拉模式和推模式
拉模式
1、数据更新频率低,则大多数请求是无效的 2、在线用户量多,则服务端的查询负载高 3、定时轮询拉取,实时性低
推模式
1、仅在数据更新时才需要推送 2、需要维护大量的在线长连接 3、数据更新后可以立即推送
基于webSocket推送
1、浏览器支持的socket编程,轻松维持服务端长连接 2、基于TCP可靠传输之上的协议,无需开发者关心通讯细节 3、提供了高度抽象的编程接口,业务开发成本较低
webSocket协议与交互
通讯流程
客户端->upgrade->服务端 客户端<-switching<-服务端 客户端->message->服务端 客户端<-message<-服务端
实现http服务端
1、webSocket是http协议upgrade而来 2、使用http标准库快速实现空接口:/ws
webSocket握手
1、使用webSocket.Upgrader完成协议握手,得到webSocket长连接 2、操作webSocket api,读取客户端消息,然后原样发送回去
封装webSocket
缺乏工程化设计
1、其他代码模块,无法直接操作webSocket连接 2、webSocket连接非线程安全,并发读/写需要同步手段
隐藏细节,封装api
1、封装Connection结构,隐藏webSocket底层连接 2、封装Connection的api,提供Send/Read/Close等线程安全接口
api原理(channel是线程安全的)
1、SendMessage将消息投递到out channel 2、ReadMessage从in channel读取消息
内部原理
1、启动读协程,循环读取webSocket,将消息投递到in channel 2、启动写协程,循环读取out channel,将消息写给webSocket
// server.go
package main
import (
"net/http"
"github.com/gorilla/websocket"
"./impl"
"time"
)
var (
upgrader = websocket.Upgrader{
//允许跨域
CheckOrigin: func(r *http.Request) bool {
return true
},
}
)
func wsHandler(w http.ResponseWriter, r *http.Request) {
var (
wsConn *websocket.Conn
err error
conn *impl.Connection
data []byte
)
//Upgrade:websocket
if wsConn, err = upgrader.Upgrade(w, r, nil); err != nil {
return
}
if conn, err = impl.InitConnection(wsConn); err != nil {
goto ERR
}
go func() {
var (
err error
)
for {
if err =conn.WriteMessage([]byte("heartbeat")); err != nil {
return
}
time.Sleep(1 * time.Second)
}
}()
for {
if data, err = conn.ReadMessage(); err != nil {
goto ERR
}
if err = conn.WriteMessage(data); err != nil {
goto ERR
}
}
ERR:
//关闭连接
conn.Close()
}
func main() {
//http:localhost:7777/ws
http.HandleFunc("/ws", wsHandler)
http.ListenAndServe("0.0.0.0:7777", nil)
}
// connection.go
package impl
import (
"github.com/gorilla/websocket"
"sync"
"github.com/influxdata/platform/kit/errors"
)
var once sync.Once
type Connection struct {
wsConn *websocket.Conn
inChan chan []byte
outChan chan []byte
closeChan chan byte
isClosed bool
mutex sync.Mutex
}
func InitConnection(wsConn *websocket.Conn) (conn *Connection, err error) {
conn = &Connection{
wsConn:wsConn,
inChan:make(chan []byte, 1000),
outChan:make(chan []byte, 1000),
closeChan:make(chan byte, 1),
}
//启动读协程
go conn.readLoop()
//启动写协程
go conn.writeLoop()
return
}
//API
func (conn *Connection) ReadMessage() (data []byte, err error) {
select {
case data = <- conn.inChan:
case <- conn.closeChan:
err = errors.New("connection is closed")
}
return
}
func (conn *Connection) WriteMessage(data []byte) (err error) {
select {
case conn.outChan <- data:
case <- conn.closeChan:
err = errors.New("connection is closed")
}
return
}
func (conn *Connection) Close() {
// 线程安全的close,可重入
conn.wsConn.Close()
conn.mutex.Lock()
if !conn.isClosed {
close(conn.closeChan)
conn.isClosed = true
}
conn.mutex.Unlock()
}
//内部实现
func (conn *Connection) readLoop() {
var (
data []byte
err error
)
for {
if _, data, err = conn.wsConn.ReadMessage(); err != nil {
goto ERR
}
//阻塞在这里,等待inChan有空位置
//但是如果writeLoop连接关闭了,这边无法得知
//conn.inChan <- data
select {
case conn.inChan <- data:
case <-conn.closeChan:
//closeChan关闭的时候,会进入此分支
goto ERR
}
}
ERR:
conn.Close()
}
func (conn *Connection) writeLoop() {
var (
data []byte
err error
)
for {
select {
case data = <- conn.outChan:
case <- conn.closeChan:
goto ERR
}
if err = conn.wsConn.WriteMessage(websocket.TextMessage, data); err != nil {
goto ERR
}
conn.outChan <- data
}
ERR:
conn.Close()
}