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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, croak on error 10 # exported functions, they croak on error
11 # and expect/generate UTF-8
8 12
9 $utf8_encoded_json_text = to_json $perl_hash_or_arrayref; 13 $utf8_encoded_json_text = encode_json $perl_hash_or_arrayref;
10 $perl_hash_or_arrayref = from_json $utf8_encoded_json_text; 14 $perl_hash_or_arrayref = decode_json $utf8_encoded_json_text;
11 15
12 # oo-interface 16 # OO-interface
13 17
14 $coder = JSON::XS->new->ascii->pretty->allow_nonref; 18 $coder = JSON::XS->new->ascii->pretty->allow_nonref;
15 $pretty_printed_unencoded = $coder->encode ($perl_scalar); 19 $pretty_printed_unencoded = $coder->encode ($perl_scalar);
16 $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.
17 29
18DESCRIPTION 30DESCRIPTION
19 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
20 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*.
21 To reach the latter goal it was written in C. 33 To reach the latter goal it was written in C.
34
35 Beginning with version 2.0 of the JSON module, when both JSON and
36 JSON::XS are installed, then JSON will fall back on JSON::XS (this can
37 be overriden) with no overhead due to emulation (by inheritign
38 constructor and methods). If JSON::XS is not available, it will fall
39 back to the compatible JSON::PP module as backend, so using JSON instead
40 of JSON::XS gives you a portable JSON API that can be fast when you need
41 and doesn't require a C compiler when that is a problem.
22 42
23 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
24 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
25 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
26 cases their maintainers are unresponsive, gone missing, or not listening 46 cases their maintainers are unresponsive, gone missing, or not listening
… …
30 50
31 See MAPPING, below, on how JSON::XS maps perl values to JSON values and 51 See MAPPING, below, on how JSON::XS maps perl values to JSON values and
32 vice versa. 52 vice versa.
33 53
34 FEATURES 54 FEATURES
35 * correct handling of unicode issues 55 * correct Unicode handling
56
36 This module knows how to handle Unicode, and even documents how and 57 This module knows how to handle Unicode, documents how and when it
37 when it does so. 58 does so, and even documents what "correct" means.
38 59
39 * round-trip integrity 60 * round-trip integrity
61
40 When you serialise a perl data structure using only datatypes 62 When you serialise a perl data structure using only datatypes
41 supported by JSON, the deserialised data structure is identical on 63 supported by JSON, the deserialised data structure is identical on
42 the Perl level. (e.g. the string "2.0" doesn't suddenly become "2"). 64 the Perl level. (e.g. the string "2.0" doesn't suddenly become "2"
65 just because it looks like a number). There minor *are* exceptions
66 to this, read the MAPPING section below to learn about those.
43 67
44 * strict checking of JSON correctness 68 * strict checking of JSON correctness
69
45 There is no guessing, no generating of illegal JSON strings by 70 There is no guessing, no generating of illegal JSON texts by
46 default, and only JSON is accepted as input by default (the latter 71 default, and only JSON is accepted as input by default (the latter
47 is a security feature). 72 is a security feature).
48 73
49 * fast 74 * fast
50 Compared to other JSON modules, this module compares favourably in
51 terms of speed, too.
52 75
76 Compared to other JSON modules and other serialisers such as
77 Storable, this module usually compares favourably in terms of speed,
78 too.
79
53 * simple to use 80 * simple to use
81
54 This module has both a simple functional interface as well as an OO 82 This module has both a simple functional interface as well as an
55 interface. 83 objetc oriented interface interface.
56 84
57 * reasonably versatile output formats 85 * reasonably versatile output formats
86
58 You can choose between the most compact guarenteed single-line 87 You can choose between the most compact guaranteed-single-line
59 format possible (nice for simple line-based protocols), a pure-ascii 88 format possible (nice for simple line-based protocols), a pure-ascii
60 format (for when your transport is not 8-bit clean), or a 89 format (for when your transport is not 8-bit clean, still supports
61 pretty-printed format (for when you want to read that stuff). Or you 90 the whole Unicode range), or a pretty-printed format (for when you
62 can combine those features in whatever way you like. 91 want to read that stuff). Or you can combine those features in
92 whatever way you like.
63 93
64FUNCTIONAL INTERFACE 94FUNCTIONAL INTERFACE
65 The following convinience methods are provided by this module. They are 95 The following convenience methods are provided by this module. They are
66 exported by default: 96 exported by default:
67 97
68 $json_string = to_json $perl_scalar 98 $json_text = encode_json $perl_scalar
69 Converts the given Perl data structure (a simple scalar or a 99 Converts the given Perl data structure to a UTF-8 encoded, binary
70 reference to a hash or array) to a UTF-8 encoded, binary string
71 (that is, the string contains octets only). Croaks on error. 100 string (that is, the string contains octets only). Croaks on error.
72 101
73 This function call is functionally identical to 102 This function call is functionally identical to:
103
74 "JSON::XS->new->utf8->encode ($perl_scalar)". 104 $json_text = JSON::XS->new->utf8->encode ($perl_scalar)
75 105
106 except being faster.
107
76 $perl_scalar = from_json $json_string 108 $perl_scalar = decode_json $json_text
77 The opposite of "to_json": expects an UTF-8 (binary) string and 109 The opposite of "encode_json": expects an UTF-8 (binary) string and
78 tries to parse that as an UTF-8 encoded JSON string, returning the 110 tries to parse that as an UTF-8 encoded JSON text, returning the
79 resulting simple scalar or reference. Croaks on error. 111 resulting reference. Croaks on error.
80 112
81 This function call is functionally identical to 113 This function call is functionally identical to:
114
82 "JSON::XS->new->utf8->decode ($json_string)". 115 $perl_scalar = JSON::XS->new->utf8->decode ($json_text)
116
117 except being faster.
118
119 $is_boolean = JSON::XS::is_bool $scalar
120 Returns true if the passed scalar represents either JSON::XS::true
121 or JSON::XS::false, two constants that act like 1 and 0,
122 respectively and are used to represent JSON "true" and "false"
123 values in Perl.
124
125 See MAPPING, below, for more information on how JSON values are
126 mapped to Perl.
127
128A FEW NOTES ON UNICODE AND PERL
129 Since this often leads to confusion, here are a few very clear words on
130 how Unicode works in Perl, modulo bugs.
131
132 1. Perl strings can store characters with ordinal values > 255.
133 This enables you to store Unicode characters as single characters in
134 a Perl string - very natural.
135
136 2. Perl does *not* associate an encoding with your strings.
137 ... until you force it to, e.g. when matching it against a regex, or
138 printing the scalar to a file, in which case Perl either interprets
139 your string as locale-encoded text, octets/binary, or as Unicode,
140 depending on various settings. In no case is an encoding stored
141 together with your data, it is *use* that decides encoding, not any
142 magical meta data.
143
144 3. The internal utf-8 flag has no meaning with regards to the encoding
145 of your string.
146 Just ignore that flag unless you debug a Perl bug, a module written
147 in XS or want to dive into the internals of perl. Otherwise it will
148 only confuse you, as, despite the name, it says nothing about how
149 your string is encoded. You can have Unicode strings with that flag
150 set, with that flag clear, and you can have binary data with that
151 flag set and that flag clear. Other possibilities exist, too.
152
153 If you didn't know about that flag, just the better, pretend it
154 doesn't exist.
155
156 4. A "Unicode String" is simply a string where each character can be
157 validly interpreted as a Unicode codepoint.
158 If you have UTF-8 encoded data, it is no longer a Unicode string,
159 but a Unicode string encoded in UTF-8, giving you a binary string.
