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1NAME 1NAME
2 JSON::XS - JSON serialising/deserialising, done correctly and fast 2 JSON::XS - JSON serialising/deserialising, done correctly and fast
3 3
4SYNOPSIS 4SYNOPSIS
5 use JSON::XS; 5 use JSON::XS;
6
7 # exported functions, they croak on error
8 # and expect/generate UTF-8
9
10 $utf8_encoded_json_text = to_json $perl_hash_or_arrayref;
11 $perl_hash_or_arrayref = from_json $utf8_encoded_json_text;
12
13 # 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. The resulting encoded JSON text can
118 be treated as a native unicode string, an ascii-encoded,
119 latin1-encoded or UTF-8 encoded string, or any other superset of
120 ASCII.
88 121
89 If $enable is false, then the "encode" method will not escape 122 If $enable is false, then the "encode" method will not escape
90 Unicode characters unless necessary. 123 Unicode characters unless required by the JSON syntax or other
124 flags. This results in a faster and more compact format.
91 125
126 The main use for this flag is to produce JSON texts that can be
127 transmitted over a 7-bit channel, as the encoded JSON texts will not
128 contain any 8 bit characters.
129
92 JSON::XS->new->ascii (1)->encode (chr 0x10401) 130 JSON::XS->new->ascii (1)->encode ([chr 0x10401])
93 => \ud801\udc01 131 => ["\ud801\udc01"]
94 132
133 $json = $json->latin1 ([$enable])
134 If $enable is true (or missing), then the "encode" method will
135 encode the resulting JSON text as latin1 (or iso-8859-1), escaping
136 any characters outside the code range 0..255. The resulting string
137 can be treated as a latin1-encoded JSON text or a native unicode
138 string. The "decode" method will not be affected in any way by this
139 flag, as "decode" by default expects unicode, which is a strict
140 superset of latin1.
141
142 If $enable is false, then the "encode" method will not escape
143 Unicode characters unless required by the JSON syntax or other
144 flags.
145
146 The main use for this flag is efficiently encoding binary data as
147 JSON text, as most octets will not be escaped, resulting in a
148 smaller encoded size. The disadvantage is that the resulting JSON
149 text is encoded in latin1 (and must correctly be treated as such
150 when storing and transfering), a rare encoding for JSON. It is
151 therefore most useful when you want to store data structures known
152 to contain binary data efficiently in files or databases, not when
153 talking to other JSON encoders/decoders.
154
155 JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]
156 => ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)
157
95 $json = $json->utf8 ($enable) 158 $json = $json->utf8 ([$enable])
96 If $enable is true, then the "encode" method will encode the JSON 159 If $enable is true (or missing), then the "encode" method will
97 string into UTF-8, as required by many protocols, while the "decode" 160 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 161 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 162 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. 163 characters outside the range 0..255, they are thus useful for
164 bytewise/binary I/O. In future versions, enabling this option might
165 enable autodetection of the UTF-16 and UTF-32 encoding families, as
166 described in RFC4627.
101 167
102 If $enable is false, then the "encode" method will return the JSON 168 If $enable is false, then the "encode" method will return the JSON
103 string as a (non-encoded) unicode string, while "decode" expects 169 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 170 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. 171 UTF-16) needs to be done yourself, e.g. using the Encode module.
106 172
173 Example, output UTF-16BE-encoded JSON:
174
175 use Encode;
176 $jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
177
178 Example, decode UTF-32LE-encoded JSON:
179
180 use Encode;
181 $object = JSON::XS->new->decode (decode "UTF-32LE", $jsontext);
182
107 $json = $json->pretty ($enable) 183 $json = $json->pretty ([$enable])
108 This enables (or disables) all of the "indent", "space_before" and 184 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 185 "space_after" (and in the future possibly more) flags in one call to
110 generate the most readable (or most compact) form possible. 186 generate the most readable (or most compact) form possible.
187
188 Example, pretty-print some simple structure:
111 189
112 my $json = JSON::XS->new->pretty(1)->encode ({a => [1,2]}) 190 my $json = JSON::XS->new->pretty(1)->encode ({a => [1,2]})
113 => 191 =>
114 { 192 {
115 "a" : [ 193 "a" : [
116 1, 194 1,
117 2 195 2
118 ] 196 ]
119 } 197 }
120 198
121 $json = $json->indent ($enable) 199 $json = $json->indent ([$enable])
122 If $enable is true, then the "encode" method will use a multiline 200 If $enable is true (or missing), then the "encode" method will use a
123 format as output, putting every array member or object/hash 201 multiline format as output, putting every array member or
124 key-value pair into its own line, identing them properly. 202 object/hash key-value pair into its own line, identing them
203 properly.
