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

Comparing JSON-XS/XS.pm (file contents):
Revision 1.85 by root, Wed Mar 19 02:55:23 2008 UTC vs.
Revision 1.110 by root, Sun Jul 20 17:55:19 2008 UTC

…		…
		1	=head1 NAME
		2
		3	JSON::XS - JSON serialising/deserialising, done correctly and fast
		4
1	=encoding utf-8	5	=encoding utf-8
2
3	=head1 NAME
4
5	JSON::XS - JSON serialising/deserialising, done correctly and fast
6		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	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)	8	(http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html)
9		9
10	=head1 SYNOPSIS	10	=head1 SYNOPSIS
37	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
38	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		39
40	Beginning with version 2.0 of the JSON module, when both JSON and	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	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	42	overridden) with no overhead due to emulation (by inheriting constructor
43	and methods). If JSON::XS is not available, it will fall back to the	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	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	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.	46	require a C compiler when that is a problem.
47		47
…		…
65	This module knows how to handle Unicode, documents how and when it does	65	This module knows how to handle Unicode, documents how and when it does
66	so, and even documents what "correct" means.	66	so, and even documents what "correct" means.
67		67
68	=item * round-trip integrity	68	=item * round-trip integrity
69		69
70	When you serialise a perl data structure using only datatypes supported	70	When you serialise a perl data structure using only data types supported
71	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.
72	(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
73	like a number). There minor I<are> exceptions to this, read the MAPPING	73	like a number). There minor I<are> exceptions to this, read the MAPPING
74	section below to learn about those.	74	section below to learn about those.
75		75
…		…
84	Compared to other JSON modules and other serialisers such as Storable,	84	Compared to other JSON modules and other serialisers such as Storable,
85	this module usually compares favourably in terms of speed, too.	85	this module usually compares favourably in terms of speed, too.
86		86
87	=item * simple to use	87	=item * simple to use
88		88
89	This module has both a simple functional interface as well as an objetc	89	This module has both a simple functional interface as well as an object
90	oriented interface interface.	90	oriented interface interface.
91		91
92	=item * reasonably versatile output formats	92	=item * reasonably versatile output formats
93		93
94	You can choose between the most compact guaranteed-single-line format	94	You can choose between the most compact guaranteed-single-line format
95	possible (nice for simple line-based protocols), a pure-ascii 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	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	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.	98	stuff). Or you can combine those features in whatever way you like.
99		99
100	=back	100	=back
101		101
102	=cut	102	=cut
103		103
104	package JSON::XS;	104	package JSON::XS;
105		105
		106	no warnings;
106	use strict;	107	use strict;
107		108
108	our $VERSION = '2.01';	109	our $VERSION = '2.2222';
109	our @ISA = qw(Exporter);	110	our @ISA = qw(Exporter);
110		111
111	our @EXPORT = qw(encode_json decode_json to_json from_json);	112	our @EXPORT = qw(encode_json decode_json to_json from_json);
112		113
113	sub to_json($) {	114	sub to_json($) {
…		…
137		138
138	This function call is functionally identical to:	139	This function call is functionally identical to:
139		140
140	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)	141	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)
141		142
142	except being faster.	143	Except being faster.
143		144
144	=item $perl_scalar = decode_json $json_text	145	=item $perl_scalar = decode_json $json_text
145		146
146	The opposite of C<encode_json>: expects an UTF-8 (binary) string and tries	147	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	to parse that as an UTF-8 encoded JSON text, returning the resulting
…		…
149		150
150	This function call is functionally identical to:	151	This function call is functionally identical to:
151		152
152	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)	153	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)
153		154
154	except being faster.	155	Except being faster.
155		156
156	=item $is_boolean = JSON::XS::is_bool $scalar	157	=item $is_boolean = JSON::XS::is_bool $scalar
157		158
158	Returns true if the passed scalar represents either JSON::XS::true or	159	Returns true if the passed scalar represents either JSON::XS::true or
159	JSON::XS::false, two constants that act like C<1> and C<0>, respectively	160	JSON::XS::false, two constants that act like C<1> and C<0>, respectively
…		…
197		198
198	If you didn't know about that flag, just the better, pretend it doesn't	199	If you didn't know about that flag, just the better, pretend it doesn't
199	exist.	200	exist.
200		201
201	=item 4. A "Unicode String" is simply a string where each character can be	202	=item 4. A "Unicode String" is simply a string where each character can be
202	validly interpreted as a Unicode codepoint.	203	validly interpreted as a Unicode code point.
203		204
204	If you have UTF-8 encoded data, it is no longer a Unicode string, but a	205	If you have UTF-8 encoded data, it is no longer a Unicode string, but a
205	Unicode string encoded in UTF-8, giving you a binary string.	206	Unicode string encoded in UTF-8, giving you a binary string.
206		207
207	=item 5. A string containing "high" (> 255) character values is I<not> a UTF-8 string.	208	=item 5. A string containing "high" (> 255) character values is I<not> a UTF-8 string.
…		…
245		246
246	If C<$enable> is false, then the C<encode> method will not escape Unicode	247	If C<$enable> is false, then the C<encode> method will not escape Unicode
247	characters unless required by the JSON syntax or other flags. This results	248	characters unless required by the JSON syntax or other flags. This results
248	in a faster and more compact format.	249	in a faster and more compact format.
249		250
		251	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		252	document.
		253
250	The main use for this flag is to produce JSON texts that can be	254	The main use for this flag is to produce JSON texts that can be
251	transmitted over a 7-bit channel, as the encoded JSON texts will not	255	transmitted over a 7-bit channel, as the encoded JSON texts will not
252	contain any 8 bit characters.	256	contain any 8 bit characters.
253		257
254	JSON::XS->new->ascii (1)->encode ([chr 0x10401])	258	JSON::XS->new->ascii (1)->encode ([chr 0x10401])
…		…
265	will not be affected in any way by this flag, as C<decode> by default	269	will not be affected in any way by this flag, as C<decode> by default
266	expects Unicode, which is a strict superset of latin1.	270	expects Unicode, which is a strict superset of latin1.
267		271
268	If C<$enable> is false, then the C<encode> method will not escape Unicode	272	If C<$enable> is false, then the C<encode> method will not escape Unicode
269	characters unless required by the JSON syntax or other flags.	273	characters unless required by the JSON syntax or other flags.
		274
		275	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		276	document.
270		277
271	The main use for this flag is efficiently encoding binary data as JSON	278	The main use for this flag is efficiently encoding binary data as JSON
272	text, as most octets will not be escaped, resulting in a smaller encoded	279	text, as most octets will not be escaped, resulting in a smaller encoded
273	size. The disadvantage is that the resulting JSON text is encoded	280	size. The disadvantage is that the resulting JSON text is encoded
274	in latin1 (and must correctly be treated as such when storing and	281	in latin1 (and must correctly be treated as such when storing and
…		…
293		300
294	If C<$enable> is false, then the C<encode> method will return the JSON	301	If C<$enable> is false, then the C<encode> method will return the JSON
295	string as a (non-encoded) Unicode string, while C<decode> expects thus a	302	string as a (non-encoded) Unicode string, while C<decode> expects thus a
296	Unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs	303	Unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs
297	to be done yourself, e.g. using the Encode module.	304	to be done yourself, e.g. using the Encode module.
		305
		306	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		307	document.
298		308
299	Example, output UTF-16BE-encoded JSON:	309	Example, output UTF-16BE-encoded JSON:
300		310
301	use Encode;	311	use Encode;
302	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);	312	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
…		…
453	Example, encode a Perl scalar as JSON value with enabled C<allow_nonref>,	463	Example, encode a Perl scalar as JSON value with enabled C<allow_nonref>,
454	resulting in an invalid JSON text:	464	resulting in an invalid JSON text:
455		465
456	JSON::XS->new->allow_nonref->encode ("Hello, World!")	466	JSON::XS->new->allow_nonref->encode ("Hello, World!")
457	=> "Hello, World!"	467	=> "Hello, World!"
		468
		469	=item $json = $json->allow_unknown ([$enable])
		470
		471	=item $enabled = $json->get_allow_unknown
		472
		473	If C<$enable> is true (or missing), then C<encode> will I<not> throw an
		474	exception when it encounters values it cannot represent in JSON (for
		475	example, filehandles) but instead will encode a JSON C<null> value. Note
		476	that blessed objects are not included here and are handled separately by
		477	c<allow_nonref>.
		478
		479	If C<$enable> is false (the default), then C<encode> will throw an
		480	exception when it encounters anything it cannot encode as JSON.
		481
		482	This option does not affect C<decode> in any way, and it is recommended to
		483	leave it off unless you know your communications partner.
458		484
459	=item $json = $json->allow_blessed ([$enable])	485	=item $json = $json->allow_blessed ([$enable])
460		486
461	=item $enabled = $json->get_allow_blessed	487	=item $enabled = $json->get_allow_blessed
462		488
…		…
603	=item $json = $json->max_depth ([$maximum_nesting_depth])	629	=item $json = $json->max_depth ([$maximum_nesting_depth])
604		630
605	=item $max_depth = $json->get_max_depth	631	=item $max_depth = $json->get_max_depth
606		632
607	Sets the maximum nesting level (default C<512>) accepted while encoding	633	Sets the maximum nesting level (default C<512>) accepted while encoding
608	or decoding. If the JSON text or Perl data structure has an equal or	634	or decoding. If a higher nesting level is detected in JSON text or a Perl
609	higher nesting level then this limit, then the encoder and decoder will	635	data structure, then the encoder and decoder will stop and croak at that
610	stop and croak at that point.	636	point.
611		637
612	Nesting level is defined by number of hash- or arrayrefs that the encoder	638	Nesting level is defined by number of hash- or arrayrefs that the encoder
613	needs to traverse to reach a given point or the number of C<{> or C<[>	639	needs to traverse to reach a given point or the number of C<{> or C<[>
614	characters without their matching closing parenthesis crossed to reach a	640	characters without their matching closing parenthesis crossed to reach a
615	given character in a string.	641	given character in a string.
616		642
617	Setting the maximum depth to one disallows any nesting, so that ensures	643	Setting the maximum depth to one disallows any nesting, so that ensures
618	that the object is only a single hash/object or array.	644	that the object is only a single hash/object or array.
619		645
620	The argument to C<max_depth> will be rounded up to the next highest power
621	of two. If no argument is given, the highest possible setting will be	646	If no argument is given, the highest possible setting will be used, which
622	used, which is rarely useful.	647	is rarely useful.
		648
		649	Note that nesting is implemented by recursion in C. The default value has
		650	been chosen to be as large as typical operating systems allow without
		651	crashing.
623		652
624	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.	653	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
625		654
626	=item $json = $json->max_size ([$maximum_string_size])	655	=item $json = $json->max_size ([$maximum_string_size])
627		656
628	=item $max_size = $json->get_max_size	657	=item $max_size = $json->get_max_size
629		658
630	Set the maximum length a JSON text may have (in bytes) where decoding is	659	Set the maximum length a JSON text may have (in bytes) where decoding is
631	being attempted. The default is C<0>, meaning no limit. When C<decode>	660	being attempted. The default is C<0>, meaning no limit. When C<decode>
632	is called on a string longer then this number of characters it will not	661	is called on a string that is longer then this many bytes, it will not
633	attempt to decode the string but throw an exception. This setting has no	662	attempt to decode the string but throw an exception. This setting has no
634	effect on C<encode> (yet).	663	effect on C<encode> (yet).
635		664
636	The argument to C<max_size> will be rounded up to the next B<highest>	665	If no argument is given, the limit check will be deactivated (same as when
637	power of two (so may be more than requested). If no argument is given, the	666	C<0> is specified).
638	limit check will be deactivated (same as when C<0> is specified).
639		667
640	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.	668	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
641		669
642	=item $json_text = $json->encode ($perl_scalar)	670	=item $json_text = $json->encode ($perl_scalar)
643		671
…		…
670		698
671	JSON::XS->new->decode_prefix ("[1] the tail")	699	JSON::XS->new->decode_prefix ("[1] the tail")
672	=> ([], 3)	700	=> ([], 3)
673		701
674	=back	702	=back
		703
		704
		705	=head1 INCREMENTAL PARSING
		706
		707	In some cases, there is the need for incremental parsing of JSON
		708	texts. While this module always has to keep both JSON text and resulting
		709	Perl data structure in memory at one time, it does allow you to parse a
		710	JSON stream incrementally. It does so by accumulating text until it has
		711	a full JSON object, which it then can decode. This process is similar to
		712	using C<decode_prefix> to see if a full JSON object is available, but
		713	is much more efficient (and can be implemented with a minimum of method
		714	calls).
		715
		716	JSON::XS will only attempt to parse the JSON text once it is sure it
		717	has enough text to get a decisive result, using a very simple but
		718	truly incremental parser. This means that it sometimes won't stop as
		719	early as the full parser, for example, it doesn't detect parenthese
		720	mismatches. The only thing it guarantees is that it starts decoding as
		721	soon as a syntactically valid JSON text has been seen. This means you need
		722	to set resource limits (e.g. C<max_size>) to ensure the parser will stop
		723	parsing in the presence if syntax errors.
		724
		725	The following methods implement this incremental parser.
		726
		727	=over 4
		728
		729	=item [void, scalar or list context] = $json->incr_parse ([$string])
		730
		731	This is the central parsing function. It can both append new text and
		732	extract objects from the stream accumulated so far (both of these
		733	functions are optional).
		734
		735	If C<$string> is given, then this string is appended to the already
		736	existing JSON fragment stored in the C<$json> object.
		737
		738	After that, if the function is called in void context, it will simply
		739	return without doing anything further. This can be used to add more text
		740	in as many chunks as you want.
		741
		742	If the method is called in scalar context, then it will try to extract
		743	exactly I<one> JSON object. If that is successful, it will return this
		744	object, otherwise it will return C<undef>. If there is a parse error,
		745	this method will croak just as C<decode> would do (one can then use
		746	C<incr_skip> to skip the errornous part). This is the most common way of
		747	using the method.
		748
		749	And finally, in list context, it will try to extract as many objects
		750	from the stream as it can find and return them, or the empty list
		751	otherwise. For this to work, there must be no separators between the JSON
		752	objects or arrays, instead they must be concatenated back-to-back. If
		753	an error occurs, an exception will be raised as in the scalar context
		754	case. Note that in this case, any previously-parsed JSON texts will be
		755	lost.
		756
		757	=item $lvalue_string = $json->incr_text
		758
		759	This method returns the currently stored JSON fragment as an lvalue, that
		760	is, you can manipulate it. This I<only> works when a preceding call to
		761	C<incr_parse> in I<scalar context> successfully returned an object. Under
		762	all other circumstances you must not call this function (I mean it.
		763	although in simple tests it might actually work, it I<will> fail under
		764	real world conditions). As a special exception, you can also call this
		765	method before having parsed anything.
		766
		767	This function is useful in two cases: a) finding the trailing text after a
		768	JSON object or b) parsing multiple JSON objects separated by non-JSON text
		769	(such as commas).
		770
		771	=item $json->incr_skip
		772
		773	This will reset the state of the incremental parser and will remove the
		774	parsed text from the input buffer. This is useful after C<incr_parse>
		775	died, in which case the input buffer and incremental parser state is left
		776	unchanged, to skip the text parsed so far and to reset the parse state.
		777
		778	=item $json->incr_reset
		779
		780	This completely resets the incremental parser, that is, after this call,
		781	it will be as if the parser had never parsed anything.
		782
		783	This is useful if you want ot repeatedly parse JSON objects and want to
		784	ignore any trailing data, which means you have to reset the parser after
		785	each successful decode.
		786
		787	=back
		788
		789	=head2 LIMITATIONS
		790
		791	All options that affect decoding are supported, except
		792	C<allow_nonref>. The reason for this is that it cannot be made to
		793	work sensibly: JSON objects and arrays are self-delimited, i.e. you can concatenate
		794	them back to back and still decode them perfectly. This does not hold true
		795	for JSON numbers, however.
		796
		797	For example, is the string C<1> a single JSON number, or is it simply the
		798	start of C<12>? Or is C<12> a single JSON number, or the concatenation
		799	of C<1> and C<2>? In neither case you can tell, and this is why JSON::XS
		800	takes the conservative route and disallows this case.
		801
		802	=head2 EXAMPLES
		803
		804	Some examples will make all this clearer. First, a simple example that
		805	works similarly to C<decode_prefix>: We want to decode the JSON object at
		806	the start of a string and identify the portion after the JSON object:
		807
		808	my $text = "[1,2,3] hello";
		809
		810	my $json = new JSON::XS;
		811
		812	my $obj = $json->incr_parse ($text)
		813	or die "expected JSON object or array at beginning of string";
		814
		815	my $tail = $json->incr_text;
		816	# $tail now contains " hello"
		817
		818	Easy, isn't it?
		819
		820	Now for a more complicated example: Imagine a hypothetical protocol where
		821	you read some requests from a TCP stream, and each request is a JSON
		822	array, without any separation between them (in fact, it is often useful to
		823	use newlines as "separators", as these get interpreted as whitespace at
		824	the start of the JSON text, which makes it possible to test said protocol
		825	with C<telnet>...).
		826
		827	Here is how you'd do it (it is trivial to write this in an event-based
		828	manner):
		829
		830	my $json = new JSON::XS;
		831
		832	# read some data from the socket
		833	while (sysread $socket, my $buf, 4096) {
		834
		835	# split and decode as many requests as possible
		836	for my $request ($json->incr_parse ($buf)) {
		837	# act on the $request
		838	}
		839	}
		840
		841	Another complicated example: Assume you have a string with JSON objects
		842	or arrays, all separated by (optional) comma characters (e.g. C<[1],[2],
		843	[3]>). To parse them, we have to skip the commas between the JSON texts,
		844	and here is where the lvalue-ness of C<incr_text> comes in useful:
		845
		846	my $text = "[1],[2], [3]";
		847	my $json = new JSON::XS;
		848
		849	# void context, so no parsing done
		850	$json->incr_parse ($text);
		851
		852	# now extract as many objects as possible. note the
		853	# use of scalar context so incr_text can be called.
		854	while (my $obj = $json->incr_parse) {
		855	# do something with $obj
		856
		857	# now skip the optional comma
		858	$json->incr_text =~ s/^ \s* , //x;
		859	}
		860
		861	Now lets go for a very complex example: Assume that you have a gigantic
		862	JSON array-of-objects, many gigabytes in size, and you want to parse it,
		863	but you cannot load it into memory fully (this has actually happened in
		864	the real world :).
		865
		866	Well, you lost, you have to implement your own JSON parser. But JSON::XS
		867	can still help you: You implement a (very simple) array parser and let
		868	JSON decode the array elements, which are all full JSON objects on their
		869	own (this wouldn't work if the array elements could be JSON numbers, for
		870	example):
		871
		872	my $json = new JSON::XS;
		873
		874	# open the monster
		875	open my $fh, "<bigfile.json"
		876	or die "bigfile: $!";
		877
		878	# first parse the initial "["
		879	for (;;) {
		880	sysread $fh, my $buf, 65536
		881	or die "read error: $!";
		882	$json->incr_parse ($buf); # void context, so no parsing
		883
		884	# Exit the loop once we found and removed(!) the initial "[".
		885	# In essence, we are (ab-)using the $json object as a simple scalar
		886	# we append data to.
		887	last if $json->incr_text =~ s/^ \s* \[ //x;
		888	}
		889
		890	# now we have the skipped the initial "[", so continue
		891	# parsing all the elements.
		892	for (;;) {
		893	# in this loop we read data until we got a single JSON object
		894	for (;;) {
		895	if (my $obj = $json->incr_parse) {
		896	# do something with $obj
		897	last;
		898	}
		899
		900	# add more data
		901	sysread $fh, my $buf, 65536
		902	or die "read error: $!";
		903	$json->incr_parse ($buf); # void context, so no parsing
		904	}
		905
		906	# in this loop we read data until we either found and parsed the
		907	# separating "," between elements, or the final "]"
		908	for (;;) {
		909	# first skip whitespace
		910	$json->incr_text =~ s/^\s*//;
		911
		912	# if we find "]", we are done
		913	if ($json->incr_text =~ s/^\]//) {
		914	print "finished.\n";
		915	exit;
		916	}
		917
		918	# if we find ",", we can continue with the next element
		919	if ($json->incr_text =~ s/^,//) {
		920	last;
		921	}
		922
		923	# if we find anything else, we have a parse error!
		924	if (length $json->incr_text) {
		925	die "parse error near ", $json->incr_text;
		926	}
		927
		928	# else add more data
		929	sysread $fh, my $buf, 65536
		930	or die "read error: $!";
		931	$json->incr_parse ($buf); # void context, so no parsing
		932	}
		933
		934	This is a complex example, but most of the complexity comes from the fact
		935	that we are trying to be correct (bear with me if I am wrong, I never ran
		936	the above example :).
		937
675		938
676		939
677	=head1 MAPPING	940	=head1 MAPPING
678		941
679	This section describes how JSON::XS maps Perl values to JSON values and	942	This section describes how JSON::XS maps Perl values to JSON values and
…		…
768	Other unblessed references are generally not allowed and will cause an	1031	Other unblessed references are generally not allowed and will cause an
769	exception to be thrown, except for references to the integers C<0> and	1032	exception to be thrown, except for references to the integers C<0> and
770	C<1>, which get turned into C<false> and C<true> atoms in JSON. You can	1033	C<1>, which get turned into C<false> and C<true> atoms in JSON. You can
771	also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability.	1034	also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability.
772		1035
773	encode_json [\0,JSON::XS::true] # yields [false,true]	1036	encode_json [\0, JSON::XS::true] # yields [false,true]
774		1037
775	=item JSON::XS::true, JSON::XS::false	1038	=item JSON::XS::true, JSON::XS::false
776		1039
777	These special values become JSON true and JSON false values,	1040	These special values become JSON true and JSON false values,
778	respectively. You can also use C<\1> and C<\0> directly if you want.	1041	respectively. You can also use C<\1> and C<\0> directly if you want.
…		…
816	my $x = "3"; # some variable containing a string	1079	my $x = "3"; # some variable containing a string
817	$x += 0; # numify it, ensuring it will be dumped as a number	1080	$x += 0; # numify it, ensuring it will be dumped as a number
818	$x *= 1; # same thing, the choice is yours.	1081	$x *= 1; # same thing, the choice is yours.
819		1082
820	You can not currently force the type in other, less obscure, ways. Tell me	1083	You can not currently force the type in other, less obscure, ways. Tell me
821	if you need this capability (but don't forget to explain why its needed	1084	if you need this capability (but don't forget to explain why it's needed
822	:).	1085	:).
823		1086
824	=back	1087	=back
825		1088
826		1089
…		…
828		1091
829	The interested reader might have seen a number of flags that signify	1092	The interested reader might have seen a number of flags that signify
830	encodings or codesets - C<utf8>, C<latin1> and C<ascii>. There seems to be	1093	encodings or codesets - C<utf8>, C<latin1> and C<ascii>. There seems to be
831	some confusion on what these do, so here is a short comparison:	1094	some confusion on what these do, so here is a short comparison:
832		1095
833	C<utf8> controls wether the JSON text created by C<encode> (and expected	1096	C<utf8> controls whether the JSON text created by C<encode> (and expected
834	by C<decode>) is UTF-8 encoded or not, while C<latin1> and C<ascii> only	1097	by C<decode>) is UTF-8 encoded or not, while C<latin1> and C<ascii> only
835	control wether C<encode> escapes character values outside their respective	1098	control whether C<encode> escapes character values outside their respective
836	codeset range. Neither of these flags conflict with each other, although	1099	codeset range. Neither of these flags conflict with each other, although
837	some combinations make less sense than others.	1100	some combinations make less sense than others.
838		1101
839	Care has been taken to make all flags symmetrical with respect to	1102	Care has been taken to make all flags symmetrical with respect to
840	C<encode> and C<decode>, that is, texts encoded with any combination of	1103	C<encode> and C<decode>, that is, texts encoded with any combination of
…		…
920	proper subset of most 8-bit and multibyte encodings in use in the world.	1183	proper subset of most 8-bit and multibyte encodings in use in the world.
