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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 texts 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_text = 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:
74 103
75 $json_text = JSON::XS->new->utf8->encode ($perl_scalar) 104 $json_text = JSON::XS->new->utf8->encode ($perl_scalar)
76 105
77 except being faster. 106 except being faster.
78 107
79 $perl_scalar = from_json $json_text 108 $perl_scalar = decode_json $json_text
80 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
81 tries to parse that as an UTF-8 encoded JSON text, returning the 110 tries to parse that as an UTF-8 encoded JSON text, returning the
82 resulting simple scalar or reference. Croaks on error. 111 resulting reference. Croaks on error.
83 112
84 This function call is functionally identical to: 113 This function call is functionally identical to:
85 114
86 $perl_scalar = JSON::XS->new->utf8->decode ($json_text) 115 $perl_scalar = JSON::XS->new->utf8->decode ($json_text)
87 116
88 except being faster. 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 :)
89 166
90OBJECT-ORIENTED INTERFACE 167OBJECT-ORIENTED INTERFACE
91 The object oriented interface lets you configure your own encoding or 168 The object oriented interface lets you configure your own encoding or
92 decoding style, within the limits of supported formats. 169 decoding style, within the limits of supported formats.
93 170
… …
101 178
102 my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]}) 179 my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]})
103 => {"a": [1, 2]} 180 => {"a": [1, 2]}
104 181
105 $json = $json->ascii ([$enable]) 182 $json = $json->ascii ([$enable])
183 $enabled = $json->get_ascii
106 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
107 generate characters outside the code range 0..127 (which is ASCII). 185 generate characters outside the code range 0..127 (which is ASCII).
108 Any unicode characters outside that range will be escaped using 186 Any Unicode characters outside that range will be escaped using
109 either a single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL 187 either a single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL
110 escape sequence, 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.
111 192
112 If $enable is false, then the "encode" method will not escape 193 If $enable is false, then the "encode" method will not escape
113 Unicode characters unless required by the JSON syntax. This results 194 Unicode characters unless required by the JSON syntax or other
114 in a faster and more compact format. 195 flags. This results in a faster and more compact format.
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.
115 203
116 JSON::XS->new->ascii (1)->encode ([chr 0x10401]) 204 JSON::XS->new->ascii (1)->encode ([chr 0x10401])
117 => ["\ud801\udc01"] 205 => ["\ud801\udc01"]
118 206
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
119 $json = $json->utf8 ([$enable]) 236 $json = $json->utf8 ([$enable])
237 $enabled = $json->get_utf8
120 If $enable is true (or missing), then the "encode" method will 238 If $enable is true (or missing), then the "encode" method will
121 encode the JSON result into UTF-8, as required by many protocols, 239 encode the JSON result into UTF-8, as required by many protocols,
122 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
123 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
124 characters outside the range 0..255, they are thus useful for 242 characters outside the range 0..255, they are thus useful for
125 bytewise/binary I/O. In future versions, enabling this option might 243 bytewise/binary I/O. In future versions, enabling this option might
126 enable autodetection of the UTF-16 and UTF-32 encoding families, as 244 enable autodetection of the UTF-16 and UTF-32 encoding families, as
127 described in RFC4627. 245 described in RFC4627.
128 246
129 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
130 string as a (non-encoded) unicode string, while "decode" expects 248 string as a (non-encoded) Unicode string, while "decode" expects
131 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
132 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.
251
252 See also the section *ENCODING/CODESET FLAG NOTES* later in this
253 document.
133 254
134 Example, output UTF-16BE-encoded JSON: 255 Example, output UTF-16BE-encoded JSON:
135 256
136 use Encode; 257 use Encode;
137 $jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object); 258 $jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
… …
156 2 277 2
157 ] 278 ]
158 } 279 }
159 280
160 $json = $json->indent ([$enable]) 281 $json = $json->indent ([$enable])
282 $enabled = $json->get_indent
161 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
162 multiline format as output, putting every array member or 284 multiline format as output, putting every array member or
163 object/hash key-value pair into its own line, identing them 285 object/hash key-value pair into its own line, indenting them
164 properly. 286 properly.
165 287
166 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
167 the resulting JSON text is guarenteed not to contain any "newlines". 289 the resulting JSON text is guaranteed not to contain any "newlines".
168 290
169 This setting has no effect when decoding JSON texts. 291 This setting has no effect when decoding JSON texts.
170 292
171 $json = $json->space_before ([$enable]) 293 $json = $json->space_before ([$enable])
294 $enabled = $json->get_space_before
172 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
173 an extra optional space before the ":" separating keys from values 296 an extra optional space before the ":" separating keys from values
174 in JSON objects. 297 in JSON objects.
175 298
176 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
… …
182 Example, space_before enabled, space_after and indent disabled: 305 Example, space_before enabled, space_after and indent disabled:
183 306
184 {"key" :"value"} 307 {"key" :"value"}
185 308
186 $json = $json->space_after ([$enable]) 309 $json = $json->space_after ([$enable])
310 $enabled = $json->get_space_after
187 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
188 an extra optional space after the ":" separating keys from values in 312 an extra optional space after the ":" separating keys from values in
189 JSON objects and extra whitespace after the "," separating key-value 313 JSON objects and extra whitespace after the "," separating key-value
190 pairs and array members. 314 pairs and array members.
191 315
… …
196 320
197 Example, space_before and indent disabled, space_after enabled: 321 Example, space_before and indent disabled, space_after enabled:
198 322
199 {"key": "value"} 323 {"key": "value"}
200 324
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
201 $json = $json->canonical ([$enable]) 367 $json = $json->canonical ([$enable])
368 $enabled = $json->get_canonical
202 If $enable is true (or missing), then the "encode" method will 369 If $enable is true (or missing), then the "encode" method will
203 output JSON objects by sorting their keys. This is adding a 370 output JSON objects by sorting their keys. This is adding a
204 comparatively high overhead. 371 comparatively high overhead.
205 372
206 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
207 pairs in the order Perl stores them (which will likely change 374 pairs in the order Perl stores them (which will likely change
208 between runs of the same script). 375 between runs of the same script).
209 376
210 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
211 encoded as the same JSON text (given the same overall settings). If 378 encoded as the same JSON text (given the same overall settings). If
212 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
213 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
214 in Perl. 381 in Perl.
