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Revision 1.19 by root, Sun Nov 29 21:35:51 2020 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, the object serialisation protocol
29 depends on a pending IANA assignment, and until that assignment is
30 official, this implementation is not interoperable with other
31 implementations (even future versions of this module) until the
32 assignment is done.
33
34 You are still invited to try out CBOR, and this module.
35
36 This module converts Perl data structures to the Concise Binary Object 26 This module converts Perl data structures to the Concise Binary Object
37 Representation (CBOR) and vice versa. CBOR is a fast binary 27 Representation (CBOR) and vice versa. CBOR is a fast binary
38 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
39 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
40 represent it in CBOR. 30 should be able to represent it in CBOR.
41 31
42 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,
43 with the added ability of supporting serialisation of Perl objects. 33 with the added ability of supporting serialisation of Perl objects.
44 (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
45 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.
46 40
47 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
48 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
49 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
50 data, the worse Storable performs in comparison. 44 data, the worse Storable performs in comparison.
51 45
52 As for compactness, "CBOR::XS" encoded data structures are usually about 46 Regarding compactness, "CBOR::XS"-encoded data structures are usually
53 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.
54 49
55 The primary goal of this module is to be *correct* and the secondary 50 In addition to the core CBOR data format, this module implements a
56 goal is to be *fast*. To reach the latter goal it was written in C. 51 number of extensions, to support cyclic and shared data structures (see
52 "allow_sharing" and "allow_cycles"), string deduplication (see
53 "pack_strings") and scalar references (always enabled).
57 54
58 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
59 vice versa. 56 vice versa.
60 57
61FUNCTIONAL INTERFACE 58FUNCTIONAL INTERFACE
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80 *disabled*. 77 *disabled*.
81 78
82 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
83 calls can be chained: 80 calls can be chained:
84 81
85 #TODO my $cbor = CBOR::XS->new->encode ({a => [1,2]}); 82 my $cbor = CBOR::XS->new->encode ({a => [1,2]});
83
84 $cbor = new_safe CBOR::XS
85 Create a new, safe/secure CBOR::XS object. This is similar to "new",
86 but configures the coder object to be safe to use with untrusted
87 data. Currently, this is equivalent to:
88
89 my $cbor = CBOR::XS
90 ->new
91 ->forbid_objects
92 ->filter (\&CBOR::XS::safe_filter)
93 ->max_size (1e8);
94
95 But is more future proof (it is better to crash because of a change
96 than to be exploited in other ways).
86 97
87 $cbor = $cbor->max_depth ([$maximum_nesting_depth]) 98 $cbor = $cbor->max_depth ([$maximum_nesting_depth])
88 $max_depth = $cbor->get_max_depth 99 $max_depth = $cbor->get_max_depth
89 Sets the maximum nesting level (default 512) accepted while encoding 100 Sets the maximum nesting level (default 512) accepted while encoding
90 or decoding. If a higher nesting level is detected in CBOR data or a 101 or decoding. If a higher nesting level is detected in CBOR data or a
… …
104 115
105 Note that nesting is implemented by recursion in C. The default 116 Note that nesting is implemented by recursion in C. The default
106 value has been chosen to be as large as typical operating systems 117 value has been chosen to be as large as typical operating systems
107 allow without crashing. 118 allow without crashing.
108 119
109 See SECURITY CONSIDERATIONS, below, for more info on why this is 120 See "SECURITY CONSIDERATIONS", below, for more info on why this is
110 useful. 121 useful.
111 122
112 $cbor = $cbor->max_size ([$maximum_string_size]) 123 $cbor = $cbor->max_size ([$maximum_string_size])
113 $max_size = $cbor->get_max_size 124 $max_size = $cbor->get_max_size
114 Set the maximum length a CBOR string may have (in bytes) where 125 Set the maximum length a CBOR string may have (in bytes) where
… …
118 exception. This setting has no effect on "encode" (yet). 129 exception. This setting has no effect on "encode" (yet).
119 130
120 If no argument is given, the limit check will be deactivated (same 131 If no argument is given, the limit check will be deactivated (same
121 as when 0 is specified). 132 as when 0 is specified).
122 133
123 See SECURITY CONSIDERATIONS, below, for more info on why this is 134 See "SECURITY CONSIDERATIONS", below, for more info on why this is
124 useful. 135 useful.
136
137 $cbor = $cbor->allow_unknown ([$enable])
138 $enabled = $cbor->get_allow_unknown
139 If $enable is true (or missing), then "encode" will *not* throw an
140 exception when it encounters values it cannot represent in CBOR (for
141 example, filehandles) but instead will encode a CBOR "error" value.
142
143 If $enable is false (the default), then "encode" will throw an
144 exception when it encounters anything it cannot encode as CBOR.
145
146 This option does not affect "decode" in any way, and it is
147 recommended to leave it off unless you know your communications
148 partner.
149
150 $cbor = $cbor->allow_sharing ([$enable])
151 $enabled = $cbor->get_allow_sharing
152 If $enable is true (or missing), then "encode" will not
153 double-encode values that have been referenced before (e.g. when the
154 same object, such as an array, is referenced multiple times), but
155 instead will emit a reference to the earlier value.
156
157 This means that such values will only be encoded once, and will not
158 result in a deep cloning of the value on decode, in decoders
159 supporting the value sharing extension. This also makes it possible
160 to encode cyclic data structures (which need "allow_cycles" to be
161 enabled to be decoded by this module).
162
163 It is recommended to leave it off unless you know your communication
164 partner supports the value sharing extensions to CBOR
165 (<http://cbor.schmorp.de/value-sharing>), as without decoder
166 support, the resulting data structure might be unusable.
167
168 Detecting shared values incurs a runtime overhead when values are
169 encoded that have a reference counter large than one, and might
170 unnecessarily increase the encoded size, as potentially shared
171 values are encoded as shareable whether or not they are actually
172 shared.
173
174 At the moment, only targets of references can be shared (e.g.
175 scalars, arrays or hashes pointed to by a reference). Weirder
176 constructs, such as an array with multiple "copies" of the *same*
177 string, which are hard but not impossible to create in Perl, are not
178 supported (this is the same as with Storable).
179
180 If $enable is false (the default), then "encode" will encode shared
181 data structures repeatedly, unsharing them in the process. Cyclic
182 data structures cannot be encoded in this mode.
