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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
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)
3 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
… …
13 # OO-interface 17 # OO-interface
14 18
15 $coder = JSON::XS->new->ascii->pretty->allow_nonref; 19 $coder = JSON::XS->new->ascii->pretty->allow_nonref;
16 $pretty_printed_unencoded = $coder->encode ($perl_scalar); 20 $pretty_printed_unencoded = $coder->encode ($perl_scalar);
17 $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.
18 30
19DESCRIPTION 31DESCRIPTION
20 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
21 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*.
22 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.
23 43
24 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
25 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
26 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
27 cases their maintainers are unresponsive, gone missing, or not listening 47 cases their maintainers are unresponsive, gone missing, or not listening
… …
31 51
32 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
33 vice versa. 53 vice versa.
34 54
35 FEATURES 55 FEATURES
36 * correct unicode handling 56 * correct Unicode handling
37 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
38 when it does so. 58 when it does so.
39 59
40 * round-trip integrity 60 * round-trip integrity
41 When you serialise a perl data structure using only datatypes 61 When you serialise a perl data structure using only datatypes
… …
55 * simple to use 75 * simple to use
56 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
57 interface. 77 interface.
58 78
59 * reasonably versatile output formats 79 * reasonably versatile output formats
60 You can choose between the most compact guarenteed single-line 80 You can choose between the most compact guaranteed single-line
61 format possible (nice for simple line-based protocols), a pure-ascii 81 format possible (nice for simple line-based protocols), a pure-ascii
62 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
63 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
64 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
65 whatever way you like. 85 whatever way you like.
66 86
67FUNCTIONAL INTERFACE 87FUNCTIONAL INTERFACE
68 The following convinience methods are provided by this module. They are 88 The following convenience methods are provided by this module. They are
69 exported by default: 89 exported by default:
70 90
71 $json_text = to_json $perl_scalar 91 $json_text = to_json $perl_scalar
72 Converts the given Perl data structure (a simple scalar or a 92 Converts the given Perl data structure to a UTF-8 encoded, binary
73 reference to a hash or array) to a UTF-8 encoded, binary string
74 (that is, the string contains octets only). Croaks on error. 93 string (that is, the string contains octets only). Croaks on error.
75 94
76 This function call is functionally identical to: 95 This function call is functionally identical to:
77 96
78 $json_text = JSON::XS->new->utf8->encode ($perl_scalar) 97 $json_text = JSON::XS->new->utf8->encode ($perl_scalar)
79 98
80 except being faster. 99 except being faster.
81 100
82 $perl_scalar = from_json $json_text 101 $perl_scalar = from_json $json_text
83 The opposite of "to_json": expects an UTF-8 (binary) string and 102 The opposite of "to_json": expects an UTF-8 (binary) string and
84 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
85 resulting simple scalar or reference. Croaks on error. 104 resulting reference. Croaks on error.
86 105
87 This function call is functionally identical to: 106 This function call is functionally identical to:
88 107
89 $perl_scalar = JSON::XS->new->utf8->decode ($json_text) 108 $perl_scalar = JSON::XS->new->utf8->decode ($json_text)
90 109
… …
97 values in Perl. 116 values in Perl.
98 117
99 See MAPPING, below, for more information on how JSON values are 118 See MAPPING, below, for more information on how JSON values are
100 mapped to Perl. 119 mapped to Perl.
101 120
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
102OBJECT-ORIENTED INTERFACE 160OBJECT-ORIENTED INTERFACE
103 The object oriented interface lets you configure your own encoding or 161 The object oriented interface lets you configure your own encoding or
104 decoding style, within the limits of supported formats. 162 decoding style, within the limits of supported formats.
105 163
106 $json = new JSON::XS 164 $json = new JSON::XS
… …
113 171
114 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]})
115 => {"a": [1, 2]} 173 => {"a": [1, 2]}
116 174
117 $json = $json->ascii ([$enable]) 175 $json = $json->ascii ([$enable])
176 $enabled = $json->get_ascii
118 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
119 generate characters outside the code range 0..127 (which is ASCII). 178 generate characters outside the code range 0..127 (which is ASCII).
