ViewVC Help
View File | Revision Log | Show Annotations | Download File
/cvs/CBOR-XS/README
(Generate patch)

Comparing CBOR-XS/README (file contents):
Revision 1.7 by root, Tue Oct 29 15:56:31 2013 UTC vs.
Revision 1.13 by root, Sun Jan 5 14:24:54 2014 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 This option does not affect "encode" in any way - shared values and
184 references will always be decoded properly if present.
185
186 $cbor = $cbor->pack_strings ([$enable])
187 $enabled = $cbor->get_pack_strings
188 If $enable is true (or missing), then "encode" will try not to
189 encode the same string twice, but will instead encode a reference to
190 the string instead. Depending on your data format, this can save a
191 lot of space, but also results in a very large runtime overhead
192 (expect encoding times to be 2-4 times as high as without).
193
194 It is recommended to leave it off unless you know your
195 communications partner supports the stringref extension to CBOR
196 (<http://cbor.schmorp.de/stringref>), as without decoder support,
197 the resulting data structure might not be usable.
198
199 If $enable is false (the default), then "encode" will encode strings
200 the standard CBOR way.
201
202 This option does not affect "decode" in any way - string references
203 will always be decoded properly if present.
204
205 $cbor = $cbor->validate_utf8 ([$enable])
206 $enabled = $cbor->get_validate_utf8
207 If $enable is true (or missing), then "decode" will validate that
208 elements (text strings) containing UTF-8 data in fact contain valid
209 UTF-8 data (instead of blindly accepting it). This validation
210 obviously takes extra time during decoding.
211
212 The concept of "valid UTF-8" used is perl's concept, which is a
213 superset of the official UTF-8.
214
215 If $enable is false (the default), then "decode" will blindly accept
216 UTF-8 data, marking them as valid UTF-8 in the resulting data
217 structure regardless of whether thats true or not.
218
219 Perl isn't too happy about corrupted UTF-8 in strings, but should
220 generally not crash or do similarly evil things. Extensions might be
221 not so forgiving, so it's recommended to turn on this setting if you
222 receive untrusted CBOR.
223
224 This option does not affect "encode" in any way - strings that are
225 supposedly valid UTF-8 will simply be dumped into the resulting CBOR
226 string without checking whether that is, in fact, true or not.
227
228 $cbor = $cbor->filter ([$cb->($tag, $value)])
229 $cb_or_undef = $cbor->get_filter
230 Sets or replaces the tagged value decoding filter (when $cb is
231 specified) or clears the filter (if no argument or "undef" is
232 provided).
233
234 The filter callback is called only during decoding, when a
235 non-enforced tagged value has been decoded (see "TAG HANDLING AND
236 EXTENSIONS" for a list of enforced tags). For specific tags, it's
237 often better to provide a default converter using the
238 %CBOR::XS::FILTER hash (see below).
239
240 The first argument is the numerical tag, the second is the (decoded)
241 value that has been tagged.
242
243 The filter function should return either exactly one value, which
244 will replace the tagged value in the decoded data structure, or no
245 values, which will result in default handling, which currently means
246 the decoder creates a "CBOR::XS::Tagged" object to hold the tag and
247 the value.
248
249 When the filter is cleared (the default state), the default filter
250 function, "CBOR::XS::default_filter", is used. This function simply
251 looks up the tag in the %CBOR::XS::FILTER hash. If an entry exists
252 it must be a code reference that is called with tag and value, and
253 is responsible for decoding the value. If no entry exists, it
254 returns no values.
255
256 Example: decode all tags not handled internally into
257 "CBOR::XS::Tagged" objects, with no other special handling (useful
258 when working with potentially "unsafe" CBOR data).
259
260 CBOR::XS->new->filter (sub { })->decode ($cbor_data);
261
262 Example: provide a global filter for tag 1347375694, converting the
263 value into some string form.
264
265 $CBOR::XS::FILTER{1347375694} = sub {
266 my ($tag, $value);
267
268 "tag 1347375694 value $value"
269 };
270
118 $cbor_data = $cbor->encode ($perl_scalar) 271 $cbor_data = $cbor->encode ($perl_scalar)
119 Converts the given Perl data structure (a scalar value) to its CBOR 272 Converts the given Perl data structure (a scalar value) to its CBOR
120 representation. 273 representation.
