… | |
… | |
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); |
|
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14 | $perl_value = $coder->decode ($binary_cbor_data); |
|
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15 | |
|
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16 | # prefix decoding |
|
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17 | |
|
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18 | my $many_cbor_strings = ...; |
|
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19 | while (length $many_cbor_strings) { |
|
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20 | my ($data, $length) = $cbor->decode_prefix ($many_cbor_strings); |
|
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21 | # data was decoded |
|
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22 | substr $many_cbor_strings, 0, $length, ""; # remove decoded cbor string |
|
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23 | } |
14 | |
24 | |
15 | DESCRIPTION |
25 | DESCRIPTION |
16 | WARNING! THIS IS A PRE-ALPHA RELEASE! IT WILL CRASH, CORRUPT YOUR DATA |
26 | 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 |
27 | AND EAT YOUR CHILDREN! (Actually, apart from being untested and a bit |
18 | feature-limited, it might already be useful). |
28 | feature-limited, it might already be useful). |
… | |
… | |
21 | Representation (CBOR) and vice versa. CBOR is a fast binary |
31 | Representation (CBOR) and vice versa. CBOR is a fast binary |
22 | serialisation format that aims to use a superset of the JSON data model, |
32 | serialisation format that aims to use a superset of the JSON data model, |
23 | i.e. when you can represent something in JSON, you should be able to |
33 | i.e. when you can represent something in JSON, you should be able to |
24 | represent it in CBOR. |
34 | represent it in CBOR. |
25 | |
35 | |
26 | This makes it a faster and more compact binary alternative to JSON. |
36 | This makes it a faster and more compact binary alternative to JSON, with |
|
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37 | the added ability of supporting serialising of perl objects. |
27 | |
38 | |
28 | The primary goal of this module is to be *correct* and the secondary |
39 | 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. |
40 | goal is to be *fast*. To reach the latter goal it was written in C. |
30 | |
41 | |
31 | See MAPPING, below, on how CBOR::XS maps perl values to CBOR values and |
42 | See MAPPING, below, on how CBOR::XS maps perl values to CBOR values and |
… | |
… | |
145 | arrays, maps |
156 | arrays, maps |
146 | CBOR arrays and CBOR maps will be converted into references to a |
157 | 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 |
158 | Perl array or hash, respectively. The keys of the map will be |
148 | stringified during this process. |
159 | stringified during this process. |
149 | |
160 | |
150 | true, false |
161 | null |
151 | These CBOR values become "CBOR::XS::true" and "CBOR::XS::false", |
162 | CBOR null becomes "undef" in Perl. |
|
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163 | |
|
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164 | true, false, undefined |
|
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165 | These CBOR values become "Types:Serialiser::true", |
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166 | "Types:Serialiser::false" and "Types::Serialiser::error", |
152 | respectively. They are overloaded to act almost exactly like the |
167 | 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 |
168 | numbers 1 and 0 (for true and false) or to throw an exception on |
154 | using the "CBOR::XS::is_bool" function. |
169 | access (for error). See the Types::Serialiser manpage for details. |
155 | |
170 | |
156 | null, undefined |
171 | CBOR tag 256 (perl object) |
157 | CBOR null and undefined values becomes "undef" in Perl (in the |
172 | The tag value 256 (TODO: pending iana registration) will be used to |
158 | future, Undefined may raise an exception or something else). |
173 | deserialise a Perl object serialised with "FREEZE". See "OBJECT |
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174 | SERIALISATION", below, for details. |
159 | |
175 | |
160 | tags |
176 | CBOR tag 55799 (magic header) |
161 | Tagged items consists of a numeric tag and another CBOR value. The |
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162 | tag 55799 is ignored (this tag implements the magic header). |
177 | The tag 55799 is ignored (this tag implements the magic header). |
163 | |
178 | |
164 | All other tags are currently converted into a CBOR::XS::Tagged |
179 | other CBOR tags |
|
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180 | Tagged items consists of a numeric tag and another CBOR value. Tags |
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181 | not handled internally are currently converted into a |
165 | object, which is simply a blessed array reference consistsing of the |
182 | CBOR::XS::Tagged object, which is simply a blessed array reference |
166 | numeric tag value followed by the (decoded) BOR value. |
183 | consisting of the numeric tag value followed by the (decoded) CBOR |
|
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184 | value. |
|
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185 | |
|
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186 | In the future, support for user-supplied conversions might get |
|
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187 | added. |
167 | |
188 | |
168 | anything else |
189 | anything else |
169 | Anything else (e.g. unsupported simple values) will raise a decoding |
190 | Anything else (e.g. unsupported simple values) will raise a decoding |
170 | error. |
191 | error. |
171 | |
192 | |
… | |
… | |
193 | CBOR::XS::Tagged objects |
214 | CBOR::XS::Tagged objects |
194 | Objects of this type must be arrays consisting of a single "[tag, |
215 | 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 |
