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Revision 1.23 by root, Fri Sep 8 20:03:06 2023 UTC

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8 $perl_value = decode_cbor $binary_cbor_data; 8 $perl_value = decode_cbor $binary_cbor_data;
9 9
10 # OO-interface 10 # OO-interface
11 11
12 $coder = CBOR::XS->new; 12 $coder = CBOR::XS->new;
13 #TODO 13 $binary_cbor_data = $coder->encode ($perl_value);
14 $perl_value = $coder->decode ($binary_cbor_data);
15
16 # prefix decoding
17
18 my $many_cbor_strings = ...;
19 while (length $many_cbor_strings) {
20 my ($data, $length) = $cbor->decode_prefix ($many_cbor_strings);
21 # data was decoded
22 substr $many_cbor_strings, 0, $length, ""; # remove decoded cbor string
23 }
14 24
15DESCRIPTION 25DESCRIPTION
16 WARNING! THIS IS A PRE-ALPHA RELEASE! IT WILL CRASH, CORRUPT YOUR DATA 26 This module converts Perl data structures to the Concise Binary Object
17 AND EAT YOUR CHILDREN! 27 Representation (CBOR) and vice versa. CBOR is a fast binary
28 serialisation format that aims to use an (almost) superset of the JSON
29 data model, i.e. when you can represent something useful in JSON, you
30 should be able to represent it in CBOR.
18 31
19 This module converts Perl data structures to CBOR and vice versa. Its 32 In short, CBOR is a faster and quite compact binary alternative to JSON,
20 primary goal is to be *correct* and its secondary goal is to be *fast*. 33 with the added ability of supporting serialisation of Perl objects.
34 (JSON often compresses better than CBOR though, so if you plan to
35 compress the data later and speed is less important you might want to
36 compare both formats first).
37
38 The primary goal of this module is to be *correct* and the secondary
21 To reach the latter goal it was written in C. 39 goal is to be *fast*. To reach the latter goal it was written in C.
40
41 To give you a general idea about speed, with texts in the megabyte
42 range, "CBOR::XS" usually encodes roughly twice as fast as Storable or
43 JSON::XS and decodes about 15%-30% faster than those. The shorter the
44 data, the worse Storable performs in comparison.
45
46 Regarding compactness, "CBOR::XS"-encoded data structures are usually
47 about 20% smaller than the same data encoded as (compact) JSON or
48 Storable.
49
50 In addition to the core CBOR data format, this module implements a
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).
22 54
23 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
24 vice versa. 56 vice versa.
25 57
26FUNCTIONAL INTERFACE 58FUNCTIONAL INTERFACE
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45 *disabled*. 77 *disabled*.
46 78
47 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
48 calls can be chained: 80 calls can be chained:
49 81
50 #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 ->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).
51 98
52 $cbor = $cbor->max_depth ([$maximum_nesting_depth]) 99 $cbor = $cbor->max_depth ([$maximum_nesting_depth])
53 $max_depth = $cbor->get_max_depth 100 $max_depth = $cbor->get_max_depth
54 Sets the maximum nesting level (default 512) accepted while encoding 101 Sets the maximum nesting level (default 512) accepted while encoding
55 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
… …
69 116
70 Note that nesting is implemented by recursion in C. The default 117 Note that nesting is implemented by recursion in C. The default
71 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
72 allow without crashing. 119 allow without crashing.
73 120
74 See SECURITY CONSIDERATIONS, below, for more info on why this is 121 See "SECURITY CONSIDERATIONS", below, for more info on why this is
75 useful. 122 useful.
76 123
77 $cbor = $cbor->max_size ([$maximum_string_size]) 124 $cbor = $cbor->max_size ([$maximum_string_size])
78 $max_size = $cbor->get_max_size 125 $max_size = $cbor->get_max_size
79 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
… …
83 exception. This setting has no effect on "encode" (yet). 130 exception. This setting has no effect on "encode" (yet).
84 131
85 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
86 as when 0 is specified). 133 as when 0 is specified).
87 134
88 See SECURITY CONSIDERATIONS, below, for more info on why this is 135 See "SECURITY CONSIDERATIONS", below, for more info on why this is
89 useful. 136 useful.
137
138 $cbor = $cbor->allow_unknown ([$enable])
139 $enabled = $cbor->get_allow_unknown
140 If $enable is true (or missing), then "encode" will *not* throw an
141 exception when it encounters values it cannot represent in CBOR (for
142 example, filehandles) but instead will encode a CBOR "error" value.
143
144 If $enable is false (the default), then "encode" will throw an
145 exception when it encounters anything it cannot encode as CBOR.
146
147 This option does not affect "decode" in any way, and it is
148 recommended to leave it off unless you know your communications
149 partner.
150
151 $cbor = $cbor->allow_sharing ([$enable])
152 $enabled = $cbor->get_allow_sharing
153 If $enable is true (or missing), then "encode" will not
154 double-encode values that have been referenced before (e.g. when the
155 same object, such as an array, is referenced multiple times), but
156 instead will emit a reference to the earlier value.
157
158 This means that such values will only be encoded once, and will not
159 result in a deep cloning of the value on decode, in decoders
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).
163
164 It is recommended to leave it off unless you know your communication
165 partner supports the value sharing extensions to CBOR
166 (<http://cbor.schmorp.de/value-sharing>), as without decoder
167 support, the resulting data structure might be unusable.
168
169 Detecting shared values incurs a runtime overhead when values are
170 encoded that have a reference counter larger than one, and might
171 unnecessarily increase the encoded size, as potentially shared
172 values are encoded as shareable whether or not they are actually
173 shared.
174
175 At the moment, only targets of references can be shared (e.g.
176 scalars, arrays or hashes pointed to by a reference). Weirder
177 constructs, such as an array with multiple "copies" of the *same*
178 string, which are hard but not impossible to create in Perl, are not
179 supported (this is the same as with Storable).
180
181 If $enable is false (the default), then "encode" will encode shared
182 data structures repeatedly, unsharing them in the process. Cyclic
183 data structures cannot be encoded in this mode.
184
185 This option does not affect "decode" in any way - shared values and
186 references will always be decoded properly if present.
187
188 $cbor = $cbor->allow_cycles ([$enable])
189 $enabled = $cbor->get_allow_cycles
190 If $enable is true (or missing), then "decode" will happily decode
191 self-referential (cyclic) data structures. By default these will not
192 be decoded, as they need manual cleanup to avoid memory leaks, so
193 code that isn't prepared for this will not leak memory.
194
195 If $enable is false (the default), then "decode" will throw an error
196 when it encounters a self-referential/cyclic data structure.
197
198 This option does not affect "encode" in any way - shared values and
199 references will always be encoded properly if present.