121 274
122 $perl_scalar = $cbor->decode ($cbor_data) 275 $perl_scalar = $cbor->decode ($cbor_data)
… …
134 the next one starts. 287 the next one starts.
135 288
136 CBOR::XS->new->decode_prefix ("......") 289 CBOR::XS->new->decode_prefix ("......")
137 => ("...", 3) 290 => ("...", 3)
138 291
292 INCREMENTAL PARSING
293 In some cases, there is the need for incremental parsing of JSON texts.
294 While this module always has to keep both CBOR text and resulting Perl
295 data structure in memory at one time, it does allow you to parse a CBOR
296 stream incrementally, using a similar to using "decode_prefix" to see if
297 a full CBOR object is available, but is much more efficient.
298
299 It basically works by parsing as much of a CBOR string as possible - if
300 the CBOR data is not complete yet, the pasrer will remember where it
301 was, to be able to restart when more data has been accumulated. Once
302 enough data is available to either decode a complete CBOR value or raise
303 an error, a real decode will be attempted.
304
305 A typical use case would be a network protocol that consists of sending
306 and receiving CBOR-encoded messages. The solution that works with CBOR
307 and about anything else is by prepending a length to every CBOR value,
308 so the receiver knows how many octets to read. More compact (and
309 slightly slower) would be to just send CBOR values back-to-back, as
310 "CBOR::XS" knows where a CBOR value ends, and doesn't need an explicit
311 length.
312
313 The following methods help with this:
314
315 @decoded = $cbor->incr_parse ($buffer)
316 This method attempts to decode exactly one CBOR value from the
317 beginning of the given $buffer. The value is removed from the
318 $buffer on success. When $buffer doesn't contain a complete value
319 yet, it returns nothing. Finally, when the $buffer doesn't start
320 with something that could ever be a valid CBOR value, it raises an
321 exception, just as "decode" would. In the latter case the decoder
322 state is undefined and must be reset before being able to parse
323 further.
324
325 This method modifies the $buffer in place. When no CBOR value can be
326 decoded, the decoder stores the current string offset. On the next
327 call, continues decoding at the place where it stopped before. For
328 this to make sense, the $buffer must begin with the same octets as
329 on previous unsuccessful calls.
330
331 You can call this method in scalar context, in which case it either
332 returns a decoded value or "undef". This makes it impossible to
333 distinguish between CBOR null values (which decode to "undef") and
334 an unsuccessful decode, which is often acceptable.
335
336 @decoded = $cbor->incr_parse_multiple ($buffer)
337 Same as "incr_parse", but attempts to decode as many CBOR values as
338 possible in one go, instead of at most one. Calls to "incr_parse"
339 and "incr_parse_multiple" can be interleaved.
340
341 $cbor->incr_reset
342 Resets the incremental decoder. This throws away any saved state, so
343 that subsequent calls to "incr_parse" or "incr_parse_multiple" start
344 to parse a new CBOR value from the beginning of the $buffer again.
345
346 This method can be caled at any time, but it *must* be called if you
347 want to change your $buffer or there was a decoding error and you
348 want to reuse the $cbor object for future incremental parsings.
349
139MAPPING 350MAPPING
140 This section describes how CBOR::XS maps Perl values to CBOR values and 351 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 352 vice versa. These mappings are designed to "do the right thing" in most
142 circumstances automatically, preserving round-tripping characteristics 353 circumstances automatically, preserving round-tripping characteristics
143 (what you put in comes out as something equivalent). 354 (what you put in comes out as something equivalent).
… …
150 integers 361 integers
151 CBOR integers become (numeric) perl scalars. On perls without 64 bit 362 CBOR integers become (numeric) perl scalars. On perls without 64 bit
152 support, 64 bit integers will be truncated or otherwise corrupted. 363 support, 64 bit integers will be truncated or otherwise corrupted.
153 364
154 byte strings 365 byte strings
155 Byte strings will become octet strings in Perl (the byte values 366 Byte strings will become octet strings in Perl (the Byte values
156 0..255 will simply become characters of the same value in Perl). 367 0..255 will simply become characters of the same value in Perl).
