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Revision 1.111 by root, Mon Jul 21 02:45:17 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
35primary 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
36I<fast>. To reach the latter goal it was written in C. 38I<fast>. To reach the latter goal it was written in C.
37 39
38Beginning 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
39JSON::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
40overriden) with no overhead due to emulation (by inheritign constructor 42overridden) with no overhead due to emulation (by inheriting constructor
41and 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
42compatible 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
43gives 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
44require a C compiler when that is a problem. 46require a C compiler when that is a problem.
45 47
47to 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
48modules, 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
49their maintainers are unresponsive, gone missing, or not listening to bug 51their maintainers are unresponsive, gone missing, or not listening to bug
50reports for other reasons. 52reports for other reasons.
51 53
52See COMPARISON, below, for a comparison to some other JSON modules.
53
54See 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
55vice versa. 55vice versa.
56 56
57=head2 FEATURES 57=head2 FEATURES
58 58
59=over 4 59=over 4
60 60
61=item * correct Unicode handling 61=item * correct Unicode handling
62 62
63This module knows how to handle Unicode, and even documents how and when 63This module knows how to handle Unicode, documents how and when it does
64it does so. 64so, and even documents what "correct" means.
65 65
66=item * round-trip integrity 66=item * round-trip integrity
67 67
68When you serialise a perl data structure using only datatypes supported 68When you serialise a perl data structure using only data types supported
69by JSON, the deserialised data structure is identical on the Perl level. 69by 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 70(e.g. the string "2.0" doesn't suddenly become "2" just because it looks
71like a number). 71like a number). There minor I<are> exceptions to this, read the MAPPING
72section below to learn about those.
72 73
73=item * strict checking of JSON correctness 74=item * strict checking of JSON correctness
74 75
75There is no guessing, no generating of illegal JSON texts by default, 76There 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 77and only JSON is accepted as input by default (the latter is a security
77feature). 78feature).
78 79
79=item * fast 80=item * fast
80 81
81Compared to other JSON modules, this module compares favourably in terms 82Compared to other JSON modules and other serialisers such as Storable,
82of speed, too. 83this module usually compares favourably in terms of speed, too.
83 84
84=item * simple to use 85=item * simple to use
85 86
86This module has both a simple functional interface as well as an OO 87This module has both a simple functional interface as well as an object
87interface. 88oriented interface interface.
88 89
89=item * reasonably versatile output formats 90=item * reasonably versatile output formats
90 91
91You can choose between the most compact guaranteed single-line format 92You can choose between the most compact guaranteed-single-line format
92possible (nice for simple line-based protocols), a pure-ascii format 93possible (nice for simple line-based protocols), a pure-ASCII format
93(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
94Unicode 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
95stuff). Or you can combine those features in whatever way you like. 96stuff). Or you can combine those features in whatever way you like.
96 97
97=back 98=back
98 99
99=cut 100=cut
100 101
101package JSON::XS; 102package JSON::XS;
102 103
104no warnings;
103use strict; 105use strict;
104 106
105our $VERSION = '2.01'; 107our $VERSION = '2.2222';
106our @ISA = qw(Exporter); 108our @ISA = qw(Exporter);
107 109
108our @EXPORT = qw(encode_json decode_json to_json from_json); 110our @EXPORT = qw(encode_json decode_json to_json from_json);
109 111
110sub to_json($) { 112sub to_json($) {
134 136
135This function call is functionally identical to: 137This function call is functionally identical to:
136 138
137 $json_text = JSON::XS->new->utf8->encode ($perl_scalar) 139 $json_text = JSON::XS->new->utf8->encode ($perl_scalar)
138 140
139except being faster. 141Except being faster.
140 142
141=item $perl_scalar = decode_json $json_text 143=item $perl_scalar = decode_json $json_text
142 144
143The 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
144to 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
146 148
147This function call is functionally identical to: 149This function call is functionally identical to:
148 150
149 $perl_scalar = JSON::XS->new->utf8->decode ($json_text) 151 $perl_scalar = JSON::XS->new->utf8->decode ($json_text)
150 152
151except being faster. 153Except being faster.
152 154
153=item $is_boolean = JSON::XS::is_bool $scalar 155=item $is_boolean = JSON::XS::is_bool $scalar
154 156
155Returns true if the passed scalar represents either JSON::XS::true or 157Returns true if the passed scalar represents either JSON::XS::true or
156JSON::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
174This enables you to store Unicode characters as single characters in a 176This enables you to store Unicode characters as single characters in a
175Perl string - very natural. 177Perl string - very natural.
176 178
177=item 2. Perl does I<not> associate an encoding with your strings. 179=item 2. Perl does I<not> associate an encoding with your strings.
