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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
4 JSON::XS - 正しくて高速な JSON 4 JSON::XS - 正しくて高速な JSON シリアライザ/デシリアライザ
5 シリアライザ/デシリアライザ
6 (http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html) 5 (http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html)
7 6
8SYNOPSIS 7SYNOPSIS
9 use JSON::XS; 8 use JSON::XS;
10 9
11 # exported functions, they croak on error 10 # exported functions, they croak on error
12 # and expect/generate UTF-8 11 # and expect/generate UTF-8
13 12
14 $utf8_encoded_json_text = to_json $perl_hash_or_arrayref; 13 $utf8_encoded_json_text = encode_json $perl_hash_or_arrayref;
15 $perl_hash_or_arrayref = from_json $utf8_encoded_json_text; 14 $perl_hash_or_arrayref = decode_json $utf8_encoded_json_text;
16 15
17 # OO-interface 16 # OO-interface
18 17
19 $coder = JSON::XS->new->ascii->pretty->allow_nonref; 18 $coder = JSON::XS->new->ascii->pretty->allow_nonref;
20 $pretty_printed_unencoded = $coder->encode ($perl_scalar); 19 $pretty_printed_unencoded = $coder->encode ($perl_scalar);
21 $perl_scalar = $coder->decode ($unicode_json_text); 20 $perl_scalar = $coder->decode ($unicode_json_text);
21
22 # Note that JSON version 2.0 and above will automatically use JSON::XS
23 # if available, at virtually no speed overhead either, so you should
24 # be able to just:
25
26 use JSON;
27
28 # and do the same things, except that you have a pure-perl fallback now.
22 29
23DESCRIPTION 30DESCRIPTION
24 This module converts Perl data structures to JSON and vice versa. Its 31 This module converts Perl data structures to JSON and vice versa. Its
25 primary goal is to be *correct* and its secondary goal is to be *fast*. 32 primary goal is to be *correct* and its secondary goal is to be *fast*.
26 To reach the latter goal it was written in C. 33 To reach the latter goal it was written in C.
34
35 Beginning with version 2.0 of the JSON module, when both JSON and
36 JSON::XS are installed, then JSON will fall back on JSON::XS (this can
37 be overriden) with no overhead due to emulation (by inheritign
38 constructor and methods). If JSON::XS is not available, it will fall
39 back to the compatible JSON::PP module as backend, so using JSON instead
40 of JSON::XS gives you a portable JSON API that can be fast when you need
41 and doesn't require a C compiler when that is a problem.
27 42
28 As this is the n-th-something JSON module on CPAN, what was the reason 43 As this is the n-th-something JSON module on CPAN, what was the reason
29 to write yet another JSON module? While it seems there are many JSON 44 to write yet another JSON module? While it seems there are many JSON
30 modules, none of them correctly handle all corner cases, and in most 45 modules, none of them correctly handle all corner cases, and in most
31 cases their maintainers are unresponsive, gone missing, or not listening 46 cases their maintainers are unresponsive, gone missing, or not listening
… …
35 50
36 See MAPPING, below, on how JSON::XS maps perl values to JSON values and 51 See MAPPING, below, on how JSON::XS maps perl values to JSON values and
37 vice versa. 52 vice versa.
38 53
39 FEATURES 54 FEATURES
40 * correct unicode handling 55 * correct Unicode handling
56
41 This module knows how to handle Unicode, and even documents how and 57 This module knows how to handle Unicode, documents how and when it
42 when it does so. 58 does so, and even documents what "correct" means.
43 59
44 * round-trip integrity 60 * round-trip integrity
61
45 When you serialise a perl data structure using only datatypes 62 When you serialise a perl data structure using only datatypes
46 supported by JSON, the deserialised data structure is identical on 63 supported by JSON, the deserialised data structure is identical on
47 the Perl level. (e.g. the string "2.0" doesn't suddenly become "2" 64 the Perl level. (e.g. the string "2.0" doesn't suddenly become "2"
48 just because it looks like a number). 65 just because it looks like a number). There minor *are* exceptions
66 to this, read the MAPPING section below to learn about those.
49 67
50 * strict checking of JSON correctness 68 * strict checking of JSON correctness
69
51 There is no guessing, no generating of illegal JSON texts by 70 There is no guessing, no generating of illegal JSON texts by
52 default, and only JSON is accepted as input by default (the latter 71 default, and only JSON is accepted as input by default (the latter
53 is a security feature). 72 is a security feature).
54 73
55 * fast 74 * fast
56 Compared to other JSON modules, this module compares favourably in
57 terms of speed, too.
58 75
76 Compared to other JSON modules and other serialisers such as
77 Storable, this module usually compares favourably in terms of speed,
78 too.
79
59 * simple to use 80 * simple to use
81
60 This module has both a simple functional interface as well as an OO 82 This module has both a simple functional interface as well as an
61 interface. 83 objetc oriented interface interface.
62 84
63 * reasonably versatile output formats 85 * reasonably versatile output formats
86
64 You can choose between the most compact guarenteed single-line 87 You can choose between the most compact guaranteed-single-line
65 format possible (nice for simple line-based protocols), a pure-ascii 88 format possible (nice for simple line-based protocols), a pure-ascii
66 format (for when your transport is not 8-bit clean, still supports 89 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 90 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 91 want to read that stuff). Or you can combine those features in
69 whatever way you like. 92 whatever way you like.
70 93
71FUNCTIONAL INTERFACE 94FUNCTIONAL INTERFACE
72 The following convinience methods are provided by this module. They are 95 The following convenience methods are provided by this module. They are
73 exported by default: 96 exported by default:
74 97
75 $json_text = to_json $perl_scalar 98 $json_text = encode_json $perl_scalar
76 Converts the given Perl data structure to a UTF-8 encoded, binary 99 Converts the given Perl data structure to a UTF-8 encoded, binary
77 string (that is, the string contains octets only). Croaks on error. 100 string (that is, the string contains octets only). Croaks on error.
78 101
79 This function call is functionally identical to: 102 This function call is functionally identical to:
80 103
81 $json_text = JSON::XS->new->utf8->encode ($perl_scalar) 104 $json_text = JSON::XS->new->utf8->encode ($perl_scalar)
82 105
83 except being faster. 106 except being faster.
84 107
85 $perl_scalar = from_json $json_text 108 $perl_scalar = decode_json $json_text
86 The opposite of "to_json": expects an UTF-8 (binary) string and 109 The opposite of "encode_json": expects an UTF-8 (binary) string and
87 tries to parse that as an UTF-8 encoded JSON text, returning the 110 tries to parse that as an UTF-8 encoded JSON text, returning the
88 resulting reference. Croaks on error. 111 resulting reference. Croaks on error.
89 112
90 This function call is functionally identical to: 113 This function call is functionally identical to:
91 114
… …
105A FEW NOTES ON UNICODE AND PERL 128A FEW NOTES ON UNICODE AND PERL
106 Since this often leads to confusion, here are a few very clear words on 129 Since this often leads to confusion, here are a few very clear words on
107 how Unicode works in Perl, modulo bugs. 130 how Unicode works in Perl, modulo bugs.
108 131
109 1. Perl strings can store characters with ordinal values > 255. 132 1. Perl strings can store characters with ordinal values > 255.
110 This enables you to store unicode characters as single characters in 133 This enables you to store Unicode characters as single characters in
111 a Perl string - very natural. 134 a Perl string - very natural.
112 135
113 2. Perl does *not* associate an encoding with your strings. 136 2. Perl does *not* associate an encoding with your strings.
