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1NAME 1NAME
2 JSON::XS - JSON serialising/deserialising, done correctly and fast 2 JSON::XS - JSON serialising/deserialising, done correctly and fast
3 3
4 JSON::XS - 正しくて高速な JSON シリアライザ/デシリアライザ
5 (http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html)
6
4SYNOPSIS 7SYNOPSIS
5 use JSON::XS; 8 use JSON::XS;
6 9
7 # exported functions, they croak on error 10 # exported functions, they croak on error
8 # and expect/generate UTF-8 11 # and expect/generate UTF-8
9 12
10 $utf8_encoded_json_text = to_json $perl_hash_or_arrayref; 13 $utf8_encoded_json_text = encode_json $perl_hash_or_arrayref;
11 $perl_hash_or_arrayref = from_json $utf8_encoded_json_text; 14 $perl_hash_or_arrayref = decode_json $utf8_encoded_json_text;
12 15
13 # OO-interface 16 # OO-interface
14 17
15 $coder = JSON::XS->new->ascii->pretty->allow_nonref; 18 $coder = JSON::XS->new->ascii->pretty->allow_nonref;
16 $pretty_printed_unencoded = $coder->encode ($perl_scalar); 19 $pretty_printed_unencoded = $coder->encode ($perl_scalar);
17 $perl_scalar = $coder->decode ($unicode_json_text); 20 $perl_scalar = $coder->decode ($unicode_json_text);
21
22 # Note that JSON version 2.0 and above will automatically use JSON::XS
23 # if available, at virtually no speed overhead either, so you should
24 # be able to just:
25
26 use JSON;
27
28 # and do the same things, except that you have a pure-perl fallback now.
18 29
19DESCRIPTION 30DESCRIPTION
20 This module converts Perl data structures to JSON and vice versa. Its 31 This module converts Perl data structures to JSON and vice versa. Its
21 primary goal is to be *correct* and its secondary goal is to be *fast*. 32 primary goal is to be *correct* and its secondary goal is to be *fast*.
22 To reach the latter goal it was written in C. 33 To reach the latter goal it was written in C.
34
35 Beginning with version 2.0 of the JSON module, when both JSON and
36 JSON::XS are installed, then JSON will fall back on JSON::XS (this can
37 be overridden) with no overhead due to emulation (by inheriting
38 constructor and methods). If JSON::XS is not available, it will fall
39 back to the compatible JSON::PP module as backend, so using JSON instead
40 of JSON::XS gives you a portable JSON API that can be fast when you need
41 and doesn't require a C compiler when that is a problem.
23 42
24 As this is the n-th-something JSON module on CPAN, what was the reason 43 As this is the n-th-something JSON module on CPAN, what was the reason
25 to write yet another JSON module? While it seems there are many JSON 44 to write yet another JSON module? While it seems there are many JSON
26 modules, none of them correctly handle all corner cases, and in most 45 modules, none of them correctly handle all corner cases, and in most
27 cases their maintainers are unresponsive, gone missing, or not listening 46 cases their maintainers are unresponsive, gone missing, or not listening
28 to bug reports for other reasons. 47 to bug reports for other reasons.
29 48
30 See COMPARISON, below, for a comparison to some other JSON modules.
31
32 See MAPPING, below, on how JSON::XS maps perl values to JSON values and 49 See MAPPING, below, on how JSON::XS maps perl values to JSON values and
33 vice versa. 50 vice versa.
34 51
35 FEATURES 52 FEATURES
36 * correct unicode handling 53 * correct Unicode handling
54
37 This module knows how to handle Unicode, and even documents how and 55 This module knows how to handle Unicode, documents how and when it
38 when it does so. 56 does so, and even documents what "correct" means.
39 57
40 * round-trip integrity 58 * round-trip integrity
59
41 When you serialise a perl data structure using only datatypes 60 When you serialise a perl data structure using only data types
42 supported by JSON, the deserialised data structure is identical on 61 supported by JSON, the deserialised data structure is identical on
43 the Perl level. (e.g. the string "2.0" doesn't suddenly become "2" 62 the Perl level. (e.g. the string "2.0" doesn't suddenly become "2"
44 just because it looks like a number). 63 just because it looks like a number). There minor *are* exceptions
64 to this, read the MAPPING section below to learn about those.
45 65
46 * strict checking of JSON correctness 66 * strict checking of JSON correctness
67
47 There is no guessing, no generating of illegal JSON texts by 68 There is no guessing, no generating of illegal JSON texts by
48 default, and only JSON is accepted as input by default (the latter 69 default, and only JSON is accepted as input by default (the latter
49 is a security feature). 70 is a security feature).
50 71
51 * fast 72 * fast
52 Compared to other JSON modules, this module compares favourably in
53 terms of speed, too.
54 73
74 Compared to other JSON modules and other serialisers such as
75 Storable, this module usually compares favourably in terms of speed,
76 too.
77
55 * simple to use 78 * simple to use
79
56 This module has both a simple functional interface as well as an OO 80 This module has both a simple functional interface as well as an
57 interface. 81 object oriented interface interface.
58 82
59 * reasonably versatile output formats 83 * reasonably versatile output formats
84
60 You can choose between the most compact guarenteed single-line 85 You can choose between the most compact guaranteed-single-line
61 format possible (nice for simple line-based protocols), a pure-ascii 86 format possible (nice for simple line-based protocols), a pure-ASCII
62 format (for when your transport is not 8-bit clean, still supports 87 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 88 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 89 want to read that stuff). Or you can combine those features in
65 whatever way you like. 90 whatever way you like.
66 91
67FUNCTIONAL INTERFACE 92FUNCTIONAL INTERFACE
68 The following convinience methods are provided by this module. They are 93 The following convenience methods are provided by this module. They are
69 exported by default: 94 exported by default:
70 95
71 $json_text = to_json $perl_scalar 96 $json_text = encode_json $perl_scalar
72 Converts the given Perl data structure (a simple scalar or a 97 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. 98 string (that is, the string contains octets only). Croaks on error.
75 99
76 This function call is functionally identical to: 100 This function call is functionally identical to:
77 101
78 $json_text = JSON::XS->new->utf8->encode ($perl_scalar) 102 $json_text = JSON::XS->new->utf8->encode ($perl_scalar)
79 103
80 except being faster. 104 Except being faster.
81 105
82 $perl_scalar = from_json $json_text 106 $perl_scalar = decode_json $json_text
83 The opposite of "to_json": expects an UTF-8 (binary) string and 107 The opposite of "encode_json": expects an UTF-8 (binary) string and
84 tries to parse that as an UTF-8 encoded JSON text, returning the 108 tries to parse that as an UTF-8 encoded JSON text, returning the
85 resulting simple scalar or reference. Croaks on error. 109 resulting reference. Croaks on error.
86 110
87 This function call is functionally identical to: 111 This function call is functionally identical to:
88 112
89 $perl_scalar = JSON::XS->new->utf8->decode ($json_text) 113 $perl_scalar = JSON::XS->new->utf8->decode ($json_text)
90 114
91 except being faster. 115 Except being faster.
92 116
93 $is_boolean = JSON::XS::is_bool $scalar 117 $is_boolean = JSON::XS::is_bool $scalar
94 Returns true if the passed scalar represents either JSON::XS::true 118 Returns true if the passed scalar represents either JSON::XS::true
95 or JSON::XS::false, two constants that act like 1 and 0, 119 or JSON::XS::false, two constants that act like 1 and 0,
96 respectively and are used to represent JSON "true" and "false" 120 respectively and are used to represent JSON "true" and "false"
97 values in Perl. 121 values in Perl.
98 122
99 See MAPPING, below, for more information on how JSON values are 123 See MAPPING, below, for more information on how JSON values are
100 mapped to Perl. 124 mapped to Perl.
