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

Comparing CBOR-XS/README (file contents):
Revision 1.10 by root, Thu Nov 28 16:09:04 2013 UTC vs.
Revision 1.18 by root, Wed Dec 7 14:14:30 2016 UTC

…		…
44	about 20% smaller than the same data encoded as (compact) JSON or	44	about 20% smaller than the same data encoded as (compact) JSON or
45	Storable.	45	Storable.
46		46
47	In addition to the core CBOR data format, this module implements a	47	In addition to the core CBOR data format, this module implements a
48	number of extensions, to support cyclic and shared data structures (see	48	number of extensions, to support cyclic and shared data structures (see
49	"allow_sharing"), string deduplication (see "pack_strings") and scalar	49	"allow_sharing" and "allow_cycles"), string deduplication (see
50	references (always enabled).	50	"pack_strings") and scalar references (always enabled).
51		51
52	The primary goal of this module is to be correct and the secondary	52	The primary goal of this module is to be correct and the secondary
53	goal is to be fast. To reach the latter goal it was written in C.	53	goal is to be fast. To reach the latter goal it was written in C.
54		54
55	See MAPPING, below, on how CBOR::XS maps perl values to CBOR values and	55	See MAPPING, below, on how CBOR::XS maps perl values to CBOR values and
…		…
78		78
79	The mutators for flags all return the CBOR object again and thus	79	The mutators for flags all return the CBOR object again and thus
80	calls can be chained:	80	calls can be chained:
81		81
82	my $cbor = CBOR::XS->new->encode ({a => [1,2]});	82	my $cbor = CBOR::XS->new->encode ({a => [1,2]});
		83
		84	$cbor = new_safe CBOR::XS
		85	Create a new, safe/secure CBOR::XS object. This is similar to "new",
		86	but configures the coder object to be safe to use with untrusted
		87	data. Currently, this is equivalent to:
		88
		89	my $cbor = CBOR::XS
		90	->new
		91	->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).
83		97
84	$cbor = $cbor->max_depth ([$maximum_nesting_depth])	98	$cbor = $cbor->max_depth ([$maximum_nesting_depth])
85	$max_depth = $cbor->get_max_depth	99	$max_depth = $cbor->get_max_depth
86	Sets the maximum nesting level (default 512) accepted while encoding	100	Sets the maximum nesting level (default 512) accepted while encoding
87	or decoding. If a higher nesting level is detected in CBOR data or a	101	or decoding. If a higher nesting level is detected in CBOR data or a
…		…
101		115
102	Note that nesting is implemented by recursion in C. The default	116	Note that nesting is implemented by recursion in C. The default
103	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
104	allow without crashing.	118	allow without crashing.
105		119
106	See SECURITY CONSIDERATIONS, below, for more info on why this is	120	See "SECURITY CONSIDERATIONS", below, for more info on why this is
107	useful.	121	useful.
108		122
109	$cbor = $cbor->max_size ([$maximum_string_size])	123	$cbor = $cbor->max_size ([$maximum_string_size])
110	$max_size = $cbor->get_max_size	124	$max_size = $cbor->get_max_size
111	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
…		…
115	exception. This setting has no effect on "encode" (yet).	129	exception. This setting has no effect on "encode" (yet).
116		130
117	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
118	as when 0 is specified).	132	as when 0 is specified).
119		133
120	See SECURITY CONSIDERATIONS, below, for more info on why this is	134	See "SECURITY CONSIDERATIONS", below, for more info on why this is
121	useful.	135	useful.
122		136
123	$cbor = $cbor->allow_unknown ([$enable])	137	$cbor = $cbor->allow_unknown ([$enable])
124	$enabled = $cbor->get_allow_unknown	138	$enabled = $cbor->get_allow_unknown
125	If $enable is true (or missing), then "encode" will not throw an	139	If $enable is true (or missing), then "encode" will not throw an
…		…
141	instead will emit a reference to the earlier value.	155	instead will emit a reference to the earlier value.
142		156
143	This means that such values will only be encoded once, and will not	157	This means that such values will only be encoded once, and will not
144	result in a deep cloning of the value on decode, in decoders	158	result in a deep cloning of the value on decode, in decoders
145	supporting the value sharing extension. This also makes it possible	159	supporting the value sharing extension. This also makes it possible
146	to encode cyclic data structures.	160	to encode cyclic data structures (which need "allow_cycles" to be
		161	enabled to be decoded by this module).
147		162
148	It is recommended to leave it off unless you know your communication	163	It is recommended to leave it off unless you know your communication
149	partner supports the value sharing extensions to CBOR	164	partner supports the value sharing extensions to CBOR
150	(<http://cbor.schmorp.de/value-sharing>), as without decoder	165	(<http://cbor.schmorp.de/value-sharing>), as without decoder
151	support, the resulting data structure might be unusable.	166	support, the resulting data structure might be unusable.
