… | |
… | |
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" and "allow_cycles"), string deduplication (see |
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50 | "pack_strings") and scalar 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 (which need "allow_cycles" to ne |
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147 | enabled to be decoded by this module). |
|
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148 | |
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149 | It is recommended to leave it off unless you know your communication |
|
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150 | partner supports the value sharing extensions to CBOR |
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151 | (<http://cbor.schmorp.de/value-sharing>), as without decoder |
|
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152 | support, the resulting data structure might be unusable. |
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153 | |
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154 | Detecting shared values incurs a runtime overhead when values are |
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155 | encoded that have a reference counter large than one, and might |
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156 | unnecessarily increase the encoded size, as potentially shared |
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157 | values are encode as shareable whether or not they are actually |
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158 | shared. |
|
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159 | |
|
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160 | At the moment, only targets of references can be shared (e.g. |
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161 | scalars, arrays or hashes pointed to by a reference). Weirder |
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162 | constructs, such as an array with multiple "copies" of the *same* |
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163 | string, which are hard but not impossible to create in Perl, are not |
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164 | supported (this is the same as with Storable). |
|
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165 | |
|
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166 | If $enable is false (the default), then "encode" will encode shared |
|
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167 | data structures repeatedly, unsharing them in the process. Cyclic |
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168 | data structures cannot be encoded in this mode. |
|
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169 | |
|
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170 | This option does not affect "decode" in any way - shared values and |
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171 | references will always be decoded properly if present. |
|
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172 | |
|
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173 | $cbor = $cbor->allow_cycles ([$enable]) |
|
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174 | $enabled = $cbor->get_allow_cycles |
|
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175 | If $enable is true (or missing), then "decode" will happily decode |
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176 | self-referential (cyclic) data structures. By default these will not |
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177 | be decoded, as they need manual cleanup to avoid memory leaks, so |
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178 | code that isn't prepared for this will not leak memory. |
|
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179 | |
|
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180 | If $enable is false (the default), then "decode" will throw an error |
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181 | when it encounters a self-referential/cyclic data structure. |
|
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182 | |
|
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183 | FUTURE DIRECTION: the motivation behind this option is to avoid |
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184 | *real* cycles - future versions of this module might chose to decode |
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185 | cyclic data structures using weak references when this option is |
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186 | off, instead of throwing an error. |
|
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187 | |
|
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188 | This option does not affect "encode" in any way - shared values and |
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189 | references will always be encoded properly if present. |
|
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190 | |
|
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191 | $cbor = $cbor->pack_strings ([$enable]) |
|
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192 | $enabled = $cbor->get_pack_strings |
|
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193 | If $enable is true (or missing), then "encode" will try not to |