216 | value]" pair. The (numerical) tag will be encoded as a CBOR tag, the |
196 | value will be encoded as appropriate for the value. |
217 | value will be encoded as appropriate for the value. |
197 | |
218 | |
198 | CBOR::XS::true, CBOR::XS::false |
219 | Types::Serialiser::true, Types::Serialiser::false, |
|
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220 | Types::Serialiser::error |
199 | These special values become CBOR true and CBOR false values, |
221 | These special values become CBOR true, CBOR false and CBOR undefined |
200 | respectively. You can also use "\1" and "\0" directly if you want. |
222 | values, respectively. You can also use "\1", "\0" and "\undef" |
|
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223 | directly if you want. |
201 | |
224 | |
202 | blessed objects |
225 | other blessed objects |
203 | Other blessed objects currently need to have a "TO_CBOR" method. It |
226 | Other blessed objects are serialised via "TO_CBOR" or "FREEZE". See |
204 | will be called on every object that is being serialised, and must |
227 | "OBJECT SERIALISATION", below, for details. |
205 | return something that can be encoded in CBOR. |
|
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206 | |
228 | |
207 | simple scalars |
229 | simple scalars |
208 | TODO Simple Perl scalars (any scalar that is not a reference) are |
230 | TODO Simple Perl scalars (any scalar that is not a reference) are |
209 | the most difficult objects to encode: CBOR::XS will encode undefined |
231 | the most difficult objects to encode: CBOR::XS will encode undefined |
210 | scalars as CBOR null values, scalars that have last been used in a |
232 | scalars as CBOR null values, scalars that have last been used in a |
… | |
… | |
245 | IEEE single format if possible without loss of precision, otherwise |
267 | IEEE single format if possible without loss of precision, otherwise |
246 | the IEEE double format will be used. Perls that use formats other |
268 | the IEEE double format will be used. Perls that use formats other |
247 | than IEEE double to represent numerical values are supported, but |
269 | than IEEE double to represent numerical values are supported, but |
248 | might suffer loss of precision. |
270 | might suffer loss of precision. |
249 | |
271 | |
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272 | OBJECT SERIALISATION |
|
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273 | This module knows two way to serialise a Perl object: The CBOR-specific |
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274 | way, and the generic way. |
|
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275 | |
|
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276 | Whenever the encoder encounters a Perl object that it cnanot serialise |
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277 | directly (most of them), it will first look up the "TO_CBOR" method on |
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278 | it. |
|
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279 | |
|
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280 | If it has a "TO_CBOR" method, it will call it with the object as only |
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281 | argument, and expects exactly one return value, which it will then |
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282 | substitute and encode it in the place of the object. |
|
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283 | |
|
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284 | Otherwise, it will look up the "FREEZE" method. If it exists, it will |
|
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285 | call it with the object as first argument, and the constant string |
|
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286 | "CBOR" as the second argument, to distinguish it from other serialisers. |
|
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287 | |
|
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288 | The "FREEZE" method can return any number of values (i.e. zero or more). |
|
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289 | These will be encoded as CBOR perl object, together with the classname. |
|
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290 | |
|
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291 | If an object supports neither "TO_CBOR" nor "FREEZE", encoding will fail |
|
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292 | with an error. |
|
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293 | |
|
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294 | Objects encoded via "TO_CBOR" cannot be automatically decoded, but |
|
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295 | objects encoded via "FREEZE" can be decoded using the following |
|
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296 | protocol: |
|
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297 | |
|
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298 | When an encoded CBOR perl object is encountered by the decoder, it will |
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299 | look up the "THAW" method, by using the stored classname, and will fail |
|
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300 | if the method cannot be found. |
|
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301 | |
|
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302 | After the lookup it will call the "THAW" method with the stored |
|
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303 | classname as first argument, the constant string "CBOR" as second |
|
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304 | argument, and all values returned by "FREEZE" as remaining arguments. |
|
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305 | |
|
|
306 | EXAMPLES |
|
|
307 | Here is an example "TO_CBOR" method: |
|
|
308 | |
|
|
309 | sub My::Object::TO_CBOR { |
|
