|
|
1 | NAME |
|
|
2 | CBOR::XS - Concise Binary Object Representation (CBOR, RFC7049) |
|
|
3 | |
|
|
4 | SYNOPSIS |
|
|
5 | use CBOR::XS; |
|
|
6 | |
|
|
7 | $binary_cbor_data = encode_cbor $perl_value; |
|
|
8 | $perl_value = decode_cbor $binary_cbor_data; |
|
|
9 | |
|
|
10 | # OO-interface |
|
|
11 | |
|
|
12 | $coder = CBOR::XS->new; |
|
|
13 | $binary_cbor_data = $coder->encode ($perl_value); |
|
|
14 | $perl_value = $coder->decode ($binary_cbor_data); |
|
|
15 | |
|
|
16 | # prefix decoding |
|
|
17 | |
|
|
18 | my $many_cbor_strings = ...; |
|
|
19 | while (length $many_cbor_strings) { |
|
|
20 | my ($data, $length) = $cbor->decode_prefix ($many_cbor_strings); |
|
|
21 | # data was decoded |
|
|
22 | substr $many_cbor_strings, 0, $length, ""; # remove decoded cbor string |
|
|
23 | } |
|
|
24 | |
|
|
25 | DESCRIPTION |
|
|
26 | This module converts Perl data structures to the Concise Binary Object |
|
|
27 | Representation (CBOR) and vice versa. CBOR is a fast binary |
|
|
28 | serialisation format that aims to use an (almost) superset of the JSON |
|
|
29 | data model, i.e. when you can represent something useful in JSON, you |
|
|
30 | should be able to represent it in CBOR. |
|
|
31 | |
|
|
32 | In short, CBOR is a faster and quite compact binary alternative to JSON, |
|
|
33 | with the added ability of supporting serialisation of Perl objects. |
|
|
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 |
|
|
36 | compare both formats first). |
|
|
37 | |
|
|
38 | 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 |
|
|
40 | JSON::XS and decodes about 15%-30% faster than those. The shorter the |
|
|
41 | data, the worse Storable performs in comparison. |
|
|
42 | |
|
|
43 | Regarding compactness, "CBOR::XS"-encoded data structures are usually |
|
|
44 | about 20% smaller than the same data encoded as (compact) JSON or |
|
|
45 | Storable. |
|
|
46 | |
|
|
47 | In addition to the core CBOR data format, this module implements a |
|
|
48 | number of extensions, to support cyclic and shared data structures (see |
|
|
49 | "allow_sharing" and "allow_cycles"), string deduplication (see |
|
|
50 | "pack_strings") and scalar references (always enabled). |
|
|
51 | |
|
|
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 |
|
|
56 | vice versa. |
|
|
57 | |
|
|
58 | FUNCTIONAL INTERFACE |
|
|
59 | The following convenience methods are provided by this module. They are |
|
|
60 | exported by default: |
|
|
61 | |
|
|
62 | $cbor_data = encode_cbor $perl_scalar |
|
|
63 | Converts the given Perl data structure to CBOR representation. |
|
|
64 | Croaks on error. |
|
|
65 | |
|
|
66 | $perl_scalar = decode_cbor $cbor_data |
|
|
67 | The opposite of "encode_cbor": expects a valid CBOR string to parse, |
|
|
68 | returning the resulting perl scalar. Croaks on error. |
|
|
69 | |
|
|
70 | OBJECT-ORIENTED INTERFACE |
|
|
71 | The object oriented interface lets you configure your own encoding or |
|
|
72 | decoding style, within the limits of supported formats. |
|
|
73 | |
|
|
74 | $cbor = new CBOR::XS |
|
|
75 | Creates a new CBOR::XS object that can be used to de/encode CBOR |
|
|
76 | strings. All boolean flags described below are by default |
|
|
77 | *disabled*. |
|
|
78 | |
|
|
79 | The mutators for flags all return the CBOR object again and thus |
|
|
80 | calls can be chained: |
|
|
81 | |
|
|
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 | ->forbid_objects |
|
|
92 | ->filter (\&CBOR::XS::safe_filter) |
|
|
93 | ->max_size (1e8); |
|
|
94 | |
|
|
95 | But is more future proof (it is better to crash because of a change |
|
|
96 | than to be exploited in other ways). |
|
|
97 | |
|
|
98 | $cbor = $cbor->max_depth ([$maximum_nesting_depth]) |
|
|
99 | $max_depth = $cbor->get_max_depth |
|
|
100 | Sets the maximum nesting level (default 512) accepted while encoding |
|
|
101 | or decoding. If a higher nesting level is detected in CBOR data or a |
|
|
102 | Perl data structure, then the encoder and decoder will stop and |
|
|
103 | croak at that point. |
|
|
104 | |
|
|
105 | Nesting level is defined by number of hash- or arrayrefs that the |
|
|
106 | encoder needs to traverse to reach a given point or the number of |
|
|
107 | "{" or "[" characters without their matching closing parenthesis |
|
|
108 | crossed to reach a given character in a string. |
|
|
109 | |
|
|
110 | Setting the maximum depth to one disallows any nesting, so that |
|
|
111 | ensures that the object is only a single hash/object or array. |
|
|
112 | |
|
|
113 | If no argument is given, the highest possible setting will be used, |
|
|
114 | which is rarely useful. |
|
|
