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Revision 1.15 by root, Mon Apr 27 20:21:53 2015 UTC vs.
Revision 1.21 by root, Tue Dec 8 08:29:44 2020 UTC

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33 with the added ability of supporting serialisation of Perl objects. 33 with the added ability of supporting serialisation of Perl objects.
34 (JSON often compresses better than CBOR though, so if you plan to 34 (JSON often compresses better than CBOR though, so if you plan to
35 compress the data later and speed is less important you might want to 35 compress the data later and speed is less important you might want to
36 compare both formats first). 36 compare both formats first).
37 37
38 The primary goal of this module is to be *correct* and the secondary
39 goal is to be *fast*. To reach the latter goal it was written in C.
40
38 To give you a general idea about speed, with texts in the megabyte 41 To give you a general idea about speed, with texts in the megabyte
39 range, "CBOR::XS" usually encodes roughly twice as fast as Storable or 42 range, "CBOR::XS" usually encodes roughly twice as fast as Storable or
40 JSON::XS and decodes about 15%-30% faster than those. The shorter the 43 JSON::XS and decodes about 15%-30% faster than those. The shorter the
41 data, the worse Storable performs in comparison. 44 data, the worse Storable performs in comparison.
42 45
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47 In addition to the core CBOR data format, this module implements a 50 In addition to the core CBOR data format, this module implements a
48 number of extensions, to support cyclic and shared data structures (see 51 number of extensions, to support cyclic and shared data structures (see
49 "allow_sharing" and "allow_cycles"), string deduplication (see 52 "allow_sharing" and "allow_cycles"), string deduplication (see
50 "pack_strings") and scalar references (always enabled). 53 "pack_strings") and scalar references (always enabled).
51 54
52 The primary goal of this module is to be *correct* and the secondary
53 goal is to be *fast*. To reach the latter goal it was written in C.
54
55 See MAPPING, below, on how CBOR::XS maps perl values to CBOR values and 55 See MAPPING, below, on how CBOR::XS maps perl values to CBOR values and
56 vice versa. 56 vice versa.
57 57
58FUNCTIONAL INTERFACE 58FUNCTIONAL INTERFACE
59 The following convenience methods are provided by this module. They are 59 The following convenience methods are provided by this module. They are
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78 78
79 The mutators for flags all return the CBOR object again and thus 79 The mutators for flags all return the CBOR object again and thus
80 calls can be chained: 80 calls can be chained:
81 81
82 my $cbor = CBOR::XS->new->encode ({a => [1,2]}); 82 my $cbor = CBOR::XS->new->encode ({a => [1,2]});
83
84 $cbor = new_safe CBOR::XS
85 Create a new, safe/secure CBOR::XS object. This is similar to "new",
86 but configures the coder object to be safe to use with untrusted
87 data. Currently, this is equivalent to:
88
89 my $cbor = CBOR::XS
90 ->new
91 ->forbid_objects
92 ->filter (\&CBOR::XS::safe_filter)
93 ->max_size (1e8);
94
95 But is more future proof (it is better to crash because of a change
96 than to be exploited in other ways).
83 97
84 $cbor = $cbor->max_depth ([$maximum_nesting_depth]) 98 $cbor = $cbor->max_depth ([$maximum_nesting_depth])
85 $max_depth = $cbor->get_max_depth 99 $max_depth = $cbor->get_max_depth
86 Sets the maximum nesting level (default 512) accepted while encoding 100 Sets the maximum nesting level (default 512) accepted while encoding
87 or decoding. If a higher nesting level is detected in CBOR data or a 101 or decoding. If a higher nesting level is detected in CBOR data or a
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101 115
102 Note that nesting is implemented by recursion in C. The default 116 Note that nesting is implemented by recursion in C. The default
103 value has been chosen to be as large as typical operating systems 117 value has been chosen to be as large as typical operating systems
104 allow without crashing. 118 allow without crashing.
105 119
106 See SECURITY CONSIDERATIONS, below, for more info on why this is 120 See "SECURITY CONSIDERATIONS", below, for more info on why this is
107 useful. 121 useful.
108 122
109 $cbor = $cbor->max_size ([$maximum_string_size]) 123 $cbor = $cbor->max_size ([$maximum_string_size])
110 $max_size = $cbor->get_max_size 124 $max_size = $cbor->get_max_size
111 Set the maximum length a CBOR string may have (in bytes) where 125 Set the maximum length a CBOR string may have (in bytes) where
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115 exception. This setting has no effect on "encode" (yet). 129 exception. This setting has no effect on "encode" (yet).
116 130
117 If no argument is given, the limit check will be deactivated (same 131 If no argument is given, the limit check will be deactivated (same
118 as when 0 is specified). 132 as when 0 is specified).
119 133
120 See SECURITY CONSIDERATIONS, below, for more info on why this is 134 See "SECURITY CONSIDERATIONS", below, for more info on why this is
121 useful. 135 useful.
