… | |
… | |
23 | } |
23 | } |
24 | |
24 | |
25 | DESCRIPTION |
25 | DESCRIPTION |
26 | WARNING! This module is very new, and not very well tested (that's up to |
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 |
27 | you to do). Furthermore, details of the implementation might change |
28 | freely before version 1.0. And lastly, the object serialisation protocol |
28 | freely before version 1.0. And lastly, most extensions depend on an IANA |
29 | depends on a pending IANA assignment, and until that assignment is |
29 | assignment, and until that assignment is official, this implementation |
30 | official, this implementation is not interoperable with other |
30 | is not interoperable with other implementations (even future versions of |
31 | implementations (even future versions of this module) until the |
31 | this module) until the assignment is done. |
32 | assignment is done. |
|
|
33 | |
32 | |
34 | You are still invited to try out CBOR, and this module. |
33 | You are still invited to try out CBOR, and this module. |
35 | |
34 | |
36 | This module converts Perl data structures to the Concise Binary Object |
35 | This module converts Perl data structures to the Concise Binary Object |
37 | Representation (CBOR) and vice versa. CBOR is a fast binary |
36 | Representation (CBOR) and vice versa. CBOR is a fast binary |
… | |
… | |
50 | data, the worse Storable performs in comparison. |
49 | data, the worse Storable performs in comparison. |
51 | |
50 | |
52 | As for compactness, "CBOR::XS" encoded data structures are usually about |
51 | As for compactness, "CBOR::XS" encoded data structures are usually about |
53 | 20% smaller than the same data encoded as (compact) JSON or Storable. |
52 | 20% smaller than the same data encoded as (compact) JSON or Storable. |
54 | |
53 | |
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54 | In addition to the core CBOR data format, this module implements a |
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55 | number of extensions, to support cyclic and self-referencing data |
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56 | structures (see "allow_sharing"), string deduplication (see |
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57 | "allow_stringref") and scalar references (always enabled). |
|
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58 | |
55 | The primary goal of this module is to be *correct* and the secondary |
59 | The primary goal of this module is to be *correct* and the secondary |
56 | goal is to be *fast*. To reach the latter goal it was written in C. |
60 | goal is to be *fast*. To reach the latter goal it was written in C. |
57 | |
61 | |
58 | See MAPPING, below, on how CBOR::XS maps perl values to CBOR values and |
62 | See MAPPING, below, on how CBOR::XS maps perl values to CBOR values and |
59 | vice versa. |
63 | vice versa. |
… | |
… | |
80 | *disabled*. |
84 | *disabled*. |
81 | |
85 | |
82 | The mutators for flags all return the CBOR object again and thus |
86 | The mutators for flags all return the CBOR object again and thus |
83 | calls can be chained: |
87 | calls can be chained: |
84 | |
88 | |
85 | #TODO my $cbor = CBOR::XS->new->encode ({a => [1,2]}); |
89 | my $cbor = CBOR::XS->new->encode ({a => [1,2]}); |
86 | |
90 | |
87 | $cbor = $cbor->max_depth ([$maximum_nesting_depth]) |
91 | $cbor = $cbor->max_depth ([$maximum_nesting_depth]) |
88 | $max_depth = $cbor->get_max_depth |
92 | $max_depth = $cbor->get_max_depth |
89 | Sets the maximum nesting level (default 512) accepted while encoding |
93 | Sets the maximum nesting level (default 512) accepted while encoding |
90 | or decoding. If a higher nesting level is detected in CBOR data or a |
94 | or decoding. If a higher nesting level is detected in CBOR data or a |
… | |
… | |
121 | as when 0 is specified). |
125 | as when 0 is specified). |
122 | |
126 | |
123 | See SECURITY CONSIDERATIONS, below, for more info on why this is |
127 | See SECURITY CONSIDERATIONS, below, for more info on why this is |
124 | useful. |
128 | useful. |
125 | |
129 | |
|
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130 | $cbor = $cbor->allow_unknown ([$enable]) |
|
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131 | $enabled = $cbor->get_allow_unknown |
|
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132 | If $enable is true (or missing), then "encode" will *not* throw an |
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133 | exception when it encounters values it cannot represent in CBOR (for |
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134 | example, filehandles) but instead will encode a CBOR "error" value. |
|
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135 | |
|
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136 | If $enable is false (the default), then "encode" will throw an |
|
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137 | exception when it encounters anything it cannot encode as CBOR. |
|
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138 | |
|
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139 | This option does not affect "decode" in any way, and it is |