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194 | encode the same string twice, but will instead encode a reference to |
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195 | the string instead. Depending on your data format, this can save a |
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196 | lot of space, but also results in a very large runtime overhead |
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197 | (expect encoding times to be 2-4 times as high as without). |
|
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198 | |
|
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199 | It is recommended to leave it off unless you know your |
|
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200 | communications partner supports the stringref extension to CBOR |
|
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201 | (<http://cbor.schmorp.de/stringref>), as without decoder support, |
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202 | the resulting data structure might not be usable. |
|
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203 | |
|
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204 | If $enable is false (the default), then "encode" will encode strings |
|
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205 | the standard CBOR way. |
|
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206 | |
|
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207 | This option does not affect "decode" in any way - string references |
|
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208 | will always be decoded properly if present. |
|
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209 | |
|
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210 | $cbor = $cbor->validate_utf8 ([$enable]) |
|
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211 | $enabled = $cbor->get_validate_utf8 |
|
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212 | If $enable is true (or missing), then "decode" will validate that |
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213 | elements (text strings) containing UTF-8 data in fact contain valid |
|
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214 | UTF-8 data (instead of blindly accepting it). This validation |
|
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215 | obviously takes extra time during decoding. |
|
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216 | |
|
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217 | The concept of "valid UTF-8" used is perl's concept, which is a |
|
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218 | superset of the official UTF-8. |
|
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219 | |
|
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220 | If $enable is false (the default), then "decode" will blindly accept |
|
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221 | UTF-8 data, marking them as valid UTF-8 in the resulting data |
|
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222 | structure regardless of whether thats true or not. |
|
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223 | |
|
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224 | Perl isn't too happy about corrupted UTF-8 in strings, but should |
|
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225 | generally not crash or do similarly evil things. Extensions might be |
|
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226 | not so forgiving, so it's recommended to turn on this setting if you |
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227 | receive untrusted CBOR. |
|
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228 | |
|
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229 | This option does not affect "encode" in any way - strings that are |
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230 | supposedly valid UTF-8 will simply be dumped into the resulting CBOR |
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231 | string without checking whether that is, in fact, true or not. |
|
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232 | |
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233 | $cbor = $cbor->filter ([$cb->($tag, $value)]) |
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234 | $cb_or_undef = $cbor->get_filter |
|
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235 | Sets or replaces the tagged value decoding filter (when $cb is |
|
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236 | specified) or clears the filter (if no argument or "undef" is |
|
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237 | provided). |
|
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238 | |
|
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239 | The filter callback is called only during decoding, when a |
|
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240 | non-enforced tagged value has been decoded (see "TAG HANDLING AND |
|
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241 | EXTENSIONS" for a list of enforced tags). For specific tags, it's |
|
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242 | often better to provide a default converter using the |
|
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243 | %CBOR::XS::FILTER hash (see below). |
