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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 $VERSION = '2.232';
106our @ISA = qw(Exporter); 108our @ISA = qw(Exporter);
107 109
108our @EXPORT = qw(encode_json decode_json to_json from_json); 110our @EXPORT = qw(encode_json decode_json to_json from_json);
109 111
110sub to_json($) { 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
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
940
941
674=head1 MAPPING 942=head1 MAPPING
675 943
676This 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
677vice versa. These mappings are designed to "do the right thing" in most 945vice versa. These mappings are designed to "do the right thing" in most
678circumstances automatically, preserving round-tripping characteristics 946circumstances automatically, preserving round-tripping characteristics
706 974
707A JSON number becomes either an integer, numeric (floating point) or 975A JSON number becomes either an integer, numeric (floating point) or
708string scalar in perl, depending on its range and any fractional parts. On 976string 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 977the Perl level, there is no difference between those as Perl handles all
710the conversion details, but an integer may take slightly less memory and 978the conversion details, but an integer may take slightly less memory and
711might represent more values exactly than (floating point) numbers. 979might represent more values exactly than floating point numbers.
712 980
713If the number consists of digits only, JSON::XS will try to represent 981If 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 982it 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 983a numeric (floating point) value if that is possible without loss of
716precision. Otherwise it will preserve the number as a string value. 984precision. Otherwise it will preserve the number as a string value (in
985which case you lose roundtripping ability, as the JSON number will be
986re-encoded toa JSON string).
717 987
718Numbers containing a fractional or exponential part will always be 988Numbers containing a fractional or exponential part will always be
719represented as numeric (floating point) values, possibly at a loss of 989represented as numeric (floating point) values, possibly at a loss of
720precision. 990precision (in which case you might lose perfect roundtripping ability, but
721 991the 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.
724 992
725=item true, false 993=item true, false
726 994
727These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>, 995These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>,
728respectively. They are overloaded to act almost exactly like the numbers 996respectively. They are overloaded to act almost exactly like the numbers
765Other unblessed references are generally not allowed and will cause an 1033Other unblessed references are generally not allowed and will cause an
766exception 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
767C<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
768also 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.
769 1037
770 encode_json [\0,JSON::XS::true] # yields [false,true] 1038 encode_json [\0, JSON::XS::true] # yields [false,true]
771 1039
772=item JSON::XS::true, JSON::XS::false 1040=item JSON::XS::true, JSON::XS::false
773 1041
774These special values become JSON true and JSON false values, 1042These special values become JSON true and JSON false values,
775respectively. 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.
813 my $x = "3"; # some variable containing a string 1081 my $x = "3"; # some variable containing a string
814 $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
815 $x *= 1; # same thing, the choice is yours. 1083 $x *= 1; # same thing, the choice is yours.
816 1084
817You 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
818if 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
819:). 1087:).
820 1088
821=back 1089=back
822 1090
823 1091
824=head1 COMPARISON 1092=head1 ENCODING/CODESET FLAG NOTES
825 1093
826As already mentioned, this module was created because none of the existing 1094The interested reader might have seen a number of flags that signify
827JSON modules could be made to work correctly. First I will describe the 1095encodings or codesets - C<utf8>, C<latin1> and C<ascii>. There seems to be
828problems (or pleasures) I encountered with various existing JSON modules, 1096some confusion on what these do, so here is a short comparison:
829followed by some benchmark values. JSON::XS was designed not to suffer 1097
830from any of these problems or limitations. 1098C<utf8> controls whether the JSON text created by C<encode> (and expected
1099by C<decode>) is UTF-8 encoded or not, while C<latin1> and C<ascii> only
1100control whether C<encode> escapes character values outside their respective
1101codeset range. Neither of these flags conflict with each other, although
1102some combinations make less sense than others.
1103
1104Care has been taken to make all flags symmetrical with respect to
1105C<encode> and C<decode>, that is, texts encoded with any combination of
1106these flag values will be correctly decoded when the same flags are used
1107- in general, if you use different flag settings while encoding vs. when
1108decoding you likely have a bug somewhere.