200
201 $cbor = $cbor->allow_weak_cycles ([$enable])
202 $enabled = $cbor->get_allow_weak_cycles
203 This works like "allow_cycles" in that it allows the resulting data
204 structures to contain cycles, but unlike "allow_cycles", those
205 cyclic rreferences will be weak. That means that code that
206 recurrsively walks the data structure must be prepared with cycles,
207 but at least not special precautions must be implemented to free
208 these data structures.
209
210 Only those references leading to actual cycles will be weakened -
211 other references, e.g. when the same hash or arrray is referenced
212 multiple times in an arrray, will be normal references.
213
214 This option does not affect "encode" in any way - shared values and
215 references will always be encoded properly if present.
216
217 $cbor = $cbor->forbid_objects ([$enable])
218 $enabled = $cbor->get_forbid_objects
219 Disables the use of the object serialiser protocol.
220
221 If $enable is true (or missing), then "encode" will will throw an
222 exception when it encounters perl objects that would be encoded
223 using the perl-object tag (26). When "decode" encounters such tags,
224 it will fall back to the general filter/tagged logic as if this were
225 an unknown tag (by default resulting in a "CBOR::XC::Tagged"
226 object).
227
228 If $enable is false (the default), then "encode" will use the
229 Types::Serialiser object serialisation protocol to serialise objects
230 into perl-object tags, and "decode" will do the same to decode such
231 tags.
232
233 See "SECURITY CONSIDERATIONS", below, for more info on why
234 forbidding this protocol can be useful.
235
236 $cbor = $cbor->pack_strings ([$enable])
237 $enabled = $cbor->get_pack_strings
238 If $enable is true (or missing), then "encode" will try not to
239 encode the same string twice, but will instead encode a reference to
240 the string instead. Depending on your data format, this can save a
241 lot of space, but also results in a very large runtime overhead
242 (expect encoding times to be 2-4 times as high as without).
243
244 It is recommended to leave it off unless you know your
245 communications partner supports the stringref extension to CBOR
246 (<http://cbor.schmorp.de/stringref>), as without decoder support,
247 the resulting data structure might not be usable.
248
249 If $enable is false (the default), then "encode" will encode strings
250 the standard CBOR way.
251
252 This option does not affect "decode" in any way - string references
253 will always be decoded properly if present.
254
255 $cbor = $cbor->text_keys ([$enable])
256 $enabled = $cbor->get_text_keys
257 If $enabled is true (or missing), then "encode" will encode all perl
258 hash keys as CBOR text strings/UTF-8 string, upgrading them as
259 needed.
260
261 If $enable is false (the default), then "encode" will encode hash
262 keys normally - upgraded perl strings (strings internally encoded as
263 UTF-8) as CBOR text strings, and downgraded perl strings as CBOR
264 byte strings.
265
266 This option does not affect "decode" in any way.
267
268 This option is useful for interoperability with CBOR decoders that
269 don't treat byte strings as a form of text. It is especially useful
270 as Perl gives very little control over hash keys.
271
272 Enabling this option can be slow, as all downgraded hash keys that
273 are encoded need to be scanned and converted to UTF-8.
274
275 $cbor = $cbor->text_strings ([$enable])
276 $enabled = $cbor->get_text_strings
277 This option works similar to "text_keys", above, but works on all
278 strings (including hash keys), so "text_keys" has no further effect
279 after enabling "text_strings".
280
281 If $enabled is true (or missing), then "encode" will encode all perl
282 strings as CBOR text strings/UTF-8 strings, upgrading them as
283 needed.
284
285 If $enable is false (the default), then "encode" will encode strings
286 normally (but see "text_keys") - upgraded perl strings (strings
287 internally encoded as UTF-8) as CBOR text strings, and downgraded
288 perl strings as CBOR byte strings.
289
290 This option does not affect "decode" in any way.
291
292 This option has similar advantages and disadvantages as "text_keys".
293 In addition, this option effectively removes the ability to
294 automatically encode byte strings, which might break some "FREEZE"
295 and "TO_CBOR" methods that rely on this.
296
297 A workaround is to use explicit type casts, which are unaffected by
298 this option.
299
300 $cbor = $cbor->validate_utf8 ([$enable])
301 $enabled = $cbor->get_validate_utf8
302 If $enable is true (or missing), then "decode" will validate that
303 elements (text strings) containing UTF-8 data in fact contain valid
304 UTF-8 data (instead of blindly accepting it). This validation
305 obviously takes extra time during decoding.
306
307 The concept of "valid UTF-8" used is perl's concept, which is a
308 superset of the official UTF-8.
309
310 If $enable is false (the default), then "decode" will blindly accept
311 UTF-8 data, marking them as valid UTF-8 in the resulting data
312 structure regardless of whether that's true or not.
313
314 Perl isn't too happy about corrupted UTF-8 in strings, but should
315 generally not crash or do similarly evil things. Extensions might be
316 not so forgiving, so it's recommended to turn on this setting if you
317 receive untrusted CBOR.
318
319 This option does not affect "encode" in any way - strings that are
320 supposedly valid UTF-8 will simply be dumped into the resulting CBOR
321 string without checking whether that is, in fact, true or not.
322
323 $cbor = $cbor->filter ([$cb->($tag, $value)])
324 $cb_or_undef = $cbor->get_filter
325 Sets or replaces the tagged value decoding filter (when $cb is
326 specified) or clears the filter (if no argument or "undef" is
327 provided).
328
329 The filter callback is called only during decoding, when a
330 non-enforced tagged value has been decoded (see "TAG HANDLING AND
331 EXTENSIONS" for a list of enforced tags). For specific tags, it's
332 often better to provide a default converter using the
333 %CBOR::XS::FILTER hash (see below).
334
335 The first argument is the numerical tag, the second is the (decoded)
336 value that has been tagged.
337
338 The filter function should return either exactly one value, which
339 will replace the tagged value in the decoded data structure, or no
340 values, which will result in default handling, which currently means
341 the decoder creates a "CBOR::XS::Tagged" object to hold the tag and
342 the value.
343
344 When the filter is cleared (the default state), the default filter
345 function, "CBOR::XS::default_filter", is used. This function simply
346 looks up the tag in the %CBOR::XS::FILTER hash. If an entry exists
347 it must be a code reference that is called with tag and value, and
348 is responsible for decoding the value. If no entry exists, it
349 returns no values. "CBOR::XS" provides a number of default filter
350 functions already, the the %CBOR::XS::FILTER hash can be freely
351 extended with more.