120 Any unicode characters outside that range will be escaped using 179 Any Unicode characters outside that range will be escaped using
121 either a single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL 180 either a single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL
122 escape sequence, as per RFC4627. The resulting encoded JSON text can 181 escape sequence, as per RFC4627. The resulting encoded JSON text can
123 be treated as a native unicode string, an ascii-encoded, 182 be treated as a native Unicode string, an ascii-encoded,
124 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
125 ASCII. 184 ASCII.
126 185
127 If $enable is false, then the "encode" method will not escape 186 If $enable is false, then the "encode" method will not escape
128 Unicode characters unless required by the JSON syntax or other 187 Unicode characters unless required by the JSON syntax or other
… …
134 193
135 JSON::XS->new->ascii (1)->encode ([chr 0x10401]) 194 JSON::XS->new->ascii (1)->encode ([chr 0x10401])
136 => ["\ud801\udc01"] 195 => ["\ud801\udc01"]
137 196
138 $json = $json->latin1 ([$enable]) 197 $json = $json->latin1 ([$enable])
198 $enabled = $json->get_latin1
139 If $enable is true (or missing), then the "encode" method will 199 If $enable is true (or missing), then the "encode" method will
140 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
141 any characters outside the code range 0..255. The resulting string 201 any characters outside the code range 0..255. The resulting string
142 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
143 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
144 flag, as "decode" by default expects unicode, which is a strict 204 flag, as "decode" by default expects Unicode, which is a strict
145 superset of latin1. 205 superset of latin1.
146 206
147 If $enable is false, then the "encode" method will not escape 207 If $enable is false, then the "encode" method will not escape
148 Unicode characters unless required by the JSON syntax or other 208 Unicode characters unless required by the JSON syntax or other
149 flags. 209 flags.
150 210
151 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
152 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
153 smaller encoded size. The disadvantage is that the resulting JSON 213 smaller encoded size. The disadvantage is that the resulting JSON
154 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
155 when storing and transfering), a rare encoding for JSON. It is 215 when storing and transferring), a rare encoding for JSON. It is
156 therefore most useful when you want to store data structures known 216 therefore most useful when you want to store data structures known
157 to contain binary data efficiently in files or databases, not when 217 to contain binary data efficiently in files or databases, not when
158 talking to other JSON encoders/decoders. 218 talking to other JSON encoders/decoders.
159 219
160 JSON::XS->new->latin1->encode (["\x{89}\x{abc}"] 220 JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]
161 => ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not) 221 => ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)
162 222
163 $json = $json->utf8 ([$enable]) 223 $json = $json->utf8 ([$enable])
224 $enabled = $json->get_utf8
164 If $enable is true (or missing), then the "encode" method will 225 If $enable is true (or missing), then the "encode" method will
165 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,
166 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
167 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
168 characters outside the range 0..255, they are thus useful for 229 characters outside the range 0..255, they are thus useful for
169 bytewise/binary I/O. In future versions, enabling this option might 230 bytewise/binary I/O. In future versions, enabling this option might
170 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
171 described in RFC4627. 232 described in RFC4627.
172 233
173 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
174 string as a (non-encoded) unicode string, while "decode" expects 235 string as a (non-encoded) Unicode string, while "decode" expects
175 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
176 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.
177 238
178 Example, output UTF-16BE-encoded JSON: 239 Example, output UTF-16BE-encoded JSON:
179 240
180 use Encode; 241 use Encode;
… …
200 2 261 2
201 ] 262 ]
202 } 263 }
203 264
204 $json = $json->indent ([$enable]) 265 $json = $json->indent ([$enable])
266 $enabled = $json->get_indent
205 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
206 multiline format as output, putting every array member or 268 multiline format as output, putting every array member or
207 object/hash key-value pair into its own line, identing them 269 object/hash key-value pair into its own line, indenting them
208 properly. 270 properly.
209 271
210 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
211 the resulting JSON text is guarenteed not to contain any "newlines". 273 the resulting JSON text is guaranteed not to contain any "newlines".