157 368
158 UTF-8 strings 369 UTF-8 strings
159 UTF-8 strings in CBOR will be decoded, i.e. the UTF-8 octets will be 370 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 371 decoded into proper Unicode code points. At the moment, the validity
… …
174 "Types:Serialiser::false" and "Types::Serialiser::error", 385 "Types:Serialiser::false" and "Types::Serialiser::error",
175 respectively. They are overloaded to act almost exactly like the 386 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 387 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. 388 access (for error). See the Types::Serialiser manpage for details.
178 389
179 CBOR tag 256 (perl object) 390 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 391 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.
193 392
194 In the future, support for user-supplied conversions might get 393 See "TAG HANDLING AND EXTENSIONS" and the description of "->filter"
195 added. 394 for details on which tags are handled how.
196 395
197 anything else 396 anything else
198 Anything else (e.g. unsupported simple values) will raise a decoding 397 Anything else (e.g. unsupported simple values) will raise a decoding
199 error. 398 error.
200 399
201 PERL -> CBOR 400 PERL -> CBOR
202 The mapping from Perl to CBOR is slightly more difficult, as Perl is a 401 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 402 typeless language. That means this module can only guess which CBOR type
204 by a Perl value. 403 is meant by a perl value.
205 404
206 hash references 405 hash references
207 Perl hash references become CBOR maps. As there is no inherent 406 Perl hash references become CBOR maps. As there is no inherent
208 ordering in hash keys (or CBOR maps), they will usually be encoded 407 ordering in hash keys (or CBOR maps), they will usually be encoded
209 in a pseudo-random order. 408 in a pseudo-random order. This order can be different each time a
409 hahs is encoded.
210 410
211 Currently, tied hashes will use the indefinite-length format, while 411 Currently, tied hashes will use the indefinite-length format, while
212 normal hashes will use the fixed-length format. 412 normal hashes will use the fixed-length format.
213 413
214 array references 414 array references
215 Perl array references become fixed-length CBOR arrays. 415 Perl array references become fixed-length CBOR arrays.
216 416
217 other references 417 other references
218 Other unblessed references are generally not allowed and will cause 418 Other unblessed references will be represented using the indirection
219 an exception to be thrown, except for references to the integers 0 419 tag extension (tag value 22098,
220 and 1, which get turned into false and true in CBOR. 420 <http://cbor.schmorp.de/indirection>). CBOR decoders are guaranteed
421 to be able to decode these values somehow, by either "doing the
422 right thing", decoding into a generic tagged object, simply ignoring
423 the tag, or something else.
221 424
222 CBOR::XS::Tagged objects 425 CBOR::XS::Tagged objects
223 Objects of this type must be arrays consisting of a single "[tag, 426 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 427 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 428 value will be encoded as appropriate for the value. You must use
226 "CBOR::XS::tag" to create such objects. 429 "CBOR::XS::tag" to create such objects.
227 430
228 Types::Serialiser::true, Types::Serialiser::false, 431 Types::Serialiser::true, Types::Serialiser::false,
229 Types::Serialiser::error 432 Types::Serialiser::error
230 These special values become CBOR true, CBOR false and CBOR undefined 433 These special values become CBOR true, CBOR false and CBOR undefined
231 values, respectively. You can also use "\1", "\0" and "\undef" 434 values, respectively. You can also use "\1", "\0" and "\undef"
232 directly if you want. 435 directly if you want.
233 436
234 other blessed objects 437 other blessed objects
235 Other blessed objects are serialised via "TO_CBOR" or "FREEZE". See 438 Other blessed objects are serialised via "TO_CBOR" or "FREEZE". See
236 "OBJECT SERIALISATION", below, for details. 439 "TAG HANDLING AND EXTENSIONS" for specific classes handled by this
440 module, and "OBJECT SERIALISATION" for generic object serialisation.
