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

Comparing CBOR-XS/README (file contents):
Revision 1.8 by root, Tue Oct 29 22:04:52 2013 UTC vs.
Revision 1.12 by root, Sun Dec 1 17:10:42 2013 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	To give you a general idea about speed, with texts in the megabyte	38	To give you a general idea about speed, with texts in the megabyte
48	range, "CBOR::XS" usually encodes roughly twice as fast as Storable or	39	range, "CBOR::XS" usually encodes roughly twice as fast as Storable or
49	JSON::XS and decodes about 15%-30% faster than those. The shorter the	40	JSON::XS and decodes about 15%-30% faster than those. The shorter the
50	data, the worse Storable performs in comparison.	41	data, the worse Storable performs in comparison.
51		42
52	As for compactness, "CBOR::XS" encoded data structures are usually about	43	Regarding compactness, "CBOR::XS"-encoded data structures are usually
53	20% smaller than the same data encoded as (compact) JSON or Storable.	44	about 20% smaller than the same data encoded as (compact) JSON or
		45	Storable.
		46
		47	In addition to the core CBOR data format, this module implements a
		48	number of extensions, to support cyclic and shared data structures (see
		49	"allow_sharing" and "allow_cycles"), string deduplication (see
		50	"pack_strings") and scalar references (always enabled).
54		51
55	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
56	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.
57		54
58	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
…		…
80	disabled.	77	disabled.
81		78
82	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
83	calls can be chained:	80	calls can be chained:
84		81
85	#TODO my $cbor = CBOR::XS->new->encode ({a => [1,2]});	82	my $cbor = CBOR::XS->new->encode ({a => [1,2]});
86		83
87	$cbor = $cbor->max_depth ([$maximum_nesting_depth])	84	$cbor = $cbor->max_depth ([$maximum_nesting_depth])
88	$max_depth = $cbor->get_max_depth	85	$max_depth = $cbor->get_max_depth
89	Sets the maximum nesting level (default 512) accepted while encoding	86	Sets the maximum nesting level (default 512) accepted while encoding
90	or decoding. If a higher nesting level is detected in CBOR data or a	87	or decoding. If a higher nesting level is detected in CBOR data or a
…		…
121	as when 0 is specified).	118	as when 0 is specified).
122		119
123	See SECURITY CONSIDERATIONS, below, for more info on why this is	120	See SECURITY CONSIDERATIONS, below, for more info on why this is
124	useful.	121	useful.
125		122
		123	$cbor = $cbor->allow_unknown ([$enable])
		124	$enabled = $cbor->get_allow_unknown
		125	If $enable is true (or missing), then "encode" will not throw an
		126	exception when it encounters values it cannot represent in CBOR (for
		127	example, filehandles) but instead will encode a CBOR "error" value.
		128
		129	If $enable is false (the default), then "encode" will throw an
		130	exception when it encounters anything it cannot encode as CBOR.
		131
		132	This option does not affect "decode" in any way, and it is
		133	recommended to leave it off unless you know your communications
		134	partner.
		135
		136	$cbor = $cbor->allow_sharing ([$enable])
		137	$enabled = $cbor->get_allow_sharing
		138	If $enable is true (or missing), then "encode" will not
		139	double-encode values that have been referenced before (e.g. when the
		140	same object, such as an array, is referenced multiple times), but
		141	instead will emit a reference to the earlier value.
		142
		143	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
		145	supporting the value sharing extension. This also makes it possible
		146	to encode cyclic data structures (which need "allow_cycles" to ne
		147	enabled to be decoded by this module).
		148
		149	It is recommended to leave it off unless you know your communication
		150	partner supports the value sharing extensions to CBOR
		151	(<http://cbor.schmorp.de/value-sharing>), as without decoder
		152	support, the resulting data structure might be unusable.
		153
		154	Detecting shared values incurs a runtime overhead when values are
		155	encoded that have a reference counter large than one, and might
		156	unnecessarily increase the encoded size, as potentially shared
		157	values are encode as shareable whether or not they are actually
		158	shared.
		159
		160	At the moment, only targets of references can be shared (e.g.
		161	scalars, arrays or hashes pointed to by a reference). Weirder
		162	constructs, such as an array with multiple "copies" of the same
		163	string, which are hard but not impossible to create in Perl, are not
		164	supported (this is the same as with Storable).
