[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 1.41 by root, Wed Nov 16 19:21:53 2016 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
…		…
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.
…		…
362	[	352	[
363	1, # this comment not allowed in JSON	353	1, # this comment not allowed in JSON
364	# neither this one...	354	# neither this one...
365	]	355	]
366		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
367	$json = $json->canonical ([$enable])	367	$json = $json->canonical ([$enable])
368	$enabled = $json->get_canonical	368	$enabled = $json->get_canonical
369	If $enable is true (or missing), then the "encode" method will	369	If $enable is true (or missing), then the "encode" method will
370	output JSON objects by sorting their keys. This is adding a	370	output JSON objects by sorting their keys. This is adding a
371	comparatively high overhead.	371	comparatively high overhead.
372		372
373	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
374	pairs in the order Perl stores them (which will likely change	374	pairs in the order Perl stores them (which will likely change
375	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).
376		377
377	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
378	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
379	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
380	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
381	in Perl.	382	in Perl.
382		383
383	This setting has no effect when decoding JSON texts.	384	This setting has no effect when decoding JSON texts.
		385
		386	This setting has currently no effect on tied hashes.
384		387
385	$json = $json->allow_nonref ([$enable])	388	$json = $json->allow_nonref ([$enable])
386	$enabled = $json->get_allow_nonref	389	$enabled = $json->get_allow_nonref
387	If $enable is true (or missing), then the "encode" method can	390	If $enable is true (or missing), then the "encode" method can
388	convert a non-reference into its corresponding string, number or	391	convert a non-reference into its corresponding string, number or
…		…
398	"allow_nonref", resulting in an invalid JSON text:	401	"allow_nonref", resulting in an invalid JSON text:
399		402
400	JSON::XS->new->allow_nonref->encode ("Hello, World!")	403	JSON::XS->new->allow_nonref->encode ("Hello, World!")
401	=> "Hello, World!"	404	=> "Hello, World!"
402		405
		406	$json = $json->allow_unknown ([$enable])
		407	$enabled = $json->get_allow_unknown
		408	If $enable is true (or missing), then "encode" will not throw an
		409	exception when it encounters values it cannot represent in JSON (for
		410	example, filehandles) but instead will encode a JSON "null" value.
		411	Note that blessed objects are not included here and are handled
		412	separately by c<allow_nonref>.
		413
		414	If $enable is false (the default), then "encode" will throw an
		415	exception when it encounters anything it cannot encode as JSON.
		416
		417	This option does not affect "decode" in any way, and it is
		418	recommended to leave it off unless you know your communications
		419	partner.
		420
403	$json = $json->allow_blessed ([$enable])	421	$json = $json->allow_blessed ([$enable])
404	$enabled = $json->get_allow_blessed	422	$enabled = $json->get_allow_blessed
		423	See "OBJECT SERIALISATION" for details.
		424
405	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
406	barf when it encounters a blessed reference. Instead, the value of	426	barf when it encounters a blessed reference that it cannot convert
407	the convert_blessed option will decide whether "null"	427	otherwise. Instead, a JSON "null" value is encoded instead of the
408	("convert_blessed" disabled or no "TO_JSON" method found) or a	428	object.
409	representation of the object ("convert_blessed" enabled and
410	"TO_JSON" method found) is being encoded. Has no effect on "decode".
411		429
412	If $enable is false (the default), then "encode" will throw an	430	If $enable is false (the default), then "encode" will throw an
413	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".
414		435
415	$json = $json->convert_blessed ([$enable])	436	$json = $json->convert_blessed ([$enable])
416	$enabled = $json->get_convert_blessed	437	$enabled = $json->get_convert_blessed
		438	See "OBJECT SERIALISATION" for details.
		439
417	If $enable is true (or missing), then "encode", upon encountering a	440	If $enable is true (or missing), then "encode", upon encountering a
418	blessed object, will check for the availability of the "TO_JSON"	441	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	442	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	443	context and the resulting scalar will be encoded instead of the
421	object. If no "TO_JSON" method is found, the value of	444	object.
422	"allow_blessed" will decide what to do.
423		445
424	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"
425	returns other blessed objects, those will be handled in the same	447	returns other blessed objects, those will be handled in the same
426	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
427	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
428	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
429	the object) are usually in upper case letters and to avoid	451	the object) are usually in upper case letters and to avoid
430	collisions with any "to_json" function or method.	452	collisions with any "to_json" function or method.
431		453
432	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
433	future, global hooks might get installed that influence "decode" and	455	this type of conversion.
434	are enabled by this setting.
435		456
436	If $enable is false, then the "allow_blessed" setting will decide	457	This setting has no effect on "decode".
437	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.
