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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.
23 34
24 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
26 modules, none of them correctly handle all corner cases, and in most
27 cases their maintainers are unresponsive, gone missing, or not listening
28 to bug reports for other reasons.
29
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 35 See MAPPING, below, on how JSON::XS maps perl values to JSON values and
33 vice versa. 36 vice versa.
34 37
35 FEATURES 38 FEATURES
36 * correct unicode handling 39 * correct Unicode handling
40
37 This module knows how to handle Unicode, and even documents how and 41 This module knows how to handle Unicode, documents how and when it
38 when it does so. 42 does so, and even documents what "correct" means.
39 43
40 * round-trip integrity 44 * round-trip integrity
45
41 When you serialise a perl data structure using only datatypes 46 When you serialise a perl data structure using only data types
42 supported by JSON, the deserialised data structure is identical on 47 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" 48 identical on the Perl level. (e.g. the string "2.0" doesn't suddenly
44 just because it looks like a number). 49 become "2" just because it looks like a number). There *are* minor
50 exceptions to this, read the MAPPING section below to learn about
51 those.
45 52
46 * strict checking of JSON correctness 53 * strict checking of JSON correctness
54
47 There is no guessing, no generating of illegal JSON texts by 55 There is no guessing, no generating of illegal JSON texts by
48 default, and only JSON is accepted as input by default (the latter 56 default, and only JSON is accepted as input by default (the latter
49 is a security feature). 57 is a security feature).
50 58
51 * fast 59 * fast
52 Compared to other JSON modules, this module compares favourably in
53 terms of speed, too.
54 60
61 Compared to other JSON modules and other serialisers such as
62 Storable, this module usually compares favourably in terms of speed,
63 too.
64
55 * simple to use 65 * simple to use
66
56 This module has both a simple functional interface as well as an OO 67 This module has both a simple functional interface as well as an
57 interface. 68 object oriented interface.
58 69
59 * reasonably versatile output formats 70 * reasonably versatile output formats
71
60 You can choose between the most compact guarenteed single-line 72 You can choose between the most compact guaranteed-single-line
61 format possible (nice for simple line-based protocols), a pure-ascii 73 format possible (nice for simple line-based protocols), a pure-ASCII
62 format (for when your transport is not 8-bit clean, still supports 74 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 75 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 76 want to read that stuff). Or you can combine those features in
65 whatever way you like. 77 whatever way you like.
66 78
67FUNCTIONAL INTERFACE 79FUNCTIONAL INTERFACE
68 The following convinience methods are provided by this module. They are 80 The following convenience methods are provided by this module. They are
69 exported by default: 81 exported by default:
70 82
71 $json_text = to_json $perl_scalar 83 $json_text = encode_json $perl_scalar
72 Converts the given Perl data structure (a simple scalar or a 84 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. 85 string (that is, the string contains octets only). Croaks on error.
75 86
76 This function call is functionally identical to: 87 This function call is functionally identical to:
77 88
78 $json_text = JSON::XS->new->utf8->encode ($perl_scalar) 89 $json_text = JSON::XS->new->utf8->encode ($perl_scalar)
79 90
80 except being faster. 91 Except being faster.
81 92
82 $perl_scalar = from_json $json_text 93 $perl_scalar = decode_json $json_text
83 The opposite of "to_json": expects an UTF-8 (binary) string and 94 The opposite of "encode_json": expects a UTF-8 (binary) string and
84 tries to parse that as an UTF-8 encoded JSON text, returning the 95 tries to parse that as a UTF-8 encoded JSON text, returning the
85 resulting simple scalar or reference. Croaks on error. 96 resulting reference. Croaks on error.
86 97
87 This function call is functionally identical to: 98 This function call is functionally identical to:
88 99
89 $perl_scalar = JSON::XS->new->utf8->decode ($json_text) 100 $perl_scalar = JSON::XS->new->utf8->decode ($json_text)
90 101
91 except being faster. 102 Except being faster.
92 103
93 $is_boolean = JSON::XS::is_bool $scalar 104A FEW NOTES ON UNICODE AND PERL
94 Returns true if the passed scalar represents either JSON::XS::true 105 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, 106 how Unicode works in Perl, modulo bugs.
96 respectively and are used to represent JSON "true" and "false"
97 values in Perl.
98 107
99 See MAPPING, below, for more information on how JSON values are 108 1. Perl strings can store characters with ordinal values > 255.
100 mapped to Perl. 109 This enables you to store Unicode characters as single characters in
110 a Perl string - very natural.
111
112 2. Perl does *not* associate an encoding with your strings.
113 ... until you force it to, e.g. when matching it against a regex, or
114 printing the scalar to a file, in which case Perl either interprets
115 your string as locale-encoded text, octets/binary, or as Unicode,
116 depending on various settings. In no case is an encoding stored
117 together with your data, it is *use* that decides encoding, not any
118 magical meta data.
119
120 3. The internal utf-8 flag has no meaning with regards to the encoding
121 of your string.
122 Just ignore that flag unless you debug a Perl bug, a module written
123 in XS or want to dive into the internals of perl. Otherwise it will
124 only confuse you, as, despite the name, it says nothing about how
125 your string is encoded. You can have Unicode strings with that flag
126 set, with that flag clear, and you can have binary data with that
127 flag set and that flag clear. Other possibilities exist, too.
128
129 If you didn't know about that flag, just the better, pretend it
130 doesn't exist.
131
132 4. A "Unicode String" is simply a string where each character can be
133 validly interpreted as a Unicode code point.
134 If you have UTF-8 encoded data, it is no longer a Unicode string,
135 but a Unicode string encoded in UTF-8, giving you a binary string.
136
137 5. A string containing "high" (> 255) character values is *not* a UTF-8
138 string.
139 It's a fact. Learn to live with it.
140
141 I hope this helps :)
101 142
102OBJECT-ORIENTED INTERFACE 143OBJECT-ORIENTED INTERFACE
103 The object oriented interface lets you configure your own encoding or 144 The object oriented interface lets you configure your own encoding or
104 decoding style, within the limits of supported formats. 145 decoding style, within the limits of supported formats.
105 146
106 $json = new JSON::XS 147 $json = new JSON::XS
107 Creates a new JSON::XS object that can be used to de/encode JSON 148 Creates a new JSON::XS object that can be used to de/encode JSON
108 strings. All boolean flags described below are by default 149 strings. All boolean flags described below are by default *disabled*
109 *disabled*. 150 (with the exception of "allow_nonref", which defaults to *enabled*
151 since version 4.0).
110 152
111 The mutators for flags all return the JSON object again and thus 153 The mutators for flags all return the JSON object again and thus
112 calls can be chained: 154 calls can be chained:
113 155
114 my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]}) 156 my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]})
115 => {"a": [1, 2]} 157 => {"a": [1, 2]}
116 158
117 $json = $json->ascii ([$enable]) 159 $json = $json->ascii ([$enable])
160 $enabled = $json->get_ascii
118 If $enable is true (or missing), then the "encode" method will not 161 If $enable is true (or missing), then the "encode" method will not
119 generate characters outside the code range 0..127 (which is ASCII). 162 generate characters outside the code range 0..127 (which is ASCII).
120 Any unicode characters outside that range will be escaped using 163 Any Unicode characters outside that range will be escaped using
121 either a single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL 164 either a single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL
122 escape sequence, as per RFC4627. The resulting encoded JSON text can 165 escape sequence, as per RFC4627. The resulting encoded JSON text can
123 be treated as a native unicode string, an ascii-encoded, 166 be treated as a native Unicode string, an ascii-encoded,
124 latin1-encoded or UTF-8 encoded string, or any other superset of 167 latin1-encoded or UTF-8 encoded string, or any other superset of
125 ASCII. 168 ASCII.
126 169
127 If $enable is false, then the "encode" method will not escape 170 If $enable is false, then the "encode" method will not escape
128 Unicode characters unless required by the JSON syntax or other 171 Unicode characters unless required by the JSON syntax or other
129 flags. This results in a faster and more compact format. 172 flags. This results in a faster and more compact format.
130 173
174 See also the section *ENCODING/CODESET FLAG NOTES* later in this
175 document.
176
131 The main use for this flag is to produce JSON texts that can be 177 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 178 transmitted over a 7-bit channel, as the encoded JSON texts will not
133 contain any 8 bit characters. 179 contain any 8 bit characters.
134 180
135 JSON::XS->new->ascii (1)->encode ([chr 0x10401]) 181 JSON::XS->new->ascii (1)->encode ([chr 0x10401])
136 => ["\ud801\udc01"] 182 => ["\ud801\udc01"]
137 183
138 $json = $json->latin1 ([$enable]) 184 $json = $json->latin1 ([$enable])
185 $enabled = $json->get_latin1
139 If $enable is true (or missing), then the "encode" method will 186 If $enable is true (or missing), then the "encode" method will
140 encode the resulting JSON text as latin1 (or iso-8859-1), escaping 187 encode the resulting JSON text as latin1 (or iso-8859-1), escaping
141 any characters outside the code range 0..255. The resulting string 188 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 189 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 190 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 191 flag, as "decode" by default expects Unicode, which is a strict
145 superset of latin1. 192 superset of latin1.
146 193
147 If $enable is false, then the "encode" method will not escape 194 If $enable is false, then the "encode" method will not escape
148 Unicode characters unless required by the JSON syntax or other 195 Unicode characters unless required by the JSON syntax or other
149 flags. 196 flags.
197
198 See also the section *ENCODING/CODESET FLAG NOTES* later in this
199 document.
150 200
151 The main use for this flag is efficiently encoding binary data as 201 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 202 JSON text, as most octets will not be escaped, resulting in a
153 smaller encoded size. The disadvantage is that the resulting JSON 203 smaller encoded size. The disadvantage is that the resulting JSON
154 text is encoded in latin1 (and must correctly be treated as such 204 text is encoded in latin1 (and must correctly be treated as such
155 when storing and transfering), a rare encoding for JSON. It is 205 when storing and transferring), a rare encoding for JSON. It is
156 therefore most useful when you want to store data structures known 206 therefore most useful when you want to store data structures known
157 to contain binary data efficiently in files or databases, not when 207 to contain binary data efficiently in files or databases, not when
158 talking to other JSON encoders/decoders. 208 talking to other JSON encoders/decoders.
159 209
160 JSON::XS->new->latin1->encode (["\x{89}\x{abc}"] 210 JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]
161 => ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not) 211 => ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)
162 212
163 $json = $json->utf8 ([$enable]) 213 $json = $json->utf8 ([$enable])
214 $enabled = $json->get_utf8
164 If $enable is true (or missing), then the "encode" method will 215 If $enable is true (or missing), then the "encode" method will
165 encode the JSON result into UTF-8, as required by many protocols, 216 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 217 while the "decode" method expects to be handed a UTF-8-encoded
167 string. Please note that UTF-8-encoded strings do not contain any 218 string. Please note that UTF-8-encoded strings do not contain any
168 characters outside the range 0..255, they are thus useful for 219 characters outside the range 0..255, they are thus useful for
169 bytewise/binary I/O. In future versions, enabling this option might 220 bytewise/binary I/O. In future versions, enabling this option might
170 enable autodetection of the UTF-16 and UTF-32 encoding families, as 221 enable autodetection of the UTF-16 and UTF-32 encoding families, as
171 described in RFC4627. 222 described in RFC4627.
