[ViewVC] Diff of: cvs/JSON-XS/README

Comparing JSON-XS/README (file contents):
Revision 1.37 by root, Thu May 23 09:32:02 2013 UTC vs.
Revision 1.42 by root, Thu Aug 17 03:47:54 2017 UTC

…		…
36	JSON::XS are installed, then JSON will fall back on JSON::XS (this can	36	JSON::XS are installed, then JSON will fall back on JSON::XS (this can
37	be overridden) with no overhead due to emulation (by inheriting	37	be overridden) with no overhead due to emulation (by inheriting
38	constructor and methods). If JSON::XS is not available, it will fall	38	constructor and methods). If JSON::XS is not available, it will fall
39	back to the compatible JSON::PP module as backend, so using JSON instead	39	back to the compatible JSON::PP module as backend, so using JSON instead
40	of JSON::XS gives you a portable JSON API that can be fast when you need	40	of JSON::XS gives you a portable JSON API that can be fast when you need
41	and doesn't require a C compiler when that is a problem.	41	it and doesn't require a C compiler when that is a problem.
42		42
43	As this is the n-th-something JSON module on CPAN, what was the reason	43	As this is the n-th-something JSON module on CPAN, what was the reason
44	to write yet another JSON module? While it seems there are many JSON	44	to write yet another JSON module? While it seems there are many JSON
45	modules, none of them correctly handle all corner cases, and in most	45	modules, none of them correctly handle all corner cases, and in most
46	cases their maintainers are unresponsive, gone missing, or not listening	46	cases their maintainers are unresponsive, gone missing, or not listening
…		…
77	too.	77	too.
78		78
79	* simple to use	79	* simple to use
80		80
81	This module has both a simple functional interface as well as an	81	This module has both a simple functional interface as well as an
82	object oriented interface interface.	82	object oriented interface.
83		83
84	* reasonably versatile output formats	84	* reasonably versatile output formats
85		85
86	You can choose between the most compact guaranteed-single-line	86	You can choose between the most compact guaranteed-single-line
87	format possible (nice for simple line-based protocols), a pure-ASCII	87	format possible (nice for simple line-based protocols), a pure-ASCII
…		…
112	This function call is functionally identical to:	112	This function call is functionally identical to:
113		113
114	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)	114	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)
115		115
116	Except being faster.	116	Except being faster.
117
118	$is_boolean = JSON::XS::is_bool $scalar
119	Returns true if the passed scalar represents either JSON::XS::true
120	or JSON::XS::false, two constants that act like 1 and 0,
121	respectively and are used to represent JSON "true" and "false"
122	values in Perl.
123
124	See MAPPING, below, for more information on how JSON values are
125	mapped to Perl.
126		117
127	A FEW NOTES ON UNICODE AND PERL	118	A FEW NOTES ON UNICODE AND PERL
128	Since this often leads to confusion, here are a few very clear words on	119	Since this often leads to confusion, here are a few very clear words on
129	how Unicode works in Perl, modulo bugs.	120	how Unicode works in Perl, modulo bugs.
130		121
…		…
361	[	352	[
362	1, # this comment not allowed in JSON	353	1, # this comment not allowed in JSON
363	# neither this one...	354	# neither this one...
364	]	355	]
365		356
		357	* literal ASCII TAB characters in strings
		358
		359	Literal ASCII TAB characters are now allowed in strings (and
		360	treated as "\t").
		361
		362	[
		363	"Hello\tWorld",
		364	"Hello<TAB>World", # literal <TAB> would not normally be allowed
		365	]
		366
366	$json = $json->canonical ([$enable])	367	$json = $json->canonical ([$enable])
367	$enabled = $json->get_canonical	368	$enabled = $json->get_canonical
368	If $enable is true (or missing), then the "encode" method will	369	If $enable is true (or missing), then the "encode" method will
369	output JSON objects by sorting their keys. This is adding a	370	output JSON objects by sorting their keys. This is adding a
370	comparatively high overhead.	371	comparatively high overhead.
…		…
417	recommended to leave it off unless you know your communications	418	recommended to leave it off unless you know your communications
418	partner.	419	partner.
419		420
420	$json = $json->allow_blessed ([$enable])	421	$json = $json->allow_blessed ([$enable])
421	$enabled = $json->get_allow_blessed	422	$enabled = $json->get_allow_blessed
		423	See "OBJECT SERIALISATION" for details.
		424
422	If $enable is true (or missing), then the "encode" method will not	425	If $enable is true (or missing), then the "encode" method will not
423	barf when it encounters a blessed reference. Instead, the value of	426	barf when it encounters a blessed reference that it cannot convert
424	the convert_blessed option will decide whether "null"	427	otherwise. Instead, a JSON "null" value is encoded instead of the
425	("convert_blessed" disabled or no "TO_JSON" method found) or a	428	object.
