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Revision 1.22 by root, Thu Oct 21 01:14:58 2021 UTC

… …
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 large 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 FUTURE DIRECTION: the motivation behind this option is to avoid
199 *real* cycles - future versions of this module might chose to decode
200 cyclic data structures using weak references when this option is
201 off, instead of throwing an error.
202
203 This option does not affect "encode" in any way - shared values and
204 references will always be encoded properly if present.
205
206 $cbor = $cbor->forbid_objects ([$enable])
207 $enabled = $cbor->get_forbid_objects
208 Disables the use of the object serialiser protocol.
209
210 If $enable is true (or missing), then "encode" will will throw an
211 exception when it encounters perl objects that would be encoded
212 using the perl-object tag (26). When "decode" encounters such tags,
213 it will fall back to the general filter/tagged logic as if this were
214 an unknown tag (by default resulting in a "CBOR::XC::Tagged"
215 object).
216
217 If $enable is false (the default), then "encode" will use the
218 Types::Serialiser object serialisation protocol to serialise objects
219 into perl-object tags, and "decode" will do the same to decode such
220 tags.
221
222 See "SECURITY CONSIDERATIONS", below, for more info on why
223 forbidding this protocol can be useful.
224
176 $cbor = $cbor->allow_stringref ([$enable]) 225 $cbor = $cbor->pack_strings ([$enable])
177 $enabled = $cbor->get_allow_stringref 226 $enabled = $cbor->get_pack_strings
178 If $enable is true (or missing), then "encode" will try not to 227 If $enable is true (or missing), then "encode" will try not to
179 encode the same string twice, but will instead encode a reference to 228 encode the same string twice, but will instead encode a reference to
180 the string instead. Depending on your data format. this can save a 229 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 230 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). 231 (expect encoding times to be 2-4 times as high as without).
183 232
184 It is recommended to leave it off unless you know your 233 It is recommended to leave it off unless you know your
185 communications partner supports the stringref extension to CBOR 234 communications partner supports the stringref extension to CBOR
186 (http://cbor.schmorp.de/stringref). 235 (<http://cbor.schmorp.de/stringref>), as without decoder support,
236 the resulting data structure might not be usable.
187 237
188 If $enable is false (the default), then "encode" will encode 238 If $enable is false (the default), then "encode" will encode strings
189 exception when it encounters anything it cannot encode as CBOR. 239 the standard CBOR way.
190 240
191 This option does not affect "decode" in any way - string references 241 This option does not affect "decode" in any way - string references
192 will always be decoded properly if present. 242 will always be decoded properly if present.
243
244 $cbor = $cbor->text_keys ([$enable])
245 $enabled = $cbor->get_text_keys
246 If $enabled is true (or missing), then "encode" will encode all perl
247 hash keys as CBOR text strings/UTF-8 string, upgrading them as
248 needed.
249
250 If $enable is false (the default), then "encode" will encode hash
251 keys normally - upgraded perl strings (strings internally encoded as
252 UTF-8) as CBOR text strings, and downgraded perl strings as CBOR
253 byte strings.
254
255 This option does not affect "decode" in any way.
256
257 This option is useful for interoperability with CBOR decoders that
258 don't treat byte strings as a form of text. It is especially useful
259 as Perl gives very little control over hash keys.
260
261 Enabling this option can be slow, as all downgraded hash keys that
262 are encoded need to be scanned and converted to UTF-8.
263
264 $cbor = $cbor->text_strings ([$enable])
265 $enabled = $cbor->get_text_strings
266 This option works similar to "text_keys", above, but works on all
267 strings (including hash keys), so "text_keys" has no further effect
268 after enabling "text_strings".
269
270 If $enabled is true (or missing), then "encode" will encode all perl
271 strings as CBOR text strings/UTF-8 strings, upgrading them as
272 needed.
273
274 If $enable is false (the default), then "encode" will encode strings
275 normally (but see "text_keys") - upgraded perl strings (strings
276 internally encoded as UTF-8) as CBOR text strings, and downgraded
277 perl strings as CBOR byte strings.
278
279 This option does not affect "decode" in any way.
280
281 This option has similar advantages and disadvantages as "text_keys".
282 In addition, this option effectively removes the ability to
283 automatically encode byte strings, which might break some "FREEZE"
284 and "TO_CBOR" methods that rely on this.
285
286 A workaround is to use explicit type casts, which are unaffected by
287 this option.
288
289 $cbor = $cbor->validate_utf8 ([$enable])
290 $enabled = $cbor->get_validate_utf8
291 If $enable is true (or missing), then "decode" will validate that
292 elements (text strings) containing UTF-8 data in fact contain valid
293 UTF-8 data (instead of blindly accepting it). This validation
294 obviously takes extra time during decoding.
295
296 The concept of "valid UTF-8" used is perl's concept, which is a
297 superset of the official UTF-8.
298
299 If $enable is false (the default), then "decode" will blindly accept
300 UTF-8 data, marking them as valid UTF-8 in the resulting data
301 structure regardless of whether that's true or not.