115 | |
|
|
116 | Note that nesting is implemented by recursion in C. The default |
|
|
117 | value has been chosen to be as large as typical operating systems |
|
|
118 | allow without crashing. |
|
|
119 | |
|
|
120 | See "SECURITY CONSIDERATIONS", below, for more info on why this is |
|
|
121 | useful. |
|
|
122 | |
|
|
123 | $cbor = $cbor->max_size ([$maximum_string_size]) |
|
|
124 | $max_size = $cbor->get_max_size |
|
|
125 | Set the maximum length a CBOR string may have (in bytes) where |
|
|
126 | decoding is being attempted. The default is 0, meaning no limit. |
|
|
127 | When "decode" is called on a string that is longer then this many |
|
|
128 | bytes, it will not attempt to decode the string but throw an |
|
|
129 | exception. This setting has no effect on "encode" (yet). |
|
|
130 | |
|
|
131 | If no argument is given, the limit check will be deactivated (same |
|
|
132 | as when 0 is specified). |
|
|
133 | |
|
|
134 | See "SECURITY CONSIDERATIONS", below, for more info on why this is |
|
|
135 | useful. |
|
|
136 | |
|
|
137 | $cbor = $cbor->allow_unknown ([$enable]) |
|
|
138 | $enabled = $cbor->get_allow_unknown |
|
|
139 | If $enable is true (or missing), then "encode" will *not* throw an |
|
|
140 | exception when it encounters values it cannot represent in CBOR (for |
|
|
141 | example, filehandles) but instead will encode a CBOR "error" value. |
|
|
142 | |
|
|
143 | If $enable is false (the default), then "encode" will throw an |
|
|
144 | exception when it encounters anything it cannot encode as CBOR. |
|
|
145 | |
|
|
146 | This option does not affect "decode" in any way, and it is |
|
|
147 | recommended to leave it off unless you know your communications |
|
|
148 | partner. |
|
|
149 | |
|
|
150 | $cbor = $cbor->allow_sharing ([$enable]) |
|
|
151 | $enabled = $cbor->get_allow_sharing |
|
|
152 | If $enable is true (or missing), then "encode" will not |
|
|
153 | double-encode values that have been referenced before (e.g. when the |
|
|
154 | same object, such as an array, is referenced multiple times), but |
|
|
155 | instead will emit a reference to the earlier value. |
|
|
156 | |
|
|
157 | This means that such values will only be encoded once, and will not |
|
|
158 | result in a deep cloning of the value on decode, in decoders |
|
|
159 | supporting the value sharing extension. This also makes it possible |
|
|
160 | to encode cyclic data structures (which need "allow_cycles" to be |
|
|
161 | enabled to be decoded by this module). |
|
|
162 | |
|
|
163 | It is recommended to leave it off unless you know your communication |
|
|
164 | partner supports the value sharing extensions to CBOR |
|
|
165 | (<http://cbor.schmorp.de/value-sharing>), as without decoder |
|
|
166 | support, the resulting data structure might be unusable. |
|
|
167 | |
|
|
168 | Detecting shared values incurs a runtime overhead when values are |
|
|
169 | encoded that have a reference counter large than one, and might |
|
|
170 | unnecessarily increase the encoded size, as potentially shared |
|
|
171 | values are encode as shareable whether or not they are actually |
|
|
172 | shared. |
|
|
173 | |
|
|
174 | At the moment, only targets of references can be shared (e.g. |
|
|
175 | scalars, arrays or hashes pointed to by a reference). Weirder |
|
|
176 | constructs, such as an array with multiple "copies" of the *same* |
|
|
177 | string, which are hard but not impossible to create in Perl, are not |
|
|
178 | supported (this is the same as with Storable). |
|
|
179 | |
|
|
180 | If $enable is false (the default), then "encode" will encode shared |
|
|
181 | data structures repeatedly, unsharing them in the process. Cyclic |
|
|
182 | data structures cannot be encoded in this mode. |
|
|
183 | |
|
|
184 | This option does not affect "decode" in any way - shared values and |
|
|
185 | references will always be decoded properly if present. |
|
|
186 | |
|
|
187 | $cbor = $cbor->allow_cycles ([$enable]) |
|
|
188 | $enabled = $cbor->get_allow_cycles |
|
|
189 | If $enable is true (or missing), then "decode" will happily decode |
|
|
190 | self-referential (cyclic) data structures. By default these will not |
|
|
191 | be decoded, as they need manual cleanup to avoid memory leaks, so |
|
|
192 | code that isn't prepared for this will not leak memory. |
|
|
193 | |
|
|
194 | If $enable is false (the default), then "decode" will throw an error |
|
|
195 | when it encounters a self-referential/cyclic data structure. |
|
|
196 | |
|
|
197 | FUTURE DIRECTION: the motivation behind this option is to avoid |
|
|
198 | *real* cycles - future versions of this module might chose to decode |
