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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
154 $json = $json->canonical ($enable) 245 $json = $json->canonical ([$enable])
155 If $enable is true, then the "encode" method will output JSON 246 If $enable is true (or missing), then the "encode" method will
156 objects by sorting their keys. This is adding a comparatively high 247 output JSON objects by sorting their keys. This is adding a
157 overhead. 248 comparatively high overhead.
158 249
159 If $enable is false, then the "encode" method will output key-value 250 If $enable is false, then the "encode" method will output key-value
160 pairs in the order Perl stores them (which will likely change 251 pairs in the order Perl stores them (which will likely change
161 between runs of the same script). 252 between runs of the same script).
162 253
163 This option is useful if you want the same data structure to be 254 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). 255 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 256 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 257 contains the same data, as key-value pairs have no inherent ordering
167 in Perl. 258 in Perl.
168 259
169 This setting has no effect when decoding JSON strings. 260 This setting has no effect when decoding JSON texts.
170 261
171 $json = $json->allow_nonref ($enable) 262 $json = $json->allow_nonref ([$enable])
172 If $enable is true, then the "encode" method can convert a 263 If $enable is true (or missing), then the "encode" method can
173 non-reference into its corresponding string, number or null JSON 264 convert a non-reference into its corresponding string, number or
174 value, which is an extension to RFC4627. Likewise, "decode" will 265 null JSON value, which is an extension to RFC4627. Likewise,
175 accept those JSON values instead of croaking. 266 "decode" will accept those JSON values instead of croaking.
176 267
177 If $enable is false, then the "encode" method will croak if it isn't 268 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 269 passed an arrayref or hashref, as JSON texts must either be an
179 object or array. Likewise, "decode" will croak if given something 270 object or array. Likewise, "decode" will croak if given something
180 that is not a JSON object or array. 271 that is not a JSON object or array.
181 272
273 Example, encode a Perl scalar as JSON value with enabled
274 "allow_nonref", resulting in an invalid JSON text:
275
276 JSON::XS->new->allow_nonref->encode ("Hello, World!")
277 => "Hello, World!"
278
279 $json = $json->allow_blessed ([$enable])
280 If $enable is true (or missing), then the "encode" method will not
281 barf when it encounters a blessed reference. Instead, the value of
282 the convert_blessed option will decide wether "null"
283 ("convert_blessed" disabled or no "to_json" method found) or a
284 representation of the object ("convert_blessed" enabled and
285 "to_json" method found) is being encoded. Has no effect on "decode".
286
287 If $enable is false (the default), then "encode" will throw an
288 exception when it encounters a blessed object.
289
290 $json = $json->convert_blessed ([$enable])
291 If $enable is true (or missing), then "encode", upon encountering a
292 blessed object, will check for the availability of the "TO_JSON"
293 method on the object's class. If found, it will be called in scalar
294 context and the resulting scalar will be encoded instead of the
295 object. If no "TO_JSON" method is found, the value of
296 "allow_blessed" will decide what to do.
297
298 The "TO_JSON" method may safely call die if it wants. If "TO_JSON"
299 returns other blessed objects, those will be handled in the same
300 way. "TO_JSON" must take care of not causing an endless recursion
301 cycle (== crash) in this case. The name of "TO_JSON" was chosen
302 because other methods called by the Perl core (== not by the user of
303 the object) are usually in upper case letters and to avoid
304 collisions with the "to_json" function.
305
306 This setting does not yet influence "decode" in any way, but in the
307 future, global hooks might get installed that influence "decode" and
308 are enabled by this setting.
309
310 If $enable is false, then the "allow_blessed" setting will decide
311 what to do when a blessed object is found.
312
313 $json = $json->filter_json_object ([$coderef->($hashref)])
314 When $coderef is specified, it will be called from "decode" each
315 time it decodes a JSON object. The only argument is a reference to
316 the newly-created hash. If the code references returns a single
317 scalar (which need not be a reference), this value (i.e. a copy of
318 that scalar to avoid aliasing) is inserted into the deserialised
319 data structure. If it returns an empty list (NOTE: *not* "undef",
320 which is a valid scalar), the original deserialised hash will be
321 inserted. This setting can slow down decoding considerably.
