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3 | JSON::XS - JSON serialising/deserialising, done correctly and fast |
3 | JSON::XS - JSON serialising/deserialising, done correctly and fast |
4 | |
4 | |
5 | =head1 SYNOPSIS |
5 | =head1 SYNOPSIS |
6 | |
6 | |
7 | use JSON::XS; |
7 | use JSON::XS; |
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8 | |
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9 | # exported functions, they croak on error |
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10 | # and expect/generate UTF-8 |
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11 | |
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12 | $utf8_encoded_json_text = to_json $perl_hash_or_arrayref; |
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13 | $perl_hash_or_arrayref = from_json $utf8_encoded_json_text; |
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14 | |
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15 | # objToJson and jsonToObj aliases to to_json and from_json |
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16 | # are exported for compatibility to the JSON module, |
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17 | # but should not be used in new code. |
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18 | |
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19 | # OO-interface |
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20 | |
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21 | $coder = JSON::XS->new->ascii->pretty->allow_nonref; |
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22 | $pretty_printed_unencoded = $coder->encode ($perl_scalar); |
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23 | $perl_scalar = $coder->decode ($unicode_json_text); |
8 | |
24 | |
9 | =head1 DESCRIPTION |
25 | =head1 DESCRIPTION |
10 | |
26 | |
11 | This module converts Perl data structures to JSON and vice versa. Its |
27 | This module converts Perl data structures to JSON and vice versa. Its |
12 | primary goal is to be I<correct> and its secondary goal is to be |
28 | primary goal is to be I<correct> and its secondary goal is to be |
… | |
… | |
18 | their maintainers are unresponsive, gone missing, or not listening to bug |
34 | their maintainers are unresponsive, gone missing, or not listening to bug |
19 | reports for other reasons. |
35 | reports for other reasons. |
20 | |
36 | |
21 | See COMPARISON, below, for a comparison to some other JSON modules. |
37 | See COMPARISON, below, for a comparison to some other JSON modules. |
22 | |
38 | |
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39 | See MAPPING, below, on how JSON::XS maps perl values to JSON values and |
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40 | vice versa. |
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41 | |
23 | =head2 FEATURES |
42 | =head2 FEATURES |
24 | |
43 | |
25 | =over 4 |
44 | =over 4 |
26 | |
45 | |
27 | =item * correct handling of unicode issues |
46 | =item * correct unicode handling |
28 | |
47 | |
29 | This module knows how to handle Unicode, and even documents how it does so. |
48 | This module knows how to handle Unicode, and even documents how and when |
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49 | it does so. |
30 | |
50 | |
31 | =item * round-trip integrity |
51 | =item * round-trip integrity |
32 | |
52 | |
33 | When you serialise a perl data structure using only datatypes supported |
53 | When you serialise a perl data structure using only datatypes supported |
34 | by JSON, the deserialised data structure is identical on the Perl level. |
54 | by JSON, the deserialised data structure is identical on the Perl level. |
35 | (e.g. the string "2.0" doesn't suddenly become "2"). |
55 | (e.g. the string "2.0" doesn't suddenly become "2" just because it looks |
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56 | like a number). |
36 | |
57 | |
37 | =item * strict checking of JSON correctness |
58 | =item * strict checking of JSON correctness |
38 | |
59 | |
39 | There is no guessing, no generating of illegal JSON strings by default, |
60 | There is no guessing, no generating of illegal JSON texts by default, |
40 | and only JSON is accepted as input (the latter is a security feature). |
61 | and only JSON is accepted as input by default (the latter is a security |
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62 | feature). |
41 | |
63 | |
42 | =item * fast |
64 | =item * fast |
43 | |
65 | |
44 | compared to other JSON modules, this module compares favourably. |
66 | Compared to other JSON modules, this module compares favourably in terms |
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67 | of speed, too. |
45 | |
68 | |
46 | =item * simple to use |
69 | =item * simple to use |
47 | |
70 | |
48 | This module has both a simple functional interface as well as an OO |
71 | This module has both a simple functional interface as well as an OO |
49 | interface. |
72 | interface. |
50 | |
73 | |
51 | =item * reasonably versatile output formats |
74 | =item * reasonably versatile output formats |
52 | |
75 | |
53 | You can choose between the most compact format possible, a pure-ascii |
76 | You can choose between the most compact guarenteed single-line format |
54 | format, or a pretty-printed format. Or you can combine those features in |
77 | possible (nice for simple line-based protocols), a pure-ascii format |
55 | whatever way you like. |
78 | (for when your transport is not 8-bit clean, still supports the whole |
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79 | unicode range), or a pretty-printed format (for when you want to read that |
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80 | stuff). Or you can combine those features in whatever way you like. |
56 | |
81 | |
57 | =back |
82 | =back |
58 | |
83 | |
59 | =cut |
84 | =cut |
60 | |
85 | |
61 | package JSON::XS; |
86 | package JSON::XS; |
62 | |
87 | |
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88 | use strict; |
