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

Comparing JSON-XS/README (file contents):
Revision 1.6 by root, Sat Mar 24 19:42:14 2007 UTC vs.
Revision 1.20 by root, Tue Nov 13 22:59:08 2007 UTC

…		…
1	NAME	1	NAME
2	JSON::XS - JSON serialising/deserialising, done correctly and fast	2	JSON::XS - JSON serialising/deserialising, done correctly and fast
3		3
		4	JSON::XS - 正しくて高速な JSON
		5	シリアライザ/デシリアライザ
		6	(http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html)
		7
4	SYNOPSIS	8	SYNOPSIS
5	use JSON::XS;	9	use JSON::XS;
6		10
7	# exported functions, croak on error	11	# exported functions, they croak on error
		12	# and expect/generate UTF-8
8		13
9	$utf8_encoded_json_text = to_json $perl_hash_or_arrayref;	14	$utf8_encoded_json_text = to_json $perl_hash_or_arrayref;
10	$perl_hash_or_arrayref = from_json $utf8_encoded_json_text;	15	$perl_hash_or_arrayref = from_json $utf8_encoded_json_text;
11		16
12	# oo-interface	17	# OO-interface
13		18
14	$coder = JSON::XS->new->ascii->pretty->allow_nonref;	19	$coder = JSON::XS->new->ascii->pretty->allow_nonref;
15	$pretty_printed_unencoded = $coder->encode ($perl_scalar);	20	$pretty_printed_unencoded = $coder->encode ($perl_scalar);
16	$perl_scalar = $coder->decode ($unicode_json_text);	21	$perl_scalar = $coder->decode ($unicode_json_text);
17		22
30		35
31	See MAPPING, below, on how JSON::XS maps perl values to JSON values and	36	See MAPPING, below, on how JSON::XS maps perl values to JSON values and
32	vice versa.	37	vice versa.
33		38
34	FEATURES	39	FEATURES
35	* correct handling of unicode issues	40	* correct Unicode handling
36	This module knows how to handle Unicode, and even documents how and	41	This module knows how to handle Unicode, and even documents how and
37	when it does so.	42	when it does so.
38		43
39	* round-trip integrity	44	* round-trip integrity
40	When you serialise a perl data structure using only datatypes	45	When you serialise a perl data structure using only datatypes
41	supported by JSON, the deserialised data structure is identical on	46	supported by JSON, the deserialised data structure is identical on
42	the Perl level. (e.g. the string "2.0" doesn't suddenly become "2").	47	the Perl level. (e.g. the string "2.0" doesn't suddenly become "2"
		48	just because it looks like a number).
43		49
44	* strict checking of JSON correctness	50	* strict checking of JSON correctness
45	There is no guessing, no generating of illegal JSON texts by	51	There is no guessing, no generating of illegal JSON texts by
46	default, and only JSON is accepted as input by default (the latter	52	default, and only JSON is accepted as input by default (the latter
47	is a security feature).	53	is a security feature).
…		…
53	* simple to use	59	* simple to use
54	This module has both a simple functional interface as well as an OO	60	This module has both a simple functional interface as well as an OO
55	interface.	61	interface.
56		62
57	* reasonably versatile output formats	63	* reasonably versatile output formats
58	You can choose between the most compact guarenteed single-line	64	You can choose between the most compact guaranteed single-line
59	format possible (nice for simple line-based protocols), a pure-ascii	65	format possible (nice for simple line-based protocols), a pure-ascii
60	format (for when your transport is not 8-bit clean), or a	66	format (for when your transport is not 8-bit clean, still supports
61	pretty-printed format (for when you want to read that stuff). Or you	67	the whole Unicode range), or a pretty-printed format (for when you
62	can combine those features in whatever way you like.	68	want to read that stuff). Or you can combine those features in
		69	whatever way you like.
63		70
64	FUNCTIONAL INTERFACE	71	FUNCTIONAL INTERFACE
65	The following convinience methods are provided by this module. They are	72	The following convenience methods are provided by this module. They are
66	exported by default:	73	exported by default:
67		74
68	$json_text = to_json $perl_scalar	75	$json_text = to_json $perl_scalar
69	Converts the given Perl data structure (a simple scalar or a	76	Converts the given Perl data structure to a UTF-8 encoded, binary
70	reference to a hash or array) to a UTF-8 encoded, binary string
71	(that is, the string contains octets only). Croaks on error.	77	string (that is, the string contains octets only). Croaks on error.
72		78
73	This function call is functionally identical to:	79	This function call is functionally identical to:
74		80
75	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)	81	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)
76		82
77	except being faster.	83	except being faster.
78		84
79	$perl_scalar = from_json $json_text	85	$perl_scalar = from_json $json_text
80	The opposite of "to_json": expects an UTF-8 (binary) string and	86	The opposite of "to_json": expects an UTF-8 (binary) string and
81	tries to parse that as an UTF-8 encoded JSON text, returning the	87	tries to parse that as an UTF-8 encoded JSON text, returning the
82	resulting simple scalar or reference. Croaks on error.	88	resulting reference. Croaks on error.
83		89
84	This function call is functionally identical to:	90	This function call is functionally identical to:
85		91
86	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)	92	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)
87		93
88	except being faster.	94	except being faster.
		95
		96	$is_boolean = JSON::XS::is_bool $scalar
		97	Returns true if the passed scalar represents either JSON::XS::true
		98	or JSON::XS::false, two constants that act like 1 and 0,
		99	respectively and are used to represent JSON "true" and "false"
		100	values in Perl.
		101
		102	See MAPPING, below, for more information on how JSON values are
		103	mapped to Perl.
		104
		105	A FEW NOTES ON UNICODE AND PERL
		106	Since this often leads to confusion, here are a few very clear words on
		107	how Unicode works in Perl, modulo bugs.
		108
		109	1. Perl strings can store characters with ordinal values > 255.
		110	This enables you to store Unicode characters as single characters in
		111	a Perl string - very natural.
		112
		113	2. Perl does not associate an encoding with your strings.
