… | |
… | |
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 | |
25 | DESCRIPTION |
25 | DESCRIPTION |
26 | WARNING! This module is very new, and not very well tested (that's up to |
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27 | you to do). Furthermore, details of the implementation might change |
|
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28 | freely before version 1.0. And lastly, the object serialisation protocol |
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29 | depends on a pending IANA assignment, and until that assignment is |
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30 | official, this implementation is not interoperable with other |
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31 | implementations (even future versions of this module) until the |
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32 | assignment is done. |
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33 | |
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34 | You are still invited to try out CBOR, and this module. |
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35 | |
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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 |
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36 | compare both formats first). |
46 | |
37 | |
47 | To give you a general idea about speed, with texts in the megabyte |
38 | To give you a general idea about speed, with texts in the megabyte |
48 | range, "CBOR::XS" usually encodes roughly twice as fast as Storable or |
39 | range, "CBOR::XS" usually encodes roughly twice as fast as Storable or |
49 | JSON::XS and decodes about 15%-30% faster than those. The shorter the |
40 | JSON::XS and decodes about 15%-30% faster than those. The shorter the |
50 | data, the worse Storable performs in comparison. |
41 | data, the worse Storable performs in comparison. |
51 | |
42 | |
52 | As for compactness, "CBOR::XS" encoded data structures are usually about |
43 | Regarding compactness, "CBOR::XS"-encoded data structures are usually |
53 | 20% smaller than the same data encoded as (compact) JSON or Storable. |
44 | about 20% smaller than the same data encoded as (compact) JSON or |
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45 | Storable. |
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46 | |
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47 | In addition to the core CBOR data format, this module implements a |
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48 | number of extensions, to support cyclic and shared data structures (see |
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49 | "allow_sharing"), string deduplication (see "pack_strings") and scalar |
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50 | references (always enabled). |
54 | |
51 | |
55 | 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 |
56 | 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. |
57 | |
54 | |
58 | 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 |
… | |
… | |
80 | *disabled*. |
77 | *disabled*. |
81 | |
78 | |
82 | 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 |
83 | calls can be chained: |
80 | calls can be chained: |
84 | |
81 | |
85 | #TODO my $cbor = CBOR::XS->new->encode ({a => [1,2]}); |
82 | my $cbor = CBOR::XS->new->encode ({a => [1,2]}); |
86 | |
83 | |
87 | $cbor = $cbor->max_depth ([$maximum_nesting_depth]) |
84 | $cbor = $cbor->max_depth ([$maximum_nesting_depth]) |
88 | $max_depth = $cbor->get_max_depth |
85 | $max_depth = $cbor->get_max_depth |
89 | Sets the maximum nesting level (default 512) accepted while encoding |
86 | 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 |
87 | or decoding. If a higher nesting level is detected in CBOR data or a |
… | |
… | |
121 | as when 0 is specified). |
118 | as when 0 is specified). |
122 | |
119 | |
123 | See SECURITY CONSIDERATIONS, below, for more info on why this is |
120 | See SECURITY CONSIDERATIONS, below, for more info on why this is |
124 | useful. |
121 | useful. |
125 | |
122 | |
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123 | $cbor = $cbor->allow_unknown ([$enable]) |
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124 | $enabled = $cbor->get_allow_unknown |
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125 | If $enable is true (or missing), then "encode" will *not* throw an |
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126 | exception when it encounters values it cannot represent in CBOR (for |
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127 | example, filehandles) but instead will encode a CBOR "error" value. |
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128 | |
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129 | If $enable is false (the default), then "encode" will throw an |
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130 | exception when it encounters anything it cannot encode as CBOR. |
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131 | |
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132 | This option does not affect "decode" in any way, and it is |
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133 | recommended to leave it off unless you know your communications |
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134 | partner. |
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135 | |
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136 | $cbor = $cbor->allow_sharing ([$enable]) |
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137 | $enabled = $cbor->get_allow_sharing |
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138 | If $enable is true (or missing), then "encode" will not |
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139 | double-encode values that have been referenced before (e.g. when the |
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140 | same object, such as an array, is referenced multiple times), but |
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141 | instead will emit a reference to the earlier value. |
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142 | |
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143 | This means that such values will only be encoded once, and will not |
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144 | result in a deep cloning of the value on decode, in decoders |
