Remove the unused cache lifetime setting (closes #69)

CacheConfig.CacheTTL was set to DefaultCacheTTL (24 hours) and never
read, so cached images never expired. Remove the field, the constant
and the line that set it. Cached source and transformed images stay
until eviction removes them to keep the cache within cache_max_bytes.

A new test caches a source and a transformed image, sets every time
pixa stores for them two days back (database rows, metadata files and
file times), and checks that both are still served from the cache
without a new upstream fetch.

Existing tests lose only the CacheTTL line of their cache config.

Model: opus-5-5

Dockerfile

@@ -33,10 +33,9 @@ COPY . .
 
 # Without -v first; on a failure, again with -v for the details, and
 # the step fails even if the second run passes. -parallel 4: by default
-# a package runs as many of its tests at once as the host has CPUs. On
-# a busy host they then wait to be scheduled, and their SQLite calls
-# queue on one lock that every database in the test process shares, so
-# a test that times a request can see it return a second late.
+# a package runs as many of its tests at once as the host has CPUs, and
+# on a busy host they then wait so long to be scheduled that a test
+# that times a request can see it return a second late.
 RUN go test -count=1 -timeout 90s -race -parallel 4 -cover ./... || \
     { echo "--- Rerunning with -v for details ---"; \
       go test -count=1 -timeout 90s -race -parallel 4 -v ./...; exit 1; }

README.md

@@ -46,9 +46,9 @@ everything in this list without further settings. The reverse proxy must:
   builds encrypted URLs from `Host`, and checks `Referer` against
   `referer_blocklist`;
 - set `X-Forwarded-For` to the client's address, with `trusted_proxies` set to
-  the address pixa sees the proxy's requests come from, so the login limit
-  counts each client by its own address (see `trusted_proxies` under
-  Configuration);
+  the address pixa sees the proxy's requests come from, so the login limit and
+  `image_requests_per_minute` count each client by its own address (see
+  `trusted_proxies` under Configuration);
 - wait for pixa's answer for at least `downstream_timeout` (default `60s`), the
   longest pixa takes to fetch, convert and send an image.
 
@@ -58,8 +58,9 @@ password there.
 
 pixa does the rest itself: it checks signatures and encrypted URLs, applies the
 allowlist, refuses upstream hosts with private or local addresses, limits login
-attempts, upstream response size and image dimensions, and sends the security
-headers, `Strict-Transport-Security` included, with every response.
+attempts, each client's image requests, upstream response size and image
+dimensions, and sends the security headers, `Strict-Transport-Security`
+included, with every response.
 
 The state directory (`state_dir`, `/var/lib/pixa` in the container) holds the
 database and the disk cache:
@@ -83,10 +84,12 @@ which answers 200 whenever pixa is running, in maintenance mode too (see
 `maintenance_mode`).
 
 On SIGTERM or SIGINT pixa stops accepting connections, gives the requests in
-progress and the images being processed 5 seconds to finish, and exits: with 0,
-or with 1 when images were still being processed after those 5 seconds or
-another part of pixa failed to stop. A request not finished by then is cut off.
-`docker stop` waits 10 seconds before it kills the container.
+progress and the images being processed 5 seconds to finish, then writes to the
+database the counts of cache hits, misses, fetches and conversions that requests
+could not write by their deadline, and exits: with 0, or with 1 when images were
+still being processed after those 5 seconds, some of those counts could not be
+written, or another part of pixa failed to stop. A request not finished by then
+is cut off. `docker stop` waits 10 seconds before it kills the container.
 
 Outside Docker, pixa needs libvips (the image has 8.16) and libheif to run, as
 it uses libvips through CGO. pixad does not start unless libvips has its JPEG XL
@@ -186,7 +189,10 @@ path under `/v1/` answers 200, in maintenance mode too.
   `Referer` names a host in `referer_blocklist`, checked before the signature,
   the cache and the upstream fetch; 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
+  address in a blocked network (see `blocked_networks`); 429 over
+  `image_requests_per_minute` (below); 415 when the upstream answers with a
+  `Content-Type` that is not one of the source formats (below), or with an image
+  whose first bytes libvips reads as another format; 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.
@@ -197,7 +203,7 @@ path under `/v1/` answers 200, in maintenance mode too.
   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; 400 for an `Accept` header that is not valid, and
-  406, 403, 502, 503 and 500, as for `/v1/image/`.
+  406, 403, 415, 429, 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`,
@@ -257,9 +263,11 @@ once, is refused with 400.
   both optional (values under Signature Specification). Both are part of what is
   cached, so each value of either is a separate cached image.
 
-The source image may be JPEG, PNG, GIF, WebP, AVIF, JPEG XL or SVG. The
-upstream's `Content-Type` must name its format, and the image's first bytes must
-match it.
+The source image may be JPEG, PNG, GIF, WebP, AVIF or JPEG XL. The upstream's
+`Content-Type` must name its format, and the image's first bytes must match it.
+An upstream answering with any other `Content-Type`, SVG included, is refused
+with 415, and so is an image whose first bytes libvips reads as another format,
+such as an SVG whose first bytes pass the check for AVIF.
 
 With the format `auto`, pixa chooses the format for each request from its
 `Accept` header, in this order:
@@ -313,6 +321,15 @@ 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.
 
+One client may send `image_requests_per_minute` requests per minute
+(default 600) to the image routes, `/v1/image/` and `/v1/e/` together, `GET` and
+`HEAD`, cache hits included; a request over the limit is refused with 429 and a
+`Retry-After` header. Clients are counted as for the login limit. A browser's
+CORS preflight is not counted. Behind a CDN or proxy whose addresses are not in
+`trusted_proxies`, all requests arriving from one proxy or CDN address count as
+one client, so such a deployment needs a higher limit, or `0`, which turns the
+limit off.
+
 ### Encrypted URLs
 
 An encrypted URL is an image URL made on pixa's own web page by someone who
@@ -482,6 +499,7 @@ tell. With no file, pixa uses the environment and the defaults.
 | `PIXA_UPSTREAM_CONNECTIONS_PER_HOST` | `upstream_connections_per_host` | Concurrent connections per upstream host; default `20`                       |
 | `PIXA_UPSTREAM_CONNECTIONS`          | `upstream_connections`          | Concurrent connections to all upstream hosts together; default `64`          |
 | `PIXA_MAX_CONCURRENT_PROCESSING`     | `max_concurrent_processing`     | Images processed at once; default the number of CPUs                         |
+| `PIXA_IMAGE_REQUESTS_PER_MINUTE`     | `image_requests_per_minute`     | Image requests per client per minute; `0` turns it off; default `600`        |
 | `PIXA_UPSTREAM_FETCH_TIMEOUT`        | `upstream_fetch_timeout`        | Time allowed for one fetch from an upstream host; default `30s`              |
 | `PIXA_UPSTREAM_MAX_RESPONSE_SIZE`    | `upstream_max_response_size`    | Largest upstream response accepted, in bytes; default 50 MiB                 |
 | `PIXA_DOWNSTREAM_TIMEOUT`            | `downstream_timeout`            | Time allowed for answering one client request; default `60s`                 |
@@ -531,13 +549,13 @@ Key settings in more detail:
   explicit list replaces the default. An invalid CIDR aborts startup. Set this
   to the address pixa sees for requests that come through your proxy, such as
   `172.17.0.1/32`, when the defaults do not cover it, or to trust nothing else
-  (see the login limit under Routes). For a proxy on the Docker host that
-  connects to pixa over `127.0.0.1`, that address is the gateway of the
-  container's Docker network (`172.17.0.1` on the default bridge), not the
-  proxy's own address; a proxy that connects through another of the host's
-  addresses is seen with that address. To be sure which address it is, set this
-  to `[]` (or `PIXA_TRUSTED_PROXIES` to empty), send a request through the
-  proxy, and read `remoteIP` in pixa's request log line for it
+  (see the login limit and `image_requests_per_minute` under Routes). For a
+  proxy on the Docker host that connects to pixa over `127.0.0.1`, that address
+  is the gateway of the container's Docker network (`172.17.0.1` on the default
+  bridge), not the proxy's own address; a proxy that connects through another of
+  the host's addresses is seen with that address. To be sure which address it
+  is, set this to `[]` (or `PIXA_TRUSTED_PROXIES` to empty), send a request
+  through the proxy, and read `remoteIP` in pixa's request log line for it
 - `upstream_fetch_timeout` — time allowed for one fetch from an upstream host,
   as a duration such as `30s` (the default) or `2m`
 - `upstream_max_response_size` — largest upstream response accepted, in bytes;
@@ -570,6 +588,12 @@ Key settings in more detail:
   container's CPU limit. A request that finds all of them in use waits up to 10
   seconds for one to free up; if none does, and `downstream_timeout` has not
   ended first, it is answered 503 the same way
+- `image_requests_per_minute` — how many requests one client may send to the
+  image routes per minute (see the limit on them under Routes); default `600`.
+  `0` turns the limit off, and a negative or non-integer value aborts startup.
+  Behind a CDN or proxy whose addresses are not in `trusted_proxies`, all
+  requests arriving from one proxy or CDN address count as one client, so raise
+  the limit there, or set `0`
 - `maintenance_mode` — while `true`, the image routes (`/v1/image/` and
   `/v1/e/`) answer every request for an image with 503, a `Retry-After` header
   and a JSON error body. The health check (`/.well-known/healthcheck.json`)

TODO.md

@@ -26,18 +26,52 @@ resolved. The disk cache is now size-bounded with LRU eviction
 
 # Next Step
 
-P2: security: per-IP rate limiting on the image routes
+P2: security: per-origin rate limiting
 
 # Completed Steps
 
-- 2026-10-08 the test phase of the `Dockerfile` runs at most 4 tests of a
-  package at once (`go test -parallel 4`, closes #224), where it ran as many as
-  the host has CPUs. On a busy host, `TestService_Get_ReturnsByItsDeadline`
-  failed because its request returned over a second after its deadline: the
-  request was waiting to be scheduled, or for SQLite calls queued on a lock
-  inside the SQLite library that every database in the test process shares.
-  `-p`, how many packages are tested at once, is unchanged, as capping it also
-  slows compiling.
+- 2026-10-13 the unused cache lifetime is removed (closes #69):
+  `CacheConfig.CacheTTL`, which pixad set to `DefaultCacheTTL` (24 hours), was
+  never read, so cached images never expired. The field and the constant are
+  removed. Cached source and transformed images stay until eviction removes them
+  to keep the cache within `cache_max_bytes`.
+- 2026-10-13 SVG sources are refused, and `orig` is never saved as JPEG in place
+  of the source's own format (closes #68): the upstream fetch no longer accepts
+  `image/svg+xml`, which libvips would render. Both image routes answer 415 for
+  an upstream `Content-Type` that is not one of the source formats, SVG
+  included, where they answered 500. Before decoding, the image processor
+  refuses with `ErrUnsupportedInputFormat`, also answered 415, any input that
+  govips' `DetermineImageType`, which picks the libvips loader from the first
+  bytes, does not name as a source format. That catches an SVG whose first bytes
+  pass the first-bytes check for another type, as an XML comment can make them
+  do for AVIF; an SVG whose first bytes do not pass that check answers 500, as
+  before, and so does a damaged image in a source format, whose first bytes
+  `DetermineImageType` names. `orig` is always the source's own format, where a
+  source the processor could not name was saved as JPEG. `README.md` no longer
+  lists SVG. The SVG detection in `internal/magic` stays: the request path does
+  not call it, and it goes with the unused code of
+  https://git.eeqj.de/sneak/pixa/issues/168.
+- 2026-10-12 per-client limit on the image routes (closes #236): the new setting
+  `image_requests_per_minute` (`PIXA_IMAGE_REQUESTS_PER_MINUTE`), default 600,
+  is how many `GET` and `HEAD` requests one client may send to `/v1/image/` and
+  `/v1/e/` together per minute, cache hits included; the next is answered 429
+  with `Retry-After`. It uses the login limit's `RateLimit` middleware, so
+  clients are told apart the same way, and runs after the CORS middleware, so a
+  preflight is not counted. `0` turns the limit off; a negative or non-integer
+  value aborts startup.
+- 2026-10-08 a request past its deadline no longer waits for the database to
+  count it (closes #224). On a busy host, `TestService_Get_ReturnsByItsDeadline`
+  failed because its request, past its deadline, still waited for its miss count
+  to be written, a write with no deadline, which in pixad waits for the one
+  database connection every request shares. Each count write now keeps the
+  request's deadline but not its cancellation. A count not written by then is
+  kept in memory, where `Stats` sees it, and one goroutine of the cache writes
+  those counts, one write at a time, and once more at shutdown before the
+  database closes. The test phase of the `Dockerfile` also runs at most 4 tests
+  of a package at once (`go test -parallel 4`), where it ran as many as the host
+  has CPUs: on a busy host they then wait so long to be scheduled that a test
+  that times a request can fail. `-p`, how many packages are tested at once, is
+  unchanged, as capping it also slows compiling.
 - 2026-10-08 every output format is saved with settings pixa sets on purpose
   (closes #232): each format has its own govips export, as JPEG XL does, in
   place of govips' generic `Export`, which sent libvips a zero for some settings
@@ -744,8 +778,6 @@ P2: security: per-IP rate limiting on the image routes
 
