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Revision 1.17 by root, Mon Aug 27 02:03:23 2007 UTC

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2 JSON::XS - JSON serialising/deserialising, done correctly and fast 2 JSON::XS - JSON serialising/deserialising, done correctly and fast
3 3
4SYNOPSIS 4SYNOPSIS
5 use JSON::XS; 5 use JSON::XS;
6 6
7 # exported functions, croak on error 7 # exported functions, they croak on error
8 # and expect/generate UTF-8
8 9
9 $utf8_encoded_json_text = to_json $perl_hash_or_arrayref; 10 $utf8_encoded_json_text = to_json $perl_hash_or_arrayref;
10 $perl_hash_or_arrayref = from_json $utf8_encoded_json_text; 11 $perl_hash_or_arrayref = from_json $utf8_encoded_json_text;
11 12
12 # oo-interface 13 # OO-interface
13 14
14 $coder = JSON::XS->new->ascii->pretty->allow_nonref; 15 $coder = JSON::XS->new->ascii->pretty->allow_nonref;
15 $pretty_printed_unencoded = $coder->encode ($perl_scalar); 16 $pretty_printed_unencoded = $coder->encode ($perl_scalar);
16 $perl_scalar = $coder->decode ($unicode_json_text); 17 $perl_scalar = $coder->decode ($unicode_json_text);
17 18
… …
30 31
31 See MAPPING, below, on how JSON::XS maps perl values to JSON values and 32 See MAPPING, below, on how JSON::XS maps perl values to JSON values and
32 vice versa. 33 vice versa.
33 34
34 FEATURES 35 FEATURES
35 * correct handling of unicode issues 36 * correct unicode handling
36 This module knows how to handle Unicode, and even documents how and 37 This module knows how to handle Unicode, and even documents how and
37 when it does so. 38 when it does so.
38 39
39 * round-trip integrity 40 * round-trip integrity
40 When you serialise a perl data structure using only datatypes 41 When you serialise a perl data structure using only datatypes
41 supported by JSON, the deserialised data structure is identical on 42 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"). 43 the Perl level. (e.g. the string "2.0" doesn't suddenly become "2"
44 just because it looks like a number).
43 45
44 * strict checking of JSON correctness 46 * strict checking of JSON correctness
45 There is no guessing, no generating of illegal JSON texts by 47 There is no guessing, no generating of illegal JSON texts by
46 default, and only JSON is accepted as input by default (the latter 48 default, and only JSON is accepted as input by default (the latter
47 is a security feature). 49 is a security feature).
… …
55 interface. 57 interface.
56 58
57 * reasonably versatile output formats 59 * reasonably versatile output formats
58 You can choose between the most compact guarenteed single-line 60 You can choose between the most compact guarenteed single-line
59 format possible (nice for simple line-based protocols), a pure-ascii 61 format possible (nice for simple line-based protocols), a pure-ascii
60 format (for when your transport is not 8-bit clean), or a 62 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 63 the whole unicode range), or a pretty-printed format (for when you
62 can combine those features in whatever way you like. 64 want to read that stuff). Or you can combine those features in
65 whatever way you like.
63 66
64FUNCTIONAL INTERFACE 67FUNCTIONAL INTERFACE
65 The following convinience methods are provided by this module. They are 68 The following convinience methods are provided by this module. They are
66 exported by default: 69 exported by default:
67 70
… …
84 This function call is functionally identical to: 87 This function call is functionally identical to:
85 88
86 $perl_scalar = JSON::XS->new->utf8->decode ($json_text) 89 $perl_scalar = JSON::XS->new->utf8->decode ($json_text)
87 90
88 except being faster. 91 except being faster.
92
93 $is_boolean = JSON::XS::is_bool $scalar
94 Returns true if the passed scalar represents either JSON::XS::true
95 or JSON::XS::false, two constants that act like 1 and 0,
96 respectively and are used to represent JSON "true" and "false"
97 values in Perl.
98
99 See MAPPING, below, for more information on how JSON values are
100 mapped to Perl.
