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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
5 シリアライザ/デシリアライザ
6 (http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html)
7
4SYNOPSIS 8SYNOPSIS
5 use JSON::XS; 9 use JSON::XS;
6 10
7 # exported functions, they croak on error 11 # exported functions, they croak on error
8 # and expect/generate UTF-8 12 # and expect/generate UTF-8
9 13
10 $utf8_encoded_json_text = to_json $perl_hash_or_arrayref; 14 $utf8_encoded_json_text = to_json $perl_hash_or_arrayref;
11 $perl_hash_or_arrayref = from_json $utf8_encoded_json_text; 15 $perl_hash_or_arrayref = from_json $utf8_encoded_json_text;
12
13 # objToJson and jsonToObj aliases to to_json and from_json
14 # are exported for compatibility to the JSON module,
15 # but should not be used in new code.
16 16
17 # OO-interface 17 # OO-interface
18 18
19 $coder = JSON::XS->new->ascii->pretty->allow_nonref; 19 $coder = JSON::XS->new->ascii->pretty->allow_nonref;
20 $pretty_printed_unencoded = $coder->encode ($perl_scalar); 20 $pretty_printed_unencoded = $coder->encode ($perl_scalar);
… …
35 35
36 See MAPPING, below, on how JSON::XS maps perl values to JSON values and 36 See MAPPING, below, on how JSON::XS maps perl values to JSON values and
37 vice versa. 37 vice versa.
38 38
39 FEATURES 39 FEATURES
40 * correct unicode handling 40 * correct Unicode handling
41 This module knows how to handle Unicode, and even documents how and 41 This module knows how to handle Unicode, and even documents how and
42 when it does so. 42 when it does so.
43 43
44 * round-trip integrity 44 * round-trip integrity
45 When you serialise a perl data structure using only datatypes 45 When you serialise a perl data structure using only datatypes
… …
59 * simple to use 59 * simple to use
60 This module has both a simple functional interface as well as an OO 60 This module has both a simple functional interface as well as an OO
61 interface. 61 interface.
62 62
63 * reasonably versatile output formats 63 * reasonably versatile output formats
64 You can choose between the most compact guarenteed single-line 64 You can choose between the most compact guaranteed single-line
65 format possible (nice for simple line-based protocols), a pure-ascii 65 format possible (nice for simple line-based protocols), a pure-ascii
66 format (for when your transport is not 8-bit clean, still supports 66 format (for when your transport is not 8-bit clean, still supports
67 the whole unicode range), or a pretty-printed format (for when you 67 the whole Unicode range), or a pretty-printed format (for when you
68 want to read that stuff). Or you can combine those features in 68 want to read that stuff). Or you can combine those features in
69 whatever way you like. 69 whatever way you like.
70 70
71FUNCTIONAL INTERFACE 71FUNCTIONAL INTERFACE
72 The following convinience methods are provided by this module. They are 72 The following convenience methods are provided by this module. They are
73 exported by default: 73 exported by default:
74 74
75 $json_text = to_json $perl_scalar 75 $json_text = to_json $perl_scalar
76 Converts the given Perl data structure (a simple scalar or a 76 Converts the given Perl data structure to a UTF-8 encoded, binary
77 reference to a hash or array) to a UTF-8 encoded, binary string
78 (that is, the string contains octets only). Croaks on error. 77 string (that is, the string contains octets only). Croaks on error.
79 78
80 This function call is functionally identical to: 79 This function call is functionally identical to:
81 80
82 $json_text = JSON::XS->new->utf8->encode ($perl_scalar) 81 $json_text = JSON::XS->new->utf8->encode ($perl_scalar)
83 82
84 except being faster. 83 except being faster.
85 84
86 $perl_scalar = from_json $json_text 85 $perl_scalar = from_json $json_text
87 The opposite of "to_json": expects an UTF-8 (binary) string and 86 The opposite of "to_json": expects an UTF-8 (binary) string and
88 tries to parse that as an UTF-8 encoded JSON text, returning the 87 tries to parse that as an UTF-8 encoded JSON text, returning the
89 resulting simple scalar or reference. Croaks on error. 88 resulting reference. Croaks on error.
90 89
91 This function call is functionally identical to: 90 This function call is functionally identical to:
92 91
93 $perl_scalar = JSON::XS->new->utf8->decode ($json_text) 92 $perl_scalar = JSON::XS->new->utf8->decode ($json_text)
94 93
95 except being faster. 94 except being faster.
95
96 $is_boolean = JSON::XS::is_bool $scalar
97 Returns true if the passed scalar represents either JSON::XS::true
98 or JSON::XS::false, two constants that act like 1 and 0,
99 respectively and are used to represent JSON "true" and "false"
100 values in Perl.
101
102 See MAPPING, below, for more information on how JSON values are
103 mapped to Perl.
104
105A FEW NOTES ON UNICODE AND PERL
106 Since this often leads to confusion, here are a few very clear words on
107 how Unicode works in Perl, modulo bugs.
108
109 1. Perl strings can store characters with ordinal values > 255.
110 This enables you to store Unicode characters as single characters in
111 a Perl string - very natural.
112
113 2. Perl does *not* associate an encoding with your strings.