152		167
153	Detecting shared values incurs a runtime overhead when values are	168	Detecting shared values incurs a runtime overhead when values are
154	encoded that have a reference counter large than one, and might	169	encoded that have a reference counter large than one, and might
155	unnecessarily increase the encoded size, as potentially shared	170	unnecessarily increase the encoded size, as potentially shared
156	values are encode as sharable whether or not they are actually	171	values are encode as shareable whether or not they are actually
157	shared.	172	shared.
158		173
159	At the moment, only targets of references can be shared (e.g.	174	At the moment, only targets of references can be shared (e.g.
160	scalars, arrays or hashes pointed to by a reference). Weirder	175	scalars, arrays or hashes pointed to by a reference). Weirder
161	constructs, such as an array with multiple "copies" of the same	176	constructs, such as an array with multiple "copies" of the same
…		…
166	data structures repeatedly, unsharing them in the process. Cyclic	181	data structures repeatedly, unsharing them in the process. Cyclic
167	data structures cannot be encoded in this mode.	182	data structures cannot be encoded in this mode.
168		183
169	This option does not affect "decode" in any way - shared values and	184	This option does not affect "decode" in any way - shared values and
170	references will always be decoded properly if present.	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.
171		223
172	$cbor = $cbor->pack_strings ([$enable])	224	$cbor = $cbor->pack_strings ([$enable])
173	$enabled = $cbor->get_pack_strings	225	$enabled = $cbor->get_pack_strings
174	If $enable is true (or missing), then "encode" will try not to	226	If $enable is true (or missing), then "encode" will try not to
175	encode the same string twice, but will instead encode a reference to	227	encode the same string twice, but will instead encode a reference to
…		…
186	the standard CBOR way.	238	the standard CBOR way.
187		239
188	This option does not affect "decode" in any way - string references	240	This option does not affect "decode" in any way - string references
189	will always be decoded properly if present.	241	will always be decoded properly if present.
190		242
		243	$cbor = $cbor->text_keys ([$enable])
		244	$enabled = $cbor->get_text_keys
		245	If $enabled is true (or missing), then "encode" will encode all perl
		246	hash keys as CBOR text strings/UTF-8 string, upgrading them as
		247	needed.
		248
		249	If $enable is false (the default), then "encode" will encode hash
		250	keys normally - upgraded perl strings (strings internally encoded as
		251	UTF-8) as CBOR text strings, and downgraded perl strings as CBOR
		252	byte strings.
		253
		254	This option does not affect "decode" in any way.
		255
		256	This option is useful for interoperability with CBOR decoders that
		257	don't treat byte strings as a form of text. It is especially useful
		258	as Perl gives very little control over hash keys.
		259
		260	Enabling this option can be slow, as all downgraded hash keys that
		261	are encoded need to be scanned and converted to UTF-8.
		262
		263	$cbor = $cbor->text_strings ([$enable])
		264	$enabled = $cbor->get_text_strings
		265	This option works similar to "text_keys", above, but works on all
		266	strings (including hash keys), so "text_keys" has no further effect
		267	after enabling "text_strings".
		268
		269	If $enabled is true (or missing), then "encode" will encode all perl
		270	strings as CBOR text strings/UTF-8 strings, upgrading them as
		271	needed.
		272
		273	If $enable is false (the default), then "encode" will encode strings
		274	normally (but see "text_keys") - upgraded perl strings (strings
		275	internally encoded as UTF-8) as CBOR text strings, and downgraded
		276	perl strings as CBOR byte strings.
		277
		278	This option does not affect "decode" in any way.
		279
		280	This option has similar advantages and disadvantages as "text_keys".
		281	In addition, this option effectively removes the ability to encode
		282	byte strings, which might break some "FREEZE" and "TO_CBOR" methods
		283	that rely on this, such as bignum encoding, so this option is mainly
		284	useful for very simple data.
		285
		286	$cbor = $cbor->validate_utf8 ([$enable])
		287	$enabled = $cbor->get_validate_utf8
		288	If $enable is true (or missing), then "decode" will validate that
		289	elements (text strings) containing UTF-8 data in fact contain valid
		290	UTF-8 data (instead of blindly accepting it). This validation
		291	obviously takes extra time during decoding.
		292
		293	The concept of "valid UTF-8" used is perl's concept, which is a
		294	superset of the official UTF-8.
		295
		296	If $enable is false (the default), then "decode" will blindly accept
		297	UTF-8 data, marking them as valid UTF-8 in the resulting data
		298	structure regardless of whether that's true or not.
		299
		300	Perl isn't too happy about corrupted UTF-8 in strings, but should
		301	generally not crash or do similarly evil things. Extensions might be
		302	not so forgiving, so it's recommended to turn on this setting if you
		303	receive untrusted CBOR.
		304
		305	This option does not affect "encode" in any way - strings that are
		306	supposedly valid UTF-8 will simply be dumped into the resulting CBOR
		307	string without checking whether that is, in fact, true or not.
		308
191	$cbor = $cbor->filter ([$cb->($tag, $value)])	309	$cbor = $cbor->filter ([$cb->($tag, $value)])
192	$cb_or_undef = $cbor->get_filter	310	$cb_or_undef = $cbor->get_filter
193	Sets or replaces the tagged value decoding filter (when $cb is	311	Sets or replaces the tagged value decoding filter (when $cb is
194	specified) or clears the filter (if no argument or "undef" is	312	specified) or clears the filter (if no argument or "undef" is
195	provided).	313	provided).
