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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
13 # objToJson and jsonToObj aliases to to_json and from_json
14 # are exported for compatibility to the JSON module,
15 # but should not be used in new code.
16
12 # oo-interface 17 # OO-interface
13 18
14 $coder = JSON::XS->new->ascii->pretty->allow_nonref; 19 $coder = JSON::XS->new->ascii->pretty->allow_nonref;
15 $pretty_printed_unencoded = $coder->encode ($perl_scalar); 20 $pretty_printed_unencoded = $coder->encode ($perl_scalar);
16 $perl_scalar = $coder->decode ($unicode_json_text); 21 $perl_scalar = $coder->decode ($unicode_json_text);
17 22
… …
30 35
31 See MAPPING, below, on how JSON::XS maps perl values to JSON values and 36 See MAPPING, below, on how JSON::XS maps perl values to JSON values and
32 vice versa. 37 vice versa.
33 38
34 FEATURES 39 FEATURES
35 * correct handling of unicode issues 40 * correct unicode handling
36 This module knows how to handle Unicode, and even documents how and 41 This module knows how to handle Unicode, and even documents how and
37 when it does so. 42 when it does so.
38 43
39 * round-trip integrity 44 * round-trip integrity
40 When you serialise a perl data structure using only datatypes 45 When you serialise a perl data structure using only datatypes
41 supported by JSON, the deserialised data structure is identical on 46 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"). 47 the Perl level. (e.g. the string "2.0" doesn't suddenly become "2"
48 just because it looks like a number).
43 49
44 * strict checking of JSON correctness 50 * strict checking of JSON correctness
45 There is no guessing, no generating of illegal JSON strings by 51 There is no guessing, no generating of illegal JSON texts by
46 default, and only JSON is accepted as input by default (the latter 52 default, and only JSON is accepted as input by default (the latter
47 is a security feature). 53 is a security feature).
48 54
49 * fast 55 * fast
50 Compared to other JSON modules, this module compares favourably in 56 Compared to other JSON modules, this module compares favourably in
… …
55 interface. 61 interface.
56 62
57 * reasonably versatile output formats 63 * reasonably versatile output formats
58 You can choose between the most compact guarenteed single-line 64 You can choose between the most compact guarenteed single-line
59 format possible (nice for simple line-based protocols), a pure-ascii 65 format possible (nice for simple line-based protocols), a pure-ascii
60 format (for when your transport is not 8-bit clean), or a 66 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 67 the whole unicode range), or a pretty-printed format (for when you
62 can combine those features in whatever way you like. 68 want to read that stuff). Or you can combine those features in
69 whatever way you like.
63 70
64FUNCTIONAL INTERFACE 71FUNCTIONAL INTERFACE
65 The following convinience methods are provided by this module. They are 72 The following convinience methods are provided by this module. They are
66 exported by default: 73 exported by default:
67 74
68 $json_string = to_json $perl_scalar 75 $json_text = to_json $perl_scalar
69 Converts the given Perl data structure (a simple scalar or a 76 Converts the given Perl data structure (a simple scalar or a
70 reference to a hash or array) to a UTF-8 encoded, binary string 77 reference to a hash or array) to a UTF-8 encoded, binary string
71 (that is, the string contains octets only). Croaks on error. 78 (that is, the string contains octets only). Croaks on error.
72 79
73 This function call is functionally identical to 80 This function call is functionally identical to:
81
74 "JSON::XS->new->utf8->encode ($perl_scalar)". 82 $json_text = JSON::XS->new->utf8->encode ($perl_scalar)
75 83
84 except being faster.
85
76 $perl_scalar = from_json $json_string 86 $perl_scalar = from_json $json_text
77 The opposite of "to_json": expects an UTF-8 (binary) string and 87 The opposite of "to_json": expects an UTF-8 (binary) string and
78 tries to parse that as an UTF-8 encoded JSON string, returning the 88 tries to parse that as an UTF-8 encoded JSON text, returning the
79 resulting simple scalar or reference. Croaks on error. 89 resulting simple scalar or reference. Croaks on error.
