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1NAME 1NAME
2 JSON::XS - JSON serialising/deserialising, done correctly and fast 2 JSON::XS - JSON serialising/deserialising, done correctly and fast
3 3
4 JSON::XS - 正しくて高速な JSON
5 シリアライザ/デシリアライザ
6 (http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html)
7
4SYNOPSIS 8SYNOPSIS
5 use JSON::XS; 9 use JSON::XS;
10
11 # exported functions, they croak on error
12 # and expect/generate UTF-8
13
14 $utf8_encoded_json_text = to_json $perl_hash_or_arrayref;
15 $perl_hash_or_arrayref = from_json $utf8_encoded_json_text;
16
17 # OO-interface
18
19 $coder = JSON::XS->new->ascii->pretty->allow_nonref;
20 $pretty_printed_unencoded = $coder->encode ($perl_scalar);
21 $perl_scalar = $coder->decode ($unicode_json_text);
6 22
7DESCRIPTION 23DESCRIPTION
8 This module converts Perl data structures to JSON and vice versa. Its 24 This module converts Perl data structures to JSON and vice versa. Its
9 primary goal is to be *correct* and its secondary goal is to be *fast*. 25 primary goal is to be *correct* and its secondary goal is to be *fast*.
10 To reach the latter goal it was written in C. 26 To reach the latter goal it was written in C.
… …
15 cases their maintainers are unresponsive, gone missing, or not listening 31 cases their maintainers are unresponsive, gone missing, or not listening
16 to bug reports for other reasons. 32 to bug reports for other reasons.
17 33
18 See COMPARISON, below, for a comparison to some other JSON modules. 34 See COMPARISON, below, for a comparison to some other JSON modules.
19 35
36 See MAPPING, below, on how JSON::XS maps perl values to JSON values and
37 vice versa.
38
20 FEATURES 39 FEATURES
21 * correct handling of unicode issues 40 * correct unicode handling
22 This module knows how to handle Unicode, and even documents how it 41 This module knows how to handle Unicode, and even documents how and
23 does so. 42 when it does so.
24 43
25 * round-trip integrity 44 * round-trip integrity
26 When you serialise a perl data structure using only datatypes 45 When you serialise a perl data structure using only datatypes
27 supported by JSON, the deserialised data structure is identical on 46 supported by JSON, the deserialised data structure is identical on
28 the Perl level. (e.g. the string "2.0" doesn't suddenly become "2"). 47 the Perl level. (e.g. the string "2.0" doesn't suddenly become "2"
48 just because it looks like a number).
29 49
30 * strict checking of JSON correctness 50 * strict checking of JSON correctness
31 There is no guessing, no generating of illegal JSON strings by 51 There is no guessing, no generating of illegal JSON texts by
32 default, and only JSON is accepted as input (the latter is a 52 default, and only JSON is accepted as input by default (the latter
33 security feature). 53 is a security feature).
34 54
35 * fast 55 * fast
36 compared to other JSON modules, this module compares favourably. 56 Compared to other JSON modules, this module compares favourably in
57 terms of speed, too.
37 58
38 * simple to use 59 * simple to use
39 This module has both a simple functional interface as well as an OO 60 This module has both a simple functional interface as well as an OO
40 interface. 61 interface.
41 62
42 * reasonably versatile output formats 63 * reasonably versatile output formats
43 You can choose between the most compact format possible, a 64 You can choose between the most compact guarenteed single-line
44 pure-ascii format, or a pretty-printed format. Or you can combine 65 format possible (nice for simple line-based protocols), a pure-ascii
66 format (for when your transport is not 8-bit clean, still supports
67 the whole unicode range), or a pretty-printed format (for when you
68 want to read that stuff). Or you can combine those features in
45 those features in whatever way you like. 69 whatever way you like.
46 70
47FUNCTIONAL INTERFACE 71FUNCTIONAL INTERFACE
48 The following convinience methods are provided by this module. They are 72 The following convinience methods are provided by this module. They are
49 exported by default: 73 exported by default:
50 74
51 $json_string = to_json $perl_scalar 75 $json_text = to_json $perl_scalar
52 Converts the given Perl data structure (a simple scalar or a 76 Converts the given Perl data structure to a UTF-8 encoded, binary
53 reference to a hash or array) to a UTF-8 encoded, binary string
54 (that is, the string contains octets only). Croaks on error. 77 string (that is, the string contains octets only). Croaks on error.
55 78
56 This function call is functionally identical to "JSON::XS->new->utf8 79 This function call is functionally identical to:
57 (1)->encode ($perl_scalar)".
58 80
81 $json_text = JSON::XS->new->utf8->encode ($perl_scalar)
82
83 except being faster.
84
59 $perl_scalar = from_json $json_string 85 $perl_scalar = from_json $json_text
60 The opposite of "to_json": expects an UTF-8 (binary) string and 86 The opposite of "to_json": expects an UTF-8 (binary) string and
61 tries to parse that as an UTF-8 encoded JSON string, returning the 87 tries to parse that as an UTF-8 encoded JSON text, returning the
62 resulting simple scalar or reference. Croaks on error. 88 resulting reference. Croaks on error.
63 89
64 This function call is functionally identical to "JSON::XS->new->utf8 90 This function call is functionally identical to:
65 (1)->decode ($json_string)". 91
92 $perl_scalar = JSON::XS->new->utf8->decode ($json_text)
93
94 except being faster.
95
96 $is_boolean = JSON::XS::is_bool $scalar
97 Returns true if the passed scalar represents either JSON::XS::true
98 or JSON::XS::false, two constants that act like 1 and 0,
99 respectively and are used to represent JSON "true" and "false"
100 values in Perl.
