next -> main (1.0.0 milestone) (#118)

Reviewed-on: #118

Dockerfile

@@ -1,4 +1,5 @@
 # Lint stage
+# Same image as Dockerfile.lint: change both pins together.
 # golangci/golangci-lint:v2.12.2-alpine, 2026-08-07
 FROM golangci/golangci-lint:v2.12.2-alpine@sha256:91b27804074a0bacea298707f016911e60cf0cdbc6c7bf5ccacb5f0606d18d60 AS lint
 
@@ -13,6 +14,9 @@ RUN go mod download
 # Copy source code
 COPY . .
 
+# Tells script/lint it is inside a container, so it runs the linter.
+ENV container=docker
+
 # Run formatting check and linter
 RUN make fmt-check
 RUN make lint
@@ -57,26 +61,30 @@ RUN apk add --no-cache \
     vips \
     libheif \
     ca-certificates \
-    tzdata
+    tzdata \
+    su-exec
 
 # Copy binary from builder
 COPY --from=builder /pixad /usr/local/bin/pixad
+COPY deploy/docker-entrypoint.sh /usr/local/bin/docker-entrypoint.sh
 
 # Create non-root user, config directory, and data directory
 RUN adduser -D -H -s /sbin/nologin pixad && \
     mkdir -p /var/lib/pixa /etc/pixa && \
     chown pixad:pixad /var/lib/pixa
 
-# Copy the image config; signing_key comes from PIXA_SIGNING_KEY.
+# No USER: the entrypoint must start as root to give a bind-mounted
-# Mount a file over /etc/pixa/config.yml to override anything else.
+# /var/lib/pixa to pixad; it then runs the server as pixad.
-COPY config.docker.yml /etc/pixa/config.yml
-
-USER pixad
 WORKDIR /var/lib/pixa
 
 EXPOSE 8080
 
+# Shell form so the probe follows PORT; a port set only in a mounted
+# config file is not seen here.
 HEALTHCHECK --interval=30s --timeout=5s --start-period=10s --retries=3 \
-    CMD wget --spider -q http://localhost:8080/.well-known/healthcheck.json || exit 1
+    CMD wget --spider -q "http://localhost:${PORT:-8080}/.well-known/healthcheck.json" || exit 1
 
-ENTRYPOINT ["/usr/local/bin/pixad", "--config", "/etc/pixa/config.yml"]
+# Settings come from PORT and the PIXA_ environment variables; only
+# PIXA_SIGNING_KEY is required. A config file mounted at
+# /etc/pixa/config.yml is optional and is read when present.
+ENTRYPOINT ["/usr/local/bin/docker-entrypoint.sh"]

Dockerfile.lint

@@ -0,0 +1,34 @@
+# Dockerfile.lint: the container script/lint builds to run golangci-lint,
+# which is never installed on the host. Pinned to the same image as the
+# Dockerfile lint stage: change both pins together, or the two run
+# different linter versions.
+#
+# golangci/golangci-lint:v2.12.2-alpine, 2026-08-07
+FROM golangci/golangci-lint:v2.12.2-alpine@sha256:91b27804074a0bacea298707f016911e60cf0cdbc6c7bf5ccacb5f0606d18d60
+
+# pixa is CGO/libvips: the type-aware linters compile every package, so
+# this image needs the same C libraries the build does.
+RUN apk add --no-cache build-base vips-dev libheif-dev pkgconfig
+
+WORKDIR /src
+
+# Modules first for layer caching; go.mod/go.sum settle this layer's
+# result, so it may safely be reused between runs.
+COPY go.mod go.sum ./
+RUN go mod download
+
+COPY . .
+
+# Tells script/lint it is inside a container, so it runs the linter.
+ENV container=docker
+
+# script/lint passes a different CACHEBUST on every run, and BuildKit
+# keys every RUN after this ARG on its value, so the lint step always
+# runs instead of returning a cached success that linted nothing.
+#
+# Go's and golangci-lint's caches (/root/.cache, hundreds of MB) go on a
+# tmpfs that is discarded after the step. Written into the layer, they
+# would pile up as build cache on every run, since no later run, with
+# its new CACHEBUST, can reuse that layer.
+ARG CACHEBUST
+RUN --mount=type=tmpfs,target=/root/.cache script/lint

Makefile

@@ -10,7 +10,7 @@ ifdef HAS_PKGCONFIG
   NIX_RUN_PREFIX =
   NIX_RUN_SUFFIX =
 else
-  NIX_RUN_PREFIX = nix-shell -p pkg-config vips libheif golangci-lint git --run '
+  NIX_RUN_PREFIX = nix-shell -p pkg-config vips libheif git --run '
   NIX_RUN_SUFFIX = '
 endif
 

README.md

@@ -27,12 +27,39 @@ make docker
 docker run -p 8080:8080 -e PIXA_SIGNING_KEY="$(openssl rand -base64 32)" pixa:latest
 ```
 
-A container is configured two ways. The signing key comes from the
+A container takes its settings from environment variables (see
-`PIXA_SIGNING_KEY` environment variable, which the baked-in config
+Configuration below for the list). Only `PIXA_SIGNING_KEY` is required; if
-reads; if it is unset the container exits at startup naming the
+it is unset the container exits at startup naming the variable. Everything
-variable. Everything else uses built-in defaults, so to change any
+else has a built-in default. A config file mounted at `/etc/pixa/config.yml`
-other setting mount your own file over `/etc/pixa/config.yml` (see
+is optional: it is read when present, and an environment variable wins over
-`config.example.yml` for the full set of keys).
+the same setting in it.
+
+## Running under upaas
+
+What the [upaas](https://git.eeqj.de/sneak/upaas) app for pixa needs:
+
+- **Port:** pixa listens on container port `8080`.
+- **Volume:** container path `/var/lib/pixa`, where pixa keeps its
+  database and cache. upaas bind-mounts the host path it is given and
+  does not create it, so the host directory must exist before the first
+  deploy.
+- **Environment variables:**
+    - `PIXA_SIGNING_KEY` (required): secret for signed and encrypted URLs
+      and login, 32+ characters, for example from
+      `openssl rand -base64 32`
+    - `PIXA_ALLOWLIST_HOSTS`: upstream hosts served without a signature,
+      comma-separated
+    - `PIXA_CACHE_MAX_BYTES`: disk cache limit in bytes; `0` disables it;
+      default 75% of free space
+    - the rest are in the table under Configuration below
+- **Health check:** the image's `HEALTHCHECK` requests
+  `/.well-known/healthcheck.json`. upaas reads the container's health 60
+  seconds after a deploy and marks the deploy failed unless it is
+  `healthy`. The probe uses the port from `PORT` (default `8080`), so a
+  port changed only in a mounted config file is not seen by it: change
+  the port with `PORT`.
+- **First run:** create the host directory. It may be owned by root: the
+  container gives it to its `pixad` user when it starts.
 
 ## Rationale
 
@@ -67,9 +94,38 @@ In-process caching of request-to-output mappings targets 1-5k r/s.
 
 Images are only fetched from origins using TLS with valid certificates.
 
+A request whose query string cannot be decoded, or gives any parameter more
+than once, is refused with 400.
+
 - `<format>`: one of `orig`, `png`, `jpeg`, `webp`
 - `<size>`: `orig` or `<width>x<height>` (e.g. `800x600`)
 
+The login form (`POST /`) is limited to 5 attempts per minute per client
+address, counting an IPv6 client by its /64; an attempt over the limit is
+refused with 429 and a `Retry-After` header. Behind a reverse proxy the client
+address comes from `X-Forwarded-For` only when the proxy's address is in
+`trusted_proxies`; otherwise all users behind the proxy are counted as one
+client. With the default `trusted_proxies` (the RFC 1918 ranges), a client
+with a private address can choose the address it is counted by through its own
+`X-Forwarded-For`, whether it connects directly or through the proxy, because
+its own address is trusted too. Setting `trusted_proxies` to the proxy's own
+address closes this.
+
+### Image Metadata
+
+pixa decodes and re-encodes every image it serves, and removes all metadata from
+the output: EXIF (GPS position, camera make, model and serial number, capture
+time, embedded thumbnail), XMP, IPTC and the ICC colour profile. This cannot be
+turned off.
+
+- The `orig` format means the source's own format, not the source's bytes: an
+  `orig` image is re-encoded and stripped like any other.
+- An image with an EXIF orientation is turned upright first, so it displays the
+  same without the tag; a requested size applies to the upright image.
+- An image with an ICC profile is converted to sRGB first, since clients show an
+  image with no profile as sRGB. Colours outside sRGB, such as the most
+  saturated ones in a Display P3 photo, are clipped.
+
 ### Source Hosts
 
 Source hosts may be allowlisted in the configuration. Non-allowlisted
@@ -79,14 +135,14 @@ hosts require an HMAC-SHA256 signature.
 
 Signatures use HMAC-SHA256 and include an expiration timestamp to
 prevent replay attacks. Signatures are **exact match only**: every
-component (host, path, query, dimensions, format, expiration) must
+component (host, path, query, dimensions, format, expiration, quality,
-match exactly what was signed. No suffix matching, wildcard matching,
+fit) must match exactly what was signed. No suffix matching, wildcard
-or partial matching is supported.
+matching, or partial matching is supported.
 
 **Signed data format** (colon-separated):
 