|
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244 | |
|
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245 | The first argument is the numerical tag, the second is the (decoded) |
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246 | value that has been tagged. |
|
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247 | |
|
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248 | The filter function should return either exactly one value, which |
|
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249 | will replace the tagged value in the decoded data structure, or no |
|
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250 | values, which will result in default handling, which currently means |
|
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251 | the decoder creates a "CBOR::XS::Tagged" object to hold the tag and |
|
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252 | the value. |
|
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253 | |
|
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254 | When the filter is cleared (the default state), the default filter |
|
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255 | function, "CBOR::XS::default_filter", is used. This function simply |
|
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256 | looks up the tag in the %CBOR::XS::FILTER hash. If an entry exists |
|
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257 | it must be a code reference that is called with tag and value, and |
|
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258 | is responsible for decoding the value. If no entry exists, it |
|
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259 | returns no values. |
|
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260 | |
|
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261 | Example: decode all tags not handled internally into |
|
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262 | "CBOR::XS::Tagged" objects, with no other special handling (useful |
|
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263 | when working with potentially "unsafe" CBOR data). |
|
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264 | |
|
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265 | CBOR::XS->new->filter (sub { })->decode ($cbor_data); |
|
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266 | |
|
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267 | Example: provide a global filter for tag 1347375694, converting the |
|
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268 | value into some string form. |
|
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269 | |
|
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270 | $CBOR::XS::FILTER{1347375694} = sub { |
|
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271 | my ($tag, $value); |
|
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272 | |
|
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273 | "tag 1347375694 value $value" |
|
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274 | }; |
|
|
275 | |
126 | $cbor_data = $cbor->encode ($perl_scalar) |
276 | $cbor_data = $cbor->encode ($perl_scalar) |
127 | Converts the given Perl data structure (a scalar value) to its CBOR |
277 | Converts the given Perl data structure (a scalar value) to its CBOR |
128 | representation. |
278 | representation. |
129 | |
279 | |
130 | $perl_scalar = $cbor->decode ($cbor_data) |
280 | $perl_scalar = $cbor->decode ($cbor_data) |
… | |
… | |
142 | the next one starts. |
292 | the next one starts. |
143 | |
293 | |
144 | CBOR::XS->new->decode_prefix ("......") |
294 | CBOR::XS->new->decode_prefix ("......") |
145 | => ("...", 3) |
295 | => ("...", 3) |
146 | |
296 | |
|
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297 | INCREMENTAL PARSING |
|
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298 | In some cases, there is the need for incremental parsing of JSON texts. |
|
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299 | While this module always has to keep both CBOR text and resulting Perl |
|
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300 | data structure in memory at one time, it does allow you to parse a CBOR |
|
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301 | stream incrementally, using a similar to using "decode_prefix" to see if |
|
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302 | a full CBOR object is available, but is much more efficient. |
|
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303 | |
|
|
304 | It basically works by parsing as much of a CBOR string as possible - if |
|
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305 | the CBOR data is not complete yet, the pasrer will remember where it |
|
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306 | was, to be able to restart when more data has been accumulated. Once |
|
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307 | enough data is available to either decode a complete CBOR value or raise |
|
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308 | an error, a real decode will be attempted. |
|
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309 | |
|
|
310 | A typical use case would be a network protocol that consists of sending |
|
