On-demand server-sent event channel

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README.md

ufeed

On-demand server-sent event channel. Create temporary channels to recieve webhook data as server-sent events.

package-lock.json

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}

package.json

{
  "name": "ufeed",
  "version": "0.0.1",
  "description": "On-demand HTTP/2 channel",
  "scripts": {
  },
  "keywords": [
  ],
  "author": "",
  "license": "Unlicense",
  "dependencies": {
    "cors": "^2.8.4",
    "express": "^4.16.3"
  }
}

server.js

const randomString = () => Math.random().toString(36).slice(2)

const SSEHeaders = {
  'Content-Type': 'text/event-stream',
  'Cache-Control': 'no-cache'
}

const createEvent = ({id, name='message', data=''}) => [
  `event: ${name}`,
  `id: ${id}`,
  `data: ${JSON.stringify(data)}\n\n`
].join('\n')

const acceptsStream = req =>
  req.get('accept').toLowerCase() === 'text/event-stream'

const setupSSE = app => {
  const channels = {}
  const createChannel = (req, target) => {
    const {params: {channel: id = randomString()}} = req
    let serial = 0
    target.set(SSEHeaders)
    target.write(createEvent({
      id: serial++,
      data: {
        id,
        url: `https://${req.hostname}${req.url}${id}`,
        remarks: 'This is the URL to send message, use search params'
      }
    }))

    channels[id] = data => {
      console.log(`Message ${serial} to ${req.ip} via channel ${id}`)
      target.write(createEvent({id: serial++, data}))
    }
    return id
  }

  const subscribe = (req, res) => {
    console.log(`Client ${req.ip} connected`)
    const id = createChannel(req, res)
    console.log(`Client ${req.ip}: created channel ${id}`)
    //TODO response docs if not accepting event-stream
    const write = channels[id]
    req.on('close', () => {
      if (write === channels[id]) {
        channels[id] = void 8
      }
      console.log(`Client ${req.ip} closed channel ${id}`)
      res.end()
    })
  }

  const sendMessage = (req, res) => {
    write = channels[req.params.channel]
    write? write(req.query): ''
    res.end('sent')
  }

  const sendOrSubscribe = (req, res) =>
    (acceptsStream(req)? subscribe: sendMessage)(req, res)

  app.get('/', subscribe)
  app.get('/:channel', sendOrSubscribe)
}

const start = () => {
  const express = require('express')
  const cors = require('cors')

  const port = process.env.PORT || 3000
  const app = express()
  app.use(express.json())
  app.use(cors({origin: true}))
  setupSSE(app)
  app.listen(port, () => console.log('Service is running on port ' + port))
}

start()