Say the source host is signed as the URL writes it (part of #246)

The Signature Specification read as though the hostname were signed
with ":" and the port appended. The code signs the host segment as the
URL writes it up to the first "/", lower-cased, so IPv6 brackets and a
":" with or without a port are kept. The README line, the TODO.md entry
and the parser comment now say so.

Model: opus-5-5

README.md

@@ -198,11 +198,9 @@ path under `/v1/` answers 200, in maintenance mode too.
   redirects to, is `localhost`, ends in `.localhost` or `.local`, or has an
   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), with a body
-  whose first bytes are not those of the format its `Content-Type` names, 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, or after
-  a body whose first bytes are not those of its `Content-Type`, for the same
+  `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.
 - `GET` or `HEAD` `/v1/e/<token>/<name>` — an image through an encrypted URL
@@ -281,12 +279,8 @@ above 8192.
 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. So is a body whose first bytes are not those of the format its
-`Content-Type` names, such as a JPEG sent as `image/png`, text sent as an image,
-or an empty body. pixa then does not fetch that source URL again for 5 minutes,
-and answers 502 for it meanwhile, as after an upstream error status. An image
-whose first bytes libvips reads as another format, such as an SVG whose first
-bytes pass the check for AVIF, is refused with 415 too.
+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:
@@ -424,7 +418,9 @@ HMAC-SHA256(secret, "host:path:query:width:height:format:expiration:quality:fit"
 
 Where:
 
-- `host` — source origin hostname (e.g. `cdn.example.com`)
+- `host` — source host as the URL writes it up to the first `/`, in lower case,
+  keeping an IPv6 address's brackets and any `:` and port after it (e.g.
+  `cdn.example.com`, `cdn.example.com:8443`, `[2001:db8::1]:8443`)
 - `path` — source path (e.g. `/photos/cat.jpg`), with each `%` written as `%25`
   and each `:` as `%3A`, so `/photos/a:b.jpg` is signed as `/photos/a%3Ab.jpg`
 - `query` — source query string, empty string if none, with `%` and `:` written
@@ -479,6 +475,12 @@ entry that is neither a host name (letters, digits, hyphens, underscores and
 dots, with at most one leading dot) nor an IP address, such as one with a port
 or a `*.` wildcard, aborts startup.
 
+pixa lower-cases the host of a `/v1/image/` URL before anything else uses it, so
+`CDN.Example.com` is matched, fetched, cached and counted against
+`upstream_connections_per_host` as `cdn.example.com`. Such a URL whose host has
+a port, as in `cdn.example.com:8443`, or a `:` with no port, needs a signature
+even when the host is allowlisted. A host holding `@` is refused with 400.
+
 ### Configuration
 
 Every setting can be given as an environment variable, in a YAML config file

TODO.md

@@ -30,15 +30,17 @@ P2: security: per-origin rate limiting
 
 # Completed Steps
 
-- 2026-10-15 a source whose first bytes do not match its `Content-Type` answers
-  415 (closes #253): a body whose first bytes are not those of the format its
-  `Content-Type` names, such as a JPEG sent as `image/png`, text, or a body
-  under 12 bytes, answered 500 on both image routes and was logged as an error
-  of pixa's, and each request for it fetched the whole body again. Both routes
-  now answer 415, and the image service logs it at warning level as a refused
-  source. It also gets a negative cache entry, as an upstream error status does,
-  so the source URL is not fetched again for 5 minutes and answers 502
-  meanwhile.
+- 2026-10-15 the host of a `/v1/image/` URL is lower-cased, and one with a port
+  needs a signature (closes #246): with `cdn.example.com` allowlisted,
+  `CDN.Example.com` and `cdn.example.com:8443` passed the allowlist too, and
+  each spelling was fetched and cached on its own and had connections of its own
+  under `upstream_connections_per_host`. The image URL parser now lower-cases
+  the host and refuses one holding `@`, which a URL reads as a user name and
+  password, with 400. A host with a port, or with a `:` and no port, needs a
+  signature even when it is allowlisted. That is checked in the image service,
+  not in `allowlist.IsAllowed`, which also matches `referer_blocklist`, where a
+  `Referer` is blocked whatever its port. A URL is signed over its host as it
+  writes it, in lower case, with any IPv6 brackets, `:` and port kept.
 - 2026-10-15 a `:` in the source path or query no longer moves where the path
   ends and the query begins (closes #247): the signed data and the cache key
   joined host, path and query with `:` and no escaping, so a URL signed for

