… | |
… | |
33 | with the added ability of supporting serialisation of Perl objects. |
33 | with the added ability of supporting serialisation of Perl objects. |
34 | (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 |
35 | compress the data later and speed is less important you might want to |
35 | compress the data later and speed is less important you might want to |
36 | compare both formats first). |
36 | compare both formats first). |
37 | |
37 | |
|
|
38 | The primary goal of this module is to be *correct* and the secondary |
|
|
39 | goal is to be *fast*. To reach the latter goal it was written in C. |
|
|
40 | |
38 | To give you a general idea about speed, with texts in the megabyte |
41 | To give you a general idea about speed, with texts in the megabyte |
39 | range, "CBOR::XS" usually encodes roughly twice as fast as Storable or |
42 | range, "CBOR::XS" usually encodes roughly twice as fast as Storable or |
40 | JSON::XS and decodes about 15%-30% faster than those. The shorter the |
43 | JSON::XS and decodes about 15%-30% faster than those. The shorter the |
41 | data, the worse Storable performs in comparison. |
44 | data, the worse Storable performs in comparison. |
42 | |
45 | |
… | |
… | |
47 | In addition to the core CBOR data format, this module implements a |
50 | In addition to the core CBOR data format, this module implements a |
48 | number of extensions, to support cyclic and shared data structures (see |
51 | number of extensions, to support cyclic and shared data structures (see |
49 | "allow_sharing" and "allow_cycles"), string deduplication (see |
52 | "allow_sharing" and "allow_cycles"), string deduplication (see |
50 | "pack_strings") and scalar references (always enabled). |
53 | "pack_strings") and scalar references (always enabled). |
51 | |
54 | |
52 | The primary goal of this module is to be *correct* and the secondary |
|
|
53 | goal is to be *fast*. To reach the latter goal it was written in C. |
|
|
54 | |
|
|
55 | 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 |
56 | vice versa. |
56 | vice versa. |
57 | |
57 | |
58 | FUNCTIONAL INTERFACE |
58 | FUNCTIONAL INTERFACE |
59 | The following convenience methods are provided by this module. They are |
59 | The following convenience methods are provided by this module. They are |
… | |
… | |
78 | |
78 | |
79 | 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 |
80 | calls can be chained: |
80 | calls can be chained: |
81 | |
81 | |
82 | my $cbor = CBOR::XS->new->encode ({a => [1,2]}); |
82 | my $cbor = CBOR::XS->new->encode ({a => [1,2]}); |
|
|
83 | |
|
|
84 | $cbor = new_safe CBOR::XS |
|
|
85 | Create a new, safe/secure CBOR::XS object. This is similar to "new", |
|
|
86 | but configures the coder object to be safe to use with untrusted |
|
|
87 | data. Currently, this is equivalent to: |
|
|
88 | |
|
|
89 | my $cbor = CBOR::XS |
|
|
90 | ->new |
|
|
91 | ->validate_utf8 |
|
|
92 | ->forbid_objects |
|
|
93 | ->filter (\&CBOR::XS::safe_filter) |
|
|
94 | ->max_size (1e8); |
|
|
95 | |
|
|
96 | But is more future proof (it is better to crash because of a change |
|
|
97 | than to be exploited in other ways). |
83 | |
98 | |
84 | $cbor = $cbor->max_depth ([$maximum_nesting_depth]) |
99 | $cbor = $cbor->max_depth ([$maximum_nesting_depth]) |
85 | $max_depth = $cbor->get_max_depth |
100 | $max_depth = $cbor->get_max_depth |
86 | Sets the maximum nesting level (default 512) accepted while encoding |
101 | Sets the maximum nesting level (default 512) accepted while encoding |
87 | or decoding. If a higher nesting level is detected in CBOR data or a |
102 | or decoding. If a higher nesting level is detected in CBOR data or a |
… | |
… | |
101 | |
116 | |
102 | Note that nesting is implemented by recursion in C. The default |
117 | Note that nesting is implemented by recursion in C. The default |
103 | value has been chosen to be as large as typical operating systems |
118 | value has been chosen to be as large as typical operating systems |
104 | allow without crashing. |
119 | allow without crashing. |
105 | |
120 | |
106 | See SECURITY CONSIDERATIONS, below, for more info on why this is |
121 | See "SECURITY CONSIDERATIONS", below, for more info on why this is |
107 | useful. |
122 | useful. |
108 | |
123 | |
109 | $cbor = $cbor->max_size ([$maximum_string_size]) |
124 | $cbor = $cbor->max_size ([$maximum_string_size]) |
110 | $max_size = $cbor->get_max_size |
125 | $max_size = $cbor->get_max_size |
111 | Set the maximum length a CBOR string may have (in bytes) where |
126 | Set the maximum length a CBOR string may have (in bytes) where |
… | |
… | |
115 | exception. This setting has no effect on "encode" (yet). |
130 | exception. This setting has no effect on "encode" (yet). |
116 | |
131 | |
117 | If no argument is given, the limit check will be deactivated (same |
132 | If no argument is given, the limit check will be deactivated (same |
118 | as when 0 is specified). |
133 | as when 0 is specified). |
119 | |
134 | |
120 | See SECURITY CONSIDERATIONS, below, for more info on why this is |
135 | See "SECURITY CONSIDERATIONS", below, for more info on why this is |
121 | useful. |
136 | useful. |
122 | |
137 | |
123 | $cbor = $cbor->allow_unknown ([$enable]) |
138 | $cbor = $cbor->allow_unknown ([$enable]) |
124 | $enabled = $cbor->get_allow_unknown |
139 | $enabled = $cbor->get_allow_unknown |
125 | If $enable is true (or missing), then "encode" will *not* throw an |
140 | If $enable is true (or missing), then "encode" will *not* throw an |
… | |
… | |
141 | instead will emit a reference to the earlier value. |
156 | instead will emit a reference to the earlier value. |
142 | |
157 | |
143 | This means that such values will only be encoded once, and will not |
158 | This means that such values will only be encoded once, and will not |
144 | result in a deep cloning of the value on decode, in decoders |
159 | result in a deep cloning of the value on decode, in decoders |
145 | supporting the value sharing extension. This also makes it possible |
