fs.WriteStream truncation

[isaacs]

This fails:

var assert = require('assert');

var fs = require('fs');
var https = require('https');
var url = require('url');
var path = require('path');
var stream = require('stream');

var resultFile = path.resolve(common.tmpDir, 'result');

var key = fs.readFileSync(common.fixturesDir + '/keys/agent1-key.pem');
var cert = fs.readFileSync(common.fixturesDir + '/keys/agent1-cert.pem');

var PORT = common.PORT;

// number of bytes discovered empirically
var data = new Buffer(99653);
var chars = 'abcdefghijklmnopqrstuvwxyz';
data.fill(chars + '\n');
var filler = new Buffer(1024).fill(chars);
filler[filler.length - 1] = 10;
data.fill(filler.toString());

syntheticTest();

function syntheticTest() {
  var res = new stream.Readable({ highWaterMark: 1024 });
  var p = 0;
  res._read = function() {
    var len = Math.min(1024, data.length - p);
    console.error('_read data len', len, p, data.length);
    if (len <= 0)
      res.push(null);
    else {
      res.push(data.slice(p, len + p));
      p += len;
    }
  };

  test(res, cb);
}

function test(res, cb) {
  var out = fs.createWriteStream(resultFile);

  var bytes = 0;
  res.on('data', function(chunk) {
    bytes += chunk.length;
    console.error('bytes', chunk.length, bytes);
  });

  res.pipe(out).on('finish', function() {
    var tmp = fs.statSync(resultFile);
    assert.strictEqual(bytes, data.length);
    assert.strictEqual(tmp.size, data.length);
    console.log('ok');
    if (cb) cb();
  });
}

But it works with a synthetic write stream, so it looks like something to do with the FS write stream specifically.