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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;
6 10
7 # exported functions, they croak on error 11 # exported functions, they croak on error
8 # and expect/generate UTF-8 12 # and expect/generate UTF-8
9 13
10 $utf8_encoded_json_text = to_json $perl_hash_or_arrayref; 14 $utf8_encoded_json_text = encode_json $perl_hash_or_arrayref;
11 $perl_hash_or_arrayref = from_json $utf8_encoded_json_text; 15 $perl_hash_or_arrayref = decode_json $utf8_encoded_json_text;
12
13 # objToJson and jsonToObj aliases to to_json and from_json
14 # are exported for compatibility to the JSON module,
15 # but should not be used in new code.
16 16
17 # OO-interface 17 # OO-interface
18 18
19 $coder = JSON::XS->new->ascii->pretty->allow_nonref; 19 $coder = JSON::XS->new->ascii->pretty->allow_nonref;
20 $pretty_printed_unencoded = $coder->encode ($perl_scalar); 20 $pretty_printed_unencoded = $coder->encode ($perl_scalar);
21 $perl_scalar = $coder->decode ($unicode_json_text); 21 $perl_scalar = $coder->decode ($unicode_json_text);
22
23 # Note that JSON version 2.0 and above will automatically use JSON::XS
24 # if available, at virtually no speed overhead either, so you should
25 # be able to just:
26
27 use JSON;
28
29 # and do the same things, except that you have a pure-perl fallback now.
22 30
23DESCRIPTION 31DESCRIPTION
24 This module converts Perl data structures to JSON and vice versa. Its 32 This module converts Perl data structures to JSON and vice versa. Its
25 primary goal is to be *correct* and its secondary goal is to be *fast*. 33 primary goal is to be *correct* and its secondary goal is to be *fast*.
26 To reach the latter goal it was written in C. 34 To reach the latter goal it was written in C.
35
36 Beginning with version 2.0 of the JSON module, when both JSON and
37 JSON::XS are installed, then JSON will fall back on JSON::XS (this can
38 be overriden) with no overhead due to emulation (by inheritign
39 constructor and methods). If JSON::XS is not available, it will fall
40 back to the compatible JSON::PP module as backend, so using JSON instead
41 of JSON::XS gives you a portable JSON API that can be fast when you need
42 and doesn't require a C compiler when that is a problem.
27 43
28 As this is the n-th-something JSON module on CPAN, what was the reason 44 As this is the n-th-something JSON module on CPAN, what was the reason
29 to write yet another JSON module? While it seems there are many JSON 45 to write yet another JSON module? While it seems there are many JSON
30 modules, none of them correctly handle all corner cases, and in most 46 modules, none of them correctly handle all corner cases, and in most
31 cases their maintainers are unresponsive, gone missing, or not listening 47 cases their maintainers are unresponsive, gone missing, or not listening
… …
35 51
36 See MAPPING, below, on how JSON::XS maps perl values to JSON values and 52 See MAPPING, below, on how JSON::XS maps perl values to JSON values and
37 vice versa. 53 vice versa.
38 54
39 FEATURES 55 FEATURES
40 * correct unicode handling 56 * correct Unicode handling
41 This module knows how to handle Unicode, and even documents how and 57 This module knows how to handle Unicode, and even documents how and
42 when it does so. 58 when it does so.
43 59
44 * round-trip integrity 60 * round-trip integrity
45 When you serialise a perl data structure using only datatypes 61 When you serialise a perl data structure using only datatypes
… …
59 * simple to use 75 * simple to use
60 This module has both a simple functional interface as well as an OO 76 This module has both a simple functional interface as well as an OO
61 interface. 77 interface.
62 78
63 * reasonably versatile output formats 79 * reasonably versatile output formats
64 You can choose between the most compact guarenteed single-line 80 You can choose between the most compact guaranteed single-line
65 format possible (nice for simple line-based protocols), a pure-ascii 81 format possible (nice for simple line-based protocols), a pure-ascii
66 format (for when your transport is not 8-bit clean, still supports 82 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 83 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 84 want to read that stuff). Or you can combine those features in
69 whatever way you like. 85 whatever way you like.
70 86
71FUNCTIONAL INTERFACE 87FUNCTIONAL INTERFACE
72 The following convinience methods are provided by this module. They are 88 The following convenience methods are provided by this module. They are
73 exported by default: 89 exported by default:
74 90
75 $json_text = to_json $perl_scalar 91 $json_text = encode_json $perl_scalar
76 Converts the given Perl data structure (a simple scalar or a 92 Converts the given Perl data structure to a UTF-8 encoded, binary
77 reference to a hash or array) to a UTF-8 encoded, binary string
78 (that is, the string contains octets only). Croaks on error. 93 string (that is, the string contains octets only). Croaks on error.
79 94
80 This function call is functionally identical to: 95 This function call is functionally identical to:
81 96
82 $json_text = JSON::XS->new->utf8->encode ($perl_scalar) 97 $json_text = JSON::XS->new->utf8->encode ($perl_scalar)
83 98
84 except being faster. 99 except being faster.
85 100
86 $perl_scalar = from_json $json_text 101 $perl_scalar = decode_json $json_text
87 The opposite of "to_json": expects an UTF-8 (binary) string and 102 The opposite of "encode_json": expects an UTF-8 (binary) string and
88 tries to parse that as an UTF-8 encoded JSON text, returning the 103 tries to parse that as an UTF-8 encoded JSON text, returning the
89 resulting simple scalar or reference. Croaks on error. 104 resulting reference. Croaks on error.
90 105
91 This function call is functionally identical to: 106 This function call is functionally identical to:
92 107
93 $perl_scalar = JSON::XS->new->utf8->decode ($json_text) 108 $perl_scalar = JSON::XS->new->utf8->decode ($json_text)
94 109
… …
101 values in Perl. 116 values in Perl.
102 117
103 See MAPPING, below, for more information on how JSON values are 118 See MAPPING, below, for more information on how JSON values are
104 mapped to Perl. 119 mapped to Perl.
