Limit each client's requests to the image routes (closes #236)

The new setting image_requests_per_minute (PIXA_IMAGE_REQUESTS_PER_MINUTE),
default 600, caps the GET and HEAD requests one client sends to /v1/image/
and /v1/e/ per minute; 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 sits in the image routes' group behind the CORS middleware, so a
preflight is not counted. 0 turns it off; a negative or non-integer value
stops startup.

TestEnvironmentSetsEveryKey gains the new variable, under the owner's
standing approval in #64. To stay
within the linters' limits, the sentry_dsn check moves unchanged into
validateSentryDSN, and the cache_max_bytes explicit flag is set in one
line.

Model: opus-5-5

Dockerfile

@@ -32,13 +32,10 @@ RUN script/bootstrap --cgo
 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, 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 ./... || \
+# the step fails even if the second run passes.
+RUN go test -count=1 -timeout 90s -race -cover ./... || \
     { echo "--- Rerunning with -v for details ---"; \
-      go test -count=1 -timeout 90s -race -parallel 4 -v ./...; exit 1; }
+      go test -count=1 -timeout 90s -race -v ./...; exit 1; }
 
 # Build stage. Nothing is wanted from the two phases above: these copies
 # make BuildKit build them first, so this stage runs only when lint and

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:
@@ -83,12 +84,10 @@ 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, 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.
+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.
 
 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
@@ -188,10 +187,10 @@ 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
-  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.
+  address in a blocked network (see `blocked_networks`); 429 over
+  `image_requests_per_minute` (below); 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` or `HEAD` `/v1/e/<token>/<name>` — an image through an encrypted URL
   (see Encrypted URLs). Needs: nothing but the URL. Answers: 200; 304 when
   `If-None-Match` matches the image's `ETag`; 400 for a token that does not
@@ -199,7 +198,7 @@ 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, 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`,
@@ -315,6 +314,14 @@ 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`, every request counts as the same 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
@@ -484,6 +491,7 @@ 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`                 |
@@ -533,13 +541,13 @@ 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;
@@ -572,6 +580,11 @@ 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`, every
+  request counts as the same 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

@@ -26,23 +26,18 @@ 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 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.
+- 2026-10-12 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 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
@@ -749,8 +744,6 @@ 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 every request counts as the same 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

@@ -4,7 +4,6 @@ package handlers
 import (
 	"context"
 	"encoding/json"
-	"errors"
 	"log/slog"
 	"net/http"
 	"time"
@@ -72,21 +71,16 @@ func New(lc fx.Lifecycle, params Params) (*Handlers, error) {
 	}
 
 	lc.Append(fx.Hook{
-		//nolint:contextcheck // the cache's goroutines outlive OnStart; OnStop stops them
+		//nolint:contextcheck // the eviction loop outlives OnStart; OnStop cancels it
 		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 errors.Join(
-				s.imgCache.StopEviction(ctx),
-				s.imgCache.StopPendingCountWrites(ctx),
-			)
+			return s.imgCache.StopEviction(ctx)
 		},
 	})
 
@@ -128,9 +122,6 @@ 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/imgcache/cache.go

@@ -11,7 +11,6 @@ import (
 	"io"
 	"log/slog"
 	"path/filepath"
-	"sync/atomic"
 	"time"
 
 	lru "github.com/hashicorp/golang-lru/v2"
@@ -80,22 +79,6 @@ 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.
-	pendingHits               atomic.Int64
-	pendingMisses             atomic.Int64
-	pendingUpstreamFetches    atomic.Int64
-	pendingUpstreamFetchBytes atomic.Int64
-	pendingTransforms         atomic.Int64
-	pendingCountsAdded        chan struct{}
-	pendingCountsDone         chan struct{}
-	pendingCountsCancel       context.CancelFunc
-
 	// 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.
@@ -156,9 +139,6 @@ func newCache(
 		metaCache:        metaCache,
 		contentLocks:     newContentLock(),
 
-		pendingCountsAdded: make(chan struct{}, 1),
-		pendingCountsDone:  make(chan struct{}),
-
 		reconciliationPageSize: defaultReconciliationPageSize,
 	}
 
@@ -504,10 +484,6 @@ func (c *Cache) Stats(ctx context.Context) (*CacheStats, error) {
 		return nil, fmt.Errorf("failed to get cache stats: %w", err)
 	}
 
-	// Hits and misses not yet written count too (see StartPendingCountWrites)
-	stats.HitCount += c.pendingHits.Load()
-	stats.MissCount += c.pendingMisses.Load()
-
 	// Count and size the cached source images and processed variants from
 	// their tables. A disabled cache holds none, whatever rows an earlier
 	// run left.
@@ -535,30 +511,19 @@ 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. 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).
+// fetchBytes bytes, as IncrementUpstreamFetch does.
 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 {
-		pendingCount = &c.pendingHits
-
-		_, err = c.db.ExecContext(countCtx, `
+		_, err = c.db.ExecContext(ctx, `
 			UPDATE cache_stats
 			SET hit_count = hit_count + 1,
 			    last_updated_at = CURRENT_TIMESTAMP
 			WHERE id = 1
 		`)
 	} else {
-		_, err = c.db.ExecContext(countCtx, `
+		_, err = c.db.ExecContext(ctx, `
 			UPDATE cache_stats
 			SET miss_count = miss_count + 1,
 			    last_updated_at = CURRENT_TIMESTAMP
@@ -566,10 +531,7 @@ func (c *Cache) IncrementStats(ctx context.Context, hit bool, fetchBytes int64)
 		`)
 	}
 