80 90
81 This function call is functionally identical to 91 This function call is functionally identical to:
92
82 "JSON::XS->new->utf8->decode ($json_string)". 93 $perl_scalar = JSON::XS->new->utf8->decode ($json_text)
94
95 except being faster.
96
97 $is_boolean = JSON::XS::is_bool $scalar
98 Returns true if the passed scalar represents either JSON::XS::true
99 or JSON::XS::false, two constants that act like 1 and 0,
100 respectively and are used to represent JSON "true" and "false"
101 values in Perl.
102
103 See MAPPING, below, for more information on how JSON values are
104 mapped to Perl.
83 105
84OBJECT-ORIENTED INTERFACE 106OBJECT-ORIENTED INTERFACE
85 The object oriented interface lets you configure your own encoding or 107 The object oriented interface lets you configure your own encoding or
86 decoding style, within the limits of supported formats. 108 decoding style, within the limits of supported formats.
87 109
… …
91 *disabled*. 113 *disabled*.
92 114
93 The mutators for flags all return the JSON object again and thus 115 The mutators for flags all return the JSON object again and thus
94 calls can be chained: 116 calls can be chained:
95 117
96 my $json = JSON::XS->new->utf8(1)->space_after(1)->encode ({a => [1,2]}) 118 my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]})
97 => {"a": [1, 2]} 119 => {"a": [1, 2]}
98 120
99 $json = $json->ascii ([$enable]) 121 $json = $json->ascii ([$enable])
100 If $enable is true (or missing), then the "encode" method will not 122 If $enable is true (or missing), then the "encode" method will not
101 generate characters outside the code range 0..127. Any unicode 123 generate characters outside the code range 0..127 (which is ASCII).
102 characters outside that range will be escaped using either a single 124 Any unicode characters outside that range will be escaped using
103 \uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence, 125 either a single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL
104 as per RFC4627. 126 escape sequence, as per RFC4627. The resulting encoded JSON text can
127 be treated as a native unicode string, an ascii-encoded,
128 latin1-encoded or UTF-8 encoded string, or any other superset of
129 ASCII.
105 130
106 If $enable is false, then the "encode" method will not escape 131 If $enable is false, then the "encode" method will not escape
107 Unicode characters unless necessary. 132 Unicode characters unless required by the JSON syntax or other
133 flags. This results in a faster and more compact format.
108 134
135 The main use for this flag is to produce JSON texts that can be
136 transmitted over a 7-bit channel, as the encoded JSON texts will not
137 contain any 8 bit characters.
138
109 JSON::XS->new->ascii (1)->encode (chr 0x10401) 139 JSON::XS->new->ascii (1)->encode ([chr 0x10401])
110 => \ud801\udc01 140 => ["\ud801\udc01"]
141
142 $json = $json->latin1 ([$enable])
143 If $enable is true (or missing), then the "encode" method will
144 encode the resulting JSON text as latin1 (or iso-8859-1), escaping
145 any characters outside the code range 0..255. The resulting string
146 can be treated as a latin1-encoded JSON text or a native unicode
147 string. The "decode" method will not be affected in any way by this
148 flag, as "decode" by default expects unicode, which is a strict
149 superset of latin1.
150
151 If $enable is false, then the "encode" method will not escape
152 Unicode characters unless required by the JSON syntax or other
153 flags.
154
155 The main use for this flag is efficiently encoding binary data as
156 JSON text, as most octets will not be escaped, resulting in a
157 smaller encoded size. The disadvantage is that the resulting JSON
158 text is encoded in latin1 (and must correctly be treated as such
159 when storing and transfering), a rare encoding for JSON. It is
160 therefore most useful when you want to store data structures known
161 to contain binary data efficiently in files or databases, not when
162 talking to other JSON encoders/decoders.