114 Unless you force it to, e.g. when matching it against a regex, or
115 printing the scalar to a file, in which case Perl either interprets
116 your string as locale-encoded text, octets/binary, or as Unicode,
117 depending on various settings. In no case is an encoding stored
118 together with your data, it is *use* that decides encoding, not any
119 magical metadata.
120
121 3. The internal utf-8 flag has no meaning with regards to the encoding
122 of your string.
123 Just ignore that flag unless you debug a Perl bug, a module written
124 in XS or want to dive into the internals of perl. Otherwise it will
125 only confuse you, as, despite the name, it says nothing about how
126 your string is encoded. You can have Unicode strings with that flag
127 set, with that flag clear, and you can have binary data with that
128 flag set and that flag clear. Other possibilities exist, too.
129
130 If you didn't know about that flag, just the better, pretend it
131 doesn't exist.
132
133 4. A "Unicode String" is simply a string where each character can be
134 validly interpreted as a Unicode codepoint.
135 If you have UTF-8 encoded data, it is no longer a Unicode string,
136 but a Unicode string encoded in UTF-8, giving you a binary string.
137
138 5. A string containing "high" (> 255) character values is *not* a UTF-8
139 string.
140 It's a fact. Learn to live with it.
141
142 I hope this helps :)
96 143
97OBJECT-ORIENTED INTERFACE 144OBJECT-ORIENTED INTERFACE
98 The object oriented interface lets you configure your own encoding or 145 The object oriented interface lets you configure your own encoding or
99 decoding style, within the limits of supported formats. 146 decoding style, within the limits of supported formats.
100 147
… …
110 => {"a": [1, 2]} 157 => {"a": [1, 2]}
111 158
112 $json = $json->ascii ([$enable]) 159 $json = $json->ascii ([$enable])
113 If $enable is true (or missing), then the "encode" method will not 160 If $enable is true (or missing), then the "encode" method will not
114 generate characters outside the code range 0..127 (which is ASCII). 161 generate characters outside the code range 0..127 (which is ASCII).
115 Any unicode characters outside that range will be escaped using 162 Any Unicode characters outside that range will be escaped using
116 either a single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL 163 either a single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL
117 escape sequence, as per RFC4627. The resulting encoded JSON text can 164 escape sequence, as per RFC4627. The resulting encoded JSON text can
118 be treated as a native unicode string, an ascii-encoded, 165 be treated as a native Unicode string, an ascii-encoded,
119 latin1-encoded or UTF-8 encoded string, or any other superset of 166 latin1-encoded or UTF-8 encoded string, or any other superset of
120 ASCII. 167 ASCII.
121 168
122 If $enable is false, then the "encode" method will not escape 169 If $enable is false, then the "encode" method will not escape
123 Unicode characters unless required by the JSON syntax or other 170 Unicode characters unless required by the JSON syntax or other
… …
132 179
133 $json = $json->latin1 ([$enable]) 180 $json = $json->latin1 ([$enable])
134 If $enable is true (or missing), then the "encode" method will 181 If $enable is true (or missing), then the "encode" method will
135 encode the resulting JSON text as latin1 (or iso-8859-1), escaping 182 encode the resulting JSON text as latin1 (or iso-8859-1), escaping
136 any characters outside the code range 0..255. The resulting string 183 any characters outside the code range 0..255. The resulting string
137 can be treated as a latin1-encoded JSON text or a native unicode 184 can be treated as a latin1-encoded JSON text or a native Unicode
138 string. The "decode" method will not be affected in any way by this 185 string. The "decode" method will not be affected in any way by this
139 flag, as "decode" by default expects unicode, which is a strict 186 flag, as "decode" by default expects Unicode, which is a strict
140 superset of latin1. 187 superset of latin1.
141 188
142 If $enable is false, then the "encode" method will not escape 189 If $enable is false, then the "encode" method will not escape
143 Unicode characters unless required by the JSON syntax or other 190 Unicode characters unless required by the JSON syntax or other
144 flags. 191 flags.
145 192
146 The main use for this flag is efficiently encoding binary data as 193 The main use for this flag is efficiently encoding binary data as
147 JSON text, as most octets will not be escaped, resulting in a 194 JSON text, as most octets will not be escaped, resulting in a
148 smaller encoded size. The disadvantage is that the resulting JSON 195 smaller encoded size. The disadvantage is that the resulting JSON
149 text is encoded in latin1 (and must correctly be treated as such 196 text is encoded in latin1 (and must correctly be treated as such
150 when storing and transfering), a rare encoding for JSON. It is 197 when storing and transferring), a rare encoding for JSON. It is
151 therefore most useful when you want to store data structures known 198 therefore most useful when you want to store data structures known
152 to contain binary data efficiently in files or databases, not when 199 to contain binary data efficiently in files or databases, not when
153 talking to other JSON encoders/decoders. 200 talking to other JSON encoders/decoders.
154 201
155 JSON::XS->new->latin1->encode (["\x{89}\x{abc}"] 202 JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]
… …
164 bytewise/binary I/O. In future versions, enabling this option might 211 bytewise/binary I/O. In future versions, enabling this option might
165 enable autodetection of the UTF-16 and UTF-32 encoding families, as 212 enable autodetection of the UTF-16 and UTF-32 encoding families, as
166 described in RFC4627. 213 described in RFC4627.
