Base64编码不会因无效字符而失败[关闭]

Question

I am trying to ensure a string coming from an http request is valid for use in a base64 url param. I've been experimenting with base64.RawURLEncoding as I assumed encoding an invalid string would throw an err, or at least decoding the result of this would fail, however it quite happily encodes/decodes the string regardless of the input.

https://play.golang.org/p/3sHUfl2NSJK

I have created the above playground showing the issue I'm having (albeit an extreme example). Is there another way of ascertaining whether a string consists entirely of valid base64 characters?

Answer 1

To clarify, Base64 is an encoding scheme which allows you to take arbitrary binary data and safely encode it into ASCII characters which can later be decoded into the original binary string.

That means that the "Base64-encode" operation can take literally any input and produce valid, encoded data. However, the "Base64-decode" operation will fail if its input string contains characters outside of set of ASCII characters that the encoding uses (meaning that the given string was not produced by a valid Base64-encoder).

To test if a string contains a valid Base64 encoded sequence, you just need to call base64.Encoding.DecodeString(...) and test if the error is "nil".

For example (Go Playground):

func IsValidBase64(s string) bool {
  _, err := base64.StdEncoding.DecodeString(s)
  return err == nil
}

func main() {
  ss := []string{"ABBA", "T0sh", "Foo=", "Bogus\x01"}

  for _, s := range ss {
    if IsValidBase64(s) {
      fmt.Printf("OK: valid Base64 %q
", s)
    } else {
      fmt.Printf("ERR: invalid Base64 %q
", s)
    }
  }
  // OK: valid Base64 "ABBA"
  // OK: valid Base64 "T0sh"
  // OK: valid Base64 "Foo="
  // ERR: invalid Base64 "Bogus\x01"
}