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Revision 1.16 by root, Mon Feb 8 04:37:12 2016 UTC vs.
Revision 1.23 by root, Fri Sep 8 20:03:06 2023 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 larger 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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178 code that isn't prepared for this will not leak memory. 193 code that isn't prepared for this will not leak memory.
179 194
180 If $enable is false (the default), then "decode" will throw an error 195 If $enable is false (the default), then "decode" will throw an error
181 when it encounters a self-referential/cyclic data structure. 196 when it encounters a self-referential/cyclic data structure.
182 197
183 FUTURE DIRECTION: the motivation behind this option is to avoid
184 *real* cycles - future versions of this module might chose to decode
185 cyclic data structures using weak references when this option is
186 off, instead of throwing an error.
187
188 This option does not affect "encode" in any way - shared values and 198 This option does not affect "encode" in any way - shared values and
189 references will always be encoded properly if present. 199 references will always be encoded properly if present.
200
201 $cbor = $cbor->allow_weak_cycles ([$enable])
202 $enabled = $cbor->get_allow_weak_cycles
203 This works like "allow_cycles" in that it allows the resulting data
204 structures to contain cycles, but unlike "allow_cycles", those
205 cyclic rreferences will be weak. That means that code that
206 recurrsively walks the data structure must be prepared with cycles,
207 but at least not special precautions must be implemented to free
208 these data structures.
209
210 Only those references leading to actual cycles will be weakened -
211 other references, e.g. when the same hash or arrray is referenced
212 multiple times in an arrray, will be normal references.
213
214 This option does not affect "encode" in any way - shared values and
215 references will always be encoded properly if present.
216
217 $cbor = $cbor->forbid_objects ([$enable])
218 $enabled = $cbor->get_forbid_objects
219 Disables the use of the object serialiser protocol.
220
221 If $enable is true (or missing), then "encode" will will throw an
222 exception when it encounters perl objects that would be encoded
223 using the perl-object tag (26). When "decode" encounters such tags,
224 it will fall back to the general filter/tagged logic as if this were
225 an unknown tag (by default resulting in a "CBOR::XC::Tagged"
226 object).
227
228 If $enable is false (the default), then "encode" will use the
229 Types::Serialiser object serialisation protocol to serialise objects
230 into perl-object tags, and "decode" will do the same to decode such
231 tags.
232
233 See "SECURITY CONSIDERATIONS", below, for more info on why
234 forbidding this protocol can be useful.
190 235
191 $cbor = $cbor->pack_strings ([$enable]) 236 $cbor = $cbor->pack_strings ([$enable])
192 $enabled = $cbor->get_pack_strings 237 $enabled = $cbor->get_pack_strings
193 If $enable is true (or missing), then "encode" will try not to 238 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 239 encode the same string twice, but will instead encode a reference to
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205 the standard CBOR way. 250 the standard CBOR way.
206 251
207 This option does not affect "decode" in any way - string references 252 This option does not affect "decode" in any way - string references
208 will always be decoded properly if present. 253 will always be decoded properly if present.
209 254
255 $cbor = $cbor->text_keys ([$enable])
256 $enabled = $cbor->get_text_keys
257 If $enabled is true (or missing), then "encode" will encode all perl
258 hash keys as CBOR text strings/UTF-8 string, upgrading them as
259 needed.
260
261 If $enable is false (the default), then "encode" will encode hash
262 keys normally - upgraded perl strings (strings internally encoded as
263 UTF-8) as CBOR text strings, and downgraded perl strings as CBOR
264 byte strings.
265
266 This option does not affect "decode" in any way.
267
268 This option is useful for interoperability with CBOR decoders that
269 don't treat byte strings as a form of text. It is especially useful
270 as Perl gives very little control over hash keys.
271
272 Enabling this option can be slow, as all downgraded hash keys that
273 are encoded need to be scanned and converted to UTF-8.