1109
1110Below comes a verbose discussion of these flags. Note that a "codeset" is
1111simply an abstract set of character-codepoint pairs, while an encoding
1112takes those codepoint numbers and I<encodes> them, in our case into
1113octets. Unicode is (among other things) a codeset, UTF-8 is an encoding,
1114and ISO-8859-1 (= latin 1) and ASCII are both codesets I<and> encodings at
1115the same time, which can be confusing.
831 1116
832=over 4 1117=over 4
833 1118
834=item JSON 1.07 1119=item C<utf8> flag disabled
835 1120
836Slow (but very portable, as it is written in pure Perl). 1121When C<utf8> is disabled (the default), then C<encode>/C<decode> generate
1122and expect Unicode strings, that is, characters with high ordinal Unicode
1123values (> 255) will be encoded as such characters, and likewise such
1124characters are decoded as-is, no canges to them will be done, except
1125"(re-)interpreting" them as Unicode codepoints or Unicode characters,
1126respectively (to Perl, these are the same thing in strings unless you do
1127funny/weird/dumb stuff).
837 1128
838Undocumented/buggy Unicode handling (how JSON handles Unicode values is 1129This is useful when you want to do the encoding yourself (e.g. when you
839undocumented. One can get far by feeding it Unicode strings and doing 1130want to have UTF-16 encoded JSON texts) or when some other layer does
840en-/decoding oneself, but Unicode escapes are not working properly). 1131the encoding for you (for example, when printing to a terminal using a
1132filehandle that transparently encodes to UTF-8 you certainly do NOT want
1133to UTF-8 encode your data first and have Perl encode it another time).
841 1134
842No round-tripping (strings get clobbered if they look like numbers, e.g. 1135=item C<utf8> flag enabled
843the string C<2.0> will encode to C<2.0> instead of C<"2.0">, and that will
844decode into the number 2.
845 1136
846=item JSON::PC 0.01 1137If the C<utf8>-flag is enabled, C<encode>/C<decode> will encode all
1138characters using the corresponding UTF-8 multi-byte sequence, and will
1139expect your input strings to be encoded as UTF-8, that is, no "character"
1140of the input string must have any value > 255, as UTF-8 does not allow
1141that.
847 1142
848Very fast. 1143The C<utf8> flag therefore switches between two modes: disabled means you
1144will get a Unicode string in Perl, enabled means you get an UTF-8 encoded
1145octet/binary string in Perl.
849 1146
850Undocumented/buggy Unicode handling. 1147=item C<latin1> or C<ascii> flags enabled
851 1148
852No round-tripping. 1149With C<latin1> (or C<ascii>) enabled, C<encode> will escape characters
1150with ordinal values > 255 (> 127 with C<ascii>) and encode the remaining
1151characters as specified by the C<utf8> flag.
853 1152
854Has problems handling many Perl values (e.g. regex results and other magic 1153If C<utf8> is disabled, then the result is also correctly encoded in those
855values will make it croak). 1154character sets (as both are proper subsets of Unicode, meaning that a
1155Unicode string with all character values < 256 is the same thing as a
1156ISO-8859-1 string, and a Unicode string with all character values < 128 is
1157the same thing as an ASCII string in Perl).
856 1158
857Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}> 1159If C<utf8> is enabled, you still get a correct UTF-8-encoded string,
858which is not a valid JSON text. 1160regardless of these flags, just some more characters will be escaped using
1161C<\uXXXX> then before.
859 1162
860Unmaintained (maintainer unresponsive for many months, bugs are not 1163Note that ISO-8859-1-I<encoded> strings are not compatible with UTF-8
861getting fixed). 1164encoding, while ASCII-encoded strings are. That is because the ISO-8859-1
1165encoding is NOT a subset of UTF-8 (despite the ISO-8859-1 I<codeset> being
1166a subset of Unicode), while ASCII is.
