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Revision 1.29 by root, Sat Nov 30 15:23:59 2013 UTC

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26 substr $many_cbor_strings, 0, $length, ""; # remove decoded cbor string 26 substr $many_cbor_strings, 0, $length, ""; # remove decoded cbor string
27 } 27 }
28 28
29=head1 DESCRIPTION 29=head1 DESCRIPTION
30 30
31WARNING! This module is very new, and not very well tested (that's up
32to you to do). Furthermore, details of the implementation might change
33freely before version 1.0. And lastly, most extensions depend on an IANA
34assignment, and until that assignment is official, this implementation is
35not interoperable with other implementations (even future versions of this
36module) until the assignment is done.
37
38You are still invited to try out CBOR, and this module.
39
40This module converts Perl data structures to the Concise Binary Object 31This module converts Perl data structures to the Concise Binary Object
41Representation (CBOR) and vice versa. CBOR is a fast binary serialisation 32Representation (CBOR) and vice versa. CBOR is a fast binary serialisation
42format that aims to use a superset of the JSON data model, i.e. when you 33format that aims to use an (almost) superset of the JSON data model, i.e.
43can represent something in JSON, you should be able to represent it in 34when you can represent something useful in JSON, you should be able to
44CBOR. 35represent it in CBOR.
45 36
46In short, CBOR is a faster and very compact binary alternative to JSON, 37In short, CBOR is a faster and quite compact binary alternative to JSON,
47with the added ability of supporting serialisation of Perl objects. (JSON 38with the added ability of supporting serialisation of Perl objects. (JSON
48often compresses better than CBOR though, so if you plan to compress the 39often compresses better than CBOR though, so if you plan to compress the
49data later you might want to compare both formats first). 40data later and speed is less important you might want to compare both
41formats first).
50 42
51To give you a general idea about speed, with texts in the megabyte range, 43To give you a general idea about speed, with texts in the megabyte range,
52C<CBOR::XS> usually encodes roughly twice as fast as L<Storable> or 44C<CBOR::XS> usually encodes roughly twice as fast as L<Storable> or
53L<JSON::XS> and decodes about 15%-30% faster than those. The shorter the 45L<JSON::XS> and decodes about 15%-30% faster than those. The shorter the
54data, the worse L<Storable> performs in comparison. 46data, the worse L<Storable> performs in comparison.
55 47
56As for compactness, C<CBOR::XS> encoded data structures are usually about 48Regarding compactness, C<CBOR::XS>-encoded data structures are usually
5720% smaller than the same data encoded as (compact) JSON or L<Storable>. 49about 20% smaller than the same data encoded as (compact) JSON or
50L<Storable>.
58 51
59In addition to the core CBOR data format, this module implements a number 52In addition to the core CBOR data format, this module implements a
60of extensions, to support cyclic and self-referencing data structures 53number of extensions, to support cyclic and shared data structures (see
61(see C<allow_sharing>), string deduplication (see C<allow_stringref>) and 54C<allow_sharing>), string deduplication (see C<pack_strings>) and scalar
62scalar references (always enabled). 55references (always enabled).
63 56
64The primary goal of this module is to be I<correct> and the secondary goal 57The primary goal of this module is to be I<correct> and the secondary goal
65is to be I<fast>. To reach the latter goal it was written in C. 58is to be I<fast>. To reach the latter goal it was written in C.
66 59
67See MAPPING, below, on how CBOR::XS maps perl values to CBOR values and 60See MAPPING, below, on how CBOR::XS maps perl values to CBOR values and
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71 64
72package CBOR::XS; 65package CBOR::XS;
73 66
74use common::sense; 67use common::sense;
75 68
76our $VERSION = 0.09; 69our $VERSION = '1.0';
77our @ISA = qw(Exporter); 70our @ISA = qw(Exporter);
78 71
79our @EXPORT = qw(encode_cbor decode_cbor); 72our @EXPORT = qw(encode_cbor decode_cbor);
80 73
81use Exporter; 74use Exporter;
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186as an array, is referenced multiple times), but instead will emit a 179as an array, is referenced multiple times), but instead will emit a
187reference to the earlier value. 180reference to the earlier value.
