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Revision 1.15 by root, Mon Apr 27 20:21:53 2015 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 To give you a general idea about speed, with texts in the megabyte
39 range, "CBOR::XS" usually encodes roughly twice as fast as Storable or
40 JSON::XS and decodes about 15%-30% faster than those. The shorter the
41 data, the worse Storable performs in comparison.
42
43 Regarding compactness, "CBOR::XS"-encoded data structures are usually
44 about 20% smaller than the same data encoded as (compact) JSON or
45 Storable.
46
47 In addition to the core CBOR data format, this module implements a
48 number of extensions, to support cyclic and shared data structures (see
49 "allow_sharing" and "allow_cycles"), string deduplication (see
50 "pack_strings") and scalar references (always enabled).
46 51
47 The primary goal of this module is to be *correct* and the secondary 52 The primary goal of this module is to be *correct* and the secondary
48 goal is to be *fast*. To reach the latter goal it was written in C. 53 goal is to be *fast*. To reach the latter goal it was written in C.
49 54
50 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
… …
72 *disabled*. 77 *disabled*.
73 78
74 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
75 calls can be chained: 80 calls can be chained:
76 81
77 #TODO my $cbor = CBOR::XS->new->encode ({a => [1,2]}); 82 my $cbor = CBOR::XS->new->encode ({a => [1,2]});
78 83
79 $cbor = $cbor->max_depth ([$maximum_nesting_depth]) 84 $cbor = $cbor->max_depth ([$maximum_nesting_depth])
80 $max_depth = $cbor->get_max_depth 85 $max_depth = $cbor->get_max_depth
81 Sets the maximum nesting level (default 512) accepted while encoding 86 Sets the maximum nesting level (default 512) accepted while encoding
82 or decoding. If a higher nesting level is detected in CBOR data or a 87 or decoding. If a higher nesting level is detected in CBOR data or a
… …
113 as when 0 is specified). 118 as when 0 is specified).
114 119
115 See SECURITY CONSIDERATIONS, below, for more info on why this is 120 See SECURITY CONSIDERATIONS, below, for more info on why this is
116 useful. 121 useful.
117 122
123 $cbor = $cbor->allow_unknown ([$enable])
124 $enabled = $cbor->get_allow_unknown
125 If $enable is true (or missing), then "encode" will *not* throw an
126 exception when it encounters values it cannot represent in CBOR (for
127 example, filehandles) but instead will encode a CBOR "error" value.
128
129 If $enable is false (the default), then "encode" will throw an
130 exception when it encounters anything it cannot encode as CBOR.
131
132 This option does not affect "decode" in any way, and it is
133 recommended to leave it off unless you know your communications
134 partner.
135
136 $cbor = $cbor->allow_sharing ([$enable])
137 $enabled = $cbor->get_allow_sharing
138 If $enable is true (or missing), then "encode" will not
139 double-encode values that have been referenced before (e.g. when the
140 same object, such as an array, is referenced multiple times), but
141 instead will emit a reference to the earlier value.
142
143 This means that such values will only be encoded once, and will not
144 result in a deep cloning of the value on decode, in decoders
145 supporting the value sharing extension. This also makes it possible
146 to encode cyclic data structures (which need "allow_cycles" to ne
147 enabled to be decoded by this module).
148
149 It is recommended to leave it off unless you know your communication
150 partner supports the value sharing extensions to CBOR
151 (<http://cbor.schmorp.de/value-sharing>), as without decoder
152 support, the resulting data structure might be unusable.
153
154 Detecting shared values incurs a runtime overhead when values are
155 encoded that have a reference counter large than one, and might
156 unnecessarily increase the encoded size, as potentially shared
157 values are encode as shareable whether or not they are actually
158 shared.
159
160 At the moment, only targets of references can be shared (e.g.
161 scalars, arrays or hashes pointed to by a reference). Weirder
162 constructs, such as an array with multiple "copies" of the *same*
163 string, which are hard but not impossible to create in Perl, are not
164 supported (this is the same as with Storable).
