<socket-io>

<socket-io> connects to a Socket.IO server and forwards received events into the Polymer event model.

Use

To avoid conflicts with other events, incoming messages are prefixed with io-, so add event listeners for io-<incoming-message-name>.

Specify which events to listen to with forwarding:

<socket-io
  auto-connecting forwarding='["new message", "user joined"]'
  on-io-new-message="handleNewMessage"
  on-io-user-joined="handleUserJoined">
</socket-io>

Or use auto-forwarding:

<socket-io
  auto-connecting auto-forwarding
  on-io-new-message="handleNewMessage"`
  on-io-user-joined="handleUserJoined">`
</socket-io>

The auto-forwarding feature may not function as you expect, due to the some workarounds it uses. Please see the auto-forwarding implementation notes for more information.

Implementation Notes

Feature: Auto-forwarding

Auto-forwarding can only be done if <socket-io> can figure out what events it needs to forward on its own, or if it can listen to all events and forward them blindly.

This leads to some interesting problems:

First, an element can't know what events it's parent is listening to (the on-<event-name> notation is processed by the parent), so <socket-io> can't use that notation to subscribe to the Socket.IO message. There is no way around this.

Second, Socket.IO has no official or public method to listen to all incoming events. There is support server side for middleware that are called for all incoming packets, but nothing similar for the browser.

This may change in the future; the Socket.IO team does not seem to be opposed to this capability, but was unable to decide between something like addGlobalListener() or io.on('*', [...]). Mirroring middleware feature to the browser would also support this.

In the meantime, there is a way to do it. By listening to the same event the Socket object itself listens to, all incoming packets can be examined (this is similar to having middleware support browser-side):

var socket = io();
socket.io.on('packet', function(packet) {
  // This event is fired immediately after a packet is fully parsed.
});

This event is a low-level firehose. It fires for all packets, not just packets from the server. Doing this also bypasses the processing the Socket object adds (currently the receive buffer feature). Any events that get buffered by the socket won't get picked up when the socket re-emits them.

Artanis/socket-io

<socket-io>

Use

Implementation Notes

Feature: Auto-forwarding