| … | |
… | |
| 30 | DESCRIPTION |
30 | DESCRIPTION |
| 31 | 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 |
| 32 | 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*. |
| 33 | To reach the latter goal it was written in C. |
33 | To reach the latter goal it was written in C. |
| 34 | |
34 | |
| 35 | Beginning with version 2.0 of the JSON module, when both JSON and |
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| 36 | JSON::XS are installed, then JSON will fall back on JSON::XS (this can |
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| 37 | be overridden) with no overhead due to emulation (by inheriting |
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| 38 | constructor and methods). If JSON::XS is not available, it will fall |
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| 39 | back to the compatible JSON::PP module as backend, so using JSON instead |
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| 40 | of JSON::XS gives you a portable JSON API that can be fast when you need |
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| 41 | and doesn't require a C compiler when that is a problem. |
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| 42 | |
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| 43 | As this is the n-th-something JSON module on CPAN, what was the reason |
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| 44 | to write yet another JSON module? While it seems there are many JSON |
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| 45 | modules, none of them correctly handle all corner cases, and in most |
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| 46 | cases their maintainers are unresponsive, gone missing, or not listening |
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| 47 | to bug reports for other reasons. |
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| 48 | |
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| 49 | See MAPPING, below, on how JSON::XS maps perl values to JSON values and |
35 | See MAPPING, below, on how JSON::XS maps perl values to JSON values and |
| 50 | vice versa. |
36 | vice versa. |
| 51 | |
37 | |
| 52 | FEATURES |
38 | FEATURES |
| 53 | * correct Unicode handling |
39 | * correct Unicode handling |
| … | |
… | |
| 56 | does so, and even documents what "correct" means. |
42 | does so, and even documents what "correct" means. |
| 57 | |
43 | |
| 58 | * round-trip integrity |
44 | * round-trip integrity |
| 59 | |
45 | |
| 60 | When you serialise a perl data structure using only data types |
46 | When you serialise a perl data structure using only data types |
| 61 | supported by JSON, the deserialised data structure is identical on |
47 | supported by JSON and Perl, the deserialised data structure is |
| 62 | the Perl level. (e.g. the string "2.0" doesn't suddenly become "2" |
48 | identical on the Perl level. (e.g. the string "2.0" doesn't suddenly |
| 63 | just because it looks like a number). There minor *are* exceptions |
49 | become "2" just because it looks like a number). There *are* minor |
| 64 | to this, read the MAPPING section below to learn about those. |
50 | exceptions to this, read the MAPPING section below to learn about |
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51 | those. |
| 65 | |
52 | |
| 66 | * strict checking of JSON correctness |
53 | * strict checking of JSON correctness |
| 67 | |
54 | |
| 68 | There is no guessing, no generating of illegal JSON texts by |
55 | There is no guessing, no generating of illegal JSON texts by |
| 69 | default, and only JSON is accepted as input by default (the latter |
56 | default, and only JSON is accepted as input by default (the latter |
| … | |
… | |
| 76 | too. |
63 | too. |
| 77 | |
64 | |
| 78 | * simple to use |
65 | * simple to use |
| 79 | |
66 | |
| 80 | This module has both a simple functional interface as well as an |
67 | This module has both a simple functional interface as well as an |
| 81 | object oriented interface interface. |
68 | object oriented interface. |
| 82 | |
69 | |
| 83 | * reasonably versatile output formats |
70 | * reasonably versatile output formats |
| 84 | |
71 | |
| 85 | You can choose between the most compact guaranteed-single-line |
72 | You can choose between the most compact guaranteed-single-line |
| 86 | format possible (nice for simple line-based protocols), a pure-ASCII |
73 | format possible (nice for simple line-based protocols), a pure-ASCII |
| … | |
… | |
| 102 | $json_text = JSON::XS->new->utf8->encode ($perl_scalar) |
89 | $json_text = JSON::XS->new->utf8->encode ($perl_scalar) |
| 103 | |
90 | |
| 104 | Except being faster. |
91 | Except being faster. |
| 105 | |
92 | |
| 106 | $perl_scalar = decode_json $json_text |
93 | $perl_scalar = decode_json $json_text |
| 107 | The opposite of "encode_json": expects an UTF-8 (binary) string and |
94 | The opposite of "encode_json": expects a UTF-8 (binary) string and |
| 108 | tries to parse that as an UTF-8 encoded JSON text, returning the |
95 | tries to parse that as a UTF-8 encoded JSON text, returning the |
| 109 | resulting reference. Croaks on error. |
96 | resulting reference. Croaks on error. |
| 110 | |
97 | |
| 111 | This function call is functionally identical to: |
98 | This function call is functionally identical to: |
| 112 | |
99 | |
| 113 | $perl_scalar = JSON::XS->new->utf8->decode ($json_text) |
100 | $perl_scalar = JSON::XS->new->utf8->decode ($json_text) |
| 114 | |
101 | |
| 115 | Except being faster. |
102 | Except being faster. |
| 116 | |
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| 117 | $is_boolean = JSON::XS::is_bool $scalar |
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| 118 | Returns true if the passed scalar represents either JSON::XS::true |
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| 119 | or JSON::XS::false, two constants that act like 1 and 0, |
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| 120 | respectively and are used to represent JSON "true" and "false" |
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| 121 | values in Perl. |
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| 122 | |
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| 123 | See MAPPING, below, for more information on how JSON values are |
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| 124 | mapped to Perl. |
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| 125 | |
103 | |
| 126 | A FEW NOTES ON UNICODE AND PERL |
104 | A FEW NOTES ON UNICODE AND PERL |
| 127 | Since this often leads to confusion, here are a few very clear words on |
105 | Since this often leads to confusion, here are a few very clear words on |
| 128 | how Unicode works in Perl, modulo bugs. |
106 | how Unicode works in Perl, modulo bugs. |
| 129 | |
107 | |
| … | |
… | |
| 166 | The object oriented interface lets you configure your own encoding or |
144 | The object oriented interface lets you configure your own encoding or |
| 167 | decoding style, within the limits of supported formats. |
145 | decoding style, within the limits of supported formats. |
| 168 | |
146 | |
| 169 | $json = new JSON::XS |
147 | $json = new JSON::XS |
| 170 | Creates a new JSON::XS object that can be used to de/encode JSON |
148 | Creates a new JSON::XS object that can be used to de/encode JSON |
| 171 | strings. All boolean flags described below are by default |
149 | strings. All boolean flags described below are by default *disabled* |
| 172 | *disabled*. |
150 | (with the exception of "allow_nonref", which defaults to *enabled* |
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151 | since version 4.0). |
| 173 | |
152 | |
| 174 | The mutators for flags all return the JSON object again and thus |
153 | The mutators for flags all return the JSON object again and thus |
| 175 | calls can be chained: |
154 | calls can be chained: |
| 176 | |
155 | |
| 177 | my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]}) |
156 | my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]}) |
| … | |
… | |
| 233 | |
212 | |
| 234 | $json = $json->utf8 ([$enable]) |
213 | $json = $json->utf8 ([$enable]) |
| 235 | $enabled = $json->get_utf8 |
214 | $enabled = $json->get_utf8 |
| 236 | If $enable is true (or missing), then the "encode" method will |
215 | If $enable is true (or missing), then the "encode" method will |
| 237 | encode the JSON result into UTF-8, as required by many protocols, |
216 | encode the JSON result into UTF-8, as required by many protocols, |
| 238 | while the "decode" method expects to be handled an UTF-8-encoded |
217 | while the "decode" method expects to be handed a UTF-8-encoded |
| 239 | string. Please note that UTF-8-encoded strings do not contain any |
218 | string. Please note that UTF-8-encoded strings do not contain any |
| 240 | characters outside the range 0..255, they are thus useful for |
219 | characters outside the range 0..255, they are thus useful for |
| 241 | bytewise/binary I/O. In future versions, enabling this option might |
220 | bytewise/binary I/O. In future versions, enabling this option might |
| 242 | enable autodetection of the UTF-16 and UTF-32 encoding families, as |
221 | enable autodetection of the UTF-16 and UTF-32 encoding families, as |
| 243 | described in RFC4627. |
222 | described in RFC4627. |
| … | |
… | |
| 322 | |
301 | |
| 323 | $json = $json->relaxed ([$enable]) |
302 | $json = $json->relaxed ([$enable]) |
| 324 | $enabled = $json->get_relaxed |
303 | $enabled = $json->get_relaxed |
| 325 | If $enable is true (or missing), then "decode" will accept some |