274
275 $cbor = $cbor->text_strings ([$enable])
276 $enabled = $cbor->get_text_strings
277 This option works similar to "text_keys", above, but works on all
278 strings (including hash keys), so "text_keys" has no further effect
279 after enabling "text_strings".
280
281 If $enabled is true (or missing), then "encode" will encode all perl
282 strings as CBOR text strings/UTF-8 strings, upgrading them as
283 needed.
284
285 If $enable is false (the default), then "encode" will encode strings
286 normally (but see "text_keys") - upgraded perl strings (strings
287 internally encoded as UTF-8) as CBOR text strings, and downgraded
288 perl strings as CBOR byte strings.
289
290 This option does not affect "decode" in any way.
291
292 This option has similar advantages and disadvantages as "text_keys".
293 In addition, this option effectively removes the ability to
294 automatically encode byte strings, which might break some "FREEZE"
295 and "TO_CBOR" methods that rely on this.
296
297 A workaround is to use explicit type casts, which are unaffected by
298 this option.
299
210 $cbor = $cbor->validate_utf8 ([$enable]) 300 $cbor = $cbor->validate_utf8 ([$enable])
211 $enabled = $cbor->get_validate_utf8 301 $enabled = $cbor->get_validate_utf8
212 If $enable is true (or missing), then "decode" will validate that 302 If $enable is true (or missing), then "decode" will validate that
213 elements (text strings) containing UTF-8 data in fact contain valid 303 elements (text strings) containing UTF-8 data in fact contain valid
214 UTF-8 data (instead of blindly accepting it). This validation 304 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 307 The concept of "valid UTF-8" used is perl's concept, which is a
218 superset of the official UTF-8. 308 superset of the official UTF-8.
219 309
220 If $enable is false (the default), then "decode" will blindly accept 310 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 311 UTF-8 data, marking them as valid UTF-8 in the resulting data
222 structure regardless of whether thats true or not. 312 structure regardless of whether that's true or not.
223 313
224 Perl isn't too happy about corrupted UTF-8 in strings, but should 314 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 315 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 316 not so forgiving, so it's recommended to turn on this setting if you
227 receive untrusted CBOR. 317 receive untrusted CBOR.
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254 When the filter is cleared (the default state), the default filter 344 When the filter is cleared (the default state), the default filter
255 function, "CBOR::XS::default_filter", is used. This function simply 345 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 346 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 347 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 348 is responsible for decoding the value. If no entry exists, it
259 returns no values. 349 returns no values. "CBOR::XS" provides a number of default filter
350 functions already, the the %CBOR::XS::FILTER hash can be freely
351 extended with more.
352
353 "CBOR::XS" additionally provides an alternative filter function that
354 is supposed to be safe to use with untrusted data (which the default
355 filter might not), called "CBOR::XS::safe_filter", which works the
356 same as the "default_filter" but uses the %CBOR::XS::SAFE_FILTER
357 variable instead. It is prepopulated with the tag decoding functions
358 that are deemed safe (basically the same as %CBOR::XS::FILTER
359 without all the bignum tags), and can be extended by user code as
360 wlel, although, obviously, one should be very careful about adding
361 decoding functions here, since the expectation is that they are safe
362 to use on untrusted data, after all.
260 363
261 Example: decode all tags not handled internally into 364 Example: decode all tags not handled internally into
262 "CBOR::XS::Tagged" objects, with no other special handling (useful 365 "CBOR::XS::Tagged" objects, with no other special handling (useful
263 when working with potentially "unsafe" CBOR data). 366 when working with potentially "unsafe" CBOR data).
264 367
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270 $CBOR::XS::FILTER{1347375694} = sub { 373 $CBOR::XS::FILTER{1347375694} = sub {
271 my ($tag, $value); 374 my ($tag, $value);
272 375
273 "tag 1347375694 value $value" 376 "tag 1347375694 value $value"
274 }; 377 };
378
379 Example: provide your own filter function that looks up tags in your
380 own hash:
381
382 my %my_filter = (
383 998347484 => sub {
384 my ($tag, $value);
385
386 "tag 998347484 value $value"
387 };
388 );
389
390 my $coder = CBOR::XS->new->filter (sub {
391 &{ $my_filter{$_[0]} or return }
392 });
393
394 Example: use the safe filter function (see "SECURITY CONSIDERATIONS"
395 for more considerations on security).
