3pid invite fails with a 500 if the IS returns a 500 (or is unreachable)

[matrixbot]

Trevor tried to do a 3pid invite by email in a small private room with me & Amandine and got a 500:

2016-05-18 11:23:47,000 - synapse.http.client - 92 - INFO - POST-674789 - Received response to  POST https://matrix.org/_matrix/identity/api/v1/store-invite: 500
2016-05-18 11:23:47,000 - synapse.http.server - 135 - ERROR - POST-674789 - Failed handle request synapse.http.server._async_render on <synapse.rest.ClientRestResource object at 0x3f44d10>: <XForwardedForRequest at 0x7fa23e7c
43f8 method=POST uri=/_matrix/client/r0/rooms/!UFXRtuwBNRjrwPSNKd:matrix.org/invite?access_token=<redacted> clientproto=HTTP/1.1 site=8080>
Traceback (most recent call last):
  File "synapse/http/server.py", line 114, in wrapped_request_handler
    yield request_handler(self, request)
  File "/mnt/disk/home/matrix/venv-synapse/local/lib/python2.7/site-packages/twisted/internet/defer.py", line 1126, in _inlineCallbacks
    result = result.throwExceptionIntoGenerator(g)
  File "/mnt/disk/home/matrix/venv-synapse/local/lib/python2.7/site-packages/twisted/python/failure.py", line 389, in throwExceptionIntoGenerator
    return g.throw(self.type, self.value, self.tb)
  File "synapse/http/server.py", line 260, in _async_render
    callback_return = yield callback(request, **kwargs)
  File "/mnt/disk/home/matrix/venv-synapse/local/lib/python2.7/site-packages/twisted/internet/defer.py", line 1126, in _inlineCallbacks
    result = result.throwExceptionIntoGenerator(g)
  File "/mnt/disk/home/matrix/venv-synapse/local/lib/python2.7/site-packages/twisted/python/failure.py", line 389, in throwExceptionIntoGenerator
    return g.throw(self.type, self.value, self.tb)
  File "synapse/rest/client/v1/room.py", line 481, in on_POST
    txn_id
  File "/mnt/disk/home/matrix/venv-synapse/local/lib/python2.7/site-packages/twisted/internet/defer.py", line 1126, in _inlineCallbacks
    result = result.throwExceptionIntoGenerator(g)
  File "/mnt/disk/home/matrix/venv-synapse/local/lib/python2.7/site-packages/twisted/python/failure.py", line 389, in throwExceptionIntoGenerator
    return g.throw(self.type, self.value, self.tb)
  File "synapse/handlers/room_member.py", line 431, in do_3pid_invite
    txn_id=txn_id
  File "/mnt/disk/home/matrix/venv-synapse/local/lib/python2.7/site-packages/twisted/internet/defer.py", line 1126, in _inlineCallbacks
    result = result.throwExceptionIntoGenerator(g)
  File "/mnt/disk/home/matrix/venv-synapse/local/lib/python2.7/site-packages/twisted/python/failure.py", line 389, in throwExceptionIntoGenerator
    return g.throw(self.type, self.value, self.tb)
  File "synapse/handlers/room_member.py", line 537, in _make_and_store_3pid_invite
    inviter_avatar_url=inviter_avatar_url
  File "/mnt/disk/home/matrix/venv-synapse/local/lib/python2.7/site-packages/twisted/internet/defer.py", line 1126, in _inlineCallbacks
    result = result.throwExceptionIntoGenerator(g)
  File "/mnt/disk/home/matrix/venv-synapse/local/lib/python2.7/site-packages/twisted/python/failure.py", line 389, in throwExceptionIntoGenerator
    return g.throw(self.type, self.value, self.tb)
  File "synapse/handlers/room_member.py", line 640, in _ask_id_server_for_third_party_invite
    invite_config
  File "/mnt/disk/home/matrix/venv-synapse/local/lib/python2.7/site-packages/twisted/internet/defer.py", line 1128, in _inlineCallbacks
    result = g.send(result)
  File "synapse/http/client.py", line 127, in post_urlencoded_get_json
    defer.returnValue(json.loads(body))
  File "/mnt/disk/home/matrix/venv-synapse/local/lib/python2.7/site-packages/simplejson/__init__.py", line 516, in loads
    return _default_decoder.decode(s)
  File "/mnt/disk/home/matrix/venv-synapse/local/lib/python2.7/site-packages/simplejson/decoder.py", line 370, in decode
    obj, end = self.raw_decode(s)
  File "/mnt/disk/home/matrix/venv-synapse/local/lib/python2.7/site-packages/simplejson/decoder.py", line 400, in raw_decode
    return self.scan_once(s, idx=_w(s, idx).end())
JSONDecodeError: Expecting value: line 1 column 1 (char 0)
2016-05-18 11:23:47,001 - synapse.access.http.8080 - 91 - INFO - POST-674789 - 46.247.9.153 - 8080 - {@&#8203;trevorm:matrix.org} Processed request: 255ms (0ms, 0ms) (0ms/0) 55B 500 "POST /_matrix/client/r0/rooms/!UFXRtuwBNRjrwPSNKd
:matrix.org/invite?access_token=<redacted> HTTP/1.1" "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_11_3) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/50.0.2661.102 Safari/537.36"

(Imported from https://matrix.org/jira/browse/SYN-698)

(Reported by @ara4n)

[matrixbot]

Jira watchers: @ara4n

[matrixbot]

Trevor was using the wrong IS (matrix.org), which 500'd him. Synapse then choked on the 500. Synapse shouldn't choke.

-- @ara4n

[reivilibre]

It's not clear what the correct error code is, though. This issue probably can't be taken seriously until that is answered.