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311 | and receiving CBOR-encoded messages. The solution that works with CBOR |
|
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312 | and about anything else is by prepending a length to every CBOR value, |
|
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313 | so the receiver knows how many octets to read. More compact (and |
|
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314 | slightly slower) would be to just send CBOR values back-to-back, as |
|
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315 | "CBOR::XS" knows where a CBOR value ends, and doesn't need an explicit |
|
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316 | length. |
|
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317 | |
|
|
318 | The following methods help with this: |
|
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319 | |
|
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320 | @decoded = $cbor->incr_parse ($buffer) |
|
|
321 | This method attempts to decode exactly one CBOR value from the |
|
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322 | beginning of the given $buffer. The value is removed from the |
|
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323 | $buffer on success. When $buffer doesn't contain a complete value |
|
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324 | yet, it returns nothing. Finally, when the $buffer doesn't start |
|
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325 | with something that could ever be a valid CBOR value, it raises an |
|
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326 | exception, just as "decode" would. In the latter case the decoder |
|
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327 | state is undefined and must be reset before being able to parse |
|
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328 | further. |
|
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329 | |
|
|
330 | This method modifies the $buffer in place. When no CBOR value can be |
|
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331 | decoded, the decoder stores the current string offset. On the next |
|
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332 | call, continues decoding at the place where it stopped before. For |
|
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333 | this to make sense, the $buffer must begin with the same octets as |
|
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334 | on previous unsuccessful calls. |
|
|
335 | |
|
|
336 | You can call this method in scalar context, in which case it either |
|
|
337 | returns a decoded value or "undef". This makes it impossible to |
|
|
338 | distinguish between CBOR null values (which decode to "undef") and |
|
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339 | an unsuccessful decode, which is often acceptable. |
|
|
340 | |
|
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341 | @decoded = $cbor->incr_parse_multiple ($buffer) |
|
|
342 | Same as "incr_parse", but attempts to decode as many CBOR values as |
|
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343 | possible in one go, instead of at most one. Calls to "incr_parse" |
|
|
344 | and "incr_parse_multiple" can be interleaved. |
|
|
345 | |
|
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346 | $cbor->incr_reset |
|
|
347 | Resets the incremental decoder. This throws away any saved state, so |
|
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348 | that subsequent calls to "incr_parse" or "incr_parse_multiple" start |
|
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349 | to parse a new CBOR value from the beginning of the $buffer again. |
|
|
350 | |
|
|
351 | This method can be caled at any time, but it *must* be called if you |
|
|
352 | want to change your $buffer or there was a decoding error and you |
|
|
353 | want to reuse the $cbor object for future incremental parsings. |
|
|
354 | |
147 | MAPPING |
355 | MAPPING |
148 | This section describes how CBOR::XS maps Perl values to CBOR values and |
356 | This section describes how CBOR::XS maps Perl values to CBOR values and |
149 | vice versa. These mappings are designed to "do the right thing" in most |
357 | vice versa. These mappings are designed to "do the right thing" in most |
150 | circumstances automatically, preserving round-tripping characteristics |
358 | circumstances automatically, preserving round-tripping characteristics |
151 | (what you put in comes out as something equivalent). |
359 | (what you put in comes out as something equivalent). |
… | |
… | |
158 | integers |
366 | integers |
159 | CBOR integers become (numeric) perl scalars. On perls without 64 bit |
367 | CBOR integers become (numeric) perl scalars. On perls without 64 bit |
160 | support, 64 bit integers will be truncated or otherwise corrupted. |
368 | support, 64 bit integers will be truncated or otherwise corrupted. |
161 | |
369 | |
162 | byte strings |
370 | byte strings |
163 | Byte strings will become octet strings in Perl (the byte values |
371 | Byte strings will become octet strings in Perl (the Byte values |
164 | 0..255 will simply become characters of the same value in Perl). |
372 | 0..255 will simply become characters of the same value in Perl). |
