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

Comparing JSON-XS/XS.pm (file contents):
Revision 1.104 by root, Thu May 8 15:33:06 2008 UTC vs.
Revision 1.159 by root, Wed Sep 7 17:14:56 2016 UTC

…		…
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
…		…
49	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
50	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
51	their maintainers are unresponsive, gone missing, or not listening to bug	51	their maintainers are unresponsive, gone missing, or not listening to bug
52	reports for other reasons.	52	reports for other reasons.
53		53
54	See COMPARISON, below, for a comparison to some other JSON modules.
55
56	See MAPPING, below, on how JSON::XS maps perl values to JSON values and	54	See MAPPING, below, on how JSON::XS maps perl values to JSON values and
57	vice versa.	55	vice versa.
58		56
59	=head2 FEATURES	57	=head2 FEATURES
60		58
…		…
65	This module knows how to handle Unicode, documents how and when it does	63	This module knows how to handle Unicode, documents how and when it does
66	so, and even documents what "correct" means.	64	so, and even documents what "correct" means.
67		65
68	=item * round-trip integrity	66	=item * round-trip integrity
69		67
70	When you serialise a perl data structure using only datatypes supported	68	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.	69	by JSON and Perl, the deserialised data structure is identical on the Perl
72	(e.g. the string "2.0" doesn't suddenly become "2" just because it looks	70	level. (e.g. the string "2.0" doesn't suddenly become "2" just because
73	like a number). There minor I<are> exceptions to this, read the MAPPING	71	it looks like a number). There I<are> minor exceptions to this, read the
74	section below to learn about those.	72	MAPPING section below to learn about those.
75		73
76	=item * strict checking of JSON correctness	74	=item * strict checking of JSON correctness
77		75
78	There is no guessing, no generating of illegal JSON texts by default,	76	There is no guessing, no generating of illegal JSON texts by default,
79	and only JSON is accepted as input by default (the latter is a security	77	and only JSON is accepted as input by default (the latter is a security
…		…
84	Compared to other JSON modules and other serialisers such as Storable,	82	Compared to other JSON modules and other serialisers such as Storable,
85	this module usually compares favourably in terms of speed, too.	83	this module usually compares favourably in terms of speed, too.
86		84
87	=item * simple to use	85	=item * simple to use
88		86
89	This module has both a simple functional interface as well as an objetc	87	This module has both a simple functional interface as well as an object
90	oriented interface interface.	88	oriented interface.
91		89
92	=item * reasonably versatile output formats	90	=item * reasonably versatile output formats
93		91
94	You can choose between the most compact guaranteed-single-line format	92	You can choose between the most compact guaranteed-single-line format
95	possible (nice for simple line-based protocols), a pure-ascii format	93	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	94	(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	95	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.	96	stuff). Or you can combine those features in whatever way you like.
99		97
100	=back	98	=back
101		99
102	=cut	100	=cut
103		101
104	package JSON::XS;	102	package JSON::XS;
105		103
106	use strict;	104	use common::sense;
107		105
108	our $VERSION = '2.2';	106	our $VERSION = 3.02;
109	our @ISA = qw(Exporter);	107	our @ISA = qw(Exporter);
110		108
111	our @EXPORT = qw(encode_json decode_json to_json from_json);	109	our @EXPORT = qw(encode_json decode_json);
112
113	sub to_json($) {
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	}
122		110
123	use Exporter;	111	use Exporter;
124	use XSLoader;	112	use XSLoader;
125		113
		114	use Types::Serialiser ();
		115
126	=head1 FUNCTIONAL INTERFACE	116	=head1 FUNCTIONAL INTERFACE
127		117
128	The following convenience methods are provided by this module. They are	118	The following convenience methods are provided by this module. They are
129	exported by default:	119	exported by default:
130		120
…		…
137		127
138	This function call is functionally identical to:	128	This function call is functionally identical to:
139		129
140	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)	130	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)
141		131
142	except being faster.	132	Except being faster.
143		133
144	=item $perl_scalar = decode_json $json_text	134	=item $perl_scalar = decode_json $json_text
145		135
146	The opposite of C<encode_json>: expects an UTF-8 (binary) string and tries	136	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	137	to parse that as an UTF-8 encoded JSON text, returning the resulting
…		…
149		139
150	This function call is functionally identical to:	140	This function call is functionally identical to:
151		141
152	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)	142	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)
153		143
154	except being faster.	144	Except being faster.
155
156	=item $is_boolean = JSON::XS::is_bool $scalar
157
158	Returns true if the passed scalar represents either JSON::XS::true or
159	JSON::XS::false, two constants that act like C<1> and C<0>, respectively
160	and are used to represent JSON C<true> and C<false> values in Perl.
161
162	See MAPPING, below, for more information on how JSON values are mapped to
163	Perl.
164		145
165	=back	146	=back
166		147
167		148
168	=head1 A FEW NOTES ON UNICODE AND PERL	149	=head1 A FEW NOTES ON UNICODE AND PERL
…		…
197		178
198	If you didn't know about that flag, just the better, pretend it doesn't	179	If you didn't know about that flag, just the better, pretend it doesn't
199	exist.	180	exist.
200		181
201	=item 4. A "Unicode String" is simply a string where each character can be	182	=item 4. A "Unicode String" is simply a string where each character can be
202	validly interpreted as a Unicode codepoint.	183	validly interpreted as a Unicode code point.
203		184
204	If you have UTF-8 encoded data, it is no longer a Unicode string, but a	185	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.	186	Unicode string encoded in UTF-8, giving you a binary string.
206		187
207	=item 5. A string containing "high" (> 255) character values is I<not> a UTF-8 string.	188	=item 5. A string containing "high" (> 255) character values is I<not> a UTF-8 string.
…		…
423	[	404	[
424	1, # this comment not allowed in JSON	405	1, # this comment not allowed in JSON
425	# neither this one...	406	# neither this one...
426	]	407	]
427		408
		409	=item * literal ASCII TAB characters in strings
		410
		411	Literal ASCII TAB characters are now allowed in strings (and treated as
		412	C<\t>).
		413
		414	[
		415	"Hello\tWorld",
		416	"Hello<TAB>World", # literal <TAB> would not normally be allowed
		417	]
		418
428	=back	419	=back
429		420
430	=item $json = $json->canonical ([$enable])	421	=item $json = $json->canonical ([$enable])
431		422
432	=item $enabled = $json->get_canonical	423	=item $enabled = $json->get_canonical
…		…
434	If C<$enable> is true (or missing), then the C<encode> method will output JSON objects	425	If C<$enable> is true (or missing), then the C<encode> method will output JSON objects
435	by sorting their keys. This is adding a comparatively high overhead.	426	by sorting their keys. This is adding a comparatively high overhead.
436		427
437	If C<$enable> is false, then the C<encode> method will output key-value	428	If C<$enable> is false, then the C<encode> method will output key-value
438	pairs in the order Perl stores them (which will likely change between runs	429	pairs in the order Perl stores them (which will likely change between runs
439	of the same script).	430	of the same script, and can change even within the same run from 5.18
		431	onwards).
440		432
441	This option is useful if you want the same data structure to be encoded as	433	This option is useful if you want the same data structure to be encoded as
442	the same JSON text (given the same overall settings). If it is disabled,	434	the same JSON text (given the same overall settings). If it is disabled,
443	the same hash might be encoded differently even if contains the same data,	435	the same hash might be encoded differently even if contains the same data,
444	as key-value pairs have no inherent ordering in Perl.	436	as key-value pairs have no inherent ordering in Perl.
445		437
446	This setting has no effect when decoding JSON texts.	438	This setting has no effect when decoding JSON texts.
		439
		440	This setting has currently no effect on tied hashes.
447		441
448	=item $json = $json->allow_nonref ([$enable])	442	=item $json = $json->allow_nonref ([$enable])
449		443
450	=item $enabled = $json->get_allow_nonref	444	=item $enabled = $json->get_allow_nonref
451		445
…		…
483		477
484	=item $json = $json->allow_blessed ([$enable])	478	=item $json = $json->allow_blessed ([$enable])
485		479
486	=item $enabled = $json->get_allow_blessed	480	=item $enabled = $json->get_allow_blessed
487		481
		482	See L<OBJECT SERIALISATION> for details.
		483
488	If C<$enable> is true (or missing), then the C<encode> method will not	484	If C<$enable> is true (or missing), then the C<encode> method will not
489	barf when it encounters a blessed reference. Instead, the value of the	485	barf when it encounters a blessed reference that it cannot convert
490	B<convert_blessed> option will decide whether C<null> (C<convert_blessed>	486	otherwise. Instead, a JSON C<null> value is encoded instead of the object.
491	disabled or no C<TO_JSON> method found) or a representation of the
492	object (C<convert_blessed> enabled and C<TO_JSON> method found) is being
493	encoded. Has no effect on C<decode>.
494		487
495	If C<$enable> is false (the default), then C<encode> will throw an	488	If C<$enable> is false (the default), then C<encode> will throw an
496	exception when it encounters a blessed object.	489	exception when it encounters a blessed object that it cannot convert
		490	otherwise.
		491
		492	This setting has no effect on C<decode>.
497		493
498	=item $json = $json->convert_blessed ([$enable])	494	=item $json = $json->convert_blessed ([$enable])
499		495
500	=item $enabled = $json->get_convert_blessed	496	=item $enabled = $json->get_convert_blessed
		497
		498	See L<OBJECT SERIALISATION> for details.
501		499
502	If C<$enable> is true (or missing), then C<encode>, upon encountering a	500	If C<$enable> is true (or missing), then C<encode>, upon encountering a
503	blessed object, will check for the availability of the C<TO_JSON> method	501	blessed object, will check for the availability of the C<TO_JSON> method
504	on the object's class. If found, it will be called in scalar context	502	on the object's class. If found, it will be called in scalar context and
505	and the resulting scalar will be encoded instead of the object. If no	503	the resulting scalar will be encoded instead of the object.
506	C<TO_JSON> method is found, the value of C<allow_blessed> will decide what
507	to do.
508		504
509	The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON>	505	The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON>
510	returns other blessed objects, those will be handled in the same	506	returns other blessed objects, those will be handled in the same
511	way. C<TO_JSON> must take care of not causing an endless recursion cycle	507	way. C<TO_JSON> must take care of not causing an endless recursion cycle
512	(== crash) in this case. The name of C<TO_JSON> was chosen because other	508	(== crash) in this case. The name of C<TO_JSON> was chosen because other
513	methods called by the Perl core (== not by the user of the object) are	509	methods called by the Perl core (== not by the user of the object) are
514	usually in upper case letters and to avoid collisions with any C<to_json>	510	usually in upper case letters and to avoid collisions with any C<to_json>
515	function or method.	511	function or method.
516		512
517	This setting does not yet influence C<decode> in any way, but in the	513	If C<$enable> is false (the default), then C<encode> will not consider
518	future, global hooks might get installed that influence C<decode> and are	514	this type of conversion.
519	enabled by this setting.
520		515
521	If C<$enable> is false, then the C<allow_blessed> setting will decide what	516	This setting has no effect on C<decode>.
522	to do when a blessed object is found.	517
		518	=item $json = $json->allow_tags ([$enable])
		519
		520	=item $enabled = $json->allow_tags
		521
		522	See L<OBJECT SERIALISATION> for details.
		523
		524	If C<$enable> is true (or missing), then C<encode>, upon encountering a
		525	blessed object, will check for the availability of the C<FREEZE> method on
		526	the object's class. If found, it will be used to serialise the object into
		527	a nonstandard tagged JSON value (that JSON decoders cannot decode).
		528
		529	It also causes C<decode> to parse such tagged JSON values and deserialise
		530	them via a call to the C<THAW> method.
		531
		532	If C<$enable> is false (the default), then C<encode> will not consider
		533	this type of conversion, and tagged JSON values will cause a parse error
		534	in C<decode>, as if tags were not part of the grammar.
523		535
524	=item $json = $json->filter_json_object ([$coderef->($hashref)])	536	=item $json = $json->filter_json_object ([$coderef->($hashref)])
525		537
526	When C<$coderef> is specified, it will be called from C<decode> each	538	When C<$coderef> is specified, it will be called from C<decode> each
527	time it decodes a JSON object. The only argument is a reference to the	539	time it decodes a JSON object. The only argument is a reference to the
…		…
666		678
667	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.	679	See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
668		680
669	=item $json_text = $json->encode ($perl_scalar)	681	=item $json_text = $json->encode ($perl_scalar)
670		682
671	Converts the given Perl data structure (a simple scalar or a reference	683	Converts the given Perl value or data structure to its JSON
672	to a hash or array) to its JSON representation. Simple scalars will be	684	representation. Croaks on error.
673	converted into JSON string or number sequences, while references to arrays
674	become JSON arrays and references to hashes become JSON objects. Undefined
675	Perl values (e.g. C<undef>) become JSON C<null> values. Neither C<true>
676	nor C<false> values will be generated.
677		685
678	=item $perl_scalar = $json->decode ($json_text)	686	=item $perl_scalar = $json->decode ($json_text)
679		687
680	The opposite of C<encode>: expects a JSON text and tries to parse it,	688	The opposite of C<encode>: expects a JSON text and tries to parse it,
681	returning the resulting simple scalar or reference. Croaks on error.	689	returning the resulting simple scalar or reference. Croaks on error.
682
683	JSON numbers and strings become simple Perl scalars. JSON arrays become
684	Perl arrayrefs and JSON objects become Perl hashrefs. C<true> becomes
685	C<1>, C<false> becomes C<0> and C<null> becomes C<undef>.
686		690
687	=item ($perl_scalar, $characters) = $json->decode_prefix ($json_text)	691	=item ($perl_scalar, $characters) = $json->decode_prefix ($json_text)
688		692
689	This works like the C<decode> method, but instead of raising an exception	693	This works like the C<decode> method, but instead of raising an exception
690	when there is trailing garbage after the first JSON object, it will	694	when there is trailing garbage after the first JSON object, it will
691	silently stop parsing there and return the number of characters consumed	695	silently stop parsing there and return the number of characters consumed
692	so far.	696	so far.
693		697
694	This is useful if your JSON texts are not delimited by an outer protocol	698	This is useful if your JSON texts are not delimited by an outer protocol
695	(which is not the brightest thing to do in the first place) and you need
696	to know where the JSON text ends.	699	and you need to know where the JSON text ends.
697		700
698	JSON::XS->new->decode_prefix ("[1] the tail")	701	JSON::XS->new->decode_prefix ("[1] the tail")
699	=> ([], 3)	702	=> ([1], 3)
700		703
701	=back	704	=back
702		705
703		706
704	=head1 INCREMENTAL PARSING	707	=head1 INCREMENTAL PARSING
705
706	[This section and the API it details is still EXPERIMENTAL]
707		708
708	In some cases, there is the need for incremental parsing of JSON	709	In some cases, there is the need for incremental parsing of JSON
709	texts. While this module always has to keep both JSON text and resulting	710	texts. While this module always has to keep both JSON text and resulting
710	Perl data structure in memory at one time, it does allow you to parse a	711	Perl data structure in memory at one time, it does allow you to parse a
711	JSON stream incrementally. It does so by accumulating text until it has	712	JSON stream incrementally. It does so by accumulating text until it has
712	a full JSON object, which it then can decode. This process is similar to	713	a full JSON object, which it then can decode. This process is similar to
713	using C<decode_prefix> to see if a full JSON object is available, but is	714	using C<decode_prefix> to see if a full JSON object is available, but
714	much more efficient (JSON::XS will only attempt to parse the JSON text	715	is much more efficient (and can be implemented with a minimum of method
		716	calls).
		717
		718	JSON::XS will only attempt to parse the JSON text once it is sure it
715	once it is sure it has enough text to get a decisive result, using a very	719	has enough text to get a decisive result, using a very simple but
716	simple but truly incremental parser).	720	truly incremental parser. This means that it sometimes won't stop as
		721	early as the full parser, for example, it doesn't detect mismatched
		722	parentheses. The only thing it guarantees is that it starts decoding as
		723	soon as a syntactically valid JSON text has been seen. This means you need
		724	to set resource limits (e.g. C<max_size>) to ensure the parser will stop
		725	parsing in the presence if syntax errors.
717		726
718	The following two methods deal with this.	727	The following methods implement this incremental parser.
719		728
720	=over 4	729	=over 4
721		730
722	=item [void, scalar or list context] = $json->incr_parse ([$string])	731	=item [void, scalar or list context] = $json->incr_parse ([$string])
723		732
…		…
734		743
735	If the method is called in scalar context, then it will try to extract	744	If the method is called in scalar context, then it will try to extract
736	exactly I<one> JSON object. If that is successful, it will return this	745	exactly I<one> JSON object. If that is successful, it will return this
737	object, otherwise it will return C<undef>. If there is a parse error,	746	object, otherwise it will return C<undef>. If there is a parse error,
738	this method will croak just as C<decode> would do (one can then use	747	this method will croak just as C<decode> would do (one can then use
739	C<incr_skip> to skip the errornous part). This is the most common way of	748	C<incr_skip> to skip the erroneous part). This is the most common way of
740	using the method.	749	using the method.
741		750
742	And finally, in list context, it will try to extract as many objects	751	And finally, in list context, it will try to extract as many objects
743	from the stream as it can find and return them, or the empty list	752	from the stream as it can find and return them, or the empty list
744	otherwise. For this to work, there must be no separators between the JSON	753	otherwise. For this to work, there must be no separators (other than
745	objects or arrays, instead they must be concatenated back-to-back. If	754	whitespace) between the JSON objects or arrays, instead they must be
746	an error occurs, an exception will be raised as in the scalar context	755	concatenated back-to-back. If an error occurs, an exception will be
747	case. Note that in this case, any previously-parsed JSON texts will be	756	raised as in the scalar context case. Note that in this case, any
748	lost.	757	previously-parsed JSON texts will be lost.
		758
		759	Example: Parse some JSON arrays/objects in a given string and return
		760	them.
		761
		762	my @objs = JSON::XS->new->incr_parse ("[5][7][1,2]");
749		763
750	=item $lvalue_string = $json->incr_text	764	=item $lvalue_string = $json->incr_text
751		765
752	This method returns the currently stored JSON fragment as an lvalue, that	766	This method returns the currently stored JSON fragment as an lvalue, that
753	is, you can manipulate it. This I<only> works when a preceding call to	767	is, you can manipulate it. This I<only> works when a preceding call to
…		…
761	JSON object or b) parsing multiple JSON objects separated by non-JSON text	775	JSON object or b) parsing multiple JSON objects separated by non-JSON text
762	(such as commas).	776	(such as commas).
763		777
764	=item $json->incr_skip	778	=item $json->incr_skip
765		779
766	This will reset the state of the incremental parser and will remove the	780	This will reset the state of the incremental parser and will remove
767	parsed text from the input buffer. This is useful after C<incr_parse>	781	the parsed text from the input buffer so far. This is useful after
768	died, in which case the input buffer and incremental parser state is left	782	C<incr_parse> died, in which case the input buffer and incremental parser
769	unchanged, to skip the text parsed so far and to reset the parse state.	783	state is left unchanged, to skip the text parsed so far and to reset the
		784	parse state.
		785
		786	The difference to C<incr_reset> is that only text until the parse error
		787	occurred is removed.
		788
		789	=item $json->incr_reset
		790
		791	This completely resets the incremental parser, that is, after this call,
		792	it will be as if the parser had never parsed anything.
		793
		794	This is useful if you want to repeatedly parse JSON objects and want to
		795	ignore any trailing data, which means you have to reset the parser after
		796	each successful decode.
770		797
771	=back	798	=back
772		799
773	=head2 LIMITATIONS	800	=head2 LIMITATIONS
774		801
775	All options that affect decoding are supported, except	802	All options that affect decoding are supported, except
776	C<allow_nonref>. The reason for this is that it cannot be made to	803	C<allow_nonref>. The reason for this is that it cannot be made to work
777	work sensibly: JSON objects and arrays are self-delimited, i.e. you can concatenate	804	sensibly: JSON objects and arrays are self-delimited, i.e. you can
778	them back to back and still decode them perfectly. This does not hold true	805	concatenate them back to back and still decode them perfectly. This does
779	for JSON numbers, however.	806	not hold true for JSON numbers, however.
780		807
781	For example, is the string C<1> a single JSON number, or is it simply the	808	For example, is the string C<1> a single JSON number, or is it simply the
782	start of C<12>? Or is C<12> a single JSON number, or the concatenation	809	start of C<12>? Or is C<12> a single JSON number, or the concatenation
783	of C<1> and C<2>? In neither case you can tell, and this is why JSON::XS	810	of C<1> and C<2>? In neither case you can tell, and this is why JSON::XS
784	takes the conservative route and disallows this case.	811	takes the conservative route and disallows this case.
…		…
963	If the number consists of digits only, JSON::XS will try to represent	990	If the number consists of digits only, JSON::XS will try to represent
964	it as an integer value. If that fails, it will try to represent it as	991	it as an integer value. If that fails, it will try to represent it as
965	a numeric (floating point) value if that is possible without loss of	992	a numeric (floating point) value if that is possible without loss of
966	precision. Otherwise it will preserve the number as a string value (in	993	precision. Otherwise it will preserve the number as a string value (in
967	which case you lose roundtripping ability, as the JSON number will be	994	which case you lose roundtripping ability, as the JSON number will be
968	re-encoded toa JSON string).	995	re-encoded to a JSON string).