438		475
439	$json = $json->filter_json_object ([$coderef->($hashref)])	476	$json = $json->filter_json_object ([$coderef->($hashref)])
440	When $coderef is specified, it will be called from "decode" each	477	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	478	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	479	the newly-created hash. If the code references returns a single
…		…
541	saving space.	578	saving space.
542		579
543	$json = $json->max_depth ([$maximum_nesting_depth])	580	$json = $json->max_depth ([$maximum_nesting_depth])
544	$max_depth = $json->get_max_depth	581	$max_depth = $json->get_max_depth
545	Sets the maximum nesting level (default 512) accepted while encoding	582	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	583	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	584	Perl data structure, then the encoder and decoder will stop and
548	will stop and croak at that point.	585	croak at that point.
549		586
550	Nesting level is defined by number of hash- or arrayrefs that the	587	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	588	encoder needs to traverse to reach a given point or the number of
552	"{" or "[" characters without their matching closing parenthesis	589	"{" or "[" characters without their matching closing parenthesis
553	crossed to reach a given character in a string.	590	crossed to reach a given character in a string.
554		591
555	Setting the maximum depth to one disallows any nesting, so that	592	Setting the maximum depth to one disallows any nesting, so that
556	ensures that the object is only a single hash/object or array.	593	ensures that the object is only a single hash/object or array.
557		594
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	595	If no argument is given, the highest possible setting will be used,
560	will be used, which is rarely useful.	596	which is rarely useful.
		597
		598	Note that nesting is implemented by recursion in C. The default
		599	value has been chosen to be as large as typical operating systems
		600	allow without crashing.
561		601
562	See SECURITY CONSIDERATIONS, below, for more info on why this is	602	See SECURITY CONSIDERATIONS, below, for more info on why this is
563	useful.	603	useful.
564		604
565	$json = $json->max_size ([$maximum_string_size])	605	$json = $json->max_size ([$maximum_string_size])
566	$max_size = $json->get_max_size	606	$max_size = $json->get_max_size
567	Set the maximum length a JSON text may have (in bytes) where	607	Set the maximum length a JSON text may have (in bytes) where
568	decoding is being attempted. The default is 0, meaning no limit.	608	decoding is being attempted. The default is 0, meaning no limit.
569	When "decode" is called on a string longer then this number of	609	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	610	bytes, it will not attempt to decode the string but throw an
571	exception. This setting has no effect on "encode" (yet).	611	exception. This setting has no effect on "encode" (yet).
572		612
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	613	If no argument is given, the limit check will be deactivated (same
576	specified).	614	as when 0 is specified).
577		615
578	See SECURITY CONSIDERATIONS, below, for more info on why this is	616	See SECURITY CONSIDERATIONS, below, for more info on why this is
579	useful.	617	useful.
580		618
581	$json_text = $json->encode ($perl_scalar)	619	$json_text = $json->encode ($perl_scalar)
582	Converts the given Perl data structure (a simple scalar or a	620	Converts the given Perl value or data structure to its JSON
583	reference to a hash or array) to its JSON representation. Simple	621	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		622
590	$perl_scalar = $json->decode ($json_text)	623	$perl_scalar = $json->decode ($json_text)
591	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,
592	returning the resulting simple scalar or reference. Croaks on error.	625	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		626
598	($perl_scalar, $characters) = $json->decode_prefix ($json_text)	627	($perl_scalar, $characters) = $json->decode_prefix ($json_text)
599	This works like the "decode" method, but instead of raising an	628	This works like the "decode" method, but instead of raising an
600	exception when there is trailing garbage after the first JSON	629	exception when there is trailing garbage after the first JSON
601	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
602	characters consumed so far.	631	characters consumed so far.
603		632
604	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
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.	634	protocol and you need to know where the JSON text ends.
607		635
608	JSON::XS->new->decode_prefix ("[1] the tail")	636	JSON::XS->new->decode_prefix ("[1] the tail")
609	=> ([], 3)	637	=> ([1], 3)
		638
		639	INCREMENTAL PARSING
		640	In some cases, there is the need for incremental parsing of JSON texts.
		641	While this module always has to keep both JSON text and resulting Perl
		642	data structure in memory at one time, it does allow you to parse a JSON
		643	stream incrementally. It does so by accumulating text until it has a
		644	full JSON object, which it then can decode. This process is similar to
		645	using "decode_prefix" to see if a full JSON object is available, but is
		646	much more efficient (and can be implemented with a minimum of method
		647	calls).