183
184 This option does not affect "decode" in any way - shared values and
185 references will always be decoded properly if present.
186
187 $cbor = $cbor->allow_cycles ([$enable])
188 $enabled = $cbor->get_allow_cycles
189 If $enable is true (or missing), then "decode" will happily decode
190 self-referential (cyclic) data structures. By default these will not
191 be decoded, as they need manual cleanup to avoid memory leaks, so
192 code that isn't prepared for this will not leak memory.
193
194 If $enable is false (the default), then "decode" will throw an error
195 when it encounters a self-referential/cyclic data structure.
196
197 FUTURE DIRECTION: the motivation behind this option is to avoid
198 *real* cycles - future versions of this module might chose to decode
199 cyclic data structures using weak references when this option is
200 off, instead of throwing an error.
201
202 This option does not affect "encode" in any way - shared values and
203 references will always be encoded properly if present.
204
205 $cbor = $cbor->forbid_objects ([$enable])
206 $enabled = $cbor->get_forbid_objects
207 Disables the use of the object serialiser protocol.
208
209 If $enable is true (or missing), then "encode" will will throw an
210 exception when it encounters perl objects that would be encoded
211 using the perl-object tag (26). When "decode" encounters such tags,
212 it will fall back to the general filter/tagged logic as if this were
213 an unknown tag (by default resulting in a "CBOR::XC::Tagged"
214 object).
215
216 If $enable is false (the default), then "encode" will use the
217 Types::Serialiser object serialisation protocol to serialise objects
218 into perl-object tags, and "decode" will do the same to decode such
219 tags.
220
221 See "SECURITY CONSIDERATIONS", below, for more info on why
222 forbidding this protocol can be useful.
223
224 $cbor = $cbor->pack_strings ([$enable])
225 $enabled = $cbor->get_pack_strings
226 If $enable is true (or missing), then "encode" will try not to
227 encode the same string twice, but will instead encode a reference to
228 the string instead. Depending on your data format, this can save a
229 lot of space, but also results in a very large runtime overhead
230 (expect encoding times to be 2-4 times as high as without).
231
232 It is recommended to leave it off unless you know your
233 communications partner supports the stringref extension to CBOR
234 (<http://cbor.schmorp.de/stringref>), as without decoder support,
235 the resulting data structure might not be usable.
236
237 If $enable is false (the default), then "encode" will encode strings
238 the standard CBOR way.
239
240 This option does not affect "decode" in any way - string references
241 will always be decoded properly if present.
242
243 $cbor = $cbor->text_keys ([$enable])
244 $enabled = $cbor->get_text_keys
245 If $enabled is true (or missing), then "encode" will encode all perl
246 hash keys as CBOR text strings/UTF-8 string, upgrading them as
247 needed.
248
249 If $enable is false (the default), then "encode" will encode hash
250 keys normally - upgraded perl strings (strings internally encoded as
251 UTF-8) as CBOR text strings, and downgraded perl strings as CBOR
252 byte strings.
253
254 This option does not affect "decode" in any way.
255
256 This option is useful for interoperability with CBOR decoders that
257 don't treat byte strings as a form of text. It is especially useful
258 as Perl gives very little control over hash keys.
259
260 Enabling this option can be slow, as all downgraded hash keys that
261 are encoded need to be scanned and converted to UTF-8.
262
263 $cbor = $cbor->text_strings ([$enable])
264 $enabled = $cbor->get_text_strings
265 This option works similar to "text_keys", above, but works on all
266 strings (including hash keys), so "text_keys" has no further effect
267 after enabling "text_strings".
268
269 If $enabled is true (or missing), then "encode" will encode all perl
270 strings as CBOR text strings/UTF-8 strings, upgrading them as
271 needed.
272
273 If $enable is false (the default), then "encode" will encode strings
274 normally (but see "text_keys") - upgraded perl strings (strings
275 internally encoded as UTF-8) as CBOR text strings, and downgraded
276 perl strings as CBOR byte strings.
277
278 This option does not affect "decode" in any way.
279
280 This option has similar advantages and disadvantages as "text_keys".
281 In addition, this option effectively removes the ability to
282 automatically encode byte strings, which might break some "FREEZE"
283 and "TO_CBOR" methods that rely on this.
284
285 A workaround is to use explicit type casts, which are unaffected by
286 this option.
287
288 $cbor = $cbor->validate_utf8 ([$enable])
289 $enabled = $cbor->get_validate_utf8
290 If $enable is true (or missing), then "decode" will validate that
291 elements (text strings) containing UTF-8 data in fact contain valid
292 UTF-8 data (instead of blindly accepting it). This validation
293 obviously takes extra time during decoding.
294
295 The concept of "valid UTF-8" used is perl's concept, which is a
296 superset of the official UTF-8.
297
298 If $enable is false (the default), then "decode" will blindly accept
299 UTF-8 data, marking them as valid UTF-8 in the resulting data
300 structure regardless of whether that's true or not.
301
302 Perl isn't too happy about corrupted UTF-8 in strings, but should
303 generally not crash or do similarly evil things. Extensions might be
304 not so forgiving, so it's recommended to turn on this setting if you
305 receive untrusted CBOR.
306
307 This option does not affect "encode" in any way - strings that are
308 supposedly valid UTF-8 will simply be dumped into the resulting CBOR
309 string without checking whether that is, in fact, true or not.
310
311 $cbor = $cbor->filter ([$cb->($tag, $value)])
312 $cb_or_undef = $cbor->get_filter
313 Sets or replaces the tagged value decoding filter (when $cb is
314 specified) or clears the filter (if no argument or "undef" is
315 provided).
316
317 The filter callback is called only during decoding, when a
318 non-enforced tagged value has been decoded (see "TAG HANDLING AND
319 EXTENSIONS" for a list of enforced tags). For specific tags, it's
320 often better to provide a default converter using the
321 %CBOR::XS::FILTER hash (see below).
322
323 The first argument is the numerical tag, the second is the (decoded)
324 value that has been tagged.
325
326 The filter function should return either exactly one value, which
327 will replace the tagged value in the decoded data structure, or no
328 values, which will result in default handling, which currently means
329 the decoder creates a "CBOR::XS::Tagged" object to hold the tag and
330 the value.