160 | supporting the value sharing extension. This also makes it possible |
146 | to encode cyclic data structures (which need "allow_cycles" to ne |
161 | to encode cyclic data structures (which need "allow_cycles" to be |
147 | enabled to be decoded by this module). |
162 | enabled to be decoded by this module). |
148 | |
163 | |
149 | It is recommended to leave it off unless you know your communication |
164 | It is recommended to leave it off unless you know your communication |
150 | partner supports the value sharing extensions to CBOR |
165 | partner supports the value sharing extensions to CBOR |
151 | (<http://cbor.schmorp.de/value-sharing>), as without decoder |
166 | (<http://cbor.schmorp.de/value-sharing>), as without decoder |
152 | support, the resulting data structure might be unusable. |
167 | support, the resulting data structure might be unusable. |
153 | |
168 | |
154 | Detecting shared values incurs a runtime overhead when values are |
169 | Detecting shared values incurs a runtime overhead when values are |
155 | encoded that have a reference counter large than one, and might |
170 | encoded that have a reference counter large than one, and might |
156 | unnecessarily increase the encoded size, as potentially shared |
171 | unnecessarily increase the encoded size, as potentially shared |
157 | values are encode as shareable whether or not they are actually |
172 | values are encoded as shareable whether or not they are actually |
158 | shared. |
173 | shared. |
159 | |
174 | |
160 | At the moment, only targets of references can be shared (e.g. |
175 | At the moment, only targets of references can be shared (e.g. |
161 | scalars, arrays or hashes pointed to by a reference). Weirder |
176 | scalars, arrays or hashes pointed to by a reference). Weirder |
162 | constructs, such as an array with multiple "copies" of the *same* |
177 | constructs, such as an array with multiple "copies" of the *same* |
… | |
… | |
178 | code that isn't prepared for this will not leak memory. |
193 | code that isn't prepared for this will not leak memory. |
179 | |
194 | |
180 | If $enable is false (the default), then "decode" will throw an error |
195 | If $enable is false (the default), then "decode" will throw an error |
181 | when it encounters a self-referential/cyclic data structure. |
196 | when it encounters a self-referential/cyclic data structure. |
182 | |
197 | |
|
|
198 | FUTURE DIRECTION: the motivation behind this option is to avoid |
|
|
199 | *real* cycles - future versions of this module might chose to decode |
|
|
200 | cyclic data structures using weak references when this option is |
|
|
201 | off, instead of throwing an error. |
|
|
202 | |
183 | This option does not affect "encode" in any way - shared values and |
203 | This option does not affect "encode" in any way - shared values and |
184 | references will always be decoded properly if present. |
204 | references will always be encoded properly if present. |
|
|
205 | |
|
|
206 | $cbor = $cbor->forbid_objects ([$enable]) |
|
|
207 | $enabled = $cbor->get_forbid_objects |
|
|
208 | Disables the use of the object serialiser protocol. |
|
|
209 | |
|
|
210 | If $enable is true (or missing), then "encode" will will throw an |
|
|
211 | exception when it encounters perl objects that would be encoded |
|
|
212 | using the perl-object tag (26). When "decode" encounters such tags, |
|
|
213 | it will fall back to the general filter/tagged logic as if this were |
|
|
214 | an unknown tag (by default resulting in a "CBOR::XC::Tagged" |
|
|
215 | object). |
|
|
216 | |
|
|
217 | If $enable is false (the default), then "encode" will use the |
|
|
218 | Types::Serialiser object serialisation protocol to serialise objects |
|
|
219 | into perl-object tags, and "decode" will do the same to decode such |
|
|
220 | tags. |
|
|
221 | |
|
|
222 | See "SECURITY CONSIDERATIONS", below, for more info on why |
|
|
223 | forbidding this protocol can be useful. |
185 | |
224 | |
186 | $cbor = $cbor->pack_strings ([$enable]) |
225 | $cbor = $cbor->pack_strings ([$enable]) |
187 | $enabled = $cbor->get_pack_strings |
226 | $enabled = $cbor->get_pack_strings |
188 | If $enable is true (or missing), then "encode" will try not to |
227 | If $enable is true (or missing), then "encode" will try not to |
189 | encode the same string twice, but will instead encode a reference to |
228 | encode the same string twice, but will instead encode a reference to |
… | |
… | |
200 | the standard CBOR way. |
239 | the standard CBOR way. |
201 | |
240 | |
202 | This option does not affect "decode" in any way - string references |
241 | This option does not affect "decode" in any way - string references |
203 | will always be decoded properly if present. |
242 | will always be decoded properly if present. |
204 | |
243 | |
|
|
244 | $cbor = $cbor->text_keys ([$enable]) |
|
|
245 | $enabled = $cbor->get_text_keys |
|
|
246 | If $enabled is true (or missing), then "encode" will encode all perl |
|
|
247 | hash keys as CBOR text strings/UTF-8 string, upgrading them as |
|
|
248 | needed. |
|
|
249 | |
|
|
250 | If $enable is false (the default), then "encode" will encode hash |
|
|
251 | keys normally - upgraded perl strings (strings internally encoded as |
|
|
252 | UTF-8) as CBOR text strings, and downgraded perl strings as CBOR |
|
|
253 | byte strings. |
|
|
254 | |
|
|
255 | This option does not affect "decode" in any way. |
|
|
256 | |
|
|
257 | This option is useful for interoperability with CBOR decoders that |
|
|
258 | don't treat byte strings as a form of text. It is especially useful |
|
|
259 | as Perl gives very little control over hash keys. |
|
|
260 | |
|
|
261 | Enabling this option can be slow, as all downgraded hash keys that |
|
|
262 | are encoded need to be scanned and converted to UTF-8. |
|
|
263 | |
|
|
264 | $cbor = $cbor->text_strings ([$enable]) |
|
|
265 | $enabled = $cbor->get_text_strings |
|
|
266 | This option works similar to "text_keys", above, but works on all |
