1 | =head1 NAME |
1 | =head1 NAME |
2 | |
2 | |
3 | JSON::XS - JSON serialising/deserialising, done correctly and fast |
3 | JSON::XS - JSON serialising/deserialising, done correctly and fast |
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4 | |
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5 | =encoding utf-8 |
4 | |
6 | |
5 | JSON::XS - 正しくて高速な JSON シリアライザ/デシリアライザ |
7 | JSON::XS - 正しくて高速な JSON シリアライザ/デシリアライザ |
6 | (http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html) |
8 | (http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html) |
7 | |
9 | |
8 | =head1 SYNOPSIS |
10 | =head1 SYNOPSIS |
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35 | primary goal is to be I<correct> and its secondary goal is to be |
37 | primary goal is to be I<correct> and its secondary goal is to be |
36 | I<fast>. To reach the latter goal it was written in C. |
38 | I<fast>. To reach the latter goal it was written in C. |
37 | |
39 | |
38 | Beginning with version 2.0 of the JSON module, when both JSON and |
40 | Beginning with version 2.0 of the JSON module, when both JSON and |
39 | JSON::XS are installed, then JSON will fall back on JSON::XS (this can be |
41 | JSON::XS are installed, then JSON will fall back on JSON::XS (this can be |
40 | overriden) with no overhead due to emulation (by inheritign constructor |
42 | overridden) with no overhead due to emulation (by inheriting constructor |
41 | and methods). If JSON::XS is not available, it will fall back to the |
43 | and methods). If JSON::XS is not available, it will fall back to the |
42 | compatible JSON::PP module as backend, so using JSON instead of JSON::XS |
44 | compatible JSON::PP module as backend, so using JSON instead of JSON::XS |
43 | gives you a portable JSON API that can be fast when you need and doesn't |
45 | gives you a portable JSON API that can be fast when you need and doesn't |
44 | require a C compiler when that is a problem. |
46 | require a C compiler when that is a problem. |
45 | |
47 | |
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47 | to write yet another JSON module? While it seems there are many JSON |
49 | to write yet another JSON module? While it seems there are many JSON |
48 | modules, none of them correctly handle all corner cases, and in most cases |
50 | modules, none of them correctly handle all corner cases, and in most cases |
49 | their maintainers are unresponsive, gone missing, or not listening to bug |
51 | their maintainers are unresponsive, gone missing, or not listening to bug |
50 | reports for other reasons. |
52 | reports for other reasons. |
51 | |
53 | |
52 | See COMPARISON, below, for a comparison to some other JSON modules. |
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53 | |
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54 | See MAPPING, below, on how JSON::XS maps perl values to JSON values and |
54 | See MAPPING, below, on how JSON::XS maps perl values to JSON values and |
55 | vice versa. |
55 | vice versa. |
56 | |
56 | |
57 | =head2 FEATURES |
57 | =head2 FEATURES |
58 | |
58 | |
59 | =over 4 |
59 | =over 4 |
60 | |
60 | |
61 | =item * correct Unicode handling |
61 | =item * correct Unicode handling |
62 | |
62 | |
63 | This module knows how to handle Unicode, and even documents how and when |
63 | This module knows how to handle Unicode, documents how and when it does |
64 | it does so. |
64 | so, and even documents what "correct" means. |
65 | |
65 | |
66 | =item * round-trip integrity |
66 | =item * round-trip integrity |
67 | |
67 | |
68 | When you serialise a perl data structure using only datatypes supported |
68 | When you serialise a perl data structure using only data types supported |
69 | by JSON, the deserialised data structure is identical on the Perl level. |
69 | by JSON, the deserialised data structure is identical on the Perl level. |
70 | (e.g. the string "2.0" doesn't suddenly become "2" just because it looks |
70 | (e.g. the string "2.0" doesn't suddenly become "2" just because it looks |
71 | like a number). |
71 | like a number). There minor I<are> exceptions to this, read the MAPPING |
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72 | section below to learn about those. |
72 | |
73 | |
73 | =item * strict checking of JSON correctness |
74 | =item * strict checking of JSON correctness |
74 | |
75 | |
75 | There is no guessing, no generating of illegal JSON texts by default, |
76 | There is no guessing, no generating of illegal JSON texts by default, |
76 | and only JSON is accepted as input by default (the latter is a security |
77 | and only JSON is accepted as input by default (the latter is a security |
77 | feature). |
78 | feature). |
78 | |
79 | |
79 | =item * fast |
80 | =item * fast |
80 | |
81 | |
81 | Compared to other JSON modules, this module compares favourably in terms |
82 | Compared to other JSON modules and other serialisers such as Storable, |
82 | of speed, too. |
83 | this module usually compares favourably in terms of speed, too. |
83 | |
84 | |
84 | =item * simple to use |
85 | =item * simple to use |
85 | |
86 | |
86 | This module has both a simple functional interface as well as an OO |
87 | This module has both a simple functional interface as well as an object |
87 | interface. |
88 | oriented interface interface. |
88 | |
89 | |
89 | =item * reasonably versatile output formats |
90 | =item * reasonably versatile output formats |
90 | |
91 | |
91 | You can choose between the most compact guaranteed single-line format |
92 | You can choose between the most compact guaranteed-single-line format |
92 | possible (nice for simple line-based protocols), a pure-ascii format |
93 | possible (nice for simple line-based protocols), a pure-ASCII format |
93 | (for when your transport is not 8-bit clean, still supports the whole |
94 | (for when your transport is not 8-bit clean, still supports the whole |
94 | Unicode range), or a pretty-printed format (for when you want to read that |
95 | Unicode range), or a pretty-printed format (for when you want to read that |
95 | stuff). Or you can combine those features in whatever way you like. |
96 | stuff). Or you can combine those features in whatever way you like. |
96 | |
97 | |
97 | =back |
98 | =back |
98 | |
99 | |
99 | =cut |
100 | =cut |
100 | |
101 | |
101 | package JSON::XS; |
102 | package JSON::XS; |
102 | |
103 | |
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104 | no warnings; |
103 | use strict; |
105 | use strict; |
104 | |
106 | |
105 | our $VERSION = '2.01'; |
107 | our $VERSION = '2.232'; |
106 | our @ISA = qw(Exporter); |
108 | our @ISA = qw(Exporter); |
107 | |
109 | |
108 | our @EXPORT = qw(encode_json decode_json to_json from_json); |
110 | our @EXPORT = qw(encode_json decode_json to_json from_json); |
109 | |
111 | |
110 | sub to_json($) { |
112 | sub to_json($) { |
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134 | |
136 | |
135 | This function call is functionally identical to: |
137 | This function call is functionally identical to: |
136 | |
138 | |
137 | $json_text = JSON::XS->new->utf8->encode ($perl_scalar) |
139 | $json_text = JSON::XS->new->utf8->encode ($perl_scalar) |
138 | |
140 | |
139 | except being faster. |
141 | Except being faster. |
140 | |
142 | |
141 | =item $perl_scalar = decode_json $json_text |
143 | =item $perl_scalar = decode_json $json_text |
142 | |
144 | |
143 | The opposite of C<encode_json>: expects an UTF-8 (binary) string and tries |
145 | The opposite of C<encode_json>: expects an UTF-8 (binary) string and tries |
144 | to parse that as an UTF-8 encoded JSON text, returning the resulting |
146 | to parse that as an UTF-8 encoded JSON text, returning the resulting |
… | |
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146 | |
148 | |
147 | This function call is functionally identical to: |
149 | This function call is functionally identical to: |
148 | |
150 | |
149 | $perl_scalar = JSON::XS->new->utf8->decode ($json_text) |
151 | $perl_scalar = JSON::XS->new->utf8->decode ($json_text) |
150 | |
152 | |
151 | except being faster. |
153 | Except being faster. |
152 | |
154 | |
153 | =item $is_boolean = JSON::XS::is_bool $scalar |
155 | =item $is_boolean = JSON::XS::is_bool $scalar |
154 | |
156 | |
155 | Returns true if the passed scalar represents either JSON::XS::true or |
157 | Returns true if the passed scalar represents either JSON::XS::true or |
156 | JSON::XS::false, two constants that act like C<1> and C<0>, respectively |
158 | JSON::XS::false, two constants that act like C<1> and C<0>, respectively |
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174 | This enables you to store Unicode characters as single characters in a |
