ViewVC Help
View File | Revision Log | Show Annotations | Download File
/cvs/JSON-XS/README
(Generate patch)

Comparing JSON-XS/README (file contents):
Revision 1.20 by root, Tue Nov 13 22:59:08 2007 UTC vs.
Revision 1.25 by root, Wed Apr 16 18:38:38 2008 UTC

1NAME 1NAME
2 JSON::XS - JSON serialising/deserialising, done correctly and fast 2 JSON::XS - JSON serialising/deserialising, done correctly and fast
3 3
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 guaranteed 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 convenience 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
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
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
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
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
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
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.
219 251
252 See also the section *ENCODING/CODESET FLAG NOTES* later in this
253 document.
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);
224 259
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, indenting them 285 object/hash key-value pair into its own line, indenting them
250 properly. 286 properly.
251 287
253 the resulting JSON text is guaranteed 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
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
355 "allow_nonref", resulting in an invalid JSON text: 398 "allow_nonref", resulting in an invalid JSON text:
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
403 $json = $json->allow_unknown ([$enable])
404 $enabled = $json->get_allow_unknown
405 If $enable is true (or missing), then "encode" will *not* throw an
406 exception when it encounters values it cannot represent in JSON (for
407 example, filehandles) but instead will encode a JSON "null" value.
408 Note that blessed objects are not included here and are handled
409 separately by c<allow_nonref>.
410
411 If $enable is false (the default), then "encode" will throw an
412 exception when it encounters anything it cannot encode as JSON.
413
414 This option does not affect "decode" in any way, and it is
415 recommended to leave it off unless you know your communications
416 partner.
417
360 $json = $json->allow_blessed ([$enable]) 418 $json = $json->allow_blessed ([$enable])
419 $enabled = $json->get_allow_blessed
361 If $enable is true (or missing), then the "encode" method will not 420 If $enable is true (or missing), then the "encode" method will not
362 barf when it encounters a blessed reference. Instead, the value of 421 barf when it encounters a blessed reference. Instead, the value of
363 the convert_blessed option will decide whether "null" 422 the convert_blessed option will decide whether "null"
364 ("convert_blessed" disabled or no "to_json" method found) or a 423 ("convert_blessed" disabled or no "TO_JSON" method found) or a
365 representation of the object ("convert_blessed" enabled and 424 representation of the object ("convert_blessed" enabled and
366 "to_json" method found) is being encoded. Has no effect on "decode". 425 "TO_JSON" method found) is being encoded. Has no effect on "decode".
367 426
368 If $enable is false (the default), then "encode" will throw an 427 If $enable is false (the default), then "encode" will throw an
369 exception when it encounters a blessed object. 428 exception when it encounters a blessed object.
370 429
371 $json = $json->convert_blessed ([$enable]) 430 $json = $json->convert_blessed ([$enable])
431 $enabled = $json->get_convert_blessed
372 If $enable is true (or missing), then "encode", upon encountering a 432 If $enable is true (or missing), then "encode", upon encountering a
373 blessed object, will check for the availability of the "TO_JSON" 433 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 434 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 435 context and the resulting scalar will be encoded instead of the
376 object. If no "TO_JSON" method is found, the value of 436 object. If no "TO_JSON" method is found, the value of
380 returns other blessed objects, those will be handled in the same 440 returns other blessed objects, those will be handled in the same
381 way. "TO_JSON" must take care of not causing an endless recursion 441 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 442 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 443 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 444 the object) are usually in upper case letters and to avoid
385 collisions with the "to_json" function. 445 collisions with any "to_json" function or method.
386 446
387 This setting does not yet influence "decode" in any way, but in the 447 This setting does not yet influence "decode" in any way, but in the
388 future, global hooks might get installed that influence "decode" and 448 future, global hooks might get installed that influence "decode" and
389 are enabled by this setting. 449 are enabled by this setting.
390 450
466 526
467 { __widget__ => $self->{id} } 527 { __widget__ => $self->{id} }
468 } 528 }
469 529
470 $json = $json->shrink ([$enable]) 530 $json = $json->shrink ([$enable])
531 $enabled = $json->get_shrink
471 Perl usually over-allocates memory a bit when allocating space for 532 Perl usually over-allocates memory a bit when allocating space for
472 strings. This flag optionally resizes strings generated by either 533 strings. This flag optionally resizes strings generated by either
473 "encode" or "decode" to their minimum size possible. This can save 534 "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 535 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 536 many short strings. It will also try to downgrade any strings to
493 converting strings that look like integers or floats into integers 554 converting strings that look like integers or floats into integers
494 or floats internally (there is no difference on the Perl level), 555 or floats internally (there is no difference on the Perl level),
495 saving space. 556 saving space.
