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Revision 1.72 by root, Sun Nov 25 19:11:07 2007 UTC vs.
Revision 1.99 by root, Thu Mar 27 06:37:35 2008 UTC

1=head1 NAME 1=head1 NAME
2
3=encoding utf-8
2 4
3JSON::XS - JSON serialising/deserialising, done correctly and fast 5JSON::XS - JSON serialising/deserialising, done correctly and fast
4 6
5JSON::XS - 正しくて高速な JSON シリアライザ/デシリアライザ 7JSON::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)
10 use JSON::XS; 12 use JSON::XS;
11 13
12 # exported functions, they croak on error 14 # exported functions, they croak on error
13 # and expect/generate UTF-8 15 # and expect/generate UTF-8
14 16
15 $utf8_encoded_json_text = to_json $perl_hash_or_arrayref; 17 $utf8_encoded_json_text = encode_json $perl_hash_or_arrayref;
16 $perl_hash_or_arrayref = from_json $utf8_encoded_json_text; 18 $perl_hash_or_arrayref = decode_json $utf8_encoded_json_text;
17 19
18 # OO-interface 20 # OO-interface
19 21
20 $coder = JSON::XS->new->ascii->pretty->allow_nonref; 22 $coder = JSON::XS->new->ascii->pretty->allow_nonref;
21 $pretty_printed_unencoded = $coder->encode ($perl_scalar); 23 $pretty_printed_unencoded = $coder->encode ($perl_scalar);
22 $perl_scalar = $coder->decode ($unicode_json_text); 24 $perl_scalar = $coder->decode ($unicode_json_text);
23 25
26 # Note that JSON version 2.0 and above will automatically use JSON::XS
27 # if available, at virtually no speed overhead either, so you should
28 # be able to just:
29
30 use JSON;
31
32 # and do the same things, except that you have a pure-perl fallback now.
33
24=head1 DESCRIPTION 34=head1 DESCRIPTION
25 35
26This module converts Perl data structures to JSON and vice versa. Its 36This module converts Perl data structures to JSON and vice versa. Its
27primary goal is to be I<correct> and its secondary goal is to be 37primary goal is to be I<correct> and its secondary goal is to be
28I<fast>. To reach the latter goal it was written in C. 38I<fast>. To reach the latter goal it was written in C.
39
40Beginning with version 2.0 of the JSON module, when both JSON and
41JSON::XS are installed, then JSON will fall back on JSON::XS (this can be
42overriden) with no overhead due to emulation (by inheritign constructor
43and methods). If JSON::XS is not available, it will fall back to the
44compatible JSON::PP module as backend, so using JSON instead of JSON::XS
45gives you a portable JSON API that can be fast when you need and doesn't
46require a C compiler when that is a problem.
29 47
30As this is the n-th-something JSON module on CPAN, what was the reason 48As this is the n-th-something JSON module on CPAN, what was the reason
31to write yet another JSON module? While it seems there are many JSON 49to write yet another JSON module? While it seems there are many JSON
32modules, none of them correctly handle all corner cases, and in most cases 50modules, none of them correctly handle all corner cases, and in most cases
33their maintainers are unresponsive, gone missing, or not listening to bug 51their maintainers are unresponsive, gone missing, or not listening to bug
42 60
43=over 4 61=over 4
44 62
45=item * correct Unicode handling 63=item * correct Unicode handling
46 64
47This module knows how to handle Unicode, and even documents how and when 65This module knows how to handle Unicode, documents how and when it does
48it does so. 66so, and even documents what "correct" means.
49 67
50=item * round-trip integrity 68=item * round-trip integrity
51 69
52When you serialise a perl data structure using only datatypes supported 70When you serialise a perl data structure using only datatypes supported
53by JSON, the deserialised data structure is identical on the Perl level. 71by JSON, the deserialised data structure is identical on the Perl level.
54(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
55like a number). 73like a number). There minor I<are> exceptions to this, read the MAPPING
74section below to learn about those.
56 75
57=item * strict checking of JSON correctness 76=item * strict checking of JSON correctness
58 77
59There is no guessing, no generating of illegal JSON texts by default, 78There is no guessing, no generating of illegal JSON texts by default,
60and only JSON is accepted as input by default (the latter is a security 79and only JSON is accepted as input by default (the latter is a security
61feature). 80feature).
62 81
63=item * fast 82=item * fast
64 83
65Compared to other JSON modules, this module compares favourably in terms 84Compared to other JSON modules and other serialisers such as Storable,
66of speed, too. 85this module usually compares favourably in terms of speed, too.
67 86
68=item * simple to use 87=item * simple to use
69 88
70This module has both a simple functional interface as well as an OO 89This module has both a simple functional interface as well as an objetc
71interface. 90oriented interface interface.
72 91
73=item * reasonably versatile output formats 92=item * reasonably versatile output formats
74 93
75You can choose between the most compact guaranteed single-line format 94You can choose between the most compact guaranteed-single-line format
76possible (nice for simple line-based protocols), a pure-ascii format 95possible (nice for simple line-based protocols), a pure-ascii format
77(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
78Unicode range), or a pretty-printed format (for when you want to read that 97Unicode range), or a pretty-printed format (for when you want to read that
79stuff). Or you can combine those features in whatever way you like. 98stuff). Or you can combine those features in whatever way you like.
