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Revision 1.77 by root, Tue Dec 4 10:37:42 2007 UTC vs.
Revision 1.104 by root, Thu May 8 15:33:06 2008 UTC

1=head1 NAME 1=head1 NAME
2 2
3JSON::XS - JSON serialising/deserialising, done correctly and fast 3JSON::XS - JSON serialising/deserialising, done correctly and fast
4
5=encoding utf-8
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)
7 9
8=head1 SYNOPSIS 10=head1 SYNOPSIS
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);
58 60
59=over 4 61=over 4
60 62
61=item * correct Unicode handling 63=item * correct Unicode handling
62 64
63This 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
64it does so. 66so, and even documents what "correct" means.
65 67
66=item * round-trip integrity 68=item * round-trip integrity
67 69
68When you serialise a perl data structure using only datatypes supported 70When you serialise a perl data structure using only datatypes supported
69by JSON, the deserialised data structure is identical on the Perl level. 71by 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
71like a number). 73like a number). There minor I<are> exceptions to this, read the MAPPING
74section below to learn about those.
72 75
73=item * strict checking of JSON correctness 76=item * strict checking of JSON correctness
74 77
75There is no guessing, no generating of illegal JSON texts by default, 78There is no guessing, no generating of illegal JSON texts by default,
76and 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
77feature). 80feature).
78 81
79=item * fast 82=item * fast
80 83
81Compared to other JSON modules, this module compares favourably in terms 84Compared to other JSON modules and other serialisers such as Storable,
82of speed, too. 85this module usually compares favourably in terms of speed, too.
83 86
84=item * simple to use 87=item * simple to use
85 88
86This 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
87interface. 90oriented interface interface.
88 91
89=item * reasonably versatile output formats 92=item * reasonably versatile output formats
90 93
91You can choose between the most compact guaranteed single-line format 94You can choose between the most compact guaranteed-single-line format
92possible (nice for simple line-based protocols), a pure-ascii format 95possible (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
94Unicode 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
95stuff). Or you can combine those features in whatever way you like. 98stuff). Or you can combine those features in whatever way you like.
96 99
100 103
101package JSON::XS; 104package JSON::XS;
102 105
103use strict; 106use strict;
104 107
105our $VERSION = '2.0'; 108our $VERSION = '2.2';
106our @ISA = qw(Exporter); 109our @ISA = qw(Exporter);
107 110
108our @EXPORT = qw(to_json from_json); 111our @EXPORT = qw(encode_json decode_json to_json from_json);
112
113sub to_json($) {
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}
109 122
110use Exporter; 123use Exporter;
111use XSLoader; 124use XSLoader;
112 125
113=head1 FUNCTIONAL INTERFACE 126=head1 FUNCTIONAL INTERFACE
115The following convenience methods are provided by this module. They are 128The following convenience methods are provided by this module. They are
116exported by default: 129exported by default:
117 130
118=over 4 131=over 4
119 132
120=item $json_text = to_json $perl_scalar 133=item $json_text = encode_json $perl_scalar
121 134
122Converts 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
123(that is, the string contains octets only). Croaks on error. 136(that is, the string contains octets only). Croaks on error.
124 137
125This function call is functionally identical to: 138This function call is functionally identical to:
126 139
127 $json_text = JSON::XS->new->utf8->encode ($perl_scalar) 140 $json_text = JSON::XS->new->utf8->encode ($perl_scalar)
128 141
129except being faster. 142except being faster.
130 143
131=item $perl_scalar = from_json $json_text 144=item $perl_scalar = decode_json $json_text
132 145
133The opposite of C<to_json>: expects an UTF-8 (binary) string and tries 146The opposite of C<encode_json>: expects an UTF-8 (binary) string and tries
134to parse that as an UTF-8 encoded JSON text, returning the resulting 147to parse that as an UTF-8 encoded JSON text, returning the resulting
135reference. Croaks on error. 148reference. Croaks on error.
136 149
137This function call is functionally identical to: 150This function call is functionally identical to:
138 151
164This enables you to store Unicode characters as single characters in a 177This enables you to store Unicode characters as single characters in a
165Perl string - very natural. 178Perl string - very natural.
166 179
167=item 2. Perl does I<not> associate an encoding with your strings. 180=item 2. Perl does I<not> associate an encoding with your strings.
168 181
169Unless you force it to, e.g. when matching it against a regex, or printing 182... until you force it to, e.g. when matching it against a regex, or
170the scalar to a file, in which case Perl either interprets your string as 183printing the scalar to a file, in which case Perl either interprets your
171locale-encoded text, octets/binary, or as Unicode, depending on various 184string as locale-encoded text, octets/binary, or as Unicode, depending
172settings. In no case is an encoding stored together with your data, it is 185on various settings. In no case is an encoding stored together with your
173I<use> that decides encoding, not any magical metadata. 186data, it is I<use> that decides encoding, not any magical meta data.
174 187
175=item 3. The internal utf-8 flag has no meaning with regards to the 188=item 3. The internal utf-8 flag has no meaning with regards to the
176encoding of your string. 189encoding of your string.
177 190
178Just ignore that flag unless you debug a Perl bug, a module written in 191Just ignore that flag unless you debug a Perl bug, a module written in
232 245
233If C<$enable> is false, then the C<encode> method will not escape Unicode 246If C<$enable> is false, then the C<encode> method will not escape Unicode
234characters unless required by the JSON syntax or other flags. This results 247characters unless required by the JSON syntax or other flags. This results
235in a faster and more compact format. 248in a faster and more compact format.