188 181
189This means that such values will only be encoded once, and will not result 182This means that such values will only be encoded once, and will not result
190in a deep cloning of the value on decode, in decoders supporting the value 183in a deep cloning of the value on decode, in decoders supporting the value
191sharing extension. 184sharing extension. This also makes it possible to encode cyclic data
185structures.
192 186
193It is recommended to leave it off unless you know your 187It is recommended to leave it off unless you know your
194communication partner supports the value sharing extensions to CBOR 188communication partner supports the value sharing extensions to CBOR
195(http://cbor.schmorp.de/value-sharing). 189(L<http://cbor.schmorp.de/value-sharing>), as without decoder support, the
190resulting data structure might be unusable.
196 191
197Detecting shared values incurs a runtime overhead when values are encoded 192Detecting shared values incurs a runtime overhead when values are encoded
198that have a reference counter large than one, and might unnecessarily 193that have a reference counter large than one, and might unnecessarily
199increase the encoded size, as potentially shared values are encode as 194increase the encoded size, as potentially shared values are encode as
200sharable whether or not they are actually shared. 195sharable whether or not they are actually shared.
201 196
202At the moment, only targets of references can be shared (e.g. scalars, 197At the moment, only targets of references can be shared (e.g. scalars,
203arrays or hashes pointed to by a reference). Weirder constructs, such as 198arrays or hashes pointed to by a reference). Weirder constructs, such as
204an array with multiple "copies" of the I<same> string, which are hard but 199an array with multiple "copies" of the I<same> string, which are hard but
205not impossible to create in Perl, are not supported (this is the same as 200not impossible to create in Perl, are not supported (this is the same as
206for L<Storable>). 201with L<Storable>).
207 202
208If C<$enable> is false (the default), then C<encode> will encode 203If C<$enable> is false (the default), then C<encode> will encode shared
209exception when it encounters anything it cannot encode as CBOR. 204data structures repeatedly, unsharing them in the process. Cyclic data
205structures cannot be encoded in this mode.
210 206
211This option does not affect C<decode> in any way - shared values and 207This option does not affect C<decode> in any way - shared values and
212references will always be decoded properly if present. 208references will always be decoded properly if present.
213 209
214=item $cbor = $cbor->allow_stringref ([$enable]) 210=item $cbor = $cbor->pack_strings ([$enable])
215 211
216=item $enabled = $cbor->get_allow_stringref 212=item $enabled = $cbor->get_pack_strings
217 213
218If C<$enable> is true (or missing), then C<encode> will try not to encode 214If C<$enable> is true (or missing), then C<encode> will try not to encode
219the same string twice, but will instead encode a reference to the string 215the same string twice, but will instead encode a reference to the string
220instead. Depending on your data format. this can save a lot of space, but 216instead. Depending on your data format, this can save a lot of space, but
221also results in a very large runtime overhead (expect encoding times to be 217also results in a very large runtime overhead (expect encoding times to be
2222-4 times as high as without). 2182-4 times as high as without).
223 219
224It is recommended to leave it off unless you know your 220It is recommended to leave it off unless you know your
225communications partner supports the stringref extension to CBOR 221communications partner supports the stringref extension to CBOR
226(http://cbor.schmorp.de/stringref). 222(L<http://cbor.schmorp.de/stringref>), as without decoder support, the
223resulting data structure might not be usable.
227 224
228If C<$enable> is false (the default), then C<encode> will encode 225If C<$enable> is false (the default), then C<encode> will encode strings
229exception when it encounters anything it cannot encode as CBOR. 226the standard CBOR way.
230 227
231This option does not affect C<decode> in any way - string references will 228This option does not affect C<decode> in any way - string references will
232always be decoded properly if present. 229always be decoded properly if present.
233 230
234=item $cbor = $cbor->filter ([$cb->($tag, $value)]) 231=item $cbor = $cbor->filter ([$cb->($tag, $value)])
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255function, C<CBOR::XS::default_filter>, is used. This function simply looks 252function, C<CBOR::XS::default_filter>, is used. This function simply looks
256up the tag in the C<%CBOR::XS::FILTER> hash. If an entry exists it must be 253up the tag in the C<%CBOR::XS::FILTER> hash. If an entry exists it must be
257a code reference that is called with tag and value, and is responsible for 254a code reference that is called with tag and value, and is responsible for
258decoding the value. If no entry exists, it returns no values. 255decoding the value. If no entry exists, it returns no values.
