[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 1.10 by root, Thu Nov 28 16:09:04 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"), string deduplication (see "pack_strings") and scalar
		50	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.
		147
		148	It is recommended to leave it off unless you know your communication
		149	partner supports the value sharing extensions to CBOR
		150	(<http://cbor.schmorp.de/value-sharing>), as without decoder
		151	support, the resulting data structure might be unusable.
		152
		153	Detecting shared values incurs a runtime overhead when values are
		154	encoded that have a reference counter large than one, and might
		155	unnecessarily increase the encoded size, as potentially shared
		156	values are encode as sharable whether or not they are actually
		157	shared.
		158
		159	At the moment, only targets of references can be shared (e.g.
		160	scalars, arrays or hashes pointed to by a reference). Weirder
		161	constructs, such as an array with multiple "copies" of the same
		162	string, which are hard but not impossible to create in Perl, are not
		163	supported (this is the same as with Storable).
		164
		165	If $enable is false (the default), then "encode" will encode shared
		166	data structures repeatedly, unsharing them in the process. Cyclic
		167	data structures cannot be encoded in this mode.
		168
		169	This option does not affect "decode" in any way - shared values and
		170	references will always be decoded properly if present.
		171
		172	$cbor = $cbor->pack_strings ([$enable])
		173	$enabled = $cbor->get_pack_strings
		174	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
		176	the string instead. Depending on your data format, this can save a
		177	lot of space, but also results in a very large runtime overhead
		178	(expect encoding times to be 2-4 times as high as without).
		179
		180	It is recommended to leave it off unless you know your
		181	communications partner supports the stringref extension to CBOR
		182	(<http://cbor.schmorp.de/stringref>), as without decoder support,
		183	the resulting data structure might not be usable.
		184
		185	If $enable is false (the default), then "encode" will encode strings
		186	the standard CBOR way.
		187
		188	This option does not affect "decode" in any way - string references
		189	will always be decoded properly if present.
		190
		191	$cbor = $cbor->filter ([$cb->($tag, $value)])
		192	$cb_or_undef = $cbor->get_filter
		193	Sets or replaces the tagged value decoding filter (when $cb is
		194	specified) or clears the filter (if no argument or "undef" is
		195	provided).
		196
		197	The filter callback is called only during decoding, when a
		198	non-enforced tagged value has been decoded (see "TAG HANDLING AND
		199	EXTENSIONS" for a list of enforced tags). For specific tags, it's
		200	often better to provide a default converter using the
		201	%CBOR::XS::FILTER hash (see below).
		202
		203	The first argument is the numerical tag, the second is the (decoded)
		204	value that has been tagged.
		205
		206	The filter function should return either exactly one value, which
		207	will replace the tagged value in the decoded data structure, or no
		208	values, which will result in default handling, which currently means
		209	the decoder creates a "CBOR::XS::Tagged" object to hold the tag and
		210	the value.
		211
		212	When the filter is cleared (the default state), the default filter
		213	function, "CBOR::XS::default_filter", is used. This function simply
		214	looks up the tag in the %CBOR::XS::FILTER hash. If an entry exists
		215	it must be a code reference that is called with tag and value, and
		216	is responsible for decoding the value. If no entry exists, it
		217	returns no values.
		218
		219	Example: decode all tags not handled internally into
		220	"CBOR::XS::Tagged" objects, with no other special handling (useful
		221	when working with potentially "unsafe" CBOR data).
		222
		223	CBOR::XS->new->filter (sub { })->decode ($cbor_data);
		224
		225	Example: provide a global filter for tag 1347375694, converting the
		226	value into some string form.
		227
		228	$CBOR::XS::FILTER{1347375694} = sub {
		229	my ($tag, $value);
		230
		231	"tag 1347375694 value $value"
		232	};
		233
126	$cbor_data = $cbor->encode ($perl_scalar)	234	$cbor_data = $cbor->encode ($perl_scalar)
127	Converts the given Perl data structure (a scalar value) to its CBOR	235	Converts the given Perl data structure (a scalar value) to its CBOR
128	representation.	236	representation.
