package Encode; use strict; our $VERSION = '0.40'; require DynaLoader; require Exporter; our @ISA = qw(Exporter DynaLoader); # Public, encouraged API is exported by default our @EXPORT = qw ( encode decode encode_utf8 decode_utf8 find_encoding encodings ); our @EXPORT_OK = qw( define_encoding define_alias from_to is_utf8 is_8bit is_16bit utf8_upgrade utf8_downgrade _utf8_on _utf8_off ); bootstrap Encode (); # Documentation moved after __END__ for speed - NI-S use Carp; # Make a %encoding package variable to allow a certain amount of cheating our %encoding; my @alias; # ordered matching list my %alias; # cached known aliases # 0 1 2 3 4 5 6 7 8 9 10 our @latin2iso_num = ( 0, 1, 2, 3, 4, 9, 10, 13, 14, 15, 16 ); our %winlatin2cp = ( 'Latin1' => 1252, 'Latin2' => 1250, 'Cyrillic' => 1251, 'Greek' => 1253, 'Turkish' => 1254, 'Hebrew' => 1255, 'Arabic' => 1256, 'Baltic' => 1257, 'Vietnamese' => 1258, ); our %external_tables = ( 'euc-cn' => 'Encode/CN.pm', gb2312 => 'Encode/CN.pm', gb12345 => 'Encode/CN.pm', gbk => 'Encode/CN.pm', cp936 => 'Encode/CN.pm', 'iso-ir-165' => 'Encode/CN.pm', 'euc-jp' => 'Encode/JP.pm', shiftjis => 'Encode/JP.pm', macjapan => 'Encode/JP.pm', cp932 => 'Encode/JP.pm', 'euc-kr' => 'Encode/KR.pm', ksc5601 => 'Encode/KR.pm', cp949 => 'Encode/KR.pm', big5 => 'Encode/TW.pm', 'big5-hkscs' => 'Encode/TW.pm', cp950 => 'Encode/TW.pm', gb18030 => 'Encode/HanExtra.pm', big5plus => 'Encode/HanExtra.pm', 'euc-tw' => 'Encode/HanExtra.pm', ); sub encodings { my ($class) = @_; return map { $_->[0] } sort { $a->[1] cmp $b->[1] } map { [$_, lc $_] } grep { $_ ne 'Internal' } keys %encoding; } sub findAlias { my $class = shift; local $_ = shift; # print "# findAlias $_\n"; unless (exists $alias{$_}) { for (my $i=0; $i < @alias; $i += 2) { my $alias = $alias[$i]; my $val = $alias[$i+1]; my $new; if (ref($alias) eq 'Regexp' && $_ =~ $alias) { $new = eval $val; } elsif (ref($alias) eq 'CODE') { $new = &{$alias}($val) } elsif (lc($_) eq lc($alias)) { $new = $val; } if (defined($new)) { next if $new eq $_; # avoid (direct) recursion on bugs my $enc = (ref($new)) ? $new : find_encoding($new); if ($enc) { $alias{$_} = $enc; last; } } } } return $alias{$_}; } sub define_alias { while (@_) { my ($alias,$name) = splice(@_,0,2); push(@alias, $alias => $name); } } # Allow variants of iso-8859-1 etc. define_alias( qr/^iso[-_]?(\d+)[-_](\d+)$/i => '"iso-$1-$2"' ); # At least HP-UX has these. define_alias( qr/^iso8859(\d+)$/i => '"iso-8859-$1"' ); # More HP stuff. define_alias( qr/^(?:hp-)?(arabic|greek|hebrew|kana|roman|thai|turkish)8$/i => '"${1}8"' ); # The Official name of ASCII. define_alias( qr/^ANSI[-_]?X3\.4[-_]?1968$/i => '"ascii"' ); # This is a font issue, not an encoding issue. # (The currency symbol of the Latin 1 upper half # has been redefined as the euro symbol.) define_alias( qr/^(.+)\@euro$/i => '"$1"' ); # Allow latin-1 style names as well define_alias( qr/^(?:iso[-_]?)?latin[-_]?(\d+)$/i => '"iso-8859-$latin2iso_num[$1]"' ); # Allow winlatin1 style names as well define_alias( qr/^win(latin[12]|cyrillic|baltic|greek|turkish|hebrew|arabic|baltic|vietnamese)$/i => '"cp$winlatin2cp{\u$1}"' ); # Common names for non-latin prefered MIME names define_alias( 'ascii' => 'US-ascii', 'cyrillic' => 'iso-8859-5', 'arabic' => 'iso-8859-6', 'greek' => 'iso-8859-7', 'hebrew' => 'iso-8859-8', 'thai' => 'iso-8859-11', 'tis620' => 'iso-8859-11', ); # At least AIX has IBM-NNN (surprisingly...) instead of cpNNN. # And Microsoft has their own naming (again, surprisingly). define_alias( qr/^(?:ibm|ms)[-_]?(\d\d\d\d?)$/i => '"cp$1"'); # Sometimes seen with a leading zero. define_alias( qr/^cp037$/i => '"cp37"'); # Ououououou. define_alias( qr/^macRomanian$/i => '"macRumanian"'); # Standardize on the dashed versions. define_alias( qr/^utf8$/i => 'utf-8' ); define_alias( qr/^koi8r$/i => 'koi8-r' ); define_alias( qr/^koi8u$/i => 'koi8-u' ); # Seen in some Linuxes. define_alias( qr/^ujis$/i => 'euc-jp' ); # CP936 doesn't have vendor-addon for GBK, so they're identical. define_alias( qr/^gbk$/i => '"cp936"'); # TODO: HP-UX '8' encodings arabic8 greek8 hebrew8 kana8 thai8 turkish8 # TODO: HP-UX '15' encodings japanese15 korean15 roi15 # TODO: Cyrillic encoding ISO-IR-111 (useful?) # TODO: Armenian encoding ARMSCII-8 # TODO: Hebrew encoding ISO-8859-8-1 # TODO: Thai encoding TCVN # TODO: Korean encoding Johab # TODO: Vietnamese encodings VPS # TODO: Japanese encoding JIS (not the same as SJIS) # TODO: Mac Asian+African encodings: Arabic Armenian Bengali Burmese # ChineseSimp ChineseTrad Devanagari Ethiopic ExtArabic # Farsi Georgian Gujarati Gurmukhi Hebrew Japanese # Kannada Khmer Korean Laotian Malayalam Mongolian # Oriya Sinhalese Symbol Tamil Telugu Tibetan Vietnamese # Map white space and _ to '-' define_alias( qr/^(\S+)[\s_]+(.