Swift-SessionDataTask断点下载文件

import UIKit
import Foundation

class PublicFunction: NSObject {
    //MARK:获取文件大小
    static func fileSizeForPath(path:String) -> UInt64 {
        var fileSize : UInt64 = 0
        do {
            let attr = try FileManager.default.attributesOfItem(atPath: path)
            fileSize = attr[FileAttributeKey.size] as! UInt64

            let dict = attr as NSDictionary
            fileSize = dict.fileSize()
        } catch {
            print("Error: \(error)")
        }
        return fileSize
    }
    //MARK:document文档目录
    static func documentPath() -> String {
        let documentPath = NSSearchPathForDirectoriesInDomains(.documentDirectory, .userDomainMask, true).first! as String
        return documentPath
    }
    //MARK:下载文件路径
    static func downloadDirectory(path:String) -> String {
        let downloadFile = PublicFunction.documentPath() + "/\(path)/"
        let fileManager = FileManager.default
        if fileManager.fileExists(atPath: downloadFile) == false {
            do {
                try fileManager.createDirectory(atPath: downloadFile, withIntermediateDirectories: true, attributes: nil)
            } catch {
                print(error)
            }
        }
        return downloadFile
    }
}

import UIKit

class DownDataTaskTool: NSObject, URLSessionTaskDelegate, URLSessionDataDelegate {
    //文件资源地址
    var downUrl:String = ""
    //保存路径
    var savePath:String = ""
    
    //文件总大小
    var totalContentLength:Float = 0
    //已下载大小
    var totalReceivedContentLength:Float = 0
    
    //下载进度回调
    var progressBlock: ((Float) -> ())?
    
    var currentSession:URLSession?
    var downloadTask:URLSessionDataTask?
    
    override init() {
        super.init()
        currentSession = URLSession(configuration: URLSessionConfiguration.default, delegate: self, delegateQueue: OperationQueue.main)
    }
    
    //MARK:创建下载
    @objc func createDownloadTask() {
        //下载地址
        let Url = URL(string: self.downUrl)
        //请求
        var request = URLRequest(url: Url!)
        //下载文件大小
        totalReceivedContentLength = Float(PublicFunction.fileSizeForPath(path:self.savePath))
        print("本地文件大小---\(totalReceivedContentLength)")
        //设置请求头
        if totalReceivedContentLength > 0 {
            let contentRange = "bytes=\(PublicFunction.fileSizeForPath(path:self.savePath))-"
            print("设置下载偏移量---\(contentRange)")
            request.addValue(contentRange, forHTTPHeaderField: "Range")
        }
        self.downloadTask = currentSession?.dataTask(with: request)
    }
    
    //MARK:启动断点续传下载请求
    func start() {
        print("下载文件大小---\(totalReceivedContentLength)")
        self.downloadTask?.resume()
    }
    
    //MARK:取消断点续传下载请求
    func cancel() {
        self.downloadTask?.suspend()
    }
    
    // 当用户确定, 继续接受数据的时候调用
    func urlSession(_ session: URLSession, dataTask: URLSessionDataTask, didReceive data: Data) {
        
        //更新进度
        totalReceivedContentLength += Float(data.count)
        
        let response:HTTPURLResponse = dataTask.response as! HTTPURLResponse
        if response.statusCode == 200 {
            totalContentLength = Float(dataTask.countOfBytesExpectedToReceive)
        } else if (response.statusCode == 206) {
            let contentRange:String = response.allHeaderFields["content-range"] as! String
            if contentRange.hasPrefix("bytes") {
                let bytes:Array = contentRange.components(separatedBy: CharacterSet.init(charactersIn: " -/"))
                if bytes.count == 4 {
                    totalContentLength = Float(bytes[3])!
                }
            }
        } else {
            print("statusCode---\(response.statusCode)")
        }
        
        
        //保存文件
        let fileHandle = FileHandle.init(forUpdatingAtPath: self.savePath)
        fileHandle?.seekToEndOfFile()//将节点跳到文件的末尾

        fileHandle?.write(data)//追加写入数据
        fileHandle?.closeFile()
        
        
        //下载进度
        let proValu:Float = Float(totalReceivedContentLength/totalContentLength)
        //print("总文件大小---\(totalReceivedContentLength)---\(totalContentLength)")
        if let onProgress = progressBlock {
            onProgress(proValu)
        }
    }
    
    // 请求完成时候调用
    func urlSession(_ session: URLSession, task: URLSessionTask, didCompleteWithError error: Error?) {
        if error == nil {
            print("下载完成---\(totalReceivedContentLength)---\(totalContentLength)")
            self.downloadTask?.cancel()
        }
    }
}

//退出，会先读取本地文件大小，跟着之前下载的进度
let downLoadManager = DownDataTaskTool()
downLoadManager.downUrl = "https://webfs.ali.kugou.com/202108021358/f8e446476833e4c950f58d07762c4827/KGTX/CLTX001/84ea1667187279849794a9cc96fa0d27.mp3"
let savePath = PublicFunction.downloadDirectory(path: "download") + "222.mp3"
downLoadManager.savePath = savePath
downLoadManager.createDownloadTask()

if !FileManager.default.fileExists(atPath: savePath) {
     print("初始化创建文件")
     FileManager.default.createFile(atPath: savePath, contents: nil, attributes: nil)
}
        
//更新下载进度
downLoadManager.progressBlock = { (progress) in
    OperationQueue.main.addOperation {
    print("下载进度：\(progress)")
    }
}
//开始下载
downLoadManager.start()
//暂停下载
downLoadManager.cancel()