|
|
267 | strings (including hash keys), so "text_keys" has no further effect |
|
|
268 | after enabling "text_strings". |
|
|
269 | |
|
|
270 | If $enabled is true (or missing), then "encode" will encode all perl |
|
|
271 | strings as CBOR text strings/UTF-8 strings, upgrading them as |
|
|
272 | needed. |
|
|
273 | |
|
|
274 | If $enable is false (the default), then "encode" will encode strings |
|
|
275 | normally (but see "text_keys") - upgraded perl strings (strings |
|
|
276 | internally encoded as UTF-8) as CBOR text strings, and downgraded |
|
|
277 | perl strings as CBOR byte strings. |
|
|
278 | |
|
|
279 | This option does not affect "decode" in any way. |
|
|
280 | |
|
|
281 | This option has similar advantages and disadvantages as "text_keys". |
|
|
282 | In addition, this option effectively removes the ability to |
|
|
283 | automatically encode byte strings, which might break some "FREEZE" |
|
|
284 | and "TO_CBOR" methods that rely on this. |
|
|
285 | |
|
|
286 | A workaround is to use explicit type casts, which are unaffected by |
|
|
287 | this option. |
|
|
288 | |
205 | $cbor = $cbor->validate_utf8 ([$enable]) |
289 | $cbor = $cbor->validate_utf8 ([$enable]) |
206 | $enabled = $cbor->get_validate_utf8 |
290 | $enabled = $cbor->get_validate_utf8 |
207 | If $enable is true (or missing), then "decode" will validate that |
291 | If $enable is true (or missing), then "decode" will validate that |
208 | elements (text strings) containing UTF-8 data in fact contain valid |
292 | elements (text strings) containing UTF-8 data in fact contain valid |
209 | UTF-8 data (instead of blindly accepting it). This validation |
293 | UTF-8 data (instead of blindly accepting it). This validation |
… | |
… | |
212 | The concept of "valid UTF-8" used is perl's concept, which is a |
296 | The concept of "valid UTF-8" used is perl's concept, which is a |
213 | superset of the official UTF-8. |
297 | superset of the official UTF-8. |
214 | |
298 | |
215 | If $enable is false (the default), then "decode" will blindly accept |
299 | If $enable is false (the default), then "decode" will blindly accept |
216 | UTF-8 data, marking them as valid UTF-8 in the resulting data |
300 | UTF-8 data, marking them as valid UTF-8 in the resulting data |
217 | structure regardless of whether thats true or not. |
301 | structure regardless of whether that's true or not. |
218 | |
302 | |
219 | Perl isn't too happy about corrupted UTF-8 in strings, but should |
303 | Perl isn't too happy about corrupted UTF-8 in strings, but should |
220 | generally not crash or do similarly evil things. Extensions might be |
304 | generally not crash or do similarly evil things. Extensions might be |
221 | not so forgiving, so it's recommended to turn on this setting if you |
305 | not so forgiving, so it's recommended to turn on this setting if you |
222 | receive untrusted CBOR. |
306 | receive untrusted CBOR. |
… | |
… | |
249 | When the filter is cleared (the default state), the default filter |
333 | When the filter is cleared (the default state), the default filter |
250 | function, "CBOR::XS::default_filter", is used. This function simply |
334 | function, "CBOR::XS::default_filter", is used. This function simply |
251 | looks up the tag in the %CBOR::XS::FILTER hash. If an entry exists |
335 | looks up the tag in the %CBOR::XS::FILTER hash. If an entry exists |
252 | it must be a code reference that is called with tag and value, and |
336 | it must be a code reference that is called with tag and value, and |
253 | is responsible for decoding the value. If no entry exists, it |
337 | is responsible for decoding the value. If no entry exists, it |
254 | returns no values. |
338 | returns no values. "CBOR::XS" provides a number of default filter |
|
|
339 | functions already, the the %CBOR::XS::FILTER hash can be freely |
|
|
340 | extended with more. |
|
|
341 | |
|
|
342 | "CBOR::XS" additionally provides an alternative filter function that |
|
|
343 | is supposed to be safe to use with untrusted data (which the default |
|
|
344 | filter might not), called "CBOR::XS::safe_filter", which works the |
|
|
345 | same as the "default_filter" but uses the %CBOR::XS::SAFE_FILTER |
|
|
346 | variable instead. It is prepopulated with the tag decoding functions |
|
|
347 | that are deemed safe (basically the same as %CBOR::XS::FILTER |
|
|
348 | without all the bignum tags), and can be extended by user code as |
|
|
349 | wlel, although, obviously, one should be very careful about adding |
|
|
350 | decoding functions here, since the expectation is that they are safe |
|
|
351 | to use on untrusted data, after all. |
255 | |
352 | |
256 | Example: decode all tags not handled internally into |
353 | Example: decode all tags not handled internally into |
257 | "CBOR::XS::Tagged" objects, with no other special handling (useful |
354 | "CBOR::XS::Tagged" objects, with no other special handling (useful |
258 | when working with potentially "unsafe" CBOR data). |
355 | when working with potentially "unsafe" CBOR data). |
259 | |
356 | |
… | |
… | |
265 | $CBOR::XS::FILTER{1347375694} = sub { |
362 | $CBOR::XS::FILTER{1347375694} = sub { |
266 | my ($tag, $value); |
363 | my ($tag, $value); |
267 | |
364 | |
268 | "tag 1347375694 value $value" |
365 | "tag 1347375694 value $value" |
269 | }; |
366 | }; |
|
|
367 | |
|
|
368 | Example: provide your own filter function that looks up tags in your |
|
|
369 | own hash: |
|
|
370 | |
|
|
371 | my %my_filter = ( |
|
|
372 | 998347484 => sub { |
|
|
373 | my ($tag, $value); |
|
|
374 | |
|
|
375 | "tag 998347484 value $value" |
|
|
376 | }; |
|
|
377 | ); |
|
|
378 | |
|
|
379 | my $coder = CBOR::XS->new->filter (sub { |
|
|
380 | &{ $my_filter{$_[0]} or return } |
|
|
381 | }); |
|
|
382 | |
|
|
383 | Example: use the safe filter function (see "SECURITY CONSIDERATIONS" |
|
|
384 | for more considerations on security). |
|
|
385 | |
|
|
386 | CBOR::XS->new->filter (\&CBOR::XS::safe_filter)->decode ($cbor_data); |
