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21 # data was decoded 21 # data was decoded
22 substr $many_cbor_strings, 0, $length, ""; # remove decoded cbor string 22 substr $many_cbor_strings, 0, $length, ""; # remove decoded cbor string
23 } 23 }
24 24
25DESCRIPTION 25DESCRIPTION
26 WARNING! This module is very new, and not very well tested (that's up to
27 you to do). Furthermore, details of the implementation might change
28 freely before version 1.0. And lastly, most extensions depend on an IANA
29 assignment, and until that assignment is official, this implementation
30 is not interoperable with other implementations (even future versions of
31 this module) until the assignment is done.
32
33 You are still invited to try out CBOR, and this module.
34
35 This module converts Perl data structures to the Concise Binary Object 26 This module converts Perl data structures to the Concise Binary Object
36 Representation (CBOR) and vice versa. CBOR is a fast binary 27 Representation (CBOR) and vice versa. CBOR is a fast binary
37 serialisation format that aims to use a superset of the JSON data model, 28 serialisation format that aims to use an (almost) superset of the JSON
38 i.e. when you can represent something in JSON, you should be able to 29 data model, i.e. when you can represent something useful in JSON, you
39 represent it in CBOR. 30 should be able to represent it in CBOR.
40 31
41 In short, CBOR is a faster and very compact binary alternative to JSON, 32 In short, CBOR is a faster and quite compact binary alternative to JSON,
42 with the added ability of supporting serialisation of Perl objects. 33 with the added ability of supporting serialisation of Perl objects.
43 (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
44 compress the data later you might want to compare both formats first). 35 compress the data later and speed is less important you might want to
36 compare both formats first).
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.
45 40
46 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
47 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
48 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
49 data, the worse Storable performs in comparison. 44 data, the worse Storable performs in comparison.
50 45
51 As for compactness, "CBOR::XS" encoded data structures are usually about 46 Regarding compactness, "CBOR::XS"-encoded data structures are usually
52 20% smaller than the same data encoded as (compact) JSON or Storable. 47 about 20% smaller than the same data encoded as (compact) JSON or
48 Storable.
53 49
54 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
55 number of extensions, to support cyclic and self-referencing data 51 number of extensions, to support cyclic and shared data structures (see
56 structures (see "allow_sharing"), string deduplication (see 52 "allow_sharing" and "allow_cycles"), string deduplication (see
57 "allow_stringref") and scalar references (always enabled). 53 "pack_strings") and scalar references (always enabled).
58
59 The primary goal of this module is to be *correct* and the secondary
60 goal is to be *fast*. To reach the latter goal it was written in C.
61 54
62 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
63 vice versa. 56 vice versa.
64 57
65FUNCTIONAL INTERFACE 58FUNCTIONAL INTERFACE
… …
85 78
86 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
87 calls can be chained: 80 calls can be chained:
88 81
89 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).
90 98
91 $cbor = $cbor->max_depth ([$maximum_nesting_depth]) 99 $cbor = $cbor->max_depth ([$maximum_nesting_depth])
92 $max_depth = $cbor->get_max_depth 100 $max_depth = $cbor->get_max_depth
93 Sets the maximum nesting level (default 512) accepted while encoding 101 Sets the maximum nesting level (default 512) accepted while encoding
94 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
… …
108 116
109 Note that nesting is implemented by recursion in C. The default 117 Note that nesting is implemented by recursion in C. The default
110 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
111 allow without crashing. 119 allow without crashing.
112 120
113 See SECURITY CONSIDERATIONS, below, for more info on why this is 121 See "SECURITY CONSIDERATIONS", below, for more info on why this is
114 useful. 122 useful.
115 123
116 $cbor = $cbor->max_size ([$maximum_string_size]) 124 $cbor = $cbor->max_size ([$maximum_string_size])
117 $max_size = $cbor->get_max_size 125 $max_size = $cbor->get_max_size
118 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
… …
122 exception. This setting has no effect on "encode" (yet). 130 exception. This setting has no effect on "encode" (yet).
123 131
124 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
125 as when 0 is specified). 133 as when 0 is specified).
126 134
127 See SECURITY CONSIDERATIONS, below, for more info on why this is 135 See "SECURITY CONSIDERATIONS", below, for more info on why this is
128 useful. 136 useful.