236 249
250See also the section I<ENCODING/CODESET FLAG NOTES> later in this
251document.
252
237The main use for this flag is to produce JSON texts that can be 253The main use for this flag is to produce JSON texts that can be
238transmitted over a 7-bit channel, as the encoded JSON texts will not 254transmitted over a 7-bit channel, as the encoded JSON texts will not
239contain any 8 bit characters. 255contain any 8 bit characters.
240 256
241 JSON::XS->new->ascii (1)->encode ([chr 0x10401]) 257 JSON::XS->new->ascii (1)->encode ([chr 0x10401])
252will not be affected in any way by this flag, as C<decode> by default 268will not be affected in any way by this flag, as C<decode> by default
253expects Unicode, which is a strict superset of latin1. 269expects Unicode, which is a strict superset of latin1.
254 270
255If C<$enable> is false, then the C<encode> method will not escape Unicode 271If C<$enable> is false, then the C<encode> method will not escape Unicode
256characters unless required by the JSON syntax or other flags. 272characters unless required by the JSON syntax or other flags.
273
274See also the section I<ENCODING/CODESET FLAG NOTES> later in this
275document.
257 276
258The main use for this flag is efficiently encoding binary data as JSON 277The main use for this flag is efficiently encoding binary data as JSON
259text, as most octets will not be escaped, resulting in a smaller encoded 278text, as most octets will not be escaped, resulting in a smaller encoded
260size. The disadvantage is that the resulting JSON text is encoded 279size. The disadvantage is that the resulting JSON text is encoded
261in latin1 (and must correctly be treated as such when storing and 280in latin1 (and must correctly be treated as such when storing and
280 299
281If C<$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
282string 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
283Unicode 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
284to be done yourself, e.g. using the Encode module. 303to be done yourself, e.g. using the Encode module.
304
305See also the section I<ENCODING/CODESET FLAG NOTES> later in this
306document.
285 307
286Example, output UTF-16BE-encoded JSON: 308Example, output UTF-16BE-encoded JSON:
287 309
288 use Encode; 310 use Encode;
289 $jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object); 311 $jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
441resulting in an invalid JSON text: 463resulting in an invalid JSON text:
442 464
443 JSON::XS->new->allow_nonref->encode ("Hello, World!") 465 JSON::XS->new->allow_nonref->encode ("Hello, World!")
444 => "Hello, World!" 466 => "Hello, World!"
445 467
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
446=item $json = $json->allow_blessed ([$enable]) 484=item $json = $json->allow_blessed ([$enable])
447 485
448=item $enabled = $json->get_allow_blessed 486=item $enabled = $json->get_allow_blessed
449 487
450If C<$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
471The 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>
472returns other blessed objects, those will be handled in the same 510returns other blessed objects, those will be handled in the same
473way. 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
474(== 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
475methods 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
476usually 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>
477function. 515function or method.
478 516
479This 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
480future, global hooks might get installed that influence C<decode> and are 518future, global hooks might get installed that influence C<decode> and are
481enabled by this setting. 519enabled by this setting.
482 520
590=item $json = $json->max_depth ([$maximum_nesting_depth]) 628=item $json = $json->max_depth ([$maximum_nesting_depth])
591 629
592=item $max_depth = $json->get_max_depth 630=item $max_depth = $json->get_max_depth
593 631
594Sets the maximum nesting level (default C<512>) accepted while encoding 632Sets the maximum nesting level (default C<512>) accepted while encoding
595or decoding. If the JSON text or Perl data structure has an equal or 633or decoding. If a higher nesting level is detected in JSON text or a Perl
596higher nesting level then this limit, then the encoder and decoder will 634data structure, then the encoder and decoder will stop and croak at that
597stop and croak at that point. 635point.
598 636
599Nesting level is defined by number of hash- or arrayrefs that the encoder 637Nesting level is defined by number of hash- or arrayrefs that the encoder
600needs to traverse to reach a given point or the number of C<{> or C<[> 638needs to traverse to reach a given point or the number of C<{> or C<[>
601characters without their matching closing parenthesis crossed to reach a 639characters without their matching closing parenthesis crossed to reach a
602given character in a string. 640given character in a string.
603 641
604Setting the maximum depth to one disallows any nesting, so that ensures 642Setting the maximum depth to one disallows any nesting, so that ensures
605that the object is only a single hash/object or array. 643that the object is only a single hash/object or array.
606 644
607The argument to C<max_depth> will be rounded up to the next highest power
608of two. If no argument is given, the highest possible setting will be 645If no argument is given, the highest possible setting will be used, which
609used, which is rarely useful. 646is rarely useful.
647
648Note that nesting is implemented by recursion in C. The default value has
649been chosen to be as large as typical operating systems allow without
650crashing.
610 651
611See SECURITY CONSIDERATIONS, below, for more info on why this is useful. 652See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
612 653
613=item $json = $json->max_size ([$maximum_string_size]) 654=item $json = $json->max_size ([$maximum_string_size])
614 655
615=item $max_size = $json->get_max_size 656=item $max_size = $json->get_max_size
616 657
617Set the maximum length a JSON text may have (in bytes) where decoding is 658Set the maximum length a JSON text may have (in bytes) where decoding is
618being attempted. The default is C<0>, meaning no limit. When C<decode> 659being attempted. The default is C<0>, meaning no limit. When C<decode>
619is called on a string longer then this number of characters it will not 660is called on a string that is longer then this many bytes, it will not
620attempt to decode the string but throw an exception. This setting has no 661attempt to decode the string but throw an exception. This setting has no
621effect on C<encode> (yet). 662effect on C<encode> (yet).
