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
178
179
180
181
182
183
184
185
186
187
188
189
190
191
192
193
194
195
196
197
198
199
200
201
202
|
'use strict';
const {
ObjectCreate,
ObjectGetPrototypeOf,
ObjectSetPrototypeOf,
Symbol,
} = primordials;
const finished = require('internal/streams/end-of-stream');
const kLastResolve = Symbol('lastResolve');
const kLastReject = Symbol('lastReject');
const kError = Symbol('error');
const kEnded = Symbol('ended');
const kLastPromise = Symbol('lastPromise');
const kHandlePromise = Symbol('handlePromise');
const kStream = Symbol('stream');
function createIterResult(value, done) {
return { value, done };
}
function readAndResolve(iter) {
const resolve = iter[kLastResolve];
if (resolve !== null) {
const data = iter[kStream].read();
// We defer if data is null. We can be expecting either 'end' or 'error'.
if (data !== null) {
iter[kLastPromise] = null;
iter[kLastResolve] = null;
iter[kLastReject] = null;
resolve(createIterResult(data, false));
}
}
}
function onReadable(iter) {
// We wait for the next tick, because it might
// emit an error with `process.nextTick()`.
process.nextTick(readAndResolve, iter);
}
function wrapForNext(lastPromise, iter) {
return (resolve, reject) => {
lastPromise.then(() => {
if (iter[kEnded]) {
resolve(createIterResult(undefined, true));
return;
}
iter[kHandlePromise](resolve, reject);
}, reject);
};
}
const AsyncIteratorPrototype = ObjectGetPrototypeOf(
ObjectGetPrototypeOf(async function* () {}).prototype);
const ReadableStreamAsyncIteratorPrototype = ObjectSetPrototypeOf({
get stream() {
return this[kStream];
},
next() {
// If we have detected an error in the meanwhile
// reject straight away.
const error = this[kError];
if (error !== null) {
return Promise.reject(error);
}
if (this[kEnded]) {
return Promise.resolve(createIterResult(undefined, true));
}
if (this[kStream].destroyed) {
// We need to defer via nextTick because if .destroy(err) is
// called, the error will be emitted via nextTick, and
// we cannot guarantee that there is no error lingering around
// waiting to be emitted.
return new Promise((resolve, reject) => {
process.nextTick(() => {
if (this[kError]) {
reject(this[kError]);
} else {
resolve(createIterResult(undefined, true));
}
});
});
}
// If we have multiple next() calls we will wait for the previous Promise to
// finish. This logic is optimized to support for await loops, where next()
// is only called once at a time.
const lastPromise = this[kLastPromise];
let promise;
if (lastPromise) {
promise = new Promise(wrapForNext(lastPromise, this));
} else {
// Fast path needed to support multiple this.push()
// without triggering the next() queue.
const data = this[kStream].read();
if (data !== null) {
return Promise.resolve(createIterResult(data, false));
}
promise = new Promise(this[kHandlePromise]);
}
this[kLastPromise] = promise;
return promise;
},
return() {
return new Promise((resolve, reject) => {
const stream = this[kStream];
// TODO(ronag): Remove this check once finished() handles
// already ended and/or destroyed streams.
const ended = stream.destroyed || stream.readableEnded ||
(stream._readableState && stream._readableState.endEmitted);
if (ended) {
resolve(createIterResult(undefined, true));
return;
}
finished(stream, (err) => {
if (err && err.code !== 'ERR_STREAM_PREMATURE_CLOSE') {
reject(err);
} else {
resolve(createIterResult(undefined, true));
}
});
stream.destroy();
});
},
}, AsyncIteratorPrototype);
const createReadableStreamAsyncIterator = (stream) => {
const iterator = ObjectCreate(ReadableStreamAsyncIteratorPrototype, {
[kStream]: { value: stream, writable: true },
[kLastResolve]: { value: null, writable: true },
[kLastReject]: { value: null, writable: true },
[kError]: { value: null, writable: true },
[kEnded]: {
value: stream.readableEnded || stream._readableState.endEmitted,
writable: true
},
// The function passed to new Promise is cached so we avoid allocating a new
// closure at every run.
[kHandlePromise]: {
value: (resolve, reject) => {
const data = iterator[kStream].read();
if (data) {
iterator[kLastPromise] = null;
iterator[kLastResolve] = null;
iterator[kLastReject] = null;
resolve(createIterResult(data, false));
} else {
iterator[kLastResolve] = resolve;
iterator[kLastReject] = reject;
}
},
writable: true,
},
});
iterator[kLastPromise] = null;
finished(stream, { writable: false }, (err) => {
if (err && err.code !== 'ERR_STREAM_PREMATURE_CLOSE') {
const reject = iterator[kLastReject];
// Reject if we are waiting for data in the Promise returned by next() and
// store the error.
if (reject !== null) {
iterator[kLastPromise] = null;
iterator[kLastResolve] = null;
iterator[kLastReject] = null;
reject(err);
}
iterator[kError] = err;
return;
}
const resolve = iterator[kLastResolve];
if (resolve !== null) {
iterator[kLastPromise] = null;
iterator[kLastResolve] = null;
iterator[kLastReject] = null;
resolve(createIterResult(undefined, true));
}
iterator[kEnded] = true;
});
stream.on('readable', onReadable.bind(null, iterator));
return iterator;
};
module.exports = createReadableStreamAsyncIterator;
|
