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1=head1 NAME
2
3JSON::XS - JSON serialising/deserialising, done correctly and fast
4
1=encoding utf-8 5=encoding utf-8
2
3=head1 NAME
4
5JSON::XS - JSON serialising/deserialising, done correctly and fast
6 6
7JSON::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
8 (http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html) 8 (http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html)
9 9
10=head1 SYNOPSIS 10=head1 SYNOPSIS
37primary 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
38I<fast>. To reach the latter goal it was written in C. 38I<fast>. To reach the latter goal it was written in C.
39 39
40Beginning with version 2.0 of the JSON module, when both JSON and 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 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 42overridden) with no overhead due to emulation (by inheriting constructor
43and methods). If JSON::XS is not available, it will fall back to the 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 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 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. 46require a C compiler when that is a problem.
47 47
49to 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
50modules, 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
51their maintainers are unresponsive, gone missing, or not listening to bug 51their maintainers are unresponsive, gone missing, or not listening to bug
52reports for other reasons. 52reports for other reasons.
53 53
54See COMPARISON, below, for a comparison to some other JSON modules.
55
56See MAPPING, below, on how JSON::XS maps perl values to JSON values and 54See MAPPING, below, on how JSON::XS maps perl values to JSON values and
57vice versa. 55vice versa.
58 56
59=head2 FEATURES 57=head2 FEATURES
60 58
65This module knows how to handle Unicode, documents how and when it does 63This module knows how to handle Unicode, documents how and when it does
66so, and even documents what "correct" means. 64so, and even documents what "correct" means.
67 65
68=item * round-trip integrity 66=item * round-trip integrity
69 67
70When you serialise a perl data structure using only datatypes supported 68When you serialise a perl data structure using only data types supported
71by JSON, the deserialised data structure is identical on the Perl level. 69by JSON, the deserialised data structure is identical on the Perl level.
72(e.g. the string "2.0" doesn't suddenly become "2" just because it looks 70(e.g. the string "2.0" doesn't suddenly become "2" just because it looks
73like a number). There minor I<are> exceptions to this, read the MAPPING 71like a number). There minor I<are> exceptions to this, read the MAPPING
74section below to learn about those. 72section below to learn about those.
75 73
84Compared to other JSON modules and other serialisers such as Storable, 82Compared to other JSON modules and other serialisers such as Storable,
85this module usually compares favourably in terms of speed, too. 83this module usually compares favourably in terms of speed, too.
86 84
87=item * simple to use 85=item * simple to use
88 86
89This module has both a simple functional interface as well as an objetc 87This module has both a simple functional interface as well as an object
90oriented interface interface. 88oriented interface interface.
91 89
92=item * reasonably versatile output formats 90=item * reasonably versatile output formats
93 91
94You can choose between the most compact guaranteed-single-line format 92You can choose between the most compact guaranteed-single-line format
95possible (nice for simple line-based protocols), a pure-ascii format 93possible (nice for simple line-based protocols), a pure-ASCII format
96(for when your transport is not 8-bit clean, still supports the whole 94(for when your transport is not 8-bit clean, still supports the whole
97Unicode range), or a pretty-printed format (for when you want to read that 95Unicode range), or a pretty-printed format (for when you want to read that
98stuff). Or you can combine those features in whatever way you like. 96stuff). Or you can combine those features in whatever way you like.
99 97
100=back 98=back
101 99
102=cut 100=cut
103 101
104package JSON::XS; 102package JSON::XS;
105 103
104no warnings;
106use strict; 105use strict;
107 106
108our $VERSION = '2.01'; 107our $VERSION = '2.231';
109our @ISA = qw(Exporter); 108our @ISA = qw(Exporter);
110 109
111our @EXPORT = qw(encode_json decode_json to_json from_json); 110our @EXPORT = qw(encode_json decode_json to_json from_json);
112 111
113sub to_json($) { 112sub to_json($) {
137 136
138This function call is functionally identical to: 137This function call is functionally identical to:
139 138
140 $json_text = JSON::XS->new->utf8->encode ($perl_scalar) 139 $json_text = JSON::XS->new->utf8->encode ($perl_scalar)
141 140
142except being faster. 141Except being faster.
