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Revision 1.18 by root, Tue Aug 28 02:06:06 2007 UTC

1NAME 1NAME
2 JSON::XS - JSON serialising/deserialising, done correctly and fast 2 JSON::XS - JSON serialising/deserialising, done correctly and fast
3 3
4SYNOPSIS 4SYNOPSIS
5 use JSON::XS; 5 use JSON::XS;
6
7 # exported functions, they croak on error
8 # and expect/generate UTF-8
9
10 $utf8_encoded_json_text = to_json $perl_hash_or_arrayref;
11 $perl_hash_or_arrayref = from_json $utf8_encoded_json_text;
12
13 # OO-interface
14
15 $coder = JSON::XS->new->ascii->pretty->allow_nonref;
16 $pretty_printed_unencoded = $coder->encode ($perl_scalar);
17 $perl_scalar = $coder->decode ($unicode_json_text);
6 18
7DESCRIPTION 19DESCRIPTION
8 This module converts Perl data structures to JSON and vice versa. Its 20 This module converts Perl data structures to JSON and vice versa. Its
9 primary goal is to be *correct* and its secondary goal is to be *fast*. 21 primary goal is to be *correct* and its secondary goal is to be *fast*.
10 To reach the latter goal it was written in C. 22 To reach the latter goal it was written in C.
… …
15 cases their maintainers are unresponsive, gone missing, or not listening 27 cases their maintainers are unresponsive, gone missing, or not listening
16 to bug reports for other reasons. 28 to bug reports for other reasons.
17 29
18 See COMPARISON, below, for a comparison to some other JSON modules. 30 See COMPARISON, below, for a comparison to some other JSON modules.
19 31
32 See MAPPING, below, on how JSON::XS maps perl values to JSON values and
33 vice versa.
34
20 FEATURES 35 FEATURES
21 * correct handling of unicode issues 36 * correct unicode handling
22 This module knows how to handle Unicode, and even documents how it 37 This module knows how to handle Unicode, and even documents how and
23 does so. 38 when it does so.
24 39
25 * round-trip integrity 40 * round-trip integrity
26 When you serialise a perl data structure using only datatypes 41 When you serialise a perl data structure using only datatypes
27 supported by JSON, the deserialised data structure is identical on 42 supported by JSON, the deserialised data structure is identical on
28 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).
29 45
30 * strict checking of JSON correctness 46 * strict checking of JSON correctness
31 There is no guessing, no generating of illegal JSON strings by 47 There is no guessing, no generating of illegal JSON texts by
32 default, and only JSON is accepted as input (the latter is a 48 default, and only JSON is accepted as input by default (the latter
33 security feature). 49 is a security feature).
34 50
35 * fast 51 * fast
36 compared to other JSON modules, this module compares favourably. 52 Compared to other JSON modules, this module compares favourably in
53 terms of speed, too.
37 54
38 * simple to use 55 * simple to use
39 This module has both a simple functional interface as well as an OO 56 This module has both a simple functional interface as well as an OO
40 interface. 57 interface.
41 58
42 * reasonably versatile output formats 59 * reasonably versatile output formats
43 You can choose between the most compact format possible, a 60 You can choose between the most compact guarenteed single-line
44 pure-ascii format, or a pretty-printed format. Or you can combine 61 format possible (nice for simple line-based protocols), a pure-ascii
62 format (for when your transport is not 8-bit clean, still supports
63 the whole unicode range), or a pretty-printed format (for when you
64 want to read that stuff). Or you can combine those features in
45 those features in whatever way you like. 65 whatever way you like.
46 66
47FUNCTIONAL INTERFACE 67FUNCTIONAL INTERFACE
48 The following convinience methods are provided by this module. They are 68 The following convinience methods are provided by this module. They are
49 exported by default: 69 exported by default:
50 70
51 $json_string = to_json $perl_scalar 71 $json_text = to_json $perl_scalar
52 Converts the given Perl data structure (a simple scalar or a 72 Converts the given Perl data structure (a simple scalar or a
53 reference to a hash or array) to a UTF-8 encoded, binary string 73 reference to a hash or array) to a UTF-8 encoded, binary string
54 (that is, the string contains octets only). Croaks on error. 74 (that is, the string contains octets only). Croaks on error.
55 75
56 This function call is functionally identical to "JSON::XS->new->utf8 76 This function call is functionally identical to:
57 (1)->encode ($perl_scalar)".
58 77
78 $json_text = JSON::XS->new->utf8->encode ($perl_scalar)
79
80 except being faster.
81
59 $perl_scalar = from_json $json_string 82 $perl_scalar = from_json $json_text
60 The opposite of "to_json": expects an UTF-8 (binary) string and 83 The opposite of "to_json": expects an UTF-8 (binary) string and
61 tries to parse that as an UTF-8 encoded JSON string, returning the 84 tries to parse that as an UTF-8 encoded JSON text, returning the
62 resulting simple scalar or reference. Croaks on error. 85 resulting simple scalar or reference. Croaks on error.
63 86
64 This function call is functionally identical to "JSON::XS->new->utf8 87 This function call is functionally identical to:
65 (1)->decode ($json_string)". 88
89 $perl_scalar = JSON::XS->new->utf8->decode ($json_text)
90
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.
