fix(node:http): socket.write not sending data in upgrade event handler

Enable streaming on the socket before emitting the "upgrade" event, matching
the existing behavior for CONNECT requests. Without this, handle.ondrain was
undefined so _write() silently skipped calling handle.write().

Also skip socket.cork() for upgrade connections since the socket is handed
off to user code and data should flow immediately.

Closes #9882

Co-Authored-By: Claude <noreply@anthropic.com>

src/js/node/_http_server.ts

@@ -602,6 +602,7 @@ Server.prototype[kRealListen] = function (tls, port, host, socketPath, reusePort
           http_res.end();
           socket.destroy();
         } else if (is_upgrade) {
+          socket[kEnableStreaming](true);
           server.emit("upgrade", http_req, socket, kEmptyBuffer);
           if (!socket._httpMessage) {
             if (canUseInternalAssignSocket) {
@@ -629,7 +630,9 @@ Server.prototype[kRealListen] = function (tls, port, host, socketPath, reusePort
           server.emit("request", http_req, http_res);
         }
 
-        socket.cork();
+        if (!is_upgrade) {
+          socket.cork();
+        }
 
         if (handle.finished || didFinish) {
           handle = undefined;

test/regression/issue/09882.test.ts

@@ -0,0 +1,162 @@
+import { expect, test } from "bun:test";
+import http from "node:http";
+import net from "node:net";
+
+test("socket.write sends data in http upgrade event handler", async () => {
+  const { promise, resolve, reject } = Promise.withResolvers<void>();
+
+  const server = http.createServer();
+  server.on("upgrade", (_req, socket) => {
+    socket.write("x", () => {
+      // After the write completes, close the socket
+      socket.end();
+    });
+  });
+
+  server.listen(0, "127.0.0.1", () => {
+    const addr = server.address() as net.AddressInfo;
+
+    const client = net.createConnection(addr.port, "127.0.0.1", () => {
+      client.write(
+        "GET / HTTP/1.1\r\n" +
+          "Host: 127.0.0.1\r\n" +
+          "Upgrade: websocket\r\n" +
+          "Connection: Upgrade\r\n" +
+          "Sec-WebSocket-Key: dGhlIHNhbXBsZSBub25jZQ==\r\n" +
+          "Sec-WebSocket-Version: 13\r\n" +
+          "\r\n",
+      );
+    });
+
+    let received = "";
+    client.on("data", (data: Buffer) => {
+      received += data.toString();
+    });
+
+    client.on("end", () => {
+      try {
+        expect(received).toBe("x");
+        resolve();
+      } catch (e) {
+        reject(e);
+      } finally {
+        server.close();
+      }
+    });
+
+    client.on("error", (err: Error) => {
+      server.close();
+      reject(err);
+    });
+  });
+
+  await promise;
+});
+
+test("socket.write with 101 handshake in http upgrade event handler", async () => {
+  const { promise, resolve, reject } = Promise.withResolvers<void>();
+
+  const server = http.createServer();
+  server.on("upgrade", (_req, socket) => {
+    socket.write(
+      "HTTP/1.1 101 Switching Protocols\r\nUpgrade: websocket\r\nConnection: Upgrade\r\n\r\nhello from upgrade",
+      () => {
+        socket.end();
+      },
+    );
+  });
+
+  server.listen(0, "127.0.0.1", () => {
+    const addr = server.address() as net.AddressInfo;
+
+    const client = net.createConnection(addr.port, "127.0.0.1", () => {
+      client.write(
+        "GET / HTTP/1.1\r\n" +
+          "Host: 127.0.0.1\r\n" +
+          "Upgrade: websocket\r\n" +
+          "Connection: Upgrade\r\n" +
+          "Sec-WebSocket-Key: dGhlIHNhbXBsZSBub25jZQ==\r\n" +
+          "Sec-WebSocket-Version: 13\r\n" +
+          "\r\n",
+      );
+    });
+
+    let received = "";
+    client.on("data", (data: Buffer) => {
+      received += data.toString();
+    });
+
+    client.on("end", () => {
+      try {
+        expect(received).toContain("HTTP/1.1 101 Switching Protocols");
+        expect(received).toContain("hello from upgrade");
+        resolve();
+      } catch (e) {
+        reject(e);
+      } finally {
+        server.close();
+      }
+    });
+
+    client.on("error", (err: Error) => {
+      server.close();
+      reject(err);
+    });
+  });
+
+  await promise;
+});
+
+test("multiple socket.write calls in http upgrade event handler", async () => {
+  const { promise, resolve, reject } = Promise.withResolvers<void>();
+
+  const server = http.createServer();
+  server.on("upgrade", (_req, socket) => {
+    socket.write("first");
+    socket.write("second");
+    socket.write("third", () => {
+      socket.end();
+    });
+  });
+
+  server.listen(0, "127.0.0.1", () => {
+    const addr = server.address() as net.AddressInfo;
+
+    const client = net.createConnection(addr.port, "127.0.0.1", () => {
+      client.write(
+        "GET / HTTP/1.1\r\n" +
+          "Host: 127.0.0.1\r\n" +
+          "Upgrade: websocket\r\n" +
+          "Connection: Upgrade\r\n" +
+          "Sec-WebSocket-Key: dGhlIHNhbXBsZSBub25jZQ==\r\n" +
+          "Sec-WebSocket-Version: 13\r\n" +
+          "\r\n",
+      );
+    });
+
+    let received = "";
+    client.on("data", (data: Buffer) => {
+      received += data.toString();
+    });
+
+    client.on("end", () => {
+      try {
+        expect(received).toContain("first");
+        expect(received).toContain("second");
+        expect(received).toContain("third");
+        resolve();
+      } catch (e) {
+        reject(e);
+      } finally {
+        server.close();
+      }
+    });
+
+    client.on("error", (err: Error) => {
+      server.close();
+      reject(err);
+    });
+  });
+
+  await promise;
+});