165 | |
373 | |
166 | UTF-8 strings |
374 | UTF-8 strings |
167 | UTF-8 strings in CBOR will be decoded, i.e. the UTF-8 octets will be |
375 | 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 |
376 | decoded into proper Unicode code points. At the moment, the validity |
… | |
… | |
182 | "Types:Serialiser::false" and "Types::Serialiser::error", |
390 | "Types:Serialiser::false" and "Types::Serialiser::error", |
183 | respectively. They are overloaded to act almost exactly like the |
391 | 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 |
392 | 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. |
393 | access (for error). See the Types::Serialiser manpage for details. |
186 | |
394 | |
187 | CBOR tag 256 (perl object) |
395 | tagged values |
188 | The tag value 256 (TODO: pending iana registration) will be used to |
|
|
189 | deserialise a Perl object serialised with "FREEZE". See OBJECT |
|
|
190 | SERIALISATION, below, for details. |
|
|
191 | |
|
|
192 | CBOR tag 55799 (magic header) |
|
|
193 | The tag 55799 is ignored (this tag implements the magic header). |
|
|
194 | |
|
|
195 | other CBOR tags |
|
|
196 | Tagged items consists of a numeric tag and another CBOR value. Tags |
396 | Tagged items consists of a numeric tag and another CBOR value. |
197 | not handled internally are currently converted into a |
|
|
198 | CBOR::XS::Tagged object, which is simply a blessed array reference |
|
|
199 | consisting of the numeric tag value followed by the (decoded) CBOR |
|
|
200 | value. |
|
|
201 | |
397 | |
202 | In the future, support for user-supplied conversions might get |
398 | See "TAG HANDLING AND EXTENSIONS" and the description of "->filter" |
203 | added. |
399 | for details on which tags are handled how. |
204 | |
400 | |
205 | anything else |
401 | anything else |
206 | Anything else (e.g. unsupported simple values) will raise a decoding |
402 | Anything else (e.g. unsupported simple values) will raise a decoding |
207 | error. |
403 | error. |
208 | |
404 | |
209 | PERL -> CBOR |
405 | PERL -> CBOR |
210 | The mapping from Perl to CBOR is slightly more difficult, as Perl is a |
406 | 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 |
407 | typeless language. That means this module can only guess which CBOR type |
212 | by a Perl value. |
408 | is meant by a perl value. |
213 | |
409 | |
214 | hash references |
410 | hash references |
215 | Perl hash references become CBOR maps. As there is no inherent |
411 | Perl hash references become CBOR maps. As there is no inherent |
216 | ordering in hash keys (or CBOR maps), they will usually be encoded |
412 | ordering in hash keys (or CBOR maps), they will usually be encoded |
217 | in a pseudo-random order. |
413 | in a pseudo-random order. This order can be different each time a |
|
|
414 | hahs is encoded. |
218 | |
415 | |
219 | Currently, tied hashes will use the indefinite-length format, while |
416 | Currently, tied hashes will use the indefinite-length format, while |
220 | normal hashes will use the fixed-length format. |
417 | normal hashes will use the fixed-length format. |
221 | |
418 | |
222 | array references |
419 | array references |
223 | Perl array references become fixed-length CBOR arrays. |
420 | Perl array references become fixed-length CBOR arrays. |
224 | |
421 | |
225 | other references |
422 | other references |
226 | Other unblessed references are generally not allowed and will cause |
423 | Other unblessed references will be represented using the indirection |
227 | an exception to be thrown, except for references to the integers 0 |
424 | tag extension (tag value 22098, |
228 | and 1, which get turned into false and true in CBOR. |
425 | <http://cbor.schmorp.de/indirection>). CBOR decoders are guaranteed |
|
|
426 | to be able to decode these values somehow, by either "doing the |
|
|
427 | right thing", decoding into a generic tagged object, simply ignoring |
|
|
428 | the tag, or something else. |
229 | |
429 | |
230 | CBOR::XS::Tagged objects |
430 | CBOR::XS::Tagged objects |
231 | Objects of this type must be arrays consisting of a single "[tag, |
431 | 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 |
432 | 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 |
433 | value will be encoded as appropriate for the value. You must use |
234 | "CBOR::XS::tag" to create such objects. |
434 | "CBOR::XS::tag" to create such objects. |
235 | |
435 | |
236 | Types::Serialiser::true, Types::Serialiser::false, |
436 | Types::Serialiser::true, Types::Serialiser::false, |
237 | Types::Serialiser::error |
437 | Types::Serialiser::error |
238 | These special values become CBOR true, CBOR false and CBOR undefined |
438 | These special values become CBOR true, CBOR false and CBOR undefined |
239 | values, respectively. You can also use "\1", "\0" and "\undef" |
439 | values, respectively. You can also use "\1", "\0" and "\undef" |
240 | directly if you want. |
440 | directly if you want. |
241 | |
441 | |
242 | other blessed objects |
442 | other blessed objects |
243 | Other blessed objects are serialised via "TO_CBOR" or "FREEZE". See |
443 | Other blessed objects are serialised via "TO_CBOR" or "FREEZE". See |
244 | "OBJECT SERIALISATION", below, for details. |
444 | "TAG HANDLING AND EXTENSIONS" for specific classes handled by this |