|
|
199 | cyclic data structures using weak references when this option is |
|
|
200 | off, instead of throwing an error. |
|
|
201 | |
|
|
202 | This option does not affect "encode" in any way - shared values and |
|
|
203 | references will always be encoded properly if present. |
|
|
204 | |
|
|
205 | $cbor = $cbor->forbid_objects ([$enable]) |
|
|
206 | $enabled = $cbor->get_forbid_objects |
|
|
207 | Disables the use of the object serialiser protocol. |
|
|
208 | |
|
|
209 | If $enable is true (or missing), then "encode" will will throw an |
|
|
210 | exception when it encounters perl objects that would be encoded |
|
|
211 | using the perl-object tag (26). When "decode" encounters such tags, |
|
|
212 | it will fall back to the general filter/tagged logic as if this were |
|
|
213 | an unknown tag (by default resulting in a "CBOR::XC::Tagged" |
|
|
214 | object). |
|
|
215 | |
|
|
216 | If $enable is false (the default), then "encode" will use the |
|
|
217 | Types::Serialiser object serialisation protocol to serialise objects |
|
|
218 | into perl-object tags, and "decode" will do the same to decode such |
|
|
219 | tags. |
|
|
220 | |
|
|
221 | See "SECURITY CONSIDERATIONS", below, for more info on why |
|
|
222 | forbidding this protocol can be useful. |
|
|
223 | |
|
|
224 | $cbor = $cbor->pack_strings ([$enable]) |
|
|
225 | $enabled = $cbor->get_pack_strings |
|
|
226 | If $enable is true (or missing), then "encode" will try not to |
|
|
227 | encode the same string twice, but will instead encode a reference to |
|
|
228 | the string instead. Depending on your data format, this can save a |
|
|
229 | lot of space, but also results in a very large runtime overhead |
|
|
230 | (expect encoding times to be 2-4 times as high as without). |
|
|
231 | |
|
|
232 | It is recommended to leave it off unless you know your |
|
|
233 | communications partner supports the stringref extension to CBOR |
|
|
234 | (<http://cbor.schmorp.de/stringref>), as without decoder support, |
|
|
235 | the resulting data structure might not be usable. |
|
|
236 | |
|
|
237 | If $enable is false (the default), then "encode" will encode strings |
|
|
238 | the standard CBOR way. |
|
|
239 | |
|
|
240 | This option does not affect "decode" in any way - string references |
|
|
241 | will always be decoded properly if present. |
|
|
242 | |
|
|
243 | $cbor = $cbor->text_keys ([$enable]) |
|
|
244 | $enabled = $cbor->get_text_keys |
|
|
245 | If $enabled is true (or missing), then "encode" will encode all perl |
|
|
246 | hash keys as CBOR text strings/UTF-8 string, upgrading them as |
|
|
247 | needed. |
|
|
248 | |
|
|
249 | If $enable is false (the default), then "encode" will encode hash |
|
|
250 | keys normally - upgraded perl strings (strings internally encoded as |
|
|
251 | UTF-8) as CBOR text strings, and downgraded perl strings as CBOR |
|
|
252 | byte strings. |
|
|
253 | |
|
|
254 | This option does not affect "decode" in any way. |
|
|
255 | |
|
|
256 | This option is useful for interoperability with CBOR decoders that |
|
|
257 | don't treat byte strings as a form of text. It is especially useful |
|
|
258 | as Perl gives very little control over hash keys. |
|
|
259 | |
|
|
260 | Enabling this option can be slow, as all downgraded hash keys that |
|
|
261 | are encoded need to be scanned and converted to UTF-8. |
|
|
262 | |
|
|
263 | $cbor = $cbor->text_strings ([$enable]) |
|
|
264 | $enabled = $cbor->get_text_strings |
|
|
265 | This option works similar to "text_keys", above, but works on all |
|
|
266 | strings (including hash keys), so "text_keys" has no further effect |
|
|
267 | after enabling "text_strings". |
|
|
268 | |
|
|
269 | If $enabled is true (or missing), then "encode" will encode all perl |
|
|
270 | strings as CBOR text strings/UTF-8 strings, upgrading them as |
|
|
271 | needed. |
|
|
272 | |
|
|
273 | If $enable is false (the default), then "encode" will encode strings |
|
|
274 | normally (but see "text_keys") - upgraded perl strings (strings |
|
|
275 | internally encoded as UTF-8) as CBOR text strings, and downgraded |
|
|
276 | perl strings as CBOR byte strings. |
|
|
277 | |
|
|
278 | This option does not affect "decode" in any way. |
|
|
279 | |
|
|
280 | This option has similar advantages and disadvantages as "text_keys". |
|
|
281 | In addition, this option effectively removes the ability to encode |
|
|
282 | byte strings, which might break some "FREEZE" and "TO_CBOR" methods |
|
|
283 | that rely on this, such as bignum encoding, so this option is mainly |
|
|
284 | useful for very simple data. |
|
|
