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

Comparing JSON-XS/README (file contents):
Revision 1.23 by root, Wed Mar 19 22:31:00 2008 UTC vs.
Revision 1.39 by root, Tue Oct 29 15:55:49 2013 UTC

…		…
20	$perl_scalar = $coder->decode ($unicode_json_text);	20	$perl_scalar = $coder->decode ($unicode_json_text);
21		21
22	# Note that JSON version 2.0 and above will automatically use JSON::XS	22	# Note that JSON version 2.0 and above will automatically use JSON::XS
23	# if available, at virtually no speed overhead either, so you should	23	# if available, at virtually no speed overhead either, so you should
24	# be able to just:	24	# be able to just:
25		25
26	use JSON;	26	use JSON;
27		27
28	# and do the same things, except that you have a pure-perl fallback now.	28	# and do the same things, except that you have a pure-perl fallback now.
29		29
30	DESCRIPTION	30	DESCRIPTION
31	This module converts Perl data structures to JSON and vice versa. Its	31	This module converts Perl data structures to JSON and vice versa. Its
32	primary goal is to be correct and its secondary goal is to be fast.	32	primary goal is to be correct and its secondary goal is to be fast.
33	To reach the latter goal it was written in C.	33	To reach the latter goal it was written in C.
34		34
35	Beginning with version 2.0 of the JSON module, when both JSON and	35	Beginning with version 2.0 of the JSON module, when both JSON and
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 overriden) with no overhead due to emulation (by inheritign	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	and doesn't require a C compiler when that is a problem.
42		42
…		…
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
47	to bug reports for other reasons.	47	to bug reports for other reasons.
48		48
49	See COMPARISON, below, for a comparison to some other JSON modules.
50
51	See MAPPING, below, on how JSON::XS maps perl values to JSON values and	49	See MAPPING, below, on how JSON::XS maps perl values to JSON values and
52	vice versa.	50	vice versa.
53		51
54	FEATURES	52	FEATURES
55	* correct Unicode handling	53	* correct Unicode handling
…		…
57	This module knows how to handle Unicode, documents how and when it	55	This module knows how to handle Unicode, documents how and when it
58	does so, and even documents what "correct" means.	56	does so, and even documents what "correct" means.
59		57
60	* round-trip integrity	58	* round-trip integrity
61		59
62	When you serialise a perl data structure using only datatypes	60	When you serialise a perl data structure using only data types
63	supported by JSON, the deserialised data structure is identical on	61	supported by JSON and Perl, the deserialised data structure is
64	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
65	just because it looks like a number). There minor are exceptions	63	become "2" just because it looks like a number). There are minor
66	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.
67		66
68	* strict checking of JSON correctness	67	* strict checking of JSON correctness
69		68
70	There is no guessing, no generating of illegal JSON texts by	69	There is no guessing, no generating of illegal JSON texts by
71	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
…		…
78	too.	77	too.
79		78
80	* simple to use	79	* simple to use
81		80
82	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
83	objetc oriented interface interface.	82	object oriented interface.
84		83
85	* reasonably versatile output formats	84	* reasonably versatile output formats
86		85
87	You can choose between the most compact guaranteed-single-line	86	You can choose between the most compact guaranteed-single-line
88	format possible (nice for simple line-based protocols), a pure-ascii	87	format possible (nice for simple line-based protocols), a pure-ASCII
89	format (for when your transport is not 8-bit clean, still supports	88	format (for when your transport is not 8-bit clean, still supports
90	the whole Unicode range), or a pretty-printed format (for when you	89	the whole Unicode range), or a pretty-printed format (for when you
91	want to read that stuff). Or you can combine those features in	90	want to read that stuff). Or you can combine those features in
92	whatever way you like.	91	whatever way you like.
93		92
…		…
101		100
102	This function call is functionally identical to:	101	This function call is functionally identical to:
103		102
104	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)	103	$json_text = JSON::XS->new->utf8->encode ($perl_scalar)
105		104
106	except being faster.	105	Except being faster.
107		106
108	$perl_scalar = decode_json $json_text	107	$perl_scalar = decode_json $json_text
109	The opposite of "encode_json": expects an UTF-8 (binary) string and	108	The opposite of "encode_json": expects an UTF-8 (binary) string and
110	tries to parse that as an UTF-8 encoded JSON text, returning the	109	tries to parse that as an UTF-8 encoded JSON text, returning the
111	resulting reference. Croaks on error.	110	resulting reference. Croaks on error.
112		111
113	This function call is functionally identical to:	112	This function call is functionally identical to:
114		113
115	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)	114	$perl_scalar = JSON::XS->new->utf8->decode ($json_text)
116		115
117	except being faster.	116	Except being faster.
118
119	$is_boolean = JSON::XS::is_bool $scalar
120	Returns true if the passed scalar represents either JSON::XS::true
121	or JSON::XS::false, two constants that act like 1 and 0,
122	respectively and are used to represent JSON "true" and "false"
123	values in Perl.
124
125	See MAPPING, below, for more information on how JSON values are
126	mapped to Perl.
127		117
128	A FEW NOTES ON UNICODE AND PERL	118	A FEW NOTES ON UNICODE AND PERL
129	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
130	how Unicode works in Perl, modulo bugs.	120	how Unicode works in Perl, modulo bugs.
131		121
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152		142
153	If you didn't know about that flag, just the better, pretend it	143	If you didn't know about that flag, just the better, pretend it
154	doesn't exist.	144	doesn't exist.
155		145
156	4. A "Unicode String" is simply a string where each character can be	146	4. A "Unicode String" is simply a string where each character can be
157	validly interpreted as a Unicode codepoint.	147	validly interpreted as a Unicode code point.
158	If you have UTF-8 encoded data, it is no longer a Unicode string,	148	If you have UTF-8 encoded data, it is no longer a Unicode string,
159	but a Unicode string encoded in UTF-8, giving you a binary string.	149	but a Unicode string encoded in UTF-8, giving you a binary string.
160		150
161	5. A string containing "high" (> 255) character values is not a UTF-8	151	5. A string containing "high" (> 255) character values is not a UTF-8
162	string.	152	string.
…		…
370	output JSON objects by sorting their keys. This is adding a	360	output JSON objects by sorting their keys. This is adding a
371	comparatively high overhead.	361	comparatively high overhead.
372		362
373	If $enable is false, then the "encode" method will output key-value	363	If $enable is false, then the "encode" method will output key-value
374	pairs in the order Perl stores them (which will likely change	364	pairs in the order Perl stores them (which will likely change
375	between runs of the same script).	365	between runs of the same script, and can change even within the same
		366	run from 5.18 onwards).
376		367
377	This option is useful if you want the same data structure to be	368	This option is useful if you want the same data structure to be
378	encoded as the same JSON text (given the same overall settings). If	369	encoded as the same JSON text (given the same overall settings). If
379	it is disabled, the same hash might be encoded differently even if	370	it is disabled, the same hash might be encoded differently even if
380	contains the same data, as key-value pairs have no inherent ordering	371	contains the same data, as key-value pairs have no inherent ordering
381	in Perl.	372	in Perl.
382		373
383	This setting has no effect when decoding JSON texts.	374	This setting has no effect when decoding JSON texts.
		375
		376	This setting has currently no effect on tied hashes.
384		377
385	$json = $json->allow_nonref ([$enable])	378	$json = $json->allow_nonref ([$enable])
386	$enabled = $json->get_allow_nonref	379	$enabled = $json->get_allow_nonref
387	If $enable is true (or missing), then the "encode" method can	380	If $enable is true (or missing), then the "encode" method can
388	convert a non-reference into its corresponding string, number or	381	convert a non-reference into its corresponding string, number or
…		…
398	"allow_nonref", resulting in an invalid JSON text:	391	"allow_nonref", resulting in an invalid JSON text:
399		392
400	JSON::XS->new->allow_nonref->encode ("Hello, World!")	393	JSON::XS->new->allow_nonref->encode ("Hello, World!")
401	=> "Hello, World!"	394	=> "Hello, World!"