143 142
144=item $perl_scalar = decode_json $json_text 143=item $perl_scalar = decode_json $json_text
145 144
146The opposite of C<encode_json>: expects an UTF-8 (binary) string and tries 145The opposite of C<encode_json>: expects an UTF-8 (binary) string and tries
147to parse that as an UTF-8 encoded JSON text, returning the resulting 146to parse that as an UTF-8 encoded JSON text, returning the resulting
149 148
150This function call is functionally identical to: 149This function call is functionally identical to:
151 150
152 $perl_scalar = JSON::XS->new->utf8->decode ($json_text) 151 $perl_scalar = JSON::XS->new->utf8->decode ($json_text)
153 152
154except being faster. 153Except being faster.
155 154
156=item $is_boolean = JSON::XS::is_bool $scalar 155=item $is_boolean = JSON::XS::is_bool $scalar
157 156
158Returns true if the passed scalar represents either JSON::XS::true or 157Returns true if the passed scalar represents either JSON::XS::true or
159JSON::XS::false, two constants that act like C<1> and C<0>, respectively 158JSON::XS::false, two constants that act like C<1> and C<0>, respectively
197 196
198If you didn't know about that flag, just the better, pretend it doesn't 197If you didn't know about that flag, just the better, pretend it doesn't
199exist. 198exist.
200 199
201=item 4. A "Unicode String" is simply a string where each character can be 200=item 4. A "Unicode String" is simply a string where each character can be
202validly interpreted as a Unicode codepoint. 201validly interpreted as a Unicode code point.
203 202
204If you have UTF-8 encoded data, it is no longer a Unicode string, but a 203If you have UTF-8 encoded data, it is no longer a Unicode string, but a
205Unicode string encoded in UTF-8, giving you a binary string. 204Unicode string encoded in UTF-8, giving you a binary string.
206 205
207=item 5. A string containing "high" (> 255) character values is I<not> a UTF-8 string. 206=item 5. A string containing "high" (> 255) character values is I<not> a UTF-8 string.
245 244
246If C<$enable> is false, then the C<encode> method will not escape Unicode 245If C<$enable> is false, then the C<encode> method will not escape Unicode
247characters unless required by the JSON syntax or other flags. This results 246characters unless required by the JSON syntax or other flags. This results
248in a faster and more compact format. 247in a faster and more compact format.
249 248
249See also the section I<ENCODING/CODESET FLAG NOTES> later in this
250document.
251
250The main use for this flag is to produce JSON texts that can be 252The main use for this flag is to produce JSON texts that can be
251transmitted over a 7-bit channel, as the encoded JSON texts will not 253transmitted over a 7-bit channel, as the encoded JSON texts will not
252contain any 8 bit characters. 254contain any 8 bit characters.
253 255
254 JSON::XS->new->ascii (1)->encode ([chr 0x10401]) 256 JSON::XS->new->ascii (1)->encode ([chr 0x10401])
265will not be affected in any way by this flag, as C<decode> by default 267will not be affected in any way by this flag, as C<decode> by default
266expects Unicode, which is a strict superset of latin1. 268expects Unicode, which is a strict superset of latin1.
267 269
268If C<$enable> is false, then the C<encode> method will not escape Unicode 270If C<$enable> is false, then the C<encode> method will not escape Unicode
269characters unless required by the JSON syntax or other flags. 271characters unless required by the JSON syntax or other flags.
272
273See also the section I<ENCODING/CODESET FLAG NOTES> later in this
274document.
270 275
271The main use for this flag is efficiently encoding binary data as JSON 276The main use for this flag is efficiently encoding binary data as JSON
272text, as most octets will not be escaped, resulting in a smaller encoded 277text, as most octets will not be escaped, resulting in a smaller encoded
273size. The disadvantage is that the resulting JSON text is encoded 278size. The disadvantage is that the resulting JSON text is encoded
274in latin1 (and must correctly be treated as such when storing and 279in latin1 (and must correctly be treated as such when storing and
293 298
294If C<$enable> is false, then the C<encode> method will return the JSON 299If C<$enable> is false, then the C<encode> method will return the JSON
295string as a (non-encoded) Unicode string, while C<decode> expects thus a 300string as a (non-encoded) Unicode string, while C<decode> expects thus a
296Unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs 301Unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs
297to be done yourself, e.g. using the Encode module. 302to be done yourself, e.g. using the Encode module.
303
304See also the section I<ENCODING/CODESET FLAG NOTES> later in this
305document.
298 306
299Example, output UTF-16BE-encoded JSON: 307Example, output UTF-16BE-encoded JSON:
300 308
301 use Encode; 309 use Encode;
302 $jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object); 310 $jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
453Example, encode a Perl scalar as JSON value with enabled C<allow_nonref>, 461Example, encode a Perl scalar as JSON value with enabled C<allow_nonref>,
454resulting in an invalid JSON text: 462resulting in an invalid JSON text:
455 463
456 JSON::XS->new->allow_nonref->encode ("Hello, World!") 464 JSON::XS->new->allow_nonref->encode ("Hello, World!")
457 => "Hello, World!" 465 => "Hello, World!"