212 274
213 This setting has no effect when decoding JSON texts. 275 This setting has no effect when decoding JSON texts.
214 276
215 $json = $json->space_before ([$enable]) 277 $json = $json->space_before ([$enable])
278 $enabled = $json->get_space_before
216 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
217 an extra optional space before the ":" separating keys from values 280 an extra optional space before the ":" separating keys from values
218 in JSON objects. 281 in JSON objects.
219 282
220 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
… …
226 Example, space_before enabled, space_after and indent disabled: 289 Example, space_before enabled, space_after and indent disabled:
227 290
228 {"key" :"value"} 291 {"key" :"value"}
229 292
230 $json = $json->space_after ([$enable]) 293 $json = $json->space_after ([$enable])
294 $enabled = $json->get_space_after
231 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
232 an extra optional space after the ":" separating keys from values in 296 an extra optional space after the ":" separating keys from values in
233 JSON objects and extra whitespace after the "," separating key-value 297 JSON objects and extra whitespace after the "," separating key-value
234 pairs and array members. 298 pairs and array members.
235 299
… …
240 304
241 Example, space_before and indent disabled, space_after enabled: 305 Example, space_before and indent disabled, space_after enabled:
242 306
243 {"key": "value"} 307 {"key": "value"}
244 308
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
245 $json = $json->canonical ([$enable]) 349 $json = $json->canonical ([$enable])
350 $enabled = $json->get_canonical
246 If $enable is true (or missing), then the "encode" method will 351 If $enable is true (or missing), then the "encode" method will
247 output JSON objects by sorting their keys. This is adding a 352 output JSON objects by sorting their keys. This is adding a
248 comparatively high overhead. 353 comparatively high overhead.
249 354
250 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
251 pairs in the order Perl stores them (which will likely change 356 pairs in the order Perl stores them (which will likely change
252 between runs of the same script). 357 between runs of the same script).
253 358
254 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
255 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
256 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
257 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
258 in Perl. 363 in Perl.
259 364
260 This setting has no effect when decoding JSON texts. 365 This setting has no effect when decoding JSON texts.
261 366
262 $json = $json->allow_nonref ([$enable]) 367 $json = $json->allow_nonref ([$enable])
368 $enabled = $json->get_allow_nonref
263 If $enable is true (or missing), then the "encode" method can 369 If $enable is true (or missing), then the "encode" method can
264 convert a non-reference into its corresponding string, number or 370 convert a non-reference into its corresponding string, number or
265 null JSON value, which is an extension to RFC4627. Likewise, 371 null JSON value, which is an extension to RFC4627. Likewise,
266 "decode" will accept those JSON values instead of croaking. 372 "decode" will accept those JSON values instead of croaking.
267 373
… …
275 381
276 JSON::XS->new->allow_nonref->encode ("Hello, World!") 382 JSON::XS->new->allow_nonref->encode ("Hello, World!")
277 => "Hello, World!" 383 => "Hello, World!"
278 384
279 $json = $json->allow_blessed ([$enable]) 385 $json = $json->allow_blessed ([$enable])
386 $enabled = $json->get_allow_blessed
280 If $enable is true (or missing), then the "encode" method will not 387 If $enable is true (or missing), then the "encode" method will not
281 barf when it encounters a blessed reference. Instead, the value of 388 barf when it encounters a blessed reference. Instead, the value of
282 the convert_blessed option will decide wether "null" 389 the convert_blessed option will decide whether "null"
283 ("convert_blessed" disabled or no "to_json" method found) or a 390 ("convert_blessed" disabled or no "TO_JSON" method found) or a
284 representation of the object ("convert_blessed" enabled and 391 representation of the object ("convert_blessed" enabled and
285 "to_json" method found) is being encoded. Has no effect on "decode". 392 "TO_JSON" method found) is being encoded. Has no effect on "decode".
286 393
287 If $enable is false (the default), then "encode" will throw an 394 If $enable is false (the default), then "encode" will throw an
288 exception when it encounters a blessed object. 395 exception when it encounters a blessed object.
