[[[NSFileManager defaultManager] attributesOfItemAtPath: FileStorePath error:nil][NSFileSize] integerValue]

- (void)URLSession:(NSURLSession *)session dataTask:(NSURLSessionDataTask *)dataTask didReceiveResponse:(NSHTTPURLResponse *)response completionHandler:(void (^)(NSURLSessionResponseDisposition))completionHandler
{
  self.totalLength = [response.allHeaderFields[@"Content-Length"] integerValue] + DownloadLength;

  NSMutableDictionary *dict = [NSMutableDictionary dictionaryWithContentsOfFile: TotalLengthPlist];

  if (dict == nil) dict = [NSMutableDictionary dictionary];
  dict[ Filename] = @(self.totalLength);

  [dict writeToFile: TotalLengthPlist atomically:YES];
}

-(void)downLoadWithURL:(NSString *)URL
       progress:(progressBlock)progressBlock
        success:(successBlock)successBlock
         faile:(faileBlock)faileBlock
{
  self.successBlock = successBlock;
  self.failedBlock = faileBlock;
  self.progressBlock = progressBlock;
  self.downLoadUrl = URL;
  [self.task resume];
}

#import <Foundation/Foundation.h>
typedef void (^successBlock) (NSString *fileStorePath);
typedef void (^faileBlock) (NSError *error);
typedef void (^progressBlock) (float progress);

@interface DownLoadManager : NSObject <NSURLSessionDataDelegate>
@property (copy) successBlock successBlock;
@property (copy) faileBlock   failedBlock;
@property (copy) progressBlock  progressBlock;


-(void)downLoadWithURL:(NSString *)URL
       progress:(progressBlock)progressBlock
        success:(successBlock)successBlock
         faile:(faileBlock)faileBlock;

+ (instancetype)sharedInstance;
-(void)stopTask;

@end

#import "DownLoadManager.h"
#import "NSString+Hash.h"

@interface DownLoadManager ()
/** 下載任務(wù) */
@property (nonatomic, strong) NSURLSessionDataTask *task;
/** session */
@property (nonatomic, strong) NSURLSession *session;
/** 寫(xiě)文件的流對(duì)象 */
@property (nonatomic, strong) NSOutputStream *stream;
/** 文件的總大小 */
@property (nonatomic, assign) NSInteger totalLength;
@property(nonatomic,strong)NSString *downLoadUrl;

@end


// 文件名（沙盒中的文件名），使用md5哈希url生成的，這樣就能保證文件名唯一
#define Filename self.downLoadUrl.md5String
// 文件的存放路徑（caches）
#define FileStorePath [[NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES) lastObject] stringByAppendingPathComponent: Filename]
// 使用plist文件存儲(chǔ)已經(jīng)下載的文件大小
#define TotalLengthPlist [[NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES) lastObject] stringByAppendingPathComponent:@"totalLength.plist"]
// 文件的已被下載的大小
#define DownloadLength [[[NSFileManager defaultManager] attributesOfItemAtPath: FileStorePath error:nil][NSFileSize] integerValue]

@implementation DownLoadManager

#pragma mark - 創(chuàng)建單例
static id _instance;

+ (instancetype)allocWithZone:(struct _NSZone *)zone
{
  static dispatch_once_t onceToken;
  dispatch_once(&onceToken, ^{
    _instance = [super allocWithZone:zone];
  });
  return _instance;
}

+ (instancetype)sharedInstance
{
  static dispatch_once_t onceToken;
  dispatch_once(&onceToken, ^{
    _instance = [[self alloc] init];
  });
  return _instance;
}

- (id)copyWithZone:(NSZone *)zone
{
  return _instance;
}

- (id)mutableCopyWithZone:(NSZone *)zone {
  return _instance;
}

#pragma mark - 公開(kāi)方法

-(void)downLoadWithURL:(NSString *)URL
       progress:(progressBlock)progressBlock
        success:(successBlock)successBlock
         faile:(faileBlock)faileBlock
{
  self.successBlock = successBlock;
  self.failedBlock = faileBlock;
  self.progressBlock = progressBlock;
  self.downLoadUrl = URL;
  [self.task resume];


}

-(void)stopTask{
  [self.task suspend ];

}


#pragma mark - getter方法
- (NSURLSession *)session
{
  if (!_session) {
    _session = [NSURLSession sessionWithConfiguration:[NSURLSessionConfiguration defaultSessionConfiguration] delegate:self delegateQueue:[[NSOperationQueue alloc] init]];
  }
  return _session;
}

- (NSOutputStream *)stream
{
  if (!_stream) {
    _stream = [NSOutputStream outputStreamToFileAtPath: FileStorePath append:YES];
  }
  return _stream;
}