178 180
179Unless you force it to, e.g. when matching it against a regex, or printing 181... until you force it to, e.g. when matching it against a regex, or
180the scalar to a file, in which case Perl either interprets your string as 182printing the scalar to a file, in which case Perl either interprets your
181locale-encoded text, octets/binary, or as Unicode, depending on various 183string as locale-encoded text, octets/binary, or as Unicode, depending
182settings. In no case is an encoding stored together with your data, it is 184on various settings. In no case is an encoding stored together with your
183I<use> that decides encoding, not any magical metadata. 185data, it is I<use> that decides encoding, not any magical meta data.
184 186
185=item 3. The internal utf-8 flag has no meaning with regards to the 187=item 3. The internal utf-8 flag has no meaning with regards to the
186encoding of your string. 188encoding of your string.
187 189
188Just ignore that flag unless you debug a Perl bug, a module written in 190Just ignore that flag unless you debug a Perl bug, a module written in
194 196
195If 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
196exist. 198exist.
197 199
198=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
199validly interpreted as a Unicode codepoint. 201validly interpreted as a Unicode code point.
200 202
201If 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
202Unicode string encoded in UTF-8, giving you a binary string. 204Unicode string encoded in UTF-8, giving you a binary string.
203 205
204=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.
242 244
243If C<$enable> is false, then the C<encode> method will not escape Unicode 245If C<$enable> is false, then the C<encode> method will not escape Unicode
244characters unless required by the JSON syntax or other flags. This results 246characters unless required by the JSON syntax or other flags. This results
245in a faster and more compact format. 247in a faster and more compact format.
246 248
249See also the section I<ENCODING/CODESET FLAG NOTES> later in this
250document.
251
247The main use for this flag is to produce JSON texts that can be 252The main use for this flag is to produce JSON texts that can be
248transmitted over a 7-bit channel, as the encoded JSON texts will not 253transmitted over a 7-bit channel, as the encoded JSON texts will not
249contain any 8 bit characters. 254contain any 8 bit characters.
250 255
251 JSON::XS->new->ascii (1)->encode ([chr 0x10401]) 256 JSON::XS->new->ascii (1)->encode ([chr 0x10401])
262will not be affected in any way by this flag, as C<decode> by default 267will not be affected in any way by this flag, as C<decode> by default
263expects Unicode, which is a strict superset of latin1. 268expects Unicode, which is a strict superset of latin1.
264 269
265If C<$enable> is false, then the C<encode> method will not escape Unicode 270If C<$enable> is false, then the C<encode> method will not escape Unicode
266characters unless required by the JSON syntax or other flags. 271characters unless required by the JSON syntax or other flags.
272
273See also the section I<ENCODING/CODESET FLAG NOTES> later in this
274document.
267 275
268The main use for this flag is efficiently encoding binary data as JSON 276The main use for this flag is efficiently encoding binary data as JSON
269text, as most octets will not be escaped, resulting in a smaller encoded 277text, as most octets will not be escaped, resulting in a smaller encoded
270size. The disadvantage is that the resulting JSON text is encoded 278size. The disadvantage is that the resulting JSON text is encoded
271in latin1 (and must correctly be treated as such when storing and 279in latin1 (and must correctly be treated as such when storing and
290 298
291If C<$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
292string 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
293Unicode 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
294to 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.
295 306
296Example, output UTF-16BE-encoded JSON: 307Example, output UTF-16BE-encoded JSON:
297 308
298 use Encode; 309 use Encode;
299 $jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object); 310 $jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
450Example, 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>,
451resulting in an invalid JSON text: 462resulting in an invalid JSON text:
452 463
453 JSON::XS->new->allow_nonref->encode ("Hello, World!") 464 JSON::XS->new->allow_nonref->encode ("Hello, World!")
454 => "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.
455 482
456=item $json = $json->allow_blessed ([$enable]) 483=item $json = $json->allow_blessed ([$enable])
457 484
458=item $enabled = $json->get_allow_blessed 485=item $enabled = $json->get_allow_blessed
459 486
600=item $json = $json->max_depth ([$maximum_nesting_depth]) 627=item $json = $json->max_depth ([$maximum_nesting_depth])
601 628
602=item $max_depth = $json->get_max_depth 629=item $max_depth = $json->get_max_depth
603 630
604Sets the maximum nesting level (default C<512>) accepted while encoding 631Sets the maximum nesting level (default C<512>) accepted while encoding
605or 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
606higher nesting level then this limit, then the encoder and decoder will 633data structure, then the encoder and decoder will stop and croak at that
607stop and croak at that point. 634point.
608 635
609Nesting 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
610needs 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<[>
611characters without their matching closing parenthesis crossed to reach a 638characters without their matching closing parenthesis crossed to reach a
612given character in a string. 639given character in a string.
613 640
614Setting the maximum depth to one disallows any nesting, so that ensures 641Setting the maximum depth to one disallows any nesting, so that ensures
615that the object is only a single hash/object or array. 642that the object is only a single hash/object or array.
