… | |
… | |
48 | Regarding compactness, C<CBOR::XS>-encoded data structures are usually |
48 | Regarding compactness, C<CBOR::XS>-encoded data structures are usually |
49 | about 20% smaller than the same data encoded as (compact) JSON or |
49 | about 20% smaller than the same data encoded as (compact) JSON or |
50 | L<Storable>. |
50 | L<Storable>. |
51 | |
51 | |
52 | In addition to the core CBOR data format, this module implements a |
52 | In addition to the core CBOR data format, this module implements a |
53 | number of extensions, to support cyclic and shared data structures (see |
53 | number of extensions, to support cyclic and shared data structures |
54 | C<allow_sharing>), string deduplication (see C<pack_strings>) and scalar |
54 | (see C<allow_sharing> and C<allow_cycles>), string deduplication (see |
55 | references (always enabled). |
55 | C<pack_strings>) and scalar references (always enabled). |
56 | |
56 | |
57 | The primary goal of this module is to be I<correct> and the secondary goal |
57 | The primary goal of this module is to be I<correct> and the secondary goal |
58 | is to be I<fast>. To reach the latter goal it was written in C. |
58 | is to be I<fast>. To reach the latter goal it was written in C. |
59 | |
59 | |
60 | See MAPPING, below, on how CBOR::XS maps perl values to CBOR values and |
60 | See MAPPING, below, on how CBOR::XS maps perl values to CBOR values and |
… | |
… | |
180 | reference to the earlier value. |
180 | reference to the earlier value. |
181 | |
181 | |
182 | This means that such values will only be encoded once, and will not result |
182 | This means that such values will only be encoded once, and will not result |
183 | in a deep cloning of the value on decode, in decoders supporting the value |
183 | in a deep cloning of the value on decode, in decoders supporting the value |
184 | sharing extension. This also makes it possible to encode cyclic data |
184 | sharing extension. This also makes it possible to encode cyclic data |
185 | structures. |
185 | structures (which need C<allow_cycles> to ne enabled to be decoded by this |
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|
186 | module). |
186 | |
187 | |
187 | It is recommended to leave it off unless you know your |
188 | It is recommended to leave it off unless you know your |
188 | communication partner supports the value sharing extensions to CBOR |
189 | communication partner supports the value sharing extensions to CBOR |
189 | (L<http://cbor.schmorp.de/value-sharing>), as without decoder support, the |
190 | (L<http://cbor.schmorp.de/value-sharing>), as without decoder support, the |
190 | resulting data structure might be unusable. |
191 | resulting data structure might be unusable. |
191 | |
192 | |
192 | Detecting shared values incurs a runtime overhead when values are encoded |
193 | Detecting shared values incurs a runtime overhead when values are encoded |
193 | that have a reference counter large than one, and might unnecessarily |
194 | that have a reference counter large than one, and might unnecessarily |
194 | increase the encoded size, as potentially shared values are encode as |
195 | increase the encoded size, as potentially shared values are encode as |
195 | sharable whether or not they are actually shared. |
196 | shareable whether or not they are actually shared. |
196 | |
197 | |
197 | At the moment, only targets of references can be shared (e.g. scalars, |
198 | At the moment, only targets of references can be shared (e.g. scalars, |
198 | arrays or hashes pointed to by a reference). Weirder constructs, such as |
199 | arrays or hashes pointed to by a reference). Weirder constructs, such as |
199 | an array with multiple "copies" of the I<same> string, which are hard but |
200 | an array with multiple "copies" of the I<same> string, which are hard but |
200 | not impossible to create in Perl, are not supported (this is the same as |
201 | not impossible to create in Perl, are not supported (this is the same as |
… | |
… | |
203 | If C<$enable> is false (the default), then C<encode> will encode shared |
204 | If C<$enable> is false (the default), then C<encode> will encode shared |
204 | data structures repeatedly, unsharing them in the process. Cyclic data |
205 | data structures repeatedly, unsharing them in the process. Cyclic data |
205 | structures cannot be encoded in this mode. |
206 | structures cannot be encoded in this mode. |
