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/httpfetcher/fetch_internal_test.go

@@ -14,6 +14,8 @@ import (
 	"sync"
 	"testing"
 	"time"
+
+	"sneak.berlin/go/pixa/internal/imagerequest"
 )
 
 // testPublicHost is a TEST-NET-1 (RFC 5737) literal. isPrivateIP treats it as
@@ -29,9 +31,9 @@ const imagePayload = "fake-jpeg-bytes"
 // would mean SSRF protection let a forbidden target reach the transport.
 var errUnexpectedDial = errors.New("unexpected dial target")
 
-// upstreamURL builds a fetch URL on the fake public host for the given path.
-func upstreamURL(path string) string {
-	return "http://" + testPublicHost + path
+// upstreamSource returns the source at path on the fake public host.
+func upstreamSource(path string) imagerequest.Source {
+	return imagerequest.Source{Host: testPublicHost, Path: path}
 }
 
 // recordingDialer records every address the transport asks it to dial and
@@ -158,7 +160,7 @@ func testContext(t *testing.T) context.Context {
 func fetchImage(t *testing.T, f *HTTPFetcher, path string) *FetchResult {
 	t.Helper()
 
-	res, err := f.Fetch(testContext(t), upstreamURL(path))
+	res, err := f.Fetch(testContext(t), upstreamSource(path))
 	if err != nil {
 		t.Fatalf("Fetch(%s) error = %v", path, err)
 	}
@@ -170,7 +172,7 @@ func fetchImage(t *testing.T, f *HTTPFetcher, path string) *FetchResult {
 func fetchExpectError(t *testing.T, f *HTTPFetcher, path string) error {
 	t.Helper()
 
-	res, err := f.Fetch(testContext(t), upstreamURL(path))
+	res, err := f.Fetch(testContext(t), upstreamSource(path))
 	if err == nil {
 		_ = res.Content.Close()
 
@@ -222,7 +224,7 @@ func TestFetchRedirectToPrivateIPBlocked(t *testing.T) {
 	srv := startUpstream(t)
 	f, dialer := newServerFetcher(t, srv, nil)
 
-	_, err := f.Fetch(testContext(t), upstreamURL("/redirect/private"))
+	_, err := f.Fetch(testContext(t), upstreamSource("/redirect/private"))
 	if !errors.Is(err, ErrSSRFBlocked) {
 		t.Fatalf("Fetch() error = %v, want ErrSSRFBlocked", err)
 	}
@@ -590,3 +592,53 @@ func TestSSRFSafeDialerAllowsPublicTarget(t *testing.T) {
 		t.Errorf("public target was SSRF-blocked: %v", err)
 	}
 }
+
+// TestFetchSchemeFollowsAllowHTTP checks that the fetcher fetches a source
+// over https, on port 443, unless AllowHTTP is set, and then over http, on
+// port 80. The test server speaks plain HTTP, so only the fetch over http
+// succeeds.
+func TestFetchSchemeFollowsAllowHTTP(t *testing.T) {
+	t.Parallel()
+
+	tests := []struct {
+		allowHTTP bool
+		wantAddr  string
+	}{
+		{false, net.JoinHostPort(testPublicHost, "443")},
+		{true, net.JoinHostPort(testPublicHost, "80")},
+	}
+
+	for _, tt := range tests {
+		t.Run(fmt.Sprintf("AllowHTTP %v", tt.allowHTTP), func(t *testing.T) {
+			t.Parallel()
+
+			srv := startUpstream(t)
+			dialer := &recordingDialer{target: srv.Listener.Addr().String()}
+
+			f := New(&Config{
+				Timeout:               30 * time.Second,
+				MaxResponseSize:       50 << 20,
+				AllowHTTP:             tt.allowHTTP,
+				MaxConnectionsPerHost: 20,
+				MaxConnections:        64,
+				DialContext:           dialer.dialContext,
+			})
+
+			res, err := f.Fetch(testContext(t), upstreamSource("/image"))
+			if err == nil {
+				_ = res.Content.Close()
+			}
+
+			dialed := dialer.dialedAddrs()
+			t.Logf("Fetch(): error %v, dialed %v", err, dialed)
+
+			if served := err == nil; served != tt.allowHTTP {
+				t.Errorf("served = %v, want %v", served, tt.allowHTTP)
+			}
+
+			if len(dialed) != 1 || dialed[0] != tt.wantAddr {
+				t.Errorf("dialed %v, want only %s", dialed, tt.wantAddr)
+			}
+		})
+	}
+}