176 | This enables you to store Unicode characters as single characters in a |
175 | Perl string - very natural. |
177 | Perl string - very natural. |
176 | |
178 | |
177 | =item 2. Perl does I<not> associate an encoding with your strings. |
179 | =item 2. Perl does I<not> associate an encoding with your strings. |
178 | |
180 | |
179 | Unless you force it to, e.g. when matching it against a regex, or printing |
181 | ... until you force it to, e.g. when matching it against a regex, or |
180 | the scalar to a file, in which case Perl either interprets your string as |
182 | printing the scalar to a file, in which case Perl either interprets your |
181 | locale-encoded text, octets/binary, or as Unicode, depending on various |
183 | string as locale-encoded text, octets/binary, or as Unicode, depending |
182 | settings. In no case is an encoding stored together with your data, it is |
184 | on various settings. In no case is an encoding stored together with your |
183 | I<use> that decides encoding, not any magical metadata. |
185 | data, it is I<use> that decides encoding, not any magical meta data. |
184 | |
186 | |
185 | =item 3. The internal utf-8 flag has no meaning with regards to the |
187 | =item 3. The internal utf-8 flag has no meaning with regards to the |
186 | encoding of your string. |
188 | encoding of your string. |
187 | |
189 | |
188 | Just ignore that flag unless you debug a Perl bug, a module written in |
190 | Just ignore that flag unless you debug a Perl bug, a module written in |
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194 | |
196 | |
195 | If you didn't know about that flag, just the better, pretend it doesn't |
197 | If you didn't know about that flag, just the better, pretend it doesn't |
196 | exist. |
198 | exist. |
197 | |
199 | |
198 | =item 4. A "Unicode String" is simply a string where each character can be |
200 | =item 4. A "Unicode String" is simply a string where each character can be |
199 | validly interpreted as a Unicode codepoint. |
201 | validly interpreted as a Unicode code point. |
200 | |
202 | |
201 | If you have UTF-8 encoded data, it is no longer a Unicode string, but a |
203 | If you have UTF-8 encoded data, it is no longer a Unicode string, but a |
202 | Unicode string encoded in UTF-8, giving you a binary string. |
204 | Unicode string encoded in UTF-8, giving you a binary string. |
203 | |
205 | |
204 | =item 5. A string containing "high" (> 255) character values is I<not> a UTF-8 string. |
206 | =item 5. A string containing "high" (> 255) character values is I<not> a UTF-8 string. |
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242 | |
244 | |
243 | If C<$enable> is false, then the C<encode> method will not escape Unicode |
245 | If C<$enable> is false, then the C<encode> method will not escape Unicode |
244 | characters unless required by the JSON syntax or other flags. This results |
246 | characters unless required by the JSON syntax or other flags. This results |
245 | in a faster and more compact format. |
247 | in a faster and more compact format. |
246 | |
248 | |
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249 | See also the section I<ENCODING/CODESET FLAG NOTES> later in this |
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250 | document. |
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251 | |
247 | The main use for this flag is to produce JSON texts that can be |
252 | The main use for this flag is to produce JSON texts that can be |
248 | transmitted over a 7-bit channel, as the encoded JSON texts will not |
253 | transmitted over a 7-bit channel, as the encoded JSON texts will not |
249 | contain any 8 bit characters. |
254 | contain any 8 bit characters. |
250 | |
255 | |
251 | JSON::XS->new->ascii (1)->encode ([chr 0x10401]) |
256 | JSON::XS->new->ascii (1)->encode ([chr 0x10401]) |
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262 | will not be affected in any way by this flag, as C<decode> by default |
267 | will not be affected in any way by this flag, as C<decode> by default |
263 | expects Unicode, which is a strict superset of latin1. |
268 | expects Unicode, which is a strict superset of latin1. |
264 | |
269 | |
265 | If C<$enable> is false, then the C<encode> method will not escape Unicode |
270 | If C<$enable> is false, then the C<encode> method will not escape Unicode |
266 | characters unless required by the JSON syntax or other flags. |
271 | characters unless required by the JSON syntax or other flags. |
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272 | |
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273 | See also the section I<ENCODING/CODESET FLAG NOTES> later in this |
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274 | document. |
267 | |
275 | |
268 | The main use for this flag is efficiently encoding binary data as JSON |
276 | The main use for this flag is efficiently encoding binary data as JSON |
269 | text, as most octets will not be escaped, resulting in a smaller encoded |
277 | text, as most octets will not be escaped, resulting in a smaller encoded |
270 | size. The disadvantage is that the resulting JSON text is encoded |
278 | size. The disadvantage is that the resulting JSON text is encoded |
271 | in latin1 (and must correctly be treated as such when storing and |
279 | in latin1 (and must correctly be treated as such when storing and |
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290 | |
298 | |
291 | If C<$enable> is false, then the C<encode> method will return the JSON |
299 | If C<$enable> is false, then the C<encode> method will return the JSON |
292 | string as a (non-encoded) Unicode string, while C<decode> expects thus a |
300 | string as a (non-encoded) Unicode string, while C<decode> expects thus a |
293 | Unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs |
301 | Unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs |
294 | to be done yourself, e.g. using the Encode module. |
302 | to be done yourself, e.g. using the Encode module. |
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303 | |
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304 | See also the section I<ENCODING/CODESET FLAG NOTES> later in this |
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305 | document. |
295 | |
306 | |
296 | Example, output UTF-16BE-encoded JSON: |
307 | Example, output UTF-16BE-encoded JSON: |
297 | |
308 | |
298 | use Encode; |
309 | use Encode; |
299 | $jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object); |
310 | $jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object); |
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450 | Example, encode a Perl scalar as JSON value with enabled C<allow_nonref>, |
461 | Example, encode a Perl scalar as JSON value with enabled C<allow_nonref>, |
451 | resulting in an invalid JSON text: |
462 | resulting in an invalid JSON text: |
452 | |
463 | |
453 | JSON::XS->new->allow_nonref->encode ("Hello, World!") |
464 | JSON::XS->new->allow_nonref->encode ("Hello, World!") |
454 | => "Hello, World!" |
465 | => "Hello, World!" |
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466 | |
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467 | =item $json = $json->allow_unknown ([$enable]) |
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468 | |
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469 | =item $enabled = $json->get_allow_unknown |
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470 | |
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471 | If C<$enable> is true (or missing), then C<encode> will I<not> throw an |
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472 | exception when it encounters values it cannot represent in JSON (for |
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473 | example, filehandles) but instead will encode a JSON C<null> value. Note |
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474 | that blessed objects are not included here and are handled separately by |
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475 | c<allow_nonref>. |
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476 | |
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477 | If C<$enable> is false (the default), then C<encode> will throw an |
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478 | exception when it encounters anything it cannot encode as JSON. |
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479 | |
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480 | This option does not affect C<decode> in any way, and it is recommended to |
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481 | leave it off unless you know your communications partner. |