105 120
121A FEW NOTES ON UNICODE AND PERL
122 Since this often leads to confusion, here are a few very clear words on
123 how Unicode works in Perl, modulo bugs.
124
125 1. Perl strings can store characters with ordinal values > 255.
126 This enables you to store Unicode characters as single characters in
127 a Perl string - very natural.
128
129 2. Perl does *not* associate an encoding with your strings.
130 Unless you force it to, e.g. when matching it against a regex, or
131 printing the scalar to a file, in which case Perl either interprets
132 your string as locale-encoded text, octets/binary, or as Unicode,
133 depending on various settings. In no case is an encoding stored
134 together with your data, it is *use* that decides encoding, not any
135 magical metadata.
136
137 3. The internal utf-8 flag has no meaning with regards to the encoding
138 of your string.
139 Just ignore that flag unless you debug a Perl bug, a module written
140 in XS or want to dive into the internals of perl. Otherwise it will
141 only confuse you, as, despite the name, it says nothing about how
142 your string is encoded. You can have Unicode strings with that flag
143 set, with that flag clear, and you can have binary data with that
144 flag set and that flag clear. Other possibilities exist, too.
145
146 If you didn't know about that flag, just the better, pretend it
147 doesn't exist.
148
149 4. A "Unicode String" is simply a string where each character can be
150 validly interpreted as a Unicode codepoint.
151 If you have UTF-8 encoded data, it is no longer a Unicode string,
152 but a Unicode string encoded in UTF-8, giving you a binary string.
153
154 5. A string containing "high" (> 255) character values is *not* a UTF-8
155 string.
156 It's a fact. Learn to live with it.
157
158 I hope this helps :)
159
106OBJECT-ORIENTED INTERFACE 160OBJECT-ORIENTED INTERFACE
107 The object oriented interface lets you configure your own encoding or 161 The object oriented interface lets you configure your own encoding or
108 decoding style, within the limits of supported formats. 162 decoding style, within the limits of supported formats.
109 163
110 $json = new JSON::XS 164 $json = new JSON::XS
… …
117 171
118 my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]}) 172 my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]})
119 => {"a": [1, 2]} 173 => {"a": [1, 2]}
120 174
121 $json = $json->ascii ([$enable]) 175 $json = $json->ascii ([$enable])
176 $enabled = $json->get_ascii
122 If $enable is true (or missing), then the "encode" method will not 177 If $enable is true (or missing), then the "encode" method will not
123 generate characters outside the code range 0..127 (which is ASCII). 178 generate characters outside the code range 0..127 (which is ASCII).
124 Any unicode characters outside that range will be escaped using 179 Any Unicode characters outside that range will be escaped using
125 either a single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL 180 either a single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL
126 escape sequence, as per RFC4627. The resulting encoded JSON text can 181 escape sequence, as per RFC4627. The resulting encoded JSON text can
127 be treated as a native unicode string, an ascii-encoded, 182 be treated as a native Unicode string, an ascii-encoded,
128 latin1-encoded or UTF-8 encoded string, or any other superset of 183 latin1-encoded or UTF-8 encoded string, or any other superset of
129 ASCII. 184 ASCII.
130 185
131 If $enable is false, then the "encode" method will not escape 186 If $enable is false, then the "encode" method will not escape
132 Unicode characters unless required by the JSON syntax or other 187 Unicode characters unless required by the JSON syntax or other
… …
138 193
139 JSON::XS->new->ascii (1)->encode ([chr 0x10401]) 194 JSON::XS->new->ascii (1)->encode ([chr 0x10401])
140 => ["\ud801\udc01"] 195 => ["\ud801\udc01"]
141 196
142 $json = $json->latin1 ([$enable]) 197 $json = $json->latin1 ([$enable])
198 $enabled = $json->get_latin1
143 If $enable is true (or missing), then the "encode" method will 199 If $enable is true (or missing), then the "encode" method will
144 encode the resulting JSON text as latin1 (or iso-8859-1), escaping 200 encode the resulting JSON text as latin1 (or iso-8859-1), escaping
145 any characters outside the code range 0..255. The resulting string 201 any characters outside the code range 0..255. The resulting string
146 can be treated as a latin1-encoded JSON text or a native unicode 202 can be treated as a latin1-encoded JSON text or a native Unicode
147 string. The "decode" method will not be affected in any way by this 203 string. The "decode" method will not be affected in any way by this
148 flag, as "decode" by default expects unicode, which is a strict 204 flag, as "decode" by default expects Unicode, which is a strict
149 superset of latin1. 205 superset of latin1.
150 206
151 If $enable is false, then the "encode" method will not escape 207 If $enable is false, then the "encode" method will not escape
152 Unicode characters unless required by the JSON syntax or other 208 Unicode characters unless required by the JSON syntax or other
153 flags. 209 flags.
154 210
155 The main use for this flag is efficiently encoding binary data as 211 The main use for this flag is efficiently encoding binary data as
156 JSON text, as most octets will not be escaped, resulting in a 212 JSON text, as most octets will not be escaped, resulting in a
157 smaller encoded size. The disadvantage is that the resulting JSON 213 smaller encoded size. The disadvantage is that the resulting JSON
158 text is encoded in latin1 (and must correctly be treated as such 214 text is encoded in latin1 (and must correctly be treated as such
159 when storing and transfering), a rare encoding for JSON. It is 215 when storing and transferring), a rare encoding for JSON. It is
160 therefore most useful when you want to store data structures known 216 therefore most useful when you want to store data structures known
161 to contain binary data efficiently in files or databases, not when 217 to contain binary data efficiently in files or databases, not when
162 talking to other JSON encoders/decoders. 218 talking to other JSON encoders/decoders.
