Socket.IO 1.4.0 ship with new features like automatic compression for XHR and WebSockets, lots of bug fixes and significant performance and memory improvements.

Compression is enabled by default, as it’s highly beneficial for most application payloads. The following example shows the savings for a realtime stream of tweets.

The compression gains will vary by transport. For example, WebSocket defaults to a window size of 32kb when DEFLATE compression is enabled. Repeated occurrences of strings within that window will be compressed.
The following demo (inspired by Julia Evans work) will highlight what the LZ77 algorithm de-duplicates from the traffic sent by the Twitter stream that matches javascript.

How this demo works: we re-implemented a part of LZ77 in JavaScript. A React component then renders the compressed strings.

The longer the string, the darker the shade of yellow displayed.

In addition to this default behavior, we’ve introduced the capability to perform selective per-message compression, by introducing the compress flag when emitting an event.

socket.compress(true).emit(‘hi’, { some: ‘data’ });

To configure the defaults, we’ve introduced the following two options that you can pass to socket.io (and engine.io) when starting the server:

• perMessageDeflate – options to customize WebSocket compression (see here) or true for defaults (true).

• httpCompression – options to customize compression for HTTP polling transports or true for defaults (true)

The memory overhead when compression is enabled is not inexistent, however. Make sure to account for a 300kb~ overhead per connection in terms of memory allocation. Read here about the parameters you can customize to change how much memory is allocated and how aggressively data is compressed.

The following improvements have been made to the server:

• Assume 443 port when passing https:// to the origins parameter – Evan Lucas
• Improve detection of binary data inside events (in the has-binary module) – Gunther Brunner
• Warn about missing error event handlers on sockets to prevent silent hard-to-debug situations
• Allow a custom function for the allowRequest function for origins verification
• Fixes for “use strict” environments – Naoyuki Kanezawa
• Prevent users calling the ack function multiple times – Kevin Jose Martin
• Fixed potential memory leaks with open sockets when upgrade fails – Naoyuki Kanezawa
• Fix lingering requests when a polling error occurs – Naoyuki Kanezawa
• Drastically more memory efficient when keeping track of clients – Damien Arrachequesne
• Drastically more memory efficient when keeping track of rooms – Jérémy Lal
• Trigger callback if the client is already in the given room when join is called – Damien Arrachequesne
• Minor parser fixes and performance improvements.

The following improvements have been made to the client:

• Fix for specifying custom ports when connecting
• 2 or more connections to the same namespace now create new sockets, instead of reusing a single one.
• Added new reserved ping and pong events when a heartbeat is emitted and received.
• Add support for environments that extend Object.prototype – Damien Arrachequesne
• Fixes for “use strict” environments – Naoyuki Kanezawa
• Added an extraHeaders feature for custom headers in HTTP transports (non-WebSocket)
• Fix handling of disconnection while in the opening state.
• Improved error handling for unmatched acknowledgements.
• Parser fixes and improvements.

We’ve also released socket.io-redis 0.2.0 with significant performance improvements.

Special thanks to Damien Arrachequesne, Naoyuki Kanezawa and Jérémy Lal for their amazing and continued contributions that made this release possible.