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How we built Pusher-JS 2.0 – part 2 – implementation (pusher.com)
33 points by knes 1515 days ago | hide | past | web | 2 comments | favorite



This is a great write-up! We learned a lot of these lessons at Poll Everywhere for http://firehose.io/, which is basically an open source version of Pusher. We do things a few things differently though:

* We only have two transport layers: http and ws. We don't bother with a Flash polyfill.

* We start the connection via HTTP long polling and upgrade to WS if its (a) present in the client and (b) the network supports it. We've seen a lot of firewalls kill WS connections, so long polling always works.

* We treat our "push" channels more like a push edge cache. Because of flakey connections you want to hang on to the past 50-100 messages published to a channel so that flakey clients can get messages if their connection drops.

Source code is up at https://github.com/polleverywhere/firehose and you can install it as a gem and have it running in 2 seconds.

I'm happy to answer questions on here if anybody's got them about building a realtime transport layer like Pusher & Firehose!


We've kept the FlashSocket option in there, as it ultimately means the user gets the benefit of a WebSocket connection without native WebSocket support; a single bidirectional connection resulting in the lowest latency possible.

Our HTTP fallback offers XHR Streaming, XHR Long-polling, IFRAME options (streaming, polling htmlfile etc.) and JSONP-polling for older browsers.

The preference is of course a WebSocket connection, then streaming (as it means a persistent connection is created), then long-polling, then standard polling. The problem with any sort of polling is that it's generally inefficient and there are periods of time where a connection isn't established - this means data on the client may not be the most up to date (stale).

We all know: WebSocket FTW! :)




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