114 Unless you force it to, e.g. when matching it against a regex, or 137 ... until you force it to, e.g. when matching it against a regex, or
115 printing the scalar to a file, in which case Perl either interprets 138 printing the scalar to a file, in which case Perl either interprets
116 your string as locale-encoded text, octets/binary, or as Unicode, 139 your string as locale-encoded text, octets/binary, or as Unicode,
117 depending on various settings. In no case is an encoding stored 140 depending on various settings. In no case is an encoding stored
118 together with your data, it is *use* that decides encoding, not any 141 together with your data, it is *use* that decides encoding, not any
119 magical metadata. 142 magical meta data.
120 143
121 3. The internal utf-8 flag has no meaning with regards to the encoding 144 3. The internal utf-8 flag has no meaning with regards to the encoding
122 of your string. 145 of your string.
123 Just ignore that flag unless you debug a Perl bug, a module written 146 Just ignore that flag unless you debug a Perl bug, a module written
124 in XS or want to dive into the internals of perl. Otherwise it will 147 in XS or want to dive into the internals of perl. Otherwise it will
125 only confuse you, as, despite the name, it says nothing about how 148 only confuse you, as, despite the name, it says nothing about how
126 your string is encoded. You can have unicode strings with that flag 149 your string is encoded. You can have Unicode strings with that flag
127 set, with that flag clear, and you can have binary data with that 150 set, with that flag clear, and you can have binary data with that
128 flag set and that flag clear. Other possibilities exist, too. 151 flag set and that flag clear. Other possibilities exist, too.
129 152
130 If you didn't know about that flag, just the better, pretend it 153 If you didn't know about that flag, just the better, pretend it
131 doesn't exist. 154 doesn't exist.
… …
135 If you have UTF-8 encoded data, it is no longer a Unicode string, 158 If you have UTF-8 encoded data, it is no longer a Unicode string,
136 but a Unicode string encoded in UTF-8, giving you a binary string. 159 but a Unicode string encoded in UTF-8, giving you a binary string.
137 160
138 5. A string containing "high" (> 255) character values is *not* a UTF-8 161 5. A string containing "high" (> 255) character values is *not* a UTF-8
139 string. 162 string.
140 Its a fact. Learn to live with it. 163 It's a fact. Learn to live with it.
141 164
142 I hope this helps :) 165 I hope this helps :)
143 166
144OBJECT-ORIENTED INTERFACE 167OBJECT-ORIENTED INTERFACE
145 The object oriented interface lets you configure your own encoding or 168 The object oriented interface lets you configure your own encoding or
… …
155 178
156 my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]}) 179 my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]})
157 => {"a": [1, 2]} 180 => {"a": [1, 2]}
158 181
159 $json = $json->ascii ([$enable]) 182 $json = $json->ascii ([$enable])
183 $enabled = $json->get_ascii
160 If $enable is true (or missing), then the "encode" method will not 184 If $enable is true (or missing), then the "encode" method will not
161 generate characters outside the code range 0..127 (which is ASCII). 185 generate characters outside the code range 0..127 (which is ASCII).
162 Any unicode characters outside that range will be escaped using 186 Any Unicode characters outside that range will be escaped using
163 either a single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL 187 either a single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL
164 escape sequence, as per RFC4627. The resulting encoded JSON text can 188 escape sequence, as per RFC4627. The resulting encoded JSON text can
165 be treated as a native unicode string, an ascii-encoded, 189 be treated as a native Unicode string, an ascii-encoded,
166 latin1-encoded or UTF-8 encoded string, or any other superset of 190 latin1-encoded or UTF-8 encoded string, or any other superset of
167 ASCII. 191 ASCII.
168 192
169 If $enable is false, then the "encode" method will not escape 193 If $enable is false, then the "encode" method will not escape
170 Unicode characters unless required by the JSON syntax or other 194 Unicode characters unless required by the JSON syntax or other
171 flags. This results in a faster and more compact format. 195 flags. This results in a faster and more compact format.
172 196
197 See also the section *ENCODING/CODESET FLAG NOTES* later in this
198 document.
199
173 The main use for this flag is to produce JSON texts that can be 200 The main use for this flag is to produce JSON texts that can be
174 transmitted over a 7-bit channel, as the encoded JSON texts will not 201 transmitted over a 7-bit channel, as the encoded JSON texts will not
175 contain any 8 bit characters. 202 contain any 8 bit characters.
176 203
177 JSON::XS->new->ascii (1)->encode ([chr 0x10401]) 204 JSON::XS->new->ascii (1)->encode ([chr 0x10401])
178 => ["\ud801\udc01"] 205 => ["\ud801\udc01"]
179 206
180 $json = $json->latin1 ([$enable]) 207 $json = $json->latin1 ([$enable])
208 $enabled = $json->get_latin1
181 If $enable is true (or missing), then the "encode" method will 209 If $enable is true (or missing), then the "encode" method will
182 encode the resulting JSON text as latin1 (or iso-8859-1), escaping 210 encode the resulting JSON text as latin1 (or iso-8859-1), escaping
183 any characters outside the code range 0..255. The resulting string 211 any characters outside the code range 0..255. The resulting string
184 can be treated as a latin1-encoded JSON text or a native unicode 212 can be treated as a latin1-encoded JSON text or a native Unicode
185 string. The "decode" method will not be affected in any way by this 213 string. The "decode" method will not be affected in any way by this
186 flag, as "decode" by default expects unicode, which is a strict 214 flag, as "decode" by default expects Unicode, which is a strict
187 superset of latin1. 215 superset of latin1.
188 216
189 If $enable is false, then the "encode" method will not escape 217 If $enable is false, then the "encode" method will not escape
190 Unicode characters unless required by the JSON syntax or other 218 Unicode characters unless required by the JSON syntax or other
191 flags. 219 flags.
220
221 See also the section *ENCODING/CODESET FLAG NOTES* later in this
222 document.
192 223
193 The main use for this flag is efficiently encoding binary data as 224 The main use for this flag is efficiently encoding binary data as
194 JSON text, as most octets will not be escaped, resulting in a 225 JSON text, as most octets will not be escaped, resulting in a
195 smaller encoded size. The disadvantage is that the resulting JSON 226 smaller encoded size. The disadvantage is that the resulting JSON
196 text is encoded in latin1 (and must correctly be treated as such 227 text is encoded in latin1 (and must correctly be treated as such
197 when storing and transfering), a rare encoding for JSON. It is 228 when storing and transferring), a rare encoding for JSON. It is
198 therefore most useful when you want to store data structures known 229 therefore most useful when you want to store data structures known
199 to contain binary data efficiently in files or databases, not when 230 to contain binary data efficiently in files or databases, not when
200 talking to other JSON encoders/decoders. 231 talking to other JSON encoders/decoders.
201 232
202 JSON::XS->new->latin1->encode (["\x{89}\x{abc}"] 233 JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]
203 => ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not) 234 => ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)
204 235
205 $json = $json->utf8 ([$enable]) 236 $json = $json->utf8 ([$enable])
237 $enabled = $json->get_utf8
206 If $enable is true (or missing), then the "encode" method will 238 If $enable is true (or missing), then the "encode" method will
207 encode the JSON result into UTF-8, as required by many protocols, 239 encode the JSON result into UTF-8, as required by many protocols,
208 while the "decode" method expects to be handled an UTF-8-encoded 240 while the "decode" method expects to be handled an UTF-8-encoded
209 string. Please note that UTF-8-encoded strings do not contain any 241 string. Please note that UTF-8-encoded strings do not contain any
210 characters outside the range 0..255, they are thus useful for 242 characters outside the range 0..255, they are thus useful for
211 bytewise/binary I/O. In future versions, enabling this option might 243 bytewise/binary I/O. In future versions, enabling this option might
212 enable autodetection of the UTF-16 and UTF-32 encoding families, as 244 enable autodetection of the UTF-16 and UTF-32 encoding families, as
213 described in RFC4627. 245 described in RFC4627.