66 101
67OBJECT-ORIENTED INTERFACE 102OBJECT-ORIENTED INTERFACE
68 The object oriented interface lets you configure your own encoding or 103 The object oriented interface lets you configure your own encoding or
69 decoding style, within the limits of supported formats. 104 decoding style, within the limits of supported formats.
70 105
… …
74 *disabled*. 109 *disabled*.
75 110
76 The mutators for flags all return the JSON object again and thus 111 The mutators for flags all return the JSON object again and thus
77 calls can be chained: 112 calls can be chained:
78 113
79 my $json = JSON::XS->new->utf8(1)->space_after(1)->encode ({a => [1,2]}) 114 my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]})
80 => {"a": [1, 2]} 115 => {"a": [1, 2]}
81 116
82 $json = $json->ascii ($enable) 117 $json = $json->ascii ([$enable])
83 If $enable is true, then the "encode" method will not generate 118 If $enable is true (or missing), then the "encode" method will not
84 characters outside the code range 0..127. Any unicode characters 119 generate characters outside the code range 0..127 (which is ASCII).
85 outside that range will be escaped using either a single \uXXXX (BMP 120 Any unicode characters outside that range will be escaped using
86 characters) or a double \uHHHH\uLLLLL escape sequence, as per 121 either a single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL
87 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.
88 126
89 If $enable is false, then the "encode" method will not escape 127 If $enable is false, then the "encode" method will not escape
90 Unicode characters unless necessary. 128 Unicode characters unless required by the JSON syntax or other
129 flags. This results in a faster and more compact format.
91 130
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.
134
92 JSON::XS->new->ascii (1)->encode (chr 0x10401) 135 JSON::XS->new->ascii (1)->encode ([chr 0x10401])
93 => \ud801\udc01 136 => ["\ud801\udc01"]
94 137
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)
162
95 $json = $json->utf8 ($enable) 163 $json = $json->utf8 ([$enable])
96 If $enable is true, then the "encode" method will encode the JSON 164 If $enable is true (or missing), then the "encode" method will
97 string into UTF-8, as required by many protocols, while the "decode" 165 encode the JSON result into UTF-8, as required by many protocols,
98 method expects to be handled an UTF-8-encoded string. Please note 166 while the "decode" method expects to be handled an UTF-8-encoded
99 that UTF-8-encoded strings do not contain any characters outside the 167 string. Please note that UTF-8-encoded strings do not contain any
100 range 0..255, they are thus useful for bytewise/binary I/O. 168 characters outside the range 0..255, they are thus useful for
169 bytewise/binary I/O. In future versions, enabling this option might
170 enable autodetection of the UTF-16 and UTF-32 encoding families, as
171 described in RFC4627.
101 172
102 If $enable is false, then the "encode" method will return the JSON 173 If $enable is false, then the "encode" method will return the JSON
103 string as a (non-encoded) unicode string, while "decode" expects 174 string as a (non-encoded) unicode string, while "decode" expects
104 thus a unicode string. Any decoding or encoding (e.g. to UTF-8 or 175 thus a unicode string. Any decoding or encoding (e.g. to UTF-8 or
105 UTF-16) needs to be done yourself, e.g. using the Encode module. 176 UTF-16) needs to be done yourself, e.g. using the Encode module.
106 177
178 Example, output UTF-16BE-encoded JSON:
179
180 use Encode;
181 $jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
182
183 Example, decode UTF-32LE-encoded JSON:
184
185 use Encode;
186 $object = JSON::XS->new->decode (decode "UTF-32LE", $jsontext);
187
107 $json = $json->pretty ($enable) 188 $json = $json->pretty ([$enable])
108 This enables (or disables) all of the "indent", "space_before" and 189 This enables (or disables) all of the "indent", "space_before" and
109 "space_after" (and in the future possibly more) flags in one call to 190 "space_after" (and in the future possibly more) flags in one call to
110 generate the most readable (or most compact) form possible. 191 generate the most readable (or most compact) form possible.
192
193 Example, pretty-print some simple structure:
111 194
112 my $json = JSON::XS->new->pretty(1)->encode ({a => [1,2]}) 195 my $json = JSON::XS->new->pretty(1)->encode ({a => [1,2]})
113 => 196 =>
114 { 197 {
115 "a" : [ 198 "a" : [
116 1, 199 1,
117 2 200 2
118 ] 201 ]
119 } 202 }
120 203
121 $json = $json->indent ($enable) 204 $json = $json->indent ([$enable])
122 If $enable is true, then the "encode" method will use a multiline 205 If $enable is true (or missing), then the "encode" method will use a
123 format as output, putting every array member or object/hash 206 multiline format as output, putting every array member or
124 key-value pair into its own line, identing them properly. 207 object/hash key-value pair into its own line, identing them
208 properly.
125 209
126 If $enable is false, no newlines or indenting will be produced, and 210 If $enable is false, no newlines or indenting will be produced, and
127 the resulting JSON strings is guarenteed not to contain any 211 the resulting JSON text is guarenteed not to contain any "newlines".
128 "newlines".
