vimproc_read_line.vim

function! s:read_line() dict
  let l:output = self.buffer
  let l:res = l:output
  while l:res !~ '\r\?\n' && !self.__eof
    let l:res = self.read(256)
    let l:output .= l:res
  endwhile

  let l:pos = match(l:output, '\v%(\r?\n|$)\zs')
  let l:line = matchstr(l:output[: l:pos - 1], '.\{-}\ze\r\?\n$')
  let self.buffer = l:output[l:pos :]
  let self.eof = (self.buffer != '') ? 0 : self.__eof

  return l:line
endfunction