		114	Unless you force it to, e.g. when matching it against a regex, or
		115	printing the scalar to a file, in which case Perl either interprets
		116	your string as locale-encoded text, octets/binary, or as Unicode,
		117	depending on various settings. In no case is an encoding stored
		118	together with your data, it is use that decides encoding, not any
		119	magical metadata.
		120
		121	3. The internal utf-8 flag has no meaning with regards to the encoding
		122	of your string.
		123	Just ignore that flag unless you debug a Perl bug, a module written
		124	in XS or want to dive into the internals of perl. Otherwise it will
		125	only confuse you, as, despite the name, it says nothing about how
		126	your string is encoded. You can have Unicode strings with that flag
		127	set, with that flag clear, and you can have binary data with that
		128	flag set and that flag clear. Other possibilities exist, too.
		129
		130	If you didn't know about that flag, just the better, pretend it
		131	doesn't exist.
		132
		133	4. A "Unicode String" is simply a string where each character can be
		134	validly interpreted as a Unicode codepoint.
		135	If you have UTF-8 encoded data, it is no longer a Unicode string,
		136	but a Unicode string encoded in UTF-8, giving you a binary string.
		137
		138	5. A string containing "high" (> 255) character values is not a UTF-8
		139	string.
		140	It's a fact. Learn to live with it.
		141
		142	I hope this helps :)
89		143
90	OBJECT-ORIENTED INTERFACE	144	OBJECT-ORIENTED INTERFACE
91	The object oriented interface lets you configure your own encoding or	145	The object oriented interface lets you configure your own encoding or
92	decoding style, within the limits of supported formats.	146	decoding style, within the limits of supported formats.
93		147
…		…
103	=> {"a": [1, 2]}	157	=> {"a": [1, 2]}
104		158
105	$json = $json->ascii ([$enable])	159	$json = $json->ascii ([$enable])
106	If $enable is true (or missing), then the "encode" method will not	160	If $enable is true (or missing), then the "encode" method will not
107	generate characters outside the code range 0..127 (which is ASCII).	161	generate characters outside the code range 0..127 (which is ASCII).
108	Any unicode characters outside that range will be escaped using	162	Any Unicode characters outside that range will be escaped using
109	either a single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL	163	either a single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL
110	escape sequence, as per RFC4627.	164	escape sequence, as per RFC4627. The resulting encoded JSON text can
		165	be treated as a native Unicode string, an ascii-encoded,
		166	latin1-encoded or UTF-8 encoded string, or any other superset of
		167	ASCII.
111		168
112	If $enable is false, then the "encode" method will not escape	169	If $enable is false, then the "encode" method will not escape
113	Unicode characters unless required by the JSON syntax. This results	170	Unicode characters unless required by the JSON syntax or other
114	in a faster and more compact format.	171	flags. This results in a faster and more compact format.
		172
		173	The main use for this flag is to produce JSON texts that can be
		174	transmitted over a 7-bit channel, as the encoded JSON texts will not
		175	contain any 8 bit characters.
115		176
116	JSON::XS->new->ascii (1)->encode ([chr 0x10401])	177	JSON::XS->new->ascii (1)->encode ([chr 0x10401])
117	=> ["\ud801\udc01"]	178	=> ["\ud801\udc01"]
		179
		180	$json = $json->latin1 ([$enable])
		181	If $enable is true (or missing), then the "encode" method will
		182	encode the resulting JSON text as latin1 (or iso-8859-1), escaping
		183	any characters outside the code range 0..255. The resulting string
		184	can be treated as a latin1-encoded JSON text or a native Unicode
		185	string. The "decode" method will not be affected in any way by this
		186	flag, as "decode" by default expects Unicode, which is a strict
		187	superset of latin1.
		188
		189	If $enable is false, then the "encode" method will not escape
		190	Unicode characters unless required by the JSON syntax or other
		191	flags.
		192
		193	The main use for this flag is efficiently encoding binary data as
		194	JSON text, as most octets will not be escaped, resulting in a
		195	smaller encoded size. The disadvantage is that the resulting JSON
		196	text is encoded in latin1 (and must correctly be treated as such
		197	when storing and transferring), a rare encoding for JSON. It is
		198	therefore most useful when you want to store data structures known
		199	to contain binary data efficiently in files or databases, not when
		200	talking to other JSON encoders/decoders.
		201
		202	JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]
		203	=> ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)
118		204
119	$json = $json->utf8 ([$enable])	205	$json = $json->utf8 ([$enable])
120	If $enable is true (or missing), then the "encode" method will	206	If $enable is true (or missing), then the "encode" method will
121	encode the JSON result into UTF-8, as required by many protocols,	207	encode the JSON result into UTF-8, as required by many protocols,
122	while the "decode" method expects to be handled an UTF-8-encoded	208	while the "decode" method expects to be handled an UTF-8-encoded
…		…
125	bytewise/binary I/O. In future versions, enabling this option might	211	bytewise/binary I/O. In future versions, enabling this option might
126	enable autodetection of the UTF-16 and UTF-32 encoding families, as	212	enable autodetection of the UTF-16 and UTF-32 encoding families, as
127	described in RFC4627.	213	described in RFC4627.
128		214
129	If $enable is false, then the "encode" method will return the JSON	215	If $enable is false, then the "encode" method will return the JSON
130	string as a (non-encoded) unicode string, while "decode" expects	216	string as a (non-encoded) Unicode string, while "decode" expects
131	thus a unicode string. Any decoding or encoding (e.g. to UTF-8 or	217	thus a Unicode string. Any decoding or encoding (e.g. to UTF-8 or
132	UTF-16) needs to be done yourself, e.g. using the Encode module.	218	UTF-16) needs to be done yourself, e.g. using the Encode module.