622 663
623The argument to C<max_size> will be rounded up to the next B<highest> 664If no argument is given, the limit check will be deactivated (same as when
624power of two (so may be more than requested). If no argument is given, the 665C<0> is specified).
625limit check will be deactivated (same as when C<0> is specified).
626 666
627See SECURITY CONSIDERATIONS, below, for more info on why this is useful. 667See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
628 668
629=item $json_text = $json->encode ($perl_scalar) 669=item $json_text = $json->encode ($perl_scalar)
630 670
659 => ([], 3) 699 => ([], 3)
660 700
661=back 701=back
662 702
663 703
704=head1 INCREMENTAL PARSING
705
706[This section and the API it details is still EXPERIMENTAL]
707
708In some cases, there is the need for incremental parsing of JSON
709texts. While this module always has to keep both JSON text and resulting
710Perl data structure in memory at one time, it does allow you to parse a
711JSON stream incrementally. It does so by accumulating text until it has
712a full JSON object, which it then can decode. This process is similar to
713using C<decode_prefix> to see if a full JSON object is available, but is
714much more efficient (JSON::XS will only attempt to parse the JSON text
715once it is sure it has enough text to get a decisive result, using a very
716simple but truly incremental parser).
717
718The following two methods deal with this.
719
720=over 4
721
722=item [void, scalar or list context] = $json->incr_parse ([$string])
723
724This is the central parsing function. It can both append new text and
725extract objects from the stream accumulated so far (both of these
726functions are optional).
727
728If C<$string> is given, then this string is appended to the already
729existing JSON fragment stored in the C<$json> object.
730
731After that, if the function is called in void context, it will simply
732return without doing anything further. This can be used to add more text
733in as many chunks as you want.
734
735If the method is called in scalar context, then it will try to extract
736exactly I<one> JSON object. If that is successful, it will return this
737object, otherwise it will return C<undef>. If there is a parse error,
738this method will croak just as C<decode> would do (one can then use
739C<incr_skip> to skip the errornous part). This is the most common way of
740using the method.
741
742And finally, in list context, it will try to extract as many objects
743from the stream as it can find and return them, or the empty list
744otherwise. For this to work, there must be no separators between the JSON
745objects or arrays, instead they must be concatenated back-to-back. If
746an error occurs, an exception will be raised as in the scalar context
747case. Note that in this case, any previously-parsed JSON texts will be
748lost.
749
750=item $lvalue_string = $json->incr_text
751
752This method returns the currently stored JSON fragment as an lvalue, that
753is, you can manipulate it. This I<only> works when a preceding call to
754C<incr_parse> in I<scalar context> successfully returned an object. Under
755all other circumstances you must not call this function (I mean it.
756although in simple tests it might actually work, it I<will> fail under
757real world conditions). As a special exception, you can also call this
758method before having parsed anything.
759
760This function is useful in two cases: a) finding the trailing text after a
761JSON object or b) parsing multiple JSON objects separated by non-JSON text
762(such as commas).
763
764=item $json->incr_skip
765
766This will reset the state of the incremental parser and will remove the
767parsed text from the input buffer. This is useful after C<incr_parse>
768died, in which case the input buffer and incremental parser state is left
769unchanged, to skip the text parsed so far and to reset the parse state.
770
771=back
772
773=head2 LIMITATIONS
774
775All options that affect decoding are supported, except
776C<allow_nonref>. The reason for this is that it cannot be made to
777work sensibly: JSON objects and arrays are self-delimited, i.e. you can concatenate
778them back to back and still decode them perfectly. This does not hold true
779for JSON numbers, however.
780
781For example, is the string C<1> a single JSON number, or is it simply the
782start of C<12>? Or is C<12> a single JSON number, or the concatenation
783of C<1> and C<2>? In neither case you can tell, and this is why JSON::XS
784takes the conservative route and disallows this case.
785
786=head2 EXAMPLES
787
788Some examples will make all this clearer. First, a simple example that
789works similarly to C<decode_prefix>: We want to decode the JSON object at
790the start of a string and identify the portion after the JSON object:
791
792 my $text = "[1,2,3] hello";
793
794 my $json = new JSON::XS;
795
796 my $obj = $json->incr_parse ($text)
797 or die "expected JSON object or array at beginning of string";
798
799 my $tail = $json->incr_text;
800 # $tail now contains " hello"
801
802Easy, isn't it?
803
804Now for a more complicated example: Imagine a hypothetical protocol where
805you read some requests from a TCP stream, and each request is a JSON
806array, without any separation between them (in fact, it is often useful to
807use newlines as "separators", as these get interpreted as whitespace at
808the start of the JSON text, which makes it possible to test said protocol
809with C<telnet>...).
