… | |
… | |
8 | $perl_value = decode_cbor $binary_cbor_data; |
8 | $perl_value = decode_cbor $binary_cbor_data; |
9 | |
9 | |
10 | # OO-interface |
10 | # OO-interface |
11 | |
11 | |
12 | $coder = CBOR::XS->new; |
12 | $coder = CBOR::XS->new; |
13 | #TODO |
13 | $binary_cbor_data = $coder->encode ($perl_value); |
|
|
14 | $perl_value = $coder->decode ($binary_cbor_data); |
|
|
15 | |
|
|
16 | # prefix decoding |
|
|
17 | |
|
|
18 | my $many_cbor_strings = ...; |
|
|
19 | while (length $many_cbor_strings) { |
|
|
20 | my ($data, $length) = $cbor->decode_prefix ($many_cbor_strings); |
|
|
21 | # data was decoded |
|
|
22 | substr $many_cbor_strings, 0, $length, ""; # remove decoded cbor string |
|
|
23 | } |
14 | |
24 | |
15 | DESCRIPTION |
25 | DESCRIPTION |
16 | WARNING! THIS IS A PRE-ALPHA RELEASE! IT WILL CRASH, CORRUPT YOUR DATA |
|
|
17 | AND EAT YOUR CHILDREN! (Actually, apart from being untested and a bit |
|
|
18 | feature-limited, it might already be useful). |
|
|
19 | |
|
|
20 | This module converts Perl data structures to the Concise Binary Object |
26 | This module converts Perl data structures to the Concise Binary Object |
21 | Representation (CBOR) and vice versa. CBOR is a fast binary |
27 | Representation (CBOR) and vice versa. CBOR is a fast binary |
22 | 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 |
23 | 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 |
24 | represent it in CBOR. |
30 | should be able to represent it in CBOR. |
25 | |
31 | |
26 | This makes it a faster and more compact binary alternative to JSON. |
32 | In short, CBOR is a faster and quite compact binary alternative to JSON, |
|
|
33 | with the added ability of supporting serialisation of Perl objects. |
|
|
34 | (JSON often compresses better than CBOR though, so if you plan to |
|
|
35 | compress the data later and speed is less important you might want to |
|
|
36 | compare both formats first). |
|
|
37 | |
|
|
38 | 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). |
27 | |
51 | |
28 | 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 |
29 | 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. |
30 | |
54 | |
31 | 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 |
… | |
… | |
53 | *disabled*. |
77 | *disabled*. |
54 | |
78 | |
55 | 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 |
56 | calls can be chained: |
80 | calls can be chained: |
57 | |
81 | |
58 | #TODO my $cbor = CBOR::XS->new->encode ({a => [1,2]}); |
82 | my $cbor = CBOR::XS->new->encode ({a => [1,2]}); |
59 | |
83 | |
60 | $cbor = $cbor->max_depth ([$maximum_nesting_depth]) |
84 | $cbor = $cbor->max_depth ([$maximum_nesting_depth]) |
61 | $max_depth = $cbor->get_max_depth |
85 | $max_depth = $cbor->get_max_depth |
62 | Sets the maximum nesting level (default 512) accepted while encoding |
86 | Sets the maximum nesting level (default 512) accepted while encoding |
63 | 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 |
… | |
… | |
94 | as when 0 is specified). |
118 | as when 0 is specified). |
95 | |
119 | |
96 | See SECURITY CONSIDERATIONS, below, for more info on why this is |
120 | See SECURITY CONSIDERATIONS, below, for more info on why this is |
97 | useful. |
121 | useful. |
98 | |
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 = $cbor->filter ([$cb->($tag, $value)]) |
|
|
206 | $cb_or_undef = $cbor->get_filter |
|
|
207 | Sets or replaces the tagged value decoding filter (when $cb is |
|
|
208 | specified) or clears the filter (if no argument or "undef" is |
|
|
209 | provided). |
|
|
210 | |
|
|
211 | The filter callback is called only during decoding, when a |
|
|
212 | non-enforced tagged value has been decoded (see "TAG HANDLING AND |
|
|
213 | EXTENSIONS" for a list of enforced tags). For specific tags, it's |
|
|
214 | often better to provide a default converter using the |
|
|
215 | %CBOR::XS::FILTER hash (see below). |
|
|
216 | |
|
|
217 | The first argument is the numerical tag, the second is the (decoded) |
|
|
218 | value that has been tagged. |
|
|
219 | |
|
|
