// 检测port是否被占用
function probe(port, callback) {

  var server = net.createServer().listen(port)

  var calledOnce = false

  var timeoutRef = setTimeout(function () {
    calledOnce = true
    callback(false,port)
  }, 2000)

  timeoutRef.unref()

  var connected = false

  server.on('listening', function() {
    clearTimeout(timeoutRef)

    if (server)
      server.close()

    if (!calledOnce) {
      calledOnce = true
      callback(true,port)
    }
  })

  server.on('error', function(err) {
    clearTimeout(timeoutRef)

    var result = true
    if (err.code === 'EADDRINUSE')
      result = false

    if (!calledOnce) {
      calledOnce = true
      callback(result,port)
    }
  })
}

function server(_port){
  var pt = _port || __port;
  probe(pt,function(bl,_pt){
    // 端口被占用 bl 返回false
    // _pt：传入的端口号
    if(bl === true){
      // ssr(_pt)
      server = http.createServer(connListener);
      server = server.listen(parseInt(_pt, 10));
      console.log("\n Static file server running at" + "\n\n=> http://localhost:" + _pt + '\n');
    }else{
      server(_pt+1)
    }
  })
}