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 1.10 by root, Thu Nov 28 16:09:04 2013 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"), string deduplication (see "pack_strings") and scalar
50 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.
147
148 It is recommended to leave it off unless you know your communication
149 partner supports the value sharing extensions to CBOR
150 (<http://cbor.schmorp.de/value-sharing>), as without decoder
151 support, the resulting data structure might be unusable.
152
153 Detecting shared values incurs a runtime overhead when values are
154 encoded that have a reference counter large than one, and might
155 unnecessarily increase the encoded size, as potentially shared
156 values are encode as sharable whether or not they are actually
157 shared.
158
159 At the moment, only targets of references can be shared (e.g.
160 scalars, arrays or hashes pointed to by a reference). Weirder
161 constructs, such as an array with multiple "copies" of the *same*
162 string, which are hard but not impossible to create in Perl, are not
163 supported (this is the same as with Storable).
164
165 If $enable is false (the default), then "encode" will encode shared
166 data structures repeatedly, unsharing them in the process. Cyclic
167 data structures cannot be encoded in this mode.
168
169 This option does not affect "decode" in any way - shared values and
170 references will always be decoded properly if present.
171
172 $cbor = $cbor->pack_strings ([$enable])
173 $enabled = $cbor->get_pack_strings
174 If $enable is true (or missing), then "encode" will try not to
175 encode the same string twice, but will instead encode a reference to
176 the string instead. Depending on your data format, this can save a
177 lot of space, but also results in a very large runtime overhead
178 (expect encoding times to be 2-4 times as high as without).
179
180 It is recommended to leave it off unless you know your
181 communications partner supports the stringref extension to CBOR
182 (<http://cbor.schmorp.de/stringref>), as without decoder support,
183 the resulting data structure might not be usable.
184
185 If $enable is false (the default), then "encode" will encode strings
186 the standard CBOR way.
187
188 This option does not affect "decode" in any way - string references
189 will always be decoded properly if present.
190
191 $cbor = $cbor->filter ([$cb->($tag, $value)])
192 $cb_or_undef = $cbor->get_filter
193 Sets or replaces the tagged value decoding filter (when $cb is
194 specified) or clears the filter (if no argument or "undef" is
195 provided).
196
197 The filter callback is called only during decoding, when a
198 non-enforced tagged value has been decoded (see "TAG HANDLING AND
199 EXTENSIONS" for a list of enforced tags). For specific tags, it's
200 often better to provide a default converter using the
201 %CBOR::XS::FILTER hash (see below).
202
203 The first argument is the numerical tag, the second is the (decoded)
204 value that has been tagged.
205
206 The filter function should return either exactly one value, which
207 will replace the tagged value in the decoded data structure, or no
208 values, which will result in default handling, which currently means
209 the decoder creates a "CBOR::XS::Tagged" object to hold the tag and
210 the value.
211
212 When the filter is cleared (the default state), the default filter
213 function, "CBOR::XS::default_filter", is used. This function simply
214 looks up the tag in the %CBOR::XS::FILTER hash. If an entry exists
215 it must be a code reference that is called with tag and value, and
216 is responsible for decoding the value. If no entry exists, it
217 returns no values.
218
219 Example: decode all tags not handled internally into
220 "CBOR::XS::Tagged" objects, with no other special handling (useful
221 when working with potentially "unsafe" CBOR data).
222
223 CBOR::XS->new->filter (sub { })->decode ($cbor_data);
224
225 Example: provide a global filter for tag 1347375694, converting the
226 value into some string form.
227
228 $CBOR::XS::FILTER{1347375694} = sub {
229 my ($tag, $value);
230
231 "tag 1347375694 value $value"
232 };
233
118 $cbor_data = $cbor->encode ($perl_scalar) 234 $cbor_data = $cbor->encode ($perl_scalar)
119 Converts the given Perl data structure (a scalar value) to its CBOR 235 Converts the given Perl data structure (a scalar value) to its CBOR
120 representation. 236 representation.
