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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 overriden) with no overhead due to emulation (by inheritign
38 constructor and methods). If JSON::XS is not available, it will fall
39 back to the compatible JSON::PP module as backend, so using JSON instead
40 of JSON::XS gives you a portable JSON API that can be fast when you need
41 and doesn't require a C compiler when that is a problem.
23 42
24 As this is the n-th-something JSON module on CPAN, what was the reason 43 As this is the n-th-something JSON module on CPAN, what was the reason
25 to write yet another JSON module? While it seems there are many JSON 44 to write yet another JSON module? While it seems there are many JSON
26 modules, none of them correctly handle all corner cases, and in most 45 modules, none of them correctly handle all corner cases, and in most
27 cases their maintainers are unresponsive, gone missing, or not listening 46 cases their maintainers are unresponsive, gone missing, or not listening
… …
31 50
32 See MAPPING, below, on how JSON::XS maps perl values to JSON values and 51 See MAPPING, below, on how JSON::XS maps perl values to JSON values and
33 vice versa. 52 vice versa.
34 53
35 FEATURES 54 FEATURES
36 * correct unicode handling 55 * correct Unicode handling
56
37 This module knows how to handle Unicode, and even documents how and 57 This module knows how to handle Unicode, documents how and when it
38 when it does so. 58 does so, and even documents what "correct" means.
39 59
40 * round-trip integrity 60 * round-trip integrity
61
41 When you serialise a perl data structure using only datatypes 62 When you serialise a perl data structure using only datatypes
42 supported by JSON, the deserialised data structure is identical on 63 supported by JSON, the deserialised data structure is identical on
43 the Perl level. (e.g. the string "2.0" doesn't suddenly become "2" 64 the Perl level. (e.g. the string "2.0" doesn't suddenly become "2"
44 just because it looks like a number). 65 just because it looks like a number). There minor *are* exceptions
66 to this, read the MAPPING section below to learn about those.
45 67
46 * strict checking of JSON correctness 68 * strict checking of JSON correctness
69
47 There is no guessing, no generating of illegal JSON texts by 70 There is no guessing, no generating of illegal JSON texts by
48 default, and only JSON is accepted as input by default (the latter 71 default, and only JSON is accepted as input by default (the latter
49 is a security feature). 72 is a security feature).
50 73
51 * fast 74 * fast
52 Compared to other JSON modules, this module compares favourably in
53 terms of speed, too.
54 75
76 Compared to other JSON modules and other serialisers such as
77 Storable, this module usually compares favourably in terms of speed,
78 too.
79
55 * simple to use 80 * simple to use
81
56 This module has both a simple functional interface as well as an OO 82 This module has both a simple functional interface as well as an
57 interface. 83 objetc oriented interface interface.
58 84
59 * reasonably versatile output formats 85 * reasonably versatile output formats
86
60 You can choose between the most compact guarenteed single-line 87 You can choose between the most compact guaranteed-single-line
61 format possible (nice for simple line-based protocols), a pure-ascii 88 format possible (nice for simple line-based protocols), a pure-ascii
62 format (for when your transport is not 8-bit clean, still supports 89 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 90 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 91 want to read that stuff). Or you can combine those features in
65 whatever way you like. 92 whatever way you like.
66 93
67FUNCTIONAL INTERFACE 94FUNCTIONAL INTERFACE
68 The following convinience methods are provided by this module. They are 95 The following convenience methods are provided by this module. They are
69 exported by default: 96 exported by default:
70 97
71 $json_text = to_json $perl_scalar 98 $json_text = encode_json $perl_scalar
72 Converts the given Perl data structure (a simple scalar or a 99 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. 100 string (that is, the string contains octets only). Croaks on error.
75 101
76 This function call is functionally identical to: 102 This function call is functionally identical to:
77 103
78 $json_text = JSON::XS->new->utf8->encode ($perl_scalar) 104 $json_text = JSON::XS->new->utf8->encode ($perl_scalar)
79 105
80 except being faster. 106 except being faster.
81 107
82 $perl_scalar = from_json $json_text 108 $perl_scalar = decode_json $json_text
83 The opposite of "to_json": expects an UTF-8 (binary) string and 109 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 110 tries to parse that as an UTF-8 encoded JSON text, returning the
85 resulting simple scalar or reference. Croaks on error. 111 resulting reference. Croaks on error.
86 112
87 This function call is functionally identical to: 113 This function call is functionally identical to:
88 114
89 $perl_scalar = JSON::XS->new->utf8->decode ($json_text) 115 $perl_scalar = JSON::XS->new->utf8->decode ($json_text)
90 116
… …
97 values in Perl. 123 values in Perl.
98 124
99 See MAPPING, below, for more information on how JSON values are 125 See MAPPING, below, for more information on how JSON values are
100 mapped to Perl. 126 mapped to Perl.
101 127
128A FEW NOTES ON UNICODE AND PERL
129 Since this often leads to confusion, here are a few very clear words on
130 how Unicode works in Perl, modulo bugs.
131
132 1. Perl strings can store characters with ordinal values > 255.
133 This enables you to store Unicode characters as single characters in
134 a Perl string - very natural.
135
136 2. Perl does *not* associate an encoding with your strings.
137 ... until you force it to, e.g. when matching it against a regex, or
138 printing the scalar to a file, in which case Perl either interprets
139 your string as locale-encoded text, octets/binary, or as Unicode,
140 depending on various settings. In no case is an encoding stored
141 together with your data, it is *use* that decides encoding, not any
142 magical meta data.
143
144 3. The internal utf-8 flag has no meaning with regards to the encoding
145 of your string.
146 Just ignore that flag unless you debug a Perl bug, a module written
147 in XS or want to dive into the internals of perl. Otherwise it will
148 only confuse you, as, despite the name, it says nothing about how
149 your string is encoded. You can have Unicode strings with that flag
150 set, with that flag clear, and you can have binary data with that
151 flag set and that flag clear. Other possibilities exist, too.
152
153 If you didn't know about that flag, just the better, pretend it
154 doesn't exist.
155
156 4. A "Unicode String" is simply a string where each character can be
157 validly interpreted as a Unicode codepoint.
158 If you have UTF-8 encoded data, it is no longer a Unicode string,
159 but a Unicode string encoded in UTF-8, giving you a binary string.
