| 1 | package Encode::Encoding; |
| 2 | # Base class for classes which implement encodings |
| 3 | use strict; |
| 4 | our $VERSION = do { my @r = (q$Revision: 2.2 $ =~ /\d+/g); sprintf "%d."."%02d" x $#r, @r }; |
| 5 | |
| 6 | require Encode; |
| 7 | |
| 8 | sub DEBUG { 0 } |
| 9 | sub Define |
| 10 | { |
| 11 | my $obj = shift; |
| 12 | my $canonical = shift; |
| 13 | $obj = bless { Name => $canonical },$obj unless ref $obj; |
| 14 | # warn "$canonical => $obj\n"; |
| 15 | Encode::define_encoding($obj, $canonical, @_); |
| 16 | } |
| 17 | |
| 18 | sub name { return shift->{'Name'} } |
| 19 | |
| 20 | # sub renew { return $_[0] } |
| 21 | |
| 22 | sub renew { |
| 23 | my $self = shift; |
| 24 | my $clone = bless { %$self } => ref($self); |
| 25 | $clone->{renewed}++; # so the caller can see it |
| 26 | DEBUG and warn $clone->{renewed}; |
| 27 | return $clone; |
| 28 | } |
| 29 | |
| 30 | sub renewed{ return $_[0]->{renewed} || 0 } |
| 31 | |
| 32 | *new_sequence = \&renew; |
| 33 | |
| 34 | sub needs_lines { 0 }; |
| 35 | |
| 36 | sub perlio_ok { |
| 37 | eval{ require PerlIO::encoding }; |
| 38 | return $@ ? 0 : 1; |
| 39 | } |
| 40 | |
| 41 | # (Temporary|legacy) methods |
| 42 | |
| 43 | sub toUnicode { shift->decode(@_) } |
| 44 | sub fromUnicode { shift->encode(@_) } |
| 45 | |
| 46 | # |
| 47 | # Needs to be overloaded or just croak |
| 48 | # |
| 49 | |
| 50 | sub encode { |
| 51 | require Carp; |
| 52 | my $obj = shift; |
| 53 | my $class = ref($obj) ? ref($obj) : $obj; |
| 54 | Carp::croak($class . "->encode() not defined!"); |
| 55 | } |
| 56 | |
| 57 | sub decode{ |
| 58 | require Carp; |
| 59 | my $obj = shift; |
| 60 | my $class = ref($obj) ? ref($obj) : $obj; |
| 61 | Carp::croak($class . "->encode() not defined!"); |
| 62 | } |
| 63 | |
| 64 | sub DESTROY {} |
| 65 | |
| 66 | 1; |
| 67 | __END__ |
| 68 | |
| 69 | =head1 NAME |
| 70 | |
| 71 | Encode::Encoding - Encode Implementation Base Class |
| 72 | |
| 73 | =head1 SYNOPSIS |
| 74 | |
| 75 | package Encode::MyEncoding; |
| 76 | use base qw(Encode::Encoding); |
| 77 | |
| 78 | __PACKAGE__->Define(qw(myCanonical myAlias)); |
| 79 | |
| 80 | =head1 DESCRIPTION |
| 81 | |
| 82 | As mentioned in L<Encode>, encodings are (in the current |
| 83 | implementation at least) defined as objects. The mapping of encoding |
| 84 | name to object is via the C<%Encode::Encoding> hash. Though you can |
| 85 | directly manipulate this hash, it is strongly encouraged to use this |
| 86 | base class module and add encode() and decode() methods. |
| 87 | |
| 88 | =head2 Methods you should implement |
| 89 | |
| 90 | You are strongly encouraged to implement methods below, at least |
| 91 | either encode() or decode(). |
| 92 | |
| 93 | =over 4 |
| 94 | |
| 95 | =item -E<gt>encode($string [,$check]) |
| 96 | |
| 97 | MUST return the octet sequence representing I<$string>. |
| 98 | |
| 99 | =over 2 |
| 100 | |
| 101 | =item * |
| 102 | |
| 103 | If I<$check> is true, it SHOULD modify I<$string> in place to remove |
| 104 | the converted part (i.e. the whole string unless there is an error). |
| 105 | If perlio_ok() is true, SHOULD becomes MUST. |
| 106 | |
| 107 | =item * |
| 108 | |
| 109 | If an error occurs, it SHOULD return the octet sequence for the |
| 110 | fragment of string that has been converted and modify $string in-place |
| 111 | to remove the converted part leaving it starting with the problem |
| 112 | fragment. If perlio_ok() is true, SHOULD becomes MUST. |
| 113 | |
| 114 | =item * |
| 115 | |
| 116 | If I<$check> is is false then C<encode> MUST make a "best effort" to |
| 117 | convert the string - for example, by using a replacement character. |
| 118 | |
| 119 | =back |
| 120 | |
| 121 | =item -E<gt>decode($octets [,$check]) |
| 122 | |
| 123 | MUST return the string that I<$octets> represents. |
| 124 | |
| 125 | =over 2 |
| 126 | |
| 127 | =item * |
| 128 | |
