sockets support in emscripten

[dudiko]

Hi,

I'm trying to write a simple client-server app in c/c++ and compile it to javascript using emscripten.
I read a lot about sockets in emscripten and I have to admit, there is a big mess!
Can please someone clarify the situation?

I understand that javascript language doesn't allow to use raw sockets and requires us to work with either HTTP or WebSocket.
So if I will write code in c/c++ that uses 'connect', 'listen' (for raw sockets) and will try to compile it using emscripten, it won't work, right? (already tried but just want to verify)
And what if I will write code in c/c++ that uses WebSocket library and will try to compile it using emscripten, I guess it won't work as well because WebSocket library internally uses raw sockets.
So, I'm wondering how should it be done? Do I need to write a pure javascript code for that mission?

Thanks,
Dudi

[dudiko]

BTW, I noticed there are tests for simple client-server under:
https://github.com/kripken/emscripten/blob/master/tests/sockets/
but it doesn't work for me!

I compiled both client and server:

emcc test_sockets_echo_client.c -o client.js -D SOCKK=9991
emcc test_sockets_echo_server.c -o server.js -D SOCKK=9991

but for the client when I run:
nodejs client.js
I get:

connect failed: Host is unreachable
emscripten_force_exit cannot actually shut down the runtime, as the build has NO_EXIT_RUNTIME set

and nothing is being sent, not even SYN packet (I recorded on loopback interface)

and for the server when I run:
nodejs server.js
I get:

atexit() called, but NO_EXIT_RUNTIME is set, so atexits() will not be called. set NO_EXIT_RUNTIME to 0 (see the FAQ)
Calling stub instead of signal()
{ [Error: Cannot find module 'ws'] code: 'MODULE_NOT_FOUND' }
{ [Error: Cannot find module 'ws'] code: 'MODULE_NOT_FOUND' }
exception thrown: abort({"code":"MODULE_NOT_FOUND"}) at Error
    at jsStackTrace (/home/emscripten/emsdk-portable/emscripten/tag-1.37.35/tests/sockets/1.js:1033:13)
    at stackTrace (/home/emscripten/emsdk-portable/emscripten/tag-1.37.35/tests/sockets/1.js:1050:12)
    at abort (/home/emscripten/emsdk-portable/emscripten/tag-1.37.35/tests/sockets/1.js:15788:44)
    at ___syscall102 (/home/emscripten/emsdk-portable/emscripten/tag-1.37.35/tests/sockets/1.js:5636:69)
    at _listen (/home/emscripten/emsdk-portable/emscripten/tag-1.37.35/tests/sockets/1.js:14576:8)
    at _main (/home/emscripten/emsdk-portable/emscripten/tag-1.37.35/tests/sockets/1.js:7534:9)
    at Object.asm._main (/home/emscripten/emsdk-portable/emscripten/tag-1.37.35/tests/sockets/1.js:15331:21)
    at Object.callMain (/home/emscripten/emsdk-portable/emscripten/tag-1.37.35/tests/sockets/1.js:15614:30)
    at doRun (/home/emscripten/emsdk-portable/emscripten/tag-1.37.35/tests/sockets/1.js:15672:60)
    at run (/home/emscripten/emsdk-portable/emscripten/tag-1.37.35/tests/sockets/1.js:15686:5)

/home/emscripten/emsdk-portable/emscripten/tag-1.37.35/tests/sockets/1.js:113
      throw ex;
      ^
abort({"code":"MODULE_NOT_FOUND"}) at Error
    at jsStackTrace (/home/emscripten/emsdk-portable/emscripten/tag-1.37.35/tests/sockets/1.js:1033:13)
    at stackTrace (/home/emscripten/emsdk-portable/emscripten/tag-1.37.35/tests/sockets/1.js:1050:12)
    at abort (/home/emscripten/emsdk-portable/emscripten/tag-1.37.35/tests/sockets/1.js:15788:44)
    at ___syscall102 (/home/emscripten/emsdk-portable/emscripten/tag-1.37.35/tests/sockets/1.js:5636:69)
    at _listen (/home/emscripten/emsdk-portable/emscripten/tag-1.37.35/tests/sockets/1.js:14576:8)
    at _main (/home/emscripten/emsdk-portable/emscripten/tag-1.37.35/tests/sockets/1.js:7534:9)
    at Object.asm._main (/home/emscripten/emsdk-portable/emscripten/tag-1.37.35/tests/sockets/1.js:15331:21)
    at Object.callMain (/home/emscripten/emsdk-portable/emscripten/tag-1.37.35/tests/sockets/1.js:15614:30)
    at doRun (/home/emscripten/emsdk-portable/emscripten/tag-1.37.35/tests/sockets/1.js:15672:60)
    at run (/home/emscripten/emsdk-portable/emscripten/tag-1.37.35/tests/sockets/1.js:15686:5)

which sounds legit cause there is no listen for javascript.