*)$/i => '"$1-$2"' ); sub define_encoding { my $obj = shift; my $name = shift; $encoding{$name} = $obj; my $lc = lc($name); define_alias($lc => $obj) unless $lc eq $name; while (@_) { my $alias = shift; define_alias($alias,$obj); } return $obj; } sub getEncoding { my ($class,$name,$skip_external) = @_; my $enc; if (ref($name) && $name->can('new_sequence')) { return $name; } my $lc = lc $name; if (exists $encoding{$name}) { return $encoding{$name}; } if (exists $encoding{$lc}) { return $encoding{$lc}; } my $oc = $class->findAlias($name); return $oc if defined $oc; $oc = $class->findAlias($lc) if $lc ne $name; return $oc if defined $oc; if (!$skip_external and exists $external_tables{$lc}) { require $external_tables{$lc}; return $encoding{$name} if exists $encoding{$name}; } return; } sub find_encoding { my ($name,$skip_external) = @_; return __PACKAGE__->getEncoding($name,$skip_external); } sub encode { my ($name,$string,$check) = @_; my $enc = find_encoding($name); croak("Unknown encoding '$name'") unless defined $enc; my $octets = $enc->encode($string,$check); return undef if ($check && length($string)); return $octets; } sub decode { my ($name,$octets,$check) = @_; my $enc = find_encoding($name); croak("Unknown encoding '$name'") unless defined $enc; my $string = $enc->decode($octets,$check); $_[1] = $octets if $check; return $string; } sub from_to { my ($string,$from,$to,$check) = @_; my $f = find_encoding($from); croak("Unknown encoding '$from'") unless defined $f; my $t = find_encoding($to); croak("Unknown encoding '$to'") unless defined $t; my $uni = $f->decode($string,$check); return undef if ($check && length($string)); $string = $t->encode($uni,$check); return undef if ($check && length($uni)); return length($_[0] = $string); } sub encode_utf8 { my ($str) = @_; utf8::encode($str); return $str; } sub decode_utf8 { my ($str) = @_; return undef unless utf8::decode($str); return $str; } require Encode::Encoding; require Encode::XS; require Encode::Internal; require Encode::Unicode; require Encode::utf8; require Encode::iso10646_1; require Encode::ucs2_le; 1; __END__ =head1 NAME Encode - character encodings =head1 SYNOPSIS use Encode; =head1 DESCRIPTION The C module provides the interfaces between Perl's strings and the rest of the system. Perl strings are sequences of B. The repertoire of characters that Perl can represent is at least that defined by the Unicode Consortium. On most platforms the ordinal values of the characters (as returned by C) is the "Unicode codepoint" for the character (the exceptions are those platforms where the legacy encoding is some variant of EBCDIC rather than a super-set of ASCII - see L). Traditionaly computer data has been moved around in 8-bit chunks often called "bytes". These chunks are also known as "octets" in networking standards. Perl is widely used to manipulate data of many types - not only strings of characters representing human or computer languages but also "binary" data being the machines representation of numbers, pixels in an image - or just about anything. When Perl is processing "binary data" the programmer wants Perl to process "sequences of bytes". This is not a problem for Perl - as a byte has 256 possible values it easily fits in Perl's much larger "logical character". Due to size concerns, each of B (Chinese, Japanese & Korean) modules are not loaded in memory until the first time they're used. Although you don't have to C the corresponding B(B|B|B|B) modules first, be aware that those encodings will not be in C<%encodings> until their module is loaded (either implicitly through using encodings contained in the same module, or via an explicit C). =head2 TERMINOLOGY =over 4 =item * I: a character in the range 0..