921		1184
922	=back	1185	=back
923		1186
924		1187
925	=head1 COMPARISON
926
927	As already mentioned, this module was created because none of the existing
928	JSON modules could be made to work correctly. First I will describe the
929	problems (or pleasures) I encountered with various existing JSON modules,
930	followed by some benchmark values. JSON::XS was designed not to suffer
931	from any of these problems or limitations.
932
933	=over 4
934
935	=item JSON 2.xx
936
937	A marvellous piece of engineering, this module either uses JSON::XS
938	directly when available (so will be 100% compatible with it, including
939	speed), or it uses JSON::PP, which is basically JSON::XS translated to
940	Pure Perl, which should be 100% compatible with JSON::XS, just a bit
941	slower.
942
943	You cannot really lose by using this module, especially as it tries very
944	hard to work even with ancient Perl versions, while JSON::XS does not.
945
946	=item JSON 1.07
947
948	Slow (but very portable, as it is written in pure Perl).
949
950	Undocumented/buggy Unicode handling (how JSON handles Unicode values is
951	undocumented. One can get far by feeding it Unicode strings and doing
952	en-/decoding oneself, but Unicode escapes are not working properly).
953
954	No round-tripping (strings get clobbered if they look like numbers, e.g.
955	the string C<2.0> will encode to C<2.0> instead of C<"2.0">, and that will
956	decode into the number 2.
957
958	=item JSON::PC 0.01
959
960	Very fast.
961
962	Undocumented/buggy Unicode handling.
963
964	No round-tripping.
965
966	Has problems handling many Perl values (e.g. regex results and other magic
967	values will make it croak).
968
969	Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}>
970	which is not a valid JSON text.
971
972	Unmaintained (maintainer unresponsive for many months, bugs are not
973	getting fixed).
974
975	=item JSON::Syck 0.21
976
977	Very buggy (often crashes).
978
979	Very inflexible (no human-readable format supported, format pretty much
980	undocumented. I need at least a format for easy reading by humans and a
981	single-line compact format for use in a protocol, and preferably a way to
982	generate ASCII-only JSON texts).
983
984	Completely broken (and confusingly documented) Unicode handling (Unicode
985	escapes are not working properly, you need to set ImplicitUnicode to
986	I<different> values on en- and decoding to get symmetric behaviour).
987
988	No round-tripping (simple cases work, but this depends on whether the scalar
989	value was used in a numeric context or not).
990
991	Dumping hashes may skip hash values depending on iterator state.
992
993	Unmaintained (maintainer unresponsive for many months, bugs are not
994	getting fixed).
995
996	Does not check input for validity (i.e. will accept non-JSON input and
997	return "something" instead of raising an exception. This is a security
998	issue: imagine two banks transferring money between each other using
999	JSON. One bank might parse a given non-JSON request and deduct money,
1000	while the other might reject the transaction with a syntax error. While a
1001	good protocol will at least recover, that is extra unnecessary work and
1002	the transaction will still not succeed).
1003
1004	=item JSON::DWIW 0.04
1005
1006	Very fast. Very natural. Very nice.
1007
1008	Undocumented Unicode handling (but the best of the pack. Unicode escapes
1009	still don't get parsed properly).
1010
1011	Very inflexible.
1012
1013	No round-tripping.
1014
1015	Does not generate valid JSON texts (key strings are often unquoted, empty keys
1016	result in nothing being output)
1017
1018	Does not check input for validity.
1019
1020	=back
1021
1022
1023	=head2 JSON and YAML	1188	=head2 JSON and YAML
1024		1189
1025	You often hear that JSON is a subset of YAML. This is, however, a mass	1190	You often hear that JSON is a subset of YAML. This is, however, a mass
1026	hysteria(*) and very far from the truth. In general, there is no way to	1191	hysteria(*) and very far from the truth (as of the time of this writing),
		1192	so let me state it clearly: I<in general, there is no way to configure
1027	configure JSON::XS to output a data structure as valid YAML that works for	1193	JSON::XS to output a data structure as valid YAML> that works in all
1028	all cases.	1194	cases.
