[ViewVC] Diff of: cvs/JSON-XS/XS.pm

Comparing JSON-XS/XS.pm (file contents):
Revision 1.72 by root, Sun Nov 25 19:11:07 2007 UTC vs.
Revision 1.92 by root, Fri Mar 21 21:47:43 2008 UTC

…		…
1	=head1 NAME	1	=head1 NAME
		2
		3	=encoding utf-8
2		4
3	JSON::XS - JSON serialising/deserialising, done correctly and fast	5	JSON::XS - JSON serialising/deserialising, done correctly and fast
4		6
5	JSON::XS - 正しくて高速な JSON シリアライザ/デシリアライザ	7	JSON::XS - 正しくて高速な JSON シリアライザ/デシリアライザ
6	(http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html)	8	(http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html)
10	use JSON::XS;	12	use JSON::XS;
11		13
12	# exported functions, they croak on error	14	# exported functions, they croak on error
13	# and expect/generate UTF-8	15	# and expect/generate UTF-8
14		16
15	$utf8_encoded_json_text = to_json $perl_hash_or_arrayref;	17	$utf8_encoded_json_text = encode_json $perl_hash_or_arrayref;
16	$perl_hash_or_arrayref = from_json $utf8_encoded_json_text;	18	$perl_hash_or_arrayref = decode_json $utf8_encoded_json_text;
17		19
18	# OO-interface	20	# OO-interface
19		21
20	$coder = JSON::XS->new->ascii->pretty->allow_nonref;	22	$coder = JSON::XS->new->ascii->pretty->allow_nonref;
21	$pretty_printed_unencoded = $coder->encode ($perl_scalar);	23	$pretty_printed_unencoded = $coder->encode ($perl_scalar);
22	$perl_scalar = $coder->decode ($unicode_json_text);	24	$perl_scalar = $coder->decode ($unicode_json_text);
23		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
24	=head1 DESCRIPTION	34	=head1 DESCRIPTION
25		35
26	This module converts Perl data structures to JSON and vice versa. Its	36	This module converts Perl data structures to JSON and vice versa. Its
27	primary goal is to be I<correct> and its secondary goal is to be	37	primary goal is to be I<correct> and its secondary goal is to be
28	I<fast>. To reach the latter goal it was written in C.	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.
29		47
30	As this is the n-th-something JSON module on CPAN, what was the reason	48	As this is the n-th-something JSON module on CPAN, what was the reason
31	to write yet another JSON module? While it seems there are many JSON	49	to write yet another JSON module? While it seems there are many JSON
32	modules, none of them correctly handle all corner cases, and in most cases	50	modules, none of them correctly handle all corner cases, and in most cases
33	their maintainers are unresponsive, gone missing, or not listening to bug	51	their maintainers are unresponsive, gone missing, or not listening to bug
…		…
42		60
43	=over 4	61	=over 4
44		62
45	=item * correct Unicode handling	63	=item * correct Unicode handling
46		64
47	This module knows how to handle Unicode, and even documents how and when	65	This module knows how to handle Unicode, documents how and when it does
48	it does so.	66	so, and even documents what "correct" means.
49		67
50	=item * round-trip integrity	68	=item * round-trip integrity
51		69
52	When you serialise a perl data structure using only datatypes supported	70	When you serialise a perl data structure using only datatypes supported
53	by JSON, the deserialised data structure is identical on the Perl level.	71	by JSON, the deserialised data structure is identical on the Perl level.
54	(e.g. the string "2.0" doesn't suddenly become "2" just because it looks	72	(e.g. the string "2.0" doesn't suddenly become "2" just because it looks
55	like a number).	73	like a number). There minor I<are> exceptions to this, read the MAPPING
		74	section below to learn about those.
56		75
57	=item * strict checking of JSON correctness	76	=item * strict checking of JSON correctness
58		77
59	There is no guessing, no generating of illegal JSON texts by default,	78	There is no guessing, no generating of illegal JSON texts by default,
60	and only JSON is accepted as input by default (the latter is a security	79	and only JSON is accepted as input by default (the latter is a security
61	feature).	80	feature).
62		81
63	=item * fast	82	=item * fast
64		83
65	Compared to other JSON modules, this module compares favourably in terms	84	Compared to other JSON modules and other serialisers such as Storable,
66	of speed, too.	85	this module usually compares favourably in terms of speed, too.
67		86
68	=item * simple to use	87	=item * simple to use
69		88
70	This module has both a simple functional interface as well as an OO	89	This module has both a simple functional interface as well as an objetc
71	interface.	90	oriented interface interface.
72		91
73	=item * reasonably versatile output formats	92	=item * reasonably versatile output formats
74		93
75	You can choose between the most compact guaranteed single-line format	94	You can choose between the most compact guaranteed-single-line format
76	possible (nice for simple line-based protocols), a pure-ascii format	95	possible (nice for simple line-based protocols), a pure-ascii format
77	(for when your transport is not 8-bit clean, still supports the whole	96	(for when your transport is not 8-bit clean, still supports the whole
78	Unicode range), or a pretty-printed format (for when you want to read that	97	Unicode range), or a pretty-printed format (for when you want to read that
79	stuff). Or you can combine those features in whatever way you like.	98	stuff). Or you can combine those features in whatever way you like.
80		99
…		…
84		103
85	package JSON::XS;	104	package JSON::XS;
86		105
87	use strict;	106	use strict;
88		107
89	our $VERSION = '1.53';	108	our $VERSION = '2.1';
90	our @ISA = qw(Exporter);	109	our @ISA = qw(Exporter);
91		110
92	our @EXPORT = qw(to_json from_json);	111	our @EXPORT = qw(encode_json decode_json to_json from_json);
		112
		113	sub to_json($) {
		114	require Carp;
		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");
		116	}
		117
		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	}
93		122
94	use Exporter;	123	use Exporter;
95	use XSLoader;	124	use XSLoader;
96		125
97	=head1 FUNCTIONAL INTERFACE	126	=head1 FUNCTIONAL INTERFACE
…		…
99	The following convenience methods are provided by this module. They are	128	The following convenience methods are provided by this module. They are
100	exported by default:	129	exported by default:
101		130
102	=over 4	131	=over 4
103		132
104	=item $json_text = to_json $perl_scalar	133	=item $json_text = encode_json $perl_scalar
105		134
106	Converts the given Perl data structure to a UTF-8 encoded, binary string	135	Converts the given Perl data structure to a UTF-8 encoded, binary string
107	(that is, the string contains octets only). Croaks on error.	136	(that is, the string contains octets only). Croaks on error.
108		137
109	This function call is functionally identical to:	138	This function call is functionally identical to:
110		139
111	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)	140	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)
112		141
113	except being faster.	142	except being faster.
114		143
115	=item $perl_scalar = from_json $json_text	144	=item $perl_scalar = decode_json $json_text
116		145
117	The opposite of C<to_json>: expects an UTF-8 (binary) string and tries	146	The opposite of C<encode_json>: expects an UTF-8 (binary) string and tries
118	to parse that as an UTF-8 encoded JSON text, returning the resulting	147	to parse that as an UTF-8 encoded JSON text, returning the resulting
119	reference. Croaks on error.	148	reference. Croaks on error.
120		149
121	This function call is functionally identical to:	150	This function call is functionally identical to:
122		151
…		…
148	This enables you to store Unicode characters as single characters in a	177	This enables you to store Unicode characters as single characters in a
149	Perl string - very natural.	178	Perl string - very natural.
150		179
151	=item 2. Perl does I<not> associate an encoding with your strings.	180	=item 2. Perl does I<not> associate an encoding with your strings.
152		181
153	Unless you force it to, e.g. when matching it against a regex, or printing	182	... until you force it to, e.g. when matching it against a regex, or
154	the scalar to a file, in which case Perl either interprets your string as	183	printing the scalar to a file, in which case Perl either interprets your
155	locale-encoded text, octets/binary, or as Unicode, depending on various	184	string as locale-encoded text, octets/binary, or as Unicode, depending
156	settings. In no case is an encoding stored together with your data, it is	185	on various settings. In no case is an encoding stored together with your
157	I<use> that decides encoding, not any magical metadata.	186	data, it is I<use> that decides encoding, not any magical meta data.
158		187
159	=item 3. The internal utf-8 flag has no meaning with regards to the	188	=item 3. The internal utf-8 flag has no meaning with regards to the
160	encoding of your string.	189	encoding of your string.
161		190
162	Just ignore that flag unless you debug a Perl bug, a module written in	191	Just ignore that flag unless you debug a Perl bug, a module written in
…		…
216		245
217	If C<$enable> is false, then the C<encode> method will not escape Unicode	246	If C<$enable> is false, then the C<encode> method will not escape Unicode
218	characters unless required by the JSON syntax or other flags. This results	247	characters unless required by the JSON syntax or other flags. This results
219	in a faster and more compact format.	248	in a faster and more compact format.
220		249
		250	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		251	document.
		252
221	The main use for this flag is to produce JSON texts that can be	253	The main use for this flag is to produce JSON texts that can be
222	transmitted over a 7-bit channel, as the encoded JSON texts will not	254	transmitted over a 7-bit channel, as the encoded JSON texts will not
223	contain any 8 bit characters.	255	contain any 8 bit characters.
224		256
225	JSON::XS->new->ascii (1)->encode ([chr 0x10401])	257	JSON::XS->new->ascii (1)->encode ([chr 0x10401])
…		…
236	will not be affected in any way by this flag, as C<decode> by default	268	will not be affected in any way by this flag, as C<decode> by default
237	expects Unicode, which is a strict superset of latin1.	269	expects Unicode, which is a strict superset of latin1.
238		270
239	If C<$enable> is false, then the C<encode> method will not escape Unicode	271	If C<$enable> is false, then the C<encode> method will not escape Unicode
240	characters unless required by the JSON syntax or other flags.	272	characters unless required by the JSON syntax or other flags.
		273
		274	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		275	document.
241		276
242	The main use for this flag is efficiently encoding binary data as JSON	277	The main use for this flag is efficiently encoding binary data as JSON
243	text, as most octets will not be escaped, resulting in a smaller encoded	278	text, as most octets will not be escaped, resulting in a smaller encoded
244	size. The disadvantage is that the resulting JSON text is encoded	279	size. The disadvantage is that the resulting JSON text is encoded
245	in latin1 (and must correctly be treated as such when storing and	280	in latin1 (and must correctly be treated as such when storing and
…		…
265	If C<$enable> is false, then the C<encode> method will return the JSON	300	If C<$enable> is false, then the C<encode> method will return the JSON
266	string as a (non-encoded) Unicode string, while C<decode> expects thus a	301	string as a (non-encoded) Unicode string, while C<decode> expects thus a
267	Unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs	302	Unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs
268	to be done yourself, e.g. using the Encode module.	303	to be done yourself, e.g. using the Encode module.
269		304
		305	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		306	document.
		307
270	Example, output UTF-16BE-encoded JSON:	308	Example, output UTF-16BE-encoded JSON:
271		309
272	use Encode;	310	use Encode;
273	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);	311	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
274		312
…		…
276		314
277	use Encode;	315	use Encode;
278	$object = JSON::XS->new->decode (decode "UTF-32LE", $jsontext);	316	$object = JSON::XS->new->decode (decode "UTF-32LE", $jsontext);
279		317
280	=item $json = $json->pretty ([$enable])	318	=item $json = $json->pretty ([$enable])
281
282	=item $enabled = $json->get_pretty
283		319
284	This enables (or disables) all of the C<indent>, C<space_before> and	320	This enables (or disables) all of the C<indent>, C<space_before> and
285	C<space_after> (and in the future possibly more) flags in one call to	321	C<space_after> (and in the future possibly more) flags in one call to
286	generate the most readable (or most compact) form possible.	322	generate the most readable (or most compact) form possible.
287		323
…		…
429	JSON::XS->new->allow_nonref->encode ("Hello, World!")	465	JSON::XS->new->allow_nonref->encode ("Hello, World!")
430	=> "Hello, World!"	466	=> "Hello, World!"
431		467
432	=item $json = $json->allow_blessed ([$enable])	468	=item $json = $json->allow_blessed ([$enable])
433		469
434	=item $enabled = $json->get_allow_bless	470	=item $enabled = $json->get_allow_blessed
435		471
436	If C<$enable> is true (or missing), then the C<encode> method will not	472	If C<$enable> is true (or missing), then the C<encode> method will not
437	barf when it encounters a blessed reference. Instead, the value of the	473	barf when it encounters a blessed reference. Instead, the value of the
438	B<convert_blessed> option will decide whether C<null> (C<convert_blessed>	474	B<convert_blessed> option will decide whether C<null> (C<convert_blessed>
439	disabled or no C<to_json> method found) or a representation of the	475	disabled or no C<TO_JSON> method found) or a representation of the
440	object (C<convert_blessed> enabled and C<to_json> method found) is being	476	object (C<convert_blessed> enabled and C<TO_JSON> method found) is being
441	encoded. Has no effect on C<decode>.	477	encoded. Has no effect on C<decode>.
442		478
443	If C<$enable> is false (the default), then C<encode> will throw an	479	If C<$enable> is false (the default), then C<encode> will throw an
444	exception when it encounters a blessed object.	480	exception when it encounters a blessed object.
445		481
…		…
457	The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON>	493	The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON>
458	returns other blessed objects, those will be handled in the same	494	returns other blessed objects, those will be handled in the same
459	way. C<TO_JSON> must take care of not causing an endless recursion cycle	495	way. C<TO_JSON> must take care of not causing an endless recursion cycle
460	(== crash) in this case. The name of C<TO_JSON> was chosen because other	496	(== crash) in this case. The name of C<TO_JSON> was chosen because other
461	methods called by the Perl core (== not by the user of the object) are	497	methods called by the Perl core (== not by the user of the object) are
462	usually in upper case letters and to avoid collisions with the C<to_json>	498	usually in upper case letters and to avoid collisions with any C<to_json>
463	function.	499	function or method.
464		500
465	This setting does not yet influence C<decode> in any way, but in the	501	This setting does not yet influence C<decode> in any way, but in the
466	future, global hooks might get installed that influence C<decode> and are	502	future, global hooks might get installed that influence C<decode> and are
467	enabled by this setting.	503	enabled by this setting.
468		504
…		…
682		718
683	A JSON number becomes either an integer, numeric (floating point) or	719	A JSON number becomes either an integer, numeric (floating point) or
684	string scalar in perl, depending on its range and any fractional parts. On	720	string scalar in perl, depending on its range and any fractional parts. On
685	the Perl level, there is no difference between those as Perl handles all	721	the Perl level, there is no difference between those as Perl handles all
686	the conversion details, but an integer may take slightly less memory and	722	the conversion details, but an integer may take slightly less memory and
687	might represent more values exactly than (floating point) numbers.	723	might represent more values exactly than floating point numbers.
688		724
689	If the number consists of digits only, JSON::XS will try to represent	725	If the number consists of digits only, JSON::XS will try to represent
690	it as an integer value. If that fails, it will try to represent it as	726	it as an integer value. If that fails, it will try to represent it as
691	a numeric (floating point) value if that is possible without loss of	727	a numeric (floating point) value if that is possible without loss of
692	precision. Otherwise it will preserve the number as a string value.	728	precision. Otherwise it will preserve the number as a string value (in
		729	which case you lose roundtripping ability, as the JSON number will be
		730	re-encoded toa JSON string).
693		731
694	Numbers containing a fractional or exponential part will always be	732	Numbers containing a fractional or exponential part will always be
695	represented as numeric (floating point) values, possibly at a loss of	733	represented as numeric (floating point) values, possibly at a loss of
696	precision.	734	precision (in which case you might lose perfect roundtripping ability, but
697		735	the JSON number will still be re-encoded as a JSON number).
698	This might create round-tripping problems as numbers might become strings,
699	but as Perl is typeless there is no other way to do it.
700		736
701	=item true, false	737	=item true, false
702		738
703	These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>,	739	These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>,
704	respectively. They are overloaded to act almost exactly like the numbers	740	respectively. They are overloaded to act almost exactly like the numbers
…		…
741	Other unblessed references are generally not allowed and will cause an	777	Other unblessed references are generally not allowed and will cause an
742	exception to be thrown, except for references to the integers C<0> and	778	exception to be thrown, except for references to the integers C<0> and
743	C<1>, which get turned into C<false> and C<true> atoms in JSON. You can	779	C<1>, which get turned into C<false> and C<true> atoms in JSON. You can
744	also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability.	780	also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability.
745		781
746	to_json [\0,JSON::XS::true] # yields [false,true]	782	encode_json [\0,JSON::XS::true] # yields [false,true]
747		783
748	=item JSON::XS::true, JSON::XS::false	784	=item JSON::XS::true, JSON::XS::false
749		785
750	These special values become JSON true and JSON false values,	786	These special values become JSON true and JSON false values,
751	respectively. You can also use C<\1> and C<\0> directly if you want.	787	respectively. You can also use C<\1> and C<\0> directly if you want.
752		788
753	=item blessed objects	789	=item blessed objects
754		790
755	Blessed objects are not allowed. JSON::XS currently tries to encode their	791	Blessed objects are not directly representable in JSON. See the
756	underlying representation (hash- or arrayref), but this behaviour might	792	C<allow_blessed> and C<convert_blessed> methods on various options on
757	change in future versions.	793	how to deal with this: basically, you can choose between throwing an
		794	exception, encoding the reference as if it weren't blessed, or provide
		795	your own serialiser method.