160
161 5. A string containing "high" (> 255) character values is *not* a UTF-8
162 string.
163 It's a fact. Learn to live with it.
164
165 I hope this helps :)
166
102OBJECT-ORIENTED INTERFACE 167OBJECT-ORIENTED INTERFACE
103 The object oriented interface lets you configure your own encoding or 168 The object oriented interface lets you configure your own encoding or
104 decoding style, within the limits of supported formats. 169 decoding style, within the limits of supported formats.
105 170
106 $json = new JSON::XS 171 $json = new JSON::XS
… …
113 178
114 my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]}) 179 my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]})
115 => {"a": [1, 2]} 180 => {"a": [1, 2]}
116 181
117 $json = $json->ascii ([$enable]) 182 $json = $json->ascii ([$enable])
183 $enabled = $json->get_ascii
118 If $enable is true (or missing), then the "encode" method will not 184 If $enable is true (or missing), then the "encode" method will not
119 generate characters outside the code range 0..127 (which is ASCII). 185 generate characters outside the code range 0..127 (which is ASCII).
120 Any unicode characters outside that range will be escaped using 186 Any Unicode characters outside that range will be escaped using
121 either a single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL 187 either a single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL
122 escape sequence, as per RFC4627. The resulting encoded JSON text can 188 escape sequence, as per RFC4627. The resulting encoded JSON text can
123 be treated as a native unicode string, an ascii-encoded, 189 be treated as a native Unicode string, an ascii-encoded,
124 latin1-encoded or UTF-8 encoded string, or any other superset of 190 latin1-encoded or UTF-8 encoded string, or any other superset of
125 ASCII. 191 ASCII.
126 192
127 If $enable is false, then the "encode" method will not escape 193 If $enable is false, then the "encode" method will not escape
128 Unicode characters unless required by the JSON syntax or other 194 Unicode characters unless required by the JSON syntax or other
129 flags. This results in a faster and more compact format. 195 flags. This results in a faster and more compact format.
130 196
197 See also the section *ENCODING/CODESET FLAG NOTES* later in this
198 document.
199
131 The main use for this flag is to produce JSON texts that can be 200 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 201 transmitted over a 7-bit channel, as the encoded JSON texts will not
133 contain any 8 bit characters. 202 contain any 8 bit characters.
134 203
135 JSON::XS->new->ascii (1)->encode ([chr 0x10401]) 204 JSON::XS->new->ascii (1)->encode ([chr 0x10401])
136 => ["\ud801\udc01"] 205 => ["\ud801\udc01"]
137 206
138 $json = $json->latin1 ([$enable]) 207 $json = $json->latin1 ([$enable])
208 $enabled = $json->get_latin1
139 If $enable is true (or missing), then the "encode" method will 209 If $enable is true (or missing), then the "encode" method will
140 encode the resulting JSON text as latin1 (or iso-8859-1), escaping 210 encode the resulting JSON text as latin1 (or iso-8859-1), escaping
141 any characters outside the code range 0..255. The resulting string 211 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 212 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 213 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 214 flag, as "decode" by default expects Unicode, which is a strict
145 superset of latin1. 215 superset of latin1.
146 216
147 If $enable is false, then the "encode" method will not escape 217 If $enable is false, then the "encode" method will not escape
148 Unicode characters unless required by the JSON syntax or other 218 Unicode characters unless required by the JSON syntax or other
149 flags. 219 flags.
220
221 See also the section *ENCODING/CODESET FLAG NOTES* later in this
222 document.
150 223
151 The main use for this flag is efficiently encoding binary data as 224 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 225 JSON text, as most octets will not be escaped, resulting in a
153 smaller encoded size. The disadvantage is that the resulting JSON 226 smaller encoded size. The disadvantage is that the resulting JSON
154 text is encoded in latin1 (and must correctly be treated as such 227 text is encoded in latin1 (and must correctly be treated as such
155 when storing and transfering), a rare encoding for JSON. It is 228 when storing and transferring), a rare encoding for JSON. It is
156 therefore most useful when you want to store data structures known 229 therefore most useful when you want to store data structures known
157 to contain binary data efficiently in files or databases, not when 230 to contain binary data efficiently in files or databases, not when
158 talking to other JSON encoders/decoders. 231 talking to other JSON encoders/decoders.
159 232
160 JSON::XS->new->latin1->encode (["\x{89}\x{abc}"] 233 JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]
161 => ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not) 234 => ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)
162 235
163 $json = $json->utf8 ([$enable]) 236 $json = $json->utf8 ([$enable])
237 $enabled = $json->get_utf8
164 If $enable is true (or missing), then the "encode" method will 238 If $enable is true (or missing), then the "encode" method will
165 encode the JSON result into UTF-8, as required by many protocols, 239 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 240 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 241 string. Please note that UTF-8-encoded strings do not contain any
168 characters outside the range 0..255, they are thus useful for 242 characters outside the range 0..255, they are thus useful for
169 bytewise/binary I/O. In future versions, enabling this option might 243 bytewise/binary I/O. In future versions, enabling this option might
170 enable autodetection of the UTF-16 and UTF-32 encoding families, as 244 enable autodetection of the UTF-16 and UTF-32 encoding families, as
171 described in RFC4627. 245 described in RFC4627.
172 246
173 If $enable is false, then the "encode" method will return the JSON 247 If $enable is false, then the "encode" method will return the JSON
174 string as a (non-encoded) unicode string, while "decode" expects 248 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 249 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. 250 UTF-16) needs to be done yourself, e.g. using the Encode module.
251
252 See also the section *ENCODING/CODESET FLAG NOTES* later in this
253 document.
177 254
178 Example, output UTF-16BE-encoded JSON: 255 Example, output UTF-16BE-encoded JSON:
179 256
180 use Encode; 257 use Encode;
181 $jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object); 258 $jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
… …
200 2 277 2
201 ] 278 ]
202 } 279 }
203 280
204 $json = $json->indent ([$enable]) 281 $json = $json->indent ([$enable])
282 $enabled = $json->get_indent
205 If $enable is true (or missing), then the "encode" method will use a 283 If $enable is true (or missing), then the "encode" method will use a
206 multiline format as output, putting every array member or 284 multiline format as output, putting every array member or
207 object/hash key-value pair into its own line, identing them 285 object/hash key-value pair into its own line, indenting them
208 properly. 286 properly.
