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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 |
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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 = '0.1'; |
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<$enable> is true, then the C<encode> method will not generate |
155 | If C<$enable> is true (or missing), then the C<encode> method will not |
122 | characters outside the code range C<0..127>. Any unicode characters |
156 | generate characters outside the code range C<0..127> (which is ASCII). Any |
123 | outside that range will be escaped using either a single \uXXXX (BMP |
157 | unicode characters outside that range will be escaped using either a |
124 | characters) or a double \uHHHH\uLLLLL escape sequence, as per RFC4627. |
158 | single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL escape sequence, |
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159 | as per RFC4627. |
125 | |
160 | |
126 | 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 |
127 | 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. |
128 | |
164 | |
129 | JSON::XS->new->ascii (1)->encode (chr 0x10401) |
165 | JSON::XS->new->ascii (1)->encode ([chr 0x10401]) |
130 | => \ud801\udc01 |
166 | => ["\ud801\udc01"] |
131 | |
167 | |
132 | =item $json = $json->utf8 ($enable) |
168 | =item $json = $json->utf8 ([$enable]) |
133 | |
169 | |
134 | If C<$enable> is true, then the C<encode> method will encode the JSON |
170 | If C<$enable> is true (or missing), then the C<encode> method will encode |
135 | string into UTF-8, as required by many protocols, while the C<decode> |
171 | the JSON result into UTF-8, as required by many protocols, while the |
136 | method expects to be handled an UTF-8-encoded string. Please note that |
172 | C<decode> method expects to be handled an UTF-8-encoded string. Please |
137 | UTF-8-encoded strings do not contain any characters outside the range |
173 | note that UTF-8-encoded strings do not contain any characters outside the |
138 | 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. |
139 | |
177 | |
140 | 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 |
141 | 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 |
142 | 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 |
143 | to be done yourself, e.g. using the Encode module. |
181 | to be done yourself, e.g. using the Encode module. |
144 | |
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 | |
145 | =item $json = $json->pretty ($enable) |
193 | =item $json = $json->pretty ([$enable]) |
146 | |
194 | |
147 | 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 |
148 | 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 |
149 | 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: |
150 | |
200 | |
151 | my $json = JSON::XS->new->pretty(1)->encode ({a => [1,2]}) |
201 | my $json = JSON::XS->new->pretty(1)->encode ({a => [1,2]}) |
152 | => |
202 | => |
153 | { |
203 | { |
154 | "a" : [ |
204 | "a" : [ |
155 | 1, |
205 | 1, |
156 | 2 |
206 | 2 |
157 | ] |
207 | ] |
158 | } |
208 | } |
159 | |
209 | |
160 | =item $json = $json->indent ($enable) |
210 | =item $json = $json->indent ([$enable]) |
161 | |
211 | |
162 | If C<$enable> is true, then the C<encode> method will use a multiline |
212 | If C<$enable> is true (or missing), then the C<encode> method will use a multiline |
163 | 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 |
164 | into its own line, identing them properly. |
214 | into its own line, identing them properly. |
165 | |
215 | |
166 | 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 |
167 | resulting JSON strings is guarenteed not to contain any C<newlines>. |
217 | resulting JSON text is guarenteed not to contain any C<newlines>. |
168 | |
218 | |
169 | This setting has no effect when decoding JSON strings. |
219 | This setting has no effect when decoding JSON texts. |
170 | |
220 | |
171 | =item $json = $json->space_before ($enable) |
221 | =item $json = $json->space_before ([$enable]) |
172 | |
222 | |
173 | If C<$enable> is true, then the C<encode> method will add an extra |
223 | If C<$enable> is true (or missing), then the C<encode> method will add an extra |
174 | 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. |
175 | |
225 | |
176 | 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 |
177 | space at those places. |
227 | space at those places. |