129		237
130	$perl_scalar = $cbor->decode ($cbor_data)	238	$perl_scalar = $cbor->decode ($cbor_data)
…		…
158	integers	266	integers
159	CBOR integers become (numeric) perl scalars. On perls without 64 bit	267	CBOR integers become (numeric) perl scalars. On perls without 64 bit
160	support, 64 bit integers will be truncated or otherwise corrupted.	268	support, 64 bit integers will be truncated or otherwise corrupted.
161		269
162	byte strings	270	byte strings
163	Byte strings will become octet strings in Perl (the byte values	271	Byte strings will become octet strings in Perl (the Byte values
164	0..255 will simply become characters of the same value in Perl).	272	0..255 will simply become characters of the same value in Perl).
165		273
166	UTF-8 strings	274	UTF-8 strings
167	UTF-8 strings in CBOR will be decoded, i.e. the UTF-8 octets will be	275	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	276	decoded into proper Unicode code points. At the moment, the validity
…		…
182	"Types:Serialiser::false" and "Types::Serialiser::error",	290	"Types:Serialiser::false" and "Types::Serialiser::error",
183	respectively. They are overloaded to act almost exactly like the	291	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	292	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.	293	access (for error). See the Types::Serialiser manpage for details.
186		294
187	CBOR tag 256 (perl object)	295	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	296	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		297
202	In the future, support for user-supplied conversions might get	298	See "TAG HANDLING AND EXTENSIONS" and the description of "->filter"
203	added.	299	for details on which tags are handled how.
204		300
205	anything else	301	anything else
206	Anything else (e.g. unsupported simple values) will raise a decoding	302	Anything else (e.g. unsupported simple values) will raise a decoding
207	error.	303	error.
208		304
209	PERL -> CBOR	305	PERL -> CBOR
210	The mapping from Perl to CBOR is slightly more difficult, as Perl is a	306	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	307	typeless language. That means this module can only guess which CBOR type
212	by a Perl value.	308	is meant by a perl value.
213		309
214	hash references	310	hash references
215	Perl hash references become CBOR maps. As there is no inherent	311	Perl hash references become CBOR maps. As there is no inherent
216	ordering in hash keys (or CBOR maps), they will usually be encoded	312	ordering in hash keys (or CBOR maps), they will usually be encoded
217	in a pseudo-random order.	313	in a pseudo-random order. This order can be different each time a
		314	hahs is encoded.
218		315
219	Currently, tied hashes will use the indefinite-length format, while	316	Currently, tied hashes will use the indefinite-length format, while
220	normal hashes will use the fixed-length format.	317	normal hashes will use the fixed-length format.
221		318
222	array references	319	array references
223	Perl array references become fixed-length CBOR arrays.	320	Perl array references become fixed-length CBOR arrays.
224		321
225	other references	322	other references
226	Other unblessed references are generally not allowed and will cause	323	Other unblessed references will be represented using the indirection
227	an exception to be thrown, except for references to the integers 0	324	tag extension (tag value 22098,
228	and 1, which get turned into false and true in CBOR.	325	<http://cbor.schmorp.de/indirection>). CBOR decoders are guaranteed
		326	to be able to decode these values somehow, by either "doing the
		327	right thing", decoding into a generic tagged object, simply ignoring
		328	the tag, or something else.
229		329
230	CBOR::XS::Tagged objects	330	CBOR::XS::Tagged objects
231	Objects of this type must be arrays consisting of a single "[tag,	331	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	332	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	333	value will be encoded as appropriate for the value. You must use
234	"CBOR::XS::tag" to create such objects.	334	"CBOR::XS::tag" to create such objects.
235		335
236	Types::Serialiser::true, Types::Serialiser::false,	336	Types::Serialiser::true, Types::Serialiser::false,
237	Types::Serialiser::error	337	Types::Serialiser::error
238	These special values become CBOR true, CBOR false and CBOR undefined	338	These special values become CBOR true, CBOR false and CBOR undefined
239	values, respectively. You can also use "\1", "\0" and "\undef"	339	values, respectively. You can also use "\1", "\0" and "\undef"
240	directly if you want.	340	directly if you want.
241		341
242	other blessed objects	342	other blessed objects
243	Other blessed objects are serialised via "TO_CBOR" or "FREEZE". See	343	Other blessed objects are serialised via "TO_CBOR" or "FREEZE". See
244	"OBJECT SERIALISATION", below, for details.	344	"TAG HANDLING AND EXTENSIONS" for specific classes handled by this
		345	module, and "OBJECT SERIALISATION" for generic object serialisation.
