func (rpc *grpcService) readFrom(request *pb.ReadRequest, reader io.ReaderAt, stream pb.ByteStream_ReadServer) error { limit := int(request.ReadLimit) if limit < 0 { return grpc.Errorf(codes.InvalidArgument, "Read(): read_limit=%d is invalid", limit) } offset := request.ReadOffset if offset < 0 { return grpc.Errorf(codes.InvalidArgument, "Read(): offset=%d is invalid", offset) } var buf []byte if limit > 0 { buf = make([]byte, limit) } else { buf = make([]byte, 1024*1024) // 1M buffer is reasonable. } bytesSent := 0 for limit == 0 || bytesSent < limit { n, err := reader.ReadAt(buf, offset) if n > 0 { if err := stream.Send(&pb.ReadResponse{Data: buf[:n]}); err != nil { return grpc.Errorf(grpc.Code(err), "Send(resourceName=%q offset=%d): %v", request.ResourceName, offset, grpc.ErrorDesc(err)) } } else if err == nil { return grpc.Errorf(codes.Internal, "nil error on empty read: io.ReaderAt contract violated") } offset += int64(n) bytesSent += n if err == io.EOF { break } if err != nil { return grpc.Errorf(codes.Unknown, "ReadAt(resourceName=%q offset=%d): %v", request.ResourceName, offset, err) } } return nil }