Disconnected agent causes invalid_state_err

[Ben Sheldon [he/him]]

(sorry to open this ticket, but I'm not sure if this is a problem on my setup or with push-it...)

Node throws an invalid_state_err when trying to send a message after refreshing the browser window. I think something isn't properly clearing the list of connected agents (i.e. trying to send to a disconnected agent), but I'm not entirely sure.

This is nodejs's console.log:

connected agent: SeKhwfqBtwYspYaveEn5B8
Agent.id(SeKhwfqBtwYspYaveEn5B8) sent message.uuid(_8iRNza40f0ANcyQ_T-yyS)
**REFRESH BROWSER**
connected agent: LaJPvL75EkCD3xJZVeEd_K
Agent.id(LaJPvL75EkCD3xJZVeEd_K) sent message.uuid(S9U-dlf8jun9DmtxqVUlPu)
disconnected agent: SeKhwfqBtwYspYaveEn5B8
Agent.id(LaJPvL75EkCD3xJZVeEd_K) sent message.uuid(LeA-VK048e0xY_XzpIO_2h)

node.js:134
        throw e; // process.nextTick error, or 'error' event on first tick
        ^
Error: INVALID_STATE_ERR
    at Error (unknown source)
    at Session.send (/Users/SlicedBread/node_modules/push-it/node_modules/sockjs/lib/transport.js:124:15)
    at Agent.send (/Users/SlicedBread/node_modules/push-it/server/models/agent.js:33:17)
    at Object.received (/Users/SlicedBread/node_modules/push-it/server/mqs/subscription_manager.js:34:26)
    at Object.callback (/Users/SlicedBread/node_modules/push-it/server/mqs/subscription_manager.js:25:12)
    at Array.<anonymous> (/Users/SlicedBread/node_modules/push-it/server/mqs/in_memory.js:47:18)
    at EventEmitter._tickCallback (node.js:126:26)

Thanks for the help and please let me know if I can better further describe the issue or help replicate it.

[Ben Sheldon [he/him]]

Tracking this down, it looks like the issue is that when agents disconnect, they are only removed from the list of agents (Agent.remove()), not unsubscribed from the channels. Thus when a new message is pushed out to a channel, it tries to send it to agents who have already disconnected. I tried wrapping SubscriptionManager.received in an error handler, at it "solved" the problem:

proto.received = function(chan, message){
  var ss = this.subscriptions[chan];
  if(ss){
    for(var agentId in ss.agents){
      try {
        // attempt to send the message
        ss.agents[agentId].send(message);
      }catch(err){
        if (err = 'invalid_state_err') {
          // agent doesn't exist, so unsubscribe
          ss.removeAgent(ss.agents[agentId]);
        }
      }
    }
  }
};

It's still a bit of spaghetti code since optimally the SubscriptionSet should be flushed in __onDisconnect. One issue is that the Agent doesn't contain a list of channels they are subscribed too, which means that when calling onDisconnect it seems like one would have to iterate through all channels to check/delete the agent.