base64.go RawHistoryFolder

1package kittygraphics
2
3import (
4	"bytes"
5	"encoding/base64"
6	"fmt"
7)
8
9// DecodeBase64 accepts both padded standard base64 and unpadded raw standard
10// base64. It deliberately does not accept URL-safe alphabets or non-base64
11// whitespace other than the CR/LF ignored by the standard encoding.
12//
13// The returned slice is freshly allocated and owned by the caller.
14func DecodeBase64(encoded []byte) ([]byte, error) {
15	// RawStdEncoding rejects '=' and otherwise accepts every input
16	// StdEncoding does (padded input has no '=' only when its length is a
17	// multiple of four, where both encodings agree), so the alphabet used is
18	// chosen by looking for padding rather than by decoding twice.
19	enc := base64.RawStdEncoding
20	if bytes.IndexByte(encoded, '=') >= 0 {
21		enc = base64.StdEncoding
22	}
23	decoded := make([]byte, enc.DecodedLen(len(encoded)))
24	n, err := enc.Decode(decoded, encoded)
25	if err == nil {
26		return decoded[:n], nil
27	}
28	if enc == base64.RawStdEncoding {
29		// Report the StdEncoding error, as the padded decoder is the
30		// documented primary format. This only runs for rejected input.
31		_, err = base64.StdEncoding.Decode(make([]byte, base64.StdEncoding.DecodedLen(len(encoded))), encoded)
32	}
33	return nil, fmt.Errorf("%w: %v", ErrInvalidBase64, err)
34}
35
36// DecodePayload is a descriptive alias for DecodeBase64.
37func DecodePayload(encoded []byte) ([]byte, error) { return DecodeBase64(encoded) }