163
164 JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]
165 => ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)
111 166
112 $json = $json->utf8 ([$enable]) 167 $json = $json->utf8 ([$enable])
113 If $enable is true (or missing), then the "encode" method will 168 If $enable is true (or missing), then the "encode" method will
114 encode the JSON string into UTF-8, as required by many protocols, 169 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 170 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 171 string. Please note that UTF-8-encoded strings do not contain any
117 characters outside the range 0..255, they are thus useful for 172 characters outside the range 0..255, they are thus useful for
118 bytewise/binary I/O. 173 bytewise/binary I/O. In future versions, enabling this option might
174 enable autodetection of the UTF-16 and UTF-32 encoding families, as
175 described in RFC4627.
119 176
120 If $enable is false, then the "encode" method will return the JSON 177 If $enable is false, then the "encode" method will return the JSON
121 string as a (non-encoded) unicode string, while "decode" expects 178 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 179 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. 180 UTF-16) needs to be done yourself, e.g. using the Encode module.
124 181
125 Example, output UTF-16-encoded JSON: 182 Example, output UTF-16BE-encoded JSON:
183
184 use Encode;
185 $jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
186
187 Example, decode UTF-32LE-encoded JSON:
188
189 use Encode;
190 $object = JSON::XS->new->decode (decode "UTF-32LE", $jsontext);
126 191
127 $json = $json->pretty ([$enable]) 192 $json = $json->pretty ([$enable])
128 This enables (or disables) all of the "indent", "space_before" and 193 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 194 "space_after" (and in the future possibly more) flags in one call to
130 generate the most readable (or most compact) form possible. 195 generate the most readable (or most compact) form possible.
… …
145 multiline format as output, putting every array member or 210 multiline format as output, putting every array member or
146 object/hash key-value pair into its own line, identing them 211 object/hash key-value pair into its own line, identing them
147 properly. 212 properly.
148 213
149 If $enable is false, no newlines or indenting will be produced, and 214 If $enable is false, no newlines or indenting will be produced, and
150 the resulting JSON strings is guarenteed not to contain any 215 the resulting JSON text is guarenteed not to contain any "newlines".
151 "newlines".
152 216
153 This setting has no effect when decoding JSON strings. 217 This setting has no effect when decoding JSON texts.
154 218
155 $json = $json->space_before ([$enable]) 219 $json = $json->space_before ([$enable])
156 If $enable is true (or missing), then the "encode" method will add 220 If $enable is true (or missing), then the "encode" method will add
157 an extra optional space before the ":" separating keys from values 221 an extra optional space before the ":" separating keys from values
158 in JSON objects. 222 in JSON objects.
159 223
160 If $enable is false, then the "encode" method will not add any extra 224 If $enable is false, then the "encode" method will not add any extra
161 space at those places. 225 space at those places.
162 226
163 This setting has no effect when decoding JSON strings. You will also 227 This setting has no effect when decoding JSON texts. You will also
164 most likely combine this setting with "space_after". 228 most likely combine this setting with "space_after".
165 229
166 Example, space_before enabled, space_after and indent disabled: 230 Example, space_before enabled, space_after and indent disabled:
167 231
168 {"key" :"value"} 232 {"key" :"value"}
… …
174 pairs and array members. 238 pairs and array members.
175 239
176 If $enable is false, then the "encode" method will not add any extra 240 If $enable is false, then the "encode" method will not add any extra
177 space at those places. 241 space at those places.
178 242
179 This setting has no effect when decoding JSON strings. 243 This setting has no effect when decoding JSON texts.
180 244
181 Example, space_before and indent disabled, space_after enabled: 245 Example, space_before and indent disabled, space_after enabled:
182 246
183 {"key": "value"} 247 {"key": "value"}
184 248
… …
190 If $enable is false, then the "encode" method will output key-value 254 If $enable is false, then the "encode" method will output key-value
191 pairs in the order Perl stores them (which will likely change 255 pairs in the order Perl stores them (which will likely change
192 between runs of the same script). 256 between runs of the same script).