(2**32-1) (or more). (What Perl's strings are made of.) =item * I: a character in the range 0..255 (A special case of a Perl character.) =item * I: 8 bits of data, with ordinal values 0..255 (Term for bytes passed to or from a non-Perl context, e.g. disk file.) =back The marker [INTERNAL] marks Internal Implementation Details, in general meant only for those who think they know what they are doing, and such details may change in future releases. =head1 ENCODINGS =head2 Characteristics of an Encoding An encoding has a "repertoire" of characters that it can represent, and for each representable character there is at least one sequence of octets that represents it. =head2 Types of Encodings Encodings can be divided into the following types: =over 4 =item * Fixed length 8-bit (or less) encodings. Each character is a single octet so may have a repertoire of up to 256 characters. ASCII and iso-8859-* are typical examples. =item * Fixed length 16-bit encodings Each character is two octets so may have a repertoire of up to 65 536 characters. Unicode's UCS-2 is an example. Also used for encodings for East Asian languages. =item * Fixed length 32-bit encodings. Not really very "encoded" encodings. The Unicode code points are just represented as 4-octet integers. None the less because different architectures use different representations of integers (so called "endian") there at least two disctinct encodings. =item * Multi-byte encodings The number of octets needed to represent a character varies. UTF-8 is a particularly complex but regular case of a multi-byte encoding. Several East Asian countries use a multi-byte encoding where 1-octet is used to cover western roman characters and Asian characters get 2-octets. (UTF-16 is strictly a multi-byte encoding taking either 2 or 4 octets to represent a Unicode code point.) =item * "Escape" encodings. These encodings embed "escape sequences" into the octet sequence which describe how the following octets are to be interpreted. The iso-2022-* family is typical. Following the escape sequence octets are encoded by an "embedded" encoding (which will be one of the above types) until another escape sequence switches to a different "embedded" encoding. These schemes are very flexible and can handle mixed languages but are very complex to process (and have state). No escape encodings are implemented for Perl yet. =back =head2 Specifying Encodings Encodings can be specified to the API described below in two ways: =over 4 =item 1. By name Encoding names are strings with characters taken from a restricted repertoire. See L. =item 2. As an object Encoding objects are returned by C. If the second parameter is true, Encode will refrain from loading external modules for CJK encodings. =back =head2 Encoding Names Encoding names are case insensitive. White space in names is ignored. In addition an encoding may have aliases. Each encoding has one "canonical" name. The "canonical" name is chosen from the names of the encoding by picking the first in the following sequence: =over 4 =item * The MIME name as defined in IETF RFCs. =item * The name in the IANA registry. =item * The name used by the organization that defined it. =back Because of all the alias issues, and because in the general case encodings have state C uses the encoding object internally once an operation is in progress. As of Perl 5.8.0, at least the following encodings are recognized (the => marks aliases): ASCII US-ASCII => ASCII The Unicode: UTF-8 UTF-16 UCS-2 ISO 10646-1 => UCS-2 The ISO 8859 and KOI: ISO 8859-1 ISO 8859-6 ISO 8859-11 KOI8-F ISO 8859-2 ISO 8859-7 (12 doesn't exist) KOI8-R ISO 8859-3 ISO 8859-8 ISO 8859-13 KOI8-U ISO 8859-4 ISO 8859-9 ISO 8859-14 ISO 8859-5 ISO 8859-10 ISO 8859-15 ISO 8859-16 Latin1 => 8859-1 Latin6 => 8859-10 Latin2 => 8859-2 Latin7 => 8859-13 Latin3 => 8859-3 Latin8 => 8859-14 Latin4 => 8859-4 Latin9 => 8859-15 Latin5 => 8859-9 Latin10 => 8859-16 Cyrillic => 8859-5 Arabic => 8859-6 Greek => 8859-7 Hebrew => 8859-8 Thai => 8859-11 TIS620 => 8859-11 