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Revision 1.11 by root, Wed May 9 16:35:21 2007 UTC

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2 JSON::XS - JSON serialising/deserialising, done correctly and fast 2 JSON::XS - JSON serialising/deserialising, done correctly and fast
3 3
4SYNOPSIS 4SYNOPSIS
5 use JSON::XS; 5 use JSON::XS;
6 6
7 # exported functions, croak on error 7 # exported functions, they croak on error
8 # and expect/generate UTF-8
8 9
9 $utf8_encoded_json_text = to_json $perl_hash_or_arrayref; 10 $utf8_encoded_json_text = to_json $perl_hash_or_arrayref;
10 $perl_hash_or_arrayref = from_json $utf8_encoded_json_text; 11 $perl_hash_or_arrayref = from_json $utf8_encoded_json_text;
11 12
13 # objToJson and jsonToObj aliases to to_json and from_json
14 # are exported for compatibility to the JSON module,
15 # but should not be used in new code.
16
12 # oo-interface 17 # OO-interface
13 18
14 $coder = JSON::XS->new->ascii->pretty->allow_nonref; 19 $coder = JSON::XS->new->ascii->pretty->allow_nonref;
15 $pretty_printed_unencoded = $coder->encode ($perl_scalar); 20 $pretty_printed_unencoded = $coder->encode ($perl_scalar);
16 $perl_scalar = $coder->decode ($unicode_json_text); 21 $perl_scalar = $coder->decode ($unicode_json_text);
17 22
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30 35
31 See MAPPING, below, on how JSON::XS maps perl values to JSON values and 36 See MAPPING, below, on how JSON::XS maps perl values to JSON values and
32 vice versa. 37 vice versa.
33 38
34 FEATURES 39 FEATURES
35 * correct handling of unicode issues 40 * correct unicode handling
36 This module knows how to handle Unicode, and even documents how and 41 This module knows how to handle Unicode, and even documents how and
37 when it does so. 42 when it does so.
38 43
39 * round-trip integrity 44 * round-trip integrity
40 When you serialise a perl data structure using only datatypes 45 When you serialise a perl data structure using only datatypes
41 supported by JSON, the deserialised data structure is identical on 46 supported by JSON, the deserialised data structure is identical on
42 the Perl level. (e.g. the string "2.0" doesn't suddenly become "2"). 47 the Perl level. (e.g. the string "2.0" doesn't suddenly become "2"
48 just because it looks like a number).
43 49
44 * strict checking of JSON correctness 50 * strict checking of JSON correctness
45 There is no guessing, no generating of illegal JSON texts by 51 There is no guessing, no generating of illegal JSON texts by
46 default, and only JSON is accepted as input by default (the latter 52 default, and only JSON is accepted as input by default (the latter
47 is a security feature). 53 is a security feature).
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55 interface. 61 interface.
56 62
57 * reasonably versatile output formats 63 * reasonably versatile output formats
58 You can choose between the most compact guarenteed single-line 64 You can choose between the most compact guarenteed single-line
59 format possible (nice for simple line-based protocols), a pure-ascii 65 format possible (nice for simple line-based protocols), a pure-ascii
60 format (for when your transport is not 8-bit clean), or a 66 format (for when your transport is not 8-bit clean, still supports
61 pretty-printed format (for when you want to read that stuff). Or you 67 the whole unicode range), or a pretty-printed format (for when you
62 can combine those features in whatever way you like. 68 want to read that stuff). Or you can combine those features in
69 whatever way you like.
63 70
64FUNCTIONAL INTERFACE 71FUNCTIONAL INTERFACE
65 The following convinience methods are provided by this module. They are 72 The following convinience methods are provided by this module. They are
66 exported by default: 73 exported by default:
67 74
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105 $json = $json->ascii ([$enable]) 112 $json = $json->ascii ([$enable])
106 If $enable is true (or missing), then the "encode" method will not 113 If $enable is true (or missing), then the "encode" method will not
107 generate characters outside the code range 0..127 (which is ASCII). 114 generate characters outside the code range 0..127 (which is ASCII).
108 Any unicode characters outside that range will be escaped using 115 Any unicode characters outside that range will be escaped using
109 either a single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL 116 either a single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL
110 escape sequence, as per RFC4627. 117 escape sequence, as per RFC4627. The resulting encoded JSON text can
118 be treated as a native unicode string, an ascii-encoded,
119 latin1-encoded or UTF-8 encoded string, or any other superset of
120 ASCII.
111 121
112 If $enable is false, then the "encode" method will not escape 122 If $enable is false, then the "encode" method will not escape
113 Unicode characters unless required by the JSON syntax. This results 123 Unicode characters unless required by the JSON syntax or other
114 in a faster and more compact format. 124 flags. This results in a faster and more compact format.
125
126 The main use for this flag is to produce JSON texts that can be
127 transmitted over a 7-bit channel, as the encoded JSON texts will not
128 contain any 8 bit characters.
115 129
116 JSON::XS->new->ascii (1)->encode ([chr 0x10401]) 130 JSON::XS->new->ascii (1)->encode ([chr 0x10401])
117 => ["\ud801\udc01"] 131 => ["\ud801\udc01"]
132
133 $json = $json->latin1 ([$enable])
134 If $enable is true (or missing), then the "encode" method will
135 encode the resulting JSON text as latin1 (or iso-8859-1), escaping
136 any characters outside the code range 0..255. The resulting string
137 can be treated as a latin1-encoded JSON text or a native unicode
138 string. The "decode" method will not be affected in any way by this
139 flag, as "decode" by default expects unicode, which is a strict
140 superset of latin1.
141
142 If $enable is false, then the "encode" method will not escape
143 Unicode characters unless required by the JSON syntax or other
144 flags.
145
146 The main use for this flag is efficiently encoding binary data as
147 JSON text, as most octets will not be escaped, resulting in a
148 smaller encoded size. The disadvantage is that the resulting JSON
149 text is encoded in latin1 (and must correctly be treated as such
150 when storing and transfering), a rare encoding for JSON. It is
151 therefore most useful when you want to store data structures known
152 to contain binary data efficiently in files or databases, not when
153 talking to other JSON encoders/decoders.
154
155 JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]
156 => ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)
118 157
119 $json = $json->utf8 ([$enable]) 158 $json = $json->utf8 ([$enable])
120 If $enable is true (or missing), then the "encode" method will 159 If $enable is true (or missing), then the "encode" method will
121 encode the JSON result into UTF-8, as required by many protocols, 160 encode the JSON result into UTF-8, as required by many protocols,
122 while the "decode" method expects to be handled an UTF-8-encoded 161 while the "decode" method expects to be handled an UTF-8-encoded
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238 "encode" or "decode" to their minimum size possible. This can save 277 "encode" or "decode" to their minimum size possible. This can save
239 memory when your JSON texts are either very very long or you have 278 memory when your JSON texts are either very very long or you have
240 many short strings. It will also try to downgrade any strings to 279 many short strings. It will also try to downgrade any strings to
241 octet-form if possible: perl stores strings internally either in an 280 octet-form if possible: perl stores strings internally either in an
242 encoding called UTF-X or in octet-form. The latter cannot store 281 encoding called UTF-X or in octet-form. The latter cannot store
243 everything but uses less space in general. 282 everything but uses less space in general (and some buggy Perl or C
283 code might even rely on that internal representation being used).
284
285 The actual definition of what shrink does might change in future
286 versions, but it will always try to save space at the expense of
287 time.
244 288
245 If $enable is true (or missing), the string returned by "encode" 289 If $enable is true (or missing), the string returned by "encode"
246 will be shrunk-to-fit, while all strings generated by "decode" will 290 will be shrunk-to-fit, while all strings generated by "decode" will
247 also be shrunk-to-fit. 291 also be shrunk-to-fit.
248 292
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251 295
252 In the future, this setting might control other things, such as 296 In the future, this setting might control other things, such as
253 converting strings that look like integers or floats into integers 297 converting strings that look like integers or floats into integers
254 or floats internally (there is no difference on the Perl level), 298 or floats internally (there is no difference on the Perl level),
255 saving space. 299 saving space.
