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Revision 1.28 by root, Thu Nov 28 16:09:04 2013 UTC vs.
Revision 1.66 by root, Tue Jun 27 02:03:24 2017 UTC

48Regarding compactness, C<CBOR::XS>-encoded data structures are usually 48Regarding compactness, C<CBOR::XS>-encoded data structures are usually
49about 20% smaller than the same data encoded as (compact) JSON or 49about 20% smaller than the same data encoded as (compact) JSON or
50L<Storable>. 50L<Storable>.
51 51
52In addition to the core CBOR data format, this module implements a 52In addition to the core CBOR data format, this module implements a
53number of extensions, to support cyclic and shared data structures (see 53number of extensions, to support cyclic and shared data structures
54C<allow_sharing>), string deduplication (see C<pack_strings>) and scalar 54(see C<allow_sharing> and C<allow_cycles>), string deduplication (see
55references (always enabled). 55C<pack_strings>) and scalar references (always enabled).
56 56
57The 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
58is 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.
59 59
60See 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
64 64
65package CBOR::XS; 65package CBOR::XS;
66 66
67use common::sense; 67use common::sense;
68 68
69our $VERSION = '1.0'; 69our $VERSION = 1.7;
70our @ISA = qw(Exporter); 70our @ISA = qw(Exporter);
71 71
72our @EXPORT = qw(encode_cbor decode_cbor); 72our @EXPORT = qw(encode_cbor decode_cbor);
73 73
74use Exporter; 74use Exporter;
112 112
113The mutators for flags all return the CBOR object again and thus calls can 113The mutators for flags all return the CBOR object again and thus calls can
114be chained: 114be chained:
115 115
116 my $cbor = CBOR::XS->new->encode ({a => [1,2]}); 116 my $cbor = CBOR::XS->new->encode ({a => [1,2]});
117
118=item $cbor = new_safe CBOR::XS
119
120Create a new, safe/secure CBOR::XS object. This is similar to C<new>,
121but configures the coder object to be safe to use with untrusted
122data. Currently, this is equivalent to:
123
124 my $cbor = CBOR::XS
125 ->new
126 ->forbid_objects
127 ->filter (\&CBOR::XS::safe_filter)
128 ->max_size (1e8);
129
130But is more future proof (it is better to crash because of a change than
131to be exploited in other ways).
132
133=cut
134
135sub new_safe {
136 CBOR::XS
137 ->new
138 ->forbid_objects
139 ->filter (\&CBOR::XS::safe_filter)
140 ->max_size (1e8)
141}
117 142
118=item $cbor = $cbor->max_depth ([$maximum_nesting_depth]) 143=item $cbor = $cbor->max_depth ([$maximum_nesting_depth])
119 144
120=item $max_depth = $cbor->get_max_depth 145=item $max_depth = $cbor->get_max_depth
121 146
137 162
138Note that nesting is implemented by recursion in C. The default value has 163Note that nesting is implemented by recursion in C. The default value has
139been chosen to be as large as typical operating systems allow without 164been chosen to be as large as typical operating systems allow without
140crashing. 165crashing.
141 166
142See SECURITY CONSIDERATIONS, below, for more info on why this is useful. 167See L<SECURITY CONSIDERATIONS>, below, for more info on why this is useful.
143 168
144=item $cbor = $cbor->max_size ([$maximum_string_size]) 169=item $cbor = $cbor->max_size ([$maximum_string_size])
145 170
146=item $max_size = $cbor->get_max_size 171=item $max_size = $cbor->get_max_size
147 172
152effect on C<encode> (yet). 177effect on C<encode> (yet).
153 178
154If no argument is given, the limit check will be deactivated (same as when 179If no argument is given, the limit check will be deactivated (same as when
155C<0> is specified). 180C<0> is specified).
156 181
157See SECURITY CONSIDERATIONS, below, for more info on why this is useful. 182See L<SECURITY CONSIDERATIONS>, below, for more info on why this is useful.
158 183
159=item $cbor = $cbor->allow_unknown ([$enable]) 184=item $cbor = $cbor->allow_unknown ([$enable])
160 185
161=item $enabled = $cbor->get_allow_unknown 186=item $enabled = $cbor->get_allow_unknown
162 187
180reference to the earlier value. 205reference to the earlier value.
181 206
182This means that such values will only be encoded once, and will not result 207This means that such values will only be encoded once, and will not result
183in a deep cloning of the value on decode, in decoders supporting the value 208in a deep cloning of the value on decode, in decoders supporting the value
184sharing extension. This also makes it possible to encode cyclic data 209sharing extension. This also makes it possible to encode cyclic data
185structures. 210structures (which need C<allow_cycles> to be enabled to be decoded by this
211module).
186 212
187It is recommended to leave it off unless you know your 213It is recommended to leave it off unless you know your
188communication partner supports the value sharing extensions to CBOR 214communication partner supports the value sharing extensions to CBOR
189(L<http://cbor.schmorp.de/value-sharing>), as without decoder support, the 215(L<http://cbor.schmorp.de/value-sharing>), as without decoder support, the
190resulting data structure might be unusable. 216resulting data structure might be unusable.
191 217
192Detecting shared values incurs a runtime overhead when values are encoded 218Detecting shared values incurs a runtime overhead when values are encoded
193that have a reference counter large than one, and might unnecessarily 219that have a reference counter large than one, and might unnecessarily
194increase the encoded size, as potentially shared values are encode as 220increase the encoded size, as potentially shared values are encode as
195sharable whether or not they are actually shared. 221shareable whether or not they are actually shared.
196 222
197At the moment, only targets of references can be shared (e.g. scalars, 223At the moment, only targets of references can be shared (e.g. scalars,
198arrays or hashes pointed to by a reference). Weirder constructs, such as 224arrays or hashes pointed to by a reference). Weirder constructs, such as
199an array with multiple "copies" of the I<same> string, which are hard but 225an array with multiple "copies" of the I<same> string, which are hard but
200not impossible to create in Perl, are not supported (this is the same as 226not impossible to create in Perl, are not supported (this is the same as
205structures cannot be encoded in this mode. 231structures cannot be encoded in this mode.
206 232
207This option does not affect C<decode> in any way - shared values and 233This option does not affect C<decode> in any way - shared values and
208references will always be decoded properly if present. 234references will always be decoded properly if present.
