Alamofire-request

一、SessionManager的总结

SessionManager 就是对外提供的管理者，这个管理者具备整个 Alamofire 的所有功能。
- 其中一个非常重要的点就是SessionManager把Session的代理移交给了一个专门的类： SessionDelegate

从上面这张图可以看出，我们的对外模块是SessionManager，他给外界的用户提供了很多的功能
但是这些工作的真正实现者是由iOS、Android、前端、后台、测试实现的！
其中单拿 iOS 模块的任务来说，有 首页、发现、我的、SDK、视频....模块要实现，但是我们的项目经理有可能都不知道这些到底是什么，怎么实现！所有来说如果全部交给SessionManager来实现，显然耦合性过强，还有任务乱七八糟，没有体现一个牛逼项目分层架构的效果。所以在 iOS 任务细化和SessionManager之间就缺了一个小管理者，对下：他知道具体事务和调度。对上：他能和SessionManager协调配合。那就是Request

二、Request初探

        SessionManager.default.request(urlString, method: .post, parameters: ["username":"dyz"]).response { (response) in
            debugPrint(response)
        }

1、method 分析 - options、get、head、post、put、patch、delete、trace、connect
get：参数拼接到url
post：参数放到了httpBody
2、url -> URLRequest -> 创建Task
3、parameters：参数处理

    @discardableResult
    open func request(
        _ url: URLConvertible,
        method: HTTPMethod = .get,
        parameters: Parameters? = nil,
        encoding: ParameterEncoding = URLEncoding.default,
        headers: HTTPHeaders? = nil)
        -> DataRequest
    {
        var originalRequest: URLRequest?

        do {
            originalRequest = try URLRequest(url: url, method: method, headers: headers)
            let encodedURLRequest = try encoding.encode(originalRequest!, with: parameters)
            return request(encodedURLRequest)
        } catch {
            return request(originalRequest, failedWith: error)
        }
    }

originalRequest = try URLRequest(url: url, method: method, headers: headers) 根据url、method和headers创建一个URLRequest
encoding.encode(originalRequest!, with: parameters) 编码，返回编码之后的URLRequest

    public func encode(_ urlRequest: URLRequestConvertible, with parameters: Parameters?) throws -> URLRequest {
        var urlRequest = try urlRequest.asURLRequest()

        guard let parameters = parameters else { return urlRequest }

        if let method = HTTPMethod(rawValue: urlRequest.httpMethod ?? "GET"), encodesParametersInURL(with: method) {
            guard let url = urlRequest.url else {
                throw AFError.parameterEncodingFailed(reason: .missingURL)
            }

            if var urlComponents = URLComponents(url: url, resolvingAgainstBaseURL: false), !parameters.isEmpty {
                let percentEncodedQuery = (urlComponents.percentEncodedQuery.map { $0 + "&" } ?? "") + query(parameters)
                urlComponents.percentEncodedQuery = percentEncodedQuery
                urlRequest.url = urlComponents.url
            }
        } else {
            if urlRequest.value(forHTTPHeaderField: "Content-Type") == nil {
                urlRequest.setValue("application/x-www-form-urlencoded; charset=utf-8", forHTTPHeaderField: "Content-Type")
            }

            urlRequest.httpBody = query(parameters).data(using: .utf8, allowLossyConversion: false)
        }

        return urlRequest
    }

encodesParametersInURL(with: method) 区分参数是拼接在url上，还是放在httpBody中
query(parameters) 参数处理
urlComponents.percentEncodedQuery = percentEncodedQuery 百分号编码，默认是ASCII码。"username=%E9%82%93%E4%BA%9A%E6%B4%B2dyz" 百分号解码网址

    private func query(_ parameters: [String: Any]) -> String {
        var components: [(String, String)] = []

        for key in parameters.keys.sorted(by: <) {
            let value = parameters[key]!
            components += queryComponents(fromKey: key, value: value)
        }
        return components.map { "\($0)=\($1)" }.joined(separator: "&")
    }

queryComponents(fromKey: key, value: value) 递归，返回一个数组，数组里面放的是元组

    public func queryComponents(fromKey key: String, value: Any) -> [(String, String)] {
        var components: [(String, String)] = []

        if let dictionary = value as? [String: Any] {
            for (nestedKey, value) in dictionary {
                components += queryComponents(fromKey: "\(key)[\(nestedKey)]", value: value)
            }
        } else if let array = value as? [Any] {
            for value in array {
                components += queryComponents(fromKey: arrayEncoding.encode(key: key), value: value)
            }
        } else if let value = value as? NSNumber {
            if value.isBool {
                components.append((escape(key), escape(boolEncoding.encode(value: value.boolValue))))
            } else {
                components.append((escape(key), escape("\(value)")))
            }
        } else if let bool = value as? Bool {
            components.append((escape(key), escape(boolEncoding.encode(value: bool))))
        } else {
            components.append((escape(key), escape("\(value)")))
        }

