Alamofie의SessionManager,SessionDelegate와TaskDelegate는 네트워크 요청의 중추이다.SessionManager는SessionDelegate 대상을 가지고 있고,SessionDelegate 대상은URLSessionDelegate,URLSessionTaskDelegate,URLSessionDataDelegate와URLSessionStreamDelegate 프로토콜을 실현한다.

SessionManager

SessionManager를 초기화하고 기본적으로 SessionDelegate 유형의 객체에 값을 부여합니다.

public init(
        configuration: URLSessionConfiguration = URLSessionConfiguration.default,
        delegate: SessionDelegate = SessionDelegate(),
        serverTrustPolicyManager: ServerTrustPolicyManager? = nil)
    {
        self.delegate = delegate
        self.session = URLSession(configuration: configuration, delegate: delegate, delegateQueue: nil)

        commonInit(serverTrustPolicyManager: serverTrustPolicyManager)
    }

    /// Creates an instance with the specified `session`, `delegate` and `serverTrustPolicyManager`.
    ///
    /// - parameter session:                  The URL session.
    /// - parameter delegate:                 The delegate of the URL session. Must equal the URL session's delegate.
    /// - parameter serverTrustPolicyManager: The server trust policy manager to use for evaluating all server trust
    ///                                       challenges. `nil` by default.
    ///
    /// - returns: The new `SessionManager` instance if the URL session's delegate matches; `nil` otherwise.
    public init?(
        session: URLSession,
        delegate: SessionDelegate,
        serverTrustPolicyManager: ServerTrustPolicyManager? = nil)
    {
        guard delegate === session.delegate else { return nil }

        self.delegate = delegate
        self.session = session

        commonInit(serverTrustPolicyManager: serverTrustPolicyManager)
    }

    private func commonInit(serverTrustPolicyManager: ServerTrustPolicyManager?) {
        session.serverTrustPolicyManager = serverTrustPolicyManager

        delegate.sessionManager = self

        delegate.sessionDidFinishEventsForBackgroundURLSession = { [weak self] session in
            guard let strongSelf = self else { return }
            DispatchQueue.main.async { strongSelf.backgroundCompletionHandler?() }
        }
    }

AFNetWorking에 비해 대기열 이름이 변경되었습니다.

let queue = DispatchQueue(label: "org.alamofire.session-manager." + UUID().uuidString)

작성자는 두 스레드가 동시에 작동하지 않도록 디렉토리를 만드는 방식으로 데이터를 업로드합니다.

   open func upload(
        multipartFormData: @escaping (MultipartFormData) -> Void,
        usingThreshold encodingMemoryThreshold: UInt64 = SessionManager.multipartFormDataEncodingMemoryThreshold,
        with urlRequest: URLRequestConvertible,
        encodingCompletion: ((MultipartFormDataEncodingResult) -> Void)?)
    {
        DispatchQueue.global(qos: .utility).async {
            let formData = MultipartFormData()
            multipartFormData(formData)

            var tempFileURL: URL?

            do {
                var urlRequestWithContentType = try urlRequest.asURLRequest()
                urlRequestWithContentType.setValue(formData.contentType, forHTTPHeaderField: "Content-Type")

                let isBackgroundSession = self.session.configuration.identifier != nil

                if formData.contentLength < encodingMemoryThreshold && !isBackgroundSession {
                    let data = try formData.encode()

                    let encodingResult = MultipartFormDataEncodingResult.success(
                        request: self.upload(data, with: urlRequestWithContentType),
                        streamingFromDisk: false,
                        streamFileURL: nil
                    )

                    DispatchQueue.main.async { encodingCompletion?(encodingResult) }
                } else {
                    let fileManager = FileManager.default
                    let tempDirectoryURL = URL(fileURLWithPath: NSTemporaryDirectory())
                    let directoryURL = tempDirectoryURL.appendingPathComponent("org.alamofire.manager/multipart.form.data")
                    let fileName = UUID().uuidString
                    let fileURL = directoryURL.appendingPathComponent(fileName)

                    tempFileURL = fileURL

                    var directoryError: Error?

