base64_decode is buggy, what to fix?

Hello, Internals! I was fixing #72152 when it became apparent that the base64_decode function is very buggy. - Null byte ends processing. - "V" produces empty result, while "V=" fails. Not very logical. - Too short padding is allowed, e.g. "VV=" works like "VV==". - Extra padding is allowed (like "V====="). - Invalid padding is allowed ("=VVV=", "VV=V=", "VVV==") except on the second place of a 24-bit run ("V=VV=" fails). - In strict mode, space between padding fails: "V V==" and "VV ==" and "VV== " are allowed, "VV= =" fails. - In strict mode, after a padding, one character is skipped, so "VVV=V" decodes to "UU" (should be "UUU"), and "VVVV=*" decodes to "UUU" instead of failing. For each of the above, what would be the preferred behaviour in default mode and strict mode? Affected existing tests: - ext/openssl/tests/bug61124.phpt uses "kzo w2RMExUTYQXW2Xzxmg==" as an invalid base64 string, based on the invalid padding. - ext/standard/tests/file/stream_rfc2397_006.phpt tests "#Zm9vYmFyIGZvb2Jhcg==" and excepts this to be valid, while "#" is clearly not valid base64. This also raises a question whether fragments should be skipped in data uri handling. Suggestions? I've created a bug-for-bug compatible rewrite of base64_decode [1], with all the bugs neatly and specifically implemented and missing features commented out, so it's now very simple to fix them one by one. I've also attached a test script that tests "all" possible combinations of data, padding, NUL and other invalid characters, and my first patch indeed provides identical results to the old implementation. Currently interesting lines in the test results:

'base64'         'default'       'strict'
'V'              ''              ''
'V='             (false)         (false)
'VV='            'U'             'U'
'VV=='           'U'             'U'
'V====='         (false)         (false)
'=VVV='          'UU'            (false)
'VV=V='          'UU'            (false)
'VVV=='          'UU'            'UU'
'V=VV='          (false)         (false)
'V V=='          'U'             'U'
'VV =='          'U'             'U'
'VV== '          'U'             'U'
'VV= ='          'U'             (false)
'VVV=V'          'UUU'           'UU'
'VVVV=*'         'UUU'           'UUU'
'VVVVVV=V'       'UUUUU'         'UUUU'
'VVVVVV=*'       'UUUU'          'UUUU'
'VVVV===*'       'UUU'           'UUU'
'VVV====V'       'UUU'           'UU'
'VVV====*'       'UU'            'UU'
'VV=====V'       'UU'            'U'
'VV=====*'       'U'             'U'
'=======*'       ''              ''

-- Lauri Kenttä

Attachment: [text/x-php] base64_decode_test.php
Attachment: [text/x-diff] base64_v0.patch