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Revision 1.9 by root, Thu Mar 29 02:45:49 2007 UTC

1NAME 1NAME
2 JSON::XS - JSON serialising/deserialising, done correctly and fast 2 JSON::XS - JSON serialising/deserialising, done correctly and fast
3 3
4SYNOPSIS 4SYNOPSIS
5 use JSON::XS; 5 use JSON::XS;
6
7 # exported functions, they croak on error
8 # and expect/generate UTF-8
9
10 $utf8_encoded_json_text = to_json $perl_hash_or_arrayref;
11 $perl_hash_or_arrayref = from_json $utf8_encoded_json_text;
12
13 # 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
17 # OO-interface
18
19 $coder = JSON::XS->new->ascii->pretty->allow_nonref;
20 $pretty_printed_unencoded = $coder->encode ($perl_scalar);
21 $perl_scalar = $coder->decode ($unicode_json_text);
6 22
7DESCRIPTION 23DESCRIPTION
8 This module converts Perl data structures to JSON and vice versa. Its 24 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*. 25 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. 26 To reach the latter goal it was written in C.
… …
15 cases their maintainers are unresponsive, gone missing, or not listening 31 cases their maintainers are unresponsive, gone missing, or not listening
16 to bug reports for other reasons. 32 to bug reports for other reasons.
17 33
18 See COMPARISON, below, for a comparison to some other JSON modules. 34 See COMPARISON, below, for a comparison to some other JSON modules.
19 35
36 See MAPPING, below, on how JSON::XS maps perl values to JSON values and
37 vice versa.
38
20 FEATURES 39 FEATURES
21 * correct handling of unicode issues 40 * correct unicode handling
22 This module knows how to handle Unicode, and even documents how it 41 This module knows how to handle Unicode, and even documents how and
23 does so. 42 when it does so.
24 43
25 * round-trip integrity 44 * round-trip integrity
26 When you serialise a perl data structure using only datatypes 45 When you serialise a perl data structure using only datatypes
27 supported by JSON, the deserialised data structure is identical on 46 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"). 47 the Perl level. (e.g. the string "2.0" doesn't suddenly become "2"
48 just because it looks like a number).
29 49
30 * strict checking of JSON correctness 50 * strict checking of JSON correctness
31 There is no guessing, no generating of illegal JSON strings by 51 There is no guessing, no generating of illegal JSON texts by
32 default, and only JSON is accepted as input (the latter is a 52 default, and only JSON is accepted as input by default (the latter
33 security feature). 53 is a security feature).
34 54
35 * fast 55 * fast
36 compared to other JSON modules, this module compares favourably. 56 Compared to other JSON modules, this module compares favourably in
57 terms of speed, too.
37 58
38 * simple to use 59 * simple to use
39 This module has both a simple functional interface as well as an OO 60 This module has both a simple functional interface as well as an OO
40 interface. 61 interface.
41 62
42 * reasonably versatile output formats 63 * reasonably versatile output formats
43 You can choose between the most compact format possible, a 64 You can choose between the most compact guarenteed single-line
44 pure-ascii format, or a pretty-printed format. Or you can combine 65 format possible (nice for simple line-based protocols), a pure-ascii
66 format (for when your transport is not 8-bit clean, still supports
67 the whole unicode range), or a pretty-printed format (for when you
68 want to read that stuff). Or you can combine those features in
45 those features in whatever way you like. 69 whatever way you like.
46 70
47FUNCTIONAL INTERFACE 71FUNCTIONAL INTERFACE
48 The following convinience methods are provided by this module. They are 72 The following convinience methods are provided by this module. They are
49 exported by default: 73 exported by default:
50 74
51 $json_string = to_json $perl_scalar 75 $json_text = to_json $perl_scalar
52 Converts the given Perl data structure (a simple scalar or a 76 Converts the given Perl data structure (a simple scalar or a
53 reference to a hash or array) to a UTF-8 encoded, binary string 77 reference to a hash or array) to a UTF-8 encoded, binary string
54 (that is, the string contains octets only). Croaks on error. 78 (that is, the string contains octets only). Croaks on error.
