Take the signature, the expiry and the URL scheme off the image request (closes #314)

The image request now holds only its source and its transform, exactly what
the variant key covers. The /v1/image/ handler checks the allowlist and
verifies the signature itself with Signer.Verify(req, sig, expires). Both
image handlers keep the URL's expiry as a local value for Cache-Control. The
image service holds no signer, allowlist or AllowHTTP, and ValidateRequest is
gone. The fetcher takes the source and builds its URL with Source.URL from its
own AllowHTTP, so no URL string is built and parsed again. chooseAutoFormat
returns the format it chooses instead of writing into the request. The signed
URL format and every route's answers are unchanged.

Model: opus-5-5

internal/handlers/image_errors_internal_test.go

@@ -14,6 +14,7 @@ import (
 
 	"github.com/go-chi/chi/v5"
 	"github.com/prometheus/client_golang/prometheus"
+	"sneak.berlin/go/pixa/internal/allowlist"
 	"sneak.berlin/go/pixa/internal/httpfetcher"
 	"sneak.berlin/go/pixa/internal/imageprocessor"
 	"sneak.berlin/go/pixa/internal/imagerequest"
@@ -26,7 +27,7 @@ import (
 const allowlistedHost = "allowed.example.com"
 
 // newImageRoute returns the image route of a Handlers whose service fetches
-// with fetcher and checks signatures with testSigningKey.
+// with fetcher, and which checks signatures with testSigningKey.
 func newImageRoute(t *testing.T, fetcher httpfetcher.Fetcher) http.Handler {
 	t.Helper()
 
@@ -46,15 +47,18 @@ func newImageRoute(t *testing.T, fetcher httpfetcher.Fetcher) http.Handler {
 			MaxInputBytes:           50 << 20,
 			MaxConcurrentProcessing: 2,
 		}),
-		SigningKey:      testSigningKey,
-		Allowlist:       []string{allowlistedHost},
 		MaxResponseSize: 50 << 20,
 	})
 	if err != nil {
 		t.Fatalf("failed to create service: %v", err)
 	}
 
-	h := &Handlers{imgSvc: svc, log: slog.New(slog.DiscardHandler)}
+	h := &Handlers{
+		imgSvc:    svc,
+		log:       slog.New(slog.DiscardHandler),
+		signer:    signature.New(testSigningKey),
+		allowlist: allowlist.New([]string{allowlistedHost}),
+	}
 
 	r := chi.NewRouter()
 	r.Get("/v1/image/*", h.HandleImage())
@@ -90,10 +94,10 @@ func photoURLWithSig(host, sig string, expires time.Time) string {
 	return fmt.Sprintf("%s?sig=%s&exp=%d", photoURL(host), sig, expires.Unix())
 }
 
-// photoSignature returns the signature of photoURL(host) at the default
-// quality and fit, made with key and expiring at expires.
-func photoSignature(key, host string, expires time.Time) string {
-	return signature.New(key).Sign(&imagerequest.Request{
+// photoRequest returns the image request of photoURL(host) at the default
+// quality and fit.
+func photoRequest(host string) *imagerequest.Request {
+	return &imagerequest.Request{
 		Source: imagerequest.Source{
 			Host: host,
 			Path: photoPath,
@@ -104,8 +108,13 @@ func photoSignature(key, host string, expires time.Time) string {
 			Quality: 85,
 			FitMode: imagerequest.FitCover,
 		},
-		Expires: expires,
-	})
+	}
+}
+
+// photoSignature returns the signature of photoURL(host) at the default
+// quality and fit, made with key and expiring at expires.
+func photoSignature(key, host string, expires time.Time) string {
+	return signature.New(key).Sign(photoRequest(host), expires)
 }
 
 // sendGet sends a GET for target to route and returns the response.
@@ -381,8 +390,7 @@ func TestHandleImage_HashInSourcePathOrQuery_Returns400(t *testing.T) {
 			Quality: 85,
 			FitMode: imagerequest.FitCover,
 		},
-		Expires: exp,
-	})
+	}, exp)
 
 	tests := []struct {
 		name   string