129 212
130 This setting has no effect when decoding JSON strings. 213 This setting has no effect when decoding JSON texts.
131 214
132 $json = $json->space_before ($enable) 215 $json = $json->space_before ([$enable])
133 If $enable is true, then the "encode" method will add an extra 216 If $enable is true (or missing), then the "encode" method will add
134 optional space before the ":" separating keys from values in JSON 217 an extra optional space before the ":" separating keys from values
135 objects. 218 in JSON objects.
136 219
137 If $enable is false, then the "encode" method will not add any extra 220 If $enable is false, then the "encode" method will not add any extra
138 space at those places. 221 space at those places.
139 222
140 This setting has no effect when decoding JSON strings. You will also 223 This setting has no effect when decoding JSON texts. You will also
141 most likely combine this setting with "space_after". 224 most likely combine this setting with "space_after".
142 225
226 Example, space_before enabled, space_after and indent disabled:
227
228 {"key" :"value"}
229
143 $json = $json->space_after ($enable) 230 $json = $json->space_after ([$enable])
144 If $enable is true, then the "encode" method will add an extra 231 If $enable is true (or missing), then the "encode" method will add
145 optional space after the ":" separating keys from values in JSON 232 an extra optional space after the ":" separating keys from values in
146 objects and extra whitespace after the "," separating key-value 233 JSON objects and extra whitespace after the "," separating key-value
147 pairs and array members. 234 pairs and array members.
148 235
149 If $enable is false, then the "encode" method will not add any extra 236 If $enable is false, then the "encode" method will not add any extra
150 space at those places. 237 space at those places.
151 238
152 This setting has no effect when decoding JSON strings. 239 This setting has no effect when decoding JSON texts.
153 240
241 Example, space_before and indent disabled, space_after enabled:
242
243 {"key": "value"}
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
273 * shell-style '#'-comments
274 Whenever JSON allows whitespace, shell-style comments are
275 additionally allowed. They are terminated by the first
276 carriage-return or line-feed character, after which more
277 white-space and comments are allowed.
278
279 [
280 1, # this comment not allowed in JSON
281 # neither this one...
282 ]
283
154 $json = $json->canonical ($enable) 284 $json = $json->canonical ([$enable])
155 If $enable is true, then the "encode" method will output JSON 285 If $enable is true (or missing), then the "encode" method will
156 objects by sorting their keys. This is adding a comparatively high 286 output JSON objects by sorting their keys. This is adding a
157 overhead. 287 comparatively high overhead.
158 288
159 If $enable is false, then the "encode" method will output key-value 289 If $enable is false, then the "encode" method will output key-value
160 pairs in the order Perl stores them (which will likely change 290 pairs in the order Perl stores them (which will likely change
161 between runs of the same script). 291 between runs of the same script).
162 292
163 This option is useful if you want the same data structure to be 293 This option is useful if you want the same data structure to be
164 encoded as the same JSON string (given the same overall settings). 294 encoded as the same JSON text (given the same overall settings). If
165 If it is disabled, the same hash migh be encoded differently even if 295 it is disabled, the same hash migh be encoded differently even if
166 contains the same data, as key-value pairs have no inherent ordering 296 contains the same data, as key-value pairs have no inherent ordering
167 in Perl. 297 in Perl.
168 298
169 This setting has no effect when decoding JSON strings. 299 This setting has no effect when decoding JSON texts.
170 300
171 $json = $json->allow_nonref ($enable) 301 $json = $json->allow_nonref ([$enable])
172 If $enable is true, then the "encode" method can convert a 302 If $enable is true (or missing), then the "encode" method can
173 non-reference into its corresponding string, number or null JSON 303 convert a non-reference into its corresponding string, number or
174 value, which is an extension to RFC4627. Likewise, "decode" will 304 null JSON value, which is an extension to RFC4627. Likewise,
175 accept those JSON values instead of croaking. 305 "decode" will accept those JSON values instead of croaking.
176 306
177 If $enable is false, then the "encode" method will croak if it isn't 307 If $enable is false, then the "encode" method will croak if it isn't
178 passed an arrayref or hashref, as JSON strings must either be an 308 passed an arrayref or hashref, as JSON texts must either be an
179 object or array. Likewise, "decode" will croak if given something 309 object or array. Likewise, "decode" will croak if given something
180 that is not a JSON object or array. 310 that is not a JSON object or array.
181 311
312 Example, encode a Perl scalar as JSON value with enabled
313 "allow_nonref", resulting in an invalid JSON text:
314
315 JSON::XS->new->allow_nonref->encode ("Hello, World!")
316 => "Hello, World!"
317
318 $json = $json->allow_blessed ([$enable])
319 If $enable is true (or missing), then the "encode" method will not
320 barf when it encounters a blessed reference. Instead, the value of
321 the convert_blessed option will decide wether "null"
322 ("convert_blessed" disabled or no "to_json" method found) or a
323 representation of the object ("convert_blessed" enabled and
324 "to_json" method found) is being encoded. Has no effect on "decode".
325
326 If $enable is false (the default), then "encode" will throw an
327 exception when it encounters a blessed object.
328
329 $json = $json->convert_blessed ([$enable])
330 If $enable is true (or missing), then "encode", upon encountering a
331 blessed object, will check for the availability of the "TO_JSON"
332 method on the object's class. If found, it will be called in scalar
333 context and the resulting scalar will be encoded instead of the
334 object. If no "TO_JSON" method is found, the value of
335 "allow_blessed" will decide what to do.
