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

Comparing JSON-XS/XS.pm (file contents):
Revision 1.77 by root, Tue Dec 4 10:37:42 2007 UTC vs.
Revision 1.95 by root, Tue Mar 25 16:56:09 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);
…		…
58		60
59	=over 4	61	=over 4
60		62
61	=item * correct Unicode handling	63	=item * correct Unicode handling
62		64
63	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
64	it does so.	66	so, and even documents what "correct" means.
65		67
66	=item * round-trip integrity	68	=item * round-trip integrity
67		69
68	When you serialise a perl data structure using only datatypes supported	70	When you serialise a perl data structure using only datatypes supported
69	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.
70	(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
71	like a number).	73	like a number). There minor I<are> exceptions to this, read the MAPPING
		74	section below to learn about those.
72		75
73	=item * strict checking of JSON correctness	76	=item * strict checking of JSON correctness
74		77
75	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,
76	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
77	feature).	80	feature).
78		81
79	=item * fast	82	=item * fast
80		83
81	Compared to other JSON modules, this module compares favourably in terms	84	Compared to other JSON modules and other serialisers such as Storable,
82	of speed, too.	85	this module usually compares favourably in terms of speed, too.
83		86
84	=item * simple to use	87	=item * simple to use
85		88
86	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
87	interface.	90	oriented interface interface.
88		91
89	=item * reasonably versatile output formats	92	=item * reasonably versatile output formats
90		93
91	You can choose between the most compact guaranteed single-line format	94	You can choose between the most compact guaranteed-single-line format
92	possible (nice for simple line-based protocols), a pure-ascii format	95	possible (nice for simple line-based protocols), a pure-ascii format
93	(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
94	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
95	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.
96		99
…		…
100		103
101	package JSON::XS;	104	package JSON::XS;
102		105
103	use strict;	106	use strict;
104		107
105	our $VERSION = '2.0';	108	our $VERSION = '2.1';
106	our @ISA = qw(Exporter);	109	our @ISA = qw(Exporter);
107		110
108	our @EXPORT = qw(to_json from_json);	111	our @EXPORT = qw(encode_json decode_json to_json from_json);
		112
		113	sub to_json($) {
		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	}
109		122
110	use Exporter;	123	use Exporter;
111	use XSLoader;	124	use XSLoader;
112		125
113	=head1 FUNCTIONAL INTERFACE	126	=head1 FUNCTIONAL INTERFACE
…		…
115	The following convenience methods are provided by this module. They are	128	The following convenience methods are provided by this module. They are
116	exported by default:	129	exported by default:
117		130
118	=over 4	131	=over 4
119		132
120	=item $json_text = to_json $perl_scalar	133	=item $json_text = encode_json $perl_scalar
121		134
122	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
123	(that is, the string contains octets only). Croaks on error.	136	(that is, the string contains octets only). Croaks on error.
124		137
125	This function call is functionally identical to:	138	This function call is functionally identical to:
126		139
127	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)	140	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)
128		141
129	except being faster.	142	except being faster.
130		143
131	=item $perl_scalar = from_json $json_text	144	=item $perl_scalar = decode_json $json_text
132		145
133	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
134	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
135	reference. Croaks on error.	148	reference. Croaks on error.
136		149
137	This function call is functionally identical to:	150	This function call is functionally identical to:
138		151
…		…
164	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
165	Perl string - very natural.	178	Perl string - very natural.
166		179
167	=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.
168		181
169	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
170	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
171	locale-encoded text, octets/binary, or as Unicode, depending on various	184	string as locale-encoded text, octets/binary, or as Unicode, depending
172	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
173	I<use> that decides encoding, not any magical metadata.	186	data, it is I<use> that decides encoding, not any magical meta data.
174		187
175	=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
176	encoding of your string.	189	encoding of your string.
