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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;
9
10 # exported functions, they croak on error
11 # and expect/generate UTF-8
12
13 $utf8_encoded_json_text = encode_json $perl_hash_or_arrayref;
14 $perl_hash_or_arrayref = decode_json $utf8_encoded_json_text;
15
16 # OO-interface
17
18 $coder = JSON::XS->new->ascii->pretty->allow_nonref;
19 $pretty_printed_unencoded = $coder->encode ($perl_scalar);
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.
6 29
7DESCRIPTION 30DESCRIPTION
8 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
9 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*.
10 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.
11 42
12 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
13 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
14 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
15 cases their maintainers are unresponsive, gone missing, or not listening 46 cases their maintainers are unresponsive, gone missing, or not listening
16 to bug reports for other reasons. 47 to bug reports for other reasons.
17 48
18 See COMPARISON, below, for a comparison to some other JSON modules. 49 See COMPARISON, below, for a comparison to some other JSON modules.
19 50
51 See MAPPING, below, on how JSON::XS maps perl values to JSON values and
52 vice versa.
53
20 FEATURES 54 FEATURES
21 * correct handling of unicode issues 55 * correct Unicode handling
56
22 This module knows how to handle Unicode, and even documents how it 57 This module knows how to handle Unicode, documents how and when it
23 does so. 58 does so, and even documents what "correct" means.
24 59
25 * round-trip integrity 60 * round-trip integrity
61
26 When you serialise a perl data structure using only datatypes 62 When you serialise a perl data structure using only datatypes
27 supported by JSON, the deserialised data structure is identical on 63 supported by JSON, the deserialised data structure is identical on
28 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.
29 67
30 * strict checking of JSON correctness 68 * strict checking of JSON correctness
69
31 There is no guessing, no generating of illegal JSON strings by 70 There is no guessing, no generating of illegal JSON texts by
32 default, and only JSON is accepted as input (the latter is a 71 default, and only JSON is accepted as input by default (the latter
33 security feature). 72 is a security feature).
34 73
35 * fast 74 * fast
36 compared to other JSON modules, this module compares favourably.
37 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
38 * simple to use 80 * simple to use
81
39 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
40 interface. 83 objetc oriented interface interface.
41 84
42 * reasonably versatile output formats 85 * reasonably versatile output formats
86
43 You can choose between the most compact format possible, a 87 You can choose between the most compact guaranteed-single-line
44 pure-ascii format, or a pretty-printed format. Or you can combine 88 format possible (nice for simple line-based protocols), a pure-ascii
89 format (for when your transport is not 8-bit clean, still supports
90 the whole Unicode range), or a pretty-printed format (for when you
91 want to read that stuff). Or you can combine those features in
45 those features in whatever way you like. 92 whatever way you like.
46 93
47FUNCTIONAL INTERFACE 94FUNCTIONAL INTERFACE
48 The following convinience methods are provided by this module. They are 95 The following convenience methods are provided by this module. They are
49 exported by default: 96 exported by default:
50 97
51 $json_string = to_json $perl_scalar 98 $json_text = encode_json $perl_scalar
52 Converts the given Perl data structure (a simple scalar or a 99 Converts the given Perl data structure to a UTF-8 encoded, binary
53 reference to a hash or array) to a UTF-8 encoded, binary string
54 (that is, the string contains octets only). Croaks on error. 100 string (that is, the string contains octets only). Croaks on error.
55 101
56 This function call is functionally identical to "JSON::XS->new->utf8 102 This function call is functionally identical to:
57 (1)->encode ($perl_scalar)".
58 103
104 $json_text = JSON::XS->new->utf8->encode ($perl_scalar)
105
106 except being faster.
107
59 $perl_scalar = from_json $json_string 108 $perl_scalar = decode_json $json_text
60 The opposite of "to_json": expects an UTF-8 (binary) string and 109 The opposite of "encode_json": expects an UTF-8 (binary) string and
61 tries to parse that as an UTF-8 encoded JSON string, returning the 110 tries to parse that as an UTF-8 encoded JSON text, returning the
62 resulting simple scalar or reference. Croaks on error. 111 resulting reference. Croaks on error.
63 112
64 This function call is functionally identical to "JSON::XS->new->utf8 113 This function call is functionally identical to:
65 (1)->decode ($json_string)". 114
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 :)
66 166
67OBJECT-ORIENTED INTERFACE 167OBJECT-ORIENTED INTERFACE
68 The object oriented interface lets you configure your own encoding or 168 The object oriented interface lets you configure your own encoding or
69 decoding style, within the limits of supported formats. 169 decoding style, within the limits of supported formats.
