iOS 中使用 webSocket

是服务器和app之间的一种通信方式

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。

Client1 ——->   cloud  ————>client2,3,4…

<——-返回ack         <——-返回ack

一，基本使用

1根据url创建socket

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

socket.write(string: sendStr)

3.接收消息，在代理方法中

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

}

二 常见问题

1.如何确保client向特定的client发送消息

“\(storeID!)-\(deviceNumber)-\(deviceGlobalID!)”.uppercased()    这些标志客户端的唯一性

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

/// 发送一条消息到指定的多个设备

///

/// - Parameters:

///   - deviceID: web socket 登陆名称数组

///   - text: 要发送的文本

func sendTextTo(deviceIDs: [String], text: String) {

if socket == nil  {

return

}

if socket.isConnected == false {

return

}

let cmdMessage = AldeloMessage(Type: 1, MsgGID: UUID().uuidString, Receivers: deviceIDs, Content: text, Time: nil, Publisher: nil, axOrderIDs: nil)

if let sendStr = AldeloMessage.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

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

firstly {

after(seconds: 3)

}.done {

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) {

firstly {

after(seconds: 3)

}.done {

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，从新发送

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

func websocketDidReceiveMessage(socket: WebSocketClient, text: String) {

printLog("Web Socket receive \(text)")

lastReceivedMessageTime = Date().timeIntervalSince1970

if text == "$" {

printLog("Received Heart Beat!!!!")

return

}

guard let messageArray = AldeloMessage.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 AldeloMessageRecord 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 AldeloMessageRecord 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

Log.shareInstance.log(message: "Websocket 收到重复消息,已忽略")

printLog("Websocket 收到重复消息,已忽略")

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

}

//            if let count = DatabaseOption().intForSql("Select count(*) from AldeloMessageRecord 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

//                Log.shareInstance.log(message: "Websocket 收到重复消息,已忽略")

//                printLog("Websocket 收到重复消息,已忽略")

//                return

//            }

//发完ACK将message存到数据库

let aMessage = AldeloMessageRecord()

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)

}

}

}

starscream地址：https://github.com/daltoniam/starscream

参考 Starscream 在 GitHub 上的项目主页 。