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Revision 1.22 by root, Thu Oct 21 01:14:58 2021 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 ->validate_utf8
92 ->forbid_objects
93 ->filter (\&CBOR::XS::safe_filter)
94 ->max_size (1e8);
95
96 But is more future proof (it is better to crash because of a change
97 than to be exploited in other ways).
83 98
84 $cbor = $cbor->max_depth ([$maximum_nesting_depth]) 99 $cbor = $cbor->max_depth ([$maximum_nesting_depth])
85 $max_depth = $cbor->get_max_depth 100 $max_depth = $cbor->get_max_depth
86 Sets the maximum nesting level (default 512) accepted while encoding 101 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 102 or decoding. If a higher nesting level is detected in CBOR data or a
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101 116
102 Note that nesting is implemented by recursion in C. The default 117 Note that nesting is implemented by recursion in C. The default
103 value has been chosen to be as large as typical operating systems 118 value has been chosen to be as large as typical operating systems
104 allow without crashing. 119 allow without crashing.
105 120
106 See SECURITY CONSIDERATIONS, below, for more info on why this is 121 See "SECURITY CONSIDERATIONS", below, for more info on why this is
107 useful. 122 useful.
108 123
109 $cbor = $cbor->max_size ([$maximum_string_size]) 124 $cbor = $cbor->max_size ([$maximum_string_size])
110 $max_size = $cbor->get_max_size 125 $max_size = $cbor->get_max_size
111 Set the maximum length a CBOR string may have (in bytes) where 126 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). 130 exception. This setting has no effect on "encode" (yet).
116 131
117 If no argument is given, the limit check will be deactivated (same 132 If no argument is given, the limit check will be deactivated (same
118 as when 0 is specified). 133 as when 0 is specified).
119 134
120 See SECURITY CONSIDERATIONS, below, for more info on why this is 135 See "SECURITY CONSIDERATIONS", below, for more info on why this is
121 useful. 136 useful.
122 137
123 $cbor = $cbor->allow_unknown ([$enable]) 138 $cbor = $cbor->allow_unknown ([$enable])
124 $enabled = $cbor->get_allow_unknown 139 $enabled = $cbor->get_allow_unknown
125 If $enable is true (or missing), then "encode" will *not* throw an 140 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. 156 instead will emit a reference to the earlier value.
142 157
143 This means that such values will only be encoded once, and will not 158 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 159 result in a deep cloning of the value on decode, in decoders
145 supporting the value sharing extension. This also makes it possible 160 supporting the value sharing extension. This also makes it possible
146 to encode cyclic data structures (which need "allow_cycles" to ne 161 to encode cyclic data structures (which need "allow_cycles" to be
147 enabled to be decoded by this module). 162 enabled to be decoded by this module).
148 163
149 It is recommended to leave it off unless you know your communication 164 It is recommended to leave it off unless you know your communication
150 partner supports the value sharing extensions to CBOR 165 partner supports the value sharing extensions to CBOR
151 (<http://cbor.schmorp.de/value-sharing>), as without decoder 166 (<http://cbor.schmorp.de/value-sharing>), as without decoder
152 support, the resulting data structure might be unusable. 167 support, the resulting data structure might be unusable.
153 168
154 Detecting shared values incurs a runtime overhead when values are 169 Detecting shared values incurs a runtime overhead when values are
155 encoded that have a reference counter large than one, and might 170 encoded that have a reference counter large than one, and might
156 unnecessarily increase the encoded size, as potentially shared 171 unnecessarily increase the encoded size, as potentially shared
157 values are encode as shareable whether or not they are actually 172 values are encoded as shareable whether or not they are actually
158 shared. 173 shared.
159 174
160 At the moment, only targets of references can be shared (e.g. 175 At the moment, only targets of references can be shared (e.g.
161 scalars, arrays or hashes pointed to by a reference). Weirder 176 scalars, arrays or hashes pointed to by a reference). Weirder
162 constructs, such as an array with multiple "copies" of the *same* 177 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 200 cyclic data structures using weak references when this option is
186 off, instead of throwing an error. 201 off, instead of throwing an error.