125 204
126 If $enable is false, no newlines or indenting will be produced, and 205 If $enable is false, no newlines or indenting will be produced, and
127 the resulting JSON strings is guarenteed not to contain any 206 the resulting JSON text is guarenteed not to contain any "newlines".
128 "newlines".
129 207
130 This setting has no effect when decoding JSON strings. 208 This setting has no effect when decoding JSON texts.
131 209
132 $json = $json->space_before ($enable) 210 $json = $json->space_before ([$enable])
133 If $enable is true, then the "encode" method will add an extra 211 If $enable is true (or missing), then the "encode" method will add
134 optional space before the ":" separating keys from values in JSON 212 an extra optional space before the ":" separating keys from values
135 objects. 213 in JSON objects.
136 214
137 If $enable is false, then the "encode" method will not add any extra 215 If $enable is false, then the "encode" method will not add any extra
138 space at those places. 216 space at those places.
139 217
140 This setting has no effect when decoding JSON strings. You will also 218 This setting has no effect when decoding JSON texts. You will also
141 most likely combine this setting with "space_after". 219 most likely combine this setting with "space_after".
142 220
221 Example, space_before enabled, space_after and indent disabled:
222
223 {"key" :"value"}
224
143 $json = $json->space_after ($enable) 225 $json = $json->space_after ([$enable])
144 If $enable is true, then the "encode" method will add an extra 226 If $enable is true (or missing), then the "encode" method will add
145 optional space after the ":" separating keys from values in JSON 227 an extra optional space after the ":" separating keys from values in
146 objects and extra whitespace after the "," separating key-value 228 JSON objects and extra whitespace after the "," separating key-value
147 pairs and array members. 229 pairs and array members.
148 230
149 If $enable is false, then the "encode" method will not add any extra 231 If $enable is false, then the "encode" method will not add any extra
150 space at those places. 232 space at those places.
151 233
152 This setting has no effect when decoding JSON strings. 234 This setting has no effect when decoding JSON texts.
153 235
236 Example, space_before and indent disabled, space_after enabled:
237
238 {"key": "value"}
239
154 $json = $json->canonical ($enable) 240 $json = $json->canonical ([$enable])
155 If $enable is true, then the "encode" method will output JSON 241 If $enable is true (or missing), then the "encode" method will
156 objects by sorting their keys. This is adding a comparatively high 242 output JSON objects by sorting their keys. This is adding a
157 overhead. 243 comparatively high overhead.
158 244
159 If $enable is false, then the "encode" method will output key-value 245 If $enable is false, then the "encode" method will output key-value
160 pairs in the order Perl stores them (which will likely change 246 pairs in the order Perl stores them (which will likely change
161 between runs of the same script). 247 between runs of the same script).
162 248
163 This option is useful if you want the same data structure to be 249 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). 250 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 251 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 252 contains the same data, as key-value pairs have no inherent ordering
167 in Perl. 253 in Perl.
168 254
169 This setting has no effect when decoding JSON strings. 255 This setting has no effect when decoding JSON texts.
170 256
171 $json = $json->allow_nonref ($enable) 257 $json = $json->allow_nonref ([$enable])
172 If $enable is true, then the "encode" method can convert a 258 If $enable is true (or missing), then the "encode" method can
173 non-reference into its corresponding string, number or null JSON 259 convert a non-reference into its corresponding string, number or
174 value, which is an extension to RFC4627. Likewise, "decode" will 260 null JSON value, which is an extension to RFC4627. Likewise,
175 accept those JSON values instead of croaking. 261 "decode" will accept those JSON values instead of croaking.
176 262
177 If $enable is false, then the "encode" method will croak if it isn't 263 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 264 passed an arrayref or hashref, as JSON texts must either be an
179 object or array. Likewise, "decode" will croak if given something 265 object or array. Likewise, "decode" will croak if given something
180 that is not a JSON object or array. 266 that is not a JSON object or array.
181 267
268 Example, encode a Perl scalar as JSON value with enabled
269 "allow_nonref", resulting in an invalid JSON text:
270
271 JSON::XS->new->allow_nonref->encode ("Hello, World!")
272 => "Hello, World!"