55 79
56 This function call is functionally identical to "JSON::XS->new->utf8 80 This function call is functionally identical to:
57 (1)->encode ($perl_scalar)".
58 81
82 $json_text = JSON::XS->new->utf8->encode ($perl_scalar)
83
84 except being faster.
85
59 $perl_scalar = from_json $json_string 86 $perl_scalar = from_json $json_text
60 The opposite of "to_json": expects an UTF-8 (binary) string and 87 The opposite of "to_json": expects an UTF-8 (binary) string and
61 tries to parse that as an UTF-8 encoded JSON string, returning the 88 tries to parse that as an UTF-8 encoded JSON text, returning the
62 resulting simple scalar or reference. Croaks on error. 89 resulting simple scalar or reference. Croaks on error.
63 90
64 This function call is functionally identical to "JSON::XS->new->utf8 91 This function call is functionally identical to:
65 (1)->decode ($json_string)". 92
93 $perl_scalar = JSON::XS->new->utf8->decode ($json_text)
94
95 except being faster.
66 96
67OBJECT-ORIENTED INTERFACE 97OBJECT-ORIENTED INTERFACE
68 The object oriented interface lets you configure your own encoding or 98 The object oriented interface lets you configure your own encoding or
69 decoding style, within the limits of supported formats. 99 decoding style, within the limits of supported formats.
70 100
… …
74 *disabled*. 104 *disabled*.
75 105
76 The mutators for flags all return the JSON object again and thus 106 The mutators for flags all return the JSON object again and thus
77 calls can be chained: 107 calls can be chained:
78 108
79 my $json = JSON::XS->new->utf8(1)->space_after(1)->encode ({a => [1,2]}) 109 my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]})
80 => {"a": [1, 2]} 110 => {"a": [1, 2]}
81 111
82 $json = $json->ascii ($enable) 112 $json = $json->ascii ([$enable])
83 If $enable is true, then the "encode" method will not generate 113 If $enable is true (or missing), then the "encode" method will not
84 characters outside the code range 0..127. Any unicode characters 114 generate characters outside the code range 0..127 (which is ASCII).
85 outside that range will be escaped using either a single \uXXXX (BMP 115 Any unicode characters outside that range will be escaped using
86 characters) or a double \uHHHH\uLLLLL escape sequence, as per 116 either a single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL
87 RFC4627. 117 escape sequence, as per RFC4627.
88 118
89 If $enable is false, then the "encode" method will not escape 119 If $enable is false, then the "encode" method will not escape
90 Unicode characters unless necessary. 120 Unicode characters unless required by the JSON syntax. This results
121 in a faster and more compact format.
91 122
92 JSON::XS->new->ascii (1)->encode (chr 0x10401) 123 JSON::XS->new->ascii (1)->encode ([chr 0x10401])
93 => \ud801\udc01 124 => ["\ud801\udc01"]
94 125
95 $json = $json->utf8 ($enable) 126 $json = $json->utf8 ([$enable])
96 If $enable is true, then the "encode" method will encode the JSON 127 If $enable is true (or missing), then the "encode" method will
97 string into UTF-8, as required by many protocols, while the "decode" 128 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 129 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 130 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. 131 characters outside the range 0..255, they are thus useful for
132 bytewise/binary I/O. In future versions, enabling this option might
133 enable autodetection of the UTF-16 and UTF-32 encoding families, as
134 described in RFC4627.
101 135
102 If $enable is false, then the "encode" method will return the JSON 136 If $enable is false, then the "encode" method will return the JSON
103 string as a (non-encoded) unicode string, while "decode" expects 137 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 138 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. 139 UTF-16) needs to be done yourself, e.g. using the Encode module.
106 140
141 Example, output UTF-16BE-encoded JSON:
142
143 use Encode;
144 $jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
145
146 Example, decode UTF-32LE-encoded JSON:
147
148 use Encode;
149 $object = JSON::XS->new->decode (decode "UTF-32LE", $jsontext);
150
107 $json = $json->pretty ($enable) 151 $json = $json->pretty ([$enable])
108 This enables (or disables) all of the "indent", "space_before" and 152 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 153 "space_after" (and in the future possibly more) flags in one call to
110 generate the most readable (or most compact) form possible. 154 generate the most readable (or most compact) form possible.