…		…
212	When the filter is cleared (the default state), the default filter	330	When the filter is cleared (the default state), the default filter
213	function, "CBOR::XS::default_filter", is used. This function simply	331	function, "CBOR::XS::default_filter", is used. This function simply
214	looks up the tag in the %CBOR::XS::FILTER hash. If an entry exists	332	looks up the tag in the %CBOR::XS::FILTER hash. If an entry exists
215	it must be a code reference that is called with tag and value, and	333	it must be a code reference that is called with tag and value, and
216	is responsible for decoding the value. If no entry exists, it	334	is responsible for decoding the value. If no entry exists, it
217	returns no values.	335	returns no values. "CBOR::XS" provides a number of default filter
		336	functions already, the the %CBOR::XS::FILTER hash can be freely
		337	extended with more.
		338
		339	"CBOR::XS" additionally provides an alternative filter function that
		340	is supposed to be safe to use with untrusted data (which the default
		341	filter might not), called "CBOR::XS::safe_filter", which works the
		342	same as the "default_filter" but uses the %CBOR::XS::SAFE_FILTER
		343	variable instead. It is prepopulated with the tag decoding functions
		344	that are deemed safe (basically the same as %CBOR::XS::FILTER
		345	without all the bignum tags), and can be extended by user code as
		346	wlel, although, obviously, one should be very careful about adding
		347	decoding functions here, since the expectation is that they are safe
		348	to use on untrusted data, after all.
218		349
219	Example: decode all tags not handled internally into	350	Example: decode all tags not handled internally into
220	"CBOR::XS::Tagged" objects, with no other special handling (useful	351	"CBOR::XS::Tagged" objects, with no other special handling (useful
221	when working with potentially "unsafe" CBOR data).	352	when working with potentially "unsafe" CBOR data).
222		353
…		…
228	$CBOR::XS::FILTER{1347375694} = sub {	359	$CBOR::XS::FILTER{1347375694} = sub {
229	my ($tag, $value);	360	my ($tag, $value);
230		361
231	"tag 1347375694 value $value"	362	"tag 1347375694 value $value"
232	};	363	};
		364
		365	Example: provide your own filter function that looks up tags in your
		366	own hash:
		367
		368	my %my_filter = (
		369	998347484 => sub {
		370	my ($tag, $value);
		371
		372	"tag 998347484 value $value"
		373	};
		374	);
		375
		376	my $coder = CBOR::XS->new->filter (sub {
		377	&{ $my_filter{$_[0]} or return }
		378	});
		379
		380	Example: use the safe filter function (see "SECURITY CONSIDERATIONS"
		381	for more considerations on security).
		382
		383	CBOR::XS->new->filter (\&CBOR::XS::safe_filter)->decode ($cbor_data);
233		384
234	$cbor_data = $cbor->encode ($perl_scalar)	385	$cbor_data = $cbor->encode ($perl_scalar)
235	Converts the given Perl data structure (a scalar value) to its CBOR	386	Converts the given Perl data structure (a scalar value) to its CBOR
236	representation.	387	representation.
237		388
…		…
249	protocol and you need to know where the first CBOR string ends amd	400	protocol and you need to know where the first CBOR string ends amd
250	the next one starts.	401	the next one starts.
251		402
252	CBOR::XS->new->decode_prefix ("......")	403	CBOR::XS->new->decode_prefix ("......")
253	=> ("...", 3)	404	=> ("...", 3)
		405
		406	INCREMENTAL PARSING
		407	In some cases, there is the need for incremental parsing of JSON texts.
		408	While this module always has to keep both CBOR text and resulting Perl
		409	data structure in memory at one time, it does allow you to parse a CBOR
		410	stream incrementally, using a similar to using "decode_prefix" to see if
		411	a full CBOR object is available, but is much more efficient.
		412
		413	It basically works by parsing as much of a CBOR string as possible - if
		414	the CBOR data is not complete yet, the pasrer will remember where it
		415	was, to be able to restart when more data has been accumulated. Once
		416	enough data is available to either decode a complete CBOR value or raise
		417	an error, a real decode will be attempted.
		418
		419	A typical use case would be a network protocol that consists of sending
		420	and receiving CBOR-encoded messages. The solution that works with CBOR
		421	and about anything else is by prepending a length to every CBOR value,
		422	so the receiver knows how many octets to read. More compact (and
		423	slightly slower) would be to just send CBOR values back-to-back, as
		424	"CBOR::XS" knows where a CBOR value ends, and doesn't need an explicit
		425	length.
		426
		427	The following methods help with this:
		428
		429	@decoded = $cbor->incr_parse ($buffer)
		430	This method attempts to decode exactly one CBOR value from the
		431	beginning of the given $buffer. The value is removed from the
		432	$buffer on success. When $buffer doesn't contain a complete value
		433	yet, it returns nothing. Finally, when the $buffer doesn't start
		434	with something that could ever be a valid CBOR value, it raises an
		435	exception, just as "decode" would. In the latter case the decoder
		436	state is undefined and must be reset before being able to parse
		437	further.
