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Revision 1.36 by root, Wed Jul 27 15:53:40 2011 UTC

1NAME 1NAME
2 JSON::XS - JSON serialising/deserialising, done correctly and fast 2 JSON::XS - JSON serialising/deserialising, done correctly and fast
3 3
4 JSON::XS - 正しくて高速な JSON シリアライザ/デシリアライザ
5 (http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html)
6
4SYNOPSIS 7SYNOPSIS
5 use JSON::XS; 8 use JSON::XS;
6 9
7 # exported functions, they croak on error 10 # exported functions, they croak on error
8 # and expect/generate UTF-8 11 # and expect/generate UTF-8
9 12
10 $utf8_encoded_json_text = to_json $perl_hash_or_arrayref; 13 $utf8_encoded_json_text = encode_json $perl_hash_or_arrayref;
11 $perl_hash_or_arrayref = from_json $utf8_encoded_json_text; 14 $perl_hash_or_arrayref = decode_json $utf8_encoded_json_text;
12 15
13 # OO-interface 16 # OO-interface
14 17
15 $coder = JSON::XS->new->ascii->pretty->allow_nonref; 18 $coder = JSON::XS->new->ascii->pretty->allow_nonref;
16 $pretty_printed_unencoded = $coder->encode ($perl_scalar); 19 $pretty_printed_unencoded = $coder->encode ($perl_scalar);
17 $perl_scalar = $coder->decode ($unicode_json_text); 20 $perl_scalar = $coder->decode ($unicode_json_text);
21
22 # Note that JSON version 2.0 and above will automatically use JSON::XS
23 # if available, at virtually no speed overhead either, so you should
24 # be able to just:
25
26 use JSON;
27
28 # and do the same things, except that you have a pure-perl fallback now.
18 29
19DESCRIPTION 30DESCRIPTION
20 This module converts Perl data structures to JSON and vice versa. Its 31 This module converts Perl data structures to JSON and vice versa. Its
21 primary goal is to be *correct* and its secondary goal is to be *fast*. 32 primary goal is to be *correct* and its secondary goal is to be *fast*.
22 To reach the latter goal it was written in C. 33 To reach the latter goal it was written in C.
34
35 Beginning with version 2.0 of the JSON module, when both JSON and
36 JSON::XS are installed, then JSON will fall back on JSON::XS (this can
37 be overridden) with no overhead due to emulation (by inheriting
38 constructor and methods). If JSON::XS is not available, it will fall
39 back to the compatible JSON::PP module as backend, so using JSON instead
40 of JSON::XS gives you a portable JSON API that can be fast when you need
41 and doesn't require a C compiler when that is a problem.
23 42
24 As this is the n-th-something JSON module on CPAN, what was the reason 43 As this is the n-th-something JSON module on CPAN, what was the reason
25 to write yet another JSON module? While it seems there are many JSON 44 to write yet another JSON module? While it seems there are many JSON
26 modules, none of them correctly handle all corner cases, and in most 45 modules, none of them correctly handle all corner cases, and in most
27 cases their maintainers are unresponsive, gone missing, or not listening 46 cases their maintainers are unresponsive, gone missing, or not listening
28 to bug reports for other reasons. 47 to bug reports for other reasons.
29 48
30 See COMPARISON, below, for a comparison to some other JSON modules.
31
32 See MAPPING, below, on how JSON::XS maps perl values to JSON values and 49 See MAPPING, below, on how JSON::XS maps perl values to JSON values and
33 vice versa. 50 vice versa.
34 51
35 FEATURES 52 FEATURES
36 * correct unicode handling 53 * correct Unicode handling
54
37 This module knows how to handle Unicode, and even documents how and 55 This module knows how to handle Unicode, documents how and when it
38 when it does so. 56 does so, and even documents what "correct" means.
39 57
40 * round-trip integrity 58 * round-trip integrity
59
41 When you serialise a perl data structure using only datatypes 60 When you serialise a perl data structure using only data types
42 supported by JSON, the deserialised data structure is identical on 61 supported by JSON and Perl, the deserialised data structure is
43 the Perl level. (e.g. the string "2.0" doesn't suddenly become "2" 62 identical on the Perl level. (e.g. the string "2.0" doesn't suddenly
44 just because it looks like a number). 63 become "2" just because it looks like a number). There *are* minor
64 exceptions to this, read the MAPPING section below to learn about
65 those.
45 66
46 * strict checking of JSON correctness 67 * strict checking of JSON correctness
68
47 There is no guessing, no generating of illegal JSON texts by 69 There is no guessing, no generating of illegal JSON texts by
48 default, and only JSON is accepted as input by default (the latter 70 default, and only JSON is accepted as input by default (the latter
49 is a security feature). 71 is a security feature).
50 72
51 * fast 73 * fast
52 Compared to other JSON modules, this module compares favourably in
53 terms of speed, too.
54 74
75 Compared to other JSON modules and other serialisers such as
76 Storable, this module usually compares favourably in terms of speed,
77 too.
78
55 * simple to use 79 * simple to use
80
56 This module has both a simple functional interface as well as an OO 81 This module has both a simple functional interface as well as an
57 interface. 82 object oriented interface interface.
58 83
59 * reasonably versatile output formats 84 * reasonably versatile output formats
85
60 You can choose between the most compact guarenteed single-line 86 You can choose between the most compact guaranteed-single-line
61 format possible (nice for simple line-based protocols), a pure-ascii 87 format possible (nice for simple line-based protocols), a pure-ASCII
62 format (for when your transport is not 8-bit clean, still supports 88 format (for when your transport is not 8-bit clean, still supports
63 the whole unicode range), or a pretty-printed format (for when you 89 the whole Unicode range), or a pretty-printed format (for when you
64 want to read that stuff). Or you can combine those features in 90 want to read that stuff). Or you can combine those features in
65 whatever way you like. 91 whatever way you like.
66 92
67FUNCTIONAL INTERFACE 93FUNCTIONAL INTERFACE
68 The following convinience methods are provided by this module. They are 94 The following convenience methods are provided by this module. They are
69 exported by default: 95 exported by default:
70 96
71 $json_text = to_json $perl_scalar 97 $json_text = encode_json $perl_scalar
72 Converts the given Perl data structure (a simple scalar or a 98 Converts the given Perl data structure to a UTF-8 encoded, binary
73 reference to a hash or array) to a UTF-8 encoded, binary string
74 (that is, the string contains octets only). Croaks on error. 99 string (that is, the string contains octets only). Croaks on error.
75 100
76 This function call is functionally identical to: 101 This function call is functionally identical to:
77 102
78 $json_text = JSON::XS->new->utf8->encode ($perl_scalar) 103 $json_text = JSON::XS->new->utf8->encode ($perl_scalar)
79 104
80 except being faster. 105 Except being faster.
81 106
82 $perl_scalar = from_json $json_text 107 $perl_scalar = decode_json $json_text
83 The opposite of "to_json": expects an UTF-8 (binary) string and 108 The opposite of "encode_json": expects an UTF-8 (binary) string and
84 tries to parse that as an UTF-8 encoded JSON text, returning the 109 tries to parse that as an UTF-8 encoded JSON text, returning the
85 resulting simple scalar or reference. Croaks on error. 110 resulting reference. Croaks on error.
86 111
87 This function call is functionally identical to: 112 This function call is functionally identical to:
88 113
89 $perl_scalar = JSON::XS->new->utf8->decode ($json_text) 114 $perl_scalar = JSON::XS->new->utf8->decode ($json_text)
90 115
91 except being faster. 116 Except being faster.
92 117
93 $is_boolean = JSON::XS::is_bool $scalar 118 $is_boolean = JSON::XS::is_bool $scalar
94 Returns true if the passed scalar represents either JSON::XS::true 119 Returns true if the passed scalar represents either JSON::XS::true
95 or JSON::XS::false, two constants that act like 1 and 0, 120 or JSON::XS::false, two constants that act like 1 and 0,
96 respectively and are used to represent JSON "true" and "false" 121 respectively and are used to represent JSON "true" and "false"
97 values in Perl. 122 values in Perl.
98 123
99 See MAPPING, below, for more information on how JSON values are 124 See MAPPING, below, for more information on how JSON values are
100 mapped to Perl. 125 mapped to Perl.
101 126
127A FEW NOTES ON UNICODE AND PERL
128 Since this often leads to confusion, here are a few very clear words on
129 how Unicode works in Perl, modulo bugs.
130
131 1. Perl strings can store characters with ordinal values > 255.
132 This enables you to store Unicode characters as single characters in
133 a Perl string - very natural.
134
135 2. Perl does *not* associate an encoding with your strings.
