// 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 == 8)
{
    int w1 = 0, w2 = 0, w3 = 0, w4 = 0;
    [data getBytes:&w1 range:NSMakeRange(0, 1)];
    [data getBytes:&w2 range:NSMakeRange(1, 1)];
    [data getBytes:&w3 range:NSMakeRange(2, 1)];
    [data getBytes:&w4 range:NSMakeRange(3, 1)];
    int w = (w1 << 24) + (w2 << 16) + (w3 << 8) + w4;
    int h1 = 0, h2 = 0, h3 = 0, h4 = 0;
    [data getBytes:&h1 range:NSMakeRange(4, 1)];
    [data getBytes:&h2 range:NSMakeRange(5, 1)];
    [data getBytes:&h3 range:NSMakeRange(6, 1)];
    [data getBytes:&h4 range:NSMakeRange(7, 1)];
    int h = (h1 << 24) + (h2 << 16) + (h3 << 8) + 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 == 4)
{
    short w1 = 0, w2 = 0;
    [data getBytes:&w1 range:NSMakeRange(0, 1)];
    [data getBytes:&w2 range:NSMakeRange(1, 1)];
    short w = w1 + (w2 << 8);
    short h1 = 0, h2 = 0;
    [data getBytes:&h1 range:NSMakeRange(2, 1)];
    [data getBytes:&h2 range:NSMakeRange(3, 1)];
    short h = h1 + (h2 << 8);
    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] < 210) {// 肯定只有一个DQT字段
    short w1 = 0, w2 = 0;
    [data getBytes:&w1 range:NSMakeRange(0x60, 0x1)];
    [data getBytes:&w2 range:NSMakeRange(0x61, 0x1)];
    short w = (w1 << 8) + w2;
    short h1 = 0, h2 = 0;
    [data getBytes:&h1 range:NSMakeRange(0x5e, 0x1)];
    [data getBytes:&h2 range:NSMakeRange(0x5f, 0x1)];
    short h = (h1 << 8) + 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 = 0, w2 = 0;
            [data getBytes:&w1 range:NSMakeRange(0xa5, 0x1)];
            [data getBytes:&w2 range:NSMakeRange(0xa6, 0x1)];
            short w = (w1 << 8) + w2;
            short h1 = 0, h2 = 0;
            [data getBytes:&h1 range:NSMakeRange(0xa3, 0x1)];
            [data getBytes:&h2 range:NSMakeRange(0xa4, 0x1)];
            short h = (h1 << 8) + h2;
            return CGSizeMake(w, h);
        } else {// 一个DQT字段
            short w1 = 0, w2 = 0;
            [data getBytes:&w1 range:NSMakeRange(0x60, 0x1)];
            [data getBytes:&w2 range:NSMakeRange(0x61, 0x1)];
            short w = (w1 << 8) + w2;
            short h1 = 0, h2 = 0;
            [data getBytes:&h1 range:NSMakeRange(0x5e, 0x1)];
            [data getBytes:&h2 range:NSMakeRange(0x5f, 0x1)];
            short h = (h1 << 8) + h2;
            return CGSizeMake(w, h);
        }
    } else {
        return CGSizeZero;
    }
}
}