187 202
188 This option does not affect "encode" in any way - shared values and 203 This option does not affect "encode" in any way - shared values and
189 references will always be encoded properly if present. 204 references will always be encoded properly if present.
205
206 $cbor = $cbor->forbid_objects ([$enable])
207 $enabled = $cbor->get_forbid_objects
208 Disables the use of the object serialiser protocol.
209
210 If $enable is true (or missing), then "encode" will will throw an
211 exception when it encounters perl objects that would be encoded
212 using the perl-object tag (26). When "decode" encounters such tags,
213 it will fall back to the general filter/tagged logic as if this were
214 an unknown tag (by default resulting in a "CBOR::XC::Tagged"
215 object).
216
217 If $enable is false (the default), then "encode" will use the
218 Types::Serialiser object serialisation protocol to serialise objects
219 into perl-object tags, and "decode" will do the same to decode such
220 tags.
221
222 See "SECURITY CONSIDERATIONS", below, for more info on why
223 forbidding this protocol can be useful.
190 224
191 $cbor = $cbor->pack_strings ([$enable]) 225 $cbor = $cbor->pack_strings ([$enable])
192 $enabled = $cbor->get_pack_strings 226 $enabled = $cbor->get_pack_strings
193 If $enable is true (or missing), then "encode" will try not to 227 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 228 encode the same string twice, but will instead encode a reference to
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205 the standard CBOR way. 239 the standard CBOR way.
206 240
207 This option does not affect "decode" in any way - string references 241 This option does not affect "decode" in any way - string references
208 will always be decoded properly if present. 242 will always be decoded properly if present.
209 243
244 $cbor = $cbor->text_keys ([$enable])
245 $enabled = $cbor->get_text_keys
246 If $enabled is true (or missing), then "encode" will encode all perl
247 hash keys as CBOR text strings/UTF-8 string, upgrading them as
248 needed.
249
250 If $enable is false (the default), then "encode" will encode hash
251 keys normally - upgraded perl strings (strings internally encoded as
252 UTF-8) as CBOR text strings, and downgraded perl strings as CBOR
253 byte strings.
254
255 This option does not affect "decode" in any way.
256
257 This option is useful for interoperability with CBOR decoders that
258 don't treat byte strings as a form of text. It is especially useful
259 as Perl gives very little control over hash keys.
260
261 Enabling this option can be slow, as all downgraded hash keys that
262 are encoded need to be scanned and converted to UTF-8.
263
264 $cbor = $cbor->text_strings ([$enable])
265 $enabled = $cbor->get_text_strings
266 This option works similar to "text_keys", above, but works on all
267 strings (including hash keys), so "text_keys" has no further effect
268 after enabling "text_strings".
269
270 If $enabled is true (or missing), then "encode" will encode all perl
271 strings as CBOR text strings/UTF-8 strings, upgrading them as
272 needed.
273
274 If $enable is false (the default), then "encode" will encode strings
275 normally (but see "text_keys") - upgraded perl strings (strings
276 internally encoded as UTF-8) as CBOR text strings, and downgraded
277 perl strings as CBOR byte strings.
278
279 This option does not affect "decode" in any way.
280
281 This option has similar advantages and disadvantages as "text_keys".
282 In addition, this option effectively removes the ability to
283 automatically encode byte strings, which might break some "FREEZE"
284 and "TO_CBOR" methods that rely on this.
285
286 A workaround is to use explicit type casts, which are unaffected by
287 this option.
288
210 $cbor = $cbor->validate_utf8 ([$enable]) 289 $cbor = $cbor->validate_utf8 ([$enable])
211 $enabled = $cbor->get_validate_utf8 290 $enabled = $cbor->get_validate_utf8
212 If $enable is true (or missing), then "decode" will validate that 291 If $enable is true (or missing), then "decode" will validate that
213 elements (text strings) containing UTF-8 data in fact contain valid 292 elements (text strings) containing UTF-8 data in fact contain valid
214 UTF-8 data (instead of blindly accepting it). This validation 293 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 296 The concept of "valid UTF-8" used is perl's concept, which is a
218 superset of the official UTF-8. 297 superset of the official UTF-8.
219 298
220 If $enable is false (the default), then "decode" will blindly accept 299 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 300 UTF-8 data, marking them as valid UTF-8 in the resulting data
222 structure regardless of whether thats true or not. 301 structure regardless of whether that's true or not.