300
301 $json = $json->max_depth ([$maximum_nesting_depth])
302 Sets the maximum nesting level (default 512) accepted while encoding
303 or decoding. If the JSON text or Perl data structure has an equal or
304 higher nesting level then this limit, then the encoder and decoder
305 will stop and croak at that point.
306
307 Nesting level is defined by number of hash- or arrayrefs that the
308 encoder needs to traverse to reach a given point or the number of
309 "{" or "[" characters without their matching closing parenthesis
310 crossed to reach a given character in a string.
311
312 Setting the maximum depth to one disallows any nesting, so that
313 ensures that the object is only a single hash/object or array.
314
315 The argument to "max_depth" will be rounded up to the next nearest
316 power of two.
317
318 See SECURITY CONSIDERATIONS, below, for more info on why this is
319 useful.
256 320
257 $json_text = $json->encode ($perl_scalar) 321 $json_text = $json->encode ($perl_scalar)
258 Converts the given Perl data structure (a simple scalar or a 322 Converts the given Perl data structure (a simple scalar or a
259 reference to a hash or array) to its JSON representation. Simple 323 reference to a hash or array) to its JSON representation. Simple
260 scalars will be converted into JSON string or number sequences, 324 scalars will be converted into JSON string or number sequences,
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269 333
270 JSON numbers and strings become simple Perl scalars. JSON arrays 334 JSON numbers and strings become simple Perl scalars. JSON arrays
271 become Perl arrayrefs and JSON objects become Perl hashrefs. "true" 335 become Perl arrayrefs and JSON objects become Perl hashrefs. "true"
272 becomes 1, "false" becomes 0 and "null" becomes "undef". 336 becomes 1, "false" becomes 0 and "null" becomes "undef".
273 337
338 ($perl_scalar, $characters) = $json->decode_prefix ($json_text)
339 This works like the "decode" method, but instead of raising an
340 exception when there is trailing garbage after the first JSON
341 object, it will silently stop parsing there and return the number of
342 characters consumed so far.
343
344 This is useful if your JSON texts are not delimited by an outer
345 protocol (which is not the brightest thing to do in the first place)
346 and you need to know where the JSON text ends.
347
348 JSON::XS->new->decode_prefix ("[1] the tail")
349 => ([], 3)
350
274MAPPING 351MAPPING
275 This section describes how JSON::XS maps Perl values to JSON values and 352 This section describes how JSON::XS maps Perl values to JSON values and
276 vice versa. These mappings are designed to "do the right thing" in most 353 vice versa. These mappings are designed to "do the right thing" in most
277 circumstances automatically, preserving round-tripping characteristics 354 circumstances automatically, preserving round-tripping characteristics
278 (what you put in comes out as something equivalent). 355 (what you put in comes out as something equivalent).
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317 truly typeless language, so we can only guess which JSON type is meant 394 truly typeless language, so we can only guess which JSON type is meant
318 by a Perl value. 395 by a Perl value.
319 396
320 hash references 397 hash references
321 Perl hash references become JSON objects. As there is no inherent 398 Perl hash references become JSON objects. As there is no inherent
322 ordering in hash keys, they will usually be encoded in a 399 ordering in hash keys (or JSON objects), they will usually be
323 pseudo-random order that can change between runs of the same program 400 encoded in a pseudo-random order that can change between runs of the
324 but stays generally the same within a single run of a program. 401 same program but stays generally the same within a single run of a
325 JSON::XS can optionally sort the hash keys (determined by the 402 program. JSON::XS can optionally sort the hash keys (determined by
326 *canonical* flag), so the same datastructure will serialise to the 403 the *canonical* flag), so the same datastructure will serialise to
327 same JSON text (given same settings and version of JSON::XS), but 404 the same JSON text (given same settings and version of JSON::XS),
328 this incurs a runtime overhead. 405 but this incurs a runtime overhead and is only rarely useful, e.g.
406 when you want to compare some JSON text against another for
407 equality.