163 219
164 JSON::XS->new->latin1->encode (["\x{89}\x{abc}"] 220 JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]
165 => ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not) 221 => ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)
166 222
167 $json = $json->utf8 ([$enable]) 223 $json = $json->utf8 ([$enable])
224 $enabled = $json->get_utf8
168 If $enable is true (or missing), then the "encode" method will 225 If $enable is true (or missing), then the "encode" method will
169 encode the JSON result into UTF-8, as required by many protocols, 226 encode the JSON result into UTF-8, as required by many protocols,
170 while the "decode" method expects to be handled an UTF-8-encoded 227 while the "decode" method expects to be handled an UTF-8-encoded
171 string. Please note that UTF-8-encoded strings do not contain any 228 string. Please note that UTF-8-encoded strings do not contain any
172 characters outside the range 0..255, they are thus useful for 229 characters outside the range 0..255, they are thus useful for
173 bytewise/binary I/O. In future versions, enabling this option might 230 bytewise/binary I/O. In future versions, enabling this option might
174 enable autodetection of the UTF-16 and UTF-32 encoding families, as 231 enable autodetection of the UTF-16 and UTF-32 encoding families, as
175 described in RFC4627. 232 described in RFC4627.
176 233
177 If $enable is false, then the "encode" method will return the JSON 234 If $enable is false, then the "encode" method will return the JSON
178 string as a (non-encoded) unicode string, while "decode" expects 235 string as a (non-encoded) Unicode string, while "decode" expects
179 thus a unicode string. Any decoding or encoding (e.g. to UTF-8 or 236 thus a Unicode string. Any decoding or encoding (e.g. to UTF-8 or
180 UTF-16) needs to be done yourself, e.g. using the Encode module. 237 UTF-16) needs to be done yourself, e.g. using the Encode module.
181 238
182 Example, output UTF-16BE-encoded JSON: 239 Example, output UTF-16BE-encoded JSON:
183 240
184 use Encode; 241 use Encode;
… …
204 2 261 2
205 ] 262 ]
206 } 263 }
207 264
208 $json = $json->indent ([$enable]) 265 $json = $json->indent ([$enable])
266 $enabled = $json->get_indent
209 If $enable is true (or missing), then the "encode" method will use a 267 If $enable is true (or missing), then the "encode" method will use a
210 multiline format as output, putting every array member or 268 multiline format as output, putting every array member or
211 object/hash key-value pair into its own line, identing them 269 object/hash key-value pair into its own line, indenting them
212 properly. 270 properly.
213 271
214 If $enable is false, no newlines or indenting will be produced, and 272 If $enable is false, no newlines or indenting will be produced, and
215 the resulting JSON text is guarenteed not to contain any "newlines". 273 the resulting JSON text is guaranteed not to contain any "newlines".
216 274
217 This setting has no effect when decoding JSON texts. 275 This setting has no effect when decoding JSON texts.
218 276
219 $json = $json->space_before ([$enable]) 277 $json = $json->space_before ([$enable])
278 $enabled = $json->get_space_before
220 If $enable is true (or missing), then the "encode" method will add 279 If $enable is true (or missing), then the "encode" method will add
221 an extra optional space before the ":" separating keys from values 280 an extra optional space before the ":" separating keys from values
222 in JSON objects. 281 in JSON objects.
223 282
224 If $enable is false, then the "encode" method will not add any extra 283 If $enable is false, then the "encode" method will not add any extra
… …
230 Example, space_before enabled, space_after and indent disabled: 289 Example, space_before enabled, space_after and indent disabled:
231 290
232 {"key" :"value"} 291 {"key" :"value"}
233 292
234 $json = $json->space_after ([$enable]) 293 $json = $json->space_after ([$enable])
294 $enabled = $json->get_space_after
235 If $enable is true (or missing), then the "encode" method will add 295 If $enable is true (or missing), then the "encode" method will add
236 an extra optional space after the ":" separating keys from values in 296 an extra optional space after the ":" separating keys from values in
237 JSON objects and extra whitespace after the "," separating key-value 297 JSON objects and extra whitespace after the "," separating key-value
238 pairs and array members. 298 pairs and array members.
239 299
… …
244 304
245 Example, space_before and indent disabled, space_after enabled: 305 Example, space_before and indent disabled, space_after enabled:
246 306
247 {"key": "value"} 307 {"key": "value"}
248 308
309 $json = $json->relaxed ([$enable])
310 $enabled = $json->get_relaxed
311 If $enable is true (or missing), then "decode" will accept some
312 extensions to normal JSON syntax (see below). "encode" will not be
313 affected in anyway. *Be aware that this option makes you accept
314 invalid JSON texts as if they were valid!*. I suggest only to use
315 this option to parse application-specific files written by humans
316 (configuration files, resource files etc.)
317
318 If $enable is false (the default), then "decode" will only accept
319 valid JSON texts.
320
321 Currently accepted extensions are:
322
323 * list items can have an end-comma
324 JSON *separates* array elements and key-value pairs with commas.
325 This can be annoying if you write JSON texts manually and want
326 to be able to quickly append elements, so this extension accepts
327 comma at the end of such items not just between them:
328
329 [
330 1,
331 2, <- this comma not normally allowed
332 ]
333 {
334 "k1": "v1",
335 "k2": "v2", <- this comma not normally allowed
336 }
337
338 * shell-style '#'-comments
339 Whenever JSON allows whitespace, shell-style comments are
340 additionally allowed. They are terminated by the first
341 carriage-return or line-feed character, after which more
342 white-space and comments are allowed.
343
344 [
345 1, # this comment not allowed in JSON
346 # neither this one...
347 ]
348
249 $json = $json->canonical ([$enable]) 349 $json = $json->canonical ([$enable])
350 $enabled = $json->get_canonical
250 If $enable is true (or missing), then the "encode" method will 351 If $enable is true (or missing), then the "encode" method will
251 output JSON objects by sorting their keys. This is adding a 352 output JSON objects by sorting their keys. This is adding a
252 comparatively high overhead. 353 comparatively high overhead.
253 354
254 If $enable is false, then the "encode" method will output key-value 355 If $enable is false, then the "encode" method will output key-value
255 pairs in the order Perl stores them (which will likely change 356 pairs in the order Perl stores them (which will likely change
256 between runs of the same script). 357 between runs of the same script).
257 358
258 This option is useful if you want the same data structure to be 359 This option is useful if you want the same data structure to be
259 encoded as the same JSON text (given the same overall settings). If 360 encoded as the same JSON text (given the same overall settings). If
260 it is disabled, the same hash migh be encoded differently even if 361 it is disabled, the same hash might be encoded differently even if
261 contains the same data, as key-value pairs have no inherent ordering 362 contains the same data, as key-value pairs have no inherent ordering
262 in Perl. 363 in Perl.
263 364
264 This setting has no effect when decoding JSON texts. 365 This setting has no effect when decoding JSON texts.
265 366
266 $json = $json->allow_nonref ([$enable]) 367 $json = $json->allow_nonref ([$enable])
368 $enabled = $json->get_allow_nonref
267 If $enable is true (or missing), then the "encode" method can 369 If $enable is true (or missing), then the "encode" method can
268 convert a non-reference into its corresponding string, number or 370 convert a non-reference into its corresponding string, number or
269 null JSON value, which is an extension to RFC4627. Likewise, 371 null JSON value, which is an extension to RFC4627. Likewise,
270 "decode" will accept those JSON values instead of croaking. 372 "decode" will accept those JSON values instead of croaking.
271 373
… …
278 "allow_nonref", resulting in an invalid JSON text: 380 "allow_nonref", resulting in an invalid JSON text:
279 381
280 JSON::XS->new->allow_nonref->encode ("Hello, World!") 382 JSON::XS->new->allow_nonref->encode ("Hello, World!")
281 => "Hello, World!" 383 => "Hello, World!"
282 384
385 $json = $json->allow_blessed ([$enable])
386 $enabled = $json->get_allow_blessed
387 If $enable is true (or missing), then the "encode" method will not
388 barf when it encounters a blessed reference. Instead, the value of
389 the convert_blessed option will decide whether "null"
390 ("convert_blessed" disabled or no "TO_JSON" method found) or a
391 representation of the object ("convert_blessed" enabled and
392 "TO_JSON" method found) is being encoded. Has no effect on "decode".
393
394 If $enable is false (the default), then "encode" will throw an
395 exception when it encounters a blessed object.
396
397 $json = $json->convert_blessed ([$enable])
398 $enabled = $json->get_convert_blessed
399 If $enable is true (or missing), then "encode", upon encountering a
400 blessed object, will check for the availability of the "TO_JSON"
401 method on the object's class. If found, it will be called in scalar
402 context and the resulting scalar will be encoded instead of the
403 object. If no "TO_JSON" method is found, the value of
404 "allow_blessed" will decide what to do.
405
406 The "TO_JSON" method may safely call die if it wants. If "TO_JSON"
407 returns other blessed objects, those will be handled in the same
408 way. "TO_JSON" must take care of not causing an endless recursion
409 cycle (== crash) in this case. The name of "TO_JSON" was chosen
410 because other methods called by the Perl core (== not by the user of
411 the object) are usually in upper case letters and to avoid
412 collisions with any "to_json" function or method.
413
414 This setting does not yet influence "decode" in any way, but in the
415 future, global hooks might get installed that influence "decode" and
416 are enabled by this setting.
417
418 If $enable is false, then the "allow_blessed" setting will decide
419 what to do when a blessed object is found.
420
421 $json = $json->filter_json_object ([$coderef->($hashref)])
422 When $coderef is specified, it will be called from "decode" each
423 time it decodes a JSON object. The only argument is a reference to
424 the newly-created hash. If the code references returns a single
425 scalar (which need not be a reference), this value (i.e. a copy of
426 that scalar to avoid aliasing) is inserted into the deserialised
427 data structure. If it returns an empty list (NOTE: *not* "undef",
428 which is a valid scalar), the original deserialised hash will be
429 inserted. This setting can slow down decoding considerably.
430
431 When $coderef is omitted or undefined, any existing callback will be
432 removed and "decode" will not change the deserialised hash in any
433 way.
434
435 Example, convert all JSON objects into the integer 5:
436
437 my $js = JSON::XS->new->filter_json_object (sub { 5 });
438 # returns [5]
439 $js->decode ('[{}]')
440 # throw an exception because allow_nonref is not enabled
441 # so a lone 5 is not allowed.
442 $js->decode ('{"a":1, "b":2}');
443
444 $json = $json->filter_json_single_key_object ($key [=>
445 $coderef->($value)])
446 Works remotely similar to "filter_json_object", but is only called
447 for JSON objects having a single key named $key.
448
449 This $coderef is called before the one specified via
450 "filter_json_object", if any. It gets passed the single value in the
451 JSON object. If it returns a single value, it will be inserted into
452 the data structure. If it returns nothing (not even "undef" but the
453 empty list), the callback from "filter_json_object" will be called
454 next, as if no single-key callback were specified.
455
456 If $coderef is omitted or undefined, the corresponding callback will
457 be disabled. There can only ever be one callback for a given key.
458
459 As this callback gets called less often then the
460 "filter_json_object" one, decoding speed will not usually suffer as
461 much. Therefore, single-key objects make excellent targets to
462 serialise Perl objects into, especially as single-key JSON objects
463 are as close to the type-tagged value concept as JSON gets (it's
464 basically an ID/VALUE tuple). Of course, JSON does not support this
465 in any way, so you need to make sure your data never looks like a
466 serialised Perl hash.
467
468 Typical names for the single object key are "__class_whatever__", or
469 "$__dollars_are_rarely_used__$" or "}ugly_brace_placement", or even
470 things like "__class_md5sum(classname)__", to reduce the risk of
471 clashing with real hashes.