167 214
168 If $enable is false, then the "encode" method will return the JSON 215 If $enable is false, then the "encode" method will return the JSON
169 string as a (non-encoded) unicode string, while "decode" expects 216 string as a (non-encoded) Unicode string, while "decode" expects
170 thus a unicode string. Any decoding or encoding (e.g. to UTF-8 or 217 thus a Unicode string. Any decoding or encoding (e.g. to UTF-8 or
171 UTF-16) needs to be done yourself, e.g. using the Encode module. 218 UTF-16) needs to be done yourself, e.g. using the Encode module.
172 219
173 Example, output UTF-16BE-encoded JSON: 220 Example, output UTF-16BE-encoded JSON:
174 221
175 use Encode; 222 use Encode;
… …
197 } 244 }
198 245
199 $json = $json->indent ([$enable]) 246 $json = $json->indent ([$enable])
200 If $enable is true (or missing), then the "encode" method will use a 247 If $enable is true (or missing), then the "encode" method will use a
201 multiline format as output, putting every array member or 248 multiline format as output, putting every array member or
202 object/hash key-value pair into its own line, identing them 249 object/hash key-value pair into its own line, indenting them
203 properly. 250 properly.
204 251
205 If $enable is false, no newlines or indenting will be produced, and 252 If $enable is false, no newlines or indenting will be produced, and
206 the resulting JSON text is guarenteed not to contain any "newlines". 253 the resulting JSON text is guaranteed not to contain any "newlines".
207 254
208 This setting has no effect when decoding JSON texts. 255 This setting has no effect when decoding JSON texts.
209 256
210 $json = $json->space_before ([$enable]) 257 $json = $json->space_before ([$enable])
211 If $enable is true (or missing), then the "encode" method will add 258 If $enable is true (or missing), then the "encode" method will add
… …
235 282
236 Example, space_before and indent disabled, space_after enabled: 283 Example, space_before and indent disabled, space_after enabled:
237 284
238 {"key": "value"} 285 {"key": "value"}
239 286
287 $json = $json->relaxed ([$enable])
288 If $enable is true (or missing), then "decode" will accept some
289 extensions to normal JSON syntax (see below). "encode" will not be
290 affected in anyway. *Be aware that this option makes you accept
291 invalid JSON texts as if they were valid!*. I suggest only to use
292 this option to parse application-specific files written by humans
293 (configuration files, resource files etc.)
294
295 If $enable is false (the default), then "decode" will only accept
296 valid JSON texts.
297
298 Currently accepted extensions are:
299
300 * list items can have an end-comma
301 JSON *separates* array elements and key-value pairs with commas.
302 This can be annoying if you write JSON texts manually and want
303 to be able to quickly append elements, so this extension accepts
304 comma at the end of such items not just between them:
305
306 [
307 1,
308 2, <- this comma not normally allowed
309 ]
310 {
311 "k1": "v1",
312 "k2": "v2", <- this comma not normally allowed
313 }
314
315 * shell-style '#'-comments
316 Whenever JSON allows whitespace, shell-style comments are
317 additionally allowed. They are terminated by the first
318 carriage-return or line-feed character, after which more
319 white-space and comments are allowed.
320
321 [
322 1, # this comment not allowed in JSON
323 # neither this one...
324 ]
325
240 $json = $json->canonical ([$enable]) 326 $json = $json->canonical ([$enable])
241 If $enable is true (or missing), then the "encode" method will 327 If $enable is true (or missing), then the "encode" method will
242 output JSON objects by sorting their keys. This is adding a 328 output JSON objects by sorting their keys. This is adding a
243 comparatively high overhead. 329 comparatively high overhead.
244 330
… …
246 pairs in the order Perl stores them (which will likely change 332 pairs in the order Perl stores them (which will likely change
247 between runs of the same script). 333 between runs of the same script).
248 334
249 This option is useful if you want the same data structure to be 335 This option is useful if you want the same data structure to be
250 encoded as the same JSON text (given the same overall settings). If 336 encoded as the same JSON text (given the same overall settings). If
251 it is disabled, the same hash migh be encoded differently even if 337 it is disabled, the same hash might be encoded differently even if
252 contains the same data, as key-value pairs have no inherent ordering 338 contains the same data, as key-value pairs have no inherent ordering
253 in Perl. 339 in Perl.
254 340
255 This setting has no effect when decoding JSON texts. 341 This setting has no effect when decoding JSON texts.
256 342
… …
268 Example, encode a Perl scalar as JSON value with enabled 354 Example, encode a Perl scalar as JSON value with enabled
269 "allow_nonref", resulting in an invalid JSON text: 355 "allow_nonref", resulting in an invalid JSON text:
270 356
271 JSON::XS->new->allow_nonref->encode ("Hello, World!") 357 JSON::XS->new->allow_nonref->encode ("Hello, World!")
272 => "Hello, World!" 358 => "Hello, World!"
359
360 $json = $json->allow_blessed ([$enable])
361 If $enable is true (or missing), then the "encode" method will not
362 barf when it encounters a blessed reference. Instead, the value of
363 the convert_blessed option will decide whether "null"
364 ("convert_blessed" disabled or no "to_json" method found) or a
365 representation of the object ("convert_blessed" enabled and
366 "to_json" method found) is being encoded. Has no effect on "decode".
367
368 If $enable is false (the default), then "encode" will throw an
369 exception when it encounters a blessed object.