496 557
497 $json = $json->max_depth ([$maximum_nesting_depth]) 558 $json = $json->max_depth ([$maximum_nesting_depth])
559 $max_depth = $json->get_max_depth
498 Sets the maximum nesting level (default 512) accepted while encoding 560 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 561 or decoding. If a higher nesting level is detected in JSON text or a
500 higher nesting level then this limit, then the encoder and decoder 562 Perl data structure, then the encoder and decoder will stop and
501 will stop and croak at that point. 563 croak at that point.
502 564
503 Nesting level is defined by number of hash- or arrayrefs that the 565 Nesting level is defined by number of hash- or arrayrefs that the
504 encoder needs to traverse to reach a given point or the number of 566 encoder needs to traverse to reach a given point or the number of
505 "{" or "[" characters without their matching closing parenthesis 567 "{" or "[" characters without their matching closing parenthesis
506 crossed to reach a given character in a string. 568 crossed to reach a given character in a string.
507 569
508 Setting the maximum depth to one disallows any nesting, so that 570 Setting the maximum depth to one disallows any nesting, so that
509 ensures that the object is only a single hash/object or array. 571 ensures that the object is only a single hash/object or array.
510 572
511 The argument to "max_depth" will be rounded up to the next highest
512 power of two. If no argument is given, the highest possible setting 573 If no argument is given, the highest possible setting will be used,
513 will be used, which is rarely useful. 574 which is rarely useful.
575
576 Note that nesting is implemented by recursion in C. The default
577 value has been chosen to be as large as typical operating systems
578 allow without crashing.
514 579
515 See SECURITY CONSIDERATIONS, below, for more info on why this is 580 See SECURITY CONSIDERATIONS, below, for more info on why this is
516 useful. 581 useful.
517 582
518 $json = $json->max_size ([$maximum_string_size]) 583 $json = $json->max_size ([$maximum_string_size])
584 $max_size = $json->get_max_size
519 Set the maximum length a JSON text may have (in bytes) where 585 Set the maximum length a JSON text may have (in bytes) where
520 decoding is being attempted. The default is 0, meaning no limit. 586 decoding is being attempted. The default is 0, meaning no limit.
521 When "decode" is called on a string longer then this number of 587 When "decode" is called on a string that is longer then this many
522 characters it will not attempt to decode the string but throw an 588 bytes, it will not attempt to decode the string but throw an
523 exception. This setting has no effect on "encode" (yet). 589 exception. This setting has no effect on "encode" (yet).
524 590
525 The argument to "max_size" will be rounded up to the next highest
526 power of two (so may be more than requested). If no argument is
527 given, the limit check will be deactivated (same as when 0 is 591 If no argument is given, the limit check will be deactivated (same
528 specified). 592 as when 0 is specified).
529 593
530 See SECURITY CONSIDERATIONS, below, for more info on why this is 594 See SECURITY CONSIDERATIONS, below, for more info on why this is
531 useful. 595 useful.
532 596
533 $json_text = $json->encode ($perl_scalar) 597 $json_text = $json->encode ($perl_scalar)
558 and you need to know where the JSON text ends. 622 and you need to know where the JSON text ends.
559 623
560 JSON::XS->new->decode_prefix ("[1] the tail") 624 JSON::XS->new->decode_prefix ("[1] the tail")
561 => ([], 3) 625 => ([], 3)
562 626
627INCREMENTAL PARSING
628 [This section and the API it details is still EXPERIMENTAL]
629
630 In some cases, there is the need for incremental parsing of JSON texts.
631 While this module always has to keep both JSON text and resulting Perl
632 data structure in memory at one time, it does allow you to parse a JSON
633 stream incrementally. It does so by accumulating text until it has a
634 full JSON object, which it then can decode. This process is similar to
635 using "decode_prefix" to see if a full JSON object is available, but is
636 much more efficient (JSON::XS will only attempt to parse the JSON text
637 once it is sure it has enough text to get a decisive result, using a
638 very simple but truly incremental parser).
639
640 The following two methods deal with this.
641
642 [void, scalar or list context] = $json->incr_parse ([$string])
643 This is the central parsing function. It can both append new text
644 and extract objects from the stream accumulated so far (both of
645 these functions are optional).
646
647 If $string is given, then this string is appended to the already
648 existing JSON fragment stored in the $json object.
649
650 After that, if the function is called in void context, it will
651 simply return without doing anything further. This can be used to
652 add more text in as many chunks as you want.
653
654 If the method is called in scalar context, then it will try to
655 extract exactly *one* JSON object. If that is successful, it will
656 return this object, otherwise it will return "undef". If there is a
657 parse error, this method will croak just as "decode" would do (one
658 can then use "incr_skip" to skip the errornous part). This is the
659 most common way of using the method.
