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fs.read into zero buffer should not throw exception #4518

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fs.read into zero buffer should not throw exception #4518

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14 changes: 14 additions & 0 deletions lib/fs.js
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Original file line number Diff line number Diff line change
Expand Up @@ -609,6 +609,12 @@ fs.read = function(fd, buffer, offset, length, position, callback) {
};
}

if (length === 0) {
return process.nextTick(function() {
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Hmmm, this is not right. There is actually a deprecated fs.read form which returns string.

So,

  1. This will actually return a buffer and the deprecated fs.read will collapse.
  2. The order of parameters to the callback, in string form, is actually string and the bytesRead.

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Actually, this calls the redefined callback function (that starts on line 600), so the right arguments should be passed to the callback function, namely: null, '', and 0.

Unless I'm missing something.

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You comment prompted me to check the fs.readSync case and the issue you describe exists there. I'll fix it and add a test.

callback && callback(null, 0, buffer);
});
}

function wrapper(err, bytesRead) {
// Retain a reference to buffer so that it can't be GC'ed too soon.
callback && callback(err, bytesRead || 0, buffer);
Expand Down Expand Up @@ -648,6 +654,14 @@ fs.readSync = function(fd, buffer, offset, length, position) {
offset = 0;
}

if (length === 0) {
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The check here means that even if the file doesn't exist/inaccessible, if the length is zero, we will return valid values.

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How do you propose to solve this? @bnoordhuis asked me to move the checks to lib/fs.js to avoid some kernel edge case.

Thoughts?

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@thefourtheye Since the fd itself is passed best we can attempt to do is read directly from it. But as @feross mentioned, there are cross platform issues that prevents this being done correctly. I don't think that assuming the fd is alright is a problem in this case.

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@trevnorris Ah, you are right. I totally missed that. Then this will not be a problem here.

if (legacy) {
return ['', 0];
} else {
return 0;
}
}

var r = binding.read(fd, buffer, offset, length, position);
if (!legacy) {
return r;
Expand Down
19 changes: 19 additions & 0 deletions test/parallel/test-fs-read-buffer-zero-length.js
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@@ -0,0 +1,19 @@
'use strict';
const common = require('../common');
const assert = require('assert');
const path = require('path');
const Buffer = require('buffer').Buffer;
const fs = require('fs');
const filepath = path.join(common.fixturesDir, 'x.txt');
const fd = fs.openSync(filepath, 'r');
const bufferAsync = new Buffer(0);
const bufferSync = new Buffer(0);

fs.read(fd, bufferAsync, 0, 0, 0, common.mustCall(function(err, bytesRead) {
assert.equal(bytesRead, 0);
assert.deepEqual(bufferAsync, new Buffer(0));
}));

const r = fs.readSync(fd, bufferSync, 0, 0, 0);
assert.deepEqual(bufferSync, new Buffer(0));
assert.equal(r, 0);
18 changes: 18 additions & 0 deletions test/parallel/test-fs-read-zero-length.js
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Original file line number Diff line number Diff line change
@@ -0,0 +1,18 @@
'use strict';
const common = require('../common');
const assert = require('assert');
const path = require('path');
const fs = require('fs');
const filepath = path.join(common.fixturesDir, 'x.txt');
const fd = fs.openSync(filepath, 'r');
const expected = '';

fs.read(fd, 0, 0, 'utf-8', common.mustCall(function(err, str, bytesRead) {
assert.ok(!err);
assert.equal(str, expected);
assert.equal(bytesRead, 0);
}));

const r = fs.readSync(fd, 0, 0, 'utf-8');
assert.equal(r[0], expected);
assert.equal(r[1], 0);