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1NAME 1NAME
2 JSON::XS - JSON serialising/deserialising, done correctly and fast 2 JSON::XS - JSON serialising/deserialising, done correctly and fast
3 3
4 JSON::XS - 正しくて高速な JSON 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 it 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
345 * shell-style '#'-comments
346
347 Whenever JSON allows whitespace, shell-style comments are
348 additionally allowed. They are terminated by the first
349 carriage-return or line-feed character, after which more
350 white-space and comments are allowed.
351
352 [
353 1, # this comment not allowed in JSON
354 # neither this one...
355 ]
356
357 * literal ASCII TAB characters in strings
358
359 Literal ASCII TAB characters are now allowed in strings (and
360 treated as "\t").
361
362 [
363 "Hello\tWorld",
364 "Hello<TAB>World", # literal <TAB> would not normally be allowed
365 ]
366
273 $json = $json->canonical ([$enable]) 367 $json = $json->canonical ([$enable])
368 $enabled = $json->get_canonical
274 If $enable is true (or missing), then the "encode" method will 369 If $enable is true (or missing), then the "encode" method will
275 output JSON objects by sorting their keys. This is adding a 370 output JSON objects by sorting their keys. This is adding a
276 comparatively high overhead. 371 comparatively high overhead.
277 372
278 If $enable is false, then the "encode" method will output key-value 373 If $enable is false, then the "encode" method will output key-value
279 pairs in the order Perl stores them (which will likely change 374 pairs in the order Perl stores them (which will likely change
280 between runs of the same script). 375 between runs of the same script, and can change even within the same
376 run from 5.18 onwards).
281 377
282 This option is useful if you want the same data structure to be 378 This option is useful if you want the same data structure to be
283 encoded as the same JSON text (given the same overall settings). If 379 encoded as the same JSON text (given the same overall settings). If
284 it is disabled, the same hash migh be encoded differently even if 380 it is disabled, the same hash might be encoded differently even if
285 contains the same data, as key-value pairs have no inherent ordering 381 contains the same data, as key-value pairs have no inherent ordering
286 in Perl. 382 in Perl.
287 383
288 This setting has no effect when decoding JSON texts. 384 This setting has no effect when decoding JSON texts.
289 385
386 This setting has currently no effect on tied hashes.
387
290 $json = $json->allow_nonref ([$enable]) 388 $json = $json->allow_nonref ([$enable])
389 $enabled = $json->get_allow_nonref
291 If $enable is true (or missing), then the "encode" method can 390 If $enable is true (or missing), then the "encode" method can
292 convert a non-reference into its corresponding string, number or 391 convert a non-reference into its corresponding string, number or
293 null JSON value, which is an extension to RFC4627. Likewise, 392 null JSON value, which is an extension to RFC4627. Likewise,
294 "decode" will accept those JSON values instead of croaking. 393 "decode" will accept those JSON values instead of croaking.
295 394
… …
302 "allow_nonref", resulting in an invalid JSON text: 401 "allow_nonref", resulting in an invalid JSON text:
303 402
304 JSON::XS->new->allow_nonref->encode ("Hello, World!") 403 JSON::XS->new->allow_nonref->encode ("Hello, World!")
305 => "Hello, World!" 404 => "Hello, World!"
306 405
406 $json = $json->allow_unknown ([$enable])
407 $enabled = $json->get_allow_unknown
408 If $enable is true (or missing), then "encode" will *not* throw an
409 exception when it encounters values it cannot represent in JSON (for
410 example, filehandles) but instead will encode a JSON "null" value.
411 Note that blessed objects are not included here and are handled
412 separately by c<allow_nonref>.
413
414 If $enable is false (the default), then "encode" will throw an
415 exception when it encounters anything it cannot encode as JSON.
416
417 This option does not affect "decode" in any way, and it is
418 recommended to leave it off unless you know your communications
419 partner.
420
307 $json = $json->allow_blessed ([$enable]) 421 $json = $json->allow_blessed ([$enable])
422 $enabled = $json->get_allow_blessed
423 See "OBJECT SERIALISATION" for details.
424
308 If $enable is true (or missing), then the "encode" method will not 425 If $enable is true (or missing), then the "encode" method will not
309 barf when it encounters a blessed reference. Instead, the value of 426 barf when it encounters a blessed reference that it cannot convert
310 the convert_blessed option will decide wether "null" 427 otherwise. Instead, a JSON "null" value is encoded instead of the
311 ("convert_blessed" disabled or no "to_json" method found) or a 428 object.
312 representation of the object ("convert_blessed" enabled and
313 "to_json" method found) is being encoded. Has no effect on "decode".
314 429
315 If $enable is false (the default), then "encode" will throw an 430 If $enable is false (the default), then "encode" will throw an
316 exception when it encounters a blessed object. 431 exception when it encounters a blessed object that it cannot convert
432 otherwise.
433
434 This setting has no effect on "decode".
317 435
318 $json = $json->convert_blessed ([$enable]) 436 $json = $json->convert_blessed ([$enable])
437 $enabled = $json->get_convert_blessed
438 See "OBJECT SERIALISATION" for details.
439
319 If $enable is true (or missing), then "encode", upon encountering a 440 If $enable is true (or missing), then "encode", upon encountering a
320 blessed object, will check for the availability of the "TO_JSON" 441 blessed object, will check for the availability of the "TO_JSON"
321 method on the object's class. If found, it will be called in scalar 442 method on the object's class. If found, it will be called in scalar
322 context and the resulting scalar will be encoded instead of the 443 context and the resulting scalar will be encoded instead of the
323 object. If no "TO_JSON" method is found, the value of 444 object.
324 "allow_blessed" will decide what to do.
325 445
326 The "TO_JSON" method may safely call die if it wants. If "TO_JSON" 446 The "TO_JSON" method may safely call die if it wants. If "TO_JSON"
327 returns other blessed objects, those will be handled in the same 447 returns other blessed objects, those will be handled in the same
328 way. "TO_JSON" must take care of not causing an endless recursion 448 way. "TO_JSON" must take care of not causing an endless recursion
329 cycle (== crash) in this case. The name of "TO_JSON" was chosen 449 cycle (== crash) in this case. The name of "TO_JSON" was chosen
330 because other methods called by the Perl core (== not by the user of 450 because other methods called by the Perl core (== not by the user of
331 the object) are usually in upper case letters and to avoid 451 the object) are usually in upper case letters and to avoid
332 collisions with the "to_json" function. 452 collisions with any "to_json" function or method.
333 453
334 This setting does not yet influence "decode" in any way, but in the 454 If $enable is false (the default), then "encode" will not consider
335 future, global hooks might get installed that influence "decode" and 455 this type of conversion.
336 are enabled by this setting.
337 456
338 If $enable is false, then the "allow_blessed" setting will decide 457 This setting has no effect on "decode".
339 what to do when a blessed object is found. 458
459 $json = $json->allow_tags ([$enable])
460 $enabled = $json->allow_tags
461 See "OBJECT SERIALISATION" for details.
462
463 If $enable is true (or missing), then "encode", upon encountering a
464 blessed object, will check for the availability of the "FREEZE"
465 method on the object's class. If found, it will be used to serialise
466 the object into a nonstandard tagged JSON value (that JSON decoders
467 cannot decode).
468
469 It also causes "decode" to parse such tagged JSON values and
470 deserialise them via a call to the "THAW" method.
471
472 If $enable is false (the default), then "encode" will not consider
473 this type of conversion, and tagged JSON values will cause a parse
474 error in "decode", as if tags were not part of the grammar.
340 475
341 $json = $json->filter_json_object ([$coderef->($hashref)]) 476 $json = $json->filter_json_object ([$coderef->($hashref)])
342 When $coderef is specified, it will be called from "decode" each 477 When $coderef is specified, it will be called from "decode" each
343 time it decodes a JSON object. The only argument is a reference to 478 time it decodes a JSON object. The only argument is a reference to
344 the newly-created hash. If the code references returns a single 479 the newly-created hash. If the code references returns a single
… …
378 513
379 As this callback gets called less often then the 514 As this callback gets called less often then the
380 "filter_json_object" one, decoding speed will not usually suffer as 515 "filter_json_object" one, decoding speed will not usually suffer as
381 much. Therefore, single-key objects make excellent targets to 516 much. Therefore, single-key objects make excellent targets to
382 serialise Perl objects into, especially as single-key JSON objects 517 serialise Perl objects into, especially as single-key JSON objects
383 are as close to the type-tagged value concept as JSON gets (its 518 are as close to the type-tagged value concept as JSON gets (it's
384 basically an ID/VALUE tuple). Of course, JSON does not support this 519 basically an ID/VALUE tuple). Of course, JSON does not support this
385 in any way, so you need to make sure your data never looks like a 520 in any way, so you need to make sure your data never looks like a
386 serialised Perl hash. 521 serialised Perl hash.
