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// Copyright 2017 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.
goog.module('mr.XhrManager');
goog.module.declareLegacyNamespace();
const Assertions = goog.require('mr.Assertions');
const PromiseResolver = goog.require('mr.PromiseResolver');
/**
* Wraps XmlHttpRequest API with additional functionalities such as queueing,
* timeout, and retries.
*/
class XhrManager {
/**
* @param {number} maxRequests The maximum number of concurrent XHR
* requests.
* @param {number} defaultTimeoutMillis The default timeout for each XHR
* request.
* @param {number} defaultNumAttempts The default number of attempts for each
* operation.
*/
constructor(maxRequests, defaultTimeoutMillis, defaultNumAttempts) {
/** @private @const {number} */
this.maxRequests_ = maxRequests;
/** @private @const {number} */
this.defaultTimeoutMillis_ = defaultTimeoutMillis;
/** @private @const {number} */
this.defaultNumAttempts_ = defaultNumAttempts;
/**
* Number of pending requests. Does not exceed this.maxRequests_.
* @private {number}
*/
this.numPendingRequests_ = 0;
/**
* Holds requests that have not yet been executed.
* @private {!Array<!QueueEntry_>}
*/
this.queuedRequests_ = [];
}
/**
* Adds a request with the given parameters.
* @param {string} url
* @param {string} method
* @param {string=} body
* @param {{timeoutMillis: (number|undefined),
* numAttempts: (number|undefined),
* headers: (!Array<!Array<string>>|undefined),
* responseType: (string|undefined)}=} overrides "headers" is an Array
* of pairs of strings. "responseType" is a valid
* XMLHttpRequest.responseType enum value.
* @return {!Promise<!XMLHttpRequest>} Resolves with the response. Rejects if
* the request timed out on all attempts.
*/
send(url, method, body = undefined, {
timeoutMillis = this.defaultTimeoutMillis_,
numAttempts = this.defaultNumAttempts_,
headers = null,
responseType = '',
} = {}) {
const entry = {
resolver: new PromiseResolver(),
url: url,
method: method,
headers: headers,
responseType: responseType,
body: body,
timeoutMillis: timeoutMillis,
numAttemptsLeft: numAttempts
};
if (this.numPendingRequests_ < this.maxRequests_) {
this.startRequest_(entry);
} else {
this.queuedRequests_.push(entry);
}
return entry.resolver.promise;
}
/**
* Starts a request from the request queue if there is room for an additional
* pending request.
* @private
*/
startNextRequestFromQueue_() {
if (this.queuedRequests_.length > 0 &&
this.numPendingRequests_ < this.maxRequests_) {
const request = this.queuedRequests_.shift();
this.startRequest_(request);
}
}
/**
* Attempts the given request once. If successful, resolves the
* PromiseResolver with the result. Otherwise, requeues the request for retry,
* or rejects the PromiseResolver if it ran out of attempts. Also processes a
* queued request, if any, at the end.
* @param {!QueueEntry_} request
* @private
*/
startRequest_(request) {
this.numPendingRequests_++;
Assertions.assert(
request.numAttemptsLeft > 0, 'request.numAttemptsLeft > 0');
request.numAttemptsLeft--;
const cleanUpAndStartNextRequest = () => {
this.numPendingRequests_--;
this.startNextRequestFromQueue_();
};
this.sendOneAttempt_(request).then(
response => {
request.resolver.resolve(response);
cleanUpAndStartNextRequest();
},
e => {
if (request.numAttemptsLeft == 0) {
request.resolver.reject(e);
} else {
// Try it again later by re-adding the request to back of queue.
this.queuedRequests_.push(request);
}
cleanUpAndStartNextRequest();
});
}
/**
* Executes a XMLHttpRequest and returns a Promise that resolves with the
* response, or rejects if the request times out.
* @param {!QueueEntry_} request
* @return {!Promise<!XMLHttpRequest>} Resolves with the response. Rejects if
* the request timed out.
* @private
*/
sendOneAttempt_(request) {
return new Promise((resolve, reject) => {
const xhr = new XMLHttpRequest();
xhr.onreadystatechange = () => {
if (xhr.readyState == XMLHttpRequest.DONE) {
resolve(xhr);
}
};
xhr.timeout = request.timeoutMillis;
xhr.ontimeout = () => {
reject(new Error('Timed out'));
};
xhr.open(request.method, request.url, true);
if (request.headers == null) {
xhr.setRequestHeader(
'Content-Type', 'application/x-www-form-urlencoded;charset=utf-8');
} else {
request.headers.forEach(
header => xhr.setRequestHeader(header[0], header[1]));
}
xhr.responseType = request.responseType;
xhr.send(request.body);
});
}
}
/** @private @record */
const QueueEntry_ = class {};
/** @type {!PromiseResolver<!XMLHttpRequest>} */
QueueEntry_.prototype.resolver;
/** @type {string} */
QueueEntry_.prototype.url;
/** @type {string} */
QueueEntry_.prototype.method;
/** @type {?Array<!Array<string>>} */
QueueEntry_.prototype.headers;
/** @type {string} */
QueueEntry_.prototype.responseType;
/** @type {string|undefined} */
QueueEntry_.prototype.body;
/** @type {number} */
QueueEntry_.prototype.timeoutMillis;
/** @type {number} */
QueueEntry_.prototype.numAttemptsLeft;
exports = XhrManager;
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