80 99
84 103
85package JSON::XS; 104package JSON::XS;
86 105
87use strict; 106use strict;
88 107
89our $VERSION = '1.53'; 108our $VERSION = '2.2';
90our @ISA = qw(Exporter); 109our @ISA = qw(Exporter);
91 110
92our @EXPORT = qw(to_json from_json); 111our @EXPORT = qw(encode_json decode_json to_json from_json);
112
113sub to_json($) {
114 require Carp;
115 Carp::croak ("JSON::XS::to_json has been renamed to encode_json, either downgrade to pre-2.0 versions of JSON::XS or rename the call");
116}
117
118sub from_json($) {
119 require Carp;
120 Carp::croak ("JSON::XS::from_json has been renamed to decode_json, either downgrade to pre-2.0 versions of JSON::XS or rename the call");
121}
93 122
94use Exporter; 123use Exporter;
95use XSLoader; 124use XSLoader;
96 125
97=head1 FUNCTIONAL INTERFACE 126=head1 FUNCTIONAL INTERFACE
99The following convenience methods are provided by this module. They are 128The following convenience methods are provided by this module. They are
100exported by default: 129exported by default:
101 130
102=over 4 131=over 4
103 132
104=item $json_text = to_json $perl_scalar 133=item $json_text = encode_json $perl_scalar
105 134
106Converts the given Perl data structure to a UTF-8 encoded, binary string 135Converts the given Perl data structure to a UTF-8 encoded, binary string
107(that is, the string contains octets only). Croaks on error. 136(that is, the string contains octets only). Croaks on error.
108 137
109This function call is functionally identical to: 138This function call is functionally identical to:
110 139
111 $json_text = JSON::XS->new->utf8->encode ($perl_scalar) 140 $json_text = JSON::XS->new->utf8->encode ($perl_scalar)
112 141
113except being faster. 142except being faster.
114 143
115=item $perl_scalar = from_json $json_text 144=item $perl_scalar = decode_json $json_text
116 145
117The opposite of C<to_json>: expects an UTF-8 (binary) string and tries 146The opposite of C<encode_json>: expects an UTF-8 (binary) string and tries
118to parse that as an UTF-8 encoded JSON text, returning the resulting 147to parse that as an UTF-8 encoded JSON text, returning the resulting
119reference. Croaks on error. 148reference. Croaks on error.
120 149
121This function call is functionally identical to: 150This function call is functionally identical to:
122 151
148This enables you to store Unicode characters as single characters in a 177This enables you to store Unicode characters as single characters in a
149Perl string - very natural. 178Perl string - very natural.
150 179
151=item 2. Perl does I<not> associate an encoding with your strings. 180=item 2. Perl does I<not> associate an encoding with your strings.
152 181
153Unless you force it to, e.g. when matching it against a regex, or printing 182... until you force it to, e.g. when matching it against a regex, or
154the scalar to a file, in which case Perl either interprets your string as 183printing the scalar to a file, in which case Perl either interprets your
155locale-encoded text, octets/binary, or as Unicode, depending on various 184string as locale-encoded text, octets/binary, or as Unicode, depending
156settings. In no case is an encoding stored together with your data, it is 185on various settings. In no case is an encoding stored together with your
157I<use> that decides encoding, not any magical metadata. 186data, it is I<use> that decides encoding, not any magical meta data.
158 187
159=item 3. The internal utf-8 flag has no meaning with regards to the 188=item 3. The internal utf-8 flag has no meaning with regards to the
160encoding of your string. 189encoding of your string.
161 190
162Just ignore that flag unless you debug a Perl bug, a module written in 191Just ignore that flag unless you debug a Perl bug, a module written in
216 245
217If C<$enable> is false, then the C<encode> method will not escape Unicode 246If C<$enable> is false, then the C<encode> method will not escape Unicode
218characters unless required by the JSON syntax or other flags. This results 247characters unless required by the JSON syntax or other flags. This results
219in a faster and more compact format. 248in a faster and more compact format.
220 249
250See also the section I<ENCODING/CODESET FLAG NOTES> later in this
251document.
252
221The main use for this flag is to produce JSON texts that can be 253The main use for this flag is to produce JSON texts that can be
222transmitted over a 7-bit channel, as the encoded JSON texts will not 254transmitted over a 7-bit channel, as the encoded JSON texts will not
223contain any 8 bit characters. 255contain any 8 bit characters.
224 256
225 JSON::XS->new->ascii (1)->encode ([chr 0x10401]) 257 JSON::XS->new->ascii (1)->encode ([chr 0x10401])
236will not be affected in any way by this flag, as C<decode> by default 268will not be affected in any way by this flag, as C<decode> by default
237expects Unicode, which is a strict superset of latin1. 269expects Unicode, which is a strict superset of latin1.
238 270
239If C<$enable> is false, then the C<encode> method will not escape Unicode 271If C<$enable> is false, then the C<encode> method will not escape Unicode
240characters unless required by the JSON syntax or other flags. 272characters unless required by the JSON syntax or other flags.
273
274See also the section I<ENCODING/CODESET FLAG NOTES> later in this
275document.
241 276
242The main use for this flag is efficiently encoding binary data as JSON 277The main use for this flag is efficiently encoding binary data as JSON
243text, as most octets will not be escaped, resulting in a smaller encoded 278text, as most octets will not be escaped, resulting in a smaller encoded
244size. The disadvantage is that the resulting JSON text is encoded 279size. The disadvantage is that the resulting JSON text is encoded
245in latin1 (and must correctly be treated as such when storing and 280in latin1 (and must correctly be treated as such when storing and
265If C<$enable> is false, then the C<encode> method will return the JSON 300If C<$enable> is false, then the C<encode> method will return the JSON
266string as a (non-encoded) Unicode string, while C<decode> expects thus a 301string as a (non-encoded) Unicode string, while C<decode> expects thus a
267Unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs 302Unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs
268to be done yourself, e.g. using the Encode module. 303to be done yourself, e.g. using the Encode module.
269 304
305See also the section I<ENCODING/CODESET FLAG NOTES> later in this
306document.
