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Revision 1.32 by root, Thu Apr 12 07:25:29 2007 UTC

4 4
5=head1 SYNOPSIS 5=head1 SYNOPSIS
6 6
7 use JSON::XS; 7 use JSON::XS;
8 8
9 # exported functions, they croak on error
10 # and expect/generate UTF-8
11
12 $utf8_encoded_json_text = to_json $perl_hash_or_arrayref;
13 $perl_hash_or_arrayref = from_json $utf8_encoded_json_text;
14
15 # objToJson and jsonToObj aliases to to_json and from_json
16 # are exported for compatibility to the JSON module,
17 # but should not be used in new code.
18
19 # OO-interface
20
21 $coder = JSON::XS->new->ascii->pretty->allow_nonref;
22 $pretty_printed_unencoded = $coder->encode ($perl_scalar);
23 $perl_scalar = $coder->decode ($unicode_json_text);
24
9=head1 DESCRIPTION 25=head1 DESCRIPTION
10 26
27This module converts Perl data structures to JSON and vice versa. Its
28primary goal is to be I<correct> and its secondary goal is to be
29I<fast>. To reach the latter goal it was written in C.
30
31As this is the n-th-something JSON module on CPAN, what was the reason
32to write yet another JSON module? While it seems there are many JSON
33modules, none of them correctly handle all corner cases, and in most cases
34their maintainers are unresponsive, gone missing, or not listening to bug
35reports for other reasons.
36
37See COMPARISON, below, for a comparison to some other JSON modules.
38
39See MAPPING, below, on how JSON::XS maps perl values to JSON values and
40vice versa.
41
42=head2 FEATURES
43
11=over 4 44=over 4
12 45
46=item * correct unicode handling
47
48This module knows how to handle Unicode, and even documents how and when
49it does so.
50
51=item * round-trip integrity
52
53When you serialise a perl data structure using only datatypes supported
54by JSON, the deserialised data structure is identical on the Perl level.
55(e.g. the string "2.0" doesn't suddenly become "2" just because it looks
56like a number).
57
58=item * strict checking of JSON correctness
59
60There is no guessing, no generating of illegal JSON texts by default,
61and only JSON is accepted as input by default (the latter is a security
62feature).
63
64=item * fast
65
66Compared to other JSON modules, this module compares favourably in terms
67of speed, too.
68
69=item * simple to use
70
71This module has both a simple functional interface as well as an OO
72interface.
73
74=item * reasonably versatile output formats
75
76You can choose between the most compact guarenteed single-line format
77possible (nice for simple line-based protocols), a pure-ascii format
78(for when your transport is not 8-bit clean, still supports the whole
79unicode range), or a pretty-printed format (for when you want to read that
80stuff). Or you can combine those features in whatever way you like.
81
82=back
83
13=cut 84=cut
14 85
15package JSON::XS; 86package JSON::XS;
16 87
88use strict;
89
17BEGIN { 90BEGIN {
18 $VERSION = '0.1'; 91 our $VERSION = '1.12';
19 @ISA = qw(Exporter); 92 our @ISA = qw(Exporter);
20 93
94 our @EXPORT = qw(to_json from_json objToJson jsonToObj);
21 require Exporter; 95 require Exporter;
22 96
23 require XSLoader; 97 require XSLoader;
24 XSLoader::load JSON::XS::, $VERSION; 98 XSLoader::load JSON::XS::, $VERSION;
25} 99}
26 100
27=item 101=head1 FUNCTIONAL INTERFACE
102
103The following convinience methods are provided by this module. They are
104exported by default:
105
106=over 4
107
108=item $json_text = to_json $perl_scalar
109
110Converts the given Perl data structure (a simple scalar or a reference to
111a hash or array) to a UTF-8 encoded, binary string (that is, the string contains
112octets only). Croaks on error.
113
114This function call is functionally identical to:
115
116 $json_text = JSON::XS->new->utf8->encode ($perl_scalar)
117
118except being faster.
