http2: improve error when server sends HTTP/1

If for some reason the server sends an HTTP/1.1 response starting with "HTTP/1.1 " (9 bytes), http2 transport interprets that as a valid frame header for an expected payload of ~4MB, and fails with non-descriptive messages like "unexpected EOF". This could happen, for example, if ALPN is misconfigured on the server's load balancer. This change attempts to improve that feedback by noting in the error messages whenever the frame header was exactly the "HTTP/1.1 " bytes. Change-Id: I7bf9ed2ee7f299b939b9004386f5bfa30a4e9032 GitHub-Last-Rev: d6e410d GitHub-Pull-Request: #224 Reviewed-on: https://go-review.googlesource.com/c/net/+/623155 LUCI-TryBot-Result: Go LUCI <golang-scoped@luci-project-accounts.iam.gserviceaccount.com> Reviewed-by: David Chase <drchase@google.com> Auto-Submit: Sean Liao <sean@liao.dev> Reviewed-by: Damien Neil <dneil@google.com> Reviewed-by: Sean Liao <sean@liao.dev>

Author: colega

http2/frame.go

@@ -225,6 +225,11 @@ var fhBytes = sync.Pool{
 },
 }
 
+func invalidHTTP1LookingFrameHeader() FrameHeader {
+fh, _ := readFrameHeader(make([]byte, frameHeaderLen), strings.NewReader("HTTP/1.1 "))
+return fh
+}
+
 // ReadFrameHeader reads 9 bytes from r and returns a FrameHeader.
 // Most users should use Framer.ReadFrame instead.
 func ReadFrameHeader(r io.Reader) (FrameHeader, error) {
@@ -503,10 +508,16 @@ func (fr *Framer) ReadFrame() (Frame, error) {
 return nil, err
 }
 if fh.Length > fr.maxReadSize {
+if fh == invalidHTTP1LookingFrameHeader() {
+return nil, fmt.Errorf("http2: failed reading the frame payload: %w, note that the frame header looked like an HTTP/1.1 header", err)
+}
 return nil, ErrFrameTooLarge
 }
 payload := fr.getReadBuf(fh.Length)
 if _, err := io.ReadFull(fr.r, payload); err != nil {
+if fh == invalidHTTP1LookingFrameHeader() {
+return nil, fmt.Errorf("http2: failed reading the frame payload: %w, note that the frame header looked like an HTTP/1.1 header", err)
+}
 return nil, err
 }
 f, err := typeFrameParser(fh.Type)(fr.frameCache, fh, fr.countError, payload)

http2/transport_test.go

@@ -272,6 +272,48 @@ func TestTransport(t *testing.T) {
 }
 }
 
+func TestTransportFailureErrorForHTTP1Response(t *testing.T) {
+const expectedHTTP1PayloadHint = "frame header looked like an HTTP/1.1 header"
+
+ts := httptest.NewServer(http.NewServeMux())
+t.Cleanup(ts.Close)
+
+for _, tc := range []struct {
+name string
+maxFrameSize uint32
+expectedErrorIs error
+}{
+{
+name: "with default max frame size",
+maxFrameSize: 0,
+},
+{
+name: "with enough frame size to start reading",
+maxFrameSize: invalidHTTP1LookingFrameHeader().Length + 1,
+},
+} {
+t.Run(tc.name, func(t *testing.T) {
+tr := &Transport{
+DialTLSContext: func(ctx context.Context, network, addr string, cfg *tls.Config) (net.Conn, error) {
+return net.Dial(network, addr)
+},
+MaxReadFrameSize: tc.maxFrameSize,
+AllowHTTP: true,
+}
+
+req, err := http.NewRequest("GET", ts.URL, nil)
+if err != nil {
+t.Fatal(err)
+}
+
+_, err = tr.RoundTrip(req)
+if !strings.Contains(err.Error(), expectedHTTP1PayloadHint) {
+t.Errorf("expected error to contain %q, got %v", expectedHTTP1PayloadHint, err)
+}
+})
+}
+}
+
 func testTransportReusesConns(t *testing.T, useClient, wantSame bool, modReq func(*http.Request)) {
 ts := newTestServer(t, func(w http.ResponseWriter, r *http.Request) {
 io.WriteString(w, r.RemoteAddr)