The CJKV: Chinese, Japanese, Korean, Vietnamese: ISO 2022 ISO 2022 JP-1 JIS 0201 GB 1988 Big5 EUC-CN ISO 2022 CN ISO 2022 JP-2 JIS 0208 GB 2312 HZ EUC-JP ISO 2022 JP ISO 2022 KR JIS 0210 GB 12345 CNS 11643 EUC-JP-0212 Shift-JIS GBK Big5-HKSCS EUC-KR VISCII ISO-IR-165 (Due to size concerns, additional Chinese encodings including C, C and C are distributed separately on CPAN, under the name L.) The PC codepages: CP37 CP852 CP861 CP866 CP949 CP1251 CP1256 CP424 CP855 CP862 CP869 CP950 CP1252 CP1257 CP737 CP856 CP863 CP874 CP1006 CP1253 CP1258 CP775 CP857 CP864 CP932 CP1047 CP1254 CP850 CP860 CP865 CP936 CP1250 CP1255 WinLatin1 => CP1252 WinLatin2 => CP1250 WinCyrillic => CP1251 WinGreek => CP1253 WinTurkiskh => CP1254 WinHebrew => CP1255 WinArabic => CP1256 WinBaltic => CP1257 WinVietnamese => CP1258 (All the CPI are available also as IBMI.) The Mac codepages: MacCentralEuropean MacJapanese MacCroatian MacRoman MacCyrillic MacRomanian MacDingbats MacSami MacGreek MacThai MacIcelandic MacTurkish MacUkraine Miscellaneous: 7bit-greek IR-197 7bit-kana NeXTstep 7bit-latin1 POSIX-BC DingBats Roman8 GSM 0338 Symbol =head1 PERL ENCODING API =head2 Generic Encoding Interface =over 4 =item * $bytes = encode(ENCODING, $string[, CHECK]) Encodes string from Perl's internal form into I and returns a sequence of octets. For CHECK see L. For example to convert (internally UTF-8 encoded) Unicode data to octets: $octets = encode("utf8", $unicode); =item * $string = decode(ENCODING, $bytes[, CHECK]) Decode sequence of octets assumed to be in I into Perl's internal form and returns the resulting string. For CHECK see L. For example to convert ISO 8859-1 data to UTF-8: $utf8 = decode("latin1", $latin1); =item * from_to($string, FROM_ENCODING, TO_ENCODING[, CHECK]) Convert B the data between two encodings. How did the data in $string originally get to be in FROM_ENCODING? Either using encode() or through PerlIO: See L. For CHECK see L. For example to convert ISO 8859-1 data to UTF-8: from_to($data, "iso-8859-1", "utf-8"); and to convert it back: from_to($data, "utf-8", "iso-8859-1"); Note that because the conversion happens in place, the data to be converted cannot be a string constant, it must be a scalar variable. =back =head2 Handling Malformed Data If CHECK is not set, C is returned. If the data is supposed to be UTF-8, an optional lexical warning (category utf8) is given. If CHECK is true but not a code reference, dies. It would desirable to have a way to indicate that transform should use the encodings "replacement character" - no such mechanism is defined yet. It is also planned to allow I to be a code reference. This is not yet implemented as there are design issues with what its arguments should be and how it returns its results. =over 4 =item Scheme 1 Passed remaining fragment of string being processed. Modifies it in place to remove bytes/characters it can understand and returns a string used to represent them. e.g. sub fixup { my $ch = substr($_[0],0,1,''); return sprintf("\x{%02X}",ord($ch); } This scheme is close to how underlying C code for Encode works, but gives the fixup routine very little context. =item Scheme 2 Passed original string, and an index into it of the problem area, and output string so far. Appends what it will to output string and returns new index into original string. For example: sub fixup { # my ($s,$i,$d) = @_; my $ch = substr($_[0],$_[1],1); $_[2] .= sprintf("\x{%02X}",ord($ch); return $_[1]+1; } This scheme gives maximal control to the fixup routine but is more complicated to code, and may need internals of Encode to be tweaked to keep original string intact. =item Other Schemes Hybrids of above. Multiple return values rather than in-place modifications. Index into the string could be pos($str) allowing s/\G...