[ViewVC] Diff of: cvs/CBOR-XS/README

Comparing CBOR-XS/README (file contents):
Revision 1.7 by root, Tue Oct 29 15:56:31 2013 UTC vs.
Revision 1.20 by root, Tue Dec 1 01:50:01 2020 UTC

…		…
21	# data was decoded	21	# data was decoded
22	substr $many_cbor_strings, 0, $length, ""; # remove decoded cbor string	22	substr $many_cbor_strings, 0, $length, ""; # remove decoded cbor string
23	}	23	}
24		24
25	DESCRIPTION	25	DESCRIPTION
26	WARNING! This module is very new, and not very well tested (that's up to
27	you to do). Furthermore, details of the implementation might change
28	freely before version 1.0. And lastly, the object serialisation protocol
29	depends on a pending IANA assignment, and until that assignment is
30	official, this implementation is not interoperable with other
31	implementations (even future versions of this module) until the
32	assignment is done.
33
34	You are still invited to try out CBOR, and this module.
35
36	This module converts Perl data structures to the Concise Binary Object	26	This module converts Perl data structures to the Concise Binary Object
37	Representation (CBOR) and vice versa. CBOR is a fast binary	27	Representation (CBOR) and vice versa. CBOR is a fast binary
38	serialisation format that aims to use a superset of the JSON data model,	28	serialisation format that aims to use an (almost) superset of the JSON
39	i.e. when you can represent something in JSON, you should be able to	29	data model, i.e. when you can represent something useful in JSON, you
40	represent it in CBOR.	30	should be able to represent it in CBOR.
41		31
42	In short, CBOR is a faster and very compact binary alternative to JSON,	32	In short, CBOR is a faster and quite compact binary alternative to JSON,
43	with the added ability of supporting serialisation of Perl objects.	33	with the added ability of supporting serialisation of Perl objects.
44	(JSON often compresses better than CBOR though, so if you plan to	34	(JSON often compresses better than CBOR though, so if you plan to
45	compress the data later you might want to compare both formats first).	35	compress the data later and speed is less important you might want to
		36	compare both formats first).
46		37
47	The primary goal of this module is to be correct and the secondary	38	The primary goal of this module is to be correct and the secondary
48	goal is to be fast. To reach the latter goal it was written in C.	39	goal is to be fast. To reach the latter goal it was written in C.
		40
		41	To give you a general idea about speed, with texts in the megabyte
		42	range, "CBOR::XS" usually encodes roughly twice as fast as Storable or
		43	JSON::XS and decodes about 15%-30% faster than those. The shorter the
		44	data, the worse Storable performs in comparison.
		45
		46	Regarding compactness, "CBOR::XS"-encoded data structures are usually
		47	about 20% smaller than the same data encoded as (compact) JSON or
		48	Storable.
		49
		50	In addition to the core CBOR data format, this module implements a
		51	number of extensions, to support cyclic and shared data structures (see
		52	"allow_sharing" and "allow_cycles"), string deduplication (see
		53	"pack_strings") and scalar references (always enabled).
49		54
50	See MAPPING, below, on how CBOR::XS maps perl values to CBOR values and	55	See MAPPING, below, on how CBOR::XS maps perl values to CBOR values and
51	vice versa.	56	vice versa.
52		57
53	FUNCTIONAL INTERFACE	58	FUNCTIONAL INTERFACE
…		…
72	disabled.	77	disabled.
73		78
74	The mutators for flags all return the CBOR object again and thus	79	The mutators for flags all return the CBOR object again and thus
75	calls can be chained:	80	calls can be chained:
76		81
77	#TODO my $cbor = CBOR::XS->new->encode ({a => [1,2]});	82	my $cbor = CBOR::XS->new->encode ({a => [1,2]});
		83
		84	$cbor = new_safe CBOR::XS
		85	Create a new, safe/secure CBOR::XS object. This is similar to "new",
		86	but configures the coder object to be safe to use with untrusted
		87	data. Currently, this is equivalent to:
		88
		89	my $cbor = CBOR::XS
		90	->new
		91	->forbid_objects
		92	->filter (\&CBOR::XS::safe_filter)
		93	->max_size (1e8);
		94
		95	But is more future proof (it is better to crash because of a change
		96	than to be exploited in other ways).
78		97
79	$cbor = $cbor->max_depth ([$maximum_nesting_depth])	98	$cbor = $cbor->max_depth ([$maximum_nesting_depth])
80	$max_depth = $cbor->get_max_depth	99	$max_depth = $cbor->get_max_depth
81	Sets the maximum nesting level (default 512) accepted while encoding	100	Sets the maximum nesting level (default 512) accepted while encoding
82	or decoding. If a higher nesting level is detected in CBOR data or a	101	or decoding. If a higher nesting level is detected in CBOR data or a
…		…
96		115
97	Note that nesting is implemented by recursion in C. The default	116	Note that nesting is implemented by recursion in C. The default
98	value has been chosen to be as large as typical operating systems	117	value has been chosen to be as large as typical operating systems
99	allow without crashing.	118	allow without crashing.
100		119
101	See SECURITY CONSIDERATIONS, below, for more info on why this is	120	See "SECURITY CONSIDERATIONS", below, for more info on why this is
102	useful.	121	useful.
103		122
104	$cbor = $cbor->max_size ([$maximum_string_size])	123	$cbor = $cbor->max_size ([$maximum_string_size])
105	$max_size = $cbor->get_max_size	124	$max_size = $cbor->get_max_size
106	Set the maximum length a CBOR string may have (in bytes) where	125	Set the maximum length a CBOR string may have (in bytes) where
…		…
110	exception. This setting has no effect on "encode" (yet).	129	exception. This setting has no effect on "encode" (yet).
111		130
112	If no argument is given, the limit check will be deactivated (same	131	If no argument is given, the limit check will be deactivated (same
113	as when 0 is specified).	132	as when 0 is specified).
114		133
115	See SECURITY CONSIDERATIONS, below, for more info on why this is	134	See "SECURITY CONSIDERATIONS", below, for more info on why this is
116	useful.	135	useful.
		136
		137	$cbor = $cbor->allow_unknown ([$enable])
		138	$enabled = $cbor->get_allow_unknown
		139	If $enable is true (or missing), then "encode" will not throw an
		140	exception when it encounters values it cannot represent in CBOR (for
		141	example, filehandles) but instead will encode a CBOR "error" value.
		142
		143	If $enable is false (the default), then "encode" will throw an
		144	exception when it encounters anything it cannot encode as CBOR.
		145
		146	This option does not affect "decode" in any way, and it is
		147	recommended to leave it off unless you know your communications
		148	partner.
