… | |
… | |
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). |
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37 | |
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38 | To give you a general idea about speed, with texts in the megabyte |
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39 | range, "CBOR::XS" usually encodes roughly twice as fast as Storable or |
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40 | JSON::XS and decodes about 15%-30% faster than those. The shorter the |
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41 | data, the worse Storable performs in comparison. |
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42 | |
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43 | Regarding compactness, "CBOR::XS"-encoded data structures are usually |
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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). |
46 | |
51 | |
47 | 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 |
48 | 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. |
49 | |
54 | |
50 | 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 |
… | |
… | |
72 | *disabled*. |
77 | *disabled*. |
73 | |
78 | |
74 | 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 |
75 | calls can be chained: |
80 | calls can be chained: |
76 | |
81 | |
77 | #TODO my $cbor = CBOR::XS->new->encode ({a => [1,2]}); |
82 | my $cbor = CBOR::XS->new->encode ({a => [1,2]}); |
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83 | |
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84 | $cbor = new_safe CBOR::XS |
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85 | Create a new, safe/secure CBOR::XS object. This is similar to "new", |
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86 | but configures the coder object to be safe to use with untrusted |
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87 | data. Currently, this is equivalent to: |
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88 | |
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89 | my $cbor = CBOR::XS |
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90 | ->new |
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91 | ->forbid_objects |
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92 | ->filter (\&CBOR::XS::safe_filter) |
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93 | ->max_size (1e8); |
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94 | |
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95 | But is more future proof (it is better to crash because of a change |
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96 | than to be exploited in other ways). |
78 | |
97 | |
79 | $cbor = $cbor->max_depth ([$maximum_nesting_depth]) |
98 | $cbor = $cbor->max_depth ([$maximum_nesting_depth]) |
80 | $max_depth = $cbor->get_max_depth |
99 | $max_depth = $cbor->get_max_depth |
81 | Sets the maximum nesting level (default 512) accepted while encoding |
100 | Sets the maximum nesting level (default 512) accepted while encoding |
82 | or decoding. If a higher nesting level is detected in CBOR data or a |
101 | or decoding. If a higher nesting level is detected in CBOR data or a |
… | |
… | |
96 | |
115 | |
97 | Note that nesting is implemented by recursion in C. The default |
116 | Note that nesting is implemented by recursion in C. The default |
98 | value has been chosen to be as large as typical operating systems |
117 | value has been chosen to be as large as typical operating systems |
99 | allow without crashing. |
118 | allow without crashing. |
100 | |
119 | |
101 | See SECURITY CONSIDERATIONS, below, for more info on why this is |
120 | See "SECURITY CONSIDERATIONS", below, for more info on why this is |
102 | useful. |
121 | useful. |
103 | |
122 | |
104 | $cbor = $cbor->max_size ([$maximum_string_size]) |
123 | $cbor = $cbor->max_size ([$maximum_string_size]) |
105 | $max_size = $cbor->get_max_size |
124 | $max_size = $cbor->get_max_size |
106 | Set the maximum length a CBOR string may have (in bytes) where |
125 | Set the maximum length a CBOR string may have (in bytes) where |
… | |
… | |
110 | exception. This setting has no effect on "encode" (yet). |
129 | exception. This setting has no effect on "encode" (yet). |
111 | |
130 | |
112 | If no argument is given, the limit check will be deactivated (same |
131 | If no argument is given, the limit check will be deactivated (same |
113 | as when 0 is specified). |
132 | as when 0 is specified). |
114 | |
133 | |
115 | See SECURITY CONSIDERATIONS, below, for more info on why this is |
134 | See "SECURITY CONSIDERATIONS", below, for more info on why this is |
116 | useful. |
135 | useful. |
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136 | |
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137 | $cbor = $cbor->allow_unknown ([$enable]) |
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138 | $enabled = $cbor->get_allow_unknown |
|
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139 | If $enable is true (or missing), then "encode" will *not* throw an |
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140 | exception when it encounters values it cannot represent in CBOR (for |
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141 | example, filehandles) but instead will encode a CBOR "error" value. |
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142 | |
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143 | If $enable is false (the default), then "encode" will throw an |
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144 | exception when it encounters anything it cannot encode as CBOR. |
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145 | |
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146 | This option does not affect "decode" in any way, and it is |
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147 | recommended to leave it off unless you know your communications |
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148 | partner. |
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149 | |
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150 | $cbor = $cbor->allow_sharing ([$enable]) |
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151 | $enabled = $cbor->get_allow_sharing |
|
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152 | If $enable is true (or missing), then "encode" will not |
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153 | double-encode values that have been referenced before (e.g. when the |
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154 | same object, such as an array, is referenced multiple times), but |
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155 | instead will emit a reference to the earlier value. |
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156 | |
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157 | This means that such values will only be encoded once, and will not |
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158 | result in a deep cloning of the value on decode, in decoders |
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159 | supporting the value sharing extension. This also makes it possible |
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160 | to encode cyclic data structures (which need "allow_cycles" to be |
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161 | enabled to be decoded by this module). |
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162 | |
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163 | It is recommended to leave it off unless you know your communication |
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164 | partner supports the value sharing extensions to CBOR |
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165 | (<http://cbor.schmorp.de/value-sharing>), as without decoder |
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166 | support, the resulting data structure might be unusable. |
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167 | |
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168 | Detecting shared values incurs a runtime overhead when values are |
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169 | encoded that have a reference counter large than one, and might |
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170 | unnecessarily increase the encoded size, as potentially shared |