101
102 See MAPPING, below, for more information on how JSON values are
103 mapped to Perl.
104
105A FEW NOTES ON UNICODE AND PERL
106 Since this often leads to confusion, here are a few very clear words on
107 how Unicode works in Perl, modulo bugs.
108
109 1. Perl strings can store characters with ordinal values > 255.
110 This enables you to store unicode characters as single characters in
111 a Perl string - very natural.
112
113 2. Perl does *not* associate an encoding with your strings.
114 Unless you force it to, e.g. when matching it against a regex, or
115 printing the scalar to a file, in which case Perl either interprets
116 your string as locale-encoded text, octets/binary, or as Unicode,
117 depending on various settings. In no case is an encoding stored
118 together with your data, it is *use* that decides encoding, not any
119 magical metadata.
120
121 3. The internal utf-8 flag has no meaning with regards to the encoding
122 of your string.
123 Just ignore that flag unless you debug a Perl bug, a module written
124 in XS or want to dive into the internals of perl. Otherwise it will
125 only confuse you, as, despite the name, it says nothing about how
126 your string is encoded. You can have unicode strings with that flag
127 set, with that flag clear, and you can have binary data with that
128 flag set and that flag clear. Other possibilities exist, too.
129
130 If you didn't know about that flag, just the better, pretend it
131 doesn't exist.
132
133 4. A "Unicode String" is simply a string where each character can be
134 validly interpreted as a Unicode codepoint.
135 If you have UTF-8 encoded data, it is no longer a Unicode string,
136 but a Unicode string encoded in UTF-8, giving you a binary string.
137
138 5. A string containing "high" (> 255) character values is *not* a UTF-8
139 string.
140 Its a fact. Learn to live with it.
141
142 I hope this helps :)
66 143
67OBJECT-ORIENTED INTERFACE 144OBJECT-ORIENTED INTERFACE
68 The object oriented interface lets you configure your own encoding or 145 The object oriented interface lets you configure your own encoding or
69 decoding style, within the limits of supported formats. 146 decoding style, within the limits of supported formats.
70 147
… …
74 *disabled*. 151 *disabled*.
75 152
76 The mutators for flags all return the JSON object again and thus 153 The mutators for flags all return the JSON object again and thus
77 calls can be chained: 154 calls can be chained:
78 155
79 my $json = JSON::XS->new->utf8(1)->space_after(1)->encode ({a => [1,2]}) 156 my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]})
80 => {"a": [1, 2]} 157 => {"a": [1, 2]}
81 158
82 $json = $json->ascii ($enable) 159 $json = $json->ascii ([$enable])
83 If $enable is true, then the "encode" method will not generate 160 If $enable is true (or missing), then the "encode" method will not
84 characters outside the code range 0..127. Any unicode characters 161 generate characters outside the code range 0..127 (which is ASCII).
85 outside that range will be escaped using either a single \uXXXX (BMP 162 Any unicode characters outside that range will be escaped using
86 characters) or a double \uHHHH\uLLLLL escape sequence, as per 163 either a single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL
87 RFC4627. 164 escape sequence, as per RFC4627. The resulting encoded JSON text can
165 be treated as a native unicode string, an ascii-encoded,
166 latin1-encoded or UTF-8 encoded string, or any other superset of
167 ASCII.
88 168
89 If $enable is false, then the "encode" method will not escape 169 If $enable is false, then the "encode" method will not escape
90 Unicode characters unless necessary. 170 Unicode characters unless required by the JSON syntax or other
171 flags. This results in a faster and more compact format.
91 172
173 The main use for this flag is to produce JSON texts that can be
174 transmitted over a 7-bit channel, as the encoded JSON texts will not
175 contain any 8 bit characters.
176
92 JSON::XS->new->ascii (1)->encode (chr 0x10401) 177 JSON::XS->new->ascii (1)->encode ([chr 0x10401])
93 => \ud801\udc01 178 => ["\ud801\udc01"]
94 179
180 $json = $json->latin1 ([$enable])
181 If $enable is true (or missing), then the "encode" method will
182 encode the resulting JSON text as latin1 (or iso-8859-1), escaping
183 any characters outside the code range 0..255. The resulting string
184 can be treated as a latin1-encoded JSON text or a native unicode
185 string. The "decode" method will not be affected in any way by this
186 flag, as "decode" by default expects unicode, which is a strict
187 superset of latin1.
188
189 If $enable is false, then the "encode" method will not escape
190 Unicode characters unless required by the JSON syntax or other
191 flags.
192
193 The main use for this flag is efficiently encoding binary data as
194 JSON text, as most octets will not be escaped, resulting in a
195 smaller encoded size. The disadvantage is that the resulting JSON
196 text is encoded in latin1 (and must correctly be treated as such
197 when storing and transfering), a rare encoding for JSON. It is
198 therefore most useful when you want to store data structures known
199 to contain binary data efficiently in files or databases, not when
200 talking to other JSON encoders/decoders.
201
202 JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]
203 => ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)
204
95 $json = $json->utf8 ($enable) 205 $json = $json->utf8 ([$enable])
96 If $enable is true, then the "encode" method will encode the JSON 206 If $enable is true (or missing), then the "encode" method will
97 string into UTF-8, as required by many protocols, while the "decode" 207 encode the JSON result into UTF-8, as required by many protocols,
98 method expects to be handled an UTF-8-encoded string. Please note 208 while the "decode" method expects to be handled an UTF-8-encoded
99 that UTF-8-encoded strings do not contain any characters outside the 209 string. Please note that UTF-8-encoded strings do not contain any
100 range 0..255, they are thus useful for bytewise/binary I/O. 210 characters outside the range 0..255, they are thus useful for
211 bytewise/binary I/O. In future versions, enabling this option might
212 enable autodetection of the UTF-16 and UTF-32 encoding families, as
213 described in RFC4627.
