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Revision 1.38 by root, Tue Oct 29 00:36:18 2013 UTC

1NAME 1NAME
2 JSON::XS - JSON serialising/deserialising, done correctly and fast 2 JSON::XS - JSON serialising/deserialising, done correctly and fast
3 3
4 JSON::XS - 正しくて高速な JSON シリアライザ/デシリアライザ
5 (http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html)
6
4SYNOPSIS 7SYNOPSIS
5 use JSON::XS; 8 use JSON::XS;
6 9
7 # exported functions, they croak on error 10 # exported functions, they croak on error
8 # and expect/generate UTF-8 11 # and expect/generate UTF-8
9 12
10 $utf8_encoded_json_text = to_json $perl_hash_or_arrayref; 13 $utf8_encoded_json_text = encode_json $perl_hash_or_arrayref;
11 $perl_hash_or_arrayref = from_json $utf8_encoded_json_text; 14 $perl_hash_or_arrayref = decode_json $utf8_encoded_json_text;
12 15
13 # OO-interface 16 # OO-interface
14 17
15 $coder = JSON::XS->new->ascii->pretty->allow_nonref; 18 $coder = JSON::XS->new->ascii->pretty->allow_nonref;
16 $pretty_printed_unencoded = $coder->encode ($perl_scalar); 19 $pretty_printed_unencoded = $coder->encode ($perl_scalar);
17 $perl_scalar = $coder->decode ($unicode_json_text); 20 $perl_scalar = $coder->decode ($unicode_json_text);
21
22 # Note that JSON version 2.0 and above will automatically use JSON::XS
23 # if available, at virtually no speed overhead either, so you should
24 # be able to just:
25
26 use JSON;
27
28 # and do the same things, except that you have a pure-perl fallback now.
18 29
19DESCRIPTION 30DESCRIPTION
20 This module converts Perl data structures to JSON and vice versa. Its 31 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*. 32 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. 33 To reach the latter goal it was written in C.
34
35 Beginning with version 2.0 of the JSON module, when both JSON and
36 JSON::XS are installed, then JSON will fall back on JSON::XS (this can
37 be overridden) with no overhead due to emulation (by inheriting
38 constructor and methods). If JSON::XS is not available, it will fall
39 back to the compatible JSON::PP module as backend, so using JSON instead
40 of JSON::XS gives you a portable JSON API that can be fast when you need
41 and doesn't require a C compiler when that is a problem.
23 42
24 As this is the n-th-something JSON module on CPAN, what was the reason 43 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 44 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 45 modules, none of them correctly handle all corner cases, and in most
27 cases their maintainers are unresponsive, gone missing, or not listening 46 cases their maintainers are unresponsive, gone missing, or not listening
28 to bug reports for other reasons. 47 to bug reports for other reasons.
29 48
30 See COMPARISON, below, for a comparison to some other JSON modules.
31
32 See MAPPING, below, on how JSON::XS maps perl values to JSON values and 49 See MAPPING, below, on how JSON::XS maps perl values to JSON values and
33 vice versa. 50 vice versa.
34 51
35 FEATURES 52 FEATURES
36 * correct unicode handling 53 * correct Unicode handling
54
37 This module knows how to handle Unicode, and even documents how and 55 This module knows how to handle Unicode, documents how and when it
38 when it does so. 56 does so, and even documents what "correct" means.
39 57
40 * round-trip integrity 58 * round-trip integrity
59
41 When you serialise a perl data structure using only datatypes 60 When you serialise a perl data structure using only data types
42 supported by JSON, the deserialised data structure is identical on 61 supported by JSON and Perl, the deserialised data structure is
43 the Perl level. (e.g. the string "2.0" doesn't suddenly become "2" 62 identical on the Perl level. (e.g. the string "2.0" doesn't suddenly
44 just because it looks like a number). 63 become "2" just because it looks like a number). There *are* minor
64 exceptions to this, read the MAPPING section below to learn about
65 those.
45 66
46 * strict checking of JSON correctness 67 * strict checking of JSON correctness
68
47 There is no guessing, no generating of illegal JSON texts by 69 There is no guessing, no generating of illegal JSON texts by
48 default, and only JSON is accepted as input by default (the latter 70 default, and only JSON is accepted as input by default (the latter
49 is a security feature). 71 is a security feature).
50 72
51 * fast 73 * fast
52 Compared to other JSON modules, this module compares favourably in
53 terms of speed, too.
54 74
75 Compared to other JSON modules and other serialisers such as
76 Storable, this module usually compares favourably in terms of speed,
77 too.
78
55 * simple to use 79 * simple to use
80
56 This module has both a simple functional interface as well as an OO 81 This module has both a simple functional interface as well as an
57 interface. 82 object oriented interface.
58 83
59 * reasonably versatile output formats 84 * reasonably versatile output formats
85
60 You can choose between the most compact guarenteed single-line 86 You can choose between the most compact guaranteed-single-line
61 format possible (nice for simple line-based protocols), a pure-ascii 87 format possible (nice for simple line-based protocols), a pure-ASCII
62 format (for when your transport is not 8-bit clean, still supports 88 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 89 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 90 want to read that stuff). Or you can combine those features in
65 whatever way you like. 91 whatever way you like.
66 92
67FUNCTIONAL INTERFACE 93FUNCTIONAL INTERFACE
68 The following convinience methods are provided by this module. They are 94 The following convenience methods are provided by this module. They are
69 exported by default: 95 exported by default:
70 96
71 $json_text = to_json $perl_scalar 97 $json_text = encode_json $perl_scalar
72 Converts the given Perl data structure (a simple scalar or a 98 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. 99 string (that is, the string contains octets only). Croaks on error.
75 100
76 This function call is functionally identical to: 101 This function call is functionally identical to:
77 102
78 $json_text = JSON::XS->new->utf8->encode ($perl_scalar) 103 $json_text = JSON::XS->new->utf8->encode ($perl_scalar)
79 104
80 except being faster. 105 Except being faster.
81 106
82 $perl_scalar = from_json $json_text 107 $perl_scalar = decode_json $json_text
83 The opposite of "to_json": expects an UTF-8 (binary) string and 108 The opposite of "encode_json": expects an UTF-8 (binary) string and
84 tries to parse that as an UTF-8 encoded JSON text, returning the 109 tries to parse that as an UTF-8 encoded JSON text, returning the
85 resulting simple scalar or reference. Croaks on error. 110 resulting reference. Croaks on error.
86 111
87 This function call is functionally identical to: 112 This function call is functionally identical to:
88 113
89 $perl_scalar = JSON::XS->new->utf8->decode ($json_text) 114 $perl_scalar = JSON::XS->new->utf8->decode ($json_text)
90 115
91 except being faster. 116 Except being faster.
92 117
93 $is_boolean = JSON::XS::is_bool $scalar 118A FEW NOTES ON UNICODE AND PERL
94 Returns true if the passed scalar represents either JSON::XS::true 119 Since this often leads to confusion, here are a few very clear words on
95 or JSON::XS::false, two constants that act like 1 and 0, 120 how Unicode works in Perl, modulo bugs.
96 respectively and are used to represent JSON "true" and "false"
97 values in Perl.
98 121
99 See MAPPING, below, for more information on how JSON values are 122 1. Perl strings can store characters with ordinal values > 255.
100 mapped to Perl. 123 This enables you to store Unicode characters as single characters in
124 a Perl string - very natural.
125
126 2. Perl does *not* associate an encoding with your strings.
127 ... until you force it to, e.g. when matching it against a regex, or
128 printing the scalar to a file, in which case Perl either interprets
129 your string as locale-encoded text, octets/binary, or as Unicode,
130 depending on various settings. In no case is an encoding stored
131 together with your data, it is *use* that decides encoding, not any
132 magical meta data.
133
134 3. The internal utf-8 flag has no meaning with regards to the encoding
135 of your string.
136 Just ignore that flag unless you debug a Perl bug, a module written
137 in XS or want to dive into the internals of perl. Otherwise it will
138 only confuse you, as, despite the name, it says nothing about how
139 your string is encoded. You can have Unicode strings with that flag
140 set, with that flag clear, and you can have binary data with that
141 flag set and that flag clear. Other possibilities exist, too.
142
143 If you didn't know about that flag, just the better, pretend it
144 doesn't exist.
145
146 4. A "Unicode String" is simply a string where each character can be
147 validly interpreted as a Unicode code point.
148 If you have UTF-8 encoded data, it is no longer a Unicode string,
149 but a Unicode string encoded in UTF-8, giving you a binary string.
150
151 5. A string containing "high" (> 255) character values is *not* a UTF-8
152 string.
153 It's a fact. Learn to live with it.
154
155 I hope this helps :)
101 156
102OBJECT-ORIENTED INTERFACE 157OBJECT-ORIENTED INTERFACE
103 The object oriented interface lets you configure your own encoding or 158 The object oriented interface lets you configure your own encoding or
104 decoding style, within the limits of supported formats. 159 decoding style, within the limits of supported formats.
105 160
… …
113 168
114 my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]}) 169 my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]})
115 => {"a": [1, 2]} 170 => {"a": [1, 2]}
116 171
117 $json = $json->ascii ([$enable]) 172 $json = $json->ascii ([$enable])
173 $enabled = $json->get_ascii
118 If $enable is true (or missing), then the "encode" method will not 174 If $enable is true (or missing), then the "encode" method will not
119 generate characters outside the code range 0..127 (which is ASCII). 175 generate characters outside the code range 0..127 (which is ASCII).
120 Any unicode characters outside that range will be escaped using 176 Any Unicode characters outside that range will be escaped using
121 either a single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL 177 either a single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL
122 escape sequence, as per RFC4627. The resulting encoded JSON text can 178 escape sequence, as per RFC4627. The resulting encoded JSON text can
123 be treated as a native unicode string, an ascii-encoded, 179 be treated as a native Unicode string, an ascii-encoded,
124 latin1-encoded or UTF-8 encoded string, or any other superset of 180 latin1-encoded or UTF-8 encoded string, or any other superset of
125 ASCII. 181 ASCII.
126 182
127 If $enable is false, then the "encode" method will not escape 183 If $enable is false, then the "encode" method will not escape
128 Unicode characters unless required by the JSON syntax or other 184 Unicode characters unless required by the JSON syntax or other
129 flags. This results in a faster and more compact format. 185 flags. This results in a faster and more compact format.
