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2 JSON::XS - JSON serialising/deserialising, done correctly and fast 2 JSON::XS - JSON serialising/deserialising, done correctly and fast
3 3
4SYNOPSIS 4SYNOPSIS
5 use JSON::XS; 5 use JSON::XS;
6 6
7 # exported functions, croak on error 7 # exported functions, they croak on error
8 # and expect/generate UTF-8
8 9
9 $utf8_encoded_json_text = to_json $perl_hash_or_arrayref; 10 $utf8_encoded_json_text = to_json $perl_hash_or_arrayref;
10 $perl_hash_or_arrayref = from_json $utf8_encoded_json_text; 11 $perl_hash_or_arrayref = from_json $utf8_encoded_json_text;
11 12
12 # oo-interface 13 # OO-interface
13 14
14 $coder = JSON::XS->new->ascii->pretty->allow_nonref; 15 $coder = JSON::XS->new->ascii->pretty->allow_nonref;
15 $pretty_printed_unencoded = $coder->encode ($perl_scalar); 16 $pretty_printed_unencoded = $coder->encode ($perl_scalar);
16 $perl_scalar = $coder->decode ($unicode_json_text); 17 $perl_scalar = $coder->decode ($unicode_json_text);
17 18
… …
30 31
31 See MAPPING, below, on how JSON::XS maps perl values to JSON values and 32 See MAPPING, below, on how JSON::XS maps perl values to JSON values and
32 vice versa. 33 vice versa.
33 34
34 FEATURES 35 FEATURES
35 * correct handling of unicode issues 36 * correct unicode handling
36 This module knows how to handle Unicode, and even documents how and 37 This module knows how to handle Unicode, and even documents how and
37 when it does so. 38 when it does so.
38 39
39 * round-trip integrity 40 * round-trip integrity
40 When you serialise a perl data structure using only datatypes 41 When you serialise a perl data structure using only datatypes
41 supported by JSON, the deserialised data structure is identical on 42 supported by JSON, the deserialised data structure is identical on
42 the Perl level. (e.g. the string "2.0" doesn't suddenly become "2"). 43 the Perl level. (e.g. the string "2.0" doesn't suddenly become "2"
44 just because it looks like a number).
43 45
44 * strict checking of JSON correctness 46 * strict checking of JSON correctness
45 There is no guessing, no generating of illegal JSON strings by 47 There is no guessing, no generating of illegal JSON texts by
46 default, and only JSON is accepted as input by default (the latter 48 default, and only JSON is accepted as input by default (the latter
47 is a security feature). 49 is a security feature).
48 50
49 * fast 51 * fast
50 Compared to other JSON modules, this module compares favourably in 52 Compared to other JSON modules, this module compares favourably in
… …
55 interface. 57 interface.
56 58
57 * reasonably versatile output formats 59 * reasonably versatile output formats
58 You can choose between the most compact guarenteed single-line 60 You can choose between the most compact guarenteed single-line
59 format possible (nice for simple line-based protocols), a pure-ascii 61 format possible (nice for simple line-based protocols), a pure-ascii
60 format (for when your transport is not 8-bit clean), or a 62 format (for when your transport is not 8-bit clean, still supports
61 pretty-printed format (for when you want to read that stuff). Or you 63 the whole unicode range), or a pretty-printed format (for when you
62 can combine those features in whatever way you like. 64 want to read that stuff). Or you can combine those features in
65 whatever way you like.
63 66
64FUNCTIONAL INTERFACE 67FUNCTIONAL INTERFACE
65 The following convinience methods are provided by this module. They are 68 The following convinience methods are provided by this module. They are
66 exported by default: 69 exported by default:
67 70
68 $json_string = to_json $perl_scalar 71 $json_text = to_json $perl_scalar
69 Converts the given Perl data structure (a simple scalar or a 72 Converts the given Perl data structure (a simple scalar or a
70 reference to a hash or array) to a UTF-8 encoded, binary string 73 reference to a hash or array) to a UTF-8 encoded, binary string
71 (that is, the string contains octets only). Croaks on error. 74 (that is, the string contains octets only). Croaks on error.