307
270Example, output UTF-16BE-encoded JSON: 308Example, output UTF-16BE-encoded JSON:
271 309
272 use Encode; 310 use Encode;
273 $jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object); 311 $jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
274 312
276 314
277 use Encode; 315 use Encode;
278 $object = JSON::XS->new->decode (decode "UTF-32LE", $jsontext); 316 $object = JSON::XS->new->decode (decode "UTF-32LE", $jsontext);
279 317
280=item $json = $json->pretty ([$enable]) 318=item $json = $json->pretty ([$enable])
281
282=item $enabled = $json->get_pretty
283 319
284This enables (or disables) all of the C<indent>, C<space_before> and 320This enables (or disables) all of the C<indent>, C<space_before> and
285C<space_after> (and in the future possibly more) flags in one call to 321C<space_after> (and in the future possibly more) flags in one call to
286generate the most readable (or most compact) form possible. 322generate the most readable (or most compact) form possible.
287 323
427resulting in an invalid JSON text: 463resulting in an invalid JSON text:
428 464
429 JSON::XS->new->allow_nonref->encode ("Hello, World!") 465 JSON::XS->new->allow_nonref->encode ("Hello, World!")
430 => "Hello, World!" 466 => "Hello, World!"
431 467
468=item $json = $json->allow_unknown ([$enable])
469
470=item $enabled = $json->get_allow_unknown
471
472If C<$enable> is true (or missing), then C<encode> will I<not> throw an
473exception when it encounters values it cannot represent in JSON (for
474example, filehandles) but instead will encode a JSON C<null> value. Note
475that blessed objects are not included here and are handled separately by
476c<allow_nonref>.
477
478If C<$enable> is false (the default), then C<encode> will throw an
479exception when it encounters anything it cannot encode as JSON.
480
481This option does not affect C<decode> in any way, and it is recommended to
482leave it off unless you know your communications partner.
483
432=item $json = $json->allow_blessed ([$enable]) 484=item $json = $json->allow_blessed ([$enable])
433 485
434=item $enabled = $json->get_allow_bless 486=item $enabled = $json->get_allow_blessed
435 487
436If C<$enable> is true (or missing), then the C<encode> method will not 488If C<$enable> is true (or missing), then the C<encode> method will not
437barf when it encounters a blessed reference. Instead, the value of the 489barf when it encounters a blessed reference. Instead, the value of the
438B<convert_blessed> option will decide whether C<null> (C<convert_blessed> 490B<convert_blessed> option will decide whether C<null> (C<convert_blessed>
439disabled or no C<to_json> method found) or a representation of the 491disabled or no C<TO_JSON> method found) or a representation of the
440object (C<convert_blessed> enabled and C<to_json> method found) is being 492object (C<convert_blessed> enabled and C<TO_JSON> method found) is being
441encoded. Has no effect on C<decode>. 493encoded. Has no effect on C<decode>.
442 494
443If C<$enable> is false (the default), then C<encode> will throw an 495If C<$enable> is false (the default), then C<encode> will throw an
444exception when it encounters a blessed object. 496exception when it encounters a blessed object.
445 497
457The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON> 509The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON>
458returns other blessed objects, those will be handled in the same 510returns other blessed objects, those will be handled in the same
459way. C<TO_JSON> must take care of not causing an endless recursion cycle 511way. C<TO_JSON> must take care of not causing an endless recursion cycle
460(== crash) in this case. The name of C<TO_JSON> was chosen because other 512(== crash) in this case. The name of C<TO_JSON> was chosen because other
461methods called by the Perl core (== not by the user of the object) are 513methods called by the Perl core (== not by the user of the object) are
462usually in upper case letters and to avoid collisions with the C<to_json> 514usually in upper case letters and to avoid collisions with any C<to_json>
463function. 515function or method.
464 516
465This setting does not yet influence C<decode> in any way, but in the 517This setting does not yet influence C<decode> in any way, but in the
466future, global hooks might get installed that influence C<decode> and are 518future, global hooks might get installed that influence C<decode> and are
467enabled by this setting. 519enabled by this setting.
468 520
645 => ([], 3) 697 => ([], 3)
646 698
647=back 699=back
648 700
649 701
702=head1 INCREMENTAL PARSING
703
704[This section and the API it details is still EXPERIMENTAL]
705
706In some cases, there is the need for incremental parsing of JSON
707texts. While this module always has to keep both JSON text and resulting
708Perl data structure in memory at one time, it does allow you to parse a
709JSON stream incrementally. It does so by accumulating text until it has
710a full JSON object, which it then can decode. This process is similar to
711using C<decode_prefix> to see if a full JSON object is available, but is
712much more efficient (JSON::XS will only attempt to parse the JSON text
713once it is sure it has enough text to get a decisive result, using a very
714simple but truly incremental parser).
715
716The following two methods deal with this.
717
718=over 4
719
720=item [void, scalar or list context] = $json->incr_parse ([$string])
721
722This is the central parsing function. It can both append new text and
723extract objects from the stream accumulated so far (both of these
724functions are optional).
725
726If C<$string> is given, then this string is appended to the already
727existing JSON fragment stored in the C<$json> object.
728
729After that, if the function is called in void context, it will simply
730return without doing anything further. This can be used to add more text
731in as many chunks as you want.
732
733If the method is called in scalar context, then it will try to extract
734exactly I<one> JSON object. If that is successful, it will return this
735object, otherwise it will return C<undef>. If there is a parse error,
736this method will croak just as C<decode> would do (one can then use
737C<incr_skip> to skip the errornous part). This is the most common way of
738using the method.
739
740And finally, in list context, it will try to extract as many objects
741from the stream as it can find and return them, or the empty list
742otherwise. For this to work, there must be no separators between the JSON
743objects or arrays, instead they must be concatenated back-to-back. If
744an error occurs, an exception will be raised as in the scalar context
745case. Note that in this case, any previously-parsed JSON texts will be
746lost.