223 302
224 Perl isn't too happy about corrupted UTF-8 in strings, but should 303 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 304 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 305 not so forgiving, so it's recommended to turn on this setting if you
227 receive untrusted CBOR. 306 receive untrusted CBOR.
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254 When the filter is cleared (the default state), the default filter 333 When the filter is cleared (the default state), the default filter
255 function, "CBOR::XS::default_filter", is used. This function simply 334 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 335 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 336 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 337 is responsible for decoding the value. If no entry exists, it
259 returns no values. 338 returns no values. "CBOR::XS" provides a number of default filter
339 functions already, the the %CBOR::XS::FILTER hash can be freely
340 extended with more.
341
342 "CBOR::XS" additionally provides an alternative filter function that
343 is supposed to be safe to use with untrusted data (which the default
344 filter might not), called "CBOR::XS::safe_filter", which works the
345 same as the "default_filter" but uses the %CBOR::XS::SAFE_FILTER
346 variable instead. It is prepopulated with the tag decoding functions
347 that are deemed safe (basically the same as %CBOR::XS::FILTER
348 without all the bignum tags), and can be extended by user code as
349 wlel, although, obviously, one should be very careful about adding
350 decoding functions here, since the expectation is that they are safe
351 to use on untrusted data, after all.
260 352
261 Example: decode all tags not handled internally into 353 Example: decode all tags not handled internally into
262 "CBOR::XS::Tagged" objects, with no other special handling (useful 354 "CBOR::XS::Tagged" objects, with no other special handling (useful
263 when working with potentially "unsafe" CBOR data). 355 when working with potentially "unsafe" CBOR data).
264 356
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270 $CBOR::XS::FILTER{1347375694} = sub { 362 $CBOR::XS::FILTER{1347375694} = sub {
271 my ($tag, $value); 363 my ($tag, $value);
272 364
273 "tag 1347375694 value $value" 365 "tag 1347375694 value $value"
274 }; 366 };
367
368 Example: provide your own filter function that looks up tags in your
369 own hash:
370
371 my %my_filter = (
372 998347484 => sub {
373 my ($tag, $value);
374
375 "tag 998347484 value $value"
376 };
377 );
378
379 my $coder = CBOR::XS->new->filter (sub {
380 &{ $my_filter{$_[0]} or return }
381 });
382
383 Example: use the safe filter function (see "SECURITY CONSIDERATIONS"
384 for more considerations on security).
385
386 CBOR::XS->new->filter (\&CBOR::XS::safe_filter)->decode ($cbor_data);
275 387
276 $cbor_data = $cbor->encode ($perl_scalar) 388 $cbor_data = $cbor->encode ($perl_scalar)
277 Converts the given Perl data structure (a scalar value) to its CBOR 389 Converts the given Perl data structure (a scalar value) to its CBOR
278 representation. 390 representation.
279 391
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287 will silently stop parsing there and return the number of characters 399 will silently stop parsing there and return the number of characters
288 consumed so far. 400 consumed so far.
289 401
290 This is useful if your CBOR texts are not delimited by an outer 402 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 403 protocol and you need to know where the first CBOR string ends amd
292 the next one starts. 404 the next one starts - CBOR strings are self-delimited, so it is
405 possible to concatenate CBOR strings without any delimiters or size
406 fields and recover their data.
293 407
294 CBOR::XS->new->decode_prefix ("......") 408 CBOR::XS->new->decode_prefix ("......")
295 => ("...", 3) 409 => ("...", 3)
296 410
297 INCREMENTAL PARSING 411 INCREMENTAL PARSING
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346 $cbor->incr_reset 460 $cbor->incr_reset
347 Resets the incremental decoder. This throws away any saved state, so 461 Resets the incremental decoder. This throws away any saved state, so
348 that subsequent calls to "incr_parse" or "incr_parse_multiple" start 462 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. 463 to parse a new CBOR value from the beginning of the $buffer again.
350 464
351 This method can be caled at any time, but it *must* be called if you 465 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 466 you want to change your $buffer or there was a decoding error and
353 want to reuse the $cbor object for future incremental parsings. 467 you want to reuse the $cbor object for future incremental parsings.