178 | |
228 | |
179 | 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 |
180 | likely combine this setting with C<space_after>. |
230 | most likely combine this setting with C<space_after>. |
181 | |
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"} |
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235 | |
182 | =item $json = $json->space_after ($enable) |
236 | =item $json = $json->space_after ([$enable]) |
183 | |
237 | |
184 | If C<$enable> is true, then the C<encode> method will add an extra |
238 | If C<$enable> is true (or missing), then the C<encode> method will add an extra |
185 | 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 |
186 | and extra whitespace after the C<,> separating key-value pairs and array |
240 | and extra whitespace after the C<,> separating key-value pairs and array |
187 | members. |
241 | members. |
188 | |
242 | |
189 | 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 |
190 | space at those places. |
244 | space at those places. |
191 | |
245 | |
192 | This setting has no effect when decoding JSON strings. |
246 | This setting has no effect when decoding JSON texts. |
193 | |
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"} |
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251 | |
194 | =item $json = $json->canonical ($enable) |
252 | =item $json = $json->canonical ([$enable]) |
195 | |
253 | |
196 | If C<$enable> is true, then the C<encode> method will output JSON objects |
254 | If C<$enable> is true (or missing), then the C<encode> method will output JSON objects |
197 | by sorting their keys. This is adding a comparatively high overhead. |
255 | by sorting their keys. This is adding a comparatively high overhead. |
198 | |
256 | |
199 | 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 |
200 | 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 |
201 | of the same script). |
259 | of the same script). |
202 | |
260 | |
203 | 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 |
204 | 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, |
205 | 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, |
206 | as key-value pairs have no inherent ordering in Perl. |
264 | as key-value pairs have no inherent ordering in Perl. |
207 | |
265 | |
208 | This setting has no effect when decoding JSON strings. |
266 | This setting has no effect when decoding JSON texts. |
209 | |
267 | |
210 | =item $json = $json->allow_nonref ($enable) |
268 | =item $json = $json->allow_nonref ([$enable]) |
211 | |
269 | |
212 | If C<$enable> is true, then the C<encode> method can convert a |
270 | If C<$enable> is true (or missing), then the C<encode> method can convert a |
213 | non-reference into its corresponding string, number or null JSON value, |
271 | non-reference into its corresponding string, number or null JSON value, |
214 | 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 |
215 | values instead of croaking. |
273 | values instead of croaking. |
216 | |
274 | |
217 | 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 |
218 | 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 |
219 | 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 |
220 | JSON object or array. |
278 | JSON object or array. |
221 | |
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!" |
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285 | |
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286 | =item $json = $json->shrink ([$enable]) |
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287 | |
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288 | Perl usually over-allocates memory a bit when allocating space for |
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289 | strings. This flag optionally resizes strings generated by either |
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290 | C<encode> or C<decode> to their minimum size possible. This can save |
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291 | memory when your JSON texts are either very very long or you have many |
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292 | short strings. It will also try to downgrade any strings to octet-form |
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293 | if possible: perl stores strings internally either in an encoding called |
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294 | UTF-X or in octet-form. The latter cannot store everything but uses less |
