go语言使用gin库实现SSE长连接_gin sse

目录

1.建立长连接

2.后端主动通知前端消息

3.调试

4.关闭长连接 

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项目需求：在go项目中实现SSE长连接，耗时操作完成后，后端主动通知前端消息。

1.建立长连接

最主要的操作是修改请求中的Content-Type类型为"text/event-stream"。

需要注意几点，后端首先不能让请求处理代码跑完，如果跑完这个请求就会断掉，保存的*gin.Context信息也就没用了，因此要新建一个range chan维持处理状态。

另外这里如果用for循环代替chan，会导致前端持续发送请求到后端。

import (
	"encoding/json"
	"fmt"
	"github.com/gin-gonic/gin"
	"github.com/labstack/gommon/log"
	"net/http"
	"strings"
	"time"
)
 
var ifChannelsMapInit = false
 
var channelsMap = map[string]chan string{}
 
func initChannelsMap() {
	channelsMap = make(map[string]chan string)
}
 
func AddChannel(userEmail string, traceId string) {
	if !ifChannelsMapInit {
		initChannelsMap()
		ifChannelsMapInit = true
	}
	var newChannel = make(chan string)
	channelsMap[userEmail+traceId] = newChannel
	log.Infof("Build SSE connection for user = " + userEmail + ", trace id = " + traceId)
}
 
func BuildNotificationChannel(userEmail string, traceId string, c *gin.Context) {
	AddChannel(userEmail, traceId)
	c.Writer.Header().Set("Content-Type", "text/event-stream")
	c.Writer.Header().Set("Cache-Control", "no-cache")
	c.Writer.Header().Set("Connection", "keep-alive")
	w := c.Writer
	flusher, _ := w.(http.Flusher)
	closeNotify := c.Request.Context().Done()
	go func() {
		<-closeNotify
		delete(channelsMap, userEmail+traceId)
		log.Infof("SSE close for user = " + userEmail + ", trace id = " + traceId)
		return
	}()
	fmt.Fprintf(w, "data: %s\n\n", "--ping--")
	flusher.Flush()
	for msg := range channelsMap[userEmail+traceId] {
		fmt.Fprintf(w, "data: %s\n\n", msg)
		flusher.Flush()
	}
}

2.后端主动通知前端消息

当耗时操作处理完成后，调用该方法，前端会收到通知。

func SendNotification(userEmail string, messageBody string, actionType string) {
	log.Infof("Send notification to user = " + userEmail)
	var msg = dao.NotificationLog{}
	msg.MessageBody = messageBody
	msg.UserEmail = userEmail
	msg.Type = actionType
	msg.Status = UNREAD
	msg.CreateTime = time.Now()
	msg.Create()
	msgBytes, _ := json.Marshal(msg)
	for key := range channelsMap {
		if strings.Contains(key, userEmail) {
			channel := channelsMap[key]
			channel <- string(msgBytes)
		}
	}
}

3.调试

准备两个接口，分别是建立SSE和触发耗时操作

GroupV1Rest.GET("/notification/socket-connection", controllers.SocketConnection)
GroupV1Rest.GET("/notification/export-excel", controllers.ExportExcel)

打开浏览器，进入调试模式，在console页输入

e = new EventSource('/business/v1/notification/socket-connection');
e.onmessage = function(event) {
    console.log(event.data);
};

看到日志打印‘--ping--’，长连接已建立

 此时发送第二个请求，调试模式看到通知被chan处理

返回浏览器，可以看到已经收到通知

4.关闭长连接 

前端关闭页面后，自动触发监听事件，后端清理连接信息