iOS开发网络编程之断点续传

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

@interface DownLoadManager ()
/** 下载任务 */
@property (nonatomic, strong) NSURLSessionDataTask *task;
/** session */
@property (nonatomic, strong) NSURLSession *session;
/** 写文件的流对象 */
@property (nonatomic, strong) NSOutputStream *stream;
/** 文件的总大小 */
@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，这样就能保证文件名唯一
#define Filename self.downLoadUrl.md5String
// 文件的存放路径（caches）
#define FileStorePath [[NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES) lastObject] stringByAppendingPathComponent: Filename]
// 使用plist文件存储已经下载的文件大小
#define TotalLengthPlist [[NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES) lastObject] stringByAppendingPathComponent:@"totalLength.plist"]
// 文件的已被下载的大小
#define DownloadLength [[[NSFileManager defaultManager] attributesOfItemAtPath: FileStorePath error:nil][NSFileSize] integerValue]

@implementation DownLoadManager

#pragma mark - 创建单例
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 - 公开方法

-(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(@"######文件已经下载过了");
      return nil;
    }

    // 创建请求
    NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:[NSURL URLWithString: self.downLoadUrl]];

    // 设置请求头
    // Range : bytes=xxx-xxx，从已经下载的长度开始到文件总长度的最后都要下载
    NSString *range = [NSString stringWithFormat:@"bytes=%zd-", DownloadLength];
    [request setValue:range forHTTPHeaderField:@"Range"];

    // 创建一个Data任务
    _task = [self.session dataTaskWithRequest:request];
  }
  return _task;
}

#pragma mark - <NSURLSessionDataDelegate>
/**
 * 1.接收到响应
 */
- (void)URLSession:(NSURLSession *)session dataTask:(NSURLSessionDataTask *)dataTask didReceiveResponse:(NSHTTPURLResponse *)response completionHandler:(void (^)(NSURLSessionResponseDisposition))completionHandler
{
  // 打开流
  [self.stream open];

  /*
   （Content-Length字段返回的是服务器对每次客户端请求要下载文件的大小）
   比如首次客户端请求下载文件A，大小为1000byte，那么第一次服务器返回的Content-Length = 1000，
   客户端下载到500byte，突然中断，再次请求的range为 “bytes=500-”，那么此时服务器返回的Content-Length为500
   所以对于单个文件进行多次下载的情况（断点续传），计算文件的总大小，必须把服务器返回的content-length加上本地存储的已经下载的文件大小
   */
  self.totalLength = [response.allHeaderFields[@"Content-Length"] integerValue] + DownloadLength;

  // 把此次已经下载的文件大小存储在plist文件
  NSMutableDictionary *dict = [NSMutableDictionary dictionaryWithContentsOfFile: TotalLengthPlist];
  if (dict == nil) dict = [NSMutableDictionary dictionary];
  dict[ Filename] = @(self.totalLength);
  [dict writeToFile: TotalLengthPlist atomically:YES];

  // 接收这个请求，允许接收服务器的数据
  completionHandler(NSURLSessionResponseAllow);
}

/**
 * 2.接收到服务器返回的数据（这个方法可能会被调用N次）
 */
- (void)URLSession:(NSURLSession *)session dataTask:(NSURLSessionDataTask *)dataTask didReceiveData:(NSData *)data
{
  // 写入数据
  [self.stream write:data.bytes maxLength:data.length];

  float progress = 1.0 * DownloadLength / self.totalLength;
  if (self.progressBlock) {
    self.progressBlock(progress);
  }
  // 下载进度
}

/**
 * 3.请求完毕（成功失败）
 */
- (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);
    }
    // 关闭流
    [self.stream close];
    self.stream = nil;
    // 清除任务
    self.task = nil;
  }
}

@end								 
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