209 287
210 If $enable is false, no newlines or indenting will be produced, and 288 If $enable is false, no newlines or indenting will be produced, and
211 the resulting JSON text is guarenteed not to contain any "newlines". 289 the resulting JSON text is guaranteed not to contain any "newlines".
212 290
213 This setting has no effect when decoding JSON texts. 291 This setting has no effect when decoding JSON texts.
214 292
215 $json = $json->space_before ([$enable]) 293 $json = $json->space_before ([$enable])
294 $enabled = $json->get_space_before
216 If $enable is true (or missing), then the "encode" method will add 295 If $enable is true (or missing), then the "encode" method will add
217 an extra optional space before the ":" separating keys from values 296 an extra optional space before the ":" separating keys from values
218 in JSON objects. 297 in JSON objects.
219 298
220 If $enable is false, then the "encode" method will not add any extra 299 If $enable is false, then the "encode" method will not add any extra
… …
226 Example, space_before enabled, space_after and indent disabled: 305 Example, space_before enabled, space_after and indent disabled:
227 306
228 {"key" :"value"} 307 {"key" :"value"}
229 308
230 $json = $json->space_after ([$enable]) 309 $json = $json->space_after ([$enable])
310 $enabled = $json->get_space_after
231 If $enable is true (or missing), then the "encode" method will add 311 If $enable is true (or missing), then the "encode" method will add
232 an extra optional space after the ":" separating keys from values in 312 an extra optional space after the ":" separating keys from values in
233 JSON objects and extra whitespace after the "," separating key-value 313 JSON objects and extra whitespace after the "," separating key-value
234 pairs and array members. 314 pairs and array members.
235 315
… …
241 Example, space_before and indent disabled, space_after enabled: 321 Example, space_before and indent disabled, space_after enabled:
242 322
243 {"key": "value"} 323 {"key": "value"}
244 324
245 $json = $json->relaxed ([$enable]) 325 $json = $json->relaxed ([$enable])
326 $enabled = $json->get_relaxed
246 If $enable is true (or missing), then "decode" will accept some 327 If $enable is true (or missing), then "decode" will accept some
247 extensions to normal JSON syntax (see below). "encode" will not be 328 extensions to normal JSON syntax (see below). "encode" will not be
248 affected in anyway. *Be aware that this option makes you accept 329 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 330 invalid JSON texts as if they were valid!*. I suggest only to use
250 this option to parse application-specific files written by humans 331 this option to parse application-specific files written by humans
… …
253 If $enable is false (the default), then "decode" will only accept 334 If $enable is false (the default), then "decode" will only accept
254 valid JSON texts. 335 valid JSON texts.
255 336
256 Currently accepted extensions are: 337 Currently accepted extensions are:
257 338
258 * list items can have an end-comma 339 * list items can have an end-comma
340
259 JSON *separates* array elements and key-value pairs with commas. 341 JSON *separates* array elements and key-value pairs with commas.
260 This can be annoying if you write JSON texts manually and want 342 This can be annoying if you write JSON texts manually and want
261 to be able to quickly append elements, so this extension accepts 343 to be able to quickly append elements, so this extension accepts
262 comma at the end of such items not just between them: 344 comma at the end of such items not just between them:
263 345
… …
268 { 350 {
269 "k1": "v1", 351 "k1": "v1",
270 "k2": "v2", <- this comma not normally allowed 352 "k2": "v2", <- this comma not normally allowed
271 } 353 }
272 354
355 * shell-style '#'-comments
356
357 Whenever JSON allows whitespace, shell-style comments are
358 additionally allowed. They are terminated by the first
359 carriage-return or line-feed character, after which more
360 white-space and comments are allowed.
361
362 [
363 1, # this comment not allowed in JSON
364 # neither this one...
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).
281 376
282 This option is useful if you want the same data structure to be 377 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 378 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 379 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 380 contains the same data, as key-value pairs have no inherent ordering
286 in Perl. 381 in Perl.
287 382
288 This setting has no effect when decoding JSON texts. 383 This setting has no effect when decoding JSON texts.
289 384
290 $json = $json->allow_nonref ([$enable]) 385 $json = $json->allow_nonref ([$enable])
386 $enabled = $json->get_allow_nonref
291 If $enable is true (or missing), then the "encode" method can 387 If $enable is true (or missing), then the "encode" method can
292 convert a non-reference into its corresponding string, number or 388 convert a non-reference into its corresponding string, number or
293 null JSON value, which is an extension to RFC4627. Likewise, 389 null JSON value, which is an extension to RFC4627. Likewise,
294 "decode" will accept those JSON values instead of croaking. 390 "decode" will accept those JSON values instead of croaking.
295 391
… …
303 399
304 JSON::XS->new->allow_nonref->encode ("Hello, World!") 400 JSON::XS->new->allow_nonref->encode ("Hello, World!")
305 => "Hello, World!" 401 => "Hello, World!"
306 402
307 $json = $json->allow_blessed ([$enable]) 403 $json = $json->allow_blessed ([$enable])
404 $enabled = $json->get_allow_blessed
308 If $enable is true (or missing), then the "encode" method will not 405 If $enable is true (or missing), then the "encode" method will not
309 barf when it encounters a blessed reference. Instead, the value of 406 barf when it encounters a blessed reference. Instead, the value of
310 the convert_blessed option will decide wether "null" 407 the convert_blessed option will decide whether "null"
311 ("convert_blessed" disabled or no "to_json" method found) or a 408 ("convert_blessed" disabled or no "TO_JSON" method found) or a
312 representation of the object ("convert_blessed" enabled and 409 representation of the object ("convert_blessed" enabled and
313 "to_json" method found) is being encoded. Has no effect on "decode". 410 "TO_JSON" method found) is being encoded. Has no effect on "decode".
314 411
315 If $enable is false (the default), then "encode" will throw an 412 If $enable is false (the default), then "encode" will throw an
316 exception when it encounters a blessed object. 413 exception when it encounters a blessed object.