133		219
134	Example, output UTF-16BE-encoded JSON:	220	Example, output UTF-16BE-encoded JSON:
135		221
136	use Encode;	222	use Encode;
…		…
158	}	244	}
159		245
160	$json = $json->indent ([$enable])	246	$json = $json->indent ([$enable])
161	If $enable is true (or missing), then the "encode" method will use a	247	If $enable is true (or missing), then the "encode" method will use a
162	multiline format as output, putting every array member or	248	multiline format as output, putting every array member or
163	object/hash key-value pair into its own line, identing them	249	object/hash key-value pair into its own line, indenting them
164	properly.	250	properly.
165		251
166	If $enable is false, no newlines or indenting will be produced, and	252	If $enable is false, no newlines or indenting will be produced, and
167	the resulting JSON text is guarenteed not to contain any "newlines".	253	the resulting JSON text is guaranteed not to contain any "newlines".
168		254
169	This setting has no effect when decoding JSON texts.	255	This setting has no effect when decoding JSON texts.
170		256
171	$json = $json->space_before ([$enable])	257	$json = $json->space_before ([$enable])
172	If $enable is true (or missing), then the "encode" method will add	258	If $enable is true (or missing), then the "encode" method will add
…		…
196		282
197	Example, space_before and indent disabled, space_after enabled:	283	Example, space_before and indent disabled, space_after enabled:
198		284
199	{"key": "value"}	285	{"key": "value"}
200		286
		287	$json = $json->relaxed ([$enable])
		288	If $enable is true (or missing), then "decode" will accept some
		289	extensions to normal JSON syntax (see below). "encode" will not be
		290	affected in anyway. *Be aware that this option makes you accept
		291	invalid JSON texts as if they were valid!*. I suggest only to use
		292	this option to parse application-specific files written by humans
		293	(configuration files, resource files etc.)
		294
		295	If $enable is false (the default), then "decode" will only accept
		296	valid JSON texts.
		297
		298	Currently accepted extensions are:
		299
		300	* list items can have an end-comma
		301	JSON separates array elements and key-value pairs with commas.
		302	This can be annoying if you write JSON texts manually and want
		303	to be able to quickly append elements, so this extension accepts
		304	comma at the end of such items not just between them:
		305
		306	[
		307	1,
		308	2, <- this comma not normally allowed
		309	]
		310	{
		311	"k1": "v1",
		312	"k2": "v2", <- this comma not normally allowed
		313	}
		314
		315	* shell-style '#'-comments
		316	Whenever JSON allows whitespace, shell-style comments are
		317	additionally allowed. They are terminated by the first
		318	carriage-return or line-feed character, after which more
		319	white-space and comments are allowed.
		320
		321	[
		322	1, # this comment not allowed in JSON
		323	# neither this one...
		324	]
		325
201	$json = $json->canonical ([$enable])	326	$json = $json->canonical ([$enable])
202	If $enable is true (or missing), then the "encode" method will	327	If $enable is true (or missing), then the "encode" method will
203	output JSON objects by sorting their keys. This is adding a	328	output JSON objects by sorting their keys. This is adding a
204	comparatively high overhead.	329	comparatively high overhead.
205		330
…		…
207	pairs in the order Perl stores them (which will likely change	332	pairs in the order Perl stores them (which will likely change
208	between runs of the same script).	333	between runs of the same script).
209		334
210	This option is useful if you want the same data structure to be	335	This option is useful if you want the same data structure to be
211	encoded as the same JSON text (given the same overall settings). If	336	encoded as the same JSON text (given the same overall settings). If
212	it is disabled, the same hash migh be encoded differently even if	337	it is disabled, the same hash might be encoded differently even if
213	contains the same data, as key-value pairs have no inherent ordering	338	contains the same data, as key-value pairs have no inherent ordering
214	in Perl.	339	in Perl.
215		340
216	This setting has no effect when decoding JSON texts.	341	This setting has no effect when decoding JSON texts.
217		342
…		…
229	Example, encode a Perl scalar as JSON value with enabled	354	Example, encode a Perl scalar as JSON value with enabled
230	"allow_nonref", resulting in an invalid JSON text:	355	"allow_nonref", resulting in an invalid JSON text:
231		356
232	JSON::XS->new->allow_nonref->encode ("Hello, World!")	357	JSON::XS->new->allow_nonref->encode ("Hello, World!")
233	=> "Hello, World!"	358	=> "Hello, World!"
		359
		360	$json = $json->allow_blessed ([$enable])
		361	If $enable is true (or missing), then the "encode" method will not
		362	barf when it encounters a blessed reference. Instead, the value of
		363	the convert_blessed option will decide whether "null"
		364	("convert_blessed" disabled or no "to_json" method found) or a
		365	representation of the object ("convert_blessed" enabled and
		366	"to_json" method found) is being encoded. Has no effect on "decode".
		367
		368	If $enable is false (the default), then "encode" will throw an
		369	exception when it encounters a blessed object.
		370
		371	$json = $json->convert_blessed ([$enable])
		372	If $enable is true (or missing), then "encode", upon encountering a
		373	blessed object, will check for the availability of the "TO_JSON"
		374	method on the object's class. If found, it will be called in scalar
		375	context and the resulting scalar will be encoded instead of the
		376	object. If no "TO_JSON" method is found, the value of
		377	"allow_blessed" will decide what to do.
		378
		379	The "TO_JSON" method may safely call die if it wants. If "TO_JSON"
		380	returns other blessed objects, those will be handled in the same
		381	way. "TO_JSON" must take care of not causing an endless recursion
		382	cycle (== crash) in this case. The name of "TO_JSON" was chosen
		383	because other methods called by the Perl core (== not by the user of
		384	the object) are usually in upper case letters and to avoid
		385	collisions with the "to_json" function.
		386
		387	This setting does not yet influence "decode" in any way, but in the
		388	future, global hooks might get installed that influence "decode" and
		389	are enabled by this setting.
		390
		391	If $enable is false, then the "allow_blessed" setting will decide
		392	what to do when a blessed object is found.
		393
		394	$json = $json->filter_json_object ([$coderef->($hashref)])
		395	When $coderef is specified, it will be called from "decode" each
		396	time it decodes a JSON object. The only argument is a reference to
		397	the newly-created hash. If the code references returns a single
		398	scalar (which need not be a reference), this value (i.e. a copy of
		399	that scalar to avoid aliasing) is inserted into the deserialised
		400	data structure. If it returns an empty list (NOTE: not "undef",
		401	which is a valid scalar), the original deserialised hash will be
		402	inserted. This setting can slow down decoding considerably.
