From a4dffc6527f412d51a786ae5bf2e9080fe1ca63c Mon Sep 17 00:00:00 2001
From: Damien Arrachequesne <damien.arrachequesne@gmail.com>
Date: Sun, 4 Jul 2021 00:39:46 +0200
Subject: [PATCH] fix: remove x-sourcemap header

This header is useless, as the client bundle already contains a
sourceMappingURL field.

Besides, Firefox prints the following warning:

> <url> is being assigned a //# sourceMappingURL, but already has one

Related: https://github.com/socketio/socket.io/issues/3958
---
 lib/index.ts      | 3 ---
 test/socket.io.ts | 2 +-
 2 files changed, 1 insertion(+), 4 deletions(-)

diff --git a/lib/index.ts b/lib/index.ts
index 53aad1188f..6f9f882ad6 100644
--- a/lib/index.ts
+++ b/lib/index.ts
@@ -515,9 +515,6 @@ export class Server<
     );
     res.setHeader("ETag", expectedEtag);
 
-    if (!isMap) {
-      res.setHeader("X-SourceMap", filename.substring(1) + ".map");
-    }
     Server.sendFile(filename, req, res);
   }
 
diff --git a/test/socket.io.ts b/test/socket.io.ts
index 206cf1d783..87c36693fb 100644
--- a/test/socket.io.ts
+++ b/test/socket.io.ts
@@ -59,7 +59,7 @@ describe("socket.io", () => {
             if (err) return done(err);
             expect(res.headers["content-type"]).to.be("application/javascript");
             expect(res.headers.etag).to.be('"' + clientVersion + '"');
-            expect(res.headers["x-sourcemap"]).to.be(filename + ".map");
+            expect(res.headers["x-sourcemap"]).to.be(undefined);
             expect(res.text).to.match(/engine\.io/);
             expect(res.status).to.be(200);
             done();