SockJS for Go III (yet another take)

It’s been a while since the last blog and this is the last in the series of “SockJS-go lessons learned”.

Version “v2”

“v2” is a compete rewrite of the SockJS-go library [1], the entire code base is much smaller thanks to using the full potential of Go’s net/http library. So no more http “hijacks” and number of go routines the library spawns internally is kept to minimum. The project also adopted versioning based on The main reason for adoption was that “v2” uses a different API compared to “v1”, which was for experimental purposes only. The aim of “v2” is to become more stable and eventually production ready library. To get the package execute:

$ go get

To import this package, add the following line to your code:

import ""

Data frames

SockJS was primarily created to enable applications running in older browsers to use WebSocket-like communication with server, or in other words provide WebSocket emulation [2]. It provides a mechanism to send messages (or data frames) in both directions, from client to server and server to client. The only properly supported frames in SockJS are text frames. So in order to send binary data it is solely responsibility of an application to properly encode/decode binary message into text messages using UTF-8 encoding. Just to make the entire picture more complete, WebSockets as defined by RFC6455 support both types of data frames: binary and text.

API Changes

As described above, SockJS (similar to WebSocket) uses data frames. A client initiates a connection to a server and creates a new sockjs session. Depending on the underlaying transport, the session can span over multiple connections. Thus the notion of sockjs session. This is reflected in the API by sockjs.Session interface. Interface is simple enough to enable receiving and sending text frames, get the session ID and close the session.

SockJS Protocol Tests

This is probably the most questioned part of SockJS for Go implementation. Not all tests pass, and there’s no plan to make them pass. However here is the list of tests that do not pass with some explanation:


Rewriting the SockJS-go library several times (9 or 10 times all together) was a perfect drill to learn Go more in deep. The latest version tries to be as simple as possible. It is also incredible to see the progress of Go since it was first introduced. The language is very much the same, but the libraries and runtime are improving at a fast pace with every release keeping the backward compatibility.


  1. SockJS-go GitHub repository
  2. SockJS-node