220 | The filter function should return either exactly one value, which |
|
|
221 | will replace the tagged value in the decoded data structure, or no |
|
|
222 | values, which will result in default handling, which currently means |
|
|
223 | the decoder creates a "CBOR::XS::Tagged" object to hold the tag and |
|
|
224 | the value. |
|
|
225 | |
|
|
226 | When the filter is cleared (the default state), the default filter |
|
|
227 | function, "CBOR::XS::default_filter", is used. This function simply |
|
|
228 | looks up the tag in the %CBOR::XS::FILTER hash. If an entry exists |
|
|
229 | it must be a code reference that is called with tag and value, and |
|
|
230 | is responsible for decoding the value. If no entry exists, it |
|
|
231 | returns no values. |
|
|
232 | |
|
|
233 | Example: decode all tags not handled internally into |
|
|
234 | "CBOR::XS::Tagged" objects, with no other special handling (useful |
|
|
235 | when working with potentially "unsafe" CBOR data). |
|
|
236 | |
|
|
237 | CBOR::XS->new->filter (sub { })->decode ($cbor_data); |
|
|
238 | |
|
|
239 | Example: provide a global filter for tag 1347375694, converting the |
|
|
240 | value into some string form. |
|
|
241 | |
|
|
242 | $CBOR::XS::FILTER{1347375694} = sub { |
|
|
243 | my ($tag, $value); |
|
|
244 | |
|
|
245 | "tag 1347375694 value $value" |
|
|
246 | }; |
|
|
247 | |
99 | $cbor_data = $cbor->encode ($perl_scalar) |
248 | $cbor_data = $cbor->encode ($perl_scalar) |
100 | Converts the given Perl data structure (a scalar value) to its CBOR |
249 | Converts the given Perl data structure (a scalar value) to its CBOR |
101 | representation. |
250 | representation. |
102 | |
251 | |
103 | $perl_scalar = $cbor->decode ($cbor_data) |
252 | $perl_scalar = $cbor->decode ($cbor_data) |
… | |
… | |
131 | integers |
280 | integers |
132 | CBOR integers become (numeric) perl scalars. On perls without 64 bit |
281 | CBOR integers become (numeric) perl scalars. On perls without 64 bit |
133 | support, 64 bit integers will be truncated or otherwise corrupted. |
282 | support, 64 bit integers will be truncated or otherwise corrupted. |
134 | |
283 | |
135 | byte strings |
284 | byte strings |
136 | Byte strings will become octet strings in Perl (the byte values |
285 | Byte strings will become octet strings in Perl (the Byte values |
137 | 0..255 will simply become characters of the same value in Perl). |
286 | 0..255 will simply become characters of the same value in Perl). |
138 | |
287 | |
139 | UTF-8 strings |
288 | UTF-8 strings |
140 | UTF-8 strings in CBOR will be decoded, i.e. the UTF-8 octets will be |
289 | UTF-8 strings in CBOR will be decoded, i.e. the UTF-8 octets will be |
141 | decoded into proper Unicode code points. At the moment, the validity |
290 | decoded into proper Unicode code points. At the moment, the validity |
… | |
… | |
145 | arrays, maps |
294 | arrays, maps |
146 | CBOR arrays and CBOR maps will be converted into references to a |
295 | CBOR arrays and CBOR maps will be converted into references to a |
147 | Perl array or hash, respectively. The keys of the map will be |
296 | Perl array or hash, respectively. The keys of the map will be |
148 | stringified during this process. |
297 | stringified during this process. |
149 | |
298 | |
150 | true, false |
299 | null |
151 | These CBOR values become "CBOR::XS::true" and "CBOR::XS::false", |
300 | CBOR null becomes "undef" in Perl. |
|
|
301 | |
|
|
302 | true, false, undefined |
|
|
303 | These CBOR values become "Types:Serialiser::true", |
|
|
304 | "Types:Serialiser::false" and "Types::Serialiser::error", |
152 | respectively. They are overloaded to act almost exactly like the |
305 | respectively. They are overloaded to act almost exactly like the |
153 | numbers 1 and 0. You can check whether a scalar is a CBOR boolean by |
306 | numbers 1 and 0 (for true and false) or to throw an exception on |
154 | using the "CBOR::XS::is_bool" function. |
307 | access (for error). See the Types::Serialiser manpage for details. |
155 | |
308 | |
156 | null, undefined |
