siimee/backend/lib/plugins/notification.js

const NotificationRoute = require('../routes/notification')

/** Heavily lifted from: https://github.com/mtharrison/susie/blob/master/lib/index.js */

const Stream = require('stream')
const PassThrough = Stream.PassThrough
const Transform = Stream.Transform

const ENDER = { event: 'end', data: '' }

const allStreams = {}

/**
 * Stringify a stream
 * ?: I don't really get what this is doing
 * @param {Stream} event
 * @returns {string}
 */
const stringifyEvent = function (event) {
    let str = ''
    const endl = '\r\n'
    for (const i in event) {
        let val = event[i]
        if (val instanceof Buffer) {
            val = val.toString()
        }
        if (typeof val === 'object') {
            val = JSON.stringify(val)
        }
        str += i + ': ' + val + endl
    }
    str += endl
    return str
}

/**
 * Transform extension
 * ?: I don't really get what this is doing
 * @param {object} options
 * @param {object} objectMode
 */
class Transformer extends Transform {
    constructor(options, objectMode) {
        super({ objectMode })
        options = options || {}
        this.counter = 1
        this.event = options.event || null
        this.generateId = options.generateId
            ? options.generateId
            : () => this.counter++
    }
    _transform(chunk, encoding, callback) {
        const event = {
            id: this.generateId(chunk),
            data: chunk,
        }
        if (this.event) {
            event.event = this.event
        }
        this.push(stringifyEvent(event))
        callback()
    }
    _flush(callback) {
        this.push(stringifyEvent(ENDER))
        callback()
    }
}

/**
 * Callback to decorate server toolkit (h)
 * !: Currently we only support ObjectMode streams
 * ?: I don't really get what this is doing
 * @param {Stream} event stream input
 * @param {Toolkit} h hapi common response toolkit
 * @param {object} streamOptions
 */
const onEvent = (event, h, streamOptions) => {
    let active
    if (event instanceof Stream.Readable) {
        if (event._readableState.objectMode) {
            active = new PassThrough()
            const through = new Transformer(streamOptions, true)
            through.pipe(active)
            event.pipe(through)
        }
        return h
            .response(active)
            .header('content-type', 'text/event-stream')
            .header('content-encoding', 'identity')
    }
}

module.exports = {
    name: 'notification-plugin',
    version: '1.0.0',
    register: async server => {
        await server.route(NotificationRoute)
        server.decorate('toolkit', 'event', onEvent)
        server.expose('streams', allStreams)
    },
}