		165
		166	If $enable is false (the default), then "encode" will encode shared
		167	data structures repeatedly, unsharing them in the process. Cyclic
		168	data structures cannot be encoded in this mode.
		169
		170	This option does not affect "decode" in any way - shared values and
		171	references will always be decoded properly if present.
		172
		173	$cbor = $cbor->allow_cycles ([$enable])
		174	$enabled = $cbor->get_allow_cycles
		175	If $enable is true (or missing), then "decode" will happily decode
		176	self-referential (cyclic) data structures. By default these will not
		177	be decoded, as they need manual cleanup to avoid memory leaks, so
		178	code that isn't prepared for this will not leak memory.
		179
		180	If $enable is false (the default), then "decode" will throw an error
		181	when it encounters a self-referential/cyclic data structure.
		182
		183	This option does not affect "encode" in any way - shared values and
		184	references will always be decoded properly if present.
		185
		186	$cbor = $cbor->pack_strings ([$enable])
		187	$enabled = $cbor->get_pack_strings
		188	If $enable is true (or missing), then "encode" will try not to
		189	encode the same string twice, but will instead encode a reference to
		190	the string instead. Depending on your data format, this can save a
		191	lot of space, but also results in a very large runtime overhead
		192	(expect encoding times to be 2-4 times as high as without).
		193
		194	It is recommended to leave it off unless you know your
		195	communications partner supports the stringref extension to CBOR
		196	(<http://cbor.schmorp.de/stringref>), as without decoder support,
		197	the resulting data structure might not be usable.
		198
		199	If $enable is false (the default), then "encode" will encode strings
		200	the standard CBOR way.
		201
		202	This option does not affect "decode" in any way - string references
		203	will always be decoded properly if present.
		204
		205	$cbor = $cbor->validate_utf8 ([$enable])
		206	$enabled = $cbor->get_validate_utf8
		207	If $enable is true (or missing), then "decode" will validate that
		208	elements (text strings) containing UTF-8 data in fact contain valid
		209	UTF-8 data (instead of blindly accepting it). This validation
		210	obviously takes extra time during decoding.
		211
		212	The concept of "valid UTF-8" used is perl's concept, which is a
		213	superset of the official UTF-8.
		214
		215	If $enable is false (the default), then "decode" will blindly accept
		216	UTF-8 data, marking them as valid UTF-8 in the resulting data
		217	structure regardless of whether thats true or not.
		218
		219	Perl isn't too happy about corrupted UTF-8 in strings, but should
		220	generally not crash or do similarly evil things. Extensions might be
		221	not so forgiving, so it's recommended to turn on this setting if you
		222	receive untrusted CBOR.
		223
		224	This option does not affect "encode" in any way - strings that are
		225	supposedly valid UTF-8 will simply be dumped into the resulting CBOR
		226	string without checking whether that is, in fact, true or not.
		227
		228	$cbor = $cbor->filter ([$cb->($tag, $value)])
		229	$cb_or_undef = $cbor->get_filter
		230	Sets or replaces the tagged value decoding filter (when $cb is
		231	specified) or clears the filter (if no argument or "undef" is
		232	provided).
		233
		234	The filter callback is called only during decoding, when a
		235	non-enforced tagged value has been decoded (see "TAG HANDLING AND
		236	EXTENSIONS" for a list of enforced tags). For specific tags, it's
		237	often better to provide a default converter using the
		238	%CBOR::XS::FILTER hash (see below).
		239
		240	The first argument is the numerical tag, the second is the (decoded)
		241	value that has been tagged.
		242
		243	The filter function should return either exactly one value, which
		244	will replace the tagged value in the decoded data structure, or no
		245	values, which will result in default handling, which currently means
		246	the decoder creates a "CBOR::XS::Tagged" object to hold the tag and
		247	the value.
		248
		249	When the filter is cleared (the default state), the default filter
		250	function, "CBOR::XS::default_filter", is used. This function simply
		251	looks up the tag in the %CBOR::XS::FILTER hash. If an entry exists
		252	it must be a code reference that is called with tag and value, and
		253	is responsible for decoding the value. If no entry exists, it
		254	returns no values.