455 | |
482 | |
456 | =item $json = $json->allow_blessed ([$enable]) |
483 | =item $json = $json->allow_blessed ([$enable]) |
457 | |
484 | |
458 | =item $enabled = $json->get_allow_blessed |
485 | =item $enabled = $json->get_allow_blessed |
459 | |
486 | |
… | |
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600 | =item $json = $json->max_depth ([$maximum_nesting_depth]) |
627 | =item $json = $json->max_depth ([$maximum_nesting_depth]) |
601 | |
628 | |
602 | =item $max_depth = $json->get_max_depth |
629 | =item $max_depth = $json->get_max_depth |
603 | |
630 | |
604 | Sets the maximum nesting level (default C<512>) accepted while encoding |
631 | Sets the maximum nesting level (default C<512>) accepted while encoding |
605 | or decoding. If the JSON text or Perl data structure has an equal or |
632 | or decoding. If a higher nesting level is detected in JSON text or a Perl |
606 | higher nesting level then this limit, then the encoder and decoder will |
633 | data structure, then the encoder and decoder will stop and croak at that |
607 | stop and croak at that point. |
634 | point. |
608 | |
635 | |
609 | Nesting level is defined by number of hash- or arrayrefs that the encoder |
636 | Nesting level is defined by number of hash- or arrayrefs that the encoder |
610 | needs to traverse to reach a given point or the number of C<{> or C<[> |
637 | needs to traverse to reach a given point or the number of C<{> or C<[> |
611 | characters without their matching closing parenthesis crossed to reach a |
638 | characters without their matching closing parenthesis crossed to reach a |
612 | given character in a string. |
639 | given character in a string. |
613 | |
640 | |
614 | Setting the maximum depth to one disallows any nesting, so that ensures |
641 | Setting the maximum depth to one disallows any nesting, so that ensures |
615 | that the object is only a single hash/object or array. |
642 | that the object is only a single hash/object or array. |
616 | |
643 | |
617 | The argument to C<max_depth> will be rounded up to the next highest power |
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618 | of two. If no argument is given, the highest possible setting will be |
644 | If no argument is given, the highest possible setting will be used, which |
619 | used, which is rarely useful. |
645 | is rarely useful. |
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646 | |
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647 | Note that nesting is implemented by recursion in C. The default value has |
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648 | been chosen to be as large as typical operating systems allow without |
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649 | crashing. |
620 | |
650 | |
621 | See SECURITY CONSIDERATIONS, below, for more info on why this is useful. |
651 | See SECURITY CONSIDERATIONS, below, for more info on why this is useful. |
622 | |
652 | |
623 | =item $json = $json->max_size ([$maximum_string_size]) |
653 | =item $json = $json->max_size ([$maximum_string_size]) |
624 | |
654 | |
625 | =item $max_size = $json->get_max_size |
655 | =item $max_size = $json->get_max_size |
626 | |
656 | |
627 | Set the maximum length a JSON text may have (in bytes) where decoding is |
657 | Set the maximum length a JSON text may have (in bytes) where decoding is |
628 | being attempted. The default is C<0>, meaning no limit. When C<decode> |
658 | being attempted. The default is C<0>, meaning no limit. When C<decode> |
629 | is called on a string longer then this number of characters it will not |
659 | is called on a string that is longer then this many bytes, it will not |
630 | attempt to decode the string but throw an exception. This setting has no |
660 | attempt to decode the string but throw an exception. This setting has no |
631 | effect on C<encode> (yet). |
661 | effect on C<encode> (yet). |
632 | |
662 | |
633 | The argument to C<max_size> will be rounded up to the next B<highest> |
663 | If no argument is given, the limit check will be deactivated (same as when |
634 | power of two (so may be more than requested). If no argument is given, the |
664 | C<0> is specified). |
635 | limit check will be deactivated (same as when C<0> is specified). |
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636 | |
665 | |
637 | See SECURITY CONSIDERATIONS, below, for more info on why this is useful. |
666 | See SECURITY CONSIDERATIONS, below, for more info on why this is useful. |
638 | |
667 | |
639 | =item $json_text = $json->encode ($perl_scalar) |
668 | =item $json_text = $json->encode ($perl_scalar) |
640 | |
669 | |
… | |
… | |
669 | => ([], 3) |
698 | => ([], 3) |
670 | |
699 | |
671 | =back |
700 | =back |
672 | |
701 | |
673 | |
702 | |
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703 | =head1 INCREMENTAL PARSING |
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704 | |
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705 | In some cases, there is the need for incremental parsing of JSON |
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706 | texts. While this module always has to keep both JSON text and resulting |
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707 | Perl data structure in memory at one time, it does allow you to parse a |
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708 | JSON stream incrementally. It does so by accumulating text until it has |
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709 | a full JSON object, which it then can decode. This process is similar to |
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710 | using C<decode_prefix> to see if a full JSON object is available, but |
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711 | is much more efficient (and can be implemented with a minimum of method |
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712 | calls). |
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713 | |
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714 | JSON::XS will only attempt to parse the JSON text once it is sure it |
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715 | has enough text to get a decisive result, using a very simple but |
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716 | truly incremental parser. This means that it sometimes won't stop as |
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717 | early as the full parser, for example, it doesn't detect parenthese |
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718 | mismatches. The only thing it guarantees is that it starts decoding as |
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719 | soon as a syntactically valid JSON text has been seen. This means you need |
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720 | to set resource limits (e.g. C<max_size>) to ensure the parser will stop |
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721 | parsing in the presence if syntax errors. |
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722 | |
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723 | The following methods implement this incremental parser. |
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724 | |
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725 | =over 4 |
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726 | |
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727 | =item [void, scalar or list context] = $json->incr_parse ([$string]) |
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728 | |
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729 | This is the central parsing function. It can both append new text and |
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730 | extract objects from the stream accumulated so far (both of these |
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731 | functions are optional). |
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732 | |
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733 | If C<$string> is given, then this string is appended to the already |
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734 | existing JSON fragment stored in the C<$json> object. |
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735 | |
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736 | After that, if the function is called in void context, it will simply |
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737 | return without doing anything further. This can be used to add more text |
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738 | in as many chunks as you want. |