273
274 $json = $json->shrink ([$enable])
275 Perl usually over-allocates memory a bit when allocating space for
276 strings. This flag optionally resizes strings generated by either
277 "encode" or "decode" to their minimum size possible. This can save
278 memory when your JSON texts are either very very long or you have
279 many short strings. It will also try to downgrade any strings to
280 octet-form if possible: perl stores strings internally either in an
281 encoding called UTF-X or in octet-form. The latter cannot store
282 everything but uses less space in general (and some buggy Perl or C
283 code might even rely on that internal representation being used).
284
285 The actual definition of what shrink does might change in future
286 versions, but it will always try to save space at the expense of
287 time.
288
289 If $enable is true (or missing), the string returned by "encode"
290 will be shrunk-to-fit, while all strings generated by "decode" will
291 also be shrunk-to-fit.
292
293 If $enable is false, then the normal perl allocation algorithms are
294 used. If you work with your data, then this is likely to be faster.
295
296 In the future, this setting might control other things, such as
297 converting strings that look like integers or floats into integers
298 or floats internally (there is no difference on the Perl level),
299 saving space.
300
301 $json = $json->max_depth ([$maximum_nesting_depth])
302 Sets the maximum nesting level (default 512) accepted while encoding
303 or decoding. If the JSON text or Perl data structure has an equal or
304 higher nesting level then this limit, then the encoder and decoder
305 will stop and croak at that point.
306
307 Nesting level is defined by number of hash- or arrayrefs that the
308 encoder needs to traverse to reach a given point or the number of
309 "{" or "[" characters without their matching closing parenthesis
310 crossed to reach a given character in a string.
311
312 Setting the maximum depth to one disallows any nesting, so that
313 ensures that the object is only a single hash/object or array.
314
315 The argument to "max_depth" will be rounded up to the next nearest
316 power of two.
317
318 See SECURITY CONSIDERATIONS, below, for more info on why this is
319 useful.
320
182 $json_string = $json->encode ($perl_scalar) 321 $json_text = $json->encode ($perl_scalar)
183 Converts the given Perl data structure (a simple scalar or a 322 Converts the given Perl data structure (a simple scalar or a
184 reference to a hash or array) to its JSON representation. Simple 323 reference to a hash or array) to its JSON representation. Simple
185 scalars will be converted into JSON string or number sequences, 324 scalars will be converted into JSON string or number sequences,
186 while references to arrays become JSON arrays and references to 325 while references to arrays become JSON arrays and references to
187 hashes become JSON objects. Undefined Perl values (e.g. "undef") 326 hashes become JSON objects. Undefined Perl values (e.g. "undef")
188 become JSON "null" values. Neither "true" nor "false" values will be 327 become JSON "null" values. Neither "true" nor "false" values will be
189 generated. 328 generated.
190 329
191 $perl_scalar = $json->decode ($json_string) 330 $perl_scalar = $json->decode ($json_text)
192 The opposite of "encode": expects a JSON string and tries to parse 331 The opposite of "encode": expects a JSON text and tries to parse it,
193 it, returning the resulting simple scalar or reference. Croaks on 332 returning the resulting simple scalar or reference. Croaks on error.
194 error.
195 333
196 JSON numbers and strings become simple Perl scalars. JSON arrays 334 JSON numbers and strings become simple Perl scalars. JSON arrays
197 become Perl arrayrefs and JSON objects become Perl hashrefs. "true" 335 become Perl arrayrefs and JSON objects become Perl hashrefs. "true"
198 becomes 1, "false" becomes 0 and "null" becomes "undef". 336 becomes 1, "false" becomes 0 and "null" becomes "undef".
337
338 ($perl_scalar, $characters) = $json->decode_prefix ($json_text)
339 This works like the "decode" method, but instead of raising an
340 exception when there is trailing garbage after the first JSON
341 object, it will silently stop parsing there and return the number of
342 characters consumed so far.
343
344 This is useful if your JSON texts are not delimited by an outer
345 protocol (which is not the brightest thing to do in the first place)
346 and you need to know where the JSON text ends.
347
348 JSON::XS->new->decode_prefix ("[1] the tail")
349 => ([], 3)
350
351MAPPING
352 This section describes how JSON::XS maps Perl values to JSON values and
353 vice versa. These mappings are designed to "do the right thing" in most
354 circumstances automatically, preserving round-tripping characteristics
355 (what you put in comes out as something equivalent).