862 1167
863=item JSON::Syck 0.21 1168Surprisingly, C<decode> will ignore these flags and so treat all input
1169values as governed by the C<utf8> flag. If it is disabled, this allows you
1170to decode ISO-8859-1- and ASCII-encoded strings, as both strict subsets of
1171Unicode. If it is enabled, you can correctly decode UTF-8 encoded strings.
864 1172
865Very buggy (often crashes). 1173So neither C<latin1> nor C<ascii> are incompatible with the C<utf8> flag -
1174they only govern when the JSON output engine escapes a character or not.
866 1175
867Very inflexible (no human-readable format supported, format pretty much 1176The main use for C<latin1> is to relatively efficiently store binary data
868undocumented. I need at least a format for easy reading by humans and a 1177as JSON, at the expense of breaking compatibility with most JSON decoders.
869single-line compact format for use in a protocol, and preferably a way to
870generate ASCII-only JSON texts).
871 1178
872Completely broken (and confusingly documented) Unicode handling (Unicode 1179The main use for C<ascii> is to force the output to not contain characters
873escapes are not working properly, you need to set ImplicitUnicode to 1180with values > 127, which means you can interpret the resulting string
874I<different> values on en- and decoding to get symmetric behaviour). 1181as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about any character set and
875 11828-bit-encoding, and still get the same data structure back. This is useful
876No round-tripping (simple cases work, but this depends on whether the scalar 1183when your channel for JSON transfer is not 8-bit clean or the encoding
877value was used in a numeric context or not). 1184might be mangled in between (e.g. in mail), and works because ASCII is a
878 1185proper subset of most 8-bit and multibyte encodings in use in the world.
879Dumping hashes may skip hash values depending on iterator state.
880
881Unmaintained (maintainer unresponsive for many months, bugs are not
882getting fixed).
883
884Does not check input for validity (i.e. will accept non-JSON input and
885return "something" instead of raising an exception. This is a security
886issue: imagine two banks transferring money between each other using
887JSON. One bank might parse a given non-JSON request and deduct money,
888while the other might reject the transaction with a syntax error. While a
889good protocol will at least recover, that is extra unnecessary work and
890the transaction will still not succeed).
891
892=item JSON::DWIW 0.04
893
894Very fast. Very natural. Very nice.
895
896Undocumented Unicode handling (but the best of the pack. Unicode escapes
897still don't get parsed properly).
898
899Very inflexible.
900
901No round-tripping.
902
903Does not generate valid JSON texts (key strings are often unquoted, empty keys
904result in nothing being output)
905
906Does not check input for validity.
907 1186
908=back 1187=back
909 1188
910 1189
1190=head2 JSON and ECMAscript
1191
1192JSON syntax is based on how literals are represented in javascript (the
1193not-standardised predecessor of ECMAscript) which is presumably why it is
1194called "JavaScript Object Notation".
1195
1196However, JSON is not a subset (and also not a superset of course) of
1197ECMAscript (the standard) or javascript (whatever browsers actually
1198implement).
1199
1200If you want to use javascript's C<eval> function to "parse" JSON, you
1201might run into parse errors for valid JSON texts, or the resulting data
1202structure might not be queryable:
1203
1204One of the problems is that U+2028 and U+2029 are valid characters inside
1205JSON strings, but are not allowed in ECMAscript string literals, so the
1206following Perl fragment will not output something that can be guaranteed
1207to be parsable by javascript's C<eval>:
1208
1209 use JSON::XS;
1210
1211 print encode_json [chr 0x2028];
1212
1213The right fix for this is to use a proper JSON parser in your javascript
1214programs, and not rely on C<eval> (see for example Douglas Crockford's
1215F<json2.js> parser).
1216
1217If this is not an option, you can, as a stop-gap measure, simply encode to
1218ASCII-only JSON:
1219
1220 use JSON::XS;
1221
1222 print JSON::XS->new->ascii->encode ([chr 0x2028]);
1223
1224Note that this will enlarge the resulting JSON text quite a bit if you
1225have many non-ASCII characters. You might be tempted to run some regexes
1226to only escape U+2028 and U+2029, e.g.:
1227
1228 # DO NOT USE THIS!