 # Future Steps
 
-- P2: security
-    - per-origin rate limiting
 - P2: HTTP response handling
     - Last-Modified headers
 - P2: configuration

configs/config.example.yml

@@ -115,6 +115,14 @@ upstream_connections: 64
 # frees up it is answered 503, unless downstream_timeout has ended first.
 # max_concurrent_processing: 4
 
+# How many requests to the image routes (/v1/image/ and /v1/e/) one client
+# may send per minute; a request over the limit is answered 429 with a
+# Retry-After header. 0 turns the limit off. Clients are told apart as for
+# the login limit, so behind a CDN or proxy whose addresses are not in
+# trusted_proxies all requests arriving from one proxy or CDN address count
+# as one client: raise the limit there, or set 0. (default: 600)
+image_requests_per_minute: 600
+
 # Time allowed for one fetch from an upstream host (default: 30s)
 upstream_fetch_timeout: 30s
 

internal/config/config.go

@@ -34,6 +34,7 @@ const (
 	DefaultUpstreamFetchTimeout       = 30 * time.Second
 	DefaultUpstreamMaxResponseSize    = 50 << 20 // 50 MiB
 	DefaultDownstreamTimeout          = 60 * time.Second
+	DefaultImageRequestsPerMinute     = 600
 )
 
 // Configuration key names.
@@ -61,6 +62,7 @@ const (
 	keyUpstreamFetchTimeout       = "upstream_fetch_timeout"
 	keyUpstreamMaxResponseSize    = "upstream_max_response_size"
 	keyDownstreamTimeout          = "downstream_timeout"
+	keyImageRequestsPerMinute     = "image_requests_per_minute"
 )
 
 // placeholderSigningKey is the dummy signing_key shipped in
@@ -158,6 +160,11 @@ type Config struct {
 	// of the per-request timeout middleware.
 	DownstreamTimeout time.Duration
 
+	// ImageRequestsPerMinute is how many requests one client may make to
+	// the image routes per minute; the next is refused with 429 Too Many
+	// Requests. 0 turns the limit off.
+	ImageRequestsPerMinute int
+
 	// BlockedNetworks are operator-supplied CIDR ranges to refuse in
 	// addition to the built-in SSRF blocklist. Enforced by the upstream
 	// fetcher's dialer; the built-in ranges always apply.
@@ -302,6 +309,8 @@ func newFromSmartConfig(sc *smartconfig.Config) (*Config, error) {
 			keyAccessControlAllowOrigin, DefaultAccessControlAllowOrigin),
 		DownstreamTimeout: loader.durationVal(
 			keyDownstreamTimeout, DefaultDownstreamTimeout),
+		ImageRequestsPerMinute: loader.intVal(
+			keyImageRequestsPerMinute, DefaultImageRequestsPerMinute),
 		CacheMaxBytes:    loader.int64Val(keyCacheMaxBytes, 0),
 		BlockedNetworks:  blockedNetworks,
 		TrustedProxies:   trustedProxies,
@@ -311,9 +320,7 @@ func newFromSmartConfig(sc *smartconfig.Config) (*Config, error) {
 	// The default for an omitted cache_max_bytes is worked out when
 	// the cache opens; here we only record whether the operator set
 	// the key explicitly.
-	if _, present := lookupValue(sc, keyCacheMaxBytes); present {
-		c.CacheMaxBytesExplicit = true
-	}
+	_, c.CacheMaxBytesExplicit = lookupValue(sc, keyCacheMaxBytes)
 
 	// 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
@@ -426,7 +433,7 @@ func isKnownConfigKey(key string) bool {
 		keyMaxConcurrentProcessing, keyCacheMaxBytes, keyBlockedNetworks,
 		keyTrustedProxies, keyAccessControlAllowOrigin, keyUpstreamFetchTimeout,
 		keyUpstreamMaxResponseSize, keyDownstreamTimeout, keyRefererBlocklist,
-		"env":
+		keyImageRequestsPerMinute, "env":
 		return true
 	}
 
@@ -461,6 +468,7 @@ func envVarNames() map[string]string {
 		keyUpstreamFetchTimeout:       "PIXA_UPSTREAM_FETCH_TIMEOUT",
 		keyUpstreamMaxResponseSize:    "PIXA_UPSTREAM_MAX_RESPONSE_SIZE",
 		keyDownstreamTimeout:          "PIXA_DOWNSTREAM_TIMEOUT",
+		keyImageRequestsPerMinute:     "PIXA_IMAGE_REQUESTS_PER_MINUTE",
 	}
 }
 
@@ -613,6 +621,14 @@ func (c *Config) validate() error {
 			settingName(keyCacheMaxBytes), c.CacheMaxBytes, errMustNotBeNegative)
 	}
 
+	// Zero is valid (it turns the limit off); only negative values are
+	// rejected.
+	if c.ImageRequestsPerMinute < 0 {
+		return fmt.Errorf("%s: value %d %w",
+			settingName(keyImageRequestsPerMinute), c.ImageRequestsPerMinute,
+			errMustNotBeNegative)
+	}
+
 	err = c.validateUpstreamMaxResponseSize()
 	if err != nil {
 		return err
@@ -625,12 +641,9 @@ func (c *Config) validate() error {
 		}
 	}
 
-	if c.SentryDSN != "" {
-		parsed, err := url.Parse(c.SentryDSN)
-		if err != nil || parsed.Scheme == "" || parsed.Host == "" {
-			return fmt.Errorf("%s: value %q is %w",
-				settingName(keySentryDSN), c.SentryDSN, errNotAValidURL)
-		}
+	err = c.validateSentryDSN()
+	if err != nil {
+		return err
 	}
 
 	if (c.MetricsUsername == "") != (c.MetricsPassword == "") {
@@ -642,6 +655,22 @@ func (c *Config) validate() error {
 	return c.validateAccessControlAllowOrigin()
 }
 
+// validateSentryDSN checks that sentry_dsn, when set, is a URL with a scheme
+// and a host.
+func (c *Config) validateSentryDSN() error {
+	if c.SentryDSN == "" {
+		return nil
+	}
+
+	parsed, err := url.Parse(c.SentryDSN)
+	if err != nil || parsed.Scheme == "" || parsed.Host == "" {
+		return fmt.Errorf("%s: value %q is %w",
+			settingName(keySentryDSN), c.SentryDSN, errNotAValidURL)
+	}
+
+	return nil
+}
+
 // validateUpstreamMaxResponseSize checks that upstream_max_response_size
 // is from 1 byte to 1 GiB. An upstream response is read whole into
 // memory, and the image processor reads one byte past this limit, which

internal/config/env_internal_test.go

@@ -70,6 +70,7 @@ func TestEnvironmentSetsEveryKey(t *testing.T) {
 	t.Setenv("PIXA_UPSTREAM_CONNECTIONS_PER_HOST", "5")
 	t.Setenv("PIXA_UPSTREAM_CONNECTIONS", "10")
 	t.Setenv("PIXA_MAX_CONCURRENT_PROCESSING", "3")
+	t.Setenv("PIXA_IMAGE_REQUESTS_PER_MINUTE", "30")
 	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")
@@ -99,6 +100,7 @@ func TestEnvironmentSetsEveryKey(t *testing.T) {
 		UpstreamConnectionsPerHost: 5,
 		UpstreamConnections:        10,
 		MaxConcurrentProcessing:    3,
+		ImageRequestsPerMinute:     30,
 		CacheMaxBytes:              1024,
 		CacheMaxBytesExplicit:      true,
 		BlockedNetworks:            []netip.Prefix{netip.MustParsePrefix("203.0.113.0/24")},

internal/config/image_requests_per_minute_internal_test.go

@@ -0,0 +1,107 @@
+package config
+
+import "testing"
+
+// testImageRequestsPerMinuteVar is the variable that sets
+// image_requests_per_minute.
+const testImageRequestsPerMinuteVar = "PIXA_IMAGE_REQUESTS_PER_MINUTE"
+
+// TestImageRequestsPerMinuteValues checks that an omitted
+// image_requests_per_minute is 600, and that 0, which turns the limit off,
+// and any larger whole number are used as given.
+func TestImageRequestsPerMinuteValues(t *testing.T) {
+	t.Parallel()
+
+	c, err := configFromYAML(t, signingKeyLine)
+	if err != nil {
+		t.Fatalf("minimal config should be valid, got error: %v", err)
+	}
+
+	if c.ImageRequestsPerMinute != 600 {
+		t.Errorf("ImageRequestsPerMinute = %d, want 600", c.ImageRequestsPerMinute)
+	}
+
+	explicit := []struct {
+		value string
+		want  int
+	}{
+		{"0", 0},
+		{"30", 30},
+	}
+
+	for _, tc := range explicit {
+		c, err := configFromYAML(t,
+			signingKeyLine+"image_requests_per_minute: "+tc.value+"\n")
+		if err != nil {
+			t.Fatalf("image_requests_per_minute: %s should load, got error: %v",
+				tc.value, err)
+		}
+
+		if c.ImageRequestsPerMinute != tc.want {
+			t.Errorf("ImageRequestsPerMinute = %d, want %d",
+				c.ImageRequestsPerMinute, tc.want)
+		}
+	}
+}
+
+// TestInvalidImageRequestsPerMinuteAbortsStartup checks that a value that is
+// negative, not a whole number, or null aborts startup naming the key and
+// the value, and the variable too where the value could have come from it.
+func TestInvalidImageRequestsPerMinuteAbortsStartup(t *testing.T) {
+	t.Parallel()
+
+	key := keyImageRequestsPerMinute
+
+	runAbortCases(t, []abortCase{
+		{
+			name: "negative",
+			yaml: signingKeyLine + key + ": -1\n",
+			wantErrSubstrings: []string{
+				key, testImageRequestsPerMinuteVar, "value -1",
+			},
+		},
+		{
+			name: "not a number",
+			yaml: signingKeyLine + key + ": plenty\n",
+			wantErrSubstrings: []string{
+				key, testImageRequestsPerMinuteVar, "plenty",
+			},
+		},
+		{
+			name:              "fractional",
+			yaml:              signingKeyLine + key + ": 2.5\n",
+			wantErrSubstrings: []string{key, "2.5"},
+		},
+		{
+			name:              "explicit null",
+			yaml:              signingKeyLine + key + ": null\n",
+			wantErrSubstrings: []string{key, nullValueText},
+		},
+	})
+}
+
+// TestImageRequestsPerMinuteFromEnvironment checks that the variable sets the
+// limit over the config file, and that an invalid value in it aborts startup
+// naming the variable and the value.
+func TestImageRequestsPerMinuteFromEnvironment(t *testing.T) {
+	t.Setenv(testImageRequestsPerMinuteVar, "0")
+
+	c, err := configFromYAML(t, signingKeyLine+"image_requests_per_minute: 30\n")
+	if err != nil {
+		t.Fatalf("limit from the environment should load: %v", err)
+	}
+
+	if c.ImageRequestsPerMinute != 0 {
+		t.Errorf("ImageRequestsPerMinute = %d, want 0 from the environment",
+			c.ImageRequestsPerMinute)
+	}
+
+	for _, value := range []string{"-5", "ten"} {
+		t.Run(value, func(t *testing.T) {
+			t.Setenv(testImageRequestsPerMinuteVar, value)
+
+			_, err := configFromYAML(t, signingKeyLine)
+			wantStartupError(t, err, testImageRequestsPerMinuteVar, value)
+		})
+	}
+}