209 235
236=item $cbor = $cbor->allow_cycles ([$enable])
237
238=item $enabled = $cbor->get_allow_cycles
239
240If C<$enable> is true (or missing), then C<decode> will happily decode
241self-referential (cyclic) data structures. By default these will not be
242decoded, as they need manual cleanup to avoid memory leaks, so code that
243isn't prepared for this will not leak memory.
244
245If C<$enable> is false (the default), then C<decode> will throw an error
246when it encounters a self-referential/cyclic data structure.
247
248FUTURE DIRECTION: the motivation behind this option is to avoid I<real>
249cycles - future versions of this module might chose to decode cyclic data
250structures using weak references when this option is off, instead of
251throwing an error.
252
253This option does not affect C<encode> in any way - shared values and
254references will always be encoded properly if present.
255
256=item $cbor = $cbor->forbid_objects ([$enable])
257
258=item $enabled = $cbor->get_forbid_objects
259
260Disables the use of the object serialiser protocol.
261
262If C<$enable> is true (or missing), then C<encode> will will throw an
263exception when it encounters perl objects that would be encoded using the
264perl-object tag (26). When C<decode> encounters such tags, it will fall
265back to the general filter/tagged logic as if this were an unknown tag (by
266default resulting in a C<CBOR::XC::Tagged> object).
267
268If C<$enable> is false (the default), then C<encode> will use the
269L<Types::Serialiser> object serialisation protocol to serialise objects
270into perl-object tags, and C<decode> will do the same to decode such tags.
271
272See L<SECURITY CONSIDERATIONS>, below, for more info on why forbidding this
273protocol can be useful.
274
210=item $cbor = $cbor->pack_strings ([$enable]) 275=item $cbor = $cbor->pack_strings ([$enable])
211 276
212=item $enabled = $cbor->get_pack_strings 277=item $enabled = $cbor->get_pack_strings
213 278
214If C<$enable> is true (or missing), then C<encode> will try not to encode 279If C<$enable> is true (or missing), then C<encode> will try not to encode
226the standard CBOR way. 291the standard CBOR way.
227 292
228This option does not affect C<decode> in any way - string references will 293This option does not affect C<decode> in any way - string references will
229always be decoded properly if present. 294always be decoded properly if present.
230 295
296=item $cbor = $cbor->text_keys ([$enable])
297
298=item $enabled = $cbor->get_text_keys
299
300If C<$enabled> is true (or missing), then C<encode> will encode all
301perl hash keys as CBOR text strings/UTF-8 string, upgrading them as needed.
302
303If C<$enable> is false (the default), then C<encode> will encode hash keys
304normally - upgraded perl strings (strings internally encoded as UTF-8) as
305CBOR text strings, and downgraded perl strings as CBOR byte strings.
306
307This option does not affect C<decode> in any way.
308
309This option is useful for interoperability with CBOR decoders that don't
310treat byte strings as a form of text. It is especially useful as Perl
311gives very little control over hash keys.
312
313Enabling this option can be slow, as all downgraded hash keys that are
314encoded need to be scanned and converted to UTF-8.
315
316=item $cbor = $cbor->text_strings ([$enable])
317
318=item $enabled = $cbor->get_text_strings
319
320This option works similar to C<text_keys>, above, but works on all strings
321(including hash keys), so C<text_keys> has no further effect after
322enabling C<text_strings>.
323
324If C<$enabled> is true (or missing), then C<encode> will encode all perl
325strings as CBOR text strings/UTF-8 strings, upgrading them as needed.
326
327If C<$enable> is false (the default), then C<encode> will encode strings
328normally (but see C<text_keys>) - upgraded perl strings (strings
329internally encoded as UTF-8) as CBOR text strings, and downgraded perl
330strings as CBOR byte strings.
331
332This option does not affect C<decode> in any way.
333
334This option has similar advantages and disadvantages as C<text_keys>. In
335addition, this option effectively removes the ability to encode byte
336strings, which might break some C<FREEZE> and C<TO_CBOR> methods that rely
337on this, such as bignum encoding, so this option is mainly useful for very
338simple data.
339
340=item $cbor = $cbor->validate_utf8 ([$enable])
341
342=item $enabled = $cbor->get_validate_utf8
343
344If C<$enable> is true (or missing), then C<decode> will validate that
345elements (text strings) containing UTF-8 data in fact contain valid UTF-8
346data (instead of blindly accepting it). This validation obviously takes
347extra time during decoding.
348
349The concept of "valid UTF-8" used is perl's concept, which is a superset
350of the official UTF-8.
351
352If C<$enable> is false (the default), then C<decode> will blindly accept
353UTF-8 data, marking them as valid UTF-8 in the resulting data structure
354regardless of whether that's true or not.
355
356Perl isn't too happy about corrupted UTF-8 in strings, but should
357generally not crash or do similarly evil things. Extensions might be not
358so forgiving, so it's recommended to turn on this setting if you receive
359untrusted CBOR.
360
361This option does not affect C<encode> in any way - strings that are
362supposedly valid UTF-8 will simply be dumped into the resulting CBOR
363string without checking whether that is, in fact, true or not.
364
231=item $cbor = $cbor->filter ([$cb->($tag, $value)]) 365=item $cbor = $cbor->filter ([$cb->($tag, $value)])
232 366
233=item $cb_or_undef = $cbor->get_filter 367=item $cb_or_undef = $cbor->get_filter
234 368
235Sets or replaces the tagged value decoding filter (when C<$cb> is 369Sets or replaces the tagged value decoding filter (when C<$cb> is
247replace the tagged value in the decoded data structure, or no values, 381replace the tagged value in the decoded data structure, or no values,
248which will result in default handling, which currently means the decoder 382which will result in default handling, which currently means the decoder
249creates a C<CBOR::XS::Tagged> object to hold the tag and the value. 383creates a C<CBOR::XS::Tagged> object to hold the tag and the value.
