3 * Copyright(c) 2014 Douglas Christopher Wilson
10 * Reference to Array slice.
13 var slice = Array.prototype.slice
16 * Execute a listener when a response is about to write headers.
19 * @return {Function} listener
23 module.exports = function onHeaders(res, listener) {
25 throw new TypeError('argument res is required')
28 if (typeof listener !== 'function') {
29 throw new TypeError('argument listener must be a function')
32 res.writeHead = createWriteHead(res.writeHead, listener)
35 function createWriteHead(prevWriteHead, listener) {
38 // return function with core name and argument list
39 return function writeHead(statusCode) {
40 // set headers from arguments
41 var args = setWriteHeadHeaders.apply(this, arguments);
48 // pass-along an updated status code
49 if (typeof args[0] === 'number' && this.statusCode !== args[0]) {
50 args[0] = this.statusCode
55 prevWriteHead.apply(this, args);
59 function setWriteHeadHeaders(statusCode) {
60 var length = arguments.length
61 var headerIndex = length > 1 && typeof arguments[1] === 'string'
65 var headers = length >= headerIndex + 1
66 ? arguments[headerIndex]
69 this.statusCode = statusCode
71 // the following block is from node.js core
72 if (Array.isArray(headers)) {
74 for (var i = 0, len = headers.length; i < len; ++i) {
75 this.setHeader(headers[i][0], headers[i][1])
79 var keys = Object.keys(headers)
80 for (var i = 0; i < keys.length; i++) {
82 if (k) this.setHeader(k, headers[k])
86 // copy leading arguments
87 var args = new Array(Math.min(length, headerIndex))
88 for (var i = 0; i < args.length; i++) {
89 args[i] = arguments[i]