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171 | values are encode as shareable whether or not they are actually |
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172 | shared. |
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173 | |
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174 | At the moment, only targets of references can be shared (e.g. |
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175 | scalars, arrays or hashes pointed to by a reference). Weirder |
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176 | constructs, such as an array with multiple "copies" of the *same* |
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177 | string, which are hard but not impossible to create in Perl, are not |
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178 | supported (this is the same as with Storable). |
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179 | |
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180 | If $enable is false (the default), then "encode" will encode shared |
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181 | data structures repeatedly, unsharing them in the process. Cyclic |
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182 | data structures cannot be encoded in this mode. |
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183 | |
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184 | This option does not affect "decode" in any way - shared values and |
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185 | references will always be decoded properly if present. |
|
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186 | |
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187 | $cbor = $cbor->allow_cycles ([$enable]) |
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188 | $enabled = $cbor->get_allow_cycles |
|
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189 | If $enable is true (or missing), then "decode" will happily decode |
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190 | self-referential (cyclic) data structures. By default these will not |
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191 | be decoded, as they need manual cleanup to avoid memory leaks, so |
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192 | code that isn't prepared for this will not leak memory. |
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193 | |
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194 | If $enable is false (the default), then "decode" will throw an error |
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195 | when it encounters a self-referential/cyclic data structure. |
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196 | |
|
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197 | FUTURE DIRECTION: the motivation behind this option is to avoid |
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198 | *real* cycles - future versions of this module might chose to decode |
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199 | cyclic data structures using weak references when this option is |
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200 | off, instead of throwing an error. |
|
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201 | |
|
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202 | This option does not affect "encode" in any way - shared values and |
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203 | references will always be encoded properly if present. |
|
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204 | |
|
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205 | $cbor = $cbor->forbid_objects ([$enable]) |
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206 | $enabled = $cbor->get_forbid_objects |
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207 | Disables the use of the object serialiser protocol. |
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208 | |
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209 | If $enable is true (or missing), then "encode" will will throw an |
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210 | exception when it encounters perl objects that would be encoded |
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211 | using the perl-object tag (26). When "decode" encounters such tags, |
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212 | it will fall back to the general filter/tagged logic as if this were |
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213 | an unknown tag (by default resulting in a "CBOR::XC::Tagged" |
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214 | object). |
|
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215 | |
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216 | If $enable is false (the default), then "encode" will use the |
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217 | Types::Serialiser object serialisation protocol to serialise objects |
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218 | into perl-object tags, and "decode" will do the same to decode such |
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219 | tags. |
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220 | |
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221 | See "SECURITY CONSIDERATIONS", below, for more info on why |
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222 | forbidding this protocol can be useful. |
|
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223 | |
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224 | $cbor = $cbor->pack_strings ([$enable]) |
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225 | $enabled = $cbor->get_pack_strings |
|
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226 | If $enable is true (or missing), then "encode" will try not to |
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227 | encode the same string twice, but will instead encode a reference to |
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228 | the string instead. Depending on your data format, this can save a |
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229 | lot of space, but also results in a very large runtime overhead |
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230 | (expect encoding times to be 2-4 times as high as without). |
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231 | |
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232 | It is recommended to leave it off unless you know your |
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233 | communications partner supports the stringref extension to CBOR |
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234 | (<http://cbor.schmorp.de/stringref>), as without decoder support, |
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235 | the resulting data structure might not be usable. |
|
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236 | |
|
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237 | If $enable is false (the default), then "encode" will encode strings |
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238 | the standard CBOR way. |
|
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239 | |
|
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240 | This option does not affect "decode" in any way - string references |
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241 | will always be decoded properly if present. |
|
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242 | |
|
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243 | $cbor = $cbor->text_keys ([$enable]) |
|
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244 | $enabled = $cbor->get_text_keys |
|
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245 | If $enabled is true (or missing), then "encode" will encode all perl |
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246 | hash keys as CBOR text strings/UTF-8 string, upgrading them as |
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247 | needed. |
|
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248 | |
|
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249 | If $enable is false (the default), then "encode" will encode hash |
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250 | keys normally - upgraded perl strings (strings internally encoded as |
