1 package Encode::Encoding;
3 # Base class for classes which implement encodings
6 our $VERSION = do { my @r = ( q$Revision: 2.5 $ =~ /\d+/g ); sprintf "%d." . "%02d" x $#r, @r };
14 my $canonical = shift;
15 $obj = bless { Name => $canonical }, $obj unless ref $obj;
17 # warn "$canonical => $obj\n";
18 Encode::define_encoding( $obj, $canonical, @_ );
21 sub name { return shift->{'Name'} }
24 require Encode::MIME::Name;
25 return Encode::MIME::Name::get_mime_name(shift->name);
28 # sub renew { return $_[0] }
32 my $clone = bless {%$self} => ref($self);
33 $clone->{renewed}++; # so the caller can see it
34 DEBUG and warn $clone->{renewed};
38 sub renewed { return $_[0]->{renewed} || 0 }
40 *new_sequence = \&renew;
45 eval { require PerlIO::encoding };
49 # (Temporary|legacy) methods
51 sub toUnicode { shift->decode(@_) }
52 sub fromUnicode { shift->encode(@_) }
55 # Needs to be overloaded or just croak
61 my $class = ref($obj) ? ref($obj) : $obj;
62 Carp::croak( $class . "->encode() not defined!" );
68 my $class = ref($obj) ? ref($obj) : $obj;
69 Carp::croak( $class . "->encode() not defined!" );
79 Encode::Encoding - Encode Implementation Base Class
83 package Encode::MyEncoding;
84 use base qw(Encode::Encoding);
86 __PACKAGE__->Define(qw(myCanonical myAlias));
90 As mentioned in L<Encode>, encodings are (in the current
91 implementation at least) defined as objects. The mapping of encoding
92 name to object is via the C<%Encode::Encoding> hash. Though you can
93 directly manipulate this hash, it is strongly encouraged to use this
94 base class module and add encode() and decode() methods.
96 =head2 Methods you should implement
98 You are strongly encouraged to implement methods below, at least
99 either encode() or decode().
103 =item -E<gt>encode($string [,$check])
105 MUST return the octet sequence representing I<$string>.
111 If I<$check> is true, it SHOULD modify I<$string> in place to remove
112 the converted part (i.e. the whole string unless there is an error).
113 If perlio_ok() is true, SHOULD becomes MUST.
117 If an error occurs, it SHOULD return the octet sequence for the
118 fragment of string that has been converted and modify $string in-place
119 to remove the converted part leaving it starting with the problem
120 fragment. If perlio_ok() is true, SHOULD becomes MUST.
124 If I<$check> is is false then C<encode> MUST make a "best effort" to
125 convert the string - for example, by using a replacement character.
129 =item -E<gt>decode($octets [,$check])
131 MUST return the string that I<$octets> represents.
137 If I<$check> is true, it SHOULD modify I<$octets> in place to remove
138 the converted part (i.e. the whole sequence unless there is an
139 error). If perlio_ok() is true, SHOULD becomes MUST.
143 If an error occurs, it SHOULD return the fragment of string that has
144 been converted and modify $octets in-place to remove the converted
145 part leaving it starting with the problem fragment. If perlio_ok() is
146 true, SHOULD becomes MUST.
150 If I<$check> is false then C<decode> should make a "best effort" to
151 convert the string - for example by using Unicode's "\x{FFFD}" as a
152 replacement character.
158 If you want your encoding to work with L<encoding> pragma, you should
159 also implement the method below.
163 =item -E<gt>cat_decode($destination, $octets, $offset, $terminator [,$check])
165 MUST decode I<$octets> with I<$offset> and concatenate it to I<$destination>.
166 Decoding will terminate when $terminator (a string) appears in output.
167 I<$offset> will be modified to the last $octets position at end of decode.
168 Returns true if $terminator appears output, else returns false.
172 =head2 Other methods defined in Encode::Encodings
174 You do not have to override methods shown below unless you have to.
182 sub name { return shift->{'Name'} }
184 MUST return the string representing the canonical name of the encoding.
186 =item -E<gt>mime_name
191 require Encode::MIME::Name;
192 return Encode::MIME::Name::get_mime_name(shift->name);
195 MUST return the string representing the IANA charset name of the encoding.
203 my $clone = bless { %$self } => ref($self);
208 This method reconstructs the encoding object if necessary. If you need
209 to store the state during encoding, this is where you clone your object.