70 170
… …
74 *disabled*. 174 *disabled*.
75 175
76 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
77 calls can be chained: 177 calls can be chained:
78 178
79 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]})
80 => {"a": [1, 2]} 180 => {"a": [1, 2]}
81 181
82 $json = $json->ascii ($enable) 182 $json = $json->ascii ([$enable])
183 $enabled = $json->get_ascii
83 If $enable is true, then the "encode" method will not generate 184 If $enable is true (or missing), then the "encode" method will not
84 characters outside the code range 0..127. Any unicode characters 185 generate characters outside the code range 0..127 (which is ASCII).
85 outside that range will be escaped using either a single \uXXXX (BMP 186 Any Unicode characters outside that range will be escaped using
86 characters) or a double \uHHHH\uLLLLL escape sequence, as per 187 either a single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL
87 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.
88 192
89 If $enable is false, then the "encode" method will not escape 193 If $enable is false, then the "encode" method will not escape
90 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.
91 196
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
92 JSON::XS->new->ascii (1)->encode (chr 0x10401) 204 JSON::XS->new->ascii (1)->encode ([chr 0x10401])
93 => \ud801\udc01 205 => ["\ud801\udc01"]
94 206
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)
235
95 $json = $json->utf8 ($enable) 236 $json = $json->utf8 ([$enable])
237 $enabled = $json->get_utf8
96 If $enable is true, then the "encode" method will encode the JSON 238 If $enable is true (or missing), then the "encode" method will
97 string into UTF-8, as required by many protocols, while the "decode" 239 encode the JSON result into UTF-8, as required by many protocols,
98 method expects to be handled an UTF-8-encoded string. Please note 240 while the "decode" method expects to be handled an UTF-8-encoded
99 that UTF-8-encoded strings do not contain any characters outside the 241 string. Please note that UTF-8-encoded strings do not contain any
100 range 0..255, they are thus useful for bytewise/binary I/O. 242 characters outside the range 0..255, they are thus useful for
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.
101 246
102 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
103 string as a (non-encoded) unicode string, while "decode" expects 248 string as a (non-encoded) Unicode string, while "decode" expects
104 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
105 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.
106 251
252 See also the section *ENCODING/CODESET FLAG NOTES* later in this
253 document.
254
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);
264
107 $json = $json->pretty ($enable) 265 $json = $json->pretty ([$enable])
108 This enables (or disables) all of the "indent", "space_before" and 266 This enables (or disables) all of the "indent", "space_before" and
109 "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
110 generate the most readable (or most compact) form possible. 268 generate the most readable (or most compact) form possible.
269
270 Example, pretty-print some simple structure:
111 271
112 my $json = JSON::XS->new->pretty(1)->encode ({a => [1,2]}) 272 my $json = JSON::XS->new->pretty(1)->encode ({a => [1,2]})
113 => 273 =>
114 { 274 {
115 "a" : [ 275 "a" : [
116 1, 276 1,
117 2 277 2
118 ] 278 ]
119 } 279 }
120 280
121 $json = $json->indent ($enable) 281 $json = $json->indent ([$enable])
282 $enabled = $json->get_indent
122 If $enable is true, then the "encode" method will use a multiline 283 If $enable is true (or missing), then the "encode" method will use a
123 format as output, putting every array member or object/hash 284 multiline format as output, putting every array member or
124 key-value pair into its own line, identing them properly. 285 object/hash key-value pair into its own line, indenting them
286 properly.
125 287
126 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
127 the resulting JSON strings is guarenteed not to contain any 289 the resulting JSON text is guaranteed not to contain any "newlines".
128 "newlines".
129 290
130 This setting has no effect when decoding JSON strings. 291 This setting has no effect when decoding JSON texts.
131 292
132 $json = $json->space_before ($enable) 293 $json = $json->space_before ([$enable])
294 $enabled = $json->get_space_before
133 If $enable is true, then the "encode" method will add an extra 295 If $enable is true (or missing), then the "encode" method will add
134 optional space before the ":" separating keys from values in JSON 296 an extra optional space before the ":" separating keys from values
135 objects. 297 in JSON objects.
136 298
137 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
138 space at those places. 300 space at those places.