130 186
187 See also the section *ENCODING/CODESET FLAG NOTES* later in this
188 document.
189
131 The main use for this flag is to produce JSON texts that can be 190 The main use for this flag is to produce JSON texts that can be
132 transmitted over a 7-bit channel, as the encoded JSON texts will not 191 transmitted over a 7-bit channel, as the encoded JSON texts will not
133 contain any 8 bit characters. 192 contain any 8 bit characters.
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.
210
211 See also the section *ENCODING/CODESET FLAG NOTES* later in this
212 document.
150 213
151 The main use for this flag is efficiently encoding binary data as 214 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 215 JSON text, as most octets will not be escaped, resulting in a
153 smaller encoded size. The disadvantage is that the resulting JSON 216 smaller encoded size. The disadvantage is that the resulting JSON
154 text is encoded in latin1 (and must correctly be treated as such 217 text is encoded in latin1 (and must correctly be treated as such
155 when storing and transfering), a rare encoding for JSON. It is 218 when storing and transferring), a rare encoding for JSON. It is
156 therefore most useful when you want to store data structures known 219 therefore most useful when you want to store data structures known
157 to contain binary data efficiently in files or databases, not when 220 to contain binary data efficiently in files or databases, not when
158 talking to other JSON encoders/decoders. 221 talking to other JSON encoders/decoders.
159 222
160 JSON::XS->new->latin1->encode (["\x{89}\x{abc}"] 223 JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]
161 => ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not) 224 => ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)
162 225
163 $json = $json->utf8 ([$enable]) 226 $json = $json->utf8 ([$enable])
227 $enabled = $json->get_utf8
164 If $enable is true (or missing), then the "encode" method will 228 If $enable is true (or missing), then the "encode" method will
165 encode the JSON result into UTF-8, as required by many protocols, 229 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 230 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 231 string. Please note that UTF-8-encoded strings do not contain any
168 characters outside the range 0..255, they are thus useful for 232 characters outside the range 0..255, they are thus useful for
169 bytewise/binary I/O. In future versions, enabling this option might 233 bytewise/binary I/O. In future versions, enabling this option might
170 enable autodetection of the UTF-16 and UTF-32 encoding families, as 234 enable autodetection of the UTF-16 and UTF-32 encoding families, as
171 described in RFC4627. 235 described in RFC4627.
172 236
173 If $enable is false, then the "encode" method will return the JSON 237 If $enable is false, then the "encode" method will return the JSON
174 string as a (non-encoded) unicode string, while "decode" expects 238 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 239 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. 240 UTF-16) needs to be done yourself, e.g. using the Encode module.
241
242 See also the section *ENCODING/CODESET FLAG NOTES* later in this
243 document.
177 244
178 Example, output UTF-16BE-encoded JSON: 245 Example, output UTF-16BE-encoded JSON:
179 246
180 use Encode; 247 use Encode;
181 $jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object); 248 $jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
… …
200 2 267 2
201 ] 268 ]
202 } 269 }
203 270
204 $json = $json->indent ([$enable]) 271 $json = $json->indent ([$enable])
272 $enabled = $json->get_indent
205 If $enable is true (or missing), then the "encode" method will use a 273 If $enable is true (or missing), then the "encode" method will use a
206 multiline format as output, putting every array member or 274 multiline format as output, putting every array member or
207 object/hash key-value pair into its own line, identing them 275 object/hash key-value pair into its own line, indenting them
208 properly. 276 properly.
209 277
210 If $enable is false, no newlines or indenting will be produced, and 278 If $enable is false, no newlines or indenting will be produced, and
211 the resulting JSON text is guarenteed not to contain any "newlines". 279 the resulting JSON text is guaranteed not to contain any "newlines".
212 280
213 This setting has no effect when decoding JSON texts. 281 This setting has no effect when decoding JSON texts.
214 282
215 $json = $json->space_before ([$enable]) 283 $json = $json->space_before ([$enable])
284 $enabled = $json->get_space_before
216 If $enable is true (or missing), then the "encode" method will add 285 If $enable is true (or missing), then the "encode" method will add
217 an extra optional space before the ":" separating keys from values 286 an extra optional space before the ":" separating keys from values
218 in JSON objects. 287 in JSON objects.
219 288
220 If $enable is false, then the "encode" method will not add any extra 289 If $enable is false, then the "encode" method will not add any extra
… …
226 Example, space_before enabled, space_after and indent disabled: 295 Example, space_before enabled, space_after and indent disabled:
227 296
228 {"key" :"value"} 297 {"key" :"value"}
229 298
230 $json = $json->space_after ([$enable]) 299 $json = $json->space_after ([$enable])
300 $enabled = $json->get_space_after
231 If $enable is true (or missing), then the "encode" method will add 301 If $enable is true (or missing), then the "encode" method will add
232 an extra optional space after the ":" separating keys from values in 302 an extra optional space after the ":" separating keys from values in
233 JSON objects and extra whitespace after the "," separating key-value 303 JSON objects and extra whitespace after the "," separating key-value
234 pairs and array members. 304 pairs and array members.
235 305
… …
241 Example, space_before and indent disabled, space_after enabled: 311 Example, space_before and indent disabled, space_after enabled:
242 312
243 {"key": "value"} 313 {"key": "value"}
244 314
245 $json = $json->relaxed ([$enable]) 315 $json = $json->relaxed ([$enable])
316 $enabled = $json->get_relaxed
246 If $enable is true (or missing), then "decode" will accept some 317 If $enable is true (or missing), then "decode" will accept some
247 extensions to normal JSON syntax (see below). "encode" will not be 318 extensions to normal JSON syntax (see below). "encode" will not be
248 affected in anyway. *Be aware that this option makes you accept 319 affected in anyway. *Be aware that this option makes you accept
249 invalid JSON texts as if they were valid!*. I suggest only to use 320 invalid JSON texts as if they were valid!*. I suggest only to use
250 this option to parse application-specific files written by humans 321 this option to parse application-specific files written by humans
… …
253 If $enable is false (the default), then "decode" will only accept 324 If $enable is false (the default), then "decode" will only accept
254 valid JSON texts. 325 valid JSON texts.
255 326
256 Currently accepted extensions are: 327 Currently accepted extensions are:
257 328
258 * list items can have an end-comma 329 * list items can have an end-comma
330
259 JSON *separates* array elements and key-value pairs with commas. 331 JSON *separates* array elements and key-value pairs with commas.
260 This can be annoying if you write JSON texts manually and want 332 This can be annoying if you write JSON texts manually and want
261 to be able to quickly append elements, so this extension accepts 333 to be able to quickly append elements, so this extension accepts
262 comma at the end of such items not just between them: 334 comma at the end of such items not just between them:
263 335
… …
268 { 340 {
269 "k1": "v1", 341 "k1": "v1",
270 "k2": "v2", <- this comma not normally allowed 342 "k2": "v2", <- this comma not normally allowed
271 } 343 }
272 344
273 * shell-style '#'-comments 345 * shell-style '#'-comments
346
274 Whenever JSON allows whitespace, shell-style comments are 347 Whenever JSON allows whitespace, shell-style comments are
275 additionally allowed. They are terminated by the first 348 additionally allowed. They are terminated by the first
276 carriage-return or line-feed character, after which more 349 carriage-return or line-feed character, after which more
277 white-space and comments are allowed. 350 white-space and comments are allowed.
278 351
… …
280 1, # this comment not allowed in JSON 353 1, # this comment not allowed in JSON
281 # neither this one... 354 # neither this one...
282 ] 355 ]
283 356
284 $json = $json->canonical ([$enable]) 357 $json = $json->canonical ([$enable])
358 $enabled = $json->get_canonical
285 If $enable is true (or missing), then the "encode" method will 359 If $enable is true (or missing), then the "encode" method will
286 output JSON objects by sorting their keys. This is adding a 360 output JSON objects by sorting their keys. This is adding a
287 comparatively high overhead. 361 comparatively high overhead.
288 362
289 If $enable is false, then the "encode" method will output key-value 363 If $enable is false, then the "encode" method will output key-value
290 pairs in the order Perl stores them (which will likely change 364 pairs in the order Perl stores them (which will likely change
291 between runs of the same script). 365 between runs of the same script, and can change even within the same
366 run from 5.18 onwards).
292 367
293 This option is useful if you want the same data structure to be 368 This option is useful if you want the same data structure to be
294 encoded as the same JSON text (given the same overall settings). If 369 encoded as the same JSON text (given the same overall settings). If
295 it is disabled, the same hash migh be encoded differently even if 370 it is disabled, the same hash might be encoded differently even if
296 contains the same data, as key-value pairs have no inherent ordering 371 contains the same data, as key-value pairs have no inherent ordering
297 in Perl. 372 in Perl.
298 373
299 This setting has no effect when decoding JSON texts. 374 This setting has no effect when decoding JSON texts.
300 375
376 This setting has currently no effect on tied hashes.
377
301 $json = $json->allow_nonref ([$enable]) 378 $json = $json->allow_nonref ([$enable])
379 $enabled = $json->get_allow_nonref
302 If $enable is true (or missing), then the "encode" method can 380 If $enable is true (or missing), then the "encode" method can
303 convert a non-reference into its corresponding string, number or 381 convert a non-reference into its corresponding string, number or
304 null JSON value, which is an extension to RFC4627. Likewise, 382 null JSON value, which is an extension to RFC4627. Likewise,
305 "decode" will accept those JSON values instead of croaking. 383 "decode" will accept those JSON values instead of croaking.
306 384
… …
313 "allow_nonref", resulting in an invalid JSON text: 391 "allow_nonref", resulting in an invalid JSON text:
314 392
315 JSON::XS->new->allow_nonref->encode ("Hello, World!") 393 JSON::XS->new->allow_nonref->encode ("Hello, World!")
316 => "Hello, World!" 394 => "Hello, World!"