129 137
130 $cbor = $cbor->allow_unknown ([$enable]) 138 $cbor = $cbor->allow_unknown ([$enable])
131 $enabled = $cbor->get_allow_unknown 139 $enabled = $cbor->get_allow_unknown
132 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
… …
147 same object, such as an array, is referenced multiple times), but 155 same object, such as an array, is referenced multiple times), but
148 instead will emit a reference to the earlier value. 156 instead will emit a reference to the earlier value.
149 157
150 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
151 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
152 supporting the value sharing extension. 160 supporting the value sharing extension. This also makes it possible
161 to encode cyclic data structures (which need "allow_cycles" to be
162 enabled to be decoded by this module).
153 163
154 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
155 partner supports the value sharing extensions to CBOR 165 partner supports the value sharing extensions to CBOR
156 (http://cbor.schmorp.de/value-sharing). 166 (<http://cbor.schmorp.de/value-sharing>), as without decoder
167 support, the resulting data structure might be unusable.
157 168
158 Detecting shared values incurs a runtime overhead when values are 169 Detecting shared values incurs a runtime overhead when values are
159 encoded that have a reference counter large than one, and might 170 encoded that have a reference counter larger than one, and might
160 unnecessarily increase the encoded size, as potentially shared 171 unnecessarily increase the encoded size, as potentially shared
161 values are encode as sharable whether or not they are actually 172 values are encoded as shareable whether or not they are actually
162 shared. 173 shared.
163 174
164 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.
165 scalars, arrays or hashes pointed to by a reference). Weirder 176 scalars, arrays or hashes pointed to by a reference). Weirder
166 constructs, such as an array with multiple "copies" of the *same* 177 constructs, such as an array with multiple "copies" of the *same*
167 string, which are hard but not impossible to create in Perl, are not 178 string, which are hard but not impossible to create in Perl, are not
168 supported (this is the same as for Storable). 179 supported (this is the same as with Storable).
169 180
170 If $enable is false (the default), then "encode" will encode 181 If $enable is false (the default), then "encode" will encode shared
171 exception when it encounters anything it cannot encode as CBOR. 182 data structures repeatedly, unsharing them in the process. Cyclic
183 data structures cannot be encoded in this mode.
172 184
173 This option does not affect "decode" in any way - shared values and 185 This option does not affect "decode" in any way - shared values and
174 references will always be decoded properly if present. 186 references will always be decoded properly if present.
175 187
188 $cbor = $cbor->allow_cycles ([$enable])
189 $enabled = $cbor->get_allow_cycles
190 If $enable is true (or missing), then "decode" will happily decode
191 self-referential (cyclic) data structures. By default these will not
192 be decoded, as they need manual cleanup to avoid memory leaks, so
193 code that isn't prepared for this will not leak memory.
194
195 If $enable is false (the default), then "decode" will throw an error
196 when it encounters a self-referential/cyclic data structure.
197
198 This option does not affect "encode" in any way - shared values and
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.
235
176 $cbor = $cbor->allow_stringref ([$enable]) 236 $cbor = $cbor->pack_strings ([$enable])
177 $enabled = $cbor->get_allow_stringref 237 $enabled = $cbor->get_pack_strings
178 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
179 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
180 the string instead. Depending on your data format. this can save a 240 the string instead. Depending on your data format, this can save a
181 lot of space, but also results in a very large runtime overhead 241 lot of space, but also results in a very large runtime overhead
182 (expect encoding times to be 2-4 times as high as without). 242 (expect encoding times to be 2-4 times as high as without).
183 243
184 It is recommended to leave it off unless you know your 244 It is recommended to leave it off unless you know your
185 communications partner supports the stringref extension to CBOR 245 communications partner supports the stringref extension to CBOR
186 (http://cbor.schmorp.de/stringref). 246 (<http://cbor.schmorp.de/stringref>), as without decoder support,
247 the resulting data structure might not be usable.
187 248
188 If $enable is false (the default), then "encode" will encode 249 If $enable is false (the default), then "encode" will encode strings
189 exception when it encounters anything it cannot encode as CBOR. 250 the standard CBOR way.
190 251
191 This option does not affect "decode" in any way - string references 252 This option does not affect "decode" in any way - string references
192 will always be decoded properly if present. 253 will always be decoded properly if present.
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
300 $cbor = $cbor->validate_utf8 ([$enable])
301 $enabled = $cbor->get_validate_utf8
302 If $enable is true (or missing), then "decode" will validate that
303 elements (text strings) containing UTF-8 data in fact contain valid
304 UTF-8 data (instead of blindly accepting it). This validation
305 obviously takes extra time during decoding.