616 643
617The argument to C<max_depth> will be rounded up to the next highest power
618of 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
619used, 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.
620 650
621See SECURITY CONSIDERATIONS, below, for more info on why this is useful. 651See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
622 652
623=item $json = $json->max_size ([$maximum_string_size]) 653=item $json = $json->max_size ([$maximum_string_size])
624 654
625=item $max_size = $json->get_max_size 655=item $max_size = $json->get_max_size
626 656
627Set 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
628being 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>
629is 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
630attempt 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
631effect on C<encode> (yet). 661effect on C<encode> (yet).
632 662
633The 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
634power of two (so may be more than requested). If no argument is given, the 664C<0> is specified).
635limit check will be deactivated (same as when C<0> is specified).
636 665
637See SECURITY CONSIDERATIONS, below, for more info on why this is useful. 666See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
638 667
639=item $json_text = $json->encode ($perl_scalar) 668=item $json_text = $json->encode ($perl_scalar)
640 669
669 => ([], 3) 698 => ([], 3)
670 699
671=back 700=back
672 701
673 702
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 the
772parsed text from the input buffer. This is useful after C<incr_parse>
773died, in which case the input buffer and incremental parser state is left
774unchanged, to skip the text parsed so far and to reset the parse state.
775
776=item $json->incr_reset
777
778This completely resets the incremental parser, that is, after this call,
779it will be as if the parser had never parsed anything.
780
781This is useful if you want ot repeatedly parse JSON objects and want to
782ignore any trailing data, which means you have to reset the parser after
783each successful decode.
784
785=back
786
787=head2 LIMITATIONS
788
789All options that affect decoding are supported, except
790C<allow_nonref>. The reason for this is that it cannot be made to
791work sensibly: JSON objects and arrays are self-delimited, i.e. you can concatenate
792them back to back and still decode them perfectly. This does not hold true
793for JSON numbers, however.
794
795For example, is the string C<1> a single JSON number, or is it simply the
796start of C<12>? Or is C<12> a single JSON number, or the concatenation
797of C<1> and C<2>? In neither case you can tell, and this is why JSON::XS
798takes the conservative route and disallows this case.
799
800=head2 EXAMPLES
801
802Some examples will make all this clearer. First, a simple example that
803works similarly to C<decode_prefix>: We want to decode the JSON object at
804the start of a string and identify the portion after the JSON object:
805
806 my $text = "[1,2,3] hello";
807
808 my $json = new JSON::XS;
809
810 my $obj = $json->incr_parse ($text)
811 or die "expected JSON object or array at beginning of string";
812
813 my $tail = $json->incr_text;
814 # $tail now contains " hello"
815
816Easy, isn't it?
817
818Now for a more complicated example: Imagine a hypothetical protocol where
819you read some requests from a TCP stream, and each request is a JSON
820array, without any separation between them (in fact, it is often useful to
821use newlines as "separators", as these get interpreted as whitespace at
822the start of the JSON text, which makes it possible to test said protocol
823with C<telnet>...).
824
825Here is how you'd do it (it is trivial to write this in an event-based
826manner):
827
828 my $json = new JSON::XS;
829
830 # read some data from the socket
831 while (sysread $socket, my $buf, 4096) {
832
833 # split and decode as many requests as possible
834 for my $request ($json->incr_parse ($buf)) {
835 # act on the $request
836 }
837 }
838
839Another complicated example: Assume you have a string with JSON objects
840or arrays, all separated by (optional) comma characters (e.g. C<[1],[2],
841[3]>). To parse them, we have to skip the commas between the JSON texts,
842and here is where the lvalue-ness of C<incr_text> comes in useful:
843
844 my $text = "[1],[2], [3]";
845 my $json = new JSON::XS;
846
847 # void context, so no parsing done
848 $json->incr_parse ($text);
849
850 # now extract as many objects as possible. note the
851 # use of scalar context so incr_text can be called.
852 while (my $obj = $json->incr_parse) {
853 # do something with $obj
854
855 # now skip the optional comma
856 $json->incr_text =~ s/^ \s* , //x;
857 }
858
859Now lets go for a very complex example: Assume that you have a gigantic
860JSON array-of-objects, many gigabytes in size, and you want to parse it,
861but you cannot load it into memory fully (this has actually happened in
862the real world :).
863
864Well, you lost, you have to implement your own JSON parser. But JSON::XS
865can still help you: You implement a (very simple) array parser and let
866JSON decode the array elements, which are all full JSON objects on their
867own (this wouldn't work if the array elements could be JSON numbers, for
868example):
869
870 my $json = new JSON::XS;
871
872 # open the monster
873 open my $fh, "<bigfile.json"
874 or die "bigfile: $!";
875
876 # first parse the initial "["
877 for (;;) {
878 sysread $fh, my $buf, 65536
879 or die "read error: $!";
880 $json->incr_parse ($buf); # void context, so no parsing
881
882 # Exit the loop once we found and removed(!) the initial "[".
