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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, croak on error 11 # exported functions, they croak on error
12 # and expect/generate UTF-8
8 13
9 $utf8_encoded_json_text = to_json $perl_hash_or_arrayref; 14 $utf8_encoded_json_text = to_json $perl_hash_or_arrayref;
10 $perl_hash_or_arrayref = from_json $utf8_encoded_json_text; 15 $perl_hash_or_arrayref = from_json $utf8_encoded_json_text;
11 16
12 # oo-interface 17 # OO-interface
13 18
14 $coder = JSON::XS->new->ascii->pretty->allow_nonref; 19 $coder = JSON::XS->new->ascii->pretty->allow_nonref;
15 $pretty_printed_unencoded = $coder->encode ($perl_scalar); 20 $pretty_printed_unencoded = $coder->encode ($perl_scalar);
16 $perl_scalar = $coder->decode ($unicode_json_text); 21 $perl_scalar = $coder->decode ($unicode_json_text);
17 22
… …
30 35
31 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
32 vice versa. 37 vice versa.
33 38
34 FEATURES 39 FEATURES
35 * correct handling of unicode issues 40 * correct unicode handling
36 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
37 when it does so. 42 when it does so.
38 43
39 * round-trip integrity 44 * round-trip integrity
40 When you serialise a perl data structure using only datatypes 45 When you serialise a perl data structure using only datatypes
41 supported by JSON, the deserialised data structure is identical on 46 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"). 47 the Perl level. (e.g. the string "2.0" doesn't suddenly become "2"
48 just because it looks like a number).
43 49
44 * strict checking of JSON correctness 50 * strict checking of JSON correctness
45 There is no guessing, no generating of illegal JSON texts by 51 There is no guessing, no generating of illegal JSON texts by
46 default, and only JSON is accepted as input by default (the latter 52 default, and only JSON is accepted as input by default (the latter
47 is a security feature). 53 is a security feature).
… …
55 interface. 61 interface.
56 62
57 * reasonably versatile output formats 63 * reasonably versatile output formats
58 You can choose between the most compact guarenteed single-line 64 You can choose between the most compact guarenteed single-line
59 format possible (nice for simple line-based protocols), a pure-ascii 65 format possible (nice for simple line-based protocols), a pure-ascii
60 format (for when your transport is not 8-bit clean), or a 66 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 67 the whole unicode range), or a pretty-printed format (for when you
62 can combine those features in whatever way you like. 68 want to read that stuff). Or you can combine those features in
69 whatever way you like.
63 70
64FUNCTIONAL INTERFACE 71FUNCTIONAL INTERFACE
65 The following convinience methods are provided by this module. They are 72 The following convinience methods are provided by this module. They are
66 exported by default: 73 exported by default:
67 74
68 $json_text = to_json $perl_scalar 75 $json_text = to_json $perl_scalar
69 Converts the given Perl data structure (a simple scalar or a 76 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. 77 string (that is, the string contains octets only). Croaks on error.
72 78
73 This function call is functionally identical to: 79 This function call is functionally identical to:
74 80
75 $json_text = JSON::XS->new->utf8->encode ($perl_scalar) 81 $json_text = JSON::XS->new->utf8->encode ($perl_scalar)
76 82
77 except being faster. 83 except being faster.
78 84
79 $perl_scalar = from_json $json_text 85 $perl_scalar = from_json $json_text
80 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
81 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
82 resulting simple scalar or reference. Croaks on error. 88 resulting reference. Croaks on error.
83 89
84 This function call is functionally identical to: 90 This function call is functionally identical to:
85 91
86 $perl_scalar = JSON::XS->new->utf8->decode ($json_text) 92 $perl_scalar = JSON::XS->new->utf8->decode ($json_text)
87 93
88 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 Its a fact. Learn to live with it.
141
142 I hope this helps :)
89 143
90OBJECT-ORIENTED INTERFACE 144OBJECT-ORIENTED INTERFACE
91 The object oriented interface lets you configure your own encoding or 145 The object oriented interface lets you configure your own encoding or
92 decoding style, within the limits of supported formats. 146 decoding style, within the limits of supported formats.
93 147
… …
105 $json = $json->ascii ([$enable]) 159 $json = $json->ascii ([$enable])
106 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
107 generate characters outside the code range 0..127 (which is ASCII). 161 generate characters outside the code range 0..127 (which is ASCII).