		149
		150	$cbor = $cbor->allow_sharing ([$enable])
		151	$enabled = $cbor->get_allow_sharing
		152	If $enable is true (or missing), then "encode" will not
		153	double-encode values that have been referenced before (e.g. when the
		154	same object, such as an array, is referenced multiple times), but
		155	instead will emit a reference to the earlier value.
		156
		157	This means that such values will only be encoded once, and will not
		158	result in a deep cloning of the value on decode, in decoders
		159	supporting the value sharing extension. This also makes it possible
		160	to encode cyclic data structures (which need "allow_cycles" to be
		161	enabled to be decoded by this module).
		162
		163	It is recommended to leave it off unless you know your communication
		164	partner supports the value sharing extensions to CBOR
		165	(<http://cbor.schmorp.de/value-sharing>), as without decoder
		166	support, the resulting data structure might be unusable.
		167
		168	Detecting shared values incurs a runtime overhead when values are
		169	encoded that have a reference counter large than one, and might
		170	unnecessarily increase the encoded size, as potentially shared
		171	values are encoded as shareable whether or not they are actually
		172	shared.
		173
		174	At the moment, only targets of references can be shared (e.g.
		175	scalars, arrays or hashes pointed to by a reference). Weirder
		176	constructs, such as an array with multiple "copies" of the same
		177	string, which are hard but not impossible to create in Perl, are not
		178	supported (this is the same as with Storable).
		179
		180	If $enable is false (the default), then "encode" will encode shared
		181	data structures repeatedly, unsharing them in the process. Cyclic
		182	data structures cannot be encoded in this mode.
		183
		184	This option does not affect "decode" in any way - shared values and
		185	references will always be decoded properly if present.
		186
		187	$cbor = $cbor->allow_cycles ([$enable])
		188	$enabled = $cbor->get_allow_cycles
		189	If $enable is true (or missing), then "decode" will happily decode
		190	self-referential (cyclic) data structures. By default these will not
		191	be decoded, as they need manual cleanup to avoid memory leaks, so
		192	code that isn't prepared for this will not leak memory.
		193
		194	If $enable is false (the default), then "decode" will throw an error
		195	when it encounters a self-referential/cyclic data structure.
		196
		197	FUTURE DIRECTION: the motivation behind this option is to avoid
		198	real cycles - future versions of this module might chose to decode
		199	cyclic data structures using weak references when this option is
		200	off, instead of throwing an error.
		201
		202	This option does not affect "encode" in any way - shared values and
		203	references will always be encoded properly if present.
		204
		205	$cbor = $cbor->forbid_objects ([$enable])
		206	$enabled = $cbor->get_forbid_objects
		207	Disables the use of the object serialiser protocol.
		208
		209	If $enable is true (or missing), then "encode" will will throw an
		210	exception when it encounters perl objects that would be encoded
		211	using the perl-object tag (26). When "decode" encounters such tags,
		212	it will fall back to the general filter/tagged logic as if this were
		213	an unknown tag (by default resulting in a "CBOR::XC::Tagged"
		214	object).
		215
		216	If $enable is false (the default), then "encode" will use the
		217	Types::Serialiser object serialisation protocol to serialise objects
		218	into perl-object tags, and "decode" will do the same to decode such
		219	tags.
		220
		221	See "SECURITY CONSIDERATIONS", below, for more info on why
		222	forbidding this protocol can be useful.
		223
		224	$cbor = $cbor->pack_strings ([$enable])
		225	$enabled = $cbor->get_pack_strings
		226	If $enable is true (or missing), then "encode" will try not to
		227	encode the same string twice, but will instead encode a reference to
		228	the string instead. Depending on your data format, this can save a
		229	lot of space, but also results in a very large runtime overhead
		230	(expect encoding times to be 2-4 times as high as without).
		231
		232	It is recommended to leave it off unless you know your
		233	communications partner supports the stringref extension to CBOR
		234	(<http://cbor.schmorp.de/stringref>), as without decoder support,
		235	the resulting data structure might not be usable.
		236
		237	If $enable is false (the default), then "encode" will encode strings
		238	the standard CBOR way.
		239
		240	This option does not affect "decode" in any way - string references
		241	will always be decoded properly if present.
		242
		243	$cbor = $cbor->text_keys ([$enable])
		244	$enabled = $cbor->get_text_keys
		245	If $enabled is true (or missing), then "encode" will encode all perl
		246	hash keys as CBOR text strings/UTF-8 string, upgrading them as
		247	needed.
		248
		249	If $enable is false (the default), then "encode" will encode hash
		250	keys normally - upgraded perl strings (strings internally encoded as
		251	UTF-8) as CBOR text strings, and downgraded perl strings as CBOR
		252	byte strings.
		253
		254	This option does not affect "decode" in any way.
		255
		256	This option is useful for interoperability with CBOR decoders that
		257	don't treat byte strings as a form of text. It is especially useful
		258	as Perl gives very little control over hash keys.
		259
		260	Enabling this option can be slow, as all downgraded hash keys that
		261	are encoded need to be scanned and converted to UTF-8.
		262
		263	$cbor = $cbor->text_strings ([$enable])
		264	$enabled = $cbor->get_text_strings
		265	This option works similar to "text_keys", above, but works on all
		266	strings (including hash keys), so "text_keys" has no further effect
		267	after enabling "text_strings".
		268
		269	If $enabled is true (or missing), then "encode" will encode all perl
		270	strings as CBOR text strings/UTF-8 strings, upgrading them as
		271	needed.
		272
		273	If $enable is false (the default), then "encode" will encode strings
		274	normally (but see "text_keys") - upgraded perl strings (strings
		275	internally encoded as UTF-8) as CBOR text strings, and downgraded
		276	perl strings as CBOR byte strings.
		277
		278	This option does not affect "decode" in any way.
		279
		280	This option has similar advantages and disadvantages as "text_keys".
		281	In addition, this option effectively removes the ability to
		282	automatically encode byte strings, which might break some "FREEZE"
		283	and "TO_CBOR" methods that rely on this.
		284
		285	A workaround is to use explicit type casts, which are unaffected by
		286	this option.
		287
		288	$cbor = $cbor->validate_utf8 ([$enable])
		289	$enabled = $cbor->get_validate_utf8
		290	If $enable is true (or missing), then "decode" will validate that
		291	elements (text strings) containing UTF-8 data in fact contain valid
		292	UTF-8 data (instead of blindly accepting it). This validation
		293	obviously takes extra time during decoding.
		294
		295	The concept of "valid UTF-8" used is perl's concept, which is a
		296	superset of the official UTF-8.
		297
		298	If $enable is false (the default), then "decode" will blindly accept
		299	UTF-8 data, marking them as valid UTF-8 in the resulting data
		300	structure regardless of whether that's true or not.
		301
		302	Perl isn't too happy about corrupted UTF-8 in strings, but should
		303	generally not crash or do similarly evil things. Extensions might be
		304	not so forgiving, so it's recommended to turn on this setting if you
		305	receive untrusted CBOR.
