Socket.IO servers

A Socket.IO server in Zorvik is a stand-in for a real one: point your app’s socket.io-client at it and watch every event, answer automatically, or emit events yourself. It speaks Socket.IO 3 and 4 (Engine.IO 4), over HTTP long-polling and WebSocket, including the upgrade from polling to WebSocket that socket.io-client makes by default.

Create one

Open the Servers sidebar, click + (New server) and choose Socket.IO server. It listens on 127.0.0.1, port 3003 (or the next port no other saved server uses), and greets each client with a welcome event. Start it, and connect:

import { io } from "socket.io-client";
const socket = io("http://127.0.0.1:3003/chat");
socket.on("welcome", (info) => console.log(info));
socket.emit("hello", "world", (answer) => console.log(answer));

Clients may join any namespace (/, /chat, /admin, …). One client connection shows as one entry in the traffic log, however many namespaces it joins; the log names the namespace before each event (/chat hello).

Answers

Mode	In the file	What happens
Echo (default)	echo	Every event is emitted back to its sender with the same arguments, and acknowledged with them when the client asks (emitWithAck, or a callback as the last argument).
Rules	rules	The first matching rule answers; other events get no answer.
Manual	manual	Nothing is sent automatically: emit from the traffic panel.
Discard	discard	Events are read and dropped.

Rules

Each rule reads: when a client emits event with arguments → acknowledge with … then emit … with …, optionally to every client of the namespace, after a delay.

Part	In the file	Description
Event	event	The event name, or * for any.
With	match, pattern	any arguments (default), arguments contain, are exactly or match regex. The pattern is checked against the arguments as JSON (["hi",{"n":1}]) and, when there is a single text argument, against that text (so are exactly hi matches emit("x", "hi")).
Acknowledge with	ack	Arguments (JSON) of the acknowledgement, when the client asks for one. Empty: an acknowledgement without arguments.
Then emit	replyEvent, replyArgs	An event to emit back and its arguments (JSON). Empty event: none.
To every client of the namespace	broadcast	Emit the reply to everyone who joined the namespace, the sender included.
After	delayMs	Wait before answering.

Arguments are JSON: an array is several arguments, anything else one. Answers can use the event’s values and templates:

Placeholder	Is
{{event.name}}	The event name, as JSON ("hello").
{{event.args}}	All arguments as a JSON array.
{{event.arg0}}, {{event.arg1}}, …	One argument as JSON (null when missing).
{{$uuid}}, {{$randomFirstName}}, …	Dynamic variables.
{{token}}	The active environment’s and the workspace’s variables.

The client’s values go in after variables are filled in, so a client sending {{token}} gets that text back, never the variable’s value. Placeholders are JSON values: write [{{event.arg0}}, "ok"], not ["{{event.arg0}}"].

Example rules

- event: join
  ack: '{"ok": true, "room": {{event.arg0}}}'
- event: say
  match: contains
  pattern: hello
  replyEvent: said
  replyArgs: '[{{event.arg0}}, "{{$isoTimestamp}}"]'
  broadcast: true
- event: "*"
  replyEvent: unknown
  replyArgs: "{{event.name}}"

A rule with an invalid regex is skipped, and the traffic log says so once.

Greeting

Event on joining is emitted to each client that joins a namespace, with Arguments (JSON, templates allowed). Leave the event empty for none.

Emitting by hand

While the server runs, the traffic panel’s composer has an event name, a namespace (/ by default) and the arguments as JSON. Emit sends to the client chosen in Send to, or to every client that joined the namespace.

Disconnect (in the traffic panel) disconnects the client from its namespaces and ends its connection.

Clients and browsers

• Path: /socket.io/ unless you change it (socket.io’s path option; clients must use the same).
• CORS: turn on Allow browsers on other origins for web apps served from another origin (long-polling requests need it; WebSocket doesn’t).
• TLS: with TLS on, clients connect to https://.
• Heartbeats: the server pings every 25 seconds and drops clients that don’t answer within 20.
• Messages and long-polling requests up to 1 MB.
• Socket.IO 2 clients (Engine.IO 3) are refused with Unsupported protocol version, as a Socket.IO 4 server does.

Saved format

servers/Chat.yaml

name: Chat
kind: socketio
host: 127.0.0.1
port: 3003
socketio:
  mode: rules
  greetingEvent: welcome
  greetingArgs: '{"id": "{{$uuid}}"}'
  rules:
    - event: join
      ack: '{"ok": true}'
  cors: true

To talk to it from Zorvik itself, use a Socket.IO request.