108 Any unicode characters outside that range will be escaped using 162 Any unicode characters outside that range will be escaped using
109 either a single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL 163 either a single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL
110 escape sequence, as per RFC4627. 164 escape sequence, as per RFC4627. The resulting encoded JSON text can
165 be treated as a native unicode string, an ascii-encoded,
166 latin1-encoded or UTF-8 encoded string, or any other superset of
167 ASCII.
111 168
112 If $enable is false, then the "encode" method will not escape 169 If $enable is false, then the "encode" method will not escape
113 Unicode characters unless required by the JSON syntax. This results 170 Unicode characters unless required by the JSON syntax or other
114 in a faster and more compact format. 171 flags. This results in a faster and more compact format.
172
173 The main use for this flag is to produce JSON texts that can be
174 transmitted over a 7-bit channel, as the encoded JSON texts will not
175 contain any 8 bit characters.
115 176
116 JSON::XS->new->ascii (1)->encode ([chr 0x10401]) 177 JSON::XS->new->ascii (1)->encode ([chr 0x10401])
117 => ["\ud801\udc01"] 178 => ["\ud801\udc01"]
179
180 $json = $json->latin1 ([$enable])
181 If $enable is true (or missing), then the "encode" method will
182 encode the resulting JSON text as latin1 (or iso-8859-1), escaping
183 any characters outside the code range 0..255. The resulting string
184 can be treated as a latin1-encoded JSON text or a native unicode
185 string. The "decode" method will not be affected in any way by this
186 flag, as "decode" by default expects unicode, which is a strict
187 superset of latin1.
188
189 If $enable is false, then the "encode" method will not escape
190 Unicode characters unless required by the JSON syntax or other
191 flags.
192
193 The main use for this flag is efficiently encoding binary data as
194 JSON text, as most octets will not be escaped, resulting in a
195 smaller encoded size. The disadvantage is that the resulting JSON
196 text is encoded in latin1 (and must correctly be treated as such
197 when storing and transfering), a rare encoding for JSON. It is
198 therefore most useful when you want to store data structures known
199 to contain binary data efficiently in files or databases, not when
200 talking to other JSON encoders/decoders.
201
202 JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]
203 => ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)
118 204
119 $json = $json->utf8 ([$enable]) 205 $json = $json->utf8 ([$enable])
120 If $enable is true (or missing), then the "encode" method will 206 If $enable is true (or missing), then the "encode" method will
121 encode the JSON result into UTF-8, as required by many protocols, 207 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 208 while the "decode" method expects to be handled an UTF-8-encoded
… …
196 282
197 Example, space_before and indent disabled, space_after enabled: 283 Example, space_before and indent disabled, space_after enabled:
198 284
199 {"key": "value"} 285 {"key": "value"}
200 286
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
201 $json = $json->canonical ([$enable]) 326 $json = $json->canonical ([$enable])
202 If $enable is true (or missing), then the "encode" method will 327 If $enable is true (or missing), then the "encode" method will
203 output JSON objects by sorting their keys. This is adding a 328 output JSON objects by sorting their keys. This is adding a
204 comparatively high overhead. 329 comparatively high overhead.
205 330
… …
229 Example, encode a Perl scalar as JSON value with enabled 354 Example, encode a Perl scalar as JSON value with enabled
230 "allow_nonref", resulting in an invalid JSON text: 355 "allow_nonref", resulting in an invalid JSON text:
231 356
232 JSON::XS->new->allow_nonref->encode ("Hello, World!") 357 JSON::XS->new->allow_nonref->encode ("Hello, World!")
233 => "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 wether "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 $coderef is omitted or undefined, the corresponding callback will
430 be disabled. There can only ever be one callback for a given key.
431
432 As this callback gets called less often then the
433 "filter_json_object" one, decoding speed will not usually suffer as
434 much. Therefore, single-key objects make excellent targets to
435 serialise Perl objects into, especially as single-key JSON objects
436 are as close to the type-tagged value concept as JSON gets (its
437 basically an ID/VALUE tuple). Of course, JSON does not support this
438 in any way, so you need to make sure your data never looks like a
439 serialised Perl hash.
440
441 Typical names for the single object key are "__class_whatever__", or
442 "$__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 }
234 469
235 $json = $json->shrink ([$enable]) 470 $json = $json->shrink ([$enable])
236 Perl usually over-allocates memory a bit when allocating space for 471 Perl usually over-allocates memory a bit when allocating space for
237 strings. This flag optionally resizes strings generated by either 472 strings. This flag optionally resizes strings generated by either
238 "encode" or "decode" to their minimum size possible. This can save 473 "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 474 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 475 many short strings. It will also try to downgrade any strings to
241 octet-form if possible: perl stores strings internally either in an 476 octet-form if possible: perl stores strings internally either in an
242 encoding called UTF-X or in octet-form. The latter cannot store 477 encoding called UTF-X or in octet-form. The latter cannot store
243 everything but uses less space in general. 478 everything but uses less space in general (and some buggy Perl or C
479 code might even rely on that internal representation being used).