139 301
140 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
141 most likely combine this setting with "space_after". 303 most likely combine this setting with "space_after".
142 304
305 Example, space_before enabled, space_after and indent disabled:
306
307 {"key" :"value"}
308
143 $json = $json->space_after ($enable) 309 $json = $json->space_after ([$enable])
310 $enabled = $json->get_space_after
144 If $enable is true, then the "encode" method will add an extra 311 If $enable is true (or missing), then the "encode" method will add
145 optional space after the ":" separating keys from values in JSON 312 an extra optional space after the ":" separating keys from values in
146 objects and extra whitespace after the "," separating key-value 313 JSON objects and extra whitespace after the "," separating key-value
147 pairs and array members. 314 pairs and array members.
148 315
149 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
150 space at those places. 317 space at those places.
151 318
152 This setting has no effect when decoding JSON strings. 319 This setting has no effect when decoding JSON texts.
153 320
321 Example, space_before and indent disabled, space_after enabled:
322
323 {"key": "value"}
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
154 $json = $json->canonical ($enable) 367 $json = $json->canonical ([$enable])
368 $enabled = $json->get_canonical
155 If $enable is true, then the "encode" method will output JSON 369 If $enable is true (or missing), then the "encode" method will
156 objects by sorting their keys. This is adding a comparatively high 370 output JSON objects by sorting their keys. This is adding a
157 overhead. 371 comparatively high overhead.
158 372
159 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
160 pairs in the order Perl stores them (which will likely change 374 pairs in the order Perl stores them (which will likely change
161 between runs of the same script). 375 between runs of the same script).
162 376
163 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
164 encoded as the same JSON string (given the same overall settings). 378 encoded as the same JSON text (given the same overall settings). If
165 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
166 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
167 in Perl. 381 in Perl.
168 382
169 This setting has no effect when decoding JSON strings. 383 This setting has no effect when decoding JSON texts.
170 384
171 $json = $json->allow_nonref ($enable) 385 $json = $json->allow_nonref ([$enable])
386 $enabled = $json->get_allow_nonref
172 If $enable is true, then the "encode" method can convert a 387 If $enable is true (or missing), then the "encode" method can
173 non-reference into its corresponding string, number or null JSON 388 convert a non-reference into its corresponding string, number or
174 value, which is an extension to RFC4627. Likewise, "decode" will 389 null JSON value, which is an extension to RFC4627. Likewise,
175 accept those JSON values instead of croaking. 390 "decode" will accept those JSON values instead of croaking.
176 391
177 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
178 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
179 object or array. Likewise, "decode" will croak if given something 394 object or array. Likewise, "decode" will croak if given something
180 that is not a JSON object or array. 395 that is not a JSON object or array.
181 396
397 Example, encode a Perl scalar as JSON value with enabled
398 "allow_nonref", resulting in an invalid JSON text:
399
400 JSON::XS->new->allow_nonref->encode ("Hello, World!")
401 => "Hello, World!"
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
515 $json = $json->shrink ([$enable])
516 $enabled = $json->get_shrink
517 Perl usually over-allocates memory a bit when allocating space for
518 strings. This flag optionally resizes strings generated by either
519 "encode" or "decode" to their minimum size possible. This can save
520 memory when your JSON texts are either very very long or you have
521 many short strings. It will also try to downgrade any strings to
522 octet-form if possible: perl stores strings internally either in an
523 encoding called UTF-X or in octet-form. The latter cannot store
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.
530
531 If $enable is true (or missing), the string returned by "encode"
532 will be shrunk-to-fit, while all strings generated by "decode" will
533 also be shrunk-to-fit.
534
535 If $enable is false, then the normal perl allocation algorithms are
536 used. If you work with your data, then this is likely to be faster.
537
538 In the future, this setting might control other things, such as
539 converting strings that look like integers or floats into integers
540 or floats internally (there is no difference on the Perl level),
541 saving space.
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
182 $json_string = $json->encode ($perl_scalar) 581 $json_text = $json->encode ($perl_scalar)
183 Converts the given Perl data structure (a simple scalar or a 582 Converts the given Perl data structure (a simple scalar or a
184 reference to a hash or array) to its JSON representation. Simple 583 reference to a hash or array) to its JSON representation. Simple
185 scalars will be converted into JSON string or number sequences, 584 scalars will be converted into JSON string or number sequences,
186 while references to arrays become JSON arrays and references to 585 while references to arrays become JSON arrays and references to
187 hashes become JSON objects. Undefined Perl values (e.g. "undef") 586 hashes become JSON objects. Undefined Perl values (e.g. "undef")
188 become JSON "null" values. Neither "true" nor "false" values will be 587 become JSON "null" values. Neither "true" nor "false" values will be
189 generated. 588 generated.