306
307 The concept of "valid UTF-8" used is perl's concept, which is a
308 superset of the official UTF-8.
309
310 If $enable is false (the default), then "decode" will blindly accept
311 UTF-8 data, marking them as valid UTF-8 in the resulting data
312 structure regardless of whether that's true or not.
313
314 Perl isn't too happy about corrupted UTF-8 in strings, but should
315 generally not crash or do similarly evil things. Extensions might be
316 not so forgiving, so it's recommended to turn on this setting if you
317 receive untrusted CBOR.
318
319 This option does not affect "encode" in any way - strings that are
320 supposedly valid UTF-8 will simply be dumped into the resulting CBOR
321 string without checking whether that is, in fact, true or not.
193 322
194 $cbor = $cbor->filter ([$cb->($tag, $value)]) 323 $cbor = $cbor->filter ([$cb->($tag, $value)])
195 $cb_or_undef = $cbor->get_filter 324 $cb_or_undef = $cbor->get_filter
196 Sets or replaces the tagged value decoding filter (when $cb is 325 Sets or replaces the tagged value decoding filter (when $cb is
197 specified) or clears the filter (if no argument or "undef" is 326 specified) or clears the filter (if no argument or "undef" is
… …
215 When the filter is cleared (the default state), the default filter 344 When the filter is cleared (the default state), the default filter
216 function, "CBOR::XS::default_filter", is used. This function simply 345 function, "CBOR::XS::default_filter", is used. This function simply
217 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
218 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
219 is responsible for decoding the value. If no entry exists, it 348 is responsible for decoding the value. If no entry exists, it
220 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.
221 363
222 Example: decode all tags not handled internally into 364 Example: decode all tags not handled internally into
223 CBOR::XS::Tagged objects, with no other special handling (useful 365 "CBOR::XS::Tagged" objects, with no other special handling (useful
224 when working with potentially "unsafe" CBOR data). 366 when working with potentially "unsafe" CBOR data).
225 367
226 CBOR::XS->new->filter (sub { })->decode ($cbor_data); 368 CBOR::XS->new->filter (sub { })->decode ($cbor_data);
227 369
228 Example: provide a global filter for tag 1347375694, converting the 370 Example: provide a global filter for tag 1347375694, converting the
… …
231 $CBOR::XS::FILTER{1347375694} = sub { 373 $CBOR::XS::FILTER{1347375694} = sub {
232 my ($tag, $value); 374 my ($tag, $value);
233 375
234 "tag 1347375694 value $value" 376 "tag 1347375694 value $value"
235 }; 377 };
378
379 Example: provide your own filter function that looks up tags in your
380 own hash:
381
382 my %my_filter = (
383 998347484 => sub {
384 my ($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);
236 398
237 $cbor_data = $cbor->encode ($perl_scalar) 399 $cbor_data = $cbor->encode ($perl_scalar)
238 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
239 representation. 401 representation.
240 402
… …
248 will silently stop parsing there and return the number of characters 410 will silently stop parsing there and return the number of characters
249 consumed so far. 411 consumed so far.
250 412
251 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
252 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
253 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.
254 418
255 CBOR::XS->new->decode_prefix ("......") 419 CBOR::XS->new->decode_prefix ("......")
256 => ("...", 3) 420 => ("...", 3)
421
422 INCREMENTAL PARSING
423 In some cases, there is the need for incremental parsing of JSON texts.
424 While this module always has to keep both CBOR text and resulting Perl
425 data structure in memory at one time, it does allow you to parse a CBOR
426 stream incrementally, using a similar to using "decode_prefix" to see if
427 a full CBOR object is available, but is much more efficient.
428
429 It basically works by parsing as much of a CBOR string as possible - if
430 the CBOR data is not complete yet, the parser will remember where it
431 was, to be able to restart when more data has been accumulated. Once
432 enough data is available to either decode a complete CBOR value or raise
433 an error, a real decode will be attempted.
434
435 A typical use case would be a network protocol that consists of sending
436 and receiving CBOR-encoded messages. The solution that works with CBOR
437 and about anything else is by prepending a length to every CBOR value,
438 so the receiver knows how many octets to read. More compact (and
439 slightly slower) would be to just send CBOR values back-to-back, as
440 "CBOR::XS" knows where a CBOR value ends, and doesn't need an explicit
441 length.