155
156 Example, pretty-print some simple structure:
111 157
112 my $json = JSON::XS->new->pretty(1)->encode ({a => [1,2]}) 158 my $json = JSON::XS->new->pretty(1)->encode ({a => [1,2]})
113 => 159 =>
114 { 160 {
115 "a" : [ 161 "a" : [
116 1, 162 1,
117 2 163 2
118 ] 164 ]
119 } 165 }
120 166
121 $json = $json->indent ($enable) 167 $json = $json->indent ([$enable])
122 If $enable is true, then the "encode" method will use a multiline 168 If $enable is true (or missing), then the "encode" method will use a
123 format as output, putting every array member or object/hash 169 multiline format as output, putting every array member or
124 key-value pair into its own line, identing them properly. 170 object/hash key-value pair into its own line, identing them
171 properly.
125 172
126 If $enable is false, no newlines or indenting will be produced, and 173 If $enable is false, no newlines or indenting will be produced, and
127 the resulting JSON strings is guarenteed not to contain any 174 the resulting JSON text is guarenteed not to contain any "newlines".
128 "newlines".
129 175
130 This setting has no effect when decoding JSON strings. 176 This setting has no effect when decoding JSON texts.
131 177
132 $json = $json->space_before ($enable) 178 $json = $json->space_before ([$enable])
133 If $enable is true, then the "encode" method will add an extra 179 If $enable is true (or missing), then the "encode" method will add
134 optional space before the ":" separating keys from values in JSON 180 an extra optional space before the ":" separating keys from values
135 objects. 181 in JSON objects.
136 182
137 If $enable is false, then the "encode" method will not add any extra 183 If $enable is false, then the "encode" method will not add any extra
138 space at those places. 184 space at those places.
139 185
140 This setting has no effect when decoding JSON strings. You will also 186 This setting has no effect when decoding JSON texts. You will also
141 most likely combine this setting with "space_after". 187 most likely combine this setting with "space_after".
142 188
189 Example, space_before enabled, space_after and indent disabled:
190
191 {"key" :"value"}
192
143 $json = $json->space_after ($enable) 193 $json = $json->space_after ([$enable])
144 If $enable is true, then the "encode" method will add an extra 194 If $enable is true (or missing), then the "encode" method will add
145 optional space after the ":" separating keys from values in JSON 195 an extra optional space after the ":" separating keys from values in
146 objects and extra whitespace after the "," separating key-value 196 JSON objects and extra whitespace after the "," separating key-value
147 pairs and array members. 197 pairs and array members.
148 198
149 If $enable is false, then the "encode" method will not add any extra 199 If $enable is false, then the "encode" method will not add any extra
150 space at those places. 200 space at those places.
151 201
152 This setting has no effect when decoding JSON strings. 202 This setting has no effect when decoding JSON texts.
153 203
204 Example, space_before and indent disabled, space_after enabled:
205
206 {"key": "value"}
207
154 $json = $json->canonical ($enable) 208 $json = $json->canonical ([$enable])
155 If $enable is true, then the "encode" method will output JSON 209 If $enable is true (or missing), then the "encode" method will
156 objects by sorting their keys. This is adding a comparatively high 210 output JSON objects by sorting their keys. This is adding a
157 overhead. 211 comparatively high overhead.
158 212
159 If $enable is false, then the "encode" method will output key-value 213 If $enable is false, then the "encode" method will output key-value
160 pairs in the order Perl stores them (which will likely change 214 pairs in the order Perl stores them (which will likely change
161 between runs of the same script). 215 between runs of the same script).
162 216
163 This option is useful if you want the same data structure to be 217 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). 218 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 219 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 220 contains the same data, as key-value pairs have no inherent ordering
167 in Perl. 221 in Perl.