122 136
123 $cbor = $cbor->allow_unknown ([$enable]) 137 $cbor = $cbor->allow_unknown ([$enable])
124 $enabled = $cbor->get_allow_unknown 138 $enabled = $cbor->get_allow_unknown
125 If $enable is true (or missing), then "encode" will *not* throw an 139 If $enable is true (or missing), then "encode" will *not* throw an
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141 instead will emit a reference to the earlier value. 155 instead will emit a reference to the earlier value.
142 156
143 This means that such values will only be encoded once, and will not 157 This means that such values will only be encoded once, and will not
144 result in a deep cloning of the value on decode, in decoders 158 result in a deep cloning of the value on decode, in decoders
145 supporting the value sharing extension. This also makes it possible 159 supporting the value sharing extension. This also makes it possible
146 to encode cyclic data structures (which need "allow_cycles" to ne 160 to encode cyclic data structures (which need "allow_cycles" to be
147 enabled to be decoded by this module). 161 enabled to be decoded by this module).
148 162
149 It is recommended to leave it off unless you know your communication 163 It is recommended to leave it off unless you know your communication
150 partner supports the value sharing extensions to CBOR 164 partner supports the value sharing extensions to CBOR
151 (<http://cbor.schmorp.de/value-sharing>), as without decoder 165 (<http://cbor.schmorp.de/value-sharing>), as without decoder
152 support, the resulting data structure might be unusable. 166 support, the resulting data structure might be unusable.
153 167
154 Detecting shared values incurs a runtime overhead when values are 168 Detecting shared values incurs a runtime overhead when values are
155 encoded that have a reference counter large than one, and might 169 encoded that have a reference counter large than one, and might
156 unnecessarily increase the encoded size, as potentially shared 170 unnecessarily increase the encoded size, as potentially shared
157 values are encode as shareable whether or not they are actually 171 values are encoded as shareable whether or not they are actually
158 shared. 172 shared.
159 173
160 At the moment, only targets of references can be shared (e.g. 174 At the moment, only targets of references can be shared (e.g.
161 scalars, arrays or hashes pointed to by a reference). Weirder 175 scalars, arrays or hashes pointed to by a reference). Weirder
162 constructs, such as an array with multiple "copies" of the *same* 176 constructs, such as an array with multiple "copies" of the *same*
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185 cyclic data structures using weak references when this option is 199 cyclic data structures using weak references when this option is
186 off, instead of throwing an error. 200 off, instead of throwing an error.
187 201
188 This option does not affect "encode" in any way - shared values and 202 This option does not affect "encode" in any way - shared values and
189 references will always be encoded properly if present. 203 references will always be encoded properly if present.
204
205 $cbor = $cbor->forbid_objects ([$enable])
206 $enabled = $cbor->get_forbid_objects
207 Disables the use of the object serialiser protocol.
208
209 If $enable is true (or missing), then "encode" will will throw an
210 exception when it encounters perl objects that would be encoded
211 using the perl-object tag (26). When "decode" encounters such tags,
212 it will fall back to the general filter/tagged logic as if this were
213 an unknown tag (by default resulting in a "CBOR::XC::Tagged"
214 object).
215
216 If $enable is false (the default), then "encode" will use the
217 Types::Serialiser object serialisation protocol to serialise objects
218 into perl-object tags, and "decode" will do the same to decode such
219 tags.
220
221 See "SECURITY CONSIDERATIONS", below, for more info on why
222 forbidding this protocol can be useful.
190 223
191 $cbor = $cbor->pack_strings ([$enable]) 224 $cbor = $cbor->pack_strings ([$enable])
192 $enabled = $cbor->get_pack_strings 225 $enabled = $cbor->get_pack_strings
193 If $enable is true (or missing), then "encode" will try not to 226 If $enable is true (or missing), then "encode" will try not to
194 encode the same string twice, but will instead encode a reference to 227 encode the same string twice, but will instead encode a reference to
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205 the standard CBOR way. 238 the standard CBOR way.
206 239
207 This option does not affect "decode" in any way - string references 240 This option does not affect "decode" in any way - string references
208 will always be decoded properly if present. 241 will always be decoded properly if present.
209 242
243 $cbor = $cbor->text_keys ([$enable])
244 $enabled = $cbor->get_text_keys
245 If $enabled is true (or missing), then "encode" will encode all perl
246 hash keys as CBOR text strings/UTF-8 string, upgrading them as
247 needed.
248
249 If $enable is false (the default), then "encode" will encode hash
250 keys normally - upgraded perl strings (strings internally encoded as
251 UTF-8) as CBOR text strings, and downgraded perl strings as CBOR
252 byte strings.
253
254 This option does not affect "decode" in any way.
255
256 This option is useful for interoperability with CBOR decoders that
257 don't treat byte strings as a form of text. It is especially useful
258 as Perl gives very little control over hash keys.
259
260 Enabling this option can be slow, as all downgraded hash keys that
261 are encoded need to be scanned and converted to UTF-8.
262
263 $cbor = $cbor->text_strings ([$enable])
264 $enabled = $cbor->get_text_strings
265 This option works similar to "text_keys", above, but works on all
266 strings (including hash keys), so "text_keys" has no further effect
267 after enabling "text_strings".