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739 | |
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740 | If the method is called in scalar context, then it will try to extract |
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741 | exactly I<one> JSON object. If that is successful, it will return this |
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742 | object, otherwise it will return C<undef>. If there is a parse error, |
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743 | this method will croak just as C<decode> would do (one can then use |
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744 | C<incr_skip> to skip the errornous part). This is the most common way of |
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745 | using the method. |
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746 | |
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747 | And finally, in list context, it will try to extract as many objects |
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748 | from the stream as it can find and return them, or the empty list |
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749 | otherwise. For this to work, there must be no separators between the JSON |
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750 | objects or arrays, instead they must be concatenated back-to-back. If |
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751 | an error occurs, an exception will be raised as in the scalar context |
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752 | case. Note that in this case, any previously-parsed JSON texts will be |
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753 | lost. |
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754 | |
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755 | =item $lvalue_string = $json->incr_text |
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756 | |
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757 | This method returns the currently stored JSON fragment as an lvalue, that |
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758 | is, you can manipulate it. This I<only> works when a preceding call to |
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759 | C<incr_parse> in I<scalar context> successfully returned an object. Under |
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760 | all other circumstances you must not call this function (I mean it. |
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761 | although in simple tests it might actually work, it I<will> fail under |
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762 | real world conditions). As a special exception, you can also call this |
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763 | method before having parsed anything. |
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764 | |
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765 | This function is useful in two cases: a) finding the trailing text after a |
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766 | JSON object or b) parsing multiple JSON objects separated by non-JSON text |
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767 | (such as commas). |
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768 | |
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769 | =item $json->incr_skip |
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770 | |
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|
771 | This will reset the state of the incremental parser and will remove |
|
|
772 | the parsed text from the input buffer so far. This is useful after |
|
|
773 | C<incr_parse> died, in which case the input buffer and incremental parser |
|
|
774 | state is left unchanged, to skip the text parsed so far and to reset the |
|
|
775 | parse state. |
|
|
776 | |
|
|
777 | The difference to C<incr_reset> is that only text until the parse error |
|
|
778 | occured is removed. |
|
|
779 | |
|
|
780 | =item $json->incr_reset |
|
|
781 | |
|
|
782 | This completely resets the incremental parser, that is, after this call, |
|
|
783 | it will be as if the parser had never parsed anything. |
|
|
784 | |
|
|
785 | This is useful if you want to repeatedly parse JSON objects and want to |
|
|
786 | ignore any trailing data, which means you have to reset the parser after |
|
|
787 | each successful decode. |
|
|
788 | |
|
|
789 | =back |
|
|
790 | |
|
|
791 | =head2 LIMITATIONS |
|
|
792 | |
|
|
793 | All options that affect decoding are supported, except |
|
|
794 | C<allow_nonref>. The reason for this is that it cannot be made to |
|
|
795 | work sensibly: JSON objects and arrays are self-delimited, i.e. you can concatenate |
|
|
796 | them back to back and still decode them perfectly. This does not hold true |
|
|
797 | for JSON numbers, however. |
|
|
798 | |
|
|
799 | For example, is the string C<1> a single JSON number, or is it simply the |
|
|
800 | start of C<12>? Or is C<12> a single JSON number, or the concatenation |
|
|
801 | of C<1> and C<2>? In neither case you can tell, and this is why JSON::XS |
|
|
802 | takes the conservative route and disallows this case. |
|
|
803 | |
|
|
804 | =head2 EXAMPLES |
|
|
805 | |
|
|
806 | Some examples will make all this clearer. First, a simple example that |
|
|
807 | works similarly to C<decode_prefix>: We want to decode the JSON object at |
|
|
808 | the start of a string and identify the portion after the JSON object: |
|
|
809 | |
|
|
810 | my $text = "[1,2,3] hello"; |
|
|
811 | |
|
|
812 | my $json = new JSON::XS; |
|
|
813 | |
|
|
814 | my $obj = $json->incr_parse ($text) |
|
|
815 | or die "expected JSON object or array at beginning of string"; |
|
|
816 | |
|
|
817 | my $tail = $json->incr_text; |
|
|
818 | # $tail now contains " hello" |
|
|
819 | |
|
|
820 | Easy, isn't it? |
|
|
821 | |
|
|
822 | Now for a more complicated example: Imagine a hypothetical protocol where |
|
|
823 | you read some requests from a TCP stream, and each request is a JSON |
|
|
824 | array, without any separation between them (in fact, it is often useful to |
|
|
825 | use newlines as "separators", as these get interpreted as whitespace at |
|
|
826 | the start of the JSON text, which makes it possible to test said protocol |
|
|
827 | with C<telnet>...). |
|
|
828 | |
|
|
829 | Here is how you'd do it (it is trivial to write this in an event-based |
|
|
830 | manner): |
|
|
831 | |
|
|
832 | my $json = new JSON::XS; |
|
|
833 | |
|
|
834 | # read some data from the socket |
|
|
835 | while (sysread $socket, my $buf, 4096) { |
|
|
836 | |
|
|
837 | # split and decode as many requests as possible |
|
|
838 | for my $request ($json->incr_parse ($buf)) { |
|
|
839 | # act on the $request |
|
|
840 | } |
|
|
841 | } |
|
|
842 | |
|
|
843 | Another complicated example: Assume you have a string with JSON objects |
|
|
844 | or arrays, all separated by (optional) comma characters (e.g. C<[1],[2], |
|
|
845 | [3]>). To parse them, we have to skip the commas between the JSON texts, |
|
|
846 | and here is where the lvalue-ness of C<incr_text> comes in useful: |
|
|
847 | |
|
|
848 | my $text = "[1],[2], [3]"; |
|
|
849 | my $json = new JSON::XS; |
|
|
850 | |
|
|
851 | # void context, so no parsing done |
|
|
852 | $json->incr_parse ($text); |
|
|
853 | |
|
|
854 | # now extract as many objects as possible. note the |
|
|
855 | # use of scalar context so incr_text can be called. |
|
|
856 | while (my $obj = $json->incr_parse) { |
|
|
857 | # do something with $obj |
|
|
858 | |
|
|
859 | # now skip the optional comma |
|
|
860 | $json->incr_text =~ s/^ \s* , //x; |
|
|
861 | } |
|
|
862 | |
|
|
863 | Now lets go for a very complex example: Assume that you have a gigantic |
|
|
864 | JSON array-of-objects, many gigabytes in size, and you want to parse it, |
|
|
865 | but you cannot load it into memory fully (this has actually happened in |
|
|
866 | the real world :). |
|
|
867 | |
|
|
868 | Well, you lost, you have to implement your own JSON parser. But JSON::XS |
|
|
869 | can still help you: You implement a (very simple) array parser and let |
|
|
870 | JSON decode the array elements, which are all full JSON objects on their |
|
|
871 | own (this wouldn't work if the array elements could be JSON numbers, for |
|
|
872 | example): |
|
|
873 | |
|
|
874 | my $json = new JSON::XS; |
|
|
875 | |
|
|
876 | # open the monster |
|
|
877 | open my $fh, "<bigfile.json" |
|
|
878 | or die "bigfile: $!"; |
|
|
879 | |
|
|
880 | # first parse the initial "[" |
|
|
881 | for (;;) { |
|
|
882 | sysread $fh, my $buf, 65536 |
|
|
883 | or die "read error: $!"; |
|
|
884 | $json->incr_parse ($buf); # void context, so no parsing |