168 222
169 This setting has no effect when decoding JSON strings. 223 This setting has no effect when decoding JSON texts.
170 224
171 $json = $json->allow_nonref ($enable) 225 $json = $json->allow_nonref ([$enable])
172 If $enable is true, then the "encode" method can convert a 226 If $enable is true (or missing), then the "encode" method can
173 non-reference into its corresponding string, number or null JSON 227 convert a non-reference into its corresponding string, number or
174 value, which is an extension to RFC4627. Likewise, "decode" will 228 null JSON value, which is an extension to RFC4627. Likewise,
175 accept those JSON values instead of croaking. 229 "decode" will accept those JSON values instead of croaking.
176 230
177 If $enable is false, then the "encode" method will croak if it isn't 231 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 232 passed an arrayref or hashref, as JSON texts must either be an
179 object or array. Likewise, "decode" will croak if given something 233 object or array. Likewise, "decode" will croak if given something
180 that is not a JSON object or array. 234 that is not a JSON object or array.
181 235
236 Example, encode a Perl scalar as JSON value with enabled
237 "allow_nonref", resulting in an invalid JSON text:
238
239 JSON::XS->new->allow_nonref->encode ("Hello, World!")
240 => "Hello, World!"
241
242 $json = $json->shrink ([$enable])
243 Perl usually over-allocates memory a bit when allocating space for
244 strings. This flag optionally resizes strings generated by either
245 "encode" or "decode" to their minimum size possible. This can save
246 memory when your JSON texts are either very very long or you have
247 many short strings. It will also try to downgrade any strings to
248 octet-form if possible: perl stores strings internally either in an
249 encoding called UTF-X or in octet-form. The latter cannot store
250 everything but uses less space in general (and some buggy Perl or C
251 code might even rely on that internal representation being used).
252
253 The actual definition of what shrink does might change in future
254 versions, but it will always try to save space at the expense of
255 time.
256
257 If $enable is true (or missing), the string returned by "encode"
258 will be shrunk-to-fit, while all strings generated by "decode" will
259 also be shrunk-to-fit.
260
261 If $enable is false, then the normal perl allocation algorithms are
262 used. If you work with your data, then this is likely to be faster.
263
264 In the future, this setting might control other things, such as
265 converting strings that look like integers or floats into integers
266 or floats internally (there is no difference on the Perl level),
267 saving space.
268
269 $json = $json->max_depth ([$maximum_nesting_depth])
270 Sets the maximum nesting level (default 4096) accepted while
271 encoding or decoding. If the JSON text or Perl data structure has an
272 equal or higher nesting level then this limit, then the encoder and
273 decoder will stop and croak at that point.
274
275 Nesting level is defined by number of hash- or arrayrefs that the
276 encoder needs to traverse to reach a given point or the number of
277 "{" or "[" characters without their matching closing parenthesis
278 crossed to reach a given character in a string.
279
280 Setting the maximum depth to one disallows any nesting, so that
281 ensures that the object is only a single hash/object or array.
282
283 The argument to "max_depth" will be rounded up to the next nearest
284 power of two.
285
286 See SECURITY CONSIDERATIONS, below, for more info on why this is
287 useful.
288
182 $json_string = $json->encode ($perl_scalar) 289 $json_text = $json->encode ($perl_scalar)
183 Converts the given Perl data structure (a simple scalar or a 290 Converts the given Perl data structure (a simple scalar or a
184 reference to a hash or array) to its JSON representation. Simple 291 reference to a hash or array) to its JSON representation. Simple
185 scalars will be converted into JSON string or number sequences, 292 scalars will be converted into JSON string or number sequences,
186 while references to arrays become JSON arrays and references to 293 while references to arrays become JSON arrays and references to
187 hashes become JSON objects. Undefined Perl values (e.g. "undef") 294 hashes become JSON objects. Undefined Perl values (e.g. "undef")
188 become JSON "null" values. Neither "true" nor "false" values will be 295 become JSON "null" values. Neither "true" nor "false" values will be
189 generated. 296 generated.
190 297
191 $perl_scalar = $json->decode ($json_string) 298 $perl_scalar = $json->decode ($json_text)
192 The opposite of "encode": expects a JSON string and tries to parse 299 The opposite of "encode": expects a JSON text and tries to parse it,
193 it, returning the resulting simple scalar or reference. Croaks on 300 returning the resulting simple scalar or reference. Croaks on error.