89 101
90OBJECT-ORIENTED INTERFACE 102OBJECT-ORIENTED INTERFACE
91 The object oriented interface lets you configure your own encoding or 103 The object oriented interface lets you configure your own encoding or
92 decoding style, within the limits of supported formats. 104 decoding style, within the limits of supported formats.
93 105
… …
105 $json = $json->ascii ([$enable]) 117 $json = $json->ascii ([$enable])
106 If $enable is true (or missing), then the "encode" method will not 118 If $enable is true (or missing), then the "encode" method will not
107 generate characters outside the code range 0..127 (which is ASCII). 119 generate characters outside the code range 0..127 (which is ASCII).
108 Any unicode characters outside that range will be escaped using 120 Any unicode characters outside that range will be escaped using
109 either a single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL 121 either a single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL
110 escape sequence, as per RFC4627. 122 escape sequence, as per RFC4627. The resulting encoded JSON text can
123 be treated as a native unicode string, an ascii-encoded,
124 latin1-encoded or UTF-8 encoded string, or any other superset of
125 ASCII.
111 126
112 If $enable is false, then the "encode" method will not escape 127 If $enable is false, then the "encode" method will not escape
113 Unicode characters unless required by the JSON syntax. This results 128 Unicode characters unless required by the JSON syntax or other
114 in a faster and more compact format. 129 flags. This results in a faster and more compact format.
130
131 The main use for this flag is to produce JSON texts that can be
132 transmitted over a 7-bit channel, as the encoded JSON texts will not
133 contain any 8 bit characters.
115 134
116 JSON::XS->new->ascii (1)->encode ([chr 0x10401]) 135 JSON::XS->new->ascii (1)->encode ([chr 0x10401])
117 => ["\ud801\udc01"] 136 => ["\ud801\udc01"]
137
138 $json = $json->latin1 ([$enable])
139 If $enable is true (or missing), then the "encode" method will
140 encode the resulting JSON text as latin1 (or iso-8859-1), escaping
141 any characters outside the code range 0..255. The resulting string
142 can be treated as a latin1-encoded JSON text or a native unicode
143 string. The "decode" method will not be affected in any way by this
144 flag, as "decode" by default expects unicode, which is a strict
145 superset of latin1.
146
147 If $enable is false, then the "encode" method will not escape
148 Unicode characters unless required by the JSON syntax or other
149 flags.
150
151 The main use for this flag is efficiently encoding binary data as
152 JSON text, as most octets will not be escaped, resulting in a
153 smaller encoded size. The disadvantage is that the resulting JSON
154 text is encoded in latin1 (and must correctly be treated as such
155 when storing and transfering), a rare encoding for JSON. It is
156 therefore most useful when you want to store data structures known
157 to contain binary data efficiently in files or databases, not when
158 talking to other JSON encoders/decoders.
159
160 JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]
161 => ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)
118 162
119 $json = $json->utf8 ([$enable]) 163 $json = $json->utf8 ([$enable])
120 If $enable is true (or missing), then the "encode" method will 164 If $enable is true (or missing), then the "encode" method will
121 encode the JSON result into UTF-8, as required by many protocols, 165 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 166 while the "decode" method expects to be handled an UTF-8-encoded
… …
196 240
197 Example, space_before and indent disabled, space_after enabled: 241 Example, space_before and indent disabled, space_after enabled:
198 242
199 {"key": "value"} 243 {"key": "value"}
200 244
245 $json = $json->relaxed ([$enable])
246 If $enable is true (or missing), then "decode" will accept some
247 extensions to normal JSON syntax (see below). "encode" will not be
248 affected in anyway. *Be aware that this option makes you accept
249 invalid JSON texts as if they were valid!*. I suggest only to use
250 this option to parse application-specific files written by humans
251 (configuration files, resource files etc.)
252
253 If $enable is false (the default), then "decode" will only accept
254 valid JSON texts.
