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stream: fix highWaterMark integer overflow #12593

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stream: fix highWaterMark integer overflow #12593

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stream: fix highWaterMark integer overflow
tniessen May 10, 2017
5e110e1
Use MAX_SAFE_INTEGER instead of 2^31-1
tniessen May 10, 2017
94e6081
Add test description
tniessen May 11, 2017
a15dacd
Use floor instead of trunc
tniessen May 15, 2017
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2 changes: 1 addition & 1 deletion lib/_stream_readable.js
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Original file line number Diff line number Diff line change
Expand Up @@ -72,7 +72,7 @@ function ReadableState(options, stream) {
this.highWaterMark = (hwm || hwm === 0) ? hwm : defaultHwm;

// cast to ints.
this.highWaterMark = ~~this.highWaterMark;
this.highWaterMark = Math.floor(this.highWaterMark);
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Minor nit: This changes the result when passed a negative floating point number.

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@thefourtheye what do you suggest? Can you make an example?
This was just changed at @mscdex suggestion from Math.trunc.

All negative values are interpreted as 0 by the machinery, so nothing should change.

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@mcollina Oh thats okay. This is just a nit. I am just making an observation here.

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It'll be even less of an issue once we start throwing on invalid values.

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@tniessen tniessen May 15, 2017 •
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This is correct, but not an actual problem. According to @mcollina:

Any negative value is interpreted by the stream machinery as a 0

Therefore, it does not matter whether the value is Math.floor(-233.5) = -234 or ~~(-233.5) = -233, not even in the special case of Math.floor(-0.5) = -1 whilst ~~(-0.5) = 0.

We are planning to throw on negative values anyway.

Edit: Sorry, the last three messages were invisible to me until now, I did not know this had already been discussed with @mcollina and @mscdex.


// A linked list is used to store data chunks instead of an array because the
// linked list can remove elements from the beginning faster than
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2 changes: 1 addition & 1 deletion lib/_stream_writable.js
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Expand Up @@ -55,7 +55,7 @@ function WritableState(options, stream) {
this.highWaterMark = (hwm || hwm === 0) ? hwm : defaultHwm;

// cast to ints.
this.highWaterMark = ~~this.highWaterMark;
this.highWaterMark = Math.floor(this.highWaterMark);

// drain event flag.
this.needDrain = false;
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18 changes: 18 additions & 0 deletions test/parallel/test-streams-highwatermark.js
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Original file line number Diff line number Diff line change
@@ -0,0 +1,18 @@
'use strict';
require('../common');

// This test ensures that the stream implementation correctly handles values
// for highWaterMark which exceed the range of signed 32 bit integers.

const assert = require('assert');
const stream = require('stream');

// This number exceeds the range of 32 bit integer arithmetic but should still
// be handled correctly.
const ovfl = Number.MAX_SAFE_INTEGER;

const readable = stream.Readable({ highWaterMark: ovfl });
assert.strictEqual(readable._readableState.highWaterMark, ovfl);

const writable = stream.Writable({ highWaterMark: ovfl });
assert.strictEqual(writable._writableState.highWaterMark, ovfl);