331
332 When the filter is cleared (the default state), the default filter
333 function, "CBOR::XS::default_filter", is used. This function simply
334 looks up the tag in the %CBOR::XS::FILTER hash. If an entry exists
335 it must be a code reference that is called with tag and value, and
336 is responsible for decoding the value. If no entry exists, it
337 returns no values. "CBOR::XS" provides a number of default filter
338 functions already, the the %CBOR::XS::FILTER hash can be freely
339 extended with more.
340
341 "CBOR::XS" additionally provides an alternative filter function that
342 is supposed to be safe to use with untrusted data (which the default
343 filter might not), called "CBOR::XS::safe_filter", which works the
344 same as the "default_filter" but uses the %CBOR::XS::SAFE_FILTER
345 variable instead. It is prepopulated with the tag decoding functions
346 that are deemed safe (basically the same as %CBOR::XS::FILTER
347 without all the bignum tags), and can be extended by user code as
348 wlel, although, obviously, one should be very careful about adding
349 decoding functions here, since the expectation is that they are safe
350 to use on untrusted data, after all.
351
352 Example: decode all tags not handled internally into
353 "CBOR::XS::Tagged" objects, with no other special handling (useful
354 when working with potentially "unsafe" CBOR data).
355
356 CBOR::XS->new->filter (sub { })->decode ($cbor_data);
357
358 Example: provide a global filter for tag 1347375694, converting the
359 value into some string form.
360
361 $CBOR::XS::FILTER{1347375694} = sub {
362 my ($tag, $value);
363
364 "tag 1347375694 value $value"
365 };
366
367 Example: provide your own filter function that looks up tags in your
368 own hash:
369
370 my %my_filter = (
371 998347484 => sub {
372 my ($tag, $value);
373
374 "tag 998347484 value $value"
375 };
376 );
377
378 my $coder = CBOR::XS->new->filter (sub {
379 &{ $my_filter{$_[0]} or return }
380 });
381
382 Example: use the safe filter function (see "SECURITY CONSIDERATIONS"
383 for more considerations on security).
384
385 CBOR::XS->new->filter (\&CBOR::XS::safe_filter)->decode ($cbor_data);
125 386
126 $cbor_data = $cbor->encode ($perl_scalar) 387 $cbor_data = $cbor->encode ($perl_scalar)
127 Converts the given Perl data structure (a scalar value) to its CBOR 388 Converts the given Perl data structure (a scalar value) to its CBOR
128 representation. 389 representation.
129 390
… …
137 will silently stop parsing there and return the number of characters 398 will silently stop parsing there and return the number of characters
138 consumed so far. 399 consumed so far.
139 400
140 This is useful if your CBOR texts are not delimited by an outer 401 This is useful if your CBOR texts are not delimited by an outer
141 protocol and you need to know where the first CBOR string ends amd 402 protocol and you need to know where the first CBOR string ends amd
142 the next one starts. 403 the next one starts - CBOR strings are self-delimited, so it is
404 possible to concatenate CBOR strings without any delimiters or size
405 fields and recover their data.
143 406
144 CBOR::XS->new->decode_prefix ("......") 407 CBOR::XS->new->decode_prefix ("......")
145 => ("...", 3) 408 => ("...", 3)
409
410 INCREMENTAL PARSING
411 In some cases, there is the need for incremental parsing of JSON texts.
412 While this module always has to keep both CBOR text and resulting Perl
413 data structure in memory at one time, it does allow you to parse a CBOR
414 stream incrementally, using a similar to using "decode_prefix" to see if
415 a full CBOR object is available, but is much more efficient.
416
417 It basically works by parsing as much of a CBOR string as possible - if
418 the CBOR data is not complete yet, the pasrer will remember where it
419 was, to be able to restart when more data has been accumulated. Once
420 enough data is available to either decode a complete CBOR value or raise
421 an error, a real decode will be attempted.
422
423 A typical use case would be a network protocol that consists of sending
424 and receiving CBOR-encoded messages. The solution that works with CBOR
425 and about anything else is by prepending a length to every CBOR value,
426 so the receiver knows how many octets to read. More compact (and
427 slightly slower) would be to just send CBOR values back-to-back, as
428 "CBOR::XS" knows where a CBOR value ends, and doesn't need an explicit
429 length.
430
431 The following methods help with this:
432
433 @decoded = $cbor->incr_parse ($buffer)
434 This method attempts to decode exactly one CBOR value from the
435 beginning of the given $buffer. The value is removed from the
436 $buffer on success. When $buffer doesn't contain a complete value
437 yet, it returns nothing. Finally, when the $buffer doesn't start
438 with something that could ever be a valid CBOR value, it raises an
439 exception, just as "decode" would. In the latter case the decoder
440 state is undefined and must be reset before being able to parse
441 further.
442
443 This method modifies the $buffer in place. When no CBOR value can be
444 decoded, the decoder stores the current string offset. On the next
445 call, continues decoding at the place where it stopped before. For
446 this to make sense, the $buffer must begin with the same octets as
447 on previous unsuccessful calls.
448
449 You can call this method in scalar context, in which case it either
450 returns a decoded value or "undef". This makes it impossible to
451 distinguish between CBOR null values (which decode to "undef") and
452 an unsuccessful decode, which is often acceptable.
453
454 @decoded = $cbor->incr_parse_multiple ($buffer)
455 Same as "incr_parse", but attempts to decode as many CBOR values as
456 possible in one go, instead of at most one. Calls to "incr_parse"
457 and "incr_parse_multiple" can be interleaved.
458
459 $cbor->incr_reset
460 Resets the incremental decoder. This throws away any saved state, so
461 that subsequent calls to "incr_parse" or "incr_parse_multiple" start
462 to parse a new CBOR value from the beginning of the $buffer again.
463
464 This method can be called at any time, but it *must* be called if
465 you want to change your $buffer or there was a decoding error and
466 you want to reuse the $cbor object for future incremental parsings.
146 467
147MAPPING 468MAPPING
148 This section describes how CBOR::XS maps Perl values to CBOR values and 469 This section describes how CBOR::XS maps Perl values to CBOR values and
149 vice versa. These mappings are designed to "do the right thing" in most 470 vice versa. These mappings are designed to "do the right thing" in most
150 circumstances automatically, preserving round-tripping characteristics 471 circumstances automatically, preserving round-tripping characteristics
… …
158 integers 479 integers
159 CBOR integers become (numeric) perl scalars. On perls without 64 bit 480 CBOR integers become (numeric) perl scalars. On perls without 64 bit
160 support, 64 bit integers will be truncated or otherwise corrupted. 481 support, 64 bit integers will be truncated or otherwise corrupted.