		438
		439	This method modifies the $buffer in place. When no CBOR value can be
		440	decoded, the decoder stores the current string offset. On the next
		441	call, continues decoding at the place where it stopped before. For
		442	this to make sense, the $buffer must begin with the same octets as
		443	on previous unsuccessful calls.
		444
		445	You can call this method in scalar context, in which case it either
		446	returns a decoded value or "undef". This makes it impossible to
		447	distinguish between CBOR null values (which decode to "undef") and
		448	an unsuccessful decode, which is often acceptable.
		449
		450	@decoded = $cbor->incr_parse_multiple ($buffer)
		451	Same as "incr_parse", but attempts to decode as many CBOR values as
		452	possible in one go, instead of at most one. Calls to "incr_parse"
		453	and "incr_parse_multiple" can be interleaved.
		454
		455	$cbor->incr_reset
		456	Resets the incremental decoder. This throws away any saved state, so
		457	that subsequent calls to "incr_parse" or "incr_parse_multiple" start
		458	to parse a new CBOR value from the beginning of the $buffer again.
		459
		460	This method can be called at any time, but it must be called if
		461	you want to change your $buffer or there was a decoding error and
		462	you want to reuse the $cbor object for future incremental parsings.
254		463
255	MAPPING	464	MAPPING
256	This section describes how CBOR::XS maps Perl values to CBOR values and	465	This section describes how CBOR::XS maps Perl values to CBOR values and
257	vice versa. These mappings are designed to "do the right thing" in most	466	vice versa. These mappings are designed to "do the right thing" in most
258	circumstances automatically, preserving round-tripping characteristics	467	circumstances automatically, preserving round-tripping characteristics
…		…
309		518
310	hash references	519	hash references
311	Perl hash references become CBOR maps. As there is no inherent	520	Perl hash references become CBOR maps. As there is no inherent
312	ordering in hash keys (or CBOR maps), they will usually be encoded	521	ordering in hash keys (or CBOR maps), they will usually be encoded
313	in a pseudo-random order. This order can be different each time a	522	in a pseudo-random order. This order can be different each time a
314	hahs is encoded.	523	hash is encoded.
315		524
316	Currently, tied hashes will use the indefinite-length format, while	525	Currently, tied hashes will use the indefinite-length format, while
317	normal hashes will use the fixed-length format.	526	normal hashes will use the fixed-length format.
318		527
319	array references	528	array references
…		…
368	my $x = 3.1; # some variable containing a number	577	my $x = 3.1; # some variable containing a number
369	"$x"; # stringified	578	"$x"; # stringified
370	$x .= ""; # another, more awkward way to stringify	579	$x .= ""; # another, more awkward way to stringify
371	print $x; # perl does it for you, too, quite often	580	print $x; # perl does it for you, too, quite often
372		581
373	You can force whether a string ie encoded as byte or text string by	582	You can force whether a string is encoded as byte or text string by
374	using "utf8::upgrade" and "utf8::downgrade"):	583	using "utf8::upgrade" and "utf8::downgrade" (if "text_strings" is
		584	disabled):
375		585
376	utf8::upgrade $x; # encode $x as text string	586	utf8::upgrade $x; # encode $x as text string
377	utf8::downgrade $x; # encode $x as byte string	587	utf8::downgrade $x; # encode $x as byte string
378		588
379	Perl doesn't define what operations up- and downgrade strings, so if	589	Perl doesn't define what operations up- and downgrade strings, so if
380	the difference between byte and text is important, you should up- or	590	the difference between byte and text is important, you should up- or
381	downgrade your string as late as possible before encoding.	591	downgrade your string as late as possible before encoding. You can
		592	also force the use of CBOR text strings by using "text_keys" or
		593	"text_strings".
382		594
383	You can force the type to be a CBOR number by numifying it:	595	You can force the type to be a CBOR number by numifying it:
384		596
385	my $x = "3"; # some variable containing a string	597	my $x = "3"; # some variable containing a string
386	$x += 0; # numify it, ensuring it will be dumped as a number	598	$x += 0; # numify it, ensuring it will be dumped as a number
…		…
396	the IEEE double format will be used. Perls that use formats other	608	the IEEE double format will be used. Perls that use formats other
397	than IEEE double to represent numerical values are supported, but	609	than IEEE double to represent numerical values are supported, but
398	might suffer loss of precision.	610	might suffer loss of precision.
399		611
400	OBJECT SERIALISATION	612	OBJECT SERIALISATION
		613	This module implements both a CBOR-specific and the generic
		614	Types::Serialier object serialisation protocol. The following
		615	subsections explain both methods.
		616
		617	ENCODING
401	This module knows two way to serialise a Perl object: The CBOR-specific	618	This module knows two way to serialise a Perl object: The CBOR-specific
402	way, and the generic way.	619	way, and the generic way.
