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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
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
154 $json = $json->canonical ($enable) 273 $json = $json->canonical ([$enable])
155 If $enable is true, then the "encode" method will output JSON 274 If $enable is true (or missing), then the "encode" method will
156 objects by sorting their keys. This is adding a comparatively high 275 output JSON objects by sorting their keys. This is adding a
157 overhead. 276 comparatively high overhead.
158 277
159 If $enable is false, then the "encode" method will output key-value 278 If $enable is false, then the "encode" method will output key-value
160 pairs in the order Perl stores them (which will likely change 279 pairs in the order Perl stores them (which will likely change
161 between runs of the same script). 280 between runs of the same script).
162 281
163 This option is useful if you want the same data structure to be 282 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). 283 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 284 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 285 contains the same data, as key-value pairs have no inherent ordering
167 in Perl. 286 in Perl.
168 287
169 This setting has no effect when decoding JSON strings. 288 This setting has no effect when decoding JSON texts.
170 289
171 $json = $json->allow_nonref ($enable) 290 $json = $json->allow_nonref ([$enable])
172 If $enable is true, then the "encode" method can convert a 291 If $enable is true (or missing), then the "encode" method can
173 non-reference into its corresponding string, number or null JSON 292 convert a non-reference into its corresponding string, number or
174 value, which is an extension to RFC4627. Likewise, "decode" will 293 null JSON value, which is an extension to RFC4627. Likewise,
175 accept those JSON values instead of croaking. 294 "decode" will accept those JSON values instead of croaking.
176 295
177 If $enable is false, then the "encode" method will croak if it isn't 296 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 297 passed an arrayref or hashref, as JSON texts must either be an
179 object or array. Likewise, "decode" will croak if given something 298 object or array. Likewise, "decode" will croak if given something
180 that is not a JSON object or array. 299 that is not a JSON object or array.
181 300
301 Example, encode a Perl scalar as JSON value with enabled
302 "allow_nonref", resulting in an invalid JSON text:
303
304 JSON::XS->new->allow_nonref->encode ("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 }
416
417 $json = $json->shrink ([$enable])
418 Perl usually over-allocates memory a bit when allocating space for
419 strings. This flag optionally resizes strings generated by either
420 "encode" or "decode" to their minimum size possible. This can save
421 memory when your JSON texts are either very very long or you have
422 many short strings. It will also try to downgrade any strings to
423 octet-form if possible: perl stores strings internally either in an
424 encoding called UTF-X or in octet-form. The latter cannot store
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.
431
432 If $enable is true (or missing), the string returned by "encode"
433 will be shrunk-to-fit, while all strings generated by "decode" will
434 also be shrunk-to-fit.
435
436 If $enable is false, then the normal perl allocation algorithms are
437 used. If you work with your data, then this is likely to be faster.
438
439 In the future, this setting might control other things, such as
440 converting strings that look like integers or floats into integers
441 or floats internally (there is no difference on the Perl level),
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.
479
182 $json_string = $json->encode ($perl_scalar) 480 $json_text = $json->encode ($perl_scalar)
183 Converts the given Perl data structure (a simple scalar or a 481 Converts the given Perl data structure (a simple scalar or a
184 reference to a hash or array) to its JSON representation. Simple 482 reference to a hash or array) to its JSON representation. Simple
185 scalars will be converted into JSON string or number sequences, 483 scalars will be converted into JSON string or number sequences,
186 while references to arrays become JSON arrays and references to 484 while references to arrays become JSON arrays and references to
187 hashes become JSON objects. Undefined Perl values (e.g. "undef") 485 hashes become JSON objects. Undefined Perl values (e.g. "undef")
188 become JSON "null" values. Neither "true" nor "false" values will be 486 become JSON "null" values. Neither "true" nor "false" values will be
189 generated. 487 generated.
190 488
191 $perl_scalar = $json->decode ($json_string) 489 $perl_scalar = $json->decode ($json_text)
192 The opposite of "encode": expects a JSON string and tries to parse 490 The opposite of "encode": expects a JSON text and tries to parse it,
193 it, returning the resulting simple scalar or reference. Croaks on 491 returning the resulting simple scalar or reference. Croaks on error.