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251 | UTF-8) as CBOR text strings, and downgraded perl strings as CBOR |
|
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252 | byte strings. |
|
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253 | |
|
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254 | This option does not affect "decode" in any way. |
|
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255 | |
|
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256 | This option is useful for interoperability with CBOR decoders that |
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257 | don't treat byte strings as a form of text. It is especially useful |
|
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258 | as Perl gives very little control over hash keys. |
|
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259 | |
|
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260 | Enabling this option can be slow, as all downgraded hash keys that |
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261 | are encoded need to be scanned and converted to UTF-8. |
|
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262 | |
|
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263 | $cbor = $cbor->text_strings ([$enable]) |
|
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264 | $enabled = $cbor->get_text_strings |
|
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265 | This option works similar to "text_keys", above, but works on all |
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266 | strings (including hash keys), so "text_keys" has no further effect |
|
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267 | after enabling "text_strings". |
|
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268 | |
|
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269 | If $enabled is true (or missing), then "encode" will encode all perl |
|
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270 | strings as CBOR text strings/UTF-8 strings, upgrading them as |
|
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271 | needed. |
|
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272 | |
|
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273 | If $enable is false (the default), then "encode" will encode strings |
|
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274 | normally (but see "text_keys") - upgraded perl strings (strings |
|
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275 | internally encoded as UTF-8) as CBOR text strings, and downgraded |
|
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276 | perl strings as CBOR byte strings. |
|
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277 | |
|
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278 | This option does not affect "decode" in any way. |
|
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279 | |
|
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280 | This option has similar advantages and disadvantages as "text_keys". |
|
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281 | In addition, this option effectively removes the ability to encode |
|
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282 | byte strings, which might break some "FREEZE" and "TO_CBOR" methods |
|
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283 | that rely on this, such as bignum encoding, so this option is mainly |
|
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284 | useful for very simple data. |
|
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285 | |
|
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286 | $cbor = $cbor->validate_utf8 ([$enable]) |
|
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287 | $enabled = $cbor->get_validate_utf8 |
|
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288 | If $enable is true (or missing), then "decode" will validate that |
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289 | elements (text strings) containing UTF-8 data in fact contain valid |
|
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290 | UTF-8 data (instead of blindly accepting it). This validation |
|
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291 | obviously takes extra time during decoding. |
|
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292 | |
|
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293 | The concept of "valid UTF-8" used is perl's concept, which is a |
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294 | superset of the official UTF-8. |
|
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295 | |
|
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296 | If $enable is false (the default), then "decode" will blindly accept |
|
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297 | UTF-8 data, marking them as valid UTF-8 in the resulting data |
|
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298 | structure regardless of whether that's true or not. |
|
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299 | |
|
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300 | Perl isn't too happy about corrupted UTF-8 in strings, but should |
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301 | generally not crash or do similarly evil things. Extensions might be |
|
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302 | not so forgiving, so it's recommended to turn on this setting if you |
|
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303 | receive untrusted CBOR. |
|
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304 | |
|
|
305 | This option does not affect "encode" in any way - strings that are |
|
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306 | supposedly valid UTF-8 will simply be dumped into the resulting CBOR |
|
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307 | string without checking whether that is, in fact, true or not. |
|
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308 | |
|
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309 | $cbor = $cbor->filter ([$cb->($tag, $value)]) |
|
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310 | $cb_or_undef = $cbor->get_filter |
|
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311 | Sets or replaces the tagged value decoding filter (when $cb is |
|
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312 | specified) or clears the filter (if no argument or "undef" is |
|
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313 | provided). |
|
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314 | |
|
|
315 | The filter callback is called only during decoding, when a |
|
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316 | non-enforced tagged value has been decoded (see "TAG HANDLING AND |
|
|
317 | EXTENSIONS" for a list of enforced tags). For specific tags, it's |
|
|
318 | often better to provide a default converter using the |
|
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319 | %CBOR::XS::FILTER hash (see below). |
|
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320 | |
|
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321 | The first argument is the numerical tag, the second is the (decoded) |
|
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322 | value that has been tagged. |
|
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323 | |
|
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324 | The filter function should return either exactly one value, which |
|
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325 | will replace the tagged value in the decoded data structure, or no |
|
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326 | values, which will result in default handling, which currently means |
|
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327 | the decoder creates a "CBOR::XS::Tagged" object to hold the tag and |
|
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328 | the value. |
|
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329 | |
|
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330 | When the filter is cleared (the default state), the default filter |
|
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331 | function, "CBOR::XS::default_filter", is used. This function simply |
|
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332 | looks up the tag in the %CBOR::XS::FILTER hash. If an entry exists |