396
397 CBOR::XS->new->filter (\&CBOR::XS::safe_filter)->decode ($cbor_data);
275 398
276 $cbor_data = $cbor->encode ($perl_scalar) 399 $cbor_data = $cbor->encode ($perl_scalar)
277 Converts the given Perl data structure (a scalar value) to its CBOR 400 Converts the given Perl data structure (a scalar value) to its CBOR
278 representation. 401 representation.
279 402
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287 will silently stop parsing there and return the number of characters 410 will silently stop parsing there and return the number of characters
288 consumed so far. 411 consumed so far.
289 412
290 This is useful if your CBOR texts are not delimited by an outer 413 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 414 protocol and you need to know where the first CBOR string ends amd
292 the next one starts. 415 the next one starts - CBOR strings are self-delimited, so it is
416 possible to concatenate CBOR strings without any delimiters or size
417 fields and recover their data.
293 418
294 CBOR::XS->new->decode_prefix ("......") 419 CBOR::XS->new->decode_prefix ("......")
295 => ("...", 3) 420 => ("...", 3)
296 421
297 INCREMENTAL PARSING 422 INCREMENTAL PARSING
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300 data structure in memory at one time, it does allow you to parse a CBOR 425 data structure in memory at one time, it does allow you to parse a CBOR
301 stream incrementally, using a similar to using "decode_prefix" to see if 426 stream incrementally, using a similar to using "decode_prefix" to see if
302 a full CBOR object is available, but is much more efficient. 427 a full CBOR object is available, but is much more efficient.
303 428
304 It basically works by parsing as much of a CBOR string as possible - if 429 It basically works by parsing as much of a CBOR string as possible - if
305 the CBOR data is not complete yet, the pasrer will remember where it 430 the CBOR data is not complete yet, the parser will remember where it
306 was, to be able to restart when more data has been accumulated. Once 431 was, to be able to restart when more data has been accumulated. Once
307 enough data is available to either decode a complete CBOR value or raise 432 enough data is available to either decode a complete CBOR value or raise
308 an error, a real decode will be attempted. 433 an error, a real decode will be attempted.
309 434
310 A typical use case would be a network protocol that consists of sending 435 A typical use case would be a network protocol that consists of sending
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346 $cbor->incr_reset 471 $cbor->incr_reset
347 Resets the incremental decoder. This throws away any saved state, so 472 Resets the incremental decoder. This throws away any saved state, so
348 that subsequent calls to "incr_parse" or "incr_parse_multiple" start 473 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. 474 to parse a new CBOR value from the beginning of the $buffer again.
350 475
351 This method can be caled at any time, but it *must* be called if you 476 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 477 you want to change your $buffer or there was a decoding error and
353 want to reuse the $cbor object for future incremental parsings. 478 you want to reuse the $cbor object for future incremental parsings.
354 479
355MAPPING 480MAPPING
356 This section describes how CBOR::XS maps Perl values to CBOR values and 481 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 482 vice versa. These mappings are designed to "do the right thing" in most
358 circumstances automatically, preserving round-tripping characteristics 483 circumstances automatically, preserving round-tripping characteristics
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409 534
410 hash references 535 hash references
411 Perl hash references become CBOR maps. As there is no inherent 536 Perl hash references become CBOR maps. As there is no inherent
412 ordering in hash keys (or CBOR maps), they will usually be encoded 537 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 538 in a pseudo-random order. This order can be different each time a
414 hahs is encoded. 539 hash is encoded.
415 540
416 Currently, tied hashes will use the indefinite-length format, while 541 Currently, tied hashes will use the indefinite-length format, while
417 normal hashes will use the fixed-length format. 542 normal hashes will use the fixed-length format.