194 error.
195 492
196 JSON numbers and strings become simple Perl scalars. JSON arrays 493 JSON numbers and strings become simple Perl scalars. JSON arrays
197 become Perl arrayrefs and JSON objects become Perl hashrefs. "true" 494 become Perl arrayrefs and JSON objects become Perl hashrefs. "true"
198 becomes 1, "false" becomes 0 and "null" becomes "undef". 495 becomes 1, "false" becomes 0 and "null" becomes "undef".
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
510MAPPING
511 This section describes how JSON::XS maps Perl values to JSON values and
512 vice versa. These mappings are designed to "do the right thing" in most
513 circumstances automatically, preserving round-tripping characteristics
514 (what you put in comes out as something equivalent).
515
516 For the more enlightened: note that in the following descriptions,
517 lowercase *perl* refers to the Perl interpreter, while uppcercase *Perl*
518 refers to the abstract Perl language itself.
519
520 JSON -> PERL
521 object
522 A JSON object becomes a reference to a hash in Perl. No ordering of
523 object keys is preserved (JSON does not preserver object key
524 ordering itself).
525
526 array
527 A JSON array becomes a reference to an array in Perl.
528
529 string
530 A JSON string becomes a string scalar in Perl - Unicode codepoints
531 in JSON are represented by the same codepoints in the Perl string,
532 so no manual decoding is necessary.
533
534 number
535 A JSON number becomes either an integer, numeric (floating point) or
536 string scalar in perl, depending on its range and any fractional
537 parts. On the Perl level, there is no difference between those as
538 Perl handles all the conversion details, but an integer may take
539 slightly less memory and might represent more values exactly than
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.
554
555 true, false
556 These JSON atoms become "JSON::XS::true" and "JSON::XS::false",
557 respectively. They are overloaded to act almost exactly like the
558 numbers 1 and 0. You can check wether a scalar is a JSON boolean by
559 using the "JSON::XS::is_bool" function.
560
561 null
562 A JSON null atom becomes "undef" in Perl.
563
564 PERL -> JSON
565 The mapping from Perl to JSON is slightly more difficult, as Perl is a
566 truly typeless language, so we can only guess which JSON type is meant
567 by a Perl value.
568
569 hash references
570 Perl hash references become JSON objects. As there is no inherent
571 ordering in hash keys (or JSON objects), they will usually be
572 encoded in a pseudo-random order that can change between runs of the
573 same program but stays generally the same within a single run of a
574 program. JSON::XS can optionally sort the hash keys (determined by
575 the *canonical* flag), so the same datastructure will serialise to
576 the same JSON text (given same settings and version of JSON::XS),
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.
580
581 array references
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.
596
597 blessed objects
598 Blessed objects are not allowed. JSON::XS currently tries to encode
599 their underlying representation (hash- or arrayref), but this
600 behaviour might change in future versions.
601
602 simple scalars
603 Simple Perl scalars (any scalar that is not a reference) are the
604 most difficult objects to encode: JSON::XS will encode undefined
605 scalars as JSON null value, scalars that have last been used in a
606 string context before encoding as JSON strings and anything else as
607 number value:
608
609 # dump as number
610 to_json [2] # yields [2]
611 to_json [-3.0e17] # yields [-3e+17]
612 my $value = 5; to_json [$value] # yields [5]
613
614 # used as string, so dump as string
615 print $value;
616 to_json [$value] # yields ["5"]
617
618 # undef becomes null
619 to_json [undef] # yields [null]
620
621 You can force the type to be a string by stringifying it:
622
623 my $x = 3.1; # some variable containing a number
624 "$x"; # stringified
625 $x .= ""; # another, more awkward way to stringify
626 print $x; # perl does it for you, too, quite often
627
628 You can force the type to be a number by numifying it:
629
630 my $x = "3"; # some variable containing a string
631 $x += 0; # numify it, ensuring it will be dumped as a number
632 $x *= 1; # same thing, the choise is yours.
