1 | NAME |
1 | NAME |
2 | JSON::XS - JSON serialising/deserialising, done correctly and fast |
2 | JSON::XS - JSON serialising/deserialising, done correctly and fast |
3 | |
3 | |
4 | JSON::XS - 正しくて高速な JSON |
4 | JSON::XS - 正しくて高速な JSON シリアライザ/デシリアライザ |
5 | シリアライザ/デシリアライザ |
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6 | (http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html) |
5 | (http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html) |
7 | |
6 | |
8 | SYNOPSIS |
7 | SYNOPSIS |
9 | use JSON::XS; |
8 | use JSON::XS; |
10 | |
9 | |
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21 | $perl_scalar = $coder->decode ($unicode_json_text); |
20 | $perl_scalar = $coder->decode ($unicode_json_text); |
22 | |
21 | |
23 | # Note that JSON version 2.0 and above will automatically use JSON::XS |
22 | # Note that JSON version 2.0 and above will automatically use JSON::XS |
24 | # if available, at virtually no speed overhead either, so you should |
23 | # if available, at virtually no speed overhead either, so you should |
25 | # be able to just: |
24 | # be able to just: |
26 | |
25 | |
27 | use JSON; |
26 | use JSON; |
28 | |
27 | |
29 | # and do the same things, except that you have a pure-perl fallback now. |
28 | # and do the same things, except that you have a pure-perl fallback now. |
30 | |
29 | |
31 | DESCRIPTION |
30 | DESCRIPTION |
32 | 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 |
33 | 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*. |
34 | To reach the latter goal it was written in C. |
33 | To reach the latter goal it was written in C. |
35 | |
34 | |
36 | Beginning with version 2.0 of the JSON module, when both JSON and |
35 | Beginning with version 2.0 of the JSON module, when both JSON and |
37 | JSON::XS are installed, then JSON will fall back on JSON::XS (this can |
36 | JSON::XS are installed, then JSON will fall back on JSON::XS (this can |
38 | be overriden) with no overhead due to emulation (by inheritign |
37 | be overridden) with no overhead due to emulation (by inheriting |
39 | constructor and methods). If JSON::XS is not available, it will fall |
38 | constructor and methods). If JSON::XS is not available, it will fall |
40 | back to the compatible JSON::PP module as backend, so using JSON instead |
39 | back to the compatible JSON::PP module as backend, so using JSON instead |
41 | of JSON::XS gives you a portable JSON API that can be fast when you need |
40 | of JSON::XS gives you a portable JSON API that can be fast when you need |
42 | and doesn't require a C compiler when that is a problem. |
41 | and doesn't require a C compiler when that is a problem. |
43 | |
42 | |
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51 | |
50 | |
52 | See MAPPING, below, on how JSON::XS maps perl values to JSON values and |
51 | See MAPPING, below, on how JSON::XS maps perl values to JSON values and |
53 | vice versa. |
52 | vice versa. |
54 | |
53 | |
55 | FEATURES |
54 | FEATURES |
56 | * correct Unicode handling |
55 | * correct Unicode handling |
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56 | |
57 | This module knows how to handle Unicode, and even documents how and |
57 | This module knows how to handle Unicode, documents how and when it |
58 | when it does so. |
58 | does so, and even documents what "correct" means. |
59 | |
59 | |
60 | * round-trip integrity |
60 | * round-trip integrity |
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61 | |
61 | When you serialise a perl data structure using only datatypes |
62 | When you serialise a perl data structure using only data types |
62 | supported by JSON, the deserialised data structure is identical on |
63 | supported by JSON, the deserialised data structure is identical on |
63 | the Perl level. (e.g. the string "2.0" doesn't suddenly become "2" |
64 | the Perl level. (e.g. the string "2.0" doesn't suddenly become "2" |
64 | just because it looks like a number). |
65 | just because it looks like a number). There minor *are* exceptions |
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66 | to this, read the MAPPING section below to learn about those. |
65 | |
67 | |
66 | * strict checking of JSON correctness |
68 | * strict checking of JSON correctness |
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69 | |
67 | There is no guessing, no generating of illegal JSON texts by |
70 | There is no guessing, no generating of illegal JSON texts by |
68 | default, and only JSON is accepted as input by default (the latter |
71 | default, and only JSON is accepted as input by default (the latter |
69 | is a security feature). |
72 | is a security feature). |
70 | |
73 | |
71 | * fast |
74 | * fast |
72 | Compared to other JSON modules, this module compares favourably in |
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73 | terms of speed, too. |
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74 | |
75 | |
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76 | Compared to other JSON modules and other serialisers such as |
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77 | Storable, this module usually compares favourably in terms of speed, |
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78 | too. |
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79 | |
75 | * simple to use |
80 | * simple to use |
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81 | |
76 | This module has both a simple functional interface as well as an OO |
82 | This module has both a simple functional interface as well as an |
77 | interface. |
83 | object oriented interface interface. |
78 | |
84 | |
79 | * reasonably versatile output formats |
85 | * reasonably versatile output formats |
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86 | |
80 | You can choose between the most compact guaranteed single-line |
87 | You can choose between the most compact guaranteed-single-line |
81 | format possible (nice for simple line-based protocols), a pure-ascii |
88 | format possible (nice for simple line-based protocols), a pure-ASCII |
82 | format (for when your transport is not 8-bit clean, still supports |
89 | format (for when your transport is not 8-bit clean, still supports |
83 | the whole Unicode range), or a pretty-printed format (for when you |
90 | the whole Unicode range), or a pretty-printed format (for when you |
84 | want to read that stuff). Or you can combine those features in |
91 | want to read that stuff). Or you can combine those features in |
85 | whatever way you like. |
92 | whatever way you like. |
86 | |
93 | |
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94 | |
101 | |
95 | This function call is functionally identical to: |
102 | This function call is functionally identical to: |
96 | |
103 | |
97 | $json_text = JSON::XS->new->utf8->encode ($perl_scalar) |
104 | $json_text = JSON::XS->new->utf8->encode ($perl_scalar) |
98 | |
105 | |
99 | except being faster. |
106 | Except being faster. |
100 | |
107 | |
101 | $perl_scalar = decode_json $json_text |
108 | $perl_scalar = decode_json $json_text |
102 | The opposite of "encode_json": expects an UTF-8 (binary) string and |
109 | The opposite of "encode_json": expects an UTF-8 (binary) string and |
103 | tries to parse that as an UTF-8 encoded JSON text, returning the |
110 | tries to parse that as an UTF-8 encoded JSON text, returning the |
104 | resulting reference. Croaks on error. |
111 | resulting reference. Croaks on error. |
105 | |
112 | |
106 | This function call is functionally identical to: |
113 | This function call is functionally identical to: |
107 | |
114 | |
108 | $perl_scalar = JSON::XS->new->utf8->decode ($json_text) |
115 | $perl_scalar = JSON::XS->new->utf8->decode ($json_text) |
109 | |
116 | |
110 | except being faster. |
117 | Except being faster. |
111 | |
118 | |
112 | $is_boolean = JSON::XS::is_bool $scalar |
119 | $is_boolean = JSON::XS::is_bool $scalar |
113 | Returns true if the passed scalar represents either JSON::XS::true |
120 | Returns true if the passed scalar represents either JSON::XS::true |
114 | or JSON::XS::false, two constants that act like 1 and 0, |