883 # In essence, we are (ab-)using the $json object as a simple scalar
884 # we append data to.
885 last if $json->incr_text =~ s/^ \s* \[ //x;
886 }
887
888 # now we have the skipped the initial "[", so continue
889 # parsing all the elements.
890 for (;;) {
891 # in this loop we read data until we got a single JSON object
892 for (;;) {
893 if (my $obj = $json->incr_parse) {
894 # do something with $obj
895 last;
896 }
897
898 # add more data
899 sysread $fh, my $buf, 65536
900 or die "read error: $!";
901 $json->incr_parse ($buf); # void context, so no parsing
902 }
903
904 # in this loop we read data until we either found and parsed the
905 # separating "," between elements, or the final "]"
906 for (;;) {
907 # first skip whitespace
908 $json->incr_text =~ s/^\s*//;
909
910 # if we find "]", we are done
911 if ($json->incr_text =~ s/^\]//) {
912 print "finished.\n";
913 exit;
914 }
915
916 # if we find ",", we can continue with the next element
917 if ($json->incr_text =~ s/^,//) {
918 last;
919 }
920
921 # if we find anything else, we have a parse error!
922 if (length $json->incr_text) {
923 die "parse error near ", $json->incr_text;
924 }
925
926 # else add more data
927 sysread $fh, my $buf, 65536
928 or die "read error: $!";
929 $json->incr_parse ($buf); # void context, so no parsing
930 }
931
932This is a complex example, but most of the complexity comes from the fact
933that we are trying to be correct (bear with me if I am wrong, I never ran
934the above example :).
935
936
937
674=head1 MAPPING 938=head1 MAPPING
675 939
676This section describes how JSON::XS maps Perl values to JSON values and 940This section describes how JSON::XS maps Perl values to JSON values and
677vice versa. These mappings are designed to "do the right thing" in most 941vice versa. These mappings are designed to "do the right thing" in most
678circumstances automatically, preserving round-tripping characteristics 942circumstances automatically, preserving round-tripping characteristics
706 970
707A JSON number becomes either an integer, numeric (floating point) or 971A JSON number becomes either an integer, numeric (floating point) or
708string scalar in perl, depending on its range and any fractional parts. On 972string scalar in perl, depending on its range and any fractional parts. On
709the Perl level, there is no difference between those as Perl handles all 973the Perl level, there is no difference between those as Perl handles all
710the conversion details, but an integer may take slightly less memory and 974the conversion details, but an integer may take slightly less memory and
711might represent more values exactly than (floating point) numbers. 975might represent more values exactly than floating point numbers.
712 976
713If the number consists of digits only, JSON::XS will try to represent 977If the number consists of digits only, JSON::XS will try to represent
714it as an integer value. If that fails, it will try to represent it as 978it as an integer value. If that fails, it will try to represent it as
715a numeric (floating point) value if that is possible without loss of 979a numeric (floating point) value if that is possible without loss of
716precision. Otherwise it will preserve the number as a string value. 980precision. Otherwise it will preserve the number as a string value (in
981which case you lose roundtripping ability, as the JSON number will be
982re-encoded toa JSON string).
717 983
718Numbers containing a fractional or exponential part will always be 984Numbers containing a fractional or exponential part will always be
719represented as numeric (floating point) values, possibly at a loss of 985represented as numeric (floating point) values, possibly at a loss of
720precision. 986precision (in which case you might lose perfect roundtripping ability, but
721 987the JSON number will still be re-encoded as a JSON number).
722This might create round-tripping problems as numbers might become strings,
723but as Perl is typeless there is no other way to do it.
724 988
725=item true, false 989=item true, false
726 990
727These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>, 991These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>,
728respectively. They are overloaded to act almost exactly like the numbers 992respectively. They are overloaded to act almost exactly like the numbers
765Other unblessed references are generally not allowed and will cause an 1029Other unblessed references are generally not allowed and will cause an
766exception to be thrown, except for references to the integers C<0> and 1030exception to be thrown, except for references to the integers C<0> and
767C<1>, which get turned into C<false> and C<true> atoms in JSON. You can 1031C<1>, which get turned into C<false> and C<true> atoms in JSON. You can
768also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability. 1032also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability.
769 1033
770 encode_json [\0,JSON::XS::true] # yields [false,true] 1034 encode_json [\0, JSON::XS::true] # yields [false,true]
771 1035
772=item JSON::XS::true, JSON::XS::false 1036=item JSON::XS::true, JSON::XS::false
773 1037
774These special values become JSON true and JSON false values, 1038These special values become JSON true and JSON false values,
775respectively. You can also use C<\1> and C<\0> directly if you want. 1039respectively. You can also use C<\1> and C<\0> directly if you want.
