1 | NAME |
1 | NAME |
2 | JSON::XS - JSON serialising/deserialising, done correctly and fast |
2 | JSON::XS - JSON serialising/deserialising, done correctly and fast |
3 | |
3 | |
4 | SYNOPSIS |
4 | SYNOPSIS |
5 | use JSON::XS; |
5 | use JSON::XS; |
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6 | |
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7 | # exported functions, they croak on error |
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8 | # and expect/generate UTF-8 |
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9 | |
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10 | $utf8_encoded_json_text = to_json $perl_hash_or_arrayref; |
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11 | $perl_hash_or_arrayref = from_json $utf8_encoded_json_text; |
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12 | |
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13 | # objToJson and jsonToObj aliases to to_json and from_json |
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14 | # are exported for compatibility to the JSON module, |
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15 | # but should not be used in new code. |
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16 | |
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17 | # OO-interface |
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18 | |
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19 | $coder = JSON::XS->new->ascii->pretty->allow_nonref; |
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20 | $pretty_printed_unencoded = $coder->encode ($perl_scalar); |
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21 | $perl_scalar = $coder->decode ($unicode_json_text); |
6 | |
22 | |
7 | DESCRIPTION |
23 | DESCRIPTION |
8 | This module converts Perl data structures to JSON and vice versa. Its |
24 | This module converts Perl data structures to JSON and vice versa. Its |
9 | primary goal is to be *correct* and its secondary goal is to be *fast*. |
25 | primary goal is to be *correct* and its secondary goal is to be *fast*. |
10 | To reach the latter goal it was written in C. |
26 | To reach the latter goal it was written in C. |
… | |
… | |
15 | cases their maintainers are unresponsive, gone missing, or not listening |
31 | cases their maintainers are unresponsive, gone missing, or not listening |
16 | to bug reports for other reasons. |
32 | to bug reports for other reasons. |
17 | |
33 | |
18 | See COMPARISON, below, for a comparison to some other JSON modules. |
34 | See COMPARISON, below, for a comparison to some other JSON modules. |
19 | |
35 | |
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36 | See MAPPING, below, on how JSON::XS maps perl values to JSON values and |
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37 | vice versa. |
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38 | |
20 | FEATURES |
39 | FEATURES |
21 | * correct handling of unicode issues |
40 | * correct unicode handling |
22 | This module knows how to handle Unicode, and even documents how it |
41 | This module knows how to handle Unicode, and even documents how and |
23 | does so. |
42 | when it does so. |
24 | |
43 | |
25 | * round-trip integrity |
44 | * round-trip integrity |
26 | When you serialise a perl data structure using only datatypes |
45 | When you serialise a perl data structure using only datatypes |
27 | supported by JSON, the deserialised data structure is identical on |
46 | supported by JSON, the deserialised data structure is identical on |
28 | the Perl level. (e.g. the string "2.0" doesn't suddenly become "2"). |
47 | the Perl level. (e.g. the string "2.0" doesn't suddenly become "2" |
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48 | just because it looks like a number). |
29 | |
49 | |
30 | * strict checking of JSON correctness |
50 | * strict checking of JSON correctness |
31 | There is no guessing, no generating of illegal JSON strings by |
51 | There is no guessing, no generating of illegal JSON texts by |
32 | default, and only JSON is accepted as input (the latter is a |
52 | default, and only JSON is accepted as input by default (the latter |
33 | security feature). |
53 | is a security feature). |
34 | |
54 | |
35 | * fast |
55 | * fast |
36 | compared to other JSON modules, this module compares favourably. |
56 | Compared to other JSON modules, this module compares favourably in |
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57 | terms of speed, too. |
37 | |
58 | |
38 | * simple to use |
59 | * simple to use |
39 | This module has both a simple functional interface as well as an OO |
60 | This module has both a simple functional interface as well as an OO |
40 | interface. |
61 | interface. |
41 | |
62 | |
42 | * reasonably versatile output formats |
63 | * reasonably versatile output formats |
43 | You can choose between the most compact format possible, a |
64 | You can choose between the most compact guarenteed single-line |
44 | pure-ascii format, or a pretty-printed format. Or you can combine |
65 | format possible (nice for simple line-based protocols), a pure-ascii |
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66 | format (for when your transport is not 8-bit clean, still supports |
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67 | the whole unicode range), or a pretty-printed format (for when you |
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68 | want to read that stuff). Or you can combine those features in |
45 | those features in whatever way you like. |
69 | whatever way you like. |
46 | |
70 | |
47 | FUNCTIONAL INTERFACE |
71 | FUNCTIONAL INTERFACE |
48 | The following convinience methods are provided by this module. They are |
72 | The following convinience methods are provided by this module. They are |
49 | exported by default: |
73 | exported by default: |
50 | |
74 | |
51 | $json_string = to_json $perl_scalar |
75 | $json_text = to_json $perl_scalar |
52 | Converts the given Perl data structure (a simple scalar or a |
76 | Converts the given Perl data structure (a simple scalar or a |
53 | reference to a hash or array) to a UTF-8 encoded, binary string |
77 | reference to a hash or array) to a UTF-8 encoded, binary string |
54 | (that is, the string contains octets only). Croaks on error. |
78 | (that is, the string contains octets only). Croaks on error. |
55 | |
79 | |
56 | This function call is functionally identical to "JSON::XS->new->utf8 |
80 | This function call is functionally identical to: |
57 | (1)->encode ($perl_scalar)". |
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58 | |
81 | |