215 382
216 This setting has no effect when decoding JSON texts. 383 This setting has no effect when decoding JSON texts.
217 384
218 $json = $json->allow_nonref ([$enable]) 385 $json = $json->allow_nonref ([$enable])
386 $enabled = $json->get_allow_nonref
219 If $enable is true (or missing), then the "encode" method can 387 If $enable is true (or missing), then the "encode" method can
220 convert a non-reference into its corresponding string, number or 388 convert a non-reference into its corresponding string, number or
221 null JSON value, which is an extension to RFC4627. Likewise, 389 null JSON value, which is an extension to RFC4627. Likewise,
222 "decode" will accept those JSON values instead of croaking. 390 "decode" will accept those JSON values instead of croaking.
223 391
… …
230 "allow_nonref", resulting in an invalid JSON text: 398 "allow_nonref", resulting in an invalid JSON text:
231 399
232 JSON::XS->new->allow_nonref->encode ("Hello, World!") 400 JSON::XS->new->allow_nonref->encode ("Hello, World!")
233 => "Hello, World!" 401 => "Hello, World!"
234 402
403 $json = $json->allow_unknown ([$enable])
404 $enabled = $json->get_allow_unknown
405 If $enable is true (or missing), then "encode" will *not* throw an
406 exception when it encounters values it cannot represent in JSON (for
407 example, filehandles) but instead will encode a JSON "null" value.
408 Note that blessed objects are not included here and are handled
409 separately by c<allow_nonref>.
410
411 If $enable is false (the default), then "encode" will throw an
412 exception when it encounters anything it cannot encode as JSON.
413
414 This option does not affect "decode" in any way, and it is
415 recommended to leave it off unless you know your communications
416 partner.
417
418 $json = $json->allow_blessed ([$enable])
419 $enabled = $json->get_allow_blessed
420 If $enable is true (or missing), then the "encode" method will not
421 barf when it encounters a blessed reference. Instead, the value of
422 the convert_blessed option will decide whether "null"
423 ("convert_blessed" disabled or no "TO_JSON" method found) or a
424 representation of the object ("convert_blessed" enabled and
425 "TO_JSON" method found) is being encoded. Has no effect on "decode".
426
427 If $enable is false (the default), then "encode" will throw an
428 exception when it encounters a blessed object.
429
430 $json = $json->convert_blessed ([$enable])
431 $enabled = $json->get_convert_blessed
432 If $enable is true (or missing), then "encode", upon encountering a
433 blessed object, will check for the availability of the "TO_JSON"
434 method on the object's class. If found, it will be called in scalar
435 context and the resulting scalar will be encoded instead of the
436 object. If no "TO_JSON" method is found, the value of
437 "allow_blessed" will decide what to do.
438
439 The "TO_JSON" method may safely call die if it wants. If "TO_JSON"
440 returns other blessed objects, those will be handled in the same
441 way. "TO_JSON" must take care of not causing an endless recursion
442 cycle (== crash) in this case. The name of "TO_JSON" was chosen
443 because other methods called by the Perl core (== not by the user of
444 the object) are usually in upper case letters and to avoid
445 collisions with any "to_json" function or method.
446
447 This setting does not yet influence "decode" in any way, but in the
448 future, global hooks might get installed that influence "decode" and
449 are enabled by this setting.
450
451 If $enable is false, then the "allow_blessed" setting will decide
452 what to do when a blessed object is found.
453
454 $json = $json->filter_json_object ([$coderef->($hashref)])
455 When $coderef is specified, it will be called from "decode" each
456 time it decodes a JSON object. The only argument is a reference to
457 the newly-created hash. If the code references returns a single
458 scalar (which need not be a reference), this value (i.e. a copy of
459 that scalar to avoid aliasing) is inserted into the deserialised
460 data structure. If it returns an empty list (NOTE: *not* "undef",
461 which is a valid scalar), the original deserialised hash will be
462 inserted. This setting can slow down decoding considerably.
463
464 When $coderef is omitted or undefined, any existing callback will be
465 removed and "decode" will not change the deserialised hash in any
466 way.
467
468 Example, convert all JSON objects into the integer 5:
469
470 my $js = JSON::XS->new->filter_json_object (sub { 5 });
471 # returns [5]
472 $js->decode ('[{}]')
473 # throw an exception because allow_nonref is not enabled
474 # so a lone 5 is not allowed.
475 $js->decode ('{"a":1, "b":2}');
476
477 $json = $json->filter_json_single_key_object ($key [=>
478 $coderef->($value)])
479 Works remotely similar to "filter_json_object", but is only called
480 for JSON objects having a single key named $key.
481
482 This $coderef is called before the one specified via
483 "filter_json_object", if any. It gets passed the single value in the
484 JSON object. If it returns a single value, it will be inserted into
485 the data structure. If it returns nothing (not even "undef" but the
486 empty list), the callback from "filter_json_object" will be called
487 next, as if no single-key callback were specified.
488
489 If $coderef is omitted or undefined, the corresponding callback will
490 be disabled. There can only ever be one callback for a given key.
491
492 As this callback gets called less often then the
493 "filter_json_object" one, decoding speed will not usually suffer as
494 much. Therefore, single-key objects make excellent targets to
495 serialise Perl objects into, especially as single-key JSON objects
496 are as close to the type-tagged value concept as JSON gets (it's
497 basically an ID/VALUE tuple). Of course, JSON does not support this
498 in any way, so you need to make sure your data never looks like a
499 serialised Perl hash.
500
501 Typical names for the single object key are "__class_whatever__", or
502 "$__dollars_are_rarely_used__$" or "}ugly_brace_placement", or even
503 things like "__class_md5sum(classname)__", to reduce the risk of
504 clashing with real hashes.
505
506 Example, decode JSON objects of the form "{ "__widget__" => <id> }"
507 into the corresponding $WIDGET{<id>} object:
508
509 # return whatever is in $WIDGET{5}:
510 JSON::XS
511 ->new
512 ->filter_json_single_key_object (__widget__ => sub {
513 $WIDGET{ $_[0] }
514 })
515 ->decode ('{"__widget__": 5')
516
517 # this can be used with a TO_JSON method in some "widget" class
518 # for serialisation to json:
519 sub WidgetBase::TO_JSON {
520 my ($self) = @_;
521
522 unless ($self->{id}) {
523 $self->{id} = ..get..some..id..;
524 $WIDGET{$self->{id}} = $self;
525 }
526
527 { __widget__ => $self->{id} }
528 }
529
235 $json = $json->shrink ([$enable]) 530 $json = $json->shrink ([$enable])
531 $enabled = $json->get_shrink
236 Perl usually over-allocates memory a bit when allocating space for 532 Perl usually over-allocates memory a bit when allocating space for
237 strings. This flag optionally resizes strings generated by either 533 strings. This flag optionally resizes strings generated by either
238 "encode" or "decode" to their minimum size possible. This can save 534 "encode" or "decode" to their minimum size possible. This can save
239 memory when your JSON texts are either very very long or you have 535 memory when your JSON texts are either very very long or you have
240 many short strings. It will also try to downgrade any strings to 536 many short strings. It will also try to downgrade any strings to
241 octet-form if possible: perl stores strings internally either in an 537 octet-form if possible: perl stores strings internally either in an
242 encoding called UTF-X or in octet-form. The latter cannot store 538 encoding called UTF-X or in octet-form. The latter cannot store
243 everything but uses less space in general. 539 everything but uses less space in general (and some buggy Perl or C
540 code might even rely on that internal representation being used).