		648
		649	JSON::XS will only attempt to parse the JSON text once it is sure it has
		650	enough text to get a decisive result, using a very simple but truly
		651	incremental parser. This means that it sometimes won't stop as early as
		652	the full parser, for example, it doesn't detect mismatched parentheses.
		653	The only thing it guarantees is that it starts decoding as soon as a
		654	syntactically valid JSON text has been seen. This means you need to set
		655	resource limits (e.g. "max_size") to ensure the parser will stop parsing
		656	in the presence if syntax errors.
		657
		658	The following methods implement this incremental parser.
		659
		660	[void, scalar or list context] = $json->incr_parse ([$string])
		661	This is the central parsing function. It can both append new text
		662	and extract objects from the stream accumulated so far (both of
		663	these functions are optional).
		664
		665	If $string is given, then this string is appended to the already
		666	existing JSON fragment stored in the $json object.
		667
		668	After that, if the function is called in void context, it will
		669	simply return without doing anything further. This can be used to
		670	add more text in as many chunks as you want.
		671
		672	If the method is called in scalar context, then it will try to
		673	extract exactly one JSON object. If that is successful, it will
		674	return this object, otherwise it will return "undef". If there is a
		675	parse error, this method will croak just as "decode" would do (one
		676	can then use "incr_skip" to skip the erroneous part). This is the
		677	most common way of using the method.
		678
		679	And finally, in list context, it will try to extract as many objects
		680	from the stream as it can find and return them, or the empty list
		681	otherwise. For this to work, there must be no separators (other than
		682	whitespace) between the JSON objects or arrays, instead they must be
		683	concatenated back-to-back. If an error occurs, an exception will be
		684	raised as in the scalar context case. Note that in this case, any
		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]");
		691
		692	$lvalue_string = $json->incr_text
		693	This method returns the currently stored JSON fragment as an lvalue,
		694	that is, you can manipulate it. This only works when a preceding
		695	call to "incr_parse" in scalar context successfully returned an
		696	object. Under all other circumstances you must not call this
		697	function (I mean it. although in simple tests it might actually
		698	work, it will fail under real world conditions). As a special
		699	exception, you can also call this method before having parsed
		700	anything.
		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
		706	This function is useful in two cases: a) finding the trailing text
		707	after a JSON object or b) parsing multiple JSON objects separated by
		708	non-JSON text (such as commas).
		709
		710	$json->incr_skip
		711	This will reset the state of the incremental parser and will remove
		712	the parsed text from the input buffer so far. This is useful after
		713	"incr_parse" died, in which case the input buffer and incremental
		714	parser state is left unchanged, to skip the text parsed so far and
		715	to reset the parse state.
		716
		717	The difference to "incr_reset" is that only text until the parse
		718	error occurred is removed.
		719
		720	$json->incr_reset
		721	This completely resets the incremental parser, that is, after this
		722	call, it will be as if the parser had never parsed anything.
		723
		724	This is useful if you want to repeatedly parse JSON objects and want
		725	to ignore any trailing data, which means you have to reset the
		726	parser after each successful decode.
		727
		728	LIMITATIONS
		729	All options that affect decoding are supported, except "allow_nonref".
		730	The reason for this is that it cannot be made to work sensibly: JSON
		731	objects and arrays are self-delimited, i.e. you can concatenate them
		732	back to back and still decode them perfectly. This does not hold true
		733	for JSON numbers, however.
		734
		735	For example, is the string 1 a single JSON number, or is it simply the
		736	start of 12? Or is 12 a single JSON number, or the concatenation of 1
		737	and 2? In neither case you can tell, and this is why JSON::XS takes the
		738	conservative route and disallows this case.
		739
		740	EXAMPLES
		741	Some examples will make all this clearer. First, a simple example that
		742	works similarly to "decode_prefix": We want to decode the JSON object at
		743	the start of a string and identify the portion after the JSON object:
		744
		745	my $text = "[1,2,3] hello";
		746
		747	my $json = new JSON::XS;
		748
		749	my $obj = $json->incr_parse ($text)
		750	or die "expected JSON object or array at beginning of string";
		751
		752	my $tail = $json->incr_text;
		753	# $tail now contains " hello"
		754
		755	Easy, isn't it?
		756
		757	Now for a more complicated example: Imagine a hypothetical protocol
		758	where you read some requests from a TCP stream, and each request is a
		759	JSON array, without any separation between them (in fact, it is often
		760	useful to use newlines as "separators", as these get interpreted as
		761	whitespace at the start of the JSON text, which makes it possible to
		762	test said protocol with "telnet"...).
