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

Comparing JSON-XS/XS.pm (file contents):
Revision 1.80 by root, Sat Dec 29 17:22:39 2007 UTC vs.
Revision 1.94 by root, Tue Mar 25 07:46:15 2008 UTC

…		…
1	=head1 NAME	1	=head1 NAME
		2
		3	=encoding utf-8
2		4
3	JSON::XS - JSON serialising/deserialising, done correctly and fast	5	JSON::XS - JSON serialising/deserialising, done correctly and fast
4		6
5	JSON::XS - 正しくて高速な JSON シリアライザ/デシリアライザ	7	JSON::XS - 正しくて高速な JSON シリアライザ/デシリアライザ
6	(http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html)	8	(http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html)
58		60
59	=over 4	61	=over 4
60		62
61	=item * correct Unicode handling	63	=item * correct Unicode handling
62		64
63	This module knows how to handle Unicode, and even documents how and when	65	This module knows how to handle Unicode, documents how and when it does
64	it does so.	66	so, and even documents what "correct" means.
65		67
66	=item * round-trip integrity	68	=item * round-trip integrity
67		69
68	When you serialise a perl data structure using only datatypes supported	70	When you serialise a perl data structure using only datatypes supported
69	by JSON, the deserialised data structure is identical on the Perl level.	71	by JSON, the deserialised data structure is identical on the Perl level.
70	(e.g. the string "2.0" doesn't suddenly become "2" just because it looks	72	(e.g. the string "2.0" doesn't suddenly become "2" just because it looks
71	like a number).	73	like a number). There minor I<are> exceptions to this, read the MAPPING
		74	section below to learn about those.
72		75
73	=item * strict checking of JSON correctness	76	=item * strict checking of JSON correctness
74		77
75	There is no guessing, no generating of illegal JSON texts by default,	78	There is no guessing, no generating of illegal JSON texts by default,
76	and only JSON is accepted as input by default (the latter is a security	79	and only JSON is accepted as input by default (the latter is a security
77	feature).	80	feature).
78		81
79	=item * fast	82	=item * fast
80		83
81	Compared to other JSON modules, this module compares favourably in terms	84	Compared to other JSON modules and other serialisers such as Storable,
82	of speed, too.	85	this module usually compares favourably in terms of speed, too.
83		86
84	=item * simple to use	87	=item * simple to use
85		88
86	This module has both a simple functional interface as well as an OO	89	This module has both a simple functional interface as well as an objetc
87	interface.	90	oriented interface interface.
88		91
89	=item * reasonably versatile output formats	92	=item * reasonably versatile output formats
90		93
91	You can choose between the most compact guaranteed single-line format	94	You can choose between the most compact guaranteed-single-line format
92	possible (nice for simple line-based protocols), a pure-ascii format	95	possible (nice for simple line-based protocols), a pure-ascii format
93	(for when your transport is not 8-bit clean, still supports the whole	96	(for when your transport is not 8-bit clean, still supports the whole
94	Unicode range), or a pretty-printed format (for when you want to read that	97	Unicode range), or a pretty-printed format (for when you want to read that
95	stuff). Or you can combine those features in whatever way you like.	98	stuff). Or you can combine those features in whatever way you like.
96		99
…		…
100		103
101	package JSON::XS;	104	package JSON::XS;
102		105
103	use strict;	106	use strict;
104		107
105	our $VERSION = '2.01';	108	our $VERSION = '2.1';
106	our @ISA = qw(Exporter);	109	our @ISA = qw(Exporter);
107		110
108	our @EXPORT = qw(encode_json decode_json to_json from_json);	111	our @EXPORT = qw(encode_json decode_json to_json from_json);
109		112
110	sub to_json($) {	113	sub to_json($) {
…		…
174	This enables you to store Unicode characters as single characters in a	177	This enables you to store Unicode characters as single characters in a
175	Perl string - very natural.	178	Perl string - very natural.
176		179
177	=item 2. Perl does I<not> associate an encoding with your strings.	180	=item 2. Perl does I<not> associate an encoding with your strings.
178		181
179	Unless you force it to, e.g. when matching it against a regex, or printing	182	... until you force it to, e.g. when matching it against a regex, or
180	the scalar to a file, in which case Perl either interprets your string as	183	printing the scalar to a file, in which case Perl either interprets your
181	locale-encoded text, octets/binary, or as Unicode, depending on various	184	string as locale-encoded text, octets/binary, or as Unicode, depending
182	settings. In no case is an encoding stored together with your data, it is	185	on various settings. In no case is an encoding stored together with your
183	I<use> that decides encoding, not any magical metadata.	186	data, it is I<use> that decides encoding, not any magical meta data.
