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Revision 1.3 by root, Sat Oct 26 11:08:34 2013 UTC vs.
Revision 1.74 by root, Mon Nov 30 18:30:29 2020 UTC

…		…
12	$perl_value = decode_cbor $binary_cbor_data;	12	$perl_value = decode_cbor $binary_cbor_data;
13		13
14	# OO-interface	14	# OO-interface
15		15
16	$coder = CBOR::XS->new;	16	$coder = CBOR::XS->new;
17	#TODO	17	$binary_cbor_data = $coder->encode ($perl_value);
		18	$perl_value = $coder->decode ($binary_cbor_data);
		19
		20	# prefix decoding
		21
		22	my $many_cbor_strings = ...;
		23	while (length $many_cbor_strings) {
		24	my ($data, $length) = $cbor->decode_prefix ($many_cbor_strings);
		25	# data was decoded
		26	substr $many_cbor_strings, 0, $length, ""; # remove decoded cbor string
		27	}
18		28
19	=head1 DESCRIPTION	29	=head1 DESCRIPTION
20		30
21	WARNING! THIS IS A PRE-ALPHA RELEASE! IT WILL CRASH, CORRUPT YOUR DATA AND	31	This module converts Perl data structures to the Concise Binary Object
22	EAT YOUR CHILDREN!	32	Representation (CBOR) and vice versa. CBOR is a fast binary serialisation
		33	format that aims to use an (almost) superset of the JSON data model, i.e.
		34	when you can represent something useful in JSON, you should be able to
		35	represent it in CBOR.
23		36
24	This module converts Perl data structures to CBOR and vice versa. Its	37	In short, CBOR is a faster and quite compact binary alternative to JSON,
		38	with the added ability of supporting serialisation of Perl objects. (JSON
		39	often compresses better than CBOR though, so if you plan to compress the
		40	data later and speed is less important you might want to compare both
		41	formats first).
		42
25	primary goal is to be I<correct> and its secondary goal is to be	43	The primary goal of this module is to be I<correct> and the secondary goal
26	I<fast>. To reach the latter goal it was written in C.	44	is to be I<fast>. To reach the latter goal it was written in C.
		45
		46	To give you a general idea about speed, with texts in the megabyte range,
		47	C<CBOR::XS> usually encodes roughly twice as fast as L<Storable> or
		48	L<JSON::XS> and decodes about 15%-30% faster than those. The shorter the
		49	data, the worse L<Storable> performs in comparison.
		50
		51	Regarding compactness, C<CBOR::XS>-encoded data structures are usually
		52	about 20% smaller than the same data encoded as (compact) JSON or
		53	L<Storable>.
		54
		55	In addition to the core CBOR data format, this module implements a
		56	number of extensions, to support cyclic and shared data structures
		57	(see C<allow_sharing> and C<allow_cycles>), string deduplication (see
		58	C<pack_strings>) and scalar references (always enabled).
27		59
28	See MAPPING, below, on how CBOR::XS maps perl values to CBOR values and	60	See MAPPING, below, on how CBOR::XS maps perl values to CBOR values and
29	vice versa.	61	vice versa.
30		62
31	=cut	63	=cut
32		64
33	package CBOR::XS;	65	package CBOR::XS;
34		66
35	use common::sense;	67	use common::sense;
36		68
37	our $VERSION = 0.02;	69	our $VERSION = 1.81;
38	our @ISA = qw(Exporter);	70	our @ISA = qw(Exporter);
39		71
40	our @EXPORT = qw(encode_cbor decode_cbor);	72	our @EXPORT = qw(encode_cbor decode_cbor);
41		73
42	use Exporter;	74	use Exporter;
43	use XSLoader;	75	use XSLoader;
44		76
		77	use Types::Serialiser;
		78
45	our $MAGIC = "\xd9\xd9\xf7";	79	our $MAGIC = "\xd9\xd9\xf7";
46		80
47	=head1 FUNCTIONAL INTERFACE	81	=head1 FUNCTIONAL INTERFACE
48		82
49	The following convenience methods are provided by this module. They are	83	The following convenience methods are provided by this module. They are
…		…
77	strings. All boolean flags described below are by default I<disabled>.	111	strings. All boolean flags described below are by default I<disabled>.
78		112
79	The mutators for flags all return the CBOR object again and thus calls can	113	The mutators for flags all return the CBOR object again and thus calls can
80	be chained:	114	be chained:
81		115
82	#TODO
83	my $cbor = CBOR::XS->new->encode ({a => [1,2]});	116	my $cbor = CBOR::XS->new->encode ({a => [1,2]});
		117
		118	=item $cbor = new_safe CBOR::XS
		119
		120	Create a new, safe/secure CBOR::XS object. This is similar to C<new>,
		121	but configures the coder object to be safe to use with untrusted
		122	data. Currently, this is equivalent to:
		123
		124	my $cbor = CBOR::XS
		125	->new
		126	->forbid_objects
		127	->filter (\&CBOR::XS::safe_filter)
		128	->max_size (1e8);
		129
		130	But is more future proof (it is better to crash because of a change than
		131	to be exploited in other ways).
		132
		133	=cut
		134
		135	sub new_safe {
		136	CBOR::XS
		137	->new
		138	->forbid_objects
		139	->filter (\&CBOR::XS::safe_filter)
		140	->max_size (1e8)
		141	}
84		142
85	=item $cbor = $cbor->max_depth ([$maximum_nesting_depth])	143	=item $cbor = $cbor->max_depth ([$maximum_nesting_depth])
86		144
87	=item $max_depth = $cbor->get_max_depth	145	=item $max_depth = $cbor->get_max_depth
88		146
…		…
104		162
105	Note that nesting is implemented by recursion in C. The default value has	163	Note that nesting is implemented by recursion in C. The default value has
106	been chosen to be as large as typical operating systems allow without	164	been chosen to be as large as typical operating systems allow without
107	crashing.	165	crashing.
108		166
109	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.	167	See L<SECURITY CONSIDERATIONS>, below, for more info on why this is useful.
110		168
111	=item $cbor = $cbor->max_size ([$maximum_string_size])	169	=item $cbor = $cbor->max_size ([$maximum_string_size])
112		170
113	=item $max_size = $cbor->get_max_size	171	=item $max_size = $cbor->get_max_size
114		172
…		…
119	effect on C<encode> (yet).	177	effect on C<encode> (yet).
120		178
121	If no argument is given, the limit check will be deactivated (same as when	179	If no argument is given, the limit check will be deactivated (same as when
122	C<0> is specified).	180	C<0> is specified).
123		181
124	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.	182	See L<SECURITY CONSIDERATIONS>, below, for more info on why this is useful.
		183
		184	=item $cbor = $cbor->allow_unknown ([$enable])
		185
		186	=item $enabled = $cbor->get_allow_unknown
		187
		188	If C<$enable> is true (or missing), then C<encode> will I<not> throw an
		189	exception when it encounters values it cannot represent in CBOR (for
		190	example, filehandles) but instead will encode a CBOR C<error> value.
		191
		192	If C<$enable> is false (the default), then C<encode> will throw an
		193	exception when it encounters anything it cannot encode as CBOR.
		194
		195	This option does not affect C<decode> in any way, and it is recommended to
		196	leave it off unless you know your communications partner.
		197
		198	=item $cbor = $cbor->allow_sharing ([$enable])
		199
		200	=item $enabled = $cbor->get_allow_sharing
		201
		202	If C<$enable> is true (or missing), then C<encode> will not double-encode
		203	values that have been referenced before (e.g. when the same object, such
		204	as an array, is referenced multiple times), but instead will emit a
		205	reference to the earlier value.
		206
		207	This means that such values will only be encoded once, and will not result
		208	in a deep cloning of the value on decode, in decoders supporting the value
		209	sharing extension. This also makes it possible to encode cyclic data
		210	structures (which need C<allow_cycles> to be enabled to be decoded by this
		211	module).
		212
		213	It is recommended to leave it off unless you know your
		214	communication partner supports the value sharing extensions to CBOR
		215	(L<http://cbor.schmorp.de/value-sharing>), as without decoder support, the
		216	resulting data structure might be unusable.
		217
		218	Detecting shared values incurs a runtime overhead when values are encoded
		219	that have a reference counter large than one, and might unnecessarily
		220	increase the encoded size, as potentially shared values are encoded as
		221	shareable whether or not they are actually shared.