internal/handlers/handlers.go

@@ -4,6 +4,7 @@ package handlers
 import (
 	"context"
 	"encoding/json"
+	"errors"
 	"log/slog"
 	"net/http"
 	"time"
@@ -71,16 +72,21 @@ func New(lc fx.Lifecycle, params Params) (*Handlers, error) {
 	}
 
 	lc.Append(fx.Hook{
-		//nolint:contextcheck // the eviction loop outlives OnStart; OnStop cancels it
+		//nolint:contextcheck // the cache's goroutines outlive OnStart; OnStop stops them
 		OnStart: func(_ context.Context) error {
 			return s.initImageService()
 		},
+		// The pending counts are written here, before the database's stop
+		// hook closes it.
 		OnStop: func(ctx context.Context) error {
 			if s.imgCache == nil {
 				return nil
 			}
 
-			return s.imgCache.StopEviction(ctx)
+			return errors.Join(
+				s.imgCache.StopEviction(ctx),
+				s.imgCache.StopPendingCountWrites(ctx),
+			)
 		},
 	})
 
@@ -100,7 +106,6 @@ func (s *Handlers) WaitForProcessing(ctx context.Context) int {
 func newCacheConfig(cfg *config.Config, log *slog.Logger) imgcache.CacheConfig {
 	return imgcache.CacheConfig{
 		StateDir:           cfg.StateDir,
-		CacheTTL:           imgcache.DefaultCacheTTL,
 		NegativeTTL:        imgcache.DefaultNegativeTTL,
 		MaxBytes:           cfg.CacheMaxBytes,
 		UseDefaultMaxBytes: !cfg.CacheMaxBytesExplicit,
@@ -122,6 +127,9 @@ func (s *Handlers) initImageService() error {
 	// write-pressure passes. No-op when the disk cache is disabled.
 	cache.StartEviction(imgcache.DefaultEvictionInterval)
 
+	// Writes the counts requests could not write by their deadline
+	cache.StartPendingCountWrites()
+
 	// Create the fetcher config
 	fetcherCfg := httpfetcher.DefaultConfig()
 	fetcherCfg.AllowHTTP = s.config.AllowHTTP

internal/handlers/handlers_internal_test.go

@@ -47,7 +47,6 @@ func setupTestHandler(t *testing.T) *testFixtures {
 
 	cache, err := imgcache.NewCache(db, imgcache.CacheConfig{
 		StateDir:    tmpDir,
-		CacheTTL:    time.Hour,
 		NegativeTTL: 5 * time.Minute,
 	})
 	if err != nil {

internal/handlers/image.go

@@ -206,6 +206,16 @@ func parseExpires(query url.Values) (time.Time, error) {
 	return time.Unix(exp, 0), nil
 }
 
+// HandleTooManyRequests answers 429 Too Many Requests with the JSON error
+// body the image routes send for their other errors. The image routes' rate
+// limit calls it for a request over the limit.
+func (s *Handlers) HandleTooManyRequests() http.HandlerFunc {
+	return func(w http.ResponseWriter, _ *http.Request) {
+		s.respondError(w, "too many requests, try again later",
+			http.StatusTooManyRequests)
+	}
+}
+
 // respondImageError maps image retrieval errors to HTTP responses.
 func (s *Handlers) respondImageError(
 	w http.ResponseWriter, req *imgcache.ImageRequest, err error,
@@ -237,6 +247,14 @@ func (s *Handlers) respondImageError(
 		return
 	}
 
+	if errors.Is(err, httpfetcher.ErrInvalidContentType) ||
+		errors.Is(err, imageprocessor.ErrUnsupportedInputFormat) {
+		s.respondError(w, "unsupported source format",
+			http.StatusUnsupportedMediaType)
+
+		return
+	}
+
 	s.respondError(w, "internal error", http.StatusInternalServerError)
 }
 

internal/handlers/image_cache_control_internal_test.go

@@ -31,7 +31,6 @@ func newSignedHostServer(
 
 	cache, err := imgcache.NewCache(setupTestDB(t), imgcache.CacheConfig{
 		StateDir:    t.TempDir(),
-		CacheTTL:    time.Hour,
 		NegativeTTL: 5 * time.Minute,
 	})
 	if err != nil {

internal/handlers/image_errors_internal_test.go

@@ -29,7 +29,6 @@ func newImageRoute(t *testing.T, fetcher httpfetcher.Fetcher) http.Handler {
 
 	cache, err := imgcache.NewCache(setupTestDB(t), imgcache.CacheConfig{
 		StateDir:    t.TempDir(),
-		CacheTTL:    time.Hour,
 		NegativeTTL: 5 * time.Minute,
 	})
 	if err != nil {

internal/handlers/imageenc.go

@@ -161,6 +161,10 @@ func (s *Handlers) handleImageError(w http.ResponseWriter, err error) {
 		errors.Is(err, imageprocessor.ErrTooManyImages):
 		s.respondError(w, "server busy, try again later",
 			http.StatusServiceUnavailable)
+	case errors.Is(err, httpfetcher.ErrInvalidContentType),
+		errors.Is(err, imageprocessor.ErrUnsupportedInputFormat):
+		s.respondError(w, "unsupported source format",
+			http.StatusUnsupportedMediaType)
 	default:
 		s.log.Error("image request failed", "error", err)
 		s.respondError(w, "internal error", http.StatusInternalServerError)

internal/handlers/referer_blocklist_internal_test.go

@@ -49,7 +49,6 @@ func newRefererRoutes(t *testing.T) (http.Handler, *Handlers, *countingFetcher)
 
 	cache, err := imgcache.NewCache(setupTestDB(t), imgcache.CacheConfig{
 		StateDir:    t.TempDir(),
-		CacheTTL:    time.Hour,
 		NegativeTTL: 5 * time.Minute,
 	})
 	if err != nil {

internal/handlers/unsupported_source_internal_test.go

@@ -0,0 +1,54 @@
+package handlers
+
+import (
+	"fmt"
+	"log/slog"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+
+	"sneak.berlin/go/pixa/internal/httpfetcher"
+	"sneak.berlin/go/pixa/internal/imageprocessor"
+	"sneak.berlin/go/pixa/internal/imgcache"
+)
+
+// TestUnsupportedSourceFormatAnswers415 checks that both image routes answer
+// 415 with a clear error when the upstream answers with a content type pixa
+// does not accept, such as SVG, and when orig is asked of a source in a
+// format the processor cannot name, wrapped as the service wraps them.
+func TestUnsupportedSourceFormatAnswers415(t *testing.T) {
+	t.Parallel()
+
+	h := &Handlers{log: slog.New(slog.DiscardHandler)}
+	req := &imgcache.ImageRequest{SourceHost: "img.example.com", SourcePath: "/a.svg"}
+
+	for _, err := range []error{
+		fmt.Errorf("upstream fetch failed: %w: image/svg+xml",
+			httpfetcher.ErrInvalidContentType),
+		fmt.Errorf("image processing failed: %w: unknown",
+			imageprocessor.ErrUnsupportedInputFormat),
+	} {
+		plain := httptest.NewRecorder()
+		h.respondImageError(plain, req, err)
+
+		encrypted := httptest.NewRecorder()
+		h.handleImageError(encrypted, err)
+
+		for route, rec := range map[string]*httptest.ResponseRecorder{
+			"HandleImage": plain, "HandleImageEnc": encrypted,
+		} {
+			t.Logf("%s for %v: %d %s", route, err, rec.Code, rec.Body.String())
+
+			if rec.Code != http.StatusUnsupportedMediaType {
+				t.Errorf("%s for %v: status = %d, want %d",
+					route, err, rec.Code, http.StatusUnsupportedMediaType)
+			}
+
+			if !strings.Contains(rec.Body.String(), "unsupported source format") {
+				t.Errorf("%s for %v: body = %q, want the unsupported source format error",
+					route, err, rec.Body.String())
+			}
+		}
+	}
+}

internal/httpfetcher/httpfetcher.go

@@ -158,7 +158,6 @@ func DefaultConfig() *Config {
 			contentTypeWebP,
 			contentTypeAVIF,
 			contentTypeJXL,
-			contentTypeSVG,
 		},
 		AllowHTTP:             false,
 		MaxConnectionsPerHost: DefaultMaxConnectionsPerHost,

internal/imageprocessor/imageprocessor.go

@@ -137,6 +137,12 @@ var ErrInputDataTooLarge = errors.New("input data exceeds maximum allowed size")
 // not supported.
 var ErrUnsupportedOutputFormat = errors.New("unsupported output format")
 
+// ErrUnsupportedInputFormat is returned, before the input is decoded, when
+// libvips reads the input's first bytes as another format than the source
+// formats, or as none: for example an SVG whose first bytes pass the
+// first-bytes check for AVIF.
+var ErrUnsupportedInputFormat = errors.New("unsupported input format")
+
 // ErrTooManyImages is returned when MaxConcurrentProcessing images are being
 // processed and none finishes within ProcessingWaitTimeout.
 var ErrTooManyImages = errors.New("too many images being processed at once")
@@ -219,6 +225,17 @@ func (p *ImageProcessor) Process(
 		return nil, ErrInputDataTooLarge
 	}
 
+	// govips picks the libvips loader from the input's first bytes with
+	// DetermineImageType. Input whose first bytes it reads as no source
+	// format, such as SVG, which librsvg would render, is refused before
+	// libvips reads it.
+	inputFormat := p.detectFormat(vips.DetermineImageType(data))
+
+	sourceFormat, err := p.formatFromString(inputFormat)
+	if err != nil {
+		return nil, err
+	}
+
 	// Decode image
 	img, err := vips.NewImageFromBuffer(data)
 	if err != nil {
@@ -237,9 +254,6 @@ func (p *ImageProcessor) Process(
 	origWidth := img.Width()
 	origHeight := img.Height()
 
-	// Detect input format
-	inputFormat := p.detectFormat(img)
-
 	// Validate input dimensions to prevent DoS via decompression bombs
 	if origWidth > MaxInputDimension || origHeight > MaxInputDimension {
 		return nil, ErrInputTooLarge
@@ -259,7 +273,7 @@ func (p *ImageProcessor) Process(
 	// orig is the source's own format; encode refuses an empty format
 	outputFormat := req.Format
 	if outputFormat == FormatOriginal {
-		outputFormat = p.formatFromString(inputFormat)
+		outputFormat = sourceFormat
 	}
 
 	// Encode to target format
@@ -403,10 +417,9 @@ func (p *ImageProcessor) acquireSlot(ctx context.Context) (func(), error) {
 	}
 }
 