184		187
185	=item 3. The internal utf-8 flag has no meaning with regards to the	188	=item 3. The internal utf-8 flag has no meaning with regards to the
186	encoding of your string.	189	encoding of your string.
187		190
188	Just ignore that flag unless you debug a Perl bug, a module written in	191	Just ignore that flag unless you debug a Perl bug, a module written in
…		…
242		245
243	If C<$enable> is false, then the C<encode> method will not escape Unicode	246	If C<$enable> is false, then the C<encode> method will not escape Unicode
244	characters unless required by the JSON syntax or other flags. This results	247	characters unless required by the JSON syntax or other flags. This results
245	in a faster and more compact format.	248	in a faster and more compact format.
246		249
		250	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		251	document.
		252
247	The main use for this flag is to produce JSON texts that can be	253	The main use for this flag is to produce JSON texts that can be
248	transmitted over a 7-bit channel, as the encoded JSON texts will not	254	transmitted over a 7-bit channel, as the encoded JSON texts will not
249	contain any 8 bit characters.	255	contain any 8 bit characters.
250		256
251	JSON::XS->new->ascii (1)->encode ([chr 0x10401])	257	JSON::XS->new->ascii (1)->encode ([chr 0x10401])
…		…
262	will not be affected in any way by this flag, as C<decode> by default	268	will not be affected in any way by this flag, as C<decode> by default
263	expects Unicode, which is a strict superset of latin1.	269	expects Unicode, which is a strict superset of latin1.
264		270
265	If C<$enable> is false, then the C<encode> method will not escape Unicode	271	If C<$enable> is false, then the C<encode> method will not escape Unicode
266	characters unless required by the JSON syntax or other flags.	272	characters unless required by the JSON syntax or other flags.
		273
		274	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		275	document.
267		276
268	The main use for this flag is efficiently encoding binary data as JSON	277	The main use for this flag is efficiently encoding binary data as JSON
269	text, as most octets will not be escaped, resulting in a smaller encoded	278	text, as most octets will not be escaped, resulting in a smaller encoded
270	size. The disadvantage is that the resulting JSON text is encoded	279	size. The disadvantage is that the resulting JSON text is encoded
271	in latin1 (and must correctly be treated as such when storing and	280	in latin1 (and must correctly be treated as such when storing and
…		…
290		299
291	If C<$enable> is false, then the C<encode> method will return the JSON	300	If C<$enable> is false, then the C<encode> method will return the JSON
292	string as a (non-encoded) Unicode string, while C<decode> expects thus a	301	string as a (non-encoded) Unicode string, while C<decode> expects thus a
293	Unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs	302	Unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs
294	to be done yourself, e.g. using the Encode module.	303	to be done yourself, e.g. using the Encode module.
		304
		305	See also the section I<ENCODING/CODESET FLAG NOTES> later in this
		306	document.
295		307
296	Example, output UTF-16BE-encoded JSON:	308	Example, output UTF-16BE-encoded JSON:
297		309
298	use Encode;	310	use Encode;
299	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);	311	$jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
…		…
669	=> ([], 3)	681	=> ([], 3)
670		682
671	=back	683	=back
672		684
673		685
		686	=head1 INCREMENTAL PARSING
		687
		688	[This section is still EXPERIMENTAL]
		689
		690	In some cases, there is the need for incremental parsing of JSON
		691	texts. While this module always has to keep both JSON text and resulting
		692	Perl data structure in memory at one time, it does allow you to parse a
		693	JSON stream incrementally. It does so by accumulating text until it has
		694	a full JSON object, which it then can decode. This process is similar to
		695	using C<decode_prefix> to see if a full JSON object is available, but is
		696	much more efficient (JSON::XS will only attempt to parse the JSON text
		697	once it is sure it has enough text to get a decisive result, using a very
		698	simple but truly incremental parser).
		699
		700	The following two methods deal with this.
		701
		702	=over 4
		703
		704	=item [void, scalar or list context] = $json->incr_parse ([$string])
		705
		706	This is the central parsing function. It can both append new text and
		707	extract objects from the stream accumulated so far (both of these
		708	functions are optional).
		709
		710	If C<$string> is given, then this string is appended to the already
		711	existing JSON fragment stored in the C<$json> object.
		712
		713	After that, if the function is called in void context, it will simply
		714	return without doing anything further. This can be used to add more text
		715	in as many chunks as you want.
		716
		717	If the method is called in scalar context, then it will try to extract
		718	exactly I<one> JSON object. If that is successful, it will return this
		719	object, otherwise it will return C<undef>. This is the most common way of
		720	using the method.