121 | or JSON::XS::false, two constants that act like 1 and 0, |
115 | respectively and are used to represent JSON "true" and "false" |
122 | respectively and are used to represent JSON "true" and "false" |
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125 | 1. Perl strings can store characters with ordinal values > 255. |
132 | 1. Perl strings can store characters with ordinal values > 255. |
126 | This enables you to store Unicode characters as single characters in |
133 | This enables you to store Unicode characters as single characters in |
127 | a Perl string - very natural. |
134 | a Perl string - very natural. |
128 | |
135 | |
129 | 2. Perl does *not* associate an encoding with your strings. |
136 | 2. Perl does *not* associate an encoding with your strings. |
130 | Unless you force it to, e.g. when matching it against a regex, or |
137 | ... until you force it to, e.g. when matching it against a regex, or |
131 | printing the scalar to a file, in which case Perl either interprets |
138 | printing the scalar to a file, in which case Perl either interprets |
132 | your string as locale-encoded text, octets/binary, or as Unicode, |
139 | your string as locale-encoded text, octets/binary, or as Unicode, |
133 | depending on various settings. In no case is an encoding stored |
140 | depending on various settings. In no case is an encoding stored |
134 | together with your data, it is *use* that decides encoding, not any |
141 | together with your data, it is *use* that decides encoding, not any |
135 | magical metadata. |
142 | magical meta data. |
136 | |
143 | |
137 | 3. The internal utf-8 flag has no meaning with regards to the encoding |
144 | 3. The internal utf-8 flag has no meaning with regards to the encoding |
138 | of your string. |
145 | of your string. |
139 | Just ignore that flag unless you debug a Perl bug, a module written |
146 | Just ignore that flag unless you debug a Perl bug, a module written |
140 | in XS or want to dive into the internals of perl. Otherwise it will |
147 | in XS or want to dive into the internals of perl. Otherwise it will |
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145 | |
152 | |
146 | If you didn't know about that flag, just the better, pretend it |
153 | If you didn't know about that flag, just the better, pretend it |
147 | doesn't exist. |
154 | doesn't exist. |
148 | |
155 | |
149 | 4. A "Unicode String" is simply a string where each character can be |
156 | 4. A "Unicode String" is simply a string where each character can be |
150 | validly interpreted as a Unicode codepoint. |
157 | validly interpreted as a Unicode code point. |
151 | If you have UTF-8 encoded data, it is no longer a Unicode string, |
158 | If you have UTF-8 encoded data, it is no longer a Unicode string, |
152 | but a Unicode string encoded in UTF-8, giving you a binary string. |
159 | but a Unicode string encoded in UTF-8, giving you a binary string. |
153 | |
160 | |
154 | 5. A string containing "high" (> 255) character values is *not* a UTF-8 |
161 | 5. A string containing "high" (> 255) character values is *not* a UTF-8 |
155 | string. |
162 | string. |
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185 | |
192 | |
186 | If $enable is false, then the "encode" method will not escape |
193 | If $enable is false, then the "encode" method will not escape |
187 | Unicode characters unless required by the JSON syntax or other |
194 | Unicode characters unless required by the JSON syntax or other |
188 | flags. This results in a faster and more compact format. |
195 | flags. This results in a faster and more compact format. |
189 | |
196 | |
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197 | See also the section *ENCODING/CODESET FLAG NOTES* later in this |
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198 | document. |
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199 | |
190 | The main use for this flag is to produce JSON texts that can be |
200 | The main use for this flag is to produce JSON texts that can be |
191 | transmitted over a 7-bit channel, as the encoded JSON texts will not |
201 | transmitted over a 7-bit channel, as the encoded JSON texts will not |
192 | contain any 8 bit characters. |
202 | contain any 8 bit characters. |
193 | |
203 | |
194 | JSON::XS->new->ascii (1)->encode ([chr 0x10401]) |
204 | JSON::XS->new->ascii (1)->encode ([chr 0x10401]) |
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205 | superset of latin1. |
215 | superset of latin1. |
206 | |
216 | |
207 | If $enable is false, then the "encode" method will not escape |
217 | If $enable is false, then the "encode" method will not escape |
208 | Unicode characters unless required by the JSON syntax or other |
218 | Unicode characters unless required by the JSON syntax or other |
209 | flags. |
219 | flags. |
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220 | |
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221 | See also the section *ENCODING/CODESET FLAG NOTES* later in this |
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222 | document. |
210 | |
223 | |
211 | The main use for this flag is efficiently encoding binary data as |
224 | The main use for this flag is efficiently encoding binary data as |
212 | JSON text, as most octets will not be escaped, resulting in a |
225 | JSON text, as most octets will not be escaped, resulting in a |
213 | smaller encoded size. The disadvantage is that the resulting JSON |
226 | smaller encoded size. The disadvantage is that the resulting JSON |
214 | text is encoded in latin1 (and must correctly be treated as such |
227 | text is encoded in latin1 (and must correctly be treated as such |
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234 | If $enable is false, then the "encode" method will return the JSON |
247 | If $enable is false, then the "encode" method will return the JSON |
235 | string as a (non-encoded) Unicode string, while "decode" expects |
248 | string as a (non-encoded) Unicode string, while "decode" expects |
236 | thus a Unicode string. Any decoding or encoding (e.g. to UTF-8 or |
249 | thus a Unicode string. Any decoding or encoding (e.g. to UTF-8 or |
237 | UTF-16) needs to be done yourself, e.g. using the Encode module. |
250 | UTF-16) needs to be done yourself, e.g. using the Encode module. |
238 | |
251 | |
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252 | See also the section *ENCODING/CODESET FLAG NOTES* later in this |
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253 | document. |
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254 | |
239 | Example, output UTF-16BE-encoded JSON: |
255 | Example, output UTF-16BE-encoded JSON: |
240 | |
256 | |
241 | use Encode; |
257 | use Encode; |
242 | $jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object); |
258 | $jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object); |
243 | |
259 | |
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318 | If $enable is false (the default), then "decode" will only accept |
334 | If $enable is false (the default), then "decode" will only accept |
319 | valid JSON texts. |
335 | valid JSON texts. |
320 | |
336 | |
321 | Currently accepted extensions are: |
337 | Currently accepted extensions are: |
322 | |
338 | |
323 | * list items can have an end-comma |
339 | * list items can have an end-comma |
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340 | |
324 | JSON *separates* array elements and key-value pairs with commas. |
341 | JSON *separates* array elements and key-value pairs with commas. |
325 | This can be annoying if you write JSON texts manually and want |
342 | This can be annoying if you write JSON texts manually and want |
326 | to be able to quickly append elements, so this extension accepts |
343 | to be able to quickly append elements, so this extension accepts |
327 | comma at the end of such items not just between them: |
344 | comma at the end of such items not just between them: |
328 | |
345 | |
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333 | { |
350 | { |
334 | "k1": "v1", |