268
269 If $enabled is true (or missing), then "encode" will encode all perl
270 strings as CBOR text strings/UTF-8 strings, upgrading them as
271 needed.
272
273 If $enable is false (the default), then "encode" will encode strings
274 normally (but see "text_keys") - upgraded perl strings (strings
275 internally encoded as UTF-8) as CBOR text strings, and downgraded
276 perl strings as CBOR byte strings.
277
278 This option does not affect "decode" in any way.
279
280 This option has similar advantages and disadvantages as "text_keys".
281 In addition, this option effectively removes the ability to
282 automatically encode byte strings, which might break some "FREEZE"
283 and "TO_CBOR" methods that rely on this.
284
285 A workaround is to use explicit type casts, which are unaffected by
286 this option.
287
210 $cbor = $cbor->validate_utf8 ([$enable]) 288 $cbor = $cbor->validate_utf8 ([$enable])
211 $enabled = $cbor->get_validate_utf8 289 $enabled = $cbor->get_validate_utf8
212 If $enable is true (or missing), then "decode" will validate that 290 If $enable is true (or missing), then "decode" will validate that
213 elements (text strings) containing UTF-8 data in fact contain valid 291 elements (text strings) containing UTF-8 data in fact contain valid
214 UTF-8 data (instead of blindly accepting it). This validation 292 UTF-8 data (instead of blindly accepting it). This validation
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217 The concept of "valid UTF-8" used is perl's concept, which is a 295 The concept of "valid UTF-8" used is perl's concept, which is a
218 superset of the official UTF-8. 296 superset of the official UTF-8.
219 297
220 If $enable is false (the default), then "decode" will blindly accept 298 If $enable is false (the default), then "decode" will blindly accept
221 UTF-8 data, marking them as valid UTF-8 in the resulting data 299 UTF-8 data, marking them as valid UTF-8 in the resulting data
222 structure regardless of whether thats true or not. 300 structure regardless of whether that's true or not.
223 301
224 Perl isn't too happy about corrupted UTF-8 in strings, but should 302 Perl isn't too happy about corrupted UTF-8 in strings, but should
225 generally not crash or do similarly evil things. Extensions might be 303 generally not crash or do similarly evil things. Extensions might be
226 not so forgiving, so it's recommended to turn on this setting if you 304 not so forgiving, so it's recommended to turn on this setting if you
227 receive untrusted CBOR. 305 receive untrusted CBOR.
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254 When the filter is cleared (the default state), the default filter 332 When the filter is cleared (the default state), the default filter
255 function, "CBOR::XS::default_filter", is used. This function simply 333 function, "CBOR::XS::default_filter", is used. This function simply
256 looks up the tag in the %CBOR::XS::FILTER hash. If an entry exists 334 looks up the tag in the %CBOR::XS::FILTER hash. If an entry exists
257 it must be a code reference that is called with tag and value, and 335 it must be a code reference that is called with tag and value, and
258 is responsible for decoding the value. If no entry exists, it 336 is responsible for decoding the value. If no entry exists, it
259 returns no values. 337 returns no values. "CBOR::XS" provides a number of default filter
338 functions already, the the %CBOR::XS::FILTER hash can be freely
339 extended with more.
340
341 "CBOR::XS" additionally provides an alternative filter function that
342 is supposed to be safe to use with untrusted data (which the default
343 filter might not), called "CBOR::XS::safe_filter", which works the
344 same as the "default_filter" but uses the %CBOR::XS::SAFE_FILTER
345 variable instead. It is prepopulated with the tag decoding functions
346 that are deemed safe (basically the same as %CBOR::XS::FILTER
347 without all the bignum tags), and can be extended by user code as
348 wlel, although, obviously, one should be very careful about adding
349 decoding functions here, since the expectation is that they are safe
350 to use on untrusted data, after all.
260 351
261 Example: decode all tags not handled internally into 352 Example: decode all tags not handled internally into
262 "CBOR::XS::Tagged" objects, with no other special handling (useful 353 "CBOR::XS::Tagged" objects, with no other special handling (useful
263 when working with potentially "unsafe" CBOR data). 354 when working with potentially "unsafe" CBOR data).
264 355
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270 $CBOR::XS::FILTER{1347375694} = sub { 361 $CBOR::XS::FILTER{1347375694} = sub {
271 my ($tag, $value); 362 my ($tag, $value);
272 363
273 "tag 1347375694 value $value" 364 "tag 1347375694 value $value"
274 }; 365 };
366
367 Example: provide your own filter function that looks up tags in your
368 own hash:
369
370 my %my_filter = (
371 998347484 => sub {
372 my ($tag, $value);
373
374 "tag 998347484 value $value"
375 };
376 );
377
378 my $coder = CBOR::XS->new->filter (sub {
379 &{ $my_filter{$_[0]} or return }
380 });
381
382 Example: use the safe filter function (see "SECURITY CONSIDERATIONS"
383 for more considerations on security).