119
120=item $perl_scalar = from_json $json_text
121
122The opposite of C<to_json>: expects an UTF-8 (binary) string and tries to
123parse that as an UTF-8 encoded JSON text, returning the resulting simple
124scalar or reference. Croaks on error.
125
126This function call is functionally identical to:
127
128 $perl_scalar = JSON::XS->new->utf8->decode ($json_text)
129
130except being faster.
131
132=back
133
134
135=head1 OBJECT-ORIENTED INTERFACE
136
137The object oriented interface lets you configure your own encoding or
138decoding style, within the limits of supported formats.
139
140=over 4
141
142=item $json = new JSON::XS
143
144Creates a new JSON::XS object that can be used to de/encode JSON
145strings. All boolean flags described below are by default I<disabled>.
146
147The mutators for flags all return the JSON object again and thus calls can
148be chained:
149
150 my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]})
151 => {"a": [1, 2]}
152
153=item $json = $json->ascii ([$enable])
154
155If C<$enable> is true (or missing), then the C<encode> method will not
156generate characters outside the code range C<0..127> (which is ASCII). Any
157unicode characters outside that range will be escaped using either a
158single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence,
159as per RFC4627. The resulting encoded JSON text can be treated as a native
160unicode string, an ascii-encoded, latin1-encoded or UTF-8 encoded string,
161or any other superset of ASCII.
162
163If C<$enable> is false, then the C<encode> method will not escape Unicode
164characters unless required by the JSON syntax. This results in a faster
165and more compact format.
166
167 JSON::XS->new->ascii (1)->encode ([chr 0x10401])
168 => ["\ud801\udc01"]
169
170=item $json = $json->utf8 ([$enable])
171
172If C<$enable> is true (or missing), then the C<encode> method will encode
173the JSON result into UTF-8, as required by many protocols, while the
174C<decode> method expects to be handled an UTF-8-encoded string. Please
175note that UTF-8-encoded strings do not contain any characters outside the
176range C<0..255>, they are thus useful for bytewise/binary I/O. In future
177versions, enabling this option might enable autodetection of the UTF-16
178and UTF-32 encoding families, as described in RFC4627.
179
180If C<$enable> is false, then the C<encode> method will return the JSON
181string as a (non-encoded) unicode string, while C<decode> expects thus a
182unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs
183to be done yourself, e.g. using the Encode module.
184
185Example, output UTF-16BE-encoded JSON:
186
187 use Encode;
188 $jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
189
190Example, decode UTF-32LE-encoded JSON:
191
192 use Encode;
193 $object = JSON::XS->new->decode (decode "UTF-32LE", $jsontext);
194
195=item $json = $json->pretty ([$enable])
196
197This enables (or disables) all of the C<indent>, C<space_before> and
198C<space_after> (and in the future possibly more) flags in one call to
199generate the most readable (or most compact) form possible.
200
201Example, pretty-print some simple structure:
202
203 my $json = JSON::XS->new->pretty(1)->encode ({a => [1,2]})
204 =>
205 {
206 "a" : [
207 1,
208 2
209 ]
210 }
211
212=item $json = $json->indent ([$enable])
213
214If C<$enable> is true (or missing), then the C<encode> method will use a multiline
215format as output, putting every array member or object/hash key-value pair
216into its own line, identing them properly.
217
218If C<$enable> is false, no newlines or indenting will be produced, and the
219resulting JSON text is guarenteed not to contain any C<newlines>.
220
221This setting has no effect when decoding JSON texts.
222
223=item $json = $json->space_before ([$enable])
224
225If C<$enable> is true (or missing), then the C<encode> method will add an extra
226optional space before the C<:> separating keys from values in JSON objects.
227
228If C<$enable> is false, then the C<encode> method will not add any extra
229space at those places.
230
231This setting has no effect when decoding JSON texts. You will also
232most likely combine this setting with C<space_after>.
233
234Example, space_before enabled, space_after and indent disabled:
235
236 {"key" :"value"}
237
238=item $json = $json->space_after ([$enable])
239
240If C<$enable> is true (or missing), then the C<encode> method will add an extra
241optional space after the C<:> separating keys from values in JSON objects
242and extra whitespace after the C<,> separating key-value pairs and array
243members.
244
245If C<$enable> is false, then the C<encode> method will not add any extra
246space at those places.
247
248This setting has no effect when decoding JSON texts.
249
250Example, space_before and indent disabled, space_after enabled:
251
252 {"key": "value"}
253
254=item $json = $json->canonical ([$enable])
255
256If C<$enable> is true (or missing), then the C<encode> method will output JSON objects
257by sorting their keys. This is adding a comparatively high overhead.
258
259If C<$enable> is false, then the C<encode> method will output key-value
260pairs in the order Perl stores them (which will likely change between runs
261of the same script).
262
263This option is useful if you want the same data structure to be encoded as
264the same JSON text (given the same overall settings). If it is disabled,
265the same hash migh be encoded differently even if contains the same data,
266as key-value pairs have no inherent ordering in Perl.
267
268This setting has no effect when decoding JSON texts.
269
270=item $json = $json->allow_nonref ([$enable])
271
272If C<$enable> is true (or missing), then the C<encode> method can convert a
273non-reference into its corresponding string, number or null JSON value,
274which is an extension to RFC4627. Likewise, C<decode> will accept those JSON
275values instead of croaking.
276
277If C<$enable> is false, then the C<encode> method will croak if it isn't
278passed an arrayref or hashref, as JSON texts must either be an object
279or array. Likewise, C<decode> will croak if given something that is not a
280JSON object or array.
281
282Example, encode a Perl scalar as JSON value with enabled C<allow_nonref>,
283resulting in an invalid JSON text:
284
285 JSON::XS->new->allow_nonref->encode ("Hello, World!")
286 => "Hello, World!"
287
288=item $json = $json->shrink ([$enable])
289
290Perl usually over-allocates memory a bit when allocating space for
291strings. This flag optionally resizes strings generated by either
292C<encode> or C<decode> to their minimum size possible. This can save
293memory when your JSON texts are either very very long or you have many
294short strings. It will also try to downgrade any strings to octet-form
295if possible: perl stores strings internally either in an encoding called
296UTF-X or in octet-form. The latter cannot store everything but uses less
297space in general (and some buggy Perl or C code might even rely on that
298internal representation being used).
299
300The actual definition of what shrink does might change in future versions,
301but it will always try to save space at the expense of time.
302
303If C<$enable> is true (or missing), the string returned by C<encode> will
304be shrunk-to-fit, while all strings generated by C<decode> will also be
305shrunk-to-fit.
306
307If C<$enable> is false, then the normal perl allocation algorithms are used.
308If you work with your data, then this is likely to be faster.
309
310In the future, this setting might control other things, such as converting
311strings that look like integers or floats into integers or floats
312internally (there is no difference on the Perl level), saving space.
313
314=item $json = $json->max_depth ([$maximum_nesting_depth])
315
316Sets the maximum nesting level (default C<512>) accepted while encoding
317or decoding. If the JSON text or Perl data structure has an equal or
318higher nesting level then this limit, then the encoder and decoder will
319stop and croak at that point.
320
321Nesting level is defined by number of hash- or arrayrefs that the encoder
322needs to traverse to reach a given point or the number of C<{> or C<[>
323characters without their matching closing parenthesis crossed to reach a
324given character in a string.
325
326Setting the maximum depth to one disallows any nesting, so that ensures
327that the object is only a single hash/object or array.
328
329The argument to C<max_depth> will be rounded up to the next nearest power
330of two.
331
332See SECURITY CONSIDERATIONS, below, for more info on why this is useful.
333
334=item $json_text = $json->encode ($perl_scalar)
335
336Converts the given Perl data structure (a simple scalar or a reference
337to a hash or array) to its JSON representation. Simple scalars will be
338converted into JSON string or number sequences, while references to arrays
339become JSON arrays and references to hashes become JSON objects. Undefined
340Perl values (e.g. C<undef>) become JSON C<null> values. Neither C<true>
341nor C<false> values will be generated.