541
542 The actual definition of what shrink does might change in future
543 versions, but it will always try to save space at the expense of
544 time.
244 545
245 If $enable is true (or missing), the string returned by "encode" 546 If $enable is true (or missing), the string returned by "encode"
246 will be shrunk-to-fit, while all strings generated by "decode" will 547 will be shrunk-to-fit, while all strings generated by "decode" will
247 also be shrunk-to-fit. 548 also be shrunk-to-fit.
248 549
… …
251 552
252 In the future, this setting might control other things, such as 553 In the future, this setting might control other things, such as
253 converting strings that look like integers or floats into integers 554 converting strings that look like integers or floats into integers
254 or floats internally (there is no difference on the Perl level), 555 or floats internally (there is no difference on the Perl level),
255 saving space. 556 saving space.
557
558 $json = $json->max_depth ([$maximum_nesting_depth])
559 $max_depth = $json->get_max_depth
560 Sets the maximum nesting level (default 512) accepted while encoding
561 or decoding. If a higher nesting level is detected in JSON text or a
562 Perl data structure, then the encoder and decoder will stop and
563 croak at that point.
564
565 Nesting level is defined by number of hash- or arrayrefs that the
566 encoder needs to traverse to reach a given point or the number of
567 "{" or "[" characters without their matching closing parenthesis
568 crossed to reach a given character in a string.
569
570 Setting the maximum depth to one disallows any nesting, so that
571 ensures that the object is only a single hash/object or array.
572
573 If no argument is given, the highest possible setting will be used,
574 which is rarely useful.
575
576 Note that nesting is implemented by recursion in C. The default
577 value has been chosen to be as large as typical operating systems
578 allow without crashing.
579
580 See SECURITY CONSIDERATIONS, below, for more info on why this is
581 useful.
582
583 $json = $json->max_size ([$maximum_string_size])
584 $max_size = $json->get_max_size
585 Set the maximum length a JSON text may have (in bytes) where
586 decoding is being attempted. The default is 0, meaning no limit.
587 When "decode" is called on a string that is longer then this many
588 bytes, it will not attempt to decode the string but throw an
589 exception. This setting has no effect on "encode" (yet).
590
591 If no argument is given, the limit check will be deactivated (same
592 as when 0 is specified).
593
594 See SECURITY CONSIDERATIONS, below, for more info on why this is
595 useful.
256 596
257 $json_text = $json->encode ($perl_scalar) 597 $json_text = $json->encode ($perl_scalar)
258 Converts the given Perl data structure (a simple scalar or a 598 Converts the given Perl data structure (a simple scalar or a
259 reference to a hash or array) to its JSON representation. Simple 599 reference to a hash or array) to its JSON representation. Simple
260 scalars will be converted into JSON string or number sequences, 600 scalars will be converted into JSON string or number sequences,
… …
269 609
270 JSON numbers and strings become simple Perl scalars. JSON arrays 610 JSON numbers and strings become simple Perl scalars. JSON arrays
271 become Perl arrayrefs and JSON objects become Perl hashrefs. "true" 611 become Perl arrayrefs and JSON objects become Perl hashrefs. "true"
272 becomes 1, "false" becomes 0 and "null" becomes "undef". 612 becomes 1, "false" becomes 0 and "null" becomes "undef".
273 613
614 ($perl_scalar, $characters) = $json->decode_prefix ($json_text)
615 This works like the "decode" method, but instead of raising an
616 exception when there is trailing garbage after the first JSON
617 object, it will silently stop parsing there and return the number of
618 characters consumed so far.
619
620 This is useful if your JSON texts are not delimited by an outer
621 protocol (which is not the brightest thing to do in the first place)
622 and you need to know where the JSON text ends.
623
624 JSON::XS->new->decode_prefix ("[1] the tail")
625 => ([], 3)
626
627INCREMENTAL PARSING
628 [This section and the API it details is still EXPERIMENTAL]
629
630 In some cases, there is the need for incremental parsing of JSON texts.
631 While this module always has to keep both JSON text and resulting Perl
632 data structure in memory at one time, it does allow you to parse a JSON
633 stream incrementally. It does so by accumulating text until it has a
634 full JSON object, which it then can decode. This process is similar to
635 using "decode_prefix" to see if a full JSON object is available, but is
636 much more efficient (JSON::XS will only attempt to parse the JSON text
637 once it is sure it has enough text to get a decisive result, using a
638 very simple but truly incremental parser).
639
640 The following two methods deal with this.
641
642 [void, scalar or list context] = $json->incr_parse ([$string])
643 This is the central parsing function. It can both append new text
644 and extract objects from the stream accumulated so far (both of
645 these functions are optional).
646
647 If $string is given, then this string is appended to the already
648 existing JSON fragment stored in the $json object.
649
650 After that, if the function is called in void context, it will
651 simply return without doing anything further. This can be used to
652 add more text in as many chunks as you want.
653
654 If the method is called in scalar context, then it will try to
655 extract exactly *one* JSON object. If that is successful, it will
656 return this object, otherwise it will return "undef". If there is a
657 parse error, this method will croak just as "decode" would do (one
658 can then use "incr_skip" to skip the errornous part). This is the
659 most common way of using the method.
660
661 And finally, in list context, it will try to extract as many objects
662 from the stream as it can find and return them, or the empty list
663 otherwise. For this to work, there must be no separators between the
664 JSON objects or arrays, instead they must be concatenated
665 back-to-back. If an error occurs, an exception will be raised as in
666 the scalar context case. Note that in this case, any
667 previously-parsed JSON texts will be lost.
668
669 $lvalue_string = $json->incr_text
670 This method returns the currently stored JSON fragment as an lvalue,
671 that is, you can manipulate it. This *only* works when a preceding
672 call to "incr_parse" in *scalar context* successfully returned an
673 object. Under all other circumstances you must not call this
674 function (I mean it. although in simple tests it might actually
675 work, it *will* fail under real world conditions). As a special
676 exception, you can also call this method before having parsed
677 anything.
