NET-Web-API-w-Angular/my-app/node_modules/needle/lib/needle.js

859 lines
29 KiB
JavaScript
Raw Normal View History

2024-02-09 00:38:41 +00:00
//////////////////////////////////////////
// Needle -- HTTP Client for Node.js
// Written by Tomás Pollak <tomas@forkhq.com>
// (c) 2012-2023 - Fork Ltd.
// MIT Licensed
//////////////////////////////////////////
var fs = require('fs'),
http = require('http'),
https = require('https'),
url = require('url'),
stream = require('stream'),
debug = require('util').debuglog('needle'),
stringify = require('./querystring').build,
multipart = require('./multipart'),
auth = require('./auth'),
cookies = require('./cookies'),
parsers = require('./parsers'),
decoder = require('./decoder'),
utils = require('./utils');
//////////////////////////////////////////
// variabilia
var version = require('../package.json').version;
var user_agent = 'Needle/' + version;
user_agent += ' (Node.js ' + process.version + '; ' + process.platform + ' ' + process.arch + ')';
var tls_options = 'pfx key passphrase cert ca ciphers rejectUnauthorized secureProtocol checkServerIdentity family';
// older versions of node (< 0.11.4) prevent the runtime from exiting
// because of connections in keep-alive state. so if this is the case
// we'll default new requests to set a Connection: close header.
var close_by_default = !http.Agent || http.Agent.defaultMaxSockets != Infinity;
// see if we have Object.assign. otherwise fall back to util._extend
var extend = Object.assign ? Object.assign : require('util')._extend;
// these are the status codes that Needle interprets as redirects.
var redirect_codes = [301, 302, 303, 307, 308];
//////////////////////////////////////////
// decompressors for gzip/deflate/br bodies
function bind_opts(fn, options) {
return fn.bind(null, options);
}
var decompressors = {};
try {
var zlib = require('zlib');
// Enable Z_SYNC_FLUSH to avoid Z_BUF_ERROR errors (Node PR #2595)
var zlib_options = {
flush: zlib.Z_SYNC_FLUSH,
finishFlush: zlib.Z_SYNC_FLUSH
};
var br_options = {
flush: zlib.BROTLI_OPERATION_FLUSH,
finishFlush: zlib.BROTLI_OPERATION_FLUSH
};
decompressors['x-deflate'] = bind_opts(zlib.Inflate, zlib_options);
decompressors['deflate'] = bind_opts(zlib.Inflate, zlib_options);
decompressors['x-gzip'] = bind_opts(zlib.Gunzip, zlib_options);
decompressors['gzip'] = bind_opts(zlib.Gunzip, zlib_options);
if (typeof zlib.BrotliDecompress === 'function') {
decompressors['br'] = bind_opts(zlib.BrotliDecompress, br_options);
}
} catch(e) { /* zlib not available */ }
//////////////////////////////////////////
// options and aliases
var defaults = {
// data
boundary : '--------------------NODENEEDLEHTTPCLIENT',
encoding : 'utf8',
parse_response : 'all', // same as true. valid options: 'json', 'xml' or false/null
proxy : null,
// agent & headers
agent : null,
headers : {},
accept : '*/*',
user_agent : user_agent,
// numbers
open_timeout : 10000,
response_timeout : 0,
read_timeout : 0,
follow_max : 0,
stream_length : -1,
// abort signal
signal : null,
// booleans
compressed : false,
decode_response : true,
parse_cookies : true,
follow_set_cookies : false,
follow_set_referer : false,
follow_keep_method : false,
follow_if_same_host : false,
follow_if_same_protocol : false,
follow_if_same_location : false,
use_proxy_from_env_var : true
}
var aliased = {
options: {
decode : 'decode_response',
parse : 'parse_response',
timeout : 'open_timeout',
follow : 'follow_max'
},
inverted: {}
}
// only once, invert aliased keys so we can get passed options.