426	representation of the object ("convert_blessed" enabled and
427	"TO_JSON" method found) is being encoded. Has no effect on "decode".
428		429
429	If $enable is false (the default), then "encode" will throw an	430	If $enable is false (the default), then "encode" will throw an
430	exception when it encounters a blessed object.	431	exception when it encounters a blessed object that it cannot convert
		432	otherwise.
		433
		434	This setting has no effect on "decode".
431		435
432	$json = $json->convert_blessed ([$enable])	436	$json = $json->convert_blessed ([$enable])
433	$enabled = $json->get_convert_blessed	437	$enabled = $json->get_convert_blessed
		438	See "OBJECT SERIALISATION" for details.
		439
434	If $enable is true (or missing), then "encode", upon encountering a	440	If $enable is true (or missing), then "encode", upon encountering a
435	blessed object, will check for the availability of the "TO_JSON"	441	blessed object, will check for the availability of the "TO_JSON"
436	method on the object's class. If found, it will be called in scalar	442	method on the object's class. If found, it will be called in scalar
437	context and the resulting scalar will be encoded instead of the	443	context and the resulting scalar will be encoded instead of the
438	object. If no "TO_JSON" method is found, the value of	444	object.
439	"allow_blessed" will decide what to do.
440		445
441	The "TO_JSON" method may safely call die if it wants. If "TO_JSON"	446	The "TO_JSON" method may safely call die if it wants. If "TO_JSON"
442	returns other blessed objects, those will be handled in the same	447	returns other blessed objects, those will be handled in the same
443	way. "TO_JSON" must take care of not causing an endless recursion	448	way. "TO_JSON" must take care of not causing an endless recursion
444	cycle (== crash) in this case. The name of "TO_JSON" was chosen	449	cycle (== crash) in this case. The name of "TO_JSON" was chosen
445	because other methods called by the Perl core (== not by the user of	450	because other methods called by the Perl core (== not by the user of
446	the object) are usually in upper case letters and to avoid	451	the object) are usually in upper case letters and to avoid
447	collisions with any "to_json" function or method.	452	collisions with any "to_json" function or method.
448		453
449	This setting does not yet influence "decode" in any way, but in the	454	If $enable is false (the default), then "encode" will not consider
450	future, global hooks might get installed that influence "decode" and	455	this type of conversion.
451	are enabled by this setting.
452		456
453	If $enable is false, then the "allow_blessed" setting will decide	457	This setting has no effect on "decode".
454	what to do when a blessed object is found.	458
		459	$json = $json->allow_tags ([$enable])
		460	$enabled = $json->allow_tags
		461	See "OBJECT SERIALISATION" for details.
		462
		463	If $enable is true (or missing), then "encode", upon encountering a
		464	blessed object, will check for the availability of the "FREEZE"
		465	method on the object's class. If found, it will be used to serialise
		466	the object into a nonstandard tagged JSON value (that JSON decoders
		467	cannot decode).
		468
		469	It also causes "decode" to parse such tagged JSON values and
		470	deserialise them via a call to the "THAW" method.
		471
		472	If $enable is false (the default), then "encode" will not consider
		473	this type of conversion, and tagged JSON values will cause a parse
		474	error in "decode", as if tags were not part of the grammar.
455		475
456	$json = $json->filter_json_object ([$coderef->($hashref)])	476	$json = $json->filter_json_object ([$coderef->($hashref)])
457	When $coderef is specified, it will be called from "decode" each	477	When $coderef is specified, it will be called from "decode" each
458	time it decodes a JSON object. The only argument is a reference to	478	time it decodes a JSON object. The only argument is a reference to
459	the newly-created hash. If the code references returns a single	479	the newly-created hash. If the code references returns a single
…		…
595		615
596	See SECURITY CONSIDERATIONS, below, for more info on why this is	616	See SECURITY CONSIDERATIONS, below, for more info on why this is
597	useful.	617	useful.
598		618
599	$json_text = $json->encode ($perl_scalar)	619	$json_text = $json->encode ($perl_scalar)
600	Converts the given Perl data structure (a simple scalar or a	620	Converts the given Perl value or data structure to its JSON
601	reference to a hash or array) to its JSON representation. Simple	621	representation. Croaks on error.
602	scalars will be converted into JSON string or number sequences,
603	while references to arrays become JSON arrays and references to
604	hashes become JSON objects. Undefined Perl values (e.g. "undef")
605	become JSON "null" values. Neither "true" nor "false" values will be
606	generated.
607		622
608	$perl_scalar = $json->decode ($json_text)	623	$perl_scalar = $json->decode ($json_text)
609	The opposite of "encode": expects a JSON text and tries to parse it,	624	The opposite of "encode": expects a JSON text and tries to parse it,
610	returning the resulting simple scalar or reference. Croaks on error.	625	returning the resulting simple scalar or reference. Croaks on error.
611
612	JSON numbers and strings become simple Perl scalars. JSON arrays
613	become Perl arrayrefs and JSON objects become Perl hashrefs. "true"
614	becomes 1, "false" becomes 0 and "null" becomes "undef".
615		626
616	($perl_scalar, $characters) = $json->decode_prefix ($json_text)	627	($perl_scalar, $characters) = $json->decode_prefix ($json_text)
617	This works like the "decode" method, but instead of raising an	628	This works like the "decode" method, but instead of raising an
618	exception when there is trailing garbage after the first JSON	629	exception when there is trailing garbage after the first JSON
619	object, it will silently stop parsing there and return the number of	630	object, it will silently stop parsing there and return the number of
620	characters consumed so far.	631	characters consumed so far.
621		632
622	This is useful if your JSON texts are not delimited by an outer	633	This is useful if your JSON texts are not delimited by an outer
623	protocol (which is not the brightest thing to do in the first place)
624	and you need to know where the JSON text ends.	634	protocol and you need to know where the JSON text ends.
625		635
626	JSON::XS->new->decode_prefix ("[1] the tail")	636	JSON::XS->new->decode_prefix ("[1] the tail")
627	=> ([], 3)	637	=> ([1], 3)
628		638
629	INCREMENTAL PARSING	639	INCREMENTAL PARSING
630	In some cases, there is the need for incremental parsing of JSON texts.	640	In some cases, there is the need for incremental parsing of JSON texts.
631	While this module always has to keep both JSON text and resulting Perl	641	While this module always has to keep both JSON text and resulting Perl
632	data structure in memory at one time, it does allow you to parse a JSON	642	data structure in memory at one time, it does allow you to parse a JSON
…		…
661		671
662	If the method is called in scalar context, then it will try to	672	If the method is called in scalar context, then it will try to
663	extract exactly one JSON object. If that is successful, it will	673	extract exactly one JSON object. If that is successful, it will
664	return this object, otherwise it will return "undef". If there is a	674	return this object, otherwise it will return "undef". If there is a
665	parse error, this method will croak just as "decode" would do (one	675	parse error, this method will croak just as "decode" would do (one
666	can then use "incr_skip" to skip the errornous part). This is the	676	can then use "incr_skip" to skip the erroneous part). This is the
667	most common way of using the method.	677	most common way of using the method.
668		678
669	And finally, in list context, it will try to extract as many objects	679	And finally, in list context, it will try to extract as many objects
670	from the stream as it can find and return them, or the empty list	680	from the stream as it can find and return them, or the empty list
671	otherwise. For this to work, there must be no separators between the	681	otherwise. For this to work, there must be no separators (other than
672	JSON objects or arrays, instead they must be concatenated	682	whitespace) between the JSON objects or arrays, instead they must be
673	back-to-back. If an error occurs, an exception will be raised as in	683	concatenated back-to-back. If an error occurs, an exception will be
674	the scalar context case. Note that in this case, any	684	raised as in the scalar context case. Note that in this case, any
675	previously-parsed JSON texts will be lost.	685	previously-parsed JSON texts will be lost.
676		686
677	Example: Parse some JSON arrays/objects in a given string and return	687	Example: Parse some JSON arrays/objects in a given string and return
678	them.	688	them.
679		689
…		…
687	function (I mean it. although in simple tests it might actually	697	function (I mean it. although in simple tests it might actually
688	work, it will fail under real world conditions). As a special	698	work, it will fail under real world conditions). As a special
689	exception, you can also call this method before having parsed	699	exception, you can also call this method before having parsed
690	anything.	700	anything.
691		701
		702	That means you can only use this function to look at or manipulate
		703	text before or after complete JSON objects, not while the parser is
		704	in the middle of parsing a JSON object.
		705
692	This function is useful in two cases: a) finding the trailing text	706	This function is useful in two cases: a) finding the trailing text
693	after a JSON object or b) parsing multiple JSON objects separated by	707	after a JSON object or b) parsing multiple JSON objects separated by
694	non-JSON text (such as commas).	708	non-JSON text (such as commas).
695		709
696	$json->incr_skip	710	$json->incr_skip
…		…
699	"incr_parse" died, in which case the input buffer and incremental	713	"incr_parse" died, in which case the input buffer and incremental
700	parser state is left unchanged, to skip the text parsed so far and	714	parser state is left unchanged, to skip the text parsed so far and
701	to reset the parse state.	715	to reset the parse state.
702		716
703	The difference to "incr_reset" is that only text until the parse	717	The difference to "incr_reset" is that only text until the parse
704	error occured is removed.	718	error occurred is removed.
705		719
706	$json->incr_reset	720	$json->incr_reset
707	This completely resets the incremental parser, that is, after this	721	This completely resets the incremental parser, that is, after this
708	call, it will be as if the parser had never parsed anything.	722	call, it will be as if the parser had never parsed anything.
709		723
…		…
893	If the number consists of digits only, JSON::XS will try to	907	If the number consists of digits only, JSON::XS will try to
894	represent it as an integer value. If that fails, it will try to	908	represent it as an integer value. If that fails, it will try to
895	represent it as a numeric (floating point) value if that is possible	909	represent it as a numeric (floating point) value if that is possible
896	without loss of precision. Otherwise it will preserve the number as	910	without loss of precision. Otherwise it will preserve the number as
897	a string value (in which case you lose roundtripping ability, as the	911	a string value (in which case you lose roundtripping ability, as the
898	JSON number will be re-encoded toa JSON string).	912	JSON number will be re-encoded to a JSON string).
899		913
900	Numbers containing a fractional or exponential part will always be	914	Numbers containing a fractional or exponential part will always be
901	represented as numeric (floating point) values, possibly at a loss	915	represented as numeric (floating point) values, possibly at a loss
902	of precision (in which case you might lose perfect roundtripping	916	of precision (in which case you might lose perfect roundtripping
903	ability, but the JSON number will still be re-encoded as a JSON	917	ability, but the JSON number will still be re-encoded as a JSON
904	number).	918	number).
905		919
906	Note that precision is not accuracy - binary floating point values	920	Note that precision is not accuracy - binary floating point values
907	cannot represent most decimal fractions exactly, and when converting	921	cannot represent most decimal fractions exactly, and when converting
908	from and to floating point, JSON::XS only guarantees precision up to	922	from and to floating point, JSON::XS only guarantees precision up to
909	but not including the leats significant bit.	923	but not including the least significant bit.
910		924
911	true, false	925	true, false
912	These JSON atoms become "JSON::XS::true" and "JSON::XS::false",	926	These JSON atoms become "Types::Serialiser::true" and
913	respectively. They are overloaded to act almost exactly like the	927	"Types::Serialiser::false", respectively. They are overloaded to act
914	numbers 1 and 0. You can check whether a scalar is a JSON boolean by	928	almost exactly like the numbers 1 and 0. You can check whether a
915	using the "JSON::XS::is_bool" function.	929	scalar is a JSON boolean by using the "Types::Serialiser::is_bool"
		930	function (after "use Types::Serialier", of course).
916		931
917	null	932	null
918	A JSON null atom becomes "undef" in Perl.	933	A JSON null atom becomes "undef" in Perl.
		934
		935	shell-style comments ("# text")
		936	As a nonstandard extension to the JSON syntax that is enabled by the
		937	"relaxed" setting, shell-style comments are allowed. They can start
		938	anywhere outside strings and go till the end of the line.
		939
		940	tagged values ("(tag)value").
		941	Another nonstandard extension to the JSON syntax, enabled with the
		942	"allow_tags" setting, are tagged values. In this implementation, the
		943	tag must be a perl package/class name encoded as a JSON string,
		944	and the value must be a JSON array encoding optional constructor
		945	arguments.
		946
		947	See "OBJECT SERIALISATION", below, for details.
919		948
920	PERL -> JSON	949	PERL -> JSON
921	The mapping from Perl to JSON is slightly more difficult, as Perl is a	950	The mapping from Perl to JSON is slightly more difficult, as Perl is a
922	truly typeless language, so we can only guess which JSON type is meant	951	truly typeless language, so we can only guess which JSON type is meant
923	by a Perl value.	952	by a Perl value.
924		953
925	hash references	954	hash references
926	Perl hash references become JSON objects. As there is no inherent	955	Perl hash references become JSON objects. As there is no inherent
927	ordering in hash keys (or JSON objects), they will usually be	956	ordering in hash keys (or JSON objects), they will usually be
928	encoded in a pseudo-random order that can change between runs of the	957	encoded in a pseudo-random order. JSON::XS can optionally sort the
929	same program but stays generally the same within a single run of a	958	hash keys (determined by the canonical flag), so the same
930	program. JSON::XS can optionally sort the hash keys (determined by	959	datastructure will serialise to the same JSON text (given same
931	the canonical flag), so the same datastructure will serialise to	960	settings and version of JSON::XS), but this incurs a runtime
932	the same JSON text (given same settings and version of JSON::XS),	961	overhead and is only rarely useful, e.g. when you want to compare
933	but this incurs a runtime overhead and is only rarely useful, e.g.	962	some JSON text against another for equality.
934	when you want to compare some JSON text against another for
935	equality.