678
679 This function is useful in two cases: a) finding the trailing text
680 after a JSON object or b) parsing multiple JSON objects separated by
681 non-JSON text (such as commas).
682
683 $json->incr_skip
684 This will reset the state of the incremental parser and will remove
685 the parsed text from the input buffer. This is useful after
686 "incr_parse" died, in which case the input buffer and incremental
687 parser state is left unchanged, to skip the text parsed so far and
688 to reset the parse state.
689
690 LIMITATIONS
691 All options that affect decoding are supported, except "allow_nonref".
692 The reason for this is that it cannot be made to work sensibly: JSON
693 objects and arrays are self-delimited, i.e. you can concatenate them
694 back to back and still decode them perfectly. This does not hold true
695 for JSON numbers, however.
696
697 For example, is the string 1 a single JSON number, or is it simply the
698 start of 12? Or is 12 a single JSON number, or the concatenation of 1
699 and 2? In neither case you can tell, and this is why JSON::XS takes the
700 conservative route and disallows this case.
701
702 EXAMPLES
703 Some examples will make all this clearer. First, a simple example that
704 works similarly to "decode_prefix": We want to decode the JSON object at
705 the start of a string and identify the portion after the JSON object:
706
707 my $text = "[1,2,3] hello";
708
709 my $json = new JSON::XS;
710
711 my $obj = $json->incr_parse ($text)
712 or die "expected JSON object or array at beginning of string";
713
714 my $tail = $json->incr_text;
715 # $tail now contains " hello"
716
717 Easy, isn't it?
718
719 Now for a more complicated example: Imagine a hypothetical protocol
720 where you read some requests from a TCP stream, and each request is a
721 JSON array, without any separation between them (in fact, it is often
722 useful to use newlines as "separators", as these get interpreted as
723 whitespace at the start of the JSON text, which makes it possible to
724 test said protocol with "telnet"...).
725
726 Here is how you'd do it (it is trivial to write this in an event-based
727 manner):
728
729 my $json = new JSON::XS;
730
731 # read some data from the socket
732 while (sysread $socket, my $buf, 4096) {
733
734 # split and decode as many requests as possible
735 for my $request ($json->incr_parse ($buf)) {
736 # act on the $request
737 }
738 }
739
740 Another complicated example: Assume you have a string with JSON objects
741 or arrays, all separated by (optional) comma characters (e.g. "[1],[2],
742 [3]"). To parse them, we have to skip the commas between the JSON texts,
743 and here is where the lvalue-ness of "incr_text" comes in useful:
744
745 my $text = "[1],[2], [3]";
746 my $json = new JSON::XS;
747
748 # void context, so no parsing done
749 $json->incr_parse ($text);
750
751 # now extract as many objects as possible. note the
752 # use of scalar context so incr_text can be called.
753 while (my $obj = $json->incr_parse) {
754 # do something with $obj
755
756 # now skip the optional comma
757 $json->incr_text =~ s/^ \s* , //x;
758 }
759
760 Now lets go for a very complex example: Assume that you have a gigantic
761 JSON array-of-objects, many gigabytes in size, and you want to parse it,
762 but you cannot load it into memory fully (this has actually happened in
763 the real world :).
764
765 Well, you lost, you have to implement your own JSON parser. But JSON::XS
766 can still help you: You implement a (very simple) array parser and let
767 JSON decode the array elements, which are all full JSON objects on their
768 own (this wouldn't work if the array elements could be JSON numbers, for
769 example):
770
771 my $json = new JSON::XS;
772
773 # open the monster
774 open my $fh, "<bigfile.json"
775 or die "bigfile: $!";
776
777 # first parse the initial "["
778 for (;;) {
779 sysread $fh, my $buf, 65536
780 or die "read error: $!";
781 $json->incr_parse ($buf); # void context, so no parsing
782
783 # Exit the loop once we found and removed(!) the initial "[".
784 # In essence, we are (ab-)using the $json object as a simple scalar
785 # we append data to.
786 last if $json->incr_text =~ s/^ \s* \[ //x;
787 }
788
789 # now we have the skipped the initial "[", so continue
790 # parsing all the elements.
791 for (;;) {
792 # in this loop we read data until we got a single JSON object
793 for (;;) {
794 if (my $obj = $json->incr_parse) {
795 # do something with $obj
796 last;
797 }
798
799 # add more data
800 sysread $fh, my $buf, 65536
801 or die "read error: $!";
802 $json->incr_parse ($buf); # void context, so no parsing
803 }
804
805 # in this loop we read data until we either found and parsed the
806 # separating "," between elements, or the final "]"
807 for (;;) {
808 # first skip whitespace
809 $json->incr_text =~ s/^\s*//;
810
811 # if we find "]", we are done
812 if ($json->incr_text =~ s/^\]//) {
813 print "finished.\n";
814 exit;
815 }
816
817 # if we find ",", we can continue with the next element
818 if ($json->incr_text =~ s/^,//) {
819 last;
820 }
821
822 # if we find anything else, we have a parse error!
823 if (length $json->incr_text) {
824 die "parse error near ", $json->incr_text;
825 }
826
827 # else add more data
828 sysread $fh, my $buf, 65536
829 or die "read error: $!";
830 $json->incr_parse ($buf); # void context, so no parsing
831 }
832
833 This is a complex example, but most of the complexity comes from the
834 fact that we are trying to be correct (bear with me if I am wrong, I
835 never ran the above example :).
836
274MAPPING 837MAPPING
275 This section describes how JSON::XS maps Perl values to JSON values and 838 This section describes how JSON::XS maps Perl values to JSON values and
276 vice versa. These mappings are designed to "do the right thing" in most 839 vice versa. These mappings are designed to "do the right thing" in most
277 circumstances automatically, preserving round-tripping characteristics 840 circumstances automatically, preserving round-tripping characteristics
278 (what you put in comes out as something equivalent). 841 (what you put in comes out as something equivalent).
279 842
280 For the more enlightened: note that in the following descriptions, 843 For the more enlightened: note that in the following descriptions,
281 lowercase *perl* refers to the Perl interpreter, while uppcercase *Perl* 844 lowercase *perl* refers to the Perl interpreter, while uppercase *Perl*
282 refers to the abstract Perl language itself. 845 refers to the abstract Perl language itself.