206 | |
207 | |
207 | This option does not affect C<decode> in any way - shared values and |
208 | This option does not affect C<decode> in any way - shared values and |
|
|
209 | references will always be decoded properly if present. |
|
|
210 | |
|
|
211 | =item $cbor = $cbor->allow_cycles ([$enable]) |
|
|
212 | |
|
|
213 | =item $enabled = $cbor->get_allow_cycles |
|
|
214 | |
|
|
215 | If C<$enable> is true (or missing), then C<decode> will happily decode |
|
|
216 | self-referential (cyclic) data structures. By default these will not be |
|
|
217 | decoded, as they need manual cleanup to avoid memory leaks, so code that |
|
|
218 | isn't prepared for this will not leak memory. |
|
|
219 | |
|
|
220 | If C<$enable> is false (the default), then C<decode> will throw an error |
|
|
221 | when it encounters a self-referential/cyclic data structure. |
|
|
222 | |
|
|
223 | This option does not affect C<encode> in any way - shared values and |
208 | references will always be decoded properly if present. |
224 | references will always be decoded properly if present. |
209 | |
225 | |
210 | =item $cbor = $cbor->pack_strings ([$enable]) |
226 | =item $cbor = $cbor->pack_strings ([$enable]) |
211 | |
227 | |
212 | =item $enabled = $cbor->get_pack_strings |
228 | =item $enabled = $cbor->get_pack_strings |
… | |
… | |
465 | |
481 | |
466 | =back |
482 | =back |
467 | |
483 | |
468 | =head2 OBJECT SERIALISATION |
484 | =head2 OBJECT SERIALISATION |
469 | |
485 | |
|
|
486 | This module implements both a CBOR-specific and the generic |
|
|
487 | L<Types::Serialier> object serialisation protocol. The following |
|
|
488 | subsections explain both methods. |
|
|
489 | |
|
|
490 | =head3 ENCODING |
|
|
491 | |
470 | This module knows two way to serialise a Perl object: The CBOR-specific |
492 | This module knows two way to serialise a Perl object: The CBOR-specific |
471 | way, and the generic way. |
493 | way, and the generic way. |
472 | |
494 | |
473 | Whenever the encoder encounters a Perl object that it cnanot serialise |
495 | Whenever the encoder encounters a Perl object that it cannot serialise |
474 | directly (most of them), it will first look up the C<TO_CBOR> method on |
496 | directly (most of them), it will first look up the C<TO_CBOR> method on |
475 | it. |
497 | it. |
476 | |
498 | |
477 | If it has a C<TO_CBOR> method, it will call it with the object as only |
499 | If it has a C<TO_CBOR> method, it will call it with the object as only |
478 | argument, and expects exactly one return value, which it will then |
500 | argument, and expects exactly one return value, which it will then |
… | |
… | |
484 | |
506 | |
485 | The C<FREEZE> method can return any number of values (i.e. zero or |
507 | The C<FREEZE> method can return any number of values (i.e. zero or |
486 | more). These will be encoded as CBOR perl object, together with the |
508 | more). These will be encoded as CBOR perl object, together with the |
487 | classname. |
509 | classname. |
488 | |
510 | |
|
|
511 | These methods I<MUST NOT> change the data structure that is being |
|
|
512 | serialised. Failure to comply to this can result in memory corruption - |
|
|
513 | and worse. |
|
|
514 | |
489 | If an object supports neither C<TO_CBOR> nor C<FREEZE>, encoding will fail |
515 | If an object supports neither C<TO_CBOR> nor C<FREEZE>, encoding will fail |
490 | with an error. |
516 | with an error. |
491 | |
517 | |
|
|
518 | =head3 DECODING |
|
|
519 | |
492 | Objects encoded via C<TO_CBOR> cannot be automatically decoded, but |
520 | Objects encoded via C<TO_CBOR> cannot (normally) be automatically decoded, |
493 | objects encoded via C<FREEZE> can be decoded using the following protocol: |
521 | but objects encoded via C<FREEZE> can be decoded using the following |
|
|
522 | protocol: |
494 | |
523 | |
495 | When an encoded CBOR perl object is encountered by the decoder, it will |
524 | When an encoded CBOR perl object is encountered by the decoder, it will |
496 | look up the C<THAW> method, by using the stored classname, and will fail |
525 | look up the C<THAW> method, by using the stored classname, and will fail |
497 | if the method cannot be found. |
526 | if the method cannot be found. |
498 | |
527 | |
499 | After the lookup it will call the C<THAW> method with the stored classname |
528 | After the lookup it will call the C<THAW> method with the stored classname |