354 468
355MAPPING 469MAPPING
356 This section describes how CBOR::XS maps Perl values to CBOR values and 470 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 471 vice versa. These mappings are designed to "do the right thing" in most
358 circumstances automatically, preserving round-tripping characteristics 472 circumstances automatically, preserving round-tripping characteristics
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409 523
410 hash references 524 hash references
411 Perl hash references become CBOR maps. As there is no inherent 525 Perl hash references become CBOR maps. As there is no inherent
412 ordering in hash keys (or CBOR maps), they will usually be encoded 526 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 527 in a pseudo-random order. This order can be different each time a
414 hahs is encoded. 528 hash is encoded.
415 529
416 Currently, tied hashes will use the indefinite-length format, while 530 Currently, tied hashes will use the indefinite-length format, while
417 normal hashes will use the fixed-length format. 531 normal hashes will use the fixed-length format.
418 532
419 array references 533 array references
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468 my $x = 3.1; # some variable containing a number 582 my $x = 3.1; # some variable containing a number
469 "$x"; # stringified 583 "$x"; # stringified
470 $x .= ""; # another, more awkward way to stringify 584 $x .= ""; # another, more awkward way to stringify
471 print $x; # perl does it for you, too, quite often 585 print $x; # perl does it for you, too, quite often
472 586
473 You can force whether a string ie encoded as byte or text string by 587 You can force whether a string is encoded as byte or text string by
474 using "utf8::upgrade" and "utf8::downgrade"): 588 using "utf8::upgrade" and "utf8::downgrade" (if "text_strings" is
589 disabled).
475 590
476 utf8::upgrade $x; # encode $x as text string 591 utf8::upgrade $x; # encode $x as text string
477 utf8::downgrade $x; # encode $x as byte string 592 utf8::downgrade $x; # encode $x as byte string
478 593
594 More options are available, see "TYPE CASTS", below, and the
595 "text_keys" and "text_strings" options.
596
479 Perl doesn't define what operations up- and downgrade strings, so if 597 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 598 the difference between byte and text is important, you should up- or
481 downgrade your string as late as possible before encoding. 599 downgrade your string as late as possible before encoding. You can
600 also force the use of CBOR text strings by using "text_keys" or
601 "text_strings".
482 602
483 You can force the type to be a CBOR number by numifying it: 603 You can force the type to be a CBOR number by numifying it:
484 604
485 my $x = "3"; # some variable containing a string 605 my $x = "3"; # some variable containing a string
486 $x += 0; # numify it, ensuring it will be dumped as a number 606 $x += 0; # numify it, ensuring it will be dumped as a number
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495 IEEE single format if possible without loss of precision, otherwise 615 IEEE single format if possible without loss of precision, otherwise
496 the IEEE double format will be used. Perls that use formats other 616 the IEEE double format will be used. Perls that use formats other
497 than IEEE double to represent numerical values are supported, but 617 than IEEE double to represent numerical values are supported, but
498 might suffer loss of precision. 618 might suffer loss of precision.
499 619
620 TYPE CASTS
621 EXPERIMENTAL: As an experimental extension, "CBOR::XS" allows you to
622 force specific CBOR types to be used when encoding. That allows you to
623 encode types not normally accessible (e.g. half floats) as well as force
624 string types even when "text_strings" is in effect.
625
626 Type forcing is done by calling a special "cast" function which keeps a
627 copy of the value and returns a new value that can be handed over to any
628 CBOR encoder function.
629
630 The following casts are currently available (all of which are unary
631 operators, that is, have a prototype of "$"):
632
633 CBOR::XS::as_int $value
634 Forces the value to be encoded as some form of (basic, not bignum)
635 integer type.
636
637 CBOR::XS::as_text $value
638 Forces the value to be encoded as (UTF-8) text values.
639
640 CBOR::XS::as_bytes $value
641 Forces the value to be encoded as a (binary) string value.
642
643 Example: encode a perl string as binary even though "text_strings"
644 is in effect.