		255
		256	Example: decode all tags not handled internally into
		257	"CBOR::XS::Tagged" objects, with no other special handling (useful
		258	when working with potentially "unsafe" CBOR data).
		259
		260	CBOR::XS->new->filter (sub { })->decode ($cbor_data);
		261
		262	Example: provide a global filter for tag 1347375694, converting the
		263	value into some string form.
		264
		265	$CBOR::XS::FILTER{1347375694} = sub {
		266	my ($tag, $value);
		267
		268	"tag 1347375694 value $value"
		269	};
		270
126	$cbor_data = $cbor->encode ($perl_scalar)	271	$cbor_data = $cbor->encode ($perl_scalar)
127	Converts the given Perl data structure (a scalar value) to its CBOR	272	Converts the given Perl data structure (a scalar value) to its CBOR
128	representation.	273	representation.
129		274
130	$perl_scalar = $cbor->decode ($cbor_data)	275	$perl_scalar = $cbor->decode ($cbor_data)
…		…
158	integers	303	integers
159	CBOR integers become (numeric) perl scalars. On perls without 64 bit	304	CBOR integers become (numeric) perl scalars. On perls without 64 bit
160	support, 64 bit integers will be truncated or otherwise corrupted.	305	support, 64 bit integers will be truncated or otherwise corrupted.
161		306
162	byte strings	307	byte strings
163	Byte strings will become octet strings in Perl (the byte values	308	Byte strings will become octet strings in Perl (the Byte values
164	0..255 will simply become characters of the same value in Perl).	309	0..255 will simply become characters of the same value in Perl).
165		310
166	UTF-8 strings	311	UTF-8 strings
167	UTF-8 strings in CBOR will be decoded, i.e. the UTF-8 octets will be	312	UTF-8 strings in CBOR will be decoded, i.e. the UTF-8 octets will be
168	decoded into proper Unicode code points. At the moment, the validity	313	decoded into proper Unicode code points. At the moment, the validity
…		…
182	"Types:Serialiser::false" and "Types::Serialiser::error",	327	"Types:Serialiser::false" and "Types::Serialiser::error",
183	respectively. They are overloaded to act almost exactly like the	328	respectively. They are overloaded to act almost exactly like the
184	numbers 1 and 0 (for true and false) or to throw an exception on	329	numbers 1 and 0 (for true and false) or to throw an exception on
185	access (for error). See the Types::Serialiser manpage for details.	330	access (for error). See the Types::Serialiser manpage for details.
186		331
187	CBOR tag 256 (perl object)	332	tagged values
188	The tag value 256 (TODO: pending iana registration) will be used to
189	deserialise a Perl object serialised with "FREEZE". See OBJECT
190	SERIALISATION, below, for details.
191
192	CBOR tag 55799 (magic header)
193	The tag 55799 is ignored (this tag implements the magic header).
194
195	other CBOR tags
196	Tagged items consists of a numeric tag and another CBOR value. Tags	333	Tagged items consists of a numeric tag and another CBOR value.
197	not handled internally are currently converted into a
198	CBOR::XS::Tagged object, which is simply a blessed array reference
199	consisting of the numeric tag value followed by the (decoded) CBOR
200	value.
201		334
202	In the future, support for user-supplied conversions might get	335	See "TAG HANDLING AND EXTENSIONS" and the description of "->filter"
203	added.	336	for details on which tags are handled how.
204		337
205	anything else	338	anything else
206	Anything else (e.g. unsupported simple values) will raise a decoding	339	Anything else (e.g. unsupported simple values) will raise a decoding
207	error.	340	error.
208		341
209	PERL -> CBOR	342	PERL -> CBOR
210	The mapping from Perl to CBOR is slightly more difficult, as Perl is a	343	The mapping from Perl to CBOR is slightly more difficult, as Perl is a
211	truly typeless language, so we can only guess which CBOR type is meant	344	typeless language. That means this module can only guess which CBOR type
212	by a Perl value.	345	is meant by a perl value.
213		346
214	hash references	347	hash references
215	Perl hash references become CBOR maps. As there is no inherent	348	Perl hash references become CBOR maps. As there is no inherent
216	ordering in hash keys (or CBOR maps), they will usually be encoded	349	ordering in hash keys (or CBOR maps), they will usually be encoded
217	in a pseudo-random order.	350	in a pseudo-random order. This order can be different each time a
		351	hahs is encoded.