Object.keys(aliased.options).map(function(k) {
var value = aliased.options[k];
aliased.inverted[value] = k;
});
//////////////////////////////////////////
// helpers
function keys_by_type(type) {
return Object.keys(defaults).map(function(el) {
if (defaults[el] !== null && defaults[el].constructor == type)
return el;
}).filter(function(el) { return el })
}
//////////////////////////////////////////
// the main act
function Needle(method, uri, data, options, callback) {
// if (!(this instanceof Needle)) {
// return new Needle(method, uri, data, options, callback);
// }
if (typeof uri !== 'string')
throw new TypeError('URL must be a string, not ' + uri);
this.method = method.toLowerCase();
this.uri = uri;
this.data = data;
if (typeof options == 'function') {
this.callback = options;
this.options = {};
} else {
this.callback = callback;
this.options = options;
}
}
Needle.prototype.setup = function(uri, options) {
function get_option(key, fallback) {
// if original is in options, return that value
if (typeof options[key] != 'undefined') return options[key];
// otherwise, return value from alias or fallback/undefined
return typeof options[aliased.inverted[key]] != 'undefined'
? options[aliased.inverted[key]] : fallback;
}
function check_value(expected, key) {
var value = get_option(key),
type = typeof value;
if (type != 'undefined' && type != expected)
throw new TypeError(type + ' received for ' + key + ', but expected a ' + expected);
return (type == expected) ? value : defaults[key];
}
//////////////////////////////////////////////////
// the basics
var config = {
http_opts : {
agent: get_option('agent', defaults.agent),
localAddress: get_option('localAddress', undefined),
lookup: get_option('lookup', undefined),
signal: get_option('signal', defaults.signal)
}, // passed later to http.request() directly
headers : {},
output : options.output,
proxy : get_option('proxy', defaults.proxy),
parser : get_option('parse_response', defaults.parse_response),
encoding : options.encoding || (options.multipart ? 'binary' : defaults.encoding)
}
keys_by_type(Boolean).forEach(function(key) {
config[key] = check_value('boolean', key);
})
keys_by_type(Number).forEach(function(key) {
config[key] = check_value('number', key);
})
if (config.http_opts.signal && !(config.http_opts.signal instanceof AbortSignal))
throw new TypeError(typeof config.http_opts.signal + ' received for signal, but expected an AbortSignal');
// populate http_opts with given TLS options
tls_options.split(' ').forEach(function(key) {
if (typeof options[key] != 'undefined') {
if (config.http_opts.agent) { // pass option to existing agent
config.http_opts.agent.options[key] = options[key];
} else {
config.http_opts[key] = options[key];
}
}
});
//////////////////////////////////////////////////
// headers, cookies
for (var key in defaults.headers)
config.headers[key] = defaults.headers[key];
config.headers['accept'] = options.accept || defaults.accept;
config.headers['user-agent'] = options.user_agent || defaults.user_agent;
if (options.content_type)
config.headers['content-type'] = options.content_type;
// set connection header if opts.connection was passed, or if node < 0.11.4 (close)
if (options.connection || close_by_default)
config.headers['connection'] = options.connection || 'close';
if ((options.compressed || defaults.compressed) && typeof zlib != 'undefined')
config.headers['accept-encoding'] = decompressors['br'] ? 'gzip, deflate, br' : 'gzip, deflate';
if (options.cookies)
config.headers['cookie'] = cookies.write(options.cookies);
//////////////////////////////////////////////////
// basic/digest auth
if (uri.match(/[^\/]@/)) { // url contains user:pass@host, so parse it.
var parts = (url.parse(uri).auth || '').split(':');
options.username = parts[0];
options.password = parts[1];
}
if (options.username) {
if (options.auth && (options.auth == 'auto' || options.auth == 'digest')) {
config.credentials = [options.username, options.password];
} else {
config.headers['authorization'] = auth.basic(options.username, options.password);
}
}
if (config.use_proxy_from_env_var) {
var env_proxy = utils.get_env_var(['HTTP_PROXY', 'HTTPS_PROXY'], true);
if (!config.proxy && env_proxy) config.proxy = env_proxy;
}
// if proxy is present, set auth header from either url or proxy_user option.
if (config.proxy) {
if (!config.use_proxy_from_env_var || utils.should_proxy_to(uri)) {
if (config.proxy.indexOf('http') === -1)
config.proxy = 'http://' + config.proxy;
if (config.proxy.indexOf('@') !== -1) {
var proxy = (url.parse(config.proxy).auth || '').split(':');
options.proxy_user = proxy[0];
options.proxy_pass = proxy[1];
}
if (options.proxy_user)
config.headers['proxy-authorization'] = auth.basic(options.proxy_user, options.proxy_pass);
} else {
delete config.proxy;
}
}
// now that all our headers are set, overwrite them if instructed.