442
443 The following methods help with this:
444
445 @decoded = $cbor->incr_parse ($buffer)
446 This method attempts to decode exactly one CBOR value from the
447 beginning of the given $buffer. The value is removed from the
448 $buffer on success. When $buffer doesn't contain a complete value
449 yet, it returns nothing. Finally, when the $buffer doesn't start
450 with something that could ever be a valid CBOR value, it raises an
451 exception, just as "decode" would. In the latter case the decoder
452 state is undefined and must be reset before being able to parse
453 further.
454
455 This method modifies the $buffer in place. When no CBOR value can be
456 decoded, the decoder stores the current string offset. On the next
457 call, continues decoding at the place where it stopped before. For
458 this to make sense, the $buffer must begin with the same octets as
459 on previous unsuccessful calls.
460
461 You can call this method in scalar context, in which case it either
462 returns a decoded value or "undef". This makes it impossible to
463 distinguish between CBOR null values (which decode to "undef") and
464 an unsuccessful decode, which is often acceptable.
465
466 @decoded = $cbor->incr_parse_multiple ($buffer)
467 Same as "incr_parse", but attempts to decode as many CBOR values as
468 possible in one go, instead of at most one. Calls to "incr_parse"
469 and "incr_parse_multiple" can be interleaved.
470
471 $cbor->incr_reset
472 Resets the incremental decoder. This throws away any saved state, so
473 that subsequent calls to "incr_parse" or "incr_parse_multiple" start
474 to parse a new CBOR value from the beginning of the $buffer again.
475
476 This method can be called at any time, but it *must* be called if
477 you want to change your $buffer or there was a decoding error and
478 you want to reuse the $cbor object for future incremental parsings.
257 479
258MAPPING 480MAPPING
259 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
260 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
261 circumstances automatically, preserving round-tripping characteristics 483 circumstances automatically, preserving round-tripping characteristics
… …
269 integers 491 integers
270 CBOR integers become (numeric) perl scalars. On perls without 64 bit 492 CBOR integers become (numeric) perl scalars. On perls without 64 bit
271 support, 64 bit integers will be truncated or otherwise corrupted. 493 support, 64 bit integers will be truncated or otherwise corrupted.
272 494
273 byte strings 495 byte strings
274 Byte strings will become octet strings in Perl (the byte values 496 Byte strings will become octet strings in Perl (the Byte values
275 0..255 will simply become characters of the same value in Perl). 497 0..255 will simply become characters of the same value in Perl).
276 498
277 UTF-8 strings 499 UTF-8 strings
278 UTF-8 strings in CBOR will be decoded, i.e. the UTF-8 octets will be 500 UTF-8 strings in CBOR will be decoded, i.e. the UTF-8 octets will be
279 decoded into proper Unicode code points. At the moment, the validity 501 decoded into proper Unicode code points. At the moment, the validity
… …
297 519
298 tagged values 520 tagged values
299 Tagged items consists of a numeric tag and another CBOR value. 521 Tagged items consists of a numeric tag and another CBOR value.
300 522
301 See "TAG HANDLING AND EXTENSIONS" and the description of "->filter" 523 See "TAG HANDLING AND EXTENSIONS" and the description of "->filter"
302 for details. 524 for details on which tags are handled how.
303 525
304 anything else 526 anything else
305 Anything else (e.g. unsupported simple values) will raise a decoding 527 Anything else (e.g. unsupported simple values) will raise a decoding
306 error. 528 error.
307 529
308 PERL -> CBOR 530 PERL -> CBOR
309 The mapping from Perl to CBOR is slightly more difficult, as Perl is a 531 The mapping from Perl to CBOR is slightly more difficult, as Perl is a
310 truly typeless language, so we can only guess which CBOR type is meant 532 typeless language. That means this module can only guess which CBOR type
311 by a Perl value. 533 is meant by a perl value.
312 534
313 hash references 535 hash references
314 Perl hash references become CBOR maps. As there is no inherent 536 Perl hash references become CBOR maps. As there is no inherent
315 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
316 in a pseudo-random order. 538 in a pseudo-random order. This order can be different each time a
539 hash is encoded.
317 540
318 Currently, tied hashes will use the indefinite-length format, while 541 Currently, tied hashes will use the indefinite-length format, while
319 normal hashes will use the fixed-length format. 542 normal hashes will use the fixed-length format.