165
166 If $enable is false (the default), then "encode" will encode shared
167 data structures repeatedly, unsharing them in the process. Cyclic
168 data structures cannot be encoded in this mode.
169
170 This option does not affect "decode" in any way - shared values and
171 references will always be decoded properly if present.
172
173 $cbor = $cbor->allow_cycles ([$enable])
174 $enabled = $cbor->get_allow_cycles
175 If $enable is true (or missing), then "decode" will happily decode
176 self-referential (cyclic) data structures. By default these will not
177 be decoded, as they need manual cleanup to avoid memory leaks, so
178 code that isn't prepared for this will not leak memory.
179
180 If $enable is false (the default), then "decode" will throw an error
181 when it encounters a self-referential/cyclic data structure.
182
183 FUTURE DIRECTION: the motivation behind this option is to avoid
184 *real* cycles - future versions of this module might chose to decode
185 cyclic data structures using weak references when this option is
186 off, instead of throwing an error.
187
188 This option does not affect "encode" in any way - shared values and
189 references will always be encoded properly if present.
190
191 $cbor = $cbor->pack_strings ([$enable])
192 $enabled = $cbor->get_pack_strings
193 If $enable is true (or missing), then "encode" will try not to
194 encode the same string twice, but will instead encode a reference to
195 the string instead. Depending on your data format, this can save a
196 lot of space, but also results in a very large runtime overhead
197 (expect encoding times to be 2-4 times as high as without).
198
199 It is recommended to leave it off unless you know your
200 communications partner supports the stringref extension to CBOR
201 (<http://cbor.schmorp.de/stringref>), as without decoder support,
202 the resulting data structure might not be usable.
203
204 If $enable is false (the default), then "encode" will encode strings
205 the standard CBOR way.
206
207 This option does not affect "decode" in any way - string references
208 will always be decoded properly if present.
209
210 $cbor = $cbor->validate_utf8 ([$enable])
211 $enabled = $cbor->get_validate_utf8
212 If $enable is true (or missing), then "decode" will validate that
213 elements (text strings) containing UTF-8 data in fact contain valid
214 UTF-8 data (instead of blindly accepting it). This validation
215 obviously takes extra time during decoding.
216
217 The concept of "valid UTF-8" used is perl's concept, which is a
218 superset of the official UTF-8.
219
220 If $enable is false (the default), then "decode" will blindly accept
221 UTF-8 data, marking them as valid UTF-8 in the resulting data
222 structure regardless of whether thats true or not.
223
224 Perl isn't too happy about corrupted UTF-8 in strings, but should
225 generally not crash or do similarly evil things. Extensions might be
226 not so forgiving, so it's recommended to turn on this setting if you
227 receive untrusted CBOR.
228
229 This option does not affect "encode" in any way - strings that are
230 supposedly valid UTF-8 will simply be dumped into the resulting CBOR
231 string without checking whether that is, in fact, true or not.
232
233 $cbor = $cbor->filter ([$cb->($tag, $value)])
234 $cb_or_undef = $cbor->get_filter
235 Sets or replaces the tagged value decoding filter (when $cb is
236 specified) or clears the filter (if no argument or "undef" is
237 provided).
238
239 The filter callback is called only during decoding, when a
240 non-enforced tagged value has been decoded (see "TAG HANDLING AND
241 EXTENSIONS" for a list of enforced tags). For specific tags, it's
242 often better to provide a default converter using the
243 %CBOR::XS::FILTER hash (see below).
244
245 The first argument is the numerical tag, the second is the (decoded)
246 value that has been tagged.
247
248 The filter function should return either exactly one value, which
249 will replace the tagged value in the decoded data structure, or no
250 values, which will result in default handling, which currently means
251 the decoder creates a "CBOR::XS::Tagged" object to hold the tag and
252 the value.
253
254 When the filter is cleared (the default state), the default filter
255 function, "CBOR::XS::default_filter", is used. This function simply
256 looks up the tag in the %CBOR::XS::FILTER hash. If an entry exists
257 it must be a code reference that is called with tag and value, and
258 is responsible for decoding the value. If no entry exists, it
259 returns no values.