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89 | |
63 | BEGIN { |
90 | BEGIN { |
64 | $VERSION = '0.2'; |
91 | our $VERSION = '0.8'; |
65 | @ISA = qw(Exporter); |
92 | our @ISA = qw(Exporter); |
66 | |
93 | |
67 | @EXPORT = qw(to_json from_json); |
94 | our @EXPORT = qw(to_json from_json objToJson jsonToObj); |
68 | require Exporter; |
95 | require Exporter; |
69 | |
96 | |
70 | require XSLoader; |
97 | require XSLoader; |
71 | XSLoader::load JSON::XS::, $VERSION; |
98 | XSLoader::load JSON::XS::, $VERSION; |
72 | } |
99 | } |
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76 | The following convinience methods are provided by this module. They are |
103 | The following convinience methods are provided by this module. They are |
77 | exported by default: |
104 | exported by default: |
78 | |
105 | |
79 | =over 4 |
106 | =over 4 |
80 | |
107 | |
81 | =item $json_string = to_json $perl_scalar |
108 | =item $json_text = to_json $perl_scalar |
82 | |
109 | |
83 | Converts the given Perl data structure (a simple scalar or a reference to |
110 | Converts the given Perl data structure (a simple scalar or a reference to |
84 | a hash or array) to a UTF-8 encoded, binary string (that is, the string contains |
111 | a hash or array) to a UTF-8 encoded, binary string (that is, the string contains |
85 | octets only). Croaks on error. |
112 | octets only). Croaks on error. |
86 | |
113 | |
87 | This function call is functionally identical to C<< JSON::XS->new->utf8 |
114 | This function call is functionally identical to: |
88 | (1)->encode ($perl_scalar) >>. |
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89 | |
115 | |
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116 | $json_text = JSON::XS->new->utf8->encode ($perl_scalar) |
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117 | |
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118 | except being faster. |
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119 | |
90 | =item $perl_scalar = from_json $json_string |
120 | =item $perl_scalar = from_json $json_text |
91 | |
121 | |
92 | The opposite of C<to_json>: expects an UTF-8 (binary) string and tries to |
122 | The opposite of C<to_json>: expects an UTF-8 (binary) string and tries to |
93 | parse that as an UTF-8 encoded JSON string, returning the resulting simple |
123 | parse that as an UTF-8 encoded JSON text, returning the resulting simple |
94 | scalar or reference. Croaks on error. |
124 | scalar or reference. Croaks on error. |
95 | |
125 | |
96 | This function call is functionally identical to C<< JSON::XS->new->utf8 |
126 | This function call is functionally identical to: |
97 | (1)->decode ($json_string) >>. |
127 | |
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128 | $perl_scalar = JSON::XS->new->utf8->decode ($json_text) |
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129 | |
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130 | except being faster. |
98 | |
131 | |
99 | =back |
132 | =back |
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133 | |
100 | |
134 | |
101 | =head1 OBJECT-ORIENTED INTERFACE |
135 | =head1 OBJECT-ORIENTED INTERFACE |
102 | |
136 | |
103 | The object oriented interface lets you configure your own encoding or |
137 | The object oriented interface lets you configure your own encoding or |
104 | decoding style, within the limits of supported formats. |
138 | decoding style, within the limits of supported formats. |
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111 | strings. All boolean flags described below are by default I<disabled>. |
145 | strings. All boolean flags described below are by default I<disabled>. |
112 | |
146 | |
113 | The mutators for flags all return the JSON object again and thus calls can |
147 | The mutators for flags all return the JSON object again and thus calls can |
114 | be chained: |
148 | be chained: |
115 | |
149 | |
116 | my $json = JSON::XS->new->utf8(1)->space_after(1)->encode ({a => [1,2]}) |
150 | my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]}) |
117 | => {"a": [1, 2]} |
151 | => {"a": [1, 2]} |
118 | |
152 | |
119 | =item $json = $json->ascii ([$enable]) |
153 | =item $json = $json->ascii ([$enable]) |
120 | |
154 | |
121 | If C<$enable> is true (or missing), then the C<encode> method will |
155 | If C<$enable> is true (or missing), then the C<encode> method will not |
122 | not generate characters outside the code range C<0..127>. Any unicode |
156 | generate characters outside the code range C<0..127> (which is ASCII). Any |
123 | characters outside that range will be escaped using either a single |
157 | unicode characters outside that range will be escaped using either a |
124 | \uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence, as per |
158 | single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence, |
125 | RFC4627. |
159 | as per RFC4627. |
126 | |
160 | |
127 | If C<$enable> is false, then the C<encode> method will not escape Unicode |
161 | If C<$enable> is false, then the C<encode> method will not escape Unicode |
128 | characters unless necessary. |
162 | characters unless required by the JSON syntax. This results in a faster |
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163 | and more compact format. |
129 | |
164 | |
130 | JSON::XS->new->ascii (1)->encode (chr 0x10401) |
165 | JSON::XS->new->ascii (1)->encode ([chr 0x10401]) |
131 | => \ud801\udc01 |
166 | => ["\ud801\udc01"] |
132 | |
167 | |
133 | =item $json = $json->utf8 ([$enable]) |
168 | =item $json = $json->utf8 ([$enable]) |
134 | |
169 | |
135 | If C<$enable> is true (or missing), then the C<encode> method will encode |
170 | If C<$enable> is true (or missing), then the C<encode> method will encode |
136 | the JSON string into UTF-8, as required by many protocols, while the |
171 | the JSON result into UTF-8, as required by many protocols, while the |
137 | C<decode> method expects to be handled an UTF-8-encoded string. Please |
172 | C<decode> method expects to be handled an UTF-8-encoded string. Please |