633
634 You can not currently output JSON booleans or force the type in
635 other, less obscure, ways. Tell me if you need this capability.
199 636
200COMPARISON 637COMPARISON
201 As already mentioned, this module was created because none of the 638 As already mentioned, this module was created because none of the
202 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
203 describe the problems (or pleasures) I encountered with various existing 640 describe the problems (or pleasures) I encountered with various existing
204 JSON modules, followed by some benchmark values. JSON::XS was designed 641 JSON modules, followed by some benchmark values. JSON::XS was designed
205 not to suffer from any of these problems or limitations. 642 not to suffer from any of these problems or limitations.
206 643
207 JSON 644 JSON 1.07
208 Slow (but very portable, as it is written in pure Perl). 645 Slow (but very portable, as it is written in pure Perl).
209 646
210 Undocumented/buggy Unicode handling (how JSON handles unicode values 647 Undocumented/buggy Unicode handling (how JSON handles unicode values
211 is undocumented. One can get far by feeding it unicode strings and 648 is undocumented. One can get far by feeding it unicode strings and
212 doing en-/decoding oneself, but unicode escapes are not working 649 doing en-/decoding oneself, but unicode escapes are not working
… …
214 651
215 No roundtripping (strings get clobbered if they look like numbers, 652 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 653 e.g. the string 2.0 will encode to 2.0 instead of "2.0", and that
217 will decode into the number 2. 654 will decode into the number 2.
218 655
219 JSON::PC 656 JSON::PC 0.01
220 Very fast. 657 Very fast.
221 658
222 Undocumented/buggy Unicode handling. 659 Undocumented/buggy Unicode handling.
223 660
224 No roundtripping. 661 No roundtripping.
225 662
226 Has problems handling many Perl values (e.g. regex results and other 663 Has problems handling many Perl values (e.g. regex results and other
227 magic values will make it croak). 664 magic values will make it croak).
228 665
229 Does not even generate valid JSON ("{1,2}" gets converted to "{1:2}" 666 Does not even generate valid JSON ("{1,2}" gets converted to "{1:2}"
230 which is not a valid JSON string. 667 which is not a valid JSON text.
231 668
232 Unmaintained (maintainer unresponsive for many months, bugs are not 669 Unmaintained (maintainer unresponsive for many months, bugs are not
233 getting fixed). 670 getting fixed).
234 671
235 JSON::Syck 672 JSON::Syck 0.21
236 Very buggy (often crashes). 673 Very buggy (often crashes).
237 674
238 Very inflexible (no human-readable format supported, format pretty 675 Very inflexible (no human-readable format supported, format pretty
239 much undocumented. I need at least a format for easy reading by 676 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 677 humans and a single-line compact format for use in a protocol, and
241 preferably a way to generate ASCII-only JSON strings). 678 preferably a way to generate ASCII-only JSON texts).
242 679
243 Completely broken (and confusingly documented) Unicode handling 680 Completely broken (and confusingly documented) Unicode handling
244 (unicode escapes are not working properly, you need to set 681 (unicode escapes are not working properly, you need to set
245 ImplicitUnicode to *different* values on en- and decoding to get 682 ImplicitUnicode to *different* values on en- and decoding to get
246 symmetric behaviour). 683 symmetric behaviour).
… …
259 other using JSON. One bank might parse a given non-JSON request and 696 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 697 deduct money, while the other might reject the transaction with a
261 syntax error. While a good protocol will at least recover, that is 698 syntax error. While a good protocol will at least recover, that is
262 extra unnecessary work and the transaction will still not succeed). 699 extra unnecessary work and the transaction will still not succeed).
263 700
264 JSON::DWIW 701 JSON::DWIW 0.04
265 Very fast. Very natural. Very nice. 702 Very fast. Very natural. Very nice.
266 703
267 Undocumented unicode handling (but the best of the pack. Unicode 704 Undocumented unicode handling (but the best of the pack. Unicode
268 escapes still don't get parsed properly). 705 escapes still don't get parsed properly).