660
661 And finally, in list context, it will try to extract as many objects
662 from the stream as it can find and return them, or the empty list
663 otherwise. For this to work, there must be no separators between the
664 JSON objects or arrays, instead they must be concatenated
665 back-to-back. If an error occurs, an exception will be raised as in
666 the scalar context case. Note that in this case, any
667 previously-parsed JSON texts will be lost.
668
669 $lvalue_string = $json->incr_text
670 This method returns the currently stored JSON fragment as an lvalue,
671 that is, you can manipulate it. This *only* works when a preceding
672 call to "incr_parse" in *scalar context* successfully returned an
673 object. Under all other circumstances you must not call this
674 function (I mean it. although in simple tests it might actually
675 work, it *will* fail under real world conditions). As a special
676 exception, you can also call this method before having parsed
677 anything.
678
679 This function is useful in two cases: a) finding the trailing text
680 after a JSON object or b) parsing multiple JSON objects separated by
681 non-JSON text (such as commas).
682
683 $json->incr_skip
684 This will reset the state of the incremental parser and will remove
685 the parsed text from the input buffer. This is useful after
686 "incr_parse" died, in which case the input buffer and incremental
687 parser state is left unchanged, to skip the text parsed so far and
688 to reset the parse state.
689
690 LIMITATIONS
691 All options that affect decoding are supported, except "allow_nonref".
692 The reason for this is that it cannot be made to work sensibly: JSON
693 objects and arrays are self-delimited, i.e. you can concatenate them
694 back to back and still decode them perfectly. This does not hold true
695 for JSON numbers, however.
696
697 For example, is the string 1 a single JSON number, or is it simply the
698 start of 12? Or is 12 a single JSON number, or the concatenation of 1
699 and 2? In neither case you can tell, and this is why JSON::XS takes the
700 conservative route and disallows this case.
701
702 EXAMPLES
703 Some examples will make all this clearer. First, a simple example that
704 works similarly to "decode_prefix": We want to decode the JSON object at
705 the start of a string and identify the portion after the JSON object:
706
707 my $text = "[1,2,3] hello";
708
709 my $json = new JSON::XS;
710
711 my $obj = $json->incr_parse ($text)
712 or die "expected JSON object or array at beginning of string";
713
714 my $tail = $json->incr_text;
715 # $tail now contains " hello"
716
717 Easy, isn't it?
718
719 Now for a more complicated example: Imagine a hypothetical protocol
720 where you read some requests from a TCP stream, and each request is a
721 JSON array, without any separation between them (in fact, it is often
722 useful to use newlines as "separators", as these get interpreted as
723 whitespace at the start of the JSON text, which makes it possible to
724 test said protocol with "telnet"...).
725
726 Here is how you'd do it (it is trivial to write this in an event-based
727 manner):
728
729 my $json = new JSON::XS;
730
731 # read some data from the socket
732 while (sysread $socket, my $buf, 4096) {
733
734 # split and decode as many requests as possible
735 for my $request ($json->incr_parse ($buf)) {
736 # act on the $request
737 }
738 }
739
740 Another complicated example: Assume you have a string with JSON objects
741 or arrays, all separated by (optional) comma characters (e.g. "[1],[2],
742 [3]"). To parse them, we have to skip the commas between the JSON texts,
743 and here is where the lvalue-ness of "incr_text" comes in useful:
744
745 my $text = "[1],[2], [3]";
746 my $json = new JSON::XS;
747
748 # void context, so no parsing done
749 $json->incr_parse ($text);
750
751 # now extract as many objects as possible. note the
752 # use of scalar context so incr_text can be called.
753 while (my $obj = $json->incr_parse) {
754 # do something with $obj
755
756 # now skip the optional comma
757 $json->incr_text =~ s/^ \s* , //x;
758 }
759
760 Now lets go for a very complex example: Assume that you have a gigantic
761 JSON array-of-objects, many gigabytes in size, and you want to parse it,
762 but you cannot load it into memory fully (this has actually happened in
763 the real world :).
764
765 Well, you lost, you have to implement your own JSON parser. But JSON::XS
766 can still help you: You implement a (very simple) array parser and let
767 JSON decode the array elements, which are all full JSON objects on their
768 own (this wouldn't work if the array elements could be JSON numbers, for
769 example):
770
771 my $json = new JSON::XS;
772
773 # open the monster
774 open my $fh, "<bigfile.json"
775 or die "bigfile: $!";
776
777 # first parse the initial "["
778 for (;;) {
779 sysread $fh, my $buf, 65536
780 or die "read error: $!";
781 $json->incr_parse ($buf); # void context, so no parsing
782
783 # Exit the loop once we found and removed(!) the initial "[".