260
261 Example: decode all tags not handled internally into
262 "CBOR::XS::Tagged" objects, with no other special handling (useful
263 when working with potentially "unsafe" CBOR data).
264
265 CBOR::XS->new->filter (sub { })->decode ($cbor_data);
266
267 Example: provide a global filter for tag 1347375694, converting the
268 value into some string form.
269
270 $CBOR::XS::FILTER{1347375694} = sub {
271 my ($tag, $value);
272
273 "tag 1347375694 value $value"
274 };
275
118 $cbor_data = $cbor->encode ($perl_scalar) 276 $cbor_data = $cbor->encode ($perl_scalar)
119 Converts the given Perl data structure (a scalar value) to its CBOR 277 Converts the given Perl data structure (a scalar value) to its CBOR
120 representation. 278 representation.
121 279
122 $perl_scalar = $cbor->decode ($cbor_data) 280 $perl_scalar = $cbor->decode ($cbor_data)
… …
134 the next one starts. 292 the next one starts.
135 293
136 CBOR::XS->new->decode_prefix ("......") 294 CBOR::XS->new->decode_prefix ("......")
137 => ("...", 3) 295 => ("...", 3)
138 296
297 INCREMENTAL PARSING
298 In some cases, there is the need for incremental parsing of JSON texts.
299 While this module always has to keep both CBOR text and resulting Perl
300 data structure in memory at one time, it does allow you to parse a CBOR
301 stream incrementally, using a similar to using "decode_prefix" to see if
302 a full CBOR object is available, but is much more efficient.
303
304 It basically works by parsing as much of a CBOR string as possible - if
305 the CBOR data is not complete yet, the pasrer will remember where it
306 was, to be able to restart when more data has been accumulated. Once
307 enough data is available to either decode a complete CBOR value or raise
308 an error, a real decode will be attempted.
309
310 A typical use case would be a network protocol that consists of sending
311 and receiving CBOR-encoded messages. The solution that works with CBOR
312 and about anything else is by prepending a length to every CBOR value,
313 so the receiver knows how many octets to read. More compact (and
314 slightly slower) would be to just send CBOR values back-to-back, as
315 "CBOR::XS" knows where a CBOR value ends, and doesn't need an explicit
316 length.
317
318 The following methods help with this:
319
320 @decoded = $cbor->incr_parse ($buffer)
321 This method attempts to decode exactly one CBOR value from the
322 beginning of the given $buffer. The value is removed from the
323 $buffer on success. When $buffer doesn't contain a complete value
324 yet, it returns nothing. Finally, when the $buffer doesn't start
325 with something that could ever be a valid CBOR value, it raises an
326 exception, just as "decode" would. In the latter case the decoder
327 state is undefined and must be reset before being able to parse
328 further.
329
330 This method modifies the $buffer in place. When no CBOR value can be
331 decoded, the decoder stores the current string offset. On the next
332 call, continues decoding at the place where it stopped before. For
333 this to make sense, the $buffer must begin with the same octets as
334 on previous unsuccessful calls.
335
336 You can call this method in scalar context, in which case it either
337 returns a decoded value or "undef". This makes it impossible to
338 distinguish between CBOR null values (which decode to "undef") and
339 an unsuccessful decode, which is often acceptable.
340
341 @decoded = $cbor->incr_parse_multiple ($buffer)
342 Same as "incr_parse", but attempts to decode as many CBOR values as
343 possible in one go, instead of at most one. Calls to "incr_parse"
344 and "incr_parse_multiple" can be interleaved.
345
346 $cbor->incr_reset
347 Resets the incremental decoder. This throws away any saved state, so
348 that subsequent calls to "incr_parse" or "incr_parse_multiple" start
349 to parse a new CBOR value from the beginning of the $buffer again.
350
351 This method can be caled at any time, but it *must* be called if you
352 want to change your $buffer or there was a decoding error and you
353 want to reuse the $cbor object for future incremental parsings.