214 246
215 If $enable is false, then the "encode" method will return the JSON 247 If $enable is false, then the "encode" method will return the JSON
216 string as a (non-encoded) unicode string, while "decode" expects 248 string as a (non-encoded) Unicode string, while "decode" expects
217 thus a unicode string. Any decoding or encoding (e.g. to UTF-8 or 249 thus a Unicode string. Any decoding or encoding (e.g. to UTF-8 or
218 UTF-16) needs to be done yourself, e.g. using the Encode module. 250 UTF-16) needs to be done yourself, e.g. using the Encode module.
251
252 See also the section *ENCODING/CODESET FLAG NOTES* later in this
253 document.
219 254
220 Example, output UTF-16BE-encoded JSON: 255 Example, output UTF-16BE-encoded JSON:
221 256
222 use Encode; 257 use Encode;
223 $jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object); 258 $jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
… …
242 2 277 2
243 ] 278 ]
244 } 279 }
245 280
246 $json = $json->indent ([$enable]) 281 $json = $json->indent ([$enable])
282 $enabled = $json->get_indent
247 If $enable is true (or missing), then the "encode" method will use a 283 If $enable is true (or missing), then the "encode" method will use a
248 multiline format as output, putting every array member or 284 multiline format as output, putting every array member or
249 object/hash key-value pair into its own line, identing them 285 object/hash key-value pair into its own line, indenting them
250 properly. 286 properly.
251 287
252 If $enable is false, no newlines or indenting will be produced, and 288 If $enable is false, no newlines or indenting will be produced, and
253 the resulting JSON text is guarenteed not to contain any "newlines". 289 the resulting JSON text is guaranteed not to contain any "newlines".
254 290
255 This setting has no effect when decoding JSON texts. 291 This setting has no effect when decoding JSON texts.
256 292
257 $json = $json->space_before ([$enable]) 293 $json = $json->space_before ([$enable])
294 $enabled = $json->get_space_before
258 If $enable is true (or missing), then the "encode" method will add 295 If $enable is true (or missing), then the "encode" method will add
259 an extra optional space before the ":" separating keys from values 296 an extra optional space before the ":" separating keys from values
260 in JSON objects. 297 in JSON objects.
261 298
262 If $enable is false, then the "encode" method will not add any extra 299 If $enable is false, then the "encode" method will not add any extra
… …
268 Example, space_before enabled, space_after and indent disabled: 305 Example, space_before enabled, space_after and indent disabled:
269 306
270 {"key" :"value"} 307 {"key" :"value"}
271 308
272 $json = $json->space_after ([$enable]) 309 $json = $json->space_after ([$enable])
310 $enabled = $json->get_space_after
273 If $enable is true (or missing), then the "encode" method will add 311 If $enable is true (or missing), then the "encode" method will add
274 an extra optional space after the ":" separating keys from values in 312 an extra optional space after the ":" separating keys from values in
275 JSON objects and extra whitespace after the "," separating key-value 313 JSON objects and extra whitespace after the "," separating key-value
276 pairs and array members. 314 pairs and array members.
277 315
… …
283 Example, space_before and indent disabled, space_after enabled: 321 Example, space_before and indent disabled, space_after enabled:
284 322
285 {"key": "value"} 323 {"key": "value"}
286 324
287 $json = $json->relaxed ([$enable]) 325 $json = $json->relaxed ([$enable])
326 $enabled = $json->get_relaxed
288 If $enable is true (or missing), then "decode" will accept some 327 If $enable is true (or missing), then "decode" will accept some
289 extensions to normal JSON syntax (see below). "encode" will not be 328 extensions to normal JSON syntax (see below). "encode" will not be
290 affected in anyway. *Be aware that this option makes you accept 329 affected in anyway. *Be aware that this option makes you accept
291 invalid JSON texts as if they were valid!*. I suggest only to use 330 invalid JSON texts as if they were valid!*. I suggest only to use
292 this option to parse application-specific files written by humans 331 this option to parse application-specific files written by humans
… …
295 If $enable is false (the default), then "decode" will only accept 334 If $enable is false (the default), then "decode" will only accept
296 valid JSON texts. 335 valid JSON texts.
297 336
298 Currently accepted extensions are: 337 Currently accepted extensions are:
299 338
300 * list items can have an end-comma 339 * list items can have an end-comma
340
301 JSON *separates* array elements and key-value pairs with commas. 341 JSON *separates* array elements and key-value pairs with commas.
302 This can be annoying if you write JSON texts manually and want 342 This can be annoying if you write JSON texts manually and want
303 to be able to quickly append elements, so this extension accepts 343 to be able to quickly append elements, so this extension accepts
304 comma at the end of such items not just between them: 344 comma at the end of such items not just between them:
305 345
… …
310 { 350 {
311 "k1": "v1", 351 "k1": "v1",
312 "k2": "v2", <- this comma not normally allowed 352 "k2": "v2", <- this comma not normally allowed
313 } 353 }
314 354
315 * shell-style '#'-comments 355 * shell-style '#'-comments
356
316 Whenever JSON allows whitespace, shell-style comments are 357 Whenever JSON allows whitespace, shell-style comments are
317 additionally allowed. They are terminated by the first 358 additionally allowed. They are terminated by the first
318 carriage-return or line-feed character, after which more 359 carriage-return or line-feed character, after which more
319 white-space and comments are allowed. 360 white-space and comments are allowed.
320 361
… …
322 1, # this comment not allowed in JSON 363 1, # this comment not allowed in JSON
323 # neither this one... 364 # neither this one...
324 ] 365 ]
325 366
326 $json = $json->canonical ([$enable]) 367 $json = $json->canonical ([$enable])
368 $enabled = $json->get_canonical
327 If $enable is true (or missing), then the "encode" method will 369 If $enable is true (or missing), then the "encode" method will
328 output JSON objects by sorting their keys. This is adding a 370 output JSON objects by sorting their keys. This is adding a
329 comparatively high overhead. 371 comparatively high overhead.
330 372
331 If $enable is false, then the "encode" method will output key-value 373 If $enable is false, then the "encode" method will output key-value
332 pairs in the order Perl stores them (which will likely change 374 pairs in the order Perl stores them (which will likely change
333 between runs of the same script). 375 between runs of the same script).
334 376
335 This option is useful if you want the same data structure to be 377 This option is useful if you want the same data structure to be
336 encoded as the same JSON text (given the same overall settings). If 378 encoded as the same JSON text (given the same overall settings). If
337 it is disabled, the same hash migh be encoded differently even if 379 it is disabled, the same hash might be encoded differently even if
338 contains the same data, as key-value pairs have no inherent ordering 380 contains the same data, as key-value pairs have no inherent ordering
339 in Perl. 381 in Perl.
340 382
341 This setting has no effect when decoding JSON texts. 383 This setting has no effect when decoding JSON texts.
342 384
343 $json = $json->allow_nonref ([$enable]) 385 $json = $json->allow_nonref ([$enable])
386 $enabled = $json->get_allow_nonref
344 If $enable is true (or missing), then the "encode" method can 387 If $enable is true (or missing), then the "encode" method can
345 convert a non-reference into its corresponding string, number or 388 convert a non-reference into its corresponding string, number or
346 null JSON value, which is an extension to RFC4627. Likewise, 389 null JSON value, which is an extension to RFC4627. Likewise,
347 "decode" will accept those JSON values instead of croaking. 390 "decode" will accept those JSON values instead of croaking.