250 384
251When the filter is cleared (the default state), the default filter 385When the filter is cleared (the default state), the default filter
252function, C<CBOR::XS::default_filter>, is used. This function simply looks 386function, C<CBOR::XS::default_filter>, is used. This function simply
253up the tag in the C<%CBOR::XS::FILTER> hash. If an entry exists it must be 387looks up the tag in the C<%CBOR::XS::FILTER> hash. If an entry exists
254a code reference that is called with tag and value, and is responsible for 388it must be a code reference that is called with tag and value, and is
255decoding the value. If no entry exists, it returns no values. 389responsible for decoding the value. If no entry exists, it returns no
390values. C<CBOR::XS> provides a number of default filter functions already,
391the the C<%CBOR::XS::FILTER> hash can be freely extended with more.
392
393C<CBOR::XS> additionally provides an alternative filter function that is
394supposed to be safe to use with untrusted data (which the default filter
395might not), called C<CBOR::XS::safe_filter>, which works the same as
396the C<default_filter> but uses the C<%CBOR::XS::SAFE_FILTER> variable
397instead. It is prepopulated with the tag decoding functions that are
398deemed safe (basically the same as C<%CBOR::XS::FILTER> without all
399the bignum tags), and can be extended by user code as wlel, although,
400obviously, one should be very careful about adding decoding functions
401here, since the expectation is that they are safe to use on untrusted
402data, after all.
256 403
257Example: decode all tags not handled internally into C<CBOR::XS::Tagged> 404Example: decode all tags not handled internally into C<CBOR::XS::Tagged>
258objects, with no other special handling (useful when working with 405objects, with no other special handling (useful when working with
259potentially "unsafe" CBOR data). 406potentially "unsafe" CBOR data).
260 407
267 my ($tag, $value); 414 my ($tag, $value);
268 415
269 "tag 1347375694 value $value" 416 "tag 1347375694 value $value"
270 }; 417 };
271 418
419Example: provide your own filter function that looks up tags in your own
420hash:
421
422 my %my_filter = (
423 998347484 => sub {
424 my ($tag, $value);
425
426 "tag 998347484 value $value"
427 };
428 );
429
430 my $coder = CBOR::XS->new->filter (sub {
431 &{ $my_filter{$_[0]} or return }
432 });
433
434
435Example: use the safe filter function (see L<SECURITY CONSIDERATIONS> for
436more considerations on security).
437
438 CBOR::XS->new->filter (\&CBOR::XS::safe_filter)->decode ($cbor_data);
439
272=item $cbor_data = $cbor->encode ($perl_scalar) 440=item $cbor_data = $cbor->encode ($perl_scalar)
273 441
274Converts the given Perl data structure (a scalar value) to its CBOR 442Converts the given Perl data structure (a scalar value) to its CBOR
275representation. 443representation.
276 444
289and you need to know where the first CBOR string ends amd the next one 457and you need to know where the first CBOR string ends amd the next one
290starts. 458starts.
291 459
292 CBOR::XS->new->decode_prefix ("......") 460 CBOR::XS->new->decode_prefix ("......")
293 => ("...", 3) 461 => ("...", 3)
462
463=back
464
465=head2 INCREMENTAL PARSING
466
467In some cases, there is the need for incremental parsing of JSON
468texts. While this module always has to keep both CBOR text and resulting
469Perl data structure in memory at one time, it does allow you to parse a
470CBOR stream incrementally, using a similar to using "decode_prefix" to see
471if a full CBOR object is available, but is much more efficient.
472
473It basically works by parsing as much of a CBOR string as possible - if
474the CBOR data is not complete yet, the pasrer will remember where it was,
475to be able to restart when more data has been accumulated. Once enough
476data is available to either decode a complete CBOR value or raise an
477error, a real decode will be attempted.
478
479A typical use case would be a network protocol that consists of sending
480and receiving CBOR-encoded messages. The solution that works with CBOR and
481about anything else is by prepending a length to every CBOR value, so the
482receiver knows how many octets to read. More compact (and slightly slower)
483would be to just send CBOR values back-to-back, as C<CBOR::XS> knows where
484a CBOR value ends, and doesn't need an explicit length.
485
486The following methods help with this:
487
488=over 4
489
490=item @decoded = $cbor->incr_parse ($buffer)
491
492This method attempts to decode exactly one CBOR value from the beginning
493of the given C<$buffer>. The value is removed from the C<$buffer> on
494success. When C<$buffer> doesn't contain a complete value yet, it returns
495nothing. Finally, when the C<$buffer> doesn't start with something
496that could ever be a valid CBOR value, it raises an exception, just as
497C<decode> would. In the latter case the decoder state is undefined and
498must be reset before being able to parse further.
499
500This method modifies the C<$buffer> in place. When no CBOR value can be
501decoded, the decoder stores the current string offset. On the next call,
502continues decoding at the place where it stopped before. For this to make
503sense, the C<$buffer> must begin with the same octets as on previous
504unsuccessful calls.
505
506You can call this method in scalar context, in which case it either
507returns a decoded value or C<undef>. This makes it impossible to
508distinguish between CBOR null values (which decode to C<undef>) and an
509unsuccessful decode, which is often acceptable.
510
511=item @decoded = $cbor->incr_parse_multiple ($buffer)
512
513Same as C<incr_parse>, but attempts to decode as many CBOR values as
514possible in one go, instead of at most one. Calls to C<incr_parse> and
515C<incr_parse_multiple> can be interleaved.
516
517=item $cbor->incr_reset
518
519Resets the incremental decoder. This throws away any saved state, so that
520subsequent calls to C<incr_parse> or C<incr_parse_multiple> start to parse
521a new CBOR value from the beginning of the C<$buffer> again.
522
523This method can be called at any time, but it I<must> be called if you want
524to change your C<$buffer> or there was a decoding error and you want to
525reuse the C<$cbor> object for future incremental parsings.
294 526
295=back 527=back
296 528
297 529
298=head1 MAPPING 530=head1 MAPPING
371 603
372=item hash references 604=item hash references
373 605
374Perl hash references become CBOR maps. As there is no inherent ordering in 606Perl hash references become CBOR maps. As there is no inherent ordering in
375hash keys (or CBOR maps), they will usually be encoded in a pseudo-random 607hash keys (or CBOR maps), they will usually be encoded in a pseudo-random
376order. This order can be different each time a hahs is encoded. 608order. This order can be different each time a hash is encoded.
