测试coturn服务器是否可用(Webrtc)

我们在使用webrtc 做视频连接的时候，如果涉及到不同网络之间的通信，往往会用到turn server来做视频中转，google也为我们提供了开源的turn server 源码，但是搭建成功后，如何能知道是否能正常使用呢？我们需要一个demo来做简单测试：

function checkTURNServer(turnConfig, timeout){  
  return new Promise(function(resolve, reject){  

    setTimeout(function(){  
      if(promiseResolved) return;  
      resolve(false);  
      promiseResolved = true;  
    }, timeout || 5000);  

    var promiseResolved = false  
      , myPeerConnection = window.RTCPeerConnection || window.mozRTCPeerConnection || window.webkitRTCPeerConnection   //compatibility for firefox and chrome  
      , pc = new myPeerConnection({iceServers:[turnConfig]})  
      , noop = function(){};  
    pc.createDataChannel("");    //create a bogus data channel  
    pc.createOffer(function(sdp){  
      if(sdp.sdp.indexOf('typ relay') > -1){ // sometimes sdp contains the ice candidates...  
        promiseResolved = true;  
        resolve(true);  
      }  
      pc.setLocalDescription(sdp, noop, noop);  
    }, noop);    // create offer and set local description  
    pc.onicecandidate = function(ice){  //listen for candidate events  
      if(promiseResolved || !ice || !ice.candidate || !ice.candidate.candidate || !(ice.candidate.candidate.indexOf('typ relay')>-1))  return;  
      promiseResolved = true;  
      resolve(true);  
    };  
  });  

}  
checkTURNServer({  
  url: 'turn:*.*.*.*',  
  username: '×××××××',  
  credential: '××××××××××',  
}).then(function(bool){  
  console.log('is my TURN server active? ', bool? 'yes':'no');  
}).catch(console.error.bind(console));

通过执行 checkTURNServer 方法，根据返回值判断是否连接成功。