193 257
194 This option is useful if you want the same data structure to be 258 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). 259 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 260 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 261 contains the same data, as key-value pairs have no inherent ordering
198 in Perl. 262 in Perl.
199 263
200 This setting has no effect when decoding JSON strings. 264 This setting has no effect when decoding JSON texts.
201 265
202 $json = $json->allow_nonref ([$enable]) 266 $json = $json->allow_nonref ([$enable])
203 If $enable is true (or missing), then the "encode" method can 267 If $enable is true (or missing), then the "encode" method can
204 convert a non-reference into its corresponding string, number or 268 convert a non-reference into its corresponding string, number or
205 null JSON value, which is an extension to RFC4627. Likewise, 269 null JSON value, which is an extension to RFC4627. Likewise,
206 "decode" will accept those JSON values instead of croaking. 270 "decode" will accept those JSON values instead of croaking.
207 271
208 If $enable is false, then the "encode" method will croak if it isn't 272 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 273 passed an arrayref or hashref, as JSON texts must either be an
210 object or array. Likewise, "decode" will croak if given something 274 object or array. Likewise, "decode" will croak if given something
211 that is not a JSON object or array. 275 that is not a JSON object or array.
212 276
213 Example, encode a Perl scalar as JSON value with enabled 277 Example, encode a Perl scalar as JSON value with enabled
214 "allow_nonref", resulting in an invalid JSON text: 278 "allow_nonref", resulting in an invalid JSON text:
… …
218 282
219 $json = $json->shrink ([$enable]) 283 $json = $json->shrink ([$enable])
220 Perl usually over-allocates memory a bit when allocating space for 284 Perl usually over-allocates memory a bit when allocating space for
221 strings. This flag optionally resizes strings generated by either 285 strings. This flag optionally resizes strings generated by either
222 "encode" or "decode" to their minimum size possible. This can save 286 "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 287 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 288 many short strings. It will also try to downgrade any strings to
225 octet-form if possible: perl stores strings internally either in an 289 octet-form if possible: perl stores strings internally either in an
226 encoding called UTF-X or in octet-form. The latter cannot store 290 encoding called UTF-X or in octet-form. The latter cannot store
227 everything but uses less space in general. 291 everything but uses less space in general (and some buggy Perl or C
292 code might even rely on that internal representation being used).
293
294 The actual definition of what shrink does might change in future
295 versions, but it will always try to save space at the expense of
296 time.
228 297
229 If $enable is true (or missing), the string returned by "encode" 298 If $enable is true (or missing), the string returned by "encode"
230 will be shrunk-to-fit, while all strings generated by "decode" will 299 will be shrunk-to-fit, while all strings generated by "decode" will
231 also be shrunk-to-fit. 300 also be shrunk-to-fit.
232 301
… …
236 In the future, this setting might control other things, such as 305 In the future, this setting might control other things, such as
237 converting strings that look like integers or floats into integers 306 converting strings that look like integers or floats into integers
238 or floats internally (there is no difference on the Perl level), 307 or floats internally (there is no difference on the Perl level),
239 saving space. 308 saving space.
240 309
310 $json = $json->max_depth ([$maximum_nesting_depth])
311 Sets the maximum nesting level (default 512) accepted while encoding
312 or decoding. If the JSON text or Perl data structure has an equal or
313 higher nesting level then this limit, then the encoder and decoder
314 will stop and croak at that point.
315
316 Nesting level is defined by number of hash- or arrayrefs that the
317 encoder needs to traverse to reach a given point or the number of
318 "{" or "[" characters without their matching closing parenthesis
319 crossed to reach a given character in a string.
320
321 Setting the maximum depth to one disallows any nesting, so that
322 ensures that the object is only a single hash/object or array.
323
324 The argument to "max_depth" will be rounded up to the next nearest
325 power of two.
326
327 See SECURITY CONSIDERATIONS, below, for more info on why this is
328 useful.
329
241 $json_string = $json->encode ($perl_scalar) 330 $json_text = $json->encode ($perl_scalar)
242 Converts the given Perl data structure (a simple scalar or a 331 Converts the given Perl data structure (a simple scalar or a
243 reference to a hash or array) to its JSON representation. Simple 332 reference to a hash or array) to its JSON representation. Simple
244 scalars will be converted into JSON string or number sequences, 333 scalars will be converted into JSON string or number sequences,
245 while references to arrays become JSON arrays and references to 334 while references to arrays become JSON arrays and references to
246 hashes become JSON objects. Undefined Perl values (e.g. "undef") 335 hashes become JSON objects. Undefined Perl values (e.g. "undef")
247 become JSON "null" values. Neither "true" nor "false" values will be 336 become JSON "null" values. Neither "true" nor "false" values will be
248 generated. 337 generated.
249 338
250 $perl_scalar = $json->decode ($json_string) 339 $perl_scalar = $json->decode ($json_text)
251 The opposite of "encode": expects a JSON string and tries to parse 340 The opposite of "encode": expects a JSON text and tries to parse it,
252 it, returning the resulting simple scalar or reference. Croaks on 341 returning the resulting simple scalar or reference. Croaks on error.
253 error.
254 342
255 JSON numbers and strings become simple Perl scalars. JSON arrays 343 JSON numbers and strings become simple Perl scalars. JSON arrays
256 become Perl arrayrefs and JSON objects become Perl hashrefs. "true" 344 become Perl arrayrefs and JSON objects become Perl hashrefs. "true"
257 becomes 1, "false" becomes 0 and "null" becomes "undef". 345 becomes 1, "false" becomes 0 and "null" becomes "undef".
346
347 ($perl_scalar, $characters) = $json->decode_prefix ($json_text)
348 This works like the "decode" method, but instead of raising an
349 exception when there is trailing garbage after the first JSON
350 object, it will silently stop parsing there and return the number of
351 characters consumed so far.
352
353 This is useful if your JSON texts are not delimited by an outer
354 protocol (which is not the brightest thing to do in the first place)
355 and you need to know where the JSON text ends.
356
357 JSON::XS->new->decode_prefix ("[1] the tail")
358 => ([], 3)
258 359
259MAPPING 360MAPPING
260 This section describes how JSON::XS maps Perl values to JSON values and 361 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 362 vice versa. These mappings are designed to "do the right thing" in most
262 circumstances automatically, preserving round-tripping characteristics 363 circumstances automatically, preserving round-tripping characteristics
… …
287 all the conversion details, but an integer may take slightly less 388 all the conversion details, but an integer may take slightly less
288 memory and might represent more values exactly than (floating point) 389 memory and might represent more values exactly than (floating point)
289 numbers. 390 numbers.
290 391
291 true, false 392 true, false
292 These JSON atoms become 0, 1, respectively. Information is lost in 393 These JSON atoms become "JSON::XS::true" and "JSON::XS::false",
293 this process. Future versions might represent those values 394 respectively. They are overloaded to act almost exactly like the
294 differently, but they will be guarenteed to act like these integers 395 numbers 1 and 0. You can check wether a scalar is a JSON boolean by
295 would normally in Perl. 396 using the "JSON::XS::is_bool" function.
296 397
297 null 398 null
298 A JSON null atom becomes "undef" in Perl. 399 A JSON null atom becomes "undef" in Perl.
299 400
300 PERL -> JSON 401 PERL -> JSON
… …
302 truly typeless language, so we can only guess which JSON type is meant 403 truly typeless language, so we can only guess which JSON type is meant
303 by a Perl value. 404 by a Perl value.