72 75
73 This function call is functionally identical to 76 This function call is functionally identical to:
77
74 "JSON::XS->new->utf8->encode ($perl_scalar)". 78 $json_text = JSON::XS->new->utf8->encode ($perl_scalar)
75 79
80 except being faster.
81
76 $perl_scalar = from_json $json_string 82 $perl_scalar = from_json $json_text
77 The opposite of "to_json": expects an UTF-8 (binary) string and 83 The opposite of "to_json": expects an UTF-8 (binary) string and
78 tries to parse that as an UTF-8 encoded JSON string, returning the 84 tries to parse that as an UTF-8 encoded JSON text, returning the
79 resulting simple scalar or reference. Croaks on error. 85 resulting simple scalar or reference. Croaks on error.
80 86
81 This function call is functionally identical to 87 This function call is functionally identical to:
88
82 "JSON::XS->new->utf8->decode ($json_string)". 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.
83 101
84OBJECT-ORIENTED INTERFACE 102OBJECT-ORIENTED INTERFACE
85 The object oriented interface lets you configure your own encoding or 103 The object oriented interface lets you configure your own encoding or
86 decoding style, within the limits of supported formats. 104 decoding style, within the limits of supported formats.
87 105
… …
91 *disabled*. 109 *disabled*.
92 110
93 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
94 calls can be chained: 112 calls can be chained:
95 113
96 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]})
97 => {"a": [1, 2]} 115 => {"a": [1, 2]}
98 116
99 $json = $json->ascii ([$enable]) 117 $json = $json->ascii ([$enable])
100 If $enable is true (or missing), then the "encode" method will not 118 If $enable is true (or missing), then the "encode" method will not
101 generate characters outside the code range 0..127. Any unicode 119 generate characters outside the code range 0..127 (which is ASCII).
102 characters outside that range will be escaped using either a single 120 Any unicode characters outside that range will be escaped using
103 \uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence, 121 either a single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL
104 as per RFC4627. 122 escape sequence, as per RFC4627. The resulting encoded JSON text can
123 be treated as a native unicode string, an ascii-encoded,
124 latin1-encoded or UTF-8 encoded string, or any other superset of
125 ASCII.
105 126
106 If $enable is false, then the "encode" method will not escape 127 If $enable is false, then the "encode" method will not escape
107 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.
108 130
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
109 JSON::XS->new->ascii (1)->encode (chr 0x10401) 135 JSON::XS->new->ascii (1)->encode ([chr 0x10401])
110 => \ud801\udc01 136 => ["\ud801\udc01"]
137
138 $json = $json->latin1 ([$enable])
139 If $enable is true (or missing), then the "encode" method will
140 encode the resulting JSON text as latin1 (or iso-8859-1), escaping
141 any characters outside the code range 0..255. The resulting string
142 can be treated as a latin1-encoded JSON text or a native unicode
143 string. The "decode" method will not be affected in any way by this
144 flag, as "decode" by default expects unicode, which is a strict
145 superset of latin1.
146
147 If $enable is false, then the "encode" method will not escape
148 Unicode characters unless required by the JSON syntax or other
149 flags.
150
151 The main use for this flag is efficiently encoding binary data as
152 JSON text, as most octets will not be escaped, resulting in a
153 smaller encoded size. The disadvantage is that the resulting JSON
154 text is encoded in latin1 (and must correctly be treated as such
155 when storing and transfering), a rare encoding for JSON. It is
156 therefore most useful when you want to store data structures known
157 to contain binary data efficiently in files or databases, not when
158 talking to other JSON encoders/decoders.
159
160 JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]
161 => ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)
111 162
112 $json = $json->utf8 ([$enable]) 163 $json = $json->utf8 ([$enable])
113 If $enable is true (or missing), then the "encode" method will 164 If $enable is true (or missing), then the "encode" method will
114 encode the JSON string into UTF-8, as required by many protocols, 165 encode the JSON result into UTF-8, as required by many protocols,
115 while the "decode" method expects to be handled an UTF-8-encoded 166 while the "decode" method expects to be handled an UTF-8-encoded
116 string. Please note that UTF-8-encoded strings do not contain any 167 string. Please note that UTF-8-encoded strings do not contain any
117 characters outside the range 0..255, they are thus useful for 168 characters outside the range 0..255, they are thus useful for
118 bytewise/binary I/O. 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.
119 172
120 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
121 string as a (non-encoded) unicode string, while "decode" expects 174 string as a (non-encoded) unicode string, while "decode" expects
122 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
123 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.
124 177
125 Example, output UTF-16-encoded JSON: 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);
126 187
127 $json = $json->pretty ([$enable]) 188 $json = $json->pretty ([$enable])
128 This enables (or disables) all of the "indent", "space_before" and 189 This enables (or disables) all of the "indent", "space_before" and
129 "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
130 generate the most readable (or most compact) form possible. 191 generate the most readable (or most compact) form possible.
… …
145 multiline format as output, putting every array member or 206 multiline format as output, putting every array member or
146 object/hash key-value pair into its own line, identing them 207 object/hash key-value pair into its own line, identing them
147 properly. 208 properly.
148 209
149 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
150 the resulting JSON strings is guarenteed not to contain any 211 the resulting JSON text is guarenteed not to contain any "newlines".
151 "newlines".
152 212
153 This setting has no effect when decoding JSON strings. 213 This setting has no effect when decoding JSON texts.
154 214
155 $json = $json->space_before ([$enable]) 215 $json = $json->space_before ([$enable])
156 If $enable is true (or missing), then the "encode" method will add 216 If $enable is true (or missing), then the "encode" method will add
157 an extra optional space before the ":" separating keys from values 217 an extra optional space before the ":" separating keys from values
158 in JSON objects. 218 in JSON objects.
159 219
160 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
161 space at those places. 221 space at those places.
162 222
163 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
164 most likely combine this setting with "space_after". 224 most likely combine this setting with "space_after".
165 225
166 Example, space_before enabled, space_after and indent disabled: 226 Example, space_before enabled, space_after and indent disabled:
167 227
168 {"key" :"value"} 228 {"key" :"value"}
… …
174 pairs and array members. 234 pairs and array members.
175 235
176 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
177 space at those places. 237 space at those places.
178 238
179 This setting has no effect when decoding JSON strings. 239 This setting has no effect when decoding JSON texts.
180 240
181 Example, space_before and indent disabled, space_after enabled: 241 Example, space_before and indent disabled, space_after enabled:
182 242
183 {"key": "value"} 243 {"key": "value"}
184 244
… …
190 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
191 pairs in the order Perl stores them (which will likely change 251 pairs in the order Perl stores them (which will likely change
192 between runs of the same script). 252 between runs of the same script).
193 253
194 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
195 encoded as the same JSON string (given the same overall settings). 255 encoded as the same JSON text (given the same overall settings). If
196 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
197 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
198 in Perl. 258 in Perl.
199 259
200 This setting has no effect when decoding JSON strings. 260 This setting has no effect when decoding JSON texts.
201 261
202 $json = $json->allow_nonref ([$enable]) 262 $json = $json->allow_nonref ([$enable])
203 If $enable is true (or missing), then the "encode" method can 263 If $enable is true (or missing), then the "encode" method can
204 convert a non-reference into its corresponding string, number or 264 convert a non-reference into its corresponding string, number or
205 null JSON value, which is an extension to RFC4627. Likewise, 265 null JSON value, which is an extension to RFC4627. Likewise,
206 "decode" will accept those JSON values instead of croaking. 266 "decode" will accept those JSON values instead of croaking.
207 267
208 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
209 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
210 object or array. Likewise, "decode" will croak if given something 270 object or array. Likewise, "decode" will croak if given something
211 that is not a JSON object or array. 271 that is not a JSON object or array.
212 272
213 Example, encode a Perl scalar as JSON value with enabled 273 Example, encode a Perl scalar as JSON value with enabled
214 "allow_nonref", resulting in an invalid JSON text: 274 "allow_nonref", resulting in an invalid JSON text:
215 275
216 JSON::XS->new->allow_nonref->encode ("Hello, World!") 276 JSON::XS->new->allow_nonref->encode ("Hello, World!")
217 => "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 }
218 388
219 $json = $json->shrink ([$enable]) 389 $json = $json->shrink ([$enable])
220 Perl usually over-allocates memory a bit when allocating space for 390 Perl usually over-allocates memory a bit when allocating space for
221 strings. This flag optionally resizes strings generated by either 391 strings. This flag optionally resizes strings generated by either
222 "encode" or "decode" to their minimum size possible. This can save 392 "encode" or "decode" to their minimum size possible. This can save
223 memory when your JSON strings are either very very long or you have 393 memory when your JSON texts are either very very long or you have
224 many short strings. It will also try to downgrade any strings to 394 many short strings. It will also try to downgrade any strings to
225 octet-form if possible: perl stores strings internally either in an 395 octet-form if possible: perl stores strings internally either in an
226 encoding called UTF-X or in octet-form. The latter cannot store 396 encoding called UTF-X or in octet-form. The latter cannot store
227 everything but uses less space in general. 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.
228 403
229 If $enable is true (or missing), the string returned by "encode" 404 If $enable is true (or missing), the string returned by "encode"
230 will be shrunk-to-fit, while all strings generated by "decode" will 405 will be shrunk-to-fit, while all strings generated by "decode" will
231 also be shrunk-to-fit. 406 also be shrunk-to-fit.
232 407
… …
236 In the future, this setting might control other things, such as 411 In the future, this setting might control other things, such as
237 converting strings that look like integers or floats into integers 412 converting strings that look like integers or floats into integers
238 or floats internally (there is no difference on the Perl level), 413 or floats internally (there is no difference on the Perl level),
239 saving space. 414 saving space.
240 415
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
241 $json_string = $json->encode ($perl_scalar) 452 $json_text = $json->encode ($perl_scalar)
242 Converts the given Perl data structure (a simple scalar or a 453 Converts the given Perl data structure (a simple scalar or a
243 reference to a hash or array) to its JSON representation. Simple 454 reference to a hash or array) to its JSON representation. Simple
244 scalars will be converted into JSON string or number sequences, 455 scalars will be converted into JSON string or number sequences,
245 while references to arrays become JSON arrays and references to 456 while references to arrays become JSON arrays and references to
246 hashes become JSON objects. Undefined Perl values (e.g. "undef") 457 hashes become JSON objects. Undefined Perl values (e.g. "undef")
247 become JSON "null" values. Neither "true" nor "false" values will be 458 become JSON "null" values. Neither "true" nor "false" values will be
248 generated. 459 generated.
249 460
250 $perl_scalar = $json->decode ($json_string) 461 $perl_scalar = $json->decode ($json_text)
251 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,
252 it, returning the resulting simple scalar or reference. Croaks on 463 returning the resulting simple scalar or reference. Croaks on error.
253 error.
254 464
255 JSON numbers and strings become simple Perl scalars. JSON arrays 465 JSON numbers and strings become simple Perl scalars. JSON arrays
256 become Perl arrayrefs and JSON objects become Perl hashrefs. "true" 466 become Perl arrayrefs and JSON objects become Perl hashrefs. "true"
257 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)
258 481
259MAPPING 482MAPPING
260 This section describes how JSON::XS maps Perl values to JSON values and 483 This section describes how JSON::XS maps Perl values to JSON values and
261 vice versa. These mappings are designed to "do the right thing" in most 484 vice versa. These mappings are designed to "do the right thing" in most
262 circumstances automatically, preserving round-tripping characteristics 485 circumstances automatically, preserving round-tripping characteristics
… …
287 all the conversion details, but an integer may take slightly less 510 all the conversion details, but an integer may take slightly less
288 memory and might represent more values exactly than (floating point) 511 memory and might represent more values exactly than (floating point)
289 numbers. 512 numbers.
290 513
291 true, false 514 true, false
292 These JSON atoms become 0, 1, respectively. Information is lost in 515 These JSON atoms become "JSON::XS::true" and "JSON::XS::false",
293 this process. Future versions might represent those values 516 respectively. They are overloaded to act almost exactly like the
294 differently, but they will be guarenteed to act like these integers 517 numbers 1 and 0. You can check wether a scalar is a JSON boolean by
295 would normally in Perl. 518 using the "JSON::XS::is_bool" function.