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295 | space in general (and some buggy Perl or C code might even rely on that |
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296 | internal representation being used). |
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297 | |
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298 | The actual definition of what shrink does might change in future versions, |
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299 | but it will always try to save space at the expense of time. |
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300 | |
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301 | If C<$enable> is true (or missing), the string returned by C<encode> will |
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302 | be shrunk-to-fit, while all strings generated by C<decode> will also be |
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303 | shrunk-to-fit. |
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304 | |
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305 | If C<$enable> is false, then the normal perl allocation algorithms are used. |
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306 | If you work with your data, then this is likely to be faster. |
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307 | |
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308 | In the future, this setting might control other things, such as converting |
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309 | strings that look like integers or floats into integers or floats |
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310 | internally (there is no difference on the Perl level), saving space. |
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311 | |
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312 | =item $json = $json->max_depth ([$maximum_nesting_depth]) |
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313 | |
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314 | Sets the maximum nesting level (default C<8192>) accepted while encoding |
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315 | or decoding. If the JSON text or Perl data structure has an equal or |
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316 | higher nesting level then this limit, then the encoder and decoder will |
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317 | stop and croak at that point. |
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318 | |
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319 | Nesting level is defined by number of hash- or arrayrefs that the encoder |
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320 | needs to traverse to reach a given point or the number of C<{> or C<[> |
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321 | characters without their matching closing parenthesis crossed to reach a |
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322 | given character in a string. |
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323 | |
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324 | Setting the maximum depth to one disallows any nesting, so that ensures |
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325 | that the object is only a single hash/object or array. |
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326 | |
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327 | The argument to C<max_depth> will be rounded up to the next nearest power |
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328 | of two. |
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329 | |
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330 | See SECURITY CONSIDERATIONS, below, for more info on why this is useful. |
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331 | |
222 | =item $json_string = $json->encode ($perl_scalar) |
332 | =item $json_text = $json->encode ($perl_scalar) |
223 | |
333 | |
224 | Converts the given Perl data structure (a simple scalar or a reference |
334 | Converts the given Perl data structure (a simple scalar or a reference |
225 | to a hash or array) to its JSON representation. Simple scalars will be |
335 | to a hash or array) to its JSON representation. Simple scalars will be |
226 | converted into JSON string or number sequences, while references to arrays |
