From 53c73749a829b2c98d9a5e45c48f0ae5a22c056c Mon Sep 17 00:00:00 2001
From: Damien Arrachequesne <damien.arrachequesne@gmail.com>
Date: Tue, 5 Jan 2021 10:38:54 +0100
Subject: [PATCH] fix: emit a connect_error event upon connection failure

Related: https://github.com/socketio/socket.io/issues/3734
---
 lib/socket.ts  | 13 +++++++++++++
 test/socket.ts | 25 +++++++++++++++++++++++++
 2 files changed, 38 insertions(+)

diff --git a/lib/socket.ts b/lib/socket.ts
index 3deb8c413..afa567e3a 100644
--- a/lib/socket.ts
+++ b/lib/socket.ts
@@ -84,6 +84,7 @@ export class Socket extends Emitter {
     this.subs = [
       on(io, "open", this.onopen.bind(this)),
       on(io, "packet", this.onpacket.bind(this)),
+      on(io, "error", this.onerror.bind(this)),
       on(io, "close", this.onclose.bind(this)),
     ];
   }
@@ -204,6 +205,18 @@ export class Socket extends Emitter {
     }
   }
 
+  /**
+   * Called upon engine or manager `error`.
+   *
+   * @param err
+   * @private
+   */
+  private onerror(err: Error) {
+    if (!this.connected) {
+      super.emit("connect_error", err);
+    }
+  }
+
   /**
    * Called upon engine `close`.
    *
diff --git a/test/socket.ts b/test/socket.ts
index b27be71d5..263404143 100644
--- a/test/socket.ts
+++ b/test/socket.ts
@@ -50,6 +50,31 @@ describe("socket", function () {
     }, 300);
   });
 
+  it("fire a connect_error event when the connection cannot be established", (done) => {
+    const socket = io("http://localhost:9823", {
+      forceNew: true,
+      timeout: 100,
+    });
+    socket.on("connect_error", () => {
+      socket.close();
+      done();
+    });
+  });
+
+  it("doesn't fire a connect_error event when the connection is already established", (done) => {
+    const socket = io({ forceNew: true });
+    socket.on("connect", () => {
+      socket.io.engine.close(true);
+    });
+    socket.on("connect_error", () => {
+      done(new Error("should not happen"));
+    });
+    setTimeout(() => {
+      socket.close();
+      done();
+    }, 300);
+  });
+
   it("should change socket.id upon reconnection", (done) => {
     const socket = io({ forceNew: true });
     socket.on("connect", () => {