270 | |
387 | |
271 | $cbor_data = $cbor->encode ($perl_scalar) |
388 | $cbor_data = $cbor->encode ($perl_scalar) |
272 | Converts the given Perl data structure (a scalar value) to its CBOR |
389 | Converts the given Perl data structure (a scalar value) to its CBOR |
273 | representation. |
390 | representation. |
274 | |
391 | |
… | |
… | |
282 | will silently stop parsing there and return the number of characters |
399 | will silently stop parsing there and return the number of characters |
283 | consumed so far. |
400 | consumed so far. |
284 | |
401 | |
285 | This is useful if your CBOR texts are not delimited by an outer |
402 | This is useful if your CBOR texts are not delimited by an outer |
286 | protocol and you need to know where the first CBOR string ends amd |
403 | protocol and you need to know where the first CBOR string ends amd |
287 | the next one starts. |
404 | the next one starts - CBOR strings are self-delimited, so it is |
|
|
405 | possible to concatenate CBOR strings without any delimiters or size |
|
|
406 | fields and recover their data. |
288 | |
407 | |
289 | CBOR::XS->new->decode_prefix ("......") |
408 | CBOR::XS->new->decode_prefix ("......") |
290 | => ("...", 3) |
409 | => ("...", 3) |
291 | |
410 | |
292 | INCREMENTAL PARSING |
411 | INCREMENTAL PARSING |
… | |
… | |
341 | $cbor->incr_reset |
460 | $cbor->incr_reset |
342 | Resets the incremental decoder. This throws away any saved state, so |
461 | Resets the incremental decoder. This throws away any saved state, so |
343 | that subsequent calls to "incr_parse" or "incr_parse_multiple" start |
462 | that subsequent calls to "incr_parse" or "incr_parse_multiple" start |
344 | to parse a new CBOR value from the beginning of the $buffer again. |
463 | to parse a new CBOR value from the beginning of the $buffer again. |
345 | |
464 | |
346 | This method can be caled at any time, but it *must* be called if you |
465 | This method can be called at any time, but it *must* be called if |
347 | want to change your $buffer or there was a decoding error and you |
466 | you want to change your $buffer or there was a decoding error and |
348 | want to reuse the $cbor object for future incremental parsings. |
467 | you want to reuse the $cbor object for future incremental parsings. |
349 | |
468 | |
350 | MAPPING |
469 | MAPPING |
351 | This section describes how CBOR::XS maps Perl values to CBOR values and |
470 | This section describes how CBOR::XS maps Perl values to CBOR values and |
352 | vice versa. These mappings are designed to "do the right thing" in most |
471 | vice versa. These mappings are designed to "do the right thing" in most |
353 | circumstances automatically, preserving round-tripping characteristics |
472 | circumstances automatically, preserving round-tripping characteristics |
… | |
… | |
404 | |
523 | |
405 | hash references |
524 | hash references |
406 | Perl hash references become CBOR maps. As there is no inherent |
525 | Perl hash references become CBOR maps. As there is no inherent |
407 | ordering in hash keys (or CBOR maps), they will usually be encoded |
526 | ordering in hash keys (or CBOR maps), they will usually be encoded |
408 | in a pseudo-random order. This order can be different each time a |
527 | in a pseudo-random order. This order can be different each time a |
409 | hahs is encoded. |
528 | hash is encoded. |
410 | |
529 | |
411 | Currently, tied hashes will use the indefinite-length format, while |
530 | Currently, tied hashes will use the indefinite-length format, while |
412 | normal hashes will use the fixed-length format. |
531 | normal hashes will use the fixed-length format. |
413 | |
532 | |
414 | array references |
533 | array references |
… | |
… | |
463 | my $x = 3.1; # some variable containing a number |
582 | my $x = 3.1; # some variable containing a number |
464 | "$x"; # stringified |
583 | "$x"; # stringified |
465 | $x .= ""; # another, more awkward way to stringify |
584 | $x .= ""; # another, more awkward way to stringify |
466 | print $x; # perl does it for you, too, quite often |
585 | print $x; # perl does it for you, too, quite often |
467 | |
586 | |
468 | You can force whether a string ie encoded as byte or text string by |
587 | You can force whether a string is encoded as byte or text string by |
469 | using "utf8::upgrade" and "utf8::downgrade"): |
588 | using "utf8::upgrade" and "utf8::downgrade" (if "text_strings" is |
|
|
589 | disabled). |
470 | |
590 | |
471 | utf8::upgrade $x; # encode $x as text string |
591 | utf8::upgrade $x; # encode $x as text string |
472 | utf8::downgrade $x; # encode $x as byte string |
592 | utf8::downgrade $x; # encode $x as byte string |
473 | |
593 | |
|
|
594 | More options are available, see "TYPE CASTS", below, and the |
|
|
595 | "text_keys" and "text_strings" options. |
|
|
596 | |
474 | Perl doesn't define what operations up- and downgrade strings, so if |
597 | Perl doesn't define what operations up- and downgrade strings, so if |
475 | the difference between byte and text is important, you should up- or |
598 | the difference between byte and text is important, you should up- or |
476 | downgrade your string as late as possible before encoding. |
599 | downgrade your string as late as possible before encoding. You can |
|
|
600 | also force the use of CBOR text strings by using "text_keys" or |
|
|
601 | "text_strings". |
477 | |
602 | |
478 | You can force the type to be a CBOR number by numifying it: |
603 | You can force the type to be a CBOR number by numifying it: |
479 | |
604 | |
480 | my $x = "3"; # some variable containing a string |
605 | my $x = "3"; # some variable containing a string |
481 | $x += 0; # numify it, ensuring it will be dumped as a number |
606 | $x += 0; # numify it, ensuring it will be dumped as a number |
… | |
… | |
490 | IEEE single format if possible without loss of precision, otherwise |
615 | IEEE single format if possible without loss of precision, otherwise |
