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112 | $json = $json->ascii ([$enable]) |
112 | $json = $json->ascii ([$enable]) |
113 | 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 |
114 | generate characters outside the code range 0..127 (which is ASCII). |
114 | generate characters outside the code range 0..127 (which is ASCII). |
115 | Any unicode characters outside that range will be escaped using |
115 | Any unicode characters outside that range will be escaped using |
116 | either a single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL |
116 | either a single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL |
117 | escape sequence, as per RFC4627. |
117 | escape sequence, as per RFC4627. The resulting encoded JSON text can |
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118 | be treated as a native unicode string, an ascii-encoded, |
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119 | latin1-encoded or UTF-8 encoded string, or any other superset of |
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120 | ASCII. |
118 | |
121 | |
119 | If $enable is false, then the "encode" method will not escape |
122 | If $enable is false, then the "encode" method will not escape |
120 | Unicode characters unless required by the JSON syntax. This results |
123 | Unicode characters unless required by the JSON syntax or other |
121 | in a faster and more compact format. |
124 | flags. This results in a faster and more compact format. |
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125 | |
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126 | The main use for this flag is to produce JSON texts that can be |
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127 | transmitted over a 7-bit channel, as the encoded JSON texts will not |
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128 | contain any 8 bit characters. |
122 | |
129 | |
123 | JSON::XS->new->ascii (1)->encode ([chr 0x10401]) |
130 | JSON::XS->new->ascii (1)->encode ([chr 0x10401]) |
124 | => ["\ud801\udc01"] |
131 | => ["\ud801\udc01"] |
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132 | |
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133 | $json = $json->latin1 ([$enable]) |
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134 | If $enable is true (or missing), then the "encode" method will |
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135 | encode the resulting JSON text as latin1 (or iso-8859-1), escaping |
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136 | any characters outside the code range 0..255. The resulting string |
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137 | can be treated as a latin1-encoded JSON text or a native unicode |
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138 | string. The "decode" method will not be affected in any way by this |
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139 | flag, as "decode" by default expects unicode, which is a strict |
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140 | superset of latin1. |
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141 | |
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142 | If $enable is false, then the "encode" method will not escape |
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143 | Unicode characters unless required by the JSON syntax or other |
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144 | flags. |
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145 | |
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146 | The main use for this flag is efficiently encoding binary data as |
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147 | JSON text, as most octets will not be escaped, resulting in a |
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148 | smaller encoded size. The disadvantage is that the resulting JSON |
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149 | text is encoded in latin1 (and must correctly be treated as such |
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150 | when storing and transfering), a rare encoding for JSON. It is |
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151 | therefore most useful when you want to store data structures known |
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152 | to contain binary data efficiently in files or databases, not when |
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153 | talking to other JSON encoders/decoders. |
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154 | |
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155 | JSON::XS->new->latin1->encode (["\x{89}\x{abc}"] |
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156 | => ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not) |
125 | |
157 | |
126 | $json = $json->utf8 ([$enable]) |
158 | $json = $json->utf8 ([$enable]) |
127 | If $enable is true (or missing), then the "encode" method will |