161 482
162 byte strings 483 byte strings
163 Byte strings will become octet strings in Perl (the byte values 484 Byte strings will become octet strings in Perl (the Byte values
164 0..255 will simply become characters of the same value in Perl). 485 0..255 will simply become characters of the same value in Perl).
165 486
166 UTF-8 strings 487 UTF-8 strings
167 UTF-8 strings in CBOR will be decoded, i.e. the UTF-8 octets will be 488 UTF-8 strings in CBOR will be decoded, i.e. the UTF-8 octets will be
168 decoded into proper Unicode code points. At the moment, the validity 489 decoded into proper Unicode code points. At the moment, the validity
… …
182 "Types:Serialiser::false" and "Types::Serialiser::error", 503 "Types:Serialiser::false" and "Types::Serialiser::error",
183 respectively. They are overloaded to act almost exactly like the 504 respectively. They are overloaded to act almost exactly like the
184 numbers 1 and 0 (for true and false) or to throw an exception on 505 numbers 1 and 0 (for true and false) or to throw an exception on
185 access (for error). See the Types::Serialiser manpage for details. 506 access (for error). See the Types::Serialiser manpage for details.
186 507
187 CBOR tag 256 (perl object) 508 tagged values
188 The tag value 256 (TODO: pending iana registration) will be used to
189 deserialise a Perl object serialised with "FREEZE". See OBJECT
190 SERIALISATION, below, for details.
191
192 CBOR tag 55799 (magic header)
193 The tag 55799 is ignored (this tag implements the magic header).
194
195 other CBOR tags
196 Tagged items consists of a numeric tag and another CBOR value. Tags 509 Tagged items consists of a numeric tag and another CBOR value.
197 not handled internally are currently converted into a
198 CBOR::XS::Tagged object, which is simply a blessed array reference
199 consisting of the numeric tag value followed by the (decoded) CBOR
200 value.
201 510
202 In the future, support for user-supplied conversions might get 511 See "TAG HANDLING AND EXTENSIONS" and the description of "->filter"
203 added. 512 for details on which tags are handled how.
204 513
205 anything else 514 anything else
206 Anything else (e.g. unsupported simple values) will raise a decoding 515 Anything else (e.g. unsupported simple values) will raise a decoding
207 error. 516 error.
208 517
209 PERL -> CBOR 518 PERL -> CBOR
210 The mapping from Perl to CBOR is slightly more difficult, as Perl is a 519 The mapping from Perl to CBOR is slightly more difficult, as Perl is a
211 truly typeless language, so we can only guess which CBOR type is meant 520 typeless language. That means this module can only guess which CBOR type
212 by a Perl value. 521 is meant by a perl value.
213 522
214 hash references 523 hash references
215 Perl hash references become CBOR maps. As there is no inherent 524 Perl hash references become CBOR maps. As there is no inherent
216 ordering in hash keys (or CBOR maps), they will usually be encoded 525 ordering in hash keys (or CBOR maps), they will usually be encoded
217 in a pseudo-random order. 526 in a pseudo-random order. This order can be different each time a
527 hash is encoded.
218 528
219 Currently, tied hashes will use the indefinite-length format, while 529 Currently, tied hashes will use the indefinite-length format, while
220 normal hashes will use the fixed-length format. 530 normal hashes will use the fixed-length format.
221 531
222 array references 532 array references
223 Perl array references become fixed-length CBOR arrays. 533 Perl array references become fixed-length CBOR arrays.
224 534
225 other references 535 other references
226 Other unblessed references are generally not allowed and will cause 536 Other unblessed references will be represented using the indirection
227 an exception to be thrown, except for references to the integers 0 537 tag extension (tag value 22098,
228 and 1, which get turned into false and true in CBOR. 538 <http://cbor.schmorp.de/indirection>). CBOR decoders are guaranteed
539 to be able to decode these values somehow, by either "doing the
540 right thing", decoding into a generic tagged object, simply ignoring
541 the tag, or something else.
229 542
230 CBOR::XS::Tagged objects 543 CBOR::XS::Tagged objects
231 Objects of this type must be arrays consisting of a single "[tag, 544 Objects of this type must be arrays consisting of a single "[tag,
232 value]" pair. The (numerical) tag will be encoded as a CBOR tag, the 545 value]" pair. The (numerical) tag will be encoded as a CBOR tag, the
233 value will be encoded as appropriate for the value. You cna use 546 value will be encoded as appropriate for the value. You must use
234 "CBOR::XS::tag" to create such objects. 547 "CBOR::XS::tag" to create such objects.
235 548
236 Types::Serialiser::true, Types::Serialiser::false, 549 Types::Serialiser::true, Types::Serialiser::false,
237 Types::Serialiser::error 550 Types::Serialiser::error
238 These special values become CBOR true, CBOR false and CBOR undefined 551 These special values become CBOR true, CBOR false and CBOR undefined
239 values, respectively. You can also use "\1", "\0" and "\undef" 552 values, respectively. You can also use "\1", "\0" and "\undef"
240 directly if you want. 553 directly if you want.
241 554
242 other blessed objects 555 other blessed objects
243 Other blessed objects are serialised via "TO_CBOR" or "FREEZE". See 556 Other blessed objects are serialised via "TO_CBOR" or "FREEZE". See
244 "OBJECT SERIALISATION", below, for details. 557 "TAG HANDLING AND EXTENSIONS" for specific classes handled by this
558 module, and "OBJECT SERIALISATION" for generic object serialisation.
