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Revision 1.19 by root, Sat Oct 13 01:57:46 2007 UTC

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;
6 10
7 # exported functions, croak on error 11 # exported functions, they croak on error
12 # and expect/generate UTF-8
8 13
9 $utf8_encoded_json_text = to_json $perl_hash_or_arrayref; 14 $utf8_encoded_json_text = to_json $perl_hash_or_arrayref;
10 $perl_hash_or_arrayref = from_json $utf8_encoded_json_text; 15 $perl_hash_or_arrayref = from_json $utf8_encoded_json_text;
11 16
12 # oo-interface 17 # OO-interface
13 18
14 $coder = JSON::XS->new->ascii->pretty->allow_nonref; 19 $coder = JSON::XS->new->ascii->pretty->allow_nonref;
15 $pretty_printed_unencoded = $coder->encode ($perl_scalar); 20 $pretty_printed_unencoded = $coder->encode ($perl_scalar);
16 $perl_scalar = $coder->decode ($unicode_json_text); 21 $perl_scalar = $coder->decode ($unicode_json_text);
17 22
… …
30 35
31 See MAPPING, below, on how JSON::XS maps perl values to JSON values and 36 See MAPPING, below, on how JSON::XS maps perl values to JSON values and
32 vice versa. 37 vice versa.
33 38
34 FEATURES 39 FEATURES
35 * correct handling of unicode issues 40 * correct unicode handling
36 This module knows how to handle Unicode, and even documents how and 41 This module knows how to handle Unicode, and even documents how and
37 when it does so. 42 when it does so.
38 43
39 * round-trip integrity 44 * round-trip integrity
40 When you serialise a perl data structure using only datatypes 45 When you serialise a perl data structure using only datatypes
41 supported by JSON, the deserialised data structure is identical on 46 supported by JSON, the deserialised data structure is identical on
42 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).
43 49
44 * strict checking of JSON correctness 50 * strict checking of JSON correctness
45 There is no guessing, no generating of illegal JSON strings by 51 There is no guessing, no generating of illegal JSON texts by
46 default, and only JSON is accepted as input by default (the latter 52 default, and only JSON is accepted as input by default (the latter
47 is a security feature). 53 is a security feature).
48 54
49 * fast 55 * fast
50 Compared to other JSON modules, this module compares favourably in 56 Compared to other JSON modules, this module compares favourably in
… …
55 interface. 61 interface.
56 62
57 * reasonably versatile output formats 63 * reasonably versatile output formats
58 You can choose between the most compact guarenteed single-line 64 You can choose between the most compact guarenteed single-line
59 format possible (nice for simple line-based protocols), a pure-ascii 65 format possible (nice for simple line-based protocols), a pure-ascii
60 format (for when your transport is not 8-bit clean), or a 66 format (for when your transport is not 8-bit clean, still supports
61 pretty-printed format (for when you want to read that stuff). Or you 67 the whole unicode range), or a pretty-printed format (for when you
62 can combine those features in whatever way you like. 68 want to read that stuff). Or you can combine those features in
69 whatever way you like.
63 70
64FUNCTIONAL INTERFACE 71FUNCTIONAL INTERFACE
65 The following convinience methods are provided by this module. They are 72 The following convinience methods are provided by this module. They are
66 exported by default: 73 exported by default:
67 74
68 $json_string = to_json $perl_scalar 75 $json_text = to_json $perl_scalar
69 Converts the given Perl data structure (a simple scalar or a 76 Converts the given Perl data structure to a UTF-8 encoded, binary
70 reference to a hash or array) to a UTF-8 encoded, binary string
71 (that is, the string contains octets only). Croaks on error. 77 string (that is, the string contains octets only). Croaks on error.
72 78
73 This function call is functionally identical to 79 This function call is functionally identical to:
80
74 "JSON::XS->new->utf8->encode ($perl_scalar)". 81 $json_text = JSON::XS->new->utf8->encode ($perl_scalar)
75 82
83 except being faster.