320 543
321 array references 544 array references
322 Perl array references become fixed-length CBOR arrays. 545 Perl array references become fixed-length CBOR arrays.
323 546
324 other references 547 other references
325 Other unblessed references are generally not allowed and will cause 548 Other unblessed references will be represented using the indirection
326 an exception to be thrown, except for references to the integers 0 549 tag extension (tag value 22098,
327 and 1, which get turned into false and true in CBOR. 550 <http://cbor.schmorp.de/indirection>). CBOR decoders are guaranteed
551 to be able to decode these values somehow, by either "doing the
552 right thing", decoding into a generic tagged object, simply ignoring
553 the tag, or something else.
328 554
329 CBOR::XS::Tagged objects 555 CBOR::XS::Tagged objects
330 Objects of this type must be arrays consisting of a single "[tag, 556 Objects of this type must be arrays consisting of a single "[tag,
331 value]" pair. The (numerical) tag will be encoded as a CBOR tag, the 557 value]" pair. The (numerical) tag will be encoded as a CBOR tag, the
332 value will be encoded as appropriate for the value. You cna use 558 value will be encoded as appropriate for the value. You must use
333 "CBOR::XS::tag" to create such objects. 559 "CBOR::XS::tag" to create such objects.
334 560
335 Types::Serialiser::true, Types::Serialiser::false, 561 Types::Serialiser::true, Types::Serialiser::false,
336 Types::Serialiser::error 562 Types::Serialiser::error
337 These special values become CBOR true, CBOR false and CBOR undefined 563 These special values become CBOR true, CBOR false and CBOR undefined
338 values, respectively. You can also use "\1", "\0" and "\undef" 564 values, respectively.
339 directly if you want.
340 565
341 other blessed objects 566 other blessed objects
342 Other blessed objects are serialised via "TO_CBOR" or "FREEZE". See 567 Other blessed objects are serialised via "TO_CBOR" or "FREEZE". See
343 "TAG HANDLING AND EXTENSIONS" for specific classes handled by this 568 "TAG HANDLING AND EXTENSIONS" for specific classes handled by this
344 module, and "OBJECT SERIALISATION" for generic object serialisation. 569 module, and "OBJECT SERIALISATION" for generic object serialisation.
… …
353 # dump as number 578 # dump as number
354 encode_cbor [2] # yields [2] 579 encode_cbor [2] # yields [2]
355 encode_cbor [-3.0e17] # yields [-3e+17] 580 encode_cbor [-3.0e17] # yields [-3e+17]
356 my $value = 5; encode_cbor [$value] # yields [5] 581 my $value = 5; encode_cbor [$value] # yields [5]
357 582
358 # used as string, so dump as string 583 # used as string, so dump as string (either byte or text)
359 print $value; 584 print $value;
360 encode_cbor [$value] # yields ["5"] 585 encode_cbor [$value] # yields ["5"]
361 586
362 # undef becomes null 587 # undef becomes null
363 encode_cbor [undef] # yields [null] 588 encode_cbor [undef] # yields [null]
… …
366 591
367 my $x = 3.1; # some variable containing a number 592 my $x = 3.1; # some variable containing a number
368 "$x"; # stringified 593 "$x"; # stringified
369 $x .= ""; # another, more awkward way to stringify 594 $x .= ""; # another, more awkward way to stringify
370 print $x; # perl does it for you, too, quite often 595 print $x; # perl does it for you, too, quite often
596
597 You can force whether a string is encoded as byte or text string by
598 using "utf8::upgrade" and "utf8::downgrade" (if "text_strings" is
599 disabled).
600
601 utf8::upgrade $x; # encode $x as text string
602 utf8::downgrade $x; # encode $x as byte string
603
604 More options are available, see "TYPE CASTS", below, and the
605 "text_keys" and "text_strings" options.
606
607 Perl doesn't define what operations up- and downgrade strings, so if
608 the difference between byte and text is important, you should up- or
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".
371 612
372 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:
373 614
374 my $x = "3"; # some variable containing a string 615 my $x = "3"; # some variable containing a string
375 $x += 0; # numify it, ensuring it will be dumped as a number 616 $x += 0; # numify it, ensuring it will be dumped as a number
… …
384 IEEE single format if possible without loss of precision, otherwise 625 IEEE single format if possible without loss of precision, otherwise
385 the IEEE double format will be used. Perls that use formats other 626 the IEEE double format will be used. Perls that use formats other
386 than IEEE double to represent numerical values are supported, but 627 than IEEE double to represent numerical values are supported, but
387 might suffer loss of precision. 628 might suffer loss of precision.