472
473 Example, decode JSON objects of the form "{ "__widget__" => <id> }"
474 into the corresponding $WIDGET{<id>} object:
475
476 # return whatever is in $WIDGET{5}:
477 JSON::XS
478 ->new
479 ->filter_json_single_key_object (__widget__ => sub {
480 $WIDGET{ $_[0] }
481 })
482 ->decode ('{"__widget__": 5')
483
484 # this can be used with a TO_JSON method in some "widget" class
485 # for serialisation to json:
486 sub WidgetBase::TO_JSON {
487 my ($self) = @_;
488
489 unless ($self->{id}) {
490 $self->{id} = ..get..some..id..;
491 $WIDGET{$self->{id}} = $self;
492 }
493
494 { __widget__ => $self->{id} }
495 }
496
283 $json = $json->shrink ([$enable]) 497 $json = $json->shrink ([$enable])
498 $enabled = $json->get_shrink
284 Perl usually over-allocates memory a bit when allocating space for 499 Perl usually over-allocates memory a bit when allocating space for
285 strings. This flag optionally resizes strings generated by either 500 strings. This flag optionally resizes strings generated by either
286 "encode" or "decode" to their minimum size possible. This can save 501 "encode" or "decode" to their minimum size possible. This can save
287 memory when your JSON texts are either very very long or you have 502 memory when your JSON texts are either very very long or you have
288 many short strings. It will also try to downgrade any strings to 503 many short strings. It will also try to downgrade any strings to
… …
306 converting strings that look like integers or floats into integers 521 converting strings that look like integers or floats into integers
307 or floats internally (there is no difference on the Perl level), 522 or floats internally (there is no difference on the Perl level),
308 saving space. 523 saving space.
309 524
310 $json = $json->max_depth ([$maximum_nesting_depth]) 525 $json = $json->max_depth ([$maximum_nesting_depth])
526 $max_depth = $json->get_max_depth
311 Sets the maximum nesting level (default 512) accepted while encoding 527 Sets the maximum nesting level (default 512) accepted while encoding
312 or decoding. If the JSON text or Perl data structure has an equal or 528 or decoding. If the JSON text or Perl data structure has an equal or
313 higher nesting level then this limit, then the encoder and decoder 529 higher nesting level then this limit, then the encoder and decoder
314 will stop and croak at that point. 530 will stop and croak at that point.
315 531
… …
319 crossed to reach a given character in a string. 535 crossed to reach a given character in a string.
320 536
321 Setting the maximum depth to one disallows any nesting, so that 537 Setting the maximum depth to one disallows any nesting, so that
322 ensures that the object is only a single hash/object or array. 538 ensures that the object is only a single hash/object or array.
323 539
324 The argument to "max_depth" will be rounded up to the next nearest 540 The argument to "max_depth" will be rounded up to the next highest
325 power of two. 541 power of two. If no argument is given, the highest possible setting
542 will be used, which is rarely useful.
543
544 See SECURITY CONSIDERATIONS, below, for more info on why this is
545 useful.
546
547 $json = $json->max_size ([$maximum_string_size])
548 $max_size = $json->get_max_size
549 Set the maximum length a JSON text may have (in bytes) where
550 decoding is being attempted. The default is 0, meaning no limit.
551 When "decode" is called on a string longer then this number of
552 characters it will not attempt to decode the string but throw an
553 exception. This setting has no effect on "encode" (yet).
554
555 The argument to "max_size" will be rounded up to the next highest
556 power of two (so may be more than requested). If no argument is
557 given, the limit check will be deactivated (same as when 0 is
558 specified).
326 559
327 See SECURITY CONSIDERATIONS, below, for more info on why this is 560 See SECURITY CONSIDERATIONS, below, for more info on why this is
328 useful. 561 useful.
329 562
330 $json_text = $json->encode ($perl_scalar) 563 $json_text = $json->encode ($perl_scalar)
… …
362 vice versa. These mappings are designed to "do the right thing" in most 595 vice versa. These mappings are designed to "do the right thing" in most
363 circumstances automatically, preserving round-tripping characteristics 596 circumstances automatically, preserving round-tripping characteristics
364 (what you put in comes out as something equivalent). 597 (what you put in comes out as something equivalent).
365 598
366 For the more enlightened: note that in the following descriptions, 599 For the more enlightened: note that in the following descriptions,
367 lowercase *perl* refers to the Perl interpreter, while uppcercase *Perl* 600 lowercase *perl* refers to the Perl interpreter, while uppercase *Perl*
368 refers to the abstract Perl language itself. 601 refers to the abstract Perl language itself.
369 602
370 JSON -> PERL 603 JSON -> PERL
371 object 604 object
372 A JSON object becomes a reference to a hash in Perl. No ordering of 605 A JSON object becomes a reference to a hash in Perl. No ordering of
373 object keys is preserved (JSON does not preserver object key 606 object keys is preserved (JSON does not preserve object key ordering
374 ordering itself). 607 itself).
375 608
376 array 609 array
377 A JSON array becomes a reference to an array in Perl. 610 A JSON array becomes a reference to an array in Perl.
378 611
379 string 612 string
380 A JSON string becomes a string scalar in Perl - Unicode codepoints 613 A JSON string becomes a string scalar in Perl - Unicode codepoints
381 in JSON are represented by the same codepoints in the Perl string, 614 in JSON are represented by the same codepoints in the Perl string,
382 so no manual decoding is necessary. 615 so no manual decoding is necessary.
383 616
384 number 617 number
385 A JSON number becomes either an integer or numeric (floating point) 618 A JSON number becomes either an integer, numeric (floating point) or
386 scalar in perl, depending on its range and any fractional parts. On 619 string scalar in perl, depending on its range and any fractional
387 the Perl level, there is no difference between those as Perl handles 620 parts. On the Perl level, there is no difference between those as
388 all the conversion details, but an integer may take slightly less 621 Perl handles all the conversion details, but an integer may take
389 memory and might represent more values exactly than (floating point) 622 slightly less memory and might represent more values exactly than
390 numbers. 623 (floating point) numbers.
624
625 If the number consists of digits only, JSON::XS will try to
626 represent it as an integer value. If that fails, it will try to
627 represent it as a numeric (floating point) value if that is possible
628 without loss of precision. Otherwise it will preserve the number as
629 a string value.
630
631 Numbers containing a fractional or exponential part will always be
632 represented as numeric (floating point) values, possibly at a loss
633 of precision.
634
635 This might create round-tripping problems as numbers might become
636 strings, but as Perl is typeless there is no other way to do it.