309 | tagged values |
157 | CBOR null and undefined values becomes "undef" in Perl (in the |
|
|
158 | future, Undefined may raise an exception or something else). |
|
|
159 | |
|
|
160 | tags |
|
|
161 | Tagged items consists of a numeric tag and another CBOR value. The |
310 | Tagged items consists of a numeric tag and another CBOR value. |
162 | tag 55799 is ignored (this tag implements the magic header). |
|
|
163 | |
311 | |
164 | All other tags are currently converted into a CBOR::XS::Tagged |
312 | See "TAG HANDLING AND EXTENSIONS" and the description of "->filter" |
165 | object, which is simply a blessed array reference consistsing of the |
313 | for details on which tags are handled how. |
166 | numeric tag value followed by the (decoded) BOR value. |
|
|
167 | |
314 | |
168 | anything else |
315 | anything else |
169 | Anything else (e.g. unsupported simple values) will raise a decoding |
316 | Anything else (e.g. unsupported simple values) will raise a decoding |
170 | error. |
317 | error. |
171 | |
318 | |
172 | PERL -> CBOR |
319 | PERL -> CBOR |
173 | The mapping from Perl to CBOR is slightly more difficult, as Perl is a |
320 | The mapping from Perl to CBOR is slightly more difficult, as Perl is a |
174 | truly typeless language, so we can only guess which CBOR type is meant |
321 | typeless language. That means this module can only guess which CBOR type |
175 | by a Perl value. |
322 | is meant by a perl value. |
176 | |
323 | |
177 | hash references |
324 | hash references |
178 | Perl hash references become CBOR maps. As there is no inherent |
325 | Perl hash references become CBOR maps. As there is no inherent |
179 | ordering in hash keys (or CBOR maps), they will usually be encoded |
326 | ordering in hash keys (or CBOR maps), they will usually be encoded |
180 | in a pseudo-random order. |
327 | in a pseudo-random order. This order can be different each time a |
|
|
328 | hahs is encoded. |
181 | |
329 | |
182 | Currently, tied hashes will use the indefinite-length format, while |
330 | Currently, tied hashes will use the indefinite-length format, while |
183 | normal hashes will use the fixed-length format. |
331 | normal hashes will use the fixed-length format. |
184 | |
332 | |
185 | array references |
333 | array references |
186 | Perl array references become fixed-length CBOR arrays. |
334 | Perl array references become fixed-length CBOR arrays. |
187 | |
335 | |
188 | other references |
336 | other references |
189 | Other unblessed references are generally not allowed and will cause |
337 | Other unblessed references will be represented using the indirection |
190 | an exception to be thrown, except for references to the integers 0 |
338 | tag extension (tag value 22098, |
191 | and 1, which get turned into false and true in CBOR. |
339 | <http://cbor.schmorp.de/indirection>). CBOR decoders are guaranteed |
|
|
340 | to be able to decode these values somehow, by either "doing the |
|
|
341 | right thing", decoding into a generic tagged object, simply ignoring |
|
|
342 | the tag, or something else. |
192 | |
343 | |
193 | CBOR::XS::Tagged objects |
344 | CBOR::XS::Tagged objects |
194 | Objects of this type must be arrays consisting of a single "[tag, |
345 | Objects of this type must be arrays consisting of a single "[tag, |
195 | value]" pair. The (numerical) tag will be encoded as a CBOR tag, the |
346 | value]" pair. The (numerical) tag will be encoded as a CBOR tag, the |
196 | value will be encoded as appropriate for the value. |
347 | value will be encoded as appropriate for the value. You must use |
|
|
348 | "CBOR::XS::tag" to create such objects. |
197 | |
349 | |
198 | CBOR::XS::true, CBOR::XS::false |
350 | Types::Serialiser::true, Types::Serialiser::false, |
|
|
351 | Types::Serialiser::error |
199 | These special values become CBOR true and CBOR false values, |
352 | These special values become CBOR true, CBOR false and CBOR undefined |
200 | respectively. You can also use "\1" and "\0" directly if you want. |
353 | values, respectively. You can also use "\1", "\0" and "\undef" |