 ```
-HMAC-SHA256(secret, "host:path:query:width:height:format:expiration")
+HMAC-SHA256(secret, "host:path:query:width:height:format:expiration:quality:fit")
 ```
 
 Where:
@@ -97,19 +153,30 @@ Where:
 - `width` — requested width in pixels, `0` for original
 - `height` — requested height in pixels, `0` for original
 - `format` — output format (jpeg, png, webp, avif, gif, orig)
-- `expiration` — Unix timestamp when signature expires
+- `expiration` — the URL's `exp` query parameter, the Unix timestamp when
+  the signature expires; a request whose `exp` is not a whole number, an
+  empty `exp=` included, is refused with 400
+- `quality` — the URL's `q` query parameter, a whole number from 1 to 100,
+  or `85` when the URL has no `q`; a request whose `q` is anything else is
+  refused with 400
+- `fit` — the URL's `fit` query parameter (cover, contain, fill, inside,
+  outside), or `cover` when the URL has no `fit`; a request whose `fit` is
+  anything else, an empty `fit=` included, is refused with 400
 
-**Example:** resize
+**Example:** resize `https://cdn.example.com/photos/cat.jpg` to 800x600
-`https://cdn.example.com/photos/cat.jpg` to 800x600 WebP with
+WebP with expiration 1704067200, default quality and fit:
-expiration 1704067200:
 
 1. Build input:
-   `cdn.example.com:/photos/cat.jpg::800:600:webp:1704067200`
+   `cdn.example.com:/photos/cat.jpg::800:600:webp:1704067200:85:cover`
 2. Compute HMAC-SHA256 with your secret key
 3. Base64URL-encode the result
 4. URL:
    `/v1/image/cdn.example.com/photos/cat.jpg/800x600.webp?sig=<base64url>&exp=1704067200`
 
+For the same image at quality 40 with fit `contain`, the input ends in
+`:40:contain` and the URL is
+`/v1/image/cdn.example.com/photos/cat.jpg/800x600.webp?sig=<base64url>&exp=1704067200&q=40&fit=contain`.
+
 **Allowlist patterns:**
 
 - **Exact match**: `cdn.example.com` — matches only that host
@@ -118,7 +185,40 @@ expiration 1704067200:
 
 ### Configuration
 
-Configured via YAML file (`--config`). Key settings:
+Every setting can be given as an environment variable, in a YAML config
+file (`--config`), or both. A variable present in the environment wins over
+the file, even when it is empty, and the file wins over the built-in
+default. The one exception is a variable named in the file's `env:` section:
+it is set while the file loads, so it overrides both the environment the
+process was started with and the file's own key. A variable's value is
+parsed as the same text in the file would be. The three lists take
+comma-separated entries, with the spaces around each trimmed; an empty
+variable is an empty list. A value that does not parse or is invalid aborts
+startup, naming the variable. A variable whose name starts with `PIXA_` but
+is not in the table below, such as a misspelled one or `PIXA_PORT`, aborts
+startup naming it, as an unknown config key does. The one other accepted
+name is `PIXA_CONFIG_PATH`, the config file's path (like `--config`). The
+variables set by the file's `env:` section are checked the same way.
+
+| Variable                             | Config key                      | Meaning                                                                      |
+| ------------------------------------ | ------------------------------- | ---------------------------------------------------------------------------- |
+| `PIXA_SIGNING_KEY`                   | `signing_key`                   | Required: secret for signed and encrypted URLs and login, 32+ characters     |
+| `PORT`                               | `port`                          | Port to listen on; default `8080`                                            |
+| `PIXA_STATE_DIR`                     | `state_dir`                     | Directory for the database and the disk cache; default `/var/lib/pixa`       |
+| `PIXA_DB_URL`                        | `db_url`                        | SQLite database URL; default `state.sqlite3` in the state directory          |
+| `PIXA_CACHE_MAX_BYTES`               | `cache_max_bytes`               | Disk cache limit in bytes; `0` disables it; default 75% of free space        |
+| `PIXA_ALLOWLIST_HOSTS`               | `allowlist_hosts`               | Upstream hosts served without a signature                                    |
+| `PIXA_BLOCKED_NETWORKS`              | `blocked_networks`              | CIDR ranges never fetched from, on top of the built-in ones                  |
+| `PIXA_TRUSTED_PROXIES`               | `trusted_proxies`               | CIDR ranges of proxies whose `X-Forwarded-For` is believed; default RFC 1918 |
+| `PIXA_ALLOW_HTTP`                    | `allow_http`                    | Allow plain-HTTP upstreams, for testing only; default `false`                |
+| `PIXA_UPSTREAM_CONNECTIONS_PER_HOST` | `upstream_connections_per_host` | Concurrent connections per upstream host; default `20`                       |
+| `PIXA_METRICS_USERNAME`              | `metrics.username`              | Username for `/metrics`, which is served only when both are set              |
+| `PIXA_METRICS_PASSWORD`              | `metrics.password`              | Password for `/metrics`; set together with the username                      |
+| `PIXA_SENTRY_DSN`                    | `sentry_dsn`                    | Sentry DSN for error reporting; empty disables it                            |
+| `PIXA_DEBUG`                         | `debug`                         | Debug logging and plain-HTTP local development; default `false`              |
+| `PIXA_MAINTENANCE_MODE`              | `maintenance_mode`              | Maintenance flag reported by the health check; default `false`               |
+
+Key settings in more detail:
 
 - `access_control_allow_origin` — CORS origin
 - `allowlist_hosts` — list of allowed upstream hosts
@@ -131,7 +231,8 @@ Configured via YAML file (`--config`). Key settings:
   inside one of these ranges; the logged and login-recorded client
   address is then the rightmost forwarded entry that is not itself a
   trusted proxy. Otherwise the direct peer address is used and the header
-  is ignored, so a client connecting directly cannot spoof its address.
+  is ignored, so a client connecting directly from an address outside
+  these ranges cannot spoof its address.
   An omitted key defaults to the RFC 1918 private ranges (`10.0.0.0/8`,
   `172.16.0.0/12`, `192.168.0.0/16`), since pixa is deployed behind a
   proxy on a private network; an explicitly empty list (`[]`) trusts no
@@ -171,7 +272,8 @@ them. We provide:
   (bootstrap, then install-precommit)
 - `script/projectname` — output the project name ("pixa")
 - `script/test` — run the test suite
-- `script/lint` — run golangci-lint
+- `script/lint` — run golangci-lint, always in a container (builds
+  `Dockerfile.lint` when run outside one)
 - `script/fmt` — format all code (writes)
 - `script/fmt-check` — check formatting (read-only)
 - `script/check` — run test, lint, and fmt-check

TODO.md

@@ -30,6 +30,90 @@ exhaustion
 
 # Completed Steps
 
+- 2026-09-28 strip metadata from processed images (closes #82): every output is
+  exported with govips' `StripMetadata`, so it carries no EXIF, XMP, IPTC or ICC
+  profile; the image is first turned upright with `AutoRotate` (before sizes are
+  worked out) and, when it has an ICC profile, converted to sRGB; the `orig`
+  format is re-encoded and stripped like any other, as pixa never serves the
+  source bytes; there is no setting to keep metadata; documented in `README.md`.
+- 2026-09-28 rate limit the login form (closes #66): `POST /` is limited to 5
+  attempts per minute per client address, and an attempt over the limit is
+  refused with 429 and a `Retry-After` header; the address is the one
+  `internal/clientip` resolves through `trusted_proxies`, an IPv6 client is
+  counted by its /64, and an IPv4-mapped address as the IPv4 address it
+  carries; the limit is a `RateLimit` middleware in `internal/middleware` on
+  `github.com/go-chi/httprate`, which the image routes can reuse; the library
+  keeps counts for the current and the previous minute only; documented in
+  `README.md`.
+- 2026-09-28 refuse an unparseable `exp` on `/v1/image/` and log swallowed
+  cache errors (closes #72): an `exp` in the URL that is not a whole
+  number, an empty `exp=` included, is a 400 naming `exp` and the value,
+  instead of being ignored and answered with 401 as if the URL had no
+  `exp`; only an `exp` missing from the URL is unchanged; `README.md` says
+  so where it documents `exp`. A failed variant `.meta` write, source
+  metadata JSON write, `Stats` count query, stats counter update, negative
+  cache write or expired negative cache delete is now logged at `warn`
+  with the path or key and the error, and stays non-fatal.
+- 2026-09-28 refuse an empty `fit` on `/v1/image/` (closes #139): a
+  `fit` in the URL with an empty value (`fit=`) is a 400 naming `fit`,
+  instead of being served as `cover` and verified against a signature
+  made for `cover`; only a `fit` missing from the URL is still `cover`;
+  any other value still goes through the existing fit-mode check;
+  `README.md` says so where it documents `fit`.
+- 2026-09-28 refuse an invalid `q` on `/v1/image/` (closes #134): a `q`
+  that is not a whole number from 1 to 100, an empty `q` included, is a
+  400 naming `q` and the value, instead of being served at the default
+  85; the route reads `q` with the generator's quality check
+  (`parseFormInt` with `minQuality` and `maxQuality`); only a `q` missing
+  from the URL is still 85; a query string that cannot be decoded, such
+  as `q=80%`, is a 400 showing it; any query parameter given more than
+  once (`q`, `fit`, `sig`, `exp` alike) is a 400 naming it, so none is
+  read from its first value only; `README.md` states the range and both
+  query-string rules.
+- 2026-09-28 unknown `PIXA_` environment variables abort startup (closes
+  #133): a variable whose name starts with `PIXA_` but is neither a
+  setting's variable nor `PIXA_CONFIG_PATH` aborts startup naming it, as
+  an unknown config key does, and `PIXA_PORT` is named with a pointer to
+  `PORT`; the check runs after the config file loads, so the variables
+  the file's `env:` section sets are checked too; documented in
+  `README.md`.
+- 2026-09-28 start on a fresh upaas volume (closes #129): the image
+  starts as root only to give `/var/lib/pixa` to `pixad` when `pixad`
+  does not own it (`deploy/docker-entrypoint.sh`), then runs the server
+  as `pixad` through `su-exec`, so a root-owned host directory
+  bind-mounted there no longer stops the container at startup;
+  `README.md` gains a "Running under upaas" section.
+- 2026-09-28 run all linting in Docker via `Dockerfile.lint` +
+  `script/lint` (closes #104): `make lint` calls `script/lint`, the only
+  way the linter is run; inside a container (both Dockerfiles set
+  `container=docker`) it runs `golangci-lint`, anywhere else it builds the
+  hash-pinned `Dockerfile.lint`, whose last step runs `script/lint` again;
+  the `Dockerfile` lint stage runs `make lint`; no host or nix-shell
+  `golangci-lint` path remains (`script/bootstrap` installs no linter);
+  a per-run `CACHEBUST` build-arg keeps the lint step from being served
+  from cache, and a tmpfs mount on that step keeps Go's and
+  golangci-lint's caches out of its layer, so a run leaves no large build
+  cache behind; `golangci-lint config verify` stays out, as it fetches its
+  schema over an unpinned live HTTPS call
+- 2026-09-28 every setting as an environment variable (closes #128, also
+  covers #99): each config key can be set by `PIXA_` plus the key in upper
+  case (`.` written as `_`), and the port by `PORT`; a variable present in
+  the environment, even empty, wins over the config file, which wins over
+  the default; the typed getters read the variable first, so every existing
+  check applies to it and a bad value aborts startup naming the variable;
+  lists are comma-separated, and an empty variable (or `""` in the file) is
+  an empty list; the Docker image no longer bakes in `config.docker.yml` or
+  passes `--config`, and its `HEALTHCHECK` probes `PORT` (default `8080`);
+  the config file is looked for under `/etc/pixa` and `~/.config/pixa`
+  instead of the daemon name `pixad`; documented in `README.md` and
+  `config.example.yml`.
+- 2026-09-28 quality and fit in the URL signature (closes #60): the signed
+  data is now `host:path:query:width:height:format:expiration:quality:fit`,
+  using `85` and `cover` when the URL has no `q` or `fit`, so one signed
+  URL can no longer be replayed across other quality and fit values to
+  create unauthorized cache entries and transcodes; the known-answer
+  vectors in `internal/signature/golden_test.go` and the README signature
+  specification describe the new format.
 - 2026-09-28 Docker image healthcheck (closes #111): a `HEALTHCHECK` in
   the runtime stage probing `/.well-known/healthcheck.json` with busybox
   `wget`; `script/docker-smoke` (`make docker-smoke`) builds the image,
@@ -58,6 +142,20 @@ exhaustion
   (IPv4-mapped forms covered); enforcement stays in the dial-time
   re-resolution so the DNS-rebinding window remains closed; documented in
   `README.md` and `config.example.yml`.
+- 2026-09-21 validate dimensions and fit mode on the encrypted-URL
+  route and the token generator (closes #62): `imgcache.ValidateDimension`
+  alone holds the `MaxDimension` bound and is used by the path parser, by
+  the new `ValidateImageRequest` (which also applies `ValidateFitMode`)
+  and by the generator; both the `/v1/image/` and `/v1/e/` routes call
+  `ValidateImageRequest`, so an over-limit size or an unknown fit mode is a
+  400 rather than an out-of-memory or a 500 from the processor; the URL
+  generator answers 400 naming the field for a `width` or `height` that is
+  not a number or fails the shared check, a `quality` that is not a number
+  from 1 to 100, a `ttl` that is not a number from 0 to the largest number
+  of seconds the expiry calculation can hold, or an unknown `fit`; an empty
+  `quality` is 85 and
+  an empty `ttl` never expires; the form's width and height inputs stop at
+  8192
 - 2026-09-21 http.Server hardening (closes #92): added
   `HTTPReadHeaderTimeout` (10s, bounds the slowloris header dribble) and
   `HTTPIdleTimeout` (120s, bounds keep-alive reuse) alongside the
@@ -159,10 +257,9 @@ exhaustion
 
 # Future Steps
 
-- P1: strip EXIF and other metadata from processed images (privacy)
 - P2: security
     - referer blacklist
-    - per-IP rate limiting
+    - per-IP rate limiting on the image routes
     - per-origin rate limiting
 - P2: HTTP response handling
     - Last-Modified headers
@@ -171,7 +268,6 @@ exhaustion
 - P2: auto format selection (format=auto based on Accept header)
 - P2: configuration
     - add all configuration options from README
-    - environment variable overrides
     - YAML config file support
 - P2: operational
     - optional Sentry error reporting

config.docker.yml

@@ -1,11 +0,0 @@
-# Pixa configuration baked into the Docker image.
-#
-# The signing key is read from the PIXA_SIGNING_KEY environment
-# variable; startup aborts naming it when it is unset. Every other key
-# is omitted so its default applies. Operators who need more (an
-# allowlist, metrics, and so on) mount their own file over
-# /etc/pixa/config.yml.
-
-signing_key: "${ENV:PIXA_SIGNING_KEY}"
-state_dir: /var/lib/pixa
-port: 8080

config.example.yml

@@ -1,4 +1,13 @@
 # Pixa Example Configuration
+#
+# Every key can also be set by an environment variable, which wins over
+# this file: PIXA_ plus the key in upper case, with "." written as "_"
+# (state_dir is PIXA_STATE_DIR, metrics.username is
+# PIXA_METRICS_USERNAME). The one exception is port, which is set by
+# PORT. In a variable, a list is comma-separated. A variable named in
+# this file's env: section is set while the file loads, so it overrides
+# both the environment the process was started with and this file's own
+# key.
 
 # Server settings
 port: 8080

deploy/docker-entrypoint.sh

@@ -0,0 +1,15 @@
+#!/bin/sh
+# deploy/docker-entrypoint.sh: the Docker image's ENTRYPOINT. It runs as
+# root only to give /var/lib/pixa to pixad: a host directory
+# bind-mounted there keeps its host owner, often root, and pixad could
+# not write to it. The server itself always runs as pixad.
+set -eu
+
+main() {
+    if [ "$(stat -c %U /var/lib/pixa)" != pixad ]; then
+        chown pixad:pixad /var/lib/pixa
+    fi
+    exec su-exec pixad /usr/local/bin/pixad "$@"
+}
+
+main "$@"

go.mod

@@ -11,6 +11,7 @@ require (
 	github.com/getsentry/sentry-go v0.40.0
 	github.com/go-chi/chi/v5 v5.2.3
 	github.com/go-chi/cors v1.2.2
+	github.com/go-chi/httprate v0.16.0
 	github.com/gorilla/csrf v1.7.3
 	github.com/gorilla/securecookie v1.1.2
 	github.com/prometheus/client_golang v1.23.2
@@ -91,6 +92,7 @@ require (
 	github.com/inconshreveable/mousetrap v1.1.0 // indirect
 	github.com/josharian/intern v1.0.0 // indirect
 	github.com/json-iterator/go v1.1.12 // indirect
+	github.com/klauspost/cpuid/v2 v2.2.10 // indirect
 	github.com/kylelemons/godebug v1.1.0 // indirect
 	github.com/mailru/easyjson v0.7.7 // indirect
 	github.com/mattn/go-colorable v0.1.13 // indirect
@@ -113,6 +115,7 @@ require (
 	github.com/tidwall/match v1.1.1 // indirect
 	github.com/tidwall/pretty v1.2.0 // indirect
 	github.com/x448/float16 v0.8.4 // indirect
+	github.com/zeebo/xxh3 v1.0.2 // indirect
 	go.etcd.io/etcd/api/v3 v3.6.2 // indirect
 	go.etcd.io/etcd/client/pkg/v3 v3.6.2 // indirect
 	go.etcd.io/etcd/client/v3 v3.6.2 // indirect

go.sum

@@ -114,6 +114,8 @@ github.com/go-chi/chi/v5 v5.2.3 h1:WQIt9uxdsAbgIYgid+BpYc+liqQZGMHRaUwp0JUcvdE=
 github.com/go-chi/chi/v5 v5.2.3/go.mod h1:L2yAIGWB3H+phAw1NxKwWM+7eUH/lU8pOMm5hHcoops=
 github.com/go-chi/cors v1.2.2 h1:Jmey33TE+b+rB7fT8MUy1u0I4L+NARQlK6LhzKPSyQE=
 github.com/go-chi/cors v1.2.2/go.mod h1:sSbTewc+6wYHBBCW7ytsFSn836hqM7JxpglAy2Vzc58=
+github.com/go-chi/httprate v0.16.0 h1:8V5DH9j6pSK6UQoBsTpvMyFxycqaKEIToyPKzHJjUa8=
+github.com/go-chi/httprate v0.16.0/go.mod h1:A8lo+qRhk+s9LiuP5saS7XCGDXRXMcrueq0NfIuCa/I=
 github.com/go-errors/errors v1.4.2 h1:J6MZopCL4uSllY1OfXM374weqZFFItUbrImctkmUxIA=
 github.com/go-errors/errors v1.4.2/go.mod h1:sIVyrIiJhuEF+Pj9Ebtd6P/rEYROXFi3BopGUQ5a5Og=
 github.com/go-jose/go-jose/v4 v4.0.5 h1:M6T8+mKZl/+fNNuFHvGIzDz7BTLQPIounk/b9dw3AaE=
@@ -251,6 +253,8 @@ github.com/kisielk/errcheck v1.5.0/go.mod h1:pFxgyoBC7bSaBwPgfKdkLd5X25qrDl4LWUI