645
646 CBOR::XS->new->text_strings->encode ([4, "text", CBOR::XS::bytes "bytevalue"]);
647
648 CBOR::XS::as_bool $value
649 Converts a Perl boolean (which can be any kind of scalar) into a
650 CBOR boolean. Strictly the same, but shorter to write, than:
651
652 $value ? Types::Serialiser::true : Types::Serialiser::false
653
654 CBOR::XS::as_float16 $value
655 Forces half-float (IEEE 754 binary16) encoding of the given value.
656
657 CBOR::XS::as_float32 $value
658 Forces single-float (IEEE 754 binary32) encoding of the given value.
659
660 CBOR::XS::as_float64 $value
661 Forces double-float (IEEE 754 binary64) encoding of the given value.
662
663 CBOR::XS::as_cbor $cbor_text
664 Not a type cast per-se, this type cast forces the argument to be
665 encoded as-is. This can be used to embed pre-encoded CBOR data.
666
667 Note that no checking on the validity of the $cbor_text is done -
668 it's the callers responsibility to correctly encode values.
669
670 CBOR::XS::as_map [key => value...]
671 Treat the array reference as key value pairs and output a CBOR map.
672 This allows you to generate CBOR maps with arbitrary key types (or,
673 if you don't care about semantics, duplicate keys or pairs in a
674 custom order), which is otherwise hard to do with Perl.
675
676 The single argument must be an array reference with an even number
677 of elements.
678
679 Note that only the reference to the array is copied, the array
680 itself is not. Modifications done to the array before calling an
681 encoding function will be reflected in the encoded output.
682
683 Example: encode a CBOR map with a string and an integer as keys.
684
685 encode_cbor CBOR::XS::as_map [string => "value", 5 => "value"]
686
500 OBJECT SERIALISATION 687 OBJECT SERIALISATION
501 This module implements both a CBOR-specific and the generic 688 This module implements both a CBOR-specific and the generic
502 Types::Serialier object serialisation protocol. The following 689 Types::Serialier object serialisation protocol. The following
503 subsections explain both methods. 690 subsections explain both methods.
504 691
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581 "$self" # encode url string 768 "$self" # encode url string
582 } 769 }
583 770
584 sub URI::THAW { 771 sub URI::THAW {
585 my ($class, $serialiser, $uri) = @_; 772 my ($class, $serialiser, $uri) = @_;
586
587 $class->new ($uri) 773 $class->new ($uri)
588 } 774 }
589 775
590 Unlike "TO_CBOR", multiple values can be returned by "FREEZE". For 776 Unlike "TO_CBOR", multiple values can be returned by "FREEZE". For
591 example, a "FREEZE" method that returns "type", "id" and "variant" 777 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 873 Future versions of this module reserve the right to special case
688 additional tags (such as base64url). 874 additional tags (such as base64url).
689 875
690 ENFORCED TAGS 876 ENFORCED TAGS
691 These tags are always handled when decoding, and their handling cannot 877 These tags are always handled when decoding, and their handling cannot
692 be overriden by the user. 878 be overridden by the user.
693 879
694 26 (perl-object, <http://cbor.schmorp.de/perl-object>) 880 26 (perl-object, <http://cbor.schmorp.de/perl-object>)
695 These tags are automatically created (and decoded) for serialisable 881 These tags are automatically created (and decoded) for serialisable
696 objects using the "FREEZE/THAW" methods (the Types::Serialier object 882 objects using the "FREEZE/THAW" methods (the Types::Serialier object
697 serialisation protocol). See "OBJECT SERIALISATION" for details. 883 serialisation protocol). See "OBJECT SERIALISATION" for details.
698 884
699 28, 29 (shareable, sharedref, L <http://cbor.schmorp.de/value-sharing>) 885 28, 29 (shareable, sharedref, <http://cbor.schmorp.de/value-sharing>)
700 These tags are automatically decoded when encountered (and they do 886 These tags are automatically decoded when encountered (and they do
701 not result in a cyclic data structure, see "allow_cycles"), 887 not result in a cyclic data structure, see "allow_cycles"),
702 resulting in shared values in the decoded object. They are only 888 resulting in shared values in the decoded object. They are only
703 encoded, however, when "allow_sharing" is enabled. 889 encoded, however, when "allow_sharing" is enabled.