194 error.
195 301
196 JSON numbers and strings become simple Perl scalars. JSON arrays 302 JSON numbers and strings become simple Perl scalars. JSON arrays
197 become Perl arrayrefs and JSON objects become Perl hashrefs. "true" 303 become Perl arrayrefs and JSON objects become Perl hashrefs. "true"
198 becomes 1, "false" becomes 0 and "null" becomes "undef". 304 becomes 1, "false" becomes 0 and "null" becomes "undef".
305
306MAPPING
307 This section describes how JSON::XS maps Perl values to JSON values and
308 vice versa. These mappings are designed to "do the right thing" in most
309 circumstances automatically, preserving round-tripping characteristics
310 (what you put in comes out as something equivalent).
311
312 For the more enlightened: note that in the following descriptions,
313 lowercase *perl* refers to the Perl interpreter, while uppcercase *Perl*
314 refers to the abstract Perl language itself.
315
316 JSON -> PERL
317 object
318 A JSON object becomes a reference to a hash in Perl. No ordering of
319 object keys is preserved (JSON does not preserver object key
320 ordering itself).
321
322 array
323 A JSON array becomes a reference to an array in Perl.
324
325 string
326 A JSON string becomes a string scalar in Perl - Unicode codepoints
327 in JSON are represented by the same codepoints in the Perl string,
328 so no manual decoding is necessary.
329
330 number
331 A JSON number becomes either an integer or numeric (floating point)
332 scalar in perl, depending on its range and any fractional parts. On
333 the Perl level, there is no difference between those as Perl handles
334 all the conversion details, but an integer may take slightly less
335 memory and might represent more values exactly than (floating point)
336 numbers.
337
338 true, false
339 These JSON atoms become 0, 1, respectively. Information is lost in
340 this process. Future versions might represent those values
341 differently, but they will be guarenteed to act like these integers
342 would normally in Perl.
343
344 null
345 A JSON null atom becomes "undef" in Perl.
346
347 PERL -> JSON
348 The mapping from Perl to JSON is slightly more difficult, as Perl is a
349 truly typeless language, so we can only guess which JSON type is meant
350 by a Perl value.
351
352 hash references
353 Perl hash references become JSON objects. As there is no inherent
354 ordering in hash keys (or JSON objects), they will usually be
355 encoded in a pseudo-random order that can change between runs of the
356 same program but stays generally the same within a single run of a
357 program. JSON::XS can optionally sort the hash keys (determined by
358 the *canonical* flag), so the same datastructure will serialise to
359 the same JSON text (given same settings and version of JSON::XS),
360 but this incurs a runtime overhead and is only rarely useful, e.g.
361 when you want to compare some JSON text against another for
362 equality.
363
364 array references
365 Perl array references become JSON arrays.
366
367 other references
368 Other unblessed references are generally not allowed and will cause
369 an exception to be thrown, except for references to the integers 0
370 and 1, which get turned into "false" and "true" atoms in JSON. You
371 can also use "JSON::XS::false" and "JSON::XS::true" to improve
372 readability.
373
374 to_json [\0,JSON::XS::true] # yields [false,true]
375
376 blessed objects
377 Blessed objects are not allowed. JSON::XS currently tries to encode
378 their underlying representation (hash- or arrayref), but this
379 behaviour might change in future versions.
380
381 simple scalars
382 Simple Perl scalars (any scalar that is not a reference) are the
383 most difficult objects to encode: JSON::XS will encode undefined
384 scalars as JSON null value, scalars that have last been used in a
385 string context before encoding as JSON strings and anything else as
386 number value:
387
388 # dump as number
389 to_json [2] # yields [2]
390 to_json [-3.0e17] # yields [-3e+17]
391 my $value = 5; to_json [$value] # yields [5]
392
393 # used as string, so dump as string
394 print $value;
395 to_json [$value] # yields ["5"]
396
397 # undef becomes null
398 to_json [undef] # yields [null]
399
400 You can force the type to be a string by stringifying it:
401
402 my $x = 3.1; # some variable containing a number
403 "$x"; # stringified
404 $x .= ""; # another, more awkward way to stringify
405 print $x; # perl does it for you, too, quite often
406
407 You can force the type to be a number by numifying it:
408
409 my $x = "3"; # some variable containing a string
410 $x += 0; # numify it, ensuring it will be dumped as a number
411 $x *= 1; # same thing, the choise is yours.