190 589
191 $perl_scalar = $json->decode ($json_string) 590 $perl_scalar = $json->decode ($json_text)
192 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,
193 it, returning the resulting simple scalar or reference. Croaks on 592 returning the resulting simple scalar or reference. Croaks on error.
194 error.
195 593
196 JSON numbers and strings become simple Perl scalars. JSON arrays 594 JSON numbers and strings become simple Perl scalars. JSON arrays
197 become Perl arrayrefs and JSON objects become Perl hashrefs. "true" 595 become Perl arrayrefs and JSON objects become Perl hashrefs. "true"
198 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)
610
611MAPPING
612 This section describes how JSON::XS maps Perl values to JSON values and
613 vice versa. These mappings are designed to "do the right thing" in most
614 circumstances automatically, preserving round-tripping characteristics
615 (what you put in comes out as something equivalent).
616
617 For the more enlightened: note that in the following descriptions,
618 lowercase *perl* refers to the Perl interpreter, while uppercase *Perl*
619 refers to the abstract Perl language itself.
620
621 JSON -> PERL
622 object
623 A JSON object becomes a reference to a hash in Perl. No ordering of
624 object keys is preserved (JSON does not preserve object key ordering
625 itself).
626
627 array
628 A JSON array becomes a reference to an array in Perl.
629
630 string
631 A JSON string becomes a string scalar in Perl - Unicode codepoints
632 in JSON are represented by the same codepoints in the Perl string,
633 so no manual decoding is necessary.
634
635 number
636 A JSON number becomes either an integer, numeric (floating point) or
637 string scalar in perl, depending on its range and any fractional
638 parts. On the Perl level, there is no difference between those as
639 Perl handles all the conversion details, but an integer may take
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
654 number).
655
656 true, false
657 These JSON atoms become "JSON::XS::true" and "JSON::XS::false",
658 respectively. They are overloaded to act almost exactly like the
659 numbers 1 and 0. You can check whether a scalar is a JSON boolean by
660 using the "JSON::XS::is_bool" function.
661
662 null
663 A JSON null atom becomes "undef" in Perl.
664
665 PERL -> JSON
666 The mapping from Perl to JSON is slightly more difficult, as Perl is a
667 truly typeless language, so we can only guess which JSON type is meant
668 by a Perl value.
669
670 hash references
671 Perl hash references become JSON objects. As there is no inherent
672 ordering in hash keys (or JSON objects), they will usually be
673 encoded in a pseudo-random order that can change between runs of the
674 same program but stays generally the same within a single run of a
675 program. JSON::XS can optionally sort the hash keys (determined by
676 the *canonical* flag), so the same datastructure will serialise to
677 the same JSON text (given same settings and version of JSON::XS),
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.
681
682 array references
683 Perl array references become JSON arrays.
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
698 blessed objects
699 Blessed objects are not directly representable in JSON. See the
700 "allow_blessed" and "convert_blessed" methods on various options on
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.
704
705 simple scalars
706 Simple Perl scalars (any scalar that is not a reference) are the
707 most difficult objects to encode: JSON::XS will encode undefined
708 scalars as JSON "null" values, scalars that have last been used in a
709 string context before encoding as JSON strings, and anything else as
710 number value:
711
712 # dump as number
713 encode_json [2] # yields [2]
714 encode_json [-3.0e17] # yields [-3e+17]
715 my $value = 5; encode_json [$value] # yields [5]
716
717 # used as string, so dump as string
718 print $value;
719 encode_json [$value] # yields ["5"]
720
721 # undef becomes null
722 encode_json [undef] # yields [null]
723
724 You can force the type to be a JSON string by stringifying it:
725
726 my $x = 3.1; # some variable containing a number
727 "$x"; # stringified
728 $x .= ""; # another, more awkward way to stringify
729 print $x; # perl does it for you, too, quite often
730
731 You can force the type to be a JSON number by numifying it:
732
733 my $x = "3"; # some variable containing a string
734 $x += 0; # numify it, ensuring it will be dumped as a number
735 $x *= 1; # same thing, the choice is yours.