-// detectFormat returns the format string from a vips image.
-func (p *ImageProcessor) detectFormat(img *vips.ImageRef) string {
-	format := img.Format()
-	switch format {
+// detectFormat returns the format string for a govips image type.
+func (p *ImageProcessor) detectFormat(imageType vips.ImageType) string {
+	switch imageType {
 	case vips.ImageTypeJPEG:
 		return "jpeg"
 	case vips.ImageTypePNG:
@@ -687,22 +700,23 @@ func jxlDistance(quality int) float64 {
 	return 53.0/3000.0*q*q - 23.0/20.0*q + 25.0
 }
 
-// formatFromString converts a format string to Format.
-func (p *ImageProcessor) formatFromString(format string) Format {
+// formatFromString converts a format string from detectFormat to Format. A
+// format detectFormat could not name is ErrUnsupportedInputFormat.
+func (p *ImageProcessor) formatFromString(format string) (Format, error) {
 	switch format {
 	case "jpeg":
-		return FormatJPEG
+		return FormatJPEG, nil
 	case "png":
-		return FormatPNG
+		return FormatPNG, nil
 	case "gif":
-		return FormatGIF
+		return FormatGIF, nil
 	case "webp":
-		return FormatWebP
+		return FormatWebP, nil
 	case string(FormatAVIF):
-		return FormatAVIF
+		return FormatAVIF, nil
 	case string(FormatJXL):
-		return FormatJXL
+		return FormatJXL, nil
 	default:
-		return FormatJPEG
+		return "", fmt.Errorf("%w: %s", ErrUnsupportedInputFormat, format)
 	}
 }

internal/imageprocessor/orig_format_internal_test.go

@@ -0,0 +1,39 @@
+package imageprocessor
+
+import (
+	"bytes"
+	"errors"
+	"testing"
+
+	"github.com/davidbyttow/govips/v2/vips"
+)
+
+// TestImageProcessor_OrigOfUnnamedFormatRefused verifies that orig of a TIFF
+// input, which is not a source format, is refused with
+// ErrUnsupportedInputFormat before it is decoded, and not saved as JPEG.
+func TestImageProcessor_OrigOfUnnamedFormatRefused(t *testing.T) {
+	t.Parallel()
+
+	img, err := vips.NewImageFromBuffer(createTestPNG(t, 20, 20))
+	if err != nil {
+		t.Fatalf("failed to decode test PNG: %v", err)
+	}
+
+	t.Cleanup(img.Close)
+
+	tiff, _, err := img.ExportTiff(vips.NewTiffExportParams())
+	if err != nil {
+		t.Fatalf("failed to save test TIFF: %v", err)
+	}
+
+	result, err := New(Params{}).Process(
+		t.Context(), bytes.NewReader(tiff), &Request{Format: FormatOriginal},
+	)
+	if result != nil {
+		t.Logf("Process() returned %s", result.ContentType)
+	}
+
+	if !errors.Is(err, ErrUnsupportedInputFormat) {
+		t.Errorf("Process() error = %v, want %v", err, ErrUnsupportedInputFormat)
+	}
+}

internal/imageprocessor/source_formats_internal_test.go

@@ -0,0 +1,46 @@
+package imageprocessor
+
+import (
+	"bytes"
+	"io"
+	"testing"
+)
+
+// TestImageProcessor_LoadsEachSourceFormat verifies that an image in each of
+// the six source formats, saved by the processor itself, is loaded and saved
+// again in its own format (orig).
+func TestImageProcessor_LoadsEachSourceFormat(t *testing.T) {
+	t.Parallel()
+
+	proc := New(Params{})
+
+	for _, format := range []Format{
+		FormatJPEG, FormatPNG, FormatGIF, FormatWebP, FormatAVIF, FormatJXL,
+	} {
+		saved, err := proc.Process(t.Context(),
+			bytes.NewReader(createTestPNG(t, 20, 20)), &Request{Format: format})
+		if err != nil {
+			t.Fatalf("saving the test image as %s: %v", format, err)
+		}
+
+		source, err := io.ReadAll(saved.Content)
+		if err != nil {
+			t.Fatalf("reading the %s image: %v", format, err)
+		}
+
+		result, err := proc.Process(t.Context(), bytes.NewReader(source),
+			&Request{Format: FormatOriginal})
+		if err != nil {
+			t.Errorf("orig of the %s image: %v", format, err)
+
+			continue
+		}
+
+		t.Logf("orig of the %s image: %s", format, result.ContentType)
+
+		if result.ContentType != FormatToMIME(format) {
+			t.Errorf("orig of the %s image is %s, want %s",
+				format, result.ContentType, FormatToMIME(format))
+		}
+	}
+}

internal/imgcache/cache.go

@@ -11,6 +11,8 @@ import (
 	"io"
 	"log/slog"
 	"path/filepath"
+	"sync"
+	"sync/atomic"
 	"time"
 
 	lru "github.com/hashicorp/golang-lru/v2"
@@ -33,7 +35,6 @@ const metaCacheSize = 10000
 // CacheConfig holds cache configuration.
 type CacheConfig struct {
 	StateDir    string
-	CacheTTL    time.Duration
 	NegativeTTL time.Duration
 
 	// MaxBytes is the disk cache size limit in bytes that eviction
@@ -79,6 +80,27 @@ type Cache struct {
 	evictionDone     chan struct{}
 	evictionCancel   context.CancelFunc
 
+	// The pending counts: hits, misses, upstream fetches and transforms
+	// whose write to the database missed its request's deadline, kept
+	// here until they are written by the goroutine that
+	// StartPendingCountWrites starts. As for eviction, the channels are
+	// created in NewCache: pendingCountsAdded wakes that goroutine, and
+	// pendingCountsDone is closed when it returns. pendingCountsCancel,
+	// set by StartPendingCountWrites, cancels its context, which tells it
+	// to finish.
+	pendingHits               atomic.Int64
+	pendingMisses             atomic.Int64
+	pendingUpstreamFetches    atomic.Int64
+	pendingUpstreamFetchBytes atomic.Int64
+	pendingTransforms         atomic.Int64
+	pendingCountsAdded        chan struct{}
+	pendingCountsDone         chan struct{}
+	pendingCountsCancel       context.CancelFunc
+
+	// Held through each write of the pending counts, and by
+	// readHitAndMissCounts to read them
+	pendingCountsWriteMutex sync.Mutex
+
 	// metaCache holds the content types of the variants most recently
 	// stored or served, so a hit does not read the variant's .meta file.
 	// It never stands in for the variant file, which is always opened.
@@ -139,6 +161,9 @@ func newCache(
 		metaCache:        metaCache,
 		contentLocks:     newContentLock(),
 
+		pendingCountsAdded: make(chan struct{}, 1),
+		pendingCountsDone:  make(chan struct{}),
+
 		reconciliationPageSize: defaultReconciliationPageSize,
 	}
 
@@ -474,12 +499,7 @@ func (c *Cache) CleanExpired(ctx context.Context) error {
 func (c *Cache) Stats(ctx context.Context) (*CacheStats, error) {
 	var stats CacheStats
 
-	// Fetch hit/miss counts from the stats table
-	err := c.db.QueryRowContext(ctx, `
-		SELECT hit_count, miss_count
-		FROM cache_stats WHERE id = 1
-	`).Scan(&stats.HitCount, &stats.MissCount)
-
+	err := c.readHitAndMissCounts(ctx, &stats)
 	if err != nil && !errors.Is(err, sql.ErrNoRows) {
 		return nil, fmt.Errorf("failed to get cache stats: %w", err)
 	}
@@ -511,19 +531,30 @@ func (c *Cache) Stats(ctx context.Context) (*CacheStats, error) {
 }
 
 // IncrementStats counts a cache hit or miss, and an upstream fetch that read
-// fetchBytes bytes, as IncrementUpstreamFetch does.
+// fetchBytes bytes, as IncrementUpstreamFetch does. Like the other Increment
+// methods, it writes to the database with ctx's deadline but not its
+// cancellation, so an ended request is still counted but does not wait for
+// the database past its deadline; a count not written by then becomes a
+// pending count (see StartPendingCountWrites).
 func (c *Cache) IncrementStats(ctx context.Context, hit bool, fetchBytes int64) {
+	countCtx, cancel := withoutCancelKeepingDeadline(ctx)
+	defer cancel()
+
 	var err error
 
+	pendingCount := &c.pendingMisses
+
 	if hit {
-		_, err = c.db.ExecContext(ctx, `
+		pendingCount = &c.pendingHits
+
+		_, err = c.db.ExecContext(countCtx, `
 			UPDATE cache_stats
 			SET hit_count = hit_count + 1,
 			    last_updated_at = CURRENT_TIMESTAMP
 			WHERE id = 1
 		`)
 	} else {
-		_, err = c.db.ExecContext(ctx, `
+		_, err = c.db.ExecContext(countCtx, `
 			UPDATE cache_stats
 			SET miss_count = miss_count + 1,
 			    last_updated_at = CURRENT_TIMESTAMP
@@ -531,7 +562,10 @@ func (c *Cache) IncrementStats(ctx context.Context, hit bool, fetchBytes int64)
 		`)
 	}
 
-	if err != nil {
+	switch {
+	case errors.Is(err, context.DeadlineExceeded):
+		c.addPendingCount(pendingCount, 1)
+	case err != nil:
 		c.log.Warn("failed to count cache hit or miss", "hit", hit, "error", err)
 	}
 
@@ -545,14 +579,22 @@ func (c *Cache) IncrementUpstreamFetch(ctx context.Context, fetchBytes int64) {
 		return
 	}
 
-	_, err := c.db.ExecContext(ctx, `
+	countCtx, cancel := withoutCancelKeepingDeadline(ctx)
+	defer cancel()
+
+	_, err := c.db.ExecContext(countCtx, `
 		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 {
+
+	switch {
+	case errors.Is(err, context.DeadlineExceeded):
+		c.addPendingCount(&c.pendingUpstreamFetches, 1)
+		c.addPendingCount(&c.pendingUpstreamFetchBytes, fetchBytes)
+	case err != nil:
 		c.log.Warn("failed to count upstream fetch",
 			"fetch_bytes", fetchBytes, "error", err)
 	}
@@ -560,17 +602,43 @@ func (c *Cache) IncrementUpstreamFetch(ctx context.Context, fetchBytes int64) {
 
 // IncrementTransformCount counts one image transcoded by the image processor.
 func (c *Cache) IncrementTransformCount(ctx context.Context) {
-	_, err := c.db.ExecContext(ctx, `
+	countCtx, cancel := withoutCancelKeepingDeadline(ctx)
+	defer cancel()
+
+	_, err := c.db.ExecContext(countCtx, `
 		UPDATE cache_stats
 		SET transform_count = transform_count + 1,
 		    last_updated_at = CURRENT_TIMESTAMP
 		WHERE id = 1
 	`)
-	if err != nil {
+
+	switch {
+	case errors.Is(err, context.DeadlineExceeded):
+		c.addPendingCount(&c.pendingTransforms, 1)
+	case err != nil:
 		c.log.Warn("failed to count transform", "error", err)
 	}
 }
 
