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

Comparing JSON-XS/XS.pm (file contents):
Revision 1.83 by root, Sun Jan 20 19:19:07 2008 UTC vs.
Revision 1.98 by root, Wed Mar 26 02:36:18 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 and the API it details 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>. If there is a parse error,
		720	this method will croak just as C<decode> would do (one can then use
		721	C<incr_skip> to skip the errornous part). This is the most common way of
		722	using the method.
		723
		724	And finally, in list context, it will try to extract as many objects
		725	from the stream as it can find and return them, or the empty list
		726	otherwise. For this to work, there must be no separators between the JSON
		727	objects or arrays, instead they must be concatenated back-to-back. If
		728	an error occurs, an exception will be raised as in the scalar context
		729	case. Note that in this case, any previously-parsed JSON texts will be
		730	lost.
		731
		732	=item $lvalue_string = $json->incr_text
		733
		734	This method returns the currently stored JSON fragment as an lvalue, that
		735	is, you can manipulate it. This I<only> works when a preceding call to
		736	C<incr_parse> in I<scalar context> successfully returned an object. Under
		737	all other circumstances you must not call this function (I mean it.
		738	although in simple tests it might actually work, it I<will> fail under
		739	real world conditions). As a special exception, you can also call this
		740	method before having parsed anything.
		741
		742	This function is useful in two cases: a) finding the trailing text after a
		743	JSON object or b) parsing multiple JSON objects separated by non-JSON text
		744	(such as commas).
		745
		746	=item $json->incr_skip
		747
		748	This will reset the state of the incremental parser and will remove the
		749	parsed text from the input buffer. This is useful after C<incr_parse>
		750	died, in which case the input buffer and incremental parser state is left
		751	unchanged, to skip the text parsed so far and to reset the parse state.
		752
		753	=back
		754
		755	=head2 LIMITATIONS
		756
		757	All options that affect decoding are supported, except
		758	C<allow_nonref>. The reason for this is that it cannot be made to
		759	work sensibly: JSON objects and arrays are self-delimited, i.e. you can concatenate
		760	them back to back and still decode them perfectly. This does not hold true
		761	for JSON numbers, however.
		762
		763	For example, is the string C<1> a single JSON number, or is it simply the
		764	start of C<12>? Or is C<12> a single JSON number, or the concatenation
		765	of C<1> and C<2>? In neither case you can tell, and this is why JSON::XS
		766	takes the conservative route and disallows this case.
		767
		768	=head2 EXAMPLES
		769
		770	Some examples will make all this clearer. First, a simple example that
		771	works similarly to C<decode_prefix>: We want to decode the JSON object at
		772	the start of a string and identify the portion after the JSON object:
		773
		774	my $text = "[1,2,3] hello";
		775
		776	my $json = new JSON::XS;
		777
		778	my $obj = $json->incr_parse ($text)
		779	or die "expected JSON object or array at beginning of string";
		780
		781	my $tail = $json->incr_text;
		782	# $tail now contains " hello"
		783
		784	Easy, isn't it?
		785
		786	Now for a more complicated example: Imagine a hypothetical protocol where
		787	you read some requests from a TCP stream, and each request is a JSON
		788	array, without any separation between them (in fact, it is often useful to
		789	use newlines as "separators", as these get interpreted as whitespace at
		790	the start of the JSON text, which makes it possible to test said protocol
		791	with C<telnet>...).
		792
		793	Here is how you'd do it (it is trivial to write this in an event-based
		794	manner):
		795
		796	my $json = new JSON::XS;
		797
		798	# read some data from the socket
		799	while (sysread $socket, my $buf, 4096) {
		800
		801	# split and decode as many requests as possible
		802	for my $request ($json->incr_parse ($buf)) {
		803	# act on the $request
		804	}
		805	}
		806
		807	Another complicated example: Assume you have a string with JSON objects
		808	or arrays, all separated by (optional) comma characters (e.g. C<[1],[2],
		809	[3]>). To parse them, we have to skip the commas between the JSON texts,
		810	and here is where the lvalue-ness of C<incr_text> comes in useful:
		811
		812	my $text = "[1],[2], [3]";
		813	my $json = new JSON::XS;
		814
		815	# void context, so no parsing done
		816	$json->incr_parse ($text);
		817
		818	# now extract as many objects as possible. note the
		819	# use of scalar context so incr_text can be called.