736
737 You can not currently force the type in other, less obscure, ways.
738 Tell me if you need this capability (but don't forget to explain why
739 its needed :).
740
741ENCODING/CODESET FLAG NOTES
742 The interested reader might have seen a number of flags that signify
743 encodings or codesets - "utf8", "latin1" and "ascii". There seems to be
744 some confusion on what these do, so here is a short comparison:
745
746 "utf8" controls wether the JSON text created by "encode" (and expected
747 by "decode") is UTF-8 encoded or not, while "latin1" and "ascii" only
748 control wether "encode" escapes character values outside their
749 respective codeset range. Neither of these flags conflict with each
750 other, although some combinations make less sense than others.
751
752 Care has been taken to make all flags symmetrical with respect to
753 "encode" and "decode", that is, texts encoded with any combination of
754 these flag values will be correctly decoded when the same flags are used
755 - in general, if you use different flag settings while encoding vs. when
756 decoding you likely have a bug somewhere.
757
758 Below comes a verbose discussion of these flags. Note that a "codeset"
759 is simply an abstract set of character-codepoint pairs, while an
760 encoding takes those codepoint numbers and *encodes* them, in our case
761 into octets. Unicode is (among other things) a codeset, UTF-8 is an
762 encoding, and ISO-8859-1 (= latin 1) and ASCII are both codesets *and*
763 encodings at the same time, which can be confusing.
764
765 "utf8" flag disabled
766 When "utf8" is disabled (the default), then "encode"/"decode"
767 generate and expect Unicode strings, that is, characters with high
768 ordinal Unicode values (> 255) will be encoded as such characters,
769 and likewise such characters are decoded as-is, no canges to them
770 will be done, except "(re-)interpreting" them as Unicode codepoints
771 or Unicode characters, respectively (to Perl, these are the same
772 thing in strings unless you do funny/weird/dumb stuff).
773
774 This is useful when you want to do the encoding yourself (e.g. when
775 you want to have UTF-16 encoded JSON texts) or when some other layer
776 does the encoding for you (for example, when printing to a terminal
777 using a filehandle that transparently encodes to UTF-8 you certainly
778 do NOT want to UTF-8 encode your data first and have Perl encode it
779 another time).
780
781 "utf8" flag enabled
782 If the "utf8"-flag is enabled, "encode"/"decode" will encode all
783 characters using the corresponding UTF-8 multi-byte sequence, and
784 will expect your input strings to be encoded as UTF-8, that is, no
785 "character" of the input string must have any value > 255, as UTF-8
786 does not allow that.
787
788 The "utf8" flag therefore switches between two modes: disabled means
789 you will get a Unicode string in Perl, enabled means you get an
790 UTF-8 encoded octet/binary string in Perl.
791
792 "latin1" or "ascii" flags enabled
793 With "latin1" (or "ascii") enabled, "encode" will escape characters
794 with ordinal values > 255 (> 127 with "ascii") and encode the
795 remaining characters as specified by the "utf8" flag.
796
797 If "utf8" is disabled, then the result is also correctly encoded in
798 those character sets (as both are proper subsets of Unicode, meaning
799 that a Unicode string with all character values < 256 is the same
800 thing as a ISO-8859-1 string, and a Unicode string with all
801 character values < 128 is the same thing as an ASCII string in
802 Perl).
803
804 If "utf8" is enabled, you still get a correct UTF-8-encoded string,
805 regardless of these flags, just some more characters will be escaped
806 using "\uXXXX" then before.
807
808 Note that ISO-8859-1-*encoded* strings are not compatible with UTF-8
809 encoding, while ASCII-encoded strings are. That is because the
810 ISO-8859-1 encoding is NOT a subset of UTF-8 (despite the ISO-8859-1
811 *codeset* being a subset of Unicode), while ASCII is.
812
813 Surprisingly, "decode" will ignore these flags and so treat all
814 input values as governed by the "utf8" flag. If it is disabled, this
815 allows you to decode ISO-8859-1- and ASCII-encoded strings, as both
816 strict subsets of Unicode. If it is enabled, you can correctly
817 decode UTF-8 encoded strings.
818
819 So neither "latin1" nor "ascii" are incompatible with the "utf8"
820 flag - they only govern when the JSON output engine escapes a
821 character or not.