|
|
445 | module, and "OBJECT SERIALISATION" for generic object serialisation. |
245 | |
446 | |
246 | simple scalars |
447 | simple scalars |
247 | TODO Simple Perl scalars (any scalar that is not a reference) are |
448 | Simple Perl scalars (any scalar that is not a reference) are the |
248 | the most difficult objects to encode: CBOR::XS will encode undefined |
449 | most difficult objects to encode: CBOR::XS will encode undefined |
249 | scalars as CBOR null values, scalars that have last been used in a |
450 | 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 |
451 | string context before encoding as CBOR strings, and anything else as |
251 | number value: |
452 | number value: |
252 | |
453 | |
253 | # dump as number |
454 | # dump as number |
254 | encode_cbor [2] # yields [2] |
455 | encode_cbor [2] # yields [2] |
255 | encode_cbor [-3.0e17] # yields [-3e+17] |
456 | encode_cbor [-3.0e17] # yields [-3e+17] |
256 | my $value = 5; encode_cbor [$value] # yields [5] |
457 | my $value = 5; encode_cbor [$value] # yields [5] |
257 | |
458 | |
258 | # used as string, so dump as string |
459 | # used as string, so dump as string (either byte or text) |
259 | print $value; |
460 | print $value; |
260 | encode_cbor [$value] # yields ["5"] |
461 | encode_cbor [$value] # yields ["5"] |
261 | |
462 | |
262 | # undef becomes null |
463 | # undef becomes null |
263 | encode_cbor [undef] # yields [null] |
464 | encode_cbor [undef] # yields [null] |
… | |
… | |
266 | |
467 | |
267 | my $x = 3.1; # some variable containing a number |
468 | my $x = 3.1; # some variable containing a number |
268 | "$x"; # stringified |
469 | "$x"; # stringified |
269 | $x .= ""; # another, more awkward way to stringify |
470 | $x .= ""; # another, more awkward way to stringify |
270 | print $x; # perl does it for you, too, quite often |
471 | print $x; # perl does it for you, too, quite often |
|
|
472 | |
|
|
473 | You can force whether a string ie encoded as byte or text string by |
|
|
474 | using "utf8::upgrade" and "utf8::downgrade"): |
|
|
475 | |
|
|
476 | utf8::upgrade $x; # encode $x as text string |
|
|
477 | utf8::downgrade $x; # encode $x as byte string |
|
|
478 | |
|
|
479 | Perl doesn't define what operations up- and downgrade strings, so if |
|
|
480 | the difference between byte and text is important, you should up- or |
|
|
481 | downgrade your string as late as possible before encoding. |
271 | |
482 | |
272 | You can force the type to be a CBOR number by numifying it: |
483 | You can force the type to be a CBOR number by numifying it: |
273 | |
484 | |
274 | my $x = "3"; # some variable containing a string |
485 | my $x = "3"; # some variable containing a string |
275 | $x += 0; # numify it, ensuring it will be dumped as a number |
486 | $x += 0; # numify it, ensuring it will be dumped as a number |
… | |
… | |
285 | the IEEE double format will be used. Perls that use formats other |
496 | the IEEE double format will be used. Perls that use formats other |
286 | than IEEE double to represent numerical values are supported, but |
497 | than IEEE double to represent numerical values are supported, but |
287 | might suffer loss of precision. |
498 | might suffer loss of precision. |
288 | |
499 | |
289 | OBJECT SERIALISATION |
500 | OBJECT SERIALISATION |
|
|
501 | This module implements both a CBOR-specific and the generic |
|
|
502 | Types::Serialier object serialisation protocol. The following |
|
|
503 | subsections explain both methods. |
|
|
504 | |
|
|
505 | ENCODING |
290 | This module knows two way to serialise a Perl object: The CBOR-specific |
506 | This module knows two way to serialise a Perl object: The CBOR-specific |
291 | way, and the generic way. |
507 | way, and the generic way. |
292 | |
508 | |
293 | Whenever the encoder encounters a Perl object that it cnanot serialise |
509 | Whenever the encoder encounters a Perl object that it cannot serialise |
294 | directly (most of them), it will first look up the "TO_CBOR" method on |
510 | directly (most of them), it will first look up the "TO_CBOR" method on |
295 | it. |
511 | it. |
296 | |
512 | |
297 | If it has a "TO_CBOR" method, it will call it with the object as only |
513 | If it has a "TO_CBOR" method, it will call it with the object as only |
298 | argument, and expects exactly one return value, which it will then |
514 | argument, and expects exactly one return value, which it will then |
… | |
… | |
303 | "CBOR" as the second argument, to distinguish it from other serialisers. |
519 | "CBOR" as the second argument, to distinguish it from other serialisers. |
304 | |
520 | |
305 | The "FREEZE" method can return any number of values (i.e. zero or more). |
521 | The "FREEZE" method can return any number of values (i.e. zero or more). |
306 | These will be encoded as CBOR perl object, together with the classname. |
522 | These will be encoded as CBOR perl object, together with the classname. |
307 | |
523 | |
|
|
524 | These methods *MUST NOT* change the data structure that is being |
|
|
525 | serialised. Failure to comply to this can result in memory corruption - |
|
|
526 | and worse. |
|
|
527 | |
308 | If an object supports neither "TO_CBOR" nor "FREEZE", encoding will fail |
528 | If an object supports neither "TO_CBOR" nor "FREEZE", encoding will fail |