402		395
		396	$json = $json->allow_unknown ([$enable])
		397	$enabled = $json->get_allow_unknown
		398	If $enable is true (or missing), then "encode" will not throw an
		399	exception when it encounters values it cannot represent in JSON (for
		400	example, filehandles) but instead will encode a JSON "null" value.
		401	Note that blessed objects are not included here and are handled
		402	separately by c<allow_nonref>.
		403
		404	If $enable is false (the default), then "encode" will throw an
		405	exception when it encounters anything it cannot encode as JSON.
		406
		407	This option does not affect "decode" in any way, and it is
		408	recommended to leave it off unless you know your communications
		409	partner.
		410
403	$json = $json->allow_blessed ([$enable])	411	$json = $json->allow_blessed ([$enable])
404	$enabled = $json->get_allow_blessed	412	$enabled = $json->get_allow_blessed
		413	See "OBJECT SERIALISATION" for details.
		414
405	If $enable is true (or missing), then the "encode" method will not	415	If $enable is true (or missing), then the "encode" method will not
406	barf when it encounters a blessed reference. Instead, the value of	416	barf when it encounters a blessed reference that it cannot convert
407	the convert_blessed option will decide whether "null"	417	otherwise. Instead, a JSON "null" value is encoded instead of the
408	("convert_blessed" disabled or no "TO_JSON" method found) or a	418	object.
409	representation of the object ("convert_blessed" enabled and
410	"TO_JSON" method found) is being encoded. Has no effect on "decode".
411		419
412	If $enable is false (the default), then "encode" will throw an	420	If $enable is false (the default), then "encode" will throw an
413	exception when it encounters a blessed object.	421	exception when it encounters a blessed object that it cannot convert
		422	otherwise.
		423
		424	This setting has no effect on "decode".
414		425
415	$json = $json->convert_blessed ([$enable])	426	$json = $json->convert_blessed ([$enable])
416	$enabled = $json->get_convert_blessed	427	$enabled = $json->get_convert_blessed
		428	See "OBJECT SERIALISATION" for details.
		429
417	If $enable is true (or missing), then "encode", upon encountering a	430	If $enable is true (or missing), then "encode", upon encountering a
418	blessed object, will check for the availability of the "TO_JSON"	431	blessed object, will check for the availability of the "TO_JSON"
419	method on the object's class. If found, it will be called in scalar	432	method on the object's class. If found, it will be called in scalar
420	context and the resulting scalar will be encoded instead of the	433	context and the resulting scalar will be encoded instead of the
421	object. If no "TO_JSON" method is found, the value of	434	object.
422	"allow_blessed" will decide what to do.
423		435
424	The "TO_JSON" method may safely call die if it wants. If "TO_JSON"	436	The "TO_JSON" method may safely call die if it wants. If "TO_JSON"
425	returns other blessed objects, those will be handled in the same	437	returns other blessed objects, those will be handled in the same
426	way. "TO_JSON" must take care of not causing an endless recursion	438	way. "TO_JSON" must take care of not causing an endless recursion
427	cycle (== crash) in this case. The name of "TO_JSON" was chosen	439	cycle (== crash) in this case. The name of "TO_JSON" was chosen
428	because other methods called by the Perl core (== not by the user of	440	because other methods called by the Perl core (== not by the user of
429	the object) are usually in upper case letters and to avoid	441	the object) are usually in upper case letters and to avoid
430	collisions with any "to_json" function or method.	442	collisions with any "to_json" function or method.
431		443
432	This setting does not yet influence "decode" in any way, but in the	444	If $enable is false (the default), then "encode" will not consider
433	future, global hooks might get installed that influence "decode" and	445	this type of conversion.
434	are enabled by this setting.
435		446
436	If $enable is false, then the "allow_blessed" setting will decide	447	This setting has no effect on "decode".
437	what to do when a blessed object is found.	448
		449	$json = $json->allow_tags ([$enable])
		450	$enabled = $json->allow_tags
		451	See "OBJECT SERIALISATION" for details.
		452
		453	If $enable is true (or missing), then "encode", upon encountering a
		454	blessed object, will check for the availability of the "FREEZE"
		455	method on the object's class. If found, it will be used to serialise
		456	the object into a nonstandard tagged JSON value (that JSON decoders
		457	cannot decode).
		458
		459	It also causes "decode" to parse such tagged JSON values and
		460	deserialise them via a call to the "THAW" method.
		461
		462	If $enable is false (the default), then "encode" will not consider
		463	this type of conversion, and tagged JSON values will cause a parse
		464	error in "decode", as if tags were not part of the grammar.
438		465
439	$json = $json->filter_json_object ([$coderef->($hashref)])	466	$json = $json->filter_json_object ([$coderef->($hashref)])
440	When $coderef is specified, it will be called from "decode" each	467	When $coderef is specified, it will be called from "decode" each
441	time it decodes a JSON object. The only argument is a reference to	468	time it decodes a JSON object. The only argument is a reference to
442	the newly-created hash. If the code references returns a single	469	the newly-created hash. If the code references returns a single
…		…
541	saving space.	568	saving space.
542		569
543	$json = $json->max_depth ([$maximum_nesting_depth])	570	$json = $json->max_depth ([$maximum_nesting_depth])
544	$max_depth = $json->get_max_depth	571	$max_depth = $json->get_max_depth
545	Sets the maximum nesting level (default 512) accepted while encoding	572	Sets the maximum nesting level (default 512) accepted while encoding
546	or decoding. If the JSON text or Perl data structure has an equal or	573	or decoding. If a higher nesting level is detected in JSON text or a
547	higher nesting level then this limit, then the encoder and decoder	574	Perl data structure, then the encoder and decoder will stop and
548	will stop and croak at that point.	575	croak at that point.
549		576
550	Nesting level is defined by number of hash- or arrayrefs that the	577	Nesting level is defined by number of hash- or arrayrefs that the
551	encoder needs to traverse to reach a given point or the number of	578	encoder needs to traverse to reach a given point or the number of
552	"{" or "[" characters without their matching closing parenthesis	579	"{" or "[" characters without their matching closing parenthesis
553	crossed to reach a given character in a string.	580	crossed to reach a given character in a string.
554		581
555	Setting the maximum depth to one disallows any nesting, so that	582	Setting the maximum depth to one disallows any nesting, so that
556	ensures that the object is only a single hash/object or array.	583	ensures that the object is only a single hash/object or array.
557		584
558	The argument to "max_depth" will be rounded up to the next highest
559	power of two. If no argument is given, the highest possible setting	585	If no argument is given, the highest possible setting will be used,
560	will be used, which is rarely useful.	586	which is rarely useful.
		587
		588	Note that nesting is implemented by recursion in C. The default
		589	value has been chosen to be as large as typical operating systems
		590	allow without crashing.
561		591
562	See SECURITY CONSIDERATIONS, below, for more info on why this is	592	See SECURITY CONSIDERATIONS, below, for more info on why this is
563	useful.	593	useful.
564		594
565	$json = $json->max_size ([$maximum_string_size])	595	$json = $json->max_size ([$maximum_string_size])
566	$max_size = $json->get_max_size	596	$max_size = $json->get_max_size
567	Set the maximum length a JSON text may have (in bytes) where	597	Set the maximum length a JSON text may have (in bytes) where
568	decoding is being attempted. The default is 0, meaning no limit.	598	decoding is being attempted. The default is 0, meaning no limit.