304 | If $enable is true (or missing), then "decode" will accept some |
| 326 | extensions to normal JSON syntax (see below). "encode" will not be |
305 | extensions to normal JSON syntax (see below). "encode" will not be |
| 327 | affected in anyway. *Be aware that this option makes you accept |
306 | affected in any way. *Be aware that this option makes you accept |
| 328 | invalid JSON texts as if they were valid!*. I suggest only to use |
307 | invalid JSON texts as if they were valid!*. I suggest only to use |
| 329 | this option to parse application-specific files written by humans |
308 | this option to parse application-specific files written by humans |
| 330 | (configuration files, resource files etc.) |
309 | (configuration files, resource files etc.) |
| 331 | |
310 | |
| 332 | If $enable is false (the default), then "decode" will only accept |
311 | If $enable is false (the default), then "decode" will only accept |
| … | |
… | |
| 360 | [ |
339 | [ |
| 361 | 1, # this comment not allowed in JSON |
340 | 1, # this comment not allowed in JSON |
| 362 | # neither this one... |
341 | # neither this one... |
| 363 | ] |
342 | ] |
| 364 | |
343 | |
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344 | * literal ASCII TAB characters in strings |
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345 | |
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346 | Literal ASCII TAB characters are now allowed in strings (and |
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347 | treated as "\t"). |
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348 | |
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349 | [ |
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350 | "Hello\tWorld", |
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351 | "Hello<TAB>World", # literal <TAB> would not normally be allowed |
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352 | ] |
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353 | |
| 365 | $json = $json->canonical ([$enable]) |
354 | $json = $json->canonical ([$enable]) |
| 366 | $enabled = $json->get_canonical |
355 | $enabled = $json->get_canonical |
| 367 | If $enable is true (or missing), then the "encode" method will |
356 | If $enable is true (or missing), then the "encode" method will |
| 368 | output JSON objects by sorting their keys. This is adding a |
357 | output JSON objects by sorting their keys. This is adding a |
| 369 | comparatively high overhead. |
358 | comparatively high overhead. |
| 370 | |
359 | |
| 371 | If $enable is false, then the "encode" method will output key-value |
360 | If $enable is false, then the "encode" method will output key-value |
| 372 | pairs in the order Perl stores them (which will likely change |
361 | pairs in the order Perl stores them (which will likely change |
| 373 | between runs of the same script). |
362 | between runs of the same script, and can change even within the same |
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363 | run from 5.18 onwards). |
| 374 | |
364 | |
| 375 | This option is useful if you want the same data structure to be |
365 | This option is useful if you want the same data structure to be |
| 376 | encoded as the same JSON text (given the same overall settings). If |
366 | encoded as the same JSON text (given the same overall settings). If |
| 377 | it is disabled, the same hash might be encoded differently even if |
367 | it is disabled, the same hash might be encoded differently even if |
| 378 | contains the same data, as key-value pairs have no inherent ordering |
368 | contains the same data, as key-value pairs have no inherent ordering |
| … | |
… | |
| 382 | |
372 | |
| 383 | This setting has currently no effect on tied hashes. |
373 | This setting has currently no effect on tied hashes. |
| 384 | |
374 | |
| 385 | $json = $json->allow_nonref ([$enable]) |
375 | $json = $json->allow_nonref ([$enable]) |
| 386 | $enabled = $json->get_allow_nonref |
376 | $enabled = $json->get_allow_nonref |
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377 | Unlike other boolean options, this opotion is enabled by default |
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378 | beginning with version 4.0. See "SECURITY CONSIDERATIONS" for the |
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379 | gory details. |
|
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380 | |
| 387 | If $enable is true (or missing), then the "encode" method can |
381 | If $enable is true (or missing), then the "encode" method can |
| 388 | convert a non-reference into its corresponding string, number or |
382 | convert a non-reference into its corresponding string, number or |
| 389 | null JSON value, which is an extension to RFC4627. Likewise, |
383 | null JSON value, which is an extension to RFC4627. Likewise, |
| 390 | "decode" will accept those JSON values instead of croaking. |
384 | "decode" will accept those JSON values instead of croaking. |
| 391 | |
385 | |
| 392 | If $enable is false, then the "encode" method will croak if it isn't |
386 | If $enable is false, then the "encode" method will croak if it isn't |
| 393 | passed an arrayref or hashref, as JSON texts must either be an |
387 | passed an arrayref or hashref, as JSON texts must either be an |
| 394 | object or array. Likewise, "decode" will croak if given something |
388 | object or array. Likewise, "decode" will croak if given something |
| 395 | that is not a JSON object or array. |
389 | that is not a JSON object or array. |
| 396 | |
390 | |
| 397 | Example, encode a Perl scalar as JSON value with enabled |
391 | Example, encode a Perl scalar as JSON value without enabled |
| 398 | "allow_nonref", resulting in an invalid JSON text: |
392 | "allow_nonref", resulting in an error: |
| 399 | |
393 | |
| 400 | JSON::XS->new->allow_nonref->encode ("Hello, World!") |
394 | JSON::XS->new->allow_nonref (0)->encode ("Hello, World!") |
| 401 | => "Hello, World!" |
395 | => hash- or arrayref expected... |
| 402 | |
396 | |
| 403 | $json = $json->allow_unknown ([$enable]) |
397 | $json = $json->allow_unknown ([$enable]) |
| 404 | $enabled = $json->get_allow_unknown |
398 | $enabled = $json->get_allow_unknown |
| 405 | If $enable is true (or missing), then "encode" will *not* throw an |
399 | If $enable is true (or missing), then "encode" will *not* throw an |
| 406 | exception when it encounters values it cannot represent in JSON (for |
400 | exception when it encounters values it cannot represent in JSON (for |
| … | |
… | |
| 415 | recommended to leave it off unless you know your communications |
409 | recommended to leave it off unless you know your communications |
| 416 | partner. |
410 | partner. |
| 417 | |
411 | |
| 418 | $json = $json->allow_blessed ([$enable]) |
412 | $json = $json->allow_blessed ([$enable]) |
| 419 | $enabled = $json->get_allow_blessed |
413 | $enabled = $json->get_allow_blessed |
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414 | See "OBJECT SERIALISATION" for details. |
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415 | |
| 420 | If $enable is true (or missing), then the "encode" method will not |
416 | If $enable is true (or missing), then the "encode" method will not |
| 421 | barf when it encounters a blessed reference. Instead, the value of |
417 | barf when it encounters a blessed reference that it cannot convert |
| 422 | the convert_blessed option will decide whether "null" |
418 | otherwise. Instead, a JSON "null" value is encoded instead of the |
| 423 | ("convert_blessed" disabled or no "TO_JSON" method found) or a |
419 | object. |
| 424 | representation of the object ("convert_blessed" enabled and |
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| 425 | "TO_JSON" method found) is being encoded. Has no effect on "decode". |
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| 426 | |
420 | |
| 427 | If $enable is false (the default), then "encode" will throw an |
421 | If $enable is false (the default), then "encode" will throw an |
| 428 | exception when it encounters a blessed object. |
422 | exception when it encounters a blessed object that it cannot convert |
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423 | otherwise. |
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424 | |
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425 | This setting has no effect on "decode". |
| 429 | |
426 | |
| 430 | $json = $json->convert_blessed ([$enable]) |
427 | $json = $json->convert_blessed ([$enable]) |
| 431 | $enabled = $json->get_convert_blessed |
428 | $enabled = $json->get_convert_blessed |
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429 | See "OBJECT SERIALISATION" for details. |
|
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430 | |
| 432 | If $enable is true (or missing), then "encode", upon encountering a |
431 | If $enable is true (or missing), then "encode", upon encountering a |
| 433 | blessed object, will check for the availability of the "TO_JSON" |
432 | blessed object, will check for the availability of the "TO_JSON" |
| 434 | method on the object's class. If found, it will be called in scalar |
433 | method on the object's class. If found, it will be called in scalar |
| 435 | context and the resulting scalar will be encoded instead of the |
434 | context and the resulting scalar will be encoded instead of the |
| 436 | object. If no "TO_JSON" method is found, the value of |
435 | object. |
| 437 | "allow_blessed" will decide what to do. |
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| 438 | |
436 | |