704 890
… …
713 references will be shared, others will not. While non-reference 899 references will be shared, others will not. While non-reference
714 shared values can be generated in Perl with some effort, they were 900 shared values can be generated in Perl with some effort, they were
715 considered too unimportant to be supported in the encoder. The 901 considered too unimportant to be supported in the encoder. The
716 decoder, however, will decode these values as shared values. 902 decoder, however, will decode these values as shared values.
717 903
718 256, 25 (stringref-namespace, stringref, L 904 256, 25 (stringref-namespace, stringref,
719 <http://cbor.schmorp.de/stringref>) 905 <http://cbor.schmorp.de/stringref>)
720 These tags are automatically decoded when encountered. They are only 906 These tags are automatically decoded when encountered. They are only
721 encoded, however, when "pack_strings" is enabled. 907 encoded, however, when "pack_strings" is enabled.
722 908
723 22098 (indirection, <http://cbor.schmorp.de/indirection>) 909 22098 (indirection, <http://cbor.schmorp.de/indirection>)
724 This tag is automatically generated when a reference are encountered 910 This tag is automatically generated when a reference are encountered
725 (with the exception of hash and array refernces). It is converted to 911 (with the exception of hash and array references). It is converted
726 a reference when decoding. 912 to a reference when decoding.
727 913
728 55799 (self-describe CBOR, RFC 7049) 914 55799 (self-describe CBOR, RFC 7049)
729 This value is not generated on encoding (unless explicitly requested 915 This value is not generated on encoding (unless explicitly requested
730 by the user), and is simply ignored when decoding. 916 by the user), and is simply ignored when decoding.
731 917
732 NON-ENFORCED TAGS 918 NON-ENFORCED TAGS
733 These tags have default filters provided when decoding. Their handling 919 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 920 can be overridden by changing the %CBOR::XS::FILTER entry for the tag,
735 by providing a custom "filter" callback when decoding. 921 or by providing a custom "filter" callback when decoding.
736 922
737 When they result in decoding into a specific Perl class, the module 923 When they result in decoding into a specific Perl class, the module
738 usually provides a corresponding "TO_CBOR" method as well. 924 usually provides a corresponding "TO_CBOR" method as well.
739 925
740 When any of these need to load additional modules that are not part of 926 When any of these need to load additional modules that are not part of
… …
755 2, 3 (positive/negative bignum) 941 2, 3 (positive/negative bignum)
756 These tags are decoded into Math::BigInt objects. The corresponding 942 These tags are decoded into Math::BigInt objects. The corresponding
757 "Math::BigInt::TO_CBOR" method encodes "small" bigints into normal 943 "Math::BigInt::TO_CBOR" method encodes "small" bigints into normal
758 CBOR integers, and others into positive/negative CBOR bignums. 944 CBOR integers, and others into positive/negative CBOR bignums.
759 945
760 4, 5 (decimal fraction/bigfloat) 946 4, 5, 264, 265 (decimal fraction/bigfloat)
761 Both decimal fractions and bigfloats are decoded into Math::BigFloat 947 Both decimal fractions and bigfloats are decoded into Math::BigFloat
762 objects. The corresponding "Math::BigFloat::TO_CBOR" method *always* 948 objects. The corresponding "Math::BigFloat::TO_CBOR" method *always*
763 encodes into a decimal fraction. 949 encodes into a decimal fraction (either tag 4 or 264).
764 950
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. 951 NaN and infinities are not encoded properly, as they cannot be
952 represented in CBOR.
953
954 See "BIGNUM SECURITY CONSIDERATIONS" for more info.
955
956 30 (rational numbers)
957 These tags are decoded into Math::BigRat objects. The corresponding
958 "Math::BigRat::TO_CBOR" method encodes rational numbers with
959 denominator 1 via their numerator only, i.e., they become normal
960 integers or "bignums".
961
962 See "BIGNUM SECURITY CONSIDERATIONS" for more info.
769 963
770 21, 22, 23 (expected later JSON conversion) 964 21, 22, 23 (expected later JSON conversion)
771 CBOR::XS is not a CBOR-to-JSON converter, and will simply ignore 965 CBOR::XS is not a CBOR-to-JSON converter, and will simply ignore
772 these tags. 966 these tags.