758		796
759	=item simple scalars	797	=item simple scalars
760		798
761	Simple Perl scalars (any scalar that is not a reference) are the most	799	Simple Perl scalars (any scalar that is not a reference) are the most
762	difficult objects to encode: JSON::XS will encode undefined scalars as	800	difficult objects to encode: JSON::XS will encode undefined scalars as
763	JSON null value, scalars that have last been used in a string context	801	JSON C<null> values, scalars that have last been used in a string context
764	before encoding as JSON strings and anything else as number value:	802	before encoding as JSON strings, and anything else as number value:
765		803
766	# dump as number	804	# dump as number
767	to_json [2] # yields [2]	805	encode_json [2] # yields [2]
768	to_json [-3.0e17] # yields [-3e+17]	806	encode_json [-3.0e17] # yields [-3e+17]
769	my $value = 5; to_json [$value] # yields [5]	807	my $value = 5; encode_json [$value] # yields [5]
770		808
771	# used as string, so dump as string	809	# used as string, so dump as string
772	print $value;	810	print $value;
773	to_json [$value] # yields ["5"]	811	encode_json [$value] # yields ["5"]
774		812
775	# undef becomes null	813	# undef becomes null
776	to_json [undef] # yields [null]	814	encode_json [undef] # yields [null]
777		815
778	You can force the type to be a JSON string by stringifying it:	816	You can force the type to be a JSON string by stringifying it:
779		817
780	my $x = 3.1; # some variable containing a number	818	my $x = 3.1; # some variable containing a number
781	"$x"; # stringified	819	"$x"; # stringified
…		…
787	my $x = "3"; # some variable containing a string	825	my $x = "3"; # some variable containing a string
788	$x += 0; # numify it, ensuring it will be dumped as a number	826	$x += 0; # numify it, ensuring it will be dumped as a number
789	$x *= 1; # same thing, the choice is yours.	827	$x *= 1; # same thing, the choice is yours.
790		828
791	You can not currently force the type in other, less obscure, ways. Tell me	829	You can not currently force the type in other, less obscure, ways. Tell me
792	if you need this capability.	830	if you need this capability (but don't forget to explain why it's needed
		831	:).
		832
		833	=back
		834
		835
		836	=head1 ENCODING/CODESET FLAG NOTES
		837
		838	The interested reader might have seen a number of flags that signify
		839	encodings or codesets - C<utf8>, C<latin1> and C<ascii>. There seems to be
		840	some confusion on what these do, so here is a short comparison:
		841
		842	C<utf8> controls whether the JSON text created by C<encode> (and expected
		843	by C<decode>) is UTF-8 encoded or not, while C<latin1> and C<ascii> only
		844	control whether C<encode> escapes character values outside their respective
		845	codeset range. Neither of these flags conflict with each other, although
		846	some combinations make less sense than others.
		847
		848	Care has been taken to make all flags symmetrical with respect to
		849	C<encode> and C<decode>, that is, texts encoded with any combination of
		850	these flag values will be correctly decoded when the same flags are used
		851	- in general, if you use different flag settings while encoding vs. when
		852	decoding you likely have a bug somewhere.
		853
		854	Below comes a verbose discussion of these flags. Note that a "codeset" is
		855	simply an abstract set of character-codepoint pairs, while an encoding
		856	takes those codepoint numbers and I<encodes> them, in our case into
		857	octets. Unicode is (among other things) a codeset, UTF-8 is an encoding,
		858	and ISO-8859-1 (= latin 1) and ASCII are both codesets I<and> encodings at
		859	the same time, which can be confusing.
		860
		861	=over 4
		862
		863	=item C<utf8> flag disabled
		864
		865	When C<utf8> is disabled (the default), then C<encode>/C<decode> generate
		866	and expect Unicode strings, that is, characters with high ordinal Unicode
		867	values (> 255) will be encoded as such characters, and likewise such
		868	characters are decoded as-is, no canges to them will be done, except
		869	"(re-)interpreting" them as Unicode codepoints or Unicode characters,
		870	respectively (to Perl, these are the same thing in strings unless you do
		871	funny/weird/dumb stuff).
		872
		873	This is useful when you want to do the encoding yourself (e.g. when you
		874	want to have UTF-16 encoded JSON texts) or when some other layer does
		875	the encoding for you (for example, when printing to a terminal using a
		876	filehandle that transparently encodes to UTF-8 you certainly do NOT want
		877	to UTF-8 encode your data first and have Perl encode it another time).
		878
		879	=item C<utf8> flag enabled
		880
		881	If the C<utf8>-flag is enabled, C<encode>/C<decode> will encode all
		882	characters using the corresponding UTF-8 multi-byte sequence, and will
		883	expect your input strings to be encoded as UTF-8, that is, no "character"
		884	of the input string must have any value > 255, as UTF-8 does not allow
		885	that.