377 609
378Currently, tied hashes will use the indefinite-length format, while normal 610Currently, tied hashes will use the indefinite-length format, while normal
379hashes will use the fixed-length format. 611hashes will use the fixed-length format.
380 612
381=item array references 613=item array references
434 my $x = 3.1; # some variable containing a number 666 my $x = 3.1; # some variable containing a number
435 "$x"; # stringified 667 "$x"; # stringified
436 $x .= ""; # another, more awkward way to stringify 668 $x .= ""; # another, more awkward way to stringify
437 print $x; # perl does it for you, too, quite often 669 print $x; # perl does it for you, too, quite often
438 670
439You can force whether a string ie encoded as byte or text string by using 671You can force whether a string is encoded as byte or text string by using
440C<utf8::upgrade> and C<utf8::downgrade>): 672C<utf8::upgrade> and C<utf8::downgrade> (if C<text_strings> is disabled):
441 673
442 utf8::upgrade $x; # encode $x as text string 674 utf8::upgrade $x; # encode $x as text string
443 utf8::downgrade $x; # encode $x as byte string 675 utf8::downgrade $x; # encode $x as byte string
444 676
445Perl doesn't define what operations up- and downgrade strings, so if the 677Perl doesn't define what operations up- and downgrade strings, so if the
446difference between byte and text is important, you should up- or downgrade 678difference between byte and text is important, you should up- or downgrade
447your string as late as possible before encoding. 679your string as late as possible before encoding. You can also force the
680use of CBOR text strings by using C<text_keys> or C<text_strings>.
448 681
449You can force the type to be a CBOR number by numifying it: 682You can force the type to be a CBOR number by numifying it:
450 683
451 my $x = "3"; # some variable containing a string 684 my $x = "3"; # some variable containing a string
452 $x += 0; # numify it, ensuring it will be dumped as a number 685 $x += 0; # numify it, ensuring it will be dumped as a number
465 698
466=back 699=back
467 700
468=head2 OBJECT SERIALISATION 701=head2 OBJECT SERIALISATION
469 702
703This module implements both a CBOR-specific and the generic
704L<Types::Serialier> object serialisation protocol. The following
705subsections explain both methods.
706
707=head3 ENCODING
708
470This module knows two way to serialise a Perl object: The CBOR-specific 709This module knows two way to serialise a Perl object: The CBOR-specific
471way, and the generic way. 710way, and the generic way.
472 711
473Whenever the encoder encounters a Perl object that it cnanot serialise 712Whenever the encoder encounters a Perl object that it cannot serialise
474directly (most of them), it will first look up the C<TO_CBOR> method on 713directly (most of them), it will first look up the C<TO_CBOR> method on
475it. 714it.
476 715
477If it has a C<TO_CBOR> method, it will call it with the object as only 716If it has a C<TO_CBOR> method, it will call it with the object as only
478argument, and expects exactly one return value, which it will then 717argument, and expects exactly one return value, which it will then
484 723
485The C<FREEZE> method can return any number of values (i.e. zero or 724The C<FREEZE> method can return any number of values (i.e. zero or
486more). These will be encoded as CBOR perl object, together with the 725more). These will be encoded as CBOR perl object, together with the
487classname. 726classname.
488 727
728These methods I<MUST NOT> change the data structure that is being
729serialised. Failure to comply to this can result in memory corruption -
730and worse.
731
489If an object supports neither C<TO_CBOR> nor C<FREEZE>, encoding will fail 732If an object supports neither C<TO_CBOR> nor C<FREEZE>, encoding will fail
490with an error. 733with an error.
491 734
735=head3 DECODING
736
492Objects encoded via C<TO_CBOR> cannot be automatically decoded, but 737Objects encoded via C<TO_CBOR> cannot (normally) be automatically decoded,
493objects encoded via C<FREEZE> can be decoded using the following protocol: 738but objects encoded via C<FREEZE> can be decoded using the following
739protocol:
494 740
495When an encoded CBOR perl object is encountered by the decoder, it will 741When an encoded CBOR perl object is encountered by the decoder, it will
496look up the C<THAW> method, by using the stored classname, and will fail 742look up the C<THAW> method, by using the stored classname, and will fail
497if the method cannot be found. 743if the method cannot be found.
498 744
499After the lookup it will call the C<THAW> method with the stored classname 745After the lookup it will call the C<THAW> method with the stored classname
500as first argument, the constant string C<CBOR> as second argument, and all 746as first argument, the constant string C<CBOR> as second argument, and all
501values returned by C<FREEZE> as remaining arguments. 747values returned by C<FREEZE> as remaining arguments.
502 748
503=head4 EXAMPLES 749=head3 EXAMPLES
504 750
505Here is an example C<TO_CBOR> method: 751Here is an example C<TO_CBOR> method:
506 752
507 sub My::Object::TO_CBOR { 753 sub My::Object::TO_CBOR {
508 my ($obj) = @_; 754 my ($obj) = @_;
540 "$self" # encode url string 786 "$self" # encode url string
541 } 787 }
542 788
543 sub URI::THAW { 789 sub URI::THAW {
544 my ($class, $serialiser, $uri) = @_; 790 my ($class, $serialiser, $uri) = @_;
545
546 $class->new ($uri) 791 $class->new ($uri)
547 } 792 }
548 793
549Unlike C<TO_CBOR>, multiple values can be returned by C<FREEZE>. For 794Unlike C<TO_CBOR>, multiple values can be returned by C<FREEZE>. For
550example, a C<FREEZE> method that returns "type", "id" and "variant" values 795example, a C<FREEZE> method that returns "type", "id" and "variant" values
681additional tags (such as base64url). 926additional tags (such as base64url).
682 927
683=head2 ENFORCED TAGS 928=head2 ENFORCED TAGS
684 929
685These tags are always handled when decoding, and their handling cannot be 930These tags are always handled when decoding, and their handling cannot be
686overriden by the user. 931overridden by the user.
687 932
688=over 4 933=over 4
689 934
690=item 26 (perl-object, L<http://cbor.schmorp.de/perl-object>) 935=item 26 (perl-object, L<http://cbor.schmorp.de/perl-object>)
691 936
692These tags are automatically created (and decoded) for serialisable 937These tags are automatically created (and decoded) for serialisable
693objects using the C<FREEZE/THAW> methods (the L<Types::Serialier> object 938objects using the C<FREEZE/THAW> methods (the L<Types::Serialier> object
694serialisation protocol). See L<OBJECT SERIALISATION> for details. 939serialisation protocol). See L<OBJECT SERIALISATION> for details.