969		996
970	Numbers containing a fractional or exponential part will always be	997	Numbers containing a fractional or exponential part will always be
971	represented as numeric (floating point) values, possibly at a loss of	998	represented as numeric (floating point) values, possibly at a loss of
972	precision (in which case you might lose perfect roundtripping ability, but	999	precision (in which case you might lose perfect roundtripping ability, but
973	the JSON number will still be re-encoded as a JSON number).	1000	the JSON number will still be re-encoded as a JSON number).
974		1001
		1002	Note that precision is not accuracy - binary floating point values cannot
		1003	represent most decimal fractions exactly, and when converting from and to
		1004	floating point, JSON::XS only guarantees precision up to but not including
		1005	the least significant bit.
		1006
975	=item true, false	1007	=item true, false
976		1008
977	These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>,	1009	These JSON atoms become C<Types::Serialiser::true> and
978	respectively. They are overloaded to act almost exactly like the numbers	1010	C<Types::Serialiser::false>, respectively. They are overloaded to act
979	C<1> and C<0>. You can check whether a scalar is a JSON boolean by using	1011	almost exactly like the numbers C<1> and C<0>. You can check whether
980	the C<JSON::XS::is_bool> function.	1012	a scalar is a JSON boolean by using the C<Types::Serialiser::is_bool>
		1013	function (after C<use Types::Serialier>, of course).
981		1014
982	=item null	1015	=item null
983		1016
984	A JSON null atom becomes C<undef> in Perl.	1017	A JSON null atom becomes C<undef> in Perl.
		1018
		1019	=item shell-style comments (C<< # I<text> >>)
		1020
		1021	As a nonstandard extension to the JSON syntax that is enabled by the
		1022	C<relaxed> setting, shell-style comments are allowed. They can start
		1023	anywhere outside strings and go till the end of the line.
		1024
		1025	=item tagged values (C<< (I<tag>)I<value> >>).
		1026
		1027	Another nonstandard extension to the JSON syntax, enabled with the
		1028	C<allow_tags> setting, are tagged values. In this implementation, the
		1029	I<tag> must be a perl package/class name encoded as a JSON string, and the
		1030	I<value> must be a JSON array encoding optional constructor arguments.
		1031
		1032	See L<OBJECT SERIALISATION>, below, for details.
985		1033
986	=back	1034	=back
987		1035
988		1036
989	=head2 PERL -> JSON	1037	=head2 PERL -> JSON
…		…
994		1042
995	=over 4	1043	=over 4
996		1044
997	=item hash references	1045	=item hash references
998		1046
999	Perl hash references become JSON objects. As there is no inherent ordering	1047	Perl hash references become JSON objects. As there is no inherent
1000	in hash keys (or JSON objects), they will usually be encoded in a	1048	ordering in hash keys (or JSON objects), they will usually be encoded
1001	pseudo-random order that can change between runs of the same program but	1049	in a pseudo-random order. JSON::XS can optionally sort the hash keys
1002	stays generally the same within a single run of a program. JSON::XS can	1050	(determined by the I<canonical> flag), so the same datastructure will
1003	optionally sort the hash keys (determined by the I<canonical> flag), so	1051	serialise to the same JSON text (given same settings and version of
1004	the same datastructure will serialise to the same JSON text (given same	1052	JSON::XS), but this incurs a runtime overhead and is only rarely useful,
1005	settings and version of JSON::XS), but this incurs a runtime overhead	1053	e.g. when you want to compare some JSON text against another for equality.
1006	and is only rarely useful, e.g. when you want to compare some JSON text
1007	against another for equality.
1008		1054
1009	=item array references	1055	=item array references
1010		1056
1011	Perl array references become JSON arrays.	1057	Perl array references become JSON arrays.
1012		1058
1013	=item other references	1059	=item other references
1014		1060
1015	Other unblessed references are generally not allowed and will cause an	1061	Other unblessed references are generally not allowed and will cause an
1016	exception to be thrown, except for references to the integers C<0> and	1062	exception to be thrown, except for references to the integers C<0> and
1017	C<1>, which get turned into C<false> and C<true> atoms in JSON. You can	1063	C<1>, which get turned into C<false> and C<true> atoms in JSON.
1018	also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability.
1019		1064
		1065	Since C<JSON::XS> uses the boolean model from L<Types::Serialiser>, you
		1066	can also C<use Types::Serialiser> and then use C<Types::Serialiser::false>
		1067	and C<Types::Serialiser::true> to improve readability.
		1068
		1069	use Types::Serialiser;
1020	encode_json [\0, JSON::XS::true] # yields [false,true]	1070	encode_json [\0, Types::Serialiser::true] # yields [false,true]
1021		1071
1022	=item JSON::XS::true, JSON::XS::false	1072	=item Types::Serialiser::true, Types::Serialiser::false
1023		1073
1024	These special values become JSON true and JSON false values,	1074	These special values from the L<Types::Serialiser> module become JSON true
1025	respectively. You can also use C<\1> and C<\0> directly if you want.	1075	and JSON false values, respectively. You can also use C<\1> and C<\0>
		1076	directly if you want.
1026		1077
1027	=item blessed objects	1078	=item blessed objects
1028		1079
1029	Blessed objects are not directly representable in JSON. See the	1080	Blessed objects are not directly representable in JSON, but C<JSON::XS>
1030	C<allow_blessed> and C<convert_blessed> methods on various options on	1081	allows various ways of handling objects. See L<OBJECT SERIALISATION>,
1031	how to deal with this: basically, you can choose between throwing an	1082	below, for details.
1032	exception, encoding the reference as if it weren't blessed, or provide
1033	your own serialiser method.
1034		1083
1035	=item simple scalars	1084	=item simple scalars
1036		1085
1037	Simple Perl scalars (any scalar that is not a reference) are the most	1086	Simple Perl scalars (any scalar that is not a reference) are the most
1038	difficult objects to encode: JSON::XS will encode undefined scalars as	1087	difficult objects to encode: JSON::XS will encode undefined scalars as
…		…
1066		1115
1067	You can not currently force the type in other, less obscure, ways. Tell me	1116	You can not currently force the type in other, less obscure, ways. Tell me
1068	if you need this capability (but don't forget to explain why it's needed	1117	if you need this capability (but don't forget to explain why it's needed
1069	:).	1118	:).
1070		1119
		1120	Note that numerical precision has the same meaning as under Perl (so
		1121	binary to decimal conversion follows the same rules as in Perl, which
		1122	can differ to other languages). Also, your perl interpreter might expose
		1123	extensions to the floating point numbers of your platform, such as
		1124	infinities or NaN's - these cannot be represented in JSON, and it is an
		1125	error to pass those in.
		1126
1071	=back	1127	=back
		1128
		1129	=head2 OBJECT SERIALISATION
		1130
		1131	As JSON cannot directly represent Perl objects, you have to choose between
		1132	a pure JSON representation (without the ability to deserialise the object
		1133	automatically again), and a nonstandard extension to the JSON syntax,
		1134	tagged values.
		1135
		1136	=head3 SERIALISATION
		1137
		1138	What happens when C<JSON::XS> encounters a Perl object depends on the
		1139	C<allow_blessed>, C<convert_blessed> and C<allow_tags> settings, which are
		1140	used in this order:
		1141
		1142	=over 4
		1143
		1144	=item 1. C<allow_tags> is enabled and the object has a C<FREEZE> method.
		1145
		1146	In this case, C<JSON::XS> uses the L<Types::Serialiser> object
		1147	serialisation protocol to create a tagged JSON value, using a nonstandard
		1148	extension to the JSON syntax.
