Add server and client support for application errors in RPC response for VTGate.SplitQuery

go/vt/vtgate/gorpcvtgateconn/conn.go

@@ -322,6 +322,9 @@ func (conn *vtgateConn) SplitQuery(ctx context.Context, keyspace string, query t
 	if err := conn.rpcConn.Call(ctx, "VTGate.SplitQuery", request, result); err != nil {
 		return nil, err
 	}
+	if err := vterrors.FromRPCError(result.Err); err != nil {
+		return nil, err
+	}
 	return result.Splits, nil
 }
 

go/vt/vtgate/gorpcvtgateservice/server.go

@@ -181,7 +181,12 @@ func (vtg *VTGate) SplitQuery(ctx context.Context, req *proto.SplitQueryRequest,
 	defer vtg.server.HandlePanic(&err)
 	ctx, cancel := context.WithDeadline(ctx, time.Now().Add(*rpcTimeout))
 	defer cancel()
-	return vtg.server.SplitQuery(ctx, req, reply)
+	vtgErr := vtg.server.SplitQuery(ctx, req, reply)
+	vtgate.AddVtGateErrorToSplitQueryResult(vtgErr, reply)
+	if *vtgate.RPCErrorOnlyInReply {
+		return nil
+	}
+	return vtgErr
 }
 
 // New returns a new VTGate service

go/vt/vtgate/proto/vtgate_proto.go

@@ -178,4 +178,5 @@ type SplitQueryPart struct {
 // SplitQueryResult is the result for SplitQueryRequest
 type SplitQueryResult struct {
 	Splits []SplitQueryPart
+	Err    *mproto.RPCError
 }

go/vt/vtgate/vtgate_error.go

@@ -41,3 +41,12 @@ func AddVtGateErrorToQueryResultList(err error, reply *proto.QueryResultList) {
 	}
 	reply.Err = rpcErrFromVtGateError(err)
 }
+
+// AddVtGateErrorToSplitQueryResult will mutate a SplitQueryResult struct to fill in the Err
+// field with details from the VTGate error.
+func AddVtGateErrorToSplitQueryResult(err error, reply *proto.SplitQueryResult) {
+	if err == nil {
+		return
+	}
+	reply.Err = rpcErrFromVtGateError(err)
+}