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

Comparing JSON-XS/README (file contents):
Revision 1.31 by root, Sat Aug 8 10:06:02 2009 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
…		…
56	does so, and even documents what "correct" means.	56	does so, and even documents what "correct" means.
57		57
58	* round-trip integrity	58	* round-trip integrity
59		59
60	When you serialise a perl data structure using only data types	60	When you serialise a perl data structure using only data types
61	supported by JSON, the deserialised data structure is identical on	61	supported by JSON and Perl, the deserialised data structure is
62	the Perl level. (e.g. the string "2.0" doesn't suddenly become "2"	62	identical on the Perl level. (e.g. the string "2.0" doesn't suddenly
63	just because it looks like a number). There minor are exceptions	63	become "2" just because it looks like a number). There are minor
64	to this, read the MAPPING section below to learn about those.	64	exceptions to this, read the MAPPING section below to learn about
		65	those.
65		66
66	* strict checking of JSON correctness	67	* strict checking of JSON correctness
67		68
68	There is no guessing, no generating of illegal JSON texts by	69	There is no guessing, no generating of illegal JSON texts by
69	default, and only JSON is accepted as input by default (the latter	70	default, and only JSON is accepted as input by default (the latter
…		…
76	too.	77	too.
77		78
78	* simple to use	79	* simple to use
79		80
80	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
81	object oriented interface interface.	82	object oriented interface.
82		83
83	* reasonably versatile output formats	84	* reasonably versatile output formats
84		85
85	You can choose between the most compact guaranteed-single-line	86	You can choose between the most compact guaranteed-single-line
86	format possible (nice for simple line-based protocols), a pure-ASCII	87	format possible (nice for simple line-based protocols), a pure-ASCII
…		…
111	This function call is functionally identical to:	112	This function call is functionally identical to:
112		113
113	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)	114	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)
114		115
115	Except being faster.	116	Except being faster.
116
117	$is_boolean = JSON::XS::is_bool $scalar
118	Returns true if the passed scalar represents either JSON::XS::true
119	or JSON::XS::false, two constants that act like 1 and 0,
120	respectively and are used to represent JSON "true" and "false"
121	values in Perl.
122
123	See MAPPING, below, for more information on how JSON values are
124	mapped to Perl.
125		117
126	A FEW NOTES ON UNICODE AND PERL	118	A FEW NOTES ON UNICODE AND PERL
127	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
128	how Unicode works in Perl, modulo bugs.	120	how Unicode works in Perl, modulo bugs.
129		121
…		…
360	[	352	[
361	1, # this comment not allowed in JSON	353	1, # this comment not allowed in JSON
362	# neither this one...	354	# neither this one...
363	]	355	]
364		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
365	$json = $json->canonical ([$enable])	367	$json = $json->canonical ([$enable])
366	$enabled = $json->get_canonical	368	$enabled = $json->get_canonical
367	If $enable is true (or missing), then the "encode" method will	369	If $enable is true (or missing), then the "encode" method will
368	output JSON objects by sorting their keys. This is adding a	370	output JSON objects by sorting their keys. This is adding a
369	comparatively high overhead.	371	comparatively high overhead.
370		372
371	If $enable is false, then the "encode" method will output key-value	373	If $enable is false, then the "encode" method will output key-value
372	pairs in the order Perl stores them (which will likely change	374	pairs in the order Perl stores them (which will likely change
373	between runs of the same script).	375	between runs of the same script, and can change even within the same
		376	run from 5.18 onwards).
374		377
375	This option is useful if you want the same data structure to be	378	This option is useful if you want the same data structure to be
376	encoded as the same JSON text (given the same overall settings). If	379	encoded as the same JSON text (given the same overall settings). If
377	it is disabled, the same hash might be encoded differently even if	380	it is disabled, the same hash might be encoded differently even if
378	contains the same data, as key-value pairs have no inherent ordering	381	contains the same data, as key-value pairs have no inherent ordering
…		…
415	recommended to leave it off unless you know your communications	418	recommended to leave it off unless you know your communications
416	partner.	419	partner.