		403
		404	When $coderef is omitted or undefined, any existing callback will be
		405	removed and "decode" will not change the deserialised hash in any
		406	way.
		407
		408	Example, convert all JSON objects into the integer 5:
		409
		410	my $js = JSON::XS->new->filter_json_object (sub { 5 });
		411	# returns [5]
		412	$js->decode ('[{}]')
		413	# throw an exception because allow_nonref is not enabled
		414	# so a lone 5 is not allowed.
		415	$js->decode ('{"a":1, "b":2}');
		416
		417	$json = $json->filter_json_single_key_object ($key [=>
		418	$coderef->($value)])
		419	Works remotely similar to "filter_json_object", but is only called
		420	for JSON objects having a single key named $key.
		421
		422	This $coderef is called before the one specified via
		423	"filter_json_object", if any. It gets passed the single value in the
		424	JSON object. If it returns a single value, it will be inserted into
		425	the data structure. If it returns nothing (not even "undef" but the
		426	empty list), the callback from "filter_json_object" will be called
		427	next, as if no single-key callback were specified.
		428
		429	If $coderef is omitted or undefined, the corresponding callback will
		430	be disabled. There can only ever be one callback for a given key.
		431
		432	As this callback gets called less often then the
		433	"filter_json_object" one, decoding speed will not usually suffer as
		434	much. Therefore, single-key objects make excellent targets to
		435	serialise Perl objects into, especially as single-key JSON objects
		436	are as close to the type-tagged value concept as JSON gets (it's
		437	basically an ID/VALUE tuple). Of course, JSON does not support this
		438	in any way, so you need to make sure your data never looks like a
		439	serialised Perl hash.
		440
		441	Typical names for the single object key are "__class_whatever__", or
		442	"$__dollars_are_rarely_used__$" or "}ugly_brace_placement", or even
		443	things like "__class_md5sum(classname)__", to reduce the risk of
		444	clashing with real hashes.
		445
		446	Example, decode JSON objects of the form "{ "__widget__" => <id> }"
		447	into the corresponding $WIDGET{<id>} object:
		448
		449	# return whatever is in $WIDGET{5}:
		450	JSON::XS
		451	->new
		452	->filter_json_single_key_object (__widget__ => sub {
		453	$WIDGET{ $_[0] }
		454	})
		455	->decode ('{"__widget__": 5')
		456
		457	# this can be used with a TO_JSON method in some "widget" class
		458	# for serialisation to json:
		459	sub WidgetBase::TO_JSON {
		460	my ($self) = @_;
		461
		462	unless ($self->{id}) {
		463	$self->{id} = ..get..some..id..;
		464	$WIDGET{$self->{id}} = $self;
		465	}
		466
		467	{ __widget__ => $self->{id} }
		468	}
234		469
235	$json = $json->shrink ([$enable])	470	$json = $json->shrink ([$enable])
236	Perl usually over-allocates memory a bit when allocating space for	471	Perl usually over-allocates memory a bit when allocating space for
237	strings. This flag optionally resizes strings generated by either	472	strings. This flag optionally resizes strings generated by either
238	"encode" or "decode" to their minimum size possible. This can save	473	"encode" or "decode" to their minimum size possible. This can save
239	memory when your JSON texts are either very very long or you have	474	memory when your JSON texts are either very very long or you have
240	many short strings. It will also try to downgrade any strings to	475	many short strings. It will also try to downgrade any strings to
241	octet-form if possible: perl stores strings internally either in an	476	octet-form if possible: perl stores strings internally either in an
242	encoding called UTF-X or in octet-form. The latter cannot store	477	encoding called UTF-X or in octet-form. The latter cannot store
243	everything but uses less space in general.	478	everything but uses less space in general (and some buggy Perl or C
		479	code might even rely on that internal representation being used).
		480
		481	The actual definition of what shrink does might change in future
		482	versions, but it will always try to save space at the expense of
		483	time.
244		484
245	If $enable is true (or missing), the string returned by "encode"	485	If $enable is true (or missing), the string returned by "encode"
246	will be shrunk-to-fit, while all strings generated by "decode" will	486	will be shrunk-to-fit, while all strings generated by "decode" will
247	also be shrunk-to-fit.	487	also be shrunk-to-fit.
248		488
…		…
251		491
252	In the future, this setting might control other things, such as	492	In the future, this setting might control other things, such as
253	converting strings that look like integers or floats into integers	493	converting strings that look like integers or floats into integers
254	or floats internally (there is no difference on the Perl level),	494	or floats internally (there is no difference on the Perl level),
255	saving space.	495	saving space.
		496
		497	$json = $json->max_depth ([$maximum_nesting_depth])
		498	Sets the maximum nesting level (default 512) accepted while encoding
		499	or decoding. If the JSON text or Perl data structure has an equal or
		500	higher nesting level then this limit, then the encoder and decoder
		501	will stop and croak at that point.
		502
		503	Nesting level is defined by number of hash- or arrayrefs that the
		504	encoder needs to traverse to reach a given point or the number of
		505	"{" or "[" characters without their matching closing parenthesis
		506	crossed to reach a given character in a string.
		507
		508	Setting the maximum depth to one disallows any nesting, so that
		509	ensures that the object is only a single hash/object or array.
		510
		511	The argument to "max_depth" will be rounded up to the next highest
		512	power of two. If no argument is given, the highest possible setting
		513	will be used, which is rarely useful.
		514
		515	See SECURITY CONSIDERATIONS, below, for more info on why this is
		516	useful.
		517
		518	$json = $json->max_size ([$maximum_string_size])
		519	Set the maximum length a JSON text may have (in bytes) where
		520	decoding is being attempted. The default is 0, meaning no limit.