internal/handlers/first_bytes_internal_test.go

@@ -1,180 +0,0 @@
-package handlers
-
-import (
-	"bytes"
-	"encoding/json"
-	"image/color"
-	"log/slog"
-	"net/http"
-	"slices"
-	"testing"
-	"testing/fstest"
-	"time"
-
-	"github.com/go-chi/chi/v5"
-	"sneak.berlin/go/pixa/internal/encurl"
-	"sneak.berlin/go/pixa/internal/httpfetcher"
-	"sneak.berlin/go/pixa/internal/imgcache"
-)
-
-// mismatchedSourcePath is the path of the source that
-// TestFirstBytesNotMatchingContentType serves on allowlistedHost. The mock
-// fetcher names a file's Content-Type from its extension, so the source is
-// sent as image/png.
-const mismatchedSourcePath = "/images/source.png"
-
-// newRoutesFetchingThrough returns both image routes, and the Handlers behind
-// them, whose image service fetches through fetcher and has allowlistedHost on
-// its allowlist. The handlers and the image service log to log.
-func newRoutesFetchingThrough(
-	t *testing.T, fetcher httpfetcher.Fetcher, log *slog.Logger,
-) (*Handlers, http.Handler) {
-	t.Helper()
-
-	cache, err := imgcache.NewCache(setupTestDB(t), imgcache.CacheConfig{
-		StateDir:    t.TempDir(),
-		NegativeTTL: 5 * time.Minute,
-	})
-	if err != nil {
-		t.Fatalf("imgcache.NewCache() error = %v", err)
-	}
-
-	svc, err := imgcache.NewService(&imgcache.ServiceConfig{
-		Cache:      cache,
-		Fetcher:    fetcher,
-		SigningKey: testSigningKey,
-		Allowlist:  []string{allowlistedHost},
-		Logger:     log,
-	})
-	if err != nil {
-		t.Fatalf("imgcache.NewService() error = %v", err)
-	}
-
-	encGen, err := encurl.NewGenerator(testSigningKey)
-	if err != nil {
-		t.Fatalf("encurl.NewGenerator() error = %v", err)
-	}
-
-	h := &Handlers{log: log, imgSvc: svc, encGen: encGen}
-
-	r := chi.NewRouter()
-	r.Get("/v1/image/*", h.HandleImage())
-	r.Get("/v1/e/{token}/*", h.HandleImageEnc())
-
-	return h, r
-}
-
-// mismatchedSourcePlainURL returns the /v1/image/ URL of mismatchedSourcePath
-// on allowlistedHost at 50x50 as a JPEG.
-func mismatchedSourcePlainURL(*testing.T, *Handlers) string {
-	return "/v1/image/" + allowlistedHost + mismatchedSourcePath + "/50x50.jpeg"
-}
-
-// mismatchedSourceEncURL returns an encrypted /v1/e/ URL, made with h's
-// generator, of mismatchedSourcePath on allowlistedHost at 50x50 as a JPEG.
-func mismatchedSourceEncURL(t *testing.T, h *Handlers) string {
-	t.Helper()
-
-	token, err := h.encGen.Generate(&encurl.Payload{
-		SourceHost: allowlistedHost,
-		SourcePath: mismatchedSourcePath,
-		Width:      50,
-		Height:     50,
-		Format:     imgcache.FormatJPEG,
-	})
-	if err != nil {
-		t.Fatalf("Generate() error = %v", err)
-	}
-
-	return "/v1/e/" + token + "/img.jpg"
-}
-