354
139MAPPING 355MAPPING
140 This section describes how CBOR::XS maps Perl values to CBOR values and 356 This section describes how CBOR::XS maps Perl values to CBOR values and
141 vice versa. These mappings are designed to "do the right thing" in most 357 vice versa. These mappings are designed to "do the right thing" in most
142 circumstances automatically, preserving round-tripping characteristics 358 circumstances automatically, preserving round-tripping characteristics
143 (what you put in comes out as something equivalent). 359 (what you put in comes out as something equivalent).
… …
150 integers 366 integers
151 CBOR integers become (numeric) perl scalars. On perls without 64 bit 367 CBOR integers become (numeric) perl scalars. On perls without 64 bit
152 support, 64 bit integers will be truncated or otherwise corrupted. 368 support, 64 bit integers will be truncated or otherwise corrupted.
153 369
154 byte strings 370 byte strings
155 Byte strings will become octet strings in Perl (the byte values 371 Byte strings will become octet strings in Perl (the Byte values
156 0..255 will simply become characters of the same value in Perl). 372 0..255 will simply become characters of the same value in Perl).
157 373
158 UTF-8 strings 374 UTF-8 strings
159 UTF-8 strings in CBOR will be decoded, i.e. the UTF-8 octets will be 375 UTF-8 strings in CBOR will be decoded, i.e. the UTF-8 octets will be
160 decoded into proper Unicode code points. At the moment, the validity 376 decoded into proper Unicode code points. At the moment, the validity
… …
174 "Types:Serialiser::false" and "Types::Serialiser::error", 390 "Types:Serialiser::false" and "Types::Serialiser::error",
175 respectively. They are overloaded to act almost exactly like the 391 respectively. They are overloaded to act almost exactly like the
176 numbers 1 and 0 (for true and false) or to throw an exception on 392 numbers 1 and 0 (for true and false) or to throw an exception on
177 access (for error). See the Types::Serialiser manpage for details. 393 access (for error). See the Types::Serialiser manpage for details.
178 394
179 CBOR tag 256 (perl object) 395 tagged values
180 The tag value 256 (TODO: pending iana registration) will be used to
181 deserialise a Perl object serialised with "FREEZE". See OBJECT
182 SERIALISATION, below, for details.
183
184 CBOR tag 55799 (magic header)
185 The tag 55799 is ignored (this tag implements the magic header).
186
187 other CBOR tags
188 Tagged items consists of a numeric tag and another CBOR value. Tags 396 Tagged items consists of a numeric tag and another CBOR value.
189 not handled internally are currently converted into a
190 CBOR::XS::Tagged object, which is simply a blessed array reference
191 consisting of the numeric tag value followed by the (decoded) CBOR
192 value.
193 397
194 In the future, support for user-supplied conversions might get 398 See "TAG HANDLING AND EXTENSIONS" and the description of "->filter"
195 added. 399 for details on which tags are handled how.
196 400
197 anything else 401 anything else
198 Anything else (e.g. unsupported simple values) will raise a decoding 402 Anything else (e.g. unsupported simple values) will raise a decoding
199 error. 403 error.
200 404
201 PERL -> CBOR 405 PERL -> CBOR
202 The mapping from Perl to CBOR is slightly more difficult, as Perl is a 406 The mapping from Perl to CBOR is slightly more difficult, as Perl is a
203 truly typeless language, so we can only guess which CBOR type is meant 407 typeless language. That means this module can only guess which CBOR type
204 by a Perl value. 408 is meant by a perl value.
205 409
206 hash references 410 hash references
207 Perl hash references become CBOR maps. As there is no inherent 411 Perl hash references become CBOR maps. As there is no inherent
208 ordering in hash keys (or CBOR maps), they will usually be encoded 412 ordering in hash keys (or CBOR maps), they will usually be encoded
209 in a pseudo-random order. 413 in a pseudo-random order. This order can be different each time a
414 hahs is encoded.
210 415
211 Currently, tied hashes will use the indefinite-length format, while 416 Currently, tied hashes will use the indefinite-length format, while
212 normal hashes will use the fixed-length format. 417 normal hashes will use the fixed-length format.