329 408
330 array references 409 array references
331 Perl array references become JSON arrays. 410 Perl array references become JSON arrays.
411
412 other references
413 Other unblessed references are generally not allowed and will cause
414 an exception to be thrown, except for references to the integers 0
415 and 1, which get turned into "false" and "true" atoms in JSON. You
416 can also use "JSON::XS::false" and "JSON::XS::true" to improve
417 readability.
418
419 to_json [\0,JSON::XS::true] # yields [false,true]
332 420
333 blessed objects 421 blessed objects
334 Blessed objects are not allowed. JSON::XS currently tries to encode 422 Blessed objects are not allowed. JSON::XS currently tries to encode
335 their underlying representation (hash- or arrayref), but this 423 their underlying representation (hash- or arrayref), but this
336 behaviour might change in future versions. 424 behaviour might change in future versions.
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367 $x += 0; # numify it, ensuring it will be dumped as a number 455 $x += 0; # numify it, ensuring it will be dumped as a number
368 $x *= 1; # same thing, the choise is yours. 456 $x *= 1; # same thing, the choise is yours.
369 457
370 You can not currently output JSON booleans or force the type in 458 You can not currently output JSON booleans or force the type in
371 other, less obscure, ways. Tell me if you need this capability. 459 other, less obscure, ways. Tell me if you need this capability.
372
373 circular data structures
374 Those will be encoded until memory or stackspace runs out.
375 460
376COMPARISON 461COMPARISON
377 As already mentioned, this module was created because none of the 462 As already mentioned, this module was created because none of the
378 existing JSON modules could be made to work correctly. First I will 463 existing JSON modules could be made to work correctly. First I will
379 describe the problems (or pleasures) I encountered with various existing 464 describe the problems (or pleasures) I encountered with various existing
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457 tables. They have been generated with the help of the "eg/bench" program 542 tables. They have been generated with the help of the "eg/bench" program
458 in the JSON::XS distribution, to make it easy to compare on your own 543 in the JSON::XS distribution, to make it easy to compare on your own
459 system. 544 system.
460 545
461 First comes a comparison between various modules using a very short JSON 546 First comes a comparison between various modules using a very short JSON
462 string (83 bytes), showing the number of encodes/decodes per second 547 string:
463 (JSON::XS is the functional interface, while JSON::XS/2 is the OO 548
549 {"method": "handleMessage", "params": ["user1", "we were just talking"], "id": null}
550
551 It shows the number of encodes/decodes per second (JSON::XS uses the
552 functional interface, while JSON::XS/2 uses the OO interface with
464 interface with pretty-printing and hashkey sorting enabled). Higher is 553 pretty-printing and hashkey sorting enabled). Higher is better:
465 better:
466 554
467 module | encode | decode | 555 module | encode | decode |
468 -----------|------------|------------| 556 -----------|------------|------------|
469 JSON | 14006 | 6820 | 557 JSON | 11488.516 | 7823.035 |
470 JSON::DWIW | 200937 | 120386 | 558 JSON::DWIW | 94708.054 | 129094.260 |
471 JSON::PC | 85065 | 129366 | 559 JSON::PC | 63884.157 | 128528.212 |
472 JSON::Syck | 59898 | 44232 | 560 JSON::Syck | 34898.677 | 42096.911 |
473 JSON::XS | 1171478 | 342435 | 561 JSON::XS | 654027.064 | 396423.669 |
474 JSON::XS/2 | 730760 | 328714 | 562 JSON::XS/2 | 371564.190 | 371725.613 |
475 -----------+------------+------------+ 563 -----------+------------+------------+
476 564
477 That is, JSON::XS is 6 times faster than than JSON::DWIW and about 80 565 That is, JSON::XS is more than six times faster than JSON::DWIW on
566 encoding, more than three times faster on decoding, and about thirty
478 times faster than JSON, even with pretty-printing and key sorting. 567 times faster than JSON, even with pretty-printing and key sorting.