784 # In essence, we are (ab-)using the $json object as a simple scalar
785 # we append data to.
786 last if $json->incr_text =~ s/^ \s* \[ //x;
787 }
788
789 # now we have the skipped the initial "[", so continue
790 # parsing all the elements.
791 for (;;) {
792 # in this loop we read data until we got a single JSON object
793 for (;;) {
794 if (my $obj = $json->incr_parse) {
795 # do something with $obj
796 last;
797 }
798
799 # add more data
800 sysread $fh, my $buf, 65536
801 or die "read error: $!";
802 $json->incr_parse ($buf); # void context, so no parsing
803 }
804
805 # in this loop we read data until we either found and parsed the
806 # separating "," between elements, or the final "]"
807 for (;;) {
808 # first skip whitespace
809 $json->incr_text =~ s/^\s*//;
810
811 # if we find "]", we are done
812 if ($json->incr_text =~ s/^\]//) {
813 print "finished.\n";
814 exit;
815 }
816
817 # if we find ",", we can continue with the next element
818 if ($json->incr_text =~ s/^,//) {
819 last;
820 }
821
822 # if we find anything else, we have a parse error!
823 if (length $json->incr_text) {
824 die "parse error near ", $json->incr_text;
825 }
826
827 # else add more data
828 sysread $fh, my $buf, 65536
829 or die "read error: $!";
830 $json->incr_parse ($buf); # void context, so no parsing
831 }
832
833 This is a complex example, but most of the complexity comes from the
834 fact that we are trying to be correct (bear with me if I am wrong, I
835 never ran the above example :).
836
563MAPPING 837MAPPING
564 This section describes how JSON::XS maps Perl values to JSON values and 838 This section describes how JSON::XS maps Perl values to JSON values and
565 vice versa. These mappings are designed to "do the right thing" in most 839 vice versa. These mappings are designed to "do the right thing" in most
566 circumstances automatically, preserving round-tripping characteristics 840 circumstances automatically, preserving round-tripping characteristics
567 (what you put in comes out as something equivalent). 841 (what you put in comes out as something equivalent).
588 A JSON number becomes either an integer, numeric (floating point) or 862 A JSON number becomes either an integer, numeric (floating point) or
589 string scalar in perl, depending on its range and any fractional 863 string scalar in perl, depending on its range and any fractional
590 parts. On the Perl level, there is no difference between those as 864 parts. On the Perl level, there is no difference between those as
591 Perl handles all the conversion details, but an integer may take 865 Perl handles all the conversion details, but an integer may take
592 slightly less memory and might represent more values exactly than 866 slightly less memory and might represent more values exactly than
593 (floating point) numbers. 867 floating point numbers.
594 868
595 If the number consists of digits only, JSON::XS will try to 869 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 870 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 871 represent it as a numeric (floating point) value if that is possible
598 without loss of precision. Otherwise it will preserve the number as 872 without loss of precision. Otherwise it will preserve the number as
599 a string value. 873 a string value (in which case you lose roundtripping ability, as the
874 JSON number will be re-encoded toa JSON string).
600 875
601 Numbers containing a fractional or exponential part will always be 876 Numbers containing a fractional or exponential part will always be
602 represented as numeric (floating point) values, possibly at a loss 877 represented as numeric (floating point) values, possibly at a loss
603 of precision. 878 of precision (in which case you might lose perfect roundtripping
604 879 ability, but the JSON number will still be re-encoded as a JSON
605 This might create round-tripping problems as numbers might become 880 number).
606 strings, but as Perl is typeless there is no other way to do it.
607 881
608 true, false 882 true, false
609 These JSON atoms become "JSON::XS::true" and "JSON::XS::false", 883 These JSON atoms become "JSON::XS::true" and "JSON::XS::false",
610 respectively. They are overloaded to act almost exactly like the 884 respectively. They are overloaded to act almost exactly like the
611 numbers 1 and 0. You can check whether a scalar is a JSON boolean by 885 numbers 1 and 0. You can check whether a scalar is a JSON boolean by
639 an exception to be thrown, except for references to the integers 0 913 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 914 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 915 can also use "JSON::XS::false" and "JSON::XS::true" to improve
642 readability. 916 readability.
643 917
644 to_json [\0,JSON::XS::true] # yields [false,true] 918 encode_json [\0,JSON::XS::true] # yields [false,true]
645 919
646 JSON::XS::true, JSON::XS::false 920 JSON::XS::true, JSON::XS::false
647 These special values become JSON true and JSON false values, 921 These special values become JSON true and JSON false values,
648 respectively. You can also use "\1" and "\0" directly if you want. 922 respectively. You can also use "\1" and "\0" directly if you want.
649 923
650 blessed objects 924 blessed objects
651 Blessed objects are not allowed. JSON::XS currently tries to encode 925 Blessed objects are not directly representable in JSON. See the
652 their underlying representation (hash- or arrayref), but this 926 "allow_blessed" and "convert_blessed" methods on various options on
653 behaviour might change in future versions. 927 how to deal with this: basically, you can choose between throwing an
928 exception, encoding the reference as if it weren't blessed, or
929 provide your own serialiser method.
654 930
655 simple scalars 931 simple scalars
656 Simple Perl scalars (any scalar that is not a reference) are the 932 Simple Perl scalars (any scalar that is not a reference) are the
657 most difficult objects to encode: JSON::XS will encode undefined 933 most difficult objects to encode: JSON::XS will encode undefined
658 scalars as JSON null value, scalars that have last been used in a 934 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 935 string context before encoding as JSON strings, and anything else as
660 number value: 936 number value:
661 937
662 # dump as number 938 # dump as number
663 to_json [2] # yields [2] 939 encode_json [2] # yields [2]
664 to_json [-3.0e17] # yields [-3e+17] 940 encode_json [-3.0e17] # yields [-3e+17]
665 my $value = 5; to_json [$value] # yields [5] 941 my $value = 5; encode_json [$value] # yields [5]
666 942
667 # used as string, so dump as string 943 # used as string, so dump as string
668 print $value; 944 print $value;
669 to_json [$value] # yields ["5"] 945 encode_json [$value] # yields ["5"]
670 946
671 # undef becomes null 947 # undef becomes null
672 to_json [undef] # yields [null] 948 encode_json [undef] # yields [null]
673 949
674 You can force the type to be a JSON string by stringifying it: 950 You can force the type to be a JSON string by stringifying it:
675 951
676 my $x = 3.1; # some variable containing a number 952 my $x = 3.1; # some variable containing a number
677 "$x"; # stringified 953 "$x"; # stringified
683 my $x = "3"; # some variable containing a string 959 my $x = "3"; # some variable containing a string
684 $x += 0; # numify it, ensuring it will be dumped as a number 960 $x += 0; # numify it, ensuring it will be dumped as a number
685 $x *= 1; # same thing, the choice is yours. 961 $x *= 1; # same thing, the choice is yours.
686 962
687 You can not currently force the type in other, less obscure, ways. 963 You can not currently force the type in other, less obscure, ways.
688 Tell me if you need this capability. 964 Tell me if you need this capability (but don't forget to explain why
965 it's needed :).
689 966
690COMPARISON 967ENCODING/CODESET FLAG NOTES
691 As already mentioned, this module was created because none of the 968 The interested reader might have seen a number of flags that signify
692 existing JSON modules could be made to work correctly. First I will 969 encodings or codesets - "utf8", "latin1" and "ascii". There seems to be
693 describe the problems (or pleasures) I encountered with various existing 970 some confusion on what these do, so here is a short comparison:
694 JSON modules, followed by some benchmark values. JSON::XS was designed
695 not to suffer from any of these problems or limitations.
696 971
697 JSON 1.07 972 "utf8" controls whether the JSON text created by "encode" (and expected
698 Slow (but very portable, as it is written in pure Perl). 973 by "decode") is UTF-8 encoded or not, while "latin1" and "ascii" only
974 control whether "encode" escapes character values outside their
975 respective codeset range. Neither of these flags conflict with each
976 other, although some combinations make less sense than others.
699 977
700 Undocumented/buggy Unicode handling (how JSON handles Unicode values 978 Care has been taken to make all flags symmetrical with respect to
701 is undocumented. One can get far by feeding it Unicode strings and 979 "encode" and "decode", that is, texts encoded with any combination of
702 doing en-/decoding oneself, but Unicode escapes are not working 980 these flag values will be correctly decoded when the same flags are used
981 - in general, if you use different flag settings while encoding vs. when
982 decoding you likely have a bug somewhere.
983
984 Below comes a verbose discussion of these flags. Note that a "codeset"
985 is simply an abstract set of character-codepoint pairs, while an
986 encoding takes those codepoint numbers and *encodes* them, in our case
987 into octets. Unicode is (among other things) a codeset, UTF-8 is an
988 encoding, and ISO-8859-1 (= latin 1) and ASCII are both codesets *and*
989 encodings at the same time, which can be confusing.
990
991 "utf8" flag disabled
992 When "utf8" is disabled (the default), then "encode"/"decode"
993 generate and expect Unicode strings, that is, characters with high
994 ordinal Unicode values (> 255) will be encoded as such characters,
995 and likewise such characters are decoded as-is, no canges to them
996 will be done, except "(re-)interpreting" them as Unicode codepoints
997 or Unicode characters, respectively (to Perl, these are the same
998 thing in strings unless you do funny/weird/dumb stuff).