for (var h in options.headers)
config.headers[h.toLowerCase()] = options.headers[h];
config.uri_modifier = get_option('uri_modifier', null);
return config;
}
Needle.prototype.start = function() {
var out = new stream.PassThrough({ objectMode: false }),
uri = this.uri,
data = this.data,
method = this.method,
callback = (typeof this.options == 'function') ? this.options : this.callback,
options = this.options || {};
// if no 'http' is found on URL, prepend it.
if (uri.indexOf('http') === -1)
uri = uri.replace(/^(\/\/)?/, 'http://');
var self = this, body, waiting = false, config = this.setup(uri, options);
// unless options.json was set to false, assume boss also wants JSON if content-type matches.
var json = options.json || (options.json !== false && config.headers['content-type'] == 'application/json');
if (data) {
if (options.multipart) { // boss says we do multipart. so we do it.
var boundary = options.boundary || defaults.boundary;
waiting = true;
multipart.build(data, boundary, function(err, parts) {
if (err) throw(err);
config.headers['content-type'] = 'multipart/form-data; boundary=' + boundary;
next(parts);
});
} else if (utils.is_stream(data)) {
if (method == 'get')
throw new Error('Refusing to pipe() a stream via GET. Did you mean .post?');
if (config.stream_length > 0 || (config.stream_length === 0 && data.path)) {
// ok, let's get the stream's length and set it as the content-length header.
// this prevents some servers from cutting us off before all the data is sent.
waiting = true;
utils.get_stream_length(data, config.stream_length, function(length) {
data.length = length;
next(data);
})
} else {
// if the boss doesn't want us to get the stream's length, or if it doesn't
// have a file descriptor for that purpose, then just head on.
body = data;
}
} else if (Buffer.isBuffer(data)) {
body = data; // use the raw buffer as request body.
} else if (method == 'get' && !json) {
// append the data to the URI as a querystring.
uri = uri.replace(/\?.*|$/, '?' + stringify(data));
} else { // string or object data, no multipart.
// if string, leave it as it is, otherwise, stringify.
body = (typeof(data) === 'string') ? data
: json ? JSON.stringify(data) : stringify(data);
// ensure we have a buffer so bytecount is correct.
body = Buffer.from(body, config.encoding);
}
}
function next(body) {
if (body) {
if (body.length) config.headers['content-length'] = body.length;
// if no content-type was passed, determine if json or not.
if (!config.headers['content-type']) {
config.headers['content-type'] = json
? 'application/json; charset=utf-8'
: 'application/x-www-form-urlencoded'; // no charset says W3 spec.
}
}
// unless a specific accept header was set, assume json: true wants JSON back.
if (options.json && (!options.accept && !(options.headers || {}).accept))
config.headers['accept'] = 'application/json';
self.send_request(1, method, uri, config, body, out, callback);
}
if (!waiting) next(body);
return out;
}
Needle.prototype.get_request_opts = function(method, uri, config) {
var opts = config.http_opts,
proxy = config.proxy,
remote = proxy ? url.parse(proxy) : url.parse(uri);
opts.protocol = remote.protocol;
opts.host = remote.hostname;
opts.port = remote.port || (remote.protocol == 'https:' ? 443 : 80);
opts.path = proxy ? uri : remote.pathname + (remote.search || '');
opts.method = method;
opts.headers = config.headers;
if (!opts.headers['host']) {
// if using proxy, make sure the host header shows the final destination
var target = proxy ? url.parse(uri) : remote;
opts.headers['host'] = target.hostname;
// and if a non standard port was passed, append it to the port header
if (target.port && [80, 443].indexOf(target.port) === -1) {
opts.headers['host'] += ':' + target.port;
}
}
return opts;
}
Needle.prototype.should_follow = function(location, config, original) {
if (!location) return false;
// returns true if location contains matching property (host or protocol)
function matches(property) {
var property = original[property];
return location.indexOf(property) !== -1;
}
// first, check whether the requested location is actually different from the original
if (!config.follow_if_same_location && location === original)
return false;
if (config.follow_if_same_host && !matches('host'))
return false; // host does not match, so not following
if (config.follow_if_same_protocol && !matches('protocol'))
return false; // procotol does not match, so not following
return true;
}
Needle.prototype.send_request = function(count, method, uri, config, post_data, out, callback) {
if (typeof config.uri_modifier === 'function') {
var modified_uri = config.uri_modifier(uri);
debug('Modifying request URI', uri + ' => ' + modified_uri);
uri = modified_uri;
}
var request,
timer,
returned = 0,
self = this,
request_opts = this.get_request_opts(method, uri, config),
protocol = request_opts.protocol == 'https:' ? https : http,
signal = request_opts.signal;
function done(err, resp) {
if (returned++ > 0)
return debug('Already finished, stopping here.');
if (timer) clearTimeout(timer);
request.removeListener('error', had_error);
out.done = true;
// An error can still be fired after closing. In particular, on macOS.
