package Encode::Encoding;# Base class for classes which implement encodingsuse strict;use warnings;our $VERSION = do { my @r = ( q$Revision: 2.5 $ =~ /\d+/g ); sprintf "%d." . "%02d" x $#r, @r };require Encode;sub DEBUG { 0 }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{    require Encode::MIME::Name;    return Encode::MIME::Name::get_mime_name(shift->name);}# sub renew { return $_[0] }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 {    eval { require PerlIO::encoding };    return $@ ? 0 : 1;}# (Temporary|legacy) methodssub toUnicode   { shift->decode(@_) }sub fromUnicode { shift->encode(@_) }## Needs to be overloaded or just croak#sub encode {    require Carp;    my $obj = shift;    my $class = ref($obj) ? ref($obj) : $obj;    Carp::croak( $class . "->encode() not defined!" );}sub decode {    require Carp;    my $obj = shift;    my $class = ref($obj) ? ref($obj) : $obj;    Carp::croak( $class . "->encode() not defined!" );}sub DESTROY { }1;__END__=head1 NAMEEncode::Encoding - Encode Implementation Base Class=head1 SYNOPSIS  package Encode::MyEncoding;  use base qw(Encode::Encoding);  __PACKAGE__->Define(qw(myCanonical myAlias));=head1 DESCRIPTIONAs mentioned in L<Encode>, encodings are (in the currentimplementation at least) defined as objects. The mapping of encodingname to object is via the C<%Encode::Encoding> hash.  Though you candirectly manipulate this hash, it is strongly encouraged to use thisbase class module and add encode() and decode() methods.=head2 Methods you should implementYou are strongly encouraged to implement methods below, at leasteither encode() or decode().=over 4=item -E<gt>encode($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 removethe 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 thefragment of string that has been converted and modify $string in-placeto remove the converted part leaving it starting with the problemfragment.  If perlio_ok() is true, SHOULD becomes MUST.=item *If I<$check> is is false then C<encode> MUST  make a "best effort" toconvert 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 removethe converted part (i.e.  the whole sequence unless there is anerror).  If perlio_ok() is true, SHOULD becomes MUST.=item *If an error occurs, it SHOULD return the fragment of string that hasbeen converted and modify $octets in-place to remove the convertedpart leaving it starting with the problem fragment.  If perlio_ok() istrue, SHOULD becomes MUST.=item *If I<$check> is false then C<decode> should make a "best effort" toconvert the string - for example by using Unicode's "\x{FFFD}" as areplacement character.=back=backIf you want your encoding to work with L<encoding> pragma, you shouldalso 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::EncodingsYou do not have to override methods shown below unless you have to.=over 4=item -E<gt>namePredefined As:  sub name  { return shift->{'Name'} }MUST return the string representing the canonical name of the encoding.=item -E<gt>mime_namePredefined As:  sub mime_name{    require Encode::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>renewPredefined 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 needto store the state during encoding, this is where you clone your object.PerlIO ALWAYS calls this method to make sure it has its own privateencoding object.=item -E<gt>renewedPredefined As:  sub renewed { $_[0]->{renewed} || 0 }Tells whether the object is renewed (and how many times).  Somemodules emit C<Use of uninitialized value in null operation> warningunless the value is numeric so return 0 for false.=item -E<gt>perlio_ok()Predefined As:  sub perlio_ok {       eval{ require PerlIO::encoding };      return $@ ? 0 : 1;  }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, youMUST define this method so it returns true.  7bit ISO-2022 encodingsare one example that needs this.  When this method is missing, falseis assumed.=back=head2 Example: Encode::ROT13  package Encode::ROT13;  use strict;  use base 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 theouter public API. The logic is that the "unchecked" case is usefulwhen the encoding is part of a stream which may be reporting errors(e.g. STDERR).  In such cases, it is desirable to get everythingthrough somehow without causing additional errors which obscure theoriginal one. Also, the encoding is best placed to know what thecorrect replacement character is, so if that is the desired behaviourthen letting low level code do it is the most efficient.By contrast, if I<$check> is true, the scheme above allows theencoding to do as much as it can and tell the layer above how muchthat was. What is lacking at present is a mechanism to report whatwent wrong. The most likely interface will be an additional methodcall to the object, or perhaps (to avoid forcing per-stream objectson otherwise stateless encodings) an additional parameter.It is also highly desirable that encoding classes inherit fromC<Encode::Encoding> as a base class. This allows that class to defineadditional behaviour for all encoding objects.  package Encode::MyEncoding;  use base qw(Encode::Encoding);  __PACKAGE__->Define(qw(myCanonical myAlias));to create an object with C<< bless {Name => ...}, $class >>, and calldefine_encoding.  They inherit their C<name> method fromC<Encode::Encoding>.=head2 Compiled EncodingsFor the sake of speed and efficiency, most of the encodings are nowsupported via a I<compiled form>: XS modules generated from UCMfiles.   Encode provides the enc2xs tool to achieve that.  Please seeL<enc2xs> for more details.=head1 SEE ALSOL<perlmod>, L<enc2xs>=begin future=over 4=item Scheme 1The fixup routine gets passed the remaining fragment of string beingprocessed.  It modifies it in place to remove bytes/characters it canunderstand and returns a string used to represent them.  For example: sub fixup {   my $ch = substr($_[0],0,1,'');   return sprintf("\x{%02X}",ord($ch); }This scheme is close to how the underlying C code for Encode works,but gives the fixup routine very little context.=item Scheme 2The fixup routine gets passed the original string, an index intoit of the problem area, and the output string so far.  It appendswhat it wants to the output string and returns a new index into theoriginal string.  For example: sub fixup {   # my ($s,$i,$d) = @_;   my $ch = substr($_[0],$_[1],1);   $_[2] .= sprintf("\x{%02X}",ord($ch);   return $_[1]+1; }This scheme gives maximal control to the fixup routine but is morecomplicated to code, and may require that the internals of Encode be tweaked tokeep the original string intact.=item Other SchemesHybrids of the above.Multiple return values rather than in-place modifications.Index into the string could be C<pos($str)> allowing C<s/\G...//>.=back=end future=cut