245 559
246 simple scalars 560 simple scalars
247 TODO Simple Perl scalars (any scalar that is not a reference) are 561 Simple Perl scalars (any scalar that is not a reference) are the
248 the most difficult objects to encode: CBOR::XS will encode undefined 562 most difficult objects to encode: CBOR::XS will encode undefined
249 scalars as CBOR null values, scalars that have last been used in a 563 scalars as CBOR null values, scalars that have last been used in a
250 string context before encoding as CBOR strings, and anything else as 564 string context before encoding as CBOR strings, and anything else as
251 number value: 565 number value:
252 566
253 # dump as number 567 # dump as number
254 encode_cbor [2] # yields [2] 568 encode_cbor [2] # yields [2]
255 encode_cbor [-3.0e17] # yields [-3e+17] 569 encode_cbor [-3.0e17] # yields [-3e+17]
256 my $value = 5; encode_cbor [$value] # yields [5] 570 my $value = 5; encode_cbor [$value] # yields [5]
257 571
258 # used as string, so dump as string 572 # used as string, so dump as string (either byte or text)
259 print $value; 573 print $value;
260 encode_cbor [$value] # yields ["5"] 574 encode_cbor [$value] # yields ["5"]
261 575
262 # undef becomes null 576 # undef becomes null
263 encode_cbor [undef] # yields [null] 577 encode_cbor [undef] # yields [null]
… …
266 580
267 my $x = 3.1; # some variable containing a number 581 my $x = 3.1; # some variable containing a number
268 "$x"; # stringified 582 "$x"; # stringified
269 $x .= ""; # another, more awkward way to stringify 583 $x .= ""; # another, more awkward way to stringify
270 print $x; # perl does it for you, too, quite often 584 print $x; # perl does it for you, too, quite often
585
586 You can force whether a string is encoded as byte or text string by
587 using "utf8::upgrade" and "utf8::downgrade" (if "text_strings" is
588 disabled).
589
590 utf8::upgrade $x; # encode $x as text string
591 utf8::downgrade $x; # encode $x as byte string
592
593 More options are available, see "TYPE CASTS", below, and the
594 "text_keys" and "text_strings" options.
595
596 Perl doesn't define what operations up- and downgrade strings, so if
597 the difference between byte and text is important, you should up- or
598 downgrade your string as late as possible before encoding. You can
599 also force the use of CBOR text strings by using "text_keys" or
600 "text_strings".
271 601
272 You can force the type to be a CBOR number by numifying it: 602 You can force the type to be a CBOR number by numifying it:
273 603
274 my $x = "3"; # some variable containing a string 604 my $x = "3"; # some variable containing a string
275 $x += 0; # numify it, ensuring it will be dumped as a number 605 $x += 0; # numify it, ensuring it will be dumped as a number
… …
284 IEEE single format if possible without loss of precision, otherwise 614 IEEE single format if possible without loss of precision, otherwise
285 the IEEE double format will be used. Perls that use formats other 615 the IEEE double format will be used. Perls that use formats other
286 than IEEE double to represent numerical values are supported, but 616 than IEEE double to represent numerical values are supported, but
287 might suffer loss of precision. 617 might suffer loss of precision.
288 618
619 TYPE CASTS
620 EXPERIMENTAL: As an experimental extension, "CBOR::XS" allows you to
621 force specific cbor types to be used when encoding. That allows you to
622 encode types not normally accessible (e.g. half floats) as well as force
623 string types even when "text_strings" is in effect.
624
625 Type forcing is done by calling a special "cast" function which keeps a
626 copy of the value and returns a new value that can be handed over to any
627 CBOR encoder function.
628
629 The following casts are currently available (all of which are unary
630 operators):
631
632 CBOR::XS::as_int $value
633 Forces the value to be encoded as some form of (basic, not bignum)
634 integer type.
635
636 CBOR::XS::as_text $value
637 Forces the value to be encoded as (UTF-8) text values.
638
639 CBOR::XS::as_bytes $value
640 Forces the value to be encoded as a (binary) string value.
641
642 CBOR::XS::as_float16 $value
643 Forces half-float (IEEE 754 binary16) encoding of the given value.
644
645 CBOR::XS::as_float32 $value
646 Forces single-float (IEEE 754 binary32) encoding of the given value.
647
648 CBOR::XS::as_float64 $value
649 Forces double-float (IEEE 754 binary64) encoding of the given value.
650
651 =item, CBOR::XS::as_cbor $cbor_text
652
653 Bot a type cast per-se, this type cast forces the argument to eb
654 encoded as-is. This can be used to embed pre-encoded CBOR data.
655
656 Note that no checking on the validity of the $cbor_text is done -
657 it's the callers responsibility to correctly encode values.
658
659 Example: encode a perl string as binary even though "text_strings" is in
660 effect.
661
662 CBOR::XS->new->text_strings->encode ([4, "text", CBOR::XS::bytes "bytevalue"]);
663
289 OBJECT SERIALISATION 664 OBJECT SERIALISATION
665 This module implements both a CBOR-specific and the generic
666 Types::Serialier object serialisation protocol. The following
667 subsections explain both methods.
668
669 ENCODING
290 This module knows two way to serialise a Perl object: The CBOR-specific 670 This module knows two way to serialise a Perl object: The CBOR-specific
291 way, and the generic way. 671 way, and the generic way.
292 672
293 Whenever the encoder encounters a Perl object that it cnanot serialise 673 Whenever the encoder encounters a Perl object that it cannot serialise
294 directly (most of them), it will first look up the "TO_CBOR" method on 674 directly (most of them), it will first look up the "TO_CBOR" method on
295 it. 675 it.
296 676
297 If it has a "TO_CBOR" method, it will call it with the object as only 677 If it has a "TO_CBOR" method, it will call it with the object as only
298 argument, and expects exactly one return value, which it will then 678 argument, and expects exactly one return value, which it will then
… …
303 "CBOR" as the second argument, to distinguish it from other serialisers. 683 "CBOR" as the second argument, to distinguish it from other serialisers.
304 684
305 The "FREEZE" method can return any number of values (i.e. zero or more). 685 The "FREEZE" method can return any number of values (i.e. zero or more).
306 These will be encoded as CBOR perl object, together with the classname. 686 These will be encoded as CBOR perl object, together with the classname.
307 687
688 These methods *MUST NOT* change the data structure that is being
689 serialised. Failure to comply to this can result in memory corruption -
690 and worse.
691
308 If an object supports neither "TO_CBOR" nor "FREEZE", encoding will fail 692 If an object supports neither "TO_CBOR" nor "FREEZE", encoding will fail
309 with an error. 693 with an error.