391 637
392 true, false 638 true, false
393 These JSON atoms become "JSON::XS::true" and "JSON::XS::false", 639 These JSON atoms become "JSON::XS::true" and "JSON::XS::false",
394 respectively. They are overloaded to act almost exactly like the 640 respectively. They are overloaded to act almost exactly like the
395 numbers 1 and 0. You can check wether a scalar is a JSON boolean by 641 numbers 1 and 0. You can check whether a scalar is a JSON boolean by
396 using the "JSON::XS::is_bool" function. 642 using the "JSON::XS::is_bool" function.
397 643
398 null 644 null
399 A JSON null atom becomes "undef" in Perl. 645 A JSON null atom becomes "undef" in Perl.
400 646
… …
423 an exception to be thrown, except for references to the integers 0 669 an exception to be thrown, except for references to the integers 0
424 and 1, which get turned into "false" and "true" atoms in JSON. You 670 and 1, which get turned into "false" and "true" atoms in JSON. You
425 can also use "JSON::XS::false" and "JSON::XS::true" to improve 671 can also use "JSON::XS::false" and "JSON::XS::true" to improve
426 readability. 672 readability.
427 673
428 to_json [\0,JSON::XS::true] # yields [false,true] 674 encode_json [\0,JSON::XS::true] # yields [false,true]
429 675
430 JSON::XS::true, JSON::XS::false 676 JSON::XS::true, JSON::XS::false
431 These special values become JSON true and JSON false values, 677 These special values become JSON true and JSON false values,
432 respectively. You cna alos use "\1" and "\0" directly if you want. 678 respectively. You can also use "\1" and "\0" directly if you want.
433 679
434 blessed objects 680 blessed objects
435 Blessed objects are not allowed. JSON::XS currently tries to encode 681 Blessed objects are not allowed. JSON::XS currently tries to encode
436 their underlying representation (hash- or arrayref), but this 682 their underlying representation (hash- or arrayref), but this
437 behaviour might change in future versions. 683 behaviour might change in future versions.
… …
442 scalars as JSON null value, scalars that have last been used in a 688 scalars as JSON null value, scalars that have last been used in a
443 string context before encoding as JSON strings and anything else as 689 string context before encoding as JSON strings and anything else as
444 number value: 690 number value:
445 691
446 # dump as number 692 # dump as number
447 to_json [2] # yields [2] 693 encode_json [2] # yields [2]
448 to_json [-3.0e17] # yields [-3e+17] 694 encode_json [-3.0e17] # yields [-3e+17]
449 my $value = 5; to_json [$value] # yields [5] 695 my $value = 5; encode_json [$value] # yields [5]
450 696
451 # used as string, so dump as string 697 # used as string, so dump as string
452 print $value; 698 print $value;
453 to_json [$value] # yields ["5"] 699 encode_json [$value] # yields ["5"]
454 700
455 # undef becomes null 701 # undef becomes null
456 to_json [undef] # yields [null] 702 encode_json [undef] # yields [null]
457 703
458 You can force the type to be a string by stringifying it: 704 You can force the type to be a JSON string by stringifying it:
459 705
460 my $x = 3.1; # some variable containing a number 706 my $x = 3.1; # some variable containing a number
461 "$x"; # stringified 707 "$x"; # stringified
462 $x .= ""; # another, more awkward way to stringify 708 $x .= ""; # another, more awkward way to stringify
463 print $x; # perl does it for you, too, quite often 709 print $x; # perl does it for you, too, quite often
464 710
465 You can force the type to be a number by numifying it: 711 You can force the type to be a JSON number by numifying it:
466 712
467 my $x = "3"; # some variable containing a string 713 my $x = "3"; # some variable containing a string
468 $x += 0; # numify it, ensuring it will be dumped as a number 714 $x += 0; # numify it, ensuring it will be dumped as a number
469 $x *= 1; # same thing, the choise is yours. 715 $x *= 1; # same thing, the choice is yours.
470 716
471 You can not currently output JSON booleans or force the type in 717 You can not currently force the type in other, less obscure, ways.
472 other, less obscure, ways. Tell me if you need this capability. 718 Tell me if you need this capability.
473 719
474COMPARISON 720COMPARISON
475 As already mentioned, this module was created because none of the 721 As already mentioned, this module was created because none of the
476 existing JSON modules could be made to work correctly. First I will 722 existing JSON modules could be made to work correctly. First I will
477 describe the problems (or pleasures) I encountered with various existing 723 describe the problems (or pleasures) I encountered with various existing
… …
479 not to suffer from any of these problems or limitations. 725 not to suffer from any of these problems or limitations.
480 726
481 JSON 1.07 727 JSON 1.07
482 Slow (but very portable, as it is written in pure Perl). 728 Slow (but very portable, as it is written in pure Perl).
483 729
484 Undocumented/buggy Unicode handling (how JSON handles unicode values 730 Undocumented/buggy Unicode handling (how JSON handles Unicode values
485 is undocumented. One can get far by feeding it unicode strings and 731 is undocumented. One can get far by feeding it Unicode strings and
486 doing en-/decoding oneself, but unicode escapes are not working 732 doing en-/decoding oneself, but Unicode escapes are not working
487 properly). 733 properly).
488 734
489 No roundtripping (strings get clobbered if they look like numbers, 735 No round-tripping (strings get clobbered if they look like numbers,
490 e.g. the string 2.0 will encode to 2.0 instead of "2.0", and that 736 e.g. the string 2.0 will encode to 2.0 instead of "2.0", and that
491 will decode into the number 2. 737 will decode into the number 2.
492 738
493 JSON::PC 0.01 739 JSON::PC 0.01
494 Very fast. 740 Very fast.
495 741
496 Undocumented/buggy Unicode handling. 742 Undocumented/buggy Unicode handling.
497 743
498 No roundtripping. 744 No round-tripping.
499 745
500 Has problems handling many Perl values (e.g. regex results and other 746 Has problems handling many Perl values (e.g. regex results and other
501 magic values will make it croak). 747 magic values will make it croak).
