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// Copyright 2018-2019 the Deno authors. All rights reserved. MIT license.
// TODO(ry) It'd be better to make Deferred a class that inherits from
// Promise, rather than an interface. This is possible in ES2016, however
// typescript produces broken code when targeting ES5 code.
// See https://github.com/Microsoft/TypeScript/issues/15202
// At the time of writing, the github issue is closed but the problem remains.
export interface Deferred<T> extends Promise<T> {
resolve: (value?: T | PromiseLike<T>) => void;
// eslint-disable-next-line @typescript-eslint/no-explicit-any
reject: (reason?: any) => void;
}
/** Creates a Promise with the `reject` and `resolve` functions
* placed as methods on the promise object itself. It allows you to do:
*
* const p = deferred<number>();
* // ...
* p.resolve(42);
*/
export function deferred<T>(): Deferred<T> {
let methods;
const promise = new Promise<T>((resolve, reject): void => {
methods = { resolve, reject };
});
return Object.assign(promise, methods)! as Deferred<T>;
}
interface TaggedYieldedValue<T> {
iterator: AsyncIterableIterator<T>;
value: T;
}
/** The MuxAsyncIterator class multiplexes multiple async iterators into a
* single stream. It currently makes a few assumptions:
* - The iterators do not throw.
* - The final result (the value returned and not yielded from the iterator)
* does not matter; if there is any, it is discarded.
*/
export class MuxAsyncIterator<T> implements AsyncIterable<T> {
private iteratorCount = 0;
private yields: Array<TaggedYieldedValue<T>> = [];
private signal: Deferred<void> = deferred();
add(iterator: AsyncIterableIterator<T>): void {
++this.iteratorCount;
this.callIteratorNext(iterator);
}
private async callIteratorNext(
iterator: AsyncIterableIterator<T>
): Promise<void> {
const { value, done } = await iterator.next();
if (done) {
--this.iteratorCount;
} else {
this.yields.push({ iterator, value });
}
this.signal.resolve();
}
async *iterate(): AsyncIterableIterator<T> {
while (this.iteratorCount > 0) {
// Sleep until any of the wrapped iterators yields.
await this.signal;
// Note that while we're looping over `yields`, new items may be added.
for (let i = 0; i < this.yields.length; i++) {
const { iterator, value } = this.yields[i];
yield value;
this.callIteratorNext(iterator);
}
// Clear the `yields` list and reset the `signal` promise.
this.yields.length = 0;
this.signal = deferred();
}
}
[Symbol.asyncIterator](): AsyncIterableIterator<T> {
return this.iterate();
}
}
/** Collects all Uint8Arrays from an AsyncIterable and retuns a single
* Uint8Array with the concatenated contents of all the collected arrays.
*/
export async function collectUint8Arrays(
it: AsyncIterable<Uint8Array>
): Promise<Uint8Array> {
const chunks = [];
let length = 0;
for await (const chunk of it) {
chunks.push(chunk);
length += chunk.length;
}
if (chunks.length === 1) {
// No need to copy.
return chunks[0];
}
const collected = new Uint8Array(length);
let offset = 0;
for (const chunk of chunks) {
collected.set(chunk, offset);
offset += chunk.length;
}
return collected;
}
// Delays the given milliseconds and resolves.
export function delay(ms: number): Promise<void> {
return new Promise((res): number =>
setTimeout((): void => {
res();
}, ms)
);
}
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