218		352
219	Currently, tied hashes will use the indefinite-length format, while	353	Currently, tied hashes will use the indefinite-length format, while
220	normal hashes will use the fixed-length format.	354	normal hashes will use the fixed-length format.
221		355
222	array references	356	array references
223	Perl array references become fixed-length CBOR arrays.	357	Perl array references become fixed-length CBOR arrays.
224		358
225	other references	359	other references
226	Other unblessed references are generally not allowed and will cause	360	Other unblessed references will be represented using the indirection
227	an exception to be thrown, except for references to the integers 0	361	tag extension (tag value 22098,
228	and 1, which get turned into false and true in CBOR.	362	<http://cbor.schmorp.de/indirection>). CBOR decoders are guaranteed
		363	to be able to decode these values somehow, by either "doing the
		364	right thing", decoding into a generic tagged object, simply ignoring
		365	the tag, or something else.
229		366
230	CBOR::XS::Tagged objects	367	CBOR::XS::Tagged objects
231	Objects of this type must be arrays consisting of a single "[tag,	368	Objects of this type must be arrays consisting of a single "[tag,
232	value]" pair. The (numerical) tag will be encoded as a CBOR tag, the	369	value]" pair. The (numerical) tag will be encoded as a CBOR tag, the
233	value will be encoded as appropriate for the value. You cna use	370	value will be encoded as appropriate for the value. You must use
234	"CBOR::XS::tag" to create such objects.	371	"CBOR::XS::tag" to create such objects.
235		372
236	Types::Serialiser::true, Types::Serialiser::false,	373	Types::Serialiser::true, Types::Serialiser::false,
237	Types::Serialiser::error	374	Types::Serialiser::error
238	These special values become CBOR true, CBOR false and CBOR undefined	375	These special values become CBOR true, CBOR false and CBOR undefined
239	values, respectively. You can also use "\1", "\0" and "\undef"	376	values, respectively. You can also use "\1", "\0" and "\undef"
240	directly if you want.	377	directly if you want.
241		378
242	other blessed objects	379	other blessed objects
243	Other blessed objects are serialised via "TO_CBOR" or "FREEZE". See	380	Other blessed objects are serialised via "TO_CBOR" or "FREEZE". See
244	"OBJECT SERIALISATION", below, for details.	381	"TAG HANDLING AND EXTENSIONS" for specific classes handled by this
		382	module, and "OBJECT SERIALISATION" for generic object serialisation.
245		383
246	simple scalars	384	simple scalars
247	TODO Simple Perl scalars (any scalar that is not a reference) are	385	Simple Perl scalars (any scalar that is not a reference) are the
248	the most difficult objects to encode: CBOR::XS will encode undefined	386	most difficult objects to encode: CBOR::XS will encode undefined
249	scalars as CBOR null values, scalars that have last been used in a	387	scalars as CBOR null values, scalars that have last been used in a
250	string context before encoding as CBOR strings, and anything else as	388	string context before encoding as CBOR strings, and anything else as
251	number value:	389	number value:
252		390
253	# dump as number	391	# dump as number
254	encode_cbor [2] # yields [2]	392	encode_cbor [2] # yields [2]
255	encode_cbor [-3.0e17] # yields [-3e+17]	393	encode_cbor [-3.0e17] # yields [-3e+17]
256	my $value = 5; encode_cbor [$value] # yields [5]	394	my $value = 5; encode_cbor [$value] # yields [5]
257		395
258	# used as string, so dump as string	396	# used as string, so dump as string (either byte or text)
259	print $value;	397	print $value;
260	encode_cbor [$value] # yields ["5"]	398	encode_cbor [$value] # yields ["5"]
261		399
262	# undef becomes null	400	# undef becomes null
263	encode_cbor [undef] # yields [null]	401	encode_cbor [undef] # yields [null]
…		…
266		404
267	my $x = 3.1; # some variable containing a number	405	my $x = 3.1; # some variable containing a number
268	"$x"; # stringified	406	"$x"; # stringified
269	$x .= ""; # another, more awkward way to stringify	407	$x .= ""; # another, more awkward way to stringify
270	print $x; # perl does it for you, too, quite often	408	print $x; # perl does it for you, too, quite often
		409
		410	You can force whether a string ie encoded as byte or text string by
		411	using "utf8::upgrade" and "utf8::downgrade"):
		412
		413	utf8::upgrade $x; # encode $x as text string
		414	utf8::downgrade $x; # encode $x as byte string
		415
		416	Perl doesn't define what operations up- and downgrade strings, so if
		417	the difference between byte and text is important, you should up- or
		418	downgrade your string as late as possible before encoding.