1229 my $json = JSON::XS->new->utf8->encode ([chr 0x2028]);
1230 $json =~ s/\xe2\x80\xa8/\\u2028/g; # escape U+2028
1231 $json =~ s/\xe2\x80\xa9/\\u2029/g; # escape U+2029
1232 print $json;
1233
1234Note that I<this is a bad idea>: the above only works for U+2028 and
1235U+2029 and thus only for fully ECMAscript-compliant parsers. Many existing
1236javascript implementations, however, have issues with other characters as
1237well - using C<eval> naively simply I<will> cause problems.
1238
1239Another problem is that some javascript implementations reserve
1240some property names for their own purposes (which probably makes
1241them non-ECMAscript-compliant). For example, Iceweasel reserves the
1242C<__proto__> property name for it's own purposes.
1243
1244If that is a problem, you could parse try to filter the resulting JSON
1245output for these property strings, e.g.:
1246
1247 $json =~ s/"__proto__"\s*:/"__proto__renamed":/g;
1248
1249This works because C<__proto__> is not valid outside of strings, so every
1250occurence of C<"__proto__"\s*:> must be a string used as property name.
1251
1252If you know of other incompatibilities, please let me know.
1253
1254
911=head2 JSON and YAML 1255=head2 JSON and YAML
912 1256
913You often hear that JSON is a subset of YAML. This is, however, a mass 1257You often hear that JSON is a subset of YAML. This is, however, a mass
914hysteria(*) and very far from the truth. In general, there is no way to 1258hysteria(*) and very far from the truth (as of the time of this writing),
1259so let me state it clearly: I<in general, there is no way to configure
915configure JSON::XS to output a data structure as valid YAML that works for 1260JSON::XS to output a data structure as valid YAML> that works in all
916all cases. 1261cases.
917 1262
918If you really must use JSON::XS to generate YAML, you should use this 1263If you really must use JSON::XS to generate YAML, you should use this
919algorithm (subject to change in future versions): 1264algorithm (subject to change in future versions):
920 1265
921 my $to_yaml = JSON::XS->new->utf8->space_after (1); 1266 my $to_yaml = JSON::XS->new->utf8->space_after (1);
924This will I<usually> generate JSON texts that also parse as valid 1269This will I<usually> generate JSON texts that also parse as valid
925YAML. Please note that YAML has hardcoded limits on (simple) object key 1270YAML. Please note that YAML has hardcoded limits on (simple) object key
926lengths that JSON doesn't have and also has different and incompatible 1271lengths that JSON doesn't have and also has different and incompatible
927unicode handling, so you should make sure that your hash keys are 1272unicode handling, so you should make sure that your hash keys are
928noticeably shorter than the 1024 "stream characters" YAML allows and that 1273noticeably shorter than the 1024 "stream characters" YAML allows and that
929you do not have codepoints with values outside the Unicode BMP (basic 1274you do not have characters with codepoint values outside the Unicode BMP
930multilingual page). YAML also does not allow C<\/> sequences in strings 1275(basic multilingual page). YAML also does not allow C<\/> sequences in
931(which JSON::XS does not I<currently> generate). 1276strings (which JSON::XS does not I<currently> generate, but other JSON
1277generators might).