283 846
284 JSON -> PERL 847 JSON -> PERL
285 object 848 object
286 A JSON object becomes a reference to a hash in Perl. No ordering of 849 A JSON object becomes a reference to a hash in Perl. No ordering of
287 object keys is preserved (JSON does not preserver object key 850 object keys is preserved (JSON does not preserve object key ordering
288 ordering itself). 851 itself).
289 852
290 array 853 array
291 A JSON array becomes a reference to an array in Perl. 854 A JSON array becomes a reference to an array in Perl.
292 855
293 string 856 string
294 A JSON string becomes a string scalar in Perl - Unicode codepoints 857 A JSON string becomes a string scalar in Perl - Unicode codepoints
295 in JSON are represented by the same codepoints in the Perl string, 858 in JSON are represented by the same codepoints in the Perl string,
296 so no manual decoding is necessary. 859 so no manual decoding is necessary.
297 860
298 number 861 number
299 A JSON number becomes either an integer or numeric (floating point) 862 A JSON number becomes either an integer, numeric (floating point) or
300 scalar in perl, depending on its range and any fractional parts. On 863 string scalar in perl, depending on its range and any fractional
301 the Perl level, there is no difference between those as Perl handles 864 parts. On the Perl level, there is no difference between those as
302 all the conversion details, but an integer may take slightly less 865 Perl handles all the conversion details, but an integer may take
303 memory and might represent more values exactly than (floating point) 866 slightly less memory and might represent more values exactly than
867 floating point numbers.
868
869 If the number consists of digits only, JSON::XS will try to
870 represent it as an integer value. If that fails, it will try to
871 represent it as a numeric (floating point) value if that is possible
872 without loss of precision. Otherwise it will preserve the number as
873 a string value (in which case you lose roundtripping ability, as the
874 JSON number will be re-encoded toa JSON string).
875
876 Numbers containing a fractional or exponential part will always be
877 represented as numeric (floating point) values, possibly at a loss
878 of precision (in which case you might lose perfect roundtripping
879 ability, but the JSON number will still be re-encoded as a JSON
304 numbers. 880 number).
305 881
306 true, false 882 true, false
307 These JSON atoms become 0, 1, respectively. Information is lost in 883 These JSON atoms become "JSON::XS::true" and "JSON::XS::false",
308 this process. Future versions might represent those values 884 respectively. They are overloaded to act almost exactly like the
309 differently, but they will be guarenteed to act like these integers 885 numbers 1 and 0. You can check whether a scalar is a JSON boolean by
310 would normally in Perl. 886 using the "JSON::XS::is_bool" function.
311 887
312 null 888 null
313 A JSON null atom becomes "undef" in Perl. 889 A JSON null atom becomes "undef" in Perl.
314 890
315 PERL -> JSON 891 PERL -> JSON
… …
317 truly typeless language, so we can only guess which JSON type is meant 893 truly typeless language, so we can only guess which JSON type is meant
318 by a Perl value. 894 by a Perl value.
319 895
320 hash references 896 hash references
321 Perl hash references become JSON objects. As there is no inherent 897 Perl hash references become JSON objects. As there is no inherent
322 ordering in hash keys, they will usually be encoded in a 898 ordering in hash keys (or JSON objects), they will usually be
323 pseudo-random order that can change between runs of the same program 899 encoded in a pseudo-random order that can change between runs of the
324 but stays generally the same within a single run of a program. 900 same program but stays generally the same within a single run of a
325 JSON::XS can optionally sort the hash keys (determined by the 901 program. JSON::XS can optionally sort the hash keys (determined by
326 *canonical* flag), so the same datastructure will serialise to the 902 the *canonical* flag), so the same datastructure will serialise to
327 same JSON text (given same settings and version of JSON::XS), but 903 the same JSON text (given same settings and version of JSON::XS),
328 this incurs a runtime overhead. 904 but this incurs a runtime overhead and is only rarely useful, e.g.
905 when you want to compare some JSON text against another for
906 equality.
329 907
330 array references 908 array references
331 Perl array references become JSON arrays. 909 Perl array references become JSON arrays.
332 910
911 other references
912 Other unblessed references are generally not allowed and will cause
913 an exception to be thrown, except for references to the integers 0
914 and 1, which get turned into "false" and "true" atoms in JSON. You
915 can also use "JSON::XS::false" and "JSON::XS::true" to improve
916 readability.
917
918 encode_json [\0,JSON::XS::true] # yields [false,true]
919
920 JSON::XS::true, JSON::XS::false
921 These special values become JSON true and JSON false values,
922 respectively. You can also use "\1" and "\0" directly if you want.
923
333 blessed objects 924 blessed objects
334 Blessed objects are not allowed. JSON::XS currently tries to encode 925 Blessed objects are not directly representable in JSON. See the
335 their underlying representation (hash- or arrayref), but this 926 "allow_blessed" and "convert_blessed" methods on various options on
336 behaviour might change in future versions. 927 how to deal with this: basically, you can choose between throwing an
928 exception, encoding the reference as if it weren't blessed, or
929 provide your own serialiser method.
337 930
338 simple scalars 931 simple scalars
339 Simple Perl scalars (any scalar that is not a reference) are the 932 Simple Perl scalars (any scalar that is not a reference) are the
340 most difficult objects to encode: JSON::XS will encode undefined 933 most difficult objects to encode: JSON::XS will encode undefined
341 scalars as JSON null value, scalars that have last been used in a 934 scalars as JSON "null" values, scalars that have last been used in a
342 string context before encoding as JSON strings and anything else as 935 string context before encoding as JSON strings, and anything else as
343 number value: 936 number value:
344 937
345 # dump as number 938 # dump as number
346 to_json [2] # yields [2] 939 encode_json [2] # yields [2]
347 to_json [-3.0e17] # yields [-3e+17] 940 encode_json [-3.0e17] # yields [-3e+17]
348 my $value = 5; to_json [$value] # yields [5] 941 my $value = 5; encode_json [$value] # yields [5]
349 942
350 # used as string, so dump as string 943 # used as string, so dump as string
351 print $value; 944 print $value;
352 to_json [$value] # yields ["5"] 945 encode_json [$value] # yields ["5"]
353 946
354 # undef becomes null 947 # undef becomes null
355 to_json [undef] # yields [null] 948 encode_json [undef] # yields [null]
356 949
357 You can force the type to be a string by stringifying it: 950 You can force the type to be a JSON string by stringifying it:
358 951
359 my $x = 3.1; # some variable containing a number 952 my $x = 3.1; # some variable containing a number
360 "$x"; # stringified 953 "$x"; # stringified
361 $x .= ""; # another, more awkward way to stringify 954 $x .= ""; # another, more awkward way to stringify
362 print $x; # perl does it for you, too, quite often 955 print $x; # perl does it for you, too, quite often
363 956
364 You can force the type to be a number by numifying it: 957 You can force the type to be a JSON number by numifying it:
365 958
366 my $x = "3"; # some variable containing a string 959 my $x = "3"; # some variable containing a string
367 $x += 0; # numify it, ensuring it will be dumped as a number 960 $x += 0; # numify it, ensuring it will be dumped as a number
368 $x *= 1; # same thing, the choise is yours. 961 $x *= 1; # same thing, the choice is yours.