+// readHitAndMissCounts sets the hit and miss counts of stats to those of the
+// cache_stats row plus the pending hits and misses (see
+// StartPendingCountWrites). It holds pendingCountsWriteMutex, so that no
+// write of the pending counts falls between the two reads.
+func (c *Cache) readHitAndMissCounts(ctx context.Context, stats *CacheStats) error {
+	c.pendingCountsWriteMutex.Lock()
+	defer c.pendingCountsWriteMutex.Unlock()
+
+	err := c.db.QueryRowContext(ctx, `
+		SELECT hit_count, miss_count
+		FROM cache_stats WHERE id = 1
+	`).Scan(&stats.HitCount, &stats.MissCount)
+
+	stats.HitCount += c.pendingHits.Load()
+	stats.MissCount += c.pendingMisses.Load()
+
+	return err
+}
+
 // loadVariantWithMeta is GetVariant for a variant metaCache does not
 // hold: it reads the content type from the variant's .meta file and
 // keeps it in metaCache, unless a StoreVariant has put one there

internal/imgcache/cache_internal_test.go

@@ -102,7 +102,6 @@ func setupTestCache(t *testing.T) *Cache {
 
 	cache, err := NewCache(db, CacheConfig{
 		StateDir:    tmpDir,
-		CacheTTL:    time.Hour,
 		NegativeTTL: 5 * time.Minute,
 	})
 	if err != nil {
@@ -241,7 +240,6 @@ func TestCache_NegativeCacheExpiry(t *testing.T) {
 	// Very short negative TTL for testing
 	cache, err := NewCache(db, CacheConfig{
 		StateDir:    tmpDir,
-		CacheTTL:    time.Hour,
 		NegativeTTL: 1 * time.Millisecond,
 	})
 	if err != nil {

internal/imgcache/eviction_internal_test.go

@@ -70,7 +70,6 @@ func newEvictionTestCache(t *testing.T, maxBytes int64) (*Cache, string) {
 	// backwards compatibility with existing fixtures.
 	cache, err := NewCache(db, CacheConfig{
 		StateDir:         tmpDir,
-		CacheTTL:         time.Hour,
 		NegativeTTL:      5 * time.Minute,
 		MaxBytes:         maxBytes,
 		DisableDiskCache: maxBytes == 0,

internal/imgcache/module.go

@@ -4,6 +4,5 @@ import "time"
 
 // CacheConfig defaults.
 const (
-	DefaultCacheTTL    = 24 * time.Hour
 	DefaultNegativeTTL = 5 * time.Minute
 )

internal/imgcache/negative_cache_internal_test.go

@@ -15,7 +15,6 @@ func TestNegativeCache_StoreAndCheck(t *testing.T) {
 
 	cache, err := NewCache(db, CacheConfig{
 		StateDir:    dir,
-		CacheTTL:    time.Hour,
 		NegativeTTL: 5 * time.Minute,
 	})
 	if err != nil {
@@ -63,7 +62,6 @@ func TestNegativeCache_Expired(t *testing.T) {
 
 	cache, err := NewCache(db, CacheConfig{
 		StateDir:    dir,
-		CacheTTL:    time.Hour,
 		NegativeTTL: 1 * time.Millisecond, // very short TTL
 	})
 	if err != nil {

internal/imgcache/pendingcounts.go

@@ -0,0 +1,149 @@
+package imgcache
+
+import (
+	"context"
+	"fmt"
+	"sync/atomic"
+)
+
+// StartPendingCountWrites starts the goroutine that writes the pending
+// counts to the database whenever there are some, one UPDATE at a time:
+// however many requests pass their deadline before their counts are
+// written, at most this one write waits for the database. It is a no-op
+// when already started. The goroutine outlives the caller, so it runs with
+// its own context, which StopPendingCountWrites cancels to tell it to
+// finish.
+func (c *Cache) StartPendingCountWrites() {
+	if c.pendingCountsCancel != nil {
+		return
+	}
+
+	ctx, cancel := context.WithCancel(context.Background())
+	c.pendingCountsCancel = cancel
+
+	go func() {
+		c.pendingCountWriteLoop(ctx)
+	}()
+}
+
+// StopPendingCountWrites tells the goroutine StartPendingCountWrites
+// started, if it did, to finish, and waits for its write under way to end
+// and for it to return. It then writes the pending counts left, so that
+// they are written before the database closes. It waits for all of this at
+// most until ctx ends, then logs the counts not written and returns an
+// error.
+func (c *Cache) StopPendingCountWrites(ctx context.Context) error {
+	var err error
+
+	if c.pendingCountsCancel != nil {
+		c.pendingCountsCancel()
+
+		select {
+		case <-c.pendingCountsDone:
+		case <-ctx.Done():
+			// The write given up on here may not reach the database:
+			// database/sql closes without waiting for a query, and a
+			// write still waiting for the connection fails when the
+			// database closes.
+			err = fmt.Errorf("pending counts still being written: %w", ctx.Err())
+		}
+	}
+
+	if err == nil {
+		err = c.writePendingCounts(ctx)
+	}
+
+	if err != nil {
+		c.log.Error("counts not written at shutdown",
+			"hits", c.pendingHits.Load(),
+			"misses", c.pendingMisses.Load(),
+			"upstream_fetches", c.pendingUpstreamFetches.Load(),
+			"upstream_fetch_bytes", c.pendingUpstreamFetchBytes.Load(),
+			"transforms", c.pendingTransforms.Load(),
+			"error", err,
+		)
+
+		return err
+	}
+
+	return nil
+}
+
+// pendingCountWriteLoop is the body of the goroutine
+// StartPendingCountWrites starts. Once ctx is cancelled it starts no write
+// and returns, but does not cut off a write under way then. A write that
+// fails leaves the counts pending, for the next write.
+func (c *Cache) pendingCountWriteLoop(ctx context.Context) {
+	defer close(c.pendingCountsDone)
+
+	for {
+		select {
+		case <-ctx.Done():
+			return
+		case <-c.pendingCountsAdded:
+		}
+
+		// select picks at random when ctx is cancelled and a wakeup
+		// waits too.
+		if ctx.Err() != nil {
+			return
+		}
+
+		err := c.writePendingCounts(context.WithoutCancel(ctx))
+		if err != nil {
+			c.log.Warn("failed to write pending counts", "error", err)
+		}
+	}
+}
+
+// addPendingCount adds n to pendingCount, one of the pending counts, and
+// wakes the goroutine that writes them. pendingCountsAdded has capacity one,
+// so a wakeup already waiting is enough.
+func (c *Cache) addPendingCount(pendingCount *atomic.Int64, n int64) {
+	pendingCount.Add(n)
+
+	select {
+	case c.pendingCountsAdded <- struct{}{}:
+	default:
+	}
+}
+
+// writePendingCounts adds the pending counts to the cache_stats row in one
+// UPDATE, then takes what it wrote out of them, leaving any added
+// meanwhile. When the UPDATE fails, they all stay pending.
+func (c *Cache) writePendingCounts(ctx context.Context) error {
+	c.pendingCountsWriteMutex.Lock()
+	defer c.pendingCountsWriteMutex.Unlock()
+
+	hits := c.pendingHits.Load()
+	misses := c.pendingMisses.Load()
+	upstreamFetches := c.pendingUpstreamFetches.Load()
+	upstreamFetchBytes := c.pendingUpstreamFetchBytes.Load()
+	transforms := c.pendingTransforms.Load()
+
+	if hits+misses+upstreamFetches+upstreamFetchBytes+transforms == 0 {
+		return nil
+	}
+
+	_, err := c.db.ExecContext(ctx, `
+		UPDATE cache_stats
+		SET hit_count = hit_count + ?,
+		    miss_count = miss_count + ?,
+		    upstream_fetch_count = upstream_fetch_count + ?,
+		    upstream_fetch_bytes = upstream_fetch_bytes + ?,
+		    transform_count = transform_count + ?,
+		    last_updated_at = CURRENT_TIMESTAMP
+		WHERE id = 1
+	`, hits, misses, upstreamFetches, upstreamFetchBytes, transforms)
+	if err != nil {
+		return fmt.Errorf("failed to write pending counts: %w", err)
+	}
+
+	c.pendingHits.Add(-hits)
+	c.pendingMisses.Add(-misses)
+	c.pendingUpstreamFetches.Add(-upstreamFetches)
+	c.pendingUpstreamFetchBytes.Add(-upstreamFetchBytes)
+	c.pendingTransforms.Add(-transforms)
+
+	return nil
+}