466
467=item $json = $json->allow_unknown ([$enable])
468
469=item $enabled = $json->get_allow_unknown
470
471If C<$enable> is true (or missing), then C<encode> will I<not> throw an
472exception when it encounters values it cannot represent in JSON (for
473example, filehandles) but instead will encode a JSON C<null> value. Note
474that blessed objects are not included here and are handled separately by
475c<allow_nonref>.
476
477If C<$enable> is false (the default), then C<encode> will throw an
478exception when it encounters anything it cannot encode as JSON.
479
480This option does not affect C<decode> in any way, and it is recommended to
481leave it off unless you know your communications partner.
458 482
459=item $json = $json->allow_blessed ([$enable]) 483=item $json = $json->allow_blessed ([$enable])
460 484
461=item $enabled = $json->get_allow_blessed 485=item $enabled = $json->get_allow_blessed
462 486
603=item $json = $json->max_depth ([$maximum_nesting_depth]) 627=item $json = $json->max_depth ([$maximum_nesting_depth])
604 628
605=item $max_depth = $json->get_max_depth 629=item $max_depth = $json->get_max_depth
606 630
607Sets the maximum nesting level (default C<512>) accepted while encoding 631Sets the maximum nesting level (default C<512>) accepted while encoding
608or decoding. If the JSON text or Perl data structure has an equal or 632or decoding. If a higher nesting level is detected in JSON text or a Perl
609higher nesting level then this limit, then the encoder and decoder will 633data structure, then the encoder and decoder will stop and croak at that
610stop and croak at that point. 634point.
611 635
612Nesting level is defined by number of hash- or arrayrefs that the encoder 636Nesting level is defined by number of hash- or arrayrefs that the encoder
613needs to traverse to reach a given point or the number of C<{> or C<[> 637needs to traverse to reach a given point or the number of C<{> or C<[>
614characters without their matching closing parenthesis crossed to reach a 638characters without their matching closing parenthesis crossed to reach a
615given character in a string. 639given character in a string.
616 640
617Setting the maximum depth to one disallows any nesting, so that ensures 641Setting the maximum depth to one disallows any nesting, so that ensures
618that the object is only a single hash/object or array. 642that the object is only a single hash/object or array.
619 643
620The argument to C<max_depth> will be rounded up to the next highest power
621of two. If no argument is given, the highest possible setting will be 644If no argument is given, the highest possible setting will be used, which
622used, which is rarely useful. 645is rarely useful.
646
647Note that nesting is implemented by recursion in C. The default value has
648been chosen to be as large as typical operating systems allow without
649crashing.
623 650
624See SECURITY CONSIDERATIONS, below, for more info on why this is useful. 651See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
625 652
626=item $json = $json->max_size ([$maximum_string_size]) 653=item $json = $json->max_size ([$maximum_string_size])
627 654
628=item $max_size = $json->get_max_size 655=item $max_size = $json->get_max_size
629 656
630Set the maximum length a JSON text may have (in bytes) where decoding is 657Set the maximum length a JSON text may have (in bytes) where decoding is
631being attempted. The default is C<0>, meaning no limit. When C<decode> 658being attempted. The default is C<0>, meaning no limit. When C<decode>
632is called on a string longer then this number of characters it will not 659is called on a string that is longer then this many bytes, it will not
633attempt to decode the string but throw an exception. This setting has no 660attempt to decode the string but throw an exception. This setting has no
634effect on C<encode> (yet). 661effect on C<encode> (yet).
635 662
636The argument to C<max_size> will be rounded up to the next B<highest> 663If no argument is given, the limit check will be deactivated (same as when
637power of two (so may be more than requested). If no argument is given, the 664C<0> is specified).
638limit check will be deactivated (same as when C<0> is specified).
639 665
640See SECURITY CONSIDERATIONS, below, for more info on why this is useful. 666See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
641 667
642=item $json_text = $json->encode ($perl_scalar) 668=item $json_text = $json->encode ($perl_scalar)
643 669
670 696
671 JSON::XS->new->decode_prefix ("[1] the tail") 697 JSON::XS->new->decode_prefix ("[1] the tail")
672 => ([], 3) 698 => ([], 3)
673 699
674=back 700=back
701
702
703=head1 INCREMENTAL PARSING
704
705In some cases, there is the need for incremental parsing of JSON
706texts. While this module always has to keep both JSON text and resulting
707Perl data structure in memory at one time, it does allow you to parse a
708JSON stream incrementally. It does so by accumulating text until it has
709a full JSON object, which it then can decode. This process is similar to
710using C<decode_prefix> to see if a full JSON object is available, but
711is much more efficient (and can be implemented with a minimum of method
712calls).
713
714JSON::XS will only attempt to parse the JSON text once it is sure it
715has enough text to get a decisive result, using a very simple but
716truly incremental parser. This means that it sometimes won't stop as
717early as the full parser, for example, it doesn't detect parenthese
718mismatches. The only thing it guarantees is that it starts decoding as
719soon as a syntactically valid JSON text has been seen. This means you need
720to set resource limits (e.g. C<max_size>) to ensure the parser will stop
721parsing in the presence if syntax errors.
722
723The following methods implement this incremental parser.
724
725=over 4
726
727=item [void, scalar or list context] = $json->incr_parse ([$string])
728
729This is the central parsing function. It can both append new text and
730extract objects from the stream accumulated so far (both of these
731functions are optional).
732
733If C<$string> is given, then this string is appended to the already
734existing JSON fragment stored in the C<$json> object.
735
736After that, if the function is called in void context, it will simply
737return without doing anything further. This can be used to add more text
738in as many chunks as you want.
739
740If the method is called in scalar context, then it will try to extract
741exactly I<one> JSON object. If that is successful, it will return this
742object, otherwise it will return C<undef>. If there is a parse error,
743this method will croak just as C<decode> would do (one can then use
744C<incr_skip> to skip the errornous part). This is the most common way of
745using the method.
746
747And finally, in list context, it will try to extract as many objects
748from the stream as it can find and return them, or the empty list
749otherwise. For this to work, there must be no separators between the JSON
750objects or arrays, instead they must be concatenated back-to-back. If
751an error occurs, an exception will be raised as in the scalar context
752case. Note that in this case, any previously-parsed JSON texts will be
753lost.
754
755=item $lvalue_string = $json->incr_text
756
757This method returns the currently stored JSON fragment as an lvalue, that
758is, you can manipulate it. This I<only> works when a preceding call to
759C<incr_parse> in I<scalar context> successfully returned an object. Under
760all other circumstances you must not call this function (I mean it.
761although in simple tests it might actually work, it I<will> fail under
762real world conditions). As a special exception, you can also call this
763method before having parsed anything.
764
765This function is useful in two cases: a) finding the trailing text after a
766JSON object or b) parsing multiple JSON objects separated by non-JSON text
767(such as commas).
768
769=item $json->incr_skip
770
771This will reset the state of the incremental parser and will remove
772the parsed text from the input buffer so far. This is useful after
773C<incr_parse> died, in which case the input buffer and incremental parser
774state is left unchanged, to skip the text parsed so far and to reset the
775parse state.
776
777The difference to C<incr_reset> is that only text until the parse error
778occured is removed.
779
780=item $json->incr_reset
781
782This completely resets the incremental parser, that is, after this call,
783it will be as if the parser had never parsed anything.
784
785This is useful if you want to repeatedly parse JSON objects and want to
786ignore any trailing data, which means you have to reset the parser after
787each successful decode.
788
789=back
790
791=head2 LIMITATIONS
792
793All options that affect decoding are supported, except
794C<allow_nonref>. The reason for this is that it cannot be made to
795work sensibly: JSON objects and arrays are self-delimited, i.e. you can concatenate
796them back to back and still decode them perfectly. This does not hold true
797for JSON numbers, however.
798
799For example, is the string C<1> a single JSON number, or is it simply the
800start of C<12>? Or is C<12> a single JSON number, or the concatenation
801of C<1> and C<2>? In neither case you can tell, and this is why JSON::XS
802takes the conservative route and disallows this case.
803
804=head2 EXAMPLES
805
806Some examples will make all this clearer. First, a simple example that
807works similarly to C<decode_prefix>: We want to decode the JSON object at
808the start of a string and identify the portion after the JSON object:
809
810 my $text = "[1,2,3] hello";
811
812 my $json = new JSON::XS;
813
814 my $obj = $json->incr_parse ($text)
815 or die "expected JSON object or array at beginning of string";
816
817 my $tail = $json->incr_text;
818 # $tail now contains " hello"
819
820Easy, isn't it?
821
822Now for a more complicated example: Imagine a hypothetical protocol where
823you read some requests from a TCP stream, and each request is a JSON
824array, without any separation between them (in fact, it is often useful to
825use newlines as "separators", as these get interpreted as whitespace at
826the start of the JSON text, which makes it possible to test said protocol
827with C<telnet>...).
828
829Here is how you'd do it (it is trivial to write this in an event-based
830manner):
831
832 my $json = new JSON::XS;
833
834 # read some data from the socket
835 while (sysread $socket, my $buf, 4096) {
836
837 # split and decode as many requests as possible
838 for my $request ($json->incr_parse ($buf)) {
839 # act on the $request
840 }
841 }
842
843Another complicated example: Assume you have a string with JSON objects
844or arrays, all separated by (optional) comma characters (e.g. C<[1],[2],
845[3]>). To parse them, we have to skip the commas between the JSON texts,
846and here is where the lvalue-ness of C<incr_text> comes in useful:
847
848 my $text = "[1],[2], [3]";
849 my $json = new JSON::XS;
850
851 # void context, so no parsing done
852 $json->incr_parse ($text);
853
854 # now extract as many objects as possible. note the
855 # use of scalar context so incr_text can be called.
856 while (my $obj = $json->incr_parse) {
857 # do something with $obj
858
859 # now skip the optional comma
860 $json->incr_text =~ s/^ \s* , //x;
861 }
862
863Now lets go for a very complex example: Assume that you have a gigantic
864JSON array-of-objects, many gigabytes in size, and you want to parse it,
865but you cannot load it into memory fully (this has actually happened in
866the real world :).
867
868Well, you lost, you have to implement your own JSON parser. But JSON::XS
869can still help you: You implement a (very simple) array parser and let
870JSON decode the array elements, which are all full JSON objects on their
871own (this wouldn't work if the array elements could be JSON numbers, for
872example):
873
874 my $json = new JSON::XS;
875
876 # open the monster
877 open my $fh, "<bigfile.json"
878 or die "bigfile: $!";
879
880 # first parse the initial "["
881 for (;;) {
882 sysread $fh, my $buf, 65536
883 or die "read error: $!";
884 $json->incr_parse ($buf); # void context, so no parsing
885
886 # Exit the loop once we found and removed(!) the initial "[".
887 # In essence, we are (ab-)using the $json object as a simple scalar
888 # we append data to.
889 last if $json->incr_text =~ s/^ \s* \[ //x;
890 }
891
892 # now we have the skipped the initial "[", so continue
893 # parsing all the elements.
894 for (;;) {
895 # in this loop we read data until we got a single JSON object
896 for (;;) {
897 if (my $obj = $json->incr_parse) {
898 # do something with $obj
899 last;
900 }
901
902 # add more data
903 sysread $fh, my $buf, 65536
904 or die "read error: $!";
905 $json->incr_parse ($buf); # void context, so no parsing
906 }
907
908 # in this loop we read data until we either found and parsed the
909 # separating "," between elements, or the final "]"
910 for (;;) {
911 # first skip whitespace
912 $json->incr_text =~ s/^\s*//;
913
914 # if we find "]", we are done
915 if ($json->incr_text =~ s/^\]//) {
916 print "finished.\n";
917 exit;
918 }
919
920 # if we find ",", we can continue with the next element
921 if ($json->incr_text =~ s/^,//) {
922 last;
923 }
924
925 # if we find anything else, we have a parse error!
926 if (length $json->incr_text) {
927 die "parse error near ", $json->incr_text;
928 }
929
930 # else add more data
931 sysread $fh, my $buf, 65536
932 or die "read error: $!";
933 $json->incr_parse ($buf); # void context, so no parsing
934 }
935
936This is a complex example, but most of the complexity comes from the fact
937that we are trying to be correct (bear with me if I am wrong, I never ran
938the above example :).
939
675 940
676 941
677=head1 MAPPING 942=head1 MAPPING
678 943
679This section describes how JSON::XS maps Perl values to JSON values and 944This section describes how JSON::XS maps Perl values to JSON values and
768Other unblessed references are generally not allowed and will cause an 1033Other unblessed references are generally not allowed and will cause an
769exception to be thrown, except for references to the integers C<0> and 1034exception to be thrown, except for references to the integers C<0> and
770C<1>, which get turned into C<false> and C<true> atoms in JSON. You can 1035C<1>, which get turned into C<false> and C<true> atoms in JSON. You can
771also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability. 1036also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability.
772 1037
773 encode_json [\0,JSON::XS::true] # yields [false,true] 1038 encode_json [\0, JSON::XS::true] # yields [false,true]
774 1039
775=item JSON::XS::true, JSON::XS::false 1040=item JSON::XS::true, JSON::XS::false
776 1041
777These special values become JSON true and JSON false values, 1042These special values become JSON true and JSON false values,
778respectively. You can also use C<\1> and C<\0> directly if you want. 1043respectively. You can also use C<\1> and C<\0> directly if you want.
816 my $x = "3"; # some variable containing a string 1081 my $x = "3"; # some variable containing a string
817 $x += 0; # numify it, ensuring it will be dumped as a number 1082 $x += 0; # numify it, ensuring it will be dumped as a number
818 $x *= 1; # same thing, the choice is yours. 1083 $x *= 1; # same thing, the choice is yours.
819 1084
820You can not currently force the type in other, less obscure, ways. Tell me 1085You can not currently force the type in other, less obscure, ways. Tell me
821if you need this capability (but don't forget to explain why its needed 1086if you need this capability (but don't forget to explain why it's needed
822:). 1087:).
823 1088
824=back 1089=back
825 1090
826 1091
828 1093
829The interested reader might have seen a number of flags that signify 1094The interested reader might have seen a number of flags that signify
830encodings or codesets - C<utf8>, C<latin1> and C<ascii>. There seems to be 1095encodings or codesets - C<utf8>, C<latin1> and C<ascii>. There seems to be
831some confusion on what these do, so here is a short comparison: 1096some confusion on what these do, so here is a short comparison:
832 1097
833C<utf8> controls wether the JSON text created by C<encode> (and expected 1098C<utf8> controls whether the JSON text created by C<encode> (and expected
834by C<decode>) is UTF-8 encoded or not, while C<latin1> and C<ascii> only 1099by C<decode>) is UTF-8 encoded or not, while C<latin1> and C<ascii> only
835control wether C<encode> escapes character values outside their respective 1100control whether C<encode> escapes character values outside their respective
836codeset range. Neither of these flags conflict with each other, although 1101codeset range. Neither of these flags conflict with each other, although
837some combinations make less sense than others. 1102some combinations make less sense than others.
838 1103
839Care has been taken to make all flags symmetrical with respect to 1104Care has been taken to make all flags symmetrical with respect to
840C<encode> and C<decode>, that is, texts encoded with any combination of 1105C<encode> and C<decode>, that is, texts encoded with any combination of
920proper subset of most 8-bit and multibyte encodings in use in the world. 1185proper subset of most 8-bit and multibyte encodings in use in the world.
921 1186
922=back 1187=back
923 1188
924 1189
925=head1 COMPARISON
926
927As already mentioned, this module was created because none of the existing
928JSON modules could be made to work correctly. First I will describe the
929problems (or pleasures) I encountered with various existing JSON modules,
930followed by some benchmark values. JSON::XS was designed not to suffer
931from any of these problems or limitations.
932
933=over 4
934
935=item JSON 2.xx
936
937A marvellous piece of engineering, this module either uses JSON::XS
938directly when available (so will be 100% compatible with it, including
939speed), or it uses JSON::PP, which is basically JSON::XS translated to
940Pure Perl, which should be 100% compatible with JSON::XS, just a bit
941slower.
942
943You cannot really lose by using this module, especially as it tries very
944hard to work even with ancient Perl versions, while JSON::XS does not.
945
946=item JSON 1.07
947
948Slow (but very portable, as it is written in pure Perl).
949
950Undocumented/buggy Unicode handling (how JSON handles Unicode values is
951undocumented. One can get far by feeding it Unicode strings and doing
952en-/decoding oneself, but Unicode escapes are not working properly).
953
954No round-tripping (strings get clobbered if they look like numbers, e.g.
955the string C<2.0> will encode to C<2.0> instead of C<"2.0">, and that will
956decode into the number 2.
957
958=item JSON::PC 0.01
959
960Very fast.
961
962Undocumented/buggy Unicode handling.
963
964No round-tripping.
965
966Has problems handling many Perl values (e.g. regex results and other magic
967values will make it croak).
968
969Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}>
970which is not a valid JSON text.
971
972Unmaintained (maintainer unresponsive for many months, bugs are not
973getting fixed).
974
975=item JSON::Syck 0.21
976
977Very buggy (often crashes).
978
979Very inflexible (no human-readable format supported, format pretty much
980undocumented. I need at least a format for easy reading by humans and a
981single-line compact format for use in a protocol, and preferably a way to
982generate ASCII-only JSON texts).
