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Revision 1.24 by root, Thu Mar 27 06:37:35 2008 UTC

1NAME 1NAME
2 JSON::XS - JSON serialising/deserialising, done correctly and fast 2 JSON::XS - JSON serialising/deserialising, done correctly and fast
3 3
4 JSON::XS - 正しくて高速な JSON シリアライザ/デシリアライザ
5 (http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html)
6
4SYNOPSIS 7SYNOPSIS
5 use JSON::XS; 8 use JSON::XS;
6 9
7 # exported functions, 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 = $json->allow_blessed ([$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
235 $json = $json->shrink ([$enable]) 515 $json = $json->shrink ([$enable])
516 $enabled = $json->get_shrink
236 Perl usually over-allocates memory a bit when allocating space for 517 Perl usually over-allocates memory a bit when allocating space for
237 strings. This flag optionally resizes strings generated by either 518 strings. This flag optionally resizes strings generated by either
238 "encode" or "decode" to their minimum size possible. This can save 519 "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 520 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 521 many short strings. It will also try to downgrade any strings to
241 octet-form if possible: perl stores strings internally either in an 522 octet-form if possible: perl stores strings internally either in an
242 encoding called UTF-X or in octet-form. The latter cannot store 523 encoding called UTF-X or in octet-form. The latter cannot store
243 everything but uses less space in general. 524 everything but uses less space in general (and some buggy Perl or C
525 code might even rely on that internal representation being used).
526
527 The actual definition of what shrink does might change in future
528 versions, but it will always try to save space at the expense of
529 time.
244 530
245 If $enable is true (or missing), the string returned by "encode" 531 If $enable is true (or missing), the string returned by "encode"
246 will be shrunk-to-fit, while all strings generated by "decode" will 532 will be shrunk-to-fit, while all strings generated by "decode" will
247 also be shrunk-to-fit. 533 also be shrunk-to-fit.
248 534
… …
251 537
252 In the future, this setting might control other things, such as 538 In the future, this setting might control other things, such as
253 converting strings that look like integers or floats into integers 539 converting strings that look like integers or floats into integers
254 or floats internally (there is no difference on the Perl level), 540 or floats internally (there is no difference on the Perl level),
255 saving space. 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.
256 580
257 $json_text = $json->encode ($perl_scalar) 581 $json_text = $json->encode ($perl_scalar)
258 Converts the given Perl data structure (a simple scalar or a 582 Converts the given Perl data structure (a simple scalar or a
259 reference to a hash or array) to its JSON representation. Simple 583 reference to a hash or array) to its JSON representation. Simple
260 scalars will be converted into JSON string or number sequences, 584 scalars will be converted into JSON string or number sequences,
… …
269 593
270 JSON numbers and strings become simple Perl scalars. JSON arrays 594 JSON numbers and strings become simple Perl scalars. JSON arrays
271 become Perl arrayrefs and JSON objects become Perl hashrefs. "true" 595 become Perl arrayrefs and JSON objects become Perl hashrefs. "true"
272 becomes 1, "false" becomes 0 and "null" becomes "undef". 596 becomes 1, "false" becomes 0 and "null" becomes "undef".
273 597
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
611INCREMENTAL PARSING
612 [This section and the API it details is still EXPERIMENTAL]
613
614 In some cases, there is the need for incremental parsing of JSON texts.
615 While this module always has to keep both JSON text and resulting Perl
616 data structure in memory at one time, it does allow you to parse a JSON
617 stream incrementally. It does so by accumulating text until it has a
618 full JSON object, which it then can decode. This process is similar to
619 using "decode_prefix" to see if a full JSON object is available, but is
620 much more efficient (JSON::XS will only attempt to parse the JSON text
621 once it is sure it has enough text to get a decisive result, using a
622 very simple but truly incremental parser).
623
624 The following two methods deal with this.
625
626 [void, scalar or list context] = $json->incr_parse ([$string])
627 This is the central parsing function. It can both append new text
628 and extract objects from the stream accumulated so far (both of
629 these functions are optional).
630
631 If $string is given, then this string is appended to the already
632 existing JSON fragment stored in the $json object.
633
634 After that, if the function is called in void context, it will
635 simply return without doing anything further. This can be used to
636 add more text in as many chunks as you want.
637
638 If the method is called in scalar context, then it will try to
639 extract exactly *one* JSON object. If that is successful, it will
640 return this object, otherwise it will return "undef". If there is a
641 parse error, this method will croak just as "decode" would do (one
642 can then use "incr_skip" to skip the errornous part). This is the
643 most common way of using the method.
