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fs: add support for async iterators to fs.writeFile #38525

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785d76d
fs: add support for async iterators to `fs.writeFile`
May 3, 2021
6f21783
fixup! fs: add support for async iterators to fs.writeFile
May 9, 2021
c0b87d6
fixup! fixup! fs: add support for async iterators to `fs.writeFile`
May 14, 2021
05a5728
fixup! fixup! fixup! fs: add support for async iterators to `fs.write…
May 17, 2021
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fixup! fs: add support for async iterators to fs.writeFile 
Fixes: #38075
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HiroyukiYagihashi committed May 9, 2021
commit 6f2178394d18b2521b927aa52560174750dcee67
34 changes: 19 additions & 15 deletions lib/fs.js
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Original file line number Diff line number Diff line change
Expand Up @@ -2045,21 +2045,16 @@ function lutimesSync(path, atime, mtime) {
function writeAll(
fd, isUserFd, buffer, offset, length, signal, encoding, callback) {
if (signal?.aborted) {
const abortError = new AbortError();
if (isUserFd) {
callback(abortError);
} else {
fs.close(fd, (err) => {
callback(aggregateTwoErrors(err, abortError));
});
}
handleWriteAllErrorCallback(fd, isUserFd, new AbortError(), callback);
return;
}

if (isCustomIterable(buffer)) {
writeAllCustomIterable(
fd, isUserFd, buffer, offset, length, signal, encoding, callback)
.catch((reason) => { throw reason; });
.catch((reason) => {
handleWriteAllErrorCallback(fd, isUserFd, reason, callback);
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@mcollina mcollina May 24, 2021

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I would schedule this via process.nextTick. If this throws synchronously for whatever reason, it will lead to an unhandled rejection.

});
return;
}
fs.write(fd, buffer, offset, length, null, (writeErr, written) => {
Expand All @@ -2082,20 +2077,29 @@ function writeAll(

async function writeAllCustomIterable(
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@mcollina mcollina May 24, 2021

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Do not use async with a callback. Mixing those two can only lead to bugs. I would recommend having a promisified version of fs.write() and just use async/await.

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@Mifrill Mifrill Nov 20, 2023

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@mcollina Thanks for your suggestion 👍 . I'm curious about the advantages of having a promisified version of fs.write() and using async/await. Could you elaborate on why this approach might be better than mixing async with a callback? I'm interested in understanding the potential benefits and how it could prevent bugs.

fd, isUserFd, buffer, offset, length, signal, encoding, callback) {
if (signal?.aborted) {
handleWriteAllErrorCallback(fd, isUserFd, new AbortError(), callback);
return;
}

const result = await buffer.next();
if (result.done) {
fs.close(fd, callback);
if (isUserFd) {
callback(null);
} else {
fs.close(fd, callback);
}
return;
}
const resultValue = result.value.toString();
fs.write(fd, resultValue, undefined,
isArrayBufferView(buffer) ? resultValue.byteLength : encoding,
const resultValue = isArrayBufferView(result.value) ?
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result.value : Buffer.from(String(result.value), encoding);
fs.write(fd, resultValue, offset, resultValue.byteLength,
null, (writeErr, _) => {
if (writeErr) {
handleWriteAllErrorCallback(fd, isUserFd, writeErr, callback);
} else {
writeAll(fd, isUserFd, buffer, offset,
length, signal, encoding, callback);
writeAllCustomIterable(fd, isUserFd, buffer, offset, length,
signal, encoding, callback);
}
}
);
Expand Down
64 changes: 64 additions & 0 deletions test/parallel/test-fs-write-file-async-iterators.js
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Expand Up @@ -44,6 +44,26 @@ tmpdir.refresh();
);
}

{
const filenameBufferIterableWithEncoding =
join(tmpdir.path, 'testBufferIterableWithEncoding.txt');
const bufferIterableWithEncoding = {
expected: 'ümlaut sechzig',
*[Symbol.iterator]() {
yield Buffer.from('ümlaut');
yield Buffer.from(' ');
yield Buffer.from('sechzig');
}
};

fs.writeFile(
filenameBufferIterableWithEncoding,
bufferIterableWithEncoding, common.mustSucceed(() => {
const data = fs.readFileSync(filenameBufferIterableWithEncoding, 'utf-8');
assert.strictEqual(bufferIterableWithEncoding.expected, data);
})
);
}

{
const filenameAsyncIterable = join(tmpdir.path, 'testAsyncIterable.txt');
Expand Down Expand Up @@ -86,3 +106,47 @@ tmpdir.refresh();
})
);
}

{
const controller = new AbortController();
const signal = controller.signal;
const filenameIterableAbort = join(tmpdir.path, 'testIterableAbort.txt');
const iterable = {
expected: 'abc',
*[Symbol.iterator]() {
yield 'a';
yield 'b';
yield 'c';
}
};


fs.writeFile(filenameIterableAbort,
iterable, { signal }, common.mustCall((err) => {
assert.strictEqual(err.name, 'AbortError');
}));

controller.abort();
}

{
const controller = new AbortController();
const signal = controller.signal;
const filenameAsyncIterableAbort =
join(tmpdir.path, 'testAsyncIterableAbort.txt');
const asyncIterable = {
expected: 'abc',
*[Symbol.asyncIterator]() {
yield 'a';
yield 'b';
yield 'c';
}
};

fs.writeFile(filenameAsyncIterableAbort,
asyncIterable, { signal }, common.mustCall((err) => {
assert.strictEqual(err.name, 'AbortError');
}));

process.nextTick(() => controller.abort());
}