177		190
178	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
…		…
232		245
233	If C<$enable> is false, then the C<encode> method will not escape Unicode	246	If C<$enable> is false, then the C<encode> method will not escape Unicode
234	characters unless required by the JSON syntax or other flags. This results	247	characters unless required by the JSON syntax or other flags. This results
235	in a faster and more compact format.	248	in a faster and more compact format.
236		249
		250	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		251	document.
		252
237	The main use for this flag is to produce JSON texts that can be	253	The main use for this flag is to produce JSON texts that can be
238	transmitted over a 7-bit channel, as the encoded JSON texts will not	254	transmitted over a 7-bit channel, as the encoded JSON texts will not
239	contain any 8 bit characters.	255	contain any 8 bit characters.
240		256
241	JSON::XS->new->ascii (1)->encode ([chr 0x10401])	257	JSON::XS->new->ascii (1)->encode ([chr 0x10401])
…		…
252	will not be affected in any way by this flag, as C<decode> by default	268	will not be affected in any way by this flag, as C<decode> by default
253	expects Unicode, which is a strict superset of latin1.	269	expects Unicode, which is a strict superset of latin1.
254		270
255	If C<$enable> is false, then the C<encode> method will not escape Unicode	271	If C<$enable> is false, then the C<encode> method will not escape Unicode
256	characters unless required by the JSON syntax or other flags.	272	characters unless required by the JSON syntax or other flags.
		273
		274	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		275	document.
257		276
258	The main use for this flag is efficiently encoding binary data as JSON	277	The main use for this flag is efficiently encoding binary data as JSON
259	text, as most octets will not be escaped, resulting in a smaller encoded	278	text, as most octets will not be escaped, resulting in a smaller encoded
260	size. The disadvantage is that the resulting JSON text is encoded	279	size. The disadvantage is that the resulting JSON text is encoded
261	in latin1 (and must correctly be treated as such when storing and	280	in latin1 (and must correctly be treated as such when storing and
…		…
280		299
281	If C<$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
282	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
283	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
284	to be done yourself, e.g. using the Encode module.	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.
285		307
286	Example, output UTF-16BE-encoded JSON:	308	Example, output UTF-16BE-encoded JSON:
287		309
288	use Encode;	310	use Encode;
289	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);	311	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
…		…
471	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>
472	returns other blessed objects, those will be handled in the same	494	returns other blessed objects, those will be handled in the same
473	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
474	(== 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
475	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
476	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>
477	function.	499	function or method.
478		500
479	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
480	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
481	enabled by this setting.	503	enabled by this setting.
482		504
…		…
659	=> ([], 3)	681	=> ([], 3)
660		682
661	=back	683	=back
662		684
663		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
664	=head1 MAPPING	894	=head1 MAPPING
665		895
666	This section describes how JSON::XS maps Perl values to JSON values and	896	This section describes how JSON::XS maps Perl values to JSON values and
667	vice versa. These mappings are designed to "do the right thing" in most	897	vice versa. These mappings are designed to "do the right thing" in most
668	circumstances automatically, preserving round-tripping characteristics	898	circumstances automatically, preserving round-tripping characteristics
…		…
696		926
697	A JSON number becomes either an integer, numeric (floating point) or	927	A JSON number becomes either an integer, numeric (floating point) or
698	string scalar in perl, depending on its range and any fractional parts. On	928	string scalar in perl, depending on its range and any fractional parts. On
699	the Perl level, there is no difference between those as Perl handles all	929	the Perl level, there is no difference between those as Perl handles all
700	the conversion details, but an integer may take slightly less memory and	930	the conversion details, but an integer may take slightly less memory and
701	might represent more values exactly than (floating point) numbers.	931	might represent more values exactly than floating point numbers.
702		932
703	If the number consists of digits only, JSON::XS will try to represent	933	If the number consists of digits only, JSON::XS will try to represent
704	it as an integer value. If that fails, it will try to represent it as	934	it as an integer value. If that fails, it will try to represent it as
705	a numeric (floating point) value if that is possible without loss of	935	a numeric (floating point) value if that is possible without loss of
706	precision. Otherwise it will preserve the number as a string value.	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).
707		939
708	Numbers containing a fractional or exponential part will always be	940	Numbers containing a fractional or exponential part will always be
709	represented as numeric (floating point) values, possibly at a loss of	941	represented as numeric (floating point) values, possibly at a loss of
710	precision.	942	precision (in which case you might lose perfect roundtripping ability, but
711		943	the JSON number will still be re-encoded as a JSON number).
712	This might create round-tripping problems as numbers might become strings,
713	but as Perl is typeless there is no other way to do it.
714		944
715	=item true, false	945	=item true, false
716		946
717	These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>,	947	These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>,
718	respectively. They are overloaded to act almost exactly like the numbers	948	respectively. They are overloaded to act almost exactly like the numbers
…		…
755	Other unblessed references are generally not allowed and will cause an	985	Other unblessed references are generally not allowed and will cause an
756	exception to be thrown, except for references to the integers C<0> and	986	exception to be thrown, except for references to the integers C<0> and
757	C<1>, which get turned into C<false> and C<true> atoms in JSON. You can	987	C<1>, which get turned into C<false> and C<true> atoms in JSON. You can
758	also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability.	988	also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability.
759		989
760	to_json [\0,JSON::XS::true] # yields [false,true]	990	encode_json [\0,JSON::XS::true] # yields [false,true]
761		991
762	=item JSON::XS::true, JSON::XS::false	992	=item JSON::XS::true, JSON::XS::false
763		993
764	These special values become JSON true and JSON false values,	994	These special values become JSON true and JSON false values,
765	respectively. You can also use C<\1> and C<\0> directly if you want.	995	respectively. You can also use C<\1> and C<\0> directly if you want.
766		996
767	=item blessed objects	997	=item blessed objects
768		998
769	Blessed objects are not allowed. JSON::XS currently tries to encode their	999	Blessed objects are not directly representable in JSON. See the
770	underlying representation (hash- or arrayref), but this behaviour might	1000	C<allow_blessed> and C<convert_blessed> methods on various options on
771	change in future versions.	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.
772		1004
773	=item simple scalars	1005	=item simple scalars
774		1006
775	Simple Perl scalars (any scalar that is not a reference) are the most	1007	Simple Perl scalars (any scalar that is not a reference) are the most
776	difficult objects to encode: JSON::XS will encode undefined scalars as	1008	difficult objects to encode: JSON::XS will encode undefined scalars as
777	JSON null value, scalars that have last been used in a string context	1009	JSON C<null> values, scalars that have last been used in a string context
778	before encoding as JSON strings and anything else as number value:	1010	before encoding as JSON strings, and anything else as number value:
779		1011
780	# dump as number	1012	# dump as number
781	to_json [2] # yields [2]	1013	encode_json [2] # yields [2]
782	to_json [-3.0e17] # yields [-3e+17]	1014	encode_json [-3.0e17] # yields [-3e+17]
783	my $value = 5; to_json [$value] # yields [5]	1015	my $value = 5; encode_json [$value] # yields [5]
784		1016
785	# used as string, so dump as string	1017	# used as string, so dump as string
786	print $value;	1018	print $value;
787	to_json [$value] # yields ["5"]	1019	encode_json [$value] # yields ["5"]
788		1020
789	# undef becomes null	1021	# undef becomes null
790	to_json [undef] # yields [null]	1022	encode_json [undef] # yields [null]
791		1023
792	You can force the type to be a JSON string by stringifying it:	1024	You can force the type to be a JSON string by stringifying it:
793		1025
794	my $x = 3.1; # some variable containing a number	1026	my $x = 3.1; # some variable containing a number
795	"$x"; # stringified	1027	"$x"; # stringified
…		…
801	my $x = "3"; # some variable containing a string	1033	my $x = "3"; # some variable containing a string
802	$x += 0; # numify it, ensuring it will be dumped as a number	1034	$x += 0; # numify it, ensuring it will be dumped as a number
803	$x *= 1; # same thing, the choice is yours.	1035	$x *= 1; # same thing, the choice is yours.
804		1036
805	You can not currently force the type in other, less obscure, ways. Tell me	1037	You can not currently force the type in other, less obscure, ways. Tell me
806	if you need this capability.	1038	if you need this capability (but don't forget to explain why it's needed
		1039	:).
807		1040
808	=back	1041	=back
809		1042
810		1043
811	=head1 COMPARISON	1044	=head1 ENCODING/CODESET FLAG NOTES
812		1045
813	As already mentioned, this module was created because none of the existing	1046	The interested reader might have seen a number of flags that signify
814	JSON modules could be made to work correctly. First I will describe the	1047	encodings or codesets - C<utf8>, C<latin1> and C<ascii>. There seems to be
815	problems (or pleasures) I encountered with various existing JSON modules,	1048	some confusion on what these do, so here is a short comparison:
816	followed by some benchmark values. JSON::XS was designed not to suffer	1049
817	from any of these problems or limitations.	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.
818		1068
819	=over 4	1069	=over 4
820		1070
821	=item JSON 1.07	1071	=item C<utf8> flag disabled
822		1072
823	Slow (but very portable, as it is written in pure Perl).	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).
824		1080
825	Undocumented/buggy Unicode handling (how JSON handles Unicode values is	1081	This is useful when you want to do the encoding yourself (e.g. when you
826	undocumented. One can get far by feeding it Unicode strings and doing	1082	want to have UTF-16 encoded JSON texts) or when some other layer does
827	en-/decoding oneself, but Unicode escapes are not working properly).	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).
828		1086
829	No round-tripping (strings get clobbered if they look like numbers, e.g.	1087	=item C<utf8> flag enabled
830	the string C<2.0> will encode to C<2.0> instead of C<"2.0">, and that will
831	decode into the number 2.
832		1088
833	=item JSON::PC 0.01	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.
834		1094
835	Very fast.	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.
836		1098
837	Undocumented/buggy Unicode handling.	1099	=item C<latin1> or C<ascii> flags enabled
838		1100
839	No round-tripping.	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.
840		1104
841	Has problems handling many Perl values (e.g. regex results and other magic	1105	If C<utf8> is disabled, then the result is also correctly encoded in those
842	values will make it croak).	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).
843		1110
844	Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}>	1111	If C<utf8> is enabled, you still get a correct UTF-8-encoded string,
845	which is not a valid JSON text.	1112	regardless of these flags, just some more characters will be escaped using
		1113	C<\uXXXX> then before.
846		1114
847	Unmaintained (maintainer unresponsive for many months, bugs are not	1115	Note that ISO-8859-1-I<encoded> strings are not compatible with UTF-8
848	getting fixed).	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.
849		1119
850	=item JSON::Syck 0.21	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.
851		1124
852	Very buggy (often crashes).	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.
853		1127
854	Very inflexible (no human-readable format supported, format pretty much	1128	The main use for C<latin1> is to relatively efficiently store binary data
855	undocumented. I need at least a format for easy reading by humans and a	1129	as JSON, at the expense of breaking compatibility with most JSON decoders.
856	single-line compact format for use in a protocol, and preferably a way to
857	generate ASCII-only JSON texts).
858		1130
859	Completely broken (and confusingly documented) Unicode handling (Unicode	1131	The main use for C<ascii> is to force the output to not contain characters
860	escapes are not working properly, you need to set ImplicitUnicode to	1132	with values > 127, which means you can interpret the resulting string
861	I<different> values on en- and decoding to get symmetric behaviour).	1133	as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about any character set and
862		1134	8-bit-encoding, and still get the same data structure back. This is useful
863	No round-tripping (simple cases work, but this depends on whether the scalar	1135	when your channel for JSON transfer is not 8-bit clean or the encoding
864	value was used in a numeric context or not).	1136	might be mangled in between (e.g. in mail), and works because ASCII is a
865		1137	proper subset of most 8-bit and multibyte encodings in use in the world.