| 129 | If I<$check> is true, it SHOULD modify I<$octets> in place to remove |
| 130 | the converted part (i.e. the whole sequence unless there is an |
| 131 | error). If perlio_ok() is true, SHOULD becomes MUST. |
| 132 | |
| 133 | =item * |
| 134 | |
| 135 | If an error occurs, it SHOULD return the fragment of string that has |
| 136 | been converted and modify $octets in-place to remove the converted |
| 137 | part leaving it starting with the problem fragment. If perlio_ok() is |
| 138 | true, SHOULD becomes MUST. |
| 139 | |
| 140 | =item * |
| 141 | |
| 142 | If I<$check> is false then C<decode> should make a "best effort" to |
| 143 | convert the string - for example by using Unicode's "\x{FFFD}" as a |
| 144 | replacement character. |
| 145 | |
| 146 | =back |
| 147 | |
| 148 | =back |
| 149 | |
| 150 | If you want your encoding to work with L<encoding> pragma, you should |
| 151 | also implement the method below. |
| 152 | |
| 153 | =over 4 |
| 154 | |
| 155 | =item -E<gt>cat_decode($destination, $octets, $offset, $terminator [,$check]) |
| 156 | |
| 157 | MUST decode I<$octets> with I<$offset> and concatenate it to I<$destination>. |
| 158 | Decoding will terminate when $terminator (a string) appears in output. |
| 159 | I<$offset> will be modified to the last $octets position at end of decode. |
| 160 | Returns true if $terminator appears output, else returns false. |
| 161 | |
| 162 | =back |
| 163 | |
| 164 | =head2 Other methods defined in Encode::Encodings |
| 165 | |
| 166 | You do not have to override methods shown below unless you have to. |
| 167 | |
| 168 | =over 4 |
| 169 | |
| 170 | =item -E<gt>name |
| 171 | |
| 172 | Predefined As: |
| 173 | |
| 174 | sub name { return shift->{'Name'} } |
| 175 | |
| 176 | MUST return the string representing the canonical name of the encoding. |
| 177 | |
| 178 | =item -E<gt>renew |
| 179 | |
| 180 | Predefined As: |
| 181 | |
| 182 | sub renew { |
| 183 | my $self = shift; |
| 184 | my $clone = bless { %$self } => ref($self); |
| 185 | $clone->{renewed}++; |
| 186 | return $clone; |
| 187 | } |
| 188 | |
| 189 | This method reconstructs the encoding object if necessary. If you need |
| 190 | to store the state during encoding, this is where you clone your object. |
| 191 | |
| 192 | PerlIO ALWAYS calls this method to make sure it has its own private |
| 193 | encoding object. |
| 194 | |
| 195 | =item -E<gt>renewed |
| 196 | |
| 197 | Predefined As: |
| 198 | |
| 199 | sub renewed { $_[0]->{renewed} || 0 } |
| 200 | |
| 201 | Tells whether the object is renewed (and how many times). Some |
| 202 | modules emit C<Use of uninitialized value in null operation> warning |
| 203 | unless the value is numeric so return 0 for false. |
| 204 | |
| 205 | =item -E<gt>perlio_ok() |
| 206 | |
| 207 | Predefined As: |
| 208 | |
| 209 | sub perlio_ok { |
| 210 | eval{ require PerlIO::encoding }; |
| 211 | return $@ ? 0 : 1; |
| 212 | } |
| 213 | |
| 214 | If your encoding does not support PerlIO for some reasons, just; |
| 215 | |
| 216 | sub perlio_ok { 0 } |
| 217 | |
| 218 | =item -E<gt>needs_lines() |
| 219 | |
| 220 | Predefined As: |
| 221 | |
| 222 | sub needs_lines { 0 }; |
| 223 | |
| 224 | If your encoding can work with PerlIO but needs line buffering, you |
| 225 | MUST define this method so it returns true. 7bit ISO-2022 encodings |
| 226 | are one example that needs this. When this method is missing, false |
| 227 | is assumed. |
| 228 | |
| 229 | =back |
| 230 | |
| 231 | =head2 Example: Encode::ROT13 |
| 232 | |
| 233 | package Encode::ROT13; |
| 234 | use strict; |
| 235 | use base qw(Encode::Encoding); |
| 236 | |
| 237 | __PACKAGE__->Define('rot13'); |
| 238 | |
| 239 | sub encode($$;$){ |
| 240 | my ($obj, $str, $chk) = @_; |
| 241 | $str =~ tr/A-Za-z/N-ZA-Mn-za-m/; |
| 242 | $_[1] = '' if $chk; # this is what in-place edit means |
| 243 | return $str; |