101 214
102 If $enable is false, then the "encode" method will return the JSON 215 If $enable is false, then the "encode" method will return the JSON
103 string as a (non-encoded) unicode string, while "decode" expects 216 string as a (non-encoded) unicode string, while "decode" expects
104 thus a unicode string. Any decoding or encoding (e.g. to UTF-8 or 217 thus a unicode string. Any decoding or encoding (e.g. to UTF-8 or
105 UTF-16) needs to be done yourself, e.g. using the Encode module. 218 UTF-16) needs to be done yourself, e.g. using the Encode module.
106 219
220 Example, output UTF-16BE-encoded JSON:
221
222 use Encode;
223 $jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
224
225 Example, decode UTF-32LE-encoded JSON:
226
227 use Encode;
228 $object = JSON::XS->new->decode (decode "UTF-32LE", $jsontext);
229
107 $json = $json->pretty ($enable) 230 $json = $json->pretty ([$enable])
108 This enables (or disables) all of the "indent", "space_before" and 231 This enables (or disables) all of the "indent", "space_before" and
109 "space_after" (and in the future possibly more) flags in one call to 232 "space_after" (and in the future possibly more) flags in one call to
110 generate the most readable (or most compact) form possible. 233 generate the most readable (or most compact) form possible.
234
235 Example, pretty-print some simple structure:
111 236
112 my $json = JSON::XS->new->pretty(1)->encode ({a => [1,2]}) 237 my $json = JSON::XS->new->pretty(1)->encode ({a => [1,2]})
113 => 238 =>
114 { 239 {
115 "a" : [ 240 "a" : [
116 1, 241 1,
117 2 242 2
118 ] 243 ]
119 } 244 }
120 245
121 $json = $json->indent ($enable) 246 $json = $json->indent ([$enable])
122 If $enable is true, then the "encode" method will use a multiline 247 If $enable is true (or missing), then the "encode" method will use a
123 format as output, putting every array member or object/hash 248 multiline format as output, putting every array member or
124 key-value pair into its own line, identing them properly. 249 object/hash key-value pair into its own line, identing them
250 properly.
125 251
126 If $enable is false, no newlines or indenting will be produced, and 252 If $enable is false, no newlines or indenting will be produced, and
127 the resulting JSON strings is guarenteed not to contain any 253 the resulting JSON text is guarenteed not to contain any "newlines".
128 "newlines".
129 254
130 This setting has no effect when decoding JSON strings. 255 This setting has no effect when decoding JSON texts.
131 256
132 $json = $json->space_before ($enable) 257 $json = $json->space_before ([$enable])
133 If $enable is true, then the "encode" method will add an extra 258 If $enable is true (or missing), then the "encode" method will add
134 optional space before the ":" separating keys from values in JSON 259 an extra optional space before the ":" separating keys from values
135 objects. 260 in JSON objects.
136 261
137 If $enable is false, then the "encode" method will not add any extra 262 If $enable is false, then the "encode" method will not add any extra
138 space at those places. 263 space at those places.
139 264
140 This setting has no effect when decoding JSON strings. You will also 265 This setting has no effect when decoding JSON texts. You will also
141 most likely combine this setting with "space_after". 266 most likely combine this setting with "space_after".
142 267
268 Example, space_before enabled, space_after and indent disabled:
269
270 {"key" :"value"}
271
143 $json = $json->space_after ($enable) 272 $json = $json->space_after ([$enable])
144 If $enable is true, then the "encode" method will add an extra 273 If $enable is true (or missing), then the "encode" method will add
145 optional space after the ":" separating keys from values in JSON 274 an extra optional space after the ":" separating keys from values in
146 objects and extra whitespace after the "," separating key-value 275 JSON objects and extra whitespace after the "," separating key-value
147 pairs and array members. 276 pairs and array members.
148 277
149 If $enable is false, then the "encode" method will not add any extra 278 If $enable is false, then the "encode" method will not add any extra
150 space at those places. 279 space at those places.
151 280
152 This setting has no effect when decoding JSON strings. 281 This setting has no effect when decoding JSON texts.
153 282
283 Example, space_before and indent disabled, space_after enabled:
284
285 {"key": "value"}
286
287 $json = $json->relaxed ([$enable])
288 If $enable is true (or missing), then "decode" will accept some
289 extensions to normal JSON syntax (see below). "encode" will not be
290 affected in anyway. *Be aware that this option makes you accept
291 invalid JSON texts as if they were valid!*. I suggest only to use
292 this option to parse application-specific files written by humans
293 (configuration files, resource files etc.)
294
295 If $enable is false (the default), then "decode" will only accept
296 valid JSON texts.
297
298 Currently accepted extensions are:
299
300 * list items can have an end-comma
301 JSON *separates* array elements and key-value pairs with commas.
302 This can be annoying if you write JSON texts manually and want
303 to be able to quickly append elements, so this extension accepts
304 comma at the end of such items not just between them:
305
306 [
307 1,
308 2, <- this comma not normally allowed
309 ]
310 {
311 "k1": "v1",
312 "k2": "v2", <- this comma not normally allowed
313 }
314
315 * shell-style '#'-comments
316 Whenever JSON allows whitespace, shell-style comments are
317 additionally allowed. They are terminated by the first
318 carriage-return or line-feed character, after which more
319 white-space and comments are allowed.