		306
		307	This option does not affect "encode" in any way - strings that are
		308	supposedly valid UTF-8 will simply be dumped into the resulting CBOR
		309	string without checking whether that is, in fact, true or not.
		310
		311	$cbor = $cbor->filter ([$cb->($tag, $value)])
		312	$cb_or_undef = $cbor->get_filter
		313	Sets or replaces the tagged value decoding filter (when $cb is
		314	specified) or clears the filter (if no argument or "undef" is
		315	provided).
		316
		317	The filter callback is called only during decoding, when a
		318	non-enforced tagged value has been decoded (see "TAG HANDLING AND
		319	EXTENSIONS" for a list of enforced tags). For specific tags, it's
		320	often better to provide a default converter using the
		321	%CBOR::XS::FILTER hash (see below).
		322
		323	The first argument is the numerical tag, the second is the (decoded)
		324	value that has been tagged.
		325
		326	The filter function should return either exactly one value, which
		327	will replace the tagged value in the decoded data structure, or no
		328	values, which will result in default handling, which currently means
		329	the decoder creates a "CBOR::XS::Tagged" object to hold the tag and
		330	the value.
		331
		332	When the filter is cleared (the default state), the default filter
		333	function, "CBOR::XS::default_filter", is used. This function simply
		334	looks up the tag in the %CBOR::XS::FILTER hash. If an entry exists
		335	it must be a code reference that is called with tag and value, and
		336	is responsible for decoding the value. If no entry exists, it
		337	returns no values. "CBOR::XS" provides a number of default filter
		338	functions already, the the %CBOR::XS::FILTER hash can be freely
		339	extended with more.
		340
		341	"CBOR::XS" additionally provides an alternative filter function that
		342	is supposed to be safe to use with untrusted data (which the default
		343	filter might not), called "CBOR::XS::safe_filter", which works the
		344	same as the "default_filter" but uses the %CBOR::XS::SAFE_FILTER
		345	variable instead. It is prepopulated with the tag decoding functions
		346	that are deemed safe (basically the same as %CBOR::XS::FILTER
		347	without all the bignum tags), and can be extended by user code as
		348	wlel, although, obviously, one should be very careful about adding
		349	decoding functions here, since the expectation is that they are safe
		350	to use on untrusted data, after all.
		351
		352	Example: decode all tags not handled internally into
		353	"CBOR::XS::Tagged" objects, with no other special handling (useful
		354	when working with potentially "unsafe" CBOR data).
		355
		356	CBOR::XS->new->filter (sub { })->decode ($cbor_data);
		357
		358	Example: provide a global filter for tag 1347375694, converting the
		359	value into some string form.
		360
		361	$CBOR::XS::FILTER{1347375694} = sub {
		362	my ($tag, $value);
		363
		364	"tag 1347375694 value $value"
		365	};
		366
		367	Example: provide your own filter function that looks up tags in your
		368	own hash:
		369
		370	my %my_filter = (
		371	998347484 => sub {
		372	my ($tag, $value);
		373
		374	"tag 998347484 value $value"
		375	};
		376	);
		377
		378	my $coder = CBOR::XS->new->filter (sub {
		379	&{ $my_filter{$_[0]} or return }
		380	});
		381
		382	Example: use the safe filter function (see "SECURITY CONSIDERATIONS"
		383	for more considerations on security).
		384
		385	CBOR::XS->new->filter (\&CBOR::XS::safe_filter)->decode ($cbor_data);
117		386
118	$cbor_data = $cbor->encode ($perl_scalar)	387	$cbor_data = $cbor->encode ($perl_scalar)
119	Converts the given Perl data structure (a scalar value) to its CBOR	388	Converts the given Perl data structure (a scalar value) to its CBOR
120	representation.	389	representation.
121		390
…		…
129	will silently stop parsing there and return the number of characters	398	will silently stop parsing there and return the number of characters
130	consumed so far.	399	consumed so far.
131		400
132	This is useful if your CBOR texts are not delimited by an outer	401	This is useful if your CBOR texts are not delimited by an outer
133	protocol and you need to know where the first CBOR string ends amd	402	protocol and you need to know where the first CBOR string ends amd
134	the next one starts.	403	the next one starts - CBOR strings are self-delimited, so it is
		404	possible to concatenate CBOR strings without any delimiters or size
		405	fields and recover their data.
135		406
136	CBOR::XS->new->decode_prefix ("......")	407	CBOR::XS->new->decode_prefix ("......")
137	=> ("...", 3)	408	=> ("...", 3)
		409
		410	INCREMENTAL PARSING
		411	In some cases, there is the need for incremental parsing of JSON texts.
		412	While this module always has to keep both CBOR text and resulting Perl
		413	data structure in memory at one time, it does allow you to parse a CBOR
		414	stream incrementally, using a similar to using "decode_prefix" to see if
		415	a full CBOR object is available, but is much more efficient.
		416
		417	It basically works by parsing as much of a CBOR string as possible - if
		418	the CBOR data is not complete yet, the pasrer will remember where it
		419	was, to be able to restart when more data has been accumulated. Once
		420	enough data is available to either decode a complete CBOR value or raise
		421	an error, a real decode will be attempted.
		422
		423	A typical use case would be a network protocol that consists of sending
		424	and receiving CBOR-encoded messages. The solution that works with CBOR
		425	and about anything else is by prepending a length to every CBOR value,
		426	so the receiver knows how many octets to read. More compact (and
		427	slightly slower) would be to just send CBOR values back-to-back, as
		428	"CBOR::XS" knows where a CBOR value ends, and doesn't need an explicit
		429	length.
		430
		431	The following methods help with this:
		432
		433	@decoded = $cbor->incr_parse ($buffer)
		434	This method attempts to decode exactly one CBOR value from the
		435	beginning of the given $buffer. The value is removed from the
		436	$buffer on success. When $buffer doesn't contain a complete value
		437	yet, it returns nothing. Finally, when the $buffer doesn't start
		438	with something that could ever be a valid CBOR value, it raises an
		439	exception, just as "decode" would. In the latter case the decoder
		440	state is undefined and must be reset before being able to parse
		441	further.
		442
		443	This method modifies the $buffer in place. When no CBOR value can be
		444	decoded, the decoder stores the current string offset. On the next
		445	call, continues decoding at the place where it stopped before. For
		446	this to make sense, the $buffer must begin with the same octets as
		447	on previous unsuccessful calls.
		448
		449	You can call this method in scalar context, in which case it either
		450	returns a decoded value or "undef". This makes it impossible to
		451	distinguish between CBOR null values (which decode to "undef") and
		452	an unsuccessful decode, which is often acceptable.