		820	while (my $obj = $json->incr_parse) {
		821	# do something with $obj
		822
		823	# now skip the optional comma
		824	$json->incr_text =~ s/^ \s* , //x;
		825	}
		826
		827	Now lets go for a very complex example: Assume that you have a gigantic
		828	JSON array-of-objects, many gigabytes in size, and you want to parse it,
		829	but you cannot load it into memory fully (this has actually happened in
		830	the real world :).
		831
		832	Well, you lost, you have to implement your own JSON parser. But JSON::XS
		833	can still help you: You implement a (very simple) array parser and let
		834	JSON decode the array elements, which are all full JSON objects on their
		835	own (this wouldn't work if the array elements could be JSON numbers, for
		836	example):
		837
		838	my $json = new JSON::XS;
		839
		840	# open the monster
		841	open my $fh, "<bigfile.json"
		842	or die "bigfile: $!";
		843
		844	# first parse the initial "["
		845	for (;;) {
		846	sysread $fh, my $buf, 65536
		847	or die "read error: $!";
		848	$json->incr_parse ($buf); # void context, so no parsing
		849
		850	# Exit the loop once we found and removed(!) the initial "[".
		851	# In essence, we are (ab-)using the $json object as a simple scalar
		852	# we append data to.
		853	last if $json->incr_text =~ s/^ \s* \[ //x;
		854	}
		855
		856	# now we have the skipped the initial "[", so continue
		857	# parsing all the elements.
		858	for (;;) {
		859	# in this loop we read data until we got a single JSON object
		860	for (;;) {
		861	if (my $obj = $json->incr_parse) {
		862	# do something with $obj
		863	last;
		864	}
		865
		866	# add more data
		867	sysread $fh, my $buf, 65536
		868	or die "read error: $!";
		869	$json->incr_parse ($buf); # void context, so no parsing
		870	}
		871
		872	# in this loop we read data until we either found and parsed the
		873	# separating "," between elements, or the final "]"
		874	for (;;) {
		875	# first skip whitespace
		876	$json->incr_text =~ s/^\s*//;
		877
		878	# if we find "]", we are done
		879	if ($json->incr_text =~ s/^\]//) {
		880	print "finished.\n";
		881	exit;
		882	}
		883
		884	# if we find ",", we can continue with the next element
		885	if ($json->incr_text =~ s/^,//) {
		886	last;
		887	}
		888
		889	# if we find anything else, we have a parse error!
		890	if (length $json->incr_text) {
		891	die "parse error near ", $json->incr_text;
		892	}
		893
		894	# else add more data
		895	sysread $fh, my $buf, 65536
		896	or die "read error: $!";
		897	$json->incr_parse ($buf); # void context, so no parsing
		898	}
		899
		900	This is a complex example, but most of the complexity comes from the fact
		901	that we are trying to be correct (bear with me if I am wrong, I never ran
		902	the above example :).
		903
		904
		905
674	=head1 MAPPING	906	=head1 MAPPING
675		907
676	This section describes how JSON::XS maps Perl values to JSON values and	908	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	909	vice versa. These mappings are designed to "do the right thing" in most
678	circumstances automatically, preserving round-tripping characteristics	910	circumstances automatically, preserving round-tripping characteristics
…		…
706		938
707	A JSON number becomes either an integer, numeric (floating point) or	939	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	940	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	941	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	942	the conversion details, but an integer may take slightly less memory and
711	might represent more values exactly than (floating point) numbers.	943	might represent more values exactly than floating point numbers.
712		944
713	If the number consists of digits only, JSON::XS will try to represent	945	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	946	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	947	a numeric (floating point) value if that is possible without loss of
716	precision. Otherwise it will preserve the number as a string value.	948	precision. Otherwise it will preserve the number as a string value (in
		949	which case you lose roundtripping ability, as the JSON number will be
		950	re-encoded toa JSON string).
