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 |
|
|
4 | |
|
|
5 | =encoding utf-8 |
|
|
6 | |
|
|
7 | JSON::XS - 正しくて高速な JSON シリアライザ/デシリアライザ |
|
|
8 | (http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html) |
4 | |
9 | |
5 | =head1 SYNOPSIS |
10 | =head1 SYNOPSIS |
6 | |
11 | |
7 | use JSON::XS; |
12 | use JSON::XS; |
8 | |
13 | |
9 | # exported functions, they croak on error |
14 | # exported functions, they croak on error |
10 | # and expect/generate UTF-8 |
15 | # and expect/generate UTF-8 |
11 | |
16 | |
12 | $utf8_encoded_json_text = to_json $perl_hash_or_arrayref; |
17 | $utf8_encoded_json_text = encode_json $perl_hash_or_arrayref; |
13 | $perl_hash_or_arrayref = from_json $utf8_encoded_json_text; |
18 | $perl_hash_or_arrayref = decode_json $utf8_encoded_json_text; |
14 | |
19 | |
15 | # OO-interface |
20 | # OO-interface |
16 | |
21 | |
17 | $coder = JSON::XS->new->ascii->pretty->allow_nonref; |
22 | $coder = JSON::XS->new->ascii->pretty->allow_nonref; |
18 | $pretty_printed_unencoded = $coder->encode ($perl_scalar); |
23 | $pretty_printed_unencoded = $coder->encode ($perl_scalar); |
19 | $perl_scalar = $coder->decode ($unicode_json_text); |
24 | $perl_scalar = $coder->decode ($unicode_json_text); |
20 | |
25 | |
|
|
26 | # Note that JSON version 2.0 and above will automatically use JSON::XS |
|
|
27 | # if available, at virtually no speed overhead either, so you should |
|
|
28 | # be able to just: |
|
|
29 | |
|
|
30 | use JSON; |
|
|
31 | |
|
|
32 | # and do the same things, except that you have a pure-perl fallback now. |
|
|
33 | |
21 | =head1 DESCRIPTION |
34 | =head1 DESCRIPTION |
22 | |
35 | |
23 | This module converts Perl data structures to JSON and vice versa. Its |
36 | This module converts Perl data structures to JSON and vice versa. Its |
24 | 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 |
25 | 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. |
|
|
39 | |
|
|
40 | Beginning with version 2.0 of the JSON module, when both JSON and |
|
|
41 | JSON::XS are installed, then JSON will fall back on JSON::XS (this can be |
|
|
42 | overridden) with no overhead due to emulation (by inheriting constructor |
|
|
43 | and methods). If JSON::XS is not available, it will fall back to the |
|
|
44 | compatible JSON::PP module as backend, so using JSON instead of JSON::XS |
|
|
45 | gives you a portable JSON API that can be fast when you need and doesn't |
|
|
46 | require a C compiler when that is a problem. |
26 | |
47 | |
27 | As this is the n-th-something JSON module on CPAN, what was the reason |
48 | As this is the n-th-something JSON module on CPAN, what was the reason |
28 | 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 |
29 | 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 |
30 | their maintainers are unresponsive, gone missing, or not listening to bug |
51 | their maintainers are unresponsive, gone missing, or not listening to bug |
31 | reports for other reasons. |
52 | reports for other reasons. |
32 | |
53 | |
33 | See COMPARISON, below, for a comparison to some other JSON modules. |
|
|
34 | |
|
|
35 | 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 |
36 | vice versa. |
55 | vice versa. |
37 | |
56 | |
38 | =head2 FEATURES |
57 | =head2 FEATURES |
39 | |
58 | |
40 | =over 4 |
59 | =over 4 |
41 | |
60 | |
42 | =item * correct unicode handling |
61 | =item * correct Unicode handling |
43 | |
62 | |
44 | 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 |
45 | it does so. |
64 | so, and even documents what "correct" means. |
46 | |
65 | |
47 | =item * round-trip integrity |
66 | =item * round-trip integrity |
48 | |
67 | |
49 | When you serialise a perl data structure using only datatypes supported |
68 | When you serialise a perl data structure using only data types supported |
50 | by JSON, the deserialised data structure is identical on the Perl level. |
69 | by JSON and Perl, the deserialised data structure is identical on the Perl |
51 | (e.g. the string "2.0" doesn't suddenly become "2" just because it looks |
70 | level. (e.g. the string "2.0" doesn't suddenly become "2" just because |
52 | like a number). |
71 | it looks like a number). There I<are> minor exceptions to this, read the |
|
|
72 | MAPPING section below to learn about those. |
53 | |
73 | |
54 | =item * strict checking of JSON correctness |
74 | =item * strict checking of JSON correctness |
55 | |
75 | |
56 | 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, |
57 | 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 |
58 | feature). |
78 | feature). |
59 | |
79 | |
60 | =item * fast |
80 | =item * fast |
61 | |
81 | |
62 | Compared to other JSON modules, this module compares favourably in terms |
82 | Compared to other JSON modules and other serialisers such as Storable, |
63 | of speed, too. |
83 | this module usually compares favourably in terms of speed, too. |
64 | |
84 | |
65 | =item * simple to use |
85 | =item * simple to use |
66 | |
86 | |
67 | 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 |
68 | interface. |
88 | oriented interface. |
69 | |
89 | |
70 | =item * reasonably versatile output formats |
90 | =item * reasonably versatile output formats |
71 | |
91 | |
72 | You can choose between the most compact guarenteed single-line format |
92 | You can choose between the most compact guaranteed-single-line format |
73 | possible (nice for simple line-based protocols), a pure-ascii format |
93 | possible (nice for simple line-based protocols), a pure-ASCII format |
74 | (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 |
75 | 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 |
76 | 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. |
77 | |
97 | |
78 | =back |
98 | =back |
79 | |
99 | |
80 | =cut |
100 | =cut |
81 | |
101 | |
82 | package JSON::XS; |
102 | package JSON::XS; |
83 | |
103 | |
84 | use strict; |
104 | use common::sense; |
85 | |
105 | |
86 | our $VERSION = '1.5'; |
106 | our $VERSION = 2.34; |
87 | our @ISA = qw(Exporter); |
107 | our @ISA = qw(Exporter); |
88 | |
108 | |
89 | our @EXPORT = qw(to_json from_json); |
109 | our @EXPORT = qw(encode_json decode_json); |
90 | |
110 | |
91 | use Exporter; |
111 | use Exporter; |
92 | use XSLoader; |
112 | use XSLoader; |
93 | |
113 | |
94 | =head1 FUNCTIONAL INTERFACE |
114 | =head1 FUNCTIONAL INTERFACE |
95 | |
115 | |
96 | The following convinience methods are provided by this module. They are |
116 | The following convenience methods are provided by this module. They are |
97 | exported by default: |
117 | exported by default: |
98 | |
118 | |
99 | =over 4 |
119 | =over 4 |
100 | |
120 | |
101 | =item $json_text = to_json $perl_scalar |
121 | =item $json_text = encode_json $perl_scalar |
102 | |
122 | |
103 | Converts the given Perl data structure (a simple scalar or a reference to |
123 | Converts the given Perl data structure to a UTF-8 encoded, binary string |
104 | a hash or array) to a UTF-8 encoded, binary string (that is, the string contains |
124 | (that is, the string contains octets only). Croaks on error. |
105 | octets only). Croaks on error. |
|
|
106 | |
125 | |
107 | This function call is functionally identical to: |
126 | This function call is functionally identical to: |
108 | |
127 | |
109 | $json_text = JSON::XS->new->utf8->encode ($perl_scalar) |
128 | $json_text = JSON::XS->new->utf8->encode ($perl_scalar) |
110 | |
129 | |
111 | except being faster. |
130 | Except being faster. |
112 | |
131 | |
113 | =item $perl_scalar = from_json $json_text |
132 | =item $perl_scalar = decode_json $json_text |
114 | |
133 | |
115 | The opposite of C<to_json>: expects an UTF-8 (binary) string and tries to |
134 | The opposite of C<encode_json>: expects an UTF-8 (binary) string and tries |
116 | parse that as an UTF-8 encoded JSON text, returning the resulting simple |
135 | to parse that as an UTF-8 encoded JSON text, returning the resulting |
117 | scalar or reference. Croaks on error. |
136 | reference. Croaks on error. |
118 | |
137 | |
119 | This function call is functionally identical to: |
138 | This function call is functionally identical to: |
120 | |
139 | |
121 | $perl_scalar = JSON::XS->new->utf8->decode ($json_text) |
140 | $perl_scalar = JSON::XS->new->utf8->decode ($json_text) |
122 | |
141 | |
123 | except being faster. |
142 | Except being faster. |
124 | |
143 | |
125 | =item $is_boolean = JSON::XS::is_bool $scalar |
144 | =item $is_boolean = JSON::XS::is_bool $scalar |
126 | |
145 | |
127 | Returns true if the passed scalar represents either JSON::XS::true or |
146 | Returns true if the passed scalar represents either JSON::XS::true or |
128 | JSON::XS::false, two constants that act like C<1> and C<0>, respectively |
147 | JSON::XS::false, two constants that act like C<1> and C<0>, respectively |
… | |
… | |
132 | Perl. |
151 | Perl. |
133 | |
152 | |
134 | =back |
153 | =back |
135 | |
154 | |
136 | |
155 | |
|
|
156 | =head1 A FEW NOTES ON UNICODE AND PERL |
|
|
157 | |
|
|
158 | Since this often leads to confusion, here are a few very clear words on |
|
|
159 | how Unicode works in Perl, modulo bugs. |
|
|
160 | |
|
|
161 | =over 4 |
|
|
162 | |
|
|
163 | =item 1. Perl strings can store characters with ordinal values > 255. |
|
|
164 | |
|
|
165 | This enables you to store Unicode characters as single characters in a |
|
|
166 | Perl string - very natural. |
|
|
167 | |
|
|
168 | =item 2. Perl does I<not> associate an encoding with your strings. |
|
|
169 | |
|
|
170 | ... until you force it to, e.g. when matching it against a regex, or |
|
|
171 | printing the scalar to a file, in which case Perl either interprets your |
|
|
172 | string as locale-encoded text, octets/binary, or as Unicode, depending |
|
|
173 | on various settings. In no case is an encoding stored together with your |
|
|
174 | data, it is I<use> that decides encoding, not any magical meta data. |
|
|
175 | |
|
|
176 | =item 3. The internal utf-8 flag has no meaning with regards to the |
|
|
177 | encoding of your string. |
|
|
178 | |
|
|
179 | Just ignore that flag unless you debug a Perl bug, a module written in |
|
|
180 | XS or want to dive into the internals of perl. Otherwise it will only |
|
|
181 | confuse you, as, despite the name, it says nothing about how your string |
|
|
182 | is encoded. You can have Unicode strings with that flag set, with that |
|
|
183 | flag clear, and you can have binary data with that flag set and that flag |
|
|
184 | clear. Other possibilities exist, too. |
|
|
185 | |
|
|
186 | If you didn't know about that flag, just the better, pretend it doesn't |
|
|
187 | exist. |
|
|
188 | |
|
|
189 | =item 4. A "Unicode String" is simply a string where each character can be |
|
|
190 | validly interpreted as a Unicode code point. |
|
|
191 | |
|
|
192 | If you have UTF-8 encoded data, it is no longer a Unicode string, but a |
|
|
193 | Unicode string encoded in UTF-8, giving you a binary string. |
|
|
194 | |
|
|
195 | =item 5. A string containing "high" (> 255) character values is I<not> a UTF-8 string. |
|
|
196 | |
|
|
197 | It's a fact. Learn to live with it. |
|
|
198 | |
|
|
199 | =back |
|
|
200 | |
|
|
201 | I hope this helps :) |
|
|
202 | |
|
|
203 | |
137 | =head1 OBJECT-ORIENTED INTERFACE |
204 | =head1 OBJECT-ORIENTED INTERFACE |
138 | |
205 | |
139 | The object oriented interface lets you configure your own encoding or |
206 | The object oriented interface lets you configure your own encoding or |
140 | decoding style, within the limits of supported formats. |
207 | decoding style, within the limits of supported formats. |
141 | |