352
353 "CBOR::XS" additionally provides an alternative filter function that
354 is supposed to be safe to use with untrusted data (which the default
355 filter might not), called "CBOR::XS::safe_filter", which works the
356 same as the "default_filter" but uses the %CBOR::XS::SAFE_FILTER
357 variable instead. It is prepopulated with the tag decoding functions
358 that are deemed safe (basically the same as %CBOR::XS::FILTER
359 without all the bignum tags), and can be extended by user code as
360 wlel, although, obviously, one should be very careful about adding
361 decoding functions here, since the expectation is that they are safe
362 to use on untrusted data, after all.
363
364 Example: decode all tags not handled internally into
365 "CBOR::XS::Tagged" objects, with no other special handling (useful
366 when working with potentially "unsafe" CBOR data).
367
368 CBOR::XS->new->filter (sub { })->decode ($cbor_data);
369
370 Example: provide a global filter for tag 1347375694, converting the
371 value into some string form.
372
373 $CBOR::XS::FILTER{1347375694} = sub {
374 my ($tag, $value);
375
376 "tag 1347375694 value $value"
377 };
378
379 Example: provide your own filter function that looks up tags in your
380 own hash:
381
382 my %my_filter = (
383 998347484 => sub {
384 my ($tag, $value);
385
386 "tag 998347484 value $value"
387 };
388 );
389
390 my $coder = CBOR::XS->new->filter (sub {
391 &{ $my_filter{$_[0]} or return }
392 });
393
394 Example: use the safe filter function (see "SECURITY CONSIDERATIONS"
395 for more considerations on security).
396
397 CBOR::XS->new->filter (\&CBOR::XS::safe_filter)->decode ($cbor_data);
90 398
91 $cbor_data = $cbor->encode ($perl_scalar) 399 $cbor_data = $cbor->encode ($perl_scalar)
92 Converts the given Perl data structure (a scalar value) to its CBOR 400 Converts the given Perl data structure (a scalar value) to its CBOR
93 representation. 401 representation.
94 402
… …
102 will silently stop parsing there and return the number of characters 410 will silently stop parsing there and return the number of characters
103 consumed so far. 411 consumed so far.
104 412
105 This is useful if your CBOR texts are not delimited by an outer 413 This is useful if your CBOR texts are not delimited by an outer
106 protocol and you need to know where the first CBOR string ends amd 414 protocol and you need to know where the first CBOR string ends amd
107 the next one starts. 415 the next one starts - CBOR strings are self-delimited, so it is
416 possible to concatenate CBOR strings without any delimiters or size
417 fields and recover their data.
108 418
109 CBOR::XS->new->decode_prefix ("......") 419 CBOR::XS->new->decode_prefix ("......")
110 => ("...", 3) 420 => ("...", 3)
421
422 INCREMENTAL PARSING
423 In some cases, there is the need for incremental parsing of JSON texts.
424 While this module always has to keep both CBOR text and resulting Perl
425 data structure in memory at one time, it does allow you to parse a CBOR
426 stream incrementally, using a similar to using "decode_prefix" to see if
427 a full CBOR object is available, but is much more efficient.
428
429 It basically works by parsing as much of a CBOR string as possible - if
430 the CBOR data is not complete yet, the parser will remember where it
431 was, to be able to restart when more data has been accumulated. Once
432 enough data is available to either decode a complete CBOR value or raise
433 an error, a real decode will be attempted.
434
435 A typical use case would be a network protocol that consists of sending
436 and receiving CBOR-encoded messages. The solution that works with CBOR
437 and about anything else is by prepending a length to every CBOR value,
438 so the receiver knows how many octets to read. More compact (and
439 slightly slower) would be to just send CBOR values back-to-back, as
440 "CBOR::XS" knows where a CBOR value ends, and doesn't need an explicit
441 length.
442
443 The following methods help with this:
444
445 @decoded = $cbor->incr_parse ($buffer)
446 This method attempts to decode exactly one CBOR value from the
447 beginning of the given $buffer. The value is removed from the
448 $buffer on success. When $buffer doesn't contain a complete value
449 yet, it returns nothing. Finally, when the $buffer doesn't start
450 with something that could ever be a valid CBOR value, it raises an
451 exception, just as "decode" would. In the latter case the decoder
452 state is undefined and must be reset before being able to parse
453 further.
454
455 This method modifies the $buffer in place. When no CBOR value can be
456 decoded, the decoder stores the current string offset. On the next
457 call, continues decoding at the place where it stopped before. For
458 this to make sense, the $buffer must begin with the same octets as
459 on previous unsuccessful calls.
460
461 You can call this method in scalar context, in which case it either
462 returns a decoded value or "undef". This makes it impossible to
463 distinguish between CBOR null values (which decode to "undef") and
464 an unsuccessful decode, which is often acceptable.
465
466 @decoded = $cbor->incr_parse_multiple ($buffer)
467 Same as "incr_parse", but attempts to decode as many CBOR values as
468 possible in one go, instead of at most one. Calls to "incr_parse"
469 and "incr_parse_multiple" can be interleaved.
470
471 $cbor->incr_reset
472 Resets the incremental decoder. This throws away any saved state, so
473 that subsequent calls to "incr_parse" or "incr_parse_multiple" start
474 to parse a new CBOR value from the beginning of the $buffer again.
475
476 This method can be called at any time, but it *must* be called if
477 you want to change your $buffer or there was a decoding error and
478 you want to reuse the $cbor object for future incremental parsings.
111 479
112MAPPING 480MAPPING
113 This section describes how CBOR::XS maps Perl values to CBOR values and 481 This section describes how CBOR::XS maps Perl values to CBOR values and
114 vice versa. These mappings are designed to "do the right thing" in most 482 vice versa. These mappings are designed to "do the right thing" in most
115 circumstances automatically, preserving round-tripping characteristics 483 circumstances automatically, preserving round-tripping characteristics
… …
118 For the more enlightened: note that in the following descriptions, 486 For the more enlightened: note that in the following descriptions,
119 lowercase *perl* refers to the Perl interpreter, while uppercase *Perl* 487 lowercase *perl* refers to the Perl interpreter, while uppercase *Perl*
120 refers to the abstract Perl language itself. 488 refers to the abstract Perl language itself.
121 489
122 CBOR -> PERL 490 CBOR -> PERL
123 True, False 491 integers
124 These CBOR values become "CBOR::XS::true" and "CBOR::XS::false", 492 CBOR integers become (numeric) perl scalars. On perls without 64 bit
493 support, 64 bit integers will be truncated or otherwise corrupted.
494
495 byte strings
496 Byte strings will become octet strings in Perl (the Byte values
497 0..255 will simply become characters of the same value in Perl).
498
499 UTF-8 strings
500 UTF-8 strings in CBOR will be decoded, i.e. the UTF-8 octets will be
501 decoded into proper Unicode code points. At the moment, the validity
502 of the UTF-8 octets will not be validated - corrupt input will
503 result in corrupted Perl strings.