302
303 Perl isn't too happy about corrupted UTF-8 in strings, but should
304 generally not crash or do similarly evil things. Extensions might be
305 not so forgiving, so it's recommended to turn on this setting if you
306 receive untrusted CBOR.
307
308 This option does not affect "encode" in any way - strings that are
309 supposedly valid UTF-8 will simply be dumped into the resulting CBOR
310 string without checking whether that is, in fact, true or not.
193 311
194 $cbor = $cbor->filter ([$cb->($tag, $value)]) 312 $cbor = $cbor->filter ([$cb->($tag, $value)])
195 $cb_or_undef = $cbor->get_filter 313 $cb_or_undef = $cbor->get_filter
196 Sets or replaces the tagged value decoding filter (when $cb is 314 Sets or replaces the tagged value decoding filter (when $cb is
197 specified) or clears the filter (if no argument or "undef" is 315 specified) or clears the filter (if no argument or "undef" is
… …
215 When the filter is cleared (the default state), the default filter 333 When the filter is cleared (the default state), the default filter
216 function, "CBOR::XS::default_filter", is used. This function simply 334 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 335 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 336 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 337 is responsible for decoding the value. If no entry exists, it
220 returns no values. 338 returns no values. "CBOR::XS" provides a number of default filter
339 functions already, the the %CBOR::XS::FILTER hash can be freely
340 extended with more.
341
342 "CBOR::XS" additionally provides an alternative filter function that
343 is supposed to be safe to use with untrusted data (which the default
344 filter might not), called "CBOR::XS::safe_filter", which works the
345 same as the "default_filter" but uses the %CBOR::XS::SAFE_FILTER
346 variable instead. It is prepopulated with the tag decoding functions
347 that are deemed safe (basically the same as %CBOR::XS::FILTER
348 without all the bignum tags), and can be extended by user code as
349 wlel, although, obviously, one should be very careful about adding
350 decoding functions here, since the expectation is that they are safe
351 to use on untrusted data, after all.
221 352
222 Example: decode all tags not handled internally into 353 Example: decode all tags not handled internally into
223 CBOR::XS::Tagged objects, with no other special handling (useful 354 "CBOR::XS::Tagged" objects, with no other special handling (useful
224 when working with potentially "unsafe" CBOR data). 355 when working with potentially "unsafe" CBOR data).
225 356
226 CBOR::XS->new->filter (sub { })->decode ($cbor_data); 357 CBOR::XS->new->filter (sub { })->decode ($cbor_data);
227 358
228 Example: provide a global filter for tag 1347375694, converting the 359 Example: provide a global filter for tag 1347375694, converting the
… …
231 $CBOR::XS::FILTER{1347375694} = sub { 362 $CBOR::XS::FILTER{1347375694} = sub {
232 my ($tag, $value); 363 my ($tag, $value);
233 364
234 "tag 1347375694 value $value" 365 "tag 1347375694 value $value"
235 }; 366 };
367
368 Example: provide your own filter function that looks up tags in your
369 own hash:
370
371 my %my_filter = (
372 998347484 => sub {
373 my ($tag, $value);
374
375 "tag 998347484 value $value"
376 };
377 );
378
379 my $coder = CBOR::XS->new->filter (sub {
380 &{ $my_filter{$_[0]} or return }
381 });
382
383 Example: use the safe filter function (see "SECURITY CONSIDERATIONS"
384 for more considerations on security).
385
386 CBOR::XS->new->filter (\&CBOR::XS::safe_filter)->decode ($cbor_data);
236 387
237 $cbor_data = $cbor->encode ($perl_scalar) 388 $cbor_data = $cbor->encode ($perl_scalar)
238 Converts the given Perl data structure (a scalar value) to its CBOR 389 Converts the given Perl data structure (a scalar value) to its CBOR
239 representation. 390 representation.
240 391
… …
248 will silently stop parsing there and return the number of characters 399 will silently stop parsing there and return the number of characters
249 consumed so far. 400 consumed so far.
250 401
251 This is useful if your CBOR texts are not delimited by an outer 402 This is useful if your CBOR texts are not delimited by an outer
252 protocol and you need to know where the first CBOR string ends amd 403 protocol and you need to know where the first CBOR string ends amd
253 the next one starts. 404 the next one starts - CBOR strings are self-delimited, so it is
405 possible to concatenate CBOR strings without any delimiters or size
406 fields and recover their data.
254 407
255 CBOR::XS->new->decode_prefix ("......") 408 CBOR::XS->new->decode_prefix ("......")
256 => ("...", 3) 409 => ("...", 3)
410
411 INCREMENTAL PARSING
412 In some cases, there is the need for incremental parsing of JSON texts.
413 While this module always has to keep both CBOR text and resulting Perl
414 data structure in memory at one time, it does allow you to parse a CBOR
415 stream incrementally, using a similar to using "decode_prefix" to see if
416 a full CBOR object is available, but is much more efficient.
417
418 It basically works by parsing as much of a CBOR string as possible - if
419 the CBOR data is not complete yet, the pasrer will remember where it
420 was, to be able to restart when more data has been accumulated. Once
421 enough data is available to either decode a complete CBOR value or raise
422 an error, a real decode will be attempted.