336
337 The "TO_JSON" method may safely call die if it wants. If "TO_JSON"
338 returns other blessed objects, those will be handled in the same
339 way. "TO_JSON" must take care of not causing an endless recursion
340 cycle (== crash) in this case. The name of "TO_JSON" was chosen
341 because other methods called by the Perl core (== not by the user of
342 the object) are usually in upper case letters and to avoid
343 collisions with the "to_json" function.
344
345 This setting does not yet influence "decode" in any way, but in the
346 future, global hooks might get installed that influence "decode" and
347 are enabled by this setting.
348
349 If $enable is false, then the "allow_blessed" setting will decide
350 what to do when a blessed object is found.
351
352 $json = $json->filter_json_object ([$coderef->($hashref)])
353 When $coderef is specified, it will be called from "decode" each
354 time it decodes a JSON object. The only argument is a reference to
355 the newly-created hash. If the code references returns a single
356 scalar (which need not be a reference), this value (i.e. a copy of
357 that scalar to avoid aliasing) is inserted into the deserialised
358 data structure. If it returns an empty list (NOTE: *not* "undef",
359 which is a valid scalar), the original deserialised hash will be
360 inserted. This setting can slow down decoding considerably.
361
362 When $coderef is omitted or undefined, any existing callback will be
363 removed and "decode" will not change the deserialised hash in any
364 way.
365
366 Example, convert all JSON objects into the integer 5:
367
368 my $js = JSON::XS->new->filter_json_object (sub { 5 });
369 # returns [5]
370 $js->decode ('[{}]')
371 # throw an exception because allow_nonref is not enabled
372 # so a lone 5 is not allowed.
373 $js->decode ('{"a":1, "b":2}');
374
375 $json = $json->filter_json_single_key_object ($key [=>
376 $coderef->($value)])
377 Works remotely similar to "filter_json_object", but is only called
378 for JSON objects having a single key named $key.
379
380 This $coderef is called before the one specified via
381 "filter_json_object", if any. It gets passed the single value in the
382 JSON object. If it returns a single value, it will be inserted into
383 the data structure. If it returns nothing (not even "undef" but the
384 empty list), the callback from "filter_json_object" will be called
385 next, as if no single-key callback were specified.
386
387 If $coderef is omitted or undefined, the corresponding callback will
388 be disabled. There can only ever be one callback for a given key.
389
390 As this callback gets called less often then the
391 "filter_json_object" one, decoding speed will not usually suffer as
392 much. Therefore, single-key objects make excellent targets to
393 serialise Perl objects into, especially as single-key JSON objects
394 are as close to the type-tagged value concept as JSON gets (its
395 basically an ID/VALUE tuple). Of course, JSON does not support this
396 in any way, so you need to make sure your data never looks like a
397 serialised Perl hash.
398
399 Typical names for the single object key are "__class_whatever__", or
400 "$__dollars_are_rarely_used__$" or "}ugly_brace_placement", or even
401 things like "__class_md5sum(classname)__", to reduce the risk of
402 clashing with real hashes.
403
404 Example, decode JSON objects of the form "{ "__widget__" => <id> }"
405 into the corresponding $WIDGET{<id>} object:
406
407 # return whatever is in $WIDGET{5}:
408 JSON::XS
409 ->new
410 ->filter_json_single_key_object (__widget__ => sub {
411 $WIDGET{ $_[0] }
412 })
413 ->decode ('{"__widget__": 5')
414
415 # this can be used with a TO_JSON method in some "widget" class
416 # for serialisation to json:
417 sub WidgetBase::TO_JSON {
418 my ($self) = @_;
419
420 unless ($self->{id}) {
421 $self->{id} = ..get..some..id..;
422 $WIDGET{$self->{id}} = $self;
423 }
424
425 { __widget__ => $self->{id} }
426 }
427
428 $json = $json->shrink ([$enable])
429 Perl usually over-allocates memory a bit when allocating space for
430 strings. This flag optionally resizes strings generated by either
431 "encode" or "decode" to their minimum size possible. This can save
432 memory when your JSON texts are either very very long or you have
433 many short strings. It will also try to downgrade any strings to
434 octet-form if possible: perl stores strings internally either in an
435 encoding called UTF-X or in octet-form. The latter cannot store
436 everything but uses less space in general (and some buggy Perl or C
437 code might even rely on that internal representation being used).
438
439 The actual definition of what shrink does might change in future
440 versions, but it will always try to save space at the expense of
441 time.
442
443 If $enable is true (or missing), the string returned by "encode"
444 will be shrunk-to-fit, while all strings generated by "decode" will
445 also be shrunk-to-fit.
446
447 If $enable is false, then the normal perl allocation algorithms are
448 used. If you work with your data, then this is likely to be faster.
449
450 In the future, this setting might control other things, such as
451 converting strings that look like integers or floats into integers
452 or floats internally (there is no difference on the Perl level),
453 saving space.
454
455 $json = $json->max_depth ([$maximum_nesting_depth])
456 Sets the maximum nesting level (default 512) accepted while encoding
457 or decoding. If the JSON text or Perl data structure has an equal or
458 higher nesting level then this limit, then the encoder and decoder
459 will stop and croak at that point.