		886
		887	The C<utf8> flag therefore switches between two modes: disabled means you
		888	will get a Unicode string in Perl, enabled means you get an UTF-8 encoded
		889	octet/binary string in Perl.
		890
		891	=item C<latin1> or C<ascii> flags enabled
		892
		893	With C<latin1> (or C<ascii>) enabled, C<encode> will escape characters
		894	with ordinal values > 255 (> 127 with C<ascii>) and encode the remaining
		895	characters as specified by the C<utf8> flag.
		896
		897	If C<utf8> is disabled, then the result is also correctly encoded in those
		898	character sets (as both are proper subsets of Unicode, meaning that a
		899	Unicode string with all character values < 256 is the same thing as a
		900	ISO-8859-1 string, and a Unicode string with all character values < 128 is
		901	the same thing as an ASCII string in Perl).
		902
		903	If C<utf8> is enabled, you still get a correct UTF-8-encoded string,
		904	regardless of these flags, just some more characters will be escaped using
		905	C<\uXXXX> then before.
		906
		907	Note that ISO-8859-1-I<encoded> strings are not compatible with UTF-8
		908	encoding, while ASCII-encoded strings are. That is because the ISO-8859-1
		909	encoding is NOT a subset of UTF-8 (despite the ISO-8859-1 I<codeset> being
		910	a subset of Unicode), while ASCII is.
		911
		912	Surprisingly, C<decode> will ignore these flags and so treat all input
		913	values as governed by the C<utf8> flag. If it is disabled, this allows you
		914	to decode ISO-8859-1- and ASCII-encoded strings, as both strict subsets of
		915	Unicode. If it is enabled, you can correctly decode UTF-8 encoded strings.
		916
		917	So neither C<latin1> nor C<ascii> are incompatible with the C<utf8> flag -
		918	they only govern when the JSON output engine escapes a character or not.
		919
		920	The main use for C<latin1> is to relatively efficiently store binary data
		921	as JSON, at the expense of breaking compatibility with most JSON decoders.
		922
		923	The main use for C<ascii> is to force the output to not contain characters
		924	with values > 127, which means you can interpret the resulting string
		925	as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about any character set and
		926	8-bit-encoding, and still get the same data structure back. This is useful
		927	when your channel for JSON transfer is not 8-bit clean or the encoding
		928	might be mangled in between (e.g. in mail), and works because ASCII is a
		929	proper subset of most 8-bit and multibyte encodings in use in the world.
793		930
794	=back	931	=back
795		932
796		933
797	=head1 COMPARISON	934	=head1 COMPARISON
…		…
801	problems (or pleasures) I encountered with various existing JSON modules,	938	problems (or pleasures) I encountered with various existing JSON modules,
802	followed by some benchmark values. JSON::XS was designed not to suffer	939	followed by some benchmark values. JSON::XS was designed not to suffer
803	from any of these problems or limitations.	940	from any of these problems or limitations.
804		941
805	=over 4	942	=over 4
		943
		944	=item JSON 2.xx
		945
		946	A marvellous piece of engineering, this module either uses JSON::XS
		947	directly when available (so will be 100% compatible with it, including
		948	speed), or it uses JSON::PP, which is basically JSON::XS translated to
		949	Pure Perl, which should be 100% compatible with JSON::XS, just a bit
		950	slower.
		951
		952	You cannot really lose by using this module, especially as it tries very
		953	hard to work even with ancient Perl versions, while JSON::XS does not.
806		954
807	=item JSON 1.07	955	=item JSON 1.07
808		956
809	Slow (but very portable, as it is written in pure Perl).	957	Slow (but very portable, as it is written in pure Perl).
810		958
…		…
881	=back	1029	=back
882		1030
883		1031
884	=head2 JSON and YAML	1032	=head2 JSON and YAML
885		1033
886	You often hear that JSON is a subset (or a close subset) of YAML. This is,	1034	You often hear that JSON is a subset of YAML. This is, however, a mass
887	however, a mass hysteria and very far from the truth. In general, there is	1035	hysteria(*) and very far from the truth (as of the time of this writing),
888	no way to configure JSON::XS to output a data structure as valid YAML.	1036	so let me state it clearly: I<in general, there is no way to configure
		1037	JSON::XS to output a data structure as valid YAML> that works in all
		1038	cases.
889		1039
890	If you really must use JSON::XS to generate YAML, you should use this	1040	If you really must use JSON::XS to generate YAML, you should use this
891	algorithm (subject to change in future versions):	1041	algorithm (subject to change in future versions):
892		1042
893	my $to_yaml = JSON::XS->new->utf8->space_after (1);	1043	my $to_yaml = JSON::XS->new->utf8->space_after (1);
894	my $yaml = $to_yaml->encode ($ref) . "\n";	1044	my $yaml = $to_yaml->encode ($ref) . "\n";
895		1045
896	This will usually generate JSON texts that also parse as valid	1046	This will I<usually> generate JSON texts that also parse as valid
897	YAML. Please note that YAML has hardcoded limits on (simple) object key	1047	YAML. Please note that YAML has hardcoded limits on (simple) object key
898	lengths that JSON doesn't have, so you should make sure that your hash	1048	lengths that JSON doesn't have and also has different and incompatible
		1049	unicode handling, so you should make sure that your hash keys are
899	keys are noticeably shorter than the 1024 characters YAML allows.	1050	noticeably shorter than the 1024 "stream characters" YAML allows and that
		1051	you do not have characters with codepoint values outside the Unicode BMP
		1052	(basic multilingual page). YAML also does not allow C<\/> sequences in
		1053	strings (which JSON::XS does not I<currently> generate, but other JSON
		1054	generators might).
900		1055
901	There might be other incompatibilities that I am not aware of. In general	1056	There might be other incompatibilities that I am not aware of (or the YAML
		1057	specification has been changed yet again - it does so quite often). In
902	you should not try to generate YAML with a JSON generator or vice versa,	1058	general you should not try to generate YAML with a JSON generator or vice
903	or try to parse JSON with a YAML parser or vice versa: chances are high	1059	versa, or try to parse JSON with a YAML parser or vice versa: chances are
904	that you will run into severe interoperability problems.	1060	high that you will run into severe interoperability problems when you
		1061	least expect it.
		1062
		1063	=over 4
		1064
		1065	=item (*)
		1066
		1067	I have been pressured multiple times by Brian Ingerson (one of the
		1068	authors of the YAML specification) to remove this paragraph, despite him
		1069	acknowledging that the actual incompatibilities exist. As I was personally
		1070	bitten by this "JSON is YAML" lie, I refused and said I will continue to
		1071	educate people about these issues, so others do not run into the same
		1072	problem again and again. After this, Brian called me a (quote)I<complete
		1073	and worthless idiot>(unquote).
		1074
		1075	In my opinion, instead of pressuring and insulting people who actually
		1076	clarify issues with YAML and the wrong statements of some of its
		1077	proponents, I would kindly suggest reading the JSON spec (which is not
		1078	that difficult or long) and finally make YAML compatible to it, and
		1079	educating users about the changes, instead of spreading lies about the
		1080	real compatibility for many I<years> and trying to silence people who
		1081	point out that it isn't true.
		1082
		1083	=back
905		1084
906		1085
907	=head2 SPEED	1086	=head2 SPEED
908		1087
909	It seems that JSON::XS is surprisingly fast, as shown in the following	1088	It seems that JSON::XS is surprisingly fast, as shown in the following
910	tables. They have been generated with the help of the C<eg/bench> program	1089	tables. They have been generated with the help of the C<eg/bench> program
911	in the JSON::XS distribution, to make it easy to compare on your own	1090	in the JSON::XS distribution, to make it easy to compare on your own
912	system.	1091	system.
913		1092
914	First comes a comparison between various modules using a very short	1093	First comes a comparison between various modules using
915	single-line JSON string:	1094	a very short single-line JSON string (also available at
		1095	L<http://dist.schmorp.de/misc/json/short.json>).
916		1096
917	{"method": "handleMessage", "params": ["user1", "we were just talking"], \	1097	{"method": "handleMessage", "params": ["user1", "we were just talking"], \
918	"id": null, "array":[1,11,234,-5,1e5,1e7, true, false]}	1098	"id": null, "array":[1,11,234,-5,1e5,1e7, true, false]}
919		1099
920	It shows the number of encodes/decodes per second (JSON::XS uses	1100	It shows the number of encodes/decodes per second (JSON::XS uses
…		…
939	about three times faster on decoding, and over forty times faster	1119	about three times faster on decoding, and over forty times faster
940	than JSON, even with pretty-printing and key sorting. It also compares	1120	than JSON, even with pretty-printing and key sorting. It also compares
941	favourably to Storable for small amounts of data.	1121	favourably to Storable for small amounts of data.
942		1122
943	Using a longer test string (roughly 18KB, generated from Yahoo! Locals	1123	Using a longer test string (roughly 18KB, generated from Yahoo! Locals
944	search API (http://nanoref.com/yahooapis/mgPdGg):	1124	search API (L<http://dist.schmorp.de/misc/json/long.json>).
