function stringToArrayBuffer(str) {
  var bytes = new Array(); 
  var len,c;
  len = str.length;
  for(var i = 0; i < len; i++){
    c = str.charCodeAt(i);
    if(c >= 0x010000 && c <= 0x10FFFF){
      bytes.push(((c >> 18) & 0x07) | 0xF0);
      bytes.push(((c >> 12) & 0x3F) | 0x80);
      bytes.push(((c >> 6) & 0x3F) | 0x80);
      bytes.push((c & 0x3F) | 0x80);
    }else if(c >= 0x000800 && c <= 0x00FFFF){
      bytes.push(((c >> 12) & 0x0F) | 0xE0);
      bytes.push(((c >> 6) & 0x3F) | 0x80);
      bytes.push((c & 0x3F) | 0x80);
    }else if(c >= 0x000080 && c <= 0x0007FF){
      bytes.push(((c >> 6) & 0x1F) | 0xC0);
      bytes.push((c & 0x3F) | 0x80);
    }else{
      bytes.push(c & 0xFF);
    }
  }
  var array = new Int8Array(bytes.length);
  for(var i in bytes){
    array[i] =bytes[i];
  }
  return array.buffer;
}

function arrayBufferToString(arr){
    if(typeof arr === 'string') {  
        return arr;  
    }  
    var dataview=new DataView(arr.data);
    var ints=new Uint8Array(arr.data.byteLength);
    for(var i=0;i<ints.length;i++){
      ints[i]=dataview.getUint8(i);
    }
    arr=ints;
    var str = '',  
        _arr = arr;  
    for(var i = 0; i < _arr.length; i++) {  
        var one = _arr[i].toString(2),  
            v = one.match(/^1+?(?=0)/);  
        if(v && one.length == 8) {  
            var bytesLength = v[0].length;  
            var store = _arr[i].toString(2).slice(7 - bytesLength);  
            for(var st = 1; st < bytesLength; st++) {  
                store += _arr[st + i].toString(2).slice(2);  
            }  
            str += String.fromCharCode(parseInt(store, 2));  
            i += bytesLength - 1;  
        } else {  
            str += String.fromCharCode(_arr[i]);  
        }  
    }  
    return str; 
}