776 1040
777=item blessed objects 1041=item blessed objects
778 1042
779Blessed objects are not allowed. JSON::XS currently tries to encode their 1043Blessed objects are not directly representable in JSON. See the
780underlying representation (hash- or arrayref), but this behaviour might 1044C<allow_blessed> and C<convert_blessed> methods on various options on
781change in future versions. 1045how to deal with this: basically, you can choose between throwing an
1046exception, encoding the reference as if it weren't blessed, or provide
1047your own serialiser method.
782 1048
783=item simple scalars 1049=item simple scalars
784 1050
785Simple Perl scalars (any scalar that is not a reference) are the most 1051Simple Perl scalars (any scalar that is not a reference) are the most
786difficult objects to encode: JSON::XS will encode undefined scalars as 1052difficult objects to encode: JSON::XS will encode undefined scalars as
787JSON null value, scalars that have last been used in a string context 1053JSON C<null> values, scalars that have last been used in a string context
788before encoding as JSON strings and anything else as number value: 1054before encoding as JSON strings, and anything else as number value:
789 1055
790 # dump as number 1056 # dump as number
791 encode_json [2] # yields [2] 1057 encode_json [2] # yields [2]
792 encode_json [-3.0e17] # yields [-3e+17] 1058 encode_json [-3.0e17] # yields [-3e+17]
793 my $value = 5; encode_json [$value] # yields [5] 1059 my $value = 5; encode_json [$value] # yields [5]
811 my $x = "3"; # some variable containing a string 1077 my $x = "3"; # some variable containing a string
812 $x += 0; # numify it, ensuring it will be dumped as a number 1078 $x += 0; # numify it, ensuring it will be dumped as a number
813 $x *= 1; # same thing, the choice is yours. 1079 $x *= 1; # same thing, the choice is yours.
814 1080
815You can not currently force the type in other, less obscure, ways. Tell me 1081You can not currently force the type in other, less obscure, ways. Tell me
816if you need this capability. 1082if you need this capability (but don't forget to explain why it's needed
1083:).
817 1084
818=back 1085=back
819 1086
820 1087
821=head1 COMPARISON 1088=head1 ENCODING/CODESET FLAG NOTES
822 1089
823As already mentioned, this module was created because none of the existing 1090The interested reader might have seen a number of flags that signify
824JSON modules could be made to work correctly. First I will describe the 1091encodings or codesets - C<utf8>, C<latin1> and C<ascii>. There seems to be
825problems (or pleasures) I encountered with various existing JSON modules, 1092some confusion on what these do, so here is a short comparison:
826followed by some benchmark values. JSON::XS was designed not to suffer 1093
827from any of these problems or limitations. 1094C<utf8> controls whether the JSON text created by C<encode> (and expected
1095by C<decode>) is UTF-8 encoded or not, while C<latin1> and C<ascii> only
1096control whether C<encode> escapes character values outside their respective
1097codeset range. Neither of these flags conflict with each other, although
1098some combinations make less sense than others.
1099
1100Care has been taken to make all flags symmetrical with respect to
1101C<encode> and C<decode>, that is, texts encoded with any combination of
1102these flag values will be correctly decoded when the same flags are used
1103- in general, if you use different flag settings while encoding vs. when
1104decoding you likely have a bug somewhere.
1105
1106Below comes a verbose discussion of these flags. Note that a "codeset" is
1107simply an abstract set of character-codepoint pairs, while an encoding
1108takes those codepoint numbers and I<encodes> them, in our case into
1109octets. Unicode is (among other things) a codeset, UTF-8 is an encoding,
1110and ISO-8859-1 (= latin 1) and ASCII are both codesets I<and> encodings at
1111the same time, which can be confusing.
828 1112
829=over 4 1113=over 4
830 1114
831=item JSON 1.07 1115=item C<utf8> flag disabled
832 1116
833Slow (but very portable, as it is written in pure Perl). 1117When C<utf8> is disabled (the default), then C<encode>/C<decode> generate
1118and expect Unicode strings, that is, characters with high ordinal Unicode
1119values (> 255) will be encoded as such characters, and likewise such
1120characters are decoded as-is, no canges to them will be done, except
1121"(re-)interpreting" them as Unicode codepoints or Unicode characters,
1122respectively (to Perl, these are the same thing in strings unless you do
1123funny/weird/dumb stuff).
834 1124
835Undocumented/buggy Unicode handling (how JSON handles Unicode values is 1125This is useful when you want to do the encoding yourself (e.g. when you
836undocumented. One can get far by feeding it Unicode strings and doing 1126want to have UTF-16 encoded JSON texts) or when some other layer does
837en-/decoding oneself, but Unicode escapes are not working properly). 1127the encoding for you (for example, when printing to a terminal using a
1128filehandle that transparently encodes to UTF-8 you certainly do NOT want
1129to UTF-8 encode your data first and have Perl encode it another time).
