NSURLSessionDownloadTask大文件断点下载

warning:逻辑不完整,可酌情参考,后面完善逻辑

<NSURLSessionDownloadDelegate>

#import "ViewController.h"

// resumeData的文件路径
#define ZYXResumeDataFile [[NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES) lastObject] stringByAppendingPathComponent:@"resumeData.tmpdata"]

@interface ViewController () <NSURLSessionDownloadDelegate>
/** 下载任务 */
@property (nonatomic, strong) NSURLSessionDownloadTask *task;
/** 保存上次的下载信息 */
@property (nonatomic, strong) NSData *resumeData;
/** session */
@property (nonatomic, strong) NSURLSession *session;
@end

@implementation ViewController

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

- (NSData *)resumeData{
    if (!_resumeData) {
        _resumeData = [NSData dataWithContentsOfFile:ZYXResumeDataFile];
    }
    return _resumeData;
}

/**
 * 开始下载
 */
- (IBAction)start:(id)sender {
    // 获得下载任务
    NSString *urlString = @"http://www.example.com:8080/resources/videos/minion_01.mp4";
    NSURL *url = [NSURL URLWithString:urlString];
    self.task = [self.session downloadTaskWithURL:url];
    [self.task resume];
}

/**
 * 暂停下载
 */
- (IBAction)pause:(id)sender {
    // 一旦这个task被取消了，就无法再恢复
    [self.task cancelByProducingResumeData:^(NSData *resumeData) {
        self.resumeData = resumeData;
        // 可以将resumeData写入沙盒，保存起来
        // 下次进入程序，就可以将resumeData读取进来，继续下载
        [resumeData writeToFile:ZYXResumeDataFile atomically:YES];
    }];
}

/**
 * 继续下载
 */
- (IBAction)goOn:(id)sender {
    self.task = [self.session downloadTaskWithResumeData:self.resumeData];
    [self.task resume];
}

#pragma mark - <NSURLSessionDownloadDelegate>

- (void)URLSession:(NSURLSession *)session
      downloadTask:(NSURLSessionDownloadTask *)downloadTask
 didResumeAtOffset:(int64_t)fileOffset
expectedTotalBytes:(int64_t)expectedTotalBytes{
    NSLog(@"%s",__func__);
}

/**
 * 每当写入数据到临时文件时，就会调用一次这个方法
 * totalBytesExpectedToWrite:总大小
 * totalBytesWritten: 已经写入的大小
 * bytesWritten: 这次写入多少
 */
- (void)URLSession:(NSURLSession *)session
      downloadTask:(NSURLSessionDownloadTask *)downloadTask
      didWriteData:(int64_t)bytesWritten
 totalBytesWritten:(int64_t)totalBytesWritten
totalBytesExpectedToWrite:(int64_t)totalBytesExpectedToWrite{
    NSLog(@"%f", 1.0 * totalBytesWritten / totalBytesExpectedToWrite);
}

/**
 * 下载完毕就会调用一次这个方法
 */
- (void)URLSession:(NSURLSession *)session
      downloadTask:(NSURLSessionDownloadTask *)downloadTask
didFinishDownloadingToURL:(NSURL *)location{
    // 文件存放的真实路径
    NSString *file = [[NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES) lastObject]
                      stringByAppendingPathComponent:downloadTask.response.suggestedFilename];
    NSLog(@"%@",file);
    // 剪切location的临时文件到真实路径
    NSFileManager *mgr = [NSFileManager defaultManager];
    [mgr moveItemAtURL:location toURL:[NSURL fileURLWithPath:file] error:nil];
}

- (void)URLSession:(NSURLSession *)session
              task:(NSURLSessionDownloadTask *)task
didCompleteWithError:(NSError *)error{
    // 保存恢复数据
    self.resumeData = error.userInfo[NSURLSessionDownloadTaskResumeData];
}

@end

实现离线断点下载

//
//  ViewController.m
//  05-掌握-大文件下载
//  Created by xiaomage on 15/7/15.
//

#import "ViewController.h"


#import "NSString+Hash.h"
#import "UIImageView+WebCache.h"

// 所需要下载的文件的URL
#define ZYXRemoteServerFileURL @"http://120.25.226.186:32812/resources/videos/minion_02.mp4"

// 文件名（沙盒中的文件名）
#define ZYXFilename ZYXRemoteServerFileURL.md5String

// 文件的存放路径（caches）
#define ZYXFileFullpath [[NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES) lastObject] stringByAppendingPathComponent:ZYXFilename]

// 存储文件总长度的文件路径（caches）
#define ZYXTotalLengthFullpath [[NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES) lastObject] stringByAppendingPathComponent:@"totalLength.info"]

// 文件的已下载长度
#define ZYXDownloadLength [[[NSFileManager defaultManager] attributesOfItemAtPath:ZYXFileFullpath error:nil][NSFileSize] integerValue]



@interface ViewController () <NSURLSessionDataDelegate>
/** 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;
/** 文件的总长度 */
@property (nonatomic, assign) NSInteger totalLength;
@end


@implementation ViewController

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

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

- (NSURLSessionDataTask *)task{
    if (!_task) {
        NSInteger totalLength = [[NSDictionary dictionaryWithContentsOfFile:ZYXTotalLengthFullpath][ZYXFilename] integerValue];
        if (totalLength && ZYXDownloadLength == totalLength) {
            NSLog(@"----文件已经下载过了");
            return nil;
        }
        
        // 创建请求
        NSURL *url = [NSURL URLWithString:ZYXRemoteServerFileURL];
        NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url];
        
        // 设置请求头
        // Range : bytes=xxx-xxx
        NSString *range = [NSString stringWithFormat:@"bytes=%zd-", ZYXDownloadLength];
        [request setValue:range forHTTPHeaderField:@"Range"];
        
        // 创建一个Data任务
        _task = [self.session dataTaskWithRequest:request];
    }
    
    return _task;
}


/**
 * 开始下载
 */
- (IBAction)start:(id)sender {
    // 启动任务
    [self.task resume];
}

/**
 * 暂停下载
 */
- (IBAction)pause:(id)sender {
    [self.task suspend];
}


#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];
    // 获得服务器这次请求 返回数据的总长度
    self.totalLength = [response.allHeaderFields[@"Content-Length"] integerValue] + ZYXDownloadLength;
    // 存储总长度
    NSMutableDictionary *dict = [NSMutableDictionary dictionaryWithContentsOfFile:ZYXTotalLengthFullpath];
    if (dict == nil) dict = [NSMutableDictionary dictionary];
    dict[ZYXFilename] = @(self.totalLength);
    [dict writeToFile:ZYXTotalLengthFullpath 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];
    // 下载进度
    NSLog(@"%f", 1.0 * ZYXDownloadLength / self.totalLength);
}

/**
 * 3.请求完毕（成功\失败）
 */
- (void)URLSession:(NSURLSession *)session
              task:(NSURLSessionTask *)task
didCompleteWithError:(NSError *)error{
    // 关闭流
    [self.stream close];
    self.stream = nil;
    // 清除任务
    self.task = nil;
}


- (void)viewDidLoad{
    [super viewDidLoad];
    
    NSLog(@"%@", ZYXFileFullpath);
    // /Users/admin/Library/Developer/CoreSimulator/Devices/95A0E48B-2AF9-45A0-83AE-6C065C293B5E/data/Containers/Data/Application/FCBA4453-906F-41BC-BE1C-094DF443D45F/Library/Caches/5b865634ad2abfa49e9ce097e87a8027
    
}

@end