Allow clients to set Host in headers (#522)

Allows Host to set the request.Host on the client and promotes
request.Host back to a Header in the handler.

Fixes #513

connect_ext_test.go

@@ -521,6 +521,64 @@ func TestHeaderBasic(t *testing.T) {
  assert.Equal(t, response.Header().Get(key), hval)
 }
 
+func TestHeaderHost(t *testing.T) {
+ t.Parallel()
+ const (
+ key = "Host"
+ cval = "buf.build"
+ )
+
+ pingServer := &pluggablePingServer{
+ ping: func(_ context.Context, request *connect.Request[pingv1.PingRequest]) (*connect.Response[pingv1.PingResponse], error) {
+ assert.Equal(t, request.Header().Get(key), cval)
+ response := connect.NewResponse(&pingv1.PingResponse{})
+ return response, nil
+ },
+ }
+
+ newHTTP2Server := func(t *testing.T) *httptest.Server {
+ t.Helper()
+ mux := http.NewServeMux()
+ mux.Handle(pingv1connect.NewPingServiceHandler(pingServer))
+ server := httptest.NewUnstartedServer(mux)
+ server.EnableHTTP2 = true
+ server.StartTLS()
+ t.Cleanup(server.Close)
+ return server
+ }
+
+ callWithHost := func(t *testing.T, client pingv1connect.PingServiceClient) {
+ t.Helper()
+
+ request := connect.NewRequest(&pingv1.PingRequest{})
+ request.Header().Set(key, cval)
+ response, err := client.Ping(context.Background(), request)
+ assert.Nil(t, err)
+ assert.Equal(t, response.Header().Get(key), "")
+ }
+
+ t.Run("connect", func(t *testing.T) {
+ t.Parallel()
+ server := newHTTP2Server(t)
+ client := pingv1connect.NewPingServiceClient(server.Client(), server.URL)
+ callWithHost(t, client)
+ })
+
+ t.Run("grpc", func(t *testing.T) {
+ t.Parallel()
+ server := newHTTP2Server(t)
+ client := pingv1connect.NewPingServiceClient(server.Client(), server.URL, connect.WithGRPC())
+ callWithHost(t, client)
+ })
+
+ t.Run("grpc-web", func(t *testing.T) {
+ t.Parallel()
+ server := newHTTP2Server(t)
+ client := pingv1connect.NewPingServiceClient(server.Client(), server.URL, connect.WithGRPCWeb())
+ callWithHost(t, client)
+ })
+}
+
 func TestTimeoutParsing(t *testing.T) {
  t.Parallel()
  const timeout = 10 * time.Minute

duplex_http_call.go

@@ -257,6 +257,11 @@ func (d *duplexHTTPCall) makeRequest() {
  // on d.responseReady, so we can't race with them.
  defer close(d.responseReady)
 
+ // Promote the header Host to the request object.
+ if host := d.request.Header.Get(headerHost); len(host) > 0 {
+ d.request.Host = host
+ }
+
  if d.onRequestSend != nil {
  d.onRequestSend(d.request)
  }

handler.go

@@ -176,7 +176,7 @@ func NewBidiStreamHandler[Req, Res any](
 
 // ServeHTTP implements [http.Handler].
 func (h *Handler) ServeHTTP(responseWriter http.ResponseWriter, request *http.Request) {
- // We don't need to defer functions  to close the request body or read to
+ // We don't need to defer functions to close the request body or read to
  // EOF: the stream we construct later on already does that, and we only
  // return early when dealing with misbehaving clients. In those cases, it's
  // okay if we can't re-use the connection.
@@ -221,6 +221,7 @@ func (h *Handler) ServeHTTP(responseWriter http.ResponseWriter, request *http.Re
 
  // Establish a stream and serve the RPC.
  setHeaderCanonical(request.Header, headerContentType, contentType)
+ setHeaderCanonical(request.Header, headerHost, request.Host)
  ctx, cancel, timeoutErr := protocolHandler.SetTimeout(request) //nolint: contextcheck
  if timeoutErr != nil {
  ctx = request.Context()

protocol.go

@@ -36,6 +36,7 @@ const (
 
 const (
  headerContentType = "Content-Type"
+ headerHost = "Host"
  headerUserAgent = "User-Agent"
  headerTrailer = "Trailer"