JezK
Edit File: Encoding.pm
package Encode::Encoding; # Base class for classes which implement encodings use strict; use warnings; our $VERSION = do { my @r = ( q$Revision: 2.8 $ =~ /\d+/g ); sprintf "%d." . "%02d" x $#r, @r }; our @CARP_NOT = qw(Encode Encode::Encoder); use Carp (); use Encode (); use Encode::MIME::Name; use constant DEBUG => !!$ENV{PERL_ENCODE_DEBUG}; sub Define { my $obj = shift; my $canonical = shift; $obj = bless { Name => $canonical }, $obj unless ref $obj; # warn "$canonical => $obj\n"; Encode::define_encoding( $obj, $canonical, @_ ); } sub name { return shift->{'Name'} } sub mime_name { return Encode::MIME::Name::get_mime_name(shift->name); } sub renew { my $self = shift; my $clone = bless {%$self} => ref($self); $clone->{renewed}++; # so the caller can see it DEBUG and warn $clone->{renewed}; return $clone; } sub renewed { return $_[0]->{renewed} || 0 } *new_sequence = \&renew; sub needs_lines { 0 } sub perlio_ok { return eval { require PerlIO::encoding } ? 1 : 0; } # (Temporary|legacy) methods sub toUnicode { shift->decode(@_) } sub fromUnicode { shift->encode(@_) } # # Needs to be overloaded or just croak # sub encode { my $obj = shift; my $class = ref($obj) ? ref($obj) : $obj; Carp::croak( $class . "->encode() not defined!" ); } sub decode { my $obj = shift; my $class = ref($obj) ? ref($obj) : $obj; Carp::croak( $class . "->encode() not defined!" ); } sub DESTROY { } 1; __END__ =head1 NAME Encode::Encoding - Encode Implementation Base Class =head1 SYNOPSIS package Encode::MyEncoding; use parent qw(Encode::Encoding); __PACKAGE__->Define(qw(myCanonical myAlias)); =head1 DESCRIPTION As mentioned in L<Encode>, encodings are (in the current implementation at least) defined as objects. The mapping of encoding name to object is via the C<%Encode::Encoding> hash. Though you can directly manipulate this hash, it is strongly encouraged to use this base class module and add encode() and decode() methods. =head2 Methods you should implement You are strongly encouraged to implement methods below, at least either encode() or decode(). =over 4 =item -E<gt>encode($string [,$check]) MUST return the octet sequence representing I<$string>. =over 2 =item * 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 perlio_ok() is true, SHOULD becomes MUST. =item * If an error occurs, it SHOULD return the octet sequence for the fragment of string that has been converted and modify $string in-place to remove the converted part leaving it starting with the problem fragment. If perlio_ok() is true, SHOULD becomes MUST. =item * If I<$check> is false then C<encode> MUST make a "best effort" to convert the string - for example, by using a replacement character. =back =item -E<gt>decode($octets [,$check]) MUST return the string that I<$octets> represents. =over 2 =item * If I<$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 perlio_ok() is true, SHOULD becomes MUST. =item * If an error occurs, it SHOULD return the fragment of string that has been converted and modify $octets in-place to remove the converted part leaving it starting with the problem fragment. If perlio_ok() is true, SHOULD becomes MUST. =item * If I<$check> is false then C<decode> should make a "best effort" to convert the string - for example by using Unicode's "\x{FFFD}" as a replacement character. =back =back If you want your encoding to work with L<encoding> pragma, you should also implement the method below. =over 4 =item -E<gt>cat_decode($destination, $octets, $offset, $terminator [,$check]) MUST decode I<$octets> with I<$offset> and concatenate it to I<$destination>. Decoding will terminate when $terminator (a string) appears in output. I<$offset> will be modified to the last $octets position at end of decode. Returns true if $terminator appears output, else returns false. =back =head2 Other methods defined in Encode::Encodings You do not have to override methods shown below unless you have to. =over 4 =item -E<gt>name Predefined As: sub name { return shift->{'Name'} } MUST