feat: make Socket#join() and Socket#leave() synchronous

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
- socketio/socket.io-redis-adapter@05f926e

Related: #3662

Author: darrachequesne

lib/socket.ts

@@ -238,38 +238,29 @@ export class Socket extends EventEmitter {
    * Joins a room.
    *
    * @param {String|Array} rooms - room or array of rooms
-   * @param {Function} fn - optional, callback
-   * @return {Socket} self
+   * @return a Promise or nothing, depending on the adapter
    * @public
    */
-  public join(rooms: Room | Array<Room>, fn?: (err: Error) => void): Socket {
-    debug("joining room %s", rooms);
+  public join(rooms: Room | Array<Room>): Promise<void> | void {
+    debug("join room %s", rooms);
 
-    this.adapter.addAll(
+    return this.adapter.addAll(
       this.id,
       new Set(Array.isArray(rooms) ? rooms : [rooms])
     );
-    debug("joined room %s", rooms);
-    fn && fn(null);
-    return this;
   }
 
   /**
    * Leaves a room.
    *
    * @param {String} room
-   * @param {Function} fn - optional, callback
-   * @return {Socket} self
+   * @return a Promise or nothing, depending on the adapter
    * @public
    */
-  public leave(room: string, fn?: (err: Error) => void): Socket {
+  public leave(room: string): Promise<void> | void {
     debug("leave room %s", room);
-    this.adapter.del(this.id, room);
 
-    debug("left room %s", room);
-    fn && fn(null);
-
-    return this;
+    return this.adapter.del(this.id, room);
   }
 
   /**

package.json

@@ -38,7 +38,7 @@
     "base64id": "~2.0.0",
     "debug": "~4.1.0",
     "engine.io": "~4.0.0",
-    "socket.io-adapter": "2.0.3-rc1",
+    "socket.io-adapter": "2.0.3-rc2",
     "socket.io-parser": "4.0.1-rc2"
   },
   "devDependencies": {

test/socket.io.ts

@@ -488,10 +488,9 @@ describe("socket.io", () => {
         const socket = client(srv);
 
         sio.on("connection", s => {
-          s.join("a", () => {
-            // FIXME not sure why process.nextTick() is needed here
-            process.nextTick(() => s.disconnect());
-          });
+          s.join("a");
+          // FIXME not sure why process.nextTick() is needed here
+          process.nextTick(() => s.disconnect());
 
           let total = 2;
           s.on("disconnecting", reason => {
@@ -578,22 +577,19 @@ describe("socket.io", () => {
         let total = 3;
         sio.of("/chat").on("connection", socket => {
           if (chatIndex++) {
-            socket.join("foo", () => {
-              chatFooSid = socket.id;
-              --total || getSockets();
-            });
+            socket.join("foo");
+            chatFooSid = socket.id;
+            --total || getSockets();
           } else {
-            socket.join("bar", () => {
-              chatBarSid = socket.id;
-              --total || getSockets();
-            });
+            socket.join("bar");
+            chatBarSid = socket.id;
+            --total || getSockets();
           }
         });
         sio.of("/other").on("connection", socket => {
-          socket.join("foo", () => {
-            otherSid = socket.id;
-            --total || getSockets();
-          });
+          socket.join("foo");
+          otherSid = socket.id;
+          --total || getSockets();
         });
       });
       async function getSockets() {
@@ -623,22 +619,19 @@ describe("socket.io", () => {
         let total = 3;
         sio.of("/chat").on("connection", socket => {
           if (chatIndex++) {
-            socket.join("foo", () => {
-              chatFooSid = socket.id;
-              --total || getSockets();
-            });
+            socket.join("foo");
+            chatFooSid = socket.id;
+            --total || getSockets();
           } else {
-            socket.join("bar", () => {
-              chatBarSid = socket.id;
-              --total || getSockets();
-            });
+            socket.join("bar");
+            chatBarSid = socket.id;
+            --total || getSockets();
           }
         });
         sio.of("/other").on("connection", socket => {
-          socket.join("foo", () => {
-            otherSid = socket.id;
-            --total || getSockets();
-          });
+          socket.join("foo");
+          otherSid = socket.id;
+          --total || getSockets();
         });
       });
       async function getSockets() {
@@ -1711,20 +1704,6 @@ describe("socket.io", () => {
       });
     });
 