932 1278
933There might be other incompatibilities that I am not aware of (or the YAML 1279There might be other incompatibilities that I am not aware of (or the YAML
934specification has been changed yet again - it does so quite often). In 1280specification has been changed yet again - it does so quite often). In
935general you should not try to generate YAML with a JSON generator or vice 1281general you should not try to generate YAML with a JSON generator or vice
936versa, or try to parse JSON with a YAML parser or vice versa: chances are 1282versa, or try to parse JSON with a YAML parser or vice versa: chances are
939 1285
940=over 4 1286=over 4
941 1287
942=item (*) 1288=item (*)
943 1289
944This is spread actively by the YAML team, however. For many years now they 1290I have been pressured multiple times by Brian Ingerson (one of the
945claim YAML were a superset of JSON, even when proven otherwise. 1291authors of the YAML specification) to remove this paragraph, despite him
1292acknowledging that the actual incompatibilities exist. As I was personally
1293bitten by this "JSON is YAML" lie, I refused and said I will continue to
1294educate people about these issues, so others do not run into the same
1295problem again and again. After this, Brian called me a (quote)I<complete
1296and worthless idiot>(unquote).
946 1297
947Even the author of this manpage was at some point accused of providing 1298In my opinion, instead of pressuring and insulting people who actually
948"incorrect" information, despite the evidence presented (claims ranged 1299clarify issues with YAML and the wrong statements of some of its
949from "your documentation contains inaccurate and negative statements about 1300proponents, I would kindly suggest reading the JSON spec (which is not
950YAML" (the only negative comment is this footnote, and it didn't exist 1301that difficult or long) and finally make YAML compatible to it, and
951back then; the question on which claims were inaccurate was never answered 1302educating users about the changes, instead of spreading lies about the
952etc.) to "the YAML spec is not up-to-date" (the *real* and supposedly 1303real compatibility for many I<years> and trying to silence people who
953JSON-compatible spec is apparently not currently publicly available) 1304point out that it isn't true.
954to actual requests to replace this section by *incorrect* information,
955suppressing information about the real problem).
956
957So whenever you are told that YAML was a superset of JSON, first check
958wether it is really true (it might be when you check it, but it certainly
959was not true when this was written). I would much prefer if the YAML team
960would spent their time on actually making JSON compatibility a truth
961(JSON, after all, has a very small and simple specification) instead of
962trying to lobby/force people into reporting untruths.
963 1305
964=back 1306=back
965 1307
966 1308
967=head2 SPEED 1309=head2 SPEED
969It seems that JSON::XS is surprisingly fast, as shown in the following 1311It seems that JSON::XS is surprisingly fast, as shown in the following
970tables. They have been generated with the help of the C<eg/bench> program 1312tables. They have been generated with the help of the C<eg/bench> program
971in the JSON::XS distribution, to make it easy to compare on your own 1313in the JSON::XS distribution, to make it easy to compare on your own
972system. 1314system.
973 1315
974First comes a comparison between various modules using a very short 1316First comes a comparison between various modules using
975single-line JSON string: 1317a very short single-line JSON string (also available at
1318L<http://dist.schmorp.de/misc/json/short.json>).
976 1319
977 {"method": "handleMessage", "params": ["user1", "we were just talking"], \ 1320 {"method": "handleMessage", "params": ["user1",
978 "id": null, "array":[1,11,234,-5,1e5,1e7, true, false]} 1321 "we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7,
1322 true, false]}
979 1323
980It shows the number of encodes/decodes per second (JSON::XS uses 1324It shows the number of encodes/decodes per second (JSON::XS uses
981the functional interface, while JSON::XS/2 uses the OO interface 1325the functional interface, while JSON::XS/2 uses the OO interface
982with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables 1326with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables
983shrink). Higher is better: 1327shrink). Higher is better:
999about three times faster on decoding, and over forty times faster 1343about three times faster on decoding, and over forty times faster
1000than JSON, even with pretty-printing and key sorting. It also compares 1344than JSON, even with pretty-printing and key sorting. It also compares
1001favourably to Storable for small amounts of data. 1345favourably to Storable for small amounts of data.
1002 1346
1003Using a longer test string (roughly 18KB, generated from Yahoo! Locals 1347Using a longer test string (roughly 18KB, generated from Yahoo! Locals
1004search API (http://nanoref.com/yahooapis/mgPdGg): 1348search API (L<http://dist.schmorp.de/misc/json/long.json>).