336 | converted into JSON string or number sequences, while references to arrays |
227 | become JSON arrays and references to hashes become JSON objects. Undefined |
337 | become JSON arrays and references to hashes become JSON objects. Undefined |
228 | Perl values (e.g. C<undef>) become JSON C<null> values. Neither C<true> |
338 | Perl values (e.g. C<undef>) become JSON C<null> values. Neither C<true> |
229 | nor C<false> values will be generated. |
339 | nor C<false> values will be generated. |
230 | |
340 | |
231 | =item $perl_scalar = $json->decode ($json_string) |
341 | =item $perl_scalar = $json->decode ($json_text) |
232 | |
342 | |
233 | The opposite of C<encode>: expects a JSON string and tries to parse it, |
343 | The opposite of C<encode>: expects a JSON text and tries to parse it, |
234 | returning the resulting simple scalar or reference. Croaks on error. |
344 | returning the resulting simple scalar or reference. Croaks on error. |
235 | |
345 | |
236 | JSON numbers and strings become simple Perl scalars. JSON arrays become |
346 | JSON numbers and strings become simple Perl scalars. JSON arrays become |
237 | Perl arrayrefs and JSON objects become Perl hashrefs. C<true> becomes |
347 | Perl arrayrefs and JSON objects become Perl hashrefs. C<true> becomes |
238 | C<1>, C<false> becomes C<0> and C<null> becomes C<undef>. |
348 | C<1>, C<false> becomes C<0> and C<null> becomes C<undef>. |
239 | |
349 | |
240 | =back |
350 | =back |
241 | |
351 | |
|
|
352 | |
|
|
353 | =head1 MAPPING |
|
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354 | |
|
|
355 | This section describes how JSON::XS maps Perl values to JSON values and |
|
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356 | vice versa. These mappings are designed to "do the right thing" in most |
|
|
357 | circumstances automatically, preserving round-tripping characteristics |
|
|
358 | (what you put in comes out as something equivalent). |
|
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359 | |
|
|
360 | For the more enlightened: note that in the following descriptions, |
|
|
361 | lowercase I<perl> refers to the Perl interpreter, while uppcercase I<Perl> |
|
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362 | refers to the abstract Perl language itself. |
|
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363 | |
|
|
364 | =head2 JSON -> PERL |
|
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365 | |
|
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366 | =over 4 |
|
|
367 | |
|
|
368 | =item object |
|
|
369 | |
|
|
370 | A JSON object becomes a reference to a hash in Perl. No ordering of object |
|
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371 | keys is preserved (JSON does not preserver object key ordering itself). |
|
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372 | |
|
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373 | =item array |
|
|
374 | |
|
|
375 | A JSON array becomes a reference to an array in Perl. |
|
|
376 | |
|
|
377 | =item string |
|
|
378 | |
|
|
379 | A JSON string becomes a string scalar in Perl - Unicode codepoints in JSON |
|
|
380 | are represented by the same codepoints in the Perl string, so no manual |
|
|
381 | decoding is necessary. |
|
|
382 | |
|
|
383 | =item number |
|
|
384 | |
|
|
385 | A JSON number becomes either an integer or numeric (floating point) |
|
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386 | scalar in perl, depending on its range and any fractional parts. On the |
|
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387 | Perl level, there is no difference between those as Perl handles all the |
|
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388 | conversion details, but an integer may take slightly less memory and might |
|
|
389 | represent more values exactly than (floating point) numbers. |
|
|
390 | |
|
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391 | =item true, false |
|
|
392 | |
|
|
393 | These JSON atoms become C<0>, C<1>, respectively. Information is lost in |
|
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394 | this process. Future versions might represent those values differently, |
|
|
395 | but they will be guarenteed to act like these integers would normally in |
|
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396 | Perl. |
|
|
397 | |
|
|
398 | =item null |
|
|
399 | |
|
|
400 | A JSON null atom becomes C<undef> in Perl. |