160
161 5. A string containing "high" (> 255) character values is *not* a UTF-8
162 string.
163 It's a fact. Learn to live with it.
164
165 I hope this helps :)
83 166
84OBJECT-ORIENTED INTERFACE 167OBJECT-ORIENTED INTERFACE
85 The object oriented interface lets you configure your own encoding or 168 The object oriented interface lets you configure your own encoding or
86 decoding style, within the limits of supported formats. 169 decoding style, within the limits of supported formats.
87 170
… …
91 *disabled*. 174 *disabled*.
92 175
93 The mutators for flags all return the JSON object again and thus 176 The mutators for flags all return the JSON object again and thus
94 calls can be chained: 177 calls can be chained:
95 178
96 my $json = JSON::XS->new->utf8(1)->space_after(1)->encode ({a => [1,2]}) 179 my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]})
97 => {"a": [1, 2]} 180 => {"a": [1, 2]}
98 181
99 $json = $json->ascii ([$enable]) 182 $json = $json->ascii ([$enable])
183 $enabled = $json->get_ascii
100 If $enable is true (or missing), then the "encode" method will not 184 If $enable is true (or missing), then the "encode" method will not
101 generate characters outside the code range 0..127. Any unicode 185 generate characters outside the code range 0..127 (which is ASCII).
102 characters outside that range will be escaped using either a single 186 Any Unicode characters outside that range will be escaped using
103 \uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence, 187 either a single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL
104 as per RFC4627. 188 escape sequence, as per RFC4627. The resulting encoded JSON text can
189 be treated as a native Unicode string, an ascii-encoded,
190 latin1-encoded or UTF-8 encoded string, or any other superset of
191 ASCII.
105 192
106 If $enable is false, then the "encode" method will not escape 193 If $enable is false, then the "encode" method will not escape
107 Unicode characters unless necessary. 194 Unicode characters unless required by the JSON syntax or other
195 flags. This results in a faster and more compact format.
108 196
197 See also the section *ENCODING/CODESET FLAG NOTES* later in this
198 document.
199
200 The main use for this flag is to produce JSON texts that can be
201 transmitted over a 7-bit channel, as the encoded JSON texts will not
202 contain any 8 bit characters.
203
109 JSON::XS->new->ascii (1)->encode (chr 0x10401) 204 JSON::XS->new->ascii (1)->encode ([chr 0x10401])
110 => \ud801\udc01 205 => ["\ud801\udc01"]
206
207 $json = $json->latin1 ([$enable])
208 $enabled = $json->get_latin1
209 If $enable is true (or missing), then the "encode" method will
210 encode the resulting JSON text as latin1 (or iso-8859-1), escaping
211 any characters outside the code range 0..255. The resulting string
212 can be treated as a latin1-encoded JSON text or a native Unicode
213 string. The "decode" method will not be affected in any way by this
214 flag, as "decode" by default expects Unicode, which is a strict
215 superset of latin1.
216
217 If $enable is false, then the "encode" method will not escape
218 Unicode characters unless required by the JSON syntax or other
219 flags.
220
221 See also the section *ENCODING/CODESET FLAG NOTES* later in this
222 document.
223
224 The main use for this flag is efficiently encoding binary data as
225 JSON text, as most octets will not be escaped, resulting in a
226 smaller encoded size. The disadvantage is that the resulting JSON
227 text is encoded in latin1 (and must correctly be treated as such
228 when storing and transferring), a rare encoding for JSON. It is
229 therefore most useful when you want to store data structures known
230 to contain binary data efficiently in files or databases, not when
231 talking to other JSON encoders/decoders.
232
233 JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]
234 => ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)
111 235
112 $json = $json->utf8 ([$enable]) 236 $json = $json->utf8 ([$enable])
237 $enabled = $json->get_utf8
113 If $enable is true (or missing), then the "encode" method will 238 If $enable is true (or missing), then the "encode" method will
114 encode the JSON string into UTF-8, as required by many protocols, 239 encode the JSON result into UTF-8, as required by many protocols,
115 while the "decode" method expects to be handled an UTF-8-encoded 240 while the "decode" method expects to be handled an UTF-8-encoded
116 string. Please note that UTF-8-encoded strings do not contain any 241 string. Please note that UTF-8-encoded strings do not contain any
117 characters outside the range 0..255, they are thus useful for 242 characters outside the range 0..255, they are thus useful for
118 bytewise/binary I/O. 243 bytewise/binary I/O. In future versions, enabling this option might
244 enable autodetection of the UTF-16 and UTF-32 encoding families, as
245 described in RFC4627.
119 246
120 If $enable is false, then the "encode" method will return the JSON 247 If $enable is false, then the "encode" method will return the JSON
121 string as a (non-encoded) unicode string, while "decode" expects 248 string as a (non-encoded) Unicode string, while "decode" expects
122 thus a unicode string. Any decoding or encoding (e.g. to UTF-8 or 249 thus a Unicode string. Any decoding or encoding (e.g. to UTF-8 or
123 UTF-16) needs to be done yourself, e.g. using the Encode module. 250 UTF-16) needs to be done yourself, e.g. using the Encode module.
124 251
252 See also the section *ENCODING/CODESET FLAG NOTES* later in this
253 document.
254
125 Example, output UTF-16-encoded JSON: 255 Example, output UTF-16BE-encoded JSON:
256
257 use Encode;
258 $jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
259
260 Example, decode UTF-32LE-encoded JSON:
261
262 use Encode;
263 $object = JSON::XS->new->decode (decode "UTF-32LE", $jsontext);
126 264
127 $json = $json->pretty ([$enable]) 265 $json = $json->pretty ([$enable])
128 This enables (or disables) all of the "indent", "space_before" and 266 This enables (or disables) all of the "indent", "space_before" and
129 "space_after" (and in the future possibly more) flags in one call to 267 "space_after" (and in the future possibly more) flags in one call to
130 generate the most readable (or most compact) form possible. 268 generate the most readable (or most compact) form possible.
… …
139 2 277 2
140 ] 278 ]
141 } 279 }
142 280
143 $json = $json->indent ([$enable]) 281 $json = $json->indent ([$enable])
282 $enabled = $json->get_indent
144 If $enable is true (or missing), then the "encode" method will use a 283 If $enable is true (or missing), then the "encode" method will use a
145 multiline format as output, putting every array member or 284 multiline format as output, putting every array member or
146 object/hash key-value pair into its own line, identing them 285 object/hash key-value pair into its own line, indenting them
147 properly. 286 properly.
148 287
149 If $enable is false, no newlines or indenting will be produced, and 288 If $enable is false, no newlines or indenting will be produced, and
150 the resulting JSON strings is guarenteed not to contain any 289 the resulting JSON text is guaranteed not to contain any "newlines".
151 "newlines".
152 290
153 This setting has no effect when decoding JSON strings. 291 This setting has no effect when decoding JSON texts.
154 292
155 $json = $json->space_before ([$enable]) 293 $json = $json->space_before ([$enable])
294 $enabled = $json->get_space_before
156 If $enable is true (or missing), then the "encode" method will add 295 If $enable is true (or missing), then the "encode" method will add
157 an extra optional space before the ":" separating keys from values 296 an extra optional space before the ":" separating keys from values
158 in JSON objects. 297 in JSON objects.
159 298
160 If $enable is false, then the "encode" method will not add any extra 299 If $enable is false, then the "encode" method will not add any extra
161 space at those places. 300 space at those places.
162 301
163 This setting has no effect when decoding JSON strings. You will also 302 This setting has no effect when decoding JSON texts. You will also
164 most likely combine this setting with "space_after". 303 most likely combine this setting with "space_after".