317 395
396 $json = $json->allow_unknown ([$enable])
397 $enabled = $json->get_allow_unknown
398 If $enable is true (or missing), then "encode" will *not* throw an
399 exception when it encounters values it cannot represent in JSON (for
400 example, filehandles) but instead will encode a JSON "null" value.
401 Note that blessed objects are not included here and are handled
402 separately by c<allow_nonref>.
403
404 If $enable is false (the default), then "encode" will throw an
405 exception when it encounters anything it cannot encode as JSON.
406
407 This option does not affect "decode" in any way, and it is
408 recommended to leave it off unless you know your communications
409 partner.
410
318 $json = $json->allow_blessed ([$enable]) 411 $json = $json->allow_blessed ([$enable])
412 $enabled = $json->get_allow_blessed
413 See "OBJECT SERIALISATION" for details.
414
319 If $enable is true (or missing), then the "encode" method will not 415 If $enable is true (or missing), then the "encode" method will not
320 barf when it encounters a blessed reference. Instead, the value of 416 barf when it encounters a blessed reference that it cannot convert
321 the convert_blessed option will decide wether "null" 417 otherwise. Instead, a JSON "null" value is encoded instead of the
322 ("convert_blessed" disabled or no "to_json" method found) or a 418 object.
323 representation of the object ("convert_blessed" enabled and
324 "to_json" method found) is being encoded. Has no effect on "decode".
325 419
326 If $enable is false (the default), then "encode" will throw an 420 If $enable is false (the default), then "encode" will throw an
327 exception when it encounters a blessed object. 421 exception when it encounters a blessed object that it cannot convert
422 otherwise.
423
424 This setting has no effect on "decode".
328 425
329 $json = $json->convert_blessed ([$enable]) 426 $json = $json->convert_blessed ([$enable])
427 $enabled = $json->get_convert_blessed
428 See "OBJECT SERIALISATION" for details.
429
330 If $enable is true (or missing), then "encode", upon encountering a 430 If $enable is true (or missing), then "encode", upon encountering a
331 blessed object, will check for the availability of the "TO_JSON" 431 blessed object, will check for the availability of the "TO_JSON"
332 method on the object's class. If found, it will be called in scalar 432 method on the object's class. If found, it will be called in scalar
333 context and the resulting scalar will be encoded instead of the 433 context and the resulting scalar will be encoded instead of the
334 object. If no "TO_JSON" method is found, the value of 434 object.
335 "allow_blessed" will decide what to do.
336 435
337 The "TO_JSON" method may safely call die if it wants. If "TO_JSON" 436 The "TO_JSON" method may safely call die if it wants. If "TO_JSON"
338 returns other blessed objects, those will be handled in the same 437 returns other blessed objects, those will be handled in the same
339 way. "TO_JSON" must take care of not causing an endless recursion 438 way. "TO_JSON" must take care of not causing an endless recursion
340 cycle (== crash) in this case. The name of "TO_JSON" was chosen 439 cycle (== crash) in this case. The name of "TO_JSON" was chosen
341 because other methods called by the Perl core (== not by the user of 440 because other methods called by the Perl core (== not by the user of
342 the object) are usually in upper case letters and to avoid 441 the object) are usually in upper case letters and to avoid
343 collisions with the "to_json" function. 442 collisions with any "to_json" function or method.
344 443
345 This setting does not yet influence "decode" in any way, but in the 444 If $enable is false (the default), then "encode" will not consider
346 future, global hooks might get installed that influence "decode" and 445 this type of conversion.
347 are enabled by this setting.
348 446
349 If $enable is false, then the "allow_blessed" setting will decide 447 This setting has no effect on "decode".
350 what to do when a blessed object is found. 448
449 $json = $json->allow_tags ([$enable])
450 $enabled = $json->allow_tags
451 See "OBJECT SERIALISATION" for details.
452
453 If $enable is true (or missing), then "encode", upon encountering a
454 blessed object, will check for the availability of the "FREEZE"
455 method on the object's class. If found, it will be used to serialise
456 the object into a nonstandard tagged JSON value (that JSON decoders
457 cannot decode).
458
459 It also causes "decode" to parse such tagged JSON values and
460 deserialise them via a call to the "THAW" method.
461
462 If $enable is false (the default), then "encode" will not consider
463 this type of conversion, and tagged JSON values will cause a parse
464 error in "decode", as if tags were not part of the grammar.
351 465
352 $json = $json->filter_json_object ([$coderef->($hashref)]) 466 $json = $json->filter_json_object ([$coderef->($hashref)])
353 When $coderef is specified, it will be called from "decode" each 467 When $coderef is specified, it will be called from "decode" each
354 time it decodes a JSON object. The only argument is a reference to 468 time it decodes a JSON object. The only argument is a reference to
355 the newly-created hash. If the code references returns a single 469 the newly-created hash. If the code references returns a single
… …
389 503
390 As this callback gets called less often then the 504 As this callback gets called less often then the
391 "filter_json_object" one, decoding speed will not usually suffer as 505 "filter_json_object" one, decoding speed will not usually suffer as
392 much. Therefore, single-key objects make excellent targets to 506 much. Therefore, single-key objects make excellent targets to
393 serialise Perl objects into, especially as single-key JSON objects 507 serialise Perl objects into, especially as single-key JSON objects
394 are as close to the type-tagged value concept as JSON gets (its 508 are as close to the type-tagged value concept as JSON gets (it's
395 basically an ID/VALUE tuple). Of course, JSON does not support this 509 basically an ID/VALUE tuple). Of course, JSON does not support this
396 in any way, so you need to make sure your data never looks like a 510 in any way, so you need to make sure your data never looks like a
397 serialised Perl hash. 511 serialised Perl hash.
398 512
399 Typical names for the single object key are "__class_whatever__", or 513 Typical names for the single object key are "__class_whatever__", or
… …
424 538
425 { __widget__ => $self->{id} } 539 { __widget__ => $self->{id} }
426 } 540 }
427 541
428 $json = $json->shrink ([$enable]) 542 $json = $json->shrink ([$enable])
543 $enabled = $json->get_shrink
429 Perl usually over-allocates memory a bit when allocating space for 544 Perl usually over-allocates memory a bit when allocating space for
430 strings. This flag optionally resizes strings generated by either 545 strings. This flag optionally resizes strings generated by either
431 "encode" or "decode" to their minimum size possible. This can save 546 "encode" or "decode" to their minimum size possible. This can save
432 memory when your JSON texts are either very very long or you have 547 memory when your JSON texts are either very very long or you have
433 many short strings. It will also try to downgrade any strings to 548 many short strings. It will also try to downgrade any strings to
… …
451 converting strings that look like integers or floats into integers 566 converting strings that look like integers or floats into integers
452 or floats internally (there is no difference on the Perl level), 567 or floats internally (there is no difference on the Perl level),
453 saving space. 568 saving space.
454 569
455 $json = $json->max_depth ([$maximum_nesting_depth]) 570 $json = $json->max_depth ([$maximum_nesting_depth])
571 $max_depth = $json->get_max_depth
456 Sets the maximum nesting level (default 512) accepted while encoding 572 Sets the maximum nesting level (default 512) accepted while encoding
457 or decoding. If the JSON text or Perl data structure has an equal or 573 or decoding. If a higher nesting level is detected in JSON text or a
458 higher nesting level then this limit, then the encoder and decoder 574 Perl data structure, then the encoder and decoder will stop and
459 will stop and croak at that point. 575 croak at that point.
460 576
461 Nesting level is defined by number of hash- or arrayrefs that the 577 Nesting level is defined by number of hash- or arrayrefs that the
462 encoder needs to traverse to reach a given point or the number of 578 encoder needs to traverse to reach a given point or the number of
463 "{" or "[" characters without their matching closing parenthesis 579 "{" or "[" characters without their matching closing parenthesis
464 crossed to reach a given character in a string. 580 crossed to reach a given character in a string.
465 581
466 Setting the maximum depth to one disallows any nesting, so that 582 Setting the maximum depth to one disallows any nesting, so that
467 ensures that the object is only a single hash/object or array. 583 ensures that the object is only a single hash/object or array.
468 584
469 The argument to "max_depth" will be rounded up to the next highest
470 power of two. If no argument is given, the highest possible setting 585 If no argument is given, the highest possible setting will be used,
471 will be used, which is rarely useful. 586 which is rarely useful.
587
588 Note that nesting is implemented by recursion in C. The default
589 value has been chosen to be as large as typical operating systems
590 allow without crashing.
472 591
473 See SECURITY CONSIDERATIONS, below, for more info on why this is 592 See SECURITY CONSIDERATIONS, below, for more info on why this is
474 useful. 593 useful.
475 594
476 $json = $json->max_size ([$maximum_string_size]) 595 $json = $json->max_size ([$maximum_string_size])
596 $max_size = $json->get_max_size
477 Set the maximum length a JSON text may have (in bytes) where 597 Set the maximum length a JSON text may have (in bytes) where
478 decoding is being attempted. The default is 0, meaning no limit. 598 decoding is being attempted. The default is 0, meaning no limit.
479 When "decode" is called on a string longer then this number of 599 When "decode" is called on a string that is longer then this many
480 characters it will not attempt to decode the string but throw an 600 bytes, it will not attempt to decode the string but throw an
481 exception. This setting has no effect on "encode" (yet). 601 exception. This setting has no effect on "encode" (yet).
482 602
483 The argument to "max_size" will be rounded up to the next highest
484 power of two (so may be more than requested). If no argument is
485 given, the limit check will be deactivated (same as when 0 is 603 If no argument is given, the limit check will be deactivated (same
486 specified). 604 as when 0 is specified).
487 605
488 See SECURITY CONSIDERATIONS, below, for more info on why this is 606 See SECURITY CONSIDERATIONS, below, for more info on why this is
489 useful. 607 useful.
490 608
491 $json_text = $json->encode ($perl_scalar) 609 $json_text = $json->encode ($perl_scalar)
492 Converts the given Perl data structure (a simple scalar or a 610 Converts the given Perl value or data structure to its JSON
493 reference to a hash or array) to its JSON representation. Simple 611 representation. Croaks on error.
