这个文件定义了几个delegate类型。TaskDelegate是DataTaskDelegate、DownloadTaskDelegate的父类；其中DataTaskDelegate是UploadTaskDelegate的父类。
1. TaskDelegate
跟SessionDelegate类似，TaskDelegate用于处理task的所有回调和执行队列的operations。
1) 属性和初始化方法
// 任务完成后，执行这个队列里的所有operations
open let queue: OperationQueue
// 服务器返回的数据，这里返回nil，然后让子类去重写
public var data: Data? { return nil }
// 整个任务过程中出现的错误
public var error: Error?
// 作者为了在get和set的时候加锁，定义了一个私有的_task
var task: URLSessionTask? {
set {
taskLock.lock(); defer { taskLock.unlock() }
_task = newValue
}
get {
taskLock.lock(); defer { taskLock.unlock() }
return _task
}
}
var initialResponseTime: CFAbsoluteTime? // 服务器最开始响应的时间
var credential: URLCredential? // URL证书
var metrics: AnyObject? // URLSessionTaskMetrics
private var _task: URLSessionTask? {
didSet { reset() }
}
private let taskLock = NSLock()
init(task: URLSessionTask?) {
_task = task
// 这里利用了一个closure来初始化queue
// 我们可以学习这种模式，可以让代码看起来更清晰
self.queue = {
let operationQueue = OperationQueue()
operationQueue.maxConcurrentOperationCount = 1
// 刚初始化，把这个属性设置为true暂时不执行队列里面的operation
operationQueue.isSuspended = true
operationQueue.qualityOfService = .utility
return operationQueue
}()
}
func reset() {
error = nil
initialResponseTime = nil
}
2) 实现URLSessionTaskDelegate
// 定义了与回调对应的closure
var taskWillPerformHTTPRedirection: ((URLSession, URLSessionTask, HTTPURLResponse, URLRequest) -> URLRequest?)?
var taskDidReceiveChallenge: ((URLSession, URLSessionTask, URLAuthenticationChallenge) -> (URLSession.AuthChallengeDisposition, URLCredential?))?
var taskNeedNewBodyStream: ((URLSession, URLSessionTask) -> InputStream?)?
var taskDidCompleteWithError: ((URLSession, URLSessionTask, Error?) -> Void)?
// 告诉代理服务器请求HTTP重定向
// @objc的意思是告诉在OC使用的时候如何显示这个方法
@objc(URLSession:task:willPerformHTTPRedirection:newRequest:completionHandler:)
func urlSession(
_ session: URLSession,
task: URLSessionTask,
willPerformHTTPRedirection response: HTTPURLResponse,
newRequest request: URLRequest,
completionHandler: @escaping (URLRequest?) -> Void)
{
var redirectRequest: URLRequest? = request
// 如果提供了taskWillPerformHTTPRedirection，则更新redirectRequest
if let taskWillPerformHTTPRedirection = taskWillPerformHTTPRedirection {
redirectRequest = taskWillPerformHTTPRedirection(session, task, response, request)
}
completionHandler(redirectRequest)
}
// 服务器请求认证
@objc(URLSession:task:didReceiveChallenge:completionHandler:)
func urlSession(
_ session: URLSession,
task: URLSessionTask,
didReceive challenge: URLAuthenticationChallenge,
completionHandler: @escaping (URLSession.AuthChallengeDisposition, URLCredential?) -> Void)
{
// 初始化一个默认的配置，就像客户端没有实现这个回调
var disposition: URLSession.AuthChallengeDisposition = .performDefaultHandling
var credential: URLCredential?
if let taskDidReceiveChallenge = taskDidReceiveChallenge {
// 如果taskDidReceiveChallenge，更新disposition和credential
(disposition, credential) = taskDidReceiveChallenge(session, task, challenge)
} else if challenge.protectionSpace.authenticationMethod == NSURLAuthenticationMethodServerTrust { // 认证方法是ServerTrust
// 获取保护区域的主机地址
let host = challenge.protectionSpace.host
// 判断我们是否提供了服务器信任策略
if let serverTrustPolicy = session.serverTrustPolicyManager?.serverTrustPolicy(forHost: host),
let serverTrust = challenge.protectionSpace.serverTrust
{
// 评估serverTrust对这个主机地址是否有效
if serverTrustPolicy.evaluate(serverTrust, forHost: host) {
// 评估通过，把disposition更新为使用证书；并更新证书
disposition = .useCredential
credential = URLCredential(trust: serverTrust)
} else {
// 评估不通过，取消认证，整个请求也会被取消
disposition = .cancelAuthenticationChallenge
}
}
} else {
if challenge.previousFailureCount > 0 { // 之前认证失败的次数大于0
// 更新disposition为rejectProtectionSpace，当前这个challenge被拒绝
disposition = .rejectProtectionSpace
} else { // 之前认证失败的次数不大于0
// 使用证书进行认证
credential = self.credential ?? session.configuration.urlCredentialStorage?.defaultCredential(for: challenge.protectionSpace)
if credential != nil {
disposition = .useCredential
}
}
}
// 最后执行completionHandler
completionHandler(disposition, credential)
}
// 服务器请求新的inputStream
@objc(URLSession:task:needNewBodyStream:)
func urlSession(
_ session: URLSession,
task: URLSessionTask,
needNewBodyStream completionHandler: @escaping (InputStream?) -> Void)
{
var bodyStream: InputStream?
if let taskNeedNewBodyStream = taskNeedNewBodyStream {
bodyStream = taskNeedNewBodyStream(session, task)
}
completionHandler(bodyStream)
}
// 任务完成
@objc(URLSession:task:didCompleteWithError:)
func urlSession(_ session: URLSession, task: URLSessionTask, didCompleteWithError error: Error?) {
// 如果有taskDidCompleteWithError，则执行
if let taskDidCompleteWithError = taskDidCompleteWithError {
taskDidCompleteWithError(session, task, error)
} else { // 没有taskDidCompleteWithError
if let error = error {
// 设置error
if self.error == nil { self.error = error }
// 如果error不为空的话，userInfo里面携带有resumeData
if let downloadDelegate = self as? DownloadTaskDelegate,
let resumeData = (error as NSError).userInfo[NSURLSessionDownloadTaskResumeData] as? Data
{
downloadDelegate.resumeData = resumeData
}
}
// 执行队列里的所有operations
queue.isSuspended = false
}
}
2. DataTaskDelegate
1) 属性和初始化方法
var dataTask: URLSessionDataTask { return task as! URLSessionDataTask }
// 重写父类的属性，服务器返回的数据
override var data: Data? {
if dataStream != nil { // 如果有dataStream去处理data，这里的data就返回nil
return nil
} else {
return mutableData // 返回从服务器接收到的数据
}
}
var progress: Progress // 进度
var progressHandler: (closure: Request.ProgressHandler, queue: DispatchQueue)?
var dataStream: ((_ data: Data) -> Void)? // 处理数据的closure
private var totalBytesReceived: Int64 = 0
private var mutableData: Data // 用于存储从服务器接收到的数据
private var expectedContentLength: Int64? // 服务器文件的总大小
override init(task: URLSessionTask?) {
mutableData = Data()
progress = Progress(totalUnitCount: 0)
super.init(task: task)
}
override func reset() {
super.reset()
progress = Progress(totalUnitCount: 0)
totalBytesReceived = 0
mutableData = Data()
expectedContentLength = nil
}
3. DownloadTaskDelegate & UploadTaskDelegate
这两个delegate与DataTaskDelegate非常类似，大家可以自己看下，如果有不懂的，欢迎留言，我会尽力解答。
有任何问题，欢迎大家留言！
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