| 244 | } |
| 245 | |
| 246 | # Jr pna or ynml yvxr guvf; |
| 247 | *decode = \&encode; |
| 248 | |
| 249 | 1; |
| 250 | |
| 251 | =head1 Why the heck Encode API is different? |
| 252 | |
| 253 | It should be noted that the I<$check> behaviour is different from the |
| 254 | outer public API. The logic is that the "unchecked" case is useful |
| 255 | when the encoding is part of a stream which may be reporting errors |
| 256 | (e.g. STDERR). In such cases, it is desirable to get everything |
| 257 | through somehow without causing additional errors which obscure the |
| 258 | original one. Also, the encoding is best placed to know what the |
| 259 | correct replacement character is, so if that is the desired behaviour |
| 260 | then letting low level code do it is the most efficient. |
| 261 | |
| 262 | By contrast, if I<$check> is true, the scheme above allows the |
| 263 | encoding to do as much as it can and tell the layer above how much |
| 264 | that was. What is lacking at present is a mechanism to report what |
| 265 | went wrong. The most likely interface will be an additional method |
| 266 | call to the object, or perhaps (to avoid forcing per-stream objects |
| 267 | on otherwise stateless encodings) an additional parameter. |
| 268 | |
| 269 | It is also highly desirable that encoding classes inherit from |
| 270 | C<Encode::Encoding> as a base class. This allows that class to define |
| 271 | additional behaviour for all encoding objects. |
| 272 | |
| 273 | package Encode::MyEncoding; |
| 274 | use base qw(Encode::Encoding); |
| 275 | |
| 276 | __PACKAGE__->Define(qw(myCanonical myAlias)); |
| 277 | |
| 278 | to create an object with C<< bless {Name => ...}, $class >>, and call |
| 279 | define_encoding. They inherit their C<name> method from |
| 280 | C<Encode::Encoding>. |
| 281 | |
| 282 | =head2 Compiled Encodings |
| 283 | |
| 284 | For the sake of speed and efficiency, most of the encodings are now |
| 285 | supported via a I<compiled form>: XS modules generated from UCM |
| 286 | files. Encode provides the enc2xs tool to achieve that. Please see |
| 287 | L<enc2xs> for more details. |
| 288 | |
| 289 | =head1 SEE ALSO |
| 290 | |
| 291 | L<perlmod>, L<enc2xs> |
| 292 | |
| 293 | =begin future |
| 294 | |
| 295 | =over 4 |
| 296 | |
| 297 | =item Scheme 1 |
| 298 | |
| 299 | The fixup routine gets passed the remaining fragment of string being |
| 300 | processed. It modifies it in place to remove bytes/characters it can |
| 301 | understand and returns a string used to represent them. For example: |
| 302 | |
| 303 | sub fixup { |
| 304 | my $ch = substr($_[0],0,1,''); |
| 305 | return sprintf("\x{%02X}",ord($ch); |
| 306 | } |
| 307 | |
| 308 | This scheme is close to how the underlying C code for Encode works, |
| 309 | but gives the fixup routine very little context. |
| 310 | |
| 311 | =item Scheme 2 |
| 312 | |
| 313 | The fixup routine gets passed the original string, an index into |
| 314 | it of the problem area, and the output string so far. It appends |
| 315 | what it wants to the output string and returns a new index into the |
| 316 | original string. For example: |
| 317 | |
| 318 | sub fixup { |
| 319 | # my ($s,$i,$d) = @_; |
| 320 | my $ch = substr($_[0],$_[1],1); |
| 321 | $_[2] .= sprintf("\x{%02X}",ord($ch); |
| 322 | return $_[1]+1; |
| 323 | } |
| 324 | |
| 325 | This scheme gives maximal control to the fixup routine but is more |
| 326 | complicated to code, and may require that the internals of Encode be tweaked to |
| 327 | keep the original string intact. |
| 328 | |
| 329 | =item Other Schemes |
| 330 | |
| 331 | Hybrids of the above. |
| 332 | |
| 333 | Multiple return values rather than in-place modifications. |
| 334 | |
| 335 | Index into the string could be C<pos($str)> allowing C<s/\G...//>. |
| 336 | |
| 337 | =back |
| 338 | |
| 339 | =end future |
| 340 | |
| 341 | =cut |