695 940
696=item 28, 29 (sharable, sharedref, L <http://cbor.schmorp.de/value-sharing>) 941=item 28, 29 (shareable, sharedref, L<http://cbor.schmorp.de/value-sharing>)
697 942
698These tags are automatically decoded when encountered, resulting in 943These tags are automatically decoded when encountered (and they do not
944result in a cyclic data structure, see C<allow_cycles>), resulting in
699shared values in the decoded object. They are only encoded, however, when 945shared values in the decoded object. They are only encoded, however, when
700C<allow_sharable> is enabled. 946C<allow_sharing> is enabled.
701 947
948Not all shared values can be successfully decoded: values that reference
949themselves will I<currently> decode as C<undef> (this is not the same
950as a reference pointing to itself, which will be represented as a value
951that contains an indirect reference to itself - these will be decoded
952properly).
953
954Note that considerably more shared value data structures can be decoded
955than will be encoded - currently, only values pointed to by references
956will be shared, others will not. While non-reference shared values can be
957generated in Perl with some effort, they were considered too unimportant
958to be supported in the encoder. The decoder, however, will decode these
959values as shared values.
960
702=item 256, 25 (stringref-namespace, stringref, L <http://cbor.schmorp.de/stringref>) 961=item 256, 25 (stringref-namespace, stringref, L<http://cbor.schmorp.de/stringref>)
703 962
704These tags are automatically decoded when encountered. They are only 963These tags are automatically decoded when encountered. They are only
705encoded, however, when C<pack_strings> is enabled. 964encoded, however, when C<pack_strings> is enabled.
706 965
707=item 22098 (indirection, L<http://cbor.schmorp.de/indirection>) 966=item 22098 (indirection, L<http://cbor.schmorp.de/indirection>)
708 967
709This tag is automatically generated when a reference are encountered (with 968This tag is automatically generated when a reference are encountered (with
710the exception of hash and array refernces). It is converted to a reference 969the exception of hash and array references). It is converted to a reference
711when decoding. 970when decoding.
712 971
713=item 55799 (self-describe CBOR, RFC 7049) 972=item 55799 (self-describe CBOR, RFC 7049)
714 973
715This value is not generated on encoding (unless explicitly requested by 974This value is not generated on encoding (unless explicitly requested by
718=back 977=back
719 978
720=head2 NON-ENFORCED TAGS 979=head2 NON-ENFORCED TAGS
721 980
722These tags have default filters provided when decoding. Their handling can 981These tags have default filters provided when decoding. Their handling can
723be overriden by changing the C<%CBOR::XS::FILTER> entry for the tag, or by 982be overridden by changing the C<%CBOR::XS::FILTER> entry for the tag, or by
724providing a custom C<filter> callback when decoding. 983providing a custom C<filter> callback when decoding.
725 984
726When they result in decoding into a specific Perl class, the module 985When they result in decoding into a specific Perl class, the module
727usually provides a corresponding C<TO_CBOR> method as well. 986usually provides a corresponding C<TO_CBOR> method as well.
728 987
731provide these modules. The decoding usually fails with an exception if the 990provide these modules. The decoding usually fails with an exception if the
732required module cannot be loaded. 991required module cannot be loaded.
733 992
734=over 4 993=over 4
735 994
995=item 0, 1 (date/time string, seconds since the epoch)
996
997These tags are decoded into L<Time::Piece> objects. The corresponding
998C<Time::Piece::TO_CBOR> method always encodes into tag 1 values currently.
999
1000The L<Time::Piece> API is generally surprisingly bad, and fractional
1001seconds are only accidentally kept intact, so watch out. On the plus side,
1002the module comes with perl since 5.10, which has to count for something.
1003
736=item 2, 3 (positive/negative bignum) 1004=item 2, 3 (positive/negative bignum)
737 1005
738These tags are decoded into L<Math::BigInt> objects. The corresponding 1006These tags are decoded into L<Math::BigInt> objects. The corresponding
739C<Math::BigInt::TO_CBOR> method encodes "small" bigints into normal CBOR 1007C<Math::BigInt::TO_CBOR> method encodes "small" bigints into normal CBOR
740integers, and others into positive/negative CBOR bignums. 1008integers, and others into positive/negative CBOR bignums.
741 1009
742=item 4, 5 (decimal fraction/bigfloat) 1010=item 4, 5, 264, 265 (decimal fraction/bigfloat)
743 1011
744Both decimal fractions and bigfloats are decoded into L<Math::BigFloat> 1012Both decimal fractions and bigfloats are decoded into L<Math::BigFloat>
745objects. The corresponding C<Math::BigFloat::TO_CBOR> method I<always> 1013objects. The corresponding C<Math::BigFloat::TO_CBOR> method I<always>
746encodes into a decimal fraction. 1014encodes into a decimal fraction (either tag 4 or 264).
747 1015
748CBOR cannot represent bigfloats with I<very> large exponents - conversion 1016NaN and infinities are not encoded properly, as they cannot be represented
749of such big float objects is undefined. 1017in CBOR.
750 1018
751Also, NaN and infinities are not encoded properly. 1019See L<BIGNUM SECURITY CONSIDERATIONS> for more info.
1020
1021=item 30 (rational numbers)
1022
1023These tags are decoded into L<Math::BigRat> objects. The corresponding
1024C<Math::BigRat::TO_CBOR> method encodes rational numbers with denominator
1025C<1> via their numerator only, i.e., they become normal integers or
1026C<bignums>.
1027
1028See L<BIGNUM SECURITY CONSIDERATIONS> for more info.
752 1029
753=item 21, 22, 23 (expected later JSON conversion) 1030=item 21, 22, 23 (expected later JSON conversion)
754 1031
755CBOR::XS is not a CBOR-to-JSON converter, and will simply ignore these 1032CBOR::XS is not a CBOR-to-JSON converter, and will simply ignore these
756tags. 1033tags.
761C<URI::TO_CBOR> method again results in a CBOR URI value. 1038C<URI::TO_CBOR> method again results in a CBOR URI value.
