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ronag committed Nov 17, 2021
1 parent 5023aa1 commit da16246
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Showing 2 changed files with 122 additions and 22 deletions.
114 changes: 107 additions & 7 deletions lib/internal/streams/operators.js
Original file line number Diff line number Diff line change
@@ -1,15 +1,115 @@
'use strict';

const console = require('console');
const { AbortController } = require('internal/abort_controller');
const { AbortError } = require('internal/errors');
const compose = require('internal/streams/compose');
const Readable = require('internal/streams/readable');
const eos = require('internal/streams/end-of-stream');

module.exports.map = function map(stream, fn) {
return compose(stream, async function* (source, { signal }) {
for await (const item of source) {
if (signal.aborted) {
throw new AbortError('The iteration has been interrupted');
module.exports.map = function map(stream, fn, options) {
// TODO: Argument validation

let concurrency = 1;
if (Number.isFinite(options)) {
concurrency = options;
} else if (options && Number.isFinite(options.concurrency)) {
concurrency = options.concurrency;
}

let highWaterMark = 1;
if (options && Number.isFinite(options.highWaterMark)) {
highWaterMark = options.highWaterMark;
}
highWaterMark = Math.max(0, highWaterMark - concurrency)

let objectMode = stream.readableObjectMode ?? stream.objectMode ?? true;
if (options && typeof options.objectMode === 'boolean') {
objectMode = options.objectMode;
}

const ac = new AbortController();
const signal = ac.signal;
const queue = [];

let reading = false;

const ret = new Readable({
objectMode,
highWaterMark,
read () {
read();
},
destroy (err, callback) {
if (!err && !this.readableEnded) {
err = new AbortError();
}
yield await fn(item, { signal });
ac.abort();
callback(err);
}
});

async function read () {
if (reading) {
return;
}

if (ret.readableLength && ret.readableLength >= ret.readableHighWaterMark) {
return;
}

try {
reading = true;
while (queue.length && !ret.destroyed) {
const [err, val] = await queue.shift();
if (err) {
ret.destroy(err);
} else if (!ret.push(val)) {
break;
} else {
pump();
}
}
reading = false;
} catch (err) {
ret.destroy(err);
}
}

async function wrap (val) {
try {
return [null, await fn(val, { signal })];
} catch (err) {
return [err, null];
}
}

function enqueue(val) {
queue.push(val);
read();
}

function pump () {
while (true) {
const val = stream.read();
if (val === null) {
return;
}

enqueue(wrap(val));

if (queue.length === concurrency) {
return;
}
}
}

eos(stream, (err) => {
enqueue([err, null]);
});

process.nextTick(pump);

stream.on('readable', pump);

return ret;
};
30 changes: 15 additions & 15 deletions test/parallel/test-stream-map.js
Original file line number Diff line number Diff line change
Expand Up @@ -36,26 +36,26 @@ const { setTimeout } = require('timers/promises');
// Map works on asynchronous streams with a asynchronous mapper
const stream = Readable.from([1, 2, 3, 4, 5]).map(async (x) => {
return x + x;
}).map((x) => x * x);
}).map((x) => x + x);
const result = [4, 8, 12, 16, 20];
(async () => {
for await (const item of stream) {
assert.strictEqual(item, result.shift());
assert.strictEqual(item, result.shift());
}
})().then(common.mustCall());
}

{
// Allow cancellation of iteration through an AbortSignal
// {
// // Allow cancellation of iteration through an AbortSignal

const stream = Readable.from([1, 2, 3, 4, 5]).map(async (x, { signal }) => {
return setTimeout(1e15, { signal });
});
(async () => {
const iterator = stream[Symbol.asyncIterator]();
iterator.next();
iterator.return();
})().catch(common.mustCall((err) => {
assert.equals(err.name, 'AbortError');
}));
}
// const stream = Readable.from([1, 2, 3, 4, 5]).map(async (x, { signal }) => {
// return setTimeout(1e5, { signal });
// });
// (async () => {
// const iterator = stream[Symbol.asyncIterator]();
// iterator.next();
// await iterator.return();
// })().catch(common.mustCall((err) => {
// assert.strictEqual(err.name, 'AbortError');
// }));
// }

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