384
385 CBOR::XS->new->filter (\&CBOR::XS::safe_filter)->decode ($cbor_data);
275 386
276 $cbor_data = $cbor->encode ($perl_scalar) 387 $cbor_data = $cbor->encode ($perl_scalar)
277 Converts the given Perl data structure (a scalar value) to its CBOR 388 Converts the given Perl data structure (a scalar value) to its CBOR
278 representation. 389 representation.
279 390
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287 will silently stop parsing there and return the number of characters 398 will silently stop parsing there and return the number of characters
288 consumed so far. 399 consumed so far.
289 400
290 This is useful if your CBOR texts are not delimited by an outer 401 This is useful if your CBOR texts are not delimited by an outer
291 protocol and you need to know where the first CBOR string ends amd 402 protocol and you need to know where the first CBOR string ends amd
292 the next one starts. 403 the next one starts - CBOR strings are self-delimited, so it is
404 possible to concatenate CBOR strings without any delimiters or size
405 fields and recover their data.
293 406
294 CBOR::XS->new->decode_prefix ("......") 407 CBOR::XS->new->decode_prefix ("......")
295 => ("...", 3) 408 => ("...", 3)
296 409
297 INCREMENTAL PARSING 410 INCREMENTAL PARSING
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346 $cbor->incr_reset 459 $cbor->incr_reset
347 Resets the incremental decoder. This throws away any saved state, so 460 Resets the incremental decoder. This throws away any saved state, so
348 that subsequent calls to "incr_parse" or "incr_parse_multiple" start 461 that subsequent calls to "incr_parse" or "incr_parse_multiple" start
349 to parse a new CBOR value from the beginning of the $buffer again. 462 to parse a new CBOR value from the beginning of the $buffer again.
350 463
351 This method can be caled at any time, but it *must* be called if you 464 This method can be called at any time, but it *must* be called if
352 want to change your $buffer or there was a decoding error and you 465 you want to change your $buffer or there was a decoding error and
353 want to reuse the $cbor object for future incremental parsings. 466 you want to reuse the $cbor object for future incremental parsings.
354 467
355MAPPING 468MAPPING
356 This section describes how CBOR::XS maps Perl values to CBOR values and 469 This section describes how CBOR::XS maps Perl values to CBOR values and
357 vice versa. These mappings are designed to "do the right thing" in most 470 vice versa. These mappings are designed to "do the right thing" in most
358 circumstances automatically, preserving round-tripping characteristics 471 circumstances automatically, preserving round-tripping characteristics
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409 522
410 hash references 523 hash references
411 Perl hash references become CBOR maps. As there is no inherent 524 Perl hash references become CBOR maps. As there is no inherent
412 ordering in hash keys (or CBOR maps), they will usually be encoded 525 ordering in hash keys (or CBOR maps), they will usually be encoded
413 in a pseudo-random order. This order can be different each time a 526 in a pseudo-random order. This order can be different each time a
414 hahs is encoded. 527 hash is encoded.
415 528
416 Currently, tied hashes will use the indefinite-length format, while 529 Currently, tied hashes will use the indefinite-length format, while
417 normal hashes will use the fixed-length format. 530 normal hashes will use the fixed-length format.
418 531
419 array references 532 array references
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468 my $x = 3.1; # some variable containing a number 581 my $x = 3.1; # some variable containing a number
469 "$x"; # stringified 582 "$x"; # stringified
470 $x .= ""; # another, more awkward way to stringify 583 $x .= ""; # another, more awkward way to stringify
471 print $x; # perl does it for you, too, quite often 584 print $x; # perl does it for you, too, quite often
472 585
473 You can force whether a string ie encoded as byte or text string by 586 You can force whether a string is encoded as byte or text string by
474 using "utf8::upgrade" and "utf8::downgrade"): 587 using "utf8::upgrade" and "utf8::downgrade" (if "text_strings" is
588 disabled).
475 589
476 utf8::upgrade $x; # encode $x as text string 590 utf8::upgrade $x; # encode $x as text string
477 utf8::downgrade $x; # encode $x as byte string 591 utf8::downgrade $x; # encode $x as byte string
478 592
593 More options are available, see "TYPE CASTS", below, and the
594 "text_keys" and "text_strings" options.
595
479 Perl doesn't define what operations up- and downgrade strings, so if 596 Perl doesn't define what operations up- and downgrade strings, so if
480 the difference between byte and text is important, you should up- or 597 the difference between byte and text is important, you should up- or
481 downgrade your string as late as possible before encoding. 598 downgrade your string as late as possible before encoding. You can
599 also force the use of CBOR text strings by using "text_keys" or
600 "text_strings".
482 601
483 You can force the type to be a CBOR number by numifying it: 602 You can force the type to be a CBOR number by numifying it:
484 603
485 my $x = "3"; # some variable containing a string 604 my $x = "3"; # some variable containing a string
486 $x += 0; # numify it, ensuring it will be dumped as a number 605 $x += 0; # numify it, ensuring it will be dumped as a number
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495 IEEE single format if possible without loss of precision, otherwise 614 IEEE single format if possible without loss of precision, otherwise
496 the IEEE double format will be used. Perls that use formats other 615 the IEEE double format will be used. Perls that use formats other
497 than IEEE double to represent numerical values are supported, but 616 than IEEE double to represent numerical values are supported, but
498 might suffer loss of precision. 617 might suffer loss of precision.