491 | the IEEE double format will be used. Perls that use formats other |
616 | the IEEE double format will be used. Perls that use formats other |
492 | than IEEE double to represent numerical values are supported, but |
617 | than IEEE double to represent numerical values are supported, but |
493 | might suffer loss of precision. |
618 | might suffer loss of precision. |
494 | |
619 | |
|
|
620 | TYPE CASTS |
|
|
621 | EXPERIMENTAL: As an experimental extension, "CBOR::XS" allows you to |
|
|
622 | force specific CBOR types to be used when encoding. That allows you to |
|
|
623 | encode types not normally accessible (e.g. half floats) as well as force |
|
|
624 | string types even when "text_strings" is in effect. |
|
|
625 | |
|
|
626 | Type forcing is done by calling a special "cast" function which keeps a |
|
|
627 | copy of the value and returns a new value that can be handed over to any |
|
|
628 | CBOR encoder function. |
|
|
629 | |
|
|
630 | The following casts are currently available (all of which are unary |
|
|
631 | operators, that is, have a prototype of "$"): |
|
|
632 | |
|
|
633 | CBOR::XS::as_int $value |
|
|
634 | Forces the value to be encoded as some form of (basic, not bignum) |
|
|
635 | integer type. |
|
|
636 | |
|
|
637 | CBOR::XS::as_text $value |
|
|
638 | Forces the value to be encoded as (UTF-8) text values. |
|
|
639 | |
|
|
640 | CBOR::XS::as_bytes $value |
|
|
641 | Forces the value to be encoded as a (binary) string value. |
|
|
642 | |
|
|
643 | Example: encode a perl string as binary even though "text_strings" |
|
|
644 | is in effect. |
|
|
645 | |
|
|
646 | CBOR::XS->new->text_strings->encode ([4, "text", CBOR::XS::bytes "bytevalue"]); |
|
|
647 | |
|
|
648 | CBOR::XS::as_bool $value |
|
|
649 | Converts a Perl boolean (which can be any kind of scalar) into a |
|
|
650 | CBOR boolean. Strictly the same, but shorter to write, than: |
|
|
651 | |
|
|
652 | $value ? Types::Serialiser::true : Types::Serialiser::false |
|
|
653 | |
|
|
654 | CBOR::XS::as_float16 $value |
|
|
655 | Forces half-float (IEEE 754 binary16) encoding of the given value. |
|
|
656 | |
|
|
657 | CBOR::XS::as_float32 $value |
|
|
658 | Forces single-float (IEEE 754 binary32) encoding of the given value. |
|
|
659 | |
|
|
660 | CBOR::XS::as_float64 $value |
|
|
661 | Forces double-float (IEEE 754 binary64) encoding of the given value. |
|
|
662 | |
|
|
663 | CBOR::XS::as_cbor $cbor_text |
|
|
664 | Not a type cast per-se, this type cast forces the argument to be |
|
|
665 | encoded as-is. This can be used to embed pre-encoded CBOR data. |
|
|
666 | |
|
|
667 | Note that no checking on the validity of the $cbor_text is done - |
|
|
668 | it's the callers responsibility to correctly encode values. |
|
|
669 | |
|
|
670 | CBOR::XS::as_map [key => value...] |
|
|
671 | Treat the array reference as key value pairs and output a CBOR map. |
|
|
672 | This allows you to generate CBOR maps with arbitrary key types (or, |
|
|
673 | if you don't care about semantics, duplicate keys or pairs in a |
|
|
674 | custom order), which is otherwise hard to do with Perl. |
|
|
675 | |
|
|
676 | The single argument must be an array reference with an even number |
|
|
677 | of elements. |
|
|
678 | |
|
|
679 | Note that only the reference to the array is copied, the array |
|
|
680 | itself is not. Modifications done to the array before calling an |
|
|
681 | encoding function will be reflected in the encoded output. |
|
|
682 | |
|
|
683 | Example: encode a CBOR map with a string and an integer as keys. |
|
|
684 | |
|
|
685 | encode_cbor CBOR::XS::as_map [string => "value", 5 => "value"] |
|
|
686 | |
495 | OBJECT SERIALISATION |
687 | OBJECT SERIALISATION |
496 | This module implements both a CBOR-specific and the generic |
688 | This module implements both a CBOR-specific and the generic |
497 | Types::Serialier object serialisation protocol. The following |
689 | Types::Serialier object serialisation protocol. The following |
498 | subsections explain both methods. |
690 | subsections explain both methods. |
499 | |
691 | |
… | |
… | |
576 | "$self" # encode url string |
768 | "$self" # encode url string |
577 | } |
769 | } |
578 | |
770 | |
579 | sub URI::THAW { |
771 | sub URI::THAW { |
580 | my ($class, $serialiser, $uri) = @_; |
772 | my ($class, $serialiser, $uri) = @_; |
581 | |
|
|
582 | $class->new ($uri) |
773 | $class->new ($uri) |
583 | } |
774 | } |
584 | |
775 | |
585 | Unlike "TO_CBOR", multiple values can be returned by "FREEZE". For |
776 | Unlike "TO_CBOR", multiple values can be returned by "FREEZE". For |
586 | example, a "FREEZE" method that returns "type", "id" and "variant" |
777 | example, a "FREEZE" method that returns "type", "id" and "variant" |
… | |
… | |
682 | Future versions of this module reserve the right to special case |
873 | Future versions of this module reserve the right to special case |
683 | additional tags (such as base64url). |
874 | additional tags (such as base64url). |
684 | |
875 | |
685 | ENFORCED TAGS |
876 | ENFORCED TAGS |
686 | These tags are always handled when decoding, and their handling cannot |
877 | These tags are always handled when decoding, and their handling cannot |
687 | be overriden by the user. |
878 | be overridden by the user. |
688 | |
879 | |
689 | 26 (perl-object, <http://cbor.schmorp.de/perl-object>) |
880 | 26 (perl-object, <http://cbor.schmorp.de/perl-object>) |
690 | These tags are automatically created (and decoded) for serialisable |
881 | These tags are automatically created (and decoded) for serialisable |
691 | objects using the "FREEZE/THAW" methods (the Types::Serialier object |
882 | objects using the "FREEZE/THAW" methods (the Types::Serialier object |
692 | serialisation protocol). See "OBJECT SERIALISATION" for details. |
883 | serialisation protocol). See "OBJECT SERIALISATION" for details. |
693 | |
884 | |
694 | 28, 29 (shareable, sharedref, L <http://cbor.schmorp.de/value-sharing>) |
885 | 28, 29 (shareable, sharedref, <http://cbor.schmorp.de/value-sharing>) |