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82 | $json_text = JSON::XS->new->utf8->encode ($perl_scalar) |
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83 | |
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84 | except being faster. |
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85 | |
59 | $perl_scalar = from_json $json_string |
86 | $perl_scalar = from_json $json_text |
60 | The opposite of "to_json": expects an UTF-8 (binary) string and |
87 | The opposite of "to_json": expects an UTF-8 (binary) string and |
61 | tries to parse that as an UTF-8 encoded JSON string, returning the |
88 | tries to parse that as an UTF-8 encoded JSON text, returning the |
62 | resulting simple scalar or reference. Croaks on error. |
89 | resulting simple scalar or reference. Croaks on error. |
63 | |
90 | |
64 | This function call is functionally identical to "JSON::XS->new->utf8 |
91 | This function call is functionally identical to: |
65 | (1)->decode ($json_string)". |
92 | |
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93 | $perl_scalar = JSON::XS->new->utf8->decode ($json_text) |
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94 | |
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95 | except being faster. |
66 | |
96 | |
67 | OBJECT-ORIENTED INTERFACE |
97 | OBJECT-ORIENTED INTERFACE |
68 | The object oriented interface lets you configure your own encoding or |
98 | The object oriented interface lets you configure your own encoding or |
69 | decoding style, within the limits of supported formats. |
99 | decoding style, within the limits of supported formats. |
70 | |
100 | |
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… | |
74 | *disabled*. |
104 | *disabled*. |
75 | |
105 | |
76 | The mutators for flags all return the JSON object again and thus |
106 | The mutators for flags all return the JSON object again and thus |
77 | calls can be chained: |
107 | calls can be chained: |
78 | |
108 | |
79 | my $json = JSON::XS->new->utf8(1)->space_after(1)->encode ({a => [1,2]}) |
109 | my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]}) |
80 | => {"a": [1, 2]} |
110 | => {"a": [1, 2]} |
81 | |
111 | |
82 | $json = $json->ascii ($enable) |
112 | $json = $json->ascii ([$enable]) |
83 | If $enable is true, then the "encode" method will not generate |
113 | If $enable is true (or missing), then the "encode" method will not |
84 | characters outside the code range 0..127. Any unicode characters |
114 | generate characters outside the code range 0..127 (which is ASCII). |
85 | outside that range will be escaped using either a single \uXXXX (BMP |
115 | Any unicode characters outside that range will be escaped using |
86 | characters) or a double \uHHHH\uLLLLL escape sequence, as per |
116 | either a single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL |
87 | RFC4627. |
117 | escape sequence, as per RFC4627. The resulting encoded JSON text can |
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118 | be treated as a native unicode string, an ascii-encoded, |
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119 | latin1-encoded or UTF-8 encoded string, or any other superset of |
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120 | ASCII. |
88 | |
121 | |
89 | If $enable is false, then the "encode" method will not escape |
122 | If $enable is false, then the "encode" method will not escape |
90 | Unicode characters unless necessary. |
123 | Unicode characters unless required by the JSON syntax or other |
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124 | flags. This results in a faster and more compact format. |
91 | |
125 | |
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126 | The main use for this flag is to produce JSON texts that can be |
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127 | transmitted over a 7-bit channel, as the encoded JSON texts will not |
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128 | contain any 8 bit characters. |
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129 | |
92 | JSON::XS->new->ascii (1)->encode (chr 0x10401) |
130 | JSON::XS->new->ascii (1)->encode ([chr 0x10401]) |
93 | => \ud801\udc01 |
131 | => ["\ud801\udc01"] |
94 | |
132 | |
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133 | $json = $json->latin1 ([$enable]) |
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134 | If $enable is true (or missing), then the "encode" method will |
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135 | encode the resulting JSON text as latin1 (or iso-8859-1), escaping |
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136 | any characters outside the code range 0..255. The resulting string |
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137 | can be treated as a latin1-encoded JSON text or a native unicode |
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138 | string. The "decode" method will not be affected in any way by this |
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139 | flag, as "decode" by default expects unicode, which is a strict |
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140 | superset of latin1. |
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141 | |
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142 | If $enable is false, then the "encode" method will not escape |
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143 | Unicode characters unless required by the JSON syntax or other |
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144 | flags. |
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145 | |
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146 | The main use for this flag is efficiently encoding binary data as |
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147 | JSON text, as most octets will not be escaped, resulting in a |
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148 | smaller encoded size. The disadvantage is that the resulting JSON |
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149 | text is encoded in latin1 (and must correctly be treated as such |
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150 | when storing and transfering), a rare encoding for JSON. It is |
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151 | therefore most useful when you want to store data structures known |
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152 | to contain binary data efficiently in files or databases, not when |
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153 | talking to other JSON encoders/decoders. |
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154 | |
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155 | JSON::XS->new->latin1->encode (["\x{89}\x{abc}"] |
