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https://github.com/b3nsn0w/koa-easy-ws

Simple Koa middleware for websocket handling
https://github.com/b3nsn0w/koa-easy-ws

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Simple Koa middleware for websocket handling

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README 

        
Simple, easy to use, composable middleware for websocket handling in Koa



# Usage



```javascript

const Koa = require('koa')

const websocket = require('koa-easy-ws')



const app = new Koa()



app.use(websocket())

app.use(async (ctx, next) => {

  // check if the current request is websocket

  if (ctx.ws) {

    const ws = await ctx.ws() // retrieve socket



    // now you have a ws instance, you can use it as you see fit

    return ws.send('hello there')

  }

  

  // we're back to regular old http here

  ctx.body = 'general kenobi'

})

```



**Note: you will also need to install the `ws` package** (`npm install --save ws` or `yarn add ws`), **it is linked only as a peer dependency.**



First, you need to pass the koa-easy-ws middleware before the one handling your request. Remember to call it as a function, `app.use(websocket())`, not `app.use(websocket)`. This sets up on-demand websocket handling for the rest of the middleware chain.



The middleware adds the `ctx.ws()` function whenever it detects an upgrade request, calling which handles the websocket and returns a [ws][ws] instance. If not called, regular Koa flow continues, likely resulting in a client-side error.



# Features



 - No magic. This is a middleware, it doesn't turn your Koa app into a KoaMagicWebSocketServer. It knows its place.

 - Integrates [ws][ws], one of the fastest and most popular websocket libraries.

 - Full composability. Since this is just a middleware, it's not picky on what other libraries you use.

 - Minimal, unopinionated 44 SLOC codebase. Seriously, this readme alone contains more code than what's imported into your project. (sorry about the tests though)

 - Two dependencies only, and it's the ws library and [debug][debug] (because apparently logs are not a bad idea). No need for more clutter in your node_modules.



# Examples and advanced configuration



You can easily compose koa-easy-ws with a routing library:



```javascript

const Koa = require('koa')

const Router = require('koa-router')

const websocket = require('koa-easy-ws')



const app = new Koa()

const router = new Router()



app

  .use(websocket())

  .use(router.routes())

  .use(router.allowedMethods())



router.get('/pow/obi', async (ctx, next) => {

  if (ctx.ws) {

    const ws = await ctx.ws()

    ws.send('chancellor palpatine is evil')

  }

})



router.get('/pow/ani', async (ctx, next) => {

  if (ctx.ws) {

    const ws = await ctx.ws()

    ws.send('the jedi are evil')

    ws.send('404')

  }

})

```



If `ctx.ws()` isn't enough for you, the websocket server instance is also exposed:



```javascript

const Koa = require('koa')

const websocket = require('koa-easy-ws')



const app = new Koa()

const websocketMiddleware = websocket()

const websocketServer = websocketMiddleware.server // this is where the fun begins



app.use(websocketMiddleware) // we already have the instance here



// 

```



This gives you access to the [ws][ws] server object, allowing to pass down custom listeners, connection validators, etc.



Alternatively, you can pass options to the underlying [ws][ws] server as part of the options object:



```javascript

app.use(websocket('ws', {

  wsOptions: {

    clientTracking: false,

    maxPayload: 69420

  }

}))

```



The `wsOptions` object will be forwarded to [ws][ws] unchanged, you can check [its documentation][ws] for the available options.



In case `ctx.ws` conflicts with something else in your code, koa-easy-ws doesn't mind changing the property name, just pass it as a property. This also lets you use multiple websocket middlewares if you ever find a reason to do so:



```javascript

const Koa = require('koa')

const websocket = require('koa-easy-ws')



const app = new Koa()



app.use(websocket('sidious')) // we just renamed ctx.ws to ctx.sidious

app.use(websocket('maul')) // attach another one for no good reason



app.use(async (ctx, next) => {

  // the first middleware detected an upgrade request

  if (ctx.sidious) {

    const socket = await ctx.sidious()

    return socket.send('this is getting out of hand')

  }



  // the second middleware detected the same upgrade request

  if (ctx.maul) {

    const socket = await ctx.maul()

    return socket.send('now there are two of them')

  }

})

```



Note: in this example `ctx.maul` is never used because there is no limit on the authority of `ctx.sidious`. However, if you define custom logic this technique could sort incoming requests to separate websocket servers.



If needed, you can also expose the websocket server on a context property, which can itself be renamed:



```javascript

const Koa = require('koa')

const websocket = require('koa-easy-ws')



const app = new Koa()



app.use(websocket('ws', { exposeServerOn: 'wss' }))



app.use(async (ctx, next) => {

  if (ctx.ws) {

    console.log('found the server', ctx.wss)

  }

})

```



In the above example, `ctx.ws` behaves as normal, but you also have the server instance available on `ctx.wss`. This saves you the trouble of having to access `websocket().server` as seen in a prior example.



From here, the sky is the limit, unless you work for SpaceX.



# Version 2 changelog



In version 2, `ws` has been moved to a peer dependency, which is a breaking change with the way dependency resolution works. It will _technically_ work if you just upgrade to v2 with no changes, especially because of the `package-lock.json` or `yarn.lock` keeping `ws` there, but it would most likely inject a weird bug. **To avoid unpredictable issues in the future, add `ws` to your own package's dependencies.**



On top of that, the peer dependency is for ws@8, not ws@7 which koa-easy-ws previously used, so refer to ws@8's breaking changes for that (but if you're fine with a warning ws@7 should continue to work).



# Special usage for Node 9 or earlier



Node's HTTP server doesn't send upgrade requests through the normal callback (and thus your Koa middleware chain) prior to version 10, preventing koa-easy-ws from handling them. Because of this, if you target Node 9 or earlier, you must pass your HTTP server to the middleware which handles the workaround:



```javascript

const server = http.createServer(app.callback())



app.use(websocket('ws', server))



// alternatively, you can pass it as part of the options object:

app.use(websocket('ws2', {

  server: server

}))



server.listen(process.env.PORT) // use this function instead of your app.listen() call

```



koa-easy-ws then automatically feeds any upgrade request into your regular middleware chain. If you wish to opt out and do this yourself, use the `noServerWorkaround` option:



```javascript

app.use(websocket('ws', {

  noServerWorkaround: true

}))

```



# Contributing



Pull requests are welcome. As always, be respectful towards each other and maybe run or create tests, as appropriate. It's on `npm test`, as usual.



koa-easy-ws uses the MIT license. Was considering the WTFPL, but I like the "no warranty" clause.



[ws]: https://github.com/websockets/ws

[debug]: https://github.com/visionmedia/debug