		521	When "decode" is called on a string longer then this number of
		522	characters it will not attempt to decode the string but throw an
		523	exception. This setting has no effect on "encode" (yet).
		524
		525	The argument to "max_size" will be rounded up to the next highest
		526	power of two (so may be more than requested). If no argument is
		527	given, the limit check will be deactivated (same as when 0 is
		528	specified).
		529
		530	See SECURITY CONSIDERATIONS, below, for more info on why this is
		531	useful.
256		532
257	$json_text = $json->encode ($perl_scalar)	533	$json_text = $json->encode ($perl_scalar)
258	Converts the given Perl data structure (a simple scalar or a	534	Converts the given Perl data structure (a simple scalar or a
259	reference to a hash or array) to its JSON representation. Simple	535	reference to a hash or array) to its JSON representation. Simple
260	scalars will be converted into JSON string or number sequences,	536	scalars will be converted into JSON string or number sequences,
…		…
269		545
270	JSON numbers and strings become simple Perl scalars. JSON arrays	546	JSON numbers and strings become simple Perl scalars. JSON arrays
271	become Perl arrayrefs and JSON objects become Perl hashrefs. "true"	547	become Perl arrayrefs and JSON objects become Perl hashrefs. "true"
272	becomes 1, "false" becomes 0 and "null" becomes "undef".	548	becomes 1, "false" becomes 0 and "null" becomes "undef".
273		549
		550	($perl_scalar, $characters) = $json->decode_prefix ($json_text)
		551	This works like the "decode" method, but instead of raising an
		552	exception when there is trailing garbage after the first JSON
		553	object, it will silently stop parsing there and return the number of
		554	characters consumed so far.
		555
		556	This is useful if your JSON texts are not delimited by an outer
		557	protocol (which is not the brightest thing to do in the first place)
		558	and you need to know where the JSON text ends.
		559
		560	JSON::XS->new->decode_prefix ("[1] the tail")
		561	=> ([], 3)
		562
274	MAPPING	563	MAPPING
275	This section describes how JSON::XS maps Perl values to JSON values and	564	This section describes how JSON::XS maps Perl values to JSON values and
276	vice versa. These mappings are designed to "do the right thing" in most	565	vice versa. These mappings are designed to "do the right thing" in most
277	circumstances automatically, preserving round-tripping characteristics	566	circumstances automatically, preserving round-tripping characteristics
278	(what you put in comes out as something equivalent).	567	(what you put in comes out as something equivalent).
279		568
280	For the more enlightened: note that in the following descriptions,	569	For the more enlightened: note that in the following descriptions,
281	lowercase perl refers to the Perl interpreter, while uppcercase Perl	570	lowercase perl refers to the Perl interpreter, while uppercase Perl
282	refers to the abstract Perl language itself.	571	refers to the abstract Perl language itself.
283		572
284	JSON -> PERL	573	JSON -> PERL
285	object	574	object
286	A JSON object becomes a reference to a hash in Perl. No ordering of	575	A JSON object becomes a reference to a hash in Perl. No ordering of
287	object keys is preserved (JSON does not preserver object key	576	object keys is preserved (JSON does not preserve object key ordering
288	ordering itself).	577	itself).
289		578
290	array	579	array
291	A JSON array becomes a reference to an array in Perl.	580	A JSON array becomes a reference to an array in Perl.
292		581
293	string	582	string
294	A JSON string becomes a string scalar in Perl - Unicode codepoints	583	A JSON string becomes a string scalar in Perl - Unicode codepoints
295	in JSON are represented by the same codepoints in the Perl string,	584	in JSON are represented by the same codepoints in the Perl string,
296	so no manual decoding is necessary.	585	so no manual decoding is necessary.
297		586
298	number	587	number
299	A JSON number becomes either an integer or numeric (floating point)	588	A JSON number becomes either an integer, numeric (floating point) or
300	scalar in perl, depending on its range and any fractional parts. On	589	string scalar in perl, depending on its range and any fractional
301	the Perl level, there is no difference between those as Perl handles	590	parts. On the Perl level, there is no difference between those as
302	all the conversion details, but an integer may take slightly less	591	Perl handles all the conversion details, but an integer may take
303	memory and might represent more values exactly than (floating point)	592	slightly less memory and might represent more values exactly than
304	numbers.	593	(floating point) numbers.
		594
		595	If the number consists of digits only, JSON::XS will try to
		596	represent it as an integer value. If that fails, it will try to
		597	represent it as a numeric (floating point) value if that is possible
		598	without loss of precision. Otherwise it will preserve the number as
		599	a string value.
		600
		601	Numbers containing a fractional or exponential part will always be
		602	represented as numeric (floating point) values, possibly at a loss
		603	of precision.
		604
		605	This might create round-tripping problems as numbers might become
		606	strings, but as Perl is typeless there is no other way to do it.
305		607
306	true, false	608	true, false
307	These JSON atoms become 0, 1, respectively. Information is lost in	609	These JSON atoms become "JSON::XS::true" and "JSON::XS::false",
308	this process. Future versions might represent those values	610	respectively. They are overloaded to act almost exactly like the
309	differently, but they will be guarenteed to act like these integers	611	numbers 1 and 0. You can check whether a scalar is a JSON boolean by
310	would normally in Perl.	612	using the "JSON::XS::is_bool" function.
311		613
312	null	614	null
313	A JSON null atom becomes "undef" in Perl.	615	A JSON null atom becomes "undef" in Perl.
314		616
315	PERL -> JSON	617	PERL -> JSON
…		…
317	truly typeless language, so we can only guess which JSON type is meant	619	truly typeless language, so we can only guess which JSON type is meant
318	by a Perl value.	620	by a Perl value.