504
505 arrays, maps
506 CBOR arrays and CBOR maps will be converted into references to a
507 Perl array or hash, respectively. The keys of the map will be
508 stringified during this process.
509
510 null
511 CBOR null becomes "undef" in Perl.
512
513 true, false, undefined
514 These CBOR values become "Types:Serialiser::true",
515 "Types:Serialiser::false" and "Types::Serialiser::error",
125 respectively. They are overloaded to act almost exactly like the 516 respectively. They are overloaded to act almost exactly like the
126 numbers 1 and 0. You can check whether a scalar is a CBOR boolean by 517 numbers 1 and 0 (for true and false) or to throw an exception on
127 using the "CBOR::XS::is_bool" function. 518 access (for error). See the Types::Serialiser manpage for details.
128 519
129 Null, Undefined 520 tagged values
130 CBOR Null and Undefined values becomes "undef" in Perl (in the 521 Tagged items consists of a numeric tag and another CBOR value.
131 future, Undefined may raise an exception). 522
523 See "TAG HANDLING AND EXTENSIONS" and the description of "->filter"
524 for details on which tags are handled how.
525
526 anything else
527 Anything else (e.g. unsupported simple values) will raise a decoding
528 error.
132 529
133 PERL -> CBOR 530 PERL -> CBOR
134 The mapping from Perl to CBOR is slightly more difficult, as Perl is a 531 The mapping from Perl to CBOR is slightly more difficult, as Perl is a
135 truly typeless language, so we can only guess which CBOR type is meant 532 typeless language. That means this module can only guess which CBOR type
136 by a Perl value. 533 is meant by a perl value.
137 534
138 hash references 535 hash references
139 Perl hash references become CBOR maps. As there is no inherent 536 Perl hash references become CBOR maps. As there is no inherent
140 ordering in hash keys (or CBOR maps), they will usually be encoded 537 ordering in hash keys (or CBOR maps), they will usually be encoded
141 in a pseudo-random order. 538 in a pseudo-random order. This order can be different each time a
539 hash is encoded.
540
541 Currently, tied hashes will use the indefinite-length format, while
542 normal hashes will use the fixed-length format.
142 543
143 array references 544 array references
144 Perl array references become CBOR arrays. 545 Perl array references become fixed-length CBOR arrays.
145 546
146 other references 547 other references
147 Other unblessed references are generally not allowed and will cause 548 Other unblessed references will be represented using the indirection
148 an exception to be thrown, except for references to the integers 0 549 tag extension (tag value 22098,
149 and 1, which get turned into "False" and "True" in CBOR. 550 <http://cbor.schmorp.de/indirection>). CBOR decoders are guaranteed
551 to be able to decode these values somehow, by either "doing the
552 right thing", decoding into a generic tagged object, simply ignoring
553 the tag, or something else.
150 554
151 CBOR::XS::true, CBOR::XS::false 555 CBOR::XS::Tagged objects
556 Objects of this type must be arrays consisting of a single "[tag,
557 value]" pair. The (numerical) tag will be encoded as a CBOR tag, the
558 value will be encoded as appropriate for the value. You must use
559 "CBOR::XS::tag" to create such objects.
560
561 Types::Serialiser::true, Types::Serialiser::false,
562 Types::Serialiser::error
152 These special values become CBOR True and CBOR False values, 563 These special values become CBOR true, CBOR false and CBOR undefined
153 respectively. You can also use "\1" and "\0" directly if you want. 564 values, respectively.
154 565
155 blessed objects 566 other blessed objects
156 Blessed objects are not directly representable in CBOR. TODO See the 567 Other blessed objects are serialised via "TO_CBOR" or "FREEZE". See
157 "allow_blessed" and "convert_blessed" methods on various options on 568 "TAG HANDLING AND EXTENSIONS" for specific classes handled by this
158 how to deal with this: basically, you can choose between throwing an 569 module, and "OBJECT SERIALISATION" for generic object serialisation.
159 exception, encoding the reference as if it weren't blessed, or
160 provide your own serialiser method.
161 570
162 simple scalars 571 simple scalars
163 TODO Simple Perl scalars (any scalar that is not a reference) are 572 Simple Perl scalars (any scalar that is not a reference) are the
164 the most difficult objects to encode: CBOR::XS will encode undefined 573 most difficult objects to encode: CBOR::XS will encode undefined
165 scalars as CBOR "Null" values, scalars that have last been used in a 574 scalars as CBOR null values, scalars that have last been used in a
166 string context before encoding as CBOR strings, and anything else as 575 string context before encoding as CBOR strings, and anything else as
167 number value: 576 number value:
168 577
169 # dump as number 578 # dump as number
170 encode_cbor [2] # yields [2] 579 encode_cbor [2] # yields [2]
171 encode_cbor [-3.0e17] # yields [-3e+17] 580 encode_cbor [-3.0e17] # yields [-3e+17]
172 my $value = 5; encode_cbor [$value] # yields [5] 581 my $value = 5; encode_cbor [$value] # yields [5]
173 582
174 # used as string, so dump as string 583 # used as string, so dump as string (either byte or text)
175 print $value; 584 print $value;
176 encode_cbor [$value] # yields ["5"] 585 encode_cbor [$value] # yields ["5"]
177 586
178 # undef becomes null 587 # undef becomes null
179 encode_cbor [undef] # yields [null] 588 encode_cbor [undef] # yields [null]
… …
183 my $x = 3.1; # some variable containing a number 592 my $x = 3.1; # some variable containing a number
184 "$x"; # stringified 593 "$x"; # stringified
185 $x .= ""; # another, more awkward way to stringify 594 $x .= ""; # another, more awkward way to stringify
186 print $x; # perl does it for you, too, quite often 595 print $x; # perl does it for you, too, quite often
187 596
597 You can force whether a string is encoded as byte or text string by
598 using "utf8::upgrade" and "utf8::downgrade" (if "text_strings" is
599 disabled).
600
601 utf8::upgrade $x; # encode $x as text string
602 utf8::downgrade $x; # encode $x as byte string
603
604 More options are available, see "TYPE CASTS", below, and the
605 "text_keys" and "text_strings" options.
606
607 Perl doesn't define what operations up- and downgrade strings, so if
608 the difference between byte and text is important, you should up- or
609 downgrade your string as late as possible before encoding. You can
610 also force the use of CBOR text strings by using "text_keys" or
611 "text_strings".
612
188 You can force the type to be a CBOR number by numifying it: 613 You can force the type to be a CBOR number by numifying it:
189 614
190 my $x = "3"; # some variable containing a string 615 my $x = "3"; # some variable containing a string
191 $x += 0; # numify it, ensuring it will be dumped as a number 616 $x += 0; # numify it, ensuring it will be dumped as a number
192 $x *= 1; # same thing, the choice is yours. 617 $x *= 1; # same thing, the choice is yours.
