// 根据图片url获取图片尺寸

+(CGSize)getImageSizeWithURL:(id)imageURL

{

    NSURL* URL = nil;

    if([imageURL isKindOfClass:[NSURL class]]){

        URL = imageURL;

    }

    if([imageURL isKindOfClass:[NSString class]]){

        URL = [NSURL URLWithString:imageURL];

    }

    if(URL == nil)

        return CGSizeZero;                  // url不正确返回CGSizeZero

    NSMutableURLRequest *request = [[NSMutableURLRequest alloc] initWithURL:URL];

    NSString* pathExtendsion = [URL.pathExtension lowercaseString];

    CGSize size = CGSizeZero;

    if([pathExtendsion isEqualToString:@"png"]){

        size =  [self getPNGImageSizeWithRequest:request];

    }

    else if([pathExtendsion isEqual:@"gif"])

    {

        size =  [self getGIFImageSizeWithRequest:request];

    }

    else{

        size = [self getJPGImageSizeWithRequest:request];

    }

    if(CGSizeEqualToSize(CGSizeZero, size))                    // 如果获取文件头信息失败,发送异步请求请求原图

    {

        NSData* data = [NSURLConnection sendSynchronousRequest:[NSURLRequest requestWithURL:URL] returningResponse:nil error:nil];

        UIImage* image = [UIImage imageWithData:data];

        if(image)

        {

            size = image.size;

        }

    }

    return size;

}

//  获取PNG图片的大小

+(CGSize)getPNGImageSizeWithRequest:(NSMutableURLRequest*)request

{

    [request setValue:@"bytes=16-23" forHTTPHeaderField:@"Range"];

    NSData* data = [NSURLConnection sendSynchronousRequest:request returningResponse:nil error:nil];

    if(data.length == )

    {

        int w1 = , w2 = , w3 = , w4 = ;

        [data getBytes:&w1 range:NSMakeRange(, )];

        [data getBytes:&w2 range:NSMakeRange(, )];

        [data getBytes:&w3 range:NSMakeRange(, )];

        [data getBytes:&w4 range:NSMakeRange(, )];

        int w = (w1 << ) + (w2 << ) + (w3 << ) + w4;

        int h1 = , h2 = , h3 = , h4 = ;

        [data getBytes:&h1 range:NSMakeRange(, )];

        [data getBytes:&h2 range:NSMakeRange(, )];

        [data getBytes:&h3 range:NSMakeRange(, )];

        [data getBytes:&h4 range:NSMakeRange(, )];

        int h = (h1 << ) + (h2 << ) + (h3 << ) + h4;

        return CGSizeMake(w, h);

    }

    return CGSizeZero;

}

//  获取gif图片的大小

+(CGSize)getGIFImageSizeWithRequest:(NSMutableURLRequest*)request

{

    [request setValue:@"bytes=6-9" forHTTPHeaderField:@"Range"];

    NSData* data = [NSURLConnection sendSynchronousRequest:request returningResponse:nil error:nil];

    if(data.length == )

    {

        short w1 = , w2 = ;

        [data getBytes:&w1 range:NSMakeRange(, )];

        [data getBytes:&w2 range:NSMakeRange(, )];

        short w = w1 + (w2 << );

        short h1 = , h2 = ;

        [data getBytes:&h1 range:NSMakeRange(, )];

        [data getBytes:&h2 range:NSMakeRange(, )];

        short h = h1 + (h2 << );

        return CGSizeMake(w, h);

    }

    return CGSizeZero;

}

//  获取jpg图片的大小

+(CGSize)getJPGImageSizeWithRequest:(NSMutableURLRequest*)request

{

    [request setValue:@"bytes=0-209" forHTTPHeaderField:@"Range"];

    NSData* data = [NSURLConnection sendSynchronousRequest:request returningResponse:nil error:nil];

    if ([data length] <= 0x58) {

        return CGSizeZero;

    }

    if ([data length] < ) {// 肯定只有一个DQT字段

        short w1 = , w2 = ;

        [data getBytes:&w1 range:NSMakeRange(0x60, 0x1)];

        [data getBytes:&w2 range:NSMakeRange(0x61, 0x1)];

        short w = (w1 << ) + w2;

        short h1 = , h2 = ;

        [data getBytes:&h1 range:NSMakeRange(0x5e, 0x1)];

        [data getBytes:&h2 range:NSMakeRange(0x5f, 0x1)];

        short h = (h1 << ) + h2;

        return CGSizeMake(w, h);

    } else {

        short word = 0x0;

        [data getBytes:&word range:NSMakeRange(0x15, 0x1)];

        if (word == 0xdb) {

            [data getBytes:&word range:NSMakeRange(0x5a, 0x1)];

            if (word == 0xdb) {// 两个DQT字段

                short w1 = , w2 = ;

                [data getBytes:&w1 range:NSMakeRange(0xa5, 0x1)];

                [data getBytes:&w2 range:NSMakeRange(0xa6, 0x1)];

                short w = (w1 << ) + w2;

                short h1 = , h2 = ;

                [data getBytes:&h1 range:NSMakeRange(0xa3, 0x1)];

                [data getBytes:&h2 range:NSMakeRange(0xa4, 0x1)];

                short h = (h1 << ) + h2;

                return CGSizeMake(w, h);

            } else {// 一个DQT字段

                short w1 = , w2 = ;

                [data getBytes:&w1 range:NSMakeRange(0x60, 0x1)];

                [data getBytes:&w2 range:NSMakeRange(0x61, 0x1)];

                short w = (w1 << ) + w2;

                short h1 = , h2 = ;

                [data getBytes:&h1 range:NSMakeRange(0x5e, 0x1)];

                [data getBytes:&h2 range:NSMakeRange(0x5f, 0x1)];

                short h = (h1 << ) + h2;

                return CGSizeMake(w, h);

            }

        } else {

            return CGSizeZero;

        }

    }

}