| /*! |
| * on-headers |
| * Copyright(c) 2014 Douglas Christopher Wilson |
| * MIT Licensed |
| */ |
| |
| 'use strict' |
| |
| /** |
| * Reference to Array slice. |
| */ |
| |
| var slice = Array.prototype.slice |
| |
| /** |
| * Execute a listener when a response is about to write headers. |
| * |
| * @param {Object} res |
| * @return {Function} listener |
| * @api public |
| */ |
| |
| module.exports = function onHeaders(res, listener) { |
| if (!res) { |
| throw new TypeError('argument res is required') |
| } |
| |
| if (typeof listener !== 'function') { |
| throw new TypeError('argument listener must be a function') |
| } |
| |
| res.writeHead = createWriteHead(res.writeHead, listener) |
| } |
| |
| function createWriteHead(prevWriteHead, listener) { |
| var fired = false; |
| |
| // return function with core name and argument list |
| return function writeHead(statusCode) { |
| // set headers from arguments |
| var args = setWriteHeadHeaders.apply(this, arguments); |
| |
| // fire listener |
| if (!fired) { |
| fired = true |
| listener.call(this) |
| |
| // pass-along an updated status code |
| if (typeof args[0] === 'number' && this.statusCode !== args[0]) { |
| args[0] = this.statusCode |
| args.length = 1 |
| } |
| } |
| |
| prevWriteHead.apply(this, args); |
| } |
| } |
| |
| function setWriteHeadHeaders(statusCode) { |
| var length = arguments.length |
| var headerIndex = length > 1 && typeof arguments[1] === 'string' |
| ? 2 |
| : 1 |
| |
| var headers = length >= headerIndex + 1 |
| ? arguments[headerIndex] |
| : undefined |
| |
| this.statusCode = statusCode |
| |
| // the following block is from node.js core |
| if (Array.isArray(headers)) { |
| // handle array case |
| for (var i = 0, len = headers.length; i < len; ++i) { |
| this.setHeader(headers[i][0], headers[i][1]) |
| } |
| } else if (headers) { |
| // handle object case |
| var keys = Object.keys(headers) |
| for (var i = 0; i < keys.length; i++) { |
| var k = keys[i] |
| if (k) this.setHeader(k, headers[k]) |
| } |
| } |
| |
| // copy leading arguments |
| var args = new Array(Math.min(length, headerIndex)) |
| for (var i = 0; i < args.length; i++) { |
| args[i] = arguments[i] |
| } |
| |
| return args |
| } |