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156 | => ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not) |
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157 | |
95 | $json = $json->utf8 ($enable) |
158 | $json = $json->utf8 ([$enable]) |
96 | If $enable is true, then the "encode" method will encode the JSON |
159 | If $enable is true (or missing), then the "encode" method will |
97 | string into UTF-8, as required by many protocols, while the "decode" |
160 | encode the JSON result into UTF-8, as required by many protocols, |
98 | method expects to be handled an UTF-8-encoded string. Please note |
161 | while the "decode" method expects to be handled an UTF-8-encoded |
99 | that UTF-8-encoded strings do not contain any characters outside the |
162 | string. Please note that UTF-8-encoded strings do not contain any |
100 | range 0..255, they are thus useful for bytewise/binary I/O. |
163 | characters outside the range 0..255, they are thus useful for |
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164 | bytewise/binary I/O. In future versions, enabling this option might |
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165 | enable autodetection of the UTF-16 and UTF-32 encoding families, as |
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166 | described in RFC4627. |
101 | |
167 | |
102 | If $enable is false, then the "encode" method will return the JSON |
168 | If $enable is false, then the "encode" method will return the JSON |
103 | string as a (non-encoded) unicode string, while "decode" expects |
169 | string as a (non-encoded) unicode string, while "decode" expects |
104 | thus a unicode string. Any decoding or encoding (e.g. to UTF-8 or |
170 | thus a unicode string. Any decoding or encoding (e.g. to UTF-8 or |
105 | UTF-16) needs to be done yourself, e.g. using the Encode module. |
171 | UTF-16) needs to be done yourself, e.g. using the Encode module. |
106 | |
172 | |
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173 | Example, output UTF-16BE-encoded JSON: |
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174 | |
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175 | use Encode; |
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176 | $jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object); |
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177 | |
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178 | Example, decode UTF-32LE-encoded JSON: |
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179 | |
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180 | use Encode; |
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181 | $object = JSON::XS->new->decode (decode "UTF-32LE", $jsontext); |
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182 | |
107 | $json = $json->pretty ($enable) |
183 | $json = $json->pretty ([$enable]) |
108 | This enables (or disables) all of the "indent", "space_before" and |
184 | This enables (or disables) all of the "indent", "space_before" and |
109 | "space_after" (and in the future possibly more) flags in one call to |
185 | "space_after" (and in the future possibly more) flags in one call to |
110 | generate the most readable (or most compact) form possible. |
186 | generate the most readable (or most compact) form possible. |
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187 | |
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188 | Example, pretty-print some simple structure: |
111 | |
189 | |
112 | my $json = JSON::XS->new->pretty(1)->encode ({a => [1,2]}) |
190 | my $json = JSON::XS->new->pretty(1)->encode ({a => [1,2]}) |
113 | => |
191 | => |
114 | { |
192 | { |
115 | "a" : [ |
193 | "a" : [ |
116 | 1, |
194 | 1, |
117 | 2 |
195 | 2 |
118 | ] |
196 | ] |
119 | } |
197 | } |
120 | |
198 | |
121 | $json = $json->indent ($enable) |
199 | $json = $json->indent ([$enable]) |
122 | If $enable is true, then the "encode" method will use a multiline |
200 | If $enable is true (or missing), then the "encode" method will use a |
123 | format as output, putting every array member or object/hash |
201 | multiline format as output, putting every array member or |
124 | key-value pair into its own line, identing them properly. |
202 | object/hash key-value pair into its own line, identing them |
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203 | properly. |
125 | |
204 | |
126 | If $enable is false, no newlines or indenting will be produced, and |
205 | If $enable is false, no newlines or indenting will be produced, and |
127 | the resulting JSON strings is guarenteed not to contain any |
206 | the resulting JSON text is guarenteed not to contain any "newlines". |
128 | "newlines". |
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129 | |
207 | |
130 | This setting has no effect when decoding JSON strings. |
208 | This setting has no effect when decoding JSON texts. |
131 | |
209 | |
132 | $json = $json->space_before ($enable) |
210 | $json = $json->space_before ([$enable]) |
133 | If $enable is true, then the "encode" method will add an extra |
211 | If $enable is true (or missing), then the "encode" method will add |
134 | optional space before the ":" separating keys from values in JSON |
212 | an extra optional space before the ":" separating keys from values |
135 | objects. |
213 | in JSON objects. |
136 | |
214 | |
137 | If $enable is false, then the "encode" method will not add any extra |
215 | If $enable is false, then the "encode" method will not add any extra |
138 | space at those places. |
216 | space at those places. |
139 | |
217 | |
140 | This setting has no effect when decoding JSON strings. You will also |
218 | This setting has no effect when decoding JSON texts. You will also |
141 | most likely combine this setting with "space_after". |
219 | most likely combine this setting with "space_after". |
142 | |
220 | |
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221 | Example, space_before enabled, space_after and indent disabled: |
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222 | |
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223 | {"key" :"value"} |
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224 | |
143 | $json = $json->space_after ($enable) |
225 | $json = $json->space_after ([$enable]) |
144 | If $enable is true, then the "encode" method will add an extra |
226 | If $enable is true (or missing), then the "encode" method will add |
145 | optional space after the ":" separating keys from values in JSON |
227 | an extra optional space after the ":" separating keys from values in |