717		951
718	Numbers containing a fractional or exponential part will always be	952	Numbers containing a fractional or exponential part will always be
719	represented as numeric (floating point) values, possibly at a loss of	953	represented as numeric (floating point) values, possibly at a loss of
720	precision.	954	precision (in which case you might lose perfect roundtripping ability, but
721		955	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		956
725	=item true, false	957	=item true, false
726		958
727	These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>,	959	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	960	respectively. They are overloaded to act almost exactly like the numbers
…		…
813	my $x = "3"; # some variable containing a string	1045	my $x = "3"; # some variable containing a string
814	$x += 0; # numify it, ensuring it will be dumped as a number	1046	$x += 0; # numify it, ensuring it will be dumped as a number
815	$x *= 1; # same thing, the choice is yours.	1047	$x *= 1; # same thing, the choice is yours.
816		1048
817	You can not currently force the type in other, less obscure, ways. Tell me	1049	You can not currently force the type in other, less obscure, ways. Tell me
818	if you need this capability (but don't forget to explain why its needed	1050	if you need this capability (but don't forget to explain why it's needed
819	:).	1051	:).
820		1052
821	=back	1053	=back
822		1054
823		1055
824	=head1 COMPARISON	1056	=head1 ENCODING/CODESET FLAG NOTES
825		1057
826	As already mentioned, this module was created because none of the existing	1058	The interested reader might have seen a number of flags that signify
827	JSON modules could be made to work correctly. First I will describe the	1059	encodings or codesets - C<utf8>, C<latin1> and C<ascii>. There seems to be
828	problems (or pleasures) I encountered with various existing JSON modules,	1060	some confusion on what these do, so here is a short comparison:
829	followed by some benchmark values. JSON::XS was designed not to suffer	1061
830	from any of these problems or limitations.	1062	C<utf8> controls whether the JSON text created by C<encode> (and expected
		1063	by C<decode>) is UTF-8 encoded or not, while C<latin1> and C<ascii> only
		1064	control whether C<encode> escapes character values outside their respective
		1065	codeset range. Neither of these flags conflict with each other, although
		1066	some combinations make less sense than others.
		1067
		1068	Care has been taken to make all flags symmetrical with respect to
		1069	C<encode> and C<decode>, that is, texts encoded with any combination of
		1070	these flag values will be correctly decoded when the same flags are used
		1071	- in general, if you use different flag settings while encoding vs. when
		1072	decoding you likely have a bug somewhere.
		1073
		1074	Below comes a verbose discussion of these flags. Note that a "codeset" is
		1075	simply an abstract set of character-codepoint pairs, while an encoding
		1076	takes those codepoint numbers and I<encodes> them, in our case into
		1077	octets. Unicode is (among other things) a codeset, UTF-8 is an encoding,
		1078	and ISO-8859-1 (= latin 1) and ASCII are both codesets I<and> encodings at
		1079	the same time, which can be confusing.
831		1080
832	=over 4	1081	=over 4
833		1082
834	=item JSON 1.07	1083	=item C<utf8> flag disabled
835		1084
836	Slow (but very portable, as it is written in pure Perl).	1085	When C<utf8> is disabled (the default), then C<encode>/C<decode> generate
		1086	and expect Unicode strings, that is, characters with high ordinal Unicode
		1087	values (> 255) will be encoded as such characters, and likewise such
		1088	characters are decoded as-is, no canges to them will be done, except
		1089	"(re-)interpreting" them as Unicode codepoints or Unicode characters,
		1090	respectively (to Perl, these are the same thing in strings unless you do
		1091	funny/weird/dumb stuff).
837		1092
838	Undocumented/buggy Unicode handling (how JSON handles Unicode values is	1093	This is useful when you want to do the encoding yourself (e.g. when you
839	undocumented. One can get far by feeding it Unicode strings and doing	1094	want to have UTF-16 encoded JSON texts) or when some other layer does
840	en-/decoding oneself, but Unicode escapes are not working properly).	1095	the encoding for you (for example, when printing to a terminal using a
		1096	filehandle that transparently encodes to UTF-8 you certainly do NOT want
		1097	to UTF-8 encode your data first and have Perl encode it another time).