296 519
297 null 520 null
298 A JSON null atom becomes "undef" in Perl. 521 A JSON null atom becomes "undef" in Perl.
299 522
300 PERL -> JSON 523 PERL -> JSON
… …
302 truly typeless language, so we can only guess which JSON type is meant 525 truly typeless language, so we can only guess which JSON type is meant
303 by a Perl value. 526 by a Perl value.
304 527
305 hash references 528 hash references
306 Perl hash references become JSON objects. As there is no inherent 529 Perl hash references become JSON objects. As there is no inherent
307 ordering in hash keys, they will usually be encoded in a 530 ordering in hash keys (or JSON objects), they will usually be
308 pseudo-random order that can change between runs of the same program 531 encoded in a pseudo-random order that can change between runs of the
309 but stays generally the same within a single run of a program. 532 same program but stays generally the same within a single run of a
310 JSON::XS can optionally sort the hash keys (determined by the 533 program. JSON::XS can optionally sort the hash keys (determined by
311 *canonical* flag), so the same datastructure will serialise to the 534 the *canonical* flag), so the same datastructure will serialise to
312 same JSON text (given same settings and version of JSON::XS), but 535 the same JSON text (given same settings and version of JSON::XS),
313 this incurs a runtime overhead. 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.
314 539
315 array references 540 array references
316 Perl array references become JSON arrays. 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.
317 555
318 blessed objects 556 blessed objects
319 Blessed objects are not allowed. JSON::XS currently tries to encode 557 Blessed objects are not allowed. JSON::XS currently tries to encode
320 their underlying representation (hash- or arrayref), but this 558 their underlying representation (hash- or arrayref), but this
321 behaviour might change in future versions. 559 behaviour might change in future versions.
… …
353 $x *= 1; # same thing, the choise is yours. 591 $x *= 1; # same thing, the choise is yours.
354 592
355 You can not currently output JSON booleans or force the type in 593 You can not currently output JSON booleans or force the type in
356 other, less obscure, ways. Tell me if you need this capability. 594 other, less obscure, ways. Tell me if you need this capability.
357 595
358 circular data structures
359 Those will be encoded until memory or stackspace runs out.
360
361COMPARISON 596COMPARISON
362 As already mentioned, this module was created because none of the 597 As already mentioned, this module was created because none of the
363 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
364 describe the problems (or pleasures) I encountered with various existing 599 describe the problems (or pleasures) I encountered with various existing
365 JSON modules, followed by some benchmark values. JSON::XS was designed 600 JSON modules, followed by some benchmark values. JSON::XS was designed
… …
386 621
387 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
388 magic values will make it croak). 623 magic values will make it croak).
389 624
390 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}"
391 which is not a valid JSON string. 626 which is not a valid JSON text.
392 627
393 Unmaintained (maintainer unresponsive for many months, bugs are not 628 Unmaintained (maintainer unresponsive for many months, bugs are not
394 getting fixed). 629 getting fixed).
395 630
396 JSON::Syck 0.21 631 JSON::Syck 0.21
397 Very buggy (often crashes). 632 Very buggy (often crashes).
398 633
399 Very inflexible (no human-readable format supported, format pretty 634 Very inflexible (no human-readable format supported, format pretty
400 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
401 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
402 preferably a way to generate ASCII-only JSON strings). 637 preferably a way to generate ASCII-only JSON texts).
403 638
404 Completely broken (and confusingly documented) Unicode handling 639 Completely broken (and confusingly documented) Unicode handling
405 (unicode escapes are not working properly, you need to set 640 (unicode escapes are not working properly, you need to set
406 ImplicitUnicode to *different* values on en- and decoding to get 641 ImplicitUnicode to *different* values on en- and decoding to get
407 symmetric behaviour). 642 symmetric behaviour).
… …
430 665
431 Very inflexible. 666 Very inflexible.
432 667
433 No roundtripping. 668 No roundtripping.
434 669
435 Does not generate valid JSON (key strings are often unquoted, empty 670 Does not generate valid JSON texts (key strings are often unquoted,
436 keys result in nothing being output) 671 empty keys result in nothing being output)
437 672
438 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.
439 697
440 SPEED 698 SPEED
441 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
442 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
443 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
444 system. 702 system.