		222
		223	At the moment, only targets of references can be shared (e.g. scalars,
		224	arrays or hashes pointed to by a reference). Weirder constructs, such as
		225	an array with multiple "copies" of the I<same> string, which are hard but
		226	not impossible to create in Perl, are not supported (this is the same as
		227	with L<Storable>).
		228
		229	If C<$enable> is false (the default), then C<encode> will encode shared
		230	data structures repeatedly, unsharing them in the process. Cyclic data
		231	structures cannot be encoded in this mode.
		232
		233	This option does not affect C<decode> in any way - shared values and
		234	references will always be decoded properly if present.
		235
		236	=item $cbor = $cbor->allow_cycles ([$enable])
		237
		238	=item $enabled = $cbor->get_allow_cycles
		239
		240	If C<$enable> is true (or missing), then C<decode> will happily decode
		241	self-referential (cyclic) data structures. By default these will not be
		242	decoded, as they need manual cleanup to avoid memory leaks, so code that
		243	isn't prepared for this will not leak memory.
		244
		245	If C<$enable> is false (the default), then C<decode> will throw an error
		246	when it encounters a self-referential/cyclic data structure.
		247
		248	FUTURE DIRECTION: the motivation behind this option is to avoid I<real>
		249	cycles - future versions of this module might chose to decode cyclic data
		250	structures using weak references when this option is off, instead of
		251	throwing an error.
		252
		253	This option does not affect C<encode> in any way - shared values and
		254	references will always be encoded properly if present.
		255
		256	=item $cbor = $cbor->forbid_objects ([$enable])
		257
		258	=item $enabled = $cbor->get_forbid_objects
		259
		260	Disables the use of the object serialiser protocol.
		261
		262	If C<$enable> is true (or missing), then C<encode> will will throw an
		263	exception when it encounters perl objects that would be encoded using the
		264	perl-object tag (26). When C<decode> encounters such tags, it will fall
		265	back to the general filter/tagged logic as if this were an unknown tag (by
		266	default resulting in a C<CBOR::XC::Tagged> object).
		267
		268	If C<$enable> is false (the default), then C<encode> will use the
		269	L<Types::Serialiser> object serialisation protocol to serialise objects
		270	into perl-object tags, and C<decode> will do the same to decode such tags.
		271
		272	See L<SECURITY CONSIDERATIONS>, below, for more info on why forbidding this
		273	protocol can be useful.
		274
		275	=item $cbor = $cbor->pack_strings ([$enable])
		276
		277	=item $enabled = $cbor->get_pack_strings
		278
		279	If C<$enable> is true (or missing), then C<encode> will try not to encode
		280	the same string twice, but will instead encode a reference to the string
		281	instead. Depending on your data format, this can save a lot of space, but
		282	also results in a very large runtime overhead (expect encoding times to be
		283	2-4 times as high as without).
		284
		285	It is recommended to leave it off unless you know your
		286	communications partner supports the stringref extension to CBOR
		287	(L<http://cbor.schmorp.de/stringref>), as without decoder support, the
		288	resulting data structure might not be usable.
		289
		290	If C<$enable> is false (the default), then C<encode> will encode strings
		291	the standard CBOR way.
		292
		293	This option does not affect C<decode> in any way - string references will
		294	always be decoded properly if present.
		295
		296	=item $cbor = $cbor->text_keys ([$enable])
		297
		298	=item $enabled = $cbor->get_text_keys
		299
		300	If C<$enabled> is true (or missing), then C<encode> will encode all
		301	perl hash keys as CBOR text strings/UTF-8 string, upgrading them as needed.
		302
		303	If C<$enable> is false (the default), then C<encode> will encode hash keys
		304	normally - upgraded perl strings (strings internally encoded as UTF-8) as
		305	CBOR text strings, and downgraded perl strings as CBOR byte strings.
		306
		307	This option does not affect C<decode> in any way.
		308
		309	This option is useful for interoperability with CBOR decoders that don't
		310	treat byte strings as a form of text. It is especially useful as Perl
		311	gives very little control over hash keys.
		312
		313	Enabling this option can be slow, as all downgraded hash keys that are
		314	encoded need to be scanned and converted to UTF-8.
		315
		316	=item $cbor = $cbor->text_strings ([$enable])
		317
		318	=item $enabled = $cbor->get_text_strings
		319
		320	This option works similar to C<text_keys>, above, but works on all strings
		321	(including hash keys), so C<text_keys> has no further effect after
		322	enabling C<text_strings>.
		323
		324	If C<$enabled> is true (or missing), then C<encode> will encode all perl
		325	strings as CBOR text strings/UTF-8 strings, upgrading them as needed.
		326
		327	If C<$enable> is false (the default), then C<encode> will encode strings
		328	normally (but see C<text_keys>) - upgraded perl strings (strings
		329	internally encoded as UTF-8) as CBOR text strings, and downgraded perl
		330	strings as CBOR byte strings.
		331
		332	This option does not affect C<decode> in any way.
		333
		334	This option has similar advantages and disadvantages as C<text_keys>. In
		335	addition, this option effectively removes the ability to automatically
		336	encode byte strings, which might break some C<FREEZE> and C<TO_CBOR>
		337	methods that rely on this.
		338
		339	A workaround is to use explicit type casts, which are unaffected by this option.
		340
		341	=item $cbor = $cbor->validate_utf8 ([$enable])
		342
		343	=item $enabled = $cbor->get_validate_utf8
		344
		345	If C<$enable> is true (or missing), then C<decode> will validate that
		346	elements (text strings) containing UTF-8 data in fact contain valid UTF-8
		347	data (instead of blindly accepting it). This validation obviously takes
		348	extra time during decoding.
		349
		350	The concept of "valid UTF-8" used is perl's concept, which is a superset
		351	of the official UTF-8.
		352
		353	If C<$enable> is false (the default), then C<decode> will blindly accept
		354	UTF-8 data, marking them as valid UTF-8 in the resulting data structure
		355	regardless of whether that's true or not.
		356
		357	Perl isn't too happy about corrupted UTF-8 in strings, but should
		358	generally not crash or do similarly evil things. Extensions might be not
		359	so forgiving, so it's recommended to turn on this setting if you receive
		360	untrusted CBOR.
		361
		362	This option does not affect C<encode> in any way - strings that are
		363	supposedly valid UTF-8 will simply be dumped into the resulting CBOR
		364	string without checking whether that is, in fact, true or not.
		365
		366	=item $cbor = $cbor->filter ([$cb->($tag, $value)])
		367
		368	=item $cb_or_undef = $cbor->get_filter
		369
		370	Sets or replaces the tagged value decoding filter (when C<$cb> is
		371	specified) or clears the filter (if no argument or C<undef> is provided).
		372
		373	The filter callback is called only during decoding, when a non-enforced
		374	tagged value has been decoded (see L<TAG HANDLING AND EXTENSIONS> for a
		375	list of enforced tags). For specific tags, it's often better to provide a
		376	default converter using the C<%CBOR::XS::FILTER> hash (see below).
		377
		378	The first argument is the numerical tag, the second is the (decoded) value
		379	that has been tagged.
		380
		381	The filter function should return either exactly one value, which will
		382	replace the tagged value in the decoded data structure, or no values,
		383	which will result in default handling, which currently means the decoder
		384	creates a C<CBOR::XS::Tagged> object to hold the tag and the value.
		385
		386	When the filter is cleared (the default state), the default filter
		387	function, C<CBOR::XS::default_filter>, is used. This function simply
		388	looks up the tag in the C<%CBOR::XS::FILTER> hash. If an entry exists
		389	it must be a code reference that is called with tag and value, and is
		390	responsible for decoding the value. If no entry exists, it returns no
		391	values. C<CBOR::XS> provides a number of default filter functions already,
		392	the the C<%CBOR::XS::FILTER> hash can be freely extended with more.
		393
		394	C<CBOR::XS> additionally provides an alternative filter function that is
		395	supposed to be safe to use with untrusted data (which the default filter
		396	might not), called C<CBOR::XS::safe_filter>, which works the same as
		397	the C<default_filter> but uses the C<%CBOR::XS::SAFE_FILTER> variable
		398	instead. It is prepopulated with the tag decoding functions that are
		399	deemed safe (basically the same as C<%CBOR::XS::FILTER> without all
		400	the bignum tags), and can be extended by user code as wlel, although,
		401	obviously, one should be very careful about adding decoding functions
		402	here, since the expectation is that they are safe to use on untrusted
		403	data, after all.