417		420
418	$json = $json->allow_blessed ([$enable])	421	$json = $json->allow_blessed ([$enable])
419	$enabled = $json->get_allow_blessed	422	$enabled = $json->get_allow_blessed
		423	See "OBJECT SERIALISATION" for details.
		424
420	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
421	barf when it encounters a blessed reference. Instead, the value of	426	barf when it encounters a blessed reference that it cannot convert
422	the convert_blessed option will decide whether "null"	427	otherwise. Instead, a JSON "null" value is encoded instead of the
423	("convert_blessed" disabled or no "TO_JSON" method found) or a	428	object.
424	representation of the object ("convert_blessed" enabled and
425	"TO_JSON" method found) is being encoded. Has no effect on "decode".
426		429
427	If $enable is false (the default), then "encode" will throw an	430	If $enable is false (the default), then "encode" will throw an
428	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".
429		435
430	$json = $json->convert_blessed ([$enable])	436	$json = $json->convert_blessed ([$enable])
431	$enabled = $json->get_convert_blessed	437	$enabled = $json->get_convert_blessed
		438	See "OBJECT SERIALISATION" for details.
		439
432	If $enable is true (or missing), then "encode", upon encountering a	440	If $enable is true (or missing), then "encode", upon encountering a
433	blessed object, will check for the availability of the "TO_JSON"	441	blessed object, will check for the availability of the "TO_JSON"
434	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
435	context and the resulting scalar will be encoded instead of the	443	context and the resulting scalar will be encoded instead of the
436	object. If no "TO_JSON" method is found, the value of	444	object.
437	"allow_blessed" will decide what to do.
438		445
439	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"
440	returns other blessed objects, those will be handled in the same	447	returns other blessed objects, those will be handled in the same
441	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
442	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
443	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
444	the object) are usually in upper case letters and to avoid	451	the object) are usually in upper case letters and to avoid
445	collisions with any "to_json" function or method.	452	collisions with any "to_json" function or method.
446		453
447	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
448	future, global hooks might get installed that influence "decode" and	455	this type of conversion.
449	are enabled by this setting.
450		456
451	If $enable is false, then the "allow_blessed" setting will decide	457	This setting has no effect on "decode".
452	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.
453		475
454	$json = $json->filter_json_object ([$coderef->($hashref)])	476	$json = $json->filter_json_object ([$coderef->($hashref)])
455	When $coderef is specified, it will be called from "decode" each	477	When $coderef is specified, it will be called from "decode" each
456	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
457	the newly-created hash. If the code references returns a single	479	the newly-created hash. If the code references returns a single
…		…
593		615
594	See SECURITY CONSIDERATIONS, below, for more info on why this is	616	See SECURITY CONSIDERATIONS, below, for more info on why this is
595	useful.	617	useful.
596		618
597	$json_text = $json->encode ($perl_scalar)	619	$json_text = $json->encode ($perl_scalar)
598	Converts the given Perl data structure (a simple scalar or a	620	Converts the given Perl value or data structure to its JSON
599	reference to a hash or array) to its JSON representation. Simple	621	representation. Croaks on error.
600	scalars will be converted into JSON string or number sequences,
601	while references to arrays become JSON arrays and references to
602	hashes become JSON objects. Undefined Perl values (e.g. "undef")
603	become JSON "null" values. Neither "true" nor "false" values will be
604	generated.
605		622
606	$perl_scalar = $json->decode ($json_text)	623	$perl_scalar = $json->decode ($json_text)
607	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,
608	returning the resulting simple scalar or reference. Croaks on error.	625	returning the resulting simple scalar or reference. Croaks on error.
609
610	JSON numbers and strings become simple Perl scalars. JSON arrays
611	become Perl arrayrefs and JSON objects become Perl hashrefs. "true"
612	becomes 1, "false" becomes 0 and "null" becomes "undef".