208 | |
… | |
… | |
152 | my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]}) |
219 | my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]}) |
153 | => {"a": [1, 2]} |
220 | => {"a": [1, 2]} |
154 | |
221 | |
155 | =item $json = $json->ascii ([$enable]) |
222 | =item $json = $json->ascii ([$enable]) |
156 | |
223 | |
|
|
224 | =item $enabled = $json->get_ascii |
|
|
225 | |
157 | If C<$enable> is true (or missing), then the C<encode> method will not |
226 | If C<$enable> is true (or missing), then the C<encode> method will not |
158 | generate characters outside the code range C<0..127> (which is ASCII). Any |
227 | generate characters outside the code range C<0..127> (which is ASCII). Any |
159 | unicode characters outside that range will be escaped using either a |
228 | Unicode characters outside that range will be escaped using either a |
160 | single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence, |
229 | single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence, |
161 | as per RFC4627. The resulting encoded JSON text can be treated as a native |
230 | as per RFC4627. The resulting encoded JSON text can be treated as a native |
162 | unicode string, an ascii-encoded, latin1-encoded or UTF-8 encoded string, |
231 | Unicode string, an ascii-encoded, latin1-encoded or UTF-8 encoded string, |
163 | or any other superset of ASCII. |
232 | or any other superset of ASCII. |
164 | |
233 | |
165 | If C<$enable> is false, then the C<encode> method will not escape Unicode |
234 | If C<$enable> is false, then the C<encode> method will not escape Unicode |
166 | characters unless required by the JSON syntax or other flags. This results |
235 | characters unless required by the JSON syntax or other flags. This results |
167 | in a faster and more compact format. |
236 | in a faster and more compact format. |
168 | |
237 | |
|
|
238 | See also the section I<ENCODING/CODESET FLAG NOTES> later in this |
|
|
239 | document. |
|
|
240 | |
169 | The main use for this flag is to produce JSON texts that can be |
241 | The main use for this flag is to produce JSON texts that can be |
170 | transmitted over a 7-bit channel, as the encoded JSON texts will not |
242 | transmitted over a 7-bit channel, as the encoded JSON texts will not |
171 | contain any 8 bit characters. |
243 | contain any 8 bit characters. |
172 | |
244 | |
173 | JSON::XS->new->ascii (1)->encode ([chr 0x10401]) |
245 | JSON::XS->new->ascii (1)->encode ([chr 0x10401]) |
174 | => ["\ud801\udc01"] |
246 | => ["\ud801\udc01"] |
175 | |
247 | |
176 | =item $json = $json->latin1 ([$enable]) |
248 | =item $json = $json->latin1 ([$enable]) |
177 | |
249 | |
|
|
250 | =item $enabled = $json->get_latin1 |
|
|
251 | |
178 | If C<$enable> is true (or missing), then the C<encode> method will encode |
252 | If C<$enable> is true (or missing), then the C<encode> method will encode |
179 | the resulting JSON text as latin1 (or iso-8859-1), escaping any characters |
253 | the resulting JSON text as latin1 (or iso-8859-1), escaping any characters |
180 | outside the code range C<0..255>. The resulting string can be treated as a |
254 | outside the code range C<0..255>. The resulting string can be treated as a |
181 | latin1-encoded JSON text or a native unicode string. The C<decode> method |
255 | latin1-encoded JSON text or a native Unicode string. The C<decode> method |
182 | will not be affected in any way by this flag, as C<decode> by default |
256 | will not be affected in any way by this flag, as C<decode> by default |
183 | expects unicode, which is a strict superset of latin1. |
257 | expects Unicode, which is a strict superset of latin1. |
184 | |
258 | |
185 | If C<$enable> is false, then the C<encode> method will not escape Unicode |
259 | If C<$enable> is false, then the C<encode> method will not escape Unicode |
186 | characters unless required by the JSON syntax or other flags. |
260 | characters unless required by the JSON syntax or other flags. |
|
|
261 | |
|
|
262 | See also the section I<ENCODING/CODESET FLAG NOTES> later in this |
|
|
263 | document. |
187 | |
264 | |
188 | The main use for this flag is efficiently encoding binary data as JSON |
265 | The main use for this flag is efficiently encoding binary data as JSON |
189 | text, as most octets will not be escaped, resulting in a smaller encoded |
266 | text, as most octets will not be escaped, resulting in a smaller encoded |
190 | size. The disadvantage is that the resulting JSON text is encoded |
267 | size. The disadvantage is that the resulting JSON text is encoded |
191 | in latin1 (and must correctly be treated as such when storing and |
268 | in latin1 (and must correctly be treated as such when storing and |
192 | transfering), a rare encoding for JSON. It is therefore most useful when |
269 | transferring), a rare encoding for JSON. It is therefore most useful when |
193 | you want to store data structures known to contain binary data efficiently |
270 | you want to store data structures known to contain binary data efficiently |
194 | in files or databases, not when talking to other JSON encoders/decoders. |
271 | in files or databases, not when talking to other JSON encoders/decoders. |
195 | |
272 | |
196 | JSON::XS->new->latin1->encode (["\x{89}\x{abc}"] |
273 | JSON::XS->new->latin1->encode (["\x{89}\x{abc}"] |
197 | => ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not) |
274 | => ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not) |
198 | |
275 | |
199 | =item $json = $json->utf8 ([$enable]) |
276 | =item $json = $json->utf8 ([$enable]) |
|
|
277 | |
|
|
278 | =item $enabled = $json->get_utf8 |
200 | |
279 | |
201 | If C<$enable> is true (or missing), then the C<encode> method will encode |
280 | If C<$enable> is true (or missing), then the C<encode> method will encode |
202 | the JSON result into UTF-8, as required by many protocols, while the |
281 | the JSON result into UTF-8, as required by many protocols, while the |
203 | C<decode> method expects to be handled an UTF-8-encoded string. Please |
282 | C<decode> method expects to be handled an UTF-8-encoded string. Please |
204 | note that UTF-8-encoded strings do not contain any characters outside the |
283 | note that UTF-8-encoded strings do not contain any characters outside the |
205 | range C<0..255>, they are thus useful for bytewise/binary I/O. In future |
284 | range C<0..255>, they are thus useful for bytewise/binary I/O. In future |
206 | versions, enabling this option might enable autodetection of the UTF-16 |
285 | versions, enabling this option might enable autodetection of the UTF-16 |
207 | and UTF-32 encoding families, as described in RFC4627. |
286 | and UTF-32 encoding families, as described in RFC4627. |
208 | |
287 | |
209 | If C<$enable> is false, then the C<encode> method will return the JSON |
288 | If C<$enable> is false, then the C<encode> method will return the JSON |
210 | string as a (non-encoded) unicode string, while C<decode> expects thus a |
289 | string as a (non-encoded) Unicode string, while C<decode> expects thus a |
211 | unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs |
290 | Unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs |
212 | to be done yourself, e.g. using the Encode module. |
291 | to be done yourself, e.g. using the Encode module. |
|
|
292 | |
|
|
293 | See also the section I<ENCODING/CODESET FLAG NOTES> later in this |
|
|
294 | document. |
213 | |
295 | |
214 | Example, output UTF-16BE-encoded JSON: |
296 | Example, output UTF-16BE-encoded JSON: |
215 | |
297 | |
216 | use Encode; |
298 | use Encode; |
217 | $jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object); |
299 | $jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object); |
… | |
… | |
238 | ] |
320 | ] |
239 | } |
321 | } |
240 | |
322 | |
241 | =item $json = $json->indent ([$enable]) |
323 | =item $json = $json->indent ([$enable]) |
242 | |
324 | |
|
|
325 | =item $enabled = $json->get_indent |
|
|
326 | |
243 | If C<$enable> is true (or missing), then the C<encode> method will use a multiline |
327 | If C<$enable> is true (or missing), then the C<encode> method will use a multiline |
244 | format as output, putting every array member or object/hash key-value pair |
328 | format as output, putting every array member or object/hash key-value pair |
245 | into its own line, identing them properly. |
329 | into its own line, indenting them properly. |
246 | |
330 | |
247 | If C<$enable> is false, no newlines or indenting will be produced, and the |
331 | If C<$enable> is false, no newlines or indenting will be produced, and the |
248 | resulting JSON text is guarenteed not to contain any C<newlines>. |
332 | resulting JSON text is guaranteed not to contain any C<newlines>. |
249 | |
333 | |
250 | This setting has no effect when decoding JSON texts. |
334 | This setting has no effect when decoding JSON texts. |
251 | |
335 | |
252 | =item $json = $json->space_before ([$enable]) |
336 | =item $json = $json->space_before ([$enable]) |
|
|
337 | |
|
|
338 | =item $enabled = $json->get_space_before |
253 | |
339 | |
254 | If C<$enable> is true (or missing), then the C<encode> method will add an extra |
340 | If C<$enable> is true (or missing), then the C<encode> method will add an extra |
255 | optional space before the C<:> separating keys from values in JSON objects. |
341 | optional space before the C<:> separating keys from values in JSON objects. |
256 | |
342 | |
257 | If C<$enable> is false, then the C<encode> method will not add any extra |
343 | If C<$enable> is false, then the C<encode> method will not add any extra |
… | |
… | |
263 | Example, space_before enabled, space_after and indent disabled: |
349 | Example, space_before enabled, space_after and indent disabled: |
264 | |
350 | |
265 | {"key" :"value"} |
351 | {"key" :"value"} |
266 | |
352 | |
267 | =item $json = $json->space_after ([$enable]) |
353 | =item $json = $json->space_after ([$enable]) |
|
|
354 | |
|
|
355 | =item $enabled = $json->get_space_after |
268 | |
356 | |
269 | If C<$enable> is true (or missing), then the C<encode> method will add an extra |
357 | If C<$enable> is true (or missing), then the C<encode> method will add an extra |
270 | optional space after the C<:> separating keys from values in JSON objects |
358 | optional space after the C<:> separating keys from values in JSON objects |
271 | and extra whitespace after the C<,> separating key-value pairs and array |
359 | and extra whitespace after the C<,> separating key-value pairs and array |
272 | members. |
360 | members. |
… | |
… | |
279 | Example, space_before and indent disabled, space_after enabled: |
367 | Example, space_before and indent disabled, space_after enabled: |
280 | |
368 | |
281 | {"key": "value"} |
369 | {"key": "value"} |
282 | |
370 | |
283 | =item $json = $json->relaxed ([$enable]) |
371 | =item $json = $json->relaxed ([$enable]) |
|
|
372 | |
|
|
373 | =item $enabled = $json->get_relaxed |
284 | |
374 | |
285 | If C<$enable> is true (or missing), then C<decode> will accept some |
375 | If C<$enable> is true (or missing), then C<decode> will accept some |
286 | extensions to normal JSON syntax (see below). C<encode> will not be |
376 | extensions to normal JSON syntax (see below). C<encode> will not be |
287 | affected in anyway. I<Be aware that this option makes you accept invalid |
377 | affected in anyway. I<Be aware that this option makes you accept invalid |
288 | JSON texts as if they were valid!>. I suggest only to use this option to |
378 | JSON texts as if they were valid!>. I suggest only to use this option to |