|
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333 | it must be a code reference that is called with tag and value, and |
|
|
334 | is responsible for decoding the value. If no entry exists, it |
|
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335 | returns no values. "CBOR::XS" provides a number of default filter |
|
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336 | functions already, the the %CBOR::XS::FILTER hash can be freely |
|
|
337 | extended with more. |
|
|
338 | |
|
|
339 | "CBOR::XS" additionally provides an alternative filter function that |
|
|
340 | is supposed to be safe to use with untrusted data (which the default |
|
|
341 | filter might not), called "CBOR::XS::safe_filter", which works the |
|
|
342 | same as the "default_filter" but uses the %CBOR::XS::SAFE_FILTER |
|
|
343 | variable instead. It is prepopulated with the tag decoding functions |
|
|
344 | that are deemed safe (basically the same as %CBOR::XS::FILTER |
|
|
345 | without all the bignum tags), and can be extended by user code as |
|
|
346 | wlel, although, obviously, one should be very careful about adding |
|
|
347 | decoding functions here, since the expectation is that they are safe |
|
|
348 | to use on untrusted data, after all. |
|
|
349 | |
|
|
350 | Example: decode all tags not handled internally into |
|
|
351 | "CBOR::XS::Tagged" objects, with no other special handling (useful |
|
|
352 | when working with potentially "unsafe" CBOR data). |
|
|
353 | |
|
|
354 | CBOR::XS->new->filter (sub { })->decode ($cbor_data); |
|
|
355 | |
|
|
356 | Example: provide a global filter for tag 1347375694, converting the |
|
|
357 | value into some string form. |
|
|
358 | |
|
|
359 | $CBOR::XS::FILTER{1347375694} = sub { |
|
|
360 | my ($tag, $value); |
|
|
361 | |
|
|
362 | "tag 1347375694 value $value" |
|
|
363 | }; |
|
|
364 | |
|
|
365 | Example: provide your own filter function that looks up tags in your |
|
|
366 | own hash: |
|
|
367 | |
|
|
368 | my %my_filter = ( |
|
|
369 | 998347484 => sub { |
|
|
370 | my ($tag, $value); |
|
|
371 | |
|
|
372 | "tag 998347484 value $value" |
|
|
373 | }; |
|
|
374 | ); |
|
|
375 | |
|
|
376 | my $coder = CBOR::XS->new->filter (sub { |
|
|
377 | &{ $my_filter{$_[0]} or return } |
|
|
378 | }); |
|
|
379 | |
|
|
380 | Example: use the safe filter function (see "SECURITY CONSIDERATIONS" |
|
|
381 | for more considerations on security). |
|
|
382 | |
|
|
383 | CBOR::XS->new->filter (\&CBOR::XS::safe_filter)->decode ($cbor_data); |
117 | |
384 | |
118 | $cbor_data = $cbor->encode ($perl_scalar) |
385 | $cbor_data = $cbor->encode ($perl_scalar) |
119 | Converts the given Perl data structure (a scalar value) to its CBOR |
386 | Converts the given Perl data structure (a scalar value) to its CBOR |
120 | representation. |
387 | representation. |
121 | |
388 | |
… | |
… | |
134 | the next one starts. |
401 | the next one starts. |
135 | |
402 | |
136 | CBOR::XS->new->decode_prefix ("......") |
403 | CBOR::XS->new->decode_prefix ("......") |
137 | => ("...", 3) |
404 | => ("...", 3) |
138 | |
405 | |
|
|
406 | INCREMENTAL PARSING |
|
|
407 | In some cases, there is the need for incremental parsing of JSON texts. |
|
|
408 | While this module always has to keep both CBOR text and resulting Perl |
|
|
409 | data structure in memory at one time, it does allow you to parse a CBOR |
|
|
410 | stream incrementally, using a similar to using "decode_prefix" to see if |
|
|
411 | a full CBOR object is available, but is much more efficient. |
|
|
412 | |
|
|
413 | It basically works by parsing as much of a CBOR string as possible - if |
|
|
414 | the CBOR data is not complete yet, the pasrer will remember where it |
|
|
415 | was, to be able to restart when more data has been accumulated. Once |
|
|
416 | enough data is available to either decode a complete CBOR value or raise |
|
|
417 | an error, a real decode will be attempted. |
|
|
418 | |
|
|
419 | A typical use case would be a network protocol that consists of sending |
|
|
420 | and receiving CBOR-encoded messages. The solution that works with CBOR |
|
|
421 | and about anything else is by prepending a length to every CBOR value, |
|
|
422 | so the receiver knows how many octets to read. More compact (and |
|
|
423 | slightly slower) would be to just send CBOR values back-to-back, as |
|
|
424 | "CBOR::XS" knows where a CBOR value ends, and doesn't need an explicit |
|
|
425 | length. |
|
|
426 | |
|
|
427 | The following methods help with this: |
|
|
428 | |
|
|
429 | @decoded = $cbor->incr_parse ($buffer) |
|
|
430 | This method attempts to decode exactly one CBOR value from the |
|
|
431 | beginning of the given $buffer. The value is removed from the |
|
|
432 | $buffer on success. When $buffer doesn't contain a complete value |
|
|
433 | yet, it returns nothing. Finally, when the $buffer doesn't start |
|
|
434 | with something that could ever be a valid CBOR value, it raises an |
|
|
435 | exception, just as "decode" would. In the latter case the decoder |
|
|
436 | state is undefined and must be reset before being able to parse |
|
|
437 | further. |
|
|
438 | |
|
|
439 | This method modifies the $buffer in place. When no CBOR value can be |
|
|
440 | decoded, the decoder stores the current string offset. On the next |
|
|
441 | call, continues decoding at the place where it stopped before. For |
|
|
442 | this to make sense, the $buffer must begin with the same octets as |
|
|
443 | on previous unsuccessful calls. |
|
|
444 | |
|
|
445 | You can call this method in scalar context, in which case it either |
|
|
446 | returns a decoded value or "undef". This makes it impossible to |
|
|
447 | distinguish between CBOR null values (which decode to "undef") and |
|
|
448 | an unsuccessful decode, which is often acceptable. |
|
|
449 | |
|
|
450 | @decoded = $cbor->incr_parse_multiple ($buffer) |
|
|
451 | Same as "incr_parse", but attempts to decode as many CBOR values as |
|
|
452 | possible in one go, instead of at most one. Calls to "incr_parse" |
|
|
453 | and "incr_parse_multiple" can be interleaved. |
|
|
454 | |
|
|
455 | $cbor->incr_reset |
|
|
456 | Resets the incremental decoder. This throws away any saved state, so |
|
|
457 | that subsequent calls to "incr_parse" or "incr_parse_multiple" start |
|
|
458 | to parse a new CBOR value from the beginning of the $buffer again. |
|
|
459 | |
|
|
460 | This method can be called at any time, but it *must* be called if |
|
|
461 | you want to change your $buffer or there was a decoding error and |
|
|
462 | you want to reuse the $cbor object for future incremental parsings. |
|
|
463 | |
139 | MAPPING |
464 | MAPPING |
140 | This section describes how CBOR::XS maps Perl values to CBOR values and |
465 | This section describes how CBOR::XS maps Perl values to CBOR values and |
141 | vice versa. These mappings are designed to "do the right thing" in most |
466 | vice versa. These mappings are designed to "do the right thing" in most |
142 | circumstances automatically, preserving round-tripping characteristics |
467 | circumstances automatically, preserving round-tripping characteristics |
143 | (what you put in comes out as something equivalent). |
468 | (what you put in comes out as something equivalent). |
… | |
… | |
150 | integers |
475 | integers |
151 | CBOR integers become (numeric) perl scalars. On perls without 64 bit |
476 | CBOR integers become (numeric) perl scalars. On perls without 64 bit |
152 | support, 64 bit integers will be truncated or otherwise corrupted. |
477 | support, 64 bit integers will be truncated or otherwise corrupted. |
153 | |
478 | |
154 | byte strings |
479 | byte strings |
155 | Byte strings will become octet strings in Perl (the byte values |
480 | Byte strings will become octet strings in Perl (the Byte values |
156 | 0..255 will simply become characters of the same value in Perl). |
481 | 0..255 will simply become characters of the same value in Perl). |
157 | |
482 | |
158 | UTF-8 strings |
483 | UTF-8 strings |
159 | UTF-8 strings in CBOR will be decoded, i.e. the UTF-8 octets will be |
484 | UTF-8 strings in CBOR will be decoded, i.e. the UTF-8 octets will be |
160 | decoded into proper Unicode code points. At the moment, the validity |
485 | decoded into proper Unicode code points. At the moment, the validity |
… | |
… | |
174 | "Types:Serialiser::false" and "Types::Serialiser::error", |