460
461 Nesting level is defined by number of hash- or arrayrefs that the
462 encoder needs to traverse to reach a given point or the number of
463 "{" or "[" characters without their matching closing parenthesis
464 crossed to reach a given character in a string.
465
466 Setting the maximum depth to one disallows any nesting, so that
467 ensures that the object is only a single hash/object or array.
468
469 The argument to "max_depth" will be rounded up to the next highest
470 power of two. If no argument is given, the highest possible setting
471 will be used, which is rarely useful.
472
473 See SECURITY CONSIDERATIONS, below, for more info on why this is
474 useful.
475
476 $json = $json->max_size ([$maximum_string_size])
477 Set the maximum length a JSON text may have (in bytes) where
478 decoding is being attempted. The default is 0, meaning no limit.
479 When "decode" is called on a string longer then this number of
480 characters it will not attempt to decode the string but throw an
481 exception. This setting has no effect on "encode" (yet).
482
483 The argument to "max_size" will be rounded up to the next highest
484 power of two (so may be more than requested). If no argument is
485 given, the limit check will be deactivated (same as when 0 is
486 specified).
487
488 See SECURITY CONSIDERATIONS, below, for more info on why this is
489 useful.
490
182 $json_string = $json->encode ($perl_scalar) 491 $json_text = $json->encode ($perl_scalar)
183 Converts the given Perl data structure (a simple scalar or a 492 Converts the given Perl data structure (a simple scalar or a
184 reference to a hash or array) to its JSON representation. Simple 493 reference to a hash or array) to its JSON representation. Simple
185 scalars will be converted into JSON string or number sequences, 494 scalars will be converted into JSON string or number sequences,
186 while references to arrays become JSON arrays and references to 495 while references to arrays become JSON arrays and references to
187 hashes become JSON objects. Undefined Perl values (e.g. "undef") 496 hashes become JSON objects. Undefined Perl values (e.g. "undef")
188 become JSON "null" values. Neither "true" nor "false" values will be 497 become JSON "null" values. Neither "true" nor "false" values will be
189 generated. 498 generated.
190 499
191 $perl_scalar = $json->decode ($json_string) 500 $perl_scalar = $json->decode ($json_text)
192 The opposite of "encode": expects a JSON string and tries to parse 501 The opposite of "encode": expects a JSON text and tries to parse it,
193 it, returning the resulting simple scalar or reference. Croaks on 502 returning the resulting simple scalar or reference. Croaks on error.
194 error.
195 503
196 JSON numbers and strings become simple Perl scalars. JSON arrays 504 JSON numbers and strings become simple Perl scalars. JSON arrays
197 become Perl arrayrefs and JSON objects become Perl hashrefs. "true" 505 become Perl arrayrefs and JSON objects become Perl hashrefs. "true"
198 becomes 1, "false" becomes 0 and "null" becomes "undef". 506 becomes 1, "false" becomes 0 and "null" becomes "undef".
507
508 ($perl_scalar, $characters) = $json->decode_prefix ($json_text)
509 This works like the "decode" method, but instead of raising an
510 exception when there is trailing garbage after the first JSON
511 object, it will silently stop parsing there and return the number of
512 characters consumed so far.
513
514 This is useful if your JSON texts are not delimited by an outer
515 protocol (which is not the brightest thing to do in the first place)
516 and you need to know where the JSON text ends.
517
518 JSON::XS->new->decode_prefix ("[1] the tail")
519 => ([], 3)
520
521MAPPING
522 This section describes how JSON::XS maps Perl values to JSON values and
523 vice versa. These mappings are designed to "do the right thing" in most
524 circumstances automatically, preserving round-tripping characteristics
525 (what you put in comes out as something equivalent).
526
527 For the more enlightened: note that in the following descriptions,
528 lowercase *perl* refers to the Perl interpreter, while uppcercase *Perl*
529 refers to the abstract Perl language itself.
530
531 JSON -> PERL
532 object
533 A JSON object becomes a reference to a hash in Perl. No ordering of
534 object keys is preserved (JSON does not preserver object key
535 ordering itself).
536
537 array
538 A JSON array becomes a reference to an array in Perl.
539
540 string
541 A JSON string becomes a string scalar in Perl - Unicode codepoints
542 in JSON are represented by the same codepoints in the Perl string,
543 so no manual decoding is necessary.
544
545 number
546 A JSON number becomes either an integer, numeric (floating point) or
547 string scalar in perl, depending on its range and any fractional
548 parts. On the Perl level, there is no difference between those as
549 Perl handles all the conversion details, but an integer may take
550 slightly less memory and might represent more values exactly than
551 (floating point) numbers.
552
553 If the number consists of digits only, JSON::XS will try to
554 represent it as an integer value. If that fails, it will try to
555 represent it as a numeric (floating point) value if that is possible
556 without loss of precision. Otherwise it will preserve the number as
557 a string value.
558
559 Numbers containing a fractional or exponential part will always be
560 represented as numeric (floating point) values, possibly at a loss
561 of precision.
562
563 This might create round-tripping problems as numbers might become
564 strings, but as Perl is typeless there is no other way to do it.
565
566 true, false
567 These JSON atoms become "JSON::XS::true" and "JSON::XS::false",
568 respectively. They are overloaded to act almost exactly like the
569 numbers 1 and 0. You can check wether a scalar is a JSON boolean by
570 using the "JSON::XS::is_bool" function.