762 1039
763=back 1040=back
764 1041
765=cut 1042=cut
766
767our %FILTER = (
768 # 0 # rfc4287 datetime, utf-8
769 # 1 # unix timestamp, any
770
771 2 => sub { # pos bigint
772 require Math::BigInt;
773 Math::BigInt->new ("0x" . unpack "H*", pop)
774 },
775
776 3 => sub { # neg bigint
777 require Math::BigInt;
778 -Math::BigInt->new ("0x" . unpack "H*", pop)
779 },
780
781 4 => sub { # decimal fraction, array
782 require Math::BigFloat;
783 Math::BigFloat->new ($_[1][1] . "E" . $_[1][0])
784 },
785
786 5 => sub { # bigfloat, array
787 require Math::BigFloat;
788 scalar Math::BigFloat->new ($_[1][1])->blsft ($_[1][0], 2)
789 },
790
791 21 => sub { pop }, # expected conversion to base64url encoding
792 22 => sub { pop }, # expected conversion to base64 encoding
793 23 => sub { pop }, # expected conversion to base16 encoding
794
795 # 24 # embedded cbor, byte string
796
797 32 => sub {
798 require URI;
799 URI->new (pop)
800 },
801
802 # 33 # base64url rfc4648, utf-8
803 # 34 # base64 rfc46484, utf-8
804 # 35 # regex pcre/ecma262, utf-8
805 # 36 # mime message rfc2045, utf-8
806);
807
808 1043
809=head1 CBOR and JSON 1044=head1 CBOR and JSON
810 1045
811CBOR is supposed to implement a superset of the JSON data model, and is, 1046CBOR is supposed to implement a superset of the JSON data model, and is,
812with some coercion, able to represent all JSON texts (something that other 1047with some coercion, able to represent all JSON texts (something that other
821CBOR intact. 1056CBOR intact.
822 1057
823 1058
824=head1 SECURITY CONSIDERATIONS 1059=head1 SECURITY CONSIDERATIONS
825 1060
826When you are using CBOR in a protocol, talking to untrusted potentially 1061Tl;dr... if you want to decode or encode CBOR from untrusted sources, you
827hostile creatures requires relatively few measures. 1062should start with a coder object created via C<new_safe>:
828 1063
1064 my $coder = CBOR::XS->new_safe;
1065
1066 my $data = $coder->decode ($cbor_text);
1067 my $cbor = $coder->encode ($data);
1068
1069Longer version: When you are using CBOR in a protocol, talking to
1070untrusted potentially hostile creatures requires some thought:
1071
1072=over 4
1073
1074=item Security of the CBOR decoder itself
1075
829First of all, your CBOR decoder should be secure, that is, should not have 1076First and foremost, your CBOR decoder should be secure, that is, should
1077not have any buffer overflows or similar bugs that could potentially be
830any buffer overflows. Obviously, this module should ensure that and I am 1078exploited. Obviously, this module should ensure that and I am trying hard
831trying hard on making that true, but you never know. 1079on making that true, but you never know.
832 1080
1081=item CBOR::XS can invoke almost arbitrary callbacks during decoding
1082
1083CBOR::XS supports object serialisation - decoding CBOR can cause calls
1084to I<any> C<THAW> method in I<any> package that exists in your process
1085(that is, CBOR::XS will not try to load modules, but any existing C<THAW>
1086method or function can be called, so they all have to be secure).
1087
1088Less obviously, it will also invoke C<TO_CBOR> and C<FREEZE> methods -
1089even if all your C<THAW> methods are secure, encoding data structures from
1090untrusted sources can invoke those and trigger bugs in those.
1091
1092So, if you are not sure about the security of all the modules you
1093have loaded (you shouldn't), you should disable this part using
1094C<forbid_objects>.
1095
1096=item CBOR can be extended with tags that call library code
1097
1098CBOR can be extended with tags, and C<CBOR::XS> has a registry of
1099conversion functions for many existing tags that can be extended via
1100third-party modules (see the C<filter> method).
1101
1102If you don't trust these, you should configure the "safe" filter function,
1103C<CBOR::XS::safe_filter>, which by default only includes conversion
1104functions that are considered "safe" by the author (but again, they can be
1105extended by third party modules).
1106
1107Depending on your level of paranoia, you can use the "safe" filter:
1108
1109 $cbor->filter (\&CBOR::XS::safe_filter);
1110
1111... your own filter...
1112
1113 $cbor->filter (sub { ... do your stuffs here ... });
1114
1115... or even no filter at all, disabling all tag decoding:
1116
1117 $cbor->filter (sub { });
1118
1119This is never a problem for encoding, as the tag mechanism only exists in
1120CBOR texts.
1121
1122=item Resource-starving attacks: object memory usage
1123
833Second, you need to avoid resource-starving attacks. That means you should 1124You need to avoid resource-starving attacks. That means you should limit
834limit the size of CBOR data you accept, or make sure then when your 1125the size of CBOR data you accept, or make sure then when your resources
835resources run out, that's just fine (e.g. by using a separate process that 1126run out, that's just fine (e.g. by using a separate process that can
836can crash safely). The size of a CBOR string in octets is usually a good 1127crash safely). The size of a CBOR string in octets is usually a good
837indication of the size of the resources required to decode it into a Perl 1128indication of the size of the resources required to decode it into a Perl
838structure. While CBOR::XS can check the size of the CBOR text, it might be 1129structure. While CBOR::XS can check the size of the CBOR text (using
839too late when you already have it in memory, so you might want to check 1130C<max_size>), it might be too late when you already have it in memory, so
840the size before you accept the string. 1131you might want to check the size before you accept the string.
841 1132
1133As for encoding, it is possible to construct data structures that are
1134relatively small but result in large CBOR texts (for example by having an
1135array full of references to the same big data structure, which will all be
1136deep-cloned during encoding by default). This is rarely an actual issue
1137(and the worst case is still just running out of memory), but you can
1138reduce this risk by using C<allow_sharing>.