138 | note that UTF-8-encoded strings do not contain any characters outside the |
173 | note that UTF-8-encoded strings do not contain any characters outside the |
139 | range C<0..255>, they are thus useful for bytewise/binary I/O. |
174 | range C<0..255>, they are thus useful for bytewise/binary I/O. In future |
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175 | versions, enabling this option might enable autodetection of the UTF-16 |
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176 | and UTF-32 encoding families, as described in RFC4627. |
140 | |
177 | |
141 | If C<$enable> is false, then the C<encode> method will return the JSON |
178 | If C<$enable> is false, then the C<encode> method will return the JSON |
142 | string as a (non-encoded) unicode string, while C<decode> expects thus a |
179 | string as a (non-encoded) unicode string, while C<decode> expects thus a |
143 | unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs |
180 | unicode string. Any decoding or encoding (e.g. to UTF-8 or UTF-16) needs |
144 | to be done yourself, e.g. using the Encode module. |
181 | to be done yourself, e.g. using the Encode module. |
145 | |
182 | |
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183 | Example, output UTF-16BE-encoded JSON: |
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184 | |
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185 | use Encode; |
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186 | $jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object); |
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187 | |
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188 | Example, decode UTF-32LE-encoded JSON: |
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189 | |
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190 | use Encode; |
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191 | $object = JSON::XS->new->decode (decode "UTF-32LE", $jsontext); |
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192 | |
146 | =item $json = $json->pretty ([$enable]) |
193 | =item $json = $json->pretty ([$enable]) |
147 | |
194 | |
148 | This enables (or disables) all of the C<indent>, C<space_before> and |
195 | This enables (or disables) all of the C<indent>, C<space_before> and |
149 | C<space_after> (and in the future possibly more) flags in one call to |
196 | C<space_after> (and in the future possibly more) flags in one call to |
150 | generate the most readable (or most compact) form possible. |
197 | generate the most readable (or most compact) form possible. |
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198 | |
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199 | Example, pretty-print some simple structure: |
151 | |
200 | |
152 | my $json = JSON::XS->new->pretty(1)->encode ({a => [1,2]}) |
201 | my $json = JSON::XS->new->pretty(1)->encode ({a => [1,2]}) |
153 | => |
202 | => |
154 | { |
203 | { |
155 | "a" : [ |
204 | "a" : [ |
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163 | If C<$enable> is true (or missing), then the C<encode> method will use a multiline |
212 | If C<$enable> is true (or missing), then the C<encode> method will use a multiline |
164 | format as output, putting every array member or object/hash key-value pair |
213 | format as output, putting every array member or object/hash key-value pair |
165 | into its own line, identing them properly. |
214 | into its own line, identing them properly. |
166 | |
215 | |
167 | If C<$enable> is false, no newlines or indenting will be produced, and the |
216 | If C<$enable> is false, no newlines or indenting will be produced, and the |
168 | resulting JSON strings is guarenteed not to contain any C<newlines>. |
217 | resulting JSON text is guarenteed not to contain any C<newlines>. |
169 | |
218 | |
170 | This setting has no effect when decoding JSON strings. |
219 | This setting has no effect when decoding JSON texts. |
171 | |
220 | |
172 | =item $json = $json->space_before ([$enable]) |
221 | =item $json = $json->space_before ([$enable]) |
173 | |
222 | |
174 | If C<$enable> is true (or missing), then the C<encode> method will add an extra |
223 | If C<$enable> is true (or missing), then the C<encode> method will add an extra |
175 | optional space before the C<:> separating keys from values in JSON objects. |
224 | optional space before the C<:> separating keys from values in JSON objects. |
176 | |
225 | |
177 | If C<$enable> is false, then the C<encode> method will not add any extra |
226 | If C<$enable> is false, then the C<encode> method will not add any extra |
178 | space at those places. |
227 | space at those places. |
179 | |
228 | |
180 | This setting has no effect when decoding JSON strings. You will also most |
229 | This setting has no effect when decoding JSON texts. You will also |
181 | likely combine this setting with C<space_after>. |
230 | most likely combine this setting with C<space_after>. |
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231 | |
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232 | Example, space_before enabled, space_after and indent disabled: |
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233 | |
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234 | {"key" :"value"} |
182 | |
235 | |
183 | =item $json = $json->space_after ([$enable]) |
236 | =item $json = $json->space_after ([$enable]) |
184 | |
237 | |
185 | If C<$enable> is true (or missing), then the C<encode> method will add an extra |
238 | If C<$enable> is true (or missing), then the C<encode> method will add an extra |
186 | optional space after the C<:> separating keys from values in JSON objects |
239 | optional space after the C<:> separating keys from values in JSON objects |
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188 | members. |
241 | members. |
189 | |
242 | |
190 | If C<$enable> is false, then the C<encode> method will not add any extra |
243 | If C<$enable> is false, then the C<encode> method will not add any extra |