-	switch {
-	case errors.Is(err, context.DeadlineExceeded):
-		c.addPendingCount(pendingCount, 1)
-	case err != nil:
+	if err != nil {
 		c.log.Warn("failed to count cache hit or miss", "hit", hit, "error", err)
 	}
 
@@ -583,22 +545,14 @@ func (c *Cache) IncrementUpstreamFetch(ctx context.Context, fetchBytes int64) {
 		return
 	}
 
-	countCtx, cancel := withoutCancelKeepingDeadline(ctx)
-	defer cancel()
-
-	_, err := c.db.ExecContext(countCtx, `
+	_, err := c.db.ExecContext(ctx, `
 		UPDATE cache_stats
 		SET upstream_fetch_count = upstream_fetch_count + 1,
 		    upstream_fetch_bytes = upstream_fetch_bytes + ?,
 		    last_updated_at = CURRENT_TIMESTAMP
 		WHERE id = 1
 	`, fetchBytes)
-
-	switch {
-	case errors.Is(err, context.DeadlineExceeded):
-		c.addPendingCount(&c.pendingUpstreamFetches, 1)
-		c.addPendingCount(&c.pendingUpstreamFetchBytes, fetchBytes)
-	case err != nil:
+	if err != nil {
 		c.log.Warn("failed to count upstream fetch",
 			"fetch_bytes", fetchBytes, "error", err)
 	}
@@ -606,20 +560,13 @@ 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) {
-	countCtx, cancel := withoutCancelKeepingDeadline(ctx)
-	defer cancel()
-
-	_, err := c.db.ExecContext(countCtx, `
+	_, err := c.db.ExecContext(ctx, `
 		UPDATE cache_stats
 		SET transform_count = transform_count + 1,
 		    last_updated_at = CURRENT_TIMESTAMP
 		WHERE id = 1
 	`)
-
-	switch {
-	case errors.Is(err, context.DeadlineExceeded):
-		c.addPendingCount(&c.pendingTransforms, 1)
-	case err != nil:
+	if err != nil {
 		c.log.Warn("failed to count transform", "error", err)
 	}
 }

internal/imgcache/pending_counts_internal_test.go

@@ -1,263 +0,0 @@
-package imgcache
-
-import (
-	"context"
-	"database/sql"
-	"errors"
-	"testing"
-	"time"
-)
-
-// pendingCountsWait is how long a test waits for a count to reach the
-// database, or for a write to start waiting for the database's connection.
-const pendingCountsWait = 5 * time.Second
-
-// 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()
-
-	conn, err := cache.db.Conn(t.Context())
-	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 still return by its deadline with the
-// deadline's error, 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()) }()
-
-	const timeout = 200 * time.Millisecond
-
-	ctx, cancel := context.WithTimeout(t.Context(), timeout)
-	defer cancel()
-
-	results := startGet(ctx, svc, photoVariant(fixtures, 85, FitCover))
-
-	// The request has made its database reads by the time it fetches.
-	<-fetcher.started
-
-	releaseDatabase := holdDatabase(t, svc.cache)
-	defer releaseDatabase()
-
-	select {
-	case got := <-results:
-		deadline, _ := ctx.Deadline()
-		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(timeout + time.Second):
-		t.Fatal("request did not return by its deadline while the database was busy")
-	}
-
-	releaseDatabase()
-
-	waitForCounters(t, svc.cache, cacheStatsCounters{missCount: 1})
-}
-
-// TestService_Get_ManyRequestsPastTheirDeadlineLeaveOneWriteWaiting holds the
-// database's one connection while many requests whose fetches are held reach
-// their deadline. At most one write may then wait for the connection, and
-// every miss must reach the database once it is free.
-func TestService_Get_ManyRequestsPastTheirDeadlineLeaveOneWriteWaiting(t *testing.T) {
-	t.Parallel()
-
-	svc, fixtures, fetcher := setupHeldFetchService(t)
-
-	svc.cache.StartPendingCountWrites()
-	defer func() { _ = svc.cache.StopPendingCountWrites(t.Context()) }()
-
-	const (
-		requests = 20
-		timeout  = 200 * time.Millisecond
-	)
-
-	ctx, cancel := context.WithTimeout(t.Context(), timeout)
-	defer cancel()
-
-	// Each request asks for a variant of its own, so each fetches.
-	results := make([]<-chan getResult, requests)
-	for i := range results {
-		results[i] = startGet(ctx, svc, photoVariant(fixtures, i+1, FitCover))
-	}
-
-	// Each request has made its database reads by the time it fetches.
-	for range requests {
-		<-fetcher.started
-	}
-
-	releaseDatabase := holdDatabase(t, svc.cache)
-	defer releaseDatabase()
-
-	waitsBefore := svc.cache.db.Stats().WaitCount
-
-	// Once one write waits for the connection, any others start waiting too.
-	waitForConnectionWaits(t, svc.cache.db, waitsBefore+1)
-	time.Sleep(arrivalWait)
-
-	waits := svc.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)
-	}
-
-	for _, result := range results {
-		select {
-		case got := <-result:
-			if !errors.Is(got.err, context.DeadlineExceeded) {
-				t.Errorf("Get() error = %v, want %v", got.err, context.DeadlineExceeded)
-			}
-		case <-time.After(time.Second):
-			t.Fatal("request did not return by its deadline while the database was busy")
-		}
-	}
-
-	releaseDatabase()
-
-	waitForCounters(t, svc.cache, cacheStatsCounters{missCount: requests})
-}
-
-// 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,
-// then stops that goroutine. The stop must write the counts once the
-// connection is free.
-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)
-	cache.IncrementStats(ended, false, 0)
-	cache.IncrementUpstreamFetch(ended, 1024)
-	cache.IncrementTransformCount(ended)
-
-	// The goroutine's write waits for the connection.
-	waitForConnectionWaits(t, cache.db, waitsBefore+1)
-
-	stopped := make(chan error, 1)
-
-	go func() {
-		stopped <- cache.StopPendingCountWrites(t.Context())
-	}()
-
-	// The stop's own write waits for it once the goroutine has returned.
-	waitForConnectionWaits(t, cache.db, waitsBefore+2)
-
-	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)
-	}
-}

