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1.2 |
NAME |
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CBOR::XS - Concise Binary Object Representation (CBOR, RFC7049) |
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SYNOPSIS |
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use CBOR::XS; |
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$binary_cbor_data = encode_cbor $perl_value; |
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$perl_value = decode_cbor $binary_cbor_data; |
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# OO-interface |
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$coder = CBOR::XS->new; |
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1.5 |
$binary_cbor_data = $coder->encode ($perl_value); |
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$perl_value = $coder->decode ($binary_cbor_data); |
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# prefix decoding |
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my $many_cbor_strings = ...; |
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while (length $many_cbor_strings) { |
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my ($data, $length) = $cbor->decode_prefix ($many_cbor_strings); |
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# data was decoded |
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substr $many_cbor_strings, 0, $length, ""; # remove decoded cbor string |
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} |
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1.2 |
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DESCRIPTION |
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1.4 |
This module converts Perl data structures to the Concise Binary Object |
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Representation (CBOR) and vice versa. CBOR is a fast binary |
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1.10 |
serialisation format that aims to use an (almost) superset of the JSON |
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data model, i.e. when you can represent something useful in JSON, you |
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should be able to represent it in CBOR. |
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1.4 |
|
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1.10 |
In short, CBOR is a faster and quite compact binary alternative to JSON, |
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1.6 |
with the added ability of supporting serialisation of Perl objects. |
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1.7 |
(JSON often compresses better than CBOR though, so if you plan to |
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1.10 |
compress the data later and speed is less important you might want to |
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compare both formats first). |
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1.4 |
|
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1.8 |
To give you a general idea about speed, with texts in the megabyte |
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range, "CBOR::XS" usually encodes roughly twice as fast as Storable or |
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JSON::XS and decodes about 15%-30% faster than those. The shorter the |
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data, the worse Storable performs in comparison. |
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1.10 |
Regarding compactness, "CBOR::XS"-encoded data structures are usually |
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about 20% smaller than the same data encoded as (compact) JSON or |
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Storable. |
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1.8 |
|
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1.9 |
In addition to the core CBOR data format, this module implements a |
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1.10 |
number of extensions, to support cyclic and shared data structures (see |
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1.11 |
"allow_sharing" and "allow_cycles"), string deduplication (see |
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"pack_strings") and scalar references (always enabled). |
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1.9 |
|
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1.4 |
The primary goal of this module is to be *correct* and the secondary |
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goal is to be *fast*. To reach the latter goal it was written in C. |
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1.2 |
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See MAPPING, below, on how CBOR::XS maps perl values to CBOR values and |
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vice versa. |
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FUNCTIONAL INTERFACE |
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The following convenience methods are provided by this module. They are |
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exported by default: |
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$cbor_data = encode_cbor $perl_scalar |
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Converts the given Perl data structure to CBOR representation. |
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Croaks on error. |
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$perl_scalar = decode_cbor $cbor_data |
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The opposite of "encode_cbor": expects a valid CBOR string to parse, |
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returning the resulting perl scalar. Croaks on error. |
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OBJECT-ORIENTED INTERFACE |
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The object oriented interface lets you configure your own encoding or |
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decoding style, within the limits of supported formats. |
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$cbor = new CBOR::XS |
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Creates a new CBOR::XS object that can be used to de/encode CBOR |
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strings. All boolean flags described below are by default |
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*disabled*. |
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The mutators for flags all return the CBOR object again and thus |
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calls can be chained: |