403		620
404	Whenever the encoder encounters a Perl object that it cnanot serialise	621	Whenever the encoder encounters a Perl object that it cannot serialise
405	directly (most of them), it will first look up the "TO_CBOR" method on	622	directly (most of them), it will first look up the "TO_CBOR" method on
406	it.	623	it.
407		624
408	If it has a "TO_CBOR" method, it will call it with the object as only	625	If it has a "TO_CBOR" method, it will call it with the object as only
409	argument, and expects exactly one return value, which it will then	626	argument, and expects exactly one return value, which it will then
…		…
414	"CBOR" as the second argument, to distinguish it from other serialisers.	631	"CBOR" as the second argument, to distinguish it from other serialisers.
415		632
416	The "FREEZE" method can return any number of values (i.e. zero or more).	633	The "FREEZE" method can return any number of values (i.e. zero or more).
417	These will be encoded as CBOR perl object, together with the classname.	634	These will be encoded as CBOR perl object, together with the classname.
418		635
		636	These methods MUST NOT change the data structure that is being
		637	serialised. Failure to comply to this can result in memory corruption -
		638	and worse.
		639
419	If an object supports neither "TO_CBOR" nor "FREEZE", encoding will fail	640	If an object supports neither "TO_CBOR" nor "FREEZE", encoding will fail
420	with an error.	641	with an error.
421		642
		643	DECODING
422	Objects encoded via "TO_CBOR" cannot be automatically decoded, but	644	Objects encoded via "TO_CBOR" cannot (normally) be automatically
423	objects encoded via "FREEZE" can be decoded using the following	645	decoded, but objects encoded via "FREEZE" can be decoded using the
424	protocol:	646	following protocol:
425		647
426	When an encoded CBOR perl object is encountered by the decoder, it will	648	When an encoded CBOR perl object is encountered by the decoder, it will
427	look up the "THAW" method, by using the stored classname, and will fail	649	look up the "THAW" method, by using the stored classname, and will fail
428	if the method cannot be found.	650	if the method cannot be found.
429		651
…		…
471	"$self" # encode url string	693	"$self" # encode url string
472	}	694	}
473		695
474	sub URI::THAW {	696	sub URI::THAW {
475	my ($class, $serialiser, $uri) = @_;	697	my ($class, $serialiser, $uri) = @_;
476
477	$class->new ($uri)	698	$class->new ($uri)
478	}	699	}
479		700
480	Unlike "TO_CBOR", multiple values can be returned by "FREEZE". For	701	Unlike "TO_CBOR", multiple values can be returned by "FREEZE". For
481	example, a "FREEZE" method that returns "type", "id" and "variant"	702	example, a "FREEZE" method that returns "type", "id" and "variant"
…		…
577	Future versions of this module reserve the right to special case	798	Future versions of this module reserve the right to special case
578	additional tags (such as base64url).	799	additional tags (such as base64url).
579		800
580	ENFORCED TAGS	801	ENFORCED TAGS
581	These tags are always handled when decoding, and their handling cannot	802	These tags are always handled when decoding, and their handling cannot
582	be overriden by the user.	803	be overridden by the user.
583		804
584	26 (perl-object, <http://cbor.schmorp.de/perl-object>)	805	26 (perl-object, <http://cbor.schmorp.de/perl-object>)
585	These tags are automatically created (and decoded) for serialisable	806	These tags are automatically created (and decoded) for serialisable
586	objects using the "FREEZE/THAW" methods (the Types::Serialier object	807	objects using the "FREEZE/THAW" methods (the Types::Serialier object
587	serialisation protocol). See "OBJECT SERIALISATION" for details.	808	serialisation protocol). See "OBJECT SERIALISATION" for details.
588		809
589	28, 29 (sharable, sharedref, L <http://cbor.schmorp.de/value-sharing>)	810	28, 29 (shareable, sharedref, <http://cbor.schmorp.de/value-sharing>)
590	These tags are automatically decoded when encountered, resulting in	811	These tags are automatically decoded when encountered (and they do
		812	not result in a cyclic data structure, see "allow_cycles"),
591	shared values in the decoded object. They are only encoded, however,	813	resulting in shared values in the decoded object. They are only
592	when "allow_sharable" is enabled.	814	encoded, however, when "allow_sharing" is enabled.
593		815
		816	Not all shared values can be successfully decoded: values that
		817	reference themselves will currently decode as "undef" (this is not
		818	the same as a reference pointing to itself, which will be
		819	represented as a value that contains an indirect reference to itself
		820	- these will be decoded properly).
		821
		822	Note that considerably more shared value data structures can be
		823	decoded than will be encoded - currently, only values pointed to by
		824	references will be shared, others will not. While non-reference
		825	shared values can be generated in Perl with some effort, they were
		826	considered too unimportant to be supported in the encoder. The
		827	decoder, however, will decode these values as shared values.
		828
594	256, 25 (stringref-namespace, stringref, L	829	256, 25 (stringref-namespace, stringref,
595	<http://cbor.schmorp.de/stringref>)	830	<http://cbor.schmorp.de/stringref>)
596	These tags are automatically decoded when encountered. They are only	831	These tags are automatically decoded when encountered. They are only
597	encoded, however, when "pack_strings" is enabled.	832	encoded, however, when "pack_strings" is enabled.