- (NSURLSessionDataTask *)task
{
  if (!_task) {
    NSInteger totalLength = [[NSDictionary dictionaryWithContentsOfFile: TotalLengthPlist][ Filename] integerValue];

    if (totalLength && DownloadLength == totalLength) {
      NSLog(@"######文件已經(jīng)下載過(guò)了");
      return nil;
    }

    // 創(chuàng)建請(qǐng)求
    NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:[NSURL URLWithString: self.downLoadUrl]];

    // 設(shè)置請(qǐng)求頭
    // Range : bytes=xxx-xxx，從已經(jīng)下載的長(zhǎng)度開(kāi)始到文件總長(zhǎng)度的最后都要下載
    NSString *range = [NSString stringWithFormat:@"bytes=%zd-", DownloadLength];
    [request setValue:range forHTTPHeaderField:@"Range"];

    // 創(chuàng)建一個(gè)Data任務(wù)
    _task = [self.session dataTaskWithRequest:request];
  }
  return _task;
}

#pragma mark - <NSURLSessionDataDelegate>
/**
 * 1.接收到響應(yīng)
 */
- (void)URLSession:(NSURLSession *)session dataTask:(NSURLSessionDataTask *)dataTask didReceiveResponse:(NSHTTPURLResponse *)response completionHandler:(void (^)(NSURLSessionResponseDisposition))completionHandler
{
  // 打開(kāi)流
  [self.stream open];

  /*
   （Content-Length字段返回的是服務(wù)器對(duì)每次客戶端請(qǐng)求要下載文件的大小）
   比如首次客戶端請(qǐng)求下載文件A，大小為1000byte，那么第一次服務(wù)器返回的Content-Length = 1000，
   客戶端下載到500byte，突然中斷，再次請(qǐng)求的range為 “bytes=500-”，那么此時(shí)服務(wù)器返回的Content-Length為500
   所以對(duì)于單個(gè)文件進(jìn)行多次下載的情況（斷點(diǎn)續(xù)傳），計(jì)算文件的總大小，必須把服務(wù)器返回的content-length加上本地存儲(chǔ)的已經(jīng)下載的文件大小
   */
  self.totalLength = [response.allHeaderFields[@"Content-Length"] integerValue] + DownloadLength;

  // 把此次已經(jīng)下載的文件大小存儲(chǔ)在plist文件
  NSMutableDictionary *dict = [NSMutableDictionary dictionaryWithContentsOfFile: TotalLengthPlist];
  if (dict == nil) dict = [NSMutableDictionary dictionary];
  dict[ Filename] = @(self.totalLength);
  [dict writeToFile: TotalLengthPlist atomically:YES];

  // 接收這個(gè)請(qǐng)求，允許接收服務(wù)器的數(shù)據(jù)
  completionHandler(NSURLSessionResponseAllow);
}

/**
 * 2.接收到服務(wù)器返回的數(shù)據(jù)（這個(gè)方法可能會(huì)被調(diào)用N次）
 */
- (void)URLSession:(NSURLSession *)session dataTask:(NSURLSessionDataTask *)dataTask didReceiveData:(NSData *)data
{
  // 寫(xiě)入數(shù)據(jù)
  [self.stream write:data.bytes maxLength:data.length];

  float progress = 1.0 * DownloadLength / self.totalLength;
  if (self.progressBlock) {
    self.progressBlock(progress);
  }
  // 下載進(jìn)度
}

/**
 * 3.請(qǐng)求完畢（成功\失敗）
 */
- (void)URLSession:(NSURLSession *)session task:(NSURLSessionTask *)task didCompleteWithError:(NSError *)error
{
  if (error) {
    if (self.failedBlock) {
      self.failedBlock(error);
    }
    self.stream = nil;
    self.task = nil;

  }else{
    if (self.successBlock) {
      self.successBlock(FileStorePath);
    }
    // 關(guān)閉流
    [self.stream close];
    self.stream = nil;
    // 清除任務(wù)
    self.task = nil;
  }
}

@end

@interface ViewController ()
@end

@implementation ViewController
/**
 * 開(kāi)始下載
 */
- (IBAction)start:(id)sender {
  // 啟動(dòng)任務(wù)
  NSString * downLoadUrl = @"http://audio.xmcdn.com/group11/M01/93/AF/wKgDa1dzzJLBL0gCAPUzeJqK84Y539.m4a";

  [[DownLoadManager sharedInstance]downLoadWithURL:downLoadUrl progress:^(float progress) {
    NSLog(@"###%f",progress);

  } success:^(NSString *fileStorePath) {
    NSLog(@"###%@",fileStorePath);

  } faile:^(NSError *error) {
    NSLog(@"###%@",error.userInfo[NSLocalizedDescriptionKey]);
  }];
}
/**
 * 暫停下載
 */
- (IBAction)pause:(id)sender {
  [[DownLoadManager sharedInstance]stopTask];
}

@end