Safely iterates line-based over an input stream.  If the input stream
    is not a :class:`LimitedStream` the `limit` parameter is mandatory.

    This uses the stream's :meth:`~file.read` method internally as opposite
    to the :meth:`~file.readline` method that is unsafe and can only be used
    in violation of the WSGI specification.  The same problem applies to the
    `__iter__` function of the input stream which calls :meth:`~file.readline`
    without arguments.

    If you need line-by-line processing it's strongly recommended to iterate
    over the input stream using this helper function.

    .. versionchanged:: 0.8
       This function now ensures that the limit was reached.

    .. versionadded:: 0.9
       added support for iterators as input stream.

    .. versionadded:: 0.11.10
       added support for the `cap_at_buffer` parameter.

    :param stream: the stream or iterate to iterate over.
    :param limit: the limit in bytes for the stream.  (Usually
                  content length.  Not necessary if the `stream`
                  is a :class:`LimitedStream`.
    :param buffer_size: The optional buffer size.
    :param cap_at_buffer: if this is set chunks are split if they are longer
                          than the buffer size.  Internally this is implemented
                          that the buffer size might be exhausted by a factor
                          of two however.

def make_line_iter(stream, limit=None, buffer_size=10 * 1024, cap_at_buffer=False):
    """Safely iterates line-based over an input stream.  If the input stream
    is not a :class:`LimitedStream` the `limit` parameter is mandatory.

    This uses the stream's :meth:`~file.read` method internally as opposite
    to the :meth:`~file.readline` method that is unsafe and can only be used
    in violation of the WSGI specification.  The same problem applies to the
    `__iter__` function of the input stream which calls :meth:`~file.readline`
    without arguments.

    If you need line-by-line processing it's strongly recommended to iterate
    over the input stream using this helper function.

    .. versionchanged:: 0.8
       This function now ensures that the limit was reached.

    .. versionadded:: 0.9
       added support for iterators as input stream.

    .. versionadded:: 0.11.10
       added support for the `cap_at_buffer` parameter.

    :param stream: the stream or iterate to iterate over.
    :param limit: the limit in bytes for the stream.  (Usually
                  content length.  Not necessary if the `stream`
                  is a :class:`LimitedStream`.
    :param buffer_size: The optional buffer size.
    :param cap_at_buffer: if this is set chunks are split if they are longer
                          than the buffer size.  Internally this is implemented
                          that the buffer size might be exhausted by a factor
                          of two however.
    """
    _iter = _make_chunk_iter(stream, limit, buffer_size)

    first_item = next(_iter, "")
    if not first_item:
        return

    s = make_literal_wrapper(first_item)
    empty = s("")
    cr = s("\r")
    lf = s("\n")
    crlf = s("\r\n")

    _iter = chain((first_item,), _iter)

    def _iter_basic_lines():
        _join = empty.join
        buffer = []
        while 1:
            new_data = next(_iter, "")
            if not new_data:
                break
            new_buf = []
            buf_size = 0
            for item in chain(buffer, new_data.splitlines(True)):
                new_buf.append(item)
                buf_size += len(item)
                if item and item[-1:] in crlf:
                    yield _join(new_buf)
                    new_buf = []
                elif cap_at_buffer and buf_size >= buffer_size:
                    rv = _join(new_buf)
                    while len(rv) >= buffer_size:
                        yield rv[:buffer_size]
                        rv = rv[buffer_size:]
                    new_buf = [rv]
            buffer = new_buf
        if buffer:
            yield _join(buffer)

    # This hackery is necessary to merge 'foo\r' and '\n' into one item
    # of 'foo\r\n' if we were unlucky and we hit a chunk boundary.
    previous = empty
    for item in _iter_basic_lines():
        if item == lf and previous[-1:] == cr:
            previous += item
            item = empty
        if previous:
            yield previous
        previous = item
    if previous:
        yield previous