 github.com/kisielk/gotool v1.0.0/go.mod h1:XhKaO+MFFWcvkIS/tQcRk01m1F5IRFswLeQ+oQHNcck=
 github.com/klauspost/compress v1.18.0 h1:c/Cqfb0r+Yi+JtIEq73FWXVkRonBlf0CRNYc8Zttxdo=
 github.com/klauspost/compress v1.18.0/go.mod h1:2Pp+KzxcywXVXMr50+X0Q/Lsb43OQHYWRCY2AiWywWQ=
+github.com/klauspost/cpuid/v2 v2.2.10 h1:tBs3QSyvjDyFTq3uoc/9xFpCuOsJQFNPiAhYdw2skhE=
+github.com/klauspost/cpuid/v2 v2.2.10/go.mod h1:hqwkgyIinND0mEev00jJYCxPNVRVXFQeu1XKlok6oO0=
 github.com/konsorten/go-windows-terminal-sequences v1.0.1/go.mod h1:T0+1ngSBFLxvqU3pZ+m/2kptfBszLMUkC4ZK/EgS/cQ=
 github.com/kr/logfmt v0.0.0-20140226030751-b84e30acd515/go.mod h1:+0opPa2QZZtGFBFZlji/RkVcI2GknAs/DXo4wKdlNEc=
 github.com/kr/pretty v0.1.0/go.mod h1:dAy3ld7l9f0ibDNOQOHHMYYIIbhfbHSm3C4ZsoJORNo=
@@ -396,6 +400,10 @@ github.com/x448/float16 v0.8.4/go.mod h1:14CWIYCyZA/cWjXOioeEpHeN/83MdbZDRQHoFcY
 github.com/yuin/goldmark v1.1.27/go.mod h1:3hX8gzYuyVAZsxl0MRgGTJEmQBFcNTphYh9decYSb74=
 github.com/yuin/goldmark v1.2.1/go.mod h1:3hX8gzYuyVAZsxl0MRgGTJEmQBFcNTphYh9decYSb74=
 github.com/yuin/goldmark v1.4.13/go.mod h1:6yULJ656Px+3vBD8DxQVa3kxgyrAnzto9xy5taEt/CY=
+github.com/zeebo/assert v1.3.0 h1:g7C04CbJuIDKNPFHmsk4hwZDO5O+kntRxzaUoNXj+IQ=
+github.com/zeebo/assert v1.3.0/go.mod h1:Pq9JiuJQpG8JLJdtkwrJESF0Foym2/D9XMU5ciN/wJ0=
+github.com/zeebo/xxh3 v1.0.2 h1:xZmwmqxHZA8AI603jOQ0tMqmBr9lPeFwGg6d+xy9DC0=
+github.com/zeebo/xxh3 v1.0.2/go.mod h1:5NWz9Sef7zIDm2JHfFlcQvNekmcEl9ekUZQQKCYaDcA=
 go.etcd.io/etcd/api/v3 v3.6.2 h1:25aCkIMjUmiiOtnBIp6PhNj4KdcURuBak0hU2P1fgRc=
 go.etcd.io/etcd/api/v3 v3.6.2/go.mod h1:eFhhvfR8Px1P6SEuLT600v+vrhdDTdcfMzmnxVXXSbk=
 go.etcd.io/etcd/client/pkg/v3 v3.6.2 h1:zw+HRghi/G8fKpgKdOcEKpnBTE4OO39T6MegA0RopVU=

internal/config/config.go

@@ -16,7 +16,6 @@ import (
 
 	"git.eeqj.de/sneak/smartconfig"
 	"go.uber.org/fx"
-	"sneak.berlin/go/pixa/internal/globals"
 	"sneak.berlin/go/pixa/internal/logger"
 )
 
@@ -59,6 +58,7 @@ var (
 	errValueRequired     = errors.New("a value is required")
 	errValueEmpty        = errors.New("value must not be empty")
 	errUnknownConfigKeys = errors.New("unknown config keys")
+	errUnknownEnvVars    = errors.New("unknown environment variables")
 	errNotAString        = errors.New("not a string")
 	errNotAnInteger      = errors.New("not an integer")
 	errNotABoolean       = errors.New("not a boolean")
@@ -92,7 +92,6 @@ var (
 type Params struct {
 	fx.In
 
-	Globals *globals.Globals
 	Logger *logger.Logger
 }
 
@@ -137,24 +136,34 @@ type Config struct {
 	CacheMaxBytes int64
 
 	// cacheMaxBytesExplicit records whether cache_max_bytes was
-	// explicitly set in the configuration file. Explicit values are
+	// explicitly set, in the environment or the configuration file.
-	// used exactly as given; only an omitted key gets the computed
+	// Explicit values are used exactly as given; only an omitted key
-	// default (and its floor) in resolveCacheMaxBytes.
+	// gets the computed default (and its floor) in resolveCacheMaxBytes.
 	cacheMaxBytesExplicit bool
 }
 
-// New creates a new Config instance by loading configuration from file.
+// New creates a new Config instance from the environment and the
+// config file.
 func New(_ fx.Lifecycle, params Params) (*Config, error) {
 	log := params.Logger.Get()
-	name := params.Globals.Appname
 
-	sc, err := loadConfigFile(log, name)
+	// Look for the config file under the project name (/etc/pixa/,
+	// ~/.config/pixa/), matching the /var/lib/pixa state directory,
+	// not under the daemon name pixad.
+	sc, err := loadConfigFile(log, "pixa")
+	if err != nil {
+		return nil, err
+	}
+
+	// Loading the config file sets the variables in its env section,
+	// so this also checks their names.
+	err = validateKnownEnvVars()
 	if err != nil {
 		return nil, err
 	}
 
 	if sc == nil {
-		log.Info("no config file found, using defaults")
+		log.Info("no config file found, using environment variables and defaults")
 	}
 
 	c, err := newFromSmartConfig(sc)
@@ -179,23 +188,24 @@ func New(_ fx.Lifecycle, params Params) (*Config, error) {
 	return c, nil
 }
 
-// newFromSmartConfig constructs a Config from a loaded smartconfig
+// newFromSmartConfig constructs a Config from the environment and a
-// instance and validates it. A nil sc means no config file was found,
+// loaded smartconfig instance, and validates it. A nil sc means no
-// in which case every option takes its default value. A key that is
+// config file was found, in which case every option the environment
-// present but unparseable or invalid is an error: defaults apply only
+// does not set takes its default value. A key that is present but
-// to omitted keys, never to invalid explicit values.
+// unparseable or invalid is an error: defaults apply only to omitted
+// keys, never to invalid explicit values.
 func newFromSmartConfig(sc *smartconfig.Config) (*Config, error) {
 	if sc != nil {
 		err := validateKnownKeys(sc)
 		if err != nil {
 			return nil, err
 		}
+	}
 
-		err = validateAllowlistHostsValue(sc)
+	err := validateAllowlistHostsValue(sc)
 	if err != nil {
 		return nil, err
 	}
-	}
 
 	blockedNetworks, err := parseCIDRList(sc, keyBlockedNetworks)
 	if err != nil {
@@ -238,23 +248,18 @@ func newFromSmartConfig(sc *smartconfig.Config) (*Config, error) {
 	// The computed default for cache_max_bytes needs a validated
 	// state_dir, so it is resolved later (resolveCacheMaxBytes); here
 	// we only record whether the operator set the key explicitly.
-	if sc != nil {
+	if _, present := lookupValue(sc, keyCacheMaxBytes); present {
-		if _, present := sc.Get(keyCacheMaxBytes); present {
 		c.cacheMaxBytesExplicit = true
 	}
-	}
 
 	// Build DBURL from StateDir if not explicitly set. The derived URL
 	// is a default: it applies only when db_url is omitted, never to an
 	// explicitly empty value.
 	c.DBURL = loader.stringVal(keyDBURL, "")
 	if c.DBURL == "" && loader.err == nil {
-		if sc != nil {
+		if _, present := lookupValue(sc, keyDBURL); present {
-			if _, present := sc.Get(keyDBURL); present {
+			return nil, fmt.Errorf("%s: %w; omit it to derive it from state_dir",
-				return nil, fmt.Errorf(
+				settingName(keyDBURL), errValueEmpty)
-					"config key %q: %w; omit the key to derive it from state_dir",
-					keyDBURL, errValueEmpty)
-			}
 		}
 
 		c.DBURL = fmt.Sprintf("file:%s/state.sqlite3?_journal_mode=WAL", c.StateDir)
@@ -356,6 +361,91 @@ func isKnownConfigKey(key string) bool {
 	return false
 }
 
+// envVarNames returns, for each configuration key, the environment
+// variable that also sets it: PIXA_ plus the key in upper case, with "."
+// written as "_", except the port, which REPO_POLICIES.md requires to be
+// PORT. metrics is set through its two subkeys; env has no variable.
+func envVarNames() map[string]string {
+	return map[string]string{ //nolint:gosec // G101: variable names, not secrets
+		keyDebug:                      "PIXA_DEBUG",
+		keyMaintenanceMode:            "PIXA_MAINTENANCE_MODE",
+		keyPort:                       "PORT",
+		keyStateDir:                   "PIXA_STATE_DIR",
+		keySentryDSN:                  "PIXA_SENTRY_DSN",
+		keyDBURL:                      "PIXA_DB_URL",
+		keyMetricsUsername:            "PIXA_METRICS_USERNAME",
+		keyMetricsPassword:            "PIXA_METRICS_PASSWORD",
+		keySigningKey:                 "PIXA_SIGNING_KEY",
+		keyAllowlistHosts:             "PIXA_ALLOWLIST_HOSTS",
+		keyAllowHTTP:                  "PIXA_ALLOW_HTTP",
+		keyUpstreamConnectionsPerHost: "PIXA_UPSTREAM_CONNECTIONS_PER_HOST",
+		keyCacheMaxBytes:              "PIXA_CACHE_MAX_BYTES",
+		keyBlockedNetworks:            "PIXA_BLOCKED_NETWORKS",
+		keyTrustedProxies:             "PIXA_TRUSTED_PROXIES",
+	}
+}
+
+// validateKnownEnvVars rejects environment variables whose names start
+// with PIXA_ but that are neither a setting's variable nor
+// PIXA_CONFIG_PATH, so a misspelled variable fails at startup instead of
+// being silently ignored, as validateKnownKeys does for config file keys.
+// New calls it after loading the config file, so the variables the
+// file's env section sets are checked too.
+func validateKnownEnvVars() error {
+	known := map[string]bool{"PIXA_CONFIG_PATH": true}
+
+	for _, name := range envVarNames() {
+		known[name] = true
+	}
+
+	var unknown []string
+
+	for _, entry := range os.Environ() {
+		name, _, _ := strings.Cut(entry, "=")
+
+		switch {
+		case !strings.HasPrefix(name, "PIXA_") || known[name]:
+			continue
+		case name == "PIXA_PORT":
+			unknown = append(unknown, name+" (use PORT for the port)")
+		default:
+			unknown = append(unknown, name)
+		}
+	}
+
+	if len(unknown) > 0 {
+		sort.Strings(unknown)
+
+		return fmt.Errorf("%w: %s", errUnknownEnvVars, strings.Join(unknown, ", "))
+	}
+
+	return nil
+}
+
+// lookupValue returns the value set for key and whether one is set. The
+// key's environment variable wins when it is present, even when empty;
+// its value is a string, read exactly as the same text quoted in the
+// config file would be. Otherwise the config file's value is used.
+func lookupValue(sc *smartconfig.Config, key string) (any, bool) {
+	value, present := os.LookupEnv(envVarNames()[key])
+	if present {
+		return value, true
+	}
+
+	if sc == nil {
+		return nil, false
+	}
+
+	return sc.Get(key)
+}
+
+// settingName names key in an error message together with its
+// environment variable, since either one may have set the value.
+func settingName(key string) string {
+	return fmt.Sprintf("config key %q (environment variable %s)",
+		key, envVarNames()[key])
+}
+
 // ensureStateDirWritable verifies at startup that StateDir can be
 // created and written to, so a misconfigured path aborts startup
 // instead of failing later at first use.
@@ -364,28 +454,28 @@ func (c *Config) ensureStateDirWritable() error {
 
 	err := os.MkdirAll(c.StateDir, stateDirPerms)
 	if err != nil {
-		return fmt.Errorf("config key %q: cannot create directory %q: %w",
+		return fmt.Errorf("%s: cannot create directory %q: %w",
-			keyStateDir, c.StateDir, err)
+			settingName(keyStateDir), c.StateDir, err)
 	}
 
 	probe, err := os.CreateTemp(c.StateDir, ".startup-write-probe-*")
 	if err != nil {
-		return fmt.Errorf("config key %q: directory %q is not writable: %w",
+		return fmt.Errorf("%s: directory %q is not writable: %w",
-			keyStateDir, c.StateDir, err)
+			settingName(keyStateDir), c.StateDir, err)
 	}
 
 	probePath := probe.Name()
 
 	err = probe.Close()
 	if err != nil {
-		return fmt.Errorf("config key %q: cannot close probe file %q: %w",
+		return fmt.Errorf("%s: cannot close probe file %q: %w",
-			keyStateDir, probePath, err)
+			settingName(keyStateDir), probePath, err)
 	}
 
 	err = os.Remove(probePath)
 	if err != nil {
-		return fmt.Errorf("config key %q: cannot remove probe file %q: %w",
+		return fmt.Errorf("%s: cannot remove probe file %q: %w",
-			keyStateDir, probePath, err)
+			settingName(keyStateDir), probePath, err)
 	}
 
 	return nil
@@ -396,18 +486,19 @@ func (c *Config) ensureStateDirWritable() error {
 // key value itself is never echoed in error messages.
 func (c *Config) validateSigningKey() error {
 	if c.SigningKey == "" {
-		return fmt.Errorf("config key %q: %w", keySigningKey, errValueRequired)
+		return fmt.Errorf("%s: %w", settingName(keySigningKey), errValueRequired)
 	}
 
 	// Minimum key length for security (32 bytes = 256 bits)
 	const minKeyLength = 32
 	if len(c.SigningKey) < minKeyLength {
-		return fmt.Errorf("config key %q: %w: must be at least %d characters, got %d",
+		return fmt.Errorf("%s: %w: must be at least %d characters, got %d",
-			keySigningKey, errValueTooShort, minKeyLength, len(c.SigningKey))
+			settingName(keySigningKey), errValueTooShort, minKeyLength,
+			len(c.SigningKey))
 	}
 
 	if c.SigningKey == placeholderSigningKey {
-		return fmt.Errorf("config key %q: %w", keySigningKey, errPlaceholderKey)
+		return fmt.Errorf("%s: %w", settingName(keySigningKey), errPlaceholderKey)
 	}
 
 	return nil
@@ -423,25 +514,25 @@ func (c *Config) validate() error {
 
 	const maxPort = 65535
 	if c.Port < 1 || c.Port > maxPort {
-		return fmt.Errorf("config key %q: value %d is %w 1-%d",
+		return fmt.Errorf("%s: value %d is %w 1-%d",
-			keyPort, c.Port, errPortOutOfRange, maxPort)
+			settingName(keyPort), c.Port, errPortOutOfRange, maxPort)
 	}
 
 	if c.UpstreamConnectionsPerHost < 1 {
-		return fmt.Errorf("config key %q: value %d %w",
+		return fmt.Errorf("%s: value %d %w",
-			keyUpstreamConnectionsPerHost, c.UpstreamConnectionsPerHost,
+			settingName(keyUpstreamConnectionsPerHost),
-			errTooFewConnections)
+			c.UpstreamConnectionsPerHost, errTooFewConnections)
 	}
 
 	if c.StateDir == "" {
-		return fmt.Errorf("config key %q: %w", keyStateDir, errValueEmpty)
+		return fmt.Errorf("%s: %w", settingName(keyStateDir), errValueEmpty)
 	}
 
 	// Zero is valid (it disables the disk cache); only negative
 	// values are rejected. No floor applies to explicit values.
 	if c.CacheMaxBytes < 0 {
-		return fmt.Errorf("config key %q: value %d %w",
+		return fmt.Errorf("%s: value %d %w",
-			keyCacheMaxBytes, c.CacheMaxBytes, errMustNotBeNegative)
+			settingName(keyCacheMaxBytes), c.CacheMaxBytes, errMustNotBeNegative)
 	}
 
 	for _, host := range c.AllowlistHosts {
@@ -454,14 +545,15 @@ func (c *Config) validate() error {
 	if c.SentryDSN != "" {
 		parsed, err := url.Parse(c.SentryDSN)
 		if err != nil || parsed.Scheme == "" || parsed.Host == "" {
-			return fmt.Errorf("config key %q: value %q is %w",
+			return fmt.Errorf("%s: value %q is %w",
-				keySentryDSN, c.SentryDSN, errNotAValidURL)
+				settingName(keySentryDSN), c.SentryDSN, errNotAValidURL)
 		}
 	}
 
 	if (c.MetricsUsername == "") != (c.MetricsPassword == "") {
-		return fmt.Errorf("config keys %q and %q %w",
+		return fmt.Errorf("%s and %s %w",
-			keyMetricsUsername, keyMetricsPassword, errMustBeSetTogether)
+			settingName(keyMetricsUsername), settingName(keyMetricsPassword),
+			errMustBeSetTogether)
 	}
 
 	return nil
@@ -476,13 +568,13 @@ func (c *Config) validate() error {
 // disable URL signing.
 func validateAllowlistHost(host string) error {
 	if strings.Contains(host, "://") || strings.ContainsAny(host, "/ \t") {
-		return fmt.Errorf("config key %q: entry %q %w",
+		return fmt.Errorf("%s: entry %q %w",
-			keyAllowlistHosts, host, errNotBareHostname)
+			settingName(keyAllowlistHosts), host, errNotBareHostname)
 	}
 
 	if strings.Trim(host, ".") == "" {
-		return fmt.Errorf("config key %q: entry %q %w",
+		return fmt.Errorf("%s: entry %q %w",
-			keyAllowlistHosts, host, errNoHostnameLabels)
+			settingName(keyAllowlistHosts), host, errNoHostnameLabels)
 	}
 
 	return nil
@@ -598,11 +690,7 @@ func (l *strictLoader) boolVal(key string, defaultVal bool) bool {
 // is omitted. A present value that is not a string, or is explicitly
 // null, is an error.
 func getString(sc *smartconfig.Config, key, defaultVal string) (string, error) {
-	if sc == nil {
+	raw, ok := lookupValue(sc, key)
-		return defaultVal, nil
-	}
-
-	raw, ok := sc.Get(key)
 	if !ok {
 		return defaultVal, nil
 	}
@@ -624,11 +712,7 @@ func getString(sc *smartconfig.Config, key, defaultVal string) (string, error) {
 // omitted. A present value that is not a whole number, or is explicitly
 // null, is an error; fractional values are never truncated.
 func getInt(sc *smartconfig.Config, key string, defaultVal int) (int, error) {
-	if sc == nil {
+	raw, ok := lookupValue(sc, key)
-		return defaultVal, nil
-	}
-
-	raw, ok := sc.Get(key)
 	if !ok {
 		return defaultVal, nil
 	}
@@ -652,8 +736,8 @@ func getInt(sc *smartconfig.Config, key string, defaultVal int) (int, error) {
 	case string:
 		parsed, err := strconv.Atoi(strings.TrimSpace(val))
 		if err != nil {
-			return 0, fmt.Errorf("config key %q: value %q is %w",
+			return 0, fmt.Errorf("%s: value %q is %w",
-				key, val, errNotAnInteger)
+				settingName(key), val, errNotAnInteger)
 		}
 
 		return parsed, nil
@@ -668,11 +752,7 @@ func getInt(sc *smartconfig.Config, key string, defaultVal int) (int, error) {
 // is explicitly null, is an error; fractional values are never
 // truncated and out-of-range values are never clamped.
 func getInt64(sc *smartconfig.Config, key string, defaultVal int64) (int64, error) {
-	if sc == nil {
+	raw, ok := lookupValue(sc, key)
-		return defaultVal, nil
-	}
-
-	raw, ok := sc.Get(key)
 	if !ok {
 		return defaultVal, nil
 	}
@@ -703,8 +783,8 @@ func getInt64(sc *smartconfig.Config, key string, defaultVal int64) (int64, erro
 	case string:
 		parsed, err := strconv.ParseInt(strings.TrimSpace(val), 10, 64)
 		if err != nil {
-			return 0, fmt.Errorf("config key %q: value %q is %w",
+			return 0, fmt.Errorf("%s: value %q is %w",
-				key, val, errNotAnInteger)
+				settingName(key), val, errNotAnInteger)
 		}
 
 		return parsed, nil
@@ -719,11 +799,7 @@ func getInt64(sc *smartconfig.Config, key string, defaultVal int64) (int64, erro
 // string), or is explicitly null, is an error; numbers are not accepted
 // as booleans.
 func getBool(sc *smartconfig.Config, key string, defaultVal bool) (bool, error) {
-	if sc == nil {
+	raw, ok := lookupValue(sc, key)
-		return defaultVal, nil
-	}
-
-	raw, ok := sc.Get(key)
 	if !ok {
 		return defaultVal, nil
 	}
@@ -738,8 +814,8 @@ func getBool(sc *smartconfig.Config, key string, defaultVal bool) (bool, error)
 	case string:
 		parsed, err := strconv.ParseBool(strings.TrimSpace(val))
 		if err != nil {
-			return false, fmt.Errorf("config key %q: value %q is %w",
+			return false, fmt.Errorf("%s: value %q is %w",
-				key, val, errNotABoolean)
+				settingName(key), val, errNotABoolean)
 		}
 
 		return parsed, nil
@@ -755,7 +831,7 @@ func getBool(sc *smartconfig.Config, key string, defaultVal bool) (bool, error)
 // (or a comma-separated string), a non-string entry, or an empty entry
 // is an error, never silently skipped.
 func validateAllowlistHostsValue(sc *smartconfig.Config) error {
-	raw, ok := sc.Get(keyAllowlistHosts)
+	raw, ok := lookupValue(sc, keyAllowlistHosts)
 	if !ok {
 		return nil
 	}
@@ -785,8 +861,8 @@ func validateAllowlistHostsValue(sc *smartconfig.Config) error {
 
 		for part := range strings.SplitSeq(val, ",") {
 			if strings.TrimSpace(part) == "" {
-				return fmt.Errorf("config key %q: value %q %w",
+				return fmt.Errorf("%s: value %q %w",
-					keyAllowlistHosts, val, errEmptyEntry)
+					settingName(keyAllowlistHosts), val, errEmptyEntry)
 			}
 		}
 	default:
@@ -802,11 +878,7 @@ func validateAllowlistHostsValue(sc *smartconfig.Config) error {
 // comma-separated string (backwards compatibility). Malformed entries
