README.md

@@ -92,8 +92,69 @@ the metadata file stored beside it.
 
 ### Routes
 
+pixa answers these routes; any other path answers 404. A path in this list asked
+with a method the list does not give answers 405, except `/static/<file>`, which
+answers any method as it answers `GET`. A browser's CORS preflight request
+(`OPTIONS` with `Origin` and `Access-Control-Request-Method` headers) to any
+path under `/v1/` answers 200, in maintenance mode too.
+
+- `GET /` — the login page, or the URL generator page with a login session
+  (see Encrypted URLs). Needs: nothing. Answers: 200.
+- `POST /` — log in with the signing key typed into the login page. Needs: the
+  login page's form (below). Answers: 303 to `/` with a login session cookie
+  that lasts 30 days for the right key; 200 with the login page and an error for
+  a wrong key; 429 over the login limit (below).
+- `POST /generate` — make an encrypted URL from the generator page's form.
+  Needs: a login session and the generator page's form (below); without a login
+  session it answers 303 to `/`. Answers: 200 with the page showing the URL; 400
+  with the page naming a field that is not valid; 500 when the URL cannot be
+  made.
+- `GET /logout` — end the login session. Needs: nothing. Answers: 303 to `/`.
+- `GET` or `HEAD` `/v1/image/<host>/<path>/<size>.<format>` — an image, fetched,
+  resized and converted (below). Needs: a signature, unless the host is
+  allowlisted (see Source Hosts). Answers: 200; 304 when `If-None-Match` matches
+  the image's `ETag`; 400 for a URL or parameter that is not valid; 401 for a
+  missing or wrong signature, a missing `exp` or an `exp` in the past; 403 when
+  the upstream host, or a host it redirects to, is `localhost`, ends in
+  `.localhost` or `.local`, or has an address in a blocked network (see
+  `blocked_networks`); 502 when the upstream answered with an error status, and
+  for 5 minutes after that for the same source URL; 503 when pixa is busy or in
+  maintenance mode; 500 for any other failure.
+- `GET /v1/e/<token>/<name>` — an image through an encrypted URL (see Encrypted
+  URLs). Needs: nothing but the URL. Answers: 200; 400 for a token that does not
+  decrypt, or that asks for a size or fit that is not valid; 410 once it has
+  expired; 504 when the upstream has not sent its response headers within
+  `upstream_fetch_timeout`, but 500 when that time runs out while the image
+  itself is still arriving; 403, 502, 503 and 500 as for `/v1/image/`.
+- `GET /robots.txt` — asks every crawler to stay away (`Disallow: /`). Needs:
+  nothing. Answers: 200.
+- `GET /.well-known/healthcheck.json` — JSON with `status` (`ok`), `now`,
+  `uptime_seconds`, `uptime_human`, `version`, `appname` and
+  `maintenance_mode`. Needs: nothing. Answers: 200, always.
+- `GET /static/<file>` — the script the login and generator pages load. Needs:
+  nothing. Answers: 200, or 404 for a file that does not exist.
+- `GET /metrics` — Prometheus metrics (see Architecture). Needs: HTTP basic
+  authentication with `metrics.username` and `metrics.password`. Answers: 200;
+  401 without them; 404 when they are not set, as the route then does not exist.
+
+Both `POST` routes accept only a form that pixa's own page served: the page puts
+a token in the form and sets a cookie to match, and a request without both is
+refused with 403, so another site cannot submit the form from a visitor's
+browser. The login and generator pages are meant to be opened over HTTPS: while
+`debug` is off, a form sent from a page opened over plain HTTP is refused with
+403, and while it is on, so is one sent from a page opened over HTTPS. Plain
+HTTP is for development on the browser's own machine: the login session cookie
+is always marked `Secure`, and over plain HTTP a browser keeps such a cookie
+only for its own machine (`localhost`), if at all. A form is also refused with
+403 when the page's host is not the `Host` header pixa receives, so a reverse
+proxy in front of pixa must pass that header on unchanged. A form body over
+1 MiB is refused with 413. The image routes answer the errors listed for them
+with JSON holding `error`, `status` and `timestamp`.
+
+An image URL has this form:
+
 ```
-/v1/image/<host>/<path>/<size>.<format>?sig=<signature>&exp=<expiration>
+/v1/image/<host>/<path>/<size>.<format>?sig=<signature>&exp=<expiration>&q=<quality>&fit=<fit>
 ```
 
 Images are only fetched from origins using TLS with valid certificates, unless
@@ -106,6 +167,11 @@ than once, is refused with 400.
 - `<format>`: one of `orig` (or `original`), `jpeg` (or `jpg`), `png`, `webp`,
   `avif`, `gif`
 - `<size>`: `orig` or `<width>x<height>` (e.g. `800x600`)
+- `sig` and `exp`: the signature and its expiry, needed unless the host is
+  allowlisted (see Signature Specification)
+- `q` and `fit`: the output quality and how the image is fitted to `<size>`,
+  both optional (values under Signature Specification). Both are part of what
+  is cached, so each value of either is a separate cached image.
 