159 | If $enable is true (or missing), then the "encode" method will |
128 | 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, |
129 | 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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265 | converting strings that look like integers or floats into integers |
297 | converting strings that look like integers or floats into integers |
266 | or floats internally (there is no difference on the Perl level), |
298 | or floats internally (there is no difference on the Perl level), |
267 | saving space. |
299 | saving space. |
268 | |
300 | |
269 | $json = $json->max_depth ([$maximum_nesting_depth]) |
301 | $json = $json->max_depth ([$maximum_nesting_depth]) |
270 | Sets the maximum nesting level (default 4096) accepted while |
302 | Sets the maximum nesting level (default 512) accepted while encoding |
271 | encoding or decoding. If the JSON text or Perl data structure has an |
303 | or decoding. If the JSON text or Perl data structure has an equal or |
272 | equal or higher nesting level then this limit, then the encoder and |
304 | higher nesting level then this limit, then the encoder and decoder |
273 | decoder will stop and croak at that point. |
305 | will stop and croak at that point. |
274 | |
306 | |
275 | Nesting level is defined by number of hash- or arrayrefs that the |
307 | Nesting level is defined by number of hash- or arrayrefs that the |
276 | encoder needs to traverse to reach a given point or the number of |
308 | encoder needs to traverse to reach a given point or the number of |
277 | "{" or "[" characters without their matching closing parenthesis |
309 | "{" or "[" characters without their matching closing parenthesis |
278 | crossed to reach a given character in a string. |
310 | crossed to reach a given character in a string. |
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300 | returning the resulting simple scalar or reference. Croaks on error. |
332 | returning the resulting simple scalar or reference. Croaks on error. |
301 | |
333 | |
302 | JSON numbers and strings become simple Perl scalars. JSON arrays |
334 | JSON numbers and strings become simple Perl scalars. JSON arrays |
303 | become Perl arrayrefs and JSON objects become Perl hashrefs. "true" |
335 | become Perl arrayrefs and JSON objects become Perl hashrefs. "true" |
304 | becomes 1, "false" becomes 0 and "null" becomes "undef". |
336 | becomes 1, "false" becomes 0 and "null" becomes "undef". |
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337 | |
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338 | ($perl_scalar, $characters) = $json->decode_prefix ($json_text) |
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339 | This works like the "decode" method, but instead of raising an |
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340 | exception when there is trailing garbage after the first JSON |
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341 | object, it will silently stop parsing there and return the number of |
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342 | characters consumed so far. |
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343 | |
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344 | This is useful if your JSON texts are not delimited by an outer |
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345 | protocol (which is not the brightest thing to do in the first place) |
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346 | and you need to know where the JSON text ends. |
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347 | |
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348 | JSON::XS->new->decode_prefix ("[1] the tail") |
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349 | => ([], 3) |
305 | |
350 | |
306 | MAPPING |
351 | MAPPING |
307 | 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 |
308 | 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 |
309 | circumstances automatically, preserving round-tripping characteristics |
354 | circumstances automatically, preserving round-tripping characteristics |
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411 | $x *= 1; # same thing, the choise is yours. |
456 | $x *= 1; # same thing, the choise is yours. |
412 | |
457 | |
413 | 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 |
414 | other, less obscure, ways. Tell me if you need this capability. |
459 | other, less obscure, ways. Tell me if you need this capability. |
415 | |
460 | |
416 | circular data structures |
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417 | Those will be encoded until memory or stackspace runs out. |
|
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418 | |
|
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419 | COMPARISON |
461 | COMPARISON |
420 | As already mentioned, this module was created because none of the |
462 | As already mentioned, this module was created because none of the |
