Large UDP messages crash the sandbox about repy_v2

[kellender]

I looked at the unit test, and get the same error for my windows machine also.
And for convenience here it is on Appveyor: https://ci.appveyor.com/project/kellender/seattlelib-v2

..\GitHub\seattlelib_v2\RUNNABLE [Large-UDP-mdgs +2 ~0 -0 !]> python utf.py -f ut_repyv2api_udp_test_datagram_sizes.r2py
Testing module: repyv2api
        Running: ut_repyv2api_udp_test_datagram_sizes.r2py          [ FAIL ]
--------------------------------------------------------------------------------
Standard error :
..............................Produced..............................
Internal Error
---
Uncaught exception!
---
Following is a full traceback, and a user traceback.
The user traceback excludes non-user modules. The most recent call is displayed last.

Full debugging traceback:
  "C:\Users\Ajay S\Documents\GitHub\seattlelib_v2\RUNNABLE\namespace.py", line 1207, in wrapped_function
  "C:\Users\Ajay S\Documents\GitHub\seattlelib_v2\RUNNABLE\emulcomm.py", line 889, in sendmessage

User traceback:

Exception (with class 'socket.error'): [Errno 10040] A message sent on a datagram socket was larger than the internal message buffer or some other network limit, or the buffer used to receive a datagram into was smaller than the datagram itself
---

..............................Expected..............................
None
--------------------------------------------------------------------------------

[aaaaalbert]

Thanks, and 👍 for doing this on AppVeyor!

Can you try and run the test outside of utf.py, please? Just the plain

python repy.py restrictions.default ut_repyv2api_udp_test_datagram_sizes.r2py 

so that we see what the size limit actually is.

[kellender]

sorry habit

C:\Users\Ajay S\Documents\GitHub\seattlelib_v2\RUNNABLE [Large-UDP-mdgs +2 ~0 -0 !]> python repy.py restrictions.default ut_repyv2api_udp_test_datagram_sizes.r2py
Message length 1000 works.
Message length 1600 works.
Message length 9216 works.
Message length 9217 works.
Message length 10000 works.
Message length 65507 works.
Message length 65508Internal Error
---
Uncaught exception!
---
Following is a full traceback, and a user traceback.
The user traceback excludes non-user modules. The most recent call is displayed last.

Full debugging traceback:
  "C:\Users\Ajay S\Documents\GitHub\seattlelib_v2\RUNNABLE\namespace.py", line 1207, in wrapped_function
  "C:\Users\Ajay S\Documents\GitHub\seattlelib_v2\RUNNABLE\emulcomm.py", line 889, in sendmessage

User traceback:

Exception (with class 'socket.error'): [Errno 10040] A message sent on a datagram socket was larger than the internal message buffer or some other network limit, or the buffer used to receive a datagram into was smaller than the datagram itself

[aaaaalbert]

Checked on Mac OS X again: First, sudo is required to modify net.inet.udp.maxdgram. In other words, Seattle cannot (safely, sanely) do this.

Second, if I increase the value to 2**16-1 (or larger), the test outcomes are like what you see on Windows and Linux, i.e. the upper datagram length limit is 65507 bytes before the socket.error arises.

[awwad]

@XuefengHuang and @vladimir-v-diaz will review this when they have time and let me know if anything seems lacking. (: