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Revision 1.1 by root, Thu Mar 22 16:40:16 2007 UTC vs.
Revision 1.94 by root, Tue Mar 25 07:46:15 2008 UTC

1	=head1 NAME	1	=head1 NAME
2		2
		3	=encoding utf-8
		4
3	JSON::XS - JSON serialising/deserialising, done correctly and fast	5	JSON::XS - JSON serialising/deserialising, done correctly and fast
4		6
		7	JSON::XS - 正しくて高速な JSON シリアライザ/デシリアライザ
		8	(http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html)
		9
5	=head1 SYNOPSIS	10	=head1 SYNOPSIS
6		11
7	use JSON::XS;	12	use JSON::XS;
8		13
		14	# exported functions, they croak on error
		15	# and expect/generate UTF-8
		16
		17	$utf8_encoded_json_text = encode_json $perl_hash_or_arrayref;
		18	$perl_hash_or_arrayref = decode_json $utf8_encoded_json_text;
		19
		20	# OO-interface
		21
		22	$coder = JSON::XS->new->ascii->pretty->allow_nonref;
		23	$pretty_printed_unencoded = $coder->encode ($perl_scalar);
		24	$perl_scalar = $coder->decode ($unicode_json_text);
		25
		26	# Note that JSON version 2.0 and above will automatically use JSON::XS
		27	# if available, at virtually no speed overhead either, so you should
		28	# be able to just:
		29
		30	use JSON;
		31
		32	# and do the same things, except that you have a pure-perl fallback now.
		33
9	=head1 DESCRIPTION	34	=head1 DESCRIPTION
10		35
		36	This module converts Perl data structures to JSON and vice versa. Its
		37	primary goal is to be I<correct> and its secondary goal is to be
		38	I<fast>. To reach the latter goal it was written in C.
		39
		40	Beginning with version 2.0 of the JSON module, when both JSON and
		41	JSON::XS are installed, then JSON will fall back on JSON::XS (this can be
		42	overriden) with no overhead due to emulation (by inheritign constructor
		43	and methods). If JSON::XS is not available, it will fall back to the
		44	compatible JSON::PP module as backend, so using JSON instead of JSON::XS
		45	gives you a portable JSON API that can be fast when you need and doesn't
		46	require a C compiler when that is a problem.
		47
		48	As this is the n-th-something JSON module on CPAN, what was the reason
		49	to write yet another JSON module? While it seems there are many JSON
		50	modules, none of them correctly handle all corner cases, and in most cases
		51	their maintainers are unresponsive, gone missing, or not listening to bug
		52	reports for other reasons.
		53
		54	See COMPARISON, below, for a comparison to some other JSON modules.
		55
		56	See MAPPING, below, on how JSON::XS maps perl values to JSON values and
		57	vice versa.
		58
		59	=head2 FEATURES
		60
11	=over 4	61	=over 4
12		62
		63	=item * correct Unicode handling
		64
		65	This module knows how to handle Unicode, documents how and when it does
		66	so, and even documents what "correct" means.
		67
		68	=item * round-trip integrity
		69
		70	When you serialise a perl data structure using only datatypes supported
		71	by JSON, the deserialised data structure is identical on the Perl level.
		72	(e.g. the string "2.0" doesn't suddenly become "2" just because it looks
		73	like a number). There minor I<are> exceptions to this, read the MAPPING
		74	section below to learn about those.
		75
		76	=item * strict checking of JSON correctness
		77
		78	There is no guessing, no generating of illegal JSON texts by default,
		79	and only JSON is accepted as input by default (the latter is a security
		80	feature).
		81
		82	=item * fast
		83
		84	Compared to other JSON modules and other serialisers such as Storable,
		85	this module usually compares favourably in terms of speed, too.
		86
		87	=item * simple to use
		88
		89	This module has both a simple functional interface as well as an objetc
		90	oriented interface interface.
		91
		92	=item * reasonably versatile output formats
		93
		94	You can choose between the most compact guaranteed-single-line format
		95	possible (nice for simple line-based protocols), a pure-ascii format
		96	(for when your transport is not 8-bit clean, still supports the whole
		97	Unicode range), or a pretty-printed format (for when you want to read that
		98	stuff). Or you can combine those features in whatever way you like.
		99
		100	=back
		101
13	=cut	102	=cut
14		103
15	package JSON::XS;	104	package JSON::XS;
16		105
17	BEGIN {	106	use strict;
		107
18	$VERSION = '0.1';	108	our $VERSION = '2.1';
19	@ISA = qw(Exporter);	109	our @ISA = qw(Exporter);
20		110
21	require Exporter;	111	our @EXPORT = qw(encode_json decode_json to_json from_json);
22		112
		113	sub to_json($) {
23	require XSLoader;	114	require Carp;
24	XSLoader::load JSON::XS::, $VERSION;	115	Carp::croak ("JSON::XS::to_json has been renamed to encode_json, either downgrade to pre-2.0 versions of JSON::XS or rename the call");
25	}	116	}
26		117
27	=item	118	sub from_json($) {
		119	require Carp;
		120	Carp::croak ("JSON::XS::from_json has been renamed to decode_json, either downgrade to pre-2.0 versions of JSON::XS or rename the call");
		121	}
		122
		123	use Exporter;
		124	use XSLoader;
		125
		126	=head1 FUNCTIONAL INTERFACE
		127
		128	The following convenience methods are provided by this module. They are
		129	exported by default:
		130
		131	=over 4
		132
		133	=item $json_text = encode_json $perl_scalar
		134
		135	Converts the given Perl data structure to a UTF-8 encoded, binary string
		136	(that is, the string contains octets only). Croaks on error.
		137
		138	This function call is functionally identical to:
		139
		140	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)
		141
		142	except being faster.
		143
		144	=item $perl_scalar = decode_json $json_text
		145
		146	The opposite of C<encode_json>: expects an UTF-8 (binary) string and tries
		147	to parse that as an UTF-8 encoded JSON text, returning the resulting
		148	reference. Croaks on error.
		149
		150	This function call is functionally identical to:
		151
		152	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)
		153
		154	except being faster.
		155
		156	=item $is_boolean = JSON::XS::is_bool $scalar
		157
		158	Returns true if the passed scalar represents either JSON::XS::true or
		159	JSON::XS::false, two constants that act like C<1> and C<0>, respectively
		160	and are used to represent JSON C<true> and C<false> values in Perl.
		161
		162	See MAPPING, below, for more information on how JSON values are mapped to
		163	Perl.
		164
		165	=back
		166
		167
		168	=head1 A FEW NOTES ON UNICODE AND PERL
		169
		170	Since this often leads to confusion, here are a few very clear words on
		171	how Unicode works in Perl, modulo bugs.
		172
		173	=over 4
		174
		175	=item 1. Perl strings can store characters with ordinal values > 255.
		176
		177	This enables you to store Unicode characters as single characters in a
		178	Perl string - very natural.
		179
		180	=item 2. Perl does I<not> associate an encoding with your strings.
		181
		182	... until you force it to, e.g. when matching it against a regex, or
		183	printing the scalar to a file, in which case Perl either interprets your
		184	string as locale-encoded text, octets/binary, or as Unicode, depending
		185	on various settings. In no case is an encoding stored together with your
		186	data, it is I<use> that decides encoding, not any magical meta data.
		187
		188	=item 3. The internal utf-8 flag has no meaning with regards to the
		189	encoding of your string.
		190
		191	Just ignore that flag unless you debug a Perl bug, a module written in
		192	XS or want to dive into the internals of perl. Otherwise it will only
		193	confuse you, as, despite the name, it says nothing about how your string
		194	is encoded. You can have Unicode strings with that flag set, with that
		195	flag clear, and you can have binary data with that flag set and that flag
		196	clear. Other possibilities exist, too.
		197
		198	If you didn't know about that flag, just the better, pretend it doesn't
		199	exist.
		200
		201	=item 4. A "Unicode String" is simply a string where each character can be
		202	validly interpreted as a Unicode codepoint.
		203
		204	If you have UTF-8 encoded data, it is no longer a Unicode string, but a
		205	Unicode string encoded in UTF-8, giving you a binary string.
		206
		207	=item 5. A string containing "high" (> 255) character values is I<not> a UTF-8 string.
		208
		209	It's a fact. Learn to live with it.
		210
		211	=back
		212
		213	I hope this helps :)
		214
		215
		216	=head1 OBJECT-ORIENTED INTERFACE
		217
		218	The object oriented interface lets you configure your own encoding or
		219	decoding style, within the limits of supported formats.
		220
		221	=over 4
		222
		223	=item $json = new JSON::XS
		224
		225	Creates a new JSON::XS object that can be used to de/encode JSON
		226	strings. All boolean flags described below are by default I<disabled>.
		227
		228	The mutators for flags all return the JSON object again and thus calls can
		229	be chained:
		230
		231	my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]})
		232	=> {"a": [1, 2]}
		233
		234	=item $json = $json->ascii ([$enable])
		235
		236	=item $enabled = $json->get_ascii
		237
		238	If C<$enable> is true (or missing), then the C<encode> method will not
		239	generate characters outside the code range C<0..127> (which is ASCII). Any
		240	Unicode characters outside that range will be escaped using either a
		241	single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence,
		242	as per RFC4627. The resulting encoded JSON text can be treated as a native
		243	Unicode string, an ascii-encoded, latin1-encoded or UTF-8 encoded string,
		244	or any other superset of ASCII.
		245
		246	If C<$enable> is false, then the C<encode> method will not escape Unicode
		247	characters unless required by the JSON syntax or other flags. This results
		248	in a faster and more compact format.
		249
		250	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		251	document.
		252
		253	The main use for this flag is to produce JSON texts that can be
		254	transmitted over a 7-bit channel, as the encoded JSON texts will not
		255	contain any 8 bit characters.
		256
		257	JSON::XS->new->ascii (1)->encode ([chr 0x10401])
		258	=> ["\ud801\udc01"]
		259
		260	=item $json = $json->latin1 ([$enable])
		261
		262	=item $enabled = $json->get_latin1
		263
		264	If C<$enable> is true (or missing), then the C<encode> method will encode
		265	the resulting JSON text as latin1 (or iso-8859-1), escaping any characters
		266	outside the code range C<0..255>. The resulting string can be treated as a
		267	latin1-encoded JSON text or a native Unicode string. The C<decode> method
		268	will not be affected in any way by this flag, as C<decode> by default
		269	expects Unicode, which is a strict superset of latin1.
		270
		271	If C<$enable> is false, then the C<encode> method will not escape Unicode
		272	characters unless required by the JSON syntax or other flags.
		273
		274	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		275	document.
		276
		277	The main use for this flag is efficiently encoding binary data as JSON
		278	text, as most octets will not be escaped, resulting in a smaller encoded
		279	size. The disadvantage is that the resulting JSON text is encoded
		280	in latin1 (and must correctly be treated as such when storing and
		281	transferring), a rare encoding for JSON. It is therefore most useful when
		282	you want to store data structures known to contain binary data efficiently
		283	in files or databases, not when talking to other JSON encoders/decoders.
		284
		285	JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]
		286	=> ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)
		287
		288	=item $json = $json->utf8 ([$enable])
		289
		290	=item $enabled = $json->get_utf8
		291
		292	If C<$enable> is true (or missing), then the C<encode> method will encode
		293	the JSON result into UTF-8, as required by many protocols, while the
		294	C<decode> method expects to be handled an UTF-8-encoded string. Please
		295	note that UTF-8-encoded strings do not contain any characters outside the
		296	range C<0..255>, they are thus useful for bytewise/binary I/O. In future
		297	versions, enabling this option might enable autodetection of the UTF-16
		298	and UTF-32 encoding families, as described in RFC4627.
		299
		300	If C<$enable> is false, then the C<encode> method will return the JSON
		301	string as a (non-encoded) Unicode string, while C<decode> expects thus a
		302	Unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs
		303	to be done yourself, e.g. using the Encode module.
		304
		305	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		306	document.
		307
		308	Example, output UTF-16BE-encoded JSON:
		309
		310	use Encode;
		311	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
		312
		313	Example, decode UTF-32LE-encoded JSON:
		314
		315	use Encode;
		316	$object = JSON::XS->new->decode (decode "UTF-32LE", $jsontext);
		317
		318	=item $json = $json->pretty ([$enable])
		319
		320	This enables (or disables) all of the C<indent>, C<space_before> and
		321	C<space_after> (and in the future possibly more) flags in one call to
		322	generate the most readable (or most compact) form possible.
		323
		324	Example, pretty-print some simple structure:
		325
		326	my $json = JSON::XS->new->pretty(1)->encode ({a => [1,2]})
		327	=>
		328	{
		329	"a" : [
		330	1,
		331	2
		332	]
		333	}
		334
		335	=item $json = $json->indent ([$enable])
		336
		337	=item $enabled = $json->get_indent
		338
		339	If C<$enable> is true (or missing), then the C<encode> method will use a multiline
		340	format as output, putting every array member or object/hash key-value pair
		341	into its own line, indenting them properly.
		342
		343	If C<$enable> is false, no newlines or indenting will be produced, and the
		344	resulting JSON text is guaranteed not to contain any C<newlines>.
		345
		346	This setting has no effect when decoding JSON texts.
		347
		348	=item $json = $json->space_before ([$enable])
		349
		350	=item $enabled = $json->get_space_before
		351
		352	If C<$enable> is true (or missing), then the C<encode> method will add an extra
		353	optional space before the C<:> separating keys from values in JSON objects.
		354
		355	If C<$enable> is false, then the C<encode> method will not add any extra
		356	space at those places.
		357
		358	This setting has no effect when decoding JSON texts. You will also
		359	most likely combine this setting with C<space_after>.
		360
		361	Example, space_before enabled, space_after and indent disabled:
		362
		363	{"key" :"value"}
		364
		365	=item $json = $json->space_after ([$enable])
		366
		367	=item $enabled = $json->get_space_after
		368
		369	If C<$enable> is true (or missing), then the C<encode> method will add an extra
		370	optional space after the C<:> separating keys from values in JSON objects
		371	and extra whitespace after the C<,> separating key-value pairs and array
		372	members.
		373
		374	If C<$enable> is false, then the C<encode> method will not add any extra
		375	space at those places.
		376
		377	This setting has no effect when decoding JSON texts.
		378
		379	Example, space_before and indent disabled, space_after enabled:
		380
		381	{"key": "value"}
		382
		383	=item $json = $json->relaxed ([$enable])
		384
		385	=item $enabled = $json->get_relaxed
		386
		387	If C<$enable> is true (or missing), then C<decode> will accept some
		388	extensions to normal JSON syntax (see below). C<encode> will not be
		389	affected in anyway. I<Be aware that this option makes you accept invalid
		390	JSON texts as if they were valid!>. I suggest only to use this option to
		391	parse application-specific files written by humans (configuration files,
		392	resource files etc.)
		393
		394	If C<$enable> is false (the default), then C<decode> will only accept
		395	valid JSON texts.
		396
		397	Currently accepted extensions are:
		398
		399	=over 4
		400
		401	=item * list items can have an end-comma
		402
		403	JSON I<separates> array elements and key-value pairs with commas. This
		404	can be annoying if you write JSON texts manually and want to be able to
		405	quickly append elements, so this extension accepts comma at the end of
		406	such items not just between them:
		407
		408	[
		409	1,
		410	2, <- this comma not normally allowed
		411	]
		412	{
		413	"k1": "v1",
		414	"k2": "v2", <- this comma not normally allowed
		415	}
		416
		417	=item * shell-style '#'-comments
		418
		419	Whenever JSON allows whitespace, shell-style comments are additionally
		420	allowed. They are terminated by the first carriage-return or line-feed
		421	character, after which more white-space and comments are allowed.
		422
		423	[
		424	1, # this comment not allowed in JSON
		425	# neither this one...
		426	]
		427
		428	=back
		429
		430	=item $json = $json->canonical ([$enable])
		431
		432	=item $enabled = $json->get_canonical
		433
		434	If C<$enable> is true (or missing), then the C<encode> method will output JSON objects
		435	by sorting their keys. This is adding a comparatively high overhead.
		436
		437	If C<$enable> is false, then the C<encode> method will output key-value
		438	pairs in the order Perl stores them (which will likely change between runs
		439	of the same script).
		440
		441	This option is useful if you want the same data structure to be encoded as
		442	the same JSON text (given the same overall settings). If it is disabled,
		443	the same hash might be encoded differently even if contains the same data,
		444	as key-value pairs have no inherent ordering in Perl.
		445
		446	This setting has no effect when decoding JSON texts.
		447
		448	=item $json = $json->allow_nonref ([$enable])
		449
		450	=item $enabled = $json->get_allow_nonref
		451
		452	If C<$enable> is true (or missing), then the C<encode> method can convert a
		453	non-reference into its corresponding string, number or null JSON value,
		454	which is an extension to RFC4627. Likewise, C<decode> will accept those JSON
		455	values instead of croaking.
		456
		457	If C<$enable> is false, then the C<encode> method will croak if it isn't
		458	passed an arrayref or hashref, as JSON texts must either be an object
		459	or array. Likewise, C<decode> will croak if given something that is not a
		460	JSON object or array.
		461
		462	Example, encode a Perl scalar as JSON value with enabled C<allow_nonref>,
		463	resulting in an invalid JSON text:
		464
		465	JSON::XS->new->allow_nonref->encode ("Hello, World!")
		466	=> "Hello, World!"
		467
		468	=item $json = $json->allow_blessed ([$enable])
		469
		470	=item $enabled = $json->get_allow_blessed
		471
		472	If C<$enable> is true (or missing), then the C<encode> method will not
		473	barf when it encounters a blessed reference. Instead, the value of the
		474	B<convert_blessed> option will decide whether C<null> (C<convert_blessed>
		475	disabled or no C<TO_JSON> method found) or a representation of the
		476	object (C<convert_blessed> enabled and C<TO_JSON> method found) is being
		477	encoded. Has no effect on C<decode>.
		478
		479	If C<$enable> is false (the default), then C<encode> will throw an
		480	exception when it encounters a blessed object.
		481
		482	=item $json = $json->convert_blessed ([$enable])
		483
		484	=item $enabled = $json->get_convert_blessed
		485
		486	If C<$enable> is true (or missing), then C<encode>, upon encountering a
		487	blessed object, will check for the availability of the C<TO_JSON> method
		488	on the object's class. If found, it will be called in scalar context
		489	and the resulting scalar will be encoded instead of the object. If no
		490	C<TO_JSON> method is found, the value of C<allow_blessed> will decide what
		491	to do.
		492
		493	The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON>
		494	returns other blessed objects, those will be handled in the same
		495	way. C<TO_JSON> must take care of not causing an endless recursion cycle
		496	(== crash) in this case. The name of C<TO_JSON> was chosen because other
		497	methods called by the Perl core (== not by the user of the object) are
		498	usually in upper case letters and to avoid collisions with any C<to_json>
		499	function or method.
		500
		501	This setting does not yet influence C<decode> in any way, but in the
		502	future, global hooks might get installed that influence C<decode> and are
		503	enabled by this setting.
		504
		505	If C<$enable> is false, then the C<allow_blessed> setting will decide what
		506	to do when a blessed object is found.
		507
		508	=item $json = $json->filter_json_object ([$coderef->($hashref)])
		509
		510	When C<$coderef> is specified, it will be called from C<decode> each
		511	time it decodes a JSON object. The only argument is a reference to the
		512	newly-created hash. If the code references returns a single scalar (which
		513	need not be a reference), this value (i.e. a copy of that scalar to avoid
		514	aliasing) is inserted into the deserialised data structure. If it returns
		515	an empty list (NOTE: I<not> C<undef>, which is a valid scalar), the
		516	original deserialised hash will be inserted. This setting can slow down
		517	decoding considerably.
		518
		519	When C<$coderef> is omitted or undefined, any existing callback will
		520	be removed and C<decode> will not change the deserialised hash in any
		521	way.
		522
		523	Example, convert all JSON objects into the integer 5:
		524
		525	my $js = JSON::XS->new->filter_json_object (sub { 5 });
		526	# returns [5]
		527	$js->decode ('[{}]')
		528	# throw an exception because allow_nonref is not enabled
		529	# so a lone 5 is not allowed.
		530	$js->decode ('{"a":1, "b":2}');
		531
		532	=item $json = $json->filter_json_single_key_object ($key [=> $coderef->($value)])
		533
		534	Works remotely similar to C<filter_json_object>, but is only called for
		535	JSON objects having a single key named C<$key>.
		536
		537	This C<$coderef> is called before the one specified via
		538	C<filter_json_object>, if any. It gets passed the single value in the JSON
		539	object. If it returns a single value, it will be inserted into the data
		540	structure. If it returns nothing (not even C<undef> but the empty list),
		541	the callback from C<filter_json_object> will be called next, as if no
		542	single-key callback were specified.
		543
		544	If C<$coderef> is omitted or undefined, the corresponding callback will be
		545	disabled. There can only ever be one callback for a given key.
		546
		547	As this callback gets called less often then the C<filter_json_object>
		548	one, decoding speed will not usually suffer as much. Therefore, single-key
		549	objects make excellent targets to serialise Perl objects into, especially
		550	as single-key JSON objects are as close to the type-tagged value concept
		551	as JSON gets (it's basically an ID/VALUE tuple). Of course, JSON does not
		552	support this in any way, so you need to make sure your data never looks
		553	like a serialised Perl hash.
		554
		555	Typical names for the single object key are C<__class_whatever__>, or
		556	C<$__dollars_are_rarely_used__$> or C<}ugly_brace_placement>, or even
		557	things like C<__class_md5sum(classname)__>, to reduce the risk of clashing
		558	with real hashes.
		559
		560	Example, decode JSON objects of the form C<< { "__widget__" => <id> } >>
		561	into the corresponding C<< $WIDGET{<id>} >> object:
		562
		563	# return whatever is in $WIDGET{5}:
		564	JSON::XS
		565	->new
		566	->filter_json_single_key_object (__widget__ => sub {
		567	$WIDGET{ $_[0] }
		568	})
		569	->decode ('{"__widget__": 5')
		570
		571	# this can be used with a TO_JSON method in some "widget" class
		572	# for serialisation to json:
		573	sub WidgetBase::TO_JSON {
		574	my ($self) = @_;
		575
		576	unless ($self->{id}) {
		577	$self->{id} = ..get..some..id..;
		578	$WIDGET{$self->{id}} = $self;
		579	}
		580
		581	{ __widget__ => $self->{id} }
		582	}
		583
		584	=item $json = $json->shrink ([$enable])
		585
		586	=item $enabled = $json->get_shrink
		587
		588	Perl usually over-allocates memory a bit when allocating space for
		589	strings. This flag optionally resizes strings generated by either
		590	C<encode> or C<decode> to their minimum size possible. This can save
		591	memory when your JSON texts are either very very long or you have many
		592	short strings. It will also try to downgrade any strings to octet-form
		593	if possible: perl stores strings internally either in an encoding called
		594	UTF-X or in octet-form. The latter cannot store everything but uses less
		595	space in general (and some buggy Perl or C code might even rely on that
		596	internal representation being used).
		597
		598	The actual definition of what shrink does might change in future versions,
		599	but it will always try to save space at the expense of time.
		600
		601	If C<$enable> is true (or missing), the string returned by C<encode> will
		602	be shrunk-to-fit, while all strings generated by C<decode> will also be
		603	shrunk-to-fit.
		604
		605	If C<$enable> is false, then the normal perl allocation algorithms are used.
		606	If you work with your data, then this is likely to be faster.
		607
		608	In the future, this setting might control other things, such as converting
		609	strings that look like integers or floats into integers or floats
		610	internally (there is no difference on the Perl level), saving space.
		611
		612	=item $json = $json->max_depth ([$maximum_nesting_depth])
		613
		614	=item $max_depth = $json->get_max_depth
		615
		616	Sets the maximum nesting level (default C<512>) accepted while encoding
		617	or decoding. If the JSON text or Perl data structure has an equal or
		618	higher nesting level then this limit, then the encoder and decoder will
		619	stop and croak at that point.
		620
		621	Nesting level is defined by number of hash- or arrayrefs that the encoder
		622	needs to traverse to reach a given point or the number of C<{> or C<[>
		623	characters without their matching closing parenthesis crossed to reach a
		624	given character in a string.
		625
		626	Setting the maximum depth to one disallows any nesting, so that ensures
		627	that the object is only a single hash/object or array.
		628
		629	The argument to C<max_depth> will be rounded up to the next highest power
		630	of two. If no argument is given, the highest possible setting will be
		631	used, which is rarely useful.
		632
		633	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
		634
		635	=item $json = $json->max_size ([$maximum_string_size])
		636
		637	=item $max_size = $json->get_max_size
		638
		639	Set the maximum length a JSON text may have (in bytes) where decoding is
		640	being attempted. The default is C<0>, meaning no limit. When C<decode>
		641	is called on a string longer then this number of characters it will not
		642	attempt to decode the string but throw an exception. This setting has no
		643	effect on C<encode> (yet).
		644
		645	The argument to C<max_size> will be rounded up to the next B<highest>
		646	power of two (so may be more than requested). If no argument is given, the
		647	limit check will be deactivated (same as when C<0> is specified).
		648
		649	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
		650
		651	=item $json_text = $json->encode ($perl_scalar)
		652
		653	Converts the given Perl data structure (a simple scalar or a reference
		654	to a hash or array) to its JSON representation. Simple scalars will be
		655	converted into JSON string or number sequences, while references to arrays
		656	become JSON arrays and references to hashes become JSON objects. Undefined
		657	Perl values (e.g. C<undef>) become JSON C<null> values. Neither C<true>
		658	nor C<false> values will be generated.
		659
		660	=item $perl_scalar = $json->decode ($json_text)
		661
		662	The opposite of C<encode>: expects a JSON text and tries to parse it,
		663	returning the resulting simple scalar or reference. Croaks on error.
		664
		665	JSON numbers and strings become simple Perl scalars. JSON arrays become
		666	Perl arrayrefs and JSON objects become Perl hashrefs. C<true> becomes
		667	C<1>, C<false> becomes C<0> and C<null> becomes C<undef>.
		668
		669	=item ($perl_scalar, $characters) = $json->decode_prefix ($json_text)
		670
		671	This works like the C<decode> method, but instead of raising an exception
		672	when there is trailing garbage after the first JSON object, it will
		673	silently stop parsing there and return the number of characters consumed
		674	so far.
		675
		676	This is useful if your JSON texts are not delimited by an outer protocol
		677	(which is not the brightest thing to do in the first place) and you need
		678	to know where the JSON text ends.
		679
		680	JSON::XS->new->decode_prefix ("[1] the tail")
		681	=> ([], 3)
		682
		683	=back
		684
		685
		686	=head1 INCREMENTAL PARSING
		687
		688	[This section is still EXPERIMENTAL]
		689
		690	In some cases, there is the need for incremental parsing of JSON
		691	texts. While this module always has to keep both JSON text and resulting
		692	Perl data structure in memory at one time, it does allow you to parse a
		693	JSON stream incrementally. It does so by accumulating text until it has
		694	a full JSON object, which it then can decode. This process is similar to
		695	using C<decode_prefix> to see if a full JSON object is available, but is
		696	much more efficient (JSON::XS will only attempt to parse the JSON text
		697	once it is sure it has enough text to get a decisive result, using a very
		698	simple but truly incremental parser).
		699
		700	The following two methods deal with this.
		701
		702	=over 4
		703
		704	=item [void, scalar or list context] = $json->incr_parse ([$string])
		705
		706	This is the central parsing function. It can both append new text and
		707	extract objects from the stream accumulated so far (both of these
		708	functions are optional).
		709
		710	If C<$string> is given, then this string is appended to the already
		711	existing JSON fragment stored in the C<$json> object.
		712
		713	After that, if the function is called in void context, it will simply
		714	return without doing anything further. This can be used to add more text
		715	in as many chunks as you want.
		716
		717	If the method is called in scalar context, then it will try to extract
		718	exactly I<one> JSON object. If that is successful, it will return this
		719	object, otherwise it will return C<undef>. This is the most common way of
		720	using the method.
		721
		722	And finally, in list context, it will try to extract as many objects
		723	from the stream as it can find and return them, or the empty list
		724	otherwise. For this to work, there must be no separators between the JSON
		725	objects or arrays, instead they must be concatenated back-to-back.
		726
		727	=item $lvalue_string = $json->incr_text
		728
		729	This method returns the currently stored JSON fragment as an lvalue, that
		730	is, you can manipulate it. This I<only> works when a preceding call to
		731	C<incr_parse> in I<scalar context> successfully returned an object. Under
		732	all other circumstances you must not call this function (I mean it.
		733	although in simple tests it might actually work, it I<will> fail under
		734	real world conditions). As a special exception, you can also call this
		735	method before having parsed anything.
		736
		737	This function is useful in two cases: a) finding the trailing text after a
		738	JSON object or b) parsing multiple JSON objects separated by non-JSON text
		739	(such as commas).
		740
		741	=back
		742
		743	=head2 LIMITATIONS
		744
		745	All options that affect decoding are supported, except
		746	C<allow_nonref>. The reason for this is that it cannot be made to
		747	work sensibly: JSON objects and arrays are self-delimited, i.e. you can concatenate
		748	them back to back and still decode them perfectly. This does not hold true
		749	for JSON numbers, however.
		750
		751	For example, is the string C<1> a single JSON number, or is it simply the
		752	start of C<12>? Or is C<12> a single JSON number, or the concatenation
		753	of C<1> and C<2>? In neither case you can tell, and this is why JSON::XS
		754	takes the conservative route and disallows this case.
		755
		756	=head2 EXAMPLES
		757
		758	Some examples will make all this clearer. First, a simple example that
		759	works similarly to C<decode_prefix>: We want to decode the JSON object at
		760	the start of a string and identify the portion after the JSON object:
		761
		762	my $text = "[1,2,3] hello";
		763
		764	my $json = new JSON::XS;
		765
		766	my $obj = $json->incr_parse ($text)
		767	or die "expected JSON object or array at beginning of string";
		768
		769	my $tail = $json->incr_text;
		770	# $tail now contains " hello"
		771
		772	Easy, isn't it?
		773
		774	Now for a more complicated example: Imagine a hypothetical protocol where
		775	you read some requests from a TCP stream, and each request is a JSON
		776	array, without any separation between them (in fact, it is often useful to
		777	use newlines as "separators", as these get interpreted as whitespace at
		778	the start of the JSON text, which makes it possible to test said protocol
		779	with C<telnet>...).
		780
		781	Here is how you'd do it (it is trivial to write this in an event-based
		782	manner):
		783
		784	my $json = new JSON::XS;
		785
		786	# read some data from the socket
		787	while (sysread $socket, my $buf, 4096) {
		788
		789	# split and decode as many requests as possible
		790	for my $request ($json->incr_parse ($buf)) {
		791	# act on the $request
		792	}
		793	}
		794
		795	Another complicated example: Assume you have a string with JSON objects
		796	or arrays, all separated by (optional) comma characters (e.g. C<[1],[2],
		797	[3]>). To parse them, we have to skip the commas between the JSON texts,
		798	and here is where the lvalue-ness of C<incr_text> comes in useful:
		799
		800	my $text = "[1],[2], [3]";
		801	my $json = new JSON::XS;
		802
		803	# void context, so no parsing done
		804	$json->incr_parse ($text);
		805
		806	# now extract as many objects as possible. note the
		807	# use of scalar context so incr_text can be called.
		808	while (my $obj = $json->incr_parse) {
		809	# do something with $obj
		810
		811	# now skip the optional comma
		812	$json->incr_text =~ s/^ \s* , //x;
		813	}
		814
		815	Now lets go for a very complex example: Assume that you have a gigantic
		816	JSON array-of-objects, many gigabytes in size, and you want to parse it,
		817	but you cannot load it into memory fully (this has actually happened in
		818	the real world :).
		819
		820	Well, you lost, you have to implement your own JSON parser. But JSON::XS
		821	can still help you: You implement a (very simple) array parser and let
		822	JSON decode the array elements, which are all full JSON objects on their
		823	own (this wouldn't work if the array elements could be JSON numbers, for
		824	example):
		825
		826	my $json = new JSON::XS;
		827
		828	# open the monster
		829	open my $fh, "<bigfile.json"
		830	or die "bigfile: $!";
		831
		832	# first parse the initial "["
		833	for (;;) {
		834	sysread $fh, my $buf, 65536
		835	or die "read error: $!";
		836	$json->incr_parse ($buf); # void context, so no parsing
		837
		838	# Exit the loop once we found and removed(!) the initial "[".
		839	# In essence, we are (ab-)using the $json object as a simple scalar
		840	# we append data to.
		841	last if $json->incr_text =~ s/^ \s* \[ //x;
		842	}
		843
		844	# now we have the skipped the initial "[", so continue
		845	# parsing all the elements.
		846	for (;;) {
		847	# in this loop we read data until we got a single JSON object
		848	for (;;) {
		849	if (my $obj = $json->incr_parse) {
		850	# do something with $obj
		851	last;
		852	}
		853
		854	# add more data
		855	sysread $fh, my $buf, 65536
		856	or die "read error: $!";
		857	$json->incr_parse ($buf); # void context, so no parsing
		858	}
		859
		860	# in this loop we read data until we either found and parsed the
		861	# separating "," between elements, or the final "]"
		862	for (;;) {
		863	# first skip whitespace
		864	$json->incr_text =~ s/^\s*//;
		865
		866	# if we find "]", we are done
		867	if ($json->incr_text =~ s/^\]//) {
		868	print "finished.\n";
		869	exit;
		870	}
		871
		872	# if we find ",", we can continue with the next element
		873	if ($json->incr_text =~ s/^,//) {
		874	last;
		875	}
		876
		877	# if we find anything else, we have a parse error!
		878	if (length $json->incr_text) {
		879	die "parse error near ", $json->incr_text;
		880	}
		881
		882	# else add more data
		883	sysread $fh, my $buf, 65536
		884	or die "read error: $!";
		885	$json->incr_parse ($buf); # void context, so no parsing
		886	}
		887
		888	This is a complex example, but most of the complexity comes from the fact
		889	that we are trying to be correct (bear with me if I am wrong, I never ran
		890	the above example :).
		891
		892
		893
		894	=head1 MAPPING
		895
		896	This section describes how JSON::XS maps Perl values to JSON values and
		897	vice versa. These mappings are designed to "do the right thing" in most
		898	circumstances automatically, preserving round-tripping characteristics
		899	(what you put in comes out as something equivalent).
		900
		901	For the more enlightened: note that in the following descriptions,
		902	lowercase I<perl> refers to the Perl interpreter, while uppercase I<Perl>
		903	refers to the abstract Perl language itself.
		904
		905
		906	=head2 JSON -> PERL
		907
		908	=over 4
		909
		910	=item object
		911
		912	A JSON object becomes a reference to a hash in Perl. No ordering of object
		913	keys is preserved (JSON does not preserve object key ordering itself).
		914
		915	=item array
		916
		917	A JSON array becomes a reference to an array in Perl.
		918
		919	=item string
		920
		921	A JSON string becomes a string scalar in Perl - Unicode codepoints in JSON
		922	are represented by the same codepoints in the Perl string, so no manual
		923	decoding is necessary.
		924
		925	=item number
		926
		927	A JSON number becomes either an integer, numeric (floating point) or
		928	string scalar in perl, depending on its range and any fractional parts. On
		929	the Perl level, there is no difference between those as Perl handles all
		930	the conversion details, but an integer may take slightly less memory and
		931	might represent more values exactly than floating point numbers.
		932
		933	If the number consists of digits only, JSON::XS will try to represent
		934	it as an integer value. If that fails, it will try to represent it as
		935	a numeric (floating point) value if that is possible without loss of
		936	precision. Otherwise it will preserve the number as a string value (in
		937	which case you lose roundtripping ability, as the JSON number will be
		938	re-encoded toa JSON string).
		939
		940	Numbers containing a fractional or exponential part will always be
		941	represented as numeric (floating point) values, possibly at a loss of
		942	precision (in which case you might lose perfect roundtripping ability, but
		943	the JSON number will still be re-encoded as a JSON number).
		944
		945	=item true, false
		946
		947	These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>,
		948	respectively. They are overloaded to act almost exactly like the numbers
		949	C<1> and C<0>. You can check whether a scalar is a JSON boolean by using
		950	the C<JSON::XS::is_bool> function.
		951
		952	=item null
		953
		954	A JSON null atom becomes C<undef> in Perl.
		955
		956	=back
		957
		958
		959	=head2 PERL -> JSON
		960
		961	The mapping from Perl to JSON is slightly more difficult, as Perl is a
		962	truly typeless language, so we can only guess which JSON type is meant by
		963	a Perl value.
		964
		965	=over 4
		966
		967	=item hash references
		968
		969	Perl hash references become JSON objects. As there is no inherent ordering
		970	in hash keys (or JSON objects), they will usually be encoded in a
		971	pseudo-random order that can change between runs of the same program but
		972	stays generally the same within a single run of a program. JSON::XS can
		973	optionally sort the hash keys (determined by the I<canonical> flag), so
		974	the same datastructure will serialise to the same JSON text (given same
		975	settings and version of JSON::XS), but this incurs a runtime overhead
		976	and is only rarely useful, e.g. when you want to compare some JSON text
		977	against another for equality.
