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zlib: fix interaction of flushing and needDrain #14527

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38 changes: 31 additions & 7 deletions lib/zlib.js
Original file line number Diff line number Diff line change
Expand Up @@ -32,11 +32,11 @@ const kRangeErrorMessage = 'Cannot create final Buffer. It would be larger ' +

const constants = process.binding('constants').zlib;
const {
Z_NO_FLUSH, Z_BLOCK, Z_SYNC_FLUSH, Z_FULL_FLUSH, Z_FINISH, Z_MIN_CHUNK,
Z_MIN_WINDOWBITS, Z_MAX_WINDOWBITS, Z_MIN_LEVEL, Z_MAX_LEVEL, Z_MIN_MEMLEVEL,
Z_MAX_MEMLEVEL, Z_DEFAULT_CHUNK, Z_DEFAULT_COMPRESSION, Z_DEFAULT_STRATEGY,
Z_DEFAULT_WINDOWBITS, Z_DEFAULT_MEMLEVEL, Z_FIXED, DEFLATE, DEFLATERAW,
INFLATE, INFLATERAW, GZIP, GUNZIP, UNZIP
Z_NO_FLUSH, Z_BLOCK, Z_PARTIAL_FLUSH, Z_SYNC_FLUSH, Z_FULL_FLUSH, Z_FINISH,
Z_MIN_CHUNK, Z_MIN_WINDOWBITS, Z_MAX_WINDOWBITS, Z_MIN_LEVEL, Z_MAX_LEVEL,
Z_MIN_MEMLEVEL, Z_MAX_MEMLEVEL, Z_DEFAULT_CHUNK, Z_DEFAULT_COMPRESSION,
Z_DEFAULT_STRATEGY, Z_DEFAULT_WINDOWBITS, Z_DEFAULT_MEMLEVEL, Z_FIXED,
DEFLATE, DEFLATERAW, INFLATE, INFLATERAW, GZIP, GUNZIP, UNZIP
} = constants;
const { inherits } = require('util');

Expand Down Expand Up @@ -254,6 +254,7 @@ function Zlib(opts, mode) {
this._strategy = strategy;
this._chunkSize = chunkSize;
this._flushFlag = flush;
this._scheduledFlushFlag = Z_NO_FLUSH;
this._origFlushFlag = flush;
this._finishFlushFlag = finishFlush;
this._info = opts && opts.info;
Expand Down Expand Up @@ -299,6 +300,22 @@ Zlib.prototype._flush = function _flush(callback) {
this._transform(Buffer.alloc(0), '', callback);
};

// If a flush is scheduled while another flush is still pending, a way to figure
// out which one is the "stronger" flush is needed.
// Roughly, the following holds:
// Z_NO_FLUSH (< Z_TREES) < Z_BLOCK < Z_PARTIAL_FLUSH <
// Z_SYNC_FLUSH < Z_FULL_FLUSH < Z_FINISH
const flushiness = [];
let i = 0;
for (const flushFlag of [Z_NO_FLUSH, Z_BLOCK, Z_PARTIAL_FLUSH,
Z_SYNC_FLUSH, Z_FULL_FLUSH, Z_FINISH]) {
flushiness[flushFlag] = i++;
}

function maxFlush(a, b) {
return flushiness[a] > flushiness[b] ? a : b;
}

Zlib.prototype.flush = function flush(kind, callback) {
var ws = this._writableState;

Expand All @@ -314,13 +331,20 @@ Zlib.prototype.flush = function flush(kind, callback) {
if (callback)
this.once('end', callback);
} else if (ws.needDrain) {
if (callback) {
const drainHandler = () => this.flush(kind, callback);
const alreadyHadFlushScheduled = this._scheduledFlushFlag !== Z_NO_FLUSH;
this._scheduledFlushFlag = maxFlush(kind, this._scheduledFlushFlag);

// If a callback was passed, always register a new `drain` + flush handler,
// mostly because that’s simpler and flush callbacks piling up is a rare
// thing anyway.
if (!alreadyHadFlushScheduled || callback) {
const drainHandler = () => this.flush(this._scheduledFlushFlag, callback);
this.once('drain', drainHandler);
}
} else {
this._flushFlag = kind;
this.write(Buffer.alloc(0), '', callback);
this._scheduledFlushFlag = Z_NO_FLUSH;
}
};

Expand Down
27 changes: 27 additions & 0 deletions test/parallel/test-zlib-flush-drain-longblock.js
Original file line number Diff line number Diff line change
@@ -0,0 +1,27 @@
'use strict';

// Regression test for https://github.com/nodejs/node/issues/14523.
// Checks that flushes interact properly with writableState.needDrain,
// even if no flush callback was passed.

const common = require('../common');
const assert = require('assert');
const zlib = require('zlib');

const zipper = zlib.createGzip({ highWaterMark: 16384 });
const unzipper = zlib.createGunzip();
zipper.pipe(unzipper);

zipper.write('A'.repeat(17000));
zipper.flush();

let received = 0;
unzipper.on('data', common.mustCall((d) => {
received += d.length;
}, 2));

// Properly `.end()`ing the streams would interfere with checking that
// `.flush()` works.
process.on('exit', () => {
assert.strictEqual(received, 17000);
});
41 changes: 41 additions & 0 deletions test/parallel/test-zlib-flush-multiple-scheduled.js
Original file line number Diff line number Diff line change
@@ -0,0 +1,41 @@
'use strict';

const common = require('../common');
const assert = require('assert');
const zlib = require('zlib');

const {
Z_PARTIAL_FLUSH, Z_SYNC_FLUSH, Z_FULL_FLUSH, Z_FINISH
} = zlib.constants;

common.crashOnUnhandledRejection();

async function getOutput(...sequenceOfFlushes) {
const zipper = zlib.createGzip({ highWaterMark: 16384 });

zipper.write('A'.repeat(17000));
for (const flush of sequenceOfFlushes) {
zipper.flush(flush);
}

const data = [];

return new Promise((resolve) => {
zipper.on('data', common.mustCall((d) => {
data.push(d);
if (data.length === 2) resolve(Buffer.concat(data));
}, 2));
});
}

(async function() {
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fancy! I wasn't aware this was possible...

assert.deepStrictEqual(await getOutput(Z_SYNC_FLUSH),
await getOutput(Z_SYNC_FLUSH, Z_PARTIAL_FLUSH));
assert.deepStrictEqual(await getOutput(Z_SYNC_FLUSH),
await getOutput(Z_PARTIAL_FLUSH, Z_SYNC_FLUSH));

assert.deepStrictEqual(await getOutput(Z_FINISH),
await getOutput(Z_FULL_FLUSH, Z_FINISH));
assert.deepStrictEqual(await getOutput(Z_FINISH),
await getOutput(Z_SYNC_FLUSH, Z_FINISH));
})();