351 | "k1": "v1", |
335 | "k2": "v2", <- this comma not normally allowed |
352 | "k2": "v2", <- this comma not normally allowed |
336 | } |
353 | } |
337 | |
354 | |
338 | * shell-style '#'-comments |
355 | * shell-style '#'-comments |
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356 | |
339 | Whenever JSON allows whitespace, shell-style comments are |
357 | Whenever JSON allows whitespace, shell-style comments are |
340 | additionally allowed. They are terminated by the first |
358 | additionally allowed. They are terminated by the first |
341 | carriage-return or line-feed character, after which more |
359 | carriage-return or line-feed character, after which more |
342 | white-space and comments are allowed. |
360 | white-space and comments are allowed. |
343 | |
361 | |
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379 | Example, encode a Perl scalar as JSON value with enabled |
397 | Example, encode a Perl scalar as JSON value with enabled |
380 | "allow_nonref", resulting in an invalid JSON text: |
398 | "allow_nonref", resulting in an invalid JSON text: |
381 | |
399 | |
382 | JSON::XS->new->allow_nonref->encode ("Hello, World!") |
400 | JSON::XS->new->allow_nonref->encode ("Hello, World!") |
383 | => "Hello, World!" |
401 | => "Hello, World!" |
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402 | |
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403 | $json = $json->allow_unknown ([$enable]) |
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404 | $enabled = $json->get_allow_unknown |
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405 | If $enable is true (or missing), then "encode" will *not* throw an |
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406 | exception when it encounters values it cannot represent in JSON (for |
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407 | example, filehandles) but instead will encode a JSON "null" value. |
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408 | Note that blessed objects are not included here and are handled |
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409 | separately by c<allow_nonref>. |
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410 | |
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411 | If $enable is false (the default), then "encode" will throw an |
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412 | exception when it encounters anything it cannot encode as JSON. |
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413 | |
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414 | This option does not affect "decode" in any way, and it is |
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415 | recommended to leave it off unless you know your communications |
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416 | partner. |
384 | |
417 | |
385 | $json = $json->allow_blessed ([$enable]) |
418 | $json = $json->allow_blessed ([$enable]) |
386 | $enabled = $json->get_allow_blessed |
419 | $enabled = $json->get_allow_blessed |
387 | If $enable is true (or missing), then the "encode" method will not |
420 | If $enable is true (or missing), then the "encode" method will not |
388 | barf when it encounters a blessed reference. Instead, the value of |
421 | barf when it encounters a blessed reference. Instead, the value of |
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523 | saving space. |
556 | saving space. |
524 | |
557 | |
525 | $json = $json->max_depth ([$maximum_nesting_depth]) |
558 | $json = $json->max_depth ([$maximum_nesting_depth]) |
526 | $max_depth = $json->get_max_depth |
559 | $max_depth = $json->get_max_depth |
527 | Sets the maximum nesting level (default 512) accepted while encoding |
560 | Sets the maximum nesting level (default 512) accepted while encoding |
528 | or decoding. If the JSON text or Perl data structure has an equal or |
561 | or decoding. If a higher nesting level is detected in JSON text or a |
529 | higher nesting level then this limit, then the encoder and decoder |
562 | Perl data structure, then the encoder and decoder will stop and |
530 | will stop and croak at that point. |
563 | croak at that point. |
531 | |
564 | |
532 | Nesting level is defined by number of hash- or arrayrefs that the |
565 | Nesting level is defined by number of hash- or arrayrefs that the |
533 | encoder needs to traverse to reach a given point or the number of |
566 | encoder needs to traverse to reach a given point or the number of |
534 | "{" or "[" characters without their matching closing parenthesis |
567 | "{" or "[" characters without their matching closing parenthesis |
535 | crossed to reach a given character in a string. |
568 | crossed to reach a given character in a string. |
536 | |
569 | |
537 | Setting the maximum depth to one disallows any nesting, so that |
570 | Setting the maximum depth to one disallows any nesting, so that |
538 | ensures that the object is only a single hash/object or array. |
571 | ensures that the object is only a single hash/object or array. |
539 | |
572 | |
540 | The argument to "max_depth" will be rounded up to the next highest |
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541 | power of two. If no argument is given, the highest possible setting |
573 | If no argument is given, the highest possible setting will be used, |
542 | will be used, which is rarely useful. |
574 | which is rarely useful. |
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575 | |
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576 | Note that nesting is implemented by recursion in C. The default |
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577 | value has been chosen to be as large as typical operating systems |
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578 | allow without crashing. |
543 | |
579 | |
544 | See SECURITY CONSIDERATIONS, below, for more info on why this is |
580 | See SECURITY CONSIDERATIONS, below, for more info on why this is |
545 | useful. |
581 | useful. |
546 | |
582 | |
547 | $json = $json->max_size ([$maximum_string_size]) |
583 | $json = $json->max_size ([$maximum_string_size]) |
548 | $max_size = $json->get_max_size |
584 | $max_size = $json->get_max_size |
549 | Set the maximum length a JSON text may have (in bytes) where |
585 | Set the maximum length a JSON text may have (in bytes) where |
550 | decoding is being attempted. The default is 0, meaning no limit. |
586 | decoding is being attempted. The default is 0, meaning no limit. |
551 | When "decode" is called on a string longer then this number of |
587 | When "decode" is called on a string that is longer then this many |
552 | characters it will not attempt to decode the string but throw an |
588 | bytes, it will not attempt to decode the string but throw an |
553 | exception. This setting has no effect on "encode" (yet). |
589 | exception. This setting has no effect on "encode" (yet). |
554 | |
590 | |
555 | The argument to "max_size" will be rounded up to the next highest |
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556 | power of two (so may be more than requested). If no argument is |
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557 | given, the limit check will be deactivated (same as when 0 is |
591 | If no argument is given, the limit check will be deactivated (same |
558 | specified). |
592 | as when 0 is specified). |
559 | |
593 | |
560 | See SECURITY CONSIDERATIONS, below, for more info on why this is |
594 | See SECURITY CONSIDERATIONS, below, for more info on why this is |
561 | useful. |
595 | useful. |
562 | |
596 | |
563 | $json_text = $json->encode ($perl_scalar) |
597 | $json_text = $json->encode ($perl_scalar) |
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588 | and you need to know where the JSON text ends. |
622 | and you need to know where the JSON text ends. |
589 | |
623 | |
590 | JSON::XS->new->decode_prefix ("[1] the tail") |
624 | JSON::XS->new->decode_prefix ("[1] the tail") |
591 | => ([], 3) |
625 | => ([], 3) |
592 | |
626 | |
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627 | INCREMENTAL PARSING |