773 967
… …
787 interoperability is improved in the future, then the goal will be to 981 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 982 ensure that decoded JSON data will round-trip encoding and decoding to
789 CBOR intact. 983 CBOR intact.
790 984
791SECURITY CONSIDERATIONS 985SECURITY CONSIDERATIONS
792 When you are using CBOR in a protocol, talking to untrusted potentially 986 Tl;dr... if you want to decode or encode CBOR from untrusted sources,
793 hostile creatures requires relatively few measures. 987 you should start with a coder object created via "new_safe" (which
988 implements the mitigations explained below):
794 989
990 my $coder = CBOR::XS->new_safe;
991
992 my $data = $coder->decode ($cbor_text);
993 my $cbor = $coder->encode ($data);
994
995 Longer version: When you are using CBOR in a protocol, talking to
996 untrusted potentially hostile creatures requires some thought:
997
998 Security of the CBOR decoder itself
795 First of all, your CBOR decoder should be secure, that is, should not 999 First and foremost, your CBOR decoder should be secure, that is,
796 have any buffer overflows. Obviously, this module should ensure that and 1000 should not have any buffer overflows or similar bugs that could
1001 potentially be exploited. Obviously, this module should ensure that
797 I am trying hard on making that true, but you never know. 1002 and I am trying hard on making that true, but you never know.
798 1003
1004 CBOR::XS can invoke almost arbitrary callbacks during decoding
1005 CBOR::XS supports object serialisation - decoding CBOR can cause
1006 calls to *any* "THAW" method in *any* package that exists in your
1007 process (that is, CBOR::XS will not try to load modules, but any
1008 existing "THAW" method or function can be called, so they all have
1009 to be secure).
1010
1011 Less obviously, it will also invoke "TO_CBOR" and "FREEZE" methods -
1012 even if all your "THAW" methods are secure, encoding data structures
1013 from untrusted sources can invoke those and trigger bugs in those.
1014
1015 So, if you are not sure about the security of all the modules you
1016 have loaded (you shouldn't), you should disable this part using
1017 "forbid_objects" or using "new_safe".
1018
1019 CBOR can be extended with tags that call library code
1020 CBOR can be extended with tags, and "CBOR::XS" has a registry of
1021 conversion functions for many existing tags that can be extended via
1022 third-party modules (see the "filter" method).
1023
1024 If you don't trust these, you should configure the "safe" filter
1025 function, "CBOR::XS::safe_filter" ("new_safe" does this), which by
1026 default only includes conversion functions that are considered
1027 "safe" by the author (but again, they can be extended by third party
1028 modules).
1029
1030 Depending on your level of paranoia, you can use the "safe" filter:
1031
1032 $cbor->filter (\&CBOR::XS::safe_filter);
1033
1034 ... your own filter...
1035
1036 $cbor->filter (sub { ... do your stuffs here ... });
1037
1038 ... or even no filter at all, disabling all tag decoding:
1039
1040 $cbor->filter (sub { });
1041
1042 This is never a problem for encoding, as the tag mechanism only
1043 exists in CBOR texts.
1044
1045 Resource-starving attacks: object memory usage
799 Second, you need to avoid resource-starving attacks. That means you 1046 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 1047 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 1048 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 1049 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 1050 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 1051 to decode it into a Perl structure. While CBOR::XS can check the
1052 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, 1053 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. 1054 want to check the size before you accept the string.
807 1055
1056 As for encoding, it is possible to construct data structures that
1057 are relatively small but result in large CBOR texts (for example by
1058 having an array full of references to the same big data structure,
1059 which will all be deep-cloned during encoding by default). This is
1060 rarely an actual issue (and the worst case is still just running out
1061 of memory), but you can reduce this risk by using "allow_sharing".
1062
1063 Resource-starving attacks: stack overflows
808 Third, CBOR::XS recurses using the C stack when decoding objects and 1064 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 1065 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 1066 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 1067 arrays but only 14k nested CBOR objects (due to perl itself
812 croak to free the temporary). If that is exceeded, the program crashes. 1068 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 1069 exceeded, the program crashes. To be conservative, the default
814 process has a smaller stack, you should adjust this setting accordingly 1070 nesting limit is set to 512. If your process has a smaller stack,
815 with the "max_depth" method. 1071 you should adjust this setting accordingly with the "max_depth"
1072 method.