-// loggedLevels reads the JSON log lines in logs and returns the messages
-// logged at each level.
-func loggedLevels(t *testing.T, logs *bytes.Buffer) map[string][]string {
-	t.Helper()
-
-	t.Logf("logged:\n%s", logs.String())
-
-	messages := make(map[string][]string)
-
-	dec := json.NewDecoder(logs)
-	for dec.More() {
-		var line struct {
-			Level string `json:"level"`
-			Msg   string `json:"msg"`
-		}
-
-		err := dec.Decode(&line)
-		if err != nil {
-			t.Fatalf("decoding log line: %v", err)
-		}
-
-		messages[line.Level] = append(messages[line.Level], line.Msg)
-	}
-
-	return messages
-}
-
-// TestFirstBytesNotMatchingContentType checks that both image routes answer
-// 415 for an upstream body whose first bytes are not those of the format its
-// Content-Type names, and log it as a refused source, not as an error of
-// pixa's. The next request for that source must answer 502 without fetching
-// it again, as after an upstream error status.
-func TestFirstBytesNotMatchingContentType(t *testing.T) {
-	t.Parallel()
-
-	bodies := map[string][]byte{
-		"JPEG sent as image/png":          generateTestJPEG(t, 10, 10, color.Black),
-		"text sent as image/png":          []byte("This is just text, not a PNG"),
-		"body too short to name a format": []byte("short"),
-	}
-
-	// The source's URL on each image route.
-	sourceURLs := map[string]func(*testing.T, *Handlers) string{
-		"plain URL":     mismatchedSourcePlainURL,
-		"encrypted URL": mismatchedSourceEncURL,
-	}
-
-	for bodyName, body := range bodies {
-		for urlName, sourceURL := range sourceURLs {
-			t.Run(urlName+", "+bodyName, func(t *testing.T) {
-				t.Parallel()
-
-				fetcher := &countingFetcher{
-					Fetcher: httpfetcher.NewMock(fstest.MapFS{
-						allowlistedHost + mismatchedSourcePath: &fstest.MapFile{
-							Data: body,
-						},
-					}),
-				}
-
-				var logs bytes.Buffer
-
-				h, routes := newRoutesFetchingThrough(t, fetcher,
-					slog.New(slog.NewJSONHandler(&logs, nil)))
-				target := sourceURL(t, h)
-
-				checkErrorBody(t, sendGet(t, routes, target),
-					http.StatusUnsupportedMediaType, "unsupported source format")
-
-				levels := loggedLevels(t, &logs)
-				if len(levels[slog.LevelError.String()]) != 0 {
-					t.Errorf("logged at error level: %q",
-						levels[slog.LevelError.String()])
-				}
-
-				if !slices.Contains(levels[slog.LevelWarn.String()], "source refused") {
-					t.Error(`no "source refused" line logged at warning level`)
-				}
-
-				checkErrorBody(t, sendGet(t, routes, target),
-					http.StatusBadGateway, "upstream error")
-
-				if n := fetcher.fetches.Load(); n != 1 {
-					t.Errorf("upstream fetched %d times, want 1", n)
-				}
-			})
-		}
-	}
-}