841		1098
842	No round-tripping (strings get clobbered if they look like numbers, e.g.	1099	=item C<utf8> flag enabled
843	the string C<2.0> will encode to C<2.0> instead of C<"2.0">, and that will
844	decode into the number 2.
845		1100
846	=item JSON::PC 0.01	1101	If the C<utf8>-flag is enabled, C<encode>/C<decode> will encode all
		1102	characters using the corresponding UTF-8 multi-byte sequence, and will
		1103	expect your input strings to be encoded as UTF-8, that is, no "character"
		1104	of the input string must have any value > 255, as UTF-8 does not allow
		1105	that.
847		1106
848	Very fast.	1107	The C<utf8> flag therefore switches between two modes: disabled means you
		1108	will get a Unicode string in Perl, enabled means you get an UTF-8 encoded
		1109	octet/binary string in Perl.
849		1110
850	Undocumented/buggy Unicode handling.	1111	=item C<latin1> or C<ascii> flags enabled
851		1112
852	No round-tripping.	1113	With C<latin1> (or C<ascii>) enabled, C<encode> will escape characters
		1114	with ordinal values > 255 (> 127 with C<ascii>) and encode the remaining
		1115	characters as specified by the C<utf8> flag.
853		1116
854	Has problems handling many Perl values (e.g. regex results and other magic	1117	If C<utf8> is disabled, then the result is also correctly encoded in those
855	values will make it croak).	1118	character sets (as both are proper subsets of Unicode, meaning that a
		1119	Unicode string with all character values < 256 is the same thing as a
		1120	ISO-8859-1 string, and a Unicode string with all character values < 128 is
		1121	the same thing as an ASCII string in Perl).
856		1122
857	Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}>	1123	If C<utf8> is enabled, you still get a correct UTF-8-encoded string,
858	which is not a valid JSON text.	1124	regardless of these flags, just some more characters will be escaped using
		1125	C<\uXXXX> then before.
859		1126
860	Unmaintained (maintainer unresponsive for many months, bugs are not	1127	Note that ISO-8859-1-I<encoded> strings are not compatible with UTF-8
861	getting fixed).	1128	encoding, while ASCII-encoded strings are. That is because the ISO-8859-1
		1129	encoding is NOT a subset of UTF-8 (despite the ISO-8859-1 I<codeset> being
		1130	a subset of Unicode), while ASCII is.
862		1131
863	=item JSON::Syck 0.21	1132	Surprisingly, C<decode> will ignore these flags and so treat all input
		1133	values as governed by the C<utf8> flag. If it is disabled, this allows you
		1134	to decode ISO-8859-1- and ASCII-encoded strings, as both strict subsets of
		1135	Unicode. If it is enabled, you can correctly decode UTF-8 encoded strings.
864		1136
865	Very buggy (often crashes).	1137	So neither C<latin1> nor C<ascii> are incompatible with the C<utf8> flag -
		1138	they only govern when the JSON output engine escapes a character or not.
866		1139
867	Very inflexible (no human-readable format supported, format pretty much	1140	The main use for C<latin1> is to relatively efficiently store binary data
868	undocumented. I need at least a format for easy reading by humans and a	1141	as JSON, at the expense of breaking compatibility with most JSON decoders.
869	single-line compact format for use in a protocol, and preferably a way to
870	generate ASCII-only JSON texts).
871		1142
872	Completely broken (and confusingly documented) Unicode handling (Unicode	1143	The main use for C<ascii> is to force the output to not contain characters
873	escapes are not working properly, you need to set ImplicitUnicode to	1144	with values > 127, which means you can interpret the resulting string
874	I<different> values on en- and decoding to get symmetric behaviour).	1145	as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about any character set and
875		1146	8-bit-encoding, and still get the same data structure back. This is useful
876	No round-tripping (simple cases work, but this depends on whether the scalar	1147	when your channel for JSON transfer is not 8-bit clean or the encoding
877	value was used in a numeric context or not).	1148	might be mangled in between (e.g. in mail), and works because ASCII is a
878		1149	proper subset of most 8-bit and multibyte encodings in use in the world.