146 | objects and extra whitespace after the "," separating key-value |
228 | JSON objects and extra whitespace after the "," separating key-value |
147 | pairs and array members. |
229 | pairs and array members. |
148 | |
230 | |
149 | If $enable is false, then the "encode" method will not add any extra |
231 | If $enable is false, then the "encode" method will not add any extra |
150 | space at those places. |
232 | space at those places. |
151 | |
233 | |
152 | This setting has no effect when decoding JSON strings. |
234 | This setting has no effect when decoding JSON texts. |
153 | |
235 | |
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236 | Example, space_before and indent disabled, space_after enabled: |
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237 | |
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238 | {"key": "value"} |
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239 | |
154 | $json = $json->canonical ($enable) |
240 | $json = $json->canonical ([$enable]) |
155 | If $enable is true, then the "encode" method will output JSON |
241 | If $enable is true (or missing), then the "encode" method will |
156 | objects by sorting their keys. This is adding a comparatively high |
242 | output JSON objects by sorting their keys. This is adding a |
157 | overhead. |
243 | comparatively high overhead. |
158 | |
244 | |
159 | If $enable is false, then the "encode" method will output key-value |
245 | If $enable is false, then the "encode" method will output key-value |
160 | pairs in the order Perl stores them (which will likely change |
246 | pairs in the order Perl stores them (which will likely change |
161 | between runs of the same script). |
247 | between runs of the same script). |
162 | |
248 | |
163 | This option is useful if you want the same data structure to be |
249 | This option is useful if you want the same data structure to be |
164 | encoded as the same JSON string (given the same overall settings). |
250 | encoded as the same JSON text (given the same overall settings). If |
165 | If it is disabled, the same hash migh be encoded differently even if |
251 | it is disabled, the same hash migh be encoded differently even if |
166 | contains the same data, as key-value pairs have no inherent ordering |
252 | contains the same data, as key-value pairs have no inherent ordering |
167 | in Perl. |
253 | in Perl. |
168 | |
254 | |
169 | This setting has no effect when decoding JSON strings. |
255 | This setting has no effect when decoding JSON texts. |
170 | |
256 | |
171 | $json = $json->allow_nonref ($enable) |
257 | $json = $json->allow_nonref ([$enable]) |
172 | If $enable is true, then the "encode" method can convert a |
258 | If $enable is true (or missing), then the "encode" method can |
173 | non-reference into its corresponding string, number or null JSON |
259 | convert a non-reference into its corresponding string, number or |
174 | value, which is an extension to RFC4627. Likewise, "decode" will |
260 | null JSON value, which is an extension to RFC4627. Likewise, |
175 | accept those JSON values instead of croaking. |
261 | "decode" will accept those JSON values instead of croaking. |
176 | |
262 | |
177 | If $enable is false, then the "encode" method will croak if it isn't |
263 | If $enable is false, then the "encode" method will croak if it isn't |
178 | passed an arrayref or hashref, as JSON strings must either be an |
264 | passed an arrayref or hashref, as JSON texts must either be an |
179 | object or array. Likewise, "decode" will croak if given something |
265 | object or array. Likewise, "decode" will croak if given something |
180 | that is not a JSON object or array. |
266 | that is not a JSON object or array. |
181 | |
267 | |
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268 | Example, encode a Perl scalar as JSON value with enabled |
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269 | "allow_nonref", resulting in an invalid JSON text: |
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270 | |
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271 | JSON::XS->new->allow_nonref->encode ("Hello, World!") |
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272 | => "Hello, World!" |
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273 | |
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274 | $json = $json->shrink ([$enable]) |
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275 | Perl usually over-allocates memory a bit when allocating space for |
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276 | strings. This flag optionally resizes strings generated by either |
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277 | "encode" or "decode" to their minimum size possible. This can save |
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278 | memory when your JSON texts are either very very long or you have |
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279 | many short strings. It will also try to downgrade any strings to |
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280 | octet-form if possible: perl stores strings internally either in an |
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281 | encoding called UTF-X or in octet-form. The latter cannot store |
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282 | everything but uses less space in general (and some buggy Perl or C |
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283 | code might even rely on that internal representation being used). |
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284 | |
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285 | The actual definition of what shrink does might change in future |
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286 | versions, but it will always try to save space at the expense of |
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287 | time. |
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288 | |
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289 | If $enable is true (or missing), the string returned by "encode" |
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290 | will be shrunk-to-fit, while all strings generated by "decode" will |
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291 | also be shrunk-to-fit. |
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292 | |
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293 | If $enable is false, then the normal perl allocation algorithms are |
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294 | used. If you work with your data, then this is likely to be faster. |
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295 | |
