Improve error when clients try bidi over HTTP/1.x (#203)

connect_ext_test.go

@@ -398,6 +398,34 @@ func TestMarshalStatusError(t *testing.T) {
 	assertInternalError(t, connect.WithGRPCWeb())
 }
 
+func TestBidiRequiresHTTP2(t *testing.T) {
+	t.Parallel()
+	handler := http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		_, err := io.WriteString(w, "hello world")
+		assert.Nil(t, err)
+	})
+	server := httptest.NewServer(handler)
+	defer server.Close()
+	client, err := pingv1connect.NewPingServiceClient(
+		server.Client(),
+		server.URL,
+		connect.WithGRPC(),
+	)
+	assert.Nil(t, err)
+	stream := client.CumSum(context.Background())
+	assert.Nil(t, stream.Send(&pingv1.CumSumRequest{}))
+	assert.Nil(t, stream.CloseSend())
+	_, err = stream.Receive()
+	assert.NotNil(t, err)
+	var connectErr *connect.Error
+	assert.True(t, errors.As(err, &connectErr))
+	assert.Equal(t, connectErr.Code(), connect.CodeUnimplemented)
+	assert.True(
+		t,
+		strings.HasSuffix(connectErr.Message(), ": bidi streams require at least HTTP/2"),
+	)
+}
+
 type failCodec struct{}
 
 func (c failCodec) Name() string {

protocol_grpc_client_stream.go

@@ -284,6 +284,15 @@ func (cs *duplexClientStream) makeRequest(prepared chan struct{}) {
 		cs.setResponseError(errorf(httpToCode(res.StatusCode), "HTTP status %v", res.Status))
 		return
 	}
+	if (cs.spec.StreamType&StreamTypeBidi) == StreamTypeBidi && res.ProtoMajor < 2 {
+		// If we somehow dialed an HTTP/1.x server, fail with an explicit message
+		// rather than returning a more cryptic error later on.
+		cs.setResponseError(errorf(
+			CodeUnimplemented,
+			"response from %q is HTTP/1.x: bidi streams require at least HTTP/2",
+			cs.url,
+		))
+	}
 	compression := res.Header.Get("Grpc-Encoding")
 	if compression == "" || compression == compressionIdentity {
 		compression = compressionIdentity