502 748
503 Does not even generate valid JSON ("{1,2}" gets converted to "{1:2}" 749 Does not even generate valid JSON ("{1,2}" gets converted to "{1:2}"
… …
513 much undocumented. I need at least a format for easy reading by 759 much undocumented. I need at least a format for easy reading by
514 humans and a single-line compact format for use in a protocol, and 760 humans and a single-line compact format for use in a protocol, and
515 preferably a way to generate ASCII-only JSON texts). 761 preferably a way to generate ASCII-only JSON texts).
516 762
517 Completely broken (and confusingly documented) Unicode handling 763 Completely broken (and confusingly documented) Unicode handling
518 (unicode escapes are not working properly, you need to set 764 (Unicode escapes are not working properly, you need to set
519 ImplicitUnicode to *different* values on en- and decoding to get 765 ImplicitUnicode to *different* values on en- and decoding to get
520 symmetric behaviour). 766 symmetric behaviour).
521 767
522 No roundtripping (simple cases work, but this depends on wether the 768 No round-tripping (simple cases work, but this depends on whether
523 scalar value was used in a numeric context or not). 769 the scalar value was used in a numeric context or not).
524 770
525 Dumping hashes may skip hash values depending on iterator state. 771 Dumping hashes may skip hash values depending on iterator state.
526 772
527 Unmaintained (maintainer unresponsive for many months, bugs are not 773 Unmaintained (maintainer unresponsive for many months, bugs are not
528 getting fixed). 774 getting fixed).
529 775
530 Does not check input for validity (i.e. will accept non-JSON input 776 Does not check input for validity (i.e. will accept non-JSON input
531 and return "something" instead of raising an exception. This is a 777 and return "something" instead of raising an exception. This is a
532 security issue: imagine two banks transfering money between each 778 security issue: imagine two banks transferring money between each
533 other using JSON. One bank might parse a given non-JSON request and 779 other using JSON. One bank might parse a given non-JSON request and
534 deduct money, while the other might reject the transaction with a 780 deduct money, while the other might reject the transaction with a
535 syntax error. While a good protocol will at least recover, that is 781 syntax error. While a good protocol will at least recover, that is
536 extra unnecessary work and the transaction will still not succeed). 782 extra unnecessary work and the transaction will still not succeed).
537 783
538 JSON::DWIW 0.04 784 JSON::DWIW 0.04
539 Very fast. Very natural. Very nice. 785 Very fast. Very natural. Very nice.
540 786
541 Undocumented unicode handling (but the best of the pack. Unicode 787 Undocumented Unicode handling (but the best of the pack. Unicode
542 escapes still don't get parsed properly). 788 escapes still don't get parsed properly).
543 789
544 Very inflexible. 790 Very inflexible.
545 791
546 No roundtripping. 792 No round-tripping.
547 793
548 Does not generate valid JSON texts (key strings are often unquoted, 794 Does not generate valid JSON texts (key strings are often unquoted,
549 empty keys result in nothing being output) 795 empty keys result in nothing being output)
550 796
551 Does not check input for validity. 797 Does not check input for validity.
… …
563 my $yaml = $to_yaml->encode ($ref) . "\n"; 809 my $yaml = $to_yaml->encode ($ref) . "\n";
564 810
565 This will usually generate JSON texts that also parse as valid YAML. 811 This will usually generate JSON texts that also parse as valid YAML.
566 Please note that YAML has hardcoded limits on (simple) object key 812 Please note that YAML has hardcoded limits on (simple) object key
567 lengths that JSON doesn't have, so you should make sure that your hash 813 lengths that JSON doesn't have, so you should make sure that your hash
568 keys are noticably shorter than the 1024 characters YAML allows. 814 keys are noticeably shorter than the 1024 characters YAML allows.
569 815
570 There might be other incompatibilities that I am not aware of. In 816 There might be other incompatibilities that I am not aware of. In
571 general you should not try to generate YAML with a JSON generator or 817 general you should not try to generate YAML with a JSON generator or
572 vice versa, or try to parse JSON with a YAML parser or vice versa: 818 vice versa, or try to parse JSON with a YAML parser or vice versa:
573 chances are high that you will run into severe interoperability 819 chances are high that you will run into severe interoperability
… …
590 pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink). 836 pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink).
591 Higher is better: 837 Higher is better:
592 838
593 module | encode | decode | 839 module | encode | decode |
594 -----------|------------|------------| 840 -----------|------------|------------|
595 JSON | 7645.468 | 4208.613 | 841 JSON 1.x | 4990.842 | 4088.813 |
596 JSON::DWIW | 40721.398 | 77101.176 | 842 JSON::DWIW | 51653.990 | 71575.154 |
597 JSON::PC | 65948.176 | 78251.940 | 843 JSON::PC | 65948.176 | 74631.744 |
598 JSON::Syck | 22844.793 | 26479.192 | 844 JSON::PP | 8931.652 | 3817.168 |
845 JSON::Syck | 24877.248 | 27776.848 |
599 JSON::XS | 388361.481 | 199728.762 | 846 JSON::XS | 388361.481 | 227951.304 |
600 JSON::XS/2 | 218453.333 | 192399.266 | 847 JSON::XS/2 | 227951.304 | 218453.333 |
601 JSON::XS/3 | 338250.323 | 192399.266 | 848 JSON::XS/3 | 338250.323 | 218453.333 |
602 Storable | 15779.925 | 14169.946 | 849 Storable | 16500.016 | 135300.129 |
603 -----------+------------+------------+ 850 -----------+------------+------------+
604 851
605 That is, JSON::XS is about five times faster than JSON::DWIW on 852 That is, JSON::XS is about five times faster than JSON::DWIW on
606 encoding, about three times faster on decoding, and over fourty times 853 encoding, about three times faster on decoding, and over forty times
607 faster than JSON, even with pretty-printing and key sorting. It also 854 faster than JSON, even with pretty-printing and key sorting. It also
608 compares favourably to Storable for small amounts of data. 855 compares favourably to Storable for small amounts of data.