		404
		405	Example: decode all tags not handled internally into C<CBOR::XS::Tagged>
		406	objects, with no other special handling (useful when working with
		407	potentially "unsafe" CBOR data).
		408
		409	CBOR::XS->new->filter (sub { })->decode ($cbor_data);
		410
		411	Example: provide a global filter for tag 1347375694, converting the value
		412	into some string form.
		413
		414	$CBOR::XS::FILTER{1347375694} = sub {
		415	my ($tag, $value);
		416
		417	"tag 1347375694 value $value"
		418	};
		419
		420	Example: provide your own filter function that looks up tags in your own
		421	hash:
		422
		423	my %my_filter = (
		424	998347484 => sub {
		425	my ($tag, $value);
		426
		427	"tag 998347484 value $value"
		428	};
		429	);
		430
		431	my $coder = CBOR::XS->new->filter (sub {
		432	&{ $my_filter{$_[0]} or return }
		433	});
		434
		435
		436	Example: use the safe filter function (see L<SECURITY CONSIDERATIONS> for
		437	more considerations on security).
		438
		439	CBOR::XS->new->filter (\&CBOR::XS::safe_filter)->decode ($cbor_data);
125		440
126	=item $cbor_data = $cbor->encode ($perl_scalar)	441	=item $cbor_data = $cbor->encode ($perl_scalar)
127		442
128	Converts the given Perl data structure (a scalar value) to its CBOR	443	Converts the given Perl data structure (a scalar value) to its CBOR
129	representation.	444	representation.
…		…
139	when there is trailing garbage after the CBOR string, it will silently	454	when there is trailing garbage after the CBOR string, it will silently
140	stop parsing there and return the number of characters consumed so far.	455	stop parsing there and return the number of characters consumed so far.
141		456
142	This is useful if your CBOR texts are not delimited by an outer protocol	457	This is useful if your CBOR texts are not delimited by an outer protocol
143	and you need to know where the first CBOR string ends amd the next one	458	and you need to know where the first CBOR string ends amd the next one
144	starts.	459	starts - CBOR strings are self-delimited, so it is possible to concatenate
		460	CBOR strings without any delimiters or size fields and recover their data.
145		461
146	CBOR::XS->new->decode_prefix ("......")	462	CBOR::XS->new->decode_prefix ("......")
147	=> ("...", 3)	463	=> ("...", 3)
		464
		465	=back
		466
		467	=head2 INCREMENTAL PARSING
		468
		469	In some cases, there is the need for incremental parsing of JSON
		470	texts. While this module always has to keep both CBOR text and resulting
		471	Perl data structure in memory at one time, it does allow you to parse a
		472	CBOR stream incrementally, using a similar to using "decode_prefix" to see
		473	if a full CBOR object is available, but is much more efficient.
		474
		475	It basically works by parsing as much of a CBOR string as possible - if
		476	the CBOR data is not complete yet, the pasrer will remember where it was,
		477	to be able to restart when more data has been accumulated. Once enough
		478	data is available to either decode a complete CBOR value or raise an
		479	error, a real decode will be attempted.
		480
		481	A typical use case would be a network protocol that consists of sending
		482	and receiving CBOR-encoded messages. The solution that works with CBOR and
		483	about anything else is by prepending a length to every CBOR value, so the
		484	receiver knows how many octets to read. More compact (and slightly slower)
		485	would be to just send CBOR values back-to-back, as C<CBOR::XS> knows where
		486	a CBOR value ends, and doesn't need an explicit length.
		487
		488	The following methods help with this:
		489
		490	=over 4
		491
		492	=item @decoded = $cbor->incr_parse ($buffer)
		493
		494	This method attempts to decode exactly one CBOR value from the beginning
		495	of the given C<$buffer>. The value is removed from the C<$buffer> on
		496	success. When C<$buffer> doesn't contain a complete value yet, it returns
		497	nothing. Finally, when the C<$buffer> doesn't start with something
		498	that could ever be a valid CBOR value, it raises an exception, just as
		499	C<decode> would. In the latter case the decoder state is undefined and
		500	must be reset before being able to parse further.
		501
		502	This method modifies the C<$buffer> in place. When no CBOR value can be
		503	decoded, the decoder stores the current string offset. On the next call,
		504	continues decoding at the place where it stopped before. For this to make
		505	sense, the C<$buffer> must begin with the same octets as on previous
		506	unsuccessful calls.
		507
		508	You can call this method in scalar context, in which case it either
		509	returns a decoded value or C<undef>. This makes it impossible to
		510	distinguish between CBOR null values (which decode to C<undef>) and an
		511	unsuccessful decode, which is often acceptable.
		512
		513	=item @decoded = $cbor->incr_parse_multiple ($buffer)
		514
		515	Same as C<incr_parse>, but attempts to decode as many CBOR values as
		516	possible in one go, instead of at most one. Calls to C<incr_parse> and
		517	C<incr_parse_multiple> can be interleaved.
		518
		519	=item $cbor->incr_reset
		520
		521	Resets the incremental decoder. This throws away any saved state, so that
		522	subsequent calls to C<incr_parse> or C<incr_parse_multiple> start to parse
		523	a new CBOR value from the beginning of the C<$buffer> again.
		524
		525	This method can be called at any time, but it I<must> be called if you want
		526	to change your C<$buffer> or there was a decoding error and you want to
		527	reuse the C<$cbor> object for future incremental parsings.
148		528
149	=back	529	=back
150		530
151		531
152	=head1 MAPPING	532	=head1 MAPPING
…		…
163		543
164	=head2 CBOR -> PERL	544	=head2 CBOR -> PERL
165		545
166	=over 4	546	=over 4
167		547
168	=item True, False	548	=item integers
169		549
170	These CBOR values become C<CBOR::XS::true> and C<CBOR::XS::false>,	550	CBOR integers become (numeric) perl scalars. On perls without 64 bit
		551	support, 64 bit integers will be truncated or otherwise corrupted.
		552
		553	=item byte strings
		554
		555	Byte strings will become octet strings in Perl (the Byte values 0..255
		556	will simply become characters of the same value in Perl).
		557
		558	=item UTF-8 strings
		559
		560	UTF-8 strings in CBOR will be decoded, i.e. the UTF-8 octets will be
		561	decoded into proper Unicode code points. At the moment, the validity of
		562	the UTF-8 octets will not be validated - corrupt input will result in
		563	corrupted Perl strings.
		564
		565	=item arrays, maps
		566
		567	CBOR arrays and CBOR maps will be converted into references to a Perl
		568	array or hash, respectively. The keys of the map will be stringified
		569	during this process.
		570
		571	=item null
		572
		573	CBOR null becomes C<undef> in Perl.
		574
		575	=item true, false, undefined
		576
		577	These CBOR values become C<Types:Serialiser::true>,
		578	C<Types:Serialiser::false> and C<Types::Serialiser::error>,
171	respectively. They are overloaded to act almost exactly like the numbers	579	respectively. They are overloaded to act almost exactly like the numbers
172	C<1> and C<0>. You can check whether a scalar is a CBOR boolean by using	580	C<1> and C<0> (for true and false) or to throw an exception on access (for
173	the C<CBOR::XS::is_bool> function.	581	error). See the L<Types::Serialiser> manpage for details.
174		582
175	=item Null, Undefined	583	=item tagged values
176		584
177	CBOR Null and Undefined values becomes C<undef> in Perl (in the future,	585	Tagged items consists of a numeric tag and another CBOR value.
178	Undefined may raise an exception).	586
		587	See L<TAG HANDLING AND EXTENSIONS> and the description of C<< ->filter >>
		588	for details on which tags are handled how.
		589
		590	=item anything else
		591
		592	Anything else (e.g. unsupported simple values) will raise a decoding
		593	error.
179		594
180	=back	595	=back
181		596
182		597
183	=head2 PERL -> CBOR	598	=head2 PERL -> CBOR
184		599
185	The mapping from Perl to CBOR is slightly more difficult, as Perl is a	600	The mapping from Perl to CBOR is slightly more difficult, as Perl is a
186	truly typeless language, so we can only guess which CBOR type is meant by	601	typeless language. That means this module can only guess which CBOR type
187	a Perl value.	602	is meant by a perl value.
188		603
189	=over 4	604	=over 4
190		605
191	=item hash references	606	=item hash references
192		607
193	Perl hash references become CBOR maps. As there is no inherent ordering	608	Perl hash references become CBOR maps. As there is no inherent ordering in
194	in hash keys (or CBOR maps), they will usually be encoded in a	609	hash keys (or CBOR maps), they will usually be encoded in a pseudo-random
195	pseudo-random order.	610	order. This order can be different each time a hash is encoded.