571
572 null
573 A JSON null atom becomes "undef" in Perl.
574
575 PERL -> JSON
576 The mapping from Perl to JSON is slightly more difficult, as Perl is a
577 truly typeless language, so we can only guess which JSON type is meant
578 by a Perl value.
579
580 hash references
581 Perl hash references become JSON objects. As there is no inherent
582 ordering in hash keys (or JSON objects), they will usually be
583 encoded in a pseudo-random order that can change between runs of the
584 same program but stays generally the same within a single run of a
585 program. JSON::XS can optionally sort the hash keys (determined by
586 the *canonical* flag), so the same datastructure will serialise to
587 the same JSON text (given same settings and version of JSON::XS),
588 but this incurs a runtime overhead and is only rarely useful, e.g.
589 when you want to compare some JSON text against another for
590 equality.
591
592 array references
593 Perl array references become JSON arrays.
594
595 other references
596 Other unblessed references are generally not allowed and will cause
597 an exception to be thrown, except for references to the integers 0
598 and 1, which get turned into "false" and "true" atoms in JSON. You
599 can also use "JSON::XS::false" and "JSON::XS::true" to improve
600 readability.
601
602 to_json [\0,JSON::XS::true] # yields [false,true]
603
604 JSON::XS::true, JSON::XS::false
605 These special values become JSON true and JSON false values,
606 respectively. You cna alos use "\1" and "\0" directly if you want.
607
608 blessed objects
609 Blessed objects are not allowed. JSON::XS currently tries to encode
610 their underlying representation (hash- or arrayref), but this
611 behaviour might change in future versions.
612
613 simple scalars
614 Simple Perl scalars (any scalar that is not a reference) are the
615 most difficult objects to encode: JSON::XS will encode undefined
616 scalars as JSON null value, scalars that have last been used in a
617 string context before encoding as JSON strings and anything else as
618 number value:
619
620 # dump as number
621 to_json [2] # yields [2]
622 to_json [-3.0e17] # yields [-3e+17]
623 my $value = 5; to_json [$value] # yields [5]
624
625 # used as string, so dump as string
626 print $value;
627 to_json [$value] # yields ["5"]
628
629 # undef becomes null
630 to_json [undef] # yields [null]
631
632 You can force the type to be a string by stringifying it:
633
634 my $x = 3.1; # some variable containing a number
635 "$x"; # stringified
636 $x .= ""; # another, more awkward way to stringify
637 print $x; # perl does it for you, too, quite often
638
639 You can force the type to be a number by numifying it:
640
641 my $x = "3"; # some variable containing a string
642 $x += 0; # numify it, ensuring it will be dumped as a number
643 $x *= 1; # same thing, the choise is yours.
644
645 You can not currently output JSON booleans or force the type in
646 other, less obscure, ways. Tell me if you need this capability.
199 647
200COMPARISON 648COMPARISON
201 As already mentioned, this module was created because none of the 649 As already mentioned, this module was created because none of the
202 existing JSON modules could be made to work correctly. First I will 650 existing JSON modules could be made to work correctly. First I will
203 describe the problems (or pleasures) I encountered with various existing 651 describe the problems (or pleasures) I encountered with various existing
204 JSON modules, followed by some benchmark values. JSON::XS was designed 652 JSON modules, followed by some benchmark values. JSON::XS was designed
205 not to suffer from any of these problems or limitations. 653 not to suffer from any of these problems or limitations.
206 654
207 JSON 655 JSON 1.07
208 Slow (but very portable, as it is written in pure Perl). 656 Slow (but very portable, as it is written in pure Perl).
209 657
210 Undocumented/buggy Unicode handling (how JSON handles unicode values 658 Undocumented/buggy Unicode handling (how JSON handles unicode values
211 is undocumented. One can get far by feeding it unicode strings and 659 is undocumented. One can get far by feeding it unicode strings and
212 doing en-/decoding oneself, but unicode escapes are not working 660 doing en-/decoding oneself, but unicode escapes are not working
… …
214 662
215 No roundtripping (strings get clobbered if they look like numbers, 663 No roundtripping (strings get clobbered if they look like numbers,
216 e.g. the string 2.0 will encode to 2.0 instead of "2.0", and that 664 e.g. the string 2.0 will encode to 2.0 instead of "2.0", and that
217 will decode into the number 2. 665 will decode into the number 2.
218 666
219 JSON::PC 667 JSON::PC 0.01
220 Very fast. 668 Very fast.
221 669
222 Undocumented/buggy Unicode handling. 670 Undocumented/buggy Unicode handling.
223 671
224 No roundtripping. 672 No roundtripping.
225 673
226 Has problems handling many Perl values (e.g. regex results and other 674 Has problems handling many Perl values (e.g. regex results and other
227 magic values will make it croak). 675 magic values will make it croak).
228 676
229 Does not even generate valid JSON ("{1,2}" gets converted to "{1:2}" 677 Does not even generate valid JSON ("{1,2}" gets converted to "{1:2}"
230 which is not a valid JSON string. 678 which is not a valid JSON text.
231 679
232 Unmaintained (maintainer unresponsive for many months, bugs are not 680 Unmaintained (maintainer unresponsive for many months, bugs are not
233 getting fixed). 681 getting fixed).