| 439 | The "TO_JSON" method may safely call die if it wants. If "TO_JSON" |
437 | The "TO_JSON" method may safely call die if it wants. If "TO_JSON" |
| 440 | returns other blessed objects, those will be handled in the same |
438 | returns other blessed objects, those will be handled in the same |
| 441 | way. "TO_JSON" must take care of not causing an endless recursion |
439 | way. "TO_JSON" must take care of not causing an endless recursion |
| 442 | cycle (== crash) in this case. The name of "TO_JSON" was chosen |
440 | cycle (== crash) in this case. The name of "TO_JSON" was chosen |
| 443 | because other methods called by the Perl core (== not by the user of |
441 | because other methods called by the Perl core (== not by the user of |
| 444 | the object) are usually in upper case letters and to avoid |
442 | the object) are usually in upper case letters and to avoid |
| 445 | collisions with any "to_json" function or method. |
443 | collisions with any "to_json" function or method. |
| 446 | |
444 | |
| 447 | This setting does not yet influence "decode" in any way, but in the |
445 | If $enable is false (the default), then "encode" will not consider |
| 448 | future, global hooks might get installed that influence "decode" and |
446 | this type of conversion. |
| 449 | are enabled by this setting. |
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| 450 | |
447 | |
| 451 | If $enable is false, then the "allow_blessed" setting will decide |
448 | This setting has no effect on "decode". |
| 452 | what to do when a blessed object is found. |
449 | |
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450 | $json = $json->allow_tags ([$enable]) |
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451 | $enabled = $json->get_allow_tags |
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452 | See "OBJECT SERIALISATION" for details. |
|
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453 | |
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454 | If $enable is true (or missing), then "encode", upon encountering a |
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455 | blessed object, will check for the availability of the "FREEZE" |
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456 | method on the object's class. If found, it will be used to serialise |
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457 | the object into a nonstandard tagged JSON value (that JSON decoders |
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458 | cannot decode). |
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459 | |
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460 | It also causes "decode" to parse such tagged JSON values and |
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461 | deserialise them via a call to the "THAW" method. |
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462 | |
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463 | If $enable is false (the default), then "encode" will not consider |
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464 | this type of conversion, and tagged JSON values will cause a parse |
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465 | error in "decode", as if tags were not part of the grammar. |
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466 | |
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467 | $json->boolean_values ([$false, $true]) |
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468 | ($false, $true) = $json->get_boolean_values |
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469 | By default, JSON booleans will be decoded as overloaded |
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470 | $Types::Serialiser::false and $Types::Serialiser::true objects. |
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471 | |
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472 | With this method you can specify your own boolean values for |
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473 | decoding - on decode, JSON "false" will be decoded as a copy of |
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474 | $false, and JSON "true" will be decoded as $true ("copy" here is the |
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475 | same thing as assigning a value to another variable, i.e. "$copy = |
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476 | $false"). |
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477 | |
|
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478 | Calling this method without any arguments will reset the booleans to |
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479 | their default values. |
|
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480 | |
|
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481 | "get_boolean_values" will return both $false and $true values, or |
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482 | the empty list when they are set to the default. |
| 453 | |
483 | |
| 454 | $json = $json->filter_json_object ([$coderef->($hashref)]) |
484 | $json = $json->filter_json_object ([$coderef->($hashref)]) |
| 455 | When $coderef is specified, it will be called from "decode" each |
485 | When $coderef is specified, it will be called from "decode" each |
| 456 | time it decodes a JSON object. The only argument is a reference to |
486 | time it decodes a JSON object. The only argument is a reference to |
| 457 | the newly-created hash. If the code references returns a single |
487 | the newly-created hash. If the code reference returns a single |
| 458 | scalar (which need not be a reference), this value (i.e. a copy of |
488 | scalar (which need not be a reference), this value (or rather a copy |
| 459 | that scalar to avoid aliasing) is inserted into the deserialised |
489 | of it) is inserted into the deserialised data structure. If it |
| 460 | data structure. If it returns an empty list (NOTE: *not* "undef", |
490 | returns an empty list (NOTE: *not* "undef", which is a valid |
| 461 | which is a valid scalar), the original deserialised hash will be |
491 | scalar), the original deserialised hash will be inserted. This |
| 462 | inserted. This setting can slow down decoding considerably. |
492 | setting can slow down decoding considerably. |
| 463 | |
493 | |
| 464 | When $coderef is omitted or undefined, any existing callback will be |
494 | When $coderef is omitted or undefined, any existing callback will be |
| 465 | removed and "decode" will not change the deserialised hash in any |
495 | removed and "decode" will not change the deserialised hash in any |
| 466 | way. |
496 | way. |
| 467 | |
497 | |
| … | |
… | |
| 593 | |
623 | |
| 594 | See SECURITY CONSIDERATIONS, below, for more info on why this is |
624 | See SECURITY CONSIDERATIONS, below, for more info on why this is |
| 595 | useful. |
625 | useful. |
| 596 | |
626 | |
| 597 | $json_text = $json->encode ($perl_scalar) |
627 | $json_text = $json->encode ($perl_scalar) |
| 598 | Converts the given Perl data structure (a simple scalar or a |
628 | Converts the given Perl value or data structure to its JSON |
| 599 | reference to a hash or array) to its JSON representation. Simple |
629 | representation. Croaks on error. |
| 600 | scalars will be converted into JSON string or number sequences, |
|
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| 601 | while references to arrays become JSON arrays and references to |
|
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| 602 | hashes become JSON objects. Undefined Perl values (e.g. "undef") |
|
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| 603 | become JSON "null" values. Neither "true" nor "false" values will be |
|
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| 604 | generated. |
|
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| 605 | |
630 | |
| 606 | $perl_scalar = $json->decode ($json_text) |
631 | $perl_scalar = $json->decode ($json_text) |
| 607 | The opposite of "encode": expects a JSON text and tries to parse it, |
632 | The opposite of "encode": expects a JSON text and tries to parse it, |
| 608 | returning the resulting simple scalar or reference. Croaks on error. |
633 | returning the resulting simple scalar or reference. Croaks on error. |
| 609 | |
|
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| 610 | JSON numbers and strings become simple Perl scalars. JSON arrays |
|
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| 611 | become Perl arrayrefs and JSON objects become Perl hashrefs. "true" |
|
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| 612 | becomes 1, "false" becomes 0 and "null" becomes "undef". |
|
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| 613 | |
634 | |
| 614 | ($perl_scalar, $characters) = $json->decode_prefix ($json_text) |
635 | ($perl_scalar, $characters) = $json->decode_prefix ($json_text) |
| 615 | This works like the "decode" method, but instead of raising an |
636 | This works like the "decode" method, but instead of raising an |
| 616 | exception when there is trailing garbage after the first JSON |
637 | exception when there is trailing garbage after the first JSON |
| 617 | object, it will silently stop parsing there and return the number of |
638 | object, it will silently stop parsing there and return the number of |
| 618 | characters consumed so far. |
639 | characters consumed so far. |
| 619 | |
640 | |
| 620 | This is useful if your JSON texts are not delimited by an outer |
641 | This is useful if your JSON texts are not delimited by an outer |
| 621 | protocol (which is not the brightest thing to do in the first place) |