271		419
272	You can force the type to be a CBOR number by numifying it:	420	You can force the type to be a CBOR number by numifying it:
273		421
274	my $x = "3"; # some variable containing a string	422	my $x = "3"; # some variable containing a string
275	$x += 0; # numify it, ensuring it will be dumped as a number	423	$x += 0; # numify it, ensuring it will be dumped as a number
…		…
285	the IEEE double format will be used. Perls that use formats other	433	the IEEE double format will be used. Perls that use formats other
286	than IEEE double to represent numerical values are supported, but	434	than IEEE double to represent numerical values are supported, but
287	might suffer loss of precision.	435	might suffer loss of precision.
288		436
289	OBJECT SERIALISATION	437	OBJECT SERIALISATION
		438	This module implements both a CBOR-specific and the generic
		439	Types::Serialier object serialisation protocol. The following
		440	subsections explain both methods.
		441
		442	ENCODING
290	This module knows two way to serialise a Perl object: The CBOR-specific	443	This module knows two way to serialise a Perl object: The CBOR-specific
291	way, and the generic way.	444	way, and the generic way.
292		445
293	Whenever the encoder encounters a Perl object that it cnanot serialise	446	Whenever the encoder encounters a Perl object that it cannot serialise
294	directly (most of them), it will first look up the "TO_CBOR" method on	447	directly (most of them), it will first look up the "TO_CBOR" method on
295	it.	448	it.
296		449
297	If it has a "TO_CBOR" method, it will call it with the object as only	450	If it has a "TO_CBOR" method, it will call it with the object as only
298	argument, and expects exactly one return value, which it will then	451	argument, and expects exactly one return value, which it will then
…		…
303	"CBOR" as the second argument, to distinguish it from other serialisers.	456	"CBOR" as the second argument, to distinguish it from other serialisers.
304		457
305	The "FREEZE" method can return any number of values (i.e. zero or more).	458	The "FREEZE" method can return any number of values (i.e. zero or more).
306	These will be encoded as CBOR perl object, together with the classname.	459	These will be encoded as CBOR perl object, together with the classname.
307		460
		461	These methods MUST NOT change the data structure that is being
		462	serialised. Failure to comply to this can result in memory corruption -
		463	and worse.
		464
308	If an object supports neither "TO_CBOR" nor "FREEZE", encoding will fail	465	If an object supports neither "TO_CBOR" nor "FREEZE", encoding will fail
309	with an error.	466	with an error.
310		467
		468	DECODING
311	Objects encoded via "TO_CBOR" cannot be automatically decoded, but	469	Objects encoded via "TO_CBOR" cannot (normally) be automatically
312	objects encoded via "FREEZE" can be decoded using the following	470	decoded, but objects encoded via "FREEZE" can be decoded using the
313	protocol:	471	following protocol:
314		472
315	When an encoded CBOR perl object is encountered by the decoder, it will	473	When an encoded CBOR perl object is encountered by the decoder, it will
316	look up the "THAW" method, by using the stored classname, and will fail	474	look up the "THAW" method, by using the stored classname, and will fail
317	if the method cannot be found.	475	if the method cannot be found.
318		476
…		…
339		497
340	sub URI::TO_CBOR {	498	sub URI::TO_CBOR {
341	my ($self) = @_;	499	my ($self) = @_;
342	my $uri = "$self"; # stringify uri	500	my $uri = "$self"; # stringify uri
343	utf8::upgrade $uri; # make sure it will be encoded as UTF-8 string	501	utf8::upgrade $uri; # make sure it will be encoded as UTF-8 string
344	CBOR::XS::tagged 32, "$_[0]"	502	CBOR::XS::tag 32, "$_[0]"
345	}	503	}
346		504
347	This will encode URIs as a UTF-8 string with tag 32, which indicates an	505	This will encode URIs as a UTF-8 string with tag 32, which indicates an
348	URI.	506	URI.
349		507
…		…
384		542
385	MAGIC HEADER	543	MAGIC HEADER
386	There is no way to distinguish CBOR from other formats programmatically.	544	There is no way to distinguish CBOR from other formats programmatically.