936		963
937	array references	964	array references
938	Perl array references become JSON arrays.	965	Perl array references become JSON arrays.
939		966
940	other references	967	other references
941	Other unblessed references are generally not allowed and will cause	968	Other unblessed references are generally not allowed and will cause
942	an exception to be thrown, except for references to the integers 0	969	an exception to be thrown, except for references to the integers 0
943	and 1, which get turned into "false" and "true" atoms in JSON. You	970	and 1, which get turned into "false" and "true" atoms in JSON.
944	can also use "JSON::XS::false" and "JSON::XS::true" to improve	971
		972	Since "JSON::XS" uses the boolean model from Types::Serialiser, you
		973	can also "use Types::Serialiser" and then use
		974	"Types::Serialiser::false" and "Types::Serialiser::true" to improve
945	readability.	975	readability.
946		976
		977	use Types::Serialiser;
947	encode_json [\0, JSON::XS::true] # yields [false,true]	978	encode_json [\0, Types::Serialiser::true] # yields [false,true]
948		979
949	JSON::XS::true, JSON::XS::false	980	Types::Serialiser::true, Types::Serialiser::false
950	These special values become JSON true and JSON false values,	981	These special values from the Types::Serialiser module become JSON
951	respectively. You can also use "\1" and "\0" directly if you want.	982	true and JSON false values, respectively. You can also use "\1" and
		983	"\0" directly if you want.
952		984
953	blessed objects	985	blessed objects
954	Blessed objects are not directly representable in JSON. See the	986	Blessed objects are not directly representable in JSON, but
955	"allow_blessed" and "convert_blessed" methods on various options on	987	"JSON::XS" allows various ways of handling objects. See "OBJECT
956	how to deal with this: basically, you can choose between throwing an	988	SERIALISATION", below, for details.
957	exception, encoding the reference as if it weren't blessed, or
958	provide your own serialiser method.
959		989
960	simple scalars	990	simple scalars
961	Simple Perl scalars (any scalar that is not a reference) are the	991	Simple Perl scalars (any scalar that is not a reference) are the
962	most difficult objects to encode: JSON::XS will encode undefined	992	most difficult objects to encode: JSON::XS will encode undefined
963	scalars as JSON "null" values, scalars that have last been used in a	993	scalars as JSON "null" values, scalars that have last been used in a
…		…
998	which can differ to other languages). Also, your perl interpreter	1028	which can differ to other languages). Also, your perl interpreter
999	might expose extensions to the floating point numbers of your	1029	might expose extensions to the floating point numbers of your
1000	platform, such as infinities or NaN's - these cannot be represented	1030	platform, such as infinities or NaN's - these cannot be represented
1001	in JSON, and it is an error to pass those in.	1031	in JSON, and it is an error to pass those in.
1002		1032
		1033	OBJECT SERIALISATION
		1034	As JSON cannot directly represent Perl objects, you have to choose
		1035	between a pure JSON representation (without the ability to deserialise
		1036	the object automatically again), and a nonstandard extension to the JSON
		1037	syntax, tagged values.
		1038
		1039	SERIALISATION
		1040	What happens when "JSON::XS" encounters a Perl object depends on the
		1041	"allow_blessed", "convert_blessed" and "allow_tags" settings, which are
		1042	used in this order:
		1043
		1044	1. "allow_tags" is enabled and the object has a "FREEZE" method.
		1045	In this case, "JSON::XS" uses the Types::Serialiser object
		1046	serialisation protocol to create a tagged JSON value, using a
		1047	nonstandard extension to the JSON syntax.
		1048
		1049	This works by invoking the "FREEZE" method on the object, with the
		1050	first argument being the object to serialise, and the second
		1051	argument being the constant string "JSON" to distinguish it from
		1052	other serialisers.
		1053
		1054	The "FREEZE" method can return any number of values (i.e. zero or
		1055	more). These values and the paclkage/classname of the object will
		1056	then be encoded as a tagged JSON value in the following format:
		1057
		1058	("classname")[FREEZE return values...]
		1059
		1060	e.g.:
		1061
		1062	("URI")["http://www.google.com/"]
		1063	("MyDate")[2013,10,29]
		1064	("ImageData::JPEG")["Z3...VlCg=="]
		1065
		1066	For example, the hypothetical "My::Object" "FREEZE" method might use
		1067	the objects "type" and "id" members to encode the object:
		1068
		1069	sub My::Object::FREEZE {
		1070	my ($self, $serialiser) = @_;
		1071
		1072	($self->{type}, $self->{id})
		1073	}
		1074
		1075	2. "convert_blessed" is enabled and the object has a "TO_JSON" method.
		1076	In this case, the "TO_JSON" method of the object is invoked in
		1077	scalar context. It must return a single scalar that can be directly
		1078	encoded into JSON. This scalar replaces the object in the JSON text.