423
424 A typical use case would be a network protocol that consists of sending
425 and receiving CBOR-encoded messages. The solution that works with CBOR
426 and about anything else is by prepending a length to every CBOR value,
427 so the receiver knows how many octets to read. More compact (and
428 slightly slower) would be to just send CBOR values back-to-back, as
429 "CBOR::XS" knows where a CBOR value ends, and doesn't need an explicit
430 length.
431
432 The following methods help with this:
433
434 @decoded = $cbor->incr_parse ($buffer)
435 This method attempts to decode exactly one CBOR value from the
436 beginning of the given $buffer. The value is removed from the
437 $buffer on success. When $buffer doesn't contain a complete value
438 yet, it returns nothing. Finally, when the $buffer doesn't start
439 with something that could ever be a valid CBOR value, it raises an
440 exception, just as "decode" would. In the latter case the decoder
441 state is undefined and must be reset before being able to parse
442 further.
443
444 This method modifies the $buffer in place. When no CBOR value can be
445 decoded, the decoder stores the current string offset. On the next
446 call, continues decoding at the place where it stopped before. For
447 this to make sense, the $buffer must begin with the same octets as
448 on previous unsuccessful calls.
449
450 You can call this method in scalar context, in which case it either
451 returns a decoded value or "undef". This makes it impossible to
452 distinguish between CBOR null values (which decode to "undef") and
453 an unsuccessful decode, which is often acceptable.
454
455 @decoded = $cbor->incr_parse_multiple ($buffer)
456 Same as "incr_parse", but attempts to decode as many CBOR values as
457 possible in one go, instead of at most one. Calls to "incr_parse"
458 and "incr_parse_multiple" can be interleaved.
459
460 $cbor->incr_reset
461 Resets the incremental decoder. This throws away any saved state, so
462 that subsequent calls to "incr_parse" or "incr_parse_multiple" start
463 to parse a new CBOR value from the beginning of the $buffer again.
464
465 This method can be called at any time, but it *must* be called if
466 you want to change your $buffer or there was a decoding error and
467 you want to reuse the $cbor object for future incremental parsings.
257 468
258MAPPING 469MAPPING
259 This section describes how CBOR::XS maps Perl values to CBOR values and 470 This section describes how CBOR::XS maps Perl values to CBOR values and
260 vice versa. These mappings are designed to "do the right thing" in most 471 vice versa. These mappings are designed to "do the right thing" in most
261 circumstances automatically, preserving round-tripping characteristics 472 circumstances automatically, preserving round-tripping characteristics
… …
269 integers 480 integers
270 CBOR integers become (numeric) perl scalars. On perls without 64 bit 481 CBOR integers become (numeric) perl scalars. On perls without 64 bit
271 support, 64 bit integers will be truncated or otherwise corrupted. 482 support, 64 bit integers will be truncated or otherwise corrupted.
272 483
273 byte strings 484 byte strings
274 Byte strings will become octet strings in Perl (the byte values 485 Byte strings will become octet strings in Perl (the Byte values
275 0..255 will simply become characters of the same value in Perl). 486 0..255 will simply become characters of the same value in Perl).
276 487
277 UTF-8 strings 488 UTF-8 strings
278 UTF-8 strings in CBOR will be decoded, i.e. the UTF-8 octets will be 489 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 490 decoded into proper Unicode code points. At the moment, the validity
… …
297 508
298 tagged values 509 tagged values
299 Tagged items consists of a numeric tag and another CBOR value. 510 Tagged items consists of a numeric tag and another CBOR value.
300 511
301 See "TAG HANDLING AND EXTENSIONS" and the description of "->filter" 512 See "TAG HANDLING AND EXTENSIONS" and the description of "->filter"
302 for details. 513 for details on which tags are handled how.
303 514
304 anything else 515 anything else
305 Anything else (e.g. unsupported simple values) will raise a decoding 516 Anything else (e.g. unsupported simple values) will raise a decoding
306 error. 517 error.
307 518
308 PERL -> CBOR 519 PERL -> CBOR
309 The mapping from Perl to CBOR is slightly more difficult, as Perl is a 520 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 521 typeless language. That means this module can only guess which CBOR type
311 by a Perl value. 522 is meant by a perl value.
312 523
313 hash references 524 hash references
314 Perl hash references become CBOR maps. As there is no inherent 525 Perl hash references become CBOR maps. As there is no inherent
315 ordering in hash keys (or CBOR maps), they will usually be encoded 526 ordering in hash keys (or CBOR maps), they will usually be encoded
316 in a pseudo-random order. 527 in a pseudo-random order. This order can be different each time a
528 hash is encoded.
317 529
318 Currently, tied hashes will use the indefinite-length format, while 530 Currently, tied hashes will use the indefinite-length format, while
319 normal hashes will use the fixed-length format. 531 normal hashes will use the fixed-length format.