695 | These tags are automatically decoded when encountered (and they do |
886 | These tags are automatically decoded when encountered (and they do |
696 | not result in a cyclic data structure, see "allow_cycles"), |
887 | not result in a cyclic data structure, see "allow_cycles"), |
697 | resulting in shared values in the decoded object. They are only |
888 | resulting in shared values in the decoded object. They are only |
698 | encoded, however, when "allow_sharing" is enabled. |
889 | encoded, however, when "allow_sharing" is enabled. |
699 | |
890 | |
… | |
… | |
708 | references will be shared, others will not. While non-reference |
899 | references will be shared, others will not. While non-reference |
709 | shared values can be generated in Perl with some effort, they were |
900 | shared values can be generated in Perl with some effort, they were |
710 | considered too unimportant to be supported in the encoder. The |
901 | considered too unimportant to be supported in the encoder. The |
711 | decoder, however, will decode these values as shared values. |
902 | decoder, however, will decode these values as shared values. |
712 | |
903 | |
713 | 256, 25 (stringref-namespace, stringref, L |
904 | 256, 25 (stringref-namespace, stringref, |
714 | <http://cbor.schmorp.de/stringref>) |
905 | <http://cbor.schmorp.de/stringref>) |
715 | These tags are automatically decoded when encountered. They are only |
906 | These tags are automatically decoded when encountered. They are only |
716 | encoded, however, when "pack_strings" is enabled. |
907 | encoded, however, when "pack_strings" is enabled. |
717 | |
908 | |
718 | 22098 (indirection, <http://cbor.schmorp.de/indirection>) |
909 | 22098 (indirection, <http://cbor.schmorp.de/indirection>) |
719 | This tag is automatically generated when a reference are encountered |
910 | This tag is automatically generated when a reference are encountered |
720 | (with the exception of hash and array refernces). It is converted to |
911 | (with the exception of hash and array references). It is converted |
721 | a reference when decoding. |
912 | to a reference when decoding. |
722 | |
913 | |
723 | 55799 (self-describe CBOR, RFC 7049) |
914 | 55799 (self-describe CBOR, RFC 7049) |
724 | This value is not generated on encoding (unless explicitly requested |
915 | This value is not generated on encoding (unless explicitly requested |
725 | by the user), and is simply ignored when decoding. |
916 | by the user), and is simply ignored when decoding. |
726 | |
917 | |
727 | NON-ENFORCED TAGS |
918 | NON-ENFORCED TAGS |
728 | These tags have default filters provided when decoding. Their handling |
919 | These tags have default filters provided when decoding. Their handling |
729 | can be overriden by changing the %CBOR::XS::FILTER entry for the tag, or |
920 | can be overridden by changing the %CBOR::XS::FILTER entry for the tag, |
730 | by providing a custom "filter" callback when decoding. |
921 | or by providing a custom "filter" callback when decoding. |
731 | |
922 | |
732 | When they result in decoding into a specific Perl class, the module |
923 | When they result in decoding into a specific Perl class, the module |
733 | usually provides a corresponding "TO_CBOR" method as well. |
924 | usually provides a corresponding "TO_CBOR" method as well. |
734 | |
925 | |
735 | When any of these need to load additional modules that are not part of |
926 | When any of these need to load additional modules that are not part of |
… | |
… | |
750 | 2, 3 (positive/negative bignum) |
941 | 2, 3 (positive/negative bignum) |
751 | These tags are decoded into Math::BigInt objects. The corresponding |
942 | These tags are decoded into Math::BigInt objects. The corresponding |
752 | "Math::BigInt::TO_CBOR" method encodes "small" bigints into normal |
943 | "Math::BigInt::TO_CBOR" method encodes "small" bigints into normal |
753 | CBOR integers, and others into positive/negative CBOR bignums. |
944 | CBOR integers, and others into positive/negative CBOR bignums. |
754 | |
945 | |
755 | 4, 5 (decimal fraction/bigfloat) |
946 | 4, 5, 264, 265 (decimal fraction/bigfloat) |
756 | Both decimal fractions and bigfloats are decoded into Math::BigFloat |
947 | Both decimal fractions and bigfloats are decoded into Math::BigFloat |
757 | objects. The corresponding "Math::BigFloat::TO_CBOR" method *always* |
948 | objects. The corresponding "Math::BigFloat::TO_CBOR" method *always* |
758 | encodes into a decimal fraction. |
949 | encodes into a decimal fraction (either tag 4 or 264). |
759 | |
950 | |
760 | CBOR cannot represent bigfloats with *very* large exponents - |
|
|
761 | conversion of such big float objects is undefined. |
|
|
762 | |
|
|
763 | Also, NaN and infinities are not encoded properly. |
951 | NaN and infinities are not encoded properly, as they cannot be |
|
|
952 | represented in CBOR. |
|
|
953 | |
|
|
954 | See "BIGNUM SECURITY CONSIDERATIONS" for more info. |
|
|
955 | |
|
|
956 | 30 (rational numbers) |
|
|
957 | These tags are decoded into Math::BigRat objects. The corresponding |
|
|
958 | "Math::BigRat::TO_CBOR" method encodes rational numbers with |
|
|
959 | denominator 1 via their numerator only, i.e., they become normal |
|
|
960 | integers or "bignums". |
|
|
961 | |
|
|
962 | See "BIGNUM SECURITY CONSIDERATIONS" for more info. |
764 | |
963 | |
765 | 21, 22, 23 (expected later JSON conversion) |
964 | 21, 22, 23 (expected later JSON conversion) |
766 | CBOR::XS is not a CBOR-to-JSON converter, and will simply ignore |
965 | CBOR::XS is not a CBOR-to-JSON converter, and will simply ignore |
767 | these tags. |
966 | these tags. |
768 | |
967 | |
… | |
… | |
782 | interoperability is improved in the future, then the goal will be to |
981 | interoperability is improved in the future, then the goal will be to |
783 | ensure that decoded JSON data will round-trip encoding and decoding to |
982 | ensure that decoded JSON data will round-trip encoding and decoding to |
784 | CBOR intact. |