|
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| 622 | and you need to know where the JSON text ends. |
642 | protocol and you need to know where the JSON text ends. |
| 623 | |
643 | |
| 624 | JSON::XS->new->decode_prefix ("[1] the tail") |
644 | JSON::XS->new->decode_prefix ("[1] the tail") |
| 625 | => ([], 3) |
645 | => ([1], 3) |
| 626 | |
646 | |
| 627 | INCREMENTAL PARSING |
647 | INCREMENTAL PARSING |
| 628 | In some cases, there is the need for incremental parsing of JSON texts. |
648 | In some cases, there is the need for incremental parsing of JSON texts. |
| 629 | While this module always has to keep both JSON text and resulting Perl |
649 | While this module always has to keep both JSON text and resulting Perl |
| 630 | data structure in memory at one time, it does allow you to parse a JSON |
650 | data structure in memory at one time, it does allow you to parse a JSON |
| … | |
… | |
| 635 | calls). |
655 | calls). |
| 636 | |
656 | |
| 637 | JSON::XS will only attempt to parse the JSON text once it is sure it has |
657 | JSON::XS will only attempt to parse the JSON text once it is sure it has |
| 638 | enough text to get a decisive result, using a very simple but truly |
658 | enough text to get a decisive result, using a very simple but truly |
| 639 | incremental parser. This means that it sometimes won't stop as early as |
659 | incremental parser. This means that it sometimes won't stop as early as |
| 640 | the full parser, for example, it doesn't detect parenthese mismatches. |
660 | the full parser, for example, it doesn't detect mismatched parentheses. |
| 641 | The only thing it guarantees is that it starts decoding as soon as a |
661 | The only thing it guarantees is that it starts decoding as soon as a |
| 642 | syntactically valid JSON text has been seen. This means you need to set |
662 | syntactically valid JSON text has been seen. This means you need to set |
| 643 | resource limits (e.g. "max_size") to ensure the parser will stop parsing |
663 | resource limits (e.g. "max_size") to ensure the parser will stop parsing |
| 644 | in the presence if syntax errors. |
664 | in the presence if syntax errors. |
| 645 | |
665 | |
| … | |
… | |
| 659 | |
679 | |
| 660 | If the method is called in scalar context, then it will try to |
680 | If the method is called in scalar context, then it will try to |
| 661 | extract exactly *one* JSON object. If that is successful, it will |
681 | extract exactly *one* JSON object. If that is successful, it will |
| 662 | return this object, otherwise it will return "undef". If there is a |
682 | return this object, otherwise it will return "undef". If there is a |
| 663 | parse error, this method will croak just as "decode" would do (one |
683 | parse error, this method will croak just as "decode" would do (one |
| 664 | can then use "incr_skip" to skip the errornous part). This is the |
684 | can then use "incr_skip" to skip the erroneous part). This is the |
| 665 | most common way of using the method. |
685 | most common way of using the method. |
| 666 | |
686 | |
| 667 | And finally, in list context, it will try to extract as many objects |
687 | And finally, in list context, it will try to extract as many objects |
| 668 | from the stream as it can find and return them, or the empty list |
688 | from the stream as it can find and return them, or the empty list |
| 669 | otherwise. For this to work, there must be no separators between the |
689 | otherwise. For this to work, there must be no separators (other than |
| 670 | JSON objects or arrays, instead they must be concatenated |
690 | whitespace) between the JSON objects or arrays, instead they must be |
| 671 | back-to-back. If an error occurs, an exception will be raised as in |
691 | concatenated back-to-back. If an error occurs, an exception will be |
| 672 | the scalar context case. Note that in this case, any |
692 | raised as in the scalar context case. Note that in this case, any |
| 673 | previously-parsed JSON texts will be lost. |
693 | previously-parsed JSON texts will be lost. |
|
|
694 | |
|
|
695 | Example: Parse some JSON arrays/objects in a given string and return |
|
|
696 | them. |
|
|
697 | |
|
|
698 | my @objs = JSON::XS->new->incr_parse ("[5][7][1,2]"); |
| 674 | |
699 | |
| 675 | $lvalue_string = $json->incr_text |
700 | $lvalue_string = $json->incr_text |
| 676 | This method returns the currently stored JSON fragment as an lvalue, |
701 | This method returns the currently stored JSON fragment as an lvalue, |
| 677 | that is, you can manipulate it. This *only* works when a preceding |
702 | that is, you can manipulate it. This *only* works when a preceding |
| 678 | call to "incr_parse" in *scalar context* successfully returned an |
703 | call to "incr_parse" in *scalar context* successfully returned an |
| … | |
… | |
| 680 | function (I mean it. although in simple tests it might actually |
705 | function (I mean it. although in simple tests it might actually |
| 681 | work, it *will* fail under real world conditions). As a special |
706 | work, it *will* fail under real world conditions). As a special |
| 682 | exception, you can also call this method before having parsed |
707 | exception, you can also call this method before having parsed |
| 683 | anything. |
708 | anything. |
| 684 | |
709 | |
|
|
710 | That means you can only use this function to look at or manipulate |
|
|
711 | text before or after complete JSON objects, not while the parser is |
|
|
712 | in the middle of parsing a JSON object. |
|
|
713 | |
| 685 | This function is useful in two cases: a) finding the trailing text |
714 | This function is useful in two cases: a) finding the trailing text |
| 686 | after a JSON object or b) parsing multiple JSON objects separated by |
715 | after a JSON object or b) parsing multiple JSON objects separated by |
| 687 | non-JSON text (such as commas). |
716 | non-JSON text (such as commas). |
| 688 | |
717 | |
| 689 | $json->incr_skip |
718 | $json->incr_skip |
| … | |
… | |
| 692 | "incr_parse" died, in which case the input buffer and incremental |
721 | "incr_parse" died, in which case the input buffer and incremental |
| 693 | parser state is left unchanged, to skip the text parsed so far and |
722 | parser state is left unchanged, to skip the text parsed so far and |
| 694 | to reset the parse state. |
723 | to reset the parse state. |
| 695 | |
724 | |
| 696 | The difference to "incr_reset" is that only text until the parse |
725 | The difference to "incr_reset" is that only text until the parse |
| 697 | error occured is removed. |
726 | error occurred is removed. |
| 698 | |
727 | |
| 699 | $json->incr_reset |
728 | $json->incr_reset |
| 700 | This completely resets the incremental parser, that is, after this |
729 | This completely resets the incremental parser, that is, after this |
| 701 | call, it will be as if the parser had never parsed anything. |
730 | call, it will be as if the parser had never parsed anything. |
| 702 | |
731 | |
| 703 | This is useful if you want to repeatedly parse JSON objects and want |
732 | This is useful if you want to repeatedly parse JSON objects and want |
| 704 | to ignore any trailing data, which means you have to reset the |
733 | to ignore any trailing data, which means you have to reset the |
| 705 | parser after each successful decode. |
734 | parser after each successful decode. |
| 706 | |
735 | |
| 707 | LIMITATIONS |
736 | LIMITATIONS |
| 708 | All options that affect decoding are supported, except "allow_nonref". |
737 | The incremental parser is a non-exact parser: it works by gathering as |
| 709 | The reason for this is that it cannot be made to work sensibly: JSON |
738 | much text as possible that *could* be a valid JSON text, followed by |
| 710 | objects and arrays are self-delimited, i.e. you can concatenate them |
739 | trying to decode it. |
| 711 | back to back and still decode them perfectly. This does not hold true |
|
|
| 712 | for JSON numbers, however. |
|
|
| 713 | |
740 | |
| 714 | For example, is the string 1 a single JSON number, or is it simply the |
741 | That means it sometimes needs to read more data than strictly necessary |
| 715 | start of 12? Or is 12 a single JSON number, or the concatenation of 1 |
742 | to diagnose an invalid JSON text. For example, after parsing the |
| 716 | and 2? In neither case you can tell, and this is why JSON::XS takes the |
743 | following fragment, the parser *could* stop with an error, as this |
| 717 | conservative route and disallows this case. |
744 | fragment *cannot* be the beginning of a valid JSON text: |
|
|
745 | |
|
|
746 | [, |
|
|
747 | |
|
|
748 | In reality, hopwever, the parser might continue to read data until a |
|
|
749 | length limit is exceeded or it finds a closing bracket. |
| 718 | |
750 | |
| 719 | EXAMPLES |
751 | EXAMPLES |
| 720 | Some examples will make all this clearer. First, a simple example that |
752 | Some examples will make all this clearer. First, a simple example that |
| 721 | works similarly to "decode_prefix": We want to decode the JSON object at |
753 | works similarly to "decode_prefix": We want to decode the JSON object at |
| 722 | the start of a string and identify the portion after the JSON object: |
754 | the start of a string and identify the portion after the JSON object: |
| … | |
… | |
| 886 | If the number consists of digits only, JSON::XS will try to |
918 | If the number consists of digits only, JSON::XS will try to |
| 887 | represent it as an integer value. If that fails, it will try to |