322
323 When $coderef is omitted or undefined, any existing callback will be
324 removed and "decode" will not change the deserialised hash in any
325 way.
326
327 Example, convert all JSON objects into the integer 5:
328
329 my $js = JSON::XS->new->filter_json_object (sub { 5 });
330 # returns [5]
331 $js->decode ('[{}]')
332 # throw an exception because allow_nonref is not enabled
333 # so a lone 5 is not allowed.
334 $js->decode ('{"a":1, "b":2}');
335
336 $json = $json->filter_json_single_key_object ($key [=>
337 $coderef->($value)])
338 Works remotely similar to "filter_json_object", but is only called
339 for JSON objects having a single key named $key.
340
341 This $coderef is called before the one specified via
342 "filter_json_object", if any. It gets passed the single value in the
343 JSON object. If it returns a single value, it will be inserted into
344 the data structure. If it returns nothing (not even "undef" but the
345 empty list), the callback from "filter_json_object" will be called
346 next, as if no single-key callback were specified.
347
348 If $coderef is omitted or undefined, the corresponding callback will
349 be disabled. There can only ever be one callback for a given key.
350
351 As this callback gets called less often then the
352 "filter_json_object" one, decoding speed will not usually suffer as
353 much. Therefore, single-key objects make excellent targets to
354 serialise Perl objects into, especially as single-key JSON objects
355 are as close to the type-tagged value concept as JSON gets (its
356 basically an ID/VALUE tuple). Of course, JSON does not support this
357 in any way, so you need to make sure your data never looks like a
358 serialised Perl hash.
359
360 Typical names for the single object key are "__class_whatever__", or
361 "$__dollars_are_rarely_used__$" or "}ugly_brace_placement", or even
362 things like "__class_md5sum(classname)__", to reduce the risk of
363 clashing with real hashes.
364
365 Example, decode JSON objects of the form "{ "__widget__" => <id> }"
366 into the corresponding $WIDGET{<id>} object:
367
368 # return whatever is in $WIDGET{5}:
369 JSON::XS
370 ->new
371 ->filter_json_single_key_object (__widget__ => sub {
372 $WIDGET{ $_[0] }
373 })
374 ->decode ('{"__widget__": 5')
375
376 # this can be used with a TO_JSON method in some "widget" class
377 # for serialisation to json:
378 sub WidgetBase::TO_JSON {
379 my ($self) = @_;
380
381 unless ($self->{id}) {
382 $self->{id} = ..get..some..id..;
383 $WIDGET{$self->{id}} = $self;
384 }
385
386 { __widget__ => $self->{id} }
387 }
388
389 $json = $json->shrink ([$enable])
390 Perl usually over-allocates memory a bit when allocating space for
391 strings. This flag optionally resizes strings generated by either
392 "encode" or "decode" to their minimum size possible. This can save
393 memory when your JSON texts are either very very long or you have
394 many short strings. It will also try to downgrade any strings to
395 octet-form if possible: perl stores strings internally either in an
396 encoding called UTF-X or in octet-form. The latter cannot store
397 everything but uses less space in general (and some buggy Perl or C
398 code might even rely on that internal representation being used).
399
400 The actual definition of what shrink does might change in future
401 versions, but it will always try to save space at the expense of
402 time.
403
404 If $enable is true (or missing), the string returned by "encode"
405 will be shrunk-to-fit, while all strings generated by "decode" will
406 also be shrunk-to-fit.
407
408 If $enable is false, then the normal perl allocation algorithms are
409 used. If you work with your data, then this is likely to be faster.
410
411 In the future, this setting might control other things, such as
412 converting strings that look like integers or floats into integers
413 or floats internally (there is no difference on the Perl level),
414 saving space.
