Except for vanilla Shift-JIS, where 0x7E is a halfwidth overline/macron.
As for Shift-JIS-2004, it has an added character (byte sequence 0x854A)
which was defined as a halfwidth macron in JIS X 0213:2000, so we use that.
By entering this character in the JIS X 0208 conversion table, we can
remove a bunch of explicit `if` clauses in different conversion filters.
It also means that U+FF5E can be converted into SJIS-mac now; I don't
know why this one SJIS variant rejected U+FF5E before, since 0x8160
means the same thing in SJIS-mac as the others.
Converting U+203E to 0x7E was especially wrong for CP932, where 0x7E
represents a tilde.
For vanilla Shift-JIS and Shift-JIS-2004, converting to 0x7E is acceptable,
since 0x7E does represent an overline/macron in those encodings.
Follow the same principle in CP51932, which is closely related to CP932.
When Microsoft created CP932 (their version of Shift-JIS), they explicitly
used bytes 0-0x7F to represent ASCII characters rather than JIS X 0201
characters.
So when converting Unicode to CP932, it is not correct to convert U+00A5
to CP932 0x5C. Fortunately, CP932 does have a multi-byte FULLWIDTH YEN SIGN
character which we can use instead.
CP51932 uses the same extended character set as CP932; while CP932 is
MicroSoft's extended version of Shift-JIS, CP51932 is their extended version
of EUC-JP. So the same reasoning applies to CP51932.
Shift-JIS-2004 is an extension of Shift-JIS, which uses 0x5C for the Yen
sign. Therefore, it is not correct to convert ASCII 0x5C (backslash) to
Shift-JIS-2004 0x5C (yen sign). JIS X 0208 does have a backslash, so we
can convert ASCII backslash to SJIS-2004 backslash instead.
From time immemorial, there has been confusion around the treatment
of 0x5C bytes on systems using legacy Japanese encodings. JIS X 0201
specified that 0x5C means a yen sign, and thus fonts on Japanese systems,
including early versions of Windows, displayed a 0x5C byte as a yen sign.
This meant that when ASCII text files were displayed on such systems,
what were meant to be backslashes would appear as yen signs. Japanese C
programmers could write character escapes using yen signs, and C compilers
built on the assumption that the input was ASCII would interpret these
escapes as desired. Likewise for shell scripts. Et cetera, et cetera...
Therefore, if the input to `mb_convert_encoding` is (for example) a C
program, and after converting to Shift-JIS-2004, the user wishes to feed
the output into a C compiler, *then* perhaps ASCII 0x5C should be mapped
to SJIS 0x5C. However, this scenario is ridiculous and will never happen.
A more realistic scenario might be: an article written in SJIS-2004 has
embedded Windows file paths (like 'C:\Program Files'), with yen signs used
as a path separator. If we convert SJIS-2004 0x5C to ASCII 0x5C, then the
path separators will be 'fixed' by the conversion.
For general written texts, it is much better to convert backslashes to...
backslashes. And yen signs, to yen signs.
Lots of problems here.
- Don't pass 'control' characters through silently in the middle of a
multi-byte character.
- Treat it as an error if a multi-byte character is truncated.
- For ESC sequences used to encode emoji on earlier Softbank phones, if an
invalid ESC sequence is found, don't pass it through. Rather, handle it as
an error and respect `mb_substitute_character`.
- In ranges used by mobile vendors for emoji, if a certain byte sequence
doesn't map to any emoji, don't emit a mangled value (actually a raw
(ku*94)+ten value, which may not even be a valid Unicode codepoint at all).
- When converting Unicode to SJIS-Mobile, don't mangle codepoints which fall
in the 2nd range of MicroSoft vendor extensions.
Some vendor-specific emoji have been mapped to standard Unicode codepoints
now, rather than 'private use area' codepoints. When the legacy code was
written, these codepoints may not have existed yet in the Unicode standard
which was current at that time.