598		833
599	22098 (indirection, <http://cbor.schmorp.de/indirection>)	834	22098 (indirection, <http://cbor.schmorp.de/indirection>)
600	This tag is automatically generated when a reference are encountered	835	This tag is automatically generated when a reference are encountered
601	(with the exception of hash and array refernces). It is converted to	836	(with the exception of hash and array references). It is converted
602	a reference when decoding.	837	to a reference when decoding.
603		838
604	55799 (self-describe CBOR, RFC 7049)	839	55799 (self-describe CBOR, RFC 7049)
605	This value is not generated on encoding (unless explicitly requested	840	This value is not generated on encoding (unless explicitly requested
606	by the user), and is simply ignored when decoding.	841	by the user), and is simply ignored when decoding.
607		842
608	NON-ENFORCED TAGS	843	NON-ENFORCED TAGS
609	These tags have default filters provided when decoding. Their handling	844	These tags have default filters provided when decoding. Their handling
610	can be overriden by changing the %CBOR::XS::FILTER entry for the tag, or	845	can be overridden by changing the %CBOR::XS::FILTER entry for the tag,
611	by providing a custom "filter" callback when decoding.	846	or by providing a custom "filter" callback when decoding.
612		847
613	When they result in decoding into a specific Perl class, the module	848	When they result in decoding into a specific Perl class, the module
614	usually provides a corresponding "TO_CBOR" method as well.	849	usually provides a corresponding "TO_CBOR" method as well.
615		850
616	When any of these need to load additional modules that are not part of	851	When any of these need to load additional modules that are not part of
617	the perl core distribution (e.g. URI), it is (currently) up to the user	852	the perl core distribution (e.g. URI), it is (currently) up to the user
618	to provide these modules. The decoding usually fails with an exception	853	to provide these modules. The decoding usually fails with an exception
619	if the required module cannot be loaded.	854	if the required module cannot be loaded.
620		855
		856	0, 1 (date/time string, seconds since the epoch)
		857	These tags are decoded into Time::Piece objects. The corresponding
		858	"Time::Piece::TO_CBOR" method always encodes into tag 1 values
		859	currently.
		860
		861	The Time::Piece API is generally surprisingly bad, and fractional
		862	seconds are only accidentally kept intact, so watch out. On the plus
		863	side, the module comes with perl since 5.10, which has to count for
		864	something.
		865
621	2, 3 (positive/negative bignum)	866	2, 3 (positive/negative bignum)
622	These tags are decoded into Math::BigInt objects. The corresponding	867	These tags are decoded into Math::BigInt objects. The corresponding
623	"Math::BigInt::TO_CBOR" method encodes "small" bigints into normal	868	"Math::BigInt::TO_CBOR" method encodes "small" bigints into normal
624	CBOR integers, and others into positive/negative CBOR bignums.	869	CBOR integers, and others into positive/negative CBOR bignums.
625		870
626	4, 5 (decimal fraction/bigfloat)	871	4, 5, 264, 265 (decimal fraction/bigfloat)
627	Both decimal fractions and bigfloats are decoded into Math::BigFloat	872	Both decimal fractions and bigfloats are decoded into Math::BigFloat
628	objects. The corresponding "Math::BigFloat::TO_CBOR" method always	873	objects. The corresponding "Math::BigFloat::TO_CBOR" method always
629	encodes into a decimal fraction.	874	encodes into a decimal fraction (either tag 4 or 264).
630		875
631	CBOR cannot represent bigfloats with very large exponents -
632	conversion of such big float objects is undefined.
633
634	Also, NaN and infinities are not encoded properly.	876	NaN and infinities are not encoded properly, as they cannot be
		877	represented in CBOR.
		878
		879	See "BIGNUM SECURITY CONSIDERATIONS" for more info.
		880
		881	30 (rational numbers)
		882	These tags are decoded into Math::BigRat objects. The corresponding
		883	"Math::BigRat::TO_CBOR" method encodes rational numbers with
		884	denominator 1 via their numerator only, i.e., they become normal
		885	integers or "bignums".
		886
		887	See "BIGNUM SECURITY CONSIDERATIONS" for more info.
635		888
636	21, 22, 23 (expected later JSON conversion)	889	21, 22, 23 (expected later JSON conversion)
637	CBOR::XS is not a CBOR-to-JSON converter, and will simply ignore	890	CBOR::XS is not a CBOR-to-JSON converter, and will simply ignore
638	these tags.	891	these tags.