        return components
    }

根据不同的数据类型，进行处理
escape 里面对参数进行百分号编码

三、Request-参数传递坑点

joined 在中间插入字符

        let arr = ["hello","world","dyz","和谐学习，不急不躁"]
        let comArr = arr.map{$0}.joined(separator: "&")
        print(comArr)

hello&world&dyz&和谐学习，不急不躁

参数里面有数组的时候，要把数组JSON序列化

        let array = [["username":"dyz","password":"123456"],["username":"Json","password":"9080"]]
        SessionManager.default.request(myGetUrlString, method: .get, parameters: ["array":getJsonFromArray(array)])
            .response { (response) in
                debugPrint(response)
        }

extension ViewController {
    fileprivate func getJsonFromArray(_ array:Array<Any>) -> String{
        let data = try? JSONSerialization.data(withJSONObject: array, options: .prettyPrinted)
        return String(data: data!, encoding: .utf8) ?? ""
    }
}

四、SessionDelegate和TaskDelegate的关系

SessionDelegate 是事件总响应者，根据不同的需求 (DataTaskDelegate、DownloadTaskDelegate、UploadTaskDelegate、TaskDelegate)，响应总代理然后根据需求的不同交给专业的人去做专业的事

代理任务下发的两种情况？

1：用户提供方案 else 系统默认
2：用户可以监听，但是还有一些任务用户做不了，我们还是要做

    @discardableResult
    open func request(_ urlRequest: URLRequestConvertible) -> DataRequest {
        var originalRequest: URLRequest?

        do {
            originalRequest = try urlRequest.asURLRequest()
            let originalTask = DataRequest.Requestable(urlRequest: originalRequest!)

            let task = try originalTask.task(session: session, adapter: adapter, queue: queue)
            let request = DataRequest(session: session, requestTask: .data(originalTask, task))

            delegate[task] = request

            if startRequestsImmediately { request.resume() }

            return request
        } catch {
            return request(originalRequest, failedWith: error)
        }
    }

delegate[task] = request request和task(URLSessionTask)绑定在一起，SessionDelegate下标法
Requestable 结构体相当与一个助理的身份，实现TaskConvertible协议的task方法

    struct Requestable: TaskConvertible {
        let urlRequest: URLRequest

        func task(session: URLSession, adapter: RequestAdapter?, queue: DispatchQueue) throws -> URLSessionTask {
            do {
                let urlRequest = try self.urlRequest.adapt(using: adapter)
                return queue.sync { session.dataTask(with: urlRequest) }
            } catch {
                throw AdaptError(error: error)
            }
        }
    }

task方法，返回一个URLSessionTask
DataRequest初始化方法

    init(session: URLSession, requestTask: RequestTask, error: Error? = nil) {
        self.session = session

        switch requestTask {
        case .data(let originalTask, let task):
            taskDelegate = DataTaskDelegate(task: task)
            self.originalTask = originalTask
        case .download(let originalTask, let task):
            taskDelegate = DownloadTaskDelegate(task: task)
            self.originalTask = originalTask
        case .upload(let originalTask, let task):
            taskDelegate = UploadTaskDelegate(task: task)
            self.originalTask = originalTask
        case .stream(let originalTask, let task):
            taskDelegate = TaskDelegate(task: task)
            self.originalTask = originalTask
        }

        delegate.error = error
        delegate.queue.addOperation { self.endTime = CFAbsoluteTimeGetCurrent() }
    }

taskDelegate = DataTaskDelegate(task: task)
DataTaskDelegate初始化方法

    override init(task: URLSessionTask?) {
        mutableData = Data()
        progress = Progress(totalUnitCount: 0)

        super.init(task: task)
    }

TaskDelegate初始化方法

    init(task: URLSessionTask?) {
        _task = task

        self.queue = {
            let operationQueue = OperationQueue()

            operationQueue.maxConcurrentOperationCount = 1
            operationQueue.isSuspended = true
            operationQueue.qualityOfService = .utility

            return operationQueue
        }()
    }

SessionDelegate下标法

    open subscript(task: URLSessionTask) -> Request? {
        get {
            lock.lock() ; defer { lock.unlock() }
            return requests[task.taskIdentifier]
        }
        set {
            lock.lock() ; defer { lock.unlock() }
            requests[task.taskIdentifier] = newValue
        }
    }

五、Charles 演示get 和 post

post