 An image is served with `Cache-Control: public, max-age=<seconds>, immutable`.
 When the URL has an expiry (an `exp`, or the TTL of an encrypted URL),
@@ -139,6 +205,39 @@ its own `X-Forwarded-For`, whether it connects directly or through the proxy,
 because its own address is trusted too. Setting `trusted_proxies` to only the
 address pixa sees for requests that come through the proxy closes this.
 
+### Encrypted URLs
+
+An encrypted URL is an image URL made on pixa's own web page by someone who
+knows the signing key. It works for any upstream host, allowlisted or not,
+without a signature, and whoever gets it can neither read the source URL from it
+nor change what it asks for.
+
+1. Open `/` in a browser over HTTPS (or over plain HTTP while `debug` is on, see
+   Routes) and log in with the signing key (`signing_key`). The login session
+   lasts 30 days, or until `/logout`.
+2. On the generator page, give the source image's URL, the width and height, the
+   format, quality and fit, and how long the URL lasts, then submit the form
+   (`POST /generate`). Width and height both empty or `0` keep the original
+   size; if only one of them is empty or `0`, that side is scaled to keep the
+   image's proportions.
+3. The page shows the URL, `https://<host>/v1/e/<token>/img.<format>`, and when
+   it expires. `<host>` is the host the page was opened on, and the URL starts
+   with `http` instead while `debug` is on. The name after the token is ignored
+   and only gives the URL a file extension, `jpg` for `orig`.
+
+The token holds the source's host, path and query and the size, format,
+quality, fit and expiry, encrypted with a key derived from `signing_key`. The
+source URL's scheme is not kept: the image is fetched like any other (see
+Routes), and the blocked networks still apply.
+
+How long the URL lasts is chosen on the page, from 1 minute to 1 year, or
+never. The expiry is fixed in the token when the URL is made and cannot be
+changed or revoked afterwards. Until then the image is served with a `max-age`
+that ends at the expiry (see Routes); after it the URL answers 410
+`URL has expired`. A URL made to last forever stops working only when
+`signing_key` changes: changing it makes every encrypted URL already handed out
+answer 400, and ends every login session.
+
 ### Image Metadata
 
 pixa decodes and re-encodes every image it serves, and removes all metadata from
@@ -237,6 +336,17 @@ 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.
 
+pixa reads at most one config file: the one given with `--config` (or `-c`),
+otherwise the one `PIXA_CONFIG_PATH` names, otherwise the first of these that
+pixa finds: `/etc/pixa/config.yml`, `/etc/pixa/config.yaml`,
+`~/.config/pixa/config.yml`, `~/.config/pixa/config.yaml`, then `config.yml`
+and `config.yaml` in the working directory. A named file that does not exist,
+cannot be read or does not parse aborts startup. Of the files pixa looks for on
+its own, one it finds but cannot read or parse aborts startup; one it cannot
+find, for any reason, is passed over without a message, even when the file is
+there in a directory pixa may not enter. With no file, pixa uses the environment
+and the defaults.
+
 | Variable                             | Config key                      | Meaning                                                                      |
 | ------------------------------------ | ------------------------------- | ---------------------------------------------------------------------------- |
 | `PIXA_SIGNING_KEY`                   | `signing_key`                   | Required: secret for signed and encrypted URLs and login, 32+ characters     |
@@ -322,12 +432,12 @@ Key settings in more detail:
   seconds for one to free up; if none does, and `downstream_timeout` has not
   ended first, it is answered 503 the same way
 - `maintenance_mode` — while `true`, the image routes (`/v1/image/` and
-  `/v1/e/`) answer every request with 503, a `Retry-After` header and a JSON
+  `/v1/e/`) answer every request for an image with 503, a `Retry-After` header
-  error body. The health check (`/.well-known/healthcheck.json`) still answers
+  and a JSON error body. The health check (`/.well-known/healthcheck.json`)
-  200 and reports `"maintenance_mode": true`. It stays 200 because the image's
+  still answers 200 and reports `"maintenance_mode": true`. It stays 200
-  Docker `HEALTHCHECK` requests it: a 503 there would make the container
+  because the image's Docker `HEALTHCHECK` requests it: a 503 there would make
-  unhealthy, and upaas marks a deploy failed when its container is unhealthy.
+  the container unhealthy, and upaas marks a deploy failed when its container
-  The login and URL generator pages and `/metrics` keep working
+  is unhealthy. The login and URL generator pages and `/metrics` keep working
 
 See `config.example.yml` for all options with defaults.
 