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628 | In some cases, there is the need for incremental parsing of JSON texts. |
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629 | While this module always has to keep both JSON text and resulting Perl |
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630 | data structure in memory at one time, it does allow you to parse a JSON |
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631 | stream incrementally. It does so by accumulating text until it has a |
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632 | full JSON object, which it then can decode. This process is similar to |
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633 | using "decode_prefix" to see if a full JSON object is available, but is |
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634 | much more efficient (and can be implemented with a minimum of method |
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635 | calls). |
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636 | |
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637 | JSON::XS will only attempt to parse the JSON text once it is sure it has |
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638 | enough text to get a decisive result, using a very simple but truly |
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639 | incremental parser. This means that it sometimes won't stop as early as |
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640 | the full parser, for example, it doesn't detect parenthese mismatches. |
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641 | The only thing it guarantees is that it starts decoding as soon as a |
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642 | syntactically valid JSON text has been seen. This means you need to set |
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643 | resource limits (e.g. "max_size") to ensure the parser will stop parsing |
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644 | in the presence if syntax errors. |
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645 | |
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646 | The following methods implement this incremental parser. |
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647 | |
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648 | [void, scalar or list context] = $json->incr_parse ([$string]) |
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649 | This is the central parsing function. It can both append new text |
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650 | and extract objects from the stream accumulated so far (both of |
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651 | these functions are optional). |
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652 | |
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653 | If $string is given, then this string is appended to the already |
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654 | existing JSON fragment stored in the $json object. |
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655 | |
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656 | After that, if the function is called in void context, it will |
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657 | simply return without doing anything further. This can be used to |
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658 | add more text in as many chunks as you want. |
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659 | |
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660 | If the method is called in scalar context, then it will try to |
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661 | extract exactly *one* JSON object. If that is successful, it will |
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662 | return this object, otherwise it will return "undef". If there is a |
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663 | parse error, this method will croak just as "decode" would do (one |
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664 | can then use "incr_skip" to skip the errornous part). This is the |
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665 | most common way of using the method. |
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666 | |
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667 | And finally, in list context, it will try to extract as many objects |
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668 | from the stream as it can find and return them, or the empty list |
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669 | otherwise. For this to work, there must be no separators between the |
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670 | JSON objects or arrays, instead they must be concatenated |
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671 | back-to-back. If an error occurs, an exception will be raised as in |
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672 | the scalar context case. Note that in this case, any |
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673 | previously-parsed JSON texts will be lost. |
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674 | |
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675 | $lvalue_string = $json->incr_text |
|
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676 | This method returns the currently stored JSON fragment as an lvalue, |
|
|
677 | that is, you can manipulate it. This *only* works when a preceding |
|
|
678 | call to "incr_parse" in *scalar context* successfully returned an |
|
|
679 | object. Under all other circumstances you must not call this |
|
|
680 | function (I mean it. although in simple tests it might actually |
|
|
681 | work, it *will* fail under real world conditions). As a special |
|
|
682 | exception, you can also call this method before having parsed |
|
|
683 | anything. |
|
|
684 | |
|
|
685 | 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 |
|
|
687 | non-JSON text (such as commas). |
|
|
688 | |
|
|
689 | $json->incr_skip |
|
|
690 | This will reset the state of the incremental parser and will remove |
|
|
691 | the parsed text from the input buffer. This is useful after |
|
|
692 | "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 |
|
|
694 | to reset the parse state. |
|
|
695 | |
|
|
696 | $json->incr_reset |
|
|
697 | This completely resets the incremental parser, that is, after this |
|
|
698 | call, it will be as if the parser had never parsed anything. |
|
|
699 | |
|
|
700 | This is useful if you want ot repeatedly parse JSON objects and want |
|
|
701 | to ignore any trailing data, which means you have to reset the |
|
|
702 | parser after each successful decode. |
|
|
703 | |
|
|
704 | LIMITATIONS |
|
|
705 | All options that affect decoding are supported, except "allow_nonref". |
|
|
706 | The reason for this is that it cannot be made to work sensibly: JSON |
|
|
707 | objects and arrays are self-delimited, i.e. you can concatenate them |
|
|
708 | back to back and still decode them perfectly. This does not hold true |
|
|
709 | for JSON numbers, however. |
|
|
710 | |
|
|
711 | For example, is the string 1 a single JSON number, or is it simply the |
|
|
712 | start of 12? Or is 12 a single JSON number, or the concatenation of 1 |
|
|
713 | and 2? In neither case you can tell, and this is why JSON::XS takes the |
|
|
714 | conservative route and disallows this case. |
|
|
715 | |
|
|
716 | EXAMPLES |
|
|
717 | Some examples will make all this clearer. First, a simple example that |
|
|
718 | works similarly to "decode_prefix": We want to decode the JSON object at |
|
|
719 | the start of a string and identify the portion after the JSON object: |
|
|
720 | |
|
|
721 | my $text = "[1,2,3] hello"; |
|
|
722 | |
|
|
723 | my $json = new JSON::XS; |
|
|
724 | |
|
|
725 | my $obj = $json->incr_parse ($text) |
|
|
726 | or die "expected JSON object or array at beginning of string"; |
|
|
727 | |
|
|
728 | my $tail = $json->incr_text; |
|
|
729 | # $tail now contains " hello" |
|
|
730 | |