211 PerlIO ALWAYS calls this method to make sure it has its own private
218 sub renewed { $_[0]->{renewed} || 0 }
220 Tells whether the object is renewed (and how many times). Some
221 modules emit C<Use of uninitialized value in null operation> warning
222 unless the value is numeric so return 0 for false.
224 =item -E<gt>perlio_ok()
229 eval{ require PerlIO::encoding };
233 If your encoding does not support PerlIO for some reasons, just;
237 =item -E<gt>needs_lines()
241 sub needs_lines { 0 };
243 If your encoding can work with PerlIO but needs line buffering, you
244 MUST define this method so it returns true. 7bit ISO-2022 encodings
245 are one example that needs this. When this method is missing, false
250 =head2 Example: Encode::ROT13
252 package Encode::ROT13;
254 use base qw(Encode::Encoding);
256 __PACKAGE__->Define('rot13');
259 my ($obj, $str, $chk) = @_;
260 $str =~ tr/A-Za-z/N-ZA-Mn-za-m/;
261 $_[1] = '' if $chk; # this is what in-place edit means
265 # Jr pna or ynml yvxr guvf;
270 =head1 Why the heck Encode API is different?
272 It should be noted that the I<$check> behaviour is different from the
273 outer public API. The logic is that the "unchecked" case is useful
274 when the encoding is part of a stream which may be reporting errors
275 (e.g. STDERR). In such cases, it is desirable to get everything
276 through somehow without causing additional errors which obscure the
277 original one. Also, the encoding is best placed to know what the
278 correct replacement character is, so if that is the desired behaviour
279 then letting low level code do it is the most efficient.
281 By contrast, if I<$check> is true, the scheme above allows the
282 encoding to do as much as it can and tell the layer above how much
283 that was. What is lacking at present is a mechanism to report what
284 went wrong. The most likely interface will be an additional method
285 call to the object, or perhaps (to avoid forcing per-stream objects
286 on otherwise stateless encodings) an additional parameter.
288 It is also highly desirable that encoding classes inherit from
289 C<Encode::Encoding> as a base class. This allows that class to define
290 additional behaviour for all encoding objects.
292 package Encode::MyEncoding;
293 use base qw(Encode::Encoding);
295 __PACKAGE__->Define(qw(myCanonical myAlias));
297 to create an object with C<< bless {Name => ...}, $class >>, and call
298 define_encoding. They inherit their C<name> method from
301 =head2 Compiled Encodings
303 For the sake of speed and efficiency, most of the encodings are now
304 supported via a I<compiled form>: XS modules generated from UCM
305 files. Encode provides the enc2xs tool to achieve that. Please see
306 L<enc2xs> for more details.
310 L<perlmod>, L<enc2xs>
318 The fixup routine gets passed the remaining fragment of string being
319 processed. It modifies it in place to remove bytes/characters it can
320 understand and returns a string used to represent them. For example:
323 my $ch = substr($_[0],0,1,'');
324 return sprintf("\x{%02X}",ord($ch);
327 This scheme is close to how the underlying C code for Encode works,
328 but gives the fixup routine very little context.
332 The fixup routine gets passed the original string, an index into
333 it of the problem area, and the output string so far. It appends
334 what it wants to the output string and returns a new index into the
335 original string. For example:
338 # my ($s,$i,$d) = @_;
339 my $ch = substr($_[0],$_[1],1);
340 $_[2] .= sprintf("\x{%02X}",ord($ch);
344 This scheme gives maximal control to the fixup routine but is more
345 complicated to code, and may require that the internals of Encode be tweaked to
346 keep the original string intact.
350 Hybrids of the above.
352 Multiple return values rather than in-place modifications.
354 Index into the string could be C<pos($str)> allowing C<s/\G...//>.