internal/imgcache/pendingcounts_internal_test.go

@@ -0,0 +1,327 @@
+package imgcache
+
+import (
+	"context"
+	"database/sql"
+	"errors"
+	"testing"
+	"time"
+)
+
+// pendingCountsWait is how long a test waits for the database's connection,
+// for a count to reach the database, for a write to start waiting for the
+// connection, for a request to return past its deadline, or for
+// StopPendingCountWrites to return.
+const pendingCountsWait = 5 * time.Second
+
+// otherWritesWait is how long a test gives other writes, once one write waits
+// for the database's connection, to start waiting for it too.
+const otherWritesWait = 100 * time.Millisecond
+
+// holdDatabase takes the one connection of cache's database, so that every
+// other query waits for it, and returns the func that frees it.
+func holdDatabase(t *testing.T, cache *Cache) func() {
+	t.Helper()
+
+	ctx, cancel := context.WithTimeout(t.Context(), pendingCountsWait)
+	defer cancel()
+
+	conn, err := cache.db.Conn(ctx)
+	if err != nil {
+		t.Fatalf("failed to take the database connection: %v", err)
+	}
+
+	return func() { _ = conn.Close() }
+}
+
+// waitForConnectionWaits waits until db.Stats().WaitCount, the number of
+// times a caller has waited for a connection, reaches waits.
+func waitForConnectionWaits(t *testing.T, db *sql.DB, waits int64) {
+	t.Helper()
+
+	deadline := time.Now().Add(pendingCountsWait)
+
+	for db.Stats().WaitCount < waits {
+		if time.Now().After(deadline) {
+			t.Fatalf("callers waited for the database connection %d times, want %d",
+				db.Stats().WaitCount, waits)
+		}
+
+		time.Sleep(10 * time.Millisecond)
+	}
+}
+
+// waitForCounters waits until the cache_stats row holds want.
+func waitForCounters(t *testing.T, cache *Cache, want cacheStatsCounters) {
+	t.Helper()
+
+	deadline := time.Now().Add(pendingCountsWait)
+
+	for {
+		got := readCacheStatsCounters(t, cache)
+		if got == want {
+			return
+		}
+
+		if time.Now().After(deadline) {
+			t.Fatalf("counters = %+v, want %+v", got, want)
+		}
+
+		time.Sleep(10 * time.Millisecond)
+	}
+}
+
+// TestService_Get_ReturnsByItsDeadlineWhileTheDatabaseIsBusy holds the
+// database's one connection while a request whose fetch is held reaches its
+// deadline. The request must return with the deadline's error while the
+// connection is still held, as it waits for no database write past its
+// deadline, and its miss must reach the database once the connection is free.
+func TestService_Get_ReturnsByItsDeadlineWhileTheDatabaseIsBusy(t *testing.T) {
+	t.Parallel()
+
+	svc, fixtures, fetcher := setupHeldFetchService(t)
+
+	svc.cache.StartPendingCountWrites()
+	defer func() { _ = svc.cache.StopPendingCountWrites(t.Context()) }()
+
+	// Room for the request to reach its fetch on a busy host
+	const timeout = 2 * time.Second
+
+	ctx, cancel := context.WithTimeout(t.Context(), timeout)
+	defer cancel()
+
+	deadline, _ := ctx.Deadline()
+
+	results := startGet(ctx, svc, photoVariant(fixtures, 85, FitCover))
+
+	// The request has made its database reads by the time it fetches.
+	select {
+	case <-fetcher.started:
+	case <-time.After(timeout):
+		t.Fatal("request did not reach its fetch by its deadline")
+	}
+
+	releaseDatabase := holdDatabase(t, svc.cache)
+	defer releaseDatabase()
+
+	select {
+	case got := <-results:
+		t.Logf("Get() returned %v after its deadline, error = %v",
+			time.Since(deadline), got.err)
+
+		if !errors.Is(got.err, context.DeadlineExceeded) {
+			t.Errorf("Get() error = %v, want %v", got.err, context.DeadlineExceeded)
+		}
+	case <-time.After(time.Until(deadline) + pendingCountsWait):
+		t.Fatal("request did not return while the database was busy")
+	}
+
+	releaseDatabase()
+
+	waitForCounters(t, svc.cache, cacheStatsCounters{missCount: 1})
+}
+
+// TestIncrementStats_ManyCountsPastTheirDeadlineLeaveOneWriteWaiting holds the
+// database's one connection while many misses are counted past their
+// deadline. At most one write may then wait for the connection, and every
+// miss must reach the database once it is free.
+func TestIncrementStats_ManyCountsPastTheirDeadlineLeaveOneWriteWaiting(t *testing.T) {
+	t.Parallel()
+
+	cache, _ := newEvictionTestCache(t, 1<<30)
+
+	cache.StartPendingCountWrites()
+	defer func() { _ = cache.StopPendingCountWrites(t.Context()) }()
+
+	releaseDatabase := holdDatabase(t, cache)
+	defer releaseDatabase()
+
+	waitsBefore := cache.db.Stats().WaitCount
+
+	// Writes given a context past its deadline fail at once.
+	ended, cancel := context.WithDeadline(t.Context(), time.Now())
+	defer cancel()
+
+	const misses = 20
+
+	for range misses {
+		cache.IncrementStats(ended, false, 0)
+	}
+
+	// Once one write waits for the connection, any others start waiting too.
+	waitForConnectionWaits(t, cache.db, waitsBefore+1)
+	time.Sleep(otherWritesWait)
+
+	waits := cache.db.Stats().WaitCount - waitsBefore
+	t.Logf("%d writes waited for the database", waits)
+
+	if waits > 1 {
+		t.Errorf("%d writes waited for the database, want at most 1", waits)
+	}
+
+	releaseDatabase()
+
+	waitForCounters(t, cache, cacheStatsCounters{missCount: misses})
+}
+
+// TestStats_IncludesPendingCounts counts hits and misses whose writes miss
+// their deadline, and checks that Stats adds them to the database's counts
+// before they are written.
+func TestStats_IncludesPendingCounts(t *testing.T) {
+	t.Parallel()
+
+	cache, _ := newEvictionTestCache(t, 1<<30)
+
+	_, err := cache.db.ExecContext(t.Context(),
+		`UPDATE cache_stats SET hit_count = 75, miss_count = 25 WHERE id = 1`)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	// Writes given a context past its deadline fail at once.
+	ended, cancel := context.WithDeadline(t.Context(), time.Now())
+	defer cancel()
+
+	cache.IncrementStats(ended, true, 0)
+	cache.IncrementStats(ended, true, 0)
+	cache.IncrementStats(ended, false, 0)
+
+	stats, err := cache.Stats(t.Context())
+	if err != nil {
+		t.Fatalf("Stats() error = %v", err)
+	}
+
+	if stats.HitCount != 77 || stats.MissCount != 26 {
+		t.Errorf("HitCount = %d, MissCount = %d, want 77 and 26",
+			stats.HitCount, stats.MissCount)
+	}
+
+	want := cacheStatsCounters{hitCount: 75, missCount: 25}
+	if got := readCacheStatsCounters(t, cache); got != want {
+		t.Errorf("counters in the database = %+v, want %+v", got, want)
+	}
+}
+
+// TestStopPendingCountWrites_WritesPendingCounts holds the database's one
+// connection while the goroutine that writes the pending counts waits for it,
+// counts more, then stops that goroutine. The stop must leave the write under
+// way to finish rather than cut it off, and once the connection is free it
+// must write the counts that write left.
+func TestStopPendingCountWrites_WritesPendingCounts(t *testing.T) {
+	t.Parallel()
+
+	cache, _ := newEvictionTestCache(t, 1<<30)
+
+	cache.StartPendingCountWrites()
+	defer func() { _ = cache.StopPendingCountWrites(t.Context()) }()
+
+	releaseDatabase := holdDatabase(t, cache)
+	defer releaseDatabase()
+
+	waitsBefore := cache.db.Stats().WaitCount
+
+	// Writes given a context past its deadline fail at once.
+	ended, cancel := context.WithDeadline(t.Context(), time.Now())
+	defer cancel()
+
+	cache.IncrementStats(ended, true, 0)
+
+	// The goroutine's write waits for the connection.
+	waitForConnectionWaits(t, cache.db, waitsBefore+1)
+
+	// Counted after that write read the pending counts
+	cache.IncrementStats(ended, false, 0)
+	cache.IncrementUpstreamFetch(ended, 1024)
+	cache.IncrementTransformCount(ended)
+
+	// The goroutine is told to finish here as well as by the stop, so that it
+	// is told before its write under way ends, however late the stop runs.
+	// The counts above then reach the database only through the stop's own
+	// write.
+	cache.pendingCountsCancel()
+
+	stopped := make(chan error, 1)
+
+	go func() {
+		stopped <- cache.StopPendingCountWrites(t.Context())
+	}()
+
+	// Had the stop cut off the write under way, its own write would wait for
+	// the connection too.
+	time.Sleep(otherWritesWait)
+
+	waits := cache.db.Stats().WaitCount - waitsBefore
+	t.Logf("%d writes waited for the database", waits)
+
+	if waits > 1 {
+		t.Errorf("%d writes waited for the database, want 1: "+
+			"the stop cut off the write under way", waits)
+	}
+
+	releaseDatabase()
+
+	select {
+	case err := <-stopped:
+		if err != nil {
+			t.Fatalf("StopPendingCountWrites() error = %v", err)
+		}
+	case <-time.After(pendingCountsWait):
+		t.Fatal("StopPendingCountWrites() did not return once the database was free")
+	}
+
+	want := cacheStatsCounters{1, 1, 1, 1024, 1}
+	if got := readCacheStatsCounters(t, cache); got != want {
+		t.Errorf("counters = %+v, want %+v", got, want)
+	}
+}
+
+// TestStopPendingCountWrites_ReturnsWhenItsContextEnds holds the database's
+// one connection while the goroutine that writes the pending counts waits for
+// it, then stops that goroutine with a context that ends first. The stop must
+// return the context's error, and the write under way must still reach the
+// database once the connection is free.
+func TestStopPendingCountWrites_ReturnsWhenItsContextEnds(t *testing.T) {
+	t.Parallel()
+
+	cache, _ := newEvictionTestCache(t, 1<<30)
+
+	cache.StartPendingCountWrites()
+	defer func() { _ = cache.StopPendingCountWrites(t.Context()) }()
+
+	releaseDatabase := holdDatabase(t, cache)
+	defer releaseDatabase()
+
+	waitsBefore := cache.db.Stats().WaitCount
+
+	// Writes given a context past its deadline fail at once.
+	ended, cancel := context.WithDeadline(t.Context(), time.Now())
+	defer cancel()
+
+	cache.IncrementStats(ended, true, 0)
+
+	// The goroutine's write waits for the connection.
+	waitForConnectionWaits(t, cache.db, waitsBefore+1)
+
+	stopCtx, cancelStop := context.WithCancel(t.Context())
+	cancelStop()
+
+	stopped := make(chan error, 1)
+
+	go func() {
+		stopped <- cache.StopPendingCountWrites(stopCtx)
+	}()
+
+	select {
+	case err := <-stopped:
+		if !errors.Is(err, context.Canceled) {
+			t.Errorf("StopPendingCountWrites() error = %v, want %v",
+				err, context.Canceled)
+		}
+	case <-time.After(pendingCountsWait):
+		t.Fatal("StopPendingCountWrites() did not return once its context ended")
+	}
+
+	releaseDatabase()
+
+	waitForCounters(t, cache, cacheStatsCounters{hitCount: 1})
+}

internal/imgcache/service.go

@@ -162,7 +162,7 @@ func (s *Service) Get(ctx context.Context, req *ImageRequest) (*ImageResponse, e
 			// Fall through to re-process
 		} else {
 			// Counted also when the request context has ended meanwhile
-			s.cache.IncrementStats(context.WithoutCancel(ctx), true, 0)
+			s.cache.IncrementStats(ctx, true, 0)
 
 			return &ImageResponse{
 				Content:       reader,
@@ -179,7 +179,7 @@ func (s *Service) Get(ctx context.Context, req *ImageRequest) (*ImageResponse, e
 	// failed or the request context has ended meanwhile
 	response, err := s.processOrWait(ctx, req)
 
-	s.cache.IncrementStats(context.WithoutCancel(ctx), false, 0)
+	s.cache.IncrementStats(ctx, false, 0)
 
 	if err != nil {
 		return nil, err
@@ -300,14 +300,8 @@ func (s *Service) processOrWait(
 				}
 			}()
 
-			processingCtx := context.WithoutCancel(ctx)
-
-			if deadline, ok := ctx.Deadline(); ok {
-				var cancel context.CancelFunc
-
-				processingCtx, cancel = context.WithDeadline(processingCtx, deadline)
-				defer cancel()
-			}
+			processingCtx, cancel := withoutCancelKeepingDeadline(ctx)
+			defer cancel()
 
 			return s.processFromSourceOrFetch(processingCtx, req, cacheKey)
 		})
@@ -344,6 +338,20 @@ func (s *Service) processOrWait(
 	}, nil
 }
 
+// withoutCancelKeepingDeadline returns ctx without its cancellation but with
+// its deadline, if it has one, and the func that releases the returned
+// context.
+func withoutCancelKeepingDeadline(
+	ctx context.Context,
+) (context.Context, context.CancelFunc) {
+	deadline, hasDeadline := ctx.Deadline()
+	if !hasDeadline {
+		return context.WithoutCancel(ctx), func() {}
+	}
+
+	return context.WithDeadline(context.WithoutCancel(ctx), deadline)
+}
+
 // loadCachedSource opens source content from cache, without reading it, and
 // returns it with its size; nil if the cached data is unavailable, empty or
 // exceeds maxResponseSize.
@@ -453,7 +461,7 @@ func (s *Service) fetchAndProcess(
 	fetchBytes := int64(len(sourceData))
 
 	// Counted also when the request context has ended meanwhile
-	s.cache.IncrementUpstreamFetch(context.WithoutCancel(ctx), fetchBytes)
+	s.cache.IncrementUpstreamFetch(ctx, fetchBytes)
 
 	if err != nil {
 		return nil, fmt.Errorf("failed to read upstream response: %w", err)
@@ -535,7 +543,7 @@ func (s *Service) processAndStore(
 	processDuration := time.Since(processStart)
 
 	// Counted also when the request context has ended meanwhile
-	s.cache.IncrementTransformCount(context.WithoutCancel(ctx))
+	s.cache.IncrementTransformCount(ctx)
 
 	// Read processed content
 	processedData, err := io.ReadAll(processResult.Content)

internal/imgcache/service_internal_test.go

@@ -2,7 +2,9 @@ package imgcache
 
 import (
 	"context"
+	"encoding/json"
 	"io"
+	"os"
 	"testing"
 	"time"
 