… | |
… | |
310 | { |
400 | { |
311 | "k1": "v1", |
401 | "k1": "v1", |
312 | "k2": "v2", <- this comma not normally allowed |
402 | "k2": "v2", <- this comma not normally allowed |
313 | } |
403 | } |
314 | |
404 | |
|
|
405 | =item * shell-style '#'-comments |
|
|
406 | |
|
|
407 | Whenever JSON allows whitespace, shell-style comments are additionally |
|
|
408 | allowed. They are terminated by the first carriage-return or line-feed |
|
|
409 | character, after which more white-space and comments are allowed. |
|
|
410 | |
|
|
411 | [ |
|
|
412 | 1, # this comment not allowed in JSON |
|
|
413 | # neither this one... |
|
|
414 | ] |
|
|
415 | |
315 | =back |
416 | =back |
316 | |
417 | |
317 | =item $json = $json->canonical ([$enable]) |
418 | =item $json = $json->canonical ([$enable]) |
|
|
419 | |
|
|
420 | =item $enabled = $json->get_canonical |
318 | |
421 | |
319 | If C<$enable> is true (or missing), then the C<encode> method will output JSON objects |
422 | If C<$enable> is true (or missing), then the C<encode> method will output JSON objects |
320 | by sorting their keys. This is adding a comparatively high overhead. |
423 | by sorting their keys. This is adding a comparatively high overhead. |
321 | |
424 | |
322 | If C<$enable> is false, then the C<encode> method will output key-value |
425 | If C<$enable> is false, then the C<encode> method will output key-value |
323 | pairs in the order Perl stores them (which will likely change between runs |
426 | pairs in the order Perl stores them (which will likely change between runs |
324 | of the same script). |
427 | of the same script, and can change even within the same run from 5.18 |
|
|
428 | onwards). |
325 | |
429 | |
326 | This option is useful if you want the same data structure to be encoded as |
430 | This option is useful if you want the same data structure to be encoded as |
327 | the same JSON text (given the same overall settings). If it is disabled, |
431 | the same JSON text (given the same overall settings). If it is disabled, |
328 | the same hash migh be encoded differently even if contains the same data, |
432 | the same hash might be encoded differently even if contains the same data, |
329 | as key-value pairs have no inherent ordering in Perl. |
433 | as key-value pairs have no inherent ordering in Perl. |
330 | |
434 | |
331 | This setting has no effect when decoding JSON texts. |
435 | This setting has no effect when decoding JSON texts. |
332 | |
436 | |
|
|
437 | This setting has currently no effect on tied hashes. |
|
|
438 | |
333 | =item $json = $json->allow_nonref ([$enable]) |
439 | =item $json = $json->allow_nonref ([$enable]) |
|
|
440 | |
|
|
441 | =item $enabled = $json->get_allow_nonref |
334 | |
442 | |
335 | If C<$enable> is true (or missing), then the C<encode> method can convert a |
443 | If C<$enable> is true (or missing), then the C<encode> method can convert a |
336 | non-reference into its corresponding string, number or null JSON value, |
444 | non-reference into its corresponding string, number or null JSON value, |
337 | which is an extension to RFC4627. Likewise, C<decode> will accept those JSON |
445 | which is an extension to RFC4627. Likewise, C<decode> will accept those JSON |
338 | values instead of croaking. |
446 | values instead of croaking. |
… | |
… | |
346 | resulting in an invalid JSON text: |
454 | resulting in an invalid JSON text: |
347 | |
455 | |
348 | JSON::XS->new->allow_nonref->encode ("Hello, World!") |
456 | JSON::XS->new->allow_nonref->encode ("Hello, World!") |
349 | => "Hello, World!" |
457 | => "Hello, World!" |
350 | |
458 | |
|
|
459 | =item $json = $json->allow_unknown ([$enable]) |
|
|
460 | |
|
|
461 | =item $enabled = $json->get_allow_unknown |
|
|
462 | |
|
|
463 | If C<$enable> is true (or missing), then C<encode> will I<not> throw an |
|
|
464 | exception when it encounters values it cannot represent in JSON (for |
|
|
465 | example, filehandles) but instead will encode a JSON C<null> value. Note |
|
|
466 | that blessed objects are not included here and are handled separately by |
|
|
467 | c<allow_nonref>. |
|
|
468 | |
|
|
469 | If C<$enable> is false (the default), then C<encode> will throw an |
|
|
470 | exception when it encounters anything it cannot encode as JSON. |
|
|
471 | |
|
|
472 | This option does not affect C<decode> in any way, and it is recommended to |
|
|
473 | leave it off unless you know your communications partner. |
|
|
474 | |
351 | =item $json = $json->allow_blessed ([$enable]) |
475 | =item $json = $json->allow_blessed ([$enable]) |
|
|
476 | |
|
|
477 | =item $enabled = $json->get_allow_blessed |
352 | |
478 | |
353 | If C<$enable> is true (or missing), then the C<encode> method will not |
479 | If C<$enable> is true (or missing), then the C<encode> method will not |
354 | barf when it encounters a blessed reference. Instead, the value of the |
480 | barf when it encounters a blessed reference. Instead, the value of the |
355 | B<convert_blessed> option will decide wether C<null> (C<convert_blessed> |
481 | B<convert_blessed> option will decide whether C<null> (C<convert_blessed> |
356 | disabled or no C<to_json> method found) or a representation of the |
482 | disabled or no C<TO_JSON> method found) or a representation of the |
357 | object (C<convert_blessed> enabled and C<to_json> method found) is being |
483 | object (C<convert_blessed> enabled and C<TO_JSON> method found) is being |
358 | encoded. Has no effect on C<decode>. |
484 | encoded. Has no effect on C<decode>. |
359 | |
485 | |
360 | If C<$enable> is false (the default), then C<encode> will throw an |
486 | If C<$enable> is false (the default), then C<encode> will throw an |
361 | exception when it encounters a blessed object. |
487 | exception when it encounters a blessed object. |
362 | |
488 | |
363 | =item $json = $json->convert_blessed ([$enable]) |
489 | =item $json = $json->convert_blessed ([$enable]) |
|
|
490 | |
|
|
491 | =item $enabled = $json->get_convert_blessed |
364 | |
492 | |
365 | If C<$enable> is true (or missing), then C<encode>, upon encountering a |
493 | If C<$enable> is true (or missing), then C<encode>, upon encountering a |
366 | blessed object, will check for the availability of the C<TO_JSON> method |
494 | blessed object, will check for the availability of the C<TO_JSON> method |
367 | on the object's class. If found, it will be called in scalar context |
495 | on the object's class. If found, it will be called in scalar context |
368 | and the resulting scalar will be encoded instead of the object. If no |
496 | and the resulting scalar will be encoded instead of the object. If no |
… | |
… | |
372 | The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON> |
500 | The C<TO_JSON> method may safely call die if it wants. If C<TO_JSON> |
373 | returns other blessed objects, those will be handled in the same |
501 | returns other blessed objects, those will be handled in the same |
374 | way. C<TO_JSON> must take care of not causing an endless recursion cycle |
502 | way. C<TO_JSON> must take care of not causing an endless recursion cycle |
375 | (== crash) in this case. The name of C<TO_JSON> was chosen because other |
503 | (== crash) in this case. The name of C<TO_JSON> was chosen because other |
376 | methods called by the Perl core (== not by the user of the object) are |
504 | methods called by the Perl core (== not by the user of the object) are |
377 | usually in upper case letters and to avoid collisions with the C<to_json> |
505 | usually in upper case letters and to avoid collisions with any C<to_json> |
378 | function. |
506 | function or method. |
379 | |
507 | |
380 | This setting does not yet influence C<decode> in any way, but in the |
508 | This setting does not yet influence C<decode> in any way, but in the |
381 | future, global hooks might get installed that influence C<decode> and are |
509 | future, global hooks might get installed that influence C<decode> and are |
382 | enabled by this setting. |
510 | enabled by this setting. |
383 | |
511 | |
… | |
… | |
425 | |
553 | |
426 | As this callback gets called less often then the C<filter_json_object> |
554 | As this callback gets called less often then the C<filter_json_object> |
427 | one, decoding speed will not usually suffer as much. Therefore, single-key |
555 | one, decoding speed will not usually suffer as much. Therefore, single-key |
428 | objects make excellent targets to serialise Perl objects into, especially |
556 | objects make excellent targets to serialise Perl objects into, especially |
429 | as single-key JSON objects are as close to the type-tagged value concept |
557 | as single-key JSON objects are as close to the type-tagged value concept |
430 | as JSON gets (its basically an ID/VALUE tuple). Of course, JSON does not |
558 | as JSON gets (it's basically an ID/VALUE tuple). Of course, JSON does not |
431 | support this in any way, so you need to make sure your data never looks |
559 | support this in any way, so you need to make sure your data never looks |
432 | like a serialised Perl hash. |
560 | like a serialised Perl hash. |
433 | |
561 | |
434 | Typical names for the single object key are C<__class_whatever__>, or |
562 | Typical names for the single object key are C<__class_whatever__>, or |
435 | C<$__dollars_are_rarely_used__$> or C<}ugly_brace_placement>, or even |
563 | C<$__dollars_are_rarely_used__$> or C<}ugly_brace_placement>, or even |
… | |
… | |
459 | |
587 | |
460 | { __widget__ => $self->{id} } |
588 | { __widget__ => $self->{id} } |
461 | } |
589 | } |
462 | |
590 | |
463 | =item $json = $json->shrink ([$enable]) |
591 | =item $json = $json->shrink ([$enable]) |
|
|
592 | |
|
|
593 | =item $enabled = $json->get_shrink |
464 | |
594 | |
465 | Perl usually over-allocates memory a bit when allocating space for |
595 | Perl usually over-allocates memory a bit when allocating space for |
466 | strings. This flag optionally resizes strings generated by either |
596 | strings. This flag optionally resizes strings generated by either |
467 | C<encode> or C<decode> to their minimum size possible. This can save |
597 | C<encode> or C<decode> to their minimum size possible. This can save |
468 | memory when your JSON texts are either very very long or you have many |
598 | memory when your JSON texts are either very very long or you have many |
… | |
… | |
486 | strings that look like integers or floats into integers or floats |
616 | strings that look like integers or floats into integers or floats |
487 | internally (there is no difference on the Perl level), saving space. |
617 | internally (there is no difference on the Perl level), saving space. |
488 | |
618 | |
489 | =item $json = $json->max_depth ([$maximum_nesting_depth]) |
619 | =item $json = $json->max_depth ([$maximum_nesting_depth]) |
490 | |
620 | |
|
|
621 | =item $max_depth = $json->get_max_depth |
|
|
622 | |
491 | Sets the maximum nesting level (default C<512>) accepted while encoding |
623 | Sets the maximum nesting level (default C<512>) accepted while encoding |
492 | or decoding. If the JSON text or Perl data structure has an equal or |
624 | or decoding. If a higher nesting level is detected in JSON text or a Perl |
493 | higher nesting level then this limit, then the encoder and decoder will |
625 | data structure, then the encoder and decoder will stop and croak at that |
494 | stop and croak at that point. |
626 | point. |
495 | |
627 | |
496 | Nesting level is defined by number of hash- or arrayrefs that the encoder |
628 | Nesting level is defined by number of hash- or arrayrefs that the encoder |
497 | needs to traverse to reach a given point or the number of C<{> or C<[> |
629 | needs to traverse to reach a given point or the number of C<{> or C<[> |
498 | characters without their matching closing parenthesis crossed to reach a |
630 | characters without their matching closing parenthesis crossed to reach a |
499 | given character in a string. |
631 | given character in a string. |
500 | |
632 | |
501 | Setting the maximum depth to one disallows any nesting, so that ensures |
633 | Setting the maximum depth to one disallows any nesting, so that ensures |
502 | that the object is only a single hash/object or array. |
634 | that the object is only a single hash/object or array. |
503 | |
635 | |
504 | The argument to C<max_depth> will be rounded up to the next highest power |
|
|
505 | of two. If no argument is given, the highest possible setting will be |
636 | If no argument is given, the highest possible setting will be used, which |
506 | used, which is rarely useful. |
637 | is rarely useful. |
|
|
638 | |
|
|
639 | Note that nesting is implemented by recursion in C. The default value has |
|
|
640 | been chosen to be as large as typical operating systems allow without |
|
|
641 | crashing. |
507 | |
642 | |
508 | See SECURITY CONSIDERATIONS, below, for more info on why this is useful. |
643 | See SECURITY CONSIDERATIONS, below, for more info on why this is useful. |
509 | |
644 | |
510 | =item $json = $json->max_size ([$maximum_string_size]) |
645 | =item $json = $json->max_size ([$maximum_string_size]) |
|
|
646 | |
|
|
647 | =item $max_size = $json->get_max_size |
511 | |
648 | |
512 | Set the maximum length a JSON text may have (in bytes) where decoding is |
649 | Set the maximum length a JSON text may have (in bytes) where decoding is |
513 | being attempted. The default is C<0>, meaning no limit. When C<decode> |
650 | being attempted. The default is C<0>, meaning no limit. When C<decode> |
514 | is called on a string longer then this number of characters it will not |
651 | is called on a string that is longer then this many bytes, it will not |
515 | attempt to decode the string but throw an exception. This setting has no |
652 | attempt to decode the string but throw an exception. This setting has no |
516 | effect on C<encode> (yet). |
653 | effect on C<encode> (yet). |
517 | |
654 | |
518 | The argument to C<max_size> will be rounded up to the next B<highest> |
655 | If no argument is given, the limit check will be deactivated (same as when |
519 | power of two (so may be more than requested). If no argument is given, the |
656 | C<0> is specified). |
520 | limit check will be deactivated (same as when C<0> is specified). |
|
|
521 | |
657 | |
522 | See SECURITY CONSIDERATIONS, below, for more info on why this is useful. |
658 | See SECURITY CONSIDERATIONS, below, for more info on why this is useful. |
523 | |
659 | |
524 | =item $json_text = $json->encode ($perl_scalar) |
660 | =item $json_text = $json->encode ($perl_scalar) |
525 | |
661 | |
526 | Converts the given Perl data structure (a simple scalar or a reference |
662 | Converts the given Perl value or data structure to its JSON |
527 | to a hash or array) to its JSON representation. Simple scalars will be |
663 | representation. Croaks on error. |
528 | converted into JSON string or number sequences, while references to arrays |
|
|
529 | become JSON arrays and references to hashes become JSON objects. Undefined |
|
|
530 | Perl values (e.g. C<undef>) become JSON C<null> values. Neither C<true> |
|
|
531 | nor C<false> values will be generated. |
|
|
532 | |
664 | |
533 | =item $perl_scalar = $json->decode ($json_text) |
665 | =item $perl_scalar = $json->decode ($json_text) |
534 | |
666 | |
535 | The opposite of C<encode>: expects a JSON text and tries to parse it, |
667 | The opposite of C<encode>: expects a JSON text and tries to parse it, |
536 | returning the resulting simple scalar or reference. Croaks on error. |
668 | returning the resulting simple scalar or reference. Croaks on error. |
537 | |
|
|
538 | JSON numbers and strings become simple Perl scalars. JSON arrays become |
|
|
539 | Perl arrayrefs and JSON objects become Perl hashrefs. C<true> becomes |
|
|
540 | C<1>, C<false> becomes C<0> and C<null> becomes C<undef>. |
|
|
541 | |
669 | |
542 | =item ($perl_scalar, $characters) = $json->decode_prefix ($json_text) |
670 | =item ($perl_scalar, $characters) = $json->decode_prefix ($json_text) |
543 | |
671 | |
544 | This works like the C<decode> method, but instead of raising an exception |
672 | This works like the C<decode> method, but instead of raising an exception |
545 | when there is trailing garbage after the first JSON object, it will |
673 | when there is trailing garbage after the first JSON object, it will |
… | |
… | |
554 | => ([], 3) |
682 | => ([], 3) |
555 | |
683 | |
556 | =back |
684 | =back |
557 | |
685 | |
558 | |
686 | |
|
|
687 | =head1 INCREMENTAL PARSING |
|
|
688 | |
|
|
689 | In some cases, there is the need for incremental parsing of JSON |
|
|
690 | texts. While this module always has to keep both JSON text and resulting |
|
|
691 | Perl data structure in memory at one time, it does allow you to parse a |
|
|
692 | JSON stream incrementally. It does so by accumulating text until it has |
|
|
693 | a full JSON object, which it then can decode. This process is similar to |
|
|
694 | using C<decode_prefix> to see if a full JSON object is available, but |
|
|
695 | is much more efficient (and can be implemented with a minimum of method |
|
|
696 | calls). |
|
|
697 | |
|
|
698 | JSON::XS will only attempt to parse the JSON text once it is sure it |
|
|
699 | has enough text to get a decisive result, using a very simple but |
|
|
700 | truly incremental parser. This means that it sometimes won't stop as |
|
|
701 | early as the full parser, for example, it doesn't detect mismatched |
|
|
702 | parentheses. The only thing it guarantees is that it starts decoding as |
|
|
703 | soon as a syntactically valid JSON text has been seen. This means you need |
|
|
704 | to set resource limits (e.g. C<max_size>) to ensure the parser will stop |
|
|
705 | parsing in the presence if syntax errors. |
|
|
706 | |
|
|
707 | The following methods implement this incremental parser. |
|
|
708 | |
|
|
709 | =over 4 |
|
|
710 | |
|
|
711 | =item [void, scalar or list context] = $json->incr_parse ([$string]) |
|
|
712 | |
|
|
713 | This is the central parsing function. It can both append new text and |
|
|
714 | extract objects from the stream accumulated so far (both of these |
|
|
715 | functions are optional). |
|
|
716 | |
|
|
717 | If C<$string> is given, then this string is appended to the already |
|
|
718 | existing JSON fragment stored in the C<$json> object. |
|
|
719 | |
|
|
720 | After that, if the function is called in void context, it will simply |
|
|
721 | return without doing anything further. This can be used to add more text |
|
|
722 | in as many chunks as you want. |
|
|
723 | |
|
|
724 | If the method is called in scalar context, then it will try to extract |
|
|
725 | exactly I<one> JSON object. If that is successful, it will return this |
|
|
726 | object, otherwise it will return C<undef>. If there is a parse error, |
|
|
727 | this method will croak just as C<decode> would do (one can then use |
|
|
728 | C<incr_skip> to skip the erroneous part). This is the most common way of |
|
|
729 | using the method. |
|
|
730 | |
|
|
731 | And finally, in list context, it will try to extract as many objects |
|
|
732 | from the stream as it can find and return them, or the empty list |
|
|
733 | otherwise. For this to work, there must be no separators between the JSON |
|
|
734 | objects or arrays, instead they must be concatenated back-to-back. If |
|
|
735 | an error occurs, an exception will be raised as in the scalar context |
|
|
736 | case. Note that in this case, any previously-parsed JSON texts will be |
|
|
737 | lost. |
|
|
738 | |
|
|
739 | Example: Parse some JSON arrays/objects in a given string and return |
|
|
740 | them. |
|
|
741 | |
|
|
742 | my @objs = JSON::XS->new->incr_parse ("[5][7][1,2]"); |
|
|
743 | |
|
|
744 | =item $lvalue_string = $json->incr_text |
|
|
745 | |
|
|
746 | This method returns the currently stored JSON fragment as an lvalue, that |
|
|
747 | is, you can manipulate it. This I<only> works when a preceding call to |
|
|
748 | C<incr_parse> in I<scalar context> successfully returned an object. Under |
|
|
749 | all other circumstances you must not call this function (I mean it. |
|
|
750 | although in simple tests it might actually work, it I<will> fail under |
|
|
751 | real world conditions). As a special exception, you can also call this |
|
|
752 | method before having parsed anything. |
|
|
753 | |
|
|
754 | This function is useful in two cases: a) finding the trailing text after a |
|
|
755 | JSON object or b) parsing multiple JSON objects separated by non-JSON text |
|
|
756 | (such as commas). |
|
|
757 | |
|
|
758 | =item $json->incr_skip |
|
|
759 | |
|
|
760 | This will reset the state of the incremental parser and will remove |
|
|
761 | the parsed text from the input buffer so far. This is useful after |
|
|
762 | C<incr_parse> died, in which case the input buffer and incremental parser |
|
|
763 | state is left unchanged, to skip the text parsed so far and to reset the |
|
|
764 | parse state. |
|
|
765 | |
|
|
766 | The difference to C<incr_reset> is that only text until the parse error |
|
|
767 | occurred is removed. |
|
|
768 | |
|
|
769 | =item $json->incr_reset |
|
|
770 | |
|
|
771 | This completely resets the incremental parser, that is, after this call, |
|
|
772 | it will be as if the parser had never parsed anything. |
|
|
773 | |
|
|
774 | This is useful if you want to repeatedly parse JSON objects and want to |
|
|
775 | ignore any trailing data, which means you have to reset the parser after |
|
|
776 | each successful decode. |
|
|
777 | |
|
|
778 | =back |
|
|
779 | |
|
|
780 | =head2 LIMITATIONS |
|
|
781 | |
|
|
782 | All options that affect decoding are supported, except |
|
|
783 | C<allow_nonref>. The reason for this is that it cannot be made to |
|
|
784 | work sensibly: JSON objects and arrays are self-delimited, i.e. you can concatenate |
|
|
785 | them back to back and still decode them perfectly. This does not hold true |
|
|
786 | for JSON numbers, however. |
|
|
787 | |
|
|
788 | For example, is the string C<1> a single JSON number, or is it simply the |
|
|
789 | start of C<12>? Or is C<12> a single JSON number, or the concatenation |
|
|
790 | of C<1> and C<2>? In neither case you can tell, and this is why JSON::XS |
|
|
791 | takes the conservative route and disallows this case. |
|
|
792 | |
|
|
793 | =head2 EXAMPLES |
|
|
794 | |
|
|
795 | Some examples will make all this clearer. First, a simple example that |
|
|
796 | works similarly to C<decode_prefix>: We want to decode the JSON object at |
|
|
797 | the start of a string and identify the portion after the JSON object: |
|
|
798 | |
|
|
799 | my $text = "[1,2,3] hello"; |
|
|
800 | |
|
|
801 | my $json = new JSON::XS; |
|
|
802 | |
|
|
803 | my $obj = $json->incr_parse ($text) |
|
|
804 | or die "expected JSON object or array at beginning of string"; |
|
|
805 | |
|
|
806 | my $tail = $json->incr_text; |
|
|
807 | # $tail now contains " hello" |
|
|
808 | |
|
|
809 | Easy, isn't it? |
|
|
810 | |
|
|
811 | Now for a more complicated example: Imagine a hypothetical protocol where |
|
|