569	When "decode" is called on a string longer then this number of	599	When "decode" is called on a string that is longer then this many
570	characters it will not attempt to decode the string but throw an	600	bytes, it will not attempt to decode the string but throw an
571	exception. This setting has no effect on "encode" (yet).	601	exception. This setting has no effect on "encode" (yet).
572		602
573	The argument to "max_size" will be rounded up to the next highest
574	power of two (so may be more than requested). If no argument is
575	given, the limit check will be deactivated (same as when 0 is	603	If no argument is given, the limit check will be deactivated (same
576	specified).	604	as when 0 is specified).
577		605
578	See SECURITY CONSIDERATIONS, below, for more info on why this is	606	See SECURITY CONSIDERATIONS, below, for more info on why this is
579	useful.	607	useful.
580		608
581	$json_text = $json->encode ($perl_scalar)	609	$json_text = $json->encode ($perl_scalar)
582	Converts the given Perl data structure (a simple scalar or a	610	Converts the given Perl value or data structure to its JSON
583	reference to a hash or array) to its JSON representation. Simple	611	representation. Croaks on error.
584	scalars will be converted into JSON string or number sequences,
585	while references to arrays become JSON arrays and references to
586	hashes become JSON objects. Undefined Perl values (e.g. "undef")
587	become JSON "null" values. Neither "true" nor "false" values will be
588	generated.
589		612
590	$perl_scalar = $json->decode ($json_text)	613	$perl_scalar = $json->decode ($json_text)
591	The opposite of "encode": expects a JSON text and tries to parse it,	614	The opposite of "encode": expects a JSON text and tries to parse it,
592	returning the resulting simple scalar or reference. Croaks on error.	615	returning the resulting simple scalar or reference. Croaks on error.
593
594	JSON numbers and strings become simple Perl scalars. JSON arrays
595	become Perl arrayrefs and JSON objects become Perl hashrefs. "true"
596	becomes 1, "false" becomes 0 and "null" becomes "undef".
597		616
598	($perl_scalar, $characters) = $json->decode_prefix ($json_text)	617	($perl_scalar, $characters) = $json->decode_prefix ($json_text)
599	This works like the "decode" method, but instead of raising an	618	This works like the "decode" method, but instead of raising an
600	exception when there is trailing garbage after the first JSON	619	exception when there is trailing garbage after the first JSON
601	object, it will silently stop parsing there and return the number of	620	object, it will silently stop parsing there and return the number of
602	characters consumed so far.	621	characters consumed so far.
603		622
604	This is useful if your JSON texts are not delimited by an outer	623	This is useful if your JSON texts are not delimited by an outer
605	protocol (which is not the brightest thing to do in the first place)
606	and you need to know where the JSON text ends.	624	protocol and you need to know where the JSON text ends.
607		625
608	JSON::XS->new->decode_prefix ("[1] the tail")	626	JSON::XS->new->decode_prefix ("[1] the tail")
609	=> ([], 3)	627	=> ([], 3)
		628
		629	INCREMENTAL PARSING
		630	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
		632	data structure in memory at one time, it does allow you to parse a JSON
		633	stream incrementally. It does so by accumulating text until it has a
		634	full JSON object, which it then can decode. This process is similar to
		635	using "decode_prefix" to see if a full JSON object is available, but is
		636	much more efficient (and can be implemented with a minimum of method
		637	calls).
		638
		639	JSON::XS will only attempt to parse the JSON text once it is sure it has
		640	enough text to get a decisive result, using a very simple but truly
		641	incremental parser. This means that it sometimes won't stop as early as
		642	the full parser, for example, it doesn't detect mismatched parentheses.
		643	The only thing it guarantees is that it starts decoding as soon as a
		644	syntactically valid JSON text has been seen. This means you need to set
		645	resource limits (e.g. "max_size") to ensure the parser will stop parsing
		646	in the presence if syntax errors.
		647
		648	The following methods implement this incremental parser.
		649
		650	[void, scalar or list context] = $json->incr_parse ([$string])
		651	This is the central parsing function. It can both append new text
		652	and extract objects from the stream accumulated so far (both of
		653	these functions are optional).
		654
		655	If $string is given, then this string is appended to the already
		656	existing JSON fragment stored in the $json object.
		657
		658	After that, if the function is called in void context, it will
		659	simply return without doing anything further. This can be used to
		660	add more text in as many chunks as you want.
		661
		662	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
		664	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
		666	can then use "incr_skip" to skip the erroneous part). This is the
		667	most common way of using the method.
		668
		669	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
		671	otherwise. For this to work, there must be no separators between the
		672	JSON objects or arrays, instead they must be concatenated
		673	back-to-back. If an error occurs, an exception will be raised as in
		674	the scalar context case. Note that in this case, any
		675	previously-parsed JSON texts will be lost.
		676
		677	Example: Parse some JSON arrays/objects in a given string and return
		678	them.
		679
		680	my @objs = JSON::XS->new->incr_parse ("[5][7][1,2]");
		681
		682	$lvalue_string = $json->incr_text
		683	This method returns the currently stored JSON fragment as an lvalue,
		684	that is, you can manipulate it. This only works when a preceding
		685	call to "incr_parse" in scalar context successfully returned an
		686	object. Under all other circumstances you must not call this
		687	function (I mean it. although in simple tests it might actually
		688	work, it will fail under real world conditions). As a special
		689	exception, you can also call this method before having parsed
		690	anything.
		691
		692	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
		694	non-JSON text (such as commas).
		695
		696	$json->incr_skip
		697	This will reset the state of the incremental parser and will remove
		698	the parsed text from the input buffer so far. This is useful after
		699	"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
		701	to reset the parse state.
		702
		703	The difference to "incr_reset" is that only text until the parse
		704	error occurred is removed.
		705
		706	$json->incr_reset
		707	This completely resets the incremental parser, that is, after this
		708	call, it will be as if the parser had never parsed anything.
		709
		710	This is useful if you want to repeatedly parse JSON objects and want
		711	to ignore any trailing data, which means you have to reset the
		712	parser after each successful decode.
		713
		714	LIMITATIONS
		715	All options that affect decoding are supported, except "allow_nonref".
		716	The reason for this is that it cannot be made to work sensibly: JSON
		717	objects and arrays are self-delimited, i.e. you can concatenate them
		718	back to back and still decode them perfectly. This does not hold true
		719	for JSON numbers, however.
		720
		721	For example, is the string 1 a single JSON number, or is it simply the
		722	start of 12? Or is 12 a single JSON number, or the concatenation of 1
		723	and 2? In neither case you can tell, and this is why JSON::XS takes the
		724	conservative route and disallows this case.
		725
		726	EXAMPLES
		727	Some examples will make all this clearer. First, a simple example that
		728	works similarly to "decode_prefix": We want to decode the JSON object at
		729	the start of a string and identify the portion after the JSON object:
		730
		731	my $text = "[1,2,3] hello";
		732
		733	my $json = new JSON::XS;
		734
		735	my $obj = $json->incr_parse ($text)
		736	or die "expected JSON object or array at beginning of string";
		737
		738	my $tail = $json->incr_text;
		739	# $tail now contains " hello"
		740
		741	Easy, isn't it?
		742
		743	Now for a more complicated example: Imagine a hypothetical protocol
		744	where you read some requests from a TCP stream, and each request is a
		745	JSON array, without any separation between them (in fact, it is often
		746	useful to use newlines as "separators", as these get interpreted as
		747	whitespace at the start of the JSON text, which makes it possible to
		748	test said protocol with "telnet"...).
