flush-on-last-write-or-end.js

var Writable = require('stream').Writable;
var util = require('util');
var assert = require('assert');

function W(o) {
  Writable.call(this, o);

  setTimeout(function() {
    this.ready = true
    this.emit('ready');
  }.bind(this), 1000);

  this.flushed = false;
  this.on('finish', function() {
    console.log('finish', this.flushed);
    assert(this.flushed);
  });
  this._writableState.decodeStrings = false;
  this.on('prefinish', function() {
    console.log('prefinish', this.flushed);
  });
}

util.inherits(W, Writable);

W.prototype._write = function(chunk, encoding, cb) {
  assert(!this.flushed);
  if (!this.ready) {
    this.once('ready', function() {
      this._write(chunk, encoding, cb);
    });
  } else {
    var state = this._writableState;
    console.error('write', chunk);
    if (state.ending && state.buffer.length === 1) {
      console.error('last write, flush trailers with it');
      this.flushed = true;
    }
    setTimeout(cb);
  }
};

W.prototype.end = function(chunk, encoding, cb) {
  if (!this.ready) {
    this.once('ready', function() {
      this.end(chunk, encoding, cb);
    });
  } else {
    if (chunk && typeof chunk !== 'function') {
      if (typeof encoding === 'function') {
        cb = encoding;
        encoding = null;
      }
      var self = this;
      this.write(chunk, encoding);
      chunk = null;
      encoding = null;
    }

    var state = this._writableState;
    if (state.buffer.length === 0) {
      console.error('no pending writes, flush trailers with it');
      this.flushed = true;
    }
    Writable.prototype.end.call(this, chunk, encoding, cb);
  }
};




f1();
function f1() {
  var w = new W();
  w.write('a');
  setTimeout(function() {
    w.end(function() {
      console.error('end cb');
      f2();
    });
  }, 200);
}

function f2() {
  var w = new W();
  w.write('a');
  w.write('b');
  w.write('c');
  w.write('d');
  w.write('e');
  w.end(function() {
    console.error('end cb');
    f3();
  });
}

function f3() {
  var w = new W();
  w.write('a');
  w.end('b', function() {
    console.error('end cb');
    f4();
  });
}

function f4() {
  var w = new W();
  w.end('a', function() {
    console.error('end cb');
  });
}