812 | you read some requests from a TCP stream, and each request is a JSON |
|
|
813 | array, without any separation between them (in fact, it is often useful to |
|
|
814 | use newlines as "separators", as these get interpreted as whitespace at |
|
|
815 | the start of the JSON text, which makes it possible to test said protocol |
|
|
816 | with C<telnet>...). |
|
|
817 | |
|
|
818 | Here is how you'd do it (it is trivial to write this in an event-based |
|
|
819 | manner): |
|
|
820 | |
|
|
821 | my $json = new JSON::XS; |
|
|
822 | |
|
|
823 | # read some data from the socket |
|
|
824 | while (sysread $socket, my $buf, 4096) { |
|
|
825 | |
|
|
826 | # split and decode as many requests as possible |
|
|
827 | for my $request ($json->incr_parse ($buf)) { |
|
|
828 | # act on the $request |
|
|
829 | } |
|
|
830 | } |
|
|
831 | |
|
|
832 | Another complicated example: Assume you have a string with JSON objects |
|
|
833 | or arrays, all separated by (optional) comma characters (e.g. C<[1],[2], |
|
|
834 | [3]>). To parse them, we have to skip the commas between the JSON texts, |
|
|
835 | and here is where the lvalue-ness of C<incr_text> comes in useful: |
|
|
836 | |
|
|
837 | my $text = "[1],[2], [3]"; |
|
|
838 | my $json = new JSON::XS; |
|
|
839 | |
|
|
840 | # void context, so no parsing done |
|
|
841 | $json->incr_parse ($text); |
|
|
842 | |
|
|
843 | # now extract as many objects as possible. note the |
|
|
844 | # use of scalar context so incr_text can be called. |
|
|
845 | while (my $obj = $json->incr_parse) { |
|
|
846 | # do something with $obj |
|
|
847 | |
|
|
848 | # now skip the optional comma |
|
|
849 | $json->incr_text =~ s/^ \s* , //x; |
|
|
850 | } |
|
|
851 | |
|
|
852 | Now lets go for a very complex example: Assume that you have a gigantic |
|
|
853 | JSON array-of-objects, many gigabytes in size, and you want to parse it, |
|
|
854 | but you cannot load it into memory fully (this has actually happened in |
|
|
855 | the real world :). |
|
|
856 | |
|
|
857 | Well, you lost, you have to implement your own JSON parser. But JSON::XS |
|
|
858 | can still help you: You implement a (very simple) array parser and let |
|
|
859 | JSON decode the array elements, which are all full JSON objects on their |
|
|
860 | own (this wouldn't work if the array elements could be JSON numbers, for |
|
|
861 | example): |
|
|
862 | |
|
|
863 | my $json = new JSON::XS; |
|
|
864 | |
|
|
865 | # open the monster |
|
|
866 | open my $fh, "<bigfile.json" |
|
|
867 | or die "bigfile: $!"; |
|
|
868 | |
|
|
869 | # first parse the initial "[" |
|
|
870 | for (;;) { |
|
|
871 | sysread $fh, my $buf, 65536 |
|
|
872 | or die "read error: $!"; |
|
|
873 | $json->incr_parse ($buf); # void context, so no parsing |
|
|
874 | |
|
|
875 | # Exit the loop once we found and removed(!) the initial "[". |
|
|
876 | # In essence, we are (ab-)using the $json object as a simple scalar |
|
|
877 | # we append data to. |
|
|
878 | last if $json->incr_text =~ s/^ \s* \[ //x; |
|
|
879 | } |
|
|
880 | |
|
|
881 | # now we have the skipped the initial "[", so continue |
|
|
882 | # parsing all the elements. |
|
|
883 | for (;;) { |
|
|
884 | # in this loop we read data until we got a single JSON object |
|
|
885 | for (;;) { |
|
|
886 | if (my $obj = $json->incr_parse) { |
|
|
887 | # do something with $obj |
|
|
888 | last; |
|
|
889 | } |
|
|
890 | |
|
|
891 | # add more data |
|
|
892 | sysread $fh, my $buf, 65536 |
|
|
893 | or die "read error: $!"; |
|
|
894 | $json->incr_parse ($buf); # void context, so no parsing |
|
|
895 | } |
|
|
896 | |
|
|
897 | # in this loop we read data until we either found and parsed the |
|
|
898 | # separating "," between elements, or the final "]" |
|
|
899 | for (;;) { |
|
|
900 | # first skip whitespace |
|
|
901 | $json->incr_text =~ s/^\s*//; |
|
|
902 | |
|
|
903 | # if we find "]", we are done |
|
|
904 | if ($json->incr_text =~ s/^\]//) { |
|
|
905 | print "finished.\n"; |
|
|
906 | exit; |
|
|
907 | } |
|
|
908 | |
|
|
909 | # if we find ",", we can continue with the next element |
|
|
910 | if ($json->incr_text =~ s/^,//) { |
|
|
911 | last; |
|
|
912 | } |
|
|
913 | |
|
|
914 | # if we find anything else, we have a parse error! |
|
|
915 | if (length $json->incr_text) { |
|
|
916 | die "parse error near ", $json->incr_text; |
|
|
917 | } |
|
|
918 | |
|
|
919 | # else add more data |
|
|
920 | sysread $fh, my $buf, 65536 |
|
|
921 | or die "read error: $!"; |
|
|
922 | $json->incr_parse ($buf); # void context, so no parsing |
|
|
923 | } |
|
|
924 | |
|
|
925 | This is a complex example, but most of the complexity comes from the fact |
|
|
926 | that we are trying to be correct (bear with me if I am wrong, I never ran |
|
|
927 | the above example :). |
|
|
928 | |
|
|
929 | |
|
|
930 | |
559 | =head1 MAPPING |
931 | =head1 MAPPING |
560 | |
932 | |
561 | This section describes how JSON::XS maps Perl values to JSON values and |
933 | This section describes how JSON::XS maps Perl values to JSON values and |
562 | vice versa. These mappings are designed to "do the right thing" in most |
934 | vice versa. These mappings are designed to "do the right thing" in most |
563 | circumstances automatically, preserving round-tripping characteristics |
935 | circumstances automatically, preserving round-tripping characteristics |
564 | (what you put in comes out as something equivalent). |
936 | (what you put in comes out as something equivalent). |
565 | |
937 | |
566 | For the more enlightened: note that in the following descriptions, |
938 | For the more enlightened: note that in the following descriptions, |
567 | lowercase I<perl> refers to the Perl interpreter, while uppcercase I<Perl> |
939 | lowercase I<perl> refers to the Perl interpreter, while uppercase I<Perl> |
568 | refers to the abstract Perl language itself. |
940 | refers to the abstract Perl language itself. |
569 | |
941 | |
570 | |
942 | |
571 | =head2 JSON -> PERL |
943 | =head2 JSON -> PERL |
572 | |
944 | |
573 | =over 4 |
945 | =over 4 |
574 | |
946 | |
575 | =item object |
947 | =item object |
576 | |
948 | |
577 | A JSON object becomes a reference to a hash in Perl. No ordering of object |
949 | A JSON object becomes a reference to a hash in Perl. No ordering of object |
578 | keys is preserved (JSON does not preserver object key ordering itself). |
950 | keys is preserved (JSON does not preserve object key ordering itself). |
579 | |
951 | |
580 | =item array |
952 | =item array |
581 | |
953 | |
582 | A JSON array becomes a reference to an array in Perl. |
954 | A JSON array becomes a reference to an array in Perl. |
583 | |
955 | |
… | |
… | |
591 | |
963 | |
592 | A JSON number becomes either an integer, numeric (floating point) or |
964 | A JSON number becomes either an integer, numeric (floating point) or |
593 | string scalar in perl, depending on its range and any fractional parts. On |
965 | string scalar in perl, depending on its range and any fractional parts. On |
594 | the Perl level, there is no difference between those as Perl handles all |
966 | the Perl level, there is no difference between those as Perl handles all |
595 | the conversion details, but an integer may take slightly less memory and |
967 | the conversion details, but an integer may take slightly less memory and |
596 | might represent more values exactly than (floating point) numbers. |
968 | might represent more values exactly than floating point numbers. |
597 | |
969 | |
598 | If the number consists of digits only, JSON::XS will try to represent |
970 | If the number consists of digits only, JSON::XS will try to represent |
599 | it as an integer value. If that fails, it will try to represent it as |
971 | it as an integer value. If that fails, it will try to represent it as |
600 | a numeric (floating point) value if that is possible without loss of |
972 | a numeric (floating point) value if that is possible without loss of |
601 | precision. Otherwise it will preserve the number as a string value. |
973 | precision. Otherwise it will preserve the number as a string value (in |
|
|
974 | which case you lose roundtripping ability, as the JSON number will be |
|
|
975 | re-encoded to a JSON string). |
602 | |
976 | |
603 | Numbers containing a fractional or exponential part will always be |
977 | Numbers containing a fractional or exponential part will always be |
604 | represented as numeric (floating point) values, possibly at a loss of |
978 | represented as numeric (floating point) values, possibly at a loss of |
605 | precision. |
979 | precision (in which case you might lose perfect roundtripping ability, but |
|
|
980 | the JSON number will still be re-encoded as a JSON number). |
606 | |
981 | |
607 | This might create round-tripping problems as numbers might become strings, |
982 | Note that precision is not accuracy - binary floating point values cannot |
608 | but as Perl is typeless there is no other way to do it. |
983 | represent most decimal fractions exactly, and when converting from and to |
|
|
984 | floating point, JSON::XS only guarantees precision up to but not including |
|
|
985 | the least significant bit. |
609 | |
986 | |
610 | =item true, false |
987 | =item true, false |
611 | |
988 | |
612 | These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>, |
989 | These JSON atoms become C<JSON::XS::true> and C<JSON::XS::false>, |
613 | respectively. They are overloaded to act almost exactly like the numbers |
990 | respectively. They are overloaded to act almost exactly like the numbers |
614 | C<1> and C<0>. You can check wether a scalar is a JSON boolean by using |
991 | C<1> and C<0>. You can check whether a scalar is a JSON boolean by using |
615 | the C<JSON::XS::is_bool> function. |
992 | the C<JSON::XS::is_bool> function. |
616 | |
993 | |
617 | =item null |
994 | =item null |
618 | |
995 | |
619 | A JSON null atom becomes C<undef> in Perl. |
996 | A JSON null atom becomes C<undef> in Perl. |
… | |
… | |
629 | |
1006 | |
630 | =over 4 |
1007 | =over 4 |
631 | |
1008 | |
632 | =item hash references |
1009 | =item hash references |
633 | |
1010 | |
634 | Perl hash references become JSON objects. As there is no inherent ordering |
1011 | Perl hash references become JSON objects. As there is no inherent |
635 | in hash keys (or JSON objects), they will usually be encoded in a |
1012 | ordering in hash keys (or JSON objects), they will usually be encoded |
636 | pseudo-random order that can change between runs of the same program but |
1013 | in a pseudo-random order. JSON::XS can optionally sort the hash keys |
637 | stays generally the same within a single run of a program. JSON::XS can |
1014 | (determined by the I<canonical> flag), so the same datastructure will |
638 | optionally sort the hash keys (determined by the I<canonical> flag), so |
1015 | serialise to the same JSON text (given same settings and version of |
639 | the same datastructure will serialise to the same JSON text (given same |
1016 | JSON::XS), but this incurs a runtime overhead and is only rarely useful, |
640 | settings and version of JSON::XS), but this incurs a runtime overhead |
1017 | e.g. when you want to compare some JSON text against another for equality. |
641 | and is only rarely useful, e.g. when you want to compare some JSON text |
|
|
642 | against another for equality. |
|
|
643 | |
1018 | |
644 | =item array references |
1019 | =item array references |
645 | |
1020 | |
646 | Perl array references become JSON arrays. |
1021 | Perl array references become JSON arrays. |
647 | |
1022 | |
… | |
… | |