747
748=item $lvalue_string = $json->incr_text
749
750This method returns the currently stored JSON fragment as an lvalue, that
751is, you can manipulate it. This I<only> works when a preceding call to
752C<incr_parse> in I<scalar context> successfully returned an object. Under
753all other circumstances you must not call this function (I mean it.
754although in simple tests it might actually work, it I<will> fail under
755real world conditions). As a special exception, you can also call this
756method before having parsed anything.
757
758This function is useful in two cases: a) finding the trailing text after a
759JSON object or b) parsing multiple JSON objects separated by non-JSON text
760(such as commas).
761
762=item $json->incr_skip
763
764This will reset the state of the incremental parser and will remove the
765parsed text from the input buffer. This is useful after C<incr_parse>
766died, in which case the input buffer and incremental parser state is left
767unchanged, to skip the text parsed so far and to reset the parse state.
768
769=back
770
771=head2 LIMITATIONS
772
773All options that affect decoding are supported, except
774C<allow_nonref>. The reason for this is that it cannot be made to
775work sensibly: JSON objects and arrays are self-delimited, i.e. you can concatenate
776them back to back and still decode them perfectly. This does not hold true
777for JSON numbers, however.
778
779For example, is the string C<1> a single JSON number, or is it simply the
780start of C<12>? Or is C<12> a single JSON number, or the concatenation
781of C<1> and C<2>? In neither case you can tell, and this is why JSON::XS
782takes the conservative route and disallows this case.
783
784=head2 EXAMPLES
785
786Some examples will make all this clearer. First, a simple example that
787works similarly to C<decode_prefix>: We want to decode the JSON object at
788the start of a string and identify the portion after the JSON object:
789
790 my $text = "[1,2,3] hello";
791
792 my $json = new JSON::XS;
793
794 my $obj = $json->incr_parse ($text)
795 or die "expected JSON object or array at beginning of string";
796
797 my $tail = $json->incr_text;
798 # $tail now contains " hello"
799
800Easy, isn't it?
801
802Now for a more complicated example: Imagine a hypothetical protocol where
803you read some requests from a TCP stream, and each request is a JSON
804array, without any separation between them (in fact, it is often useful to
805use newlines as "separators", as these get interpreted as whitespace at
806the start of the JSON text, which makes it possible to test said protocol
807with C<telnet>...).
808
809Here is how you'd do it (it is trivial to write this in an event-based
810manner):
811
812 my $json = new JSON::XS;
813
814 # read some data from the socket
815 while (sysread $socket, my $buf, 4096) {
816
817 # split and decode as many requests as possible
818 for my $request ($json->incr_parse ($buf)) {
819 # act on the $request
820 }
821 }
822
823Another complicated example: Assume you have a string with JSON objects
824or arrays, all separated by (optional) comma characters (e.g. C<[1],[2],
825[3]>). To parse them, we have to skip the commas between the JSON texts,
826and here is where the lvalue-ness of C<incr_text> comes in useful:
827
828 my $text = "[1],[2], [3]";
829 my $json = new JSON::XS;
830
831 # void context, so no parsing done
832 $json->incr_parse ($text);
833
834 # now extract as many objects as possible. note the
835 # use of scalar context so incr_text can be called.
836 while (my $obj = $json->incr_parse) {
837 # do something with $obj
838
839 # now skip the optional comma
840 $json->incr_text =~ s/^ \s* , //x;
841 }
842
843Now lets go for a very complex example: Assume that you have a gigantic
844JSON array-of-objects, many gigabytes in size, and you want to parse it,
845but you cannot load it into memory fully (this has actually happened in
846the real world :).
847
848Well, you lost, you have to implement your own JSON parser. But JSON::XS
849can still help you: You implement a (very simple) array parser and let
850JSON decode the array elements, which are all full JSON objects on their
851own (this wouldn't work if the array elements could be JSON numbers, for
852example):
853
854 my $json = new JSON::XS;
855
856 # open the monster
857 open my $fh, "<bigfile.json"
858 or die "bigfile: $!";
859
860 # first parse the initial "["
861 for (;;) {
862 sysread $fh, my $buf, 65536
863 or die "read error: $!";
864 $json->incr_parse ($buf); # void context, so no parsing
865
866 # Exit the loop once we found and removed(!) the initial "[".
867 # In essence, we are (ab-)using the $json object as a simple scalar
868 # we append data to.
869 last if $json->incr_text =~ s/^ \s* \[ //x;
870 }
871
872 # now we have the skipped the initial "[", so continue
873 # parsing all the elements.
874 for (;;) {
875 # in this loop we read data until we got a single JSON object
876 for (;;) {
877 if (my $obj = $json->incr_parse) {
878 # do something with $obj
879 last;
880 }
881
882 # add more data
883 sysread $fh, my $buf, 65536
884 or die "read error: $!";
885 $json->incr_parse ($buf); # void context, so no parsing
886 }
887
888 # in this loop we read data until we either found and parsed the
889 # separating "," between elements, or the final "]"
890 for (;;) {
891 # first skip whitespace
892 $json->incr_text =~ s/^\s*//;
893
894 # if we find "]", we are done
895 if ($json->incr_text =~ s/^\]//) {
896 print "finished.\n";
897 exit;
898 }
899
900 # if we find ",", we can continue with the next element
901 if ($json->incr_text =~ s/^,//) {
902 last;
903 }
904
905 # if we find anything else, we have a parse error!
906 if (length $json->incr_text) {
907 die "parse error near ", $json->incr_text;
908 }
909
910 # else add more data
911 sysread $fh, my $buf, 65536
912 or die "read error: $!";
913 $json->incr_parse ($buf); # void context, so no parsing
914 }
915
916This is a complex example, but most of the complexity comes from the fact
917that we are trying to be correct (bear with me if I am wrong, I never ran
918the above example :).
