perf(node): fire-and-forget response send on the serve() path

src/adapters/_node/request.ts

@@ -24,6 +24,10 @@ export const NodeRequest: {
 
   class Request implements Partial<ServerRequest> {
     runtime: ServerRequest["runtime"];
+    // Declared so the post-construction `request.waitUntil = ...` assignment
+    // in the adapters doesn't add a property (hidden-class transition) per
+    // request.
+    waitUntil?: ServerRequest["waitUntil"];
 
     #req: NodeServerRequest;
     #url?: URL;
@@ -134,21 +138,33 @@ export const NodeRequest: {
       return this.#bodyStream;
     }
 
+    // Buffer the raw request body once; consumers add their own single
+    // continuation (`.toString()` / `JSON.parse`) so no extra promise or
+    // microtask hop is introduced vs. inlining the read.
+    #readBuffered() {
+      return readBody(this.#req, this.#maxRequestBodySize);
+    }
+
     text() {
       if (this.#request) {
         return this.#request.text();
       }
       if (this.#bodyStream !== undefined) {
         return this.#bodyStream ? new Response(this.#bodyStream).text() : Promise.resolve("");
       }
-      return readBody(this.#req, this.#maxRequestBodySize).then((buf) => buf.toString());
+      return this.#readBuffered().then((buf) => buf.toString());
     }
 
     json() {
       if (this.#request) {
         return this.#request.json();
       }
-      return this.text().then((text) => JSON.parse(text));
+      if (this.#bodyStream !== undefined) {
+        return this.text().then((text) => JSON.parse(text));
+      }
+      // Parse in a single continuation (readBody -> parse) instead of going
+      // through text() — one less promise + microtask hop per body read.
+      return this.#readBuffered().then((buf) => JSON.parse(buf.toString()));
     }
 
     get _request(): globalThis.Request {

src/adapters/_node/send.ts

@@ -4,13 +4,66 @@ import type NodeHttp from "node:http";
 import type { NodeServerResponse } from "../../types.ts";
 import type { NodeResponse } from "./response.ts";
 
-export async function sendNodeResponse(
+/**
+ * Sends a web `Response` to a Node.js `ServerResponse`.
+ *
+ * The returned promise resolves once the response has been fully sent
+ * (kept for `toNodeHandler` consumers that await completion).
+ */
+export function sendNodeResponse(
   nodeRes: NodeServerResponse,
   webRes: Response | NodeResponse,
 ): Promise<void> {
+  try {
+    return _sendNodeResponse(nodeRes, webRes, false) || Promise.resolve();
+  } catch (error) {
+    return Promise.reject(error);
+  }
+}
+
+/**
+ * Fire-and-forget variant for the internal `serve()` path: node:http ignores
+ * the request listener's return value, so tracking `end()` completion with a
+ * per-response Promise (and the microtask hops to settle it) is pure overhead
+ * there. Streaming bodies still return their tracking promise (it drives
+ * their own cleanup).
+ *
+ * A synchronous throw during serialization (e.g. an invalid header value in
+ * `writeHead`) must not escape the request listener — that would surface as an
+ * `uncaughtException` and take the process down. Guard it here and fail the
+ * single response instead.
+ *
+ * @internal
+ */
+export function sendNodeResponseDetached(
+  nodeRes: NodeServerResponse,
+  webRes: Response | NodeResponse,
+): Promise<void> | void {
+  try {
+    return _sendNodeResponse(nodeRes, webRes, true);
+  } catch (error) {
+    handleSendError(nodeRes, error);
+  }
+}
+
+function handleSendError(nodeRes: NodeServerResponse, _error: unknown): void {
+  if (nodeRes.headersSent) {
+    // Response already committed — the only recovery is to tear down the socket.
+    nodeRes.destroy();
+  } else {
+    nodeRes.statusCode = 500;
+    nodeRes.end();
+  }
+}
+
+function _sendNodeResponse(
+  nodeRes: NodeServerResponse,
+  webRes: Response | NodeResponse,
+  detached: boolean,
+): Promise<void> | void {
   if (!webRes) {
     nodeRes.statusCode = 500;
-    return endNodeResponse(nodeRes);
+    return endNodeResponse(nodeRes, detached);
   }
 
   // Fast path for NodeResponse
@@ -31,7 +84,7 @@ export async function sendNodeResponse(
     } else {
       writeHead(nodeRes, res.status, res.statusText, res.headers);
     }
-    return endNodeResponse(nodeRes);
+    return endNodeResponse(nodeRes, detached);
   }
 
   const rawHeaders: string[] = [];
@@ -40,7 +93,7 @@ export async function sendNodeResponse(
   }
   writeHead(nodeRes, webRes.status, webRes.statusText, rawHeaders);
 
-  return webRes.body ? streamBody(webRes.body, nodeRes) : endNodeResponse(nodeRes);
+  return webRes.body ? streamBody(webRes.body, nodeRes) : endNodeResponse(nodeRes, detached);
 }
 
 function writeHead(
@@ -66,7 +119,11 @@ function writeHead(
   }
 }
 
-function endNodeResponse(nodeRes: NodeServerResponse) {
+function endNodeResponse(nodeRes: NodeServerResponse, detached?: boolean): Promise<void> | void {
+  if (detached) {
+    nodeRes.end();
+    return;
+  }
   return new Promise<void>((resolve) => nodeRes.end(resolve));
 }
 
@@ -106,7 +163,7 @@ function pipeBody(
       stream.off("readable", onReadable);
       stream.destroy();
       writeHead(nodeRes, 500, "Internal Server Error", []);
-      endNodeResponse(nodeRes).then(resolve);
+      (endNodeResponse(nodeRes) as Promise<void>).then(resolve);
     }
     function onReadable() {
       stream.off("error", onEarlyError);

src/adapters/node.ts

@@ -1,4 +1,4 @@
-import { sendNodeResponse } from "./_node/send.ts";
+import { sendNodeResponseDetached } from "./_node/send.ts";
 import { NodeRequest } from "./_node/request.ts";
 import {
   fmtURL,
@@ -82,9 +82,11 @@ class NodeServer implements Server {
       });
       request.waitUntil = this.#wait?.waitUntil;
       const res = fetchHandler(request);
+      // node:http ignores the listener's return value — use the detached
+      // variant to skip the per-response end-tracking Promise.
       return res instanceof Promise
-        ? res.then((resolvedRes) => sendNodeResponse(nodeRes, resolvedRes))
-        : sendNodeResponse(nodeRes, res);
+        ? res.then((resolvedRes) => sendNodeResponseDetached(nodeRes, resolvedRes))
+        : sendNodeResponseDetached(nodeRes, res);
     };
 
     this.node = { handler, server: undefined };