//. =back =head2 UTF-8 / utf8 The Unicode consortium defines the UTF-8 standard as a way of encoding the entire Unicode repertiore as sequences of octets. This encoding is expected to become very widespread. Perl can use this form internaly to represent strings, so conversions to and from this form are particularly efficient (as octets in memory do not have to change, just the meta-data that tells Perl how to treat them). =over 4 =item * $bytes = encode_utf8($string); The characters that comprise string are encoded in Perl's superset of UTF-8 and the resulting octets returned as a sequence of bytes. All possible characters have a UTF-8 representation so this function cannot fail. =item * $string = decode_utf8($bytes [,CHECK]); The sequence of octets represented by $bytes is decoded from UTF-8 into a sequence of logical characters. Not all sequences of octets form valid UTF-8 encodings, so it is possible for this call to fail. For CHECK see L. =back =head2 Other Encodings of Unicode UTF-16 is similar to UCS-2, 16 bit or 2-byte chunks. UCS-2 can only represent 0..0xFFFF, while UTF-16 has a I scheme which allows it to cover the whole Unicode range. Surrogates are code points set aside to encode the 0x01000..0x10FFFF range of Unicode code points in pairs of 16-bit units. The I are the range 0xD800..0xDBFF, and the I are the range 0xDC00..0xDFFFF. The surrogate encoding is $hi = ($uni - 0x10000) / 0x400 + 0xD800; $lo = ($uni - 0x10000) % 0x400 + 0xDC00; and the decoding is $uni = 0x10000 + ($hi - 0xD8000) * 0x400 + ($lo - 0xDC00); Encode implements big-endian UCS-2 aliased to "iso-10646-1" as that happens to be the name used by that representation when used with X11 fonts. UTF-32 or UCS-4 is 32-bit or 4-byte chunks. Perl's logical characters can be considered as being in this form without encoding. An encoding to transfer strings in this form (e.g. to write them to a file) would need to pack('L*', unpack('U*', $string)); # native or pack('V*', unpack('U*', $string)); # little-endian or pack('N*', unpack('U*', $string)); # big-endian depending on the endianness required. No UTF-32 encodings are implemented yet. Both UCS-2 and UCS-4 style encodings can have "byte order marks" by representing the code point 0xFFFE as the very first thing in a file. =head2 Listing available encodings use Encode qw(encodings); @list = encodings(); Returns a list of the canonical names of the available encodings. =head2 Defining Aliases use Encode qw(define_alias); define_alias( newName => ENCODING); Allows newName to be used as am alias for ENCODING. ENCODING may be either the name of an encoding or and encoding object (as above). Currently I can be specified in the following ways: =over 4 =item As a simple string. =item As a qr// compiled regular expression, e.g.: define_alias( qr/^iso8859-(\d+)$/i => '"iso-8859-$1"' ); In this case if I is not a reference it is C-ed to allow C<$1> etc. to be subsituted. The example is one way to names as used in X11 font names to alias the MIME names for the iso-8859-* family. =item As a code reference, e.g.: define_alias( sub { return /^iso8859-(\d+)$/i ? "iso-8859-$1" : undef } , ''); In this case C<$_> will be set to the name that is being looked up and I is passed to the sub as its first argument. The example is another way to names as used in X11 font names to alias the MIME names for the iso-8859-* family. =back =head2 Defining Encodings use Encode qw(define_alias); define_encoding( $object, 'canonicalName' [,alias...]); Causes I to be associated with I<$object>. The object should provide the interface described in L below. If more than two arguments are provided then additional arguments are taken as aliases for I<$object> as for C. =head1 Encoding and IO It is very common to want to do encoding transformations when reading or writing files, network connections, pipes etc. If Perl is configured to use the new 'perlio' IO system then C provides a "layer" (See L) which can transform data as it is read or written. Here is how the blind poet would modernise the encoding: use Encode; open(my $iliad,'<:encoding(iso-8859-7)','iliad.greek'); open(my $utf8,'>:utf8','iliad.utf8'); my @epic = <$iliad>; print $utf8 @epic; close($utf8); close($illiad); In addition the new IO system can also be configured to read/write UTF-8 encoded characters (as noted above this is efficient): open(my $fh,'>:utf8','anything'); print $fh "Any \x{0021} string \N{SMILEY FACE}\n"; Either of the above forms of "layer" specifications can be made the default for a lexical scope with the C pragma. See L. Once a handle is open