@@ -430,6 +432,172 @@ func TestService_Get_Caching(t *testing.T) {
 	}
 }
 
+// TestService_Get_ServesSourceAndVariantCachedTwoDaysAgo caches a source and
+// a variant of it and sets back two days every time pixa stored for them.
+// For the source: fetched_at in source_metadata, fetched_at and
+// last_accessed_at in source_content, the fetched_at in its metadata file,
+// and the access and modification times of its file and of its metadata
+// file. For the variant: created_at and last_accessed_at in variant_content,
+// the created_at in its .meta file, and the access and modification times of
+// its file and of its .meta file. It then checks that the variant is still
+// served from the cache and that a new variant is made from the cached source
+// without fetching it again.
+//
+// Left at the present: the files' status change and birth times, which a
+// program cannot set, and the times of the directories holding the files,
+// which other entries share. The source's stored response headers are empty,
+// as the mock fetcher sends none. expires_at, etag and last_modified in
+// source_metadata and in the metadata file are never written, nor are the
+// request_cache and output_content tables.
+func TestService_Get_ServesSourceAndVariantCachedTwoDaysAgo(t *testing.T) {
+	t.Parallel()
+
+	svc, fixtures := SetupTestService(t)
+	variant := photoVariant(fixtures, 85, FitCover)
+
+	resp, err := svc.Get(t.Context(), variant)
+	if err != nil {
+		t.Fatalf("Get() first request error = %v", err)
+	}
+
+	_ = resp.Content.Close()
+
+	twoDaysAgo := time.Now().AddDate(0, 0, -2)
+	backdateSource(t, svc.cache, variant, twoDaysAgo)
+	backdateVariant(t, svc.cache, variant, twoDaysAgo)
+
+	resp, err = svc.Get(t.Context(), variant)
+	if err != nil {
+		t.Fatalf("Get() of the cached variant error = %v", err)
+	}
+
+	_ = resp.Content.Close()
+
+	if resp.CacheStatus != CacheHit {
+		t.Errorf("cached variant CacheStatus = %q, want %q",
+			resp.CacheStatus, CacheHit)
+	}
+
+	// Another quality is a new variant, made from the cached source
+	resp, err = svc.Get(t.Context(), photoVariant(fixtures, 40, FitCover))
+	if err != nil {
+		t.Fatalf("Get() of a new variant error = %v", err)
+	}
+
+	_ = resp.Content.Close()
+
+	fetches := readCacheStatsCounters(t, svc.cache).upstreamFetchCount
+	if fetches != 1 {
+		t.Errorf("upstream fetches = %d, want 1", fetches)
+	}
+}
+
+// backdateSource sets every time pixa stored for req's cached source to when,
+// as listed on TestService_Get_ServesSourceAndVariantCachedTwoDaysAgo.
+func backdateSource(
+	t *testing.T, cache *Cache, req *ImageRequest, when time.Time,
+) {
+	t.Helper()
+
+	pathHash := HashPath(req.SourcePath + "?" + req.SourceQuery)
+
+	meta, err := cache.srcMetadata.Load(req.SourceHost, pathHash)
+	if err != nil {
+		t.Fatalf("reading the source's metadata file: %v", err)
+	}
+
+	meta.FetchedAt = when.Unix()
+
+	err = cache.srcMetadata.Store(req.SourceHost, pathHash, meta)
+	if err != nil {
+		t.Fatalf("writing the source's metadata file: %v", err)
+	}
+
+	dbTime := when.UTC().Format(sqliteTimestampFormat)
+
+	updateOneRow(t, cache, `
+		UPDATE source_metadata SET fetched_at = ?
+		WHERE source_host = ? AND source_path = ? AND source_query = ?
+	`, dbTime, req.SourceHost, req.SourcePath, req.SourceQuery)
+	updateOneRow(t, cache,
+		`UPDATE source_content SET fetched_at = ? WHERE content_hash = ?`,
+		dbTime, meta.ContentHash)
+	setSourceLastAccessed(t, cache, ContentHash(meta.ContentHash), when)
+
+	for _, path := range []string{
+		cache.srcContent.hashToPath(ContentHash(meta.ContentHash)),
+		cache.srcMetadata.metaPath(req.SourceHost, pathHash),
+	} {
+		err = os.Chtimes(path, when, when)
+		if err != nil {
+			t.Fatalf("setting back the times of %s: %v", path, err)
+		}
+	}
+}
+
+// backdateVariant sets every time pixa stored for the cached variant req asks
+// for to when, as listed on
+// TestService_Get_ServesSourceAndVariantCachedTwoDaysAgo.
+func backdateVariant(
+	t *testing.T, cache *Cache, req *ImageRequest, when time.Time,
+) {
+	t.Helper()
+
+	key := CacheKey(req)
+
+	content, size, contentType, err := cache.variants.LoadWithMeta(key)
+	if err != nil || contentType == "" {
+		t.Fatalf("reading the variant's .meta file: content type %q, error %v",
+			contentType, err)
+	}
+
+	_ = content.Close()
+
+	meta, err := json.Marshal(VariantMeta{
+		ContentType: contentType,
+		Size:        size,
+		CreatedAt:   when.Unix(),
+	})
+	if err != nil {
+		t.Fatalf("encoding the variant's .meta file: %v", err)
+	}
+
+	path := cache.variants.keyToPath(key)
+
+	err = os.WriteFile(path+variantMetaSuffix, meta, StorageFilePerm)
+	if err != nil {
+		t.Fatalf("writing the variant's .meta file: %v", err)
+	}
+
+	updateOneRow(t, cache,
+		`UPDATE variant_content SET created_at = ? WHERE cache_key = ?`,
+		when.UTC().Format(sqliteTimestampFormat), string(key))
+	setVariantLastAccessed(t, cache, key, when)
+
+	for _, file := range []string{path, path + variantMetaSuffix} {
+		err = os.Chtimes(file, when, when)
+		if err != nil {
+			t.Fatalf("setting back the times of %s: %v", file, err)
+		}
+	}
+}
+
+// updateOneRow runs the UPDATE statement query and fails the test unless it
+// changed exactly one row.
+func updateOneRow(t *testing.T, cache *Cache, query string, args ...any) {
+	t.Helper()
+
+	result, err := cache.db.ExecContext(t.Context(), query, args...)
+	if err != nil {
+		t.Fatalf("%s: %v", query, err)
+	}
+
+	rows, err := result.RowsAffected()
+	if err != nil || rows != 1 {
+		t.Fatalf("%s: rows = %d, error = %v, want 1 row", query, rows, err)
+	}
+}
+
 func TestService_Get_DifferentSizes(t *testing.T) {
 	t.Parallel()
 

internal/imgcache/stats_internal_test.go

@@ -43,7 +43,6 @@ func TestStats_HitRateIsRatio(t *testing.T) {
 
 	cache, err := NewCache(db, CacheConfig{
 		StateDir:    dir,
-		CacheTTL:    time.Hour,
 		NegativeTTL: 5 * time.Minute,
 	})
 	if err != nil {
@@ -91,7 +90,6 @@ func TestStats_ZeroCounts(t *testing.T) {
 
 	cache, err := NewCache(db, CacheConfig{
 		StateDir:    dir,
-		CacheTTL:    time.Hour,
 		NegativeTTL: 5 * time.Minute,
 	})
 	if err != nil {
@@ -120,7 +118,6 @@ func TestStats_LogsFailedCountQueries(t *testing.T) {
 
 	cache, err := NewCache(db, CacheConfig{
 		StateDir:    t.TempDir(),
-		CacheTTL:    time.Hour,
 		NegativeTTL: 5 * time.Minute,
 		Logger:      slog.New(slog.NewJSONHandler(&logBuf, nil)),
 	})
@@ -162,7 +159,6 @@ func TestIncrementStats_LogsFailedUpdates(t *testing.T) {
 
 	cache, err := NewCache(db, CacheConfig{
 		StateDir:    t.TempDir(),
-		CacheTTL:    time.Hour,
 		NegativeTTL: 5 * time.Minute,
 		Logger:      slog.New(slog.NewJSONHandler(&logBuf, nil)),
 	})
@@ -232,7 +228,6 @@ func TestStats_DisabledCacheReportsNoItems(t *testing.T) {
 
 	disabled, err := NewCache(enabled.db, CacheConfig{
 		StateDir:         t.TempDir(),
-		CacheTTL:         time.Hour,
 		NegativeTTL:      5 * time.Minute,
 		DisableDiskCache: true,
 	})

internal/imgcache/testutil_internal_test.go

@@ -185,7 +185,6 @@ func SetupTestService(
 
 	cache, err := NewCache(db, CacheConfig{
 		StateDir:    tmpDir,
-		CacheTTL:    time.Hour,
 		NegativeTTL: 5 * time.Minute,
 	})
 	if err != nil {

internal/middleware/middleware.go

@@ -98,9 +98,10 @@ func (s *Middleware) ClientIP() func(http.Handler) http.Handler {
 // 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.
+// stays bounded. limitHandler writes the 429 after Retry-After is set; nil
+// keeps the rate limit library's plain-text "Too Many Requests".
 func (s *Middleware) RateLimit(
-	requestLimit int, window time.Duration,
+	requestLimit int, window time.Duration, limitHandler http.HandlerFunc,
 ) func(http.Handler) http.Handler {
 	return httprate.LimitBy(requestLimit, window,
 		func(r *http.Request) (string, error) {
@@ -112,7 +113,8 @@ func (s *Middleware) RateLimit(
 			}
 
 			return httprate.CanonicalizeIP(ip), nil
-		})
+		},
+		httprate.WithLimitHandler(limitHandler))
 }
 