255
256 Currently accepted extensions are:
257
258 * list items can have an end-comma
259 JSON *separates* array elements and key-value pairs with commas.
260 This can be annoying if you write JSON texts manually and want
261 to be able to quickly append elements, so this extension accepts
262 comma at the end of such items not just between them:
263
264 [
265 1,
266 2, <- this comma not normally allowed
267 ]
268 {
269 "k1": "v1",
270 "k2": "v2", <- this comma not normally allowed
271 }
272
201 $json = $json->canonical ([$enable]) 273 $json = $json->canonical ([$enable])
202 If $enable is true (or missing), then the "encode" method will 274 If $enable is true (or missing), then the "encode" method will
203 output JSON objects by sorting their keys. This is adding a 275 output JSON objects by sorting their keys. This is adding a
204 comparatively high overhead. 276 comparatively high overhead.
205 277
… …
229 Example, encode a Perl scalar as JSON value with enabled 301 Example, encode a Perl scalar as JSON value with enabled
230 "allow_nonref", resulting in an invalid JSON text: 302 "allow_nonref", resulting in an invalid JSON text:
231 303
232 JSON::XS->new->allow_nonref->encode ("Hello, World!") 304 JSON::XS->new->allow_nonref->encode ("Hello, World!")
233 => "Hello, World!" 305 => "Hello, World!"
306
307 $json = $json->allow_blessed ([$enable])
308 If $enable is true (or missing), then the "encode" method will not
309 barf when it encounters a blessed reference. Instead, the value of
310 the convert_blessed option will decide wether "null"
311 ("convert_blessed" disabled or no "to_json" method found) or a
312 representation of the object ("convert_blessed" enabled and
313 "to_json" method found) is being encoded. Has no effect on "decode".
314
315 If $enable is false (the default), then "encode" will throw an
316 exception when it encounters a blessed object.
317
318 $json = $json->convert_blessed ([$enable])
319 If $enable is true (or missing), then "encode", upon encountering a
320 blessed object, will check for the availability of the "TO_JSON"
321 method on the object's class. If found, it will be called in scalar
322 context and the resulting scalar will be encoded instead of the
323 object. If no "TO_JSON" method is found, the value of
324 "allow_blessed" will decide what to do.
325
326 The "TO_JSON" method may safely call die if it wants. If "TO_JSON"
327 returns other blessed objects, those will be handled in the same
328 way. "TO_JSON" must take care of not causing an endless recursion
329 cycle (== crash) in this case. The name of "TO_JSON" was chosen
330 because other methods called by the Perl core (== not by the user of
331 the object) are usually in upper case letters and to avoid
332 collisions with the "to_json" function.
333
334 This setting does not yet influence "decode" in any way, but in the
335 future, global hooks might get installed that influence "decode" and
336 are enabled by this setting.
337
338 If $enable is false, then the "allow_blessed" setting will decide
339 what to do when a blessed object is found.
340
341 $json = $json->filter_json_object ([$coderef->($hashref)])
342 When $coderef is specified, it will be called from "decode" each
343 time it decodes a JSON object. The only argument is a reference to
344 the newly-created hash. If the code references returns a single
345 scalar (which need not be a reference), this value (i.e. a copy of
346 that scalar to avoid aliasing) is inserted into the deserialised
347 data structure. If it returns an empty list (NOTE: *not* "undef",
348 which is a valid scalar), the original deserialised hash will be
349 inserted. This setting can slow down decoding considerably.
350
351 When $coderef is omitted or undefined, any existing callback will be
352 removed and "decode" will not change the deserialised hash in any
353 way.
354
355 Example, convert all JSON objects into the integer 5:
356
357 my $js = JSON::XS->new->filter_json_object (sub { 5 });
358 # returns [5]
359 $js->decode ('[{}]')
360 # throw an exception because allow_nonref is not enabled
361 # so a lone 5 is not allowed.
362 $js->decode ('{"a":1, "b":2}');
363
364 $json = $json->filter_json_single_key_object ($key [=>
365 $coderef->($value)])
366 Works remotely similar to "filter_json_object", but is only called
367 for JSON objects having a single key named $key.