356
357 For the more enlightened: note that in the following descriptions,
358 lowercase *perl* refers to the Perl interpreter, while uppcercase *Perl*
359 refers to the abstract Perl language itself.
360
361 JSON -> PERL
362 object
363 A JSON object becomes a reference to a hash in Perl. No ordering of
364 object keys is preserved (JSON does not preserver object key
365 ordering itself).
366
367 array
368 A JSON array becomes a reference to an array in Perl.
369
370 string
371 A JSON string becomes a string scalar in Perl - Unicode codepoints
372 in JSON are represented by the same codepoints in the Perl string,
373 so no manual decoding is necessary.
374
375 number
376 A JSON number becomes either an integer or numeric (floating point)
377 scalar in perl, depending on its range and any fractional parts. On
378 the Perl level, there is no difference between those as Perl handles
379 all the conversion details, but an integer may take slightly less
380 memory and might represent more values exactly than (floating point)
381 numbers.
382
383 true, false
384 These JSON atoms become 0, 1, respectively. Information is lost in
385 this process. Future versions might represent those values
386 differently, but they will be guarenteed to act like these integers
387 would normally in Perl.
388
389 null
390 A JSON null atom becomes "undef" in Perl.
391
392 PERL -> JSON
393 The mapping from Perl to JSON is slightly more difficult, as Perl is a
394 truly typeless language, so we can only guess which JSON type is meant
395 by a Perl value.
396
397 hash references
398 Perl hash references become JSON objects. As there is no inherent
399 ordering in hash keys (or JSON objects), they will usually be
400 encoded in a pseudo-random order that can change between runs of the
401 same program but stays generally the same within a single run of a
402 program. JSON::XS can optionally sort the hash keys (determined by
403 the *canonical* flag), so the same datastructure will serialise to
404 the same JSON text (given same settings and version of JSON::XS),
405 but this incurs a runtime overhead and is only rarely useful, e.g.
406 when you want to compare some JSON text against another for
407 equality.
408
409 array references
410 Perl array references become JSON arrays.
411
412 other references
413 Other unblessed references are generally not allowed and will cause
414 an exception to be thrown, except for references to the integers 0
415 and 1, which get turned into "false" and "true" atoms in JSON. You
416 can also use "JSON::XS::false" and "JSON::XS::true" to improve
417 readability.
418
419 to_json [\0,JSON::XS::true] # yields [false,true]
420
421 blessed objects
422 Blessed objects are not allowed. JSON::XS currently tries to encode
423 their underlying representation (hash- or arrayref), but this
424 behaviour might change in future versions.
425
426 simple scalars
427 Simple Perl scalars (any scalar that is not a reference) are the
428 most difficult objects to encode: JSON::XS will encode undefined
429 scalars as JSON null value, scalars that have last been used in a
430 string context before encoding as JSON strings and anything else as
431 number value:
432
433 # dump as number
434 to_json [2] # yields [2]
435 to_json [-3.0e17] # yields [-3e+17]
436 my $value = 5; to_json [$value] # yields [5]
437
438 # used as string, so dump as string
439 print $value;
440 to_json [$value] # yields ["5"]
441
442 # undef becomes null
443 to_json [undef] # yields [null]
444
445 You can force the type to be a string by stringifying it:
446
447 my $x = 3.1; # some variable containing a number
448 "$x"; # stringified
449 $x .= ""; # another, more awkward way to stringify
450 print $x; # perl does it for you, too, quite often
451
452 You can force the type to be a number by numifying it:
453
454 my $x = "3"; # some variable containing a string
455 $x += 0; # numify it, ensuring it will be dumped as a number
456 $x *= 1; # same thing, the choise is yours.
457
458 You can not currently output JSON booleans or force the type in
459 other, less obscure, ways. Tell me if you need this capability.
199 460
200COMPARISON 461COMPARISON
201 As already mentioned, this module was created because none of the 462 As already mentioned, this module was created because none of the
202 existing JSON modules could be made to work correctly. First I will 463 existing JSON modules could be made to work correctly. First I will
203 describe the problems (or pleasures) I encountered with various existing 464 describe the problems (or pleasures) I encountered with various existing
… …
225 486
226 Has problems handling many Perl values (e.g. regex results and other 487 Has problems handling many Perl values (e.g. regex results and other
227 magic values will make it croak). 488 magic values will make it croak).