		1079
		1080	For example, the following "TO_JSON" method will convert all URI
		1081	objects to JSON strings when serialised. The fatc that these values
		1082	originally were URI objects is lost.
		1083
		1084	sub URI::TO_JSON {
		1085	my ($uri) = @_;
		1086	$uri->as_string
		1087	}
		1088
		1089	3. "allow_blessed" is enabled.
		1090	The object will be serialised as a JSON null value.
		1091
		1092	4. none of the above
		1093	If none of the settings are enabled or the respective methods are
		1094	missing, "JSON::XS" throws an exception.
		1095
		1096	DESERIALISATION
		1097	For deserialisation there are only two cases to consider: either
		1098	nonstandard tagging was used, in which case "allow_tags" decides, or
		1099	objects cannot be automatically be deserialised, in which case you can
		1100	use postprocessing or the "filter_json_object" or
		1101	"filter_json_single_key_object" callbacks to get some real objects our
		1102	of your JSON.
		1103
		1104	This section only considers the tagged value case: I a tagged JSON
		1105	object is encountered during decoding and "allow_tags" is disabled, a
		1106	parse error will result (as if tagged values were not part of the
		1107	grammar).
		1108
		1109	If "allow_tags" is enabled, "JSON::XS" will look up the "THAW" method of
		1110	the package/classname used during serialisation (it will not attempt to
		1111	load the package as a Perl module). If there is no such method, the
		1112	decoding will fail with an error.
		1113
		1114	Otherwise, the "THAW" method is invoked with the classname as first
		1115	argument, the constant string "JSON" as second argument, and all the
		1116	values from the JSON array (the values originally returned by the
		1117	"FREEZE" method) as remaining arguments.
		1118
		1119	The method must then return the object. While technically you can return
		1120	any Perl scalar, you might have to enable the "enable_nonref" setting to
		1121	make that work in all cases, so better return an actual blessed
		1122	reference.
		1123
		1124	As an example, let's implement a "THAW" function that regenerates the
		1125	"My::Object" from the "FREEZE" example earlier:
		1126
		1127	sub My::Object::THAW {
		1128	my ($class, $serialiser, $type, $id) = @_;
		1129
		1130	$class->new (type => $type, id => $id)
		1131	}
		1132
1003	ENCODING/CODESET FLAG NOTES	1133	ENCODING/CODESET FLAG NOTES
1004	The interested reader might have seen a number of flags that signify	1134	The interested reader might have seen a number of flags that signify
1005	encodings or codesets - "utf8", "latin1" and "ascii". There seems to be	1135	encodings or codesets - "utf8", "latin1" and "ascii". There seems to be
1006	some confusion on what these do, so here is a short comparison:	1136	some confusion on what these do, so here is a short comparison:
1007		1137
…		…
1026		1156
1027	"utf8" flag disabled	1157	"utf8" flag disabled
1028	When "utf8" is disabled (the default), then "encode"/"decode"	1158	When "utf8" is disabled (the default), then "encode"/"decode"
1029	generate and expect Unicode strings, that is, characters with high	1159	generate and expect Unicode strings, that is, characters with high
1030	ordinal Unicode values (> 255) will be encoded as such characters,	1160	ordinal Unicode values (> 255) will be encoded as such characters,
1031	and likewise such characters are decoded as-is, no canges to them	1161	and likewise such characters are decoded as-is, no changes to them
1032	will be done, except "(re-)interpreting" them as Unicode codepoints	1162	will be done, except "(re-)interpreting" them as Unicode codepoints
1033	or Unicode characters, respectively (to Perl, these are the same	1163	or Unicode characters, respectively (to Perl, these are the same
1034	thing in strings unless you do funny/weird/dumb stuff).	1164	thing in strings unless you do funny/weird/dumb stuff).
1035		1165
1036	This is useful when you want to do the encoding yourself (e.g. when	1166	This is useful when you want to do the encoding yourself (e.g. when
…		…
1152	output for these property strings, e.g.:	1282	output for these property strings, e.g.:
1153		1283
1154	$json =~ s/"__proto__"\s*:/"__proto__renamed":/g;	1284	$json =~ s/"__proto__"\s*:/"__proto__renamed":/g;
1155		1285
1156	This works because "__proto__" is not valid outside of strings, so every	1286	This works because "__proto__" is not valid outside of strings, so every
1157	occurence of ""__proto__"\s*:" must be a string used as property name.	1287	occurrence of ""__proto__"\s*:" must be a string used as property name.
1158		1288
1159	If you know of other incompatibilities, please let me know.	1289	If you know of other incompatibilities, please let me know.