1139
1140=item Resource-starving attacks: stack overflows
1141
842Third, CBOR::XS recurses using the C stack when decoding objects and 1142CBOR::XS recurses using the C stack when decoding objects and arrays. The
843arrays. The C stack is a limited resource: for instance, on my amd64 1143C stack is a limited resource: for instance, on my amd64 machine with 8MB
844machine with 8MB of stack size I can decode around 180k nested arrays but 1144of stack size I can decode around 180k nested arrays but only 14k nested
845only 14k nested CBOR objects (due to perl itself recursing deeply on croak 1145CBOR objects (due to perl itself recursing deeply on croak to free the
846to free the temporary). If that is exceeded, the program crashes. To be 1146temporary). If that is exceeded, the program crashes. To be conservative,
847conservative, the default nesting limit is set to 512. If your process 1147the default nesting limit is set to 512. If your process has a smaller
848has a smaller stack, you should adjust this setting accordingly with the 1148stack, you should adjust this setting accordingly with the C<max_depth>
849C<max_depth> method. 1149method.
1150
1151=item Resource-starving attacks: CPU en-/decoding complexity
1152
1153CBOR::XS will use the L<Math::BigInt>, L<Math::BigFloat> and
1154L<Math::BigRat> libraries to represent encode/decode bignums. These can
1155be very slow (as in, centuries of CPU time) and can even crash your
1156program (and are generally not very trustworthy). See the next section for
1157details.
1158
1159=item Data breaches: leaking information in error messages
1160
1161CBOR::XS might leak contents of your Perl data structures in its error
1162messages, so when you serialise sensitive information you might want to
1163make sure that exceptions thrown by CBOR::XS will not end up in front of
1164untrusted eyes.
1165
1166=item Something else...
850 1167
851Something else could bomb you, too, that I forgot to think of. In that 1168Something else could bomb you, too, that I forgot to think of. In that
852case, you get to keep the pieces. I am always open for hints, though... 1169case, you get to keep the pieces. I am always open for hints, though...
853 1170
854Also keep in mind that CBOR::XS might leak contents of your Perl data 1171=back
855structures in its error messages, so when you serialise sensitive 1172
856information you might want to make sure that exceptions thrown by CBOR::XS 1173
857will not end up in front of untrusted eyes. 1174=head1 BIGNUM SECURITY CONSIDERATIONS
1175
1176CBOR::XS provides a C<TO_CBOR> method for both L<Math::BigInt> and
1177L<Math::BigFloat> that tries to encode the number in the simplest possible
1178way, that is, either a CBOR integer, a CBOR bigint/decimal fraction (tag
11794) or an arbitrary-exponent decimal fraction (tag 264). Rational numbers
1180(L<Math::BigRat>, tag 30) can also contain bignums as members.
1181
1182CBOR::XS will also understand base-2 bigfloat or arbitrary-exponent
1183bigfloats (tags 5 and 265), but it will never generate these on its own.
1184
1185Using the built-in L<Math::BigInt::Calc> support, encoding and decoding
1186decimal fractions is generally fast. Decoding bigints can be slow for very
1187big numbers (tens of thousands of digits, something that could potentially
1188be caught by limiting the size of CBOR texts), and decoding bigfloats or
1189arbitrary-exponent bigfloats can be I<extremely> slow (minutes, decades)
1190for large exponents (roughly 40 bit and longer).
1191
1192Additionally, L<Math::BigInt> can take advantage of other bignum
1193libraries, such as L<Math::GMP>, which cannot handle big floats with large
1194exponents, and might simply abort or crash your program, due to their code
1195quality.
1196
1197This can be a concern if you want to parse untrusted CBOR. If it is, you
1198might want to disable decoding of tag 2 (bigint) and 3 (negative bigint)
1199types. You should also disable types 5 and 265, as these can be slow even
1200without bigints.
1201
1202Disabling bigints will also partially or fully disable types that rely on
1203them, e.g. rational numbers that use bignums.
1204
858 1205
859=head1 CBOR IMPLEMENTATION NOTES 1206=head1 CBOR IMPLEMENTATION NOTES
860 1207
861This section contains some random implementation notes. They do not 1208This section contains some random implementation notes. They do not
862describe guaranteed behaviour, but merely behaviour as-is implemented 1209describe guaranteed behaviour, but merely behaviour as-is implemented
871Only the double data type is supported for NV data types - when Perl uses 1218Only the double data type is supported for NV data types - when Perl uses
872long double to represent floating point values, they might not be encoded 1219long double to represent floating point values, they might not be encoded
873properly. Half precision types are accepted, but not encoded. 1220properly. Half precision types are accepted, but not encoded.
874 1221
875Strict mode and canonical mode are not implemented. 1222Strict mode and canonical mode are not implemented.
1223
1224
1225=head1 LIMITATIONS ON PERLS WITHOUT 64-BIT INTEGER SUPPORT
1226
1227On perls that were built without 64 bit integer support (these are rare
1228nowadays, even on 32 bit architectures, as all major Perl distributions
1229are built with 64 bit integer support), support for any kind of 64 bit
1230integer in CBOR is very limited - most likely, these 64 bit values will
1231be truncated, corrupted, or otherwise not decoded correctly. This also
1232includes string, array and map sizes that are stored as 64 bit integers.
876 1233
877 1234
878=head1 THREADS 1235=head1 THREADS
879 1236
880This module is I<not> guaranteed to be thread safe and there are no 1237This module is I<not> guaranteed to be thread safe and there are no
894Please refrain from using rt.cpan.org or any other bug reporting 1251Please refrain from using rt.cpan.org or any other bug reporting
895service. I put the contact address into my modules for a reason. 1252service. I put the contact address into my modules for a reason.
896 1253
897=cut 1254=cut
898 1255
1256# clumsy and slow hv_store-in-hash helper function
1257sub _hv_store {
1258 $_[0]{$_[1]} = $_[2];
1259}
1260
899our %FILTER = ( 1261our %FILTER = (
900 # 0 # rfc4287 datetime, utf-8 1262 0 => sub { # rfc4287 datetime, utf-8
901 # 1 # unix timestamp, any 1263 require Time::Piece;
1264 # Time::Piece::Strptime uses the "incredibly flexible date parsing routine"
1265 # from FreeBSD, which can't parse ISO 8601, RFC3339, RFC4287 or much of anything
1266 # else either. Whats incredibe over standard strptime totally escapes me.
1267 # doesn't do fractional times, either. sigh.