879	Dumping hashes may skip hash values depending on iterator state.
880
881	Unmaintained (maintainer unresponsive for many months, bugs are not
882	getting fixed).
883
884	Does not check input for validity (i.e. will accept non-JSON input and
885	return "something" instead of raising an exception. This is a security
886	issue: imagine two banks transferring money between each other using
887	JSON. One bank might parse a given non-JSON request and deduct money,
888	while the other might reject the transaction with a syntax error. While a
889	good protocol will at least recover, that is extra unnecessary work and
890	the transaction will still not succeed).
891
892	=item JSON::DWIW 0.04
893
894	Very fast. Very natural. Very nice.
895
896	Undocumented Unicode handling (but the best of the pack. Unicode escapes
897	still don't get parsed properly).
898
899	Very inflexible.
900
901	No round-tripping.
902
903	Does not generate valid JSON texts (key strings are often unquoted, empty keys
904	result in nothing being output)
905
906	Does not check input for validity.
907		1150
908	=back	1151	=back
909		1152
910		1153
911	=head2 JSON and YAML	1154	=head2 JSON and YAML
912		1155
913	You often hear that JSON is a subset of YAML. This is, however, a mass	1156	You often hear that JSON is a subset of YAML. This is, however, a mass
914	hysteria(*) and very far from the truth. In general, there is no way to	1157	hysteria(*) and very far from the truth (as of the time of this writing),
		1158	so let me state it clearly: I<in general, there is no way to configure
915	configure JSON::XS to output a data structure as valid YAML that works for	1159	JSON::XS to output a data structure as valid YAML> that works in all
916	all cases.	1160	cases.
917		1161
918	If you really must use JSON::XS to generate YAML, you should use this	1162	If you really must use JSON::XS to generate YAML, you should use this
919	algorithm (subject to change in future versions):	1163	algorithm (subject to change in future versions):
920		1164
921	my $to_yaml = JSON::XS->new->utf8->space_after (1);	1165	my $to_yaml = JSON::XS->new->utf8->space_after (1);
…		…
924	This will I<usually> generate JSON texts that also parse as valid	1168	This will I<usually> generate JSON texts that also parse as valid
925	YAML. Please note that YAML has hardcoded limits on (simple) object key	1169	YAML. Please note that YAML has hardcoded limits on (simple) object key
926	lengths that JSON doesn't have and also has different and incompatible	1170	lengths that JSON doesn't have and also has different and incompatible
927	unicode handling, so you should make sure that your hash keys are	1171	unicode handling, so you should make sure that your hash keys are
928	noticeably shorter than the 1024 "stream characters" YAML allows and that	1172	noticeably shorter than the 1024 "stream characters" YAML allows and that
929	you do not have codepoints with values outside the Unicode BMP (basic	1173	you do not have characters with codepoint values outside the Unicode BMP
930	multilingual page). YAML also does not allow C<\/> sequences in strings	1174	(basic multilingual page). YAML also does not allow C<\/> sequences in
931	(which JSON::XS does not I<currently> generate).	1175	strings (which JSON::XS does not I<currently> generate, but other JSON
		1176	generators might).
932		1177
933	There might be other incompatibilities that I am not aware of (or the YAML	1178	There might be other incompatibilities that I am not aware of (or the YAML
934	specification has been changed yet again - it does so quite often). In	1179	specification has been changed yet again - it does so quite often). In
935	general you should not try to generate YAML with a JSON generator or vice	1180	general you should not try to generate YAML with a JSON generator or vice
936	versa, or try to parse JSON with a YAML parser or vice versa: chances are	1181	versa, or try to parse JSON with a YAML parser or vice versa: chances are
…		…
939		1184
940	=over 4	1185	=over 4
941		1186
942	=item (*)	1187	=item (*)
943		1188
944	This is spread actively by the YAML team, however. For many years now they	1189	I have been pressured multiple times by Brian Ingerson (one of the
945	claim YAML were a superset of JSON, even when proven otherwise.	1190	authors of the YAML specification) to remove this paragraph, despite him
		1191	acknowledging that the actual incompatibilities exist. As I was personally
		1192	bitten by this "JSON is YAML" lie, I refused and said I will continue to
		1193	educate people about these issues, so others do not run into the same
		1194	problem again and again. After this, Brian called me a (quote)I<complete
		1195	and worthless idiot>(unquote).