369 962
370 You can not currently output JSON booleans or force the type in 963 You can not currently force the type in other, less obscure, ways.
371 other, less obscure, ways. Tell me if you need this capability. 964 Tell me if you need this capability (but don't forget to explain why
965 it's needed :).
372 966
373 circular data structures 967ENCODING/CODESET FLAG NOTES
374 Those will be encoded until memory or stackspace runs out. 968 The interested reader might have seen a number of flags that signify
969 encodings or codesets - "utf8", "latin1" and "ascii". There seems to be
970 some confusion on what these do, so here is a short comparison:
375 971
376COMPARISON 972 "utf8" controls whether the JSON text created by "encode" (and expected
377 As already mentioned, this module was created because none of the 973 by "decode") is UTF-8 encoded or not, while "latin1" and "ascii" only
378 existing JSON modules could be made to work correctly. First I will 974 control whether "encode" escapes character values outside their
379 describe the problems (or pleasures) I encountered with various existing 975 respective codeset range. Neither of these flags conflict with each
380 JSON modules, followed by some benchmark values. JSON::XS was designed 976 other, although some combinations make less sense than others.
381 not to suffer from any of these problems or limitations.
382 977
383 JSON 1.07 978 Care has been taken to make all flags symmetrical with respect to
384 Slow (but very portable, as it is written in pure Perl). 979 "encode" and "decode", that is, texts encoded with any combination of
980 these flag values will be correctly decoded when the same flags are used
981 - in general, if you use different flag settings while encoding vs. when
982 decoding you likely have a bug somewhere.
385 983
386 Undocumented/buggy Unicode handling (how JSON handles unicode values 984 Below comes a verbose discussion of these flags. Note that a "codeset"
387 is undocumented. One can get far by feeding it unicode strings and 985 is simply an abstract set of character-codepoint pairs, while an
388 doing en-/decoding oneself, but unicode escapes are not working 986 encoding takes those codepoint numbers and *encodes* them, in our case
987 into octets. Unicode is (among other things) a codeset, UTF-8 is an
988 encoding, and ISO-8859-1 (= latin 1) and ASCII are both codesets *and*
989 encodings at the same time, which can be confusing.
990
991 "utf8" flag disabled
992 When "utf8" is disabled (the default), then "encode"/"decode"
993 generate and expect Unicode strings, that is, characters with high
994 ordinal Unicode values (> 255) will be encoded as such characters,
995 and likewise such characters are decoded as-is, no canges to them
996 will be done, except "(re-)interpreting" them as Unicode codepoints
997 or Unicode characters, respectively (to Perl, these are the same
998 thing in strings unless you do funny/weird/dumb stuff).
999
1000 This is useful when you want to do the encoding yourself (e.g. when
1001 you want to have UTF-16 encoded JSON texts) or when some other layer
1002 does the encoding for you (for example, when printing to a terminal
1003 using a filehandle that transparently encodes to UTF-8 you certainly
1004 do NOT want to UTF-8 encode your data first and have Perl encode it
1005 another time).
1006
1007 "utf8" flag enabled
1008 If the "utf8"-flag is enabled, "encode"/"decode" will encode all
1009 characters using the corresponding UTF-8 multi-byte sequence, and
1010 will expect your input strings to be encoded as UTF-8, that is, no
1011 "character" of the input string must have any value > 255, as UTF-8
1012 does not allow that.
1013
1014 The "utf8" flag therefore switches between two modes: disabled means
1015 you will get a Unicode string in Perl, enabled means you get an
1016 UTF-8 encoded octet/binary string in Perl.
1017
1018 "latin1" or "ascii" flags enabled
1019 With "latin1" (or "ascii") enabled, "encode" will escape characters
1020 with ordinal values > 255 (> 127 with "ascii") and encode the
1021 remaining characters as specified by the "utf8" flag.
1022
1023 If "utf8" is disabled, then the result is also correctly encoded in
1024 those character sets (as both are proper subsets of Unicode, meaning
1025 that a Unicode string with all character values < 256 is the same
1026 thing as a ISO-8859-1 string, and a Unicode string with all
1027 character values < 128 is the same thing as an ASCII string in
389 properly). 1028 Perl).
390 1029
391 No roundtripping (strings get clobbered if they look like numbers, 1030 If "utf8" is enabled, you still get a correct UTF-8-encoded string,
392 e.g. the string 2.0 will encode to 2.0 instead of "2.0", and that 1031 regardless of these flags, just some more characters will be escaped
393 will decode into the number 2. 1032 using "\uXXXX" then before.
394 1033
395 JSON::PC 0.01 1034 Note that ISO-8859-1-*encoded* strings are not compatible with UTF-8
396 Very fast. 1035 encoding, while ASCII-encoded strings are. That is because the
1036 ISO-8859-1 encoding is NOT a subset of UTF-8 (despite the ISO-8859-1
1037 *codeset* being a subset of Unicode), while ASCII is.
397 1038
398 Undocumented/buggy Unicode handling. 1039 Surprisingly, "decode" will ignore these flags and so treat all
1040 input values as governed by the "utf8" flag. If it is disabled, this
1041 allows you to decode ISO-8859-1- and ASCII-encoded strings, as both
1042 strict subsets of Unicode. If it is enabled, you can correctly
1043 decode UTF-8 encoded strings.
399 1044
400 No roundtripping. 1045 So neither "latin1" nor "ascii" are incompatible with the "utf8"
1046 flag - they only govern when the JSON output engine escapes a
1047 character or not.
401 1048
402 Has problems handling many Perl values (e.g. regex results and other 1049 The main use for "latin1" is to relatively efficiently store binary
403 magic values will make it croak). 1050 data as JSON, at the expense of breaking compatibility with most
1051 JSON decoders.
404 1052
405 Does not even generate valid JSON ("{1,2}" gets converted to "{1:2}" 1053 The main use for "ascii" is to force the output to not contain
406 which is not a valid JSON text. 1054 characters with values > 127, which means you can interpret the
1055 resulting string as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about
1056 any character set and 8-bit-encoding, and still get the same data
1057 structure back. This is useful when your channel for JSON transfer
1058 is not 8-bit clean or the encoding might be mangled in between (e.g.