237 441
238 simple scalars 442 simple scalars
239 TODO Simple Perl scalars (any scalar that is not a reference) are 443 Simple Perl scalars (any scalar that is not a reference) are the
240 the most difficult objects to encode: CBOR::XS will encode undefined 444 most difficult objects to encode: CBOR::XS will encode undefined
241 scalars as CBOR null values, scalars that have last been used in a 445 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 446 string context before encoding as CBOR strings, and anything else as
243 number value: 447 number value:
244 448
245 # dump as number 449 # dump as number
246 encode_cbor [2] # yields [2] 450 encode_cbor [2] # yields [2]
247 encode_cbor [-3.0e17] # yields [-3e+17] 451 encode_cbor [-3.0e17] # yields [-3e+17]
248 my $value = 5; encode_cbor [$value] # yields [5] 452 my $value = 5; encode_cbor [$value] # yields [5]
249 453
250 # used as string, so dump as string 454 # used as string, so dump as string (either byte or text)
251 print $value; 455 print $value;
252 encode_cbor [$value] # yields ["5"] 456 encode_cbor [$value] # yields ["5"]
253 457
254 # undef becomes null 458 # undef becomes null
255 encode_cbor [undef] # yields [null] 459 encode_cbor [undef] # yields [null]
… …
258 462
259 my $x = 3.1; # some variable containing a number 463 my $x = 3.1; # some variable containing a number
260 "$x"; # stringified 464 "$x"; # stringified
261 $x .= ""; # another, more awkward way to stringify 465 $x .= ""; # another, more awkward way to stringify
262 print $x; # perl does it for you, too, quite often 466 print $x; # perl does it for you, too, quite often
467
468 You can force whether a string ie encoded as byte or text string by
469 using "utf8::upgrade" and "utf8::downgrade"):
470
471 utf8::upgrade $x; # encode $x as text string
472 utf8::downgrade $x; # encode $x as byte string
473
474 Perl doesn't define what operations up- and downgrade strings, so if
475 the difference between byte and text is important, you should up- or
476 downgrade your string as late as possible before encoding.
263 477
264 You can force the type to be a CBOR number by numifying it: 478 You can force the type to be a CBOR number by numifying it:
265 479
266 my $x = "3"; # some variable containing a string 480 my $x = "3"; # some variable containing a string
267 $x += 0; # numify it, ensuring it will be dumped as a number 481 $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 491 the IEEE double format will be used. Perls that use formats other
278 than IEEE double to represent numerical values are supported, but 492 than IEEE double to represent numerical values are supported, but
279 might suffer loss of precision. 493 might suffer loss of precision.
280 494
281 OBJECT SERIALISATION 495 OBJECT SERIALISATION
496 This module implements both a CBOR-specific and the generic
497 Types::Serialier object serialisation protocol. The following
498 subsections explain both methods.
499
500 ENCODING
282 This module knows two way to serialise a Perl object: The CBOR-specific 501 This module knows two way to serialise a Perl object: The CBOR-specific
283 way, and the generic way. 502 way, and the generic way.
284 503
285 Whenever the encoder encounters a Perl object that it cnanot serialise 504 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 505 directly (most of them), it will first look up the "TO_CBOR" method on
287 it. 506 it.
288 507
289 If it has a "TO_CBOR" method, it will call it with the object as only 508 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 509 argument, and expects exactly one return value, which it will then
… …
295 "CBOR" as the second argument, to distinguish it from other serialisers. 514 "CBOR" as the second argument, to distinguish it from other serialisers.
296 515
297 The "FREEZE" method can return any number of values (i.e. zero or more). 516 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. 517 These will be encoded as CBOR perl object, together with the classname.
299 518
519 These methods *MUST NOT* change the data structure that is being
520 serialised. Failure to comply to this can result in memory corruption -
521 and worse.
522
300 If an object supports neither "TO_CBOR" nor "FREEZE", encoding will fail 523 If an object supports neither "TO_CBOR" nor "FREEZE", encoding will fail
301 with an error. 524 with an error.
302 525
526 DECODING
303 Objects encoded via "TO_CBOR" cannot be automatically decoded, but 527 Objects encoded via "TO_CBOR" cannot (normally) be automatically
304 objects encoded via "FREEZE" can be decoded using the following 528 decoded, but objects encoded via "FREEZE" can be decoded using the
305 protocol: 529 following protocol:
306 530
307 When an encoded CBOR perl object is encountered by the decoder, it will 531 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 532 look up the "THAW" method, by using the stored classname, and will fail
309 if the method cannot be found. 533 if the method cannot be found.