 // are rejected beforehand by validateAllowlistHostsValue.
 func getStringSlice(sc *smartconfig.Config) []string {
-	if sc == nil {
+	val, ok := lookupValue(sc, keyAllowlistHosts)
-		return nil
-	}
-
-	val, ok := sc.Get(keyAllowlistHosts)
 	if !ok || val == nil {
 		return nil
 	}
@@ -866,11 +938,7 @@ func defaultTrustedProxies() []netip.Prefix {
 // aborts startup naming the key and the offending value; the default
 // (an empty list) applies only to an omitted key.
 func parseCIDRList(sc *smartconfig.Config, key string) ([]netip.Prefix, error) {
-	if sc == nil {
+	raw, ok := lookupValue(sc, key)
-		return nil, nil
-	}
-
-	raw, ok := sc.Get(key)
 	if !ok {
 		return nil, nil
 	}
@@ -889,8 +957,8 @@ func parseCIDRList(sc *smartconfig.Config, key string) ([]netip.Prefix, error) {
 	for _, entry := range entries {
 		prefix, err := netip.ParsePrefix(entry)
 		if err != nil {
-			return nil, fmt.Errorf("config key %q: value %q is %w",
+			return nil, fmt.Errorf("%s: value %q is %w",
-				key, entry, errNotAValidCIDR)
+				settingName(key), entry, errNotAValidCIDR)
 		}
 
 		prefixes = append(prefixes, prefix)
@@ -901,7 +969,8 @@ func parseCIDRList(sc *smartconfig.Config, key string) ([]netip.Prefix, error) {
 
 // cidrListEntries extracts the raw entries of the named CIDR-list key as
 // trimmed, non-empty strings, from either a YAML list of strings or a
-// comma-separated string. Any other shape is a configuration error.
+// comma-separated string; an empty string is an empty list, as for
+// allowlist_hosts. Any other shape is a configuration error.
 func cidrListEntries(raw any, key string) ([]string, error) {
 	switch val := raw.(type) {
 	case []any:
@@ -926,11 +995,15 @@ func cidrListEntries(raw any, key string) ([]string, error) {
 	case string:
 		entries := make([]string, 0)
 
+		if strings.TrimSpace(val) == "" {
+			return entries, nil
+		}
+
 		for part := range strings.SplitSeq(val, ",") {
 			trimmed := strings.TrimSpace(part)
 			if trimmed == "" {
-				return nil, fmt.Errorf("config key %q: value %q %w",
+				return nil, fmt.Errorf("%s: value %q %w",
-					key, val, errEmptyEntry)
+					settingName(key), val, errEmptyEntry)
 			}
 
 			entries = append(entries, trimmed)

internal/config/env_internal_test.go

@@ -0,0 +1,367 @@
+package config
+
+import (
+	"net/netip"
+	"os"
+	"path/filepath"
+	"reflect"
+	"slices"
+	"strings"
+	"testing"
+
+	"sneak.berlin/go/pixa/internal/globals"
+	"sneak.berlin/go/pixa/internal/logger"
+)
+
+// TestMain unsets PORT and every PIXA_ environment variable before the
+// tests run, so each test sees only the variables it sets itself, not
+// whatever the shell running the tests exports.
+func TestMain(m *testing.M) {
+	for _, entry := range os.Environ() {
+		name, _, _ := strings.Cut(entry, "=")
+		if name != "PORT" && !strings.HasPrefix(name, "PIXA_") {
+			continue
+		}
+
+		err := os.Unsetenv(name)
+		if err != nil {
+			panic(err)
+		}
+	}
+
+	m.Run()
+}
+
+// wantStartupError fails the test unless err is a startup error that
+// mentions every one of wants.
+func wantStartupError(t *testing.T, err error, wants ...string) {
+	t.Helper()
+
+	if err == nil {
+		t.Fatalf("want a startup error mentioning %q, got none", wants)
+	}
+
+	t.Logf("got expected error: %v", err)
+
+	for _, want := range wants {
+		if !strings.Contains(err.Error(), want) {
+			t.Errorf("error %q does not mention %q", err.Error(), want)
+		}
+	}
+}
+
+// TestEnvironmentSetsEveryKey sets every key from its environment
+// variable, with no config file at all: PORT for the port, and PIXA_
+// plus the key in upper case, "." written as "_", for every other key.
+func TestEnvironmentSetsEveryKey(t *testing.T) {
+	t.Setenv("PIXA_DEBUG", "true")
+	t.Setenv("PIXA_MAINTENANCE_MODE", "1")
+	t.Setenv("PORT", "9090")
+	t.Setenv("PIXA_STATE_DIR", "/srv/pixa-env")
+	t.Setenv("PIXA_SENTRY_DSN", "https://abc123@sentry.example.com/42")
+	t.Setenv("PIXA_DB_URL", "file:/srv/pixa-env/other.sqlite3")
+	t.Setenv("PIXA_METRICS_USERNAME", "metricsuser")
+	t.Setenv("PIXA_METRICS_PASSWORD", "metricspass")
+	t.Setenv("PIXA_SIGNING_KEY", validTestSigningKey)
+	t.Setenv("PIXA_ALLOWLIST_HOSTS", "s3.sneak.cloud,.example.com")
+	t.Setenv("PIXA_ALLOW_HTTP", "true")
+	t.Setenv("PIXA_UPSTREAM_CONNECTIONS_PER_HOST", "5")
+	t.Setenv("PIXA_CACHE_MAX_BYTES", "1024")
+	t.Setenv("PIXA_BLOCKED_NETWORKS", "203.0.113.0/24")
+	t.Setenv("PIXA_TRUSTED_PROXIES", "192.0.2.0/24")
+
+	c, err := newFromSmartConfig(nil)
+	if err != nil {
+		t.Fatalf("configuration from the environment alone should load: %v", err)
+	}
+
+	want := Config{
+		Debug:                      true,
+		MaintenanceMode:            true,
+		Port:                       9090,
+		StateDir:                   "/srv/pixa-env",
+		SentryDSN:                  "https://abc123@sentry.example.com/42",
+		DBURL:                      "file:/srv/pixa-env/other.sqlite3",
+		MetricsUsername:            "metricsuser",
+		MetricsPassword:            "metricspass",
+		SigningKey:                 validTestSigningKey,
+		AllowlistHosts:             []string{testHostS3, ".example.com"},
+		AllowHTTP:                  true,
+		UpstreamConnectionsPerHost: 5,
+		CacheMaxBytes:              1024,
+		cacheMaxBytesExplicit:      true,
+		BlockedNetworks:            []netip.Prefix{netip.MustParsePrefix("203.0.113.0/24")},
+		TrustedProxies:             []netip.Prefix{netip.MustParsePrefix("192.0.2.0/24")},
+	}
+
+	if !reflect.DeepEqual(*c, want) {
+		t.Errorf("config from the environment =\n%+v\nwant\n%+v", *c, want)
+	}
+}
+
+// TestUnknownPixaVariableAbortsStartup checks that a PIXA_ variable that
+// is not a setting's variable, such as a misspelled one, aborts startup
+// naming it, as an unknown config key does, instead of being ignored.
+func TestUnknownPixaVariableAbortsStartup(t *testing.T) {
+	t.Setenv("PIXA_TRUSTED_PROXY", "192.0.2.0/24")
+	t.Setenv("PIXA_SIGNINGKEY", validTestSigningKey)
+
+	err := validateKnownEnvVars()
+	wantStartupError(t, err, "PIXA_TRUSTED_PROXY", "PIXA_SIGNINGKEY")
+}
+
+// TestPixaPortAbortsStartupPointingToPort checks that PIXA_PORT aborts
+// startup with a message saying to use PORT, which sets the port.
+func TestPixaPortAbortsStartupPointingToPort(t *testing.T) {
+	t.Setenv("PIXA_PORT", "9090")
+
+	err := validateKnownEnvVars()
+	wantStartupError(t, err, "PIXA_PORT", "use PORT")
+}
+
+// TestSettingVariablesAndConfigPathAreAccepted checks that every
+// setting's variable and PIXA_CONFIG_PATH pass the check for unknown
+// PIXA_ variables. TestEnvironmentSetsEveryKey pins the names in the list.
+func TestSettingVariablesAndConfigPathAreAccepted(t *testing.T) {
+	// A config file's env section loaded by another test can leave a
+	// PIXA_ variable set for the whole process, so every one is unset
+	// here first; t.Setenv restores each when the test ends.
+	for _, entry := range os.Environ() {
+		name, _, _ := strings.Cut(entry, "=")
+		if !strings.HasPrefix(name, "PIXA_") {
+			continue
+		}
+
+		t.Setenv(name, "")
+
+		err := os.Unsetenv(name)
+		if err != nil {
+			t.Fatalf("failed to unset %s: %v", name, err)
+		}
+	}
+
+	t.Setenv("PIXA_CONFIG_PATH", "/etc/pixa/config.yml")
+
+	for _, name := range envVarNames() {
+		t.Setenv(name, "")
+	}
+
+	err := validateKnownEnvVars()
+	if err != nil {
+		t.Fatalf("PIXA_CONFIG_PATH and every setting's variable "+
+			"must be accepted: %v", err)
+	}
+}
+
+// configFromNew writes yamlContent to a temporary config file, points
+// PIXA_CONFIG_PATH at it, and runs New, as the server does at startup.
+// The state directory is a temporary one and the disk cache is off, so
+// New succeeds unless something in the test is wrong.
+func configFromNew(t *testing.T, yamlContent string) (*Config, error) {
+	t.Helper()
+
+	tmpDir := t.TempDir()
+	configPath := filepath.Join(tmpDir, "config.yml")
+
+	err := os.WriteFile(configPath, []byte(yamlContent), 0o600)
+	if err != nil {
+		t.Fatalf("failed to write test config: %v", err)
+	}
+
+	t.Setenv("PIXA_CONFIG_PATH", configPath)
+	t.Setenv("PIXA_STATE_DIR", filepath.Join(tmpDir, "state"))
+	t.Setenv("PIXA_CACHE_MAX_BYTES", "0")
+
+	testLogger, err := logger.New(nil, logger.Params{Globals: &globals.Globals{}})
+	if err != nil {
+		t.Fatalf("failed to create logger: %v", err)
+	}
+
+	return New(nil, Params{Logger: testLogger})
+}
+
+// TestUnknownPixaVariableAbortsNew checks that New, which the server
+// calls at startup, aborts on a misspelled PIXA_ variable.
+func TestUnknownPixaVariableAbortsNew(t *testing.T) {
+	t.Setenv("PIXA_TRUSTED_PROXY", "192.0.2.0/24")
+
+	_, err := configFromNew(t, signingKeyLine)
+	wantStartupError(t, err, "PIXA_TRUSTED_PROXY")
+}
+
+// TestUnknownPixaVariableInEnvSectionAbortsNew checks that New aborts
+// on a misspelled PIXA_ name in the config file's env section, which
+// loading the file sets as an environment variable.
+func TestUnknownPixaVariableInEnvSectionAbortsNew(t *testing.T) {
+	// The variable must be absent until the file loads. t.Setenv makes
+	// sure the one the file sets is removed when the test ends.
+	t.Setenv("PIXA_TRUSTED_PROXY", "")
+
+	err := os.Unsetenv("PIXA_TRUSTED_PROXY")
+	if err != nil {
+		t.Fatalf("failed to unset PIXA_TRUSTED_PROXY: %v", err)
+	}
+
+	_, err = configFromNew(t, signingKeyLine+
+		"env:\n  PIXA_TRUSTED_PROXY: 192.0.2.0/24\n")
+	wantStartupError(t, err, "PIXA_TRUSTED_PROXY")
+}
+
+// TestPortFromEnvironmentOverridesConfigFile checks that PORT wins over
+// the port in the config file.
+func TestPortFromEnvironmentOverridesConfigFile(t *testing.T) {
+	t.Setenv("PORT", "9090")
+
+	c, err := configFromYAML(t, signingKeyLine+"port: 8080\n")
+	if err != nil {
+		t.Fatalf("PORT=9090 with port 8080 in the file should load: %v", err)
+	}
+
+	if c.Port != 9090 {
+		t.Errorf("Port = %d, want 9090 from PORT, not 8080 from the file", c.Port)
+	}
+}
+
+// TestInvalidPortFromEnvironmentAbortsStartup checks that a PORT that is
+// not a number, or is outside the port range, aborts startup naming PORT
+// and the value, even though the file's port is valid.
+func TestInvalidPortFromEnvironmentAbortsStartup(t *testing.T) {
+	t.Setenv("PORT", "banana")
+
+	_, err := configFromYAML(t, signingKeyLine+"port: 8080\n")
+	wantStartupError(t, err, "PORT", "banana")
+
+	t.Setenv("PORT", "70000")
+
+	_, err = configFromYAML(t, signingKeyLine+"port: 8080\n")
+	wantStartupError(t, err, "PORT", "70000")
+}
+
+// TestListFromEnvironmentReplacesConfigFileList checks that a list
+// variable replaces the file's list, split on commas with the spaces
+// around each entry trimmed.
+func TestListFromEnvironmentReplacesConfigFileList(t *testing.T) {
+	t.Setenv("PIXA_ALLOWLIST_HOSTS", " cdn.example.com , .example.org ")
+
+	c, err := configFromYAML(t, signingKeyLine+
+		"allowlist_hosts:\n  - s3.sneak.cloud\n  - sneak.berlin\n")
+	if err != nil {
+		t.Fatalf("PIXA_ALLOWLIST_HOSTS should load: %v", err)
+	}
+
+	want := []string{"cdn.example.com", ".example.org"}
+	if !slices.Equal(c.AllowlistHosts, want) {
+		t.Errorf("AllowlistHosts = %v, want %v from PIXA_ALLOWLIST_HOSTS",
+			c.AllowlistHosts, want)
+	}
+}
+
+// TestInvalidBlockedNetworksFromEnvironmentAbortsStartup checks that an
+// invalid CIDR, or an empty entry, in PIXA_BLOCKED_NETWORKS aborts
+// startup naming the variable, as the same list in the file does.
+func TestInvalidBlockedNetworksFromEnvironmentAbortsStartup(t *testing.T) {
+	t.Setenv("PIXA_BLOCKED_NETWORKS", "203.0.113.0/24,not-a-cidr")
+
+	_, err := configFromYAML(t, signingKeyLine)
+	wantStartupError(t, err, "PIXA_BLOCKED_NETWORKS", "not-a-cidr")
+
+	t.Setenv("PIXA_BLOCKED_NETWORKS", "203.0.113.0/24,,198.51.100.0/24")
+
+	_, err = configFromYAML(t, signingKeyLine)
+	wantStartupError(t, err, "PIXA_BLOCKED_NETWORKS")
+}
+
+// TestInvalidDebugFromEnvironmentAbortsStartup checks that a PIXA_DEBUG
+// that strconv.ParseBool rejects aborts startup instead of defaulting.
+func TestInvalidDebugFromEnvironmentAbortsStartup(t *testing.T) {
+	t.Setenv("PIXA_DEBUG", "maybe")
+
+	_, err := configFromYAML(t, signingKeyLine)
+	wantStartupError(t, err, "PIXA_DEBUG", "maybe")
+}
+
+// TestConfigFileAloneBehavesAsBefore checks that with no variables set
+// (TestMain unsets them) the config file's values are used and omitted
+// keys take their defaults.
+func TestConfigFileAloneBehavesAsBefore(t *testing.T) {
+	t.Parallel()
+
+	c, err := configFromYAML(t, signingKeyLine+"port: 9191\n")
+	if err != nil {
+		t.Fatalf("config file should load: %v", err)
+	}
+
+	if c.Port != 9191 {
+		t.Errorf("Port = %d, want 9191 from the file", c.Port)
+	}
+
+	if c.StateDir != DefaultStateDir {
+		t.Errorf("StateDir = %q, want default %q", c.StateDir, DefaultStateDir)
+	}
+
+	if !slices.Equal(c.TrustedProxies, defaultTrustedProxies()) {
+		t.Errorf("TrustedProxies = %v, want default %v",
+			c.TrustedProxies, defaultTrustedProxies())
+	}
+}
+
+// TestEmptyTrustedProxiesFromEnvironmentTrustsNoOne checks that an empty
+// PIXA_TRUSTED_PROXIES is an empty list, like [] in the file: it trusts
+// no proxy instead of taking the default ranges.
+func TestEmptyTrustedProxiesFromEnvironmentTrustsNoOne(t *testing.T) {
+	t.Setenv("PIXA_TRUSTED_PROXIES", "")
+
+	c, err := configFromYAML(t, signingKeyLine)
+	if err != nil {
+		t.Fatalf("empty PIXA_TRUSTED_PROXIES should load: %v", err)
+	}
+
+	if len(c.TrustedProxies) != 0 {
+		t.Errorf("TrustedProxies = %v, want none", c.TrustedProxies)
+	}
+}
+
+// TestEmptyVariableDoesNotFallBackToConfigFile checks that a variable
+// that is present but empty is a set value: an empty PIXA_STATE_DIR
+// aborts startup like state_dir: "" in the file, instead of falling
+// through to the file's state_dir.
+func TestEmptyVariableDoesNotFallBackToConfigFile(t *testing.T) {
+	t.Setenv("PIXA_STATE_DIR", "")
+
+	_, err := configFromYAML(t, signingKeyLine+"state_dir: /srv/pixa-file\n")
+	wantStartupError(t, err, "PIXA_STATE_DIR")
+}
+
+// TestMissingSigningKeyNamesItsVariable checks that with no config file
+// and no PIXA_SIGNING_KEY, startup aborts naming the variable, which is
+// how a container started without it reports the problem.
+func TestMissingSigningKeyNamesItsVariable(t *testing.T) {
+	t.Parallel()
+
+	_, err := newFromSmartConfig(nil)
+	wantStartupError(t, err, "PIXA_SIGNING_KEY")
+}
+
+// TestSecretsFromEnvironmentAreNotPrinted checks that errors about the
+// signing key and the metrics password name their variables but never
+// print their values.
+func TestSecretsFromEnvironmentAreNotPrinted(t *testing.T) {
+	t.Setenv("PIXA_SIGNING_KEY", "short-signing-secret")
+
+	_, err := newFromSmartConfig(nil)
+	wantStartupError(t, err, "PIXA_SIGNING_KEY")
+
+	if strings.Contains(err.Error(), "short-signing-secret") {
+		t.Errorf("error %q prints the signing key", err.Error())
+	}
+
+	t.Setenv("PIXA_SIGNING_KEY", validTestSigningKey)
+	t.Setenv("PIXA_METRICS_PASSWORD", "metrics-password-secret")
+
+	_, err = newFromSmartConfig(nil)
+	wantStartupError(t, err, "PIXA_METRICS_PASSWORD")
+
+	if strings.Contains(err.Error(), "metrics-password-secret") {
+		t.Errorf("error %q prints the metrics password", err.Error())
+	}
+}

internal/handlers/auth.go

@@ -1,8 +1,12 @@
 package handlers
 
 import (
+	"bytes"
 	"crypto/subtle"
+	"errors"
+	"fmt"
 	"html/template"
+	"math"
 	"net/http"
 	"net/url"
 	"strconv"
@@ -14,6 +18,20 @@ import (
 	"sneak.berlin/go/pixa/internal/templates"
 )
 
+// errInvalidFormField reports a generator form field, or the q or exp
+// parameter of /v1/image/, whose value is non-numeric or out of range. The
+// offending field name is wrapped in so the response can name it.
+var errInvalidFormField = errors.New("invalid")
+
+// Bounds for the generator's quality and ttl fields; the quality bounds also
+// apply to the q parameter of /v1/image/. maxTTL is in seconds: the expiry
+// calculation time.Duration(ttl) * time.Second overflows above it.
+const (
+	minQuality = 1
+	maxQuality = 100
+	maxTTL     = int(math.MaxInt64 / time.Second)
+)
+
 // HandleRoot serves the login page or generator page based on authentication state.
 func (s *Handlers) HandleRoot() http.HandlerFunc {
 	return func(w http.ResponseWriter, r *http.Request) {
@@ -101,18 +119,26 @@ func (s *Handlers) HandleGenerateURL() http.HandlerFunc {
 		// Validate source URL
 		parsed, err := url.Parse(sourceURL)
 		if err != nil || parsed.Host == "" {
-			s.renderGeneratorWithForm(w, r, "Invalid source URL", r.Form)
+			s.renderGeneratorWithForm(w, r, "Invalid source URL", r.Form,
+				http.StatusBadRequest)
 
 			return
 		}
 
-		payload, expiresAt, ttl := buildGeneratePayload(parsed, r.Form)
+		payload, expiresAt, ttl, err := buildGeneratePayload(parsed, r.Form)
+		if err != nil {
+			s.renderGeneratorWithForm(w, r, err.Error(), r.Form,
+				http.StatusBadRequest)
+
+			return
+		}
 
 		// Generate encrypted token
 		token, err := s.encGen.Generate(payload)
 		if err != nil {
 			s.log.Error("failed to generate encrypted URL", "error", err)
-			s.renderGeneratorWithForm(w, r, "Failed to generate URL", r.Form)
+			s.renderGeneratorWithForm(w, r, "Failed to generate URL", r.Form,
+				http.StatusInternalServerError)
 
 			return
 		}
@@ -140,17 +166,40 @@ func (s *Handlers) HandleGenerateURL() http.HandlerFunc {
 }
 
 // buildGeneratePayload parses the numeric form fields and assembles the
-// encrypted URL payload. ttl=0 means never expires (ExpiresAt stays 0).
+// encrypted URL payload. ttl=0 means never expires (ExpiresAt stays 0). A
+// non-numeric or out-of-range width, height, quality or ttl, or an
+// unrecognized fit mode, is a client error naming the offending field. The
+// format field is passed through unchecked.
 func buildGeneratePayload(
 	parsed *url.URL, form url.Values,
-) (*encurl.Payload, time.Time, int) {
+) (*encurl.Payload, time.Time, int, error) {
-	width, _ := strconv.Atoi(form.Get("width"))
+	width, err := parseFormDimension(form, "width")
-	height, _ := strconv.Atoi(form.Get("height"))
+	if err != nil {
-	quality, _ := strconv.Atoi(form.Get("quality"))
+		return nil, time.Time{}, 0, err
-	ttl, _ := strconv.Atoi(form.Get("ttl"))
+	}
 
-	if quality <= 0 {
+	height, err := parseFormDimension(form, "height")
-		quality = 85
+	if err != nil {
+		return nil, time.Time{}, 0, err
+	}
+
+	quality, err := parseFormInt(form, "quality",
+		encurl.DefaultQuality, minQuality, maxQuality)
+	if err != nil {
+		return nil, time.Time{}, 0, err
+	}
+
+	ttl, err := parseFormInt(form, "ttl", 0, 0, maxTTL)
+	if err != nil {
+		return nil, time.Time{}, 0, err
+	}
+
+	fitMode := imgcache.FitMode(form.Get("fit"))
+
+	err = imgcache.ValidateFitMode(fitMode)
+	if err != nil {