412
413 You can not currently output JSON booleans or force the type in
414 other, less obscure, ways. Tell me if you need this capability.
415
416 circular data structures
417 Those will be encoded until memory or stackspace runs out.
199 418
200COMPARISON 419COMPARISON
201 As already mentioned, this module was created because none of the 420 As already mentioned, this module was created because none of the
202 existing JSON modules could be made to work correctly. First I will 421 existing JSON modules could be made to work correctly. First I will
203 describe the problems (or pleasures) I encountered with various existing 422 describe the problems (or pleasures) I encountered with various existing
… …
225 444
226 Has problems handling many Perl values (e.g. regex results and other 445 Has problems handling many Perl values (e.g. regex results and other
227 magic values will make it croak). 446 magic values will make it croak).
228 447
229 Does not even generate valid JSON ("{1,2}" gets converted to "{1:2}" 448 Does not even generate valid JSON ("{1,2}" gets converted to "{1:2}"
230 which is not a valid JSON string. 449 which is not a valid JSON text.
231 450
232 Unmaintained (maintainer unresponsive for many months, bugs are not 451 Unmaintained (maintainer unresponsive for many months, bugs are not
233 getting fixed). 452 getting fixed).
234 453
235 JSON::Syck 0.21 454 JSON::Syck 0.21
236 Very buggy (often crashes). 455 Very buggy (often crashes).
237 456
238 Very inflexible (no human-readable format supported, format pretty 457 Very inflexible (no human-readable format supported, format pretty
239 much undocumented. I need at least a format for easy reading by 458 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 459 humans and a single-line compact format for use in a protocol, and
241 preferably a way to generate ASCII-only JSON strings). 460 preferably a way to generate ASCII-only JSON texts).
242 461
243 Completely broken (and confusingly documented) Unicode handling 462 Completely broken (and confusingly documented) Unicode handling
244 (unicode escapes are not working properly, you need to set 463 (unicode escapes are not working properly, you need to set
245 ImplicitUnicode to *different* values on en- and decoding to get 464 ImplicitUnicode to *different* values on en- and decoding to get
246 symmetric behaviour). 465 symmetric behaviour).
… …
269 488
270 Very inflexible. 489 Very inflexible.
271 490
272 No roundtripping. 491 No roundtripping.
273 492
274 Does not generate valid JSON (key strings are often unquoted, empty 493 Does not generate valid JSON texts (key strings are often unquoted,
275 keys result in nothing being output) 494 empty keys result in nothing being output)
276 495
277 Does not check input for validity. 496 Does not check input for validity.
278 497
279 SPEED 498 SPEED
280 It seems that JSON::XS is surprisingly fast, as shown in the following 499 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 500 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 501 in the JSON::XS distribution, to make it easy to compare on your own
283 system. 502 system.
284 503
285 First is a comparison between various modules using a very simple JSON 504 First comes a comparison between various modules using a very short JSON
505 string:
506
507 {"method": "handleMessage", "params": ["user1", "we were just talking"], "id": null}
508
286 string, showing the number of encodes/decodes per second (JSON::XS is 509 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 510 functional interface, while JSON::XS/2 uses the OO interface with
288 pretty-printing and hashkey sorting enabled). 511 pretty-printing and hashkey sorting enabled). Higher is better:
289 512
290 module | encode | decode | 513 module | encode | decode |
291 -----------|------------|------------| 514 -----------|------------|------------|
292 JSON | 14006 | 6820 | 515 JSON | 11488.516 | 7823.035 |
293 JSON::DWIW | 200937 | 120386 | 516 JSON::DWIW | 94708.054 | 129094.260 |
294 JSON::PC | 85065 | 129366 | 517 JSON::PC | 63884.157 | 128528.212 |
295 JSON::Syck | 59898 | 44232 | 518 JSON::Syck | 34898.677 | 42096.911 |
296 JSON::XS | 1171478 | 342435 | 519 JSON::XS | 654027.064 | 396423.669 |
297 JSON::XS/2 | 730760 | 328714 | 520 JSON::XS/2 | 371564.190 | 371725.613 |
298 -----------+------------+------------+ 521 -----------+------------+------------+
299 522
300 That is, JSON::XS is 6 times faster than than JSON::DWIW and about 80 523 That is, JSON::XS is more than six times faster than JSON::DWIW on
524 encoding, more than three times faster on decoding, and about thirty
301 times faster than JSON, even with pretty-printing and key sorting. 525 times faster than JSON, even with pretty-printing and key sorting.