		721
		722	And finally, in list context, it will try to extract as many objects
		723	from the stream as it can find and return them, or the empty list
		724	otherwise. For this to work, there must be no separators between the JSON
		725	objects or arrays, instead they must be concatenated back-to-back.
		726
		727	=item $lvalue_string = $json->incr_text
		728
		729	This method returns the currently stored JSON fragment as an lvalue, that
		730	is, you can manipulate it. This I<only> works when a preceding call to
		731	C<incr_parse> in I<scalar context> successfully returned an object. Under
		732	all other circumstances you must not call this function (I mean it.
		733	although in simple tests it might actually work, it I<will> fail under
		734	real world conditions). As a special exception, you can also call this
		735	method before having parsed anything.
		736
		737	This function is useful in two cases: a) finding the trailing text after a
		738	JSON object or b) parsing multiple JSON objects separated by non-JSON text
		739	(such as commas).
		740
		741	=back
		742
		743	=head2 LIMITATIONS
		744
		745	All options that affect decoding are supported, except
		746	C<allow_nonref>. The reason for this is that it cannot be made to
		747	work sensibly: JSON objects and arrays are self-delimited, i.e. you can concatenate
		748	them back to back and still decode them perfectly. This does not hold true
		749	for JSON numbers, however.
		750
		751	For example, is the string C<1> a single JSON number, or is it simply the
		752	start of C<12>? Or is C<12> a single JSON number, or the concatenation
		753	of C<1> and C<2>? In neither case you can tell, and this is why JSON::XS
		754	takes the conservative route and disallows this case.
		755
		756	=head2 EXAMPLES
		757
		758	Some examples will make all this clearer. First, a simple example that
		759	works similarly to C<decode_prefix>: We want to decode the JSON object at
		760	the start of a string and identify the portion after the JSON object:
		761
		762	my $text = "[1,2,3] hello";
		763
		764	my $json = new JSON::XS;
		765
		766	my $obj = $json->incr_parse ($text)
		767	or die "expected JSON object or array at beginning of string";
		768
		769	my $tail = $json->incr_text;
		770	# $tail now contains " hello"
		771
		772	Easy, isn't it?
		773
		774	Now for a more complicated example: Imagine a hypothetical protocol where
		775	you read some requests from a TCP stream, and each request is a JSON
		776	array, without any separation between them (in fact, it is often useful to
		777	use newlines as "separators", as these get interpreted as whitespace at
		778	the start of the JSON text, which makes it possible to test said protocol
		779	with C<telnet>...).
		780
		781	Here is how you'd do it (it is trivial to write this in an event-based
		782	manner):
		783
		784	my $json = new JSON::XS;
		785
		786	# read some data from the socket
		787	while (sysread $socket, my $buf, 4096) {
		788
		789	# split and decode as many requests as possible
		790	for my $request ($json->incr_parse ($buf)) {
		791	# act on the $request
		792	}
		793	}
		794
		795	Another complicated example: Assume you have a string with JSON objects
		796	or arrays, all separated by (optional) comma characters (e.g. C<[1],[2],
		797	[3]>). To parse them, we have to skip the commas between the JSON texts,
		798	and here is where the lvalue-ness of C<incr_text> comes in useful:
		799
		800	my $text = "[1],[2], [3]";
		801	my $json = new JSON::XS;
		802
		803	# void context, so no parsing done
		804	$json->incr_parse ($text);
		805
		806	# now extract as many objects as possible. note the
		807	# use of scalar context so incr_text can be called.
		808	while (my $obj = $json->incr_parse) {
		809	# do something with $obj
		810
		811	# now skip the optional comma
		812	$json->incr_text =~ s/^ \s* , //x;
		813	}
		814
		815	Now lets go for a very complex example: Assume that you have a gigantic
		816	JSON array-of-objects, many gigabytes in size, and you want to parse it,
		817	but you cannot load it into memory fully (this has actually happened in
		818	the real world :).
		819
		820	Well, you lost, you have to implement your own JSON parser. But JSON::XS
		821	can still help you: You implement a (very simple) array parser and let
		822	JSON decode the array elements, which are all full JSON objects on their
		823	own (this wouldn't work if the array elements could be JSON numbers, for
		824	example):
		825
		826	my $json = new JSON::XS;
		827
		828	# open the monster
		829	open my $fh, "<bigfile.json"
		830	or die "bigfile: $!";
		831
		832	# first parse the initial "["
		833	for (;;) {
		834	sysread $fh, my $buf, 65536
		835	or die "read error: $!";
		836	$json->incr_parse ($buf); # void context, so no parsing
		837
		838	# Exit the loop once we found and removed(!) the initial "[".