1160		1290
1161	JSON and YAML	1291	JSON and YAML
1162	You often hear that JSON is a subset of YAML. This is, however, a mass	1292	You often hear that JSON is a subset of YAML. This is, however, a mass
…		…
1313	to see whether you are vulnerable to some common attack vectors (which	1443	to see whether you are vulnerable to some common attack vectors (which
1314	really are browser design bugs, but it is still you who will have to	1444	really are browser design bugs, but it is still you who will have to
1315	deal with it, as major browser developers care only for features, not	1445	deal with it, as major browser developers care only for features, not
1316	about getting security right).	1446	about getting security right).
1317		1447
		1448	"OLD" VS. "NEW" JSON (RFC 4627 VS. RFC 7159)
		1449	TL;DR: Due to security concerns, JSON::XS will not allow scalar data in
		1450	JSON texts by default - you need to create your own JSON::XS object and
		1451	enable "allow_nonref":
		1452
		1453	my $json = JSON::XS->new->allow_nonref;
		1454
		1455	$text = $json->encode ($data);
		1456	$data = $json->decode ($text);
		1457
		1458	The long version: JSON being an important and supposedly stable format,
		1459	the IETF standardised it as RFC 4627 in 2006. Unfortunately, the
		1460	inventor of JSON, Dougles Crockford, unilaterally changed the definition
		1461	of JSON in javascript. Rather than create a fork, the IETF decided to
		1462	standardise the new syntax (apparently, so Iw as told, without finding
		1463	it very amusing).
		1464
		1465	The biggest difference between thed original JSON and the new JSON is
		1466	that the new JSON supports scalars (anything other than arrays and
		1467	objects) at the toplevel of a JSON text. While this is strictly
		1468	backwards compatible to older versions, it breaks a number of protocols
		1469	that relied on sending JSON back-to-back, and is a minor security
		1470	concern.
		1471
		1472	For example, imagine you have two banks communicating, and on one side,
		1473	trhe JSON coder gets upgraded. Two messages, such as 10 and 1000 might
		1474	then be confused to mean 101000, something that couldn't happen in the
		1475	original JSON, because niether of these messages would be valid JSON.
		1476
		1477	If one side accepts these messages, then an upgrade in the coder on
		1478	either side could result in this becoming exploitable.
		1479
		1480	This module has always allowed these messages as an optional extension,
		1481	by default disabled. The security concerns are the reason why the
		1482	default is still disabled, but future versions might/will likely upgrade
		1483	to the newer RFC as default format, so you are advised to check your
		1484	implementation and/or override the default with "->allow_nonref (0)" to
		1485	ensure that future versions are safe.
		1486
		1487	INTEROPERABILITY WITH OTHER MODULES
		1488	"JSON::XS" uses the Types::Serialiser module to provide boolean
		1489	constants. That means that the JSON true and false values will be
		1490	comaptible to true and false values of other modules that do the same,
		1491	such as JSON::PP and CBOR::XS.
		1492
		1493	INTEROPERABILITY WITH OTHER JSON DECODERS
		1494	As long as you only serialise data that can be directly expressed in
		1495	JSON, "JSON::XS" is incapable of generating invalid JSON output (modulo
		1496	bugs, but "JSON::XS" has found more bugs in the official JSON testsuite
		1497	(1) than the official JSON testsuite has found in "JSON::XS" (0)).
		1498
		1499	When you have trouble decoding JSON generated by this module using other
		1500	decoders, then it is very likely that you have an encoding mismatch or
		1501	the other decoder is broken.
		1502
		1503	When decoding, "JSON::XS" is strict by default and will likely catch all
		1504	errors. There are currently two settings that change this: "relaxed"
		1505	makes "JSON::XS" accept (but not generate) some non-standard extensions,
		1506	and "allow_tags" will allow you to encode and decode Perl objects, at
		1507	the cost of not outputting valid JSON anymore.
		1508
		1509	TAGGED VALUE SYNTAX AND STANDARD JSON EN/DECODERS
		1510	When you use "allow_tags" to use the extended (and also nonstandard and
		1511	invalid) JSON syntax for serialised objects, and you still want to
		1512	decode the generated When you want to serialise objects, you can run a
		1513	regex to replace the tagged syntax by standard JSON arrays (it only
		1514	works for "normal" package names without comma, newlines or single
		1515	colons). First, the readable Perl version:
		1516
		1517	# if your FREEZE methods return no values, you need this replace first:
		1518	$json =~ s/$ \s* (" (?: [^\\":,]+\|\\.\|::)* ") \s* $ \s* \[\s*\]/[$1]/gx;
		1519
		1520	# this works for non-empty constructor arg lists:
		1521	$json =~ s/$ \s* (" (?: [^\\":,]+\|\\.\|::)* ") \s* $ \s* \[/[$1,/gx;
		1522
		1523	And here is a less readable version that is easy to adapt to other
		1524	languages:
		1525
		1526	$json =~ s/$\s("([^\\":,]+\|\\.\|::)")\s$\s\[/[$1,/g;
		1527
		1528	Here is an ECMAScript version (same regex):
		1529
		1530	json = json.replace (/$\s("([^\\":,]+\|\\.\|::)")\s$\s\[/g, "[$1,");
		1531
		1532	Since this syntax converts to standard JSON arrays, it might be hard to
		1533	distinguish serialised objects from normal arrays. You can prepend a
		1534	"magic number" as first array element to reduce chances of a collision:
		1535
		1536	$json =~ s/$\s("([^\\":,]+\|\\.\|::)")\s$\s\[/["XU1peReLzT4ggEllLanBYq4G9VzliwKF",$1,/g;
		1537
		1538	And after decoding the JSON text, you could walk the data structure
		1539	looking for arrays with a first element of
		1540	"XU1peReLzT4ggEllLanBYq4G9VzliwKF".