internal/handlers/image.go

@@ -15,7 +15,6 @@ import (
 	"sneak.berlin/go/pixa/internal/httpfetcher"
 	"sneak.berlin/go/pixa/internal/imageprocessor"
 	"sneak.berlin/go/pixa/internal/imgcache"
-	"sneak.berlin/go/pixa/internal/magic"
 )
 
 // HandleImage handles the main image proxy route:
@@ -221,18 +220,6 @@ func (s *Handlers) HandleTooManyRequests() http.HandlerFunc {
 func (s *Handlers) respondImageError(
 	w http.ResponseWriter, req *imgcache.ImageRequest, err error,
 ) {
-	// An upstream body whose first bytes are not those of the format its
-	// Content-Type names is the upstream's error, not pixa's: the image
-	// service has logged it as a refused source.
-	if errors.Is(err, magic.ErrMagicByteMismatch) ||
-		errors.Is(err, magic.ErrUnknownFormat) ||
-		errors.Is(err, magic.ErrNotEnoughData) {
-		s.respondError(w, "unsupported source format",
-			http.StatusUnsupportedMediaType)
-
-		return
-	}
-
 	s.log.Error("failed to get image",
 		"host", req.SourceHost,
 		"path", req.SourcePath,

internal/handlers/imageenc.go

@@ -15,7 +15,6 @@ import (
 	"sneak.berlin/go/pixa/internal/httpfetcher"
 	"sneak.berlin/go/pixa/internal/imageprocessor"
 	"sneak.berlin/go/pixa/internal/imgcache"
-	"sneak.berlin/go/pixa/internal/magic"
 )
 
 // HandleImageEnc handles requests to /v1/e/{token}/* for encrypted
@@ -163,10 +162,7 @@ func (s *Handlers) handleImageError(w http.ResponseWriter, err error) {
 		s.respondError(w, "server busy, try again later",
 			http.StatusServiceUnavailable)
 	case errors.Is(err, httpfetcher.ErrInvalidContentType),
-		errors.Is(err, imageprocessor.ErrUnsupportedInputFormat),
-		errors.Is(err, magic.ErrMagicByteMismatch),
-		errors.Is(err, magic.ErrUnknownFormat),
-		errors.Is(err, magic.ErrNotEnoughData):
+		errors.Is(err, imageprocessor.ErrUnsupportedInputFormat):
 		s.respondError(w, "unsupported source format",
 			http.StatusUnsupportedMediaType)
 	case errors.Is(err, imageprocessor.ErrOutputTooLarge):

internal/imgcache/service.go

@@ -9,6 +9,7 @@ import (
 	"log/slog"
 	"net/url"
 	"runtime/debug"
+	"strings"
 	"time"
 
 	"github.com/dustin/go-humanize"
@@ -218,7 +219,16 @@ func (s *Service) ValidateRequest(req *ImageRequest) error {
 		return fmt.Errorf("invalid source URL: %w", err)
 	}
 
-	if s.allowlist.IsAllowed(parsedURL) {
+	// An allowlist entry names no port, so a host followed by ":", with or
+	// without a port, needs a signature. The port is read from the parsed
+	// URL, as the fetcher reads it: in an IPv6 address written without
+	// brackets, such as 2001:db8::1:8443, it is what follows the last ":".
+	// This is checked here and not in allowlist.IsAllowed, which also matches
+	// referer_blocklist, where a Referer must be blocked whatever its port.
+	hostHasPort := parsedURL.Port() != "" ||
+		strings.HasSuffix(parsedURL.Host, ":")
+
+	if !hostHasPort && s.allowlist.IsAllowed(parsedURL) {
 		return nil
 	}
 
@@ -438,7 +448,13 @@ func (s *Service) fetchAndProcess(
 	if err != nil {
 		// Store negative cache for certain errors
 		if isNegativeCacheable(err) {
-			s.storeNegative(ctx, req, extractStatusCode(err), err)
+			statusCode := extractStatusCode(err)
+
+			storeErr := s.cache.StoreNegative(ctx, req, statusCode, err.Error())
+			if storeErr != nil {
+				s.log.Warn("failed to store negative cache entry",
+					"host", req.SourceHost, "path", req.SourcePath, "error", storeErr)
+			}
 		}
 
 		return nil, fmt.Errorf("upstream fetch failed: %w", err)
@@ -484,16 +500,9 @@ func (s *Service) fetchAndProcess(
 		"cipher", fetchResult.TLSCipherSuite,
 	)
 
-	// Validate magic bytes match content type. A body that does not is the
-	// upstream's error, so it gets a negative cache entry, as an upstream
-	// error status does.
+	// Validate magic bytes match content type
 	err = magic.ValidateMagicBytes(sourceData, fetchResult.ContentType)
 	if err != nil {
-		s.log.Warn("source refused", "request_id", middleware.GetReqID(ctx),
-			"host", req.SourceHost, "path", req.SourcePath,
-			"content_type", fetchResult.ContentType, "error", err)
-		s.storeNegative(ctx, req, httpStatusUnsupportedMediaType, err)
-
 		return nil, fmt.Errorf("content validation failed: %w", err)
 	}
 