+		return nil, time.Time{}, 0,
+			fmt.Errorf("%w: %s", imgcache.ErrInvalidFitMode, form.Get("fit"))
 	}
 
 	var (
@@ -171,11 +220,57 @@ func buildGeneratePayload(
 		Height:      height,
 		Format:      imgcache.ImageFormat(form.Get("format")),
 		Quality:     quality,
-		FitMode:     imgcache.FitMode(form.Get("fit")),
+		FitMode:     fitMode,
 		ExpiresAt:   expiresAtUnix,
 	}
 
-	return payload, expiresAt, ttl
+	return payload, expiresAt, ttl, nil
+}
+
+// parseFormDimension reads an optional width or height form field. An empty
+// value means "original size" (0). A non-numeric value, or one
+// imgcache.ValidateDimension rejects, is an error naming the field.
+func parseFormDimension(form url.Values, field string) (int, error) {
+	raw := form.Get(field)
+	if raw == "" {
+		return 0, nil
+	}
+
+	value, err := strconv.Atoi(raw)
+	if err != nil {
+		return 0, fmt.Errorf("%w %s: not a number", errInvalidFormField, field)
+	}
+
+	err = imgcache.ValidateDimension(field, value)
+	if err != nil {
+		return 0, err
+	}
+
+	return value, nil
+}
+
+// parseFormInt reads an optional integer form field or URL query parameter,
+// returning def when the field is empty and an error naming the field when the
+// value is non-numeric or outside minValue to maxValue.
+func parseFormInt(
+	form url.Values, field string, def, minValue, maxValue int,
+) (int, error) {
+	raw := form.Get(field)
+	if raw == "" {
+		return def, nil
+	}
+
+	value, err := strconv.Atoi(raw)
+	if err != nil {
+		return 0, fmt.Errorf("%w %s: not a number", errInvalidFormField, field)
+	}
+
+	if value < minValue || value > maxValue {
+		return 0, fmt.Errorf("%w %s: must be from %d to %d",
+			errInvalidFormField, field, minValue, maxValue)
+	}
+
+	return value, nil
 }
 
 // generatorData holds template data for the generator page.
@@ -215,6 +310,15 @@ func (s *Handlers) renderLogin(
 
 func (s *Handlers) renderGenerator(
 	w http.ResponseWriter, r *http.Request, data *generatorData,
+) {
+	s.renderGeneratorStatus(w, r, data, http.StatusOK)
+}
+
+// renderGeneratorStatus renders the generator page with an explicit HTTP
+// status; a rejected form uses 400. The page is rendered into a buffer before
+// the status is written, so a template failure can still answer 500.
+func (s *Handlers) renderGeneratorStatus(
+	w http.ResponseWriter, r *http.Request, data *generatorData, status int,
 ) {
 	w.Header().Set("Content-Type", "text/html; charset=utf-8")
 
@@ -224,17 +328,29 @@ func (s *Handlers) renderGenerator(
 
 	data.CSRFField = csrfField(r)
 
-	err := templates.Render(w, "generator.html", data)
+	var page bytes.Buffer
+
+	err := templates.Render(&page, "generator.html", data)
 	if err != nil {
 		s.log.Error("failed to render generator template", "error", err)
 		http.Error(w, "Internal server error", http.StatusInternalServerError)
+
+		return
+	}
+
+	w.WriteHeader(status)
+
+	_, err = page.WriteTo(w)
+	if err != nil {
+		s.log.Error("failed to write generator page", "error", err)
 	}
 }
 
 func (s *Handlers) renderGeneratorWithForm(
-	w http.ResponseWriter, r *http.Request, errorMsg string, form url.Values,
+	w http.ResponseWriter, r *http.Request, errorMsg string,
+	form url.Values, status int,
 ) {
-	s.renderGenerator(w, r, &generatorData{
+	s.renderGeneratorStatus(w, r, &generatorData{
 		Error:       errorMsg,
 		FormURL:     form.Get("url"),
 		FormWidth:   form.Get("width"),
@@ -243,7 +359,7 @@ func (s *Handlers) renderGeneratorWithForm(
 		FormQuality: form.Get("quality"),
 		FormFit:     form.Get("fit"),
 		FormTTL:     form.Get("ttl"),
-	})
+	}, status)
 }
 
 func (s *Handlers) buildGeneratedURL(r *http.Request, token, format string) string {

internal/handlers/auth_generate_internal_test.go

@@ -0,0 +1,163 @@
+package handlers
+
+import (
+	"maps"
+	"net/http"
+	"net/http/httptest"
+	"net/url"
+	"strconv"
+	"strings"
+	"testing"
+	"time"
+
+	"sneak.berlin/go/pixa/internal/encurl"
+	"sneak.berlin/go/pixa/internal/imgcache"
+)
+
+// Generator form field names, and a value that is not a number.
+const (
+	widthField   = "width"
+	heightField  = "height"
+	qualityField = "quality"
+	ttlField     = "ttl"
+	fitField     = "fit"
+	notANumber   = "abc"
+)
+
+// generatePost submits the /generate form with a valid session and CSRF token
+// plus the caller's extra fields, returning the recorder.
+func generatePost(
+	t *testing.T, extra url.Values,
+) *httptest.ResponseRecorder {
+	t.Helper()
+
+	h, srv := newCSRFTestRouter(t)
+
+	sessionCookie := newSessionCookie(t, h)
+	cookies, token := csrfCredentials(t, srv, []*http.Cookie{sessionCookie})
+	cookies = append(cookies, sessionCookie)
+
+	form := url.Values{
+		sourceURLField: {testSourceURL},
+		csrfTokenField: {token},
+	}
+	maps.Copy(form, extra)
+
+	return postForm(srv, "/generate", cookies, form)
+}
+
+// TestGeneratePostRejectsNonNumericWidth verifies that a non-numeric width is
+// rejected with 400 naming the field rather than being coerced to 0 and
+// minting a 0-width token.
+func TestGeneratePostRejectsNonNumericWidth(t *testing.T) {
+	t.Parallel()
+
+	rec := generatePost(t, url.Values{"width": {"abc"}})
+
+	if rec.Code != http.StatusBadRequest {
+		t.Fatalf("status = %d, want %d", rec.Code, http.StatusBadRequest)
+	}
+
+	if strings.Contains(rec.Body.String(), "/v1/e/") {
+		t.Error("a token was generated for non-numeric width")
+	}
+}
+
+// TestGeneratePostRejectsOverLimitWidth verifies that a width beyond
+// MaxDimension is rejected at generation time so an unusable token cannot be
+// minted.
+func TestGeneratePostRejectsOverLimitWidth(t *testing.T) {
+	t.Parallel()
+
+	rec := generatePost(t, url.Values{"width": {"100000"}})
+
+	if rec.Code != http.StatusBadRequest {
+		t.Fatalf("status = %d, want %d", rec.Code, http.StatusBadRequest)
+	}
+
+	if strings.Contains(rec.Body.String(), "/v1/e/") {
+		t.Error("a token was generated for an over-limit width")
+	}
+}
+
+// TestGeneratePostRejectsBadField verifies that each generator field whose
+// value is not a number, out of range, or unrecognized is rejected with 400,
+// mints no token, and is named in the error shown on the page.
+func TestGeneratePostRejectsBadField(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		field, value, wantError string
+	}{
+		{widthField, notANumber, "invalid width: not a number"},
+		{widthField, "-1", "width is negative"},
+		{widthField, "8193", "width is above 8192"},
+		{heightField, notANumber, "invalid height: not a number"},
+		{heightField, "8193", "height is above 8192"},
+		{qualityField, notANumber, "invalid quality: not a number"},
+		{qualityField, "0", "invalid quality: must be from 1 to 100"},
+		{qualityField, "101", "invalid quality: must be from 1 to 100"},
+		{ttlField, notANumber, "invalid ttl: not a number"},
+		{ttlField, "-1", "invalid ttl: must be from 0 to"},
+		{ttlField, "10000000000", "invalid ttl: must be from 0 to"},
+		{fitField, "bogus", "invalid fit mode: bogus"},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.field+"="+tt.value, func(t *testing.T) {
+			t.Parallel()
+
+			rec := generatePost(t, url.Values{tt.field: {tt.value}})
+			body := rec.Body.String()
+
+			if rec.Code != http.StatusBadRequest {
+				t.Fatalf("status = %d, want %d", rec.Code, http.StatusBadRequest)
+			}
+
+			if strings.Contains(body, "/v1/e/") {
+				t.Error("a token was generated")
+			}
+
+			if !strings.Contains(body, tt.wantError) {
+				t.Errorf("page does not show %q", tt.wantError)
+			}
+		})
+	}
+}
+
+// TestBuildGeneratePayloadDefaultAndLimits verifies that an empty quality
+// takes the default, and that the largest accepted width, height, quality and
+// ttl are accepted with an expiry still in the future.
+func TestBuildGeneratePayloadDefaultAndLimits(t *testing.T) {
+	t.Parallel()
+
+	parsed, err := url.Parse(testSourceURL)
+	if err != nil {
+		t.Fatalf("url.Parse() error = %v", err)
+	}
+
+	payload, _, _, err := buildGeneratePayload(parsed, url.Values{})
+	if err != nil {
+		t.Fatalf("empty form: error = %v", err)
+	}
+
+	if payload.Quality != encurl.DefaultQuality {
+		t.Errorf("empty quality gave %d, want %d",
+			payload.Quality, encurl.DefaultQuality)
+	}
+
+	_, expiresAt, _, err := buildGeneratePayload(parsed, url.Values{
+		widthField:   {strconv.Itoa(imgcache.MaxDimension)},
+		heightField:  {strconv.Itoa(imgcache.MaxDimension)},
+		qualityField: {strconv.Itoa(maxQuality)},
+		ttlField:     {strconv.Itoa(maxTTL)},
+	})
+	if err != nil {
+		t.Fatalf("largest accepted values: error = %v", err)
+	}
+
+	if !expiresAt.After(time.Now()) {
+		t.Errorf("ttl %d gave expiry %v, want a time in the future",
+			maxTTL, expiresAt)
+	}
+}

internal/handlers/handlers_internal_test.go

@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"context"
 	"database/sql"
+	"encoding/json"
 	"image"
 	"image/color"
 	"image/jpeg"
@@ -276,3 +277,120 @@ func TestHandleImage_ETagHeader(t *testing.T) {
 		t.Errorf("ETag should be quoted, got %q", etag)
 	}
 }
+
+// TestHandleImage_InvalidFitMode_Returns400 verifies that the plain image
+// route rejects an unrecognized fit mode with 400.
+func TestHandleImage_InvalidFitMode_Returns400(t *testing.T) {
+	t.Parallel()
+
+	fix := setupTestHandler(t)
+
+	status := getImage(t, fix,
+		"/v1/image/"+fix.goodHost+"/images/photo.jpg/50x50.jpeg?fit=bogus")
+
+	if status != http.StatusBadRequest {
+		t.Fatalf("status = %d, want %d", status, http.StatusBadRequest)
+	}
+}
+
+// TestHandleImage_InvalidQuery_Returns400 verifies that the plain image route
+// answers a q that is not a whole number from 1 to 100, an empty one
+// included, with 400 naming q and the value, a parameter given more than once
+// with 400 naming it, and a query string that cannot be decoded with 400
+// showing it, instead of serving the image at the default quality 85 or at
+// the first value given.
+func TestHandleImage_InvalidQuery_Returns400(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		query, wantError string
+	}{
+		{"q=banana", `invalid q: not a number, got "banana"`},
+		{"q=0", `invalid q: must be from 1 to 100, got "0"`},
+		{"q=101", `invalid q: must be from 1 to 100, got "101"`},
+		{"q=", `invalid q: not a number, got ""`},
+		{"q=80&q=500", `invalid q: given more than once`},
+		{"q=80&q=", `invalid q: given more than once`},
+		{"fit=cover&fit=contain", `invalid fit: given more than once`},
+		{"q=80%", `invalid query string "q=80%": invalid URL escape "%"`},
+		{
+			"q=50;fit=contain",
+			`invalid query string "q=50;fit=contain": ` +
+				`invalid semicolon separator in query`,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.query, func(t *testing.T) {
+			t.Parallel()
+
+			fix := setupTestHandler(t)
+
+			r := chi.NewRouter()
+			r.Get("/v1/image/*", fix.handler.HandleImage())
+
+			req := httptest.NewRequestWithContext(t.Context(), http.MethodGet,
+				"/v1/image/"+fix.goodHost+"/images/photo.jpg/50x50.jpeg?"+tt.query, nil)
+			rec := httptest.NewRecorder()
+
+			r.ServeHTTP(rec, req)
+
+			if rec.Code != http.StatusBadRequest {
+				t.Fatalf("status = %d, want %d", rec.Code, http.StatusBadRequest)
+			}
+
+			t.Logf("GET %s: %d %s", req.URL, rec.Code, rec.Body)
+
+			var body struct {
+				Error string `json:"error"`
+			}
+
+			err := json.NewDecoder(rec.Body).Decode(&body)
+			if err != nil {
+				t.Fatalf("decoding response body: %v", err)
+			}
+
+			if body.Error != tt.wantError {
+				t.Errorf("error = %q, want %q", body.Error, tt.wantError)
+			}
+		})
+	}
+}
+
+// TestHandleImage_EmptyFit_Returns400 verifies that the plain image route
+// answers a fit that is in the URL but empty with 400 naming fit, instead of
+// serving the image as cover. Only a fit missing from the URL means cover.
+func TestHandleImage_EmptyFit_Returns400(t *testing.T) {
+	t.Parallel()
+
+	fix := setupTestHandler(t)
+
+	r := chi.NewRouter()
+	r.Get("/v1/image/*", fix.handler.HandleImage())
+
+	req := httptest.NewRequestWithContext(t.Context(), http.MethodGet,
+		"/v1/image/"+fix.goodHost+"/images/photo.jpg/50x50.jpeg?fit=", nil)
+	rec := httptest.NewRecorder()
+
+	r.ServeHTTP(rec, req)
+
+	if rec.Code != http.StatusBadRequest {
+		t.Fatalf("status = %d, want %d", rec.Code, http.StatusBadRequest)
+	}
+
+	t.Logf("GET %s: %d %s", req.URL, rec.Code, rec.Body)
+
+	var body struct {
+		Error string `json:"error"`
+	}
+
+	err := json.NewDecoder(rec.Body).Decode(&body)
+	if err != nil {
+		t.Fatalf("decoding response body: %v", err)
+	}
+
+	wantError := `invalid fit: not a fit mode, got ""`
+	if body.Error != wantError {
+		t.Errorf("error = %q, want %q", body.Error, wantError)
+	}
+}

internal/handlers/image.go

@@ -2,12 +2,15 @@ package handlers
 
 import (
 	"errors"
+	"fmt"
 	"io"
 	"net/http"
+	"net/url"
 	"strconv"
 	"time"
 
 	"github.com/go-chi/chi/v5"
+	"sneak.berlin/go/pixa/internal/encurl"
 	"sneak.berlin/go/pixa/internal/httpfetcher"
 	"sneak.berlin/go/pixa/internal/imgcache"
 )
@@ -89,39 +92,66 @@ func (s *Handlers) parseImageRequest(
 	// Convert to ImageRequest
 	req := parsed.ToImageRequest()
 
-	// Parse signature params from query string
+	// Parse signature params from query string. r.URL.Query() would silently
-	query := r.URL.Query()
+	// drop a pair it cannot decode, such as q=80%, so that q would be served
-	req.Signature = query.Get("sig")
+	// at 85; a query string that cannot be decoded is refused instead. A
+	// parameter given more than once is refused too, as only its first value
+	// would be read.
+	query, err := url.ParseQuery(r.URL.RawQuery)
+	if err != nil {
+		s.respondError(w, fmt.Sprintf("invalid query string %q: %v",
+			r.URL.RawQuery, err), http.StatusBadRequest)
 
-	if expStr := query.Get("exp"); expStr != "" {
+		return nil, false
-		exp, parseErr := strconv.ParseInt(expStr, 10, 64)
-		if parseErr == nil {
-			req.Expires = time.Unix(exp, 0)
-		}
 	}
 
-	// Parse optional quality and fit params
+	for name, values := range query {
-	if qStr := query.Get("q"); qStr != "" {
+		if len(values) > 1 {
-		q, parseErr := strconv.Atoi(qStr)
+			s.respondError(w, fmt.Sprintf("invalid %s: given more than once",
-		if parseErr == nil && q > 0 && q <= 100 {
+				name), http.StatusBadRequest)
-			req.Quality = q
-		}
-	}
-
-	if fit := query.Get("fit"); fit != "" {
-		req.FitMode = imgcache.FitMode(fit)
-
-		fitErr := imgcache.ValidateFitMode(req.FitMode)
-		if fitErr != nil {
-			s.respondError(w, "invalid fit mode: "+fit, http.StatusBadRequest)
 
 			return nil, false
 		}
 	}
 
-	// Default quality if not set
+	req.Signature = query.Get("sig")
-	if req.Quality == 0 {
+
-		req.Quality = 85
+	req.Expires, err = parseExpires(query)
+	if err != nil {
+		s.respondError(w, err.Error(), http.StatusBadRequest)
+
+		return nil, false
+	}
+
+	// Parse optional quality and fit params. Only a q missing from the URL is
+	// 85. A q in the URL that is not a whole number from 1 to 100, an empty
+	// one included, is refused, checked as the generator checks its quality
+	// field; that check alone would take an empty q as missing.
+	qStr := query.Get("q")
+	if query.Has("q") && qStr == "" {
+		s.respondError(w, `invalid q: not a number, got ""`,
+			http.StatusBadRequest)
+
+		return nil, false
+	}
+
+	req.Quality, err = parseFormInt(query, "q",
+		encurl.DefaultQuality, minQuality, maxQuality)
+	if err != nil {
+		s.respondError(w, fmt.Sprintf("%v, got %q", err, qStr),
+			http.StatusBadRequest)
+
+		return nil, false
+	}
+
+	// Only a fit missing from the URL is cover. A fit in the URL that is not a
+	// fit mode is refused by the fit-mode check below; that check would take an
+	// empty fit as missing, so an empty one is refused here.
+	req.FitMode = imgcache.FitMode(query.Get("fit"))
+	if query.Has("fit") && req.FitMode == "" {
+		s.respondError(w, `invalid fit: not a fit mode, got ""`, http.StatusBadRequest)
+
+		return nil, false
 	}
 
 	// Default fit mode if not set
@@ -129,9 +159,41 @@ func (s *Handlers) parseImageRequest(
 		req.FitMode = imgcache.FitCover
 	}
 
+	// Enforce dimension and fit-mode bounds, shared with the encrypted-URL
+	// route. Dimensions are already bounded by the path parser above; this
+	// also rejects an unrecognized fit mode with 400 instead of letting it
+	// reach the processor as a 500.
+	err = imgcache.ValidateImageRequest(req)
+	if err != nil {
+		s.respondError(w, "invalid image request: "+err.Error(),
+			http.StatusBadRequest)
+
+		return nil, false
+	}
+
 	return req, true
 }
 
+// parseExpires reads the exp query parameter, a Unix time in seconds. An exp
+// missing from the URL gives the zero time, which the signature check takes
+// as no expiration. An exp in the URL that is not a whole number, an empty
+// one included, is an error naming exp and the value.
+func parseExpires(query url.Values) (time.Time, error) {
+	if !query.Has("exp") {
+		return time.Time{}, nil
+	}
+
+	expStr := query.Get("exp")
+
+	exp, err := strconv.ParseInt(expStr, 10, 64)
+	if err != nil {
+		return time.Time{}, fmt.Errorf("%w exp: not a number, got %q",
+			errInvalidFormField, expStr)
+	}
+
+	return time.Unix(exp, 0), nil
+}
+
 // respondImageError maps image retrieval errors to HTTP responses.
 func (s *Handlers) respondImageError(
 	w http.ResponseWriter, req *imgcache.ImageRequest, err error,

internal/handlers/image_signature_internal_test.go

@@ -0,0 +1,171 @@
+package handlers
+
+import (
+	"encoding/json"
+	"fmt"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+	"time"
+
+	"github.com/go-chi/chi/v5"
+	"sneak.berlin/go/pixa/internal/imgcache"
+	"sneak.berlin/go/pixa/internal/signature"
+)
+
+// signedHost is not on the allowlist setupTestHandler builds, so a request
+// for it needs a valid signature. No image is served for it: a request that
+// passes the signature check gets 502 from the failed fetch, and one that
+// fails the check gets 401.
+const signedHost = "signed.example.com"
+
+// getImage sends a GET for target to the image route of fix and returns the
+// response status.
+func getImage(t *testing.T, fix *testFixtures, target string) int {
+	t.Helper()
+
+	r := chi.NewRouter()
+	r.Get("/v1/image/*", fix.handler.HandleImage())
+
+	req := httptest.NewRequestWithContext(t.Context(), http.MethodGet, target, nil)
+	rec := httptest.NewRecorder()
+
+	r.ServeHTTP(rec, req)
+	t.Logf("GET %s: %d", target, rec.Code)
+
+	return rec.Code
+}
+
+// TestHandleImage_SignatureCoversQualityAndFit signs a URL for quality 85
+// and fit cover, the values the route uses when a URL has no q or fit, and
+// sends that signature with each q and fit below.
+func TestHandleImage_SignatureCoversQualityAndFit(t *testing.T) {
+	t.Parallel()
+
+	expires := time.Now().Add(time.Hour)