|
|
401 | |
|
|
402 | =back |
|
|
403 | |
|
|
404 | =head2 PERL -> JSON |
|
|
405 | |
|
|
406 | The mapping from Perl to JSON is slightly more difficult, as Perl is a |
|
|
407 | truly typeless language, so we can only guess which JSON type is meant by |
|
|
408 | a Perl value. |
|
|
409 | |
|
|
410 | =over 4 |
|
|
411 | |
|
|
412 | =item hash references |
|
|
413 | |
|
|
414 | Perl hash references become JSON objects. As there is no inherent ordering |
|
|
415 | in hash keys, they will usually be encoded in a pseudo-random order that |
|
|
416 | can change between runs of the same program but stays generally the same |
|
|
417 | within a single run of a program. JSON::XS can optionally sort the hash |
|
|
418 | keys (determined by the I<canonical> flag), so the same datastructure |
|
|
419 | will serialise to the same JSON text (given same settings and version of |
|
|
420 | JSON::XS), but this incurs a runtime overhead. |
|
|
421 | |
|
|
422 | =item array references |
|
|
423 | |
|
|
424 | Perl array references become JSON arrays. |
|
|
425 | |
|
|
426 | =item blessed objects |
|
|
427 | |
|
|
428 | Blessed objects are not allowed. JSON::XS currently tries to encode their |
|
|
429 | underlying representation (hash- or arrayref), but this behaviour might |
|
|
430 | change in future versions. |
|
|
431 | |
|
|
432 | =item simple scalars |
|
|
433 | |
|
|
434 | Simple Perl scalars (any scalar that is not a reference) are the most |
|
|
435 | difficult objects to encode: JSON::XS will encode undefined scalars as |
|
|
436 | JSON null value, scalars that have last been used in a string context |
|
|
437 | before encoding as JSON strings and anything else as number value: |
|
|
438 | |
|
|
439 | # dump as number |
|
|
440 | to_json [2] # yields [2] |
|
|
441 | to_json [-3.0e17] # yields [-3e+17] |
|
|
442 | my $value = 5; to_json [$value] # yields [5] |
|
|
443 | |
|
|
444 | # used as string, so dump as string |
|
|
445 | print $value; |
|
|
446 | to_json [$value] # yields ["5"] |
|
|
447 | |
|
|
448 | # undef becomes null |
|
|
449 | to_json [undef] # yields [null] |
|
|
450 | |
|
|
451 | You can force the type to be a string by stringifying it: |
|
|
452 | |
|
|
453 | my $x = 3.1; # some variable containing a number |
|
|
454 | "$x"; # stringified |
|
|
455 | $x .= ""; # another, more awkward way to stringify |
|
|
456 | print $x; # perl does it for you, too, quite often |
|
|
457 | |
|
|
458 | You can force the type to be a number by numifying it: |
|
|
459 | |
|
|
460 | my $x = "3"; # some variable containing a string |
|
|
461 | $x += 0; # numify it, ensuring it will be dumped as a number |
|
|
462 | $x *= 1; # same thing, the choise is yours. |
|
|
463 | |
|
|
464 | You can not currently output JSON booleans or force the type in other, |
|
|
465 | less obscure, ways. Tell me if you need this capability. |
|
|
466 | |
|
|
467 | =item circular data structures |
|
|
468 | |
|
|
469 | Those will be encoded until memory or stackspace runs out. |
|
|
470 | |
|
|
471 | =back |
|
|
472 | |
|
|
473 | |
242 | =head1 COMPARISON |
474 | =head1 COMPARISON |
243 | |
475 | |
244 | As already mentioned, this module was created because none of the existing |
476 | As already mentioned, this module was created because none of the existing |
245 | JSON modules could be made to work correctly. First I will describe the |
477 | JSON modules could be made to work correctly. First I will describe the |
246 | problems (or pleasures) I encountered with various existing JSON modules, |
478 | problems (or pleasures) I encountered with various existing JSON modules, |
247 | followed by some benchmark values. |
479 | followed by some benchmark values. JSON::XS was designed not to suffer |
|
|
480 | from any of these problems or limitations. |
248 | |
481 | |
249 | =over 4 |
482 | =over 4 |
250 | |
483 | |
251 | =item JSON |
484 | =item JSON 1.07 |
252 | |
485 | |
253 | Slow (but very portable, as it is written in pure Perl). |
486 | Slow (but very portable, as it is written in pure Perl). |
254 | |
487 | |
255 | Undocumented/buggy Unicode handling (how JSON handles unicode values is |
488 | Undocumented/buggy Unicode handling (how JSON handles unicode values is |
256 | undocumented. One can get far by feeding it unicode strings and doing |
489 | undocumented. One can get far by feeding it unicode strings and doing |
… | |
… | |
258 | |
491 | |