415
416 $json = $json->max_depth ([$maximum_nesting_depth])
417 Sets the maximum nesting level (default 512) accepted while encoding
418 or decoding. If the JSON text or Perl data structure has an equal or
419 higher nesting level then this limit, then the encoder and decoder
420 will stop and croak at that point.
421
422 Nesting level is defined by number of hash- or arrayrefs that the
423 encoder needs to traverse to reach a given point or the number of
424 "{" or "[" characters without their matching closing parenthesis
425 crossed to reach a given character in a string.
426
427 Setting the maximum depth to one disallows any nesting, so that
428 ensures that the object is only a single hash/object or array.
429
430 The argument to "max_depth" will be rounded up to the next highest
431 power of two. If no argument is given, the highest possible setting
432 will be used, which is rarely useful.
433
434 See SECURITY CONSIDERATIONS, below, for more info on why this is
435 useful.
436
437 $json = $json->max_size ([$maximum_string_size])
438 Set the maximum length a JSON text may have (in bytes) where
439 decoding is being attempted. The default is 0, meaning no limit.
440 When "decode" is called on a string longer then this number of
441 characters it will not attempt to decode the string but throw an
442 exception. This setting has no effect on "encode" (yet).
443
444 The argument to "max_size" will be rounded up to the next highest
445 power of two (so may be more than requested). If no argument is
446 given, the limit check will be deactivated (same as when 0 is
447 specified).
448
449 See SECURITY CONSIDERATIONS, below, for more info on why this is
450 useful.
451
182 $json_string = $json->encode ($perl_scalar) 452 $json_text = $json->encode ($perl_scalar)
183 Converts the given Perl data structure (a simple scalar or a 453 Converts the given Perl data structure (a simple scalar or a
184 reference to a hash or array) to its JSON representation. Simple 454 reference to a hash or array) to its JSON representation. Simple
185 scalars will be converted into JSON string or number sequences, 455 scalars will be converted into JSON string or number sequences,
186 while references to arrays become JSON arrays and references to 456 while references to arrays become JSON arrays and references to
187 hashes become JSON objects. Undefined Perl values (e.g. "undef") 457 hashes become JSON objects. Undefined Perl values (e.g. "undef")
188 become JSON "null" values. Neither "true" nor "false" values will be 458 become JSON "null" values. Neither "true" nor "false" values will be
189 generated. 459 generated.
190 460
191 $perl_scalar = $json->decode ($json_string) 461 $perl_scalar = $json->decode ($json_text)
192 The opposite of "encode": expects a JSON string and tries to parse 462 The opposite of "encode": expects a JSON text and tries to parse it,
193 it, returning the resulting simple scalar or reference. Croaks on 463 returning the resulting simple scalar or reference. Croaks on error.
194 error.
195 464
196 JSON numbers and strings become simple Perl scalars. JSON arrays 465 JSON numbers and strings become simple Perl scalars. JSON arrays
197 become Perl arrayrefs and JSON objects become Perl hashrefs. "true" 466 become Perl arrayrefs and JSON objects become Perl hashrefs. "true"
198 becomes 1, "false" becomes 0 and "null" becomes "undef". 467 becomes 1, "false" becomes 0 and "null" becomes "undef".
468
469 ($perl_scalar, $characters) = $json->decode_prefix ($json_text)
470 This works like the "decode" method, but instead of raising an
471 exception when there is trailing garbage after the first JSON
472 object, it will silently stop parsing there and return the number of
473 characters consumed so far.
474
475 This is useful if your JSON texts are not delimited by an outer
476 protocol (which is not the brightest thing to do in the first place)
477 and you need to know where the JSON text ends.
478
479 JSON::XS->new->decode_prefix ("[1] the tail")
480 => ([], 3)
481
482MAPPING
483 This section describes how JSON::XS maps Perl values to JSON values and
484 vice versa. These mappings are designed to "do the right thing" in most
485 circumstances automatically, preserving round-tripping characteristics
486 (what you put in comes out as something equivalent).