320 532
321 array references 533 array references
322 Perl array references become fixed-length CBOR arrays. 534 Perl array references become fixed-length CBOR arrays.
323 535
324 other references 536 other references
325 Other unblessed references are generally not allowed and will cause 537 Other unblessed references will be represented using the indirection
326 an exception to be thrown, except for references to the integers 0 538 tag extension (tag value 22098,
327 and 1, which get turned into false and true in CBOR. 539 <http://cbor.schmorp.de/indirection>). CBOR decoders are guaranteed
540 to be able to decode these values somehow, by either "doing the
541 right thing", decoding into a generic tagged object, simply ignoring
542 the tag, or something else.
328 543
329 CBOR::XS::Tagged objects 544 CBOR::XS::Tagged objects
330 Objects of this type must be arrays consisting of a single "[tag, 545 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 546 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 547 value will be encoded as appropriate for the value. You must use
333 "CBOR::XS::tag" to create such objects. 548 "CBOR::XS::tag" to create such objects.
334 549
335 Types::Serialiser::true, Types::Serialiser::false, 550 Types::Serialiser::true, Types::Serialiser::false,
336 Types::Serialiser::error 551 Types::Serialiser::error
337 These special values become CBOR true, CBOR false and CBOR undefined 552 These special values become CBOR true, CBOR false and CBOR undefined
… …
353 # dump as number 568 # dump as number
354 encode_cbor [2] # yields [2] 569 encode_cbor [2] # yields [2]
355 encode_cbor [-3.0e17] # yields [-3e+17] 570 encode_cbor [-3.0e17] # yields [-3e+17]
356 my $value = 5; encode_cbor [$value] # yields [5] 571 my $value = 5; encode_cbor [$value] # yields [5]
357 572
358 # used as string, so dump as string 573 # used as string, so dump as string (either byte or text)
359 print $value; 574 print $value;
360 encode_cbor [$value] # yields ["5"] 575 encode_cbor [$value] # yields ["5"]
361 576
362 # undef becomes null 577 # undef becomes null
363 encode_cbor [undef] # yields [null] 578 encode_cbor [undef] # yields [null]
… …
366 581
367 my $x = 3.1; # some variable containing a number 582 my $x = 3.1; # some variable containing a number
368 "$x"; # stringified 583 "$x"; # stringified
369 $x .= ""; # another, more awkward way to stringify 584 $x .= ""; # another, more awkward way to stringify
370 print $x; # perl does it for you, too, quite often 585 print $x; # perl does it for you, too, quite often
586
587 You can force whether a string is encoded as byte or text string by
588 using "utf8::upgrade" and "utf8::downgrade" (if "text_strings" is
589 disabled).
590
591 utf8::upgrade $x; # encode $x as text string
592 utf8::downgrade $x; # encode $x as byte string
593
594 More options are available, see "TYPE CASTS", below, and the
595 "text_keys" and "text_strings" options.
596
597 Perl doesn't define what operations up- and downgrade strings, so if
598 the difference between byte and text is important, you should up- or
599 downgrade your string as late as possible before encoding. You can
600 also force the use of CBOR text strings by using "text_keys" or
601 "text_strings".
371 602
372 You can force the type to be a CBOR number by numifying it: 603 You can force the type to be a CBOR number by numifying it:
373 604
374 my $x = "3"; # some variable containing a string 605 my $x = "3"; # some variable containing a string
375 $x += 0; # numify it, ensuring it will be dumped as a number 606 $x += 0; # numify it, ensuring it will be dumped as a number
… …
384 IEEE single format if possible without loss of precision, otherwise 615 IEEE single format if possible without loss of precision, otherwise
385 the IEEE double format will be used. Perls that use formats other 616 the IEEE double format will be used. Perls that use formats other
386 than IEEE double to represent numerical values are supported, but 617 than IEEE double to represent numerical values are supported, but
387 might suffer loss of precision. 618 might suffer loss of precision.
388 619
620 TYPE CASTS
621 EXPERIMENTAL: As an experimental extension, "CBOR::XS" allows you to
622 force specific CBOR types to be used when encoding. That allows you to
623 encode types not normally accessible (e.g. half floats) as well as force
624 string types even when "text_strings" is in effect.
625
626 Type forcing is done by calling a special "cast" function which keeps a
627 copy of the value and returns a new value that can be handed over to any
628 CBOR encoder function.
629
630 The following casts are currently available (all of which are unary
631 operators, that is, have a prototype of "$"):
632
633 CBOR::XS::as_int $value
634 Forces the value to be encoded as some form of (basic, not bignum)
635 integer type.
636
637 CBOR::XS::as_text $value
638 Forces the value to be encoded as (UTF-8) text values.
639
640 CBOR::XS::as_bytes $value
641 Forces the value to be encoded as a (binary) string value.
642
643 Example: encode a perl string as binary even though "text_strings"
644 is in effect.