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140 | recommended to leave it off unless you know your communications |
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141 | partner. |
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142 | |
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143 | $cbor = $cbor->allow_sharing ([$enable]) |
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144 | $enabled = $cbor->get_allow_sharing |
|
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145 | If $enable is true (or missing), then "encode" will not |
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146 | double-encode values that have been referenced before (e.g. when the |
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147 | same object, such as an array, is referenced multiple times), but |
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148 | instead will emit a reference to the earlier value. |
|
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149 | |
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150 | This means that such values will only be encoded once, and will not |
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151 | result in a deep cloning of the value on decode, in decoders |
|
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152 | supporting the value sharing extension. |
|
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153 | |
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154 | It is recommended to leave it off unless you know your communication |
|
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155 | partner supports the value sharing extensions to CBOR |
|
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156 | (http://cbor.schmorp.de/value-sharing). |
|
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157 | |
|
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158 | Detecting shared values incurs a runtime overhead when values are |
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159 | encoded that have a reference counter large than one, and might |
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160 | unnecessarily increase the encoded size, as potentially shared |
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161 | values are encode as sharable whether or not they are actually |
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162 | shared. |
|
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163 | |
|
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164 | At the moment, only targets of references can be shared (e.g. |
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165 | scalars, arrays or hashes pointed to by a reference). Weirder |
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166 | constructs, such as an array with multiple "copies" of the *same* |
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167 | string, which are hard but not impossible to create in Perl, are not |
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168 | supported (this is the same as for Storable). |
|
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169 | |
|
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170 | If $enable is false (the default), then "encode" will encode |
|
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171 | exception when it encounters anything it cannot encode as CBOR. |
|
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172 | |
|
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173 | This option does not affect "decode" in any way - shared values and |
|
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174 | references will always be decoded properly if present. |
|
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175 | |
|
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176 | $cbor = $cbor->allow_stringref ([$enable]) |
|
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177 | $enabled = $cbor->get_allow_stringref |
|
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178 | If $enable is true (or missing), then "encode" will try not to |
|
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179 | encode the same string twice, but will instead encode a reference to |
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180 | the string instead. Depending on your data format. this can save a |
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181 | lot of space, but also results in a very large runtime overhead |
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182 | (expect encoding times to be 2-4 times as high as without). |
|
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183 | |
|
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184 | It is recommended to leave it off unless you know your |
|
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185 | communications partner supports the stringref extension to CBOR |
|
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186 | (http://cbor.schmorp.de/stringref). |
|
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187 | |
|
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188 | If $enable is false (the default), then "encode" will encode |
|