644
645 And finally, in list context, it will try to extract as many objects
646 from the stream as it can find and return them, or the empty list
647 otherwise. For this to work, there must be no separators between the
648 JSON objects or arrays, instead they must be concatenated
649 back-to-back. If an error occurs, an exception will be raised as in
650 the scalar context case. Note that in this case, any
651 previously-parsed JSON texts will be lost.
652
653 $lvalue_string = $json->incr_text
654 This method returns the currently stored JSON fragment as an lvalue,
655 that is, you can manipulate it. This *only* works when a preceding
656 call to "incr_parse" in *scalar context* successfully returned an
657 object. Under all other circumstances you must not call this
658 function (I mean it. although in simple tests it might actually
659 work, it *will* fail under real world conditions). As a special
660 exception, you can also call this method before having parsed
661 anything.
662
663 This function is useful in two cases: a) finding the trailing text
664 after a JSON object or b) parsing multiple JSON objects separated by
665 non-JSON text (such as commas).
666
667 $json->incr_skip
668 This will reset the state of the incremental parser and will remove
669 the parsed text from the input buffer. This is useful after
670 "incr_parse" died, in which case the input buffer and incremental
671 parser state is left unchanged, to skip the text parsed so far and
672 to reset the parse state.
673
674 LIMITATIONS
675 All options that affect decoding are supported, except "allow_nonref".
676 The reason for this is that it cannot be made to work sensibly: JSON
677 objects and arrays are self-delimited, i.e. you can concatenate them
678 back to back and still decode them perfectly. This does not hold true
679 for JSON numbers, however.
680
681 For example, is the string 1 a single JSON number, or is it simply the
682 start of 12? Or is 12 a single JSON number, or the concatenation of 1
683 and 2? In neither case you can tell, and this is why JSON::XS takes the
684 conservative route and disallows this case.
685
686 EXAMPLES
687 Some examples will make all this clearer. First, a simple example that
688 works similarly to "decode_prefix": We want to decode the JSON object at
689 the start of a string and identify the portion after the JSON object:
690
691 my $text = "[1,2,3] hello";
692
693 my $json = new JSON::XS;
694
695 my $obj = $json->incr_parse ($text)
696 or die "expected JSON object or array at beginning of string";
697
698 my $tail = $json->incr_text;
699 # $tail now contains " hello"
700
701 Easy, isn't it?
702
703 Now for a more complicated example: Imagine a hypothetical protocol
704 where you read some requests from a TCP stream, and each request is a
705 JSON array, without any separation between them (in fact, it is often
706 useful to use newlines as "separators", as these get interpreted as
707 whitespace at the start of the JSON text, which makes it possible to
708 test said protocol with "telnet"...).
709
710 Here is how you'd do it (it is trivial to write this in an event-based
711 manner):
712
713 my $json = new JSON::XS;
714
715 # read some data from the socket
716 while (sysread $socket, my $buf, 4096) {
717
718 # split and decode as many requests as possible
719 for my $request ($json->incr_parse ($buf)) {
720 # act on the $request
721 }
722 }
723
724 Another complicated example: Assume you have a string with JSON objects
725 or arrays, all separated by (optional) comma characters (e.g. "[1],[2],
726 [3]"). To parse them, we have to skip the commas between the JSON texts,
727 and here is where the lvalue-ness of "incr_text" comes in useful:
728
729 my $text = "[1],[2], [3]";
730 my $json = new JSON::XS;
731
732 # void context, so no parsing done
733 $json->incr_parse ($text);
734
735 # now extract as many objects as possible. note the
736 # use of scalar context so incr_text can be called.
737 while (my $obj = $json->incr_parse) {
738 # do something with $obj
739
740 # now skip the optional comma
741 $json->incr_text =~ s/^ \s* , //x;
742 }
743
744 Now lets go for a very complex example: Assume that you have a gigantic
745 JSON array-of-objects, many gigabytes in size, and you want to parse it,
746 but you cannot load it into memory fully (this has actually happened in
747 the real world :).
748
749 Well, you lost, you have to implement your own JSON parser. But JSON::XS
750 can still help you: You implement a (very simple) array parser and let
751 JSON decode the array elements, which are all full JSON objects on their
752 own (this wouldn't work if the array elements could be JSON numbers, for
753 example):
754
755 my $json = new JSON::XS;
756
757 # open the monster
758 open my $fh, "<bigfile.json"
759 or die "bigfile: $!";
760
761 # first parse the initial "["
762 for (;;) {
763 sysread $fh, my $buf, 65536
764 or die "read error: $!";
765 $json->incr_parse ($buf); # void context, so no parsing
766
767 # Exit the loop once we found and removed(!) the initial "[".