310 694
695 DECODING
311 Objects encoded via "TO_CBOR" cannot be automatically decoded, but 696 Objects encoded via "TO_CBOR" cannot (normally) be automatically
312 objects encoded via "FREEZE" can be decoded using the following 697 decoded, but objects encoded via "FREEZE" can be decoded using the
313 protocol: 698 following protocol:
314 699
315 When an encoded CBOR perl object is encountered by the decoder, it will 700 When an encoded CBOR perl object is encountered by the decoder, it will
316 look up the "THAW" method, by using the stored classname, and will fail 701 look up the "THAW" method, by using the stored classname, and will fail
317 if the method cannot be found. 702 if the method cannot be found.
318 703
… …
339 724
340 sub URI::TO_CBOR { 725 sub URI::TO_CBOR {
341 my ($self) = @_; 726 my ($self) = @_;
342 my $uri = "$self"; # stringify uri 727 my $uri = "$self"; # stringify uri
343 utf8::upgrade $uri; # make sure it will be encoded as UTF-8 string 728 utf8::upgrade $uri; # make sure it will be encoded as UTF-8 string
344 CBOR::XS::tagged 32, "$_[0]" 729 CBOR::XS::tag 32, "$_[0]"
345 } 730 }
346 731
347 This will encode URIs as a UTF-8 string with tag 32, which indicates an 732 This will encode URIs as a UTF-8 string with tag 32, which indicates an
348 URI. 733 URI.
349 734
… …
360 "$self" # encode url string 745 "$self" # encode url string
361 } 746 }
362 747
363 sub URI::THAW { 748 sub URI::THAW {
364 my ($class, $serialiser, $uri) = @_; 749 my ($class, $serialiser, $uri) = @_;
365
366 $class->new ($uri) 750 $class->new ($uri)
367 } 751 }
368 752
369 Unlike "TO_CBOR", multiple values can be returned by "FREEZE". For 753 Unlike "TO_CBOR", multiple values can be returned by "FREEZE". For
370 example, a "FREEZE" method that returns "type", "id" and "variant" 754 example, a "FREEZE" method that returns "type", "id" and "variant"
… …
384 768
385MAGIC HEADER 769MAGIC HEADER
386 There is no way to distinguish CBOR from other formats programmatically. 770 There is no way to distinguish CBOR from other formats programmatically.
387 To make it easier to distinguish CBOR from other formats, the CBOR 771 To make it easier to distinguish CBOR from other formats, the CBOR
388 specification has a special "magic string" that can be prepended to any 772 specification has a special "magic string" that can be prepended to any
389 CBOR string without changing it's meaning. 773 CBOR string without changing its meaning.
390 774
391 This string is available as $CBOR::XS::MAGIC. This module does not 775 This string is available as $CBOR::XS::MAGIC. This module does not
392 prepend this string tot he CBOR data it generates, but it will ignroe it 776 prepend this string to the CBOR data it generates, but it will ignore it
393 if present, so users can prepend this string as a "file type" indicator 777 if present, so users can prepend this string as a "file type" indicator
394 as required. 778 as required.
395 779
396THE CBOR::XS::Tagged CLASS 780THE CBOR::XS::Tagged CLASS
397 CBOR has the concept of tagged values - any CBOR value can be tagged 781 CBOR has the concept of tagged values - any CBOR value can be tagged
… …
448 Wrap CBOR data in CBOR: 832 Wrap CBOR data in CBOR:
449 833
450 my $cbor_cbor = encode_cbor 834 my $cbor_cbor = encode_cbor
451 CBOR::XS::tag 24, 835 CBOR::XS::tag 24,
452 encode_cbor [1, 2, 3]; 836 encode_cbor [1, 2, 3];
837
838TAG HANDLING AND EXTENSIONS
839 This section describes how this module handles specific tagged values
840 and extensions. If a tag is not mentioned here and no additional filters
841 are provided for it, then the default handling applies (creating a
842 CBOR::XS::Tagged object on decoding, and only encoding the tag when
843 explicitly requested).
844
845 Tags not handled specifically are currently converted into a
846 CBOR::XS::Tagged object, which is simply a blessed array reference
847 consisting of the numeric tag value followed by the (decoded) CBOR
848 value.
849
850 Future versions of this module reserve the right to special case
851 additional tags (such as base64url).
852
853 ENFORCED TAGS
854 These tags are always handled when decoding, and their handling cannot
855 be overridden by the user.
856
857 26 (perl-object, <http://cbor.schmorp.de/perl-object>)
858 These tags are automatically created (and decoded) for serialisable
859 objects using the "FREEZE/THAW" methods (the Types::Serialier object
860 serialisation protocol). See "OBJECT SERIALISATION" for details.
861
862 28, 29 (shareable, sharedref, <http://cbor.schmorp.de/value-sharing>)
863 These tags are automatically decoded when encountered (and they do
864 not result in a cyclic data structure, see "allow_cycles"),
865 resulting in shared values in the decoded object. They are only
866 encoded, however, when "allow_sharing" is enabled.
867
868 Not all shared values can be successfully decoded: values that
869 reference themselves will *currently* decode as "undef" (this is not
870 the same as a reference pointing to itself, which will be
871 represented as a value that contains an indirect reference to itself
872 - these will be decoded properly).
873
874 Note that considerably more shared value data structures can be
875 decoded than will be encoded - currently, only values pointed to by
876 references will be shared, others will not. While non-reference
877 shared values can be generated in Perl with some effort, they were
878 considered too unimportant to be supported in the encoder. The
879 decoder, however, will decode these values as shared values.
880
881 256, 25 (stringref-namespace, stringref,
882 <http://cbor.schmorp.de/stringref>)
883 These tags are automatically decoded when encountered. They are only
884 encoded, however, when "pack_strings" is enabled.
885
886 22098 (indirection, <http://cbor.schmorp.de/indirection>)
887 This tag is automatically generated when a reference are encountered
888 (with the exception of hash and array references). It is converted
889 to a reference when decoding.
890
891 55799 (self-describe CBOR, RFC 7049)
892 This value is not generated on encoding (unless explicitly requested
893 by the user), and is simply ignored when decoding.
894
895 NON-ENFORCED TAGS
896 These tags have default filters provided when decoding. Their handling
897 can be overridden by changing the %CBOR::XS::FILTER entry for the tag,
898 or by providing a custom "filter" callback when decoding.
899
900 When they result in decoding into a specific Perl class, the module
901 usually provides a corresponding "TO_CBOR" method as well.