983
984Completely broken (and confusingly documented) Unicode handling (Unicode
985escapes are not working properly, you need to set ImplicitUnicode to
986I<different> values on en- and decoding to get symmetric behaviour).
987
988No round-tripping (simple cases work, but this depends on whether the scalar
989value was used in a numeric context or not).
990
991Dumping hashes may skip hash values depending on iterator state.
992
993Unmaintained (maintainer unresponsive for many months, bugs are not
994getting fixed).
995
996Does not check input for validity (i.e. will accept non-JSON input and
997return "something" instead of raising an exception. This is a security
998issue: imagine two banks transferring money between each other using
999JSON. One bank might parse a given non-JSON request and deduct money,
1000while the other might reject the transaction with a syntax error. While a
1001good protocol will at least recover, that is extra unnecessary work and
1002the transaction will still not succeed).
1003
1004=item JSON::DWIW 0.04
1005
1006Very fast. Very natural. Very nice.
1007
1008Undocumented Unicode handling (but the best of the pack. Unicode escapes
1009still don't get parsed properly).
1010
1011Very inflexible.
1012
1013No round-tripping.
1014
1015Does not generate valid JSON texts (key strings are often unquoted, empty keys
1016result in nothing being output)
1017
1018Does not check input for validity.
1019
1020=back
1021
1022
1023=head2 JSON and YAML 1190=head2 JSON and YAML
1024 1191
1025You often hear that JSON is a subset of YAML. This is, however, a mass 1192You often hear that JSON is a subset of YAML. This is, however, a mass
1026hysteria(*) and very far from the truth. In general, there is no way to 1193hysteria(*) and very far from the truth (as of the time of this writing),
1194so let me state it clearly: I<in general, there is no way to configure
1027configure JSON::XS to output a data structure as valid YAML that works for 1195JSON::XS to output a data structure as valid YAML> that works in all
1028all cases. 1196cases.
1029 1197
1030If you really must use JSON::XS to generate YAML, you should use this 1198If you really must use JSON::XS to generate YAML, you should use this
1031algorithm (subject to change in future versions): 1199algorithm (subject to change in future versions):
1032 1200
1033 my $to_yaml = JSON::XS->new->utf8->space_after (1); 1201 my $to_yaml = JSON::XS->new->utf8->space_after (1);
1036This will I<usually> generate JSON texts that also parse as valid 1204This will I<usually> generate JSON texts that also parse as valid
1037YAML. Please note that YAML has hardcoded limits on (simple) object key 1205YAML. Please note that YAML has hardcoded limits on (simple) object key
1038lengths that JSON doesn't have and also has different and incompatible 1206lengths that JSON doesn't have and also has different and incompatible
1039unicode handling, so you should make sure that your hash keys are 1207unicode handling, so you should make sure that your hash keys are
1040noticeably shorter than the 1024 "stream characters" YAML allows and that 1208noticeably shorter than the 1024 "stream characters" YAML allows and that
1041you do not have codepoints with values outside the Unicode BMP (basic 1209you do not have characters with codepoint values outside the Unicode BMP
1042multilingual page). YAML also does not allow C<\/> sequences in strings 1210(basic multilingual page). YAML also does not allow C<\/> sequences in
1043(which JSON::XS does not I<currently> generate). 1211strings (which JSON::XS does not I<currently> generate, but other JSON
1212generators might).
1044 1213
1045There might be other incompatibilities that I am not aware of (or the YAML 1214There might be other incompatibilities that I am not aware of (or the YAML
1046specification has been changed yet again - it does so quite often). In 1215specification has been changed yet again - it does so quite often). In
1047general you should not try to generate YAML with a JSON generator or vice 1216general you should not try to generate YAML with a JSON generator or vice
1048versa, or try to parse JSON with a YAML parser or vice versa: chances are 1217versa, or try to parse JSON with a YAML parser or vice versa: chances are
1051 1220
1052=over 4 1221=over 4
1053 1222
1054=item (*) 1223=item (*)
1055 1224
1056This is spread actively by the YAML team, however. For many years now they 1225I have been pressured multiple times by Brian Ingerson (one of the
1057claim YAML were a superset of JSON, even when proven otherwise. 1226authors of the YAML specification) to remove this paragraph, despite him
1227acknowledging that the actual incompatibilities exist. As I was personally
1228bitten by this "JSON is YAML" lie, I refused and said I will continue to
1229educate people about these issues, so others do not run into the same
1230problem again and again. After this, Brian called me a (quote)I<complete
1231and worthless idiot>(unquote).