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189 | exception when it encounters anything it cannot encode as CBOR. |
|
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190 | |
|
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191 | This option does not affect "decode" in any way - string references |
|
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192 | will always be decoded properly if present. |
|
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193 | |
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194 | $cbor = $cbor->filter ([$cb->($tag, $value)]) |
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195 | $cb_or_undef = $cbor->get_filter |
|
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196 | Sets or replaces the tagged value decoding filter (when $cb is |
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197 | specified) or clears the filter (if no argument or "undef" is |
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198 | provided). |
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199 | |
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200 | The filter callback is called only during decoding, when a |
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201 | non-enforced tagged value has been decoded (see "TAG HANDLING AND |
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202 | EXTENSIONS" for a list of enforced tags). For specific tags, it's |
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203 | often better to provide a default converter using the |
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204 | %CBOR::XS::FILTER hash (see below). |
|
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205 | |
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206 | The first argument is the numerical tag, the second is the (decoded) |
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207 | value that has been tagged. |
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208 | |
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209 | The filter function should return either exactly one value, which |
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210 | will replace the tagged value in the decoded data structure, or no |
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211 | values, which will result in default handling, which currently means |
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212 | the decoder creates a "CBOR::XS::Tagged" object to hold the tag and |
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213 | the value. |
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214 | |
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215 | When the filter is cleared (the default state), the default filter |
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216 | function, "CBOR::XS::default_filter", is used. This function simply |
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217 | looks up the tag in the %CBOR::XS::FILTER hash. If an entry exists |
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218 | it must be a code reference that is called with tag and value, and |
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219 | is responsible for decoding the value. If no entry exists, it |
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220 | returns no values. |
|
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221 | |
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222 | Example: decode all tags not handled internally into |
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223 | CBOR::XS::Tagged objects, with no other special handling (useful |
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224 | when working with potentially "unsafe" CBOR data). |
|
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225 | |
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226 | CBOR::XS->new->filter (sub { })->decode ($cbor_data); |
|
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227 | |
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228 | Example: provide a global filter for tag 1347375694, converting the |
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229 | value into some string form. |
|
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230 | |
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231 | $CBOR::XS::FILTER{1347375694} = sub { |
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232 | my ($tag, $value); |
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233 | |
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234 | "tag 1347375694 value $value" |
|
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235 | }; |
|
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236 | |
126 | $cbor_data = $cbor->encode ($perl_scalar) |
237 | $cbor_data = $cbor->encode ($perl_scalar) |
127 | Converts the given Perl data structure (a scalar value) to its CBOR |
238 | Converts the given Perl data structure (a scalar value) to its CBOR |
128 | representation. |
239 | representation. |
129 | |
240 | |
130 | $perl_scalar = $cbor->decode ($cbor_data) |
241 | $perl_scalar = $cbor->decode ($cbor_data) |
… | |
… | |
182 | "Types:Serialiser::false" and "Types::Serialiser::error", |
