Encode/Decode base64 - base64

Question

here is my code and I don't understand why the decode function doesn't work.
Little insight would be great please.
func EncodeB64(message string) (retour string) {
base64Text := make([]byte, base64.StdEncoding.EncodedLen(len(message)))
base64.StdEncoding.Encode(base64Text, []byte(message))
return string(base64Text)
}
func DecodeB64(message string) (retour string) {
base64Text := make([]byte, base64.StdEncoding.DecodedLen(len(message)))
base64.StdEncoding.Decode(base64Text, []byte(message))
fmt.Printf("base64: %s\n", base64Text)
return string(base64Text)
}
It gaves me :
[Decode error - output not utf-8][Decode error - output not utf-8]

Answer 1

The len prefix is superficial and causes the invalid utf-8 error:
package main
import (
"encoding/base64"
"fmt"
"log"
)
func main() {
str := base64.StdEncoding.EncodeToString([]byte("Hello, playground"))
fmt.Println(str)
data, err := base64.StdEncoding.DecodeString(str)
if err != nil {
log.Fatal("error:", err)
}
fmt.Printf("%q\n", data)
}
(Also here)
Output
SGVsbG8sIHBsYXlncm91bmQ=
"Hello, playground"
EDIT: I read too fast, the len was not used as a prefix. dystroy got it right.

Answer 2

DecodedLen returns the maximal length.
This length is useful for sizing your buffer but part of the buffer won't be written and thus won't be valid UTF-8.
You have to use only the real written length returned by the Decode function.
l, _ := base64.StdEncoding.Decode(base64Text, []byte(message))
log.Printf("base64: %s\n", base64Text[:l])

Answer 3

To sum up the other two posts, here are two simple functions to encode/decode Base64 strings with Go:
// Dont forget to import "encoding/base64"!
func base64Encode(str string) string {
return base64.StdEncoding.EncodeToString([]byte(str))
}
func base64Decode(str string) (string, bool) {
data, err := base64.StdEncoding.DecodeString(str)
if err != nil {
return "", true
}
return string(data), false
}
Try it!

Answer 4

#Denys Séguret's answer is almost 100% correct. As an improvement to avoid wasting memory with non used space in base64Text, you should use base64.DecodedLen. Take a look at how base64.DecodeString uses it.
It should look like this:
func main() {
message := base64.StdEncoding.EncodeToString([]byte("Hello, playground"))
base64Text := make([]byte, base64.StdEncoding.DecodedLen(len(message)))
n, _ := base64.StdEncoding.Decode(base64Text, []byte(message))
fmt.Println("base64Text:", string(base64Text[:n]))
}
Try it here.

Answer 5

More or less like above, but using []bytes and part of a bigger struct:
func (s secure) encodePayload(body []byte) string {
//Base64 Encode
return base64.StdEncoding.EncodeToString(body)
}
func (s secure) decodePayload(body []byte) ([]byte, error) {
//Base64 Decode
b64 := make([]byte, base64.StdEncoding.DecodedLen(len(body)))
n, err := base64.StdEncoding.Decode(b64, body)
if err != nil {
return nil, err
}
return b64[:n], nil
}