418 543
419 array references 544 array references
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434 "CBOR::XS::tag" to create such objects. 559 "CBOR::XS::tag" to create such objects.
435 560
436 Types::Serialiser::true, Types::Serialiser::false, 561 Types::Serialiser::true, Types::Serialiser::false,
437 Types::Serialiser::error 562 Types::Serialiser::error
438 These special values become CBOR true, CBOR false and CBOR undefined 563 These special values become CBOR true, CBOR false and CBOR undefined
439 values, respectively. You can also use "\1", "\0" and "\undef" 564 values, respectively.
440 directly if you want.
441 565
442 other blessed objects 566 other blessed objects
443 Other blessed objects are serialised via "TO_CBOR" or "FREEZE". See 567 Other blessed objects are serialised via "TO_CBOR" or "FREEZE". See
444 "TAG HANDLING AND EXTENSIONS" for specific classes handled by this 568 "TAG HANDLING AND EXTENSIONS" for specific classes handled by this
445 module, and "OBJECT SERIALISATION" for generic object serialisation. 569 module, and "OBJECT SERIALISATION" for generic object serialisation.
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468 my $x = 3.1; # some variable containing a number 592 my $x = 3.1; # some variable containing a number
469 "$x"; # stringified 593 "$x"; # stringified
470 $x .= ""; # another, more awkward way to stringify 594 $x .= ""; # another, more awkward way to stringify
471 print $x; # perl does it for you, too, quite often 595 print $x; # perl does it for you, too, quite often
472 596
473 You can force whether a string ie encoded as byte or text string by 597 You can force whether a string is encoded as byte or text string by
474 using "utf8::upgrade" and "utf8::downgrade"): 598 using "utf8::upgrade" and "utf8::downgrade" (if "text_strings" is
599 disabled).
475 600
476 utf8::upgrade $x; # encode $x as text string 601 utf8::upgrade $x; # encode $x as text string
477 utf8::downgrade $x; # encode $x as byte string 602 utf8::downgrade $x; # encode $x as byte string
478 603
604 More options are available, see "TYPE CASTS", below, and the
605 "text_keys" and "text_strings" options.
606
479 Perl doesn't define what operations up- and downgrade strings, so if 607 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 608 the difference between byte and text is important, you should up- or
481 downgrade your string as late as possible before encoding. 609 downgrade your string as late as possible before encoding. You can
610 also force the use of CBOR text strings by using "text_keys" or
611 "text_strings".
482 612
483 You can force the type to be a CBOR number by numifying it: 613 You can force the type to be a CBOR number by numifying it:
484 614
485 my $x = "3"; # some variable containing a string 615 my $x = "3"; # some variable containing a string
486 $x += 0; # numify it, ensuring it will be dumped as a number 616 $x += 0; # numify it, ensuring it will be dumped as a number
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495 IEEE single format if possible without loss of precision, otherwise 625 IEEE single format if possible without loss of precision, otherwise
496 the IEEE double format will be used. Perls that use formats other 626 the IEEE double format will be used. Perls that use formats other
497 than IEEE double to represent numerical values are supported, but 627 than IEEE double to represent numerical values are supported, but
498 might suffer loss of precision. 628 might suffer loss of precision.
499 629
630 TYPE CASTS
631 EXPERIMENTAL: As an experimental extension, "CBOR::XS" allows you to
632 force specific CBOR types to be used when encoding. That allows you to
633 encode types not normally accessible (e.g. half floats) as well as force
634 string types even when "text_strings" is in effect.
635
636 Type forcing is done by calling a special "cast" function which keeps a
637 copy of the value and returns a new value that can be handed over to any
638 CBOR encoder function.
639
640 The following casts are currently available (all of which are unary
641 operators, that is, have a prototype of "$"):
642
643 CBOR::XS::as_int $value
644 Forces the value to be encoded as some form of (basic, not bignum)
645 integer type.