|
|
885 | |
|
|
886 | # Exit the loop once we found and removed(!) the initial "[". |
|
|
887 | # In essence, we are (ab-)using the $json object as a simple scalar |
|
|
888 | # we append data to. |
|
|
889 | last if $json->incr_text =~ s/^ \s* \[ //x; |
|
|
890 | } |
|
|
891 | |
|
|
892 | # now we have the skipped the initial "[", so continue |
|
|
893 | # parsing all the elements. |
|
|
894 | for (;;) { |
|
|
895 | # in this loop we read data until we got a single JSON object |
|
|
896 | for (;;) { |
|
|
897 | if (my $obj = $json->incr_parse) { |
|
|
898 | # do something with $obj |
|
|
899 | last; |
|
|
900 | } |
|
|
901 | |
|
|
902 | # add more data |
|
|
903 | sysread $fh, my $buf, 65536 |
|
|
904 | or die "read error: $!"; |
|
|
905 | $json->incr_parse ($buf); # void context, so no parsing |
|
|
906 | } |
|
|
907 | |
|
|
908 | # in this loop we read data until we either found and parsed the |
|
|
909 | # separating "," between elements, or the final "]" |
|
|
910 | for (;;) { |
|
|
911 | # first skip whitespace |
|
|
912 | $json->incr_text =~ s/^\s*//; |
|
|
913 | |
|
|
914 | # if we find "]", we are done |
|
|
915 | if ($json->incr_text =~ s/^\]//) { |
|
|
916 | print "finished.\n"; |
|
|
917 | exit; |
|
|
918 | } |
|
|
919 | |
|
|
920 | # if we find ",", we can continue with the next element |
|
|
921 | if ($json->incr_text =~ s/^,//) { |
|
|
922 | last; |
|
|
923 | } |
|
|
924 | |
|
|
925 | # if we find anything else, we have a parse error! |
|
|
926 | if (length $json->incr_text) { |
|
|
927 | die "parse error near ", $json->incr_text; |
|
|
928 | } |
|
|
929 | |
|
|
930 | # else add more data |
|
|
931 | sysread $fh, my $buf, 65536 |
|
|
932 | or die "read error: $!"; |
|
|
933 | $json->incr_parse ($buf); # void context, so no parsing |
|
|
934 | } |
|
|
935 | |
|
|
936 | This is a complex example, but most of the complexity comes from the fact |
|
|
937 | that we are trying to be correct (bear with me if I am wrong, I never ran |
|
|
938 | the above example :). |
|
|
939 | |
|
|
940 | |
|
|
941 | |
674 | =head1 MAPPING |
942 | =head1 MAPPING |
675 | |
943 | |
676 | This section describes how JSON::XS maps Perl values to JSON values and |
944 | This section describes how JSON::XS maps Perl values to JSON values and |
677 | vice versa. These mappings are designed to "do the right thing" in most |
945 | vice versa. These mappings are designed to "do the right thing" in most |
678 | circumstances automatically, preserving round-tripping characteristics |
946 | circumstances automatically, preserving round-tripping characteristics |
… | |
… | |
706 | |
974 | |
707 | A JSON number becomes either an integer, numeric (floating point) or |
975 | A JSON number becomes either an integer, numeric (floating point) or |
708 | string scalar in perl, depending on its range and any fractional parts. On |
976 | string scalar in perl, depending on its range and any fractional parts. On |
709 | the Perl level, there is no difference between those as Perl handles all |
977 | the Perl level, there is no difference between those as Perl handles all |
710 | the conversion details, but an integer may take slightly less memory and |
978 | the conversion details, but an integer may take slightly less memory and |
711 | might represent more values exactly than (floating point) numbers. |
979 | might represent more values exactly than floating point numbers. |
712 | |
980 | |
713 | If the number consists of digits only, JSON::XS will try to represent |
981 | If the number consists of digits only, JSON::XS will try to represent |
714 | it as an integer value. If that fails, it will try to represent it as |
982 | it as an integer value. If that fails, it will try to represent it as |
715 | a numeric (floating point) value if that is possible without loss of |
983 | a numeric (floating point) value if that is possible without loss of |
716 | precision. Otherwise it will preserve the number as a string value. |
984 | precision. Otherwise it will preserve the number as a string value (in |
|
|
985 | which case you lose roundtripping ability, as the JSON number will be |
|
|
986 | re-encoded toa JSON string). |
717 | |
987 | |
718 | Numbers containing a fractional or exponential part will always be |
988 | Numbers containing a fractional or exponential part will always be |
719 | represented as numeric (floating point) values, possibly at a loss of |
989 | represented as numeric (floating point) values, possibly at a loss of |
720 | precision. |
990 | precision (in which case you might lose perfect roundtripping ability, but |
721 | |
991 | the JSON number will still be re-encoded as a JSON number). |
722 | This might create round-tripping problems as numbers might become strings, |
|
|
723 | but as Perl is typeless there is no other way to do it. |
|
|
724 | |
992 | |
725 | =item true, false |
993 | =item true, false |
726 | |
994 | |
727 | These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>, |
995 | These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>, |
728 | respectively. They are overloaded to act almost exactly like the numbers |
996 | respectively. They are overloaded to act almost exactly like the numbers |
… | |
… | |
765 | Other unblessed references are generally not allowed and will cause an |
1033 | Other unblessed references are generally not allowed and will cause an |
766 | exception to be thrown, except for references to the integers C<0> and |
1034 | exception to be thrown, except for references to the integers C<0> and |
767 | C<1>, which get turned into C<false> and C<true> atoms in JSON. You can |
1035 | C<1>, which get turned into C<false> and C<true> atoms in JSON. You can |
768 | also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability. |
1036 | also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability. |
769 | |
1037 | |
770 | encode_json [\0,JSON::XS::true] # yields [false,true] |
1038 | encode_json [\0, JSON::XS::true] # yields [false,true] |
771 | |
1039 | |
772 | =item JSON::XS::true, JSON::XS::false |
1040 | =item JSON::XS::true, JSON::XS::false |
773 | |
1041 | |
774 | These special values become JSON true and JSON false values, |
1042 | These special values become JSON true and JSON false values, |
775 | respectively. You can also use C<\1> and C<\0> directly if you want. |
1043 | respectively. You can also use C<\1> and C<\0> directly if you want. |
776 | |
1044 | |
777 | =item blessed objects |
1045 | =item blessed objects |
778 | |
1046 | |
779 | Blessed objects are not allowed. JSON::XS currently tries to encode their |
1047 | Blessed objects are not directly representable in JSON. See the |
780 | underlying representation (hash- or arrayref), but this behaviour might |
1048 | C<allow_blessed> and C<convert_blessed> methods on various options on |
781 | change in future versions. |
1049 | how to deal with this: basically, you can choose between throwing an |
|
|
1050 | exception, encoding the reference as if it weren't blessed, or provide |
|
|
1051 | your own serialiser method. |
782 | |
1052 | |
783 | =item simple scalars |
1053 | =item simple scalars |
784 | |
1054 | |
785 | Simple Perl scalars (any scalar that is not a reference) are the most |
1055 | Simple Perl scalars (any scalar that is not a reference) are the most |
786 | difficult objects to encode: JSON::XS will encode undefined scalars as |
1056 | difficult objects to encode: JSON::XS will encode undefined scalars as |
787 | JSON null value, scalars that have last been used in a string context |
1057 | JSON C<null> values, scalars that have last been used in a string context |
788 | before encoding as JSON strings and anything else as number value: |
1058 | before encoding as JSON strings, and anything else as number value: |
789 | |
1059 | |
790 | # dump as number |
1060 | # dump as number |
791 | encode_json [2] # yields [2] |
1061 | encode_json [2] # yields [2] |
792 | encode_json [-3.0e17] # yields [-3e+17] |
1062 | encode_json [-3.0e17] # yields [-3e+17] |
793 | my $value = 5; encode_json [$value] # yields [5] |
1063 | my $value = 5; encode_json [$value] # yields [5] |
… | |
… | |
811 | my $x = "3"; # some variable containing a string |
1081 | my $x = "3"; # some variable containing a string |
812 | $x += 0; # numify it, ensuring it will be dumped as a number |
1082 | $x += 0; # numify it, ensuring it will be dumped as a number |
813 | $x *= 1; # same thing, the choice is yours. |
1083 | $x *= 1; # same thing, the choice is yours. |
814 | |
1084 | |
815 | You can not currently force the type in other, less obscure, ways. Tell me |
1085 | You can not currently force the type in other, less obscure, ways. Tell me |