		611
		612	Currently, tied hashes will use the indefinite-length format, while normal
		613	hashes will use the fixed-length format.
196		614
197	=item array references	615	=item array references
198		616
199	Perl array references become CBOR arrays.	617	Perl array references become fixed-length CBOR arrays.
200		618
201	=item other references	619	=item other references
202		620
203	Other unblessed references are generally not allowed and will cause an	621	Other unblessed references will be represented using
204	exception to be thrown, except for references to the integers C<0> and	622	the indirection tag extension (tag value C<22098>,
205	C<1>, which get turned into C<False> and C<True> in CBOR.	623	L<http://cbor.schmorp.de/indirection>). CBOR decoders are guaranteed
		624	to be able to decode these values somehow, by either "doing the right
		625	thing", decoding into a generic tagged object, simply ignoring the tag, or
		626	something else.
206		627
207	=item CBOR::XS::true, CBOR::XS::false	628	=item CBOR::XS::Tagged objects
208		629
		630	Objects of this type must be arrays consisting of a single C<[tag, value]>
		631	pair. The (numerical) tag will be encoded as a CBOR tag, the value will
		632	be encoded as appropriate for the value. You must use C<CBOR::XS::tag> to
		633	create such objects.
		634
		635	=item Types::Serialiser::true, Types::Serialiser::false, Types::Serialiser::error
		636
209	These special values become CBOR True and CBOR False values,	637	These special values become CBOR true, CBOR false and CBOR undefined
210	respectively. You can also use C<\1> and C<\0> directly if you want.	638	values, respectively. You can also use C<\1>, C<\0> and C<\undef> directly
		639	if you want.
211		640
212	=item blessed objects	641	=item other blessed objects
213		642
214	Blessed objects are not directly representable in CBOR. TODO	643	Other blessed objects are serialised via C<TO_CBOR> or C<FREEZE>. See
215	See the	644	L<TAG HANDLING AND EXTENSIONS> for specific classes handled by this
216	C<allow_blessed> and C<convert_blessed> methods on various options on	645	module, and L<OBJECT SERIALISATION> for generic object serialisation.
217	how to deal with this: basically, you can choose between throwing an
218	exception, encoding the reference as if it weren't blessed, or provide
219	your own serialiser method.
220		646
221	=item simple scalars	647	=item simple scalars
222		648
223	TODO
224	Simple Perl scalars (any scalar that is not a reference) are the most	649	Simple Perl scalars (any scalar that is not a reference) are the most
225	difficult objects to encode: CBOR::XS will encode undefined scalars as	650	difficult objects to encode: CBOR::XS will encode undefined scalars as
226	CBOR C<Null> values, scalars that have last been used in a string context	651	CBOR null values, scalars that have last been used in a string context
227	before encoding as CBOR strings, and anything else as number value:	652	before encoding as CBOR strings, and anything else as number value:
228		653
229	# dump as number	654	# dump as number
230	encode_cbor [2] # yields [2]	655	encode_cbor [2] # yields [2]
231	encode_cbor [-3.0e17] # yields [-3e+17]	656	encode_cbor [-3.0e17] # yields [-3e+17]
232	my $value = 5; encode_cbor [$value] # yields [5]	657	my $value = 5; encode_cbor [$value] # yields [5]
233		658
234	# used as string, so dump as string	659	# used as string, so dump as string (either byte or text)
235	print $value;	660	print $value;
236	encode_cbor [$value] # yields ["5"]	661	encode_cbor [$value] # yields ["5"]
237		662
238	# undef becomes null	663	# undef becomes null
239	encode_cbor [undef] # yields [null]	664	encode_cbor [undef] # yields [null]
…		…
243	my $x = 3.1; # some variable containing a number	668	my $x = 3.1; # some variable containing a number
244	"$x"; # stringified	669	"$x"; # stringified
245	$x .= ""; # another, more awkward way to stringify	670	$x .= ""; # another, more awkward way to stringify
246	print $x; # perl does it for you, too, quite often	671	print $x; # perl does it for you, too, quite often
247		672
		673	You can force whether a string is encoded as byte or text string by using
		674	C<utf8::upgrade> and C<utf8::downgrade> (if C<text_strings> is disabled).
		675
		676	utf8::upgrade $x; # encode $x as text string
		677	utf8::downgrade $x; # encode $x as byte string
		678
		679	More options are available, see L<TYPE CASTS>, below, and the C<text_keys>
		680	and C<text_strings> options.
		681
		682	Perl doesn't define what operations up- and downgrade strings, so if the
		683	difference between byte and text is important, you should up- or downgrade
		684	your string as late as possible before encoding. You can also force the
		685	use of CBOR text strings by using C<text_keys> or C<text_strings>.
		686
248	You can force the type to be a CBOR number by numifying it:	687	You can force the type to be a CBOR number by numifying it:
249		688
250	my $x = "3"; # some variable containing a string	689	my $x = "3"; # some variable containing a string
251	$x += 0; # numify it, ensuring it will be dumped as a number	690	$x += 0; # numify it, ensuring it will be dumped as a number
252	$x *= 1; # same thing, the choice is yours.	691	$x *= 1; # same thing, the choice is yours.
253		692
254	You can not currently force the type in other, less obscure, ways. Tell me	693	You can not currently force the type in other, less obscure, ways. Tell me
255	if you need this capability (but don't forget to explain why it's needed	694	if you need this capability (but don't forget to explain why it's needed
256	:).	695	:).
257		696
258	Note that numerical precision has the same meaning as under Perl (so	697	Perl values that seem to be integers generally use the shortest possible
259	binary to decimal conversion follows the same rules as in Perl, which	698	representation. Floating-point values will use either the IEEE single
260	can differ to other languages). Also, your perl interpreter might expose	699	format if possible without loss of precision, otherwise the IEEE double
261	extensions to the floating point numbers of your platform, such as	700	format will be used. Perls that use formats other than IEEE double to
262	infinities or NaN's - these cannot be represented in CBOR, and it is an	701	represent numerical values are supported, but might suffer loss of
263	error to pass those in.	702	precision.
264		703
265	=back	704	=back
266		705
		706	=head2 TYPE CASTS
267		707
		708	B<EXPERIMENTAL>: As an experimental extension, C<CBOR::XS> allows you to
		709	force specific cbor types to be used when encoding. That allows you to
		710	encode types not normally accessible (e.g. half floats) as well as force
		711	string types even when C<text_strings> is in effect.
		712
		713	Type forcing is done by calling a special "cast" function which keeps a
		714	copy of the value and returns a new value that can be handed over to any
		715	CBOR encoder function.
		716
		717	The following casts are currently available (all of which are unary operators):
		718
		719	=over
		720
		721	=item CBOR::XS::as_int $value
		722
		723	Forces the value to be encoded as some form of (basic, not bignum) integer
		724	type.
		725
		726	=item CBOR::XS::as_text $value
		727
		728	Forces the value to be encoded as (UTF-8) text values.
		729
		730	=item CBOR::XS::as_bytes $value
		731
		732	Forces the value to be encoded as a (binary) string value.
		733
		734	=item CBOR::XS::as_float16 $value
		735
		736	Forces half-float (IEEE 754 binary16) encoding of the given value.
		737
		738	=item CBOR::XS::as_float32 $value
		739
		740	Forces single-float (IEEE 754 binary32) encoding of the given value.
		741
		742	=item CBOR::XS::as_float64 $value
		743
		744	Forces double-float (IEEE 754 binary64) encoding of the given value.
		745
		746	=item, CBOR::XS::as_cbor $cbor_text
		747
		748	Bot a type cast per-se, this type cast forces the argument to eb encoded
		749	as-is. This can be used to embed pre-encoded CBOR data.
		750
		751	Note that no checking on the validity of the C<$cbor_text> is done - it's
		752	the callers responsibility to correctly encode values.
		753
		754	=back
		755
		756	Example: encode a perl string as binary even though C<text_strings> is in
		757	effect.