304 405
305 hash references 406 hash references
306 Perl hash references become JSON objects. As there is no inherent 407 Perl hash references become JSON objects. As there is no inherent
307 ordering in hash keys, they will usually be encoded in a 408 ordering in hash keys (or JSON objects), they will usually be
308 pseudo-random order that can change between runs of the same program 409 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. 410 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 411 program. JSON::XS can optionally sort the hash keys (determined by
311 *canonical* flag), so the same datastructure will serialise to the 412 the *canonical* flag), so the same datastructure will serialise to
312 same JSON text (given same settings and version of JSON::XS), but 413 the same JSON text (given same settings and version of JSON::XS),
313 this incurs a runtime overhead. 414 but this incurs a runtime overhead and is only rarely useful, e.g.
415 when you want to compare some JSON text against another for
416 equality.
314 417
315 array references 418 array references
316 Perl array references become JSON arrays. 419 Perl array references become JSON arrays.
420
421 other references
422 Other unblessed references are generally not allowed and will cause
423 an exception to be thrown, except for references to the integers 0
424 and 1, which get turned into "false" and "true" atoms in JSON. You
425 can also use "JSON::XS::false" and "JSON::XS::true" to improve
426 readability.
427
428 to_json [\0,JSON::XS::true] # yields [false,true]
429
430 JSON::XS::true, JSON::XS::false
431 These special values become JSON true and JSON false values,
432 respectively. You cna alos use "\1" and "\0" directly if you want.
317 433
318 blessed objects 434 blessed objects
319 Blessed objects are not allowed. JSON::XS currently tries to encode 435 Blessed objects are not allowed. JSON::XS currently tries to encode
320 their underlying representation (hash- or arrayref), but this 436 their underlying representation (hash- or arrayref), but this
321 behaviour might change in future versions. 437 behaviour might change in future versions.
… …
353 $x *= 1; # same thing, the choise is yours. 469 $x *= 1; # same thing, the choise is yours.
354 470
355 You can not currently output JSON booleans or force the type in 471 You can not currently output JSON booleans or force the type in
356 other, less obscure, ways. Tell me if you need this capability. 472 other, less obscure, ways. Tell me if you need this capability.
357 473
358 circular data structures
359 Those will be encoded until memory or stackspace runs out.
360
361COMPARISON 474COMPARISON
362 As already mentioned, this module was created because none of the 475 As already mentioned, this module was created because none of the
363 existing JSON modules could be made to work correctly. First I will 476 existing JSON modules could be made to work correctly. First I will
364 describe the problems (or pleasures) I encountered with various existing 477 describe the problems (or pleasures) I encountered with various existing
365 JSON modules, followed by some benchmark values. JSON::XS was designed 478 JSON modules, followed by some benchmark values. JSON::XS was designed
… …
386 499
387 Has problems handling many Perl values (e.g. regex results and other 500 Has problems handling many Perl values (e.g. regex results and other
388 magic values will make it croak). 501 magic values will make it croak).
389 502
390 Does not even generate valid JSON ("{1,2}" gets converted to "{1:2}" 503 Does not even generate valid JSON ("{1,2}" gets converted to "{1:2}"
391 which is not a valid JSON string. 504 which is not a valid JSON text.
392 505
393 Unmaintained (maintainer unresponsive for many months, bugs are not 506 Unmaintained (maintainer unresponsive for many months, bugs are not
394 getting fixed). 507 getting fixed).
395 508
396 JSON::Syck 0.21 509 JSON::Syck 0.21
397 Very buggy (often crashes). 510 Very buggy (often crashes).
398 511
399 Very inflexible (no human-readable format supported, format pretty 512 Very inflexible (no human-readable format supported, format pretty
400 much undocumented. I need at least a format for easy reading by 513 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 514 humans and a single-line compact format for use in a protocol, and
402 preferably a way to generate ASCII-only JSON strings). 515 preferably a way to generate ASCII-only JSON texts).
403 516
404 Completely broken (and confusingly documented) Unicode handling 517 Completely broken (and confusingly documented) Unicode handling
405 (unicode escapes are not working properly, you need to set 518 (unicode escapes are not working properly, you need to set
406 ImplicitUnicode to *different* values on en- and decoding to get 519 ImplicitUnicode to *different* values on en- and decoding to get
407 symmetric behaviour). 520 symmetric behaviour).
