http: fix rawHeaders exceeding maxHeadersCount limit

Fixes: https://github.com/nodejs/node/issues/61284
PR-URL: https://github.com/nodejs/node/pull/61285
Reviewed-By: Tim Perry <pimterry@gmail.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: René <contact.9a5d6388@renegade334.me.uk>
Reviewed-By: Ethan Arrowood <ethan@arrowood.dev>

lib/_http_common.js

@@ -59,9 +59,11 @@ const MAX_HEADER_PAIRS = 2000;
 // called to process trailing HTTP headers.
 function parserOnHeaders(headers, url) {
   // Once we exceeded headers limit - stop collecting them
-  if (this.maxHeaderPairs <= 0 ||
-      this._headers.length < this.maxHeaderPairs) {
+  const capacity = this.maxHeaderPairs - this._headers.length;
+  if (this.maxHeaderPairs <= 0 || capacity >= headers.length) {
     this._headers.push(...headers);
+  } else if (capacity > 0) {
+    this._headers.push(...headers.slice(0, capacity));
   }
   this._url += url;
 }

test/parallel/test-http-rawheaders-limit.js

@@ -0,0 +1,26 @@
+'use strict';
+const common = require('../common');
+const assert = require('assert');
+const http = require('http');
+const net = require('net');
+
+const server = http.createServer(common.mustCall((req, res) => {
+  const limit = server.maxHeadersCount * 2;
+  assert.ok(req.rawHeaders.length <= limit,
+            `rawHeaders.length (${req.rawHeaders.length}) exceeds limit (${limit})`);
+  res.end();
+  server.close();
+}));
+
+server.maxHeadersCount = 50;
+
+server.listen(0, common.mustCall(() => {
+  const port = server.address().port;
+  const headers = Array.from({ length: 65 }, (_, i) => `X-${i}:v`).join('\r\n');
+  const req = `GET / HTTP/1.1\r\nHost: localhost\r\n${headers}\r\n\r\n`;
+
+  net.createConnection(port, 'localhost', function() {
+    this.write(req);
+    this.once('data', () => this.end());
+  });
+}));