// See also:
// - https://github.com/tomas/needle/issues/391
// - https://github.com/less/less.js/issues/3693
// - https://github.com/nodejs/node/issues/27916
request.once('error', function() {});
if (callback)
return callback(err, resp, resp ? resp.body : undefined);
// NOTE: this event used to be called 'end', but the behaviour was confusing
// when errors ocurred, because the stream would still emit an 'end' event.
out.emit('done', err);
// trigger the 'done' event on streams we're being piped to, if any
var pipes = out._readableState.pipes || [];
if (!pipes.forEach) pipes = [pipes];
pipes.forEach(function(st) { st.emit('done', err); })
}
function had_error(err) {
debug('Request error', err);
out.emit('err', err);
done(err || new Error('Unknown error when making request.'));
}
function abort_handler() {
out.emit('err', new Error('Aborted by signal.'));
request.destroy();
}
function set_timeout(type, milisecs) {
if (timer) clearTimeout(timer);
if (milisecs <= 0) return;
timer = setTimeout(function() {
out.emit('timeout', type);
request.destroy();
// also invoke done() to terminate job on read_timeout
if (type == 'read') done(new Error(type + ' timeout'));
signal && signal.removeEventListener('abort', abort_handler);
}, milisecs);
}
debug('Making request #' + count, request_opts);
request = protocol.request(request_opts, function(resp) {
var headers = resp.headers;
debug('Got response', resp.statusCode, headers);
out.emit('response', resp);
set_timeout('read', config.read_timeout);
// if we got cookies, parse them unless we were instructed not to. make sure to include any
// cookies that might have been set on previous redirects.
if (config.parse_cookies && (headers['set-cookie'] || config.previous_resp_cookies)) {
resp.cookies = extend(config.previous_resp_cookies || {}, cookies.read(headers['set-cookie']));
debug('Got cookies', resp.cookies);
}
// if redirect code is found, determine if we should follow it according to the given options.
if (redirect_codes.indexOf(resp.statusCode) !== -1 && self.should_follow(headers.location, config, uri)) {
// clear timer before following redirects to prevent unexpected setTimeout consequence
clearTimeout(timer);
if (count <= config.follow_max) {
out.emit('redirect', headers.location);
// unless 'follow_keep_method' is true, rewrite the request to GET before continuing.
if (!config.follow_keep_method) {
method = 'GET';
post_data = null;
delete config.headers['content-length']; // in case the original was a multipart POST request.
}
// if follow_set_cookies is true, insert cookies in the next request's headers.
// we set both the original request cookies plus any response cookies we might have received.
if (config.follow_set_cookies && utils.host_and_ports_match(headers.location, uri)) {
var request_cookies = cookies.read(config.headers['cookie']);
config.previous_resp_cookies = resp.cookies;
if (Object.keys(request_cookies).length || Object.keys(resp.cookies || {}).length) {
config.headers['cookie'] = cookies.write(extend(request_cookies, resp.cookies));
}
} else if (config.headers['cookie']) {
debug('Clearing original request cookie', config.headers['cookie']);
delete config.headers['cookie'];
}
if (config.follow_set_referer)
config.headers['referer'] = encodeURI(uri); // the original, not the destination URL.
config.headers['host'] = null; // clear previous Host header to avoid conflicts.
var redirect_url = utils.resolve_url(headers.location, uri);
debug('Redirecting to ' + redirect_url.toString());
return self.send_request(++count, method, redirect_url.toString(), config, post_data, out, callback);
} else if (config.follow_max > 0) {
return done(new Error('Max redirects reached. Possible loop in: ' + headers.location));
}
}
// if auth is requested and credentials were not passed, resend request, provided we have user/pass.