172 223
173 If $enable is false, then the "encode" method will return the JSON 224 If $enable is false, then the "encode" method will return the JSON
174 string as a (non-encoded) unicode string, while "decode" expects 225 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 226 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. 227 UTF-16) needs to be done yourself, e.g. using the Encode module.
228
229 See also the section *ENCODING/CODESET FLAG NOTES* later in this
230 document.
177 231
178 Example, output UTF-16BE-encoded JSON: 232 Example, output UTF-16BE-encoded JSON:
179 233
180 use Encode; 234 use Encode;
181 $jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object); 235 $jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
… …
200 2 254 2
201 ] 255 ]
202 } 256 }
203 257
204 $json = $json->indent ([$enable]) 258 $json = $json->indent ([$enable])
259 $enabled = $json->get_indent
205 If $enable is true (or missing), then the "encode" method will use a 260 If $enable is true (or missing), then the "encode" method will use a
206 multiline format as output, putting every array member or 261 multiline format as output, putting every array member or
207 object/hash key-value pair into its own line, identing them 262 object/hash key-value pair into its own line, indenting them
208 properly. 263 properly.
209 264
210 If $enable is false, no newlines or indenting will be produced, and 265 If $enable is false, no newlines or indenting will be produced, and
211 the resulting JSON text is guarenteed not to contain any "newlines". 266 the resulting JSON text is guaranteed not to contain any "newlines".
212 267
213 This setting has no effect when decoding JSON texts. 268 This setting has no effect when decoding JSON texts.
214 269
215 $json = $json->space_before ([$enable]) 270 $json = $json->space_before ([$enable])
271 $enabled = $json->get_space_before
216 If $enable is true (or missing), then the "encode" method will add 272 If $enable is true (or missing), then the "encode" method will add
217 an extra optional space before the ":" separating keys from values 273 an extra optional space before the ":" separating keys from values
218 in JSON objects. 274 in JSON objects.
219 275
220 If $enable is false, then the "encode" method will not add any extra 276 If $enable is false, then the "encode" method will not add any extra
… …
226 Example, space_before enabled, space_after and indent disabled: 282 Example, space_before enabled, space_after and indent disabled:
227 283
228 {"key" :"value"} 284 {"key" :"value"}
229 285
230 $json = $json->space_after ([$enable]) 286 $json = $json->space_after ([$enable])
287 $enabled = $json->get_space_after
231 If $enable is true (or missing), then the "encode" method will add 288 If $enable is true (or missing), then the "encode" method will add
232 an extra optional space after the ":" separating keys from values in 289 an extra optional space after the ":" separating keys from values in
233 JSON objects and extra whitespace after the "," separating key-value 290 JSON objects and extra whitespace after the "," separating key-value
234 pairs and array members. 291 pairs and array members.
235 292
… …
240 297
241 Example, space_before and indent disabled, space_after enabled: 298 Example, space_before and indent disabled, space_after enabled:
242 299
243 {"key": "value"} 300 {"key": "value"}
244 301
302 $json = $json->relaxed ([$enable])
303 $enabled = $json->get_relaxed
304 If $enable is true (or missing), then "decode" will accept some
305 extensions to normal JSON syntax (see below). "encode" will not be
306 affected in any way. *Be aware that this option makes you accept
307 invalid JSON texts as if they were valid!*. I suggest only to use
308 this option to parse application-specific files written by humans
309 (configuration files, resource files etc.)
310
311 If $enable is false (the default), then "decode" will only accept
312 valid JSON texts.
313
314 Currently accepted extensions are:
315
316 * list items can have an end-comma
317
318 JSON *separates* array elements and key-value pairs with commas.
319 This can be annoying if you write JSON texts manually and want
320 to be able to quickly append elements, so this extension accepts
321 comma at the end of such items not just between them:
322
323 [
324 1,
325 2, <- this comma not normally allowed
326 ]
327 {
328 "k1": "v1",
329 "k2": "v2", <- this comma not normally allowed
330 }
331
332 * shell-style '#'-comments
333
334 Whenever JSON allows whitespace, shell-style comments are
335 additionally allowed. They are terminated by the first
336 carriage-return or line-feed character, after which more
337 white-space and comments are allowed.
338
339 [
340 1, # this comment not allowed in JSON
341 # neither this one...
342 ]
343
344 * literal ASCII TAB characters in strings
345
346 Literal ASCII TAB characters are now allowed in strings (and
347 treated as "\t").
348
349 [
350 "Hello\tWorld",
351 "Hello<TAB>World", # literal <TAB> would not normally be allowed
352 ]
353
245 $json = $json->canonical ([$enable]) 354 $json = $json->canonical ([$enable])
355 $enabled = $json->get_canonical
246 If $enable is true (or missing), then the "encode" method will 356 If $enable is true (or missing), then the "encode" method will
247 output JSON objects by sorting their keys. This is adding a 357 output JSON objects by sorting their keys. This is adding a
248 comparatively high overhead. 358 comparatively high overhead.
249 359
250 If $enable is false, then the "encode" method will output key-value 360 If $enable is false, then the "encode" method will output key-value
251 pairs in the order Perl stores them (which will likely change 361 pairs in the order Perl stores them (which will likely change
252 between runs of the same script). 362 between runs of the same script, and can change even within the same
363 run from 5.18 onwards).
253 364
254 This option is useful if you want the same data structure to be 365 This option is useful if you want the same data structure to be
255 encoded as the same JSON text (given the same overall settings). If 366 encoded as the same JSON text (given the same overall settings). If
256 it is disabled, the same hash migh be encoded differently even if 367 it is disabled, the same hash might be encoded differently even if
257 contains the same data, as key-value pairs have no inherent ordering 368 contains the same data, as key-value pairs have no inherent ordering
258 in Perl. 369 in Perl.
259 370
260 This setting has no effect when decoding JSON texts. 371 This setting has no effect when decoding JSON texts.
261 372
373 This setting has currently no effect on tied hashes.
374
262 $json = $json->allow_nonref ([$enable]) 375 $json = $json->allow_nonref ([$enable])
376 $enabled = $json->get_allow_nonref
377 Unlike other boolean options, this opotion is enabled by default
378 beginning with version 4.0. See "SECURITY CONSIDERATIONS" for the
379 gory details.
380
263 If $enable is true (or missing), then the "encode" method can 381 If $enable is true (or missing), then the "encode" method can
264 convert a non-reference into its corresponding string, number or 382 convert a non-reference into its corresponding string, number or
265 null JSON value, which is an extension to RFC4627. Likewise, 383 null JSON value, which is an extension to RFC4627. Likewise,
266 "decode" will accept those JSON values instead of croaking. 384 "decode" will accept those JSON values instead of croaking.
267 385
268 If $enable is false, then the "encode" method will croak if it isn't 386 If $enable is false, then the "encode" method will croak if it isn't
269 passed an arrayref or hashref, as JSON texts must either be an 387 passed an arrayref or hashref, as JSON texts must either be an
270 object or array. Likewise, "decode" will croak if given something 388 object or array. Likewise, "decode" will croak if given something
271 that is not a JSON object or array. 389 that is not a JSON object or array.
272 390
273 Example, encode a Perl scalar as JSON value with enabled 391 Example, encode a Perl scalar as JSON value without enabled
274 "allow_nonref", resulting in an invalid JSON text: 392 "allow_nonref", resulting in an error:
275 393
276 JSON::XS->new->allow_nonref->encode ("Hello, World!") 394 JSON::XS->new->allow_nonref (0)->encode ("Hello, World!")
277 => "Hello, World!" 395 => hash- or arrayref expected...
396
397 $json = $json->allow_unknown ([$enable])
398 $enabled = $json->get_allow_unknown
399 If $enable is true (or missing), then "encode" will *not* throw an
400 exception when it encounters values it cannot represent in JSON (for
401 example, filehandles) but instead will encode a JSON "null" value.
402 Note that blessed objects are not included here and are handled
403 separately by c<allow_nonref>.
404
405 If $enable is false (the default), then "encode" will throw an
406 exception when it encounters anything it cannot encode as JSON.
407
408 This option does not affect "decode" in any way, and it is
409 recommended to leave it off unless you know your communications
410 partner.
278 411
279 $json = $json->allow_blessed ([$enable]) 412 $json = $json->allow_blessed ([$enable])
413 $enabled = $json->get_allow_blessed
414 See "OBJECT SERIALISATION" for details.
415
280 If $enable is true (or missing), then the "encode" method will not 416 If $enable is true (or missing), then the "encode" method will not
281 barf when it encounters a blessed reference. Instead, the value of 417 barf when it encounters a blessed reference that it cannot convert
282 the convert_blessed option will decide wether "null" 418 otherwise. Instead, a JSON "null" value is encoded instead of the
283 ("convert_blessed" disabled or no "to_json" method found) or a 419 object.
284 representation of the object ("convert_blessed" enabled and
285 "to_json" method found) is being encoded. Has no effect on "decode".
286 420
287 If $enable is false (the default), then "encode" will throw an 421 If $enable is false (the default), then "encode" will throw an
288 exception when it encounters a blessed object. 422 exception when it encounters a blessed object that it cannot convert
423 otherwise.
424
425 This setting has no effect on "decode".
289 426
290 $json = $json->convert_blessed ([$enable]) 427 $json = $json->convert_blessed ([$enable])
428 $enabled = $json->get_convert_blessed
429 See "OBJECT SERIALISATION" for details.
430
291 If $enable is true (or missing), then "encode", upon encountering a 431 If $enable is true (or missing), then "encode", upon encountering a
292 blessed object, will check for the availability of the "TO_JSON" 432 blessed object, will check for the availability of the "TO_JSON"
293 method on the object's class. If found, it will be called in scalar 433 method on the object's class. If found, it will be called in scalar
294 context and the resulting scalar will be encoded instead of the 434 context and the resulting scalar will be encoded instead of the
295 object. If no "TO_JSON" method is found, the value of 435 object.
296 "allow_blessed" will decide what to do.
297 436
298 The "TO_JSON" method may safely call die if it wants. If "TO_JSON" 437 The "TO_JSON" method may safely call die if it wants. If "TO_JSON"
299 returns other blessed objects, those will be handled in the same 438 returns other blessed objects, those will be handled in the same
300 way. "TO_JSON" must take care of not causing an endless recursion 439 way. "TO_JSON" must take care of not causing an endless recursion
301 cycle (== crash) in this case. The name of "TO_JSON" was chosen 440 cycle (== crash) in this case. The name of "TO_JSON" was chosen
302 because other methods called by the Perl core (== not by the user of 441 because other methods called by the Perl core (== not by the user of
303 the object) are usually in upper case letters and to avoid 442 the object) are usually in upper case letters and to avoid
304 collisions with the "to_json" function. 443 collisions with any "to_json" function or method.
305 444
306 This setting does not yet influence "decode" in any way, but in the 445 If $enable is false (the default), then "encode" will not consider
307 future, global hooks might get installed that influence "decode" and 446 this type of conversion.