-    it("should always trigger the callback (if provided) when joining a room", done => {
-      const srv = createServer();
-      const sio = new Server(srv);
-
-      srv.listen(() => {
-        const socket = client(srv);
-        sio.on("connection", s => {
-          s.join("a", () => {
-            s.join("a", done);
-          });
-        });
-      });
-    });
-
     it("should throw on reserved event", done => {
       const srv = createServer();
       const sio = new Server(srv);
@@ -1861,13 +1840,13 @@ describe("socket.io", () => {
         socket1.on("a", () => {
           done();
         });
-        socket1.emit("join", "woot", () => {
-          socket1.emit("emit", "woot");
-        });
+        socket1.emit("join", "woot");
+        socket1.emit("emit", "woot");
 
         sio.on("connection", socket => {
           socket.on("join", (room, fn) => {
-            socket.join(room, fn);
+            socket.join(room);
+            fn && fn();
           });
 
           socket.on("emit", room => {
@@ -1904,7 +1883,8 @@ describe("socket.io", () => {
 
         sio.on("connection", socket => {
           socket.on("join", (room, fn) => {
-            socket.join(room, fn);
+            socket.join(room);
+            fn && fn();
           });
 
           socket.on("emit", room => {
@@ -1949,7 +1929,8 @@ describe("socket.io", () => {
 
         sio.on("connection", socket => {
           socket.on("join", (room, fn) => {
-            socket.join(room, fn);
+            socket.join(room);
+            fn && fn();
           });
 
           socket.on("broadcast", () => {
@@ -1996,7 +1977,8 @@ describe("socket.io", () => {
 
         sio.on("connection", socket => {
           socket.on("join", (room, fn) => {
-            socket.join(room, fn);
+            socket.join(room);
+            fn && fn();
           });
           socket.on("broadcast", () => {
             socket.broadcast.to("test").emit("bin", Buffer.alloc(5));
@@ -2013,21 +1995,17 @@ describe("socket.io", () => {
       srv.listen(() => {
         const socket = client(srv);
         sio.on("connection", s => {
-          s.join("a", () => {
-            expect(s.rooms).to.contain(s.id, "a");
-            s.join("b", () => {
-              expect(s.rooms).to.contain(s.id, "a", "b");
-              s.join("c", () => {
-                expect(s.rooms).to.contain(s.id, "a", "b", "c");
-                s.leave("b", () => {
-                  expect(s.rooms).to.contain(s.id, "a", "c");
-                  s.leaveAll();
-                  expect(s.rooms.size).to.eql(0);
-                  done();
-                });
-              });
-            });
-          });
+          s.join("a");
+          expect(s.rooms).to.contain(s.id, "a");
+          s.join("b");
+          expect(s.rooms).to.contain(s.id, "a", "b");
+          s.join("c");
+          expect(s.rooms).to.contain(s.id, "a", "b", "c");
+          s.leave("b");
+          expect(s.rooms).to.contain(s.id, "a", "c");
+          s.leaveAll();
+          expect(s.rooms.size).to.eql(0);
+          done();
         });
       });
     });
@@ -2039,13 +2017,11 @@ describe("socket.io", () => {
       srv.listen(() => {
         const socket = client(srv);
         sio.on("connection", s => {
-          s.join("a", () => {
-            expect(s.nsp.adapter.rooms).to.contain("a");
-            s.leave("a", () => {
-              expect(s.nsp.adapter.rooms).to.not.contain("a");
-              done();
-            });
-          });
+          s.join("a");
+          expect(s.nsp.adapter.rooms).to.contain("a");
+          s.leave("a");
+          expect(s.nsp.adapter.rooms).to.not.contain("a");
+          done();
         });
       });
     });
@@ -2057,18 +2033,15 @@ describe("socket.io", () => {
       srv.listen(() => {
         const socket = client(srv);
         sio.on("connection", s => {
-          s.join("a", () => {
-            expect(s.rooms).to.contain(s.id, "a");
-            s.join("b", () => {
-              expect(s.rooms).to.contain(s.id, "a", "b");
-              s.leave("unknown", () => {
-                expect(s.rooms).to.contain(s.id, "a", "b");
-                s.leaveAll();
-                expect(s.rooms.size).to.eql(0);
-                done();
-              });
-            });
-          });
+          s.join("a");
+          expect(s.rooms).to.contain(s.id, "a");
+          s.join("b");
+          expect(s.rooms).to.contain(s.id, "a", "b");
+          s.leave("unknown");
+          expect(s.rooms).to.contain(s.id, "a", "b");
+          s.leaveAll();
+          expect(s.rooms.size).to.eql(0);
+          done();
         });
       });
     });
@@ -2080,10 +2053,9 @@ describe("socket.io", () => {
       srv.listen(() => {
         const socket = client(srv);
         sio.on("connection", s => {
-          s.join(["a", "b", "c"], () => {
-            expect(s.rooms).to.contain(s.id, "a", "b", "c");
-            done();
-          });
+          s.join(["a", "b", "c"]);
+          expect(s.rooms).to.contain(s.id, "a", "b", "c");
+          done();
         });
       });
     });