388 629
630 TYPE CASTS
631 EXPERIMENTAL: As an experimental extension, "CBOR::XS" allows you to
632 force specific CBOR types to be used when encoding. That allows you to
633 encode types not normally accessible (e.g. half floats) as well as force
634 string types even when "text_strings" is in effect.
635
636 Type forcing is done by calling a special "cast" function which keeps a
637 copy of the value and returns a new value that can be handed over to any
638 CBOR encoder function.
639
640 The following casts are currently available (all of which are unary
641 operators, that is, have a prototype of "$"):
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
389 OBJECT SERIALISATION 697 OBJECT SERIALISATION
698 This module implements both a CBOR-specific and the generic
699 Types::Serialier object serialisation protocol. The following
700 subsections explain both methods.
701
702 ENCODING
390 This module knows two way to serialise a Perl object: The CBOR-specific 703 This module knows two way to serialise a Perl object: The CBOR-specific
391 way, and the generic way. 704 way, and the generic way.
392 705
393 Whenever the encoder encounters a Perl object that it cnanot serialise 706 Whenever the encoder encounters a Perl object that it cannot serialise
394 directly (most of them), it will first look up the "TO_CBOR" method on 707 directly (most of them), it will first look up the "TO_CBOR" method on
395 it. 708 it.
396 709
397 If it has a "TO_CBOR" method, it will call it with the object as only 710 If it has a "TO_CBOR" method, it will call it with the object as only
398 argument, and expects exactly one return value, which it will then 711 argument, and expects exactly one return value, which it will then
… …
403 "CBOR" as the second argument, to distinguish it from other serialisers. 716 "CBOR" as the second argument, to distinguish it from other serialisers.
404 717
405 The "FREEZE" method can return any number of values (i.e. zero or more). 718 The "FREEZE" method can return any number of values (i.e. zero or more).
406 These will be encoded as CBOR perl object, together with the classname. 719 These will be encoded as CBOR perl object, together with the classname.
407 720
721 These methods *MUST NOT* change the data structure that is being
722 serialised. Failure to comply to this can result in memory corruption -
723 and worse.
724
408 If an object supports neither "TO_CBOR" nor "FREEZE", encoding will fail 725 If an object supports neither "TO_CBOR" nor "FREEZE", encoding will fail
409 with an error. 726 with an error.
410 727
728 DECODING
411 Objects encoded via "TO_CBOR" cannot be automatically decoded, but 729 Objects encoded via "TO_CBOR" cannot (normally) be automatically
412 objects encoded via "FREEZE" can be decoded using the following 730 decoded, but objects encoded via "FREEZE" can be decoded using the
413 protocol: 731 following protocol:
414 732
415 When an encoded CBOR perl object is encountered by the decoder, it will 733 When an encoded CBOR perl object is encountered by the decoder, it will
416 look up the "THAW" method, by using the stored classname, and will fail 734 look up the "THAW" method, by using the stored classname, and will fail
417 if the method cannot be found. 735 if the method cannot be found.
418 736
… …
439 757
440 sub URI::TO_CBOR { 758 sub URI::TO_CBOR {
441 my ($self) = @_; 759 my ($self) = @_;
442 my $uri = "$self"; # stringify uri 760 my $uri = "$self"; # stringify uri
443 utf8::upgrade $uri; # make sure it will be encoded as UTF-8 string 761 utf8::upgrade $uri; # make sure it will be encoded as UTF-8 string
444 CBOR::XS::tagged 32, "$_[0]" 762 CBOR::XS::tag 32, "$_[0]"
445 } 763 }
446 764
447 This will encode URIs as a UTF-8 string with tag 32, which indicates an 765 This will encode URIs as a UTF-8 string with tag 32, which indicates an
448 URI. 766 URI.
449 767
… …
460 "$self" # encode url string 778 "$self" # encode url string
461 } 779 }
462 780
463 sub URI::THAW { 781 sub URI::THAW {
464 my ($class, $serialiser, $uri) = @_; 782 my ($class, $serialiser, $uri) = @_;
465
466 $class->new ($uri) 783 $class->new ($uri)
467 } 784 }
468 785
469 Unlike "TO_CBOR", multiple values can be returned by "FREEZE". For 786 Unlike "TO_CBOR", multiple values can be returned by "FREEZE". For
470 example, a "FREEZE" method that returns "type", "id" and "variant" 787 example, a "FREEZE" method that returns "type", "id" and "variant"
… …
566 Future versions of this module reserve the right to special case 883 Future versions of this module reserve the right to special case
567 additional tags (such as base64url). 884 additional tags (such as base64url).