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296 | In the future, this setting might control other things, such as |
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297 | converting strings that look like integers or floats into integers |
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298 | or floats internally (there is no difference on the Perl level), |
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299 | saving space. |
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300 | |
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301 | $json = $json->max_depth ([$maximum_nesting_depth]) |
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302 | Sets the maximum nesting level (default 512) accepted while encoding |
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303 | or decoding. If the JSON text or Perl data structure has an equal or |
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304 | higher nesting level then this limit, then the encoder and decoder |
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305 | will stop and croak at that point. |
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306 | |
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307 | Nesting level is defined by number of hash- or arrayrefs that the |
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308 | encoder needs to traverse to reach a given point or the number of |
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309 | "{" or "[" characters without their matching closing parenthesis |
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310 | crossed to reach a given character in a string. |
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311 | |
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312 | Setting the maximum depth to one disallows any nesting, so that |
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313 | ensures that the object is only a single hash/object or array. |
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314 | |
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315 | The argument to "max_depth" will be rounded up to the next nearest |
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316 | power of two. |
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317 | |
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318 | See SECURITY CONSIDERATIONS, below, for more info on why this is |
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319 | useful. |
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320 | |
182 | $json_string = $json->encode ($perl_scalar) |
321 | $json_text = $json->encode ($perl_scalar) |
183 | Converts the given Perl data structure (a simple scalar or a |
322 | Converts the given Perl data structure (a simple scalar or a |
184 | reference to a hash or array) to its JSON representation. Simple |
323 | reference to a hash or array) to its JSON representation. Simple |
185 | scalars will be converted into JSON string or number sequences, |
324 | scalars will be converted into JSON string or number sequences, |
186 | while references to arrays become JSON arrays and references to |
325 | while references to arrays become JSON arrays and references to |
187 | hashes become JSON objects. Undefined Perl values (e.g. "undef") |
326 | hashes become JSON objects. Undefined Perl values (e.g. "undef") |
188 | become JSON "null" values. Neither "true" nor "false" values will be |
327 | become JSON "null" values. Neither "true" nor "false" values will be |
189 | generated. |
328 | generated. |
190 | |
329 | |
191 | $perl_scalar = $json->decode ($json_string) |
330 | $perl_scalar = $json->decode ($json_text) |
192 | The opposite of "encode": expects a JSON string and tries to parse |
331 | The opposite of "encode": expects a JSON text and tries to parse it, |
193 | it, returning the resulting simple scalar or reference. Croaks on |
332 | returning the resulting simple scalar or reference. Croaks on error. |
194 | error. |
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195 | |
333 | |
196 | JSON numbers and strings become simple Perl scalars. JSON arrays |
334 | JSON numbers and strings become simple Perl scalars. JSON arrays |
197 | become Perl arrayrefs and JSON objects become Perl hashrefs. "true" |
335 | become Perl arrayrefs and JSON objects become Perl hashrefs. "true" |
198 | becomes 1, "false" becomes 0 and "null" becomes "undef". |
336 | becomes 1, "false" becomes 0 and "null" becomes "undef". |
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337 | |
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338 | ($perl_scalar, $characters) = $json->decode_prefix ($json_text) |
|
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339 | This works like the "decode" method, but instead of raising an |
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340 | exception when there is trailing garbage after the first JSON |
|
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341 | object, it will silently stop parsing there and return the number of |
|
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342 | characters consumed so far. |
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343 | |
|
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344 | This is useful if your JSON texts are not delimited by an outer |
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345 | protocol (which is not the brightest thing to do in the first place) |
|
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346 | and you need to know where the JSON text ends. |
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347 | |
|
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348 | JSON::XS->new->decode_prefix ("[1] the tail") |
|
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349 | => ([], 3) |
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350 | |
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351 | MAPPING |
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352 | This section describes how JSON::XS maps Perl values to JSON values and |
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353 | vice versa. These mappings are designed to "do the right thing" in most |
|
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354 | circumstances automatically, preserving round-tripping characteristics |
|
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355 | (what you put in comes out as something equivalent). |
|
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356 | |
|
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357 | For the more enlightened: note that in the following descriptions, |