613		626
614	($perl_scalar, $characters) = $json->decode_prefix ($json_text)	627	($perl_scalar, $characters) = $json->decode_prefix ($json_text)
615	This works like the "decode" method, but instead of raising an	628	This works like the "decode" method, but instead of raising an
616	exception when there is trailing garbage after the first JSON	629	exception when there is trailing garbage after the first JSON
617	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
618	characters consumed so far.	631	characters consumed so far.
619		632
620	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
621	protocol (which is not the brightest thing to do in the first place)
622	and you need to know where the JSON text ends.	634	protocol and you need to know where the JSON text ends.
623		635
624	JSON::XS->new->decode_prefix ("[1] the tail")	636	JSON::XS->new->decode_prefix ("[1] the tail")
625	=> ([], 3)	637	=> ([1], 3)
626		638
627	INCREMENTAL PARSING	639	INCREMENTAL PARSING
628	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.
629	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
630	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
…		…
635	calls).	647	calls).
636		648
637	JSON::XS will only attempt to parse the JSON text once it is sure it has	649	JSON::XS will only attempt to parse the JSON text once it is sure it has
638	enough text to get a decisive result, using a very simple but truly	650	enough text to get a decisive result, using a very simple but truly
639	incremental parser. This means that it sometimes won't stop as early as	651	incremental parser. This means that it sometimes won't stop as early as
640	the full parser, for example, it doesn't detect parenthese mismatches.	652	the full parser, for example, it doesn't detect mismatched parentheses.
641	The only thing it guarantees is that it starts decoding as soon as a	653	The only thing it guarantees is that it starts decoding as soon as a
642	syntactically valid JSON text has been seen. This means you need to set	654	syntactically valid JSON text has been seen. This means you need to set
643	resource limits (e.g. "max_size") to ensure the parser will stop parsing	655	resource limits (e.g. "max_size") to ensure the parser will stop parsing
644	in the presence if syntax errors.	656	in the presence if syntax errors.
645		657
…		…
659		671
660	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
661	extract exactly one JSON object. If that is successful, it will	673	extract exactly one JSON object. If that is successful, it will
662	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
663	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
664	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
665	most common way of using the method.	677	most common way of using the method.
666		678
667	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
668	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
669	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
670	JSON objects or arrays, instead they must be concatenated	682	whitespace) between the JSON objects or arrays, instead they must be
671	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
672	the scalar context case. Note that in this case, any	684	raised as in the scalar context case. Note that in this case, any
673	previously-parsed JSON texts will be lost.	685	previously-parsed JSON texts will be lost.
		686
		687	Example: Parse some JSON arrays/objects in a given string and return
		688	them.
		689
		690	my @objs = JSON::XS->new->incr_parse ("[5][7][1,2]");
674		691
675	$lvalue_string = $json->incr_text	692	$lvalue_string = $json->incr_text
676	This method returns the currently stored JSON fragment as an lvalue,	693	This method returns the currently stored JSON fragment as an lvalue,
677	that is, you can manipulate it. This only works when a preceding	694	that is, you can manipulate it. This only works when a preceding
678	call to "incr_parse" in scalar context successfully returned an	695	call to "incr_parse" in scalar context successfully returned an
…		…
680	function (I mean it. although in simple tests it might actually	697	function (I mean it. although in simple tests it might actually
681	work, it will fail under real world conditions). As a special	698	work, it will fail under real world conditions). As a special
682	exception, you can also call this method before having parsed	699	exception, you can also call this method before having parsed
683	anything.	700	anything.
684		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
685	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
686	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
687	non-JSON text (such as commas).	708	non-JSON text (such as commas).
688		709
689	$json->incr_skip	710	$json->incr_skip
…		…
692	"incr_parse" died, in which case the input buffer and incremental	713	"incr_parse" died, in which case the input buffer and incremental
693	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
694	to reset the parse state.	715	to reset the parse state.