		978
		979	=item array references
		980
		981	Perl array references become JSON arrays.
		982
		983	=item other references
		984
		985	Other unblessed references are generally not allowed and will cause an
		986	exception to be thrown, except for references to the integers C<0> and
		987	C<1>, which get turned into C<false> and C<true> atoms in JSON. You can
		988	also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability.
		989
		990	encode_json [\0,JSON::XS::true] # yields [false,true]
		991
		992	=item JSON::XS::true, JSON::XS::false
		993
		994	These special values become JSON true and JSON false values,
		995	respectively. You can also use C<\1> and C<\0> directly if you want.
		996
		997	=item blessed objects
		998
		999	Blessed objects are not directly representable in JSON. See the
		1000	C<allow_blessed> and C<convert_blessed> methods on various options on
		1001	how to deal with this: basically, you can choose between throwing an
		1002	exception, encoding the reference as if it weren't blessed, or provide
		1003	your own serialiser method.
		1004
		1005	=item simple scalars
		1006
		1007	Simple Perl scalars (any scalar that is not a reference) are the most
		1008	difficult objects to encode: JSON::XS will encode undefined scalars as
		1009	JSON C<null> values, scalars that have last been used in a string context
		1010	before encoding as JSON strings, and anything else as number value:
		1011
		1012	# dump as number
		1013	encode_json [2] # yields [2]
		1014	encode_json [-3.0e17] # yields [-3e+17]
		1015	my $value = 5; encode_json [$value] # yields [5]
		1016
		1017	# used as string, so dump as string
		1018	print $value;
		1019	encode_json [$value] # yields ["5"]
		1020
		1021	# undef becomes null
		1022	encode_json [undef] # yields [null]
		1023
		1024	You can force the type to be a JSON string by stringifying it:
		1025
		1026	my $x = 3.1; # some variable containing a number
		1027	"$x"; # stringified
		1028	$x .= ""; # another, more awkward way to stringify
		1029	print $x; # perl does it for you, too, quite often
		1030
		1031	You can force the type to be a JSON number by numifying it:
		1032
		1033	my $x = "3"; # some variable containing a string
		1034	$x += 0; # numify it, ensuring it will be dumped as a number
		1035	$x *= 1; # same thing, the choice is yours.
		1036
		1037	You can not currently force the type in other, less obscure, ways. Tell me
		1038	if you need this capability (but don't forget to explain why it's needed
		1039	:).
		1040
		1041	=back
		1042
		1043
		1044	=head1 ENCODING/CODESET FLAG NOTES
		1045
		1046	The interested reader might have seen a number of flags that signify
		1047	encodings or codesets - C<utf8>, C<latin1> and C<ascii>. There seems to be
		1048	some confusion on what these do, so here is a short comparison:
		1049
		1050	C<utf8> controls whether the JSON text created by C<encode> (and expected
		1051	by C<decode>) is UTF-8 encoded or not, while C<latin1> and C<ascii> only
		1052	control whether C<encode> escapes character values outside their respective
		1053	codeset range. Neither of these flags conflict with each other, although
		1054	some combinations make less sense than others.
		1055
		1056	Care has been taken to make all flags symmetrical with respect to
		1057	C<encode> and C<decode>, that is, texts encoded with any combination of
		1058	these flag values will be correctly decoded when the same flags are used
		1059	- in general, if you use different flag settings while encoding vs. when
		1060	decoding you likely have a bug somewhere.
		1061
		1062	Below comes a verbose discussion of these flags. Note that a "codeset" is
		1063	simply an abstract set of character-codepoint pairs, while an encoding
		1064	takes those codepoint numbers and I<encodes> them, in our case into
		1065	octets. Unicode is (among other things) a codeset, UTF-8 is an encoding,
		1066	and ISO-8859-1 (= latin 1) and ASCII are both codesets I<and> encodings at
		1067	the same time, which can be confusing.
		1068
		1069	=over 4
		1070
		1071	=item C<utf8> flag disabled
		1072
		1073	When C<utf8> is disabled (the default), then C<encode>/C<decode> generate
		1074	and expect Unicode strings, that is, characters with high ordinal Unicode
		1075	values (> 255) will be encoded as such characters, and likewise such
		1076	characters are decoded as-is, no canges to them will be done, except
		1077	"(re-)interpreting" them as Unicode codepoints or Unicode characters,
		1078	respectively (to Perl, these are the same thing in strings unless you do
		1079	funny/weird/dumb stuff).
		1080
		1081	This is useful when you want to do the encoding yourself (e.g. when you
		1082	want to have UTF-16 encoded JSON texts) or when some other layer does
		1083	the encoding for you (for example, when printing to a terminal using a
		1084	filehandle that transparently encodes to UTF-8 you certainly do NOT want
		1085	to UTF-8 encode your data first and have Perl encode it another time).
		1086
		1087	=item C<utf8> flag enabled
		1088
		1089	If the C<utf8>-flag is enabled, C<encode>/C<decode> will encode all
		1090	characters using the corresponding UTF-8 multi-byte sequence, and will
		1091	expect your input strings to be encoded as UTF-8, that is, no "character"
		1092	of the input string must have any value > 255, as UTF-8 does not allow
		1093	that.
		1094
		1095	The C<utf8> flag therefore switches between two modes: disabled means you
		1096	will get a Unicode string in Perl, enabled means you get an UTF-8 encoded
		1097	octet/binary string in Perl.
		1098
		1099	=item C<latin1> or C<ascii> flags enabled
		1100
		1101	With C<latin1> (or C<ascii>) enabled, C<encode> will escape characters
		1102	with ordinal values > 255 (> 127 with C<ascii>) and encode the remaining
		1103	characters as specified by the C<utf8> flag.
		1104
		1105	If C<utf8> is disabled, then the result is also correctly encoded in those
		1106	character sets (as both are proper subsets of Unicode, meaning that a
		1107	Unicode string with all character values < 256 is the same thing as a
		1108	ISO-8859-1 string, and a Unicode string with all character values < 128 is
		1109	the same thing as an ASCII string in Perl).
		1110
		1111	If C<utf8> is enabled, you still get a correct UTF-8-encoded string,
		1112	regardless of these flags, just some more characters will be escaped using
		1113	C<\uXXXX> then before.
		1114
		1115	Note that ISO-8859-1-I<encoded> strings are not compatible with UTF-8
		1116	encoding, while ASCII-encoded strings are. That is because the ISO-8859-1
		1117	encoding is NOT a subset of UTF-8 (despite the ISO-8859-1 I<codeset> being
		1118	a subset of Unicode), while ASCII is.
		1119
		1120	Surprisingly, C<decode> will ignore these flags and so treat all input
		1121	values as governed by the C<utf8> flag. If it is disabled, this allows you
		1122	to decode ISO-8859-1- and ASCII-encoded strings, as both strict subsets of
		1123	Unicode. If it is enabled, you can correctly decode UTF-8 encoded strings.
		1124
		1125	So neither C<latin1> nor C<ascii> are incompatible with the C<utf8> flag -
		1126	they only govern when the JSON output engine escapes a character or not.
		1127
		1128	The main use for C<latin1> is to relatively efficiently store binary data
		1129	as JSON, at the expense of breaking compatibility with most JSON decoders.