285 | |
|
|
286 | $cbor = $cbor->validate_utf8 ([$enable]) |
|
|
287 | $enabled = $cbor->get_validate_utf8 |
|
|
288 | If $enable is true (or missing), then "decode" will validate that |
|
|
289 | elements (text strings) containing UTF-8 data in fact contain valid |
|
|
290 | UTF-8 data (instead of blindly accepting it). This validation |
|
|
291 | obviously takes extra time during decoding. |
|
|
292 | |
|
|
293 | The concept of "valid UTF-8" used is perl's concept, which is a |
|
|
294 | superset of the official UTF-8. |
|
|
295 | |
|
|
296 | If $enable is false (the default), then "decode" will blindly accept |
|
|
297 | UTF-8 data, marking them as valid UTF-8 in the resulting data |
|
|
298 | structure regardless of whether that's true or not. |
|
|
299 | |
|
|
300 | Perl isn't too happy about corrupted UTF-8 in strings, but should |
|
|
301 | generally not crash or do similarly evil things. Extensions might be |
|
|
302 | not so forgiving, so it's recommended to turn on this setting if you |
|
|
303 | receive untrusted CBOR. |
|
|
304 | |
|
|
305 | This option does not affect "encode" in any way - strings that are |
|
|
306 | supposedly valid UTF-8 will simply be dumped into the resulting CBOR |
|
|
307 | string without checking whether that is, in fact, true or not. |
|
|
308 | |
|
|
309 | $cbor = $cbor->filter ([$cb->($tag, $value)]) |
|
|
310 | $cb_or_undef = $cbor->get_filter |
|
|
311 | Sets or replaces the tagged value decoding filter (when $cb is |
|
|
312 | specified) or clears the filter (if no argument or "undef" is |
|
|
313 | provided). |
|
|
314 | |
|
|
315 | The filter callback is called only during decoding, when a |
|
|
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 |
|
|
319 | %CBOR::XS::FILTER hash (see below). |
|
|
320 | |
|
|
321 | The first argument is the numerical tag, the second is the (decoded) |
|
|
322 | value that has been tagged. |
|
|
323 | |
|
|
324 | The filter function should return either exactly one value, which |
|
|
325 | will replace the tagged value in the decoded data structure, or no |
|
|
326 | values, which will result in default handling, which currently means |
|
|
327 | the decoder creates a "CBOR::XS::Tagged" object to hold the tag and |
|
|
328 | the value. |
|
|
329 | |
|
|
330 | When the filter is cleared (the default state), the default filter |
|
|
331 | function, "CBOR::XS::default_filter", is used. This function simply |
|
|
332 | looks up the tag in the %CBOR::XS::FILTER hash. If an entry exists |
|
|
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 |
|
|
335 | returns no values. "CBOR::XS" provides a number of default filter |
|
|
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); |
|
|
384 | |
|
|
385 | $cbor_data = $cbor->encode ($perl_scalar) |
|
|
386 | Converts the given Perl data structure (a scalar value) to its CBOR |
|
|
387 | representation. |
|
|
388 | |
|
|
389 | $perl_scalar = $cbor->decode ($cbor_data) |
|
|
390 | The opposite of "encode": expects CBOR data and tries to parse it, |
|
|
391 | returning the resulting simple scalar or reference. Croaks on error. |
|
|
392 | |
|
|
393 | ($perl_scalar, $octets) = $cbor->decode_prefix ($cbor_data) |
|
|
394 | This works like the "decode" method, but instead of raising an |
|
|
395 | exception when there is trailing garbage after the CBOR string, it |
|
|
396 | will silently stop parsing there and return the number of characters |
|
|
397 | consumed so far. |
|
|
398 | |
|
|
399 | This is useful if your CBOR texts are not delimited by an outer |
|
|
400 | protocol and you need to know where the first CBOR string ends amd |
|
|
401 | the next one starts. |
|
|
402 | |
|
|
403 | CBOR::XS->new->decode_prefix ("......") |
|
|
404 | => ("...", 3) |
|
|
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 | |
|
|
464 | MAPPING |
|
|
465 | This section describes how CBOR::XS maps Perl values to CBOR values and |
|
|
466 | vice versa. These mappings are designed to "do the right thing" in most |
|
|
467 | circumstances automatically, preserving round-tripping characteristics |
|
|
468 | (what you put in comes out as something equivalent). |
|
|
469 | |
|
|
470 | For the more enlightened: note that in the following descriptions, |
|
|
471 | lowercase *perl* refers to the Perl interpreter, while uppercase *Perl* |
|
|
472 | refers to the abstract Perl language itself. |
|
|
473 | |
|
|
474 | CBOR -> PERL |
|
|
475 | integers |
|
|
476 | CBOR integers become (numeric) perl scalars. On perls without 64 bit |
|
|
477 | support, 64 bit integers will be truncated or otherwise corrupted. |
|
|
478 | |
|
|
479 | byte strings |
|
|