368
369 This $coderef is called before the one specified via
370 "filter_json_object", if any. It gets passed the single value in the
371 JSON object. If it returns a single value, it will be inserted into
372 the data structure. If it returns nothing (not even "undef" but the
373 empty list), the callback from "filter_json_object" will be called
374 next, as if no single-key callback were specified.
375
376 If $coderef is omitted or undefined, the corresponding callback will
377 be disabled. There can only ever be one callback for a given key.
378
379 As this callback gets called less often then the
380 "filter_json_object" one, decoding speed will not usually suffer as
381 much. Therefore, single-key objects make excellent targets to
382 serialise Perl objects into, especially as single-key JSON objects
383 are as close to the type-tagged value concept as JSON gets (its
384 basically an ID/VALUE tuple). Of course, JSON does not support this
385 in any way, so you need to make sure your data never looks like a
386 serialised Perl hash.
387
388 Typical names for the single object key are "__class_whatever__", or
389 "$__dollars_are_rarely_used__$" or "}ugly_brace_placement", or even
390 things like "__class_md5sum(classname)__", to reduce the risk of
391 clashing with real hashes.
392
393 Example, decode JSON objects of the form "{ "__widget__" => <id> }"
394 into the corresponding $WIDGET{<id>} object:
395
396 # return whatever is in $WIDGET{5}:
397 JSON::XS
398 ->new
399 ->filter_json_single_key_object (__widget__ => sub {
400 $WIDGET{ $_[0] }
401 })
402 ->decode ('{"__widget__": 5')
403
404 # this can be used with a TO_JSON method in some "widget" class
405 # for serialisation to json:
406 sub WidgetBase::TO_JSON {
407 my ($self) = @_;
408
409 unless ($self->{id}) {
410 $self->{id} = ..get..some..id..;
411 $WIDGET{$self->{id}} = $self;
412 }
413
414 { __widget__ => $self->{id} }
415 }
234 416
235 $json = $json->shrink ([$enable]) 417 $json = $json->shrink ([$enable])
236 Perl usually over-allocates memory a bit when allocating space for 418 Perl usually over-allocates memory a bit when allocating space for
237 strings. This flag optionally resizes strings generated by either 419 strings. This flag optionally resizes strings generated by either
238 "encode" or "decode" to their minimum size possible. This can save 420 "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 421 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 422 many short strings. It will also try to downgrade any strings to
241 octet-form if possible: perl stores strings internally either in an 423 octet-form if possible: perl stores strings internally either in an
242 encoding called UTF-X or in octet-form. The latter cannot store 424 encoding called UTF-X or in octet-form. The latter cannot store
243 everything but uses less space in general. 425 everything but uses less space in general (and some buggy Perl or C
426 code might even rely on that internal representation being used).
427
428 The actual definition of what shrink does might change in future
429 versions, but it will always try to save space at the expense of
430 time.
244 431
245 If $enable is true (or missing), the string returned by "encode" 432 If $enable is true (or missing), the string returned by "encode"
246 will be shrunk-to-fit, while all strings generated by "decode" will 433 will be shrunk-to-fit, while all strings generated by "decode" will
247 also be shrunk-to-fit. 434 also be shrunk-to-fit.
248 435
… …
251 438
252 In the future, this setting might control other things, such as 439 In the future, this setting might control other things, such as
253 converting strings that look like integers or floats into integers 440 converting strings that look like integers or floats into integers
254 or floats internally (there is no difference on the Perl level), 441 or floats internally (there is no difference on the Perl level),
255 saving space. 442 saving space.
443
444 $json = $json->max_depth ([$maximum_nesting_depth])
445 Sets the maximum nesting level (default 512) accepted while encoding
446 or decoding. If the JSON text or Perl data structure has an equal or
447 higher nesting level then this limit, then the encoder and decoder
448 will stop and croak at that point.