348 391
… …
356 399
357 JSON::XS->new->allow_nonref->encode ("Hello, World!") 400 JSON::XS->new->allow_nonref->encode ("Hello, World!")
358 => "Hello, World!" 401 => "Hello, World!"
359 402
360 $json = $json->allow_blessed ([$enable]) 403 $json = $json->allow_blessed ([$enable])
404 $enabled = $json->get_allow_blessed
361 If $enable is true (or missing), then the "encode" method will not 405 If $enable is true (or missing), then the "encode" method will not
362 barf when it encounters a blessed reference. Instead, the value of 406 barf when it encounters a blessed reference. Instead, the value of
363 the convert_blessed option will decide wether "null" 407 the convert_blessed option will decide whether "null"
364 ("convert_blessed" disabled or no "to_json" method found) or a 408 ("convert_blessed" disabled or no "TO_JSON" method found) or a
365 representation of the object ("convert_blessed" enabled and 409 representation of the object ("convert_blessed" enabled and
366 "to_json" method found) is being encoded. Has no effect on "decode". 410 "TO_JSON" method found) is being encoded. Has no effect on "decode".
367 411
368 If $enable is false (the default), then "encode" will throw an 412 If $enable is false (the default), then "encode" will throw an
369 exception when it encounters a blessed object. 413 exception when it encounters a blessed object.
370 414
371 $json = $json->convert_blessed ([$enable]) 415 $json = $json->convert_blessed ([$enable])
416 $enabled = $json->get_convert_blessed
372 If $enable is true (or missing), then "encode", upon encountering a 417 If $enable is true (or missing), then "encode", upon encountering a
373 blessed object, will check for the availability of the "TO_JSON" 418 blessed object, will check for the availability of the "TO_JSON"
374 method on the object's class. If found, it will be called in scalar 419 method on the object's class. If found, it will be called in scalar
375 context and the resulting scalar will be encoded instead of the 420 context and the resulting scalar will be encoded instead of the
376 object. If no "TO_JSON" method is found, the value of 421 object. If no "TO_JSON" method is found, the value of
… …
380 returns other blessed objects, those will be handled in the same 425 returns other blessed objects, those will be handled in the same
381 way. "TO_JSON" must take care of not causing an endless recursion 426 way. "TO_JSON" must take care of not causing an endless recursion
382 cycle (== crash) in this case. The name of "TO_JSON" was chosen 427 cycle (== crash) in this case. The name of "TO_JSON" was chosen
383 because other methods called by the Perl core (== not by the user of 428 because other methods called by the Perl core (== not by the user of
384 the object) are usually in upper case letters and to avoid 429 the object) are usually in upper case letters and to avoid
385 collisions with the "to_json" function. 430 collisions with any "to_json" function or method.
386 431
387 This setting does not yet influence "decode" in any way, but in the 432 This setting does not yet influence "decode" in any way, but in the
388 future, global hooks might get installed that influence "decode" and 433 future, global hooks might get installed that influence "decode" and
389 are enabled by this setting. 434 are enabled by this setting.
390 435
… …
431 476
432 As this callback gets called less often then the 477 As this callback gets called less often then the
433 "filter_json_object" one, decoding speed will not usually suffer as 478 "filter_json_object" one, decoding speed will not usually suffer as
434 much. Therefore, single-key objects make excellent targets to 479 much. Therefore, single-key objects make excellent targets to
435 serialise Perl objects into, especially as single-key JSON objects 480 serialise Perl objects into, especially as single-key JSON objects
436 are as close to the type-tagged value concept as JSON gets (its 481 are as close to the type-tagged value concept as JSON gets (it's
437 basically an ID/VALUE tuple). Of course, JSON does not support this 482 basically an ID/VALUE tuple). Of course, JSON does not support this
438 in any way, so you need to make sure your data never looks like a 483 in any way, so you need to make sure your data never looks like a
439 serialised Perl hash. 484 serialised Perl hash.
440 485
441 Typical names for the single object key are "__class_whatever__", or 486 Typical names for the single object key are "__class_whatever__", or
… …
466 511
467 { __widget__ => $self->{id} } 512 { __widget__ => $self->{id} }
468 } 513 }
469 514
470 $json = $json->shrink ([$enable]) 515 $json = $json->shrink ([$enable])
516 $enabled = $json->get_shrink
471 Perl usually over-allocates memory a bit when allocating space for 517 Perl usually over-allocates memory a bit when allocating space for
472 strings. This flag optionally resizes strings generated by either 518 strings. This flag optionally resizes strings generated by either
473 "encode" or "decode" to their minimum size possible. This can save 519 "encode" or "decode" to their minimum size possible. This can save
474 memory when your JSON texts are either very very long or you have 520 memory when your JSON texts are either very very long or you have
475 many short strings. It will also try to downgrade any strings to 521 many short strings. It will also try to downgrade any strings to
… …
493 converting strings that look like integers or floats into integers 539 converting strings that look like integers or floats into integers
494 or floats internally (there is no difference on the Perl level), 540 or floats internally (there is no difference on the Perl level),
495 saving space. 541 saving space.
496 542
497 $json = $json->max_depth ([$maximum_nesting_depth]) 543 $json = $json->max_depth ([$maximum_nesting_depth])
544 $max_depth = $json->get_max_depth
498 Sets the maximum nesting level (default 512) accepted while encoding 545 Sets the maximum nesting level (default 512) accepted while encoding
499 or decoding. If the JSON text or Perl data structure has an equal or 546 or decoding. If the JSON text or Perl data structure has an equal or
500 higher nesting level then this limit, then the encoder and decoder 547 higher nesting level then this limit, then the encoder and decoder
501 will stop and croak at that point. 548 will stop and croak at that point.
502 549
… …
514 561
515 See SECURITY CONSIDERATIONS, below, for more info on why this is 562 See SECURITY CONSIDERATIONS, below, for more info on why this is
516 useful. 563 useful.
517 564
518 $json = $json->max_size ([$maximum_string_size]) 565 $json = $json->max_size ([$maximum_string_size])
566 $max_size = $json->get_max_size
519 Set the maximum length a JSON text may have (in bytes) where 567 Set the maximum length a JSON text may have (in bytes) where
520 decoding is being attempted. The default is 0, meaning no limit. 568 decoding is being attempted. The default is 0, meaning no limit.
521 When "decode" is called on a string longer then this number of 569 When "decode" is called on a string longer then this number of
522 characters it will not attempt to decode the string but throw an 570 characters it will not attempt to decode the string but throw an
523 exception. This setting has no effect on "encode" (yet). 571 exception. This setting has no effect on "encode" (yet).
… …
565 vice versa. These mappings are designed to "do the right thing" in most 613 vice versa. These mappings are designed to "do the right thing" in most
566 circumstances automatically, preserving round-tripping characteristics 614 circumstances automatically, preserving round-tripping characteristics
567 (what you put in comes out as something equivalent). 615 (what you put in comes out as something equivalent).
568 616
569 For the more enlightened: note that in the following descriptions, 617 For the more enlightened: note that in the following descriptions,
570 lowercase *perl* refers to the Perl interpreter, while uppcercase *Perl* 618 lowercase *perl* refers to the Perl interpreter, while uppercase *Perl*
571 refers to the abstract Perl language itself. 619 refers to the abstract Perl language itself.
