Monkey patch for h11. Although HTTP uses CRLF as line-breaks in headers, some implementations may still use LF. The script provides CRLF insensitive patch for ReceiveBuffer from h11.

monkey_patch_h11.py

from h11._receivebuffer import ReceiveBuffer

def monkey_patch():
    def _maybe_extract_lines_crlf_insensitive(self):
        if self._data[self._start : self._start + 2] == b"\r\n":
            self._start += 2
            return []
        elif self._data[self._start : self._start + 1] == b"\n":
            self._start += 1
            return []
        else:
            data = self.maybe_extract_until_next(b"\r\n\r\n") \
                    or self.maybe_extract_until_next(b"\n\n")
            if data is None:
                # header not finish 
                return None
            
            lines = []
            lf_lines = data.split(b"\r\n")
            for lf_line in lf_lines:
                lines += lf_line.split(b"\n")
            assert lines[-2] == lines[-1] == b""
            del lines[-2:]
            return lines

    _original_ReceiveBuffer_maybe_extract_lines = ReceiveBuffer.maybe_extract_lines
    ReceiveBuffer.maybe_extract_lines = _maybe_extract_lines_crlf_insensitive
    
    def _recover():
        ReceiveBuffer.maybe_extract_lines = _original_ReceiveBuffer_maybe_extract_lines

    return _recover

The following header may cause error in h11 when trying to decode it since there are CRLFs and LFs.

HTTP/1.1 200 OK\r\nCache-Control: private, max-age=604800, pre-check=604800\nPragma: private\nExpires: Thu, 28 Nov 2019 06:29:17 GMT\nLast-Modified: Thu, 23 May 2019 07:32:40 GMT\nContent-Type: image/jpeg\nContent-Length: 59967\nContent-Transfer-Encoding: binary\r\n\r\n

LocalProtocolError or RemoteProtocolError may be raised with the message malformed data.

File "/.../site-packages/requests_async/api.py", line 6, in request
    return await session.request(method=method, url=url, **kwargs)
  File "/.../site-packages/requests_async/sessions.py", line 79, in request
    resp = await self.send(prep, **send_kwargs)
  File "/.../site-packages/requests_async/sessions.py", line 136, in send
    r = await adapter.send(request, **kwargs)
  File "/.../site-packages/requests_async/adapters.py", line 55, in send
    timeout=timeout,
  File "/.../site-packages/http3/interfaces.py", line 49, in request
    return await self.send(request, verify=verify, cert=cert, timeout=timeout)
  File "/.../site-packages/http3/dispatch/connection_pool.py", line 130, in send
    raise exc
  File "/.../site-packages/http3/dispatch/connection_pool.py", line 121, in send
    request, verify=verify, cert=cert, timeout=timeout
  File "/.../site-packages/http3/dispatch/connection.py", line 59, in send
    response = await self.h11_connection.send(request, timeout=timeout)
  File "/.../site-packages/http3/dispatch/http11.py", line 58, in send
    http_version, status_code, headers = await self._receive_response(timeout)
  File "/.../site-packages/http3/dispatch/http11.py", line 130, in _receive_response
    event = await self._receive_event(timeout)
  File "/.../site-packages/http3/dispatch/http11.py", line 161, in _receive_event
    event = self.h11_state.next_event()
  File "/.../site-packages/h11/_connection.py", line 439, in next_event
    exc._reraise_as_remote_protocol_error()
  File "/.../site-packages/h11/_util.py", line 72, in _reraise_as_remote_protocol_error
    raise self
  File "/.../site-packages/h11/_connection.py", line 420, in next_event
    event = self._extract_next_receive_event()
  File "/.../site-packages/h11/_connection.py", line 361, in _extract_next_receive_event
    event = self._reader(self._receive_buffer)
  File "/.../site-packages/h11/_readers.py", line 88, in maybe_read_from_SEND_RESPONSE_server
    return class_(headers=list(_decode_header_lines(lines[1:])),
  File "/.../site-packages/h11/_readers.py", line 58, in _decode_header_lines
    matches = validate(header_field_re, bytes(line))
  File "/.../site-packages/h11/_util.py", line 96, in validate
    raise LocalProtocolError(msg)
h11._util.RemoteProtocolError: malformed data

---

Patching the library before any HTTP requests fixes the error.

from monkey_patch_h11 import monkey_patch
recover_h11 = monkey_patch()

# use recover_h11 () to recover