上传大文件服务端报错，排查了比较久
还是查Google靠谱
upload big file php post data is null
https://stackoverflow.com/questions/7852910/php-empty-post-and-files-when-uploading-larger-files
受下面的限制：
php.ini 的两个属性
post_max_size = 80M
upload_max_filesize = 500M
nginx一个属性
client_max_body_size 80m;
修改后ok