… …
430 543
431 Very inflexible. 544 Very inflexible.
432 545
433 No roundtripping. 546 No roundtripping.
434 547
435 Does not generate valid JSON (key strings are often unquoted, empty 548 Does not generate valid JSON texts (key strings are often unquoted,
436 keys result in nothing being output) 549 empty keys result in nothing being output)
437 550
438 Does not check input for validity. 551 Does not check input for validity.
552
553 JSON and YAML
554 You often hear that JSON is a subset (or a close subset) of YAML. This
555 is, however, a mass hysteria and very far from the truth. In general,
556 there is no way to configure JSON::XS to output a data structure as
557 valid YAML.
558
559 If you really must use JSON::XS to generate YAML, you should use this
560 algorithm (subject to change in future versions):
561
562 my $to_yaml = JSON::XS->new->utf8->space_after (1);
563 my $yaml = $to_yaml->encode ($ref) . "\n";
564
565 This will usually generate JSON texts that also parse as valid YAML.
566 Please note that YAML has hardcoded limits on (simple) object key
567 lengths that JSON doesn't have, so you should make sure that your hash
568 keys are noticably shorter than the 1024 characters YAML allows.
569
570 There might be other incompatibilities that I am not aware of. In
571 general you should not try to generate YAML with a JSON generator or
572 vice versa, or try to parse JSON with a YAML parser or vice versa:
573 chances are high that you will run into severe interoperability
574 problems.
439 575
440 SPEED 576 SPEED
441 It seems that JSON::XS is surprisingly fast, as shown in the following 577 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 578 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 579 in the JSON::XS distribution, to make it easy to compare on your own
444 system. 580 system.
445 581
446 First comes a comparison between various modules using a very short JSON 582 First comes a comparison between various modules using a very short
447 string (83 bytes), showing the number of encodes/decodes per second 583 single-line JSON string:
448 (JSON::XS is the functional interface, while JSON::XS/2 is the OO 584
449 interface with pretty-printing and hashkey sorting enabled). Higher is 585 {"method": "handleMessage", "params": ["user1", "we were just talking"], \
450 better: 586 "id": null, "array":[1,11,234,-5,1e5,1e7, true, false]}
587
588 It shows the number of encodes/decodes per second (JSON::XS uses the
589 functional interface, while JSON::XS/2 uses the OO interface with
590 pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink).
591 Higher is better:
451 592
452 module | encode | decode | 593 module | encode | decode |
453 -----------|------------|------------| 594 -----------|------------|------------|
454 JSON | 14006 | 6820 | 595 JSON | 7645.468 | 4208.613 |
455 JSON::DWIW | 200937 | 120386 | 596 JSON::DWIW | 40721.398 | 77101.176 |
456 JSON::PC | 85065 | 129366 | 597 JSON::PC | 65948.176 | 78251.940 |
457 JSON::Syck | 59898 | 44232 | 598 JSON::Syck | 22844.793 | 26479.192 |
458 JSON::XS | 1171478 | 342435 | 599 JSON::XS | 388361.481 | 199728.762 |
459 JSON::XS/2 | 730760 | 328714 | 600 JSON::XS/2 | 218453.333 | 192399.266 |
601 JSON::XS/3 | 338250.323 | 192399.266 |
602 Storable | 15779.925 | 14169.946 |
460 -----------+------------+------------+ 603 -----------+------------+------------+
461 604
462 That is, JSON::XS is 6 times faster than than JSON::DWIW and about 80 605 That is, JSON::XS is about five times faster than JSON::DWIW on
606 encoding, about three times faster on decoding, and over fourty times
463 times faster than JSON, even with pretty-printing and key sorting. 607 faster than JSON, even with pretty-printing and key sorting. It also
608 compares favourably to Storable for small amounts of data.