228 489
229 Does not even generate valid JSON ("{1,2}" gets converted to "{1:2}" 490 Does not even generate valid JSON ("{1,2}" gets converted to "{1:2}"
230 which is not a valid JSON string. 491 which is not a valid JSON text.
231 492
232 Unmaintained (maintainer unresponsive for many months, bugs are not 493 Unmaintained (maintainer unresponsive for many months, bugs are not
233 getting fixed). 494 getting fixed).
234 495
235 JSON::Syck 0.21 496 JSON::Syck 0.21
236 Very buggy (often crashes). 497 Very buggy (often crashes).
237 498
238 Very inflexible (no human-readable format supported, format pretty 499 Very inflexible (no human-readable format supported, format pretty
239 much undocumented. I need at least a format for easy reading by 500 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 501 humans and a single-line compact format for use in a protocol, and
241 preferably a way to generate ASCII-only JSON strings). 502 preferably a way to generate ASCII-only JSON texts).
242 503
243 Completely broken (and confusingly documented) Unicode handling 504 Completely broken (and confusingly documented) Unicode handling
244 (unicode escapes are not working properly, you need to set 505 (unicode escapes are not working properly, you need to set
245 ImplicitUnicode to *different* values on en- and decoding to get 506 ImplicitUnicode to *different* values on en- and decoding to get
246 symmetric behaviour). 507 symmetric behaviour).
… …
269 530
270 Very inflexible. 531 Very inflexible.
271 532
272 No roundtripping. 533 No roundtripping.
273 534
274 Does not generate valid JSON (key strings are often unquoted, empty 535 Does not generate valid JSON texts (key strings are often unquoted,
275 keys result in nothing being output) 536 empty keys result in nothing being output)
276 537
277 Does not check input for validity. 538 Does not check input for validity.
539
540 JSON and YAML
541 You often hear that JSON is a subset (or a close subset) of YAML. This
542 is, however, a mass hysteria and very far from the truth. In general,
543 there is no way to configure JSON::XS to output a data structure as
544 valid YAML.
545
546 If you really must use JSON::XS to generate YAML, you should use this
547 algorithm (subject to change in future versions):
548
549 my $to_yaml = JSON::XS->new->utf8->space_after (1);
550 my $yaml = $to_yaml->encode ($ref) . "\n";
551
552 This will usually generate JSON texts that also parse as valid YAML.
553 Please note that YAML has hardcoded limits on (simple) object key
554 lengths that JSON doesn't have, so you should make sure that your hash
555 keys are noticably shorter than the 1024 characters YAML allows.
556
557 There might be other incompatibilities that I am not aware of. In
558 general you should not try to generate YAML with a JSON generator or
559 vice versa, or try to parse JSON with a YAML parser or vice versa:
560 chances are high that you will run into severe interoperability
561 problems.
278 562
279 SPEED 563 SPEED
280 It seems that JSON::XS is surprisingly fast, as shown in the following 564 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 565 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 566 in the JSON::XS distribution, to make it easy to compare on your own
283 system. 567 system.
284 568
285 First is a comparison between various modules using a very simple JSON 569 First comes a comparison between various modules using a very short
570 single-line JSON string:
571
572 {"method": "handleMessage", "params": ["user1", "we were just talking"], \
573 "id": null, "array":[1,11,234,-5,1e5,1e7, true, false]}
574
286 string, showing the number of encodes/decodes per second (JSON::XS is 575 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 576 functional interface, while JSON::XS/2 uses the OO interface with
288 pretty-printing and hashkey sorting enabled). 577 pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink).
578 Higher is better:
289 579
290 module | encode | decode | 580 module | encode | decode |
291 -----------|------------|------------| 581 -----------|------------|------------|
292 JSON | 14006 | 6820 | 582 JSON | 7645.468 | 4208.613 |
293 JSON::DWIW | 200937 | 120386 | 583 JSON::DWIW | 40721.398 | 77101.176 |
294 JSON::PC | 85065 | 129366 | 584 JSON::PC | 65948.176 | 78251.940 |
295 JSON::Syck | 59898 | 44232 | 585 JSON::Syck | 22844.793 | 26479.192 |
296 JSON::XS | 1171478 | 342435 | 586 JSON::XS | 388361.481 | 199728.762 |
297 JSON::XS/2 | 730760 | 328714 | 587 JSON::XS/2 | 218453.333 | 192399.266 |
588 JSON::XS/3 | 338250.323 | 192399.266 |
589 Storable | 15779.925 | 14169.946 |
298 -----------+------------+------------+ 590 -----------+------------+------------+
299 591
300 That is, JSON::XS is 6 times faster than than JSON::DWIW and about 80 592 That is, JSON::XS is about five times faster than JSON::DWIW on
593 encoding, about three times faster on decoding, and over fourty times
301 times faster than JSON, even with pretty-printing and key sorting. 594 faster than JSON, even with pretty-printing and key sorting. It also
595 compares favourably to Storable for small amounts of data.