645
646 CBOR::XS->new->text_strings->encode ([4, "text", CBOR::XS::bytes "bytevalue"]);
647
648 CBOR::XS::as_bool $value
649 Converts a Perl boolean (which can be any kind of scalar) into a
650 CBOR boolean. Strictly the same, but shorter to write, than:
651
652 $value ? Types::Serialiser::true : Types::Serialiser::false
653
654 CBOR::XS::as_float16 $value
655 Forces half-float (IEEE 754 binary16) encoding of the given value.
656
657 CBOR::XS::as_float32 $value
658 Forces single-float (IEEE 754 binary32) encoding of the given value.
659
660 CBOR::XS::as_float64 $value
661 Forces double-float (IEEE 754 binary64) encoding of the given value.
662
663 CBOR::XS::as_cbor $cbor_text
664 Not a type cast per-se, this type cast forces the argument to be
665 encoded as-is. This can be used to embed pre-encoded CBOR data.
666
667 Note that no checking on the validity of the $cbor_text is done -
668 it's the callers responsibility to correctly encode values.
669
670 CBOR::XS::as_map [key => value...]
671 Treat the array reference as key value pairs and output a CBOR map.
672 This allows you to generate CBOR maps with arbitrary key types (or,
673 if you don't care about semantics, duplicate keys or pairs in a
674 custom order), which is otherwise hard to do with Perl.
675
676 The single argument must be an array reference with an even number
677 of elements.
678
679 Note that only the reference to the array is copied, the array
680 itself is not. Modifications done to the array before calling an
681 encoding function will be reflected in the encoded output.
682
683 Example: encode a CBOR map with a string and an integer as keys.
684
685 encode_cbor CBOR::XS::as_map [string => "value", 5 => "value"]
686
389 OBJECT SERIALISATION 687 OBJECT SERIALISATION
688 This module implements both a CBOR-specific and the generic
689 Types::Serialier object serialisation protocol. The following
690 subsections explain both methods.
691
692 ENCODING
390 This module knows two way to serialise a Perl object: The CBOR-specific 693 This module knows two way to serialise a Perl object: The CBOR-specific
391 way, and the generic way. 694 way, and the generic way.
392 695
393 Whenever the encoder encounters a Perl object that it cnanot serialise 696 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 697 directly (most of them), it will first look up the "TO_CBOR" method on
395 it. 698 it.
396 699
397 If it has a "TO_CBOR" method, it will call it with the object as only 700 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 701 argument, and expects exactly one return value, which it will then
… …
403 "CBOR" as the second argument, to distinguish it from other serialisers. 706 "CBOR" as the second argument, to distinguish it from other serialisers.
404 707
405 The "FREEZE" method can return any number of values (i.e. zero or more). 708 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. 709 These will be encoded as CBOR perl object, together with the classname.
407 710
711 These methods *MUST NOT* change the data structure that is being
712 serialised. Failure to comply to this can result in memory corruption -
713 and worse.
714
408 If an object supports neither "TO_CBOR" nor "FREEZE", encoding will fail 715 If an object supports neither "TO_CBOR" nor "FREEZE", encoding will fail
409 with an error. 716 with an error.
410 717
718 DECODING
411 Objects encoded via "TO_CBOR" cannot be automatically decoded, but 719 Objects encoded via "TO_CBOR" cannot (normally) be automatically
412 objects encoded via "FREEZE" can be decoded using the following 720 decoded, but objects encoded via "FREEZE" can be decoded using the
413 protocol: 721 following protocol:
414 722
415 When an encoded CBOR perl object is encountered by the decoder, it will 723 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 724 look up the "THAW" method, by using the stored classname, and will fail
417 if the method cannot be found. 725 if the method cannot be found.
418 726
… …
439 747
440 sub URI::TO_CBOR { 748 sub URI::TO_CBOR {
441 my ($self) = @_; 749 my ($self) = @_;
442 my $uri = "$self"; # stringify uri 750 my $uri = "$self"; # stringify uri
443 utf8::upgrade $uri; # make sure it will be encoded as UTF-8 string 751 utf8::upgrade $uri; # make sure it will be encoded as UTF-8 string
444 CBOR::XS::tagged 32, "$_[0]" 752 CBOR::XS::tag 32, "$_[0]"
445 } 753 }
446 754
447 This will encode URIs as a UTF-8 string with tag 32, which indicates an 755 This will encode URIs as a UTF-8 string with tag 32, which indicates an
448 URI. 756 URI.
449 757
… …
460 "$self" # encode url string 768 "$self" # encode url string
461 } 769 }
462 770
463 sub URI::THAW { 771 sub URI::THAW {
464 my ($class, $serialiser, $uri) = @_; 772 my ($class, $serialiser, $uri) = @_;
465
466 $class->new ($uri) 773 $class->new ($uri)
467 } 774 }
468 775
469 Unlike "TO_CBOR", multiple values can be returned by "FREEZE". For 776 Unlike "TO_CBOR", multiple values can be returned by "FREEZE". For
470 example, a "FREEZE" method that returns "type", "id" and "variant" 777 example, a "FREEZE" method that returns "type", "id" and "variant"
… …
566 Future versions of this module reserve the right to special case 873 Future versions of this module reserve the right to special case
567 additional tags (such as base64url). 874 additional tags (such as base64url).
568 875
569 ENFORCED TAGS 876 ENFORCED TAGS
570 These tags are always handled when decoding, and their handling cannot 877 These tags are always handled when decoding, and their handling cannot
571 be overriden by the user. 878 be overridden by the user.