494 scalars will be converted into JSON string or number sequences,
495 while references to arrays become JSON arrays and references to
496 hashes become JSON objects. Undefined Perl values (e.g. "undef")
497 become JSON "null" values. Neither "true" nor "false" values will be
498 generated.
499 612
500 $perl_scalar = $json->decode ($json_text) 613 $perl_scalar = $json->decode ($json_text)
501 The opposite of "encode": expects a JSON text and tries to parse it, 614 The opposite of "encode": expects a JSON text and tries to parse it,
502 returning the resulting simple scalar or reference. Croaks on error. 615 returning the resulting simple scalar or reference. Croaks on error.
503
504 JSON numbers and strings become simple Perl scalars. JSON arrays
505 become Perl arrayrefs and JSON objects become Perl hashrefs. "true"
506 becomes 1, "false" becomes 0 and "null" becomes "undef".
507 616
508 ($perl_scalar, $characters) = $json->decode_prefix ($json_text) 617 ($perl_scalar, $characters) = $json->decode_prefix ($json_text)
509 This works like the "decode" method, but instead of raising an 618 This works like the "decode" method, but instead of raising an
510 exception when there is trailing garbage after the first JSON 619 exception when there is trailing garbage after the first JSON
511 object, it will silently stop parsing there and return the number of 620 object, it will silently stop parsing there and return the number of
512 characters consumed so far. 621 characters consumed so far.
513 622
514 This is useful if your JSON texts are not delimited by an outer 623 This is useful if your JSON texts are not delimited by an outer
515 protocol (which is not the brightest thing to do in the first place)
516 and you need to know where the JSON text ends. 624 protocol and you need to know where the JSON text ends.
517 625
518 JSON::XS->new->decode_prefix ("[1] the tail") 626 JSON::XS->new->decode_prefix ("[1] the tail")
519 => ([], 3) 627 => ([], 3)
628
629INCREMENTAL PARSING
630 In some cases, there is the need for incremental parsing of JSON texts.
631 While this module always has to keep both JSON text and resulting Perl
632 data structure in memory at one time, it does allow you to parse a JSON
633 stream incrementally. It does so by accumulating text until it has a
634 full JSON object, which it then can decode. This process is similar to
635 using "decode_prefix" to see if a full JSON object is available, but is
636 much more efficient (and can be implemented with a minimum of method
637 calls).
638
639 JSON::XS will only attempt to parse the JSON text once it is sure it has
640 enough text to get a decisive result, using a very simple but truly
641 incremental parser. This means that it sometimes won't stop as early as
642 the full parser, for example, it doesn't detect mismatched parentheses.
643 The only thing it guarantees is that it starts decoding as soon as a
644 syntactically valid JSON text has been seen. This means you need to set
645 resource limits (e.g. "max_size") to ensure the parser will stop parsing
646 in the presence if syntax errors.
647
648 The following methods implement this incremental parser.
649
650 [void, scalar or list context] = $json->incr_parse ([$string])
651 This is the central parsing function. It can both append new text
652 and extract objects from the stream accumulated so far (both of
653 these functions are optional).
654
655 If $string is given, then this string is appended to the already
656 existing JSON fragment stored in the $json object.
657
658 After that, if the function is called in void context, it will
659 simply return without doing anything further. This can be used to
660 add more text in as many chunks as you want.
661
662 If the method is called in scalar context, then it will try to
663 extract exactly *one* JSON object. If that is successful, it will
664 return this object, otherwise it will return "undef". If there is a
665 parse error, this method will croak just as "decode" would do (one
666 can then use "incr_skip" to skip the erroneous part). This is the
667 most common way of using the method.
668
669 And finally, in list context, it will try to extract as many objects
670 from the stream as it can find and return them, or the empty list
671 otherwise. For this to work, there must be no separators between the
672 JSON objects or arrays, instead they must be concatenated
673 back-to-back. If an error occurs, an exception will be raised as in
674 the scalar context case. Note that in this case, any
675 previously-parsed JSON texts will be lost.
676
677 Example: Parse some JSON arrays/objects in a given string and return
678 them.
679
680 my @objs = JSON::XS->new->incr_parse ("[5][7][1,2]");
681
682 $lvalue_string = $json->incr_text
683 This method returns the currently stored JSON fragment as an lvalue,
684 that is, you can manipulate it. This *only* works when a preceding
685 call to "incr_parse" in *scalar context* successfully returned an
686 object. Under all other circumstances you must not call this
687 function (I mean it. although in simple tests it might actually
688 work, it *will* fail under real world conditions). As a special
689 exception, you can also call this method before having parsed
690 anything.
691
692 This function is useful in two cases: a) finding the trailing text
693 after a JSON object or b) parsing multiple JSON objects separated by
694 non-JSON text (such as commas).
695
696 $json->incr_skip
697 This will reset the state of the incremental parser and will remove
698 the parsed text from the input buffer so far. This is useful after
699 "incr_parse" died, in which case the input buffer and incremental
700 parser state is left unchanged, to skip the text parsed so far and
701 to reset the parse state.
702
703 The difference to "incr_reset" is that only text until the parse
704 error occurred is removed.
705
706 $json->incr_reset
707 This completely resets the incremental parser, that is, after this
708 call, it will be as if the parser had never parsed anything.
709
710 This is useful if you want to repeatedly parse JSON objects and want
711 to ignore any trailing data, which means you have to reset the
712 parser after each successful decode.
713
714 LIMITATIONS
715 All options that affect decoding are supported, except "allow_nonref".
716 The reason for this is that it cannot be made to work sensibly: JSON
717 objects and arrays are self-delimited, i.e. you can concatenate them
718 back to back and still decode them perfectly. This does not hold true
719 for JSON numbers, however.
720
721 For example, is the string 1 a single JSON number, or is it simply the
722 start of 12? Or is 12 a single JSON number, or the concatenation of 1
723 and 2? In neither case you can tell, and this is why JSON::XS takes the
724 conservative route and disallows this case.
725
726 EXAMPLES
727 Some examples will make all this clearer. First, a simple example that
728 works similarly to "decode_prefix": We want to decode the JSON object at
729 the start of a string and identify the portion after the JSON object:
730
731 my $text = "[1,2,3] hello";
732
733 my $json = new JSON::XS;
734
735 my $obj = $json->incr_parse ($text)
736 or die "expected JSON object or array at beginning of string";
737
738 my $tail = $json->incr_text;
739 # $tail now contains " hello"
740
741 Easy, isn't it?
742
743 Now for a more complicated example: Imagine a hypothetical protocol
744 where you read some requests from a TCP stream, and each request is a
745 JSON array, without any separation between them (in fact, it is often
746 useful to use newlines as "separators", as these get interpreted as
747 whitespace at the start of the JSON text, which makes it possible to
748 test said protocol with "telnet"...).
749
750 Here is how you'd do it (it is trivial to write this in an event-based
751 manner):
752
753 my $json = new JSON::XS;
754
755 # read some data from the socket
756 while (sysread $socket, my $buf, 4096) {
757
758 # split and decode as many requests as possible
759 for my $request ($json->incr_parse ($buf)) {
760 # act on the $request
761 }
762 }
763
764 Another complicated example: Assume you have a string with JSON objects
765 or arrays, all separated by (optional) comma characters (e.g. "[1],[2],
766 [3]"). To parse them, we have to skip the commas between the JSON texts,
767 and here is where the lvalue-ness of "incr_text" comes in useful:
768
769 my $text = "[1],[2], [3]";
770 my $json = new JSON::XS;
771
772 # void context, so no parsing done
773 $json->incr_parse ($text);
774
775 # now extract as many objects as possible. note the
776 # use of scalar context so incr_text can be called.
777 while (my $obj = $json->incr_parse) {
778 # do something with $obj
779
780 # now skip the optional comma
781 $json->incr_text =~ s/^ \s* , //x;
782 }
783
784 Now lets go for a very complex example: Assume that you have a gigantic
785 JSON array-of-objects, many gigabytes in size, and you want to parse it,
786 but you cannot load it into memory fully (this has actually happened in
787 the real world :).
788
789 Well, you lost, you have to implement your own JSON parser. But JSON::XS
790 can still help you: You implement a (very simple) array parser and let
791 JSON decode the array elements, which are all full JSON objects on their
792 own (this wouldn't work if the array elements could be JSON numbers, for
793 example):
794
795 my $json = new JSON::XS;
796
797 # open the monster
798 open my $fh, "<bigfile.json"
799 or die "bigfile: $!";
800
801 # first parse the initial "["
802 for (;;) {
803 sysread $fh, my $buf, 65536
804 or die "read error: $!";
805 $json->incr_parse ($buf); # void context, so no parsing
806
807 # Exit the loop once we found and removed(!) the initial "[".
808 # In essence, we are (ab-)using the $json object as a simple scalar
809 # we append data to.
810 last if $json->incr_text =~ s/^ \s* \[ //x;
811 }
812
813 # now we have the skipped the initial "[", so continue
814 # parsing all the elements.
815 for (;;) {
816 # in this loop we read data until we got a single JSON object
817 for (;;) {
818 if (my $obj = $json->incr_parse) {
819 # do something with $obj
820 last;
821 }
822
823 # add more data
824 sysread $fh, my $buf, 65536
825 or die "read error: $!";
826 $json->incr_parse ($buf); # void context, so no parsing
827 }
828
829 # in this loop we read data until we either found and parsed the
830 # separating "," between elements, or the final "]"
831 for (;;) {
832 # first skip whitespace
833 $json->incr_text =~ s/^\s*//;
834
835 # if we find "]", we are done
836 if ($json->incr_text =~ s/^\]//) {
837 print "finished.\n";
838 exit;
839 }
840
841 # if we find ",", we can continue with the next element
842 if ($json->incr_text =~ s/^,//) {
843 last;
844 }
845
846 # if we find anything else, we have a parse error!