695		716
696	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
697	error occured is removed.	718	error occurred is removed.
698		719
699	$json->incr_reset	720	$json->incr_reset
700	This completely resets the incremental parser, that is, after this	721	This completely resets the incremental parser, that is, after this
701	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.
702		723
…		…
886	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
887	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
888	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
889	without loss of precision. Otherwise it will preserve the number as	910	without loss of precision. Otherwise it will preserve the number as
890	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
891	JSON number will be re-encoded toa JSON string).	912	JSON number will be re-encoded to a JSON string).
892		913
893	Numbers containing a fractional or exponential part will always be	914	Numbers containing a fractional or exponential part will always be
894	represented as numeric (floating point) values, possibly at a loss	915	represented as numeric (floating point) values, possibly at a loss
895	of precision (in which case you might lose perfect roundtripping	916	of precision (in which case you might lose perfect roundtripping
896	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
897	number).	918	number).
898		919
		920	Note that precision is not accuracy - binary floating point values
		921	cannot represent most decimal fractions exactly, and when converting
		922	from and to floating point, JSON::XS only guarantees precision up to
		923	but not including the least significant bit.
		924
899	true, false	925	true, false
900	These JSON atoms become "JSON::XS::true" and "JSON::XS::false",	926	These JSON atoms become "Types::Serialiser::true" and
901	respectively. They are overloaded to act almost exactly like the	927	"Types::Serialiser::false", respectively. They are overloaded to act
902	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
903	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).
904		931
905	null	932	null
906	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.
907		948
908	PERL -> JSON	949	PERL -> JSON
909	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
910	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
911	by a Perl value.	952	by a Perl value.
912		953
913	hash references	954	hash references
914	Perl hash references become JSON objects. As there is no inherent	955	Perl hash references become JSON objects. As there is no inherent
915	ordering in hash keys (or JSON objects), they will usually be	956	ordering in hash keys (or JSON objects), they will usually be
916	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
917	same program but stays generally the same within a single run of a	958	hash keys (determined by the canonical flag), so the same
918	program. JSON::XS can optionally sort the hash keys (determined by	959	datastructure will serialise to the same JSON text (given same
919	the canonical flag), so the same datastructure will serialise to	960	settings and version of JSON::XS), but this incurs a runtime
920	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
921	but this incurs a runtime overhead and is only rarely useful, e.g.	962	some JSON text against another for equality.
922	when you want to compare some JSON text against another for
923	equality.
924		963
925	array references	964	array references
926	Perl array references become JSON arrays.	965	Perl array references become JSON arrays.
927		966
928	other references	967	other references
929	Other unblessed references are generally not allowed and will cause	968	Other unblessed references are generally not allowed and will cause
930	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
931	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.
932	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
933	readability.	975	readability.
934		976
		977	use Types::Serialiser;
935	encode_json [\0, JSON::XS::true] # yields [false,true]	978	encode_json [\0, Types::Serialiser::true] # yields [false,true]
936		979
937	JSON::XS::true, JSON::XS::false	980	Types::Serialiser::true, Types::Serialiser::false
938	These special values become JSON true and JSON false values,	981	These special values from the Types::Serialiser module become JSON
939	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.
940		984
941	blessed objects	985	blessed objects
942	Blessed objects are not directly representable in JSON. See the	986	Blessed objects are not directly representable in JSON, but
943	"allow_blessed" and "convert_blessed" methods on various options on	987	"JSON::XS" allows various ways of handling objects. See "OBJECT
944	how to deal with this: basically, you can choose between throwing an	988	SERIALISATION", below, for details.
945	exception, encoding the reference as if it weren't blessed, or
946	provide your own serialiser method.
947		989
948	simple scalars	990	simple scalars
949	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
950	most difficult objects to encode: JSON::XS will encode undefined	992	most difficult objects to encode: JSON::XS will encode undefined
951	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
…		…
979		1021
980	You can not currently force the type in other, less obscure, ways.	1022	You can not currently force the type in other, less obscure, ways.