136 ... until you force it to, e.g. when matching it against a regex, or
137 printing the scalar to a file, in which case Perl either interprets
138 your string as locale-encoded text, octets/binary, or as Unicode,
139 depending on various settings. In no case is an encoding stored
140 together with your data, it is *use* that decides encoding, not any
141 magical meta data.
142
143 3. The internal utf-8 flag has no meaning with regards to the encoding
144 of your string.
145 Just ignore that flag unless you debug a Perl bug, a module written
146 in XS or want to dive into the internals of perl. Otherwise it will
147 only confuse you, as, despite the name, it says nothing about how
148 your string is encoded. You can have Unicode strings with that flag
149 set, with that flag clear, and you can have binary data with that
150 flag set and that flag clear. Other possibilities exist, too.
151
152 If you didn't know about that flag, just the better, pretend it
153 doesn't exist.
154
155 4. A "Unicode String" is simply a string where each character can be
156 validly interpreted as a Unicode code point.
157 If you have UTF-8 encoded data, it is no longer a Unicode string,
158 but a Unicode string encoded in UTF-8, giving you a binary string.
159
160 5. A string containing "high" (> 255) character values is *not* a UTF-8
161 string.
162 It's a fact. Learn to live with it.
163
164 I hope this helps :)
165
102OBJECT-ORIENTED INTERFACE 166OBJECT-ORIENTED INTERFACE
103 The object oriented interface lets you configure your own encoding or 167 The object oriented interface lets you configure your own encoding or
104 decoding style, within the limits of supported formats. 168 decoding style, within the limits of supported formats.
105 169
106 $json = new JSON::XS 170 $json = new JSON::XS
… …
113 177
114 my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]}) 178 my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]})
115 => {"a": [1, 2]} 179 => {"a": [1, 2]}
116 180
117 $json = $json->ascii ([$enable]) 181 $json = $json->ascii ([$enable])
182 $enabled = $json->get_ascii
118 If $enable is true (or missing), then the "encode" method will not 183 If $enable is true (or missing), then the "encode" method will not
119 generate characters outside the code range 0..127 (which is ASCII). 184 generate characters outside the code range 0..127 (which is ASCII).
120 Any unicode characters outside that range will be escaped using 185 Any Unicode characters outside that range will be escaped using
121 either a single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL 186 either a single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL
122 escape sequence, as per RFC4627. The resulting encoded JSON text can 187 escape sequence, as per RFC4627. The resulting encoded JSON text can
123 be treated as a native unicode string, an ascii-encoded, 188 be treated as a native Unicode string, an ascii-encoded,
124 latin1-encoded or UTF-8 encoded string, or any other superset of 189 latin1-encoded or UTF-8 encoded string, or any other superset of
125 ASCII. 190 ASCII.
126 191
127 If $enable is false, then the "encode" method will not escape 192 If $enable is false, then the "encode" method will not escape
128 Unicode characters unless required by the JSON syntax or other 193 Unicode characters unless required by the JSON syntax or other
129 flags. This results in a faster and more compact format. 194 flags. This results in a faster and more compact format.
130 195
196 See also the section *ENCODING/CODESET FLAG NOTES* later in this
197 document.
198
131 The main use for this flag is to produce JSON texts that can be 199 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 200 transmitted over a 7-bit channel, as the encoded JSON texts will not
133 contain any 8 bit characters. 201 contain any 8 bit characters.
134 202
135 JSON::XS->new->ascii (1)->encode ([chr 0x10401]) 203 JSON::XS->new->ascii (1)->encode ([chr 0x10401])
136 => ["\ud801\udc01"] 204 => ["\ud801\udc01"]
137 205
138 $json = $json->latin1 ([$enable]) 206 $json = $json->latin1 ([$enable])
207 $enabled = $json->get_latin1
139 If $enable is true (or missing), then the "encode" method will 208 If $enable is true (or missing), then the "encode" method will
140 encode the resulting JSON text as latin1 (or iso-8859-1), escaping 209 encode the resulting JSON text as latin1 (or iso-8859-1), escaping
141 any characters outside the code range 0..255. The resulting string 210 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 211 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 212 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 213 flag, as "decode" by default expects Unicode, which is a strict
145 superset of latin1. 214 superset of latin1.
146 215
147 If $enable is false, then the "encode" method will not escape 216 If $enable is false, then the "encode" method will not escape
148 Unicode characters unless required by the JSON syntax or other 217 Unicode characters unless required by the JSON syntax or other
149 flags. 218 flags.
219
220 See also the section *ENCODING/CODESET FLAG NOTES* later in this
221 document.
150 222
151 The main use for this flag is efficiently encoding binary data as 223 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 224 JSON text, as most octets will not be escaped, resulting in a
153 smaller encoded size. The disadvantage is that the resulting JSON 225 smaller encoded size. The disadvantage is that the resulting JSON
154 text is encoded in latin1 (and must correctly be treated as such 226 text is encoded in latin1 (and must correctly be treated as such
155 when storing and transfering), a rare encoding for JSON. It is 227 when storing and transferring), a rare encoding for JSON. It is
156 therefore most useful when you want to store data structures known 228 therefore most useful when you want to store data structures known
157 to contain binary data efficiently in files or databases, not when 229 to contain binary data efficiently in files or databases, not when
158 talking to other JSON encoders/decoders. 230 talking to other JSON encoders/decoders.
159 231
160 JSON::XS->new->latin1->encode (["\x{89}\x{abc}"] 232 JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]
161 => ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not) 233 => ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)
162 234
163 $json = $json->utf8 ([$enable]) 235 $json = $json->utf8 ([$enable])
236 $enabled = $json->get_utf8
164 If $enable is true (or missing), then the "encode" method will 237 If $enable is true (or missing), then the "encode" method will
165 encode the JSON result into UTF-8, as required by many protocols, 238 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 239 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 240 string. Please note that UTF-8-encoded strings do not contain any
168 characters outside the range 0..255, they are thus useful for 241 characters outside the range 0..255, they are thus useful for
169 bytewise/binary I/O. In future versions, enabling this option might 242 bytewise/binary I/O. In future versions, enabling this option might
170 enable autodetection of the UTF-16 and UTF-32 encoding families, as 243 enable autodetection of the UTF-16 and UTF-32 encoding families, as
171 described in RFC4627. 244 described in RFC4627.
172 245
173 If $enable is false, then the "encode" method will return the JSON 246 If $enable is false, then the "encode" method will return the JSON
174 string as a (non-encoded) unicode string, while "decode" expects 247 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 248 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. 249 UTF-16) needs to be done yourself, e.g. using the Encode module.
250
251 See also the section *ENCODING/CODESET FLAG NOTES* later in this
252 document.
177 253
178 Example, output UTF-16BE-encoded JSON: 254 Example, output UTF-16BE-encoded JSON:
179 255
180 use Encode; 256 use Encode;
181 $jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object); 257 $jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
… …
200 2 276 2
201 ] 277 ]
202 } 278 }
203 279
204 $json = $json->indent ([$enable]) 280 $json = $json->indent ([$enable])
281 $enabled = $json->get_indent
205 If $enable is true (or missing), then the "encode" method will use a 282 If $enable is true (or missing), then the "encode" method will use a
206 multiline format as output, putting every array member or 283 multiline format as output, putting every array member or
207 object/hash key-value pair into its own line, identing them 284 object/hash key-value pair into its own line, indenting them
208 properly. 285 properly.
209 286
210 If $enable is false, no newlines or indenting will be produced, and 287 If $enable is false, no newlines or indenting will be produced, and
211 the resulting JSON text is guarenteed not to contain any "newlines". 288 the resulting JSON text is guaranteed not to contain any "newlines".
212 289
213 This setting has no effect when decoding JSON texts. 290 This setting has no effect when decoding JSON texts.
214 291
215 $json = $json->space_before ([$enable]) 292 $json = $json->space_before ([$enable])
293 $enabled = $json->get_space_before
216 If $enable is true (or missing), then the "encode" method will add 294 If $enable is true (or missing), then the "encode" method will add
217 an extra optional space before the ":" separating keys from values 295 an extra optional space before the ":" separating keys from values
218 in JSON objects. 296 in JSON objects.
219 297
220 If $enable is false, then the "encode" method will not add any extra 298 If $enable is false, then the "encode" method will not add any extra
… …
226 Example, space_before enabled, space_after and indent disabled: 304 Example, space_before enabled, space_after and indent disabled:
227 305
228 {"key" :"value"} 306 {"key" :"value"}
229 307
230 $json = $json->space_after ([$enable]) 308 $json = $json->space_after ([$enable])
309 $enabled = $json->get_space_after
231 If $enable is true (or missing), then the "encode" method will add 310 If $enable is true (or missing), then the "encode" method will add
232 an extra optional space after the ":" separating keys from values in 311 an extra optional space after the ":" separating keys from values in
233 JSON objects and extra whitespace after the "," separating key-value 312 JSON objects and extra whitespace after the "," separating key-value
234 pairs and array members. 313 pairs and array members.
235 314
… …
240 319
241 Example, space_before and indent disabled, space_after enabled: 320 Example, space_before and indent disabled, space_after enabled:
242 321
243 {"key": "value"} 322 {"key": "value"}
244 323
324 $json = $json->relaxed ([$enable])
325 $enabled = $json->get_relaxed
326 If $enable is true (or missing), then "decode" will accept some
327 extensions to normal JSON syntax (see below). "encode" will not be
328 affected in anyway. *Be aware that this option makes you accept
329 invalid JSON texts as if they were valid!*. I suggest only to use
330 this option to parse application-specific files written by humans
331 (configuration files, resource files etc.)
332
333 If $enable is false (the default), then "decode" will only accept
334 valid JSON texts.
335
336 Currently accepted extensions are:
337
338 * list items can have an end-comma
339
340 JSON *separates* array elements and key-value pairs with commas.
341 This can be annoying if you write JSON texts manually and want
342 to be able to quickly append elements, so this extension accepts
343 comma at the end of such items not just between them:
344
345 [
346 1,
347 2, <- this comma not normally allowed
348 ]
349 {
350 "k1": "v1",
351 "k2": "v2", <- this comma not normally allowed
352 }
353
354 * shell-style '#'-comments
355
356 Whenever JSON allows whitespace, shell-style comments are
357 additionally allowed. They are terminated by the first
358 carriage-return or line-feed character, after which more
359 white-space and comments are allowed.
360
361 [
362 1, # this comment not allowed in JSON
363 # neither this one...
364 ]
365
245 $json = $json->canonical ([$enable]) 366 $json = $json->canonical ([$enable])
367 $enabled = $json->get_canonical
246 If $enable is true (or missing), then the "encode" method will 368 If $enable is true (or missing), then the "encode" method will
247 output JSON objects by sorting their keys. This is adding a 369 output JSON objects by sorting their keys. This is adding a
248 comparatively high overhead. 370 comparatively high overhead.
249 371
250 If $enable is false, then the "encode" method will output key-value 372 If $enable is false, then the "encode" method will output key-value
251 pairs in the order Perl stores them (which will likely change 373 pairs in the order Perl stores them (which will likely change
252 between runs of the same script). 374 between runs of the same script).
253 375
254 This option is useful if you want the same data structure to be 376 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 377 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 378 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 379 contains the same data, as key-value pairs have no inherent ordering
258 in Perl. 380 in Perl.
259 381
260 This setting has no effect when decoding JSON texts. 382 This setting has no effect when decoding JSON texts.
261 383
384 This setting has currently no effect on tied hashes.
385
262 $json = $json->allow_nonref ([$enable]) 386 $json = $json->allow_nonref ([$enable])
387 $enabled = $json->get_allow_nonref
263 If $enable is true (or missing), then the "encode" method can 388 If $enable is true (or missing), then the "encode" method can
264 convert a non-reference into its corresponding string, number or 389 convert a non-reference into its corresponding string, number or
265 null JSON value, which is an extension to RFC4627. Likewise, 390 null JSON value, which is an extension to RFC4627. Likewise,
266 "decode" will accept those JSON values instead of croaking. 391 "decode" will accept those JSON values instead of croaking.
267 392
… …
274 "allow_nonref", resulting in an invalid JSON text: 399 "allow_nonref", resulting in an invalid JSON text:
275 400
276 JSON::XS->new->allow_nonref->encode ("Hello, World!") 401 JSON::XS->new->allow_nonref->encode ("Hello, World!")
277 => "Hello, World!" 402 => "Hello, World!"
278 403
404 $json = $json->allow_unknown ([$enable])
405 $enabled = $json->get_allow_unknown
406 If $enable is true (or missing), then "encode" will *not* throw an
407 exception when it encounters values it cannot represent in JSON (for
408 example, filehandles) but instead will encode a JSON "null" value.
409 Note that blessed objects are not included here and are handled
410 separately by c<allow_nonref>.
411
412 If $enable is false (the default), then "encode" will throw an
413 exception when it encounters anything it cannot encode as JSON.
414
415 This option does not affect "decode" in any way, and it is
416 recommended to leave it off unless you know your communications
417 partner.
418
279 $json = $json->allow_blessed ([$enable]) 419 $json = $json->allow_blessed ([$enable])
420 $enabled = $json->get_allow_blessed
280 If $enable is true (or missing), then the "encode" method will not 421 If $enable is true (or missing), then the "encode" method will not
281 barf when it encounters a blessed reference. Instead, the value of 422 barf when it encounters a blessed reference. Instead, the value of
282 the convert_blessed option will decide wether "null" 423 the convert_blessed option will decide whether "null"
283 ("convert_blessed" disabled or no "to_json" method found) or a 424 ("convert_blessed" disabled or no "TO_JSON" method found) or a
284 representation of the object ("convert_blessed" enabled and 425 representation of the object ("convert_blessed" enabled and
285 "to_json" method found) is being encoded. Has no effect on "decode". 426 "TO_JSON" method found) is being encoded. Has no effect on "decode".
286 427
287 If $enable is false (the default), then "encode" will throw an 428 If $enable is false (the default), then "encode" will throw an
288 exception when it encounters a blessed object. 429 exception when it encounters a blessed object.
289 430
290 $json = $json->convert_blessed ([$enable]) 431 $json = $json->convert_blessed ([$enable])
432 $enabled = $json->get_convert_blessed
291 If $enable is true (or missing), then "encode", upon encountering a 433 If $enable is true (or missing), then "encode", upon encountering a
292 blessed object, will check for the availability of the "TO_JSON" 434 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 435 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 436 context and the resulting scalar will be encoded instead of the
295 object. If no "TO_JSON" method is found, the value of 437 object. If no "TO_JSON" method is found, the value of
… …
299 returns other blessed objects, those will be handled in the same 441 returns other blessed objects, those will be handled in the same
300 way. "TO_JSON" must take care of not causing an endless recursion 442 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 443 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 444 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 445 the object) are usually in upper case letters and to avoid
304 collisions with the "to_json" function. 446 collisions with any "to_json" function or method.
305 447
306 This setting does not yet influence "decode" in any way, but in the 448 This setting does not yet influence "decode" in any way, but in the
307 future, global hooks might get installed that influence "decode" and 449 future, global hooks might get installed that influence "decode" and
308 are enabled by this setting. 450 are enabled by this setting.
309 451
… …
350 492
351 As this callback gets called less often then the 493 As this callback gets called less often then the
352 "filter_json_object" one, decoding speed will not usually suffer as 494 "filter_json_object" one, decoding speed will not usually suffer as
353 much. Therefore, single-key objects make excellent targets to 495 much. Therefore, single-key objects make excellent targets to
354 serialise Perl objects into, especially as single-key JSON objects 496 serialise Perl objects into, especially as single-key JSON objects
355 are as close to the type-tagged value concept as JSON gets (its 497 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 498 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 499 in any way, so you need to make sure your data never looks like a
358 serialised Perl hash. 500 serialised Perl hash.
359 501
360 Typical names for the single object key are "__class_whatever__", or 502 Typical names for the single object key are "__class_whatever__", or
… …
385 527
386 { __widget__ => $self->{id} } 528 { __widget__ => $self->{id} }
387 } 529 }
388 530
389 $json = $json->shrink ([$enable]) 531 $json = $json->shrink ([$enable])
532 $enabled = $json->get_shrink
390 Perl usually over-allocates memory a bit when allocating space for 533 Perl usually over-allocates memory a bit when allocating space for
391 strings. This flag optionally resizes strings generated by either 534 strings. This flag optionally resizes strings generated by either
392 "encode" or "decode" to their minimum size possible. This can save 535 "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 536 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 537 many short strings. It will also try to downgrade any strings to
… …
412 converting strings that look like integers or floats into integers 555 converting strings that look like integers or floats into integers
413 or floats internally (there is no difference on the Perl level), 556 or floats internally (there is no difference on the Perl level),
414 saving space. 557 saving space.
415 558
416 $json = $json->max_depth ([$maximum_nesting_depth]) 559 $json = $json->max_depth ([$maximum_nesting_depth])
560 $max_depth = $json->get_max_depth
417 Sets the maximum nesting level (default 512) accepted while encoding 561 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 562 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 563 Perl data structure, then the encoder and decoder will stop and
420 will stop and croak at that point. 564 croak at that point.
421 565
422 Nesting level is defined by number of hash- or arrayrefs that the 566 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 567 encoder needs to traverse to reach a given point or the number of
424 "{" or "[" characters without their matching closing parenthesis 568 "{" or "[" characters without their matching closing parenthesis
425 crossed to reach a given character in a string. 569 crossed to reach a given character in a string.
426 570
427 Setting the maximum depth to one disallows any nesting, so that 571 Setting the maximum depth to one disallows any nesting, so that
428 ensures that the object is only a single hash/object or array. 572 ensures that the object is only a single hash/object or array.
429 573
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 574 If no argument is given, the highest possible setting will be used,
432 will be used, which is rarely useful. 575 which is rarely useful.
576
577 Note that nesting is implemented by recursion in C. The default
578 value has been chosen to be as large as typical operating systems
579 allow without crashing.
433 580
434 See SECURITY CONSIDERATIONS, below, for more info on why this is 581 See SECURITY CONSIDERATIONS, below, for more info on why this is
435 useful. 582 useful.
436 583
437 $json = $json->max_size ([$maximum_string_size]) 584 $json = $json->max_size ([$maximum_string_size])
585 $max_size = $json->get_max_size
438 Set the maximum length a JSON text may have (in bytes) where 586 Set the maximum length a JSON text may have (in bytes) where
439 decoding is being attempted. The default is 0, meaning no limit. 587 decoding is being attempted. The default is 0, meaning no limit.
440 When "decode" is called on a string longer then this number of 588 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 589 bytes, it will not attempt to decode the string but throw an
442 exception. This setting has no effect on "encode" (yet). 590 exception. This setting has no effect on "encode" (yet).
443 591
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 592 If no argument is given, the limit check will be deactivated (same
447 specified). 593 as when 0 is specified).
448 594
449 See SECURITY CONSIDERATIONS, below, for more info on why this is 595 See SECURITY CONSIDERATIONS, below, for more info on why this is
450 useful. 596 useful.
451 597
452 $json_text = $json->encode ($perl_scalar) 598 $json_text = $json->encode ($perl_scalar)
… …
477 and you need to know where the JSON text ends. 623 and you need to know where the JSON text ends.
478 624
479 JSON::XS->new->decode_prefix ("[1] the tail") 625 JSON::XS->new->decode_prefix ("[1] the tail")
480 => ([], 3) 626 => ([], 3)
481 627
628INCREMENTAL PARSING
629 In some cases, there is the need for incremental parsing of JSON texts.
630 While this module always has to keep both JSON text and resulting Perl
631 data structure in memory at one time, it does allow you to parse a JSON
632 stream incrementally. It does so by accumulating text until it has a
633 full JSON object, which it then can decode. This process is similar to
634 using "decode_prefix" to see if a full JSON object is available, but is
635 much more efficient (and can be implemented with a minimum of method
636 calls).
637
638 JSON::XS will only attempt to parse the JSON text once it is sure it has
639 enough text to get a decisive result, using a very simple but truly
640 incremental parser. This means that it sometimes won't stop as early as
641 the full parser, for example, it doesn't detect mismatched parentheses.
642 The only thing it guarantees is that it starts decoding as soon as a
643 syntactically valid JSON text has been seen. This means you need to set
644 resource limits (e.g. "max_size") to ensure the parser will stop parsing
645 in the presence if syntax errors.
646
647 The following methods implement this incremental parser.
648
649 [void, scalar or list context] = $json->incr_parse ([$string])
650 This is the central parsing function. It can both append new text
651 and extract objects from the stream accumulated so far (both of
652 these functions are optional).
653
654 If $string is given, then this string is appended to the already
655 existing JSON fragment stored in the $json object.
656
657 After that, if the function is called in void context, it will
658 simply return without doing anything further. This can be used to
659 add more text in as many chunks as you want.
660
661 If the method is called in scalar context, then it will try to
662 extract exactly *one* JSON object. If that is successful, it will
663 return this object, otherwise it will return "undef". If there is a
664 parse error, this method will croak just as "decode" would do (one
665 can then use "incr_skip" to skip the errornous part). This is the
666 most common way of using the method.
667
668 And finally, in list context, it will try to extract as many objects
669 from the stream as it can find and return them, or the empty list
670 otherwise. For this to work, there must be no separators between the
671 JSON objects or arrays, instead they must be concatenated
672 back-to-back. If an error occurs, an exception will be raised as in
673 the scalar context case. Note that in this case, any
674 previously-parsed JSON texts will be lost.
675
676 Example: Parse some JSON arrays/objects in a given string and return
677 them.
678
679 my @objs = JSON::XS->new->incr_parse ("[5][7][1,2]");
680
681 $lvalue_string = $json->incr_text
682 This method returns the currently stored JSON fragment as an lvalue,
683 that is, you can manipulate it. This *only* works when a preceding
684 call to "incr_parse" in *scalar context* successfully returned an
685 object. Under all other circumstances you must not call this
686 function (I mean it. although in simple tests it might actually
687 work, it *will* fail under real world conditions). As a special
688 exception, you can also call this method before having parsed
689 anything.
690
691 This function is useful in two cases: a) finding the trailing text
692 after a JSON object or b) parsing multiple JSON objects separated by
693 non-JSON text (such as commas).
694
695 $json->incr_skip
696 This will reset the state of the incremental parser and will remove
697 the parsed text from the input buffer so far. This is useful after
698 "incr_parse" died, in which case the input buffer and incremental
699 parser state is left unchanged, to skip the text parsed so far and
700 to reset the parse state.
701
702 The difference to "incr_reset" is that only text until the parse
703 error occured is removed.
704
705 $json->incr_reset
706 This completely resets the incremental parser, that is, after this
707 call, it will be as if the parser had never parsed anything.
708
709 This is useful if you want to repeatedly parse JSON objects and want
710 to ignore any trailing data, which means you have to reset the
711 parser after each successful decode.
712
713 LIMITATIONS
714 All options that affect decoding are supported, except "allow_nonref".
715 The reason for this is that it cannot be made to work sensibly: JSON
716 objects and arrays are self-delimited, i.e. you can concatenate them
717 back to back and still decode them perfectly. This does not hold true
718 for JSON numbers, however.
719
720 For example, is the string 1 a single JSON number, or is it simply the
721 start of 12? Or is 12 a single JSON number, or the concatenation of 1
722 and 2? In neither case you can tell, and this is why JSON::XS takes the
723 conservative route and disallows this case.
724
725 EXAMPLES
726 Some examples will make all this clearer. First, a simple example that
727 works similarly to "decode_prefix": We want to decode the JSON object at
728 the start of a string and identify the portion after the JSON object:
729
730 my $text = "[1,2,3] hello";
731
732 my $json = new JSON::XS;
733
734 my $obj = $json->incr_parse ($text)
735 or die "expected JSON object or array at beginning of string";
736
737 my $tail = $json->incr_text;
738 # $tail now contains " hello"
739
740 Easy, isn't it?
741
742 Now for a more complicated example: Imagine a hypothetical protocol
743 where you read some requests from a TCP stream, and each request is a
744 JSON array, without any separation between them (in fact, it is often
745 useful to use newlines as "separators", as these get interpreted as
746 whitespace at the start of the JSON text, which makes it possible to
747 test said protocol with "telnet"...).
748
749 Here is how you'd do it (it is trivial to write this in an event-based
750 manner):
751
752 my $json = new JSON::XS;
753
754 # read some data from the socket
755 while (sysread $socket, my $buf, 4096) {
756
757 # split and decode as many requests as possible
758 for my $request ($json->incr_parse ($buf)) {
759 # act on the $request
760 }
761 }
762
763 Another complicated example: Assume you have a string with JSON objects
764 or arrays, all separated by (optional) comma characters (e.g. "[1],[2],
765 [3]"). To parse them, we have to skip the commas between the JSON texts,
766 and here is where the lvalue-ness of "incr_text" comes in useful:
767
768 my $text = "[1],[2], [3]";
769 my $json = new JSON::XS;
770
771 # void context, so no parsing done
772 $json->incr_parse ($text);
773
774 # now extract as many objects as possible. note the
775 # use of scalar context so incr_text can be called.
776 while (my $obj = $json->incr_parse) {
777 # do something with $obj
778
779 # now skip the optional comma
780 $json->incr_text =~ s/^ \s* , //x;
781 }
782
783 Now lets go for a very complex example: Assume that you have a gigantic
784 JSON array-of-objects, many gigabytes in size, and you want to parse it,
785 but you cannot load it into memory fully (this has actually happened in
786 the real world :).