1005 1349
1006 module | encode | decode | 1350 module | encode | decode |
1007 -----------|------------|------------| 1351 -----------|------------|------------|
1008 JSON 1.x | 55.260 | 34.971 | 1352 JSON 1.x | 55.260 | 34.971 |
1009 JSON::DWIW | 825.228 | 1082.513 | 1353 JSON::DWIW | 825.228 | 1082.513 |
1051to free the temporary). If that is exceeded, the program crashes. To be 1395to free the temporary). If that is exceeded, the program crashes. To be
1052conservative, the default nesting limit is set to 512. If your process 1396conservative, the default nesting limit is set to 512. If your process
1053has a smaller stack, you should adjust this setting accordingly with the 1397has a smaller stack, you should adjust this setting accordingly with the
1054C<max_depth> method. 1398C<max_depth> method.
1055 1399
1056And last but least, something else could bomb you that I forgot to think 1400Something else could bomb you, too, that I forgot to think of. In that
1057of. In that case, you get to keep the pieces. I am always open for hints, 1401case, you get to keep the pieces. I am always open for hints, though...
1058though... 1402
1403Also keep in mind that JSON::XS might leak contents of your Perl data
1404structures in its error messages, so when you serialise sensitive
1405information you might want to make sure that exceptions thrown by JSON::XS
1406will not end up in front of untrusted eyes.
1059 1407
1060If you are using JSON::XS to return packets to consumption 1408If you are using JSON::XS to return packets to consumption
1061by JavaScript scripts in a browser you should have a look at 1409by JavaScript scripts in a browser you should have a look at
1062L<http://jpsykes.com/47/practical-csrf-and-json-security> to see whether 1410L<http://jpsykes.com/47/practical-csrf-and-json-security> to see whether
1063you are vulnerable to some common attack vectors (which really are browser 1411you are vulnerable to some common attack vectors (which really are browser
1069=head1 THREADS 1417=head1 THREADS
1070 1418
1071This module is I<not> guaranteed to be thread safe and there are no 1419This module is I<not> guaranteed to be thread safe and there are no
1072plans to change this until Perl gets thread support (as opposed to the 1420plans to change this until Perl gets thread support (as opposed to the
1073horribly slow so-called "threads" which are simply slow and bloated 1421horribly slow so-called "threads" which are simply slow and bloated
1074process simulations - use fork, its I<much> faster, cheaper, better). 1422process simulations - use fork, it's I<much> faster, cheaper, better).
1075 1423
1076(It might actually work, but you have been warned). 1424(It might actually work, but you have been warned).
1077 1425
1078 1426
1079=head1 BUGS 1427=head1 BUGS
1080 1428
1081While the goal of this module is to be correct, that unfortunately does 1429While the goal of this module is to be correct, that unfortunately does
1082not mean its bug-free, only that I think its design is bug-free. It is 1430not mean it's bug-free, only that I think its design is bug-free. If you
1083still relatively early in its development. If you keep reporting bugs they 1431keep reporting bugs they will be fixed swiftly, though.
1084will be fixed swiftly, though.
1085 1432
1086Please refrain from using rt.cpan.org or any other bug reporting 1433Please refrain from using rt.cpan.org or any other bug reporting
1087service. I put the contact address into my modules for a reason. 1434service. I put the contact address into my modules for a reason.
1088 1435
1089=cut 1436=cut
1109 "--" => sub { $_[0] = ${$_[0]} - 1 }, 1456 "--" => sub { $_[0] = ${$_[0]} - 1 },
1110 fallback => 1; 1457 fallback => 1;
1111 1458
11121; 14591;
1113 1460
1461=head1 SEE ALSO
1462
1463The F<json_xs> command line utility for quick experiments.
1464
1114=head1 AUTHOR 1465=head1 AUTHOR
1115 1466
1116 Marc Lehmann <schmorp@schmorp.de> 1467 Marc Lehmann <schmorp@schmorp.de>
1117 http://home.schmorp.de/ 1468 http://home.schmorp.de/
1118 1469

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