101 125
126A FEW NOTES ON UNICODE AND PERL
127 Since this often leads to confusion, here are a few very clear words on
128 how Unicode works in Perl, modulo bugs.
129
130 1. Perl strings can store characters with ordinal values > 255.
131 This enables you to store Unicode characters as single characters in
132 a Perl string - very natural.
133
134 2. Perl does *not* associate an encoding with your strings.
135 ... until you force it to, e.g. when matching it against a regex, or
136 printing the scalar to a file, in which case Perl either interprets
137 your string as locale-encoded text, octets/binary, or as Unicode,
138 depending on various settings. In no case is an encoding stored
139 together with your data, it is *use* that decides encoding, not any
140 magical meta data.
141
142 3. The internal utf-8 flag has no meaning with regards to the encoding
143 of your string.
144 Just ignore that flag unless you debug a Perl bug, a module written
145 in XS or want to dive into the internals of perl. Otherwise it will
146 only confuse you, as, despite the name, it says nothing about how
147 your string is encoded. You can have Unicode strings with that flag
148 set, with that flag clear, and you can have binary data with that
149 flag set and that flag clear. Other possibilities exist, too.
150
151 If you didn't know about that flag, just the better, pretend it
152 doesn't exist.
153
154 4. A "Unicode String" is simply a string where each character can be
155 validly interpreted as a Unicode code point.
156 If you have UTF-8 encoded data, it is no longer a Unicode string,
157 but a Unicode string encoded in UTF-8, giving you a binary string.
158
159 5. A string containing "high" (> 255) character values is *not* a UTF-8
160 string.
161 It's a fact. Learn to live with it.
162
163 I hope this helps :)
164
102OBJECT-ORIENTED INTERFACE 165OBJECT-ORIENTED INTERFACE
103 The object oriented interface lets you configure your own encoding or 166 The object oriented interface lets you configure your own encoding or
104 decoding style, within the limits of supported formats. 167 decoding style, within the limits of supported formats.
105 168
106 $json = new JSON::XS 169 $json = new JSON::XS
… …
113 176
114 my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]}) 177 my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]})
115 => {"a": [1, 2]} 178 => {"a": [1, 2]}
116 179
117 $json = $json->ascii ([$enable]) 180 $json = $json->ascii ([$enable])
181 $enabled = $json->get_ascii
118 If $enable is true (or missing), then the "encode" method will not 182 If $enable is true (or missing), then the "encode" method will not
119 generate characters outside the code range 0..127 (which is ASCII). 183 generate characters outside the code range 0..127 (which is ASCII).
120 Any unicode characters outside that range will be escaped using 184 Any Unicode characters outside that range will be escaped using
121 either a single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL 185 either a single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL
122 escape sequence, as per RFC4627. The resulting encoded JSON text can 186 escape sequence, as per RFC4627. The resulting encoded JSON text can
123 be treated as a native unicode string, an ascii-encoded, 187 be treated as a native Unicode string, an ascii-encoded,
124 latin1-encoded or UTF-8 encoded string, or any other superset of 188 latin1-encoded or UTF-8 encoded string, or any other superset of
125 ASCII. 189 ASCII.
126 190
127 If $enable is false, then the "encode" method will not escape 191 If $enable is false, then the "encode" method will not escape
128 Unicode characters unless required by the JSON syntax or other 192 Unicode characters unless required by the JSON syntax or other
129 flags. This results in a faster and more compact format. 193 flags. This results in a faster and more compact format.
130 194
195 See also the section *ENCODING/CODESET FLAG NOTES* later in this
196 document.
197
131 The main use for this flag is to produce JSON texts that can be 198 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 199 transmitted over a 7-bit channel, as the encoded JSON texts will not
133 contain any 8 bit characters. 200 contain any 8 bit characters.
134 201
135 JSON::XS->new->ascii (1)->encode ([chr 0x10401]) 202 JSON::XS->new->ascii (1)->encode ([chr 0x10401])
136 => ["\ud801\udc01"] 203 => ["\ud801\udc01"]
137 204
138 $json = $json->latin1 ([$enable]) 205 $json = $json->latin1 ([$enable])
206 $enabled = $json->get_latin1
139 If $enable is true (or missing), then the "encode" method will 207 If $enable is true (or missing), then the "encode" method will
140 encode the resulting JSON text as latin1 (or iso-8859-1), escaping 208 encode the resulting JSON text as latin1 (or iso-8859-1), escaping
141 any characters outside the code range 0..255. The resulting string 209 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 210 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 211 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 212 flag, as "decode" by default expects Unicode, which is a strict
145 superset of latin1. 213 superset of latin1.
146 214
147 If $enable is false, then the "encode" method will not escape 215 If $enable is false, then the "encode" method will not escape
148 Unicode characters unless required by the JSON syntax or other 216 Unicode characters unless required by the JSON syntax or other
149 flags. 217 flags.
218
219 See also the section *ENCODING/CODESET FLAG NOTES* later in this
220 document.
150 221
151 The main use for this flag is efficiently encoding binary data as 222 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 223 JSON text, as most octets will not be escaped, resulting in a
153 smaller encoded size. The disadvantage is that the resulting JSON 224 smaller encoded size. The disadvantage is that the resulting JSON
154 text is encoded in latin1 (and must correctly be treated as such 225 text is encoded in latin1 (and must correctly be treated as such
155 when storing and transfering), a rare encoding for JSON. It is 226 when storing and transferring), a rare encoding for JSON. It is
156 therefore most useful when you want to store data structures known 227 therefore most useful when you want to store data structures known
157 to contain binary data efficiently in files or databases, not when 228 to contain binary data efficiently in files or databases, not when
158 talking to other JSON encoders/decoders. 229 talking to other JSON encoders/decoders.
159 230
160 JSON::XS->new->latin1->encode (["\x{89}\x{abc}"] 231 JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]
161 => ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not) 232 => ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)
162 233
163 $json = $json->utf8 ([$enable]) 234 $json = $json->utf8 ([$enable])
235 $enabled = $json->get_utf8
164 If $enable is true (or missing), then the "encode" method will 236 If $enable is true (or missing), then the "encode" method will
165 encode the JSON result into UTF-8, as required by many protocols, 237 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 238 while the "decode" method expects to be handled an UTF-8-encoded
167 string. Please note that UTF-8-encoded strings do not contain any 239 string. Please note that UTF-8-encoded strings do not contain any
168 characters outside the range 0..255, they are thus useful for 240 characters outside the range 0..255, they are thus useful for
169 bytewise/binary I/O. In future versions, enabling this option might 241 bytewise/binary I/O. In future versions, enabling this option might
170 enable autodetection of the UTF-16 and UTF-32 encoding families, as 242 enable autodetection of the UTF-16 and UTF-32 encoding families, as
171 described in RFC4627. 243 described in RFC4627.
172 244
173 If $enable is false, then the "encode" method will return the JSON 245 If $enable is false, then the "encode" method will return the JSON
174 string as a (non-encoded) unicode string, while "decode" expects 246 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 247 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. 248 UTF-16) needs to be done yourself, e.g. using the Encode module.
249
250 See also the section *ENCODING/CODESET FLAG NOTES* later in this
251 document.
177 252
178 Example, output UTF-16BE-encoded JSON: 253 Example, output UTF-16BE-encoded JSON:
179 254
180 use Encode; 255 use Encode;
181 $jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object); 256 $jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
… …
200 2 275 2
201 ] 276 ]
202 } 277 }
203 278
204 $json = $json->indent ([$enable]) 279 $json = $json->indent ([$enable])
280 $enabled = $json->get_indent
205 If $enable is true (or missing), then the "encode" method will use a 281 If $enable is true (or missing), then the "encode" method will use a
206 multiline format as output, putting every array member or 282 multiline format as output, putting every array member or
207 object/hash key-value pair into its own line, identing them 283 object/hash key-value pair into its own line, indenting them
208 properly. 284 properly.