919 | represent it as an integer value. If that fails, it will try to |
| 888 | represent it as a numeric (floating point) value if that is possible |
920 | represent it as a numeric (floating point) value if that is possible |
| 889 | without loss of precision. Otherwise it will preserve the number as |
921 | without loss of precision. Otherwise it will preserve the number as |
| 890 | a string value (in which case you lose roundtripping ability, as the |
922 | a string value (in which case you lose roundtripping ability, as the |
| 891 | JSON number will be re-encoded toa JSON string). |
923 | JSON number will be re-encoded to a JSON string). |
| 892 | |
924 | |
| 893 | Numbers containing a fractional or exponential part will always be |
925 | Numbers containing a fractional or exponential part will always be |
| 894 | represented as numeric (floating point) values, possibly at a loss |
926 | represented as numeric (floating point) values, possibly at a loss |
| 895 | of precision (in which case you might lose perfect roundtripping |
927 | of precision (in which case you might lose perfect roundtripping |
| 896 | ability, but the JSON number will still be re-encoded as a JSON |
928 | ability, but the JSON number will still be re-encoded as a JSON |
| 897 | number). |
929 | number). |
| 898 | |
930 | |
|
|
931 | Note that precision is not accuracy - binary floating point values |
|
|
932 | cannot represent most decimal fractions exactly, and when converting |
|
|
933 | from and to floating point, JSON::XS only guarantees precision up to |
|
|
934 | but not including the least significant bit. |
|
|
935 | |
| 899 | true, false |
936 | true, false |
| 900 | These JSON atoms become "JSON::XS::true" and "JSON::XS::false", |
937 | These JSON atoms become "Types::Serialiser::true" and |
| 901 | respectively. They are overloaded to act almost exactly like the |
938 | "Types::Serialiser::false", respectively. They are overloaded to act |
| 902 | numbers 1 and 0. You can check whether a scalar is a JSON boolean by |
939 | almost exactly like the numbers 1 and 0. You can check whether a |
| 903 | using the "JSON::XS::is_bool" function. |
940 | scalar is a JSON boolean by using the "Types::Serialiser::is_bool" |
|
|
941 | function (after "use Types::Serialier", of course). |
| 904 | |
942 | |
| 905 | null |
943 | null |
| 906 | A JSON null atom becomes "undef" in Perl. |
944 | A JSON null atom becomes "undef" in Perl. |
|
|
945 | |
|
|
946 | shell-style comments ("# *text*") |
|
|
947 | As a nonstandard extension to the JSON syntax that is enabled by the |
|
|
948 | "relaxed" setting, shell-style comments are allowed. They can start |
|
|
949 | anywhere outside strings and go till the end of the line. |
|
|
950 | |
|
|
951 | tagged values ("(*tag*)*value*"). |
|
|
952 | Another nonstandard extension to the JSON syntax, enabled with the |
|
|
953 | "allow_tags" setting, are tagged values. In this implementation, the |
|
|
954 | *tag* must be a perl package/class name encoded as a JSON string, |
|
|
955 | and the *value* must be a JSON array encoding optional constructor |
|
|
956 | arguments. |
|
|
957 | |
|
|
958 | See "OBJECT SERIALISATION", below, for details. |
| 907 | |
959 | |
| 908 | PERL -> JSON |
960 | PERL -> JSON |
| 909 | The mapping from Perl to JSON is slightly more difficult, as Perl is a |
961 | The mapping from Perl to JSON is slightly more difficult, as Perl is a |
| 910 | truly typeless language, so we can only guess which JSON type is meant |
962 | truly typeless language, so we can only guess which JSON type is meant |
| 911 | by a Perl value. |
963 | by a Perl value. |
| 912 | |
964 | |
| 913 | hash references |
965 | hash references |
| 914 | Perl hash references become JSON objects. As there is no inherent |
966 | Perl hash references become JSON objects. As there is no inherent |
| 915 | ordering in hash keys (or JSON objects), they will usually be |
967 | ordering in hash keys (or JSON objects), they will usually be |
| 916 | encoded in a pseudo-random order that can change between runs of the |
968 | encoded in a pseudo-random order. JSON::XS can optionally sort the |
| 917 | same program but stays generally the same within a single run of a |
969 | hash keys (determined by the *canonical* flag), so the same |
| 918 | program. JSON::XS can optionally sort the hash keys (determined by |
970 | datastructure will serialise to the same JSON text (given same |
| 919 | the *canonical* flag), so the same datastructure will serialise to |
971 | settings and version of JSON::XS), but this incurs a runtime |
| 920 | the same JSON text (given same settings and version of JSON::XS), |
972 | overhead and is only rarely useful, e.g. when you want to compare |
| 921 | but this incurs a runtime overhead and is only rarely useful, e.g. |
973 | some JSON text against another for equality. |
| 922 | when you want to compare some JSON text against another for |
|
|
| 923 | equality. |
|
|
| 924 | |
974 | |
| 925 | array references |
975 | array references |
| 926 | Perl array references become JSON arrays. |
976 | Perl array references become JSON arrays. |
| 927 | |
977 | |
| 928 | other references |
978 | other references |
| 929 | Other unblessed references are generally not allowed and will cause |
979 | Other unblessed references are generally not allowed and will cause |
| 930 | an exception to be thrown, except for references to the integers 0 |
980 | an exception to be thrown, except for references to the integers 0 |
| 931 | and 1, which get turned into "false" and "true" atoms in JSON. You |
981 | and 1, which get turned into "false" and "true" atoms in JSON. |
| 932 | can also use "JSON::XS::false" and "JSON::XS::true" to improve |
982 | |
|
|
983 | Since "JSON::XS" uses the boolean model from Types::Serialiser, you |
|
|
984 | can also "use Types::Serialiser" and then use |
|
|
985 | "Types::Serialiser::false" and "Types::Serialiser::true" to improve |
| 933 | readability. |
986 | readability. |
| 934 | |
987 | |
|
|
988 | use Types::Serialiser; |
| 935 | encode_json [\0, JSON::XS::true] # yields [false,true] |
989 | encode_json [\0, Types::Serialiser::true] # yields [false,true] |
| 936 | |
990 | |
| 937 | JSON::XS::true, JSON::XS::false |
991 | Types::Serialiser::true, Types::Serialiser::false |
| 938 | These special values become JSON true and JSON false values, |
992 | These special values from the Types::Serialiser module become JSON |
| 939 | respectively. You can also use "\1" and "\0" directly if you want. |
993 | true and JSON false values, respectively. You can also use "\1" and |
|
|
994 | "\0" directly if you want. |
| 940 | |
995 | |
| 941 | blessed objects |
996 | blessed objects |
| 942 | Blessed objects are not directly representable in JSON. See the |
997 | Blessed objects are not directly representable in JSON, but |
| 943 | "allow_blessed" and "convert_blessed" methods on various options on |
998 | "JSON::XS" allows various ways of handling objects. See "OBJECT |
| 944 | how to deal with this: basically, you can choose between throwing an |
999 | SERIALISATION", below, for details. |
| 945 | exception, encoding the reference as if it weren't blessed, or |
|
|
| 946 | provide your own serialiser method. |
|
|
| 947 | |
1000 | |
| 948 | simple scalars |
1001 | simple scalars |
| 949 | Simple Perl scalars (any scalar that is not a reference) are the |
1002 | Simple Perl scalars (any scalar that is not a reference) are the |
| 950 | most difficult objects to encode: JSON::XS will encode undefined |
1003 | most difficult objects to encode: JSON::XS will encode undefined |
| 951 | scalars as JSON "null" values, scalars that have last been used in a |
1004 | scalars as JSON "null" values, scalars that have last been used in a |
| … | |
… | |
| 979 | |
1032 | |
| 980 | You can not currently force the type in other, less obscure, ways. |
1033 | You can not currently force the type in other, less obscure, ways. |
| 981 | Tell me if you need this capability (but don't forget to explain why |
1034 | Tell me if you need this capability (but don't forget to explain why |
| 982 | it's needed :). |
1035 | it's needed :). |
| 983 | |
1036 | |
|
|
1037 | Note that numerical precision has the same meaning as under Perl (so |
|
|
1038 | binary to decimal conversion follows the same rules as in Perl, |
|
|
1039 | which can differ to other languages). Also, your perl interpreter |
|
|
1040 | might expose extensions to the floating point numbers of your |
|
|
1041 | platform, such as infinities or NaN's - these cannot be represented |
|
|
1042 | in JSON, and it is an error to pass those in. |
|
|
1043 | |
|
|
1044 | OBJECT SERIALISATION |
|
|
1045 | As JSON cannot directly represent Perl objects, you have to choose |
|
|
1046 | between a pure JSON representation (without the ability to deserialise |
|
|
1047 | the object automatically again), and a nonstandard extension to the JSON |
|
|
1048 | syntax, tagged values. |
|
|
1049 | |
|
|
1050 | SERIALISATION |
|
|
1051 | What happens when "JSON::XS" encounters a Perl object depends on the |
|
|
1052 | "allow_blessed", "convert_blessed" and "allow_tags" settings, which are |
|
|
1053 | used in this order: |
|
|
1054 | |
|
|
1055 | 1. "allow_tags" is enabled and the object has a "FREEZE" method. |
|
|
1056 | In this case, "JSON::XS" uses the Types::Serialiser object |
|
|
1057 | serialisation protocol to create a tagged JSON value, using a |
|
|
1058 | nonstandard extension to the JSON syntax. |
|
|
1059 | |
|
|
1060 | This works by invoking the "FREEZE" method on the object, with the |
|
|
