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