TODO.md

@@ -29,6 +29,14 @@ P2: security: referer blacklist
 
 # Completed Steps
 
+- 2026-10-04 routes, encrypted URLs and config file documented (closes #75):
+  "Routes" in `README.md` lists every route with its method, purpose, what it
+  needs and the status codes it answers with, and says `q` and `fit` are part
+  of what is cached; "Encrypted URLs" covers logging in, making one on the
+  generator page, how long it lasts and the 410 once it has expired;
+  "Configuration" gives the order in which pixa looks for its config file;
+  `config.example.yml` lists `db_url` and `env` and gives every key's default;
+  `scripts/manual-test.sh` is left to #97.
 - 2026-10-04 shutdown stops cache eviction in progress (closes #102):
   `StartEviction` runs the eviction goroutine with its own context, which
   `StopEviction` cancels, so a pass in progress stops at its next database
@@ -441,7 +449,5 @@ P2: security: referer blacklist
     - integration tests for the image proxy flow
     - load tests to verify the 1k to 5k req/s target
 - P2: documentation
-    - configuration options
-    - API endpoints
     - deployment guide
     - example nginx or caddy reverse proxy config

config.example.yml

@@ -12,27 +12,38 @@
 # Durations are Go duration strings such as 30s or 2m and must be
 # positive; a bare number has no unit and aborts startup. Sizes are a
 # whole number of bytes.
+#
+# A key left out takes the default its comment gives.
 
-# Server settings
+# Port to listen on (default: 8080)
 port: 8080
+
+# Debug logging and plain-HTTP local development (default: false)
 debug: false
 
 # While true, the image routes (/v1/image/ and /v1/e/) answer every request
-# with 503 and a Retry-After header. The health check keeps answering 200 and
+# for an image with 503 and a Retry-After header. The health check keeps
-# reports maintenance_mode as true. It stays 200 because the image's Docker
+# answering 200 and reports maintenance_mode as true. It stays 200 because
-# HEALTHCHECK requests it: a 503 there would make the container unhealthy, and
+# the image's Docker HEALTHCHECK requests it: a 503 there would make the
-# upaas marks a deploy failed when its container is unhealthy.
+# container unhealthy, and upaas marks a deploy failed when its container is
+# unhealthy. (default: false)
 maintenance_mode: false
 
 # Data directory for SQLite database and cache files
+# (default: /var/lib/pixa)
 state_dir: ./data
 
+# SQLite database URL (default:
+# file:<state_dir>/state.sqlite3?_journal_mode=WAL). An empty value aborts
+# startup; leave the key out to use the default.
+# db_url: "file:./data/state.sqlite3?_journal_mode=WAL"
+
 # Image proxy settings
 # HMAC signing key for URL signatures (required, at least 32 characters)
 # Generate with: openssl rand -base64 32
 signing_key: "CHANGE_ME_generate_with_openssl_rand_base64_32"
 
-# Hosts that don't require signatures
+# Hosts that don't require signatures (default: none)
 # Use "." prefix for wildcard subdomain matching (e.g., ".example.com" matches "cdn.example.com")
 allowlist_hosts:
   - s3.sneak.cloud
@@ -45,7 +56,7 @@ allowlist_hosts:
 # SSRF protection. These are added to the always-enforced built-in ranges
 # (loopback, RFC 1918 private, link-local, CGNAT, benchmark, NAT64, and
 # similar), never replacing them. Each entry must be a valid CIDR in IPv4
-# or IPv6 form; an invalid entry aborts startup.
+# or IPv6 form; an invalid entry aborts startup. (default: none)
 # blocked_networks:
 #   - 100.64.0.0/10
 #   - 2001:db8::/32
@@ -72,6 +83,7 @@ allowlist_hosts:
 #   - 2001:db8::/32
 
 # Allow HTTP upstream (only for testing, always use HTTPS in production)
+# (default: false)
 allow_http: false
 
 # Maximum concurrent connections per upstream host (default: 20)
@@ -121,10 +133,16 @@ access_control_allow_origin: "*"
 # with a minimum of 500 MiB.
 # cache_max_bytes: 10737418240
 
-# Sentry error reporting (optional)
+# Sentry DSN for error reporting (default: empty, which turns it off)
 sentry_dsn: ""
 
-# Metrics endpoint authentication (optional)
+# Username and password for /metrics, set together (default: unset). Metrics
+# are measured and /metrics is served only when both are set.
 # metrics:
 #   username: "admin"
 #   password: "secret"
+
+# Environment variables set while this file loads, as described at the top
+# (default: none)
+# env:
+#   PIXA_DEBUG: "true"