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310 | my ($obj) = @_; |
|
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311 | |
|
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312 | ["this is a serialised My::Object object", $obj->{id}] |
|
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313 | } |
|
|
314 | |
|
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315 | When a "My::Object" is encoded to CBOR, it will instead encode a simple |
|
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316 | array with two members: a string, and the "object id". Decoding this |
|
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317 | CBOR string will yield a normal perl array reference in place of the |
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318 | object. |
|
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319 | |
|
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320 | A more useful and practical example would be a serialisation method for |
|
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321 | the URI module. CBOR has a custom tag value for URIs, namely 32: |
|
|
322 | |
|
|
323 | sub URI::TO_CBOR { |
|
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324 | my ($self) = @_; |
|
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325 | my $uri = "$self"; # stringify uri |
|
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326 | utf8::upgrade $uri; # make sure it will be encoded as UTF-8 string |
|
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327 | CBOR::XS::tagged 32, "$_[0]" |
|
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328 | } |
|
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329 | |
|
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330 | This will encode URIs as a UTF-8 string with tag 32, which indicates an |
|
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331 | URI. |
|
|
332 | |
|
|
333 | Decoding such an URI will not (currently) give you an URI object, but |
|
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334 | instead a CBOR::XS::Tagged object with tag number 32 and the string - |
|
|
335 | exactly what was returned by "TO_CBOR". |
|
|
336 | |
|
|
337 | To serialise an object so it can automatically be deserialised, you need |
|
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338 | to use "FREEZE" and "THAW". To take the URI module as example, this |
|
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339 | would be a possible implementation: |
|
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340 | |
|
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341 | sub URI::FREEZE { |
|
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342 | my ($self, $serialiser) = @_; |
|
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343 | "$self" # encode url string |
|
|
344 | } |
|
|
345 | |
|
|
346 | sub URI::THAW { |
|
|
347 | my ($class, $serialiser, $uri) = @_; |
|
|
348 | |
|
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349 | $class->new ($uri) |
|
|
350 | } |
|
|
351 | |
|
|
352 | Unlike "TO_CBOR", multiple values can be returned by "FREEZE". For |
|
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353 | example, a "FREEZE" method that returns "type", "id" and "variant" |
|
|
354 | values would cause an invocation of "THAW" with 5 arguments: |
|
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355 | |
|
|
356 | sub My::Object::FREEZE { |
|
|
357 | my ($self, $serialiser) = @_; |
|
|
358 | |
|
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359 | ($self->{type}, $self->{id}, $self->{variant}) |
|
|
360 | } |
|
|
361 | |
|
|
362 | sub My::Object::THAW { |
|
|
363 | my ($class, $serialiser, $type, $id, $variant) = @_; |
|
|
364 | |
|
|
365 | $class-<new (type => $type, id => $id, variant => $variant) |
|
|
366 | } |
|
|
367 | |
250 | MAGIC HEADER |
368 | MAGIC HEADER |
251 | There is no way to distinguish CBOR from other formats programmatically. |
369 | There is no way to distinguish CBOR from other formats programmatically. |
252 | To make it easier to distinguish CBOR from other formats, the CBOR |
370 | 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 |
371 | specification has a special "magic string" that can be prepended to any |
254 | CBOR string without changing it's meaning. |
372 | CBOR string without changing it's meaning. |
255 | |
373 | |
256 | This string is available as $CBOR::XS::MAGIC. This module does not |
374 | 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 |
375 | prepend this string tot he CBOR data it generates, but it will ignroe it |
258 | if present, so users can prepend this string as a "file type" indicator |
376 | if present, so users can prepend this string as a "file type" indicator |
259 | as required. |
377 | as required. |
260 | |
378 | |
261 | CBOR and JSON |
379 | CBOR and JSON |
262 | CBOR is supposed to implement a superset of the JSON data model, and is, |
380 | 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 |
381 | with some coercion, able to represent all JSON texts (something that |
264 | other "binary JSON" formats such as BSON generally do not support). |
382 | other "binary JSON" formats such as BSON generally do not support). |
265 | |
383 | |
266 | CBOR implements some extra hints and support for JSON interoperability, |
384 | CBOR implements some extra hints and support for JSON interoperability, |
… | |
… | |
340 | |
458 | |
341 | SEE ALSO |
459 | SEE ALSO |
342 | The JSON and JSON::XS modules that do similar, but human-readable, |
460 | The JSON and JSON::XS modules that do similar, but human-readable, |
343 | serialisation. |
461 | serialisation. |
344 | |
462 | |
|
|
463 | The Types::Serialiser module provides the data model for true, false and |
|
|
464 | error values. |
|
|
465 | |
345 | AUTHOR |
466 | AUTHOR |
346 | Marc Lehmann <schmorp@schmorp.de> |
467 | Marc Lehmann <schmorp@schmorp.de> |
347 | http://home.schmorp.de/ |
468 | http://home.schmorp.de/ |
348 | |
469 | |