816 1073
1074 Resource-starving attacks: CPU en-/decoding complexity
1075 CBOR::XS will use the Math::BigInt, Math::BigFloat and Math::BigRat
1076 libraries to represent encode/decode bignums. These can be very slow
1077 (as in, centuries of CPU time) and can even crash your program (and
1078 are generally not very trustworthy). See the next section on bignum
1079 security for details.
1080
1081 Data breaches: leaking information in error messages
1082 CBOR::XS might leak contents of your Perl data structures in its
1083 error messages, so when you serialise sensitive information you
1084 might want to make sure that exceptions thrown by CBOR::XS will not
1085 end up in front of untrusted eyes.
1086
1087 Something else...
817 Something else could bomb you, too, that I forgot to think of. In that 1088 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... 1089 that case, you get to keep the pieces. I am always open for hints,
1090 though...
819 1091
820 Also keep in mind that CBOR::XS might leak contents of your Perl data 1092BIGNUM SECURITY CONSIDERATIONS
821 structures in its error messages, so when you serialise sensitive 1093 CBOR::XS provides a "TO_CBOR" method for both Math::BigInt and
822 information you might want to make sure that exceptions thrown by 1094 Math::BigFloat that tries to encode the number in the simplest possible
823 CBOR::XS will not end up in front of untrusted eyes. 1095 way, that is, either a CBOR integer, a CBOR bigint/decimal fraction (tag
1096 4) or an arbitrary-exponent decimal fraction (tag 264). Rational numbers
1097 (Math::BigRat, tag 30) can also contain bignums as members.
1098
1099 CBOR::XS will also understand base-2 bigfloat or arbitrary-exponent
1100 bigfloats (tags 5 and 265), but it will never generate these on its own.
1101
1102 Using the built-in Math::BigInt::Calc support, encoding and decoding
1103 decimal fractions is generally fast. Decoding bigints can be slow for
1104 very big numbers (tens of thousands of digits, something that could
1105 potentially be caught by limiting the size of CBOR texts), and decoding
1106 bigfloats or arbitrary-exponent bigfloats can be *extremely* slow
1107 (minutes, decades) for large exponents (roughly 40 bit and longer).
1108
1109 Additionally, Math::BigInt can take advantage of other bignum libraries,
1110 such as Math::GMP, which cannot handle big floats with large exponents,
1111 and might simply abort or crash your program, due to their code quality.
1112
1113 This can be a concern if you want to parse untrusted CBOR. If it is, you
1114 might want to disable decoding of tag 2 (bigint) and 3 (negative bigint)
1115 types. You should also disable types 5 and 265, as these can be slow
1116 even without bigints.
1117
1118 Disabling bigints will also partially or fully disable types that rely
1119 on them, e.g. rational numbers that use bignums.
824 1120
825CBOR IMPLEMENTATION NOTES 1121CBOR IMPLEMENTATION NOTES
826 This section contains some random implementation notes. They do not 1122 This section contains some random implementation notes. They do not
827 describe guaranteed behaviour, but merely behaviour as-is implemented 1123 describe guaranteed behaviour, but merely behaviour as-is implemented
828 right now. 1124 right now.
… …
841 1137
842LIMITATIONS ON PERLS WITHOUT 64-BIT INTEGER SUPPORT 1138LIMITATIONS ON PERLS WITHOUT 64-BIT INTEGER SUPPORT
843 On perls that were built without 64 bit integer support (these are rare 1139 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 1140 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 1141 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 1142 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 1143 truncated, corrupted, or otherwise not decoded correctly. This also
848 includes string, array and map sizes that are stored as 64 bit integers. 1144 includes string, float, array and map sizes that are stored as 64 bit
1145 integers.
849 1146
850THREADS 1147THREADS
851 This module is *not* guaranteed to be thread safe and there are no plans 1148 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 1149 to change this until Perl gets thread support (as opposed to the
853 horribly slow so-called "threads" which are simply slow and bloated 1150 horribly slow so-called "threads" which are simply slow and bloated

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