983 | CBOR intact. |
785 | |
984 | |
786 | SECURITY CONSIDERATIONS |
985 | SECURITY CONSIDERATIONS |
787 | When you are using CBOR in a protocol, talking to untrusted potentially |
986 | Tl;dr... if you want to decode or encode CBOR from untrusted sources, |
788 | hostile creatures requires relatively few measures. |
987 | you should start with a coder object created via "new_safe" (which |
|
|
988 | implements the mitigations explained below): |
789 | |
989 | |
|
|
990 | my $coder = CBOR::XS->new_safe; |
|
|
991 | |
|
|
992 | my $data = $coder->decode ($cbor_text); |
|
|
993 | my $cbor = $coder->encode ($data); |
|
|
994 | |
|
|
995 | Longer version: When you are using CBOR in a protocol, talking to |
|
|
996 | untrusted potentially hostile creatures requires some thought: |
|
|
997 | |
|
|
998 | Security of the CBOR decoder itself |
790 | First of all, your CBOR decoder should be secure, that is, should not |
999 | First and foremost, your CBOR decoder should be secure, that is, |
791 | have any buffer overflows. Obviously, this module should ensure that and |
1000 | should not have any buffer overflows or similar bugs that could |
|
|
1001 | potentially be exploited. Obviously, this module should ensure that |
792 | I am trying hard on making that true, but you never know. |
1002 | and I am trying hard on making that true, but you never know. |
793 | |
1003 | |
|
|
1004 | CBOR::XS can invoke almost arbitrary callbacks during decoding |
|
|
1005 | CBOR::XS supports object serialisation - decoding CBOR can cause |
|
|
1006 | calls to *any* "THAW" method in *any* package that exists in your |
|
|
1007 | process (that is, CBOR::XS will not try to load modules, but any |
|
|
1008 | existing "THAW" method or function can be called, so they all have |
|
|
1009 | to be secure). |
|
|
1010 | |
|
|
1011 | Less obviously, it will also invoke "TO_CBOR" and "FREEZE" methods - |
|
|
1012 | even if all your "THAW" methods are secure, encoding data structures |
|
|
1013 | from untrusted sources can invoke those and trigger bugs in those. |
|
|
1014 | |
|
|
1015 | So, if you are not sure about the security of all the modules you |
|
|
1016 | have loaded (you shouldn't), you should disable this part using |
|
|
1017 | "forbid_objects" or using "new_safe". |
|
|
1018 | |
|
|
1019 | CBOR can be extended with tags that call library code |
|
|
1020 | CBOR can be extended with tags, and "CBOR::XS" has a registry of |
|
|
1021 | conversion functions for many existing tags that can be extended via |
|
|
1022 | third-party modules (see the "filter" method). |
|
|
1023 | |
|
|
1024 | If you don't trust these, you should configure the "safe" filter |
|
|
1025 | function, "CBOR::XS::safe_filter" ("new_safe" does this), which by |
|
|
1026 | default only includes conversion functions that are considered |
|
|
1027 | "safe" by the author (but again, they can be extended by third party |
|
|
1028 | modules). |
|
|
1029 | |
|
|
1030 | Depending on your level of paranoia, you can use the "safe" filter: |
|
|
1031 | |
|
|
1032 | $cbor->filter (\&CBOR::XS::safe_filter); |
|
|
1033 | |
|
|
1034 | ... your own filter... |
|
|
1035 | |
|
|
1036 | $cbor->filter (sub { ... do your stuffs here ... }); |
|
|
1037 | |
|
|
1038 | ... or even no filter at all, disabling all tag decoding: |
|
|
1039 | |
|
|
1040 | $cbor->filter (sub { }); |
|
|
1041 | |
|
|
1042 | This is never a problem for encoding, as the tag mechanism only |
|
|
1043 | exists in CBOR texts. |
|
|
1044 | |
|
|
1045 | Resource-starving attacks: object memory usage |
794 | Second, you need to avoid resource-starving attacks. That means you |
1046 | You need to avoid resource-starving attacks. That means you should |
795 | should limit the size of CBOR data you accept, or make sure then when |
1047 | limit the size of CBOR data you accept, or make sure then when your |
796 | your resources run out, that's just fine (e.g. by using a separate |
1048 | resources run out, that's just fine (e.g. by using a separate |
797 | process that can crash safely). The size of a CBOR string in octets is |
1049 | process that can crash safely). The size of a CBOR string in octets |
798 | usually a good indication of the size of the resources required to |
1050 | is usually a good indication of the size of the resources required |
799 | decode it into a Perl structure. While CBOR::XS can check the size of |
1051 | to decode it into a Perl structure. While CBOR::XS can check the |
|
|
1052 | size of the CBOR text (using "max_size" - done by "new_safe"), it |
800 | the CBOR text, it might be too late when you already have it in memory, |
1053 | might be too late when you already have it in memory, so you might |
801 | so you might want to check the size before you accept the string. |
1054 | want to check the size before you accept the string. |
802 | |
1055 | |
|
|
1056 | As for encoding, it is possible to construct data structures that |
|
|
1057 | are relatively small but result in large CBOR texts (for example by |
|
|
1058 | having an array full of references to the same big data structure, |
|
|
1059 | which will all be deep-cloned during encoding by default). This is |
|
|
1060 | rarely an actual issue (and the worst case is still just running out |
|
|
1061 | of memory), but you can reduce this risk by using "allow_sharing". |
|
|
1062 | |
|
|
1063 | Resource-starving attacks: stack overflows |
803 | Third, CBOR::XS recurses using the C stack when decoding objects and |
1064 | CBOR::XS recurses using the C stack when decoding objects and |
804 | arrays. The C stack is a limited resource: for instance, on my amd64 |
1065 | arrays. The C stack is a limited resource: for instance, on my amd64 |
805 | machine with 8MB of stack size I can decode around 180k nested arrays |
1066 | machine with 8MB of stack size I can decode around 180k nested |
806 | but only 14k nested CBOR objects (due to perl itself recursing deeply on |
1067 | arrays but only 14k nested CBOR objects (due to perl itself |