		758
		759	CBOR::XS->new->text_strings->encode ([4, "text", CBOR::XS::bytes "bytevalue"]);
		760
		761	=cut
		762
		763	sub CBOR::XS::as_cbor ($) { bless [$_[0], 0, undef], CBOR::XS::Tagged:: }
		764	sub CBOR::XS::as_int ($) { bless [$_[0], 1, undef], CBOR::XS::Tagged:: }
		765	sub CBOR::XS::as_bytes ($) { bless [$_[0], 2, undef], CBOR::XS::Tagged:: }
		766	sub CBOR::XS::as_text ($) { bless [$_[0], 3, undef], CBOR::XS::Tagged:: }
		767	sub CBOR::XS::as_float16 ($) { bless [$_[0], 4, undef], CBOR::XS::Tagged:: }
		768	sub CBOR::XS::as_float32 ($) { bless [$_[0], 5, undef], CBOR::XS::Tagged:: }
		769	sub CBOR::XS::as_float64 ($) { bless [$_[0], 6, undef], CBOR::XS::Tagged:: }
		770
		771	=head2 OBJECT SERIALISATION
		772
		773	This module implements both a CBOR-specific and the generic
		774	L<Types::Serialier> object serialisation protocol. The following
		775	subsections explain both methods.
		776
		777	=head3 ENCODING
		778
		779	This module knows two way to serialise a Perl object: The CBOR-specific
		780	way, and the generic way.
		781
		782	Whenever the encoder encounters a Perl object that it cannot serialise
		783	directly (most of them), it will first look up the C<TO_CBOR> method on
		784	it.
		785
		786	If it has a C<TO_CBOR> method, it will call it with the object as only
		787	argument, and expects exactly one return value, which it will then
		788	substitute and encode it in the place of the object.
		789
		790	Otherwise, it will look up the C<FREEZE> method. If it exists, it will
		791	call it with the object as first argument, and the constant string C<CBOR>
		792	as the second argument, to distinguish it from other serialisers.
		793
		794	The C<FREEZE> method can return any number of values (i.e. zero or
		795	more). These will be encoded as CBOR perl object, together with the
		796	classname.
		797
		798	These methods I<MUST NOT> change the data structure that is being
		799	serialised. Failure to comply to this can result in memory corruption -
		800	and worse.
		801
		802	If an object supports neither C<TO_CBOR> nor C<FREEZE>, encoding will fail
		803	with an error.
		804
		805	=head3 DECODING
		806
		807	Objects encoded via C<TO_CBOR> cannot (normally) be automatically decoded,
		808	but objects encoded via C<FREEZE> can be decoded using the following
		809	protocol:
		810
		811	When an encoded CBOR perl object is encountered by the decoder, it will
		812	look up the C<THAW> method, by using the stored classname, and will fail
		813	if the method cannot be found.
		814
		815	After the lookup it will call the C<THAW> method with the stored classname
		816	as first argument, the constant string C<CBOR> as second argument, and all
		817	values returned by C<FREEZE> as remaining arguments.
		818
		819	=head3 EXAMPLES
		820
		821	Here is an example C<TO_CBOR> method:
		822
		823	sub My::Object::TO_CBOR {
		824	my ($obj) = @_;
		825
		826	["this is a serialised My::Object object", $obj->{id}]
		827	}
		828
		829	When a C<My::Object> is encoded to CBOR, it will instead encode a simple
		830	array with two members: a string, and the "object id". Decoding this CBOR
		831	string will yield a normal perl array reference in place of the object.
		832
		833	A more useful and practical example would be a serialisation method for
		834	the URI module. CBOR has a custom tag value for URIs, namely 32:
		835
		836	sub URI::TO_CBOR {
		837	my ($self) = @_;
		838	my $uri = "$self"; # stringify uri
		839	utf8::upgrade $uri; # make sure it will be encoded as UTF-8 string
		840	CBOR::XS::tag 32, "$_[0]"
		841	}
		842
		843	This will encode URIs as a UTF-8 string with tag 32, which indicates an
		844	URI.
		845
		846	Decoding such an URI will not (currently) give you an URI object, but
		847	instead a CBOR::XS::Tagged object with tag number 32 and the string -
		848	exactly what was returned by C<TO_CBOR>.
		849
		850	To serialise an object so it can automatically be deserialised, you need
		851	to use C<FREEZE> and C<THAW>. To take the URI module as example, this
		852	would be a possible implementation:
		853
		854	sub URI::FREEZE {
		855	my ($self, $serialiser) = @_;
		856	"$self" # encode url string
		857	}
		858
		859	sub URI::THAW {
		860	my ($class, $serialiser, $uri) = @_;
		861	$class->new ($uri)
		862	}
		863
		864	Unlike C<TO_CBOR>, multiple values can be returned by C<FREEZE>. For
		865	example, a C<FREEZE> method that returns "type", "id" and "variant" values
		866	would cause an invocation of C<THAW> with 5 arguments:
		867
		868	sub My::Object::FREEZE {
		869	my ($self, $serialiser) = @_;
		870
		871	($self->{type}, $self->{id}, $self->{variant})
		872	}
		873
		874	sub My::Object::THAW {
		875	my ($class, $serialiser, $type, $id, $variant) = @_;
		876
		877	$class-<new (type => $type, id => $id, variant => $variant)
		878	}
		879
		880
268	=head2 MAGIC HEADER	881	=head1 MAGIC HEADER
269		882
270	There is no way to distinguish CBOR from other formats	883	There is no way to distinguish CBOR from other formats
271	programmatically. To make it easier to distinguish CBOR from other	884	programmatically. To make it easier to distinguish CBOR from other
272	formats, the CBOR specification has a special "magic string" that can be	885	formats, the CBOR specification has a special "magic string" that can be
273	prepended to any CBOR string without changing it's meaning.	886	prepended to any CBOR string without changing its meaning.
274		887
275	This string is available as C<$CBOR::XS::MAGIC>. This module does not	888	This string is available as C<$CBOR::XS::MAGIC>. This module does not
276	prepend this string tot he CBOR data it generates, but it will ignroe it	889	prepend this string to the CBOR data it generates, but it will ignore it
277	if present, so users can prepend this string as a "file type" indicator as	890	if present, so users can prepend this string as a "file type" indicator as
278	required.	891	required.
279		892
280		893
		894	=head1 THE CBOR::XS::Tagged CLASS
		895
		896	CBOR has the concept of tagged values - any CBOR value can be tagged with
		897	a numeric 64 bit number, which are centrally administered.
		898
		899	C<CBOR::XS> handles a few tags internally when en- or decoding. You can
		900	also create tags yourself by encoding C<CBOR::XS::Tagged> objects, and the
		901	decoder will create C<CBOR::XS::Tagged> objects itself when it hits an
		902	unknown tag.
		903
		904	These objects are simply blessed array references - the first member of
		905	the array being the numerical tag, the second being the value.
		906
		907	You can interact with C<CBOR::XS::Tagged> objects in the following ways:
		908
		909	=over 4
		910
		911	=item $tagged = CBOR::XS::tag $tag, $value
		912
		913	This function(!) creates a new C<CBOR::XS::Tagged> object using the given
		914	C<$tag> (0..2**64-1) to tag the given C<$value> (which can be any Perl
		915	value that can be encoded in CBOR, including serialisable Perl objects and
		916	C<CBOR::XS::Tagged> objects).
		917
		918	=item $tagged->[0]
		919
		920	=item $tagged->[0] = $new_tag
		921
		922	=item $tag = $tagged->tag
		923
		924	=item $new_tag = $tagged->tag ($new_tag)
		925
		926	Access/mutate the tag.
		927
		928	=item $tagged->[1]
		929
		930	=item $tagged->[1] = $new_value
		931
		932	=item $value = $tagged->value
		933
		934	=item $new_value = $tagged->value ($new_value)
		935
		936	Access/mutate the tagged value.
		937
		938	=back
		939
		940	=cut
		941
		942	sub tag($$) {
		943	bless [@_], CBOR::XS::Tagged::;
		944	}
		945
		946	sub CBOR::XS::Tagged::tag {
		947	$_[0][0] = $_[1] if $#_;
		948	$_[0][0]
		949	}
		950
		951	sub CBOR::XS::Tagged::value {
		952	$_[0][1] = $_[1] if $#_;
		953	$_[0][1]
		954	}
		955
		956	=head2 EXAMPLES
		957
		958	Here are some examples of C<CBOR::XS::Tagged> uses to tag objects.
		959
		960	You can look up CBOR tag value and emanings in the IANA registry at
		961	L<http://www.iana.org/assignments/cbor-tags/cbor-tags.xhtml>.
		962
		963	Prepend a magic header (C<$CBOR::XS::MAGIC>):
		964
		965	my $cbor = encode_cbor CBOR::XS::tag 55799, $value;
		966	# same as:
		967	my $cbor = $CBOR::XS::MAGIC . encode_cbor $value;
		968
		969	Serialise some URIs and a regex in an array:
		970
		971	my $cbor = encode_cbor [
		972	(CBOR::XS::tag 32, "http://www.nethype.de/"),
		973	(CBOR::XS::tag 32, "http://software.schmorp.de/"),
		974	(CBOR::XS::tag 35, "^[Pp][Ee][Rr][lL]\$"),
		975	];
		976
		977	Wrap CBOR data in CBOR:
		978
		979	my $cbor_cbor = encode_cbor
		980	CBOR::XS::tag 24,
		981	encode_cbor [1, 2, 3];
		982
		983	=head1 TAG HANDLING AND EXTENSIONS
		984
		985	This section describes how this module handles specific tagged values
		986	and extensions. If a tag is not mentioned here and no additional filters
		987	are provided for it, then the default handling applies (creating a
		988	CBOR::XS::Tagged object on decoding, and only encoding the tag when
		989	explicitly requested).