387 522
388 Typical names for the single object key are "__class_whatever__", or 523 Typical names for the single object key are "__class_whatever__", or
… …
413 548
414 { __widget__ => $self->{id} } 549 { __widget__ => $self->{id} }
415 } 550 }
416 551
417 $json = $json->shrink ([$enable]) 552 $json = $json->shrink ([$enable])
553 $enabled = $json->get_shrink
418 Perl usually over-allocates memory a bit when allocating space for 554 Perl usually over-allocates memory a bit when allocating space for
419 strings. This flag optionally resizes strings generated by either 555 strings. This flag optionally resizes strings generated by either
420 "encode" or "decode" to their minimum size possible. This can save 556 "encode" or "decode" to their minimum size possible. This can save
421 memory when your JSON texts are either very very long or you have 557 memory when your JSON texts are either very very long or you have
422 many short strings. It will also try to downgrade any strings to 558 many short strings. It will also try to downgrade any strings to
… …
440 converting strings that look like integers or floats into integers 576 converting strings that look like integers or floats into integers
441 or floats internally (there is no difference on the Perl level), 577 or floats internally (there is no difference on the Perl level),
442 saving space. 578 saving space.
443 579
444 $json = $json->max_depth ([$maximum_nesting_depth]) 580 $json = $json->max_depth ([$maximum_nesting_depth])
581 $max_depth = $json->get_max_depth
445 Sets the maximum nesting level (default 512) accepted while encoding 582 Sets the maximum nesting level (default 512) accepted while encoding
446 or decoding. If the JSON text or Perl data structure has an equal or 583 or decoding. If a higher nesting level is detected in JSON text or a
447 higher nesting level then this limit, then the encoder and decoder 584 Perl data structure, then the encoder and decoder will stop and
448 will stop and croak at that point. 585 croak at that point.
449 586
450 Nesting level is defined by number of hash- or arrayrefs that the 587 Nesting level is defined by number of hash- or arrayrefs that the
451 encoder needs to traverse to reach a given point or the number of 588 encoder needs to traverse to reach a given point or the number of
452 "{" or "[" characters without their matching closing parenthesis 589 "{" or "[" characters without their matching closing parenthesis
453 crossed to reach a given character in a string. 590 crossed to reach a given character in a string.
454 591
455 Setting the maximum depth to one disallows any nesting, so that 592 Setting the maximum depth to one disallows any nesting, so that
456 ensures that the object is only a single hash/object or array. 593 ensures that the object is only a single hash/object or array.
457 594
458 The argument to "max_depth" will be rounded up to the next highest
459 power of two. If no argument is given, the highest possible setting 595 If no argument is given, the highest possible setting will be used,
460 will be used, which is rarely useful. 596 which is rarely useful.
597
598 Note that nesting is implemented by recursion in C. The default
599 value has been chosen to be as large as typical operating systems
600 allow without crashing.
461 601
462 See SECURITY CONSIDERATIONS, below, for more info on why this is 602 See SECURITY CONSIDERATIONS, below, for more info on why this is
463 useful. 603 useful.
464 604
465 $json = $json->max_size ([$maximum_string_size]) 605 $json = $json->max_size ([$maximum_string_size])
606 $max_size = $json->get_max_size
466 Set the maximum length a JSON text may have (in bytes) where 607 Set the maximum length a JSON text may have (in bytes) where
467 decoding is being attempted. The default is 0, meaning no limit. 608 decoding is being attempted. The default is 0, meaning no limit.
468 When "decode" is called on a string longer then this number of 609 When "decode" is called on a string that is longer then this many
469 characters it will not attempt to decode the string but throw an 610 bytes, it will not attempt to decode the string but throw an
470 exception. This setting has no effect on "encode" (yet). 611 exception. This setting has no effect on "encode" (yet).
471 612
472 The argument to "max_size" will be rounded up to the next highest
473 power of two (so may be more than requested). If no argument is
474 given, the limit check will be deactivated (same as when 0 is 613 If no argument is given, the limit check will be deactivated (same
475 specified). 614 as when 0 is specified).
476 615
477 See SECURITY CONSIDERATIONS, below, for more info on why this is 616 See SECURITY CONSIDERATIONS, below, for more info on why this is
478 useful. 617 useful.
479 618
480 $json_text = $json->encode ($perl_scalar) 619 $json_text = $json->encode ($perl_scalar)
481 Converts the given Perl data structure (a simple scalar or a 620 Converts the given Perl value or data structure to its JSON
482 reference to a hash or array) to its JSON representation. Simple 621 representation. Croaks on error.
483 scalars will be converted into JSON string or number sequences,
484 while references to arrays become JSON arrays and references to
485 hashes become JSON objects. Undefined Perl values (e.g. "undef")
486 become JSON "null" values. Neither "true" nor "false" values will be
487 generated.
488 622
489 $perl_scalar = $json->decode ($json_text) 623 $perl_scalar = $json->decode ($json_text)
490 The opposite of "encode": expects a JSON text and tries to parse it, 624 The opposite of "encode": expects a JSON text and tries to parse it,
491 returning the resulting simple scalar or reference. Croaks on error. 625 returning the resulting simple scalar or reference. Croaks on error.
492
493 JSON numbers and strings become simple Perl scalars. JSON arrays
494 become Perl arrayrefs and JSON objects become Perl hashrefs. "true"
495 becomes 1, "false" becomes 0 and "null" becomes "undef".
496 626
497 ($perl_scalar, $characters) = $json->decode_prefix ($json_text) 627 ($perl_scalar, $characters) = $json->decode_prefix ($json_text)
498 This works like the "decode" method, but instead of raising an 628 This works like the "decode" method, but instead of raising an
499 exception when there is trailing garbage after the first JSON 629 exception when there is trailing garbage after the first JSON
500 object, it will silently stop parsing there and return the number of 630 object, it will silently stop parsing there and return the number of
501 characters consumed so far. 631 characters consumed so far.
502 632
503 This is useful if your JSON texts are not delimited by an outer 633 This is useful if your JSON texts are not delimited by an outer
504 protocol (which is not the brightest thing to do in the first place)
505 and you need to know where the JSON text ends. 634 protocol and you need to know where the JSON text ends.
506 635
507 JSON::XS->new->decode_prefix ("[1] the tail") 636 JSON::XS->new->decode_prefix ("[1] the tail")
508 => ([], 3) 637 => ([1], 3)
638
639INCREMENTAL PARSING
640 In some cases, there is the need for incremental parsing of JSON texts.
641 While this module always has to keep both JSON text and resulting Perl
642 data structure in memory at one time, it does allow you to parse a JSON
643 stream incrementally. It does so by accumulating text until it has a
644 full JSON object, which it then can decode. This process is similar to
645 using "decode_prefix" to see if a full JSON object is available, but is
646 much more efficient (and can be implemented with a minimum of method
647 calls).
648
649 JSON::XS will only attempt to parse the JSON text once it is sure it has
650 enough text to get a decisive result, using a very simple but truly
651 incremental parser. This means that it sometimes won't stop as early as
652 the full parser, for example, it doesn't detect mismatched parentheses.
653 The only thing it guarantees is that it starts decoding as soon as a
654 syntactically valid JSON text has been seen. This means you need to set
655 resource limits (e.g. "max_size") to ensure the parser will stop parsing
656 in the presence if syntax errors.
657
658 The following methods implement this incremental parser.
659
660 [void, scalar or list context] = $json->incr_parse ([$string])
661 This is the central parsing function. It can both append new text
662 and extract objects from the stream accumulated so far (both of
663 these functions are optional).
664
665 If $string is given, then this string is appended to the already
666 existing JSON fragment stored in the $json object.
667
668 After that, if the function is called in void context, it will
669 simply return without doing anything further. This can be used to
670 add more text in as many chunks as you want.
671
672 If the method is called in scalar context, then it will try to
673 extract exactly *one* JSON object. If that is successful, it will
674 return this object, otherwise it will return "undef". If there is a
675 parse error, this method will croak just as "decode" would do (one
676 can then use "incr_skip" to skip the erroneous part). This is the
677 most common way of using the method.
678
679 And finally, in list context, it will try to extract as many objects
680 from the stream as it can find and return them, or the empty list
681 otherwise. For this to work, there must be no separators (other than
682 whitespace) between the JSON objects or arrays, instead they must be
683 concatenated back-to-back. If an error occurs, an exception will be
684 raised as in the scalar context case. Note that in this case, any
685 previously-parsed JSON texts will be lost.
686
687 Example: Parse some JSON arrays/objects in a given string and return
688 them.
689
690 my @objs = JSON::XS->new->incr_parse ("[5][7][1,2]");
691
692 $lvalue_string = $json->incr_text
693 This method returns the currently stored JSON fragment as an lvalue,
694 that is, you can manipulate it. This *only* works when a preceding
695 call to "incr_parse" in *scalar context* successfully returned an
696 object. Under all other circumstances you must not call this
697 function (I mean it. although in simple tests it might actually
698 work, it *will* fail under real world conditions). As a special
699 exception, you can also call this method before having parsed
700 anything.
701
702 That means you can only use this function to look at or manipulate
703 text before or after complete JSON objects, not while the parser is
704 in the middle of parsing a JSON object.
705
706 This function is useful in two cases: a) finding the trailing text
707 after a JSON object or b) parsing multiple JSON objects separated by
708 non-JSON text (such as commas).
709
710 $json->incr_skip
711 This will reset the state of the incremental parser and will remove
712 the parsed text from the input buffer so far. This is useful after
713 "incr_parse" died, in which case the input buffer and incremental
714 parser state is left unchanged, to skip the text parsed so far and
715 to reset the parse state.
716
717 The difference to "incr_reset" is that only text until the parse
718 error occurred is removed.
719
720 $json->incr_reset
721 This completely resets the incremental parser, that is, after this
722 call, it will be as if the parser had never parsed anything.
723
724 This is useful if you want to repeatedly parse JSON objects and want
725 to ignore any trailing data, which means you have to reset the
726 parser after each successful decode.
727
728 LIMITATIONS
729 All options that affect decoding are supported, except "allow_nonref".
730 The reason for this is that it cannot be made to work sensibly: JSON
731 objects and arrays are self-delimited, i.e. you can concatenate them
732 back to back and still decode them perfectly. This does not hold true
733 for JSON numbers, however.
734
735 For example, is the string 1 a single JSON number, or is it simply the
736 start of 12? Or is 12 a single JSON number, or the concatenation of 1
737 and 2? In neither case you can tell, and this is why JSON::XS takes the
738 conservative route and disallows this case.
739
740 EXAMPLES
741 Some examples will make all this clearer. First, a simple example that
742 works similarly to "decode_prefix": We want to decode the JSON object at
743 the start of a string and identify the portion after the JSON object:
744
745 my $text = "[1,2,3] hello";
746
747 my $json = new JSON::XS;
748
749 my $obj = $json->incr_parse ($text)
750 or die "expected JSON object or array at beginning of string";
751
752 my $tail = $json->incr_text;
753 # $tail now contains " hello"
754
755 Easy, isn't it?
756
757 Now for a more complicated example: Imagine a hypothetical protocol
758 where you read some requests from a TCP stream, and each request is a
759 JSON array, without any separation between them (in fact, it is often
760 useful to use newlines as "separators", as these get interpreted as
761 whitespace at the start of the JSON text, which makes it possible to
762 test said protocol with "telnet"...).
763
764 Here is how you'd do it (it is trivial to write this in an event-based
765 manner):
766
767 my $json = new JSON::XS;
768
769 # read some data from the socket
770 while (sysread $socket, my $buf, 4096) {
771
772 # split and decode as many requests as possible
773 for my $request ($json->incr_parse ($buf)) {
774 # act on the $request
775 }
776 }
777
778 Another complicated example: Assume you have a string with JSON objects
779 or arrays, all separated by (optional) comma characters (e.g. "[1],[2],
780 [3]"). To parse them, we have to skip the commas between the JSON texts,
781 and here is where the lvalue-ness of "incr_text" comes in useful:
782
783 my $text = "[1],[2], [3]";
784 my $json = new JSON::XS;
785
786 # void context, so no parsing done
787 $json->incr_parse ($text);
788
789 # now extract as many objects as possible. note the
790 # use of scalar context so incr_text can be called.
791 while (my $obj = $json->incr_parse) {
792 # do something with $obj
793
794 # now skip the optional comma
795 $json->incr_text =~ s/^ \s* , //x;
796 }
797
798 Now lets go for a very complex example: Assume that you have a gigantic
799 JSON array-of-objects, many gigabytes in size, and you want to parse it,
800 but you cannot load it into memory fully (this has actually happened in
801 the real world :).
802
803 Well, you lost, you have to implement your own JSON parser. But JSON::XS
804 can still help you: You implement a (very simple) array parser and let
805 JSON decode the array elements, which are all full JSON objects on their
806 own (this wouldn't work if the array elements could be JSON numbers, for
807 example):
808
809 my $json = new JSON::XS;
810
811 # open the monster
812 open my $fh, "<bigfile.json"
813 or die "bigfile: $!";
814
815 # first parse the initial "["
816 for (;;) {
817 sysread $fh, my $buf, 65536
818 or die "read error: $!";
819 $json->incr_parse ($buf); # void context, so no parsing
820
821 # Exit the loop once we found and removed(!) the initial "[".
822 # In essence, we are (ab-)using the $json object as a simple scalar
823 # we append data to.
824 last if $json->incr_text =~ s/^ \s* \[ //x;
825 }
826
827 # now we have the skipped the initial "[", so continue
828 # parsing all the elements.
829 for (;;) {
830 # in this loop we read data until we got a single JSON object
831 for (;;) {
832 if (my $obj = $json->incr_parse) {
833 # do something with $obj
834 last;
835 }
836
837 # add more data
838 sysread $fh, my $buf, 65536
839 or die "read error: $!";
840 $json->incr_parse ($buf); # void context, so no parsing
841 }
842
843 # in this loop we read data until we either found and parsed the
844 # separating "," between elements, or the final "]"
845 for (;;) {
846 # first skip whitespace
847 $json->incr_text =~ s/^\s*//;
848
849 # if we find "]", we are done
850 if ($json->incr_text =~ s/^\]//) {
851 print "finished.\n";
852 exit;
853 }
854
855 # if we find ",", we can continue with the next element
856 if ($json->incr_text =~ s/^,//) {
857 last;
858 }
859
860 # if we find anything else, we have a parse error!
861 if (length $json->incr_text) {
862 die "parse error near ", $json->incr_text;
863 }
864
865 # else add more data
866 sysread $fh, my $buf, 65536
867 or die "read error: $!";
868 $json->incr_parse ($buf); # void context, so no parsing
869 }
870
871 This is a complex example, but most of the complexity comes from the
872 fact that we are trying to be correct (bear with me if I am wrong, I
873 never ran the above example :).
509 874
510MAPPING 875MAPPING
511 This section describes how JSON::XS maps Perl values to JSON values and 876 This section describes how JSON::XS maps Perl values to JSON values and
512 vice versa. These mappings are designed to "do the right thing" in most 877 vice versa. These mappings are designed to "do the right thing" in most
513 circumstances automatically, preserving round-tripping characteristics 878 circumstances automatically, preserving round-tripping characteristics
514 (what you put in comes out as something equivalent). 879 (what you put in comes out as something equivalent).
515 880
516 For the more enlightened: note that in the following descriptions, 881 For the more enlightened: note that in the following descriptions,
517 lowercase *perl* refers to the Perl interpreter, while uppcercase *Perl* 882 lowercase *perl* refers to the Perl interpreter, while uppercase *Perl*
518 refers to the abstract Perl language itself. 883 refers to the abstract Perl language itself.
519 884
520 JSON -> PERL 885 JSON -> PERL
521 object 886 object
522 A JSON object becomes a reference to a hash in Perl. No ordering of 887 A JSON object becomes a reference to a hash in Perl. No ordering of
523 object keys is preserved (JSON does not preserver object key 888 object keys is preserved (JSON does not preserve object key ordering
524 ordering itself). 889 itself).
525 890
526 array 891 array
527 A JSON array becomes a reference to an array in Perl. 892 A JSON array becomes a reference to an array in Perl.
528 893
529 string 894 string
… …
535 A JSON number becomes either an integer, numeric (floating point) or 900 A JSON number becomes either an integer, numeric (floating point) or
536 string scalar in perl, depending on its range and any fractional 901 string scalar in perl, depending on its range and any fractional
537 parts. On the Perl level, there is no difference between those as 902 parts. On the Perl level, there is no difference between those as
538 Perl handles all the conversion details, but an integer may take 903 Perl handles all the conversion details, but an integer may take
539 slightly less memory and might represent more values exactly than 904 slightly less memory and might represent more values exactly than
540 (floating point) numbers. 905 floating point numbers.
541 906
542 If the number consists of digits only, JSON::XS will try to 907 If the number consists of digits only, JSON::XS will try to
543 represent it as an integer value. If that fails, it will try to 908 represent it as an integer value. If that fails, it will try to
544 represent it as a numeric (floating point) value if that is possible 909 represent it as a numeric (floating point) value if that is possible
545 without loss of precision. Otherwise it will preserve the number as 910 without loss of precision. Otherwise it will preserve the number as
546 a string value. 911 a string value (in which case you lose roundtripping ability, as the
912 JSON number will be re-encoded to a JSON string).
547 913
548 Numbers containing a fractional or exponential part will always be 914 Numbers containing a fractional or exponential part will always be
549 represented as numeric (floating point) values, possibly at a loss 915 represented as numeric (floating point) values, possibly at a loss
550 of precision. 916 of precision (in which case you might lose perfect roundtripping
917 ability, but the JSON number will still be re-encoded as a JSON
918 number).