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358 | lowercase *perl* refers to the Perl interpreter, while uppcercase *Perl* |
|
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359 | refers to the abstract Perl language itself. |
|
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360 | |
|
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361 | JSON -> PERL |
|
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362 | object |
|
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363 | A JSON object becomes a reference to a hash in Perl. No ordering of |
|
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364 | object keys is preserved (JSON does not preserver object key |
|
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365 | ordering itself). |
|
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366 | |
|
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367 | array |
|
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368 | A JSON array becomes a reference to an array in Perl. |
|
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369 | |
|
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370 | string |
|
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371 | A JSON string becomes a string scalar in Perl - Unicode codepoints |
|
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372 | in JSON are represented by the same codepoints in the Perl string, |
|
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373 | so no manual decoding is necessary. |
|
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374 | |
|
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375 | number |
|
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376 | A JSON number becomes either an integer or numeric (floating point) |
|
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377 | scalar in perl, depending on its range and any fractional parts. On |
|
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378 | the Perl level, there is no difference between those as Perl handles |
|
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379 | all the conversion details, but an integer may take slightly less |
|
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380 | memory and might represent more values exactly than (floating point) |
|
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381 | numbers. |
|
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382 | |
|
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383 | true, false |
|
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384 | These JSON atoms become 0, 1, respectively. Information is lost in |
|
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385 | this process. Future versions might represent those values |
|
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386 | differently, but they will be guarenteed to act like these integers |
|
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387 | would normally in Perl. |
|
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388 | |
|
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389 | null |
|
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390 | A JSON null atom becomes "undef" in Perl. |
|
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391 | |
|
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392 | PERL -> JSON |
|
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393 | The mapping from Perl to JSON is slightly more difficult, as Perl is a |
|
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394 | truly typeless language, so we can only guess which JSON type is meant |
|
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395 | by a Perl value. |
|
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396 | |
|
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397 | hash references |
|
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398 | Perl hash references become JSON objects. As there is no inherent |
|
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399 | ordering in hash keys (or JSON objects), they will usually be |
|
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400 | encoded in a pseudo-random order that can change between runs of the |
|
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401 | same program but stays generally the same within a single run of a |
|
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402 | program. JSON::XS can optionally sort the hash keys (determined by |
|
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403 | the *canonical* flag), so the same datastructure will serialise to |
|
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404 | the same JSON text (given same settings and version of JSON::XS), |
|
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405 | but this incurs a runtime overhead and is only rarely useful, e.g. |
|
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406 | when you want to compare some JSON text against another for |
|
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407 | equality. |
|
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408 | |
|
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409 | array references |
|
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410 | Perl array references become JSON arrays. |
|
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411 | |
|
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412 | other references |
|
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413 | Other unblessed references are generally not allowed and will cause |
|
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414 | an exception to be thrown, except for references to the integers 0 |
|
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415 | and 1, which get turned into "false" and "true" atoms in JSON. You |
|
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416 | can also use "JSON::XS::false" and "JSON::XS::true" to improve |
|
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417 | readability. |
|
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418 | |
|
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419 | to_json [\0,JSON::XS::true] # yields [false,true] |
|
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420 | |
|
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421 | blessed objects |
|
|
422 | Blessed objects are not allowed. JSON::XS currently tries to encode |
|
|
423 | their underlying representation (hash- or arrayref), but this |
|
|
424 | behaviour might change in future versions. |
|
|
425 | |
|
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426 | simple scalars |