245		346
246	simple scalars	347	simple scalars
247	TODO Simple Perl scalars (any scalar that is not a reference) are	348	Simple Perl scalars (any scalar that is not a reference) are the
248	the most difficult objects to encode: CBOR::XS will encode undefined	349	most difficult objects to encode: CBOR::XS will encode undefined
249	scalars as CBOR null values, scalars that have last been used in a	350	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	351	string context before encoding as CBOR strings, and anything else as
251	number value:	352	number value:
252		353
253	# dump as number	354	# dump as number
254	encode_cbor [2] # yields [2]	355	encode_cbor [2] # yields [2]
255	encode_cbor [-3.0e17] # yields [-3e+17]	356	encode_cbor [-3.0e17] # yields [-3e+17]
256	my $value = 5; encode_cbor [$value] # yields [5]	357	my $value = 5; encode_cbor [$value] # yields [5]
257		358
258	# used as string, so dump as string	359	# used as string, so dump as string (either byte or text)
259	print $value;	360	print $value;
260	encode_cbor [$value] # yields ["5"]	361	encode_cbor [$value] # yields ["5"]
261		362
262	# undef becomes null	363	# undef becomes null
263	encode_cbor [undef] # yields [null]	364	encode_cbor [undef] # yields [null]
…		…
266		367
267	my $x = 3.1; # some variable containing a number	368	my $x = 3.1; # some variable containing a number
268	"$x"; # stringified	369	"$x"; # stringified
269	$x .= ""; # another, more awkward way to stringify	370	$x .= ""; # another, more awkward way to stringify
270	print $x; # perl does it for you, too, quite often	371	print $x; # perl does it for you, too, quite often
		372
		373	You can force whether a string ie encoded as byte or text string by
		374	using "utf8::upgrade" and "utf8::downgrade"):
		375
		376	utf8::upgrade $x; # encode $x as text string
		377	utf8::downgrade $x; # encode $x as byte string
		378
		379	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
		381	downgrade your string as late as possible before encoding.
271		382
272	You can force the type to be a CBOR number by numifying it:	383	You can force the type to be a CBOR number by numifying it:
273		384
274	my $x = "3"; # some variable containing a string	385	my $x = "3"; # some variable containing a string
275	$x += 0; # numify it, ensuring it will be dumped as a number	386	$x += 0; # numify it, ensuring it will be dumped as a number
…		…
339		450
340	sub URI::TO_CBOR {	451	sub URI::TO_CBOR {
341	my ($self) = @_;	452	my ($self) = @_;
342	my $uri = "$self"; # stringify uri	453	my $uri = "$self"; # stringify uri
343	utf8::upgrade $uri; # make sure it will be encoded as UTF-8 string	454	utf8::upgrade $uri; # make sure it will be encoded as UTF-8 string
344	CBOR::XS::tagged 32, "$_[0]"	455	CBOR::XS::tag 32, "$_[0]"
345	}	456	}
346		457
347	This will encode URIs as a UTF-8 string with tag 32, which indicates an	458	This will encode URIs as a UTF-8 string with tag 32, which indicates an
348	URI.	459	URI.
349		460
…		…
384		495
385	MAGIC HEADER	496	MAGIC HEADER
386	There is no way to distinguish CBOR from other formats programmatically.	497	There is no way to distinguish CBOR from other formats programmatically.
387	To make it easier to distinguish CBOR from other formats, the CBOR	498	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	499	specification has a special "magic string" that can be prepended to any
389	CBOR string without changing it's meaning.	500	CBOR string without changing its meaning.
390		501
391	This string is available as $CBOR::XS::MAGIC. This module does not	502	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	503	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	504	if present, so users can prepend this string as a "file type" indicator
394	as required.	505	as required.