		990
		991	Tags not handled specifically are currently converted into a
		992	L<CBOR::XS::Tagged> object, which is simply a blessed array reference
		993	consisting of the numeric tag value followed by the (decoded) CBOR value.
		994
		995	Future versions of this module reserve the right to special case
		996	additional tags (such as base64url).
		997
		998	=head2 ENFORCED TAGS
		999
		1000	These tags are always handled when decoding, and their handling cannot be
		1001	overridden by the user.
		1002
		1003	=over 4
		1004
		1005	=item 26 (perl-object, L<http://cbor.schmorp.de/perl-object>)
		1006
		1007	These tags are automatically created (and decoded) for serialisable
		1008	objects using the C<FREEZE/THAW> methods (the L<Types::Serialier> object
		1009	serialisation protocol). See L<OBJECT SERIALISATION> for details.
		1010
		1011	=item 28, 29 (shareable, sharedref, L<http://cbor.schmorp.de/value-sharing>)
		1012
		1013	These tags are automatically decoded when encountered (and they do not
		1014	result in a cyclic data structure, see C<allow_cycles>), resulting in
		1015	shared values in the decoded object. They are only encoded, however, when
		1016	C<allow_sharing> is enabled.
		1017
		1018	Not all shared values can be successfully decoded: values that reference
		1019	themselves will I<currently> decode as C<undef> (this is not the same
		1020	as a reference pointing to itself, which will be represented as a value
		1021	that contains an indirect reference to itself - these will be decoded
		1022	properly).
		1023
		1024	Note that considerably more shared value data structures can be decoded
		1025	than will be encoded - currently, only values pointed to by references
		1026	will be shared, others will not. While non-reference shared values can be
		1027	generated in Perl with some effort, they were considered too unimportant
		1028	to be supported in the encoder. The decoder, however, will decode these
		1029	values as shared values.
		1030
		1031	=item 256, 25 (stringref-namespace, stringref, L<http://cbor.schmorp.de/stringref>)
		1032
		1033	These tags are automatically decoded when encountered. They are only
		1034	encoded, however, when C<pack_strings> is enabled.
		1035
		1036	=item 22098 (indirection, L<http://cbor.schmorp.de/indirection>)
		1037
		1038	This tag is automatically generated when a reference are encountered (with
		1039	the exception of hash and array references). It is converted to a reference
		1040	when decoding.
		1041
		1042	=item 55799 (self-describe CBOR, RFC 7049)
		1043
		1044	This value is not generated on encoding (unless explicitly requested by
		1045	the user), and is simply ignored when decoding.
		1046
		1047	=back
		1048
		1049	=head2 NON-ENFORCED TAGS
		1050
		1051	These tags have default filters provided when decoding. Their handling can
		1052	be overridden by changing the C<%CBOR::XS::FILTER> entry for the tag, or by
		1053	providing a custom C<filter> callback when decoding.
		1054
		1055	When they result in decoding into a specific Perl class, the module
		1056	usually provides a corresponding C<TO_CBOR> method as well.
		1057
		1058	When any of these need to load additional modules that are not part of the
		1059	perl core distribution (e.g. L<URI>), it is (currently) up to the user to
		1060	provide these modules. The decoding usually fails with an exception if the
		1061	required module cannot be loaded.
		1062
		1063	=over 4
		1064
		1065	=item 0, 1 (date/time string, seconds since the epoch)
		1066
		1067	These tags are decoded into L<Time::Piece> objects. The corresponding
		1068	C<Time::Piece::TO_CBOR> method always encodes into tag 1 values currently.
		1069
		1070	The L<Time::Piece> API is generally surprisingly bad, and fractional
		1071	seconds are only accidentally kept intact, so watch out. On the plus side,
		1072	the module comes with perl since 5.10, which has to count for something.
		1073
		1074	=item 2, 3 (positive/negative bignum)
		1075
		1076	These tags are decoded into L<Math::BigInt> objects. The corresponding
		1077	C<Math::BigInt::TO_CBOR> method encodes "small" bigints into normal CBOR
		1078	integers, and others into positive/negative CBOR bignums.
		1079
		1080	=item 4, 5, 264, 265 (decimal fraction/bigfloat)
		1081
		1082	Both decimal fractions and bigfloats are decoded into L<Math::BigFloat>
		1083	objects. The corresponding C<Math::BigFloat::TO_CBOR> method I<always>
		1084	encodes into a decimal fraction (either tag 4 or 264).
		1085
		1086	NaN and infinities are not encoded properly, as they cannot be represented
		1087	in CBOR.
		1088
		1089	See L<BIGNUM SECURITY CONSIDERATIONS> for more info.
		1090
		1091	=item 30 (rational numbers)
		1092
		1093	These tags are decoded into L<Math::BigRat> objects. The corresponding
		1094	C<Math::BigRat::TO_CBOR> method encodes rational numbers with denominator
		1095	C<1> via their numerator only, i.e., they become normal integers or
		1096	C<bignums>.
		1097
		1098	See L<BIGNUM SECURITY CONSIDERATIONS> for more info.
		1099
		1100	=item 21, 22, 23 (expected later JSON conversion)
		1101
		1102	CBOR::XS is not a CBOR-to-JSON converter, and will simply ignore these
		1103	tags.
		1104
		1105	=item 32 (URI)
		1106
		1107	These objects decode into L<URI> objects. The corresponding
		1108	C<URI::TO_CBOR> method again results in a CBOR URI value.
		1109
		1110	=back
		1111
		1112	=cut
		1113
281	=head2 CBOR and JSON	1114	=head1 CBOR and JSON
282		1115
283	TODO	1116	CBOR is supposed to implement a superset of the JSON data model, and is,
		1117	with some coercion, able to represent all JSON texts (something that other
		1118	"binary JSON" formats such as BSON generally do not support).
		1119
		1120	CBOR implements some extra hints and support for JSON interoperability,
		1121	and the spec offers further guidance for conversion between CBOR and
		1122	JSON. None of this is currently implemented in CBOR, and the guidelines
		1123	in the spec do not result in correct round-tripping of data. If JSON
		1124	interoperability is improved in the future, then the goal will be to
		1125	ensure that decoded JSON data will round-trip encoding and decoding to
		1126	CBOR intact.
284		1127
285		1128
286	=head1 SECURITY CONSIDERATIONS	1129	=head1 SECURITY CONSIDERATIONS
287		1130
288	When you are using CBOR in a protocol, talking to untrusted potentially	1131	Tl;dr... if you want to decode or encode CBOR from untrusted sources, you
289	hostile creatures requires relatively few measures.	1132	should start with a coder object created via C<new_safe> (which implements
		1133	the mitigations explained below):
290		1134
		1135	my $coder = CBOR::XS->new_safe;
		1136
		1137	my $data = $coder->decode ($cbor_text);
		1138	my $cbor = $coder->encode ($data);
		1139
		1140	Longer version: When you are using CBOR in a protocol, talking to
		1141	untrusted potentially hostile creatures requires some thought:
		1142
		1143	=over 4
		1144
		1145	=item Security of the CBOR decoder itself
		1146
291	First of all, your CBOR decoder should be secure, that is, should not have	1147	First and foremost, your CBOR decoder should be secure, that is, should
		1148	not have any buffer overflows or similar bugs that could potentially be
292	any buffer overflows. Obviously, this module should ensure that and I am	1149	exploited. Obviously, this module should ensure that and I am trying hard
293	trying hard on making that true, but you never know.	1150	on making that true, but you never know.
