go的encoding/base64有四种编码方式：
编码方式 | 说明 |
StdEncoding | 常规编码 |
URLEncoding | URL safe 编码，相当于替换掉字符串中的特殊字符，+ 和 / |
RawStdEncoding | 常规编码，末尾不补 = |
RawURLEncoding | URL safe 编码，末尾不补 = |
package main
import (
"encoding/base64"
"fmt"
)
func main() {
msg := []byte("Hello world. 你好，世界！")
// 标准编码
encoded := base64.StdEncoding.EncodeToString(msg)
fmt.Println(encoded)
// SGVsbG8gd29ybGQuIOS9oOWlve+8jOS4lueVjO+8gQ==
decoded, _ := base64.StdEncoding.DecodeString(encoded)
fmt.Println(string(decoded))
// Hello world. 你好，世界！
// 常规编码，末尾不补 =
encoded = base64.RawStdEncoding.EncodeToString(msg)
fmt.Println(encoded)
// SGVsbG8gd29ybGQuIOS9oOWlve+8jOS4lueVjO+8gQ
decoded, _ = base64.RawStdEncoding.DecodeString(encoded)
fmt.Println(string(decoded))
// Hello world. 你好，世界！
// URL safe 编码
encoded = base64.URLEncoding.EncodeToString(msg)
fmt.Println(encoded)
// SGVsbG8gd29ybGQuIOS9oOWlve-8jOS4lueVjO-8gQ==
decoded, _ = base64.URLEncoding.DecodeString(encoded)
fmt.Println(string(decoded))
// Hello world. 你好，世界！
// URL safe 编码，末尾不补 =
encoded = base64.RawURLEncoding.EncodeToString(msg)
fmt.Println(encoded)
// SGVsbG8gd29ybGQuIOS9oOWlve-8jOS4lueVjO-8gQ
decoded, _ = base64.RawURLEncoding.DecodeString(encoded)
fmt.Println(string(decoded))
// Hello world. 你好，世界！
}
参考
https://syaning.github.io/go-pkgs/encoding/base64.html
https://www.rfc-editor.org/rfc/rfc4648
http://doc.golang.ltd/pkg/encoding_base64.htm
https://base64.us/