|
|
354 | directly if you want. |
201 | |
355 | |
202 | blessed objects |
356 | other blessed objects |
203 | Other blessed objects currently need to have a "TO_CBOR" method. It |
357 | Other blessed objects are serialised via "TO_CBOR" or "FREEZE". See |
204 | will be called on every object that is being serialised, and must |
358 | "TAG HANDLING AND EXTENSIONS" for specific classes handled by this |
205 | return something that can be encoded in CBOR. |
359 | module, and "OBJECT SERIALISATION" for generic object serialisation. |
206 | |
360 | |
207 | simple scalars |
361 | simple scalars |
208 | TODO Simple Perl scalars (any scalar that is not a reference) are |
362 | Simple Perl scalars (any scalar that is not a reference) are the |
209 | the most difficult objects to encode: CBOR::XS will encode undefined |
363 | most difficult objects to encode: CBOR::XS will encode undefined |
210 | scalars as CBOR null values, scalars that have last been used in a |
364 | scalars as CBOR null values, scalars that have last been used in a |
211 | string context before encoding as CBOR strings, and anything else as |
365 | string context before encoding as CBOR strings, and anything else as |
212 | number value: |
366 | number value: |
213 | |
367 | |
214 | # dump as number |
368 | # dump as number |
215 | encode_cbor [2] # yields [2] |
369 | encode_cbor [2] # yields [2] |
216 | encode_cbor [-3.0e17] # yields [-3e+17] |
370 | encode_cbor [-3.0e17] # yields [-3e+17] |
217 | my $value = 5; encode_cbor [$value] # yields [5] |
371 | my $value = 5; encode_cbor [$value] # yields [5] |
218 | |
372 | |
219 | # used as string, so dump as string |
373 | # used as string, so dump as string (either byte or text) |
220 | print $value; |
374 | print $value; |
221 | encode_cbor [$value] # yields ["5"] |
375 | encode_cbor [$value] # yields ["5"] |
222 | |
376 | |
223 | # undef becomes null |
377 | # undef becomes null |
224 | encode_cbor [undef] # yields [null] |
378 | encode_cbor [undef] # yields [null] |
… | |
… | |
227 | |
381 | |
228 | my $x = 3.1; # some variable containing a number |
382 | my $x = 3.1; # some variable containing a number |
229 | "$x"; # stringified |
383 | "$x"; # stringified |
230 | $x .= ""; # another, more awkward way to stringify |
384 | $x .= ""; # another, more awkward way to stringify |
231 | print $x; # perl does it for you, too, quite often |
385 | print $x; # perl does it for you, too, quite often |
|
|
386 | |
|
|
387 | You can force whether a string ie encoded as byte or text string by |
|
|
388 | using "utf8::upgrade" and "utf8::downgrade"): |
|
|
389 | |
|
|
390 | utf8::upgrade $x; # encode $x as text string |
|
|
391 | utf8::downgrade $x; # encode $x as byte string |
|
|
392 | |
|
|
393 | Perl doesn't define what operations up- and downgrade strings, so if |
|
|
394 | the difference between byte and text is important, you should up- or |
|
|
395 | downgrade your string as late as possible before encoding. |
232 | |
396 | |
233 | You can force the type to be a CBOR number by numifying it: |
397 | You can force the type to be a CBOR number by numifying it: |
234 | |
398 | |
235 | my $x = "3"; # some variable containing a string |
399 | my $x = "3"; # some variable containing a string |
236 | $x += 0; # numify it, ensuring it will be dumped as a number |
400 | $x += 0; # numify it, ensuring it will be dumped as a number |
… | |
… | |
245 | IEEE single format if possible without loss of precision, otherwise |
409 | IEEE single format if possible without loss of precision, otherwise |
246 | the IEEE double format will be used. Perls that use formats other |
410 | the IEEE double format will be used. Perls that use formats other |
247 | than IEEE double to represent numerical values are supported, but |
411 | than IEEE double to represent numerical values are supported, but |
248 | might suffer loss of precision. |
412 | might suffer loss of precision. |
249 | |
413 | |
|
|
414 | OBJECT SERIALISATION |
|
|
415 | This module implements both a CBOR-specific and the generic |