1058 1232
1059Even the author of this manpage was at some point accused of providing 1233In my opinion, instead of pressuring and insulting people who actually
1060"incorrect" information, despite the evidence presented (claims ranged 1234clarify issues with YAML and the wrong statements of some of its
1061from "your documentation contains inaccurate and negative statements about 1235proponents, I would kindly suggest reading the JSON spec (which is not
1062YAML" (the only negative comment is this footnote, and it didn't exist 1236that difficult or long) and finally make YAML compatible to it, and
1063back then; the question on which claims were inaccurate was never answered 1237educating users about the changes, instead of spreading lies about the
1064etc.) to "the YAML spec is not up-to-date" (the *real* and supposedly 1238real compatibility for many I<years> and trying to silence people who
1065JSON-compatible spec is apparently not currently publicly available) 1239point out that it isn't true.
1066to actual requests to replace this section by *incorrect* information,
1067suppressing information about the real problem).
1068
1069So whenever you are told that YAML was a superset of JSON, first check
1070wether it is really true (it might be when you check it, but it certainly
1071was not true when this was written). I would much prefer if the YAML team
1072would spent their time on actually making JSON compatibility a truth
1073(JSON, after all, has a very small and simple specification) instead of
1074trying to lobby/force people into reporting untruths.
1075 1240
1076=back 1241=back
1077 1242
1078 1243
1079=head2 SPEED 1244=head2 SPEED
1085 1250
1086First comes a comparison between various modules using 1251First comes a comparison between various modules using
1087a very short single-line JSON string (also available at 1252a very short single-line JSON string (also available at
1088L<http://dist.schmorp.de/misc/json/short.json>). 1253L<http://dist.schmorp.de/misc/json/short.json>).
1089 1254
1090 {"method": "handleMessage", "params": ["user1", "we were just talking"], \ 1255 {"method": "handleMessage", "params": ["user1",
1091 "id": null, "array":[1,11,234,-5,1e5,1e7, true, false]} 1256 "we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7,
1257 true, false]}
1092 1258
1093It shows the number of encodes/decodes per second (JSON::XS uses 1259It shows the number of encodes/decodes per second (JSON::XS uses
1094the functional interface, while JSON::XS/2 uses the OO interface 1260the functional interface, while JSON::XS/2 uses the OO interface
1095with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables 1261with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables
1096shrink). Higher is better: 1262shrink). Higher is better:
1186=head1 THREADS 1352=head1 THREADS
1187 1353
1188This module is I<not> guaranteed to be thread safe and there are no 1354This module is I<not> guaranteed to be thread safe and there are no
1189plans to change this until Perl gets thread support (as opposed to the 1355plans to change this until Perl gets thread support (as opposed to the
1190horribly slow so-called "threads" which are simply slow and bloated 1356horribly slow so-called "threads" which are simply slow and bloated
1191process simulations - use fork, its I<much> faster, cheaper, better). 1357process simulations - use fork, it's I<much> faster, cheaper, better).
1192 1358
1193(It might actually work, but you have been warned). 1359(It might actually work, but you have been warned).
1194 1360
1195 1361
1196=head1 BUGS 1362=head1 BUGS
1197 1363
1198While the goal of this module is to be correct, that unfortunately does 1364While the goal of this module is to be correct, that unfortunately does
1199not mean its bug-free, only that I think its design is bug-free. It is 1365not mean it's bug-free, only that I think its design is bug-free. If you
1200still relatively early in its development. If you keep reporting bugs they 1366keep reporting bugs they will be fixed swiftly, though.
1201will be fixed swiftly, though.
1202 1367
1203Please refrain from using rt.cpan.org or any other bug reporting 1368Please refrain from using rt.cpan.org or any other bug reporting
1204service. I put the contact address into my modules for a reason. 1369service. I put the contact address into my modules for a reason.
1205 1370
1206=cut 1371=cut
1226 "--" => sub { $_[0] = ${$_[0]} - 1 }, 1391 "--" => sub { $_[0] = ${$_[0]} - 1 },
1227 fallback => 1; 1392 fallback => 1;
1228 1393
12291; 13941;
1230 1395
1396=head1 SEE ALSO
1397
1398The F<json_xs> command line utility for quick experiments.
1399
1231=head1 AUTHOR 1400=head1 AUTHOR
1232 1401
1233 Marc Lehmann <schmorp@schmorp.de> 1402 Marc Lehmann <schmorp@schmorp.de>
1234 http://home.schmorp.de/ 1403 http://home.schmorp.de/
1235 1404

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