		1149
		1150	This works by invoking the C<FREEZE> method on the object, with the first
		1151	argument being the object to serialise, and the second argument being the
		1152	constant string C<JSON> to distinguish it from other serialisers.
		1153
		1154	The C<FREEZE> method can return any number of values (i.e. zero or
		1155	more). These values and the paclkage/classname of the object will then be
		1156	encoded as a tagged JSON value in the following format:
		1157
		1158	("classname")[FREEZE return values...]
		1159
		1160	e.g.:
		1161
		1162	("URI")["http://www.google.com/"]
		1163	("MyDate")[2013,10,29]
		1164	("ImageData::JPEG")["Z3...VlCg=="]
		1165
		1166	For example, the hypothetical C<My::Object> C<FREEZE> method might use the
		1167	objects C<type> and C<id> members to encode the object:
		1168
		1169	sub My::Object::FREEZE {
		1170	my ($self, $serialiser) = @_;
		1171
		1172	($self->{type}, $self->{id})
		1173	}
		1174
		1175	=item 2. C<convert_blessed> is enabled and the object has a C<TO_JSON> method.
		1176
		1177	In this case, the C<TO_JSON> method of the object is invoked in scalar
		1178	context. It must return a single scalar that can be directly encoded into
		1179	JSON. This scalar replaces the object in the JSON text.
		1180
		1181	For example, the following C<TO_JSON> method will convert all L<URI>
		1182	objects to JSON strings when serialised. The fatc that these values
		1183	originally were L<URI> objects is lost.
		1184
		1185	sub URI::TO_JSON {
		1186	my ($uri) = @_;
		1187	$uri->as_string
		1188	}
		1189
		1190	=item 3. C<allow_blessed> is enabled.
		1191
		1192	The object will be serialised as a JSON null value.
		1193
		1194	=item 4. none of the above
		1195
		1196	If none of the settings are enabled or the respective methods are missing,
		1197	C<JSON::XS> throws an exception.
		1198
		1199	=back
		1200
		1201	=head3 DESERIALISATION
		1202
		1203	For deserialisation there are only two cases to consider: either
		1204	nonstandard tagging was used, in which case C<allow_tags> decides,
		1205	or objects cannot be automatically be deserialised, in which
		1206	case you can use postprocessing or the C<filter_json_object> or
		1207	C<filter_json_single_key_object> callbacks to get some real objects our of
		1208	your JSON.
		1209
		1210	This section only considers the tagged value case: I a tagged JSON object
		1211	is encountered during decoding and C<allow_tags> is disabled, a parse
		1212	error will result (as if tagged values were not part of the grammar).
		1213
		1214	If C<allow_tags> is enabled, C<JSON::XS> will look up the C<THAW> method
		1215	of the package/classname used during serialisation (it will not attempt
		1216	to load the package as a Perl module). If there is no such method, the
		1217	decoding will fail with an error.
		1218
		1219	Otherwise, the C<THAW> method is invoked with the classname as first
		1220	argument, the constant string C<JSON> as second argument, and all the
		1221	values from the JSON array (the values originally returned by the
		1222	C<FREEZE> method) as remaining arguments.
		1223
		1224	The method must then return the object. While technically you can return
		1225	any Perl scalar, you might have to enable the C<enable_nonref> setting to
		1226	make that work in all cases, so better return an actual blessed reference.
		1227
		1228	As an example, let's implement a C<THAW> function that regenerates the
		1229	C<My::Object> from the C<FREEZE> example earlier:
		1230
		1231	sub My::Object::THAW {
		1232	my ($class, $serialiser, $type, $id) = @_;
		1233
		1234	$class->new (type => $type, id => $id)
		1235	}
1072		1236
1073		1237
1074	=head1 ENCODING/CODESET FLAG NOTES	1238	=head1 ENCODING/CODESET FLAG NOTES
1075		1239
1076	The interested reader might have seen a number of flags that signify	1240	The interested reader might have seen a number of flags that signify
…		…
1101	=item C<utf8> flag disabled	1265	=item C<utf8> flag disabled
1102		1266
1103	When C<utf8> is disabled (the default), then C<encode>/C<decode> generate	1267	When C<utf8> is disabled (the default), then C<encode>/C<decode> generate
1104	and expect Unicode strings, that is, characters with high ordinal Unicode	1268	and expect Unicode strings, that is, characters with high ordinal Unicode
1105	values (> 255) will be encoded as such characters, and likewise such	1269	values (> 255) will be encoded as such characters, and likewise such
1106	characters are decoded as-is, no canges to them will be done, except	1270	characters are decoded as-is, no changes to them will be done, except
1107	"(re-)interpreting" them as Unicode codepoints or Unicode characters,	1271	"(re-)interpreting" them as Unicode codepoints or Unicode characters,
1108	respectively (to Perl, these are the same thing in strings unless you do	1272	respectively (to Perl, these are the same thing in strings unless you do
1109	funny/weird/dumb stuff).	1273	funny/weird/dumb stuff).
1110		1274
1111	This is useful when you want to do the encoding yourself (e.g. when you	1275	This is useful when you want to do the encoding yourself (e.g. when you
…		…
1167	proper subset of most 8-bit and multibyte encodings in use in the world.	1331	proper subset of most 8-bit and multibyte encodings in use in the world.
1168		1332
1169	=back	1333	=back
1170		1334
1171		1335
		1336	=head2 JSON and ECMAscript
		1337
		1338	JSON syntax is based on how literals are represented in javascript (the
		1339	not-standardised predecessor of ECMAscript) which is presumably why it is
		1340	called "JavaScript Object Notation".
		1341
		1342	However, JSON is not a subset (and also not a superset of course) of
		1343	ECMAscript (the standard) or javascript (whatever browsers actually
		1344	implement).
		1345
		1346	If you want to use javascript's C<eval> function to "parse" JSON, you
		1347	might run into parse errors for valid JSON texts, or the resulting data
		1348	structure might not be queryable:
		1349
		1350	One of the problems is that U+2028 and U+2029 are valid characters inside
		1351	JSON strings, but are not allowed in ECMAscript string literals, so the
		1352	following Perl fragment will not output something that can be guaranteed
		1353	to be parsable by javascript's C<eval>:
		1354
		1355	use JSON::XS;
		1356
		1357	print encode_json [chr 0x2028];
		1358
		1359	The right fix for this is to use a proper JSON parser in your javascript
		1360	programs, and not rely on C<eval> (see for example Douglas Crockford's
		1361	F<json2.js> parser).
		1362
		1363	If this is not an option, you can, as a stop-gap measure, simply encode to
		1364	ASCII-only JSON:
		1365
		1366	use JSON::XS;
		1367
		1368	print JSON::XS->new->ascii->encode ([chr 0x2028]);
		1369
		1370	Note that this will enlarge the resulting JSON text quite a bit if you
		1371	have many non-ASCII characters. You might be tempted to run some regexes
		1372	to only escape U+2028 and U+2029, e.g.:
		1373
		1374	# DO NOT USE THIS!
		1375	my $json = JSON::XS->new->utf8->encode ([chr 0x2028]);
		1376	$json =~ s/\xe2\x80\xa8/\\u2028/g; # escape U+2028
		1377	$json =~ s/\xe2\x80\xa9/\\u2029/g; # escape U+2029
		1378	print $json;
		1379
		1380	Note that I<this is a bad idea>: the above only works for U+2028 and
		1381	U+2029 and thus only for fully ECMAscript-compliant parsers. Many existing
		1382	javascript implementations, however, have issues with other characters as
		1383	well - using C<eval> naively simply I<will> cause problems.
