index.js

var fs = require('fs'),
    assert = require('assert')

// Default data
var resources = {
    '/feed': [
        {link: '/post/1'},
        {link: '/post/2'},
        {link: '/post/3'}
    ],
    '/post/1': {subject: 'First!',
                body: 'First post OMGGG!!!!',
                date: 1715618080011},

    '/post/2': {subject: 'Second...',
                body: `Once upon a time,
I ate a big fish.
It was really tasty.`,
                date: 1715618080012},

    '/post/3': {subject: 'Tois.',
                body: "It's nice when things come in threes.",
                date: 1715618080013},

    '/users': {
        'mike@braid.org': {
            name: 'Michael Toomim',
            email: 'mike@braid.org',
            pic: 'https://invisible.college/toomim/toom-headup.jpg'
        }
    }
}
var curr_version = () => [ (resources['/feed'].length + '') ]


// Load real data from db
try {
    var resources = JSON.parse(fs.readFileSync('db'))
} catch (e) {}
function save_db () { fs.writeFileSync('db', JSON.stringify(resources, null, 2)) }


// Subscriptions
var subscriptions = {}
var rhash = (req) => JSON.stringify([req.headers.peer, req.url])


// The main Braidmail request handler!
function handler (req, res, next) {
    var feed_name = '/feed',
        post_name = '/post/',
        users_name = '/users'

    require('braid-http').http_server(req, res)

    // We'll give each request a random ID, if it's not alraedy provided to us
    req.headers.peer ??= Math.random().toString(36).substr(3)

    // console.log('req:', {
    //     url: req.url,
    //     post: req.url.startsWith(post_name),
    //     users: req.url === users_name
    // })

    // Feed only supports get
    if (req.url === feed_name && req.method === 'GET')
        getter(req, res)

    else if (req.url.startsWith(post_name) || req.url === users_name) {

        // GET /post/*
        if (req.method === 'GET')
            getter(req, res)

        // PUT /post/*
        else if (req.method === 'PUT') {
            var is_new_post = !(req.url in resources)

            // Download the post body
            var body = ''
            req.on('data', chunk => {body += chunk.toString()})
            req.on('end', () => {

                // Now update the post
                resources[req.url] = JSON.parse(body)

                // Update subscribers
                post_changed(req)

                // Update the feed
                if (is_new_post)   // Update this when we delete posts
                    append_to_feed(req)

                res.end()
            })
        }            

        // DELETE /post/*
        else if (req.method === 'DELETE') {
            if (!req.url in resources || resources[req.url] === null)
                res.status = 404
            else {
                resources[req.url] = null

                // And kill the post in the feed
                var feed = resources['/feed']
                for (var i=0; i < feed.length; i++)
                    if (feed[i] && feed[i].link === req.url)
                        feed[i] = null

                res.status = 200
                post_changed(req)
            }
        }
    }
}

// GET the /feed or a /post/
//   - handles subscriptions
//   - and regular GETs
function getter (req, res) {
    // Make sure URL is valid
    if (!(req.url in resources) || resources[req.url] === null) {
        res.statusCode = 404
        res.end()
        return
    }

    // Set headers
    res.setHeader('content-type', 'application/json')
    res.setHeader('editable', 'true')
    if (req.url === '/feed') {
        res.setHeader('Version-Type', 'arraystream')
        res.setHeader('Current-Version', curr_version().map(JSON.stringify).join(', '))
    }

    // Honor any subscription request
    if (req.subscribe) {
        console.log('Incoming subscription!!!', req.url)
        res.startSubscription({ onClose: _=> {
            delete subscriptions[rhash(req)]
            console.log('Disconnect! Now there are',
                        Object.keys(subscriptions).length, 'subscriptions')
        }})
        subscriptions[rhash(req)] = res
        console.log('Now there are', Object.keys(subscriptions).length, 'subscriptions')
    } else
        res.statusCode = 200


    // Feed resubscribers get a shortcut update
    if (req.parents && req.url === '/feed'
        // If they have to have a valid parents header
        && req.parents.length === 1
        && typeof parseInt(req.parents[0]) === 'number'
        && parseInt(req.parents[0]) > 0
        && parseInt(req.parents[0]) <= resources[req.url].length) {

        if (JSON.stringify(curr_version()) === JSON.stringify(req.parents)) {
            // Skip the update entirely if we're already at the current version
        } else
            // Send a slice of the recent feed
            res.sendUpdate({
                version: curr_version(),
                parents: req.parents,
                patches: [{
                    unit:'json',
                    range: '[-0:-0]',
                    content: JSON.stringify(
                        resources[req.url].slice(parseInt(req.parents[0]))
                    )
                }]
            })
    }
    else
        // Send a snapshot of state to first-timers
        res.sendUpdate({
            version: req.url === '/feed' ? curr_version() : undefined,
            body: JSON.stringify(resources[req.url])
        })

    if (!req.subscribe)
        res.end()
}


// Add a post to the feed.  Update all subscribers.
function append_to_feed (post_req) {
    var post_entry = {link: post_req.url}

    // Add the post to the feed
    resources['/feed'].push(post_entry)

    // Save the new database
    save_db()

    // console.log('Updating /feed listners from',
    //             {subscriptions: Object.keys(subscriptions)})

    // Tell everyone about it
    for (var k in subscriptions) {
        var [peer, url] = JSON.parse(k)
        if (peer !== post_req.headers.peer && url === '/feed') {
            console.log('Telling peer', peer, 'about the new', post_entry, 'in /feed')
            subscriptions[k].sendUpdate({
                version: curr_version(),
                patches: [{
                    unit: 'json',
                    range: '[-0:-0]',
                    content: JSON.stringify([post_entry])
                }]
            })
        }
    }
}

// Notify everyone when a post changes
function post_changed (req) {
    // Save the new database.
    save_db()

    // Tell everyone
    for (var k in subscriptions) {
        var [peer, url] = JSON.parse(k)
        if (peer !== req.headers.peer && url === req.url) {
            console.log('Telling peer', peer, 'about new post', url)
            subscriptions[k].sendUpdate({
                body: JSON.stringify(resources[req.url])
            })
        }
    }
}

module.exports = handler