165 304
166 Example, space_before enabled, space_after and indent disabled: 305 Example, space_before enabled, space_after and indent disabled:
167 306
168 {"key" :"value"} 307 {"key" :"value"}
169 308
170 $json = $json->space_after ([$enable]) 309 $json = $json->space_after ([$enable])
310 $enabled = $json->get_space_after
171 If $enable is true (or missing), then the "encode" method will add 311 If $enable is true (or missing), then the "encode" method will add
172 an extra optional space after the ":" separating keys from values in 312 an extra optional space after the ":" separating keys from values in
173 JSON objects and extra whitespace after the "," separating key-value 313 JSON objects and extra whitespace after the "," separating key-value
174 pairs and array members. 314 pairs and array members.
175 315
176 If $enable is false, then the "encode" method will not add any extra 316 If $enable is false, then the "encode" method will not add any extra
177 space at those places. 317 space at those places.
178 318
179 This setting has no effect when decoding JSON strings. 319 This setting has no effect when decoding JSON texts.
180 320
181 Example, space_before and indent disabled, space_after enabled: 321 Example, space_before and indent disabled, space_after enabled:
182 322
183 {"key": "value"} 323 {"key": "value"}
184 324
325 $json = $json->relaxed ([$enable])
326 $enabled = $json->get_relaxed
327 If $enable is true (or missing), then "decode" will accept some
328 extensions to normal JSON syntax (see below). "encode" will not be
329 affected in anyway. *Be aware that this option makes you accept
330 invalid JSON texts as if they were valid!*. I suggest only to use
331 this option to parse application-specific files written by humans
332 (configuration files, resource files etc.)
333
334 If $enable is false (the default), then "decode" will only accept
335 valid JSON texts.
336
337 Currently accepted extensions are:
338
339 * list items can have an end-comma
340
341 JSON *separates* array elements and key-value pairs with commas.
342 This can be annoying if you write JSON texts manually and want
343 to be able to quickly append elements, so this extension accepts
344 comma at the end of such items not just between them:
345
346 [
347 1,
348 2, <- this comma not normally allowed
349 ]
350 {
351 "k1": "v1",
352 "k2": "v2", <- this comma not normally allowed
353 }
354
355 * shell-style '#'-comments
356
357 Whenever JSON allows whitespace, shell-style comments are
358 additionally allowed. They are terminated by the first
359 carriage-return or line-feed character, after which more
360 white-space and comments are allowed.
361
362 [
363 1, # this comment not allowed in JSON
364 # neither this one...
365 ]
366
185 $json = $json->canonical ([$enable]) 367 $json = $json->canonical ([$enable])
368 $enabled = $json->get_canonical
186 If $enable is true (or missing), then the "encode" method will 369 If $enable is true (or missing), then the "encode" method will
187 output JSON objects by sorting their keys. This is adding a 370 output JSON objects by sorting their keys. This is adding a
188 comparatively high overhead. 371 comparatively high overhead.
189 372
190 If $enable is false, then the "encode" method will output key-value 373 If $enable is false, then the "encode" method will output key-value
191 pairs in the order Perl stores them (which will likely change 374 pairs in the order Perl stores them (which will likely change
192 between runs of the same script). 375 between runs of the same script).
193 376
194 This option is useful if you want the same data structure to be 377 This option is useful if you want the same data structure to be
195 encoded as the same JSON string (given the same overall settings). 378 encoded as the same JSON text (given the same overall settings). If
196 If it is disabled, the same hash migh be encoded differently even if 379 it is disabled, the same hash might be encoded differently even if
197 contains the same data, as key-value pairs have no inherent ordering 380 contains the same data, as key-value pairs have no inherent ordering
198 in Perl. 381 in Perl.
199 382
200 This setting has no effect when decoding JSON strings. 383 This setting has no effect when decoding JSON texts.
201 384
202 $json = $json->allow_nonref ([$enable]) 385 $json = $json->allow_nonref ([$enable])
386 $enabled = $json->get_allow_nonref
203 If $enable is true (or missing), then the "encode" method can 387 If $enable is true (or missing), then the "encode" method can
204 convert a non-reference into its corresponding string, number or 388 convert a non-reference into its corresponding string, number or
205 null JSON value, which is an extension to RFC4627. Likewise, 389 null JSON value, which is an extension to RFC4627. Likewise,
206 "decode" will accept those JSON values instead of croaking. 390 "decode" will accept those JSON values instead of croaking.
207 391
208 If $enable is false, then the "encode" method will croak if it isn't 392 If $enable is false, then the "encode" method will croak if it isn't
209 passed an arrayref or hashref, as JSON strings must either be an 393 passed an arrayref or hashref, as JSON texts must either be an
210 object or array. Likewise, "decode" will croak if given something 394 object or array. Likewise, "decode" will croak if given something
211 that is not a JSON object or array. 395 that is not a JSON object or array.
212 396
213 Example, encode a Perl scalar as JSON value with enabled 397 Example, encode a Perl scalar as JSON value with enabled
214 "allow_nonref", resulting in an invalid JSON text: 398 "allow_nonref", resulting in an invalid JSON text:
215 399
216 JSON::XS->new->allow_nonref->encode ("Hello, World!") 400 JSON::XS->new->allow_nonref->encode ("Hello, World!")
217 => "Hello, World!" 401 => "Hello, World!"
218 402
403 $json = $json->allow_blessed ([$enable])
404 $enabled = $json->get_allow_blessed
405 If $enable is true (or missing), then the "encode" method will not
406 barf when it encounters a blessed reference. Instead, the value of
407 the convert_blessed option will decide whether "null"
408 ("convert_blessed" disabled or no "TO_JSON" method found) or a
409 representation of the object ("convert_blessed" enabled and
410 "TO_JSON" method found) is being encoded. Has no effect on "decode".
411
412 If $enable is false (the default), then "encode" will throw an
413 exception when it encounters a blessed object.
414
415 $json = $json->convert_blessed ([$enable])
416 $enabled = $json->get_convert_blessed
417 If $enable is true (or missing), then "encode", upon encountering a
418 blessed object, will check for the availability of the "TO_JSON"
419 method on the object's class. If found, it will be called in scalar
420 context and the resulting scalar will be encoded instead of the
421 object. If no "TO_JSON" method is found, the value of
422 "allow_blessed" will decide what to do.
423
424 The "TO_JSON" method may safely call die if it wants. If "TO_JSON"
425 returns other blessed objects, those will be handled in the same
426 way. "TO_JSON" must take care of not causing an endless recursion
427 cycle (== crash) in this case. The name of "TO_JSON" was chosen
428 because other methods called by the Perl core (== not by the user of
429 the object) are usually in upper case letters and to avoid
430 collisions with any "to_json" function or method.
431
432 This setting does not yet influence "decode" in any way, but in the
433 future, global hooks might get installed that influence "decode" and
434 are enabled by this setting.
435
436 If $enable is false, then the "allow_blessed" setting will decide
437 what to do when a blessed object is found.
438
439 $json = $json->filter_json_object ([$coderef->($hashref)])
440 When $coderef is specified, it will be called from "decode" each
441 time it decodes a JSON object. The only argument is a reference to
442 the newly-created hash. If the code references returns a single
443 scalar (which need not be a reference), this value (i.e. a copy of
444 that scalar to avoid aliasing) is inserted into the deserialised
445 data structure. If it returns an empty list (NOTE: *not* "undef",
446 which is a valid scalar), the original deserialised hash will be
447 inserted. This setting can slow down decoding considerably.
