test/parallel/test-stream-big-packet.js

// Copyright Joyent, Inc. and other Node contributors.
//
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//
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// OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
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'use strict';
require('../common');
const assert = require('assert');
const stream = require('stream');

let passed = false;

class TestStream extends stream.Transform {
  _transform(chunk, encoding, done) {
    // Char 'a' only exists in the last write
    passed ||= chunk.toString().includes('a');
    done();
  }
}

const s1 = new stream.Transform({
  transform(chunk, encoding, cb) {
    process.nextTick(cb, null, chunk);
  }
});
const s2 = new stream.PassThrough();
const s3 = new TestStream();
s1.pipe(s3);
// Don't let s2 auto close which may close s3
s2.pipe(s3, { end: false });

// We must write a buffer larger than highWaterMark
const big = Buffer.alloc(s1.writableHighWaterMark + 1, 'x');

// Since big is larger than highWaterMark, it will be buffered internally.
assert(!s1.write(big));
// 'tiny' is small enough to pass through internal buffer.
assert(s2.write('tiny'));

// Write some small data in next IO loop, which will never be written to s3
// Because 'drain' event is not emitted from s1 and s1 is still paused
setImmediate(s1.write.bind(s1), 'later');

// Assert after two IO loops when all operations have been done.
process.on('exit', function() {
  assert(passed, 'Large buffer is not handled properly by Writable Stream');
});