In order to ease the migration to Socket.IO v3, the Socket.IO server
can now communicate with v2 clients.
```js
const io = require("socket.io")({
allowEIO3: true
});
```
This feature is disabled by default.
Depending on the adapter, Socket#join() may return:
- nothing (in-memory and Redis adapters)
- a promise (custom adapters)
Breaking change: Socket#join() and Socket#leave() do not accept a
callback argument anymore.
Before:
```js
socket.join("room1", () => {
io.to("room1").emit("hello");
});
```
After:
```
socket.join("room1");
io.to("room1").emit("hello");
// or await socket.join("room1"); for custom adapters
```
Note: the need for an asynchronous method came from the Redis adapter,
which did override the Adapter#add() method in earlier versions, but
this is not the case anymore.
Reference:
- https://github.com/socketio/socket.io/blob/2.3.0/lib/socket.js#L236-L258
- https://github.com/socketio/socket.io-adapter/blob/1.1.2/index.js#L56-L65
- 05f926e13e
Related: https://github.com/socketio/socket.io/issues/3662
The client bundles are included in the repository in order to remove
socket.io-client from the list of production dependencies and thus to
reduce the total number of dependencies when installing the server.
This means the release of the client and the server must now be in sync
(which is almost always the case actually).
The minified build is now served:
- /<path>/socket.io.js
- /<path>/socket.io.js.map
- /<path>/socket.io.min.js
- /<path>/socket.io.min.js.map
The content will now be compressed as well.
Both the "connected" and the "_sockets" maps were used to track the
Socket instances in the namespace.
Let's merge them into "sockets". It's a breaking change, but:
- the "sockets" object did already exist in Socket.IO v2 (and appears in some examples/tutorials)
- "sockets" makes more sense than "connected" in my opinion
- there was already a breaking change regarding the "connected" property (from object to Map)
Breaking change: the "connected" map is renamed to "sockets"
Both CommonJS and ES6 import are now supported:
- with `{ "type": "commonjs" }` in the package.json file
```js
const io = require("socket.io")(8080);
// or
const { Server } = require("socket.io");
const io = new Server(8080);
```
- with `{ "type": "module" }`
```js
import { Server } from "socket.io";
const io = new Server(8080);
```
Related: https://nodejs.org/api/packages.html#packages_dual_commonjs_es_module_packages
In previous versions, the Socket#id attribute was equal (or derived,
for a non-default namespace) to the underlying Engine.IO id, which is
used as a mean to authenticate the user throughout the Engine.IO
session and thus is sensitive information that should be kept secret.
The problem with reusing the Engine.IO id is that users could be
tempted to transmit this id to other clients, in order to implement
private messaging for example.
So we'll now generate a new random id for each new socket.
Please note that this id will now be different from the one found in
the query parameters of the HTTP requests.
In previous versions, a client was always connected to the default
namespace, even if it requested access to another namespace.
This meant that the middlewares registered for the default namespace
were triggered in any case, which is a surprising behavior for end
users.
This also meant that the query option of the Socket on the client-side
was not sent in the Socket.IO CONNECT packet for the default namespace:
```js
// default namespace: query sent in the query params
const socket = io({
query: {
abc: "def"
}
});
// another namespace: query sent in the query params + the CONNECT packet
const socket = io("/admin", {
query: {
abc: "def"
}
});
```
The client will now send a CONNECT packet in any case, and the query
option of the Socket is renamed to "auth", in order to make a clear
distinction with the query option of the Manager (included in the query
parameters of the HTTP requests).
```js
// server-side
io.use((socket, next) => {
// not triggered anymore
});
io.of("/admin").use((socket, next => {
// triggered
console.log(socket.handshake.query.abc); // "def"
console.log(socket.handshake.auth.abc); // "123"
});
// client-side
const socket = io("/admin", {
query: {
abc: "def"
},
auth: {
abc: "123"
}
});
```
So that the call to the `has-binary` method can be skipped. Usage:
```
// with binary data
socket.binary(true).emit("binary", obj);
// without binary data
socket.binary(false).emit("string", obj);
// call to hasBin
socket.emit("guess", obj);
```