259 256
260Example: decode all tags not handled internally into CBOR::XS::Tagged 257Example: decode all tags not handled internally into C<CBOR::XS::Tagged>
261objects, with no other special handling (useful when working with 258objects, with no other special handling (useful when working with
262potentially "unsafe" CBOR data). 259potentially "unsafe" CBOR data).
263 260
264 CBOR::XS->new->filter (sub { })->decode ($cbor_data); 261 CBOR::XS->new->filter (sub { })->decode ($cbor_data);
265 262
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319CBOR integers become (numeric) perl scalars. On perls without 64 bit 316CBOR integers become (numeric) perl scalars. On perls without 64 bit
320support, 64 bit integers will be truncated or otherwise corrupted. 317support, 64 bit integers will be truncated or otherwise corrupted.
321 318
322=item byte strings 319=item byte strings
323 320
324Byte strings will become octet strings in Perl (the byte values 0..255 321Byte strings will become octet strings in Perl (the Byte values 0..255
325will simply become characters of the same value in Perl). 322will simply become characters of the same value in Perl).
326 323
327=item UTF-8 strings 324=item UTF-8 strings
328 325
329UTF-8 strings in CBOR will be decoded, i.e. the UTF-8 octets will be 326UTF-8 strings in CBOR will be decoded, i.e. the UTF-8 octets will be
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352=item tagged values 349=item tagged values
353 350
354Tagged items consists of a numeric tag and another CBOR value. 351Tagged items consists of a numeric tag and another CBOR value.
355 352
356See L<TAG HANDLING AND EXTENSIONS> and the description of C<< ->filter >> 353See L<TAG HANDLING AND EXTENSIONS> and the description of C<< ->filter >>
357for details. 354for details on which tags are handled how.
358 355
359=item anything else 356=item anything else
360 357
361Anything else (e.g. unsupported simple values) will raise a decoding 358Anything else (e.g. unsupported simple values) will raise a decoding
362error. 359error.
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365 362
366 363
367=head2 PERL -> CBOR 364=head2 PERL -> CBOR
368 365
369The mapping from Perl to CBOR is slightly more difficult, as Perl is a 366The mapping from Perl to CBOR is slightly more difficult, as Perl is a
370truly typeless language, so we can only guess which CBOR type is meant by 367typeless language. That means this module can only guess which CBOR type
371a Perl value. 368is meant by a perl value.
372 369
373=over 4 370=over 4
374 371
375=item hash references 372=item hash references
376 373
377Perl hash references become CBOR maps. As there is no inherent ordering in 374Perl hash references become CBOR maps. As there is no inherent ordering in
378hash keys (or CBOR maps), they will usually be encoded in a pseudo-random 375hash keys (or CBOR maps), they will usually be encoded in a pseudo-random
379order. 376order. This order can be different each time a hahs is encoded.
380 377
381Currently, tied hashes will use the indefinite-length format, while normal 378Currently, tied hashes will use the indefinite-length format, while normal
382hashes will use the fixed-length format. 379hashes will use the fixed-length format.
383 380
384=item array references 381=item array references
385 382
386Perl array references become fixed-length CBOR arrays. 383Perl array references become fixed-length CBOR arrays.
387 384
388=item other references 385=item other references
389 386
390Other unblessed references are generally not allowed and will cause an 387Other unblessed references will be represented using
391exception to be thrown, except for references to the integers C<0> and 388the indirection tag extension (tag value C<22098>,
392C<1>, which get turned into false and true in CBOR. 389L<http://cbor.schmorp.de/indirection>). CBOR decoders are guaranteed
390to be able to decode these values somehow, by either "doing the right
391thing", decoding into a generic tagged object, simply ignoring the tag, or
392something else.
393 393
394=item CBOR::XS::Tagged objects 394=item CBOR::XS::Tagged objects
395 395
396Objects of this type must be arrays consisting of a single C<[tag, value]> 396Objects of this type must be arrays consisting of a single C<[tag, value]>
397pair. The (numerical) tag will be encoded as a CBOR tag, the value will 397pair. The (numerical) tag will be encoded as a CBOR tag, the value will
398be encoded as appropriate for the value. You cna use C<CBOR::XS::tag> to 398be encoded as appropriate for the value. You must use C<CBOR::XS::tag> to
399create such objects. 399create such objects.