639		892
…		…
653	interoperability is improved in the future, then the goal will be to	906	interoperability is improved in the future, then the goal will be to
654	ensure that decoded JSON data will round-trip encoding and decoding to	907	ensure that decoded JSON data will round-trip encoding and decoding to
655	CBOR intact.	908	CBOR intact.
656		909
657	SECURITY CONSIDERATIONS	910	SECURITY CONSIDERATIONS
658	When you are using CBOR in a protocol, talking to untrusted potentially	911	Tl;dr... if you want to decode or encode CBOR from untrusted sources,
659	hostile creatures requires relatively few measures.	912	you should start with a coder object created via "new_safe":
660		913
		914	my $coder = CBOR::XS->new_safe;
		915
		916	my $data = $coder->decode ($cbor_text);
		917	my $cbor = $coder->encode ($data);
		918
		919	Longer version: When you are using CBOR in a protocol, talking to
		920	untrusted potentially hostile creatures requires some thought:
		921
		922	Security of the CBOR decoder itself
661	First of all, your CBOR decoder should be secure, that is, should not	923	First and foremost, your CBOR decoder should be secure, that is,
662	have any buffer overflows. Obviously, this module should ensure that and	924	should not have any buffer overflows or similar bugs that could
		925	potentially be exploited. Obviously, this module should ensure that
663	I am trying hard on making that true, but you never know.	926	and I am trying hard on making that true, but you never know.
664		927
		928	CBOR::XS can invoke almost arbitrary callbacks during decoding
		929	CBOR::XS supports object serialisation - decoding CBOR can cause
		930	calls to any "THAW" method in any package that exists in your
		931	process (that is, CBOR::XS will not try to load modules, but any
		932	existing "THAW" method or function can be called, so they all have
		933	to be secure).
		934
		935	Less obviously, it will also invoke "TO_CBOR" and "FREEZE" methods -
		936	even if all your "THAW" methods are secure, encoding data structures
		937	from untrusted sources can invoke those and trigger bugs in those.
		938
		939	So, if you are not sure about the security of all the modules you
		940	have loaded (you shouldn't), you should disable this part using
		941	"forbid_objects".
		942
		943	CBOR can be extended with tags that call library code
		944	CBOR can be extended with tags, and "CBOR::XS" has a registry of
		945	conversion functions for many existing tags that can be extended via
		946	third-party modules (see the "filter" method).
		947
		948	If you don't trust these, you should configure the "safe" filter
		949	function, "CBOR::XS::safe_filter", which by default only includes
		950	conversion functions that are considered "safe" by the author (but
		951	again, they can be extended by third party modules).
		952
		953	Depending on your level of paranoia, you can use the "safe" filter:
		954
		955	$cbor->filter (\&CBOR::XS::safe_filter);
		956
		957	... your own filter...
		958
		959	$cbor->filter (sub { ... do your stuffs here ... });
		960
		961	... or even no filter at all, disabling all tag decoding:
		962
		963	$cbor->filter (sub { });
		964
		965	This is never a problem for encoding, as the tag mechanism only
		966	exists in CBOR texts.
		967
		968	Resource-starving attacks: object memory usage
665	Second, you need to avoid resource-starving attacks. That means you	969	You need to avoid resource-starving attacks. That means you should
666	should limit the size of CBOR data you accept, or make sure then when	970	limit the size of CBOR data you accept, or make sure then when your
667	your resources run out, that's just fine (e.g. by using a separate	971	resources run out, that's just fine (e.g. by using a separate
668	process that can crash safely). The size of a CBOR string in octets is	972	process that can crash safely). The size of a CBOR string in octets
669	usually a good indication of the size of the resources required to	973	is usually a good indication of the size of the resources required
670	decode it into a Perl structure. While CBOR::XS can check the size of	974	to decode it into a Perl structure. While CBOR::XS can check the
671	the CBOR text, it might be too late when you already have it in memory,	975	size of the CBOR text (using "max_size"), it might be too late when
672	so you might want to check the size before you accept the string.	976	you already have it in memory, so you might want to check the size
		977	before you accept the string.
673		978
		979	As for encoding, it is possible to construct data structures that
		980	are relatively small but result in large CBOR texts (for example by
		981	having an array full of references to the same big data structure,
		982	which will all be deep-cloned during encoding by default). This is
		983	rarely an actual issue (and the worst case is still just running out
		984	of memory), but you can reduce this risk by using "allow_sharing".
		985
		986	Resource-starving attacks: stack overflows
674	Third, CBOR::XS recurses using the C stack when decoding objects and	987	CBOR::XS recurses using the C stack when decoding objects and
675	arrays. The C stack is a limited resource: for instance, on my amd64	988	arrays. The C stack is a limited resource: for instance, on my amd64
676	machine with 8MB of stack size I can decode around 180k nested arrays	989	machine with 8MB of stack size I can decode around 180k nested
677	but only 14k nested CBOR objects (due to perl itself recursing deeply on	990	arrays but only 14k nested CBOR objects (due to perl itself
678	croak to free the temporary). If that is exceeded, the program crashes.	991	recursing deeply on croak to free the temporary). If that is
679	To be conservative, the default nesting limit is set to 512. If your	992	exceeded, the program crashes. To be conservative, the default
680	process has a smaller stack, you should adjust this setting accordingly	993	nesting limit is set to 512. If your process has a smaller stack,
681	with the "max_depth" method.	994	you should adjust this setting accordingly with the "max_depth"
		995	method.