479 568
480 Using a longer test string (roughly 18KB, generated from Yahoo! Locals 569 Using a longer test string (roughly 18KB, generated from Yahoo! Locals
481 search API (http://nanoref.com/yahooapis/mgPdGg): 570 search API (http://nanoref.com/yahooapis/mgPdGg):
482 571
483 module | encode | decode | 572 module | encode | decode |
484 -----------|------------|------------| 573 -----------|------------|------------|
485 JSON | 673 | 38 | 574 JSON | 273.023 | 44.674 |
486 JSON::DWIW | 5271 | 770 | 575 JSON::DWIW | 1089.383 | 1145.704 |
487 JSON::PC | 9901 | 2491 | 576 JSON::PC | 3097.419 | 2393.921 |
488 JSON::Syck | 2360 | 786 | 577 JSON::Syck | 514.060 | 843.053 |
489 JSON::XS | 37398 | 3202 | 578 JSON::XS | 6479.668 | 3636.364 |
490 JSON::XS/2 | 13765 | 3153 | 579 JSON::XS/2 | 3774.221 | 3599.124 |
491 -----------+------------+------------+ 580 -----------+------------+------------+
492 581
493 Again, JSON::XS leads by far in the encoding case, while still beating 582 Again, JSON::XS leads by far.
494 every other module in the decoding case.
495 583
496 On large strings containing lots of unicode characters, some modules 584 On large strings containing lots of high unicode characters, some
497 (such as JSON::PC) decode faster than JSON::XS, but the result will be 585 modules (such as JSON::PC) seem to decode faster than JSON::XS, but the
498 broken due to missing unicode handling. Others refuse to decode or 586 result will be broken due to missing (or wrong) unicode handling. Others
499 encode properly, so it was impossible to prepare a fair comparison table 587 refuse to decode or encode properly, so it was impossible to prepare a
500 for that case. 588 fair comparison table for that case.
501 589
502RESOURCE LIMITS 590SECURITY CONSIDERATIONS
503 JSON::XS does not impose any limits on the size of JSON texts or Perl 591 When you are using JSON in a protocol, talking to untrusted potentially
504 values they represent - if your machine can handle it, JSON::XS will 592 hostile creatures requires relatively few measures.
505 encode or decode it. Future versions might optionally impose structure 593
506 depth and memory use resource limits. 594 First of all, your JSON decoder should be secure, that is, should not
595 have any buffer overflows. Obviously, this module should ensure that and
596 I am trying hard on making that true, but you never know.
597
598 Second, you need to avoid resource-starving attacks. That means you
599 should limit the size of JSON texts you accept, or make sure then when
600 your resources run out, thats just fine (e.g. by using a separate
601 process that can crash safely). The size of a JSON text in octets or
602 characters is usually a good indication of the size of the resources
603 required to decode it into a Perl structure.
604
605 Third, JSON::XS recurses using the C stack when decoding objects and
606 arrays. The C stack is a limited resource: for instance, on my amd64
607 machine with 8MB of stack size I can decode around 180k nested arrays
608 but only 14k nested JSON objects (due to perl itself recursing deeply on
609 croak to free the temporary). If that is exceeded, the program crashes.
610 to be conservative, the default nesting limit is set to 512. If your
611 process has a smaller stack, you should adjust this setting accordingly
612 with the "max_depth" method.
613
614 And last but least, something else could bomb you that I forgot to think
615 of. In that case, you get to keep the pieces. I am always open for
616 hints, though...
507 617
508BUGS 618BUGS
509 While the goal of this module is to be correct, that unfortunately does 619 While the goal of this module is to be correct, that unfortunately does
510 not mean its bug-free, only that I think its design is bug-free. It is 620 not mean its bug-free, only that I think its design is bug-free. It is
511 still very young and not well-tested. If you keep reporting bugs they 621 still relatively early in its development. If you keep reporting bugs
512 will be fixed swiftly, though. 622 they will be fixed swiftly, though.
513 623
514AUTHOR 624AUTHOR
515 Marc Lehmann <schmorp@schmorp.de> 625 Marc Lehmann <schmorp@schmorp.de>
516 http://home.schmorp.de/ 626 http://home.schmorp.de/
517 627

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