		749
		750	Here is how you'd do it (it is trivial to write this in an event-based
		751	manner):
		752
		753	my $json = new JSON::XS;
		754
		755	# read some data from the socket
		756	while (sysread $socket, my $buf, 4096) {
		757
		758	# split and decode as many requests as possible
		759	for my $request ($json->incr_parse ($buf)) {
		760	# act on the $request
		761	}
		762	}
		763
		764	Another complicated example: Assume you have a string with JSON objects
		765	or arrays, all separated by (optional) comma characters (e.g. "[1],[2],
		766	[3]"). To parse them, we have to skip the commas between the JSON texts,
		767	and here is where the lvalue-ness of "incr_text" comes in useful:
		768
		769	my $text = "[1],[2], [3]";
		770	my $json = new JSON::XS;
		771
		772	# void context, so no parsing done
		773	$json->incr_parse ($text);
		774
		775	# now extract as many objects as possible. note the
		776	# use of scalar context so incr_text can be called.
		777	while (my $obj = $json->incr_parse) {
		778	# do something with $obj
		779
		780	# now skip the optional comma
		781	$json->incr_text =~ s/^ \s* , //x;
		782	}
		783
		784	Now lets go for a very complex example: Assume that you have a gigantic
		785	JSON array-of-objects, many gigabytes in size, and you want to parse it,
		786	but you cannot load it into memory fully (this has actually happened in
		787	the real world :).
		788
		789	Well, you lost, you have to implement your own JSON parser. But JSON::XS
		790	can still help you: You implement a (very simple) array parser and let
		791	JSON decode the array elements, which are all full JSON objects on their
		792	own (this wouldn't work if the array elements could be JSON numbers, for
		793	example):
		794
		795	my $json = new JSON::XS;
		796
		797	# open the monster
		798	open my $fh, "<bigfile.json"
		799	or die "bigfile: $!";
		800
		801	# first parse the initial "["
		802	for (;;) {
		803	sysread $fh, my $buf, 65536
		804	or die "read error: $!";
		805	$json->incr_parse ($buf); # void context, so no parsing
		806
		807	# Exit the loop once we found and removed(!) the initial "[".
		808	# In essence, we are (ab-)using the $json object as a simple scalar
		809	# we append data to.
		810	last if $json->incr_text =~ s/^ \s* \[ //x;
		811	}
		812
		813	# now we have the skipped the initial "[", so continue
		814	# parsing all the elements.
		815	for (;;) {
		816	# in this loop we read data until we got a single JSON object
		817	for (;;) {
		818	if (my $obj = $json->incr_parse) {
		819	# do something with $obj
		820	last;
		821	}
		822
		823	# add more data
		824	sysread $fh, my $buf, 65536
		825	or die "read error: $!";
		826	$json->incr_parse ($buf); # void context, so no parsing
		827	}
		828
		829	# in this loop we read data until we either found and parsed the
		830	# separating "," between elements, or the final "]"
		831	for (;;) {
		832	# first skip whitespace
		833	$json->incr_text =~ s/^\s*//;
		834
		835	# if we find "]", we are done
		836	if ($json->incr_text =~ s/^\]//) {
		837	print "finished.\n";
		838	exit;
		839	}
		840
		841	# if we find ",", we can continue with the next element
		842	if ($json->incr_text =~ s/^,//) {
		843	last;
		844	}
		845
		846	# if we find anything else, we have a parse error!
		847	if (length $json->incr_text) {
		848	die "parse error near ", $json->incr_text;
		849	}
		850
		851	# else add more data
		852	sysread $fh, my $buf, 65536
		853	or die "read error: $!";
		854	$json->incr_parse ($buf); # void context, so no parsing
		855	}
		856
		857	This is a complex example, but most of the complexity comes from the
		858	fact that we are trying to be correct (bear with me if I am wrong, I
		859	never ran the above example :).
610		860
611	MAPPING	861	MAPPING
612	This section describes how JSON::XS maps Perl values to JSON values and	862	This section describes how JSON::XS maps Perl values to JSON values and
613	vice versa. These mappings are designed to "do the right thing" in most	863	vice versa. These mappings are designed to "do the right thing" in most
614	circumstances automatically, preserving round-tripping characteristics	864	circumstances automatically, preserving round-tripping characteristics
…		…
643	If the number consists of digits only, JSON::XS will try to	893	If the number consists of digits only, JSON::XS will try to
644	represent it as an integer value. If that fails, it will try to	894	represent it as an integer value. If that fails, it will try to
645	represent it as a numeric (floating point) value if that is possible	895	represent it as a numeric (floating point) value if that is possible
646	without loss of precision. Otherwise it will preserve the number as	896	without loss of precision. Otherwise it will preserve the number as
647	a string value (in which case you lose roundtripping ability, as the	897	a string value (in which case you lose roundtripping ability, as the
648	JSON number will be re-encoded toa JSON string).	898	JSON number will be re-encoded to a JSON string).
649		899
650	Numbers containing a fractional or exponential part will always be	900	Numbers containing a fractional or exponential part will always be
651	represented as numeric (floating point) values, possibly at a loss	901	represented as numeric (floating point) values, possibly at a loss
652	of precision (in which case you might lose perfect roundtripping	902	of precision (in which case you might lose perfect roundtripping
653	ability, but the JSON number will still be re-encoded as a JSON	903	ability, but the JSON number will still be re-encoded as a JSON
654	number).	904	number).
655		905
		906	Note that precision is not accuracy - binary floating point values
		907	cannot represent most decimal fractions exactly, and when converting
		908	from and to floating point, JSON::XS only guarantees precision up to
		909	but not including the least significant bit.
		910
656	true, false	911	true, false
657	These JSON atoms become "JSON::XS::true" and "JSON::XS::false",	912	These JSON atoms become "Types::Serialiser::true" and
658	respectively. They are overloaded to act almost exactly like the	913	"Types::Serialiser::false", respectively. They are overloaded to act
659	numbers 1 and 0. You can check whether a scalar is a JSON boolean by	914	almost exactly like the numbers 1 and 0. You can check whether a
660	using the "JSON::XS::is_bool" function.	915	scalar is a JSON boolean by using the "Types::Serialiser::is_bool"
		916	function (after "use Types::Serialier", of course).
661		917
662	null	918	null
663	A JSON null atom becomes "undef" in Perl.	919	A JSON null atom becomes "undef" in Perl.
		920
		921	shell-style comments ("# text")
		922	As a nonstandard extension to the JSON syntax that is enabled by the
		923	"relaxed" setting, shell-style comments are allowed. They can start
		924	anywhere outside strings and go till the end of the line.
		925
		926	tagged values ("(tag)value").
		927	Another nonstandard extension to the JSON syntax, enabled with the
		928	"allow_tags" setting, are tagged values. In this implementation, the
		929	tag must be a perl package/class name encoded as a JSON string,
		930	and the value must be a JSON array encoding optional constructor
		931	arguments.
		932
		933	See "OBJECT SERIALISATION", below, for details.
664		934
665	PERL -> JSON	935	PERL -> JSON
666	The mapping from Perl to JSON is slightly more difficult, as Perl is a	936	The mapping from Perl to JSON is slightly more difficult, as Perl is a
667	truly typeless language, so we can only guess which JSON type is meant	937	truly typeless language, so we can only guess which JSON type is meant
668	by a Perl value.	938	by a Perl value.
