fix(spanner): inject "x-goog-spanner-request-id" into outgoing client context (#11544)

Injects metadata derived from the associated gax.CallOptions that were
correctly being generated and tested, but accidentally not injected
into the outgoing context.

Fixes #11543

Co-authored-by: Knut Olav Løite <[email protected]>

Author: odeke-em

spanner/request_id_header.go

@@ -116,7 +116,7 @@ func (r requestID) augmentErrorWithRequestID(err error) error {
 	}
 }
 
-func gRPCCallOptionsToRequestID(opts []grpc.CallOption) (reqID requestID, found bool) {
+func gRPCCallOptionsToRequestID(opts []grpc.CallOption) (md metadata.MD, reqID requestID, found bool) {
 	for _, opt := range opts {
 		hdrOpt, ok := opt.(grpc.HeaderCallOption)
 		if !ok {
@@ -126,6 +126,7 @@ func gRPCCallOptionsToRequestID(opts []grpc.CallOption) (reqID requestID, found
 		metadata := hdrOpt.HeaderAddr
 		reqIDs := metadata.Get(xSpannerRequestIDHeader)
 		if len(reqIDs) != 0 && len(reqIDs[0]) != 0 {
+			md = *metadata
 			reqID = requestID(reqIDs[0])
 			found = true
 			break
@@ -137,7 +138,11 @@ func gRPCCallOptionsToRequestID(opts []grpc.CallOption) (reqID requestID, found
 func (wr *requestIDHeaderInjector) interceptUnary(ctx context.Context, method string, req, reply any, cc *grpc.ClientConn, invoker grpc.UnaryInvoker, opts ...grpc.CallOption) error {
 	// It is imperative to search for the requestID before the call
 	// because gRPC's internals will consume the headers.
-	reqID, foundRequestID := gRPCCallOptionsToRequestID(opts)
+	metadataWithRequestID, reqID, foundRequestID := gRPCCallOptionsToRequestID(opts)
+	if foundRequestID {
+		ctx = metadata.NewOutgoingContext(ctx, metadataWithRequestID)
+	}
+
 	err := invoker(ctx, method, req, reply, cc, opts...)
 	if !foundRequestID {
 		return err
@@ -174,7 +179,11 @@ type requestIDHeaderInjector int
 func (wr *requestIDHeaderInjector) interceptStream(ctx context.Context, desc *grpc.StreamDesc, cc *grpc.ClientConn, method string, streamer grpc.Streamer, opts ...grpc.CallOption) (grpc.ClientStream, error) {
 	// It is imperative to search for the requestID before the call
 	// because gRPC's internals will consume the headers.
-	reqID, foundRequestID := gRPCCallOptionsToRequestID(opts)
+	metadataWithRequestID, reqID, foundRequestID := gRPCCallOptionsToRequestID(opts)
+	if foundRequestID {
+		ctx = metadata.NewOutgoingContext(ctx, metadataWithRequestID)
+	}
+
 	cs, err := streamer(ctx, desc, cc, method, opts...)
 	if !foundRequestID {
 		return cs, err