572 879
573 <unassigned> (perl-object, <http://cbor.schmorp.de/perl-object>) 880 26 (perl-object, <http://cbor.schmorp.de/perl-object>)
574 These tags are automatically created (and decoded) for serialisable 881 These tags are automatically created (and decoded) for serialisable
575 objects using the "FREEZE/THAW" methods (the Types::Serialier object 882 objects using the "FREEZE/THAW" methods (the Types::Serialier object
576 serialisation protocol). See "OBJECT SERIALISATION" for details. 883 serialisation protocol). See "OBJECT SERIALISATION" for details.
577 884
578 <unassigned>, <unassigned> (sharable, sharedref, L 885 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 886 These tags are automatically decoded when encountered (and they do
887 not result in a cyclic data structure, see "allow_cycles"),
581 shared values in the decoded object. They are only encoded, however, 888 resulting in shared values in the decoded object. They are only
582 when "allow_sharable" is enabled. 889 encoded, however, when "allow_sharing" is enabled.
583 890
584 <unassigned>, <unassigned> (stringref-namespace, stringref, L 891 Not all shared values can be successfully decoded: values that
892 reference themselves will *currently* decode as "undef" (this is not
893 the same as a reference pointing to itself, which will be
894 represented as a value that contains an indirect reference to itself
895 - these will be decoded properly).
896
897 Note that considerably more shared value data structures can be
898 decoded than will be encoded - currently, only values pointed to by
899 references will be shared, others will not. While non-reference
900 shared values can be generated in Perl with some effort, they were
901 considered too unimportant to be supported in the encoder. The
902 decoder, however, will decode these values as shared values.
903
904 256, 25 (stringref-namespace, stringref,
585 <http://cbor.schmorp.de/stringref>) 905 <http://cbor.schmorp.de/stringref>)
586 These tags are automatically decoded when encountered. They are only 906 These tags are automatically decoded when encountered. They are only
587 encoded, however, when "allow_stringref" is enabled. 907 encoded, however, when "pack_strings" is enabled.
588 908
589 22098 (indirection, <http://cbor.schmorp.de/indirection>) 909 22098 (indirection, <http://cbor.schmorp.de/indirection>)
590 This tag is automatically generated when a reference are encountered 910 This tag is automatically generated when a reference are encountered
591 (with the exception of hash and array refernces). It is converted to 911 (with the exception of hash and array references). It is converted
592 a reference when decoding. 912 to a reference when decoding.
593 913
594 55799 (self-describe CBOR, RFC 7049) 914 55799 (self-describe CBOR, RFC 7049)
595 This value is not generated on encoding (unless explicitly requested 915 This value is not generated on encoding (unless explicitly requested
596 by the user), and is simply ignored when decoding. 916 by the user), and is simply ignored when decoding.
597 917
598 NON-ENFORCED TAGS 918 NON-ENFORCED TAGS
599 These tags have default filters provided when decoding. Their handling 919 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 920 can be overridden by changing the %CBOR::XS::FILTER entry for the tag,
601 by providing a custom "filter" callback when decoding. 921 or by providing a custom "filter" callback when decoding.
602 922
603 When they result in decoding into a specific Perl class, the module 923 When they result in decoding into a specific Perl class, the module
604 usually provides a corresponding "TO_CBOR" method as well. 924 usually provides a corresponding "TO_CBOR" method as well.
605 925
606 When any of these need to load additional modules that are not part of 926 When any of these need to load additional modules that are not part of
607 the perl core distribution (e.g. URI), it is (currently) up to the user 927 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 928 to provide these modules. The decoding usually fails with an exception
609 if the required module cannot be loaded. 929 if the required module cannot be loaded.
610 930
931 0, 1 (date/time string, seconds since the epoch)
932 These tags are decoded into Time::Piece objects. The corresponding
933 "Time::Piece::TO_CBOR" method always encodes into tag 1 values
934 currently.
935
936 The Time::Piece API is generally surprisingly bad, and fractional
937 seconds are only accidentally kept intact, so watch out. On the plus
938 side, the module comes with perl since 5.10, which has to count for
939 something.
940
611 2, 3 (positive/negative bignum) 941 2, 3 (positive/negative bignum)
612 These tags are decoded into Math::BigInt objects. The corresponding 942 These tags are decoded into Math::BigInt objects. The corresponding
613 "Math::BigInt::TO_CBOR" method encodes "small" bigints into normal 943 "Math::BigInt::TO_CBOR" method encodes "small" bigints into normal
614 CBOR integers, and others into positive/negative CBOR bignums. 944 CBOR integers, and others into positive/negative CBOR bignums.
615 945
616 4, 5 (decimal fraction/bigfloat) 946 4, 5, 264, 265 (decimal fraction/bigfloat)
617 Both decimal fractions and bigfloats are decoded into Math::BigFloat 947 Both decimal fractions and bigfloats are decoded into Math::BigFloat
618 objects. The corresponding "Math::BigFloat::TO_CBOR" method *always* 948 objects. The corresponding "Math::BigFloat::TO_CBOR" method *always*
619 encodes into a decimal fraction. 949 encodes into a decimal fraction (either tag 4 or 264).