193 618
194 You can not currently force the type in other, less obscure, ways. 619 You can not currently force the type in other, less obscure, ways.
195 Tell me if you need this capability (but don't forget to explain why 620 Tell me if you need this capability (but don't forget to explain why
196 it's needed :). 621 it's needed :).
197 622
198 Note that numerical precision has the same meaning as under Perl (so 623 Perl values that seem to be integers generally use the shortest
199 binary to decimal conversion follows the same rules as in Perl, 624 possible representation. Floating-point values will use either the
200 which can differ to other languages). Also, your perl interpreter 625 IEEE single format if possible without loss of precision, otherwise
201 might expose extensions to the floating point numbers of your 626 the IEEE double format will be used. Perls that use formats other
202 platform, such as infinities or NaN's - these cannot be represented 627 than IEEE double to represent numerical values are supported, but
203 in CBOR, and it is an error to pass those in. 628 might suffer loss of precision.
204 629
630 TYPE CASTS
631 EXPERIMENTAL: As an experimental extension, "CBOR::XS" allows you to
632 force specific CBOR types to be used when encoding. That allows you to
633 encode types not normally accessible (e.g. half floats) as well as force
634 string types even when "text_strings" is in effect.
635
636 Type forcing is done by calling a special "cast" function which keeps a
637 copy of the value and returns a new value that can be handed over to any
638 CBOR encoder function.
639
640 The following casts are currently available (all of which are unary
641 operators, that is, have a prototype of "$"):
642
643 CBOR::XS::as_int $value
644 Forces the value to be encoded as some form of (basic, not bignum)
645 integer type.
646
647 CBOR::XS::as_text $value
648 Forces the value to be encoded as (UTF-8) text values.
649
650 CBOR::XS::as_bytes $value
651 Forces the value to be encoded as a (binary) string value.
652
653 Example: encode a perl string as binary even though "text_strings"
654 is in effect.
655
656 CBOR::XS->new->text_strings->encode ([4, "text", CBOR::XS::bytes "bytevalue"]);
657
658 CBOR::XS::as_bool $value
659 Converts a Perl boolean (which can be any kind of scalar) into a
660 CBOR boolean. Strictly the same, but shorter to write, than:
661
662 $value ? Types::Serialiser::true : Types::Serialiser::false
663
664 CBOR::XS::as_float16 $value
665 Forces half-float (IEEE 754 binary16) encoding of the given value.
666
667 CBOR::XS::as_float32 $value
668 Forces single-float (IEEE 754 binary32) encoding of the given value.
669
670 CBOR::XS::as_float64 $value
671 Forces double-float (IEEE 754 binary64) encoding of the given value.
672
673 CBOR::XS::as_cbor $cbor_text
674 Not a type cast per-se, this type cast forces the argument to be
675 encoded as-is. This can be used to embed pre-encoded CBOR data.
676
677 Note that no checking on the validity of the $cbor_text is done -
678 it's the callers responsibility to correctly encode values.
679
680 CBOR::XS::as_map [key => value...]
681 Treat the array reference as key value pairs and output a CBOR map.
682 This allows you to generate CBOR maps with arbitrary key types (or,
683 if you don't care about semantics, duplicate keys or pairs in a
684 custom order), which is otherwise hard to do with Perl.
685
686 The single argument must be an array reference with an even number
687 of elements.
688
689 Note that only the reference to the array is copied, the array
690 itself is not. Modifications done to the array before calling an
691 encoding function will be reflected in the encoded output.
692
693 Example: encode a CBOR map with a string and an integer as keys.
694
695 encode_cbor CBOR::XS::as_map [string => "value", 5 => "value"]
696
697 OBJECT SERIALISATION
698 This module implements both a CBOR-specific and the generic
699 Types::Serialier object serialisation protocol. The following
700 subsections explain both methods.
701
702 ENCODING
703 This module knows two way to serialise a Perl object: The CBOR-specific
704 way, and the generic way.
705
706 Whenever the encoder encounters a Perl object that it cannot serialise
707 directly (most of them), it will first look up the "TO_CBOR" method on
708 it.
709
710 If it has a "TO_CBOR" method, it will call it with the object as only
711 argument, and expects exactly one return value, which it will then
712 substitute and encode it in the place of the object.
713
714 Otherwise, it will look up the "FREEZE" method. If it exists, it will
715 call it with the object as first argument, and the constant string
716 "CBOR" as the second argument, to distinguish it from other serialisers.
717
718 The "FREEZE" method can return any number of values (i.e. zero or more).
719 These will be encoded as CBOR perl object, together with the classname.
720
721 These methods *MUST NOT* change the data structure that is being
722 serialised. Failure to comply to this can result in memory corruption -
723 and worse.
724
725 If an object supports neither "TO_CBOR" nor "FREEZE", encoding will fail
726 with an error.
727
728 DECODING
729 Objects encoded via "TO_CBOR" cannot (normally) be automatically
730 decoded, but objects encoded via "FREEZE" can be decoded using the
731 following protocol:
732
733 When an encoded CBOR perl object is encountered by the decoder, it will
734 look up the "THAW" method, by using the stored classname, and will fail
735 if the method cannot be found.
736
737 After the lookup it will call the "THAW" method with the stored
738 classname as first argument, the constant string "CBOR" as second
739 argument, and all values returned by "FREEZE" as remaining arguments.
740
741 EXAMPLES
742 Here is an example "TO_CBOR" method:
743
744 sub My::Object::TO_CBOR {
745 my ($obj) = @_;
746
747 ["this is a serialised My::Object object", $obj->{id}]
748 }
749
750 When a "My::Object" is encoded to CBOR, it will instead encode a simple
751 array with two members: a string, and the "object id". Decoding this
752 CBOR string will yield a normal perl array reference in place of the
753 object.
754
755 A more useful and practical example would be a serialisation method for
756 the URI module. CBOR has a custom tag value for URIs, namely 32:
757
758 sub URI::TO_CBOR {
759 my ($self) = @_;
760 my $uri = "$self"; # stringify uri
761 utf8::upgrade $uri; # make sure it will be encoded as UTF-8 string
762 CBOR::XS::tag 32, "$_[0]"
763 }
764
765 This will encode URIs as a UTF-8 string with tag 32, which indicates an
766 URI.
767
768 Decoding such an URI will not (currently) give you an URI object, but
769 instead a CBOR::XS::Tagged object with tag number 32 and the string -
770 exactly what was returned by "TO_CBOR".