646
647 CBOR::XS::as_text $value
648 Forces the value to be encoded as (UTF-8) text values.
649
650 CBOR::XS::as_bytes $value
651 Forces the value to be encoded as a (binary) string value.
652
653 Example: encode a perl string as binary even though "text_strings"
654 is in effect.
655
656 CBOR::XS->new->text_strings->encode ([4, "text", CBOR::XS::bytes "bytevalue"]);
657
658 CBOR::XS::as_bool $value
659 Converts a Perl boolean (which can be any kind of scalar) into a
660 CBOR boolean. Strictly the same, but shorter to write, than:
661
662 $value ? Types::Serialiser::true : Types::Serialiser::false
663
664 CBOR::XS::as_float16 $value
665 Forces half-float (IEEE 754 binary16) encoding of the given value.
666
667 CBOR::XS::as_float32 $value
668 Forces single-float (IEEE 754 binary32) encoding of the given value.
669
670 CBOR::XS::as_float64 $value
671 Forces double-float (IEEE 754 binary64) encoding of the given value.
672
673 CBOR::XS::as_cbor $cbor_text
674 Not a type cast per-se, this type cast forces the argument to be
675 encoded as-is. This can be used to embed pre-encoded CBOR data.
676
677 Note that no checking on the validity of the $cbor_text is done -
678 it's the callers responsibility to correctly encode values.
679
680 CBOR::XS::as_map [key => value...]
681 Treat the array reference as key value pairs and output a CBOR map.
682 This allows you to generate CBOR maps with arbitrary key types (or,
683 if you don't care about semantics, duplicate keys or pairs in a
684 custom order), which is otherwise hard to do with Perl.
685
686 The single argument must be an array reference with an even number
687 of elements.
688
689 Note that only the reference to the array is copied, the array
690 itself is not. Modifications done to the array before calling an
691 encoding function will be reflected in the encoded output.
692
693 Example: encode a CBOR map with a string and an integer as keys.
694
695 encode_cbor CBOR::XS::as_map [string => "value", 5 => "value"]
696
500 OBJECT SERIALISATION 697 OBJECT SERIALISATION
501 This module implements both a CBOR-specific and the generic 698 This module implements both a CBOR-specific and the generic
502 Types::Serialier object serialisation protocol. The following 699 Types::Serialier object serialisation protocol. The following
503 subsections explain both methods. 700 subsections explain both methods.
504 701
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581 "$self" # encode url string 778 "$self" # encode url string
582 } 779 }
583 780
584 sub URI::THAW { 781 sub URI::THAW {
585 my ($class, $serialiser, $uri) = @_; 782 my ($class, $serialiser, $uri) = @_;
586
587 $class->new ($uri) 783 $class->new ($uri)
588 } 784 }
589 785
590 Unlike "TO_CBOR", multiple values can be returned by "FREEZE". For 786 Unlike "TO_CBOR", multiple values can be returned by "FREEZE". For
591 example, a "FREEZE" method that returns "type", "id" and "variant" 787 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 883 Future versions of this module reserve the right to special case
688 additional tags (such as base64url). 884 additional tags (such as base64url).
689 885
690 ENFORCED TAGS 886 ENFORCED TAGS
691 These tags are always handled when decoding, and their handling cannot 887 These tags are always handled when decoding, and their handling cannot
692 be overriden by the user. 888 be overridden by the user.
693 889
694 26 (perl-object, <http://cbor.schmorp.de/perl-object>) 890 26 (perl-object, <http://cbor.schmorp.de/perl-object>)
695 These tags are automatically created (and decoded) for serialisable 891 These tags are automatically created (and decoded) for serialisable
696 objects using the "FREEZE/THAW" methods (the Types::Serialier object 892 objects using the "FREEZE/THAW" methods (the Types::Serialier object
697 serialisation protocol). See "OBJECT SERIALISATION" for details. 893 serialisation protocol). See "OBJECT SERIALISATION" for details.