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1.9 |
my $cbor = CBOR::XS->new->encode ({a => [1,2]}); |
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1.2 |
|
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1.18 |
$cbor = new_safe CBOR::XS |
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Create a new, safe/secure CBOR::XS object. This is similar to "new", |
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but configures the coder object to be safe to use with untrusted |
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data. Currently, this is equivalent to: |
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my $cbor = CBOR::XS |
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->new |
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->forbid_objects |
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->filter (\&CBOR::XS::safe_filter) |
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->max_size (1e8); |
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But is more future proof (it is better to crash because of a change |
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than to be exploited in other ways). |
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1.2 |
$cbor = $cbor->max_depth ([$maximum_nesting_depth]) |
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$max_depth = $cbor->get_max_depth |
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Sets the maximum nesting level (default 512) accepted while encoding |
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or decoding. If a higher nesting level is detected in CBOR data or a |
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Perl data structure, then the encoder and decoder will stop and |
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croak at that point. |
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Nesting level is defined by number of hash- or arrayrefs that the |
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encoder needs to traverse to reach a given point or the number of |
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"{" or "[" characters without their matching closing parenthesis |
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crossed to reach a given character in a string. |
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Setting the maximum depth to one disallows any nesting, so that |
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ensures that the object is only a single hash/object or array. |
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If no argument is given, the highest possible setting will be used, |
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which is rarely useful. |
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Note that nesting is implemented by recursion in C. The default |
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value has been chosen to be as large as typical operating systems |
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allow without crashing. |
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1.18 |
See "SECURITY CONSIDERATIONS", below, for more info on why this is |
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1.2 |
useful. |
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$cbor = $cbor->max_size ([$maximum_string_size]) |
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$max_size = $cbor->get_max_size |
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Set the maximum length a CBOR string may have (in bytes) where |
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decoding is being attempted. The default is 0, meaning no limit. |
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When "decode" is called on a string that is longer then this many |
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bytes, it will not attempt to decode the string but throw an |
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exception. This setting has no effect on "encode" (yet). |
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If no argument is given, the limit check will be deactivated (same |
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as when 0 is specified). |
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1.18 |
See "SECURITY CONSIDERATIONS", below, for more info on why this is |
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1.2 |
useful. |
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1.9 |
$cbor = $cbor->allow_unknown ([$enable]) |
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$enabled = $cbor->get_allow_unknown |
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If $enable is true (or missing), then "encode" will *not* throw an |
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exception when it encounters values it cannot represent in CBOR (for |
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example, filehandles) but instead will encode a CBOR "error" value. |
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If $enable is false (the default), then "encode" will throw an |
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exception when it encounters anything it cannot encode as CBOR. |
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This option does not affect "decode" in any way, and it is |
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recommended to leave it off unless you know your communications |
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partner. |
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$cbor = $cbor->allow_sharing ([$enable]) |
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$enabled = $cbor->get_allow_sharing |
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If $enable is true (or missing), then "encode" will not |
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double-encode values that have been referenced before (e.g. when the |
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same object, such as an array, is referenced multiple times), but |
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instead will emit a reference to the earlier value. |
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This means that such values will only be encoded once, and will not |
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result in a deep cloning of the value on decode, in decoders |
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1.10 |
supporting the value sharing extension. This also makes it possible |
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1.18 |
to encode cyclic data structures (which need "allow_cycles" to be |