84
76 $perl_scalar = from_json $json_string 85 $perl_scalar = from_json $json_text
77 The opposite of "to_json": expects an UTF-8 (binary) string and 86 The opposite of "to_json": expects an UTF-8 (binary) string and
78 tries to parse that as an UTF-8 encoded JSON string, returning the 87 tries to parse that as an UTF-8 encoded JSON text, returning the
79 resulting simple scalar or reference. Croaks on error. 88 resulting reference. Croaks on error.
80 89
81 This function call is functionally identical to 90 This function call is functionally identical to:
91
82 "JSON::XS->new->utf8->decode ($json_string)". 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 :)
83 143
84OBJECT-ORIENTED INTERFACE 144OBJECT-ORIENTED INTERFACE
85 The object oriented interface lets you configure your own encoding or 145 The object oriented interface lets you configure your own encoding or
86 decoding style, within the limits of supported formats. 146 decoding style, within the limits of supported formats.
87 147
… …
91 *disabled*. 151 *disabled*.
92 152
93 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
94 calls can be chained: 154 calls can be chained:
95 155
96 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]})
97 => {"a": [1, 2]} 157 => {"a": [1, 2]}
98 158
99 $json = $json->ascii ([$enable]) 159 $json = $json->ascii ([$enable])
100 If $enable is true (or missing), then the "encode" method will not 160 If $enable is true (or missing), then the "encode" method will not
101 generate characters outside the code range 0..127. Any unicode 161 generate characters outside the code range 0..127 (which is ASCII).
102 characters outside that range will be escaped using either a single 162 Any unicode characters outside that range will be escaped using
103 \uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence, 163 either a single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL
104 as per 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.
105 168
106 If $enable is false, then the "encode" method will not escape 169 If $enable is false, then the "encode" method will not escape
107 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.
108 172
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
109 JSON::XS->new->ascii (1)->encode (chr 0x10401) 177 JSON::XS->new->ascii (1)->encode ([chr 0x10401])
110 => \ud801\udc01 178 => ["\ud801\udc01"]
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)
111 204
112 $json = $json->utf8 ([$enable]) 205 $json = $json->utf8 ([$enable])
113 If $enable is true (or missing), then the "encode" method will 206 If $enable is true (or missing), then the "encode" method will
114 encode the JSON string into UTF-8, as required by many protocols, 207 encode the JSON result into UTF-8, as required by many protocols,
115 while the "decode" method expects to be handled an UTF-8-encoded 208 while the "decode" method expects to be handled an UTF-8-encoded
116 string. Please note that UTF-8-encoded strings do not contain any 209 string. Please note that UTF-8-encoded strings do not contain any
117 characters outside the range 0..255, they are thus useful for 210 characters outside the range 0..255, they are thus useful for
118 bytewise/binary I/O. 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.
119 214
120 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
121 string as a (non-encoded) unicode string, while "decode" expects 216 string as a (non-encoded) unicode string, while "decode" expects
122 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
123 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.
124 219
125 Example, output UTF-16-encoded JSON: 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);
126 229
127 $json = $json->pretty ([$enable]) 230 $json = $json->pretty ([$enable])
128 This enables (or disables) all of the "indent", "space_before" and 231 This enables (or disables) all of the "indent", "space_before" and
129 "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
130 generate the most readable (or most compact) form possible. 233 generate the most readable (or most compact) form possible.
… …
145 multiline format as output, putting every array member or 248 multiline format as output, putting every array member or
146 object/hash key-value pair into its own line, identing them 249 object/hash key-value pair into its own line, identing them
147 properly. 250 properly.
148 251
149 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
150 the resulting JSON strings is guarenteed not to contain any 253 the resulting JSON text is guarenteed not to contain any "newlines".
151 "newlines".
152 254
153 This setting has no effect when decoding JSON strings. 255 This setting has no effect when decoding JSON texts.
154 256
155 $json = $json->space_before ([$enable]) 257 $json = $json->space_before ([$enable])
156 If $enable is true (or missing), then the "encode" method will add 258 If $enable is true (or missing), then the "encode" method will add
157 an extra optional space before the ":" separating keys from values 259 an extra optional space before the ":" separating keys from values
158 in JSON objects. 260 in JSON objects.