568 885
569 ENFORCED TAGS 886 ENFORCED TAGS
570 These tags are always handled when decoding, and their handling cannot 887 These tags are always handled when decoding, and their handling cannot
571 be overriden by the user. 888 be overridden by the user.
572 889
573 <unassigned> (perl-object, <http://cbor.schmorp.de/perl-object>) 890 26 (perl-object, <http://cbor.schmorp.de/perl-object>)
574 These tags are automatically created (and decoded) for serialisable 891 These tags are automatically created (and decoded) for serialisable
575 objects using the "FREEZE/THAW" methods (the Types::Serialier object 892 objects using the "FREEZE/THAW" methods (the Types::Serialier object
576 serialisation protocol). See "OBJECT SERIALISATION" for details. 893 serialisation protocol). See "OBJECT SERIALISATION" for details.
577 894
578 <unassigned>, <unassigned> (sharable, sharedref, L 895 28, 29 (shareable, sharedref, <http://cbor.schmorp.de/value-sharing>)
579 <http://cbor.schmorp.de/value-sharing>)
580 These tags are automatically decoded when encountered, resulting in 896 These tags are automatically decoded when encountered (and they do
897 not result in a cyclic data structure, see "allow_cycles"),
581 shared values in the decoded object. They are only encoded, however, 898 resulting in shared values in the decoded object. They are only
582 when "allow_sharable" is enabled. 899 encoded, however, when "allow_sharing" is enabled.
583 900
584 <unassigned>, <unassigned> (stringref-namespace, stringref, L 901 Not all shared values can be successfully decoded: values that
902 reference themselves will *currently* decode as "undef" (this is not
903 the same as a reference pointing to itself, which will be
904 represented as a value that contains an indirect reference to itself
905 - these will be decoded properly).
906
907 Note that considerably more shared value data structures can be
908 decoded than will be encoded - currently, only values pointed to by
909 references will be shared, others will not. While non-reference
910 shared values can be generated in Perl with some effort, they were
911 considered too unimportant to be supported in the encoder. The
912 decoder, however, will decode these values as shared values.
913
914 256, 25 (stringref-namespace, stringref,
585 <http://cbor.schmorp.de/stringref>) 915 <http://cbor.schmorp.de/stringref>)
586 These tags are automatically decoded when encountered. They are only 916 These tags are automatically decoded when encountered. They are only
587 encoded, however, when "allow_stringref" is enabled. 917 encoded, however, when "pack_strings" is enabled.
588 918
589 22098 (indirection, <http://cbor.schmorp.de/indirection>) 919 22098 (indirection, <http://cbor.schmorp.de/indirection>)
590 This tag is automatically generated when a reference are encountered 920 This tag is automatically generated when a reference are encountered
591 (with the exception of hash and array refernces). It is converted to 921 (with the exception of hash and array references). It is converted
592 a reference when decoding. 922 to a reference when decoding.
593 923
594 55799 (self-describe CBOR, RFC 7049) 924 55799 (self-describe CBOR, RFC 7049)
595 This value is not generated on encoding (unless explicitly requested 925 This value is not generated on encoding (unless explicitly requested
596 by the user), and is simply ignored when decoding. 926 by the user), and is simply ignored when decoding.
597 927
598 NON-ENFORCED TAGS 928 NON-ENFORCED TAGS
599 These tags have default filters provided when decoding. Their handling 929 These tags have default filters provided when decoding. Their handling
600 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,
601 by providing a custom "filter" callback when decoding. 931 or by providing a custom "filter" callback when decoding.
602 932
603 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
604 usually provides a corresponding "TO_CBOR" method as well. 934 usually provides a corresponding "TO_CBOR" method as well.
605 935
606 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
607 the perl core distribution (e.g. URI), it is (currently) up to the user 937 the perl core distribution (e.g. URI), it is (currently) up to the user
608 to provide these modules. The decoding usually fails with an exception 938 to provide these modules. The decoding usually fails with an exception
609 if the required module cannot be loaded. 939 if the required module cannot be loaded.
610 940
941 0, 1 (date/time string, seconds since the epoch)
942 These tags are decoded into Time::Piece objects. The corresponding
943 "Time::Piece::TO_CBOR" method always encodes into tag 1 values
944 currently.
945
946 The Time::Piece API is generally surprisingly bad, and fractional
947 seconds are only accidentally kept intact, so watch out. On the plus
948 side, the module comes with perl since 5.10, which has to count for
949 something.