480
481 The actual definition of what shrink does might change in future
482 versions, but it will always try to save space at the expense of
483 time.
244 484
245 If $enable is true (or missing), the string returned by "encode" 485 If $enable is true (or missing), the string returned by "encode"
246 will be shrunk-to-fit, while all strings generated by "decode" will 486 will be shrunk-to-fit, while all strings generated by "decode" will
247 also be shrunk-to-fit. 487 also be shrunk-to-fit.
248 488
… …
251 491
252 In the future, this setting might control other things, such as 492 In the future, this setting might control other things, such as
253 converting strings that look like integers or floats into integers 493 converting strings that look like integers or floats into integers
254 or floats internally (there is no difference on the Perl level), 494 or floats internally (there is no difference on the Perl level),
255 saving space. 495 saving space.
496
497 $json = $json->max_depth ([$maximum_nesting_depth])
498 Sets the maximum nesting level (default 512) accepted while encoding
499 or decoding. If the JSON text or Perl data structure has an equal or
500 higher nesting level then this limit, then the encoder and decoder
501 will stop and croak at that point.
502
503 Nesting level is defined by number of hash- or arrayrefs that the
504 encoder needs to traverse to reach a given point or the number of
505 "{" or "[" characters without their matching closing parenthesis
506 crossed to reach a given character in a string.
507
508 Setting the maximum depth to one disallows any nesting, so that
509 ensures that the object is only a single hash/object or array.
510
511 The argument to "max_depth" will be rounded up to the next highest
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).
529
530 See SECURITY CONSIDERATIONS, below, for more info on why this is
531 useful.
256 532
257 $json_text = $json->encode ($perl_scalar) 533 $json_text = $json->encode ($perl_scalar)
258 Converts the given Perl data structure (a simple scalar or a 534 Converts the given Perl data structure (a simple scalar or a
259 reference to a hash or array) to its JSON representation. Simple 535 reference to a hash or array) to its JSON representation. Simple
260 scalars will be converted into JSON string or number sequences, 536 scalars will be converted into JSON string or number sequences,
… …
269 545
270 JSON numbers and strings become simple Perl scalars. JSON arrays 546 JSON numbers and strings become simple Perl scalars. JSON arrays
271 become Perl arrayrefs and JSON objects become Perl hashrefs. "true" 547 become Perl arrayrefs and JSON objects become Perl hashrefs. "true"
272 becomes 1, "false" becomes 0 and "null" becomes "undef". 548 becomes 1, "false" becomes 0 and "null" becomes "undef".
273 549
550 ($perl_scalar, $characters) = $json->decode_prefix ($json_text)
551 This works like the "decode" method, but instead of raising an
552 exception when there is trailing garbage after the first JSON
553 object, it will silently stop parsing there and return the number of
554 characters consumed so far.
555
556 This is useful if your JSON texts are not delimited by an outer
557 protocol (which is not the brightest thing to do in the first place)
558 and you need to know where the JSON text ends.
559
560 JSON::XS->new->decode_prefix ("[1] the tail")
561 => ([], 3)
562
274MAPPING 563MAPPING
275 This section describes how JSON::XS maps Perl values to JSON values and 564 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 565 vice versa. These mappings are designed to "do the right thing" in most
277 circumstances automatically, preserving round-tripping characteristics 566 circumstances automatically, preserving round-tripping characteristics
278 (what you put in comes out as something equivalent). 567 (what you put in comes out as something equivalent).
… …
294 A JSON string becomes a string scalar in Perl - Unicode codepoints 583 A JSON string becomes a string scalar in Perl - Unicode codepoints
295 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,
296 so no manual decoding is necessary. 585 so no manual decoding is necessary.
297 586
298 number 587 number
299 A JSON number becomes either an integer or numeric (floating point) 588 A JSON number becomes either an integer, numeric (floating point) or
300 scalar in perl, depending on its range and any fractional parts. On 589 string scalar in perl, depending on its range and any fractional
301 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
302 all the conversion details, but an integer may take slightly less 591 Perl handles all the conversion details, but an integer may take
303 memory and might represent more values exactly than (floating point) 592 slightly less memory and might represent more values exactly than
304 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.