is layers can be altered using C. Without any such configuration, or if Perl itself is built using system's own IO, then write operations assume that file handle accepts only I and will C if a character larger than 255 is written to the handle. When reading, each octet from the handle becomes a byte-in-a-character. Note that this default is the same behaviour as bytes-only languages (including Perl before v5.6) would have, and is sufficient to handle native 8-bit encodings e.g. iso-8859-1, EBCDIC etc. and any legacy mechanisms for handling other encodings and binary data. In other cases it is the programs responsibility to transform characters into bytes using the API above before doing writes, and to transform the bytes read from a handle into characters before doing "character operations" (e.g. C, C, ...). You can also use PerlIO to convert larger amounts of data you don't want to bring into memory. For example to convert between ISO 8859-1 (Latin 1) and UTF-8 (or UTF-EBCDIC in EBCDIC machines): open(F, "<:encoding(iso-8859-1)", "data.txt") or die $!; open(G, ">:utf8", "data.utf") or die $!; while () { print G } # Could also do "print G " but that would pull # the whole file into memory just to write it out again. More examples: open(my $f, "<:encoding(cp1252)") open(my $g, ">:encoding(iso-8859-2)") open(my $h, ">:encoding(latin9)") # iso-8859-15 See L for more information. See also L for how to change the default encoding of the data in your script. =head1 Encoding How to ... To do: =over 4 =item * IO with mixed content (faking iso-2020-*) =item * MIME's Content-Length: =item * UTF-8 strings in binary data. =item * Perl/Encode wrappers on non-Unicode XS modules. =back =head1 Messing with Perl's Internals The following API uses parts of Perl's internals in the current implementation. As such they are efficient, but may change. =over 4 =item * is_utf8(STRING [, CHECK]) [INTERNAL] Test whether the UTF-8 flag is turned on in the STRING. If CHECK is true, also checks the data in STRING for being well-formed UTF-8. Returns true if successful, false otherwise. =item * valid_utf8(STRING) [INTERNAL] Test whether STRING is in a consistent state. Will return true if string is held as bytes, or is well-formed UTF-8 and has the UTF-8 flag on. Main reason for this routine is to allow Perl's testsuite to check that operations have left strings in a consistent state. =item * _utf8_on(STRING) [INTERNAL] Turn on the UTF-8 flag in STRING. The data in STRING is B checked for being well-formed UTF-8. Do not use unless you B that the STRING is well-formed UTF-8. Returns the previous state of the UTF-8 flag (so please don't test the return value as I success or failure), or C if STRING is not a string. =item * _utf8_off(STRING) [INTERNAL] Turn off the UTF-8 flag in STRING. Do not use frivolously. Returns the previous state of the UTF-8 flag (so please don't test the return value as I success or failure), or C if STRING is not a string. =back =head1 IMPLEMENTATION CLASSES As mentioned above encodings are (in the current implementation at least) defined by objects. The mapping of encoding name to object is via the C<%encodings> hash. The values of the hash can currently be either strings or objects. The string form may go away in the future. The string form occurs when C has scanned C<@INC> for loadable encodings but has not actually loaded the encoding in question. This is because the current "loading" process is all Perl and a bit slow. Once an encoding is loaded then value of the hash is object which implements the encoding. The object should provide the following interface: =over 4 =item -Ename Should return the string representing the canonical name of the encoding. =item -Enew_sequence This is a placeholder for encodings with state. It should return an object which implements this interface, all current implementations return the original object. =item -Eencode($string,$check) Should return the octet sequence representing I<$string>. If I<$check> is true it should modify I<$string> in place to remove the converted part (i.e. the whole string unless there is an error). If an error occurs it should return the octet sequence for the