342
343=item $perl_scalar = $json->decode ($json_text)
344
345The opposite of C<encode>: expects a JSON text and tries to parse it,
346returning the resulting simple scalar or reference. Croaks on error.
347
348JSON numbers and strings become simple Perl scalars. JSON arrays become
349Perl arrayrefs and JSON objects become Perl hashrefs. C<true> becomes
350C<1>, C<false> becomes C<0> and C<null> becomes C<undef>.
351
352=back
353
354
355=head1 MAPPING
356
357This section describes how JSON::XS maps Perl values to JSON values and
358vice versa. These mappings are designed to "do the right thing" in most
359circumstances automatically, preserving round-tripping characteristics
360(what you put in comes out as something equivalent).
361
362For the more enlightened: note that in the following descriptions,
363lowercase I<perl> refers to the Perl interpreter, while uppcercase I<Perl>
364refers to the abstract Perl language itself.
365
366=head2 JSON -> PERL
367
368=over 4
369
370=item object
371
372A JSON object becomes a reference to a hash in Perl. No ordering of object
373keys is preserved (JSON does not preserver object key ordering itself).
374
375=item array
376
377A JSON array becomes a reference to an array in Perl.
378
379=item string
380
381A JSON string becomes a string scalar in Perl - Unicode codepoints in JSON
382are represented by the same codepoints in the Perl string, so no manual
383decoding is necessary.
384
385=item number
386
387A JSON number becomes either an integer or numeric (floating point)
388scalar in perl, depending on its range and any fractional parts. On the
389Perl level, there is no difference between those as Perl handles all the
390conversion details, but an integer may take slightly less memory and might
391represent more values exactly than (floating point) numbers.
392
393=item true, false
394
395These JSON atoms become C<0>, C<1>, respectively. Information is lost in
396this process. Future versions might represent those values differently,
397but they will be guarenteed to act like these integers would normally in
398Perl.
399
400=item null
401
402A JSON null atom becomes C<undef> in Perl.
403
404=back
405
406=head2 PERL -> JSON
407
408The mapping from Perl to JSON is slightly more difficult, as Perl is a
409truly typeless language, so we can only guess which JSON type is meant by
410a Perl value.
411
412=over 4
413
414=item hash references
415
416Perl hash references become JSON objects. As there is no inherent ordering
417in hash keys (or JSON objects), they will usually be encoded in a
418pseudo-random order that can change between runs of the same program but
419stays generally the same within a single run of a program. JSON::XS can
420optionally sort the hash keys (determined by the I<canonical> flag), so
421the same datastructure will serialise to the same JSON text (given same
422settings and version of JSON::XS), but this incurs a runtime overhead
423and is only rarely useful, e.g. when you want to compare some JSON text
424against another for equality.
425
426=item array references
427
428Perl array references become JSON arrays.
429
430=item other references
431
432Other unblessed references are generally not allowed and will cause an
433exception to be thrown, except for references to the integers C<0> and
434C<1>, which get turned into C<false> and C<true> atoms in JSON. You can
435also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability.
436
437 to_json [\0,JSON::XS::true] # yields [false,true]
438
439=item blessed objects
440
441Blessed objects are not allowed. JSON::XS currently tries to encode their
442underlying representation (hash- or arrayref), but this behaviour might
443change in future versions.
444
445=item simple scalars
446
447Simple Perl scalars (any scalar that is not a reference) are the most
448difficult objects to encode: JSON::XS will encode undefined scalars as
449JSON null value, scalars that have last been used in a string context
450before encoding as JSON strings and anything else as number value:
451
452 # dump as number
453 to_json [2] # yields [2]
454 to_json [-3.0e17] # yields [-3e+17]
455 my $value = 5; to_json [$value] # yields [5]
456
457 # used as string, so dump as string
458 print $value;
459 to_json [$value] # yields ["5"]
460
461 # undef becomes null
462 to_json [undef] # yields [null]
463
464You can force the type to be a string by stringifying it:
465
466 my $x = 3.1; # some variable containing a number
467 "$x"; # stringified
468 $x .= ""; # another, more awkward way to stringify
469 print $x; # perl does it for you, too, quite often
470
471You can force the type to be a number by numifying it:
472
473 my $x = "3"; # some variable containing a string
474 $x += 0; # numify it, ensuring it will be dumped as a number
475 $x *= 1; # same thing, the choise is yours.
