fix enabling compression by trimming whitespaces in accept encoding header

internal/transport/transport.go

@@ -28,6 +28,7 @@ import (
 	"fmt"
 	"io"
 	"net"
+	"strings"
 	"sync"
 	"sync/atomic"
 	"time"
@@ -362,8 +363,12 @@ func (s *Stream) SendCompress() string {
 
 // ClientAdvertisedCompressors returns the compressor names advertised by the
 // client via grpc-accept-encoding header.
-func (s *Stream) ClientAdvertisedCompressors() string {
-	return s.clientAdvertisedCompressors
+func (s *Stream) ClientAdvertisedCompressors() []string {
+	values := strings.Split(s.clientAdvertisedCompressors, ",")
+	for i, v := range values {
+		values[i] = strings.TrimSpace(v)
+	}
+	return values
 }
 
 // Done returns a channel which is closed when it receives the final status

server.go

@@ -2119,7 +2119,7 @@ func ClientSupportedCompressors(ctx context.Context) ([]string, error) {
 		return nil, fmt.Errorf("failed to fetch the stream from the given context %v", ctx)
 	}
 
-	return strings.Split(stream.ClientAdvertisedCompressors(), ","), nil
+	return stream.ClientAdvertisedCompressors(), nil
 }
 
 // SetTrailer sets the trailer metadata that will be sent when an RPC returns.
@@ -2159,7 +2159,7 @@ func (c *channelzServer) ChannelzMetric() *channelz.ServerInternalMetric {
 
 // validateSendCompressor returns an error when given compressor name cannot be
 // handled by the server or the client based on the advertised compressors.
-func validateSendCompressor(name, clientCompressors string) error {
+func validateSendCompressor(name string, clientCompressors []string) error {
 	if name == encoding.Identity {
 		return nil
 	}
@@ -2168,7 +2168,7 @@ func validateSendCompressor(name, clientCompressors string) error {
 		return fmt.Errorf("compressor not registered %q", name)
 	}
 
-	for _, c := range strings.Split(clientCompressors, ",") {
+	for _, c := range clientCompressors {
 		if c == name {
 			return nil // found match
 		}

test/compressor_test.go

@@ -566,6 +566,13 @@ func (s) TestClientSupportedCompressors(t *testing.T) {
 			),
 			want: []string{"gzip"},
 		},
+		{
+			desc: "With additional grpc-accept-encoding header with spaces between values",
+			ctx: metadata.AppendToOutgoingContext(ctx,
+				"grpc-accept-encoding", "identity, deflate",
+			),
+			want: []string{"gzip", "identity", "deflate"},
+		},
 	} {
 		t.Run(tt.desc, func(t *testing.T) {
 			ss := &stubserver.StubServer{