		839	# In essence, we are (ab-)using the $json object as a simple scalar
		840	# we append data to.
		841	last if $json->incr_text =~ s/^ \s* \[ //x;
		842	}
		843
		844	# now we have the skipped the initial "[", so continue
		845	# parsing all the elements.
		846	for (;;) {
		847	# in this loop we read data until we got a single JSON object
		848	for (;;) {
		849	if (my $obj = $json->incr_parse) {
		850	# do something with $obj
		851	last;
		852	}
		853
		854	# add more data
		855	sysread $fh, my $buf, 65536
		856	or die "read error: $!";
		857	$json->incr_parse ($buf); # void context, so no parsing
		858	}
		859
		860	# in this loop we read data until we either found and parsed the
		861	# separating "," between elements, or the final "]"
		862	for (;;) {
		863	# first skip whitespace
		864	$json->incr_text =~ s/^\s*//;
		865
		866	# if we find "]", we are done
		867	if ($json->incr_text =~ s/^\]//) {
		868	print "finished.\n";
		869	exit;
		870	}
		871
		872	# if we find ",", we can continue with the next element
		873	if ($json->incr_text =~ s/^,//) {
		874	last;
		875	}
		876
		877	# if we find anything else, we have a parse error!
		878	if (length $json->incr_text) {
		879	die "parse error near ", $json->incr_text;
		880	}
		881
		882	# else add more data
		883	sysread $fh, my $buf, 65536
		884	or die "read error: $!";
		885	$json->incr_parse ($buf); # void context, so no parsing
		886	}
		887
		888	This is a complex example, but most of the complexity comes from the fact
		889	that we are trying to be correct (bear with me if I am wrong, I never ran
		890	the above example :).
		891
		892
		893
674	=head1 MAPPING	894	=head1 MAPPING
675		895
676	This section describes how JSON::XS maps Perl values to JSON values and	896	This section describes how JSON::XS maps Perl values to JSON values and
677	vice versa. These mappings are designed to "do the right thing" in most	897	vice versa. These mappings are designed to "do the right thing" in most
678	circumstances automatically, preserving round-tripping characteristics	898	circumstances automatically, preserving round-tripping characteristics
…		…
706		926
707	A JSON number becomes either an integer, numeric (floating point) or	927	A JSON number becomes either an integer, numeric (floating point) or
708	string scalar in perl, depending on its range and any fractional parts. On	928	string scalar in perl, depending on its range and any fractional parts. On
709	the Perl level, there is no difference between those as Perl handles all	929	the Perl level, there is no difference between those as Perl handles all
710	the conversion details, but an integer may take slightly less memory and	930	the conversion details, but an integer may take slightly less memory and
711	might represent more values exactly than (floating point) numbers.	931	might represent more values exactly than floating point numbers.
712		932
713	If the number consists of digits only, JSON::XS will try to represent	933	If the number consists of digits only, JSON::XS will try to represent
714	it as an integer value. If that fails, it will try to represent it as	934	it as an integer value. If that fails, it will try to represent it as
715	a numeric (floating point) value if that is possible without loss of	935	a numeric (floating point) value if that is possible without loss of
716	precision. Otherwise it will preserve the number as a string value.	936	precision. Otherwise it will preserve the number as a string value (in
		937	which case you lose roundtripping ability, as the JSON number will be
		938	re-encoded toa JSON string).
717		939
718	Numbers containing a fractional or exponential part will always be	940	Numbers containing a fractional or exponential part will always be
719	represented as numeric (floating point) values, possibly at a loss of	941	represented as numeric (floating point) values, possibly at a loss of
720	precision.	942	precision (in which case you might lose perfect roundtripping ability, but
721		943	the JSON number will still be re-encoded as a JSON number).
722	This might create round-tripping problems as numbers might become strings,
723	but as Perl is typeless there is no other way to do it.
724		944
725	=item true, false	945	=item true, false
726		946
727	These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>,	947	These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>,
728	respectively. They are overloaded to act almost exactly like the numbers	948	respectively. They are overloaded to act almost exactly like the numbers
…		…
774	These special values become JSON true and JSON false values,	994	These special values become JSON true and JSON false values,
775	respectively. You can also use C<\1> and C<\0> directly if you want.	995	respectively. You can also use C<\1> and C<\0> directly if you want.
776		996
777	=item blessed objects	997	=item blessed objects
778		998
779	Blessed objects are not allowed. JSON::XS currently tries to encode their	999	Blessed objects are not directly representable in JSON. See the
780	underlying representation (hash- or arrayref), but this behaviour might	1000	C<allow_blessed> and C<convert_blessed> methods on various options on
781	change in future versions.	1001	how to deal with this: basically, you can choose between throwing an
		1002	exception, encoding the reference as if it weren't blessed, or provide
		1003	your own serialiser method.