159 261
160 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
161 space at those places. 263 space at those places.
162 264
163 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
164 most likely combine this setting with "space_after". 266 most likely combine this setting with "space_after".
165 267
166 Example, space_before enabled, space_after and indent disabled: 268 Example, space_before enabled, space_after and indent disabled:
167 269
168 {"key" :"value"} 270 {"key" :"value"}
… …
174 pairs and array members. 276 pairs and array members.
175 277
176 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
177 space at those places. 279 space at those places.
178 280
179 This setting has no effect when decoding JSON strings. 281 This setting has no effect when decoding JSON texts.
180 282
181 Example, space_before and indent disabled, space_after enabled: 283 Example, space_before and indent disabled, space_after enabled:
182 284
183 {"key": "value"} 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 ]
184 325
185 $json = $json->canonical ([$enable]) 326 $json = $json->canonical ([$enable])
186 If $enable is true (or missing), then the "encode" method will 327 If $enable is true (or missing), then the "encode" method will
187 output JSON objects by sorting their keys. This is adding a 328 output JSON objects by sorting their keys. This is adding a
188 comparatively high overhead. 329 comparatively high overhead.
… …
190 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
191 pairs in the order Perl stores them (which will likely change 332 pairs in the order Perl stores them (which will likely change
192 between runs of the same script). 333 between runs of the same script).
193 334
194 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
195 encoded as the same JSON string (given the same overall settings). 336 encoded as the same JSON text (given the same overall settings). If
196 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
197 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
198 in Perl. 339 in Perl.
199 340
200 This setting has no effect when decoding JSON strings. 341 This setting has no effect when decoding JSON texts.
201 342
202 $json = $json->allow_nonref ([$enable]) 343 $json = $json->allow_nonref ([$enable])
203 If $enable is true (or missing), then the "encode" method can 344 If $enable is true (or missing), then the "encode" method can
204 convert a non-reference into its corresponding string, number or 345 convert a non-reference into its corresponding string, number or
205 null JSON value, which is an extension to RFC4627. Likewise, 346 null JSON value, which is an extension to RFC4627. Likewise,
206 "decode" will accept those JSON values instead of croaking. 347 "decode" will accept those JSON values instead of croaking.
207 348
208 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
209 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
210 object or array. Likewise, "decode" will croak if given something 351 object or array. Likewise, "decode" will croak if given something
211 that is not a JSON object or array. 352 that is not a JSON object or array.
212 353
213 Example, encode a Perl scalar as JSON value with enabled 354 Example, encode a Perl scalar as JSON value with enabled
214 "allow_nonref", resulting in an invalid JSON text: 355 "allow_nonref", resulting in an invalid JSON text:
215 356
216 JSON::XS->new->allow_nonref->encode ("Hello, World!") 357 JSON::XS->new->allow_nonref->encode ("Hello, World!")
217 => "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 }
218 469
219 $json = $json->shrink ([$enable]) 470 $json = $json->shrink ([$enable])
220 Perl usually over-allocates memory a bit when allocating space for 471 Perl usually over-allocates memory a bit when allocating space for
221 strings. This flag optionally resizes strings generated by either 472 strings. This flag optionally resizes strings generated by either
222 "encode" or "decode" to their minimum size possible. This can save 473 "encode" or "decode" to their minimum size possible. This can save
223 memory when your JSON strings are either very very long or you have 474 memory when your JSON texts are either very very long or you have
224 many short strings. It will also try to downgrade any strings to 475 many short strings. It will also try to downgrade any strings to
225 octet-form if possible: perl stores strings internally either in an 476 octet-form if possible: perl stores strings internally either in an
226 encoding called UTF-X or in octet-form. The latter cannot store 477 encoding called UTF-X or in octet-form. The latter cannot store
227 everything but uses less space in general. 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.