289 396
290 $json = $json->convert_blessed ([$enable]) 397 $json = $json->convert_blessed ([$enable])
398 $enabled = $json->get_convert_blessed
291 If $enable is true (or missing), then "encode", upon encountering a 399 If $enable is true (or missing), then "encode", upon encountering a
292 blessed object, will check for the availability of the "TO_JSON" 400 blessed object, will check for the availability of the "TO_JSON"
293 method on the object's class. If found, it will be called in scalar 401 method on the object's class. If found, it will be called in scalar
294 context and the resulting scalar will be encoded instead of the 402 context and the resulting scalar will be encoded instead of the
295 object. If no "TO_JSON" method is found, the value of 403 object. If no "TO_JSON" method is found, the value of
… …
350 458
351 As this callback gets called less often then the 459 As this callback gets called less often then the
352 "filter_json_object" one, decoding speed will not usually suffer as 460 "filter_json_object" one, decoding speed will not usually suffer as
353 much. Therefore, single-key objects make excellent targets to 461 much. Therefore, single-key objects make excellent targets to
354 serialise Perl objects into, especially as single-key JSON objects 462 serialise Perl objects into, especially as single-key JSON objects
355 are as close to the type-tagged value concept as JSON gets (its 463 are as close to the type-tagged value concept as JSON gets (it's
356 basically an ID/VALUE tuple). Of course, JSON does not support this 464 basically an ID/VALUE tuple). Of course, JSON does not support this
357 in any way, so you need to make sure your data never looks like a 465 in any way, so you need to make sure your data never looks like a
358 serialised Perl hash. 466 serialised Perl hash.
359 467
360 Typical names for the single object key are "__class_whatever__", or 468 Typical names for the single object key are "__class_whatever__", or
… …
385 493
386 { __widget__ => $self->{id} } 494 { __widget__ => $self->{id} }
387 } 495 }
388 496
389 $json = $json->shrink ([$enable]) 497 $json = $json->shrink ([$enable])
498 $enabled = $json->get_shrink
390 Perl usually over-allocates memory a bit when allocating space for 499 Perl usually over-allocates memory a bit when allocating space for
391 strings. This flag optionally resizes strings generated by either 500 strings. This flag optionally resizes strings generated by either
392 "encode" or "decode" to their minimum size possible. This can save 501 "encode" or "decode" to their minimum size possible. This can save
393 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
394 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
… …
412 converting strings that look like integers or floats into integers 521 converting strings that look like integers or floats into integers
413 or floats internally (there is no difference on the Perl level), 522 or floats internally (there is no difference on the Perl level),
414 saving space. 523 saving space.
415 524
416 $json = $json->max_depth ([$maximum_nesting_depth]) 525 $json = $json->max_depth ([$maximum_nesting_depth])
526 $max_depth = $json->get_max_depth
417 Sets the maximum nesting level (default 512) accepted while encoding 527 Sets the maximum nesting level (default 512) accepted while encoding
418 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
419 higher nesting level then this limit, then the encoder and decoder 529 higher nesting level then this limit, then the encoder and decoder
420 will stop and croak at that point. 530 will stop and croak at that point.
421 531
… …
433 543
434 See SECURITY CONSIDERATIONS, below, for more info on why this is 544 See SECURITY CONSIDERATIONS, below, for more info on why this is
435 useful. 545 useful.
436 546
437 $json = $json->max_size ([$maximum_string_size]) 547 $json = $json->max_size ([$maximum_string_size])
548 $max_size = $json->get_max_size
438 Set the maximum length a JSON text may have (in bytes) where 549 Set the maximum length a JSON text may have (in bytes) where
439 decoding is being attempted. The default is 0, meaning no limit. 550 decoding is being attempted. The default is 0, meaning no limit.
440 When "decode" is called on a string longer then this number of 551 When "decode" is called on a string longer then this number of
441 characters it will not attempt to decode the string but throw an 552 characters it will not attempt to decode the string but throw an
442 exception. This setting has no effect on "encode" (yet). 553 exception. This setting has no effect on "encode" (yet).
… …
484 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
485 circumstances automatically, preserving round-tripping characteristics 596 circumstances automatically, preserving round-tripping characteristics
486 (what you put in comes out as something equivalent). 597 (what you put in comes out as something equivalent).
487 598
488 For the more enlightened: note that in the following descriptions, 599 For the more enlightened: note that in the following descriptions,
489 lowercase *perl* refers to the Perl interpreter, while uppcercase *Perl* 600 lowercase *perl* refers to the Perl interpreter, while uppercase *Perl*
490 refers to the abstract Perl language itself. 601 refers to the abstract Perl language itself.