476
477You can not currently output JSON booleans or force the type in other,
478less obscure, ways. Tell me if you need this capability.
479
480=back
481
482
483=head1 COMPARISON
484
485As already mentioned, this module was created because none of the existing
486JSON modules could be made to work correctly. First I will describe the
487problems (or pleasures) I encountered with various existing JSON modules,
488followed by some benchmark values. JSON::XS was designed not to suffer
489from any of these problems or limitations.
490
491=over 4
492
493=item JSON 1.07
494
495Slow (but very portable, as it is written in pure Perl).
496
497Undocumented/buggy Unicode handling (how JSON handles unicode values is
498undocumented. One can get far by feeding it unicode strings and doing
499en-/decoding oneself, but unicode escapes are not working properly).
500
501No roundtripping (strings get clobbered if they look like numbers, e.g.
502the string C<2.0> will encode to C<2.0> instead of C<"2.0">, and that will
503decode into the number 2.
504
505=item JSON::PC 0.01
506
507Very fast.
508
509Undocumented/buggy Unicode handling.
510
511No roundtripping.
512
513Has problems handling many Perl values (e.g. regex results and other magic
514values will make it croak).
515
516Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}>
517which is not a valid JSON text.
518
519Unmaintained (maintainer unresponsive for many months, bugs are not
520getting fixed).
521
522=item JSON::Syck 0.21
523
524Very buggy (often crashes).
525
526Very inflexible (no human-readable format supported, format pretty much
527undocumented. I need at least a format for easy reading by humans and a
528single-line compact format for use in a protocol, and preferably a way to
529generate ASCII-only JSON texts).
530
531Completely broken (and confusingly documented) Unicode handling (unicode
532escapes are not working properly, you need to set ImplicitUnicode to
533I<different> values on en- and decoding to get symmetric behaviour).
534
535No roundtripping (simple cases work, but this depends on wether the scalar
536value was used in a numeric context or not).
537
538Dumping hashes may skip hash values depending on iterator state.
539
540Unmaintained (maintainer unresponsive for many months, bugs are not
541getting fixed).
542
543Does not check input for validity (i.e. will accept non-JSON input and
544return "something" instead of raising an exception. This is a security
545issue: imagine two banks transfering money between each other using
546JSON. One bank might parse a given non-JSON request and deduct money,
547while the other might reject the transaction with a syntax error. While a
548good protocol will at least recover, that is extra unnecessary work and
549the transaction will still not succeed).
550
551=item JSON::DWIW 0.04
552
553Very fast. Very natural. Very nice.
554
555Undocumented unicode handling (but the best of the pack. Unicode escapes
556still don't get parsed properly).
557
558Very inflexible.
559
560No roundtripping.
561
562Does not generate valid JSON texts (key strings are often unquoted, empty keys
563result in nothing being output)
564
565Does not check input for validity.
566
567=back
568
569=head2 SPEED
570
571It seems that JSON::XS is surprisingly fast, as shown in the following
572tables. They have been generated with the help of the C<eg/bench> program
573in the JSON::XS distribution, to make it easy to compare on your own
574system.
575
576First comes a comparison between various modules using a very short JSON
577string:
578
579 {"method": "handleMessage", "params": ["user1", "we were just talking"], "id": null}
580
581It shows the number of encodes/decodes per second (JSON::XS uses the
582functional interface, while JSON::XS/2 uses the OO interface with
583pretty-printing and hashkey sorting enabled). Higher is better:
584
585 module | encode | decode |
586 -----------|------------|------------|
587 JSON | 11488.516 | 7823.035 |
588 JSON::DWIW | 94708.054 | 129094.260 |
589 JSON::PC | 63884.157 | 128528.212 |
590 JSON::Syck | 34898.677 | 42096.911 |
591 JSON::XS | 654027.064 | 396423.669 |
592 JSON::XS/2 | 371564.190 | 371725.613 |
593 -----------+------------+------------+
594
595That is, JSON::XS is more than six times faster than JSON::DWIW on
596encoding, more than three times faster on decoding, and about thirty times
597faster than JSON, even with pretty-printing and key sorting.