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1.11 |
enabled to be decoded by this module). |
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1.9 |
|
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It is recommended to leave it off unless you know your communication |
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partner supports the value sharing extensions to CBOR |
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1.10 |
(<http://cbor.schmorp.de/value-sharing>), as without decoder |
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support, the resulting data structure might be unusable. |
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1.9 |
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Detecting shared values incurs a runtime overhead when values are |
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encoded that have a reference counter large than one, and might |
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unnecessarily increase the encoded size, as potentially shared |
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1.11 |
values are encode as shareable whether or not they are actually |
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1.9 |
shared. |
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At the moment, only targets of references can be shared (e.g. |
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scalars, arrays or hashes pointed to by a reference). Weirder |
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constructs, such as an array with multiple "copies" of the *same* |
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string, which are hard but not impossible to create in Perl, are not |
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1.10 |
supported (this is the same as with Storable). |
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1.9 |
|
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1.10 |
If $enable is false (the default), then "encode" will encode shared |
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data structures repeatedly, unsharing them in the process. Cyclic |
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data structures cannot be encoded in this mode. |
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1.9 |
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This option does not affect "decode" in any way - shared values and |
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references will always be decoded properly if present. |
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1.11 |
$cbor = $cbor->allow_cycles ([$enable]) |
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$enabled = $cbor->get_allow_cycles |
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If $enable is true (or missing), then "decode" will happily decode |
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self-referential (cyclic) data structures. By default these will not |
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be decoded, as they need manual cleanup to avoid memory leaks, so |
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code that isn't prepared for this will not leak memory. |
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If $enable is false (the default), then "decode" will throw an error |
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when it encounters a self-referential/cyclic data structure. |
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1.14 |
FUTURE DIRECTION: the motivation behind this option is to avoid |
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*real* cycles - future versions of this module might chose to decode |
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cyclic data structures using weak references when this option is |
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off, instead of throwing an error. |
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root |
1.11 |
This option does not affect "encode" in any way - shared values and |
203 |
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1.14 |
references will always be encoded properly if present. |
204 |
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1.11 |
|
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1.18 |
$cbor = $cbor->forbid_objects ([$enable]) |
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$enabled = $cbor->get_forbid_objects |
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Disables the use of the object serialiser protocol. |
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If $enable is true (or missing), then "encode" will will throw an |
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exception when it encounters perl objects that would be encoded |
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using the perl-object tag (26). When "decode" encounters such tags, |
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it will fall back to the general filter/tagged logic as if this were |
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an unknown tag (by default resulting in a "CBOR::XC::Tagged" |
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object). |
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If $enable is false (the default), then "encode" will use the |
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Types::Serialiser object serialisation protocol to serialise objects |
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into perl-object tags, and "decode" will do the same to decode such |
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tags. |
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See "SECURITY CONSIDERATIONS", below, for more info on why |
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forbidding this protocol can be useful. |
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root |
1.10 |
$cbor = $cbor->pack_strings ([$enable]) |
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$enabled = $cbor->get_pack_strings |
226 |
root |
1.9 |
If $enable is true (or missing), then "encode" will try not to |
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encode the same string twice, but will instead encode a reference to |
228 |
root |
1.10 |
the string instead. Depending on your data format, this can save a |
229 |
root |
1.9 |
lot of space, but also results in a very large runtime overhead |
230 |
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(expect encoding times to be 2-4 times as high as without). |
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It is recommended to leave it off unless you know your |
