continuation passing yield.js

var _copyFile = function(
  iName,
  oName,
  _ret
)
{
  var CHUNK_SIZE = 65536;

  var _copy = function(iF, oF, size, _ret)
  {
    var freeBuffersStack = [];
    var pos = 0;
    
    var _read = function(){
      var b = freeBuffersStack.pop() || Buffer(CHUNK_SIZE);
      var p = pos;

      fs.read(iF, b, 0, CHUNK_SIZE, p, function(err)
      { 
        if(err) return _ret(err); 
        _write(b, p);

        pos += CHUNK_SIZE;
        if(pos < size) setTimeout(_read);
      })
    };
    
    var _write = function(b, pos)
    {
      fs.write(oF, b, 0, CHUNK_SIZE, pos, function(err)
      { 
        if(err) return _ret(err);
        freeBuffersStack.push(b);
        if(pos >= size) _ret()
      })
    };
    
  };
  
  var _run = function() {
    var __beforeRet = _run, // ala `defer` from Go, but contunuation passing version
      _beforeRet = function(_fn){ 
        var _old = __beforeRet; 
        __beforeRet = function(){ _fn(_old) }; 
      }
    ;
    
    try
    {
      var iF; fs.open(iName,  'r', 0, function(errArg, fArg){ err = errArg; iF = fArg; _run() });
      yield;
      if(err) throw err;
      _beforeRet(function(_next){ fs.close(iF, _next) });

      var oF; fs.open(oName,  'w', 0, function(errArg, fArg){ err = errArg; oF = fArg; _run() });
      yield;
      if(err) throw err;
      _beforeRet(function(_next){ fs.close(oF, _next) });

      var size; fs.stat(iName, function(errArg, stat){ if(err) errArg = err else size = stat.size; _run() })
      yield;
      if(err) throw err;
      
      _copy(iF, oF, size, function(errArg){ err = errArg; _run() })
      yield;
      if(err) throw err;
    }
    catch(errArg)
    {
      err = errArg;
    }
    
    setTimeout(_beforeRet, 0)
    yield;
    return _ret(err);
    
  };
  
  _run();
};