209 285
210 If $enable is false, no newlines or indenting will be produced, and 286 If $enable is false, no newlines or indenting will be produced, and
211 the resulting JSON text is guarenteed not to contain any "newlines". 287 the resulting JSON text is guaranteed not to contain any "newlines".
212 288
213 This setting has no effect when decoding JSON texts. 289 This setting has no effect when decoding JSON texts.
214 290
215 $json = $json->space_before ([$enable]) 291 $json = $json->space_before ([$enable])
292 $enabled = $json->get_space_before
216 If $enable is true (or missing), then the "encode" method will add 293 If $enable is true (or missing), then the "encode" method will add
217 an extra optional space before the ":" separating keys from values 294 an extra optional space before the ":" separating keys from values
218 in JSON objects. 295 in JSON objects.
219 296
220 If $enable is false, then the "encode" method will not add any extra 297 If $enable is false, then the "encode" method will not add any extra
… …
226 Example, space_before enabled, space_after and indent disabled: 303 Example, space_before enabled, space_after and indent disabled:
227 304
228 {"key" :"value"} 305 {"key" :"value"}
229 306
230 $json = $json->space_after ([$enable]) 307 $json = $json->space_after ([$enable])
308 $enabled = $json->get_space_after
231 If $enable is true (or missing), then the "encode" method will add 309 If $enable is true (or missing), then the "encode" method will add
232 an extra optional space after the ":" separating keys from values in 310 an extra optional space after the ":" separating keys from values in
233 JSON objects and extra whitespace after the "," separating key-value 311 JSON objects and extra whitespace after the "," separating key-value
234 pairs and array members. 312 pairs and array members.
235 313
… …
240 318
241 Example, space_before and indent disabled, space_after enabled: 319 Example, space_before and indent disabled, space_after enabled:
242 320
243 {"key": "value"} 321 {"key": "value"}
244 322
323 $json = $json->relaxed ([$enable])
324 $enabled = $json->get_relaxed
325 If $enable is true (or missing), then "decode" will accept some
326 extensions to normal JSON syntax (see below). "encode" will not be
327 affected in anyway. *Be aware that this option makes you accept
328 invalid JSON texts as if they were valid!*. I suggest only to use
329 this option to parse application-specific files written by humans
330 (configuration files, resource files etc.)
331
332 If $enable is false (the default), then "decode" will only accept
333 valid JSON texts.
334
335 Currently accepted extensions are:
336
337 * list items can have an end-comma
338
339 JSON *separates* array elements and key-value pairs with commas.
340 This can be annoying if you write JSON texts manually and want
341 to be able to quickly append elements, so this extension accepts
342 comma at the end of such items not just between them:
343
344 [
345 1,
346 2, <- this comma not normally allowed
347 ]
348 {
349 "k1": "v1",
350 "k2": "v2", <- this comma not normally allowed
351 }
352
353 * shell-style '#'-comments
354
355 Whenever JSON allows whitespace, shell-style comments are
356 additionally allowed. They are terminated by the first
357 carriage-return or line-feed character, after which more
358 white-space and comments are allowed.
359
360 [
361 1, # this comment not allowed in JSON
362 # neither this one...
363 ]
364
245 $json = $json->canonical ([$enable]) 365 $json = $json->canonical ([$enable])
366 $enabled = $json->get_canonical
246 If $enable is true (or missing), then the "encode" method will 367 If $enable is true (or missing), then the "encode" method will
247 output JSON objects by sorting their keys. This is adding a 368 output JSON objects by sorting their keys. This is adding a
248 comparatively high overhead. 369 comparatively high overhead.
249 370
250 If $enable is false, then the "encode" method will output key-value 371 If $enable is false, then the "encode" method will output key-value
251 pairs in the order Perl stores them (which will likely change 372 pairs in the order Perl stores them (which will likely change
252 between runs of the same script). 373 between runs of the same script).
253 374
254 This option is useful if you want the same data structure to be 375 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 376 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 377 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 378 contains the same data, as key-value pairs have no inherent ordering
258 in Perl. 379 in Perl.
259 380
260 This setting has no effect when decoding JSON texts. 381 This setting has no effect when decoding JSON texts.
261 382
262 $json = $json->allow_nonref ([$enable]) 383 $json = $json->allow_nonref ([$enable])
384 $enabled = $json->get_allow_nonref
263 If $enable is true (or missing), then the "encode" method can 385 If $enable is true (or missing), then the "encode" method can
264 convert a non-reference into its corresponding string, number or 386 convert a non-reference into its corresponding string, number or
265 null JSON value, which is an extension to RFC4627. Likewise, 387 null JSON value, which is an extension to RFC4627. Likewise,
266 "decode" will accept those JSON values instead of croaking. 388 "decode" will accept those JSON values instead of croaking.
267 389
… …
274 "allow_nonref", resulting in an invalid JSON text: 396 "allow_nonref", resulting in an invalid JSON text:
275 397
276 JSON::XS->new->allow_nonref->encode ("Hello, World!") 398 JSON::XS->new->allow_nonref->encode ("Hello, World!")
277 => "Hello, World!" 399 => "Hello, World!"
278 400
401 $json = $json->allow_unknown ([$enable])
402 $enabled = $json->get_allow_unknown
403 If $enable is true (or missing), then "encode" will *not* throw an
404 exception when it encounters values it cannot represent in JSON (for
405 example, filehandles) but instead will encode a JSON "null" value.
406 Note that blessed objects are not included here and are handled
407 separately by c<allow_nonref>.
408
409 If $enable is false (the default), then "encode" will throw an
410 exception when it encounters anything it cannot encode as JSON.
411
412 This option does not affect "decode" in any way, and it is
413 recommended to leave it off unless you know your communications
414 partner.
415
279 $json = $json->allow_blessed ([$enable]) 416 $json = $json->allow_blessed ([$enable])
417 $enabled = $json->get_allow_blessed
280 If $enable is true (or missing), then the "encode" method will not 418 If $enable is true (or missing), then the "encode" method will not
281 barf when it encounters a blessed reference. Instead, the value of 419 barf when it encounters a blessed reference. Instead, the value of
282 the convert_blessed option will decide wether "null" 420 the convert_blessed option will decide whether "null"
283 ("convert_blessed" disabled or no "to_json" method found) or a 421 ("convert_blessed" disabled or no "TO_JSON" method found) or a
284 representation of the object ("convert_blessed" enabled and 422 representation of the object ("convert_blessed" enabled and
285 "to_json" method found) is being encoded. Has no effect on "decode". 423 "TO_JSON" method found) is being encoded. Has no effect on "decode".
286 424
287 If $enable is false (the default), then "encode" will throw an 425 If $enable is false (the default), then "encode" will throw an
288 exception when it encounters a blessed object. 426 exception when it encounters a blessed object.
289 427
290 $json = $json->convert_blessed ([$enable]) 428 $json = $json->convert_blessed ([$enable])
429 $enabled = $json->get_convert_blessed
291 If $enable is true (or missing), then "encode", upon encountering a 430 If $enable is true (or missing), then "encode", upon encountering a
292 blessed object, will check for the availability of the "TO_JSON" 431 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 432 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 433 context and the resulting scalar will be encoded instead of the
295 object. If no "TO_JSON" method is found, the value of 434 object. If no "TO_JSON" method is found, the value of
… …
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 This setting does not yet influence "decode" in any way, but in the
307 future, global hooks might get installed that influence "decode" and 446 future, global hooks might get installed that influence "decode" and
308 are enabled by this setting. 447 are enabled by this setting.