782		1004
783	=item simple scalars	1005	=item simple scalars
784		1006
785	Simple Perl scalars (any scalar that is not a reference) are the most	1007	Simple Perl scalars (any scalar that is not a reference) are the most
786	difficult objects to encode: JSON::XS will encode undefined scalars as	1008	difficult objects to encode: JSON::XS will encode undefined scalars as
787	JSON null value, scalars that have last been used in a string context	1009	JSON C<null> values, scalars that have last been used in a string context
788	before encoding as JSON strings and anything else as number value:	1010	before encoding as JSON strings, and anything else as number value:
789		1011
790	# dump as number	1012	# dump as number
791	encode_json [2] # yields [2]	1013	encode_json [2] # yields [2]
792	encode_json [-3.0e17] # yields [-3e+17]	1014	encode_json [-3.0e17] # yields [-3e+17]
793	my $value = 5; encode_json [$value] # yields [5]	1015	my $value = 5; encode_json [$value] # yields [5]
…		…
811	my $x = "3"; # some variable containing a string	1033	my $x = "3"; # some variable containing a string
812	$x += 0; # numify it, ensuring it will be dumped as a number	1034	$x += 0; # numify it, ensuring it will be dumped as a number
813	$x *= 1; # same thing, the choice is yours.	1035	$x *= 1; # same thing, the choice is yours.
814		1036
815	You can not currently force the type in other, less obscure, ways. Tell me	1037	You can not currently force the type in other, less obscure, ways. Tell me
816	if you need this capability.	1038	if you need this capability (but don't forget to explain why it's needed
		1039	:).
		1040
		1041	=back
		1042
		1043
		1044	=head1 ENCODING/CODESET FLAG NOTES
		1045
		1046	The interested reader might have seen a number of flags that signify
		1047	encodings or codesets - C<utf8>, C<latin1> and C<ascii>. There seems to be
		1048	some confusion on what these do, so here is a short comparison:
		1049
		1050	C<utf8> controls whether the JSON text created by C<encode> (and expected
		1051	by C<decode>) is UTF-8 encoded or not, while C<latin1> and C<ascii> only
		1052	control whether C<encode> escapes character values outside their respective
		1053	codeset range. Neither of these flags conflict with each other, although
		1054	some combinations make less sense than others.
		1055
		1056	Care has been taken to make all flags symmetrical with respect to
		1057	C<encode> and C<decode>, that is, texts encoded with any combination of
		1058	these flag values will be correctly decoded when the same flags are used
		1059	- in general, if you use different flag settings while encoding vs. when
		1060	decoding you likely have a bug somewhere.
		1061
		1062	Below comes a verbose discussion of these flags. Note that a "codeset" is
		1063	simply an abstract set of character-codepoint pairs, while an encoding
		1064	takes those codepoint numbers and I<encodes> them, in our case into
		1065	octets. Unicode is (among other things) a codeset, UTF-8 is an encoding,
		1066	and ISO-8859-1 (= latin 1) and ASCII are both codesets I<and> encodings at
		1067	the same time, which can be confusing.
		1068
		1069	=over 4
		1070
		1071	=item C<utf8> flag disabled
		1072
		1073	When C<utf8> is disabled (the default), then C<encode>/C<decode> generate
		1074	and expect Unicode strings, that is, characters with high ordinal Unicode
		1075	values (> 255) will be encoded as such characters, and likewise such
		1076	characters are decoded as-is, no canges to them will be done, except
		1077	"(re-)interpreting" them as Unicode codepoints or Unicode characters,
		1078	respectively (to Perl, these are the same thing in strings unless you do
		1079	funny/weird/dumb stuff).
		1080
		1081	This is useful when you want to do the encoding yourself (e.g. when you
		1082	want to have UTF-16 encoded JSON texts) or when some other layer does
		1083	the encoding for you (for example, when printing to a terminal using a
		1084	filehandle that transparently encodes to UTF-8 you certainly do NOT want
		1085	to UTF-8 encode your data first and have Perl encode it another time).
		1086
		1087	=item C<utf8> flag enabled
		1088
		1089	If the C<utf8>-flag is enabled, C<encode>/C<decode> will encode all
		1090	characters using the corresponding UTF-8 multi-byte sequence, and will
		1091	expect your input strings to be encoded as UTF-8, that is, no "character"
		1092	of the input string must have any value > 255, as UTF-8 does not allow
		1093	that.