810
811Here is how you'd do it (it is trivial to write this in an event-based
812manner):
813
814 my $json = new JSON::XS;
815
816 # read some data from the socket
817 while (sysread $socket, my $buf, 4096) {
818
819 # split and decode as many requests as possible
820 for my $request ($json->incr_parse ($buf)) {
821 # act on the $request
822 }
823 }
824
825Another complicated example: Assume you have a string with JSON objects
826or arrays, all separated by (optional) comma characters (e.g. C<[1],[2],
827[3]>). To parse them, we have to skip the commas between the JSON texts,
828and here is where the lvalue-ness of C<incr_text> comes in useful:
829
830 my $text = "[1],[2], [3]";
831 my $json = new JSON::XS;
832
833 # void context, so no parsing done
834 $json->incr_parse ($text);
835
836 # now extract as many objects as possible. note the
837 # use of scalar context so incr_text can be called.
838 while (my $obj = $json->incr_parse) {
839 # do something with $obj
840
841 # now skip the optional comma
842 $json->incr_text =~ s/^ \s* , //x;
843 }
844
845Now lets go for a very complex example: Assume that you have a gigantic
846JSON array-of-objects, many gigabytes in size, and you want to parse it,
847but you cannot load it into memory fully (this has actually happened in
848the real world :).
849
850Well, you lost, you have to implement your own JSON parser. But JSON::XS
851can still help you: You implement a (very simple) array parser and let
852JSON decode the array elements, which are all full JSON objects on their
853own (this wouldn't work if the array elements could be JSON numbers, for
854example):
855
856 my $json = new JSON::XS;
857
858 # open the monster
859 open my $fh, "<bigfile.json"
860 or die "bigfile: $!";
861
862 # first parse the initial "["
863 for (;;) {
864 sysread $fh, my $buf, 65536
865 or die "read error: $!";
866 $json->incr_parse ($buf); # void context, so no parsing
867
868 # Exit the loop once we found and removed(!) the initial "[".
869 # In essence, we are (ab-)using the $json object as a simple scalar
870 # we append data to.
871 last if $json->incr_text =~ s/^ \s* \[ //x;
872 }
873
874 # now we have the skipped the initial "[", so continue
875 # parsing all the elements.
876 for (;;) {
877 # in this loop we read data until we got a single JSON object
878 for (;;) {
879 if (my $obj = $json->incr_parse) {
880 # do something with $obj
881 last;
882 }
883
884 # add more data
885 sysread $fh, my $buf, 65536
886 or die "read error: $!";
887 $json->incr_parse ($buf); # void context, so no parsing
888 }
889
890 # in this loop we read data until we either found and parsed the
891 # separating "," between elements, or the final "]"
892 for (;;) {
893 # first skip whitespace
894 $json->incr_text =~ s/^\s*//;
895
896 # if we find "]", we are done
897 if ($json->incr_text =~ s/^\]//) {
898 print "finished.\n";
899 exit;
900 }
901
902 # if we find ",", we can continue with the next element
903 if ($json->incr_text =~ s/^,//) {
904 last;
905 }
906
907 # if we find anything else, we have a parse error!
908 if (length $json->incr_text) {
909 die "parse error near ", $json->incr_text;
910 }
911
912 # else add more data
913 sysread $fh, my $buf, 65536
914 or die "read error: $!";
915 $json->incr_parse ($buf); # void context, so no parsing
916 }
917
918This is a complex example, but most of the complexity comes from the fact
919that we are trying to be correct (bear with me if I am wrong, I never ran
920the above example :).
921
922
923
664=head1 MAPPING 924=head1 MAPPING
665 925
666This section describes how JSON::XS maps Perl values to JSON values and 926This section describes how JSON::XS maps Perl values to JSON values and
667vice versa. These mappings are designed to "do the right thing" in most 927vice versa. These mappings are designed to "do the right thing" in most
668circumstances automatically, preserving round-tripping characteristics 928circumstances automatically, preserving round-tripping characteristics
696 956
697A JSON number becomes either an integer, numeric (floating point) or 957A JSON number becomes either an integer, numeric (floating point) or
698string scalar in perl, depending on its range and any fractional parts. On 958string scalar in perl, depending on its range and any fractional parts. On
699the Perl level, there is no difference between those as Perl handles all 959the Perl level, there is no difference between those as Perl handles all
700the conversion details, but an integer may take slightly less memory and 960the conversion details, but an integer may take slightly less memory and
701might represent more values exactly than (floating point) numbers. 961might represent more values exactly than floating point numbers.
702 962
703If the number consists of digits only, JSON::XS will try to represent 963If the number consists of digits only, JSON::XS will try to represent
704it as an integer value. If that fails, it will try to represent it as 964it as an integer value. If that fails, it will try to represent it as
705a numeric (floating point) value if that is possible without loss of 965a numeric (floating point) value if that is possible without loss of
706precision. Otherwise it will preserve the number as a string value. 966precision. Otherwise it will preserve the number as a string value (in
967which case you lose roundtripping ability, as the JSON number will be
968re-encoded toa JSON string).
707 969
708Numbers containing a fractional or exponential part will always be 970Numbers containing a fractional or exponential part will always be
709represented as numeric (floating point) values, possibly at a loss of 971represented as numeric (floating point) values, possibly at a loss of
710precision. 972precision (in which case you might lose perfect roundtripping ability, but
711 973the JSON number will still be re-encoded as a JSON number).
712This might create round-tripping problems as numbers might become strings,
713but as Perl is typeless there is no other way to do it.