448
449 When $coderef is omitted or undefined, any existing callback will be
450 removed and "decode" will not change the deserialised hash in any
451 way.
452
453 Example, convert all JSON objects into the integer 5:
454
455 my $js = JSON::XS->new->filter_json_object (sub { 5 });
456 # returns [5]
457 $js->decode ('[{}]')
458 # throw an exception because allow_nonref is not enabled
459 # so a lone 5 is not allowed.
460 $js->decode ('{"a":1, "b":2}');
461
462 $json = $json->filter_json_single_key_object ($key [=>
463 $coderef->($value)])
464 Works remotely similar to "filter_json_object", but is only called
465 for JSON objects having a single key named $key.
466
467 This $coderef is called before the one specified via
468 "filter_json_object", if any. It gets passed the single value in the
469 JSON object. If it returns a single value, it will be inserted into
470 the data structure. If it returns nothing (not even "undef" but the
471 empty list), the callback from "filter_json_object" will be called
472 next, as if no single-key callback were specified.
473
474 If $coderef is omitted or undefined, the corresponding callback will
475 be disabled. There can only ever be one callback for a given key.
476
477 As this callback gets called less often then the
478 "filter_json_object" one, decoding speed will not usually suffer as
479 much. Therefore, single-key objects make excellent targets to
480 serialise Perl objects into, especially as single-key JSON objects
481 are as close to the type-tagged value concept as JSON gets (it's
482 basically an ID/VALUE tuple). Of course, JSON does not support this
483 in any way, so you need to make sure your data never looks like a
484 serialised Perl hash.
485
486 Typical names for the single object key are "__class_whatever__", or
487 "$__dollars_are_rarely_used__$" or "}ugly_brace_placement", or even
488 things like "__class_md5sum(classname)__", to reduce the risk of
489 clashing with real hashes.
490
491 Example, decode JSON objects of the form "{ "__widget__" => <id> }"
492 into the corresponding $WIDGET{<id>} object:
493
494 # return whatever is in $WIDGET{5}:
495 JSON::XS
496 ->new
497 ->filter_json_single_key_object (__widget__ => sub {
498 $WIDGET{ $_[0] }
499 })
500 ->decode ('{"__widget__": 5')
501
502 # this can be used with a TO_JSON method in some "widget" class
503 # for serialisation to json:
504 sub WidgetBase::TO_JSON {
505 my ($self) = @_;
506
507 unless ($self->{id}) {
508 $self->{id} = ..get..some..id..;
509 $WIDGET{$self->{id}} = $self;
510 }
511
512 { __widget__ => $self->{id} }
513 }
514
219 $json = $json->shrink ([$enable]) 515 $json = $json->shrink ([$enable])
516 $enabled = $json->get_shrink
220 Perl usually over-allocates memory a bit when allocating space for 517 Perl usually over-allocates memory a bit when allocating space for
221 strings. This flag optionally resizes strings generated by either 518 strings. This flag optionally resizes strings generated by either
222 "encode" or "decode" to their minimum size possible. This can save 519 "encode" or "decode" to their minimum size possible. This can save
223 memory when your JSON strings are either very very long or you have 520 memory when your JSON texts are either very very long or you have
224 many short strings. It will also try to downgrade any strings to 521 many short strings. It will also try to downgrade any strings to
225 octet-form if possible: perl stores strings internally either in an 522 octet-form if possible: perl stores strings internally either in an
226 encoding called UTF-X or in octet-form. The latter cannot store 523 encoding called UTF-X or in octet-form. The latter cannot store
227 everything but uses less space in general. 524 everything but uses less space in general (and some buggy Perl or C
525 code might even rely on that internal representation being used).
526
527 The actual definition of what shrink does might change in future
528 versions, but it will always try to save space at the expense of
529 time.
228 530
229 If $enable is true (or missing), the string returned by "encode" 531 If $enable is true (or missing), the string returned by "encode"
230 will be shrunk-to-fit, while all strings generated by "decode" will 532 will be shrunk-to-fit, while all strings generated by "decode" will
231 also be shrunk-to-fit. 533 also be shrunk-to-fit.
232 534
… …
236 In the future, this setting might control other things, such as 538 In the future, this setting might control other things, such as
237 converting strings that look like integers or floats into integers 539 converting strings that look like integers or floats into integers
238 or floats internally (there is no difference on the Perl level), 540 or floats internally (there is no difference on the Perl level),
239 saving space. 541 saving space.
240 542
543 $json = $json->max_depth ([$maximum_nesting_depth])
544 $max_depth = $json->get_max_depth
545 Sets the maximum nesting level (default 512) accepted while encoding
546 or decoding. If the JSON text or Perl data structure has an equal or
547 higher nesting level then this limit, then the encoder and decoder
548 will stop and croak at that point.
549
550 Nesting level is defined by number of hash- or arrayrefs that the
551 encoder needs to traverse to reach a given point or the number of
552 "{" or "[" characters without their matching closing parenthesis
553 crossed to reach a given character in a string.
554
555 Setting the maximum depth to one disallows any nesting, so that
556 ensures that the object is only a single hash/object or array.
557
558 The argument to "max_depth" will be rounded up to the next highest
559 power of two. If no argument is given, the highest possible setting
560 will be used, which is rarely useful.
561
562 See SECURITY CONSIDERATIONS, below, for more info on why this is
563 useful.
564
565 $json = $json->max_size ([$maximum_string_size])
566 $max_size = $json->get_max_size
567 Set the maximum length a JSON text may have (in bytes) where
568 decoding is being attempted. The default is 0, meaning no limit.
569 When "decode" is called on a string longer then this number of
570 characters it will not attempt to decode the string but throw an
571 exception. This setting has no effect on "encode" (yet).
572
573 The argument to "max_size" will be rounded up to the next highest
574 power of two (so may be more than requested). If no argument is
575 given, the limit check will be deactivated (same as when 0 is
576 specified).
577
578 See SECURITY CONSIDERATIONS, below, for more info on why this is
579 useful.
580
241 $json_string = $json->encode ($perl_scalar) 581 $json_text = $json->encode ($perl_scalar)
242 Converts the given Perl data structure (a simple scalar or a 582 Converts the given Perl data structure (a simple scalar or a
243 reference to a hash or array) to its JSON representation. Simple 583 reference to a hash or array) to its JSON representation. Simple
244 scalars will be converted into JSON string or number sequences, 584 scalars will be converted into JSON string or number sequences,
245 while references to arrays become JSON arrays and references to 585 while references to arrays become JSON arrays and references to
246 hashes become JSON objects. Undefined Perl values (e.g. "undef") 586 hashes become JSON objects. Undefined Perl values (e.g. "undef")
247 become JSON "null" values. Neither "true" nor "false" values will be 587 become JSON "null" values. Neither "true" nor "false" values will be
248 generated. 588 generated.
249 589
250 $perl_scalar = $json->decode ($json_string) 590 $perl_scalar = $json->decode ($json_text)
251 The opposite of "encode": expects a JSON string and tries to parse 591 The opposite of "encode": expects a JSON text and tries to parse it,
252 it, returning the resulting simple scalar or reference. Croaks on 592 returning the resulting simple scalar or reference. Croaks on error.
253 error.
254 593
255 JSON numbers and strings become simple Perl scalars. JSON arrays 594 JSON numbers and strings become simple Perl scalars. JSON arrays
256 become Perl arrayrefs and JSON objects become Perl hashrefs. "true" 595 become Perl arrayrefs and JSON objects become Perl hashrefs. "true"
257 becomes 1, "false" becomes 0 and "null" becomes "undef". 596 becomes 1, "false" becomes 0 and "null" becomes "undef".