|
|
731 | Easy, isn't it? |
|
|
732 | |
|
|
733 | Now for a more complicated example: Imagine a hypothetical protocol |
|
|
734 | where you read some requests from a TCP stream, and each request is a |
|
|
735 | JSON array, without any separation between them (in fact, it is often |
|
|
736 | useful to use newlines as "separators", as these get interpreted as |
|
|
737 | whitespace at the start of the JSON text, which makes it possible to |
|
|
738 | test said protocol with "telnet"...). |
|
|
739 | |
|
|
740 | Here is how you'd do it (it is trivial to write this in an event-based |
|
|
741 | manner): |
|
|
742 | |
|
|
743 | my $json = new JSON::XS; |
|
|
744 | |
|
|
745 | # read some data from the socket |
|
|
746 | while (sysread $socket, my $buf, 4096) { |
|
|
747 | |
|
|
748 | # split and decode as many requests as possible |
|
|
749 | for my $request ($json->incr_parse ($buf)) { |
|
|
750 | # act on the $request |
|
|
751 | } |
|
|
752 | } |
|
|
753 | |
|
|
754 | Another complicated example: Assume you have a string with JSON objects |
|
|
755 | or arrays, all separated by (optional) comma characters (e.g. "[1],[2], |
|
|
756 | [3]"). To parse them, we have to skip the commas between the JSON texts, |
|
|
757 | and here is where the lvalue-ness of "incr_text" comes in useful: |
|
|
758 | |
|
|
759 | my $text = "[1],[2], [3]"; |
|
|
760 | my $json = new JSON::XS; |
|
|
761 | |
|
|
762 | # void context, so no parsing done |
|
|
763 | $json->incr_parse ($text); |
|
|
764 | |
|
|
765 | # now extract as many objects as possible. note the |
|
|
766 | # use of scalar context so incr_text can be called. |
|
|
767 | while (my $obj = $json->incr_parse) { |
|
|
768 | # do something with $obj |
|
|
769 | |
|
|
770 | # now skip the optional comma |
|
|
771 | $json->incr_text =~ s/^ \s* , //x; |
|
|
772 | } |
|
|
773 | |
|
|
774 | Now lets go for a very complex example: Assume that you have a gigantic |
|
|
775 | JSON array-of-objects, many gigabytes in size, and you want to parse it, |
|
|
776 | but you cannot load it into memory fully (this has actually happened in |
|
|
777 | the real world :). |
|
|
778 | |
|
|
779 | Well, you lost, you have to implement your own JSON parser. But JSON::XS |
|
|
780 | can still help you: You implement a (very simple) array parser and let |
|
|
781 | JSON decode the array elements, which are all full JSON objects on their |
|
|
782 | own (this wouldn't work if the array elements could be JSON numbers, for |
|
|
783 | example): |
|
|
784 | |
|
|
785 | my $json = new JSON::XS; |
|
|
786 | |
|
|
787 | # open the monster |
|
|
788 | open my $fh, "<bigfile.json" |
|
|
789 | or die "bigfile: $!"; |
|
|
790 | |
|
|
791 | # first parse the initial "[" |
|
|
792 | for (;;) { |
|
|
793 | sysread $fh, my $buf, 65536 |
|
|
794 | or die "read error: $!"; |
|
|
795 | $json->incr_parse ($buf); # void context, so no parsing |
|
|
796 | |
|
|
797 | # Exit the loop once we found and removed(!) the initial "[". |
|
|
798 | # In essence, we are (ab-)using the $json object as a simple scalar |
|
|
799 | # we append data to. |
|
|
800 | last if $json->incr_text =~ s/^ \s* \[ //x; |
|
|
801 | } |
|
|
802 | |
|
|
803 | # now we have the skipped the initial "[", so continue |
|
|
804 | # parsing all the elements. |
|
|
805 | for (;;) { |
|
|
806 | # in this loop we read data until we got a single JSON object |
|
|
807 | for (;;) { |
|
|
808 | if (my $obj = $json->incr_parse) { |
|
|
809 | # do something with $obj |
|
|
810 | last; |
|
|
811 | } |
|
|
812 | |
|
|
813 | # add more data |
|
|
814 | sysread $fh, my $buf, 65536 |
|
|
815 | or die "read error: $!"; |
|
|
816 | $json->incr_parse ($buf); # void context, so no parsing |
|
|
817 | } |
|
|
818 | |
|
|
819 | # in this loop we read data until we either found and parsed the |
|
|
820 | # separating "," between elements, or the final "]" |
|
|
821 | for (;;) { |
|
|
822 | # first skip whitespace |
|
|
823 | $json->incr_text =~ s/^\s*//; |
|
|
824 | |
|
|
825 | # if we find "]", we are done |
|
|
826 | if ($json->incr_text =~ s/^\]//) { |
|
|
827 | print "finished.\n"; |
|
|
828 | exit; |
|
|
829 | } |
|
|
830 | |
|
|
831 | # if we find ",", we can continue with the next element |
|
|
832 | if ($json->incr_text =~ s/^,//) { |
|
|
833 | last; |
|
|
834 | } |
|
|
835 | |
|
|
836 | # if we find anything else, we have a parse error! |
|
|
837 | if (length $json->incr_text) { |
|
|
838 | die "parse error near ", $json->incr_text; |
|
|
839 | } |
|
|
840 | |
|
|
841 | # else add more data |
|
|
842 | sysread $fh, my $buf, 65536 |
|
|
843 | or die "read error: $!"; |
|
|
844 | $json->incr_parse ($buf); # void context, so no parsing |
|
|
845 | } |
|
|
846 | |
|
|
847 | This is a complex example, but most of the complexity comes from the |
|
|
848 | fact that we are trying to be correct (bear with me if I am wrong, I |
|
|
849 | never ran the above example :). |
|
|
850 | |
593 | MAPPING |
851 | MAPPING |
594 | This section describes how JSON::XS maps Perl values to JSON values and |
852 | This section describes how JSON::XS maps Perl values to JSON values and |
595 | vice versa. These mappings are designed to "do the right thing" in most |
853 | vice versa. These mappings are designed to "do the right thing" in most |
596 | circumstances automatically, preserving round-tripping characteristics |
854 | circumstances automatically, preserving round-tripping characteristics |
597 | (what you put in comes out as something equivalent). |
855 | (what you put in comes out as something equivalent). |
… | |
… | |
618 | A JSON number becomes either an integer, numeric (floating point) or |
876 | A JSON number becomes either an integer, numeric (floating point) or |
619 | string scalar in perl, depending on its range and any fractional |
877 | string scalar in perl, depending on its range and any fractional |
620 | parts. On the Perl level, there is no difference between those as |
878 | parts. On the Perl level, there is no difference between those as |
621 | Perl handles all the conversion details, but an integer may take |
879 | Perl handles all the conversion details, but an integer may take |
622 | slightly less memory and might represent more values exactly than |
880 | slightly less memory and might represent more values exactly than |
623 | (floating point) numbers. |
881 | floating point numbers. |
624 | |
882 | |
625 | If the number consists of digits only, JSON::XS will try to |
883 | If the number consists of digits only, JSON::XS will try to |
626 | represent it as an integer value. If that fails, it will try to |
884 | represent it as an integer value. If that fails, it will try to |
627 | represent it as a numeric (floating point) value if that is possible |
885 | represent it as a numeric (floating point) value if that is possible |
628 | without loss of precision. Otherwise it will preserve the number as |
886 | without loss of precision. Otherwise it will preserve the number as |
629 | a string value. |
887 | a string value (in which case you lose roundtripping ability, as the |
|
|
888 | JSON number will be re-encoded toa JSON string). |
630 | |
889 | |
631 | Numbers containing a fractional or exponential part will always be |
890 | Numbers containing a fractional or exponential part will always be |
632 | represented as numeric (floating point) values, possibly at a loss |
891 | represented as numeric (floating point) values, possibly at a loss |
633 | of precision. |
892 | of precision (in which case you might lose perfect roundtripping |
634 | |
893 | ability, but the JSON number will still be re-encoded as a JSON |
635 | This might create round-tripping problems as numbers might become |
894 | number). |
636 | strings, but as Perl is typeless there is no other way to do it. |
|
|
637 | |
895 | |
638 | true, false |
896 | true, false |
639 | These JSON atoms become "JSON::XS::true" and "JSON::XS::false", |
897 | These JSON atoms become "JSON::XS::true" and "JSON::XS::false", |
640 | respectively. They are overloaded to act almost exactly like the |
898 | respectively. They are overloaded to act almost exactly like the |
