socket.io client connection cannot be made on the 2nd time

Question

Currently, I am implementing an API using nodejs express, then it needs to connect to socket.io and send event.

The API is located in socket.io-client (client), and it connects to socket.io (server)

1st API call: success

The connection is made for the 1st call of the API, message is sent and socket can be disconnected, with the 'disconnect' callback is invoked both on client and server side.

2nd API call: failure

When the API is invoked the 2nd time, the connection to server cannot be made, 'client' callback on client side is not called.

3rd API call: success

Then I tried to restart the client side, keeping other things unchanged. The API is called again, and the connection to socket.io is made successfully and everything is fine.

Can anyone explain the logistics behind this?

Updated

client.js

   App.getByUserId(message.to_id, function(error, app) {
  var  socket = io.connect('http://127.0.0.1:9002');
  socket.on('connect', function(){
  console.log("client connect socket id:" + socket.id);
    console.log("appkey:" + app.private_token);
    socket.emit('appkey.check',{appkey: app.private_token, uuid: message.to_id.uuid},    function(data){
        socket.emit("forceDisconnect");
        socket = null;

    });
});

Answer 1

You just hit one of Socket.IO's many "features" or "bugs" depending how you see this. Socket.IO tries to be smart and re-use connections (which causes a lot of connection issues actually) The way around this is use the force new connection option in your io.connect:

io.connect('http://127.0.0.1:9002', { 'force new connection': true });

What you could also do is use https://github.com/primus/primus which wraps Socket.IO if you use the socket.io transformer. Internally, it completely removes the use of the io.connect and uses the much more lower level io.Socket constructor to create more stable connections that you would get with a stock socket.io.