一、什么是webSocket
webSocket是HTML5开始提供的一种浏览器与服务器进行全双工通讯的网络技术，属于应用层协议。它基于TCP传输协议，并复用HTTP的握手通道。对大部分web开发者来说，上面这段描述有点枯燥，其实只要记住几点：
- WebSocket可以在浏览器里使用
- 支持双向通信
- 使用很简单
有哪些优点
说到优点，这里的对比参照物是HTTP协议，概括地说就是：支持双向通信，更灵活，更高效，可扩展性更好。
- 支持双向通信，实时性更强。
- 更好的二进制支持。
- 较少的控制开销。连接创建后，ws客户端、服务端进行数据交换时，协议控制的数据包头部较小。在不包含头部的情况下，服务端到客户端的包头只有2~10字节（取决于数据包长度），客户端到服务端的的话，需要加上额外的4字节的掩码。而HTTP协议每次通信都需要携带完整的头部。
- 支持扩展。ws协议定义了扩展，用户可以扩展协议，或者实现自定义的子协议。（比如支持自定义压缩算法等）
二、iOS中如何使用webSocket
webSocket 实现了服务端推机制（主动向客户端发送消息）。新的 web 浏览器全都支持 WebSocket，这使得它的使用超级简单。通过 WebSocket 能够打开持久连接，大部分网络都能轻松处理 WebSocket 连接。在 iOS 中使用 WebSocket 比较麻烦，你必须进行大量的设置，而且内置的 API 根本帮不上忙。这时 Starscream 出现了------这个小巧、易于使用的库让你所有的烦恼不翼而飞。
1、根据url创建socket
Swift
var request = URLRequest(url: URL(string: "url")!)
request.timeoutInterval = 5//超时时间
socket = WebSocket(request: request)
socket.delegate = self//接收到消息走代理方法2、发送消息
Swift
socket.write(string: sendStr)3、接收消息，在代理方法中
Swift
func websocketDidReceiveMessage(socket: WebSocketClient, text: String) {
//接收到字符串消息
}
func websocketDidReceiveData(socket: WebSocketClient, data: Data) {
printLog("\(data)")//接收到data消息
}三、常见问题
1、如何确保client向特定的client发送消息
发送消息时带着要发送给哪些client（唯一标识性数组）发送给cloud，cloud根据要发送给的client数组向相应的client发送消息
Swift
func sendTextTo(deviceIDs: [String], text: String) {
if socket == nil {
return
}
if socket.isConnected == false {
return
}
let cmdMessage = DQMessage(Type: 1, MsgGID: UUID().uuidString, Receivers: deviceIDs, Content: text, Time: nil, Publisher: nil, axOrderIDs: nil)
if let sendStr = DQMessage.toJsonString(messages: [cmdMessage]) {
socket.write(string: sendStr)
}
}2.如何保持链接
十分钟发送一次心跳包，app进入前台时，app断网重连时，app失去web连接时，重新连接
Swift
NotificationCenter.default.addObserver(self, selector: #selector(appDidBecomeActive), name: UIApplication.didBecomeActiveNotification, object: nil)
do {
try reachability.startNotifier()
} catch {
print("Unable to start notifier")
}
reachability.whenReachable = { [weak self] reachability in
self?.reconnectTimes = 10
if self?.socket == nil {
return
}
self?.socket.connect()
}
if #available(iOS 10.0, *) {
timer = Timer.scheduledTimer(withTimeInterval: 30, repeats: true) { timer in
let now = Date().timeIntervalSince1970
let s = now - self.lastReceivedMessageTime
if s >= 600 && s <= 660 {
self.sendHeartBeat()
} else if s > 660 {
self.reconnect()
}
}
} else {
timer = Timer.scheduledTimer(timeInterval: 30, target: self, selector: #selector(handleTimer), userInfo: nil, repeats: true)
}
@objc func handleTimer(timer: Timer) {
let now = Date().timeIntervalSince1970
let s = now - self.lastReceivedMessageTime
if s >= 600 && s <= 660 {
self.sendHeartBeat()
} else if s > 660 {
self.reconnect()
}
}
@objc func appDidBecomeActive(_ application: UIApplication) {
if self.socket == nil {
return
}
if self.socket.isConnected == false && self.reachability.connection != .none {
self.socket.connect()
}
}3.如何保证消息送达
client到cloud：client中维护一个message数据表（包括字段是否发送成功sent）cloud收到消息之后向client返回ack，client收到ack后将该条message标记为sent=1已发送，60秒client未收到ack，视为发送失败，重新发送， cloud端message表中已经存在该条消息，则忽略，但是向客户端client发送ack
cloud到clinet：client收到消息后向cloud返回ack，cloud收到ack标记消息为已发送成功， 60秒cloud未收到ack，视为发送失败，从新发送，client端message表中已经存在该条消息，则忽略，但是向客户端client发送ack
Swift
func websocketDidReceiveMessage(socket: WebSocketClient, text: String) {
printLog("Web Socket receive \(text)")
lastReceivedMessageTime = Date().timeIntervalSince1970
if text == "$" {
printLog("Received Heart Beat!!!!")