|
|
416 | Types::Serialier object serialisation protocol. The following |
|
|
417 | subsections explain both methods. |
|
|
418 | |
|
|
419 | ENCODING |
|
|
420 | This module knows two way to serialise a Perl object: The CBOR-specific |
|
|
421 | way, and the generic way. |
|
|
422 | |
|
|
423 | Whenever the encoder encounters a Perl object that it cannot serialise |
|
|
424 | directly (most of them), it will first look up the "TO_CBOR" method on |
|
|
425 | it. |
|
|
426 | |
|
|
427 | If it has a "TO_CBOR" method, it will call it with the object as only |
|
|
428 | argument, and expects exactly one return value, which it will then |
|
|
429 | substitute and encode it in the place of the object. |
|
|
430 | |
|
|
431 | Otherwise, it will look up the "FREEZE" method. If it exists, it will |
|
|
432 | call it with the object as first argument, and the constant string |
|
|
433 | "CBOR" as the second argument, to distinguish it from other serialisers. |
|
|
434 | |
|
|
435 | The "FREEZE" method can return any number of values (i.e. zero or more). |
|
|
436 | These will be encoded as CBOR perl object, together with the classname. |
|
|
437 | |
|
|
438 | These methods *MUST NOT* change the data structure that is being |
|
|
439 | serialised. Failure to comply to this can result in memory corruption - |
|
|
440 | and worse. |
|
|
441 | |
|
|
442 | If an object supports neither "TO_CBOR" nor "FREEZE", encoding will fail |
|
|
443 | with an error. |
|
|
444 | |
|
|
445 | DECODING |
|
|
446 | Objects encoded via "TO_CBOR" cannot (normally) be automatically |
|
|
447 | decoded, but objects encoded via "FREEZE" can be decoded using the |
|
|
448 | following protocol: |
|
|
449 | |
|
|
450 | When an encoded CBOR perl object is encountered by the decoder, it will |
|
|
451 | look up the "THAW" method, by using the stored classname, and will fail |
|
|
452 | if the method cannot be found. |
|
|
453 | |
|
|
454 | After the lookup it will call the "THAW" method with the stored |
|
|
455 | classname as first argument, the constant string "CBOR" as second |
|
|
456 | argument, and all values returned by "FREEZE" as remaining arguments. |
|
|
457 | |
|
|
458 | EXAMPLES |
|
|
459 | Here is an example "TO_CBOR" method: |
|
|
460 | |
|
|
461 | sub My::Object::TO_CBOR { |
|
|
462 | my ($obj) = @_; |
|
|
463 | |
|
|
464 | ["this is a serialised My::Object object", $obj->{id}] |
|
|
465 | } |
|
|
466 | |
|
|
467 | When a "My::Object" is encoded to CBOR, it will instead encode a simple |
|
|
468 | array with two members: a string, and the "object id". Decoding this |
|
|
469 | CBOR string will yield a normal perl array reference in place of the |
|
|
470 | object. |
|
|
471 | |
|
|
472 | A more useful and practical example would be a serialisation method for |
|
|
473 | the URI module. CBOR has a custom tag value for URIs, namely 32: |
|
|
474 | |
|
|
475 | sub URI::TO_CBOR { |
|
|
476 | my ($self) = @_; |
|
|
477 | my $uri = "$self"; # stringify uri |
|
|
478 | utf8::upgrade $uri; # make sure it will be encoded as UTF-8 string |
|
|
479 | CBOR::XS::tag 32, "$_[0]" |
|
|
480 | } |
|
|
481 | |
|
|
482 | This will encode URIs as a UTF-8 string with tag 32, which indicates an |
|
|
483 | URI. |
|
|
484 | |
|
|
485 | Decoding such an URI will not (currently) give you an URI object, but |
|
|
486 | instead a CBOR::XS::Tagged object with tag number 32 and the string - |
|
|
487 | exactly what was returned by "TO_CBOR". |
|
|
488 | |
|
|
489 | To serialise an object so it can automatically be deserialised, you need |
|
|
490 | to use "FREEZE" and "THAW". To take the URI module as example, this |
|
|
491 | would be a possible implementation: |
|
|
492 | |
|
|
493 | sub URI::FREEZE { |
|
|
494 | my ($self, $serialiser) = @_; |
|
|
495 | "$self" # encode url string |
|
|
496 | } |
|
|
497 | |
|
|
498 | sub URI::THAW { |
|
|
499 | my ($class, $serialiser, $uri) = @_; |
|
|
500 | |
|
|
501 | $class->new ($uri) |
|
|
502 | } |
|
|
503 | |
|
|
504 | Unlike "TO_CBOR", multiple values can be returned by "FREEZE". For |
|
|
