1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
176
177
|
/* Copyright 2015 The TensorFlow Authors. All Rights Reserved.
Licensed under the Apache License, Version 2.0 (the 'License');
you may not use this file except in compliance with the License.
You may obtain a copy of the License at
http://www.apache.org/licenses/LICENSE-2.0
Unless required by applicable law or agreed to in writing, software
distributed under the License is distributed on an 'AS IS' BASIS,
WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
See the License for the specific language governing permissions and
limitations under the License.
==============================================================================*/
interface ResolveReject {
resolve: Function;
reject: Function;
}
/**
* Manages many fetch requests. Launches up to nSimultaneousRequests
* simultaneously, and maintains a LIFO queue of requests to process when
* more urls are requested than can be handled at once. The queue can be
* cleared.
*
* When a request is made, a Promise is returned which resolves with the
* parsed JSON result from the request.
*/
export class RequestCancellationError extends Error {
public name = 'RequestCancellationError';
}
export class RequestNetworkError extends Error {
public name: string;
public req: XMLHttpRequest;
public url: string;
constructor(req: XMLHttpRequest, url) {
super();
this.message = `RequestNetworkError: ${req.status} at ${url}`;
this.name = 'RequestNetworkError';
this.req = req;
this.url = url;
}
}
export class RequestManager {
private _queue: ResolveReject[];
private _maxRetries: number;
private _nActiveRequests: number;
private _nSimultaneousRequests: number;
constructor(nSimultaneousRequests = 10, maxRetries = 3) {
this._queue = [];
this._nActiveRequests = 0;
this._nSimultaneousRequests = nSimultaneousRequests;
this._maxRetries = maxRetries;
}
/**
* Gives a promise that loads assets from given url (respects queuing). If
* postData is provided, this request will use POST, not GET. This is an
* object mapping POST keys to string values.
*/
public request(url: string, postData?: {[key: string]: string}):
Promise<any> {
const promise =
new Promise((resolve, reject) => {
const resolver = {resolve: resolve, reject: reject};
this._queue.push(resolver);
this.launchRequests();
})
.then(() => {
return this.promiseWithRetries(url, this._maxRetries, postData);
})
.then(
(response) => {
// Success - Let's free space for another active
// reqest, and launch it
this._nActiveRequests--;
this.launchRequests();
return response;
},
(rejection) => {
if (rejection.name === 'RequestNetworkError') {
// If we failed due to network error, we should
// decrement
// _nActiveRequests because this request was
// active
this._nActiveRequests--;
this.launchRequests();
}
return Promise.reject(rejection);
});
return promise;
}
public clearQueue() {
while (this._queue.length > 0) {
this._queue.pop().reject(
new RequestCancellationError('Request cancelled by clearQueue'));
}
}
/* Return number of currently pending requests */
public activeRequests(): number {
return this._nActiveRequests;
}
/* Return total number of outstanding requests (includes queue) */
public outstandingRequests(): number {
return this._nActiveRequests + this._queue.length;
}
private launchRequests() {
while (this._nActiveRequests < this._nSimultaneousRequests &&
this._queue.length > 0) {
this._nActiveRequests++;
this._queue.pop().resolve();
}
}
/**
* Try to request a given URL using overwritable _promiseFromUrl method.
* If the request fails for any reason, we will retry up to maxRetries
* times. In practice, this will help us paper over transient network issues
* like '502 Bad Gateway'.
* By default, Chrome displays network errors in console, so
* the user will be able to tell when the requests are failing. I think this
* is a feature, if the request failures and retries are causing any
* pain to users, they can see it and file issues.
*/
private promiseWithRetries(
url: string, maxRetries: number, postData?: {[key: string]: string}) {
var success = (x) => x;
var failure = (x) => {
if (maxRetries > 0) {
return this.promiseWithRetries(url, maxRetries - 1, postData);
} else {
return Promise.reject(x);
}
};
return this._promiseFromUrl(url, postData).then(success, failure);
}
/* Actually get promise from url using XMLHttpRequest */
protected _promiseFromUrl(url: string, postData?: {[key: string]: string}) {
return new Promise((resolve, reject) => {
let req = new XMLHttpRequest();
req.open(postData ? 'POST' : 'GET', url);
let formData;
if (postData) {
// We are to make a POST request.
formData = new FormData();
for (let postKey in postData) {
if (postKey) {
// The linter requires 'for in' loops to be filtered by an if
// condition.
formData.append(postKey, postData[postKey]);
}
}
}
req.onload = function() {
if (req.status === 200) {
resolve(JSON.parse(req.responseText));
} else {
reject(new RequestNetworkError(req, url));
}
};
req.onerror = function() {
reject(new RequestNetworkError(req, url));
};
req.send(formData);
});
}
}
|