Also do a major code cleanup -- remove dead code, rearrange what is left,
use some new macros and helper functions to make the code clearer...
These constants indicate that a text encoding uses 2+ bytes for each character,
and is either big endian or little endian (respectively). But nothing in
mbstring cares about the difference between MBFL_ENCTYPE_MWC2BE and
MBFL_ENCTYPE_MWC2LE.
(Actually, nothing cares about whether these flags are set at all...
maybe we should just remove them?)
These flags identify text encodings in mbstring which use a constant number of
bytes per character. While some parts of the code do use these flags, usually
to detect cases which can be optimized due to constant-width encoding, nothing
cares whether the encodings are 'LE' (little-endian) or 'BE' (big-endian).
So we can simplify things by combining constants.
Similarly to JIS X 0208, mbstring would pass kuten codes which are not mapped
in the JIS X 0212, JIS X 0213, or CP932 character sets through silently when
converting to another Japanese encoding.
Many Japanese encodings, such as JIS7/8, Shift JIS, ISO-2022-JP, EUC-JP, and
so on encode characters from the JIS X 0208 character set. JIS X 0208 is based
on the concept of a 94x94 table, with numbered rows and columns. However,
more than a thousand of the cells in that table are empty; JIS X 0208 does not
actually use all 94x94=8,836 possible kuten codes.
mbstring had a dubious feature whereby, if a Japanese string contained one of
these 'unmapped' kuten codes, and it was being converted to another Japanese
encoding which was also based on JIS X 0208, the non-existent character would
be silently passed through, and the unmapped kuten code would be re-encoded
using the normal encoding method of the target text encoding.
Again, this _only_ happened if converting the text with the funky kuten code
to a Japanese encoding. If one tried converting it to Unicode, mbstring would
treat that as an error.
If somebody, somewhere, made their own private extension to JIS X 0208, and
used the regular Japanese encodings like Shift JIS and EUC-JP to encode this
private character set, then this feature might conceivably be useful. But how
likely is that? If someone is using Shift JIS, EUC-JP, ISO-2022-JP, etc. to
encode a funky version of JIS X 0208 with extra characters added, then that
should be treated as a separate text encoding.
The code which flags such characters with MBFL_WCSPLANE_JIS0208 is retained
solely for error reporting in `mbfl_filt_conv_illegal_output`.
- Don't allow control characters to appear in the middle of a multi-byte
character. (This was a strange feature of mbstring; it doesn't make much
sense, and iconv doesn't allow it.)
- Treat truncated multi-byte characters as an error.
- For consistency with UTF-16, UTF-32, and UCS-4, strip leading byte
order marks.
- Treat it as an error if string is truncated (i.e. has an odd number
of bytes).
To give the background on this issue, here is an excerpt from JAPANESE.txt,
from the Unicode Consortium:
Apple has defined a block of 32 corporate characters as "transcoding
hints." These are used in combination with standard Unicode characters
to force them to be treated in a special way for mapping to other
encodings; they have no other effect. Sixteen of these transcoding
hints are "grouping hints" - they indicate that the next 2-4 Unicode
characters should be treated as a single entity for transcoding. The
other sixteen transcoding hints are "variant tags" - they are like
combining characters, and can follow a standard Unicode (or a sequence
consisting of a base character and other combining characters) to
cause it to be treated in a special way for transcoding. These always
terminate a combining-character sequence.
The transcoding coding hints used in this mapping table are:
0xF860 group next 2 characters as a single entity for transcoding
0xF861 group next 3 characters as a single entity for transcoding
0xF862 group next 4 characters as a single entity for transcoding
0xF87A variant tag for "negative" (i.e. black & white reversed)
0xF87E variant tag for vertical form
0xF87F variant tag for other alternate form
For example, the Apple addition character 0x85AB is Roman numeral
thirteen. There is no single Unicode for this (although there are
standard Unicodes for Roman numerals 1-12). Using the grouping hint
0xF862 in combination with standard Unicodes, we can map this as
0xF862+0x0058+0x0049+0x0049+0x0049 (i.e. X + I + I + I).