597
598 ($perl_scalar, $characters) = $json->decode_prefix ($json_text)
599 This works like the "decode" method, but instead of raising an
600 exception when there is trailing garbage after the first JSON
601 object, it will silently stop parsing there and return the number of
602 characters consumed so far.
603
604 This is useful if your JSON texts are not delimited by an outer
605 protocol (which is not the brightest thing to do in the first place)
606 and you need to know where the JSON text ends.
607
608 JSON::XS->new->decode_prefix ("[1] the tail")
609 => ([], 3)
258 610
259MAPPING 611MAPPING
260 This section describes how JSON::XS maps Perl values to JSON values and 612 This section describes how JSON::XS maps Perl values to JSON values and
261 vice versa. These mappings are designed to "do the right thing" in most 613 vice versa. These mappings are designed to "do the right thing" in most
262 circumstances automatically, preserving round-tripping characteristics 614 circumstances automatically, preserving round-tripping characteristics
263 (what you put in comes out as something equivalent). 615 (what you put in comes out as something equivalent).
264 616
265 For the more enlightened: note that in the following descriptions, 617 For the more enlightened: note that in the following descriptions,
266 lowercase *perl* refers to the Perl interpreter, while uppcercase *Perl* 618 lowercase *perl* refers to the Perl interpreter, while uppercase *Perl*
267 refers to the abstract Perl language itself. 619 refers to the abstract Perl language itself.
268 620
269 JSON -> PERL 621 JSON -> PERL
270 object 622 object
271 A JSON object becomes a reference to a hash in Perl. No ordering of 623 A JSON object becomes a reference to a hash in Perl. No ordering of
272 object keys is preserved (JSON does not preserver object key 624 object keys is preserved (JSON does not preserve object key ordering
273 ordering itself). 625 itself).
274 626
275 array 627 array
276 A JSON array becomes a reference to an array in Perl. 628 A JSON array becomes a reference to an array in Perl.
277 629
278 string 630 string
279 A JSON string becomes a string scalar in Perl - Unicode codepoints 631 A JSON string becomes a string scalar in Perl - Unicode codepoints
280 in JSON are represented by the same codepoints in the Perl string, 632 in JSON are represented by the same codepoints in the Perl string,
281 so no manual decoding is necessary. 633 so no manual decoding is necessary.
282 634
283 number 635 number
284 A JSON number becomes either an integer or numeric (floating point) 636 A JSON number becomes either an integer, numeric (floating point) or
285 scalar in perl, depending on its range and any fractional parts. On 637 string scalar in perl, depending on its range and any fractional
286 the Perl level, there is no difference between those as Perl handles 638 parts. On the Perl level, there is no difference between those as
287 all the conversion details, but an integer may take slightly less 639 Perl handles all the conversion details, but an integer may take
288 memory and might represent more values exactly than (floating point) 640 slightly less memory and might represent more values exactly than
641 floating point numbers.
642
643 If the number consists of digits only, JSON::XS will try to
644 represent it as an integer value. If that fails, it will try to
645 represent it as a numeric (floating point) value if that is possible
646 without loss of precision. Otherwise it will preserve the number as
647 a string value (in which case you lose roundtripping ability, as the
648 JSON number will be re-encoded toa JSON string).
649
650 Numbers containing a fractional or exponential part will always be
651 represented as numeric (floating point) values, possibly at a loss
652 of precision (in which case you might lose perfect roundtripping
653 ability, but the JSON number will still be re-encoded as a JSON
289 numbers. 654 number).
290 655
291 true, false 656 true, false
292 These JSON atoms become 0, 1, respectively. Information is lost in 657 These JSON atoms become "JSON::XS::true" and "JSON::XS::false",
293 this process. Future versions might represent those values 658 respectively. They are overloaded to act almost exactly like the
294 differently, but they will be guarenteed to act like these integers 659 numbers 1 and 0. You can check whether a scalar is a JSON boolean by
295 would normally in Perl. 660 using the "JSON::XS::is_bool" function.
296 661
297 null 662 null
298 A JSON null atom becomes "undef" in Perl. 663 A JSON null atom becomes "undef" in Perl.
299 664
300 PERL -> JSON 665 PERL -> JSON
… …
302 truly typeless language, so we can only guess which JSON type is meant 667 truly typeless language, so we can only guess which JSON type is meant
303 by a Perl value. 668 by a Perl value.
304 669
305 hash references 670 hash references
306 Perl hash references become JSON objects. As there is no inherent 671 Perl hash references become JSON objects. As there is no inherent
307 ordering in hash keys, they will usually be encoded in a 672 ordering in hash keys (or JSON objects), they will usually be
308 pseudo-random order that can change between runs of the same program 673 encoded in a pseudo-random order that can change between runs of the
309 but stays generally the same within a single run of a program. 674 same program but stays generally the same within a single run of a
310 JSON::XS can optionally sort the hash keys (determined by the 675 program. JSON::XS can optionally sort the hash keys (determined by
311 *canonical* flag), so the same datastructure will serialise to the 676 the *canonical* flag), so the same datastructure will serialise to
312 same JSON text (given same settings and version of JSON::XS), but 677 the same JSON text (given same settings and version of JSON::XS),
313 this incurs a runtime overhead. 678 but this incurs a runtime overhead and is only rarely useful, e.g.
679 when you want to compare some JSON text against another for
680 equality.
314 681
315 array references 682 array references
316 Perl array references become JSON arrays. 683 Perl array references become JSON arrays.
317 684
685 other references
686 Other unblessed references are generally not allowed and will cause
687 an exception to be thrown, except for references to the integers 0
688 and 1, which get turned into "false" and "true" atoms in JSON. You
689 can also use "JSON::XS::false" and "JSON::XS::true" to improve
690 readability.
691
692 encode_json [\0,JSON::XS::true] # yields [false,true]
693
694 JSON::XS::true, JSON::XS::false
695 These special values become JSON true and JSON false values,
696 respectively. You can also use "\1" and "\0" directly if you want.
697
318 blessed objects 698 blessed objects
319 Blessed objects are not allowed. JSON::XS currently tries to encode 699 Blessed objects are not directly representable in JSON. See the
320 their underlying representation (hash- or arrayref), but this 700 "allow_blessed" and "convert_blessed" methods on various options on
321 behaviour might change in future versions. 701 how to deal with this: basically, you can choose between throwing an
702 exception, encoding the reference as if it weren't blessed, or
703 provide your own serialiser method.
322 704
323 simple scalars 705 simple scalars
324 Simple Perl scalars (any scalar that is not a reference) are the 706 Simple Perl scalars (any scalar that is not a reference) are the
325 most difficult objects to encode: JSON::XS will encode undefined 707 most difficult objects to encode: JSON::XS will encode undefined
326 scalars as JSON null value, scalars that have last been used in a 708 scalars as JSON "null" values, scalars that have last been used in a
327 string context before encoding as JSON strings and anything else as 709 string context before encoding as JSON strings, and anything else as
328 number value: 710 number value:
329 711
330 # dump as number 712 # dump as number
331 to_json [2] # yields [2] 713 encode_json [2] # yields [2]
332 to_json [-3.0e17] # yields [-3e+17] 714 encode_json [-3.0e17] # yields [-3e+17]
333 my $value = 5; to_json [$value] # yields [5] 715 my $value = 5; encode_json [$value] # yields [5]
334 716
335 # used as string, so dump as string 717 # used as string, so dump as string
336 print $value; 718 print $value;
337 to_json [$value] # yields ["5"] 719 encode_json [$value] # yields ["5"]
338 720
339 # undef becomes null 721 # undef becomes null
340 to_json [undef] # yields [null] 722 encode_json [undef] # yields [null]
341 723
342 You can force the type to be a string by stringifying it: 724 You can force the type to be a JSON string by stringifying it:
343 725
344 my $x = 3.1; # some variable containing a number 726 my $x = 3.1; # some variable containing a number
345 "$x"; # stringified 727 "$x"; # stringified
346 $x .= ""; # another, more awkward way to stringify 728 $x .= ""; # another, more awkward way to stringify
347 print $x; # perl does it for you, too, quite often 729 print $x; # perl does it for you, too, quite often
348 730
349 You can force the type to be a number by numifying it: 731 You can force the type to be a JSON number by numifying it:
350 732
351 my $x = "3"; # some variable containing a string 733 my $x = "3"; # some variable containing a string
352 $x += 0; # numify it, ensuring it will be dumped as a number 734 $x += 0; # numify it, ensuring it will be dumped as a number
353 $x *= 1; # same thing, the choise is yours. 735 $x *= 1; # same thing, the choice is yours.
