Fail blocking socket operations loudly

[thomasballinger]

Would it make sense to fail blocking socket operations fail with an error code or a JavaScript exception?

@tiran encountered a TypeError: Cannot read property 'stream' of undefined error when calling accept on a blocking socket that was more confusing than Error: accept call on blocking socket is not supported would have been.

[tiran]

The full traceback is:

/python-wasm/cpython/builddir/node/python.js:158
   throw ex;
   ^

TypeError: Cannot read property 'stream' of undefined
    at Object.accept (/python-wasm/cpython/builddir/node/python.js:5354:12)
    at ___syscall_accept4 (/python-wasm/cpython/builddir/node/python.js:5609:31)
    at _emscripten_receive_on_main_thread_js (/python-wasm/cpython/builddir/node/python.js:7065:14)
    at _do_call (<anonymous>:wasm-function[8329]:0x2e657c)
    at emscripten_current_thread_process_queued_calls (<anonymous>:wasm-function[8323]:0x2e5bc8)
    at emscripten_main_thread_process_queued_calls (<anonymous>:wasm-function[8335]:0x2e671b)
    at /python-wasm/cpython/builddir/node/python.js:1321:20
    at Worker.worker.onmessage (/python-wasm/cpython/builddir/node/python.js:1607:5)
    at Worker.<anonymous> (/python-wasm/cpython/builddir/node/python.js:1656:12)
    at Worker.emit (events.js:400:28)
Emitted 'error' event on process instance at:
    at emitUnhandledRejectionOrErr (internal/event_target.js:579:11)
    at MessagePort.[nodejs.internal.kHybridDispatch] (internal/event_target.js:403:9)
    at MessagePort.exports.emitMessage (internal/per_context/messageport.js:18:26)

console log of the listening socket

<ref *1> {
  family: 2,
  type: 1,
  protocol: 0,
  server: WebSocketServer {
    _events: [Object: null prototype] {
      connection: [Function (anonymous)],
      closed: [Function (anonymous)],
      error: [Function (anonymous)]
    },
    _eventsCount: 3,
    _maxListeners: undefined,
    _server: Server {
      maxHeaderSize: undefined,
      insecureHTTPParser: undefined,
      _events: [Object: null prototype],
      _eventsCount: 5,
      _maxListeners: undefined,
      _connections: 0,
      _handle: [TCP],
      _usingWorkers: false,
      _workers: [],
      _unref: false,
      allowHalfOpen: true,
      pauseOnConnect: false,
      httpAllowHalfOpen: false,
      timeout: 0,
      keepAliveTimeout: 5000,
      maxHeadersCount: null,
      headersTimeout: 60000,
      requestTimeout: 0,
      _connectionKey: '4:127.0.0.1:0',
      [Symbol(IncomingMessage)]: [Function: IncomingMessage],
      [Symbol(ServerResponse)]: [Function: ServerResponse],
      [Symbol(kCapture)]: false,
      [Symbol(async_id_symbol)]: 15
    },
    _removeListeners: [Function: removeListeners],
    clients: Set(0) {},
    _shouldEmitClose: false,
    options: {
      maxPayload: 104857600,
      skipUTF8Validation: false,
      perMessageDeflate: false,
      handleProtocols: null,
      clientTracking: true,
      verifyClient: null,
      noServer: false,
      backlog: null,
      server: null,
      host: '127.0.0.1',
      path: null,
      port: 0
    },
    _state: 0,
    [Symbol(kCapture)]: false
  },
  error: null,
  peers: {},
  pending: [],
  recv_queue: [],
  sock_ops: {
    createPeer: [Function: createPeer],
    getPeer: [Function: getPeer],
    addPeer: [Function: addPeer],
    removePeer: [Function: removePeer],
    handlePeerEvents: [Function: handlePeerEvents],
    poll: [Function: poll],
    ioctl: [Function: ioctl],
    close: [Function: close],
    bind: [Function: bind],
    connect: [Function: connect],
    listen: [Function: listen],
    accept: [Function: accept],
    getname: [Function: getname],
    sendmsg: [Function: sendmsg],
    recvmsg: [Function: recvmsg]
  },
  stream: {
    path: 'socket[0]',
    node: FSNode {
      parent: [FSNode],
      mount: [Object],
      mounted: null,
      id: 19,
      name: 'socket[0]',
      mode: 49152,
      node_ops: {},
      stream_ops: {},
      rdev: 0,
      name_next: undefined,
      sock: [Circular *1]
    },
    flags: 2,
    seekable: false,
    stream_ops: {
      poll: [Function: poll],
      ioctl: [Function: ioctl],
      read: [Function: read],
      write: [Function: write],
      close: [Function: close]
    },
    fd: 3
  },
  saddr: '127.0.0.1',
  sport: 0
}

[sbc100]

Looks like a bug in accept, it should surely be checking the a non-empty listensock.pending or the result of the shift here:

emscripten/src/library_sockfs.js

Lines 565 to 567 in 583000b

	var newsock = listensock.pending.shift();
	newsock.stream.flags = listensock.stream.flags;
	return newsock;

Looks like an easy fix if you have time to write a PR.

[thomasballinger]

So a blocking accept call should is fine, it's only an error if it can't be fulfilled synchronously? Sounds good if so.

[sbc100]

Yes, I don't think crash relates specifically to blocking vs non-blocking.

At the same time, I don't see any support in the code there for blocking (but that isn't the proximate cause of the crash).

[RReverser]

It seems this issue was resolved & can be closed?