		1384
		1385	Another problem is that some javascript implementations reserve
		1386	some property names for their own purposes (which probably makes
		1387	them non-ECMAscript-compliant). For example, Iceweasel reserves the
		1388	C<__proto__> property name for its own purposes.
		1389
		1390	If that is a problem, you could parse try to filter the resulting JSON
		1391	output for these property strings, e.g.:
		1392
		1393	$json =~ s/"__proto__"\s*:/"__proto__renamed":/g;
		1394
		1395	This works because C<__proto__> is not valid outside of strings, so every
		1396	occurrence of C<"__proto__"\s*:> must be a string used as property name.
		1397
		1398	If you know of other incompatibilities, please let me know.
		1399
		1400
1172	=head2 JSON and YAML	1401	=head2 JSON and YAML
1173		1402
1174	You often hear that JSON is a subset of YAML. This is, however, a mass	1403	You often hear that JSON is a subset of YAML. This is, however, a mass
1175	hysteria(*) and very far from the truth (as of the time of this writing),	1404	hysteria(*) and very far from the truth (as of the time of this writing),
1176	so let me state it clearly: I<in general, there is no way to configure	1405	so let me state it clearly: I<in general, there is no way to configure
…		…
1184	my $yaml = $to_yaml->encode ($ref) . "\n";	1413	my $yaml = $to_yaml->encode ($ref) . "\n";
1185		1414
1186	This will I<usually> generate JSON texts that also parse as valid	1415	This will I<usually> generate JSON texts that also parse as valid
1187	YAML. Please note that YAML has hardcoded limits on (simple) object key	1416	YAML. Please note that YAML has hardcoded limits on (simple) object key
1188	lengths that JSON doesn't have and also has different and incompatible	1417	lengths that JSON doesn't have and also has different and incompatible
1189	unicode handling, so you should make sure that your hash keys are	1418	unicode character escape syntax, so you should make sure that your hash
1190	noticeably shorter than the 1024 "stream characters" YAML allows and that	1419	keys are noticeably shorter than the 1024 "stream characters" YAML allows
1191	you do not have characters with codepoint values outside the Unicode BMP	1420	and that you do not have characters with codepoint values outside the
1192	(basic multilingual page). YAML also does not allow C<\/> sequences in	1421	Unicode BMP (basic multilingual page). YAML also does not allow C<\/>
1193	strings (which JSON::XS does not I<currently> generate, but other JSON	1422	sequences in strings (which JSON::XS does not I<currently> generate, but
1194	generators might).	1423	other JSON generators might).
1195		1424
1196	There might be other incompatibilities that I am not aware of (or the YAML	1425	There might be other incompatibilities that I am not aware of (or the YAML
1197	specification has been changed yet again - it does so quite often). In	1426	specification has been changed yet again - it does so quite often). In
1198	general you should not try to generate YAML with a JSON generator or vice	1427	general you should not try to generate YAML with a JSON generator or vice
1199	versa, or try to parse JSON with a YAML parser or vice versa: chances are	1428	versa, or try to parse JSON with a YAML parser or vice versa: chances are
…		…
1218	that difficult or long) and finally make YAML compatible to it, and	1447	that difficult or long) and finally make YAML compatible to it, and
1219	educating users about the changes, instead of spreading lies about the	1448	educating users about the changes, instead of spreading lies about the
1220	real compatibility for many I<years> and trying to silence people who	1449	real compatibility for many I<years> and trying to silence people who
1221	point out that it isn't true.	1450	point out that it isn't true.
1222		1451
		1452	Addendum/2009: the YAML 1.2 spec is still incompatible with JSON, even
		1453	though the incompatibilities have been documented (and are known to Brian)
		1454	for many years and the spec makes explicit claims that YAML is a superset
		1455	of JSON. It would be so easy to fix, but apparently, bullying people and
		1456	corrupting userdata is so much easier.
		1457
1223	=back	1458	=back
1224		1459
1225		1460
1226	=head2 SPEED	1461	=head2 SPEED
1227		1462
…		…
1234	a very short single-line JSON string (also available at	1469	a very short single-line JSON string (also available at
1235	L<http://dist.schmorp.de/misc/json/short.json>).	1470	L<http://dist.schmorp.de/misc/json/short.json>).
1236		1471
1237	{"method": "handleMessage", "params": ["user1",	1472	{"method": "handleMessage", "params": ["user1",
1238	"we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7,	1473	"we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7,
1239	true, false]}	1474	1, 0]}
1240		1475
1241	It shows the number of encodes/decodes per second (JSON::XS uses	1476	It shows the number of encodes/decodes per second (JSON::XS uses
1242	the functional interface, while JSON::XS/2 uses the OO interface	1477	the functional interface, while JSON::XS/2 uses the OO interface
1243	with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables	1478	with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables
1244	shrink). Higher is better:	1479	shrink. JSON::DWIW/DS uses the deserialise function, while JSON::DWIW::FJ
		1480	uses the from_json method). Higher is better:
1245		1481
1246	module \| encode \| decode \|	1482	module \| encode \| decode \|
1247	-----------\|------------\|------------\|	1483	--------------\|------------\|------------\|
1248	JSON 1.x \| 4990.842 \| 4088.813 \|	1484	JSON::DWIW/DS \| 86302.551 \| 102300.098 \|
1249	JSON::DWIW \| 51653.990 \| 71575.154 \|	1485	JSON::DWIW/FJ \| 86302.551 \| 75983.768 \|
1250	JSON::PC \| 65948.176 \| 74631.744 \|	1486	JSON::PP \| 15827.562 \| 6638.658 \|
1251	JSON::PP \| 8931.652 \| 3817.168 \|	1487	JSON::Syck \| 63358.066 \| 47662.545 \|
1252	JSON::Syck \| 24877.248 \| 27776.848 \|	1488	JSON::XS \| 511500.488 \| 511500.488 \|
1253	JSON::XS \| 388361.481 \| 227951.304 \|	1489	JSON::XS/2 \| 291271.111 \| 388361.481 \|
1254	JSON::XS/2 \| 227951.304 \| 218453.333 \|	1490	JSON::XS/3 \| 361577.931 \| 361577.931 \|
1255	JSON::XS/3 \| 338250.323 \| 218453.333 \|	1491	Storable \| 66788.280 \| 265462.278 \|
1256	Storable \| 16500.016 \| 135300.129 \|
1257	-----------+------------+------------+	1492	--------------+------------+------------+
1258		1493
1259	That is, JSON::XS is about five times faster than JSON::DWIW on encoding,	1494	That is, JSON::XS is almost six times faster than JSON::DWIW on encoding,
1260	about three times faster on decoding, and over forty times faster	1495	about five times faster on decoding, and over thirty to seventy times
1261	than JSON, even with pretty-printing and key sorting. It also compares	1496	faster than JSON's pure perl implementation. It also compares favourably
1262	favourably to Storable for small amounts of data.	1497	to Storable for small amounts of data.