400 400
401=item Types::Serialiser::true, Types::Serialiser::false, Types::Serialiser::error 401=item Types::Serialiser::true, Types::Serialiser::false, Types::Serialiser::error
402 402
403These special values become CBOR true, CBOR false and CBOR undefined 403These special values become CBOR true, CBOR false and CBOR undefined
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420 # dump as number 420 # dump as number
421 encode_cbor [2] # yields [2] 421 encode_cbor [2] # yields [2]
422 encode_cbor [-3.0e17] # yields [-3e+17] 422 encode_cbor [-3.0e17] # yields [-3e+17]
423 my $value = 5; encode_cbor [$value] # yields [5] 423 my $value = 5; encode_cbor [$value] # yields [5]
424 424
425 # used as string, so dump as string 425 # used as string, so dump as string (either byte or text)
426 print $value; 426 print $value;
427 encode_cbor [$value] # yields ["5"] 427 encode_cbor [$value] # yields ["5"]
428 428
429 # undef becomes null 429 # undef becomes null
430 encode_cbor [undef] # yields [null] 430 encode_cbor [undef] # yields [null]
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433 433
434 my $x = 3.1; # some variable containing a number 434 my $x = 3.1; # some variable containing a number
435 "$x"; # stringified 435 "$x"; # stringified
436 $x .= ""; # another, more awkward way to stringify 436 $x .= ""; # another, more awkward way to stringify
437 print $x; # perl does it for you, too, quite often 437 print $x; # perl does it for you, too, quite often
438
439You can force whether a string ie encoded as byte or text string by using
440C<utf8::upgrade> and C<utf8::downgrade>):
441
442 utf8::upgrade $x; # encode $x as text string
443 utf8::downgrade $x; # encode $x as byte string
444
445Perl doesn't define what operations up- and downgrade strings, so if the
446difference between byte and text is important, you should up- or downgrade
447your string as late as possible before encoding.
438 448
439You can force the type to be a CBOR number by numifying it: 449You can force the type to be a CBOR number by numifying it:
440 450
441 my $x = "3"; # some variable containing a string 451 my $x = "3"; # some variable containing a string
442 $x += 0; # numify it, ensuring it will be dumped as a number 452 $x += 0; # numify it, ensuring it will be dumped as a number
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455 465
456=back 466=back
457 467
458=head2 OBJECT SERIALISATION 468=head2 OBJECT SERIALISATION
459 469
470This module implements both a CBOR-specific and the generic
471L<Types::Serialier> object serialisation protocol. The following
472subsections explain both methods.
473
474=head3 ENCODING
475
460This module knows two way to serialise a Perl object: The CBOR-specific 476This module knows two way to serialise a Perl object: The CBOR-specific
461way, and the generic way. 477way, and the generic way.
462 478
463Whenever the encoder encounters a Perl object that it cnanot serialise 479Whenever the encoder encounters a Perl object that it cannot serialise
464directly (most of them), it will first look up the C<TO_CBOR> method on 480directly (most of them), it will first look up the C<TO_CBOR> method on
465it. 481it.
466 482
467If it has a C<TO_CBOR> method, it will call it with the object as only 483If it has a C<TO_CBOR> method, it will call it with the object as only
468argument, and expects exactly one return value, which it will then 484argument, and expects exactly one return value, which it will then
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474 490
475The C<FREEZE> method can return any number of values (i.e. zero or 491The C<FREEZE> method can return any number of values (i.e. zero or
476more). These will be encoded as CBOR perl object, together with the 492more). These will be encoded as CBOR perl object, together with the
477classname. 493classname.
478 494
495These methods I<MUST NOT> change the data structure that is being
496serialised. Failure to comply to this can result in memory corruption -
497and worse.
498
479If an object supports neither C<TO_CBOR> nor C<FREEZE>, encoding will fail 499If an object supports neither C<TO_CBOR> nor C<FREEZE>, encoding will fail
480with an error. 500with an error.