981	Tell me if you need this capability (but don't forget to explain why	1023	Tell me if you need this capability (but don't forget to explain why
982	it's needed :).	1024	it's needed :).
983		1025
		1026	Note that numerical precision has the same meaning as under Perl (so
		1027	binary to decimal conversion follows the same rules as in Perl,
		1028	which can differ to other languages). Also, your perl interpreter
		1029	might expose extensions to the floating point numbers of your
		1030	platform, such as infinities or NaN's - these cannot be represented
		1031	in JSON, and it is an error to pass those in.
		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
984	ENCODING/CODESET FLAG NOTES	1133	ENCODING/CODESET FLAG NOTES
985	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
986	encodings or codesets - "utf8", "latin1" and "ascii". There seems to be	1135	encodings or codesets - "utf8", "latin1" and "ascii". There seems to be
987	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:
988		1137
…		…
1007		1156
1008	"utf8" flag disabled	1157	"utf8" flag disabled
1009	When "utf8" is disabled (the default), then "encode"/"decode"	1158	When "utf8" is disabled (the default), then "encode"/"decode"
1010	generate and expect Unicode strings, that is, characters with high	1159	generate and expect Unicode strings, that is, characters with high
1011	ordinal Unicode values (> 255) will be encoded as such characters,	1160	ordinal Unicode values (> 255) will be encoded as such characters,
1012	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
1013	will be done, except "(re-)interpreting" them as Unicode codepoints	1162	will be done, except "(re-)interpreting" them as Unicode codepoints
1014	or Unicode characters, respectively (to Perl, these are the same	1163	or Unicode characters, respectively (to Perl, these are the same
1015	thing in strings unless you do funny/weird/dumb stuff).	1164	thing in strings unless you do funny/weird/dumb stuff).
1016		1165
1017	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
…		…
1125	characters as well - using "eval" naively simply will cause problems.	1274	characters as well - using "eval" naively simply will cause problems.
1126		1275
1127	Another problem is that some javascript implementations reserve some	1276	Another problem is that some javascript implementations reserve some
1128	property names for their own purposes (which probably makes them	1277	property names for their own purposes (which probably makes them
1129	non-ECMAscript-compliant). For example, Iceweasel reserves the	1278	non-ECMAscript-compliant). For example, Iceweasel reserves the
1130	"__proto__" property name for it's own purposes.	1279	"__proto__" property name for its own purposes.
1131		1280
1132	If that is a problem, you could parse try to filter the resulting JSON	1281	If that is a problem, you could parse try to filter the resulting JSON
1133	output for these property strings, e.g.:	1282	output for these property strings, e.g.:
1134		1283
1135	$json =~ s/"__proto__"\s*:/"__proto__renamed":/g;	1284	$json =~ s/"__proto__"\s*:/"__proto__renamed":/g;
1136		1285
1137	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
1138	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.
1139		1288
1140	If you know of other incompatibilities, please let me know.	1289	If you know of other incompatibilities, please let me know.
1141		1290
1142	JSON and YAML	1291	JSON and YAML
1143	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
…		…
1153	my $yaml = $to_yaml->encode ($ref) . "\n";	1302	my $yaml = $to_yaml->encode ($ref) . "\n";
1154		1303
1155	This will usually generate JSON texts that also parse as valid YAML.	1304	This will usually generate JSON texts that also parse as valid YAML.
1156	Please note that YAML has hardcoded limits on (simple) object key	1305	Please note that YAML has hardcoded limits on (simple) object key
1157	lengths that JSON doesn't have and also has different and incompatible	1306	lengths that JSON doesn't have and also has different and incompatible
1158	unicode handling, so you should make sure that your hash keys are	1307	unicode character escape syntax, so you should make sure that your hash
1159	noticeably shorter than the 1024 "stream characters" YAML allows and	1308	keys are noticeably shorter than the 1024 "stream characters" YAML
1160	that you do not have characters with codepoint values outside the	1309	allows and that you do not have characters with codepoint values outside
1161	Unicode BMP (basic multilingual page). YAML also does not allow "\/"	1310	the Unicode BMP (basic multilingual page). YAML also does not allow "\/"
1162	sequences in strings (which JSON::XS does not currently generate, but	1311	sequences in strings (which JSON::XS does not currently generate, but
1163	other JSON generators might).	1312	other JSON generators might).