… …
720 These tags are automatically decoded when encountered. They are only 916 These tags are automatically decoded when encountered. They are only
721 encoded, however, when "pack_strings" is enabled. 917 encoded, however, when "pack_strings" is enabled.
722 918
723 22098 (indirection, <http://cbor.schmorp.de/indirection>) 919 22098 (indirection, <http://cbor.schmorp.de/indirection>)
724 This tag is automatically generated when a reference are encountered 920 This tag is automatically generated when a reference are encountered
725 (with the exception of hash and array refernces). It is converted to 921 (with the exception of hash and array references). It is converted
726 a reference when decoding. 922 to a reference when decoding.
727 923
728 55799 (self-describe CBOR, RFC 7049) 924 55799 (self-describe CBOR, RFC 7049)
729 This value is not generated on encoding (unless explicitly requested 925 This value is not generated on encoding (unless explicitly requested
730 by the user), and is simply ignored when decoding. 926 by the user), and is simply ignored when decoding.
731 927
732 NON-ENFORCED TAGS 928 NON-ENFORCED TAGS
733 These tags have default filters provided when decoding. Their handling 929 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 930 can be overridden by changing the %CBOR::XS::FILTER entry for the tag,
735 by providing a custom "filter" callback when decoding. 931 or by providing a custom "filter" callback when decoding.
736 932
737 When they result in decoding into a specific Perl class, the module 933 When they result in decoding into a specific Perl class, the module
738 usually provides a corresponding "TO_CBOR" method as well. 934 usually provides a corresponding "TO_CBOR" method as well.
739 935
740 When any of these need to load additional modules that are not part of 936 When any of these need to load additional modules that are not part of
… …
755 2, 3 (positive/negative bignum) 951 2, 3 (positive/negative bignum)
756 These tags are decoded into Math::BigInt objects. The corresponding 952 These tags are decoded into Math::BigInt objects. The corresponding
757 "Math::BigInt::TO_CBOR" method encodes "small" bigints into normal 953 "Math::BigInt::TO_CBOR" method encodes "small" bigints into normal
758 CBOR integers, and others into positive/negative CBOR bignums. 954 CBOR integers, and others into positive/negative CBOR bignums.
759 955
760 4, 5 (decimal fraction/bigfloat) 956 4, 5, 264, 265 (decimal fraction/bigfloat)
761 Both decimal fractions and bigfloats are decoded into Math::BigFloat 957 Both decimal fractions and bigfloats are decoded into Math::BigFloat
762 objects. The corresponding "Math::BigFloat::TO_CBOR" method *always* 958 objects. The corresponding "Math::BigFloat::TO_CBOR" method *always*
763 encodes into a decimal fraction. 959 encodes into a decimal fraction (either tag 4 or 264).
764 960
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. 961 NaN and infinities are not encoded properly, as they cannot be
962 represented in CBOR.
963
964 See "BIGNUM SECURITY CONSIDERATIONS" for more info.
965
966 30 (rational numbers)
967 These tags are decoded into Math::BigRat objects. The corresponding
968 "Math::BigRat::TO_CBOR" method encodes rational numbers with
969 denominator 1 via their numerator only, i.e., they become normal
970 integers or "bignums".
971
972 See "BIGNUM SECURITY CONSIDERATIONS" for more info.
769 973
770 21, 22, 23 (expected later JSON conversion) 974 21, 22, 23 (expected later JSON conversion)
771 CBOR::XS is not a CBOR-to-JSON converter, and will simply ignore 975 CBOR::XS is not a CBOR-to-JSON converter, and will simply ignore
772 these tags. 976 these tags.