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communications partner supports the stringref extension to CBOR |
234 |
root |
1.10 |
(<http://cbor.schmorp.de/stringref>), as without decoder support, |
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the resulting data structure might not be usable. |
236 |
root |
1.9 |
|
237 |
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1.10 |
If $enable is false (the default), then "encode" will encode strings |
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the standard CBOR way. |
239 |
root |
1.9 |
|
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This option does not affect "decode" in any way - string references |
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will always be decoded properly if present. |
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1.17 |
$cbor = $cbor->text_keys ([$enable]) |
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$enabled = $cbor->get_text_keys |
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If $enabled is true (or missing), then "encode" will encode all perl |
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hash keys as CBOR text strings/UTF-8 string, upgrading them as |
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needed. |
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249 |
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If $enable is false (the default), then "encode" will encode hash |
250 |
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keys normally - upgraded perl strings (strings internally encoded as |
251 |
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UTF-8) as CBOR text strings, and downgraded perl strings as CBOR |
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byte strings. |
253 |
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254 |
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This option does not affect "decode" in any way. |
255 |
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|
256 |
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This option is useful for interoperability with CBOR decoders that |
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don't treat byte strings as a form of text. It is especially useful |
258 |
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as Perl gives very little control over hash keys. |
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260 |
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Enabling this option can be slow, as all downgraded hash keys that |
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are encoded need to be scanned and converted to UTF-8. |
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263 |
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$cbor = $cbor->text_strings ([$enable]) |
264 |
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$enabled = $cbor->get_text_strings |
265 |
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This option works similar to "text_keys", above, but works on all |
266 |
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strings (including hash keys), so "text_keys" has no further effect |
267 |
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after enabling "text_strings". |
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269 |
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If $enabled is true (or missing), then "encode" will encode all perl |
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strings as CBOR text strings/UTF-8 strings, upgrading them as |
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needed. |
272 |
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|
273 |
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If $enable is false (the default), then "encode" will encode strings |
274 |
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normally (but see "text_keys") - upgraded perl strings (strings |
275 |
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internally encoded as UTF-8) as CBOR text strings, and downgraded |
276 |
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perl strings as CBOR byte strings. |
277 |
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|
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This option does not affect "decode" in any way. |
279 |
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|
280 |
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This option has similar advantages and disadvantages as "text_keys". |
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In addition, this option effectively removes the ability to encode |
282 |
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byte strings, which might break some "FREEZE" and "TO_CBOR" methods |
283 |
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that rely on this, such as bignum encoding, so this option is mainly |
284 |
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useful for very simple data. |
285 |
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|
286 |
root |
1.12 |
$cbor = $cbor->validate_utf8 ([$enable]) |
287 |
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$enabled = $cbor->get_validate_utf8 |
288 |
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If $enable is true (or missing), then "decode" will validate that |
289 |
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elements (text strings) containing UTF-8 data in fact contain valid |
290 |
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UTF-8 data (instead of blindly accepting it). This validation |
291 |
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obviously takes extra time during decoding. |
292 |
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293 |
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The concept of "valid UTF-8" used is perl's concept, which is a |
294 |
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superset of the official UTF-8. |
295 |
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296 |
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If $enable is false (the default), then "decode" will blindly accept |
297 |
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UTF-8 data, marking them as valid UTF-8 in the resulting data |
298 |
root |
1.17 |
structure regardless of whether that's true or not. |
299 |
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1.12 |
|
300 |
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Perl isn't too happy about corrupted UTF-8 in strings, but should |
301 |
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generally not crash or do similarly evil things. Extensions might be |