191 | space at those places. |
244 | space at those places. |
192 | |
245 | |
193 | This setting has no effect when decoding JSON strings. |
246 | This setting has no effect when decoding JSON texts. |
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247 | |
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248 | Example, space_before and indent disabled, space_after enabled: |
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249 | |
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250 | {"key": "value"} |
194 | |
251 | |
195 | =item $json = $json->canonical ([$enable]) |
252 | =item $json = $json->canonical ([$enable]) |
196 | |
253 | |
197 | If C<$enable> is true (or missing), then the C<encode> method will output JSON objects |
254 | If C<$enable> is true (or missing), then the C<encode> method will output JSON objects |
198 | by sorting their keys. This is adding a comparatively high overhead. |
255 | by sorting their keys. This is adding a comparatively high overhead. |
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200 | If C<$enable> is false, then the C<encode> method will output key-value |
257 | If C<$enable> is false, then the C<encode> method will output key-value |
201 | pairs in the order Perl stores them (which will likely change between runs |
258 | pairs in the order Perl stores them (which will likely change between runs |
202 | of the same script). |
259 | of the same script). |
203 | |
260 | |
204 | This option is useful if you want the same data structure to be encoded as |
261 | This option is useful if you want the same data structure to be encoded as |
205 | the same JSON string (given the same overall settings). If it is disabled, |
262 | the same JSON text (given the same overall settings). If it is disabled, |
206 | the same hash migh be encoded differently even if contains the same data, |
263 | the same hash migh be encoded differently even if contains the same data, |
207 | as key-value pairs have no inherent ordering in Perl. |
264 | as key-value pairs have no inherent ordering in Perl. |
208 | |
265 | |
209 | This setting has no effect when decoding JSON strings. |
266 | This setting has no effect when decoding JSON texts. |
210 | |
267 | |
211 | =item $json = $json->allow_nonref ([$enable]) |
268 | =item $json = $json->allow_nonref ([$enable]) |
212 | |
269 | |
213 | If C<$enable> is true (or missing), then the C<encode> method can convert a |
270 | If C<$enable> is true (or missing), then the C<encode> method can convert a |
214 | non-reference into its corresponding string, number or null JSON value, |
271 | non-reference into its corresponding string, number or null JSON value, |
215 | which is an extension to RFC4627. Likewise, C<decode> will accept those JSON |
272 | which is an extension to RFC4627. Likewise, C<decode> will accept those JSON |
216 | values instead of croaking. |
273 | values instead of croaking. |
217 | |
274 | |
218 | If C<$enable> is false, then the C<encode> method will croak if it isn't |
275 | If C<$enable> is false, then the C<encode> method will croak if it isn't |
219 | passed an arrayref or hashref, as JSON strings must either be an object |
276 | passed an arrayref or hashref, as JSON texts must either be an object |
220 | or array. Likewise, C<decode> will croak if given something that is not a |
277 | or array. Likewise, C<decode> will croak if given something that is not a |
221 | JSON object or array. |
278 | JSON object or array. |
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279 | |
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280 | Example, encode a Perl scalar as JSON value with enabled C<allow_nonref>, |
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281 | resulting in an invalid JSON text: |
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282 | |
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283 | JSON::XS->new->allow_nonref->encode ("Hello, World!") |
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284 | => "Hello, World!" |
222 | |
285 | |
223 | =item $json = $json->shrink ([$enable]) |
286 | =item $json = $json->shrink ([$enable]) |
224 | |
287 | |
225 | Perl usually over-allocates memory a bit when allocating space for |
288 | Perl usually over-allocates memory a bit when allocating space for |
226 | strings. This flag optionally resizes strings generated by either |
289 | strings. This flag optionally resizes strings generated by either |
227 | C<encode> or C<decode> to their minimum size possible. This can save |
290 | C<encode> or C<decode> to their minimum size possible. This can save |
228 | memory when your JSON strings are either very very long or you have many |
291 | memory when your JSON texts are either very very long or you have many |
229 | short strings. It will also try to downgrade any strings to octet-form |
292 | short strings. It will also try to downgrade any strings to octet-form |
230 | if possible: perl stores strings internally either in an encoding called |
293 | if possible: perl stores strings internally either in an encoding called |
231 | UTF-X or in octet-form. The latter cannot store everything but uses less |
294 | UTF-X or in octet-form. The latter cannot store everything but uses less |
232 | space in general. |
295 | space in general. |
233 | |
296 | |
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239 | |
302 | |
240 | In the future, this setting might control other things, such as converting |
303 | In the future, this setting might control other things, such as converting |
241 | strings that look like integers or floats into integers or floats |
304 | strings that look like integers or floats into integers or floats |
242 | internally (there is no difference on the Perl level), saving space. |
305 | internally (there is no difference on the Perl level), saving space. |
243 | |
306 | |
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307 | =item $json = $json->max_depth ([$maximum_nesting_depth]) |
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308 | |