771
772 To serialise an object so it can automatically be deserialised, you need
773 to use "FREEZE" and "THAW". To take the URI module as example, this
774 would be a possible implementation:
775
776 sub URI::FREEZE {
777 my ($self, $serialiser) = @_;
778 "$self" # encode url string
779 }
780
781 sub URI::THAW {
782 my ($class, $serialiser, $uri) = @_;
783 $class->new ($uri)
784 }
785
786 Unlike "TO_CBOR", multiple values can be returned by "FREEZE". For
787 example, a "FREEZE" method that returns "type", "id" and "variant"
788 values would cause an invocation of "THAW" with 5 arguments:
789
790 sub My::Object::FREEZE {
791 my ($self, $serialiser) = @_;
792
793 ($self->{type}, $self->{id}, $self->{variant})
794 }
795
796 sub My::Object::THAW {
797 my ($class, $serialiser, $type, $id, $variant) = @_;
798
799 $class-<new (type => $type, id => $id, variant => $variant)
800 }
801
205 MAGIC HEADER 802MAGIC HEADER
206 There is no way to distinguish CBOR from other formats programmatically. 803 There is no way to distinguish CBOR from other formats programmatically.
207 To make it easier to distinguish CBOR from other formats, the CBOR 804 To make it easier to distinguish CBOR from other formats, the CBOR
208 specification has a special "magic string" that can be prepended to any 805 specification has a special "magic string" that can be prepended to any
209 CBOR string without changing it's meaning. 806 CBOR string without changing its meaning.
210 807
211 This string is available as $CBOR::XS::MAGIC. This module does not 808 This string is available as $CBOR::XS::MAGIC. This module does not
212 prepend this string tot he CBOR data it generates, but it will ignroe it 809 prepend this string to the CBOR data it generates, but it will ignore it
213 if present, so users can prepend this string as a "file type" indicator 810 if present, so users can prepend this string as a "file type" indicator
214 as required. 811 as required.
215 812
813THE CBOR::XS::Tagged CLASS
814 CBOR has the concept of tagged values - any CBOR value can be tagged
815 with a numeric 64 bit number, which are centrally administered.
816
817 "CBOR::XS" handles a few tags internally when en- or decoding. You can
818 also create tags yourself by encoding "CBOR::XS::Tagged" objects, and
819 the decoder will create "CBOR::XS::Tagged" objects itself when it hits
820 an unknown tag.
821
822 These objects are simply blessed array references - the first member of
823 the array being the numerical tag, the second being the value.
824
825 You can interact with "CBOR::XS::Tagged" objects in the following ways:
826
827 $tagged = CBOR::XS::tag $tag, $value
828 This function(!) creates a new "CBOR::XS::Tagged" object using the
829 given $tag (0..2**64-1) to tag the given $value (which can be any
830 Perl value that can be encoded in CBOR, including serialisable Perl
831 objects and "CBOR::XS::Tagged" objects).
832
833 $tagged->[0]
834 $tagged->[0] = $new_tag
835 $tag = $tagged->tag
836 $new_tag = $tagged->tag ($new_tag)
837 Access/mutate the tag.
838
839 $tagged->[1]
840 $tagged->[1] = $new_value
841 $value = $tagged->value
842 $new_value = $tagged->value ($new_value)
843 Access/mutate the tagged value.
844
845 EXAMPLES
846 Here are some examples of "CBOR::XS::Tagged" uses to tag objects.
847
848 You can look up CBOR tag value and emanings in the IANA registry at
849 <http://www.iana.org/assignments/cbor-tags/cbor-tags.xhtml>.
850
851 Prepend a magic header ($CBOR::XS::MAGIC):
852
853 my $cbor = encode_cbor CBOR::XS::tag 55799, $value;
854 # same as:
855 my $cbor = $CBOR::XS::MAGIC . encode_cbor $value;
856
857 Serialise some URIs and a regex in an array:
858
859 my $cbor = encode_cbor [
860 (CBOR::XS::tag 32, "http://www.nethype.de/"),
861 (CBOR::XS::tag 32, "http://software.schmorp.de/"),
862 (CBOR::XS::tag 35, "^[Pp][Ee][Rr][lL]\$"),
863 ];
864
865 Wrap CBOR data in CBOR:
866
867 my $cbor_cbor = encode_cbor
868 CBOR::XS::tag 24,
869 encode_cbor [1, 2, 3];
870
871TAG HANDLING AND EXTENSIONS
872 This section describes how this module handles specific tagged values
873 and extensions. If a tag is not mentioned here and no additional filters
874 are provided for it, then the default handling applies (creating a
875 CBOR::XS::Tagged object on decoding, and only encoding the tag when
876 explicitly requested).
877
878 Tags not handled specifically are currently converted into a
879 CBOR::XS::Tagged object, which is simply a blessed array reference
880 consisting of the numeric tag value followed by the (decoded) CBOR
881 value.
882
883 Future versions of this module reserve the right to special case
884 additional tags (such as base64url).
885
886 ENFORCED TAGS
887 These tags are always handled when decoding, and their handling cannot
888 be overridden by the user.
889
890 26 (perl-object, <http://cbor.schmorp.de/perl-object>)
891 These tags are automatically created (and decoded) for serialisable
892 objects using the "FREEZE/THAW" methods (the Types::Serialier object
893 serialisation protocol). See "OBJECT SERIALISATION" for details.
894
895 28, 29 (shareable, sharedref, <http://cbor.schmorp.de/value-sharing>)
896 These tags are automatically decoded when encountered (and they do
897 not result in a cyclic data structure, see "allow_cycles"),
898 resulting in shared values in the decoded object. They are only
899 encoded, however, when "allow_sharing" is enabled.
900
901 Not all shared values can be successfully decoded: values that
902 reference themselves will *currently* decode as "undef" (this is not
903 the same as a reference pointing to itself, which will be
904 represented as a value that contains an indirect reference to itself
905 - these will be decoded properly).
906
907 Note that considerably more shared value data structures can be
908 decoded than will be encoded - currently, only values pointed to by
909 references will be shared, others will not. While non-reference
910 shared values can be generated in Perl with some effort, they were
911 considered too unimportant to be supported in the encoder. The
912 decoder, however, will decode these values as shared values.
913
914 256, 25 (stringref-namespace, stringref,
915 <http://cbor.schmorp.de/stringref>)
916 These tags are automatically decoded when encountered. They are only
917 encoded, however, when "pack_strings" is enabled.
918
919 22098 (indirection, <http://cbor.schmorp.de/indirection>)
920 This tag is automatically generated when a reference are encountered
921 (with the exception of hash and array references). It is converted
922 to a reference when decoding.
923
924 55799 (self-describe CBOR, RFC 7049)
925 This value is not generated on encoding (unless explicitly requested
926 by the user), and is simply ignored when decoding.