919
920
921
650=head1 MAPPING 922=head1 MAPPING
651 923
652This section describes how JSON::XS maps Perl values to JSON values and 924This section describes how JSON::XS maps Perl values to JSON values and
653vice versa. These mappings are designed to "do the right thing" in most 925vice versa. These mappings are designed to "do the right thing" in most
654circumstances automatically, preserving round-tripping characteristics 926circumstances automatically, preserving round-tripping characteristics
682 954
683A JSON number becomes either an integer, numeric (floating point) or 955A JSON number becomes either an integer, numeric (floating point) or
684string scalar in perl, depending on its range and any fractional parts. On 956string scalar in perl, depending on its range and any fractional parts. On
685the Perl level, there is no difference between those as Perl handles all 957the Perl level, there is no difference between those as Perl handles all
686the conversion details, but an integer may take slightly less memory and 958the conversion details, but an integer may take slightly less memory and
687might represent more values exactly than (floating point) numbers. 959might represent more values exactly than floating point numbers.
688 960
689If the number consists of digits only, JSON::XS will try to represent 961If the number consists of digits only, JSON::XS will try to represent
690it as an integer value. If that fails, it will try to represent it as 962it as an integer value. If that fails, it will try to represent it as
691a numeric (floating point) value if that is possible without loss of 963a numeric (floating point) value if that is possible without loss of
692precision. Otherwise it will preserve the number as a string value. 964precision. Otherwise it will preserve the number as a string value (in
965which case you lose roundtripping ability, as the JSON number will be
966re-encoded toa JSON string).
693 967
694Numbers containing a fractional or exponential part will always be 968Numbers containing a fractional or exponential part will always be
695represented as numeric (floating point) values, possibly at a loss of 969represented as numeric (floating point) values, possibly at a loss of
696precision. 970precision (in which case you might lose perfect roundtripping ability, but
697 971the JSON number will still be re-encoded as a JSON number).
698This might create round-tripping problems as numbers might become strings,
699but as Perl is typeless there is no other way to do it.
700 972
701=item true, false 973=item true, false
702 974
703These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>, 975These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>,
704respectively. They are overloaded to act almost exactly like the numbers 976respectively. They are overloaded to act almost exactly like the numbers
741Other unblessed references are generally not allowed and will cause an 1013Other unblessed references are generally not allowed and will cause an
742exception to be thrown, except for references to the integers C<0> and 1014exception to be thrown, except for references to the integers C<0> and
743C<1>, which get turned into C<false> and C<true> atoms in JSON. You can 1015C<1>, which get turned into C<false> and C<true> atoms in JSON. You can
744also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability. 1016also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability.
745 1017
746 to_json [\0,JSON::XS::true] # yields [false,true] 1018 encode_json [\0,JSON::XS::true] # yields [false,true]
747 1019
748=item JSON::XS::true, JSON::XS::false 1020=item JSON::XS::true, JSON::XS::false
749 1021
750These special values become JSON true and JSON false values, 1022These special values become JSON true and JSON false values,
751respectively. You can also use C<\1> and C<\0> directly if you want. 1023respectively. You can also use C<\1> and C<\0> directly if you want.
752 1024
753=item blessed objects 1025=item blessed objects
754 1026
755Blessed objects are not allowed. JSON::XS currently tries to encode their 1027Blessed objects are not directly representable in JSON. See the
756underlying representation (hash- or arrayref), but this behaviour might 1028C<allow_blessed> and C<convert_blessed> methods on various options on
757change in future versions. 1029how to deal with this: basically, you can choose between throwing an
1030exception, encoding the reference as if it weren't blessed, or provide
1031your own serialiser method.
758 1032
759=item simple scalars 1033=item simple scalars
760 1034
761Simple Perl scalars (any scalar that is not a reference) are the most 1035Simple Perl scalars (any scalar that is not a reference) are the most
762difficult objects to encode: JSON::XS will encode undefined scalars as 1036difficult objects to encode: JSON::XS will encode undefined scalars as
763JSON null value, scalars that have last been used in a string context 1037JSON C<null> values, scalars that have last been used in a string context
764before encoding as JSON strings and anything else as number value: 1038before encoding as JSON strings, and anything else as number value:
765 1039
766 # dump as number 1040 # dump as number
767 to_json [2] # yields [2] 1041 encode_json [2] # yields [2]
768 to_json [-3.0e17] # yields [-3e+17] 1042 encode_json [-3.0e17] # yields [-3e+17]
769 my $value = 5; to_json [$value] # yields [5] 1043 my $value = 5; encode_json [$value] # yields [5]
770 1044
771 # used as string, so dump as string 1045 # used as string, so dump as string
772 print $value; 1046 print $value;
773 to_json [$value] # yields ["5"] 1047 encode_json [$value] # yields ["5"]
774 1048
775 # undef becomes null 1049 # undef becomes null
776 to_json [undef] # yields [null] 1050 encode_json [undef] # yields [null]
777 1051
778You can force the type to be a JSON string by stringifying it: 1052You can force the type to be a JSON string by stringifying it:
779 1053
780 my $x = 3.1; # some variable containing a number 1054 my $x = 3.1; # some variable containing a number
781 "$x"; # stringified 1055 "$x"; # stringified
787 my $x = "3"; # some variable containing a string 1061 my $x = "3"; # some variable containing a string
788 $x += 0; # numify it, ensuring it will be dumped as a number 1062 $x += 0; # numify it, ensuring it will be dumped as a number
789 $x *= 1; # same thing, the choice is yours. 1063 $x *= 1; # same thing, the choice is yours.
790 1064
791You can not currently force the type in other, less obscure, ways. Tell me 1065You can not currently force the type in other, less obscure, ways. Tell me
792if you need this capability. 1066if you need this capability (but don't forget to explain why it's needed
1067:).