847 if (length $json->incr_text) {
848 die "parse error near ", $json->incr_text;
849 }
850
851 # else add more data
852 sysread $fh, my $buf, 65536
853 or die "read error: $!";
854 $json->incr_parse ($buf); # void context, so no parsing
855 }
856
857 This is a complex example, but most of the complexity comes from the
858 fact that we are trying to be correct (bear with me if I am wrong, I
859 never ran the above example :).
520 860
521MAPPING 861MAPPING
522 This section describes how JSON::XS maps Perl values to JSON values and 862 This section describes how JSON::XS maps Perl values to JSON values and
523 vice versa. These mappings are designed to "do the right thing" in most 863 vice versa. These mappings are designed to "do the right thing" in most
524 circumstances automatically, preserving round-tripping characteristics 864 circumstances automatically, preserving round-tripping characteristics
525 (what you put in comes out as something equivalent). 865 (what you put in comes out as something equivalent).
526 866
527 For the more enlightened: note that in the following descriptions, 867 For the more enlightened: note that in the following descriptions,
528 lowercase *perl* refers to the Perl interpreter, while uppcercase *Perl* 868 lowercase *perl* refers to the Perl interpreter, while uppercase *Perl*
529 refers to the abstract Perl language itself. 869 refers to the abstract Perl language itself.
530 870
531 JSON -> PERL 871 JSON -> PERL
532 object 872 object
533 A JSON object becomes a reference to a hash in Perl. No ordering of 873 A JSON object becomes a reference to a hash in Perl. No ordering of
534 object keys is preserved (JSON does not preserver object key 874 object keys is preserved (JSON does not preserve object key ordering
535 ordering itself). 875 itself).
536 876
537 array 877 array
538 A JSON array becomes a reference to an array in Perl. 878 A JSON array becomes a reference to an array in Perl.
539 879
540 string 880 string
… …
546 A JSON number becomes either an integer, numeric (floating point) or 886 A JSON number becomes either an integer, numeric (floating point) or
547 string scalar in perl, depending on its range and any fractional 887 string scalar in perl, depending on its range and any fractional
548 parts. On the Perl level, there is no difference between those as 888 parts. On the Perl level, there is no difference between those as
549 Perl handles all the conversion details, but an integer may take 889 Perl handles all the conversion details, but an integer may take
550 slightly less memory and might represent more values exactly than 890 slightly less memory and might represent more values exactly than
551 (floating point) numbers. 891 floating point numbers.
552 892
553 If the number consists of digits only, JSON::XS will try to 893 If the number consists of digits only, JSON::XS will try to
554 represent it as an integer value. If that fails, it will try to 894 represent it as an integer value. If that fails, it will try to
555 represent it as a numeric (floating point) value if that is possible 895 represent it as a numeric (floating point) value if that is possible
556 without loss of precision. Otherwise it will preserve the number as 896 without loss of precision. Otherwise it will preserve the number as
557 a string value. 897 a string value (in which case you lose roundtripping ability, as the
898 JSON number will be re-encoded to a JSON string).
558 899
559 Numbers containing a fractional or exponential part will always be 900 Numbers containing a fractional or exponential part will always be
560 represented as numeric (floating point) values, possibly at a loss 901 represented as numeric (floating point) values, possibly at a loss
561 of precision. 902 of precision (in which case you might lose perfect roundtripping
903 ability, but the JSON number will still be re-encoded as a JSON
904 number).
562 905
563 This might create round-tripping problems as numbers might become 906 Note that precision is not accuracy - binary floating point values
564 strings, but as Perl is typeless there is no other way to do it. 907 cannot represent most decimal fractions exactly, and when converting
908 from and to floating point, JSON::XS only guarantees precision up to
909 but not including the least significant bit.
565 910
566 true, false 911 true, false
567 These JSON atoms become "JSON::XS::true" and "JSON::XS::false", 912 These JSON atoms become "Types::Serialiser::true" and
568 respectively. They are overloaded to act almost exactly like the 913 "Types::Serialiser::false", respectively. They are overloaded to act
569 numbers 1 and 0. You can check wether a scalar is a JSON boolean by 914 almost exactly like the numbers 1 and 0. You can check whether a
570 using the "JSON::XS::is_bool" function. 915 scalar is a JSON boolean by using the "Types::Serialiser::is_bool"
916 function (after "use Types::Serialier", of course).
571 917
572 null 918 null
573 A JSON null atom becomes "undef" in Perl. 919 A JSON null atom becomes "undef" in Perl.
920
921 shell-style comments ("# *text*")
922 As a nonstandard extension to the JSON syntax that is enabled by the
923 "relaxed" setting, shell-style comments are allowed. They can start
924 anywhere outside strings and go till the end of the line.
925
926 tagged values ("(*tag*)*value*").
927 Another nonstandard extension to the JSON syntax, enabled with the
928 "allow_tags" setting, are tagged values. In this implementation, the
929 *tag* must be a perl package/class name encoded as a JSON string,
930 and the *value* must be a JSON array encoding optional constructor
931 arguments.
932
933 See "OBJECT SERIALISATION", below, for details.
574 934
575 PERL -> JSON 935 PERL -> JSON
576 The mapping from Perl to JSON is slightly more difficult, as Perl is a 936 The mapping from Perl to JSON is slightly more difficult, as Perl is a
577 truly typeless language, so we can only guess which JSON type is meant 937 truly typeless language, so we can only guess which JSON type is meant
578 by a Perl value. 938 by a Perl value.
579 939
580 hash references 940 hash references
581 Perl hash references become JSON objects. As there is no inherent 941 Perl hash references become JSON objects. As there is no inherent
582 ordering in hash keys (or JSON objects), they will usually be 942 ordering in hash keys (or JSON objects), they will usually be
583 encoded in a pseudo-random order that can change between runs of the 943 encoded in a pseudo-random order. JSON::XS can optionally sort the
584 same program but stays generally the same within a single run of a 944 hash keys (determined by the *canonical* flag), so the same
585 program. JSON::XS can optionally sort the hash keys (determined by 945 datastructure will serialise to the same JSON text (given same
586 the *canonical* flag), so the same datastructure will serialise to 946 settings and version of JSON::XS), but this incurs a runtime
587 the same JSON text (given same settings and version of JSON::XS), 947 overhead and is only rarely useful, e.g. when you want to compare
588 but this incurs a runtime overhead and is only rarely useful, e.g. 948 some JSON text against another for equality.
589 when you want to compare some JSON text against another for
590 equality.
591 949
592 array references 950 array references
593 Perl array references become JSON arrays. 951 Perl array references become JSON arrays.
594 952
595 other references 953 other references
596 Other unblessed references are generally not allowed and will cause 954 Other unblessed references are generally not allowed and will cause
597 an exception to be thrown, except for references to the integers 0 955 an exception to be thrown, except for references to the integers 0
598 and 1, which get turned into "false" and "true" atoms in JSON. You 956 and 1, which get turned into "false" and "true" atoms in JSON.
599 can also use "JSON::XS::false" and "JSON::XS::true" to improve 957
958 Since "JSON::XS" uses the boolean model from Types::Serialiser, you
959 can also "use Types::Serialiser" and then use
960 "Types::Serialiser::false" and "Types::Serialiser::true" to improve
600 readability. 961 readability.
601 962
963 use Types::Serialiser;
602 to_json [\0,JSON::XS::true] # yields [false,true] 964 encode_json [\0, Types::Serialiser::true] # yields [false,true]
603 965
604 JSON::XS::true, JSON::XS::false 966 Types::Serialiser::true, Types::Serialiser::false
605 These special values become JSON true and JSON false values, 967 These special values from the Types::Serialiser module become JSON
606 respectively. You cna alos use "\1" and "\0" directly if you want. 968 true and JSON false values, respectively. You can also use "\1" and
969 "\0" directly if you want.
607 970
608 blessed objects 971 blessed objects
609 Blessed objects are not allowed. JSON::XS currently tries to encode 972 Blessed objects are not directly representable in JSON, but
610 their underlying representation (hash- or arrayref), but this 973 "JSON::XS" allows various ways of handling objects. See "OBJECT
611 behaviour might change in future versions. 974 SERIALISATION", below, for details.
612 975
613 simple scalars 976 simple scalars
614 Simple Perl scalars (any scalar that is not a reference) are the 977 Simple Perl scalars (any scalar that is not a reference) are the
615 most difficult objects to encode: JSON::XS will encode undefined 978 most difficult objects to encode: JSON::XS will encode undefined
616 scalars as JSON null value, scalars that have last been used in a 979 scalars as JSON "null" values, scalars that have last been used in a
617 string context before encoding as JSON strings and anything else as 980 string context before encoding as JSON strings, and anything else as
618 number value: 981 number value:
619 982
620 # dump as number 983 # dump as number
621 to_json [2] # yields [2] 984 encode_json [2] # yields [2]
622 to_json [-3.0e17] # yields [-3e+17] 985 encode_json [-3.0e17] # yields [-3e+17]
623 my $value = 5; to_json [$value] # yields [5] 986 my $value = 5; encode_json [$value] # yields [5]
624 987
625 # used as string, so dump as string 988 # used as string, so dump as string
626 print $value; 989 print $value;
627 to_json [$value] # yields ["5"] 990 encode_json [$value] # yields ["5"]
628 991
629 # undef becomes null 992 # undef becomes null
630 to_json [undef] # yields [null] 993 encode_json [undef] # yields [null]
631 994
632 You can force the type to be a string by stringifying it: 995 You can force the type to be a JSON string by stringifying it:
633 996
634 my $x = 3.1; # some variable containing a number 997 my $x = 3.1; # some variable containing a number
635 "$x"; # stringified 998 "$x"; # stringified
636 $x .= ""; # another, more awkward way to stringify 999 $x .= ""; # another, more awkward way to stringify
637 print $x; # perl does it for you, too, quite often 1000 print $x; # perl does it for you, too, quite often
638 1001
639 You can force the type to be a number by numifying it: 1002 You can force the type to be a JSON number by numifying it:
640 1003
641 my $x = "3"; # some variable containing a string 1004 my $x = "3"; # some variable containing a string
642 $x += 0; # numify it, ensuring it will be dumped as a number 1005 $x += 0; # numify it, ensuring it will be dumped as a number
643 $x *= 1; # same thing, the choise is yours. 1006 $x *= 1; # same thing, the choice is yours.