370
371 $json = $json->convert_blessed ([$enable])
372 If $enable is true (or missing), then "encode", upon encountering a
373 blessed object, will check for the availability of the "TO_JSON"
374 method on the object's class. If found, it will be called in scalar
375 context and the resulting scalar will be encoded instead of the
376 object. If no "TO_JSON" method is found, the value of
377 "allow_blessed" will decide what to do.
378
379 The "TO_JSON" method may safely call die if it wants. If "TO_JSON"
380 returns other blessed objects, those will be handled in the same
381 way. "TO_JSON" must take care of not causing an endless recursion
382 cycle (== crash) in this case. The name of "TO_JSON" was chosen
383 because other methods called by the Perl core (== not by the user of
384 the object) are usually in upper case letters and to avoid
385 collisions with the "to_json" function.
386
387 This setting does not yet influence "decode" in any way, but in the
388 future, global hooks might get installed that influence "decode" and
389 are enabled by this setting.
390
391 If $enable is false, then the "allow_blessed" setting will decide
392 what to do when a blessed object is found.
393
394 $json = $json->filter_json_object ([$coderef->($hashref)])
395 When $coderef is specified, it will be called from "decode" each
396 time it decodes a JSON object. The only argument is a reference to
397 the newly-created hash. If the code references returns a single
398 scalar (which need not be a reference), this value (i.e. a copy of
399 that scalar to avoid aliasing) is inserted into the deserialised
400 data structure. If it returns an empty list (NOTE: *not* "undef",
401 which is a valid scalar), the original deserialised hash will be
402 inserted. This setting can slow down decoding considerably.
403
404 When $coderef is omitted or undefined, any existing callback will be
405 removed and "decode" will not change the deserialised hash in any
406 way.
407
408 Example, convert all JSON objects into the integer 5:
409
410 my $js = JSON::XS->new->filter_json_object (sub { 5 });
411 # returns [5]
412 $js->decode ('[{}]')
413 # throw an exception because allow_nonref is not enabled
414 # so a lone 5 is not allowed.
415 $js->decode ('{"a":1, "b":2}');
416
417 $json = $json->filter_json_single_key_object ($key [=>
418 $coderef->($value)])
419 Works remotely similar to "filter_json_object", but is only called
420 for JSON objects having a single key named $key.
421
422 This $coderef is called before the one specified via
423 "filter_json_object", if any. It gets passed the single value in the
424 JSON object. If it returns a single value, it will be inserted into
425 the data structure. If it returns nothing (not even "undef" but the
426 empty list), the callback from "filter_json_object" will be called
427 next, as if no single-key callback were specified.
428
429 If $coderef is omitted or undefined, the corresponding callback will
430 be disabled. There can only ever be one callback for a given key.
431
432 As this callback gets called less often then the
433 "filter_json_object" one, decoding speed will not usually suffer as
434 much. Therefore, single-key objects make excellent targets to
435 serialise Perl objects into, especially as single-key JSON objects
436 are as close to the type-tagged value concept as JSON gets (it's
437 basically an ID/VALUE tuple). Of course, JSON does not support this
438 in any way, so you need to make sure your data never looks like a
439 serialised Perl hash.
440
441 Typical names for the single object key are "__class_whatever__", or
442 "$__dollars_are_rarely_used__$" or "}ugly_brace_placement", or even
443 things like "__class_md5sum(classname)__", to reduce the risk of
444 clashing with real hashes.
445
446 Example, decode JSON objects of the form "{ "__widget__" => <id> }"
447 into the corresponding $WIDGET{<id>} object:
448
449 # return whatever is in $WIDGET{5}:
450 JSON::XS
451 ->new
452 ->filter_json_single_key_object (__widget__ => sub {
453 $WIDGET{ $_[0] }
454 })
455 ->decode ('{"__widget__": 5')
456
457 # this can be used with a TO_JSON method in some "widget" class
458 # for serialisation to json:
459 sub WidgetBase::TO_JSON {
460 my ($self) = @_;
461
462 unless ($self->{id}) {
463 $self->{id} = ..get..some..id..;
464 $WIDGET{$self->{id}} = $self;
465 }
466
467 { __widget__ => $self->{id} }
468 }
273 469
274 $json = $json->shrink ([$enable]) 470 $json = $json->shrink ([$enable])
275 Perl usually over-allocates memory a bit when allocating space for 471 Perl usually over-allocates memory a bit when allocating space for
276 strings. This flag optionally resizes strings generated by either 472 strings. This flag optionally resizes strings generated by either
277 "encode" or "decode" to their minimum size possible. This can save 473 "encode" or "decode" to their minimum size possible. This can save
… …
310 crossed to reach a given character in a string. 506 crossed to reach a given character in a string.
311 507
312 Setting the maximum depth to one disallows any nesting, so that 508 Setting the maximum depth to one disallows any nesting, so that
313 ensures that the object is only a single hash/object or array. 509 ensures that the object is only a single hash/object or array.
314 510
315 The argument to "max_depth" will be rounded up to the next nearest 511 The argument to "max_depth" will be rounded up to the next highest
316 power of two. 512 power of two. If no argument is given, the highest possible setting
513 will be used, which is rarely useful.
514
515 See SECURITY CONSIDERATIONS, below, for more info on why this is
516 useful.