480 | Byte strings will become octet strings in Perl (the Byte values |
|
|
481 | 0..255 will simply become characters of the same value in Perl). |
|
|
482 | |
|
|
483 | UTF-8 strings |
|
|
484 | UTF-8 strings in CBOR will be decoded, i.e. the UTF-8 octets will be |
|
|
485 | decoded into proper Unicode code points. At the moment, the validity |
|
|
486 | of the UTF-8 octets will not be validated - corrupt input will |
|
|
487 | result in corrupted Perl strings. |
|
|
488 | |
|
|
489 | arrays, maps |
|
|
490 | CBOR arrays and CBOR maps will be converted into references to a |
|
|
491 | Perl array or hash, respectively. The keys of the map will be |
|
|
492 | stringified during this process. |
|
|
493 | |
|
|
494 | null |
|
|
495 | CBOR null becomes "undef" in Perl. |
|
|
496 | |
|
|
497 | true, false, undefined |
|
|
498 | These CBOR values become "Types:Serialiser::true", |
|
|
499 | "Types:Serialiser::false" and "Types::Serialiser::error", |
|
|
500 | respectively. They are overloaded to act almost exactly like the |
|
|
501 | numbers 1 and 0 (for true and false) or to throw an exception on |
|
|
502 | access (for error). See the Types::Serialiser manpage for details. |
|
|
503 | |
|
|
504 | tagged values |
|
|
505 | Tagged items consists of a numeric tag and another CBOR value. |
|
|
506 | |
|
|
507 | See "TAG HANDLING AND EXTENSIONS" and the description of "->filter" |
|
|
508 | for details on which tags are handled how. |
|
|
509 | |
|
|
510 | anything else |
|
|
511 | Anything else (e.g. unsupported simple values) will raise a decoding |
|
|
512 | error. |
|
|
513 | |
|
|
514 | PERL -> CBOR |
|
|
515 | The mapping from Perl to CBOR is slightly more difficult, as Perl is a |
|
|
516 | typeless language. That means this module can only guess which CBOR type |
|
|
517 | is meant by a perl value. |
|
|
518 | |
|
|
519 | hash references |
|
|
520 | Perl hash references become CBOR maps. As there is no inherent |
|
|
521 | ordering in hash keys (or CBOR maps), they will usually be encoded |
|
|
522 | in a pseudo-random order. This order can be different each time a |
|
|
523 | hash is encoded. |
|
|
524 | |
|
|
525 | Currently, tied hashes will use the indefinite-length format, while |
|
|
526 | normal hashes will use the fixed-length format. |
|
|
527 | |
|
|
528 | array references |
|
|
529 | Perl array references become fixed-length CBOR arrays. |
|
|
530 | |
|
|
531 | other references |
|
|
532 | Other unblessed references will be represented using the indirection |
|
|
533 | tag extension (tag value 22098, |
|
|
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. |
|
|
538 | |
|
|
539 | CBOR::XS::Tagged objects |
|
|
540 | Objects of this type must be arrays consisting of a single "[tag, |
|
|
541 | value]" pair. The (numerical) tag will be encoded as a CBOR tag, the |
|
|
542 | value will be encoded as appropriate for the value. You must use |
|
|
543 | "CBOR::XS::tag" to create such objects. |
|
|
544 | |
|
|
545 | Types::Serialiser::true, Types::Serialiser::false, |
|
|
546 | Types::Serialiser::error |
|
|
547 | These special values become CBOR true, CBOR false and CBOR undefined |
|
|
548 | values, respectively. You can also use "\1", "\0" and "\undef" |
|
|
549 | directly if you want. |
|
|
550 | |
|
|
551 | other blessed objects |
|
|
552 | Other blessed objects are serialised via "TO_CBOR" or "FREEZE". See |
|
|
553 | "TAG HANDLING AND EXTENSIONS" for specific classes handled by this |
|
|
554 | module, and "OBJECT SERIALISATION" for generic object serialisation. |
|
|
555 | |
|
|
556 | simple scalars |
|
|
557 | Simple Perl scalars (any scalar that is not a reference) are the |
|
|
558 | most difficult objects to encode: CBOR::XS will encode undefined |
|
|
559 | scalars as CBOR null values, scalars that have last been used in a |
|
|
560 | string context before encoding as CBOR strings, and anything else as |
|
|
561 | number value: |
|
|
562 | |
|
|
563 | # dump as number |
|
|
564 | encode_cbor [2] # yields [2] |
|
|
565 | encode_cbor [-3.0e17] # yields [-3e+17] |
|
|
566 | my $value = 5; encode_cbor [$value] # yields [5] |
|
|
567 | |
|
|
568 | # used as string, so dump as string (either byte or text) |
|
|
569 | print $value; |
|
|
570 | encode_cbor [$value] # yields ["5"] |
|
|
571 | |
|
|
572 | # undef becomes null |
|
|
573 | encode_cbor [undef] # yields [null] |
|
|
574 | |
|
|
575 | You can force the type to be a CBOR string by stringifying it: |
|
|
576 | |
|
|
577 | my $x = 3.1; # some variable containing a number |
|
|
578 | "$x"; # stringified |
|
|
579 | $x .= ""; # another, more awkward way to stringify |
|
|