320
321 [
322 1, # this comment not allowed in JSON
323 # neither this one...
324 ]
325
154 $json = $json->canonical ($enable) 326 $json = $json->canonical ([$enable])
155 If $enable is true, then the "encode" method will output JSON 327 If $enable is true (or missing), then the "encode" method will
156 objects by sorting their keys. This is adding a comparatively high 328 output JSON objects by sorting their keys. This is adding a
157 overhead. 329 comparatively high overhead.
158 330
159 If $enable is false, then the "encode" method will output key-value 331 If $enable is false, then the "encode" method will output key-value
160 pairs in the order Perl stores them (which will likely change 332 pairs in the order Perl stores them (which will likely change
161 between runs of the same script). 333 between runs of the same script).
162 334
163 This option is useful if you want the same data structure to be 335 This option is useful if you want the same data structure to be
164 encoded as the same JSON string (given the same overall settings). 336 encoded as the same JSON text (given the same overall settings). If
165 If it is disabled, the same hash migh be encoded differently even if 337 it is disabled, the same hash migh be encoded differently even if
166 contains the same data, as key-value pairs have no inherent ordering 338 contains the same data, as key-value pairs have no inherent ordering
167 in Perl. 339 in Perl.
168 340
169 This setting has no effect when decoding JSON strings. 341 This setting has no effect when decoding JSON texts.
170 342
171 $json = $json->allow_nonref ($enable) 343 $json = $json->allow_nonref ([$enable])
172 If $enable is true, then the "encode" method can convert a 344 If $enable is true (or missing), then the "encode" method can
173 non-reference into its corresponding string, number or null JSON 345 convert a non-reference into its corresponding string, number or
174 value, which is an extension to RFC4627. Likewise, "decode" will 346 null JSON value, which is an extension to RFC4627. Likewise,
175 accept those JSON values instead of croaking. 347 "decode" will accept those JSON values instead of croaking.
176 348
177 If $enable is false, then the "encode" method will croak if it isn't 349 If $enable is false, then the "encode" method will croak if it isn't
178 passed an arrayref or hashref, as JSON strings must either be an 350 passed an arrayref or hashref, as JSON texts must either be an
179 object or array. Likewise, "decode" will croak if given something 351 object or array. Likewise, "decode" will croak if given something
180 that is not a JSON object or array. 352 that is not a JSON object or array.
181 353
354 Example, encode a Perl scalar as JSON value with enabled
355 "allow_nonref", resulting in an invalid JSON text:
356
357 JSON::XS->new->allow_nonref->encode ("Hello, World!")
358 => "Hello, World!"
359
360 $json = $json->allow_blessed ([$enable])
361 If $enable is true (or missing), then the "encode" method will not
362 barf when it encounters a blessed reference. Instead, the value of
363 the convert_blessed option will decide wether "null"
364 ("convert_blessed" disabled or no "to_json" method found) or a
365 representation of the object ("convert_blessed" enabled and
366 "to_json" method found) is being encoded. Has no effect on "decode".
367
368 If $enable is false (the default), then "encode" will throw an
369 exception when it encounters a blessed object.
370
371 $json = $json->convert_blessed ([$enable])
372 If $enable is true (or missing), then "encode", upon encountering a
373 blessed object, will check for the availability of the "TO_JSON"
374 method on the object's class. If found, it will be called in scalar
375 context and the resulting scalar will be encoded instead of the
376 object. If no "TO_JSON" method is found, the value of
377 "allow_blessed" will decide what to do.
378
379 The "TO_JSON" method may safely call die if it wants. If "TO_JSON"
380 returns other blessed objects, those will be handled in the same
381 way. "TO_JSON" must take care of not causing an endless recursion
382 cycle (== crash) in this case. The name of "TO_JSON" was chosen
383 because other methods called by the Perl core (== not by the user of
384 the object) are usually in upper case letters and to avoid
385 collisions with the "to_json" function.
386
387 This setting does not yet influence "decode" in any way, but in the
388 future, global hooks might get installed that influence "decode" and
389 are enabled by this setting.
390
391 If $enable is false, then the "allow_blessed" setting will decide
392 what to do when a blessed object is found.
393
394 $json = $json->filter_json_object ([$coderef->($hashref)])
395 When $coderef is specified, it will be called from "decode" each
396 time it decodes a JSON object. The only argument is a reference to
397 the newly-created hash. If the code references returns a single
398 scalar (which need not be a reference), this value (i.e. a copy of
399 that scalar to avoid aliasing) is inserted into the deserialised
400 data structure. If it returns an empty list (NOTE: *not* "undef",
401 which is a valid scalar), the original deserialised hash will be
402 inserted. This setting can slow down decoding considerably.
403
404 When $coderef is omitted or undefined, any existing callback will be
405 removed and "decode" will not change the deserialised hash in any
406 way.
407
408 Example, convert all JSON objects into the integer 5:
409
410 my $js = JSON::XS->new->filter_json_object (sub { 5 });
411 # returns [5]
412 $js->decode ('[{}]')
413 # throw an exception because allow_nonref is not enabled
414 # so a lone 5 is not allowed.
415 $js->decode ('{"a":1, "b":2}');
416
417 $json = $json->filter_json_single_key_object ($key [=>
418 $coderef->($value)])
419 Works remotely similar to "filter_json_object", but is only called
420 for JSON objects having a single key named $key.
421
422 This $coderef is called before the one specified via
423 "filter_json_object", if any. It gets passed the single value in the
424 JSON object. If it returns a single value, it will be inserted into
425 the data structure. If it returns nothing (not even "undef" but the
426 empty list), the callback from "filter_json_object" will be called
427 next, as if no single-key callback were specified.