838 1130
839No round-tripping (strings get clobbered if they look like numbers, e.g. 1131=item C<utf8> flag enabled
840the string C<2.0> will encode to C<2.0> instead of C<"2.0">, and that will
841decode into the number 2.
842 1132
843=item JSON::PC 0.01 1133If the C<utf8>-flag is enabled, C<encode>/C<decode> will encode all
1134characters using the corresponding UTF-8 multi-byte sequence, and will
1135expect your input strings to be encoded as UTF-8, that is, no "character"
1136of the input string must have any value > 255, as UTF-8 does not allow
1137that.
844 1138
845Very fast. 1139The C<utf8> flag therefore switches between two modes: disabled means you
1140will get a Unicode string in Perl, enabled means you get an UTF-8 encoded
1141octet/binary string in Perl.
846 1142
847Undocumented/buggy Unicode handling. 1143=item C<latin1> or C<ascii> flags enabled
848 1144
849No round-tripping. 1145With C<latin1> (or C<ascii>) enabled, C<encode> will escape characters
1146with ordinal values > 255 (> 127 with C<ascii>) and encode the remaining
1147characters as specified by the C<utf8> flag.
850 1148
851Has problems handling many Perl values (e.g. regex results and other magic 1149If C<utf8> is disabled, then the result is also correctly encoded in those
852values will make it croak). 1150character sets (as both are proper subsets of Unicode, meaning that a
1151Unicode string with all character values < 256 is the same thing as a
1152ISO-8859-1 string, and a Unicode string with all character values < 128 is
1153the same thing as an ASCII string in Perl).
853 1154
854Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}> 1155If C<utf8> is enabled, you still get a correct UTF-8-encoded string,
855which is not a valid JSON text. 1156regardless of these flags, just some more characters will be escaped using
1157C<\uXXXX> then before.
856 1158
857Unmaintained (maintainer unresponsive for many months, bugs are not 1159Note that ISO-8859-1-I<encoded> strings are not compatible with UTF-8
858getting fixed). 1160encoding, while ASCII-encoded strings are. That is because the ISO-8859-1
1161encoding is NOT a subset of UTF-8 (despite the ISO-8859-1 I<codeset> being
1162a subset of Unicode), while ASCII is.
859 1163
860=item JSON::Syck 0.21 1164Surprisingly, C<decode> will ignore these flags and so treat all input
1165values as governed by the C<utf8> flag. If it is disabled, this allows you
1166to decode ISO-8859-1- and ASCII-encoded strings, as both strict subsets of
1167Unicode. If it is enabled, you can correctly decode UTF-8 encoded strings.
861 1168
862Very buggy (often crashes). 1169So neither C<latin1> nor C<ascii> are incompatible with the C<utf8> flag -
1170they only govern when the JSON output engine escapes a character or not.
863 1171
864Very inflexible (no human-readable format supported, format pretty much 1172The main use for C<latin1> is to relatively efficiently store binary data
865undocumented. I need at least a format for easy reading by humans and a 1173as JSON, at the expense of breaking compatibility with most JSON decoders.
866single-line compact format for use in a protocol, and preferably a way to
867generate ASCII-only JSON texts).
868 1174
869Completely broken (and confusingly documented) Unicode handling (Unicode 1175The main use for C<ascii> is to force the output to not contain characters
870escapes are not working properly, you need to set ImplicitUnicode to 1176with values > 127, which means you can interpret the resulting string
871I<different> values on en- and decoding to get symmetric behaviour). 1177as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about any character set and
872 11788-bit-encoding, and still get the same data structure back. This is useful
873No round-tripping (simple cases work, but this depends on whether the scalar 1179when your channel for JSON transfer is not 8-bit clean or the encoding
874value was used in a numeric context or not). 1180might be mangled in between (e.g. in mail), and works because ASCII is a
875 1181proper subset of most 8-bit and multibyte encodings in use in the world.
876Dumping hashes may skip hash values depending on iterator state.
877
878Unmaintained (maintainer unresponsive for many months, bugs are not
879getting fixed).
880
881Does not check input for validity (i.e. will accept non-JSON input and
882return "something" instead of raising an exception. This is a security
883issue: imagine two banks transferring money between each other using
884JSON. One bank might parse a given non-JSON request and deduct money,
885while the other might reject the transaction with a syntax error. While a
886good protocol will at least recover, that is extra unnecessary work and
887the transaction will still not succeed).
888
889=item JSON::DWIW 0.04
890
891Very fast. Very natural. Very nice.
892
893Undocumented Unicode handling (but the best of the pack. Unicode escapes
894still don't get parsed properly).
895
896Very inflexible.
897
898No round-tripping.