950
611 2, 3 (positive/negative bignum) 951 2, 3 (positive/negative bignum)
612 These tags are decoded into Math::BigInt objects. The corresponding 952 These tags are decoded into Math::BigInt objects. The corresponding
613 "Math::BigInt::TO_CBOR" method encodes "small" bigints into normal 953 "Math::BigInt::TO_CBOR" method encodes "small" bigints into normal
614 CBOR integers, and others into positive/negative CBOR bignums. 954 CBOR integers, and others into positive/negative CBOR bignums.
615 955
616 4, 5 (decimal fraction/bigfloat) 956 4, 5, 264, 265 (decimal fraction/bigfloat)
617 Both decimal fractions and bigfloats are decoded into Math::BigFloat 957 Both decimal fractions and bigfloats are decoded into Math::BigFloat
618 objects. The corresponding "Math::BigFloat::TO_CBOR" method *always* 958 objects. The corresponding "Math::BigFloat::TO_CBOR" method *always*
619 encodes into a decimal fraction. 959 encodes into a decimal fraction (either tag 4 or 264).
620 960
621 CBOR cannot represent bigfloats with *very* large exponents -
622 conversion of such big float objects is undefined.
623
624 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.
625 973
626 21, 22, 23 (expected later JSON conversion) 974 21, 22, 23 (expected later JSON conversion)
627 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
628 these tags. 976 these tags.
629 977
… …
643 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
644 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
645 CBOR intact. 993 CBOR intact.
646 994
647SECURITY CONSIDERATIONS 995SECURITY CONSIDERATIONS
648 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,
649 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):
650 999
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
651 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,
652 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
653 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.
654 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
655 Second, you need to avoid resource-starving attacks. That means you 1056 You need to avoid resource-starving attacks. That means you should
656 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
657 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
658 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
659 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
660 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
661 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
662 so you might want to check the size before you accept the string. 1064 want to check the size before you accept the string.
663 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
664 Third, CBOR::XS recurses using the C stack when decoding objects and 1074 CBOR::XS recurses using the C stack when decoding objects and
665 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
666 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
667 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
668 croak to free the temporary). If that is exceeded, the program crashes. 1078 recursing deeply on croak to free the temporary). If that is
669 To be conservative, the default nesting limit is set to 512. If your 1079 exceeded, the program crashes. To be conservative, the default
670 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,
671 with the "max_depth" method. 1081 you should adjust this setting accordingly with the "max_depth"
1082 method.
672 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...
673 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
674 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...
675 1101
676 Also keep in mind that CBOR::XS might leak contents of your Perl data 1102BIGNUM SECURITY CONSIDERATIONS
677 structures in its error messages, so when you serialise sensitive 1103 CBOR::XS provides a "TO_CBOR" method for both Math::BigInt and
678 information you might want to make sure that exceptions thrown by 1104 Math::BigFloat that tries to encode the number in the simplest possible
679 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.
680 1130
681CBOR IMPLEMENTATION NOTES 1131CBOR IMPLEMENTATION NOTES
682 This section contains some random implementation notes. They do not 1132 This section contains some random implementation notes. They do not
683 describe guaranteed behaviour, but merely behaviour as-is implemented 1133 describe guaranteed behaviour, but merely behaviour as-is implemented
684 right now. 1134 right now.
… …
692 Only the double data type is supported for NV data types - when Perl 1142 Only the double data type is supported for NV data types - when Perl
693 uses long double to represent floating point values, they might not be 1143 uses long double to represent floating point values, they might not be
694 encoded properly. Half precision types are accepted, but not encoded. 1144 encoded properly. Half precision types are accepted, but not encoded.
695 1145
696 Strict mode and canonical mode are not implemented. 1146 Strict mode and canonical mode are not implemented.
1147
1148LIMITATIONS ON PERLS WITHOUT 64-BIT INTEGER SUPPORT
1149 On perls that were built without 64 bit integer support (these are rare
1150 nowadays, even on 32 bit architectures, as all major Perl distributions
1151 are built with 64 bit integer support), support for any kind of 64 bit
1152 value in CBOR is very limited - most likely, these 64 bit values will be
1153 truncated, corrupted, or otherwise not decoded correctly. This also
1154 includes string, float, array and map sizes that are stored as 64 bit
1155 integers.
697 1156
698THREADS 1157THREADS
699 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
700 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
701 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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