481 501
502=head3 DECODING
503
482Objects encoded via C<TO_CBOR> cannot be automatically decoded, but 504Objects encoded via C<TO_CBOR> cannot (normally) be automatically decoded,
483objects encoded via C<FREEZE> can be decoded using the following protocol: 505but objects encoded via C<FREEZE> can be decoded using the following
506protocol:
484 507
485When an encoded CBOR perl object is encountered by the decoder, it will 508When an encoded CBOR perl object is encountered by the decoder, it will
486look up the C<THAW> method, by using the stored classname, and will fail 509look up the C<THAW> method, by using the stored classname, and will fail
487if the method cannot be found. 510if the method cannot be found.
488 511
489After the lookup it will call the C<THAW> method with the stored classname 512After the lookup it will call the C<THAW> method with the stored classname
490as first argument, the constant string C<CBOR> as second argument, and all 513as first argument, the constant string C<CBOR> as second argument, and all
491values returned by C<FREEZE> as remaining arguments. 514values returned by C<FREEZE> as remaining arguments.
492 515
493=head4 EXAMPLES 516=head3 EXAMPLES
494 517
495Here is an example C<TO_CBOR> method: 518Here is an example C<TO_CBOR> method:
496 519
497 sub My::Object::TO_CBOR { 520 sub My::Object::TO_CBOR {
498 my ($obj) = @_; 521 my ($obj) = @_;
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509 532
510 sub URI::TO_CBOR { 533 sub URI::TO_CBOR {
511 my ($self) = @_; 534 my ($self) = @_;
512 my $uri = "$self"; # stringify uri 535 my $uri = "$self"; # stringify uri
513 utf8::upgrade $uri; # make sure it will be encoded as UTF-8 string 536 utf8::upgrade $uri; # make sure it will be encoded as UTF-8 string
514 CBOR::XS::tagged 32, "$_[0]" 537 CBOR::XS::tag 32, "$_[0]"
515 } 538 }
516 539
517This will encode URIs as a UTF-8 string with tag 32, which indicates an 540This will encode URIs as a UTF-8 string with tag 32, which indicates an
518URI. 541URI.
519 542
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675These tags are always handled when decoding, and their handling cannot be 698These tags are always handled when decoding, and their handling cannot be
676overriden by the user. 699overriden by the user.
677 700
678=over 4 701=over 4
679 702
680=item <unassigned> (perl-object, L<http://cbor.schmorp.de/perl-object>) 703=item 26 (perl-object, L<http://cbor.schmorp.de/perl-object>)
681 704
682These tags are automatically created (and decoded) for serialisable 705These tags are automatically created (and decoded) for serialisable
683objects using the C<FREEZE/THAW> methods (the L<Types::Serialier> object 706objects using the C<FREEZE/THAW> methods (the L<Types::Serialier> object
684serialisation protocol). See L<OBJECT SERIALISATION> for details. 707serialisation protocol). See L<OBJECT SERIALISATION> for details.
685 708
686=item <unassigned>, <unassigned> (sharable, sharedref, L <http://cbor.schmorp.de/value-sharing>) 709=item 28, 29 (sharable, sharedref, L <http://cbor.schmorp.de/value-sharing>)
687 710
688These tags are automatically decoded when encountered, resulting in 711These tags are automatically decoded when encountered, resulting in
689shared values in the decoded object. They are only encoded, however, when 712shared values in the decoded object. They are only encoded, however, when
690C<allow_sharable> is enabled. 713C<allow_sharable> is enabled.
691 714
692=item <unassigned>, <unassigned> (stringref-namespace, stringref, L <http://cbor.schmorp.de/stringref>) 715=item 256, 25 (stringref-namespace, stringref, L <http://cbor.schmorp.de/stringref>)
693 716
694These tags are automatically decoded when encountered. They are only 717These tags are automatically decoded when encountered. They are only
695encoded, however, when C<allow_stringref> is enabled. 718encoded, however, when C<pack_strings> is enabled.
696 719
697=item 22098 (indirection, L<http://cbor.schmorp.de/indirection>) 720=item 22098 (indirection, L<http://cbor.schmorp.de/indirection>)
698 721
699This tag is automatically generated when a reference are encountered (with 722This tag is automatically generated when a reference are encountered (with
700the exception of hash and array refernces). It is converted to a reference 723the exception of hash and array refernces). It is converted to a reference

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