768 # In essence, we are (ab-)using the $json object as a simple scalar
769 # we append data to.
770 last if $json->incr_text =~ s/^ \s* \[ //x;
771 }
772
773 # now we have the skipped the initial "[", so continue
774 # parsing all the elements.
775 for (;;) {
776 # in this loop we read data until we got a single JSON object
777 for (;;) {
778 if (my $obj = $json->incr_parse) {
779 # do something with $obj
780 last;
781 }
782
783 # add more data
784 sysread $fh, my $buf, 65536
785 or die "read error: $!";
786 $json->incr_parse ($buf); # void context, so no parsing
787 }
788
789 # in this loop we read data until we either found and parsed the
790 # separating "," between elements, or the final "]"
791 for (;;) {
792 # first skip whitespace
793 $json->incr_text =~ s/^\s*//;
794
795 # if we find "]", we are done
796 if ($json->incr_text =~ s/^\]//) {
797 print "finished.\n";
798 exit;
799 }
800
801 # if we find ",", we can continue with the next element
802 if ($json->incr_text =~ s/^,//) {
803 last;
804 }
805
806 # if we find anything else, we have a parse error!
807 if (length $json->incr_text) {
808 die "parse error near ", $json->incr_text;
809 }
810
811 # else add more data
812 sysread $fh, my $buf, 65536
813 or die "read error: $!";
814 $json->incr_parse ($buf); # void context, so no parsing
815 }
816
817 This is a complex example, but most of the complexity comes from the
818 fact that we are trying to be correct (bear with me if I am wrong, I
819 never ran the above example :).
820
274MAPPING 821MAPPING
275 This section describes how JSON::XS maps Perl values to JSON values and 822 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 823 vice versa. These mappings are designed to "do the right thing" in most
277 circumstances automatically, preserving round-tripping characteristics 824 circumstances automatically, preserving round-tripping characteristics
278 (what you put in comes out as something equivalent). 825 (what you put in comes out as something equivalent).
279 826
280 For the more enlightened: note that in the following descriptions, 827 For the more enlightened: note that in the following descriptions,
281 lowercase *perl* refers to the Perl interpreter, while uppcercase *Perl* 828 lowercase *perl* refers to the Perl interpreter, while uppercase *Perl*
282 refers to the abstract Perl language itself. 829 refers to the abstract Perl language itself.
283 830
284 JSON -> PERL 831 JSON -> PERL
285 object 832 object
286 A JSON object becomes a reference to a hash in Perl. No ordering of 833 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 834 object keys is preserved (JSON does not preserve object key ordering
288 ordering itself). 835 itself).
289 836
290 array 837 array
291 A JSON array becomes a reference to an array in Perl. 838 A JSON array becomes a reference to an array in Perl.
292 839
293 string 840 string
294 A JSON string becomes a string scalar in Perl - Unicode codepoints 841 A JSON string becomes a string scalar in Perl - Unicode codepoints
295 in JSON are represented by the same codepoints in the Perl string, 842 in JSON are represented by the same codepoints in the Perl string,
296 so no manual decoding is necessary. 843 so no manual decoding is necessary.
297 844
298 number 845 number
299 A JSON number becomes either an integer or numeric (floating point) 846 A JSON number becomes either an integer, numeric (floating point) or
300 scalar in perl, depending on its range and any fractional parts. On 847 string scalar in perl, depending on its range and any fractional
301 the Perl level, there is no difference between those as Perl handles 848 parts. On the Perl level, there is no difference between those as
302 all the conversion details, but an integer may take slightly less 849 Perl handles all the conversion details, but an integer may take
303 memory and might represent more values exactly than (floating point) 850 slightly less memory and might represent more values exactly than
851 floating point numbers.
852
853 If the number consists of digits only, JSON::XS will try to
854 represent it as an integer value. If that fails, it will try to
855 represent it as a numeric (floating point) value if that is possible
856 without loss of precision. Otherwise it will preserve the number as
857 a string value (in which case you lose roundtripping ability, as the
858 JSON number will be re-encoded toa JSON string).
859
860 Numbers containing a fractional or exponential part will always be
861 represented as numeric (floating point) values, possibly at a loss
862 of precision (in which case you might lose perfect roundtripping
863 ability, but the JSON number will still be re-encoded as a JSON
304 numbers. 864 number).