445 703
446 First comes a comparison between various modules using a very short JSON 704 First comes a comparison between various modules using a very short
447 string (83 bytes), showing the number of encodes/decodes per second 705 single-line JSON string:
448 (JSON::XS is the functional interface, while JSON::XS/2 is the OO
449 interface with pretty-printing and hashkey sorting enabled). Higher is
450 better:
451 706
707 {"method": "handleMessage", "params": ["user1", "we were just talking"], \
708 "id": null, "array":[1,11,234,-5,1e5,1e7, true, false]}
709
710 It shows the number of encodes/decodes per second (JSON::XS uses the
711 functional interface, while JSON::XS/2 uses the OO interface with
712 pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink).
713 Higher is better:
714
715 Storable | 15779.925 | 14169.946 |
716 -----------+------------+------------+
452 module | encode | decode | 717 module | encode | decode |
453 -----------|------------|------------| 718 -----------|------------|------------|
454 JSON | 14006 | 6820 | 719 JSON | 4990.842 | 4088.813 |
455 JSON::DWIW | 200937 | 120386 | 720 JSON::DWIW | 51653.990 | 71575.154 |
456 JSON::PC | 85065 | 129366 | 721 JSON::PC | 65948.176 | 74631.744 |
457 JSON::Syck | 59898 | 44232 | 722 JSON::PP | 8931.652 | 3817.168 |
458 JSON::XS | 1171478 | 342435 | 723 JSON::Syck | 24877.248 | 27776.848 |
459 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 |
460 -----------+------------+------------+ 728 -----------+------------+------------+
461 729
462 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
463 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.
464 734
465 Using a longer test string (roughly 18KB, generated from Yahoo! Locals 735 Using a longer test string (roughly 18KB, generated from Yahoo! Locals
466 search API (http://nanoref.com/yahooapis/mgPdGg): 736 search API (http://nanoref.com/yahooapis/mgPdGg):
467 737
468 module | encode | decode | 738 module | encode | decode |
469 -----------|------------|------------| 739 -----------|------------|------------|
470 JSON | 673 | 38 | 740 JSON | 55.260 | 34.971 |
471 JSON::DWIW | 5271 | 770 | 741 JSON::DWIW | 825.228 | 1082.513 |
742 JSON::PC | 3571.444 | 2394.829 |
472 JSON::PC | 9901 | 2491 | 743 JSON::PP | 210.987 | 32.574 |
473 JSON::Syck | 2360 | 786 | 744 JSON::Syck | 552.551 | 787.544 |
474 JSON::XS | 37398 | 3202 | 745 JSON::XS | 5780.463 | 4854.519 |
475 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 |
476 -----------+------------+------------+ 749 -----------+------------+------------+
477 750
478 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
479 every other module in the decoding case. 752 decodes faster).
480 753
481 On large strings containing lots of unicode characters, some modules 754 On large strings containing lots of high unicode characters, some
482 (such as JSON::PC) decode faster than JSON::XS, but the result will be 755 modules (such as JSON::PC) seem to decode faster than JSON::XS, but the
483 broken due to missing unicode handling. Others refuse to decode or 756 result will be broken due to missing (or wrong) unicode handling. Others
484 encode properly, so it was impossible to prepare a fair comparison table 757 refuse to decode or encode properly, so it was impossible to prepare a
485 for that case. 758 fair comparison table for that case.
486 759
487RESOURCE LIMITS 760SECURITY CONSIDERATIONS
488 JSON::XS does not impose any limits on the size of JSON texts or Perl 761 When you are using JSON in a protocol, talking to untrusted potentially
489 values they represent - if your machine can handle it, JSON::XS will 762 hostile creatures requires relatively few measures.
490 encode or decode it. Future versions might optionally impose structure 763
491 depth and memory use resource limits. 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).
492 798
493BUGS 799BUGS
494 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
495 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
496 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
497 will be fixed swiftly, though. 803 they will be fixed swiftly, though.
498 804
499AUTHOR 805AUTHOR
500 Marc Lehmann <schmorp@schmorp.de> 806 Marc Lehmann <schmorp@schmorp.de>
501 http://home.schmorp.de/ 807 http://home.schmorp.de/
502 808

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