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since this iconv implementation's output is stateless, it's necessary
to know before writing anything to the output buffer whether the
conversion of the current input character will fit.
previously we used a hard-coded table of the output size needed for
each supported output encoding, but failed to update the table when
adding support for conversion to jis-based encodings and again when
adding separate encoding identifiers for implicit-endianness utf-16/32
and ucs-2/4 variants, resulting in out-of-bound table reads and
incorrect size checks. no buffer overflow was possible, but the
affected characters could be converted incorrectly, and iconv could
potentially produce an incorrect return value as a result.
remove the hard-coded table, and instead perform the recursive iconv
conversion to a temporary buffer, measuring the output size and
transferring it to the actual output buffer only if the whole
converted result fits.
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this case is handled with a recursive call to iconv using a
specially-constructed conversion descriptor. the constant 0 was used
as the offset for utf-8, since utf-8 appears first in the charmaps
table, but the offset used needs to point into the charmap entry, past
the name/aliases at the beginning, to the byte identifying the
encoding. as a result of this error, junk was produced.
instead, call find_charmap so we don't have to hard-code a nontrivial
offset. with this change, the code has been tested and found to work
in the case of converting the affected hkscs characters to utf-8.
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maintainer's notes:
commit 95c6044e2ae85846330814c4ac5ebf4102dbe02c split UTF-32 and
UTF-32BE but neglected to add a case for the former as a destination
encoding, resulting in it wrongly being handled by the default case.
the intent was that the value of the macro be chosen to encode "big
endian" in the low bits, so that no code would be needed, but this was
botched; instead, handle it the way UCS2 is handled.
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maintainer's notes:
commit a223dbd27ae36fe53f9f67f86caf685b729593fc added the reverse
conversions to JIS-based encodings, but omitted the check for remining
buffer space in the case where the next character to be written was
single-byte, allowing conversion to continue past the end of the
destination buffer.
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in the unified code for handling utf-16 and ucs2 output, the check for
ucs2 wrongly looked at the source charset rather than the destination
charset.
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previously, the charset names without endianness specified were always
interpreted as big endian. unicode specifies that UTF-16 and UTF-32
have BOM-determined endianness if BOM is present, and are otherwise
big endian. since commit 5b546faa67544af395d6407553762b37e9711157
added support for stateful encodings, it is now possible to implement
BOM support via the conversion descriptor state.
for conversions to these charsets, the output is always big endian and
does not have a BOM.
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these encodings are still commonly used in messaging protocols and
such. the reverse mapping is implemented as a binary search of a list
of the jis 0208 characters in unicode order; the existing forward
table is used to perform the comparison in the search.
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previously, 8-bit codepages could only remap the high 128 bytes; the
low range was assumed/forced to agree with ascii. interpretation of
codepage table headers has been changed so that it's possible to
represent mappings for up to 256 slots (fewer if the initial portion
of the map is elided because it coincides with unicode codepoints).
this requires consuming a bit more of the 10-bit space of characters
that can be represented in 8-bit codepages, but there's still a plenty
left. the size of the legacy_chars table is actually reduced now by
eliding the first 256 entries and considering them to map implicitly
via the identity map.
before these changes, there seem to have been minor bugs/omissions in
codepage table generation, so it's likely that some actual bug fixes
are silently included in this commit. round-trip testing of a few
codepages was performed on the new version of the code, but no
differential testing against the old version was done.
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this implementation aims to match the baseline defined by rfc1468 (the
original mime charset definition) plus the halfwidth katakana
extension included in the whatwg definition of the charset. rejection
of si/so controls and newlines in doublebyte state are not currently
enforced. the jis x 0201 mode is currently interpreted as having the
yen sign and overline character in place of backslash and tilde; ascii
mode has the standard ascii characters in those slots.
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assuming pointers obtained from malloc have some nonzero alignment,
repurpose the low bit of iconv_t as an indicator that the descriptor
is a stateless value representing the source and destination character
encodings.
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the special case where mbrtowc returns 0 but consumed 1 byte of input
does not need to be considered, because the short-circuit for low
bytes already covered that case.
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short-circuiting low bytes before the switch precluded support for
character encodings that don't coincide with ascii in this range. this
limitation affected iso-2022 encodings, which use the esc byte to
introduce a shift sequence, and things like ebcdic.
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this is in preparation to support stateful conversion descriptors,
which are necessarily allocated and thus must be freed in iconv_close.
putting it in a separate TU will avoid pulling in free if iconv_close
is not referenced.
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this change is made to avoid having assumptions about the encoding
spread out across the file, and to facilitate future change to a form
that can accommodate allocted, stateful descriptors when needed.
this commit should not produce any functional changes; with the
compiler tested the only change to code generation was minor
reordering of local variables on stack.
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commit 97bd6b09dbe7478d5a90a06ecd9e5b59389d8eb9 refactored the table
lookup into a function and introduced an error in index computation.
the error caused garbage to be read from the table if the given charmap
had a non-zero number of elided entries.