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309 | Sets the maximum nesting level (default C<8192>) accepted while encoding |
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310 | or decoding. If the JSON text or Perl data structure has an equal or |
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311 | higher nesting level then this limit, then the encoder and decoder will |
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312 | stop and croak at that point. |
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313 | |
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314 | Nesting level is defined by number of hash- or arrayrefs that the encoder |
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315 | needs to traverse to reach a given point or the number of C<{> or C<[> |
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316 | characters without their matching closing parenthesis crossed to reach a |
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317 | given character in a string. |
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318 | |
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319 | Setting the maximum depth to one disallows any nesting, so that ensures |
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320 | that the object is only a single hash/object or array. |
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321 | |
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322 | The argument to C<max_depth> will be rounded up to the next nearest power |
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323 | of two. |
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324 | |
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325 | See SECURITY CONSIDERATIONS, below, for more info on why this is useful. |
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326 | |
244 | =item $json_string = $json->encode ($perl_scalar) |
327 | =item $json_text = $json->encode ($perl_scalar) |
245 | |
328 | |
246 | Converts the given Perl data structure (a simple scalar or a reference |
329 | Converts the given Perl data structure (a simple scalar or a reference |
247 | to a hash or array) to its JSON representation. Simple scalars will be |
330 | to a hash or array) to its JSON representation. Simple scalars will be |
248 | converted into JSON string or number sequences, while references to arrays |
331 | converted into JSON string or number sequences, while references to arrays |
249 | become JSON arrays and references to hashes become JSON objects. Undefined |
332 | become JSON arrays and references to hashes become JSON objects. Undefined |
250 | Perl values (e.g. C<undef>) become JSON C<null> values. Neither C<true> |
333 | Perl values (e.g. C<undef>) become JSON C<null> values. Neither C<true> |
251 | nor C<false> values will be generated. |
334 | nor C<false> values will be generated. |
252 | |
335 | |
253 | =item $perl_scalar = $json->decode ($json_string) |
336 | =item $perl_scalar = $json->decode ($json_text) |
254 | |
337 | |
255 | The opposite of C<encode>: expects a JSON string and tries to parse it, |
338 | The opposite of C<encode>: expects a JSON text and tries to parse it, |
256 | returning the resulting simple scalar or reference. Croaks on error. |
339 | returning the resulting simple scalar or reference. Croaks on error. |
257 | |
340 | |
258 | JSON numbers and strings become simple Perl scalars. JSON arrays become |
341 | JSON numbers and strings become simple Perl scalars. JSON arrays become |
259 | Perl arrayrefs and JSON objects become Perl hashrefs. C<true> becomes |
342 | Perl arrayrefs and JSON objects become Perl hashrefs. C<true> becomes |
260 | C<1>, C<false> becomes C<0> and C<null> becomes C<undef>. |
343 | C<1>, C<false> becomes C<0> and C<null> becomes C<undef>. |
261 | |
344 | |
262 | =back |
345 | =back |
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346 | |
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347 | |
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348 | =head1 MAPPING |
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349 | |
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350 | This section describes how JSON::XS maps Perl values to JSON values and |
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351 | vice versa. These mappings are designed to "do the right thing" in most |
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352 | circumstances automatically, preserving round-tripping characteristics |
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353 | (what you put in comes out as something equivalent). |
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354 | |
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355 | For the more enlightened: note that in the following descriptions, |
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356 | lowercase I<perl> refers to the Perl interpreter, while uppcercase I<Perl> |
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357 | refers to the abstract Perl language itself. |
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358 | |
|
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359 | =head2 JSON -> PERL |
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360 | |
|
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361 | =over 4 |
|
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362 | |
|
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363 | =item object |
|
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364 | |
|
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365 | A JSON object becomes a reference to a hash in Perl. No ordering of object |
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366 | keys is preserved (JSON does not preserver object key ordering itself). |
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367 | |
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368 | =item array |
|
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369 | |