487
488 For the more enlightened: note that in the following descriptions,
489 lowercase *perl* refers to the Perl interpreter, while uppcercase *Perl*
490 refers to the abstract Perl language itself.
491
492 JSON -> PERL
493 object
494 A JSON object becomes a reference to a hash in Perl. No ordering of
495 object keys is preserved (JSON does not preserver object key
496 ordering itself).
497
498 array
499 A JSON array becomes a reference to an array in Perl.
500
501 string
502 A JSON string becomes a string scalar in Perl - Unicode codepoints
503 in JSON are represented by the same codepoints in the Perl string,
504 so no manual decoding is necessary.
505
506 number
507 A JSON number becomes either an integer or numeric (floating point)
508 scalar in perl, depending on its range and any fractional parts. On
509 the Perl level, there is no difference between those as Perl handles
510 all the conversion details, but an integer may take slightly less
511 memory and might represent more values exactly than (floating point)
512 numbers.
513
514 true, false
515 These JSON atoms become "JSON::XS::true" and "JSON::XS::false",
516 respectively. They are overloaded to act almost exactly like the
517 numbers 1 and 0. You can check wether a scalar is a JSON boolean by
518 using the "JSON::XS::is_bool" function.
519
520 null
521 A JSON null atom becomes "undef" in Perl.
522
523 PERL -> JSON
524 The mapping from Perl to JSON is slightly more difficult, as Perl is a
525 truly typeless language, so we can only guess which JSON type is meant
526 by a Perl value.
527
528 hash references
529 Perl hash references become JSON objects. As there is no inherent
530 ordering in hash keys (or JSON objects), they will usually be
531 encoded in a pseudo-random order that can change between runs of the
532 same program but stays generally the same within a single run of a
533 program. JSON::XS can optionally sort the hash keys (determined by
534 the *canonical* flag), so the same datastructure will serialise to
535 the same JSON text (given same settings and version of JSON::XS),
536 but this incurs a runtime overhead and is only rarely useful, e.g.
537 when you want to compare some JSON text against another for
538 equality.
539
540 array references
541 Perl array references become JSON arrays.
542
543 other references
544 Other unblessed references are generally not allowed and will cause
545 an exception to be thrown, except for references to the integers 0
546 and 1, which get turned into "false" and "true" atoms in JSON. You
547 can also use "JSON::XS::false" and "JSON::XS::true" to improve
548 readability.
549
550 to_json [\0,JSON::XS::true] # yields [false,true]
551
552 JSON::XS::true, JSON::XS::false
553 These special values become JSON true and JSON false values,
554 respectively. You cna alos use "\1" and "\0" directly if you want.
555
556 blessed objects
557 Blessed objects are not allowed. JSON::XS currently tries to encode
558 their underlying representation (hash- or arrayref), but this
559 behaviour might change in future versions.
560
561 simple scalars
562 Simple Perl scalars (any scalar that is not a reference) are the
563 most difficult objects to encode: JSON::XS will encode undefined
564 scalars as JSON null value, scalars that have last been used in a
565 string context before encoding as JSON strings and anything else as
566 number value:
567
568 # dump as number
569 to_json [2] # yields [2]
570 to_json [-3.0e17] # yields [-3e+17]
571 my $value = 5; to_json [$value] # yields [5]
572
573 # used as string, so dump as string
574 print $value;
575 to_json [$value] # yields ["5"]
576
577 # undef becomes null
578 to_json [undef] # yields [null]
579
580 You can force the type to be a string by stringifying it:
581
582 my $x = 3.1; # some variable containing a number
583 "$x"; # stringified
584 $x .= ""; # another, more awkward way to stringify
585 print $x; # perl does it for you, too, quite often
586
587 You can force the type to be a number by numifying it:
588
589 my $x = "3"; # some variable containing a string
590 $x += 0; # numify it, ensuring it will be dumped as a number
591 $x *= 1; # same thing, the choise is yours.
592
593 You can not currently output JSON booleans or force the type in
594 other, less obscure, ways. Tell me if you need this capability.