899
900Does not generate valid JSON texts (key strings are often unquoted, empty keys
901result in nothing being output)
902
903Does not check input for validity.
904 1182
905=back 1183=back
906 1184
907 1185
908=head2 JSON and YAML 1186=head2 JSON and YAML
909 1187
910You often hear that JSON is a subset of YAML. This is, however, a mass 1188You often hear that JSON is a subset of YAML. This is, however, a mass
911hysteria and very far from the truth. In general, there is no way to 1189hysteria(*) and very far from the truth (as of the time of this writing),
1190so let me state it clearly: I<in general, there is no way to configure
912configure JSON::XS to output a data structure as valid YAML that works for 1191JSON::XS to output a data structure as valid YAML> that works in all
913all cases. 1192cases.
914 1193
915If you really must use JSON::XS to generate YAML, you should use this 1194If you really must use JSON::XS to generate YAML, you should use this
916algorithm (subject to change in future versions): 1195algorithm (subject to change in future versions):
917 1196
918 my $to_yaml = JSON::XS->new->utf8->space_after (1); 1197 my $to_yaml = JSON::XS->new->utf8->space_after (1);
919 my $yaml = $to_yaml->encode ($ref) . "\n"; 1198 my $yaml = $to_yaml->encode ($ref) . "\n";
920 1199
921This will usually generate JSON texts that also parse as valid 1200This will I<usually> generate JSON texts that also parse as valid
922YAML. Please note that YAML has hardcoded limits on (simple) object key 1201YAML. Please note that YAML has hardcoded limits on (simple) object key
923lengths that JSON doesn't have and also has different and incompatible 1202lengths that JSON doesn't have and also has different and incompatible
924unicode handling, so you should make sure that your hash keys are 1203unicode handling, so you should make sure that your hash keys are
925noticeably shorter than the 1024 "stream characters" YAML allows and that 1204noticeably shorter than the 1024 "stream characters" YAML allows and that
926you do not have codepoints with values outside the Unicode BMP (basic 1205you do not have characters with codepoint values outside the Unicode BMP
927multilingual page). 1206(basic multilingual page). YAML also does not allow C<\/> sequences in
1207strings (which JSON::XS does not I<currently> generate, but other JSON
1208generators might).
928 1209
929There might be other incompatibilities that I am not aware of. In general 1210There might be other incompatibilities that I am not aware of (or the YAML
1211specification has been changed yet again - it does so quite often). In
930you should not try to generate YAML with a JSON generator or vice versa, 1212general you should not try to generate YAML with a JSON generator or vice
931or try to parse JSON with a YAML parser or vice versa: chances are high 1213versa, or try to parse JSON with a YAML parser or vice versa: chances are
932that you will run into severe interoperability problems when you least 1214high that you will run into severe interoperability problems when you
933expect it. 1215least expect it.
1216
1217=over 4
1218
1219=item (*)
1220
1221I have been pressured multiple times by Brian Ingerson (one of the
1222authors of the YAML specification) to remove this paragraph, despite him
1223acknowledging that the actual incompatibilities exist. As I was personally
1224bitten by this "JSON is YAML" lie, I refused and said I will continue to
1225educate people about these issues, so others do not run into the same
1226problem again and again. After this, Brian called me a (quote)I<complete
1227and worthless idiot>(unquote).
1228
1229In my opinion, instead of pressuring and insulting people who actually
1230clarify issues with YAML and the wrong statements of some of its
1231proponents, I would kindly suggest reading the JSON spec (which is not
1232that difficult or long) and finally make YAML compatible to it, and
1233educating users about the changes, instead of spreading lies about the
1234real compatibility for many I<years> and trying to silence people who
1235point out that it isn't true.
1236
1237=back
934 1238
935 1239
936=head2 SPEED 1240=head2 SPEED
937 1241
938It seems that JSON::XS is surprisingly fast, as shown in the following 1242It seems that JSON::XS is surprisingly fast, as shown in the following
939tables. They have been generated with the help of the C<eg/bench> program 1243tables. They have been generated with the help of the C<eg/bench> program
940in the JSON::XS distribution, to make it easy to compare on your own 1244in the JSON::XS distribution, to make it easy to compare on your own
941system. 1245system.
942 1246
943First comes a comparison between various modules using a very short 1247First comes a comparison between various modules using
944single-line JSON string: 1248a very short single-line JSON string (also available at
1249L<http://dist.schmorp.de/misc/json/short.json>).