302 526
303 Using a longer test string (roughly 8KB, generated from Yahoo! Locals 527 Using a longer test string (roughly 18KB, generated from Yahoo! Locals
304 search API (http://nanoref.com/yahooapis/mgPdGg): 528 search API (http://nanoref.com/yahooapis/mgPdGg):
305 529
306 module | encode | decode | 530 module | encode | decode |
307 -----------|------------|------------| 531 -----------|------------|------------|
308 JSON | 673 | 38 | 532 JSON | 273.023 | 44.674 |
309 JSON::DWIW | 5271 | 770 | 533 JSON::DWIW | 1089.383 | 1145.704 |
310 JSON::PC | 9901 | 2491 | 534 JSON::PC | 3097.419 | 2393.921 |
311 JSON::Syck | 2360 | 786 | 535 JSON::Syck | 514.060 | 843.053 |
312 JSON::XS | 37398 | 3202 | 536 JSON::XS | 6479.668 | 3636.364 |
313 JSON::XS/2 | 13765 | 3153 | 537 JSON::XS/2 | 3774.221 | 3599.124 |
314 -----------+------------+------------+ 538 -----------+------------+------------+
315 539
316 Again, JSON::XS leads by far in the encoding case, while still beating 540 Again, JSON::XS leads by far.
317 every other module in the decoding case.
318 541
319 Last example is an almost 8MB large hash with many large binary values 542 On large strings containing lots of high unicode characters, some
320 (PNG files), resulting in a lot of escaping: 543 modules (such as JSON::PC) seem to decode faster than JSON::XS, but the
544 result will be broken due to missing (or wrong) unicode handling. Others
545 refuse to decode or encode properly, so it was impossible to prepare a
546 fair comparison table for that case.
547
548SECURITY CONSIDERATIONS
549 When you are using JSON in a protocol, talking to untrusted potentially
550 hostile creatures requires relatively few measures.
551
552 First of all, your JSON decoder should be secure, that is, should not
553 have any buffer overflows. Obviously, this module should ensure that and
554 I am trying hard on making that true, but you never know.
555
556 Second, you need to avoid resource-starving attacks. That means you
557 should limit the size of JSON texts you accept, or make sure then when
558 your resources run out, thats just fine (e.g. by using a separate
559 process that can crash safely). The size of a JSON text in octets or
560 characters is usually a good indication of the size of the resources
561 required to decode it into a Perl structure.
562
563 Third, JSON::XS recurses using the C stack when decoding objects and
564 arrays. The C stack is a limited resource: for instance, on my amd64
565 machine with 8MB of stack size I can decode around 180k nested arrays
566 but only 14k nested JSON objects. If that is exceeded, the program
567 crashes. Thats why the default nesting limit is set to 4096. If your
568 process has a smaller stack, you should adjust this setting accordingly
569 with the "max_depth" method.
570
571 And last but least, something else could bomb you that I forgot to think
572 of. In that case, you get to keep the pieces. I am alway sopen for
573 hints, though...
321 574
322BUGS 575BUGS
323 While the goal of this module is to be correct, that unfortunately does 576 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 577 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 578 still relatively early in its development. If you keep reporting bugs
326 will be fixed swiftly, though. 579 they will be fixed swiftly, though.
327 580
328AUTHOR 581AUTHOR
329 Marc Lehmann <schmorp@schmorp.de> 582 Marc Lehmann <schmorp@schmorp.de>
330 http://home.schmorp.de/ 583 http://home.schmorp.de/
331 584

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