902
903 When any of these need to load additional modules that are not part of
904 the perl core distribution (e.g. URI), it is (currently) up to the user
905 to provide these modules. The decoding usually fails with an exception
906 if the required module cannot be loaded.
907
908 0, 1 (date/time string, seconds since the epoch)
909 These tags are decoded into Time::Piece objects. The corresponding
910 "Time::Piece::TO_CBOR" method always encodes into tag 1 values
911 currently.
912
913 The Time::Piece API is generally surprisingly bad, and fractional
914 seconds are only accidentally kept intact, so watch out. On the plus
915 side, the module comes with perl since 5.10, which has to count for
916 something.
917
918 2, 3 (positive/negative bignum)
919 These tags are decoded into Math::BigInt objects. The corresponding
920 "Math::BigInt::TO_CBOR" method encodes "small" bigints into normal
921 CBOR integers, and others into positive/negative CBOR bignums.
922
923 4, 5, 264, 265 (decimal fraction/bigfloat)
924 Both decimal fractions and bigfloats are decoded into Math::BigFloat
925 objects. The corresponding "Math::BigFloat::TO_CBOR" method *always*
926 encodes into a decimal fraction (either tag 4 or 264).
927
928 NaN and infinities are not encoded properly, as they cannot be
929 represented in CBOR.
930
931 See "BIGNUM SECURITY CONSIDERATIONS" for more info.
932
933 30 (rational numbers)
934 These tags are decoded into Math::BigRat objects. The corresponding
935 "Math::BigRat::TO_CBOR" method encodes rational numbers with
936 denominator 1 via their numerator only, i.e., they become normal
937 integers or "bignums".
938
939 See "BIGNUM SECURITY CONSIDERATIONS" for more info.
940
941 21, 22, 23 (expected later JSON conversion)
942 CBOR::XS is not a CBOR-to-JSON converter, and will simply ignore
943 these tags.
944
945 32 (URI)
946 These objects decode into URI objects. The corresponding
947 "URI::TO_CBOR" method again results in a CBOR URI value.
453 948
454CBOR and JSON 949CBOR and JSON
455 CBOR is supposed to implement a superset of the JSON data model, and is, 950 CBOR is supposed to implement a superset of the JSON data model, and is,
456 with some coercion, able to represent all JSON texts (something that 951 with some coercion, able to represent all JSON texts (something that
457 other "binary JSON" formats such as BSON generally do not support). 952 other "binary JSON" formats such as BSON generally do not support).
… …
463 interoperability is improved in the future, then the goal will be to 958 interoperability is improved in the future, then the goal will be to
464 ensure that decoded JSON data will round-trip encoding and decoding to 959 ensure that decoded JSON data will round-trip encoding and decoding to
465 CBOR intact. 960 CBOR intact.
466 961
467SECURITY CONSIDERATIONS 962SECURITY CONSIDERATIONS
468 When you are using CBOR in a protocol, talking to untrusted potentially 963 Tl;dr... if you want to decode or encode CBOR from untrusted sources,
469 hostile creatures requires relatively few measures. 964 you should start with a coder object created via "new_safe" (which
965 implements the mitigations explained below):
470 966
967 my $coder = CBOR::XS->new_safe;
968
969 my $data = $coder->decode ($cbor_text);
970 my $cbor = $coder->encode ($data);
971
972 Longer version: When you are using CBOR in a protocol, talking to
973 untrusted potentially hostile creatures requires some thought:
974
975 Security of the CBOR decoder itself
471 First of all, your CBOR decoder should be secure, that is, should not 976 First and foremost, your CBOR decoder should be secure, that is,
472 have any buffer overflows. Obviously, this module should ensure that and 977 should not have any buffer overflows or similar bugs that could
978 potentially be exploited. Obviously, this module should ensure that
473 I am trying hard on making that true, but you never know. 979 and I am trying hard on making that true, but you never know.
474 980
981 CBOR::XS can invoke almost arbitrary callbacks during decoding
982 CBOR::XS supports object serialisation - decoding CBOR can cause
983 calls to *any* "THAW" method in *any* package that exists in your
984 process (that is, CBOR::XS will not try to load modules, but any
985 existing "THAW" method or function can be called, so they all have
986 to be secure).
987
988 Less obviously, it will also invoke "TO_CBOR" and "FREEZE" methods -
989 even if all your "THAW" methods are secure, encoding data structures
990 from untrusted sources can invoke those and trigger bugs in those.
991
992 So, if you are not sure about the security of all the modules you
993 have loaded (you shouldn't), you should disable this part using
994 "forbid_objects" or using "new_safe".
995
996 CBOR can be extended with tags that call library code
997 CBOR can be extended with tags, and "CBOR::XS" has a registry of
998 conversion functions for many existing tags that can be extended via
999 third-party modules (see the "filter" method).
1000
1001 If you don't trust these, you should configure the "safe" filter
1002 function, "CBOR::XS::safe_filter" ("new_safe" does this), which by
1003 default only includes conversion functions that are considered
1004 "safe" by the author (but again, they can be extended by third party
1005 modules).
1006
1007 Depending on your level of paranoia, you can use the "safe" filter:
1008
1009 $cbor->filter (\&CBOR::XS::safe_filter);
1010
1011 ... your own filter...
1012
1013 $cbor->filter (sub { ... do your stuffs here ... });
1014
1015 ... or even no filter at all, disabling all tag decoding:
1016
1017 $cbor->filter (sub { });
1018
1019 This is never a problem for encoding, as the tag mechanism only
1020 exists in CBOR texts.
1021
1022 Resource-starving attacks: object memory usage
475 Second, you need to avoid resource-starving attacks. That means you 1023 You need to avoid resource-starving attacks. That means you should
476 should limit the size of CBOR data you accept, or make sure then when 1024 limit the size of CBOR data you accept, or make sure then when your
477 your resources run out, that's just fine (e.g. by using a separate 1025 resources run out, that's just fine (e.g. by using a separate
478 process that can crash safely). The size of a CBOR string in octets is 1026 process that can crash safely). The size of a CBOR string in octets
479 usually a good indication of the size of the resources required to 1027 is usually a good indication of the size of the resources required
480 decode it into a Perl structure. While CBOR::XS can check the size of 1028 to decode it into a Perl structure. While CBOR::XS can check the
1029 size of the CBOR text (using "max_size" - done by "new_safe"), it
481 the CBOR text, it might be too late when you already have it in memory, 1030 might be too late when you already have it in memory, so you might
482 so you might want to check the size before you accept the string. 1031 want to check the size before you accept the string.
