Events from the page, in Express

Pages send events to the rooms they are in, straight through WordPlus Cloud, with no request to your server: chat messages, typing, read ticks, a cursor. A room rule says which events its pages may send.

What a room allows

// The chat of Ann and Ben: they send messages, typing, reactions and read ticks. The messages and reactions reach this
// server by webhook, which keeps the conversation.
realtime.room( 'chat:{a}:{b}', { history: 50, emit: [ 'message', 'typing', 'reaction', 'read' ], webhook: [ 'message', 'reaction' ] },
    ( user, { a, b } ) => [ a, b ].includes( String( user ) ) );

• emit lists the names, or '*' for any. None by default: a room your server alone sends to.
• webhook names those your server gets too, to keep them (below).
• history keeps the last events of the room for 30 minutes: what a page that reconnects missed comes again from it.
• The answer for one user can narrow it: { emit: [ 'typing' ] }, or { readOnly: true }.
• Reserved: joined, join, leave, count and error are the names kept for the room itself.

Sending

A page sends to a room it has joined, and hears what the others send:

const chat = rt.join( 'chat:34:42' );

chat.emit( 'message', { text: 'Hi' } );                                // sent, nothing waited for
const { id, at } = await chat.emitWithAck( 'message', { text: 'Hi' } ); // WordPlus Cloud took it: checked, kept, sent
chat.volatile.emit( 'typing', { on: true } );                          // dropped rather than queued while off line, never kept
await chat.timeout( 5000 ).emitWithAck( 'message', { text: 'Hi' } );   // an ack waited for 5 seconds at most

chat.on( 'message', ( data, meta ) => draw( data.text, meta.from ) );   // meta: { from, id, at }

• Everyone in the room gets it, the other tabs and devices of the sender too. The tab that sent it does not, so it draws its own at once.
• emitWithAck resolves with the kept event id and time, or rejects with a code: not_allowed (the rule does not list it), forbidden, rate_limited, too_large.
• meta.from is the sender user id, as your server vouched for them: a page cannot send as someone else.
• Binary: an ArrayBuffer, Uint8Array or Blob may be anywhere in the data. It is sealed as binary.
• Limits: 1 MB an event, 50 a second a connection, in bursts of up to 100.

Typing, done the usual way

let sent = 0;
input.addEventListener( 'input', () => {
    if ( Date.now() - sent < 2000 ) return;   // at most every 2 seconds
    sent = Date.now();
    chat.volatile.emit( 'typing', { on: true } );
} );

chat.on( 'typing', ( data, meta ) => showTyping( meta.from, data.on ) );   // and hide it after 4 seconds of nothing

Keeping the conversation

The conversation is for your app to keep, in its own database, as Better Messages keeps its own in the WordPress database. A room keeps its events for 30 minutes, for pages that reconnect. Your server gets the events the rule names in webhook (webhooks) and saves them by event_id, the id the pages saw as meta.id. A route gives them back, a page at a time:

realtime.on( 'message', ( { room, from, data, event_id, at } ) => db.messages.upsert( { id: event_id, room, from, text: data.text, at } ) );

// The newest 50, or with ?before=<id> the 50 before that one, oldest first. Only its two people may read it.
app.get( '/chat/:a/:b/messages', async ( req, res ) => {
    const { a, b } = req.params;
    if ( ! [ a, b ].includes( String( req.session.userId ) ) ) return res.status( 403 ).end();
    res.json( await db.messages.page( `chat:${ a }:${ b }`, req.query.before, 50 ) );   // { messages: [ { id, from, text, at, reactions } ], more }
} );

• Check there anything that matters: the events do not go through your server before they are sent on.
• at is in milliseconds, and reactions maps each reaction to who chose it. A reaction comes as { id, key }: the one reaction of the user to message id, an empty key taking it back.

Ready-made: the chat

The Better Messages conversation, on any room: your server conversation paged back as the reader scrolls up, the room filling in what came since, the day separators, the messages of a sender stacked, typing, reactions, the read ticks and the composer. It is one element:

<wordplus-chat room="chat:34:42" messages="/chat/34/42/messages" placeholder="Write a message"></wordplus-chat>

await rt.callScreen();   // loads the elements and the call screen, rt.ui() the elements without calls

• messages is your route, asked with the page cookies. chat.load = async ( before ) => ( { messages, more } ) replaces it, for a token or another shape: before is null for the newest page, or the oldest message shown ({ id, at }). With neither, it shows what the room still has.
• Its room rule lets it send what it uses: emit: [ 'message', 'typing', 'reaction', 'read' ], and names message and reaction in webhook for your server to keep.
• What it sends is what you would: message as { text } with an ack, typing as { on } and read as { id }, both volatile, and reaction as { id, key }. Your own pages and apps on the same room read it.
• Names and pictures come from your directory.
• reactions sets the reactions offered (reactions="1f44d 2764 1f602"), and max-length the longest message.
• It fills the height its place gives it. Its look is that of Better Messages, in a shadow root. Its colours are CSS custom properties your page sets.

<wordplus-typing room="…"> is the typing line alone, for a page that draws its own messages.

More, with PHP and Python side by side: events in depth.