Our SJIS-mac conversion code actually recognizes some special sequences
which start with an Apple 'transcoding hint'. However, if a transcoding
hint is misplaced and is not followed by one of the expected sequences,
we can just emit one error marker for the bad transcoding hint and then
process the following codepoint as normal.
When converting Unicode to MacJapanese, some special sequences of Unicode
codepoints are collapsed into a single SJIS character. When the implementation
sees a codepoint which *might* begin such a sequence, it is cached and examined
again after the next codepoint arrives.
If it turns out that it wasn't one of the 'special' sequences, then a 'fallback'
conversion table is consulted to convert the cached codepoint. Then we re-enter
the regular conversion code to convert the immediately following codepoint.
BUT, local variables need to be reinitialized properly when doing this!
Because the locals weren't reinitialized, the sad result was that some codepoints
would get chopped up into bit salad and emitted as something totally bogus
(which might not even be valid SJIS-mac text at all).
Since 1993, Unicode has had a specific codepoint for a fullwidth Yen sign.
Likewise, MacJapanese has separate kuten codes for halfwidth and fullwidth
Yen signs. But mbstring mapped _both_ Yen sign codepoints to the
MacJapanese fullwidth Yen sign.
It's probably more appropriate to map the 'ordinary' Yen sign to the
MacJapanese halfwidth Yen sign. Besides, this means that the conversion
between Unicode and MacJapanese is closer to being lossless and reversible.
Also, don't accept 1st bytes above 0xED, since none of the possible 2-byte
sequences starting with 0xEE and above are actually mapped to any character.
Unicode has 'combining' characters which join with another following character.
Japanese hiragana and katakana with the 'two dots' voice mark can be represented
in this way, with one Unicode character for the 'base' kana and another one which
adds the voice mark.
In SJIS-2004, however, there are dedicated characters for voiced and unvoiced
kana. So some special checks are done to identify sequences of Unicode characters
which need to be 'collapsed' into a single SJIS-2004 character.
If a kana is immediately followed by some other unrelated character, like a
Cyrillic letter, then the cached kana should be output 'as is' and we
proceed with encoding the unrelated character. When doing this, though,
we need to re-initialize local variables, or else the unrelated character
will be mangled in some cases.
If the 2nd byte of a 2-byte character is invalid, then mb_substitute_character()
should be respected. Instead, what mbstring was doing was 'swallowing' the
first byte, then emitting the 2nd byte as if it was an ASCII character.
Likewise, if the 2nd byte is missing, instead of just keeping quiet, report an
illegal character as specified by mb_substitute_character().
This faulty binary search would never reject values at the very high
end of the range being searched, even if they were not actually in
the table.
Among other things, this meant that some Unicode codepoints which do
not correspond to any character in JIS X 0213 would be converted to
bogus Shift-JIS-2004 values rather than being rejected.
Each flush function in a chain of mbstring conversion filters always
calls the next flush function in the chain. So it is not necessary to
explicitly flush the second filter in a chain. (Due to this bug, in many
cases, flush functions were actually being called three times.)
Previously, the unit tests for these text encodings covered all mappings
from legacy -> Unicode, and all _reversible_ mappings from Unicode -> legacy.
However, we should also test the few Unicode -> legacy mappings which
are not reversible.
mbstring had an 'identify filter' for almost every supported text encoding
which was used when auto-detecting the most likely encoding for a string.
It would run over the string and set a 'flag' if it saw anything which
did not appear likely to be the encoding in question.
One problem with this scheme was that encodings which merely appeared
less likely to be the correct one were completely rejected, even if there
was no better candidate. Another problem was that the 'identify filters'
had a huge amount of code duplication with the 'conversion filters'.