 // requestIDPattern is what a request's own X-Request-Id must look like to be

internal/server/image_rate_limit_internal_test.go

@@ -0,0 +1,204 @@
+package server
+
+import (
+	"encoding/json"
+	"net/http"
+	"net/http/httptest"
+	"strconv"
+	"testing"
+
+	"sneak.berlin/go/pixa/internal/config"
+)
+
+// requestImageFrom sends method path to s from remoteAddr and returns the
+// response. The image handlers refuse an unsigned image URL with 401 and a
+// token they cannot decrypt with 400, so either status shows the limit let
+// the request through.
+func requestImageFrom(
+	t *testing.T, s *Server, method, path, remoteAddr string,
+) *httptest.ResponseRecorder {
+	t.Helper()
+
+	req := httptest.NewRequestWithContext(t.Context(), method, path, nil)
+	req.RemoteAddr = remoteAddr
+
+	rec := httptest.NewRecorder()
+	s.ServeHTTP(rec, req)
+
+	return rec
+}
+
+// TestImageRequestLimitRefusesRequestOverLimit verifies that GET and HEAD on
+// both image routes count toward one limit per client, and that the request
+// after image_requests_per_minute of them is refused with 429 and a
+// Retry-After header.
+func TestImageRequestLimitRefusesRequestOverLimit(t *testing.T) {
+	t.Parallel()
+
+	requests := []struct {
+		method string
+		path   string
+		want   int
+	}{
+		{http.MethodGet, unsignedImagePath, http.StatusUnauthorized},
+		{http.MethodHead, unsignedImagePath, http.StatusUnauthorized},
+		{http.MethodGet, encryptedImagePath, http.StatusBadRequest},
+	}
+
+	s := newTestServer(t)
+	s.config.ImageRequestsPerMinute = len(requests)
+	s.SetupRoutes()
+
+	for _, tc := range requests {
+		rec := requestImageFrom(t, s, tc.method, tc.path, firstClient)
+		if rec.Code != tc.want {
+			t.Fatalf("%s %s within the limit status = %d, want %d",
+				tc.method, tc.path, rec.Code, tc.want)
+		}
+	}
+
+	rec := requestImageFrom(t, s, http.MethodHead, encryptedImagePath, firstClient)
+	if rec.Code != http.StatusTooManyRequests {
+		t.Fatalf("request over the limit status = %d, want %d",
+			rec.Code, http.StatusTooManyRequests)
+	}
+
+	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)
+	}
+}
+
+// TestImageRequestLimitAnswersWithJSONError verifies that the 429 for a
+// request over the limit carries Retry-After and the JSON error body the
+// image routes send for their other errors.
+func TestImageRequestLimitAnswersWithJSONError(t *testing.T) {
+	t.Parallel()
+
+	s := newTestServer(t)
+	s.config.ImageRequestsPerMinute = 1
+	s.SetupRoutes()
+
+	requestImageFrom(t, s, http.MethodGet, unsignedImagePath, firstClient)
+
+	rec := requestImageFrom(t, s, http.MethodGet, unsignedImagePath, firstClient)
+	t.Logf("status %d, body %s", rec.Code, rec.Body.String())
+
+	if rec.Code != http.StatusTooManyRequests {
+		t.Fatalf("request over the limit status = %d, want %d",
+			rec.Code, http.StatusTooManyRequests)
+	}
+
+	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)
+	}
+
+	contentType := rec.Header().Get("Content-Type")
+	if contentType != "application/json" {
+		t.Errorf("Content-Type = %q, want %q", contentType, "application/json")
+	}
+
+	var body struct {
+		Error     string `json:"error"`
+		Status    int    `json:"status"`
+		Timestamp string `json:"timestamp"`
+	}
+
+	err = json.NewDecoder(rec.Body).Decode(&body)
+	if err != nil {
+		t.Fatalf("body is not JSON: %v", err)
+	}
+
+	if body.Error == "" || body.Status != http.StatusTooManyRequests ||
+		body.Timestamp == "" {
+		t.Errorf("body = %+v, want an error, status %d and a timestamp",
+			body, http.StatusTooManyRequests)
+	}
+}
+
+// TestImageRequestLimitCountsClientsSeparately verifies that one client going
+// over the limit does not limit another.
+func TestImageRequestLimitCountsClientsSeparately(t *testing.T) {
+	t.Parallel()
+
+	s := newTestServer(t)
+	s.config.ImageRequestsPerMinute = 1
+	s.SetupRoutes()
+
+	rec := requestImageFrom(t, s, http.MethodGet, unsignedImagePath, firstClient)
+	if rec.Code != http.StatusUnauthorized {
+		t.Fatalf("first client's first request status = %d, want %d",
+			rec.Code, http.StatusUnauthorized)
+	}
+
+	rec = requestImageFrom(t, s, http.MethodGet, unsignedImagePath, firstClient)
+	if rec.Code != http.StatusTooManyRequests {
+		t.Fatalf("first client's second request status = %d, want %d",
+			rec.Code, http.StatusTooManyRequests)
+	}
+
+	rec = requestImageFrom(t, s, http.MethodGet, unsignedImagePath, secondClient)
+	if rec.Code != http.StatusUnauthorized {
+		t.Errorf("second client's first request status = %d, want %d",
+			rec.Code, http.StatusUnauthorized)
+	}
+}
+
+// TestImageRequestLimitZeroLetsEveryRequestThrough verifies that with
+// image_requests_per_minute set to 0 no image request is refused with 429,
+// not even past the default limit.
+func TestImageRequestLimitZeroLetsEveryRequestThrough(t *testing.T) {
+	t.Parallel()
+
+	s := newTestServer(t)
+	s.config.ImageRequestsPerMinute = 0
+	s.SetupRoutes()
+
+	for request := range config.DefaultImageRequestsPerMinute + 1 {
+		rec := requestImageFrom(t, s, http.MethodGet, unsignedImagePath, firstClient)
+		if rec.Code != http.StatusUnauthorized {
+			t.Fatalf("request %d status = %d, want %d",
+				request+1, rec.Code, http.StatusUnauthorized)
+		}
+	}
+}
+
+// TestImageRequestLimitDoesNotCountPreflight verifies that a browser's CORS
+// preflight request to an image route is answered without being counted, so
+// a client that has sent several still gets its image request through.
+func TestImageRequestLimitDoesNotCountPreflight(t *testing.T) {
+	t.Parallel()
+
+	s := newTestServer(t)
+	s.config.AccessControlAllowOrigin = config.DefaultAccessControlAllowOrigin
+	s.config.ImageRequestsPerMinute = 1
+	s.SetupRoutes()
+
+	for range 3 {
+		req := httptest.NewRequestWithContext(
+			t.Context(), http.MethodOptions, unsignedImagePath, nil)
+		req.RemoteAddr = firstClient
+		req.Header.Set("Origin", "https://app.example.com")
+		req.Header.Set("Access-Control-Request-Method", http.MethodGet)
+
+		rec := httptest.NewRecorder()
+		s.ServeHTTP(rec, req)
+
+		if rec.Code != http.StatusOK {
+			t.Fatalf("preflight status = %d, want %d", rec.Code, http.StatusOK)
+		}
+	}
+
+	rec := requestImageFrom(t, s, http.MethodGet, unsignedImagePath, firstClient)
+	if rec.Code != http.StatusUnauthorized {
+		t.Errorf("image request after preflights status = %d, want %d",
+			rec.Code, http.StatusUnauthorized)
+	}
+}

internal/server/routes.go

@@ -66,7 +66,7 @@ func (s *Server) SetupRoutes() {
 		r.Use(s.h.LimitBody(handlers.MaxFormBytes))
 		r.Use(s.h.CSRF())
 		r.Get("/", s.h.HandleRoot())
-		r.With(s.mw.RateLimit(LoginAttemptsPerMinute, time.Minute)).
+		r.With(s.mw.RateLimit(LoginAttemptsPerMinute, time.Minute, nil)).
 			Post("/", s.h.HandleRoot())
 		r.Post("/generate", s.h.HandleGenerateURL())
 	})
@@ -88,6 +88,15 @@ func (s *Server) SetupRoutes() {
 		r.Group(func(r chi.Router) {
 			r.Use(s.refuseDuringMaintenance)
 
+			// Limited per client, as the login POST is, but the 429 has
+			// the image routes' JSON error body; 0 turns the limit off.
+			// The CORS middleware answers a preflight before it gets
+			// here, so a preflight is not counted.
+			if s.config.ImageRequestsPerMinute > 0 {
+				r.Use(s.mw.RateLimit(s.config.ImageRequestsPerMinute,
+					time.Minute, s.h.HandleTooManyRequests()))
+			}
+
 			// Main image proxy route
 			// /v1/image/<host>/<path>/<width>x<height>.<format>, or with no
 			// format /v1/image/<host>/<path>/<width>x<height>

internal/server/svg_as_avif_internal_test.go

@@ -0,0 +1,71 @@
+package server
+
+import (
+	"io"
+	"net/http"
+	"net/http/httptest"
+	"strings"
+	"testing"
+
+	"sneak.berlin/go/pixa/internal/encurl"
+	"sneak.berlin/go/pixa/internal/imgcache"
+)
+
+// svgServedAsAVIF is an SVG whose first bytes pass the first-bytes check for
+// AVIF: its XML comment puts "ftypavis" at bytes 4 to 11, where an AVIF file
+// has its ftyp box and brand. libvips would load it as SVG.
+const svgServedAsAVIF = `<!--ftypavis--><svg xmlns="http://www.w3.org/2000/svg" ` +
+	`width="64" height="48"><rect width="64" height="48"/></svg>`
+
+// TestImageProxyRefusesSVGServedAsAVIF requests svgServedAsAVIF, which the
+// upstream answers as image/avif, through both image routes, resized as PNG
+// and in its own format (orig). Each request is answered 415, as for an SVG
+// source, never with an image.
+func TestImageProxyRefusesSVGServedAsAVIF(t *testing.T) {
+	t.Parallel()
+
+	upstream := httptest.NewServer(http.HandlerFunc(
+		func(w http.ResponseWriter, _ *http.Request) {
+			w.Header().Set("Content-Type", "image/avif")
+			_, _ = io.WriteString(w, svgServedAsAVIF)
+		}))
+	t.Cleanup(upstream.Close)
+
+	s, _, _ := startImageProxy(t, upstream)
+
+	generator, err := encurl.NewGenerator(testSigningKey)
+	if err != nil {
+		t.Fatalf("encurl.NewGenerator: %v", err)
+	}
+
+	encryptedURL := func(format imgcache.ImageFormat) string {
+		token, err := generator.Generate(&encurl.Payload{
+			SourceHost: upstreamHost, SourcePath: "/drawing.avif",
+			Width: 32, Height: 24, Format: format,
+		})
+		if err != nil {
+			t.Fatalf("encurl Generate: %v", err)
+		}
+
+		return "/v1/e/" + token + "/drawing." + string(format)
+	}
+
+	for _, target := range []string{
+		"/v1/image/" + upstreamHost + "/drawing.avif/32x24.png",
+		"/v1/image/" + upstreamHost + "/drawing.avif/64x48.orig",
+		encryptedURL(imgcache.FormatPNG),
+		encryptedURL(imgcache.FormatOriginal),
+	} {
+		rec := httptest.NewRecorder()
+		s.ServeHTTP(rec, httptest.NewRequestWithContext(
+			t.Context(), http.MethodGet, target, nil))
+		t.Logf("GET %s: %d, Content-Type %s, body %q",
+			target, rec.Code, rec.Header().Get("Content-Type"), rec.Body.String())
+
+		if rec.Code != http.StatusUnsupportedMediaType ||
+			!strings.Contains(rec.Body.String(), "unsupported source format") {
+			t.Errorf("GET %s: %d %q, want %d unsupported source format",
+				target, rec.Code, rec.Body.String(), http.StatusUnsupportedMediaType)
+		}
+	}
+}

internal/server/svg_internal_test.go

@@ -0,0 +1,41 @@
+package server
+
+import (
+	"io"
+	"net/http"
+	"net/http/httptest"
+	"testing"
+)
+
+// TestImageProxyRefusesSVG requests an image the upstream answers as SVG,
+// in its own format (orig) and resized as PNG, through pixa's router,
+// upstream fetcher and image processor. pixa does not accept SVG as a
+// source, so each request is answered 415, never with an image.
+func TestImageProxyRefusesSVG(t *testing.T) {
+	t.Parallel()
+
+	upstream := httptest.NewServer(http.HandlerFunc(
+		func(w http.ResponseWriter, _ *http.Request) {
+			w.Header().Set("Content-Type", "image/svg+xml")
+			_, _ = io.WriteString(w, `<svg xmlns="http://www.w3.org/2000/svg" `+
+				`width="64" height="48"><rect width="64" height="48"/></svg>`)
+		}))
+	t.Cleanup(upstream.Close)
+
+	s, _, _ := startImageProxy(t, upstream)
+
+	for _, sizeFormat := range []string{"64x48.orig", "32x24.png"} {
+		target := "/v1/image/" + upstreamHost + "/drawing.svg/" + sizeFormat
+
+		rec := httptest.NewRecorder()
+		s.ServeHTTP(rec, httptest.NewRequestWithContext(
+			t.Context(), http.MethodGet, target, nil))
+		t.Logf("GET %s: %d, Content-Type %s, body %s",
+			target, rec.Code, rec.Header().Get("Content-Type"), rec.Body.String())
+
+		if rec.Code != http.StatusUnsupportedMediaType {
+			t.Errorf("GET %s status = %d, want %d",
+				target, rec.Code, http.StatusUnsupportedMediaType)
+		}
+	}
+}

script/loadtest

@@ -94,7 +94,8 @@ main() {
 }
 
 # start_containers starts a new origin and a new pixad, and waits up to 30
-# seconds for pixad's health check to pass.
+# seconds for pixad's health check to pass. pixad sees all of vegeta's
+# requests come from one address, so its image request limit is off.
 start_containers() {
     docker run -d --name "$run-origin" \
         --network "$run" --network-alias origin \
@@ -104,6 +105,7 @@ start_containers() {
         --network "$run" -p 127.0.0.1::8080 --health-interval=1s \
         -e PIXA_SIGNING_KEY="$(head -c 32 /dev/urandom | base64)" \
         -e PIXA_ALLOWLIST_HOSTS=origin -e PIXA_ALLOW_HTTP=true \
+        -e PIXA_IMAGE_REQUESTS_PER_MINUTE=0 \
         "$image" >/dev/null
 
     waited=0