if (resp.statusCode == 401 && headers['www-authenticate'] && config.credentials) {
if (!config.headers['authorization']) { // only if authentication hasn't been sent
var auth_header = auth.header(headers['www-authenticate'], config.credentials, request_opts);
if (auth_header) {
config.headers['authorization'] = auth_header;
return self.send_request(count, method, uri, config, post_data, out, callback);
}
}
}
// ok, so we got a valid (non-redirect & authorized) response. let's notify the stream guys.
out.emit('header', resp.statusCode, headers);
out.emit('headers', headers);
var pipeline = [],
mime = utils.parse_content_type(headers['content-type']),
text_response = mime.type && (mime.type.indexOf('text/') != -1 || !!mime.type.match(/(\/|\+)(xml|json)$/));
// To start, if our body is compressed and we're able to inflate it, do it.
if (headers['content-encoding'] && decompressors[headers['content-encoding']]) {
var decompressor = decompressors[headers['content-encoding']]();
// make sure we catch errors triggered by the decompressor.
decompressor.on('error', had_error);
pipeline.push(decompressor);
}
// If parse is enabled and we have a parser for it, then go for it.
if (config.parser && parsers[mime.type]) {
// If a specific parser was requested, make sure we don't parse other types.
var parser_name = config.parser.toString().toLowerCase();
if (['xml', 'json'].indexOf(parser_name) == -1 || parsers[mime.type].name == parser_name) {
// OK, so either we're parsing all content types or the one requested matches.
out.parser = parsers[mime.type].name;
pipeline.push(parsers[mime.type].fn());
// Set objectMode on out stream to improve performance.
out._writableState.objectMode = true;
out._readableState.objectMode = true;
}
// If we're not parsing, and unless decoding was disabled, we'll try
// decoding non UTF-8 bodies to UTF-8, using the iconv-lite library.
} else if (text_response && config.decode_response && mime.charset) {
pipeline.push(decoder(mime.charset));
}
// And `out` is the stream we finally push the decoded/parsed output to.
pipeline.push(out);
// Now, release the kraken!
utils.pump_streams([resp].concat(pipeline), function(err) {
if (err) debug(err)
// on node v8.x, if an error ocurrs on the receiving end,
// then we want to abort the request to avoid having dangling sockets
if (err && err.message == 'write after end') request.destroy();
});
// If the user has requested and output file, pipe the output stream to it.
// In stream mode, we will still get the response stream to play with.
if (config.output && resp.statusCode == 200) {
// for some reason, simply piping resp to the writable stream doesn't
// work all the time (stream gets cut in the middle with no warning).
// so we'll manually need to do the readable/write(chunk) trick.
var file = fs.createWriteStream(config.output);
file.on('error', had_error);
out.on('end', function() {
if (file.writable) file.end();
});
file.on('close', function() {
delete out.file;
})
out.on('readable', function() {
var chunk;
while ((chunk = this.read()) !== null) {
if (file.writable) file.write(chunk);
// if callback was requested, also push it to resp.body
if (resp.body) resp.body.push(chunk);
}
})
out.file = file;
}
// Only aggregate the full body if a callback was requested.
if (callback) {
resp.raw = [];
resp.body = [];
resp.bytes = 0;
// Gather and count the amount of (raw) bytes using a PassThrough stream.
var clean_pipe = new stream.PassThrough();
clean_pipe.on('readable', function() {
var chunk;
while ((chunk = this.read()) != null) {
resp.bytes += chunk.length;
resp.raw.push(chunk);
}
})
utils.pump_streams([resp, clean_pipe], function(err) {
if (err) debug(err);
});
// Listen on the 'readable' event to aggregate the chunks, but only if
// file output wasn't requested. Otherwise we'd have two stream readers.
if (!config.output || resp.statusCode != 200) {
out.on('readable', function() {
var chunk;
while ((chunk = this.read()) !== null) {
// We're either pushing buffers or objects, never strings.
if (typeof chunk == 'string') chunk = Buffer.from(chunk);
// Push all chunks to resp.body. We'll bind them in resp.end().
resp.body.push(chunk);
}
})
}
}
// And set the .body property once all data is in.
out.on('end', function() {
if (resp.body) { // callback mode
// we want to be able to access to the raw data later, so keep a reference.
resp.raw = Buffer.concat(resp.raw);
// if parse was successful, we should have an array with one object
if (resp.body[0] !== undefined && !Buffer.isBuffer(resp.body[0])) {
// that's our body right there.
resp.body = resp.body[0];
// set the parser property on our response. we may want to check.
if (out.parser) resp.parser = out.parser;
} else { // we got one or several buffers. string or binary.
resp.body = Buffer.concat(resp.body);
// if we're here and parsed is true, it means we tried to but it didn't work.