927
928 NON-ENFORCED TAGS
929 These tags have default filters provided when decoding. Their handling
930 can be overridden by changing the %CBOR::XS::FILTER entry for the tag,
931 or by providing a custom "filter" callback when decoding.
932
933 When they result in decoding into a specific Perl class, the module
934 usually provides a corresponding "TO_CBOR" method as well.
935
936 When any of these need to load additional modules that are not part of
937 the perl core distribution (e.g. URI), it is (currently) up to the user
938 to provide these modules. The decoding usually fails with an exception
939 if the required module cannot be loaded.
940
941 0, 1 (date/time string, seconds since the epoch)
942 These tags are decoded into Time::Piece objects. The corresponding
943 "Time::Piece::TO_CBOR" method always encodes into tag 1 values
944 currently.
945
946 The Time::Piece API is generally surprisingly bad, and fractional
947 seconds are only accidentally kept intact, so watch out. On the plus
948 side, the module comes with perl since 5.10, which has to count for
949 something.
950
951 2, 3 (positive/negative bignum)
952 These tags are decoded into Math::BigInt objects. The corresponding
953 "Math::BigInt::TO_CBOR" method encodes "small" bigints into normal
954 CBOR integers, and others into positive/negative CBOR bignums.
955
956 4, 5, 264, 265 (decimal fraction/bigfloat)
957 Both decimal fractions and bigfloats are decoded into Math::BigFloat
958 objects. The corresponding "Math::BigFloat::TO_CBOR" method *always*
959 encodes into a decimal fraction (either tag 4 or 264).
960
961 NaN and infinities are not encoded properly, as they cannot be
962 represented in CBOR.
963
964 See "BIGNUM SECURITY CONSIDERATIONS" for more info.
965
966 30 (rational numbers)
967 These tags are decoded into Math::BigRat objects. The corresponding
968 "Math::BigRat::TO_CBOR" method encodes rational numbers with
969 denominator 1 via their numerator only, i.e., they become normal
970 integers or "bignums".
971
972 See "BIGNUM SECURITY CONSIDERATIONS" for more info.
973
974 21, 22, 23 (expected later JSON conversion)
975 CBOR::XS is not a CBOR-to-JSON converter, and will simply ignore
976 these tags.
977
978 32 (URI)
979 These objects decode into URI objects. The corresponding
980 "URI::TO_CBOR" method again results in a CBOR URI value.
981
216 CBOR and JSON 982CBOR and JSON
217 TODO 983 CBOR is supposed to implement a superset of the JSON data model, and is,
984 with some coercion, able to represent all JSON texts (something that
985 other "binary JSON" formats such as BSON generally do not support).
986
987 CBOR implements some extra hints and support for JSON interoperability,
988 and the spec offers further guidance for conversion between CBOR and
989 JSON. None of this is currently implemented in CBOR, and the guidelines
990 in the spec do not result in correct round-tripping of data. If JSON
991 interoperability is improved in the future, then the goal will be to
992 ensure that decoded JSON data will round-trip encoding and decoding to
993 CBOR intact.
218 994
219SECURITY CONSIDERATIONS 995SECURITY CONSIDERATIONS
220 When you are using CBOR in a protocol, talking to untrusted potentially 996 Tl;dr... if you want to decode or encode CBOR from untrusted sources,
221 hostile creatures requires relatively few measures. 997 you should start with a coder object created via "new_safe" (which
998 implements the mitigations explained below):
222 999
1000 my $coder = CBOR::XS->new_safe;
1001
1002 my $data = $coder->decode ($cbor_text);
1003 my $cbor = $coder->encode ($data);
1004
1005 Longer version: When you are using CBOR in a protocol, talking to
1006 untrusted potentially hostile creatures requires some thought:
1007
1008 Security of the CBOR decoder itself
223 First of all, your CBOR decoder should be secure, that is, should not 1009 First and foremost, your CBOR decoder should be secure, that is,
224 have any buffer overflows. Obviously, this module should ensure that and 1010 should not have any buffer overflows or similar bugs that could
1011 potentially be exploited. Obviously, this module should ensure that
225 I am trying hard on making that true, but you never know. 1012 and I am trying hard on making that true, but you never know.
226 1013
1014 CBOR::XS can invoke almost arbitrary callbacks during decoding
1015 CBOR::XS supports object serialisation - decoding CBOR can cause
1016 calls to *any* "THAW" method in *any* package that exists in your
1017 process (that is, CBOR::XS will not try to load modules, but any
1018 existing "THAW" method or function can be called, so they all have
1019 to be secure).
1020
1021 Less obviously, it will also invoke "TO_CBOR" and "FREEZE" methods -
1022 even if all your "THAW" methods are secure, encoding data structures
1023 from untrusted sources can invoke those and trigger bugs in those.
1024
1025 So, if you are not sure about the security of all the modules you
1026 have loaded (you shouldn't), you should disable this part using
1027 "forbid_objects" or using "new_safe".
1028
1029 CBOR can be extended with tags that call library code
1030 CBOR can be extended with tags, and "CBOR::XS" has a registry of
1031 conversion functions for many existing tags that can be extended via
1032 third-party modules (see the "filter" method).
1033
1034 If you don't trust these, you should configure the "safe" filter
1035 function, "CBOR::XS::safe_filter" ("new_safe" does this), which by
1036 default only includes conversion functions that are considered
1037 "safe" by the author (but again, they can be extended by third party
1038 modules).
1039
1040 Depending on your level of paranoia, you can use the "safe" filter:
1041
1042 $cbor->filter (\&CBOR::XS::safe_filter);
1043
1044 ... your own filter...
1045
1046 $cbor->filter (sub { ... do your stuffs here ... });
1047
1048 ... or even no filter at all, disabling all tag decoding:
1049
1050 $cbor->filter (sub { });
1051
1052 This is never a problem for encoding, as the tag mechanism only
1053 exists in CBOR texts.
1054
1055 Resource-starving attacks: object memory usage
227 Second, you need to avoid resource-starving attacks. That means you 1056 You need to avoid resource-starving attacks. That means you should
228 should limit the size of CBOR data you accept, or make sure then when 1057 limit the size of CBOR data you accept, or make sure then when your
229 your resources run out, that's just fine (e.g. by using a separate 1058 resources run out, that's just fine (e.g. by using a separate
230 process that can crash safely). The size of a CBOR string in octets is 1059 process that can crash safely). The size of a CBOR string in octets
231 usually a good indication of the size of the resources required to 1060 is usually a good indication of the size of the resources required
232 decode it into a Perl structure. While CBOR::XS can check the size of 1061 to decode it into a Perl structure. While CBOR::XS can check the
1062 size of the CBOR text (using "max_size" - done by "new_safe"), it
233 the CBOR text, it might be too late when you already have it in memory, 1063 might be too late when you already have it in memory, so you might
234 so you might want to check the size before you accept the string. 1064 want to check the size before you accept the string.