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145 | supporting the value sharing extension. This also makes it possible |
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146 | to encode cyclic data structures. |
|
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147 | |
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148 | It is recommended to leave it off unless you know your communication |
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149 | partner supports the value sharing extensions to CBOR |
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150 | (<http://cbor.schmorp.de/value-sharing>), as without decoder |
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151 | support, the resulting data structure might be unusable. |
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152 | |
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153 | Detecting shared values incurs a runtime overhead when values are |
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154 | encoded that have a reference counter large than one, and might |
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155 | unnecessarily increase the encoded size, as potentially shared |
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156 | values are encode as sharable whether or not they are actually |
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157 | shared. |
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158 | |
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159 | At the moment, only targets of references can be shared (e.g. |
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160 | scalars, arrays or hashes pointed to by a reference). Weirder |
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161 | constructs, such as an array with multiple "copies" of the *same* |
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162 | string, which are hard but not impossible to create in Perl, are not |
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163 | supported (this is the same as with Storable). |
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164 | |
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165 | If $enable is false (the default), then "encode" will encode shared |
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166 | data structures repeatedly, unsharing them in the process. Cyclic |
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167 | data structures cannot be encoded in this mode. |
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168 | |
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169 | This option does not affect "decode" in any way - shared values and |
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170 | references will always be decoded properly if present. |
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171 | |
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172 | $cbor = $cbor->pack_strings ([$enable]) |
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173 | $enabled = $cbor->get_pack_strings |
|
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174 | If $enable is true (or missing), then "encode" will try not to |
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175 | encode the same string twice, but will instead encode a reference to |
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176 | the string instead. Depending on your data format, this can save a |
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177 | lot of space, but also results in a very large runtime overhead |
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178 | (expect encoding times to be 2-4 times as high as without). |
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179 | |
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180 | It is recommended to leave it off unless you know your |
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181 | communications partner supports the stringref extension to CBOR |
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182 | (<http://cbor.schmorp.de/stringref>), as without decoder support, |
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183 | the resulting data structure might not be usable. |
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184 | |
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185 | If $enable is false (the default), then "encode" will encode strings |
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186 | the standard CBOR way. |
|
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187 | |
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188 | This option does not affect "decode" in any way - string references |
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189 | will always be decoded properly if present. |
|
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190 | |
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191 | $cbor = $cbor->filter ([$cb->($tag, $value)]) |
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192 | $cb_or_undef = $cbor->get_filter |
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193 | Sets or replaces the tagged value decoding filter (when $cb is |
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194 | specified) or clears the filter (if no argument or "undef" is |
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195 | provided). |
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196 | |
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197 | The filter callback is called only during decoding, when a |
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198 | non-enforced tagged value has been decoded (see "TAG HANDLING AND |
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199 | EXTENSIONS" for a list of enforced tags). For specific tags, it's |
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200 | often better to provide a default converter using the |
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201 | %CBOR::XS::FILTER hash (see below). |
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202 | |
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203 | The first argument is the numerical tag, the second is the (decoded) |
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204 | value that has been tagged. |
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205 | |
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206 | The filter function should return either exactly one value, which |