945 1250
946 {"method": "handleMessage", "params": ["user1", "we were just talking"], \ 1251 {"method": "handleMessage", "params": ["user1",
947 "id": null, "array":[1,11,234,-5,1e5,1e7, true, false]} 1252 "we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7,
1253 true, false]}
948 1254
949It shows the number of encodes/decodes per second (JSON::XS uses 1255It shows the number of encodes/decodes per second (JSON::XS uses
950the functional interface, while JSON::XS/2 uses the OO interface 1256the functional interface, while JSON::XS/2 uses the OO interface
951with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables 1257with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables
952shrink). Higher is better: 1258shrink). Higher is better:
968about three times faster on decoding, and over forty times faster 1274about three times faster on decoding, and over forty times faster
969than JSON, even with pretty-printing and key sorting. It also compares 1275than JSON, even with pretty-printing and key sorting. It also compares
970favourably to Storable for small amounts of data. 1276favourably to Storable for small amounts of data.
971 1277
972Using a longer test string (roughly 18KB, generated from Yahoo! Locals 1278Using a longer test string (roughly 18KB, generated from Yahoo! Locals
973search API (http://nanoref.com/yahooapis/mgPdGg): 1279search API (L<http://dist.schmorp.de/misc/json/long.json>).
974 1280
975 module | encode | decode | 1281 module | encode | decode |
976 -----------|------------|------------| 1282 -----------|------------|------------|
977 JSON 1.x | 55.260 | 34.971 | 1283 JSON 1.x | 55.260 | 34.971 |
978 JSON::DWIW | 825.228 | 1082.513 | 1284 JSON::DWIW | 825.228 | 1082.513 |
1020to free the temporary). If that is exceeded, the program crashes. To be 1326to free the temporary). If that is exceeded, the program crashes. To be
1021conservative, the default nesting limit is set to 512. If your process 1327conservative, the default nesting limit is set to 512. If your process
1022has a smaller stack, you should adjust this setting accordingly with the 1328has a smaller stack, you should adjust this setting accordingly with the
1023C<max_depth> method. 1329C<max_depth> method.
1024 1330
1025And last but least, something else could bomb you that I forgot to think 1331Something else could bomb you, too, that I forgot to think of. In that
1026of. In that case, you get to keep the pieces. I am always open for hints, 1332case, you get to keep the pieces. I am always open for hints, though...
1027though... 1333
1334Also keep in mind that JSON::XS might leak contents of your Perl data
1335structures in its error messages, so when you serialise sensitive
1336information you might want to make sure that exceptions thrown by JSON::XS
1337will not end up in front of untrusted eyes.
1028 1338
1029If you are using JSON::XS to return packets to consumption 1339If you are using JSON::XS to return packets to consumption
1030by JavaScript scripts in a browser you should have a look at 1340by JavaScript scripts in a browser you should have a look at
1031L<http://jpsykes.com/47/practical-csrf-and-json-security> to see whether 1341L<http://jpsykes.com/47/practical-csrf-and-json-security> to see whether
1032you are vulnerable to some common attack vectors (which really are browser 1342you are vulnerable to some common attack vectors (which really are browser
1038=head1 THREADS 1348=head1 THREADS
1039 1349
1040This module is I<not> guaranteed to be thread safe and there are no 1350This module is I<not> guaranteed to be thread safe and there are no
1041plans to change this until Perl gets thread support (as opposed to the 1351plans to change this until Perl gets thread support (as opposed to the
1042horribly slow so-called "threads" which are simply slow and bloated 1352horribly slow so-called "threads" which are simply slow and bloated
1043process simulations - use fork, its I<much> faster, cheaper, better). 1353process simulations - use fork, it's I<much> faster, cheaper, better).
1044 1354
1045(It might actually work, but you have been warned). 1355(It might actually work, but you have been warned).
1046 1356
1047 1357
1048=head1 BUGS 1358=head1 BUGS
1049 1359
1050While the goal of this module is to be correct, that unfortunately does 1360While the goal of this module is to be correct, that unfortunately does
1051not mean its bug-free, only that I think its design is bug-free. It is 1361not mean it's bug-free, only that I think its design is bug-free. If you
1052still relatively early in its development. If you keep reporting bugs they 1362keep reporting bugs they will be fixed swiftly, though.
1053will be fixed swiftly, though.
1054 1363
1055Please refrain from using rt.cpan.org or any other bug reporting 1364Please refrain from using rt.cpan.org or any other bug reporting
1056service. I put the contact address into my modules for a reason. 1365service. I put the contact address into my modules for a reason.
1057 1366
1058=cut 1367=cut
1078 "--" => sub { $_[0] = ${$_[0]} - 1 }, 1387 "--" => sub { $_[0] = ${$_[0]} - 1 },
1079 fallback => 1; 1388 fallback => 1;
1080 1389
10811; 13901;
1082 1391
1392=head1 SEE ALSO
1393
1394The F<json_xs> command line utility for quick experiments.
1395
1083=head1 AUTHOR 1396=head1 AUTHOR
1084 1397
1085 Marc Lehmann <schmorp@schmorp.de> 1398 Marc Lehmann <schmorp@schmorp.de>
1086 http://home.schmorp.de/ 1399 http://home.schmorp.de/
1087 1400

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