999
1000 This is useful when you want to do the encoding yourself (e.g. when
1001 you want to have UTF-16 encoded JSON texts) or when some other layer
1002 does the encoding for you (for example, when printing to a terminal
1003 using a filehandle that transparently encodes to UTF-8 you certainly
1004 do NOT want to UTF-8 encode your data first and have Perl encode it
1005 another time).
1006
1007 "utf8" flag enabled
1008 If the "utf8"-flag is enabled, "encode"/"decode" will encode all
1009 characters using the corresponding UTF-8 multi-byte sequence, and
1010 will expect your input strings to be encoded as UTF-8, that is, no
1011 "character" of the input string must have any value > 255, as UTF-8
1012 does not allow that.
1013
1014 The "utf8" flag therefore switches between two modes: disabled means
1015 you will get a Unicode string in Perl, enabled means you get an
1016 UTF-8 encoded octet/binary string in Perl.
1017
1018 "latin1" or "ascii" flags enabled
1019 With "latin1" (or "ascii") enabled, "encode" will escape characters
1020 with ordinal values > 255 (> 127 with "ascii") and encode the
1021 remaining characters as specified by the "utf8" flag.
1022
1023 If "utf8" is disabled, then the result is also correctly encoded in
1024 those character sets (as both are proper subsets of Unicode, meaning
1025 that a Unicode string with all character values < 256 is the same
1026 thing as a ISO-8859-1 string, and a Unicode string with all
1027 character values < 128 is the same thing as an ASCII string in
703 properly). 1028 Perl).
704 1029
705 No round-tripping (strings get clobbered if they look like numbers, 1030 If "utf8" is enabled, you still get a correct UTF-8-encoded string,
706 e.g. the string 2.0 will encode to 2.0 instead of "2.0", and that 1031 regardless of these flags, just some more characters will be escaped
707 will decode into the number 2. 1032 using "\uXXXX" then before.
708 1033
709 JSON::PC 0.01 1034 Note that ISO-8859-1-*encoded* strings are not compatible with UTF-8
710 Very fast. 1035 encoding, while ASCII-encoded strings are. That is because the
1036 ISO-8859-1 encoding is NOT a subset of UTF-8 (despite the ISO-8859-1
1037 *codeset* being a subset of Unicode), while ASCII is.
711 1038
712 Undocumented/buggy Unicode handling. 1039 Surprisingly, "decode" will ignore these flags and so treat all
1040 input values as governed by the "utf8" flag. If it is disabled, this
1041 allows you to decode ISO-8859-1- and ASCII-encoded strings, as both
1042 strict subsets of Unicode. If it is enabled, you can correctly
1043 decode UTF-8 encoded strings.
713 1044
714 No round-tripping. 1045 So neither "latin1" nor "ascii" are incompatible with the "utf8"
1046 flag - they only govern when the JSON output engine escapes a
1047 character or not.
715 1048
716 Has problems handling many Perl values (e.g. regex results and other 1049 The main use for "latin1" is to relatively efficiently store binary
717 magic values will make it croak). 1050 data as JSON, at the expense of breaking compatibility with most
1051 JSON decoders.
718 1052
719 Does not even generate valid JSON ("{1,2}" gets converted to "{1:2}" 1053 The main use for "ascii" is to force the output to not contain
720 which is not a valid JSON text. 1054 characters with values > 127, which means you can interpret the
721 1055 resulting string as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about
722 Unmaintained (maintainer unresponsive for many months, bugs are not 1056 any character set and 8-bit-encoding, and still get the same data
723 getting fixed). 1057 structure back. This is useful when your channel for JSON transfer
724 1058 is not 8-bit clean or the encoding might be mangled in between (e.g.
725 JSON::Syck 0.21 1059 in mail), and works because ASCII is a proper subset of most 8-bit
726 Very buggy (often crashes). 1060 and multibyte encodings in use in the world.
727
728 Very inflexible (no human-readable format supported, format pretty
729 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
731 preferably a way to generate ASCII-only JSON texts).
732
733 Completely broken (and confusingly documented) Unicode handling
734 (Unicode escapes are not working properly, you need to set
735 ImplicitUnicode to *different* values on en- and decoding to get
736 symmetric behaviour).
737
738 No round-tripping (simple cases work, but this depends on whether
739 the scalar value was used in a numeric context or not).
740
741 Dumping hashes may skip hash values depending on iterator state.
742
743 Unmaintained (maintainer unresponsive for many months, bugs are not
744 getting fixed).
745
746 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
748 security issue: imagine two banks transferring money between each
749 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
751 syntax error. While a good protocol will at least recover, that is
752 extra unnecessary work and the transaction will still not succeed).