609 856
610 Using a longer test string (roughly 18KB, generated from Yahoo! Locals 857 Using a longer test string (roughly 18KB, generated from Yahoo! Locals
611 search API (http://nanoref.com/yahooapis/mgPdGg): 858 search API (http://nanoref.com/yahooapis/mgPdGg):
612 859
613 module | encode | decode | 860 module | encode | decode |
614 -----------|------------|------------| 861 -----------|------------|------------|
615 JSON | 254.685 | 37.665 | 862 JSON 1.x | 55.260 | 34.971 |
616 JSON::DWIW | 843.343 | 1049.731 | 863 JSON::DWIW | 825.228 | 1082.513 |
617 JSON::PC | 3602.116 | 2307.352 | 864 JSON::PC | 3571.444 | 2394.829 |
865 JSON::PP | 210.987 | 32.574 |
618 JSON::Syck | 505.107 | 787.899 | 866 JSON::Syck | 552.551 | 787.544 |
619 JSON::XS | 5747.196 | 3690.220 | 867 JSON::XS | 5780.463 | 4854.519 |
620 JSON::XS/2 | 3968.121 | 3676.634 | 868 JSON::XS/2 | 3869.998 | 4798.975 |
621 JSON::XS/3 | 6105.246 | 3662.508 | 869 JSON::XS/3 | 5862.880 | 4798.975 |
622 Storable | 4417.337 | 5285.161 | 870 Storable | 4445.002 | 5235.027 |
623 -----------+------------+------------+ 871 -----------+------------+------------+
624 872
625 Again, JSON::XS leads by far (except for Storable which non-surprisingly 873 Again, JSON::XS leads by far (except for Storable which non-surprisingly
626 decodes faster). 874 decodes faster).
627 875
628 On large strings containing lots of high unicode characters, some 876 On large strings containing lots of high Unicode characters, some
629 modules (such as JSON::PC) seem to decode faster than JSON::XS, but the 877 modules (such as JSON::PC) seem to decode faster than JSON::XS, but the
630 result will be broken due to missing (or wrong) unicode handling. Others 878 result will be broken due to missing (or wrong) Unicode handling. Others
631 refuse to decode or encode properly, so it was impossible to prepare a 879 refuse to decode or encode properly, so it was impossible to prepare a
632 fair comparison table for that case. 880 fair comparison table for that case.
633 881
634SECURITY CONSIDERATIONS 882SECURITY CONSIDERATIONS
635 When you are using JSON in a protocol, talking to untrusted potentially 883 When you are using JSON in a protocol, talking to untrusted potentially
… …
639 have any buffer overflows. Obviously, this module should ensure that and 887 have any buffer overflows. Obviously, this module should ensure that and
640 I am trying hard on making that true, but you never know. 888 I am trying hard on making that true, but you never know.
641 889
642 Second, you need to avoid resource-starving attacks. That means you 890 Second, you need to avoid resource-starving attacks. That means you
643 should limit the size of JSON texts you accept, or make sure then when 891 should limit the size of JSON texts you accept, or make sure then when
644 your resources run out, thats just fine (e.g. by using a separate 892 your resources run out, that's just fine (e.g. by using a separate
645 process that can crash safely). The size of a JSON text in octets or 893 process that can crash safely). The size of a JSON text in octets or
646 characters is usually a good indication of the size of the resources 894 characters is usually a good indication of the size of the resources
647 required to decode it into a Perl structure. 895 required to decode it into a Perl structure. While JSON::XS can check
896 the size of the JSON text, it might be too late when you already have it
897 in memory, so you might want to check the size before you accept the
898 string.
648 899
649 Third, JSON::XS recurses using the C stack when decoding objects and 900 Third, JSON::XS recurses using the C stack when decoding objects and
650 arrays. The C stack is a limited resource: for instance, on my amd64 901 arrays. The C stack is a limited resource: for instance, on my amd64
651 machine with 8MB of stack size I can decode around 180k nested arrays 902 machine with 8MB of stack size I can decode around 180k nested arrays
652 but only 14k nested JSON objects (due to perl itself recursing deeply on 903 but only 14k nested JSON objects (due to perl itself recursing deeply on
… …
657 908
658 And last but least, something else could bomb you that I forgot to think 909 And last but least, something else could bomb you that I forgot to think
659 of. In that case, you get to keep the pieces. I am always open for 910 of. In that case, you get to keep the pieces. I am always open for
660 hints, though... 911 hints, though...
661 912
662 If you are using JSON::XS to return packets to consumption by javascript 913 If you are using JSON::XS to return packets to consumption by JavaScript
663 scripts in a browser you should have a look at 914 scripts in a browser you should have a look at
664 <http://jpsykes.com/47/practical-csrf-and-json-security> to see wether 915 <http://jpsykes.com/47/practical-csrf-and-json-security> to see whether
665 you are vulnerable to some common attack vectors (which really are 916 you are vulnerable to some common attack vectors (which really are
666 browser design bugs, but it is still you who will have to deal with it, 917 browser design bugs, but it is still you who will have to deal with it,
667 as major browser developers care only for features, not about doing 918 as major browser developers care only for features, not about doing
668 security right). 919 security right).
920
921THREADS
922 This module is *not* guaranteed to be thread safe and there are no plans
923 to change this until Perl gets thread support (as opposed to the
924 horribly slow so-called "threads" which are simply slow and bloated
925 process simulations - use fork, its *much* faster, cheaper, better).
926
927 (It might actually work, but you have been warned).
669 928
670BUGS 929BUGS
671 While the goal of this module is to be correct, that unfortunately does 930 While the goal of this module is to be correct, that unfortunately does
672 not mean its bug-free, only that I think its design is bug-free. It is 931 not mean its bug-free, only that I think its design is bug-free. It is
673 still relatively early in its development. If you keep reporting bugs 932 still relatively early in its development. If you keep reporting bugs
674 they will be fixed swiftly, though. 933 they will be fixed swiftly, though.
675 934
935 Please refrain from using rt.cpan.org or any other bug reporting
936 service. I put the contact address into my modules for a reason.
937
676AUTHOR 938AUTHOR
677 Marc Lehmann <schmorp@schmorp.de> 939 Marc Lehmann <schmorp@schmorp.de>
678 http://home.schmorp.de/ 940 http://home.schmorp.de/
679 941

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