499 618
619 TYPE CASTS
620 EXPERIMENTAL: As an experimental extension, "CBOR::XS" allows you to
621 force specific cbor types to be used when encoding. That allows you to
622 encode types not normally accessible (e.g. half floats) as well as force
623 string types even when "text_strings" is in effect.
624
625 Type forcing is done by calling a special "cast" function which keeps a
626 copy of the value and returns a new value that can be handed over to any
627 CBOR encoder function.
628
629 The following casts are currently available (all of which are unary
630 operators):
631
632 CBOR::XS::as_int $value
633 Forces the value to be encoded as some form of (basic, not bignum)
634 integer type.
635
636 CBOR::XS::as_text $value
637 Forces the value to be encoded as (UTF-8) text values.
638
639 CBOR::XS::as_bytes $value
640 Forces the value to be encoded as a (binary) string value.
641
642 Example: encode a perl string as binary even though "text_strings"
643 is in effect.
644
645 CBOR::XS->new->text_strings->encode ([4, "text", CBOR::XS::bytes "bytevalue"]);
646
647 CBOR::XS::as_bool $value
648 Converts a Perl boolean (which can be any kind of scalar) into a
649 CBOR boolean. Strictly the same, but shorter to write, than:
650
651 $value ? Types::Serialiser::true : Types::Serialiser::false
652
653 CBOR::XS::as_float16 $value
654 Forces half-float (IEEE 754 binary16) encoding of the given value.
655
656 CBOR::XS::as_float32 $value
657 Forces single-float (IEEE 754 binary32) encoding of the given value.
658
659 CBOR::XS::as_float64 $value
660 Forces double-float (IEEE 754 binary64) encoding of the given value.
661
662 CBOR::XS::as_cbor $cbor_text
663 Not a type cast per-se, this type cast forces the argument to eb
664 encoded as-is. This can be used to embed pre-encoded CBOR data.
665
666 Note that no checking on the validity of the $cbor_text is done -
667 it's the callers responsibility to correctly encode values.
668
669 CBOR::XS::as_map [key => value...]
670 Treat the array reference as key value pairs and output a CBOR map.
671 This allows you to generate CBOR maps with arbitrary key types (or,
672 if you don't care about semantics, duplicate keys or prairs in a
673 custom order), which is otherwise hard to do with Perl.
674
675 The single argument must be an array reference with an even number
676 of elements.
677
678 Example: encode a CBOR map with a string and an integer as keys.
679
680 encode_cbor CBOR::XS::as_map [string => "value", 5 => "value"]
681
500 OBJECT SERIALISATION 682 OBJECT SERIALISATION
501 This module implements both a CBOR-specific and the generic 683 This module implements both a CBOR-specific and the generic
502 Types::Serialier object serialisation protocol. The following 684 Types::Serialier object serialisation protocol. The following
503 subsections explain both methods. 685 subsections explain both methods.
504 686
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581 "$self" # encode url string 763 "$self" # encode url string
582 } 764 }
583 765
584 sub URI::THAW { 766 sub URI::THAW {
585 my ($class, $serialiser, $uri) = @_; 767 my ($class, $serialiser, $uri) = @_;
586
587 $class->new ($uri) 768 $class->new ($uri)
588 } 769 }
589 770
590 Unlike "TO_CBOR", multiple values can be returned by "FREEZE". For 771 Unlike "TO_CBOR", multiple values can be returned by "FREEZE". For
591 example, a "FREEZE" method that returns "type", "id" and "variant" 772 example, a "FREEZE" method that returns "type", "id" and "variant"
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687 Future versions of this module reserve the right to special case 868 Future versions of this module reserve the right to special case
688 additional tags (such as base64url). 869 additional tags (such as base64url).
689 870
690 ENFORCED TAGS 871 ENFORCED TAGS
691 These tags are always handled when decoding, and their handling cannot 872 These tags are always handled when decoding, and their handling cannot
692 be overriden by the user. 873 be overridden by the user.
693 874
694 26 (perl-object, <http://cbor.schmorp.de/perl-object>) 875 26 (perl-object, <http://cbor.schmorp.de/perl-object>)
695 These tags are automatically created (and decoded) for serialisable 876 These tags are automatically created (and decoded) for serialisable
696 objects using the "FREEZE/THAW" methods (the Types::Serialier object 877 objects using the "FREEZE/THAW" methods (the Types::Serialier object
697 serialisation protocol). See "OBJECT SERIALISATION" for details. 878 serialisation protocol). See "OBJECT SERIALISATION" for details.