1061 | first argument being the object to serialise, and the second |
|
|
1062 | argument being the constant string "JSON" to distinguish it from |
|
|
1063 | other serialisers. |
|
|
1064 | |
|
|
1065 | The "FREEZE" method can return any number of values (i.e. zero or |
|
|
1066 | more). These values and the paclkage/classname of the object will |
|
|
1067 | then be encoded as a tagged JSON value in the following format: |
|
|
1068 | |
|
|
1069 | ("classname")[FREEZE return values...] |
|
|
1070 | |
|
|
1071 | e.g.: |
|
|
1072 | |
|
|
1073 | ("URI")["http://www.google.com/"] |
|
|
1074 | ("MyDate")[2013,10,29] |
|
|
1075 | ("ImageData::JPEG")["Z3...VlCg=="] |
|
|
1076 | |
|
|
1077 | For example, the hypothetical "My::Object" "FREEZE" method might use |
|
|
1078 | the objects "type" and "id" members to encode the object: |
|
|
1079 | |
|
|
1080 | sub My::Object::FREEZE { |
|
|
1081 | my ($self, $serialiser) = @_; |
|
|
1082 | |
|
|
1083 | ($self->{type}, $self->{id}) |
|
|
1084 | } |
|
|
1085 | |
|
|
1086 | 2. "convert_blessed" is enabled and the object has a "TO_JSON" method. |
|
|
1087 | In this case, the "TO_JSON" method of the object is invoked in |
|
|
1088 | scalar context. It must return a single scalar that can be directly |
|
|
1089 | encoded into JSON. This scalar replaces the object in the JSON text. |
|
|
1090 | |
|
|
1091 | For example, the following "TO_JSON" method will convert all URI |
|
|
1092 | objects to JSON strings when serialised. The fatc that these values |
|
|
1093 | originally were URI objects is lost. |
|
|
1094 | |
|
|
1095 | sub URI::TO_JSON { |
|
|
1096 | my ($uri) = @_; |
|
|
1097 | $uri->as_string |
|
|
1098 | } |
|
|
1099 | |
|
|
1100 | 3. "allow_blessed" is enabled. |
|
|
1101 | The object will be serialised as a JSON null value. |
|
|
1102 | |
|
|
1103 | 4. none of the above |
|
|
1104 | If none of the settings are enabled or the respective methods are |
|
|
1105 | missing, "JSON::XS" throws an exception. |
|
|
1106 | |
|
|
1107 | DESERIALISATION |
|
|
1108 | For deserialisation there are only two cases to consider: either |
|
|
1109 | nonstandard tagging was used, in which case "allow_tags" decides, or |
|
|
1110 | objects cannot be automatically be deserialised, in which case you can |
|
|
1111 | use postprocessing or the "filter_json_object" or |
|
|
1112 | "filter_json_single_key_object" callbacks to get some real objects our |
|
|
1113 | of your JSON. |
|
|
1114 | |
|
|
1115 | This section only considers the tagged value case: I a tagged JSON |
|
|
1116 | object is encountered during decoding and "allow_tags" is disabled, a |
|
|
1117 | parse error will result (as if tagged values were not part of the |
|
|
1118 | grammar). |
|
|
1119 | |
|
|
1120 | If "allow_tags" is enabled, "JSON::XS" will look up the "THAW" method of |
|
|
1121 | the package/classname used during serialisation (it will not attempt to |
|
|
1122 | load the package as a Perl module). If there is no such method, the |
|
|
1123 | decoding will fail with an error. |
|
|
1124 | |
|
|
1125 | Otherwise, the "THAW" method is invoked with the classname as first |
|
|
1126 | argument, the constant string "JSON" as second argument, and all the |
|
|
1127 | values from the JSON array (the values originally returned by the |
|
|
1128 | "FREEZE" method) as remaining arguments. |
|
|
1129 | |
|
|
1130 | The method must then return the object. While technically you can return |
|
|
1131 | any Perl scalar, you might have to enable the "enable_nonref" setting to |
|
|
1132 | make that work in all cases, so better return an actual blessed |
|
|
1133 | reference. |
|
|
1134 | |
|
|
1135 | As an example, let's implement a "THAW" function that regenerates the |
|
|
1136 | "My::Object" from the "FREEZE" example earlier: |
|
|
1137 | |
|
|
1138 | sub My::Object::THAW { |
|
|
1139 | my ($class, $serialiser, $type, $id) = @_; |
|
|
1140 | |
|
|
1141 | $class->new (type => $type, id => $id) |
|
|
1142 | } |
|
|
1143 | |
| 984 | ENCODING/CODESET FLAG NOTES |
1144 | ENCODING/CODESET FLAG NOTES |
| 985 | The interested reader might have seen a number of flags that signify |
1145 | The interested reader might have seen a number of flags that signify |
| 986 | encodings or codesets - "utf8", "latin1" and "ascii". There seems to be |
1146 | encodings or codesets - "utf8", "latin1" and "ascii". There seems to be |
| 987 | some confusion on what these do, so here is a short comparison: |
1147 | some confusion on what these do, so here is a short comparison: |
| 988 | |
1148 | |
| … | |
… | |
| 1007 | |
1167 | |
| 1008 | "utf8" flag disabled |
1168 | "utf8" flag disabled |
| 1009 | When "utf8" is disabled (the default), then "encode"/"decode" |
1169 | When "utf8" is disabled (the default), then "encode"/"decode" |
| 1010 | generate and expect Unicode strings, that is, characters with high |
1170 | generate and expect Unicode strings, that is, characters with high |
| 1011 | ordinal Unicode values (> 255) will be encoded as such characters, |
1171 | ordinal Unicode values (> 255) will be encoded as such characters, |
| 1012 | and likewise such characters are decoded as-is, no canges to them |
1172 | and likewise such characters are decoded as-is, no changes to them |
| 1013 | will be done, except "(re-)interpreting" them as Unicode codepoints |
1173 | will be done, except "(re-)interpreting" them as Unicode codepoints |
| 1014 | or Unicode characters, respectively (to Perl, these are the same |
1174 | or Unicode characters, respectively (to Perl, these are the same |
| 1015 | thing in strings unless you do funny/weird/dumb stuff). |
1175 | thing in strings unless you do funny/weird/dumb stuff). |
| 1016 | |
1176 | |
| 1017 | This is useful when you want to do the encoding yourself (e.g. when |
1177 | This is useful when you want to do the encoding yourself (e.g. when |
| … | |
… | |
| 1027 | will expect your input strings to be encoded as UTF-8, that is, no |
1187 | will expect your input strings to be encoded as UTF-8, that is, no |
| 1028 | "character" of the input string must have any value > 255, as UTF-8 |
1188 | "character" of the input string must have any value > 255, as UTF-8 |
| 1029 | does not allow that. |
1189 | does not allow that. |
| 1030 | |
1190 | |
| 1031 | The "utf8" flag therefore switches between two modes: disabled means |
1191 | The "utf8" flag therefore switches between two modes: disabled means |
| 1032 | you will get a Unicode string in Perl, enabled means you get an |
1192 | you will get a Unicode string in Perl, enabled means you get a UTF-8 |
| 1033 | UTF-8 encoded octet/binary string in Perl. |
1193 | encoded octet/binary string in Perl. |
| 1034 | |
1194 | |
| 1035 | "latin1" or "ascii" flags enabled |
1195 | "latin1" or "ascii" flags enabled |
| 1036 | With "latin1" (or "ascii") enabled, "encode" will escape characters |
1196 | With "latin1" (or "ascii") enabled, "encode" will escape characters |
| 1037 | with ordinal values > 255 (> 127 with "ascii") and encode the |
1197 | with ordinal values > 255 (> 127 with "ascii") and encode the |
| 1038 | remaining characters as specified by the "utf8" flag. |
1198 | remaining characters as specified by the "utf8" flag. |
| … | |
… | |
| 1125 | characters as well - using "eval" naively simply *will* cause problems. |
1285 | characters as well - using "eval" naively simply *will* cause problems. |
| 1126 | |
1286 | |
| 1127 | Another problem is that some javascript implementations reserve some |
1287 | Another problem is that some javascript implementations reserve some |
| 1128 | property names for their own purposes (which probably makes them |
1288 | property names for their own purposes (which probably makes them |
| 1129 | non-ECMAscript-compliant). For example, Iceweasel reserves the |
1289 | non-ECMAscript-compliant). For example, Iceweasel reserves the |
| 1130 | "__proto__" property name for it's own purposes. |
1290 | "__proto__" property name for its own purposes. |
| 1131 | |
1291 | |
| 1132 | If that is a problem, you could parse try to filter the resulting JSON |
1292 | If that is a problem, you could parse try to filter the resulting JSON |
| 1133 | output for these property strings, e.g.: |
1293 | output for these property strings, e.g.: |
| 1134 | |
1294 | |
| 1135 | $json =~ s/"__proto__"\s*:/"__proto__renamed":/g; |
1295 | $json =~ s/"__proto__"\s*:/"__proto__renamed":/g; |
| 1136 | |
1296 | |
| 1137 | This works because "__proto__" is not valid outside of strings, so every |
1297 | This works because "__proto__" is not valid outside of strings, so every |
| 1138 | occurence of ""__proto__"\s*:" must be a string used as property name. |
1298 | occurrence of ""__proto__"\s*:" must be a string used as property name. |
| 1139 | |
1299 | |
| 1140 | If you know of other incompatibilities, please let me know. |
1300 | If you know of other incompatibilities, please let me know. |
| 1141 | |
1301 | |
| 1142 | JSON and YAML |
1302 | JSON and YAML |
| 1143 | You often hear that JSON is a subset of YAML. This is, however, a mass |
1303 | You often hear that JSON is a subset of YAML. This is, however, a mass |
| … | |
… | |
| 1183 | (which is not that difficult or long) and finally make YAML |
1343 | (which is not that difficult or long) and finally make YAML |
| 1184 | compatible to it, and educating users about the changes, instead of |
1344 | compatible to it, and educating users about the changes, instead of |
| 1185 | spreading lies about the real compatibility for many *years* and |
1345 | spreading lies about the real compatibility for many *years* and |
| 1186 | trying to silence people who point out that it isn't true. |