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370 | A JSON array becomes a reference to an array in Perl. |
|
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371 | |
|
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372 | =item string |
|
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373 | |
|
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374 | A JSON string becomes a string scalar in Perl - Unicode codepoints in JSON |
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375 | are represented by the same codepoints in the Perl string, so no manual |
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376 | decoding is necessary. |
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377 | |
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378 | =item number |
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379 | |
|
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380 | A JSON number becomes either an integer or numeric (floating point) |
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381 | scalar in perl, depending on its range and any fractional parts. On the |
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382 | Perl level, there is no difference between those as Perl handles all the |
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383 | conversion details, but an integer may take slightly less memory and might |
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384 | represent more values exactly than (floating point) numbers. |
|
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385 | |
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386 | =item true, false |
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387 | |
|
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388 | These JSON atoms become C<0>, C<1>, respectively. Information is lost in |
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389 | this process. Future versions might represent those values differently, |
|
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390 | but they will be guarenteed to act like these integers would normally in |
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391 | Perl. |
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392 | |
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393 | =item null |
|
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394 | |
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395 | A JSON null atom becomes C<undef> in Perl. |
|
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396 | |
|
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397 | =back |
|
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398 | |
|
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399 | =head2 PERL -> JSON |
|
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400 | |
|
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401 | The mapping from Perl to JSON is slightly more difficult, as Perl is a |
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402 | truly typeless language, so we can only guess which JSON type is meant by |
|
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403 | a Perl value. |
|
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404 | |
|
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405 | =over 4 |
|
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406 | |
|
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407 | =item hash references |
|
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408 | |
|
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409 | Perl hash references become JSON objects. As there is no inherent ordering |
|
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410 | in hash keys, they will usually be encoded in a pseudo-random order that |
|
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411 | can change between runs of the same program but stays generally the same |
|
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412 | within a single run of a program. JSON::XS can optionally sort the hash |
|
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413 | keys (determined by the I<canonical> flag), so the same datastructure |
|
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414 | will serialise to the same JSON text (given same settings and version of |
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415 | JSON::XS), but this incurs a runtime overhead. |
|
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416 | |
|
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417 | =item array references |
|
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418 | |
|
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419 | Perl array references become JSON arrays. |
|
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420 | |
|
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421 | =item blessed objects |
|
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422 | |
|
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423 | Blessed objects are not allowed. JSON::XS currently tries to encode their |
|
|
424 | underlying representation (hash- or arrayref), but this behaviour might |
|
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425 | change in future versions. |
|
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426 | |
|
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427 | =item simple scalars |
|
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428 | |
|
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429 | Simple Perl scalars (any scalar that is not a reference) are the most |
|
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430 | difficult objects to encode: JSON::XS will encode undefined scalars as |
|
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431 | JSON null value, scalars that have last been used in a string context |
|
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432 | before encoding as JSON strings and anything else as number value: |
|
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433 | |