714 974
715=item true, false 975=item true, false
716 976
717These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>, 977These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>,
718respectively. They are overloaded to act almost exactly like the numbers 978respectively. They are overloaded to act almost exactly like the numbers
755Other unblessed references are generally not allowed and will cause an 1015Other unblessed references are generally not allowed and will cause an
756exception to be thrown, except for references to the integers C<0> and 1016exception to be thrown, except for references to the integers C<0> and
757C<1>, which get turned into C<false> and C<true> atoms in JSON. You can 1017C<1>, which get turned into C<false> and C<true> atoms in JSON. You can
758also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability. 1018also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability.
759 1019
760 to_json [\0,JSON::XS::true] # yields [false,true] 1020 encode_json [\0, JSON::XS::true] # yields [false,true]
761 1021
762=item JSON::XS::true, JSON::XS::false 1022=item JSON::XS::true, JSON::XS::false
763 1023
764These special values become JSON true and JSON false values, 1024These special values become JSON true and JSON false values,
765respectively. You can also use C<\1> and C<\0> directly if you want. 1025respectively. You can also use C<\1> and C<\0> directly if you want.
766 1026
767=item blessed objects 1027=item blessed objects
768 1028
769Blessed objects are not allowed. JSON::XS currently tries to encode their 1029Blessed objects are not directly representable in JSON. See the
770underlying representation (hash- or arrayref), but this behaviour might 1030C<allow_blessed> and C<convert_blessed> methods on various options on
771change in future versions. 1031how to deal with this: basically, you can choose between throwing an
1032exception, encoding the reference as if it weren't blessed, or provide
1033your own serialiser method.
772 1034
773=item simple scalars 1035=item simple scalars
774 1036
775Simple Perl scalars (any scalar that is not a reference) are the most 1037Simple Perl scalars (any scalar that is not a reference) are the most
776difficult objects to encode: JSON::XS will encode undefined scalars as 1038difficult objects to encode: JSON::XS will encode undefined scalars as
777JSON null value, scalars that have last been used in a string context 1039JSON C<null> values, scalars that have last been used in a string context
778before encoding as JSON strings and anything else as number value: 1040before encoding as JSON strings, and anything else as number value:
779 1041
780 # dump as number 1042 # dump as number
781 to_json [2] # yields [2] 1043 encode_json [2] # yields [2]
782 to_json [-3.0e17] # yields [-3e+17] 1044 encode_json [-3.0e17] # yields [-3e+17]
783 my $value = 5; to_json [$value] # yields [5] 1045 my $value = 5; encode_json [$value] # yields [5]
784 1046
785 # used as string, so dump as string 1047 # used as string, so dump as string
786 print $value; 1048 print $value;
787 to_json [$value] # yields ["5"] 1049 encode_json [$value] # yields ["5"]
788 1050
789 # undef becomes null 1051 # undef becomes null
790 to_json [undef] # yields [null] 1052 encode_json [undef] # yields [null]
791 1053
792You can force the type to be a JSON string by stringifying it: 1054You can force the type to be a JSON string by stringifying it:
793 1055
794 my $x = 3.1; # some variable containing a number 1056 my $x = 3.1; # some variable containing a number
795 "$x"; # stringified 1057 "$x"; # stringified
801 my $x = "3"; # some variable containing a string 1063 my $x = "3"; # some variable containing a string
802 $x += 0; # numify it, ensuring it will be dumped as a number 1064 $x += 0; # numify it, ensuring it will be dumped as a number
803 $x *= 1; # same thing, the choice is yours. 1065 $x *= 1; # same thing, the choice is yours.
804 1066
805You can not currently force the type in other, less obscure, ways. Tell me 1067You can not currently force the type in other, less obscure, ways. Tell me
806if you need this capability. 1068if you need this capability (but don't forget to explain why it's needed
1069:).
807 1070
808=back 1071=back
809 1072
810 1073
811=head1 COMPARISON 1074=head1 ENCODING/CODESET FLAG NOTES
812 1075
813As already mentioned, this module was created because none of the existing 1076The interested reader might have seen a number of flags that signify
814JSON modules could be made to work correctly. First I will describe the 1077encodings or codesets - C<utf8>, C<latin1> and C<ascii>. There seems to be
815problems (or pleasures) I encountered with various existing JSON modules, 1078some confusion on what these do, so here is a short comparison:
816followed by some benchmark values. JSON::XS was designed not to suffer 1079
817from any of these problems or limitations. 1080C<utf8> controls whether the JSON text created by C<encode> (and expected
1081by C<decode>) is UTF-8 encoded or not, while C<latin1> and C<ascii> only
1082control whether C<encode> escapes character values outside their respective
1083codeset range. Neither of these flags conflict with each other, although
1084some combinations make less sense than others.
1085
1086Care has been taken to make all flags symmetrical with respect to
1087C<encode> and C<decode>, that is, texts encoded with any combination of
1088these flag values will be correctly decoded when the same flags are used
1089- in general, if you use different flag settings while encoding vs. when
1090decoding you likely have a bug somewhere.
1091
1092Below comes a verbose discussion of these flags. Note that a "codeset" is
1093simply an abstract set of character-codepoint pairs, while an encoding
1094takes those codepoint numbers and I<encodes> them, in our case into
1095octets. Unicode is (among other things) a codeset, UTF-8 is an encoding,
1096and ISO-8859-1 (= latin 1) and ASCII are both codesets I<and> encodings at
1097the same time, which can be confusing.