                    // Create directory inside serial queue to ensure two threads don't do this in parallel
                    self.queue.sync {
                        do {
                            try fileManager.createDirectory(at: directoryURL, withIntermediateDirectories: true, attributes: nil)
                        } catch {
                            directoryError = error
                        }
                    }

                    if let directoryError = directoryError { throw directoryError }

                    try formData.writeEncodedData(to: fileURL)

                    let upload = self.upload(fileURL, with: urlRequestWithContentType)

                    // Cleanup the temp file once the upload is complete
                    upload.delegate.queue.addOperation {
                        do {
                            try FileManager.default.removeItem(at: fileURL)
                        } catch {
                            // No-op
                        }
                    }

                    DispatchQueue.main.async {
                        let encodingResult = MultipartFormDataEncodingResult.success(
                            request: upload,
                            streamingFromDisk: true,
                            streamFileURL: fileURL
                        )

                        encodingCompletion?(encodingResult)
                    }
                }
            } catch {
                // Cleanup the temp file in the event that the multipart form data encoding failed
                if let tempFileURL = tempFileURL {
                    do {
                        try FileManager.default.removeItem(at: tempFileURL)
                    } catch {
                        // No-op
                    }
                }

                DispatchQueue.main.async { encodingCompletion?(.failure(error)) }
            }
        }
    }

SessionDelegate & TaskDelegate

SessionDelegate 대상은URLSessionDelegate,URLSessionTaskDelegate,URLSessionDataDelegate와URLSessionStreamDelegate 프로토콜을 실현합니다.

    open func urlSession(
        _ session: URLSession,
        downloadTask: URLSessionDownloadTask,
        didWriteData bytesWritten: Int64,
        totalBytesWritten: Int64,
        totalBytesExpectedToWrite: Int64)
    {
        if let downloadTaskDidWriteData = downloadTaskDidWriteData {
            downloadTaskDidWriteData(session, downloadTask, bytesWritten, totalBytesWritten, totalBytesExpectedToWrite)
        } else if let delegate = self[downloadTask]?.delegate as? DownloadTaskDelegate {
            delegate.urlSession(
                session,
                downloadTask: downloadTask,
                didWriteData: bytesWritten,
                totalBytesWritten: totalBytesWritten,
                totalBytesExpectedToWrite: totalBytesExpectedToWrite
            )
        }
    }

SessionDelegate는 사용자 정의 아래 첨자를 통해 TaskDelegate의 코드를 제거하는 것이 비교적 참고할 만한 가치가 있습니다.

  /// Access the task delegate for the specified task in a thread-safe manner.
    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
        }
    }

TaskDelegate의 하위 클래스 DownloadTaskDelegate 다운로드 진행 방법에 대한 리셋 구현:

   func urlSession(
        _ session: URLSession,
        downloadTask: URLSessionDownloadTask,
        didWriteData bytesWritten: Int64,
        totalBytesWritten: Int64,
        totalBytesExpectedToWrite: Int64)
    {
        if initialResponseTime == nil { initialResponseTime = CFAbsoluteTimeGetCurrent() }

        if let downloadTaskDidWriteData = downloadTaskDidWriteData {
            downloadTaskDidWriteData(
                session,
                downloadTask,
                bytesWritten,
                totalBytesWritten,
                totalBytesExpectedToWrite
            )
        } else {
            progress.totalUnitCount = totalBytesExpectedToWrite
            progress.completedUnitCount = totalBytesWritten

            if let progressHandler = progressHandler {
                progressHandler.queue.async { progressHandler.closure(self.progress) }
            }
        }
    }

DispatchQueue

Alamofire는 DispatchQueue 호출 대기열 설정 매개변수 유형을 간단하게 확장합니다.