309 448
… …
350 489
351 As this callback gets called less often then the 490 As this callback gets called less often then the
352 "filter_json_object" one, decoding speed will not usually suffer as 491 "filter_json_object" one, decoding speed will not usually suffer as
353 much. Therefore, single-key objects make excellent targets to 492 much. Therefore, single-key objects make excellent targets to
354 serialise Perl objects into, especially as single-key JSON objects 493 serialise Perl objects into, especially as single-key JSON objects
355 are as close to the type-tagged value concept as JSON gets (its 494 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 495 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 496 in any way, so you need to make sure your data never looks like a
358 serialised Perl hash. 497 serialised Perl hash.
359 498
360 Typical names for the single object key are "__class_whatever__", or 499 Typical names for the single object key are "__class_whatever__", or
… …
385 524
386 { __widget__ => $self->{id} } 525 { __widget__ => $self->{id} }
387 } 526 }
388 527
389 $json = $json->shrink ([$enable]) 528 $json = $json->shrink ([$enable])
529 $enabled = $json->get_shrink
390 Perl usually over-allocates memory a bit when allocating space for 530 Perl usually over-allocates memory a bit when allocating space for
391 strings. This flag optionally resizes strings generated by either 531 strings. This flag optionally resizes strings generated by either
392 "encode" or "decode" to their minimum size possible. This can save 532 "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 533 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 534 many short strings. It will also try to downgrade any strings to
… …
412 converting strings that look like integers or floats into integers 552 converting strings that look like integers or floats into integers
413 or floats internally (there is no difference on the Perl level), 553 or floats internally (there is no difference on the Perl level),
414 saving space. 554 saving space.
415 555
416 $json = $json->max_depth ([$maximum_nesting_depth]) 556 $json = $json->max_depth ([$maximum_nesting_depth])
557 $max_depth = $json->get_max_depth
417 Sets the maximum nesting level (default 512) accepted while encoding 558 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 559 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 560 Perl data structure, then the encoder and decoder will stop and
420 will stop and croak at that point. 561 croak at that point.
421 562
422 Nesting level is defined by number of hash- or arrayrefs that the 563 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 564 encoder needs to traverse to reach a given point or the number of
424 "{" or "[" characters without their matching closing parenthesis 565 "{" or "[" characters without their matching closing parenthesis
425 crossed to reach a given character in a string. 566 crossed to reach a given character in a string.
426 567
427 Setting the maximum depth to one disallows any nesting, so that 568 Setting the maximum depth to one disallows any nesting, so that
428 ensures that the object is only a single hash/object or array. 569 ensures that the object is only a single hash/object or array.
429 570
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 571 If no argument is given, the highest possible setting will be used,
432 will be used, which is rarely useful. 572 which is rarely useful.
573
574 Note that nesting is implemented by recursion in C. The default
575 value has been chosen to be as large as typical operating systems
576 allow without crashing.
433 577
434 See SECURITY CONSIDERATIONS, below, for more info on why this is 578 See SECURITY CONSIDERATIONS, below, for more info on why this is
435 useful. 579 useful.
436 580
437 $json = $json->max_size ([$maximum_string_size]) 581 $json = $json->max_size ([$maximum_string_size])
582 $max_size = $json->get_max_size
438 Set the maximum length a JSON text may have (in bytes) where 583 Set the maximum length a JSON text may have (in bytes) where
439 decoding is being attempted. The default is 0, meaning no limit. 584 decoding is being attempted. The default is 0, meaning no limit.
440 When "decode" is called on a string longer then this number of 585 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 586 bytes, it will not attempt to decode the string but throw an
442 exception. This setting has no effect on "encode" (yet). 587 exception. This setting has no effect on "encode" (yet).
443 588
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 589 If no argument is given, the limit check will be deactivated (same
447 specified). 590 as when 0 is specified).
448 591
449 See SECURITY CONSIDERATIONS, below, for more info on why this is 592 See SECURITY CONSIDERATIONS, below, for more info on why this is
450 useful. 593 useful.
451 594
452 $json_text = $json->encode ($perl_scalar) 595 $json_text = $json->encode ($perl_scalar)
… …
477 and you need to know where the JSON text ends. 620 and you need to know where the JSON text ends.
478 621
479 JSON::XS->new->decode_prefix ("[1] the tail") 622 JSON::XS->new->decode_prefix ("[1] the tail")
480 => ([], 3) 623 => ([], 3)
481 624
625INCREMENTAL PARSING
626 In some cases, there is the need for incremental parsing of JSON texts.
627 While this module always has to keep both JSON text and resulting Perl
628 data structure in memory at one time, it does allow you to parse a JSON
629 stream incrementally. It does so by accumulating text until it has a
630 full JSON object, which it then can decode. This process is similar to
631 using "decode_prefix" to see if a full JSON object is available, but is
632 much more efficient (and can be implemented with a minimum of method
633 calls).
634
635 JSON::XS will only attempt to parse the JSON text once it is sure it has
636 enough text to get a decisive result, using a very simple but truly
637 incremental parser. This means that it sometimes won't stop as early as
638 the full parser, for example, it doesn't detect parenthese mismatches.
639 The only thing it guarantees is that it starts decoding as soon as a
640 syntactically valid JSON text has been seen. This means you need to set
641 resource limits (e.g. "max_size") to ensure the parser will stop parsing
642 in the presence if syntax errors.
643
644 The following methods implement this incremental parser.
645
646 [void, scalar or list context] = $json->incr_parse ([$string])
647 This is the central parsing function. It can both append new text
648 and extract objects from the stream accumulated so far (both of
649 these functions are optional).
650
651 If $string is given, then this string is appended to the already
652 existing JSON fragment stored in the $json object.
653
654 After that, if the function is called in void context, it will
655 simply return without doing anything further. This can be used to
656 add more text in as many chunks as you want.
657
658 If the method is called in scalar context, then it will try to
659 extract exactly *one* JSON object. If that is successful, it will
660 return this object, otherwise it will return "undef". If there is a
661 parse error, this method will croak just as "decode" would do (one
662 can then use "incr_skip" to skip the errornous part). This is the
663 most common way of using the method.
664
665 And finally, in list context, it will try to extract as many objects
666 from the stream as it can find and return them, or the empty list
667 otherwise. For this to work, there must be no separators between the
668 JSON objects or arrays, instead they must be concatenated
669 back-to-back. If an error occurs, an exception will be raised as in
670 the scalar context case. Note that in this case, any
671 previously-parsed JSON texts will be lost.
672
673 $lvalue_string = $json->incr_text
674 This method returns the currently stored JSON fragment as an lvalue,
675 that is, you can manipulate it. This *only* works when a preceding
676 call to "incr_parse" in *scalar context* successfully returned an
677 object. Under all other circumstances you must not call this
678 function (I mean it. although in simple tests it might actually
679 work, it *will* fail under real world conditions). As a special
680 exception, you can also call this method before having parsed
681 anything.
682
683 This function is useful in two cases: a) finding the trailing text
684 after a JSON object or b) parsing multiple JSON objects separated by
685 non-JSON text (such as commas).
686
687 $json->incr_skip
688 This will reset the state of the incremental parser and will remove
689 the parsed text from the input buffer so far. This is useful after
690 "incr_parse" died, in which case the input buffer and incremental
691 parser state is left unchanged, to skip the text parsed so far and
692 to reset the parse state.
693
694 The difference to "incr_reset" is that only text until the parse
695 error occured is removed.
696
697 $json->incr_reset
698 This completely resets the incremental parser, that is, after this
699 call, it will be as if the parser had never parsed anything.
700
701 This is useful if you want to repeatedly parse JSON objects and want
702 to ignore any trailing data, which means you have to reset the
703 parser after each successful decode.
704
705 LIMITATIONS
706 All options that affect decoding are supported, except "allow_nonref".
707 The reason for this is that it cannot be made to work sensibly: JSON
708 objects and arrays are self-delimited, i.e. you can concatenate them
709 back to back and still decode them perfectly. This does not hold true
710 for JSON numbers, however.