		763
		764	Here is how you'd do it (it is trivial to write this in an event-based
		765	manner):
		766
		767	my $json = new JSON::XS;
		768
		769	# read some data from the socket
		770	while (sysread $socket, my $buf, 4096) {
		771
		772	# split and decode as many requests as possible
		773	for my $request ($json->incr_parse ($buf)) {
		774	# act on the $request
		775	}
		776	}
		777
		778	Another complicated example: Assume you have a string with JSON objects
		779	or arrays, all separated by (optional) comma characters (e.g. "[1],[2],
		780	[3]"). To parse them, we have to skip the commas between the JSON texts,
		781	and here is where the lvalue-ness of "incr_text" comes in useful:
		782
		783	my $text = "[1],[2], [3]";
		784	my $json = new JSON::XS;
		785
		786	# void context, so no parsing done
		787	$json->incr_parse ($text);
		788
		789	# now extract as many objects as possible. note the
		790	# use of scalar context so incr_text can be called.
		791	while (my $obj = $json->incr_parse) {
		792	# do something with $obj
		793
		794	# now skip the optional comma
		795	$json->incr_text =~ s/^ \s* , //x;
		796	}
		797
		798	Now lets go for a very complex example: Assume that you have a gigantic
		799	JSON array-of-objects, many gigabytes in size, and you want to parse it,
		800	but you cannot load it into memory fully (this has actually happened in
		801	the real world :).
		802
		803	Well, you lost, you have to implement your own JSON parser. But JSON::XS
		804	can still help you: You implement a (very simple) array parser and let
		805	JSON decode the array elements, which are all full JSON objects on their
		806	own (this wouldn't work if the array elements could be JSON numbers, for
		807	example):
		808
		809	my $json = new JSON::XS;
		810
		811	# open the monster
		812	open my $fh, "<bigfile.json"
		813	or die "bigfile: $!";
		814
		815	# first parse the initial "["
		816	for (;;) {
		817	sysread $fh, my $buf, 65536
		818	or die "read error: $!";
		819	$json->incr_parse ($buf); # void context, so no parsing
		820
		821	# Exit the loop once we found and removed(!) the initial "[".
		822	# In essence, we are (ab-)using the $json object as a simple scalar
		823	# we append data to.
		824	last if $json->incr_text =~ s/^ \s* \[ //x;
		825	}
		826
		827	# now we have the skipped the initial "[", so continue
		828	# parsing all the elements.
		829	for (;;) {
		830	# in this loop we read data until we got a single JSON object
		831	for (;;) {
		832	if (my $obj = $json->incr_parse) {
		833	# do something with $obj
		834	last;
		835	}
		836
		837	# add more data
		838	sysread $fh, my $buf, 65536
		839	or die "read error: $!";
		840	$json->incr_parse ($buf); # void context, so no parsing
		841	}
		842
		843	# in this loop we read data until we either found and parsed the
		844	# separating "," between elements, or the final "]"
		845	for (;;) {
		846	# first skip whitespace
		847	$json->incr_text =~ s/^\s*//;
		848
		849	# if we find "]", we are done
		850	if ($json->incr_text =~ s/^\]//) {
		851	print "finished.\n";
		852	exit;
		853	}
		854
		855	# if we find ",", we can continue with the next element
		856	if ($json->incr_text =~ s/^,//) {
		857	last;
		858	}
		859
		860	# if we find anything else, we have a parse error!
		861	if (length $json->incr_text) {
		862	die "parse error near ", $json->incr_text;
		863	}
		864
		865	# else add more data
		866	sysread $fh, my $buf, 65536
		867	or die "read error: $!";
		868	$json->incr_parse ($buf); # void context, so no parsing
		869	}
		870
		871	This is a complex example, but most of the complexity comes from the
		872	fact that we are trying to be correct (bear with me if I am wrong, I
		873	never ran the above example :).
610		874
611	MAPPING	875	MAPPING
612	This section describes how JSON::XS maps Perl values to JSON values and	876	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	877	vice versa. These mappings are designed to "do the right thing" in most
614	circumstances automatically, preserving round-tripping characteristics	878	circumstances automatically, preserving round-tripping characteristics
…		…
643	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
644	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
645	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
646	without loss of precision. Otherwise it will preserve the number as	910	without loss of precision. Otherwise it will preserve the number as
647	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
648	JSON number will be re-encoded toa JSON string).	912	JSON number will be re-encoded to a JSON string).
649		913
650	Numbers containing a fractional or exponential part will always be	914	Numbers containing a fractional or exponential part will always be
651	represented as numeric (floating point) values, possibly at a loss	915	represented as numeric (floating point) values, possibly at a loss
652	of precision (in which case you might lose perfect roundtripping	916	of precision (in which case you might lose perfect roundtripping
653	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
654	number).	918	number).