945		1125
946	module \| encode \| decode \|	1126	module \| encode \| decode \|
947	-----------\|------------\|------------\|	1127	-----------\|------------\|------------\|
948	JSON 1.x \| 55.260 \| 34.971 \|	1128	JSON 1.x \| 55.260 \| 34.971 \|
949	JSON::DWIW \| 825.228 \| 1082.513 \|	1129	JSON::DWIW \| 825.228 \| 1082.513 \|
…		…
986		1166
987	Third, JSON::XS recurses using the C stack when decoding objects and	1167	Third, JSON::XS recurses using the C stack when decoding objects and
988	arrays. The C stack is a limited resource: for instance, on my amd64	1168	arrays. The C stack is a limited resource: for instance, on my amd64
989	machine with 8MB of stack size I can decode around 180k nested arrays but	1169	machine with 8MB of stack size I can decode around 180k nested arrays but
990	only 14k nested JSON objects (due to perl itself recursing deeply on croak	1170	only 14k nested JSON objects (due to perl itself recursing deeply on croak
991	to free the temporary). If that is exceeded, the program crashes. to be	1171	to free the temporary). If that is exceeded, the program crashes. To be
992	conservative, the default nesting limit is set to 512. If your process	1172	conservative, the default nesting limit is set to 512. If your process
993	has a smaller stack, you should adjust this setting accordingly with the	1173	has a smaller stack, you should adjust this setting accordingly with the
994	C<max_depth> method.	1174	C<max_depth> method.
995		1175
996	And last but least, something else could bomb you that I forgot to think	1176	Something else could bomb you, too, that I forgot to think of. In that
997	of. In that case, you get to keep the pieces. I am always open for hints,	1177	case, you get to keep the pieces. I am always open for hints, though...
998	though...	1178
		1179	Also keep in mind that JSON::XS might leak contents of your Perl data
		1180	structures in its error messages, so when you serialise sensitive
		1181	information you might want to make sure that exceptions thrown by JSON::XS
		1182	will not end up in front of untrusted eyes.
999		1183
1000	If you are using JSON::XS to return packets to consumption	1184	If you are using JSON::XS to return packets to consumption
1001	by JavaScript scripts in a browser you should have a look at	1185	by JavaScript scripts in a browser you should have a look at
1002	L<http://jpsykes.com/47/practical-csrf-and-json-security> to see whether	1186	L<http://jpsykes.com/47/practical-csrf-and-json-security> to see whether
1003	you are vulnerable to some common attack vectors (which really are browser	1187	you are vulnerable to some common attack vectors (which really are browser
1004	design bugs, but it is still you who will have to deal with it, as major	1188	design bugs, but it is still you who will have to deal with it, as major
1005	browser developers care only for features, not about doing security	1189	browser developers care only for features, not about getting security
1006	right).	1190	right).
1007		1191
1008		1192
1009	=head1 THREADS	1193	=head1 THREADS
1010		1194
1011	This module is I<not> guaranteed to be thread safe and there are no	1195	This module is I<not> guaranteed to be thread safe and there are no
1012	plans to change this until Perl gets thread support (as opposed to the	1196	plans to change this until Perl gets thread support (as opposed to the
1013	horribly slow so-called "threads" which are simply slow and bloated	1197	horribly slow so-called "threads" which are simply slow and bloated
1014	process simulations - use fork, its I<much> faster, cheaper, better).	1198	process simulations - use fork, it's I<much> faster, cheaper, better).
1015		1199
1016	(It might actually work, but you have been warned).	1200	(It might actually work, but you have been warned).
1017		1201
1018		1202
1019	=head1 BUGS	1203	=head1 BUGS
1020		1204
1021	While the goal of this module is to be correct, that unfortunately does	1205	While the goal of this module is to be correct, that unfortunately does
1022	not mean its bug-free, only that I think its design is bug-free. It is	1206	not mean it's bug-free, only that I think its design is bug-free. It is
1023	still relatively early in its development. If you keep reporting bugs they	1207	still relatively early in its development. If you keep reporting bugs they
1024	will be fixed swiftly, though.	1208	will be fixed swiftly, though.
1025		1209
1026	Please refrain from using rt.cpan.org or any other bug reporting	1210	Please refrain from using rt.cpan.org or any other bug reporting
1027	service. I put the contact address into my modules for a reason.	1211	service. I put the contact address into my modules for a reason.

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Comparing JSON-XS/XS.pm (file contents):
Revision 1.72 by root, Sun Nov 25 19:11:07 2007 UTC vs.
Revision 1.92 by root, Fri Mar 21 21:47:43 2008 UTC