213 418
214 array references 419 array references
215 Perl array references become fixed-length CBOR arrays. 420 Perl array references become fixed-length CBOR arrays.
216 421
217 other references 422 other references
218 Other unblessed references are generally not allowed and will cause 423 Other unblessed references will be represented using the indirection
219 an exception to be thrown, except for references to the integers 0 424 tag extension (tag value 22098,
220 and 1, which get turned into false and true in CBOR. 425 <http://cbor.schmorp.de/indirection>). CBOR decoders are guaranteed
426 to be able to decode these values somehow, by either "doing the
427 right thing", decoding into a generic tagged object, simply ignoring
428 the tag, or something else.
221 429
222 CBOR::XS::Tagged objects 430 CBOR::XS::Tagged objects
223 Objects of this type must be arrays consisting of a single "[tag, 431 Objects of this type must be arrays consisting of a single "[tag,
224 value]" pair. The (numerical) tag will be encoded as a CBOR tag, the 432 value]" pair. The (numerical) tag will be encoded as a CBOR tag, the
225 value will be encoded as appropriate for the value. You cna use 433 value will be encoded as appropriate for the value. You must use
226 "CBOR::XS::tag" to create such objects. 434 "CBOR::XS::tag" to create such objects.
227 435
228 Types::Serialiser::true, Types::Serialiser::false, 436 Types::Serialiser::true, Types::Serialiser::false,
229 Types::Serialiser::error 437 Types::Serialiser::error
230 These special values become CBOR true, CBOR false and CBOR undefined 438 These special values become CBOR true, CBOR false and CBOR undefined
231 values, respectively. You can also use "\1", "\0" and "\undef" 439 values, respectively. You can also use "\1", "\0" and "\undef"
232 directly if you want. 440 directly if you want.
233 441
234 other blessed objects 442 other blessed objects
235 Other blessed objects are serialised via "TO_CBOR" or "FREEZE". See 443 Other blessed objects are serialised via "TO_CBOR" or "FREEZE". See
236 "OBJECT SERIALISATION", below, for details. 444 "TAG HANDLING AND EXTENSIONS" for specific classes handled by this
445 module, and "OBJECT SERIALISATION" for generic object serialisation.
237 446
238 simple scalars 447 simple scalars
239 TODO Simple Perl scalars (any scalar that is not a reference) are 448 Simple Perl scalars (any scalar that is not a reference) are the
240 the most difficult objects to encode: CBOR::XS will encode undefined 449 most difficult objects to encode: CBOR::XS will encode undefined
241 scalars as CBOR null values, scalars that have last been used in a 450 scalars as CBOR null values, scalars that have last been used in a
242 string context before encoding as CBOR strings, and anything else as 451 string context before encoding as CBOR strings, and anything else as
243 number value: 452 number value:
244 453
245 # dump as number 454 # dump as number
246 encode_cbor [2] # yields [2] 455 encode_cbor [2] # yields [2]
247 encode_cbor [-3.0e17] # yields [-3e+17] 456 encode_cbor [-3.0e17] # yields [-3e+17]
248 my $value = 5; encode_cbor [$value] # yields [5] 457 my $value = 5; encode_cbor [$value] # yields [5]
249 458
250 # used as string, so dump as string 459 # used as string, so dump as string (either byte or text)
251 print $value; 460 print $value;
252 encode_cbor [$value] # yields ["5"] 461 encode_cbor [$value] # yields ["5"]
253 462
254 # undef becomes null 463 # undef becomes null
255 encode_cbor [undef] # yields [null] 464 encode_cbor [undef] # yields [null]
… …
258 467
259 my $x = 3.1; # some variable containing a number 468 my $x = 3.1; # some variable containing a number
260 "$x"; # stringified 469 "$x"; # stringified
261 $x .= ""; # another, more awkward way to stringify 470 $x .= ""; # another, more awkward way to stringify
262 print $x; # perl does it for you, too, quite often 471 print $x; # perl does it for you, too, quite often
472
473 You can force whether a string ie encoded as byte or text string by
474 using "utf8::upgrade" and "utf8::downgrade"):
475
476 utf8::upgrade $x; # encode $x as text string
477 utf8::downgrade $x; # encode $x as byte string
478
479 Perl doesn't define what operations up- and downgrade strings, so if
480 the difference between byte and text is important, you should up- or
481 downgrade your string as late as possible before encoding.