199 595
200COMPARISON 596COMPARISON
201 As already mentioned, this module was created because none of the 597 As already mentioned, this module was created because none of the
202 existing JSON modules could be made to work correctly. First I will 598 existing JSON modules could be made to work correctly. First I will
203 describe the problems (or pleasures) I encountered with various existing 599 describe the problems (or pleasures) I encountered with various existing
204 JSON modules, followed by some benchmark values. JSON::XS was designed 600 JSON modules, followed by some benchmark values. JSON::XS was designed
205 not to suffer from any of these problems or limitations. 601 not to suffer from any of these problems or limitations.
206 602
207 JSON 603 JSON 1.07
208 Slow (but very portable, as it is written in pure Perl). 604 Slow (but very portable, as it is written in pure Perl).
209 605
210 Undocumented/buggy Unicode handling (how JSON handles unicode values 606 Undocumented/buggy Unicode handling (how JSON handles unicode values
211 is undocumented. One can get far by feeding it unicode strings and 607 is undocumented. One can get far by feeding it unicode strings and
212 doing en-/decoding oneself, but unicode escapes are not working 608 doing en-/decoding oneself, but unicode escapes are not working
… …
214 610
215 No roundtripping (strings get clobbered if they look like numbers, 611 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 612 e.g. the string 2.0 will encode to 2.0 instead of "2.0", and that
217 will decode into the number 2. 613 will decode into the number 2.
218 614
219 JSON::PC 615 JSON::PC 0.01
220 Very fast. 616 Very fast.
221 617
222 Undocumented/buggy Unicode handling. 618 Undocumented/buggy Unicode handling.
223 619
224 No roundtripping. 620 No roundtripping.
225 621
226 Has problems handling many Perl values (e.g. regex results and other 622 Has problems handling many Perl values (e.g. regex results and other
227 magic values will make it croak). 623 magic values will make it croak).
228 624
229 Does not even generate valid JSON ("{1,2}" gets converted to "{1:2}" 625 Does not even generate valid JSON ("{1,2}" gets converted to "{1:2}"
230 which is not a valid JSON string. 626 which is not a valid JSON text.
231 627
232 Unmaintained (maintainer unresponsive for many months, bugs are not 628 Unmaintained (maintainer unresponsive for many months, bugs are not
233 getting fixed). 629 getting fixed).
234 630
235 JSON::Syck 631 JSON::Syck 0.21
236 Very buggy (often crashes). 632 Very buggy (often crashes).
237 633
238 Very inflexible (no human-readable format supported, format pretty 634 Very inflexible (no human-readable format supported, format pretty
239 much undocumented. I need at least a format for easy reading by 635 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 636 humans and a single-line compact format for use in a protocol, and
241 preferably a way to generate ASCII-only JSON strings). 637 preferably a way to generate ASCII-only JSON texts).
242 638
243 Completely broken (and confusingly documented) Unicode handling 639 Completely broken (and confusingly documented) Unicode handling
244 (unicode escapes are not working properly, you need to set 640 (unicode escapes are not working properly, you need to set
245 ImplicitUnicode to *different* values on en- and decoding to get 641 ImplicitUnicode to *different* values on en- and decoding to get
246 symmetric behaviour). 642 symmetric behaviour).
… …
259 other using JSON. One bank might parse a given non-JSON request and 655 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 656 deduct money, while the other might reject the transaction with a
261 syntax error. While a good protocol will at least recover, that is 657 syntax error. While a good protocol will at least recover, that is
262 extra unnecessary work and the transaction will still not succeed). 658 extra unnecessary work and the transaction will still not succeed).
263 659
264 JSON::DWIW 660 JSON::DWIW 0.04
265 Very fast. Very natural. Very nice. 661 Very fast. Very natural. Very nice.
266 662
267 Undocumented unicode handling (but the best of the pack. Unicode 663 Undocumented unicode handling (but the best of the pack. Unicode
268 escapes still don't get parsed properly). 664 escapes still don't get parsed properly).