317 414
318 $json = $json->convert_blessed ([$enable]) 415 $json = $json->convert_blessed ([$enable])
416 $enabled = $json->get_convert_blessed
319 If $enable is true (or missing), then "encode", upon encountering a 417 If $enable is true (or missing), then "encode", upon encountering a
320 blessed object, will check for the availability of the "TO_JSON" 418 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 419 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 420 context and the resulting scalar will be encoded instead of the
323 object. If no "TO_JSON" method is found, the value of 421 object. If no "TO_JSON" method is found, the value of
… …
327 returns other blessed objects, those will be handled in the same 425 returns other blessed objects, those will be handled in the same
328 way. "TO_JSON" must take care of not causing an endless recursion 426 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 427 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 428 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 429 the object) are usually in upper case letters and to avoid
332 collisions with the "to_json" function. 430 collisions with any "to_json" function or method.
333 431
334 This setting does not yet influence "decode" in any way, but in the 432 This setting does not yet influence "decode" in any way, but in the
335 future, global hooks might get installed that influence "decode" and 433 future, global hooks might get installed that influence "decode" and
336 are enabled by this setting. 434 are enabled by this setting.
337 435
… …
378 476
379 As this callback gets called less often then the 477 As this callback gets called less often then the
380 "filter_json_object" one, decoding speed will not usually suffer as 478 "filter_json_object" one, decoding speed will not usually suffer as
381 much. Therefore, single-key objects make excellent targets to 479 much. Therefore, single-key objects make excellent targets to
382 serialise Perl objects into, especially as single-key JSON objects 480 serialise Perl objects into, especially as single-key JSON objects
383 are as close to the type-tagged value concept as JSON gets (its 481 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 482 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 483 in any way, so you need to make sure your data never looks like a
386 serialised Perl hash. 484 serialised Perl hash.
387 485
388 Typical names for the single object key are "__class_whatever__", or 486 Typical names for the single object key are "__class_whatever__", or
… …
413 511
414 { __widget__ => $self->{id} } 512 { __widget__ => $self->{id} }
415 } 513 }
416 514
417 $json = $json->shrink ([$enable]) 515 $json = $json->shrink ([$enable])
516 $enabled = $json->get_shrink
418 Perl usually over-allocates memory a bit when allocating space for 517 Perl usually over-allocates memory a bit when allocating space for
419 strings. This flag optionally resizes strings generated by either 518 strings. This flag optionally resizes strings generated by either
420 "encode" or "decode" to their minimum size possible. This can save 519 "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 520 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 521 many short strings. It will also try to downgrade any strings to
… …
440 converting strings that look like integers or floats into integers 539 converting strings that look like integers or floats into integers
441 or floats internally (there is no difference on the Perl level), 540 or floats internally (there is no difference on the Perl level),
442 saving space. 541 saving space.
443 542
444 $json = $json->max_depth ([$maximum_nesting_depth]) 543 $json = $json->max_depth ([$maximum_nesting_depth])
544 $max_depth = $json->get_max_depth
445 Sets the maximum nesting level (default 512) accepted while encoding 545 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 546 or decoding. If the JSON text or Perl data structure has an equal or
447 higher nesting level then this limit, then the encoder and decoder 547 higher nesting level then this limit, then the encoder and decoder
448 will stop and croak at that point. 548 will stop and croak at that point.
449 549
… …
461 561
462 See SECURITY CONSIDERATIONS, below, for more info on why this is 562 See SECURITY CONSIDERATIONS, below, for more info on why this is
463 useful. 563 useful.
464 564
465 $json = $json->max_size ([$maximum_string_size]) 565 $json = $json->max_size ([$maximum_string_size])
566 $max_size = $json->get_max_size
466 Set the maximum length a JSON text may have (in bytes) where 567 Set the maximum length a JSON text may have (in bytes) where
467 decoding is being attempted. The default is 0, meaning no limit. 568 decoding is being attempted. The default is 0, meaning no limit.
468 When "decode" is called on a string longer then this number of 569 When "decode" is called on a string longer then this number of
469 characters it will not attempt to decode the string but throw an 570 characters it will not attempt to decode the string but throw an
470 exception. This setting has no effect on "encode" (yet). 571 exception. This setting has no effect on "encode" (yet).
… …
512 vice versa. These mappings are designed to "do the right thing" in most 613 vice versa. These mappings are designed to "do the right thing" in most
513 circumstances automatically, preserving round-tripping characteristics 614 circumstances automatically, preserving round-tripping characteristics
514 (what you put in comes out as something equivalent). 615 (what you put in comes out as something equivalent).
515 616
516 For the more enlightened: note that in the following descriptions, 617 For the more enlightened: note that in the following descriptions,
517 lowercase *perl* refers to the Perl interpreter, while uppcercase *Perl* 618 lowercase *perl* refers to the Perl interpreter, while uppercase *Perl*
518 refers to the abstract Perl language itself. 619 refers to the abstract Perl language itself.
519 620
520 JSON -> PERL 621 JSON -> PERL
521 object 622 object
522 A JSON object becomes a reference to a hash in Perl. No ordering of 623 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 624 object keys is preserved (JSON does not preserve object key ordering
524 ordering itself). 625 itself).
525 626
526 array 627 array
527 A JSON array becomes a reference to an array in Perl. 628 A JSON array becomes a reference to an array in Perl.
528 629
529 string 630 string
… …
535 A JSON number becomes either an integer, numeric (floating point) or 636 A JSON number becomes either an integer, numeric (floating point) or
536 string scalar in perl, depending on its range and any fractional 637 string scalar in perl, depending on its range and any fractional
537 parts. On the Perl level, there is no difference between those as 638 parts. On the Perl level, there is no difference between those as
538 Perl handles all the conversion details, but an integer may take 639 Perl handles all the conversion details, but an integer may take
539 slightly less memory and might represent more values exactly than 640 slightly less memory and might represent more values exactly than
540 (floating point) numbers. 641 floating point numbers.
541 642
542 If the number consists of digits only, JSON::XS will try to 643 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 644 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 645 represent it as a numeric (floating point) value if that is possible
545 without loss of precision. Otherwise it will preserve the number as 646 without loss of precision. Otherwise it will preserve the number as
546 a string value. 647 a string value (in which case you lose roundtripping ability, as the
648 JSON number will be re-encoded toa JSON string).
547 649
548 Numbers containing a fractional or exponential part will always be 650 Numbers containing a fractional or exponential part will always be
549 represented as numeric (floating point) values, possibly at a loss 651 represented as numeric (floating point) values, possibly at a loss
550 of precision. 652 of precision (in which case you might lose perfect roundtripping
551 653 ability, but the JSON number will still be re-encoded as a JSON
552 This might create round-tripping problems as numbers might become 654 number).
553 strings, but as Perl is typeless there is no other way to do it.