305 607
306 true, false 608 true, false
307 These JSON atoms become 0, 1, respectively. Information is lost in 609 These JSON atoms become "JSON::XS::true" and "JSON::XS::false",
308 this process. Future versions might represent those values 610 respectively. They are overloaded to act almost exactly like the
309 differently, but they will be guarenteed to act like these integers 611 numbers 1 and 0. You can check wether a scalar is a JSON boolean by
310 would normally in Perl. 612 using the "JSON::XS::is_bool" function.
311 613
312 null 614 null
313 A JSON null atom becomes "undef" in Perl. 615 A JSON null atom becomes "undef" in Perl.
314 616
315 PERL -> JSON 617 PERL -> JSON
… …
317 truly typeless language, so we can only guess which JSON type is meant 619 truly typeless language, so we can only guess which JSON type is meant
318 by a Perl value. 620 by a Perl value.
319 621
320 hash references 622 hash references
321 Perl hash references become JSON objects. As there is no inherent 623 Perl hash references become JSON objects. As there is no inherent
322 ordering in hash keys, they will usually be encoded in a 624 ordering in hash keys (or JSON objects), they will usually be
323 pseudo-random order that can change between runs of the same program 625 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. 626 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 627 program. JSON::XS can optionally sort the hash keys (determined by
326 *canonical* flag), so the same datastructure will serialise to the 628 the *canonical* flag), so the same datastructure will serialise to
327 same JSON text (given same settings and version of JSON::XS), but 629 the same JSON text (given same settings and version of JSON::XS),
328 this incurs a runtime overhead. 630 but this incurs a runtime overhead and is only rarely useful, e.g.
631 when you want to compare some JSON text against another for
632 equality.
329 633
330 array references 634 array references
331 Perl array references become JSON arrays. 635 Perl array references become JSON arrays.
636
637 other references
638 Other unblessed references are generally not allowed and will cause
639 an exception to be thrown, except for references to the integers 0
640 and 1, which get turned into "false" and "true" atoms in JSON. You
641 can also use "JSON::XS::false" and "JSON::XS::true" to improve
642 readability.
643
644 to_json [\0,JSON::XS::true] # yields [false,true]
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.
332 649
333 blessed objects 650 blessed objects
334 Blessed objects are not allowed. JSON::XS currently tries to encode 651 Blessed objects are not allowed. JSON::XS currently tries to encode
335 their underlying representation (hash- or arrayref), but this 652 their underlying representation (hash- or arrayref), but this
336 behaviour might change in future versions. 653 behaviour might change in future versions.
… …
367 $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
368 $x *= 1; # same thing, the choise is yours. 685 $x *= 1; # same thing, the choise is yours.
369 686
370 You can not currently output JSON booleans or force the type in 687 You can not currently output JSON booleans or force the type in
371 other, less obscure, ways. Tell me if you need this capability. 688 other, less obscure, ways. Tell me if you need this capability.
372
373 circular data structures
374 Those will be encoded until memory or stackspace runs out.
375 689
376COMPARISON 690COMPARISON
377 As already mentioned, this module was created because none of the 691 As already mentioned, this module was created because none of the
378 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
379 describe the problems (or pleasures) I encountered with various existing 693 describe the problems (or pleasures) I encountered with various existing
… …
450 Does not generate valid JSON texts (key strings are often unquoted, 764 Does not generate valid JSON texts (key strings are often unquoted,
451 empty keys result in nothing being output) 765 empty keys result in nothing being output)
452 766
453 Does not check input for validity. 767 Does not check input for validity.
454 768
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 noticably 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.
791
455 SPEED 792 SPEED
456 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
457 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
458 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
459 system. 796 system.
460 797
461 First comes a comparison between various modules using a very short JSON 798 First comes a comparison between various modules using a very short
462 string: 799 single-line JSON string:
463 800
464 {"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]}
465 803
466 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
467 functional interface, while JSON::XS/2 uses the OO interface with 805 functional interface, while JSON::XS/2 uses the OO interface with
468 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:
469 808
809 Storable | 15779.925 | 14169.946 |
810 -----------+------------+------------+
470 module | encode | decode | 811 module | encode | decode |
471 -----------|------------|------------| 812 -----------|------------|------------|
472 JSON | 11488.516 | 7823.035 | 813 JSON | 4990.842 | 4088.813 |
473 JSON::DWIW | 94708.054 | 129094.260 | 814 JSON::DWIW | 51653.990 | 71575.154 |
474 JSON::PC | 63884.157 | 128528.212 | 815 JSON::PC | 65948.176 | 74631.744 |
816 JSON::PP | 8931.652 | 3817.168 |
475 JSON::Syck | 34898.677 | 42096.911 | 817 JSON::Syck | 24877.248 | 27776.848 |
476 JSON::XS | 654027.064 | 396423.669 | 818 JSON::XS | 388361.481 | 227951.304 |
477 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 |
478 -----------+------------+------------+ 822 -----------+------------+------------+
479 823
480 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
481 encoding, more than three times faster on decoding, and about thirty 825 encoding, about three times faster on decoding, and over fourty times
482 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.