|
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427 | Simple Perl scalars (any scalar that is not a reference) are the |
|
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428 | most difficult objects to encode: JSON::XS will encode undefined |
|
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429 | scalars as JSON null value, scalars that have last been used in a |
|
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430 | string context before encoding as JSON strings and anything else as |
|
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431 | number value: |
|
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432 | |
|
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433 | # dump as number |
|
|
434 | to_json [2] # yields [2] |
|
|
435 | to_json [-3.0e17] # yields [-3e+17] |
|
|
436 | my $value = 5; to_json [$value] # yields [5] |
|
|
437 | |
|
|
438 | # used as string, so dump as string |
|
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439 | print $value; |
|
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440 | to_json [$value] # yields ["5"] |
|
|
441 | |
|
|
442 | # undef becomes null |
|
|
443 | to_json [undef] # yields [null] |
|
|
444 | |
|
|
445 | You can force the type to be a string by stringifying it: |
|
|
446 | |
|
|
447 | my $x = 3.1; # some variable containing a number |
|
|
448 | "$x"; # stringified |
|
|
449 | $x .= ""; # another, more awkward way to stringify |
|
|
450 | print $x; # perl does it for you, too, quite often |
|
|
451 | |
|
|
452 | You can force the type to be a number by numifying it: |
|
|
453 | |
|
|
454 | my $x = "3"; # some variable containing a string |
|
|
455 | $x += 0; # numify it, ensuring it will be dumped as a number |
|
|
456 | $x *= 1; # same thing, the choise is yours. |
|
|
457 | |
|
|
458 | You can not currently output JSON booleans or force the type in |
|
|
459 | other, less obscure, ways. Tell me if you need this capability. |
199 | |
460 | |
200 | COMPARISON |
461 | COMPARISON |
201 | As already mentioned, this module was created because none of the |
462 | As already mentioned, this module was created because none of the |
202 | existing JSON modules could be made to work correctly. First I will |
463 | existing JSON modules could be made to work correctly. First I will |
203 | describe the problems (or pleasures) I encountered with various existing |
464 | describe the problems (or pleasures) I encountered with various existing |
… | |
… | |
225 | |
486 | |
226 | Has problems handling many Perl values (e.g. regex results and other |
487 | Has problems handling many Perl values (e.g. regex results and other |
227 | magic values will make it croak). |
488 | magic values will make it croak). |
228 | |
489 | |
229 | Does not even generate valid JSON ("{1,2}" gets converted to "{1:2}" |
490 | Does not even generate valid JSON ("{1,2}" gets converted to "{1:2}" |
230 | which is not a valid JSON string. |
491 | which is not a valid JSON text. |
231 | |
492 | |
232 | Unmaintained (maintainer unresponsive for many months, bugs are not |
493 | Unmaintained (maintainer unresponsive for many months, bugs are not |
233 | getting fixed). |
494 | getting fixed). |
234 | |
495 | |
235 | JSON::Syck 0.21 |
496 | JSON::Syck 0.21 |
236 | Very buggy (often crashes). |
497 | Very buggy (often crashes). |
237 | |
498 | |
238 | Very inflexible (no human-readable format supported, format pretty |
499 | Very inflexible (no human-readable format supported, format pretty |
239 | much undocumented. I need at least a format for easy reading by |
500 | much undocumented. I need at least a format for easy reading by |
240 | humans and a single-line compact format for use in a protocol, and |
501 | humans and a single-line compact format for use in a protocol, and |
241 | preferably a way to generate ASCII-only JSON strings). |
502 | preferably a way to generate ASCII-only JSON texts). |
242 | |
503 | |
243 | Completely broken (and confusingly documented) Unicode handling |
504 | Completely broken (and confusingly documented) Unicode handling |
244 | (unicode escapes are not working properly, you need to set |
505 | (unicode escapes are not working properly, you need to set |
245 | ImplicitUnicode to *different* values on en- and decoding to get |
506 | ImplicitUnicode to *different* values on en- and decoding to get |
246 | symmetric behaviour). |
507 | symmetric behaviour). |
… | |
… | |
269 | |
530 | |
270 | Very inflexible. |
531 | Very inflexible. |
271 | |
532 | |
272 | No roundtripping. |
533 | No roundtripping. |
273 | |
534 | |
274 | Does not generate valid JSON (key strings are often unquoted, empty |
535 | Does not generate valid JSON texts (key strings are often unquoted, |
275 | keys result in nothing being output) |
536 | empty keys result in nothing being output) |
276 | |
537 | |
277 | Does not check input for validity. |
538 | Does not check input for validity. |
|
|
539 | |
|
|
540 | JSON and YAML |
|
|
541 | You often hear that JSON is a subset (or a close subset) of YAML. This |
|
|
542 | is, however, a mass hysteria and very far from the truth. In general, |
|
|
543 | there is no way to configure JSON::XS to output a data structure as |
|
|
544 | valid YAML. |
|
|
545 | |
|
|
546 | If you really must use JSON::XS to generate YAML, you should use this |
|
|
547 | algorithm (subject to change in future versions): |
|
|
548 | |
|
|
549 | my $to_yaml = JSON::XS->new->utf8->space_after (1); |
|
|
550 | my $yaml = $to_yaml->encode ($ref) . "\n"; |
|
|
551 | |
|
|
552 | This will usually generate JSON texts that also parse as valid YAML. |
|
|
553 | Please note that YAML has hardcoded limits on (simple) object key |
|
|
554 | lengths that JSON doesn't have, so you should make sure that your hash |
|
|
555 | keys are noticably shorter than the 1024 characters YAML allows. |
|
|
556 | |
|
|
557 | There might be other incompatibilities that I am not aware of. In |
|
|
558 | general you should not try to generate YAML with a JSON generator or |
|
|
559 | vice versa, or try to parse JSON with a YAML parser or vice versa: |
|
|
560 | chances are high that you will run into severe interoperability |
|
|
561 | problems. |
278 | |
562 | |
279 | SPEED |
563 | SPEED |
280 | It seems that JSON::XS is surprisingly fast, as shown in the following |
564 | It seems that JSON::XS is surprisingly fast, as shown in the following |
281 | tables. They have been generated with the help of the "eg/bench" program |
565 | tables. They have been generated with the help of the "eg/bench" program |
282 | in the JSON::XS distribution, to make it easy to compare on your own |
