Legacy conversion code for '7bit' to '8bit' inserts error markers

The use of a special 'vtbl' for converting between '7bit' and
'8bit' text meant that '7bit' text would not be converted

Legacy conversion code for '7bit' to '8bit' inserts error markers

The use of a special 'vtbl' for converting between '7bit' and
'8bit' text meant that '7bit' text would not be converted to
wchars before going to '8bit'. This meant that the special
value MBFL_BAD_INPUT, which we use to flag an erroneous byte
sequence in input text (and which is required by functions
like mb_check_encoding), would pass directly to the output,
instead of being converted to the error marker specified
by mb_substitute_character.

This issue dates back to the time when I removed the mbfl
'identify filters' and made encoding validity checking and
encoding detection rely only on the conversion filters.

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Imitate legacy behavior when converting non-encodings using mbstring

Fuzzing revealed that something was missed here when making the new
encoding conversion code match the behavior of th

Imitate legacy behavior when converting non-encodings using mbstring

Fuzzing revealed that something was missed here when making the new
encoding conversion code match the behavior of the old code. In the
next major release of PHP, support for these non-encodings will be
dropped, but in the meantime, it is better to match the legacy
behavior.

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Merge branch 'PHP-8.1'

* PHP-8.1:
mb_check_encoding($str, '7bit') rejects strings with bytes over 0x7F

mb_check_encoding($str, '7bit') rejects strings with bytes over 0x7F

This was the old behavior of mb_check_encoding() before 3e7acf901d,
but yours truly broke it. If only we had more tho

mb_check_encoding($str, '7bit') rejects strings with bytes over 0x7F

This was the old behavior of mb_check_encoding() before 3e7acf901d,
but yours truly broke it. If only we had more thorough tests at that
time, this might not have slipped through the cracks.

Thanks to divinity76 for the report.

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Merge branch 'PHP-8.1'

* PHP-8.1:
mb_detect_encoding will not return non-encodings
Improve detection accuracy of mb_detect_encoding

mb_detect_encoding will not return non-encodings

Among the text encodings supported by mbstring are several which are
not really 'text encodings'. These include Base64, QPrint, UUencode,

mb_detect_encoding will not return non-encodings

Among the text encodings supported by mbstring are several which are
not really 'text encodings'. These include Base64, QPrint, UUencode,
HTML entities, '7 bit', and '8 bit'.

Rather than providing an explicit list of text encodings which they are
interested in, users may pass the output of mb_list_encodings to
mb_detect_encoding. Since Base64, QPrint, and so on are included in
the output of mb_list_encodings, mb_detect_encoding can return one of
these as its 'detected encoding' (and in fact, this often happens).
Before mb_detect_encoding was enhanced so it could detect any of the
supported text encodings, this did not happen, and it is never desired.

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Add more tests for UCS-4 text conversion

Add another test for UCS-2 text conversion

mbstring no longer provides 'long' substitutions for erroneous input bytes

Previously, mbstring had a special mode whereby it would convert
erroneous input byte sequences to output like

mbstring no longer provides 'long' substitutions for erroneous input bytes

Previously, mbstring had a special mode whereby it would convert
erroneous input byte sequences to output like "BAD+XXXX", where "XXXX"
would be the erroneous bytes expressed in hexadecimal. This mode could
be enabled by calling `mb_substitute_character("long")`.

However, accurately reproducing input byte sequences from the cached
state of a conversion filter is often tricky, and this significantly
complicates the implementation. Further, the means used for passing
the erroneous bytes through to where the "BAD+XXXX" text is generated
only allows for up to 3 bytes to be passed, meaning that some erroneous
byte sequences are truncated anyways.

More to the point, a search of publically available PHP code indicates
that nobody is really using this feature anyways.

Incidentally, this feature also provided error output like "JIS+XXXX"
if the input 'should have' represented a JISX 0208 codepoint, but it
decodes to a codepoint which does not exist in the JISX 0208 charset.
Similarly, specific error output was provided for non-existent
JISX 0212 codepoints, and likewise for JISX 0213, CP932, and a few
other charsets. All of that is now consigned to the flames.

However, "long" error markers also include a somewhat more useful
"U+XXXX" marker for Unicode codepoints which were successfully
decoded from the input text, but cannot be represented in the output
encoding. Those are still supported.

With this change, there is no need to use a variety of special values
in the high bits of a wchar to represent different types of error
values. We can (and will) just use a single error value. This will be
equal to -1.

One complicating factor: Text conversion functions return an integer to
indicate whether the conversion operation should be immediately
aborted, and the magic 'abort' marker is -1. Also, almost all of these
functions would return the received byte/codepoint to indicate success.
That doesn't work with the new error value; if an input filter detects
an error and passes -1 to the output filter, and the output filter
returns it back, that would be taken to mean 'abort'.

Therefore, amend all these functions to return 0 for success.

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Add tests for UCS-4 text conversion

Add tests for UCS-2 text encoding

Add tests for '7bit' and '8bit' text encodings in mbstring