1029		1195
1030	If you really must use JSON::XS to generate YAML, you should use this	1196	If you really must use JSON::XS to generate YAML, you should use this
1031	algorithm (subject to change in future versions):	1197	algorithm (subject to change in future versions):
1032		1198
1033	my $to_yaml = JSON::XS->new->utf8->space_after (1);	1199	my $to_yaml = JSON::XS->new->utf8->space_after (1);
…		…
1036	This will I<usually> generate JSON texts that also parse as valid	1202	This will I<usually> generate JSON texts that also parse as valid
1037	YAML. Please note that YAML has hardcoded limits on (simple) object key	1203	YAML. Please note that YAML has hardcoded limits on (simple) object key
1038	lengths that JSON doesn't have and also has different and incompatible	1204	lengths that JSON doesn't have and also has different and incompatible
1039	unicode handling, so you should make sure that your hash keys are	1205	unicode handling, so you should make sure that your hash keys are
1040	noticeably shorter than the 1024 "stream characters" YAML allows and that	1206	noticeably shorter than the 1024 "stream characters" YAML allows and that
1041	you do not have codepoints with values outside the Unicode BMP (basic	1207	you do not have characters with codepoint values outside the Unicode BMP
1042	multilingual page). YAML also does not allow C<\/> sequences in strings	1208	(basic multilingual page). YAML also does not allow C<\/> sequences in
1043	(which JSON::XS does not I<currently> generate).	1209	strings (which JSON::XS does not I<currently> generate, but other JSON
		1210	generators might).
1044		1211
1045	There might be other incompatibilities that I am not aware of (or the YAML	1212	There might be other incompatibilities that I am not aware of (or the YAML
1046	specification has been changed yet again - it does so quite often). In	1213	specification has been changed yet again - it does so quite often). In
1047	general you should not try to generate YAML with a JSON generator or vice	1214	general you should not try to generate YAML with a JSON generator or vice
1048	versa, or try to parse JSON with a YAML parser or vice versa: chances are	1215	versa, or try to parse JSON with a YAML parser or vice versa: chances are
…		…
1051		1218
1052	=over 4	1219	=over 4
1053		1220
1054	=item (*)	1221	=item (*)
1055		1222
1056	This is spread actively by the YAML team, however. For many years now they	1223	I have been pressured multiple times by Brian Ingerson (one of the
1057	claim YAML were a superset of JSON, even when proven otherwise.	1224	authors of the YAML specification) to remove this paragraph, despite him
		1225	acknowledging that the actual incompatibilities exist. As I was personally
		1226	bitten by this "JSON is YAML" lie, I refused and said I will continue to
		1227	educate people about these issues, so others do not run into the same
		1228	problem again and again. After this, Brian called me a (quote)I<complete
		1229	and worthless idiot>(unquote).
1058		1230
1059	Even the author of this manpage was at some point accused of providing	1231	In my opinion, instead of pressuring and insulting people who actually
1060	"incorrect" information, despite the evidence presented (claims ranged	1232	clarify issues with YAML and the wrong statements of some of its
1061	from "your documentation contains inaccurate and negative statements about	1233	proponents, I would kindly suggest reading the JSON spec (which is not
1062	YAML" (the only negative comment is this footnote, and it didn't exist	1234	that difficult or long) and finally make YAML compatible to it, and
1063	back then; the question on which claims were inaccurate was never answered	1235	educating users about the changes, instead of spreading lies about the
1064	etc.) to "the YAML spec is not up-to-date" (the real and supposedly	1236	real compatibility for many I<years> and trying to silence people who
1065	JSON-compatible spec is apparently not currently publicly available)	1237	point out that it isn't true.
1066	to actual requests to replace this section by incorrect information,
1067	suppressing information about the real problem).
1068
1069	So whenever you are told that YAML was a superset of JSON, first check
1070	wether it is really true (it might be when you check it, but it certainly
1071	was not true when this was written). I would much prefer if the YAML team
1072	would spent their time on actually making JSON compatibility a truth
1073	(JSON, after all, has a very small and simple specification) instead of
1074	trying to lobby/force people into reporting untruths.
1075		1238
1076	=back	1239	=back
1077		1240
1078		1241
1079	=head2 SPEED	1242	=head2 SPEED
…		…
1081	It seems that JSON::XS is surprisingly fast, as shown in the following	1244	It seems that JSON::XS is surprisingly fast, as shown in the following
1082	tables. They have been generated with the help of the C<eg/bench> program	1245	tables. They have been generated with the help of the C<eg/bench> program
1083	in the JSON::XS distribution, to make it easy to compare on your own	1246	in the JSON::XS distribution, to make it easy to compare on your own
1084	system.	1247	system.
1085		1248
1086	First comes a comparison between various modules using a very short	1249	First comes a comparison between various modules using
1087	single-line JSON string:	1250	a very short single-line JSON string (also available at
		1251	L<http://dist.schmorp.de/misc/json/short.json>).
1088		1252
1089	{"method": "handleMessage", "params": ["user1", "we were just talking"], \	1253	{"method": "handleMessage", "params": ["user1",
1090	"id": null, "array":[1,11,234,-5,1e5,1e7, true, false]}	1254	"we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7,
		1255	true, false]}
1091		1256
1092	It shows the number of encodes/decodes per second (JSON::XS uses	1257	It shows the number of encodes/decodes per second (JSON::XS uses
1093	the functional interface, while JSON::XS/2 uses the OO interface	1258	the functional interface, while JSON::XS/2 uses the OO interface
1094	with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables	1259	with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables
1095	shrink). Higher is better:	1260	shrink). Higher is better:
…		…
1111	about three times faster on decoding, and over forty times faster	1276	about three times faster on decoding, and over forty times faster
1112	than JSON, even with pretty-printing and key sorting. It also compares	1277	than JSON, even with pretty-printing and key sorting. It also compares
1113	favourably to Storable for small amounts of data.	1278	favourably to Storable for small amounts of data.