		453
		454	@decoded = $cbor->incr_parse_multiple ($buffer)
		455	Same as "incr_parse", but attempts to decode as many CBOR values as
		456	possible in one go, instead of at most one. Calls to "incr_parse"
		457	and "incr_parse_multiple" can be interleaved.
		458
		459	$cbor->incr_reset
		460	Resets the incremental decoder. This throws away any saved state, so
		461	that subsequent calls to "incr_parse" or "incr_parse_multiple" start
		462	to parse a new CBOR value from the beginning of the $buffer again.
		463
		464	This method can be called at any time, but it must be called if
		465	you want to change your $buffer or there was a decoding error and
		466	you want to reuse the $cbor object for future incremental parsings.
138		467
139	MAPPING	468	MAPPING
140	This section describes how CBOR::XS maps Perl values to CBOR values and	469	This section describes how CBOR::XS maps Perl values to CBOR values and
141	vice versa. These mappings are designed to "do the right thing" in most	470	vice versa. These mappings are designed to "do the right thing" in most
142	circumstances automatically, preserving round-tripping characteristics	471	circumstances automatically, preserving round-tripping characteristics
…		…
150	integers	479	integers
151	CBOR integers become (numeric) perl scalars. On perls without 64 bit	480	CBOR integers become (numeric) perl scalars. On perls without 64 bit
152	support, 64 bit integers will be truncated or otherwise corrupted.	481	support, 64 bit integers will be truncated or otherwise corrupted.
153		482
154	byte strings	483	byte strings
155	Byte strings will become octet strings in Perl (the byte values	484	Byte strings will become octet strings in Perl (the Byte values
156	0..255 will simply become characters of the same value in Perl).	485	0..255 will simply become characters of the same value in Perl).
157		486
158	UTF-8 strings	487	UTF-8 strings
159	UTF-8 strings in CBOR will be decoded, i.e. the UTF-8 octets will be	488	UTF-8 strings in CBOR will be decoded, i.e. the UTF-8 octets will be
160	decoded into proper Unicode code points. At the moment, the validity	489	decoded into proper Unicode code points. At the moment, the validity
…		…
174	"Types:Serialiser::false" and "Types::Serialiser::error",	503	"Types:Serialiser::false" and "Types::Serialiser::error",
175	respectively. They are overloaded to act almost exactly like the	504	respectively. They are overloaded to act almost exactly like the
176	numbers 1 and 0 (for true and false) or to throw an exception on	505	numbers 1 and 0 (for true and false) or to throw an exception on
177	access (for error). See the Types::Serialiser manpage for details.	506	access (for error). See the Types::Serialiser manpage for details.
178		507
179	CBOR tag 256 (perl object)	508	tagged values
180	The tag value 256 (TODO: pending iana registration) will be used to
181	deserialise a Perl object serialised with "FREEZE". See OBJECT
182	SERIALISATION, below, for details.
183
184	CBOR tag 55799 (magic header)
185	The tag 55799 is ignored (this tag implements the magic header).
186
187	other CBOR tags
188	Tagged items consists of a numeric tag and another CBOR value. Tags	509	Tagged items consists of a numeric tag and another CBOR value.
189	not handled internally are currently converted into a
190	CBOR::XS::Tagged object, which is simply a blessed array reference
191	consisting of the numeric tag value followed by the (decoded) CBOR
192	value.
193		510
194	In the future, support for user-supplied conversions might get	511	See "TAG HANDLING AND EXTENSIONS" and the description of "->filter"
195	added.	512	for details on which tags are handled how.
196		513
197	anything else	514	anything else
198	Anything else (e.g. unsupported simple values) will raise a decoding	515	Anything else (e.g. unsupported simple values) will raise a decoding
199	error.	516	error.
200		517
201	PERL -> CBOR	518	PERL -> CBOR
202	The mapping from Perl to CBOR is slightly more difficult, as Perl is a	519	The mapping from Perl to CBOR is slightly more difficult, as Perl is a
203	truly typeless language, so we can only guess which CBOR type is meant	520	typeless language. That means this module can only guess which CBOR type
204	by a Perl value.	521	is meant by a perl value.
205		522
206	hash references	523	hash references
207	Perl hash references become CBOR maps. As there is no inherent	524	Perl hash references become CBOR maps. As there is no inherent
208	ordering in hash keys (or CBOR maps), they will usually be encoded	525	ordering in hash keys (or CBOR maps), they will usually be encoded
209	in a pseudo-random order.	526	in a pseudo-random order. This order can be different each time a
		527	hash is encoded.
210		528
211	Currently, tied hashes will use the indefinite-length format, while	529	Currently, tied hashes will use the indefinite-length format, while
212	normal hashes will use the fixed-length format.	530	normal hashes will use the fixed-length format.
213		531
214	array references	532	array references
215	Perl array references become fixed-length CBOR arrays.	533	Perl array references become fixed-length CBOR arrays.
216		534
217	other references	535	other references
218	Other unblessed references are generally not allowed and will cause	536	Other unblessed references will be represented using the indirection
219	an exception to be thrown, except for references to the integers 0	537	tag extension (tag value 22098,
220	and 1, which get turned into false and true in CBOR.	538	<http://cbor.schmorp.de/indirection>). CBOR decoders are guaranteed
		539	to be able to decode these values somehow, by either "doing the
		540	right thing", decoding into a generic tagged object, simply ignoring
		541	the tag, or something else.
221		542
222	CBOR::XS::Tagged objects	543	CBOR::XS::Tagged objects
223	Objects of this type must be arrays consisting of a single "[tag,	544	Objects of this type must be arrays consisting of a single "[tag,
224	value]" pair. The (numerical) tag will be encoded as a CBOR tag, the	545	value]" pair. The (numerical) tag will be encoded as a CBOR tag, the
225	value will be encoded as appropriate for the value. You cna use	546	value will be encoded as appropriate for the value. You must use
226	"CBOR::XS::tag" to create such objects.	547	"CBOR::XS::tag" to create such objects.
227		548
228	Types::Serialiser::true, Types::Serialiser::false,	549	Types::Serialiser::true, Types::Serialiser::false,
229	Types::Serialiser::error	550	Types::Serialiser::error
230	These special values become CBOR true, CBOR false and CBOR undefined	551	These special values become CBOR true, CBOR false and CBOR undefined
231	values, respectively. You can also use "\1", "\0" and "\undef"	552	values, respectively. You can also use "\1", "\0" and "\undef"
232	directly if you want.	553	directly if you want.
233		554
234	other blessed objects	555	other blessed objects
235	Other blessed objects are serialised via "TO_CBOR" or "FREEZE". See	556	Other blessed objects are serialised via "TO_CBOR" or "FREEZE". See
236	"OBJECT SERIALISATION", below, for details.	557	"TAG HANDLING AND EXTENSIONS" for specific classes handled by this
		558	module, and "OBJECT SERIALISATION" for generic object serialisation.