669		939
670	hash references	940	hash references
671	Perl hash references become JSON objects. As there is no inherent	941	Perl hash references become JSON objects. As there is no inherent
672	ordering in hash keys (or JSON objects), they will usually be	942	ordering in hash keys (or JSON objects), they will usually be
673	encoded in a pseudo-random order that can change between runs of the	943	encoded in a pseudo-random order. JSON::XS can optionally sort the
674	same program but stays generally the same within a single run of a	944	hash keys (determined by the canonical flag), so the same
675	program. JSON::XS can optionally sort the hash keys (determined by	945	datastructure will serialise to the same JSON text (given same
676	the canonical flag), so the same datastructure will serialise to	946	settings and version of JSON::XS), but this incurs a runtime
677	the same JSON text (given same settings and version of JSON::XS),	947	overhead and is only rarely useful, e.g. when you want to compare
678	but this incurs a runtime overhead and is only rarely useful, e.g.	948	some JSON text against another for equality.
679	when you want to compare some JSON text against another for
680	equality.
681		949
682	array references	950	array references
683	Perl array references become JSON arrays.	951	Perl array references become JSON arrays.
684		952
685	other references	953	other references
686	Other unblessed references are generally not allowed and will cause	954	Other unblessed references are generally not allowed and will cause
687	an exception to be thrown, except for references to the integers 0	955	an exception to be thrown, except for references to the integers 0
688	and 1, which get turned into "false" and "true" atoms in JSON. You	956	and 1, which get turned into "false" and "true" atoms in JSON.
689	can also use "JSON::XS::false" and "JSON::XS::true" to improve	957
		958	Since "JSON::XS" uses the boolean model from Types::Serialiser, you
		959	can also "use Types::Serialiser" and then use
		960	"Types::Serialiser::false" and "Types::Serialiser::true" to improve
690	readability.	961	readability.
691		962
		963	use Types::Serialiser;
692	encode_json [\0,JSON::XS::true] # yields [false,true]	964	encode_json [\0, Types::Serialiser::true] # yields [false,true]
693		965
694	JSON::XS::true, JSON::XS::false	966	Types::Serialiser::true, Types::Serialiser::false
695	These special values become JSON true and JSON false values,	967	These special values from the Types::Serialiser module become JSON
696	respectively. You can also use "\1" and "\0" directly if you want.	968	true and JSON false values, respectively. You can also use "\1" and
		969	"\0" directly if you want.
697		970
698	blessed objects	971	blessed objects
699	Blessed objects are not directly representable in JSON. See the	972	Blessed objects are not directly representable in JSON, but
700	"allow_blessed" and "convert_blessed" methods on various options on	973	"JSON::XS" allows various ways of handling objects. See "OBJECT
701	how to deal with this: basically, you can choose between throwing an	974	SERIALISATION", below, for details.
702	exception, encoding the reference as if it weren't blessed, or
703	provide your own serialiser method.
704		975
705	simple scalars	976	simple scalars
706	Simple Perl scalars (any scalar that is not a reference) are the	977	Simple Perl scalars (any scalar that is not a reference) are the
707	most difficult objects to encode: JSON::XS will encode undefined	978	most difficult objects to encode: JSON::XS will encode undefined
708	scalars as JSON "null" values, scalars that have last been used in a	979	scalars as JSON "null" values, scalars that have last been used in a
…		…
734	$x += 0; # numify it, ensuring it will be dumped as a number	1005	$x += 0; # numify it, ensuring it will be dumped as a number
735	$x *= 1; # same thing, the choice is yours.	1006	$x *= 1; # same thing, the choice is yours.
736		1007
737	You can not currently force the type in other, less obscure, ways.	1008	You can not currently force the type in other, less obscure, ways.
738	Tell me if you need this capability (but don't forget to explain why	1009	Tell me if you need this capability (but don't forget to explain why
739	its needed :).	1010	it's needed :).
		1011
		1012	Note that numerical precision has the same meaning as under Perl (so
		1013	binary to decimal conversion follows the same rules as in Perl,
		1014	which can differ to other languages). Also, your perl interpreter
		1015	might expose extensions to the floating point numbers of your
		1016	platform, such as infinities or NaN's - these cannot be represented
		1017	in JSON, and it is an error to pass those in.
		1018
		1019	OBJECT SERIALISATION
		1020	As JSON cannot directly represent Perl objects, you have to choose
		1021	between a pure JSON representation (without the ability to deserialise
		1022	the object automatically again), and a nonstandard extension to the JSON
		1023	syntax, tagged values.
		1024
		1025	SERIALISATION
		1026	What happens when "JSON::XS" encounters a Perl object depends on the
		1027	"allow_blessed", "convert_blessed" and "allow_tags" settings, which are
		1028	used in this order:
		1029
		1030	1. "allow_tags" is enabled and the object has a "FREEZE" method.
		1031	In this case, "JSON::XS" uses the Types::Serialiser object
		1032	serialisation protocol to create a tagged JSON value, using a
		1033	nonstandard extension to the JSON syntax.
		1034
		1035	This works by invoking the "FREEZE" method on the object, with the
		1036	first argument being the object to serialise, and the second
		1037	argument being the constant string "JSON" to distinguish it from
		1038	other serialisers.
		1039
		1040	The "FREEZE" method can return any number of values (i.e. zero or
		1041	more). These values and the paclkage/classname of the object will
		1042	then be encoded as a tagged JSON value in the following format:
		1043
		1044	("classname")[FREEZE return values...]
		1045
		1046	e.g.:
		1047
		1048	("URI")["http://www.google.com/"]
		1049	("MyDate")[2013,10,29]
		1050	("ImageData::JPEG")["Z3...VlCg=="]
		1051
		1052	For example, the hypothetical "My::Object" "FREEZE" method might use
		1053	the objects "type" and "id" members to encode the object:
		1054
		1055	sub My::Object::FREEZE {
		1056	my ($self, $serialiser) = @_;
		1057
		1058	($self->{type}, $self->{id})
		1059	}
		1060
		1061	2. "convert_blessed" is enabled and the object has a "TO_JSON" method.
		1062	In this case, the "TO_JSON" method of the object is invoked in
		1063	scalar context. It must return a single scalar that can be directly
		1064	encoded into JSON. This scalar replaces the object in the JSON text.
		1065
		1066	For example, the following "TO_JSON" method will convert all URI
		1067	objects to JSON strings when serialised. The fatc that these values
		1068	originally were URI objects is lost.
		1069
		1070	sub URI::TO_JSON {
		1071	my ($uri) = @_;
		1072	$uri->as_string
		1073	}
		1074
		1075	3. "allow_blessed" is enabled.
		1076	The object will be serialised as a JSON null value.
		1077
		1078	4. none of the above
		1079	If none of the settings are enabled or the respective methods are
		1080	missing, "JSON::XS" throws an exception.
		1081
		1082	DESERIALISATION
		1083	For deserialisation there are only two cases to consider: either
		1084	nonstandard tagging was used, in which case "allow_tags" decides, or
		1085	objects cannot be automatically be deserialised, in which case you can
		1086	use postprocessing or the "filter_json_object" or
		1087	"filter_json_single_key_object" callbacks to get some real objects our
		1088	of your JSON.
		1089
		1090	This section only considers the tagged value case: I a tagged JSON
		1091	object is encountered during decoding and "allow_tags" is disabled, a
		1092	parse error will result (as if tagged values were not part of the
		1093	grammar).
		1094
		1095	If "allow_tags" is enabled, "JSON::XS" will look up the "THAW" method of
		1096	the package/classname used during serialisation (it will not attempt to
		1097	load the package as a Perl module). If there is no such method, the
		1098	decoding will fail with an error.