753
754 JSON::DWIW 0.04
755 Very fast. Very natural. Very nice.
756
757 Undocumented Unicode handling (but the best of the pack. Unicode
758 escapes still don't get parsed properly).
759
760 Very inflexible.
761
762 No round-tripping.
763
764 Does not generate valid JSON texts (key strings are often unquoted,
765 empty keys result in nothing being output)
766
767 Does not check input for validity.
768 1061
769 JSON and YAML 1062 JSON and YAML
770 You often hear that JSON is a subset (or a close subset) of YAML. This 1063 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, 1064 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 1065 writing), so let me state it clearly: *in general, there is no way to
773 valid YAML. 1066 configure JSON::XS to output a data structure as valid YAML* that works
1067 in all cases.
774 1068
775 If you really must use JSON::XS to generate YAML, you should use this 1069 If you really must use JSON::XS to generate YAML, you should use this
776 algorithm (subject to change in future versions): 1070 algorithm (subject to change in future versions):
777 1071
778 my $to_yaml = JSON::XS->new->utf8->space_after (1); 1072 my $to_yaml = JSON::XS->new->utf8->space_after (1);
779 my $yaml = $to_yaml->encode ($ref) . "\n"; 1073 my $yaml = $to_yaml->encode ($ref) . "\n";
780 1074
781 This will usually generate JSON texts that also parse as valid YAML. 1075 This will *usually* generate JSON texts that also parse as valid YAML.
782 Please note that YAML has hardcoded limits on (simple) object key 1076 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 1077 lengths that JSON doesn't have and also has different and incompatible
1078 unicode handling, so you should make sure that your hash keys are
784 keys are noticeably shorter than the 1024 characters YAML allows. 1079 noticeably shorter than the 1024 "stream characters" YAML allows and
1080 that you do not have characters with codepoint values outside the
1081 Unicode BMP (basic multilingual page). YAML also does not allow "\/"
1082 sequences in strings (which JSON::XS does not *currently* generate, but
1083 other JSON generators might).
785 1084
786 There might be other incompatibilities that I am not aware of. In 1085 There might be other incompatibilities that I am not aware of (or the
1086 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 1087 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: 1088 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 1089 chances are high that you will run into severe interoperability problems
790 problems. 1090 when you least expect it.
1091
1092 (*) I have been pressured multiple times by Brian Ingerson (one of the
1093 authors of the YAML specification) to remove this paragraph, despite
1094 him acknowledging that the actual incompatibilities exist. As I was
1095 personally bitten by this "JSON is YAML" lie, I refused and said I
1096 will continue to educate people about these issues, so others do not
1097 run into the same problem again and again. After this, Brian called
1098 me a (quote)*complete and worthless idiot*(unquote).
1099
1100 In my opinion, instead of pressuring and insulting people who
1101 actually clarify issues with YAML and the wrong statements of some
1102 of its proponents, I would kindly suggest reading the JSON spec
1103 (which is not that difficult or long) and finally make YAML
1104 compatible to it, and educating users about the changes, instead of
1105 spreading lies about the real compatibility for many *years* and
1106 trying to silence people who point out that it isn't true.
791 1107
792 SPEED 1108 SPEED
793 It seems that JSON::XS is surprisingly fast, as shown in the following 1109 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 1110 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 1111 in the JSON::XS distribution, to make it easy to compare on your own
796 system. 1112 system.
797 1113
798 First comes a comparison between various modules using a very short 1114 First comes a comparison between various modules using a very short
799 single-line JSON string: 1115 single-line JSON string (also available at
1116 <http://dist.schmorp.de/misc/json/short.json>).
800 1117
801 {"method": "handleMessage", "params": ["user1", "we were just talking"], \ 1118 {"method": "handleMessage", "params": ["user1",
802 "id": null, "array":[1,11,234,-5,1e5,1e7, true, false]} 1119 "we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7,
1120 true, false]}
803 1121
804 It shows the number of encodes/decodes per second (JSON::XS uses the 1122 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 1123 functional interface, while JSON::XS/2 uses the OO interface with
806 pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink). 1124 pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink).