572 620
573 JSON -> PERL 621 JSON -> PERL
574 object 622 object
575 A JSON object becomes a reference to a hash in Perl. No ordering of 623 A JSON object becomes a reference to a hash in Perl. No ordering of
576 object keys is preserved (JSON does not preserver object key 624 object keys is preserved (JSON does not preserve object key ordering
577 ordering itself). 625 itself).
578 626
579 array 627 array
580 A JSON array becomes a reference to an array in Perl. 628 A JSON array becomes a reference to an array in Perl.
581 629
582 string 630 string
… …
588 A JSON number becomes either an integer, numeric (floating point) or 636 A JSON number becomes either an integer, numeric (floating point) or
589 string scalar in perl, depending on its range and any fractional 637 string scalar in perl, depending on its range and any fractional
590 parts. On the Perl level, there is no difference between those as 638 parts. On the Perl level, there is no difference between those as
591 Perl handles all the conversion details, but an integer may take 639 Perl handles all the conversion details, but an integer may take
592 slightly less memory and might represent more values exactly than 640 slightly less memory and might represent more values exactly than
593 (floating point) numbers. 641 floating point numbers.
594 642
595 If the number consists of digits only, JSON::XS will try to 643 If the number consists of digits only, JSON::XS will try to
596 represent it as an integer value. If that fails, it will try to 644 represent it as an integer value. If that fails, it will try to
597 represent it as a numeric (floating point) value if that is possible 645 represent it as a numeric (floating point) value if that is possible
598 without loss of precision. Otherwise it will preserve the number as 646 without loss of precision. Otherwise it will preserve the number as
599 a string value. 647 a string value (in which case you lose roundtripping ability, as the
648 JSON number will be re-encoded toa JSON string).
600 649
601 Numbers containing a fractional or exponential part will always be 650 Numbers containing a fractional or exponential part will always be
602 represented as numeric (floating point) values, possibly at a loss 651 represented as numeric (floating point) values, possibly at a loss
603 of precision. 652 of precision (in which case you might lose perfect roundtripping
604 653 ability, but the JSON number will still be re-encoded as a JSON
605 This might create round-tripping problems as numbers might become 654 number).
606 strings, but as Perl is typeless there is no other way to do it.
607 655
608 true, false 656 true, false
609 These JSON atoms become "JSON::XS::true" and "JSON::XS::false", 657 These JSON atoms become "JSON::XS::true" and "JSON::XS::false",
610 respectively. They are overloaded to act almost exactly like the 658 respectively. They are overloaded to act almost exactly like the
611 numbers 1 and 0. You can check wether a scalar is a JSON boolean by 659 numbers 1 and 0. You can check whether a scalar is a JSON boolean by
612 using the "JSON::XS::is_bool" function. 660 using the "JSON::XS::is_bool" function.
613 661
614 null 662 null
615 A JSON null atom becomes "undef" in Perl. 663 A JSON null atom becomes "undef" in Perl.
616 664
… …
639 an exception to be thrown, except for references to the integers 0 687 an exception to be thrown, except for references to the integers 0
640 and 1, which get turned into "false" and "true" atoms in JSON. You 688 and 1, which get turned into "false" and "true" atoms in JSON. You
641 can also use "JSON::XS::false" and "JSON::XS::true" to improve 689 can also use "JSON::XS::false" and "JSON::XS::true" to improve
642 readability. 690 readability.
643 691
644 to_json [\0,JSON::XS::true] # yields [false,true] 692 encode_json [\0,JSON::XS::true] # yields [false,true]
645 693
646 JSON::XS::true, JSON::XS::false 694 JSON::XS::true, JSON::XS::false
647 These special values become JSON true and JSON false values, 695 These special values become JSON true and JSON false values,
648 respectively. You can also use "\1" and "\0" directly if you want. 696 respectively. You can also use "\1" and "\0" directly if you want.
649 697
650 blessed objects 698 blessed objects
651 Blessed objects are not allowed. JSON::XS currently tries to encode 699 Blessed objects are not directly representable in JSON. See the
652 their underlying representation (hash- or arrayref), but this 700 "allow_blessed" and "convert_blessed" methods on various options on
653 behaviour might change in future versions. 701 how to deal with this: basically, you can choose between throwing an
702 exception, encoding the reference as if it weren't blessed, or
703 provide your own serialiser method.
654 704
655 simple scalars 705 simple scalars
656 Simple Perl scalars (any scalar that is not a reference) are the 706 Simple Perl scalars (any scalar that is not a reference) are the
657 most difficult objects to encode: JSON::XS will encode undefined 707 most difficult objects to encode: JSON::XS will encode undefined
658 scalars as JSON null value, scalars that have last been used in a 708 scalars as JSON "null" values, scalars that have last been used in a
659 string context before encoding as JSON strings and anything else as 709 string context before encoding as JSON strings, and anything else as
660 number value: 710 number value:
661 711
662 # dump as number 712 # dump as number
663 to_json [2] # yields [2] 713 encode_json [2] # yields [2]
664 to_json [-3.0e17] # yields [-3e+17] 714 encode_json [-3.0e17] # yields [-3e+17]
665 my $value = 5; to_json [$value] # yields [5] 715 my $value = 5; encode_json [$value] # yields [5]
666 716
667 # used as string, so dump as string 717 # used as string, so dump as string
668 print $value; 718 print $value;
669 to_json [$value] # yields ["5"] 719 encode_json [$value] # yields ["5"]
670 720
671 # undef becomes null 721 # undef becomes null
672 to_json [undef] # yields [null] 722 encode_json [undef] # yields [null]
673 723
674 You can force the type to be a string by stringifying it: 724 You can force the type to be a JSON string by stringifying it:
675 725
676 my $x = 3.1; # some variable containing a number 726 my $x = 3.1; # some variable containing a number
677 "$x"; # stringified 727 "$x"; # stringified
678 $x .= ""; # another, more awkward way to stringify 728 $x .= ""; # another, more awkward way to stringify
679 print $x; # perl does it for you, too, quite often 729 print $x; # perl does it for you, too, quite often
680 730
681 You can force the type to be a number by numifying it: 731 You can force the type to be a JSON number by numifying it:
682 732
683 my $x = "3"; # some variable containing a string 733 my $x = "3"; # some variable containing a string
684 $x += 0; # numify it, ensuring it will be dumped as a number 734 $x += 0; # numify it, ensuring it will be dumped as a number
685 $x *= 1; # same thing, the choise is yours. 735 $x *= 1; # same thing, the choice is yours.
686 736
687 You can not currently output JSON booleans or force the type in 737 You can not currently force the type in other, less obscure, ways.
688 other, less obscure, ways. Tell me if you need this capability. 738 Tell me if you need this capability (but don't forget to explain why
739 its needed :).
740
741ENCODING/CODESET FLAG NOTES
742 The interested reader might have seen a number of flags that signify
743 encodings or codesets - "utf8", "latin1" and "ascii". There seems to be
744 some confusion on what these do, so here is a short comparison:
745
746 "utf8" controls wether the JSON text created by "encode" (and expected
747 by "decode") is UTF-8 encoded or not, while "latin1" and "ascii" only
748 control wether "encode" escapes character values outside their
749 respective codeset range. Neither of these flags conflict with each
750 other, although some combinations make less sense than others.
751
752 Care has been taken to make all flags symmetrical with respect to
753 "encode" and "decode", that is, texts encoded with any combination of
754 these flag values will be correctly decoded when the same flags are used
755 - in general, if you use different flag settings while encoding vs. when
756 decoding you likely have a bug somewhere.