773 977
… …
787 interoperability is improved in the future, then the goal will be to 991 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 992 ensure that decoded JSON data will round-trip encoding and decoding to
789 CBOR intact. 993 CBOR intact.
790 994
791SECURITY CONSIDERATIONS 995SECURITY CONSIDERATIONS
792 When you are using CBOR in a protocol, talking to untrusted potentially 996 Tl;dr... if you want to decode or encode CBOR from untrusted sources,
793 hostile creatures requires relatively few measures. 997 you should start with a coder object created via "new_safe" (which
998 implements the mitigations explained below):
794 999
1000 my $coder = CBOR::XS->new_safe;
1001
1002 my $data = $coder->decode ($cbor_text);
1003 my $cbor = $coder->encode ($data);
1004
1005 Longer version: When you are using CBOR in a protocol, talking to
1006 untrusted potentially hostile creatures requires some thought:
1007
1008 Security of the CBOR decoder itself
795 First of all, your CBOR decoder should be secure, that is, should not 1009 First and foremost, your CBOR decoder should be secure, that is,
796 have any buffer overflows. Obviously, this module should ensure that and 1010 should not have any buffer overflows or similar bugs that could
1011 potentially be exploited. Obviously, this module should ensure that
797 I am trying hard on making that true, but you never know. 1012 and I am trying hard on making that true, but you never know.
798 1013
1014 CBOR::XS can invoke almost arbitrary callbacks during decoding
1015 CBOR::XS supports object serialisation - decoding CBOR can cause
1016 calls to *any* "THAW" method in *any* package that exists in your
1017 process (that is, CBOR::XS will not try to load modules, but any
1018 existing "THAW" method or function can be called, so they all have
1019 to be secure).
1020
1021 Less obviously, it will also invoke "TO_CBOR" and "FREEZE" methods -
1022 even if all your "THAW" methods are secure, encoding data structures
1023 from untrusted sources can invoke those and trigger bugs in those.
1024
1025 So, if you are not sure about the security of all the modules you
1026 have loaded (you shouldn't), you should disable this part using
1027 "forbid_objects" or using "new_safe".
1028
1029 CBOR can be extended with tags that call library code
1030 CBOR can be extended with tags, and "CBOR::XS" has a registry of
1031 conversion functions for many existing tags that can be extended via
1032 third-party modules (see the "filter" method).
1033
1034 If you don't trust these, you should configure the "safe" filter
1035 function, "CBOR::XS::safe_filter" ("new_safe" does this), which by
1036 default only includes conversion functions that are considered
1037 "safe" by the author (but again, they can be extended by third party
1038 modules).
1039
1040 Depending on your level of paranoia, you can use the "safe" filter:
1041
1042 $cbor->filter (\&CBOR::XS::safe_filter);
1043
1044 ... your own filter...
1045
1046 $cbor->filter (sub { ... do your stuffs here ... });
1047
1048 ... or even no filter at all, disabling all tag decoding:
1049
1050 $cbor->filter (sub { });
1051
1052 This is never a problem for encoding, as the tag mechanism only
1053 exists in CBOR texts.
1054
1055 Resource-starving attacks: object memory usage
799 Second, you need to avoid resource-starving attacks. That means you 1056 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 1057 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 1058 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 1059 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 1060 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 1061 to decode it into a Perl structure. While CBOR::XS can check the
1062 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, 1063 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. 1064 want to check the size before you accept the string.
807 1065
1066 As for encoding, it is possible to construct data structures that
1067 are relatively small but result in large CBOR texts (for example by
1068 having an array full of references to the same big data structure,
1069 which will all be deep-cloned during encoding by default). This is
1070 rarely an actual issue (and the worst case is still just running out
1071 of memory), but you can reduce this risk by using "allow_sharing".
1072
1073 Resource-starving attacks: stack overflows
808 Third, CBOR::XS recurses using the C stack when decoding objects and 1074 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 1075 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 1076 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 1077 arrays but only 14k nested CBOR objects (due to perl itself
812 croak to free the temporary). If that is exceeded, the program crashes. 1078 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 1079 exceeded, the program crashes. To be conservative, the default
814 process has a smaller stack, you should adjust this setting accordingly 1080 nesting limit is set to 512. If your process has a smaller stack,
815 with the "max_depth" method. 1081 you should adjust this setting accordingly with the "max_depth"
1082 method.