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". |
|
|
594 | |
|
|
595 | You can force the type to be a CBOR number by numifying it: |
|
|
596 | |
|
|
597 | my $x = "3"; # some variable containing a string |
|
|
598 | $x += 0; # numify it, ensuring it will be dumped as a number |
|
|
599 | $x *= 1; # same thing, the choice is yours. |
|
|
600 | |
|
|
601 | You can not currently force the type in other, less obscure, ways. |
|
|
602 | Tell me if you need this capability (but don't forget to explain why |
|
|
603 | it's needed :). |
|
|
604 | |
|
|
605 | Perl values that seem to be integers generally use the shortest |
|
|
606 | possible representation. Floating-point values will use either the |
|
|
607 | IEEE single format if possible without loss of precision, otherwise |
|
|
608 | the IEEE double format will be used. Perls that use formats other |
|
|
609 | than IEEE double to represent numerical values are supported, but |
|
|
610 | might suffer loss of precision. |
|
|
611 | |
|
|
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 |
|
|
618 | This module knows two way to serialise a Perl object: The CBOR-specific |
|
|
619 | way, and the generic way. |
|
|
620 | |
|
|
621 | Whenever the encoder encounters a Perl object that it cannot serialise |
|
|
622 | directly (most of them), it will first look up the "TO_CBOR" method on |
|
|
623 | it. |
|
|
624 | |
|
|
625 | If it has a "TO_CBOR" method, it will call it with the object as only |
|
|
626 | argument, and expects exactly one return value, which it will then |
|
|
627 | substitute and encode it in the place of the object. |
|
|
628 | |
|
|
629 | Otherwise, it will look up the "FREEZE" method. If it exists, it will |
|
|
630 | call it with the object as first argument, and the constant string |
|
|
631 | "CBOR" as the second argument, to distinguish it from other serialisers. |
|
|
632 | |
|
|
633 | The "FREEZE" method can return any number of values (i.e. zero or more). |
|
|
634 | These will be encoded as CBOR perl object, together with the classname. |
|
|
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 | |
|
|
640 | If an object supports neither "TO_CBOR" nor "FREEZE", encoding will fail |
|
|
641 | with an error. |
|
|
642 | |
|
|
643 | DECODING |
|
|
644 | Objects encoded via "TO_CBOR" cannot (normally) be automatically |
|
|
645 | decoded, but objects encoded via "FREEZE" can be decoded using the |
|
|
646 | following protocol: |
|
|
647 | |
|
|
648 | When an encoded CBOR perl object is encountered by the decoder, it will |
|
|
649 | look up the "THAW" method, by using the stored classname, and will fail |
|
|
650 | if the method cannot be found. |
|
|
651 | |
|
|
652 | After the lookup it will call the "THAW" method with the stored |
|
|
653 | classname as first argument, the constant string "CBOR" as second |
|
|
654 | argument, and all values returned by "FREEZE" as remaining arguments. |
|
|
655 | |
|
|
656 | EXAMPLES |
|
|
657 | Here is an example "TO_CBOR" method: |
|
|
658 | |
|
|
659 | sub My::Object::TO_CBOR { |
|
|
660 | my ($obj) = @_; |
|
|
661 | |
|
|
662 | ["this is a serialised My::Object object", $obj->{id}] |
|
|
663 | } |
|
|
664 | |
|
|
665 | When a "My::Object" is encoded to CBOR, it will instead encode a simple |
|
|
666 | array with two members: a string, and the "object id". Decoding this |
|
|
667 | CBOR string will yield a normal perl array reference in place of the |
|
|
668 | object. |
|
|
669 | |
|
|
670 | A more useful and practical example would be a serialisation method for |
|
|
671 | the URI module. CBOR has a custom tag value for URIs, namely 32: |
|
|
672 | |
|
|
673 | sub URI::TO_CBOR { |
|
|
674 | my ($self) = @_; |
|
|
675 | my $uri = "$self"; # stringify uri |
|
|
676 | utf8::upgrade $uri; # make sure it will be encoded as UTF-8 string |
|
|
677 | CBOR::XS::tag 32, "$_[0]" |
|
|
678 | } |
|
|
679 | |
|
|
680 | This will encode URIs as a UTF-8 string with tag 32, which indicates an |
|
|
681 | URI. |
|
|
682 | |
|
|
683 | Decoding such an URI will not (currently) give you an URI object, but |
|
|
684 | instead a CBOR::XS::Tagged object with tag number 32 and the string - |
|
|
685 | exactly what was returned by "TO_CBOR". |
|
|
686 | |
|
|
687 | To serialise an object so it can automatically be deserialised, you need |
|
|
688 | to use "FREEZE" and "THAW". To take the URI module as example, this |
|
|
689 | would be a possible implementation: |
|
|
690 | |
|
|
691 | sub URI::FREEZE { |
|
|
692 | my ($self, $serialiser) = @_; |
|
|
693 | "$self" # encode url string |
|
|
694 | } |
|
|
695 | |
|
|
696 | sub URI::THAW { |
|
|
697 | my ($class, $serialiser, $uri) = @_; |