757
758 Below comes a verbose discussion of these flags. Note that a "codeset"
759 is simply an abstract set of character-codepoint pairs, while an
760 encoding takes those codepoint numbers and *encodes* them, in our case
761 into octets. Unicode is (among other things) a codeset, UTF-8 is an
762 encoding, and ISO-8859-1 (= latin 1) and ASCII are both codesets *and*
763 encodings at the same time, which can be confusing.
764
765 "utf8" flag disabled
766 When "utf8" is disabled (the default), then "encode"/"decode"
767 generate and expect Unicode strings, that is, characters with high
768 ordinal Unicode values (> 255) will be encoded as such characters,
769 and likewise such characters are decoded as-is, no canges to them
770 will be done, except "(re-)interpreting" them as Unicode codepoints
771 or Unicode characters, respectively (to Perl, these are the same
772 thing in strings unless you do funny/weird/dumb stuff).
773
774 This is useful when you want to do the encoding yourself (e.g. when
775 you want to have UTF-16 encoded JSON texts) or when some other layer
776 does the encoding for you (for example, when printing to a terminal
777 using a filehandle that transparently encodes to UTF-8 you certainly
778 do NOT want to UTF-8 encode your data first and have Perl encode it
779 another time).
780
781 "utf8" flag enabled
782 If the "utf8"-flag is enabled, "encode"/"decode" will encode all
783 characters using the corresponding UTF-8 multi-byte sequence, and
784 will expect your input strings to be encoded as UTF-8, that is, no
785 "character" of the input string must have any value > 255, as UTF-8
786 does not allow that.
787
788 The "utf8" flag therefore switches between two modes: disabled means
789 you will get a Unicode string in Perl, enabled means you get an
790 UTF-8 encoded octet/binary string in Perl.
791
792 "latin1" or "ascii" flags enabled
793 With "latin1" (or "ascii") enabled, "encode" will escape characters
794 with ordinal values > 255 (> 127 with "ascii") and encode the
795 remaining characters as specified by the "utf8" flag.
796
797 If "utf8" is disabled, then the result is also correctly encoded in
798 those character sets (as both are proper subsets of Unicode, meaning
799 that a Unicode string with all character values < 256 is the same
800 thing as a ISO-8859-1 string, and a Unicode string with all
801 character values < 128 is the same thing as an ASCII string in
802 Perl).
803
804 If "utf8" is enabled, you still get a correct UTF-8-encoded string,
805 regardless of these flags, just some more characters will be escaped
806 using "\uXXXX" then before.
807
808 Note that ISO-8859-1-*encoded* strings are not compatible with UTF-8
809 encoding, while ASCII-encoded strings are. That is because the
810 ISO-8859-1 encoding is NOT a subset of UTF-8 (despite the ISO-8859-1
811 *codeset* being a subset of Unicode), while ASCII is.
812
813 Surprisingly, "decode" will ignore these flags and so treat all
814 input values as governed by the "utf8" flag. If it is disabled, this
815 allows you to decode ISO-8859-1- and ASCII-encoded strings, as both
816 strict subsets of Unicode. If it is enabled, you can correctly
817 decode UTF-8 encoded strings.
818
819 So neither "latin1" nor "ascii" are incompatible with the "utf8"
820 flag - they only govern when the JSON output engine escapes a
821 character or not.
822
823 The main use for "latin1" is to relatively efficiently store binary
824 data as JSON, at the expense of breaking compatibility with most
825 JSON decoders.
826
827 The main use for "ascii" is to force the output to not contain
828 characters with values > 127, which means you can interpret the
829 resulting string as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about
830 any character set and 8-bit-encoding, and still get the same data
831 structure back. This is useful when your channel for JSON transfer
832 is not 8-bit clean or the encoding might be mangled in between (e.g.
833 in mail), and works because ASCII is a proper subset of most 8-bit
834 and multibyte encodings in use in the world.
689 835
690COMPARISON 836COMPARISON
691 As already mentioned, this module was created because none of the 837 As already mentioned, this module was created because none of the
692 existing JSON modules could be made to work correctly. First I will 838 existing JSON modules could be made to work correctly. First I will
693 describe the problems (or pleasures) I encountered with various existing 839 describe the problems (or pleasures) I encountered with various existing
694 JSON modules, followed by some benchmark values. JSON::XS was designed 840 JSON modules, followed by some benchmark values. JSON::XS was designed
695 not to suffer from any of these problems or limitations. 841 not to suffer from any of these problems or limitations.
696 842
843 JSON 2.xx
844 A marvellous piece of engineering, this module either uses JSON::XS
845 directly when available (so will be 100% compatible with it,
846 including speed), or it uses JSON::PP, which is basically JSON::XS
847 translated to Pure Perl, which should be 100% compatible with
848 JSON::XS, just a bit slower.
849
850 You cannot really lose by using this module, especially as it tries
851 very hard to work even with ancient Perl versions, while JSON::XS
852 does not.
853
697 JSON 1.07 854 JSON 1.07
698 Slow (but very portable, as it is written in pure Perl). 855 Slow (but very portable, as it is written in pure Perl).
699 856
700 Undocumented/buggy Unicode handling (how JSON handles unicode values 857 Undocumented/buggy Unicode handling (how JSON handles Unicode values
701 is undocumented. One can get far by feeding it unicode strings and 858 is undocumented. One can get far by feeding it Unicode strings and
702 doing en-/decoding oneself, but unicode escapes are not working 859 doing en-/decoding oneself, but Unicode escapes are not working
703 properly). 860 properly).
704 861
705 No roundtripping (strings get clobbered if they look like numbers, 862 No round-tripping (strings get clobbered if they look like numbers,
706 e.g. the string 2.0 will encode to 2.0 instead of "2.0", and that 863 e.g. the string 2.0 will encode to 2.0 instead of "2.0", and that
707 will decode into the number 2. 864 will decode into the number 2.
708 865
709 JSON::PC 0.01 866 JSON::PC 0.01
710 Very fast. 867 Very fast.
711 868
712 Undocumented/buggy Unicode handling. 869 Undocumented/buggy Unicode handling.
713 870
714 No roundtripping. 871 No round-tripping.
715 872
716 Has problems handling many Perl values (e.g. regex results and other 873 Has problems handling many Perl values (e.g. regex results and other
717 magic values will make it croak). 874 magic values will make it croak).
718 875
719 Does not even generate valid JSON ("{1,2}" gets converted to "{1:2}" 876 Does not even generate valid JSON ("{1,2}" gets converted to "{1:2}"
… …
729 much undocumented. I need at least a format for easy reading by 886 much undocumented. I need at least a format for easy reading by
730 humans and a single-line compact format for use in a protocol, and 887 humans and a single-line compact format for use in a protocol, and
731 preferably a way to generate ASCII-only JSON texts). 888 preferably a way to generate ASCII-only JSON texts).
732 889
733 Completely broken (and confusingly documented) Unicode handling 890 Completely broken (and confusingly documented) Unicode handling
734 (unicode escapes are not working properly, you need to set 891 (Unicode escapes are not working properly, you need to set
735 ImplicitUnicode to *different* values on en- and decoding to get 892 ImplicitUnicode to *different* values on en- and decoding to get
736 symmetric behaviour). 893 symmetric behaviour).
737 894
738 No roundtripping (simple cases work, but this depends on wether the 895 No round-tripping (simple cases work, but this depends on whether
739 scalar value was used in a numeric context or not). 896 the scalar value was used in a numeric context or not).
