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
}