711
712 For example, is the string 1 a single JSON number, or is it simply the
713 start of 12? Or is 12 a single JSON number, or the concatenation of 1
714 and 2? In neither case you can tell, and this is why JSON::XS takes the
715 conservative route and disallows this case.
716
717 EXAMPLES
718 Some examples will make all this clearer. First, a simple example that
719 works similarly to "decode_prefix": We want to decode the JSON object at
720 the start of a string and identify the portion after the JSON object:
721
722 my $text = "[1,2,3] hello";
723
724 my $json = new JSON::XS;
725
726 my $obj = $json->incr_parse ($text)
727 or die "expected JSON object or array at beginning of string";
728
729 my $tail = $json->incr_text;
730 # $tail now contains " hello"
731
732 Easy, isn't it?
733
734 Now for a more complicated example: Imagine a hypothetical protocol
735 where you read some requests from a TCP stream, and each request is a
736 JSON array, without any separation between them (in fact, it is often
737 useful to use newlines as "separators", as these get interpreted as
738 whitespace at the start of the JSON text, which makes it possible to
739 test said protocol with "telnet"...).
740
741 Here is how you'd do it (it is trivial to write this in an event-based
742 manner):
743
744 my $json = new JSON::XS;
745
746 # read some data from the socket
747 while (sysread $socket, my $buf, 4096) {
748
749 # split and decode as many requests as possible
750 for my $request ($json->incr_parse ($buf)) {
751 # act on the $request
752 }
753 }
754
755 Another complicated example: Assume you have a string with JSON objects
756 or arrays, all separated by (optional) comma characters (e.g. "[1],[2],
757 [3]"). To parse them, we have to skip the commas between the JSON texts,
758 and here is where the lvalue-ness of "incr_text" comes in useful:
759
760 my $text = "[1],[2], [3]";
761 my $json = new JSON::XS;
762
763 # void context, so no parsing done
764 $json->incr_parse ($text);
765
766 # now extract as many objects as possible. note the
767 # use of scalar context so incr_text can be called.
768 while (my $obj = $json->incr_parse) {
769 # do something with $obj
770
771 # now skip the optional comma
772 $json->incr_text =~ s/^ \s* , //x;
773 }
774
775 Now lets go for a very complex example: Assume that you have a gigantic
776 JSON array-of-objects, many gigabytes in size, and you want to parse it,
777 but you cannot load it into memory fully (this has actually happened in
778 the real world :).
779
780 Well, you lost, you have to implement your own JSON parser. But JSON::XS
781 can still help you: You implement a (very simple) array parser and let
782 JSON decode the array elements, which are all full JSON objects on their
783 own (this wouldn't work if the array elements could be JSON numbers, for
784 example):
785
786 my $json = new JSON::XS;
787
788 # open the monster
789 open my $fh, "<bigfile.json"
790 or die "bigfile: $!";
791
792 # first parse the initial "["
793 for (;;) {
794 sysread $fh, my $buf, 65536
795 or die "read error: $!";
796 $json->incr_parse ($buf); # void context, so no parsing
797
798 # Exit the loop once we found and removed(!) the initial "[".
799 # In essence, we are (ab-)using the $json object as a simple scalar
800 # we append data to.
801 last if $json->incr_text =~ s/^ \s* \[ //x;
802 }
803
804 # now we have the skipped the initial "[", so continue
805 # parsing all the elements.
806 for (;;) {
807 # in this loop we read data until we got a single JSON object
808 for (;;) {
809 if (my $obj = $json->incr_parse) {
810 # do something with $obj
811 last;
812 }
813
814 # add more data
815 sysread $fh, my $buf, 65536
816 or die "read error: $!";
817 $json->incr_parse ($buf); # void context, so no parsing
818 }
819
820 # in this loop we read data until we either found and parsed the
821 # separating "," between elements, or the final "]"
822 for (;;) {
823 # first skip whitespace
824 $json->incr_text =~ s/^\s*//;
825
826 # if we find "]", we are done
827 if ($json->incr_text =~ s/^\]//) {
828 print "finished.\n";
829 exit;
830 }
831
832 # if we find ",", we can continue with the next element
833 if ($json->incr_text =~ s/^,//) {
834 last;
835 }
836
837 # if we find anything else, we have a parse error!
838 if (length $json->incr_text) {
839 die "parse error near ", $json->incr_text;
840 }
841
842 # else add more data
843 sysread $fh, my $buf, 65536
844 or die "read error: $!";
845 $json->incr_parse ($buf); # void context, so no parsing
846 }
847
848 This is a complex example, but most of the complexity comes from the
849 fact that we are trying to be correct (bear with me if I am wrong, I
850 never ran the above example :).
851
482MAPPING 852MAPPING
483 This section describes how JSON::XS maps Perl values to JSON values and 853 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 854 vice versa. These mappings are designed to "do the right thing" in most
485 circumstances automatically, preserving round-tripping characteristics 855 circumstances automatically, preserving round-tripping characteristics
486 (what you put in comes out as something equivalent). 856 (what you put in comes out as something equivalent).
487 857
488 For the more enlightened: note that in the following descriptions, 858 For the more enlightened: note that in the following descriptions,
489 lowercase *perl* refers to the Perl interpreter, while uppcercase *Perl* 859 lowercase *perl* refers to the Perl interpreter, while uppercase *Perl*
490 refers to the abstract Perl language itself. 860 refers to the abstract Perl language itself.
491 861
492 JSON -> PERL 862 JSON -> PERL
493 object 863 object
494 A JSON object becomes a reference to a hash in Perl. No ordering of 864 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 865 object keys is preserved (JSON does not preserve object key ordering
496 ordering itself). 866 itself).
497 867
498 array 868 array
499 A JSON array becomes a reference to an array in Perl. 869 A JSON array becomes a reference to an array in Perl.
500 870
501 string 871 string
502 A JSON string becomes a string scalar in Perl - Unicode codepoints 872 A JSON string becomes a string scalar in Perl - Unicode codepoints
503 in JSON are represented by the same codepoints in the Perl string, 873 in JSON are represented by the same codepoints in the Perl string,
504 so no manual decoding is necessary. 874 so no manual decoding is necessary.
505 875
506 number 876 number
507 A JSON number becomes either an integer or numeric (floating point) 877 A JSON number becomes either an integer, numeric (floating point) or
508 scalar in perl, depending on its range and any fractional parts. On 878 string scalar in perl, depending on its range and any fractional
509 the Perl level, there is no difference between those as Perl handles 879 parts. On the Perl level, there is no difference between those as
510 all the conversion details, but an integer may take slightly less 880 Perl handles all the conversion details, but an integer may take
511 memory and might represent more values exactly than (floating point) 881 slightly less memory and might represent more values exactly than
882 floating point numbers.
883
884 If the number consists of digits only, JSON::XS will try to
885 represent it as an integer value. If that fails, it will try to
886 represent it as a numeric (floating point) value if that is possible
887 without loss of precision. Otherwise it will preserve the number as
888 a string value (in which case you lose roundtripping ability, as the
889 JSON number will be re-encoded toa JSON string).
890
891 Numbers containing a fractional or exponential part will always be
892 represented as numeric (floating point) values, possibly at a loss
893 of precision (in which case you might lose perfect roundtripping
894 ability, but the JSON number will still be re-encoded as a JSON
512 numbers. 895 number).
513 896
514 true, false 897 true, false
515 These JSON atoms become "JSON::XS::true" and "JSON::XS::false", 898 These JSON atoms become "JSON::XS::true" and "JSON::XS::false",
516 respectively. They are overloaded to act almost exactly like the 899 respectively. They are overloaded to act almost exactly like the
517 numbers 1 and 0. You can check wether a scalar is a JSON boolean by 900 numbers 1 and 0. You can check whether a scalar is a JSON boolean by
518 using the "JSON::XS::is_bool" function. 901 using the "JSON::XS::is_bool" function.