302 |
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not so forgiving, so it's recommended to turn on this setting if you |
303 |
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receive untrusted CBOR. |
304 |
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|
305 |
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This option does not affect "encode" in any way - strings that are |
306 |
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supposedly valid UTF-8 will simply be dumped into the resulting CBOR |
307 |
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string without checking whether that is, in fact, true or not. |
308 |
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|
309 |
root |
1.9 |
$cbor = $cbor->filter ([$cb->($tag, $value)]) |
310 |
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$cb_or_undef = $cbor->get_filter |
311 |
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Sets or replaces the tagged value decoding filter (when $cb is |
312 |
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specified) or clears the filter (if no argument or "undef" is |
313 |
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provided). |
314 |
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315 |
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The filter callback is called only during decoding, when a |
316 |
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non-enforced tagged value has been decoded (see "TAG HANDLING AND |
317 |
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EXTENSIONS" for a list of enforced tags). For specific tags, it's |
318 |
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often better to provide a default converter using the |
319 |
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%CBOR::XS::FILTER hash (see below). |
320 |
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|
321 |
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The first argument is the numerical tag, the second is the (decoded) |
322 |
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value that has been tagged. |
323 |
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|
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The filter function should return either exactly one value, which |
325 |
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will replace the tagged value in the decoded data structure, or no |
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values, which will result in default handling, which currently means |
327 |
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the decoder creates a "CBOR::XS::Tagged" object to hold the tag and |
328 |
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the value. |
329 |
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|
330 |
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When the filter is cleared (the default state), the default filter |
331 |
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function, "CBOR::XS::default_filter", is used. This function simply |
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looks up the tag in the %CBOR::XS::FILTER hash. If an entry exists |
333 |
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it must be a code reference that is called with tag and value, and |
334 |
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is responsible for decoding the value. If no entry exists, it |
335 |
root |
1.18 |
returns no values. "CBOR::XS" provides a number of default filter |
336 |
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functions already, the the %CBOR::XS::FILTER hash can be freely |
337 |
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extended with more. |
338 |
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|
339 |
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"CBOR::XS" additionally provides an alternative filter function that |
340 |
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is supposed to be safe to use with untrusted data (which the default |
341 |
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filter might not), called "CBOR::XS::safe_filter", which works the |
342 |
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same as the "default_filter" but uses the %CBOR::XS::SAFE_FILTER |
343 |
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variable instead. It is prepopulated with the tag decoding functions |
344 |
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that are deemed safe (basically the same as %CBOR::XS::FILTER |
345 |
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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 |
root |
1.9 |
|
350 |
|
|
Example: decode all tags not handled internally into |
351 |
root |
1.10 |
"CBOR::XS::Tagged" objects, with no other special handling (useful |
352 |
root |
1.9 |
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 $value" |
363 |
|
|
}; |
364 |
|
|
|
365 |
root |
1.18 |
Example: provide your own filter function that looks up tags in your |
366 |
|
|
own hash: |
367 |
|
|
|
368 |
|
|
my %my_filter = ( |
369 |
|
|
998347484 => sub { |
370 |
|
|
my ($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 |
root |
1.2 |
$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 |
root |
1.13 |
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 |
root |
1.18 |
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 |
root |
1.13 |
|
464 |
root |
1.2 |
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 |
root |
1.4 |
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 |
root |
1.10 |
Byte strings will become octet strings in Perl (the Byte values |
481 |
root |
1.4 |
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 |
root |
1.5 |
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 |
root |
1.2 |
respectively. They are overloaded to act almost exactly like the |
501 |
root |
1.5 |
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 |
root |
1.9 |
tagged values |
505 |
|
|
Tagged items consists of a numeric tag and another CBOR value. |
506 |
root |
1.2 |
|
507 |
root |
1.9 |
See "TAG HANDLING AND EXTENSIONS" and the description of "->filter" |
508 |
root |
1.10 |
for details on which tags are handled how. |
509 |
root |
1.4 |
|
510 |
|
|
anything else |
511 |
|
|
Anything else (e.g. unsupported simple values) will raise a decoding |
512 |
|
|
error. |
513 |
root |
1.2 |
|
514 |
|
|
PERL -> CBOR |
515 |
|
|
The mapping from Perl to CBOR is slightly more difficult, as Perl is a |
516 |
root |
1.10 |
typeless language. That means this module can only guess which CBOR type |
517 |