Eliminate the identify filters. Instead, when auto-detecting text
encoding, use conversion filters to see whether the input string is valid
in candidate encodings or not. At the same type, watch the type of
codepoints which the string decodes to and mark it as less likely if
non-printable characters (ESC, form feed, bell, etc.) or 'private use
area' codepoints are seen.
Interestingly, one old test case in which JIS text was misidentified
as UTF-8 (and this wrong behavior was enshrined in the test) was 'fixed'
and the JIS string is now auto-detected as JIS.
- Don't allow control characters to appear in the middle of a multi-byte
character. (A strange feature, or perhaps misfeature, of mbstring which is
not present in other libraries such as iconv.)
- When checking whether string is valid, reject kuten codes which do not
map to any character, whether converting from EUC-JP to another encoding,
or converting another encoding which uses JIS X 0208/0212 charsets to
EUC-JP.
- Truncated multi-byte characters are treated as an error.
- Reject otherwise valid kuten codes which don't map to anything in JIS X 0208.
- Handle truncated multi-byte characters as an error.
- Convert Shift-JIS 0x7E to Unicode 0x203E (overline) as recommended by the
Unicode Consortium, and as iconv does.
- Convert Shift-JIS 0x5C to Unicode 0xA5 (yen sign) as recommended by the
Unicode Consortium, and as iconv does.
(NOTE: This will affect PHP scripts which use an internal encoding of
Shift-JIS! PHP assigns a special meaning to 0x5C, the backslash. For example,
it is used for escapes in double-quoted strings. Mapping the Shift-JIS yen
sign to the Unicode yen sign means the yen sign will not be usable for
C escapes in double-quoted strings. Japanese PHP programmers who want to
write their source code in Shift-JIS for some strange reason will have to
use the JIS X 0208 backlash or 'REVERSE SOLIDUS' character for their C
escapes.)
- Convert Unicode 0x5C (backslash) to Shift-JIS 0x815F (reverse solidus).
- Immediately handle error if first Shift-JIS byte is over 0xEF, rather than
waiting to see the next byte. (Previously, the value used was 0xFC, which is
the limit for the 2nd byte and not the 1st byte of a multi-byte character.)
- Don't allow 'control characters' to appear in the middle of a multi-byte
character.
The test case for bug 47399 is now obsolete. That test assumed that a number
of Shift-JIS byte sequences which don't map to any character were 'valid'
(because the byte values were within the legal ranges).
There is no meaningful difference between these and UCS-{2,4}. They are
just a little bit more lax about passing errors silently. They also have
no known use.
Alias to UCS-{2,4} in case someone, somewhere is using them.
- Identify filter was completely wrong.
- Respect `mb_substitute_character` rather than converting invalid bytes to
Unicode 0xFFFD (generic replacement character).
- Don't convert Unicode 0xFFFD to a valid ARMSCII-8 character.
- When converting ARMSCII-8 to ARMSCII-8, don't pass invalid bytes through
silently.
Previously, `mb_check_encoding` did an awful lot of unneeded work. In order to
determine whether a string was valid or not, it would convert the whole string
into wchar (code points), which required dynamically allocating a (potentially
large) buffer. Then it would turn right around and convert that big 'ol buffer
of code points back to the original encoding again. Finally, it would check
whether any invalid bytes were detected during that long and onerous process.
The thing is, mbstring _already_ has machinery for detecting whether a string
is valid in a certain encoding or not, and it doesn't require copying any data
around or allocating buffers. Better yet, it can fail fast when an invalid byte
is found. Why not use it? It's sure a lot faster!
Further, the legacy code was also badly broken. Why? Because aside from
checking whether illegal characters were detected, it would also check whether
the conversion to and from wchars was lossless. But, some encodings have
more than one valid encoding for the same character. In such cases, it is
not possible to make the conversion to and from wchars lossless for every
valid character. So `mb_check_encoding` would actually reject good strings
in a lot of encodings!