822
823 The main use for "latin1" is to relatively efficiently store binary
824 data as JSON, at the expense of breaking compatibility with most
825 JSON decoders.
826
827 The main use for "ascii" is to force the output to not contain
828 characters with values > 127, which means you can interpret the
829 resulting string as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about
830 any character set and 8-bit-encoding, and still get the same data
831 structure back. This is useful when your channel for JSON transfer
832 is not 8-bit clean or the encoding might be mangled in between (e.g.
833 in mail), and works because ASCII is a proper subset of most 8-bit
834 and multibyte encodings in use in the world.
199 835
200COMPARISON 836COMPARISON
201 As already mentioned, this module was created because none of the 837 As already mentioned, this module was created because none of the
202 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
203 describe the problems (or pleasures) I encountered with various existing 839 describe the problems (or pleasures) I encountered with various existing
204 JSON modules, followed by some benchmark values. JSON::XS was designed 840 JSON modules, followed by some benchmark values. JSON::XS was designed
205 not to suffer from any of these problems or limitations. 841 not to suffer from any of these problems or limitations.
206 842
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
207 JSON 1.07 854 JSON 1.07
208 Slow (but very portable, as it is written in pure Perl). 855 Slow (but very portable, as it is written in pure Perl).
209 856
210 Undocumented/buggy Unicode handling (how JSON handles unicode values 857 Undocumented/buggy Unicode handling (how JSON handles Unicode values
211 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
212 doing en-/decoding oneself, but unicode escapes are not working 859 doing en-/decoding oneself, but Unicode escapes are not working
213 properly). 860 properly).
214 861
215 No roundtripping (strings get clobbered if they look like numbers, 862 No round-tripping (strings get clobbered if they look like numbers,
216 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
217 will decode into the number 2. 864 will decode into the number 2.
218 865
219 JSON::PC 0.01 866 JSON::PC 0.01
220 Very fast. 867 Very fast.
221 868
222 Undocumented/buggy Unicode handling. 869 Undocumented/buggy Unicode handling.
223 870
224 No roundtripping. 871 No round-tripping.
225 872
226 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
227 magic values will make it croak). 874 magic values will make it croak).
228 875
229 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}"
230 which is not a valid JSON string. 877 which is not a valid JSON text.
231 878
232 Unmaintained (maintainer unresponsive for many months, bugs are not 879 Unmaintained (maintainer unresponsive for many months, bugs are not
233 getting fixed). 880 getting fixed).
234 881
235 JSON::Syck 0.21 882 JSON::Syck 0.21
236 Very buggy (often crashes). 883 Very buggy (often crashes).
237 884
238 Very inflexible (no human-readable format supported, format pretty 885 Very inflexible (no human-readable format supported, format pretty
239 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
240 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
241 preferably a way to generate ASCII-only JSON strings). 888 preferably a way to generate ASCII-only JSON texts).
242 889
243 Completely broken (and confusingly documented) Unicode handling 890 Completely broken (and confusingly documented) Unicode handling
244 (unicode escapes are not working properly, you need to set 891 (Unicode escapes are not working properly, you need to set
245 ImplicitUnicode to *different* values on en- and decoding to get 892 ImplicitUnicode to *different* values on en- and decoding to get
246 symmetric behaviour). 893 symmetric behaviour).
247 894
248 No roundtripping (simple cases work, but this depends on wether the 895 No round-tripping (simple cases work, but this depends on whether
249 scalar value was used in a numeric context or not). 896 the scalar value was used in a numeric context or not).
250 897
251 Dumping hashes may skip hash values depending on iterator state. 898 Dumping hashes may skip hash values depending on iterator state.
252 899
253 Unmaintained (maintainer unresponsive for many months, bugs are not 900 Unmaintained (maintainer unresponsive for many months, bugs are not
254 getting fixed). 901 getting fixed).
255 902
256 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
257 and return "something" instead of raising an exception. This is a 904 and return "something" instead of raising an exception. This is a
258 security issue: imagine two banks transfering money between each 905 security issue: imagine two banks transferring money between each
259 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
260 deduct money, while the other might reject the transaction with a 907 deduct money, while the other might reject the transaction with a
261 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
262 extra unnecessary work and the transaction will still not succeed). 909 extra unnecessary work and the transaction will still not succeed).
263 910
264 JSON::DWIW 0.04 911 JSON::DWIW 0.04
265 Very fast. Very natural. Very nice. 912 Very fast. Very natural. Very nice.
266 913
267 Undocumented unicode handling (but the best of the pack. Unicode 914 Undocumented Unicode handling (but the best of the pack. Unicode
268 escapes still don't get parsed properly). 915 escapes still don't get parsed properly).