428
429 If $coderef is omitted or undefined, the corresponding callback will
430 be disabled. There can only ever be one callback for a given key.
431
432 As this callback gets called less often then the
433 "filter_json_object" one, decoding speed will not usually suffer as
434 much. Therefore, single-key objects make excellent targets to
435 serialise Perl objects into, especially as single-key JSON objects
436 are as close to the type-tagged value concept as JSON gets (its
437 basically an ID/VALUE tuple). Of course, JSON does not support this
438 in any way, so you need to make sure your data never looks like a
439 serialised Perl hash.
440
441 Typical names for the single object key are "__class_whatever__", or
442 "$__dollars_are_rarely_used__$" or "}ugly_brace_placement", or even
443 things like "__class_md5sum(classname)__", to reduce the risk of
444 clashing with real hashes.
445
446 Example, decode JSON objects of the form "{ "__widget__" => <id> }"
447 into the corresponding $WIDGET{<id>} object:
448
449 # return whatever is in $WIDGET{5}:
450 JSON::XS
451 ->new
452 ->filter_json_single_key_object (__widget__ => sub {
453 $WIDGET{ $_[0] }
454 })
455 ->decode ('{"__widget__": 5')
456
457 # this can be used with a TO_JSON method in some "widget" class
458 # for serialisation to json:
459 sub WidgetBase::TO_JSON {
460 my ($self) = @_;
461
462 unless ($self->{id}) {
463 $self->{id} = ..get..some..id..;
464 $WIDGET{$self->{id}} = $self;
465 }
466
467 { __widget__ => $self->{id} }
468 }
469
470 $json = $json->shrink ([$enable])
471 Perl usually over-allocates memory a bit when allocating space for
472 strings. This flag optionally resizes strings generated by either
473 "encode" or "decode" to their minimum size possible. This can save
474 memory when your JSON texts are either very very long or you have
475 many short strings. It will also try to downgrade any strings to
476 octet-form if possible: perl stores strings internally either in an
477 encoding called UTF-X or in octet-form. The latter cannot store
478 everything but uses less space in general (and some buggy Perl or C
479 code might even rely on that internal representation being used).
480
481 The actual definition of what shrink does might change in future
482 versions, but it will always try to save space at the expense of
483 time.
484
485 If $enable is true (or missing), the string returned by "encode"
486 will be shrunk-to-fit, while all strings generated by "decode" will
487 also be shrunk-to-fit.
488
489 If $enable is false, then the normal perl allocation algorithms are
490 used. If you work with your data, then this is likely to be faster.
491
492 In the future, this setting might control other things, such as
493 converting strings that look like integers or floats into integers
494 or floats internally (there is no difference on the Perl level),
495 saving space.
496
497 $json = $json->max_depth ([$maximum_nesting_depth])
498 Sets the maximum nesting level (default 512) accepted while encoding
499 or decoding. If the JSON text or Perl data structure has an equal or
500 higher nesting level then this limit, then the encoder and decoder
501 will stop and croak at that point.
502
503 Nesting level is defined by number of hash- or arrayrefs that the
504 encoder needs to traverse to reach a given point or the number of
505 "{" or "[" characters without their matching closing parenthesis
506 crossed to reach a given character in a string.
507
508 Setting the maximum depth to one disallows any nesting, so that
509 ensures that the object is only a single hash/object or array.
510
511 The argument to "max_depth" will be rounded up to the next highest
512 power of two. If no argument is given, the highest possible setting
513 will be used, which is rarely useful.
514
515 See SECURITY CONSIDERATIONS, below, for more info on why this is
516 useful.
517
518 $json = $json->max_size ([$maximum_string_size])
519 Set the maximum length a JSON text may have (in bytes) where
520 decoding is being attempted. The default is 0, meaning no limit.
521 When "decode" is called on a string longer then this number of
522 characters it will not attempt to decode the string but throw an
523 exception. This setting has no effect on "encode" (yet).
524
525 The argument to "max_size" will be rounded up to the next highest
526 power of two (so may be more than requested). If no argument is
527 given, the limit check will be deactivated (same as when 0 is
528 specified).
529
530 See SECURITY CONSIDERATIONS, below, for more info on why this is
531 useful.
532
182 $json_string = $json->encode ($perl_scalar) 533 $json_text = $json->encode ($perl_scalar)
183 Converts the given Perl data structure (a simple scalar or a 534 Converts the given Perl data structure (a simple scalar or a
184 reference to a hash or array) to its JSON representation. Simple 535 reference to a hash or array) to its JSON representation. Simple
185 scalars will be converted into JSON string or number sequences, 536 scalars will be converted into JSON string or number sequences,
186 while references to arrays become JSON arrays and references to 537 while references to arrays become JSON arrays and references to
187 hashes become JSON objects. Undefined Perl values (e.g. "undef") 538 hashes become JSON objects. Undefined Perl values (e.g. "undef")
188 become JSON "null" values. Neither "true" nor "false" values will be 539 become JSON "null" values. Neither "true" nor "false" values will be
189 generated. 540 generated.
190 541
191 $perl_scalar = $json->decode ($json_string) 542 $perl_scalar = $json->decode ($json_text)
192 The opposite of "encode": expects a JSON string and tries to parse 543 The opposite of "encode": expects a JSON text and tries to parse it,
193 it, returning the resulting simple scalar or reference. Croaks on 544 returning the resulting simple scalar or reference. Croaks on error.
194 error.