551 919
552 This might create round-tripping problems as numbers might become 920 Note that precision is not accuracy - binary floating point values
553 strings, but as Perl is typeless there is no other way to do it. 921 cannot represent most decimal fractions exactly, and when converting
922 from and to floating point, JSON::XS only guarantees precision up to
923 but not including the least significant bit.
554 924
555 true, false 925 true, false
556 These JSON atoms become "JSON::XS::true" and "JSON::XS::false", 926 These JSON atoms become "Types::Serialiser::true" and
557 respectively. They are overloaded to act almost exactly like the 927 "Types::Serialiser::false", respectively. They are overloaded to act
558 numbers 1 and 0. You can check wether a scalar is a JSON boolean by 928 almost exactly like the numbers 1 and 0. You can check whether a
559 using the "JSON::XS::is_bool" function. 929 scalar is a JSON boolean by using the "Types::Serialiser::is_bool"
930 function (after "use Types::Serialier", of course).
560 931
561 null 932 null
562 A JSON null atom becomes "undef" in Perl. 933 A JSON null atom becomes "undef" in Perl.
934
935 shell-style comments ("# *text*")
936 As a nonstandard extension to the JSON syntax that is enabled by the
937 "relaxed" setting, shell-style comments are allowed. They can start
938 anywhere outside strings and go till the end of the line.
939
940 tagged values ("(*tag*)*value*").
941 Another nonstandard extension to the JSON syntax, enabled with the
942 "allow_tags" setting, are tagged values. In this implementation, the
943 *tag* must be a perl package/class name encoded as a JSON string,
944 and the *value* must be a JSON array encoding optional constructor
945 arguments.
946
947 See "OBJECT SERIALISATION", below, for details.
563 948
564 PERL -> JSON 949 PERL -> JSON
565 The mapping from Perl to JSON is slightly more difficult, as Perl is a 950 The mapping from Perl to JSON is slightly more difficult, as Perl is a
566 truly typeless language, so we can only guess which JSON type is meant 951 truly typeless language, so we can only guess which JSON type is meant
567 by a Perl value. 952 by a Perl value.
568 953
569 hash references 954 hash references
570 Perl hash references become JSON objects. As there is no inherent 955 Perl hash references become JSON objects. As there is no inherent
571 ordering in hash keys (or JSON objects), they will usually be 956 ordering in hash keys (or JSON objects), they will usually be
572 encoded in a pseudo-random order that can change between runs of the 957 encoded in a pseudo-random order. JSON::XS can optionally sort the
573 same program but stays generally the same within a single run of a 958 hash keys (determined by the *canonical* flag), so the same
574 program. JSON::XS can optionally sort the hash keys (determined by 959 datastructure will serialise to the same JSON text (given same
575 the *canonical* flag), so the same datastructure will serialise to 960 settings and version of JSON::XS), but this incurs a runtime
576 the same JSON text (given same settings and version of JSON::XS), 961 overhead and is only rarely useful, e.g. when you want to compare
577 but this incurs a runtime overhead and is only rarely useful, e.g. 962 some JSON text against another for equality.
578 when you want to compare some JSON text against another for
579 equality.
580 963
581 array references 964 array references
582 Perl array references become JSON arrays. 965 Perl array references become JSON arrays.
583 966
584 other references 967 other references
585 Other unblessed references are generally not allowed and will cause 968 Other unblessed references are generally not allowed and will cause
586 an exception to be thrown, except for references to the integers 0 969 an exception to be thrown, except for references to the integers 0
587 and 1, which get turned into "false" and "true" atoms in JSON. You 970 and 1, which get turned into "false" and "true" atoms in JSON.
588 can also use "JSON::XS::false" and "JSON::XS::true" to improve 971
972 Since "JSON::XS" uses the boolean model from Types::Serialiser, you
973 can also "use Types::Serialiser" and then use
974 "Types::Serialiser::false" and "Types::Serialiser::true" to improve
589 readability. 975 readability.
590 976
977 use Types::Serialiser;
591 to_json [\0,JSON::XS::true] # yields [false,true] 978 encode_json [\0, Types::Serialiser::true] # yields [false,true]
592 979
593 JSON::XS::true, JSON::XS::false 980 Types::Serialiser::true, Types::Serialiser::false
594 These special values become JSON true and JSON false values, 981 These special values from the Types::Serialiser module become JSON
595 respectively. You cna alos use "\1" and "\0" directly if you want. 982 true and JSON false values, respectively. You can also use "\1" and
983 "\0" directly if you want.
596 984
597 blessed objects 985 blessed objects
598 Blessed objects are not allowed. JSON::XS currently tries to encode 986 Blessed objects are not directly representable in JSON, but
599 their underlying representation (hash- or arrayref), but this 987 "JSON::XS" allows various ways of handling objects. See "OBJECT
600 behaviour might change in future versions. 988 SERIALISATION", below, for details.
601 989
602 simple scalars 990 simple scalars
603 Simple Perl scalars (any scalar that is not a reference) are the 991 Simple Perl scalars (any scalar that is not a reference) are the
604 most difficult objects to encode: JSON::XS will encode undefined 992 most difficult objects to encode: JSON::XS will encode undefined
605 scalars as JSON null value, scalars that have last been used in a 993 scalars as JSON "null" values, scalars that have last been used in a
606 string context before encoding as JSON strings and anything else as 994 string context before encoding as JSON strings, and anything else as
607 number value: 995 number value:
608 996
609 # dump as number 997 # dump as number
610 to_json [2] # yields [2] 998 encode_json [2] # yields [2]
611 to_json [-3.0e17] # yields [-3e+17] 999 encode_json [-3.0e17] # yields [-3e+17]
612 my $value = 5; to_json [$value] # yields [5] 1000 my $value = 5; encode_json [$value] # yields [5]
613 1001
614 # used as string, so dump as string 1002 # used as string, so dump as string
615 print $value; 1003 print $value;
616 to_json [$value] # yields ["5"] 1004 encode_json [$value] # yields ["5"]
617 1005
618 # undef becomes null 1006 # undef becomes null
619 to_json [undef] # yields [null] 1007 encode_json [undef] # yields [null]
620 1008
621 You can force the type to be a string by stringifying it: 1009 You can force the type to be a JSON string by stringifying it:
622 1010
623 my $x = 3.1; # some variable containing a number 1011 my $x = 3.1; # some variable containing a number
624 "$x"; # stringified 1012 "$x"; # stringified
625 $x .= ""; # another, more awkward way to stringify 1013 $x .= ""; # another, more awkward way to stringify
626 print $x; # perl does it for you, too, quite often 1014 print $x; # perl does it for you, too, quite often
627 1015
628 You can force the type to be a number by numifying it: 1016 You can force the type to be a JSON number by numifying it:
629 1017
630 my $x = "3"; # some variable containing a string 1018 my $x = "3"; # some variable containing a string
631 $x += 0; # numify it, ensuring it will be dumped as a number 1019 $x += 0; # numify it, ensuring it will be dumped as a number
632 $x *= 1; # same thing, the choise is yours. 1020 $x *= 1; # same thing, the choice is yours.
633 1021
634 You can not currently output JSON booleans or force the type in 1022 You can not currently force the type in other, less obscure, ways.
635 other, less obscure, ways. Tell me if you need this capability. 1023 Tell me if you need this capability (but don't forget to explain why
1024 it's needed :).
636 1025
637COMPARISON 1026 Note that numerical precision has the same meaning as under Perl (so
638 As already mentioned, this module was created because none of the 1027 binary to decimal conversion follows the same rules as in Perl,
639 existing JSON modules could be made to work correctly. First I will 1028 which can differ to other languages). Also, your perl interpreter
640 describe the problems (or pleasures) I encountered with various existing 1029 might expose extensions to the floating point numbers of your
641 JSON modules, followed by some benchmark values. JSON::XS was designed 1030 platform, such as infinities or NaN's - these cannot be represented
642 not to suffer from any of these problems or limitations. 1031 in JSON, and it is an error to pass those in.
643 1032
644 JSON 1.07 1033 OBJECT SERIALISATION
645 Slow (but very portable, as it is written in pure Perl). 1034 As JSON cannot directly represent Perl objects, you have to choose
1035 between a pure JSON representation (without the ability to deserialise
1036 the object automatically again), and a nonstandard extension to the JSON
1037 syntax, tagged values.