269 706
270 Very inflexible. 707 Very inflexible.
271 708
272 No roundtripping. 709 No roundtripping.
273 710
274 Does not generate valid JSON (key strings are often unquoted, empty 711 Does not generate valid JSON texts (key strings are often unquoted,
275 keys result in nothing being output) 712 empty keys result in nothing being output)
276 713
277 Does not check input for validity. 714 Does not check input for validity.
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.
278 738
279 SPEED 739 SPEED
280 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
281 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
282 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
283 system. 743 system.
284 744
285 First is a comparison between various modules using a very simple JSON 745 First comes a comparison between various modules using a very short
746 single-line JSON string:
747
748 {"method": "handleMessage", "params": ["user1", "we were just talking"], \
749 "id": null, "array":[1,11,234,-5,1e5,1e7, true, false]}
750
286 string, showing the number of encodes/decodes per second (JSON::XS is 751 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 752 functional interface, while JSON::XS/2 uses the OO interface with
288 pretty-printing and hashkey sorting enabled). 753 pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink).
754 Higher is better:
289 755
756 Storable | 15779.925 | 14169.946 |
757 -----------+------------+------------+
290 module | encode | decode | 758 module | encode | decode |
291 -----------|------------|------------| 759 -----------|------------|------------|
292 JSON | 14006 | 6820 | 760 JSON | 4990.842 | 4088.813 |
293 JSON::DWIW | 200937 | 120386 | 761 JSON::DWIW | 51653.990 | 71575.154 |
294 JSON::PC | 85065 | 129366 | 762 JSON::PC | 65948.176 | 74631.744 |
295 JSON::Syck | 59898 | 44232 | 763 JSON::PP | 8931.652 | 3817.168 |
296 JSON::XS | 1171478 | 342435 | 764 JSON::Syck | 24877.248 | 27776.848 |
297 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 |
298 -----------+------------+------------+ 769 -----------+------------+------------+
299 770
300 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
301 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.
302 775
303 Using a longer test string (roughly 8KB, generated from Yahoo! Locals 776 Using a longer test string (roughly 18KB, generated from Yahoo! Locals
304 search API (http://nanoref.com/yahooapis/mgPdGg): 777 search API (http://nanoref.com/yahooapis/mgPdGg):
305 778
306 module | encode | decode | 779 module | encode | decode |
307 -----------|------------|------------| 780 -----------|------------|------------|
308 JSON | 673 | 38 | 781 JSON | 55.260 | 34.971 |
309 JSON::DWIW | 5271 | 770 | 782 JSON::DWIW | 825.228 | 1082.513 |
783 JSON::PC | 3571.444 | 2394.829 |
310 JSON::PC | 9901 | 2491 | 784 JSON::PP | 210.987 | 32.574 |
311 JSON::Syck | 2360 | 786 | 785 JSON::Syck | 552.551 | 787.544 |
312 JSON::XS | 37398 | 3202 | 786 JSON::XS | 5780.463 | 4854.519 |
313 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 |
314 -----------+------------+------------+ 790 -----------+------------+------------+
315 791
316 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
317 every other module in the decoding case. 793 decodes faster).
318 794
319 Last example is an almost 8MB large hash with many large binary values 795 On large strings containing lots of high unicode characters, some
320 (PNG files), resulting in a lot of escaping: 796 modules (such as JSON::PC) seem to decode faster than JSON::XS, but the
797 result will be broken due to missing (or wrong) unicode handling. Others
798 refuse to decode or encode properly, so it was impossible to prepare a
799 fair comparison table for that case.
800
801SECURITY CONSIDERATIONS
802 When you are using JSON in a protocol, talking to untrusted potentially
803 hostile creatures requires relatively few measures.
804
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).
321 839
322BUGS 840BUGS
323 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
324 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
325 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
326 will be fixed swiftly, though. 844 they will be fixed swiftly, though.
327 845
328AUTHOR 846AUTHOR
329 Marc Lehmann <schmorp@schmorp.de> 847 Marc Lehmann <schmorp@schmorp.de>
330 http://home.schmorp.de/ 848 http://home.schmorp.de/
331 849

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