269 665
270 Very inflexible. 666 Very inflexible.
271 667
272 No roundtripping. 668 No roundtripping.
273 669
274 Does not generate valid JSON (key strings are often unquoted, empty 670 Does not generate valid JSON texts (key strings are often unquoted,
275 keys result in nothing being output) 671 empty keys result in nothing being output)
276 672
277 Does not check input for validity. 673 Does not check input for validity.
674
675 JSON and YAML
676 You often hear that JSON is a subset (or a close subset) of YAML. This
677 is, however, a mass hysteria and very far from the truth. In general,
678 there is no way to configure JSON::XS to output a data structure as
679 valid YAML.
680
681 If you really must use JSON::XS to generate YAML, you should use this
682 algorithm (subject to change in future versions):
683
684 my $to_yaml = JSON::XS->new->utf8->space_after (1);
685 my $yaml = $to_yaml->encode ($ref) . "\n";
686
687 This will usually generate JSON texts that also parse as valid YAML.
688 Please note that YAML has hardcoded limits on (simple) object key
689 lengths that JSON doesn't have, so you should make sure that your hash
690 keys are noticably shorter than the 1024 characters YAML allows.
691
692 There might be other incompatibilities that I am not aware of. In
693 general you should not try to generate YAML with a JSON generator or
694 vice versa, or try to parse JSON with a YAML parser or vice versa:
695 chances are high that you will run into severe interoperability
696 problems.
278 697
279 SPEED 698 SPEED
280 It seems that JSON::XS is surprisingly fast, as shown in the following 699 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 700 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 701 in the JSON::XS distribution, to make it easy to compare on your own
283 system. 702 system.
284 703
285 First is a comparison between various modules using a very simple JSON 704 First comes a comparison between various modules using a very short
705 single-line JSON string:
706
707 {"method": "handleMessage", "params": ["user1", "we were just talking"], \
708 "id": null, "array":[1,11,234,-5,1e5,1e7, true, false]}
709
286 string, showing the number of encodes/decodes per second (JSON::XS is 710 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 711 functional interface, while JSON::XS/2 uses the OO interface with
288 pretty-printing and hashkey sorting enabled). 712 pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink).
713 Higher is better:
289 714
715 Storable | 15779.925 | 14169.946 |
716 -----------+------------+------------+
290 module | encode | decode | 717 module | encode | decode |
291 -----------|------------|------------| 718 -----------|------------|------------|
292 JSON | 14006 | 6820 | 719 JSON | 4990.842 | 4088.813 |
293 JSON::DWIW | 200937 | 120386 | 720 JSON::DWIW | 51653.990 | 71575.154 |
294 JSON::PC | 85065 | 129366 | 721 JSON::PC | 65948.176 | 74631.744 |
295 JSON::Syck | 59898 | 44232 | 722 JSON::PP | 8931.652 | 3817.168 |
296 JSON::XS | 1171478 | 342435 | 723 JSON::Syck | 24877.248 | 27776.848 |
297 JSON::XS/2 | 730760 | 328714 | 724 JSON::XS | 388361.481 | 227951.304 |
725 JSON::XS/2 | 227951.304 | 218453.333 |
726 JSON::XS/3 | 338250.323 | 218453.333 |
727 Storable | 16500.016 | 135300.129 |
298 -----------+------------+------------+ 728 -----------+------------+------------+
299 729
300 That is, JSON::XS is 6 times faster than than JSON::DWIW and about 80 730 That is, JSON::XS is about five times faster than JSON::DWIW on
731 encoding, about three times faster on decoding, and over fourty times
301 times faster than JSON, even with pretty-printing and key sorting. 732 faster than JSON, even with pretty-printing and key sorting. It also
733 compares favourably to Storable for small amounts of data.