655		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
656	true, false	925	true, false
657	These JSON atoms become "JSON::XS::true" and "JSON::XS::false",	926	These JSON atoms become "Types::Serialiser::true" and
658	respectively. They are overloaded to act almost exactly like the	927	"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	928	almost exactly like the numbers 1 and 0. You can check whether a
660	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).
661		931
662	null	932	null
663	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.
664		948
665	PERL -> JSON	949	PERL -> JSON
666	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
667	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
668	by a Perl value.	952	by a Perl value.
669		953
670	hash references	954	hash references
671	Perl hash references become JSON objects. As there is no inherent	955	Perl hash references become JSON objects. As there is no inherent
672	ordering in hash keys (or JSON objects), they will usually be	956	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	957	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	958	hash keys (determined by the canonical flag), so the same
675	program. JSON::XS can optionally sort the hash keys (determined by	959	datastructure will serialise to the same JSON text (given same
676	the canonical flag), so the same datastructure will serialise to	960	settings and version of JSON::XS), but this incurs a runtime
677	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
678	but this incurs a runtime overhead and is only rarely useful, e.g.	962	some JSON text against another for equality.
679	when you want to compare some JSON text against another for
680	equality.
681		963
682	array references	964	array references
683	Perl array references become JSON arrays.	965	Perl array references become JSON arrays.
684		966
685	other references	967	other references
686	Other unblessed references are generally not allowed and will cause	968	Other unblessed references are generally not allowed and will cause
687	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
688	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.
689	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
690	readability.	975	readability.
691		976
		977	use Types::Serialiser;
692	encode_json [\0,JSON::XS::true] # yields [false,true]	978	encode_json [\0, Types::Serialiser::true] # yields [false,true]
693		979
694	JSON::XS::true, JSON::XS::false	980	Types::Serialiser::true, Types::Serialiser::false
695	These special values become JSON true and JSON false values,	981	These special values from the Types::Serialiser module become JSON
696	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.
697		984
698	blessed objects	985	blessed objects
699	Blessed objects are not directly representable in JSON. See the	986	Blessed objects are not directly representable in JSON, but
700	"allow_blessed" and "convert_blessed" methods on various options on	987	"JSON::XS" allows various ways of handling objects. See "OBJECT
701	how to deal with this: basically, you can choose between throwing an	988	SERIALISATION", below, for details.
702	exception, encoding the reference as if it weren't blessed, or
703	provide your own serialiser method.
704		989
705	simple scalars	990	simple scalars
706	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
707	most difficult objects to encode: JSON::XS will encode undefined	992	most difficult objects to encode: JSON::XS will encode undefined
708	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
…		…
734	$x += 0; # numify it, ensuring it will be dumped as a number	1019	$x += 0; # numify it, ensuring it will be dumped as a number
735	$x *= 1; # same thing, the choice is yours.	1020	$x *= 1; # same thing, the choice is yours.
736		1021
737	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.
738	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
739	its needed :).	1024	it's needed :).
		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	}
740		1132
741	ENCODING/CODESET FLAG NOTES	1133	ENCODING/CODESET FLAG NOTES
742	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
743	encodings or codesets - "utf8", "latin1" and "ascii". There seems to be	1135	encodings or codesets - "utf8", "latin1" and "ascii". There seems to be
744	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:
745		1137
746	"utf8" controls wether the JSON text created by "encode" (and expected	1138	"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	1139	by "decode") is UTF-8 encoded or not, while "latin1" and "ascii" only
748	control wether "encode" escapes character values outside their	1140	control whether "encode" escapes character values outside their
749	respective codeset range. Neither of these flags conflict with each	1141	respective codeset range. Neither of these flags conflict with each
750	other, although some combinations make less sense than others.	1142	other, although some combinations make less sense than others.
751		1143
752	Care has been taken to make all flags symmetrical with respect to	1144	Care has been taken to make all flags symmetrical with respect to
753	"encode" and "decode", that is, texts encoded with any combination of	1145	"encode" and "decode", that is, texts encoded with any combination of
…		…
764		1156
765	"utf8" flag disabled	1157	"utf8" flag disabled
766	When "utf8" is disabled (the default), then "encode"/"decode"	1158	When "utf8" is disabled (the default), then "encode"/"decode"
767	generate and expect Unicode strings, that is, characters with high	1159	generate and expect Unicode strings, that is, characters with high
768	ordinal Unicode values (> 255) will be encoded as such characters,	1160	ordinal Unicode values (> 255) will be encoded as such characters,
769	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
770	will be done, except "(re-)interpreting" them as Unicode codepoints	1162	will be done, except "(re-)interpreting" them as Unicode codepoints
771	or Unicode characters, respectively (to Perl, these are the same	1163	or Unicode characters, respectively (to Perl, these are the same
772	thing in strings unless you do funny/weird/dumb stuff).	1164	thing in strings unless you do funny/weird/dumb stuff).