866	Dumping hashes may skip hash values depending on iterator state.
867
868	Unmaintained (maintainer unresponsive for many months, bugs are not
869	getting fixed).
870
871	Does not check input for validity (i.e. will accept non-JSON input and
872	return "something" instead of raising an exception. This is a security
873	issue: imagine two banks transferring money between each other using
874	JSON. One bank might parse a given non-JSON request and deduct money,
875	while the other might reject the transaction with a syntax error. While a
876	good protocol will at least recover, that is extra unnecessary work and
877	the transaction will still not succeed).
878
879	=item JSON::DWIW 0.04
880
881	Very fast. Very natural. Very nice.
882
883	Undocumented Unicode handling (but the best of the pack. Unicode escapes
884	still don't get parsed properly).
885
886	Very inflexible.
887
888	No round-tripping.
889
890	Does not generate valid JSON texts (key strings are often unquoted, empty keys
891	result in nothing being output)
892
893	Does not check input for validity.
894		1138
895	=back	1139	=back
896		1140
897		1141
898	=head2 JSON and YAML	1142	=head2 JSON and YAML
899		1143
900	You often hear that JSON is a subset (or a close subset) of YAML. This is,	1144	You often hear that JSON is a subset of YAML. This is, however, a mass
901	however, a mass hysteria and very far from the truth. In general, there is	1145	hysteria(*) and very far from the truth (as of the time of this writing),
902	no way to configure JSON::XS to output a data structure as valid YAML.	1146	so let me state it clearly: I<in general, there is no way to configure
		1147	JSON::XS to output a data structure as valid YAML> that works in all
		1148	cases.
903		1149
904	If you really must use JSON::XS to generate YAML, you should use this	1150	If you really must use JSON::XS to generate YAML, you should use this
905	algorithm (subject to change in future versions):	1151	algorithm (subject to change in future versions):
906		1152
907	my $to_yaml = JSON::XS->new->utf8->space_after (1);	1153	my $to_yaml = JSON::XS->new->utf8->space_after (1);
908	my $yaml = $to_yaml->encode ($ref) . "\n";	1154	my $yaml = $to_yaml->encode ($ref) . "\n";
909		1155
910	This will usually generate JSON texts that also parse as valid	1156	This will I<usually> generate JSON texts that also parse as valid
911	YAML. Please note that YAML has hardcoded limits on (simple) object key	1157	YAML. Please note that YAML has hardcoded limits on (simple) object key
912	lengths that JSON doesn't have, so you should make sure that your hash	1158	lengths that JSON doesn't have and also has different and incompatible
		1159	unicode handling, so you should make sure that your hash keys are
913	keys are noticeably shorter than the 1024 characters YAML allows.	1160	noticeably shorter than the 1024 "stream characters" YAML allows and that
		1161	you do not have characters with codepoint values outside the Unicode BMP
		1162	(basic multilingual page). YAML also does not allow C<\/> sequences in
		1163	strings (which JSON::XS does not I<currently> generate, but other JSON
		1164	generators might).
914		1165
915	There might be other incompatibilities that I am not aware of. In general	1166	There might be other incompatibilities that I am not aware of (or the YAML
		1167	specification has been changed yet again - it does so quite often). In
916	you should not try to generate YAML with a JSON generator or vice versa,	1168	general you should not try to generate YAML with a JSON generator or vice
917	or try to parse JSON with a YAML parser or vice versa: chances are high	1169	versa, or try to parse JSON with a YAML parser or vice versa: chances are
918	that you will run into severe interoperability problems.	1170	high that you will run into severe interoperability problems when you
		1171	least expect it.
		1172
		1173	=over 4
		1174
		1175	=item (*)
		1176
		1177	I have been pressured multiple times by Brian Ingerson (one of the
		1178	authors of the YAML specification) to remove this paragraph, despite him
		1179	acknowledging that the actual incompatibilities exist. As I was personally
		1180	bitten by this "JSON is YAML" lie, I refused and said I will continue to
		1181	educate people about these issues, so others do not run into the same
		1182	problem again and again. After this, Brian called me a (quote)I<complete
		1183	and worthless idiot>(unquote).