517
518 $json = $json->max_size ([$maximum_string_size])
519 Set the maximum length a JSON text may have (in bytes) where
520 decoding is being attempted. The default is 0, meaning no limit.
521 When "decode" is called on a string longer then this number of
522 characters it will not attempt to decode the string but throw an
523 exception. This setting has no effect on "encode" (yet).
524
525 The argument to "max_size" will be rounded up to the next highest
526 power of two (so may be more than requested). If no argument is
527 given, the limit check will be deactivated (same as when 0 is
528 specified).
317 529
318 See SECURITY CONSIDERATIONS, below, for more info on why this is 530 See SECURITY CONSIDERATIONS, below, for more info on why this is
319 useful. 531 useful.
320 532
321 $json_text = $json->encode ($perl_scalar) 533 $json_text = $json->encode ($perl_scalar)
… …
353 vice versa. These mappings are designed to "do the right thing" in most 565 vice versa. These mappings are designed to "do the right thing" in most
354 circumstances automatically, preserving round-tripping characteristics 566 circumstances automatically, preserving round-tripping characteristics
355 (what you put in comes out as something equivalent). 567 (what you put in comes out as something equivalent).
356 568
357 For the more enlightened: note that in the following descriptions, 569 For the more enlightened: note that in the following descriptions,
358 lowercase *perl* refers to the Perl interpreter, while uppcercase *Perl* 570 lowercase *perl* refers to the Perl interpreter, while uppercase *Perl*
359 refers to the abstract Perl language itself. 571 refers to the abstract Perl language itself.
360 572
361 JSON -> PERL 573 JSON -> PERL
362 object 574 object
363 A JSON object becomes a reference to a hash in Perl. No ordering of 575 A JSON object becomes a reference to a hash in Perl. No ordering of
364 object keys is preserved (JSON does not preserver object key 576 object keys is preserved (JSON does not preserve object key ordering
365 ordering itself). 577 itself).
366 578
367 array 579 array
368 A JSON array becomes a reference to an array in Perl. 580 A JSON array becomes a reference to an array in Perl.
369 581
370 string 582 string
371 A JSON string becomes a string scalar in Perl - Unicode codepoints 583 A JSON string becomes a string scalar in Perl - Unicode codepoints
372 in JSON are represented by the same codepoints in the Perl string, 584 in JSON are represented by the same codepoints in the Perl string,
373 so no manual decoding is necessary. 585 so no manual decoding is necessary.
374 586
375 number 587 number
376 A JSON number becomes either an integer or numeric (floating point) 588 A JSON number becomes either an integer, numeric (floating point) or
377 scalar in perl, depending on its range and any fractional parts. On 589 string scalar in perl, depending on its range and any fractional
378 the Perl level, there is no difference between those as Perl handles 590 parts. On the Perl level, there is no difference between those as
379 all the conversion details, but an integer may take slightly less 591 Perl handles all the conversion details, but an integer may take
380 memory and might represent more values exactly than (floating point) 592 slightly less memory and might represent more values exactly than
381 numbers. 593 (floating point) numbers.
594
595 If the number consists of digits only, JSON::XS will try to
596 represent it as an integer value. If that fails, it will try to
597 represent it as a numeric (floating point) value if that is possible
598 without loss of precision. Otherwise it will preserve the number as
599 a string value.
600
601 Numbers containing a fractional or exponential part will always be
602 represented as numeric (floating point) values, possibly at a loss
603 of precision.
604
605 This might create round-tripping problems as numbers might become
606 strings, but as Perl is typeless there is no other way to do it.
382 607
383 true, false 608 true, false
384 These JSON atoms become 0, 1, respectively. Information is lost in 609 These JSON atoms become "JSON::XS::true" and "JSON::XS::false",
385 this process. Future versions might represent those values 610 respectively. They are overloaded to act almost exactly like the
386 differently, but they will be guarenteed to act like these integers 611 numbers 1 and 0. You can check whether a scalar is a JSON boolean by
387 would normally in Perl. 612 using the "JSON::XS::is_bool" function.
388 613
389 null 614 null
390 A JSON null atom becomes "undef" in Perl. 615 A JSON null atom becomes "undef" in Perl.
391 616
392 PERL -> JSON 617 PERL -> JSON
… …
416 can also use "JSON::XS::false" and "JSON::XS::true" to improve 641 can also use "JSON::XS::false" and "JSON::XS::true" to improve
417 readability. 642 readability.
418 643
419 to_json [\0,JSON::XS::true] # yields [false,true] 644 to_json [\0,JSON::XS::true] # yields [false,true]
420 645
646 JSON::XS::true, JSON::XS::false
647 These special values become JSON true and JSON false values,
648 respectively. You can also use "\1" and "\0" directly if you want.
649
421 blessed objects 650 blessed objects
422 Blessed objects are not allowed. JSON::XS currently tries to encode 651 Blessed objects are not allowed. JSON::XS currently tries to encode
423 their underlying representation (hash- or arrayref), but this 652 their underlying representation (hash- or arrayref), but this
424 behaviour might change in future versions. 653 behaviour might change in future versions.
