Detailed introduction to server push events

Server-sent Events are a one-way communication based on the WebSocket protocol in which the server sends events & data to the client. Currently all major browsers support server-sent events, except of course Internet Explorer. 2333...

The WebSocket protocol is another server-client communication protocol after the HTTP protocol. Unlike HTTP, which is a simple client requesting a server response, it supports a one-way communication mode. Two-way communication between server and client.

Use of Server-sent Events

Server-sent Events (hereinafter referred to as SSE) as the server=> For the client communication method, the client must have the corresponding service address and response method, and the server must have the corresponding data sending method; without further ado, let’s get to the code!

Client-side JS code

 H5页面需添加如下JS代码：     <script>         if (typeof (EventSource) !== "undefined") {             //推送服务接口地址 var eventSource = new EventSource("http://localhost:2242/webservice/ServerSent/SentNews");             //当通往服务器的连接被打开 eventSource.onopen = function () {                 console.log("连接打开...");             }              //当错误发生  eventSource.onerror= function (e) {                  console.log(e);              };              //当接收到消息，此事件为默认事件  eventSource.onmessage = function (event) {                  console.log("onmessage...");          　　　　 eventSource.close()//关闭SSE链接
              };              //服务器推送sentMessage事件  eventSource.addEventListener('sentMessage', function (event) { 
                  var data = eval('('+event.data+')');//服务器端推送的数据，eval装换Json对象  var origin = event.origin;//服务器 URL 的域名部分，即协议、域名和端口，表示消息的来源。  var lastEventId = event.lastEventId;////数据的编号，由服务器端发送。如果没有编号，这个属性为空。  //此处根据需求编写业务逻辑  console.log(data);              }, false);          } else {              //浏览器不支持server-sent events 所有主流浏览器均支持服务器发送事件，除了 Internet Explorer。  document.getElementById("result").innerHTML = "Sorry, your browser does not support server-sent events...";          }      </script>

Server-side

What data format should the server return? What kind of response should be given to the client? Let’s take a .Net example first

 　　　　/// <summary>/// 推送消息/// </summary>/// <returns></returns>        [HttpGet]public HttpResponseMessage SentNews()
        {
            HttpResponseMessage response = Request.CreateResponse(HttpStatusCode.OK);try{//response.Headers.Add("Access-Control-Allow-Origin", "*");//如需要跨域可配置string data_str = “推送至客户端的数据”;//当然可以是json字符串格式string even = "", data = "";if (!string.IsNullOrWhiteSpace(data_str))
                {
                    even = "event:sentMessage\n";
                    data = "data:" + data_str + "\n\n";
                }string retry = "retry:" + 1000 + "\n";//连接断开后重连时间（毫秒），其实可以理解为轮询时间 2333...byte[] array = Encoding.UTF8.GetBytes(even + data + retry);
                Stream stream_result = new MemoryStream(array);
                response.Content = new StreamContent(stream_result);
                response.Content.Headers.ContentType = new MediaTypeHeaderValue("text/event-stream");//此处一定要配置response.Headers.CacheControl = new CacheControlHeaderValue();
                response.Headers.CacheControl.NoCache = false;
            }catch (Exception ex)
            {
                LogHelper.WriteWebLog(ex);
            }return response;
        }

After reading the above code, I think you should have an idea. The response method is still HTTPResponse response, but always A little request:

• The response header "Content-Type" should be set to "text/event-stream"

The response data format should also pay attention to the "data:", "event:" and "retry:" tags in the above code:

1. event: Indicates the type of event this line is used to declare. When the browser receives data, it will generate events of the corresponding type.

2. data: Indicates that the row contains data. Lines starting with data can appear multiple times. All these rows are data for that event.

3. retry: Indicates that this line is used to declare the waiting time of the browser before reconnecting after the connection is disconnected.

4. id: Indicates the identifier (that is, the number of the data) used by this row to declare the event, which is not commonly used.

The above is a simple application of Server-sent Events. I will not show the effect anymore. If you are interested, you can operate it yourself to achieve the effect!

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