@@ -509,19 +518,6 @@ func (s *Service) fetchAndProcess(
 	)
 }
 
-// storeNegative stores a negative cache entry for req's source, whose fetch
-// failed with err, so the source is not fetched again until the entry
-// expires. A failure to store the entry is only logged.
-func (s *Service) storeNegative(
-	ctx context.Context, req *ImageRequest, statusCode int, err error,
-) {
-	storeErr := s.cache.StoreNegative(ctx, req, statusCode, err.Error())
-	if storeErr != nil {
-		s.log.Warn("failed to store negative cache entry",
-			"host", req.SourceHost, "path", req.SourcePath, "error", storeErr)
-	}
-}
-
 // processedVariant is a variant as processAndStore made it. Each request that
 // shared its processing serves it through a reader of its own.
 type processedVariant struct {
@@ -632,7 +628,6 @@ func signatureRequest(req *ImageRequest) *signature.Request {
 const (
 	httpStatusBadGateway    = 502
 	httpStatusInternalError = 500
-	httpStatusUnsupportedMediaType = 415
 )
 
 // isNegativeCacheable returns true if the error should be cached.

internal/imgcache/service_internal_test.go

@@ -250,6 +250,97 @@ func TestService_ValidateRequest_SignatureExactHostMatch(t *testing.T) {
 	}
 }
 
+// TestService_ValidateRequest_HostWithPortNeedsSignature verifies that a host
+// followed by a port, or by a colon with no port, matches no allowlist entry,
+// so that a request for it without a signature is refused, while the same
+// host with no port is allowlisted.
+func TestService_ValidateRequest_HostWithPortNeedsSignature(t *testing.T) {
+	t.Parallel()
+
+	svc, _ := SetupTestService(t,
+		WithSigningKey(testSigningKey),
+		WithAllowlist(testHostCDN, "203.0.113.5", "2001:db8::1"),
+	)
+
+	tests := []struct {
+		host        string
+		allowlisted bool
+	}{
+		{testHostCDN, true},
+		{"cdn.example.com:8443", false},
+		{"cdn.example.com:443", false},
+		{"cdn.example.com:", false},
+		{"203.0.113.5", true},
+		{"203.0.113.5:8080", false},
+		{"[2001:db8::1]", true},
+		{"[2001:db8::1]:8443", false},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.host, func(t *testing.T) {
+			t.Parallel()
+
+			req := &ImageRequest{
+				SourceHost: tt.host,
+				SourcePath: testPathCat,
+				Size:       Size{Width: 50, Height: 50},
+				Format:     FormatJPEG,
+				Quality:    85,
+				FitMode:    FitCover,
+			}
+
+			err := svc.ValidateRequest(req)
+			t.Logf("ValidateRequest() for host %q with no signature: %v",
+				tt.host, err)
+
+			if allowlisted := err == nil; allowlisted != tt.allowlisted {
+				t.Errorf("host %q served without a signature = %v, want %v",
+					tt.host, allowlisted, tt.allowlisted)
+			}
+		})
+	}
+}
+
+// TestService_ValidateRequest_UnbracketedIPv6PortNeedsSignature verifies that
+// an allowlisted IPv6 address written without brackets and followed by a
+// port, or by a colon with no port, needs a signature. Go's URL parser, which
+// the fetcher uses, reads 2001:db8::1:8443 as the host 2001:db8::1 with the
+// port 8443.
+func TestService_ValidateRequest_UnbracketedIPv6PortNeedsSignature(
+	t *testing.T,
+) {
+	t.Parallel()
+
+	svc, _ := SetupTestService(t,
+		WithSigningKey(testSigningKey),
+		WithAllowlist("2001:db8::1"),
+	)
+
+	for _, host := range []string{"2001:db8::1:8443", "2001:db8::1:"} {
+		t.Run(host, func(t *testing.T) {
+			t.Parallel()
+
+			req := &ImageRequest{
+				SourceHost: host,
+				SourcePath: testPathCat,
+				Size:       Size{Width: 50, Height: 50},
+				Format:     FormatJPEG,
+				Quality:    85,
+				FitMode:    FitCover,
+			}
+
+			err := svc.ValidateRequest(req)
+			t.Logf("ValidateRequest() for host %q with no signature: %v",
+				host, err)
+
+			if err == nil {
+				t.Errorf("host %q served without a signature, want refused",
+					host)
+			}
+		})
+	}
+}
+
 func TestService_Get_InvalidFile(t *testing.T) {
 	t.Parallel()
 