1059 in mail), and works because ASCII is a proper subset of most 8-bit
1060 and multibyte encodings in use in the world.
407 1061
408 Unmaintained (maintainer unresponsive for many months, bugs are not 1062 JSON and YAML
409 getting fixed). 1063 You often hear that JSON is a subset of YAML. This is, however, a mass
1064 hysteria(*) and very far from the truth (as of the time of this
1065 writing), so let me state it clearly: *in general, there is no way to
1066 configure JSON::XS to output a data structure as valid YAML* that works
1067 in all cases.
410 1068
411 JSON::Syck 0.21 1069 If you really must use JSON::XS to generate YAML, you should use this
412 Very buggy (often crashes). 1070 algorithm (subject to change in future versions):
413 1071
414 Very inflexible (no human-readable format supported, format pretty 1072 my $to_yaml = JSON::XS->new->utf8->space_after (1);
415 much undocumented. I need at least a format for easy reading by 1073 my $yaml = $to_yaml->encode ($ref) . "\n";
416 humans and a single-line compact format for use in a protocol, and
417 preferably a way to generate ASCII-only JSON texts).
418 1074
419 Completely broken (and confusingly documented) Unicode handling 1075 This will *usually* generate JSON texts that also parse as valid YAML.
420 (unicode escapes are not working properly, you need to set 1076 Please note that YAML has hardcoded limits on (simple) object key
421 ImplicitUnicode to *different* values on en- and decoding to get 1077 lengths that JSON doesn't have and also has different and incompatible
422 symmetric behaviour). 1078 unicode handling, so you should make sure that your hash keys are
1079 noticeably shorter than the 1024 "stream characters" YAML allows and
1080 that you do not have characters with codepoint values outside the
1081 Unicode BMP (basic multilingual page). YAML also does not allow "\/"
1082 sequences in strings (which JSON::XS does not *currently* generate, but
1083 other JSON generators might).
423 1084
424 No roundtripping (simple cases work, but this depends on wether the 1085 There might be other incompatibilities that I am not aware of (or the
425 scalar value was used in a numeric context or not). 1086 YAML specification has been changed yet again - it does so quite often).
1087 In general you should not try to generate YAML with a JSON generator or
1088 vice versa, or try to parse JSON with a YAML parser or vice versa:
1089 chances are high that you will run into severe interoperability problems
1090 when you least expect it.
426 1091
427 Dumping hashes may skip hash values depending on iterator state. 1092 (*) I have been pressured multiple times by Brian Ingerson (one of the
1093 authors of the YAML specification) to remove this paragraph, despite
1094 him acknowledging that the actual incompatibilities exist. As I was
1095 personally bitten by this "JSON is YAML" lie, I refused and said I
1096 will continue to educate people about these issues, so others do not
1097 run into the same problem again and again. After this, Brian called
1098 me a (quote)*complete and worthless idiot*(unquote).
428 1099
429 Unmaintained (maintainer unresponsive for many months, bugs are not 1100 In my opinion, instead of pressuring and insulting people who
430 getting fixed). 1101 actually clarify issues with YAML and the wrong statements of some
431 1102 of its proponents, I would kindly suggest reading the JSON spec
432 Does not check input for validity (i.e. will accept non-JSON input 1103 (which is not that difficult or long) and finally make YAML
433 and return "something" instead of raising an exception. This is a 1104 compatible to it, and educating users about the changes, instead of
434 security issue: imagine two banks transfering money between each 1105 spreading lies about the real compatibility for many *years* and
435 other using JSON. One bank might parse a given non-JSON request and 1106 trying to silence people who point out that it isn't true.
436 deduct money, while the other might reject the transaction with a
437 syntax error. While a good protocol will at least recover, that is
438 extra unnecessary work and the transaction will still not succeed).
439
440 JSON::DWIW 0.04
441 Very fast. Very natural. Very nice.
442
443 Undocumented unicode handling (but the best of the pack. Unicode
444 escapes still don't get parsed properly).
445
446 Very inflexible.
447
448 No roundtripping.
449
450 Does not generate valid JSON texts (key strings are often unquoted,
451 empty keys result in nothing being output)
452
453 Does not check input for validity.
454 1107
455 SPEED 1108 SPEED
456 It seems that JSON::XS is surprisingly fast, as shown in the following 1109 It seems that JSON::XS is surprisingly fast, as shown in the following
457 tables. They have been generated with the help of the "eg/bench" program 1110 tables. They have been generated with the help of the "eg/bench" program
458 in the JSON::XS distribution, to make it easy to compare on your own 1111 in the JSON::XS distribution, to make it easy to compare on your own
459 system. 1112 system.
460 1113
461 First comes a comparison between various modules using a very short JSON 1114 First comes a comparison between various modules using a very short
462 string: 1115 single-line JSON string (also available at
1116 <http://dist.schmorp.de/misc/json/short.json>).
463 1117
464 {"method": "handleMessage", "params": ["user1", "we were just talking"], "id": null} 1118 {"method": "handleMessage", "params": ["user1",
1119 "we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7,
1120 true, false]}
465 1121
466 It shows the number of encodes/decodes per second (JSON::XS uses the 1122 It shows the number of encodes/decodes per second (JSON::XS uses the
467 functional interface, while JSON::XS/2 uses the OO interface with 1123 functional interface, while JSON::XS/2 uses the OO interface with
468 pretty-printing and hashkey sorting enabled). Higher is better: 1124 pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink).
1125 Higher is better:
469 1126
470 module | encode | decode | 1127 module | encode | decode |
471 -----------|------------|------------| 1128 -----------|------------|------------|
472 JSON | 11488.516 | 7823.035 | 1129 JSON 1.x | 4990.842 | 4088.813 |
473 JSON::DWIW | 94708.054 | 129094.260 | 1130 JSON::DWIW | 51653.990 | 71575.154 |
474 JSON::PC | 63884.157 | 128528.212 | 1131 JSON::PC | 65948.176 | 74631.744 |
1132 JSON::PP | 8931.652 | 3817.168 |
475 JSON::Syck | 34898.677 | 42096.911 | 1133 JSON::Syck | 24877.248 | 27776.848 |
476 JSON::XS | 654027.064 | 396423.669 | 1134 JSON::XS | 388361.481 | 227951.304 |
477 JSON::XS/2 | 371564.190 | 371725.613 | 1135 JSON::XS/2 | 227951.304 | 218453.333 |
1136 JSON::XS/3 | 338250.323 | 218453.333 |
1137 Storable | 16500.016 | 135300.129 |
478 -----------+------------+------------+ 1138 -----------+------------+------------+
479 1139
480 That is, JSON::XS is more than six times faster than JSON::DWIW on 1140 That is, JSON::XS is about five times faster than JSON::DWIW on
481 encoding, more than three times faster on decoding, and about thirty 1141 encoding, about three times faster on decoding, and over forty times
482 times faster than JSON, even with pretty-printing and key sorting. 1142 faster than JSON, even with pretty-printing and key sorting. It also
1143 compares favourably to Storable for small amounts of data.