641 | numbers 1 and 0. You can check whether a scalar is a JSON boolean by |
899 | numbers 1 and 0. You can check whether a scalar is a JSON boolean by |
… | |
… | |
669 | an exception to be thrown, except for references to the integers 0 |
927 | an exception to be thrown, except for references to the integers 0 |
670 | and 1, which get turned into "false" and "true" atoms in JSON. You |
928 | and 1, which get turned into "false" and "true" atoms in JSON. You |
671 | can also use "JSON::XS::false" and "JSON::XS::true" to improve |
929 | can also use "JSON::XS::false" and "JSON::XS::true" to improve |
672 | readability. |
930 | readability. |
673 | |
931 | |
674 | encode_json [\0,JSON::XS::true] # yields [false,true] |
932 | encode_json [\0, JSON::XS::true] # yields [false,true] |
675 | |
933 | |
676 | JSON::XS::true, JSON::XS::false |
934 | JSON::XS::true, JSON::XS::false |
677 | These special values become JSON true and JSON false values, |
935 | These special values become JSON true and JSON false values, |
678 | respectively. You can also use "\1" and "\0" directly if you want. |
936 | respectively. You can also use "\1" and "\0" directly if you want. |
679 | |
937 | |
680 | blessed objects |
938 | blessed objects |
681 | Blessed objects are not allowed. JSON::XS currently tries to encode |
939 | Blessed objects are not directly representable in JSON. See the |
682 | their underlying representation (hash- or arrayref), but this |
940 | "allow_blessed" and "convert_blessed" methods on various options on |
683 | behaviour might change in future versions. |
941 | how to deal with this: basically, you can choose between throwing an |
|
|
942 | exception, encoding the reference as if it weren't blessed, or |
|
|
943 | provide your own serialiser method. |
684 | |
944 | |
685 | simple scalars |
945 | simple scalars |
686 | Simple Perl scalars (any scalar that is not a reference) are the |
946 | Simple Perl scalars (any scalar that is not a reference) are the |
687 | most difficult objects to encode: JSON::XS will encode undefined |
947 | most difficult objects to encode: JSON::XS will encode undefined |
688 | scalars as JSON null value, scalars that have last been used in a |
948 | scalars as JSON "null" values, scalars that have last been used in a |
689 | string context before encoding as JSON strings and anything else as |
949 | string context before encoding as JSON strings, and anything else as |
690 | number value: |
950 | number value: |
691 | |
951 | |
692 | # dump as number |
952 | # dump as number |
693 | encode_json [2] # yields [2] |
953 | encode_json [2] # yields [2] |
694 | encode_json [-3.0e17] # yields [-3e+17] |
954 | encode_json [-3.0e17] # yields [-3e+17] |
… | |
… | |
713 | my $x = "3"; # some variable containing a string |
973 | my $x = "3"; # some variable containing a string |
714 | $x += 0; # numify it, ensuring it will be dumped as a number |
974 | $x += 0; # numify it, ensuring it will be dumped as a number |
715 | $x *= 1; # same thing, the choice is yours. |
975 | $x *= 1; # same thing, the choice is yours. |
716 | |
976 | |
717 | You can not currently force the type in other, less obscure, ways. |
977 | You can not currently force the type in other, less obscure, ways. |
718 | Tell me if you need this capability. |
978 | Tell me if you need this capability (but don't forget to explain why |
|
|
979 | it's needed :). |
719 | |
980 | |
720 | COMPARISON |
981 | ENCODING/CODESET FLAG NOTES |
721 | As already mentioned, this module was created because none of the |
982 | The interested reader might have seen a number of flags that signify |
722 | existing JSON modules could be made to work correctly. First I will |
983 | encodings or codesets - "utf8", "latin1" and "ascii". There seems to be |
723 | describe the problems (or pleasures) I encountered with various existing |
984 | some confusion on what these do, so here is a short comparison: |
724 | JSON modules, followed by some benchmark values. JSON::XS was designed |
|
|
725 | not to suffer from any of these problems or limitations. |
|
|
726 | |
985 | |
727 | JSON 1.07 |
986 | "utf8" controls whether the JSON text created by "encode" (and expected |
728 | Slow (but very portable, as it is written in pure Perl). |
987 | by "decode") is UTF-8 encoded or not, while "latin1" and "ascii" only |
|
|
988 | control whether "encode" escapes character values outside their |
|
|
989 | respective codeset range. Neither of these flags conflict with each |
|
|
990 | other, although some combinations make less sense than others. |
729 | |
991 | |
730 | Undocumented/buggy Unicode handling (how JSON handles Unicode values |
992 | Care has been taken to make all flags symmetrical with respect to |
731 | is undocumented. One can get far by feeding it Unicode strings and |
993 | "encode" and "decode", that is, texts encoded with any combination of |
732 | doing en-/decoding oneself, but Unicode escapes are not working |
994 | these flag values will be correctly decoded when the same flags are used |
|
|
995 | - in general, if you use different flag settings while encoding vs. when |
|
|
996 | decoding you likely have a bug somewhere. |
|
|
997 | |
|
|
998 | Below comes a verbose discussion of these flags. Note that a "codeset" |
|
|
999 | is simply an abstract set of character-codepoint pairs, while an |
|
|
1000 | encoding takes those codepoint numbers and *encodes* them, in our case |
|
|
1001 | into octets. Unicode is (among other things) a codeset, UTF-8 is an |
|
|
1002 | encoding, and ISO-8859-1 (= latin 1) and ASCII are both codesets *and* |
|
|
1003 | encodings at the same time, which can be confusing. |
|
|
1004 | |
|
|
1005 | "utf8" flag disabled |
|
|
1006 | When "utf8" is disabled (the default), then "encode"/"decode" |
|
|
1007 | generate and expect Unicode strings, that is, characters with high |
|
|
1008 | ordinal Unicode values (> 255) will be encoded as such characters, |
|
|
1009 | and likewise such characters are decoded as-is, no canges to them |
|
|
1010 | will be done, except "(re-)interpreting" them as Unicode codepoints |
|
|
1011 | or Unicode characters, respectively (to Perl, these are the same |
|
|
1012 | thing in strings unless you do funny/weird/dumb stuff). |
|
|
1013 | |
|
|
1014 | This is useful when you want to do the encoding yourself (e.g. when |
|
|
1015 | you want to have UTF-16 encoded JSON texts) or when some other layer |
|
|
1016 | does the encoding for you (for example, when printing to a terminal |
|
|
1017 | using a filehandle that transparently encodes to UTF-8 you certainly |
|
|
1018 | do NOT want to UTF-8 encode your data first and have Perl encode it |
|
|
1019 | another time). |
|
|
1020 | |
|
|
1021 | "utf8" flag enabled |
|
|
1022 | If the "utf8"-flag is enabled, "encode"/"decode" will encode all |
|
|
1023 | characters using the corresponding UTF-8 multi-byte sequence, and |
|
|
1024 | will expect your input strings to be encoded as UTF-8, that is, no |
|
|
1025 | "character" of the input string must have any value > 255, as UTF-8 |
|
|
1026 | does not allow that. |
|
|
1027 | |
|
|
1028 | The "utf8" flag therefore switches between two modes: disabled means |
|
|
1029 | you will get a Unicode string in Perl, enabled means you get an |
|
|
1030 | UTF-8 encoded octet/binary string in Perl. |
|
|
1031 | |
|
|
1032 | "latin1" or "ascii" flags enabled |
|
|
1033 | With "latin1" (or "ascii") enabled, "encode" will escape characters |
|
|
1034 | with ordinal values > 255 (> 127 with "ascii") and encode the |
|
|
1035 | remaining characters as specified by the "utf8" flag. |
|
|
1036 | |
|
|
1037 | If "utf8" is disabled, then the result is also correctly encoded in |
|
|
1038 | those character sets (as both are proper subsets of Unicode, meaning |
|
|
1039 | that a Unicode string with all character values < 256 is the same |
|
|
1040 | thing as a ISO-8859-1 string, and a Unicode string with all |
|
|
1041 | character values < 128 is the same thing as an ASCII string in |
733 | properly). |
1042 | Perl). |
734 | |
1043 | |
735 | No round-tripping (strings get clobbered if they look like numbers, |