1268 # In fact, it's all a lie, it uses whatever strptime it wants, and of course,
1269 # they are all incompatible. The openbsd one simply ignores %z (but according to the
1270 # docs, it would be much more incredibly flexible indeed. If it worked, that is.).
1271 scalar eval {
1272 my $s = $_[1];
1273
1274 $s =~ s/Z$/+00:00/;
1275 $s =~ s/(\.[0-9]+)?([+-][0-9][0-9]):([0-9][0-9])$//
1276 or die;
1277
1278 my $b = $1 - ($2 * 60 + $3) * 60; # fractional part + offset. hopefully
1279 my $d = Time::Piece->strptime ($s, "%Y-%m-%dT%H:%M:%S");
1280
1281 Time::Piece::gmtime ($d->epoch + $b)
1282 } || die "corrupted CBOR date/time string ($_[0])";
1283 },
1284
1285 1 => sub { # seconds since the epoch, possibly fractional
1286 require Time::Piece;
1287 scalar Time::Piece::gmtime (pop)
1288 },
902 1289
903 2 => sub { # pos bigint 1290 2 => sub { # pos bigint
904 require Math::BigInt; 1291 require Math::BigInt;
905 Math::BigInt->new ("0x" . unpack "H*", pop) 1292 Math::BigInt->new ("0x" . unpack "H*", pop)
906 }, 1293 },
913 4 => sub { # decimal fraction, array 1300 4 => sub { # decimal fraction, array
914 require Math::BigFloat; 1301 require Math::BigFloat;
915 Math::BigFloat->new ($_[1][1] . "E" . $_[1][0]) 1302 Math::BigFloat->new ($_[1][1] . "E" . $_[1][0])
916 }, 1303 },
917 1304
1305 264 => sub { # decimal fraction with arbitrary exponent
1306 require Math::BigFloat;
1307 Math::BigFloat->new ($_[1][1] . "E" . $_[1][0])
1308 },
1309
918 5 => sub { # bigfloat, array 1310 5 => sub { # bigfloat, array
919 require Math::BigFloat; 1311 require Math::BigFloat;
920 scalar Math::BigFloat->new ($_[1][1])->blsft ($_[1][0], 2) 1312 scalar Math::BigFloat->new ($_[1][1]) * Math::BigFloat->new (2)->bpow ($_[1][0])
1313 },
1314
1315 265 => sub { # bigfloat with arbitrary exponent
1316 require Math::BigFloat;
1317 scalar Math::BigFloat->new ($_[1][1]) * Math::BigFloat->new (2)->bpow ($_[1][0])
1318 },
1319
1320 30 => sub { # rational number
1321 require Math::BigRat;
1322 Math::BigRat->new ("$_[1][0]/$_[1][1]") # separate parameters only work in recent versons
921 }, 1323 },
922 1324
923 21 => sub { pop }, # expected conversion to base64url encoding 1325 21 => sub { pop }, # expected conversion to base64url encoding
924 22 => sub { pop }, # expected conversion to base64 encoding 1326 22 => sub { pop }, # expected conversion to base64 encoding
925 23 => sub { pop }, # expected conversion to base16 encoding 1327 23 => sub { pop }, # expected conversion to base16 encoding
935 # 34 # base64 rfc46484, utf-8 1337 # 34 # base64 rfc46484, utf-8
936 # 35 # regex pcre/ecma262, utf-8 1338 # 35 # regex pcre/ecma262, utf-8
937 # 36 # mime message rfc2045, utf-8 1339 # 36 # mime message rfc2045, utf-8
938); 1340);
939 1341
940sub CBOR::XS::default_filter { 1342sub default_filter {
941 &{ $FILTER{$_[0]} or return } 1343 &{ $FILTER{$_[0]} or return }
1344}
1345
1346our %SAFE_FILTER = map { $_ => $FILTER{$_} } 0, 1, 21, 22, 23, 32;
1347
1348sub safe_filter {
1349 &{ $SAFE_FILTER{$_[0]} or return }
942} 1350}
943 1351
944sub URI::TO_CBOR { 1352sub URI::TO_CBOR {
945 my $uri = $_[0]->as_string; 1353 my $uri = $_[0]->as_string;
946 utf8::upgrade $uri; 1354 utf8::upgrade $uri;
947 CBOR::XS::tag 32, $uri 1355 tag 32, $uri
948} 1356}
949 1357
950sub Math::BigInt::TO_CBOR { 1358sub Math::BigInt::TO_CBOR {
951 if ($_[0] >= -2147483648 && $_[0] <= 2147483647) { 1359 if (-2147483648 <= $_[0] && $_[0] <= 2147483647) {
952 $_[0]->numify 1360 $_[0]->numify
953 } else { 1361 } else {
954 my $hex = substr $_[0]->as_hex, 2; 1362 my $hex = substr $_[0]->as_hex, 2;
955 $hex = "0$hex" if 1 & length $hex; # sigh 1363 $hex = "0$hex" if 1 & length $hex; # sigh
956 CBOR::XS::tag $_[0] >= 0 ? 2 : 3, pack "H*", $hex 1364 tag $_[0] >= 0 ? 2 : 3, pack "H*", $hex
957 } 1365 }
958} 1366}
959 1367
960sub Math::BigFloat::TO_CBOR { 1368sub Math::BigFloat::TO_CBOR {
961 my ($m, $e) = $_[0]->parts; 1369 my ($m, $e) = $_[0]->parts;
1370
1371 -9223372036854775808 <= $e && $e <= 18446744073709551615
962 CBOR::XS::tag 4, [$e->numify, $m] 1372 ? tag 4, [$e->numify, $m]
1373 : tag 264, [$e, $m]
1374}
1375
1376sub Math::BigRat::TO_CBOR {
1377 my ($n, $d) = $_[0]->parts;
1378
1379 # older versions of BigRat need *1, as they not always return numbers
1380
1381 $d*1 == 1
1382 ? $n*1
1383 : tag 30, [$n*1, $d*1]
1384}
1385
1386sub Time::Piece::TO_CBOR {
1387 tag 1, 0 + $_[0]->epoch
963} 1388}
964 1389
965XSLoader::load "CBOR::XS", $VERSION; 1390XSLoader::load "CBOR::XS", $VERSION;
966 1391
967=head1 SEE ALSO 1392=head1 SEE ALSO

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