		1094
		1095	The C<utf8> flag therefore switches between two modes: disabled means you
		1096	will get a Unicode string in Perl, enabled means you get an UTF-8 encoded
		1097	octet/binary string in Perl.
		1098
		1099	=item C<latin1> or C<ascii> flags enabled
		1100
		1101	With C<latin1> (or C<ascii>) enabled, C<encode> will escape characters
		1102	with ordinal values > 255 (> 127 with C<ascii>) and encode the remaining
		1103	characters as specified by the C<utf8> flag.
		1104
		1105	If C<utf8> is disabled, then the result is also correctly encoded in those
		1106	character sets (as both are proper subsets of Unicode, meaning that a
		1107	Unicode string with all character values < 256 is the same thing as a
		1108	ISO-8859-1 string, and a Unicode string with all character values < 128 is
		1109	the same thing as an ASCII string in Perl).
		1110
		1111	If C<utf8> is enabled, you still get a correct UTF-8-encoded string,
		1112	regardless of these flags, just some more characters will be escaped using
		1113	C<\uXXXX> then before.
		1114
		1115	Note that ISO-8859-1-I<encoded> strings are not compatible with UTF-8
		1116	encoding, while ASCII-encoded strings are. That is because the ISO-8859-1
		1117	encoding is NOT a subset of UTF-8 (despite the ISO-8859-1 I<codeset> being
		1118	a subset of Unicode), while ASCII is.
		1119
		1120	Surprisingly, C<decode> will ignore these flags and so treat all input
		1121	values as governed by the C<utf8> flag. If it is disabled, this allows you
		1122	to decode ISO-8859-1- and ASCII-encoded strings, as both strict subsets of
		1123	Unicode. If it is enabled, you can correctly decode UTF-8 encoded strings.
		1124
		1125	So neither C<latin1> nor C<ascii> are incompatible with the C<utf8> flag -
		1126	they only govern when the JSON output engine escapes a character or not.
		1127
		1128	The main use for C<latin1> is to relatively efficiently store binary data
		1129	as JSON, at the expense of breaking compatibility with most JSON decoders.
		1130
		1131	The main use for C<ascii> is to force the output to not contain characters
		1132	with values > 127, which means you can interpret the resulting string
		1133	as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about any character set and
		1134	8-bit-encoding, and still get the same data structure back. This is useful
		1135	when your channel for JSON transfer is not 8-bit clean or the encoding
		1136	might be mangled in between (e.g. in mail), and works because ASCII is a
		1137	proper subset of most 8-bit and multibyte encodings in use in the world.
817		1138
818	=back	1139	=back
819		1140
820		1141
821	=head1 COMPARISON	1142	=head1 COMPARISON
…		…
825	problems (or pleasures) I encountered with various existing JSON modules,	1146	problems (or pleasures) I encountered with various existing JSON modules,
826	followed by some benchmark values. JSON::XS was designed not to suffer	1147	followed by some benchmark values. JSON::XS was designed not to suffer
827	from any of these problems or limitations.	1148	from any of these problems or limitations.
828		1149
829	=over 4	1150	=over 4
		1151
		1152	=item JSON 2.xx
		1153
		1154	A marvellous piece of engineering, this module either uses JSON::XS
		1155	directly when available (so will be 100% compatible with it, including
		1156	speed), or it uses JSON::PP, which is basically JSON::XS translated to
		1157	Pure Perl, which should be 100% compatible with JSON::XS, just a bit
		1158	slower.
		1159
		1160	You cannot really lose by using this module, especially as it tries very
		1161	hard to work even with ancient Perl versions, while JSON::XS does not.
830		1162
831	=item JSON 1.07	1163	=item JSON 1.07
832		1164
833	Slow (but very portable, as it is written in pure Perl).	1165	Slow (but very portable, as it is written in pure Perl).
834		1166
…		…
906		1238
907		1239
908	=head2 JSON and YAML	1240	=head2 JSON and YAML
909		1241
910	You often hear that JSON is a subset of YAML. This is, however, a mass	1242	You often hear that JSON is a subset of YAML. This is, however, a mass
911	hysteria and very far from the truth. In general, there is no way to	1243	hysteria(*) and very far from the truth (as of the time of this writing),
		1244	so let me state it clearly: I<in general, there is no way to configure
912	configure JSON::XS to output a data structure as valid YAML that works for	1245	JSON::XS to output a data structure as valid YAML> that works in all
913	all cases.	1246	cases.