499 | "Types:Serialiser::false" and "Types::Serialiser::error", |
175 | respectively. They are overloaded to act almost exactly like the |
500 | respectively. They are overloaded to act almost exactly like the |
176 | numbers 1 and 0 (for true and false) or to throw an exception on |
501 | numbers 1 and 0 (for true and false) or to throw an exception on |
177 | access (for error). See the Types::Serialiser manpage for details. |
502 | access (for error). See the Types::Serialiser manpage for details. |
178 | |
503 | |
179 | CBOR tag 256 (perl object) |
504 | tagged values |
180 | The tag value 256 (TODO: pending iana registration) will be used to |
|
|
181 | deserialise a Perl object serialised with "FREEZE". See OBJECT |
|
|
182 | SERIALISATION, below, for details. |
|
|
183 | |
|
|
184 | CBOR tag 55799 (magic header) |
|
|
185 | The tag 55799 is ignored (this tag implements the magic header). |
|
|
186 | |
|
|
187 | other CBOR tags |
|
|
188 | Tagged items consists of a numeric tag and another CBOR value. Tags |
505 | Tagged items consists of a numeric tag and another CBOR value. |
189 | not handled internally are currently converted into a |
|
|
190 | CBOR::XS::Tagged object, which is simply a blessed array reference |
|
|
191 | consisting of the numeric tag value followed by the (decoded) CBOR |
|
|
192 | value. |
|
|
193 | |
506 | |
194 | In the future, support for user-supplied conversions might get |
507 | See "TAG HANDLING AND EXTENSIONS" and the description of "->filter" |
195 | added. |
508 | for details on which tags are handled how. |
196 | |
509 | |
197 | anything else |
510 | anything else |
198 | Anything else (e.g. unsupported simple values) will raise a decoding |
511 | Anything else (e.g. unsupported simple values) will raise a decoding |
199 | error. |
512 | error. |
200 | |
513 | |
201 | PERL -> CBOR |
514 | PERL -> CBOR |
202 | The mapping from Perl to CBOR is slightly more difficult, as Perl is a |
515 | The mapping from Perl to CBOR is slightly more difficult, as Perl is a |
203 | truly typeless language, so we can only guess which CBOR type is meant |
516 | typeless language. That means this module can only guess which CBOR type |
204 | by a Perl value. |
517 | is meant by a perl value. |
205 | |
518 | |
206 | hash references |
519 | hash references |
207 | Perl hash references become CBOR maps. As there is no inherent |
520 | Perl hash references become CBOR maps. As there is no inherent |
208 | ordering in hash keys (or CBOR maps), they will usually be encoded |
521 | ordering in hash keys (or CBOR maps), they will usually be encoded |
209 | in a pseudo-random order. |
522 | in a pseudo-random order. This order can be different each time a |
|
|
523 | hash is encoded. |
210 | |
524 | |
211 | Currently, tied hashes will use the indefinite-length format, while |
525 | Currently, tied hashes will use the indefinite-length format, while |
212 | normal hashes will use the fixed-length format. |
526 | normal hashes will use the fixed-length format. |
213 | |
527 | |
214 | array references |
528 | array references |
215 | Perl array references become fixed-length CBOR arrays. |
529 | Perl array references become fixed-length CBOR arrays. |
216 | |
530 | |
217 | other references |
531 | other references |
218 | Other unblessed references are generally not allowed and will cause |
532 | Other unblessed references will be represented using the indirection |
219 | an exception to be thrown, except for references to the integers 0 |
533 | tag extension (tag value 22098, |
220 | and 1, which get turned into false and true in CBOR. |
534 | <http://cbor.schmorp.de/indirection>). CBOR decoders are guaranteed |
|
|
535 | to be able to decode these values somehow, by either "doing the |
|
|
536 | right thing", decoding into a generic tagged object, simply ignoring |
|
|
537 | the tag, or something else. |
221 | |
538 | |
222 | CBOR::XS::Tagged objects |
539 | CBOR::XS::Tagged objects |
223 | Objects of this type must be arrays consisting of a single "[tag, |
540 | Objects of this type must be arrays consisting of a single "[tag, |
224 | value]" pair. The (numerical) tag will be encoded as a CBOR tag, the |
541 | value]" pair. The (numerical) tag will be encoded as a CBOR tag, the |
225 | value will be encoded as appropriate for the value. You cna use |
542 | value will be encoded as appropriate for the value. You must use |
226 | "CBOR::XS::tag" to create such objects. |
543 | "CBOR::XS::tag" to create such objects. |
227 | |
544 | |
228 | Types::Serialiser::true, Types::Serialiser::false, |
545 | Types::Serialiser::true, Types::Serialiser::false, |
229 | Types::Serialiser::error |
546 | Types::Serialiser::error |
230 | These special values become CBOR true, CBOR false and CBOR undefined |
547 | These special values become CBOR true, CBOR false and CBOR undefined |
231 | values, respectively. You can also use "\1", "\0" and "\undef" |
548 | values, respectively. You can also use "\1", "\0" and "\undef" |
232 | directly if you want. |
549 | directly if you want. |
233 | |
550 | |
234 | other blessed objects |
551 | other blessed objects |
235 | Other blessed objects are serialised via "TO_CBOR" or "FREEZE". See |
552 | Other blessed objects are serialised via "TO_CBOR" or "FREEZE". See |
236 | "OBJECT SERIALISATION", below, for details. |
553 | "TAG HANDLING AND EXTENSIONS" for specific classes handled by this |
|
|
554 | module, and "OBJECT SERIALISATION" for generic object serialisation. |
237 | |
555 | |
238 | simple scalars |
556 | simple scalars |
239 | TODO Simple Perl scalars (any scalar that is not a reference) are |
557 | Simple Perl scalars (any scalar that is not a reference) are the |
240 | the most difficult objects to encode: CBOR::XS will encode undefined |
558 | most difficult objects to encode: CBOR::XS will encode undefined |
241 | scalars as CBOR null values, scalars that have last been used in a |
559 | scalars as CBOR null values, scalars that have last been used in a |
242 | string context before encoding as CBOR strings, and anything else as |
560 | string context before encoding as CBOR strings, and anything else as |
243 | number value: |
561 | number value: |
244 | |
562 | |
245 | # dump as number |
563 | # dump as number |
246 | encode_cbor [2] # yields [2] |
564 | encode_cbor [2] # yields [2] |
247 | encode_cbor [-3.0e17] # yields [-3e+17] |
565 | encode_cbor [-3.0e17] # yields [-3e+17] |
248 | my $value = 5; encode_cbor [$value] # yields [5] |
566 | my $value = 5; encode_cbor [$value] # yields [5] |
249 | |
567 | |
250 | # used as string, so dump as string |
568 | # used as string, so dump as string (either byte or text) |
251 | print $value; |
569 | print $value; |
252 | encode_cbor [$value] # yields ["5"] |
570 | encode_cbor [$value] # yields ["5"] |
253 | |
571 | |
254 | # undef becomes null |
572 | # undef becomes null |
255 | encode_cbor [undef] # yields [null] |
573 | encode_cbor [undef] # yields [null] |
… | |
… | |
258 | |
576 | |
259 | my $x = 3.1; # some variable containing a number |
577 | my $x = 3.1; # some variable containing a number |
260 | "$x"; # stringified |
578 | "$x"; # stringified |
261 | $x .= ""; # another, more awkward way to stringify |
579 | $x .= ""; # another, more awkward way to stringify |
262 | print $x; # perl does it for you, too, quite often |
580 | print $x; # perl does it for you, too, quite often |
|
|
581 | |
|
|
582 | You can force whether a string is encoded as byte or text string by |
|
|
583 | using "utf8::upgrade" and "utf8::downgrade" (if "text_strings" is |
|
|
584 | disabled): |
|
|
585 | |
|
|
586 | utf8::upgrade $x; # encode $x as text string |
|
|
587 | utf8::downgrade $x; # encode $x as byte string |
|
|
588 | |
|
|
589 | Perl doesn't define what operations up- and downgrade strings, so if |
|
|
590 | the difference between byte and text is important, you should up- or |
|
|
591 | downgrade your string as late as possible before encoding. You can |
|
|
592 | also force the use of CBOR text strings by using "text_keys" or |
|
|
593 | "text_strings". |
263 | |
594 | |
264 | You can force the type to be a CBOR number by numifying it: |
595 | You can force the type to be a CBOR number by numifying it: |
265 | |
596 | |
266 | my $x = "3"; # some variable containing a string |
597 | my $x = "3"; # some variable containing a string |