620 950
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. 951 NaN and infinities are not encoded properly, as they cannot be
952 represented in CBOR.
953
954 See "BIGNUM SECURITY CONSIDERATIONS" for more info.
955
956 30 (rational numbers)
957 These tags are decoded into Math::BigRat objects. The corresponding
958 "Math::BigRat::TO_CBOR" method encodes rational numbers with
959 denominator 1 via their numerator only, i.e., they become normal
960 integers or "bignums".
961
962 See "BIGNUM SECURITY CONSIDERATIONS" for more info.
625 963
626 21, 22, 23 (expected later JSON conversion) 964 21, 22, 23 (expected later JSON conversion)
627 CBOR::XS is not a CBOR-to-JSON converter, and will simply ignore 965 CBOR::XS is not a CBOR-to-JSON converter, and will simply ignore
628 these tags. 966 these tags.
629 967
… …
643 interoperability is improved in the future, then the goal will be to 981 interoperability is improved in the future, then the goal will be to
644 ensure that decoded JSON data will round-trip encoding and decoding to 982 ensure that decoded JSON data will round-trip encoding and decoding to
645 CBOR intact. 983 CBOR intact.
646 984
647SECURITY CONSIDERATIONS 985SECURITY CONSIDERATIONS
648 When you are using CBOR in a protocol, talking to untrusted potentially 986 Tl;dr... if you want to decode or encode CBOR from untrusted sources,
649 hostile creatures requires relatively few measures. 987 you should start with a coder object created via "new_safe" (which
988 implements the mitigations explained below):
650 989
990 my $coder = CBOR::XS->new_safe;
991
992 my $data = $coder->decode ($cbor_text);
993 my $cbor = $coder->encode ($data);
994
995 Longer version: When you are using CBOR in a protocol, talking to
996 untrusted potentially hostile creatures requires some thought:
997
998 Security of the CBOR decoder itself
651 First of all, your CBOR decoder should be secure, that is, should not 999 First and foremost, your CBOR decoder should be secure, that is,
652 have any buffer overflows. Obviously, this module should ensure that and 1000 should not have any buffer overflows or similar bugs that could
1001 potentially be exploited. Obviously, this module should ensure that
653 I am trying hard on making that true, but you never know. 1002 and I am trying hard on making that true, but you never know.
654 1003
1004 CBOR::XS can invoke almost arbitrary callbacks during decoding
1005 CBOR::XS supports object serialisation - decoding CBOR can cause
1006 calls to *any* "THAW" method in *any* package that exists in your
1007 process (that is, CBOR::XS will not try to load modules, but any
1008 existing "THAW" method or function can be called, so they all have
1009 to be secure).
1010
1011 Less obviously, it will also invoke "TO_CBOR" and "FREEZE" methods -
1012 even if all your "THAW" methods are secure, encoding data structures
1013 from untrusted sources can invoke those and trigger bugs in those.
1014
1015 So, if you are not sure about the security of all the modules you
1016 have loaded (you shouldn't), you should disable this part using
1017 "forbid_objects" or using "new_safe".
1018
1019 CBOR can be extended with tags that call library code
1020 CBOR can be extended with tags, and "CBOR::XS" has a registry of
1021 conversion functions for many existing tags that can be extended via
1022 third-party modules (see the "filter" method).
1023
1024 If you don't trust these, you should configure the "safe" filter
1025 function, "CBOR::XS::safe_filter" ("new_safe" does this), which by
1026 default only includes conversion functions that are considered
1027 "safe" by the author (but again, they can be extended by third party
1028 modules).
1029
1030 Depending on your level of paranoia, you can use the "safe" filter:
1031
1032 $cbor->filter (\&CBOR::XS::safe_filter);
1033
1034 ... your own filter...
1035
1036 $cbor->filter (sub { ... do your stuffs here ... });
1037
1038 ... or even no filter at all, disabling all tag decoding:
1039
1040 $cbor->filter (sub { });
1041
1042 This is never a problem for encoding, as the tag mechanism only
1043 exists in CBOR texts.
1044
1045 Resource-starving attacks: object memory usage
655 Second, you need to avoid resource-starving attacks. That means you 1046 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 1047 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 1048 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 1049 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 1050 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 1051 to decode it into a Perl structure. While CBOR::XS can check the
1052 size of the CBOR text (using "max_size" - done by "new_safe"), it
661 the CBOR text, it might be too late when you already have it in memory, 1053 might be too late when you already have it in memory, so you might
662 so you might want to check the size before you accept the string. 1054 want to check the size before you accept the string.
663 1055
1056 As for encoding, it is possible to construct data structures that
1057 are relatively small but result in large CBOR texts (for example by
1058 having an array full of references to the same big data structure,
1059 which will all be deep-cloned during encoding by default). This is
1060 rarely an actual issue (and the worst case is still just running out
1061 of memory), but you can reduce this risk by using "allow_sharing".