305 865
306 true, false 866 true, false
307 These JSON atoms become 0, 1, respectively. Information is lost in 867 These JSON atoms become "JSON::XS::true" and "JSON::XS::false",
308 this process. Future versions might represent those values 868 respectively. They are overloaded to act almost exactly like the
309 differently, but they will be guarenteed to act like these integers 869 numbers 1 and 0. You can check whether a scalar is a JSON boolean by
310 would normally in Perl. 870 using the "JSON::XS::is_bool" function.
311 871
312 null 872 null
313 A JSON null atom becomes "undef" in Perl. 873 A JSON null atom becomes "undef" in Perl.
314 874
315 PERL -> JSON 875 PERL -> JSON
… …
317 truly typeless language, so we can only guess which JSON type is meant 877 truly typeless language, so we can only guess which JSON type is meant
318 by a Perl value. 878 by a Perl value.
319 879
320 hash references 880 hash references
321 Perl hash references become JSON objects. As there is no inherent 881 Perl hash references become JSON objects. As there is no inherent
322 ordering in hash keys, they will usually be encoded in a 882 ordering in hash keys (or JSON objects), they will usually be
323 pseudo-random order that can change between runs of the same program 883 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. 884 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 885 program. JSON::XS can optionally sort the hash keys (determined by
326 *canonical* flag), so the same datastructure will serialise to the 886 the *canonical* flag), so the same datastructure will serialise to
327 same JSON text (given same settings and version of JSON::XS), but 887 the same JSON text (given same settings and version of JSON::XS),
328 this incurs a runtime overhead. 888 but this incurs a runtime overhead and is only rarely useful, e.g.
889 when you want to compare some JSON text against another for
890 equality.
329 891
330 array references 892 array references
331 Perl array references become JSON arrays. 893 Perl array references become JSON arrays.
332 894
895 other references
896 Other unblessed references are generally not allowed and will cause
897 an exception to be thrown, except for references to the integers 0
898 and 1, which get turned into "false" and "true" atoms in JSON. You
899 can also use "JSON::XS::false" and "JSON::XS::true" to improve
900 readability.
901
902 encode_json [\0,JSON::XS::true] # yields [false,true]
903
904 JSON::XS::true, JSON::XS::false
905 These special values become JSON true and JSON false values,
906 respectively. You can also use "\1" and "\0" directly if you want.
907
333 blessed objects 908 blessed objects
334 Blessed objects are not allowed. JSON::XS currently tries to encode 909 Blessed objects are not directly representable in JSON. See the
335 their underlying representation (hash- or arrayref), but this 910 "allow_blessed" and "convert_blessed" methods on various options on
336 behaviour might change in future versions. 911 how to deal with this: basically, you can choose between throwing an
912 exception, encoding the reference as if it weren't blessed, or
913 provide your own serialiser method.
337 914
338 simple scalars 915 simple scalars
339 Simple Perl scalars (any scalar that is not a reference) are the 916 Simple Perl scalars (any scalar that is not a reference) are the
340 most difficult objects to encode: JSON::XS will encode undefined 917 most difficult objects to encode: JSON::XS will encode undefined
341 scalars as JSON null value, scalars that have last been used in a 918 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 919 string context before encoding as JSON strings, and anything else as
343 number value: 920 number value:
344 921
345 # dump as number 922 # dump as number
346 to_json [2] # yields [2] 923 encode_json [2] # yields [2]
347 to_json [-3.0e17] # yields [-3e+17] 924 encode_json [-3.0e17] # yields [-3e+17]
348 my $value = 5; to_json [$value] # yields [5] 925 my $value = 5; encode_json [$value] # yields [5]
349 926
350 # used as string, so dump as string 927 # used as string, so dump as string
351 print $value; 928 print $value;
352 to_json [$value] # yields ["5"] 929 encode_json [$value] # yields ["5"]
353 930
354 # undef becomes null 931 # undef becomes null
355 to_json [undef] # yields [null] 932 encode_json [undef] # yields [null]
356 933
357 You can force the type to be a string by stringifying it: 934 You can force the type to be a JSON string by stringifying it:
358 935
359 my $x = 3.1; # some variable containing a number 936 my $x = 3.1; # some variable containing a number
360 "$x"; # stringified 937 "$x"; # stringified
361 $x .= ""; # another, more awkward way to stringify 938 $x .= ""; # another, more awkward way to stringify
362 print $x; # perl does it for you, too, quite often 939 print $x; # perl does it for you, too, quite often
363 940
364 You can force the type to be a number by numifying it: 941 You can force the type to be a JSON number by numifying it:
365 942
366 my $x = "3"; # some variable containing a string 943 my $x = "3"; # some variable containing a string
367 $x += 0; # numify it, ensuring it will be dumped as a number 944 $x += 0; # numify it, ensuring it will be dumped as a number
368 $x *= 1; # same thing, the choise is yours. 945 $x *= 1; # same thing, the choice is yours.