// so given that we got a text response, let's stringify it.
if (text_response || out.parser) {
resp.body = resp.body.toString();
}
}
}
// if an output file is being written to, make sure the callback
// is triggered after all data has been written to it.
if (out.file) {
out.file.on('close', function() {
done(null, resp);
})
} else { // elvis has left the building.
done(null, resp);
}
});
// out.on('error', function(err) {
// had_error(err);
// if (err.code == 'ERR_STREAM_DESTROYED' || err.code == 'ERR_STREAM_PREMATURE_CLOSE') {
// request.abort();
// }
// })
}); // end request call
// unless open_timeout was disabled, set a timeout to abort the request.
set_timeout('open', config.open_timeout);
// handle errors on the request object. things might get bumpy.
request.on('error', had_error);
// make sure timer is cleared if request is aborted (issue #257)
request.once('abort', function() {
if (timer) clearTimeout(timer);
})
// set response timeout once we get a valid socket
request.once('socket', function(socket) {
if (socket.connecting) {
socket.once('connect', function() {
set_timeout('response', config.response_timeout);
})
} else {
set_timeout('response', config.response_timeout);
}
})
if (post_data) {
if (utils.is_stream(post_data)) {
utils.pump_streams([post_data, request], function(err) {
if (err) debug(err);
});
} else {
request.write(post_data, config.encoding);
request.end();
}
} else {
request.end();
}
if (signal) { // abort signal given, so handle it
if (signal.aborted === true) {
abort_handler();
} else {
signal.addEventListener('abort', abort_handler, { once: true });
}
}
out.abort = function() { request.destroy() }; // easier access
out.request = request;
return out;
}
//////////////////////////////////////////
// exports
if (typeof Promise !== 'undefined') {
module.exports = function() {
var verb, args = [].slice.call(arguments);
if (args[0].match(/\.|\//)) // first argument looks like a URL
verb = (args.length > 2) ? 'post' : 'get';
else
verb = args.shift();
if (verb.match(/get|head/i) && args.length == 2)
args.splice(1, 0, null); // assume no data if head/get with two args (url, options)
return new Promise(function(resolve, reject) {
module.exports.request(verb, args[0], args[1], args[2], function(err, resp) {
return err ? reject(err) : resolve(resp);
});
})
}
}
module.exports.version = version;
module.exports.defaults = function(obj) {
for (var key in obj) {
var target_key = aliased.options[key] || key;
if (defaults.hasOwnProperty(target_key) && typeof obj[key] != 'undefined') {
if (target_key != 'parse_response' && target_key != 'proxy' && target_key != 'agent' && target_key != 'signal') {
// ensure type matches the original, except for proxy/parse_response that can be null/bool or string, and signal that can be null/AbortSignal
var valid_type = defaults[target_key].constructor.name;
if (obj[key].constructor.name != valid_type)
throw new TypeError('Invalid type for ' + key + ', should be ' + valid_type);
} else if (target_key === 'signal' && obj[key] !== null && !(obj[key] instanceof AbortSignal)) {
throw new TypeError('Invalid type for ' + key + ', should be AbortSignal');
}
defaults[target_key] = obj[key];
} else {
throw new Error('Invalid property for defaults:' + target_key);
}
}
return defaults;
}
'head get'.split(' ').forEach(function(method) {
module.exports[method] = function(uri, options, callback) {
return new Needle(method, uri, null, options, callback).start();
}
})
'post put patch delete'.split(' ').forEach(function(method) {
module.exports[method] = function(uri, data, options, callback) {
return new Needle(method, uri, data, options, callback).start();
}
})
module.exports.request = function(method, uri, data, opts, callback) {
return new Needle(method, uri, data, opts, callback).start();
};