554 655
555 true, false 656 true, false
556 These JSON atoms become "JSON::XS::true" and "JSON::XS::false", 657 These JSON atoms become "JSON::XS::true" and "JSON::XS::false",
557 respectively. They are overloaded to act almost exactly like the 658 respectively. They are overloaded to act almost exactly like the
558 numbers 1 and 0. You can check wether a scalar is a JSON boolean by 659 numbers 1 and 0. You can check whether a scalar is a JSON boolean by
559 using the "JSON::XS::is_bool" function. 660 using the "JSON::XS::is_bool" function.
560 661
561 null 662 null
562 A JSON null atom becomes "undef" in Perl. 663 A JSON null atom becomes "undef" in Perl.
563 664
… …
586 an exception to be thrown, except for references to the integers 0 687 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 688 and 1, which get turned into "false" and "true" atoms in JSON. You
588 can also use "JSON::XS::false" and "JSON::XS::true" to improve 689 can also use "JSON::XS::false" and "JSON::XS::true" to improve
589 readability. 690 readability.
590 691
591 to_json [\0,JSON::XS::true] # yields [false,true] 692 encode_json [\0,JSON::XS::true] # yields [false,true]
592 693
593 JSON::XS::true, JSON::XS::false 694 JSON::XS::true, JSON::XS::false
594 These special values become JSON true and JSON false values, 695 These special values become JSON true and JSON false values,
595 respectively. You cna alos use "\1" and "\0" directly if you want. 696 respectively. You can also use "\1" and "\0" directly if you want.
596 697
597 blessed objects 698 blessed objects
598 Blessed objects are not allowed. JSON::XS currently tries to encode 699 Blessed objects are not directly representable in JSON. See the
599 their underlying representation (hash- or arrayref), but this 700 "allow_blessed" and "convert_blessed" methods on various options on
600 behaviour might change in future versions. 701 how to deal with this: basically, you can choose between throwing an
702 exception, encoding the reference as if it weren't blessed, or
703 provide your own serialiser method.
601 704
602 simple scalars 705 simple scalars
603 Simple Perl scalars (any scalar that is not a reference) are the 706 Simple Perl scalars (any scalar that is not a reference) are the
604 most difficult objects to encode: JSON::XS will encode undefined 707 most difficult objects to encode: JSON::XS will encode undefined
605 scalars as JSON null value, scalars that have last been used in a 708 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 709 string context before encoding as JSON strings, and anything else as
607 number value: 710 number value:
608 711
609 # dump as number 712 # dump as number
610 to_json [2] # yields [2] 713 encode_json [2] # yields [2]
611 to_json [-3.0e17] # yields [-3e+17] 714 encode_json [-3.0e17] # yields [-3e+17]
612 my $value = 5; to_json [$value] # yields [5] 715 my $value = 5; encode_json [$value] # yields [5]
613 716
614 # used as string, so dump as string 717 # used as string, so dump as string
615 print $value; 718 print $value;
616 to_json [$value] # yields ["5"] 719 encode_json [$value] # yields ["5"]
617 720
618 # undef becomes null 721 # undef becomes null
619 to_json [undef] # yields [null] 722 encode_json [undef] # yields [null]
620 723
621 You can force the type to be a string by stringifying it: 724 You can force the type to be a JSON string by stringifying it:
622 725
623 my $x = 3.1; # some variable containing a number 726 my $x = 3.1; # some variable containing a number
624 "$x"; # stringified 727 "$x"; # stringified
625 $x .= ""; # another, more awkward way to stringify 728 $x .= ""; # another, more awkward way to stringify
626 print $x; # perl does it for you, too, quite often 729 print $x; # perl does it for you, too, quite often
627 730
628 You can force the type to be a number by numifying it: 731 You can force the type to be a JSON number by numifying it:
629 732
630 my $x = "3"; # some variable containing a string 733 my $x = "3"; # some variable containing a string
631 $x += 0; # numify it, ensuring it will be dumped as a number 734 $x += 0; # numify it, ensuring it will be dumped as a number
632 $x *= 1; # same thing, the choise is yours. 735 $x *= 1; # same thing, the choice is yours.
633 736
634 You can not currently output JSON booleans or force the type in 737 You can not currently force the type in other, less obscure, ways.
635 other, less obscure, ways. Tell me if you need this capability. 738 Tell me if you need this capability (but don't forget to explain why
739 its needed :).
740
741ENCODING/CODESET FLAG NOTES
742 The interested reader might have seen a number of flags that signify
743 encodings or codesets - "utf8", "latin1" and "ascii". There seems to be
744 some confusion on what these do, so here is a short comparison:
745
746 "utf8" controls wether the JSON text created by "encode" (and expected
747 by "decode") is UTF-8 encoded or not, while "latin1" and "ascii" only
748 control wether "encode" escapes character values outside their
749 respective codeset range. Neither of these flags conflict with each
750 other, although some combinations make less sense than others.
751
752 Care has been taken to make all flags symmetrical with respect to
753 "encode" and "decode", that is, texts encoded with any combination of
754 these flag values will be correctly decoded when the same flags are used
755 - in general, if you use different flag settings while encoding vs. when
756 decoding you likely have a bug somewhere.
757
758 Below comes a verbose discussion of these flags. Note that a "codeset"
759 is simply an abstract set of character-codepoint pairs, while an
760 encoding takes those codepoint numbers and *encodes* them, in our case
761 into octets. Unicode is (among other things) a codeset, UTF-8 is an
762 encoding, and ISO-8859-1 (= latin 1) and ASCII are both codesets *and*
763 encodings at the same time, which can be confusing.
764
765 "utf8" flag disabled
766 When "utf8" is disabled (the default), then "encode"/"decode"
767 generate and expect Unicode strings, that is, characters with high
768 ordinal Unicode values (> 255) will be encoded as such characters,
769 and likewise such characters are decoded as-is, no canges to them
770 will be done, except "(re-)interpreting" them as Unicode codepoints
771 or Unicode characters, respectively (to Perl, these are the same
772 thing in strings unless you do funny/weird/dumb stuff).