369 946
370 You can not currently output JSON booleans or force the type in 947 You can not currently force the type in other, less obscure, ways.
371 other, less obscure, ways. Tell me if you need this capability. 948 Tell me if you need this capability (but don't forget to explain why
949 it's needed :).
372 950
373 circular data structures 951ENCODING/CODESET FLAG NOTES
374 Those will be encoded until memory or stackspace runs out. 952 The interested reader might have seen a number of flags that signify
953 encodings or codesets - "utf8", "latin1" and "ascii". There seems to be
954 some confusion on what these do, so here is a short comparison:
375 955
376COMPARISON 956 "utf8" controls whether the JSON text created by "encode" (and expected
377 As already mentioned, this module was created because none of the 957 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 958 control whether "encode" escapes character values outside their
379 describe the problems (or pleasures) I encountered with various existing 959 respective codeset range. Neither of these flags conflict with each
380 JSON modules, followed by some benchmark values. JSON::XS was designed 960 other, although some combinations make less sense than others.
381 not to suffer from any of these problems or limitations.
382 961
383 JSON 1.07 962 Care has been taken to make all flags symmetrical with respect to
384 Slow (but very portable, as it is written in pure Perl). 963 "encode" and "decode", that is, texts encoded with any combination of
964 these flag values will be correctly decoded when the same flags are used
965 - in general, if you use different flag settings while encoding vs. when
966 decoding you likely have a bug somewhere.
385 967
386 Undocumented/buggy Unicode handling (how JSON handles unicode values 968 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 969 is simply an abstract set of character-codepoint pairs, while an
388 doing en-/decoding oneself, but unicode escapes are not working 970 encoding takes those codepoint numbers and *encodes* them, in our case
971 into octets. Unicode is (among other things) a codeset, UTF-8 is an
972 encoding, and ISO-8859-1 (= latin 1) and ASCII are both codesets *and*
973 encodings at the same time, which can be confusing.
974
975 "utf8" flag disabled
976 When "utf8" is disabled (the default), then "encode"/"decode"
977 generate and expect Unicode strings, that is, characters with high
978 ordinal Unicode values (> 255) will be encoded as such characters,
979 and likewise such characters are decoded as-is, no canges to them
980 will be done, except "(re-)interpreting" them as Unicode codepoints
981 or Unicode characters, respectively (to Perl, these are the same
982 thing in strings unless you do funny/weird/dumb stuff).
983
984 This is useful when you want to do the encoding yourself (e.g. when
985 you want to have UTF-16 encoded JSON texts) or when some other layer
986 does the encoding for you (for example, when printing to a terminal
987 using a filehandle that transparently encodes to UTF-8 you certainly
988 do NOT want to UTF-8 encode your data first and have Perl encode it
989 another time).
990
991 "utf8" flag enabled
992 If the "utf8"-flag is enabled, "encode"/"decode" will encode all
993 characters using the corresponding UTF-8 multi-byte sequence, and
994 will expect your input strings to be encoded as UTF-8, that is, no
995 "character" of the input string must have any value > 255, as UTF-8
996 does not allow that.
997
998 The "utf8" flag therefore switches between two modes: disabled means
999 you will get a Unicode string in Perl, enabled means you get an
1000 UTF-8 encoded octet/binary string in Perl.
1001
1002 "latin1" or "ascii" flags enabled
1003 With "latin1" (or "ascii") enabled, "encode" will escape characters
1004 with ordinal values > 255 (> 127 with "ascii") and encode the
1005 remaining characters as specified by the "utf8" flag.
1006
1007 If "utf8" is disabled, then the result is also correctly encoded in
1008 those character sets (as both are proper subsets of Unicode, meaning
1009 that a Unicode string with all character values < 256 is the same
1010 thing as a ISO-8859-1 string, and a Unicode string with all
1011 character values < 128 is the same thing as an ASCII string in
389 properly). 1012 Perl).
390 1013
391 No roundtripping (strings get clobbered if they look like numbers, 1014 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 1015 regardless of these flags, just some more characters will be escaped
393 will decode into the number 2. 1016 using "\uXXXX" then before.
