Braid-HTTP

This ponyfill library extends the HTTP implementations of Browsers and Nodejs with Braid-HTTP; transforming them from state transfer to state synchronization systems.

These features are provided in an elegant, backwards-compatible way:

• Browsers: get a drop-in replacement for fetch()
• Nodejs: get a route handler that adds abilities to the http, https, and http2 modules

It conforms to the Braid-HTTP v04 specification, with the additional HTTP Multiresponse and Multiplexing v1.0 extensions.

Developed in braid.org.

Installing

Browsers:

<script src="https://unpkg.com/braid-http/braid-http-client.js"></script>
<script>
  // To live on the cutting edge, you can now replace the browser's fetch() if desired:
  // window.fetch = braid_fetch
</script>

Node.js:

npm install braid-http

// Import with require()
require('braid-http').fetch       // A polyfill for fetch
require('braid-http').http_client // A polyfill for require('http') clients
require('braid-http').http_server // A polyfill for require('http') servers

// Or as es6 module
import {fetch, http_client, http_server} from 'braid-http'

Using it in Browsers

This library adds a {subscribe: true} option to fetch(), and lets you access the result of a subscription with two new fields on the fetch response:

• response.subscribe( update => ... )
• response.subscription: an iterator that can be used with for await

Example Subscription with Promises

Here is an example of subscribing to a Braid resource using promises:

fetch('https://braid.org/chat', {subscribe: true}).then(
    res => res.subscribe(
        (update) => {
            console.log('We got a new update!', update)
            // {
            //   version: ["me"],
            //   parents: ["mom", "dad"],
            //   patches: [{
            //.      unit: "json",
            //       range: ".foo",
            //       content: new Uint8Array([51]),
            //       content_text: "3" <-- getter
            //.  }],
            //   body: new Uint8Array([51]),
            //   body_text: "3" <-- getter
            // }
            //
            // Note that `update` will contain either patches *or* body
        }
    )
)

If you want automatic reconnections, this library add a {retry: true} option to fetch().

fetch('https://braid.org/chat', {subscribe: true, retry: true}).then(
    res => res.subscribe(
        (update) => {
            console.log('We got a new update!', update)
            // Do something with the update
        }
    )
)

For use in conjunction with {retry: true}, it's possible to make the parents param equal to a function, which will be called to get the current parents each time the fetch establishes a new connection.

fetch('https://braid.org/chat', {subscribe: true, retry: true, parents: () => {
        return current_parents
    }}).then(
    res => res.subscribe(
        (update) => {
            console.log('We got a new update!', update)
            // Do something with the update
        }
    )
)

Example Subscription with Async/Await

(await fetch('/chat', {subscribe: true, retry: true})).subscribe(
    (update) => {
        // We got a new update!
    })

Example Subscription with for await

var subscription_iterator = (await fetch('/chat',
    {subscribe: true, retry: true})).subscription
for await (var update of subscription_iterator) {
    // Updates might come in the form of patches:
    if (update.patches)
        chat = apply_patches(update.patches, chat)

    // Or complete snapshots:
    else
        // Beware the server doesn't send these yet.
        chat = JSON.parse(update.body_text)

    render_stuff()
}

Using it in Nodejs

You can braidify your nodejs server with:

var braidify = require('braid-http').http_server

Braidify adds these new abilities to requests and responses:

• req.subscribe
• req.startSubscription({onClose: cb})
• await req.parseUpdate()
• res.sendUpdate()

You can call it in two ways:

1. braidify((req, res) => ...) wraps your HTTP request handler, and gives it perfectly braidified requests and responses.
2. braidify(req, res, next) will add arguments to your existing requests and responses. You can use this as express middleware.