449
450 Nesting level is defined by number of hash- or arrayrefs that the
451 encoder needs to traverse to reach a given point or the number of
452 "{" or "[" characters without their matching closing parenthesis
453 crossed to reach a given character in a string.
454
455 Setting the maximum depth to one disallows any nesting, so that
456 ensures that the object is only a single hash/object or array.
457
458 The argument to "max_depth" will be rounded up to the next highest
459 power of two. If no argument is given, the highest possible setting
460 will be used, which is rarely useful.
461
462 See SECURITY CONSIDERATIONS, below, for more info on why this is
463 useful.
464
465 $json = $json->max_size ([$maximum_string_size])
466 Set the maximum length a JSON text may have (in bytes) where
467 decoding is being attempted. The default is 0, meaning no limit.
468 When "decode" is called on a string longer then this number of
469 characters it will not attempt to decode the string but throw an
470 exception. This setting has no effect on "encode" (yet).
471
472 The argument to "max_size" will be rounded up to the next highest
473 power of two (so may be more than requested). If no argument is
474 given, the limit check will be deactivated (same as when 0 is
475 specified).
476
477 See SECURITY CONSIDERATIONS, below, for more info on why this is
478 useful.
256 479
257 $json_text = $json->encode ($perl_scalar) 480 $json_text = $json->encode ($perl_scalar)
258 Converts the given Perl data structure (a simple scalar or a 481 Converts the given Perl data structure (a simple scalar or a
259 reference to a hash or array) to its JSON representation. Simple 482 reference to a hash or array) to its JSON representation. Simple
260 scalars will be converted into JSON string or number sequences, 483 scalars will be converted into JSON string or number sequences,
… …
269 492
270 JSON numbers and strings become simple Perl scalars. JSON arrays 493 JSON numbers and strings become simple Perl scalars. JSON arrays
271 become Perl arrayrefs and JSON objects become Perl hashrefs. "true" 494 become Perl arrayrefs and JSON objects become Perl hashrefs. "true"
272 becomes 1, "false" becomes 0 and "null" becomes "undef". 495 becomes 1, "false" becomes 0 and "null" becomes "undef".
273 496
497 ($perl_scalar, $characters) = $json->decode_prefix ($json_text)
498 This works like the "decode" method, but instead of raising an
499 exception when there is trailing garbage after the first JSON
500 object, it will silently stop parsing there and return the number of
501 characters consumed so far.
502
503 This is useful if your JSON texts are not delimited by an outer
504 protocol (which is not the brightest thing to do in the first place)
505 and you need to know where the JSON text ends.
506
507 JSON::XS->new->decode_prefix ("[1] the tail")
508 => ([], 3)
509
274MAPPING 510MAPPING
275 This section describes how JSON::XS maps Perl values to JSON values and 511 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 512 vice versa. These mappings are designed to "do the right thing" in most
277 circumstances automatically, preserving round-tripping characteristics 513 circumstances automatically, preserving round-tripping characteristics
278 (what you put in comes out as something equivalent). 514 (what you put in comes out as something equivalent).
… …
294 A JSON string becomes a string scalar in Perl - Unicode codepoints 530 A JSON string becomes a string scalar in Perl - Unicode codepoints
295 in JSON are represented by the same codepoints in the Perl string, 531 in JSON are represented by the same codepoints in the Perl string,
296 so no manual decoding is necessary. 532 so no manual decoding is necessary.
297 533
298 number 534 number
299 A JSON number becomes either an integer or numeric (floating point) 535 A JSON number becomes either an integer, numeric (floating point) or
300 scalar in perl, depending on its range and any fractional parts. On 536 string scalar in perl, depending on its range and any fractional
301 the Perl level, there is no difference between those as Perl handles 537 parts. On the Perl level, there is no difference between those as
302 all the conversion details, but an integer may take slightly less 538 Perl handles all the conversion details, but an integer may take
303 memory and might represent more values exactly than (floating point) 539 slightly less memory and might represent more values exactly than
304 numbers. 540 (floating point) numbers.