354 736
355 You can not currently output JSON booleans or force the type in 737 You can not currently force the type in other, less obscure, ways.
356 other, less obscure, ways. Tell me if you need this capability. 738 Tell me if you need this capability (but don't forget to explain why
739 its needed :).
357 740
358 circular data structures 741ENCODING/CODESET FLAG NOTES
359 Those will be encoded until memory or stackspace runs out. 742 The interested reader might have seen a number of flags that signify
743 encodings or codesets - "utf8", "latin1" and "ascii". There seems to be
744 some confusion on what these do, so here is a short comparison:
745
746 "utf8" controls wether the JSON text created by "encode" (and expected
747 by "decode") is UTF-8 encoded or not, while "latin1" and "ascii" only
748 control wether "encode" escapes character values outside their
749 respective codeset range. Neither of these flags conflict with each
750 other, although some combinations make less sense than others.
751
752 Care has been taken to make all flags symmetrical with respect to
753 "encode" and "decode", that is, texts encoded with any combination of
754 these flag values will be correctly decoded when the same flags are used
755 - in general, if you use different flag settings while encoding vs. when
756 decoding you likely have a bug somewhere.
757
758 Below comes a verbose discussion of these flags. Note that a "codeset"
759 is simply an abstract set of character-codepoint pairs, while an
760 encoding takes those codepoint numbers and *encodes* them, in our case
761 into octets. Unicode is (among other things) a codeset, UTF-8 is an
762 encoding, and ISO-8859-1 (= latin 1) and ASCII are both codesets *and*
763 encodings at the same time, which can be confusing.
764
765 "utf8" flag disabled
766 When "utf8" is disabled (the default), then "encode"/"decode"
767 generate and expect Unicode strings, that is, characters with high
768 ordinal Unicode values (> 255) will be encoded as such characters,
769 and likewise such characters are decoded as-is, no canges to them
770 will be done, except "(re-)interpreting" them as Unicode codepoints
771 or Unicode characters, respectively (to Perl, these are the same
772 thing in strings unless you do funny/weird/dumb stuff).
773
774 This is useful when you want to do the encoding yourself (e.g. when
775 you want to have UTF-16 encoded JSON texts) or when some other layer
776 does the encoding for you (for example, when printing to a terminal
777 using a filehandle that transparently encodes to UTF-8 you certainly
778 do NOT want to UTF-8 encode your data first and have Perl encode it
779 another time).
780
781 "utf8" flag enabled
782 If the "utf8"-flag is enabled, "encode"/"decode" will encode all
783 characters using the corresponding UTF-8 multi-byte sequence, and
784 will expect your input strings to be encoded as UTF-8, that is, no
785 "character" of the input string must have any value > 255, as UTF-8
786 does not allow that.
787
788 The "utf8" flag therefore switches between two modes: disabled means
789 you will get a Unicode string in Perl, enabled means you get an
790 UTF-8 encoded octet/binary string in Perl.
791
792 "latin1" or "ascii" flags enabled
793 With "latin1" (or "ascii") enabled, "encode" will escape characters
794 with ordinal values > 255 (> 127 with "ascii") and encode the
795 remaining characters as specified by the "utf8" flag.
796
797 If "utf8" is disabled, then the result is also correctly encoded in
798 those character sets (as both are proper subsets of Unicode, meaning
799 that a Unicode string with all character values < 256 is the same
800 thing as a ISO-8859-1 string, and a Unicode string with all
801 character values < 128 is the same thing as an ASCII string in
802 Perl).
803
804 If "utf8" is enabled, you still get a correct UTF-8-encoded string,
805 regardless of these flags, just some more characters will be escaped
806 using "\uXXXX" then before.
807
808 Note that ISO-8859-1-*encoded* strings are not compatible with UTF-8
809 encoding, while ASCII-encoded strings are. That is because the
810 ISO-8859-1 encoding is NOT a subset of UTF-8 (despite the ISO-8859-1
811 *codeset* being a subset of Unicode), while ASCII is.
812
813 Surprisingly, "decode" will ignore these flags and so treat all
814 input values as governed by the "utf8" flag. If it is disabled, this
815 allows you to decode ISO-8859-1- and ASCII-encoded strings, as both
816 strict subsets of Unicode. If it is enabled, you can correctly
817 decode UTF-8 encoded strings.
818
819 So neither "latin1" nor "ascii" are incompatible with the "utf8"
820 flag - they only govern when the JSON output engine escapes a
821 character or not.
822
823 The main use for "latin1" is to relatively efficiently store binary
824 data as JSON, at the expense of breaking compatibility with most
825 JSON decoders.
826
827 The main use for "ascii" is to force the output to not contain
828 characters with values > 127, which means you can interpret the
829 resulting string as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about
830 any character set and 8-bit-encoding, and still get the same data
831 structure back. This is useful when your channel for JSON transfer
832 is not 8-bit clean or the encoding might be mangled in between (e.g.
833 in mail), and works because ASCII is a proper subset of most 8-bit
834 and multibyte encodings in use in the world.
360 835
361COMPARISON 836COMPARISON
362 As already mentioned, this module was created because none of the 837 As already mentioned, this module was created because none of the
363 existing JSON modules could be made to work correctly. First I will 838 existing JSON modules could be made to work correctly. First I will
364 describe the problems (or pleasures) I encountered with various existing 839 describe the problems (or pleasures) I encountered with various existing
365 JSON modules, followed by some benchmark values. JSON::XS was designed 840 JSON modules, followed by some benchmark values. JSON::XS was designed
366 not to suffer from any of these problems or limitations. 841 not to suffer from any of these problems or limitations.
367 842
843 JSON 2.xx
844 A marvellous piece of engineering, this module either uses JSON::XS
845 directly when available (so will be 100% compatible with it,
846 including speed), or it uses JSON::PP, which is basically JSON::XS
847 translated to Pure Perl, which should be 100% compatible with
848 JSON::XS, just a bit slower.
849
850 You cannot really lose by using this module, especially as it tries
851 very hard to work even with ancient Perl versions, while JSON::XS
852 does not.
853
368 JSON 1.07 854 JSON 1.07
369 Slow (but very portable, as it is written in pure Perl). 855 Slow (but very portable, as it is written in pure Perl).
370 856
371 Undocumented/buggy Unicode handling (how JSON handles unicode values 857 Undocumented/buggy Unicode handling (how JSON handles Unicode values
372 is undocumented. One can get far by feeding it unicode strings and 858 is undocumented. One can get far by feeding it Unicode strings and
373 doing en-/decoding oneself, but unicode escapes are not working 859 doing en-/decoding oneself, but Unicode escapes are not working
374 properly). 860 properly).