121 237
122 $perl_scalar = $cbor->decode ($cbor_data) 238 $perl_scalar = $cbor->decode ($cbor_data)
150 integers 266 integers
151 CBOR integers become (numeric) perl scalars. On perls without 64 bit 267 CBOR integers become (numeric) perl scalars. On perls without 64 bit
152 support, 64 bit integers will be truncated or otherwise corrupted. 268 support, 64 bit integers will be truncated or otherwise corrupted.
153 269
154 byte strings 270 byte strings
155 Byte strings will become octet strings in Perl (the byte values 271 Byte strings will become octet strings in Perl (the Byte values
156 0..255 will simply become characters of the same value in Perl). 272 0..255 will simply become characters of the same value in Perl).
157 273
158 UTF-8 strings 274 UTF-8 strings
159 UTF-8 strings in CBOR will be decoded, i.e. the UTF-8 octets will be 275 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 276 decoded into proper Unicode code points. At the moment, the validity
174 "Types:Serialiser::false" and "Types::Serialiser::error", 290 "Types:Serialiser::false" and "Types::Serialiser::error",
175 respectively. They are overloaded to act almost exactly like the 291 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 292 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. 293 access (for error). See the Types::Serialiser manpage for details.
178 294
179 CBOR tag 256 (perl object) 295 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 296 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.
193 297
194 In the future, support for user-supplied conversions might get 298 See "TAG HANDLING AND EXTENSIONS" and the description of "->filter"
195 added. 299 for details on which tags are handled how.
196 300
197 anything else 301 anything else
198 Anything else (e.g. unsupported simple values) will raise a decoding 302 Anything else (e.g. unsupported simple values) will raise a decoding
199 error. 303 error.
200 304
201 PERL -> CBOR 305 PERL -> CBOR
202 The mapping from Perl to CBOR is slightly more difficult, as Perl is a 306 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 307 typeless language. That means this module can only guess which CBOR type
204 by a Perl value. 308 is meant by a perl value.
205 309
206 hash references 310 hash references
207 Perl hash references become CBOR maps. As there is no inherent 311 Perl hash references become CBOR maps. As there is no inherent
208 ordering in hash keys (or CBOR maps), they will usually be encoded 312 ordering in hash keys (or CBOR maps), they will usually be encoded
209 in a pseudo-random order. 313 in a pseudo-random order. This order can be different each time a
314 hahs is encoded.
210 315
211 Currently, tied hashes will use the indefinite-length format, while 316 Currently, tied hashes will use the indefinite-length format, while
212 normal hashes will use the fixed-length format. 317 normal hashes will use the fixed-length format.
213 318
214 array references 319 array references
215 Perl array references become fixed-length CBOR arrays. 320 Perl array references become fixed-length CBOR arrays.
216 321
217 other references 322 other references
218 Other unblessed references are generally not allowed and will cause 323 Other unblessed references will be represented using the indirection
219 an exception to be thrown, except for references to the integers 0 324 tag extension (tag value 22098,
220 and 1, which get turned into false and true in CBOR. 325 <http://cbor.schmorp.de/indirection>). CBOR decoders are guaranteed
326 to be able to decode these values somehow, by either "doing the
327 right thing", decoding into a generic tagged object, simply ignoring
328 the tag, or something else.
221 329
222 CBOR::XS::Tagged objects 330 CBOR::XS::Tagged objects
223 Objects of this type must be arrays consisting of a single "[tag, 331 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 332 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 333 value will be encoded as appropriate for the value. You must use
226 "CBOR::XS::tag" to create such objects. 334 "CBOR::XS::tag" to create such objects.
227 335
228 Types::Serialiser::true, Types::Serialiser::false, 336 Types::Serialiser::true, Types::Serialiser::false,
229 Types::Serialiser::error 337 Types::Serialiser::error
230 These special values become CBOR true, CBOR false and CBOR undefined 338 These special values become CBOR true, CBOR false and CBOR undefined
231 values, respectively. You can also use "\1", "\0" and "\undef" 339 values, respectively. You can also use "\1", "\0" and "\undef"
232 directly if you want. 340 directly if you want.
233 341
234 other blessed objects 342 other blessed objects
235 Other blessed objects are serialised via "TO_CBOR" or "FREEZE". See 343 Other blessed objects are serialised via "TO_CBOR" or "FREEZE". See
236 "OBJECT SERIALISATION", below, for details. 344 "TAG HANDLING AND EXTENSIONS" for specific classes handled by this
345 module, and "OBJECT SERIALISATION" for generic object serialisation.
