serverSideEmit should be allowed

[lkho]

I think the default adapter should either loopback or ignore (if the event is not intended to be received locally) the emit, instead of throwing. This makes the default adapter incompatible with other real cluster mode adapters and cannot be used as a drop in replacement in tests.

https://github.com/socketio/socket.io-adapter/blob/d4ef54cccb7e4a1b89fd4cdb46eefd192c69b5b8/lib/index.ts#L274-L278

[darrachequesne]

Hi! That's an interesting point. However, if I'm not mistaken the other adapters do not loopback on the given server (when serverSideEmit is used on serverA, it gets emitted on serverB and serverC, but not on serverA).

So we could probably ignore it here, but in that case, does it make sense to run the tests with this adapter?

[lkho]

it's fine to just ignore the events, but just don't throw errors. IMHO, this adapter should be a drop in replacement with other adapters (and vice versa), and should behave the same in user code. if it throws, then the user code need to check explicitly what the underlying implementation is.

In order to catch that error, I need to write some hacky code like this:

  // work around default adapter will throw error. fallback to local emit
  let serverSideEmitNotSupported = false;
  const tryServerSideEmit = (ev, ...args) => {
    try {
      if (serverSideEmitNotSupported) {
        // no need to loop back in this case
        // nsp._onServerSideEmit([ev, ...args]);
      } else {
        nsp.serverSideEmit(ev, ...args);
      }
    } catch (e) {
      if (e.message.indexOf('serverSideEmit()') >= 0) {
        serverSideEmitNotSupported = true;
        return tryServerSideEmit(ev, ...args);
      }
      throw e;
    }
  };

[lkho]

As for tests, in my deployment environment, I have a production (with redis) and UAT (no redis, single node process) server. I need to use the above hacky code to make it work when deployed on both servers.

[darrachequesne]

This should be fixed by https://github.com/socketio/socket.io-adapter/commit/808c0450d858bb0abc7d93c2b650ad5a2a20dda8, included in socket.io-adapter@2.4.0 (and socket.io@4.5.0).

Please reopen if needed.

[MatanYemini]

this adapter does not support the serverSideEmit() functionality

Still get's it. Version 2.5.2

[darrachequesne]

@MatanYemini you mean, the warning in the console? In that case, this is expected, as it warns users that calling serverSideEmit() is no-op with the in-memory adapter.