follow-redirects.js

'use strict';
var url = require('url');
var assert = require('assert');
var http = require('http');
var https = require('https');
var Writable = require('stream').Writable;

var nativeProtocols = {'http:': http, 'https:': https};
var schemes = {};
var exports = module.exports = {
	maxRedirects: 21
};
// RFC7231§4.2.1: Of the request methods defined by this specification,
// the GET, HEAD, OPTIONS, and TRACE methods are defined to be safe.
var safeMethods = {GET: true, HEAD: true, OPTIONS: true, TRACE: true};

// Create handlers that pass events from native requests
var eventHandlers = Object.create(null);
['abort', 'aborted', 'error', 'socket'].forEach(function (event) {
	eventHandlers[event] = function (arg) {
		this._redirectable.emit(event, arg);
	};
});

// An HTTP(S) request that can be redirected
function RedirectableRequest(options, responseCallback) {
	// Initialize the request
	Writable.call(this);
	this._options = options;
	this._redirectCount = 0;
	this._bufferedWrites = [];

	// Attach a callback if passed
	if (responseCallback) {
		this.on('response', responseCallback);
	}

	// React to responses of native requests
	var self = this;
	this._onNativeResponse = function (response) {
		self._processResponse(response);
	};

	// Perform the first request
	this._performRequest();
}
RedirectableRequest.prototype = Object.create(Writable.prototype);

// Executes the next native request (initial or redirect)
RedirectableRequest.prototype._performRequest = function () {
	// If specified, use the agent corresponding to the protocol
	// (HTTP and HTTPS use different types of agents)
	var protocol = this._options.protocol;
	if (this._options.agents) {
		this._options.agent = this._options.agents[schemes[protocol]];
	}

	// Create the native request
	var nativeProtocol = nativeProtocols[this._options.protocol];
	var request = this._currentRequest =
				nativeProtocol.request(this._options, this._onNativeResponse);
	this._currentUrl = url.format(this._options);

	// Set up event handlers
	request._redirectable = this;
	for (var event in eventHandlers) {
		if (event) {
			request.on(event, eventHandlers[event]);
		}
	}

	// End a redirected request
	// (The first request must be ended explicitly with RedirectableRequest#end)
	if (this._currentResponse) {
		// If no body was written to the original request, or the method was changed to GET,
		// end the redirected request (without writing a body).
		var bufferedWrites = this._bufferedWrites;
		if (bufferedWrites.length === 0 || this._options.method === 'GET') {
			request.end();
		// The body of the original request must be added to the redirected request.
		} else {
			var i = 0;
			(function writeNext() {
				if (i < bufferedWrites.length) {
					var bufferedWrite = bufferedWrites[i++];
					request.write(bufferedWrite.data, bufferedWrite.encoding, writeNext);
				} else {
					request.end();
				}
			})();
		}
	}
};

// Processes a response from the current native request
RedirectableRequest.prototype._processResponse = function (response) {
	// RFC7231§6.4: The 3xx (Redirection) class of status code indicates
	// that further action needs to be taken by the user agent in order to
	// fulfill the request. If a Location header field is provided,
	// the user agent MAY automatically redirect its request to the URI
	// referenced by the Location field value,
	// even if the specific status code is not understood.
	var location = response.headers.location;
	if (location && this._options.followRedirects !== false &&
			response.statusCode >= 300 && response.statusCode < 400) {
		// RFC7231§6.4: A client SHOULD detect and intervene
		// in cyclical redirections (i.e., "infinite" redirection loops).
		if (++this._redirectCount > this._options.maxRedirects) {
			return this.emit('error', new Error('Max redirects exceeded.'));
		}

		// RFC7231§6.4.7: The 307 (Temporary Redirect) status code indicates
		// that the target resource resides temporarily under a different URI
		// and the user agent MUST NOT change the request method
		// if it performs an automatic redirection to that URI.
		if (response.statusCode !== 307) {
			// RFC7231§6.4: Automatic redirection needs to done with
			// care for methods not known to be safe […],
			// since the user might not wish to redirect an unsafe request.
			if (!(this._options.method in safeMethods)) {
				this._options.method = 'GET';
			}
		}

		// Perform the redirected request
		var redirectUrl = url.resolve(this._currentUrl, location);
		Object.assign(this._options, url.parse(redirectUrl));
		this._currentResponse = response;
		this._performRequest();
	} else {
		// The response is not a redirect; return it as-is
		response.responseUrl = this._currentUrl;
		this.emit('response', response);

		// Clean up
		delete this._options;
		delete this._bufferedWrites;
	}
};

// Aborts the current native request
RedirectableRequest.prototype.abort = function () {
	this._currentRequest.abort();
};

// Flushes the headers of the current native request
RedirectableRequest.prototype.flushHeaders = function () {
	this._currentRequest.flushHeaders();
};

// Sets the noDelay option of the current native request
RedirectableRequest.prototype.setNoDelay = function (noDelay) {
	this._currentRequest.setNoDelay(noDelay);
};

// Sets the socketKeepAlive option of the current native request
RedirectableRequest.prototype.setSocketKeepAlive = function (enable, initialDelay) {
	this._currentRequest.setSocketKeepAlive(enable, initialDelay);
};

// Sets the timeout option of the current native request
RedirectableRequest.prototype.setTimeout = function (timeout, callback) {
	this._currentRequest.setTimeout(timeout, callback);
};

// Writes buffered data to the current native request
RedirectableRequest.prototype._write = function (data, encoding, callback) {
	this._currentRequest.write(data, encoding, callback);
	this._bufferedWrites.push({data: data, encoding: encoding});
};

// Ends the current native request
RedirectableRequest.prototype.end = function (data, encoding, callback) {
	this._currentRequest.end(data, encoding, callback);
	if (data) {
		this._bufferedWrites.push({data: data, encoding: encoding});
	}
};

// Export a redirecting wrapper for each native protocol
Object.keys(nativeProtocols).forEach(function (protocol) {
	var scheme = schemes[protocol] = protocol.substr(0, protocol.length - 1);
	var nativeProtocol = nativeProtocols[protocol];
	var wrappedProtocol = exports[scheme] = Object.create(nativeProtocol);

	// Executes an HTTP request, following redirects
	wrappedProtocol.request = function (options, callback) {
		if (typeof options === 'string') {
			options = url.parse(options);
			options.maxRedirects = exports.maxRedirects;
		} else {
			options = Object.assign({
				maxRedirects: exports.maxRedirects,
				protocol: protocol
			}, options);
		}
		assert.equal(options.protocol, protocol, 'protocol mismatch');

		return new RedirectableRequest(options, callback);
	};

	// Executes a GET request, following redirects
	wrappedProtocol.get = function (options, callback) {
		var request = wrappedProtocol.request(options, callback);
		request.end();
		return request;
	};
});