|
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434 | # dump as number |
|
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435 | to_json [2] # yields [2] |
|
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436 | to_json [-3.0e17] # yields [-3e+17] |
|
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437 | my $value = 5; to_json [$value] # yields [5] |
|
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438 | |
|
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439 | # used as string, so dump as string |
|
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440 | print $value; |
|
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441 | to_json [$value] # yields ["5"] |
|
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442 | |
|
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443 | # undef becomes null |
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444 | to_json [undef] # yields [null] |
|
|
445 | |
|
|
446 | You can force the type to be a string by stringifying it: |
|
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447 | |
|
|
448 | my $x = 3.1; # some variable containing a number |
|
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449 | "$x"; # stringified |
|
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450 | $x .= ""; # another, more awkward way to stringify |
|
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451 | print $x; # perl does it for you, too, quite often |
|
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452 | |
|
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453 | You can force the type to be a number by numifying it: |
|
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454 | |
|
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455 | my $x = "3"; # some variable containing a string |
|
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456 | $x += 0; # numify it, ensuring it will be dumped as a number |
|
|
457 | $x *= 1; # same thing, the choise is yours. |
|
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458 | |
|
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459 | You can not currently output JSON booleans or force the type in other, |
|
|
460 | less obscure, ways. Tell me if you need this capability. |
|
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461 | |
|
|
462 | =item circular data structures |
|
|
463 | |
|
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464 | Those will be encoded until memory or stackspace runs out. |
|
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465 | |
|
|
466 | =back |
|
|
467 | |
263 | |
468 | |
264 | =head1 COMPARISON |
469 | =head1 COMPARISON |
265 | |
470 | |
266 | As already mentioned, this module was created because none of the existing |
471 | As already mentioned, this module was created because none of the existing |
267 | JSON modules could be made to work correctly. First I will describe the |
472 | JSON modules could be made to work correctly. First I will describe the |
… | |
… | |
293 | |
498 | |
294 | Has problems handling many Perl values (e.g. regex results and other magic |
499 | Has problems handling many Perl values (e.g. regex results and other magic |
295 | values will make it croak). |
500 | values will make it croak). |
296 | |
501 | |
297 | Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}> |
502 | Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}> |
298 | which is not a valid JSON string. |
503 | which is not a valid JSON text. |
299 | |
504 | |
300 | Unmaintained (maintainer unresponsive for many months, bugs are not |
505 | Unmaintained (maintainer unresponsive for many months, bugs are not |
301 | getting fixed). |
506 | getting fixed). |
302 | |
507 | |
303 | =item JSON::Syck 0.21 |
508 | =item JSON::Syck 0.21 |
… | |
… | |
305 | Very buggy (often crashes). |
510 | Very buggy (often crashes). |
306 | |
511 | |
307 | Very inflexible (no human-readable format supported, format pretty much |
512 | Very inflexible (no human-readable format supported, format pretty much |
308 | undocumented. I need at least a format for easy reading by humans and a |
513 | undocumented. I need at least a format for easy reading by humans and a |
309 | single-line compact format for use in a protocol, and preferably a way to |
514 | single-line compact format for use in a protocol, and preferably a way to |
310 | generate ASCII-only JSON strings). |
515 | generate ASCII-only JSON texts). |
311 | |
516 | |
312 | Completely broken (and confusingly documented) Unicode handling (unicode |
517 | Completely broken (and confusingly documented) Unicode handling (unicode |
313 | escapes are not working properly, you need to set ImplicitUnicode to |
518 | escapes are not working properly, you need to set ImplicitUnicode to |
314 | I<different> values on en- and decoding to get symmetric behaviour). |
519 | I<different> values on en- and decoding to get symmetric behaviour). |
315 | |
520 | |
… | |
… | |
338 | |
543 | |
339 | Very inflexible. |
544 | Very inflexible. |
340 | |
545 | |
341 | No roundtripping. |
546 | No roundtripping. |
342 | |
547 | |
343 | Does not generate valid JSON (key strings are often unquoted, empty keys |
548 | Does not generate valid JSON texts (key strings are often unquoted, empty keys |
344 | result in nothing being output) |
549 | result in nothing being output) |
345 | |
550 | |
346 | Does not check input for validity. |
551 | Does not check input for validity. |
347 | |
552 | |
348 | =back |
553 | =back |
… | |
… | |
352 | It seems that JSON::XS is surprisingly fast, as shown in the following |
557 | It seems that JSON::XS is surprisingly fast, as shown in the following |
353 | tables. They have been generated with the help of the C<eg/bench> program |
558 | tables. They have been generated with the help of the C<eg/bench> program |
354 | in the JSON::XS distribution, to make it easy to compare on your own |
559 | in the JSON::XS distribution, to make it easy to compare on your own |
355 | system. |
560 | system. |