519 902
520 null 903 null
521 A JSON null atom becomes "undef" in Perl. 904 A JSON null atom becomes "undef" in Perl.
522 905
… …
545 an exception to be thrown, except for references to the integers 0 928 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 929 and 1, which get turned into "false" and "true" atoms in JSON. You
547 can also use "JSON::XS::false" and "JSON::XS::true" to improve 930 can also use "JSON::XS::false" and "JSON::XS::true" to improve
548 readability. 931 readability.
549 932
550 to_json [\0,JSON::XS::true] # yields [false,true] 933 encode_json [\0, JSON::XS::true] # yields [false,true]
551 934
552 JSON::XS::true, JSON::XS::false 935 JSON::XS::true, JSON::XS::false
553 These special values become JSON true and JSON false values, 936 These special values become JSON true and JSON false values,
554 respectively. You cna alos use "\1" and "\0" directly if you want. 937 respectively. You can also use "\1" and "\0" directly if you want.
555 938
556 blessed objects 939 blessed objects
557 Blessed objects are not allowed. JSON::XS currently tries to encode 940 Blessed objects are not directly representable in JSON. See the
558 their underlying representation (hash- or arrayref), but this 941 "allow_blessed" and "convert_blessed" methods on various options on
559 behaviour might change in future versions. 942 how to deal with this: basically, you can choose between throwing an
943 exception, encoding the reference as if it weren't blessed, or
944 provide your own serialiser method.
560 945
561 simple scalars 946 simple scalars
562 Simple Perl scalars (any scalar that is not a reference) are the 947 Simple Perl scalars (any scalar that is not a reference) are the
563 most difficult objects to encode: JSON::XS will encode undefined 948 most difficult objects to encode: JSON::XS will encode undefined
564 scalars as JSON null value, scalars that have last been used in a 949 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 950 string context before encoding as JSON strings, and anything else as
566 number value: 951 number value:
567 952
568 # dump as number 953 # dump as number
569 to_json [2] # yields [2] 954 encode_json [2] # yields [2]
570 to_json [-3.0e17] # yields [-3e+17] 955 encode_json [-3.0e17] # yields [-3e+17]
571 my $value = 5; to_json [$value] # yields [5] 956 my $value = 5; encode_json [$value] # yields [5]
572 957
573 # used as string, so dump as string 958 # used as string, so dump as string
574 print $value; 959 print $value;
575 to_json [$value] # yields ["5"] 960 encode_json [$value] # yields ["5"]
576 961
577 # undef becomes null 962 # undef becomes null
578 to_json [undef] # yields [null] 963 encode_json [undef] # yields [null]
579 964
580 You can force the type to be a string by stringifying it: 965 You can force the type to be a JSON string by stringifying it:
581 966
582 my $x = 3.1; # some variable containing a number 967 my $x = 3.1; # some variable containing a number
583 "$x"; # stringified 968 "$x"; # stringified
584 $x .= ""; # another, more awkward way to stringify 969 $x .= ""; # another, more awkward way to stringify
585 print $x; # perl does it for you, too, quite often 970 print $x; # perl does it for you, too, quite often
586 971
587 You can force the type to be a number by numifying it: 972 You can force the type to be a JSON number by numifying it:
588 973
589 my $x = "3"; # some variable containing a string 974 my $x = "3"; # some variable containing a string
590 $x += 0; # numify it, ensuring it will be dumped as a number 975 $x += 0; # numify it, ensuring it will be dumped as a number
591 $x *= 1; # same thing, the choise is yours. 976 $x *= 1; # same thing, the choice is yours.
592 977
593 You can not currently output JSON booleans or force the type in 978 You can not currently force the type in other, less obscure, ways.
594 other, less obscure, ways. Tell me if you need this capability. 979 Tell me if you need this capability (but don't forget to explain why
980 it's needed :).
595 981
596COMPARISON 982ENCODING/CODESET FLAG NOTES
597 As already mentioned, this module was created because none of the 983 The interested reader might have seen a number of flags that signify
598 existing JSON modules could be made to work correctly. First I will 984 encodings or codesets - "utf8", "latin1" and "ascii". There seems to be
599 describe the problems (or pleasures) I encountered with various existing 985 some confusion on what these do, so here is a short comparison:
600 JSON modules, followed by some benchmark values. JSON::XS was designed
601 not to suffer from any of these problems or limitations.
602 986
603 JSON 1.07 987 "utf8" controls whether the JSON text created by "encode" (and expected
604 Slow (but very portable, as it is written in pure Perl). 988 by "decode") is UTF-8 encoded or not, while "latin1" and "ascii" only
989 control whether "encode" escapes character values outside their
990 respective codeset range. Neither of these flags conflict with each
991 other, although some combinations make less sense than others.
605 992
606 Undocumented/buggy Unicode handling (how JSON handles unicode values 993 Care has been taken to make all flags symmetrical with respect to
607 is undocumented. One can get far by feeding it unicode strings and 994 "encode" and "decode", that is, texts encoded with any combination of
608 doing en-/decoding oneself, but unicode escapes are not working 995 these flag values will be correctly decoded when the same flags are used
996 - in general, if you use different flag settings while encoding vs. when
997 decoding you likely have a bug somewhere.
998
999 Below comes a verbose discussion of these flags. Note that a "codeset"
1000 is simply an abstract set of character-codepoint pairs, while an
1001 encoding takes those codepoint numbers and *encodes* them, in our case
1002 into octets. Unicode is (among other things) a codeset, UTF-8 is an
1003 encoding, and ISO-8859-1 (= latin 1) and ASCII are both codesets *and*
1004 encodings at the same time, which can be confusing.
1005
1006 "utf8" flag disabled
1007 When "utf8" is disabled (the default), then "encode"/"decode"
1008 generate and expect Unicode strings, that is, characters with high
1009 ordinal Unicode values (> 255) will be encoded as such characters,
1010 and likewise such characters are decoded as-is, no canges to them
1011 will be done, except "(re-)interpreting" them as Unicode codepoints
1012 or Unicode characters, respectively (to Perl, these are the same
1013 thing in strings unless you do funny/weird/dumb stuff).
1014
1015 This is useful when you want to do the encoding yourself (e.g. when
1016 you want to have UTF-16 encoded JSON texts) or when some other layer
1017 does the encoding for you (for example, when printing to a terminal
1018 using a filehandle that transparently encodes to UTF-8 you certainly
1019 do NOT want to UTF-8 encode your data first and have Perl encode it
1020 another time).
1021
1022 "utf8" flag enabled
1023 If the "utf8"-flag is enabled, "encode"/"decode" will encode all
1024 characters using the corresponding UTF-8 multi-byte sequence, and
1025 will expect your input strings to be encoded as UTF-8, that is, no
1026 "character" of the input string must have any value > 255, as UTF-8
1027 does not allow that.
1028
1029 The "utf8" flag therefore switches between two modes: disabled means
1030 you will get a Unicode string in Perl, enabled means you get an
1031 UTF-8 encoded octet/binary string in Perl.
1032
1033 "latin1" or "ascii" flags enabled
1034 With "latin1" (or "ascii") enabled, "encode" will escape characters
1035 with ordinal values > 255 (> 127 with "ascii") and encode the
1036 remaining characters as specified by the "utf8" flag.
1037
1038 If "utf8" is disabled, then the result is also correctly encoded in
1039 those character sets (as both are proper subsets of Unicode, meaning
1040 that a Unicode string with all character values < 256 is the same
1041 thing as a ISO-8859-1 string, and a Unicode string with all
1042 character values < 128 is the same thing as an ASCII string in
609 properly). 1043 Perl).
610 1044
611 No roundtripping (strings get clobbered if they look like numbers, 1045 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 1046 regardless of these flags, just some more characters will be escaped
613 will decode into the number 2. 1047 using "\uXXXX" then before.