+	signer := signature.New("test-signing-key-must-be-32-chars")
+	sig := signer.Sign(&signature.Request{
+		SourceHost: signedHost,
+		SourcePath: "/images/photo.jpg",
+		Width:      50,
+		Height:     50,
+		Format:     string(imgcache.FormatJPEG),
+		Quality:    85,
+		FitMode:    string(imgcache.FitCover),
+		Expires:    expires,
+	})
+	signedURL := fmt.Sprintf("/v1/image/%s/images/photo.jpg/50x50.jpeg?sig=%s&exp=%d",
+		signedHost, sig, expires.Unix())
+
+	tests := []struct {
+		name       string
+		query      string
+		wantStatus int
+	}{
+		{"no q or fit", "", http.StatusBadGateway},
+		{"q=85 and fit=cover", "&q=85&fit=cover", http.StatusBadGateway},
+		{"replayed with q=40", "&q=40", http.StatusUnauthorized},
+		{"replayed with fit=contain", "&fit=contain", http.StatusUnauthorized},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+
+			status := getImage(t, setupTestHandler(t), signedURL+tt.query)
+			if status != tt.wantStatus {
+				t.Errorf("status = %d, want %d", status, tt.wantStatus)
+			}
+		})
+	}
+}
+
+// TestHandleImage_GeneratedSignedURLVerifies sends URLs built by the
+// service's signed-URL generator to the route.
+func TestHandleImage_GeneratedSignedURLVerifies(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		name    string
+		quality int
+		fitMode imgcache.FitMode
+	}{
+		{"quality 40 and fit contain", 40, imgcache.FitContain},
+		{"quality and fit unset", 0, ""},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+
+			fix := setupTestHandler(t)
+
+			signedURL, err := fix.service.GenerateSignedURL("", &imgcache.ImageRequest{
+				SourceHost: signedHost,
+				SourcePath: "/images/photo.jpg",
+				Size:       imgcache.Size{Width: 50, Height: 50},
+				Format:     imgcache.FormatJPEG,
+				Quality:    tt.quality,
+				FitMode:    tt.fitMode,
+			}, time.Hour)
+			if err != nil {
+				t.Fatalf("GenerateSignedURL() error = %v", err)
+			}
+
+			status := getImage(t, fix, signedURL)
+			if status != http.StatusBadGateway {
+				t.Errorf("status = %d, want %d", status, http.StatusBadGateway)
+			}
+		})
+	}
+}
+
+// TestHandleImage_InvalidExp_Returns400 sends a signed-host URL whose exp is
+// not a whole number, and one whose exp is empty. Each is refused with 400
+// naming exp and the value, not with the 401 a URL without exp still gets.
+func TestHandleImage_InvalidExp_Returns400(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		query      string
+		wantStatus int
+		wantError  string
+	}{
+		{"sig=x&exp=banana", http.StatusBadRequest,
+			`invalid exp: not a number, got "banana"`},
+		{"sig=x&exp=", http.StatusBadRequest, `invalid exp: not a number, got ""`},
+		{"sig=x", http.StatusUnauthorized, "unauthorized"},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.query, func(t *testing.T) {
+			t.Parallel()
+
+			fix := setupTestHandler(t)
+
+			r := chi.NewRouter()
+			r.Get("/v1/image/*", fix.handler.HandleImage())
+
+			req := httptest.NewRequestWithContext(t.Context(), http.MethodGet,
+				"/v1/image/"+signedHost+"/images/photo.jpg/50x50.jpeg?"+tt.query, nil)
+			rec := httptest.NewRecorder()
+
+			r.ServeHTTP(rec, req)
+			t.Logf("GET %s: %d %s", req.URL, rec.Code, rec.Body)
+
+			var body struct {
+				Error string `json:"error"`
+			}
+
+			err := json.NewDecoder(rec.Body).Decode(&body)
+			if err != nil {
+				t.Fatalf("decoding response body: %v", err)
+			}
+
+			if rec.Code != tt.wantStatus || body.Error != tt.wantError {
+				t.Errorf("got %d %q, want %d %q",
+					rec.Code, body.Error, tt.wantStatus, tt.wantError)
+			}
+		})
+	}
+}

internal/handlers/imageenc.go

@@ -50,6 +50,19 @@ func (s *Handlers) HandleImageEnc() http.HandlerFunc {
 		// Convert payload to ImageRequest
 		req := payload.ToImageRequest()
 
+		// Apply the same dimension and fit-mode bounds as the plain image
+		// route: a sealed payload is trusted for its origin, not for staying
+		// within limits, so an over-limit size or unknown fit mode is a 400
+		// here rather than an out-of-memory or a 500 from the processor.
+		err = imgcache.ValidateImageRequest(req)
+		if err != nil {
+			s.log.Debug("encrypted URL failed validation", "error", err)
+			s.respondError(w, "invalid encrypted URL: "+err.Error(),
+				http.StatusBadRequest)
+
+			return
+		}
+
 		// Log the request
 		s.log.Debug("encrypted image request",
 			"host", req.SourceHost,

internal/handlers/imageenc_internal_test.go

@@ -0,0 +1,98 @@
+package handlers
+
+import (
+	"context"
+	"log/slog"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"github.com/go-chi/chi/v5"
+
+	"sneak.berlin/go/pixa/internal/encurl"
+	"sneak.berlin/go/pixa/internal/imgcache"
+)
+
+// newEncTestServer builds a router serving the encrypted-URL route with a
+// generator seeded by the shared test signing key. The image service is left
+// nil: these tests exercise validation that rejects a token before any image
+// is fetched, so the handler must never reach the service.
+func newEncTestServer(t *testing.T) (*encurl.Generator, http.Handler) {
+	t.Helper()
+
+	encGen, err := encurl.NewGenerator(testSigningKey)
+	if err != nil {
+		t.Fatalf("encurl.NewGenerator() error = %v", err)
+	}
+
+	h := &Handlers{
+		log:    slog.New(slog.DiscardHandler),
+		encGen: encGen,
+	}
+
+	r := chi.NewRouter()
+	r.Get("/v1/e/{token}/*", h.HandleImageEnc())
+
+	return encGen, r
+}
+
+// getEncToken issues a GET for the given token and returns the recorder.
+func getEncToken(srv http.Handler, token string) *httptest.ResponseRecorder {
+	req := httptest.NewRequestWithContext(
+		context.Background(), http.MethodGet, "/v1/e/"+token+"/img.jpg", nil)
+	rec := httptest.NewRecorder()
+	srv.ServeHTTP(rec, req)
+
+	return rec
+}
+
+// TestHandleImageEnc_OverLimitDimension_Returns400 verifies that a decrypted
+// token requesting a dimension beyond MaxDimension is rejected with 400
+// instead of reaching the image processor and libvips.
+func TestHandleImageEnc_OverLimitDimension_Returns400(t *testing.T) {
+	t.Parallel()
+
+	encGen, srv := newEncTestServer(t)
+
+	token, err := encGen.Generate(&encurl.Payload{
+		SourceHost: "cdn.example.com",
+		SourcePath: "/photo.jpg",
+		Width:      100000,
+		Height:     100000,
+	})
+	if err != nil {
+		t.Fatalf("Generate() error = %v", err)
+	}
+
+	rec := getEncToken(srv, token)
+
+	if rec.Code != http.StatusBadRequest {
+		t.Fatalf("status = %d, want %d", rec.Code, http.StatusBadRequest)
+	}
+}
+
+// TestHandleImageEnc_InvalidFitMode_Returns400 verifies that a decrypted token
+// carrying an unrecognized fit mode is rejected with 400 rather than surfacing
+// as a 500 from the image processor's default branch.
+func TestHandleImageEnc_InvalidFitMode_Returns400(t *testing.T) {
+	t.Parallel()
+
+	encGen, srv := newEncTestServer(t)
+
+	token, err := encGen.Generate(&encurl.Payload{
+		SourceHost: "cdn.example.com",
+		SourcePath: "/photo.jpg",
+		Width:      800,
+		Height:     600,
+		FitMode:    imgcache.FitMode("bogus"),
+	})
+	if err != nil {
+		t.Fatalf("Generate() error = %v", err)
+	}
+
+	rec := getEncToken(srv, token)
+
+	if rec.Code != http.StatusBadRequest {
+		t.Fatalf("status = %d, want %d", rec.Code, http.StatusBadRequest)
+	}
+}

internal/imageprocessor/imageprocessor.go

@@ -161,6 +161,13 @@ func (p *ImageProcessor) Process(
 	}
 	defer img.Close()
 
+	// Turn the image upright now: encode strips the EXIF orientation tag,
+	// and sizes below must be worked out on the upright image.
+	err = img.AutoRotate()
+	if err != nil {
+		return nil, fmt.Errorf("failed to auto-rotate: %w", err)
+	}
+
 	// Get original dimensions
 	origWidth := img.Width()
 	origHeight := img.Height()
@@ -404,6 +411,21 @@ func (p *ImageProcessor) encode(
 		return nil, fmt.Errorf("%w: %s", ErrUnsupportedOutputFormat, format)
 	}
 
+	// Stripping drops the ICC profile as well, and clients show an image
+	// with no profile as sRGB, so convert to sRGB first. "srgb" names
+	// libvips' built-in profile; govips' own sRGB path variable is set on
+	// first use but read without a lock, so concurrent requests race on it.
+	if img.HasICCProfile() {
+		err := img.TransformICCProfileWithFallback("srgb", "srgb")
+		if err != nil {
+			return nil, fmt.Errorf("failed to convert to sRGB: %w", err)
+		}
+	}
+
+	// Drop EXIF, XMP, IPTC and the ICC profile. govips ignores this for
+	// GIF, which carries none of them.
+	params.StripMetadata = true
+
 	output, _, err := img.Export(&params)
 	if err != nil {
 		return nil, err

internal/imageprocessor/imageprocessor_internal_test.go

@@ -9,7 +9,9 @@ import (
 	"image/jpeg"
 	"image/png"
 	"io"
+	"math"
 	"os"
+	"slices"
 	"testing"
 
 	"github.com/davidbyttow/govips/v2/vips"
@@ -561,3 +563,152 @@ func TestImageProcessor_EncodeAVIF(t *testing.T) {
 
 	encodeAndCheck(t, FormatAVIF, 85, mimeAVIF)
 }
+
+// processAndDecode runs input through Process and decodes the output with
+// vips, so a test can inspect the image a client would receive.
+func processAndDecode(t *testing.T, input []byte, req *Request) *vips.ImageRef {
+	t.Helper()
+
+	result, err := New(Params{}).Process(
+		context.Background(), bytes.NewReader(input), req,
+	)
+	if err != nil {
+		t.Fatalf("Process() error = %v", err)
+	}
+
+	defer func() { _ = result.Content.Close() }()
+
+	data, err := io.ReadAll(result.Content)
+	if err != nil {
+		t.Fatalf("failed to read result: %v", err)
+	}
+
+	output, err := vips.NewImageFromBuffer(data)
+	if err != nil {
+		t.Fatalf("failed to decode output: %v", err)
+	}
+
+	t.Cleanup(output.Close)
+
+	return output
+}
+
+func TestImageProcessor_StripsEXIF(t *testing.T) {
+	t.Parallel()
+
+	// gps-exif.jpg carries GPS coordinates, a camera make, model and serial
+	// number, and a capture time.
+	input, err := os.ReadFile("testdata/gps-exif.jpg")
+	if err != nil {
+		t.Fatalf("failed to read test JPEG: %v", err)
+	}
+
+	fixture, err := vips.NewImageFromBuffer(input)
+	if err != nil {
+		t.Fatalf("failed to decode test JPEG: %v", err)
+	}
+
+	t.Cleanup(fixture.Close)
+
+	if !slices.Contains(fixture.GetFields(), "exif-ifd3-GPSLatitude") {
+		t.Fatal("testdata/gps-exif.jpg has no GPS latitude")
+	}
+
+	formats := []Format{
+		FormatJPEG, FormatPNG, FormatWebP, FormatAVIF, FormatGIF, FormatOriginal,
+	}
+
+	for _, format := range formats {
+		t.Run(string(format), func(t *testing.T) {
+			t.Parallel()
+
+			output := processAndDecode(t, input, &Request{Format: format})
+
+			if output.HasExif() {
+				t.Errorf("output has EXIF: %v", output.GetExif())
+			}
+		})
+	}
+}
+
+func TestImageProcessor_AppliesEXIFOrientation(t *testing.T) {
+	t.Parallel()
+
+	// orientation-6.jpg is stored 16x8, red on the left and blue on the
+	// right, with EXIF orientation 6 (turn 90 degrees clockwise to view).
+	// Upright it is 8x16, red on top and blue below.
+	input, err := os.ReadFile("testdata/orientation-6.jpg")
+	if err != nil {
+		t.Fatalf("failed to read test JPEG: %v", err)
+	}
+
+	tests := []struct {
+		name  string
+		size  Size
+		wantW int
+		wantH int
+	}{
+		{name: "original size", size: Size{}, wantW: 8, wantH: 16},
+		{name: "width only", size: Size{Width: 4}, wantW: 4, wantH: 8},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+
+			output := processAndDecode(t, input, &Request{
+				Size:   tt.size,
+				Format: FormatPNG,
+			})
+
+			if output.Width() != tt.wantW || output.Height() != tt.wantH {
+				t.Fatalf("output is %dx%d, want %dx%d",
+					output.Width(), output.Height(), tt.wantW, tt.wantH)
+			}
+
+			top, err := output.GetPoint(tt.wantW/2, 0)
+			if err != nil {
+				t.Fatalf("GetPoint() error = %v", err)
+			}
+
+			bottom, err := output.GetPoint(tt.wantW/2, tt.wantH-1)
+			if err != nil {
+				t.Fatalf("GetPoint() error = %v", err)
+			}
+
+			if top[0] <= top[2] || bottom[2] <= bottom[0] {
+				t.Errorf("top pixel = %v, bottom pixel = %v, want red above blue",
+					top, bottom)
+			}
+		})
+	}
+}
+
+func TestImageProcessor_ConvertsWideGamutToSRGB(t *testing.T) {
+	t.Parallel()
+
+	// display-p3.jpg is a flat 8x8 image with the Display P3 profile
+	// embedded, filled with Display P3 (234, 51, 35), which is sRGB red.
+	input, err := os.ReadFile("testdata/display-p3.jpg")
+	if err != nil {
+		t.Fatalf("failed to read test JPEG: %v", err)
+	}
+
+	output := processAndDecode(t, input, &Request{Format: FormatPNG})
+
+	if output.HasICCProfile() {
+		t.Error("output has an ICC profile")
+	}
+
+	pixel, err := output.GetPoint(4, 4)
+	if err != nil {
+		t.Fatalf("GetPoint() error = %v", err)
+	}
+
+	want := []float64{255, 0, 0}
+	for i := range want {
+		if math.Abs(pixel[i]-want[i]) > 5 {
+			t.Fatalf("pixel = %v, want within 5 of %v", pixel, want)
+		}
+	}
+}

internal/imgcache/cache.go

@@ -125,7 +125,7 @@ func NewCache(db *sql.DB, config CacheConfig) (*Cache, error) {
 	}
 
 	variants, err := NewVariantStorage(
-		filepath.Join(config.StateDir, "cache", "variants"),
+		filepath.Join(config.StateDir, "cache", "variants"), log,
 	)
 	if err != nil {
 		return nil, fmt.Errorf("failed to create variant storage: %w", err)
@@ -263,23 +263,7 @@ func (c *Cache) StoreSource(
 		return "", fmt.Errorf("failed to insert source metadata: %w", err)
 	}
 
-	// Store metadata JSON file
+	c.writeMetadataSidecar(req, pathHash, contentHash, result)
-	meta := &SourceMetadata{
-		Host:            req.SourceHost,
-		Path:            req.SourcePath,
-		Query:           req.SourceQuery,
-		ContentHash:     string(contentHash),
-		StatusCode:      result.StatusCode,
-		ContentType:     result.ContentType,
-		ContentLength:   result.ContentLength,
-		ResponseHeaders: result.Headers,
-		FetchedAt:       time.Now().UTC().Unix(),
-		FetchDurationMs: result.FetchDurationMs,
-		RemoteAddr:      result.RemoteAddr,
-	}
-
-	// A failure here is non-fatal; the metadata is in the database.
-	_ = c.srcMetadata.Store(req.SourceHost, pathHash, meta)
 
 	c.notifyWritePressure()
 
@@ -436,12 +420,19 @@ func (c *Cache) Stats(ctx context.Context) (*CacheStats, error) {
 	}
 
 	// Get actual item count and total size from content tables
-	_ = c.db.QueryRowContext(ctx,
+	err = c.db.QueryRowContext(ctx,
 		`SELECT COUNT(*) FROM request_cache`,
 	).Scan(&stats.TotalItems)
-	_ = c.db.QueryRowContext(ctx,
+	if err != nil {
+		c.log.Warn("failed to count cache items for stats", "error", err)
+	}
+
+	err = c.db.QueryRowContext(ctx,
 		`SELECT COALESCE(SUM(size_bytes), 0) FROM output_content`,
 	).Scan(&stats.TotalSizeBytes)
+	if err != nil {
+		c.log.Warn("failed to sum cache size for stats", "error", err)
+	}
 
 	// Compute hit rate as a ratio
 	if stats.HitCount+stats.MissCount > 0 {
@@ -453,15 +444,17 @@ func (c *Cache) Stats(ctx context.Context) (*CacheStats, error) {
 
 // IncrementStats increments cache statistics.
 func (c *Cache) IncrementStats(ctx context.Context, hit bool, fetchBytes int64) {
+	var err error
+
 	if hit {
-		_, _ = c.db.ExecContext(ctx, `
+		_, err = c.db.ExecContext(ctx, `
 			UPDATE cache_stats
 			SET hit_count = hit_count + 1,
 			    last_updated_at = CURRENT_TIMESTAMP
 			WHERE id = 1
 		`)
 	} else {
-		_, _ = c.db.ExecContext(ctx, `
+		_, err = c.db.ExecContext(ctx, `
 			UPDATE cache_stats
 			SET miss_count = miss_count + 1,
 			    last_updated_at = CURRENT_TIMESTAMP
@@ -469,14 +462,52 @@ func (c *Cache) IncrementStats(ctx context.Context, hit bool, fetchBytes int64)
 		`)
 	}
 
+	if err != nil {
+		c.log.Warn("failed to count cache hit or miss", "hit", hit, "error", err)
+	}
+
 	if fetchBytes > 0 {
-		_, _ = c.db.ExecContext(ctx, `
+		_, err = c.db.ExecContext(ctx, `
 			UPDATE cache_stats
 			SET upstream_fetch_count = upstream_fetch_count + 1,
 			    upstream_fetch_bytes = upstream_fetch_bytes + ?,
 			    last_updated_at = CURRENT_TIMESTAMP
 			WHERE id = 1
 		`, fetchBytes)
+		if err != nil {
+			c.log.Warn("failed to count upstream fetch",
+				"fetch_bytes", fetchBytes, "error", err)
+		}
+	}
+}
+
+// writeMetadataSidecar writes the JSON metadata sidecar of a stored source.
+// A failure is logged and is otherwise non-fatal; the metadata is in the
+// database.
+func (c *Cache) writeMetadataSidecar(
+	req *ImageRequest,
+	pathHash PathHash,
+	contentHash ContentHash,
+	result *httpfetcher.FetchResult,
+) {
+	meta := &SourceMetadata{
+		Host:            req.SourceHost,
+		Path:            req.SourcePath,
+		Query:           req.SourceQuery,
+		ContentHash:     string(contentHash),
+		StatusCode:      result.StatusCode,
+		ContentType:     result.ContentType,
+		ContentLength:   result.ContentLength,
+		ResponseHeaders: result.Headers,
+		FetchedAt:       time.Now().UTC().Unix(),
+		FetchDurationMs: result.FetchDurationMs,
+		RemoteAddr:      result.RemoteAddr,
+	}
+
+	err := c.srcMetadata.Store(req.SourceHost, pathHash, meta)
+	if err != nil {
+		c.log.Warn("failed to write metadata sidecar",
+			"host", req.SourceHost, "path_hash", pathHash, "error", err)
 	}
 }
 
@@ -528,10 +559,14 @@ func (c *Cache) checkNegativeCache(
 	// Check if expired
 	if time.Now().After(expiresAt) {
 		// Clean up expired entry
-		_, _ = c.db.ExecContext(ctx, `
+		_, err = c.db.ExecContext(ctx, `
 			DELETE FROM negative_cache
 			WHERE source_host = ? AND source_path = ? AND source_query = ?
 		`, req.SourceHost, req.SourcePath, req.SourceQuery)
+		if err != nil {
+			c.log.Warn("failed to delete expired negative cache entry",
+				"host", req.SourceHost, "path", req.SourcePath, "error", err)
+		}
 
 		return false, nil
 	}

internal/imgcache/imgcache.go

@@ -59,6 +59,24 @@ func ValidateFitMode(fit FitMode) error {
 	}
 }
 
+// ValidateImageRequest checks a request's width and height with
+// ValidateDimension and its fit mode with ValidateFitMode. Both the plain
+// /v1/image/ route and the encrypted /v1/e/ route validate through this
+// function so a request from either source enforces identical bounds.
+func ValidateImageRequest(req *ImageRequest) error {
+	err := ValidateDimension("width", req.Size.Width)
+	if err != nil {
+		return err
+	}
+
+	err = ValidateDimension("height", req.Size.Height)
+	if err != nil {
+		return err
+	}
+
+	return ValidateFitMode(req.FitMode)
+}
+
 // ImageRequest represents a request for a processed image
 type ImageRequest struct {
 	// SourceHost is the origin host (e.g., "cdn.example.com")

internal/imgcache/service.go

@@ -205,12 +205,23 @@ func (s *Service) ValidateRequest(req *ImageRequest) error {
 	return s.signer.Verify(signatureRequest(req))
 }
 
-// GenerateSignedURL generates a signed URL for the given request.
+// GenerateSignedURL generates a signed URL for the given request. The URL
+// carries q and fit next to sig and exp, so the image route verifies it for