698 879
699 28, 29 (shareable, sharedref, L <http://cbor.schmorp.de/value-sharing>) 880 28, 29 (shareable, sharedref, <http://cbor.schmorp.de/value-sharing>)
700 These tags are automatically decoded when encountered (and they do 881 These tags are automatically decoded when encountered (and they do
701 not result in a cyclic data structure, see "allow_cycles"), 882 not result in a cyclic data structure, see "allow_cycles"),
702 resulting in shared values in the decoded object. They are only 883 resulting in shared values in the decoded object. They are only
703 encoded, however, when "allow_sharing" is enabled. 884 encoded, however, when "allow_sharing" is enabled.
704 885
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713 references will be shared, others will not. While non-reference 894 references will be shared, others will not. While non-reference
714 shared values can be generated in Perl with some effort, they were 895 shared values can be generated in Perl with some effort, they were
715 considered too unimportant to be supported in the encoder. The 896 considered too unimportant to be supported in the encoder. The
716 decoder, however, will decode these values as shared values. 897 decoder, however, will decode these values as shared values.
717 898
718 256, 25 (stringref-namespace, stringref, L 899 256, 25 (stringref-namespace, stringref,
719 <http://cbor.schmorp.de/stringref>) 900 <http://cbor.schmorp.de/stringref>)
720 These tags are automatically decoded when encountered. They are only 901 These tags are automatically decoded when encountered. They are only
721 encoded, however, when "pack_strings" is enabled. 902 encoded, however, when "pack_strings" is enabled.
722 903
723 22098 (indirection, <http://cbor.schmorp.de/indirection>) 904 22098 (indirection, <http://cbor.schmorp.de/indirection>)
724 This tag is automatically generated when a reference are encountered 905 This tag is automatically generated when a reference are encountered
725 (with the exception of hash and array refernces). It is converted to 906 (with the exception of hash and array references). It is converted
726 a reference when decoding. 907 to a reference when decoding.
727 908
728 55799 (self-describe CBOR, RFC 7049) 909 55799 (self-describe CBOR, RFC 7049)
729 This value is not generated on encoding (unless explicitly requested 910 This value is not generated on encoding (unless explicitly requested
730 by the user), and is simply ignored when decoding. 911 by the user), and is simply ignored when decoding.
731 912
732 NON-ENFORCED TAGS 913 NON-ENFORCED TAGS
733 These tags have default filters provided when decoding. Their handling 914 These tags have default filters provided when decoding. Their handling
734 can be overriden by changing the %CBOR::XS::FILTER entry for the tag, or 915 can be overridden by changing the %CBOR::XS::FILTER entry for the tag,
735 by providing a custom "filter" callback when decoding. 916 or by providing a custom "filter" callback when decoding.
736 917
737 When they result in decoding into a specific Perl class, the module 918 When they result in decoding into a specific Perl class, the module
738 usually provides a corresponding "TO_CBOR" method as well. 919 usually provides a corresponding "TO_CBOR" method as well.
739 920
740 When any of these need to load additional modules that are not part of 921 When any of these need to load additional modules that are not part of
… …
755 2, 3 (positive/negative bignum) 936 2, 3 (positive/negative bignum)
756 These tags are decoded into Math::BigInt objects. The corresponding 937 These tags are decoded into Math::BigInt objects. The corresponding
757 "Math::BigInt::TO_CBOR" method encodes "small" bigints into normal 938 "Math::BigInt::TO_CBOR" method encodes "small" bigints into normal
758 CBOR integers, and others into positive/negative CBOR bignums. 939 CBOR integers, and others into positive/negative CBOR bignums.
759 940
760 4, 5 (decimal fraction/bigfloat) 941 4, 5, 264, 265 (decimal fraction/bigfloat)
761 Both decimal fractions and bigfloats are decoded into Math::BigFloat 942 Both decimal fractions and bigfloats are decoded into Math::BigFloat
762 objects. The corresponding "Math::BigFloat::TO_CBOR" method *always* 943 objects. The corresponding "Math::BigFloat::TO_CBOR" method *always*
763 encodes into a decimal fraction. 944 encodes into a decimal fraction (either tag 4 or 264).
764 945
765 CBOR cannot represent bigfloats with *very* large exponents -
766 conversion of such big float objects is undefined.
767
768 Also, NaN and infinities are not encoded properly. 946 NaN and infinities are not encoded properly, as they cannot be
947 represented in CBOR.
948
949 See "BIGNUM SECURITY CONSIDERATIONS" for more info.
950
951 30 (rational numbers)
952 These tags are decoded into Math::BigRat objects. The corresponding
953 "Math::BigRat::TO_CBOR" method encodes rational numbers with
954 denominator 1 via their numerator only, i.e., they become normal
955 integers or "bignums".
956
957 See "BIGNUM SECURITY CONSIDERATIONS" for more info.
769 958
770 21, 22, 23 (expected later JSON conversion) 959 21, 22, 23 (expected later JSON conversion)
771 CBOR::XS is not a CBOR-to-JSON converter, and will simply ignore 960 CBOR::XS is not a CBOR-to-JSON converter, and will simply ignore
772 these tags. 961 these tags.