646 1038
647 Undocumented/buggy Unicode handling (how JSON handles unicode values 1039 SERIALISATION
648 is undocumented. One can get far by feeding it unicode strings and 1040 What happens when "JSON::XS" encounters a Perl object depends on the
649 doing en-/decoding oneself, but unicode escapes are not working 1041 "allow_blessed", "convert_blessed" and "allow_tags" settings, which are
1042 used in this order:
1043
1044 1. "allow_tags" is enabled and the object has a "FREEZE" method.
1045 In this case, "JSON::XS" uses the Types::Serialiser object
1046 serialisation protocol to create a tagged JSON value, using a
1047 nonstandard extension to the JSON syntax.
1048
1049 This works by invoking the "FREEZE" method on the object, with the
1050 first argument being the object to serialise, and the second
1051 argument being the constant string "JSON" to distinguish it from
1052 other serialisers.
1053
1054 The "FREEZE" method can return any number of values (i.e. zero or
1055 more). These values and the paclkage/classname of the object will
1056 then be encoded as a tagged JSON value in the following format:
1057
1058 ("classname")[FREEZE return values...]
1059
1060 e.g.:
1061
1062 ("URI")["http://www.google.com/"]
1063 ("MyDate")[2013,10,29]
1064 ("ImageData::JPEG")["Z3...VlCg=="]
1065
1066 For example, the hypothetical "My::Object" "FREEZE" method might use
1067 the objects "type" and "id" members to encode the object:
1068
1069 sub My::Object::FREEZE {
1070 my ($self, $serialiser) = @_;
1071
1072 ($self->{type}, $self->{id})
1073 }
1074
1075 2. "convert_blessed" is enabled and the object has a "TO_JSON" method.
1076 In this case, the "TO_JSON" method of the object is invoked in
1077 scalar context. It must return a single scalar that can be directly
1078 encoded into JSON. This scalar replaces the object in the JSON text.
1079
1080 For example, the following "TO_JSON" method will convert all URI
1081 objects to JSON strings when serialised. The fatc that these values
1082 originally were URI objects is lost.
1083
1084 sub URI::TO_JSON {
1085 my ($uri) = @_;
1086 $uri->as_string
1087 }
1088
1089 3. "allow_blessed" is enabled.
1090 The object will be serialised as a JSON null value.
1091
1092 4. none of the above
1093 If none of the settings are enabled or the respective methods are
1094 missing, "JSON::XS" throws an exception.
1095
1096 DESERIALISATION
1097 For deserialisation there are only two cases to consider: either
1098 nonstandard tagging was used, in which case "allow_tags" decides, or
1099 objects cannot be automatically be deserialised, in which case you can
1100 use postprocessing or the "filter_json_object" or
1101 "filter_json_single_key_object" callbacks to get some real objects our
1102 of your JSON.
1103
1104 This section only considers the tagged value case: I a tagged JSON
1105 object is encountered during decoding and "allow_tags" is disabled, a
1106 parse error will result (as if tagged values were not part of the
1107 grammar).
1108
1109 If "allow_tags" is enabled, "JSON::XS" will look up the "THAW" method of
1110 the package/classname used during serialisation (it will not attempt to
1111 load the package as a Perl module). If there is no such method, the
1112 decoding will fail with an error.
1113
1114 Otherwise, the "THAW" method is invoked with the classname as first
1115 argument, the constant string "JSON" as second argument, and all the
1116 values from the JSON array (the values originally returned by the
1117 "FREEZE" method) as remaining arguments.
1118
1119 The method must then return the object. While technically you can return
1120 any Perl scalar, you might have to enable the "enable_nonref" setting to
1121 make that work in all cases, so better return an actual blessed
1122 reference.
1123
1124 As an example, let's implement a "THAW" function that regenerates the
1125 "My::Object" from the "FREEZE" example earlier:
1126
1127 sub My::Object::THAW {
1128 my ($class, $serialiser, $type, $id) = @_;
1129
1130 $class->new (type => $type, id => $id)
1131 }
1132
1133ENCODING/CODESET FLAG NOTES
1134 The interested reader might have seen a number of flags that signify
1135 encodings or codesets - "utf8", "latin1" and "ascii". There seems to be
1136 some confusion on what these do, so here is a short comparison:
1137
1138 "utf8" controls whether the JSON text created by "encode" (and expected
1139 by "decode") is UTF-8 encoded or not, while "latin1" and "ascii" only
1140 control whether "encode" escapes character values outside their
1141 respective codeset range. Neither of these flags conflict with each
1142 other, although some combinations make less sense than others.
1143
1144 Care has been taken to make all flags symmetrical with respect to
1145 "encode" and "decode", that is, texts encoded with any combination of
1146 these flag values will be correctly decoded when the same flags are used
1147 - in general, if you use different flag settings while encoding vs. when
1148 decoding you likely have a bug somewhere.
1149
1150 Below comes a verbose discussion of these flags. Note that a "codeset"
1151 is simply an abstract set of character-codepoint pairs, while an
1152 encoding takes those codepoint numbers and *encodes* them, in our case
1153 into octets. Unicode is (among other things) a codeset, UTF-8 is an
1154 encoding, and ISO-8859-1 (= latin 1) and ASCII are both codesets *and*
1155 encodings at the same time, which can be confusing.
1156
1157 "utf8" flag disabled
1158 When "utf8" is disabled (the default), then "encode"/"decode"
1159 generate and expect Unicode strings, that is, characters with high
1160 ordinal Unicode values (> 255) will be encoded as such characters,
1161 and likewise such characters are decoded as-is, no changes to them
1162 will be done, except "(re-)interpreting" them as Unicode codepoints
1163 or Unicode characters, respectively (to Perl, these are the same
1164 thing in strings unless you do funny/weird/dumb stuff).
1165
1166 This is useful when you want to do the encoding yourself (e.g. when
1167 you want to have UTF-16 encoded JSON texts) or when some other layer
1168 does the encoding for you (for example, when printing to a terminal
1169 using a filehandle that transparently encodes to UTF-8 you certainly
1170 do NOT want to UTF-8 encode your data first and have Perl encode it
1171 another time).
1172
1173 "utf8" flag enabled
1174 If the "utf8"-flag is enabled, "encode"/"decode" will encode all
1175 characters using the corresponding UTF-8 multi-byte sequence, and
1176 will expect your input strings to be encoded as UTF-8, that is, no
1177 "character" of the input string must have any value > 255, as UTF-8
1178 does not allow that.
1179
1180 The "utf8" flag therefore switches between two modes: disabled means
1181 you will get a Unicode string in Perl, enabled means you get an
1182 UTF-8 encoded octet/binary string in Perl.
1183
1184 "latin1" or "ascii" flags enabled
1185 With "latin1" (or "ascii") enabled, "encode" will escape characters
1186 with ordinal values > 255 (> 127 with "ascii") and encode the
1187 remaining characters as specified by the "utf8" flag.
1188
1189 If "utf8" is disabled, then the result is also correctly encoded in
1190 those character sets (as both are proper subsets of Unicode, meaning
1191 that a Unicode string with all character values < 256 is the same
1192 thing as a ISO-8859-1 string, and a Unicode string with all
1193 character values < 128 is the same thing as an ASCII string in
650 properly). 1194 Perl).
651 1195
652 No roundtripping (strings get clobbered if they look like numbers, 1196 If "utf8" is enabled, you still get a correct UTF-8-encoded string,
653 e.g. the string 2.0 will encode to 2.0 instead of "2.0", and that 1197 regardless of these flags, just some more characters will be escaped
654 will decode into the number 2. 1198 using "\uXXXX" then before.
655 1199
656 JSON::PC 0.01 1200 Note that ISO-8859-1-*encoded* strings are not compatible with UTF-8
657 Very fast. 1201 encoding, while ASCII-encoded strings are. That is because the
1202 ISO-8859-1 encoding is NOT a subset of UTF-8 (despite the ISO-8859-1
1203 *codeset* being a subset of Unicode), while ASCII is.
658 1204
659 Undocumented/buggy Unicode handling. 1205 Surprisingly, "decode" will ignore these flags and so treat all
1206 input values as governed by the "utf8" flag. If it is disabled, this
1207 allows you to decode ISO-8859-1- and ASCII-encoded strings, as both
1208 strict subsets of Unicode. If it is enabled, you can correctly
1209 decode UTF-8 encoded strings.
660 1210
661 No roundtripping. 1211 So neither "latin1" nor "ascii" are incompatible with the "utf8"
1212 flag - they only govern when the JSON output engine escapes a
1213 character or not.