Example Nodejs server with the built-in HTTP module

var braidify = require('braid-http').http_server
// or:
import {http_server as braidify} from 'braid-http'

require('http').createServer(
    braidify((req, res) => {
        // Now braid stuff is available on req and res

        // So you can easily handle subscriptions
        if (req.subscribe)
            res.startSubscription({ onClose: _=> null })
            // startSubscription automatically sets statusCode = 209
        else
            res.statusCode = 200

        // And send updates over a subscription
        res.sendUpdate({
            version: ['greg'],
            body: JSON.stringify({greg: 'greg'})
        })
    })
).listen(9935)

You can also use braidify within a request handler like this:

require('http').createServer(
    (req, res) => {
        braidify(req, res); if (req.is_multiplexer) return
        // Now braid stuff is available on req and res

        // ...
    })
).listen(9935)

The is_multiplexer test in this form is only necessary if multiplexing is enabled.

Example Nodejs server with Express

Or if you're using express, you can just call app.use(braidify) to get braid features added to every request and response.

var braidify = require('braid-http').http_server
// or:
import {http_server as braidify} from 'braid-http'

var app = require('express')()

app.use(braidify)    // Add braid stuff to req and res

app.get('/', (req, res) => {
    // Now use it
    if (req.subscribe)
        res.startSubscription({ onClose: _=> null })
        // startSubscription automatically sets statusCode = 209
    else
        res.statusCode = 200

    // Send the current version
    res.sendUpdate({
        version: ['greg'],
        parents: ['gr','eg'],
        body: JSON.stringify({greg: 'greg'})
    })

    // Or you can send patches like this:
    // res.sendUpdate({
    //     version: ['greg'],
    //     parents: ['gr','eg'],
    //     patches: [{range: '.greg', unit: 'json', content: '"greg"'}]
    // })
})

require('http').createServer(app).listen(8583)

Example Nodejs client with require('http')

// Use this line if necessary for self-signed certs
// process.env["NODE_TLS_REJECT_UNAUTHORIZED"] = 0

var https = require('braid-http').http_client(require('https'))
// or:
// import braid_http from 'braid-http'
// https = braid_http.http_client(require('https'))

https.get(
   'https://braid.org/chat',
   {subscribe: true},
   (res) => {
      res.on('update', (update) => {
          console.log('well we got one', update)
      })
   }
)

To get auto-reconnections use:

function connect () {
    https.get(
        'https://braid.org/chat',
        {subscribe: true},
        (res) => {
            res.on('update', (update) => {
                // {
                //   version: ["me"],
                //   parents: ["mom", "dad"],
                //   patches: [{
                //.      unit: "json",
                //       range: ".foo",
                //       content: new Uint8Array([51]),
                //       content_text: "3" <-- getter
                //.  }],
                //   body: new Uint8Array([51]),
                //   body_text: "3" <-- getter
                // }
                // Update will contain either patches *or* body, but not both
                console.log('We got a new update!', update)
            })

            res.on('end',   e => setTimeout(connect, 1000))
            res.on('error', e => setTimeout(connect, 1000))
        })
}
connect()

Example Nodejs client with fetch()

var fetch = require('braid-http').fetch
// or:
import {fetch} from 'braid-http'

// process.env["NODE_TLS_REJECT_UNAUTHORIZED"] = 0

fetch('https://localhost:3009/chat',
      {subscribe: true}).andThen(
          x => console.log('Got ', x)
      )

Configuring Multiplexing

You shouldn't need to, but can, configure which requests the library will multiplex. You can configure multiplexing on both the client and the server. They both need multiplexing enabled for it to happen.

Client

A client can globally disable multiplexing on braid_fetch() with:

braid_fetch.enable_multiplex = false

It can enable multiplexing for all GET requests with:

braid_fetch.enable_multiplex = true

It can also set it to multiplex after N connections to an origin with:

braid_fetch.enable_multiplex = {after: N}

The default value is {after: 1}.

A client can override this global setting per-request by passing the same value into braid_fetch(url, {multiplex: <value>}), such as with:

braid_fetch('/example', {multiplex: true, subscription: true})
braid_fetch('/example', {multiplex: false, subscription: true})
// or
braid_fetch('/example', {multiplex: {after: 1}, subscription: true})

Server

Configure mutliplexing with:

var braidify = require('braid-http').http-server
nbraidify.enable_multiplex = true   // or false