237		559
238	simple scalars	560	simple scalars
239	TODO Simple Perl scalars (any scalar that is not a reference) are	561	Simple Perl scalars (any scalar that is not a reference) are the
240	the most difficult objects to encode: CBOR::XS will encode undefined	562	most difficult objects to encode: CBOR::XS will encode undefined
241	scalars as CBOR null values, scalars that have last been used in a	563	scalars as CBOR null values, scalars that have last been used in a
242	string context before encoding as CBOR strings, and anything else as	564	string context before encoding as CBOR strings, and anything else as
243	number value:	565	number value:
244		566
245	# dump as number	567	# dump as number
246	encode_cbor [2] # yields [2]	568	encode_cbor [2] # yields [2]
247	encode_cbor [-3.0e17] # yields [-3e+17]	569	encode_cbor [-3.0e17] # yields [-3e+17]
248	my $value = 5; encode_cbor [$value] # yields [5]	570	my $value = 5; encode_cbor [$value] # yields [5]
249		571
250	# used as string, so dump as string	572	# used as string, so dump as string (either byte or text)
251	print $value;	573	print $value;
252	encode_cbor [$value] # yields ["5"]	574	encode_cbor [$value] # yields ["5"]
253		575
254	# undef becomes null	576	# undef becomes null
255	encode_cbor [undef] # yields [null]	577	encode_cbor [undef] # yields [null]
…		…
258		580
259	my $x = 3.1; # some variable containing a number	581	my $x = 3.1; # some variable containing a number
260	"$x"; # stringified	582	"$x"; # stringified
261	$x .= ""; # another, more awkward way to stringify	583	$x .= ""; # another, more awkward way to stringify
262	print $x; # perl does it for you, too, quite often	584	print $x; # perl does it for you, too, quite often
		585
		586	You can force whether a string is encoded as byte or text string by
		587	using "utf8::upgrade" and "utf8::downgrade" (if "text_strings" is
		588	disabled).
		589
		590	utf8::upgrade $x; # encode $x as text string
		591	utf8::downgrade $x; # encode $x as byte string
		592
		593	More options are available, see "TYPE CASTS", below, and the
		594	"text_keys" and "text_strings" options.
		595
		596	Perl doesn't define what operations up- and downgrade strings, so if
		597	the difference between byte and text is important, you should up- or
		598	downgrade your string as late as possible before encoding. You can
		599	also force the use of CBOR text strings by using "text_keys" or
		600	"text_strings".
263		601
264	You can force the type to be a CBOR number by numifying it:	602	You can force the type to be a CBOR number by numifying it:
265		603
266	my $x = "3"; # some variable containing a string	604	my $x = "3"; # some variable containing a string
267	$x += 0; # numify it, ensuring it will be dumped as a number	605	$x += 0; # numify it, ensuring it will be dumped as a number
…		…
276	IEEE single format if possible without loss of precision, otherwise	614	IEEE single format if possible without loss of precision, otherwise
277	the IEEE double format will be used. Perls that use formats other	615	the IEEE double format will be used. Perls that use formats other
278	than IEEE double to represent numerical values are supported, but	616	than IEEE double to represent numerical values are supported, but
279	might suffer loss of precision.	617	might suffer loss of precision.
280		618
		619	TYPE CASTS
		620	EXPERIMENTAL: As an experimental extension, "CBOR::XS" allows you to
		621	force specific cbor types to be used when encoding. That allows you to
		622	encode types not normally accessible (e.g. half floats) as well as force
		623	string types even when "text_strings" is in effect.
		624
		625	Type forcing is done by calling a special "cast" function which keeps a
		626	copy of the value and returns a new value that can be handed over to any
		627	CBOR encoder function.
		628
		629	The following casts are currently available (all of which are unary
		630	operators):
		631
		632	CBOR::XS::as_int $value
		633	Forces the value to be encoded as some form of (basic, not bignum)
		634	integer type.
		635
		636	CBOR::XS::as_text $value
		637	Forces the value to be encoded as (UTF-8) text values.
		638
		639	CBOR::XS::as_bytes $value
		640	Forces the value to be encoded as a (binary) string value.
		641
		642	CBOR::XS::as_bool $value
		643	Converts a Perl boolean (which can be any kind of scalar) into a
		644	CBOR boolean. Strictly the same, but shorter to write, than:
		645
		646	$value ? Types::Serialiser::true : Types::Serialiser::false
		647
		648	CBOR::XS::as_float16 $value
		649	Forces half-float (IEEE 754 binary16) encoding of the given value.
		650
		651	CBOR::XS::as_float32 $value
		652	Forces single-float (IEEE 754 binary32) encoding of the given value.
		653
		654	CBOR::XS::as_float64 $value
		655	Forces double-float (IEEE 754 binary64) encoding of the given value.
		656
		657	=item, CBOR::XS::as_cbor $cbor_text
		658
		659	Bot a type cast per-se, this type cast forces the argument to eb
		660	encoded as-is. This can be used to embed pre-encoded CBOR data.
		661
		662	Note that no checking on the validity of the $cbor_text is done -
		663	it's the callers responsibility to correctly encode values.
		664
		665	Example: encode a perl string as binary even though "text_strings" is in
		666	effect.
		667
		668	CBOR::XS->new->text_strings->encode ([4, "text", CBOR::XS::bytes "bytevalue"]);
		669
281	OBJECT SERIALISATION	670	OBJECT SERIALISATION
		671	This module implements both a CBOR-specific and the generic
		672	Types::Serialier object serialisation protocol. The following
		673	subsections explain both methods.
		674
		675	ENCODING
282	This module knows two way to serialise a Perl object: The CBOR-specific	676	This module knows two way to serialise a Perl object: The CBOR-specific
283	way, and the generic way.	677	way, and the generic way.
284		678
285	Whenever the encoder encounters a Perl object that it cnanot serialise	679	Whenever the encoder encounters a Perl object that it cannot serialise
286	directly (most of them), it will first look up the "TO_CBOR" method on	680	directly (most of them), it will first look up the "TO_CBOR" method on
287	it.	681	it.
288		682
289	If it has a "TO_CBOR" method, it will call it with the object as only	683	If it has a "TO_CBOR" method, it will call it with the object as only
290	argument, and expects exactly one return value, which it will then	684	argument, and expects exactly one return value, which it will then
…		…
295	"CBOR" as the second argument, to distinguish it from other serialisers.	689	"CBOR" as the second argument, to distinguish it from other serialisers.
296		690
297	The "FREEZE" method can return any number of values (i.e. zero or more).	691	The "FREEZE" method can return any number of values (i.e. zero or more).
298	These will be encoded as CBOR perl object, together with the classname.	692	These will be encoded as CBOR perl object, together with the classname.