293 | "Types:Serialiser::false" and "Types::Serialiser::error", |
183 | respectively. They are overloaded to act almost exactly like the |
294 | respectively. They are overloaded to act almost exactly like the |
184 | numbers 1 and 0 (for true and false) or to throw an exception on |
295 | numbers 1 and 0 (for true and false) or to throw an exception on |
185 | access (for error). See the Types::Serialiser manpage for details. |
296 | access (for error). See the Types::Serialiser manpage for details. |
186 | |
297 | |
187 | CBOR tag 256 (perl object) |
298 | tagged values |
188 | The tag value 256 (TODO: pending iana registration) will be used to |
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189 | deserialise a Perl object serialised with "FREEZE". See OBJECT |
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190 | SERIALISATION, below, for details. |
|
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191 | |
|
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192 | CBOR tag 55799 (magic header) |
|
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193 | The tag 55799 is ignored (this tag implements the magic header). |
|
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194 | |
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195 | other CBOR tags |
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196 | Tagged items consists of a numeric tag and another CBOR value. Tags |
299 | Tagged items consists of a numeric tag and another CBOR value. |
197 | not handled internally are currently converted into a |
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198 | CBOR::XS::Tagged object, which is simply a blessed array reference |
|
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199 | consisting of the numeric tag value followed by the (decoded) CBOR |
|
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200 | value. |
|
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201 | |
300 | |
202 | In the future, support for user-supplied conversions might get |
301 | See "TAG HANDLING AND EXTENSIONS" and the description of "->filter" |
203 | added. |
302 | for details. |
204 | |
303 | |
205 | anything else |
304 | anything else |
206 | Anything else (e.g. unsupported simple values) will raise a decoding |
305 | Anything else (e.g. unsupported simple values) will raise a decoding |
207 | error. |
306 | error. |
208 | |
307 | |
… | |
… | |
239 | values, respectively. You can also use "\1", "\0" and "\undef" |
338 | values, respectively. You can also use "\1", "\0" and "\undef" |
240 | directly if you want. |
339 | directly if you want. |
241 | |
340 | |
242 | other blessed objects |
341 | other blessed objects |
243 | Other blessed objects are serialised via "TO_CBOR" or "FREEZE". See |
342 | Other blessed objects are serialised via "TO_CBOR" or "FREEZE". See |
244 | "OBJECT SERIALISATION", below, for details. |
343 | "TAG HANDLING AND EXTENSIONS" for specific classes handled by this |
|
|
344 | module, and "OBJECT SERIALISATION" for generic object serialisation. |
245 | |
345 | |
246 | simple scalars |
346 | simple scalars |
247 | TODO Simple Perl scalars (any scalar that is not a reference) are |
347 | Simple Perl scalars (any scalar that is not a reference) are the |
248 | the most difficult objects to encode: CBOR::XS will encode undefined |
348 | most difficult objects to encode: CBOR::XS will encode undefined |
249 | scalars as CBOR null values, scalars that have last been used in a |
349 | scalars as CBOR null values, scalars that have last been used in a |
250 | string context before encoding as CBOR strings, and anything else as |
350 | string context before encoding as CBOR strings, and anything else as |
251 | number value: |
351 | number value: |
252 | |
352 | |
253 | # dump as number |
353 | # dump as number |
… | |
… | |
384 | |
484 | |
385 | MAGIC HEADER |
485 | MAGIC HEADER |
386 | There is no way to distinguish CBOR from other formats programmatically. |
486 | There is no way to distinguish CBOR from other formats programmatically. |
387 | To make it easier to distinguish CBOR from other formats, the CBOR |
487 | To make it easier to distinguish CBOR from other formats, the CBOR |
388 | specification has a special "magic string" that can be prepended to any |
488 | specification has a special "magic string" that can be prepended to any |
389 | CBOR string without changing it's meaning. |
489 | CBOR string without changing its meaning. |
390 | |
490 | |
391 | This string is available as $CBOR::XS::MAGIC. This module does not |
491 | This string is available as $CBOR::XS::MAGIC. This module does not |
392 | prepend this string tot he CBOR data it generates, but it will ignroe it |
492 | prepend this string to the CBOR data it generates, but it will ignore it |
393 | if present, so users can prepend this string as a "file type" indicator |
493 | if present, so users can prepend this string as a "file type" indicator |
394 | as required. |
494 | as required. |
395 | |
495 | |
396 | THE CBOR::XS::Tagged CLASS |
496 | THE CBOR::XS::Tagged CLASS |
397 | CBOR has the concept of tagged values - any CBOR value can be tagged |
497 | CBOR has the concept of tagged values - any CBOR value can be tagged |