		1099
		1100	Otherwise, the "THAW" method is invoked with the classname as first
		1101	argument, the constant string "JSON" as second argument, and all the
		1102	values from the JSON array (the values originally returned by the
		1103	"FREEZE" method) as remaining arguments.
		1104
		1105	The method must then return the object. While technically you can return
		1106	any Perl scalar, you might have to enable the "enable_nonref" setting to
		1107	make that work in all cases, so better return an actual blessed
		1108	reference.
		1109
		1110	As an example, let's implement a "THAW" function that regenerates the
		1111	"My::Object" from the "FREEZE" example earlier:
		1112
		1113	sub My::Object::THAW {
		1114	my ($class, $serialiser, $type, $id) = @_;
		1115
		1116	$class->new (type => $type, id => $id)
		1117	}
740		1118
741	ENCODING/CODESET FLAG NOTES	1119	ENCODING/CODESET FLAG NOTES
742	The interested reader might have seen a number of flags that signify	1120	The interested reader might have seen a number of flags that signify
743	encodings or codesets - "utf8", "latin1" and "ascii". There seems to be	1121	encodings or codesets - "utf8", "latin1" and "ascii". There seems to be
744	some confusion on what these do, so here is a short comparison:	1122	some confusion on what these do, so here is a short comparison:
745		1123
746	"utf8" controls wether the JSON text created by "encode" (and expected	1124	"utf8" controls whether the JSON text created by "encode" (and expected
747	by "decode") is UTF-8 encoded or not, while "latin1" and "ascii" only	1125	by "decode") is UTF-8 encoded or not, while "latin1" and "ascii" only
748	control wether "encode" escapes character values outside their	1126	control whether "encode" escapes character values outside their
749	respective codeset range. Neither of these flags conflict with each	1127	respective codeset range. Neither of these flags conflict with each
750	other, although some combinations make less sense than others.	1128	other, although some combinations make less sense than others.
751		1129
752	Care has been taken to make all flags symmetrical with respect to	1130	Care has been taken to make all flags symmetrical with respect to
753	"encode" and "decode", that is, texts encoded with any combination of	1131	"encode" and "decode", that is, texts encoded with any combination of
…		…
764		1142
765	"utf8" flag disabled	1143	"utf8" flag disabled
766	When "utf8" is disabled (the default), then "encode"/"decode"	1144	When "utf8" is disabled (the default), then "encode"/"decode"
767	generate and expect Unicode strings, that is, characters with high	1145	generate and expect Unicode strings, that is, characters with high
768	ordinal Unicode values (> 255) will be encoded as such characters,	1146	ordinal Unicode values (> 255) will be encoded as such characters,
769	and likewise such characters are decoded as-is, no canges to them	1147	and likewise such characters are decoded as-is, no changes to them
770	will be done, except "(re-)interpreting" them as Unicode codepoints	1148	will be done, except "(re-)interpreting" them as Unicode codepoints
771	or Unicode characters, respectively (to Perl, these are the same	1149	or Unicode characters, respectively (to Perl, these are the same
772	thing in strings unless you do funny/weird/dumb stuff).	1150	thing in strings unless you do funny/weird/dumb stuff).
773		1151
774	This is useful when you want to do the encoding yourself (e.g. when	1152	This is useful when you want to do the encoding yourself (e.g. when
…		…
831	structure back. This is useful when your channel for JSON transfer	1209	structure back. This is useful when your channel for JSON transfer
832	is not 8-bit clean or the encoding might be mangled in between (e.g.	1210	is not 8-bit clean or the encoding might be mangled in between (e.g.
833	in mail), and works because ASCII is a proper subset of most 8-bit	1211	in mail), and works because ASCII is a proper subset of most 8-bit
834	and multibyte encodings in use in the world.	1212	and multibyte encodings in use in the world.
835		1213
836	COMPARISON	1214	JSON and ECMAscript
837	As already mentioned, this module was created because none of the	1215	JSON syntax is based on how literals are represented in javascript (the
838	existing JSON modules could be made to work correctly. First I will	1216	not-standardised predecessor of ECMAscript) which is presumably why it
839	describe the problems (or pleasures) I encountered with various existing	1217	is called "JavaScript Object Notation".
840	JSON modules, followed by some benchmark values. JSON::XS was designed
841	not to suffer from any of these problems or limitations.
842		1218
843	JSON 2.xx	1219	However, JSON is not a subset (and also not a superset of course) of
844	A marvellous piece of engineering, this module either uses JSON::XS	1220	ECMAscript (the standard) or javascript (whatever browsers actually
845	directly when available (so will be 100% compatible with it,	1221	implement).
846	including speed), or it uses JSON::PP, which is basically JSON::XS
847	translated to Pure Perl, which should be 100% compatible with
848	JSON::XS, just a bit slower.
849		1222
850	You cannot really lose by using this module, especially as it tries	1223	If you want to use javascript's "eval" function to "parse" JSON, you
851	very hard to work even with ancient Perl versions, while JSON::XS	1224	might run into parse errors for valid JSON texts, or the resulting data
852	does not.	1225	structure might not be queryable:
853		1226
854	JSON 1.07	1227	One of the problems is that U+2028 and U+2029 are valid characters
855	Slow (but very portable, as it is written in pure Perl).	1228	inside JSON strings, but are not allowed in ECMAscript string literals,
		1229	so the following Perl fragment will not output something that can be
		1230	guaranteed to be parsable by javascript's "eval":
856		1231
857	Undocumented/buggy Unicode handling (how JSON handles Unicode values	1232	use JSON::XS;
858	is undocumented. One can get far by feeding it Unicode strings and
859	doing en-/decoding oneself, but Unicode escapes are not working
860	properly).
861		1233
862	No round-tripping (strings get clobbered if they look like numbers,	1234	print encode_json [chr 0x2028];
863	e.g. the string 2.0 will encode to 2.0 instead of "2.0", and that
864	will decode into the number 2.
865		1235
866	JSON::PC 0.01	1236	The right fix for this is to use a proper JSON parser in your javascript
867	Very fast.	1237	programs, and not rely on "eval" (see for example Douglas Crockford's
		1238	json2.js parser).
868		1239
869	Undocumented/buggy Unicode handling.	1240	If this is not an option, you can, as a stop-gap measure, simply encode
		1241	to ASCII-only JSON:
870		1242
871	No round-tripping.	1243	use JSON::XS;
872		1244
873	Has problems handling many Perl values (e.g. regex results and other	1245	print JSON::XS->new->ascii->encode ([chr 0x2028]);
874	magic values will make it croak).
875		1246
876	Does not even generate valid JSON ("{1,2}" gets converted to "{1:2}"	1247	Note that this will enlarge the resulting JSON text quite a bit if you
877	which is not a valid JSON text.	1248	have many non-ASCII characters. You might be tempted to run some regexes
		1249	to only escape U+2028 and U+2029, e.g.:
878		1250
879	Unmaintained (maintainer unresponsive for many months, bugs are not	1251	# DO NOT USE THIS!
880	getting fixed).	1252	my $json = JSON::XS->new->utf8->encode ([chr 0x2028]);
		1253	$json =~ s/\xe2\x80\xa8/\\u2028/g; # escape U+2028
		1254	$json =~ s/\xe2\x80\xa9/\\u2029/g; # escape U+2029
		1255	print $json;
881		1256
882	JSON::Syck 0.21	1257	Note that this is a bad idea: the above only works for U+2028 and
883	Very buggy (often crashes).	1258	U+2029 and thus only for fully ECMAscript-compliant parsers. Many
		1259	existing javascript implementations, however, have issues with other
		1260	characters as well - using "eval" naively simply will cause problems.