259 | No roundtripping (strings get clobbered if they look like numbers, e.g. |
492 | No roundtripping (strings get clobbered if they look like numbers, e.g. |
260 | the string C<2.0> will encode to C<2.0> instead of C<"2.0">, and that will |
493 | the string C<2.0> will encode to C<2.0> instead of C<"2.0">, and that will |
261 | decode into the number 2. |
494 | decode into the number 2. |
262 | |
495 | |
263 | =item JSON::PC |
496 | =item JSON::PC 0.01 |
264 | |
497 | |
265 | Very fast. |
498 | Very fast. |
|
|
499 | |
|
|
500 | Undocumented/buggy Unicode handling. |
|
|
501 | |
|
|
502 | No roundtripping. |
|
|
503 | |
|
|
504 | Has problems handling many Perl values (e.g. regex results and other magic |
|
|
505 | values will make it croak). |
|
|
506 | |
|
|
507 | Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}> |
|
|
508 | which is not a valid JSON text. |
|
|
509 | |
|
|
510 | Unmaintained (maintainer unresponsive for many months, bugs are not |
|
|
511 | getting fixed). |
|
|
512 | |
|
|
513 | =item JSON::Syck 0.21 |
|
|
514 | |
|
|
515 | Very buggy (often crashes). |
266 | |
516 | |
267 | Very inflexible (no human-readable format supported, format pretty much |
517 | Very inflexible (no human-readable format supported, format pretty much |
268 | undocumented. I need at least a format for easy reading by humans and a |
518 | undocumented. I need at least a format for easy reading by humans and a |
269 | single-line compact format for use in a protocol, and preferably a way to |
519 | single-line compact format for use in a protocol, and preferably a way to |
270 | generate ASCII-only JSON strings). |
520 | generate ASCII-only JSON texts). |
271 | |
|
|
272 | Undocumented/buggy Unicode handling. |
|
|
273 | |
|
|
274 | No roundtripping. |
|
|
275 | |
|
|
276 | Has problems handling many Perl values. |
|
|
277 | |
|
|
278 | Does not even generate valid JSON (C<{1,2}> gets converted to C<{1:2}> |
|
|
279 | which is not a valid JSON string. |
|
|
280 | |
|
|
281 | Unmaintained (maintainer unresponsive for many months, bugs are not |
|
|
282 | getting fixed). |
|
|
283 | |
|
|
284 | =item JSON::Syck |
|
|
285 | |
|
|
286 | Very buggy (often crashes). |
|
|
287 | |
|
|
288 | Very inflexible. |
|
|
289 | |
521 | |
290 | Completely broken (and confusingly documented) Unicode handling (unicode |
522 | Completely broken (and confusingly documented) Unicode handling (unicode |
291 | escapes are not working properly, you need to set ImplicitUnicode to |
523 | escapes are not working properly, you need to set ImplicitUnicode to |
292 | I<different> values on en- and decoding to get symmetric behaviour). |
524 | I<different> values on en- and decoding to get symmetric behaviour). |
293 | |
525 | |
… | |
… | |
305 | JSON. One bank might parse a given non-JSON request and deduct money, |
537 | JSON. One bank might parse a given non-JSON request and deduct money, |
306 | while the other might reject the transaction with a syntax error. While a |
538 | while the other might reject the transaction with a syntax error. While a |
307 | good protocol will at least recover, that is extra unnecessary work and |
539 | good protocol will at least recover, that is extra unnecessary work and |
308 | the transaction will still not succeed). |
540 | the transaction will still not succeed). |
309 | |
541 | |
310 | =item JSON::DWIW |
542 | =item JSON::DWIW 0.04 |
311 | |
543 | |
312 | Very fast. Very natural. Very nice. |
544 | Very fast. Very natural. Very nice. |
313 | |
545 | |
314 | Undocumented unicode handling (but the best of the pack. Unicode escapes |
546 | Undocumented unicode handling (but the best of the pack. Unicode escapes |
315 | still don't get parsed properly). |
547 | still don't get parsed properly). |
316 | |
548 | |
317 | Very inflexible. |
549 | Very inflexible. |
318 | |
550 | |
319 | No roundtripping. |
551 | No roundtripping. |
320 | |
552 | |
|
|
553 | Does not generate valid JSON texts (key strings are often unquoted, empty keys |
|
|
554 | result in nothing being output) |
|
|
555 | |
321 | Does not check input for validity. |
556 | Does not check input for validity. |
322 | |
557 | |
323 | =back |
558 | =back |
324 | |
559 | |
325 | =head2 SPEED |
560 | =head2 SPEED |
|
|
561 | |
|
|
562 | It seems that JSON::XS is surprisingly fast, as shown in the following |
|
|
563 | tables. They have been generated with the help of the C<eg/bench> program |
|
|