773 962
… …
787 interoperability is improved in the future, then the goal will be to 976 interoperability is improved in the future, then the goal will be to
788 ensure that decoded JSON data will round-trip encoding and decoding to 977 ensure that decoded JSON data will round-trip encoding and decoding to
789 CBOR intact. 978 CBOR intact.
790 979
791SECURITY CONSIDERATIONS 980SECURITY CONSIDERATIONS
792 When you are using CBOR in a protocol, talking to untrusted potentially 981 Tl;dr... if you want to decode or encode CBOR from untrusted sources,
793 hostile creatures requires relatively few measures. 982 you should start with a coder object created via "new_safe" (which
983 implements the mitigations explained below):
794 984
985 my $coder = CBOR::XS->new_safe;
986
987 my $data = $coder->decode ($cbor_text);
988 my $cbor = $coder->encode ($data);
989
990 Longer version: When you are using CBOR in a protocol, talking to
991 untrusted potentially hostile creatures requires some thought:
992
993 Security of the CBOR decoder itself
795 First of all, your CBOR decoder should be secure, that is, should not 994 First and foremost, your CBOR decoder should be secure, that is,
796 have any buffer overflows. Obviously, this module should ensure that and 995 should not have any buffer overflows or similar bugs that could
996 potentially be exploited. Obviously, this module should ensure that
797 I am trying hard on making that true, but you never know. 997 and I am trying hard on making that true, but you never know.
798 998
999 CBOR::XS can invoke almost arbitrary callbacks during decoding
1000 CBOR::XS supports object serialisation - decoding CBOR can cause
1001 calls to *any* "THAW" method in *any* package that exists in your
1002 process (that is, CBOR::XS will not try to load modules, but any
1003 existing "THAW" method or function can be called, so they all have
1004 to be secure).
1005
1006 Less obviously, it will also invoke "TO_CBOR" and "FREEZE" methods -
1007 even if all your "THAW" methods are secure, encoding data structures
1008 from untrusted sources can invoke those and trigger bugs in those.
1009
1010 So, if you are not sure about the security of all the modules you
1011 have loaded (you shouldn't), you should disable this part using
1012 "forbid_objects" or using "new_safe".
1013
1014 CBOR can be extended with tags that call library code
1015 CBOR can be extended with tags, and "CBOR::XS" has a registry of
1016 conversion functions for many existing tags that can be extended via
1017 third-party modules (see the "filter" method).
1018
1019 If you don't trust these, you should configure the "safe" filter
1020 function, "CBOR::XS::safe_filter" ("new_safe" does this), which by
1021 default only includes conversion functions that are considered
1022 "safe" by the author (but again, they can be extended by third party
1023 modules).
1024
1025 Depending on your level of paranoia, you can use the "safe" filter:
1026
1027 $cbor->filter (\&CBOR::XS::safe_filter);
1028
1029 ... your own filter...
1030
1031 $cbor->filter (sub { ... do your stuffs here ... });
1032
1033 ... or even no filter at all, disabling all tag decoding:
1034
1035 $cbor->filter (sub { });
1036
1037 This is never a problem for encoding, as the tag mechanism only
1038 exists in CBOR texts.
1039
1040 Resource-starving attacks: object memory usage
799 Second, you need to avoid resource-starving attacks. That means you 1041 You need to avoid resource-starving attacks. That means you should
800 should limit the size of CBOR data you accept, or make sure then when 1042 limit the size of CBOR data you accept, or make sure then when your
801 your resources run out, that's just fine (e.g. by using a separate 1043 resources run out, that's just fine (e.g. by using a separate
802 process that can crash safely). The size of a CBOR string in octets is 1044 process that can crash safely). The size of a CBOR string in octets
803 usually a good indication of the size of the resources required to 1045 is usually a good indication of the size of the resources required
804 decode it into a Perl structure. While CBOR::XS can check the size of 1046 to decode it into a Perl structure. While CBOR::XS can check the
1047 size of the CBOR text (using "max_size" - done by "new_safe"), it
805 the CBOR text, it might be too late when you already have it in memory, 1048 might be too late when you already have it in memory, so you might
806 so you might want to check the size before you accept the string. 1049 want to check the size before you accept the string.
807 1050
1051 As for encoding, it is possible to construct data structures that
1052 are relatively small but result in large CBOR texts (for example by
1053 having an array full of references to the same big data structure,
1054 which will all be deep-cloned during encoding by default). This is
1055 rarely an actual issue (and the worst case is still just running out
1056 of memory), but you can reduce this risk by using "allow_sharing".
1057
1058 Resource-starving attacks: stack overflows
808 Third, CBOR::XS recurses using the C stack when decoding objects and 1059 CBOR::XS recurses using the C stack when decoding objects and
809 arrays. The C stack is a limited resource: for instance, on my amd64 1060 arrays. The C stack is a limited resource: for instance, on my amd64
810 machine with 8MB of stack size I can decode around 180k nested arrays 1061 machine with 8MB of stack size I can decode around 180k nested
811 but only 14k nested CBOR objects (due to perl itself recursing deeply on 1062 arrays but only 14k nested CBOR objects (due to perl itself
812 croak to free the temporary). If that is exceeded, the program crashes. 1063 recursing deeply on croak to free the temporary). If that is
813 To be conservative, the default nesting limit is set to 512. If your 1064 exceeded, the program crashes. To be conservative, the default
814 process has a smaller stack, you should adjust this setting accordingly 1065 nesting limit is set to 512. If your process has a smaller stack,
815 with the "max_depth" method. 1066 you should adjust this setting accordingly with the "max_depth"
1067 method.
