iOS 快速只获取Http响应头

iOS 快速只获取Http响应头
有些时候需要某个Http的响应头不需要响应文件
如对于一个.mp4的连接怎么快速获取文件大小或者是否经过了302跳转等。

//代码开始时间和结束时间
#define TICK   NSDate *startTime = [NSDate date]
#define TOCK NSLog(@"__func__%s \r\n", __func__);\
NSLog(@"code runing Time duration : %f", -[startTime timeIntervalSinceNow]);\
NSLog(@"\n");

//这样获取的是全部文件 下面给出正确方案
    NSURL *url = [NSURL URLWithString:@"/videofiles/20121214/9533522808.f4v.mp4"];
    NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url];
     = @"GET";
    //[request setHTTPMethod:@"HEAD"];
    NSURLSessionConfiguration *config = [NSURLSessionConfiguration defaultSessionConfiguration];
     = NSURLRequestReloadIgnoringLocalCacheData;
    NSURLSession *urlSession = [NSURLSession sessionWithConfiguration:config delegate:nil delegateQueue:[NSOperationQueue currentQueue]];
    NSURLSessionDataTask *task = [urlSession dataTaskWithRequest:request completionHandler:^(NSData * _Nullable data, NSURLResponse * _Nullable response, NSError * _Nullable error) {
        TOCK;
        NSHTTPURLResponse *res = (NSHTTPURLResponse *)response;
        NSDictionary *allHeaderFields = ;
        TOCK;
        if ([ containsString:urlStr] == NO) {
            NSLog(@"302");
        }
        
        if ([ containsObject:@"Content-Length"]) {
            NSNumber *lengthObj = [allHeaderFields objectForKey:@"Content-Length"];
            //fileLength = [lengthObj integerValue];
        }
        
        NSLog(@"allHeaderFields is %@", allHeaderFields);
    }];
    
    [task resume];

//正确的只获取视频文件的响应头
    TICK;
    NSURL *url = [NSURL URLWithString:@"/videofiles/20121214/9533522808.f4v.mp4"];
    NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:url];
    //只获取响应头 大概100ms就能返回
    [request setHTTPMethod:@"HEAD"];
    NSURLSessionConfiguration *config = [NSURLSessionConfiguration defaultSessionConfiguration];
     = NSURLRequestReloadIgnoringLocalCacheData;
    NSURLSession *urlSession = [NSURLSession sessionWithConfiguration:config delegate:nil delegateQueue:[NSOperationQueue currentQueue]];
    NSURLSessionDataTask *task = [urlSession dataTaskWithRequest:request completionHandler:^(NSData * _Nullable data, NSURLResponse * _Nullable response, NSError * _Nullable error) {
        TOCK;
        NSHTTPURLResponse *res = (NSHTTPURLResponse *)response;
        NSDictionary *allHeaderFields = ;
        if ([ containsString:urlStr] == NO) {
            NSLog(@"302");
        }
        
        if ([ containsObject:@"Content-Length"]) {
            NSNumber *lengthObj = [allHeaderFields objectForKey:@"Content-Length"];
            //fileLength = [lengthObj integerValue];
        }
        
        NSLog(@"allHeaderFields is %@", allHeaderFields);
    }];
    
    [task resume];