464 609
465 Using a longer test string (roughly 18KB, generated from Yahoo! Locals 610 Using a longer test string (roughly 18KB, generated from Yahoo! Locals
466 search API (http://nanoref.com/yahooapis/mgPdGg): 611 search API (http://nanoref.com/yahooapis/mgPdGg):
467 612
468 module | encode | decode | 613 module | encode | decode |
469 -----------|------------|------------| 614 -----------|------------|------------|
470 JSON | 673 | 38 | 615 JSON | 254.685 | 37.665 |
471 JSON::DWIW | 5271 | 770 | 616 JSON::DWIW | 843.343 | 1049.731 |
472 JSON::PC | 9901 | 2491 | 617 JSON::PC | 3602.116 | 2307.352 |
473 JSON::Syck | 2360 | 786 | 618 JSON::Syck | 505.107 | 787.899 |
474 JSON::XS | 37398 | 3202 | 619 JSON::XS | 5747.196 | 3690.220 |
475 JSON::XS/2 | 13765 | 3153 | 620 JSON::XS/2 | 3968.121 | 3676.634 |
621 JSON::XS/3 | 6105.246 | 3662.508 |
622 Storable | 4417.337 | 5285.161 |
476 -----------+------------+------------+ 623 -----------+------------+------------+
477 624
478 Again, JSON::XS leads by far in the encoding case, while still beating 625 Again, JSON::XS leads by far (except for Storable which non-surprisingly
479 every other module in the decoding case. 626 decodes faster).
480 627
481 On large strings containing lots of unicode characters, some modules 628 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 629 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 630 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 631 refuse to decode or encode properly, so it was impossible to prepare a
485 for that case. 632 fair comparison table for that case.
486 633
487RESOURCE LIMITS 634SECURITY CONSIDERATIONS
488 JSON::XS does not impose any limits on the size of JSON texts or Perl 635 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 636 hostile creatures requires relatively few measures.
490 encode or decode it. Future versions might optionally impose structure 637
491 depth and memory use resource limits. 638 First of all, your JSON decoder should be secure, that is, should not
639 have any buffer overflows. Obviously, this module should ensure that and
640 I am trying hard on making that true, but you never know.
641
642 Second, you need to avoid resource-starving attacks. That means you
643 should limit the size of JSON texts you accept, or make sure then when
644 your resources run out, thats just fine (e.g. by using a separate
645 process that can crash safely). The size of a JSON text in octets or
646 characters is usually a good indication of the size of the resources
647 required to decode it into a Perl structure.
648
649 Third, JSON::XS recurses using the C stack when decoding objects and
650 arrays. The C stack is a limited resource: for instance, on my amd64
651 machine with 8MB of stack size I can decode around 180k nested arrays
652 but only 14k nested JSON objects (due to perl itself recursing deeply on
653 croak to free the temporary). If that is exceeded, the program crashes.
654 to be conservative, the default nesting limit is set to 512. If your
655 process has a smaller stack, you should adjust this setting accordingly
656 with the "max_depth" method.
657
658 And last but least, something else could bomb you that I forgot to think
659 of. In that case, you get to keep the pieces. I am always open for
660 hints, though...
661
662 If you are using JSON::XS to return packets to consumption by javascript
663 scripts in a browser you should have a look at
664 <http://jpsykes.com/47/practical-csrf-and-json-security> to see wether
665 you are vulnerable to some common attack vectors (which really are
666 browser design bugs, but it is still you who will have to deal with it,
667 as major browser developers care only for features, not about doing
668 security right).
492 669
493BUGS 670BUGS
494 While the goal of this module is to be correct, that unfortunately does 671 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 672 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 673 still relatively early in its development. If you keep reporting bugs
497 will be fixed swiftly, though. 674 they will be fixed swiftly, though.
498 675
499AUTHOR 676AUTHOR
500 Marc Lehmann <schmorp@schmorp.de> 677 Marc Lehmann <schmorp@schmorp.de>
501 http://home.schmorp.de/ 678 http://home.schmorp.de/
502 679

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