491 602
492 JSON -> PERL 603 JSON -> PERL
493 object 604 object
494 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
495 object keys is preserved (JSON does not preserver object key 606 object keys is preserved (JSON does not preserve object key ordering
496 ordering itself). 607 itself).
497 608
498 array 609 array
499 A JSON array becomes a reference to an array in Perl. 610 A JSON array becomes a reference to an array in Perl.
500 611
501 string 612 string
… …
525 strings, but as Perl is typeless there is no other way to do it. 636 strings, but as Perl is typeless there is no other way to do it.
526 637
527 true, false 638 true, false
528 These JSON atoms become "JSON::XS::true" and "JSON::XS::false", 639 These JSON atoms become "JSON::XS::true" and "JSON::XS::false",
529 respectively. They are overloaded to act almost exactly like the 640 respectively. They are overloaded to act almost exactly like the
530 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
531 using the "JSON::XS::is_bool" function. 642 using the "JSON::XS::is_bool" function.
532 643
533 null 644 null
534 A JSON null atom becomes "undef" in Perl. 645 A JSON null atom becomes "undef" in Perl.
535 646
… …
562 673
563 to_json [\0,JSON::XS::true] # yields [false,true] 674 to_json [\0,JSON::XS::true] # yields [false,true]
564 675
565 JSON::XS::true, JSON::XS::false 676 JSON::XS::true, JSON::XS::false
566 These special values become JSON true and JSON false values, 677 These special values become JSON true and JSON false values,
567 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.
568 679
569 blessed objects 680 blessed objects
570 Blessed objects are not allowed. JSON::XS currently tries to encode 681 Blessed objects are not allowed. JSON::XS currently tries to encode
571 their underlying representation (hash- or arrayref), but this 682 their underlying representation (hash- or arrayref), but this
572 behaviour might change in future versions. 683 behaviour might change in future versions.
… …
588 to_json [$value] # yields ["5"] 699 to_json [$value] # yields ["5"]
589 700
590 # undef becomes null 701 # undef becomes null
591 to_json [undef] # yields [null] 702 to_json [undef] # yields [null]
592 703
593 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:
594 705
595 my $x = 3.1; # some variable containing a number 706 my $x = 3.1; # some variable containing a number
596 "$x"; # stringified 707 "$x"; # stringified
597 $x .= ""; # another, more awkward way to stringify 708 $x .= ""; # another, more awkward way to stringify
598 print $x; # perl does it for you, too, quite often 709 print $x; # perl does it for you, too, quite often
599 710
600 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:
601 712
602 my $x = "3"; # some variable containing a string 713 my $x = "3"; # some variable containing a string
603 $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
604 $x *= 1; # same thing, the choise is yours. 715 $x *= 1; # same thing, the choice is yours.
605 716
606 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.
607 other, less obscure, ways. Tell me if you need this capability. 718 Tell me if you need this capability.
608 719
609COMPARISON 720COMPARISON
610 As already mentioned, this module was created because none of the 721 As already mentioned, this module was created because none of the
611 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
612 describe the problems (or pleasures) I encountered with various existing 723 describe the problems (or pleasures) I encountered with various existing
… …
614 not to suffer from any of these problems or limitations. 725 not to suffer from any of these problems or limitations.
615 726
616 JSON 1.07 727 JSON 1.07
617 Slow (but very portable, as it is written in pure Perl). 728 Slow (but very portable, as it is written in pure Perl).
618 729
619 Undocumented/buggy Unicode handling (how JSON handles unicode values 730 Undocumented/buggy Unicode handling (how JSON handles Unicode values
620 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
621 doing en-/decoding oneself, but unicode escapes are not working 732 doing en-/decoding oneself, but Unicode escapes are not working
622 properly). 733 properly).
623 734
624 No roundtripping (strings get clobbered if they look like numbers, 735 No round-tripping (strings get clobbered if they look like numbers,
625 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
626 will decode into the number 2. 737 will decode into the number 2.