fragment of string that has been converted, and modify $string in-place to remove the converted part leaving it starting with the problem fragment. If check is is false then C should make a "best effort" to convert the string - for example by using a replacement character. =item -Edecode($octets,$check) Should return the string that I<$octets> represents. If I<$check> is true it should modify I<$octets> in place to remove the converted part (i.e. the whole sequence unless there is an error). If an error occurs it should return the fragment of string that has been converted, and modify $octets in-place to remove the converted part leaving it starting with the problem fragment. If check is is false then C should make a "best effort" to convert the string - for example by using Unicode's "\x{FFFD}" as a replacement character. =back It should be noted that the check behaviour is different from the outer public API. The logic is that the "unchecked" case is useful when encoding is part of a stream which may be reporting errors (e.g. STDERR). In such cases it is desirable to get everything through somehow without causing additional errors which obscure the original one. Also the encoding is best placed to know what the correct replacement character is, so if that is the desired behaviour then letting low level code do it is the most efficient. In contrast if check is true, the scheme above allows the encoding to do as much as it can and tell layer above how much that was. What is lacking at present is a mechanism to report what went wrong. The most likely interface will be an additional method call to the object, or perhaps (to avoid forcing per-stream objects on otherwise stateless encodings) and additional parameter. It is also highly desirable that encoding classes inherit from C as a base class. This allows that class to define additional behaviour for all encoding objects. For example built in Unicode, UCS-2 and UTF-8 classes use : package Encode::MyEncoding; use base qw(Encode::Encoding); __PACKAGE__->Define(qw(myCanonical myAlias)); To create an object with bless {Name => ...},$class, and call define_encoding. They inherit their C method from C. =head2 Compiled Encodings F provides a class C which provides the interface described above. It calls a generic octet-sequence to octet-sequence "engine" that is driven by tables (defined in F). The same engine is used for both encode and decode. C's C forces Perl's characters to their UTF-8 form and then treats them as just another multibyte encoding. C's C transforms the sequence and then turns the UTF-8-ness flag as that is the form that the tables are defined to produce. For details of the engine see the comments in F. The tables are produced by the Perl script F (the name needs to change so we can eventually install it somewhere). F can currently read two formats: =over 4 =item *.enc This is a coined format used by Tcl. It is documented in Encode/EncodeFormat.pod. =item *.ucm This is the semi-standard format used by IBM's ICU package. =back F can write the following forms: =over 4 =item *.ucm See above - the F files provided with the distribution have been created from the original Tcl .enc files using this approach. =item *.c Produces tables as C data structures - this is used to build in encodings into F/F. =item *.xs In theory this allows encodings to be stand-alone loadable Perl extensions. The process has not yet been tested. The plan is to use this approach for large East Asian encodings. =back The set of encodings built-in to F/F is determined by F. The current set is as follows: =over 4 =item ascii and iso-8859-* That is all the common 8-bit "western" encodings. =item IBM-1047 and two other variants of EBCDIC. These are the same variants that are supported by EBCDIC Perl as "native" encodings. They are included to prove "reversibility" of some constructs in EBCDIC Perl. =item symbol and dingbats as used by Tk on X11. (The reason Encode got started was to support Perl/Tk.) =back That set is rather ad hoc and has been driven by the needs of the tests rather than the needs of typical applications. It is likely to be rationalized. =head1 SEE ALSO L, L, L, L, L =cut