541
542 If the number consists of digits only, JSON::XS will try to
543 represent it as an integer value. If that fails, it will try to
544 represent it as a numeric (floating point) value if that is possible
545 without loss of precision. Otherwise it will preserve the number as
546 a string value.
547
548 Numbers containing a fractional or exponential part will always be
549 represented as numeric (floating point) values, possibly at a loss
550 of precision.
551
552 This might create round-tripping problems as numbers might become
553 strings, but as Perl is typeless there is no other way to do it.
305 554
306 true, false 555 true, false
307 These JSON atoms become 0, 1, respectively. Information is lost in 556 These JSON atoms become "JSON::XS::true" and "JSON::XS::false",
308 this process. Future versions might represent those values 557 respectively. They are overloaded to act almost exactly like the
309 differently, but they will be guarenteed to act like these integers 558 numbers 1 and 0. You can check wether a scalar is a JSON boolean by
310 would normally in Perl. 559 using the "JSON::XS::is_bool" function.
311 560
312 null 561 null
313 A JSON null atom becomes "undef" in Perl. 562 A JSON null atom becomes "undef" in Perl.
314 563
315 PERL -> JSON 564 PERL -> JSON
… …
317 truly typeless language, so we can only guess which JSON type is meant 566 truly typeless language, so we can only guess which JSON type is meant
318 by a Perl value. 567 by a Perl value.
319 568
320 hash references 569 hash references
321 Perl hash references become JSON objects. As there is no inherent 570 Perl hash references become JSON objects. As there is no inherent
322 ordering in hash keys, they will usually be encoded in a 571 ordering in hash keys (or JSON objects), they will usually be
323 pseudo-random order that can change between runs of the same program 572 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. 573 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 574 program. JSON::XS can optionally sort the hash keys (determined by
326 *canonical* flag), so the same datastructure will serialise to the 575 the *canonical* flag), so the same datastructure will serialise to
327 same JSON text (given same settings and version of JSON::XS), but 576 the same JSON text (given same settings and version of JSON::XS),
328 this incurs a runtime overhead. 577 but this incurs a runtime overhead and is only rarely useful, e.g.
578 when you want to compare some JSON text against another for
579 equality.
329 580
330 array references 581 array references
331 Perl array references become JSON arrays. 582 Perl array references become JSON arrays.
583
584 other references
585 Other unblessed references are generally not allowed and will cause
586 an exception to be thrown, except for references to the integers 0
587 and 1, which get turned into "false" and "true" atoms in JSON. You
588 can also use "JSON::XS::false" and "JSON::XS::true" to improve
589 readability.
590
591 to_json [\0,JSON::XS::true] # yields [false,true]
592
593 JSON::XS::true, JSON::XS::false
594 These special values become JSON true and JSON false values,
595 respectively. You cna alos use "\1" and "\0" directly if you want.
332 596
333 blessed objects 597 blessed objects
334 Blessed objects are not allowed. JSON::XS currently tries to encode 598 Blessed objects are not allowed. JSON::XS currently tries to encode
335 their underlying representation (hash- or arrayref), but this 599 their underlying representation (hash- or arrayref), but this
336 behaviour might change in future versions. 600 behaviour might change in future versions.
… …
367 $x += 0; # numify it, ensuring it will be dumped as a number 631 $x += 0; # numify it, ensuring it will be dumped as a number
368 $x *= 1; # same thing, the choise is yours. 632 $x *= 1; # same thing, the choise is yours.
369 633
370 You can not currently output JSON booleans or force the type in 634 You can not currently output JSON booleans or force the type in
371 other, less obscure, ways. Tell me if you need this capability. 635 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.