1263		1498
1264	Using a longer test string (roughly 18KB, generated from Yahoo! Locals	1499	Using a longer test string (roughly 18KB, generated from Yahoo! Locals
1265	search API (L<http://dist.schmorp.de/misc/json/long.json>).	1500	search API (L<http://dist.schmorp.de/misc/json/long.json>).
1266		1501
1267	module \| encode \| decode \|	1502	module \| encode \| decode \|
1268	-----------\|------------\|------------\|	1503	--------------\|------------\|------------\|
1269	JSON 1.x \| 55.260 \| 34.971 \|	1504	JSON::DWIW/DS \| 1647.927 \| 2673.916 \|
1270	JSON::DWIW \| 825.228 \| 1082.513 \|	1505	JSON::DWIW/FJ \| 1630.249 \| 2596.128 \|
1271	JSON::PC \| 3571.444 \| 2394.829 \|
1272	JSON::PP \| 210.987 \| 32.574 \|	1506	JSON::PP \| 400.640 \| 62.311 \|
1273	JSON::Syck \| 552.551 \| 787.544 \|	1507	JSON::Syck \| 1481.040 \| 1524.869 \|
1274	JSON::XS \| 5780.463 \| 4854.519 \|	1508	JSON::XS \| 20661.596 \| 9541.183 \|
1275	JSON::XS/2 \| 3869.998 \| 4798.975 \|	1509	JSON::XS/2 \| 10683.403 \| 9416.938 \|
1276	JSON::XS/3 \| 5862.880 \| 4798.975 \|	1510	JSON::XS/3 \| 20661.596 \| 9400.054 \|
1277	Storable \| 4445.002 \| 5235.027 \|	1511	Storable \| 19765.806 \| 10000.725 \|
1278	-----------+------------+------------+	1512	--------------+------------+------------+
1279		1513
1280	Again, JSON::XS leads by far (except for Storable which non-surprisingly	1514	Again, JSON::XS leads by far (except for Storable which non-surprisingly
1281	decodes faster).	1515	decodes a bit faster).
1282		1516
1283	On large strings containing lots of high Unicode characters, some modules	1517	On large strings containing lots of high Unicode characters, some modules
1284	(such as JSON::PC) seem to decode faster than JSON::XS, but the result	1518	(such as JSON::PC) seem to decode faster than JSON::XS, but the result
1285	will be broken due to missing (or wrong) Unicode handling. Others refuse	1519	will be broken due to missing (or wrong) Unicode handling. Others refuse
1286	to decode or encode properly, so it was impossible to prepare a fair	1520	to decode or encode properly, so it was impossible to prepare a fair
…		…
1322	information you might want to make sure that exceptions thrown by JSON::XS	1556	information you might want to make sure that exceptions thrown by JSON::XS
1323	will not end up in front of untrusted eyes.	1557	will not end up in front of untrusted eyes.
1324		1558
1325	If you are using JSON::XS to return packets to consumption	1559	If you are using JSON::XS to return packets to consumption
1326	by JavaScript scripts in a browser you should have a look at	1560	by JavaScript scripts in a browser you should have a look at
1327	L<http://jpsykes.com/47/practical-csrf-and-json-security> to see whether	1561	L<http://blog.archive.jpsykes.com/47/practical-csrf-and-json-security/> to
1328	you are vulnerable to some common attack vectors (which really are browser	1562	see whether you are vulnerable to some common attack vectors (which really
1329	design bugs, but it is still you who will have to deal with it, as major	1563	are browser design bugs, but it is still you who will have to deal with
1330	browser developers care only for features, not about getting security	1564	it, as major browser developers care only for features, not about getting
1331	right).	1565	security right).
		1566
		1567
		1568	=head1 "OLD" VS. "NEW" JSON (RFC 4627 VS. RFC 7159)
		1569
		1570	TL;DR: Due to security concerns, JSON::XS will not allow scalar data in
		1571	JSON texts by default - you need to create your own JSON::XS object and
		1572	enable C<allow_nonref>:
		1573
		1574
		1575	my $json = JSON::XS->new->allow_nonref;
		1576
		1577	$text = $json->encode ($data);
		1578	$data = $json->decode ($text);
		1579
		1580	The long version: JSON being an important and supposedly stable format,
		1581	the IETF standardised it as RFC 4627 in 2006. Unfortunately, the inventor
		1582	of JSON, Dougles Crockford, unilaterally changed the definition of JSON in
		1583	javascript. Rather than create a fork, the IETF decided to standardise the
		1584	new syntax (apparently, so Iw as told, without finding it very amusing).
		1585
		1586	The biggest difference between thed original JSON and the new JSON is that
		1587	the new JSON supports scalars (anything other than arrays and objects) at
		1588	the toplevel of a JSON text. While this is strictly backwards compatible
		1589	to older versions, it breaks a number of protocols that relied on sending
		1590	JSON back-to-back, and is a minor security concern.
		1591
		1592	For example, imagine you have two banks communicating, and on one side,
		1593	trhe JSON coder gets upgraded. Two messages, such as C<10> and C<1000>
		1594	might then be confused to mean C<101000>, something that couldn't happen
		1595	in the original JSON, because niether of these messages would be valid
		1596	JSON.
		1597
		1598	If one side accepts these messages, then an upgrade in the coder on either
		1599	side could result in this becoming exploitable.
		1600
		1601	This module has always allowed these messages as an optional extension, by
		1602	default disabled. The security concerns are the reason why the default is
		1603	still disabled, but future versions might/will likely upgrade to the newer
		1604	RFC as default format, so you are advised to check your implementation
		1605	and/or override the default with C<< ->allow_nonref (0) >> to ensure that
		1606	future versions are safe.
		1607
		1608
		1609	=head1 INTEROPERABILITY WITH OTHER MODULES
		1610
		1611	C<JSON::XS> uses the L<Types::Serialiser> module to provide boolean
		1612	constants. That means that the JSON true and false values will be
		1613	comaptible to true and false values of other modules that do the same,
		1614	such as L<JSON::PP> and L<CBOR::XS>.
		1615
		1616
		1617	=head1 INTEROPERABILITY WITH OTHER JSON DECODERS
		1618
		1619	As long as you only serialise data that can be directly expressed in JSON,
		1620	C<JSON::XS> is incapable of generating invalid JSON output (modulo bugs,
		1621	but C<JSON::XS> has found more bugs in the official JSON testsuite (1)
		1622	than the official JSON testsuite has found in C<JSON::XS> (0)).
		1623
		1624	When you have trouble decoding JSON generated by this module using other
		1625	decoders, then it is very likely that you have an encoding mismatch or the
		1626	other decoder is broken.
		1627
		1628	When decoding, C<JSON::XS> is strict by default and will likely catch all
		1629	errors. There are currently two settings that change this: C<relaxed>
		1630	makes C<JSON::XS> accept (but not generate) some non-standard extensions,
		1631	and C<allow_tags> will allow you to encode and decode Perl objects, at the
		1632	cost of not outputting valid JSON anymore.