309 | with an error. |
529 | with an error. |
310 | |
530 | |
|
|
531 | DECODING |
311 | Objects encoded via "TO_CBOR" cannot be automatically decoded, but |
532 | Objects encoded via "TO_CBOR" cannot (normally) be automatically |
312 | objects encoded via "FREEZE" can be decoded using the following |
533 | decoded, but objects encoded via "FREEZE" can be decoded using the |
313 | protocol: |
534 | following protocol: |
314 | |
535 | |
315 | When an encoded CBOR perl object is encountered by the decoder, it will |
536 | When an encoded CBOR perl object is encountered by the decoder, it will |
316 | look up the "THAW" method, by using the stored classname, and will fail |
537 | look up the "THAW" method, by using the stored classname, and will fail |
317 | if the method cannot be found. |
538 | if the method cannot be found. |
318 | |
539 | |
… | |
… | |
339 | |
560 | |
340 | sub URI::TO_CBOR { |
561 | sub URI::TO_CBOR { |
341 | my ($self) = @_; |
562 | my ($self) = @_; |
342 | my $uri = "$self"; # stringify uri |
563 | my $uri = "$self"; # stringify uri |
343 | utf8::upgrade $uri; # make sure it will be encoded as UTF-8 string |
564 | utf8::upgrade $uri; # make sure it will be encoded as UTF-8 string |
344 | CBOR::XS::tagged 32, "$_[0]" |
565 | CBOR::XS::tag 32, "$_[0]" |
345 | } |
566 | } |
346 | |
567 | |
347 | This will encode URIs as a UTF-8 string with tag 32, which indicates an |
568 | This will encode URIs as a UTF-8 string with tag 32, which indicates an |
348 | URI. |
569 | URI. |
349 | |
570 | |
… | |
… | |
384 | |
605 | |
385 | MAGIC HEADER |
606 | MAGIC HEADER |
386 | There is no way to distinguish CBOR from other formats programmatically. |
607 | There is no way to distinguish CBOR from other formats programmatically. |
387 | To make it easier to distinguish CBOR from other formats, the CBOR |
608 | 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 |
609 | specification has a special "magic string" that can be prepended to any |
389 | CBOR string without changing it's meaning. |
610 | CBOR string without changing its meaning. |
390 | |
611 | |
391 | This string is available as $CBOR::XS::MAGIC. This module does not |
612 | 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 |
613 | 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 |
614 | if present, so users can prepend this string as a "file type" indicator |
394 | as required. |
615 | as required. |
395 | |
616 | |
396 | THE CBOR::XS::Tagged CLASS |
617 | THE CBOR::XS::Tagged CLASS |
397 | CBOR has the concept of tagged values - any CBOR value can be tagged |
618 | CBOR has the concept of tagged values - any CBOR value can be tagged |
… | |
… | |
448 | Wrap CBOR data in CBOR: |
669 | Wrap CBOR data in CBOR: |
449 | |
670 | |
450 | my $cbor_cbor = encode_cbor |
671 | my $cbor_cbor = encode_cbor |
451 | CBOR::XS::tag 24, |
672 | CBOR::XS::tag 24, |
452 | encode_cbor [1, 2, 3]; |
673 | encode_cbor [1, 2, 3]; |
|
|
674 | |
|
|
675 | TAG HANDLING AND EXTENSIONS |
|
|
676 | This section describes how this module handles specific tagged values |
|
|
677 | and extensions. If a tag is not mentioned here and no additional filters |
|
|
678 | are provided for it, then the default handling applies (creating a |
|
|
679 | CBOR::XS::Tagged object on decoding, and only encoding the tag when |
|
|
680 | explicitly requested). |
|
|
681 | |
|
|
682 | Tags not handled specifically are currently converted into a |
|
|
683 | CBOR::XS::Tagged object, which is simply a blessed array reference |
|
|
684 | consisting of the numeric tag value followed by the (decoded) CBOR |
|
|
685 | value. |
|
|
686 | |
|
|
687 | Future versions of this module reserve the right to special case |
|
|
688 | additional tags (such as base64url). |
|
|
689 | |
|
|
690 | ENFORCED TAGS |
|
|
691 | These tags are always handled when decoding, and their handling cannot |
|
|
692 | be overriden by the user. |
|
|
693 | |
|
|
694 | 26 (perl-object, <http://cbor.schmorp.de/perl-object>) |
|
|
695 | These tags are automatically created (and decoded) for serialisable |
|
|
696 | objects using the "FREEZE/THAW" methods (the Types::Serialier object |
|
|
697 | serialisation protocol). See "OBJECT SERIALISATION" for details. |
|
|
698 | |
|
|
699 | 28, 29 (shareable, sharedref, L <http://cbor.schmorp.de/value-sharing>) |
|
|
700 | These tags are automatically decoded when encountered (and they do |
|
|
701 | not result in a cyclic data structure, see "allow_cycles"), |
|
|
702 | resulting in shared values in the decoded object. They are only |
|
|
703 | encoded, however, when "allow_sharing" is enabled. |
|
|
704 | |
|
|
705 | Not all shared values can be successfully decoded: values that |
|
|
706 | reference themselves will *currently* decode as "undef" (this is not |
|
|
707 | the same as a reference pointing to itself, which will be |
|
|
708 | represented as a value that contains an indirect reference to itself |
|
|
709 | - these will be decoded properly). |
|
|
710 | |
|
|
711 | Note that considerably more shared value data structures can be |
|
|
712 | decoded than will be encoded - currently, only values pointed to by |
|
|
713 | references will be shared, others will not. While non-reference |
|
|
714 | shared values can be generated in Perl with some effort, they were |
|
|