195 545
196 JSON numbers and strings become simple Perl scalars. JSON arrays 546 JSON numbers and strings become simple Perl scalars. JSON arrays
197 become Perl arrayrefs and JSON objects become Perl hashrefs. "true" 547 become Perl arrayrefs and JSON objects become Perl hashrefs. "true"
198 becomes 1, "false" becomes 0 and "null" becomes "undef". 548 becomes 1, "false" becomes 0 and "null" becomes "undef".
549
550 ($perl_scalar, $characters) = $json->decode_prefix ($json_text)
551 This works like the "decode" method, but instead of raising an
552 exception when there is trailing garbage after the first JSON
553 object, it will silently stop parsing there and return the number of
554 characters consumed so far.
555
556 This is useful if your JSON texts are not delimited by an outer
557 protocol (which is not the brightest thing to do in the first place)
558 and you need to know where the JSON text ends.
559
560 JSON::XS->new->decode_prefix ("[1] the tail")
561 => ([], 3)
562
563MAPPING
564 This section describes how JSON::XS maps Perl values to JSON values and
565 vice versa. These mappings are designed to "do the right thing" in most
566 circumstances automatically, preserving round-tripping characteristics
567 (what you put in comes out as something equivalent).
568
569 For the more enlightened: note that in the following descriptions,
570 lowercase *perl* refers to the Perl interpreter, while uppcercase *Perl*
571 refers to the abstract Perl language itself.
572
573 JSON -> PERL
574 object
575 A JSON object becomes a reference to a hash in Perl. No ordering of
576 object keys is preserved (JSON does not preserver object key
577 ordering itself).
578
579 array
580 A JSON array becomes a reference to an array in Perl.
581
582 string
583 A JSON string becomes a string scalar in Perl - Unicode codepoints
584 in JSON are represented by the same codepoints in the Perl string,
585 so no manual decoding is necessary.
586
587 number
588 A JSON number becomes either an integer, numeric (floating point) or
589 string scalar in perl, depending on its range and any fractional
590 parts. On the Perl level, there is no difference between those as
591 Perl handles all the conversion details, but an integer may take
592 slightly less memory and might represent more values exactly than
593 (floating point) numbers.
594
595 If the number consists of digits only, JSON::XS will try to
596 represent it as an integer value. If that fails, it will try to
597 represent it as a numeric (floating point) value if that is possible
598 without loss of precision. Otherwise it will preserve the number as
599 a string value.
600
601 Numbers containing a fractional or exponential part will always be
602 represented as numeric (floating point) values, possibly at a loss
603 of precision.
604
605 This might create round-tripping problems as numbers might become
606 strings, but as Perl is typeless there is no other way to do it.
607
608 true, false
609 These JSON atoms become "JSON::XS::true" and "JSON::XS::false",
610 respectively. They are overloaded to act almost exactly like the
611 numbers 1 and 0. You can check wether a scalar is a JSON boolean by
612 using the "JSON::XS::is_bool" function.
613
614 null
615 A JSON null atom becomes "undef" in Perl.
616
617 PERL -> JSON
618 The mapping from Perl to JSON is slightly more difficult, as Perl is a
619 truly typeless language, so we can only guess which JSON type is meant
620 by a Perl value.
621
622 hash references
623 Perl hash references become JSON objects. As there is no inherent
624 ordering in hash keys (or JSON objects), they will usually be
625 encoded in a pseudo-random order that can change between runs of the
626 same program but stays generally the same within a single run of a
627 program. JSON::XS can optionally sort the hash keys (determined by
628 the *canonical* flag), so the same datastructure will serialise to
629 the same JSON text (given same settings and version of JSON::XS),
630 but this incurs a runtime overhead and is only rarely useful, e.g.
631 when you want to compare some JSON text against another for
632 equality.
633
634 array references
635 Perl array references become JSON arrays.
636
637 other references
638 Other unblessed references are generally not allowed and will cause
639 an exception to be thrown, except for references to the integers 0
640 and 1, which get turned into "false" and "true" atoms in JSON. You
641 can also use "JSON::XS::false" and "JSON::XS::true" to improve
642 readability.
643
644 to_json [\0,JSON::XS::true] # yields [false,true]
645
646 JSON::XS::true, JSON::XS::false
647 These special values become JSON true and JSON false values,
648 respectively. You can also use "\1" and "\0" directly if you want.
649
650 blessed objects
651 Blessed objects are not allowed. JSON::XS currently tries to encode
652 their underlying representation (hash- or arrayref), but this
653 behaviour might change in future versions.
654
655 simple scalars
656 Simple Perl scalars (any scalar that is not a reference) are the
657 most difficult objects to encode: JSON::XS will encode undefined
658 scalars as JSON null value, scalars that have last been used in a
659 string context before encoding as JSON strings and anything else as
660 number value:
661
662 # dump as number
663 to_json [2] # yields [2]
664 to_json [-3.0e17] # yields [-3e+17]
665 my $value = 5; to_json [$value] # yields [5]
666
667 # used as string, so dump as string
668 print $value;
669 to_json [$value] # yields ["5"]
670
671 # undef becomes null
672 to_json [undef] # yields [null]
673
674 You can force the type to be a string by stringifying it:
675
676 my $x = 3.1; # some variable containing a number
677 "$x"; # stringified
678 $x .= ""; # another, more awkward way to stringify
679 print $x; # perl does it for you, too, quite often
680
681 You can force the type to be a number by numifying it:
682
683 my $x = "3"; # some variable containing a string
684 $x += 0; # numify it, ensuring it will be dumped as a number
685 $x *= 1; # same thing, the choise is yours.