		1633
		1634	=head2 TAGGED VALUE SYNTAX AND STANDARD JSON EN/DECODERS
		1635
		1636	When you use C<allow_tags> to use the extended (and also nonstandard and
		1637	invalid) JSON syntax for serialised objects, and you still want to decode
		1638	the generated When you want to serialise objects, you can run a regex
		1639	to replace the tagged syntax by standard JSON arrays (it only works for
		1640	"normal" package names without comma, newlines or single colons). First,
		1641	the readable Perl version:
		1642
		1643	# if your FREEZE methods return no values, you need this replace first:
		1644	$json =~ s/$ \s* (" (?: [^\\":,]+\|\\.\|::)* ") \s* $ \s* \[\s*\]/[$1]/gx;
		1645
		1646	# this works for non-empty constructor arg lists:
		1647	$json =~ s/$ \s* (" (?: [^\\":,]+\|\\.\|::)* ") \s* $ \s* \[/[$1,/gx;
		1648
		1649	And here is a less readable version that is easy to adapt to other
		1650	languages:
		1651
		1652	$json =~ s/$\s("([^\\":,]+\|\\.\|::)")\s$\s\[/[$1,/g;
		1653
		1654	Here is an ECMAScript version (same regex):
		1655
		1656	json = json.replace (/$\s("([^\\":,]+\|\\.\|::)")\s$\s\[/g, "[$1,");
		1657
		1658	Since this syntax converts to standard JSON arrays, it might be hard to
		1659	distinguish serialised objects from normal arrays. You can prepend a
		1660	"magic number" as first array element to reduce chances of a collision:
		1661
		1662	$json =~ s/$\s("([^\\":,]+\|\\.\|::)")\s$\s\[/["XU1peReLzT4ggEllLanBYq4G9VzliwKF",$1,/g;
		1663
		1664	And after decoding the JSON text, you could walk the data
		1665	structure looking for arrays with a first element of
		1666	C<XU1peReLzT4ggEllLanBYq4G9VzliwKF>.
		1667
		1668	The same approach can be used to create the tagged format with another
		1669	encoder. First, you create an array with the magic string as first member,
		1670	the classname as second, and constructor arguments last, encode it as part
		1671	of your JSON structure, and then:
		1672
		1673	$json =~ s/\[\s"XU1peReLzT4ggEllLanBYq4G9VzliwKF"\s,\s("([^\\":,]+\|\\.\|::)")\s*,/($1)[/g;
		1674
		1675	Again, this has some limitations - the magic string must not be encoded
		1676	with character escapes, and the constructor arguments must be non-empty.
		1677
		1678
		1679	=head1 RFC7159
		1680
		1681	Since this module was written, Google has written a new JSON RFC, RFC 7159
		1682	(and RFC7158). Unfortunately, this RFC breaks compatibility with both the
		1683	original JSON specification on www.json.org and RFC4627.
		1684
		1685	As far as I can see, you can get partial compatibility when parsing by
		1686	using C<< ->allow_nonref >>. However, consider the security implications
		1687	of doing so.
		1688
		1689	I haven't decided yet when to break compatibility with RFC4627 by default
		1690	(and potentially leave applications insecure) and change the default to
		1691	follow RFC7159, but application authors are well advised to call C<<
		1692	->allow_nonref(0) >> even if this is the current default, if they cannot
		1693	handle non-reference values, in preparation for the day when the default
		1694	will change.
1332		1695
1333		1696
1334	=head1 THREADS	1697	=head1 THREADS
1335		1698
1336	This module is I<not> guaranteed to be thread safe and there are no	1699	This module is I<not> guaranteed to be thread safe and there are no
…		…
1339	process simulations - use fork, it's I<much> faster, cheaper, better).	1702	process simulations - use fork, it's I<much> faster, cheaper, better).
1340		1703
1341	(It might actually work, but you have been warned).	1704	(It might actually work, but you have been warned).
1342		1705
1343		1706
		1707	=head1 THE PERILS OF SETLOCALE
		1708
		1709	Sometimes people avoid the Perl locale support and directly call the
		1710	system's setlocale function with C<LC_ALL>.
		1711
		1712	This breaks both perl and modules such as JSON::XS, as stringification of
		1713	numbers no longer works correctly (e.g. C<$x = 0.1; print "$x"+1> might
		1714	print C<1>, and JSON::XS might output illegal JSON as JSON::XS relies on
		1715	perl to stringify numbers).
		1716
		1717	The solution is simple: don't call C<setlocale>, or use it for only those
		1718	categories you need, such as C<LC_MESSAGES> or C<LC_CTYPE>.
		1719
		1720	If you need C<LC_NUMERIC>, you should enable it only around the code that
		1721	actually needs it (avoiding stringification of numbers), and restore it
		1722	afterwards.
		1723
		1724
1344	=head1 BUGS	1725	=head1 BUGS
1345		1726
1346	While the goal of this module is to be correct, that unfortunately does	1727	While the goal of this module is to be correct, that unfortunately does
1347	not mean it's bug-free, only that I think its design is bug-free. If you	1728	not mean it's bug-free, only that I think its design is bug-free. If you
1348	keep reporting bugs they will be fixed swiftly, though.	1729	keep reporting bugs they will be fixed swiftly, though.
…		…
1350	Please refrain from using rt.cpan.org or any other bug reporting	1731	Please refrain from using rt.cpan.org or any other bug reporting
1351	service. I put the contact address into my modules for a reason.	1732	service. I put the contact address into my modules for a reason.
1352		1733
1353	=cut	1734	=cut
1354		1735
1355	our $true = do { bless \(my $dummy = 1), "JSON::XS::Boolean" };	1736	BEGIN {
1356	our $false = do { bless \(my $dummy = 0), "JSON::XS::Boolean" };	1737	*true = \$Types::Serialiser::true;
		1738	*true = \&Types::Serialiser::true;
		1739	*false = \$Types::Serialiser::false;
		1740	*false = \&Types::Serialiser::false;
		1741	*is_bool = \&Types::Serialiser::is_bool;
1357		1742
1358	sub true() { $true }	1743	JSON::XS::Boolean:: = Types::Serialiser::Boolean::;
1359	sub false() { $false }
1360
1361	sub is_bool($) {
1362	UNIVERSAL::isa $_[0], "JSON::XS::Boolean"
1363	# or UNIVERSAL::isa $_[0], "JSON::Literal"
1364	}	1744	}
1365		1745
1366	XSLoader::load "JSON::XS", $VERSION;	1746	XSLoader::load "JSON::XS", $VERSION;
1367
1368	package JSON::XS::Boolean;
1369
1370	use overload
1371	"0+" => sub { ${$_[0]} },
1372	"++" => sub { $_[0] = ${$_[0]} + 1 },
1373	"--" => sub { $_[0] = ${$_[0]} - 1 },
1374	fallback => 1;
1375
1376	1;
1377		1747
1378	=head1 SEE ALSO	1748	=head1 SEE ALSO
1379		1749
1380	The F<json_xs> command line utility for quick experiments.	1750	The F<json_xs> command line utility for quick experiments.
1381		1751
…		…
1384	Marc Lehmann <schmorp@schmorp.de>	1754	Marc Lehmann <schmorp@schmorp.de>
1385	http://home.schmorp.de/	1755	http://home.schmorp.de/
1386		1756
1387	=cut	1757	=cut
1388		1758
		1759	1
		1760

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Comparing JSON-XS/XS.pm (file contents): Revision 1.104 by root, Thu May 8 15:33:06 2008 UTC vs. Revision 1.159 by root, Wed Sep 7 17:14:56 2016 UTC

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Comparing JSON-XS/XS.pm (file contents):
Revision 1.104 by root, Thu May 8 15:33:06 2008 UTC vs.
Revision 1.159 by root, Wed Sep 7 17:14:56 2016 UTC