263 482
264 You can force the type to be a CBOR number by numifying it: 483 You can force the type to be a CBOR number by numifying it:
265 484
266 my $x = "3"; # some variable containing a string 485 my $x = "3"; # some variable containing a string
267 $x += 0; # numify it, ensuring it will be dumped as a number 486 $x += 0; # numify it, ensuring it will be dumped as a number
… …
277 the IEEE double format will be used. Perls that use formats other 496 the IEEE double format will be used. Perls that use formats other
278 than IEEE double to represent numerical values are supported, but 497 than IEEE double to represent numerical values are supported, but
279 might suffer loss of precision. 498 might suffer loss of precision.
280 499
281 OBJECT SERIALISATION 500 OBJECT SERIALISATION
501 This module implements both a CBOR-specific and the generic
502 Types::Serialier object serialisation protocol. The following
503 subsections explain both methods.
504
505 ENCODING
282 This module knows two way to serialise a Perl object: The CBOR-specific 506 This module knows two way to serialise a Perl object: The CBOR-specific
283 way, and the generic way. 507 way, and the generic way.
284 508
285 Whenever the encoder encounters a Perl object that it cnanot serialise 509 Whenever the encoder encounters a Perl object that it cannot serialise
286 directly (most of them), it will first look up the "TO_CBOR" method on 510 directly (most of them), it will first look up the "TO_CBOR" method on
287 it. 511 it.
288 512
289 If it has a "TO_CBOR" method, it will call it with the object as only 513 If it has a "TO_CBOR" method, it will call it with the object as only
290 argument, and expects exactly one return value, which it will then 514 argument, and expects exactly one return value, which it will then
… …
295 "CBOR" as the second argument, to distinguish it from other serialisers. 519 "CBOR" as the second argument, to distinguish it from other serialisers.
296 520
297 The "FREEZE" method can return any number of values (i.e. zero or more). 521 The "FREEZE" method can return any number of values (i.e. zero or more).
298 These will be encoded as CBOR perl object, together with the classname. 522 These will be encoded as CBOR perl object, together with the classname.
299 523
524 These methods *MUST NOT* change the data structure that is being
525 serialised. Failure to comply to this can result in memory corruption -
526 and worse.
527
300 If an object supports neither "TO_CBOR" nor "FREEZE", encoding will fail 528 If an object supports neither "TO_CBOR" nor "FREEZE", encoding will fail
301 with an error. 529 with an error.
302 530
531 DECODING
303 Objects encoded via "TO_CBOR" cannot be automatically decoded, but 532 Objects encoded via "TO_CBOR" cannot (normally) be automatically
304 objects encoded via "FREEZE" can be decoded using the following 533 decoded, but objects encoded via "FREEZE" can be decoded using the
305 protocol: 534 following protocol:
306 535
307 When an encoded CBOR perl object is encountered by the decoder, it will 536 When an encoded CBOR perl object is encountered by the decoder, it will
308 look up the "THAW" method, by using the stored classname, and will fail 537 look up the "THAW" method, by using the stored classname, and will fail
309 if the method cannot be found. 538 if the method cannot be found.
310 539
… …
331 560
332 sub URI::TO_CBOR { 561 sub URI::TO_CBOR {
333 my ($self) = @_; 562 my ($self) = @_;
334 my $uri = "$self"; # stringify uri 563 my $uri = "$self"; # stringify uri
335 utf8::upgrade $uri; # make sure it will be encoded as UTF-8 string 564 utf8::upgrade $uri; # make sure it will be encoded as UTF-8 string
336 CBOR::XS::tagged 32, "$_[0]" 565 CBOR::XS::tag 32, "$_[0]"
337 } 566 }
338 567
339 This will encode URIs as a UTF-8 string with tag 32, which indicates an 568 This will encode URIs as a UTF-8 string with tag 32, which indicates an
340 URI. 569 URI.
341 570
… …
376 605
377MAGIC HEADER 606MAGIC HEADER
378 There is no way to distinguish CBOR from other formats programmatically. 607 There is no way to distinguish CBOR from other formats programmatically.