816 | if you need this capability. |
1086 | if you need this capability (but don't forget to explain why it's needed |
|
|
1087 | :). |
817 | |
1088 | |
818 | =back |
1089 | =back |
819 | |
1090 | |
820 | |
1091 | |
821 | =head1 COMPARISON |
1092 | =head1 ENCODING/CODESET FLAG NOTES |
822 | |
1093 | |
823 | As already mentioned, this module was created because none of the existing |
1094 | The interested reader might have seen a number of flags that signify |
824 | JSON modules could be made to work correctly. First I will describe the |
1095 | encodings or codesets - C<utf8>, C<latin1> and C<ascii>. There seems to be |
825 | problems (or pleasures) I encountered with various existing JSON modules, |
1096 | some confusion on what these do, so here is a short comparison: |
826 | followed by some benchmark values. JSON::XS was designed not to suffer |
1097 | |
827 | from any of these problems or limitations. |
1098 | C<utf8> controls whether the JSON text created by C<encode> (and expected |
|
|
1099 | by C<decode>) is UTF-8 encoded or not, while C<latin1> and C<ascii> only |
|
|
1100 | control whether C<encode> escapes character values outside their respective |
|
|
1101 | codeset range. Neither of these flags conflict with each other, although |
|
|
1102 | some combinations make less sense than others. |
|
|
1103 | |
|
|
1104 | Care has been taken to make all flags symmetrical with respect to |
|
|
1105 | C<encode> and C<decode>, that is, texts encoded with any combination of |
|
|
1106 | these flag values will be correctly decoded when the same flags are used |
|
|
1107 | - in general, if you use different flag settings while encoding vs. when |
|
|
1108 | decoding you likely have a bug somewhere. |
|
|
1109 | |
|
|
1110 | Below comes a verbose discussion of these flags. Note that a "codeset" is |
|
|
1111 | simply an abstract set of character-codepoint pairs, while an encoding |
|
|
1112 | takes those codepoint numbers and I<encodes> them, in our case into |
|
|
1113 | octets. Unicode is (among other things) a codeset, UTF-8 is an encoding, |
|
|
1114 | and ISO-8859-1 (= latin 1) and ASCII are both codesets I<and> encodings at |
|
|
1115 | the same time, which can be confusing. |
828 | |
1116 | |
829 | =over 4 |
1117 | =over 4 |
830 | |
1118 | |
831 | =item JSON 1.07 |
1119 | =item C<utf8> flag disabled |
832 | |
1120 | |
833 | Slow (but very portable, as it is written in pure Perl). |
1121 | When C<utf8> is disabled (the default), then C<encode>/C<decode> generate |
|
|
1122 | and expect Unicode strings, that is, characters with high ordinal Unicode |
|
|
1123 | values (> 255) will be encoded as such characters, and likewise such |
|
|
1124 | characters are decoded as-is, no canges to them will be done, except |
|
|
1125 | "(re-)interpreting" them as Unicode codepoints or Unicode characters, |
|
|
1126 | respectively (to Perl, these are the same thing in strings unless you do |
|
|
1127 | funny/weird/dumb stuff). |
834 | |
1128 | |
835 | Undocumented/buggy Unicode handling (how JSON handles Unicode values is |
1129 | This is useful when you want to do the encoding yourself (e.g. when you |
836 | undocumented. One can get far by feeding it Unicode strings and doing |
1130 | want to have UTF-16 encoded JSON texts) or when some other layer does |
837 | en-/decoding oneself, but Unicode escapes are not working properly). |
1131 | the encoding for you (for example, when printing to a terminal using a |
|
|
1132 | filehandle that transparently encodes to UTF-8 you certainly do NOT want |
|
|
1133 | to UTF-8 encode your data first and have Perl encode it another time). |
838 | |
1134 | |
839 | No round-tripping (strings get clobbered if they look like numbers, e.g. |
1135 | =item C<utf8> flag enabled |
840 | the string C<2.0> will encode to C<2.0> instead of C<"2.0">, and that will |
|
|
841 | decode into the number 2. |
|
|
842 | |
1136 | |
843 | =item JSON::PC 0.01 |
1137 | If the C<utf8>-flag is enabled, C<encode>/C<decode> will encode all |
|
|
1138 | characters using the corresponding UTF-8 multi-byte sequence, and will |
|
|
1139 | expect your input strings to be encoded as UTF-8, that is, no "character" |
|
|
1140 | of the input string must have any value > 255, as UTF-8 does not allow |
|
|
1141 | that. |
844 | |
1142 | |
845 | Very fast. |
1143 | The C<utf8> flag therefore switches between two modes: disabled means you |
|
|
1144 | will get a Unicode string in Perl, enabled means you get an UTF-8 encoded |
|
|
1145 | octet/binary string in Perl. |
846 | |
1146 | |
847 | Undocumented/buggy Unicode handling. |
1147 | =item C<latin1> or C<ascii> flags enabled |
848 | |
1148 | |
849 | No round-tripping. |
1149 | With C<latin1> (or C<ascii>) enabled, C<encode> will escape characters |
|
|
1150 | with ordinal values > 255 (> 127 with C<ascii>) and encode the remaining |
|
|
1151 | characters as specified by the C<utf8> flag. |
850 | |
1152 | |
851 | Has problems handling many Perl values (e.g. regex results and other magic |
1153 | If C<utf8> is disabled, then the result is also correctly encoded in those |
852 | values will make it croak). |
1154 | character sets (as both are proper subsets of Unicode, meaning that a |
|
|
1155 | Unicode string with all character values < 256 is the same thing as a |
|
|
1156 | ISO-8859-1 string, and a Unicode string with all character values < 128 is |
|
|
1157 | the same thing as an ASCII string in Perl). |
853 | |
1158 | |
854 | Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}> |
1159 | If C<utf8> is enabled, you still get a correct UTF-8-encoded string, |
855 | which is not a valid JSON text. |
1160 | regardless of these flags, just some more characters will be escaped using |
|
|
1161 | C<\uXXXX> then before. |
856 | |
1162 | |
857 | Unmaintained (maintainer unresponsive for many months, bugs are not |
1163 | Note that ISO-8859-1-I<encoded> strings are not compatible with UTF-8 |
858 | getting fixed). |
1164 | encoding, while ASCII-encoded strings are. That is because the ISO-8859-1 |
|
|
1165 | encoding is NOT a subset of UTF-8 (despite the ISO-8859-1 I<codeset> being |
|
|
1166 | a subset of Unicode), while ASCII is. |
859 | |
1167 | |
860 | =item JSON::Syck 0.21 |
1168 | Surprisingly, C<decode> will ignore these flags and so treat all input |
|
|
1169 | values as governed by the C<utf8> flag. If it is disabled, this allows you |
|
|
1170 | to decode ISO-8859-1- and ASCII-encoded strings, as both strict subsets of |
|
|
1171 | Unicode. If it is enabled, you can correctly decode UTF-8 encoded strings. |
861 | |
1172 | |
862 | Very buggy (often crashes). |
1173 | So neither C<latin1> nor C<ascii> are incompatible with the C<utf8> flag - |
|
|
1174 | they only govern when the JSON output engine escapes a character or not. |
863 | |
1175 | |
864 | Very inflexible (no human-readable format supported, format pretty much |
1176 | The main use for C<latin1> is to relatively efficiently store binary data |
865 | undocumented. I need at least a format for easy reading by humans and a |
1177 | as JSON, at the expense of breaking compatibility with most JSON decoders. |
866 | single-line compact format for use in a protocol, and preferably a way to |
|
|
867 | generate ASCII-only JSON texts). |
|
|
868 | |
1178 | |
869 | Completely broken (and confusingly documented) Unicode handling (Unicode |
1179 | The main use for C<ascii> is to force the output to not contain characters |
870 | escapes are not working properly, you need to set ImplicitUnicode to |
1180 | with values > 127, which means you can interpret the resulting string |
871 | I<different> values on en- and decoding to get symmetric behaviour). |
1181 | as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about any character set and |
872 | |
1182 | 8-bit-encoding, and still get the same data structure back. This is useful |
873 | No round-tripping (simple cases work, but this depends on whether the scalar |
1183 | when your channel for JSON transfer is not 8-bit clean or the encoding |
874 | value was used in a numeric context or not). |
1184 | might be mangled in between (e.g. in mail), and works because ASCII is a |
875 | |
1185 | proper subset of most 8-bit and multibyte encodings in use in the world. |
876 | Dumping hashes may skip hash values depending on iterator state. |
|
|
877 | |
|
|
878 | Unmaintained (maintainer unresponsive for many months, bugs are not |
|
|
879 | getting fixed). |
|
|
880 | |
|
|
881 | Does not check input for validity (i.e. will accept non-JSON input and |
|
|
882 | return "something" instead of raising an exception. This is a security |
|
|
883 | issue: imagine two banks transferring money between each other using |
|
|
