feat: add autoUnref option

With autoUnref set to true (default: false), the Socket.IO client will
allow the program to exit if there is no other active timer/socket in
the event system.

```js
const socket = io({
  autoUnref: true
});
```

Note: this option only applies to Node.js clients.

Related: #1446

lib/manager.ts

@@ -256,6 +256,13 @@ export interface ManagerOptions extends EngineOptions {
    */
   autoConnect: boolean;
 
+  /**
+   * weather we should unref the reconnect timer when it is
+   * create automatically
+   * @default false
+   */
+  autoUnref: boolean;
+
   /**
    * the parser to use. Defaults to an instance of the Parser that ships with socket.io.
    */
@@ -531,6 +538,10 @@ export class Manager<
         socket.emit("error", new Error("timeout"));
       }, timeout);
 
+      if (this.opts.autoUnref) {
+        timer.unref();
+      }
+
       this.subs.push(function subDestroy(): void {
         clearTimeout(timer);
       });
@@ -769,6 +780,10 @@ export class Manager<
         });
       }, delay);
 
+      if (this.opts.autoUnref) {
+        timer.unref();
+      }
+
       this.subs.push(function subDestroy() {
         clearTimeout(timer);
       });

package.json

@@ -31,7 +31,7 @@
     "backo2": "~1.0.2",
     "component-emitter": "~1.3.0",
     "debug": "~4.3.1",
-    "engine.io-client": "~4.1.0",
+    "engine.io-client": "~5.0.0",
     "parseuri": "0.0.6",
     "socket.io-parser": "~4.0.4"
   },
@@ -108,5 +108,8 @@
   },
   "tsd": {
     "directory": "test"
+  },
+  "browser": {
+    "./test/node.ts": false
   }
 }

test/fixtures/no-unref.ts

@@ -0,0 +1,8 @@
+const io = require("../..");
+const socket = io("http://localhost:3211", {
+  autoUnref: false,
+});
+
+setTimeout(() => {
+  console.log("process should not exit");
+}, 500);

test/fixtures/unref-during-reconnection.ts

@@ -0,0 +1,12 @@
+const io = require("../..");
+const socket = io("http://localhost:3211", {
+  autoUnref: true,
+});
+
+socket.on("open", () => {
+  console.log("open");
+});
+
+setTimeout(() => {
+  console.log("process should exit now");
+}, 500);

test/fixtures/unref-polling-only.ts

@@ -0,0 +1,13 @@
+const io = require("../..");
+const socket = io("http://localhost:3210", {
+  autoUnref: true,
+  transports: ["polling"],
+});
+
+socket.on("open", () => {
+  console.log("open");
+});
+
+setTimeout(() => {
+  console.log("process should exit now");
+}, 500);

test/fixtures/unref-websocket-only.ts

@@ -0,0 +1,13 @@
+const io = require("../..");
+const socket = io("http://localhost:3210", {
+  autoUnref: true,
+  transports: ["websocket"],
+});
+
+socket.on("open", () => {
+  console.log("open");
+});
+
+setTimeout(() => {
+  console.log("process should exit now");
+}, 500);

test/fixtures/unref.ts

@@ -0,0 +1,12 @@
+const io = require("../..");
+const socket = io("http://localhost:3210", {
+  autoUnref: true,
+});
+
+socket.on("open", () => {
+  console.log("open");
+});
+
+setTimeout(() => {
+  console.log("process should exit now");
+}, 500);

test/index.js

@@ -3,6 +3,8 @@ const { browser } = require("./support/env");
 // whitelist some globals to avoid warnings
 if (browser) {
   window.mocha.globals(["___eio", "eio_iframe_*"]);
+} else {
+  require("./node.ts");
 }
 
 require("./url.ts");

test/node.ts

@@ -0,0 +1,33 @@
+const path = require("path");
+const { exec } = require("child_process");
+
+describe("autoRef option", () => {
+  const fixture = (filename) =>
+    process.execPath + " " + path.join(__dirname, "fixtures", filename);
+
+  it("should stop once the timer is triggered", (done) => {
+    exec(fixture("unref.ts"), done);
+  });
+
+  it("should stop once the timer is triggered (even when trying to reconnect)", (done) => {
+    exec(fixture("unref-during-reconnection.ts"), done);
+  });
+
+  it("should stop once the timer is triggered (polling)", (done) => {
+    exec(fixture("unref-polling-only.ts"), done);
+  });
+
+  it("should stop once the timer is triggered (websocket)", (done) => {
+    exec(fixture("unref-websocket-only.ts"), done);
+  });
+
+  it("should not stop with autoUnref set to false", (done) => {
+    const process = exec(fixture("no-unref.ts"), () => {
+      done(new Error("should not happen"));
+    });
+    setTimeout(() => {
+      process.kill();
+      done();
+    }, 1000);
+  });
+});