375 861
376 No roundtripping (strings get clobbered if they look like numbers, 862 No round-tripping (strings get clobbered if they look like numbers,
377 e.g. the string 2.0 will encode to 2.0 instead of "2.0", and that 863 e.g. the string 2.0 will encode to 2.0 instead of "2.0", and that
378 will decode into the number 2. 864 will decode into the number 2.
379 865
380 JSON::PC 0.01 866 JSON::PC 0.01
381 Very fast. 867 Very fast.
382 868
383 Undocumented/buggy Unicode handling. 869 Undocumented/buggy Unicode handling.
384 870
385 No roundtripping. 871 No round-tripping.
386 872
387 Has problems handling many Perl values (e.g. regex results and other 873 Has problems handling many Perl values (e.g. regex results and other
388 magic values will make it croak). 874 magic values will make it croak).
389 875
390 Does not even generate valid JSON ("{1,2}" gets converted to "{1:2}" 876 Does not even generate valid JSON ("{1,2}" gets converted to "{1:2}"
391 which is not a valid JSON string. 877 which is not a valid JSON text.
392 878
393 Unmaintained (maintainer unresponsive for many months, bugs are not 879 Unmaintained (maintainer unresponsive for many months, bugs are not
394 getting fixed). 880 getting fixed).
395 881
396 JSON::Syck 0.21 882 JSON::Syck 0.21
397 Very buggy (often crashes). 883 Very buggy (often crashes).
398 884
399 Very inflexible (no human-readable format supported, format pretty 885 Very inflexible (no human-readable format supported, format pretty
400 much undocumented. I need at least a format for easy reading by 886 much undocumented. I need at least a format for easy reading by
401 humans and a single-line compact format for use in a protocol, and 887 humans and a single-line compact format for use in a protocol, and
402 preferably a way to generate ASCII-only JSON strings). 888 preferably a way to generate ASCII-only JSON texts).
403 889
404 Completely broken (and confusingly documented) Unicode handling 890 Completely broken (and confusingly documented) Unicode handling
405 (unicode escapes are not working properly, you need to set 891 (Unicode escapes are not working properly, you need to set
406 ImplicitUnicode to *different* values on en- and decoding to get 892 ImplicitUnicode to *different* values on en- and decoding to get
407 symmetric behaviour). 893 symmetric behaviour).
408 894
409 No roundtripping (simple cases work, but this depends on wether the 895 No round-tripping (simple cases work, but this depends on whether
410 scalar value was used in a numeric context or not). 896 the scalar value was used in a numeric context or not).
411 897
412 Dumping hashes may skip hash values depending on iterator state. 898 Dumping hashes may skip hash values depending on iterator state.
413 899
414 Unmaintained (maintainer unresponsive for many months, bugs are not 900 Unmaintained (maintainer unresponsive for many months, bugs are not
415 getting fixed). 901 getting fixed).
416 902
417 Does not check input for validity (i.e. will accept non-JSON input 903 Does not check input for validity (i.e. will accept non-JSON input
418 and return "something" instead of raising an exception. This is a 904 and return "something" instead of raising an exception. This is a
419 security issue: imagine two banks transfering money between each 905 security issue: imagine two banks transferring money between each
420 other using JSON. One bank might parse a given non-JSON request and 906 other using JSON. One bank might parse a given non-JSON request and
421 deduct money, while the other might reject the transaction with a 907 deduct money, while the other might reject the transaction with a
422 syntax error. While a good protocol will at least recover, that is 908 syntax error. While a good protocol will at least recover, that is
423 extra unnecessary work and the transaction will still not succeed). 909 extra unnecessary work and the transaction will still not succeed).
424 910
425 JSON::DWIW 0.04 911 JSON::DWIW 0.04
426 Very fast. Very natural. Very nice. 912 Very fast. Very natural. Very nice.
427 913
428 Undocumented unicode handling (but the best of the pack. Unicode 914 Undocumented Unicode handling (but the best of the pack. Unicode
429 escapes still don't get parsed properly). 915 escapes still don't get parsed properly).
430 916
431 Very inflexible. 917 Very inflexible.
432 918
433 No roundtripping. 919 No round-tripping.
434 920
435 Does not generate valid JSON (key strings are often unquoted, empty 921 Does not generate valid JSON texts (key strings are often unquoted,
436 keys result in nothing being output) 922 empty keys result in nothing being output)
437 923
438 Does not check input for validity. 924 Does not check input for validity.
925
926 JSON and YAML
927 You often hear that JSON is a subset of YAML. This is, however, a mass
928 hysteria(*) and very far from the truth (as of the time of this
929 writing), so let me state it clearly: *in general, there is no way to
930 configure JSON::XS to output a data structure as valid YAML* that works
931 in all cases.
932
933 If you really must use JSON::XS to generate YAML, you should use this
934 algorithm (subject to change in future versions):
935
936 my $to_yaml = JSON::XS->new->utf8->space_after (1);
937 my $yaml = $to_yaml->encode ($ref) . "\n";
938
939 This will *usually* generate JSON texts that also parse as valid YAML.
940 Please note that YAML has hardcoded limits on (simple) object key
941 lengths that JSON doesn't have and also has different and incompatible
942 unicode handling, so you should make sure that your hash keys are
943 noticeably shorter than the 1024 "stream characters" YAML allows and
944 that you do not have characters with codepoint values outside the
945 Unicode BMP (basic multilingual page). YAML also does not allow "\/"
946 sequences in strings (which JSON::XS does not *currently* generate, but
947 other JSON generators might).
948
949 There might be other incompatibilities that I am not aware of (or the
950 YAML specification has been changed yet again - it does so quite often).
951 In general you should not try to generate YAML with a JSON generator or
952 vice versa, or try to parse JSON with a YAML parser or vice versa:
953 chances are high that you will run into severe interoperability problems
954 when you least expect it.
955
956 (*) I have been pressured multiple times by Brian Ingerson (one of the
957 authors of the YAML specification) to remove this paragraph, despite
958 him acknowledging that the actual incompatibilities exist. As I was
959 personally bitten by this "JSON is YAML" lie, I refused and said I
960 will continue to educate people about these issues, so others do not
961 run into the same problem again and again. After this, Brian called
962 me a (quote)*complete and worthless idiot*(unquote).
963
964 In my opinion, instead of pressuring and insulting people who
965 actually clarify issues with YAML and the wrong statements of some
966 of its proponents, I would kindly suggest reading the JSON spec
967 (which is not that difficult or long) and finally make YAML
968 compatible to it, and educating users about the changes, instead of
969 spreading lies about the real compatibility for many *years* and
970 trying to silence people who point out that it isn't true.
439 971
440 SPEED 972 SPEED
441 It seems that JSON::XS is surprisingly fast, as shown in the following 973 It seems that JSON::XS is surprisingly fast, as shown in the following
442 tables. They have been generated with the help of the "eg/bench" program 974 tables. They have been generated with the help of the "eg/bench" program
443 in the JSON::XS distribution, to make it easy to compare on your own 975 in the JSON::XS distribution, to make it easy to compare on your own
444 system. 976 system.
445 977
446 First comes a comparison between various modules using a very short JSON 978 First comes a comparison between various modules using a very short
447 string (83 bytes), showing the number of encodes/decodes per second 979 single-line JSON string (also available at
448 (JSON::XS is the functional interface, while JSON::XS/2 is the OO 980 <http://dist.schmorp.de/misc/json/short.json>).