308 are enabled by this setting.
309 447
310 If $enable is false, then the "allow_blessed" setting will decide 448 This setting has no effect on "decode".
311 what to do when a blessed object is found. 449
450 $json = $json->allow_tags ([$enable])
451 $enabled = $json->get_allow_tags
452 See "OBJECT SERIALISATION" for details.
453
454 If $enable is true (or missing), then "encode", upon encountering a
455 blessed object, will check for the availability of the "FREEZE"
456 method on the object's class. If found, it will be used to serialise
457 the object into a nonstandard tagged JSON value (that JSON decoders
458 cannot decode).
459
460 It also causes "decode" to parse such tagged JSON values and
461 deserialise them via a call to the "THAW" method.
462
463 If $enable is false (the default), then "encode" will not consider
464 this type of conversion, and tagged JSON values will cause a parse
465 error in "decode", as if tags were not part of the grammar.
466
467 $json->boolean_values ([$false, $true])
468 ($false, $true) = $json->get_boolean_values
469 By default, JSON booleans will be decoded as overloaded
470 $Types::Serialiser::false and $Types::Serialiser::true objects.
471
472 With this method you can specify your own boolean values for
473 decoding - on decode, JSON "false" will be decoded as a copy of
474 $false, and JSON "true" will be decoded as $true ("copy" here is the
475 same thing as assigning a value to another variable, i.e. "$copy =
476 $false").
477
478 Calling this method without any arguments will reset the booleans to
479 their default values.
480
481 "get_boolean_values" will return both $false and $true values, or
482 the empty list when they are set to the default.
312 483
313 $json = $json->filter_json_object ([$coderef->($hashref)]) 484 $json = $json->filter_json_object ([$coderef->($hashref)])
314 When $coderef is specified, it will be called from "decode" each 485 When $coderef is specified, it will be called from "decode" each
315 time it decodes a JSON object. The only argument is a reference to 486 time it decodes a JSON object. The only argument is a reference to
316 the newly-created hash. If the code references returns a single 487 the newly-created hash. If the code reference returns a single
317 scalar (which need not be a reference), this value (i.e. a copy of 488 scalar (which need not be a reference), this value (or rather a copy
318 that scalar to avoid aliasing) is inserted into the deserialised 489 of it) is inserted into the deserialised data structure. If it
319 data structure. If it returns an empty list (NOTE: *not* "undef", 490 returns an empty list (NOTE: *not* "undef", which is a valid
320 which is a valid scalar), the original deserialised hash will be 491 scalar), the original deserialised hash will be inserted. This
321 inserted. This setting can slow down decoding considerably. 492 setting can slow down decoding considerably.
322 493
323 When $coderef is omitted or undefined, any existing callback will be 494 When $coderef is omitted or undefined, any existing callback will be
324 removed and "decode" will not change the deserialised hash in any 495 removed and "decode" will not change the deserialised hash in any
325 way. 496 way.
326 497
… …
350 521
351 As this callback gets called less often then the 522 As this callback gets called less often then the
352 "filter_json_object" one, decoding speed will not usually suffer as 523 "filter_json_object" one, decoding speed will not usually suffer as
353 much. Therefore, single-key objects make excellent targets to 524 much. Therefore, single-key objects make excellent targets to
354 serialise Perl objects into, especially as single-key JSON objects 525 serialise Perl objects into, especially as single-key JSON objects
355 are as close to the type-tagged value concept as JSON gets (its 526 are as close to the type-tagged value concept as JSON gets (it's
356 basically an ID/VALUE tuple). Of course, JSON does not support this 527 basically an ID/VALUE tuple). Of course, JSON does not support this
357 in any way, so you need to make sure your data never looks like a 528 in any way, so you need to make sure your data never looks like a
358 serialised Perl hash. 529 serialised Perl hash.
359 530
360 Typical names for the single object key are "__class_whatever__", or 531 Typical names for the single object key are "__class_whatever__", or
… …
385 556
386 { __widget__ => $self->{id} } 557 { __widget__ => $self->{id} }
387 } 558 }
388 559
389 $json = $json->shrink ([$enable]) 560 $json = $json->shrink ([$enable])
561 $enabled = $json->get_shrink
390 Perl usually over-allocates memory a bit when allocating space for 562 Perl usually over-allocates memory a bit when allocating space for
391 strings. This flag optionally resizes strings generated by either 563 strings. This flag optionally resizes strings generated by either
392 "encode" or "decode" to their minimum size possible. This can save 564 "encode" or "decode" to their minimum size possible. This can save
393 memory when your JSON texts are either very very long or you have 565 memory when your JSON texts are either very very long or you have
394 many short strings. It will also try to downgrade any strings to 566 many short strings. It will also try to downgrade any strings to
… …
412 converting strings that look like integers or floats into integers 584 converting strings that look like integers or floats into integers
413 or floats internally (there is no difference on the Perl level), 585 or floats internally (there is no difference on the Perl level),
414 saving space. 586 saving space.
415 587
416 $json = $json->max_depth ([$maximum_nesting_depth]) 588 $json = $json->max_depth ([$maximum_nesting_depth])
589 $max_depth = $json->get_max_depth
417 Sets the maximum nesting level (default 512) accepted while encoding 590 Sets the maximum nesting level (default 512) accepted while encoding
418 or decoding. If the JSON text or Perl data structure has an equal or 591 or decoding. If a higher nesting level is detected in JSON text or a
419 higher nesting level then this limit, then the encoder and decoder 592 Perl data structure, then the encoder and decoder will stop and
420 will stop and croak at that point. 593 croak at that point.
421 594
422 Nesting level is defined by number of hash- or arrayrefs that the 595 Nesting level is defined by number of hash- or arrayrefs that the
423 encoder needs to traverse to reach a given point or the number of 596 encoder needs to traverse to reach a given point or the number of
424 "{" or "[" characters without their matching closing parenthesis 597 "{" or "[" characters without their matching closing parenthesis
425 crossed to reach a given character in a string. 598 crossed to reach a given character in a string.
426 599
427 Setting the maximum depth to one disallows any nesting, so that 600 Setting the maximum depth to one disallows any nesting, so that
428 ensures that the object is only a single hash/object or array. 601 ensures that the object is only a single hash/object or array.
429 602
430 The argument to "max_depth" will be rounded up to the next highest
431 power of two. If no argument is given, the highest possible setting 603 If no argument is given, the highest possible setting will be used,
432 will be used, which is rarely useful. 604 which is rarely useful.
605
606 Note that nesting is implemented by recursion in C. The default
607 value has been chosen to be as large as typical operating systems
608 allow without crashing.
433 609
434 See SECURITY CONSIDERATIONS, below, for more info on why this is 610 See SECURITY CONSIDERATIONS, below, for more info on why this is
435 useful. 611 useful.
436 612
437 $json = $json->max_size ([$maximum_string_size]) 613 $json = $json->max_size ([$maximum_string_size])
614 $max_size = $json->get_max_size
438 Set the maximum length a JSON text may have (in bytes) where 615 Set the maximum length a JSON text may have (in bytes) where
439 decoding is being attempted. The default is 0, meaning no limit. 616 decoding is being attempted. The default is 0, meaning no limit.
440 When "decode" is called on a string longer then this number of 617 When "decode" is called on a string that is longer then this many
441 characters it will not attempt to decode the string but throw an 618 bytes, it will not attempt to decode the string but throw an
442 exception. This setting has no effect on "encode" (yet). 619 exception. This setting has no effect on "encode" (yet).
443 620
444 The argument to "max_size" will be rounded up to the next highest
445 power of two (so may be more than requested). If no argument is
446 given, the limit check will be deactivated (same as when 0 is 621 If no argument is given, the limit check will be deactivated (same
447 specified). 622 as when 0 is specified).
448 623
449 See SECURITY CONSIDERATIONS, below, for more info on why this is 624 See SECURITY CONSIDERATIONS, below, for more info on why this is
450 useful. 625 useful.
451 626
452 $json_text = $json->encode ($perl_scalar) 627 $json_text = $json->encode ($perl_scalar)
453 Converts the given Perl data structure (a simple scalar or a 628 Converts the given Perl value or data structure to its JSON
454 reference to a hash or array) to its JSON representation. Simple 629 representation. Croaks on error.
455 scalars will be converted into JSON string or number sequences,
456 while references to arrays become JSON arrays and references to
457 hashes become JSON objects. Undefined Perl values (e.g. "undef")
458 become JSON "null" values. Neither "true" nor "false" values will be
459 generated.
460 630
461 $perl_scalar = $json->decode ($json_text) 631 $perl_scalar = $json->decode ($json_text)
462 The opposite of "encode": expects a JSON text and tries to parse it, 632 The opposite of "encode": expects a JSON text and tries to parse it,
463 returning the resulting simple scalar or reference. Croaks on error. 633 returning the resulting simple scalar or reference. Croaks on error.
464
465 JSON numbers and strings become simple Perl scalars. JSON arrays
466 become Perl arrayrefs and JSON objects become Perl hashrefs. "true"
467 becomes 1, "false" becomes 0 and "null" becomes "undef".
468 634
469 ($perl_scalar, $characters) = $json->decode_prefix ($json_text) 635 ($perl_scalar, $characters) = $json->decode_prefix ($json_text)
470 This works like the "decode" method, but instead of raising an 636 This works like the "decode" method, but instead of raising an
471 exception when there is trailing garbage after the first JSON 637 exception when there is trailing garbage after the first JSON
472 object, it will silently stop parsing there and return the number of 638 object, it will silently stop parsing there and return the number of
473 characters consumed so far. 639 characters consumed so far.
474 640
475 This is useful if your JSON texts are not delimited by an outer 641 This is useful if your JSON texts are not delimited by an outer
476 protocol (which is not the brightest thing to do in the first place)
477 and you need to know where the JSON text ends. 642 protocol and you need to know where the JSON text ends.
478 643
479 JSON::XS->new->decode_prefix ("[1] the tail") 644 JSON::XS->new->decode_prefix ("[1] the tail")
480 => ([], 3) 645 => ([1], 3)
646
647INCREMENTAL PARSING
648 In some cases, there is the need for incremental parsing of JSON texts.
649 While this module always has to keep both JSON text and resulting Perl
650 data structure in memory at one time, it does allow you to parse a JSON
651 stream incrementally. It does so by accumulating text until it has a
652 full JSON object, which it then can decode. This process is similar to
653 using "decode_prefix" to see if a full JSON object is available, but is
654 much more efficient (and can be implemented with a minimum of method
655 calls).
656
657 JSON::XS will only attempt to parse the JSON text once it is sure it has
658 enough text to get a decisive result, using a very simple but truly
659 incremental parser. This means that it sometimes won't stop as early as
660 the full parser, for example, it doesn't detect mismatched parentheses.
661 The only thing it guarantees is that it starts decoding as soon as a
662 syntactically valid JSON text has been seen. This means you need to set
663 resource limits (e.g. "max_size") to ensure the parser will stop parsing
664 in the presence if syntax errors.
665
666 The following methods implement this incremental parser.
667
668 [void, scalar or list context] = $json->incr_parse ([$string])
669 This is the central parsing function. It can both append new text
670 and extract objects from the stream accumulated so far (both of
671 these functions are optional).