483 828
484 Using a longer test string (roughly 18KB, generated from Yahoo! Locals 829 Using a longer test string (roughly 18KB, generated from Yahoo! Locals
485 search API (http://nanoref.com/yahooapis/mgPdGg): 830 search API (http://nanoref.com/yahooapis/mgPdGg):
486 831
487 module | encode | decode | 832 module | encode | decode |
488 -----------|------------|------------| 833 -----------|------------|------------|
489 JSON | 273.023 | 44.674 | 834 JSON | 55.260 | 34.971 |
490 JSON::DWIW | 1089.383 | 1145.704 | 835 JSON::DWIW | 825.228 | 1082.513 |
491 JSON::PC | 3097.419 | 2393.921 | 836 JSON::PC | 3571.444 | 2394.829 |
492 JSON::Syck | 514.060 | 843.053 | 837 JSON::PP | 210.987 | 32.574 |
493 JSON::XS | 6479.668 | 3636.364 | 838 JSON::Syck | 552.551 | 787.544 |
494 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 |
495 -----------+------------+------------+ 843 -----------+------------+------------+
496 844
497 Again, JSON::XS leads by far. 845 Again, JSON::XS leads by far (except for Storable which non-surprisingly
846 decodes faster).
498 847
499 On large strings containing lots of high unicode characters, some 848 On large strings containing lots of high unicode characters, some
500 modules (such as JSON::PC) seem to decode faster than JSON::XS, but the 849 modules (such as JSON::PC) seem to decode faster than JSON::XS, but the
501 result will be broken due to missing (or wrong) unicode handling. Others 850 result will be broken due to missing (or wrong) unicode handling. Others
502 refuse to decode or encode properly, so it was impossible to prepare a 851 refuse to decode or encode properly, so it was impossible to prepare a
503 fair comparison table for that case. 852 fair comparison table for that case.
504 853
505RESOURCE LIMITS 854SECURITY CONSIDERATIONS
506 JSON::XS does not impose any limits on the size of JSON texts or Perl 855 When you are using JSON in a protocol, talking to untrusted potentially
507 values they represent - if your machine can handle it, JSON::XS will 856 hostile creatures requires relatively few measures.
508 encode or decode it. Future versions might optionally impose structure 857
509 depth and memory use resource limits. 858 First of all, your JSON decoder should be secure, that is, should not
859 have any buffer overflows. Obviously, this module should ensure that and
860 I am trying hard on making that true, but you never know.
861
862 Second, you need to avoid resource-starving attacks. That means you
863 should limit the size of JSON texts you accept, or make sure then when
864 your resources run out, thats just fine (e.g. by using a separate
865 process that can crash safely). The size of a JSON text in octets or
866 characters is usually a good indication of the size of the resources
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.
871
872 Third, JSON::XS recurses using the C stack when decoding objects and
873 arrays. The C stack is a limited resource: for instance, on my amd64
874 machine with 8MB of stack size I can decode around 180k nested arrays
875 but only 14k nested JSON objects (due to perl itself recursing deeply on
876 croak to free the temporary). If that is exceeded, the program crashes.
877 to be conservative, the default nesting limit is set to 512. If your
878 process has a smaller stack, you should adjust this setting accordingly
879 with the "max_depth" method.
880
881 And last but least, something else could bomb you that I forgot to think
882 of. In that case, you get to keep the pieces. I am always open for
883 hints, though...
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 wether
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* guarenteed 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 ahve ben warned).
510 900
511BUGS 901BUGS
512 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
513 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
514 still very young and not well-tested. If you keep reporting bugs they 904 still relatively early in its development. If you keep reporting bugs
515 will be fixed swiftly, though. 905 they will be fixed swiftly, though.
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.
516 909
517AUTHOR 910AUTHOR
518 Marc Lehmann <schmorp@schmorp.de> 911 Marc Lehmann <schmorp@schmorp.de>
519 http://home.schmorp.de/ 912 http://home.schmorp.de/
520 913

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