return the string representing the canonical name of the encoding. =item -E<gt>mime_name Predefined As: sub mime_name{ return Encode::MIME::Name::get_mime_name(shift->name); } MUST return the string representing the IANA charset name of the encoding. =item -E<gt>renew Predefined As: sub renew { my $self = shift; my $clone = bless { %$self } => ref($self); $clone->{renewed}++; return $clone; } This method reconstructs the encoding object if necessary. If you need to store the state during encoding, this is where you clone your object. PerlIO ALWAYS calls this method to make sure it has its own private encoding object. =item -E<gt>renewed Predefined As: sub renewed { $_[0]->{renewed} || 0 } Tells whether the object is renewed (and how many times). Some modules emit C<Use of uninitialized value in null operation> warning unless the value is numeric so return 0 for false. =item -E<gt>perlio_ok() Predefined As: sub perlio_ok { return eval { require PerlIO::encoding } ? 1 : 0; } If your encoding does not support PerlIO for some reasons, just; sub perlio_ok { 0 } =item -E<gt>needs_lines() Predefined As: sub needs_lines { 0 }; If your encoding can work with PerlIO but needs line buffering, you MUST define this method so it returns true. 7bit ISO-2022 encodings are one example that needs this. When this method is missing, false is assumed. =back =head2 Example: Encode::ROT13 package Encode::ROT13; use strict; use parent qw(Encode::Encoding); __PACKAGE__->Define('rot13'); sub encode($$;$){ my ($obj, $str, $chk) = @_; $str =~ tr/A-Za-z/N-ZA-Mn-za-m/; $_[1] = '' if $chk; # this is what in-place edit means return $str; } # Jr pna or ynml yvxr guvf; *decode = \&encode; 1; =head1 Why the heck Encode API is different? It should be noted that the I<$check> behaviour is different from the outer public API. The logic is that the "unchecked" case is useful when the 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. By contrast, if I<$check> is true, the scheme above allows the encoding to do as much as it can and tell the 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) an additional parameter. It is also highly desirable that encoding classes inherit from C<Encode::Encoding> as a base class. This allows that class to define additional behaviour for all encoding objects. package Encode::MyEncoding; use parent qw(Encode::Encoding); __PACKAGE__->Define(qw(myCanonical myAlias)); to create an object with C<< bless {Name => ...}, $class >>, and call define_encoding. They inherit their C<name> method from C<Encode::Encoding>. =head2 Compiled Encodings For the sake of speed and efficiency, most of the encodings are now supported via a I<compiled form>: XS modules generated from UCM files. Encode provides the enc2xs tool to achieve that. Please see L<enc2xs> for more details. =head1 SEE ALSO L<perlmod>, L<enc2xs> =begin future =over 4 =item Scheme 1 The fixup routine gets passed the remaining fragment of string being processed. It modifies it in place to remove bytes/characters it can understand and returns a string used to represent them. For example: sub fixup { my $ch = substr($_[0],0,1,''); return sprintf("\x{%02X}",ord($ch); } This scheme is close to how the underlying C code for Encode works, but gives the fixup routine very little context. =item Scheme 2 The fixup routine gets passed the original string, an index into it of the problem area, and the output string so far. It appends what it wants to the output string and returns a new index into the original string. For example: sub fixup { # my ($s,$i,$d) = @_; my $ch = substr($_[0],$_[1],1); $_[2] .= sprintf("\x{%02X}",ord($ch); return $_[1]+1; } This scheme gives maximal control to the fixup routine but is more complicated to code, and may require that the internals of Encode be tweaked to keep the original string intact. =item Other Schemes Hybrids of the above. Multiple return values rather than in-place modifications. Index into the string could be C<pos($str)> allowing C<s/\G...//>. =back =end future =cut