672
673 If $string is given, then this string is appended to the already
674 existing JSON fragment stored in the $json object.
675
676 After that, if the function is called in void context, it will
677 simply return without doing anything further. This can be used to
678 add more text in as many chunks as you want.
679
680 If the method is called in scalar context, then it will try to
681 extract exactly *one* JSON object. If that is successful, it will
682 return this object, otherwise it will return "undef". If there is a
683 parse error, this method will croak just as "decode" would do (one
684 can then use "incr_skip" to skip the erroneous part). This is the
685 most common way of using the method.
686
687 And finally, in list context, it will try to extract as many objects
688 from the stream as it can find and return them, or the empty list
689 otherwise. For this to work, there must be no separators (other than
690 whitespace) between the JSON objects or arrays, instead they must be
691 concatenated back-to-back. If an error occurs, an exception will be
692 raised as in the scalar context case. Note that in this case, any
693 previously-parsed JSON texts will be lost.
694
695 Example: Parse some JSON arrays/objects in a given string and return
696 them.
697
698 my @objs = JSON::XS->new->incr_parse ("[5][7][1,2]");
699
700 $lvalue_string = $json->incr_text
701 This method returns the currently stored JSON fragment as an lvalue,
702 that is, you can manipulate it. This *only* works when a preceding
703 call to "incr_parse" in *scalar context* successfully returned an
704 object. Under all other circumstances you must not call this
705 function (I mean it. although in simple tests it might actually
706 work, it *will* fail under real world conditions). As a special
707 exception, you can also call this method before having parsed
708 anything.
709
710 That means you can only use this function to look at or manipulate
711 text before or after complete JSON objects, not while the parser is
712 in the middle of parsing a JSON object.
713
714 This function is useful in two cases: a) finding the trailing text
715 after a JSON object or b) parsing multiple JSON objects separated by
716 non-JSON text (such as commas).
717
718 $json->incr_skip
719 This will reset the state of the incremental parser and will remove
720 the parsed text from the input buffer so far. This is useful after
721 "incr_parse" died, in which case the input buffer and incremental
722 parser state is left unchanged, to skip the text parsed so far and
723 to reset the parse state.
724
725 The difference to "incr_reset" is that only text until the parse
726 error occurred is removed.
727
728 $json->incr_reset
729 This completely resets the incremental parser, that is, after this
730 call, it will be as if the parser had never parsed anything.
731
732 This is useful if you want to repeatedly parse JSON objects and want
733 to ignore any trailing data, which means you have to reset the
734 parser after each successful decode.
735
736 LIMITATIONS
737 The incremental parser is a non-exact parser: it works by gathering as
738 much text as possible that *could* be a valid JSON text, followed by
739 trying to decode it.
740
741 That means it sometimes needs to read more data than strictly necessary
742 to diagnose an invalid JSON text. For example, after parsing the
743 following fragment, the parser *could* stop with an error, as this
744 fragment *cannot* be the beginning of a valid JSON text:
745
746 [,
747
748 In reality, hopwever, the parser might continue to read data until a
749 length limit is exceeded or it finds a closing bracket.
750
751 EXAMPLES
752 Some examples will make all this clearer. First, a simple example that
753 works similarly to "decode_prefix": We want to decode the JSON object at
754 the start of a string and identify the portion after the JSON object:
755
756 my $text = "[1,2,3] hello";
757
758 my $json = new JSON::XS;
759
760 my $obj = $json->incr_parse ($text)
761 or die "expected JSON object or array at beginning of string";
762
763 my $tail = $json->incr_text;
764 # $tail now contains " hello"
765
766 Easy, isn't it?
767
768 Now for a more complicated example: Imagine a hypothetical protocol
769 where you read some requests from a TCP stream, and each request is a
770 JSON array, without any separation between them (in fact, it is often
771 useful to use newlines as "separators", as these get interpreted as
772 whitespace at the start of the JSON text, which makes it possible to
773 test said protocol with "telnet"...).
774
775 Here is how you'd do it (it is trivial to write this in an event-based
776 manner):
777
778 my $json = new JSON::XS;
779
780 # read some data from the socket
781 while (sysread $socket, my $buf, 4096) {
782
783 # split and decode as many requests as possible
784 for my $request ($json->incr_parse ($buf)) {
785 # act on the $request
786 }
787 }
788
789 Another complicated example: Assume you have a string with JSON objects
790 or arrays, all separated by (optional) comma characters (e.g. "[1],[2],
791 [3]"). To parse them, we have to skip the commas between the JSON texts,
792 and here is where the lvalue-ness of "incr_text" comes in useful:
793
794 my $text = "[1],[2], [3]";
795 my $json = new JSON::XS;
796
797 # void context, so no parsing done
798 $json->incr_parse ($text);
799
800 # now extract as many objects as possible. note the
801 # use of scalar context so incr_text can be called.
802 while (my $obj = $json->incr_parse) {
803 # do something with $obj
804
805 # now skip the optional comma
806 $json->incr_text =~ s/^ \s* , //x;
807 }
808
809 Now lets go for a very complex example: Assume that you have a gigantic
810 JSON array-of-objects, many gigabytes in size, and you want to parse it,
811 but you cannot load it into memory fully (this has actually happened in
812 the real world :).
813
814 Well, you lost, you have to implement your own JSON parser. But JSON::XS
815 can still help you: You implement a (very simple) array parser and let
816 JSON decode the array elements, which are all full JSON objects on their
817 own (this wouldn't work if the array elements could be JSON numbers, for
818 example):
819
820 my $json = new JSON::XS;
821
822 # open the monster
823 open my $fh, "<bigfile.json"
824 or die "bigfile: $!";
825
826 # first parse the initial "["
827 for (;;) {
828 sysread $fh, my $buf, 65536
829 or die "read error: $!";
830 $json->incr_parse ($buf); # void context, so no parsing
831
832 # Exit the loop once we found and removed(!) the initial "[".
833 # In essence, we are (ab-)using the $json object as a simple scalar
834 # we append data to.
835 last if $json->incr_text =~ s/^ \s* \[ //x;
836 }
837
838 # now we have the skipped the initial "[", so continue
839 # parsing all the elements.
840 for (;;) {
841 # in this loop we read data until we got a single JSON object
842 for (;;) {
843 if (my $obj = $json->incr_parse) {
844 # do something with $obj
845 last;
846 }
847
848 # add more data
849 sysread $fh, my $buf, 65536
850 or die "read error: $!";
851 $json->incr_parse ($buf); # void context, so no parsing
852 }
853
854 # in this loop we read data until we either found and parsed the
855 # separating "," between elements, or the final "]"
856 for (;;) {
857 # first skip whitespace
858 $json->incr_text =~ s/^\s*//;
859
860 # if we find "]", we are done
861 if ($json->incr_text =~ s/^\]//) {
862 print "finished.\n";
863 exit;
864 }
865
866 # if we find ",", we can continue with the next element
867 if ($json->incr_text =~ s/^,//) {
868 last;
869 }
870
871 # if we find anything else, we have a parse error!
872 if (length $json->incr_text) {
873 die "parse error near ", $json->incr_text;
874 }
875
876 # else add more data
877 sysread $fh, my $buf, 65536
878 or die "read error: $!";
879 $json->incr_parse ($buf); # void context, so no parsing
880 }
881
882 This is a complex example, but most of the complexity comes from the
883 fact that we are trying to be correct (bear with me if I am wrong, I
884 never ran the above example :).
481 885
482MAPPING 886MAPPING
483 This section describes how JSON::XS maps Perl values to JSON values and 887 This section describes how JSON::XS maps Perl values to JSON values and
484 vice versa. These mappings are designed to "do the right thing" in most 888 vice versa. These mappings are designed to "do the right thing" in most
485 circumstances automatically, preserving round-tripping characteristics 889 circumstances automatically, preserving round-tripping characteristics
486 (what you put in comes out as something equivalent). 890 (what you put in comes out as something equivalent).
487 891
488 For the more enlightened: note that in the following descriptions, 892 For the more enlightened: note that in the following descriptions,
489 lowercase *perl* refers to the Perl interpreter, while uppcercase *Perl* 893 lowercase *perl* refers to the Perl interpreter, while uppercase *Perl*
490 refers to the abstract Perl language itself. 894 refers to the abstract Perl language itself.
491 895
492 JSON -> PERL 896 JSON -> PERL
493 object 897 object
494 A JSON object becomes a reference to a hash in Perl. No ordering of 898 A JSON object becomes a reference to a hash in Perl. No ordering of
495 object keys is preserved (JSON does not preserver object key 899 object keys is preserved (JSON does not preserve object key ordering
496 ordering itself). 900 itself).
497 901
498 array 902 array
499 A JSON array becomes a reference to an array in Perl. 903 A JSON array becomes a reference to an array in Perl.
500 904
501 string 905 string
502 A JSON string becomes a string scalar in Perl - Unicode codepoints 906 A JSON string becomes a string scalar in Perl - Unicode codepoints
503 in JSON are represented by the same codepoints in the Perl string, 907 in JSON are represented by the same codepoints in the Perl string,
504 so no manual decoding is necessary. 908 so no manual decoding is necessary.
505 909
506 number 910 number
507 A JSON number becomes either an integer or numeric (floating point) 911 A JSON number becomes either an integer, numeric (floating point) or
508 scalar in perl, depending on its range and any fractional parts. On 912 string scalar in perl, depending on its range and any fractional
509 the Perl level, there is no difference between those as Perl handles 913 parts. On the Perl level, there is no difference between those as
510 all the conversion details, but an integer may take slightly less 914 Perl handles all the conversion details, but an integer may take
511 memory and might represent more values exactly than (floating point) 915 slightly less memory and might represent more values exactly than
916 floating point numbers.
917
918 If the number consists of digits only, JSON::XS will try to
919 represent it as an integer value. If that fails, it will try to
920 represent it as a numeric (floating point) value if that is possible
921 without loss of precision. Otherwise it will preserve the number as
922 a string value (in which case you lose roundtripping ability, as the
923 JSON number will be re-encoded to a JSON string).
924
925 Numbers containing a fractional or exponential part will always be
926 represented as numeric (floating point) values, possibly at a loss
927 of precision (in which case you might lose perfect roundtripping
928 ability, but the JSON number will still be re-encoded as a JSON
512 numbers. 929 number).
930
931 Note that precision is not accuracy - binary floating point values
932 cannot represent most decimal fractions exactly, and when converting
933 from and to floating point, JSON::XS only guarantees precision up to
934 but not including the least significant bit.
513 935
514 true, false 936 true, false
515 These JSON atoms become "JSON::XS::true" and "JSON::XS::false", 937 These JSON atoms become "Types::Serialiser::true" and
516 respectively. They are overloaded to act almost exactly like the 938 "Types::Serialiser::false", respectively. They are overloaded to act
517 numbers 1 and 0. You can check wether a scalar is a JSON boolean by 939 almost exactly like the numbers 1 and 0. You can check whether a
518 using the "JSON::XS::is_bool" function. 940 scalar is a JSON boolean by using the "Types::Serialiser::is_bool"
941 function (after "use Types::Serialier", of course).