946		1196
947	Even the author of this manpage was at some point accused of providing	1197	In my opinion, instead of pressuring and insulting people who actually
948	"incorrect" information, despite the evidence presented (claims ranged	1198	clarify issues with YAML and the wrong statements of some of its
949	from "your documentation contains inaccurate and negative statements about	1199	proponents, I would kindly suggest reading the JSON spec (which is not
950	YAML" (the only negative comment is this footnote, and it didn't exist	1200	that difficult or long) and finally make YAML compatible to it, and
951	back then; the question on which claims were inaccurate was never answered	1201	educating users about the changes, instead of spreading lies about the
952	etc.) to "the YAML spec is not up-to-date" (the real and supposedly	1202	real compatibility for many I<years> and trying to silence people who
953	JSON-compatible spec is apparently not currently publicly available)	1203	point out that it isn't true.
954	to actual requests to replace this section by incorrect information,
955	suppressing information about the real problem).
956
957	So whenever you are told that YAML was a superset of JSON, first check
958	wether it is really true (it might be when you check it, but it certainly
959	was not true when this was written). I would much prefer if the YAML team
960	would spent their time on actually making JSON compatibility a truth
961	(JSON, after all, has a very small and simple specification) instead of
962	trying to lobby/force people into reporting untruths.
963		1204
964	=back	1205	=back
965		1206
966		1207
967	=head2 SPEED	1208	=head2 SPEED
…		…
969	It seems that JSON::XS is surprisingly fast, as shown in the following	1210	It seems that JSON::XS is surprisingly fast, as shown in the following
970	tables. They have been generated with the help of the C<eg/bench> program	1211	tables. They have been generated with the help of the C<eg/bench> program
971	in the JSON::XS distribution, to make it easy to compare on your own	1212	in the JSON::XS distribution, to make it easy to compare on your own
972	system.	1213	system.
973		1214
974	First comes a comparison between various modules using a very short	1215	First comes a comparison between various modules using
975	single-line JSON string:	1216	a very short single-line JSON string (also available at
		1217	L<http://dist.schmorp.de/misc/json/short.json>).
976		1218
977	{"method": "handleMessage", "params": ["user1", "we were just talking"], \	1219	{"method": "handleMessage", "params": ["user1", "we were just talking"], \
978	"id": null, "array":[1,11,234,-5,1e5,1e7, true, false]}	1220	"id": null, "array":[1,11,234,-5,1e5,1e7, true, false]}
979		1221
980	It shows the number of encodes/decodes per second (JSON::XS uses	1222	It shows the number of encodes/decodes per second (JSON::XS uses
…		…
999	about three times faster on decoding, and over forty times faster	1241	about three times faster on decoding, and over forty times faster
1000	than JSON, even with pretty-printing and key sorting. It also compares	1242	than JSON, even with pretty-printing and key sorting. It also compares
1001	favourably to Storable for small amounts of data.	1243	favourably to Storable for small amounts of data.
1002		1244
1003	Using a longer test string (roughly 18KB, generated from Yahoo! Locals	1245	Using a longer test string (roughly 18KB, generated from Yahoo! Locals
1004	search API (http://nanoref.com/yahooapis/mgPdGg):	1246	search API (L<http://dist.schmorp.de/misc/json/long.json>).