302 734
303 Using a longer test string (roughly 8KB, generated from Yahoo! Locals 735 Using a longer test string (roughly 18KB, generated from Yahoo! Locals
304 search API (http://nanoref.com/yahooapis/mgPdGg): 736 search API (http://nanoref.com/yahooapis/mgPdGg):
305 737
306 module | encode | decode | 738 module | encode | decode |
307 -----------|------------|------------| 739 -----------|------------|------------|
308 JSON | 673 | 38 | 740 JSON | 55.260 | 34.971 |
309 JSON::DWIW | 5271 | 770 | 741 JSON::DWIW | 825.228 | 1082.513 |
742 JSON::PC | 3571.444 | 2394.829 |
310 JSON::PC | 9901 | 2491 | 743 JSON::PP | 210.987 | 32.574 |
311 JSON::Syck | 2360 | 786 | 744 JSON::Syck | 552.551 | 787.544 |
312 JSON::XS | 37398 | 3202 | 745 JSON::XS | 5780.463 | 4854.519 |
313 JSON::XS/2 | 13765 | 3153 | 746 JSON::XS/2 | 3869.998 | 4798.975 |
747 JSON::XS/3 | 5862.880 | 4798.975 |
748 Storable | 4445.002 | 5235.027 |
314 -----------+------------+------------+ 749 -----------+------------+------------+
315 750
316 Again, JSON::XS leads by far in the encoding case, while still beating 751 Again, JSON::XS leads by far (except for Storable which non-surprisingly
317 every other module in the decoding case. 752 decodes faster).
318 753
319 Last example is an almost 8MB large hash with many large binary values 754 On large strings containing lots of high unicode characters, some
320 (PNG files), resulting in a lot of escaping: 755 modules (such as JSON::PC) seem to decode faster than JSON::XS, but the
756 result will be broken due to missing (or wrong) unicode handling. Others
757 refuse to decode or encode properly, so it was impossible to prepare a
758 fair comparison table for that case.
759
760SECURITY CONSIDERATIONS
761 When you are using JSON in a protocol, talking to untrusted potentially
762 hostile creatures requires relatively few measures.
763
764 First of all, your JSON decoder should be secure, that is, should not
765 have any buffer overflows. Obviously, this module should ensure that and
766 I am trying hard on making that true, but you never know.
767
768 Second, you need to avoid resource-starving attacks. That means you
769 should limit the size of JSON texts you accept, or make sure then when
770 your resources run out, thats just fine (e.g. by using a separate
771 process that can crash safely). The size of a JSON text in octets or
772 characters is usually a good indication of the size of the resources
773 required to decode it into a Perl structure. While JSON::XS can check
774 the size of the JSON text, it might be too late when you already have it
775 in memory, so you might want to check the size before you accept the
776 string.
777
778 Third, JSON::XS recurses using the C stack when decoding objects and
779 arrays. The C stack is a limited resource: for instance, on my amd64
780 machine with 8MB of stack size I can decode around 180k nested arrays
781 but only 14k nested JSON objects (due to perl itself recursing deeply on
782 croak to free the temporary). If that is exceeded, the program crashes.
783 to be conservative, the default nesting limit is set to 512. If your
784 process has a smaller stack, you should adjust this setting accordingly
785 with the "max_depth" method.
786
787 And last but least, something else could bomb you that I forgot to think
788 of. In that case, you get to keep the pieces. I am always open for
789 hints, though...
790
791 If you are using JSON::XS to return packets to consumption by javascript
792 scripts in a browser you should have a look at
793 <http://jpsykes.com/47/practical-csrf-and-json-security> to see wether
794 you are vulnerable to some common attack vectors (which really are
795 browser design bugs, but it is still you who will have to deal with it,
796 as major browser developers care only for features, not about doing
797 security right).
321 798
322BUGS 799BUGS
323 While the goal of this module is to be correct, that unfortunately does 800 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 801 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 802 still relatively early in its development. If you keep reporting bugs
326 will be fixed swiftly, though. 803 they will be fixed swiftly, though.
327 804
328AUTHOR 805AUTHOR
329 Marc Lehmann <schmorp@schmorp.de> 806 Marc Lehmann <schmorp@schmorp.de>
330 http://home.schmorp.de/ 807 http://home.schmorp.de/
331 808

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