针对我们下载图片地址的动态性. 例如: 服务器给到我们图片的地址, 只是一段字符: NSString * urlStr = @"les://BEC0200F32374CD1B2255F4449B61CF8"
然后利用urlStr去发送post请求, 获取到对应的url 和 header参数.
例如: downURL: https://sample.com
header参数: X-Les-Date --> date
X-Les-Length --> length
Authorization --> auth
这时, 需要自行构造https请求头, 请求头header的参数是动态.
那么这时如何利用SDWebImage框架来做呢:
代码如下:

   先创建类属性, headersDict , 
   key: 图片地址downURL  value: 一个字典保存有header的各种参数

    NSMutableDictionary * header = [NSMutableDictionary dictionary];
    [header setValue:date forKey:@"X-Les-Date"];
    [header setValue:length forKey:@" X-Les-Length"];
    [header setValue:auth forKey:@"Authorization"];
    [self.headersDict setValue:header forKey:downURL];
    //这里来设置header, 利用headersFilter, 将对应的downURL的header取出来设置好.
    [SDWebImageManager sharedManager].imageDownloader.headersFilter = ^(NSURL *url, NSDictionary * headers){
       //这里的url, 就是来下载的downURL
        NSMutableDictionary * headerDic = [NSMutableDictionary dictionary];
        [headerDic setDictionary:headers];
        [headerDic setDictionary:[self.headersDict valueForKey:url.absoluteString]];
        return headerDic;
    };
    
    // options: SDWebImageAllowInvalidSSLCertificates针对https地址没有域名或者证书过期等问题, 跳过检测, 后续会有另外方法在解决
    [[SDWebImageManager sharedManager] downloadImageWithURL:[NSURL URLWithString:downURL] options:SDWebImageAllowInvalidSSLCertificates progress:nil completed:^(UIImage *image, NSError *error, SDImageCacheType cacheType, BOOL finished, NSURL *imageURL) {
        //如果要传出去缓存的地址
        NSString *cacheImageKey = [[SDWebImageManager sharedManager] cacheKeyForURL:[NSURL URLWithString:downURL]];
        NSString *cacheImagePath = [[SDImageCache sharedImageCache] defaultCachePathForKey:cacheImageKey];
        NSLog(@"哈哈😝%@", cacheImagePath);
         if (!image) {
             // 外层自己封装的回调block, 需要传出去什么值,自己定
            completion(NO, @"下载图片失败", nil, nil);
        }else{
            completion(YES, nil, image, cacheImagePath);
         }
    }];

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