File checksum
File checksum
https://golang.org/pkg/io/#Copy
https://blog.iphpo.com/blog/2017/03/golang-產生檔案的md5-hash-generate-file-md5-hash-in-golang/
https://golang.org/pkg/io/#Copy
https://blog.iphpo.com/blog/2017/03/golang-產生檔案的md5-hash-generate-file-md5-hash-in-golang/