http: add maxHeaderSize property

This commit exposes the value of --max-http-header-size
as a property of the http module.

Backport-PR-URL: #25218
PR-URL: #24860
Reviewed-By: Richard Lau <riclau@uk.ibm.com>
Reviewed-By: Matteo Collina <matteo.collina@gmail.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>
Reviewed-By: Shelley Vohr <codebytere@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

doc/api/http.md

@@ -1581,6 +1581,16 @@ added: v0.5.9
 Global instance of `Agent` which is used as the default for all HTTP client
 requests.
 
+## http.maxHeaderSize
+<!-- YAML
+added: REPLACEME
+-->
+
+* {number}
+
+Read-only property specifying the maximum allowed size of HTTP headers in bytes.
+Defaults to 8KB. Configurable using the [`--max-http-header-size`][] CLI option.
+
 ## http.request(options[, callback])
 <!-- YAML
 added: v0.3.6
@@ -1698,6 +1708,7 @@ There are a few special headers that should be noted.
 * Sending an Authorization header will override using the `auth` option
   to compute basic authentication.
 
+[`--max-http-header-size`]: cli.html#cli_max_http_header_size_size
 [`'checkContinue'`]: #http_event_checkcontinue
 [`'listening'`]: net.html#net_event_listening
 [`'request'`]: #http_event_request

lib/http.js

@@ -19,6 +19,8 @@ const server = require('_http_server');
 exports.ServerResponse = server.ServerResponse;
 exports.STATUS_CODES = server.STATUS_CODES;
 
+let maxHeaderSize;
+
 
 const agent = require('_http_agent');
 const Agent = exports.Agent = agent.Agent;
@@ -92,8 +94,21 @@ Client.prototype.request = function(method, path, headers) {
   return c;
 };
 
+
 exports.Client = internalUtil.deprecate(Client, 'http.Client is deprecated.');
 
 exports.createClient = internalUtil.deprecate(function(port, host) {
   return new Client(port, host);
 }, 'http.createClient is deprecated. Use http.request instead.');
+
+Object.defineProperty(module.exports, 'maxHeaderSize', {
+  configurable: true,
+  enumerable: true,
+  get() {
+    if (maxHeaderSize === undefined) {
+      maxHeaderSize = process.binding('config').maxHTTPHeaderSize;
+    }
+
+    return maxHeaderSize;
+  }
+});

test/parallel/test-http-max-header-size.js

@@ -0,0 +1,11 @@
+'use strict';
+
+require('../common');
+const assert = require('assert');
+const { spawnSync } = require('child_process');
+const http = require('http');
+
+assert.strictEqual(http.maxHeaderSize, 8 * 1024);
+const child = spawnSync(process.execPath, ['--max-http-header-size=10', '-p',
+                                           'http.maxHeaderSize']);
+assert.strictEqual(+child.stdout.toString().trim(), 10);