644 1007
645 You can not currently output JSON booleans or force the type in 1008 You can not currently force the type in other, less obscure, ways.
646 other, less obscure, ways. Tell me if you need this capability. 1009 Tell me if you need this capability (but don't forget to explain why
1010 it's needed :).
647 1011
648COMPARISON 1012 Note that numerical precision has the same meaning as under Perl (so
649 As already mentioned, this module was created because none of the 1013 binary to decimal conversion follows the same rules as in Perl,
650 existing JSON modules could be made to work correctly. First I will 1014 which can differ to other languages). Also, your perl interpreter
651 describe the problems (or pleasures) I encountered with various existing 1015 might expose extensions to the floating point numbers of your
652 JSON modules, followed by some benchmark values. JSON::XS was designed 1016 platform, such as infinities or NaN's - these cannot be represented
653 not to suffer from any of these problems or limitations. 1017 in JSON, and it is an error to pass those in.
654 1018
655 JSON 1.07 1019 OBJECT SERIALISATION
656 Slow (but very portable, as it is written in pure Perl). 1020 As JSON cannot directly represent Perl objects, you have to choose
1021 between a pure JSON representation (without the ability to deserialise
1022 the object automatically again), and a nonstandard extension to the JSON
1023 syntax, tagged values.
657 1024
658 Undocumented/buggy Unicode handling (how JSON handles unicode values 1025 SERIALISATION
659 is undocumented. One can get far by feeding it unicode strings and 1026 What happens when "JSON::XS" encounters a Perl object depends on the
660 doing en-/decoding oneself, but unicode escapes are not working 1027 "allow_blessed", "convert_blessed" and "allow_tags" settings, which are
1028 used in this order:
1029
1030 1. "allow_tags" is enabled and the object has a "FREEZE" method.
1031 In this case, "JSON::XS" uses the Types::Serialiser object
1032 serialisation protocol to create a tagged JSON value, using a
1033 nonstandard extension to the JSON syntax.
1034
1035 This works by invoking the "FREEZE" method on the object, with the
1036 first argument being the object to serialise, and the second
1037 argument being the constant string "JSON" to distinguish it from
1038 other serialisers.
1039
1040 The "FREEZE" method can return any number of values (i.e. zero or
1041 more). These values and the paclkage/classname of the object will
1042 then be encoded as a tagged JSON value in the following format:
1043
1044 ("classname")[FREEZE return values...]
1045
1046 For example, the hypothetical "My::Object" "FREEZE" method might use
1047 the objects "type" and "id" members to encode the object:
1048
1049 sub My::Object::FREEZE {
1050 my ($self, $serialiser) = @_;
1051
1052 ($self->{type}, $self->{id})
1053 }
1054
1055 2. "convert_blessed" is enabled and the object has a "TO_JSON" method.
1056 In this case, the "TO_JSON" method of the object is invoked in
1057 scalar context. It must return a single scalar that can be directly
1058 encoded into JSON. This scalar replaces the object in the JSON text.
1059
1060 For example, the following "TO_JSON" method will convert all URI
1061 objects to JSON strings when serialised. The fatc that these values
1062 originally were URI objects is lost.
1063
1064 sub URI::TO_JSON {
1065 my ($uri) = @_;
1066 $uri->as_string
1067 }
1068
1069 3. "allow_blessed" is enabled.
1070 The object will be serialised as a JSON null value.
1071
1072 4. none of the above
1073 If none of the settings are enabled or the respective methods are
1074 missing, "JSON::XS" throws an exception.
1075
1076 DESERIALISATION
1077 For deserialisation there are only two cases to consider: either
1078 nonstandard tagging was used, in which case "allow_tags" decides, or
1079 objects cannot be automatically be deserialised, in which case you can
1080 use postprocessing or the "filter_json_object" or
1081 "filter_json_single_key_object" callbacks to get some real objects our
1082 of your JSON.
1083
1084 This section only considers the tagged value case: I a tagged JSON
1085 object is encountered during decoding and "allow_tags" is disabled, a
1086 parse error will result (as if tagged values were not part of the
1087 grammar).
1088
1089 If "allow_tags" is enabled, "JSON::XS" will look up the "THAW" method of
1090 the package/classname used during serialisation (it will not attempt to
1091 load the package as a Perl module). If there is no such method, the
1092 decoding will fail with an error.
1093
1094 Otherwise, the "THAW" method is invoked with the classname as first
1095 argument, the constant string "JSON" as second argument, and all the
1096 values from the JSON array (the values originally returned by the
1097 "FREEZE" method) as remaining arguments.
1098
1099 The method must then return the object. While technically you can return
1100 any Perl scalar, you might have to enable the "enable_nonref" setting to
1101 make that work in all cases, so better return an actual blessed
1102 reference.
1103
1104 As an example, let's implement a "THAW" function that regenerates the
1105 "My::Object" from the "FREEZE" example earlier:
1106
1107 sub My::Object::THAW {
1108 my ($class, $serialiser, $type, $id) = @_;
1109
1110 $class->new (type => $type, id => $id)
1111 }
1112
1113ENCODING/CODESET FLAG NOTES
1114 The interested reader might have seen a number of flags that signify
1115 encodings or codesets - "utf8", "latin1" and "ascii". There seems to be
1116 some confusion on what these do, so here is a short comparison:
1117
1118 "utf8" controls whether the JSON text created by "encode" (and expected
1119 by "decode") is UTF-8 encoded or not, while "latin1" and "ascii" only
1120 control whether "encode" escapes character values outside their
1121 respective codeset range. Neither of these flags conflict with each
1122 other, although some combinations make less sense than others.
1123
1124 Care has been taken to make all flags symmetrical with respect to
1125 "encode" and "decode", that is, texts encoded with any combination of
1126 these flag values will be correctly decoded when the same flags are used
1127 - in general, if you use different flag settings while encoding vs. when
1128 decoding you likely have a bug somewhere.
1129
1130 Below comes a verbose discussion of these flags. Note that a "codeset"
1131 is simply an abstract set of character-codepoint pairs, while an
1132 encoding takes those codepoint numbers and *encodes* them, in our case
1133 into octets. Unicode is (among other things) a codeset, UTF-8 is an
1134 encoding, and ISO-8859-1 (= latin 1) and ASCII are both codesets *and*
1135 encodings at the same time, which can be confusing.
1136
1137 "utf8" flag disabled
1138 When "utf8" is disabled (the default), then "encode"/"decode"
1139 generate and expect Unicode strings, that is, characters with high
1140 ordinal Unicode values (> 255) will be encoded as such characters,
1141 and likewise such characters are decoded as-is, no changes to them
1142 will be done, except "(re-)interpreting" them as Unicode codepoints
1143 or Unicode characters, respectively (to Perl, these are the same
1144 thing in strings unless you do funny/weird/dumb stuff).
1145
1146 This is useful when you want to do the encoding yourself (e.g. when
1147 you want to have UTF-16 encoded JSON texts) or when some other layer
1148 does the encoding for you (for example, when printing to a terminal
1149 using a filehandle that transparently encodes to UTF-8 you certainly
1150 do NOT want to UTF-8 encode your data first and have Perl encode it
1151 another time).
1152
1153 "utf8" flag enabled
1154 If the "utf8"-flag is enabled, "encode"/"decode" will encode all
1155 characters using the corresponding UTF-8 multi-byte sequence, and
1156 will expect your input strings to be encoded as UTF-8, that is, no
1157 "character" of the input string must have any value > 255, as UTF-8
1158 does not allow that.
1159
1160 The "utf8" flag therefore switches between two modes: disabled means
1161 you will get a Unicode string in Perl, enabled means you get an
1162 UTF-8 encoded octet/binary string in Perl.
1163
1164 "latin1" or "ascii" flags enabled
1165 With "latin1" (or "ascii") enabled, "encode" will escape characters
1166 with ordinal values > 255 (> 127 with "ascii") and encode the
1167 remaining characters as specified by the "utf8" flag.
1168
1169 If "utf8" is disabled, then the result is also correctly encoded in
1170 those character sets (as both are proper subsets of Unicode, meaning
1171 that a Unicode string with all character values < 256 is the same
1172 thing as a ISO-8859-1 string, and a Unicode string with all
1173 character values < 128 is the same thing as an ASCII string in
661 properly). 1174 Perl).
662 1175
663 No roundtripping (strings get clobbered if they look like numbers, 1176 If "utf8" is enabled, you still get a correct UTF-8-encoded string,
664 e.g. the string 2.0 will encode to 2.0 instead of "2.0", and that 1177 regardless of these flags, just some more characters will be escaped
665 will decode into the number 2. 1178 using "\uXXXX" then before.
666 1179
667 JSON::PC 0.01 1180 Note that ISO-8859-1-*encoded* strings are not compatible with UTF-8
668 Very fast. 1181 encoding, while ASCII-encoded strings are. That is because the
1182 ISO-8859-1 encoding is NOT a subset of UTF-8 (despite the ISO-8859-1
1183 *codeset* being a subset of Unicode), while ASCII is.
669 1184
670 Undocumented/buggy Unicode handling. 1185 Surprisingly, "decode" will ignore these flags and so treat all
1186 input values as governed by the "utf8" flag. If it is disabled, this
1187 allows you to decode ISO-8859-1- and ASCII-encoded strings, as both
1188 strict subsets of Unicode. If it is enabled, you can correctly
1189 decode UTF-8 encoded strings.
671 1190
672 No roundtripping. 1191 So neither "latin1" nor "ascii" are incompatible with the "utf8"
1192 flag - they only govern when the JSON output engine escapes a
1193 character or not.
673 1194
674 Has problems handling many Perl values (e.g. regex results and other 1195 The main use for "latin1" is to relatively efficiently store binary
675 magic values will make it croak). 1196 data as JSON, at the expense of breaking compatibility with most
1197 JSON decoders.
676 1198
677 Does not even generate valid JSON ("{1,2}" gets converted to "{1:2}" 1199 The main use for "ascii" is to force the output to not contain
678 which is not a valid JSON text. 1200 characters with values > 127, which means you can interpret the
1201 resulting string as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about
1202 any character set and 8-bit-encoding, and still get the same data
1203 structure back. This is useful when your channel for JSON transfer
1204 is not 8-bit clean or the encoding might be mangled in between (e.g.