375 636
376COMPARISON 637COMPARISON
377 As already mentioned, this module was created because none of the 638 As already mentioned, this module was created because none of the
378 existing JSON modules could be made to work correctly. First I will 639 existing JSON modules could be made to work correctly. First I will
379 describe the problems (or pleasures) I encountered with various existing 640 describe the problems (or pleasures) I encountered with various existing
… …
450 Does not generate valid JSON texts (key strings are often unquoted, 711 Does not generate valid JSON texts (key strings are often unquoted,
451 empty keys result in nothing being output) 712 empty keys result in nothing being output)
452 713
453 Does not check input for validity. 714 Does not check input for validity.
454 715
716 JSON and YAML
717 You often hear that JSON is a subset (or a close subset) of YAML. This
718 is, however, a mass hysteria and very far from the truth. In general,
719 there is no way to configure JSON::XS to output a data structure as
720 valid YAML.
721
722 If you really must use JSON::XS to generate YAML, you should use this
723 algorithm (subject to change in future versions):
724
725 my $to_yaml = JSON::XS->new->utf8->space_after (1);
726 my $yaml = $to_yaml->encode ($ref) . "\n";
727
728 This will usually generate JSON texts that also parse as valid YAML.
729 Please note that YAML has hardcoded limits on (simple) object key
730 lengths that JSON doesn't have, so you should make sure that your hash
731 keys are noticably shorter than the 1024 characters YAML allows.
732
733 There might be other incompatibilities that I am not aware of. In
734 general you should not try to generate YAML with a JSON generator or
735 vice versa, or try to parse JSON with a YAML parser or vice versa:
736 chances are high that you will run into severe interoperability
737 problems.
738
455 SPEED 739 SPEED
456 It seems that JSON::XS is surprisingly fast, as shown in the following 740 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 741 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 742 in the JSON::XS distribution, to make it easy to compare on your own
459 system. 743 system.
460 744
461 First comes a comparison between various modules using a very short JSON 745 First comes a comparison between various modules using a very short
462 string (83 bytes), showing the number of encodes/decodes per second 746 single-line JSON string:
463 (JSON::XS is the functional interface, while JSON::XS/2 is the OO
464 interface with pretty-printing and hashkey sorting enabled). Higher is
465 better:
466 747
748 {"method": "handleMessage", "params": ["user1", "we were just talking"], \
749 "id": null, "array":[1,11,234,-5,1e5,1e7, true, false]}
750
751 It shows the number of encodes/decodes per second (JSON::XS uses the
752 functional interface, while JSON::XS/2 uses the OO interface with
753 pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink).
754 Higher is better:
755
756 Storable | 15779.925 | 14169.946 |
757 -----------+------------+------------+
467 module | encode | decode | 758 module | encode | decode |
468 -----------|------------|------------| 759 -----------|------------|------------|
469 JSON | 14006 | 6820 | 760 JSON | 4990.842 | 4088.813 |
470 JSON::DWIW | 200937 | 120386 | 761 JSON::DWIW | 51653.990 | 71575.154 |
471 JSON::PC | 85065 | 129366 | 762 JSON::PC | 65948.176 | 74631.744 |
472 JSON::Syck | 59898 | 44232 | 763 JSON::PP | 8931.652 | 3817.168 |
473 JSON::XS | 1171478 | 342435 | 764 JSON::Syck | 24877.248 | 27776.848 |
474 JSON::XS/2 | 730760 | 328714 | 765 JSON::XS | 388361.481 | 227951.304 |
766 JSON::XS/2 | 227951.304 | 218453.333 |
767 JSON::XS/3 | 338250.323 | 218453.333 |
768 Storable | 16500.016 | 135300.129 |
475 -----------+------------+------------+ 769 -----------+------------+------------+
476 770
477 That is, JSON::XS is 6 times faster than than JSON::DWIW and about 80 771 That is, JSON::XS is about five times faster than JSON::DWIW on
772 encoding, about three times faster on decoding, and over fourty times
478 times faster than JSON, even with pretty-printing and key sorting. 773 faster than JSON, even with pretty-printing and key sorting. It also
774 compares favourably to Storable for small amounts of data.