650 | Other unblessed references are generally not allowed and will cause an |
1025 | Other unblessed references are generally not allowed and will cause an |
651 | exception to be thrown, except for references to the integers C<0> and |
1026 | exception to be thrown, except for references to the integers C<0> and |
652 | C<1>, which get turned into C<false> and C<true> atoms in JSON. You can |
1027 | C<1>, which get turned into C<false> and C<true> atoms in JSON. You can |
653 | also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability. |
1028 | also use C<JSON::XS::false> and C<JSON::XS::true> to improve readability. |
654 | |
1029 | |
655 | to_json [\0,JSON::XS::true] # yields [false,true] |
1030 | encode_json [\0, JSON::XS::true] # yields [false,true] |
656 | |
1031 | |
657 | =item JSON::XS::true, JSON::XS::false |
1032 | =item JSON::XS::true, JSON::XS::false |
658 | |
1033 | |
659 | These special values become JSON true and JSON false values, |
1034 | These special values become JSON true and JSON false values, |
660 | respectively. You cna alos use C<\1> and C<\0> directly if you want. |
1035 | respectively. You can also use C<\1> and C<\0> directly if you want. |
661 | |
1036 | |
662 | =item blessed objects |
1037 | =item blessed objects |
663 | |
1038 | |
664 | Blessed objects are not allowed. JSON::XS currently tries to encode their |
1039 | Blessed objects are not directly representable in JSON. See the |
665 | underlying representation (hash- or arrayref), but this behaviour might |
1040 | C<allow_blessed> and C<convert_blessed> methods on various options on |
666 | change in future versions. |
1041 | how to deal with this: basically, you can choose between throwing an |
|
|
1042 | exception, encoding the reference as if it weren't blessed, or provide |
|
|
1043 | your own serialiser method. |
667 | |
1044 | |
668 | =item simple scalars |
1045 | =item simple scalars |
669 | |
1046 | |
670 | Simple Perl scalars (any scalar that is not a reference) are the most |
1047 | Simple Perl scalars (any scalar that is not a reference) are the most |
671 | difficult objects to encode: JSON::XS will encode undefined scalars as |
1048 | difficult objects to encode: JSON::XS will encode undefined scalars as |
672 | JSON null value, scalars that have last been used in a string context |
1049 | JSON C<null> values, scalars that have last been used in a string context |
673 | before encoding as JSON strings and anything else as number value: |
1050 | before encoding as JSON strings, and anything else as number value: |
674 | |
1051 | |
675 | # dump as number |
1052 | # dump as number |
676 | to_json [2] # yields [2] |
1053 | encode_json [2] # yields [2] |
677 | to_json [-3.0e17] # yields [-3e+17] |
1054 | encode_json [-3.0e17] # yields [-3e+17] |
678 | my $value = 5; to_json [$value] # yields [5] |
1055 | my $value = 5; encode_json [$value] # yields [5] |
679 | |
1056 | |
680 | # used as string, so dump as string |
1057 | # used as string, so dump as string |
681 | print $value; |
1058 | print $value; |
682 | to_json [$value] # yields ["5"] |
1059 | encode_json [$value] # yields ["5"] |
683 | |
1060 | |
684 | # undef becomes null |
1061 | # undef becomes null |
685 | to_json [undef] # yields [null] |
1062 | encode_json [undef] # yields [null] |
686 | |
1063 | |
687 | You can force the type to be a string by stringifying it: |
1064 | You can force the type to be a JSON string by stringifying it: |
688 | |
1065 | |
689 | my $x = 3.1; # some variable containing a number |
1066 | my $x = 3.1; # some variable containing a number |
690 | "$x"; # stringified |
1067 | "$x"; # stringified |
691 | $x .= ""; # another, more awkward way to stringify |
1068 | $x .= ""; # another, more awkward way to stringify |
692 | print $x; # perl does it for you, too, quite often |
1069 | print $x; # perl does it for you, too, quite often |
693 | |
1070 | |
694 | You can force the type to be a number by numifying it: |
1071 | You can force the type to be a JSON number by numifying it: |
695 | |
1072 | |
696 | my $x = "3"; # some variable containing a string |
1073 | my $x = "3"; # some variable containing a string |
697 | $x += 0; # numify it, ensuring it will be dumped as a number |
1074 | $x += 0; # numify it, ensuring it will be dumped as a number |
698 | $x *= 1; # same thing, the choise is yours. |
1075 | $x *= 1; # same thing, the choice is yours. |
699 | |
1076 | |
700 | You can not currently output JSON booleans or force the type in other, |
1077 | You can not currently force the type in other, less obscure, ways. Tell me |
701 | less obscure, ways. Tell me if you need this capability. |
1078 | if you need this capability (but don't forget to explain why it's needed |
|
|
1079 | :). |
|
|
1080 | |
|
|
1081 | Note that numerical precision has the same meaning as under Perl (so |
|
|
1082 | binary to decimal conversion follows the same rules as in Perl, which |
|
|
1083 | can differ to other languages). Also, your perl interpreter might expose |
|
|
1084 | extensions to the floating point numbers of your platform, such as |
|
|
1085 | infinities or NaN's - these cannot be represented in JSON, and it is an |
|
|
1086 | error to pass those in. |
702 | |
1087 | |
703 | =back |
1088 | =back |
704 | |
1089 | |
705 | |
1090 | |
706 | =head1 COMPARISON |
1091 | =head1 ENCODING/CODESET FLAG NOTES |
707 | |
1092 | |
708 | As already mentioned, this module was created because none of the existing |
1093 | The interested reader might have seen a number of flags that signify |
709 | JSON modules could be made to work correctly. First I will describe the |
1094 | encodings or codesets - C<utf8>, C<latin1> and C<ascii>. There seems to be |
710 | problems (or pleasures) I encountered with various existing JSON modules, |
1095 | some confusion on what these do, so here is a short comparison: |
711 | followed by some benchmark values. JSON::XS was designed not to suffer |
1096 | |
712 | from any of these problems or limitations. |
1097 | C<utf8> controls whether the JSON text created by C<encode> (and expected |
|
|
1098 | by C<decode>) is UTF-8 encoded or not, while C<latin1> and C<ascii> only |
|
|
1099 | control whether C<encode> escapes character values outside their respective |
|
|
1100 | codeset range. Neither of these flags conflict with each other, although |
|
|
1101 | some combinations make less sense than others. |
|
|
1102 | |
|
|
1103 | Care has been taken to make all flags symmetrical with respect to |
|
|
1104 | C<encode> and C<decode>, that is, texts encoded with any combination of |
|
|
1105 | these flag values will be correctly decoded when the same flags are used |
|
|
1106 | - in general, if you use different flag settings while encoding vs. when |
|
|
1107 | decoding you likely have a bug somewhere. |
|
|
1108 | |
|
|
1109 | Below comes a verbose discussion of these flags. Note that a "codeset" is |
|
|
1110 | simply an abstract set of character-codepoint pairs, while an encoding |
|
|
1111 | takes those codepoint numbers and I<encodes> them, in our case into |
|
|
1112 | octets. Unicode is (among other things) a codeset, UTF-8 is an encoding, |
|
|
1113 | and ISO-8859-1 (= latin 1) and ASCII are both codesets I<and> encodings at |
|
|
1114 | the same time, which can be confusing. |
713 | |
1115 | |
714 | =over 4 |
1116 | =over 4 |
715 | |
1117 | |
716 | =item JSON 1.07 |
1118 | =item C<utf8> flag disabled |
717 | |
1119 | |
718 | Slow (but very portable, as it is written in pure Perl). |
1120 | When C<utf8> is disabled (the default), then C<encode>/C<decode> generate |
|
|
1121 | and expect Unicode strings, that is, characters with high ordinal Unicode |
|
|
1122 | values (> 255) will be encoded as such characters, and likewise such |
|
|
1123 | characters are decoded as-is, no changes to them will be done, except |
|
|
1124 | "(re-)interpreting" them as Unicode codepoints or Unicode characters, |
|
|
1125 | respectively (to Perl, these are the same thing in strings unless you do |
|
|
1126 | funny/weird/dumb stuff). |
719 | |
1127 | |
720 | Undocumented/buggy Unicode handling (how JSON handles unicode values is |
1128 | This is useful when you want to do the encoding yourself (e.g. when you |
721 | undocumented. One can get far by feeding it unicode strings and doing |
1129 | want to have UTF-16 encoded JSON texts) or when some other layer does |
722 | en-/decoding oneself, but unicode escapes are not working properly). |
1130 | the encoding for you (for example, when printing to a terminal using a |
|
|
1131 | filehandle that transparently encodes to UTF-8 you certainly do NOT want |
|
|
1132 | to UTF-8 encode your data first and have Perl encode it another time). |
723 | |
1133 | |
724 | No roundtripping (strings get clobbered if they look like numbers, e.g. |
1134 | =item C<utf8> flag enabled |
725 | the string C<2.0> will encode to C<2.0> instead of C<"2.0">, and that will |
|
|
726 | decode into the number 2. |
|
|
727 | |
1135 | |
728 | =item JSON::PC 0.01 |
1136 | If the C<utf8>-flag is enabled, C<encode>/C<decode> will encode all |
|
|
1137 | characters using the corresponding UTF-8 multi-byte sequence, and will |
|
|
1138 | expect your input strings to be encoded as UTF-8, that is, no "character" |
|
|
1139 | of the input string must have any value > 255, as UTF-8 does not allow |
|
|
1140 | that. |
729 | |
1141 | |
730 | Very fast. |
1142 | The C<utf8> flag therefore switches between two modes: disabled means you |
|
|
1143 | will get a Unicode string in Perl, enabled means you get an UTF-8 encoded |
|
|
1144 | octet/binary string in Perl. |
731 | |
1145 | |
732 | Undocumented/buggy Unicode handling. |
1146 | =item C<latin1> or C<ascii> flags enabled |
733 | |
1147 | |
734 | No roundtripping. |
1148 | With C<latin1> (or C<ascii>) enabled, C<encode> will escape characters |
|
|
1149 | with ordinal values > 255 (> 127 with C<ascii>) and encode the remaining |
|
|
1150 | characters as specified by the C<utf8> flag. |
735 | |
1151 | |
736 | Has problems handling many Perl values (e.g. regex results and other magic |
1152 | If C<utf8> is disabled, then the result is also correctly encoded in those |
737 | values will make it croak). |
1153 | character sets (as both are proper subsets of Unicode, meaning that a |
|
|
1154 | Unicode string with all character values < 256 is the same thing as a |
|
|
1155 | ISO-8859-1 string, and a Unicode string with all character values < 128 is |
|
|
1156 | the same thing as an ASCII string in Perl). |
738 | |
1157 | |
739 | Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}> |
1158 | If C<utf8> is enabled, you still get a correct UTF-8-encoded string, |
740 | which is not a valid JSON text. |
1159 | regardless of these flags, just some more characters will be escaped using |
|
|
1160 | C<\uXXXX> then before. |
741 | |
1161 | |
742 | Unmaintained (maintainer unresponsive for many months, bugs are not |
1162 | Note that ISO-8859-1-I<encoded> strings are not compatible with UTF-8 |
743 | getting fixed). |
1163 | encoding, while ASCII-encoded strings are. That is because the ISO-8859-1 |
|
|
1164 | encoding is NOT a subset of UTF-8 (despite the ISO-8859-1 I<codeset> being |
|
|
1165 | a subset of Unicode), while ASCII is. |
744 | |
1166 | |
745 | =item JSON::Syck 0.21 |
1167 | Surprisingly, C<decode> will ignore these flags and so treat all input |
|
|
1168 | values as governed by the C<utf8> flag. If it is disabled, this allows you |
|
|
1169 | to decode ISO-8859-1- and ASCII-encoded strings, as both strict subsets of |
|
|
1170 | Unicode. If it is enabled, you can correctly decode UTF-8 encoded strings. |