884 | JSON. One bank might parse a given non-JSON request and deduct money, |
|
|
885 | while the other might reject the transaction with a syntax error. While a |
|
|
886 | good protocol will at least recover, that is extra unnecessary work and |
|
|
887 | the transaction will still not succeed). |
|
|
888 | |
|
|
889 | =item JSON::DWIW 0.04 |
|
|
890 | |
|
|
891 | Very fast. Very natural. Very nice. |
|
|
892 | |
|
|
893 | Undocumented Unicode handling (but the best of the pack. Unicode escapes |
|
|
894 | still don't get parsed properly). |
|
|
895 | |
|
|
896 | Very inflexible. |
|
|
897 | |
|
|
898 | No round-tripping. |
|
|
899 | |
|
|
900 | Does not generate valid JSON texts (key strings are often unquoted, empty keys |
|
|
901 | result in nothing being output) |
|
|
902 | |
|
|
903 | Does not check input for validity. |
|
|
904 | |
1186 | |
905 | =back |
1187 | =back |
906 | |
1188 | |
907 | |
1189 | |
|
|
1190 | =head2 JSON and ECMAscript |
|
|
1191 | |
|
|
1192 | JSON syntax is based on how literals are represented in javascript (the |
|
|
1193 | not-standardised predecessor of ECMAscript) which is presumably why it is |
|
|
1194 | called "JavaScript Object Notation". |
|
|
1195 | |
|
|
1196 | However, JSON is not a subset (and also not a superset of course) of |
|
|
1197 | ECMAscript (the standard) or javascript (whatever browsers actually |
|
|
1198 | implement). |
|
|
1199 | |
|
|
1200 | If you want to use javascript's C<eval> function to "parse" JSON, you |
|
|
1201 | might run into parse errors for valid JSON texts, or the resulting data |
|
|
1202 | structure might not be queryable: |
|
|
1203 | |
|
|
1204 | One of the problems is that U+2028 and U+2029 are valid characters inside |
|
|
1205 | JSON strings, but are not allowed in ECMAscript string literals, so the |
|
|
1206 | following Perl fragment will not output something that can be guaranteed |
|
|
1207 | to be parsable by javascript's C<eval>: |
|
|
1208 | |
|
|
1209 | use JSON::XS; |
|
|
1210 | |
|
|
1211 | print encode_json [chr 0x2028]; |
|
|
1212 | |
|
|
1213 | The right fix for this is to use a proper JSON parser in your javascript |
|
|
1214 | programs, and not rely on C<eval>. |
|
|
1215 | |
|
|
1216 | If this is not an option, you can, as a stop-gap measure, simply encode to |
|
|
1217 | ASCII-only JSON: |
|
|
1218 | |
|
|
1219 | use JSON::XS; |
|
|
1220 | |
|
|
1221 | print JSON::XS->new->ascii->encode ([chr 0x2028]); |
|
|
1222 | |
|
|
1223 | And if you are concerned about the size of the resulting JSON text, you |
|
|
1224 | can run some regexes to only escape U+2028 and U+2029: |
|
|
1225 | |
|
|
1226 | use JSON::XS; |
|
|
1227 | |
|
|
1228 | my $json = JSON::XS->new->utf8->encode ([chr 0x2028]); |
|
|
1229 | $json =~ s/\xe2\x80\xa8/\\u2028/g; # escape U+2028 |
|
|
1230 | $json =~ s/\xe2\x80\xa9/\\u2029/g; # escape U+2029 |
|
|
1231 | print $json; |
|
|
1232 | |
|
|
1233 | This works because U+2028/U+2029 are not allowed outside of strings and |
|
|
1234 | are not used for syntax, so replacing them unconditionally just works. |
|
|
1235 | |
|
|
1236 | Note, however, that fixing the broken JSON parser is better than working |
|
|
1237 | around it in every other generator. The above regexes should work well in |
|
|
1238 | other languages, as long as they operate on UTF-8. It is equally valid to |
|
|
1239 | replace all occurences of U+2028/2029 directly by their \\u-escaped forms |
|
|
1240 | in unicode texts, so they can simply be used to fix any parsers relying on |
|
|
1241 | C<eval> by first applying the regexes on the encoded texts. |
|
|
1242 | |
|
|
1243 | Another problem is that some javascript implementations reserve |
|
|
1244 | some property names for their own purposes (which probably makes |
|
|
1245 | them non-ECMAscript-compliant). For example, Iceweasel reserves the |
|
|
1246 | C<__proto__> property name for it's own purposes. |
|
|
1247 | |
|
|
1248 | If that is a problem, you could parse try to filter the resulting JSON |
|
|
1249 | output for these property strings, e.g.: |
|
|
1250 | |
|
|
1251 | $json =~ s/"__proto__"\s*:/"__proto__renamed":/g; |
|
|
1252 | |
|
|
1253 | This works because C<__proto__> is not valid outside of strings, so every |
|
|
1254 | occurence of C<"__proto__"\s*:> must be a string used as property name. |
|
|
1255 | |
|
|
1256 | If you know of other incompatibilities, please let me know. |
|
|
1257 | |
|
|
1258 | |
908 | =head2 JSON and YAML |
1259 | =head2 JSON and YAML |
909 | |
1260 | |
910 | You often hear that JSON is a subset of YAML. This is, however, a mass |
1261 | You often hear that JSON is a subset of YAML. This is, however, a mass |
911 | hysteria(*) and very far from the truth. In general, there is no way to |
1262 | hysteria(*) and very far from the truth (as of the time of this writing), |
|
|
1263 | so let me state it clearly: I<in general, there is no way to configure |
912 | configure JSON::XS to output a data structure as valid YAML that works for |
1264 | JSON::XS to output a data structure as valid YAML> that works in all |
913 | all cases. |
1265 | cases. |
914 | |
1266 | |
915 | If you really must use JSON::XS to generate YAML, you should use this |
1267 | If you really must use JSON::XS to generate YAML, you should use this |
916 | algorithm (subject to change in future versions): |
1268 | algorithm (subject to change in future versions): |
917 | |
1269 | |
918 | my $to_yaml = JSON::XS->new->utf8->space_after (1); |
1270 | my $to_yaml = JSON::XS->new->utf8->space_after (1); |
919 | my $yaml = $to_yaml->encode ($ref) . "\n"; |
1271 | my $yaml = $to_yaml->encode ($ref) . "\n"; |
920 | |
1272 | |
921 | This will usually generate JSON texts that also parse as valid |
1273 | This will I<usually> generate JSON texts that also parse as valid |
922 | YAML. Please note that YAML has hardcoded limits on (simple) object key |
1274 | YAML. Please note that YAML has hardcoded limits on (simple) object key |
923 | lengths that JSON doesn't have and also has different and incompatible |
1275 | lengths that JSON doesn't have and also has different and incompatible |
924 | unicode handling, so you should make sure that your hash keys are |
1276 | unicode handling, so you should make sure that your hash keys are |
925 | noticeably shorter than the 1024 "stream characters" YAML allows and that |
1277 | noticeably shorter than the 1024 "stream characters" YAML allows and that |
926 | you do not have codepoints with values outside the Unicode BMP (basic |
1278 | you do not have characters with codepoint values outside the Unicode BMP |
927 | multilingual page). YAML also does not allow C<\/> sequences in strings |
1279 | (basic multilingual page). YAML also does not allow C<\/> sequences in |
928 | (which JSON::XS does not I<currently> generate). |
1280 | strings (which JSON::XS does not I<currently> generate, but other JSON |
|
|
1281 | generators might). |
929 | |
1282 | |
930 | There might be other incompatibilities that I am not aware of. In general |
1283 | There might be other incompatibilities that I am not aware of (or the YAML |
|
|
1284 | specification has been changed yet again - it does so quite often). In |
931 | you should not try to generate YAML with a JSON generator or vice versa, |
1285 | general you should not try to generate YAML with a JSON generator or vice |
932 | or try to parse JSON with a YAML parser or vice versa: chances are high |
1286 | versa, or try to parse JSON with a YAML parser or vice versa: chances are |
933 | that you will run into severe interoperability problems when you least |
1287 | high that you will run into severe interoperability problems when you |
934 | expect it. |
1288 | least expect it. |
935 | |
1289 | |
936 | =over 4 |
1290 | =over 4 |
937 | |
1291 | |
938 | =item (*) |
1292 | =item (*) |
939 | |
1293 | |
940 | This is spread actively by the YAML team, however. For many years now they |
1294 | I have been pressured multiple times by Brian Ingerson (one of the |
941 | claim YAML were a superset of JSON, even when proven otherwise. |
1295 | authors of the YAML specification) to remove this paragraph, despite him |
|
|
1296 | acknowledging that the actual incompatibilities exist. As I was personally |
|
|
1297 | bitten by this "JSON is YAML" lie, I refused and said I will continue to |
|
|
1298 | educate people about these issues, so others do not run into the same |
|
|
1299 | problem again and again. After this, Brian called me a (quote)I<complete |
|
|
1300 | and worthless idiot>(unquote). |
942 | |
1301 | |
943 | Even the author of this manpage was at some point accused of providing |
1302 | In my opinion, instead of pressuring and insulting people who actually |