505 | example, a "FREEZE" method that returns "type", "id" and "variant" |
|
|
506 | values would cause an invocation of "THAW" with 5 arguments: |
|
|
507 | |
|
|
508 | sub My::Object::FREEZE { |
|
|
509 | my ($self, $serialiser) = @_; |
|
|
510 | |
|
|
511 | ($self->{type}, $self->{id}, $self->{variant}) |
|
|
512 | } |
|
|
513 | |
|
|
514 | sub My::Object::THAW { |
|
|
515 | my ($class, $serialiser, $type, $id, $variant) = @_; |
|
|
516 | |
|
|
517 | $class-<new (type => $type, id => $id, variant => $variant) |
|
|
518 | } |
|
|
519 | |
250 | MAGIC HEADER |
520 | MAGIC HEADER |
251 | There is no way to distinguish CBOR from other formats programmatically. |
521 | There is no way to distinguish CBOR from other formats programmatically. |
252 | To make it easier to distinguish CBOR from other formats, the CBOR |
522 | To make it easier to distinguish CBOR from other formats, the CBOR |
253 | specification has a special "magic string" that can be prepended to any |
523 | specification has a special "magic string" that can be prepended to any |
254 | CBOR string without changing it's meaning. |
524 | CBOR string without changing its meaning. |
255 | |
525 | |
256 | This string is available as $CBOR::XS::MAGIC. This module does not |
526 | This string is available as $CBOR::XS::MAGIC. This module does not |
257 | prepend this string tot he CBOR data it generates, but it will ignroe it |
527 | prepend this string to the CBOR data it generates, but it will ignore it |
258 | if present, so users can prepend this string as a "file type" indicator |
528 | if present, so users can prepend this string as a "file type" indicator |
259 | as required. |
529 | as required. |
260 | |
530 | |
|
|
531 | THE CBOR::XS::Tagged CLASS |
|
|
532 | CBOR has the concept of tagged values - any CBOR value can be tagged |
|
|
533 | with a numeric 64 bit number, which are centrally administered. |
|
|
534 | |
|
|
535 | "CBOR::XS" handles a few tags internally when en- or decoding. You can |
|
|
536 | also create tags yourself by encoding "CBOR::XS::Tagged" objects, and |
|
|
537 | the decoder will create "CBOR::XS::Tagged" objects itself when it hits |
|
|
538 | an unknown tag. |
|
|
539 | |
|
|
540 | These objects are simply blessed array references - the first member of |
|
|
541 | the array being the numerical tag, the second being the value. |
|
|
542 | |
|
|
543 | You can interact with "CBOR::XS::Tagged" objects in the following ways: |
|
|
544 | |
|
|
545 | $tagged = CBOR::XS::tag $tag, $value |
|
|
546 | This function(!) creates a new "CBOR::XS::Tagged" object using the |
|
|
547 | given $tag (0..2**64-1) to tag the given $value (which can be any |
|
|
548 | Perl value that can be encoded in CBOR, including serialisable Perl |
|
|
549 | objects and "CBOR::XS::Tagged" objects). |
|
|
550 | |
|
|
551 | $tagged->[0] |
|
|
552 | $tagged->[0] = $new_tag |
|
|
553 | $tag = $tagged->tag |
|
|
554 | $new_tag = $tagged->tag ($new_tag) |
|
|
555 | Access/mutate the tag. |
|
|
556 | |
|
|
557 | $tagged->[1] |
|
|
558 | $tagged->[1] = $new_value |
|
|
559 | $value = $tagged->value |
|
|
560 | $new_value = $tagged->value ($new_value) |
|
|
561 | Access/mutate the tagged value. |
|
|
562 | |
|
|
563 | EXAMPLES |
|
|
564 | Here are some examples of "CBOR::XS::Tagged" uses to tag objects. |
|
|
565 | |
|
|
566 | You can look up CBOR tag value and emanings in the IANA registry at |
|
|
567 | <http://www.iana.org/assignments/cbor-tags/cbor-tags.xhtml>. |
|
|
568 | |
|
|
569 | Prepend a magic header ($CBOR::XS::MAGIC): |
|
|
570 | |
|
|
571 | my $cbor = encode_cbor CBOR::XS::tag 55799, $value; |
|
|
572 | # same as: |
|
|
573 | my $cbor = $CBOR::XS::MAGIC . encode_cbor $value; |
|
|
574 | |
|
|
575 | Serialise some URIs and a regex in an array: |
|
|
576 | |
|
|
577 | my $cbor = encode_cbor [ |
|
|
578 | (CBOR::XS::tag 32, "http://www.nethype.de/"), |
|
|
579 | (CBOR::XS::tag 32, "http://software.schmorp.de/"), |
|
|
580 | (CBOR::XS::tag 35, "^[Pp][Ee][Rr][lL]\$"), |
|
|
581 | ]; |
|
|
582 | |
|
|
583 | Wrap CBOR data in CBOR: |
|
|
584 | |
|
|