662 1214
663 Has problems handling many Perl values (e.g. regex results and other 1215 The main use for "latin1" is to relatively efficiently store binary
664 magic values will make it croak). 1216 data as JSON, at the expense of breaking compatibility with most
1217 JSON decoders.
665 1218
666 Does not even generate valid JSON ("{1,2}" gets converted to "{1:2}" 1219 The main use for "ascii" is to force the output to not contain
667 which is not a valid JSON text. 1220 characters with values > 127, which means you can interpret the
1221 resulting string as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about
1222 any character set and 8-bit-encoding, and still get the same data
1223 structure back. This is useful when your channel for JSON transfer
1224 is not 8-bit clean or the encoding might be mangled in between (e.g.
1225 in mail), and works because ASCII is a proper subset of most 8-bit
1226 and multibyte encodings in use in the world.
668 1227
669 Unmaintained (maintainer unresponsive for many months, bugs are not 1228 JSON and ECMAscript
670 getting fixed). 1229 JSON syntax is based on how literals are represented in javascript (the
1230 not-standardised predecessor of ECMAscript) which is presumably why it
1231 is called "JavaScript Object Notation".
671 1232
672 JSON::Syck 0.21 1233 However, JSON is not a subset (and also not a superset of course) of
673 Very buggy (often crashes). 1234 ECMAscript (the standard) or javascript (whatever browsers actually
1235 implement).
674 1236
675 Very inflexible (no human-readable format supported, format pretty 1237 If you want to use javascript's "eval" function to "parse" JSON, you
676 much undocumented. I need at least a format for easy reading by 1238 might run into parse errors for valid JSON texts, or the resulting data
677 humans and a single-line compact format for use in a protocol, and 1239 structure might not be queryable:
678 preferably a way to generate ASCII-only JSON texts).
679 1240
680 Completely broken (and confusingly documented) Unicode handling 1241 One of the problems is that U+2028 and U+2029 are valid characters
681 (unicode escapes are not working properly, you need to set 1242 inside JSON strings, but are not allowed in ECMAscript string literals,
682 ImplicitUnicode to *different* values on en- and decoding to get 1243 so the following Perl fragment will not output something that can be
683 symmetric behaviour). 1244 guaranteed to be parsable by javascript's "eval":
684 1245
685 No roundtripping (simple cases work, but this depends on wether the 1246 use JSON::XS;
686 scalar value was used in a numeric context or not).
687 1247
688 Dumping hashes may skip hash values depending on iterator state. 1248 print encode_json [chr 0x2028];
689 1249
690 Unmaintained (maintainer unresponsive for many months, bugs are not 1250 The right fix for this is to use a proper JSON parser in your javascript
691 getting fixed). 1251 programs, and not rely on "eval" (see for example Douglas Crockford's
1252 json2.js parser).
692 1253
693 Does not check input for validity (i.e. will accept non-JSON input 1254 If this is not an option, you can, as a stop-gap measure, simply encode
694 and return "something" instead of raising an exception. This is a 1255 to ASCII-only JSON:
695 security issue: imagine two banks transfering money between each
696 other using JSON. One bank might parse a given non-JSON request and
697 deduct money, while the other might reject the transaction with a
698 syntax error. While a good protocol will at least recover, that is
699 extra unnecessary work and the transaction will still not succeed).
700 1256
701 JSON::DWIW 0.04 1257 use JSON::XS;
702 Very fast. Very natural. Very nice.
703 1258
704 Undocumented unicode handling (but the best of the pack. Unicode 1259 print JSON::XS->new->ascii->encode ([chr 0x2028]);
705 escapes still don't get parsed properly).
706 1260
707 Very inflexible. 1261 Note that this will enlarge the resulting JSON text quite a bit if you
1262 have many non-ASCII characters. You might be tempted to run some regexes
1263 to only escape U+2028 and U+2029, e.g.:
708 1264
709 No roundtripping. 1265 # DO NOT USE THIS!
1266 my $json = JSON::XS->new->utf8->encode ([chr 0x2028]);
1267 $json =~ s/\xe2\x80\xa8/\\u2028/g; # escape U+2028
1268 $json =~ s/\xe2\x80\xa9/\\u2029/g; # escape U+2029
1269 print $json;
710 1270
711 Does not generate valid JSON texts (key strings are often unquoted, 1271 Note that *this is a bad idea*: the above only works for U+2028 and
712 empty keys result in nothing being output) 1272 U+2029 and thus only for fully ECMAscript-compliant parsers. Many
1273 existing javascript implementations, however, have issues with other
1274 characters as well - using "eval" naively simply *will* cause problems.
713 1275
714 Does not check input for validity. 1276 Another problem is that some javascript implementations reserve some
1277 property names for their own purposes (which probably makes them
1278 non-ECMAscript-compliant). For example, Iceweasel reserves the
1279 "__proto__" property name for its own purposes.
1280
1281 If that is a problem, you could parse try to filter the resulting JSON
1282 output for these property strings, e.g.:
1283
1284 $json =~ s/"__proto__"\s*:/"__proto__renamed":/g;
1285
1286 This works because "__proto__" is not valid outside of strings, so every
1287 occurrence of ""__proto__"\s*:" must be a string used as property name.
1288
1289 If you know of other incompatibilities, please let me know.
715 1290
716 JSON and YAML 1291 JSON and YAML
717 You often hear that JSON is a subset (or a close subset) of YAML. This 1292 You often hear that JSON is a subset of YAML. This is, however, a mass
718 is, however, a mass hysteria and very far from the truth. In general, 1293 hysteria(*) and very far from the truth (as of the time of this
719 there is no way to configure JSON::XS to output a data structure as 1294 writing), so let me state it clearly: *in general, there is no way to
720 valid YAML. 1295 configure JSON::XS to output a data structure as valid YAML* that works
1296 in all cases.
721 1297
722 If you really must use JSON::XS to generate YAML, you should use this 1298 If you really must use JSON::XS to generate YAML, you should use this
723 algorithm (subject to change in future versions): 1299 algorithm (subject to change in future versions):
724 1300
725 my $to_yaml = JSON::XS->new->utf8->space_after (1); 1301 my $to_yaml = JSON::XS->new->utf8->space_after (1);
726 my $yaml = $to_yaml->encode ($ref) . "\n"; 1302 my $yaml = $to_yaml->encode ($ref) . "\n";
727 1303
728 This will usually generate JSON texts that also parse as valid YAML. 1304 This will *usually* generate JSON texts that also parse as valid YAML.
729 Please note that YAML has hardcoded limits on (simple) object key 1305 Please note that YAML has hardcoded limits on (simple) object key
730 lengths that JSON doesn't have, so you should make sure that your hash 1306 lengths that JSON doesn't have and also has different and incompatible
1307 unicode character escape syntax, so you should make sure that your hash
731 keys are noticably shorter than the 1024 characters YAML allows. 1308 keys are noticeably shorter than the 1024 "stream characters" YAML
1309 allows and that you do not have characters with codepoint values outside
1310 the Unicode BMP (basic multilingual page). YAML also does not allow "\/"
1311 sequences in strings (which JSON::XS does not *currently* generate, but
1312 other JSON generators might).
732 1313
733 There might be other incompatibilities that I am not aware of. In 1314 There might be other incompatibilities that I am not aware of (or the
1315 YAML specification has been changed yet again - it does so quite often).
734 general you should not try to generate YAML with a JSON generator or 1316 In general you should not try to generate YAML with a JSON generator or
735 vice versa, or try to parse JSON with a YAML parser or vice versa: 1317 vice versa, or try to parse JSON with a YAML parser or vice versa:
736 chances are high that you will run into severe interoperability 1318 chances are high that you will run into severe interoperability problems
737 problems. 1319 when you least expect it.
1320
1321 (*) I have been pressured multiple times by Brian Ingerson (one of the
1322 authors of the YAML specification) to remove this paragraph, despite
1323 him acknowledging that the actual incompatibilities exist. As I was
1324 personally bitten by this "JSON is YAML" lie, I refused and said I
1325 will continue to educate people about these issues, so others do not
1326 run into the same problem again and again. After this, Brian called
1327 me a (quote)*complete and worthless idiot*(unquote).
1328
1329 In my opinion, instead of pressuring and insulting people who
1330 actually clarify issues with YAML and the wrong statements of some
1331 of its proponents, I would kindly suggest reading the JSON spec
1332 (which is not that difficult or long) and finally make YAML
1333 compatible to it, and educating users about the changes, instead of
1334 spreading lies about the real compatibility for many *years* and
1335 trying to silence people who point out that it isn't true.
1336
1337 Addendum/2009: the YAML 1.2 spec is still incompatible with JSON,
1338 even though the incompatibilities have been documented (and are
1339 known to Brian) for many years and the spec makes explicit claims
1340 that YAML is a superset of JSON. It would be so easy to fix, but
1341 apparently, bullying people and corrupting userdata is so much
1342 easier.