816 1068
1069 Resource-starving attacks: CPU en-/decoding complexity
1070 CBOR::XS will use the Math::BigInt, Math::BigFloat and Math::BigRat
1071 libraries to represent encode/decode bignums. These can be very slow
1072 (as in, centuries of CPU time) and can even crash your program (and
1073 are generally not very trustworthy). See the next section on bignum
1074 security for details.
1075
1076 Data breaches: leaking information in error messages
1077 CBOR::XS might leak contents of your Perl data structures in its
1078 error messages, so when you serialise sensitive information you
1079 might want to make sure that exceptions thrown by CBOR::XS will not
1080 end up in front of untrusted eyes.
1081
1082 Something else...
817 Something else could bomb you, too, that I forgot to think of. In that 1083 Something else could bomb you, too, that I forgot to think of. In
818 case, you get to keep the pieces. I am always open for hints, though... 1084 that case, you get to keep the pieces. I am always open for hints,
1085 though...
819 1086
820 Also keep in mind that CBOR::XS might leak contents of your Perl data 1087BIGNUM SECURITY CONSIDERATIONS
821 structures in its error messages, so when you serialise sensitive 1088 CBOR::XS provides a "TO_CBOR" method for both Math::BigInt and
822 information you might want to make sure that exceptions thrown by 1089 Math::BigFloat that tries to encode the number in the simplest possible
823 CBOR::XS will not end up in front of untrusted eyes. 1090 way, that is, either a CBOR integer, a CBOR bigint/decimal fraction (tag
1091 4) or an arbitrary-exponent decimal fraction (tag 264). Rational numbers
1092 (Math::BigRat, tag 30) can also contain bignums as members.
1093
1094 CBOR::XS will also understand base-2 bigfloat or arbitrary-exponent
1095 bigfloats (tags 5 and 265), but it will never generate these on its own.
1096
1097 Using the built-in Math::BigInt::Calc support, encoding and decoding
1098 decimal fractions is generally fast. Decoding bigints can be slow for
1099 very big numbers (tens of thousands of digits, something that could
1100 potentially be caught by limiting the size of CBOR texts), and decoding
1101 bigfloats or arbitrary-exponent bigfloats can be *extremely* slow
1102 (minutes, decades) for large exponents (roughly 40 bit and longer).
1103
1104 Additionally, Math::BigInt can take advantage of other bignum libraries,
1105 such as Math::GMP, which cannot handle big floats with large exponents,
1106 and might simply abort or crash your program, due to their code quality.
1107
1108 This can be a concern if you want to parse untrusted CBOR. If it is, you
1109 might want to disable decoding of tag 2 (bigint) and 3 (negative bigint)
1110 types. You should also disable types 5 and 265, as these can be slow
1111 even without bigints.
1112
1113 Disabling bigints will also partially or fully disable types that rely
1114 on them, e.g. rational numbers that use bignums.
824 1115
825CBOR IMPLEMENTATION NOTES 1116CBOR IMPLEMENTATION NOTES
826 This section contains some random implementation notes. They do not 1117 This section contains some random implementation notes. They do not
827 describe guaranteed behaviour, but merely behaviour as-is implemented 1118 describe guaranteed behaviour, but merely behaviour as-is implemented
828 right now. 1119 right now.
… …
841 1132
842LIMITATIONS ON PERLS WITHOUT 64-BIT INTEGER SUPPORT 1133LIMITATIONS ON PERLS WITHOUT 64-BIT INTEGER SUPPORT
843 On perls that were built without 64 bit integer support (these are rare 1134 On perls that were built without 64 bit integer support (these are rare
844 nowadays, even on 32 bit architectures, as all major Perl distributions 1135 nowadays, even on 32 bit architectures, as all major Perl distributions
845 are built with 64 bit integer support), support for any kind of 64 bit 1136 are built with 64 bit integer support), support for any kind of 64 bit
846 integer in CBOR is very limited - most likely, these 64 bit values will 1137 value in CBOR is very limited - most likely, these 64 bit values will be
847 be truncated, corrupted, or otherwise not decoded correctly. This also 1138 truncated, corrupted, or otherwise not decoded correctly. This also
848 includes string, array and map sizes that are stored as 64 bit integers. 1139 includes string, float, array and map sizes that are stored as 64 bit
1140 integers.
849 1141
850THREADS 1142THREADS
851 This module is *not* guaranteed to be thread safe and there are no plans 1143 This module is *not* guaranteed to be thread safe and there are no plans
852 to change this until Perl gets thread support (as opposed to the 1144 to change this until Perl gets thread support (as opposed to the
853 horribly slow so-called "threads" which are simply slow and bloated 1145 horribly slow so-called "threads" which are simply slow and bloated

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