1346 | trying to silence people who point out that it isn't true. |
| 1187 | |
1347 | |
| 1188 | Addendum/2009: the YAML 1.2 spec is still incomaptible with JSON, |
1348 | Addendum/2009: the YAML 1.2 spec is still incompatible with JSON, |
| 1189 | even though the incompatibilities have been documented (and are |
1349 | even though the incompatibilities have been documented (and are |
| 1190 | known to Brian) for many years and the spec makes explicit claims |
1350 | known to Brian) for many years and the spec makes explicit claims |
| 1191 | that YAML is a superset of JSON. It would be so easy to fix, but |
1351 | that YAML is a superset of JSON. It would be so easy to fix, but |
| 1192 | apparently, bullying and corrupting userdata is so much easier. |
1352 | apparently, bullying people and corrupting userdata is so much |
|
|
1353 | easier. |
| 1193 | |
1354 | |
| 1194 | SPEED |
1355 | SPEED |
| 1195 | It seems that JSON::XS is surprisingly fast, as shown in the following |
1356 | It seems that JSON::XS is surprisingly fast, as shown in the following |
| 1196 | tables. They have been generated with the help of the "eg/bench" program |
1357 | tables. They have been generated with the help of the "eg/bench" program |
| 1197 | in the JSON::XS distribution, to make it easy to compare on your own |
1358 | in the JSON::XS distribution, to make it easy to compare on your own |
| … | |
… | |
| 1201 | single-line JSON string (also available at |
1362 | single-line JSON string (also available at |
| 1202 | <http://dist.schmorp.de/misc/json/short.json>). |
1363 | <http://dist.schmorp.de/misc/json/short.json>). |
| 1203 | |
1364 | |
| 1204 | {"method": "handleMessage", "params": ["user1", |
1365 | {"method": "handleMessage", "params": ["user1", |
| 1205 | "we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7, |
1366 | "we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7, |
| 1206 | true, false]} |
1367 | 1, 0]} |
| 1207 | |
1368 | |
| 1208 | It shows the number of encodes/decodes per second (JSON::XS uses the |
1369 | It shows the number of encodes/decodes per second (JSON::XS uses the |
| 1209 | functional interface, while JSON::XS/2 uses the OO interface with |
1370 | functional interface, while JSON::XS/2 uses the OO interface with |
| 1210 | pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink). |
1371 | pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink. |
| 1211 | Higher is better: |
1372 | JSON::DWIW/DS uses the deserialise function, while JSON::DWIW::FJ uses |
|
|
1373 | the from_json method). Higher is better: |
| 1212 | |
1374 | |
| 1213 | module | encode | decode | |
1375 | module | encode | decode | |
| 1214 | -----------|------------|------------| |
1376 | --------------|------------|------------| |
| 1215 | JSON 1.x | 4990.842 | 4088.813 | |
1377 | JSON::DWIW/DS | 86302.551 | 102300.098 | |
| 1216 | JSON::DWIW | 51653.990 | 71575.154 | |
1378 | JSON::DWIW/FJ | 86302.551 | 75983.768 | |
| 1217 | JSON::PC | 65948.176 | 74631.744 | |
1379 | JSON::PP | 15827.562 | 6638.658 | |
| 1218 | JSON::PP | 8931.652 | 3817.168 | |
1380 | JSON::Syck | 63358.066 | 47662.545 | |
| 1219 | JSON::Syck | 24877.248 | 27776.848 | |
1381 | JSON::XS | 511500.488 | 511500.488 | |
| 1220 | JSON::XS | 388361.481 | 227951.304 | |
1382 | JSON::XS/2 | 291271.111 | 388361.481 | |
| 1221 | JSON::XS/2 | 227951.304 | 218453.333 | |
1383 | JSON::XS/3 | 361577.931 | 361577.931 | |
| 1222 | JSON::XS/3 | 338250.323 | 218453.333 | |
1384 | Storable | 66788.280 | 265462.278 | |
| 1223 | Storable | 16500.016 | 135300.129 | |
|
|
| 1224 | -----------+------------+------------+ |
1385 | --------------+------------+------------+ |
| 1225 | |
1386 | |
| 1226 | That is, JSON::XS is about five times faster than JSON::DWIW on |
1387 | That is, JSON::XS is almost six times faster than JSON::DWIW on |
| 1227 | encoding, about three times faster on decoding, and over forty times |
1388 | encoding, about five times faster on decoding, and over thirty to |
| 1228 | faster than JSON, even with pretty-printing and key sorting. It also |
1389 | seventy times faster than JSON's pure perl implementation. It also |
| 1229 | compares favourably to Storable for small amounts of data. |
1390 | compares favourably to Storable for small amounts of data. |
| 1230 | |
1391 | |
| 1231 | Using a longer test string (roughly 18KB, generated from Yahoo! Locals |
1392 | Using a longer test string (roughly 18KB, generated from Yahoo! Locals |
| 1232 | search API (<http://dist.schmorp.de/misc/json/long.json>). |
1393 | search API (<http://dist.schmorp.de/misc/json/long.json>). |
| 1233 | |
1394 | |
| 1234 | module | encode | decode | |
1395 | module | encode | decode | |
| 1235 | -----------|------------|------------| |
1396 | --------------|------------|------------| |
| 1236 | JSON 1.x | 55.260 | 34.971 | |
1397 | JSON::DWIW/DS | 1647.927 | 2673.916 | |
| 1237 | JSON::DWIW | 825.228 | 1082.513 | |
1398 | JSON::DWIW/FJ | 1630.249 | 2596.128 | |
| 1238 | JSON::PC | 3571.444 | 2394.829 | |
|
|
| 1239 | JSON::PP | 210.987 | 32.574 | |
1399 | JSON::PP | 400.640 | 62.311 | |
| 1240 | JSON::Syck | 552.551 | 787.544 | |
1400 | JSON::Syck | 1481.040 | 1524.869 | |
| 1241 | JSON::XS | 5780.463 | 4854.519 | |
1401 | JSON::XS | 20661.596 | 9541.183 | |
| 1242 | JSON::XS/2 | 3869.998 | 4798.975 | |
1402 | JSON::XS/2 | 10683.403 | 9416.938 | |
| 1243 | JSON::XS/3 | 5862.880 | 4798.975 | |
1403 | JSON::XS/3 | 20661.596 | 9400.054 | |
| 1244 | Storable | 4445.002 | 5235.027 | |
1404 | Storable | 19765.806 | 10000.725 | |
| 1245 | -----------+------------+------------+ |
1405 | --------------+------------+------------+ |
| 1246 | |
1406 | |
| 1247 | Again, JSON::XS leads by far (except for Storable which non-surprisingly |
1407 | Again, JSON::XS leads by far (except for Storable which non-surprisingly |
| 1248 | decodes faster). |
1408 | decodes a bit faster). |
| 1249 | |
1409 | |
| 1250 | On large strings containing lots of high Unicode characters, some |
1410 | On large strings containing lots of high Unicode characters, some |
| 1251 | modules (such as JSON::PC) seem to decode faster than JSON::XS, but the |
1411 | modules (such as JSON::PC) seem to decode faster than JSON::XS, but the |
| 1252 | result will be broken due to missing (or wrong) Unicode handling. Others |
1412 | result will be broken due to missing (or wrong) Unicode handling. Others |
| 1253 | refuse to decode or encode properly, so it was impossible to prepare a |
1413 | refuse to decode or encode properly, so it was impossible to prepare a |
| … | |
… | |
| 1294 | to see whether you are vulnerable to some common attack vectors (which |
1454 | to see whether you are vulnerable to some common attack vectors (which |
| 1295 | really are browser design bugs, but it is still you who will have to |
1455 | really are browser design bugs, but it is still you who will have to |
| 1296 | deal with it, as major browser developers care only for features, not |
1456 | deal with it, as major browser developers care only for features, not |
| 1297 | about getting security right). |
1457 | about getting security right). |
| 1298 | |
1458 | |
|
|
1459 | "OLD" VS. "NEW" JSON (RFC4627 VS. RFC7159) |
|
|
1460 | JSON originally required JSON texts to represent an array or object - |
|
|
1461 | scalar values were explicitly not allowed. This has changed, and |
|
|
1462 | versions of JSON::XS beginning with 4.0 reflect this by allowing scalar |
|
|
1463 | values by default. |
|
|
1464 | |
|
|
1465 | One reason why one might not want this is that this removes a |
|
|
1466 | fundamental property of JSON texts, namely that they are self-delimited |
|
|
1467 | and self-contained, or in other words, you could take any number of |
|
|
1468 | "old" JSON texts and paste them together, and the result would be |
|
|
1469 | unambiguously parseable: |
|
|
1470 | |
|
|
1471 | [1,3]{"k":5}[][null] # four JSON texts, without doubt |
|
|
1472 | |
|
|
1473 | By allowing scalars, this property is lost: in the following example, is |
|
|
1474 | this one JSON text (the number 12) or two JSON texts (the numbers 1 and |
|
|
1475 | 2): |
|
|
1476 | |
|
|
1477 | 12 # could be 12, or 1 and 2 |
|
|
1478 | |
|
|
1479 | Another lost property of "old" JSON is that no lookahead is required to |
|
|
1480 | know the end of a JSON text, i.e. the JSON text definitely ended at the |
|
|
1481 | last "]" or "}" character, there was no need to read extra characters. |
|
|
1482 | |
|
|
1483 | For example, a viable network protocol with "old" JSON was to simply |
|
|
1484 | exchange JSON texts without delimiter. For "new" JSON, you have to use a |
|
|
1485 | suitable delimiter (such as a newline) after every JSON text or ensure |
|
|
1486 | you never encode/decode scalar values. |
|
|
1487 | |
|
|
1488 | Most protocols do work by only transferring arrays or objects, and the |
|
|
1489 | easiest way to avoid problems with the "new" JSON definition is to |
|
|
1490 | explicitly disallow scalar values in your encoder and decoder: |
|
|
1491 | |
|
|
1492 | $json_coder = JSON::XS->new->allow_nonref (0) |
|
|
1493 | |
|
|
1494 | This is a somewhat unhappy situation, and the blame can fully be put on |
|
|
1495 | JSON's inmventor, Douglas Crockford, who unilaterally changed the format |
|
|
1496 | in 2006 without consulting the IETF, forcing the IETF to either fork the |
|
|
1497 | format or go with it (as I was told, the IETF wasn't amused). |
|
|
1498 | |
|
|
1499 | RELATIONSHIP WITH I-JSON |
|
|
1500 | JSON is a somewhat sloppily-defined format - it carries around obvious |
|
|