319		621
320	hash references	622	hash references
321	Perl hash references become JSON objects. As there is no inherent	623	Perl hash references become JSON objects. As there is no inherent
322	ordering in hash keys, they will usually be encoded in a	624	ordering in hash keys (or JSON objects), they will usually be
323	pseudo-random order that can change between runs of the same program	625	encoded in a pseudo-random order that can change between runs of the
324	but stays generally the same within a single run of a program.	626	same program but stays generally the same within a single run of a
325	JSON::XS can optionally sort the hash keys (determined by the	627	program. JSON::XS can optionally sort the hash keys (determined by
326	canonical flag), so the same datastructure will serialise to the	628	the canonical flag), so the same datastructure will serialise to
327	same JSON text (given same settings and version of JSON::XS), but	629	the same JSON text (given same settings and version of JSON::XS),
328	this incurs a runtime overhead.	630	but this incurs a runtime overhead and is only rarely useful, e.g.
		631	when you want to compare some JSON text against another for
		632	equality.
329		633
330	array references	634	array references
331	Perl array references become JSON arrays.	635	Perl array references become JSON arrays.
		636
		637	other references
		638	Other unblessed references are generally not allowed and will cause
		639	an exception to be thrown, except for references to the integers 0
		640	and 1, which get turned into "false" and "true" atoms in JSON. You
		641	can also use "JSON::XS::false" and "JSON::XS::true" to improve
		642	readability.
		643
		644	to_json [\0,JSON::XS::true] # yields [false,true]
		645
		646	JSON::XS::true, JSON::XS::false
		647	These special values become JSON true and JSON false values,
		648	respectively. You can also use "\1" and "\0" directly if you want.
332		649
333	blessed objects	650	blessed objects
334	Blessed objects are not allowed. JSON::XS currently tries to encode	651	Blessed objects are not allowed. JSON::XS currently tries to encode
335	their underlying representation (hash- or arrayref), but this	652	their underlying representation (hash- or arrayref), but this
336	behaviour might change in future versions.	653	behaviour might change in future versions.
…		…
352	to_json [$value] # yields ["5"]	669	to_json [$value] # yields ["5"]
353		670
354	# undef becomes null	671	# undef becomes null
355	to_json [undef] # yields [null]	672	to_json [undef] # yields [null]
356		673
357	You can force the type to be a string by stringifying it:	674	You can force the type to be a JSON string by stringifying it:
358		675
359	my $x = 3.1; # some variable containing a number	676	my $x = 3.1; # some variable containing a number
360	"$x"; # stringified	677	"$x"; # stringified
361	$x .= ""; # another, more awkward way to stringify	678	$x .= ""; # another, more awkward way to stringify
362	print $x; # perl does it for you, too, quite often	679	print $x; # perl does it for you, too, quite often
363		680
364	You can force the type to be a number by numifying it:	681	You can force the type to be a JSON number by numifying it:
365		682
366	my $x = "3"; # some variable containing a string	683	my $x = "3"; # some variable containing a string
367	$x += 0; # numify it, ensuring it will be dumped as a number	684	$x += 0; # numify it, ensuring it will be dumped as a number
368	$x *= 1; # same thing, the choise is yours.	685	$x *= 1; # same thing, the choice is yours.
369		686
370	You can not currently output JSON booleans or force the type in	687	You can not currently force the type in other, less obscure, ways.
371	other, less obscure, ways. Tell me if you need this capability.	688	Tell me if you need this capability.
372
373	circular data structures
374	Those will be encoded until memory or stackspace runs out.
375		689
376	COMPARISON	690	COMPARISON
377	As already mentioned, this module was created because none of the	691	As already mentioned, this module was created because none of the
378	existing JSON modules could be made to work correctly. First I will	692	existing JSON modules could be made to work correctly. First I will
379	describe the problems (or pleasures) I encountered with various existing	693	describe the problems (or pleasures) I encountered with various existing
…		…
381	not to suffer from any of these problems or limitations.	695	not to suffer from any of these problems or limitations.
382		696
383	JSON 1.07	697	JSON 1.07
384	Slow (but very portable, as it is written in pure Perl).	698	Slow (but very portable, as it is written in pure Perl).
385		699
386	Undocumented/buggy Unicode handling (how JSON handles unicode values	700	Undocumented/buggy Unicode handling (how JSON handles Unicode values
387	is undocumented. One can get far by feeding it unicode strings and	701	is undocumented. One can get far by feeding it Unicode strings and
388	doing en-/decoding oneself, but unicode escapes are not working	702	doing en-/decoding oneself, but Unicode escapes are not working
389	properly).	703	properly).
390		704
391	No roundtripping (strings get clobbered if they look like numbers,	705	No round-tripping (strings get clobbered if they look like numbers,
392	e.g. the string 2.0 will encode to 2.0 instead of "2.0", and that	706	e.g. the string 2.0 will encode to 2.0 instead of "2.0", and that
393	will decode into the number 2.	707	will decode into the number 2.
394		708
395	JSON::PC 0.01	709	JSON::PC 0.01
396	Very fast.	710	Very fast.
397		711
398	Undocumented/buggy Unicode handling.	712	Undocumented/buggy Unicode handling.
399		713
400	No roundtripping.	714	No round-tripping.
401		715
402	Has problems handling many Perl values (e.g. regex results and other	716	Has problems handling many Perl values (e.g. regex results and other
403	magic values will make it croak).	717	magic values will make it croak).
404		718
405	Does not even generate valid JSON ("{1,2}" gets converted to "{1:2}"	719	Does not even generate valid JSON ("{1,2}" gets converted to "{1:2}"
…		…
415	much undocumented. I need at least a format for easy reading by	729	much undocumented. I need at least a format for easy reading by
416	humans and a single-line compact format for use in a protocol, and	730	humans and a single-line compact format for use in a protocol, and
417	preferably a way to generate ASCII-only JSON texts).	731	preferably a way to generate ASCII-only JSON texts).
418		732
419	Completely broken (and confusingly documented) Unicode handling	733	Completely broken (and confusingly documented) Unicode handling
420	(unicode escapes are not working properly, you need to set	734	(Unicode escapes are not working properly, you need to set
421	ImplicitUnicode to different values on en- and decoding to get	735	ImplicitUnicode to different values on en- and decoding to get
422	symmetric behaviour).	736	symmetric behaviour).
