client: fix ForceCodec to set content-type header appropriately

Author: dfawley

rpc_util.go

@@ -429,9 +429,10 @@ func (o ContentSubtypeCallOption) before(c *callInfo) error {
 }
 func (o ContentSubtypeCallOption) after(c *callInfo, attempt *csAttempt) {}
 
-// ForceCodec returns a CallOption that will set codec to be
-// used for all request and response messages for a call. The result of calling
-// Name() will be used as the content-subtype in a case-insensitive manner.
+// ForceCodec returns a CallOption that will set codec to be used for all
+// request and response messages for a call. The result of calling Name() will
+// be used as the content-subtype after converting to lowercase, unless
+// CallContentSubtype is also used.
 //
 // See Content-Type on
 // https://github.com/grpc/grpc/blob/master/doc/PROTOCOL-HTTP2.md#requests for

stream.go

@@ -24,6 +24,7 @@ import (
 	"io"
 	"math"
 	"strconv"
+	"strings"
 	"sync"
 	"time"
 
@@ -246,6 +247,16 @@ func newClientStreamWithParams(ctx context.Context, desc *StreamDesc, cc *Client
 		return nil, err
 	}
 
+	// Set the content subtype if it is already unset and ForceCodec is used.
+	if c.codec != nil && c.contentSubtype == "" {
+		// c.codec is a baseCodec to hide the difference between grpc.Codec and
+		// encoding.Codec (Name vs. String method name).  We only support
+		// setting content subtype from encoding.Codec to avoid a behavior
+		// change with the deprecated version.
+		if ec, ok := c.codec.(encoding.Codec); ok {
+			c.contentSubtype = strings.ToLower(ec.Name())
+		}
+	}
 	callHdr := &transport.CallHdr{
 		Host:           cc.authority,
 		Method:         method,

test/end2end_test.go

@@ -5284,6 +5284,53 @@ func (s) TestGRPCMethod(t *testing.T) {
 	}
 }
 
+// renameProtoCodec is an encoding.Codec wrapper that allows customizing the
+// Name() of another codec.
+type renameProtoCodec struct {
+	encoding.Codec
+	name string
+}
+
+func (r *renameProtoCodec) Name() string { return r.name }
+
+func (s) TestForceCodecName(t *testing.T) {
+	wantContentTypeCh := make(chan string, 1)
+	defer close(wantContentTypeCh)
+
+	ss := &stubserver.StubServer{
+		EmptyCallF: func(ctx context.Context, in *testpb.Empty) (*testpb.Empty, error) {
+			md, ok := metadata.FromIncomingContext(ctx)
+			if !ok {
+				return nil, status.Errorf(codes.Internal, "no metadata in context")
+			}
+			if got, want := md["content-type"], <-wantContentTypeCh; len(got) != 1 || got[0] != want {
+				return nil, status.Errorf(codes.Internal, "got content-type=%q; want [%q]", got, want)
+			}
+			return &testpb.Empty{}, nil
+		},
+	}
+	protoCodec := encoding.GetCodec("proto")
+	if err := ss.Start([]grpc.ServerOption{grpc.ForceServerCodec(encoding.GetCodec("proto"))}); err != nil {
+		t.Fatalf("Error starting endpoint server: %v", err)
+	}
+	defer ss.Stop()
+
+	ctx, cancel := context.WithTimeout(context.Background(), 2*time.Second)
+	defer cancel()
+
+	codec := &renameProtoCodec{Codec: protoCodec, name: "some-test-name"}
+	wantContentTypeCh <- "application/grpc+some-test-name"
+	if _, err := ss.Client.EmptyCall(ctx, &testpb.Empty{}, grpc.ForceCodec(codec)); err != nil {
+		t.Fatalf("ss.Client.EmptyCall(_, _) = _, %v; want _, nil", err)
+	}
+
+	codec.name = "aNoTHeRNaME"
+	wantContentTypeCh <- "application/grpc+anothername"
+	if _, err := ss.Client.EmptyCall(ctx, &testpb.Empty{}, grpc.ForceCodec(codec)); err != nil {
+		t.Fatalf("ss.Client.EmptyCall(_, _) = _, %v; want _, nil", err)
+	}
+}
+
 func (s) TestForceServerCodec(t *testing.T) {
 	ss := &stubserver.StubServer{
 		EmptyCallF: func(ctx context.Context, in *testpb.Empty) (*testpb.Empty, error) {