3 files changed, 60 insertions, 3 deletions

diff --git a/src/js/node/http.ts b/src/js/node/http.ts
index a745f9b32..42388b32e 100644
--- a/src/js/node/http.ts
+++ b/src/js/node/http.ts
@@ -957,6 +957,7 @@ export class OutgoingMessage extends Writable {
   }
 }
 
+let OriginalWriteHeadFn, OriginalImplicitHeadFn;
 export class ServerResponse extends Writable {
   declare _writableState: any;
 
@@ -989,9 +990,11 @@ export class ServerResponse extends Writable {
   _removedContLen = false;
   #deferred: (() => void) | undefined = undefined;
   #finished = false;
-
   // Express "compress" package uses this
-  _implicitHeader() {}
+  _implicitHeader() {
+    // @ts-ignore
+    this.writeHead(this.statusCode);
+  }
 
   _write(chunk, encoding, callback) {
     if (!this.#firstWrite && !this.headersSent) {
@@ -1053,11 +1056,20 @@ export class ServerResponse extends Writable {
     );
   }
 
+  #drainHeadersIfObservable() {
+    if (this._implicitHeader === OriginalImplicitHeadFn && this.writeHead === OriginalWriteHeadFn) {
+      return;
+    }
+
+    this._implicitHeader();
+  }
+
   _final(callback) {
     if (!this.headersSent) {
       var data = this.#firstWrite || "";
       this.#firstWrite = undefined;
       this.#finished = true;
+      this.#drainHeadersIfObservable();
       this._reply(
         new Response(data, {
           headers: this.#headers,
@@ -1176,6 +1188,9 @@ export class ServerResponse extends Writable {
   }
 }
 
+OriginalWriteHeadFn = ServerResponse.prototype.writeHead;
+OriginalImplicitHeadFn = ServerResponse.prototype._implicitHeader;
+
 export class ClientRequest extends OutgoingMessage {
   #timeout;
   #res: IncomingMessage | null = null;
diff --git a/src/js/out/modules/node/http.js b/src/js/out/modules/node/http.js
index 13ee7fded..d0937a945 100644
--- a/src/js/out/modules/node/http.js
+++ b/src/js/out/modules/node/http.js
@@ -626,6 +626,7 @@ class OutgoingMessage extends Writable {
     return this;
   }
 }
+var OriginalWriteHeadFn, OriginalImplicitHeadFn;
 
 class ServerResponse extends Writable {
   constructor({ req, reply }) {
@@ -648,6 +649,7 @@ class ServerResponse extends Writable {
   #deferred = void 0;
   #finished = !1;
   _implicitHeader() {
+    this.writeHead(this.statusCode);
   }
   _write(chunk, encoding, callback) {
     if (!this.#firstWrite && !this.headersSent) {
@@ -691,10 +693,15 @@ class ServerResponse extends Writable {
       statusText: this.statusMessage ?? STATUS_CODES[this.statusCode]
     }));
   }
+  #drainHeadersIfObservable() {
+    if (this._implicitHeader === OriginalImplicitHeadFn && this.writeHead === OriginalWriteHeadFn)
+      return;
+    this._implicitHeader();
+  }
   _final(callback) {
     if (!this.headersSent) {
       var data = this.#firstWrite || "";
-      this.#firstWrite = void 0, this.#finished = !0, this._reply(new Response(data, {
+      this.#firstWrite = void 0, this.#finished = !0, this.#drainHeadersIfObservable(), this._reply(new Response(data, {
         headers: this.#headers,
         status: this.statusCode,
         statusText: this.statusMessage ?? STATUS_CODES[this.statusCode]
@@ -780,6 +787,8 @@ class ServerResponse extends Writable {
     return _writeHead(statusCode, statusMessage, headers, this), this;
   }
 }
+OriginalWriteHeadFn = ServerResponse.prototype.writeHead;
+OriginalImplicitHeadFn = ServerResponse.prototype._implicitHeader;
 
 class ClientRequest extends OutgoingMessage {
   #timeout;
diff --git a/test/js/node/http/node-http.test.ts b/test/js/node/http/node-http.test.ts
index 3e7da9d34..0e7b3ca13 100644
--- a/test/js/node/http/node-http.test.ts
+++ b/test/js/node/http/node-http.test.ts
@@ -146,6 +146,29 @@ describe("node:http", () => {
             res.end("Path correct!\n");
             return;
           }
+          if (reqUrl.pathname === "/customWriteHead") {
+            function createWriteHead(prevWriteHead, listener) {
+              let fired = false;
+              return function writeHead() {
+                if (!fired) {
+                  fired = true;
+                  listener.call(this);
+                }
+                return prevWriteHead.apply(this, arguments);
+              };
+            }
+
+            function addPoweredBy() {
+              if (!this.getHeader("X-Powered-By")) {
+                this.setHeader("X-Powered-By", "Bun");
+              }
+            }
+
+            res.writeHead = createWriteHead(res.writeHead, addPoweredBy);
+            res.setHeader("Content-Type", "text/plain");
+            res.end("Hello World");
+            return;
+          }
         }
 
         res.writeHead(200, { "Content-Type": "text/plain" });
@@ -507,6 +530,16 @@ describe("node:http", () => {
         req.end();
       });
     });
+    it("reassign writeHead method, issue#3585", done => {
+      runTest(done, (server, serverPort, done) => {
+        const req = request(`http://localhost:${serverPort}/customWriteHead`, res => {
+          expect(res.headers["content-type"]).toBe("text/plain");
+          expect(res.headers["x-powered-by"]).toBe("Bun");
+          done();
+        });
+        req.end();
+      });
+    });
   });
 
   describe("signal", () => {