From 44ed73f53995d35ef0c8d10df6806d5687238282 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Erdin=C3=A7=20C=C3=BCrebal?= <erdinccurebal@hotmail.com>
Date: Wed, 4 Mar 2026 11:07:02 +0300
Subject: [PATCH] fix(eio): emit initial_headers and headers events in uServer
 (#5460)

The uServer (uWebSockets.js) implementation did not emit
"initial_headers" and "headers" events during WebSocket upgrades,
unlike the regular Server which does this via the ws "headers" event.

Related: https://github.com/socketio/socket.io/issues/5300
---
 packages/engine.io/lib/userver.ts | 14 ++++++++++++++
 packages/engine.io/test/server.js | 10 ++--------
 2 files changed, 16 insertions(+), 8 deletions(-)

diff --git a/packages/engine.io/lib/userver.ts b/packages/engine.io/lib/userver.ts
index 71ed616f..54d34a60 100644
--- a/packages/engine.io/lib/userver.ts
+++ b/packages/engine.io/lib/userver.ts
@@ -226,9 +226,23 @@ export class uServer extends BaseServer {
         }
       }
 
+      // emit headers events for WebSocket upgrades
+      const additionalHeaders = {};
+      const isInitialRequest = !id;
+
+      if (isInitialRequest) {
+        this.emit("initial_headers", additionalHeaders, req);
+      }
+
+      this.emit("headers", additionalHeaders, req);
+
       // calling writeStatus() triggers the flushing of any header added in a middleware
       req.res.writeStatus("101 Switching Protocols");
 
+      Object.keys(additionalHeaders).forEach((key) => {
+        req.res.writeHeader(key, additionalHeaders[key]);
+      });
+
       res.upgrade(
         {
           transport,
diff --git a/packages/engine.io/test/server.js b/packages/engine.io/test/server.js
index 1795b00b..75b287c1 100644
--- a/packages/engine.io/test/server.js
+++ b/packages/engine.io/test/server.js
@@ -3598,10 +3598,7 @@ describe("server", () => {
     });
 
     it("should emit a 'initial_headers' event (websocket)", function (done) {
-      if (
-        process.env.EIO_WS_ENGINE === "eiows" ||
-        process.env.EIO_WS_ENGINE === "uws"
-      ) {
+      if (process.env.EIO_WS_ENGINE === "eiows") {
         return this.skip();
       }
       const partialDone = createPartialDone(done, 2);
@@ -3644,10 +3641,7 @@ describe("server", () => {
     });
 
     it("should emit several 'headers' events per connection", function (done) {
-      if (
-        process.env.EIO_WS_ENGINE === "eiows" ||
-        process.env.EIO_WS_ENGINE === "uws"
-      ) {
+      if (process.env.EIO_WS_ENGINE === "eiows") {
         return this.skip();
       }
       const partialDone = createPartialDone(done, 4);