267 | $x += 0; # numify it, ensuring it will be dumped as a number |
598 | $x += 0; # numify it, ensuring it will be dumped as a number |
… | |
… | |
277 | the IEEE double format will be used. Perls that use formats other |
608 | the IEEE double format will be used. Perls that use formats other |
278 | than IEEE double to represent numerical values are supported, but |
609 | than IEEE double to represent numerical values are supported, but |
279 | might suffer loss of precision. |
610 | might suffer loss of precision. |
280 | |
611 | |
281 | OBJECT SERIALISATION |
612 | OBJECT SERIALISATION |
|
|
613 | This module implements both a CBOR-specific and the generic |
|
|
614 | Types::Serialier object serialisation protocol. The following |
|
|
615 | subsections explain both methods. |
|
|
616 | |
|
|
617 | ENCODING |
282 | This module knows two way to serialise a Perl object: The CBOR-specific |
618 | This module knows two way to serialise a Perl object: The CBOR-specific |
283 | way, and the generic way. |
619 | way, and the generic way. |
284 | |
620 | |
285 | Whenever the encoder encounters a Perl object that it cnanot serialise |
621 | Whenever the encoder encounters a Perl object that it cannot serialise |
286 | directly (most of them), it will first look up the "TO_CBOR" method on |
622 | directly (most of them), it will first look up the "TO_CBOR" method on |
287 | it. |
623 | it. |
288 | |
624 | |
289 | If it has a "TO_CBOR" method, it will call it with the object as only |
625 | If it has a "TO_CBOR" method, it will call it with the object as only |
290 | argument, and expects exactly one return value, which it will then |
626 | argument, and expects exactly one return value, which it will then |
… | |
… | |
295 | "CBOR" as the second argument, to distinguish it from other serialisers. |
631 | "CBOR" as the second argument, to distinguish it from other serialisers. |
296 | |
632 | |
297 | The "FREEZE" method can return any number of values (i.e. zero or more). |
633 | The "FREEZE" method can return any number of values (i.e. zero or more). |
298 | These will be encoded as CBOR perl object, together with the classname. |
634 | These will be encoded as CBOR perl object, together with the classname. |
299 | |
635 | |
|
|
636 | These methods *MUST NOT* change the data structure that is being |
|
|
637 | serialised. Failure to comply to this can result in memory corruption - |
|
|
638 | and worse. |
|
|
639 | |
300 | If an object supports neither "TO_CBOR" nor "FREEZE", encoding will fail |
640 | If an object supports neither "TO_CBOR" nor "FREEZE", encoding will fail |
301 | with an error. |
641 | with an error. |
302 | |
642 | |
|
|
643 | DECODING |
303 | Objects encoded via "TO_CBOR" cannot be automatically decoded, but |
644 | Objects encoded via "TO_CBOR" cannot (normally) be automatically |
304 | objects encoded via "FREEZE" can be decoded using the following |
645 | decoded, but objects encoded via "FREEZE" can be decoded using the |
305 | protocol: |
646 | following protocol: |
306 | |
647 | |
307 | When an encoded CBOR perl object is encountered by the decoder, it will |
648 | When an encoded CBOR perl object is encountered by the decoder, it will |
308 | look up the "THAW" method, by using the stored classname, and will fail |
649 | look up the "THAW" method, by using the stored classname, and will fail |
309 | if the method cannot be found. |
650 | if the method cannot be found. |
310 | |
651 | |
… | |
… | |
331 | |
672 | |
332 | sub URI::TO_CBOR { |
673 | sub URI::TO_CBOR { |
333 | my ($self) = @_; |
674 | my ($self) = @_; |
334 | my $uri = "$self"; # stringify uri |
675 | my $uri = "$self"; # stringify uri |
335 | utf8::upgrade $uri; # make sure it will be encoded as UTF-8 string |
676 | utf8::upgrade $uri; # make sure it will be encoded as UTF-8 string |
336 | CBOR::XS::tagged 32, "$_[0]" |
677 | CBOR::XS::tag 32, "$_[0]" |
337 | } |
678 | } |
338 | |
679 | |
339 | This will encode URIs as a UTF-8 string with tag 32, which indicates an |
680 | This will encode URIs as a UTF-8 string with tag 32, which indicates an |
340 | URI. |
681 | URI. |
341 | |
682 | |
… | |
… | |
352 | "$self" # encode url string |
693 | "$self" # encode url string |
353 | } |
694 | } |
354 | |
695 | |
355 | sub URI::THAW { |
696 | sub URI::THAW { |
356 | my ($class, $serialiser, $uri) = @_; |
697 | my ($class, $serialiser, $uri) = @_; |
357 | |
|
|
358 | $class->new ($uri) |
698 | $class->new ($uri) |
359 | } |
699 | } |
360 | |
700 | |
361 | Unlike "TO_CBOR", multiple values can be returned by "FREEZE". For |
701 | Unlike "TO_CBOR", multiple values can be returned by "FREEZE". For |
362 | example, a "FREEZE" method that returns "type", "id" and "variant" |
702 | example, a "FREEZE" method that returns "type", "id" and "variant" |
… | |
… | |
376 | |
716 | |
377 | MAGIC HEADER |
717 | MAGIC HEADER |
378 | There is no way to distinguish CBOR from other formats programmatically. |
718 | There is no way to distinguish CBOR from other formats programmatically. |
379 | To make it easier to distinguish CBOR from other formats, the CBOR |
719 | To make it easier to distinguish CBOR from other formats, the CBOR |
380 | specification has a special "magic string" that can be prepended to any |
720 | specification has a special "magic string" that can be prepended to any |
381 | CBOR string without changing it's meaning. |
721 | CBOR string without changing its meaning. |
382 | |
722 | |
383 | This string is available as $CBOR::XS::MAGIC. This module does not |
723 | This string is available as $CBOR::XS::MAGIC. This module does not |
384 | prepend this string tot he CBOR data it generates, but it will ignroe it |
724 | prepend this string to the CBOR data it generates, but it will ignore it |
385 | if present, so users can prepend this string as a "file type" indicator |
725 | if present, so users can prepend this string as a "file type" indicator |
386 | as required. |
726 | as required. |
387 | |
727 | |
388 | THE CBOR::XS::Tagged CLASS |
728 | THE CBOR::XS::Tagged CLASS |
389 | CBOR has the concept of tagged values - any CBOR value can be tagged |
729 | CBOR has the concept of tagged values - any CBOR value can be tagged |
… | |
… | |
440 | Wrap CBOR data in CBOR: |
780 | Wrap CBOR data in CBOR: |
441 | |
781 | |
442 | my $cbor_cbor = encode_cbor |
782 | my $cbor_cbor = encode_cbor |
443 | CBOR::XS::tag 24, |
783 | CBOR::XS::tag 24, |
444 | encode_cbor [1, 2, 3]; |
784 | encode_cbor [1, 2, 3]; |
|
|
785 | |
|
|
786 | TAG HANDLING AND EXTENSIONS |
|
|
787 | This section describes how this module handles specific tagged values |
|
|
788 | and extensions. If a tag is not mentioned here and no additional filters |
|
|
789 | are provided for it, then the default handling applies (creating a |
|
|
790 | CBOR::XS::Tagged object on decoding, and only encoding the tag when |
|
|
791 | explicitly requested). |
|
|
792 | |
|
|
793 | Tags not handled specifically are currently converted into a |
|
|
794 | CBOR::XS::Tagged object, which is simply a blessed array reference |
|
|
795 | consisting of the numeric tag value followed by the (decoded) CBOR |
|
|
796 | value. |
|
|
797 | |
|
|
798 | Future versions of this module reserve the right to special case |
|
|
799 | additional tags (such as base64url). |
|
|
800 | |
|
|
801 | ENFORCED TAGS |
|
|
802 | These tags are always handled when decoding, and their handling cannot |
|
|
803 | be overridden by the user. |
|
|
804 | |
|
|
805 | 26 (perl-object, <http://cbor.schmorp.de/perl-object>) |
|
|
806 | These tags are automatically created (and decoded) for serialisable |
|
|
807 | objects using the "FREEZE/THAW" methods (the Types::Serialier object |
|
|
808 | serialisation protocol). See "OBJECT SERIALISATION" for details. |
|
|
809 | |
|
|
810 | 28, 29 (shareable, sharedref, <http://cbor.schmorp.de/value-sharing>) |
|
|
811 | These tags are automatically decoded when encountered (and they do |
|
|
812 | not result in a cyclic data structure, see "allow_cycles"), |
|
|
813 | resulting in shared values in the decoded object. They are only |
|
|
814 | encoded, however, when "allow_sharing" is enabled. |
|
|
815 | |
|
|
816 | Not all shared values can be successfully decoded: values that |
|
|
817 | reference themselves will *currently* decode as "undef" (this is not |
|
|
818 | the same as a reference pointing to itself, which will be |
|
|