294		1151
		1152	=item CBOR::XS can invoke almost arbitrary callbacks during decoding
		1153
		1154	CBOR::XS supports object serialisation - decoding CBOR can cause calls
		1155	to I<any> C<THAW> method in I<any> package that exists in your process
		1156	(that is, CBOR::XS will not try to load modules, but any existing C<THAW>
		1157	method or function can be called, so they all have to be secure).
		1158
		1159	Less obviously, it will also invoke C<TO_CBOR> and C<FREEZE> methods -
		1160	even if all your C<THAW> methods are secure, encoding data structures from
		1161	untrusted sources can invoke those and trigger bugs in those.
		1162
		1163	So, if you are not sure about the security of all the modules you
		1164	have loaded (you shouldn't), you should disable this part using
		1165	C<forbid_objects> or using C<new_safe>.
		1166
		1167	=item CBOR can be extended with tags that call library code
		1168
		1169	CBOR can be extended with tags, and C<CBOR::XS> has a registry of
		1170	conversion functions for many existing tags that can be extended via
		1171	third-party modules (see the C<filter> method).
		1172
		1173	If you don't trust these, you should configure the "safe" filter function,
		1174	C<CBOR::XS::safe_filter> (C<new_safe> does this), which by default only
		1175	includes conversion functions that are considered "safe" by the author
		1176	(but again, they can be extended by third party modules).
		1177
		1178	Depending on your level of paranoia, you can use the "safe" filter:
		1179
		1180	$cbor->filter (\&CBOR::XS::safe_filter);
		1181
		1182	... your own filter...
		1183
		1184	$cbor->filter (sub { ... do your stuffs here ... });
		1185
		1186	... or even no filter at all, disabling all tag decoding:
		1187
		1188	$cbor->filter (sub { });
		1189
		1190	This is never a problem for encoding, as the tag mechanism only exists in
		1191	CBOR texts.
		1192
		1193	=item Resource-starving attacks: object memory usage
		1194
295	Second, you need to avoid resource-starving attacks. That means you should	1195	You need to avoid resource-starving attacks. That means you should limit
296	limit the size of CBOR data you accept, or make sure then when your	1196	the size of CBOR data you accept, or make sure then when your resources
297	resources run out, that's just fine (e.g. by using a separate process that	1197	run out, that's just fine (e.g. by using a separate process that can
298	can crash safely). The size of a CBOR string in octets is usually a good	1198	crash safely). The size of a CBOR string in octets is usually a good
299	indication of the size of the resources required to decode it into a Perl	1199	indication of the size of the resources required to decode it into a Perl
300	structure. While CBOR::XS can check the size of the CBOR text, it might be	1200	structure. While CBOR::XS can check the size of the CBOR text (using
301	too late when you already have it in memory, so you might want to check	1201	C<max_size> - done by C<new_safe>), it might be too late when you already
302	the size before you accept the string.	1202	have it in memory, so you might want to check the size before you accept
		1203	the string.
303		1204
		1205	As for encoding, it is possible to construct data structures that are
		1206	relatively small but result in large CBOR texts (for example by having an
		1207	array full of references to the same big data structure, which will all be
		1208	deep-cloned during encoding by default). This is rarely an actual issue
		1209	(and the worst case is still just running out of memory), but you can
		1210	reduce this risk by using C<allow_sharing>.
		1211
		1212	=item Resource-starving attacks: stack overflows
		1213
304	Third, CBOR::XS recurses using the C stack when decoding objects and	1214	CBOR::XS recurses using the C stack when decoding objects and arrays. The
305	arrays. The C stack is a limited resource: for instance, on my amd64	1215	C stack is a limited resource: for instance, on my amd64 machine with 8MB
306	machine with 8MB of stack size I can decode around 180k nested arrays but	1216	of stack size I can decode around 180k nested arrays but only 14k nested
307	only 14k nested CBOR objects (due to perl itself recursing deeply on croak	1217	CBOR objects (due to perl itself recursing deeply on croak to free the
308	to free the temporary). If that is exceeded, the program crashes. To be	1218	temporary). If that is exceeded, the program crashes. To be conservative,
309	conservative, the default nesting limit is set to 512. If your process	1219	the default nesting limit is set to 512. If your process has a smaller
310	has a smaller stack, you should adjust this setting accordingly with the	1220	stack, you should adjust this setting accordingly with the C<max_depth>
311	C<max_depth> method.	1221	method.
		1222
		1223	=item Resource-starving attacks: CPU en-/decoding complexity
		1224
		1225	CBOR::XS will use the L<Math::BigInt>, L<Math::BigFloat> and
		1226	L<Math::BigRat> libraries to represent encode/decode bignums. These can be
		1227	very slow (as in, centuries of CPU time) and can even crash your program
		1228	(and are generally not very trustworthy). See the next section on bignum
		1229	security for details.
		1230
		1231	=item Data breaches: leaking information in error messages
		1232
		1233	CBOR::XS might leak contents of your Perl data structures in its error
		1234	messages, so when you serialise sensitive information you might want to
		1235	make sure that exceptions thrown by CBOR::XS will not end up in front of
		1236	untrusted eyes.
		1237
		1238	=item Something else...
312		1239
313	Something else could bomb you, too, that I forgot to think of. In that	1240	Something else could bomb you, too, that I forgot to think of. In that
314	case, you get to keep the pieces. I am always open for hints, though...	1241	case, you get to keep the pieces. I am always open for hints, though...
315		1242
316	Also keep in mind that CBOR::XS might leak contents of your Perl data	1243	=back
317	structures in its error messages, so when you serialise sensitive	1244
318	information you might want to make sure that exceptions thrown by CBOR::XS	1245
319	will not end up in front of untrusted eyes.	1246	=head1 BIGNUM SECURITY CONSIDERATIONS
		1247
		1248	CBOR::XS provides a C<TO_CBOR> method for both L<Math::BigInt> and
		1249	L<Math::BigFloat> that tries to encode the number in the simplest possible
		1250	way, that is, either a CBOR integer, a CBOR bigint/decimal fraction (tag
		1251	4) or an arbitrary-exponent decimal fraction (tag 264). Rational numbers
		1252	(L<Math::BigRat>, tag 30) can also contain bignums as members.
		1253
		1254	CBOR::XS will also understand base-2 bigfloat or arbitrary-exponent
		1255	bigfloats (tags 5 and 265), but it will never generate these on its own.
		1256
		1257	Using the built-in L<Math::BigInt::Calc> support, encoding and decoding
		1258	decimal fractions is generally fast. Decoding bigints can be slow for very
		1259	big numbers (tens of thousands of digits, something that could potentially
		1260	be caught by limiting the size of CBOR texts), and decoding bigfloats or
		1261	arbitrary-exponent bigfloats can be I<extremely> slow (minutes, decades)
		1262	for large exponents (roughly 40 bit and longer).
		1263
		1264	Additionally, L<Math::BigInt> can take advantage of other bignum
		1265	libraries, such as L<Math::GMP>, which cannot handle big floats with large
		1266	exponents, and might simply abort or crash your program, due to their code
		1267	quality.
		1268
		1269	This can be a concern if you want to parse untrusted CBOR. If it is, you
		1270	might want to disable decoding of tag 2 (bigint) and 3 (negative bigint)
		1271	types. You should also disable types 5 and 265, as these can be slow even
		1272	without bigints.
		1273
		1274	Disabling bigints will also partially or fully disable types that rely on
		1275	them, e.g. rational numbers that use bignums.
		1276
320		1277
321	=head1 CBOR IMPLEMENTATION NOTES	1278	=head1 CBOR IMPLEMENTATION NOTES
322		1279
323	This section contains some random implementation notes. They do not	1280	This section contains some random implementation notes. They do not
324	describe guaranteed behaviour, but merely behaviour as-is implemented	1281	describe guaranteed behaviour, but merely behaviour as-is implemented
…		…
333	Only the double data type is supported for NV data types - when Perl uses	1290	Only the double data type is supported for NV data types - when Perl uses
334	long double to represent floating point values, they might not be encoded	1291	long double to represent floating point values, they might not be encoded
335	properly. Half precision types are accepted, but not encoded.	1292	properly. Half precision types are accepted, but not encoded.