1205 in mail), and works because ASCII is a proper subset of most 8-bit
1206 and multibyte encodings in use in the world.
679 1207
680 Unmaintained (maintainer unresponsive for many months, bugs are not 1208 JSON and ECMAscript
681 getting fixed). 1209 JSON syntax is based on how literals are represented in javascript (the
1210 not-standardised predecessor of ECMAscript) which is presumably why it
1211 is called "JavaScript Object Notation".
682 1212
683 JSON::Syck 0.21 1213 However, JSON is not a subset (and also not a superset of course) of
684 Very buggy (often crashes). 1214 ECMAscript (the standard) or javascript (whatever browsers actually
1215 implement).
685 1216
686 Very inflexible (no human-readable format supported, format pretty 1217 If you want to use javascript's "eval" function to "parse" JSON, you
687 much undocumented. I need at least a format for easy reading by 1218 might run into parse errors for valid JSON texts, or the resulting data
688 humans and a single-line compact format for use in a protocol, and 1219 structure might not be queryable:
689 preferably a way to generate ASCII-only JSON texts).
690 1220
691 Completely broken (and confusingly documented) Unicode handling 1221 One of the problems is that U+2028 and U+2029 are valid characters
692 (unicode escapes are not working properly, you need to set 1222 inside JSON strings, but are not allowed in ECMAscript string literals,
693 ImplicitUnicode to *different* values on en- and decoding to get 1223 so the following Perl fragment will not output something that can be
694 symmetric behaviour). 1224 guaranteed to be parsable by javascript's "eval":
695 1225
696 No roundtripping (simple cases work, but this depends on wether the 1226 use JSON::XS;
697 scalar value was used in a numeric context or not).
698 1227
699 Dumping hashes may skip hash values depending on iterator state. 1228 print encode_json [chr 0x2028];
700 1229
701 Unmaintained (maintainer unresponsive for many months, bugs are not 1230 The right fix for this is to use a proper JSON parser in your javascript
702 getting fixed). 1231 programs, and not rely on "eval" (see for example Douglas Crockford's
1232 json2.js parser).
703 1233
704 Does not check input for validity (i.e. will accept non-JSON input 1234 If this is not an option, you can, as a stop-gap measure, simply encode
705 and return "something" instead of raising an exception. This is a 1235 to ASCII-only JSON:
706 security issue: imagine two banks transfering money between each
707 other using JSON. One bank might parse a given non-JSON request and
708 deduct money, while the other might reject the transaction with a
709 syntax error. While a good protocol will at least recover, that is
710 extra unnecessary work and the transaction will still not succeed).
711 1236
712 JSON::DWIW 0.04 1237 use JSON::XS;
713 Very fast. Very natural. Very nice.
714 1238
715 Undocumented unicode handling (but the best of the pack. Unicode 1239 print JSON::XS->new->ascii->encode ([chr 0x2028]);
716 escapes still don't get parsed properly).
717 1240
718 Very inflexible. 1241 Note that this will enlarge the resulting JSON text quite a bit if you
1242 have many non-ASCII characters. You might be tempted to run some regexes
1243 to only escape U+2028 and U+2029, e.g.:
719 1244
720 No roundtripping. 1245 # DO NOT USE THIS!
1246 my $json = JSON::XS->new->utf8->encode ([chr 0x2028]);
1247 $json =~ s/\xe2\x80\xa8/\\u2028/g; # escape U+2028
1248 $json =~ s/\xe2\x80\xa9/\\u2029/g; # escape U+2029
1249 print $json;
721 1250
722 Does not generate valid JSON texts (key strings are often unquoted, 1251 Note that *this is a bad idea*: the above only works for U+2028 and
723 empty keys result in nothing being output) 1252 U+2029 and thus only for fully ECMAscript-compliant parsers. Many
1253 existing javascript implementations, however, have issues with other
1254 characters as well - using "eval" naively simply *will* cause problems.
724 1255
725 Does not check input for validity. 1256 Another problem is that some javascript implementations reserve some
1257 property names for their own purposes (which probably makes them
1258 non-ECMAscript-compliant). For example, Iceweasel reserves the
1259 "__proto__" property name for its own purposes.
1260
1261 If that is a problem, you could parse try to filter the resulting JSON
1262 output for these property strings, e.g.:
1263
1264 $json =~ s/"__proto__"\s*:/"__proto__renamed":/g;
1265
1266 This works because "__proto__" is not valid outside of strings, so every
1267 occurrence of ""__proto__"\s*:" must be a string used as property name.
1268
1269 If you know of other incompatibilities, please let me know.
726 1270
727 JSON and YAML 1271 JSON and YAML
728 You often hear that JSON is a subset (or a close subset) of YAML. This 1272 You often hear that JSON is a subset of YAML. This is, however, a mass
729 is, however, a mass hysteria and very far from the truth. In general, 1273 hysteria(*) and very far from the truth (as of the time of this
730 there is no way to configure JSON::XS to output a data structure as 1274 writing), so let me state it clearly: *in general, there is no way to
731 valid YAML. 1275 configure JSON::XS to output a data structure as valid YAML* that works
1276 in all cases.
732 1277
733 If you really must use JSON::XS to generate YAML, you should use this 1278 If you really must use JSON::XS to generate YAML, you should use this
734 algorithm (subject to change in future versions): 1279 algorithm (subject to change in future versions):
735 1280
736 my $to_yaml = JSON::XS->new->utf8->space_after (1); 1281 my $to_yaml = JSON::XS->new->utf8->space_after (1);
737 my $yaml = $to_yaml->encode ($ref) . "\n"; 1282 my $yaml = $to_yaml->encode ($ref) . "\n";
738 1283
739 This will usually generate JSON texts that also parse as valid YAML. 1284 This will *usually* generate JSON texts that also parse as valid YAML.
740 Please note that YAML has hardcoded limits on (simple) object key 1285 Please note that YAML has hardcoded limits on (simple) object key
741 lengths that JSON doesn't have, so you should make sure that your hash 1286 lengths that JSON doesn't have and also has different and incompatible
1287 unicode character escape syntax, so you should make sure that your hash
742 keys are noticably shorter than the 1024 characters YAML allows. 1288 keys are noticeably shorter than the 1024 "stream characters" YAML
1289 allows and that you do not have characters with codepoint values outside
1290 the Unicode BMP (basic multilingual page). YAML also does not allow "\/"
1291 sequences in strings (which JSON::XS does not *currently* generate, but
1292 other JSON generators might).
743 1293
744 There might be other incompatibilities that I am not aware of. In 1294 There might be other incompatibilities that I am not aware of (or the
1295 YAML specification has been changed yet again - it does so quite often).
745 general you should not try to generate YAML with a JSON generator or 1296 In general you should not try to generate YAML with a JSON generator or
746 vice versa, or try to parse JSON with a YAML parser or vice versa: 1297 vice versa, or try to parse JSON with a YAML parser or vice versa:
747 chances are high that you will run into severe interoperability 1298 chances are high that you will run into severe interoperability problems
748 problems. 1299 when you least expect it.
1300
1301 (*) I have been pressured multiple times by Brian Ingerson (one of the
1302 authors of the YAML specification) to remove this paragraph, despite
1303 him acknowledging that the actual incompatibilities exist. As I was
1304 personally bitten by this "JSON is YAML" lie, I refused and said I
1305 will continue to educate people about these issues, so others do not
1306 run into the same problem again and again. After this, Brian called
1307 me a (quote)*complete and worthless idiot*(unquote).
1308
1309 In my opinion, instead of pressuring and insulting people who
1310 actually clarify issues with YAML and the wrong statements of some
1311 of its proponents, I would kindly suggest reading the JSON spec
1312 (which is not that difficult or long) and finally make YAML
1313 compatible to it, and educating users about the changes, instead of
1314 spreading lies about the real compatibility for many *years* and
1315 trying to silence people who point out that it isn't true.
1316
1317 Addendum/2009: the YAML 1.2 spec is still incompatible with JSON,
1318 even though the incompatibilities have been documented (and are
1319 known to Brian) for many years and the spec makes explicit claims
1320 that YAML is a superset of JSON. It would be so easy to fix, but
1321 apparently, bullying people and corrupting userdata is so much
1322 easier.
749 1323
750 SPEED 1324 SPEED
751 It seems that JSON::XS is surprisingly fast, as shown in the following 1325 It seems that JSON::XS is surprisingly fast, as shown in the following
752 tables. They have been generated with the help of the "eg/bench" program 1326 tables. They have been generated with the help of the "eg/bench" program
753 in the JSON::XS distribution, to make it easy to compare on your own 1327 in the JSON::XS distribution, to make it easy to compare on your own
754 system. 1328 system.
755 1329
756 First comes a comparison between various modules using a very short 1330 First comes a comparison between various modules using a very short
757 single-line JSON string: 1331 single-line JSON string (also available at
1332 <http://dist.schmorp.de/misc/json/short.json>).
758 1333
759 {"method": "handleMessage", "params": ["user1", "we were just talking"], \ 1334 {"method": "handleMessage", "params": ["user1",
760 "id": null, "array":[1,11,234,-5,1e5,1e7, true, false]} 1335 "we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7,
1336 1, 0]}
761 1337
762 It shows the number of encodes/decodes per second (JSON::XS uses the 1338 It shows the number of encodes/decodes per second (JSON::XS uses the
763 functional interface, while JSON::XS/2 uses the OO interface with 1339 functional interface, while JSON::XS/2 uses the OO interface with
764 pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink). 1340 pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink.
