server: ClientSupportedCompressors and SetSendCompressor break when using Opentelemetry metrics plugin

[arjan-bal]

Both SetSendCompressor and downcast the the ServerTransport to a concrete struct (*transport.ServerStream) to call methods which are not available on the ServerTransport interface.

grpc-go/server.go

Lines 2153 to 2157 in 5fdb6d0

	func SetSendCompressor(ctx context.Context, name string) error {
	stream, ok := ServerTransportStreamFromContext(ctx).(*transport.ServerStream)
	if !ok || stream == nil {
	return fmt.Errorf("failed to fetch the stream from the given context")
	}

grpc-go/server.go

Lines 2175 to 2179 in 5fdb6d0

	func ClientSupportedCompressors(ctx context.Context) ([]string, error) {
	stream, ok := ServerTransportStreamFromContext(ctx).(*transport.ServerStream)
	if !ok || stream == nil {
	return nil, fmt.Errorf("failed to fetch the stream from the given context %v", ctx)
	}

The Opentelemetry plugin wraps the ServerTransport type for unary calls, which causes the downcasts to fail:

grpc-go/stats/opentelemetry/server_metrics.go

Lines 93 to 105 in 5fdb6d0

	func (h *serverMetricsHandler) unaryInterceptor(ctx context.Context, req any, _ *grpc.UnaryServerInfo, handler grpc.UnaryHandler) (any, error) {
	var metadataExchangeLabels metadata.MD
	if h.options.MetricsOptions.pluginOption != nil {
	metadataExchangeLabels = h.options.MetricsOptions.pluginOption.GetMetadata()
	}
	sts := grpc.ServerTransportStreamFromContext(ctx)
	alts := &attachLabelsTransportStream{
	ServerTransportStream: sts,
	metadataExchangeLabels: metadataExchangeLabels,
	}
	ctx = grpc.NewContextWithServerTransportStream(ctx, alts)