627 738
628 JSON::PC 0.01 739 JSON::PC 0.01
629 Very fast. 740 Very fast.
630 741
631 Undocumented/buggy Unicode handling. 742 Undocumented/buggy Unicode handling.
632 743
633 No roundtripping. 744 No round-tripping.
634 745
635 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
636 magic values will make it croak). 747 magic values will make it croak).
637 748
638 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}"
… …
648 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
649 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
650 preferably a way to generate ASCII-only JSON texts). 761 preferably a way to generate ASCII-only JSON texts).
651 762
652 Completely broken (and confusingly documented) Unicode handling 763 Completely broken (and confusingly documented) Unicode handling
653 (unicode escapes are not working properly, you need to set 764 (Unicode escapes are not working properly, you need to set
654 ImplicitUnicode to *different* values on en- and decoding to get 765 ImplicitUnicode to *different* values on en- and decoding to get
655 symmetric behaviour). 766 symmetric behaviour).
656 767
657 No roundtripping (simple cases work, but this depends on wether the 768 No round-tripping (simple cases work, but this depends on whether
658 scalar value was used in a numeric context or not). 769 the scalar value was used in a numeric context or not).
659 770
660 Dumping hashes may skip hash values depending on iterator state. 771 Dumping hashes may skip hash values depending on iterator state.
661 772
662 Unmaintained (maintainer unresponsive for many months, bugs are not 773 Unmaintained (maintainer unresponsive for many months, bugs are not
663 getting fixed). 774 getting fixed).
664 775
665 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
666 and return "something" instead of raising an exception. This is a 777 and return "something" instead of raising an exception. This is a
667 security issue: imagine two banks transfering money between each 778 security issue: imagine two banks transferring money between each
668 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
669 deduct money, while the other might reject the transaction with a 780 deduct money, while the other might reject the transaction with a
670 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
671 extra unnecessary work and the transaction will still not succeed). 782 extra unnecessary work and the transaction will still not succeed).
672 783
673 JSON::DWIW 0.04 784 JSON::DWIW 0.04
674 Very fast. Very natural. Very nice. 785 Very fast. Very natural. Very nice.
675 786
676 Undocumented unicode handling (but the best of the pack. Unicode 787 Undocumented Unicode handling (but the best of the pack. Unicode
677 escapes still don't get parsed properly). 788 escapes still don't get parsed properly).
678 789
679 Very inflexible. 790 Very inflexible.
680 791
681 No roundtripping. 792 No round-tripping.
682 793
683 Does not generate valid JSON texts (key strings are often unquoted, 794 Does not generate valid JSON texts (key strings are often unquoted,
684 empty keys result in nothing being output) 795 empty keys result in nothing being output)
685 796
686 Does not check input for validity. 797 Does not check input for validity.
… …
698 my $yaml = $to_yaml->encode ($ref) . "\n"; 809 my $yaml = $to_yaml->encode ($ref) . "\n";
699 810
700 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.
701 Please note that YAML has hardcoded limits on (simple) object key 812 Please note that YAML has hardcoded limits on (simple) object key
702 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
703 keys are noticably shorter than the 1024 characters YAML allows. 814 keys are noticeably shorter than the 1024 characters YAML allows.
704 815
705 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
706 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
707 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:
708 chances are high that you will run into severe interoperability 819 chances are high that you will run into severe interoperability
… …
723 It shows the number of encodes/decodes per second (JSON::XS uses the 834 It shows the number of encodes/decodes per second (JSON::XS uses the
724 functional interface, while JSON::XS/2 uses the OO interface with 835 functional interface, while JSON::XS/2 uses the OO interface with
725 pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink). 836 pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink).