1062
1063 Resource-starving attacks: stack overflows
664 Third, CBOR::XS recurses using the C stack when decoding objects and 1064 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 1065 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 1066 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 1067 arrays but only 14k nested CBOR objects (due to perl itself
668 croak to free the temporary). If that is exceeded, the program crashes. 1068 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 1069 exceeded, the program crashes. To be conservative, the default
670 process has a smaller stack, you should adjust this setting accordingly 1070 nesting limit is set to 512. If your process has a smaller stack,
671 with the "max_depth" method. 1071 you should adjust this setting accordingly with the "max_depth"
1072 method.
672 1073
1074 Resource-starving attacks: CPU en-/decoding complexity
1075 CBOR::XS will use the Math::BigInt, Math::BigFloat and Math::BigRat
1076 libraries to represent encode/decode bignums. These can be very slow
1077 (as in, centuries of CPU time) and can even crash your program (and
1078 are generally not very trustworthy). See the next section on bignum
1079 security for details.
1080
1081 Data breaches: leaking information in error messages
1082 CBOR::XS might leak contents of your Perl data structures in its
1083 error messages, so when you serialise sensitive information you
1084 might want to make sure that exceptions thrown by CBOR::XS will not
1085 end up in front of untrusted eyes.
1086
1087 Something else...
673 Something else could bomb you, too, that I forgot to think of. In that 1088 Something else could bomb you, too, that I forgot to think of. In
674 case, you get to keep the pieces. I am always open for hints, though... 1089 that case, you get to keep the pieces. I am always open for hints,
1090 though...
675 1091
676 Also keep in mind that CBOR::XS might leak contents of your Perl data 1092BIGNUM SECURITY CONSIDERATIONS
677 structures in its error messages, so when you serialise sensitive 1093 CBOR::XS provides a "TO_CBOR" method for both Math::BigInt and
678 information you might want to make sure that exceptions thrown by 1094 Math::BigFloat that tries to encode the number in the simplest possible
679 CBOR::XS will not end up in front of untrusted eyes. 1095 way, that is, either a CBOR integer, a CBOR bigint/decimal fraction (tag
1096 4) or an arbitrary-exponent decimal fraction (tag 264). Rational numbers
1097 (Math::BigRat, tag 30) can also contain bignums as members.
1098
1099 CBOR::XS will also understand base-2 bigfloat or arbitrary-exponent
1100 bigfloats (tags 5 and 265), but it will never generate these on its own.
1101
1102 Using the built-in Math::BigInt::Calc support, encoding and decoding
1103 decimal fractions is generally fast. Decoding bigints can be slow for
1104 very big numbers (tens of thousands of digits, something that could
1105 potentially be caught by limiting the size of CBOR texts), and decoding
1106 bigfloats or arbitrary-exponent bigfloats can be *extremely* slow
1107 (minutes, decades) for large exponents (roughly 40 bit and longer).
1108
1109 Additionally, Math::BigInt can take advantage of other bignum libraries,
1110 such as Math::GMP, which cannot handle big floats with large exponents,
1111 and might simply abort or crash your program, due to their code quality.
1112
1113 This can be a concern if you want to parse untrusted CBOR. If it is, you
1114 might want to disable decoding of tag 2 (bigint) and 3 (negative bigint)
1115 types. You should also disable types 5 and 265, as these can be slow
1116 even without bigints.
1117
1118 Disabling bigints will also partially or fully disable types that rely
1119 on them, e.g. rational numbers that use bignums.
680 1120
681CBOR IMPLEMENTATION NOTES 1121CBOR IMPLEMENTATION NOTES
682 This section contains some random implementation notes. They do not 1122 This section contains some random implementation notes. They do not
683 describe guaranteed behaviour, but merely behaviour as-is implemented 1123 describe guaranteed behaviour, but merely behaviour as-is implemented
684 right now. 1124 right now.
… …
692 Only the double data type is supported for NV data types - when Perl 1132 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 1133 uses long double to represent floating point values, they might not be
694 encoded properly. Half precision types are accepted, but not encoded. 1134 encoded properly. Half precision types are accepted, but not encoded.
695 1135
696 Strict mode and canonical mode are not implemented. 1136 Strict mode and canonical mode are not implemented.
1137
1138LIMITATIONS ON PERLS WITHOUT 64-BIT INTEGER SUPPORT
1139 On perls that were built without 64 bit integer support (these are rare
1140 nowadays, even on 32 bit architectures, as all major Perl distributions
1141 are built with 64 bit integer support), support for any kind of 64 bit
1142 value in CBOR is very limited - most likely, these 64 bit values will be
1143 truncated, corrupted, or otherwise not decoded correctly. This also
1144 includes string, float, array and map sizes that are stored as 64 bit
1145 integers.
697 1146
698THREADS 1147THREADS
699 This module is *not* guaranteed to be thread safe and there are no plans 1148 This module is *not* guaranteed to be thread safe and there are no plans
700 to change this until Perl gets thread support (as opposed to the 1149 to change this until Perl gets thread support (as opposed to the
701 horribly slow so-called "threads" which are simply slow and bloated 1150 horribly slow so-called "threads" which are simply slow and bloated

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