585 | my $cbor_cbor = encode_cbor |
|
|
586 | CBOR::XS::tag 24, |
|
|
587 | encode_cbor [1, 2, 3]; |
|
|
588 | |
|
|
589 | TAG HANDLING AND EXTENSIONS |
|
|
590 | This section describes how this module handles specific tagged values |
|
|
591 | and extensions. If a tag is not mentioned here and no additional filters |
|
|
592 | are provided for it, then the default handling applies (creating a |
|
|
593 | CBOR::XS::Tagged object on decoding, and only encoding the tag when |
|
|
594 | explicitly requested). |
|
|
595 | |
|
|
596 | Tags not handled specifically are currently converted into a |
|
|
597 | CBOR::XS::Tagged object, which is simply a blessed array reference |
|
|
598 | consisting of the numeric tag value followed by the (decoded) CBOR |
|
|
599 | value. |
|
|
600 | |
|
|
601 | Future versions of this module reserve the right to special case |
|
|
602 | additional tags (such as base64url). |
|
|
603 | |
|
|
604 | ENFORCED TAGS |
|
|
605 | These tags are always handled when decoding, and their handling cannot |
|
|
606 | be overriden by the user. |
|
|
607 | |
|
|
608 | 26 (perl-object, <http://cbor.schmorp.de/perl-object>) |
|
|
609 | These tags are automatically created (and decoded) for serialisable |
|
|
610 | objects using the "FREEZE/THAW" methods (the Types::Serialier object |
|
|
611 | serialisation protocol). See "OBJECT SERIALISATION" for details. |
|
|
612 | |
|
|
613 | 28, 29 (shareable, sharedref, L <http://cbor.schmorp.de/value-sharing>) |
|
|
614 | These tags are automatically decoded when encountered (and they do |
|
|
615 | not result in a cyclic data structure, see "allow_cycles"), |
|
|
616 | resulting in shared values in the decoded object. They are only |
|
|
617 | encoded, however, when "allow_sharing" is enabled. |
|
|
618 | |
|
|
619 | Not all shared values can be successfully decoded: values that |
|
|
620 | reference themselves will *currently* decode as "undef" (this is not |
|
|
621 | the same as a reference pointing to itself, which will be |
|
|
622 | represented as a value that contains an indirect reference to itself |
|
|
623 | - these will be decoded properly). |
|
|
624 | |
|
|
625 | Note that considerably more shared value data structures can be |
|
|
626 | decoded than will be encoded - currently, only values pointed to by |
|
|
627 | references will be shared, others will not. While non-reference |
|
|
628 | shared values can be generated in Perl with some effort, they were |
|
|
629 | considered too unimportant to be supported in the encoder. The |
|
|
630 | decoder, however, will decode these values as shared values. |
|
|
631 | |
|
|
632 | 256, 25 (stringref-namespace, stringref, L |
|
|
633 | <http://cbor.schmorp.de/stringref>) |
|
|
634 | These tags are automatically decoded when encountered. They are only |
|
|
635 | encoded, however, when "pack_strings" is enabled. |
|
|
636 | |
|
|
637 | 22098 (indirection, <http://cbor.schmorp.de/indirection>) |
|
|
638 | This tag is automatically generated when a reference are encountered |
|
|
639 | (with the exception of hash and array refernces). It is converted to |
|
|
640 | a reference when decoding. |
|
|
641 | |
|
|
642 | 55799 (self-describe CBOR, RFC 7049) |
|
|
643 | This value is not generated on encoding (unless explicitly requested |
|
|
644 | by the user), and is simply ignored when decoding. |
|
|
645 | |
|
|
646 | NON-ENFORCED TAGS |
|
|
647 | These tags have default filters provided when decoding. Their handling |
|
|
648 | can be overriden by changing the %CBOR::XS::FILTER entry for the tag, or |
|
|
649 | by providing a custom "filter" callback when decoding. |
|
|
650 | |
|
|
651 | When they result in decoding into a specific Perl class, the module |
|
|
652 | usually provides a corresponding "TO_CBOR" method as well. |
|
|
653 | |
|
|
654 | When any of these need to load additional modules that are not part of |
|
|
655 | the perl core distribution (e.g. URI), it is (currently) up to the user |
|
|
656 | to provide these modules. The decoding usually fails with an exception |
|
|
