'WSGI callable to begin the HTTP response.'

def start_response(self, status, headers, exc_info=None):

    if (self.started_response and (not exc_info)):
        raise AssertionError('WSGI    start_response    called    a    second    time    with    no    exc_info.')
    self.started_response = True
    if self.req.sent_headers:
        try:
            raise exc_info[0], exc_info[1], exc_info[2]
        finally:
            exc_info = None
    self.req.status = status
    for (k, v) in headers:
        if (not isinstance(k, str)):
            raise TypeError(('WSGI    response    header    key    %r    is    not    of    type    str.' % k))
        if (not isinstance(v, str)):
            raise TypeError(('WSGI    response    header    value    %r    is    not    of    type    str.' % v))
        if (k.lower() == 'content-length'):
            self.remaining_bytes_out = int(v)
    self.req.outheaders.extend(headers)
    return self.write