+// the quality and fit it was signed with. An unset quality or fit is first
+// set to 85 or cover, the values the route uses when a URL has no q or fit.
 func (s *Service) GenerateSignedURL(
 	baseURL string,
 	req *ImageRequest,
 	ttl time.Duration,
 ) (string, error) {
+	if req.Quality == 0 {
+		req.Quality = 85
+	}
+
+	if req.FitMode == "" {
+		req.FitMode = FitCover
+	}
+
 	sigReq := signatureRequest(req)
 	path, sig, exp := s.signer.GenerateSignedURL(sigReq, ttl)
 
@@ -218,7 +229,8 @@ func (s *Service) GenerateSignedURL(
 	req.Expires = sigReq.Expires
 	req.Signature = sigReq.Signature
 
-	return fmt.Sprintf("%s%s?sig=%s&exp=%d", baseURL, path, sig, exp), nil
+	return fmt.Sprintf("%s%s?sig=%s&exp=%d&q=%d&fit=%s",
+		baseURL, path, sig, exp, req.Quality, req.FitMode), nil
 }
 
 // loadCachedSource attempts to load source content from cache, returning nil
@@ -310,7 +322,12 @@ func (s *Service) fetchAndProcess(
 		// Store negative cache for certain errors
 		if isNegativeCacheable(err) {
 			statusCode := extractStatusCode(err)
-			_ = s.cache.StoreNegative(ctx, req, statusCode, err.Error())
+
+			storeErr := s.cache.StoreNegative(ctx, req, statusCode, err.Error())
+			if storeErr != nil {
+				s.log.Warn("failed to store negative cache entry",
+					"host", req.SourceHost, "path", req.SourcePath, "error", storeErr)
+			}
 		}
 
 		return nil, fmt.Errorf("upstream fetch failed: %w", err)
@@ -452,6 +469,8 @@ func signatureRequest(req *ImageRequest) *signature.Request {
 		Width:       req.Size.Width,
 		Height:      req.Size.Height,
 		Format:      string(req.Format),
+		Quality:     req.Quality,
+		FitMode:     string(req.FitMode),
 		Signature:   req.Signature,
 		Expires:     req.Expires,
 	}

internal/imgcache/stats_internal_test.go

@@ -1,9 +1,12 @@
 package imgcache
 
 import (
+	"bytes"
 	"context"
 	"database/sql"
+	"log/slog"
 	"math"
+	"strings"
 	"testing"
 	"time"
 
@@ -101,3 +104,82 @@ func TestStats_ZeroCounts(t *testing.T) {
 		t.Errorf("HitRate = %f, want 0.0 for zero counts", stats.HitRate)
 	}
 }
+
+// TestStats_LogsFailedCountQueries verifies that a failed item count query
+// and a failed size query are each logged at warn and Stats still succeeds.
+func TestStats_LogsFailedCountQueries(t *testing.T) {
+	t.Parallel()
+
+	db := setupStatsTestDB(t)
+
+	var logBuf bytes.Buffer
+
+	cache, err := NewCache(db, CacheConfig{
+		StateDir:    t.TempDir(),
+		CacheTTL:    time.Hour,
+		NegativeTTL: 5 * time.Minute,
+		Logger:      slog.New(slog.NewJSONHandler(&logBuf, nil)),
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	_, err = db.ExecContext(t.Context(),
+		`DROP TABLE request_cache; DROP TABLE output_content`)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	_, err = cache.Stats(t.Context())
+	if err != nil {
+		t.Fatalf("Stats() error = %v, want nil", err)
+	}
+
+	for _, msg := range []string{
+		"failed to count cache items for stats",
+		"failed to sum cache size for stats",
+	} {
+		want := `"level":"WARN","msg":"` + msg + `"`
+		if !strings.Contains(logBuf.String(), want) {
+			t.Errorf("log missing %s; got %q", want, logBuf.String())
+		}
+	}
+}
+
+// TestIncrementStats_LogsFailedUpdates verifies that a failed hit or miss
+// count update and a failed upstream fetch count update are each logged at
+// warn.
+func TestIncrementStats_LogsFailedUpdates(t *testing.T) {
+	t.Parallel()
+
+	db := setupStatsTestDB(t)
+
+	var logBuf bytes.Buffer
+
+	cache, err := NewCache(db, CacheConfig{
+		StateDir:    t.TempDir(),
+		CacheTTL:    time.Hour,
+		NegativeTTL: 5 * time.Minute,
+		Logger:      slog.New(slog.NewJSONHandler(&logBuf, nil)),
+	})
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	_, err = db.ExecContext(t.Context(), `DROP TABLE cache_stats`)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	cache.IncrementStats(t.Context(), false, 1024)
+
+	for _, msg := range []string{
+		"failed to count cache hit or miss",
+		"failed to count upstream fetch",
+	} {
+		want := `"level":"WARN","msg":"` + msg + `"`
+		if !strings.Contains(logBuf.String(), want) {
+			t.Errorf("log missing %s; got %q", want, logBuf.String())
+		}
+	}
+}

internal/imgcache/storage.go

@@ -7,6 +7,7 @@ import (
 	"errors"
 	"fmt"
 	"io"
+	"log/slog"
 	"os"
 	"path/filepath"
 	"time"
@@ -392,6 +393,7 @@ func CacheKey(req *ImageRequest) VariantKey {
 // Unlike ContentStorage, the key is provided by the caller (not computed from content).
 type VariantStorage struct {
 	baseDir string
+	log     *slog.Logger
 }
 
 // VariantMeta contains metadata about a cached variant.
@@ -404,13 +406,14 @@ type VariantMeta struct {
 }
 
 // NewVariantStorage creates a new variant storage at the given base directory.
-func NewVariantStorage(baseDir string) (*VariantStorage, error) {
+// A failed .meta write is logged to log.
+func NewVariantStorage(baseDir string, log *slog.Logger) (*VariantStorage, error) {
 	err := os.MkdirAll(baseDir, StorageDirPerm)
 	if err != nil {
 		return nil, fmt.Errorf("failed to create variant storage directory: %w", err)
 	}
 
-	return &VariantStorage{baseDir: baseDir}, nil
+	return &VariantStorage{baseDir: baseDir, log: log}, nil
 }
 
 // Store writes content and metadata to storage at the given key.
@@ -478,7 +481,11 @@ func (s *VariantStorage) Store(
 	}
 
 	// Metadata write failure is non-fatal; content is already stored.
-	_ = os.WriteFile(metaPath, metaData, StorageFilePerm)
+	err = os.WriteFile(metaPath, metaData, StorageFilePerm)
+	if err != nil {
+		s.log.Warn("failed to write variant metadata sidecar",
+			"path", metaPath, "error", err)
+	}
 
 	return size, nil
 }

internal/imgcache/storage_internal_test.go

@@ -4,8 +4,10 @@ import (
 	"bytes"
 	"errors"
 	"io"
+	"log/slog"
 	"os"
 	"path/filepath"
+	"strings"
 	"testing"
 )
 
@@ -404,3 +406,35 @@ func TestCacheKey(t *testing.T) {
 		t.Error("CacheKey() produced same key for different quality")
 	}
 }
+
+// TestVariantStorage_StoreLogsFailedMetaWrite verifies that a .meta write
+// that fails is logged at warn and the store still succeeds.
+func TestVariantStorage_StoreLogsFailedMetaWrite(t *testing.T) {
+	t.Parallel()
+
+	var logBuf bytes.Buffer
+
+	storage, err := NewVariantStorage(
+		t.TempDir(), slog.New(slog.NewJSONHandler(&logBuf, nil)))
+	if err != nil {
+		t.Fatalf("NewVariantStorage() error = %v", err)
+	}
+
+	key := CacheKey(&ImageRequest{SourceHost: testHostCDN, SourcePath: testPathCat})
+
+	// A directory where the .meta file goes makes the .meta write fail.
+	err = os.MkdirAll(storage.keyToPath(key)+".meta", StorageDirPerm)
+	if err != nil {
+		t.Fatalf("failed to create directory: %v", err)
+	}
+
+	_, err = storage.Store(key, bytes.NewReader([]byte("variant data")), "image/webp")
+	if err != nil {
+		t.Fatalf("Store() error = %v, want nil", err)
+	}
+
+	want := `"level":"WARN","msg":"failed to write variant metadata sidecar"`
+	if !strings.Contains(logBuf.String(), want) {
+		t.Errorf("log missing %s; got %q", want, logBuf.String())
+	}
+}

internal/imgcache/urlparser.go

@@ -23,6 +23,21 @@ var (
 // MaxDimension is the maximum allowed width or height.
 const MaxDimension = 8192
 
+// ValidateDimension checks one requested width or height; name ("width" or
+// "height") appears in the error. 0 means "original size" and is valid.
+func ValidateDimension(name string, value int) error {
+	if value < 0 {
+		return fmt.Errorf("%w: %s is negative", ErrInvalidSize, name)
+	}
+
+	if value > MaxDimension {
+		return fmt.Errorf("%w: %s is above %d",
+			ErrDimensionTooLarge, name, MaxDimension)
+	}
+
+	return nil
+}
+
 // sizeFormatRegex matches patterns like "800x600.webp", "0x0.jpeg", "orig.png"
 var sizeFormatRegex = regexp.MustCompile(`^(\d+)x(\d+)\.(\w+)$|^(orig)\.(\w+)$`)
 
@@ -225,14 +240,20 @@ func parseSizeFormat(s string) (Size, ImageFormat, error) {
 			return Size{}, "", ErrInvalidSize
 		}
 
-		if width > MaxDimension || height > MaxDimension {
-			return Size{}, "", ErrDimensionTooLarge
-		}
-
 		size = Size{Width: width, Height: height}
 		formatStr = matches[3]
 	}
 
+	err := ValidateDimension("width", size.Width)
+	if err != nil {
+		return Size{}, "", err
+	}
+
+	err = ValidateDimension("height", size.Height)
+	if err != nil {
+		return Size{}, "", err
+	}
+
 	format, err := parseFormat(formatStr)
 	if err != nil {
 		return Size{}, "", err

internal/imgcache/validate_internal_test.go

@@ -0,0 +1,64 @@
+package imgcache
+
+import (
+	"errors"
+	"testing"
+)
+
+func TestValidateImageRequest(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		name    string
+		req     ImageRequest
+		wantErr error
+	}{
+		{
+			name: "within bounds",
+			req:  ImageRequest{Size: Size{Width: 800, Height: 600}, FitMode: FitCover},
+		},
+		{
+			name: "original size and empty fit",
+			req:  ImageRequest{Size: Size{Width: 0, Height: 0}},
+		},
+		{
+			name:    "width over limit",
+			req:     ImageRequest{Size: Size{Width: MaxDimension + 1, Height: 600}},
+			wantErr: ErrDimensionTooLarge,
+		},
+		{
+			name:    "height over limit",
+			req:     ImageRequest{Size: Size{Width: 800, Height: MaxDimension + 1}},
+			wantErr: ErrDimensionTooLarge,
+		},
+		{
+			name:    "negative width",
+			req:     ImageRequest{Size: Size{Width: -1, Height: 600}},
+			wantErr: ErrInvalidSize,
+		},
+		{
+			name:    "invalid fit mode",
+			req:     ImageRequest{Size: Size{Width: 800, Height: 600}, FitMode: "bogus"},
+			wantErr: ErrInvalidFitMode,
+		},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+
+			err := ValidateImageRequest(&tt.req)
+			if tt.wantErr == nil {
+				if err != nil {
+					t.Fatalf("ValidateImageRequest() error = %v, want nil", err)
+				}
+
+				return
+			}
+
+			if !errors.Is(err, tt.wantErr) {
+				t.Fatalf("ValidateImageRequest() error = %v, want %v", err, tt.wantErr)
+			}
+		})
+	}
+}

internal/middleware/middleware.go

@@ -4,11 +4,13 @@ package middleware
 import (
 	"log/slog"
 	"net/http"
+	"net/netip"
 	"time"
 
 	basicauth "github.com/99designs/basicauth-go"
 	"github.com/go-chi/chi/v5/middleware"
 	"github.com/go-chi/cors"
+	"github.com/go-chi/httprate"
 	metrics "github.com/slok/go-http-metrics/metrics/prometheus"
 	ghmm "github.com/slok/go-http-metrics/middleware"
 	"github.com/slok/go-http-metrics/middleware/std"
@@ -88,6 +90,31 @@ func (s *Middleware) ClientIP() func(http.Handler) http.Handler {
 	}
 }
 
+// RateLimit returns a middleware that limits each client to requestLimit
+// requests per window and refuses a request over the limit with 429 Too Many
+// Requests and a Retry-After header. Clients are told apart by the address
+// the ClientIP middleware stored in the request context, so ClientIP must
+// run first. An IPv6 client is counted by its /64, which one client usually
+// holds whole; an IPv4-mapped address (::ffff:a.b.c.d) is counted as the
+// IPv4 address it carries, since every such address falls in the same /64.
+// Counts are kept only for the current and the previous window, so memory
+// stays bounded.
+func (s *Middleware) RateLimit(
+	requestLimit int, window time.Duration,
+) func(http.Handler) http.Handler {
+	return httprate.LimitBy(requestLimit, window,
+		func(r *http.Request) (string, error) {
+			ip := clientip.FromContext(r.Context())
+
+			addr, err := netip.ParseAddr(ip)
+			if err == nil {
+				ip = addr.Unmap().String()
+			}
+
+			return httprate.CanonicalizeIP(ip), nil
+		})
+}
+
 type loggingResponseWriter struct {
 	http.ResponseWriter
 

internal/server/login_rate_limit_internal_test.go

@@ -0,0 +1,280 @@
+package server
+
+import (
+	"io"
+	"net/http"
+	"net/http/httptest"
+	"net/netip"
+	"net/url"
+	"path/filepath"
+	"regexp"
+	"strconv"
+	"strings"
+	"testing"
+
+	"go.uber.org/fx/fxtest"
+
+	"sneak.berlin/go/pixa/internal/config"
+	"sneak.berlin/go/pixa/internal/database"
+	"sneak.berlin/go/pixa/internal/globals"
+	"sneak.berlin/go/pixa/internal/handlers"
+	"sneak.berlin/go/pixa/internal/logger"
+	"sneak.berlin/go/pixa/internal/middleware"
+)
+
+// testSigningKey is a throwaway signing key; submitting it logs in.
+const testSigningKey = "test-signing-key-0123456789abcdef"
+
+// wrongKey is submitted for a failed login.
+const wrongKey = "not-the-signing-key"
+
+// Addresses for the login rate limit tests. The test server trusts
+// 10.0.0.0/8 as its proxies, so the X-Forwarded-For sent by proxyPeer is
+// believed and the one sent by firstClient or secondClient is ignored.
+const (
+	firstClient     = "198.51.100.1:40000"
+	secondClient    = "198.51.100.2:40000"
+	proxyPeer       = "10.0.0.1:40000"
+	firstForwarded  = "203.0.113.1"
+	secondForwarded = "203.0.113.2"
+)
+
+// csrfFieldPattern extracts the CSRF token rendered into the login form.
+var csrfFieldPattern = regexp.MustCompile(
+	`name="gorilla\.csrf\.Token" value="([^"]+)"`)
+
+// newTestServer builds the server's real routes from the constructors
+// cmd/pixad uses, with a throwaway state directory. Debug marks requests
+// as plain HTTP, so the CSRF check runs without an https Referer.
+func newTestServer(t *testing.T) *Server {
+	t.Helper()
+
+	stateDir := t.TempDir()
+	cfg := &config.Config{
+		Debug:          true,
+		SigningKey:     testSigningKey,
+		StateDir:       stateDir,
+		DBURL:          "file:" + filepath.Join(stateDir, "state.sqlite3"),
+		TrustedProxies: []netip.Prefix{netip.MustParsePrefix("10.0.0.0/8")},
+	}
+
+	lc := fxtest.NewLifecycle(t)
+
+	log, err := logger.New(lc, logger.Params{Globals: &globals.Globals{}})
+	if err != nil {
+		t.Fatalf("logger.New() error = %v", err)
+	}
+
+	db, err := database.New(lc, database.Params{Logger: log, Config: cfg})
+	if err != nil {
+		t.Fatalf("database.New() error = %v", err)
+	}
+
+	h, err := handlers.New(lc, handlers.Params{
+		Logger: log, Database: db, Config: cfg,
+	})
+	if err != nil {
+		t.Fatalf("handlers.New() error = %v", err)
+	}
+
+	mw, err := middleware.New(lc, middleware.Params{Logger: log, Config: cfg})
+	if err != nil {
+		t.Fatalf("middleware.New() error = %v", err)
+	}
+
+	lc.RequireStart()
+	t.Cleanup(lc.RequireStop)
+
+	s := &Server{config: cfg, mw: mw, h: h}
+	s.SetupRoutes()
+
+	return s
+}
+
+// clientRequest builds a request for / arriving from remoteAddr, carrying
+// forwardedFor as its X-Forwarded-For header when that is not empty.
+func clientRequest(
+	t *testing.T, method string, body io.Reader, remoteAddr, forwardedFor string,
+) *http.Request {
+	t.Helper()
+
+	req := httptest.NewRequestWithContext(t.Context(), method, "/", body)
+	req.RemoteAddr = remoteAddr
+
+	if forwardedFor != "" {
+		req.Header.Set("X-Forwarded-For", forwardedFor)
+	}
+
+	return req
+}
+
+// postLogin loads the login form with GET / and submits key in it with
+// POST /, as a browser does, both from the same client. GET / is not rate
+// limited, so the form must load even for a client over the limit.
+func postLogin(
+	t *testing.T, s *Server, remoteAddr, forwardedFor, key string,
+) *httptest.ResponseRecorder {
+	t.Helper()
+
+	page := httptest.NewRecorder()
+	s.ServeHTTP(page,
+		clientRequest(t, http.MethodGet, nil, remoteAddr, forwardedFor))
+
+	if page.Code != http.StatusOK {
+		t.Fatalf("GET / status = %d, want %d", page.Code, http.StatusOK)
+	}
+
+	match := csrfFieldPattern.FindStringSubmatch(page.Body.String())
+	if match == nil {
+		t.Fatalf("no CSRF token field found in the login form")
+	}
+
+	form := url.Values{"key": {key}, "gorilla.csrf.Token": {match[1]}}
+	req := clientRequest(t, http.MethodPost,
+		strings.NewReader(form.Encode()), remoteAddr, forwardedFor)
+	req.Header.Set("Content-Type", "application/x-www-form-urlencoded")
+
+	for _, c := range page.Result().Cookies() {
+		req.AddCookie(c)
+	}
+
+	rec := httptest.NewRecorder()
+	s.ServeHTTP(rec, req)
+
+	return rec
+}
+
+// tripLoginRateLimit makes LoginAttemptsPerMinute failed logins from one
+// client, each answered with the login form again, then one more, which
+// must be refused with 429. It returns the response to that last attempt.
+func tripLoginRateLimit(
+	t *testing.T, s *Server, remoteAddr, forwardedFor string,
+) *httptest.ResponseRecorder {
+	t.Helper()
+
+	for attempt := range LoginAttemptsPerMinute {
+		rec := postLogin(t, s, remoteAddr, forwardedFor, wrongKey)
+		if rec.Code != http.StatusOK {
+			t.Fatalf("failed login %d status = %d, want %d",
+				attempt+1, rec.Code, http.StatusOK)
+		}
+	}
+
+	rec := postLogin(t, s, remoteAddr, forwardedFor, wrongKey)
+	if rec.Code != http.StatusTooManyRequests {
+		t.Fatalf("login over the limit status = %d, want %d",
+			rec.Code, http.StatusTooManyRequests)
+	}
+
+	return rec
+}
+
+// TestLoginRateLimitRefusesAttemptOverLimit verifies the login attempt
+// after LoginAttemptsPerMinute failed ones from one client is refused with
+// 429 and a Retry-After header, and that the client cannot get around the
+// limit by sending X-Forwarded-For: from a peer that is not a trusted
+// proxy, the header is ignored.
+func TestLoginRateLimitRefusesAttemptOverLimit(t *testing.T) {
+	t.Parallel()
+
+	s := newTestServer(t)
+
+	rec := tripLoginRateLimit(t, s, firstClient, "")
+
+	retryAfter := rec.Header().Get("Retry-After")
+
+	seconds, err := strconv.Atoi(retryAfter)
+	if err != nil || seconds <= 0 {
+		t.Errorf("Retry-After = %q, want a positive number of seconds",
+			retryAfter)
+	}
+
+	rec = postLogin(t, s, firstClient, secondForwarded, wrongKey)
+	if rec.Code != http.StatusTooManyRequests {
+		t.Errorf("login with X-Forwarded-For from an untrusted peer "+
+			"status = %d, want %d", rec.Code, http.StatusTooManyRequests)
+	}
+}
+
+// TestLoginRateLimitLeavesOtherClientsAlone verifies one client going over
+// the limit does not limit another: a failed login from a different
+// address is answered with the login form, and the signing key still logs
+// it in.
+func TestLoginRateLimitLeavesOtherClientsAlone(t *testing.T) {
+	t.Parallel()
+
+	s := newTestServer(t)
+
+	tripLoginRateLimit(t, s, firstClient, "")
+
+	rec := postLogin(t, s, secondClient, "", wrongKey)
+	if rec.Code != http.StatusOK {
+		t.Errorf("failed login from another client status = %d, want %d",
+			rec.Code, http.StatusOK)
+	}
+
+	rec = postLogin(t, s, secondClient, "", testSigningKey)
+	if rec.Code != http.StatusSeeOther {
+		t.Errorf("login with the signing key from another client "+
+			"status = %d, want %d", rec.Code, http.StatusSeeOther)
+	}
+}
+
+// TestLoginRateLimitCountsClientsBehindProxySeparately verifies the limit
+// counts the client address resolved from X-Forwarded-For, not the address
+// of the trusted proxy the requests arrive from, so two clients behind the
+// same proxy are counted separately.
+func TestLoginRateLimitCountsClientsBehindProxySeparately(t *testing.T) {