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207 | will replace the tagged value in the decoded data structure, or no |
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208 | values, which will result in default handling, which currently means |
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209 | the decoder creates a "CBOR::XS::Tagged" object to hold the tag and |
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210 | the value. |
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211 | |
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212 | When the filter is cleared (the default state), the default filter |
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213 | function, "CBOR::XS::default_filter", is used. This function simply |
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214 | looks up the tag in the %CBOR::XS::FILTER hash. If an entry exists |
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215 | it must be a code reference that is called with tag and value, and |
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216 | is responsible for decoding the value. If no entry exists, it |
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217 | returns no values. |
|
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218 | |
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219 | Example: decode all tags not handled internally into |
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220 | "CBOR::XS::Tagged" objects, with no other special handling (useful |
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221 | when working with potentially "unsafe" CBOR data). |
|
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222 | |
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223 | CBOR::XS->new->filter (sub { })->decode ($cbor_data); |
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224 | |
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225 | Example: provide a global filter for tag 1347375694, converting the |
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226 | value into some string form. |
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227 | |
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228 | $CBOR::XS::FILTER{1347375694} = sub { |
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229 | my ($tag, $value); |
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230 | |
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231 | "tag 1347375694 value $value" |
|
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232 | }; |
|
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233 | |
126 | $cbor_data = $cbor->encode ($perl_scalar) |
234 | $cbor_data = $cbor->encode ($perl_scalar) |
127 | 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 |
128 | representation. |
236 | representation. |
129 | |
237 | |
130 | $perl_scalar = $cbor->decode ($cbor_data) |
238 | $perl_scalar = $cbor->decode ($cbor_data) |
… | |
… | |
158 | integers |
266 | integers |
159 | CBOR integers become (numeric) perl scalars. On perls without 64 bit |
267 | CBOR integers become (numeric) perl scalars. On perls without 64 bit |
160 | support, 64 bit integers will be truncated or otherwise corrupted. |
268 | support, 64 bit integers will be truncated or otherwise corrupted. |
161 | |
269 | |
162 | byte strings |
270 | byte strings |
163 | Byte strings will become octet strings in Perl (the byte values |
271 | Byte strings will become octet strings in Perl (the Byte values |
164 | 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). |
165 | |
273 | |
166 | UTF-8 strings |
274 | UTF-8 strings |
167 | 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 |
168 | decoded into proper Unicode code points. At the moment, the validity |
276 | decoded into proper Unicode code points. At the moment, the validity |
… | |
… | |
182 | "Types:Serialiser::false" and "Types::Serialiser::error", |
290 | "Types:Serialiser::false" and "Types::Serialiser::error", |
183 | respectively. They are overloaded to act almost exactly like the |
291 | 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 |
292 | 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. |
293 | access (for error). See the Types::Serialiser manpage for details. |
186 | |
294 | |
187 | CBOR tag 256 (perl object) |
295 | 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 |
296 | 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 | |
297 | |
202 | In the future, support for user-supplied conversions might get |
298 | See "TAG HANDLING AND EXTENSIONS" and the description of "->filter" |
203 | added. |
299 | for details on which tags are handled how. |
204 | |
300 | |
205 | anything else |
301 | anything else |
206 | Anything else (e.g. unsupported simple values) will raise a decoding |
302 | Anything else (e.g. unsupported simple values) will raise a decoding |
207 | error. |
303 | error. |
208 | |
304 | |
209 | PERL -> CBOR |
305 | PERL -> CBOR |
210 | 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 |
211 | 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 |
212 | by a Perl value. |
308 | is meant by a perl value. |
213 | |
309 | |
214 | hash references |
310 | hash references |
215 | Perl hash references become CBOR maps. As there is no inherent |
311 | Perl hash references become CBOR maps. As there is no inherent |
216 | 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 |
217 | in a pseudo-random order. |
313 | in a pseudo-random order. This order can be different each time a |
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314 | hahs is encoded. |
218 | |
315 | |
219 | Currently, tied hashes will use the indefinite-length format, while |
316 | Currently, tied hashes will use the indefinite-length format, while |
220 | normal hashes will use the fixed-length format. |
317 | normal hashes will use the fixed-length format. |
221 | |
318 | |
222 | array references |
319 | array references |
223 | Perl array references become fixed-length CBOR arrays. |
320 | Perl array references become fixed-length CBOR arrays. |
224 | |
321 | |
225 | other references |
322 | other references |
226 | Other unblessed references are generally not allowed and will cause |
323 | Other unblessed references will be represented using the indirection |
227 | an exception to be thrown, except for references to the integers 0 |
324 | tag extension (tag value 22098, |
228 | and 1, which get turned into false and true in CBOR. |