310 534
… …
331 555
332 sub URI::TO_CBOR { 556 sub URI::TO_CBOR {
333 my ($self) = @_; 557 my ($self) = @_;
334 my $uri = "$self"; # stringify uri 558 my $uri = "$self"; # stringify uri
335 utf8::upgrade $uri; # make sure it will be encoded as UTF-8 string 559 utf8::upgrade $uri; # make sure it will be encoded as UTF-8 string
336 CBOR::XS::tagged 32, "$_[0]" 560 CBOR::XS::tag 32, "$_[0]"
337 } 561 }
338 562
339 This will encode URIs as a UTF-8 string with tag 32, which indicates an 563 This will encode URIs as a UTF-8 string with tag 32, which indicates an
340 URI. 564 URI.
341 565
… …
376 600
377MAGIC HEADER 601MAGIC HEADER
378 There is no way to distinguish CBOR from other formats programmatically. 602 There is no way to distinguish CBOR from other formats programmatically.
379 To make it easier to distinguish CBOR from other formats, the CBOR 603 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 604 specification has a special "magic string" that can be prepended to any
381 CBOR string without changing it's meaning. 605 CBOR string without changing its meaning.
382 606
383 This string is available as $CBOR::XS::MAGIC. This module does not 607 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 608 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 609 if present, so users can prepend this string as a "file type" indicator
386 as required. 610 as required.
387 611
388THE CBOR::XS::Tagged CLASS 612THE CBOR::XS::Tagged CLASS
389 CBOR has the concept of tagged values - any CBOR value can be tagged 613 CBOR has the concept of tagged values - any CBOR value can be tagged
… …
440 Wrap CBOR data in CBOR: 664 Wrap CBOR data in CBOR:
441 665
442 my $cbor_cbor = encode_cbor 666 my $cbor_cbor = encode_cbor
443 CBOR::XS::tag 24, 667 CBOR::XS::tag 24,
444 encode_cbor [1, 2, 3]; 668 encode_cbor [1, 2, 3];
669
670TAG HANDLING AND EXTENSIONS
671 This section describes how this module handles specific tagged values
672 and extensions. If a tag is not mentioned here and no additional filters
673 are provided for it, then the default handling applies (creating a
674 CBOR::XS::Tagged object on decoding, and only encoding the tag when
675 explicitly requested).
676
677 Tags not handled specifically are currently converted into a
678 CBOR::XS::Tagged object, which is simply a blessed array reference
679 consisting of the numeric tag value followed by the (decoded) CBOR
680 value.
681
682 Future versions of this module reserve the right to special case
683 additional tags (such as base64url).
684
685 ENFORCED TAGS
686 These tags are always handled when decoding, and their handling cannot
687 be overriden by the user.
688
689 26 (perl-object, <http://cbor.schmorp.de/perl-object>)
690 These tags are automatically created (and decoded) for serialisable
691 objects using the "FREEZE/THAW" methods (the Types::Serialier object
692 serialisation protocol). See "OBJECT SERIALISATION" for details.
693
694 28, 29 (shareable, sharedref, L <http://cbor.schmorp.de/value-sharing>)
695 These tags are automatically decoded when encountered (and they do
696 not result in a cyclic data structure, see "allow_cycles"),
697 resulting in shared values in the decoded object. They are only
698 encoded, however, when "allow_sharing" is enabled.
699
700 Not all shared values can be successfully decoded: values that
701 reference themselves will *currently* decode as "undef" (this is not
702 the same as a reference pointing to itself, which will be
703 represented as a value that contains an indirect reference to itself
704 - these will be decoded properly).
705
706 Note that considerably more shared value data structures can be
707 decoded than will be encoded - currently, only values pointed to by
708 references will be shared, others will not. While non-reference
709 shared values can be generated in Perl with some effort, they were
710 considered too unimportant to be supported in the encoder. The
711 decoder, however, will decode these values as shared values.