425 654
… …
440 to_json [$value] # yields ["5"] 669 to_json [$value] # yields ["5"]
441 670
442 # undef becomes null 671 # undef becomes null
443 to_json [undef] # yields [null] 672 to_json [undef] # yields [null]
444 673
445 You can force the type to be a string by stringifying it: 674 You can force the type to be a JSON string by stringifying it:
446 675
447 my $x = 3.1; # some variable containing a number 676 my $x = 3.1; # some variable containing a number
448 "$x"; # stringified 677 "$x"; # stringified
449 $x .= ""; # another, more awkward way to stringify 678 $x .= ""; # another, more awkward way to stringify
450 print $x; # perl does it for you, too, quite often 679 print $x; # perl does it for you, too, quite often
451 680
452 You can force the type to be a number by numifying it: 681 You can force the type to be a JSON number by numifying it:
453 682
454 my $x = "3"; # some variable containing a string 683 my $x = "3"; # some variable containing a string
455 $x += 0; # numify it, ensuring it will be dumped as a number 684 $x += 0; # numify it, ensuring it will be dumped as a number
456 $x *= 1; # same thing, the choise is yours. 685 $x *= 1; # same thing, the choice is yours.
457 686
458 You can not currently output JSON booleans or force the type in 687 You can not currently force the type in other, less obscure, ways.
459 other, less obscure, ways. Tell me if you need this capability. 688 Tell me if you need this capability.
460 689
461COMPARISON 690COMPARISON
462 As already mentioned, this module was created because none of the 691 As already mentioned, this module was created because none of the
463 existing JSON modules could be made to work correctly. First I will 692 existing JSON modules could be made to work correctly. First I will
464 describe the problems (or pleasures) I encountered with various existing 693 describe the problems (or pleasures) I encountered with various existing
… …
466 not to suffer from any of these problems or limitations. 695 not to suffer from any of these problems or limitations.
467 696
468 JSON 1.07 697 JSON 1.07
469 Slow (but very portable, as it is written in pure Perl). 698 Slow (but very portable, as it is written in pure Perl).
470 699
471 Undocumented/buggy Unicode handling (how JSON handles unicode values 700 Undocumented/buggy Unicode handling (how JSON handles Unicode values
472 is undocumented. One can get far by feeding it unicode strings and 701 is undocumented. One can get far by feeding it Unicode strings and
473 doing en-/decoding oneself, but unicode escapes are not working 702 doing en-/decoding oneself, but Unicode escapes are not working
474 properly). 703 properly).
475 704
476 No roundtripping (strings get clobbered if they look like numbers, 705 No round-tripping (strings get clobbered if they look like numbers,
477 e.g. the string 2.0 will encode to 2.0 instead of "2.0", and that 706 e.g. the string 2.0 will encode to 2.0 instead of "2.0", and that
478 will decode into the number 2. 707 will decode into the number 2.
479 708
480 JSON::PC 0.01 709 JSON::PC 0.01
481 Very fast. 710 Very fast.
482 711
483 Undocumented/buggy Unicode handling. 712 Undocumented/buggy Unicode handling.
484 713
485 No roundtripping. 714 No round-tripping.
486 715
487 Has problems handling many Perl values (e.g. regex results and other 716 Has problems handling many Perl values (e.g. regex results and other
488 magic values will make it croak). 717 magic values will make it croak).
489 718
490 Does not even generate valid JSON ("{1,2}" gets converted to "{1:2}" 719 Does not even generate valid JSON ("{1,2}" gets converted to "{1:2}"
… …
500 much undocumented. I need at least a format for easy reading by 729 much undocumented. I need at least a format for easy reading by
501 humans and a single-line compact format for use in a protocol, and 730 humans and a single-line compact format for use in a protocol, and
502 preferably a way to generate ASCII-only JSON texts). 731 preferably a way to generate ASCII-only JSON texts).
503 732
504 Completely broken (and confusingly documented) Unicode handling 733 Completely broken (and confusingly documented) Unicode handling
505 (unicode escapes are not working properly, you need to set 734 (Unicode escapes are not working properly, you need to set
506 ImplicitUnicode to *different* values on en- and decoding to get 735 ImplicitUnicode to *different* values on en- and decoding to get
507 symmetric behaviour). 736 symmetric behaviour).
508 737
509 No roundtripping (simple cases work, but this depends on wether the 738 No round-tripping (simple cases work, but this depends on whether
510 scalar value was used in a numeric context or not). 739 the scalar value was used in a numeric context or not).
511 740
512 Dumping hashes may skip hash values depending on iterator state. 741 Dumping hashes may skip hash values depending on iterator state.
513 742
514 Unmaintained (maintainer unresponsive for many months, bugs are not 743 Unmaintained (maintainer unresponsive for many months, bugs are not
515 getting fixed). 744 getting fixed).
516 745
517 Does not check input for validity (i.e. will accept non-JSON input 746 Does not check input for validity (i.e. will accept non-JSON input
518 and return "something" instead of raising an exception. This is a 747 and return "something" instead of raising an exception. This is a
519 security issue: imagine two banks transfering money between each 748 security issue: imagine two banks transferring money between each
520 other using JSON. One bank might parse a given non-JSON request and 749 other using JSON. One bank might parse a given non-JSON request and
521 deduct money, while the other might reject the transaction with a 750 deduct money, while the other might reject the transaction with a
522 syntax error. While a good protocol will at least recover, that is 751 syntax error. While a good protocol will at least recover, that is
523 extra unnecessary work and the transaction will still not succeed). 752 extra unnecessary work and the transaction will still not succeed).