483 1032
1033 As for encoding, it is possible to construct data structures that
1034 are relatively small but result in large CBOR texts (for example by
1035 having an array full of references to the same big data structure,
1036 which will all be deep-cloned during encoding by default). This is
1037 rarely an actual issue (and the worst case is still just running out
1038 of memory), but you can reduce this risk by using "allow_sharing".
1039
1040 Resource-starving attacks: stack overflows
484 Third, CBOR::XS recurses using the C stack when decoding objects and 1041 CBOR::XS recurses using the C stack when decoding objects and
485 arrays. The C stack is a limited resource: for instance, on my amd64 1042 arrays. The C stack is a limited resource: for instance, on my amd64
486 machine with 8MB of stack size I can decode around 180k nested arrays 1043 machine with 8MB of stack size I can decode around 180k nested
487 but only 14k nested CBOR objects (due to perl itself recursing deeply on 1044 arrays but only 14k nested CBOR objects (due to perl itself
488 croak to free the temporary). If that is exceeded, the program crashes. 1045 recursing deeply on croak to free the temporary). If that is
489 To be conservative, the default nesting limit is set to 512. If your 1046 exceeded, the program crashes. To be conservative, the default
490 process has a smaller stack, you should adjust this setting accordingly 1047 nesting limit is set to 512. If your process has a smaller stack,
491 with the "max_depth" method. 1048 you should adjust this setting accordingly with the "max_depth"
1049 method.
492 1050
1051 Resource-starving attacks: CPU en-/decoding complexity
1052 CBOR::XS will use the Math::BigInt, Math::BigFloat and Math::BigRat
1053 libraries to represent encode/decode bignums. These can be very slow
1054 (as in, centuries of CPU time) and can even crash your program (and
1055 are generally not very trustworthy). See the next section on bignum
1056 security for details.
1057
1058 Data breaches: leaking information in error messages
1059 CBOR::XS might leak contents of your Perl data structures in its
1060 error messages, so when you serialise sensitive information you
1061 might want to make sure that exceptions thrown by CBOR::XS will not
1062 end up in front of untrusted eyes.
1063
1064 Something else...
493 Something else could bomb you, too, that I forgot to think of. In that 1065 Something else could bomb you, too, that I forgot to think of. In
494 case, you get to keep the pieces. I am always open for hints, though... 1066 that case, you get to keep the pieces. I am always open for hints,
1067 though...
495 1068
496 Also keep in mind that CBOR::XS might leak contents of your Perl data 1069BIGNUM SECURITY CONSIDERATIONS
497 structures in its error messages, so when you serialise sensitive 1070 CBOR::XS provides a "TO_CBOR" method for both Math::BigInt and
498 information you might want to make sure that exceptions thrown by 1071 Math::BigFloat that tries to encode the number in the simplest possible
499 CBOR::XS will not end up in front of untrusted eyes. 1072 way, that is, either a CBOR integer, a CBOR bigint/decimal fraction (tag
1073 4) or an arbitrary-exponent decimal fraction (tag 264). Rational numbers
1074 (Math::BigRat, tag 30) can also contain bignums as members.
1075
1076 CBOR::XS will also understand base-2 bigfloat or arbitrary-exponent
1077 bigfloats (tags 5 and 265), but it will never generate these on its own.
1078
1079 Using the built-in Math::BigInt::Calc support, encoding and decoding
1080 decimal fractions is generally fast. Decoding bigints can be slow for
1081 very big numbers (tens of thousands of digits, something that could
1082 potentially be caught by limiting the size of CBOR texts), and decoding
1083 bigfloats or arbitrary-exponent bigfloats can be *extremely* slow
1084 (minutes, decades) for large exponents (roughly 40 bit and longer).
1085
1086 Additionally, Math::BigInt can take advantage of other bignum libraries,
1087 such as Math::GMP, which cannot handle big floats with large exponents,
1088 and might simply abort or crash your program, due to their code quality.
1089
1090 This can be a concern if you want to parse untrusted CBOR. If it is, you
1091 might want to disable decoding of tag 2 (bigint) and 3 (negative bigint)
1092 types. You should also disable types 5 and 265, as these can be slow
1093 even without bigints.
1094
1095 Disabling bigints will also partially or fully disable types that rely
1096 on them, e.g. rational numbers that use bignums.
500 1097
501CBOR IMPLEMENTATION NOTES 1098CBOR IMPLEMENTATION NOTES
502 This section contains some random implementation notes. They do not 1099 This section contains some random implementation notes. They do not
503 describe guaranteed behaviour, but merely behaviour as-is implemented 1100 describe guaranteed behaviour, but merely behaviour as-is implemented
504 right now. 1101 right now.
… …
512 Only the double data type is supported for NV data types - when Perl 1109 Only the double data type is supported for NV data types - when Perl
513 uses long double to represent floating point values, they might not be 1110 uses long double to represent floating point values, they might not be
514 encoded properly. Half precision types are accepted, but not encoded. 1111 encoded properly. Half precision types are accepted, but not encoded.
515 1112
516 Strict mode and canonical mode are not implemented. 1113 Strict mode and canonical mode are not implemented.
1114
1115LIMITATIONS ON PERLS WITHOUT 64-BIT INTEGER SUPPORT
1116 On perls that were built without 64 bit integer support (these are rare
1117 nowadays, even on 32 bit architectures, as all major Perl distributions
1118 are built with 64 bit integer support), support for any kind of 64 bit
1119 value in CBOR is very limited - most likely, these 64 bit values will be
1120 truncated, corrupted, or otherwise not decoded correctly. This also
1121 includes string, float, array and map sizes that are stored as 64 bit
1122 integers.
517 1123
518THREADS 1124THREADS
519 This module is *not* guaranteed to be thread safe and there are no plans 1125 This module is *not* guaranteed to be thread safe and there are no plans
520 to change this until Perl gets thread support (as opposed to the 1126 to change this until Perl gets thread support (as opposed to the
521 horribly slow so-called "threads" which are simply slow and bloated 1127 horribly slow so-called "threads" which are simply slow and bloated

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