base64 - the encoding of RFC 4648.
EncodeToString uses the standard alphabet and pads with "=", which is what most things expect. URLEncodeToString uses "-" and "_" instead of "+" and "/", for what travels inside a URL or a filename.
¶EncodedLen = fn(n)source
EncodedLen is how long the encoding of n bytes is, padding included.
¶EncodeToString = fn(data)source
EncodeToString returns the base64 form of data, a string or bytes.
¶URLEncodeToString = fn(data)source
URLEncodeToString is EncodeToString with the URL safe alphabet and no padding, the form a token or a filename is written in.
¶DecodeString = fn(s)source
DecodeString returns the bytes s stands for. Both alphabets are understood and the padding is optional, since it carries nothing the length doesn't.