395		506
396	THE CBOR::XS::Tagged CLASS	507	THE CBOR::XS::Tagged CLASS
397	CBOR has the concept of tagged values - any CBOR value can be tagged	508	CBOR has the concept of tagged values - any CBOR value can be tagged
…		…
448	Wrap CBOR data in CBOR:	559	Wrap CBOR data in CBOR:
449		560
450	my $cbor_cbor = encode_cbor	561	my $cbor_cbor = encode_cbor
451	CBOR::XS::tag 24,	562	CBOR::XS::tag 24,
452	encode_cbor [1, 2, 3];	563	encode_cbor [1, 2, 3];
		564
		565	TAG HANDLING AND EXTENSIONS
		566	This section describes how this module handles specific tagged values
		567	and extensions. If a tag is not mentioned here and no additional filters
		568	are provided for it, then the default handling applies (creating a
		569	CBOR::XS::Tagged object on decoding, and only encoding the tag when
		570	explicitly requested).
		571
		572	Tags not handled specifically are currently converted into a
		573	CBOR::XS::Tagged object, which is simply a blessed array reference
		574	consisting of the numeric tag value followed by the (decoded) CBOR
		575	value.
		576
		577	Future versions of this module reserve the right to special case
		578	additional tags (such as base64url).
		579
		580	ENFORCED TAGS
		581	These tags are always handled when decoding, and their handling cannot
		582	be overriden by the user.
		583
		584	26 (perl-object, <http://cbor.schmorp.de/perl-object>)
		585	These tags are automatically created (and decoded) for serialisable
		586	objects using the "FREEZE/THAW" methods (the Types::Serialier object
		587	serialisation protocol). See "OBJECT SERIALISATION" for details.
		588
		589	28, 29 (sharable, sharedref, L <http://cbor.schmorp.de/value-sharing>)
		590	These tags are automatically decoded when encountered, resulting in
		591	shared values in the decoded object. They are only encoded, however,
		592	when "allow_sharable" is enabled.
		593
		594	256, 25 (stringref-namespace, stringref, L
		595	<http://cbor.schmorp.de/stringref>)
		596	These tags are automatically decoded when encountered. They are only
		597	encoded, however, when "pack_strings" is enabled.
		598
		599	22098 (indirection, <http://cbor.schmorp.de/indirection>)
		600	This tag is automatically generated when a reference are encountered
		601	(with the exception of hash and array refernces). It is converted to
		602	a reference when decoding.
		603
		604	55799 (self-describe CBOR, RFC 7049)
		605	This value is not generated on encoding (unless explicitly requested
		606	by the user), and is simply ignored when decoding.
		607
		608	NON-ENFORCED TAGS
		609	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
		611	by providing a custom "filter" callback when decoding.
		612
		613	When they result in decoding into a specific Perl class, the module
		614	usually provides a corresponding "TO_CBOR" method as well.
		615
		616	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
		618	to provide these modules. The decoding usually fails with an exception
		619	if the required module cannot be loaded.
		620
		621	2, 3 (positive/negative bignum)
		622	These tags are decoded into Math::BigInt objects. The corresponding
		623	"Math::BigInt::TO_CBOR" method encodes "small" bigints into normal
		624	CBOR integers, and others into positive/negative CBOR bignums.
		625
		626	4, 5 (decimal fraction/bigfloat)
		627	Both decimal fractions and bigfloats are decoded into Math::BigFloat
		628	objects. The corresponding "Math::BigFloat::TO_CBOR" method always
		629	encodes into a decimal fraction.
		630
		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.
		635
		636	21, 22, 23 (expected later JSON conversion)
		637	CBOR::XS is not a CBOR-to-JSON converter, and will simply ignore
		638	these tags.
		639
		640	32 (URI)
		641	These objects decode into URI objects. The corresponding
		642	"URI::TO_CBOR" method again results in a CBOR URI value.
453		643
454	CBOR and JSON	644	CBOR and JSON
455	CBOR is supposed to implement a superset of the JSON data model, and is,	645	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	646	with some coercion, able to represent all JSON texts (something that
457	other "binary JSON" formats such as BSON generally do not support).	647	other "binary JSON" formats such as BSON generally do not support).

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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 1.10 by root, Thu Nov 28 16:09:04 2013 UTC

Diff Legend

Comparing CBOR-XS/README (file contents):
Revision 1.8 by root, Tue Oct 29 22:04:52 2013 UTC vs.
Revision 1.10 by root, Thu Nov 28 16:09:04 2013 UTC