+	t.Parallel()
+
+	s := newTestServer(t)
+
+	tripLoginRateLimit(t, s, proxyPeer, firstForwarded)
+
+	rec := postLogin(t, s, proxyPeer, secondForwarded, wrongKey)
+	if rec.Code != http.StatusOK {
+		t.Errorf("failed login from a second client behind the proxy "+
+			"status = %d, want %d", rec.Code, http.StatusOK)
+	}
+}
+
+// TestLoginRateLimitCountsIPv6ClientsByPrefix verifies an IPv6 client is
+// counted by its /64: another address in the same /64 is refused too,
+// while an address in a different /64 is not.
+func TestLoginRateLimitCountsIPv6ClientsByPrefix(t *testing.T) {
+	t.Parallel()
+
+	s := newTestServer(t)
+
+	tripLoginRateLimit(t, s, proxyPeer, "2001:db8::1")
+
+	rec := postLogin(t, s, proxyPeer, "2001:db8::2", wrongKey)
+	if rec.Code != http.StatusTooManyRequests {
+		t.Errorf("login from the same /64 status = %d, want %d",
+			rec.Code, http.StatusTooManyRequests)
+	}
+
+	rec = postLogin(t, s, proxyPeer, "2001:db8:0:1::1", wrongKey)
+	if rec.Code != http.StatusOK {
+		t.Errorf("login from another /64 status = %d, want %d",
+			rec.Code, http.StatusOK)
+	}
+}
+
+// TestLoginRateLimitCountsIPv4MappedClientsSeparately verifies an IPv4
+// client that the proxy forwards in IPv4-mapped IPv6 form (::ffff:a.b.c.d)
+// is counted by its IPv4 address, not by the /64 that every such address
+// shares, so two of them behind the proxy are counted separately.
+func TestLoginRateLimitCountsIPv4MappedClientsSeparately(t *testing.T) {
+	t.Parallel()
+
+	s := newTestServer(t)
+
+	tripLoginRateLimit(t, s, proxyPeer, "::ffff:"+firstForwarded)
+
+	rec := postLogin(t, s, proxyPeer, "::ffff:"+secondForwarded, wrongKey)
+	if rec.Code != http.StatusOK {
+		t.Errorf("failed login from a second IPv4-mapped client "+
+			"status = %d, want %d", rec.Code, http.StatusOK)
+	}
+}

internal/server/routes.go

@@ -2,6 +2,7 @@ package server
 
 import (
 	"net/http"
+	"time"
 
 	sentryhttp "github.com/getsentry/sentry-go/http"
 	"github.com/go-chi/chi/v5"
@@ -12,6 +13,10 @@ import (
 	"sneak.berlin/go/pixa/internal/static"
 )
 
+// LoginAttemptsPerMinute is how many login attempts (POST /) one client may
+// make per minute; the next is refused with 429 Too Many Requests.
+const LoginAttemptsPerMinute = 5
+
 // SetupRoutes configures all HTTP routes.
 func (s *Server) SetupRoutes() {
 	s.router = chi.NewRouter()
@@ -50,11 +55,14 @@ func (s *Server) SetupRoutes() {
 	// token cookie is independent of the session cookie, so it also
 	// covers the login POST, where no session exists yet. LimitBody caps
 	// the POST body ahead of CSRF, which reads its token from that body.
+	// The login POST is rate limited per client after both, so every
+	// attempt that reaches the signing key comparison is counted.
 	s.router.Group(func(r chi.Router) {
 		r.Use(s.h.LimitBody(handlers.MaxFormBytes))
 		r.Use(s.h.CSRF())
 		r.Get("/", s.h.HandleRoot())
-		r.Post("/", s.h.HandleRoot())
+		r.With(s.mw.RateLimit(LoginAttemptsPerMinute, time.Minute)).
+			Post("/", s.h.HandleRoot())
 		r.Post("/generate", s.h.HandleGenerateURL())
 	})
 

internal/signature/golden_test.go

@@ -41,9 +41,12 @@ func goldenVectors() []goldenVector {
 				Width:       800,
 				Height:      600,
 				Format:      testFormatWebP,
+				Quality:     85,
+				FitMode:     testFitCover,
 			},
-			// Signed data: "cdn.example.com:/photos/cat.jpg::800:600:webp:1704067200"
+			// Signed data:
-			wantSignature:  "x5PfPp8QSDo0cJT96od-AEgrQyOVLfqifH5sst61_-w=",
+			// "cdn.example.com:/photos/cat.jpg::800:600:webp:1704067200:85:cover"
+			wantSignature:  "kdqeGoW2SX7qnaYtoB970wEnLydn0UnIgQYQLfAnjXQ=",
 			wantSignedPath: testSignedPath,
 		},
 		{
@@ -55,10 +58,12 @@ func goldenVectors() []goldenVector {
 				Width:       800,
 				Height:      600,
 				Format:      testFormatWebP,
+				Quality:     85,
+				FitMode:     testFitCover,
 			},
 			// Signed data:
-			// "cdn.example.com:/photos/cat.jpg:token=abc&v=2:800:600:webp:1704067200"
+			// "cdn.example.com:/photos/cat.jpg:token=abc&v=2:800:600:webp:1704067200:85:cover"
-			wantSignature: "394_Vf9TdQFkpQ3XKFDQSyxgqKq8N7mApf2S4QaHqyo=",
+			wantSignature: "pKgVBOTd_Q_EikI7MNQLC9Q8Hurdxzyv3EIYvVhqc2I=",
 			wantSignedPath: "/v1/image/cdn.example.com/photos/cat.jpg" +
 				"%3Ftoken=abc&v=2/800x600.webp",
 		},
@@ -71,11 +76,34 @@ func goldenVectors() []goldenVector {
 				Width:       0,
 				Height:      0,
 				Format:      testFormatPNG,
+				Quality:     85,
+				FitMode:     testFitCover,
 			},
-			// Signed data: "cdn.example.com:/photos/cat.jpg::0:0:png:1704067200"
+			// Signed data:
-			wantSignature:  "7Be7oteeQwvnSPU4bchyQ4ZGYGsAGBKpeEtuQ02ox60=",
+			// "cdn.example.com:/photos/cat.jpg::0:0:png:1704067200:85:cover"
+			wantSignature:  "6_rZ0yyVbGZRs8kG7n7HLgLi5Jt8vjiWQljIEL1jbIs=",
 			wantSignedPath: "/v1/image/cdn.example.com/photos/cat.jpg/orig.png",
 		},
+		{
+			name: "non-default quality and fit",
+			req: signature.Request{
+				SourceHost:  testHost,
+				SourcePath:  testPath,
+				SourceQuery: "",
+				Width:       800,
+				Height:      600,
+				Format:      testFormatWebP,
+				Quality:     40,
+				FitMode:     testFitContain,
+			},
+			// Signed data:
+			// "cdn.example.com:/photos/cat.jpg::800:600:webp:1704067200:40:contain"
+			wantSignature: "pGaXpPUbI3A7nMx-4T9bfq9bYWBNL0kY4bxlcv3g1F8=",
+			// The path is the same as for the default quality and fit:
+			// q=40&fit=contain go in the query string next to sig and
+			// exp (imgcache.Service.GenerateSignedURL adds all four).
+			wantSignedPath: testSignedPath,
+		},
 	}
 }
 
@@ -84,11 +112,9 @@ func goldenVectors() []goldenVector {
 // hardcoded signing key.
 //
 // If any of these assertions fail, the signed byte format
-// ("host:path:query:width:height:format:expiration"), the base64url
+// ("host:path:query:width:height:format:expiration:quality:fit"), the
-// encoding, or the signed URL layout has changed. Such a change breaks
+// base64url encoding, or the signed URL layout has changed. Update these
-// every signature already issued to clients, so it must be made
+// constants only when that change is intended.
-// deliberately: update these constants only as part of an intentional,
-// documented signature format migration.
 func TestSigner_GoldenVectors(t *testing.T) {
 	t.Parallel()
 

internal/signature/quality_fit_test.go

@@ -0,0 +1,68 @@
+package signature_test
+
+import (
+	"errors"
+	"testing"
+	"time"
+
+	"sneak.berlin/go/pixa/internal/signature"
+)
+
+// signedQualityFitRequest returns a request signed for quality 85 and fit
+// mode "cover", the effective defaults the handler applies before
+// verification.
+func signedQualityFitRequest(signer *signature.Signer) *signature.Request {
+	req := &signature.Request{
+		SourceHost: testHost,
+		SourcePath: testPath,
+		Width:      800,
+		Height:     600,
+		Format:     testFormatWebP,
+		Quality:    85,
+		FitMode:    testFitCover,
+		Expires:    time.Now().Add(1 * time.Hour),
+	}
+	req.Signature = signer.Sign(req)
+
+	return req
+}
+
+// TestSigner_Verify_QualityAndFitAreSigned proves that quality and fit are
+// covered by the signature: a URL signed for one quality or fit mode must
+// not verify when replayed with a different quality or fit mode. This is the
+// amplification vector from the issue — one signed URL replayed across many
+// quality and fit values yields many unauthorized cache entries and
+// transcodes — so it must be rejected.
+func TestSigner_Verify_QualityAndFitAreSigned(t *testing.T) {
+	t.Parallel()
+
+	signer := signature.New("test-secret-key")
+
+	cases := []struct {
+		name   string
+		tamper func(r *signature.Request)
+	}{
+		{
+			name:   "replayed with different quality",
+			tamper: func(r *signature.Request) { r.Quality = 40 },
+		},
+		{
+			name:   "replayed with different fit mode",
+			tamper: func(r *signature.Request) { r.FitMode = testFitContain },
+		},
+	}
+
+	for _, tt := range cases {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+
+			req := signedQualityFitRequest(signer)
+			tt.tamper(req)
+
+			err := signer.Verify(req)
+			if !errors.Is(err, signature.ErrInvalid) {
+				t.Errorf("Verify() = %v, want %v", err, signature.ErrInvalid)
+			}
+		})
+	}
+}

internal/signature/signature.go

@@ -37,6 +37,15 @@ type Request struct {
 	Height int
 	// Format is the requested output format (e.g. "webp").
 	Format string
+	// Quality is the requested output quality (1-100) for lossy formats.
+	// It is the effective value the request resolves to: callers pass the
+	// default quality when the request omits the parameter, so an omitted
+	// quality signs identically to that same value stated explicitly.
+	Quality int
+	// FitMode is how the image is fit into the requested dimensions
+	// (e.g. "cover"). Like Quality it is the effective value: callers pass
+	// the default fit mode when the request omits the parameter.
+	FitMode string
 	// Signature is the HMAC signature to verify.
 	Signature string
 	// Expires is the signature expiration timestamp.
@@ -56,7 +65,8 @@ func New(secretKey string) *Signer {
 }
 
 // Sign generates an HMAC-SHA256 signature for the given request.
-// The signature covers: host + path + query + width + height + format + expiration.
+// The signature covers: host + path + query + width + height + format +
+// expiration + quality + fit.
 func (s *Signer) Sign(req *Request) string {
 	data := s.buildSignatureData(req)
 	mac := hmac.New(sha256.New, s.secretKey)
@@ -68,7 +78,8 @@ func (s *Signer) Sign(req *Request) string {
 
 // Verify checks if the signature on the request is valid and not expired.
 // Signatures are exact-match only: every component of the signed data
-// (host, path, query, dimensions, format, expiration) must match exactly.
+// (host, path, query, dimensions, format, expiration, quality, fit) must
+// match exactly.
 // No suffix matching, wildcard matching, or partial matching is supported.
 // A signature for "cdn.example.com" will NOT verify for "example.com" or
 // "other.cdn.example.com", and vice versa.
@@ -142,11 +153,13 @@ func (s *Signer) GenerateSignedURL(
 }
 
 // buildSignatureData creates the string to be signed.
-// Format: "host:path:query:width:height:format:expiration"
+// Format: "host:path:query:width:height:format:expiration:quality:fit"
 // All components are used verbatim (exact match). No normalization,
-// suffix matching, or wildcard expansion is performed.
+// suffix matching, or wildcard expansion is performed. Quality and fit
+// are the effective transform values, so replaying a signed URL with a
+// different quality or fit mode fails verification.
 func (s *Signer) buildSignatureData(req *Request) string {
-	return fmt.Sprintf("%s:%s:%s:%d:%d:%s:%d",
+	return fmt.Sprintf("%s:%s:%s:%d:%d:%s:%d:%d:%s",
 		req.SourceHost,
 		req.SourcePath,
 		req.SourceQuery,
@@ -154,6 +167,8 @@ func (s *Signer) buildSignatureData(req *Request) string {
 		req.Height,
 		req.Format,
 		req.Expires.Unix(),
+		req.Quality,
+		req.FitMode,
 	)
 }
 

internal/signature/signature_test.go

@@ -15,6 +15,8 @@ const (
 	testPath       = "/photos/cat.jpg"
 	testFormatWebP = "webp"
 	testFormatPNG  = "png"
+	testFitCover   = "cover"
+	testFitContain = "contain"
 	testSignedPath = "/v1/image/cdn.example.com/photos/cat.jpg/800x600.webp"
 	testSig        = "abc123"
 )

internal/templates/generator.html

@@ -73,7 +73,7 @@
                         id="width"
                         name="width"
                         min="0"
-                        max="10000"
+                        max="8192"
                         value="{{if .FormWidth}}{{.FormWidth}}{{else}}0{{end}}"
                         placeholder="0 = original"
                         class="w-full px-3 py-2 border border-gray-300 rounded-md shadow-sm focus:outline-none focus:ring-2 focus:ring-blue-500 focus:border-blue-500"
@@ -88,7 +88,7 @@
                         id="height"
                         name="height"
                         min="0"
-                        max="10000"
+                        max="8192"
                         value="{{if .FormHeight}}{{.FormHeight}}{{else}}0{{end}}"
                         placeholder="0 = original"
                         class="w-full px-3 py-2 border border-gray-300 rounded-md shadow-sm focus:outline-none focus:ring-2 focus:ring-blue-500 focus:border-blue-500"

script/bootstrap

@@ -3,20 +3,14 @@
 # this repo. Idempotent: every install is guarded by a check so already
 # installed tools are skipped. Base tooling comes from nix, apt, brew,
 # or apk (detected in that order); assumes NOTHING is present (not git,
-# make, or go). golangci-lint is packaged in nix, brew, and apk; on apt
+# make, or go). The linter is never installed on the host: golangci-lint
-# it is installed from a hash-verified GitHub release archive (never
+# runs only inside a container, Dockerfile.lint or the Dockerfile lint
-# curl | sh). CGO image libraries (pkg-config, vips, libheif) are
+# stage (see script/lint). CGO image libraries (pkg-config, vips,
-# installed for the govips bindings.
+# libheif) are installed for the govips bindings.
 set -eu
 
 ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"
 
-# Pinned versions, 2026-08-07. Never "latest"; exact versions only.
-GOLANGCI_LINT_VERSION="2.12.2"
-# sha256 of golangci-lint-2.12.2-linux-<arch>.tar.gz release archives
-GOLANGCI_LINT_SHA256_AMD64="8df580d2670fed8fa984aac0507099af8df275e665215f5c7a2ae3943893a553"
-GOLANGCI_LINT_SHA256_ARM64="44cd40a8c76c86755375adfeea52cfd3533cb43d7bd647771e0ae065e166df3a"
-
 PKGMGR=""
 SUDO=""
 
@@ -57,52 +51,6 @@ missing() {
     ! command -v "$1" >/dev/null 2>&1
 }
 
-# verify_sha256 <file> <expected-hash>
-verify_sha256() {
-    if command -v sha256sum >/dev/null 2>&1; then
-        actual="$(sha256sum "$1" | cut -d' ' -f1)"
-    else
-        actual="$(shasum -a 256 "$1" | cut -d' ' -f1)"
-    fi
-    if [ "$actual" != "$2" ]; then
-        echo "bootstrap: sha256 mismatch for $1" >&2
-        echo "  expected: $2" >&2
-        echo "  actual:   $actual" >&2
-        exit 1
-    fi
-}
-
-# apt has no golangci-lint package: install a pinned release archive
-# from GitHub, verified by hardcoded sha256 (never curl | sh).
-install_golangci_lint_release() {
-    case "$(uname -m)" in
-        x86_64) goarch="amd64"; sha="$GOLANGCI_LINT_SHA256_AMD64" ;;
-        aarch64|arm64) goarch="arm64"; sha="$GOLANGCI_LINT_SHA256_ARM64" ;;
-        *)
-            echo "bootstrap: unsupported architecture $(uname -m)" >&2
-            exit 1
-            ;;
-    esac
-    if missing curl; then pkg_install curl curl curl curl; fi
-    name="golangci-lint-${GOLANGCI_LINT_VERSION}-linux-${goarch}"
-    tmp="$(mktemp -d)"
-    curl -fsSL -o "$tmp/$name.tar.gz" \
-        "https://github.com/golangci/golangci-lint/releases/download/v${GOLANGCI_LINT_VERSION}/${name}.tar.gz"
-    verify_sha256 "$tmp/$name.tar.gz" "$sha"
-    tar -xzf "$tmp/$name.tar.gz" -C "$tmp"
-    $SUDO install -m 0755 "$tmp/$name/golangci-lint" /usr/local/bin/golangci-lint
-    rm -rf "$tmp"
-}
-
-ensure_golangci_lint() {
-    if ! missing golangci-lint; then return 0; fi
-    detect_pkgmgr
-    case "$PKGMGR" in
-        apt) install_golangci_lint_release ;;
-        *) pkg_install golangci-lint golangci-lint golangci-lint golangci-lint ;;
-    esac
-}
-
 # CGO dependencies for govips (image processing)
 ensure_cgo_deps() {
     if missing pkg-config; then
@@ -123,9 +71,8 @@ main() {
     if missing git; then pkg_install git git git git; fi
     if missing make; then pkg_install gnumake make make make; fi
 
-    # Go toolchain and linter
+    # Go toolchain
     if missing go; then pkg_install go golang go go; fi
-    ensure_golangci_lint
 
     # CGO image libraries
     ensure_cgo_deps

script/docker-smoke

@@ -16,8 +16,10 @@ main() {
     # removed on exit.
     key="$(head -c 32 /dev/urandom | base64)"
 
-    # --health-interval=1s overrides the image's 30s interval so the
+    # Docker 25 and later probe every 5 seconds during the image's
-    # first probe does not use up the whole wait.
+    # 10-second start period. --health-interval=1s makes it probe every
+    # second after that instead of every 30, so a slow start still shows
+    # as healthy within the 30-second wait.
     cid="$(docker create --health-interval=1s \
         -e PIXA_SIGNING_KEY="$key" "$("$SCRIPT_DIR/projectname")")"
     # Remove the container on any exit; turning signals into exit makes

script/lint

@@ -1,23 +1,37 @@
 #!/bin/sh
-# script/lint: run the linter. CGO dependencies (pkg-config, vips,
+# script/lint: run golangci-lint over the whole tree. This is the only
-# libheif) come from nix-shell when not already available (e.g. inside
+# way the linter is run, everywhere; it is never installed on the host.
-# a Docker build or an existing nix-shell).
+#
+# Inside a container it runs the linter. Anywhere else it builds
+# Dockerfile.lint, whose last step runs this script again inside that
+# container.
+#
+# Dockerfile.lint and the Dockerfile lint stage set container=docker
+# (the systemd convention for marking a container) to say where we are.
+# /.dockerenv cannot: it is missing inside build steps, and present on
+# hosts that are themselves containers.
 set -eu
 
 ROOT="$(cd "$(dirname "$0")/.." && pwd -P)"
 
-run_with_cgo_deps() {
+main() {
-    if command -v pkg-config >/dev/null 2>&1; then
+    cd "$ROOT"
-        sh -c "$1"
+    if [ "${container:-}" = docker ]; then
+        # `golangci-lint config verify` is not run: it fetches its JSON
+        # schema over an unpinned live HTTPS call, which REPO_POLICIES.md
+        # forbids.
+        echo "Running linter..."
+        golangci-lint run --config .golangci.yml ./...
     else
-        nix-shell -p pkg-config vips libheif golangci-lint git --run "$1"
+        # A new CACHEBUST on every run means the lint step is never
+        # served from cache (see Dockerfile.lint). The cacheonly output
+        # leaves no image behind.
+        docker build \
+            --progress=plain \
+            --build-arg CACHEBUST="$(date +%s)-$$" \
+            --output=type=cacheonly \
+            -f Dockerfile.lint .
     fi
 }
 
-main() {
-    cd "$ROOT"
-    echo "Running linter..."
-    run_with_cgo_deps "golangci-lint run"
-}
-
 main "$@"

script/test

@@ -10,7 +10,7 @@ run_with_cgo_deps() {
     if command -v pkg-config >/dev/null 2>&1; then
         sh -c "$1"
     else
-        nix-shell -p pkg-config vips libheif golangci-lint git --run "$1"
+        nix-shell -p pkg-config vips libheif git --run "$1"
     fi
 }