… | |
… | |
448 | Wrap CBOR data in CBOR: |
548 | Wrap CBOR data in CBOR: |
449 | |
549 | |
450 | my $cbor_cbor = encode_cbor |
550 | my $cbor_cbor = encode_cbor |
451 | CBOR::XS::tag 24, |
551 | CBOR::XS::tag 24, |
452 | encode_cbor [1, 2, 3]; |
552 | encode_cbor [1, 2, 3]; |
|
|
553 | |
|
|
554 | TAG HANDLING AND EXTENSIONS |
|
|
555 | This section describes how this module handles specific tagged values |
|
|
556 | and extensions. If a tag is not mentioned here and no additional filters |
|
|
557 | are provided for it, then the default handling applies (creating a |
|
|
558 | CBOR::XS::Tagged object on decoding, and only encoding the tag when |
|
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559 | explicitly requested). |
|
|
560 | |
|
|
561 | Tags not handled specifically are currently converted into a |
|
|
562 | CBOR::XS::Tagged object, which is simply a blessed array reference |
|
|
563 | consisting of the numeric tag value followed by the (decoded) CBOR |
|
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564 | value. |
|
|
565 | |
|
|
566 | Future versions of this module reserve the right to special case |
|
|
567 | additional tags (such as base64url). |
|
|
568 | |
|
|
569 | ENFORCED TAGS |
|
|
570 | These tags are always handled when decoding, and their handling cannot |
|
|
571 | be overriden by the user. |
|
|
572 | |
|
|
573 | <unassigned> (perl-object, <http://cbor.schmorp.de/perl-object>) |
|
|
574 | These tags are automatically created (and decoded) for serialisable |
|
|
575 | objects using the "FREEZE/THAW" methods (the Types::Serialier object |
|
|
576 | serialisation protocol). See "OBJECT SERIALISATION" for details. |
|
|
577 | |
|
|
578 | <unassigned>, <unassigned> (sharable, sharedref, L |
|
|
579 | <http://cbor.schmorp.de/value-sharing>) |
|
|
580 | These tags are automatically decoded when encountered, resulting in |
|
|
581 | shared values in the decoded object. They are only encoded, however, |
|
|
582 | when "allow_sharable" is enabled. |
|
|
583 | |
|
|
584 | <unassigned>, <unassigned> (stringref-namespace, stringref, L |
|
|
585 | <http://cbor.schmorp.de/stringref>) |
|
|
586 | These tags are automatically decoded when encountered. They are only |
|
|
587 | encoded, however, when "allow_stringref" is enabled. |
|
|
588 | |
|
|
589 | 22098 (indirection, <http://cbor.schmorp.de/indirection>) |
|
|
590 | This tag is automatically generated when a reference are encountered |
|
|
591 | (with the exception of hash and array refernces). It is converted to |
|
|
592 | a reference when decoding. |
|
|
593 | |
|
|
594 | 55799 (self-describe CBOR, RFC 7049) |
|
|
595 | This value is not generated on encoding (unless explicitly requested |
|
|
596 | by the user), and is simply ignored when decoding. |
|
|
597 | |
|
|
598 | NON-ENFORCED TAGS |
|
|
599 | These tags have default filters provided when decoding. Their handling |
|
|
600 | can be overriden by changing the %CBOR::XS::FILTER entry for the tag, or |
|
|
601 | by providing a custom "filter" callback when decoding. |
|
|
602 | |
|
|
603 | When they result in decoding into a specific Perl class, the module |
|
|
604 | usually provides a corresponding "TO_CBOR" method as well. |
|
|
605 | |
|
|
606 | When any of these need to load additional modules that are not part of |
|
|
607 | the perl core distribution (e.g. URI), it is (currently) up to the user |
|
|
608 | to provide these modules. The decoding usually fails with an exception |
|
|
609 | if the required module cannot be loaded. |
|
|
610 | |
|
|
611 | 2, 3 (positive/negative bignum) |
|
|
612 | These tags are decoded into Math::BigInt objects. The corresponding |
|
|
613 | "Math::BigInt::TO_CBOR" method encodes "small" bigints into normal |
|
|
614 | CBOR integers, and others into positive/negative CBOR bignums. |
|
|
615 | |
|
|
616 | 4, 5 (decimal fraction/bigfloat) |
|
|
617 | Both decimal fractions and bigfloats are decoded into Math::BigFloat |
|
|
618 | objects. The corresponding "Math::BigFloat::TO_CBOR" method *always* |
|
|
619 | encodes into a decimal fraction. |
|
|
620 | |
|
|
621 | CBOR cannot represent bigfloats with *very* large exponents - |
|
|
622 | conversion of such big float objects is undefined. |
|
|
623 | |
|
|
624 | Also, NaN and infinities are not encoded properly. |
|
|
625 | |
|
|
626 | 21, 22, 23 (expected later JSON conversion) |
|
|
627 | CBOR::XS is not a CBOR-to-JSON converter, and will simply ignore |
|
|
628 | these tags. |
|
|
629 | |
|
|
630 | 32 (URI) |
|
|
631 | These objects decode into URI objects. The corresponding |
|
|
632 | "URI::TO_CBOR" method again results in a CBOR URI value. |
453 | |
633 | |
454 | CBOR and JSON |
634 | CBOR and JSON |
455 | CBOR is supposed to implement a superset of the JSON data model, and is, |
635 | CBOR is supposed to implement a superset of the JSON data model, and is, |
456 | with some coercion, able to represent all JSON texts (something that |
636 | with some coercion, able to represent all JSON texts (something that |
457 | other "binary JSON" formats such as BSON generally do not support). |
637 | other "binary JSON" formats such as BSON generally do not support). |