大文件断点下载

ViewController.m

//
//  ViewController.m
//  005-urlsession
//
//  Created by 李建舜 on 15/02/2017.
//  Copyright © 2017 李建舜. All rights reserved.
//

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

// 所需要下载的文件的url
#define JSFileURL @"http://video.pearvideo.com/mp4/short/20170215/cont-1034279-10200514-hd.mp4"

// 文件名(沙盒中的文件名)
#define JSFileName JSFileURL.md5String

// 文件存放的路径
#define JSFileFullPath [[NSSearchPathForDirectoriesInDomains(NSCachesDirectory, NSUserDomainMask, YES) lastObject] stringByAppendingPathComponent:JSFileName]

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

// 文件的已下载的长度
#define JSDownloadLength [[[NSFileManager defaultManager] attributesOfItemAtPath:JSFileFullPath error:nil][NSFileSize] integerValue]

@interface ViewController () <NSURLSessionDataDelegate>

/** 下载任务 */
@property (nonatomic, strong) NSURLSessionDataTask *task;

/** 保存上次下载信息 */
//@property (nonatomic, strong) NSData *resumeData;
/** 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:JSFileFullPath append:YES];
    }
    return _stream;
}


- (NSURLSessionDataTask *)task {
    if (!_task) {
        
        NSInteger totalLength = [[NSDictionary dictionaryWithContentsOfFile:JSTotalLengthFullPath][JSFileName] integerValue];
        if (totalLength && JSDownloadLength == totalLength) {
            NSLog(@"--文件已下载--");
            return nil;
        }
        
        // 创建请求
        NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:[NSURL URLWithString:@"http://video.pearvideo.com/mp4/short/20170215/cont-1034279-10200514-hd.mp4"]];
        
        // 设置请求头
        // Range : bytes=xxx-xxx
        NSString *range = [NSString stringWithFormat:@"bytes=%zd-", JSDownloadLength];
        [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 {
    
    [self.task resume];
    
}

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


- (void)viewDidLoad {
    [super viewDidLoad];
    
}


#pragma mark - NSURLSessionDataDelegate
/**
 *  接收到响应
 */
- (void)URLSession:(NSURLSession *)session dataTask:(NSURLSessionDataTask *)dataTask didReceiveResponse:(NSHTTPURLResponse *)response completionHandler:(void (^)(NSURLSessionResponseDisposition disposition))completionHandler {
    // 打开流
    [self.stream open];
    
    // 获得服务器这次请求返回数据的总长度 + 文件现在的长度
    self.totalLength = [response.allHeaderFields[@"Content-Length"] integerValue] + JSDownloadLength;
    
    // 存储总长度
    NSMutableDictionary *dict = [NSMutableDictionary dictionaryWithContentsOfFile:JSTotalLengthFullPath];
    if (dict == nil) {
        dict = [NSMutableDictionary dictionary];
    }
    dict[JSFileName] = @(self.totalLength);
    [dict writeToFile:JSTotalLengthFullPath atomically:YES];
    
    // 允许接受服务器的数据
    completionHandler(NSURLSessionResponseAllow);
    
}

- (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(@"%.2f", 1.0 * JSDownloadLength / self.totalLength);
    
}

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


- (void)didReceiveMemoryWarning {
    [super didReceiveMemoryWarning];
    // Dispose of any resources that can be recreated.
}


@end