738 1343
739 SPEED 1344 SPEED
740 It seems that JSON::XS is surprisingly fast, as shown in the following 1345 It seems that JSON::XS is surprisingly fast, as shown in the following
741 tables. They have been generated with the help of the "eg/bench" program 1346 tables. They have been generated with the help of the "eg/bench" program
742 in the JSON::XS distribution, to make it easy to compare on your own 1347 in the JSON::XS distribution, to make it easy to compare on your own
743 system. 1348 system.
744 1349
745 First comes a comparison between various modules using a very short 1350 First comes a comparison between various modules using a very short
746 single-line JSON string: 1351 single-line JSON string (also available at
1352 <http://dist.schmorp.de/misc/json/short.json>).
747 1353
748 {"method": "handleMessage", "params": ["user1", "we were just talking"], \ 1354 {"method": "handleMessage", "params": ["user1",
749 "id": null, "array":[1,11,234,-5,1e5,1e7, true, false]} 1355 "we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7,
1356 1, 0]}
750 1357
751 It shows the number of encodes/decodes per second (JSON::XS uses the 1358 It shows the number of encodes/decodes per second (JSON::XS uses the
752 functional interface, while JSON::XS/2 uses the OO interface with 1359 functional interface, while JSON::XS/2 uses the OO interface with
753 pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink). 1360 pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink.
754 Higher is better: 1361 JSON::DWIW/DS uses the deserialise function, while JSON::DWIW::FJ uses
1362 the from_json method). Higher is better:
755 1363
756 Storable | 15779.925 | 14169.946 |
757 -----------+------------+------------+
758 module | encode | decode | 1364 module | encode | decode |
759 -----------|------------|------------| 1365 --------------|------------|------------|
760 JSON | 4990.842 | 4088.813 | 1366 JSON::DWIW/DS | 86302.551 | 102300.098 |
761 JSON::DWIW | 51653.990 | 71575.154 | 1367 JSON::DWIW/FJ | 86302.551 | 75983.768 |
762 JSON::PC | 65948.176 | 74631.744 | 1368 JSON::PP | 15827.562 | 6638.658 |
763 JSON::PP | 8931.652 | 3817.168 | 1369 JSON::Syck | 63358.066 | 47662.545 |
764 JSON::Syck | 24877.248 | 27776.848 | 1370 JSON::XS | 511500.488 | 511500.488 |
765 JSON::XS | 388361.481 | 227951.304 | 1371 JSON::XS/2 | 291271.111 | 388361.481 |
766 JSON::XS/2 | 227951.304 | 218453.333 | 1372 JSON::XS/3 | 361577.931 | 361577.931 |
767 JSON::XS/3 | 338250.323 | 218453.333 | 1373 Storable | 66788.280 | 265462.278 |
768 Storable | 16500.016 | 135300.129 |
769 -----------+------------+------------+ 1374 --------------+------------+------------+
770 1375
771 That is, JSON::XS is about five times faster than JSON::DWIW on 1376 That is, JSON::XS is almost six times faster than JSON::DWIW on
772 encoding, about three times faster on decoding, and over fourty times 1377 encoding, about five times faster on decoding, and over thirty to
773 faster than JSON, even with pretty-printing and key sorting. It also 1378 seventy times faster than JSON's pure perl implementation. It also
774 compares favourably to Storable for small amounts of data. 1379 compares favourably to Storable for small amounts of data.
775 1380
776 Using a longer test string (roughly 18KB, generated from Yahoo! Locals 1381 Using a longer test string (roughly 18KB, generated from Yahoo! Locals
777 search API (http://nanoref.com/yahooapis/mgPdGg): 1382 search API (<http://dist.schmorp.de/misc/json/long.json>).
778 1383
779 module | encode | decode | 1384 module | encode | decode |
780 -----------|------------|------------| 1385 --------------|------------|------------|
781 JSON | 55.260 | 34.971 | 1386 JSON::DWIW/DS | 1647.927 | 2673.916 |
782 JSON::DWIW | 825.228 | 1082.513 | 1387 JSON::DWIW/FJ | 1630.249 | 2596.128 |
783 JSON::PC | 3571.444 | 2394.829 |
784 JSON::PP | 210.987 | 32.574 | 1388 JSON::PP | 400.640 | 62.311 |
785 JSON::Syck | 552.551 | 787.544 | 1389 JSON::Syck | 1481.040 | 1524.869 |
786 JSON::XS | 5780.463 | 4854.519 | 1390 JSON::XS | 20661.596 | 9541.183 |
787 JSON::XS/2 | 3869.998 | 4798.975 | 1391 JSON::XS/2 | 10683.403 | 9416.938 |
788 JSON::XS/3 | 5862.880 | 4798.975 | 1392 JSON::XS/3 | 20661.596 | 9400.054 |
789 Storable | 4445.002 | 5235.027 | 1393 Storable | 19765.806 | 10000.725 |
790 -----------+------------+------------+ 1394 --------------+------------+------------+
791 1395
792 Again, JSON::XS leads by far (except for Storable which non-surprisingly 1396 Again, JSON::XS leads by far (except for Storable which non-surprisingly
793 decodes faster). 1397 decodes a bit faster).
794 1398
795 On large strings containing lots of high unicode characters, some 1399 On large strings containing lots of high Unicode characters, some
796 modules (such as JSON::PC) seem to decode faster than JSON::XS, but the 1400 modules (such as JSON::PC) seem to decode faster than JSON::XS, but the
797 result will be broken due to missing (or wrong) unicode handling. Others 1401 result will be broken due to missing (or wrong) Unicode handling. Others
798 refuse to decode or encode properly, so it was impossible to prepare a 1402 refuse to decode or encode properly, so it was impossible to prepare a
799 fair comparison table for that case. 1403 fair comparison table for that case.
800 1404
801SECURITY CONSIDERATIONS 1405SECURITY CONSIDERATIONS
802 When you are using JSON in a protocol, talking to untrusted potentially 1406 When you are using JSON in a protocol, talking to untrusted potentially
… …
806 have any buffer overflows. Obviously, this module should ensure that and 1410 have any buffer overflows. Obviously, this module should ensure that and
807 I am trying hard on making that true, but you never know. 1411 I am trying hard on making that true, but you never know.
808 1412
809 Second, you need to avoid resource-starving attacks. That means you 1413 Second, you need to avoid resource-starving attacks. That means you
810 should limit the size of JSON texts you accept, or make sure then when 1414 should limit the size of JSON texts you accept, or make sure then when
811 your resources run out, thats just fine (e.g. by using a separate 1415 your resources run out, that's just fine (e.g. by using a separate
812 process that can crash safely). The size of a JSON text in octets or 1416 process that can crash safely). The size of a JSON text in octets or
813 characters is usually a good indication of the size of the resources 1417 characters is usually a good indication of the size of the resources
814 required to decode it into a Perl structure. While JSON::XS can check 1418 required to decode it into a Perl structure. While JSON::XS can check
815 the size of the JSON text, it might be too late when you already have it 1419 the size of the JSON text, it might be too late when you already have it
816 in memory, so you might want to check the size before you accept the 1420 in memory, so you might want to check the size before you accept the
… …
819 Third, JSON::XS recurses using the C stack when decoding objects and 1423 Third, JSON::XS recurses using the C stack when decoding objects and
820 arrays. The C stack is a limited resource: for instance, on my amd64 1424 arrays. The C stack is a limited resource: for instance, on my amd64
821 machine with 8MB of stack size I can decode around 180k nested arrays 1425 machine with 8MB of stack size I can decode around 180k nested arrays
822 but only 14k nested JSON objects (due to perl itself recursing deeply on 1426 but only 14k nested JSON objects (due to perl itself recursing deeply on
823 croak to free the temporary). If that is exceeded, the program crashes. 1427 croak to free the temporary). If that is exceeded, the program crashes.
824 to be conservative, the default nesting limit is set to 512. If your 1428 To be conservative, the default nesting limit is set to 512. If your
825 process has a smaller stack, you should adjust this setting accordingly 1429 process has a smaller stack, you should adjust this setting accordingly
826 with the "max_depth" method. 1430 with the "max_depth" method.
827 1431
828 And last but least, something else could bomb you that I forgot to think 1432 Something else could bomb you, too, that I forgot to think of. In that
829 of. In that case, you get to keep the pieces. I am always open for 1433 case, you get to keep the pieces. I am always open for hints, though...
830 hints, though...