564 | in the JSON::XS distribution, to make it easy to compare on your own |
|
|
565 | system. |
|
|
566 | |
|
|
567 | First comes a comparison between various modules using a very short JSON |
|
|
568 | string: |
|
|
569 | |
|
|
570 | {"method": "handleMessage", "params": ["user1", "we were just talking"], "id": null} |
|
|
571 | |
|
|
572 | It shows the number of encodes/decodes per second (JSON::XS uses the |
|
|
573 | functional interface, while JSON::XS/2 uses the OO interface with |
|
|
574 | pretty-printing and hashkey sorting enabled). Higher is better: |
|
|
575 | |
|
|
576 | module | encode | decode | |
|
|
577 | -----------|------------|------------| |
|
|
578 | JSON | 11488.516 | 7823.035 | |
|
|
579 | JSON::DWIW | 94708.054 | 129094.260 | |
|
|
580 | JSON::PC | 63884.157 | 128528.212 | |
|
|
581 | JSON::Syck | 34898.677 | 42096.911 | |
|
|
582 | JSON::XS | 654027.064 | 396423.669 | |
|
|
583 | JSON::XS/2 | 371564.190 | 371725.613 | |
|
|
584 | -----------+------------+------------+ |
|
|
585 | |
|
|
586 | That is, JSON::XS is more than six times faster than JSON::DWIW on |
|
|
587 | encoding, more than three times faster on decoding, and about thirty times |
|
|
588 | faster than JSON, even with pretty-printing and key sorting. |
|
|
589 | |
|
|
590 | Using a longer test string (roughly 18KB, generated from Yahoo! Locals |
|
|
591 | search API (http://nanoref.com/yahooapis/mgPdGg): |
|
|
592 | |
|
|
593 | module | encode | decode | |
|
|
594 | -----------|------------|------------| |
|
|
595 | JSON | 273.023 | 44.674 | |
|
|
596 | JSON::DWIW | 1089.383 | 1145.704 | |
|
|
597 | JSON::PC | 3097.419 | 2393.921 | |
|
|
598 | JSON::Syck | 514.060 | 843.053 | |
|
|
599 | JSON::XS | 6479.668 | 3636.364 | |
|
|
600 | JSON::XS/2 | 3774.221 | 3599.124 | |
|
|
601 | -----------+------------+------------+ |
|
|
602 | |
|
|
603 | Again, JSON::XS leads by far. |
|
|
604 | |
|
|
605 | On large strings containing lots of high unicode characters, some modules |
|
|
606 | (such as JSON::PC) seem to decode faster than JSON::XS, but the result |
|
|
607 | will be broken due to missing (or wrong) unicode handling. Others refuse |
|
|
608 | to decode or encode properly, so it was impossible to prepare a fair |
|
|
609 | comparison table for that case. |
|
|
610 | |
|
|
611 | |
|
|
612 | =head1 SECURITY CONSIDERATIONS |
|
|
613 | |
|
|
614 | When you are using JSON in a protocol, talking to untrusted potentially |
|
|
615 | hostile creatures requires relatively few measures. |
|
|
616 | |
|
|
617 | First of all, your JSON decoder should be secure, that is, should not have |
|
|
618 | any buffer overflows. Obviously, this module should ensure that and I am |
|
|
619 | trying hard on making that true, but you never know. |
|
|
620 | |
|
|
621 | Second, you need to avoid resource-starving attacks. That means you should |
|
|
622 | limit the size of JSON texts you accept, or make sure then when your |
|
|
623 | resources run out, thats just fine (e.g. by using a separate process that |
|
|
624 | can crash safely). The size of a JSON text in octets or characters is |
|
|
625 | usually a good indication of the size of the resources required to decode |
|
|
626 | it into a Perl structure. |
|
|
627 | |
|
|
628 | Third, JSON::XS recurses using the C stack when decoding objects and |
|
|
629 | arrays. The C stack is a limited resource: for instance, on my amd64 |
|
|
630 | machine with 8MB of stack size I can decode around 180k nested arrays |
|
|
631 | but only 14k nested JSON objects. If that is exceeded, the program |
|
|
632 | crashes. Thats why the default nesting limit is set to 8192. If your |
|
|
633 | process has a smaller stack, you should adjust this setting accordingly |
|
|
634 | with the C<max_depth> method. |
|
|
635 | |
|
|
636 | And last but least, something else could bomb you that I forgot to think |
|
|
637 | of. In that case, you get to keep the pieces. I am alway sopen for hints, |
|
|
638 | though... |
|
|
639 | |
|
|
640 | |
|
|
641 | =head1 BUGS |
|
|
642 | |
|
|
643 | While the goal of this module is to be correct, that unfortunately does |
|
|
644 | not mean its bug-free, only that I think its design is bug-free. It is |
|
|
645 | still relatively early in its development. If you keep reporting bugs they |
|
|
646 | will be fixed swiftly, though. |
326 | |
647 | |
327 | =cut |
648 | =cut |
328 | |
649 | |
329 | 1; |
650 | 1; |
330 | |
651 | |