		1130
		1131	The main use for C<ascii> is to force the output to not contain characters
		1132	with values > 127, which means you can interpret the resulting string
		1133	as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about any character set and
		1134	8-bit-encoding, and still get the same data structure back. This is useful
		1135	when your channel for JSON transfer is not 8-bit clean or the encoding
		1136	might be mangled in between (e.g. in mail), and works because ASCII is a
		1137	proper subset of most 8-bit and multibyte encodings in use in the world.
		1138
		1139	=back
		1140
		1141
		1142	=head1 COMPARISON
		1143
		1144	As already mentioned, this module was created because none of the existing
		1145	JSON modules could be made to work correctly. First I will describe the
		1146	problems (or pleasures) I encountered with various existing JSON modules,
		1147	followed by some benchmark values. JSON::XS was designed not to suffer
		1148	from any of these problems or limitations.
		1149
		1150	=over 4
		1151
		1152	=item JSON 2.xx
		1153
		1154	A marvellous piece of engineering, this module either uses JSON::XS
		1155	directly when available (so will be 100% compatible with it, including
		1156	speed), or it uses JSON::PP, which is basically JSON::XS translated to
		1157	Pure Perl, which should be 100% compatible with JSON::XS, just a bit
		1158	slower.
		1159
		1160	You cannot really lose by using this module, especially as it tries very
		1161	hard to work even with ancient Perl versions, while JSON::XS does not.
		1162
		1163	=item JSON 1.07
		1164
		1165	Slow (but very portable, as it is written in pure Perl).
		1166
		1167	Undocumented/buggy Unicode handling (how JSON handles Unicode values is
		1168	undocumented. One can get far by feeding it Unicode strings and doing
		1169	en-/decoding oneself, but Unicode escapes are not working properly).
		1170
		1171	No round-tripping (strings get clobbered if they look like numbers, e.g.
		1172	the string C<2.0> will encode to C<2.0> instead of C<"2.0">, and that will
		1173	decode into the number 2.
		1174
		1175	=item JSON::PC 0.01
		1176
		1177	Very fast.
		1178
		1179	Undocumented/buggy Unicode handling.
		1180
		1181	No round-tripping.
		1182
		1183	Has problems handling many Perl values (e.g. regex results and other magic
		1184	values will make it croak).
		1185
		1186	Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}>
		1187	which is not a valid JSON text.
		1188
		1189	Unmaintained (maintainer unresponsive for many months, bugs are not
		1190	getting fixed).
		1191
		1192	=item JSON::Syck 0.21
		1193
		1194	Very buggy (often crashes).
		1195
		1196	Very inflexible (no human-readable format supported, format pretty much
		1197	undocumented. I need at least a format for easy reading by humans and a
		1198	single-line compact format for use in a protocol, and preferably a way to
		1199	generate ASCII-only JSON texts).
		1200
		1201	Completely broken (and confusingly documented) Unicode handling (Unicode
		1202	escapes are not working properly, you need to set ImplicitUnicode to
		1203	I<different> values on en- and decoding to get symmetric behaviour).
		1204
		1205	No round-tripping (simple cases work, but this depends on whether the scalar
		1206	value was used in a numeric context or not).
		1207
		1208	Dumping hashes may skip hash values depending on iterator state.
		1209
		1210	Unmaintained (maintainer unresponsive for many months, bugs are not
		1211	getting fixed).
		1212
		1213	Does not check input for validity (i.e. will accept non-JSON input and
		1214	return "something" instead of raising an exception. This is a security
		1215	issue: imagine two banks transferring money between each other using
		1216	JSON. One bank might parse a given non-JSON request and deduct money,
		1217	while the other might reject the transaction with a syntax error. While a
		1218	good protocol will at least recover, that is extra unnecessary work and
		1219	the transaction will still not succeed).
		1220
		1221	=item JSON::DWIW 0.04
		1222
		1223	Very fast. Very natural. Very nice.
		1224
		1225	Undocumented Unicode handling (but the best of the pack. Unicode escapes
		1226	still don't get parsed properly).
		1227
		1228	Very inflexible.
		1229
		1230	No round-tripping.
		1231
		1232	Does not generate valid JSON texts (key strings are often unquoted, empty keys
		1233	result in nothing being output)
		1234
		1235	Does not check input for validity.
		1236
		1237	=back
		1238
		1239
		1240	=head2 JSON and YAML
		1241
		1242	You often hear that JSON is a subset of YAML. This is, however, a mass
		1243	hysteria(*) and very far from the truth (as of the time of this writing),
		1244	so let me state it clearly: I<in general, there is no way to configure
		1245	JSON::XS to output a data structure as valid YAML> that works in all
		1246	cases.
		1247
		1248	If you really must use JSON::XS to generate YAML, you should use this
		1249	algorithm (subject to change in future versions):
		1250
		1251	my $to_yaml = JSON::XS->new->utf8->space_after (1);
		1252	my $yaml = $to_yaml->encode ($ref) . "\n";
		1253
		1254	This will I<usually> generate JSON texts that also parse as valid
		1255	YAML. Please note that YAML has hardcoded limits on (simple) object key
		1256	lengths that JSON doesn't have and also has different and incompatible
		1257	unicode handling, so you should make sure that your hash keys are
		1258	noticeably shorter than the 1024 "stream characters" YAML allows and that
		1259	you do not have characters with codepoint values outside the Unicode BMP
		1260	(basic multilingual page). YAML also does not allow C<\/> sequences in
		1261	strings (which JSON::XS does not I<currently> generate, but other JSON
		1262	generators might).
		1263
		1264	There might be other incompatibilities that I am not aware of (or the YAML
		1265	specification has been changed yet again - it does so quite often). In
		1266	general you should not try to generate YAML with a JSON generator or vice
		1267	versa, or try to parse JSON with a YAML parser or vice versa: chances are
		1268	high that you will run into severe interoperability problems when you
		1269	least expect it.
		1270
		1271	=over 4
		1272
		1273	=item (*)
		1274
		1275	I have been pressured multiple times by Brian Ingerson (one of the
		1276	authors of the YAML specification) to remove this paragraph, despite him
		1277	acknowledging that the actual incompatibilities exist. As I was personally
		1278	bitten by this "JSON is YAML" lie, I refused and said I will continue to
		1279	educate people about these issues, so others do not run into the same
		1280	problem again and again. After this, Brian called me a (quote)I<complete
		1281	and worthless idiot>(unquote).
		1282
		1283	In my opinion, instead of pressuring and insulting people who actually
		1284	clarify issues with YAML and the wrong statements of some of its
		1285	proponents, I would kindly suggest reading the JSON spec (which is not
		1286	that difficult or long) and finally make YAML compatible to it, and
		1287	educating users about the changes, instead of spreading lies about the
		1288	real compatibility for many I<years> and trying to silence people who
		1289	point out that it isn't true.
		1290
		1291	=back
		1292
		1293
		1294	=head2 SPEED
		1295
		1296	It seems that JSON::XS is surprisingly fast, as shown in the following
		1297	tables. They have been generated with the help of the C<eg/bench> program
		1298	in the JSON::XS distribution, to make it easy to compare on your own
		1299	system.