884		1261
885	Very inflexible (no human-readable format supported, format pretty	1262	Another problem is that some javascript implementations reserve some
886	much undocumented. I need at least a format for easy reading by	1263	property names for their own purposes (which probably makes them
887	humans and a single-line compact format for use in a protocol, and	1264	non-ECMAscript-compliant). For example, Iceweasel reserves the
888	preferably a way to generate ASCII-only JSON texts).	1265	"__proto__" property name for its own purposes.
889		1266
890	Completely broken (and confusingly documented) Unicode handling	1267	If that is a problem, you could parse try to filter the resulting JSON
891	(Unicode escapes are not working properly, you need to set	1268	output for these property strings, e.g.:
892	ImplicitUnicode to different values on en- and decoding to get
893	symmetric behaviour).
894		1269
895	No round-tripping (simple cases work, but this depends on whether	1270	$json =~ s/"__proto__"\s*:/"__proto__renamed":/g;
896	the scalar value was used in a numeric context or not).
897		1271
898	Dumping hashes may skip hash values depending on iterator state.	1272	This works because "__proto__" is not valid outside of strings, so every
		1273	occurrence of ""__proto__"\s*:" must be a string used as property name.
899		1274
900	Unmaintained (maintainer unresponsive for many months, bugs are not	1275	If you know of other incompatibilities, please let me know.
901	getting fixed).
902
903	Does not check input for validity (i.e. will accept non-JSON input
904	and return "something" instead of raising an exception. This is a
905	security issue: imagine two banks transferring money between each
906	other using JSON. One bank might parse a given non-JSON request and
907	deduct money, while the other might reject the transaction with a
908	syntax error. While a good protocol will at least recover, that is
909	extra unnecessary work and the transaction will still not succeed).
910
911	JSON::DWIW 0.04
912	Very fast. Very natural. Very nice.
913
914	Undocumented Unicode handling (but the best of the pack. Unicode
915	escapes still don't get parsed properly).
916
917	Very inflexible.
918
919	No round-tripping.
920
921	Does not generate valid JSON texts (key strings are often unquoted,
922	empty keys result in nothing being output)
923
924	Does not check input for validity.
925		1276
926	JSON and YAML	1277	JSON and YAML
927	You often hear that JSON is a subset of YAML. This is, however, a mass	1278	You often hear that JSON is a subset of YAML. This is, however, a mass
928	hysteria(*) and very far from the truth (as of the time of this	1279	hysteria(*) and very far from the truth (as of the time of this
929	writing), so let me state it clearly: *in general, there is no way to	1280	writing), so let me state it clearly: *in general, there is no way to
…		…
937	my $yaml = $to_yaml->encode ($ref) . "\n";	1288	my $yaml = $to_yaml->encode ($ref) . "\n";
938		1289
939	This will usually generate JSON texts that also parse as valid YAML.	1290	This will usually generate JSON texts that also parse as valid YAML.
940	Please note that YAML has hardcoded limits on (simple) object key	1291	Please note that YAML has hardcoded limits on (simple) object key
941	lengths that JSON doesn't have and also has different and incompatible	1292	lengths that JSON doesn't have and also has different and incompatible
942	unicode handling, so you should make sure that your hash keys are	1293	unicode character escape syntax, so you should make sure that your hash
943	noticeably shorter than the 1024 "stream characters" YAML allows and	1294	keys are noticeably shorter than the 1024 "stream characters" YAML
944	that you do not have characters with codepoint values outside the	1295	allows and that you do not have characters with codepoint values outside
945	Unicode BMP (basic multilingual page). YAML also does not allow "\/"	1296	the Unicode BMP (basic multilingual page). YAML also does not allow "\/"
946	sequences in strings (which JSON::XS does not currently generate, but	1297	sequences in strings (which JSON::XS does not currently generate, but
947	other JSON generators might).	1298	other JSON generators might).
948		1299
949	There might be other incompatibilities that I am not aware of (or the	1300	There might be other incompatibilities that I am not aware of (or the
950	YAML specification has been changed yet again - it does so quite often).	1301	YAML specification has been changed yet again - it does so quite often).
…		…
967	(which is not that difficult or long) and finally make YAML	1318	(which is not that difficult or long) and finally make YAML
968	compatible to it, and educating users about the changes, instead of	1319	compatible to it, and educating users about the changes, instead of
969	spreading lies about the real compatibility for many years and	1320	spreading lies about the real compatibility for many years and
970	trying to silence people who point out that it isn't true.	1321	trying to silence people who point out that it isn't true.
971		1322
		1323	Addendum/2009: the YAML 1.2 spec is still incompatible with JSON,
		1324	even though the incompatibilities have been documented (and are
		1325	known to Brian) for many years and the spec makes explicit claims
		1326	that YAML is a superset of JSON. It would be so easy to fix, but
		1327	apparently, bullying people and corrupting userdata is so much
		1328	easier.
		1329
972	SPEED	1330	SPEED
973	It seems that JSON::XS is surprisingly fast, as shown in the following	1331	It seems that JSON::XS is surprisingly fast, as shown in the following
974	tables. They have been generated with the help of the "eg/bench" program	1332	tables. They have been generated with the help of the "eg/bench" program
975	in the JSON::XS distribution, to make it easy to compare on your own	1333	in the JSON::XS distribution, to make it easy to compare on your own
976	system.	1334	system.
977		1335
978	First comes a comparison between various modules using a very short	1336	First comes a comparison between various modules using a very short
979	single-line JSON string (also available at	1337	single-line JSON string (also available at
980	<http://dist.schmorp.de/misc/json/short.json>).	1338	<http://dist.schmorp.de/misc/json/short.json>).
981		1339
982	{"method": "handleMessage", "params": ["user1", "we were just talking"], \	1340	{"method": "handleMessage", "params": ["user1",
983	"id": null, "array":[1,11,234,-5,1e5,1e7, true, false]}	1341	"we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7,
		1342	1, 0]}
984		1343
985	It shows the number of encodes/decodes per second (JSON::XS uses the	1344	It shows the number of encodes/decodes per second (JSON::XS uses the
986	functional interface, while JSON::XS/2 uses the OO interface with	1345	functional interface, while JSON::XS/2 uses the OO interface with
987	pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink).	1346	pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink.
988	Higher is better:	1347	JSON::DWIW/DS uses the deserialise function, while JSON::DWIW::FJ uses
		1348	the from_json method). Higher is better:
989		1349
990	module \| encode \| decode \|	1350	module \| encode \| decode \|
991	-----------\|------------\|------------\|	1351	--------------\|------------\|------------\|
992	JSON 1.x \| 4990.842 \| 4088.813 \|	1352	JSON::DWIW/DS \| 86302.551 \| 102300.098 \|
993	JSON::DWIW \| 51653.990 \| 71575.154 \|	1353	JSON::DWIW/FJ \| 86302.551 \| 75983.768 \|
994	JSON::PC \| 65948.176 \| 74631.744 \|	1354	JSON::PP \| 15827.562 \| 6638.658 \|
995	JSON::PP \| 8931.652 \| 3817.168 \|	1355	JSON::Syck \| 63358.066 \| 47662.545 \|
996	JSON::Syck \| 24877.248 \| 27776.848 \|	1356	JSON::XS \| 511500.488 \| 511500.488 \|
997	JSON::XS \| 388361.481 \| 227951.304 \|	1357	JSON::XS/2 \| 291271.111 \| 388361.481 \|
998	JSON::XS/2 \| 227951.304 \| 218453.333 \|	1358	JSON::XS/3 \| 361577.931 \| 361577.931 \|
999	JSON::XS/3 \| 338250.323 \| 218453.333 \|	1359	Storable \| 66788.280 \| 265462.278 \|
1000	Storable \| 16500.016 \| 135300.129 \|
1001	-----------+------------+------------+	1360	--------------+------------+------------+
1002		1361
1003	That is, JSON::XS is about five times faster than JSON::DWIW on	1362	That is, JSON::XS is almost six times faster than JSON::DWIW on
1004	encoding, about three times faster on decoding, and over forty times	1363	encoding, about five times faster on decoding, and over thirty to
1005	faster than JSON, even with pretty-printing and key sorting. It also	1364	seventy times faster than JSON's pure perl implementation. It also
1006	compares favourably to Storable for small amounts of data.	1365	compares favourably to Storable for small amounts of data.