819 | represented as a value that contains an indirect reference to itself |
|
|
820 | - these will be decoded properly). |
|
|
821 | |
|
|
822 | Note that considerably more shared value data structures can be |
|
|
823 | decoded than will be encoded - currently, only values pointed to by |
|
|
824 | references will be shared, others will not. While non-reference |
|
|
825 | shared values can be generated in Perl with some effort, they were |
|
|
826 | considered too unimportant to be supported in the encoder. The |
|
|
827 | decoder, however, will decode these values as shared values. |
|
|
828 | |
|
|
829 | 256, 25 (stringref-namespace, stringref, |
|
|
830 | <http://cbor.schmorp.de/stringref>) |
|
|
831 | These tags are automatically decoded when encountered. They are only |
|
|
832 | encoded, however, when "pack_strings" is enabled. |
|
|
833 | |
|
|
834 | 22098 (indirection, <http://cbor.schmorp.de/indirection>) |
|
|
835 | This tag is automatically generated when a reference are encountered |
|
|
836 | (with the exception of hash and array references). It is converted |
|
|
837 | to a reference when decoding. |
|
|
838 | |
|
|
839 | 55799 (self-describe CBOR, RFC 7049) |
|
|
840 | This value is not generated on encoding (unless explicitly requested |
|
|
841 | by the user), and is simply ignored when decoding. |
|
|
842 | |
|
|
843 | NON-ENFORCED TAGS |
|
|
844 | These tags have default filters provided when decoding. Their handling |
|
|
845 | can be overridden by changing the %CBOR::XS::FILTER entry for the tag, |
|
|
846 | or by providing a custom "filter" callback when decoding. |
|
|
847 | |
|
|
848 | When they result in decoding into a specific Perl class, the module |
|
|
849 | usually provides a corresponding "TO_CBOR" method as well. |
|
|
850 | |
|
|
851 | When any of these need to load additional modules that are not part of |
|
|
852 | the perl core distribution (e.g. URI), it is (currently) up to the user |
|
|
853 | to provide these modules. The decoding usually fails with an exception |
|
|
854 | if the required module cannot be loaded. |
|
|
855 | |
|
|
856 | 0, 1 (date/time string, seconds since the epoch) |
|
|
857 | These tags are decoded into Time::Piece objects. The corresponding |
|
|
858 | "Time::Piece::TO_CBOR" method always encodes into tag 1 values |
|
|
859 | currently. |
|
|
860 | |
|
|
861 | The Time::Piece API is generally surprisingly bad, and fractional |
|
|
862 | seconds are only accidentally kept intact, so watch out. On the plus |
|
|
863 | side, the module comes with perl since 5.10, which has to count for |
|
|
864 | something. |
|
|
865 | |
|
|
866 | 2, 3 (positive/negative bignum) |
|
|
867 | These tags are decoded into Math::BigInt objects. The corresponding |
|
|
868 | "Math::BigInt::TO_CBOR" method encodes "small" bigints into normal |
|
|
869 | CBOR integers, and others into positive/negative CBOR bignums. |
|
|
870 | |
|
|
871 | 4, 5, 264, 265 (decimal fraction/bigfloat) |
|
|
872 | Both decimal fractions and bigfloats are decoded into Math::BigFloat |
|
|
873 | objects. The corresponding "Math::BigFloat::TO_CBOR" method *always* |
|
|
874 | encodes into a decimal fraction (either tag 4 or 264). |
|
|
875 | |
|
|
876 | NaN and infinities are not encoded properly, as they cannot be |
|
|
877 | represented in CBOR. |
|
|
878 | |
|
|
879 | See "BIGNUM SECURITY CONSIDERATIONS" for more info. |
|
|
880 | |
|
|
881 | 30 (rational numbers) |
|
|
882 | These tags are decoded into Math::BigRat objects. The corresponding |
|
|
883 | "Math::BigRat::TO_CBOR" method encodes rational numbers with |
|
|
884 | denominator 1 via their numerator only, i.e., they become normal |
|
|
885 | integers or "bignums". |
|
|
886 | |
|
|
887 | See "BIGNUM SECURITY CONSIDERATIONS" for more info. |
|
|
888 | |
|
|
889 | 21, 22, 23 (expected later JSON conversion) |
|
|
890 | CBOR::XS is not a CBOR-to-JSON converter, and will simply ignore |
|
|
891 | these tags. |
|
|
892 | |
|
|
893 | 32 (URI) |
|
|
894 | These objects decode into URI objects. The corresponding |
|
|
895 | "URI::TO_CBOR" method again results in a CBOR URI value. |
445 | |
896 | |
446 | CBOR and JSON |
897 | CBOR and JSON |
447 | CBOR is supposed to implement a superset of the JSON data model, and is, |
898 | CBOR is supposed to implement a superset of the JSON data model, and is, |
448 | with some coercion, able to represent all JSON texts (something that |
899 | with some coercion, able to represent all JSON texts (something that |
449 | other "binary JSON" formats such as BSON generally do not support). |
900 | other "binary JSON" formats such as BSON generally do not support). |
… | |
… | |
455 | interoperability is improved in the future, then the goal will be to |
906 | interoperability is improved in the future, then the goal will be to |
456 | ensure that decoded JSON data will round-trip encoding and decoding to |
907 | ensure that decoded JSON data will round-trip encoding and decoding to |
457 | CBOR intact. |
908 | CBOR intact. |
458 | |
909 | |
459 | SECURITY CONSIDERATIONS |
910 | SECURITY CONSIDERATIONS |
460 | When you are using CBOR in a protocol, talking to untrusted potentially |
911 | Tl;dr... if you want to decode or encode CBOR from untrusted sources, |
461 | hostile creatures requires relatively few measures. |
912 | you should start with a coder object created via "new_safe": |
462 | |
913 | |
|
|
914 | my $coder = CBOR::XS->new_safe; |
|
|
915 | |
|
|
916 | my $data = $coder->decode ($cbor_text); |
|
|
917 | my $cbor = $coder->encode ($data); |
|
|
918 | |
|
|
919 | Longer version: When you are using CBOR in a protocol, talking to |
|
|
920 | untrusted potentially hostile creatures requires some thought: |
|
|
921 | |
|
|
922 | Security of the CBOR decoder itself |
463 | First of all, your CBOR decoder should be secure, that is, should not |
923 | First and foremost, your CBOR decoder should be secure, that is, |
464 | have any buffer overflows. Obviously, this module should ensure that and |
924 | should not have any buffer overflows or similar bugs that could |
|
|
925 | potentially be exploited. Obviously, this module should ensure that |
465 | I am trying hard on making that true, but you never know. |
926 | and I am trying hard on making that true, but you never know. |
466 | |
927 | |
|
|
928 | CBOR::XS can invoke almost arbitrary callbacks during decoding |
|
|
929 | CBOR::XS supports object serialisation - decoding CBOR can cause |
|
|
930 | calls to *any* "THAW" method in *any* package that exists in your |
|
|
931 | process (that is, CBOR::XS will not try to load modules, but any |
|
|
932 | existing "THAW" method or function can be called, so they all have |
|
|
933 | to be secure). |
|
|
934 | |
|
|
935 | Less obviously, it will also invoke "TO_CBOR" and "FREEZE" methods - |
|
|
936 | even if all your "THAW" methods are secure, encoding data structures |
|
|
937 | from untrusted sources can invoke those and trigger bugs in those. |
|
|
938 | |
|
|
939 | So, if you are not sure about the security of all the modules you |
|
|
940 | have loaded (you shouldn't), you should disable this part using |
|
|
941 | "forbid_objects". |
|
|
942 | |
|
|
943 | CBOR can be extended with tags that call library code |
|
|
944 | CBOR can be extended with tags, and "CBOR::XS" has a registry of |
|
|
945 | conversion functions for many existing tags that can be extended via |
|
|
946 | third-party modules (see the "filter" method). |
|
|
947 | |
|
|
948 | If you don't trust these, you should configure the "safe" filter |
|
|
949 | function, "CBOR::XS::safe_filter", which by default only includes |
|
|
950 | conversion functions that are considered "safe" by the author (but |
|
|
951 | again, they can be extended by third party modules). |
|
|
952 | |
|
|
953 | Depending on your level of paranoia, you can use the "safe" filter: |
|
|
954 | |
|
|
955 | $cbor->filter (\&CBOR::XS::safe_filter); |
|
|
956 | |
|
|
957 | ... your own filter... |
|
|
958 | |
|
|
959 | $cbor->filter (sub { ... do your stuffs here ... }); |
|
|
960 | |
|
|
961 | ... or even no filter at all, disabling all tag decoding: |
|
|
962 | |
|
|
963 | $cbor->filter (sub { }); |
|
|
964 | |
|
|
965 | This is never a problem for encoding, as the tag mechanism only |
|
|
966 | exists in CBOR texts. |
|
|
967 | |
|
|
968 | Resource-starving attacks: object memory usage |
467 | Second, you need to avoid resource-starving attacks. That means you |
