如何使用 URLSessionStreamTask 和 URLSession 进行分块编码传输

You do, however, have an option as to how you receive the returned data. If you use the URLSession convenience APIs (dataTask(with:completionHandler:) and so on), URLSession will buffer all the incoming data and then pass it to your completion handler in one large Data value. That’s convenient in many situations but it doesn’t work well with a streamed resource. In that case you need to use the URLSession delegate-based APIs (dataTask(with:) and so on), which will call the urlSession(_:dataTask:didReceive:) session delegate method with chunks of data as they arrive.

至于我正在测试的特定端点，发现了以下内容:如果客户端向其发送流式请求，服务器似乎仅启用其流式响应(分块传输编码).这有点奇怪，而且 HTTP 规范绝对不需要.

As for the specific endpoint I was testing, the following was uncovered: It seems that the server only enables its streaming response (the chunked transfer encoding) if the client sends it a streaming request. That’s kinda weird, and definitely not required by the HTTP spec.

幸运的是，可以强制 URLSession 发送流式请求:

Fortunately, it is possible to force URLSession to send a streaming request:

1. 使用 uploadTask(withStreamedRequest:)

实现 urlSession(_:task:needNewBodyStream:) 委托方法以返回输入流，读取时返回请求正文

Implement the urlSession(_:task:needNewBodyStream:) delegate method to return an input stream that, when read, returns the request body

利润！

我附上了一些测试代码来展示这一点.在这种情况下，它使用一对绑定的流，将输入流传递给请求(按照上面的步骤 2)并保持输出流.

I’ve attached some test code that shows this in action. In this case it uses a bound pair of streams, passing the input stream to the request (per step 2 above) and holding on to the output stream.

如果您想实际发送数据作为请求正文的一部分，您可以通过写入输出流来实现.

If you want to actually send data as part of the request body you can do so by writing to the output stream.

class NetworkManager : NSObject, URLSessionDataDelegate {

static var shared = NetworkManager()

private var session: URLSession! = nil

override init() {
    super.init()
    let config = URLSessionConfiguration.default
    config.requestCachePolicy = .reloadIgnoringLocalCacheData
    self.session = URLSession(configuration: config, delegate: self, delegateQueue: .main)
}

private var streamingTask: URLSessionDataTask? = nil

var isStreaming: Bool { return self.streamingTask != nil }

func startStreaming() {
    precondition( !self.isStreaming )

    let url = URL(string: "ENTER STREAMING URL HERE")!
    let request = URLRequest(url: url)
    let task = self.session.uploadTask(withStreamedRequest: request)
    self.streamingTask = task
    task.resume()
}

func stopStreaming() {
    guard let task = self.streamingTask else {
        return
    }
    self.streamingTask = nil
    task.cancel()
    self.closeStream()
}

var outputStream: OutputStream? = nil

private func closeStream() {
    if let stream = self.outputStream {
        stream.close()
        self.outputStream = nil
    }
}

func urlSession(_ session: URLSession, task: URLSessionTask, needNewBodyStream completionHandler: @escaping (InputStream?) -> Void) {
    self.closeStream()

    var inStream: InputStream? = nil
    var outStream: OutputStream? = nil
    Stream.getBoundStreams(withBufferSize: 4096, inputStream: &inStream, outputStream: &outStream)
    self.outputStream = outStream

    completionHandler(inStream)
}

func urlSession(_ session: URLSession, dataTask: URLSessionDataTask, didReceive data: Data) {
    NSLog("task data: %@", data as NSData)
}

func urlSession(_ session: URLSession, task: URLSessionTask, didCompleteWithError error: Error?) {
    if let error = error as NSError? {
        NSLog("task error: %@ / %d", error.domain, error.code)
    } else {
        NSLog("task complete")
    }
}
}

您可以从任何地方调用网络代码，例如:

And you can call the networking code from anywhere such as:

class MainViewController : UITableViewController {

override func tableView(_ tableView: UITableView, didSelectRowAt indexPath: IndexPath) {
    if NetworkManager.shared.isStreaming {  
       NetworkManager.shared.stopStreaming() 
    } else {
       NetworkManager.shared.startStreaming() 
    }
    self.tableView.deselectRow(at: indexPath, animated: true)
}
}

希望这会有所帮助.

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