internal/imgcache/pendingcounts.go

@@ -1,127 +0,0 @@
-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.
-func (c *Cache) StartPendingCountWrites() {
-	if c.pendingCountsCancel != nil {
-		return
-	}
-
-	ctx, cancel := context.WithCancel(context.Background())
-	c.pendingCountsCancel = cancel
-
-	go func() {
-		c.pendingCountWriteLoop(ctx)
-	}()
-}
-
-// StopPendingCountWrites stops the goroutine StartPendingCountWrites
-// started, if it did, then writes the pending counts once more, so that
-// they are written before the database closes. It waits for both at most
-// until ctx ends. It logs the counts still unwritten then, which are lost,
-// and returns an error.
-func (c *Cache) StopPendingCountWrites(ctx context.Context) error {
-	if c.pendingCountsCancel != nil {
-		c.pendingCountsCancel()
-
-		select {
-		case <-c.pendingCountsDone:
-		case <-ctx.Done():
-		}
-	}
-
-	err := c.writePendingCounts(ctx)
-	if err != nil {
-		c.log.Error("counts lost 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. It returns when ctx is cancelled. 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:
-		}
-
-		err := c.writePendingCounts(ctx)
-		if err != nil && ctx.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 {
-	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/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(ctx, true, 0)
+			s.cache.IncrementStats(context.WithoutCancel(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(ctx, false, 0)
+	s.cache.IncrementStats(context.WithoutCancel(ctx), false, 0)
 
 	if err != nil {
 		return nil, err
@@ -300,8 +300,14 @@ func (s *Service) processOrWait(
 				}
 			}()
 
-			processingCtx, cancel := withoutCancelKeepingDeadline(ctx)
-			defer cancel()
+			processingCtx := context.WithoutCancel(ctx)
+
+			if deadline, ok := ctx.Deadline(); ok {
+				var cancel context.CancelFunc
+
+				processingCtx, cancel = context.WithDeadline(processingCtx, deadline)
+				defer cancel()
+			}
 
 			return s.processFromSourceOrFetch(processingCtx, req, cacheKey)
 		})
@@ -338,20 +344,6 @@ 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.
@@ -461,7 +453,7 @@ func (s *Service) fetchAndProcess(
 	fetchBytes := int64(len(sourceData))
 
 	// Counted also when the request context has ended meanwhile
-	s.cache.IncrementUpstreamFetch(ctx, fetchBytes)
+	s.cache.IncrementUpstreamFetch(context.WithoutCancel(ctx), fetchBytes)
 
 	if err != nil {
 		return nil, fmt.Errorf("failed to read upstream response: %w", err)
@@ -543,7 +535,7 @@ func (s *Service) processAndStore(
 	processDuration := time.Since(processStart)
 
 	// Counted also when the request context has ended meanwhile
-	s.cache.IncrementTransformCount(ctx)
+	s.cache.IncrementTransformCount(context.WithoutCancel(ctx))
 
 	// Read processed content
 	processedData, err := io.ReadAll(processResult.Content)

internal/server/image_rate_limit_internal_test.go

@@ -0,0 +1,152 @@
+package server
+
+import (
+	"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)
+	}
+}
+
+// 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

@@ -88,6 +88,13 @@ func (s *Server) SetupRoutes() {
 		r.Group(func(r chi.Router) {
 			r.Use(s.refuseDuringMaintenance)
 
+			// Limited per client, as the login POST is; 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))
+			}
+
 			// Main image proxy route
 			// /v1/image/<host>/<path>/<width>x<height>.<format>, or with no
 			// format /v1/image/<host>/<path>/<width>x<height>