944 | "incorrect" information, despite the evidence presented (claims ranged |
1303 | clarify issues with YAML and the wrong statements of some of its |
945 | from "your documentation contains inaccurate and negative statements about |
1304 | proponents, I would kindly suggest reading the JSON spec (which is not |
946 | YAML" (the only negative comment is this footnote, and it didn't exist |
1305 | that difficult or long) and finally make YAML compatible to it, and |
947 | back then; the question on which claims were inaccurate was never answered |
1306 | educating users about the changes, instead of spreading lies about the |
948 | etc.) to "the YAML spec is not up-to-date" (the *real* and suppsedly |
1307 | real compatibility for many I<years> and trying to silence people who |
949 | JSON-compatible spec is apparently not currently publicly available) |
1308 | point out that it isn't true. |
950 | to actual requests to replace this section by *incorrect* information, |
|
|
951 | suppressing information about the real problem). |
|
|
952 | |
|
|
953 | So whenever you are told that YAML was a superset of JSON, first check |
|
|
954 | wether it is really true (it might be when you check it, but it cetrainly |
|
|
955 | is not true when this was written). I would much prefer if the YAML team |
|
|
956 | would spent their time on actually making JSON compatibility a truth |
|
|
957 | (JSON, after all, has a very small and simple specification) instead of |
|
|
958 | trying to lobby/force people into reporting untruths. |
|
|
959 | |
1309 | |
960 | =back |
1310 | =back |
961 | |
1311 | |
962 | |
1312 | |
963 | =head2 SPEED |
1313 | =head2 SPEED |
… | |
… | |
965 | It seems that JSON::XS is surprisingly fast, as shown in the following |
1315 | It seems that JSON::XS is surprisingly fast, as shown in the following |
966 | tables. They have been generated with the help of the C<eg/bench> program |
1316 | tables. They have been generated with the help of the C<eg/bench> program |
967 | in the JSON::XS distribution, to make it easy to compare on your own |
1317 | in the JSON::XS distribution, to make it easy to compare on your own |
968 | system. |
1318 | system. |
969 | |
1319 | |
970 | First comes a comparison between various modules using a very short |
1320 | First comes a comparison between various modules using |
971 | single-line JSON string: |
1321 | a very short single-line JSON string (also available at |
|
|
1322 | L<http://dist.schmorp.de/misc/json/short.json>). |
972 | |
1323 | |
973 | {"method": "handleMessage", "params": ["user1", "we were just talking"], \ |
1324 | {"method": "handleMessage", "params": ["user1", |
974 | "id": null, "array":[1,11,234,-5,1e5,1e7, true, false]} |
1325 | "we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7, |
|
|
1326 | true, false]} |
975 | |
1327 | |
976 | It shows the number of encodes/decodes per second (JSON::XS uses |
1328 | It shows the number of encodes/decodes per second (JSON::XS uses |
977 | the functional interface, while JSON::XS/2 uses the OO interface |
1329 | the functional interface, while JSON::XS/2 uses the OO interface |
978 | with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables |
1330 | with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables |
979 | shrink). Higher is better: |
1331 | shrink). Higher is better: |
… | |
… | |
995 | about three times faster on decoding, and over forty times faster |
1347 | about three times faster on decoding, and over forty times faster |
996 | than JSON, even with pretty-printing and key sorting. It also compares |
1348 | than JSON, even with pretty-printing and key sorting. It also compares |
997 | favourably to Storable for small amounts of data. |
1349 | favourably to Storable for small amounts of data. |
998 | |
1350 | |
999 | Using a longer test string (roughly 18KB, generated from Yahoo! Locals |
1351 | Using a longer test string (roughly 18KB, generated from Yahoo! Locals |
1000 | search API (http://nanoref.com/yahooapis/mgPdGg): |
1352 | search API (L<http://dist.schmorp.de/misc/json/long.json>). |
1001 | |
1353 | |
1002 | module | encode | decode | |
1354 | module | encode | decode | |
1003 | -----------|------------|------------| |
1355 | -----------|------------|------------| |
1004 | JSON 1.x | 55.260 | 34.971 | |
1356 | JSON 1.x | 55.260 | 34.971 | |
1005 | JSON::DWIW | 825.228 | 1082.513 | |
1357 | JSON::DWIW | 825.228 | 1082.513 | |
… | |
… | |
1047 | to free the temporary). If that is exceeded, the program crashes. To be |
1399 | to free the temporary). If that is exceeded, the program crashes. To be |
1048 | conservative, the default nesting limit is set to 512. If your process |
1400 | conservative, the default nesting limit is set to 512. If your process |
1049 | has a smaller stack, you should adjust this setting accordingly with the |
1401 | has a smaller stack, you should adjust this setting accordingly with the |
1050 | C<max_depth> method. |
1402 | C<max_depth> method. |
1051 | |
1403 | |
1052 | And last but least, something else could bomb you that I forgot to think |
1404 | Something else could bomb you, too, that I forgot to think of. In that |
1053 | of. In that case, you get to keep the pieces. I am always open for hints, |
1405 | case, you get to keep the pieces. I am always open for hints, though... |
1054 | though... |
1406 | |
|
|
1407 | Also keep in mind that JSON::XS might leak contents of your Perl data |
|
|
1408 | structures in its error messages, so when you serialise sensitive |
|
|
1409 | information you might want to make sure that exceptions thrown by JSON::XS |
|
|
1410 | will not end up in front of untrusted eyes. |
1055 | |
1411 | |
1056 | If you are using JSON::XS to return packets to consumption |
1412 | If you are using JSON::XS to return packets to consumption |
1057 | by JavaScript scripts in a browser you should have a look at |
1413 | by JavaScript scripts in a browser you should have a look at |
1058 | L<http://jpsykes.com/47/practical-csrf-and-json-security> to see whether |
1414 | L<http://jpsykes.com/47/practical-csrf-and-json-security> to see whether |
1059 | you are vulnerable to some common attack vectors (which really are browser |
1415 | you are vulnerable to some common attack vectors (which really are browser |
… | |
… | |
1065 | =head1 THREADS |
1421 | =head1 THREADS |
1066 | |
1422 | |
1067 | This module is I<not> guaranteed to be thread safe and there are no |
1423 | This module is I<not> guaranteed to be thread safe and there are no |
1068 | plans to change this until Perl gets thread support (as opposed to the |
1424 | plans to change this until Perl gets thread support (as opposed to the |
1069 | horribly slow so-called "threads" which are simply slow and bloated |
1425 | horribly slow so-called "threads" which are simply slow and bloated |
1070 | process simulations - use fork, its I<much> faster, cheaper, better). |
1426 | process simulations - use fork, it's I<much> faster, cheaper, better). |
1071 | |
1427 | |
1072 | (It might actually work, but you have been warned). |
1428 | (It might actually work, but you have been warned). |
1073 | |
1429 | |
1074 | |
1430 | |
1075 | =head1 BUGS |
1431 | =head1 BUGS |
1076 | |
1432 | |
1077 | While the goal of this module is to be correct, that unfortunately does |
1433 | While the goal of this module is to be correct, that unfortunately does |
1078 | not mean its bug-free, only that I think its design is bug-free. It is |
1434 | not mean it's bug-free, only that I think its design is bug-free. If you |
1079 | still relatively early in its development. If you keep reporting bugs they |
1435 | keep reporting bugs they will be fixed swiftly, though. |
1080 | will be fixed swiftly, though. |
|
|
1081 | |
1436 | |
1082 | Please refrain from using rt.cpan.org or any other bug reporting |
1437 | Please refrain from using rt.cpan.org or any other bug reporting |
1083 | service. I put the contact address into my modules for a reason. |
1438 | service. I put the contact address into my modules for a reason. |
1084 | |
1439 | |
1085 | =cut |
1440 | =cut |
… | |
… | |
1105 | "--" => sub { $_[0] = ${$_[0]} - 1 }, |
1460 | "--" => sub { $_[0] = ${$_[0]} - 1 }, |
1106 | fallback => 1; |
1461 | fallback => 1; |
1107 | |
1462 | |
1108 | 1; |
1463 | 1; |
1109 | |
1464 | |
|
|
1465 | =head1 SEE ALSO |
|
|
1466 | |
|
|
1467 | The F<json_xs> command line utility for quick experiments. |
|
|
1468 | |
1110 | =head1 AUTHOR |
1469 | =head1 AUTHOR |
1111 | |
1470 | |
1112 | Marc Lehmann <schmorp@schmorp.de> |
1471 | Marc Lehmann <schmorp@schmorp.de> |
1113 | http://home.schmorp.de/ |
1472 | http://home.schmorp.de/ |
1114 | |
1473 | |