793 1068
794=back 1069=back
795 1070
796 1071
797=head1 COMPARISON 1072=head1 ENCODING/CODESET FLAG NOTES
798 1073
799As already mentioned, this module was created because none of the existing 1074The interested reader might have seen a number of flags that signify
800JSON modules could be made to work correctly. First I will describe the 1075encodings or codesets - C<utf8>, C<latin1> and C<ascii>. There seems to be
801problems (or pleasures) I encountered with various existing JSON modules, 1076some confusion on what these do, so here is a short comparison:
802followed by some benchmark values. JSON::XS was designed not to suffer 1077
803from any of these problems or limitations. 1078C<utf8> controls whether the JSON text created by C<encode> (and expected
1079by C<decode>) is UTF-8 encoded or not, while C<latin1> and C<ascii> only
1080control whether C<encode> escapes character values outside their respective
1081codeset range. Neither of these flags conflict with each other, although
1082some combinations make less sense than others.
1083
1084Care has been taken to make all flags symmetrical with respect to
1085C<encode> and C<decode>, that is, texts encoded with any combination of
1086these flag values will be correctly decoded when the same flags are used
1087- in general, if you use different flag settings while encoding vs. when
1088decoding you likely have a bug somewhere.
1089
1090Below comes a verbose discussion of these flags. Note that a "codeset" is
1091simply an abstract set of character-codepoint pairs, while an encoding
1092takes those codepoint numbers and I<encodes> them, in our case into
1093octets. Unicode is (among other things) a codeset, UTF-8 is an encoding,
1094and ISO-8859-1 (= latin 1) and ASCII are both codesets I<and> encodings at
1095the same time, which can be confusing.
804 1096
805=over 4 1097=over 4
806 1098
807=item JSON 1.07 1099=item C<utf8> flag disabled
808 1100
809Slow (but very portable, as it is written in pure Perl). 1101When C<utf8> is disabled (the default), then C<encode>/C<decode> generate
1102and expect Unicode strings, that is, characters with high ordinal Unicode
1103values (> 255) will be encoded as such characters, and likewise such
1104characters are decoded as-is, no canges to them will be done, except
1105"(re-)interpreting" them as Unicode codepoints or Unicode characters,
1106respectively (to Perl, these are the same thing in strings unless you do
1107funny/weird/dumb stuff).
810 1108
811Undocumented/buggy Unicode handling (how JSON handles Unicode values is 1109This is useful when you want to do the encoding yourself (e.g. when you
812undocumented. One can get far by feeding it Unicode strings and doing 1110want to have UTF-16 encoded JSON texts) or when some other layer does
813en-/decoding oneself, but Unicode escapes are not working properly). 1111the encoding for you (for example, when printing to a terminal using a
1112filehandle that transparently encodes to UTF-8 you certainly do NOT want
1113to UTF-8 encode your data first and have Perl encode it another time).
814 1114
815No round-tripping (strings get clobbered if they look like numbers, e.g. 1115=item C<utf8> flag enabled
816the string C<2.0> will encode to C<2.0> instead of C<"2.0">, and that will
817decode into the number 2.
818 1116
819=item JSON::PC 0.01 1117If the C<utf8>-flag is enabled, C<encode>/C<decode> will encode all
1118characters using the corresponding UTF-8 multi-byte sequence, and will
1119expect your input strings to be encoded as UTF-8, that is, no "character"
1120of the input string must have any value > 255, as UTF-8 does not allow
1121that.
820 1122
821Very fast. 1123The C<utf8> flag therefore switches between two modes: disabled means you
1124will get a Unicode string in Perl, enabled means you get an UTF-8 encoded
1125octet/binary string in Perl.
822 1126
823Undocumented/buggy Unicode handling. 1127=item C<latin1> or C<ascii> flags enabled
824 1128
825No round-tripping. 1129With C<latin1> (or C<ascii>) enabled, C<encode> will escape characters
1130with ordinal values > 255 (> 127 with C<ascii>) and encode the remaining
1131characters as specified by the C<utf8> flag.
826 1132
827Has problems handling many Perl values (e.g. regex results and other magic 1133If C<utf8> is disabled, then the result is also correctly encoded in those
828values will make it croak). 1134character sets (as both are proper subsets of Unicode, meaning that a
1135Unicode string with all character values < 256 is the same thing as a
1136ISO-8859-1 string, and a Unicode string with all character values < 128 is
1137the same thing as an ASCII string in Perl).
829 1138
830Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}> 1139If C<utf8> is enabled, you still get a correct UTF-8-encoded string,
831which is not a valid JSON text. 1140regardless of these flags, just some more characters will be escaped using
1141C<\uXXXX> then before.
832 1142
833Unmaintained (maintainer unresponsive for many months, bugs are not 1143Note that ISO-8859-1-I<encoded> strings are not compatible with UTF-8
834getting fixed). 1144encoding, while ASCII-encoded strings are. That is because the ISO-8859-1
1145encoding is NOT a subset of UTF-8 (despite the ISO-8859-1 I<codeset> being
1146a subset of Unicode), while ASCII is.
835 1147
836=item JSON::Syck 0.21 1148Surprisingly, C<decode> will ignore these flags and so treat all input
1149values as governed by the C<utf8> flag. If it is disabled, this allows you
1150to decode ISO-8859-1- and ASCII-encoded strings, as both strict subsets of
1151Unicode. If it is enabled, you can correctly decode UTF-8 encoded strings.
837 1152
838Very buggy (often crashes). 1153So neither C<latin1> nor C<ascii> are incompatible with the C<utf8> flag -
1154they only govern when the JSON output engine escapes a character or not.
839 1155
840Very inflexible (no human-readable format supported, format pretty much 1156The main use for C<latin1> is to relatively efficiently store binary data
841undocumented. I need at least a format for easy reading by humans and a 1157as JSON, at the expense of breaking compatibility with most JSON decoders.
842single-line compact format for use in a protocol, and preferably a way to
843generate ASCII-only JSON texts).