773		1165
774	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
…		…
831	structure back. This is useful when your channel for JSON transfer	1223	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.	1224	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	1225	in mail), and works because ASCII is a proper subset of most 8-bit
834	and multibyte encodings in use in the world.	1226	and multibyte encodings in use in the world.
835		1227
836	COMPARISON	1228	JSON and ECMAscript
837	As already mentioned, this module was created because none of the	1229	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	1230	not-standardised predecessor of ECMAscript) which is presumably why it
839	describe the problems (or pleasures) I encountered with various existing	1231	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		1232
843	JSON 2.xx	1233	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	1234	ECMAscript (the standard) or javascript (whatever browsers actually
845	directly when available (so will be 100% compatible with it,	1235	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		1236
850	You cannot really lose by using this module, especially as it tries	1237	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	1238	might run into parse errors for valid JSON texts, or the resulting data
852	does not.	1239	structure might not be queryable:
853		1240
854	JSON 1.07	1241	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).	1242	inside JSON strings, but are not allowed in ECMAscript string literals,
		1243	so the following Perl fragment will not output something that can be
		1244	guaranteed to be parsable by javascript's "eval":
856		1245
857	Undocumented/buggy Unicode handling (how JSON handles Unicode values	1246	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		1247
862	No round-tripping (strings get clobbered if they look like numbers,	1248	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		1249
866	JSON::PC 0.01	1250	The right fix for this is to use a proper JSON parser in your javascript
867	Very fast.	1251	programs, and not rely on "eval" (see for example Douglas Crockford's
		1252	json2.js parser).
868		1253
869	Undocumented/buggy Unicode handling.	1254	If this is not an option, you can, as a stop-gap measure, simply encode
		1255	to ASCII-only JSON:
870		1256
871	No round-tripping.	1257	use JSON::XS;
872		1258
873	Has problems handling many Perl values (e.g. regex results and other	1259	print JSON::XS->new->ascii->encode ([chr 0x2028]);
874	magic values will make it croak).
875		1260
876	Does not even generate valid JSON ("{1,2}" gets converted to "{1:2}"	1261	Note that this will enlarge the resulting JSON text quite a bit if you
877	which is not a valid JSON text.	1262	have many non-ASCII characters. You might be tempted to run some regexes
		1263	to only escape U+2028 and U+2029, e.g.:
878		1264
879	Unmaintained (maintainer unresponsive for many months, bugs are not	1265	# DO NOT USE THIS!
880	getting fixed).	1266	my $json = JSON::XS->new->utf8->encode ([chr 0x2028]);
		1267	$json =~ s/\xe2\x80\xa8/\\u2028/g; # escape U+2028
		1268	$json =~ s/\xe2\x80\xa9/\\u2029/g; # escape U+2029
		1269	print $json;
881		1270
882	JSON::Syck 0.21	1271	Note that this is a bad idea: the above only works for U+2028 and
883	Very buggy (often crashes).	1272	U+2029 and thus only for fully ECMAscript-compliant parsers. Many
		1273	existing javascript implementations, however, have issues with other
		1274	characters as well - using "eval" naively simply will cause problems.
884		1275
885	Very inflexible (no human-readable format supported, format pretty	1276	Another problem is that some javascript implementations reserve some
886	much undocumented. I need at least a format for easy reading by	1277	property names for their own purposes (which probably makes them
887	humans and a single-line compact format for use in a protocol, and	1278	non-ECMAscript-compliant). For example, Iceweasel reserves the
888	preferably a way to generate ASCII-only JSON texts).	1279	"__proto__" property name for its own purposes.
889		1280
890	Completely broken (and confusingly documented) Unicode handling	1281	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	1282	output for these property strings, e.g.:
892	ImplicitUnicode to different values on en- and decoding to get
893	symmetric behaviour).
894		1283
895	No round-tripping (simple cases work, but this depends on whether	1284	$json =~ s/"__proto__"\s*:/"__proto__renamed":/g;
896	the scalar value was used in a numeric context or not).
897		1285
898	Dumping hashes may skip hash values depending on iterator state.	1286	This works because "__proto__" is not valid outside of strings, so every
		1287	occurrence of ""__proto__"\s*:" must be a string used as property name.