237 346
238 simple scalars 347 simple scalars
239 TODO Simple Perl scalars (any scalar that is not a reference) are 348 Simple Perl scalars (any scalar that is not a reference) are the
240 the most difficult objects to encode: CBOR::XS will encode undefined 349 most difficult objects to encode: CBOR::XS will encode undefined
241 scalars as CBOR null values, scalars that have last been used in a 350 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 351 string context before encoding as CBOR strings, and anything else as
243 number value: 352 number value:
244 353
245 # dump as number 354 # dump as number
246 encode_cbor [2] # yields [2] 355 encode_cbor [2] # yields [2]
247 encode_cbor [-3.0e17] # yields [-3e+17] 356 encode_cbor [-3.0e17] # yields [-3e+17]
248 my $value = 5; encode_cbor [$value] # yields [5] 357 my $value = 5; encode_cbor [$value] # yields [5]
249 358
250 # used as string, so dump as string 359 # used as string, so dump as string (either byte or text)
251 print $value; 360 print $value;
252 encode_cbor [$value] # yields ["5"] 361 encode_cbor [$value] # yields ["5"]
253 362
254 # undef becomes null 363 # undef becomes null
255 encode_cbor [undef] # yields [null] 364 encode_cbor [undef] # yields [null]
258 367
259 my $x = 3.1; # some variable containing a number 368 my $x = 3.1; # some variable containing a number
260 "$x"; # stringified 369 "$x"; # stringified
261 $x .= ""; # another, more awkward way to stringify 370 $x .= ""; # another, more awkward way to stringify
262 print $x; # perl does it for you, too, quite often 371 print $x; # perl does it for you, too, quite often
372
373 You can force whether a string ie encoded as byte or text string by
374 using "utf8::upgrade" and "utf8::downgrade"):
375
376 utf8::upgrade $x; # encode $x as text string
377 utf8::downgrade $x; # encode $x as byte string
378
379 Perl doesn't define what operations up- and downgrade strings, so if
380 the difference between byte and text is important, you should up- or
381 downgrade your string as late as possible before encoding.
263 382
264 You can force the type to be a CBOR number by numifying it: 383 You can force the type to be a CBOR number by numifying it:
265 384
266 my $x = "3"; # some variable containing a string 385 my $x = "3"; # some variable containing a string
267 $x += 0; # numify it, ensuring it will be dumped as a number 386 $x += 0; # numify it, ensuring it will be dumped as a number
331 450
332 sub URI::TO_CBOR { 451 sub URI::TO_CBOR {
333 my ($self) = @_; 452 my ($self) = @_;
334 my $uri = "$self"; # stringify uri 453 my $uri = "$self"; # stringify uri
335 utf8::upgrade $uri; # make sure it will be encoded as UTF-8 string 454 utf8::upgrade $uri; # make sure it will be encoded as UTF-8 string
336 CBOR::XS::tagged 32, "$_[0]" 455 CBOR::XS::tag 32, "$_[0]"
337 } 456 }
338 457
339 This will encode URIs as a UTF-8 string with tag 32, which indicates an 458 This will encode URIs as a UTF-8 string with tag 32, which indicates an
340 URI. 459 URI.
341 460
376 495
377MAGIC HEADER 496MAGIC HEADER
378 There is no way to distinguish CBOR from other formats programmatically. 497 There is no way to distinguish CBOR from other formats programmatically.
379 To make it easier to distinguish CBOR from other formats, the CBOR 498 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 499 specification has a special "magic string" that can be prepended to any
381 CBOR string without changing it's meaning. 500 CBOR string without changing its meaning.
382 501
383 This string is available as $CBOR::XS::MAGIC. This module does not 502 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 503 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 504 if present, so users can prepend this string as a "file type" indicator
386 as required. 505 as required.