614 1048
615 JSON::PC 0.01 1049 Note that ISO-8859-1-*encoded* strings are not compatible with UTF-8
616 Very fast. 1050 encoding, while ASCII-encoded strings are. That is because the
1051 ISO-8859-1 encoding is NOT a subset of UTF-8 (despite the ISO-8859-1
1052 *codeset* being a subset of Unicode), while ASCII is.
617 1053
618 Undocumented/buggy Unicode handling. 1054 Surprisingly, "decode" will ignore these flags and so treat all
1055 input values as governed by the "utf8" flag. If it is disabled, this
1056 allows you to decode ISO-8859-1- and ASCII-encoded strings, as both
1057 strict subsets of Unicode. If it is enabled, you can correctly
1058 decode UTF-8 encoded strings.
619 1059
620 No roundtripping. 1060 So neither "latin1" nor "ascii" are incompatible with the "utf8"
1061 flag - they only govern when the JSON output engine escapes a
1062 character or not.
621 1063
622 Has problems handling many Perl values (e.g. regex results and other 1064 The main use for "latin1" is to relatively efficiently store binary
623 magic values will make it croak). 1065 data as JSON, at the expense of breaking compatibility with most
1066 JSON decoders.
624 1067
625 Does not even generate valid JSON ("{1,2}" gets converted to "{1:2}" 1068 The main use for "ascii" is to force the output to not contain
626 which is not a valid JSON text. 1069 characters with values > 127, which means you can interpret the
1070 resulting string as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about
1071 any character set and 8-bit-encoding, and still get the same data
1072 structure back. This is useful when your channel for JSON transfer
1073 is not 8-bit clean or the encoding might be mangled in between (e.g.
1074 in mail), and works because ASCII is a proper subset of most 8-bit
1075 and multibyte encodings in use in the world.
627 1076
628 Unmaintained (maintainer unresponsive for many months, bugs are not 1077 JSON and ECMAscript
629 getting fixed). 1078 JSON syntax is based on how literals are represented in javascript (the
1079 not-standardised predecessor of ECMAscript) which is presumably why it
1080 is called "JavaScript Object Notation".
630 1081
631 JSON::Syck 0.21 1082 However, JSON is not a subset (and also not a superset of course) of
632 Very buggy (often crashes). 1083 ECMAscript (the standard) or javascript (whatever browsers actually
1084 implement).
633 1085
634 Very inflexible (no human-readable format supported, format pretty 1086 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 1087 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 1088 structure might not be queryable:
637 preferably a way to generate ASCII-only JSON texts).
638 1089
639 Completely broken (and confusingly documented) Unicode handling 1090 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 1091 inside JSON strings, but are not allowed in ECMAscript string literals,
641 ImplicitUnicode to *different* values on en- and decoding to get 1092 so the following Perl fragment will not output something that can be
642 symmetric behaviour). 1093 guaranteed to be parsable by javascript's "eval":
643 1094
644 No roundtripping (simple cases work, but this depends on wether the 1095 use JSON::XS;
645 scalar value was used in a numeric context or not).
646 1096
647 Dumping hashes may skip hash values depending on iterator state. 1097 print encode_json [chr 0x2028];
648 1098
649 Unmaintained (maintainer unresponsive for many months, bugs are not 1099 The right fix for this is to use a proper JSON parser in your javascript
650 getting fixed). 1100 programs, and not rely on "eval" (see for example Douglas Crockford's
1101 json2.js parser).
651 1102
652 Does not check input for validity (i.e. will accept non-JSON input 1103 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 1104 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 1105
660 JSON::DWIW 0.04 1106 use JSON::XS;
661 Very fast. Very natural. Very nice.
662 1107
663 Undocumented unicode handling (but the best of the pack. Unicode 1108 print JSON::XS->new->ascii->encode ([chr 0x2028]);
664 escapes still don't get parsed properly).
665 1109
666 Very inflexible. 1110 Note that this will enlarge the resulting JSON text quite a bit if you
1111 have many non-ASCII characters. You might be tempted to run some regexes
1112 to only escape U+2028 and U+2029, e.g.:
667 1113
668 No roundtripping. 1114 # DO NOT USE THIS!
1115 my $json = JSON::XS->new->utf8->encode ([chr 0x2028]);
1116 $json =~ s/\xe2\x80\xa8/\\u2028/g; # escape U+2028
1117 $json =~ s/\xe2\x80\xa9/\\u2029/g; # escape U+2029
1118 print $json;
669 1119
670 Does not generate valid JSON texts (key strings are often unquoted, 1120 Note that *this is a bad idea*: the above only works for U+2028 and
671 empty keys result in nothing being output) 1121 U+2029 and thus only for fully ECMAscript-compliant parsers. Many
1122 existing javascript implementations, however, have issues with other
1123 characters as well - using "eval" naively simply *will* cause problems.
672 1124
673 Does not check input for validity. 1125 Another problem is that some javascript implementations reserve some
1126 property names for their own purposes (which probably makes them
1127 non-ECMAscript-compliant). For example, Iceweasel reserves the
1128 "__proto__" property name for it's own purposes.
1129
1130 If that is a problem, you could parse try to filter the resulting JSON
1131 output for these property strings, e.g.:
1132
1133 $json =~ s/"__proto__"\s*:/"__proto__renamed":/g;
1134
1135 This works because "__proto__" is not valid outside of strings, so every
1136 occurence of ""__proto__"\s*:" must be a string used as property name.
1137
1138 If you know of other incompatibilities, please let me know.
674 1139
675 JSON and YAML 1140 JSON and YAML
676 You often hear that JSON is a subset (or a close subset) of YAML. This 1141 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, 1142 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 1143 writing), so let me state it clearly: *in general, there is no way to
679 valid YAML. 1144 configure JSON::XS to output a data structure as valid YAML* that works
1145 in all cases.
680 1146
681 If you really must use JSON::XS to generate YAML, you should use this 1147 If you really must use JSON::XS to generate YAML, you should use this
682 algorithm (subject to change in future versions): 1148 algorithm (subject to change in future versions):
683 1149
684 my $to_yaml = JSON::XS->new->utf8->space_after (1); 1150 my $to_yaml = JSON::XS->new->utf8->space_after (1);
685 my $yaml = $to_yaml->encode ($ref) . "\n"; 1151 my $yaml = $to_yaml->encode ($ref) . "\n";
686 1152
687 This will usually generate JSON texts that also parse as valid YAML. 1153 This will *usually* generate JSON texts that also parse as valid YAML.
688 Please note that YAML has hardcoded limits on (simple) object key 1154 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 1155 lengths that JSON doesn't have and also has different and incompatible
1156 unicode handling, so you should make sure that your hash keys are
690 keys are noticably shorter than the 1024 characters YAML allows. 1157 noticeably shorter than the 1024 "stream characters" YAML allows and
1158 that you do not have characters with codepoint values outside the
1159 Unicode BMP (basic multilingual page). YAML also does not allow "\/"
1160 sequences in strings (which JSON::XS does not *currently* generate, but
1161 other JSON generators might).
691 1162
692 There might be other incompatibilities that I am not aware of. In 1163 There might be other incompatibilities that I am not aware of (or the
1164 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 1165 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: 1166 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 1167 chances are high that you will run into severe interoperability problems
696 problems. 1168 when you least expect it.
1169
1170 (*) I have been pressured multiple times by Brian Ingerson (one of the
1171 authors of the YAML specification) to remove this paragraph, despite
1172 him acknowledging that the actual incompatibilities exist. As I was
1173 personally bitten by this "JSON is YAML" lie, I refused and said I
1174 will continue to educate people about these issues, so others do not
1175 run into the same problem again and again. After this, Brian called
1176 me a (quote)*complete and worthless idiot*(unquote).