387	To make it easier to distinguish CBOR from other formats, the CBOR	545	To make it easier to distinguish CBOR from other formats, the CBOR
388	specification has a special "magic string" that can be prepended to any	546	specification has a special "magic string" that can be prepended to any
389	CBOR string without changing it's meaning.	547	CBOR string without changing its meaning.
390		548
391	This string is available as $CBOR::XS::MAGIC. This module does not	549	This string is available as $CBOR::XS::MAGIC. This module does not
392	prepend this string tot he CBOR data it generates, but it will ignroe it	550	prepend this string to the CBOR data it generates, but it will ignore it
393	if present, so users can prepend this string as a "file type" indicator	551	if present, so users can prepend this string as a "file type" indicator
394	as required.	552	as required.
395		553
396	THE CBOR::XS::Tagged CLASS	554	THE CBOR::XS::Tagged CLASS
397	CBOR has the concept of tagged values - any CBOR value can be tagged	555	CBOR has the concept of tagged values - any CBOR value can be tagged
…		…
448	Wrap CBOR data in CBOR:	606	Wrap CBOR data in CBOR:
449		607
450	my $cbor_cbor = encode_cbor	608	my $cbor_cbor = encode_cbor
451	CBOR::XS::tag 24,	609	CBOR::XS::tag 24,
452	encode_cbor [1, 2, 3];	610	encode_cbor [1, 2, 3];
		611
		612	TAG HANDLING AND EXTENSIONS
		613	This section describes how this module handles specific tagged values
		614	and extensions. If a tag is not mentioned here and no additional filters
		615	are provided for it, then the default handling applies (creating a
		616	CBOR::XS::Tagged object on decoding, and only encoding the tag when
		617	explicitly requested).
		618
		619	Tags not handled specifically are currently converted into a
		620	CBOR::XS::Tagged object, which is simply a blessed array reference
		621	consisting of the numeric tag value followed by the (decoded) CBOR
		622	value.
		623
		624	Future versions of this module reserve the right to special case
		625	additional tags (such as base64url).
		626
		627	ENFORCED TAGS
		628	These tags are always handled when decoding, and their handling cannot
		629	be overriden by the user.
		630
		631	26 (perl-object, <http://cbor.schmorp.de/perl-object>)
		632	These tags are automatically created (and decoded) for serialisable
		633	objects using the "FREEZE/THAW" methods (the Types::Serialier object
		634	serialisation protocol). See "OBJECT SERIALISATION" for details.
		635
		636	28, 29 (shareable, sharedref, L <http://cbor.schmorp.de/value-sharing>)
		637	These tags are automatically decoded when encountered (and they do
		638	not result in a cyclic data structure, see "allow_cycles"),
		639	resulting in shared values in the decoded object. They are only
		640	encoded, however, when "allow_sharing" is enabled.
		641
		642	Not all shared values can be successfully decoded: values that
		643	reference themselves will currently decode as "undef" (this is not
		644	the same as a reference pointing to itself, which will be
		645	represented as a value that contains an indirect reference to itself
		646	- these will be decoded properly).
		647
		648	Note that considerably more shared value data structures can be
		649	decoded than will be encoded - currently, only values pointed to by
		650	references will be shared, others will not. While non-reference
		651	shared values can be generated in Perl with some effort, they were
		652	considered too unimportant to be supported in the encoder. The
		653	decoder, however, will decode these values as shared values.
		654
		655	256, 25 (stringref-namespace, stringref, L
		656	<http://cbor.schmorp.de/stringref>)
		657	These tags are automatically decoded when encountered. They are only
		658	encoded, however, when "pack_strings" is enabled.
		659
		660	22098 (indirection, <http://cbor.schmorp.de/indirection>)
		661	This tag is automatically generated when a reference are encountered
		662	(with the exception of hash and array refernces). It is converted to
		663	a reference when decoding.
		664
		665	55799 (self-describe CBOR, RFC 7049)
		666	This value is not generated on encoding (unless explicitly requested
		667	by the user), and is simply ignored when decoding.