394 1017
395 JSON::PC 0.01 1018 Note that ISO-8859-1-*encoded* strings are not compatible with UTF-8
396 Very fast. 1019 encoding, while ASCII-encoded strings are. That is because the
1020 ISO-8859-1 encoding is NOT a subset of UTF-8 (despite the ISO-8859-1
1021 *codeset* being a subset of Unicode), while ASCII is.
397 1022
398 Undocumented/buggy Unicode handling. 1023 Surprisingly, "decode" will ignore these flags and so treat all
1024 input values as governed by the "utf8" flag. If it is disabled, this
1025 allows you to decode ISO-8859-1- and ASCII-encoded strings, as both
1026 strict subsets of Unicode. If it is enabled, you can correctly
1027 decode UTF-8 encoded strings.
399 1028
400 No roundtripping. 1029 So neither "latin1" nor "ascii" are incompatible with the "utf8"
1030 flag - they only govern when the JSON output engine escapes a
1031 character or not.
401 1032
402 Has problems handling many Perl values (e.g. regex results and other 1033 The main use for "latin1" is to relatively efficiently store binary
403 magic values will make it croak). 1034 data as JSON, at the expense of breaking compatibility with most
1035 JSON decoders.
404 1036
405 Does not even generate valid JSON ("{1,2}" gets converted to "{1:2}" 1037 The main use for "ascii" is to force the output to not contain
406 which is not a valid JSON text. 1038 characters with values > 127, which means you can interpret the
1039 resulting string as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about
1040 any character set and 8-bit-encoding, and still get the same data
1041 structure back. This is useful when your channel for JSON transfer
1042 is not 8-bit clean or the encoding might be mangled in between (e.g.
1043 in mail), and works because ASCII is a proper subset of most 8-bit
1044 and multibyte encodings in use in the world.
407 1045
408 Unmaintained (maintainer unresponsive for many months, bugs are not 1046 JSON and YAML
409 getting fixed). 1047 You often hear that JSON is a subset of YAML. This is, however, a mass
1048 hysteria(*) and very far from the truth (as of the time of this
1049 writing), so let me state it clearly: *in general, there is no way to
1050 configure JSON::XS to output a data structure as valid YAML* that works
1051 in all cases.
410 1052
411 JSON::Syck 0.21 1053 If you really must use JSON::XS to generate YAML, you should use this
412 Very buggy (often crashes). 1054 algorithm (subject to change in future versions):
413 1055
414 Very inflexible (no human-readable format supported, format pretty 1056 my $to_yaml = JSON::XS->new->utf8->space_after (1);
415 much undocumented. I need at least a format for easy reading by 1057 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 1058
419 Completely broken (and confusingly documented) Unicode handling 1059 This will *usually* generate JSON texts that also parse as valid YAML.
420 (unicode escapes are not working properly, you need to set 1060 Please note that YAML has hardcoded limits on (simple) object key
421 ImplicitUnicode to *different* values on en- and decoding to get 1061 lengths that JSON doesn't have and also has different and incompatible
422 symmetric behaviour). 1062 unicode handling, so you should make sure that your hash keys are
1063 noticeably shorter than the 1024 "stream characters" YAML allows and
1064 that you do not have characters with codepoint values outside the
1065 Unicode BMP (basic multilingual page). YAML also does not allow "\/"
1066 sequences in strings (which JSON::XS does not *currently* generate, but
1067 other JSON generators might).
423 1068
424 No roundtripping (simple cases work, but this depends on wether the 1069 There might be other incompatibilities that I am not aware of (or the
425 scalar value was used in a numeric context or not). 1070 YAML specification has been changed yet again - it does so quite often).
1071 In general you should not try to generate YAML with a JSON generator or
1072 vice versa, or try to parse JSON with a YAML parser or vice versa:
1073 chances are high that you will run into severe interoperability problems
1074 when you least expect it.
426 1075
427 Dumping hashes may skip hash values depending on iterator state. 1076 (*) I have been pressured multiple times by Brian Ingerson (one of the
1077 authors of the YAML specification) to remove this paragraph, despite
1078 him acknowledging that the actual incompatibilities exist. As I was
1079 personally bitten by this "JSON is YAML" lie, I refused and said I
1080 will continue to educate people about these issues, so others do not
1081 run into the same problem again and again. After this, Brian called
1082 me a (quote)*complete and worthless idiot*(unquote).