914		1247
915	If you really must use JSON::XS to generate YAML, you should use this	1248	If you really must use JSON::XS to generate YAML, you should use this
916	algorithm (subject to change in future versions):	1249	algorithm (subject to change in future versions):
917		1250
918	my $to_yaml = JSON::XS->new->utf8->space_after (1);	1251	my $to_yaml = JSON::XS->new->utf8->space_after (1);
919	my $yaml = $to_yaml->encode ($ref) . "\n";	1252	my $yaml = $to_yaml->encode ($ref) . "\n";
920		1253
921	This will usually generate JSON texts that also parse as valid	1254	This will I<usually> generate JSON texts that also parse as valid
922	YAML. Please note that YAML has hardcoded limits on (simple) object key	1255	YAML. Please note that YAML has hardcoded limits on (simple) object key
923	lengths that JSON doesn't have and also has different and incompatible	1256	lengths that JSON doesn't have and also has different and incompatible
924	unicode handling, so you should make sure that your hash keys are	1257	unicode handling, so you should make sure that your hash keys are
925	noticeably shorter than the 1024 "stream characters" YAML allows and that	1258	noticeably shorter than the 1024 "stream characters" YAML allows and that
926	you do not have codepoints with values outside the Unicode BMP (basic	1259	you do not have characters with codepoint values outside the Unicode BMP
927	multilingual page).	1260	(basic multilingual page). YAML also does not allow C<\/> sequences in
		1261	strings (which JSON::XS does not I<currently> generate, but other JSON
		1262	generators might).
928		1263
929	There might be other incompatibilities that I am not aware of. In general	1264	There might be other incompatibilities that I am not aware of (or the YAML
		1265	specification has been changed yet again - it does so quite often). In
930	you should not try to generate YAML with a JSON generator or vice versa,	1266	general you should not try to generate YAML with a JSON generator or vice
931	or try to parse JSON with a YAML parser or vice versa: chances are high	1267	versa, or try to parse JSON with a YAML parser or vice versa: chances are
932	that you will run into severe interoperability problems when you least	1268	high that you will run into severe interoperability problems when you
933	expect it.	1269	least expect it.
		1270
		1271	=over 4
		1272
		1273	=item (*)
		1274
		1275	I have been pressured multiple times by Brian Ingerson (one of the
		1276	authors of the YAML specification) to remove this paragraph, despite him
		1277	acknowledging that the actual incompatibilities exist. As I was personally
		1278	bitten by this "JSON is YAML" lie, I refused and said I will continue to
		1279	educate people about these issues, so others do not run into the same
		1280	problem again and again. After this, Brian called me a (quote)I<complete
		1281	and worthless idiot>(unquote).
		1282
		1283	In my opinion, instead of pressuring and insulting people who actually
		1284	clarify issues with YAML and the wrong statements of some of its
		1285	proponents, I would kindly suggest reading the JSON spec (which is not
		1286	that difficult or long) and finally make YAML compatible to it, and
		1287	educating users about the changes, instead of spreading lies about the
		1288	real compatibility for many I<years> and trying to silence people who
		1289	point out that it isn't true.
		1290
		1291	=back
934		1292
935		1293
936	=head2 SPEED	1294	=head2 SPEED
937		1295
938	It seems that JSON::XS is surprisingly fast, as shown in the following	1296	It seems that JSON::XS is surprisingly fast, as shown in the following
939	tables. They have been generated with the help of the C<eg/bench> program	1297	tables. They have been generated with the help of the C<eg/bench> program
940	in the JSON::XS distribution, to make it easy to compare on your own	1298	in the JSON::XS distribution, to make it easy to compare on your own
941	system.	1299	system.
942		1300
943	First comes a comparison between various modules using a very short	1301	First comes a comparison between various modules using
944	single-line JSON string:	1302	a very short single-line JSON string (also available at
		1303	L<http://dist.schmorp.de/misc/json/short.json>).
945		1304
946	{"method": "handleMessage", "params": ["user1", "we were just talking"], \	1305	{"method": "handleMessage", "params": ["user1", "we were just talking"], \
947	"id": null, "array":[1,11,234,-5,1e5,1e7, true, false]}	1306	"id": null, "array":[1,11,234,-5,1e5,1e7, true, false]}
948		1307
949	It shows the number of encodes/decodes per second (JSON::XS uses	1308	It shows the number of encodes/decodes per second (JSON::XS uses
…		…
968	about three times faster on decoding, and over forty times faster	1327	about three times faster on decoding, and over forty times faster
969	than JSON, even with pretty-printing and key sorting. It also compares	1328	than JSON, even with pretty-printing and key sorting. It also compares
970	favourably to Storable for small amounts of data.	1329	favourably to Storable for small amounts of data.