818 1098
819=over 4 1099=over 4
820 1100
821=item JSON 1.07 1101=item C<utf8> flag disabled
822 1102
823Slow (but very portable, as it is written in pure Perl). 1103When C<utf8> is disabled (the default), then C<encode>/C<decode> generate
1104and expect Unicode strings, that is, characters with high ordinal Unicode
1105values (> 255) will be encoded as such characters, and likewise such
1106characters are decoded as-is, no canges to them will be done, except
1107"(re-)interpreting" them as Unicode codepoints or Unicode characters,
1108respectively (to Perl, these are the same thing in strings unless you do
1109funny/weird/dumb stuff).
824 1110
825Undocumented/buggy Unicode handling (how JSON handles Unicode values is 1111This is useful when you want to do the encoding yourself (e.g. when you
826undocumented. One can get far by feeding it Unicode strings and doing 1112want to have UTF-16 encoded JSON texts) or when some other layer does
827en-/decoding oneself, but Unicode escapes are not working properly). 1113the encoding for you (for example, when printing to a terminal using a
1114filehandle that transparently encodes to UTF-8 you certainly do NOT want
1115to UTF-8 encode your data first and have Perl encode it another time).
828 1116
829No round-tripping (strings get clobbered if they look like numbers, e.g. 1117=item C<utf8> flag enabled
830the string C<2.0> will encode to C<2.0> instead of C<"2.0">, and that will
831decode into the number 2.
832 1118
833=item JSON::PC 0.01 1119If the C<utf8>-flag is enabled, C<encode>/C<decode> will encode all
1120characters using the corresponding UTF-8 multi-byte sequence, and will
1121expect your input strings to be encoded as UTF-8, that is, no "character"
1122of the input string must have any value > 255, as UTF-8 does not allow
1123that.
834 1124
835Very fast. 1125The C<utf8> flag therefore switches between two modes: disabled means you
1126will get a Unicode string in Perl, enabled means you get an UTF-8 encoded
1127octet/binary string in Perl.
836 1128
837Undocumented/buggy Unicode handling. 1129=item C<latin1> or C<ascii> flags enabled
838 1130
839No round-tripping. 1131With C<latin1> (or C<ascii>) enabled, C<encode> will escape characters
1132with ordinal values > 255 (> 127 with C<ascii>) and encode the remaining
1133characters as specified by the C<utf8> flag.
840 1134
841Has problems handling many Perl values (e.g. regex results and other magic 1135If C<utf8> is disabled, then the result is also correctly encoded in those
842values will make it croak). 1136character sets (as both are proper subsets of Unicode, meaning that a
1137Unicode string with all character values < 256 is the same thing as a
1138ISO-8859-1 string, and a Unicode string with all character values < 128 is
1139the same thing as an ASCII string in Perl).
843 1140
844Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}> 1141If C<utf8> is enabled, you still get a correct UTF-8-encoded string,
845which is not a valid JSON text. 1142regardless of these flags, just some more characters will be escaped using
1143C<\uXXXX> then before.
846 1144
847Unmaintained (maintainer unresponsive for many months, bugs are not 1145Note that ISO-8859-1-I<encoded> strings are not compatible with UTF-8
848getting fixed). 1146encoding, while ASCII-encoded strings are. That is because the ISO-8859-1
1147encoding is NOT a subset of UTF-8 (despite the ISO-8859-1 I<codeset> being
1148a subset of Unicode), while ASCII is.
849 1149
850=item JSON::Syck 0.21 1150Surprisingly, C<decode> will ignore these flags and so treat all input
1151values as governed by the C<utf8> flag. If it is disabled, this allows you
1152to decode ISO-8859-1- and ASCII-encoded strings, as both strict subsets of
1153Unicode. If it is enabled, you can correctly decode UTF-8 encoded strings.
851 1154
852Very buggy (often crashes). 1155So neither C<latin1> nor C<ascii> are incompatible with the C<utf8> flag -
1156they only govern when the JSON output engine escapes a character or not.
853 1157
854Very inflexible (no human-readable format supported, format pretty much 1158The main use for C<latin1> is to relatively efficiently store binary data
855undocumented. I need at least a format for easy reading by humans and a 1159as JSON, at the expense of breaking compatibility with most JSON decoders.
856single-line compact format for use in a protocol, and preferably a way to
857generate ASCII-only JSON texts).
858 1160
859Completely broken (and confusingly documented) Unicode handling (Unicode 1161The main use for C<ascii> is to force the output to not contain characters
860escapes are not working properly, you need to set ImplicitUnicode to 1162with values > 127, which means you can interpret the resulting string
861I<different> values on en- and decoding to get symmetric behaviour). 1163as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about any character set and
862 11648-bit-encoding, and still get the same data structure back. This is useful
863No round-tripping (simple cases work, but this depends on whether the scalar 1165when your channel for JSON transfer is not 8-bit clean or the encoding
864value was used in a numeric context or not). 1166might be mangled in between (e.g. in mail), and works because ASCII is a
865 1167proper subset of most 8-bit and multibyte encodings in use in the world.
866Dumping hashes may skip hash values depending on iterator state.
867
868Unmaintained (maintainer unresponsive for many months, bugs are not
869getting fixed).
870
871Does not check input for validity (i.e. will accept non-JSON input and
872return "something" instead of raising an exception. This is a security
873issue: imagine two banks transferring money between each other using
874JSON. One bank might parse a given non-JSON request and deduct money,
875while the other might reject the transaction with a syntax error. While a
876good protocol will at least recover, that is extra unnecessary work and
877the transaction will still not succeed).