519 942
520 null 943 null
521 A JSON null atom becomes "undef" in Perl. 944 A JSON null atom becomes "undef" in Perl.
945
946 shell-style comments ("# *text*")
947 As a nonstandard extension to the JSON syntax that is enabled by the
948 "relaxed" setting, shell-style comments are allowed. They can start
949 anywhere outside strings and go till the end of the line.
950
951 tagged values ("(*tag*)*value*").
952 Another nonstandard extension to the JSON syntax, enabled with the
953 "allow_tags" setting, are tagged values. In this implementation, the
954 *tag* must be a perl package/class name encoded as a JSON string,
955 and the *value* must be a JSON array encoding optional constructor
956 arguments.
957
958 See "OBJECT SERIALISATION", below, for details.
522 959
523 PERL -> JSON 960 PERL -> JSON
524 The mapping from Perl to JSON is slightly more difficult, as Perl is a 961 The mapping from Perl to JSON is slightly more difficult, as Perl is a
525 truly typeless language, so we can only guess which JSON type is meant 962 truly typeless language, so we can only guess which JSON type is meant
526 by a Perl value. 963 by a Perl value.
527 964
528 hash references 965 hash references
529 Perl hash references become JSON objects. As there is no inherent 966 Perl hash references become JSON objects. As there is no inherent
530 ordering in hash keys (or JSON objects), they will usually be 967 ordering in hash keys (or JSON objects), they will usually be
531 encoded in a pseudo-random order that can change between runs of the 968 encoded in a pseudo-random order. JSON::XS can optionally sort the
532 same program but stays generally the same within a single run of a 969 hash keys (determined by the *canonical* flag), so the same
533 program. JSON::XS can optionally sort the hash keys (determined by 970 datastructure will serialise to the same JSON text (given same
534 the *canonical* flag), so the same datastructure will serialise to 971 settings and version of JSON::XS), but this incurs a runtime
535 the same JSON text (given same settings and version of JSON::XS), 972 overhead and is only rarely useful, e.g. when you want to compare
536 but this incurs a runtime overhead and is only rarely useful, e.g. 973 some JSON text against another for equality.
537 when you want to compare some JSON text against another for
538 equality.
539 974
540 array references 975 array references
541 Perl array references become JSON arrays. 976 Perl array references become JSON arrays.
542 977
543 other references 978 other references
544 Other unblessed references are generally not allowed and will cause 979 Other unblessed references are generally not allowed and will cause
545 an exception to be thrown, except for references to the integers 0 980 an exception to be thrown, except for references to the integers 0
546 and 1, which get turned into "false" and "true" atoms in JSON. You 981 and 1, which get turned into "false" and "true" atoms in JSON.
547 can also use "JSON::XS::false" and "JSON::XS::true" to improve 982
983 Since "JSON::XS" uses the boolean model from Types::Serialiser, you
984 can also "use Types::Serialiser" and then use
985 "Types::Serialiser::false" and "Types::Serialiser::true" to improve
548 readability. 986 readability.
549 987
988 use Types::Serialiser;
550 to_json [\0,JSON::XS::true] # yields [false,true] 989 encode_json [\0, Types::Serialiser::true] # yields [false,true]
551 990
552 JSON::XS::true, JSON::XS::false 991 Types::Serialiser::true, Types::Serialiser::false
553 These special values become JSON true and JSON false values, 992 These special values from the Types::Serialiser module become JSON
554 respectively. You cna alos use "\1" and "\0" directly if you want. 993 true and JSON false values, respectively. You can also use "\1" and
994 "\0" directly if you want.
555 995
556 blessed objects 996 blessed objects
557 Blessed objects are not allowed. JSON::XS currently tries to encode 997 Blessed objects are not directly representable in JSON, but
558 their underlying representation (hash- or arrayref), but this 998 "JSON::XS" allows various ways of handling objects. See "OBJECT
559 behaviour might change in future versions. 999 SERIALISATION", below, for details.
560 1000
561 simple scalars 1001 simple scalars
562 Simple Perl scalars (any scalar that is not a reference) are the 1002 Simple Perl scalars (any scalar that is not a reference) are the
563 most difficult objects to encode: JSON::XS will encode undefined 1003 most difficult objects to encode: JSON::XS will encode undefined
564 scalars as JSON null value, scalars that have last been used in a 1004 scalars as JSON "null" values, scalars that have last been used in a
565 string context before encoding as JSON strings and anything else as 1005 string context before encoding as JSON strings, and anything else as
566 number value: 1006 number value:
567 1007
568 # dump as number 1008 # dump as number
569 to_json [2] # yields [2] 1009 encode_json [2] # yields [2]
570 to_json [-3.0e17] # yields [-3e+17] 1010 encode_json [-3.0e17] # yields [-3e+17]
571 my $value = 5; to_json [$value] # yields [5] 1011 my $value = 5; encode_json [$value] # yields [5]
572 1012
573 # used as string, so dump as string 1013 # used as string, so dump as string
574 print $value; 1014 print $value;
575 to_json [$value] # yields ["5"] 1015 encode_json [$value] # yields ["5"]
576 1016
577 # undef becomes null 1017 # undef becomes null
578 to_json [undef] # yields [null] 1018 encode_json [undef] # yields [null]
579 1019
580 You can force the type to be a string by stringifying it: 1020 You can force the type to be a JSON string by stringifying it:
581 1021
582 my $x = 3.1; # some variable containing a number 1022 my $x = 3.1; # some variable containing a number
583 "$x"; # stringified 1023 "$x"; # stringified
584 $x .= ""; # another, more awkward way to stringify 1024 $x .= ""; # another, more awkward way to stringify
585 print $x; # perl does it for you, too, quite often 1025 print $x; # perl does it for you, too, quite often
586 1026
587 You can force the type to be a number by numifying it: 1027 You can force the type to be a JSON number by numifying it:
588 1028
589 my $x = "3"; # some variable containing a string 1029 my $x = "3"; # some variable containing a string
590 $x += 0; # numify it, ensuring it will be dumped as a number 1030 $x += 0; # numify it, ensuring it will be dumped as a number
591 $x *= 1; # same thing, the choise is yours. 1031 $x *= 1; # same thing, the choice is yours.
592 1032
593 You can not currently output JSON booleans or force the type in 1033 You can not currently force the type in other, less obscure, ways.
594 other, less obscure, ways. Tell me if you need this capability. 1034 Tell me if you need this capability (but don't forget to explain why
1035 it's needed :).
595 1036
596COMPARISON 1037 Note that numerical precision has the same meaning as under Perl (so
597 As already mentioned, this module was created because none of the 1038 binary to decimal conversion follows the same rules as in Perl,
598 existing JSON modules could be made to work correctly. First I will 1039 which can differ to other languages). Also, your perl interpreter
599 describe the problems (or pleasures) I encountered with various existing 1040 might expose extensions to the floating point numbers of your
600 JSON modules, followed by some benchmark values. JSON::XS was designed 1041 platform, such as infinities or NaN's - these cannot be represented
601 not to suffer from any of these problems or limitations. 1042 in JSON, and it is an error to pass those in.
602 1043
603 JSON 1.07 1044 OBJECT SERIALISATION
604 Slow (but very portable, as it is written in pure Perl). 1045 As JSON cannot directly represent Perl objects, you have to choose
1046 between a pure JSON representation (without the ability to deserialise
1047 the object automatically again), and a nonstandard extension to the JSON
1048 syntax, tagged values.
605 1049
606 Undocumented/buggy Unicode handling (how JSON handles unicode values 1050 SERIALISATION
607 is undocumented. One can get far by feeding it unicode strings and 1051 What happens when "JSON::XS" encounters a Perl object depends on the
608 doing en-/decoding oneself, but unicode escapes are not working 1052 "allow_blessed", "convert_blessed" and "allow_tags" settings, which are
1053 used in this order:
1054
1055 1. "allow_tags" is enabled and the object has a "FREEZE" method.
1056 In this case, "JSON::XS" uses the Types::Serialiser object
1057 serialisation protocol to create a tagged JSON value, using a
1058 nonstandard extension to the JSON syntax.
1059
1060 This works by invoking the "FREEZE" method on the object, with the
1061 first argument being the object to serialise, and the second
1062 argument being the constant string "JSON" to distinguish it from
1063 other serialisers.
1064
1065 The "FREEZE" method can return any number of values (i.e. zero or
1066 more). These values and the paclkage/classname of the object will
1067 then be encoded as a tagged JSON value in the following format:
1068
1069 ("classname")[FREEZE return values...]
1070
1071 e.g.:
1072
1073 ("URI")["http://www.google.com/"]
1074 ("MyDate")[2013,10,29]
1075 ("ImageData::JPEG")["Z3...VlCg=="]
1076
1077 For example, the hypothetical "My::Object" "FREEZE" method might use
1078 the objects "type" and "id" members to encode the object:
1079
1080 sub My::Object::FREEZE {
1081 my ($self, $serialiser) = @_;
1082
1083 ($self->{type}, $self->{id})
1084 }
1085
1086 2. "convert_blessed" is enabled and the object has a "TO_JSON" method.
1087 In this case, the "TO_JSON" method of the object is invoked in
1088 scalar context. It must return a single scalar that can be directly
1089 encoded into JSON. This scalar replaces the object in the JSON text.
1090
1091 For example, the following "TO_JSON" method will convert all URI
1092 objects to JSON strings when serialised. The fatc that these values
1093 originally were URI objects is lost.
1094
1095 sub URI::TO_JSON {
1096 my ($uri) = @_;
1097 $uri->as_string
1098 }
1099
1100 3. "allow_blessed" is enabled.
1101 The object will be serialised as a JSON null value.
1102
1103 4. none of the above
1104 If none of the settings are enabled or the respective methods are
1105 missing, "JSON::XS" throws an exception.
1106
1107 DESERIALISATION
1108 For deserialisation there are only two cases to consider: either
1109 nonstandard tagging was used, in which case "allow_tags" decides, or
1110 objects cannot be automatically be deserialised, in which case you can
1111 use postprocessing or the "filter_json_object" or
1112 "filter_json_single_key_object" callbacks to get some real objects our
1113 of your JSON.
1114
1115 This section only considers the tagged value case: I a tagged JSON
1116 object is encountered during decoding and "allow_tags" is disabled, a
1117 parse error will result (as if tagged values were not part of the
1118 grammar).
1119
1120 If "allow_tags" is enabled, "JSON::XS" will look up the "THAW" method of
1121 the package/classname used during serialisation (it will not attempt to
1122 load the package as a Perl module). If there is no such method, the
1123 decoding will fail with an error.
1124
1125 Otherwise, the "THAW" method is invoked with the classname as first
1126 argument, the constant string "JSON" as second argument, and all the
1127 values from the JSON array (the values originally returned by the
1128 "FREEZE" method) as remaining arguments.
1129
1130 The method must then return the object. While technically you can return
1131 any Perl scalar, you might have to enable the "enable_nonref" setting to
1132 make that work in all cases, so better return an actual blessed
1133 reference.