internal/imgcache/urlparser.go

@@ -15,6 +15,7 @@ import (
 var (
 	ErrInvalidPath       = errors.New("invalid image path")
 	ErrMissingHost       = errors.New("missing source host")
+	ErrInvalidHost       = errors.New("invalid source host")
 	ErrMissingSize       = errors.New("missing size specification")
 	ErrInvalidSize       = errors.New("invalid size format")
 	ErrInvalidFormat     = errors.New("invalid or unsupported format")
@@ -143,6 +144,17 @@ func parseImageComponents(remainder string) (*ParsedURL, error) {
 		return nil, ErrMissingHost
 	}
 
+	// A URL reads what comes before "@" as a user name and password, and the
+	// rest as the host
+	if strings.Contains(host, "@") {
+		return nil, fmt.Errorf("%w: %q holds @", ErrInvalidHost, host)
+	}
+
+	// Host names do not depend on letter case, so the allowlist, the upstream
+	// connection limits, the cache and the signature see one spelling of each
+	// host
+	host = strings.ToLower(host)
+
 	// Extract query string if present in path
 	if qIndex := strings.Index(path, "?"); qIndex != -1 {
 		query = path[qIndex+1:]

internal/imgcache/urlparser_internal_test.go

@@ -234,6 +234,49 @@ func TestParseImagePath(t *testing.T) {
 	}
 }
 
+// TestParseImagePath_LowerCasesHost verifies that the host is lower-cased, so
+// that every spelling of its letter case is the same host to the allowlist,
+// the upstream connection limits and the cache, and that the path keeps its
+// case.
+func TestParseImagePath_LowerCasesHost(t *testing.T) {
+	t.Parallel()
+
+	got, err := ParseImagePath("CDN.Example.COM/Photos/Cat.jpg/800x600.webp")
+	if err != nil {
+		t.Fatalf("ParseImagePath() error = %v", err)
+	}
+
+	t.Logf("parsed host %q, path %q", got.Host, got.Path)
+
+	if got.Host != testHostCDN {
+		t.Errorf("Host = %q, want %q", got.Host, testHostCDN)
+	}
+
+	if got.Path != "/Photos/Cat.jpg" {
+		t.Errorf("Path = %q, want %q", got.Path, "/Photos/Cat.jpg")
+	}
+}
+
+// TestParseImagePath_RefusesUserinfo verifies that a host holding "@" is
+// refused: a URL reads what comes before the "@" as a user name and password
+// and the rest as the host.
+func TestParseImagePath_RefusesUserinfo(t *testing.T) {
+	t.Parallel()
+
+	for _, input := range []string{
+		"user@cdn.example.com/photos/cat.jpg/800x600.webp",
+		"user:password@cdn.example.com/photos/cat.jpg/800x600.webp",
+	} {
+		got, err := ParseImagePath(input)
+		t.Logf("ParseImagePath(%q) = %+v, error = %v", input, got, err)
+
+		if !errors.Is(err, ErrInvalidHost) {
+			t.Errorf("ParseImagePath(%q) error = %v, want %v",
+				input, err, ErrInvalidHost)
+		}
+	}
+}
+
 func TestParsedURL_ToImageRequest(t *testing.T) {
 	t.Parallel()