483 1144
484 Using a longer test string (roughly 18KB, generated from Yahoo! Locals 1145 Using a longer test string (roughly 18KB, generated from Yahoo! Locals
485 search API (http://nanoref.com/yahooapis/mgPdGg): 1146 search API (<http://dist.schmorp.de/misc/json/long.json>).
486 1147
487 module | encode | decode | 1148 module | encode | decode |
488 -----------|------------|------------| 1149 -----------|------------|------------|
489 JSON | 273.023 | 44.674 | 1150 JSON 1.x | 55.260 | 34.971 |
490 JSON::DWIW | 1089.383 | 1145.704 | 1151 JSON::DWIW | 825.228 | 1082.513 |
491 JSON::PC | 3097.419 | 2393.921 | 1152 JSON::PC | 3571.444 | 2394.829 |
492 JSON::Syck | 514.060 | 843.053 | 1153 JSON::PP | 210.987 | 32.574 |
493 JSON::XS | 6479.668 | 3636.364 | 1154 JSON::Syck | 552.551 | 787.544 |
494 JSON::XS/2 | 3774.221 | 3599.124 | 1155 JSON::XS | 5780.463 | 4854.519 |
1156 JSON::XS/2 | 3869.998 | 4798.975 |
1157 JSON::XS/3 | 5862.880 | 4798.975 |
1158 Storable | 4445.002 | 5235.027 |
495 -----------+------------+------------+ 1159 -----------+------------+------------+
496 1160
497 Again, JSON::XS leads by far. 1161 Again, JSON::XS leads by far (except for Storable which non-surprisingly
1162 decodes faster).
498 1163
499 On large strings containing lots of high unicode characters, some 1164 On large strings containing lots of high Unicode characters, some
500 modules (such as JSON::PC) seem to decode faster than JSON::XS, but the 1165 modules (such as JSON::PC) seem to decode faster than JSON::XS, but the
501 result will be broken due to missing (or wrong) unicode handling. Others 1166 result will be broken due to missing (or wrong) Unicode handling. Others
502 refuse to decode or encode properly, so it was impossible to prepare a 1167 refuse to decode or encode properly, so it was impossible to prepare a
503 fair comparison table for that case. 1168 fair comparison table for that case.
504 1169
505RESOURCE LIMITS 1170SECURITY CONSIDERATIONS
506 JSON::XS does not impose any limits on the size of JSON texts or Perl 1171 When you are using JSON in a protocol, talking to untrusted potentially
507 values they represent - if your machine can handle it, JSON::XS will 1172 hostile creatures requires relatively few measures.
508 encode or decode it. Future versions might optionally impose structure 1173
509 depth and memory use resource limits. 1174 First of all, your JSON decoder should be secure, that is, should not
1175 have any buffer overflows. Obviously, this module should ensure that and
1176 I am trying hard on making that true, but you never know.
1177
1178 Second, you need to avoid resource-starving attacks. That means you
1179 should limit the size of JSON texts you accept, or make sure then when
1180 your resources run out, that's just fine (e.g. by using a separate
1181 process that can crash safely). The size of a JSON text in octets or
1182 characters is usually a good indication of the size of the resources
1183 required to decode it into a Perl structure. While JSON::XS can check
1184 the size of the JSON text, it might be too late when you already have it
1185 in memory, so you might want to check the size before you accept the
1186 string.
1187
1188 Third, JSON::XS recurses using the C stack when decoding objects and
1189 arrays. The C stack is a limited resource: for instance, on my amd64
1190 machine with 8MB of stack size I can decode around 180k nested arrays
1191 but only 14k nested JSON objects (due to perl itself recursing deeply on
1192 croak to free the temporary). If that is exceeded, the program crashes.
1193 To be conservative, the default nesting limit is set to 512. If your
1194 process has a smaller stack, you should adjust this setting accordingly
1195 with the "max_depth" method.
1196
1197 Something else could bomb you, too, that I forgot to think of. In that
1198 case, you get to keep the pieces. I am always open for hints, though...
1199
1200 Also keep in mind that JSON::XS might leak contents of your Perl data
1201 structures in its error messages, so when you serialise sensitive
1202 information you might want to make sure that exceptions thrown by
1203 JSON::XS will not end up in front of untrusted eyes.
1204
1205 If you are using JSON::XS to return packets to consumption by JavaScript
1206 scripts in a browser you should have a look at
1207 <http://jpsykes.com/47/practical-csrf-and-json-security> to see whether
1208 you are vulnerable to some common attack vectors (which really are
1209 browser design bugs, but it is still you who will have to deal with it,
1210 as major browser developers care only for features, not about getting
1211 security right).
1212
1213THREADS
1214 This module is *not* guaranteed to be thread safe and there are no plans
1215 to change this until Perl gets thread support (as opposed to the
1216 horribly slow so-called "threads" which are simply slow and bloated
1217 process simulations - use fork, it's *much* faster, cheaper, better).
1218
1219 (It might actually work, but you have been warned).
510 1220
511BUGS 1221BUGS
512 While the goal of this module is to be correct, that unfortunately does 1222 While the goal of this module is to be correct, that unfortunately does
513 not mean its bug-free, only that I think its design is bug-free. It is 1223 not mean it's bug-free, only that I think its design is bug-free. It is
514 still very young and not well-tested. If you keep reporting bugs they 1224 still relatively early in its development. If you keep reporting bugs
515 will be fixed swiftly, though. 1225 they will be fixed swiftly, though.
1226
1227 Please refrain from using rt.cpan.org or any other bug reporting
1228 service. I put the contact address into my modules for a reason.
1229
1230SEE ALSO
1231 The json_xs command line utility for quick experiments.
516 1232
517AUTHOR 1233AUTHOR
518 Marc Lehmann <schmorp@schmorp.de> 1234 Marc Lehmann <schmorp@schmorp.de>
519 http://home.schmorp.de/ 1235 http://home.schmorp.de/
520 1236

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