1177
1178 In my opinion, instead of pressuring and insulting people who
1179 actually clarify issues with YAML and the wrong statements of some
1180 of its proponents, I would kindly suggest reading the JSON spec
1181 (which is not that difficult or long) and finally make YAML
1182 compatible to it, and educating users about the changes, instead of
1183 spreading lies about the real compatibility for many *years* and
1184 trying to silence people who point out that it isn't true.
697 1185
698 SPEED 1186 SPEED
699 It seems that JSON::XS is surprisingly fast, as shown in the following 1187 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 1188 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 1189 in the JSON::XS distribution, to make it easy to compare on your own
702 system. 1190 system.
703 1191
704 First comes a comparison between various modules using a very short 1192 First comes a comparison between various modules using a very short
705 single-line JSON string: 1193 single-line JSON string (also available at
1194 <http://dist.schmorp.de/misc/json/short.json>).
706 1195
707 {"method": "handleMessage", "params": ["user1", "we were just talking"], \ 1196 {"method": "handleMessage", "params": ["user1",
708 "id": null, "array":[1,11,234,-5,1e5,1e7, true, false]} 1197 "we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7,
1198 true, false]}
709 1199
710 It shows the number of encodes/decodes per second (JSON::XS uses the 1200 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 1201 functional interface, while JSON::XS/2 uses the OO interface with
712 pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink). 1202 pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink).
713 Higher is better: 1203 Higher is better:
714 1204
715 Storable | 15779.925 | 14169.946 |
716 -----------+------------+------------+
717 module | encode | decode | 1205 module | encode | decode |
718 -----------|------------|------------| 1206 -----------|------------|------------|
719 JSON | 4990.842 | 4088.813 | 1207 JSON 1.x | 4990.842 | 4088.813 |
720 JSON::DWIW | 51653.990 | 71575.154 | 1208 JSON::DWIW | 51653.990 | 71575.154 |
721 JSON::PC | 65948.176 | 74631.744 | 1209 JSON::PC | 65948.176 | 74631.744 |
722 JSON::PP | 8931.652 | 3817.168 | 1210 JSON::PP | 8931.652 | 3817.168 |
723 JSON::Syck | 24877.248 | 27776.848 | 1211 JSON::Syck | 24877.248 | 27776.848 |
724 JSON::XS | 388361.481 | 227951.304 | 1212 JSON::XS | 388361.481 | 227951.304 |
… …
726 JSON::XS/3 | 338250.323 | 218453.333 | 1214 JSON::XS/3 | 338250.323 | 218453.333 |
727 Storable | 16500.016 | 135300.129 | 1215 Storable | 16500.016 | 135300.129 |
728 -----------+------------+------------+ 1216 -----------+------------+------------+
729 1217
730 That is, JSON::XS is about five times faster than JSON::DWIW on 1218 That is, JSON::XS is about five times faster than JSON::DWIW on
731 encoding, about three times faster on decoding, and over fourty times 1219 encoding, about three times faster on decoding, and over forty times
732 faster than JSON, even with pretty-printing and key sorting. It also 1220 faster than JSON, even with pretty-printing and key sorting. It also
733 compares favourably to Storable for small amounts of data. 1221 compares favourably to Storable for small amounts of data.
734 1222
735 Using a longer test string (roughly 18KB, generated from Yahoo! Locals 1223 Using a longer test string (roughly 18KB, generated from Yahoo! Locals
736 search API (http://nanoref.com/yahooapis/mgPdGg): 1224 search API (<http://dist.schmorp.de/misc/json/long.json>).
737 1225
738 module | encode | decode | 1226 module | encode | decode |
739 -----------|------------|------------| 1227 -----------|------------|------------|
740 JSON | 55.260 | 34.971 | 1228 JSON 1.x | 55.260 | 34.971 |
741 JSON::DWIW | 825.228 | 1082.513 | 1229 JSON::DWIW | 825.228 | 1082.513 |
742 JSON::PC | 3571.444 | 2394.829 | 1230 JSON::PC | 3571.444 | 2394.829 |
743 JSON::PP | 210.987 | 32.574 | 1231 JSON::PP | 210.987 | 32.574 |
744 JSON::Syck | 552.551 | 787.544 | 1232 JSON::Syck | 552.551 | 787.544 |
745 JSON::XS | 5780.463 | 4854.519 | 1233 JSON::XS | 5780.463 | 4854.519 |
… …
749 -----------+------------+------------+ 1237 -----------+------------+------------+
750 1238
751 Again, JSON::XS leads by far (except for Storable which non-surprisingly 1239 Again, JSON::XS leads by far (except for Storable which non-surprisingly
752 decodes faster). 1240 decodes faster).
753 1241
754 On large strings containing lots of high unicode characters, some 1242 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 1243 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 1244 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 1245 refuse to decode or encode properly, so it was impossible to prepare a
758 fair comparison table for that case. 1246 fair comparison table for that case.
759 1247
760SECURITY CONSIDERATIONS 1248SECURITY CONSIDERATIONS
761 When you are using JSON in a protocol, talking to untrusted potentially 1249 When you are using JSON in a protocol, talking to untrusted potentially
… …
765 have any buffer overflows. Obviously, this module should ensure that and 1253 have any buffer overflows. Obviously, this module should ensure that and
766 I am trying hard on making that true, but you never know. 1254 I am trying hard on making that true, but you never know.
767 1255
768 Second, you need to avoid resource-starving attacks. That means you 1256 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 1257 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 1258 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 1259 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 1260 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 1261 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 1262 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 1263 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 1266 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 1267 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 1268 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 1269 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. 1270 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 1271 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 1272 process has a smaller stack, you should adjust this setting accordingly
785 with the "max_depth" method. 1273 with the "max_depth" method.
786 1274
787 And last but least, something else could bomb you that I forgot to think 1275 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 1276 case, you get to keep the pieces. I am always open for hints, though...
789 hints, though...
790 1277
1278 Also keep in mind that JSON::XS might leak contents of your Perl data
1279 structures in its error messages, so when you serialise sensitive
1280 information you might want to make sure that exceptions thrown by
1281 JSON::XS will not end up in front of untrusted eyes.
1282
791 If you are using JSON::XS to return packets to consumption by javascript 1283 If you are using JSON::XS to return packets to consumption by JavaScript
792 scripts in a browser you should have a look at 1284 scripts in a browser you should have a look at
793 <http://jpsykes.com/47/practical-csrf-and-json-security> to see wether 1285 <http://jpsykes.com/47/practical-csrf-and-json-security> to see whether
794 you are vulnerable to some common attack vectors (which really are 1286 you are vulnerable to some common attack vectors (which really are
795 browser design bugs, but it is still you who will have to deal with it, 1287 browser design bugs, but it is still you who will have to deal with it,
796 as major browser developers care only for features, not about doing 1288 as major browser developers care only for features, not about getting
797 security right). 1289 security right).
1290
1291THREADS
1292 This module is *not* guaranteed to be thread safe and there are no plans
1293 to change this until Perl gets thread support (as opposed to the
1294 horribly slow so-called "threads" which are simply slow and bloated
1295 process simulations - use fork, it's *much* faster, cheaper, better).
1296
1297 (It might actually work, but you have been warned).
798 1298
799BUGS 1299BUGS
800 While the goal of this module is to be correct, that unfortunately does 1300 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 1301 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. 1302 keep reporting bugs they will be fixed swiftly, though.
1303
1304 Please refrain from using rt.cpan.org or any other bug reporting
1305 service. I put the contact address into my modules for a reason.
1306
1307SEE ALSO
1308 The json_xs command line utility for quick experiments.
804 1309
805AUTHOR 1310AUTHOR
806 Marc Lehmann <schmorp@schmorp.de> 1311 Marc Lehmann <schmorp@schmorp.de>
807 http://home.schmorp.de/ 1312 http://home.schmorp.de/
808 1313

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