encoding/base64: encoding doesn't support every possible alphabet

[josselin-c]

What version of Go are you using (go version)?

Go 1.8

What did you expect to see?

Some alphabets accepted by encoding/base64 NewEncoding cannot be decoded: alphabets containing "\n", "\r" or padChar.
See: https://play.golang.org/p/fNJfbH3QgA

Maybe NewEncoding documentation could state that we don't support theses cases or we should fix our implementation.

[ianlancetaylor]

We could have NewEncoding check for and reject \n or \r. I don't see any way to handle padChar other than documentation, since one can call WithPadding after calling NewEncoding.

[gopherbot]

CL https://golang.org/cl/37838 mentions this issue.