971		1330
972	Using a longer test string (roughly 18KB, generated from Yahoo! Locals	1331	Using a longer test string (roughly 18KB, generated from Yahoo! Locals
973	search API (http://nanoref.com/yahooapis/mgPdGg):	1332	search API (L<http://dist.schmorp.de/misc/json/long.json>).
974		1333
975	module \| encode \| decode \|	1334	module \| encode \| decode \|
976	-----------\|------------\|------------\|	1335	-----------\|------------\|------------\|
977	JSON 1.x \| 55.260 \| 34.971 \|	1336	JSON 1.x \| 55.260 \| 34.971 \|
978	JSON::DWIW \| 825.228 \| 1082.513 \|	1337	JSON::DWIW \| 825.228 \| 1082.513 \|
…		…
1020	to free the temporary). If that is exceeded, the program crashes. To be	1379	to free the temporary). If that is exceeded, the program crashes. To be
1021	conservative, the default nesting limit is set to 512. If your process	1380	conservative, the default nesting limit is set to 512. If your process
1022	has a smaller stack, you should adjust this setting accordingly with the	1381	has a smaller stack, you should adjust this setting accordingly with the
1023	C<max_depth> method.	1382	C<max_depth> method.
1024		1383
1025	And last but least, something else could bomb you that I forgot to think	1384	Something else could bomb you, too, that I forgot to think of. In that
1026	of. In that case, you get to keep the pieces. I am always open for hints,	1385	case, you get to keep the pieces. I am always open for hints, though...
1027	though...	1386
		1387	Also keep in mind that JSON::XS might leak contents of your Perl data
		1388	structures in its error messages, so when you serialise sensitive
		1389	information you might want to make sure that exceptions thrown by JSON::XS
		1390	will not end up in front of untrusted eyes.
1028		1391
1029	If you are using JSON::XS to return packets to consumption	1392	If you are using JSON::XS to return packets to consumption
1030	by JavaScript scripts in a browser you should have a look at	1393	by JavaScript scripts in a browser you should have a look at
1031	L<http://jpsykes.com/47/practical-csrf-and-json-security> to see whether	1394	L<http://jpsykes.com/47/practical-csrf-and-json-security> to see whether
1032	you are vulnerable to some common attack vectors (which really are browser	1395	you are vulnerable to some common attack vectors (which really are browser
…		…
1038	=head1 THREADS	1401	=head1 THREADS
1039		1402
1040	This module is I<not> guaranteed to be thread safe and there are no	1403	This module is I<not> guaranteed to be thread safe and there are no
1041	plans to change this until Perl gets thread support (as opposed to the	1404	plans to change this until Perl gets thread support (as opposed to the
1042	horribly slow so-called "threads" which are simply slow and bloated	1405	horribly slow so-called "threads" which are simply slow and bloated
1043	process simulations - use fork, its I<much> faster, cheaper, better).	1406	process simulations - use fork, it's I<much> faster, cheaper, better).
1044		1407
1045	(It might actually work, but you have been warned).	1408	(It might actually work, but you have been warned).
1046		1409
1047		1410
1048	=head1 BUGS	1411	=head1 BUGS
1049		1412
1050	While the goal of this module is to be correct, that unfortunately does	1413	While the goal of this module is to be correct, that unfortunately does
1051	not mean its bug-free, only that I think its design is bug-free. It is	1414	not mean it's bug-free, only that I think its design is bug-free. It is
1052	still relatively early in its development. If you keep reporting bugs they	1415	still relatively early in its development. If you keep reporting bugs they
1053	will be fixed swiftly, though.	1416	will be fixed swiftly, though.
1054		1417
1055	Please refrain from using rt.cpan.org or any other bug reporting	1418	Please refrain from using rt.cpan.org or any other bug reporting
1056	service. I put the contact address into my modules for a reason.	1419	service. I put the contact address into my modules for a reason.
…		…
1078	"--" => sub { $_[0] = ${$_[0]} - 1 },	1441	"--" => sub { $_[0] = ${$_[0]} - 1 },
1079	fallback => 1;	1442	fallback => 1;
1080		1443
1081	1;	1444	1;
1082		1445
		1446	=head1 SEE ALSO
		1447
		1448	The F<json_xs> command line utility for quick experiments.
		1449
1083	=head1 AUTHOR	1450	=head1 AUTHOR
1084		1451
1085	Marc Lehmann <schmorp@schmorp.de>	1452	Marc Lehmann <schmorp@schmorp.de>
1086	http://home.schmorp.de/	1453	http://home.schmorp.de/
1087		1454

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Revision 1.94 by root, Tue Mar 25 07:46:15 2008 UTC