740 897
741 Dumping hashes may skip hash values depending on iterator state. 898 Dumping hashes may skip hash values depending on iterator state.
742 899
743 Unmaintained (maintainer unresponsive for many months, bugs are not 900 Unmaintained (maintainer unresponsive for many months, bugs are not
744 getting fixed). 901 getting fixed).
745 902
746 Does not check input for validity (i.e. will accept non-JSON input 903 Does not check input for validity (i.e. will accept non-JSON input
747 and return "something" instead of raising an exception. This is a 904 and return "something" instead of raising an exception. This is a
748 security issue: imagine two banks transfering money between each 905 security issue: imagine two banks transferring money between each
749 other using JSON. One bank might parse a given non-JSON request and 906 other using JSON. One bank might parse a given non-JSON request and
750 deduct money, while the other might reject the transaction with a 907 deduct money, while the other might reject the transaction with a
751 syntax error. While a good protocol will at least recover, that is 908 syntax error. While a good protocol will at least recover, that is
752 extra unnecessary work and the transaction will still not succeed). 909 extra unnecessary work and the transaction will still not succeed).
753 910
754 JSON::DWIW 0.04 911 JSON::DWIW 0.04
755 Very fast. Very natural. Very nice. 912 Very fast. Very natural. Very nice.
756 913
757 Undocumented unicode handling (but the best of the pack. Unicode 914 Undocumented Unicode handling (but the best of the pack. Unicode
758 escapes still don't get parsed properly). 915 escapes still don't get parsed properly).
759 916
760 Very inflexible. 917 Very inflexible.
761 918
762 No roundtripping. 919 No round-tripping.
763 920
764 Does not generate valid JSON texts (key strings are often unquoted, 921 Does not generate valid JSON texts (key strings are often unquoted,
765 empty keys result in nothing being output) 922 empty keys result in nothing being output)
766 923
767 Does not check input for validity. 924 Does not check input for validity.
768 925
769 JSON and YAML 926 JSON and YAML
770 You often hear that JSON is a subset (or a close subset) of YAML. This 927 You often hear that JSON is a subset of YAML. This is, however, a mass
771 is, however, a mass hysteria and very far from the truth. In general, 928 hysteria(*) and very far from the truth (as of the time of this
772 there is no way to configure JSON::XS to output a data structure as 929 writing), so let me state it clearly: *in general, there is no way to
773 valid YAML. 930 configure JSON::XS to output a data structure as valid YAML* that works
931 in all cases.
774 932
775 If you really must use JSON::XS to generate YAML, you should use this 933 If you really must use JSON::XS to generate YAML, you should use this
776 algorithm (subject to change in future versions): 934 algorithm (subject to change in future versions):
777 935
778 my $to_yaml = JSON::XS->new->utf8->space_after (1); 936 my $to_yaml = JSON::XS->new->utf8->space_after (1);
779 my $yaml = $to_yaml->encode ($ref) . "\n"; 937 my $yaml = $to_yaml->encode ($ref) . "\n";
780 938
781 This will usually generate JSON texts that also parse as valid YAML. 939 This will *usually* generate JSON texts that also parse as valid YAML.
782 Please note that YAML has hardcoded limits on (simple) object key 940 Please note that YAML has hardcoded limits on (simple) object key
783 lengths that JSON doesn't have, so you should make sure that your hash 941 lengths that JSON doesn't have and also has different and incompatible
942 unicode handling, so you should make sure that your hash keys are
784 keys are noticably shorter than the 1024 characters YAML allows. 943 noticeably shorter than the 1024 "stream characters" YAML allows and
944 that you do not have characters with codepoint values outside the
945 Unicode BMP (basic multilingual page). YAML also does not allow "\/"
946 sequences in strings (which JSON::XS does not *currently* generate, but
947 other JSON generators might).
785 948
786 There might be other incompatibilities that I am not aware of. In 949 There might be other incompatibilities that I am not aware of (or the
950 YAML specification has been changed yet again - it does so quite often).
787 general you should not try to generate YAML with a JSON generator or 951 In general you should not try to generate YAML with a JSON generator or
788 vice versa, or try to parse JSON with a YAML parser or vice versa: 952 vice versa, or try to parse JSON with a YAML parser or vice versa:
789 chances are high that you will run into severe interoperability 953 chances are high that you will run into severe interoperability problems
790 problems. 954 when you least expect it.
955
956 (*) I have been pressured multiple times by Brian Ingerson (one of the
957 authors of the YAML specification) to remove this paragraph, despite
958 him acknowledging that the actual incompatibilities exist. As I was
959 personally bitten by this "JSON is YAML" lie, I refused and said I
960 will continue to educate people about these issues, so others do not
961 run into the same problem again and again. After this, Brian called
962 me a (quote)*complete and worthless idiot*(unquote).
963
964 In my opinion, instead of pressuring and insulting people who
965 actually clarify issues with YAML and the wrong statements of some
966 of its proponents, I would kindly suggest reading the JSON spec
967 (which is not that difficult or long) and finally make YAML
968 compatible to it, and educating users about the changes, instead of
969 spreading lies about the real compatibility for many *years* and
970 trying to silence people who point out that it isn't true.
791 971
792 SPEED 972 SPEED
793 It seems that JSON::XS is surprisingly fast, as shown in the following 973 It seems that JSON::XS is surprisingly fast, as shown in the following
794 tables. They have been generated with the help of the "eg/bench" program 974 tables. They have been generated with the help of the "eg/bench" program
795 in the JSON::XS distribution, to make it easy to compare on your own 975 in the JSON::XS distribution, to make it easy to compare on your own
796 system. 976 system.
797 977
798 First comes a comparison between various modules using a very short 978 First comes a comparison between various modules using a very short
799 single-line JSON string: 979 single-line JSON string (also available at
980 <http://dist.schmorp.de/misc/json/short.json>).
800 981
801 {"method": "handleMessage", "params": ["user1", "we were just talking"], \ 982 {"method": "handleMessage", "params": ["user1", "we were just talking"], \
802 "id": null, "array":[1,11,234,-5,1e5,1e7, true, false]} 983 "id": null, "array":[1,11,234,-5,1e5,1e7, true, false]}
803 984
804 It shows the number of encodes/decodes per second (JSON::XS uses the 985 It shows the number of encodes/decodes per second (JSON::XS uses the
805 functional interface, while JSON::XS/2 uses the OO interface with 986 functional interface, while JSON::XS/2 uses the OO interface with
806 pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink). 987 pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink).
807 Higher is better: 988 Higher is better:
808 989
809 Storable | 15779.925 | 14169.946 |
810 -----------+------------+------------+
811 module | encode | decode | 990 module | encode | decode |
812 -----------|------------|------------| 991 -----------|------------|------------|
813 JSON | 4990.842 | 4088.813 | 992 JSON 1.x | 4990.842 | 4088.813 |
814 JSON::DWIW | 51653.990 | 71575.154 | 993 JSON::DWIW | 51653.990 | 71575.154 |
815 JSON::PC | 65948.176 | 74631.744 | 994 JSON::PC | 65948.176 | 74631.744 |
816 JSON::PP | 8931.652 | 3817.168 | 995 JSON::PP | 8931.652 | 3817.168 |
817 JSON::Syck | 24877.248 | 27776.848 | 996 JSON::Syck | 24877.248 | 27776.848 |
818 JSON::XS | 388361.481 | 227951.304 | 997 JSON::XS | 388361.481 | 227951.304 |
… …
820 JSON::XS/3 | 338250.323 | 218453.333 | 999 JSON::XS/3 | 338250.323 | 218453.333 |
821 Storable | 16500.016 | 135300.129 | 1000 Storable | 16500.016 | 135300.129 |
822 -----------+------------+------------+ 1001 -----------+------------+------------+
823 1002
824 That is, JSON::XS is about five times faster than JSON::DWIW on 1003 That is, JSON::XS is about five times faster than JSON::DWIW on
825 encoding, about three times faster on decoding, and over fourty times 1004 encoding, about three times faster on decoding, and over forty times
826 faster than JSON, even with pretty-printing and key sorting. It also 1005 faster than JSON, even with pretty-printing and key sorting. It also
827 compares favourably to Storable for small amounts of data. 1006 compares favourably to Storable for small amounts of data.