325 | <http://cbor.schmorp.de/indirection>). CBOR decoders are guaranteed |
|
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326 | to be able to decode these values somehow, by either "doing the |
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327 | right thing", decoding into a generic tagged object, simply ignoring |
|
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328 | the tag, or something else. |
229 | |
329 | |
230 | CBOR::XS::Tagged objects |
330 | CBOR::XS::Tagged objects |
231 | 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, |
232 | 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 |
233 | 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 |
234 | "CBOR::XS::tag" to create such objects. |
334 | "CBOR::XS::tag" to create such objects. |
235 | |
335 | |
236 | Types::Serialiser::true, Types::Serialiser::false, |
336 | Types::Serialiser::true, Types::Serialiser::false, |
237 | Types::Serialiser::error |
337 | Types::Serialiser::error |
238 | These special values become CBOR true, CBOR false and CBOR undefined |
338 | These special values become CBOR true, CBOR false and CBOR undefined |
239 | values, respectively. You can also use "\1", "\0" and "\undef" |
339 | values, respectively. You can also use "\1", "\0" and "\undef" |
240 | directly if you want. |
340 | directly if you want. |
241 | |
341 | |
242 | other blessed objects |
342 | other blessed objects |
243 | Other blessed objects are serialised via "TO_CBOR" or "FREEZE". See |
343 | Other blessed objects are serialised via "TO_CBOR" or "FREEZE". See |
244 | "OBJECT SERIALISATION", below, for details. |
344 | "TAG HANDLING AND EXTENSIONS" for specific classes handled by this |
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345 | module, and "OBJECT SERIALISATION" for generic object serialisation. |
245 | |
346 | |
246 | simple scalars |
347 | simple scalars |
247 | 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 |
248 | the most difficult objects to encode: CBOR::XS will encode undefined |
349 | most difficult objects to encode: CBOR::XS will encode undefined |
249 | 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 |
250 | string context before encoding as CBOR strings, and anything else as |
351 | string context before encoding as CBOR strings, and anything else as |
251 | number value: |
352 | number value: |
252 | |
353 | |
253 | # dump as number |
354 | # dump as number |
254 | encode_cbor [2] # yields [2] |
355 | encode_cbor [2] # yields [2] |
255 | encode_cbor [-3.0e17] # yields [-3e+17] |
356 | encode_cbor [-3.0e17] # yields [-3e+17] |
256 | my $value = 5; encode_cbor [$value] # yields [5] |
357 | my $value = 5; encode_cbor [$value] # yields [5] |
257 | |
358 | |
258 | # used as string, so dump as string |
359 | # used as string, so dump as string (either byte or text) |
259 | print $value; |
360 | print $value; |
260 | encode_cbor [$value] # yields ["5"] |
361 | encode_cbor [$value] # yields ["5"] |
261 | |
362 | |
262 | # undef becomes null |
363 | # undef becomes null |
263 | encode_cbor [undef] # yields [null] |
364 | encode_cbor [undef] # yields [null] |
… | |
… | |
266 | |
367 | |
267 | my $x = 3.1; # some variable containing a number |
368 | my $x = 3.1; # some variable containing a number |
268 | "$x"; # stringified |
369 | "$x"; # stringified |
269 | $x .= ""; # another, more awkward way to stringify |
370 | $x .= ""; # another, more awkward way to stringify |
270 | 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 |
|
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380 | the difference between byte and text is important, you should up- or |
|
|
381 | downgrade your string as late as possible before encoding. |
271 | |
382 | |
272 | 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: |
273 | |
384 | |
274 | my $x = "3"; # some variable containing a string |
385 | my $x = "3"; # some variable containing a string |
275 | $x += 0; # numify it, ensuring it will be dumped as a number |
386 | $x += 0; # numify it, ensuring it will be dumped as a number |
… | |
… | |
339 | |
450 | |
340 | sub URI::TO_CBOR { |
451 | sub URI::TO_CBOR { |
341 | my ($self) = @_; |
452 | my ($self) = @_; |
342 | my $uri = "$self"; # stringify uri |
453 | my $uri = "$self"; # stringify uri |
343 | utf8::upgrade $uri; # make sure it will be encoded as UTF-8 string |
454 | utf8::upgrade $uri; # make sure it will be encoded as UTF-8 string |
344 | CBOR::XS::tagged 32, "$_[0]" |
455 | CBOR::XS::tag 32, "$_[0]" |
345 | } |
456 | } |
346 | |
457 | |
347 | 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 |
348 | URI. |
459 | URI. |
349 | |
460 | |
… | |
… | |
384 | |
495 | |
385 | MAGIC HEADER |
496 | MAGIC HEADER |
386 | There is no way to distinguish CBOR from other formats programmatically. |
497 | There is no way to distinguish CBOR from other formats programmatically. |
387 | 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 |
388 | 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 |
389 | CBOR string without changing it's meaning. |
500 | CBOR string without changing its meaning. |
390 | |
501 | |
391 | 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 |
392 | 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 |
393 | 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 |
394 | as required. |
505 | as required. |
395 | |
506 | |
396 | THE CBOR::XS::Tagged CLASS |
507 | THE CBOR::XS::Tagged CLASS |
397 | 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 |
… | |
… | |
448 | Wrap CBOR data in CBOR: |
559 | Wrap CBOR data in CBOR: |
449 | |
560 | |
450 | my $cbor_cbor = encode_cbor |
561 | my $cbor_cbor = encode_cbor |
451 | CBOR::XS::tag 24, |
562 | CBOR::XS::tag 24, |
452 | encode_cbor [1, 2, 3]; |
563 | encode_cbor [1, 2, 3]; |
|
|
564 | |
|
|
565 | TAG 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 |
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|
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 |
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|
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. |
453 | |
643 | |
454 | CBOR and JSON |
644 | CBOR and JSON |
455 | 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, |
456 | with some coercion, able to represent all JSON texts (something that |
646 | with some coercion, able to represent all JSON texts (something that |
457 | other "binary JSON" formats such as BSON generally do not support). |
647 | other "binary JSON" formats such as BSON generally do not support). |