899		1288
900	Unmaintained (maintainer unresponsive for many months, bugs are not	1289	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		1290
926	JSON and YAML	1291	JSON and YAML
927	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
928	hysteria(*) and very far from the truth (as of the time of this	1293	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	1294	writing), so let me state it clearly: *in general, there is no way to
…		…
937	my $yaml = $to_yaml->encode ($ref) . "\n";	1302	my $yaml = $to_yaml->encode ($ref) . "\n";
938		1303
939	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.
940	Please note that YAML has hardcoded limits on (simple) object key	1305	Please note that YAML has hardcoded limits on (simple) object key
941	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
942	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
943	noticeably shorter than the 1024 "stream characters" YAML allows and	1308	keys are noticeably shorter than the 1024 "stream characters" YAML
944	that you do not have characters with codepoint values outside the	1309	allows and that you do not have characters with codepoint values outside
945	Unicode BMP (basic multilingual page). YAML also does not allow "\/"	1310	the Unicode BMP (basic multilingual page). YAML also does not allow "\/"
946	sequences in strings (which JSON::XS does not currently generate, but	1311	sequences in strings (which JSON::XS does not currently generate, but
947	other JSON generators might).	1312	other JSON generators might).
948		1313
949	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
950	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).
…		…
967	(which is not that difficult or long) and finally make YAML	1332	(which is not that difficult or long) and finally make YAML
968	compatible to it, and educating users about the changes, instead of	1333	compatible to it, and educating users about the changes, instead of
969	spreading lies about the real compatibility for many years and	1334	spreading lies about the real compatibility for many years and
970	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.
971		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
972	SPEED	1344	SPEED
973	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
974	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
975	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
976	system.	1348	system.
977		1349
978	First comes a comparison between various modules using a very short	1350	First comes a comparison between various modules using a very short
979	single-line JSON string (also available at	1351	single-line JSON string (also available at
980	<http://dist.schmorp.de/misc/json/short.json>).	1352	<http://dist.schmorp.de/misc/json/short.json>).
981		1353
982	{"method": "handleMessage", "params": ["user1", "we were just talking"], \	1354	{"method": "handleMessage", "params": ["user1",
983	"id": null, "array":[1,11,234,-5,1e5,1e7, true, false]}	1355	"we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7,
		1356	1, 0]}
984		1357
985	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
986	functional interface, while JSON::XS/2 uses the OO interface with	1359	functional interface, while JSON::XS/2 uses the OO interface with
987	pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink).	1360	pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink.
988	Higher is better:	1361	JSON::DWIW/DS uses the deserialise function, while JSON::DWIW::FJ uses
		1362	the from_json method). Higher is better:
989		1363
990	module \| encode \| decode \|	1364	module \| encode \| decode \|
991	-----------\|------------\|------------\|	1365	--------------\|------------\|------------\|
992	JSON 1.x \| 4990.842 \| 4088.813 \|	1366	JSON::DWIW/DS \| 86302.551 \| 102300.098 \|
993	JSON::DWIW \| 51653.990 \| 71575.154 \|	1367	JSON::DWIW/FJ \| 86302.551 \| 75983.768 \|
994	JSON::PC \| 65948.176 \| 74631.744 \|	1368	JSON::PP \| 15827.562 \| 6638.658 \|
995	JSON::PP \| 8931.652 \| 3817.168 \|	1369	JSON::Syck \| 63358.066 \| 47662.545 \|
996	JSON::Syck \| 24877.248 \| 27776.848 \|	1370	JSON::XS \| 511500.488 \| 511500.488 \|
997	JSON::XS \| 388361.481 \| 227951.304 \|	1371	JSON::XS/2 \| 291271.111 \| 388361.481 \|
998	JSON::XS/2 \| 227951.304 \| 218453.333 \|	1372	JSON::XS/3 \| 361577.931 \| 361577.931 \|
999	JSON::XS/3 \| 338250.323 \| 218453.333 \|	1373	Storable \| 66788.280 \| 265462.278 \|
1000	Storable \| 16500.016 \| 135300.129 \|
1001	-----------+------------+------------+	1374	--------------+------------+------------+
1002		1375
1003	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
1004	encoding, about three times faster on decoding, and over forty times	1377	encoding, about five times faster on decoding, and over thirty to
1005	faster than JSON, even with pretty-printing and key sorting. It also	1378	seventy times faster than JSON's pure perl implementation. It also
1006	compares favourably to Storable for small amounts of data.	1379	compares favourably to Storable for small amounts of data.
1007		1380
1008	Using a longer test string (roughly 18KB, generated from Yahoo! Locals	1381	Using a longer test string (roughly 18KB, generated from Yahoo! Locals
1009	search API (<http://dist.schmorp.de/misc/json/long.json>).	1382	search API (<http://dist.schmorp.de/misc/json/long.json>).
