Repository: onevcat/Kingfisher
File: Sources/Networking/ImageDownloader.swift (Swift)

Code before:

    // MARK: Initializers

    /// Creates a downloader with name.
    ///
    /// - Parameter name: The name for the downloader. It should not be empty.
    public init(name: String) {
        if name.isEmpty {
            fatalError("[Kingfisher] You should specify a name for the downloader. "
                + "A downloader with empty name is not permitted.")
        }

        self.name = name

        sessionDelegate = SessionDelegate()
        session = URLSession(
            configuration: sessionConfiguration,
            delegate: sessionDelegate,
            delegateQueue: nil)

        authenticationChallengeResponder = self
        setupSessionHandler()
    }
    
    /// You could set the extra handler before a downloading task starts.
    public weak var extraSessionDelegateHandler:URLSessionDataDelegate? {
        set {sessionDelegate.setExtraHandler(newValue)}
        get {return sessionDelegate.getExtraHandler()}
    }
    
    deinit { session.invalidateAndCancel() }

    private func setupSessionHandler() {
        sessionDelegate.onReceiveSessionChallenge.delegate(on: self) { (self, invoke) in
            self.authenticationChallengeResponder?.downloader(self, didReceive: invoke.1, completionHandler: invoke.2)
        }
        sessionDelegate.onReceiveSessionTaskChallenge.delegate(on: self) { (self, invoke) in
            self.authenticationChallengeResponder?.downloader(
                self, task: invoke.1, didReceive: invoke.2, completionHandler: invoke.3)
        }
        sessionDelegate.onValidStatusCode.delegate(on: self) { (self, code) in
            return (self.delegate ?? self).isValidStatusCode(code, for: self)
        }
        sessionDelegate.onDownloadingFinished.delegate(on: self) { (self, value) in
            let (url, result) = value
            do {
                let value = try result.get()
                self.delegate?.imageDownloader(self, didFinishDownloadingImageForURL: url, with: value, error: nil)
            } catch {
                self.delegate?.imageDownloader(self, didFinishDownloadingImageForURL: url, with: nil, error: error)
            }

Review comment (suggestion):
```suggestion
    public var extraSessionDelegateHandler:URLSessionDataDelegate? {
```

For a getter/setter, there should be no need to mark it as `weak`.

Code after:

    // MARK: Initializers

    /// Creates a downloader with name.
    ///
    /// - Parameter name: The name for the downloader. It should not be empty.
    public init(name: String) {
        if name.isEmpty {
            fatalError("[Kingfisher] You should specify a name for the downloader. "
                + "A downloader with empty name is not permitted.")
        }

        self.name = name

        sessionDelegate = SessionDelegate()
        session = URLSession(
            configuration: sessionConfiguration,
            delegate: sessionDelegate,
            delegateQueue: nil)

        authenticationChallengeResponder = self
        setupSessionHandler()
    }
    
    /// You could set the extra handler before a downloading task starts.
    public var extraSessionDelegateHandler:URLSessionDataDelegate? {
        set {sessionDelegate.extraHandler = newValue}
        get {return sessionDelegate.extraHandler}
    }
    
    deinit { session.invalidateAndCancel() }

    private func setupSessionHandler() {
        sessionDelegate.onReceiveSessionChallenge.delegate(on: self) { (self, invoke) in
            self.authenticationChallengeResponder?.downloader(self, didReceive: invoke.1, completionHandler: invoke.2)
        }
        sessionDelegate.onReceiveSessionTaskChallenge.delegate(on: self) { (self, invoke) in
            self.authenticationChallengeResponder?.downloader(
                self, task: invoke.1, didReceive: invoke.2, completionHandler: invoke.3)
        }
        sessionDelegate.onValidStatusCode.delegate(on: self) { (self, code) in
            return (self.delegate ?? self).isValidStatusCode(code, for: self)
        }
        sessionDelegate.onDownloadingFinished.delegate(on: self) { (self, value) in
            let (url, result) = value
            do {
                let value = try result.get()
                self.delegate?.imageDownloader(self, didFinishDownloadingImageForURL: url, with: value, error: nil)
            } catch {
                self.delegate?.imageDownloader(self, didFinishDownloadingImageForURL: url, with: nil, error: error)
            }