500 | as first argument, the constant string C<CBOR> as second argument, and all |
529 | as first argument, the constant string C<CBOR> as second argument, and all |
501 | values returned by C<FREEZE> as remaining arguments. |
530 | values returned by C<FREEZE> as remaining arguments. |
502 | |
531 | |
503 | =head4 EXAMPLES |
532 | =head3 EXAMPLES |
504 | |
533 | |
505 | Here is an example C<TO_CBOR> method: |
534 | Here is an example C<TO_CBOR> method: |
506 | |
535 | |
507 | sub My::Object::TO_CBOR { |
536 | sub My::Object::TO_CBOR { |
508 | my ($obj) = @_; |
537 | my ($obj) = @_; |
… | |
… | |
691 | |
720 | |
692 | These tags are automatically created (and decoded) for serialisable |
721 | These tags are automatically created (and decoded) for serialisable |
693 | objects using the C<FREEZE/THAW> methods (the L<Types::Serialier> object |
722 | objects using the C<FREEZE/THAW> methods (the L<Types::Serialier> object |
694 | serialisation protocol). See L<OBJECT SERIALISATION> for details. |
723 | serialisation protocol). See L<OBJECT SERIALISATION> for details. |
695 | |
724 | |
696 | =item 28, 29 (sharable, sharedref, L <http://cbor.schmorp.de/value-sharing>) |
725 | =item 28, 29 (shareable, sharedref, L <http://cbor.schmorp.de/value-sharing>) |
697 | |
726 | |
698 | These tags are automatically decoded when encountered, resulting in |
727 | These tags are automatically decoded when encountered (and they do not |
|
|
728 | result in a cyclic data structure, see C<allow_cycles>), resulting in |
699 | shared values in the decoded object. They are only encoded, however, when |
729 | shared values in the decoded object. They are only encoded, however, when |
700 | C<allow_sharable> is enabled. |
730 | C<allow_sharing> is enabled. |
|
|
731 | |
|
|
732 | Not all shared values can be successfully decoded: values that reference |
|
|
733 | themselves will I<currently> decode as C<undef> (this is not the same |
|
|
734 | as a reference pointing to itself, which will be represented as a value |
|
|
735 | that contains an indirect reference to itself - these will be decoded |
|
|
736 | properly). |
|
|
737 | |
|
|
738 | Note that considerably more shared value data structures can be decoded |
|
|
739 | than will be encoded - currently, only values pointed to by references |
|
|
740 | will be shared, others will not. While non-reference shared values can be |
|
|
741 | generated in Perl with some effort, they were considered too unimportant |
|
|
742 | to be supported in the encoder. The decoder, however, will decode these |
|
|
743 | values as shared values. |
701 | |
744 | |
702 | =item 256, 25 (stringref-namespace, stringref, L <http://cbor.schmorp.de/stringref>) |
745 | =item 256, 25 (stringref-namespace, stringref, L <http://cbor.schmorp.de/stringref>) |
703 | |
746 | |
704 | These tags are automatically decoded when encountered. They are only |
747 | These tags are automatically decoded when encountered. They are only |
705 | encoded, however, when C<pack_strings> is enabled. |
748 | encoded, however, when C<pack_strings> is enabled. |
… | |
… | |
871 | Only the double data type is supported for NV data types - when Perl uses |
914 | Only the double data type is supported for NV data types - when Perl uses |
872 | long double to represent floating point values, they might not be encoded |
915 | long double to represent floating point values, they might not be encoded |
873 | properly. Half precision types are accepted, but not encoded. |
916 | properly. Half precision types are accepted, but not encoded. |
874 | |
917 | |
875 | Strict mode and canonical mode are not implemented. |
918 | Strict mode and canonical mode are not implemented. |
|
|
919 | |
|
|
920 | |
|
|
921 | =head1 LIMITATIONS ON PERLS WITHOUT 64-BIT INTEGER SUPPORT |
|
|
922 | |
|
|
923 | On perls that were built without 64 bit integer support (these are rare |
|
|
924 | nowadays, even on 32 bit architectures), support for any kind of 64 bit |
|
|
925 | integer in CBOR is very limited - most likely, these 64 bit values will |
|
|
926 | be truncated, corrupted, or otherwise not decoded correctly. This also |
|
|
927 | includes string, array and map sizes that are stored as 64 bit integers. |
876 | |
928 | |
877 | |
929 | |
878 | =head1 THREADS |
930 | =head1 THREADS |
879 | |
931 | |
880 | This module is I<not> guaranteed to be thread safe and there are no |
932 | This module is I<not> guaranteed to be thread safe and there are no |