773
774 This is useful when you want to do the encoding yourself (e.g. when
775 you want to have UTF-16 encoded JSON texts) or when some other layer
776 does the encoding for you (for example, when printing to a terminal
777 using a filehandle that transparently encodes to UTF-8 you certainly
778 do NOT want to UTF-8 encode your data first and have Perl encode it
779 another time).
780
781 "utf8" flag enabled
782 If the "utf8"-flag is enabled, "encode"/"decode" will encode all
783 characters using the corresponding UTF-8 multi-byte sequence, and
784 will expect your input strings to be encoded as UTF-8, that is, no
785 "character" of the input string must have any value > 255, as UTF-8
786 does not allow that.
787
788 The "utf8" flag therefore switches between two modes: disabled means
789 you will get a Unicode string in Perl, enabled means you get an
790 UTF-8 encoded octet/binary string in Perl.
791
792 "latin1" or "ascii" flags enabled
793 With "latin1" (or "ascii") enabled, "encode" will escape characters
794 with ordinal values > 255 (> 127 with "ascii") and encode the
795 remaining characters as specified by the "utf8" flag.
796
797 If "utf8" is disabled, then the result is also correctly encoded in
798 those character sets (as both are proper subsets of Unicode, meaning
799 that a Unicode string with all character values < 256 is the same
800 thing as a ISO-8859-1 string, and a Unicode string with all
801 character values < 128 is the same thing as an ASCII string in
802 Perl).
803
804 If "utf8" is enabled, you still get a correct UTF-8-encoded string,
805 regardless of these flags, just some more characters will be escaped
806 using "\uXXXX" then before.
807
808 Note that ISO-8859-1-*encoded* strings are not compatible with UTF-8
809 encoding, while ASCII-encoded strings are. That is because the
810 ISO-8859-1 encoding is NOT a subset of UTF-8 (despite the ISO-8859-1
811 *codeset* being a subset of Unicode), while ASCII is.
812
813 Surprisingly, "decode" will ignore these flags and so treat all
814 input values as governed by the "utf8" flag. If it is disabled, this
815 allows you to decode ISO-8859-1- and ASCII-encoded strings, as both
816 strict subsets of Unicode. If it is enabled, you can correctly
817 decode UTF-8 encoded strings.
818
819 So neither "latin1" nor "ascii" are incompatible with the "utf8"
820 flag - they only govern when the JSON output engine escapes a
821 character or not.
822
823 The main use for "latin1" is to relatively efficiently store binary
824 data as JSON, at the expense of breaking compatibility with most
825 JSON decoders.
826
827 The main use for "ascii" is to force the output to not contain
828 characters with values > 127, which means you can interpret the
829 resulting string as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about
830 any character set and 8-bit-encoding, and still get the same data
831 structure back. This is useful when your channel for JSON transfer
832 is not 8-bit clean or the encoding might be mangled in between (e.g.
833 in mail), and works because ASCII is a proper subset of most 8-bit
834 and multibyte encodings in use in the world.
636 835
637COMPARISON 836COMPARISON
638 As already mentioned, this module was created because none of the 837 As already mentioned, this module was created because none of the
639 existing JSON modules could be made to work correctly. First I will 838 existing JSON modules could be made to work correctly. First I will
640 describe the problems (or pleasures) I encountered with various existing 839 describe the problems (or pleasures) I encountered with various existing
641 JSON modules, followed by some benchmark values. JSON::XS was designed 840 JSON modules, followed by some benchmark values. JSON::XS was designed
642 not to suffer from any of these problems or limitations. 841 not to suffer from any of these problems or limitations.
643 842
843 JSON 2.xx
844 A marvellous piece of engineering, this module either uses JSON::XS
845 directly when available (so will be 100% compatible with it,
846 including speed), or it uses JSON::PP, which is basically JSON::XS
847 translated to Pure Perl, which should be 100% compatible with
848 JSON::XS, just a bit slower.
849
850 You cannot really lose by using this module, especially as it tries
851 very hard to work even with ancient Perl versions, while JSON::XS
852 does not.
853
644 JSON 1.07 854 JSON 1.07
645 Slow (but very portable, as it is written in pure Perl). 855 Slow (but very portable, as it is written in pure Perl).
646 856
647 Undocumented/buggy Unicode handling (how JSON handles unicode values 857 Undocumented/buggy Unicode handling (how JSON handles Unicode values
648 is undocumented. One can get far by feeding it unicode strings and 858 is undocumented. One can get far by feeding it Unicode strings and
649 doing en-/decoding oneself, but unicode escapes are not working 859 doing en-/decoding oneself, but Unicode escapes are not working
650 properly). 860 properly).
651 861
652 No roundtripping (strings get clobbered if they look like numbers, 862 No round-tripping (strings get clobbered if they look like numbers,
653 e.g. the string 2.0 will encode to 2.0 instead of "2.0", and that 863 e.g. the string 2.0 will encode to 2.0 instead of "2.0", and that
654 will decode into the number 2. 864 will decode into the number 2.
655 865
656 JSON::PC 0.01 866 JSON::PC 0.01
657 Very fast. 867 Very fast.
658 868
659 Undocumented/buggy Unicode handling. 869 Undocumented/buggy Unicode handling.
660 870
661 No roundtripping. 871 No round-tripping.
662 872
663 Has problems handling many Perl values (e.g. regex results and other 873 Has problems handling many Perl values (e.g. regex results and other
664 magic values will make it croak). 874 magic values will make it croak).
665 875
666 Does not even generate valid JSON ("{1,2}" gets converted to "{1:2}" 876 Does not even generate valid JSON ("{1,2}" gets converted to "{1:2}"
… …
676 much undocumented. I need at least a format for easy reading by 886 much undocumented. I need at least a format for easy reading by
677 humans and a single-line compact format for use in a protocol, and 887 humans and a single-line compact format for use in a protocol, and
678 preferably a way to generate ASCII-only JSON texts). 888 preferably a way to generate ASCII-only JSON texts).