|
|
698 | $class->new ($uri) |
|
|
699 | } |
|
|
700 | |
|
|
701 | Unlike "TO_CBOR", multiple values can be returned by "FREEZE". For |
|
|
702 | example, a "FREEZE" method that returns "type", "id" and "variant" |
|
|
703 | values would cause an invocation of "THAW" with 5 arguments: |
|
|
704 | |
|
|
705 | sub My::Object::FREEZE { |
|
|
706 | my ($self, $serialiser) = @_; |
|
|
707 | |
|
|
708 | ($self->{type}, $self->{id}, $self->{variant}) |
|
|
709 | } |
|
|
710 | |
|
|
711 | sub My::Object::THAW { |
|
|
712 | my ($class, $serialiser, $type, $id, $variant) = @_; |
|
|
713 | |
|
|
714 | $class-<new (type => $type, id => $id, variant => $variant) |
|
|
715 | } |
|
|
716 | |
|
|
717 | MAGIC HEADER |
|
|
718 | There is no way to distinguish CBOR from other formats programmatically. |
|
|
719 | To make it easier to distinguish CBOR from other formats, the CBOR |
|
|
720 | specification has a special "magic string" that can be prepended to any |
|
|
721 | CBOR string without changing its meaning. |
|
|
722 | |
|
|
723 | This string is available as $CBOR::XS::MAGIC. This module does not |
|
|
724 | prepend this string to the CBOR data it generates, but it will ignore it |
|
|
725 | if present, so users can prepend this string as a "file type" indicator |
|
|
726 | as required. |
|
|
727 | |
|
|
728 | THE CBOR::XS::Tagged CLASS |
|
|
729 | CBOR has the concept of tagged values - any CBOR value can be tagged |
|
|
730 | with a numeric 64 bit number, which are centrally administered. |
|
|
731 | |
|
|
732 | "CBOR::XS" handles a few tags internally when en- or decoding. You can |
|
|
733 | also create tags yourself by encoding "CBOR::XS::Tagged" objects, and |
|
|
734 | the decoder will create "CBOR::XS::Tagged" objects itself when it hits |
|
|
735 | an unknown tag. |
|
|
736 | |
|
|
737 | These objects are simply blessed array references - the first member of |
|
|
738 | the array being the numerical tag, the second being the value. |
|
|
739 | |
|
|
740 | You can interact with "CBOR::XS::Tagged" objects in the following ways: |
|
|
741 | |
|
|
742 | $tagged = CBOR::XS::tag $tag, $value |
|
|
743 | This function(!) creates a new "CBOR::XS::Tagged" object using the |
|
|
744 | given $tag (0..2**64-1) to tag the given $value (which can be any |
|
|
745 | Perl value that can be encoded in CBOR, including serialisable Perl |
|
|
746 | objects and "CBOR::XS::Tagged" objects). |
|
|
747 | |
|
|
748 | $tagged->[0] |
|
|
749 | $tagged->[0] = $new_tag |
|
|
750 | $tag = $tagged->tag |
|
|
751 | $new_tag = $tagged->tag ($new_tag) |
|
|
752 | Access/mutate the tag. |
|
|
753 | |
|
|
754 | $tagged->[1] |
|
|
755 | $tagged->[1] = $new_value |
|
|
756 | $value = $tagged->value |
|
|
757 | $new_value = $tagged->value ($new_value) |
|
|
758 | Access/mutate the tagged value. |
|
|
759 | |
|
|
760 | EXAMPLES |
|
|
761 | Here are some examples of "CBOR::XS::Tagged" uses to tag objects. |
|
|
762 | |
|
|
763 | You can look up CBOR tag value and emanings in the IANA registry at |
|
|
764 | <http://www.iana.org/assignments/cbor-tags/cbor-tags.xhtml>. |
|
|
765 | |
|
|
766 | Prepend a magic header ($CBOR::XS::MAGIC): |
|
|
767 | |
|
|
768 | my $cbor = encode_cbor CBOR::XS::tag 55799, $value; |
|
|
769 | # same as: |
|
|
770 | my $cbor = $CBOR::XS::MAGIC . encode_cbor $value; |
|
|
771 | |
|
|
772 | Serialise some URIs and a regex in an array: |
|
|
773 | |
|
|
774 | my $cbor = encode_cbor [ |
|
|
775 | (CBOR::XS::tag 32, "http://www.nethype.de/"), |
|
|
776 | (CBOR::XS::tag 32, "http://software.schmorp.de/"), |
|
|
777 | (CBOR::XS::tag 35, "^[Pp][Ee][Rr][lL]\$"), |
|
|
778 | ]; |
|
|
779 | |
|
|
780 | Wrap CBOR data in CBOR: |
|
|
781 | |
|
|
782 | my $cbor_cbor = encode_cbor |
|
|
783 | CBOR::XS::tag 24, |
|
|
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. |
|
|
896 | |
|
|
897 | CBOR and JSON |
|
|
898 | CBOR is supposed to implement a superset of the JSON data model, and is, |
|
|
899 | with some coercion, able to represent all JSON texts (something that |
|
|
900 | other "binary JSON" formats such as BSON generally do not support). |
|
|
901 | |
|
|
902 | CBOR implements some extra hints and support for JSON interoperability, |
|
|
903 | and the spec offers further guidance for conversion between CBOR and |
|
|
904 | JSON. None of this is currently implemented in CBOR, and the guidelines |
|
|
905 | in the spec do not result in correct round-tripping of data. If JSON |
|
|
906 | interoperability is improved in the future, then the goal will be to |
|
|
907 | ensure that decoded JSON data will round-trip encoding and decoding to |
|
|
908 | CBOR intact. |