1114		1279
1115	Using a longer test string (roughly 18KB, generated from Yahoo! Locals	1280	Using a longer test string (roughly 18KB, generated from Yahoo! Locals
1116	search API (http://nanoref.com/yahooapis/mgPdGg):	1281	search API (L<http://dist.schmorp.de/misc/json/long.json>).
1117		1282
1118	module \| encode \| decode \|	1283	module \| encode \| decode \|
1119	-----------\|------------\|------------\|	1284	-----------\|------------\|------------\|
1120	JSON 1.x \| 55.260 \| 34.971 \|	1285	JSON 1.x \| 55.260 \| 34.971 \|
1121	JSON::DWIW \| 825.228 \| 1082.513 \|	1286	JSON::DWIW \| 825.228 \| 1082.513 \|
…		…
1163	to free the temporary). If that is exceeded, the program crashes. To be	1328	to free the temporary). If that is exceeded, the program crashes. To be
1164	conservative, the default nesting limit is set to 512. If your process	1329	conservative, the default nesting limit is set to 512. If your process
1165	has a smaller stack, you should adjust this setting accordingly with the	1330	has a smaller stack, you should adjust this setting accordingly with the
1166	C<max_depth> method.	1331	C<max_depth> method.
1167		1332
1168	And last but least, something else could bomb you that I forgot to think	1333	Something else could bomb you, too, that I forgot to think of. In that
1169	of. In that case, you get to keep the pieces. I am always open for hints,	1334	case, you get to keep the pieces. I am always open for hints, though...
1170	though...	1335
		1336	Also keep in mind that JSON::XS might leak contents of your Perl data
		1337	structures in its error messages, so when you serialise sensitive
		1338	information you might want to make sure that exceptions thrown by JSON::XS
		1339	will not end up in front of untrusted eyes.
1171		1340
1172	If you are using JSON::XS to return packets to consumption	1341	If you are using JSON::XS to return packets to consumption
1173	by JavaScript scripts in a browser you should have a look at	1342	by JavaScript scripts in a browser you should have a look at
1174	L<http://jpsykes.com/47/practical-csrf-and-json-security> to see whether	1343	L<http://jpsykes.com/47/practical-csrf-and-json-security> to see whether
1175	you are vulnerable to some common attack vectors (which really are browser	1344	you are vulnerable to some common attack vectors (which really are browser
…		…
1181	=head1 THREADS	1350	=head1 THREADS
1182		1351
1183	This module is I<not> guaranteed to be thread safe and there are no	1352	This module is I<not> guaranteed to be thread safe and there are no
1184	plans to change this until Perl gets thread support (as opposed to the	1353	plans to change this until Perl gets thread support (as opposed to the
1185	horribly slow so-called "threads" which are simply slow and bloated	1354	horribly slow so-called "threads" which are simply slow and bloated
1186	process simulations - use fork, its I<much> faster, cheaper, better).	1355	process simulations - use fork, it's I<much> faster, cheaper, better).
1187		1356
1188	(It might actually work, but you have been warned).	1357	(It might actually work, but you have been warned).
1189		1358
1190		1359
1191	=head1 BUGS	1360	=head1 BUGS
1192		1361
1193	While the goal of this module is to be correct, that unfortunately does	1362	While the goal of this module is to be correct, that unfortunately does
1194	not mean its bug-free, only that I think its design is bug-free. It is	1363	not mean it's bug-free, only that I think its design is bug-free. If you
1195	still relatively early in its development. If you keep reporting bugs they	1364	keep reporting bugs they will be fixed swiftly, though.
1196	will be fixed swiftly, though.
1197		1365
1198	Please refrain from using rt.cpan.org or any other bug reporting	1366	Please refrain from using rt.cpan.org or any other bug reporting
1199	service. I put the contact address into my modules for a reason.	1367	service. I put the contact address into my modules for a reason.
1200		1368
1201	=cut	1369	=cut
…		…
1221	"--" => sub { $_[0] = ${$_[0]} - 1 },	1389	"--" => sub { $_[0] = ${$_[0]} - 1 },
1222	fallback => 1;	1390	fallback => 1;
1223		1391
1224	1;	1392	1;
1225		1393
		1394	=head1 SEE ALSO
		1395
		1396	The F<json_xs> command line utility for quick experiments.
		1397
1226	=head1 AUTHOR	1398	=head1 AUTHOR
1227		1399
1228	Marc Lehmann <schmorp@schmorp.de>	1400	Marc Lehmann <schmorp@schmorp.de>
1229	http://home.schmorp.de/	1401	http://home.schmorp.de/
1230		1402

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Revision 1.110 by root, Sun Jul 20 17:55:19 2008 UTC