		668
		669	NON-ENFORCED TAGS
		670	These tags have default filters provided when decoding. Their handling
		671	can be overriden by changing the %CBOR::XS::FILTER entry for the tag, or
		672	by providing a custom "filter" callback when decoding.
		673
		674	When they result in decoding into a specific Perl class, the module
		675	usually provides a corresponding "TO_CBOR" method as well.
		676
		677	When any of these need to load additional modules that are not part of
		678	the perl core distribution (e.g. URI), it is (currently) up to the user
		679	to provide these modules. The decoding usually fails with an exception
		680	if the required module cannot be loaded.
		681
		682	0, 1 (date/time string, seconds since the epoch)
		683	These tags are decoded into Time::Piece objects. The corresponding
		684	"Time::Piece::TO_CBOR" method always encodes into tag 1 values
		685	currently.
		686
		687	The Time::Piece API is generally surprisingly bad, and fractional
		688	seconds are only accidentally kept intact, so watch out. On the plus
		689	side, the module comes with perl since 5.10, which has to count for
		690	something.
		691
		692	2, 3 (positive/negative bignum)
		693	These tags are decoded into Math::BigInt objects. The corresponding
		694	"Math::BigInt::TO_CBOR" method encodes "small" bigints into normal
		695	CBOR integers, and others into positive/negative CBOR bignums.
		696
		697	4, 5 (decimal fraction/bigfloat)
		698	Both decimal fractions and bigfloats are decoded into Math::BigFloat
		699	objects. The corresponding "Math::BigFloat::TO_CBOR" method always
		700	encodes into a decimal fraction.
		701
		702	CBOR cannot represent bigfloats with very large exponents -
		703	conversion of such big float objects is undefined.
		704
		705	Also, NaN and infinities are not encoded properly.
		706
		707	21, 22, 23 (expected later JSON conversion)
		708	CBOR::XS is not a CBOR-to-JSON converter, and will simply ignore
		709	these tags.
		710
		711	32 (URI)
		712	These objects decode into URI objects. The corresponding
		713	"URI::TO_CBOR" method again results in a CBOR URI value.
453		714
454	CBOR and JSON	715	CBOR and JSON
455	CBOR is supposed to implement a superset of the JSON data model, and is,	716	CBOR is supposed to implement a superset of the JSON data model, and is,
456	with some coercion, able to represent all JSON texts (something that	717	with some coercion, able to represent all JSON texts (something that
457	other "binary JSON" formats such as BSON generally do not support).	718	other "binary JSON" formats such as BSON generally do not support).
…		…
513	uses long double to represent floating point values, they might not be	774	uses long double to represent floating point values, they might not be
514	encoded properly. Half precision types are accepted, but not encoded.	775	encoded properly. Half precision types are accepted, but not encoded.
515		776
516	Strict mode and canonical mode are not implemented.	777	Strict mode and canonical mode are not implemented.
517		778
		779	LIMITATIONS ON PERLS WITHOUT 64-BIT INTEGER SUPPORT
		780	On perls that were built without 64 bit integer support (these are rare
		781	nowadays, even on 32 bit architectures), support for any kind of 64 bit
		782	integer in CBOR is very limited - most likely, these 64 bit values will
		783	be truncated, corrupted, or otherwise not decoded correctly. This also
		784	includes string, array and map sizes that are stored as 64 bit integers.
		785
518	THREADS	786	THREADS
519	This module is not guaranteed to be thread safe and there are no plans	787	This module is not guaranteed to be thread safe and there are no plans
520	to change this until Perl gets thread support (as opposed to the	788	to change this until Perl gets thread support (as opposed to the
521	horribly slow so-called "threads" which are simply slow and bloated	789	horribly slow so-called "threads" which are simply slow and bloated
522	process simulations - use fork, it's much faster, cheaper, better).	790	process simulations - use fork, it's much faster, cheaper, better).

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Comparing CBOR-XS/README (file contents): Revision 1.8 by root, Tue Oct 29 22:04:52 2013 UTC vs. Revision 1.12 by root, Sun Dec 1 17:10:42 2013 UTC

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Comparing CBOR-XS/README (file contents):
Revision 1.8 by root, Tue Oct 29 22:04:52 2013 UTC vs.
Revision 1.12 by root, Sun Dec 1 17:10:42 2013 UTC