return
}
guard let messageArray = DQMessage.from(jsonData: text.data(using: .utf8)!) else { return }
for message in messageArray {
if message.Type == 99 { //ACK
DBPool.write { db in
try? db.execute("Update MessageRecord Set sent = 1 Where messageGID = '\(message.MsgGID)'")
}
continue
}
//收到消息后回复ACK,这样服务器会标记这条消息发送成功
sendACK(message: message)
//从收到的消息列表中对比msgid, 如果已经收到过,则忽略这条消息, 去重处理
var shouldReturn = false
DBQueue.inDatabase { db in
do {
if let count = try Int.fetchOne(db, "Select count(*) from MessageRecord where messageGID = '\(message.MsgGID)'"), count > 0 {
//数据库里有这条消息,说明已经收到过,忽略掉
shouldReturn = true
}
} catch {
Log.shareInstance.log(message: "读取数据库错误")
printLog("读取数据库错误")
self.createTable()
}
}
if shouldReturn == true {
return
}
//发完ACK将message存到数据库
let aMessage = essageRecord()
aMessage.messageGID = message.MsgGID
aMessage.type = message.Type
aMessage.time = message.Time
aMessage.publisher = message.Publisher
if message.Type == 1 { //text
guard let content = message.Content else { continue }
aMessage.message = message.Content
if content.hasPrefix("cmd::") {
let ar = content.components(separatedBy: "::")
var para: String? = nil
if ar.count == 3 {
para = ar[2]
}
let cmdString = "\(ar[0])::\(ar[1])".lowercased()
let command = AldeloCommand(rawValue: cmdString) ?? AldeloCommand.unknown
if command == .clinePrint {
if let ar = para?.components(separatedBy: ","), ar.count == 2 {
if let orderID = Int64(ar[0]), orderID > 0 {
gotPrintCommandBlock?([orderID],ar[1].boolValue(),true, message)
delegate?.receivedPrintCommand(axOrderIDs: [orderID], packingPrint: ar[1].boolValue(), isClientWebSocket: true)
}
}
} else {
gotCommandBlock?(command,para, message)
delegate?.receivedCommand(cmd: command,parameter: para, message: message)
}
} else {
gotMessageBlock?(message)
delegate?.receivedMessage(message: message)
}
} else if message.Type == 2 { //print
guard let orderIDs = message.axOrderIDs else { return }
aMessage.message = "\(orderIDs)"
gotPrintCommandBlock?(orderIDs,true,false,message)
delegate?.receivedPrintCommand(axOrderIDs: orderIDs, packingPrint: true, isClientWebSocket: false)
} else if message.Type == 3 { //QR payment
guard let content = message.Content else { continue }
aMessage.message = content
gotQRPaymentBlock?(content)
delegate?.receivedQRPayment(content: content)
} else if message.Type == 4 { //cloud 强制反激活
printLog("cloud 强制反激活 .....")
}
DBPool.write { db in
try? aMessage.insert(db)
}
}
}