726 Higher is better: 837 Higher is better:
727 838
728 Storable | 15779.925 | 14169.946 |
729 -----------+------------+------------+
730 module | encode | decode | 839 module | encode | decode |
731 -----------|------------|------------| 840 -----------|------------|------------|
732 JSON | 4990.842 | 4088.813 | 841 JSON 1.x | 4990.842 | 4088.813 |
733 JSON::DWIW | 51653.990 | 71575.154 | 842 JSON::DWIW | 51653.990 | 71575.154 |
734 JSON::PC | 65948.176 | 74631.744 | 843 JSON::PC | 65948.176 | 74631.744 |
735 JSON::PP | 8931.652 | 3817.168 | 844 JSON::PP | 8931.652 | 3817.168 |
736 JSON::Syck | 24877.248 | 27776.848 | 845 JSON::Syck | 24877.248 | 27776.848 |
737 JSON::XS | 388361.481 | 227951.304 | 846 JSON::XS | 388361.481 | 227951.304 |
… …
739 JSON::XS/3 | 338250.323 | 218453.333 | 848 JSON::XS/3 | 338250.323 | 218453.333 |
740 Storable | 16500.016 | 135300.129 | 849 Storable | 16500.016 | 135300.129 |
741 -----------+------------+------------+ 850 -----------+------------+------------+
742 851
743 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
744 encoding, about three times faster on decoding, and over fourty times 853 encoding, about three times faster on decoding, and over forty times
745 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
746 compares favourably to Storable for small amounts of data. 855 compares favourably to Storable for small amounts of data.
747 856
748 Using a longer test string (roughly 18KB, generated from Yahoo! Locals 857 Using a longer test string (roughly 18KB, generated from Yahoo! Locals
749 search API (http://nanoref.com/yahooapis/mgPdGg): 858 search API (http://nanoref.com/yahooapis/mgPdGg):
750 859
751 module | encode | decode | 860 module | encode | decode |
752 -----------|------------|------------| 861 -----------|------------|------------|
753 JSON | 55.260 | 34.971 | 862 JSON 1.x | 55.260 | 34.971 |
754 JSON::DWIW | 825.228 | 1082.513 | 863 JSON::DWIW | 825.228 | 1082.513 |
755 JSON::PC | 3571.444 | 2394.829 | 864 JSON::PC | 3571.444 | 2394.829 |
756 JSON::PP | 210.987 | 32.574 | 865 JSON::PP | 210.987 | 32.574 |
757 JSON::Syck | 552.551 | 787.544 | 866 JSON::Syck | 552.551 | 787.544 |
758 JSON::XS | 5780.463 | 4854.519 | 867 JSON::XS | 5780.463 | 4854.519 |
… …
762 -----------+------------+------------+ 871 -----------+------------+------------+
763 872
764 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
765 decodes faster). 874 decodes faster).
766 875
767 On large strings containing lots of high unicode characters, some 876 On large strings containing lots of high Unicode characters, some
768 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
769 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
770 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
771 fair comparison table for that case. 880 fair comparison table for that case.
772 881
773SECURITY CONSIDERATIONS 882SECURITY CONSIDERATIONS
774 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
… …
778 have any buffer overflows. Obviously, this module should ensure that and 887 have any buffer overflows. Obviously, this module should ensure that and
779 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.
780 889
781 Second, you need to avoid resource-starving attacks. That means you 890 Second, you need to avoid resource-starving attacks. That means you
782 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
783 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
784 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
785 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
786 required to decode it into a Perl structure. While JSON::XS can check 895 required to decode it into a Perl structure. While JSON::XS can check
787 the size of the JSON text, it might be too late when you already have it 896 the size of the JSON text, it might be too late when you already have it
788 in memory, so you might want to check the size before you accept the 897 in memory, so you might want to check the size before you accept the
… …
799 908
800 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
801 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
802 hints, though... 911 hints, though...
803 912
804 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
805 scripts in a browser you should have a look at 914 scripts in a browser you should have a look at
806 <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
807 you are vulnerable to some common attack vectors (which really are 916 you are vulnerable to some common attack vectors (which really are
808 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,
809 as major browser developers care only for features, not about doing 918 as major browser developers care only for features, not about doing
810 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).
811 928
812BUGS 929BUGS
813 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
814 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
815 still relatively early in its development. If you keep reporting bugs 932 still relatively early in its development. If you keep reporting bugs
816 they will be fixed swiftly, though. 933 they will be fixed swiftly, though.
817 934
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
818AUTHOR 938AUTHOR
819 Marc Lehmann <schmorp@schmorp.de> 939 Marc Lehmann <schmorp@schmorp.de>
820 http://home.schmorp.de/ 940 http://home.schmorp.de/
821 941

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