379 To make it easier to distinguish CBOR from other formats, the CBOR 608 To make it easier to distinguish CBOR from other formats, the CBOR
380 specification has a special "magic string" that can be prepended to any 609 specification has a special "magic string" that can be prepended to any
381 CBOR string without changing it's meaning. 610 CBOR string without changing its meaning.
382 611
383 This string is available as $CBOR::XS::MAGIC. This module does not 612 This string is available as $CBOR::XS::MAGIC. This module does not
384 prepend this string tot he CBOR data it generates, but it will ignroe it 613 prepend this string to the CBOR data it generates, but it will ignore it
385 if present, so users can prepend this string as a "file type" indicator 614 if present, so users can prepend this string as a "file type" indicator
386 as required. 615 as required.
387 616
388THE CBOR::XS::Tagged CLASS 617THE CBOR::XS::Tagged CLASS
389 CBOR has the concept of tagged values - any CBOR value can be tagged 618 CBOR has the concept of tagged values - any CBOR value can be tagged
… …
440 Wrap CBOR data in CBOR: 669 Wrap CBOR data in CBOR:
441 670
442 my $cbor_cbor = encode_cbor 671 my $cbor_cbor = encode_cbor
443 CBOR::XS::tag 24, 672 CBOR::XS::tag 24,
444 encode_cbor [1, 2, 3]; 673 encode_cbor [1, 2, 3];
674
675TAG HANDLING AND EXTENSIONS
676 This section describes how this module handles specific tagged values
677 and extensions. If a tag is not mentioned here and no additional filters
678 are provided for it, then the default handling applies (creating a
679 CBOR::XS::Tagged object on decoding, and only encoding the tag when
680 explicitly requested).
681
682 Tags not handled specifically are currently converted into a
683 CBOR::XS::Tagged object, which is simply a blessed array reference
684 consisting of the numeric tag value followed by the (decoded) CBOR
685 value.
686
687 Future versions of this module reserve the right to special case
688 additional tags (such as base64url).
689
690 ENFORCED TAGS
691 These tags are always handled when decoding, and their handling cannot
692 be overriden by the user.
693
694 26 (perl-object, <http://cbor.schmorp.de/perl-object>)
695 These tags are automatically created (and decoded) for serialisable
696 objects using the "FREEZE/THAW" methods (the Types::Serialier object
697 serialisation protocol). See "OBJECT SERIALISATION" for details.
698
699 28, 29 (shareable, sharedref, L <http://cbor.schmorp.de/value-sharing>)
700 These tags are automatically decoded when encountered (and they do
701 not result in a cyclic data structure, see "allow_cycles"),
702 resulting in shared values in the decoded object. They are only
703 encoded, however, when "allow_sharing" is enabled.
704
705 Not all shared values can be successfully decoded: values that
706 reference themselves will *currently* decode as "undef" (this is not
707 the same as a reference pointing to itself, which will be
708 represented as a value that contains an indirect reference to itself
709 - these will be decoded properly).
710
711 Note that considerably more shared value data structures can be
712 decoded than will be encoded - currently, only values pointed to by
713 references will be shared, others will not. While non-reference
714 shared values can be generated in Perl with some effort, they were
715 considered too unimportant to be supported in the encoder. The
716 decoder, however, will decode these values as shared values.
717
718 256, 25 (stringref-namespace, stringref, L
719 <http://cbor.schmorp.de/stringref>)
720 These tags are automatically decoded when encountered. They are only
721 encoded, however, when "pack_strings" is enabled.
722
723 22098 (indirection, <http://cbor.schmorp.de/indirection>)
724 This tag is automatically generated when a reference are encountered
725 (with the exception of hash and array refernces). It is converted to
726 a reference when decoding.