421 | 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 |
422 | describe the problems (or pleasures) I encountered with various existing |
464 | describe the problems (or pleasures) I encountered with various existing |
423 | JSON modules, followed by some benchmark values. JSON::XS was designed |
465 | JSON modules, followed by some benchmark values. JSON::XS was designed |
… | |
… | |
493 | Does not generate valid JSON texts (key strings are often unquoted, |
535 | Does not generate valid JSON texts (key strings are often unquoted, |
494 | empty keys result in nothing being output) |
536 | empty keys result in nothing being output) |
495 | |
537 | |
496 | Does not check input for validity. |
538 | Does not check input for validity. |
497 | |
539 | |
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540 | JSON and YAML |
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541 | You often hear that JSON is a subset (or a close subset) of YAML. This |
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542 | is, however, a mass hysteria and very far from the truth. In general, |
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|
543 | there is no way to configure JSON::XS to output a data structure as |
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544 | valid YAML. |
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545 | |
|
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546 | If you really must use JSON::XS to generate YAML, you should use this |
|
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547 | algorithm (subject to change in future versions): |
|
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548 | |
|
|
549 | my $to_yaml = JSON::XS->new->utf8->space_after (1); |
|
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550 | my $yaml = $to_yaml->encode ($ref) . "\n"; |
|
|
551 | |
|
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552 | This will usually generate JSON texts that also parse as valid YAML. |
|
|
553 | Please note that YAML has hardcoded limits on (simple) object key |
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554 | lengths that JSON doesn't have, so you should make sure that your hash |
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555 | keys are noticably shorter than the 1024 characters YAML allows. |
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556 | |
|
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557 | There might be other incompatibilities that I am not aware of. In |
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558 | general you should not try to generate YAML with a JSON generator or |
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559 | vice versa, or try to parse JSON with a YAML parser or vice versa: |
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560 | chances are high that you will run into severe interoperability |
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|
561 | problems. |
|
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562 | |
498 | SPEED |
563 | SPEED |
499 | It seems that JSON::XS is surprisingly fast, as shown in the following |
564 | It seems that JSON::XS is surprisingly fast, as shown in the following |
500 | tables. They have been generated with the help of the "eg/bench" program |
565 | tables. They have been generated with the help of the "eg/bench" program |
501 | in the JSON::XS distribution, to make it easy to compare on your own |
566 | in the JSON::XS distribution, to make it easy to compare on your own |
502 | system. |
567 | system. |
503 | |
568 | |
504 | First comes a comparison between various modules using a very short JSON |
569 | First comes a comparison between various modules using a very short |
505 | string: |
570 | single-line JSON string: |
506 | |
571 | |
507 | {"method": "handleMessage", "params": ["user1", "we were just talking"], "id": null} |
572 | {"method": "handleMessage", "params": ["user1", "we were just talking"], \ |
|
|
573 | "id": null, "array":[1,11,234,-5,1e5,1e7, true, false]} |
508 | |
574 | |
509 | It shows the number of encodes/decodes per second (JSON::XS uses the |
575 | It shows the number of encodes/decodes per second (JSON::XS uses the |
510 | functional interface, while JSON::XS/2 uses the OO interface with |
576 | functional interface, while JSON::XS/2 uses the OO interface with |
511 | pretty-printing and hashkey sorting enabled). Higher is better: |
577 | pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink). |
|
|
578 | Higher is better: |
512 | |
579 | |
513 | module | encode | decode | |
580 | module | encode | decode | |
514 | -----------|------------|------------| |
581 | -----------|------------|------------| |
515 | JSON | 11488.516 | 7823.035 | |
582 | JSON | 7645.468 | 4208.613 | |
516 | JSON::DWIW | 94708.054 | 129094.260 | |
583 | JSON::DWIW | 40721.398 | 77101.176 | |
517 | JSON::PC | 63884.157 | 128528.212 | |