1164		1313
1165	There might be other incompatibilities that I am not aware of (or the	1314	There might be other incompatibilities that I am not aware of (or the
1166	YAML specification has been changed yet again - it does so quite often).	1315	YAML specification has been changed yet again - it does so quite often).
…		…
1183	(which is not that difficult or long) and finally make YAML	1332	(which is not that difficult or long) and finally make YAML
1184	compatible to it, and educating users about the changes, instead of	1333	compatible to it, and educating users about the changes, instead of
1185	spreading lies about the real compatibility for many years and	1334	spreading lies about the real compatibility for many years and
1186	trying to silence people who point out that it isn't true.	1335	trying to silence people who point out that it isn't true.
1187		1336
		1337	Addendum/2009: the YAML 1.2 spec is still incompatible with JSON,
		1338	even though the incompatibilities have been documented (and are
		1339	known to Brian) for many years and the spec makes explicit claims
		1340	that YAML is a superset of JSON. It would be so easy to fix, but
		1341	apparently, bullying people and corrupting userdata is so much
		1342	easier.
		1343
1188	SPEED	1344	SPEED
1189	It seems that JSON::XS is surprisingly fast, as shown in the following	1345	It seems that JSON::XS is surprisingly fast, as shown in the following
1190	tables. They have been generated with the help of the "eg/bench" program	1346	tables. They have been generated with the help of the "eg/bench" program
1191	in the JSON::XS distribution, to make it easy to compare on your own	1347	in the JSON::XS distribution, to make it easy to compare on your own
1192	system.	1348	system.
…		…
1195	single-line JSON string (also available at	1351	single-line JSON string (also available at
1196	<http://dist.schmorp.de/misc/json/short.json>).	1352	<http://dist.schmorp.de/misc/json/short.json>).
1197		1353
1198	{"method": "handleMessage", "params": ["user1",	1354	{"method": "handleMessage", "params": ["user1",
1199	"we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7,	1355	"we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7,
1200	true, false]}	1356	1, 0]}
1201		1357
1202	It shows the number of encodes/decodes per second (JSON::XS uses the	1358	It shows the number of encodes/decodes per second (JSON::XS uses the
1203	functional interface, while JSON::XS/2 uses the OO interface with	1359	functional interface, while JSON::XS/2 uses the OO interface with
1204	pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink).	1360	pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink.
1205	Higher is better:	1361	JSON::DWIW/DS uses the deserialise function, while JSON::DWIW::FJ uses
		1362	the from_json method). Higher is better:
1206		1363
1207	module \| encode \| decode \|	1364	module \| encode \| decode \|
1208	-----------\|------------\|------------\|	1365	--------------\|------------\|------------\|
1209	JSON 1.x \| 4990.842 \| 4088.813 \|	1366	JSON::DWIW/DS \| 86302.551 \| 102300.098 \|
1210	JSON::DWIW \| 51653.990 \| 71575.154 \|	1367	JSON::DWIW/FJ \| 86302.551 \| 75983.768 \|
1211	JSON::PC \| 65948.176 \| 74631.744 \|	1368	JSON::PP \| 15827.562 \| 6638.658 \|
1212	JSON::PP \| 8931.652 \| 3817.168 \|	1369	JSON::Syck \| 63358.066 \| 47662.545 \|
1213	JSON::Syck \| 24877.248 \| 27776.848 \|	1370	JSON::XS \| 511500.488 \| 511500.488 \|
1214	JSON::XS \| 388361.481 \| 227951.304 \|	1371	JSON::XS/2 \| 291271.111 \| 388361.481 \|
1215	JSON::XS/2 \| 227951.304 \| 218453.333 \|	1372	JSON::XS/3 \| 361577.931 \| 361577.931 \|
1216	JSON::XS/3 \| 338250.323 \| 218453.333 \|	1373	Storable \| 66788.280 \| 265462.278 \|
1217	Storable \| 16500.016 \| 135300.129 \|
1218	-----------+------------+------------+	1374	--------------+------------+------------+
1219		1375
1220	That is, JSON::XS is about five times faster than JSON::DWIW on	1376	That is, JSON::XS is almost six times faster than JSON::DWIW on
1221	encoding, about three times faster on decoding, and over forty times	1377	encoding, about five times faster on decoding, and over thirty to
1222	faster than JSON, even with pretty-printing and key sorting. It also	1378	seventy times faster than JSON's pure perl implementation. It also
1223	compares favourably to Storable for small amounts of data.	1379	compares favourably to Storable for small amounts of data.