765 Higher is better: 1341 JSON::DWIW/DS uses the deserialise function, while JSON::DWIW::FJ uses
1342 the from_json method). Higher is better:
766 1343
767 Storable | 15779.925 | 14169.946 |
768 -----------+------------+------------+
769 module | encode | decode | 1344 module | encode | decode |
770 -----------|------------|------------| 1345 --------------|------------|------------|
771 JSON | 4990.842 | 4088.813 | 1346 JSON::DWIW/DS | 86302.551 | 102300.098 |
772 JSON::DWIW | 51653.990 | 71575.154 | 1347 JSON::DWIW/FJ | 86302.551 | 75983.768 |
773 JSON::PC | 65948.176 | 74631.744 | 1348 JSON::PP | 15827.562 | 6638.658 |
774 JSON::PP | 8931.652 | 3817.168 | 1349 JSON::Syck | 63358.066 | 47662.545 |
775 JSON::Syck | 24877.248 | 27776.848 | 1350 JSON::XS | 511500.488 | 511500.488 |
776 JSON::XS | 388361.481 | 227951.304 | 1351 JSON::XS/2 | 291271.111 | 388361.481 |
777 JSON::XS/2 | 227951.304 | 218453.333 | 1352 JSON::XS/3 | 361577.931 | 361577.931 |
778 JSON::XS/3 | 338250.323 | 218453.333 | 1353 Storable | 66788.280 | 265462.278 |
779 Storable | 16500.016 | 135300.129 |
780 -----------+------------+------------+ 1354 --------------+------------+------------+
781 1355
782 That is, JSON::XS is about five times faster than JSON::DWIW on 1356 That is, JSON::XS is almost six times faster than JSON::DWIW on
783 encoding, about three times faster on decoding, and over fourty times 1357 encoding, about five times faster on decoding, and over thirty to
784 faster than JSON, even with pretty-printing and key sorting. It also 1358 seventy times faster than JSON's pure perl implementation. It also
785 compares favourably to Storable for small amounts of data. 1359 compares favourably to Storable for small amounts of data.
786 1360
787 Using a longer test string (roughly 18KB, generated from Yahoo! Locals 1361 Using a longer test string (roughly 18KB, generated from Yahoo! Locals
788 search API (http://nanoref.com/yahooapis/mgPdGg): 1362 search API (<http://dist.schmorp.de/misc/json/long.json>).
789 1363
790 module | encode | decode | 1364 module | encode | decode |
791 -----------|------------|------------| 1365 --------------|------------|------------|
792 JSON | 55.260 | 34.971 | 1366 JSON::DWIW/DS | 1647.927 | 2673.916 |
793 JSON::DWIW | 825.228 | 1082.513 | 1367 JSON::DWIW/FJ | 1630.249 | 2596.128 |
794 JSON::PC | 3571.444 | 2394.829 |
795 JSON::PP | 210.987 | 32.574 | 1368 JSON::PP | 400.640 | 62.311 |
796 JSON::Syck | 552.551 | 787.544 | 1369 JSON::Syck | 1481.040 | 1524.869 |
797 JSON::XS | 5780.463 | 4854.519 | 1370 JSON::XS | 20661.596 | 9541.183 |
798 JSON::XS/2 | 3869.998 | 4798.975 | 1371 JSON::XS/2 | 10683.403 | 9416.938 |
799 JSON::XS/3 | 5862.880 | 4798.975 | 1372 JSON::XS/3 | 20661.596 | 9400.054 |
800 Storable | 4445.002 | 5235.027 | 1373 Storable | 19765.806 | 10000.725 |
801 -----------+------------+------------+ 1374 --------------+------------+------------+
802 1375
803 Again, JSON::XS leads by far (except for Storable which non-surprisingly 1376 Again, JSON::XS leads by far (except for Storable which non-surprisingly
804 decodes faster). 1377 decodes a bit faster).
805 1378
806 On large strings containing lots of high unicode characters, some 1379 On large strings containing lots of high Unicode characters, some
807 modules (such as JSON::PC) seem to decode faster than JSON::XS, but the 1380 modules (such as JSON::PC) seem to decode faster than JSON::XS, but the
808 result will be broken due to missing (or wrong) unicode handling. Others 1381 result will be broken due to missing (or wrong) Unicode handling. Others
809 refuse to decode or encode properly, so it was impossible to prepare a 1382 refuse to decode or encode properly, so it was impossible to prepare a
810 fair comparison table for that case. 1383 fair comparison table for that case.
811 1384
812SECURITY CONSIDERATIONS 1385SECURITY CONSIDERATIONS
813 When you are using JSON in a protocol, talking to untrusted potentially 1386 When you are using JSON in a protocol, talking to untrusted potentially
… …
817 have any buffer overflows. Obviously, this module should ensure that and 1390 have any buffer overflows. Obviously, this module should ensure that and
818 I am trying hard on making that true, but you never know. 1391 I am trying hard on making that true, but you never know.
819 1392
820 Second, you need to avoid resource-starving attacks. That means you 1393 Second, you need to avoid resource-starving attacks. That means you
821 should limit the size of JSON texts you accept, or make sure then when 1394 should limit the size of JSON texts you accept, or make sure then when
822 your resources run out, thats just fine (e.g. by using a separate 1395 your resources run out, that's just fine (e.g. by using a separate
823 process that can crash safely). The size of a JSON text in octets or 1396 process that can crash safely). The size of a JSON text in octets or
824 characters is usually a good indication of the size of the resources 1397 characters is usually a good indication of the size of the resources
825 required to decode it into a Perl structure. While JSON::XS can check 1398 required to decode it into a Perl structure. While JSON::XS can check
826 the size of the JSON text, it might be too late when you already have it 1399 the size of the JSON text, it might be too late when you already have it
827 in memory, so you might want to check the size before you accept the 1400 in memory, so you might want to check the size before you accept the
… …
830 Third, JSON::XS recurses using the C stack when decoding objects and 1403 Third, JSON::XS recurses using the C stack when decoding objects and
831 arrays. The C stack is a limited resource: for instance, on my amd64 1404 arrays. The C stack is a limited resource: for instance, on my amd64
832 machine with 8MB of stack size I can decode around 180k nested arrays 1405 machine with 8MB of stack size I can decode around 180k nested arrays
833 but only 14k nested JSON objects (due to perl itself recursing deeply on 1406 but only 14k nested JSON objects (due to perl itself recursing deeply on
834 croak to free the temporary). If that is exceeded, the program crashes. 1407 croak to free the temporary). If that is exceeded, the program crashes.
835 to be conservative, the default nesting limit is set to 512. If your 1408 To be conservative, the default nesting limit is set to 512. If your
836 process has a smaller stack, you should adjust this setting accordingly 1409 process has a smaller stack, you should adjust this setting accordingly
837 with the "max_depth" method. 1410 with the "max_depth" method.
838 1411
839 And last but least, something else could bomb you that I forgot to think 1412 Something else could bomb you, too, that I forgot to think of. In that
840 of. In that case, you get to keep the pieces. I am always open for 1413 case, you get to keep the pieces. I am always open for hints, though...
841 hints, though...
842 1414
1415 Also keep in mind that JSON::XS might leak contents of your Perl data
1416 structures in its error messages, so when you serialise sensitive
1417 information you might want to make sure that exceptions thrown by
1418 JSON::XS will not end up in front of untrusted eyes.
1419
843 If you are using JSON::XS to return packets to consumption by javascript 1420 If you are using JSON::XS to return packets to consumption by JavaScript
844 scripts in a browser you should have a look at 1421 scripts in a browser you should have a look at
845 <http://jpsykes.com/47/practical-csrf-and-json-security> to see wether 1422 <http://blog.archive.jpsykes.com/47/practical-csrf-and-json-security/>
846 you are vulnerable to some common attack vectors (which really are 1423 to see whether you are vulnerable to some common attack vectors (which
847 browser design bugs, but it is still you who will have to deal with it, 1424 really are browser design bugs, but it is still you who will have to
848 as major browser developers care only for features, not about doing 1425 deal with it, as major browser developers care only for features, not
849 security right). 1426 about getting security right).
1427
1428INTEROPERABILITY WITH OTHER MODULES
1429 "JSON::XS" uses the Types::Serialiser module to provide boolean
1430 constants. That means that the JSON true and false values will be
1431 comaptible to true and false values of iother modules that do the same,
1432 such as JSON::PP and CBOR::XS.
1433
1434THREADS
1435 This module is *not* guaranteed to be thread safe and there are no plans
1436 to change this until Perl gets thread support (as opposed to the
1437 horribly slow so-called "threads" which are simply slow and bloated
1438 process simulations - use fork, it's *much* faster, cheaper, better).
1439
1440 (It might actually work, but you have been warned).
1441
1442THE PERILS OF SETLOCALE
1443 Sometimes people avoid the Perl locale support and directly call the
1444 system's setlocale function with "LC_ALL".
1445
1446 This breaks both perl and modules such as JSON::XS, as stringification
1447 of numbers no longer works correctly (e.g. "$x = 0.1; print "$x"+1"
1448 might print 1, and JSON::XS might output illegal JSON as JSON::XS relies
1449 on perl to stringify numbers).
1450
1451 The solution is simple: don't call "setlocale", or use it for only those
1452 categories you need, such as "LC_MESSAGES" or "LC_CTYPE".
1453
1454 If you need "LC_NUMERIC", you should enable it only around the code that
1455 actually needs it (avoiding stringification of numbers), and restore it
1456 afterwards.
850 1457
851BUGS 1458BUGS
852 While the goal of this module is to be correct, that unfortunately does 1459 While the goal of this module is to be correct, that unfortunately does
853 not mean its bug-free, only that I think its design is bug-free. It is 1460 not mean it's bug-free, only that I think its design is bug-free. If you
854 still relatively early in its development. If you keep reporting bugs
855 they will be fixed swiftly, though. 1461 keep reporting bugs they will be fixed swiftly, though.
1462
1463 Please refrain from using rt.cpan.org or any other bug reporting
1464 service. I put the contact address into my modules for a reason.
1465
1466SEE ALSO
1467 The json_xs command line utility for quick experiments.
856 1468
857AUTHOR 1469AUTHOR
858 Marc Lehmann <schmorp@schmorp.de> 1470 Marc Lehmann <schmorp@schmorp.de>
859 http://home.schmorp.de/ 1471 http://home.schmorp.de/
860 1472

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