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there was missing reverse-conversion logic for the case, handled
specially in the character set tables, where a byte represents a
unicode codepoint with the same value.
this patch adds code to handle the case, and refactors the two-level
10-bit table lookup for legacy character sets into a function to avoid
repeating it yet another time as part of the fix.
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this patch adjusts libc components which use the multibyte functions
internally, and which depend on them operating in a particular
encoding, to make the appropriate locale changes before calling them
and restore the calling thread's locale afterwards. activating the
byte-based C locale without these changes would cause regressions in
stdio and iconv.
in the case of iconv, the current implementation was simply using the
multibyte functions as UTF-8 conversions. setting a multibyte UTF-8
locale for the duration of the iconv operation allows the code to
continue working.
in the case of stdio, POSIX requires that FILE streams have an
encoding rule bound at the time of setting wide orientation. as long
as all locales, including the C locale, used the same encoding,
treating high bytes as UTF-8, there was no need to store an encoding
rule as part of the stream's state.
a new locale field in the FILE structure points to the locale that
should be made active during fgetwc/fputwc/ungetwc on the stream. it
cannot point to the locale active at the time the stream becomes
oriented, because this locale could be mutable (the global locale) or
could be destroyed (locale_t objects produced by newlocale) before the
stream is closed. instead, a pointer to the static C or C.UTF-8 locale
object added in commit commit aeeac9ca5490d7d90fe061ab72da446c01ddf746
is used. this is valid since categories other than LC_CTYPE will not
affect these functions.
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the comment claimed that EUC/GBK/Big5 are not implemented, which has
been incorrect since commit 19b4a0a20efc6b9df98b6a43536ecdd628ba4643.
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while not a requirement, it's common convention in other iconv
implementations to accept "CHAR" as an alias for nl_langinfo(CODESET),
meaning the encoding used for char[] strings in the current locale,
and also "" as an alternate form. supporting this is not costly and
improves compatibility.
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with these changes, the character set implemented as "big5" in musl is
a pure superset of cp950, the canonical "big5", and agrees with the
normative parts of Unicode. this means it has minor differences from
both hkscs and big5-2003:
- the range A2CC-A2CE maps to CJK ideographs rather than numerals,
contrary to changes made in big5-2003.
- C6CD maps to a CJK ideograph rather than its corresponding Kangxi
radical character, contrary to changes made in hkscs.
- F9FE maps to U+2593 rather than U+FFED.
of these differences, none but the last are visually distinct, and the
last is a character used purely for text-based graphics, not to convey
linguistic content.
should there be future demand for strict conformance to big5-2003 or
hkscs mappings, the present charset aliases can be replaced with
distinct variants.
reportedly there are other non-standard big5 extensions in common use
in Taiwan and perhaps elsewhere, which could also be added as layers
on top of the existing big5 support.
there may be additional characters which should be added to the hkscs
table: the whatwg standard for big5 defines what appears to be a
superset of hkscs.
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at this point, it is just the common base charset equivalent to
Windows CP 950, with no further extensions. HKSCS and possibly other
supersets will be added later. other aliases may need to be added too.
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like for other character sets, stateful iso-2022 form is not supported
yet but everything else should work. all charset aliases are treated
the same, as Windows codepage 949, because reportedly the EUC-KR
charset name is in widespread (mis?)usage in email and on the web for
data which actually uses the extended characters outside the standard
93x94 grid. this could easily be changed if desired.
the principle of this converter for handling the giant bulk of rare
Hangul syllables outside of the standard KS X 1001 93x94 grid is the
same as the GB18030 converter's treatment of non-explicitly-coded
Unicode codepoints: sequences in the extension range are mapped to an
integer index N, and the converter explicitly computes the Nth Hangul
syllable not explicitly encoded in the character map. empirically,
this requires at most 7 passes over the grid. this approach reduces
the table size required for Korean legacy encodings from roughly 44k
to 17k and should have minimal performance impact on real-world text
conversions since the "slow" characters are rare. where it does have
impact, the cost is merely a large constant time factor.
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this seems to have been a simple copy-and-paste error from the code
for converting from legacy codepages.
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to deal with the fact that the public headers may be used with pre-c99
compilers, __restrict is used in place of restrict, and defined
appropriately for any supported compiler. we also avoid the form
[restrict] since older versions of gcc rejected it due to a bug in the
original c99 standard, and instead use the form *restrict.
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apparently this was never tested before.
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also support (and restrict to subsets) older chinese sets, and
explicitly refuse to convert to cjk (since there's no code for it yet)
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this broke most uses of iconv in real-world programs, especially
glib's iconv wrappers.
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sadly the C language does not specify any such implicit conversion, so
this is not a matter of just fixing warnings (as gcc treats it) but
actual errors. i would like to revisit a number of these changes and
possibly revise the types used to reduce the number of casts required.
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