423		737
424	No roundtripping (simple cases work, but this depends on wether the	738	No round-tripping (simple cases work, but this depends on whether
425	scalar value was used in a numeric context or not).	739	the scalar value was used in a numeric context or not).
426		740
427	Dumping hashes may skip hash values depending on iterator state.	741	Dumping hashes may skip hash values depending on iterator state.
428		742
429	Unmaintained (maintainer unresponsive for many months, bugs are not	743	Unmaintained (maintainer unresponsive for many months, bugs are not
430	getting fixed).	744	getting fixed).
431		745
432	Does not check input for validity (i.e. will accept non-JSON input	746	Does not check input for validity (i.e. will accept non-JSON input
433	and return "something" instead of raising an exception. This is a	747	and return "something" instead of raising an exception. This is a
434	security issue: imagine two banks transfering money between each	748	security issue: imagine two banks transferring money between each
435	other using JSON. One bank might parse a given non-JSON request and	749	other using JSON. One bank might parse a given non-JSON request and
436	deduct money, while the other might reject the transaction with a	750	deduct money, while the other might reject the transaction with a
437	syntax error. While a good protocol will at least recover, that is	751	syntax error. While a good protocol will at least recover, that is
438	extra unnecessary work and the transaction will still not succeed).	752	extra unnecessary work and the transaction will still not succeed).
439		753
440	JSON::DWIW 0.04	754	JSON::DWIW 0.04
441	Very fast. Very natural. Very nice.	755	Very fast. Very natural. Very nice.
442		756
443	Undocumented unicode handling (but the best of the pack. Unicode	757	Undocumented Unicode handling (but the best of the pack. Unicode
444	escapes still don't get parsed properly).	758	escapes still don't get parsed properly).
445		759
446	Very inflexible.	760	Very inflexible.
447		761
448	No roundtripping.	762	No round-tripping.
449		763
450	Does not generate valid JSON texts (key strings are often unquoted,	764	Does not generate valid JSON texts (key strings are often unquoted,
451	empty keys result in nothing being output)	765	empty keys result in nothing being output)
452		766
453	Does not check input for validity.	767	Does not check input for validity.
		768
		769	JSON and YAML
		770	You often hear that JSON is a subset (or a close subset) of YAML. This
		771	is, however, a mass hysteria and very far from the truth. In general,
		772	there is no way to configure JSON::XS to output a data structure as
		773	valid YAML.
		774
		775	If you really must use JSON::XS to generate YAML, you should use this
		776	algorithm (subject to change in future versions):
		777
		778	my $to_yaml = JSON::XS->new->utf8->space_after (1);
		779	my $yaml = $to_yaml->encode ($ref) . "\n";
		780
		781	This will usually generate JSON texts that also parse as valid YAML.
		782	Please note that YAML has hardcoded limits on (simple) object key
		783	lengths that JSON doesn't have, so you should make sure that your hash
		784	keys are noticeably shorter than the 1024 characters YAML allows.
		785
		786	There might be other incompatibilities that I am not aware of. In
		787	general you should not try to generate YAML with a JSON generator or
		788	vice versa, or try to parse JSON with a YAML parser or vice versa:
		789	chances are high that you will run into severe interoperability
		790	problems.
454		791
455	SPEED	792	SPEED
456	It seems that JSON::XS is surprisingly fast, as shown in the following	793	It seems that JSON::XS is surprisingly fast, as shown in the following
457	tables. They have been generated with the help of the "eg/bench" program	794	tables. They have been generated with the help of the "eg/bench" program
458	in the JSON::XS distribution, to make it easy to compare on your own	795	in the JSON::XS distribution, to make it easy to compare on your own
459	system.	796	system.
460		797
461	First comes a comparison between various modules using a very short JSON	798	First comes a comparison between various modules using a very short
462	string (83 bytes), showing the number of encodes/decodes per second	799	single-line JSON string:
463	(JSON::XS is the functional interface, while JSON::XS/2 is the OO
464	interface with pretty-printing and hashkey sorting enabled). Higher is
465	better:
466		800
		801	{"method": "handleMessage", "params": ["user1", "we were just talking"], \
		802	"id": null, "array":[1,11,234,-5,1e5,1e7, true, false]}
		803
		804	It shows the number of encodes/decodes per second (JSON::XS uses the
		805	functional interface, while JSON::XS/2 uses the OO interface with
		806	pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink).
		807	Higher is better:
		808
		809	Storable \| 15779.925 \| 14169.946 \|
		810	-----------+------------+------------+
467	module \| encode \| decode \|	811	module \| encode \| decode \|
468	-----------\|------------\|------------\|	812	-----------\|------------\|------------\|
469	JSON \| 14006 \| 6820 \|	813	JSON \| 4990.842 \| 4088.813 \|
470	JSON::DWIW \| 200937 \| 120386 \|	814	JSON::DWIW \| 51653.990 \| 71575.154 \|
471	JSON::PC \| 85065 \| 129366 \|	815	JSON::PC \| 65948.176 \| 74631.744 \|
472	JSON::Syck \| 59898 \| 44232 \|	816	JSON::PP \| 8931.652 \| 3817.168 \|
473	JSON::XS \| 1171478 \| 342435 \|	817	JSON::Syck \| 24877.248 \| 27776.848 \|
474	JSON::XS/2 \| 730760 \| 328714 \|	818	JSON::XS \| 388361.481 \| 227951.304 \|
		819	JSON::XS/2 \| 227951.304 \| 218453.333 \|
		820	JSON::XS/3 \| 338250.323 \| 218453.333 \|
		821	Storable \| 16500.016 \| 135300.129 \|
475	-----------+------------+------------+	822	-----------+------------+------------+
476		823
477	That is, JSON::XS is 6 times faster than than JSON::DWIW and about 80	824	That is, JSON::XS is about five times faster than JSON::DWIW on
		825	encoding, about three times faster on decoding, and over forty times
478	times faster than JSON, even with pretty-printing and key sorting.	826	faster than JSON, even with pretty-printing and key sorting. It also
		827	compares favourably to Storable for small amounts of data.