807 | croak to free the temporary). If that is exceeded, the program crashes. |
1068 | recursing deeply on croak to free the temporary). If that is |
808 | To be conservative, the default nesting limit is set to 512. If your |
1069 | exceeded, the program crashes. To be conservative, the default |
809 | process has a smaller stack, you should adjust this setting accordingly |
1070 | nesting limit is set to 512. If your process has a smaller stack, |
810 | with the "max_depth" method. |
1071 | you should adjust this setting accordingly with the "max_depth" |
|
|
1072 | method. |
811 | |
1073 | |
|
|
1074 | Resource-starving attacks: CPU en-/decoding complexity |
|
|
1075 | CBOR::XS will use the Math::BigInt, Math::BigFloat and Math::BigRat |
|
|
1076 | libraries to represent encode/decode bignums. These can be very slow |
|
|
1077 | (as in, centuries of CPU time) and can even crash your program (and |
|
|
1078 | are generally not very trustworthy). See the next section on bignum |
|
|
1079 | security for details. |
|
|
1080 | |
|
|
1081 | Data breaches: leaking information in error messages |
|
|
1082 | CBOR::XS might leak contents of your Perl data structures in its |
|
|
1083 | error messages, so when you serialise sensitive information you |
|
|
1084 | might want to make sure that exceptions thrown by CBOR::XS will not |
|
|
1085 | end up in front of untrusted eyes. |
|
|
1086 | |
|
|
1087 | Something else... |
812 | Something else could bomb you, too, that I forgot to think of. In that |
1088 | Something else could bomb you, too, that I forgot to think of. In |
813 | case, you get to keep the pieces. I am always open for hints, though... |
1089 | that case, you get to keep the pieces. I am always open for hints, |
|
|
1090 | though... |
814 | |
1091 | |
815 | Also keep in mind that CBOR::XS might leak contents of your Perl data |
1092 | BIGNUM SECURITY CONSIDERATIONS |
816 | structures in its error messages, so when you serialise sensitive |
1093 | CBOR::XS provides a "TO_CBOR" method for both Math::BigInt and |
817 | information you might want to make sure that exceptions thrown by |
1094 | Math::BigFloat that tries to encode the number in the simplest possible |
818 | CBOR::XS will not end up in front of untrusted eyes. |
1095 | way, that is, either a CBOR integer, a CBOR bigint/decimal fraction (tag |
|
|
1096 | 4) or an arbitrary-exponent decimal fraction (tag 264). Rational numbers |
|
|
1097 | (Math::BigRat, tag 30) can also contain bignums as members. |
|
|
1098 | |
|
|
1099 | CBOR::XS will also understand base-2 bigfloat or arbitrary-exponent |
|
|
1100 | bigfloats (tags 5 and 265), but it will never generate these on its own. |
|
|
1101 | |
|
|
1102 | Using the built-in Math::BigInt::Calc support, encoding and decoding |
|
|
1103 | decimal fractions is generally fast. Decoding bigints can be slow for |
|
|
1104 | very big numbers (tens of thousands of digits, something that could |
|
|
1105 | potentially be caught by limiting the size of CBOR texts), and decoding |
|
|
1106 | bigfloats or arbitrary-exponent bigfloats can be *extremely* slow |
|
|
1107 | (minutes, decades) for large exponents (roughly 40 bit and longer). |
|
|
1108 | |
|
|
1109 | Additionally, Math::BigInt can take advantage of other bignum libraries, |
|
|
1110 | such as Math::GMP, which cannot handle big floats with large exponents, |
|
|
1111 | and might simply abort or crash your program, due to their code quality. |
|
|
1112 | |
|
|
1113 | This can be a concern if you want to parse untrusted CBOR. If it is, you |
|
|
1114 | might want to disable decoding of tag 2 (bigint) and 3 (negative bigint) |
|
|
1115 | types. You should also disable types 5 and 265, as these can be slow |
|
|
1116 | even without bigints. |
|
|
1117 | |
|
|
1118 | Disabling bigints will also partially or fully disable types that rely |
|
|
1119 | on them, e.g. rational numbers that use bignums. |
819 | |
1120 | |
820 | CBOR IMPLEMENTATION NOTES |
1121 | CBOR IMPLEMENTATION NOTES |
821 | This section contains some random implementation notes. They do not |
1122 | This section contains some random implementation notes. They do not |
822 | describe guaranteed behaviour, but merely behaviour as-is implemented |
1123 | describe guaranteed behaviour, but merely behaviour as-is implemented |
823 | right now. |
1124 | right now. |
… | |
… | |
834 | |
1135 | |
835 | Strict mode and canonical mode are not implemented. |
1136 | Strict mode and canonical mode are not implemented. |
836 | |
1137 | |
837 | LIMITATIONS ON PERLS WITHOUT 64-BIT INTEGER SUPPORT |
1138 | LIMITATIONS ON PERLS WITHOUT 64-BIT INTEGER SUPPORT |
838 | On perls that were built without 64 bit integer support (these are rare |
1139 | On perls that were built without 64 bit integer support (these are rare |
839 | nowadays, even on 32 bit architectures), support for any kind of 64 bit |
1140 | nowadays, even on 32 bit architectures, as all major Perl distributions |
|
|
1141 | are built with 64 bit integer support), support for any kind of 64 bit |
840 | integer in CBOR is very limited - most likely, these 64 bit values will |
1142 | value in CBOR is very limited - most likely, these 64 bit values will be |
841 | be truncated, corrupted, or otherwise not decoded correctly. This also |
1143 | truncated, corrupted, or otherwise not decoded correctly. This also |
842 | includes string, array and map sizes that are stored as 64 bit integers. |
1144 | includes string, float, array and map sizes that are stored as 64 bit |
|
|
1145 | integers. |
843 | |
1146 | |
844 | THREADS |
1147 | THREADS |
845 | This module is *not* guaranteed to be thread safe and there are no plans |
1148 | This module is *not* guaranteed to be thread safe and there are no plans |
846 | to change this until Perl gets thread support (as opposed to the |
1149 | to change this until Perl gets thread support (as opposed to the |
847 | horribly slow so-called "threads" which are simply slow and bloated |
1150 | horribly slow so-called "threads" which are simply slow and bloated |