Function decode_b

Lib/email/_encoded_words.py:100–136

(encoded)

#

def decode_b(encoded):
    # First try encoding with validate=True, fixing the padding if needed.
    # This will succeed only if encoded includes no invalid characters.
    pad_err = len(encoded) % 4
    missing_padding = b'==='[:4-pad_err] if pad_err else b''
    try:
        return (
            base64.b64decode(encoded + missing_padding, validate=True),
            [errors.InvalidBase64PaddingDefect()] if pad_err else [],
        )
    except binascii.Error:
        # Since we had correct padding, this is likely an invalid char error.
        #
        # The non-alphabet characters are ignored as far as padding
        # goes, but we don't know how many there are.  So try without adding
        # padding to see if it works.
        try:
            return (
                base64.b64decode(encoded, validate=False),
                [errors.InvalidBase64CharactersDefect()],
            )
        except binascii.Error:
            # Add as much padding as could possibly be necessary (extra padding
            # is ignored).
            try:
                return (
                    base64.b64decode(encoded + b'==', validate=False),
                    [errors.InvalidBase64CharactersDefect(),
                     errors.InvalidBase64PaddingDefect()],
                )
            except binascii.Error:
                # This only happens when the encoded string's length is 1 more
                # than a multiple of 4, which is invalid.
                #
                # bpo-27397: Just return the encoded string since there's no
                # way to decode.
                return encoded, [errors.InvalidBase64LengthDefect()]

def encode_b(bstring):
    return base64.b64encode(bstring).decode('ascii')