Reads lines from source. Make one with make_line_reader, read with read_line and give its
buffer back with free_line_reader. It does not close source.
Fields
- source: Reader
- limit: s64
- buffer: [..] u8
- start: s64
- The line being read starts here;
scannedbytes after it are known to hold no newline. - scanned: s64
- ended: bool
- unterminated: bool
- Set by
read_line: whether the line it just returned had no line ending.