		1300
		1301	First comes a comparison between various modules using
		1302	a very short single-line JSON string (also available at
		1303	L<http://dist.schmorp.de/misc/json/short.json>).
		1304
		1305	{"method": "handleMessage", "params": ["user1", "we were just talking"], \
		1306	"id": null, "array":[1,11,234,-5,1e5,1e7, true, false]}
		1307
		1308	It shows the number of encodes/decodes per second (JSON::XS uses
		1309	the functional interface, while JSON::XS/2 uses the OO interface
		1310	with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables
		1311	shrink). Higher is better:
		1312
		1313	module | encode | decode |
		1314	-----------|------------|------------|
		1315	JSON 1.x | 4990.842 | 4088.813 |
		1316	JSON::DWIW | 51653.990 | 71575.154 |
		1317	JSON::PC | 65948.176 | 74631.744 |
		1318	JSON::PP | 8931.652 | 3817.168 |
		1319	JSON::Syck | 24877.248 | 27776.848 |
		1320	JSON::XS | 388361.481 | 227951.304 |
		1321	JSON::XS/2 | 227951.304 | 218453.333 |
		1322	JSON::XS/3 | 338250.323 | 218453.333 |
		1323	Storable | 16500.016 | 135300.129 |
		1324	-----------+------------+------------+
		1325
		1326	That is, JSON::XS is about five times faster than JSON::DWIW on encoding,
		1327	about three times faster on decoding, and over forty times faster
		1328	than JSON, even with pretty-printing and key sorting. It also compares
		1329	favourably to Storable for small amounts of data.
		1330
		1331	Using a longer test string (roughly 18KB, generated from Yahoo! Locals
		1332	search API (L<http://dist.schmorp.de/misc/json/long.json>).
		1333
		1334	module | encode | decode |
		1335	-----------|------------|------------|
		1336	JSON 1.x | 55.260 | 34.971 |
		1337	JSON::DWIW | 825.228 | 1082.513 |
		1338	JSON::PC | 3571.444 | 2394.829 |
		1339	JSON::PP | 210.987 | 32.574 |
		1340	JSON::Syck | 552.551 | 787.544 |
		1341	JSON::XS | 5780.463 | 4854.519 |
		1342	JSON::XS/2 | 3869.998 | 4798.975 |
		1343	JSON::XS/3 | 5862.880 | 4798.975 |
		1344	Storable | 4445.002 | 5235.027 |
		1345	-----------+------------+------------+
		1346
		1347	Again, JSON::XS leads by far (except for Storable which non-surprisingly
		1348	decodes faster).
		1349
		1350	On large strings containing lots of high Unicode characters, some modules
		1351	(such as JSON::PC) seem to decode faster than JSON::XS, but the result
		1352	will be broken due to missing (or wrong) Unicode handling. Others refuse
		1353	to decode or encode properly, so it was impossible to prepare a fair
		1354	comparison table for that case.
		1355
		1356
		1357	=head1 SECURITY CONSIDERATIONS
		1358
		1359	When you are using JSON in a protocol, talking to untrusted potentially
		1360	hostile creatures requires relatively few measures.
		1361
		1362	First of all, your JSON decoder should be secure, that is, should not have
		1363	any buffer overflows. Obviously, this module should ensure that and I am
		1364	trying hard on making that true, but you never know.
		1365
		1366	Second, you need to avoid resource-starving attacks. That means you should
		1367	limit the size of JSON texts you accept, or make sure then when your
		1368	resources run out, that's just fine (e.g. by using a separate process that
		1369	can crash safely). The size of a JSON text in octets or characters is
		1370	usually a good indication of the size of the resources required to decode
		1371	it into a Perl structure. While JSON::XS can check the size of the JSON
		1372	text, it might be too late when you already have it in memory, so you
		1373	might want to check the size before you accept the string.
		1374
		1375	Third, JSON::XS recurses using the C stack when decoding objects and
		1376	arrays. The C stack is a limited resource: for instance, on my amd64
		1377	machine with 8MB of stack size I can decode around 180k nested arrays but
		1378	only 14k nested JSON objects (due to perl itself recursing deeply on croak
		1379	to free the temporary). If that is exceeded, the program crashes. To be
		1380	conservative, the default nesting limit is set to 512. If your process
		1381	has a smaller stack, you should adjust this setting accordingly with the
		1382	C<max_depth> method.
		1383
		1384	Something else could bomb you, too, that I forgot to think of. In that
		1385	case, you get to keep the pieces. I am always open for hints, though...
		1386
		1387	Also keep in mind that JSON::XS might leak contents of your Perl data
		1388	structures in its error messages, so when you serialise sensitive
		1389	information you might want to make sure that exceptions thrown by JSON::XS
		1390	will not end up in front of untrusted eyes.
		1391
		1392	If you are using JSON::XS to return packets to consumption
		1393	by JavaScript scripts in a browser you should have a look at
		1394	L<http://jpsykes.com/47/practical-csrf-and-json-security> to see whether
		1395	you are vulnerable to some common attack vectors (which really are browser
		1396	design bugs, but it is still you who will have to deal with it, as major
		1397	browser developers care only for features, not about getting security
		1398	right).
		1399
		1400
		1401	=head1 THREADS
		1402
		1403	This module is I<not> guaranteed to be thread safe and there are no
		1404	plans to change this until Perl gets thread support (as opposed to the
		1405	horribly slow so-called "threads" which are simply slow and bloated
		1406	process simulations - use fork, it's I<much> faster, cheaper, better).
		1407
		1408	(It might actually work, but you have been warned).
		1409
		1410
		1411	=head1 BUGS
		1412
		1413	While the goal of this module is to be correct, that unfortunately does
		1414	not mean it's bug-free, only that I think its design is bug-free. It is
		1415	still relatively early in its development. If you keep reporting bugs they
		1416	will be fixed swiftly, though.
		1417
		1418	Please refrain from using rt.cpan.org or any other bug reporting
		1419	service. I put the contact address into my modules for a reason.
28		1420
29	=cut	1421	=cut
30		1422
31	use JSON::DWIW;	1423	our $true = do { bless \(my $dummy = 1), "JSON::XS::Boolean" };
32	use Benchmark;	1424	our $false = do { bless \(my $dummy = 0), "JSON::XS::Boolean" };
33		1425
34	use utf8;	1426	sub true() { $true }
35	#my $json = '{"ü":1,"a":[1,{"3":4},2],"b":5,"üü":2}';	1427	sub false() { $false }
36	my $json = '{"test":9555555555555555555,"hu" : -1e+5, "arr" : [ 1,2,3,4,5]}';
37		1428
38	my $js = JSON::XS->new;	1429	sub is_bool($) {
39	warn $js->indent (0);	1430	UNIVERSAL::isa $_[0], "JSON::XS::Boolean"
40	warn $js->canonical (0);	1431	# or UNIVERSAL::isa $_[0], "JSON::Literal"
41	warn $js->ascii (0);	1432	}
42	warn $js->space_after (0);
43	use Data::Dumper;
44	warn Dumper $js->decode ($json);
45	warn Dumper $js->encode ($js->decode ($json));
46	#my $x = {"üü" => 2, "ü" => 1, "a" => [1,{3,4},2], b => 5};
47		1433
48	#my $js2 = JSON::DWIW->new;	1434	XSLoader::load "JSON::XS", $VERSION;
49	#	1435
50	#timethese 200000, {	1436	package JSON::XS::Boolean;
51	# a => sub { $js->encode ($x) },	1437
52	# b => sub { $js2->to_json ($x) },	1438	use overload
53	#};	1439	"0+" => sub { ${$_[0]} },
		1440	"++" => sub { $_[0] = ${$_[0]} + 1 },
		1441	"--" => sub { $_[0] = ${$_[0]} - 1 },
		1442	fallback => 1;
54		1443
55	1;	1444	1;
56		1445
57	=back	1446	=head1 SEE ALSO
		1447
		1448	The F<json_xs> command line utility for quick experiments.
58		1449
59	=head1 AUTHOR	1450	=head1 AUTHOR
60		1451
61	Marc Lehmann <schmorp@schmorp.de>	1452	Marc Lehmann <schmorp@schmorp.de>
62	http://home.schmorp.de/	1453	http://home.schmorp.de/

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