524 753
525 JSON::DWIW 0.04 754 JSON::DWIW 0.04
526 Very fast. Very natural. Very nice. 755 Very fast. Very natural. Very nice.
527 756
528 Undocumented unicode handling (but the best of the pack. Unicode 757 Undocumented Unicode handling (but the best of the pack. Unicode
529 escapes still don't get parsed properly). 758 escapes still don't get parsed properly).
530 759
531 Very inflexible. 760 Very inflexible.
532 761
533 No roundtripping. 762 No round-tripping.
534 763
535 Does not generate valid JSON texts (key strings are often unquoted, 764 Does not generate valid JSON texts (key strings are often unquoted,
536 empty keys result in nothing being output) 765 empty keys result in nothing being output)
537 766
538 Does not check input for validity. 767 Does not check input for validity.
768
769 JSON and YAML
770 You often hear that JSON is a subset (or a close subset) of YAML. This
771 is, however, a mass hysteria and very far from the truth. In general,
772 there is no way to configure JSON::XS to output a data structure as
773 valid YAML.
774
775 If you really must use JSON::XS to generate YAML, you should use this
776 algorithm (subject to change in future versions):
777
778 my $to_yaml = JSON::XS->new->utf8->space_after (1);
779 my $yaml = $to_yaml->encode ($ref) . "\n";
780
781 This will usually generate JSON texts that also parse as valid YAML.
782 Please note that YAML has hardcoded limits on (simple) object key
783 lengths that JSON doesn't have, so you should make sure that your hash
784 keys are noticeably shorter than the 1024 characters YAML allows.
785
786 There might be other incompatibilities that I am not aware of. In
787 general you should not try to generate YAML with a JSON generator or
788 vice versa, or try to parse JSON with a YAML parser or vice versa:
789 chances are high that you will run into severe interoperability
790 problems.
539 791
540 SPEED 792 SPEED
541 It seems that JSON::XS is surprisingly fast, as shown in the following 793 It seems that JSON::XS is surprisingly fast, as shown in the following
542 tables. They have been generated with the help of the "eg/bench" program 794 tables. They have been generated with the help of the "eg/bench" program
543 in the JSON::XS distribution, to make it easy to compare on your own 795 in the JSON::XS distribution, to make it easy to compare on your own
544 system. 796 system.
545 797
546 First comes a comparison between various modules using a very short JSON 798 First comes a comparison between various modules using a very short
547 string: 799 single-line JSON string:
548 800
549 {"method": "handleMessage", "params": ["user1", "we were just talking"], "id": null} 801 {"method": "handleMessage", "params": ["user1", "we were just talking"], \
802 "id": null, "array":[1,11,234,-5,1e5,1e7, true, false]}
550 803
551 It shows the number of encodes/decodes per second (JSON::XS uses the 804 It shows the number of encodes/decodes per second (JSON::XS uses the
552 functional interface, while JSON::XS/2 uses the OO interface with 805 functional interface, while JSON::XS/2 uses the OO interface with
553 pretty-printing and hashkey sorting enabled). Higher is better: 806 pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink).
807 Higher is better:
554 808
809 Storable | 15779.925 | 14169.946 |
810 -----------+------------+------------+
555 module | encode | decode | 811 module | encode | decode |
556 -----------|------------|------------| 812 -----------|------------|------------|
557 JSON | 11488.516 | 7823.035 | 813 JSON | 4990.842 | 4088.813 |
558 JSON::DWIW | 94708.054 | 129094.260 | 814 JSON::DWIW | 51653.990 | 71575.154 |
559 JSON::PC | 63884.157 | 128528.212 | 815 JSON::PC | 65948.176 | 74631.744 |
816 JSON::PP | 8931.652 | 3817.168 |
560 JSON::Syck | 34898.677 | 42096.911 | 817 JSON::Syck | 24877.248 | 27776.848 |
561 JSON::XS | 654027.064 | 396423.669 | 818 JSON::XS | 388361.481 | 227951.304 |
562 JSON::XS/2 | 371564.190 | 371725.613 | 819 JSON::XS/2 | 227951.304 | 218453.333 |
820 JSON::XS/3 | 338250.323 | 218453.333 |
821 Storable | 16500.016 | 135300.129 |
563 -----------+------------+------------+ 822 -----------+------------+------------+
564 823
565 That is, JSON::XS is more than six times faster than JSON::DWIW on 824 That is, JSON::XS is about five times faster than JSON::DWIW on
566 encoding, more than three times faster on decoding, and about thirty 825 encoding, about three times faster on decoding, and over forty times
567 times faster than JSON, even with pretty-printing and key sorting. 826 faster than JSON, even with pretty-printing and key sorting. It also
827 compares favourably to Storable for small amounts of data.