234 682
235 JSON::Syck 683 JSON::Syck 0.21
236 Very buggy (often crashes). 684 Very buggy (often crashes).
237 685
238 Very inflexible (no human-readable format supported, format pretty 686 Very inflexible (no human-readable format supported, format pretty
239 much undocumented. I need at least a format for easy reading by 687 much undocumented. I need at least a format for easy reading by
240 humans and a single-line compact format for use in a protocol, and 688 humans and a single-line compact format for use in a protocol, and
241 preferably a way to generate ASCII-only JSON strings). 689 preferably a way to generate ASCII-only JSON texts).
242 690
243 Completely broken (and confusingly documented) Unicode handling 691 Completely broken (and confusingly documented) Unicode handling
244 (unicode escapes are not working properly, you need to set 692 (unicode escapes are not working properly, you need to set
245 ImplicitUnicode to *different* values on en- and decoding to get 693 ImplicitUnicode to *different* values on en- and decoding to get
246 symmetric behaviour). 694 symmetric behaviour).
… …
259 other using JSON. One bank might parse a given non-JSON request and 707 other using JSON. One bank might parse a given non-JSON request and
260 deduct money, while the other might reject the transaction with a 708 deduct money, while the other might reject the transaction with a
261 syntax error. While a good protocol will at least recover, that is 709 syntax error. While a good protocol will at least recover, that is
262 extra unnecessary work and the transaction will still not succeed). 710 extra unnecessary work and the transaction will still not succeed).
263 711
264 JSON::DWIW 712 JSON::DWIW 0.04
265 Very fast. Very natural. Very nice. 713 Very fast. Very natural. Very nice.
266 714
267 Undocumented unicode handling (but the best of the pack. Unicode 715 Undocumented unicode handling (but the best of the pack. Unicode
268 escapes still don't get parsed properly). 716 escapes still don't get parsed properly).
269 717
270 Very inflexible. 718 Very inflexible.
271 719
272 No roundtripping. 720 No roundtripping.
273 721
274 Does not generate valid JSON (key strings are often unquoted, empty 722 Does not generate valid JSON texts (key strings are often unquoted,
275 keys result in nothing being output) 723 empty keys result in nothing being output)
276 724
277 Does not check input for validity. 725 Does not check input for validity.
726
727 JSON and YAML
728 You often hear that JSON is a subset (or a close subset) of YAML. This
729 is, however, a mass hysteria and very far from the truth. In general,
730 there is no way to configure JSON::XS to output a data structure as
731 valid YAML.
732
733 If you really must use JSON::XS to generate YAML, you should use this
734 algorithm (subject to change in future versions):
735
736 my $to_yaml = JSON::XS->new->utf8->space_after (1);
737 my $yaml = $to_yaml->encode ($ref) . "\n";
738
739 This will usually generate JSON texts that also parse as valid YAML.
740 Please note that YAML has hardcoded limits on (simple) object key
741 lengths that JSON doesn't have, so you should make sure that your hash
742 keys are noticably shorter than the 1024 characters YAML allows.
743
744 There might be other incompatibilities that I am not aware of. In
745 general you should not try to generate YAML with a JSON generator or
746 vice versa, or try to parse JSON with a YAML parser or vice versa:
747 chances are high that you will run into severe interoperability
748 problems.
278 749
279 SPEED 750 SPEED
280 It seems that JSON::XS is surprisingly fast, as shown in the following 751 It seems that JSON::XS is surprisingly fast, as shown in the following
281 tables. They have been generated with the help of the "eg/bench" program 752 tables. They have been generated with the help of the "eg/bench" program
282 in the JSON::XS distribution, to make it easy to compare on your own 753 in the JSON::XS distribution, to make it easy to compare on your own
283 system. 754 system.
284 755
285 First is a comparison between various modules using a very simple JSON 756 First comes a comparison between various modules using a very short
757 single-line JSON string:
758
759 {"method": "handleMessage", "params": ["user1", "we were just talking"], \
760 "id": null, "array":[1,11,234,-5,1e5,1e7, true, false]}
761
286 string, showing the number of encodes/decodes per second (JSON::XS is 762 It shows the number of encodes/decodes per second (JSON::XS uses the
287 the functional interface, while JSON::XS/2 is the OO interface with 763 functional interface, while JSON::XS/2 uses the OO interface with
288 pretty-printing and hashkey sorting enabled). 764 pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink).
765 Higher is better:
289 766
767 Storable | 15779.925 | 14169.946 |
768 -----------+------------+------------+
290 module | encode | decode | 769 module | encode | decode |
291 -----------|------------|------------| 770 -----------|------------|------------|
292 JSON | 14006 | 6820 | 771 JSON | 4990.842 | 4088.813 |
293 JSON::DWIW | 200937 | 120386 | 772 JSON::DWIW | 51653.990 | 71575.154 |
294 JSON::PC | 85065 | 129366 | 773 JSON::PC | 65948.176 | 74631.744 |
295 JSON::Syck | 59898 | 44232 | 774 JSON::PP | 8931.652 | 3817.168 |
296 JSON::XS | 1171478 | 342435 | 775 JSON::Syck | 24877.248 | 27776.848 |
297 JSON::XS/2 | 730760 | 328714 | 776 JSON::XS | 388361.481 | 227951.304 |
777 JSON::XS/2 | 227951.304 | 218453.333 |
778 JSON::XS/3 | 338250.323 | 218453.333 |
779 Storable | 16500.016 | 135300.129 |
298 -----------+------------+------------+ 780 -----------+------------+------------+
299 781
300 That is, JSON::XS is 6 times faster than than JSON::DWIW and about 80 782 That is, JSON::XS is about five times faster than JSON::DWIW on
783 encoding, about three times faster on decoding, and over fourty times
301 times faster than JSON, even with pretty-printing and key sorting. 784 faster than JSON, even with pretty-printing and key sorting. It also
785 compares favourably to Storable for small amounts of data.