387 506
388THE CBOR::XS::Tagged CLASS 507THE CBOR::XS::Tagged CLASS
389 CBOR has the concept of tagged values - any CBOR value can be tagged 508 CBOR has the concept of tagged values - any CBOR value can be tagged
440 Wrap CBOR data in CBOR: 559 Wrap CBOR data in CBOR:
441 560
442 my $cbor_cbor = encode_cbor 561 my $cbor_cbor = encode_cbor
443 CBOR::XS::tag 24, 562 CBOR::XS::tag 24,
444 encode_cbor [1, 2, 3]; 563 encode_cbor [1, 2, 3];
564
565TAG HANDLING AND EXTENSIONS
566 This section describes how this module handles specific tagged values
567 and extensions. If a tag is not mentioned here and no additional filters
568 are provided for it, then the default handling applies (creating a
569 CBOR::XS::Tagged object on decoding, and only encoding the tag when
570 explicitly requested).
571
572 Tags not handled specifically are currently converted into a
573 CBOR::XS::Tagged object, which is simply a blessed array reference
574 consisting of the numeric tag value followed by the (decoded) CBOR
575 value.
576
577 Future versions of this module reserve the right to special case
578 additional tags (such as base64url).
579
580 ENFORCED TAGS
581 These tags are always handled when decoding, and their handling cannot
582 be overriden by the user.
583
584 26 (perl-object, <http://cbor.schmorp.de/perl-object>)
585 These tags are automatically created (and decoded) for serialisable
586 objects using the "FREEZE/THAW" methods (the Types::Serialier object
587 serialisation protocol). See "OBJECT SERIALISATION" for details.
588
589 28, 29 (sharable, sharedref, L <http://cbor.schmorp.de/value-sharing>)
590 These tags are automatically decoded when encountered, resulting in
591 shared values in the decoded object. They are only encoded, however,
592 when "allow_sharable" is enabled.
593
594 256, 25 (stringref-namespace, stringref, L
595 <http://cbor.schmorp.de/stringref>)
596 These tags are automatically decoded when encountered. They are only
597 encoded, however, when "pack_strings" is enabled.
598
599 22098 (indirection, <http://cbor.schmorp.de/indirection>)
600 This tag is automatically generated when a reference are encountered
601 (with the exception of hash and array refernces). It is converted to
602 a reference when decoding.
603
604 55799 (self-describe CBOR, RFC 7049)
605 This value is not generated on encoding (unless explicitly requested
606 by the user), and is simply ignored when decoding.
607
608 NON-ENFORCED TAGS
609 These tags have default filters provided when decoding. Their handling
610 can be overriden by changing the %CBOR::XS::FILTER entry for the tag, or
611 by providing a custom "filter" callback when decoding.
612
613 When they result in decoding into a specific Perl class, the module
614 usually provides a corresponding "TO_CBOR" method as well.
615
616 When any of these need to load additional modules that are not part of
617 the perl core distribution (e.g. URI), it is (currently) up to the user
618 to provide these modules. The decoding usually fails with an exception
619 if the required module cannot be loaded.
620
621 2, 3 (positive/negative bignum)
622 These tags are decoded into Math::BigInt objects. The corresponding
623 "Math::BigInt::TO_CBOR" method encodes "small" bigints into normal
624 CBOR integers, and others into positive/negative CBOR bignums.
625
626 4, 5 (decimal fraction/bigfloat)
627 Both decimal fractions and bigfloats are decoded into Math::BigFloat
628 objects. The corresponding "Math::BigFloat::TO_CBOR" method *always*
629 encodes into a decimal fraction.
630
631 CBOR cannot represent bigfloats with *very* large exponents -
632 conversion of such big float objects is undefined.
633
634 Also, NaN and infinities are not encoded properly.
635
636 21, 22, 23 (expected later JSON conversion)
637 CBOR::XS is not a CBOR-to-JSON converter, and will simply ignore
638 these tags.
639
640 32 (URI)
641 These objects decode into URI objects. The corresponding
642 "URI::TO_CBOR" method again results in a CBOR URI value.
445 643
446CBOR and JSON 644CBOR and JSON
447 CBOR is supposed to implement a superset of the JSON data model, and is, 645 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 646 with some coercion, able to represent all JSON texts (something that
449 other "binary JSON" formats such as BSON generally do not support). 647 other "binary JSON" formats such as BSON generally do not support).

Diff Legend

Removed lines
+ Added lines
< Changed lines
> Changed lines