428 1083
429 Unmaintained (maintainer unresponsive for many months, bugs are not 1084 In my opinion, instead of pressuring and insulting people who
430 getting fixed). 1085 actually clarify issues with YAML and the wrong statements of some
431 1086 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 1087 (which is not that difficult or long) and finally make YAML
433 and return "something" instead of raising an exception. This is a 1088 compatible to it, and educating users about the changes, instead of
434 security issue: imagine two banks transfering money between each 1089 spreading lies about the real compatibility for many *years* and
435 other using JSON. One bank might parse a given non-JSON request and 1090 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 1091
455 SPEED 1092 SPEED
456 It seems that JSON::XS is surprisingly fast, as shown in the following 1093 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 1094 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 1095 in the JSON::XS distribution, to make it easy to compare on your own
459 system. 1096 system.
460 1097
461 First comes a comparison between various modules using a very short JSON 1098 First comes a comparison between various modules using a very short
462 string (83 bytes), showing the number of encodes/decodes per second 1099 single-line JSON string (also available at
463 (JSON::XS is the functional interface, while JSON::XS/2 is the OO 1100 <http://dist.schmorp.de/misc/json/short.json>).
464 interface with pretty-printing and hashkey sorting enabled). Higher is 1101
465 better: 1102 {"method": "handleMessage", "params": ["user1", "we were just talking"], \
1103 "id": null, "array":[1,11,234,-5,1e5,1e7, true, false]}
1104
1105 It shows the number of encodes/decodes per second (JSON::XS uses the
1106 functional interface, while JSON::XS/2 uses the OO interface with
1107 pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink).
1108 Higher is better:
466 1109
467 module | encode | decode | 1110 module | encode | decode |
468 -----------|------------|------------| 1111 -----------|------------|------------|
469 JSON | 14006 | 6820 | 1112 JSON 1.x | 4990.842 | 4088.813 |
470 JSON::DWIW | 200937 | 120386 | 1113 JSON::DWIW | 51653.990 | 71575.154 |
471 JSON::PC | 85065 | 129366 | 1114 JSON::PC | 65948.176 | 74631.744 |
472 JSON::Syck | 59898 | 44232 | 1115 JSON::PP | 8931.652 | 3817.168 |
473 JSON::XS | 1171478 | 342435 | 1116 JSON::Syck | 24877.248 | 27776.848 |
474 JSON::XS/2 | 730760 | 328714 | 1117 JSON::XS | 388361.481 | 227951.304 |
1118 JSON::XS/2 | 227951.304 | 218453.333 |
1119 JSON::XS/3 | 338250.323 | 218453.333 |
1120 Storable | 16500.016 | 135300.129 |
475 -----------+------------+------------+ 1121 -----------+------------+------------+
476 1122
477 That is, JSON::XS is 6 times faster than than JSON::DWIW and about 80 1123 That is, JSON::XS is about five times faster than JSON::DWIW on
1124 encoding, about three times faster on decoding, and over forty times
478 times faster than JSON, even with pretty-printing and key sorting. 1125 faster than JSON, even with pretty-printing and key sorting. It also
1126 compares favourably to Storable for small amounts of data.
479 1127
480 Using a longer test string (roughly 18KB, generated from Yahoo! Locals 1128 Using a longer test string (roughly 18KB, generated from Yahoo! Locals
481 search API (http://nanoref.com/yahooapis/mgPdGg): 1129 search API (<http://dist.schmorp.de/misc/json/long.json>).
482 1130
483 module | encode | decode | 1131 module | encode | decode |
484 -----------|------------|------------| 1132 -----------|------------|------------|
485 JSON | 673 | 38 | 1133 JSON 1.x | 55.260 | 34.971 |
486 JSON::DWIW | 5271 | 770 | 1134 JSON::DWIW | 825.228 | 1082.513 |
1135 JSON::PC | 3571.444 | 2394.829 |
487 JSON::PC | 9901 | 2491 | 1136 JSON::PP | 210.987 | 32.574 |
488 JSON::Syck | 2360 | 786 | 1137 JSON::Syck | 552.551 | 787.544 |
489 JSON::XS | 37398 | 3202 | 1138 JSON::XS | 5780.463 | 4854.519 |
490 JSON::XS/2 | 13765 | 3153 | 1139 JSON::XS/2 | 3869.998 | 4798.975 |
1140 JSON::XS/3 | 5862.880 | 4798.975 |
1141 Storable | 4445.002 | 5235.027 |
491 -----------+------------+------------+ 1142 -----------+------------+------------+
492 1143
493 Again, JSON::XS leads by far in the encoding case, while still beating 1144 Again, JSON::XS leads by far (except for Storable which non-surprisingly
494 every other module in the decoding case. 1145 decodes faster).