299		693
		694	These methods MUST NOT change the data structure that is being
		695	serialised. Failure to comply to this can result in memory corruption -
		696	and worse.
		697
300	If an object supports neither "TO_CBOR" nor "FREEZE", encoding will fail	698	If an object supports neither "TO_CBOR" nor "FREEZE", encoding will fail
301	with an error.	699	with an error.
302		700
		701	DECODING
303	Objects encoded via "TO_CBOR" cannot be automatically decoded, but	702	Objects encoded via "TO_CBOR" cannot (normally) be automatically
304	objects encoded via "FREEZE" can be decoded using the following	703	decoded, but objects encoded via "FREEZE" can be decoded using the
305	protocol:	704	following protocol:
306		705
307	When an encoded CBOR perl object is encountered by the decoder, it will	706	When an encoded CBOR perl object is encountered by the decoder, it will
308	look up the "THAW" method, by using the stored classname, and will fail	707	look up the "THAW" method, by using the stored classname, and will fail
309	if the method cannot be found.	708	if the method cannot be found.
310		709
…		…
331		730
332	sub URI::TO_CBOR {	731	sub URI::TO_CBOR {
333	my ($self) = @_;	732	my ($self) = @_;
334	my $uri = "$self"; # stringify uri	733	my $uri = "$self"; # stringify uri
335	utf8::upgrade $uri; # make sure it will be encoded as UTF-8 string	734	utf8::upgrade $uri; # make sure it will be encoded as UTF-8 string
336	CBOR::XS::tagged 32, "$_[0]"	735	CBOR::XS::tag 32, "$_[0]"
337	}	736	}
338		737
339	This will encode URIs as a UTF-8 string with tag 32, which indicates an	738	This will encode URIs as a UTF-8 string with tag 32, which indicates an
340	URI.	739	URI.
341		740
…		…
352	"$self" # encode url string	751	"$self" # encode url string
353	}	752	}
354		753
355	sub URI::THAW {	754	sub URI::THAW {
356	my ($class, $serialiser, $uri) = @_;	755	my ($class, $serialiser, $uri) = @_;
357
358	$class->new ($uri)	756	$class->new ($uri)
359	}	757	}
360		758
361	Unlike "TO_CBOR", multiple values can be returned by "FREEZE". For	759	Unlike "TO_CBOR", multiple values can be returned by "FREEZE". For
362	example, a "FREEZE" method that returns "type", "id" and "variant"	760	example, a "FREEZE" method that returns "type", "id" and "variant"
…		…
376		774
377	MAGIC HEADER	775	MAGIC HEADER
378	There is no way to distinguish CBOR from other formats programmatically.	776	There is no way to distinguish CBOR from other formats programmatically.
379	To make it easier to distinguish CBOR from other formats, the CBOR	777	To make it easier to distinguish CBOR from other formats, the CBOR
380	specification has a special "magic string" that can be prepended to any	778	specification has a special "magic string" that can be prepended to any
381	CBOR string without changing it's meaning.	779	CBOR string without changing its meaning.
382		780
383	This string is available as $CBOR::XS::MAGIC. This module does not	781	This string is available as $CBOR::XS::MAGIC. This module does not
384	prepend this string tot he CBOR data it generates, but it will ignroe it	782	prepend this string to the CBOR data it generates, but it will ignore it
385	if present, so users can prepend this string as a "file type" indicator	783	if present, so users can prepend this string as a "file type" indicator
386	as required.	784	as required.
387		785
388	THE CBOR::XS::Tagged CLASS	786	THE CBOR::XS::Tagged CLASS
389	CBOR has the concept of tagged values - any CBOR value can be tagged	787	CBOR has the concept of tagged values - any CBOR value can be tagged
…		…
440	Wrap CBOR data in CBOR:	838	Wrap CBOR data in CBOR:
441		839
442	my $cbor_cbor = encode_cbor	840	my $cbor_cbor = encode_cbor
443	CBOR::XS::tag 24,	841	CBOR::XS::tag 24,
444	encode_cbor [1, 2, 3];	842	encode_cbor [1, 2, 3];
		843
		844	TAG HANDLING AND EXTENSIONS
		845	This section describes how this module handles specific tagged values
		846	and extensions. If a tag is not mentioned here and no additional filters
		847	are provided for it, then the default handling applies (creating a
		848	CBOR::XS::Tagged object on decoding, and only encoding the tag when
		849	explicitly requested).
		850
		851	Tags not handled specifically are currently converted into a
		852	CBOR::XS::Tagged object, which is simply a blessed array reference
		853	consisting of the numeric tag value followed by the (decoded) CBOR
		854	value.
		855
		856	Future versions of this module reserve the right to special case
		857	additional tags (such as base64url).
		858
		859	ENFORCED TAGS
		860	These tags are always handled when decoding, and their handling cannot
		861	be overridden by the user.
		862
		863	26 (perl-object, <http://cbor.schmorp.de/perl-object>)
		864	These tags are automatically created (and decoded) for serialisable
		865	objects using the "FREEZE/THAW" methods (the Types::Serialier object
		866	serialisation protocol). See "OBJECT SERIALISATION" for details.
		867
		868	28, 29 (shareable, sharedref, <http://cbor.schmorp.de/value-sharing>)
		869	These tags are automatically decoded when encountered (and they do
		870	not result in a cyclic data structure, see "allow_cycles"),
		871	resulting in shared values in the decoded object. They are only
		872	encoded, however, when "allow_sharing" is enabled.
		873
		874	Not all shared values can be successfully decoded: values that
		875	reference themselves will currently decode as "undef" (this is not
		876	the same as a reference pointing to itself, which will be
		877	represented as a value that contains an indirect reference to itself
		878	- these will be decoded properly).
		879
		880	Note that considerably more shared value data structures can be
		881	decoded than will be encoded - currently, only values pointed to by
		882	references will be shared, others will not. While non-reference
		883	shared values can be generated in Perl with some effort, they were
		884	considered too unimportant to be supported in the encoder. The
		885	decoder, however, will decode these values as shared values.
		886
		887	256, 25 (stringref-namespace, stringref,
		888	<http://cbor.schmorp.de/stringref>)
		889	These tags are automatically decoded when encountered. They are only
		890	encoded, however, when "pack_strings" is enabled.
		891
		892	22098 (indirection, <http://cbor.schmorp.de/indirection>)
		893	This tag is automatically generated when a reference are encountered
		894	(with the exception of hash and array references). It is converted
		895	to a reference when decoding.
		896
		897	55799 (self-describe CBOR, RFC 7049)
		898	This value is not generated on encoding (unless explicitly requested
		899	by the user), and is simply ignored when decoding.
		900
		901	NON-ENFORCED TAGS
		902	These tags have default filters provided when decoding. Their handling
		903	can be overridden by changing the %CBOR::XS::FILTER entry for the tag,
		904	or by providing a custom "filter" callback when decoding.