816 1083
1084 Resource-starving attacks: CPU en-/decoding complexity
1085 CBOR::XS will use the Math::BigInt, Math::BigFloat and Math::BigRat
1086 libraries to represent encode/decode bignums. These can be very slow
1087 (as in, centuries of CPU time) and can even crash your program (and
1088 are generally not very trustworthy). See the next section on bignum
1089 security for details.
1090
1091 Data breaches: leaking information in error messages
1092 CBOR::XS might leak contents of your Perl data structures in its
1093 error messages, so when you serialise sensitive information you
1094 might want to make sure that exceptions thrown by CBOR::XS will not
1095 end up in front of untrusted eyes.
1096
1097 Something else...
817 Something else could bomb you, too, that I forgot to think of. In that 1098 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... 1099 that case, you get to keep the pieces. I am always open for hints,
1100 though...
819 1101
820 Also keep in mind that CBOR::XS might leak contents of your Perl data 1102BIGNUM SECURITY CONSIDERATIONS
821 structures in its error messages, so when you serialise sensitive 1103 CBOR::XS provides a "TO_CBOR" method for both Math::BigInt and
822 information you might want to make sure that exceptions thrown by 1104 Math::BigFloat that tries to encode the number in the simplest possible
823 CBOR::XS will not end up in front of untrusted eyes. 1105 way, that is, either a CBOR integer, a CBOR bigint/decimal fraction (tag
1106 4) or an arbitrary-exponent decimal fraction (tag 264). Rational numbers
1107 (Math::BigRat, tag 30) can also contain bignums as members.
1108
1109 CBOR::XS will also understand base-2 bigfloat or arbitrary-exponent
1110 bigfloats (tags 5 and 265), but it will never generate these on its own.
1111
1112 Using the built-in Math::BigInt::Calc support, encoding and decoding
1113 decimal fractions is generally fast. Decoding bigints can be slow for
1114 very big numbers (tens of thousands of digits, something that could
1115 potentially be caught by limiting the size of CBOR texts), and decoding
1116 bigfloats or arbitrary-exponent bigfloats can be *extremely* slow
1117 (minutes, decades) for large exponents (roughly 40 bit and longer).
1118
1119 Additionally, Math::BigInt can take advantage of other bignum libraries,
1120 such as Math::GMP, which cannot handle big floats with large exponents,
1121 and might simply abort or crash your program, due to their code quality.
1122
1123 This can be a concern if you want to parse untrusted CBOR. If it is, you
1124 might want to disable decoding of tag 2 (bigint) and 3 (negative bigint)
1125 types. You should also disable types 5 and 265, as these can be slow
1126 even without bigints.
1127
1128 Disabling bigints will also partially or fully disable types that rely
1129 on them, e.g. rational numbers that use bignums.
824 1130
825CBOR IMPLEMENTATION NOTES 1131CBOR IMPLEMENTATION NOTES
826 This section contains some random implementation notes. They do not 1132 This section contains some random implementation notes. They do not
827 describe guaranteed behaviour, but merely behaviour as-is implemented 1133 describe guaranteed behaviour, but merely behaviour as-is implemented
828 right now. 1134 right now.
… …
841 1147
842LIMITATIONS ON PERLS WITHOUT 64-BIT INTEGER SUPPORT 1148LIMITATIONS ON PERLS WITHOUT 64-BIT INTEGER SUPPORT
843 On perls that were built without 64 bit integer support (these are rare 1149 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 1150 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 1151 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 1152 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 1153 truncated, corrupted, or otherwise not decoded correctly. This also
848 includes string, array and map sizes that are stored as 64 bit integers. 1154 includes string, float, array and map sizes that are stored as 64 bit
1155 integers.
849 1156
850THREADS 1157THREADS
851 This module is *not* guaranteed to be thread safe and there are no plans 1158 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 1159 to change this until Perl gets thread support (as opposed to the
853 horribly slow so-called "threads" which are simply slow and bloated 1160 horribly slow so-called "threads" which are simply slow and bloated

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