302 786
303 Using a longer test string (roughly 8KB, generated from Yahoo! Locals 787 Using a longer test string (roughly 18KB, generated from Yahoo! Locals
304 search API (http://nanoref.com/yahooapis/mgPdGg): 788 search API (http://nanoref.com/yahooapis/mgPdGg):
305 789
306 module | encode | decode | 790 module | encode | decode |
307 -----------|------------|------------| 791 -----------|------------|------------|
308 JSON | 673 | 38 | 792 JSON | 55.260 | 34.971 |
309 JSON::DWIW | 5271 | 770 | 793 JSON::DWIW | 825.228 | 1082.513 |
794 JSON::PC | 3571.444 | 2394.829 |
310 JSON::PC | 9901 | 2491 | 795 JSON::PP | 210.987 | 32.574 |
311 JSON::Syck | 2360 | 786 | 796 JSON::Syck | 552.551 | 787.544 |
312 JSON::XS | 37398 | 3202 | 797 JSON::XS | 5780.463 | 4854.519 |
313 JSON::XS/2 | 13765 | 3153 | 798 JSON::XS/2 | 3869.998 | 4798.975 |
799 JSON::XS/3 | 5862.880 | 4798.975 |
800 Storable | 4445.002 | 5235.027 |
314 -----------+------------+------------+ 801 -----------+------------+------------+
315 802
316 Again, JSON::XS leads by far in the encoding case, while still beating 803 Again, JSON::XS leads by far (except for Storable which non-surprisingly
317 every other module in the decoding case. 804 decodes faster).
318 805
319 Last example is an almost 8MB large hash with many large binary values 806 On large strings containing lots of high unicode characters, some
320 (PNG files), resulting in a lot of escaping: 807 modules (such as JSON::PC) seem to decode faster than JSON::XS, but the
808 result will be broken due to missing (or wrong) unicode handling. Others
809 refuse to decode or encode properly, so it was impossible to prepare a
810 fair comparison table for that case.
811
812SECURITY CONSIDERATIONS
813 When you are using JSON in a protocol, talking to untrusted potentially
814 hostile creatures requires relatively few measures.
815
816 First of all, your JSON decoder should be secure, that is, should not
817 have any buffer overflows. Obviously, this module should ensure that and
818 I am trying hard on making that true, but you never know.
819
820 Second, you need to avoid resource-starving attacks. That means you
821 should limit the size of JSON texts you accept, or make sure then when
822 your resources run out, thats just fine (e.g. by using a separate
823 process that can crash safely). The size of a JSON text in octets or
824 characters is usually a good indication of the size of the resources
825 required to decode it into a Perl structure. While JSON::XS can check
826 the size of the JSON text, it might be too late when you already have it
827 in memory, so you might want to check the size before you accept the
828 string.
829
830 Third, JSON::XS recurses using the C stack when decoding objects and
831 arrays. The C stack is a limited resource: for instance, on my amd64
832 machine with 8MB of stack size I can decode around 180k nested arrays
833 but only 14k nested JSON objects (due to perl itself recursing deeply on
834 croak to free the temporary). If that is exceeded, the program crashes.
835 to be conservative, the default nesting limit is set to 512. If your
836 process has a smaller stack, you should adjust this setting accordingly
837 with the "max_depth" method.
838
839 And last but least, something else could bomb you that I forgot to think
840 of. In that case, you get to keep the pieces. I am always open for
841 hints, though...
842
843 If you are using JSON::XS to return packets to consumption by javascript
844 scripts in a browser you should have a look at
845 <http://jpsykes.com/47/practical-csrf-and-json-security> to see wether
846 you are vulnerable to some common attack vectors (which really are
847 browser design bugs, but it is still you who will have to deal with it,
848 as major browser developers care only for features, not about doing
849 security right).
321 850
322BUGS 851BUGS
323 While the goal of this module is to be correct, that unfortunately does 852 While the goal of this module is to be correct, that unfortunately does
324 not mean its bug-free, only that I think its design is bug-free. It is 853 not mean its bug-free, only that I think its design is bug-free. It is
325 still very young and not well-tested. If you keep reporting bugs they 854 still relatively early in its development. If you keep reporting bugs
326 will be fixed swiftly, though. 855 they will be fixed swiftly, though.
327 856
328AUTHOR 857AUTHOR
329 Marc Lehmann <schmorp@schmorp.de> 858 Marc Lehmann <schmorp@schmorp.de>
330 http://home.schmorp.de/ 859 http://home.schmorp.de/
331 860

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