1134
1135 As an example, let's implement a "THAW" function that regenerates the
1136 "My::Object" from the "FREEZE" example earlier:
1137
1138 sub My::Object::THAW {
1139 my ($class, $serialiser, $type, $id) = @_;
1140
1141 $class->new (type => $type, id => $id)
1142 }
1143
1144ENCODING/CODESET FLAG NOTES
1145 The interested reader might have seen a number of flags that signify
1146 encodings or codesets - "utf8", "latin1" and "ascii". There seems to be
1147 some confusion on what these do, so here is a short comparison:
1148
1149 "utf8" controls whether the JSON text created by "encode" (and expected
1150 by "decode") is UTF-8 encoded or not, while "latin1" and "ascii" only
1151 control whether "encode" escapes character values outside their
1152 respective codeset range. Neither of these flags conflict with each
1153 other, although some combinations make less sense than others.
1154
1155 Care has been taken to make all flags symmetrical with respect to
1156 "encode" and "decode", that is, texts encoded with any combination of
1157 these flag values will be correctly decoded when the same flags are used
1158 - in general, if you use different flag settings while encoding vs. when
1159 decoding you likely have a bug somewhere.
1160
1161 Below comes a verbose discussion of these flags. Note that a "codeset"
1162 is simply an abstract set of character-codepoint pairs, while an
1163 encoding takes those codepoint numbers and *encodes* them, in our case
1164 into octets. Unicode is (among other things) a codeset, UTF-8 is an
1165 encoding, and ISO-8859-1 (= latin 1) and ASCII are both codesets *and*
1166 encodings at the same time, which can be confusing.
1167
1168 "utf8" flag disabled
1169 When "utf8" is disabled (the default), then "encode"/"decode"
1170 generate and expect Unicode strings, that is, characters with high
1171 ordinal Unicode values (> 255) will be encoded as such characters,
1172 and likewise such characters are decoded as-is, no changes to them
1173 will be done, except "(re-)interpreting" them as Unicode codepoints
1174 or Unicode characters, respectively (to Perl, these are the same
1175 thing in strings unless you do funny/weird/dumb stuff).
1176
1177 This is useful when you want to do the encoding yourself (e.g. when
1178 you want to have UTF-16 encoded JSON texts) or when some other layer
1179 does the encoding for you (for example, when printing to a terminal
1180 using a filehandle that transparently encodes to UTF-8 you certainly
1181 do NOT want to UTF-8 encode your data first and have Perl encode it
1182 another time).
1183
1184 "utf8" flag enabled
1185 If the "utf8"-flag is enabled, "encode"/"decode" will encode all
1186 characters using the corresponding UTF-8 multi-byte sequence, and
1187 will expect your input strings to be encoded as UTF-8, that is, no
1188 "character" of the input string must have any value > 255, as UTF-8
1189 does not allow that.
1190
1191 The "utf8" flag therefore switches between two modes: disabled means
1192 you will get a Unicode string in Perl, enabled means you get a UTF-8
1193 encoded octet/binary string in Perl.
1194
1195 "latin1" or "ascii" flags enabled
1196 With "latin1" (or "ascii") enabled, "encode" will escape characters
1197 with ordinal values > 255 (> 127 with "ascii") and encode the
1198 remaining characters as specified by the "utf8" flag.
1199
1200 If "utf8" is disabled, then the result is also correctly encoded in
1201 those character sets (as both are proper subsets of Unicode, meaning
1202 that a Unicode string with all character values < 256 is the same
1203 thing as a ISO-8859-1 string, and a Unicode string with all
1204 character values < 128 is the same thing as an ASCII string in
609 properly). 1205 Perl).
610 1206
611 No roundtripping (strings get clobbered if they look like numbers, 1207 If "utf8" is enabled, you still get a correct UTF-8-encoded string,
612 e.g. the string 2.0 will encode to 2.0 instead of "2.0", and that 1208 regardless of these flags, just some more characters will be escaped
613 will decode into the number 2. 1209 using "\uXXXX" then before.
614 1210
615 JSON::PC 0.01 1211 Note that ISO-8859-1-*encoded* strings are not compatible with UTF-8
616 Very fast. 1212 encoding, while ASCII-encoded strings are. That is because the
1213 ISO-8859-1 encoding is NOT a subset of UTF-8 (despite the ISO-8859-1
1214 *codeset* being a subset of Unicode), while ASCII is.
617 1215
618 Undocumented/buggy Unicode handling. 1216 Surprisingly, "decode" will ignore these flags and so treat all
1217 input values as governed by the "utf8" flag. If it is disabled, this
1218 allows you to decode ISO-8859-1- and ASCII-encoded strings, as both
1219 strict subsets of Unicode. If it is enabled, you can correctly
1220 decode UTF-8 encoded strings.
619 1221
620 No roundtripping. 1222 So neither "latin1" nor "ascii" are incompatible with the "utf8"
1223 flag - they only govern when the JSON output engine escapes a
1224 character or not.
621 1225
622 Has problems handling many Perl values (e.g. regex results and other 1226 The main use for "latin1" is to relatively efficiently store binary
623 magic values will make it croak). 1227 data as JSON, at the expense of breaking compatibility with most
1228 JSON decoders.
624 1229
625 Does not even generate valid JSON ("{1,2}" gets converted to "{1:2}" 1230 The main use for "ascii" is to force the output to not contain
626 which is not a valid JSON text. 1231 characters with values > 127, which means you can interpret the
1232 resulting string as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about
1233 any character set and 8-bit-encoding, and still get the same data
1234 structure back. This is useful when your channel for JSON transfer
1235 is not 8-bit clean or the encoding might be mangled in between (e.g.
1236 in mail), and works because ASCII is a proper subset of most 8-bit
1237 and multibyte encodings in use in the world.
627 1238
628 Unmaintained (maintainer unresponsive for many months, bugs are not 1239 JSON and ECMAscript
629 getting fixed). 1240 JSON syntax is based on how literals are represented in javascript (the
1241 not-standardised predecessor of ECMAscript) which is presumably why it
1242 is called "JavaScript Object Notation".
630 1243
631 JSON::Syck 0.21 1244 However, JSON is not a subset (and also not a superset of course) of
632 Very buggy (often crashes). 1245 ECMAscript (the standard) or javascript (whatever browsers actually
1246 implement).
633 1247
634 Very inflexible (no human-readable format supported, format pretty 1248 If you want to use javascript's "eval" function to "parse" JSON, you
635 much undocumented. I need at least a format for easy reading by 1249 might run into parse errors for valid JSON texts, or the resulting data
636 humans and a single-line compact format for use in a protocol, and 1250 structure might not be queryable:
637 preferably a way to generate ASCII-only JSON texts).
638 1251
639 Completely broken (and confusingly documented) Unicode handling 1252 One of the problems is that U+2028 and U+2029 are valid characters
640 (unicode escapes are not working properly, you need to set 1253 inside JSON strings, but are not allowed in ECMAscript string literals,
641 ImplicitUnicode to *different* values on en- and decoding to get 1254 so the following Perl fragment will not output something that can be
642 symmetric behaviour). 1255 guaranteed to be parsable by javascript's "eval":
643 1256
644 No roundtripping (simple cases work, but this depends on wether the 1257 use JSON::XS;
645 scalar value was used in a numeric context or not).
646 1258
647 Dumping hashes may skip hash values depending on iterator state. 1259 print encode_json [chr 0x2028];
648 1260
649 Unmaintained (maintainer unresponsive for many months, bugs are not 1261 The right fix for this is to use a proper JSON parser in your javascript
650 getting fixed). 1262 programs, and not rely on "eval" (see for example Douglas Crockford's
1263 json2.js parser).
651 1264
652 Does not check input for validity (i.e. will accept non-JSON input 1265 If this is not an option, you can, as a stop-gap measure, simply encode
653 and return "something" instead of raising an exception. This is a 1266 to ASCII-only JSON:
654 security issue: imagine two banks transfering money between each
655 other using JSON. One bank might parse a given non-JSON request and
656 deduct money, while the other might reject the transaction with a
657 syntax error. While a good protocol will at least recover, that is
658 extra unnecessary work and the transaction will still not succeed).
659 1267
660 JSON::DWIW 0.04 1268 use JSON::XS;
661 Very fast. Very natural. Very nice.
662 1269
663 Undocumented unicode handling (but the best of the pack. Unicode 1270 print JSON::XS->new->ascii->encode ([chr 0x2028]);
664 escapes still don't get parsed properly).
665 1271
666 Very inflexible. 1272 Note that this will enlarge the resulting JSON text quite a bit if you
1273 have many non-ASCII characters. You might be tempted to run some regexes
1274 to only escape U+2028 and U+2029, e.g.:
667 1275
668 No roundtripping. 1276 # DO NOT USE THIS!
1277 my $json = JSON::XS->new->utf8->encode ([chr 0x2028]);
1278 $json =~ s/\xe2\x80\xa8/\\u2028/g; # escape U+2028
1279 $json =~ s/\xe2\x80\xa9/\\u2029/g; # escape U+2029
1280 print $json;
669 1281
670 Does not generate valid JSON texts (key strings are often unquoted, 1282 Note that *this is a bad idea*: the above only works for U+2028 and
671 empty keys result in nothing being output) 1283 U+2029 and thus only for fully ECMAscript-compliant parsers. Many
1284 existing javascript implementations, however, have issues with other
1285 characters as well - using "eval" naively simply *will* cause problems.
672 1286
673 Does not check input for validity. 1287 Another problem is that some javascript implementations reserve some
1288 property names for their own purposes (which probably makes them
1289 non-ECMAscript-compliant). For example, Iceweasel reserves the
1290 "__proto__" property name for its own purposes.
1291
1292 If that is a problem, you could parse try to filter the resulting JSON
1293 output for these property strings, e.g.:
1294
1295 $json =~ s/"__proto__"\s*:/"__proto__renamed":/g;
1296
1297 This works because "__proto__" is not valid outside of strings, so every
1298 occurrence of ""__proto__"\s*:" must be a string used as property name.
1299
1300 If you know of other incompatibilities, please let me know.
674 1301
675 JSON and YAML 1302 JSON and YAML
676 You often hear that JSON is a subset (or a close subset) of YAML. This 1303 You often hear that JSON is a subset of YAML. This is, however, a mass
677 is, however, a mass hysteria and very far from the truth. In general, 1304 hysteria(*) and very far from the truth (as of the time of this
678 there is no way to configure JSON::XS to output a data structure as 1305 writing), so let me state it clearly: *in general, there is no way to
679 valid YAML. 1306 configure JSON::XS to output a data structure as valid YAML* that works
1307 in all cases.
680 1308
681 If you really must use JSON::XS to generate YAML, you should use this 1309 If you really must use JSON::XS to generate YAML, you should use this
682 algorithm (subject to change in future versions): 1310 algorithm (subject to change in future versions):
683 1311
684 my $to_yaml = JSON::XS->new->utf8->space_after (1); 1312 my $to_yaml = JSON::XS->new->utf8->space_after (1);
685 my $yaml = $to_yaml->encode ($ref) . "\n"; 1313 my $yaml = $to_yaml->encode ($ref) . "\n";
686 1314
687 This will usually generate JSON texts that also parse as valid YAML. 1315 This will *usually* generate JSON texts that also parse as valid YAML.