807 Higher is better: 1125 Higher is better:
808 1126
809 Storable | 15779.925 | 14169.946 |
810 -----------+------------+------------+
811 module | encode | decode | 1127 module | encode | decode |
812 -----------|------------|------------| 1128 -----------|------------|------------|
813 JSON | 4990.842 | 4088.813 | 1129 JSON 1.x | 4990.842 | 4088.813 |
814 JSON::DWIW | 51653.990 | 71575.154 | 1130 JSON::DWIW | 51653.990 | 71575.154 |
815 JSON::PC | 65948.176 | 74631.744 | 1131 JSON::PC | 65948.176 | 74631.744 |
816 JSON::PP | 8931.652 | 3817.168 | 1132 JSON::PP | 8931.652 | 3817.168 |
817 JSON::Syck | 24877.248 | 27776.848 | 1133 JSON::Syck | 24877.248 | 27776.848 |
818 JSON::XS | 388361.481 | 227951.304 | 1134 JSON::XS | 388361.481 | 227951.304 |
825 encoding, about three times faster on decoding, and over forty times 1141 encoding, about three times faster on decoding, and over forty times
826 faster than JSON, even with pretty-printing and key sorting. It also 1142 faster than JSON, even with pretty-printing and key sorting. It also
827 compares favourably to Storable for small amounts of data. 1143 compares favourably to Storable for small amounts of data.
828 1144
829 Using a longer test string (roughly 18KB, generated from Yahoo! Locals 1145 Using a longer test string (roughly 18KB, generated from Yahoo! Locals
830 search API (http://nanoref.com/yahooapis/mgPdGg): 1146 search API (<http://dist.schmorp.de/misc/json/long.json>).
831 1147
832 module | encode | decode | 1148 module | encode | decode |
833 -----------|------------|------------| 1149 -----------|------------|------------|
834 JSON | 55.260 | 34.971 | 1150 JSON 1.x | 55.260 | 34.971 |
835 JSON::DWIW | 825.228 | 1082.513 | 1151 JSON::DWIW | 825.228 | 1082.513 |
836 JSON::PC | 3571.444 | 2394.829 | 1152 JSON::PC | 3571.444 | 2394.829 |
837 JSON::PP | 210.987 | 32.574 | 1153 JSON::PP | 210.987 | 32.574 |
838 JSON::Syck | 552.551 | 787.544 | 1154 JSON::Syck | 552.551 | 787.544 |
839 JSON::XS | 5780.463 | 4854.519 | 1155 JSON::XS | 5780.463 | 4854.519 |
872 Third, JSON::XS recurses using the C stack when decoding objects and 1188 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 1189 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 1190 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 1191 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. 1192 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 1193 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 1194 process has a smaller stack, you should adjust this setting accordingly
879 with the "max_depth" method. 1195 with the "max_depth" method.
880 1196
881 And last but least, something else could bomb you that I forgot to think 1197 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 1198 case, you get to keep the pieces. I am always open for hints, though...
883 hints, though... 1199
1200 Also keep in mind that JSON::XS might leak contents of your Perl data
1201 structures in its error messages, so when you serialise sensitive
1202 information you might want to make sure that exceptions thrown by
1203 JSON::XS will not end up in front of untrusted eyes.
884 1204
885 If you are using JSON::XS to return packets to consumption by JavaScript 1205 If you are using JSON::XS to return packets to consumption by JavaScript
886 scripts in a browser you should have a look at 1206 scripts in a browser you should have a look at
887 <http://jpsykes.com/47/practical-csrf-and-json-security> to see whether 1207 <http://jpsykes.com/47/practical-csrf-and-json-security> to see whether
888 you are vulnerable to some common attack vectors (which really are 1208 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, 1209 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 1210 as major browser developers care only for features, not about getting
891 security right). 1211 security right).
892 1212
893THREADS 1213THREADS
894 This module is *not* guaranteed to be thread safe and there are no plans 1214 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 1215 to change this until Perl gets thread support (as opposed to the
896 horribly slow so-called "threads" which are simply slow and bloated 1216 horribly slow so-called "threads" which are simply slow and bloated
897 process simulations - use fork, its *much* faster, cheaper, better). 1217 process simulations - use fork, it's *much* faster, cheaper, better).
898 1218
899 (It might actually work, but you have been warned). 1219 (It might actually work, but you have been warned).
900 1220
901BUGS 1221BUGS
902 While the goal of this module is to be correct, that unfortunately does 1222 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 1223 not mean it's 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 1224 still relatively early in its development. If you keep reporting bugs
905 they will be fixed swiftly, though. 1225 they will be fixed swiftly, though.
906 1226
907 Please refrain from using rt.cpan.org or any other bug reporting 1227 Please refrain from using rt.cpan.org or any other bug reporting
908 service. I put the contact address into my modules for a reason. 1228 service. I put the contact address into my modules for a reason.
1229
1230SEE ALSO
1231 The json_xs command line utility for quick experiments.
909 1232
910AUTHOR 1233AUTHOR
911 Marc Lehmann <schmorp@schmorp.de> 1234 Marc Lehmann <schmorp@schmorp.de>
912 http://home.schmorp.de/ 1235 http://home.schmorp.de/
913 1236

Diff Legend

Removed lines
+ Added lines
< Changed lines
> Changed lines