727
728 55799 (self-describe CBOR, RFC 7049)
729 This value is not generated on encoding (unless explicitly requested
730 by the user), and is simply ignored when decoding.
731
732 NON-ENFORCED TAGS
733 These tags have default filters provided when decoding. Their handling
734 can be overriden by changing the %CBOR::XS::FILTER entry for the tag, or
735 by providing a custom "filter" callback when decoding.
736
737 When they result in decoding into a specific Perl class, the module
738 usually provides a corresponding "TO_CBOR" method as well.
739
740 When any of these need to load additional modules that are not part of
741 the perl core distribution (e.g. URI), it is (currently) up to the user
742 to provide these modules. The decoding usually fails with an exception
743 if the required module cannot be loaded.
744
745 0, 1 (date/time string, seconds since the epoch)
746 These tags are decoded into Time::Piece objects. The corresponding
747 "Time::Piece::TO_CBOR" method always encodes into tag 1 values
748 currently.
749
750 The Time::Piece API is generally surprisingly bad, and fractional
751 seconds are only accidentally kept intact, so watch out. On the plus
752 side, the module comes with perl since 5.10, which has to count for
753 something.
754
755 2, 3 (positive/negative bignum)
756 These tags are decoded into Math::BigInt objects. The corresponding
757 "Math::BigInt::TO_CBOR" method encodes "small" bigints into normal
758 CBOR integers, and others into positive/negative CBOR bignums.
759
760 4, 5 (decimal fraction/bigfloat)
761 Both decimal fractions and bigfloats are decoded into Math::BigFloat
762 objects. The corresponding "Math::BigFloat::TO_CBOR" method *always*
763 encodes into a decimal fraction.
764
765 CBOR cannot represent bigfloats with *very* large exponents -
766 conversion of such big float objects is undefined.
767
768 Also, NaN and infinities are not encoded properly.
769
770 21, 22, 23 (expected later JSON conversion)
771 CBOR::XS is not a CBOR-to-JSON converter, and will simply ignore
772 these tags.
773
774 32 (URI)
775 These objects decode into URI objects. The corresponding
776 "URI::TO_CBOR" method again results in a CBOR URI value.
445 777
446CBOR and JSON 778CBOR and JSON
447 CBOR is supposed to implement a superset of the JSON data model, and is, 779 CBOR is supposed to implement a superset of the JSON data model, and is,
448 with some coercion, able to represent all JSON texts (something that 780 with some coercion, able to represent all JSON texts (something that
449 other "binary JSON" formats such as BSON generally do not support). 781 other "binary JSON" formats such as BSON generally do not support).
… …
505 uses long double to represent floating point values, they might not be 837 uses long double to represent floating point values, they might not be
506 encoded properly. Half precision types are accepted, but not encoded. 838 encoded properly. Half precision types are accepted, but not encoded.
507 839
508 Strict mode and canonical mode are not implemented. 840 Strict mode and canonical mode are not implemented.
509 841
842LIMITATIONS ON PERLS WITHOUT 64-BIT INTEGER SUPPORT
843 On perls that were built without 64 bit integer support (these are rare
844 nowadays, even on 32 bit architectures, as all major Perl distributions
845 are built with 64 bit integer support), support for any kind of 64 bit
846 integer in CBOR is very limited - most likely, these 64 bit values will
847 be truncated, corrupted, or otherwise not decoded correctly. This also
848 includes string, array and map sizes that are stored as 64 bit integers.
849
510THREADS 850THREADS
511 This module is *not* guaranteed to be thread safe and there are no plans 851 This module is *not* guaranteed to be thread safe and there are no plans
512 to change this until Perl gets thread support (as opposed to the 852 to change this until Perl gets thread support (as opposed to the
513 horribly slow so-called "threads" which are simply slow and bloated 853 horribly slow so-called "threads" which are simply slow and bloated
514 process simulations - use fork, it's *much* faster, cheaper, better). 854 process simulations - use fork, it's *much* faster, cheaper, better).

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