|
|
909 | |
|
|
910 | SECURITY CONSIDERATIONS |
|
|
911 | Tl;dr... if you want to decode or encode CBOR from untrusted sources, |
|
|
912 | you should start with a coder object created via "new_safe": |
|
|
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 |
|
|
923 | First and foremost, your CBOR decoder should be secure, that is, |
|
|
924 | should not have any buffer overflows or similar bugs that could |
|
|
925 | potentially be exploited. Obviously, this module should ensure that |
|
|
926 | and I am trying hard on making that true, but you never know. |
|
|
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 |
|
|
969 | You need to avoid resource-starving attacks. That means you should |
|
|
970 | limit the size of CBOR data you accept, or make sure then when your |
|
|
971 | resources run out, that's just fine (e.g. by using a separate |
|
|
972 | process that can crash safely). The size of a CBOR string in octets |
|
|
973 | is usually a good indication of the size of the resources required |
|
|
974 | to decode it into a Perl structure. While CBOR::XS can check the |
|
|
975 | size of the CBOR text (using "max_size"), it might be too late when |
|
|
976 | you already have it in memory, so you might want to check the size |
|
|
977 | before you accept the string. |
|
|
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 |
|
|
987 | CBOR::XS recurses using the C stack when decoding objects and |
|
|
988 | arrays. The C stack is a limited resource: for instance, on my amd64 |
|
|
989 | machine with 8MB of stack size I can decode around 180k nested |
|
|
990 | arrays but only 14k nested CBOR objects (due to perl itself |
|
|
991 | recursing deeply on croak to free the temporary). If that is |
|
|
992 | exceeded, the program crashes. To be conservative, the default |
|
|
993 | nesting limit is set to 512. If your process has a smaller stack, |
|
|
994 | you should adjust this setting accordingly with the "max_depth" |
|
|
995 | method. |
|
|
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... |
|
|
1011 | Something else could bomb you, too, that I forgot to think of. In |
|
|
1012 | that case, you get to keep the pieces. I am always open for hints, |
|
|
1013 | though... |
|
|
1014 | |
|
|
1015 | BIGNUM SECURITY CONSIDERATIONS |
|
|
1016 | CBOR::XS provides a "TO_CBOR" method for both Math::BigInt and |
|
|
1017 | Math::BigFloat that tries to encode the number in the simplest possible |
|
|
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. |
|
|
1043 | |
|
|
1044 | CBOR IMPLEMENTATION NOTES |
|
|
1045 | This section contains some random implementation notes. They do not |
|
|
1046 | describe guaranteed behaviour, but merely behaviour as-is implemented |
|
|
1047 | right now. |
|
|
1048 | |
|
|
1049 | 64 bit integers are only properly decoded when Perl was built with 64 |
|
|
1050 | bit support. |
|
|
1051 | |
|
|
1052 | Strings and arrays are encoded with a definite length. Hashes as well, |
|
|
1053 | unless they are tied (or otherwise magical). |
|
|
1054 | |
|
|
1055 | Only the double data type is supported for NV data types - when Perl |
|
|
1056 | uses long double to represent floating point values, they might not be |
|
|
1057 | encoded properly. Half precision types are accepted, but not encoded. |
|
|
1058 | |
|
|
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. |
|
|
1068 | |
|
|
1069 | THREADS |
|
|
1070 | This module is *not* guaranteed to be thread safe and there are no plans |
|
|
1071 | to change this until Perl gets thread support (as opposed to the |
|
|
1072 | horribly slow so-called "threads" which are simply slow and bloated |
|
|
1073 | process simulations - use fork, it's *much* faster, cheaper, better). |
|
|
1074 | |
|
|
1075 | (It might actually work, but you have been warned). |
|
|
1076 | |
|
|
1077 | BUGS |
|
|
1078 | While the goal of this module is to be correct, that unfortunately does |
|
|
1079 | not mean it's bug-free, only that I think its design is bug-free. If you |
|
|
1080 | keep reporting bugs they will be fixed swiftly, though. |
|
|
1081 | |
|
|
1082 | Please refrain from using rt.cpan.org or any other bug reporting |
|
|
1083 | service. I put the contact address into my modules for a reason. |
|
|
1084 | |
|
|
1085 | SEE ALSO |
|
|
1086 | The JSON and JSON::XS modules that do similar, but human-readable, |
|
|
1087 | serialisation. |
|
|
1088 | |
|
|
1089 | The Types::Serialiser module provides the data model for true, false and |
|
|
1090 | error values. |
|
|
1091 | |
|
|
1092 | AUTHOR |
|
|
1093 | Marc Lehmann <schmorp@schmorp.de> |
|
|
1094 | http://home.schmorp.de/ |
|
|
1095 | |