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fs: nullish coalescing to respect zero positional reads
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When the file read position is moved passing zero is
not respected and `null` is used instead. PR fixes the
issues by using nullish coalescing which will return
the rhs only when the lhs is `null` or `undefined`;
respecting the zero.

Fixes: #40715

PR-URL: #40716
Fixes: #40699
Reviewed-By: Robert Nagy <ronagy@icloud.com>
Reviewed-By: Luigi Pinca <luigipinca@gmail.com>
Reviewed-By: Ruben Bridgewater <ruben@bridgewater.de>
Reviewed-By: Tobias Nießen <tniessen@tnie.de>
Reviewed-By: Evan Lucas <evanlucas@me.com>
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mihilmy authored and danielleadams committed Feb 1, 2022
1 parent 86bbb42 commit 0377edc
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Showing 2 changed files with 21 additions and 1 deletion.
2 changes: 1 addition & 1 deletion lib/internal/fs/promises.js
Original file line number Diff line number Diff line change
Expand Up @@ -469,7 +469,7 @@ async function read(handle, bufferOrOptions, offset, length, position) {
}
offset = bufferOrOptions.offset || 0;
length = buffer.byteLength;
position = bufferOrOptions.position || null;
position = bufferOrOptions.position ?? null;
}

if (offset == null) {
Expand Down
20 changes: 20 additions & 0 deletions test/parallel/test-fs-promises-file-handle-read.js
Original file line number Diff line number Diff line change
Expand Up @@ -68,6 +68,25 @@ async function validateReadNoParams() {
await fileHandle.read();
}

// Validates that the zero position is respected after the position has been
// moved. The test iterates over the xyz chars twice making sure that the values
// are read from the correct position.
async function validateReadWithPositionZero() {
const opts = { useConf: true };
const filePath = fixtures.path('x.txt');
const fileHandle = await open(filePath, 'r');
const expectedSequence = ['x', 'y', 'z'];

for (let i = 0; i < expectedSequence.length * 2; i++) {
const len = 1;
const pos = i % 3;
const buf = Buffer.alloc(len);
const { bytesRead } = await read(fileHandle, buf, 0, len, pos, opts);
assert.strictEqual(bytesRead, len);
assert.strictEqual(buf.toString(), expectedSequence[pos]);
}
}


(async function() {
tmpdir.refresh();
Expand All @@ -78,4 +97,5 @@ async function validateReadNoParams() {
await validateLargeRead({ useConf: false });
await validateLargeRead({ useConf: true });
await validateReadNoParams();
await validateReadWithPositionZero();
})().then(common.mustCall());

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