746 | |
1171 | |
747 | Very buggy (often crashes). |
1172 | So neither C<latin1> nor C<ascii> are incompatible with the C<utf8> flag - |
|
|
1173 | they only govern when the JSON output engine escapes a character or not. |
748 | |
1174 | |
749 | Very inflexible (no human-readable format supported, format pretty much |
1175 | The main use for C<latin1> is to relatively efficiently store binary data |
750 | undocumented. I need at least a format for easy reading by humans and a |
1176 | as JSON, at the expense of breaking compatibility with most JSON decoders. |
751 | single-line compact format for use in a protocol, and preferably a way to |
|
|
752 | generate ASCII-only JSON texts). |
|
|
753 | |
1177 | |
754 | Completely broken (and confusingly documented) Unicode handling (unicode |
1178 | The main use for C<ascii> is to force the output to not contain characters |
755 | escapes are not working properly, you need to set ImplicitUnicode to |
1179 | with values > 127, which means you can interpret the resulting string |
756 | I<different> values on en- and decoding to get symmetric behaviour). |
1180 | as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about any character set and |
757 | |
1181 | 8-bit-encoding, and still get the same data structure back. This is useful |
758 | No roundtripping (simple cases work, but this depends on wether the scalar |
1182 | when your channel for JSON transfer is not 8-bit clean or the encoding |
759 | value was used in a numeric context or not). |
1183 | might be mangled in between (e.g. in mail), and works because ASCII is a |
760 | |
1184 | proper subset of most 8-bit and multibyte encodings in use in the world. |
761 | Dumping hashes may skip hash values depending on iterator state. |
|
|
762 | |
|
|
763 | Unmaintained (maintainer unresponsive for many months, bugs are not |
|
|
764 | getting fixed). |
|
|
765 | |
|
|
766 | Does not check input for validity (i.e. will accept non-JSON input and |
|
|
767 | return "something" instead of raising an exception. This is a security |
|
|
768 | issue: imagine two banks transfering money between each other using |
|
|
769 | JSON. One bank might parse a given non-JSON request and deduct money, |
|
|
770 | while the other might reject the transaction with a syntax error. While a |
|
|
771 | good protocol will at least recover, that is extra unnecessary work and |
|
|
772 | the transaction will still not succeed). |
|
|
773 | |
|
|
774 | =item JSON::DWIW 0.04 |
|
|
775 | |
|
|
776 | Very fast. Very natural. Very nice. |
|
|
777 | |
|
|
778 | Undocumented unicode handling (but the best of the pack. Unicode escapes |
|
|
779 | still don't get parsed properly). |
|
|
780 | |
|
|
781 | Very inflexible. |
|
|
782 | |
|
|
783 | No roundtripping. |
|
|
784 | |
|
|
785 | Does not generate valid JSON texts (key strings are often unquoted, empty keys |
|
|
786 | result in nothing being output) |
|
|
787 | |
|
|
788 | Does not check input for validity. |
|
|
789 | |
1185 | |
790 | =back |
1186 | =back |
791 | |
1187 | |
792 | |
1188 | |
|
|
1189 | =head2 JSON and ECMAscript |
|
|
1190 | |
|
|
1191 | JSON syntax is based on how literals are represented in javascript (the |
|
|
1192 | not-standardised predecessor of ECMAscript) which is presumably why it is |
|
|
1193 | called "JavaScript Object Notation". |
|
|
1194 | |
|
|
1195 | However, JSON is not a subset (and also not a superset of course) of |
|
|
1196 | ECMAscript (the standard) or javascript (whatever browsers actually |
|
|
1197 | implement). |
|
|
1198 | |
|
|
1199 | If you want to use javascript's C<eval> function to "parse" JSON, you |
|
|
1200 | might run into parse errors for valid JSON texts, or the resulting data |
|
|
1201 | structure might not be queryable: |
|
|
1202 | |
|
|
1203 | One of the problems is that U+2028 and U+2029 are valid characters inside |
|
|
1204 | JSON strings, but are not allowed in ECMAscript string literals, so the |
|
|
1205 | following Perl fragment will not output something that can be guaranteed |
|
|
1206 | to be parsable by javascript's C<eval>: |
|
|
1207 | |
|
|
1208 | use JSON::XS; |
|
|
1209 | |
|
|
1210 | print encode_json [chr 0x2028]; |
|
|
1211 | |
|
|
1212 | The right fix for this is to use a proper JSON parser in your javascript |
|
|
1213 | programs, and not rely on C<eval> (see for example Douglas Crockford's |
|
|
1214 | F<json2.js> parser). |
|
|
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 | Note that this will enlarge the resulting JSON text quite a bit if you |
|
|
1224 | have many non-ASCII characters. You might be tempted to run some regexes |
|
|
1225 | to only escape U+2028 and U+2029, e.g.: |
|
|
1226 | |
|
|
1227 | # DO NOT USE THIS! |
|
|
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 | Note that I<this is a bad idea>: the above only works for U+2028 and |
|
|
1234 | U+2029 and thus only for fully ECMAscript-compliant parsers. Many existing |
|
|
1235 | javascript implementations, however, have issues with other characters as |
|
|
1236 | well - using C<eval> naively simply I<will> cause problems. |
|
|
1237 | |
|
|
1238 | Another problem is that some javascript implementations reserve |
|
|
1239 | some property names for their own purposes (which probably makes |
|
|
1240 | them non-ECMAscript-compliant). For example, Iceweasel reserves the |
|
|
1241 | C<__proto__> property name for its own purposes. |
|
|
1242 | |
|
|
1243 | If that is a problem, you could parse try to filter the resulting JSON |
|
|
1244 | output for these property strings, e.g.: |
|
|
1245 | |
|
|
1246 | $json =~ s/"__proto__"\s*:/"__proto__renamed":/g; |
|
|
1247 | |
|
|
1248 | This works because C<__proto__> is not valid outside of strings, so every |
|
|
1249 | occurrence of C<"__proto__"\s*:> must be a string used as property name. |
|
|
1250 | |
|
|
1251 | If you know of other incompatibilities, please let me know. |
|
|
1252 | |
|
|
1253 | |
793 | =head2 JSON and YAML |
1254 | =head2 JSON and YAML |
794 | |
1255 | |
795 | You often hear that JSON is a subset (or a close subset) of YAML. This is, |
1256 | You often hear that JSON is a subset of YAML. This is, however, a mass |
796 | however, a mass hysteria and very far from the truth. In general, there is |
1257 | hysteria(*) and very far from the truth (as of the time of this writing), |
797 | no way to configure JSON::XS to output a data structure as valid YAML. |
1258 | so let me state it clearly: I<in general, there is no way to configure |
|
|
1259 | JSON::XS to output a data structure as valid YAML> that works in all |
|
|
1260 | cases. |
798 | |
1261 | |
799 | If you really must use JSON::XS to generate YAML, you should use this |
1262 | If you really must use JSON::XS to generate YAML, you should use this |
800 | algorithm (subject to change in future versions): |
1263 | algorithm (subject to change in future versions): |
801 | |
1264 | |
802 | my $to_yaml = JSON::XS->new->utf8->space_after (1); |
1265 | my $to_yaml = JSON::XS->new->utf8->space_after (1); |
803 | my $yaml = $to_yaml->encode ($ref) . "\n"; |
1266 | my $yaml = $to_yaml->encode ($ref) . "\n"; |
804 | |
1267 | |
805 | This will usually generate JSON texts that also parse as valid |
1268 | This will I<usually> generate JSON texts that also parse as valid |
806 | YAML. Please note that YAML has hardcoded limits on (simple) object key |
1269 | YAML. Please note that YAML has hardcoded limits on (simple) object key |
807 | lengths that JSON doesn't have, so you should make sure that your hash |
1270 | lengths that JSON doesn't have and also has different and incompatible |
|
|
1271 | unicode character escape syntax, so you should make sure that your hash |
808 | keys are noticably shorter than the 1024 characters YAML allows. |
1272 | keys are noticeably shorter than the 1024 "stream characters" YAML allows |
|
|
1273 | and that you do not have characters with codepoint values outside the |
|
|
1274 | Unicode BMP (basic multilingual page). YAML also does not allow C<\/> |
|
|
1275 | sequences in strings (which JSON::XS does not I<currently> generate, but |
|
|
1276 | other JSON generators might). |
809 | |
1277 | |
810 | There might be other incompatibilities that I am not aware of. In general |
1278 | There might be other incompatibilities that I am not aware of (or the YAML |
|
|
1279 | specification has been changed yet again - it does so quite often). In |
811 | you should not try to generate YAML with a JSON generator or vice versa, |
1280 | general you should not try to generate YAML with a JSON generator or vice |
812 | or try to parse JSON with a YAML parser or vice versa: chances are high |
1281 | versa, or try to parse JSON with a YAML parser or vice versa: chances are |
813 | that you will run into severe interoperability problems. |
1282 | high that you will run into severe interoperability problems when you |
|
|
1283 | least expect it. |
|
|
1284 | |
|
|
1285 | =over 4 |
|
|
1286 | |
|
|
1287 | =item (*) |
|
|
1288 | |
|
|
1289 | I have been pressured multiple times by Brian Ingerson (one of the |
|
|
1290 | authors of the YAML specification) to remove this paragraph, despite him |
|
|
1291 | acknowledging that the actual incompatibilities exist. As I was personally |
|
|
1292 | bitten by this "JSON is YAML" lie, I refused and said I will continue to |
|
|
1293 | educate people about these issues, so others do not run into the same |
|
|
1294 | problem again and again. After this, Brian called me a (quote)I<complete |
|
|
1295 | and worthless idiot>(unquote). |
|
|
1296 | |
|
|
1297 | In my opinion, instead of pressuring and insulting people who actually |
|
|
1298 | clarify issues with YAML and the wrong statements of some of its |
|
|
1299 | proponents, I would kindly suggest reading the JSON spec (which is not |
|
|
1300 | that difficult or long) and finally make YAML compatible to it, and |
|
|
1301 | educating users about the changes, instead of spreading lies about the |
|
|
1302 | real compatibility for many I<years> and trying to silence people who |
|
|
1303 | point out that it isn't true. |
|
|
1304 | |
|
|
1305 | Addendum/2009: the YAML 1.2 spec is still incompatible with JSON, even |
|
|
1306 | though the incompatibilities have been documented (and are known to Brian) |
|
|
1307 | for many years and the spec makes explicit claims that YAML is a superset |
|
|
1308 | of JSON. It would be so easy to fix, but apparently, bullying people and |
|
|
1309 | corrupting userdata is so much easier. |
|
|
1310 | |
|
|
1311 | =back |
814 | |
1312 | |
815 | |
1313 | |
816 | =head2 SPEED |
1314 | =head2 SPEED |
817 | |
1315 | |
818 | It seems that JSON::XS is surprisingly fast, as shown in the following |
1316 | It seems that JSON::XS is surprisingly fast, as shown in the following |
819 | tables. They have been generated with the help of the C<eg/bench> program |
1317 | tables. They have been generated with the help of the C<eg/bench> program |
820 | in the JSON::XS distribution, to make it easy to compare on your own |
1318 | in the JSON::XS distribution, to make it easy to compare on your own |
821 | system. |
1319 | system. |
822 | |
1320 | |
823 | First comes a comparison between various modules using a very short |
1321 | First comes a comparison between various modules using |
824 | single-line JSON string: |
1322 | a very short single-line JSON string (also available at |
|
|
1323 | L<http://dist.schmorp.de/misc/json/short.json>). |
825 | |
1324 | |
826 | {"method": "handleMessage", "params": ["user1", "we were just talking"], \ |
1325 | {"method": "handleMessage", "params": ["user1", |
