SSE: server-sent events

　　当客户端需要定时轮询服务器获取一些消息的时候，可以使用 servser-sent events

　　.NET 服务端:　　

1         public void ProcessRequest(HttpContext context)
2         {
3             context.Response.ContentType = "text/event-stream";
4             context.Response.Write("retry: 1000
");//告诉客户端请求的时间间隔
5             context.Response.Write("data: " + DateTime.Now.ToString() + " 

");//返回的数据格式 data:...
6             context.Response.Flush();
7         }

　　客户端：　　

 1 <!DOCTYPE html>
 2 <html xmlns="http://www.w3.org/1999/xhtml">
 3 <head>
 4 <meta http-equiv="Content-Type" content="text/html; charset=utf-8"/>
 5     <title></title>
 6     <script>
 7         function listener(event) {
 8             var div = document.getElementById("main");
 9             div.innerHTML += event.data +"<br/>";
10         }
11 
12         var es = new EventSource("/SSE_Server.ashx");
13 
14         es.addEventListener("open", function (e) {
15             var msg = "";
16             if (e.target.readyState == EventSource.CONNECTING) {
17                 msg = "链接中...";
18             } else if (e.target.readyState == EventSource.OPEN) {
19                 msg = "OPEN";
20             } else if (e.target.readyState == EventSource.CLOSED) {
21                 msg = "CLOSED";
22             }
23             var div = document.getElementById("main");
24             div.innerHTML += msg + "<br/>";
25         });
26         es.addEventListener("message", listener);
27         es.addEventListener("error", function (e) {
28             var msg ="";
29             if(e.target.readyState==EventSource.CONNECTING)
30             {
31                 msg = "等待链接";
32             } else if (e.target.readyState == EventSource.CLOSED)
33             {
34                 msg = "链接失败";
35             }
36             var div = document.getElementById("main");
37             div.innerHTML += msg + "<br/>";
38         });
39     </script>
40 </head>
41 <body>
42     <div id="main">
43     </div>
44 </body>
45 </html>

　　效果展示:

附：

服务器可返回下列字段格式：

 1 Fields
 2 
 3 The following field names are defined by the specification:
 4 
 5 event
 6 　　The event's type. If this is specified, an event will be dispatched on the browser to the listener for the specified event name; 
　　the web site source code should use addEventListener() to listen for named events. The onmessage handler is called if no event name is specified for a message.
 7 data
 8 　　The data field for the message. When the EventSource receives multiple consecutive lines that begin with data:, it will concatenate them, inserting a newline character between each one. 
　　Trailing newlines are removed.
 9 id
10 　　The event ID to set the EventSource object's last event ID value.
11 retry
12 　　The reconnection time to use when attempting to send the event. [What code handles this?] This must be an integer, specifying the reconnection time in milliseconds. 
   If a non-integer value is specified the field is ignored.