1044 | If "utf8" is enabled, you still get a correct UTF-8-encoded string, |
736 | e.g. the string 2.0 will encode to 2.0 instead of "2.0", and that |
1045 | regardless of these flags, just some more characters will be escaped |
737 | will decode into the number 2. |
1046 | using "\uXXXX" then before. |
738 | |
1047 | |
739 | JSON::PC 0.01 |
1048 | Note that ISO-8859-1-*encoded* strings are not compatible with UTF-8 |
740 | Very fast. |
1049 | encoding, while ASCII-encoded strings are. That is because the |
|
|
1050 | ISO-8859-1 encoding is NOT a subset of UTF-8 (despite the ISO-8859-1 |
|
|
1051 | *codeset* being a subset of Unicode), while ASCII is. |
741 | |
1052 | |
742 | Undocumented/buggy Unicode handling. |
1053 | Surprisingly, "decode" will ignore these flags and so treat all |
|
|
1054 | input values as governed by the "utf8" flag. If it is disabled, this |
|
|
1055 | allows you to decode ISO-8859-1- and ASCII-encoded strings, as both |
|
|
1056 | strict subsets of Unicode. If it is enabled, you can correctly |
|
|
1057 | decode UTF-8 encoded strings. |
743 | |
1058 | |
744 | No round-tripping. |
1059 | So neither "latin1" nor "ascii" are incompatible with the "utf8" |
|
|
1060 | flag - they only govern when the JSON output engine escapes a |
|
|
1061 | character or not. |
745 | |
1062 | |
746 | Has problems handling many Perl values (e.g. regex results and other |
1063 | The main use for "latin1" is to relatively efficiently store binary |
747 | magic values will make it croak). |
1064 | data as JSON, at the expense of breaking compatibility with most |
|
|
1065 | JSON decoders. |
748 | |
1066 | |
749 | Does not even generate valid JSON ("{1,2}" gets converted to "{1:2}" |
1067 | The main use for "ascii" is to force the output to not contain |
750 | which is not a valid JSON text. |
1068 | characters with values > 127, which means you can interpret the |
751 | |
1069 | resulting string as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about |
752 | Unmaintained (maintainer unresponsive for many months, bugs are not |
1070 | any character set and 8-bit-encoding, and still get the same data |
753 | getting fixed). |
1071 | structure back. This is useful when your channel for JSON transfer |
754 | |
1072 | is not 8-bit clean or the encoding might be mangled in between (e.g. |
755 | JSON::Syck 0.21 |
1073 | in mail), and works because ASCII is a proper subset of most 8-bit |
756 | Very buggy (often crashes). |
1074 | and multibyte encodings in use in the world. |
757 | |
|
|
758 | Very inflexible (no human-readable format supported, format pretty |
|
|
759 | much undocumented. I need at least a format for easy reading by |
|
|
760 | humans and a single-line compact format for use in a protocol, and |
|
|
761 | preferably a way to generate ASCII-only JSON texts). |
|
|
762 | |
|
|
763 | Completely broken (and confusingly documented) Unicode handling |
|
|
764 | (Unicode escapes are not working properly, you need to set |
|
|
765 | ImplicitUnicode to *different* values on en- and decoding to get |
|
|
766 | symmetric behaviour). |
|
|
767 | |
|
|
768 | No round-tripping (simple cases work, but this depends on whether |
|
|
769 | the scalar value was used in a numeric context or not). |
|
|
770 | |
|
|
771 | Dumping hashes may skip hash values depending on iterator state. |
|
|
772 | |
|
|
773 | Unmaintained (maintainer unresponsive for many months, bugs are not |
|
|
774 | getting fixed). |
|
|
775 | |
|
|
776 | Does not check input for validity (i.e. will accept non-JSON input |
|
|
777 | and return "something" instead of raising an exception. This is a |
|
|
778 | security issue: imagine two banks transferring money between each |
|
|
779 | other using JSON. One bank might parse a given non-JSON request and |
|
|
780 | deduct money, while the other might reject the transaction with a |
|
|
781 | syntax error. While a good protocol will at least recover, that is |
|
|
782 | extra unnecessary work and the transaction will still not succeed). |
|
|
783 | |
|
|
784 | JSON::DWIW 0.04 |
|
|
785 | Very fast. Very natural. Very nice. |
|
|
786 | |
|
|
787 | Undocumented Unicode handling (but the best of the pack. Unicode |
|
|
788 | escapes still don't get parsed properly). |
|
|
789 | |
|
|
790 | Very inflexible. |
|
|
791 | |
|
|
792 | No round-tripping. |
|
|
793 | |
|
|
794 | Does not generate valid JSON texts (key strings are often unquoted, |
|
|
795 | empty keys result in nothing being output) |
|
|
796 | |
|
|
797 | Does not check input for validity. |
|
|
798 | |
1075 | |
799 | JSON and YAML |
1076 | JSON and YAML |
800 | You often hear that JSON is a subset (or a close subset) of YAML. This |
1077 | You often hear that JSON is a subset of YAML. This is, however, a mass |
801 | is, however, a mass hysteria and very far from the truth. In general, |
1078 | hysteria(*) and very far from the truth (as of the time of this |
802 | there is no way to configure JSON::XS to output a data structure as |
1079 | writing), so let me state it clearly: *in general, there is no way to |
803 | valid YAML. |
1080 | configure JSON::XS to output a data structure as valid YAML* that works |
|
|
1081 | in all cases. |
804 | |
1082 | |
805 | If you really must use JSON::XS to generate YAML, you should use this |
1083 | If you really must use JSON::XS to generate YAML, you should use this |
806 | algorithm (subject to change in future versions): |
1084 | algorithm (subject to change in future versions): |
807 | |
1085 | |
808 | my $to_yaml = JSON::XS->new->utf8->space_after (1); |
1086 | my $to_yaml = JSON::XS->new->utf8->space_after (1); |
809 | my $yaml = $to_yaml->encode ($ref) . "\n"; |
1087 | my $yaml = $to_yaml->encode ($ref) . "\n"; |
810 | |
1088 | |
811 | This will usually generate JSON texts that also parse as valid YAML. |
1089 | This will *usually* generate JSON texts that also parse as valid YAML. |
812 | Please note that YAML has hardcoded limits on (simple) object key |
1090 | Please note that YAML has hardcoded limits on (simple) object key |
813 | lengths that JSON doesn't have, so you should make sure that your hash |
1091 | lengths that JSON doesn't have and also has different and incompatible |
|
|
1092 | unicode handling, so you should make sure that your hash keys are |
814 | keys are noticeably shorter than the 1024 characters YAML allows. |
1093 | noticeably shorter than the 1024 "stream characters" YAML allows and |
|
|
1094 | that you do not have characters with codepoint values outside the |
|
|
1095 | Unicode BMP (basic multilingual page). YAML also does not allow "\/" |
|
|
1096 | sequences in strings (which JSON::XS does not *currently* generate, but |
|
|
1097 | other JSON generators might). |
815 | |
1098 | |
816 | There might be other incompatibilities that I am not aware of. In |
1099 | There might be other incompatibilities that I am not aware of (or the |
|
|
1100 | YAML specification has been changed yet again - it does so quite often). |
817 | general you should not try to generate YAML with a JSON generator or |
1101 | In general you should not try to generate YAML with a JSON generator or |
818 | vice versa, or try to parse JSON with a YAML parser or vice versa: |
1102 | vice versa, or try to parse JSON with a YAML parser or vice versa: |
819 | chances are high that you will run into severe interoperability |
1103 | chances are high that you will run into severe interoperability problems |
820 | problems. |
1104 | when you least expect it. |
|
|
1105 | |
|
|
1106 | (*) I have been pressured multiple times by Brian Ingerson (one of the |
|
|
1107 | authors of the YAML specification) to remove this paragraph, despite |
|
|
1108 | him acknowledging that the actual incompatibilities exist. As I was |
|
|
1109 | personally bitten by this "JSON is YAML" lie, I refused and said I |
|
|
1110 | will continue to educate people about these issues, so others do not |
|
|
1111 | run into the same problem again and again. After this, Brian called |
|
|
1112 | me a (quote)*complete and worthless idiot*(unquote). |
|
|
1113 | |
|
|