844 1158
845Completely broken (and confusingly documented) Unicode handling (Unicode 1159The main use for C<ascii> is to force the output to not contain characters
846escapes are not working properly, you need to set ImplicitUnicode to 1160with values > 127, which means you can interpret the resulting string
847I<different> values on en- and decoding to get symmetric behaviour). 1161as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about any character set and
848 11628-bit-encoding, and still get the same data structure back. This is useful
849No round-tripping (simple cases work, but this depends on whether the scalar 1163when your channel for JSON transfer is not 8-bit clean or the encoding
850value was used in a numeric context or not). 1164might be mangled in between (e.g. in mail), and works because ASCII is a
851 1165proper subset of most 8-bit and multibyte encodings in use in the world.
852Dumping hashes may skip hash values depending on iterator state.
853
854Unmaintained (maintainer unresponsive for many months, bugs are not
855getting fixed).
856
857Does not check input for validity (i.e. will accept non-JSON input and
858return "something" instead of raising an exception. This is a security
859issue: imagine two banks transferring money between each other using
860JSON. One bank might parse a given non-JSON request and deduct money,
861while the other might reject the transaction with a syntax error. While a
862good protocol will at least recover, that is extra unnecessary work and
863the transaction will still not succeed).
864
865=item JSON::DWIW 0.04
866
867Very fast. Very natural. Very nice.
868
869Undocumented Unicode handling (but the best of the pack. Unicode escapes
870still don't get parsed properly).
871
872Very inflexible.
873
874No round-tripping.
875
876Does not generate valid JSON texts (key strings are often unquoted, empty keys
877result in nothing being output)
878
879Does not check input for validity.
880 1166
881=back 1167=back
882 1168
883 1169
884=head2 JSON and YAML 1170=head2 JSON and YAML
885 1171
886You often hear that JSON is a subset (or a close subset) of YAML. This is, 1172You often hear that JSON is a subset of YAML. This is, however, a mass
887however, a mass hysteria and very far from the truth. In general, there is 1173hysteria(*) and very far from the truth (as of the time of this writing),
888no way to configure JSON::XS to output a data structure as valid YAML. 1174so let me state it clearly: I<in general, there is no way to configure
1175JSON::XS to output a data structure as valid YAML> that works in all
1176cases.
889 1177
890If you really must use JSON::XS to generate YAML, you should use this 1178If you really must use JSON::XS to generate YAML, you should use this
891algorithm (subject to change in future versions): 1179algorithm (subject to change in future versions):
892 1180
893 my $to_yaml = JSON::XS->new->utf8->space_after (1); 1181 my $to_yaml = JSON::XS->new->utf8->space_after (1);
894 my $yaml = $to_yaml->encode ($ref) . "\n"; 1182 my $yaml = $to_yaml->encode ($ref) . "\n";
895 1183
896This will usually generate JSON texts that also parse as valid 1184This will I<usually> generate JSON texts that also parse as valid
897YAML. Please note that YAML has hardcoded limits on (simple) object key 1185YAML. Please note that YAML has hardcoded limits on (simple) object key
898lengths that JSON doesn't have, so you should make sure that your hash 1186lengths that JSON doesn't have and also has different and incompatible
1187unicode handling, so you should make sure that your hash keys are
899keys are noticeably shorter than the 1024 characters YAML allows. 1188noticeably shorter than the 1024 "stream characters" YAML allows and that
1189you do not have characters with codepoint values outside the Unicode BMP
1190(basic multilingual page). YAML also does not allow C<\/> sequences in
1191strings (which JSON::XS does not I<currently> generate, but other JSON
1192generators might).
900 1193
901There might be other incompatibilities that I am not aware of. In general 1194There might be other incompatibilities that I am not aware of (or the YAML
1195specification has been changed yet again - it does so quite often). In
902you should not try to generate YAML with a JSON generator or vice versa, 1196general you should not try to generate YAML with a JSON generator or vice
903or try to parse JSON with a YAML parser or vice versa: chances are high 1197versa, or try to parse JSON with a YAML parser or vice versa: chances are
904that you will run into severe interoperability problems. 1198high that you will run into severe interoperability problems when you
1199least expect it.
1200
1201=over 4
1202
1203=item (*)
1204
1205I have been pressured multiple times by Brian Ingerson (one of the
1206authors of the YAML specification) to remove this paragraph, despite him
1207acknowledging that the actual incompatibilities exist. As I was personally
1208bitten by this "JSON is YAML" lie, I refused and said I will continue to
1209educate people about these issues, so others do not run into the same
1210problem again and again. After this, Brian called me a (quote)I<complete
1211and worthless idiot>(unquote).
1212
1213In my opinion, instead of pressuring and insulting people who actually
1214clarify issues with YAML and the wrong statements of some of its
1215proponents, I would kindly suggest reading the JSON spec (which is not
1216that difficult or long) and finally make YAML compatible to it, and
1217educating users about the changes, instead of spreading lies about the
1218real compatibility for many I<years> and trying to silence people who
1219point out that it isn't true.
1220
1221=back
905 1222
906 1223
907=head2 SPEED 1224=head2 SPEED
908 1225
909It seems that JSON::XS is surprisingly fast, as shown in the following 1226It seems that JSON::XS is surprisingly fast, as shown in the following
910tables. They have been generated with the help of the C<eg/bench> program 1227tables. They have been generated with the help of the C<eg/bench> program
911in the JSON::XS distribution, to make it easy to compare on your own 1228in the JSON::XS distribution, to make it easy to compare on your own
912system. 1229system.
913 1230
914First comes a comparison between various modules using a very short 1231First comes a comparison between various modules using
915single-line JSON string: 1232a very short single-line JSON string (also available at
1233L<http://dist.schmorp.de/misc/json/short.json>).