969 | You need to avoid resource-starving attacks. That means you should |
468 | should limit the size of CBOR data you accept, or make sure then when |
970 | limit the size of CBOR data you accept, or make sure then when your |
469 | your resources run out, that's just fine (e.g. by using a separate |
971 | resources run out, that's just fine (e.g. by using a separate |
470 | process that can crash safely). The size of a CBOR string in octets is |
972 | process that can crash safely). The size of a CBOR string in octets |
471 | usually a good indication of the size of the resources required to |
973 | is usually a good indication of the size of the resources required |
472 | decode it into a Perl structure. While CBOR::XS can check the size of |
974 | to decode it into a Perl structure. While CBOR::XS can check the |
473 | the CBOR text, it might be too late when you already have it in memory, |
975 | size of the CBOR text (using "max_size"), it might be too late when |
474 | so you might want to check the size before you accept the string. |
976 | you already have it in memory, so you might want to check the size |
|
|
977 | before you accept the string. |
475 | |
978 | |
|
|
979 | As for encoding, it is possible to construct data structures that |
|
|
980 | are relatively small but result in large CBOR texts (for example by |
|
|
981 | having an array full of references to the same big data structure, |
|
|
982 | which will all be deep-cloned during encoding by default). This is |
|
|
983 | rarely an actual issue (and the worst case is still just running out |
|
|
984 | of memory), but you can reduce this risk by using "allow_sharing". |
|
|
985 | |
|
|
986 | Resource-starving attacks: stack overflows |
476 | Third, CBOR::XS recurses using the C stack when decoding objects and |
987 | CBOR::XS recurses using the C stack when decoding objects and |
477 | arrays. The C stack is a limited resource: for instance, on my amd64 |
988 | arrays. The C stack is a limited resource: for instance, on my amd64 |
478 | machine with 8MB of stack size I can decode around 180k nested arrays |
989 | machine with 8MB of stack size I can decode around 180k nested |
479 | but only 14k nested CBOR objects (due to perl itself recursing deeply on |
990 | arrays but only 14k nested CBOR objects (due to perl itself |
480 | croak to free the temporary). If that is exceeded, the program crashes. |
991 | recursing deeply on croak to free the temporary). If that is |
481 | To be conservative, the default nesting limit is set to 512. If your |
992 | exceeded, the program crashes. To be conservative, the default |
482 | process has a smaller stack, you should adjust this setting accordingly |
993 | nesting limit is set to 512. If your process has a smaller stack, |
483 | with the "max_depth" method. |
994 | you should adjust this setting accordingly with the "max_depth" |
|
|
995 | method. |
484 | |
996 | |
|
|
997 | Resource-starving attacks: CPU en-/decoding complexity |
|
|
998 | CBOR::XS will use the Math::BigInt, Math::BigFloat and Math::BigRat |
|
|
999 | libraries to represent encode/decode bignums. These can be very slow |
|
|
1000 | (as in, centuries of CPU time) and can even crash your program (and |
|
|
1001 | are generally not very trustworthy). See the next section for |
|
|
1002 | details. |
|
|
1003 | |
|
|
1004 | Data breaches: leaking information in error messages |
|
|
1005 | CBOR::XS might leak contents of your Perl data structures in its |
|
|
1006 | error messages, so when you serialise sensitive information you |
|
|
1007 | might want to make sure that exceptions thrown by CBOR::XS will not |
|
|
1008 | end up in front of untrusted eyes. |
|
|
1009 | |
|
|
1010 | Something else... |
485 | Something else could bomb you, too, that I forgot to think of. In that |
1011 | Something else could bomb you, too, that I forgot to think of. In |
486 | case, you get to keep the pieces. I am always open for hints, though... |
1012 | that case, you get to keep the pieces. I am always open for hints, |
|
|
1013 | though... |
487 | |
1014 | |
488 | Also keep in mind that CBOR::XS might leak contents of your Perl data |
1015 | BIGNUM SECURITY CONSIDERATIONS |
489 | structures in its error messages, so when you serialise sensitive |
1016 | CBOR::XS provides a "TO_CBOR" method for both Math::BigInt and |
490 | information you might want to make sure that exceptions thrown by |
1017 | Math::BigFloat that tries to encode the number in the simplest possible |
491 | CBOR::XS will not end up in front of untrusted eyes. |
1018 | way, that is, either a CBOR integer, a CBOR bigint/decimal fraction (tag |
|
|
1019 | 4) or an arbitrary-exponent decimal fraction (tag 264). Rational numbers |
|
|
1020 | (Math::BigRat, tag 30) can also contain bignums as members. |
|
|
1021 | |
|
|
1022 | CBOR::XS will also understand base-2 bigfloat or arbitrary-exponent |
|
|
1023 | bigfloats (tags 5 and 265), but it will never generate these on its own. |
|
|
1024 | |
|
|
1025 | Using the built-in Math::BigInt::Calc support, encoding and decoding |
|
|
1026 | decimal fractions is generally fast. Decoding bigints can be slow for |
|
|
1027 | very big numbers (tens of thousands of digits, something that could |
|
|
1028 | potentially be caught by limiting the size of CBOR texts), and decoding |
|
|
1029 | bigfloats or arbitrary-exponent bigfloats can be *extremely* slow |
|
|
1030 | (minutes, decades) for large exponents (roughly 40 bit and longer). |
|
|
1031 | |
|
|
1032 | Additionally, Math::BigInt can take advantage of other bignum libraries, |
|
|
1033 | such as Math::GMP, which cannot handle big floats with large exponents, |
|
|
1034 | and might simply abort or crash your program, due to their code quality. |
|
|
1035 | |
|
|
1036 | This can be a concern if you want to parse untrusted CBOR. If it is, you |
|
|
1037 | might want to disable decoding of tag 2 (bigint) and 3 (negative bigint) |
|
|
1038 | types. You should also disable types 5 and 265, as these can be slow |
|
|
1039 | even without bigints. |
|
|
1040 | |
|
|
1041 | Disabling bigints will also partially or fully disable types that rely |
|
|
1042 | on them, e.g. rational numbers that use bignums. |
492 | |
1043 | |
493 | CBOR IMPLEMENTATION NOTES |
1044 | CBOR IMPLEMENTATION NOTES |
494 | This section contains some random implementation notes. They do not |
1045 | This section contains some random implementation notes. They do not |
495 | describe guaranteed behaviour, but merely behaviour as-is implemented |
1046 | describe guaranteed behaviour, but merely behaviour as-is implemented |
496 | right now. |
1047 | right now. |
… | |
… | |
504 | Only the double data type is supported for NV data types - when Perl |
1055 | Only the double data type is supported for NV data types - when Perl |
505 | uses long double to represent floating point values, they might not be |
1056 | uses long double to represent floating point values, they might not be |
506 | encoded properly. Half precision types are accepted, but not encoded. |
1057 | encoded properly. Half precision types are accepted, but not encoded. |
507 | |
1058 | |
508 | Strict mode and canonical mode are not implemented. |
1059 | Strict mode and canonical mode are not implemented. |
|
|
1060 | |
|
|
1061 | LIMITATIONS ON PERLS WITHOUT 64-BIT INTEGER SUPPORT |
|
|
1062 | On perls that were built without 64 bit integer support (these are rare |
|
|
1063 | nowadays, even on 32 bit architectures, as all major Perl distributions |
|
|
1064 | are built with 64 bit integer support), support for any kind of 64 bit |
|
|
1065 | integer in CBOR is very limited - most likely, these 64 bit values will |
|
|
1066 | be truncated, corrupted, or otherwise not decoded correctly. This also |
|
|
1067 | includes string, array and map sizes that are stored as 64 bit integers. |
509 | |
1068 | |
510 | THREADS |
1069 | THREADS |
511 | This module is *not* guaranteed to be thread safe and there are no plans |
1070 | This module is *not* guaranteed to be thread safe and there are no plans |
512 | to change this until Perl gets thread support (as opposed to the |
1071 | to change this until Perl gets thread support (as opposed to the |
513 | horribly slow so-called "threads" which are simply slow and bloated |
1072 | horribly slow so-called "threads" which are simply slow and bloated |