686
687 You can not currently output JSON booleans or force the type in
688 other, less obscure, ways. Tell me if you need this capability.
199 689
200COMPARISON 690COMPARISON
201 As already mentioned, this module was created because none of the 691 As already mentioned, this module was created because none of the
202 existing JSON modules could be made to work correctly. First I will 692 existing JSON modules could be made to work correctly. First I will
203 describe the problems (or pleasures) I encountered with various existing 693 describe the problems (or pleasures) I encountered with various existing
… …
225 715
226 Has problems handling many Perl values (e.g. regex results and other 716 Has problems handling many Perl values (e.g. regex results and other
227 magic values will make it croak). 717 magic values will make it croak).
228 718
229 Does not even generate valid JSON ("{1,2}" gets converted to "{1:2}" 719 Does not even generate valid JSON ("{1,2}" gets converted to "{1:2}"
230 which is not a valid JSON string. 720 which is not a valid JSON text.
231 721
232 Unmaintained (maintainer unresponsive for many months, bugs are not 722 Unmaintained (maintainer unresponsive for many months, bugs are not
233 getting fixed). 723 getting fixed).
234 724
235 JSON::Syck 0.21 725 JSON::Syck 0.21
236 Very buggy (often crashes). 726 Very buggy (often crashes).
237 727
238 Very inflexible (no human-readable format supported, format pretty 728 Very inflexible (no human-readable format supported, format pretty
239 much undocumented. I need at least a format for easy reading by 729 much undocumented. I need at least a format for easy reading by
240 humans and a single-line compact format for use in a protocol, and 730 humans and a single-line compact format for use in a protocol, and
241 preferably a way to generate ASCII-only JSON strings). 731 preferably a way to generate ASCII-only JSON texts).
242 732
243 Completely broken (and confusingly documented) Unicode handling 733 Completely broken (and confusingly documented) Unicode handling
244 (unicode escapes are not working properly, you need to set 734 (unicode escapes are not working properly, you need to set
245 ImplicitUnicode to *different* values on en- and decoding to get 735 ImplicitUnicode to *different* values on en- and decoding to get
246 symmetric behaviour). 736 symmetric behaviour).
… …
269 759
270 Very inflexible. 760 Very inflexible.
271 761
272 No roundtripping. 762 No roundtripping.
273 763
274 Does not generate valid JSON (key strings are often unquoted, empty 764 Does not generate valid JSON texts (key strings are often unquoted,
275 keys result in nothing being output) 765 empty keys result in nothing being output)
276 766
277 Does not check input for validity. 767 Does not check input for validity.
768
769 JSON and YAML
770 You often hear that JSON is a subset (or a close subset) of YAML. This
771 is, however, a mass hysteria and very far from the truth. In general,
772 there is no way to configure JSON::XS to output a data structure as
773 valid YAML.
774
775 If you really must use JSON::XS to generate YAML, you should use this
776 algorithm (subject to change in future versions):
777
778 my $to_yaml = JSON::XS->new->utf8->space_after (1);
779 my $yaml = $to_yaml->encode ($ref) . "\n";
780
781 This will usually generate JSON texts that also parse as valid YAML.
782 Please note that YAML has hardcoded limits on (simple) object key
783 lengths that JSON doesn't have, so you should make sure that your hash
784 keys are noticably shorter than the 1024 characters YAML allows.
785
786 There might be other incompatibilities that I am not aware of. In
787 general you should not try to generate YAML with a JSON generator or
788 vice versa, or try to parse JSON with a YAML parser or vice versa:
789 chances are high that you will run into severe interoperability
790 problems.
278 791
279 SPEED 792 SPEED
280 It seems that JSON::XS is surprisingly fast, as shown in the following 793 It seems that JSON::XS is surprisingly fast, as shown in the following
281 tables. They have been generated with the help of the "eg/bench" program 794 tables. They have been generated with the help of the "eg/bench" program
282 in the JSON::XS distribution, to make it easy to compare on your own 795 in the JSON::XS distribution, to make it easy to compare on your own
283 system. 796 system.
284 797
285 First is a comparison between various modules using a very simple JSON 798 First comes a comparison between various modules using a very short
799 single-line JSON string:
800
801 {"method": "handleMessage", "params": ["user1", "we were just talking"], \
802 "id": null, "array":[1,11,234,-5,1e5,1e7, true, false]}
803
286 string, showing the number of encodes/decodes per second (JSON::XS is 804 It shows the number of encodes/decodes per second (JSON::XS uses the
287 the functional interface, while JSON::XS/2 is the OO interface with 805 functional interface, while JSON::XS/2 uses the OO interface with
288 pretty-printing and hashkey sorting enabled). 806 pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink).
807 Higher is better:
289 808
809 Storable | 15779.925 | 14169.946 |
810 -----------+------------+------------+
290 module | encode | decode | 811 module | encode | decode |
291 -----------|------------|------------| 812 -----------|------------|------------|
292 JSON | 14006 | 6820 | 813 JSON | 4990.842 | 4088.813 |
293 JSON::DWIW | 200937 | 120386 | 814 JSON::DWIW | 51653.990 | 71575.154 |
294 JSON::PC | 85065 | 129366 | 815 JSON::PC | 65948.176 | 74631.744 |
295 JSON::Syck | 59898 | 44232 | 816 JSON::PP | 8931.652 | 3817.168 |
296 JSON::XS | 1171478 | 342435 | 817 JSON::Syck | 24877.248 | 27776.848 |
297 JSON::XS/2 | 730760 | 328714 | 818 JSON::XS | 388361.481 | 227951.304 |
819 JSON::XS/2 | 227951.304 | 218453.333 |
820 JSON::XS/3 | 338250.323 | 218453.333 |
821 Storable | 16500.016 | 135300.129 |
298 -----------+------------+------------+ 822 -----------+------------+------------+
299 823
300 That is, JSON::XS is 6 times faster than than JSON::DWIW and about 80 824 That is, JSON::XS is about five times faster than JSON::DWIW on
825 encoding, about three times faster on decoding, and over fourty times
301 times faster than JSON, even with pretty-printing and key sorting. 826 faster than JSON, even with pretty-printing and key sorting. It also
827 compares favourably to Storable for small amounts of data.