228 484
229 If $enable is true (or missing), the string returned by "encode" 485 If $enable is true (or missing), the string returned by "encode"
230 will be shrunk-to-fit, while all strings generated by "decode" will 486 will be shrunk-to-fit, while all strings generated by "decode" will
231 also be shrunk-to-fit. 487 also be shrunk-to-fit.
232 488
… …
236 In the future, this setting might control other things, such as 492 In the future, this setting might control other things, such as
237 converting strings that look like integers or floats into integers 493 converting strings that look like integers or floats into integers
238 or floats internally (there is no difference on the Perl level), 494 or floats internally (there is no difference on the Perl level),
239 saving space. 495 saving space.
240 496
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
241 $json_string = $json->encode ($perl_scalar) 533 $json_text = $json->encode ($perl_scalar)
242 Converts the given Perl data structure (a simple scalar or a 534 Converts the given Perl data structure (a simple scalar or a
243 reference to a hash or array) to its JSON representation. Simple 535 reference to a hash or array) to its JSON representation. Simple
244 scalars will be converted into JSON string or number sequences, 536 scalars will be converted into JSON string or number sequences,
245 while references to arrays become JSON arrays and references to 537 while references to arrays become JSON arrays and references to
246 hashes become JSON objects. Undefined Perl values (e.g. "undef") 538 hashes become JSON objects. Undefined Perl values (e.g. "undef")
247 become JSON "null" values. Neither "true" nor "false" values will be 539 become JSON "null" values. Neither "true" nor "false" values will be
248 generated. 540 generated.
249 541
250 $perl_scalar = $json->decode ($json_string) 542 $perl_scalar = $json->decode ($json_text)
251 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,
252 it, returning the resulting simple scalar or reference. Croaks on 544 returning the resulting simple scalar or reference. Croaks on error.
253 error.
254 545
255 JSON numbers and strings become simple Perl scalars. JSON arrays 546 JSON numbers and strings become simple Perl scalars. JSON arrays
256 become Perl arrayrefs and JSON objects become Perl hashrefs. "true" 547 become Perl arrayrefs and JSON objects become Perl hashrefs. "true"
257 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)
258 562
259MAPPING 563MAPPING
260 This section describes how JSON::XS maps Perl values to JSON values and 564 This section describes how JSON::XS maps Perl values to JSON values and
261 vice versa. These mappings are designed to "do the right thing" in most 565 vice versa. These mappings are designed to "do the right thing" in most
262 circumstances automatically, preserving round-tripping characteristics 566 circumstances automatically, preserving round-tripping characteristics
… …
267 refers to the abstract Perl language itself. 571 refers to the abstract Perl language itself.
268 572
269 JSON -> PERL 573 JSON -> PERL
270 object 574 object
271 A JSON object becomes a reference to a hash in Perl. No ordering of 575 A JSON object becomes a reference to a hash in Perl. No ordering of
272 object keys is preserved. 576 object keys is preserved (JSON does not preserver object key
577 ordering itself).
273 578
274 array 579 array
275 A JSON array becomes a reference to an array in Perl. 580 A JSON array becomes a reference to an array in Perl.
276 581
277 string 582 string
278 A JSON string becomes a string scalar in Perl - Unicode codepoints 583 A JSON string becomes a string scalar in Perl - Unicode codepoints
279 in JSON are represented by the same codepoints in the Perl string, 584 in JSON are represented by the same codepoints in the Perl string,
280 so no manual decoding is necessary. 585 so no manual decoding is necessary.
281 586
282 number 587 number
283 A JSON number becomes either an integer or numeric (floating point) 588 A JSON number becomes either an integer, numeric (floating point) or
284 scalar in perl, depending on its range and any fractional parts. On 589 string scalar in perl, depending on its range and any fractional
285 the Perl level, there is no difference between those as Perl handles 590 parts. On the Perl level, there is no difference between those as
286 all the conversion details, but an integer may take slightly less 591 Perl handles all the conversion details, but an integer may take
287 memory and might represent more values exactly than (floating point) 592 slightly less memory and might represent more values exactly than
288 numbers. 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.