682		996
		997	Resource-starving attacks: CPU en-/decoding complexity
		998	CBOR::XS will use the Math::BigInt, Math::BigFloat and Math::BigRat
		999	libraries to represent encode/decode bignums. These can be very slow
		1000	(as in, centuries of CPU time) and can even crash your program (and
		1001	are generally not very trustworthy). See the next section for
		1002	details.
		1003
		1004	Data breaches: leaking information in error messages
		1005	CBOR::XS might leak contents of your Perl data structures in its
		1006	error messages, so when you serialise sensitive information you
		1007	might want to make sure that exceptions thrown by CBOR::XS will not
		1008	end up in front of untrusted eyes.
		1009
		1010	Something else...
683	Something else could bomb you, too, that I forgot to think of. In that	1011	Something else could bomb you, too, that I forgot to think of. In
684	case, you get to keep the pieces. I am always open for hints, though...	1012	that case, you get to keep the pieces. I am always open for hints,
		1013	though...
685		1014
686	Also keep in mind that CBOR::XS might leak contents of your Perl data	1015	BIGNUM SECURITY CONSIDERATIONS
687	structures in its error messages, so when you serialise sensitive	1016	CBOR::XS provides a "TO_CBOR" method for both Math::BigInt and
688	information you might want to make sure that exceptions thrown by	1017	Math::BigFloat that tries to encode the number in the simplest possible
689	CBOR::XS will not end up in front of untrusted eyes.	1018	way, that is, either a CBOR integer, a CBOR bigint/decimal fraction (tag
		1019	4) or an arbitrary-exponent decimal fraction (tag 264). Rational numbers
		1020	(Math::BigRat, tag 30) can also contain bignums as members.
		1021
		1022	CBOR::XS will also understand base-2 bigfloat or arbitrary-exponent
		1023	bigfloats (tags 5 and 265), but it will never generate these on its own.
		1024
		1025	Using the built-in Math::BigInt::Calc support, encoding and decoding
		1026	decimal fractions is generally fast. Decoding bigints can be slow for
		1027	very big numbers (tens of thousands of digits, something that could
		1028	potentially be caught by limiting the size of CBOR texts), and decoding
		1029	bigfloats or arbitrary-exponent bigfloats can be extremely slow
		1030	(minutes, decades) for large exponents (roughly 40 bit and longer).
		1031
		1032	Additionally, Math::BigInt can take advantage of other bignum libraries,
		1033	such as Math::GMP, which cannot handle big floats with large exponents,
		1034	and might simply abort or crash your program, due to their code quality.
		1035
		1036	This can be a concern if you want to parse untrusted CBOR. If it is, you
		1037	might want to disable decoding of tag 2 (bigint) and 3 (negative bigint)
		1038	types. You should also disable types 5 and 265, as these can be slow
		1039	even without bigints.
		1040
		1041	Disabling bigints will also partially or fully disable types that rely
		1042	on them, e.g. rational numbers that use bignums.
690		1043
691	CBOR IMPLEMENTATION NOTES	1044	CBOR IMPLEMENTATION NOTES
692	This section contains some random implementation notes. They do not	1045	This section contains some random implementation notes. They do not
693	describe guaranteed behaviour, but merely behaviour as-is implemented	1046	describe guaranteed behaviour, but merely behaviour as-is implemented
694	right now.	1047	right now.
…		…
702	Only the double data type is supported for NV data types - when Perl	1055	Only the double data type is supported for NV data types - when Perl
703	uses long double to represent floating point values, they might not be	1056	uses long double to represent floating point values, they might not be
704	encoded properly. Half precision types are accepted, but not encoded.	1057	encoded properly. Half precision types are accepted, but not encoded.
705		1058
706	Strict mode and canonical mode are not implemented.	1059	Strict mode and canonical mode are not implemented.
		1060
		1061	LIMITATIONS ON PERLS WITHOUT 64-BIT INTEGER SUPPORT
		1062	On perls that were built without 64 bit integer support (these are rare
		1063	nowadays, even on 32 bit architectures, as all major Perl distributions
		1064	are built with 64 bit integer support), support for any kind of 64 bit
		1065	integer in CBOR is very limited - most likely, these 64 bit values will
		1066	be truncated, corrupted, or otherwise not decoded correctly. This also
		1067	includes string, array and map sizes that are stored as 64 bit integers.
707		1068
708	THREADS	1069	THREADS
709	This module is not guaranteed to be thread safe and there are no plans	1070	This module is not guaranteed to be thread safe and there are no plans
710	to change this until Perl gets thread support (as opposed to the	1071	to change this until Perl gets thread support (as opposed to the
711	horribly slow so-called "threads" which are simply slow and bloated	1072	horribly slow so-called "threads" which are simply slow and bloated

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Comparing CBOR-XS/README (file contents): Revision 1.10 by root, Thu Nov 28 16:09:04 2013 UTC vs. Revision 1.18 by root, Wed Dec 7 14:14:30 2016 UTC

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Comparing CBOR-XS/README (file contents):
Revision 1.10 by root, Thu Nov 28 16:09:04 2013 UTC vs.
Revision 1.18 by root, Wed Dec 7 14:14:30 2016 UTC