1114 | In my opinion, instead of pressuring and insulting people who |
|
|
1115 | actually clarify issues with YAML and the wrong statements of some |
|
|
1116 | of its proponents, I would kindly suggest reading the JSON spec |
|
|
1117 | (which is not that difficult or long) and finally make YAML |
|
|
1118 | compatible to it, and educating users about the changes, instead of |
|
|
1119 | spreading lies about the real compatibility for many *years* and |
|
|
1120 | trying to silence people who point out that it isn't true. |
821 | |
1121 | |
822 | SPEED |
1122 | SPEED |
823 | It seems that JSON::XS is surprisingly fast, as shown in the following |
1123 | It seems that JSON::XS is surprisingly fast, as shown in the following |
824 | tables. They have been generated with the help of the "eg/bench" program |
1124 | tables. They have been generated with the help of the "eg/bench" program |
825 | in the JSON::XS distribution, to make it easy to compare on your own |
1125 | in the JSON::XS distribution, to make it easy to compare on your own |
826 | system. |
1126 | system. |
827 | |
1127 | |
828 | First comes a comparison between various modules using a very short |
1128 | First comes a comparison between various modules using a very short |
829 | single-line JSON string: |
1129 | single-line JSON string (also available at |
|
|
1130 | <http://dist.schmorp.de/misc/json/short.json>). |
830 | |
1131 | |
831 | {"method": "handleMessage", "params": ["user1", "we were just talking"], \ |
1132 | {"method": "handleMessage", "params": ["user1", |
832 | "id": null, "array":[1,11,234,-5,1e5,1e7, true, false]} |
1133 | "we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7, |
|
|
1134 | true, false]} |
833 | |
1135 | |
834 | It shows the number of encodes/decodes per second (JSON::XS uses the |
1136 | It shows the number of encodes/decodes per second (JSON::XS uses the |
835 | functional interface, while JSON::XS/2 uses the OO interface with |
1137 | functional interface, while JSON::XS/2 uses the OO interface with |
836 | pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink). |
1138 | pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink). |
837 | Higher is better: |
1139 | Higher is better: |
… | |
… | |
853 | encoding, about three times faster on decoding, and over forty times |
1155 | encoding, about three times faster on decoding, and over forty times |
854 | faster than JSON, even with pretty-printing and key sorting. It also |
1156 | faster than JSON, even with pretty-printing and key sorting. It also |
855 | compares favourably to Storable for small amounts of data. |
1157 | compares favourably to Storable for small amounts of data. |
856 | |
1158 | |
857 | Using a longer test string (roughly 18KB, generated from Yahoo! Locals |
1159 | Using a longer test string (roughly 18KB, generated from Yahoo! Locals |
858 | search API (http://nanoref.com/yahooapis/mgPdGg): |
1160 | search API (<http://dist.schmorp.de/misc/json/long.json>). |
859 | |
1161 | |
860 | module | encode | decode | |
1162 | module | encode | decode | |
861 | -----------|------------|------------| |
1163 | -----------|------------|------------| |
862 | JSON 1.x | 55.260 | 34.971 | |
1164 | JSON 1.x | 55.260 | 34.971 | |
863 | JSON::DWIW | 825.228 | 1082.513 | |
1165 | JSON::DWIW | 825.228 | 1082.513 | |
… | |
… | |
900 | Third, JSON::XS recurses using the C stack when decoding objects and |
1202 | Third, JSON::XS recurses using the C stack when decoding objects and |
901 | arrays. The C stack is a limited resource: for instance, on my amd64 |
1203 | arrays. The C stack is a limited resource: for instance, on my amd64 |
902 | machine with 8MB of stack size I can decode around 180k nested arrays |
1204 | machine with 8MB of stack size I can decode around 180k nested arrays |
903 | but only 14k nested JSON objects (due to perl itself recursing deeply on |
1205 | but only 14k nested JSON objects (due to perl itself recursing deeply on |
904 | croak to free the temporary). If that is exceeded, the program crashes. |
1206 | croak to free the temporary). If that is exceeded, the program crashes. |
905 | to be conservative, the default nesting limit is set to 512. If your |
1207 | To be conservative, the default nesting limit is set to 512. If your |
906 | process has a smaller stack, you should adjust this setting accordingly |
1208 | process has a smaller stack, you should adjust this setting accordingly |
907 | with the "max_depth" method. |
1209 | with the "max_depth" method. |
908 | |
1210 | |
909 | And last but least, something else could bomb you that I forgot to think |
1211 | Something else could bomb you, too, that I forgot to think of. In that |
910 | of. In that case, you get to keep the pieces. I am always open for |
1212 | case, you get to keep the pieces. I am always open for hints, though... |
911 | hints, though... |
1213 | |
|
|
1214 | Also keep in mind that JSON::XS might leak contents of your Perl data |
|
|
1215 | structures in its error messages, so when you serialise sensitive |
|
|
1216 | information you might want to make sure that exceptions thrown by |
|
|
1217 | JSON::XS will not end up in front of untrusted eyes. |
912 | |
1218 | |
913 | If you are using JSON::XS to return packets to consumption by JavaScript |
1219 | If you are using JSON::XS to return packets to consumption by JavaScript |
914 | scripts in a browser you should have a look at |
1220 | scripts in a browser you should have a look at |
915 | <http://jpsykes.com/47/practical-csrf-and-json-security> to see whether |
1221 | <http://jpsykes.com/47/practical-csrf-and-json-security> to see whether |
916 | you are vulnerable to some common attack vectors (which really are |
1222 | you are vulnerable to some common attack vectors (which really are |
917 | browser design bugs, but it is still you who will have to deal with it, |
1223 | browser design bugs, but it is still you who will have to deal with it, |
918 | as major browser developers care only for features, not about doing |
1224 | as major browser developers care only for features, not about getting |
919 | security right). |
1225 | security right). |
920 | |
1226 | |
921 | THREADS |
1227 | THREADS |
922 | This module is *not* guaranteed to be thread safe and there are no plans |
1228 | This module is *not* guaranteed to be thread safe and there are no plans |
923 | to change this until Perl gets thread support (as opposed to the |
1229 | to change this until Perl gets thread support (as opposed to the |
924 | horribly slow so-called "threads" which are simply slow and bloated |
1230 | horribly slow so-called "threads" which are simply slow and bloated |
925 | process simulations - use fork, its *much* faster, cheaper, better). |
1231 | process simulations - use fork, it's *much* faster, cheaper, better). |
926 | |
1232 | |
927 | (It might actually work, but you have been warned). |
1233 | (It might actually work, but you have been warned). |
928 | |
1234 | |
929 | BUGS |
1235 | BUGS |
930 | While the goal of this module is to be correct, that unfortunately does |
1236 | While the goal of this module is to be correct, that unfortunately does |
931 | not mean its bug-free, only that I think its design is bug-free. It is |
1237 | not mean it's bug-free, only that I think its design is bug-free. If you |
932 | still relatively early in its development. If you keep reporting bugs |
|
|
933 | they will be fixed swiftly, though. |
1238 | keep reporting bugs they will be fixed swiftly, though. |
934 | |
1239 | |
935 | Please refrain from using rt.cpan.org or any other bug reporting |
1240 | Please refrain from using rt.cpan.org or any other bug reporting |
936 | service. I put the contact address into my modules for a reason. |
1241 | service. I put the contact address into my modules for a reason. |
|
|
1242 | |
|
|
1243 | SEE ALSO |
|
|
1244 | The json_xs command line utility for quick experiments. |
937 | |
1245 | |
938 | AUTHOR |
1246 | AUTHOR |
939 | Marc Lehmann <schmorp@schmorp.de> |
1247 | Marc Lehmann <schmorp@schmorp.de> |
940 | http://home.schmorp.de/ |
1248 | http://home.schmorp.de/ |
941 | |
1249 | |