787
788 Well, you lost, you have to implement your own JSON parser. But JSON::XS
789 can still help you: You implement a (very simple) array parser and let
790 JSON decode the array elements, which are all full JSON objects on their
791 own (this wouldn't work if the array elements could be JSON numbers, for
792 example):
793
794 my $json = new JSON::XS;
795
796 # open the monster
797 open my $fh, "<bigfile.json"
798 or die "bigfile: $!";
799
800 # first parse the initial "["
801 for (;;) {
802 sysread $fh, my $buf, 65536
803 or die "read error: $!";
804 $json->incr_parse ($buf); # void context, so no parsing
805
806 # Exit the loop once we found and removed(!) the initial "[".
807 # In essence, we are (ab-)using the $json object as a simple scalar
808 # we append data to.
809 last if $json->incr_text =~ s/^ \s* \[ //x;
810 }
811
812 # now we have the skipped the initial "[", so continue
813 # parsing all the elements.
814 for (;;) {
815 # in this loop we read data until we got a single JSON object
816 for (;;) {
817 if (my $obj = $json->incr_parse) {
818 # do something with $obj
819 last;
820 }
821
822 # add more data
823 sysread $fh, my $buf, 65536
824 or die "read error: $!";
825 $json->incr_parse ($buf); # void context, so no parsing
826 }
827
828 # in this loop we read data until we either found and parsed the
829 # separating "," between elements, or the final "]"
830 for (;;) {
831 # first skip whitespace
832 $json->incr_text =~ s/^\s*//;
833
834 # if we find "]", we are done
835 if ($json->incr_text =~ s/^\]//) {
836 print "finished.\n";
837 exit;
838 }
839
840 # if we find ",", we can continue with the next element
841 if ($json->incr_text =~ s/^,//) {
842 last;
843 }
844
845 # if we find anything else, we have a parse error!
846 if (length $json->incr_text) {
847 die "parse error near ", $json->incr_text;
848 }
849
850 # else add more data
851 sysread $fh, my $buf, 65536
852 or die "read error: $!";
853 $json->incr_parse ($buf); # void context, so no parsing
854 }
855
856 This is a complex example, but most of the complexity comes from the
857 fact that we are trying to be correct (bear with me if I am wrong, I
858 never ran the above example :).
859
482MAPPING 860MAPPING
483 This section describes how JSON::XS maps Perl values to JSON values and 861 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 862 vice versa. These mappings are designed to "do the right thing" in most
485 circumstances automatically, preserving round-tripping characteristics 863 circumstances automatically, preserving round-tripping characteristics
486 (what you put in comes out as something equivalent). 864 (what you put in comes out as something equivalent).
487 865
488 For the more enlightened: note that in the following descriptions, 866 For the more enlightened: note that in the following descriptions,
489 lowercase *perl* refers to the Perl interpreter, while uppcercase *Perl* 867 lowercase *perl* refers to the Perl interpreter, while uppercase *Perl*
490 refers to the abstract Perl language itself. 868 refers to the abstract Perl language itself.
491 869
492 JSON -> PERL 870 JSON -> PERL
493 object 871 object
494 A JSON object becomes a reference to a hash in Perl. No ordering of 872 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 873 object keys is preserved (JSON does not preserve object key ordering
496 ordering itself). 874 itself).
497 875
498 array 876 array
499 A JSON array becomes a reference to an array in Perl. 877 A JSON array becomes a reference to an array in Perl.
500 878
501 string 879 string
… …
507 A JSON number becomes either an integer, numeric (floating point) or 885 A JSON number becomes either an integer, numeric (floating point) or
508 string scalar in perl, depending on its range and any fractional 886 string scalar in perl, depending on its range and any fractional
509 parts. On the Perl level, there is no difference between those as 887 parts. On the Perl level, there is no difference between those as
510 Perl handles all the conversion details, but an integer may take 888 Perl handles all the conversion details, but an integer may take
511 slightly less memory and might represent more values exactly than 889 slightly less memory and might represent more values exactly than
512 (floating point) numbers. 890 floating point numbers.
513 891
514 If the number consists of digits only, JSON::XS will try to 892 If the number consists of digits only, JSON::XS will try to
515 represent it as an integer value. If that fails, it will try to 893 represent it as an integer value. If that fails, it will try to
516 represent it as a numeric (floating point) value if that is possible 894 represent it as a numeric (floating point) value if that is possible
517 without loss of precision. Otherwise it will preserve the number as 895 without loss of precision. Otherwise it will preserve the number as
518 a string value. 896 a string value (in which case you lose roundtripping ability, as the
897 JSON number will be re-encoded toa JSON string).
519 898
520 Numbers containing a fractional or exponential part will always be 899 Numbers containing a fractional or exponential part will always be
521 represented as numeric (floating point) values, possibly at a loss 900 represented as numeric (floating point) values, possibly at a loss
522 of precision. 901 of precision (in which case you might lose perfect roundtripping
902 ability, but the JSON number will still be re-encoded as a JSON
903 number).
523 904
524 This might create round-tripping problems as numbers might become 905 Note that precision is not accuracy - binary floating point values
525 strings, but as Perl is typeless there is no other way to do it. 906 cannot represent most decimal fractions exactly, and when converting
907 from and to floating point, JSON::XS only guarantees precision up to
908 but not including the leats significant bit.
526 909
527 true, false 910 true, false
528 These JSON atoms become "JSON::XS::true" and "JSON::XS::false", 911 These JSON atoms become "JSON::XS::true" and "JSON::XS::false",
529 respectively. They are overloaded to act almost exactly like the 912 respectively. They are overloaded to act almost exactly like the
530 numbers 1 and 0. You can check wether a scalar is a JSON boolean by 913 numbers 1 and 0. You can check whether a scalar is a JSON boolean by
531 using the "JSON::XS::is_bool" function. 914 using the "JSON::XS::is_bool" function.
532 915
533 null 916 null
534 A JSON null atom becomes "undef" in Perl. 917 A JSON null atom becomes "undef" in Perl.
535 918
… …
558 an exception to be thrown, except for references to the integers 0 941 an exception to be thrown, except for references to the integers 0
559 and 1, which get turned into "false" and "true" atoms in JSON. You 942 and 1, which get turned into "false" and "true" atoms in JSON. You
560 can also use "JSON::XS::false" and "JSON::XS::true" to improve 943 can also use "JSON::XS::false" and "JSON::XS::true" to improve
561 readability. 944 readability.
562 945
563 to_json [\0,JSON::XS::true] # yields [false,true] 946 encode_json [\0, JSON::XS::true] # yields [false,true]
564 947
565 JSON::XS::true, JSON::XS::false 948 JSON::XS::true, JSON::XS::false
566 These special values become JSON true and JSON false values, 949 These special values become JSON true and JSON false values,
567 respectively. You cna alos use "\1" and "\0" directly if you want. 950 respectively. You can also use "\1" and "\0" directly if you want.
568 951
569 blessed objects 952 blessed objects
570 Blessed objects are not allowed. JSON::XS currently tries to encode 953 Blessed objects are not directly representable in JSON. See the
571 their underlying representation (hash- or arrayref), but this 954 "allow_blessed" and "convert_blessed" methods on various options on
572 behaviour might change in future versions. 955 how to deal with this: basically, you can choose between throwing an
956 exception, encoding the reference as if it weren't blessed, or
957 provide your own serialiser method.
573 958
574 simple scalars 959 simple scalars
575 Simple Perl scalars (any scalar that is not a reference) are the 960 Simple Perl scalars (any scalar that is not a reference) are the
576 most difficult objects to encode: JSON::XS will encode undefined 961 most difficult objects to encode: JSON::XS will encode undefined
577 scalars as JSON null value, scalars that have last been used in a 962 scalars as JSON "null" values, scalars that have last been used in a
578 string context before encoding as JSON strings and anything else as 963 string context before encoding as JSON strings, and anything else as
579 number value: 964 number value:
580 965
581 # dump as number 966 # dump as number
582 to_json [2] # yields [2] 967 encode_json [2] # yields [2]
583 to_json [-3.0e17] # yields [-3e+17] 968 encode_json [-3.0e17] # yields [-3e+17]
584 my $value = 5; to_json [$value] # yields [5] 969 my $value = 5; encode_json [$value] # yields [5]
585 970
586 # used as string, so dump as string 971 # used as string, so dump as string
587 print $value; 972 print $value;
588 to_json [$value] # yields ["5"] 973 encode_json [$value] # yields ["5"]
589 974
590 # undef becomes null 975 # undef becomes null
591 to_json [undef] # yields [null] 976 encode_json [undef] # yields [null]
592 977
593 You can force the type to be a string by stringifying it: 978 You can force the type to be a JSON string by stringifying it:
594 979
595 my $x = 3.1; # some variable containing a number 980 my $x = 3.1; # some variable containing a number
596 "$x"; # stringified 981 "$x"; # stringified
597 $x .= ""; # another, more awkward way to stringify 982 $x .= ""; # another, more awkward way to stringify
598 print $x; # perl does it for you, too, quite often 983 print $x; # perl does it for you, too, quite often
599 984
600 You can force the type to be a number by numifying it: 985 You can force the type to be a JSON number by numifying it:
601 986
602 my $x = "3"; # some variable containing a string 987 my $x = "3"; # some variable containing a string
603 $x += 0; # numify it, ensuring it will be dumped as a number 988 $x += 0; # numify it, ensuring it will be dumped as a number
604 $x *= 1; # same thing, the choise is yours. 989 $x *= 1; # same thing, the choice is yours.
