oc下如果通过二进制文件数据判断zip格式

具体实现如下，通过文件头获取指定长度的十六进制字符串进行判断

- (BOOL)isRealZipFileForNSData:(NSData *)fileData {
    if (!fileData || [fileData length] == 0) {
        return NO;
    }
    NSMutableString *hexHeaderString = [[NSMutableString alloc] initWithCapacity:[fileData length]];
    
    [fileData enumerateByteRangesUsingBlock:^(const void *bytes, NSRange byteRange, BOOL *stop) {
        unsigned char *dataBytes = (unsigned char*)bytes;
        
        for (NSInteger i = 0; i < byteRange.length; i++) {
            NSString *hexStr = [NSString stringWithFormat:@"%x", (dataBytes[i]) & 0xff];
            if ([hexStr length] == 2) {
                [hexHeaderString appendString:hexStr];
            } else {
                [hexHeaderString appendFormat:@"0%@", hexStr];
            }
            
            if (hexHeaderString.length > 8) {
                break;
            }
        }
    }];
    
    // 504B0304 表示文件格式是zip的十六进制 文件头
    if ([hexHeaderString hasPrefix:@"504b0304"] || [hexHeaderString hasPrefix:@"504B0304"]) {
        return YES;
    }
    
    return NO;
}