289 607
290 true, false 608 true, false
291 These JSON atoms become 0, 1, respectively. Information is lost in 609 These JSON atoms become "JSON::XS::true" and "JSON::XS::false",
292 this process. Future versions might represent those values 610 respectively. They are overloaded to act almost exactly like the
293 differently, but they will be guarenteed to act like these integers 611 numbers 1 and 0. You can check wether a scalar is a JSON boolean by
294 would normally in Perl. 612 using the "JSON::XS::is_bool" function.
295 613
296 null 614 null
297 A JSON null atom becomes "undef" in Perl. 615 A JSON null atom becomes "undef" in Perl.
298 616
299 PERL -> JSON 617 PERL -> JSON
… …
301 truly typeless language, so we can only guess which JSON type is meant 619 truly typeless language, so we can only guess which JSON type is meant
302 by a Perl value. 620 by a Perl value.
303 621
304 hash references 622 hash references
305 Perl hash references become JSON objects. As there is no inherent 623 Perl hash references become JSON objects. As there is no inherent
306 ordering in hash keys, they will usually be encoded in a 624 ordering in hash keys (or JSON objects), they will usually be
307 pseudo-random order that can change between runs of the same program 625 encoded in a pseudo-random order that can change between runs of the
308 but stays generally the same within the single run of a program. 626 same program but stays generally the same within a single run of a
309 JSON::XS can optionally sort the hash keys (determined by the 627 program. JSON::XS can optionally sort the hash keys (determined by
310 *canonical* flag), so the same datastructure will serialise to the 628 the *canonical* flag), so the same datastructure will serialise to
311 same JSON text (given same settings and version of JSON::XS), but 629 the same JSON text (given same settings and version of JSON::XS),
312 this incurs a runtime overhead. 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.
313 633
314 array references 634 array references
315 Perl array references become JSON arrays. 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.
316 649
317 blessed objects 650 blessed objects
318 Blessed objects are not allowed. JSON::XS currently tries to encode 651 Blessed objects are not allowed. JSON::XS currently tries to encode
319 their underlying representation (hash- or arrayref), but this 652 their underlying representation (hash- or arrayref), but this
320 behaviour might change in future versions. 653 behaviour might change in future versions.
… …
352 $x *= 1; # same thing, the choise is yours. 685 $x *= 1; # same thing, the choise is yours.
353 686
354 You can not currently output JSON booleans or force the type in 687 You can not currently output JSON booleans or force the type in
355 other, less obscure, ways. Tell me if you need this capability. 688 other, less obscure, ways. Tell me if you need this capability.
356 689
357 circular data structures
358 Those will be encoded until memory or stackspace runs out.
359
360COMPARISON 690COMPARISON
361 As already mentioned, this module was created because none of the 691 As already mentioned, this module was created because none of the
362 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
363 describe the problems (or pleasures) I encountered with various existing 693 describe the problems (or pleasures) I encountered with various existing
364 JSON modules, followed by some benchmark values. JSON::XS was designed 694 JSON modules, followed by some benchmark values. JSON::XS was designed
… …
385 715
386 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
387 magic values will make it croak). 717 magic values will make it croak).
388 718
389 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}"
390 which is not a valid JSON string. 720 which is not a valid JSON text.
391 721
392 Unmaintained (maintainer unresponsive for many months, bugs are not 722 Unmaintained (maintainer unresponsive for many months, bugs are not
393 getting fixed). 723 getting fixed).
394 724
395 JSON::Syck 0.21 725 JSON::Syck 0.21
396 Very buggy (often crashes). 726 Very buggy (often crashes).
397 727
398 Very inflexible (no human-readable format supported, format pretty 728 Very inflexible (no human-readable format supported, format pretty
399 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
400 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
401 preferably a way to generate ASCII-only JSON strings). 731 preferably a way to generate ASCII-only JSON texts).