605 990
606 You can not currently output JSON booleans or force the type in 991 You can not currently force the type in other, less obscure, ways.
607 other, less obscure, ways. Tell me if you need this capability. 992 Tell me if you need this capability (but don't forget to explain why
993 it's needed :).
608 994
609COMPARISON 995 Note that numerical precision has the same meaning as under Perl (so
610 As already mentioned, this module was created because none of the 996 binary to decimal conversion follows the same rules as in Perl,
611 existing JSON modules could be made to work correctly. First I will 997 which can differ to other languages). Also, your perl interpreter
612 describe the problems (or pleasures) I encountered with various existing 998 might expose extensions to the floating point numbers of your
613 JSON modules, followed by some benchmark values. JSON::XS was designed 999 platform, such as infinities or NaN's - these cannot be represented
614 not to suffer from any of these problems or limitations. 1000 in JSON, and it is an error to pass those in.
615 1001
616 JSON 1.07 1002ENCODING/CODESET FLAG NOTES
617 Slow (but very portable, as it is written in pure Perl). 1003 The interested reader might have seen a number of flags that signify
1004 encodings or codesets - "utf8", "latin1" and "ascii". There seems to be
1005 some confusion on what these do, so here is a short comparison:
618 1006
619 Undocumented/buggy Unicode handling (how JSON handles unicode values 1007 "utf8" controls whether the JSON text created by "encode" (and expected
620 is undocumented. One can get far by feeding it unicode strings and 1008 by "decode") is UTF-8 encoded or not, while "latin1" and "ascii" only
621 doing en-/decoding oneself, but unicode escapes are not working 1009 control whether "encode" escapes character values outside their
1010 respective codeset range. Neither of these flags conflict with each
1011 other, although some combinations make less sense than others.
1012
1013 Care has been taken to make all flags symmetrical with respect to
1014 "encode" and "decode", that is, texts encoded with any combination of
1015 these flag values will be correctly decoded when the same flags are used
1016 - in general, if you use different flag settings while encoding vs. when
1017 decoding you likely have a bug somewhere.
1018
1019 Below comes a verbose discussion of these flags. Note that a "codeset"
1020 is simply an abstract set of character-codepoint pairs, while an
1021 encoding takes those codepoint numbers and *encodes* them, in our case
1022 into octets. Unicode is (among other things) a codeset, UTF-8 is an
1023 encoding, and ISO-8859-1 (= latin 1) and ASCII are both codesets *and*
1024 encodings at the same time, which can be confusing.
1025
1026 "utf8" flag disabled
1027 When "utf8" is disabled (the default), then "encode"/"decode"
1028 generate and expect Unicode strings, that is, characters with high
1029 ordinal Unicode values (> 255) will be encoded as such characters,
1030 and likewise such characters are decoded as-is, no canges to them
1031 will be done, except "(re-)interpreting" them as Unicode codepoints
1032 or Unicode characters, respectively (to Perl, these are the same
1033 thing in strings unless you do funny/weird/dumb stuff).
1034
1035 This is useful when you want to do the encoding yourself (e.g. when
1036 you want to have UTF-16 encoded JSON texts) or when some other layer
1037 does the encoding for you (for example, when printing to a terminal
1038 using a filehandle that transparently encodes to UTF-8 you certainly
1039 do NOT want to UTF-8 encode your data first and have Perl encode it
1040 another time).
1041
1042 "utf8" flag enabled
1043 If the "utf8"-flag is enabled, "encode"/"decode" will encode all
1044 characters using the corresponding UTF-8 multi-byte sequence, and
1045 will expect your input strings to be encoded as UTF-8, that is, no
1046 "character" of the input string must have any value > 255, as UTF-8
1047 does not allow that.
1048
1049 The "utf8" flag therefore switches between two modes: disabled means
1050 you will get a Unicode string in Perl, enabled means you get an
1051 UTF-8 encoded octet/binary string in Perl.
1052
1053 "latin1" or "ascii" flags enabled
1054 With "latin1" (or "ascii") enabled, "encode" will escape characters
1055 with ordinal values > 255 (> 127 with "ascii") and encode the
1056 remaining characters as specified by the "utf8" flag.
1057
1058 If "utf8" is disabled, then the result is also correctly encoded in
1059 those character sets (as both are proper subsets of Unicode, meaning
1060 that a Unicode string with all character values < 256 is the same
1061 thing as a ISO-8859-1 string, and a Unicode string with all
1062 character values < 128 is the same thing as an ASCII string in
622 properly). 1063 Perl).
623 1064
624 No roundtripping (strings get clobbered if they look like numbers, 1065 If "utf8" is enabled, you still get a correct UTF-8-encoded string,
625 e.g. the string 2.0 will encode to 2.0 instead of "2.0", and that 1066 regardless of these flags, just some more characters will be escaped
626 will decode into the number 2. 1067 using "\uXXXX" then before.
627 1068
628 JSON::PC 0.01 1069 Note that ISO-8859-1-*encoded* strings are not compatible with UTF-8
629 Very fast. 1070 encoding, while ASCII-encoded strings are. That is because the
1071 ISO-8859-1 encoding is NOT a subset of UTF-8 (despite the ISO-8859-1
1072 *codeset* being a subset of Unicode), while ASCII is.
630 1073
631 Undocumented/buggy Unicode handling. 1074 Surprisingly, "decode" will ignore these flags and so treat all
1075 input values as governed by the "utf8" flag. If it is disabled, this
1076 allows you to decode ISO-8859-1- and ASCII-encoded strings, as both
1077 strict subsets of Unicode. If it is enabled, you can correctly
1078 decode UTF-8 encoded strings.
632 1079
633 No roundtripping. 1080 So neither "latin1" nor "ascii" are incompatible with the "utf8"
1081 flag - they only govern when the JSON output engine escapes a
1082 character or not.
634 1083
635 Has problems handling many Perl values (e.g. regex results and other 1084 The main use for "latin1" is to relatively efficiently store binary
636 magic values will make it croak). 1085 data as JSON, at the expense of breaking compatibility with most
1086 JSON decoders.
637 1087
638 Does not even generate valid JSON ("{1,2}" gets converted to "{1:2}" 1088 The main use for "ascii" is to force the output to not contain
639 which is not a valid JSON text. 1089 characters with values > 127, which means you can interpret the
1090 resulting string as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about
1091 any character set and 8-bit-encoding, and still get the same data
1092 structure back. This is useful when your channel for JSON transfer
1093 is not 8-bit clean or the encoding might be mangled in between (e.g.
1094 in mail), and works because ASCII is a proper subset of most 8-bit
1095 and multibyte encodings in use in the world.
640 1096
641 Unmaintained (maintainer unresponsive for many months, bugs are not 1097 JSON and ECMAscript
642 getting fixed). 1098 JSON syntax is based on how literals are represented in javascript (the
1099 not-standardised predecessor of ECMAscript) which is presumably why it
1100 is called "JavaScript Object Notation".
643 1101
644 JSON::Syck 0.21 1102 However, JSON is not a subset (and also not a superset of course) of
645 Very buggy (often crashes). 1103 ECMAscript (the standard) or javascript (whatever browsers actually
1104 implement).
646 1105
647 Very inflexible (no human-readable format supported, format pretty 1106 If you want to use javascript's "eval" function to "parse" JSON, you
648 much undocumented. I need at least a format for easy reading by 1107 might run into parse errors for valid JSON texts, or the resulting data
649 humans and a single-line compact format for use in a protocol, and 1108 structure might not be queryable:
650 preferably a way to generate ASCII-only JSON texts).
651 1109
652 Completely broken (and confusingly documented) Unicode handling 1110 One of the problems is that U+2028 and U+2029 are valid characters
653 (unicode escapes are not working properly, you need to set 1111 inside JSON strings, but are not allowed in ECMAscript string literals,
654 ImplicitUnicode to *different* values on en- and decoding to get 1112 so the following Perl fragment will not output something that can be
655 symmetric behaviour). 1113 guaranteed to be parsable by javascript's "eval":
656 1114
657 No roundtripping (simple cases work, but this depends on wether the 1115 use JSON::XS;
658 scalar value was used in a numeric context or not).