302 596
303 Using a longer test string (roughly 8KB, generated from Yahoo! Locals 597 Using a longer test string (roughly 18KB, generated from Yahoo! Locals
304 search API (http://nanoref.com/yahooapis/mgPdGg): 598 search API (http://nanoref.com/yahooapis/mgPdGg):
305 599
306 module | encode | decode | 600 module | encode | decode |
307 -----------|------------|------------| 601 -----------|------------|------------|
308 JSON | 673 | 38 | 602 JSON | 254.685 | 37.665 |
309 JSON::DWIW | 5271 | 770 | 603 JSON::DWIW | 843.343 | 1049.731 |
310 JSON::PC | 9901 | 2491 | 604 JSON::PC | 3602.116 | 2307.352 |
311 JSON::Syck | 2360 | 786 | 605 JSON::Syck | 505.107 | 787.899 |
312 JSON::XS | 37398 | 3202 | 606 JSON::XS | 5747.196 | 3690.220 |
313 JSON::XS/2 | 13765 | 3153 | 607 JSON::XS/2 | 3968.121 | 3676.634 |
608 JSON::XS/3 | 6105.246 | 3662.508 |
609 Storable | 4417.337 | 5285.161 |
314 -----------+------------+------------+ 610 -----------+------------+------------+
315 611
316 Again, JSON::XS leads by far in the encoding case, while still beating 612 Again, JSON::XS leads by far (except for Storable which non-surprisingly
317 every other module in the decoding case. 613 decodes faster).
318 614
319 Last example is an almost 8MB large hash with many large binary values 615 On large strings containing lots of high unicode characters, some
320 (PNG files), resulting in a lot of escaping: 616 modules (such as JSON::PC) seem to decode faster than JSON::XS, but the
617 result will be broken due to missing (or wrong) unicode handling. Others
618 refuse to decode or encode properly, so it was impossible to prepare a
619 fair comparison table for that case.
620
621SECURITY CONSIDERATIONS
622 When you are using JSON in a protocol, talking to untrusted potentially
623 hostile creatures requires relatively few measures.
624
625 First of all, your JSON decoder should be secure, that is, should not
626 have any buffer overflows. Obviously, this module should ensure that and
627 I am trying hard on making that true, but you never know.
628
629 Second, you need to avoid resource-starving attacks. That means you
630 should limit the size of JSON texts you accept, or make sure then when
631 your resources run out, thats just fine (e.g. by using a separate
632 process that can crash safely). The size of a JSON text in octets or
633 characters is usually a good indication of the size of the resources
634 required to decode it into a Perl structure.
635
636 Third, JSON::XS recurses using the C stack when decoding objects and
637 arrays. The C stack is a limited resource: for instance, on my amd64
638 machine with 8MB of stack size I can decode around 180k nested arrays
639 but only 14k nested JSON objects (due to perl itself recursing deeply on
640 croak to free the temporary). If that is exceeded, the program crashes.
641 to be conservative, the default nesting limit is set to 512. If your
642 process has a smaller stack, you should adjust this setting accordingly
643 with the "max_depth" method.
644
645 And last but least, something else could bomb you that I forgot to think
646 of. In that case, you get to keep the pieces. I am always open for
647 hints, though...
321 648
322BUGS 649BUGS
323 While the goal of this module is to be correct, that unfortunately does 650 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 651 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 652 still relatively early in its development. If you keep reporting bugs
326 will be fixed swiftly, though. 653 they will be fixed swiftly, though.
327 654
328AUTHOR 655AUTHOR
329 Marc Lehmann <schmorp@schmorp.de> 656 Marc Lehmann <schmorp@schmorp.de>
330 http://home.schmorp.de/ 657 http://home.schmorp.de/
331 658

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