本地图片大小74KB，IOS通过：
NSData *photoData = UIImageJPEGRepresentation([UIImage imageNamed:@"IMG_7160.JPG"], 1.0);

QNUploadManager *magager = [[QNUploadManager alloc] init];
QNUploadOption *opt = [[QNUploadOption alloc] initWithMime:nil progressHandler: ^(NSString *key, float percent) {
    NSLog(@"progress: %f", percent);
} params:nil checkCrc:NO cancellationSignal: ^BOOL () {
    return flag;
}];

上传到七牛服务器286 KB，为什么，怎么保证大小一致啊？