WebRTC - 傳送訊息

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現在讓我們建立一個簡單的例子。首先，透過“node server”執行我們在“信令伺服器”教程中建立的信令伺服器。

頁面上將有三個文字輸入框，一個用於登入，一個用於使用者名稱，一個用於我們想要傳送給另一個對等節點的訊息。建立一個index.html檔案並新增以下程式碼 -

<html lang = "en"> 
   <head> 
      <meta charset = "utf-8" /> 
   </head>
	
   <body> 
      <div> 
         <input type = "text" id = "loginInput" /> 
         <button id = "loginBtn">Login</button> 
      </div> 
		
      <div> 
         <input type = "text" id = "otherUsernameInput" /> 
         <button id = "connectToOtherUsernameBtn">Establish connection</button> 
      </div> 
		
      <div> 
         <input type = "text" id = "msgInput" /> 
         <button id = "sendMsgBtn">Send text message</button> 
      </div> 
		
      <script src = "client.js"></script>
   </body>
	
</html>

我們還添加了三個按鈕，用於登入、建立連線和傳送訊息。現在建立一個client.js檔案並新增以下程式碼 -

var connection = new WebSocket('ws://:9090'); 
var name = "";

var loginInput = document.querySelector('#loginInput'); 
var loginBtn = document.querySelector('#loginBtn'); 

var otherUsernameInput = document.querySelector('#otherUsernameInput'); 
var connectToOtherUsernameBtn = document.querySelector('#connectToOtherUsernameBtn'); 
var msgInput = document.querySelector('#msgInput'); 
var sendMsgBtn = document.querySelector('#sendMsgBtn'); 
var connectedUser, myConnection, dataChannel;
  
//when a user clicks the login button 
loginBtn.addEventListener("click", function(event) { 
   name = loginInput.value; 
	
   if(name.length > 0) { 
      send({ 
         type: "login", 
         name: name 
      }); 
   } 
}); 
 
//handle messages from the server 
connection.onmessage = function (message) { 
   console.log("Got message", message.data); 
   var data = JSON.parse(message.data); 
	
   switch(data.type) { 
      case "login": 
         onLogin(data.success); 
         break; 
      case "offer": 
         onOffer(data.offer, data.name); 
         break; 
      case "answer":
         onAnswer(data.answer); 
         break; 
      case "candidate": 
         onCandidate(data.candidate); 
         break; 
      default: 
         break; 
   } 
}; 
 
//when a user logs in 
function onLogin(success) { 

   if (success === false) { 
      alert("oops...try a different username"); 
   } else { 
      //creating our RTCPeerConnection object 
      var configuration = { 
         "iceServers": [{ "url": "stun:stun.1.google.com:19302" }] 
      }; 
		
      myConnection = new webkitRTCPeerConnection(configuration, { 
         optional: [{RtpDataChannels: true}] 
      }); 
		
      console.log("RTCPeerConnection object was created"); 
      console.log(myConnection); 
  
      //setup ice handling 
      //when the browser finds an ice candidate we send it to another peer 
      myConnection.onicecandidate = function (event) { 
		
         if (event.candidate) { 
            send({ 
               type: "candidate", 
               candidate: event.candidate 
            });
         } 
      }; 
		
      openDataChannel();
		
   } 
};
  
connection.onopen = function () { 
   console.log("Connected"); 
}; 
 
connection.onerror = function (err) { 
   console.log("Got error", err); 
};
  
// Alias for sending messages in JSON format 
function send(message) { 
   if (connectedUser) { 
      message.name = connectedUser; 
   }
	
   connection.send(JSON.stringify(message)); 
};

您可以看到我們建立了一個到信令伺服器的套接字連線。當用戶點選登入按鈕時，應用程式將其使用者名稱傳送到伺服器。如果登入成功，應用程式將建立RTCPeerConnection物件並設定onicecandidate處理程式，該處理程式將所有找到的 icecandidates 傳送到另一個對等節點。它還執行openDataChannel()函式，該函式建立一個dataChannel。請注意，在建立RTCPeerConnection物件時，建構函式中的第二個引數是可選的：[{RtpDataChannels: true}]，如果您使用的是Chrome或Opera，則此引數是必需的。下一步是向另一個對等節點發出一個Offer。將以下程式碼新增到您的client.js檔案中 -

//setup a peer connection with another user 
connectToOtherUsernameBtn.addEventListener("click", function () {
  
   var otherUsername = otherUsernameInput.value;
   connectedUser = otherUsername;
	
   if (otherUsername.length > 0) { 
      //make an offer 
      myConnection.createOffer(function (offer) { 
         console.log(); 
			
         send({ 
            type: "offer", 
            offer: offer 
         }); 
			
         myConnection.setLocalDescription(offer); 
      }, function (error) { 
         alert("An error has occurred."); 
      }); 
   } 
});
  
//when somebody wants to call us 
function onOffer(offer, name) { 
   connectedUser = name; 
   myConnection.setRemoteDescription(new RTCSessionDescription(offer));
	
   myConnection.createAnswer(function (answer) { 
      myConnection.setLocalDescription(answer); 
		
      send({ 
         type: "answer", 
         answer: answer 
      }); 
		
   }, function (error) { 
      alert("oops...error"); 
   }); 
}

//when another user answers to our offer 
function onAnswer(answer) { 
   myConnection.setRemoteDescription(new RTCSessionDescription(answer)); 
}
  
//when we got ice candidate from another user 
function onCandidate(candidate) { 
   myConnection.addIceCandidate(new RTCIceCandidate(candidate)); 
}

您可以看到，當用戶點選“建立連線”按鈕時，應用程式會向另一個對等節點發出一個SDP Offer。我們還設定了onAnswer和onCandidate處理程式。最後，讓我們實現openDataChannel()函式，該函式建立我們的dataChannel。將以下程式碼新增到您的client.js檔案中 -

//creating data channel 
function openDataChannel() { 

   var dataChannelOptions = { 
      reliable:true 
   }; 
	
   dataChannel = myConnection.createDataChannel("myDataChannel", dataChannelOptions);
	
   dataChannel.onerror = function (error) { 
      console.log("Error:", error); 
   };
	
   dataChannel.onmessage = function (event) { 
      console.log("Got message:", event.data); 
   };  
}
  
//when a user clicks the send message button 
sendMsgBtn.addEventListener("click", function (event) { 
   console.log("send message");
   var val = msgInput.value; 
   dataChannel.send(val); 
});

在這裡，我們為我們的連線建立了dataChannel，併為“傳送訊息”按鈕添加了事件處理程式。現在在兩個標籤頁中開啟此頁面，使用兩個使用者登入，建立連線，並嘗試傳送訊息。您應該在控制檯輸出中看到它們。請注意，以上示例在Opera中進行了測試。

Example in Opera

現在您可能會發現RTCDataChannel是WebRTC API中極其強大的部分。此物件還有許多其他用例，例如點對點遊戲或基於 torrent 的檔案共享。

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