1010		1383
1011	module \| encode \| decode \|	1384	module \| encode \| decode \|
1012	-----------\|------------\|------------\|	1385	--------------\|------------\|------------\|
1013	JSON 1.x \| 55.260 \| 34.971 \|	1386	JSON::DWIW/DS \| 1647.927 \| 2673.916 \|
1014	JSON::DWIW \| 825.228 \| 1082.513 \|	1387	JSON::DWIW/FJ \| 1630.249 \| 2596.128 \|
1015	JSON::PC \| 3571.444 \| 2394.829 \|
1016	JSON::PP \| 210.987 \| 32.574 \|	1388	JSON::PP \| 400.640 \| 62.311 \|
1017	JSON::Syck \| 552.551 \| 787.544 \|	1389	JSON::Syck \| 1481.040 \| 1524.869 \|
1018	JSON::XS \| 5780.463 \| 4854.519 \|	1390	JSON::XS \| 20661.596 \| 9541.183 \|
1019	JSON::XS/2 \| 3869.998 \| 4798.975 \|	1391	JSON::XS/2 \| 10683.403 \| 9416.938 \|
1020	JSON::XS/3 \| 5862.880 \| 4798.975 \|	1392	JSON::XS/3 \| 20661.596 \| 9400.054 \|
1021	Storable \| 4445.002 \| 5235.027 \|	1393	Storable \| 19765.806 \| 10000.725 \|
1022	-----------+------------+------------+	1394	--------------+------------+------------+
1023		1395
1024	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
1025	decodes faster).	1397	decodes a bit faster).
1026		1398
1027	On large strings containing lots of high Unicode characters, some	1399	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	1400	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	1401	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	1402	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	1437	information you might want to make sure that exceptions thrown by
1066	JSON::XS will not end up in front of untrusted eyes.	1438	JSON::XS will not end up in front of untrusted eyes.
1067		1439
1068	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
1069	scripts in a browser you should have a look at	1441	scripts in a browser you should have a look at
1070	<http://jpsykes.com/47/practical-csrf-and-json-security> to see whether	1442	<http://blog.archive.jpsykes.com/47/practical-csrf-and-json-security/>
1071	you are vulnerable to some common attack vectors (which really are	1443	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,	1444	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	1445	deal with it, as major browser developers care only for features, not
1074	security right).	1446	about getting security right).
		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.
1075		1567
1076	THREADS	1568	THREADS
1077	This module is not guaranteed to be thread safe and there are no plans	1569	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	1570	to change this until Perl gets thread support (as opposed to the
1079	horribly slow so-called "threads" which are simply slow and bloated	1571	horribly slow so-called "threads" which are simply slow and bloated
1080	process simulations - use fork, its much faster, cheaper, better).	1572	process simulations - use fork, it's much faster, cheaper, better).
1081		1573
1082	(It might actually work, but you have been warned).	1574	(It might actually work, but you have been warned).
		1575
		1576	THE PERILS OF SETLOCALE
		1577	Sometimes people avoid the Perl locale support and directly call the
		1578	system's setlocale function with "LC_ALL".
		1579
		1580	This breaks both perl and modules such as JSON::XS, as stringification
		1581	of numbers no longer works correctly (e.g. "$x = 0.1; print "$x"+1"
		1582	might print 1, and JSON::XS might output illegal JSON as JSON::XS relies
		1583	on perl to stringify numbers).
		1584
		1585	The solution is simple: don't call "setlocale", or use it for only those
		1586	categories you need, such as "LC_MESSAGES" or "LC_CTYPE".
		1587
		1588	If you need "LC_NUMERIC", you should enable it only around the code that
		1589	actually needs it (avoiding stringification of numbers), and restore it
		1590	afterwards.
1083		1591
1084	BUGS	1592	BUGS
1085	While the goal of this module is to be correct, that unfortunately does	1593	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	1594	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.	1595	keep reporting bugs they will be fixed swiftly, though.
1089		1596
1090	Please refrain from using rt.cpan.org or any other bug reporting	1597	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.	1598	service. I put the contact address into my modules for a reason.
		1599
		1600	SEE ALSO
		1601	The json_xs command line utility for quick experiments.
1092		1602
1093	AUTHOR	1603	AUTHOR
1094	Marc Lehmann <schmorp@schmorp.de>	1604	Marc Lehmann <schmorp@schmorp.de>
1095	http://home.schmorp.de/	1605	http://home.schmorp.de/
1096		1606

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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 1.41 by root, Wed Nov 16 19:21:53 2016 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 1.41 by root, Wed Nov 16 19:21:53 2016 UTC