[Bug] Decode URL Safe Base64 in Shadowsocks share link

[ricky9w]

Commit d2f1118

Cannot correctly process URL Safe Base64 encoded user info (aka method:password) fields if the length of encoded field is not a multiple of 4.

The decodeBase64URLSafe function in the current code does not use = to fill the string length to a multiple of 4 and then hands the string to the base64 library for parsing:

func decodeBase64URLSafe(content string) (string, error) {
	content = strings.ReplaceAll(content, " ", "-")
	content = strings.ReplaceAll(content, "/", "_")
	content = strings.ReplaceAll(content, "+", "-")
	content = strings.ReplaceAll(content, "=", "")
	result, err := base64.StdEncoding.DecodeString(content)
	return string(result), err
}

https://github.com/ricky9w/serenity/blob/474ab7e4299d1395cf790036a07ecee23612599c/subscription/parser/raw.go#L37C1-L44C2