如何在 Swift 3 中同时发出 https 请求

Question

我在执行 https 请求时遇到问题，如果请求没有任何错误，我永远不会收到消息，这是一个命令行工具应用程序，我有一个允许 http 请求的 plist，我总是查看完成块。

typealias escHandler = ( URLResponse?, Data? ) -> Void

func getRequest(url : URL, _ handler : @escaping escHandler){    
let session = URLSession.shared
var request = URLRequest(url:url)
request.cachePolicy = .reloadIgnoringLocalCacheData
request.httpMethod = "GET"
let task = session.dataTask(with: url ){ (data,response,error) in
        handler(response,data)
}

task.resume()
}


func startOp(action : @escaping () -> Void) -> BlockOperation{

let exOp = BlockOperation(block: action)    
exOp.completionBlock = {

print("Finished")

}
return exOp
}

     for sUrl in textFile.components(separatedBy: "\n"){
     let url = URL(string: sUrl)!

        let queu = startOp {
            getRequest(url: url){  response, data  in

                print("REACHED")



            }

        }
      operationQueue.addOperation(queu)
      operationQueue.waitUntilAllOperationsAreFinished()

Answer 1

一个问题是您的操作只是启动请求，但由于请求是异步执行的，因此操作会立即完成，而不是实际等待请求完成。您不想在异步请求完成之前完成操作。

如果您想对操作队列执行此操作，诀窍是您必须子class Operation 并为isExecuting 和isFinished 执行必要的KVO。然后，您在开始请求时更改 isExecuting，在完成请求时更改 isFinished，并为两者关联 KVO。 Concurrency Programming Guide: Defining a Custom Operation Object, notably in the Configuring Operations for Concurrent Execution 部分对此进行了概述。（请注意，本指南有点过时（它指的是 isConcurrent 属性，已被替换为 isAsynchronous；它专注于 Objective-C；等），但是它向您介绍了问题。

无论如何，这是一个抽象class，我用它来封装所有这些愚蠢的异步操作：

/// Asynchronous Operation base class
///
/// This class performs all of the necessary KVN of `isFinished` and
/// `isExecuting` for a concurrent `NSOperation` subclass. So, to developer
/// a concurrent NSOperation subclass, you instead subclass this class which:
///
/// - must override `main()` with the tasks that initiate the asynchronous task;
///
/// - must call `completeOperation()` function when the asynchronous task is done;
///
/// - optionally, periodically check `self.cancelled` status, performing any clean-up
///   necessary and then ensuring that `completeOperation()` is called; or
///   override `cancel` method, calling `super.cancel()` and then cleaning-up
///   and ensuring `completeOperation()` is called.

public class AsynchronousOperation : Operation {

    override public var isAsynchronous: Bool { return true }

    private let lock = NSLock()

    private var _executing: Bool = false
    override private(set) public var isExecuting: Bool {
        get {
            return lock.synchronize { _executing }
        }
        set {
            willChangeValue(forKey: "isExecuting")
            lock.synchronize { _executing = newValue }
            didChangeValue(forKey: "isExecuting")
        }
    }

    private var _finished: Bool = false
    override private(set) public var isFinished: Bool {
        get {
            return lock.synchronize { _finished }
        }
        set {
            willChangeValue(forKey: "isFinished")
            lock.synchronize { _finished = newValue }
            didChangeValue(forKey: "isFinished")
        }
    }

    /// Complete the operation
    ///
    /// This will result in the appropriate KVN of isFinished and isExecuting

    public func completeOperation() {
        if isExecuting {
            isExecuting = false
            isFinished = true
        }
    }

    override public func start() {
        if isCancelled {
            isFinished = true
            return
        }

        isExecuting = true

        main()
    }
}

并且我将此 Apple 扩展程序用于 NSLocking 以确保同步上面的状态更改（他们是 NSLock 上名为 withCriticalSection 的扩展程序，但这是一个稍微更通用的再现，处理任何符合 NSLocking 并处理抛出错误的闭包）：

extension NSLocking {

    /// Perform closure within lock.
    ///
    /// An extension to `NSLocking` to simplify executing critical code.
    ///
    /// - parameter block: The closure to be performed.

    func synchronize<T>(block: () throws -> T) rethrows -> T {
        lock()
        defer { unlock() }
        return try block()
    }
}

然后，我可以创建一个 NetworkOperation 并使用它：

class NetworkOperation: AsynchronousOperation {
    var task: URLSessionTask!

    init(session: URLSession, url: URL, requestCompletionHandler: @escaping (Data?, URLResponse?, Error?) -> ()) {
        super.init()

        task = session.dataTask(with: url) { data, response, error in
            requestCompletionHandler(data, response, error)
            self.completeOperation()
        }
    }

    override func main() {
        task.resume()
    }

    override func cancel() {
        task.cancel()
        super.cancel()
    }
}

无论如何，完成后，我现在可以为网络请求创建操作，例如：

let queue = OperationQueue()
queue.name = "com.domain.app.network"

let url = URL(string: "http://...")!
let operation = NetworkOperation(session: .shared, url: url) { data, response, error in
    guard let data = data, error == nil else {
        print("\(error)")
        return
    }

    let string = String(data: data, encoding: .utf8)
    print("\(string)")
    // do something with `data` here
}

let operation2 = BlockOperation {
    print("done")
}

operation2.addDependency(operation)

queue.addOperations([operation, operation2], waitUntilFinished: false) // if you're using command line app, you'd might use `true` for `waitUntilFinished`, but with standard Cocoa apps, you generally would not

注意，在上面的例子中，我添加了第二个操作，它只打印了一些东西，使其依赖于第一个操作，以说明第一个操作在网络请求完成后才完成。

显然，您通常不会使用原始示例中的 waitUntilAllOperationsAreFinished，也不会在我的示例中使用 addOperations 中的 waitUntilFinished 选项。但是因为您正在处理一个您不想在这些请求完成之前退出的命令行应用程序，所以这种模式是可以接受的。（我只是为了让未来的读者对 waitUntilFinished 的随心所欲的使用感到惊讶而提及这一点，这通常是不可取的。）

如何在 Swift 3 中同时发出 https 请求

How to make simultaneous https requests in Swift 3

http

concurrency

swift3

nsoperation

nsoperationqueue