679 889
680 Completely broken (and confusingly documented) Unicode handling 890 Completely broken (and confusingly documented) Unicode handling
681 (unicode escapes are not working properly, you need to set 891 (Unicode escapes are not working properly, you need to set
682 ImplicitUnicode to *different* values on en- and decoding to get 892 ImplicitUnicode to *different* values on en- and decoding to get
683 symmetric behaviour). 893 symmetric behaviour).
684 894
685 No roundtripping (simple cases work, but this depends on wether the 895 No round-tripping (simple cases work, but this depends on whether
686 scalar value was used in a numeric context or not). 896 the scalar value was used in a numeric context or not).
687 897
688 Dumping hashes may skip hash values depending on iterator state. 898 Dumping hashes may skip hash values depending on iterator state.
689 899
690 Unmaintained (maintainer unresponsive for many months, bugs are not 900 Unmaintained (maintainer unresponsive for many months, bugs are not
691 getting fixed). 901 getting fixed).
692 902
693 Does not check input for validity (i.e. will accept non-JSON input 903 Does not check input for validity (i.e. will accept non-JSON input
694 and return "something" instead of raising an exception. This is a 904 and return "something" instead of raising an exception. This is a
695 security issue: imagine two banks transfering money between each 905 security issue: imagine two banks transferring money between each
696 other using JSON. One bank might parse a given non-JSON request and 906 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 907 deduct money, while the other might reject the transaction with a
698 syntax error. While a good protocol will at least recover, that is 908 syntax error. While a good protocol will at least recover, that is
699 extra unnecessary work and the transaction will still not succeed). 909 extra unnecessary work and the transaction will still not succeed).
700 910
701 JSON::DWIW 0.04 911 JSON::DWIW 0.04
702 Very fast. Very natural. Very nice. 912 Very fast. Very natural. Very nice.
703 913
704 Undocumented unicode handling (but the best of the pack. Unicode 914 Undocumented Unicode handling (but the best of the pack. Unicode
705 escapes still don't get parsed properly). 915 escapes still don't get parsed properly).
706 916
707 Very inflexible. 917 Very inflexible.
708 918
709 No roundtripping. 919 No round-tripping.
710 920
711 Does not generate valid JSON texts (key strings are often unquoted, 921 Does not generate valid JSON texts (key strings are often unquoted,
712 empty keys result in nothing being output) 922 empty keys result in nothing being output)
713 923
714 Does not check input for validity. 924 Does not check input for validity.
715 925
716 JSON and YAML 926 JSON and YAML
717 You often hear that JSON is a subset (or a close subset) of YAML. This 927 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, 928 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 929 writing), so let me state it clearly: *in general, there is no way to
720 valid YAML. 930 configure JSON::XS to output a data structure as valid YAML* that works
931 in all cases.
721 932
722 If you really must use JSON::XS to generate YAML, you should use this 933 If you really must use JSON::XS to generate YAML, you should use this
723 algorithm (subject to change in future versions): 934 algorithm (subject to change in future versions):
724 935
725 my $to_yaml = JSON::XS->new->utf8->space_after (1); 936 my $to_yaml = JSON::XS->new->utf8->space_after (1);
726 my $yaml = $to_yaml->encode ($ref) . "\n"; 937 my $yaml = $to_yaml->encode ($ref) . "\n";
727 938
728 This will usually generate JSON texts that also parse as valid YAML. 939 This will *usually* generate JSON texts that also parse as valid YAML.
729 Please note that YAML has hardcoded limits on (simple) object key 940 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 941 lengths that JSON doesn't have and also has different and incompatible
942 unicode handling, so you should make sure that your hash keys are
731 keys are noticably shorter than the 1024 characters YAML allows. 943 noticeably shorter than the 1024 "stream characters" YAML allows and
944 that you do not have characters with codepoint values outside the
945 Unicode BMP (basic multilingual page). YAML also does not allow "\/"
946 sequences in strings (which JSON::XS does not *currently* generate, but
947 other JSON generators might).
732 948
733 There might be other incompatibilities that I am not aware of. In 949 There might be other incompatibilities that I am not aware of (or the
950 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 951 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: 952 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 953 chances are high that you will run into severe interoperability problems
737 problems. 954 when you least expect it.
955
956 (*) I have been pressured multiple times by Brian Ingerson (one of the
957 authors of the YAML specification) to remove this paragraph, despite
958 him acknowledging that the actual incompatibilities exist. As I was
959 personally bitten by this "JSON is YAML" lie, I refused and said I
960 will continue to educate people about these issues, so others do not
961 run into the same problem again and again. After this, Brian called
962 me a (quote)*complete and worthless idiot*(unquote).
963
964 In my opinion, instead of pressuring and insulting people who
965 actually clarify issues with YAML and the wrong statements of some
966 of its proponents, I would kindly suggest reading the JSON spec
967 (which is not that difficult or long) and finally make YAML
968 compatible to it, and educating users about the changes, instead of
969 spreading lies about the real compatibility for many *years* and
970 trying to silence people who point out that it isn't true.
738 971
739 SPEED 972 SPEED
740 It seems that JSON::XS is surprisingly fast, as shown in the following 973 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 974 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 975 in the JSON::XS distribution, to make it easy to compare on your own
743 system. 976 system.
744 977
745 First comes a comparison between various modules using a very short 978 First comes a comparison between various modules using a very short
746 single-line JSON string: 979 single-line JSON string (also available at
980 <http://dist.schmorp.de/misc/json/short.json>).
747 981
748 {"method": "handleMessage", "params": ["user1", "we were just talking"], \ 982 {"method": "handleMessage", "params": ["user1", "we were just talking"], \
749 "id": null, "array":[1,11,234,-5,1e5,1e7, true, false]} 983 "id": null, "array":[1,11,234,-5,1e5,1e7, true, false]}
750 984
751 It shows the number of encodes/decodes per second (JSON::XS uses the 985 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 986 functional interface, while JSON::XS/2 uses the OO interface with
753 pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink). 987 pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink).