712
713 256, 25 (stringref-namespace, stringref, L
714 <http://cbor.schmorp.de/stringref>)
715 These tags are automatically decoded when encountered. They are only
716 encoded, however, when "pack_strings" is enabled.
717
718 22098 (indirection, <http://cbor.schmorp.de/indirection>)
719 This tag is automatically generated when a reference are encountered
720 (with the exception of hash and array refernces). It is converted to
721 a reference when decoding.
722
723 55799 (self-describe CBOR, RFC 7049)
724 This value is not generated on encoding (unless explicitly requested
725 by the user), and is simply ignored when decoding.
726
727 NON-ENFORCED TAGS
728 These tags have default filters provided when decoding. Their handling
729 can be overriden by changing the %CBOR::XS::FILTER entry for the tag, or
730 by providing a custom "filter" callback when decoding.
731
732 When they result in decoding into a specific Perl class, the module
733 usually provides a corresponding "TO_CBOR" method as well.
734
735 When any of these need to load additional modules that are not part of
736 the perl core distribution (e.g. URI), it is (currently) up to the user
737 to provide these modules. The decoding usually fails with an exception
738 if the required module cannot be loaded.
739
740 0, 1 (date/time string, seconds since the epoch)
741 These tags are decoded into Time::Piece objects. The corresponding
742 "Time::Piece::TO_CBOR" method always encodes into tag 1 values
743 currently.
744
745 The Time::Piece API is generally surprisingly bad, and fractional
746 seconds are only accidentally kept intact, so watch out. On the plus
747 side, the module comes with perl since 5.10, which has to count for
748 something.
749
750 2, 3 (positive/negative bignum)
751 These tags are decoded into Math::BigInt objects. The corresponding
752 "Math::BigInt::TO_CBOR" method encodes "small" bigints into normal
753 CBOR integers, and others into positive/negative CBOR bignums.
754
755 4, 5 (decimal fraction/bigfloat)
756 Both decimal fractions and bigfloats are decoded into Math::BigFloat
757 objects. The corresponding "Math::BigFloat::TO_CBOR" method *always*
758 encodes into a decimal fraction.
759
760 CBOR cannot represent bigfloats with *very* large exponents -
761 conversion of such big float objects is undefined.
762
763 Also, NaN and infinities are not encoded properly.
764
765 21, 22, 23 (expected later JSON conversion)
766 CBOR::XS is not a CBOR-to-JSON converter, and will simply ignore
767 these tags.
768
769 32 (URI)
770 These objects decode into URI objects. The corresponding
771 "URI::TO_CBOR" method again results in a CBOR URI value.
445 772
446CBOR and JSON 773CBOR and JSON
447 CBOR is supposed to implement a superset of the JSON data model, and is, 774 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 775 with some coercion, able to represent all JSON texts (something that
449 other "binary JSON" formats such as BSON generally do not support). 776 other "binary JSON" formats such as BSON generally do not support).
… …
505 uses long double to represent floating point values, they might not be 832 uses long double to represent floating point values, they might not be
506 encoded properly. Half precision types are accepted, but not encoded. 833 encoded properly. Half precision types are accepted, but not encoded.
507 834
508 Strict mode and canonical mode are not implemented. 835 Strict mode and canonical mode are not implemented.
509 836
837LIMITATIONS ON PERLS WITHOUT 64-BIT INTEGER SUPPORT
838 On perls that were built without 64 bit integer support (these are rare
839 nowadays, even on 32 bit architectures), support for any kind of 64 bit
840 integer in CBOR is very limited - most likely, these 64 bit values will
841 be truncated, corrupted, or otherwise not decoded correctly. This also
842 includes string, array and map sizes that are stored as 64 bit integers.
843
510THREADS 844THREADS
511 This module is *not* guaranteed to be thread safe and there are no plans 845 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 846 to change this until Perl gets thread support (as opposed to the
513 horribly slow so-called "threads" which are simply slow and bloated 847 horribly slow so-called "threads" which are simply slow and bloated
514 process simulations - use fork, it's *much* faster, cheaper, better). 848 process simulations - use fork, it's *much* faster, cheaper, better).

Diff Legend

– Removed lines
+ Added lines
< Changed lines
> Changed lines