479		828
480	Using a longer test string (roughly 18KB, generated from Yahoo! Locals	829	Using a longer test string (roughly 18KB, generated from Yahoo! Locals
481	search API (http://nanoref.com/yahooapis/mgPdGg):	830	search API (http://nanoref.com/yahooapis/mgPdGg):
482		831
483	module \| encode \| decode \|	832	module \| encode \| decode \|
484	-----------\|------------\|------------\|	833	-----------\|------------\|------------\|
485	JSON \| 673 \| 38 \|	834	JSON \| 55.260 \| 34.971 \|
486	JSON::DWIW \| 5271 \| 770 \|	835	JSON::DWIW \| 825.228 \| 1082.513 \|
		836	JSON::PC \| 3571.444 \| 2394.829 \|
487	JSON::PC \| 9901 \| 2491 \|	837	JSON::PP \| 210.987 \| 32.574 \|
488	JSON::Syck \| 2360 \| 786 \|	838	JSON::Syck \| 552.551 \| 787.544 \|
489	JSON::XS \| 37398 \| 3202 \|	839	JSON::XS \| 5780.463 \| 4854.519 \|
490	JSON::XS/2 \| 13765 \| 3153 \|	840	JSON::XS/2 \| 3869.998 \| 4798.975 \|
		841	JSON::XS/3 \| 5862.880 \| 4798.975 \|
		842	Storable \| 4445.002 \| 5235.027 \|
491	-----------+------------+------------+	843	-----------+------------+------------+
492		844
493	Again, JSON::XS leads by far in the encoding case, while still beating	845	Again, JSON::XS leads by far (except for Storable which non-surprisingly
494	every other module in the decoding case.	846	decodes faster).
495		847
496	On large strings containing lots of unicode characters, some modules	848	On large strings containing lots of high Unicode characters, some
497	(such as JSON::PC) decode faster than JSON::XS, but the result will be	849	modules (such as JSON::PC) seem to decode faster than JSON::XS, but the
498	broken due to missing unicode handling. Others refuse to decode or	850	result will be broken due to missing (or wrong) Unicode handling. Others
499	encode properly, so it was impossible to prepare a fair comparison table	851	refuse to decode or encode properly, so it was impossible to prepare a
500	for that case.	852	fair comparison table for that case.
501		853
502	RESOURCE LIMITS	854	SECURITY CONSIDERATIONS
503	JSON::XS does not impose any limits on the size of JSON texts or Perl	855	When you are using JSON in a protocol, talking to untrusted potentially
504	values they represent - if your machine can handle it, JSON::XS will	856	hostile creatures requires relatively few measures.
505	encode or decode it. Future versions might optionally impose structure	857
506	depth and memory use resource limits.	858	First of all, your JSON decoder should be secure, that is, should not
		859	have any buffer overflows. Obviously, this module should ensure that and
		860	I am trying hard on making that true, but you never know.
		861
		862	Second, you need to avoid resource-starving attacks. That means you
		863	should limit the size of JSON texts you accept, or make sure then when
		864	your resources run out, that's just fine (e.g. by using a separate
		865	process that can crash safely). The size of a JSON text in octets or
		866	characters is usually a good indication of the size of the resources
		867	required to decode it into a Perl structure. While JSON::XS can check
		868	the size of the JSON text, it might be too late when you already have it
		869	in memory, so you might want to check the size before you accept the
		870	string.
		871
		872	Third, JSON::XS recurses using the C stack when decoding objects and
		873	arrays. The C stack is a limited resource: for instance, on my amd64
		874	machine with 8MB of stack size I can decode around 180k nested arrays
		875	but only 14k nested JSON objects (due to perl itself recursing deeply on
		876	croak to free the temporary). If that is exceeded, the program crashes.
		877	to be conservative, the default nesting limit is set to 512. If your
		878	process has a smaller stack, you should adjust this setting accordingly
		879	with the "max_depth" method.
		880
		881	And last but least, something else could bomb you that I forgot to think
		882	of. In that case, you get to keep the pieces. I am always open for
		883	hints, though...
		884
		885	If you are using JSON::XS to return packets to consumption by JavaScript
		886	scripts in a browser you should have a look at
		887	<http://jpsykes.com/47/practical-csrf-and-json-security> to see whether
		888	you are vulnerable to some common attack vectors (which really are
		889	browser design bugs, but it is still you who will have to deal with it,
		890	as major browser developers care only for features, not about doing
		891	security right).
		892
		893	THREADS
		894	This module is not guaranteed to be thread safe and there are no plans
		895	to change this until Perl gets thread support (as opposed to the
		896	horribly slow so-called "threads" which are simply slow and bloated
		897	process simulations - use fork, its much faster, cheaper, better).
		898
		899	(It might actually work, but you have been warned).
507		900
508	BUGS	901	BUGS
509	While the goal of this module is to be correct, that unfortunately does	902	While the goal of this module is to be correct, that unfortunately does
510	not mean its bug-free, only that I think its design is bug-free. It is	903	not mean its bug-free, only that I think its design is bug-free. It is
511	still very young and not well-tested. If you keep reporting bugs they	904	still relatively early in its development. If you keep reporting bugs
512	will be fixed swiftly, though.	905	they will be fixed swiftly, though.
		906
		907	Please refrain from using rt.cpan.org or any other bug reporting
		908	service. I put the contact address into my modules for a reason.
513		909
514	AUTHOR	910	AUTHOR
515	Marc Lehmann <schmorp@schmorp.de>	911	Marc Lehmann <schmorp@schmorp.de>
516	http://home.schmorp.de/	912	http://home.schmorp.de/
517		913

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Comparing JSON-XS/README (file contents): Revision 1.6 by root, Sat Mar 24 19:42:14 2007 UTC vs. Revision 1.20 by root, Tue Nov 13 22:59:08 2007 UTC

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Comparing JSON-XS/README (file contents):
Revision 1.6 by root, Sat Mar 24 19:42:14 2007 UTC vs.
Revision 1.20 by root, Tue Nov 13 22:59:08 2007 UTC