715 | considered too unimportant to be supported in the encoder. The |
|
|
716 | decoder, however, will decode these values as shared values. |
|
|
717 | |
|
|
718 | 256, 25 (stringref-namespace, stringref, L |
|
|
719 | <http://cbor.schmorp.de/stringref>) |
|
|
720 | These tags are automatically decoded when encountered. They are only |
|
|
721 | encoded, however, when "pack_strings" is enabled. |
|
|
722 | |
|
|
723 | 22098 (indirection, <http://cbor.schmorp.de/indirection>) |
|
|
724 | This tag is automatically generated when a reference are encountered |
|
|
725 | (with the exception of hash and array refernces). It is converted to |
|
|
726 | a reference when decoding. |
|
|
727 | |
|
|
728 | 55799 (self-describe CBOR, RFC 7049) |
|
|
729 | This value is not generated on encoding (unless explicitly requested |
|
|
730 | by the user), and is simply ignored when decoding. |
|
|
731 | |
|
|
732 | NON-ENFORCED TAGS |
|
|
733 | These tags have default filters provided when decoding. Their handling |
|
|
734 | can be overriden by changing the %CBOR::XS::FILTER entry for the tag, or |
|
|
735 | by providing a custom "filter" callback when decoding. |
|
|
736 | |
|
|
737 | When they result in decoding into a specific Perl class, the module |
|
|
738 | usually provides a corresponding "TO_CBOR" method as well. |
|
|
739 | |
|
|
740 | When any of these need to load additional modules that are not part of |
|
|
741 | the perl core distribution (e.g. URI), it is (currently) up to the user |
|
|
742 | to provide these modules. The decoding usually fails with an exception |
|
|
743 | if the required module cannot be loaded. |
|
|
744 | |
|
|
745 | 0, 1 (date/time string, seconds since the epoch) |
|
|
746 | These tags are decoded into Time::Piece objects. The corresponding |
|
|
747 | "Time::Piece::TO_CBOR" method always encodes into tag 1 values |
|
|
748 | currently. |
|
|
749 | |
|
|
750 | The Time::Piece API is generally surprisingly bad, and fractional |
|
|
751 | seconds are only accidentally kept intact, so watch out. On the plus |
|
|
752 | side, the module comes with perl since 5.10, which has to count for |
|
|
753 | something. |
|
|
754 | |
|
|
755 | 2, 3 (positive/negative bignum) |
|
|
756 | These tags are decoded into Math::BigInt objects. The corresponding |
|
|
757 | "Math::BigInt::TO_CBOR" method encodes "small" bigints into normal |
|
|
758 | CBOR integers, and others into positive/negative CBOR bignums. |
|
|
759 | |
|
|
760 | 4, 5 (decimal fraction/bigfloat) |
|
|
761 | Both decimal fractions and bigfloats are decoded into Math::BigFloat |
|
|
762 | objects. The corresponding "Math::BigFloat::TO_CBOR" method *always* |
|
|
763 | encodes into a decimal fraction. |
|
|
764 | |
|
|
765 | CBOR cannot represent bigfloats with *very* large exponents - |
|
|
766 | conversion of such big float objects is undefined. |
|
|
767 | |
|
|
768 | Also, NaN and infinities are not encoded properly. |
|
|
769 | |
|
|
770 | 21, 22, 23 (expected later JSON conversion) |
|
|
771 | CBOR::XS is not a CBOR-to-JSON converter, and will simply ignore |
|
|
772 | these tags. |
|
|
773 | |
|
|
774 | 32 (URI) |
|
|
775 | These objects decode into URI objects. The corresponding |
|
|
776 | "URI::TO_CBOR" method again results in a CBOR URI value. |
453 | |
777 | |
454 | CBOR and JSON |
778 | CBOR and JSON |
455 | CBOR is supposed to implement a superset of the JSON data model, and is, |
779 | 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 |
780 | with some coercion, able to represent all JSON texts (something that |
457 | other "binary JSON" formats such as BSON generally do not support). |
781 | other "binary JSON" formats such as BSON generally do not support). |
… | |
… | |
513 | uses long double to represent floating point values, they might not be |
837 | uses long double to represent floating point values, they might not be |
514 | encoded properly. Half precision types are accepted, but not encoded. |
838 | encoded properly. Half precision types are accepted, but not encoded. |
515 | |
839 | |
516 | Strict mode and canonical mode are not implemented. |
840 | Strict mode and canonical mode are not implemented. |
517 | |
841 | |
|
|
842 | LIMITATIONS ON PERLS WITHOUT 64-BIT INTEGER SUPPORT |
|
|
843 | On perls that were built without 64 bit integer support (these are rare |
|
|
844 | nowadays, even on 32 bit architectures), support for any kind of 64 bit |
|
|
845 | integer in CBOR is very limited - most likely, these 64 bit values will |
|
|
846 | be truncated, corrupted, or otherwise not decoded correctly. This also |
|
|
847 | includes string, array and map sizes that are stored as 64 bit integers. |
|
|
848 | |
518 | THREADS |
849 | THREADS |
519 | This module is *not* guaranteed to be thread safe and there are no plans |
850 | This module is *not* guaranteed to be thread safe and there are no plans |
520 | to change this until Perl gets thread support (as opposed to the |
851 | to change this until Perl gets thread support (as opposed to the |
521 | horribly slow so-called "threads" which are simply slow and bloated |
852 | horribly slow so-called "threads" which are simply slow and bloated |
522 | process simulations - use fork, it's *much* faster, cheaper, better). |
853 | process simulations - use fork, it's *much* faster, cheaper, better). |