269 916
270 Very inflexible. 917 Very inflexible.
271 918
272 No roundtripping. 919 No round-tripping.
273 920
274 Does not generate valid JSON (key strings are often unquoted, empty 921 Does not generate valid JSON texts (key strings are often unquoted,
275 keys result in nothing being output) 922 empty keys result in nothing being output)
276 923
277 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.
278 971
279 SPEED 972 SPEED
280 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
281 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
282 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
283 system. 976 system.
284 977
285 First is a comparison between various modules using a very simple JSON 978 First comes a comparison between various modules using a very short
979 single-line JSON string (also available at
980 <http://dist.schmorp.de/misc/json/short.json>).
981
982 {"method": "handleMessage", "params": ["user1", "we were just talking"], \
983 "id": null, "array":[1,11,234,-5,1e5,1e7, true, false]}
984
286 string, showing the number of encodes/decodes per second (JSON::XS is 985 It shows the number of encodes/decodes per second (JSON::XS uses the
287 the functional interface, while JSON::XS/2 is the OO interface with 986 functional interface, while JSON::XS/2 uses the OO interface with
288 pretty-printing and hashkey sorting enabled). 987 pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink).
988 Higher is better:
289 989
290 module | encode | decode | 990 module | encode | decode |
291 -----------|------------|------------| 991 -----------|------------|------------|
292 JSON | 14006 | 6820 | 992 JSON 1.x | 4990.842 | 4088.813 |
293 JSON::DWIW | 200937 | 120386 | 993 JSON::DWIW | 51653.990 | 71575.154 |
294 JSON::PC | 85065 | 129366 | 994 JSON::PC | 65948.176 | 74631.744 |
295 JSON::Syck | 59898 | 44232 | 995 JSON::PP | 8931.652 | 3817.168 |
296 JSON::XS | 1171478 | 342435 | 996 JSON::Syck | 24877.248 | 27776.848 |
297 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 |
298 -----------+------------+------------+ 1001 -----------+------------+------------+
299 1002
300 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
301 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.
302 1007
303 Using a longer test string (roughly 8KB, generated from Yahoo! Locals 1008 Using a longer test string (roughly 18KB, generated from Yahoo! Locals
304 search API (http://nanoref.com/yahooapis/mgPdGg): 1009 search API (<http://dist.schmorp.de/misc/json/long.json>).
305 1010
306 module | encode | decode | 1011 module | encode | decode |
307 -----------|------------|------------| 1012 -----------|------------|------------|
308 JSON | 673 | 38 | 1013 JSON 1.x | 55.260 | 34.971 |
309 JSON::DWIW | 5271 | 770 | 1014 JSON::DWIW | 825.228 | 1082.513 |
1015 JSON::PC | 3571.444 | 2394.829 |
310 JSON::PC | 9901 | 2491 | 1016 JSON::PP | 210.987 | 32.574 |
311 JSON::Syck | 2360 | 786 | 1017 JSON::Syck | 552.551 | 787.544 |
312 JSON::XS | 37398 | 3202 | 1018 JSON::XS | 5780.463 | 4854.519 |
313 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 |
314 -----------+------------+------------+ 1022 -----------+------------+------------+
315 1023
316 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
317 every other module in the decoding case. 1025 decodes faster).
318 1026
319 Last example is an almost 8MB large hash with many large binary values 1027 On large strings containing lots of high Unicode characters, some
320 (PNG files), resulting in a lot of escaping: 1028 modules (such as JSON::PC) seem to decode faster than JSON::XS, but the
1029 result will be broken due to missing (or wrong) Unicode handling. Others
1030 refuse to decode or encode properly, so it was impossible to prepare a
1031 fair comparison table for that case.
1032
1033SECURITY CONSIDERATIONS
1034 When you are using JSON in a protocol, talking to untrusted potentially
1035 hostile creatures requires relatively few measures.
1036
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).
321 1083
322BUGS 1084BUGS
323 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
324 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
325 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
326 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.
327 1092
328AUTHOR 1093AUTHOR
329 Marc Lehmann <schmorp@schmorp.de> 1094 Marc Lehmann <schmorp@schmorp.de>
330 http://home.schmorp.de/ 1095 http://home.schmorp.de/
331 1096

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