size_t header_or_error_bytes_sent;
// Number of bytes we are into the stream (ie., the end of last send).
- // Only relevant for SENDING_DATA.
+ // -1 means we want to send from the end of the backlog (the normal case),
+ // -2 means we want to send from the _beginning_ of the backlog.
+ // Once we go into SENDING_DATA, these negative values will be translated
+ // to real numbers.
size_t stream_pos;
// Number of bytes we've sent of data. Only relevant for SENDING_DATA.