878
879=item JSON::DWIW 0.04
880
881Very fast. Very natural. Very nice.
882
883Undocumented Unicode handling (but the best of the pack. Unicode escapes
884still don't get parsed properly).
885
886Very inflexible.
887
888No round-tripping.
889
890Does not generate valid JSON texts (key strings are often unquoted, empty keys
891result in nothing being output)
892
893Does not check input for validity.
894 1168
895=back 1169=back
896 1170
897 1171
898=head2 JSON and YAML 1172=head2 JSON and YAML
899 1173
900You often hear that JSON is a subset (or a close subset) of YAML. This is, 1174You often hear that JSON is a subset of YAML. This is, however, a mass
901however, a mass hysteria and very far from the truth. In general, there is 1175hysteria(*) and very far from the truth (as of the time of this writing),
902no way to configure JSON::XS to output a data structure as valid YAML. 1176so let me state it clearly: I<in general, there is no way to configure
1177JSON::XS to output a data structure as valid YAML> that works in all
1178cases.
903 1179
904If you really must use JSON::XS to generate YAML, you should use this 1180If you really must use JSON::XS to generate YAML, you should use this
905algorithm (subject to change in future versions): 1181algorithm (subject to change in future versions):
906 1182
907 my $to_yaml = JSON::XS->new->utf8->space_after (1); 1183 my $to_yaml = JSON::XS->new->utf8->space_after (1);
908 my $yaml = $to_yaml->encode ($ref) . "\n"; 1184 my $yaml = $to_yaml->encode ($ref) . "\n";
909 1185
910This will usually generate JSON texts that also parse as valid 1186This will I<usually> generate JSON texts that also parse as valid
911YAML. Please note that YAML has hardcoded limits on (simple) object key 1187YAML. Please note that YAML has hardcoded limits on (simple) object key
912lengths that JSON doesn't have, so you should make sure that your hash 1188lengths that JSON doesn't have and also has different and incompatible
1189unicode handling, so you should make sure that your hash keys are
913keys are noticeably shorter than the 1024 characters YAML allows. 1190noticeably shorter than the 1024 "stream characters" YAML allows and that
1191you do not have characters with codepoint values outside the Unicode BMP
1192(basic multilingual page). YAML also does not allow C<\/> sequences in
1193strings (which JSON::XS does not I<currently> generate, but other JSON
1194generators might).
914 1195
915There might be other incompatibilities that I am not aware of. In general 1196There might be other incompatibilities that I am not aware of (or the YAML
1197specification has been changed yet again - it does so quite often). In
916you should not try to generate YAML with a JSON generator or vice versa, 1198general you should not try to generate YAML with a JSON generator or vice
917or try to parse JSON with a YAML parser or vice versa: chances are high 1199versa, or try to parse JSON with a YAML parser or vice versa: chances are
918that you will run into severe interoperability problems. 1200high that you will run into severe interoperability problems when you
1201least expect it.
1202
1203=over 4
1204
1205=item (*)
1206
1207I have been pressured multiple times by Brian Ingerson (one of the
1208authors of the YAML specification) to remove this paragraph, despite him
1209acknowledging that the actual incompatibilities exist. As I was personally
1210bitten by this "JSON is YAML" lie, I refused and said I will continue to
1211educate people about these issues, so others do not run into the same
1212problem again and again. After this, Brian called me a (quote)I<complete
1213and worthless idiot>(unquote).
1214
1215In my opinion, instead of pressuring and insulting people who actually
1216clarify issues with YAML and the wrong statements of some of its
1217proponents, I would kindly suggest reading the JSON spec (which is not
1218that difficult or long) and finally make YAML compatible to it, and
1219educating users about the changes, instead of spreading lies about the
1220real compatibility for many I<years> and trying to silence people who
1221point out that it isn't true.
1222
1223=back
919 1224
920 1225
921=head2 SPEED 1226=head2 SPEED
922 1227
923It seems that JSON::XS is surprisingly fast, as shown in the following 1228It seems that JSON::XS is surprisingly fast, as shown in the following
924tables. They have been generated with the help of the C<eg/bench> program 1229tables. They have been generated with the help of the C<eg/bench> program
925in the JSON::XS distribution, to make it easy to compare on your own 1230in the JSON::XS distribution, to make it easy to compare on your own
926system. 1231system.
927 1232
928First comes a comparison between various modules using a very short 1233First comes a comparison between various modules using
929single-line JSON string: 1234a very short single-line JSON string (also available at
1235L<http://dist.schmorp.de/misc/json/short.json>).
930 1236
931 {"method": "handleMessage", "params": ["user1", "we were just talking"], \ 1237 {"method": "handleMessage", "params": ["user1",
932 "id": null, "array":[1,11,234,-5,1e5,1e7, true, false]} 1238 "we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7,
1239 true, false]}
933 1240
934It shows the number of encodes/decodes per second (JSON::XS uses 1241It shows the number of encodes/decodes per second (JSON::XS uses
935the functional interface, while JSON::XS/2 uses the OO interface 1242the functional interface, while JSON::XS/2 uses the OO interface
936with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables 1243with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables
937shrink). Higher is better: 1244shrink). Higher is better:
953about three times faster on decoding, and over forty times faster 1260about three times faster on decoding, and over forty times faster
954than JSON, even with pretty-printing and key sorting. It also compares 1261than JSON, even with pretty-printing and key sorting. It also compares
955favourably to Storable for small amounts of data. 1262favourably to Storable for small amounts of data.
956 1263
957Using a longer test string (roughly 18KB, generated from Yahoo! Locals 1264Using a longer test string (roughly 18KB, generated from Yahoo! Locals
958search API (http://nanoref.com/yahooapis/mgPdGg): 1265search API (L<http://dist.schmorp.de/misc/json/long.json>).
959 1266
960 module | encode | decode | 1267 module | encode | decode |
961 -----------|------------|------------| 1268 -----------|------------|------------|
962 JSON 1.x | 55.260 | 34.971 | 1269 JSON 1.x | 55.260 | 34.971 |
963 JSON::DWIW | 825.228 | 1082.513 | 1270 JSON::DWIW | 825.228 | 1082.513 |
1000 1307
1001Third, JSON::XS recurses using the C stack when decoding objects and 1308Third, JSON::XS recurses using the C stack when decoding objects and
1002arrays. The C stack is a limited resource: for instance, on my amd64 1309arrays. The C stack is a limited resource: for instance, on my amd64
1003machine with 8MB of stack size I can decode around 180k nested arrays but 1310machine with 8MB of stack size I can decode around 180k nested arrays but
1004only 14k nested JSON objects (due to perl itself recursing deeply on croak 1311only 14k nested JSON objects (due to perl itself recursing deeply on croak
1005to free the temporary). If that is exceeded, the program crashes. to be 1312to free the temporary). If that is exceeded, the program crashes. To be
1006conservative, the default nesting limit is set to 512. If your process 1313conservative, the default nesting limit is set to 512. If your process
1007has a smaller stack, you should adjust this setting accordingly with the 1314has a smaller stack, you should adjust this setting accordingly with the
1008C<max_depth> method. 1315C<max_depth> method.
1009 1316
1010And last but least, something else could bomb you that I forgot to think 1317Something else could bomb you, too, that I forgot to think of. In that
1011of. In that case, you get to keep the pieces. I am always open for hints, 1318case, you get to keep the pieces. I am always open for hints, though...
1012though... 1319
1320Also keep in mind that JSON::XS might leak contents of your Perl data
1321structures in its error messages, so when you serialise sensitive
1322information you might want to make sure that exceptions thrown by JSON::XS
1323will not end up in front of untrusted eyes.
1013 1324
1014If you are using JSON::XS to return packets to consumption 1325If you are using JSON::XS to return packets to consumption
1015by JavaScript scripts in a browser you should have a look at 1326by JavaScript scripts in a browser you should have a look at
1016L<http://jpsykes.com/47/practical-csrf-and-json-security> to see whether 1327L<http://jpsykes.com/47/practical-csrf-and-json-security> to see whether
1017you are vulnerable to some common attack vectors (which really are browser 1328you are vulnerable to some common attack vectors (which really are browser
1018design bugs, but it is still you who will have to deal with it, as major 1329design bugs, but it is still you who will have to deal with it, as major
1019browser developers care only for features, not about doing security 1330browser developers care only for features, not about getting security
1020right). 1331right).
1021 1332
1022 1333
1023=head1 THREADS 1334=head1 THREADS
1024 1335
1025This module is I<not> guaranteed to be thread safe and there are no 1336This module is I<not> guaranteed to be thread safe and there are no
1026plans to change this until Perl gets thread support (as opposed to the 1337plans to change this until Perl gets thread support (as opposed to the
1027horribly slow so-called "threads" which are simply slow and bloated 1338horribly slow so-called "threads" which are simply slow and bloated
1028process simulations - use fork, its I<much> faster, cheaper, better). 1339process simulations - use fork, it's I<much> faster, cheaper, better).
1029 1340
1030(It might actually work, but you have been warned). 1341(It might actually work, but you have been warned).
1031 1342
1032 1343
1033=head1 BUGS 1344=head1 BUGS
1034 1345
1035While the goal of this module is to be correct, that unfortunately does 1346While the goal of this module is to be correct, that unfortunately does
1036not mean its bug-free, only that I think its design is bug-free. It is 1347not mean it's bug-free, only that I think its design is bug-free. If you
1037still relatively early in its development. If you keep reporting bugs they 1348keep reporting bugs they will be fixed swiftly, though.
1038will be fixed swiftly, though.
1039 1349
1040Please refrain from using rt.cpan.org or any other bug reporting 1350Please refrain from using rt.cpan.org or any other bug reporting
1041service. I put the contact address into my modules for a reason. 1351service. I put the contact address into my modules for a reason.
1042 1352
1043=cut 1353=cut
1063 "--" => sub { $_[0] = ${$_[0]} - 1 }, 1373 "--" => sub { $_[0] = ${$_[0]} - 1 },
1064 fallback => 1; 1374 fallback => 1;
1065 1375
10661; 13761;
1067 1377
1378=head1 SEE ALSO
1379
1380The F<json_xs> command line utility for quick experiments.
1381
1068=head1 AUTHOR 1382=head1 AUTHOR
1069 1383
1070 Marc Lehmann <schmorp@schmorp.de> 1384 Marc Lehmann <schmorp@schmorp.de>
1071 http://home.schmorp.de/ 1385 http://home.schmorp.de/
1072 1386

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