|
|
is meant by a perl value. |
518 |
root |
1.2 |
|
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 |
root |
1.10 |
in a pseudo-random order. This order can be different each time a |
523 |
root |
1.17 |
hash is encoded. |
524 |
root |
1.2 |
|
525 |
root |
1.4 |
Currently, tied hashes will use the indefinite-length format, while |
526 |
|
|
normal hashes will use the fixed-length format. |
527 |
|
|
|
528 |
root |
1.2 |
array references |
529 |
root |
1.4 |
Perl array references become fixed-length CBOR arrays. |
530 |
root |
1.2 |
|
531 |
|
|
other references |
532 |
root |
1.10 |
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 |
root |
1.4 |
|
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 |
root |
1.10 |
value will be encoded as appropriate for the value. You must use |
543 |
root |
1.7 |
"CBOR::XS::tag" to create such objects. |
544 |
root |
1.2 |
|
545 |
root |
1.5 |
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 |
root |
1.9 |
"TAG HANDLING AND EXTENSIONS" for specific classes handled by this |
554 |
|
|
module, and "OBJECT SERIALISATION" for generic object serialisation. |
555 |
root |
1.2 |
|
556 |
|
|
simple scalars |
557 |
root |
1.9 |
Simple Perl scalars (any scalar that is not a reference) are the |
558 |
|
|
most difficult objects to encode: CBOR::XS will encode undefined |
559 |
root |
1.4 |
scalars as CBOR null values, scalars that have last been used in a |
560 |
root |
1.2 |
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 |
root |
1.10 |
# used as string, so dump as string (either byte or text) |
569 |
root |
1.2 |
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 |
root |
1.17 |
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 |
root |
1.10 |
|
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 |
root |
1.17 |
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 |
root |
1.10 |
|
595 |
root |
1.2 |
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 |
root |
1.4 |
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 |
root |
1.2 |
|
612 |
root |
1.5 |
OBJECT SERIALISATION |
613 |
root |
1.11 |
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 |
root |
1.5 |
This module knows two way to serialise a Perl object: The CBOR-specific |
619 |
|
|
way, and the generic way. |
620 |
|
|
|
621 |
root |
1.11 |
Whenever the encoder encounters a Perl object that it cannot serialise |
622 |
root |
1.5 |
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 |
root |
1.11 |
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 |
root |
1.5 |
If an object supports neither "TO_CBOR" nor "FREEZE", encoding will fail |
641 |
|
|
with an error. |
642 |
|
|
|
643 |
root |
1.11 |
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 |
root |
1.5 |
|
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 $uri; # make sure it will be encoded as UTF-8 string |
677 |
root |
1.10 |
CBOR::XS::tag 32, "$_[0]" |
678 |
root |
1.5 |
} |
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 |
root |
1.3 |
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 |
root |
1.9 |
CBOR string without changing its meaning. |
722 |
root |
1.3 |
|
723 |
|
|
This string is available as $CBOR::XS::MAGIC. This module does not |
724 |
root |
1.9 |
prepend this string to the CBOR data it generates, but it will ignore it |
725 |
root |
1.3 |
if present, so users can prepend this string as a "file type" indicator |
726 |
|
|
as required. |
727 |
|
|
|
728 |
root |
1.7 |
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 |
root |
1.9 |
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 |
root |
1.17 |
be overridden by the user. |
804 |
root |
1.9 |
|
805 |
root |
1.10 |
26 (perl-object, <http://cbor.schmorp.de/perl-object>) |
806 |
root |
1.9 |
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 |
root |
1.16 |
28, 29 (shareable, sharedref, <http://cbor.schmorp.de/value-sharing>) |
811 |
root |
1.11 |
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 |
root |
1.9 |
|
829 |
root |
1.16 |
256, 25 (stringref-namespace, stringref, |
830 |
root |
1.9 |
<http://cbor.schmorp.de/stringref>) |
831 |
|
|
These tags are automatically decoded when encountered. They are only |
832 |
root |
1.10 |
encoded, however, when "pack_strings" is enabled. |
833 |
root |
1.9 |
|
834 |
|
|
22098 (indirection, <http://cbor.schmorp.de/indirection>) |
835 |
|
|
This tag is automatically generated when a reference are encountered |
836 |
root |
1.17 |
(with the exception of hash and array references). It is converted |
837 |
|
|
to a reference when decoding. |
838 |
root |
1.9 |
|
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 |
root |
1.17 |
can be overridden by changing the %CBOR::XS::FILTER entry for the tag, |
846 |
|
|
or by providing a custom "filter" callback when decoding. |
847 |
root |
1.9 |
|
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 |
root |
1.12 |
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 |
root |
1.9 |
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 |
root |
1.17 |
4, 5, 264, 265 (decimal fraction/bigfloat) |
872 |
root |
1.9 |
Both decimal fractions and bigfloats are decoded into Math::BigFloat |
873 |
|
|
objects. The corresponding "Math::BigFloat::TO_CBOR" method *always* |
874 |
root |
1.17 |
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 |
root |
1.9 |
|
879 |
root |
1.17 |
See "BIGNUM SECURITY CONSIDERATIONS" for more info. |
880 |
root |
1.9 |
|
881 |
root |
1.17 |
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 |
root |
1.9 |
|
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 |
root |
1.5 |
CBOR and JSON |
898 |
root |
1.4 |
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 |
root |
1.2 |
|
910 |
|
|
SECURITY CONSIDERATIONS |
911 |
root |
1.18 |
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 |
root |
1.2 |
|
919 |
root |
1.18 |
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 |
root |
1.2 |
|
1015 |
root |
1.17 |
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 |
root |
1.2 |
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 |
root |
1.11 |
LIMITATIONS ON PERLS WITHOUT 64-BIT INTEGER SUPPORT |
1062 |
|
|
On perls that were built without 64 bit integer support (these are rare |
1063 |
root |
1.15 |
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 |
root |
1.11 |
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 |
root |
1.2 |
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 |
root |
1.5 |
The Types::Serialiser module provides the data model for true, false and |
1090 |
|
|
error values. |
1091 |
|
|
|
1092 |
root |
1.2 |
AUTHOR |
1093 |
|
|
Marc Lehmann <schmorp@schmorp.de> |
1094 |
|
|
http://home.schmorp.de/ |
1095 |
|
|
|