1224		1380
1225	Using a longer test string (roughly 18KB, generated from Yahoo! Locals	1381	Using a longer test string (roughly 18KB, generated from Yahoo! Locals
1226	search API (<http://dist.schmorp.de/misc/json/long.json>).	1382	search API (<http://dist.schmorp.de/misc/json/long.json>).
1227		1383
1228	module \| encode \| decode \|	1384	module \| encode \| decode \|
1229	-----------\|------------\|------------\|	1385	--------------\|------------\|------------\|
1230	JSON 1.x \| 55.260 \| 34.971 \|	1386	JSON::DWIW/DS \| 1647.927 \| 2673.916 \|
1231	JSON::DWIW \| 825.228 \| 1082.513 \|	1387	JSON::DWIW/FJ \| 1630.249 \| 2596.128 \|
1232	JSON::PC \| 3571.444 \| 2394.829 \|
1233	JSON::PP \| 210.987 \| 32.574 \|	1388	JSON::PP \| 400.640 \| 62.311 \|
1234	JSON::Syck \| 552.551 \| 787.544 \|	1389	JSON::Syck \| 1481.040 \| 1524.869 \|
1235	JSON::XS \| 5780.463 \| 4854.519 \|	1390	JSON::XS \| 20661.596 \| 9541.183 \|
1236	JSON::XS/2 \| 3869.998 \| 4798.975 \|	1391	JSON::XS/2 \| 10683.403 \| 9416.938 \|
1237	JSON::XS/3 \| 5862.880 \| 4798.975 \|	1392	JSON::XS/3 \| 20661.596 \| 9400.054 \|
1238	Storable \| 4445.002 \| 5235.027 \|	1393	Storable \| 19765.806 \| 10000.725 \|
1239	-----------+------------+------------+	1394	--------------+------------+------------+
1240		1395
1241	Again, JSON::XS leads by far (except for Storable which non-surprisingly	1396	Again, JSON::XS leads by far (except for Storable which non-surprisingly
1242	decodes faster).	1397	decodes a bit faster).
1243		1398
1244	On large strings containing lots of high Unicode characters, some	1399	On large strings containing lots of high Unicode characters, some
1245	modules (such as JSON::PC) seem to decode faster than JSON::XS, but the	1400	modules (such as JSON::PC) seem to decode faster than JSON::XS, but the
1246	result will be broken due to missing (or wrong) Unicode handling. Others	1401	result will be broken due to missing (or wrong) Unicode handling. Others
1247	refuse to decode or encode properly, so it was impossible to prepare a	1402	refuse to decode or encode properly, so it was impossible to prepare a
…		…
1282	information you might want to make sure that exceptions thrown by	1437	information you might want to make sure that exceptions thrown by