		1184
		1185	In my opinion, instead of pressuring and insulting people who actually
		1186	clarify issues with YAML and the wrong statements of some of its
		1187	proponents, I would kindly suggest reading the JSON spec (which is not
		1188	that difficult or long) and finally make YAML compatible to it, and
		1189	educating users about the changes, instead of spreading lies about the
		1190	real compatibility for many I<years> and trying to silence people who
		1191	point out that it isn't true.
		1192
		1193	=back
919		1194
920		1195
921	=head2 SPEED	1196	=head2 SPEED
922		1197
923	It seems that JSON::XS is surprisingly fast, as shown in the following	1198	It seems that JSON::XS is surprisingly fast, as shown in the following
924	tables. They have been generated with the help of the C<eg/bench> program	1199	tables. They have been generated with the help of the C<eg/bench> program
925	in the JSON::XS distribution, to make it easy to compare on your own	1200	in the JSON::XS distribution, to make it easy to compare on your own
926	system.	1201	system.
927		1202
928	First comes a comparison between various modules using a very short	1203	First comes a comparison between various modules using
929	single-line JSON string:	1204	a very short single-line JSON string (also available at
		1205	L<http://dist.schmorp.de/misc/json/short.json>).
930		1206
931	{"method": "handleMessage", "params": ["user1", "we were just talking"], \	1207	{"method": "handleMessage", "params": ["user1", "we were just talking"], \
932	"id": null, "array":[1,11,234,-5,1e5,1e7, true, false]}	1208	"id": null, "array":[1,11,234,-5,1e5,1e7, true, false]}
933		1209
934	It shows the number of encodes/decodes per second (JSON::XS uses	1210	It shows the number of encodes/decodes per second (JSON::XS uses
…		…
953	about three times faster on decoding, and over forty times faster	1229	about three times faster on decoding, and over forty times faster
954	than JSON, even with pretty-printing and key sorting. It also compares	1230	than JSON, even with pretty-printing and key sorting. It also compares
955	favourably to Storable for small amounts of data.	1231	favourably to Storable for small amounts of data.
956		1232
957	Using a longer test string (roughly 18KB, generated from Yahoo! Locals	1233	Using a longer test string (roughly 18KB, generated from Yahoo! Locals
958	search API (http://nanoref.com/yahooapis/mgPdGg):	1234	search API (L<http://dist.schmorp.de/misc/json/long.json>).
959		1235
960	module \| encode \| decode \|	1236	module \| encode \| decode \|
961	-----------\|------------\|------------\|	1237	-----------\|------------\|------------\|
962	JSON 1.x \| 55.260 \| 34.971 \|	1238	JSON 1.x \| 55.260 \| 34.971 \|
963	JSON::DWIW \| 825.228 \| 1082.513 \|	1239	JSON::DWIW \| 825.228 \| 1082.513 \|
…		…
1000		1276
1001	Third, JSON::XS recurses using the C stack when decoding objects and	1277	Third, JSON::XS recurses using the C stack when decoding objects and
1002	arrays. The C stack is a limited resource: for instance, on my amd64	1278	arrays. The C stack is a limited resource: for instance, on my amd64
1003	machine with 8MB of stack size I can decode around 180k nested arrays but	1279	machine with 8MB of stack size I can decode around 180k nested arrays but
1004	only 14k nested JSON objects (due to perl itself recursing deeply on croak	1280	only 14k nested JSON objects (due to perl itself recursing deeply on croak
1005	to free the temporary). If that is exceeded, the program crashes. to be	1281	to free the temporary). If that is exceeded, the program crashes. To be
1006	conservative, the default nesting limit is set to 512. If your process	1282	conservative, the default nesting limit is set to 512. If your process
1007	has a smaller stack, you should adjust this setting accordingly with the	1283	has a smaller stack, you should adjust this setting accordingly with the
1008	C<max_depth> method.	1284	C<max_depth> method.
1009		1285
1010	And last but least, something else could bomb you that I forgot to think	1286	Something else could bomb you, too, that I forgot to think of. In that
1011	of. In that case, you get to keep the pieces. I am always open for hints,	1287	case, you get to keep the pieces. I am always open for hints, though...