So, how should I make it work?

And of course, when I'm compiling with gcc, everything work just perfect

[kripken]

Do they pass when running in the test suite? ./tests/runner.py sockets.test_... (the test runner sets up the server with websockify etc. in a way that should work)

[dudiko]

emscripten@dudi-Latitude-E7450:~/emsdk-portable/emscripten/tag-1.37.35/tests$ ./runner.py sockets
WARNING:root:use EM_ALL_ENGINES=1 in the env to run against all JS engines, which is slower but provides more coverage
Test suites:
['test_sockets']
Running test_sockets: (21 tests)
ERROR

======================================================================
ERROR: setUpClass (test_sockets.sockets)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "/home/emscripten/emsdk-portable/emscripten/tag-1.37.35/tests/test_sockets.py", line 132, in setUpClass
    super(sockets, self).setUpClass()
  File "/home/emscripten/emsdk-portable/emscripten/tag-1.37.35/tests/runner.py", line 788, in setUpClass
    self.harness_queue = multiprocessing.Queue()
  File "/usr/lib/python2.7/multiprocessing/__init__.py", line 218, in Queue
    return Queue(maxsize)
  File "/usr/lib/python2.7/multiprocessing/queues.py", line 63, in __init__
    self._rlock = Lock()
  File "/usr/lib/python2.7/multiprocessing/synchronize.py", line 147, in __init__
    SemLock.__init__(self, SEMAPHORE, 1, 1)
  File "/usr/lib/python2.7/multiprocessing/synchronize.py", line 75, in __init__
    sl = self._semlock = _multiprocessing.SemLock(kind, value, maxvalue)
OSError: [Errno 38] Function not implemented

----------------------------------------------------------------------
Ran 0 tests in 0.002s

FAILED (errors=1)

BUT, I succeed! Apparently what was missing for me was to install ws library for nodejs...
and there is a significant progress...

Now, the client is sending traffic but the server crushes:

emscripten@dudi-Latitude-E7450:~/emsdk-portable/emscripten/tag-1.37.35/tests/sockets$ nodejs server.js 
atexit() called, but NO_EXIT_RUNTIME is set, so atexits() will not be called. set NO_EXIT_RUNTIME to 0 (see the FAQ)
Calling stub instead of signal()
/home/emscripten/emsdk-portable/emscripten/tag-1.37.35/tests/sockets/server.js:113
      throw ex;
      ^

TypeError: Cannot read property 'binary' of undefined
    at WebSocket.<anonymous> (/home/emscripten/emsdk-portable/emscripten/tag-1.37.35/tests/sockets/server.js:4713:26)
    at WebSocket.emit (events.js:180:13)
    at Receiver.receiverOnMessage (/home/node_modules/ws/lib/websocket.js:715:20)
    at Receiver.emit (events.js:180:13)
    at Receiver.dataMessage (/home/node_modules/ws/lib/receiver.js:405:14)
    at Receiver.getData (/home/node_modules/ws/lib/receiver.js:346:17)
    at Receiver.startLoop (/home/node_modules/ws/lib/receiver.js:133:22)
    at Receiver._write (/home/node_modules/ws/lib/receiver.js:69:10)
    at doWrite (_stream_writable.js:406:12)
    at writeOrBuffer (_stream_writable.js:392:5)

and the wireshark shows:

GET / HTTP/1.1
Sec-WebSocket-Version: 13
Sec-WebSocket-Key: SXJSB2nb4zZlEnjGiZAexg==
Connection: Upgrade
Upgrade: websocket
Sec-WebSocket-Extensions: permessage-deflate; client_max_window_bits
Host: 127.0.0.1:1337

HTTP/1.1 101 Switching Protocols
Upgrade: websocket
Connection: Upgrade
Sec-WebSocket-Accept: hEKNs+pm+aMovfHFBLsgEVAbK9k=

..y. .w. ....aPf..>...$...?..a

Any explanation?

[ternaam]

Seems related to #5971
@dudiko did you find a workaround eventually?