598
599Using a longer test string (roughly 18KB, generated from Yahoo! Locals
600search API (http://nanoref.com/yahooapis/mgPdGg):
601
602 module | encode | decode |
603 -----------|------------|------------|
604 JSON | 273.023 | 44.674 |
605 JSON::DWIW | 1089.383 | 1145.704 |
606 JSON::PC | 3097.419 | 2393.921 |
607 JSON::Syck | 514.060 | 843.053 |
608 JSON::XS | 6479.668 | 3636.364 |
609 JSON::XS/2 | 3774.221 | 3599.124 |
610 -----------+------------+------------+
611
612Again, JSON::XS leads by far.
613
614On large strings containing lots of high unicode characters, some modules
615(such as JSON::PC) seem to decode faster than JSON::XS, but the result
616will be broken due to missing (or wrong) unicode handling. Others refuse
617to decode or encode properly, so it was impossible to prepare a fair
618comparison table for that case.
619
620
621=head1 SECURITY CONSIDERATIONS
622
623When you are using JSON in a protocol, talking to untrusted potentially
624hostile creatures requires relatively few measures.
625
626First of all, your JSON decoder should be secure, that is, should not have
627any buffer overflows. Obviously, this module should ensure that and I am
628trying hard on making that true, but you never know.
629
630Second, you need to avoid resource-starving attacks. That means you should
631limit the size of JSON texts you accept, or make sure then when your
632resources run out, thats just fine (e.g. by using a separate process that
633can crash safely). The size of a JSON text in octets or characters is
634usually a good indication of the size of the resources required to decode
635it into a Perl structure.
636
637Third, JSON::XS recurses using the C stack when decoding objects and
638arrays. The C stack is a limited resource: for instance, on my amd64
639machine with 8MB of stack size I can decode around 180k nested arrays but
640only 14k nested JSON objects (due to perl itself recursing deeply on croak
641to free the temporary). If that is exceeded, the program crashes. to be
642conservative, the default nesting limit is set to 512. If your process
643has a smaller stack, you should adjust this setting accordingly with the
644C<max_depth> method.
645
646And last but least, something else could bomb you that I forgot to think
647of. In that case, you get to keep the pieces. I am always open for hints,
648though...
649
650
651=head1 BUGS
652
653While the goal of this module is to be correct, that unfortunately does
654not mean its bug-free, only that I think its design is bug-free. It is
655still relatively early in its development. If you keep reporting bugs they
656will be fixed swiftly, though.
28 657
29=cut 658=cut
30 659
31use JSON::DWIW; 660sub true() { \1 }
32use Benchmark; 661sub false() { \0 }
33
34use utf8;
35#my $json = '{"ü":1,"a":[1,{"3":4},2],"b":5,"üü":2}';
36my $json = '{"test":9555555555555555555,"hu" : -1e+5, "arr" : [ 1,2,3,4,5]}';
37
38my $js = JSON::XS->new;
39warn $js->indent (0);
40warn $js->canonical (0);
41warn $js->ascii (0);
42warn $js->space_after (0);
43use Data::Dumper;
44warn Dumper $js->decode ($json);
45warn Dumper $js->encode ($js->decode ($json));
46#my $x = {"üü" => 2, "ü" => 1, "a" => [1,{3,4},2], b => 5};
47
48#my $js2 = JSON::DWIW->new;
49#
50#timethese 200000, {
51# a => sub { $js->encode ($x) },
52# b => sub { $js2->to_json ($x) },
53#};
54 662
551; 6631;
56
57=back
58 664
59=head1 AUTHOR 665=head1 AUTHOR
60 666
61 Marc Lehmann <schmorp@schmorp.de> 667 Marc Lehmann <schmorp@schmorp.de>
62 http://home.schmorp.de/ 668 http://home.schmorp.de/

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