http: 451 status code "Unavailable For Legal Reasons"

This http code allows us to provide a fair reason when
we can't return some data to the client by legal issues.

IETF https://datatracker.ietf.org/doc/draft-ietf-httpbis-legally-restricted-status/

Fixes: #4376
PR-URL: https://github.com/nodejs/node/pull/4377
Reviewed-By: Rich Trott <rtrott@gmail.com>
Reviewed-By: James M Snell <jasnell@gmail.com>

lib/_http_server.js

@@ -65,6 +65,7 @@ const STATUS_CODES = exports.STATUS_CODES = {
   428: 'Precondition Required',      // RFC 6585
   429: 'Too Many Requests',          // RFC 6585
   431: 'Request Header Fields Too Large', // RFC 6585
+  451: 'Unavailable For Legal Reasons',
   500: 'Internal Server Error',
   501: 'Not Implemented',
   502: 'Bad Gateway',

test/parallel/test-http-status-code.js

@@ -7,7 +7,7 @@ var http = require('http');
 // ServerResponse.prototype.statusCode
 
 var testsComplete = 0;
-var tests = [200, 202, 300, 404, 500];
+var tests = [200, 202, 300, 404, 451, 500];
 var testIdx = 0;
 
 var s = http.createServer(function(req, res) {
@@ -42,6 +42,6 @@ function nextTest() {
 
 
 process.on('exit', function() {
-  assert.equal(4, testsComplete);
+  assert.equal(5, testsComplete);
 });