Stated server.maxHeadersCount default is off by a factor of two

[arynh]

Affected URL(s)

https://nodejs.org/docs/latest-v24.x/api/http.html#servermaxheaderscount
https://nodejs.org/docs/latest-v26.x/api/http.html#servermaxheaderscount

Description of the problem

In PR #12039, this limit was raised with the justification that it's set to 2000 in code. However the reference was pointing to the default max header pairs, not header count. Pairs defaults to 2000 here:

node/lib/_http_common.js

Line 53 in e65df3b

const MAX_HEADER_PAIRS = 2000;

Each incoming header consumes two pairs.

Here's a minimal reproduction:

const http = require("http");

const server = http.createServer((req, res) => {
  res.writeHead(200);
  res.end(String(req.rawHeaders.length << 1)); // this should be the line count
});

server.listen(0, () => {
  const port = server.address().port;
  const headers = {};

  // add 999 headers, bringing total to 1001 including host and connection
  // keep size small to not run into size limit
  for (let i = 0; i < 999; i++) {
    headers[`h-${i}`] = "v";
  }

  http.get({ port, headers }, (res) => {
    let body = "";
    res.on("data", (c) => (body += c));
    res.on("end", () => {
      console.log(`Status: ${res.statusCode}`);
      server.close();
    });
  });
});

I would expect this to work given the stated 2000 default, but I get 431:

$ node --version; node header-count-bug.js
v24.19.0
Status: 431