657 | if the required module cannot be loaded. |
|
|
658 | |
|
|
659 | 2, 3 (positive/negative bignum) |
|
|
660 | These tags are decoded into Math::BigInt objects. The corresponding |
|
|
661 | "Math::BigInt::TO_CBOR" method encodes "small" bigints into normal |
|
|
662 | CBOR integers, and others into positive/negative CBOR bignums. |
|
|
663 | |
|
|
664 | 4, 5 (decimal fraction/bigfloat) |
|
|
665 | Both decimal fractions and bigfloats are decoded into Math::BigFloat |
|
|
666 | objects. The corresponding "Math::BigFloat::TO_CBOR" method *always* |
|
|
667 | encodes into a decimal fraction. |
|
|
668 | |
|
|
669 | CBOR cannot represent bigfloats with *very* large exponents - |
|
|
670 | conversion of such big float objects is undefined. |
|
|
671 | |
|
|
672 | Also, NaN and infinities are not encoded properly. |
|
|
673 | |
|
|
674 | 21, 22, 23 (expected later JSON conversion) |
|
|
675 | CBOR::XS is not a CBOR-to-JSON converter, and will simply ignore |
|
|
676 | these tags. |
|
|
677 | |
|
|
678 | 32 (URI) |
|
|
679 | These objects decode into URI objects. The corresponding |
|
|
680 | "URI::TO_CBOR" method again results in a CBOR URI value. |
|
|
681 | |
261 | CBOR and JSON |
682 | CBOR and JSON |
262 | CBOR is supposed to implement a superset of the JSON data model, and is, |
683 | CBOR is supposed to implement a superset of the JSON data model, and is, |
263 | with some coercion, able to represent all JSON texts (something that |
684 | with some coercion, able to represent all JSON texts (something that |
264 | other "binary JSON" formats such as BSON generally do not support). |
685 | other "binary JSON" formats such as BSON generally do not support). |
265 | |
686 | |
266 | CBOR implements some extra hints and support for JSON interoperability, |
687 | CBOR implements some extra hints and support for JSON interoperability, |
… | |
… | |
320 | uses long double to represent floating point values, they might not be |
741 | uses long double to represent floating point values, they might not be |
321 | encoded properly. Half precision types are accepted, but not encoded. |
742 | encoded properly. Half precision types are accepted, but not encoded. |
322 | |
743 | |
323 | Strict mode and canonical mode are not implemented. |
744 | Strict mode and canonical mode are not implemented. |
324 | |
745 | |
|
|
746 | LIMITATIONS ON PERLS WITHOUT 64-BIT INTEGER SUPPORT |
|
|
747 | On perls that were built without 64 bit integer support (these are rare |
|
|
748 | nowadays, even on 32 bit architectures), support for any kind of 64 bit |
|
|
749 | integer in CBOR is very limited - most likely, these 64 bit values will |
|
|
750 | be truncated, corrupted, or otherwise not decoded correctly. This also |
|
|
751 | includes string, array and map sizes that are stored as 64 bit integers. |
|
|
752 | |
325 | THREADS |
753 | THREADS |
326 | This module is *not* guaranteed to be thread safe and there are no plans |
754 | This module is *not* guaranteed to be thread safe and there are no plans |
327 | to change this until Perl gets thread support (as opposed to the |
755 | to change this until Perl gets thread support (as opposed to the |
328 | horribly slow so-called "threads" which are simply slow and bloated |
756 | horribly slow so-called "threads" which are simply slow and bloated |
329 | process simulations - use fork, it's *much* faster, cheaper, better). |
757 | process simulations - use fork, it's *much* faster, cheaper, better). |
… | |
… | |
340 | |
768 | |
341 | SEE ALSO |
769 | SEE ALSO |
342 | The JSON and JSON::XS modules that do similar, but human-readable, |
770 | The JSON and JSON::XS modules that do similar, but human-readable, |
343 | serialisation. |
771 | serialisation. |
344 | |
772 | |
|
|
773 | The Types::Serialiser module provides the data model for true, false and |
|
|
774 | error values. |
|
|
775 | |
345 | AUTHOR |
776 | AUTHOR |
346 | Marc Lehmann <schmorp@schmorp.de> |
777 | Marc Lehmann <schmorp@schmorp.de> |
347 | http://home.schmorp.de/ |
778 | http://home.schmorp.de/ |
348 | |
779 | |