688 Please note that YAML has hardcoded limits on (simple) object key 1316 Please note that YAML has hardcoded limits on (simple) object key
689 lengths that JSON doesn't have, so you should make sure that your hash 1317 lengths that JSON doesn't have and also has different and incompatible
1318 unicode character escape syntax, so you should make sure that your hash
690 keys are noticably shorter than the 1024 characters YAML allows. 1319 keys are noticeably shorter than the 1024 "stream characters" YAML
1320 allows and that you do not have characters with codepoint values outside
1321 the Unicode BMP (basic multilingual page). YAML also does not allow "\/"
1322 sequences in strings (which JSON::XS does not *currently* generate, but
1323 other JSON generators might).
691 1324
692 There might be other incompatibilities that I am not aware of. In 1325 There might be other incompatibilities that I am not aware of (or the
1326 YAML specification has been changed yet again - it does so quite often).
693 general you should not try to generate YAML with a JSON generator or 1327 In general you should not try to generate YAML with a JSON generator or
694 vice versa, or try to parse JSON with a YAML parser or vice versa: 1328 vice versa, or try to parse JSON with a YAML parser or vice versa:
695 chances are high that you will run into severe interoperability 1329 chances are high that you will run into severe interoperability problems
696 problems. 1330 when you least expect it.
1331
1332 (*) I have been pressured multiple times by Brian Ingerson (one of the
1333 authors of the YAML specification) to remove this paragraph, despite
1334 him acknowledging that the actual incompatibilities exist. As I was
1335 personally bitten by this "JSON is YAML" lie, I refused and said I
1336 will continue to educate people about these issues, so others do not
1337 run into the same problem again and again. After this, Brian called
1338 me a (quote)*complete and worthless idiot*(unquote).
1339
1340 In my opinion, instead of pressuring and insulting people who
1341 actually clarify issues with YAML and the wrong statements of some
1342 of its proponents, I would kindly suggest reading the JSON spec
1343 (which is not that difficult or long) and finally make YAML
1344 compatible to it, and educating users about the changes, instead of
1345 spreading lies about the real compatibility for many *years* and
1346 trying to silence people who point out that it isn't true.
1347
1348 Addendum/2009: the YAML 1.2 spec is still incompatible with JSON,
1349 even though the incompatibilities have been documented (and are
1350 known to Brian) for many years and the spec makes explicit claims
1351 that YAML is a superset of JSON. It would be so easy to fix, but
1352 apparently, bullying people and corrupting userdata is so much
1353 easier.
697 1354
698 SPEED 1355 SPEED
699 It seems that JSON::XS is surprisingly fast, as shown in the following 1356 It seems that JSON::XS is surprisingly fast, as shown in the following
700 tables. They have been generated with the help of the "eg/bench" program 1357 tables. They have been generated with the help of the "eg/bench" program
701 in the JSON::XS distribution, to make it easy to compare on your own 1358 in the JSON::XS distribution, to make it easy to compare on your own
702 system. 1359 system.
703 1360
704 First comes a comparison between various modules using a very short 1361 First comes a comparison between various modules using a very short
705 single-line JSON string: 1362 single-line JSON string (also available at
1363 <http://dist.schmorp.de/misc/json/short.json>).
706 1364
707 {"method": "handleMessage", "params": ["user1", "we were just talking"], \ 1365 {"method": "handleMessage", "params": ["user1",
708 "id": null, "array":[1,11,234,-5,1e5,1e7, true, false]} 1366 "we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7,
1367 1, 0]}
709 1368
710 It shows the number of encodes/decodes per second (JSON::XS uses the 1369 It shows the number of encodes/decodes per second (JSON::XS uses the
711 functional interface, while JSON::XS/2 uses the OO interface with 1370 functional interface, while JSON::XS/2 uses the OO interface with
712 pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink). 1371 pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink.
713 Higher is better: 1372 JSON::DWIW/DS uses the deserialise function, while JSON::DWIW::FJ uses
1373 the from_json method). Higher is better:
714 1374
715 Storable | 15779.925 | 14169.946 |
716 -----------+------------+------------+
717 module | encode | decode | 1375 module | encode | decode |
718 -----------|------------|------------| 1376 --------------|------------|------------|
719 JSON | 4990.842 | 4088.813 | 1377 JSON::DWIW/DS | 86302.551 | 102300.098 |
720 JSON::DWIW | 51653.990 | 71575.154 | 1378 JSON::DWIW/FJ | 86302.551 | 75983.768 |
721 JSON::PC | 65948.176 | 74631.744 | 1379 JSON::PP | 15827.562 | 6638.658 |
722 JSON::PP | 8931.652 | 3817.168 | 1380 JSON::Syck | 63358.066 | 47662.545 |
723 JSON::Syck | 24877.248 | 27776.848 | 1381 JSON::XS | 511500.488 | 511500.488 |
724 JSON::XS | 388361.481 | 227951.304 | 1382 JSON::XS/2 | 291271.111 | 388361.481 |
725 JSON::XS/2 | 227951.304 | 218453.333 | 1383 JSON::XS/3 | 361577.931 | 361577.931 |
726 JSON::XS/3 | 338250.323 | 218453.333 | 1384 Storable | 66788.280 | 265462.278 |
727 Storable | 16500.016 | 135300.129 |
728 -----------+------------+------------+ 1385 --------------+------------+------------+
729 1386
730 That is, JSON::XS is about five times faster than JSON::DWIW on 1387 That is, JSON::XS is almost six times faster than JSON::DWIW on
731 encoding, about three times faster on decoding, and over fourty times 1388 encoding, about five times faster on decoding, and over thirty to
732 faster than JSON, even with pretty-printing and key sorting. It also 1389 seventy times faster than JSON's pure perl implementation. It also
733 compares favourably to Storable for small amounts of data. 1390 compares favourably to Storable for small amounts of data.
734 1391
735 Using a longer test string (roughly 18KB, generated from Yahoo! Locals 1392 Using a longer test string (roughly 18KB, generated from Yahoo! Locals
736 search API (http://nanoref.com/yahooapis/mgPdGg): 1393 search API (<http://dist.schmorp.de/misc/json/long.json>).
737 1394
738 module | encode | decode | 1395 module | encode | decode |
739 -----------|------------|------------| 1396 --------------|------------|------------|
740 JSON | 55.260 | 34.971 | 1397 JSON::DWIW/DS | 1647.927 | 2673.916 |
741 JSON::DWIW | 825.228 | 1082.513 | 1398 JSON::DWIW/FJ | 1630.249 | 2596.128 |
742 JSON::PC | 3571.444 | 2394.829 |
743 JSON::PP | 210.987 | 32.574 | 1399 JSON::PP | 400.640 | 62.311 |
744 JSON::Syck | 552.551 | 787.544 | 1400 JSON::Syck | 1481.040 | 1524.869 |
745 JSON::XS | 5780.463 | 4854.519 | 1401 JSON::XS | 20661.596 | 9541.183 |
746 JSON::XS/2 | 3869.998 | 4798.975 | 1402 JSON::XS/2 | 10683.403 | 9416.938 |
747 JSON::XS/3 | 5862.880 | 4798.975 | 1403 JSON::XS/3 | 20661.596 | 9400.054 |
748 Storable | 4445.002 | 5235.027 | 1404 Storable | 19765.806 | 10000.725 |
749 -----------+------------+------------+ 1405 --------------+------------+------------+
750 1406
751 Again, JSON::XS leads by far (except for Storable which non-surprisingly 1407 Again, JSON::XS leads by far (except for Storable which non-surprisingly
752 decodes faster). 1408 decodes a bit faster).
753 1409
754 On large strings containing lots of high unicode characters, some 1410 On large strings containing lots of high Unicode characters, some
755 modules (such as JSON::PC) seem to decode faster than JSON::XS, but the 1411 modules (such as JSON::PC) seem to decode faster than JSON::XS, but the
756 result will be broken due to missing (or wrong) unicode handling. Others 1412 result will be broken due to missing (or wrong) Unicode handling. Others
757 refuse to decode or encode properly, so it was impossible to prepare a 1413 refuse to decode or encode properly, so it was impossible to prepare a
758 fair comparison table for that case. 1414 fair comparison table for that case.
759 1415
760SECURITY CONSIDERATIONS 1416SECURITY CONSIDERATIONS
761 When you are using JSON in a protocol, talking to untrusted potentially 1417 When you are using JSON in a protocol, talking to untrusted potentially
… …
765 have any buffer overflows. Obviously, this module should ensure that and 1421 have any buffer overflows. Obviously, this module should ensure that and
766 I am trying hard on making that true, but you never know. 1422 I am trying hard on making that true, but you never know.
767 1423
768 Second, you need to avoid resource-starving attacks. That means you 1424 Second, you need to avoid resource-starving attacks. That means you
769 should limit the size of JSON texts you accept, or make sure then when 1425 should limit the size of JSON texts you accept, or make sure then when
770 your resources run out, thats just fine (e.g. by using a separate 1426 your resources run out, that's just fine (e.g. by using a separate
771 process that can crash safely). The size of a JSON text in octets or 1427 process that can crash safely). The size of a JSON text in octets or
772 characters is usually a good indication of the size of the resources 1428 characters is usually a good indication of the size of the resources
773 required to decode it into a Perl structure. While JSON::XS can check 1429 required to decode it into a Perl structure. While JSON::XS can check
774 the size of the JSON text, it might be too late when you already have it 1430 the size of the JSON text, it might be too late when you already have it
775 in memory, so you might want to check the size before you accept the 1431 in memory, so you might want to check the size before you accept the
… …
778 Third, JSON::XS recurses using the C stack when decoding objects and 1434 Third, JSON::XS recurses using the C stack when decoding objects and
779 arrays. The C stack is a limited resource: for instance, on my amd64 1435 arrays. The C stack is a limited resource: for instance, on my amd64
780 machine with 8MB of stack size I can decode around 180k nested arrays 1436 machine with 8MB of stack size I can decode around 180k nested arrays
781 but only 14k nested JSON objects (due to perl itself recursing deeply on 1437 but only 14k nested JSON objects (due to perl itself recursing deeply on
782 croak to free the temporary). If that is exceeded, the program crashes. 1438 croak to free the temporary). If that is exceeded, the program crashes.
783 to be conservative, the default nesting limit is set to 512. If your 1439 To be conservative, the default nesting limit is set to 512. If your
784 process has a smaller stack, you should adjust this setting accordingly 1440 process has a smaller stack, you should adjust this setting accordingly
785 with the "max_depth" method. 1441 with the "max_depth" method.
786 1442
787 And last but least, something else could bomb you that I forgot to think 1443 Something else could bomb you, too, that I forgot to think of. In that
788 of. In that case, you get to keep the pieces. I am always open for 1444 case, you get to keep the pieces. I am always open for hints, though...
789 hints, though...