568 828
569 Using a longer test string (roughly 18KB, generated from Yahoo! Locals 829 Using a longer test string (roughly 18KB, generated from Yahoo! Locals
570 search API (http://nanoref.com/yahooapis/mgPdGg): 830 search API (http://nanoref.com/yahooapis/mgPdGg):
571 831
572 module | encode | decode | 832 module | encode | decode |
573 -----------|------------|------------| 833 -----------|------------|------------|
574 JSON | 273.023 | 44.674 | 834 JSON | 55.260 | 34.971 |
575 JSON::DWIW | 1089.383 | 1145.704 | 835 JSON::DWIW | 825.228 | 1082.513 |
576 JSON::PC | 3097.419 | 2393.921 | 836 JSON::PC | 3571.444 | 2394.829 |
577 JSON::Syck | 514.060 | 843.053 | 837 JSON::PP | 210.987 | 32.574 |
578 JSON::XS | 6479.668 | 3636.364 | 838 JSON::Syck | 552.551 | 787.544 |
579 JSON::XS/2 | 3774.221 | 3599.124 | 839 JSON::XS | 5780.463 | 4854.519 |
840 JSON::XS/2 | 3869.998 | 4798.975 |
841 JSON::XS/3 | 5862.880 | 4798.975 |
842 Storable | 4445.002 | 5235.027 |
580 -----------+------------+------------+ 843 -----------+------------+------------+
581 844
582 Again, JSON::XS leads by far. 845 Again, JSON::XS leads by far (except for Storable which non-surprisingly
846 decodes faster).
583 847
584 On large strings containing lots of high unicode characters, some 848 On large strings containing lots of high Unicode characters, some
585 modules (such as JSON::PC) seem to decode faster than JSON::XS, but the 849 modules (such as JSON::PC) seem to decode faster than JSON::XS, but the
586 result will be broken due to missing (or wrong) unicode handling. Others 850 result will be broken due to missing (or wrong) Unicode handling. Others
587 refuse to decode or encode properly, so it was impossible to prepare a 851 refuse to decode or encode properly, so it was impossible to prepare a
588 fair comparison table for that case. 852 fair comparison table for that case.
589 853
590SECURITY CONSIDERATIONS 854SECURITY CONSIDERATIONS
591 When you are using JSON in a protocol, talking to untrusted potentially 855 When you are using JSON in a protocol, talking to untrusted potentially
… …
595 have any buffer overflows. Obviously, this module should ensure that and 859 have any buffer overflows. Obviously, this module should ensure that and
596 I am trying hard on making that true, but you never know. 860 I am trying hard on making that true, but you never know.
597 861
598 Second, you need to avoid resource-starving attacks. That means you 862 Second, you need to avoid resource-starving attacks. That means you
599 should limit the size of JSON texts you accept, or make sure then when 863 should limit the size of JSON texts you accept, or make sure then when
600 your resources run out, thats just fine (e.g. by using a separate 864 your resources run out, that's just fine (e.g. by using a separate
601 process that can crash safely). The size of a JSON text in octets or 865 process that can crash safely). The size of a JSON text in octets or
602 characters is usually a good indication of the size of the resources 866 characters is usually a good indication of the size of the resources
603 required to decode it into a Perl structure. 867 required to decode it into a Perl structure. While JSON::XS can check
868 the size of the JSON text, it might be too late when you already have it
869 in memory, so you might want to check the size before you accept the
870 string.
604 871
605 Third, JSON::XS recurses using the C stack when decoding objects and 872 Third, JSON::XS recurses using the C stack when decoding objects and
606 arrays. The C stack is a limited resource: for instance, on my amd64 873 arrays. The C stack is a limited resource: for instance, on my amd64
607 machine with 8MB of stack size I can decode around 180k nested arrays 874 machine with 8MB of stack size I can decode around 180k nested arrays
608 but only 14k nested JSON objects (due to perl itself recursing deeply on 875 but only 14k nested JSON objects (due to perl itself recursing deeply on
… …
613 880
614 And last but least, something else could bomb you that I forgot to think 881 And last but least, something else could bomb you that I forgot to think
615 of. In that case, you get to keep the pieces. I am always open for 882 of. In that case, you get to keep the pieces. I am always open for
616 hints, though... 883 hints, though...
617 884
885 If you are using JSON::XS to return packets to consumption by JavaScript
886 scripts in a browser you should have a look at
887 <http://jpsykes.com/47/practical-csrf-and-json-security> to see whether
888 you are vulnerable to some common attack vectors (which really are
889 browser design bugs, but it is still you who will have to deal with it,
890 as major browser developers care only for features, not about doing
891 security right).
892
893THREADS
894 This module is *not* guaranteed to be thread safe and there are no plans
895 to change this until Perl gets thread support (as opposed to the
896 horribly slow so-called "threads" which are simply slow and bloated
897 process simulations - use fork, its *much* faster, cheaper, better).
898
899 (It might actually work, but you have been warned).
900
618BUGS 901BUGS
619 While the goal of this module is to be correct, that unfortunately does 902 While the goal of this module is to be correct, that unfortunately does
620 not mean its bug-free, only that I think its design is bug-free. It is 903 not mean its bug-free, only that I think its design is bug-free. It is
621 still relatively early in its development. If you keep reporting bugs 904 still relatively early in its development. If you keep reporting bugs
622 they will be fixed swiftly, though. 905 they will be fixed swiftly, though.
623 906
907 Please refrain from using rt.cpan.org or any other bug reporting
908 service. I put the contact address into my modules for a reason.
909
624AUTHOR 910AUTHOR
625 Marc Lehmann <schmorp@schmorp.de> 911 Marc Lehmann <schmorp@schmorp.de>
626 http://home.schmorp.de/ 912 http://home.schmorp.de/
627 913

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