495 1146
496 On large strings containing lots of unicode characters, some modules 1147 On large strings containing lots of high Unicode characters, some
497 (such as JSON::PC) decode faster than JSON::XS, but the result will be 1148 modules (such as JSON::PC) seem to decode faster than JSON::XS, but the
498 broken due to missing unicode handling. Others refuse to decode or 1149 result will be broken due to missing (or wrong) Unicode handling. Others
499 encode properly, so it was impossible to prepare a fair comparison table 1150 refuse to decode or encode properly, so it was impossible to prepare a
500 for that case. 1151 fair comparison table for that case.
501 1152
502RESOURCE LIMITS 1153SECURITY CONSIDERATIONS
503 JSON::XS does not impose any limits on the size of JSON texts or Perl 1154 When you are using JSON in a protocol, talking to untrusted potentially
504 values they represent - if your machine can handle it, JSON::XS will 1155 hostile creatures requires relatively few measures.
505 encode or decode it. Future versions might optionally impose structure 1156
506 depth and memory use resource limits. 1157 First of all, your JSON decoder should be secure, that is, should not
1158 have any buffer overflows. Obviously, this module should ensure that and
1159 I am trying hard on making that true, but you never know.
1160
1161 Second, you need to avoid resource-starving attacks. That means you
1162 should limit the size of JSON texts you accept, or make sure then when
1163 your resources run out, that's just fine (e.g. by using a separate
1164 process that can crash safely). The size of a JSON text in octets or
1165 characters is usually a good indication of the size of the resources
1166 required to decode it into a Perl structure. While JSON::XS can check
1167 the size of the JSON text, it might be too late when you already have it
1168 in memory, so you might want to check the size before you accept the
1169 string.
1170
1171 Third, JSON::XS recurses using the C stack when decoding objects and
1172 arrays. The C stack is a limited resource: for instance, on my amd64
1173 machine with 8MB of stack size I can decode around 180k nested arrays
1174 but only 14k nested JSON objects (due to perl itself recursing deeply on
1175 croak to free the temporary). If that is exceeded, the program crashes.
1176 To be conservative, the default nesting limit is set to 512. If your
1177 process has a smaller stack, you should adjust this setting accordingly
1178 with the "max_depth" method.
1179
1180 Something else could bomb you, too, that I forgot to think of. In that
1181 case, you get to keep the pieces. I am always open for hints, though...
1182
1183 Also keep in mind that JSON::XS might leak contents of your Perl data
1184 structures in its error messages, so when you serialise sensitive
1185 information you might want to make sure that exceptions thrown by
1186 JSON::XS will not end up in front of untrusted eyes.
1187
1188 If you are using JSON::XS to return packets to consumption by JavaScript
1189 scripts in a browser you should have a look at
1190 <http://jpsykes.com/47/practical-csrf-and-json-security> to see whether
1191 you are vulnerable to some common attack vectors (which really are
1192 browser design bugs, but it is still you who will have to deal with it,
1193 as major browser developers care only for features, not about getting
1194 security right).
1195
1196THREADS
1197 This module is *not* guaranteed to be thread safe and there are no plans
1198 to change this until Perl gets thread support (as opposed to the
1199 horribly slow so-called "threads" which are simply slow and bloated
1200 process simulations - use fork, it's *much* faster, cheaper, better).
1201
1202 (It might actually work, but you have been warned).
507 1203
508BUGS 1204BUGS
509 While the goal of this module is to be correct, that unfortunately does 1205 While the goal of this module is to be correct, that unfortunately does
510 not mean its bug-free, only that I think its design is bug-free. It is 1206 not mean it's bug-free, only that I think its design is bug-free. It is
511 still very young and not well-tested. If you keep reporting bugs they 1207 still relatively early in its development. If you keep reporting bugs
512 will be fixed swiftly, though. 1208 they will be fixed swiftly, though.
1209
1210 Please refrain from using rt.cpan.org or any other bug reporting
1211 service. I put the contact address into my modules for a reason.
1212
1213SEE ALSO
1214 The json_xs command line utility for quick experiments.
513 1215
514AUTHOR 1216AUTHOR
515 Marc Lehmann <schmorp@schmorp.de> 1217 Marc Lehmann <schmorp@schmorp.de>
516 http://home.schmorp.de/ 1218 http://home.schmorp.de/
517 1219

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