827 | "id": null, "array":[1,11,234,-5,1e5,1e7, true, false]} |
1326 | "we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7, |
|
|
1327 | 1, 0]} |
828 | |
1328 | |
829 | It shows the number of encodes/decodes per second (JSON::XS uses |
1329 | It shows the number of encodes/decodes per second (JSON::XS uses |
830 | the functional interface, while JSON::XS/2 uses the OO interface |
1330 | the functional interface, while JSON::XS/2 uses the OO interface |
831 | with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables |
1331 | with pretty-printing and hashkey sorting enabled, JSON::XS/3 enables |
832 | shrink). Higher is better: |
1332 | shrink. JSON::DWIW/DS uses the deserialise function, while JSON::DWIW::FJ |
|
|
1333 | uses the from_json method). Higher is better: |
833 | |
1334 | |
834 | Storable | 15779.925 | 14169.946 | |
|
|
835 | -----------+------------+------------+ |
|
|
836 | module | encode | decode | |
1335 | module | encode | decode | |
837 | -----------|------------|------------| |
1336 | --------------|------------|------------| |
838 | JSON | 4990.842 | 4088.813 | |
1337 | JSON::DWIW/DS | 86302.551 | 102300.098 | |
839 | JSON::DWIW | 51653.990 | 71575.154 | |
1338 | JSON::DWIW/FJ | 86302.551 | 75983.768 | |
840 | JSON::PC | 65948.176 | 74631.744 | |
1339 | JSON::PP | 15827.562 | 6638.658 | |
841 | JSON::PP | 8931.652 | 3817.168 | |
1340 | JSON::Syck | 63358.066 | 47662.545 | |
842 | JSON::Syck | 24877.248 | 27776.848 | |
1341 | JSON::XS | 511500.488 | 511500.488 | |
843 | JSON::XS | 388361.481 | 227951.304 | |
1342 | JSON::XS/2 | 291271.111 | 388361.481 | |
844 | JSON::XS/2 | 227951.304 | 218453.333 | |
1343 | JSON::XS/3 | 361577.931 | 361577.931 | |
845 | JSON::XS/3 | 338250.323 | 218453.333 | |
1344 | Storable | 66788.280 | 265462.278 | |
846 | Storable | 16500.016 | 135300.129 | |
|
|
847 | -----------+------------+------------+ |
1345 | --------------+------------+------------+ |
848 | |
1346 | |
849 | That is, JSON::XS is about five times faster than JSON::DWIW on encoding, |
1347 | That is, JSON::XS is almost six times faster than JSON::DWIW on encoding, |
850 | about three times faster on decoding, and over fourty times faster |
1348 | about five times faster on decoding, and over thirty to seventy times |
851 | than JSON, even with pretty-printing and key sorting. It also compares |
1349 | faster than JSON's pure perl implementation. It also compares favourably |
852 | favourably to Storable for small amounts of data. |
1350 | to Storable for small amounts of data. |
853 | |
1351 | |
854 | Using a longer test string (roughly 18KB, generated from Yahoo! Locals |
1352 | Using a longer test string (roughly 18KB, generated from Yahoo! Locals |
855 | search API (http://nanoref.com/yahooapis/mgPdGg): |
1353 | search API (L<http://dist.schmorp.de/misc/json/long.json>). |
856 | |
1354 | |
857 | module | encode | decode | |
1355 | module | encode | decode | |
858 | -----------|------------|------------| |
1356 | --------------|------------|------------| |
859 | JSON | 55.260 | 34.971 | |
1357 | JSON::DWIW/DS | 1647.927 | 2673.916 | |
860 | JSON::DWIW | 825.228 | 1082.513 | |
1358 | JSON::DWIW/FJ | 1630.249 | 2596.128 | |
861 | JSON::PC | 3571.444 | 2394.829 | |
|
|
862 | JSON::PP | 210.987 | 32.574 | |
1359 | JSON::PP | 400.640 | 62.311 | |
863 | JSON::Syck | 552.551 | 787.544 | |
1360 | JSON::Syck | 1481.040 | 1524.869 | |
864 | JSON::XS | 5780.463 | 4854.519 | |
1361 | JSON::XS | 20661.596 | 9541.183 | |
865 | JSON::XS/2 | 3869.998 | 4798.975 | |
1362 | JSON::XS/2 | 10683.403 | 9416.938 | |
866 | JSON::XS/3 | 5862.880 | 4798.975 | |
1363 | JSON::XS/3 | 20661.596 | 9400.054 | |
867 | Storable | 4445.002 | 5235.027 | |
1364 | Storable | 19765.806 | 10000.725 | |
868 | -----------+------------+------------+ |
1365 | --------------+------------+------------+ |
869 | |
1366 | |
870 | Again, JSON::XS leads by far (except for Storable which non-surprisingly |
1367 | Again, JSON::XS leads by far (except for Storable which non-surprisingly |
871 | decodes faster). |
1368 | decodes a bit faster). |
872 | |
1369 | |
873 | On large strings containing lots of high unicode characters, some modules |
1370 | On large strings containing lots of high Unicode characters, some modules |
874 | (such as JSON::PC) seem to decode faster than JSON::XS, but the result |
1371 | (such as JSON::PC) seem to decode faster than JSON::XS, but the result |
875 | will be broken due to missing (or wrong) unicode handling. Others refuse |
1372 | will be broken due to missing (or wrong) Unicode handling. Others refuse |
876 | to decode or encode properly, so it was impossible to prepare a fair |
1373 | to decode or encode properly, so it was impossible to prepare a fair |
877 | comparison table for that case. |
1374 | comparison table for that case. |
878 | |
1375 | |
879 | |
1376 | |
880 | =head1 SECURITY CONSIDERATIONS |
1377 | =head1 SECURITY CONSIDERATIONS |
… | |
… | |
886 | any buffer overflows. Obviously, this module should ensure that and I am |
1383 | any buffer overflows. Obviously, this module should ensure that and I am |
887 | trying hard on making that true, but you never know. |
1384 | trying hard on making that true, but you never know. |
888 | |
1385 | |
889 | Second, you need to avoid resource-starving attacks. That means you should |
1386 | Second, you need to avoid resource-starving attacks. That means you should |
890 | limit the size of JSON texts you accept, or make sure then when your |
1387 | limit the size of JSON texts you accept, or make sure then when your |
891 | resources run out, thats just fine (e.g. by using a separate process that |
1388 | resources run out, that's just fine (e.g. by using a separate process that |
892 | can crash safely). The size of a JSON text in octets or characters is |
1389 | can crash safely). The size of a JSON text in octets or characters is |
893 | usually a good indication of the size of the resources required to decode |
1390 | usually a good indication of the size of the resources required to decode |
894 | it into a Perl structure. While JSON::XS can check the size of the JSON |
1391 | it into a Perl structure. While JSON::XS can check the size of the JSON |
895 | text, it might be too late when you already have it in memory, so you |
1392 | text, it might be too late when you already have it in memory, so you |
896 | might want to check the size before you accept the string. |
1393 | might want to check the size before you accept the string. |
897 | |
1394 | |
898 | Third, JSON::XS recurses using the C stack when decoding objects and |
1395 | Third, JSON::XS recurses using the C stack when decoding objects and |
899 | arrays. The C stack is a limited resource: for instance, on my amd64 |
1396 | arrays. The C stack is a limited resource: for instance, on my amd64 |
900 | machine with 8MB of stack size I can decode around 180k nested arrays but |
1397 | machine with 8MB of stack size I can decode around 180k nested arrays but |
901 | only 14k nested JSON objects (due to perl itself recursing deeply on croak |
1398 | only 14k nested JSON objects (due to perl itself recursing deeply on croak |
902 | 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 |
903 | 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 |
904 | 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 |
905 | C<max_depth> method. |
1402 | C<max_depth> method. |
906 | |
1403 | |
907 | 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 |
908 | 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... |
909 | 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. |
910 | |
1411 | |
911 | If you are using JSON::XS to return packets to consumption |
1412 | If you are using JSON::XS to return packets to consumption |
912 | 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 |
913 | L<http://jpsykes.com/47/practical-csrf-and-json-security> to see wether |
1414 | L<http://blog.archive.jpsykes.com/47/practical-csrf-and-json-security/> to |
914 | you are vulnerable to some common attack vectors (which really are browser |
1415 | see whether you are vulnerable to some common attack vectors (which really |
915 | design bugs, but it is still you who will have to deal with it, as major |
1416 | are browser design bugs, but it is still you who will have to deal with |
916 | browser developers care only for features, not about doing security |
1417 | it, as major browser developers care only for features, not about getting |
917 | right). |
1418 | security right). |
|
|
1419 | |
|
|
1420 | |
|
|
1421 | =head1 THREADS |
|
|
1422 | |
|
|
1423 | This module is I<not> guaranteed to be thread safe and there are no |
|
|
1424 | plans to change this until Perl gets thread support (as opposed to the |
|
|
1425 | horribly slow so-called "threads" which are simply slow and bloated |
|
|
1426 | process simulations - use fork, it's I<much> faster, cheaper, better). |
|
|
1427 | |
|
|
1428 | (It might actually work, but you have been warned). |
|
|
1429 | |
|
|
1430 | |
|
|
1431 | =head1 THE PERILS OF SETLOCALE |
|
|
1432 | |
|
|
1433 | Sometimes people avoid the Perl locale support and directly call the |
|
|
1434 | system's setlocale function with C<LC_ALL>. |
|
|
1435 | |
|
|
1436 | This breaks both perl and modules such as JSON::XS, as stringification of |
|
|
1437 | numbers no longer works correctly (e.g. C<$x = 0.1; print "$x"+1> might |
|
|
1438 | print C<1>, and JSON::XS might output illegal JSON as JSON::XS relies on |
|
|
1439 | perl to stringify numbers). |
|
|
1440 | |
|
|
1441 | The solution is simple: don't call C<setlocale>, or use it for only those |
|
|
1442 | categories you need, such as C<LC_MESSAGES> or C<LC_CTYPE>. |
|
|
1443 | |
|
|
1444 | If you need C<LC_NUMERIC>, you should enable it only around the code that |
|
|
1445 | actually needs it (avoiding stringification of numbers), and restore it |
|
|
1446 | afterwards. |
918 | |
1447 | |
919 | |
1448 | |
920 | =head1 BUGS |
1449 | =head1 BUGS |
921 | |
1450 | |
922 | While the goal of this module is to be correct, that unfortunately does |
1451 | While the goal of this module is to be correct, that unfortunately does |
923 | not mean its bug-free, only that I think its design is bug-free. It is |
1452 | not mean it's bug-free, only that I think its design is bug-free. If you |
924 | still relatively early in its development. If you keep reporting bugs they |
1453 | keep reporting bugs they will be fixed swiftly, though. |
925 | will be fixed swiftly, though. |
1454 | |
|
|
1455 | Please refrain from using rt.cpan.org or any other bug reporting |
|
|
1456 | service. I put the contact address into my modules for a reason. |
926 | |
1457 | |
927 | =cut |
1458 | =cut |
928 | |
1459 | |
929 | our $true = do { bless \(my $dummy = 1), "JSON::XS::Boolean" }; |
1460 | our $true = do { bless \(my $dummy = 1), "JSON::XS::Boolean" }; |
930 | our $false = do { bless \(my $dummy = 0), "JSON::XS::Boolean" }; |
1461 | our $false = do { bless \(my $dummy = 0), "JSON::XS::Boolean" }; |
… | |
… | |
947 | "--" => sub { $_[0] = ${$_[0]} - 1 }, |
1478 | "--" => sub { $_[0] = ${$_[0]} - 1 }, |
948 | fallback => 1; |
1479 | fallback => 1; |
949 | |
1480 | |
950 | 1; |
1481 | 1; |
951 | |
1482 | |
|
|
1483 | =head1 SEE ALSO |
|
|
1484 | |
|
|
1485 | The F<json_xs> command line utility for quick experiments. |
|
|
1486 | |
952 | =head1 AUTHOR |
1487 | =head1 AUTHOR |
953 | |
1488 | |
954 | Marc Lehmann <schmorp@schmorp.de> |
1489 | Marc Lehmann <schmorp@schmorp.de> |
955 | http://home.schmorp.de/ |
1490 | http://home.schmorp.de/ |
956 | |
1491 | |