831 1434
1435 Also keep in mind that JSON::XS might leak contents of your Perl data
1436 structures in its error messages, so when you serialise sensitive
1437 information you might want to make sure that exceptions thrown by
1438 JSON::XS will not end up in front of untrusted eyes.
1439
832 If you are using JSON::XS to return packets to consumption by javascript 1440 If you are using JSON::XS to return packets to consumption by JavaScript
833 scripts in a browser you should have a look at 1441 scripts in a browser you should have a look at
834 <http://jpsykes.com/47/practical-csrf-and-json-security> to see wether 1442 <http://blog.archive.jpsykes.com/47/practical-csrf-and-json-security/>
835 you are vulnerable to some common attack vectors (which really are 1443 to see whether you are vulnerable to some common attack vectors (which
836 browser design bugs, but it is still you who will have to deal with it, 1444 really are browser design bugs, but it is still you who will have to
837 as major browser developers care only for features, not about doing 1445 deal with it, as major browser developers care only for features, not
838 security right). 1446 about getting security right).
1447
1448"OLD" VS. "NEW" JSON (RFC 4627 VS. RFC 7159)
1449 TL;DR: Due to security concerns, JSON::XS will not allow scalar data in
1450 JSON texts by default - you need to create your own JSON::XS object and
1451 enable "allow_nonref":
1452
1453 my $json = JSON::XS->new->allow_nonref;
1454
1455 $text = $json->encode ($data);
1456 $data = $json->decode ($text);
1457
1458 The long version: JSON being an important and supposedly stable format,
1459 the IETF standardised it as RFC 4627 in 2006. Unfortunately, the
1460 inventor of JSON, Dougles Crockford, unilaterally changed the definition
1461 of JSON in javascript. Rather than create a fork, the IETF decided to
1462 standardise the new syntax (apparently, so Iw as told, without finding
1463 it very amusing).
1464
1465 The biggest difference between thed original JSON and the new JSON is
1466 that the new JSON supports scalars (anything other than arrays and
1467 objects) at the toplevel of a JSON text. While this is strictly
1468 backwards compatible to older versions, it breaks a number of protocols
1469 that relied on sending JSON back-to-back, and is a minor security
1470 concern.
1471
1472 For example, imagine you have two banks communicating, and on one side,
1473 trhe JSON coder gets upgraded. Two messages, such as 10 and 1000 might
1474 then be confused to mean 101000, something that couldn't happen in the
1475 original JSON, because niether of these messages would be valid JSON.
1476
1477 If one side accepts these messages, then an upgrade in the coder on
1478 either side could result in this becoming exploitable.
1479
1480 This module has always allowed these messages as an optional extension,
1481 by default disabled. The security concerns are the reason why the
1482 default is still disabled, but future versions might/will likely upgrade
1483 to the newer RFC as default format, so you are advised to check your
1484 implementation and/or override the default with "->allow_nonref (0)" to
1485 ensure that future versions are safe.
1486
1487INTEROPERABILITY WITH OTHER MODULES
1488 "JSON::XS" uses the Types::Serialiser module to provide boolean
1489 constants. That means that the JSON true and false values will be
1490 comaptible to true and false values of other modules that do the same,
1491 such as JSON::PP and CBOR::XS.
1492
1493INTEROPERABILITY WITH OTHER JSON DECODERS
1494 As long as you only serialise data that can be directly expressed in
1495 JSON, "JSON::XS" is incapable of generating invalid JSON output (modulo
1496 bugs, but "JSON::XS" has found more bugs in the official JSON testsuite
1497 (1) than the official JSON testsuite has found in "JSON::XS" (0)).
1498
1499 When you have trouble decoding JSON generated by this module using other
1500 decoders, then it is very likely that you have an encoding mismatch or
1501 the other decoder is broken.
1502
1503 When decoding, "JSON::XS" is strict by default and will likely catch all
1504 errors. There are currently two settings that change this: "relaxed"
1505 makes "JSON::XS" accept (but not generate) some non-standard extensions,
1506 and "allow_tags" will allow you to encode and decode Perl objects, at
1507 the cost of not outputting valid JSON anymore.
1508
1509 TAGGED VALUE SYNTAX AND STANDARD JSON EN/DECODERS
1510 When you use "allow_tags" to use the extended (and also nonstandard and
1511 invalid) JSON syntax for serialised objects, and you still want to
1512 decode the generated When you want to serialise objects, you can run a
1513 regex to replace the tagged syntax by standard JSON arrays (it only
1514 works for "normal" package names without comma, newlines or single
1515 colons). First, the readable Perl version:
1516
1517 # if your FREEZE methods return no values, you need this replace first:
1518 $json =~ s/\( \s* (" (?: [^\\":,]+|\\.|::)* ") \s* \) \s* \[\s*\]/[$1]/gx;
1519
1520 # this works for non-empty constructor arg lists:
1521 $json =~ s/\( \s* (" (?: [^\\":,]+|\\.|::)* ") \s* \) \s* \[/[$1,/gx;
1522
1523 And here is a less readable version that is easy to adapt to other
1524 languages:
1525
1526 $json =~ s/\(\s*("([^\\":,]+|\\.|::)*")\s*\)\s*\[/[$1,/g;
1527
1528 Here is an ECMAScript version (same regex):
1529
1530 json = json.replace (/\(\s*("([^\\":,]+|\\.|::)*")\s*\)\s*\[/g, "[$1,");
1531
1532 Since this syntax converts to standard JSON arrays, it might be hard to
1533 distinguish serialised objects from normal arrays. You can prepend a
1534 "magic number" as first array element to reduce chances of a collision:
1535
1536 $json =~ s/\(\s*("([^\\":,]+|\\.|::)*")\s*\)\s*\[/["XU1peReLzT4ggEllLanBYq4G9VzliwKF",$1,/g;
1537
1538 And after decoding the JSON text, you could walk the data structure
1539 looking for arrays with a first element of
1540 "XU1peReLzT4ggEllLanBYq4G9VzliwKF".
1541
1542 The same approach can be used to create the tagged format with another
1543 encoder. First, you create an array with the magic string as first
1544 member, the classname as second, and constructor arguments last, encode
1545 it as part of your JSON structure, and then:
1546
1547 $json =~ s/\[\s*"XU1peReLzT4ggEllLanBYq4G9VzliwKF"\s*,\s*("([^\\":,]+|\\.|::)*")\s*,/($1)[/g;
1548
1549 Again, this has some limitations - the magic string must not be encoded
1550 with character escapes, and the constructor arguments must be non-empty.
1551
1552RFC7159
1553 Since this module was written, Google has written a new JSON RFC, RFC
1554 7159 (and RFC7158). Unfortunately, this RFC breaks compatibility with
1555 both the original JSON specification on www.json.org and RFC4627.
1556
1557 As far as I can see, you can get partial compatibility when parsing by
1558 using "->allow_nonref". However, consider the security implications of
1559 doing so.
1560
1561 I haven't decided yet when to break compatibility with RFC4627 by
1562 default (and potentially leave applications insecure) and change the
1563 default to follow RFC7159, but application authors are well advised to
1564 call "->allow_nonref(0)" even if this is the current default, if they
1565 cannot handle non-reference values, in preparation for the day when the
1566 default will change.
1567
1568(I-)THREADS
1569 This module is *not* guaranteed to be ithread (or MULTIPLICITY-) safe
1570 and there are no plans to change this. Note that perl's builtin
1571 so-called theeads/ithreads are officially deprecated and should not be
1572 used.
1573
1574THE PERILS OF SETLOCALE
1575 Sometimes people avoid the Perl locale support and directly call the
1576 system's setlocale function with "LC_ALL".
1577
1578 This breaks both perl and modules such as JSON::XS, as stringification
1579 of numbers no longer works correctly (e.g. "$x = 0.1; print "$x"+1"
1580 might print 1, and JSON::XS might output illegal JSON as JSON::XS relies
1581 on perl to stringify numbers).
1582
1583 The solution is simple: don't call "setlocale", or use it for only those
1584 categories you need, such as "LC_MESSAGES" or "LC_CTYPE".
1585
1586 If you need "LC_NUMERIC", you should enable it only around the code that
1587 actually needs it (avoiding stringification of numbers), and restore it
1588 afterwards.
839 1589
840BUGS 1590BUGS
841 While the goal of this module is to be correct, that unfortunately does 1591 While the goal of this module is to be correct, that unfortunately does
842 not mean its bug-free, only that I think its design is bug-free. It is 1592 not mean it's bug-free, only that I think its design is bug-free. If you
843 still relatively early in its development. If you keep reporting bugs
844 they will be fixed swiftly, though. 1593 keep reporting bugs they will be fixed swiftly, though.
1594
1595 Please refrain from using rt.cpan.org or any other bug reporting
1596 service. I put the contact address into my modules for a reason.
1597
1598SEE ALSO
1599 The json_xs command line utility for quick experiments.
845 1600
846AUTHOR 1601AUTHOR
847 Marc Lehmann <schmorp@schmorp.de> 1602 Marc Lehmann <schmorp@schmorp.de>
848 http://home.schmorp.de/ 1603 http://home.schmorp.de/
849 1604

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