916 1234
917 {"method": "handleMessage", "params": ["user1", "we were just talking"], \ 1235 {"method": "handleMessage", "params": ["user1", "we were just talking"], \
918 "id": null, "array":[1,11,234,-5,1e5,1e7, true, false]} 1236 "id": null, "array":[1,11,234,-5,1e5,1e7, true, false]}
919 1237
920It shows the number of encodes/decodes per second (JSON::XS uses 1238It shows the number of encodes/decodes per second (JSON::XS uses
939about three times faster on decoding, and over forty times faster 1257about three times faster on decoding, and over forty times faster
940than JSON, even with pretty-printing and key sorting. It also compares 1258than JSON, even with pretty-printing and key sorting. It also compares
941favourably to Storable for small amounts of data. 1259favourably to Storable for small amounts of data.
942 1260
943Using a longer test string (roughly 18KB, generated from Yahoo! Locals 1261Using a longer test string (roughly 18KB, generated from Yahoo! Locals
944search API (http://nanoref.com/yahooapis/mgPdGg): 1262search API (L<http://dist.schmorp.de/misc/json/long.json>).
945 1263
946 module | encode | decode | 1264 module | encode | decode |
947 -----------|------------|------------| 1265 -----------|------------|------------|
948 JSON 1.x | 55.260 | 34.971 | 1266 JSON 1.x | 55.260 | 34.971 |
949 JSON::DWIW | 825.228 | 1082.513 | 1267 JSON::DWIW | 825.228 | 1082.513 |
986 1304
987Third, JSON::XS recurses using the C stack when decoding objects and 1305Third, JSON::XS recurses using the C stack when decoding objects and
988arrays. The C stack is a limited resource: for instance, on my amd64 1306arrays. The C stack is a limited resource: for instance, on my amd64
989machine with 8MB of stack size I can decode around 180k nested arrays but 1307machine with 8MB of stack size I can decode around 180k nested arrays but
990only 14k nested JSON objects (due to perl itself recursing deeply on croak 1308only 14k nested JSON objects (due to perl itself recursing deeply on croak
991to free the temporary). If that is exceeded, the program crashes. to be 1309to free the temporary). If that is exceeded, the program crashes. To be
992conservative, the default nesting limit is set to 512. If your process 1310conservative, the default nesting limit is set to 512. If your process
993has a smaller stack, you should adjust this setting accordingly with the 1311has a smaller stack, you should adjust this setting accordingly with the
994C<max_depth> method. 1312C<max_depth> method.
995 1313
996And last but least, something else could bomb you that I forgot to think 1314Something else could bomb you, too, that I forgot to think of. In that
997of. In that case, you get to keep the pieces. I am always open for hints, 1315case, you get to keep the pieces. I am always open for hints, though...
998though... 1316
1317Also keep in mind that JSON::XS might leak contents of your Perl data
1318structures in its error messages, so when you serialise sensitive
1319information you might want to make sure that exceptions thrown by JSON::XS
1320will not end up in front of untrusted eyes.
999 1321
1000If you are using JSON::XS to return packets to consumption 1322If you are using JSON::XS to return packets to consumption
1001by JavaScript scripts in a browser you should have a look at 1323by JavaScript scripts in a browser you should have a look at
1002L<http://jpsykes.com/47/practical-csrf-and-json-security> to see whether 1324L<http://jpsykes.com/47/practical-csrf-and-json-security> to see whether
1003you are vulnerable to some common attack vectors (which really are browser 1325you are vulnerable to some common attack vectors (which really are browser
1004design bugs, but it is still you who will have to deal with it, as major 1326design bugs, but it is still you who will have to deal with it, as major
1005browser developers care only for features, not about doing security 1327browser developers care only for features, not about getting security
1006right). 1328right).
1007 1329
1008 1330
1009=head1 THREADS 1331=head1 THREADS
1010 1332
1011This module is I<not> guaranteed to be thread safe and there are no 1333This module is I<not> guaranteed to be thread safe and there are no
1012plans to change this until Perl gets thread support (as opposed to the 1334plans to change this until Perl gets thread support (as opposed to the
1013horribly slow so-called "threads" which are simply slow and bloated 1335horribly slow so-called "threads" which are simply slow and bloated
1014process simulations - use fork, its I<much> faster, cheaper, better). 1336process simulations - use fork, it's I<much> faster, cheaper, better).
1015 1337
1016(It might actually work, but you have been warned). 1338(It might actually work, but you have been warned).
1017 1339
1018 1340
1019=head1 BUGS 1341=head1 BUGS
1020 1342
1021While the goal of this module is to be correct, that unfortunately does 1343While the goal of this module is to be correct, that unfortunately does
1022not mean its bug-free, only that I think its design is bug-free. It is 1344not mean it's bug-free, only that I think its design is bug-free. It is
1023still relatively early in its development. If you keep reporting bugs they 1345still relatively early in its development. If you keep reporting bugs they
1024will be fixed swiftly, though. 1346will be fixed swiftly, though.
1025 1347
1026Please refrain from using rt.cpan.org or any other bug reporting 1348Please refrain from using rt.cpan.org or any other bug reporting
1027service. I put the contact address into my modules for a reason. 1349service. I put the contact address into my modules for a reason.
1049 "--" => sub { $_[0] = ${$_[0]} - 1 }, 1371 "--" => sub { $_[0] = ${$_[0]} - 1 },
1050 fallback => 1; 1372 fallback => 1;
1051 1373
10521; 13741;
1053 1375
1376=head1 SEE ALSO
1377
1378The F<json_xs> command line utility for quick experiments.
1379
1054=head1 AUTHOR 1380=head1 AUTHOR
1055 1381
1056 Marc Lehmann <schmorp@schmorp.de> 1382 Marc Lehmann <schmorp@schmorp.de>
1057 http://home.schmorp.de/ 1383 http://home.schmorp.de/
1058 1384

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