828 1007
829 Using a longer test string (roughly 18KB, generated from Yahoo! Locals 1008 Using a longer test string (roughly 18KB, generated from Yahoo! Locals
830 search API (http://nanoref.com/yahooapis/mgPdGg): 1009 search API (<http://dist.schmorp.de/misc/json/long.json>).
831 1010
832 module | encode | decode | 1011 module | encode | decode |
833 -----------|------------|------------| 1012 -----------|------------|------------|
834 JSON | 55.260 | 34.971 | 1013 JSON 1.x | 55.260 | 34.971 |
835 JSON::DWIW | 825.228 | 1082.513 | 1014 JSON::DWIW | 825.228 | 1082.513 |
836 JSON::PC | 3571.444 | 2394.829 | 1015 JSON::PC | 3571.444 | 2394.829 |
837 JSON::PP | 210.987 | 32.574 | 1016 JSON::PP | 210.987 | 32.574 |
838 JSON::Syck | 552.551 | 787.544 | 1017 JSON::Syck | 552.551 | 787.544 |
839 JSON::XS | 5780.463 | 4854.519 | 1018 JSON::XS | 5780.463 | 4854.519 |
… …
843 -----------+------------+------------+ 1022 -----------+------------+------------+
844 1023
845 Again, JSON::XS leads by far (except for Storable which non-surprisingly 1024 Again, JSON::XS leads by far (except for Storable which non-surprisingly
846 decodes faster). 1025 decodes faster).
847 1026
848 On large strings containing lots of high unicode characters, some 1027 On large strings containing lots of high Unicode characters, some
849 modules (such as JSON::PC) seem to decode faster than JSON::XS, but the 1028 modules (such as JSON::PC) seem to decode faster than JSON::XS, but the
850 result will be broken due to missing (or wrong) unicode handling. Others 1029 result will be broken due to missing (or wrong) Unicode handling. Others
851 refuse to decode or encode properly, so it was impossible to prepare a 1030 refuse to decode or encode properly, so it was impossible to prepare a
852 fair comparison table for that case. 1031 fair comparison table for that case.
853 1032
854SECURITY CONSIDERATIONS 1033SECURITY CONSIDERATIONS
855 When you are using JSON in a protocol, talking to untrusted potentially 1034 When you are using JSON in a protocol, talking to untrusted potentially
… …
859 have any buffer overflows. Obviously, this module should ensure that and 1038 have any buffer overflows. Obviously, this module should ensure that and
860 I am trying hard on making that true, but you never know. 1039 I am trying hard on making that true, but you never know.
861 1040
862 Second, you need to avoid resource-starving attacks. That means you 1041 Second, you need to avoid resource-starving attacks. That means you
863 should limit the size of JSON texts you accept, or make sure then when 1042 should limit the size of JSON texts you accept, or make sure then when
864 your resources run out, thats just fine (e.g. by using a separate 1043 your resources run out, that's just fine (e.g. by using a separate
865 process that can crash safely). The size of a JSON text in octets or 1044 process that can crash safely). The size of a JSON text in octets or
866 characters is usually a good indication of the size of the resources 1045 characters is usually a good indication of the size of the resources
867 required to decode it into a Perl structure. While JSON::XS can check 1046 required to decode it into a Perl structure. While JSON::XS can check
868 the size of the JSON text, it might be too late when you already have it 1047 the size of the JSON text, it might be too late when you already have it
869 in memory, so you might want to check the size before you accept the 1048 in memory, so you might want to check the size before you accept the
… …
872 Third, JSON::XS recurses using the C stack when decoding objects and 1051 Third, JSON::XS recurses using the C stack when decoding objects and
873 arrays. The C stack is a limited resource: for instance, on my amd64 1052 arrays. The C stack is a limited resource: for instance, on my amd64
874 machine with 8MB of stack size I can decode around 180k nested arrays 1053 machine with 8MB of stack size I can decode around 180k nested arrays
875 but only 14k nested JSON objects (due to perl itself recursing deeply on 1054 but only 14k nested JSON objects (due to perl itself recursing deeply on
876 croak to free the temporary). If that is exceeded, the program crashes. 1055 croak to free the temporary). If that is exceeded, the program crashes.
877 to be conservative, the default nesting limit is set to 512. If your 1056 To be conservative, the default nesting limit is set to 512. If your
878 process has a smaller stack, you should adjust this setting accordingly 1057 process has a smaller stack, you should adjust this setting accordingly
879 with the "max_depth" method. 1058 with the "max_depth" method.
880 1059
881 And last but least, something else could bomb you that I forgot to think 1060 Something else could bomb you, too, that I forgot to think of. In that
882 of. In that case, you get to keep the pieces. I am always open for 1061 case, you get to keep the pieces. I am always open for hints, though...
883 hints, though...
884 1062
1063 Also keep in mind that JSON::XS might leak contents of your Perl data
1064 structures in its error messages, so when you serialise sensitive
1065 information you might want to make sure that exceptions thrown by
1066 JSON::XS will not end up in front of untrusted eyes.
1067
885 If you are using JSON::XS to return packets to consumption by javascript 1068 If you are using JSON::XS to return packets to consumption by JavaScript
886 scripts in a browser you should have a look at 1069 scripts in a browser you should have a look at
887 <http://jpsykes.com/47/practical-csrf-and-json-security> to see wether 1070 <http://jpsykes.com/47/practical-csrf-and-json-security> to see whether
888 you are vulnerable to some common attack vectors (which really are 1071 you are vulnerable to some common attack vectors (which really are
889 browser design bugs, but it is still you who will have to deal with it, 1072 browser design bugs, but it is still you who will have to deal with it,
890 as major browser developers care only for features, not about doing 1073 as major browser developers care only for features, not about getting
891 security right). 1074 security right).
892 1075
893THREADS 1076THREADS
894 This module is *not* guarenteed to be thread safe and there are no plans 1077 This module is *not* guaranteed to be thread safe and there are no plans
895 to change this until Perl gets thread support (as opposed to the 1078 to change this until Perl gets thread support (as opposed to the
896 horribly slow so-called "threads" which are simply slow and bloated 1079 horribly slow so-called "threads" which are simply slow and bloated
897 process simulations - use fork, its *much* faster, cheaper, better). 1080 process simulations - use fork, its *much* faster, cheaper, better).
898 1081
899 (It might actually work, but you ahve ben warned). 1082 (It might actually work, but you have been warned).
900 1083
901BUGS 1084BUGS
902 While the goal of this module is to be correct, that unfortunately does 1085 While the goal of this module is to be correct, that unfortunately does
903 not mean its bug-free, only that I think its design is bug-free. It is 1086 not mean its bug-free, only that I think its design is bug-free. It is
904 still relatively early in its development. If you keep reporting bugs 1087 still relatively early in its development. If you keep reporting bugs

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