500 when content-type is 'application/json' and body is None

[explosic4]

I am using webargs with aiohttp.
When the incoming request has header Content-Type: application/json and has no body, the server returns 500 error.
Below is the error log.

[2018-05-25 16:38:46,436] ERROR Error handling request
Traceback (most recent call last):
  File "/Users/explosic4/anaconda3/envs/qb/lib/python3.6/site-packages/aiohttp/web_protocol.py", line 381, in start
    resp = await self._request_handler(request)
  File "/Users/explosic4/anaconda3/envs/qb/lib/python3.6/site-packages/aiohttp/web_app.py", line 322, in _handle
    resp = await handler(request)
  File "/Users/explosic4/anaconda3/envs/qb/lib/python3.6/site-packages/aiohttp/web_middlewares.py", line 88, in impl
    return await handler(request)
  File "/Users/explosic4/qb/ot-rpc/warehouse/utils.py", line 76, in handler_middleware
    args = await parser.parse(args, request)
  File "/Users/explosic4/anaconda3/envs/qb/lib/python3.6/site-packages/webargs/async.py", line 71, in parse
    parsed = yield from self._parse_request(schema=schema, req=req, locations=locations)
  File "/Users/explosic4/anaconda3/envs/qb/lib/python3.6/site-packages/webargs/async.py", line 45, in _parse_request
    parsed_value = yield from self.parse_arg(argname, field_obj, req, locations)
  File "/Users/explosic4/anaconda3/envs/qb/lib/python3.6/site-packages/webargs/async.py", line 102, in parse_arg
    value = yield from self._get_value(name, field, req=req, location=location)
  File "/Users/explosic4/anaconda3/envs/qb/lib/python3.6/site-packages/webargs/async.py", line 119, in _get_value
    value = yield from function(req, name, argobj)
  File "/Users/explosic4/anaconda3/envs/qb/lib/python3.6/site-packages/webargs/aiohttpparser.py", line 102, in parse_json
    self._cache['json'] = json_data = yield from req.json()
  File "/Users/explosic4/anaconda3/envs/qb/lib/python3.6/site-packages/aiohttp/web_request.py", line 537, in json
    return loads(body)
  File "/Users/explosic4/anaconda3/envs/qb/lib/python3.6/json/__init__.py", line 354, in loads
    return _default_decoder.decode(s)
  File "/Users/explosic4/anaconda3/envs/qb/lib/python3.6/json/decoder.py", line 339, in decode
    obj, end = self.raw_decode(s, idx=_w(s, 0).end())
  File "/Users/explosic4/anaconda3/envs/qb/lib/python3.6/json/decoder.py", line 357, in raw_decode
    raise JSONDecodeError("Expecting value", s, err.value) from None
json.decoder.JSONDecodeError: Expecting value: line 1 column 1 (char 0)

[sloria]

Looks like a possible bug in aiohttp. I would expect yield from req.json() to return either None or raise a more specific error. I suggest reporting this issue on their issue tracker.

For now, webargs should probably handle this case. PRs welcome!

[foresmac]

Falcon has a similar behavior because it also passes the body directly to json.dumps and when that raises an error, it's internal media handling raises a bad request or something similar. falconry/falcon#1216

[fmqa]

I think this can be fixed by catching the JSONDecodeError and inspecting the exception object's doc member. I submitted PR #297 illustrating this workaround.

[sloria]

This is fixed in 4.1.1.