		905
		906	When they result in decoding into a specific Perl class, the module
		907	usually provides a corresponding "TO_CBOR" method as well.
		908
		909	When any of these need to load additional modules that are not part of
		910	the perl core distribution (e.g. URI), it is (currently) up to the user
		911	to provide these modules. The decoding usually fails with an exception
		912	if the required module cannot be loaded.
		913
		914	0, 1 (date/time string, seconds since the epoch)
		915	These tags are decoded into Time::Piece objects. The corresponding
		916	"Time::Piece::TO_CBOR" method always encodes into tag 1 values
		917	currently.
		918
		919	The Time::Piece API is generally surprisingly bad, and fractional
		920	seconds are only accidentally kept intact, so watch out. On the plus
		921	side, the module comes with perl since 5.10, which has to count for
		922	something.
		923
		924	2, 3 (positive/negative bignum)
		925	These tags are decoded into Math::BigInt objects. The corresponding
		926	"Math::BigInt::TO_CBOR" method encodes "small" bigints into normal
		927	CBOR integers, and others into positive/negative CBOR bignums.
		928
		929	4, 5, 264, 265 (decimal fraction/bigfloat)
		930	Both decimal fractions and bigfloats are decoded into Math::BigFloat
		931	objects. The corresponding "Math::BigFloat::TO_CBOR" method always
		932	encodes into a decimal fraction (either tag 4 or 264).
		933
		934	NaN and infinities are not encoded properly, as they cannot be
		935	represented in CBOR.
		936
		937	See "BIGNUM SECURITY CONSIDERATIONS" for more info.
		938
		939	30 (rational numbers)
		940	These tags are decoded into Math::BigRat objects. The corresponding
		941	"Math::BigRat::TO_CBOR" method encodes rational numbers with
		942	denominator 1 via their numerator only, i.e., they become normal
		943	integers or "bignums".
		944
		945	See "BIGNUM SECURITY CONSIDERATIONS" for more info.
		946
		947	21, 22, 23 (expected later JSON conversion)
		948	CBOR::XS is not a CBOR-to-JSON converter, and will simply ignore
		949	these tags.
		950
		951	32 (URI)
		952	These objects decode into URI objects. The corresponding
		953	"URI::TO_CBOR" method again results in a CBOR URI value.
445		954
446	CBOR and JSON	955	CBOR and JSON
447	CBOR is supposed to implement a superset of the JSON data model, and is,	956	CBOR is supposed to implement a superset of the JSON data model, and is,
448	with some coercion, able to represent all JSON texts (something that	957	with some coercion, able to represent all JSON texts (something that
449	other "binary JSON" formats such as BSON generally do not support).	958	other "binary JSON" formats such as BSON generally do not support).
…		…
455	interoperability is improved in the future, then the goal will be to	964	interoperability is improved in the future, then the goal will be to
456	ensure that decoded JSON data will round-trip encoding and decoding to	965	ensure that decoded JSON data will round-trip encoding and decoding to
457	CBOR intact.	966	CBOR intact.
458		967
459	SECURITY CONSIDERATIONS	968	SECURITY CONSIDERATIONS
460	When you are using CBOR in a protocol, talking to untrusted potentially	969	Tl;dr... if you want to decode or encode CBOR from untrusted sources,
461	hostile creatures requires relatively few measures.	970	you should start with a coder object created via "new_safe" (which
		971	implements the mitigations explained below):
462		972
		973	my $coder = CBOR::XS->new_safe;
		974
		975	my $data = $coder->decode ($cbor_text);
		976	my $cbor = $coder->encode ($data);
		977
		978	Longer version: When you are using CBOR in a protocol, talking to
		979	untrusted potentially hostile creatures requires some thought:
		980
		981	Security of the CBOR decoder itself
463	First of all, your CBOR decoder should be secure, that is, should not	982	First and foremost, your CBOR decoder should be secure, that is,
464	have any buffer overflows. Obviously, this module should ensure that and	983	should not have any buffer overflows or similar bugs that could
		984	potentially be exploited. Obviously, this module should ensure that
465	I am trying hard on making that true, but you never know.	985	and I am trying hard on making that true, but you never know.
466		986
		987	CBOR::XS can invoke almost arbitrary callbacks during decoding
		988	CBOR::XS supports object serialisation - decoding CBOR can cause
		989	calls to any "THAW" method in any package that exists in your
		990	process (that is, CBOR::XS will not try to load modules, but any
		991	existing "THAW" method or function can be called, so they all have
		992	to be secure).
		993
		994	Less obviously, it will also invoke "TO_CBOR" and "FREEZE" methods -
		995	even if all your "THAW" methods are secure, encoding data structures
		996	from untrusted sources can invoke those and trigger bugs in those.
		997
		998	So, if you are not sure about the security of all the modules you
		999	have loaded (you shouldn't), you should disable this part using
		1000	"forbid_objects" or using "new_safe".
		1001
		1002	CBOR can be extended with tags that call library code
		1003	CBOR can be extended with tags, and "CBOR::XS" has a registry of
		1004	conversion functions for many existing tags that can be extended via
		1005	third-party modules (see the "filter" method).
		1006
		1007	If you don't trust these, you should configure the "safe" filter
		1008	function, "CBOR::XS::safe_filter" ("new_safe" does this), which by
		1009	default only includes conversion functions that are considered
		1010	"safe" by the author (but again, they can be extended by third party
		1011	modules).
		1012
		1013	Depending on your level of paranoia, you can use the "safe" filter:
		1014
		1015	$cbor->filter (\&CBOR::XS::safe_filter);
		1016
		1017	... your own filter...
		1018
		1019	$cbor->filter (sub { ... do your stuffs here ... });
		1020
		1021	... or even no filter at all, disabling all tag decoding:
		1022
		1023	$cbor->filter (sub { });
		1024
		1025	This is never a problem for encoding, as the tag mechanism only
		1026	exists in CBOR texts.
		1027
		1028	Resource-starving attacks: object memory usage
467	Second, you need to avoid resource-starving attacks. That means you	1029	You need to avoid resource-starving attacks. That means you should
468	should limit the size of CBOR data you accept, or make sure then when	1030	limit the size of CBOR data you accept, or make sure then when your
469	your resources run out, that's just fine (e.g. by using a separate	1031	resources run out, that's just fine (e.g. by using a separate
470	process that can crash safely). The size of a CBOR string in octets is	1032	process that can crash safely). The size of a CBOR string in octets
471	usually a good indication of the size of the resources required to	1033	is usually a good indication of the size of the resources required
472	decode it into a Perl structure. While CBOR::XS can check the size of	1034	to decode it into a Perl structure. While CBOR::XS can check the
		1035	size of the CBOR text (using "max_size" - done by "new_safe"), it
473	the CBOR text, it might be too late when you already have it in memory,	1036	might be too late when you already have it in memory, so you might
474	so you might want to check the size before you accept the string.	1037	want to check the size before you accept the string.
