遭遇json.decoder.JSONDecodeError，请求排查Django接口POST解析问题

错误现象 #

在Django项目的/voice_chat/rooms接口处理POST请求时，触发json.decoder.JSONDecodeError，具体错误信息为：

json.decoder.JSONDecodeError: Expecting value: line 1 column 1 (char 0)

完整错误栈 #

ERROR 2022-11-08 13:29:54,926: Internal Server Error: /voice_chat/rooms
Traceback (most recent call last):
  File "C:\Users\15512\anaconda3\lib\site-packages\asgiref\sync.py", line 451, in thread_handler
    raise exc_info[1]
  File "C:\Users\15512\anaconda3\lib\site-packages\django\core\handlers\exception.py", line 38, in inner
    response = await get_response(request)
  File "C:\Users\15512\anaconda3\lib\site-packages\django\core\handlers\base.py", line 233, in _get_response_async
    response = await wrapped_callback(request, *callback_args, **callback_kwargs)
  File "C:\Users\15512\anaconda3\lib\site-packages\asgiref\sync.py", line 414, in __call__
    ret = await asyncio.wait_for(future, timeout=None)
  File "C:\Users\15512\anaconda3\lib\asyncio\tasks.py", line 455, in wait_for
    return await fut
  File "C:\Users\15512\anaconda3\lib\concurrent\futures\thread.py", line 57, in run
    result = self.fn(*self.args, **self.kwargs)
  File "C:\Users\15512\anaconda3\lib\site-packages\asgiref\sync.py", line 455, in thread_handler
    return func(*args, **kwargs)
  File "C:\Users\15512\anaconda3\lib\site-packages\django\views\generic\base.py", line 69, in view
    return self.dispatch(request, *args, **kwargs)
    request_body = json.loads(decode_request)
  File "C:\Users\15512\anaconda3\lib\json\__init__.py", line 357, in loads
    return _default_decoder.decode(s)
  File "C:\Users\15512\anaconda3\lib\json\decoder.py", line 337, in decode
    obj, end = self.raw_decode(s, idx=_w(s, 0).end())
  File "C:\Users\15512\anaconda3\lib\json\decoder.py", line 355, in raw_decode
    raise JSONDecodeError("Expecting value", s, err.value) from None
json.decoder.JSONDecodeError: Expecting value: line 1 column 1 (char 0)
ERROR 2022-11-08 13:29:54,959: HTTP POST /voice_chat/rooms 500 [0.32, 127.0.0.1:54258]

问题根源 #

代码中通过json.loads()解析请求体，但实际接收到的是x-www-form-urlencoded格式的键值对参数（包含AccountSid、roomName等字段），而非预期的JSON格式，导致JSON解析失败。

原代码示例 #

def post(self, request, *args, **kwargs):
    decode_request = request.body.decode("utf-8")
    print('decoded request body', decode_request)
    request_body = json.loads(decode_request)
    # print('request body', request_body)
    room_name = request_body.get("roomName")
    participant_label = request_body["participantLabel"]
    # print('username', curr_username)
    response = VoiceResponse()
    dial = Dial()
    dial.conference(
        name=room_name,
        participant_label=participant_label,
        start_conference_on_enter=True,
    )
    response.append(dial)
    return HttpResponse(response.to_xml(), content_type="text/xml")

请求体对比 #

预期JSON格式请求体 #

{"roomName":"testingUseremmanuelS21","participantLabel":"emmanuelS21","matchedUser":"testingUser"}

实际接收的x-www-form-urlencoded格式内容 #

AccountSid=***&ApiVersion=2010-04-01&ApplicationSid=***&CallSid=CAf4e
***&CallStatus=ringing&Called=&Caller=client%3AemmanuelS21&Direction=inbound&From=client%3AemmanuelS21&To=&participantLabel=emmanuelS21&roomName=testingUseremmanuelS21

修复方案 #

Django会自动解析x-www-form-urlencoded格式的请求体，直接通过request.POST获取参数即可，无需手动解析请求体。如果需要同时兼容JSON和表单两种格式，可以先判断请求的Content-Type头，再选择对应的解析方式。

修复后代码 #

def post(self, request, *args, **kwargs):
    # 直接从request.POST获取表单格式的参数
    room_name = request.POST.get("roomName")
    participant_label = request.POST.get("participantLabel")
    
    # 如果需要兼容JSON格式，可以添加如下判断
    # if request.content_type == 'application/json':
    #     decode_request = request.body.decode("utf-8")
    #     request_body = json.loads(decode_request)
    #     room_name = request_body.get("roomName")
    #     participant_label = request_body.get("participantLabel")

    response = VoiceResponse()
    dial = Dial()
    dial.conference(
        name=room_name,
        participant_label=participant_label,
        start_conference_on_enter=True,
    )
    response.append(dial)
    return HttpResponse(response.to_xml(), content_type="text/xml")

内容的提问来源于stack exchange，提问作者Emm