1283	JSON::XS will not end up in front of untrusted eyes.	1438	JSON::XS will not end up in front of untrusted eyes.
1284		1439
1285	If you are using JSON::XS to return packets to consumption by JavaScript	1440	If you are using JSON::XS to return packets to consumption by JavaScript
1286	scripts in a browser you should have a look at	1441	scripts in a browser you should have a look at
1287	<http://jpsykes.com/47/practical-csrf-and-json-security> to see whether	1442	<http://blog.archive.jpsykes.com/47/practical-csrf-and-json-security/>
1288	you are vulnerable to some common attack vectors (which really are	1443	to see whether you are vulnerable to some common attack vectors (which
1289	browser design bugs, but it is still you who will have to deal with it,	1444	really are browser design bugs, but it is still you who will have to
1290	as major browser developers care only for features, not about getting	1445	deal with it, as major browser developers care only for features, not
1291	security right).	1446	about getting security right).
1292		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*,/($1)[/g;
		1548
		1549	Again, this has some limitations - the magic string must not be encoded
		1550	with character escapes, and the constructor arguments must be non-empty.
		1551
		1552	RFC7159
		1553	Since this module was written, Google has written a new JSON RFC, RFC
		1554	7159 (and RFC7158). Unfortunately, this RFC breaks compatibility with
		1555	both the original JSON specification on www.json.org and RFC4627.
		1556
		1557	As far as I can see, you can get partial compatibility when parsing by
		1558	using "->allow_nonref". However, consider the security implications of
		1559	doing so.
		1560
		1561	I haven't decided yet when to break compatibility with RFC4627 by
		1562	default (and potentially leave applications insecure) and change the
		1563	default to follow RFC7159, but application authors are well advised to
		1564	call "->allow_nonref(0)" even if this is the current default, if they
		1565	cannot handle non-reference values, in preparation for the day when the
		1566	default will change.
		1567
1293	THREADS	1568	(I-)THREADS
1294	This module is not guaranteed to be thread safe and there are no plans	1569	This module is not guaranteed to be ithread (or MULTIPLICITY-) safe
1295	to change this until Perl gets thread support (as opposed to the	1570	and there are no plans to change this. Note that perl's builtin
1296	horribly slow so-called "threads" which are simply slow and bloated	1571	so-called theeads/ithreads are officially deprecated and should not be
1297	process simulations - use fork, it's much faster, cheaper, better).	1572	used.
1298		1573
1299	(It might actually work, but you have been warned).	1574	THE PERILS OF SETLOCALE
		1575	Sometimes people avoid the Perl locale support and directly call the
		1576	system's setlocale function with "LC_ALL".
		1577
		1578	This breaks both perl and modules such as JSON::XS, as stringification
		1579	of numbers no longer works correctly (e.g. "$x = 0.1; print "$x"+1"
		1580	might print 1, and JSON::XS might output illegal JSON as JSON::XS relies
		1581	on perl to stringify numbers).
		1582
		1583	The solution is simple: don't call "setlocale", or use it for only those
		1584	categories you need, such as "LC_MESSAGES" or "LC_CTYPE".
		1585
		1586	If you need "LC_NUMERIC", you should enable it only around the code that
		1587	actually needs it (avoiding stringification of numbers), and restore it
		1588	afterwards.
1300		1589
1301	BUGS	1590	BUGS
1302	While the goal of this module is to be correct, that unfortunately does	1591	While the goal of this module is to be correct, that unfortunately does
1303	not mean it's bug-free, only that I think its design is bug-free. If you	1592	not mean it's bug-free, only that I think its design is bug-free. If you
1304	keep reporting bugs they will be fixed swiftly, though.	1593	keep reporting bugs they will be fixed swiftly, though.

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Comparing JSON-XS/README (file contents): Revision 1.31 by root, Sat Aug 8 10:06:02 2009 UTC vs. Revision 1.42 by root, Thu Aug 17 03:47:54 2017 UTC

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Comparing JSON-XS/README (file contents):
Revision 1.31 by root, Sat Aug 8 10:06:02 2009 UTC vs.
Revision 1.42 by root, Thu Aug 17 03:47:54 2017 UTC