		1541
		1542	The same approach can be used to create the tagged format with another
		1543	encoder. First, you create an array with the magic string as first
		1544	member, the classname as second, and constructor arguments last, encode
		1545	it as part of your JSON structure, and then:
		1546
		1547	$json =~ s/\[\s"XU1peReLzT4ggEllLanBYq4G9VzliwKF"\s,\s("([^\\":,]+\|\\.\|::)")\s*,/($1)[/g;
		1548
		1549	Again, this has some limitations - the magic string must not be encoded
		1550	with character escapes, and the constructor arguments must be non-empty.
		1551
		1552	RFC7159
		1553	Since this module was written, Google has written a new JSON RFC, RFC
		1554	7159 (and RFC7158). Unfortunately, this RFC breaks compatibility with
		1555	both the original JSON specification on www.json.org and RFC4627.
		1556
		1557	As far as I can see, you can get partial compatibility when parsing by
		1558	using "->allow_nonref". However, consider the security implications of
		1559	doing so.
		1560
		1561	I haven't decided yet when to break compatibility with RFC4627 by
		1562	default (and potentially leave applications insecure) and change the
		1563	default to follow RFC7159, but application authors are well advised to
		1564	call "->allow_nonref(0)" even if this is the current default, if they
		1565	cannot handle non-reference values, in preparation for the day when the
		1566	default will change.
		1567
1318	THREADS	1568	(I-)THREADS
1319	This module is not guaranteed to be thread safe and there are no plans	1569	This module is not guaranteed to be ithread (or MULTIPLICITY-) safe
1320	to change this until Perl gets thread support (as opposed to the	1570	and there are no plans to change this. Note that perl's builtin
1321	horribly slow so-called "threads" which are simply slow and bloated	1571	so-called theeads/ithreads are officially deprecated and should not be
1322	process simulations - use fork, it's much faster, cheaper, better).	1572	used.
1323
1324	(It might actually work, but you have been warned).
1325		1573
1326	THE PERILS OF SETLOCALE	1574	THE PERILS OF SETLOCALE
1327	Sometimes people avoid the Perl locale support and directly call the	1575	Sometimes people avoid the Perl locale support and directly call the
1328	system's setlocale function with "LC_ALL".	1576	system's setlocale function with "LC_ALL".
1329		1577
1330	This breaks both perl and modules such as JSON::XS, as stringification	1578	This breaks both perl and modules such as JSON::XS, as stringification
1331	of numbers no longer works correcly (e.g. "$x = 0.1; print "$x"+1" might	1579	of numbers no longer works correctly (e.g. "$x = 0.1; print "$x"+1"
1332	print 1, and JSON::XS might output illegal JSON as JSON::XS relies on	1580	might print 1, and JSON::XS might output illegal JSON as JSON::XS relies
1333	perl to stringify numbers).	1581	on perl to stringify numbers).
1334		1582
1335	The solution is simple: don't call "setlocale", or use it for only those	1583	The solution is simple: don't call "setlocale", or use it for only those
1336	categories you need, such as "LC_MESSAGES" or "LC_CTYPE".	1584	categories you need, such as "LC_MESSAGES" or "LC_CTYPE".
1337		1585
1338	If you need "LC_NUMERIC", you should enable it only around the code that	1586	If you need "LC_NUMERIC", you should enable it only around the code that

Diff Legend

-–
+Removed lines
-+
+Added lines
-<
+Changed lines
->
+Changed lines

Comparing JSON-XS/README (file contents): Revision 1.37 by root, Thu May 23 09:32:02 2013 UTC vs. Revision 1.42 by root, Thu Aug 17 03:47:54 2017 UTC

Diff Legend

Comparing JSON-XS/README (file contents):
Revision 1.37 by root, Thu May 23 09:32:02 2013 UTC vs.
Revision 1.42 by root, Thu Aug 17 03:47:54 2017 UTC