You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: base64.go
    path of file: ./repos/k6/vendor/github.com/lestrrat-go/jwx/v2/internal/base64
    
    the code of the file until where you have to start completion: package base64

import (
	"bytes"
	"encoding/base64"
	"encoding/binary"
	"fmt"
	"sync"
)

type Decoder interface {
	Decode([]byte) ([]byte, error)
}

type Encoder interface {
	Encod
    
func Guess(src []byte) int {
	var isRaw = !bytes.HasSuffix(src, []byte{'='})
	var isURL = !bytes.ContainsAny(src, "+/")
	switch {
	case isRaw && isURL:
		return RawURL
	case isURL:
		return URL
	case isRaw:
		return RawStd
	default:
		return Std
	}
}