356 | |
561 | |
357 | First is a comparison between various modules using a very simple JSON |
562 | First comes a comparison between various modules using a very short JSON |
|
|
563 | string: |
|
|
564 | |
|
|
565 | {"method": "handleMessage", "params": ["user1", "we were just talking"], "id": null} |
|
|
566 | |
358 | string, showing the number of encodes/decodes per second (JSON::XS is |
567 | It shows the number of encodes/decodes per second (JSON::XS uses the |
359 | the functional interface, while JSON::XS/2 is the OO interface with |
568 | functional interface, while JSON::XS/2 uses the OO interface with |
360 | pretty-printing and hashkey sorting enabled). |
569 | pretty-printing and hashkey sorting enabled). Higher is better: |
361 | |
570 | |
362 | module | encode | decode | |
571 | module | encode | decode | |
363 | -----------|------------|------------| |
572 | -----------|------------|------------| |
364 | JSON | 14006 | 6820 | |
573 | JSON | 11488.516 | 7823.035 | |
365 | JSON::DWIW | 200937 | 120386 | |
574 | JSON::DWIW | 94708.054 | 129094.260 | |
366 | JSON::PC | 85065 | 129366 | |
575 | JSON::PC | 63884.157 | 128528.212 | |
367 | JSON::Syck | 59898 | 44232 | |
576 | JSON::Syck | 34898.677 | 42096.911 | |
368 | JSON::XS | 1171478 | 342435 | |
577 | JSON::XS | 654027.064 | 396423.669 | |
369 | JSON::XS/2 | 730760 | 328714 | |
578 | JSON::XS/2 | 371564.190 | 371725.613 | |
370 | -----------+------------+------------+ |
579 | -----------+------------+------------+ |
371 | |
580 | |
372 | That is, JSON::XS is 6 times faster than than JSON::DWIW and about 80 |
581 | That is, JSON::XS is more than six times faster than JSON::DWIW on |
|
|
582 | encoding, more than three times faster on decoding, and about thirty times |
373 | times faster than JSON, even with pretty-printing and key sorting. |
583 | faster than JSON, even with pretty-printing and key sorting. |
374 | |
584 | |
375 | Using a longer test string (roughly 8KB, generated from Yahoo! Locals |
585 | Using a longer test string (roughly 18KB, generated from Yahoo! Locals |
376 | search API (http://nanoref.com/yahooapis/mgPdGg): |
586 | search API (http://nanoref.com/yahooapis/mgPdGg): |
377 | |
587 | |
378 | module | encode | decode | |
588 | module | encode | decode | |
379 | -----------|------------|------------| |
589 | -----------|------------|------------| |
380 | JSON | 673 | 38 | |
590 | JSON | 273.023 | 44.674 | |
381 | JSON::DWIW | 5271 | 770 | |
591 | JSON::DWIW | 1089.383 | 1145.704 | |
382 | JSON::PC | 9901 | 2491 | |
592 | JSON::PC | 3097.419 | 2393.921 | |
383 | JSON::Syck | 2360 | 786 | |
593 | JSON::Syck | 514.060 | 843.053 | |
384 | JSON::XS | 37398 | 3202 | |
594 | JSON::XS | 6479.668 | 3636.364 | |
385 | JSON::XS/2 | 13765 | 3153 | |
595 | JSON::XS/2 | 3774.221 | 3599.124 | |
386 | -----------+------------+------------+ |
596 | -----------+------------+------------+ |
387 | |
597 | |
388 | Again, JSON::XS leads by far in the encoding case, while still beating |
598 | Again, JSON::XS leads by far. |
389 | every other module in the decoding case. |
|
|
390 | |
599 | |
391 | Last example is an almost 8MB large hash with many large binary values |
600 | On large strings containing lots of high unicode characters, some modules |
392 | (PNG files), resulting in a lot of escaping: |
601 | (such as JSON::PC) seem to decode faster than JSON::XS, but the result |
|
|
602 | will be broken due to missing (or wrong) unicode handling. Others refuse |
|
|
603 | to decode or encode properly, so it was impossible to prepare a fair |
|
|
604 | comparison table for that case. |
|
|
605 | |
|
|
606 | |
|
|
607 | =head1 SECURITY CONSIDERATIONS |
|
|
608 | |
|
|
609 | When you are using JSON in a protocol, talking to untrusted potentially |
|
|
610 | hostile creatures requires relatively few measures. |
|
|
611 | |
|
|
612 | First of all, your JSON decoder should be secure, that is, should not have |
|
|
613 | any buffer overflows. Obviously, this module should ensure that and I am |
|
|
614 | trying hard on making that true, but you never know. |
|
|
615 | |
|
|
616 | Second, you need to avoid resource-starving attacks. That means you should |
|
|
617 | limit the size of JSON texts you accept, or make sure then when your |
|
|
618 | resources run out, thats just fine (e.g. by using a separate process that |
|
|
619 | can crash safely). The size of a JSON text in octets or characters is |
|
|
620 | usually a good indication of the size of the resources required to decode |
|
|
621 | it into a Perl structure. |
|
|
622 | |
|
|
623 | Third, JSON::XS recurses using the C stack when decoding objects and |
|
|
624 | arrays. The C stack is a limited resource: for instance, on my amd64 |
|
|
625 | machine with 8MB of stack size I can decode around 180k nested arrays |
|
|
626 | but only 14k nested JSON objects. If that is exceeded, the program |
|
|
627 | crashes. Thats why the default nesting limit is set to 8192. If your |
|
|
628 | process has a smaller stack, you should adjust this setting accordingly |
|
|
629 | with the C<max_depth> method. |
|
|
630 | |
|
|
631 | And last but least, something else could bomb you that I forgot to think |
|
|
632 | of. In that case, you get to keep the pieces. I am alway sopen for hints, |
|
|
633 | though... |
|
|
634 | |
393 | |
635 | |
394 | =head1 BUGS |
636 | =head1 BUGS |
395 | |
637 | |
396 | While the goal of this module is to be correct, that unfortunately does |
638 | While the goal of this module is to be correct, that unfortunately does |
397 | not mean its bug-free, only that I think its design is bug-free. It is |
639 | not mean its bug-free, only that I think its design is bug-free. It is |
398 | still very young and not well-tested. If you keep reporting bugs they will |
640 | still relatively early in its development. If you keep reporting bugs they |
399 | be fixed swiftly, though. |
641 | will be fixed swiftly, though. |
400 | |
642 | |
401 | =cut |
643 | =cut |
402 | |
644 | |
403 | 1; |
645 | 1; |
404 | |
646 | |