1005		1247
1006	module \| encode \| decode \|	1248	module \| encode \| decode \|
1007	-----------\|------------\|------------\|	1249	-----------\|------------\|------------\|
1008	JSON 1.x \| 55.260 \| 34.971 \|	1250	JSON 1.x \| 55.260 \| 34.971 \|
1009	JSON::DWIW \| 825.228 \| 1082.513 \|	1251	JSON::DWIW \| 825.228 \| 1082.513 \|
…		…
1051	to free the temporary). If that is exceeded, the program crashes. To be	1293	to free the temporary). If that is exceeded, the program crashes. To be
1052	conservative, the default nesting limit is set to 512. If your process	1294	conservative, the default nesting limit is set to 512. If your process
1053	has a smaller stack, you should adjust this setting accordingly with the	1295	has a smaller stack, you should adjust this setting accordingly with the
1054	C<max_depth> method.	1296	C<max_depth> method.
1055		1297
1056	And last but least, something else could bomb you that I forgot to think	1298	Something else could bomb you, too, that I forgot to think of. In that
1057	of. In that case, you get to keep the pieces. I am always open for hints,	1299	case, you get to keep the pieces. I am always open for hints, though...
1058	though...	1300
		1301	Also keep in mind that JSON::XS might leak contents of your Perl data
		1302	structures in its error messages, so when you serialise sensitive
		1303	information you might want to make sure that exceptions thrown by JSON::XS
		1304	will not end up in front of untrusted eyes.
1059		1305
1060	If you are using JSON::XS to return packets to consumption	1306	If you are using JSON::XS to return packets to consumption
1061	by JavaScript scripts in a browser you should have a look at	1307	by JavaScript scripts in a browser you should have a look at
1062	L<http://jpsykes.com/47/practical-csrf-and-json-security> to see whether	1308	L<http://jpsykes.com/47/practical-csrf-and-json-security> to see whether
1063	you are vulnerable to some common attack vectors (which really are browser	1309	you are vulnerable to some common attack vectors (which really are browser
…		…
1069	=head1 THREADS	1315	=head1 THREADS
1070		1316
1071	This module is I<not> guaranteed to be thread safe and there are no	1317	This module is I<not> guaranteed to be thread safe and there are no
1072	plans to change this until Perl gets thread support (as opposed to the	1318	plans to change this until Perl gets thread support (as opposed to the
1073	horribly slow so-called "threads" which are simply slow and bloated	1319	horribly slow so-called "threads" which are simply slow and bloated
1074	process simulations - use fork, its I<much> faster, cheaper, better).	1320	process simulations - use fork, it's I<much> faster, cheaper, better).
1075		1321
1076	(It might actually work, but you have been warned).	1322	(It might actually work, but you have been warned).
1077		1323
1078		1324
1079	=head1 BUGS	1325	=head1 BUGS
1080		1326
1081	While the goal of this module is to be correct, that unfortunately does	1327	While the goal of this module is to be correct, that unfortunately does
1082	not mean its bug-free, only that I think its design is bug-free. It is	1328	not mean it's bug-free, only that I think its design is bug-free. It is
1083	still relatively early in its development. If you keep reporting bugs they	1329	still relatively early in its development. If you keep reporting bugs they
1084	will be fixed swiftly, though.	1330	will be fixed swiftly, though.
1085		1331
1086	Please refrain from using rt.cpan.org or any other bug reporting	1332	Please refrain from using rt.cpan.org or any other bug reporting
1087	service. I put the contact address into my modules for a reason.	1333	service. I put the contact address into my modules for a reason.
…		…
1109	"--" => sub { $_[0] = ${$_[0]} - 1 },	1355	"--" => sub { $_[0] = ${$_[0]} - 1 },
1110	fallback => 1;	1356	fallback => 1;
1111		1357
1112	1;	1358	1;
1113		1359
		1360	=head1 SEE ALSO
		1361
		1362	The F<json_xs> command line utility for quick experiments.
		1363
1114	=head1 AUTHOR	1364	=head1 AUTHOR
1115		1365
1116	Marc Lehmann <schmorp@schmorp.de>	1366	Marc Lehmann <schmorp@schmorp.de>
1117	http://home.schmorp.de/	1367	http://home.schmorp.de/
1118		1368

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Comparing JSON-XS/XS.pm (file contents):
Revision 1.83 by root, Sun Jan 20 19:19:07 2008 UTC vs.
Revision 1.98 by root, Wed Mar 26 02:36:18 2008 UTC