235 1065
1066 As for encoding, it is possible to construct data structures that
1067 are relatively small but result in large CBOR texts (for example by
1068 having an array full of references to the same big data structure,
1069 which will all be deep-cloned during encoding by default). This is
1070 rarely an actual issue (and the worst case is still just running out
1071 of memory), but you can reduce this risk by using "allow_sharing".
1072
1073 Resource-starving attacks: stack overflows
236 Third, CBOR::XS recurses using the C stack when decoding objects and 1074 CBOR::XS recurses using the C stack when decoding objects and
237 arrays. The C stack is a limited resource: for instance, on my amd64 1075 arrays. The C stack is a limited resource: for instance, on my amd64
238 machine with 8MB of stack size I can decode around 180k nested arrays 1076 machine with 8MB of stack size I can decode around 180k nested
239 but only 14k nested CBOR objects (due to perl itself recursing deeply on 1077 arrays but only 14k nested CBOR objects (due to perl itself
240 croak to free the temporary). If that is exceeded, the program crashes. 1078 recursing deeply on croak to free the temporary). If that is
241 To be conservative, the default nesting limit is set to 512. If your 1079 exceeded, the program crashes. To be conservative, the default
242 process has a smaller stack, you should adjust this setting accordingly 1080 nesting limit is set to 512. If your process has a smaller stack,
243 with the "max_depth" method. 1081 you should adjust this setting accordingly with the "max_depth"
1082 method.
244 1083
1084 Resource-starving attacks: CPU en-/decoding complexity
1085 CBOR::XS will use the Math::BigInt, Math::BigFloat and Math::BigRat
1086 libraries to represent encode/decode bignums. These can be very slow
1087 (as in, centuries of CPU time) and can even crash your program (and
1088 are generally not very trustworthy). See the next section on bignum
1089 security for details.
1090
1091 Data breaches: leaking information in error messages
1092 CBOR::XS might leak contents of your Perl data structures in its
1093 error messages, so when you serialise sensitive information you
1094 might want to make sure that exceptions thrown by CBOR::XS will not
1095 end up in front of untrusted eyes.
1096
1097 Something else...
245 Something else could bomb you, too, that I forgot to think of. In that 1098 Something else could bomb you, too, that I forgot to think of. In
246 case, you get to keep the pieces. I am always open for hints, though... 1099 that case, you get to keep the pieces. I am always open for hints,
1100 though...
247 1101
248 Also keep in mind that CBOR::XS might leak contents of your Perl data 1102BIGNUM SECURITY CONSIDERATIONS
249 structures in its error messages, so when you serialise sensitive 1103 CBOR::XS provides a "TO_CBOR" method for both Math::BigInt and
250 information you might want to make sure that exceptions thrown by 1104 Math::BigFloat that tries to encode the number in the simplest possible
251 CBOR::XS will not end up in front of untrusted eyes. 1105 way, that is, either a CBOR integer, a CBOR bigint/decimal fraction (tag
1106 4) or an arbitrary-exponent decimal fraction (tag 264). Rational numbers
1107 (Math::BigRat, tag 30) can also contain bignums as members.
1108
1109 CBOR::XS will also understand base-2 bigfloat or arbitrary-exponent
1110 bigfloats (tags 5 and 265), but it will never generate these on its own.
1111
1112 Using the built-in Math::BigInt::Calc support, encoding and decoding
1113 decimal fractions is generally fast. Decoding bigints can be slow for
1114 very big numbers (tens of thousands of digits, something that could
1115 potentially be caught by limiting the size of CBOR texts), and decoding
1116 bigfloats or arbitrary-exponent bigfloats can be *extremely* slow
1117 (minutes, decades) for large exponents (roughly 40 bit and longer).
1118
1119 Additionally, Math::BigInt can take advantage of other bignum libraries,
1120 such as Math::GMP, which cannot handle big floats with large exponents,
1121 and might simply abort or crash your program, due to their code quality.
1122
1123 This can be a concern if you want to parse untrusted CBOR. If it is, you
1124 might want to disable decoding of tag 2 (bigint) and 3 (negative bigint)
1125 types. You should also disable types 5 and 265, as these can be slow
1126 even without bigints.
1127
1128 Disabling bigints will also partially or fully disable types that rely
1129 on them, e.g. rational numbers that use bignums.
252 1130
253CBOR IMPLEMENTATION NOTES 1131CBOR IMPLEMENTATION NOTES
254 This section contains some random implementation notes. They do not 1132 This section contains some random implementation notes. They do not
255 describe guaranteed behaviour, but merely behaviour as-is implemented 1133 describe guaranteed behaviour, but merely behaviour as-is implemented
256 right now. 1134 right now.
… …
264 Only the double data type is supported for NV data types - when Perl 1142 Only the double data type is supported for NV data types - when Perl
265 uses long double to represent floating point values, they might not be 1143 uses long double to represent floating point values, they might not be
266 encoded properly. Half precision types are accepted, but not encoded. 1144 encoded properly. Half precision types are accepted, but not encoded.
267 1145
268 Strict mode and canonical mode are not implemented. 1146 Strict mode and canonical mode are not implemented.
1147
1148LIMITATIONS ON PERLS WITHOUT 64-BIT INTEGER SUPPORT
1149 On perls that were built without 64 bit integer support (these are rare
1150 nowadays, even on 32 bit architectures, as all major Perl distributions
1151 are built with 64 bit integer support), support for any kind of 64 bit
1152 value in CBOR is very limited - most likely, these 64 bit values will be
1153 truncated, corrupted, or otherwise not decoded correctly. This also
1154 includes string, float, array and map sizes that are stored as 64 bit
1155 integers.
269 1156
270THREADS 1157THREADS
271 This module is *not* guaranteed to be thread safe and there are no plans 1158 This module is *not* guaranteed to be thread safe and there are no plans
272 to change this until Perl gets thread support (as opposed to the 1159 to change this until Perl gets thread support (as opposed to the
273 horribly slow so-called "threads" which are simply slow and bloated 1160 horribly slow so-called "threads" which are simply slow and bloated
… …
285 1172
286SEE ALSO 1173SEE ALSO
287 The JSON and JSON::XS modules that do similar, but human-readable, 1174 The JSON and JSON::XS modules that do similar, but human-readable,
288 serialisation. 1175 serialisation.
289 1176
1177 The Types::Serialiser module provides the data model for true, false and
1178 error values.
1179
290AUTHOR 1180AUTHOR
291 Marc Lehmann <schmorp@schmorp.de> 1181 Marc Lehmann <schmorp@schmorp.de>
292 http://home.schmorp.de/ 1182 http://home.schmorp.de/
293 1183

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