1501 | Javascript baggage, such as not really defining number range, probably |
|
|
1502 | because Javascript only has one type of numbers: IEEE 64 bit floats |
|
|
1503 | ("binary64"). |
|
|
1504 | |
|
|
1505 | For this reaosn, RFC7493 defines "Internet JSON", which is a restricted |
|
|
1506 | subset of JSON that is supposedly more interoperable on the internet. |
|
|
1507 | |
|
|
1508 | While "JSON::XS" does not offer specific support for I-JSON, it of |
|
|
1509 | course accepts valid I-JSON and by default implements some of the |
|
|
1510 | limitations of I-JSON, such as parsing numbers as perl numbers, which |
|
|
1511 | are usually a superset of binary64 numbers. |
|
|
1512 | |
|
|
1513 | To generate I-JSON, follow these rules: |
|
|
1514 | |
|
|
1515 | * always generate UTF-8 |
|
|
1516 | |
|
|
1517 | I-JSON must be encoded in UTF-8, the default for "encode_json". |
|
|
1518 | |
|
|
1519 | * numbers should be within IEEE 754 binary64 range |
|
|
1520 | |
|
|
1521 | Basically all existing perl installations use binary64 to represent |
|
|
1522 | floating point numbers, so all you need to do is to avoid large |
|
|
1523 | integers. |
|
|
1524 | |
|
|
1525 | * objects must not have duplicate keys |
|
|
1526 | |
|
|
1527 | This is trivially done, as "JSON::XS" does not allow duplicate keys. |
|
|
1528 | |
|
|
1529 | * do not generate scalar JSON texts, use "->allow_nonref (0)" |
|
|
1530 | |
|
|
1531 | I-JSON strongly requests you to only encode arrays and objects into |
|
|
1532 | JSON. |
|
|
1533 | |
|
|
1534 | * times should be strings in ISO 8601 format |
|
|
1535 | |
|
|
1536 | There are a myriad of modules on CPAN dealing with ISO 8601 - search |
|
|
1537 | for "ISO8601" on CPAN and use one. |
|
|
1538 | |
|
|
1539 | * encode binary data as base64 |
|
|
1540 | |
|
|
1541 | While it's tempting to just dump binary data as a string (and let |
|
|
1542 | "JSON::XS" do the escaping), for I-JSON, it's *recommended* to |
|
|
1543 | encode binary data as base64. |
|
|
1544 | |
|
|
1545 | There are some other considerations - read RFC7493 for the details if |
|
|
1546 | interested. |
|
|
1547 | |
|
|
1548 | INTEROPERABILITY WITH OTHER MODULES |
|
|
1549 | "JSON::XS" uses the Types::Serialiser module to provide boolean |
|
|
1550 | constants. That means that the JSON true and false values will be |
|
|
1551 | comaptible to true and false values of other modules that do the same, |
|
|
1552 | such as JSON::PP and CBOR::XS. |
|
|
1553 | |
|
|
1554 | INTEROPERABILITY WITH OTHER JSON DECODERS |
|
|
1555 | As long as you only serialise data that can be directly expressed in |
|
|
1556 | JSON, "JSON::XS" is incapable of generating invalid JSON output (modulo |
|
|
1557 | bugs, but "JSON::XS" has found more bugs in the official JSON testsuite |
|
|
1558 | (1) than the official JSON testsuite has found in "JSON::XS" (0)). |
|
|
1559 | |
|
|
1560 | When you have trouble decoding JSON generated by this module using other |
|
|
1561 | decoders, then it is very likely that you have an encoding mismatch or |
|
|
1562 | the other decoder is broken. |
|
|
1563 | |
|
|
1564 | When decoding, "JSON::XS" is strict by default and will likely catch all |
|
|
1565 | errors. There are currently two settings that change this: "relaxed" |
|
|
1566 | makes "JSON::XS" accept (but not generate) some non-standard extensions, |
|
|
1567 | and "allow_tags" will allow you to encode and decode Perl objects, at |
|
|
1568 | the cost of not outputting valid JSON anymore. |
|
|
1569 | |
|
|
1570 | TAGGED VALUE SYNTAX AND STANDARD JSON EN/DECODERS |
|
|
1571 | When you use "allow_tags" to use the extended (and also nonstandard and |
|
|
1572 | invalid) JSON syntax for serialised objects, and you still want to |
|
|
1573 | decode the generated When you want to serialise objects, you can run a |
|
|
1574 | regex to replace the tagged syntax by standard JSON arrays (it only |
|
|
1575 | works for "normal" package names without comma, newlines or single |
|
|
1576 | colons). First, the readable Perl version: |
|
|
1577 | |
|
|
1578 | # if your FREEZE methods return no values, you need this replace first: |
|
|
1579 | $json =~ s/\( \s* (" (?: [^\\":,]+|\\.|::)* ") \s* \) \s* \[\s*\]/[$1]/gx; |
|
|
1580 | |
|
|
1581 | # this works for non-empty constructor arg lists: |
|
|
1582 | $json =~ s/\( \s* (" (?: [^\\":,]+|\\.|::)* ") \s* \) \s* \[/[$1,/gx; |
|
|
1583 | |
|
|
1584 | And here is a less readable version that is easy to adapt to other |
|
|
1585 | languages: |
|
|
1586 | |
|
|
1587 | $json =~ s/\(\s*("([^\\":,]+|\\.|::)*")\s*\)\s*\[/[$1,/g; |
|
|
1588 | |
|
|
1589 | Here is an ECMAScript version (same regex): |
|
|
1590 | |
|
|
1591 | json = json.replace (/\(\s*("([^\\":,]+|\\.|::)*")\s*\)\s*\[/g, "[$1,"); |
|
|
1592 | |
|
|
1593 | Since this syntax converts to standard JSON arrays, it might be hard to |
|
|
1594 | distinguish serialised objects from normal arrays. You can prepend a |
|
|
1595 | "magic number" as first array element to reduce chances of a collision: |
|
|
1596 | |
|
|
1597 | $json =~ s/\(\s*("([^\\":,]+|\\.|::)*")\s*\)\s*\[/["XU1peReLzT4ggEllLanBYq4G9VzliwKF",$1,/g; |
|
|
1598 | |
|
|
1599 | And after decoding the JSON text, you could walk the data structure |
|
|
1600 | looking for arrays with a first element of |
|
|
1601 | "XU1peReLzT4ggEllLanBYq4G9VzliwKF". |
|
|
1602 | |
|
|
1603 | The same approach can be used to create the tagged format with another |
|
|
1604 | encoder. First, you create an array with the magic string as first |
|
|
1605 | member, the classname as second, and constructor arguments last, encode |
|
|
1606 | it as part of your JSON structure, and then: |
|
|
1607 | |
|
|
1608 | $json =~ s/\[\s*"XU1peReLzT4ggEllLanBYq4G9VzliwKF"\s*,\s*("([^\\":,]+|\\.|::)*")\s*,/($1)[/g; |
|
|
1609 | |
|
|
1610 | Again, this has some limitations - the magic string must not be encoded |
|
|
1611 | with character escapes, and the constructor arguments must be non-empty. |
|
|
1612 | |
| 1299 | THREADS |
1613 | (I-)THREADS |
| 1300 | This module is *not* guaranteed to be thread safe and there are no plans |
1614 | This module is *not* guaranteed to be ithread (or MULTIPLICITY-) safe |
| 1301 | to change this until Perl gets thread support (as opposed to the |
1615 | and there are no plans to change this. Note that perl's builtin |
| 1302 | horribly slow so-called "threads" which are simply slow and bloated |
1616 | so-called threads/ithreads are officially deprecated and should not be |
| 1303 | process simulations - use fork, it's *much* faster, cheaper, better). |
1617 | used. |
| 1304 | |
1618 | |
| 1305 | (It might actually work, but you have been warned). |
1619 | THE PERILS OF SETLOCALE |
|
|
1620 | Sometimes people avoid the Perl locale support and directly call the |
|
|
1621 | system's setlocale function with "LC_ALL". |
|
|
1622 | |
|
|
1623 | This breaks both perl and modules such as JSON::XS, as stringification |
|
|
1624 | of numbers no longer works correctly (e.g. "$x = 0.1; print "$x"+1" |
|
|
1625 | might print 1, and JSON::XS might output illegal JSON as JSON::XS relies |
|
|
1626 | on perl to stringify numbers). |
|
|
1627 | |
|
|
1628 | The solution is simple: don't call "setlocale", or use it for only those |
|
|
1629 | categories you need, such as "LC_MESSAGES" or "LC_CTYPE". |
|
|
1630 | |
|
|
1631 | If you need "LC_NUMERIC", you should enable it only around the code that |
|
|
1632 | actually needs it (avoiding stringification of numbers), and restore it |
|
|
1633 | afterwards. |
|
|
1634 | |
|
|
1635 | SOME HISTORY |
|
|
1636 | At the time this module was created there already were a number of JSON |
|
|
1637 | modules available on CPAN, so what was the reason to write yet another |
|
|
1638 | JSON module? While it seems there are many JSON modules, none of them |
|
|
1639 | correctly handled all corner cases, and in most cases their maintainers |
|
|
1640 | are unresponsive, gone missing, or not listening to bug reports for |
|
|
1641 | other reasons. |
|
|
1642 | |
|
|
1643 | Beginning with version 2.0 of the JSON module, when both JSON and |
|
|
1644 | JSON::XS are installed, then JSON will fall back on JSON::XS (this can |
|
|
1645 | be overridden) with no overhead due to emulation (by inheriting |
|
|
1646 | constructor and methods). If JSON::XS is not available, it will fall |
|
|
1647 | back to the compatible JSON::PP module as backend, so using JSON instead |
|
|
1648 | of JSON::XS gives you a portable JSON API that can be fast when you need |
|
|
1649 | it and doesn't require a C compiler when that is a problem. |
|
|
1650 | |
|
|
1651 | Somewhere around version 3, this module was forked into |
|
|
1652 | "Cpanel::JSON::XS", because its maintainer had serious trouble |
|
|
1653 | understanding JSON and insisted on a fork with many bugs "fixed" that |
|
|
1654 | weren't actually bugs, while spreading FUD about this module without |
|
|
1655 | actually giving any details on his accusations. You be the judge, but in |
|
|
1656 | my personal opinion, if you want quality, you will stay away from |
|
|
1657 | dangerous forks like that. |
| 1306 | |
1658 | |
| 1307 | BUGS |
1659 | BUGS |
| 1308 | While the goal of this module is to be correct, that unfortunately does |
1660 | While the goal of this module is to be correct, that unfortunately does |
| 1309 | not mean it's bug-free, only that I think its design is bug-free. If you |
1661 | not mean it's bug-free, only that I think its design is bug-free. If you |
| 1310 | keep reporting bugs they will be fixed swiftly, though. |
1662 | keep reporting bugs they will be fixed swiftly, though. |