584 | JSON::PC | 65948.176 | 78251.940 | |
518 | JSON::Syck | 34898.677 | 42096.911 | |
585 | JSON::Syck | 22844.793 | 26479.192 | |
519 | JSON::XS | 654027.064 | 396423.669 | |
586 | JSON::XS | 388361.481 | 199728.762 | |
520 | JSON::XS/2 | 371564.190 | 371725.613 | |
587 | JSON::XS/2 | 218453.333 | 192399.266 | |
|
|
588 | JSON::XS/3 | 338250.323 | 192399.266 | |
|
|
589 | Storable | 15779.925 | 14169.946 | |
521 | -----------+------------+------------+ |
590 | -----------+------------+------------+ |
522 | |
591 | |
523 | That is, JSON::XS is more than six times faster than JSON::DWIW on |
592 | That is, JSON::XS is about five times faster than JSON::DWIW on |
524 | encoding, more than three times faster on decoding, and about thirty |
593 | encoding, about three times faster on decoding, and over fourty times |
525 | times faster than JSON, even with pretty-printing and key sorting. |
594 | faster than JSON, even with pretty-printing and key sorting. It also |
|
|
595 | compares favourably to Storable for small amounts of data. |
526 | |
596 | |
527 | Using a longer test string (roughly 18KB, generated from Yahoo! Locals |
597 | Using a longer test string (roughly 18KB, generated from Yahoo! Locals |
528 | search API (http://nanoref.com/yahooapis/mgPdGg): |
598 | search API (http://nanoref.com/yahooapis/mgPdGg): |
529 | |
599 | |
530 | module | encode | decode | |
600 | module | encode | decode | |
531 | -----------|------------|------------| |
601 | -----------|------------|------------| |
532 | JSON | 273.023 | 44.674 | |
602 | JSON | 254.685 | 37.665 | |
533 | JSON::DWIW | 1089.383 | 1145.704 | |
603 | JSON::DWIW | 843.343 | 1049.731 | |
534 | JSON::PC | 3097.419 | 2393.921 | |
604 | JSON::PC | 3602.116 | 2307.352 | |
535 | JSON::Syck | 514.060 | 843.053 | |
605 | JSON::Syck | 505.107 | 787.899 | |
536 | JSON::XS | 6479.668 | 3636.364 | |
606 | JSON::XS | 5747.196 | 3690.220 | |
537 | JSON::XS/2 | 3774.221 | 3599.124 | |
607 | JSON::XS/2 | 3968.121 | 3676.634 | |
|
|
608 | JSON::XS/3 | 6105.246 | 3662.508 | |
|
|
609 | Storable | 4417.337 | 5285.161 | |
538 | -----------+------------+------------+ |
610 | -----------+------------+------------+ |
539 | |
611 | |
540 | Again, JSON::XS leads by far. |
612 | Again, JSON::XS leads by far (except for Storable which non-surprisingly |
|
|
613 | decodes faster). |
541 | |
614 | |
542 | On large strings containing lots of high unicode characters, some |
615 | On large strings containing lots of high unicode characters, some |
543 | modules (such as JSON::PC) seem to decode faster than JSON::XS, but the |
616 | modules (such as JSON::PC) seem to decode faster than JSON::XS, but the |
544 | result will be broken due to missing (or wrong) unicode handling. Others |
617 | result will be broken due to missing (or wrong) unicode handling. Others |
545 | refuse to decode or encode properly, so it was impossible to prepare a |
618 | refuse to decode or encode properly, so it was impossible to prepare a |
… | |
… | |
561 | required to decode it into a Perl structure. |
634 | required to decode it into a Perl structure. |
562 | |
635 | |
563 | Third, JSON::XS recurses using the C stack when decoding objects and |
636 | Third, JSON::XS recurses using the C stack when decoding objects and |
564 | arrays. The C stack is a limited resource: for instance, on my amd64 |
637 | arrays. The C stack is a limited resource: for instance, on my amd64 |
565 | machine with 8MB of stack size I can decode around 180k nested arrays |
638 | machine with 8MB of stack size I can decode around 180k nested arrays |
566 | but only 14k nested JSON objects. If that is exceeded, the program |
639 | but only 14k nested JSON objects (due to perl itself recursing deeply on |
|
|
640 | croak to free the temporary). If that is exceeded, the program crashes. |
567 | crashes. Thats why the default nesting limit is set to 4096. If your |
641 | to be conservative, the default nesting limit is set to 512. If your |
568 | process has a smaller stack, you should adjust this setting accordingly |
642 | process has a smaller stack, you should adjust this setting accordingly |
569 | with the "max_depth" method. |
643 | with the "max_depth" method. |
570 | |
644 | |
571 | And last but least, something else could bomb you that I forgot to think |
645 | And last but least, something else could bomb you that I forgot to think |
572 | of. In that case, you get to keep the pieces. I am alway sopen for |
646 | of. In that case, you get to keep the pieces. I am always open for |
573 | hints, though... |
647 | hints, though... |
574 | |
648 | |
575 | BUGS |
649 | BUGS |
576 | While the goal of this module is to be correct, that unfortunately does |
650 | While the goal of this module is to be correct, that unfortunately does |
577 | not mean its bug-free, only that I think its design is bug-free. It is |
651 | not mean its bug-free, only that I think its design is bug-free. It is |