chore: Clean converter code and add doc

common/convert/base64.go

@@ -0,0 +1,45 @@
+package convert
+
+import (
+	"encoding/base64"
+	"strings"
+)
+
+var (
+	encRaw = base64.RawStdEncoding
+	enc    = base64.StdEncoding
+)
+
+// DecodeBase64 try to decode content from the given bytes,
+// which can be in base64.RawStdEncoding, base64.StdEncoding or just plaintext.
+func DecodeBase64(buf []byte) []byte {
+	result, err := tryDecodeBase64(buf)
+	if err != nil {
+		return buf
+	}
+	return result
+}
+
+func tryDecodeBase64(buf []byte) ([]byte, error) {
+	dBuf := make([]byte, encRaw.DecodedLen(len(buf)))
+	n, err := encRaw.Decode(dBuf, buf)
+	if err != nil {
+		n, err = enc.Decode(dBuf, buf)
+		if err != nil {
+			return nil, err
+		}
+	}
+	return dBuf[:n], nil
+}
+
+func urlSafe(data string) string {
+	return strings.NewReplacer("+", "-", "/", "_").Replace(data)
+}
+
+func decodeUrlSafe(data string) string {
+	dcBuf, err := base64.RawURLEncoding.DecodeString(data)
+	if err != nil {
+		return ""
+	}
+	return string(dcBuf)
+}