402 732
403 Completely broken (and confusingly documented) Unicode handling 733 Completely broken (and confusingly documented) Unicode handling
404 (unicode escapes are not working properly, you need to set 734 (unicode escapes are not working properly, you need to set
405 ImplicitUnicode to *different* values on en- and decoding to get 735 ImplicitUnicode to *different* values on en- and decoding to get
406 symmetric behaviour). 736 symmetric behaviour).
… …
429 759
430 Very inflexible. 760 Very inflexible.
431 761
432 No roundtripping. 762 No roundtripping.
433 763
434 Does not generate valid JSON (key strings are often unquoted, empty 764 Does not generate valid JSON texts (key strings are often unquoted,
435 keys result in nothing being output) 765 empty keys result in nothing being output)
436 766
437 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.
438 791
439 SPEED 792 SPEED
440 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
441 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
442 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
443 system. 796 system.
444 797
445 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
446 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
447 the functional interface, while JSON::XS/2 is the OO interface with 805 functional interface, while JSON::XS/2 uses the OO interface with
448 pretty-printing and hashkey sorting enabled). 806 pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink).
807 Higher is better:
449 808
809 Storable | 15779.925 | 14169.946 |
810 -----------+------------+------------+
450 module | encode | decode | 811 module | encode | decode |
451 -----------|------------|------------| 812 -----------|------------|------------|
452 JSON | 14006 | 6820 | 813 JSON | 4990.842 | 4088.813 |
453 JSON::DWIW | 200937 | 120386 | 814 JSON::DWIW | 51653.990 | 71575.154 |
454 JSON::PC | 85065 | 129366 | 815 JSON::PC | 65948.176 | 74631.744 |
455 JSON::Syck | 59898 | 44232 | 816 JSON::PP | 8931.652 | 3817.168 |
456 JSON::XS | 1171478 | 342435 | 817 JSON::Syck | 24877.248 | 27776.848 |
457 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 |
458 -----------+------------+------------+ 822 -----------+------------+------------+
459 823
460 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
461 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.
462 828
463 Using a longer test string (roughly 8KB, generated from Yahoo! Locals 829 Using a longer test string (roughly 18KB, generated from Yahoo! Locals
464 search API (http://nanoref.com/yahooapis/mgPdGg): 830 search API (http://nanoref.com/yahooapis/mgPdGg):
465 831
466 module | encode | decode | 832 module | encode | decode |
467 -----------|------------|------------| 833 -----------|------------|------------|
468 JSON | 673 | 38 | 834 JSON | 55.260 | 34.971 |
469 JSON::DWIW | 5271 | 770 | 835 JSON::DWIW | 825.228 | 1082.513 |
836 JSON::PC | 3571.444 | 2394.829 |
470 JSON::PC | 9901 | 2491 | 837 JSON::PP | 210.987 | 32.574 |
471 JSON::Syck | 2360 | 786 | 838 JSON::Syck | 552.551 | 787.544 |
472 JSON::XS | 37398 | 3202 | 839 JSON::XS | 5780.463 | 4854.519 |
473 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 |
474 -----------+------------+------------+ 843 -----------+------------+------------+
475 844
476 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
477 every other module in the decoding case. 846 decodes faster).
478 847
479RESOURCE LIMITS 848 On large strings containing lots of high unicode characters, some
480 JSON::XS does not impose any limits on the size of JSON texts or Perl 849 modules (such as JSON::PC) seem to decode faster than JSON::XS, but the
481 values they represent - if your machine can handle it, JSON::XS will 850 result will be broken due to missing (or wrong) unicode handling. Others
482 encode or decode it. Future versions might optionally impose structure 851 refuse to decode or encode properly, so it was impossible to prepare a
483 depth and memory use resource limits. 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).
484 900
485BUGS 901BUGS
486 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
487 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
488 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
489 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.
490 909
491AUTHOR 910AUTHOR
492 Marc Lehmann <schmorp@schmorp.de> 911 Marc Lehmann <schmorp@schmorp.de>
493 http://home.schmorp.de/ 912 http://home.schmorp.de/
494 913

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