790 1445
1446 Also keep in mind that JSON::XS might leak contents of your Perl data
1447 structures in its error messages, so when you serialise sensitive
1448 information you might want to make sure that exceptions thrown by
1449 JSON::XS will not end up in front of untrusted eyes.
1450
791 If you are using JSON::XS to return packets to consumption by javascript 1451 If you are using JSON::XS to return packets to consumption by JavaScript
792 scripts in a browser you should have a look at 1452 scripts in a browser you should have a look at
793 <http://jpsykes.com/47/practical-csrf-and-json-security> to see wether 1453 <http://blog.archive.jpsykes.com/47/practical-csrf-and-json-security/>
794 you are vulnerable to some common attack vectors (which really are 1454 to see whether you are vulnerable to some common attack vectors (which
795 browser design bugs, but it is still you who will have to deal with it, 1455 really are browser design bugs, but it is still you who will have to
796 as major browser developers care only for features, not about doing 1456 deal with it, as major browser developers care only for features, not
797 security right). 1457 about getting security right).
1458
1459 "OLD" VS. "NEW" JSON (RFC4627 VS. RFC7159)
1460 JSON originally required JSON texts to represent an array or object -
1461 scalar values were explicitly not allowed. This has changed, and
1462 versions of JSON::XS beginning with 4.0 reflect this by allowing scalar
1463 values by default.
1464
1465 One reason why one might not want this is that this removes a
1466 fundamental property of JSON texts, namely that they are self-delimited
1467 and self-contained, or in other words, you could take any number of
1468 "old" JSON texts and paste them together, and the result would be
1469 unambiguously parseable:
1470
1471 [1,3]{"k":5}[][null] # four JSON texts, without doubt
1472
1473 By allowing scalars, this property is lost: in the following example, is
1474 this one JSON text (the number 12) or two JSON texts (the numbers 1 and
1475 2):
1476
1477 12 # could be 12, or 1 and 2
1478
1479 Another lost property of "old" JSON is that no lookahead is required to
1480 know the end of a JSON text, i.e. the JSON text definitely ended at the
1481 last "]" or "}" character, there was no need to read extra characters.
1482
1483 For example, a viable network protocol with "old" JSON was to simply
1484 exchange JSON texts without delimiter. For "new" JSON, you have to use a
1485 suitable delimiter (such as a newline) after every JSON text or ensure
1486 you never encode/decode scalar values.
1487
1488 Most protocols do work by only transferring arrays or objects, and the
1489 easiest way to avoid problems with the "new" JSON definition is to
1490 explicitly disallow scalar values in your encoder and decoder:
1491
1492 $json_coder = JSON::XS->new->allow_nonref (0)
1493
1494 This is a somewhat unhappy situation, and the blame can fully be put on
1495 JSON's inmventor, Douglas Crockford, who unilaterally changed the format
1496 in 2006 without consulting the IETF, forcing the IETF to either fork the
1497 format or go with it (as I was told, the IETF wasn't amused).
1498
1499RELATIONSHIP WITH I-JSON
1500 JSON is a somewhat sloppily-defined format - it carries around obvious
1501 Javascript baggage, such as not really defining number range, probably
1502 because Javascript only has one type of numbers: IEEE 64 bit floats
1503 ("binary64").
1504
1505 For this reaosn, RFC7493 defines "Internet JSON", which is a restricted
1506 subset of JSON that is supposedly more interoperable on the internet.
1507
1508 While "JSON::XS" does not offer specific support for I-JSON, it of
1509 course accepts valid I-JSON and by default implements some of the
1510 limitations of I-JSON, such as parsing numbers as perl numbers, which
1511 are usually a superset of binary64 numbers.
1512
1513 To generate I-JSON, follow these rules:
1514
1515 * always generate UTF-8
1516
1517 I-JSON must be encoded in UTF-8, the default for "encode_json".
1518
1519 * numbers should be within IEEE 754 binary64 range
1520
1521 Basically all existing perl installations use binary64 to represent
1522 floating point numbers, so all you need to do is to avoid large
1523 integers.
1524
1525 * objects must not have duplicate keys
1526
1527 This is trivially done, as "JSON::XS" does not allow duplicate keys.
1528
1529 * do not generate scalar JSON texts, use "->allow_nonref (0)"
1530
1531 I-JSON strongly requests you to only encode arrays and objects into
1532 JSON.
1533
1534 * times should be strings in ISO 8601 format
1535
1536 There are a myriad of modules on CPAN dealing with ISO 8601 - search
1537 for "ISO8601" on CPAN and use one.
1538
1539 * encode binary data as base64
1540
1541 While it's tempting to just dump binary data as a string (and let
1542 "JSON::XS" do the escaping), for I-JSON, it's *recommended* to
1543 encode binary data as base64.
1544
1545 There are some other considerations - read RFC7493 for the details if
1546 interested.
1547
1548INTEROPERABILITY WITH OTHER MODULES
1549 "JSON::XS" uses the Types::Serialiser module to provide boolean
1550 constants. That means that the JSON true and false values will be
1551 comaptible to true and false values of other modules that do the same,
1552 such as JSON::PP and CBOR::XS.
1553
1554INTEROPERABILITY WITH OTHER JSON DECODERS
1555 As long as you only serialise data that can be directly expressed in
1556 JSON, "JSON::XS" is incapable of generating invalid JSON output (modulo
1557 bugs, but "JSON::XS" has found more bugs in the official JSON testsuite
1558 (1) than the official JSON testsuite has found in "JSON::XS" (0)).
1559
1560 When you have trouble decoding JSON generated by this module using other
1561 decoders, then it is very likely that you have an encoding mismatch or
1562 the other decoder is broken.
1563
1564 When decoding, "JSON::XS" is strict by default and will likely catch all
1565 errors. There are currently two settings that change this: "relaxed"
1566 makes "JSON::XS" accept (but not generate) some non-standard extensions,
1567 and "allow_tags" will allow you to encode and decode Perl objects, at
1568 the cost of not outputting valid JSON anymore.
1569
1570 TAGGED VALUE SYNTAX AND STANDARD JSON EN/DECODERS
1571 When you use "allow_tags" to use the extended (and also nonstandard and
1572 invalid) JSON syntax for serialised objects, and you still want to
1573 decode the generated When you want to serialise objects, you can run a
1574 regex to replace the tagged syntax by standard JSON arrays (it only
1575 works for "normal" package names without comma, newlines or single
1576 colons). First, the readable Perl version:
1577
1578 # if your FREEZE methods return no values, you need this replace first:
1579 $json =~ s/\( \s* (" (?: [^\\":,]+|\\.|::)* ") \s* \) \s* \[\s*\]/[$1]/gx;
1580
1581 # this works for non-empty constructor arg lists:
1582 $json =~ s/\( \s* (" (?: [^\\":,]+|\\.|::)* ") \s* \) \s* \[/[$1,/gx;
1583
1584 And here is a less readable version that is easy to adapt to other
1585 languages:
1586
1587 $json =~ s/\(\s*("([^\\":,]+|\\.|::)*")\s*\)\s*\[/[$1,/g;
1588
1589 Here is an ECMAScript version (same regex):
1590
1591 json = json.replace (/\(\s*("([^\\":,]+|\\.|::)*")\s*\)\s*\[/g, "[$1,");
1592
1593 Since this syntax converts to standard JSON arrays, it might be hard to
1594 distinguish serialised objects from normal arrays. You can prepend a
1595 "magic number" as first array element to reduce chances of a collision:
1596
1597 $json =~ s/\(\s*("([^\\":,]+|\\.|::)*")\s*\)\s*\[/["XU1peReLzT4ggEllLanBYq4G9VzliwKF",$1,/g;
1598
1599 And after decoding the JSON text, you could walk the data structure
1600 looking for arrays with a first element of
1601 "XU1peReLzT4ggEllLanBYq4G9VzliwKF".
1602
1603 The same approach can be used to create the tagged format with another
1604 encoder. First, you create an array with the magic string as first
1605 member, the classname as second, and constructor arguments last, encode
1606 it as part of your JSON structure, and then:
1607
1608 $json =~ s/\[\s*"XU1peReLzT4ggEllLanBYq4G9VzliwKF"\s*,\s*("([^\\":,]+|\\.|::)*")\s*,/($1)[/g;
1609
1610 Again, this has some limitations - the magic string must not be encoded
1611 with character escapes, and the constructor arguments must be non-empty.
1612
1613(I-)THREADS
1614 This module is *not* guaranteed to be ithread (or MULTIPLICITY-) safe
1615 and there are no plans to change this. Note that perl's builtin
1616 so-called threads/ithreads are officially deprecated and should not be
1617 used.
1618
1619THE PERILS OF SETLOCALE
1620 Sometimes people avoid the Perl locale support and directly call the
1621 system's setlocale function with "LC_ALL".
1622
1623 This breaks both perl and modules such as JSON::XS, as stringification
1624 of numbers no longer works correctly (e.g. "$x = 0.1; print "$x"+1"
1625 might print 1, and JSON::XS might output illegal JSON as JSON::XS relies
1626 on perl to stringify numbers).
1627
1628 The solution is simple: don't call "setlocale", or use it for only those
1629 categories you need, such as "LC_MESSAGES" or "LC_CTYPE".
1630
1631 If you need "LC_NUMERIC", you should enable it only around the code that
1632 actually needs it (avoiding stringification of numbers), and restore it
1633 afterwards.
1634
1635SOME HISTORY
1636 At the time this module was created there already were a number of JSON
1637 modules available on CPAN, so what was the reason to write yet another
1638 JSON module? While it seems there are many JSON modules, none of them
1639 correctly handled all corner cases, and in most cases their maintainers
1640 are unresponsive, gone missing, or not listening to bug reports for
1641 other reasons.
1642
1643 Beginning with version 2.0 of the JSON module, when both JSON and
1644 JSON::XS are installed, then JSON will fall back on JSON::XS (this can
1645 be overridden) with no overhead due to emulation (by inheriting
1646 constructor and methods). If JSON::XS is not available, it will fall
1647 back to the compatible JSON::PP module as backend, so using JSON instead
1648 of JSON::XS gives you a portable JSON API that can be fast when you need
1649 it and doesn't require a C compiler when that is a problem.
1650
1651 Somewhere around version 3, this module was forked into
1652 "Cpanel::JSON::XS", because its maintainer had serious trouble
1653 understanding JSON and insisted on a fork with many bugs "fixed" that
1654 weren't actually bugs, while spreading FUD about this module without
1655 actually giving any details on his accusations. You be the judge, but in
1656 my personal opinion, if you want quality, you will stay away from
1657 dangerous forks like that.
798 1658
799BUGS 1659BUGS
800 While the goal of this module is to be correct, that unfortunately does 1660 While the goal of this module is to be correct, that unfortunately does
801 not mean its bug-free, only that I think its design is bug-free. It is 1661 not mean it's bug-free, only that I think its design is bug-free. If you
802 still relatively early in its development. If you keep reporting bugs
803 they will be fixed swiftly, though. 1662 keep reporting bugs they will be fixed swiftly, though.
1663
1664 Please refrain from using rt.cpan.org or any other bug reporting
1665 service. I put the contact address into my modules for a reason.
1666
1667SEE ALSO
1668 The json_xs command line utility for quick experiments.
804 1669
805AUTHOR 1670AUTHOR
806 Marc Lehmann <schmorp@schmorp.de> 1671 Marc Lehmann <schmorp@schmorp.de>
807 http://home.schmorp.de/ 1672 http://home.schmorp.de/
808 1673

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