659 1116
660 Dumping hashes may skip hash values depending on iterator state. 1117 print encode_json [chr 0x2028];
661 1118
662 Unmaintained (maintainer unresponsive for many months, bugs are not 1119 The right fix for this is to use a proper JSON parser in your javascript
663 getting fixed). 1120 programs, and not rely on "eval" (see for example Douglas Crockford's
1121 json2.js parser).
664 1122
665 Does not check input for validity (i.e. will accept non-JSON input 1123 If this is not an option, you can, as a stop-gap measure, simply encode
666 and return "something" instead of raising an exception. This is a 1124 to ASCII-only JSON:
667 security issue: imagine two banks transfering money between each
668 other using JSON. One bank might parse a given non-JSON request and
669 deduct money, while the other might reject the transaction with a
670 syntax error. While a good protocol will at least recover, that is
671 extra unnecessary work and the transaction will still not succeed).
672 1125
673 JSON::DWIW 0.04 1126 use JSON::XS;
674 Very fast. Very natural. Very nice.
675 1127
676 Undocumented unicode handling (but the best of the pack. Unicode 1128 print JSON::XS->new->ascii->encode ([chr 0x2028]);
677 escapes still don't get parsed properly).
678 1129
679 Very inflexible. 1130 Note that this will enlarge the resulting JSON text quite a bit if you
1131 have many non-ASCII characters. You might be tempted to run some regexes
1132 to only escape U+2028 and U+2029, e.g.:
680 1133
681 No roundtripping. 1134 # DO NOT USE THIS!
1135 my $json = JSON::XS->new->utf8->encode ([chr 0x2028]);
1136 $json =~ s/\xe2\x80\xa8/\\u2028/g; # escape U+2028
1137 $json =~ s/\xe2\x80\xa9/\\u2029/g; # escape U+2029
1138 print $json;
682 1139
683 Does not generate valid JSON texts (key strings are often unquoted, 1140 Note that *this is a bad idea*: the above only works for U+2028 and
684 empty keys result in nothing being output) 1141 U+2029 and thus only for fully ECMAscript-compliant parsers. Many
1142 existing javascript implementations, however, have issues with other
1143 characters as well - using "eval" naively simply *will* cause problems.
685 1144
686 Does not check input for validity. 1145 Another problem is that some javascript implementations reserve some
1146 property names for their own purposes (which probably makes them
1147 non-ECMAscript-compliant). For example, Iceweasel reserves the
1148 "__proto__" property name for its own purposes.
1149
1150 If that is a problem, you could parse try to filter the resulting JSON
1151 output for these property strings, e.g.:
1152
1153 $json =~ s/"__proto__"\s*:/"__proto__renamed":/g;
1154
1155 This works because "__proto__" is not valid outside of strings, so every
1156 occurence of ""__proto__"\s*:" must be a string used as property name.
1157
1158 If you know of other incompatibilities, please let me know.
687 1159
688 JSON and YAML 1160 JSON and YAML
689 You often hear that JSON is a subset (or a close subset) of YAML. This 1161 You often hear that JSON is a subset of YAML. This is, however, a mass
690 is, however, a mass hysteria and very far from the truth. In general, 1162 hysteria(*) and very far from the truth (as of the time of this
691 there is no way to configure JSON::XS to output a data structure as 1163 writing), so let me state it clearly: *in general, there is no way to
692 valid YAML. 1164 configure JSON::XS to output a data structure as valid YAML* that works
1165 in all cases.
693 1166
694 If you really must use JSON::XS to generate YAML, you should use this 1167 If you really must use JSON::XS to generate YAML, you should use this
695 algorithm (subject to change in future versions): 1168 algorithm (subject to change in future versions):
696 1169
697 my $to_yaml = JSON::XS->new->utf8->space_after (1); 1170 my $to_yaml = JSON::XS->new->utf8->space_after (1);
698 my $yaml = $to_yaml->encode ($ref) . "\n"; 1171 my $yaml = $to_yaml->encode ($ref) . "\n";
699 1172
700 This will usually generate JSON texts that also parse as valid YAML. 1173 This will *usually* generate JSON texts that also parse as valid YAML.
701 Please note that YAML has hardcoded limits on (simple) object key 1174 Please note that YAML has hardcoded limits on (simple) object key
702 lengths that JSON doesn't have, so you should make sure that your hash 1175 lengths that JSON doesn't have and also has different and incompatible
1176 unicode character escape syntax, so you should make sure that your hash
703 keys are noticably shorter than the 1024 characters YAML allows. 1177 keys are noticeably shorter than the 1024 "stream characters" YAML
1178 allows and that you do not have characters with codepoint values outside
1179 the Unicode BMP (basic multilingual page). YAML also does not allow "\/"
1180 sequences in strings (which JSON::XS does not *currently* generate, but
1181 other JSON generators might).
704 1182
705 There might be other incompatibilities that I am not aware of. In 1183 There might be other incompatibilities that I am not aware of (or the
1184 YAML specification has been changed yet again - it does so quite often).
706 general you should not try to generate YAML with a JSON generator or 1185 In general you should not try to generate YAML with a JSON generator or
707 vice versa, or try to parse JSON with a YAML parser or vice versa: 1186 vice versa, or try to parse JSON with a YAML parser or vice versa:
708 chances are high that you will run into severe interoperability 1187 chances are high that you will run into severe interoperability problems
709 problems. 1188 when you least expect it.
1189
1190 (*) I have been pressured multiple times by Brian Ingerson (one of the
1191 authors of the YAML specification) to remove this paragraph, despite
1192 him acknowledging that the actual incompatibilities exist. As I was
1193 personally bitten by this "JSON is YAML" lie, I refused and said I
1194 will continue to educate people about these issues, so others do not
1195 run into the same problem again and again. After this, Brian called
1196 me a (quote)*complete and worthless idiot*(unquote).
1197
1198 In my opinion, instead of pressuring and insulting people who
1199 actually clarify issues with YAML and the wrong statements of some
1200 of its proponents, I would kindly suggest reading the JSON spec
1201 (which is not that difficult or long) and finally make YAML
1202 compatible to it, and educating users about the changes, instead of
1203 spreading lies about the real compatibility for many *years* and
1204 trying to silence people who point out that it isn't true.
1205
1206 Addendum/2009: the YAML 1.2 spec is still incompatible with JSON,
1207 even though the incompatibilities have been documented (and are
1208 known to Brian) for many years and the spec makes explicit claims
1209 that YAML is a superset of JSON. It would be so easy to fix, but
1210 apparently, bullying people and corrupting userdata is so much
1211 easier.
710 1212
711 SPEED 1213 SPEED
712 It seems that JSON::XS is surprisingly fast, as shown in the following 1214 It seems that JSON::XS is surprisingly fast, as shown in the following
713 tables. They have been generated with the help of the "eg/bench" program 1215 tables. They have been generated with the help of the "eg/bench" program
714 in the JSON::XS distribution, to make it easy to compare on your own 1216 in the JSON::XS distribution, to make it easy to compare on your own
715 system. 1217 system.
716 1218
717 First comes a comparison between various modules using a very short 1219 First comes a comparison between various modules using a very short
718 single-line JSON string: 1220 single-line JSON string (also available at
1221 <http://dist.schmorp.de/misc/json/short.json>).
719 1222
720 {"method": "handleMessage", "params": ["user1", "we were just talking"], \ 1223 {"method": "handleMessage", "params": ["user1",
721 "id": null, "array":[1,11,234,-5,1e5,1e7, true, false]} 1224 "we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7,
1225 1, 0]}
722 1226
723 It shows the number of encodes/decodes per second (JSON::XS uses the 1227 It shows the number of encodes/decodes per second (JSON::XS uses the
724 functional interface, while JSON::XS/2 uses the OO interface with 1228 functional interface, while JSON::XS/2 uses the OO interface with
725 pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink). 1229 pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink.
