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stream: improve Readable.from error handling #37158

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stream: improve Readable.from error handling #37158

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stream: improve Readable.from error handling
benjamingr Jan 31, 2021
0f9324a
fixup! lint
benjamingr Jan 31, 2021
11fe4f2
fixup! comment
benjamingr Jan 31, 2021
0bce498
fixup! code review
benjamingr Feb 1, 2021
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33 changes: 15 additions & 18 deletions lib/internal/streams/from.js
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Original file line number Diff line number Diff line change
Expand Up @@ -43,9 +43,6 @@ function from(Readable, iterable, opts) {
// being called before last iteration completion.
let reading = false;

// Flag for when iterator needs to be explicitly closed.
let needToClose = false;

readable._read = function() {
if (!reading) {
reading = true;
Expand All @@ -54,19 +51,23 @@ function from(Readable, iterable, opts) {
};

readable._destroy = function(error, cb) {
if (needToClose) {
needToClose = false;
PromisePrototypeThen(
close(),
() => process.nextTick(cb, error),
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(e) => process.nextTick(cb, error || e),
);
} else {
cb(error);
}
PromisePrototypeThen(
close(error),
() => process.nextTick(cb, error), // nextTick is here in case cb throws
(e) => process.nextTick(cb, e || error),
);
};

async function close() {
async function close(error) {
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This is tricky and I want feedback on the semantics, basically:

  • If we had an error ( .destroy(err) ) we call .throw - this aligns the behaviour of .from with other methods and means stuff like addAbortSignal automagically "works".
  • If after calling throw the iterator did not finish - we also call .return

const hadError = (error !== undefined) && (error !== null);
const hasThrow = typeof iterator.throw === 'function';
if (hadError && hasThrow) {
const { value, done } = await iterator.throw(error);
await value;
if (done) {
return;
}
}
if (typeof iterator.return === 'function') {
const { value } = await iterator.return();
await value;
Expand All @@ -75,13 +76,9 @@ function from(Readable, iterable, opts) {

async function next() {
try {
needToClose = false;
const { value, done } = await iterator.next();
needToClose = !done;
if (done) {
readable.push(null);
} else if (readable.destroyed) {
await close();
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This check is no longer necessary without needToClose since _destroy is called and if the stream is destroyed the iterator is closed.

} else {
const res = await value;
if (res === null) {
Expand Down
23 changes: 22 additions & 1 deletion test/parallel/test-readable-from.js
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Original file line number Diff line number Diff line change
Expand Up @@ -4,6 +4,7 @@ const { mustCall } = require('../common');
const { once } = require('events');
const { Readable } = require('stream');
const { strictEqual, throws } = require('assert');
const common = require('../common');

{
throws(() => {
Expand Down Expand Up @@ -187,6 +188,25 @@ async function endWithError() {
}
}

async function destroyingStreamWithErrorThrowsInGenerator() {
const validateError = common.mustCall((e) => {
strictEqual(e, 'Boum');
});
async function* generate() {
try {
yield 1;
yield 2;
yield 3;
throw new Error();
} catch (e) {
validateError(e);
}
}
const stream = Readable.from(generate());
stream.read();
stream.once('error', common.mustCall());
stream.destroy('Boum');
}

Promise.all([
toReadableBasicSupport(),
Expand All @@ -198,5 +218,6 @@ Promise.all([
toReadableOnDataNonObject(),
destroysTheStreamWhenThrowing(),
asTransformStream(),
endWithError()
endWithError(),
destroyingStreamWithErrorThrowsInGenerator(),
]).then(mustCall());