import Dispatch
import Foundation

extension DispatchQueue {
    static var userInteractive: DispatchQueue { return DispatchQueue.global(qos: .userInteractive) }
    static var userInitiated: DispatchQueue { return DispatchQueue.global(qos: .userInitiated) }
    static var utility: DispatchQueue { return DispatchQueue.global(qos: .utility) }
    static var background: DispatchQueue { return DispatchQueue.global(qos: .background) }

    func after(_ delay: TimeInterval, execute closure: @escaping () -> Void) {
        asyncAfter(deadline: .now() + delay, execute: closure)
    }
}

MultipartFormData

MultipartFormData에서 boundaryType에 대한 판단 및 패키지 코드:

open class MultipartFormData {

    // MARK: - Helper Types

    struct EncodingCharacters {
        static let crlf = "\r
"
    }

    struct BoundaryGenerator {
        enum BoundaryType {
            case initial, encapsulated, final
        }

        static func randomBoundary() -> String {
            return String(format: "alamofire.boundary.%08x%08x", arc4random(), arc4random())
        }

        static func boundaryData(forBoundaryType boundaryType: BoundaryType, boundary: String) -> Data {
            let boundaryText: String

            switch boundaryType {
            case .initial:
                boundaryText = "--\(boundary)\(EncodingCharacters.crlf)"
            case .encapsulated:
                boundaryText = "\(EncodingCharacters.crlf)--\(boundary)\(EncodingCharacters.crlf)"
            case .final:
                boundaryText = "\(EncodingCharacters.crlf)--\(boundary)--\(EncodingCharacters.crlf)"
            }

            return boundaryText.data(using: String.Encoding.utf8, allowLossyConversion: false)!
        }
    }

저자 append 방법의 주석을 보았을 때 순간적으로 작가에게 경건함을 느꼈습니다.

   public func append(_ fileURL: URL, withName name: String, fileName: String, mimeType: String) {
        let headers = contentHeaders(withName: name, fileName: fileName, mimeType: mimeType)

        //============================================================
        //                 Check 1 - is file URL?
        //============================================================

        guard fileURL.isFileURL else {
            setBodyPartError(withReason: .bodyPartURLInvalid(url: fileURL))
            return
        }

        //============================================================
        //              Check 2 - is file URL reachable?
        //============================================================

        do {
            let isReachable = try fileURL.checkPromisedItemIsReachable()
            guard isReachable else {
                setBodyPartError(withReason: .bodyPartFileNotReachable(at: fileURL))
                return
            }
        } catch {
            setBodyPartError(withReason: .bodyPartFileNotReachableWithError(atURL: fileURL, error: error))
            return
        }

        //============================================================
        //            Check 3 - is file URL a directory?
        //============================================================

        var isDirectory: ObjCBool = false
        let path = fileURL.path

        guard FileManager.default.fileExists(atPath: path, isDirectory: &isDirectory) && !isDirectory.boolValue else {
            setBodyPartError(withReason: .bodyPartFileIsDirectory(at: fileURL))
            return
        }

        //============================================================
        //          Check 4 - can the file size be extracted?
        //============================================================

        let bodyContentLength: UInt64

        do {
            guard let fileSize = try FileManager.default.attributesOfItem(atPath: path)[.size] as? NSNumber else {
                setBodyPartError(withReason: .bodyPartFileSizeNotAvailable(at: fileURL))
                return
            }

            bodyContentLength = fileSize.uint64Value
        }
        catch {
            setBodyPartError(withReason: .bodyPartFileSizeQueryFailedWithError(forURL: fileURL, error: error))
            return
        }

        //============================================================
        //       Check 5 - can a stream be created from file URL?
        //============================================================

        guard let stream = InputStream(url: fileURL) else {
            setBodyPartError(withReason: .bodyPartInputStreamCreationFailed(for: fileURL))
            return
        }

        append(stream, withLength: bodyContentLength, headers: headers)
    }