1012	though...	1288
		1289	Also keep in mind that JSON::XS might leak contents of your Perl data
		1290	structures in its error messages, so when you serialise sensitive
		1291	information you might want to make sure that exceptions thrown by JSON::XS
		1292	will not end up in front of untrusted eyes.
1013		1293
1014	If you are using JSON::XS to return packets to consumption	1294	If you are using JSON::XS to return packets to consumption
1015	by JavaScript scripts in a browser you should have a look at	1295	by JavaScript scripts in a browser you should have a look at
1016	L<http://jpsykes.com/47/practical-csrf-and-json-security> to see whether	1296	L<http://jpsykes.com/47/practical-csrf-and-json-security> to see whether
1017	you are vulnerable to some common attack vectors (which really are browser	1297	you are vulnerable to some common attack vectors (which really are browser
1018	design bugs, but it is still you who will have to deal with it, as major	1298	design bugs, but it is still you who will have to deal with it, as major
1019	browser developers care only for features, not about doing security	1299	browser developers care only for features, not about getting security
1020	right).	1300	right).
1021		1301
1022		1302
1023	=head1 THREADS	1303	=head1 THREADS
1024		1304
1025	This module is I<not> guaranteed to be thread safe and there are no	1305	This module is I<not> guaranteed to be thread safe and there are no
1026	plans to change this until Perl gets thread support (as opposed to the	1306	plans to change this until Perl gets thread support (as opposed to the
1027	horribly slow so-called "threads" which are simply slow and bloated	1307	horribly slow so-called "threads" which are simply slow and bloated
1028	process simulations - use fork, its I<much> faster, cheaper, better).	1308	process simulations - use fork, it's I<much> faster, cheaper, better).
1029		1309
1030	(It might actually work, but you have been warned).	1310	(It might actually work, but you have been warned).
1031		1311
1032		1312
1033	=head1 BUGS	1313	=head1 BUGS
1034		1314
1035	While the goal of this module is to be correct, that unfortunately does	1315	While the goal of this module is to be correct, that unfortunately does
1036	not mean its bug-free, only that I think its design is bug-free. It is	1316	not mean it's bug-free, only that I think its design is bug-free. It is
1037	still relatively early in its development. If you keep reporting bugs they	1317	still relatively early in its development. If you keep reporting bugs they
1038	will be fixed swiftly, though.	1318	will be fixed swiftly, though.
1039		1319
1040	Please refrain from using rt.cpan.org or any other bug reporting	1320	Please refrain from using rt.cpan.org or any other bug reporting
1041	service. I put the contact address into my modules for a reason.	1321	service. I put the contact address into my modules for a reason.
…		…
1063	"--" => sub { $_[0] = ${$_[0]} - 1 },	1343	"--" => sub { $_[0] = ${$_[0]} - 1 },
1064	fallback => 1;	1344	fallback => 1;
1065		1345
1066	1;	1346	1;
1067		1347
		1348	=head1 SEE ALSO
		1349
		1350	The F<json_xs> command line utility for quick experiments.
		1351
1068	=head1 AUTHOR	1352	=head1 AUTHOR
1069		1353
1070	Marc Lehmann <schmorp@schmorp.de>	1354	Marc Lehmann <schmorp@schmorp.de>
1071	http://home.schmorp.de/	1355	http://home.schmorp.de/
1072		1356

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Revision 1.77 by root, Tue Dec 4 10:37:42 2007 UTC vs.
Revision 1.95 by root, Tue Mar 25 16:56:09 2008 UTC