336		1293
337	Strict mode and canonical mode are not implemented.	1294	Strict mode and canonical mode are not implemented.
		1295
		1296
		1297	=head1 LIMITATIONS ON PERLS WITHOUT 64-BIT INTEGER SUPPORT
		1298
		1299	On perls that were built without 64 bit integer support (these are rare
		1300	nowadays, even on 32 bit architectures, as all major Perl distributions
		1301	are built with 64 bit integer support), support for any kind of 64 bit
		1302	value in CBOR is very limited - most likely, these 64 bit values will
		1303	be truncated, corrupted, or otherwise not decoded correctly. This also
		1304	includes string, float, array and map sizes that are stored as 64 bit
		1305	integers.
338		1306
339		1307
340	=head1 THREADS	1308	=head1 THREADS
341		1309
342	This module is I<not> guaranteed to be thread safe and there are no	1310	This module is I<not> guaranteed to be thread safe and there are no
…		…
356	Please refrain from using rt.cpan.org or any other bug reporting	1324	Please refrain from using rt.cpan.org or any other bug reporting
357	service. I put the contact address into my modules for a reason.	1325	service. I put the contact address into my modules for a reason.
358		1326
359	=cut	1327	=cut
360		1328
361	our $true = do { bless \(my $dummy = 1), "CBOR::XS::Boolean" };	1329	# clumsy and slow hv_store-in-hash helper function
362	our $false = do { bless \(my $dummy = 0), "CBOR::XS::Boolean" };	1330	sub _hv_store {
363		1331	$_[0]{$_[1]} = $_[2];
364	sub true() { $true }
365	sub false() { $false }
366
367	sub is_bool($) {
368	UNIVERSAL::isa $_[0], "CBOR::XS::Boolean"
369	# or UNIVERSAL::isa $_[0], "CBOR::Literal"
370	}	1332	}
371		1333
		1334	our %FILTER = (
		1335	0 => sub { # rfc4287 datetime, utf-8
		1336	require Time::Piece;
		1337	# Time::Piece::Strptime uses the "incredibly flexible date parsing routine"
		1338	# from FreeBSD, which can't parse ISO 8601, RFC3339, RFC4287 or much of anything
		1339	# else either. Whats incredibe over standard strptime totally escapes me.
		1340	# doesn't do fractional times, either. sigh.
		1341	# In fact, it's all a lie, it uses whatever strptime it wants, and of course,
		1342	# they are all incompatible. The openbsd one simply ignores %z (but according to the
		1343	# docs, it would be much more incredibly flexible indeed. If it worked, that is.).
		1344	scalar eval {
		1345	my $s = $_[1];
		1346
		1347	$s =~ s/Z$/+00:00/;
		1348	$s =~ s/(\.[0-9]+)?([+-][0-9][0-9]):([0-9][0-9])$//
		1349	or die;
		1350
		1351	my $b = $1 - ($2 * 60 + $3) * 60; # fractional part + offset. hopefully
		1352	my $d = Time::Piece->strptime ($s, "%Y-%m-%dT%H:%M:%S");
		1353
		1354	Time::Piece::gmtime ($d->epoch + $b)
		1355	} || die "corrupted CBOR date/time string ($_[0])";
		1356	},
		1357
		1358	1 => sub { # seconds since the epoch, possibly fractional
		1359	require Time::Piece;
		1360	scalar Time::Piece::gmtime (pop)
		1361	},
		1362
		1363	2 => sub { # pos bigint
		1364	require Math::BigInt;
		1365	Math::BigInt->new ("0x" . unpack "H*", pop)
		1366	},
		1367
		1368	3 => sub { # neg bigint
		1369	require Math::BigInt;
		1370	-Math::BigInt->new ("0x" . unpack "H*", pop)
		1371	},
		1372
		1373	4 => sub { # decimal fraction, array
		1374	require Math::BigFloat;
		1375	Math::BigFloat->new ($_[1][1] . "E" . $_[1][0])
		1376	},
		1377
		1378	264 => sub { # decimal fraction with arbitrary exponent
		1379	require Math::BigFloat;
		1380	Math::BigFloat->new ($_[1][1] . "E" . $_[1][0])
		1381	},
		1382
		1383	5 => sub { # bigfloat, array
		1384	require Math::BigFloat;
		1385	scalar Math::BigFloat->new ($_[1][1]) * Math::BigFloat->new (2)->bpow ($_[1][0])
		1386	},
		1387
		1388	265 => sub { # bigfloat with arbitrary exponent
		1389	require Math::BigFloat;
		1390	scalar Math::BigFloat->new ($_[1][1]) * Math::BigFloat->new (2)->bpow ($_[1][0])
		1391	},
		1392
		1393	30 => sub { # rational number
		1394	require Math::BigRat;
		1395	Math::BigRat->new ("$_[1][0]/$_[1][1]") # separate parameters only work in recent versons
		1396	},
		1397
		1398	21 => sub { pop }, # expected conversion to base64url encoding
		1399	22 => sub { pop }, # expected conversion to base64 encoding
		1400	23 => sub { pop }, # expected conversion to base16 encoding
		1401
		1402	# 24 # embedded cbor, byte string
		1403
		1404	32 => sub {
		1405	require URI;
		1406	URI->new (pop)
		1407	},
		1408
		1409	# 33 # base64url rfc4648, utf-8
		1410	# 34 # base64 rfc46484, utf-8
		1411	# 35 # regex pcre/ecma262, utf-8
		1412	# 36 # mime message rfc2045, utf-8
		1413	);
		1414
		1415	sub default_filter {
		1416	&{ $FILTER{$_[0]} or return }
		1417	}
		1418
		1419	our %SAFE_FILTER = map { $_ => $FILTER{$_} } 0, 1, 21, 22, 23, 32;
		1420
		1421	sub safe_filter {
		1422	&{ $SAFE_FILTER{$_[0]} or return }
		1423	}
		1424
		1425	sub URI::TO_CBOR {
		1426	my $uri = $_[0]->as_string;
		1427	utf8::upgrade $uri;
		1428	tag 32, $uri
		1429	}
		1430
		1431	sub Math::BigInt::TO_CBOR {
		1432	if (-2147483648 <= $_[0] && $_[0] <= 2147483647) {
		1433	$_[0]->numify
		1434	} else {
		1435	my $hex = substr $_[0]->as_hex, 2;
		1436	$hex = "0$hex" if 1 & length $hex; # sigh
		1437	tag $_[0] >= 0 ? 2 : 3, pack "H*", $hex
		1438	}
		1439	}
		1440
		1441	sub Math::BigFloat::TO_CBOR {
		1442	my ($m, $e) = $_[0]->parts;
		1443
		1444	-9223372036854775808 <= $e && $e <= 18446744073709551615
		1445	? tag 4, [$e->numify, $m]
		1446	: tag 264, [$e, $m]
		1447	}
		1448
		1449	sub Math::BigRat::TO_CBOR {
		1450	my ($n, $d) = $_[0]->parts;
		1451
		1452	# older versions of BigRat need *1, as they not always return numbers
		1453
		1454	$d*1 == 1
		1455	? $n*1
		1456	: tag 30, [$n*1, $d*1]
		1457	}
		1458
		1459	sub Time::Piece::TO_CBOR {
		1460	tag 1, 0 + $_[0]->epoch
		1461	}
		1462
372	XSLoader::load "CBOR::XS", $VERSION;	1463	XSLoader::load "CBOR::XS", $VERSION;
373
374	package CBOR::XS::Boolean;
375
376	use overload
377	"0+" => sub { ${$_[0]} },
378	"++" => sub { $_[0] = ${$_[0]} + 1 },
379	"--" => sub { $_[0] = ${$_[0]} - 1 },
380	fallback => 1;
381
382	1;
383		1464
384	=head1 SEE ALSO	1465	=head1 SEE ALSO
385		1466
386	The L<JSON> and L<JSON::XS> modules that do similar, but human-readable,	1467	The L<JSON> and L<JSON::XS> modules that do similar, but human-readable,
387	serialisation.	1468	serialisation.
388		1469
		1470	The L<Types::Serialiser> module provides the data model for true, false
		1471	and error values.
		1472
389	=head1 AUTHOR	1473	=head1 AUTHOR
390		1474
391	Marc Lehmann <schmorp@schmorp.de>	1475	Marc Lehmann <schmorp@schmorp.de>
392	http://home.schmorp.de/	1476	http://home.schmorp.de/
393		1477
394	=cut	1478	=cut
395		1479
		1480	1
		1481

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