(Server-sent Events) A brief discussion of server push events in H5

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

WebSocket protocol is another server-client communication protocol after the HTTP protocol. Different from HTTP's simple one-way communication mode where the client requests the server to respond, it supports two-way communication between the server and the client. .

The use of Server-sent Events

Server-sent Events (hereinafter referred to as SSE) as the server => client communication method is inevitable The client must have a corresponding service address and response method, and the server must have a corresponding data sending method.

Client JS code

The H5 page needs to add the following JS code:

     <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(&#39;sentMessage&#39;, function (event) { 
                  var data = eval(&#39;(&#39;+event.data+&#39;)&#39;);//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>

Service Terminal

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

　　　　/// <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 it is always a bit small. Requirements:

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

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

1.event: Indicates the type of event used by this line to declare an event. 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.

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