449 interface with pretty-printing and hashkey sorting enabled). Higher is 981
450 better: 982 {"method": "handleMessage", "params": ["user1", "we were just talking"], \
983 "id": null, "array":[1,11,234,-5,1e5,1e7, true, false]}
984
985 It shows the number of encodes/decodes per second (JSON::XS uses the
986 functional interface, while JSON::XS/2 uses the OO interface with
987 pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink).
988 Higher is better:
451 989
452 module | encode | decode | 990 module | encode | decode |
453 -----------|------------|------------| 991 -----------|------------|------------|
454 JSON | 14006 | 6820 | 992 JSON 1.x | 4990.842 | 4088.813 |
455 JSON::DWIW | 200937 | 120386 | 993 JSON::DWIW | 51653.990 | 71575.154 |
456 JSON::PC | 85065 | 129366 | 994 JSON::PC | 65948.176 | 74631.744 |
457 JSON::Syck | 59898 | 44232 | 995 JSON::PP | 8931.652 | 3817.168 |
458 JSON::XS | 1171478 | 342435 | 996 JSON::Syck | 24877.248 | 27776.848 |
459 JSON::XS/2 | 730760 | 328714 | 997 JSON::XS | 388361.481 | 227951.304 |
998 JSON::XS/2 | 227951.304 | 218453.333 |
999 JSON::XS/3 | 338250.323 | 218453.333 |
1000 Storable | 16500.016 | 135300.129 |
460 -----------+------------+------------+ 1001 -----------+------------+------------+
461 1002
462 That is, JSON::XS is 6 times faster than than JSON::DWIW and about 80 1003 That is, JSON::XS is about five times faster than JSON::DWIW on
1004 encoding, about three times faster on decoding, and over forty times
463 times faster than JSON, even with pretty-printing and key sorting. 1005 faster than JSON, even with pretty-printing and key sorting. It also
1006 compares favourably to Storable for small amounts of data.
464 1007
465 Using a longer test string (roughly 18KB, generated from Yahoo! Locals 1008 Using a longer test string (roughly 18KB, generated from Yahoo! Locals
466 search API (http://nanoref.com/yahooapis/mgPdGg): 1009 search API (<http://dist.schmorp.de/misc/json/long.json>).
467 1010
468 module | encode | decode | 1011 module | encode | decode |
469 -----------|------------|------------| 1012 -----------|------------|------------|
470 JSON | 673 | 38 | 1013 JSON 1.x | 55.260 | 34.971 |
471 JSON::DWIW | 5271 | 770 | 1014 JSON::DWIW | 825.228 | 1082.513 |
1015 JSON::PC | 3571.444 | 2394.829 |
472 JSON::PC | 9901 | 2491 | 1016 JSON::PP | 210.987 | 32.574 |
473 JSON::Syck | 2360 | 786 | 1017 JSON::Syck | 552.551 | 787.544 |
474 JSON::XS | 37398 | 3202 | 1018 JSON::XS | 5780.463 | 4854.519 |
475 JSON::XS/2 | 13765 | 3153 | 1019 JSON::XS/2 | 3869.998 | 4798.975 |
1020 JSON::XS/3 | 5862.880 | 4798.975 |
1021 Storable | 4445.002 | 5235.027 |
476 -----------+------------+------------+ 1022 -----------+------------+------------+
477 1023
478 Again, JSON::XS leads by far in the encoding case, while still beating 1024 Again, JSON::XS leads by far (except for Storable which non-surprisingly
479 every other module in the decoding case. 1025 decodes faster).
480 1026
481 On large strings containing lots of unicode characters, some modules 1027 On large strings containing lots of high Unicode characters, some
482 (such as JSON::PC) decode faster than JSON::XS, but the result will be 1028 modules (such as JSON::PC) seem to decode faster than JSON::XS, but the
483 broken due to missing unicode handling. Others refuse to decode or 1029 result will be broken due to missing (or wrong) Unicode handling. Others
484 encode properly, so it was impossible to prepare a fair comparison table 1030 refuse to decode or encode properly, so it was impossible to prepare a
485 for that case. 1031 fair comparison table for that case.
486 1032
487RESOURCE LIMITS 1033SECURITY CONSIDERATIONS
488 JSON::XS does not impose any limits on the size of JSON texts or Perl 1034 When you are using JSON in a protocol, talking to untrusted potentially
489 values they represent - if your machine can handle it, JSON::XS will 1035 hostile creatures requires relatively few measures.
490 encode or decode it. Future versions might optionally impose structure 1036
491 depth and memory use resource limits. 1037 First of all, your JSON decoder should be secure, that is, should not
1038 have any buffer overflows. Obviously, this module should ensure that and
1039 I am trying hard on making that true, but you never know.
1040
1041 Second, you need to avoid resource-starving attacks. That means you
1042 should limit the size of JSON texts you accept, or make sure then when
1043 your resources run out, that's just fine (e.g. by using a separate
1044 process that can crash safely). The size of a JSON text in octets or
1045 characters is usually a good indication of the size of the resources
1046 required to decode it into a Perl structure. While JSON::XS can check
1047 the size of the JSON text, it might be too late when you already have it
1048 in memory, so you might want to check the size before you accept the
1049 string.
1050
1051 Third, JSON::XS recurses using the C stack when decoding objects and
1052 arrays. The C stack is a limited resource: for instance, on my amd64
1053 machine with 8MB of stack size I can decode around 180k nested arrays
1054 but only 14k nested JSON objects (due to perl itself recursing deeply on
1055 croak to free the temporary). If that is exceeded, the program crashes.
1056 To be conservative, the default nesting limit is set to 512. If your
1057 process has a smaller stack, you should adjust this setting accordingly
1058 with the "max_depth" method.
1059
1060 Something else could bomb you, too, that I forgot to think of. In that
1061 case, you get to keep the pieces. I am always open for hints, though...
1062
1063 Also keep in mind that JSON::XS might leak contents of your Perl data
1064 structures in its error messages, so when you serialise sensitive
1065 information you might want to make sure that exceptions thrown by
1066 JSON::XS will not end up in front of untrusted eyes.
1067
1068 If you are using JSON::XS to return packets to consumption by JavaScript
1069 scripts in a browser you should have a look at
1070 <http://jpsykes.com/47/practical-csrf-and-json-security> to see whether
1071 you are vulnerable to some common attack vectors (which really are
1072 browser design bugs, but it is still you who will have to deal with it,
1073 as major browser developers care only for features, not about getting
1074 security right).
1075
1076THREADS
1077 This module is *not* guaranteed to be thread safe and there are no plans
1078 to change this until Perl gets thread support (as opposed to the
1079 horribly slow so-called "threads" which are simply slow and bloated
1080 process simulations - use fork, its *much* faster, cheaper, better).
1081
1082 (It might actually work, but you have been warned).
492 1083
493BUGS 1084BUGS
494 While the goal of this module is to be correct, that unfortunately does 1085 While the goal of this module is to be correct, that unfortunately does
495 not mean its bug-free, only that I think its design is bug-free. It is 1086 not mean its bug-free, only that I think its design is bug-free. It is
496 still very young and not well-tested. If you keep reporting bugs they 1087 still relatively early in its development. If you keep reporting bugs
497 will be fixed swiftly, though. 1088 they will be fixed swiftly, though.
1089
1090 Please refrain from using rt.cpan.org or any other bug reporting
1091 service. I put the contact address into my modules for a reason.
498 1092
499AUTHOR 1093AUTHOR
500 Marc Lehmann <schmorp@schmorp.de> 1094 Marc Lehmann <schmorp@schmorp.de>
501 http://home.schmorp.de/ 1095 http://home.schmorp.de/
502 1096

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