754 Higher is better: 988 Higher is better:
755 989
756 Storable | 15779.925 | 14169.946 |
757 -----------+------------+------------+
758 module | encode | decode | 990 module | encode | decode |
759 -----------|------------|------------| 991 -----------|------------|------------|
760 JSON | 4990.842 | 4088.813 | 992 JSON 1.x | 4990.842 | 4088.813 |
761 JSON::DWIW | 51653.990 | 71575.154 | 993 JSON::DWIW | 51653.990 | 71575.154 |
762 JSON::PC | 65948.176 | 74631.744 | 994 JSON::PC | 65948.176 | 74631.744 |
763 JSON::PP | 8931.652 | 3817.168 | 995 JSON::PP | 8931.652 | 3817.168 |
764 JSON::Syck | 24877.248 | 27776.848 | 996 JSON::Syck | 24877.248 | 27776.848 |
765 JSON::XS | 388361.481 | 227951.304 | 997 JSON::XS | 388361.481 | 227951.304 |
… …
767 JSON::XS/3 | 338250.323 | 218453.333 | 999 JSON::XS/3 | 338250.323 | 218453.333 |
768 Storable | 16500.016 | 135300.129 | 1000 Storable | 16500.016 | 135300.129 |
769 -----------+------------+------------+ 1001 -----------+------------+------------+
770 1002
771 That is, JSON::XS is about five times faster than JSON::DWIW on 1003 That is, JSON::XS is about five times faster than JSON::DWIW on
772 encoding, about three times faster on decoding, and over fourty times 1004 encoding, about three times faster on decoding, and over forty times
773 faster than JSON, even with pretty-printing and key sorting. It also 1005 faster than JSON, even with pretty-printing and key sorting. It also
774 compares favourably to Storable for small amounts of data. 1006 compares favourably to Storable for small amounts of data.
775 1007
776 Using a longer test string (roughly 18KB, generated from Yahoo! Locals 1008 Using a longer test string (roughly 18KB, generated from Yahoo! Locals
777 search API (http://nanoref.com/yahooapis/mgPdGg): 1009 search API (<http://dist.schmorp.de/misc/json/long.json>).
778 1010
779 module | encode | decode | 1011 module | encode | decode |
780 -----------|------------|------------| 1012 -----------|------------|------------|
781 JSON | 55.260 | 34.971 | 1013 JSON 1.x | 55.260 | 34.971 |
782 JSON::DWIW | 825.228 | 1082.513 | 1014 JSON::DWIW | 825.228 | 1082.513 |
783 JSON::PC | 3571.444 | 2394.829 | 1015 JSON::PC | 3571.444 | 2394.829 |
784 JSON::PP | 210.987 | 32.574 | 1016 JSON::PP | 210.987 | 32.574 |
785 JSON::Syck | 552.551 | 787.544 | 1017 JSON::Syck | 552.551 | 787.544 |
786 JSON::XS | 5780.463 | 4854.519 | 1018 JSON::XS | 5780.463 | 4854.519 |
… …
790 -----------+------------+------------+ 1022 -----------+------------+------------+
791 1023
792 Again, JSON::XS leads by far (except for Storable which non-surprisingly 1024 Again, JSON::XS leads by far (except for Storable which non-surprisingly
793 decodes faster). 1025 decodes faster).
794 1026
795 On large strings containing lots of high unicode characters, some 1027 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 1028 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 1029 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 1030 refuse to decode or encode properly, so it was impossible to prepare a
799 fair comparison table for that case. 1031 fair comparison table for that case.
800 1032
801SECURITY CONSIDERATIONS 1033SECURITY CONSIDERATIONS
802 When you are using JSON in a protocol, talking to untrusted potentially 1034 When you are using JSON in a protocol, talking to untrusted potentially
… …
806 have any buffer overflows. Obviously, this module should ensure that and 1038 have any buffer overflows. Obviously, this module should ensure that and
807 I am trying hard on making that true, but you never know. 1039 I am trying hard on making that true, but you never know.
808 1040
809 Second, you need to avoid resource-starving attacks. That means you 1041 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 1042 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 1043 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 1044 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 1045 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 1046 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 1047 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 1048 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 1051 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 1052 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 1053 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 1054 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. 1055 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 1056 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 1057 process has a smaller stack, you should adjust this setting accordingly
826 with the "max_depth" method. 1058 with the "max_depth" method.
827 1059
828 And last but least, something else could bomb you that I forgot to think 1060 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 1061 case, you get to keep the pieces. I am always open for hints, though...
830 hints, though...
831 1062
1063 Also keep in mind that JSON::XS might leak contents of your Perl data
1064 structures in its error messages, so when you serialise sensitive
1065 information you might want to make sure that exceptions thrown by
1066 JSON::XS will not end up in front of untrusted eyes.
1067
832 If you are using JSON::XS to return packets to consumption by javascript 1068 If you are using JSON::XS to return packets to consumption by JavaScript
833 scripts in a browser you should have a look at 1069 scripts in a browser you should have a look at
834 <http://jpsykes.com/47/practical-csrf-and-json-security> to see wether 1070 <http://jpsykes.com/47/practical-csrf-and-json-security> to see whether
835 you are vulnerable to some common attack vectors (which really are 1071 you are vulnerable to some common attack vectors (which really are
836 browser design bugs, but it is still you who will have to deal with it, 1072 browser design bugs, but it is still you who will have to deal with it,
837 as major browser developers care only for features, not about doing 1073 as major browser developers care only for features, not about getting
838 security right). 1074 security right).
1075
1076THREADS
1077 This module is *not* guaranteed to be thread safe and there are no plans
1078 to change this until Perl gets thread support (as opposed to the
1079 horribly slow so-called "threads" which are simply slow and bloated
1080 process simulations - use fork, its *much* faster, cheaper, better).
1081
1082 (It might actually work, but you have been warned).
839 1083
840BUGS 1084BUGS
841 While the goal of this module is to be correct, that unfortunately does 1085 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 1086 not mean its bug-free, only that I think its design is bug-free. It is
843 still relatively early in its development. If you keep reporting bugs 1087 still relatively early in its development. If you keep reporting bugs
844 they will be fixed swiftly, though. 1088 they will be fixed swiftly, though.
845 1089
1090 Please refrain from using rt.cpan.org or any other bug reporting
1091 service. I put the contact address into my modules for a reason.
1092
846AUTHOR 1093AUTHOR
847 Marc Lehmann <schmorp@schmorp.de> 1094 Marc Lehmann <schmorp@schmorp.de>
848 http://home.schmorp.de/ 1095 http://home.schmorp.de/
849 1096

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