Make client.Send(nil) send request headers

Adding to the StreamingHandlerConn interface isn't backward-compatible,
but we need a way for clients to send request headers without a body.
This commit removes the previous commit's `SendHeaders` method, but makes
`Send(nil)` accomplish the same thing.

client_stream.go

@@ -59,6 +59,9 @@ func (c *ClientStreamForClient[Req, Res]) Send(request *Req) error {
 	if c.err != nil {
 		return c.err
 	}
+	if request == nil {
+		return c.conn.Send(nil)
+	}
 	return c.conn.Send(request)
 }
 
@@ -184,11 +187,6 @@ func (b *BidiStreamForClient[_, _]) Peer() Peer {
 	return b.conn.Peer()
 }
 
-// SendHeaders sends the request headers.
-func (b *BidiStreamForClient[_, _]) SendHeaders() {
-	b.conn.SendHeaders()
-}
-
 // RequestHeader returns the request headers. Headers are sent with the first
 // call to Send.
 func (b *BidiStreamForClient[Req, Res]) RequestHeader() http.Header {
@@ -199,7 +197,8 @@ func (b *BidiStreamForClient[Req, Res]) RequestHeader() http.Header {
 }
 
 // Send a message to the server. The first call to Send also sends the request
-// headers.
+// headers. To send just the request headers, without a body, call Send with a
+// nil pointer.
 //
 // If the server returns an error, Send returns an error that wraps [io.EOF].
 // Clients should check for EOF using the standard library's [errors.Is] and
@@ -208,6 +207,9 @@ func (b *BidiStreamForClient[Req, Res]) Send(msg *Req) error {
 	if b.err != nil {
 		return b.err
 	}
+	if msg == nil {
+		return b.conn.Send(nil)
+	}
 	return b.conn.Send(msg)
 }
 

connect.go

@@ -103,10 +103,9 @@ type StreamingClientConn interface {
 	Spec() Spec
 	Peer() Peer
 
-	// Send, SendHeaders, RequestHeader, and CloseRequest may race with each other,
-	// but must be safe to call concurrently with all other methods.
+	// Send, RequestHeader, and CloseRequest may race with each other, but must
+	// be safe to call concurrently with all other methods.
 	Send(any) error
-	SendHeaders()
 	RequestHeader() http.Header
 	CloseRequest() error
 

connect_ext_test.go

@@ -1343,7 +1343,7 @@ func TestClientWithSendMaxBytes(t *testing.T) {
 	})
 }
 
-func TestBidiStreamForClientSendHeaders(t *testing.T) {
+func TestBidiStreamServerSendsFirstMessage(t *testing.T) {
 	t.Parallel()
 	run := func(t *testing.T, opts ...connect.ClientOption) {
 		t.Helper()
@@ -1372,7 +1372,7 @@ func TestBidiStreamForClientSendHeaders(t *testing.T) {
 			assert.Nil(t, stream.CloseRequest())
 			assert.Nil(t, stream.CloseResponse())
 		})
-		stream.SendHeaders()
+		assert.Nil(t, stream.Send(nil))
 		select {
 		case <-time.After(time.Second):
 			t.Error("timed out to get request headers")

envelope.go

@@ -58,6 +58,15 @@ type envelopeWriter struct {
 }
 
 func (w *envelopeWriter) Marshal(message any) *Error {
+	if message == nil {
+		if _, err := w.writer.Write(nil); err != nil {
+			if connectErr, ok := asError(err); ok {
+				return connectErr
+			}
+			return NewError(CodeUnknown, err)
+		}
+		return nil
+	}
 	raw, err := w.codec.Marshal(message)
 	if err != nil {
 		return errorf(CodeInternal, "marshal message: %w", err)

handler_stream.go

@@ -104,6 +104,9 @@ func (s *ServerStream[Res]) ResponseTrailer() http.Header {
 // Send a message to the client. The first call to Send also sends the response
 // headers.
 func (s *ServerStream[Res]) Send(msg *Res) error {
+	if msg == nil {
+		return s.conn.Send(nil)
+	}
 	return s.conn.Send(msg)
 }
 
@@ -161,6 +164,9 @@ func (b *BidiStream[Req, Res]) ResponseTrailer() http.Header {
 // Send a message to the client. The first call to Send also sends the response
 // headers.
 func (b *BidiStream[Req, Res]) Send(msg *Res) error {
+	if msg == nil {
+		return b.conn.Send(nil)
+	}
 	return b.conn.Send(msg)
 }
 

protocol_connect.go

@@ -357,10 +357,6 @@ func (cc *connectUnaryClientConn) Send(msg any) error {
 	return nil // must be a literal nil: nil *Error is a non-nil error
 }
 
-func (cc *connectUnaryClientConn) SendHeaders() {
-	cc.duplexCall.ensureRequestMade()
-}
-
 func (cc *connectUnaryClientConn) RequestHeader() http.Header {
 	return cc.duplexCall.Header()
 }
@@ -460,10 +456,6 @@ func (cc *connectStreamingClientConn) Send(msg any) error {
 	return nil // must be a literal nil: nil *Error is a non-nil error
 }
 
-func (cc *connectStreamingClientConn) SendHeaders() {
-	cc.duplexCall.ensureRequestMade()
-}
-
 func (cc *connectStreamingClientConn) RequestHeader() http.Header {
 	return cc.duplexCall.Header()
 }
@@ -753,6 +745,9 @@ type connectUnaryMarshaler struct {
 }
 
 func (m *connectUnaryMarshaler) Marshal(message any) *Error {
+	if message == nil {
+		return m.write(nil)
+	}
 	data, err := m.codec.Marshal(message)
 	if err != nil {
 		return errorf(CodeInternal, "marshal message: %w", err)

protocol_grpc.go

@@ -325,10 +325,6 @@ func (cc *grpcClientConn) Send(msg any) error {
 	return nil // must be a literal nil: nil *Error is a non-nil error
 }
 
-func (cc *grpcClientConn) SendHeaders() {
-	cc.duplexCall.ensureRequestMade()
-}
-
 func (cc *grpcClientConn) RequestHeader() http.Header {
 	return cc.duplexCall.Header()
 }