302 828
303 Using a longer test string (roughly 8KB, generated from Yahoo! Locals 829 Using a longer test string (roughly 18KB, generated from Yahoo! Locals
304 search API (http://nanoref.com/yahooapis/mgPdGg): 830 search API (http://nanoref.com/yahooapis/mgPdGg):
305 831
306 module | encode | decode | 832 module | encode | decode |
307 -----------|------------|------------| 833 -----------|------------|------------|
308 JSON | 673 | 38 | 834 JSON | 55.260 | 34.971 |
309 JSON::DWIW | 5271 | 770 | 835 JSON::DWIW | 825.228 | 1082.513 |
836 JSON::PC | 3571.444 | 2394.829 |
310 JSON::PC | 9901 | 2491 | 837 JSON::PP | 210.987 | 32.574 |
311 JSON::Syck | 2360 | 786 | 838 JSON::Syck | 552.551 | 787.544 |
312 JSON::XS | 37398 | 3202 | 839 JSON::XS | 5780.463 | 4854.519 |
313 JSON::XS/2 | 13765 | 3153 | 840 JSON::XS/2 | 3869.998 | 4798.975 |
841 JSON::XS/3 | 5862.880 | 4798.975 |
842 Storable | 4445.002 | 5235.027 |
314 -----------+------------+------------+ 843 -----------+------------+------------+
315 844
316 Again, JSON::XS leads by far in the encoding case, while still beating 845 Again, JSON::XS leads by far (except for Storable which non-surprisingly
317 every other module in the decoding case. 846 decodes faster).
318 847
319 Last example is an almost 8MB large hash with many large binary values 848 On large strings containing lots of high unicode characters, some
320 (PNG files), resulting in a lot of escaping: 849 modules (such as JSON::PC) seem to decode faster than JSON::XS, but the
850 result will be broken due to missing (or wrong) unicode handling. Others
851 refuse to decode or encode properly, so it was impossible to prepare a
852 fair comparison table for that case.
853
854SECURITY CONSIDERATIONS
855 When you are using JSON in a protocol, talking to untrusted potentially
856 hostile creatures requires relatively few measures.
857
858 First of all, your JSON decoder should be secure, that is, should not
859 have any buffer overflows. Obviously, this module should ensure that and
860 I am trying hard on making that true, but you never know.
861
862 Second, you need to avoid resource-starving attacks. That means you
863 should limit the size of JSON texts you accept, or make sure then when
864 your resources run out, thats just fine (e.g. by using a separate
865 process that can crash safely). The size of a JSON text in octets or
866 characters is usually a good indication of the size of the resources
867 required to decode it into a Perl structure. While JSON::XS can check
868 the size of the JSON text, it might be too late when you already have it
869 in memory, so you might want to check the size before you accept the
870 string.
871
872 Third, JSON::XS recurses using the C stack when decoding objects and
873 arrays. The C stack is a limited resource: for instance, on my amd64
874 machine with 8MB of stack size I can decode around 180k nested arrays
875 but only 14k nested JSON objects (due to perl itself recursing deeply on
876 croak to free the temporary). If that is exceeded, the program crashes.
877 to be conservative, the default nesting limit is set to 512. If your
878 process has a smaller stack, you should adjust this setting accordingly
879 with the "max_depth" method.
880
881 And last but least, something else could bomb you that I forgot to think
882 of. In that case, you get to keep the pieces. I am always open for
883 hints, though...
884
885 If you are using JSON::XS to return packets to consumption by javascript
886 scripts in a browser you should have a look at
887 <http://jpsykes.com/47/practical-csrf-and-json-security> to see wether
888 you are vulnerable to some common attack vectors (which really are
889 browser design bugs, but it is still you who will have to deal with it,
890 as major browser developers care only for features, not about doing
891 security right).
892
893THREADS
894 This module is *not* guarenteed to be thread safe and there are no plans
895 to change this until Perl gets thread support (as opposed to the
896 horribly slow so-called "threads" which are simply slow and bloated
897 process simulations - use fork, its *much* faster, cheaper, better).
898
899 (It might actually work, but you ahve ben warned).
321 900
322BUGS 901BUGS
323 While the goal of this module is to be correct, that unfortunately does 902 While the goal of this module is to be correct, that unfortunately does
324 not mean its bug-free, only that I think its design is bug-free. It is 903 not mean its bug-free, only that I think its design is bug-free. It is
325 still very young and not well-tested. If you keep reporting bugs they 904 still relatively early in its development. If you keep reporting bugs
326 will be fixed swiftly, though. 905 they will be fixed swiftly, though.
906
907 Please refrain from using rt.cpan.org or any other bug reporting
908 service. I put the contact address into my modules for a reason.
327 909
328AUTHOR 910AUTHOR
329 Marc Lehmann <schmorp@schmorp.de> 911 Marc Lehmann <schmorp@schmorp.de>
330 http://home.schmorp.de/ 912 http://home.schmorp.de/
331 913

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