479 775
480 Using a longer test string (roughly 18KB, generated from Yahoo! Locals 776 Using a longer test string (roughly 18KB, generated from Yahoo! Locals
481 search API (http://nanoref.com/yahooapis/mgPdGg): 777 search API (http://nanoref.com/yahooapis/mgPdGg):
482 778
483 module | encode | decode | 779 module | encode | decode |
484 -----------|------------|------------| 780 -----------|------------|------------|
485 JSON | 673 | 38 | 781 JSON | 55.260 | 34.971 |
486 JSON::DWIW | 5271 | 770 | 782 JSON::DWIW | 825.228 | 1082.513 |
783 JSON::PC | 3571.444 | 2394.829 |
487 JSON::PC | 9901 | 2491 | 784 JSON::PP | 210.987 | 32.574 |
488 JSON::Syck | 2360 | 786 | 785 JSON::Syck | 552.551 | 787.544 |
489 JSON::XS | 37398 | 3202 | 786 JSON::XS | 5780.463 | 4854.519 |
490 JSON::XS/2 | 13765 | 3153 | 787 JSON::XS/2 | 3869.998 | 4798.975 |
788 JSON::XS/3 | 5862.880 | 4798.975 |
789 Storable | 4445.002 | 5235.027 |
491 -----------+------------+------------+ 790 -----------+------------+------------+
492 791
493 Again, JSON::XS leads by far in the encoding case, while still beating 792 Again, JSON::XS leads by far (except for Storable which non-surprisingly
494 every other module in the decoding case. 793 decodes faster).
495 794
496 On large strings containing lots of unicode characters, some modules 795 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 796 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 797 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 798 refuse to decode or encode properly, so it was impossible to prepare a
500 for that case. 799 fair comparison table for that case.
501 800
502RESOURCE LIMITS 801SECURITY CONSIDERATIONS
503 JSON::XS does not impose any limits on the size of JSON texts or Perl 802 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 803 hostile creatures requires relatively few measures.
505 encode or decode it. Future versions might optionally impose structure 804
506 depth and memory use resource limits. 805 First of all, your JSON decoder should be secure, that is, should not
806 have any buffer overflows. Obviously, this module should ensure that and
807 I am trying hard on making that true, but you never know.
808
809 Second, you need to avoid resource-starving attacks. That means you
810 should limit the size of JSON texts you accept, or make sure then when
811 your resources run out, thats just fine (e.g. by using a separate
812 process that can crash safely). The size of a JSON text in octets or
813 characters is usually a good indication of the size of the resources
814 required to decode it into a Perl structure. While JSON::XS can check
815 the size of the JSON text, it might be too late when you already have it
816 in memory, so you might want to check the size before you accept the
817 string.
818
819 Third, JSON::XS recurses using the C stack when decoding objects and
820 arrays. The C stack is a limited resource: for instance, on my amd64
821 machine with 8MB of stack size I can decode around 180k nested arrays
822 but only 14k nested JSON objects (due to perl itself recursing deeply on
823 croak to free the temporary). If that is exceeded, the program crashes.
824 to be conservative, the default nesting limit is set to 512. If your
825 process has a smaller stack, you should adjust this setting accordingly
826 with the "max_depth" method.
827
828 And last but least, something else could bomb you that I forgot to think
829 of. In that case, you get to keep the pieces. I am always open for
830 hints, though...
831
832 If you are using JSON::XS to return packets to consumption by javascript
833 scripts in a browser you should have a look at
834 <http://jpsykes.com/47/practical-csrf-and-json-security> to see wether
835 you are vulnerable to some common attack vectors (which really are
836 browser design bugs, but it is still you who will have to deal with it,
837 as major browser developers care only for features, not about doing
838 security right).
507 839
508BUGS 840BUGS
509 While the goal of this module is to be correct, that unfortunately does 841 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 842 not mean its 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 843 still relatively early in its development. If you keep reporting bugs
512 will be fixed swiftly, though. 844 they will be fixed swiftly, though.
513 845
514AUTHOR 846AUTHOR
515 Marc Lehmann <schmorp@schmorp.de> 847 Marc Lehmann <schmorp@schmorp.de>
516 http://home.schmorp.de/ 848 http://home.schmorp.de/
517 849

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