Question

I can happily send messages to the clients from the server and also to the server from the clients. I, however, seem to need to send (broadcast) messages to the (server) sockets from the server itself — and I don’t know how to go about it.

The case is that the server learns (via a Redis subscription) that a subset of the possibly very numerous clients need to be sent a message. Each server side socket can determine on its own if it needs to fire or not. I just don’t know how to let them know they have to do the check (possibly in much the same way as ‘normally’ by a message from the client (?)).

FWIW the check can be made by using the handshakeData only (and other non-socket-instance-specific server side structures). If there’s a way to get to the handshakeData ‘from the outside’, it’s also a possibility; but by no means really pretty.

Any thoughts/pointers anyone?

Answer 1

I seem to have got it finally (by debugging the socket.io code).

Within a message handler fetch the socket in question and have a ‘params’ array set with the event and other attributes (usually a ‘data’ object with additional info). With these two call socket.$emit.apply(socket, params).

In actual code:

for (var socketId in io.namespaces['/mynamespace'].sockets) {
    var socket = io.namespaces['/mynamespace'].sockets[socketId];
    var params = ['test event', {'foo': 'bar'}];
    socket.$emit.apply(socket, params);
}