1007		1366
1008	Using a longer test string (roughly 18KB, generated from Yahoo! Locals	1367	Using a longer test string (roughly 18KB, generated from Yahoo! Locals
1009	search API (<http://dist.schmorp.de/misc/json/long.json>).	1368	search API (<http://dist.schmorp.de/misc/json/long.json>).
1010		1369
1011	module \| encode \| decode \|	1370	module \| encode \| decode \|
1012	-----------\|------------\|------------\|	1371	--------------\|------------\|------------\|
1013	JSON 1.x \| 55.260 \| 34.971 \|	1372	JSON::DWIW/DS \| 1647.927 \| 2673.916 \|
1014	JSON::DWIW \| 825.228 \| 1082.513 \|	1373	JSON::DWIW/FJ \| 1630.249 \| 2596.128 \|
1015	JSON::PC \| 3571.444 \| 2394.829 \|
1016	JSON::PP \| 210.987 \| 32.574 \|	1374	JSON::PP \| 400.640 \| 62.311 \|
1017	JSON::Syck \| 552.551 \| 787.544 \|	1375	JSON::Syck \| 1481.040 \| 1524.869 \|
1018	JSON::XS \| 5780.463 \| 4854.519 \|	1376	JSON::XS \| 20661.596 \| 9541.183 \|
1019	JSON::XS/2 \| 3869.998 \| 4798.975 \|	1377	JSON::XS/2 \| 10683.403 \| 9416.938 \|
1020	JSON::XS/3 \| 5862.880 \| 4798.975 \|	1378	JSON::XS/3 \| 20661.596 \| 9400.054 \|
1021	Storable \| 4445.002 \| 5235.027 \|	1379	Storable \| 19765.806 \| 10000.725 \|
1022	-----------+------------+------------+	1380	--------------+------------+------------+
1023		1381
1024	Again, JSON::XS leads by far (except for Storable which non-surprisingly	1382	Again, JSON::XS leads by far (except for Storable which non-surprisingly
1025	decodes faster).	1383	decodes a bit faster).
1026		1384
1027	On large strings containing lots of high Unicode characters, some	1385	On large strings containing lots of high Unicode characters, some
1028	modules (such as JSON::PC) seem to decode faster than JSON::XS, but the	1386	modules (such as JSON::PC) seem to decode faster than JSON::XS, but the
1029	result will be broken due to missing (or wrong) Unicode handling. Others	1387	result will be broken due to missing (or wrong) Unicode handling. Others
1030	refuse to decode or encode properly, so it was impossible to prepare a	1388	refuse to decode or encode properly, so it was impossible to prepare a
…		…
1065	information you might want to make sure that exceptions thrown by	1423	information you might want to make sure that exceptions thrown by
1066	JSON::XS will not end up in front of untrusted eyes.	1424	JSON::XS will not end up in front of untrusted eyes.
1067		1425
1068	If you are using JSON::XS to return packets to consumption by JavaScript	1426	If you are using JSON::XS to return packets to consumption by JavaScript
1069	scripts in a browser you should have a look at	1427	scripts in a browser you should have a look at
1070	<http://jpsykes.com/47/practical-csrf-and-json-security> to see whether	1428	<http://blog.archive.jpsykes.com/47/practical-csrf-and-json-security/>
1071	you are vulnerable to some common attack vectors (which really are	1429	to see whether you are vulnerable to some common attack vectors (which
1072	browser design bugs, but it is still you who will have to deal with it,	1430	really are browser design bugs, but it is still you who will have to
1073	as major browser developers care only for features, not about getting	1431	deal with it, as major browser developers care only for features, not
1074	security right).	1432	about getting security right).
		1433
		1434	INTEROPERABILITY WITH OTHER MODULES
		1435	"JSON::XS" uses the Types::Serialiser module to provide boolean
		1436	constants. That means that the JSON true and false values will be
		1437	comaptible to true and false values of iother modules that do the same,
		1438	such as JSON::PP and CBOR::XS.
1075		1439
1076	THREADS	1440	THREADS
1077	This module is not guaranteed to be thread safe and there are no plans	1441	This module is not guaranteed to be thread safe and there are no plans
1078	to change this until Perl gets thread support (as opposed to the	1442	to change this until Perl gets thread support (as opposed to the
1079	horribly slow so-called "threads" which are simply slow and bloated	1443	horribly slow so-called "threads" which are simply slow and bloated
1080	process simulations - use fork, its much faster, cheaper, better).	1444	process simulations - use fork, it's much faster, cheaper, better).
1081		1445
1082	(It might actually work, but you have been warned).	1446	(It might actually work, but you have been warned).
		1447
		1448	THE PERILS OF SETLOCALE
		1449	Sometimes people avoid the Perl locale support and directly call the
		1450	system's setlocale function with "LC_ALL".
		1451
		1452	This breaks both perl and modules such as JSON::XS, as stringification
		1453	of numbers no longer works correctly (e.g. "$x = 0.1; print "$x"+1"
		1454	might print 1, and JSON::XS might output illegal JSON as JSON::XS relies
		1455	on perl to stringify numbers).
		1456
		1457	The solution is simple: don't call "setlocale", or use it for only those
		1458	categories you need, such as "LC_MESSAGES" or "LC_CTYPE".
		1459
		1460	If you need "LC_NUMERIC", you should enable it only around the code that
		1461	actually needs it (avoiding stringification of numbers), and restore it
		1462	afterwards.
1083		1463
1084	BUGS	1464	BUGS
1085	While the goal of this module is to be correct, that unfortunately does	1465	While the goal of this module is to be correct, that unfortunately does
1086	not mean its bug-free, only that I think its design is bug-free. It is	1466	not mean it's bug-free, only that I think its design is bug-free. If you
1087	still relatively early in its development. If you keep reporting bugs
1088	they will be fixed swiftly, though.	1467	keep reporting bugs they will be fixed swiftly, though.
1089		1468
1090	Please refrain from using rt.cpan.org or any other bug reporting	1469	Please refrain from using rt.cpan.org or any other bug reporting
1091	service. I put the contact address into my modules for a reason.	1470	service. I put the contact address into my modules for a reason.
		1471
		1472	SEE ALSO
		1473	The json_xs command line utility for quick experiments.
1092		1474
1093	AUTHOR	1475	AUTHOR
1094	Marc Lehmann <schmorp@schmorp.de>	1476	Marc Lehmann <schmorp@schmorp.de>
1095	http://home.schmorp.de/	1477	http://home.schmorp.de/
1096		1478

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Comparing JSON-XS/README (file contents): Revision 1.23 by root, Wed Mar 19 22:31:00 2008 UTC vs. Revision 1.39 by root, Tue Oct 29 15:55:49 2013 UTC

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Comparing JSON-XS/README (file contents):
Revision 1.23 by root, Wed Mar 19 22:31:00 2008 UTC vs.
Revision 1.39 by root, Tue Oct 29 15:55:49 2013 UTC