475		1038
		1039	As for encoding, it is possible to construct data structures that
		1040	are relatively small but result in large CBOR texts (for example by
		1041	having an array full of references to the same big data structure,
		1042	which will all be deep-cloned during encoding by default). This is
		1043	rarely an actual issue (and the worst case is still just running out
		1044	of memory), but you can reduce this risk by using "allow_sharing".
		1045
		1046	Resource-starving attacks: stack overflows
476	Third, CBOR::XS recurses using the C stack when decoding objects and	1047	CBOR::XS recurses using the C stack when decoding objects and
477	arrays. The C stack is a limited resource: for instance, on my amd64	1048	arrays. The C stack is a limited resource: for instance, on my amd64
478	machine with 8MB of stack size I can decode around 180k nested arrays	1049	machine with 8MB of stack size I can decode around 180k nested
479	but only 14k nested CBOR objects (due to perl itself recursing deeply on	1050	arrays but only 14k nested CBOR objects (due to perl itself
480	croak to free the temporary). If that is exceeded, the program crashes.	1051	recursing deeply on croak to free the temporary). If that is
481	To be conservative, the default nesting limit is set to 512. If your	1052	exceeded, the program crashes. To be conservative, the default
482	process has a smaller stack, you should adjust this setting accordingly	1053	nesting limit is set to 512. If your process has a smaller stack,
483	with the "max_depth" method.	1054	you should adjust this setting accordingly with the "max_depth"
		1055	method.
484		1056
		1057	Resource-starving attacks: CPU en-/decoding complexity
		1058	CBOR::XS will use the Math::BigInt, Math::BigFloat and Math::BigRat
		1059	libraries to represent encode/decode bignums. These can be very slow
		1060	(as in, centuries of CPU time) and can even crash your program (and
		1061	are generally not very trustworthy). See the next section on bignum
		1062	security for details.
		1063
		1064	Data breaches: leaking information in error messages
		1065	CBOR::XS might leak contents of your Perl data structures in its
		1066	error messages, so when you serialise sensitive information you
		1067	might want to make sure that exceptions thrown by CBOR::XS will not
		1068	end up in front of untrusted eyes.
		1069
		1070	Something else...
485	Something else could bomb you, too, that I forgot to think of. In that	1071	Something else could bomb you, too, that I forgot to think of. In
486	case, you get to keep the pieces. I am always open for hints, though...	1072	that case, you get to keep the pieces. I am always open for hints,
		1073	though...
487		1074
488	Also keep in mind that CBOR::XS might leak contents of your Perl data	1075	BIGNUM SECURITY CONSIDERATIONS
489	structures in its error messages, so when you serialise sensitive	1076	CBOR::XS provides a "TO_CBOR" method for both Math::BigInt and
490	information you might want to make sure that exceptions thrown by	1077	Math::BigFloat that tries to encode the number in the simplest possible
491	CBOR::XS will not end up in front of untrusted eyes.	1078	way, that is, either a CBOR integer, a CBOR bigint/decimal fraction (tag
		1079	4) or an arbitrary-exponent decimal fraction (tag 264). Rational numbers
		1080	(Math::BigRat, tag 30) can also contain bignums as members.
		1081
		1082	CBOR::XS will also understand base-2 bigfloat or arbitrary-exponent
		1083	bigfloats (tags 5 and 265), but it will never generate these on its own.
		1084
		1085	Using the built-in Math::BigInt::Calc support, encoding and decoding
		1086	decimal fractions is generally fast. Decoding bigints can be slow for
		1087	very big numbers (tens of thousands of digits, something that could
		1088	potentially be caught by limiting the size of CBOR texts), and decoding
		1089	bigfloats or arbitrary-exponent bigfloats can be extremely slow
		1090	(minutes, decades) for large exponents (roughly 40 bit and longer).
		1091
		1092	Additionally, Math::BigInt can take advantage of other bignum libraries,
		1093	such as Math::GMP, which cannot handle big floats with large exponents,
		1094	and might simply abort or crash your program, due to their code quality.
		1095
		1096	This can be a concern if you want to parse untrusted CBOR. If it is, you
		1097	might want to disable decoding of tag 2 (bigint) and 3 (negative bigint)
		1098	types. You should also disable types 5 and 265, as these can be slow
		1099	even without bigints.
		1100
		1101	Disabling bigints will also partially or fully disable types that rely
		1102	on them, e.g. rational numbers that use bignums.
492		1103
493	CBOR IMPLEMENTATION NOTES	1104	CBOR IMPLEMENTATION NOTES
494	This section contains some random implementation notes. They do not	1105	This section contains some random implementation notes. They do not
495	describe guaranteed behaviour, but merely behaviour as-is implemented	1106	describe guaranteed behaviour, but merely behaviour as-is implemented
496	right now.	1107	right now.
…		…
504	Only the double data type is supported for NV data types - when Perl	1115	Only the double data type is supported for NV data types - when Perl
505	uses long double to represent floating point values, they might not be	1116	uses long double to represent floating point values, they might not be
506	encoded properly. Half precision types are accepted, but not encoded.	1117	encoded properly. Half precision types are accepted, but not encoded.
507		1118
508	Strict mode and canonical mode are not implemented.	1119	Strict mode and canonical mode are not implemented.
		1120
		1121	LIMITATIONS ON PERLS WITHOUT 64-BIT INTEGER SUPPORT
		1122	On perls that were built without 64 bit integer support (these are rare
		1123	nowadays, even on 32 bit architectures, as all major Perl distributions
		1124	are built with 64 bit integer support), support for any kind of 64 bit
		1125	value in CBOR is very limited - most likely, these 64 bit values will be
		1126	truncated, corrupted, or otherwise not decoded correctly. This also
		1127	includes string, float, array and map sizes that are stored as 64 bit
		1128	integers.
509		1129
510	THREADS	1130	THREADS
511	This module is not guaranteed to be thread safe and there are no plans	1131	This module is not guaranteed to be thread safe and there are no plans
512	to change this until Perl gets thread support (as opposed to the	1132	to change this until Perl gets thread support (as opposed to the
513	horribly slow so-called "threads" which are simply slow and bloated	1133	horribly slow so-called "threads" which are simply slow and bloated

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Comparing CBOR-XS/README (file contents): Revision 1.7 by root, Tue Oct 29 15:56:31 2013 UTC vs. Revision 1.20 by root, Tue Dec 1 01:50:01 2020 UTC

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Comparing CBOR-XS/README (file contents):
Revision 1.7 by root, Tue Oct 29 15:56:31 2013 UTC vs.
Revision 1.20 by root, Tue Dec 1 01:50:01 2020 UTC