internal/gomote: add object name to UploadFile endpoint

This change adds the object name as one of the fields returned to the
caller. The object name is not included in the URL. The object name is
required for any subsequent calls needed to pass the file along to the
gomote instances.

For golang/go#47521
Updates golang/go#48742

Change-Id: I5437ab2029907460806f2f3b6a19f6dec22115da
Reviewed-on: https://go-review.googlesource.com/c/build/+/405535
TryBot-Result: Gopher Robot <[email protected]>
Auto-Submit: Carlos Amedee <[email protected]>
Reviewed-by: Dmitri Shuralyov <[email protected]>
Reviewed-by: Dmitri Shuralyov <[email protected]>
Reviewed-by: Carlos Amedee <[email protected]>
Run-TryBot: Carlos Amedee <[email protected]>

Author: cagedmantis

internal/gomote/gomote.go

@@ -401,14 +401,16 @@ func (s *Server) UploadFile(ctx context.Context, req *protos.UploadFileRequest)
 	if err != nil {
 		return nil, status.Errorf(codes.Unauthenticated, "request does not contain the required authentication")
 	}
-	url, fields, err := s.signURLForUpload(uuid.NewString())
+	objectName := uuid.NewString()
+	url, fields, err := s.signURLForUpload(objectName)
 	if err != nil {
 		log.Printf("unable to create signed URL: %s", err)
 		return nil, status.Errorf(codes.Internal, "unable to create signed url")
 	}
 	return &protos.UploadFileResponse{
-		Url:    url,
-		Fields: fields,
+		Url:        url,
+		Fields:     fields,
+		ObjectName: objectName,
 	}, nil
 }