726 Higher is better: 1230 JSON::DWIW/DS uses the deserialise function, while JSON::DWIW::FJ uses
1231 the from_json method). Higher is better:
727 1232
728 Storable | 15779.925 | 14169.946 |
729 -----------+------------+------------+
730 module | encode | decode | 1233 module | encode | decode |
731 -----------|------------|------------| 1234 --------------|------------|------------|
732 JSON | 4990.842 | 4088.813 | 1235 JSON::DWIW/DS | 86302.551 | 102300.098 |
733 JSON::DWIW | 51653.990 | 71575.154 | 1236 JSON::DWIW/FJ | 86302.551 | 75983.768 |
734 JSON::PC | 65948.176 | 74631.744 | 1237 JSON::PP | 15827.562 | 6638.658 |
735 JSON::PP | 8931.652 | 3817.168 | 1238 JSON::Syck | 63358.066 | 47662.545 |
736 JSON::Syck | 24877.248 | 27776.848 | 1239 JSON::XS | 511500.488 | 511500.488 |
737 JSON::XS | 388361.481 | 227951.304 | 1240 JSON::XS/2 | 291271.111 | 388361.481 |
738 JSON::XS/2 | 227951.304 | 218453.333 | 1241 JSON::XS/3 | 361577.931 | 361577.931 |
739 JSON::XS/3 | 338250.323 | 218453.333 | 1242 Storable | 66788.280 | 265462.278 |
740 Storable | 16500.016 | 135300.129 |
741 -----------+------------+------------+ 1243 --------------+------------+------------+
742 1244
743 That is, JSON::XS is about five times faster than JSON::DWIW on 1245 That is, JSON::XS is almost six times faster than JSON::DWIW on
744 encoding, about three times faster on decoding, and over fourty times 1246 encoding, about five times faster on decoding, and over thirty to
745 faster than JSON, even with pretty-printing and key sorting. It also 1247 seventy times faster than JSON's pure perl implementation. It also
746 compares favourably to Storable for small amounts of data. 1248 compares favourably to Storable for small amounts of data.
747 1249
748 Using a longer test string (roughly 18KB, generated from Yahoo! Locals 1250 Using a longer test string (roughly 18KB, generated from Yahoo! Locals
749 search API (http://nanoref.com/yahooapis/mgPdGg): 1251 search API (<http://dist.schmorp.de/misc/json/long.json>).
750 1252
751 module | encode | decode | 1253 module | encode | decode |
752 -----------|------------|------------| 1254 --------------|------------|------------|
753 JSON | 55.260 | 34.971 | 1255 JSON::DWIW/DS | 1647.927 | 2673.916 |
754 JSON::DWIW | 825.228 | 1082.513 | 1256 JSON::DWIW/FJ | 1630.249 | 2596.128 |
755 JSON::PC | 3571.444 | 2394.829 |
756 JSON::PP | 210.987 | 32.574 | 1257 JSON::PP | 400.640 | 62.311 |
757 JSON::Syck | 552.551 | 787.544 | 1258 JSON::Syck | 1481.040 | 1524.869 |
758 JSON::XS | 5780.463 | 4854.519 | 1259 JSON::XS | 20661.596 | 9541.183 |
759 JSON::XS/2 | 3869.998 | 4798.975 | 1260 JSON::XS/2 | 10683.403 | 9416.938 |
760 JSON::XS/3 | 5862.880 | 4798.975 | 1261 JSON::XS/3 | 20661.596 | 9400.054 |
761 Storable | 4445.002 | 5235.027 | 1262 Storable | 19765.806 | 10000.725 |
762 -----------+------------+------------+ 1263 --------------+------------+------------+
763 1264
764 Again, JSON::XS leads by far (except for Storable which non-surprisingly 1265 Again, JSON::XS leads by far (except for Storable which non-surprisingly
765 decodes faster). 1266 decodes a bit faster).
766 1267
767 On large strings containing lots of high unicode characters, some 1268 On large strings containing lots of high Unicode characters, some
768 modules (such as JSON::PC) seem to decode faster than JSON::XS, but the 1269 modules (such as JSON::PC) seem to decode faster than JSON::XS, but the
769 result will be broken due to missing (or wrong) unicode handling. Others 1270 result will be broken due to missing (or wrong) Unicode handling. Others
770 refuse to decode or encode properly, so it was impossible to prepare a 1271 refuse to decode or encode properly, so it was impossible to prepare a
771 fair comparison table for that case. 1272 fair comparison table for that case.
772 1273
773SECURITY CONSIDERATIONS 1274SECURITY CONSIDERATIONS
774 When you are using JSON in a protocol, talking to untrusted potentially 1275 When you are using JSON in a protocol, talking to untrusted potentially
… …
778 have any buffer overflows. Obviously, this module should ensure that and 1279 have any buffer overflows. Obviously, this module should ensure that and
779 I am trying hard on making that true, but you never know. 1280 I am trying hard on making that true, but you never know.
780 1281
781 Second, you need to avoid resource-starving attacks. That means you 1282 Second, you need to avoid resource-starving attacks. That means you
782 should limit the size of JSON texts you accept, or make sure then when 1283 should limit the size of JSON texts you accept, or make sure then when
783 your resources run out, thats just fine (e.g. by using a separate 1284 your resources run out, that's just fine (e.g. by using a separate
784 process that can crash safely). The size of a JSON text in octets or 1285 process that can crash safely). The size of a JSON text in octets or
785 characters is usually a good indication of the size of the resources 1286 characters is usually a good indication of the size of the resources
786 required to decode it into a Perl structure. While JSON::XS can check 1287 required to decode it into a Perl structure. While JSON::XS can check
787 the size of the JSON text, it might be too late when you already have it 1288 the size of the JSON text, it might be too late when you already have it
788 in memory, so you might want to check the size before you accept the 1289 in memory, so you might want to check the size before you accept the
… …
791 Third, JSON::XS recurses using the C stack when decoding objects and 1292 Third, JSON::XS recurses using the C stack when decoding objects and
792 arrays. The C stack is a limited resource: for instance, on my amd64 1293 arrays. The C stack is a limited resource: for instance, on my amd64
793 machine with 8MB of stack size I can decode around 180k nested arrays 1294 machine with 8MB of stack size I can decode around 180k nested arrays
794 but only 14k nested JSON objects (due to perl itself recursing deeply on 1295 but only 14k nested JSON objects (due to perl itself recursing deeply on
795 croak to free the temporary). If that is exceeded, the program crashes. 1296 croak to free the temporary). If that is exceeded, the program crashes.
796 to be conservative, the default nesting limit is set to 512. If your 1297 To be conservative, the default nesting limit is set to 512. If your
797 process has a smaller stack, you should adjust this setting accordingly 1298 process has a smaller stack, you should adjust this setting accordingly
798 with the "max_depth" method. 1299 with the "max_depth" method.
799 1300
800 And last but least, something else could bomb you that I forgot to think 1301 Something else could bomb you, too, that I forgot to think of. In that
801 of. In that case, you get to keep the pieces. I am always open for 1302 case, you get to keep the pieces. I am always open for hints, though...
802 hints, though...
803 1303
1304 Also keep in mind that JSON::XS might leak contents of your Perl data
1305 structures in its error messages, so when you serialise sensitive
1306 information you might want to make sure that exceptions thrown by
1307 JSON::XS will not end up in front of untrusted eyes.
1308
804 If you are using JSON::XS to return packets to consumption by javascript 1309 If you are using JSON::XS to return packets to consumption by JavaScript
805 scripts in a browser you should have a look at 1310 scripts in a browser you should have a look at
806 <http://jpsykes.com/47/practical-csrf-and-json-security> to see wether 1311 <http://blog.archive.jpsykes.com/47/practical-csrf-and-json-security/>
807 you are vulnerable to some common attack vectors (which really are 1312 to see whether you are vulnerable to some common attack vectors (which
808 browser design bugs, but it is still you who will have to deal with it, 1313 really are browser design bugs, but it is still you who will have to
809 as major browser developers care only for features, not about doing 1314 deal with it, as major browser developers care only for features, not
810 security right). 1315 about getting security right).
1316
1317THREADS
1318 This module is *not* guaranteed to be thread safe and there are no plans
1319 to change this until Perl gets thread support (as opposed to the
1320 horribly slow so-called "threads" which are simply slow and bloated
1321 process simulations - use fork, it's *much* faster, cheaper, better).
1322
1323 (It might actually work, but you have been warned).
811 1324
812BUGS 1325BUGS
813 While the goal of this module is to be correct, that unfortunately does 1326 While the goal of this module is to be correct, that unfortunately does
814 not mean its bug-free, only that I think its design is bug-free. It is 1327 not mean it's bug-free, only that I think its design is bug-free. If you
815 still relatively early in its development. If you keep reporting bugs
816 they will be fixed swiftly, though. 1328 keep reporting bugs they will be fixed swiftly, though.
1329
1330 Please refrain from using rt.cpan.org or any other bug reporting
1331 service. I put the contact address into my modules for a reason.
1332
1333SEE ALSO
1334 The json_xs command line utility for quick experiments.
817 1335
818AUTHOR 1336AUTHOR
819 Marc Lehmann <schmorp@schmorp.de> 1337 Marc Lehmann <schmorp@schmorp.de>
820 http://home.schmorp.de/ 1338 http://home.schmorp.de/
821 1339

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