网络编程(03)NSURLSessionDataTask大文件下载

@interface AAAViewController ()<NSURLSessionDataDelegate>

/**
 NSFileHandle 文件句柄
 特点:在写数据的时候边写边移动位置
 使用步骤:
 1> 创建空的文件
 2> 创建文件句柄指针 指向该文件
 3> 当接收到数据的时候,使用该句柄来写数据
 4> 当所有的数据写完,应该关闭句柄指针
 */
@property(nonatomic, strong)NSFileHandle *fileHandle;
@property(nonatomic, assign)long long totalSize;
@property(nonatomic, assign)long long currentSize;
@end

@implementation AAAViewController


-(void)download:(NSString *)urlStr{
    
    // 1 创建URL
    NSURL *url = [NSURL URLWithString:urlStr];
    
    //2. 创建请求
    NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url];
// POST 请求才设置
//    //3. 设置请求的方式
//    request.HTTPMethod = @"POST";
//    //4. 设置请求体
//    request.HTTPBody =data;
    
    //5. 创建sesstion
    NSURLSessionConfiguration *config = [[NSURLSessionConfiguration alloc] init];
    NSURLSession *session = [NSURLSession sessionWithConfiguration:config
                                                          delegate:self
                                                     delegateQueue:[[NSOperationQueue alloc] init]];
    //6. 创建下载任务
    NSURLSessionDataTask *dataTask = [session dataTaskWithRequest:request];
    [dataTask resume];
    
}

#pragma mark- NSURLSessionDataDelegate
//1. 接收到响应头就会响应
    -(void)URLSession:(NSURLSession *)session
             dataTask:(NSURLSessionDataTask *)dataTask
    didReceiveResponse:(NSURLResponse *)response
    completionHandler:(void (^)(NSURLSessionResponseDisposition))completionHandler{

        
        //1. 获取文件建议名称
        NSString *suggestName = [response suggestedFilename]; // 文件建议的名称,URL 的最后一个节点
        NSString *cachepath = @"usr/default/";
        NSString *fullPath = [NSString stringWithFormat:@"%@/%@",cachepath,suggestName];
        //创建一个空的文件
        [[NSFileManager defaultManager] createFileAtPath:fullPath contents:nil attributes:nil];
        
        //2. 创建文件句柄
        self.fileHandle = [NSFileHandle fileHandleForWritingAtPath:fullPath];
        
        
        //2. 获取下载文件总大小
        self.totalSize = [response expectedContentLength];
        
        /**
         NSURLSessionResponseCancel         // 取消请求
         NSURLSessionResponseAllow          //  接收数据
         NSURLSessionResponseBecomeDownload //
         NSURLSessionResponseBecomeStream   //
         */
        completionHandler(NSURLSessionResponseAllow);
    
}

//2. 接收到数据就会调用
-(void)URLSession:(NSURLSession *)session
         dataTask:(NSURLSessionDataTask *)dataTask
   didReceiveData:(NSData *)data{
    
    // 不断的拼接服务器返回的数据
    [self.fileHandle writeData:data];
    self.currentSize += data.length;
    
     CGFloat progress = 1.0 *self.currentSize / self.totalSize;
    NSLog(@"当前下载进度: %f",progress);
   
}

//3. 下载完成或者是失败就会调用
-(void)URLSession:(NSURLSession *)session
             task:(nonnull NSURLSessionTask *)task
didCompleteWithError:(nullable NSError *)error{
    
    if (error == nil) {
        // 得到请求的响应头信息
        [self.fileHandle closeFile];
    }
    
}
@end