566 | in the JSON::XS distribution, to make it easy to compare on your own |
283 | system. |
567 | system. |
284 | |
568 | |
285 | First is a comparison between various modules using a very simple JSON |
569 | First comes a comparison between various modules using a very short |
|
|
570 | single-line JSON string: |
|
|
571 | |
|
|
572 | {"method": "handleMessage", "params": ["user1", "we were just talking"], \ |
|
|
573 | "id": null, "array":[1,11,234,-5,1e5,1e7, true, false]} |
|
|
574 | |
286 | string, showing the number of encodes/decodes per second (JSON::XS is |
575 | It shows the number of encodes/decodes per second (JSON::XS uses the |
287 | the functional interface, while JSON::XS/2 is the OO interface with |
576 | functional interface, while JSON::XS/2 uses the OO interface with |
288 | pretty-printing and hashkey sorting enabled). |
577 | pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink). |
|
|
578 | Higher is better: |
289 | |
579 | |
290 | module | encode | decode | |
580 | module | encode | decode | |
291 | -----------|------------|------------| |
581 | -----------|------------|------------| |
292 | JSON | 14006 | 6820 | |
582 | JSON | 7645.468 | 4208.613 | |
293 | JSON::DWIW | 200937 | 120386 | |
583 | JSON::DWIW | 40721.398 | 77101.176 | |
294 | JSON::PC | 85065 | 129366 | |
584 | JSON::PC | 65948.176 | 78251.940 | |
295 | JSON::Syck | 59898 | 44232 | |
585 | JSON::Syck | 22844.793 | 26479.192 | |
296 | JSON::XS | 1171478 | 342435 | |
586 | JSON::XS | 388361.481 | 199728.762 | |
297 | JSON::XS/2 | 730760 | 328714 | |
587 | JSON::XS/2 | 218453.333 | 192399.266 | |
|
|
588 | JSON::XS/3 | 338250.323 | 192399.266 | |
|
|
589 | Storable | 15779.925 | 14169.946 | |
298 | -----------+------------+------------+ |
590 | -----------+------------+------------+ |
299 | |
591 | |
300 | That is, JSON::XS is 6 times faster than than JSON::DWIW and about 80 |
592 | That is, JSON::XS is about five times faster than JSON::DWIW on |
|
|
593 | encoding, about three times faster on decoding, and over fourty times |
301 | times faster than JSON, even with pretty-printing and key sorting. |
594 | faster than JSON, even with pretty-printing and key sorting. It also |
|
|
595 | compares favourably to Storable for small amounts of data. |
302 | |
596 | |
303 | Using a longer test string (roughly 8KB, generated from Yahoo! Locals |
597 | Using a longer test string (roughly 18KB, generated from Yahoo! Locals |
304 | search API (http://nanoref.com/yahooapis/mgPdGg): |
598 | search API (http://nanoref.com/yahooapis/mgPdGg): |
305 | |
599 | |
306 | module | encode | decode | |
600 | module | encode | decode | |
307 | -----------|------------|------------| |
601 | -----------|------------|------------| |
308 | JSON | 673 | 38 | |
602 | JSON | 254.685 | 37.665 | |
309 | JSON::DWIW | 5271 | 770 | |
603 | JSON::DWIW | 843.343 | 1049.731 | |
310 | JSON::PC | 9901 | 2491 | |
604 | JSON::PC | 3602.116 | 2307.352 | |
311 | JSON::Syck | 2360 | 786 | |
605 | JSON::Syck | 505.107 | 787.899 | |
312 | JSON::XS | 37398 | 3202 | |
606 | JSON::XS | 5747.196 | 3690.220 | |
313 | JSON::XS/2 | 13765 | 3153 | |
607 | JSON::XS/2 | 3968.121 | 3676.634 | |
|
|
608 | JSON::XS/3 | 6105.246 | 3662.508 | |
|
|
609 | Storable | 4417.337 | 5285.161 | |
314 | -----------+------------+------------+ |
610 | -----------+------------+------------+ |
315 | |
611 | |
316 | Again, JSON::XS leads by far in the encoding case, while still beating |
612 | Again, JSON::XS leads by far (except for Storable which non-surprisingly |
317 | every other module in the decoding case. |
613 | decodes faster). |
318 | |
614 | |
319 | Last example is an almost 8MB large hash with many large binary values |
615 | On large strings containing lots of high unicode characters, some |
320 | (PNG files), resulting in a lot of escaping: |
616 | modules (such as JSON::PC) seem to decode faster than JSON::XS, but the |
|
|
617 | result will be broken due to missing (or wrong) unicode handling. Others |
|
|
618 | refuse to decode or encode properly, so it was impossible to prepare a |
|
|
619 | fair comparison table for that case. |
|
|
620 | |
|
|
621 | SECURITY CONSIDERATIONS |
|
|
622 | When you are using JSON in a protocol, talking to untrusted potentially |
|
|
623 | hostile creatures requires relatively few measures. |
|
|
624 | |
|
|
625 | First of all, your JSON decoder should be secure, that is, should not |
|
|
626 | have any buffer overflows. Obviously, this module should ensure that and |
|
|
627 | I am trying hard on making that true, but you never know. |
|
|
628 | |
|
|
629 | Second, you need to avoid resource-starving attacks. That means you |
|
|
630 | should limit the size of JSON texts you accept, or make sure then when |
|
|
631 | your resources run out, thats just fine (e.g. by using a separate |
|
|
632 | process that can crash safely). The size of a JSON text in octets or |
|
|
633 | characters is usually a good indication of the size of the resources |
|
|
634 | required to decode it into a Perl structure. |
|
|
635 | |
|
|
636 | Third, JSON::XS recurses using the C stack when decoding objects and |
|
|
637 | arrays. The C stack is a limited resource: for instance, on my amd64 |
|
|
638 | machine with 8MB of stack size I can decode around 180k nested arrays |
|
|
639 | but only 14k nested JSON objects (due to perl itself recursing deeply on |
|
|
640 | croak to free the temporary). If that is exceeded, the program crashes. |
|
|
641 | to be conservative, the default nesting limit is set to 512. If your |
|
|
642 | process has a smaller stack, you should adjust this setting accordingly |
|
|
643 | with the "max_depth" method. |
|
|
644 | |
|
|
645 | And last but least, something else could bomb you that I forgot to think |
|
|
646 | of. In that case, you get to keep the pieces. I am always open for |
|
|
647 | hints, though... |
321 | |
648 | |
322 | BUGS |
649 | BUGS |
323 | While the goal of this module is to be correct, that unfortunately does |
650 | While the goal of this module is to be correct, that unfortunately does |
324 | not mean its bug-free, only that I think its design is bug-free. It is |
651 | not mean its bug-free, only that I think its design is bug-free. It is |
325 | still very young and not well-tested. If you keep reporting bugs they |
652 | still relatively early in its development. If you keep reporting bugs |
326 | will be fixed swiftly, though. |
653 | they will be fixed swiftly, though. |
327 | |
654 | |
328 | AUTHOR |
655 | AUTHOR |
329 | Marc Lehmann <schmorp@schmorp.de> |
656 | Marc Lehmann <schmorp@schmorp.de> |
330 | http://home.schmorp.de/ |
657 | http://home.schmorp.de/ |
331 | |
658 | |