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 | |
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4 | JSON::XS - 正しくて高速な JSON |
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5 | シリアライザ/デシリアライザ |
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6 | (http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html) |
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7 | |
4 | SYNOPSIS |
8 | SYNOPSIS |
5 | use JSON::XS; |
9 | use JSON::XS; |
6 | |
10 | |
7 | # exported functions, they croak on error |
11 | # exported functions, they croak on error |
8 | # and expect/generate UTF-8 |
12 | # and expect/generate UTF-8 |
9 | |
13 | |
10 | $utf8_encoded_json_text = to_json $perl_hash_or_arrayref; |
14 | $utf8_encoded_json_text = to_json $perl_hash_or_arrayref; |
11 | $perl_hash_or_arrayref = from_json $utf8_encoded_json_text; |
15 | $perl_hash_or_arrayref = from_json $utf8_encoded_json_text; |
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 | |
16 | |
17 | # OO-interface |
17 | # OO-interface |
18 | |
18 | |
19 | $coder = JSON::XS->new->ascii->pretty->allow_nonref; |
19 | $coder = JSON::XS->new->ascii->pretty->allow_nonref; |
20 | $pretty_printed_unencoded = $coder->encode ($perl_scalar); |
20 | $pretty_printed_unencoded = $coder->encode ($perl_scalar); |
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71 | FUNCTIONAL INTERFACE |
71 | FUNCTIONAL INTERFACE |
72 | The following convinience methods are provided by this module. They are |
72 | The following convinience methods are provided by this module. They are |
73 | exported by default: |
73 | exported by default: |
74 | |
74 | |
75 | $json_text = to_json $perl_scalar |
75 | $json_text = to_json $perl_scalar |
76 | Converts the given Perl data structure (a simple scalar or a |
76 | Converts the given Perl data structure to a UTF-8 encoded, binary |
77 | reference to a hash or array) to a UTF-8 encoded, binary string |
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78 | (that is, the string contains octets only). Croaks on error. |
77 | string (that is, the string contains octets only). Croaks on error. |
79 | |
78 | |
80 | This function call is functionally identical to: |
79 | This function call is functionally identical to: |
81 | |
80 | |
82 | $json_text = JSON::XS->new->utf8->encode ($perl_scalar) |
81 | $json_text = JSON::XS->new->utf8->encode ($perl_scalar) |
83 | |
82 | |
84 | except being faster. |
83 | except being faster. |
85 | |
84 | |
86 | $perl_scalar = from_json $json_text |
85 | $perl_scalar = from_json $json_text |
87 | The opposite of "to_json": expects an UTF-8 (binary) string and |
86 | The opposite of "to_json": expects an UTF-8 (binary) string and |
88 | tries to parse that as an UTF-8 encoded JSON text, returning the |
87 | tries to parse that as an UTF-8 encoded JSON text, returning the |
89 | resulting simple scalar or reference. Croaks on error. |
88 | resulting reference. Croaks on error. |
90 | |
89 | |
91 | This function call is functionally identical to: |
90 | This function call is functionally identical to: |
92 | |
91 | |
93 | $perl_scalar = JSON::XS->new->utf8->decode ($json_text) |
92 | $perl_scalar = JSON::XS->new->utf8->decode ($json_text) |
94 | |
93 | |
95 | except being faster. |
94 | except being faster. |
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95 | |
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96 | $is_boolean = JSON::XS::is_bool $scalar |
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97 | Returns true if the passed scalar represents either JSON::XS::true |
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98 | or JSON::XS::false, two constants that act like 1 and 0, |
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99 | respectively and are used to represent JSON "true" and "false" |
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100 | values in Perl. |
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101 | |
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102 | See MAPPING, below, for more information on how JSON values are |
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103 | mapped to Perl. |
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104 | |
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105 | A FEW NOTES ON UNICODE AND PERL |
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106 | Since this often leads to confusion, here are a few very clear words on |
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107 | how Unicode works in Perl, modulo bugs. |
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108 | |
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109 | 1. Perl strings can store characters with ordinal values > 255. |
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110 | This enables you to store unicode characters as single characters in |
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111 | a Perl string - very natural. |
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112 | |
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113 | 2. Perl does *not* associate an encoding with your strings. |
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114 | Unless you force it to, e.g. when matching it against a regex, or |
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115 | printing the scalar to a file, in which case Perl either interprets |
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116 | your string as locale-encoded text, octets/binary, or as Unicode, |
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117 | depending on various settings. In no case is an encoding stored |
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118 | together with your data, it is *use* that decides encoding, not any |
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119 | magical metadata. |
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120 | |
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121 | 3. The internal utf-8 flag has no meaning with regards to the encoding |
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122 | of your string. |
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123 | Just ignore that flag unless you debug a Perl bug, a module written |
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124 | in XS or want to dive into the internals of perl. Otherwise it will |
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125 | only confuse you, as, despite the name, it says nothing about how |
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126 | your string is encoded. You can have unicode strings with that flag |
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127 | set, with that flag clear, and you can have binary data with that |
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128 | flag set and that flag clear. Other possibilities exist, too. |
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129 | |
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130 | If you didn't know about that flag, just the better, pretend it |
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131 | doesn't exist. |
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132 | |
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133 | 4. A "Unicode String" is simply a string where each character can be |
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134 | validly interpreted as a Unicode codepoint. |
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135 | If you have UTF-8 encoded data, it is no longer a Unicode string, |
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136 | but a Unicode string encoded in UTF-8, giving you a binary string. |
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137 | |
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138 | 5. A string containing "high" (> 255) character values is *not* a UTF-8 |
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139 | string. |
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140 | Its a fact. Learn to live with it. |
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141 | |
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142 | I hope this helps :) |
96 | |
143 | |
97 | OBJECT-ORIENTED INTERFACE |
144 | OBJECT-ORIENTED INTERFACE |
98 | The object oriented interface lets you configure your own encoding or |
145 | The object oriented interface lets you configure your own encoding or |
99 | decoding style, within the limits of supported formats. |
146 | decoding style, within the limits of supported formats. |
100 | |
147 | |
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112 | $json = $json->ascii ([$enable]) |
159 | $json = $json->ascii ([$enable]) |
113 | If $enable is true (or missing), then the "encode" method will not |
160 | If $enable is true (or missing), then the "encode" method will not |
114 | generate characters outside the code range 0..127 (which is ASCII). |
161 | generate characters outside the code range 0..127 (which is ASCII). |
115 | Any unicode characters outside that range will be escaped using |
162 | Any unicode characters outside that range will be escaped using |
116 | either a single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL |
163 | either a single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL |
117 | escape sequence, as per RFC4627. |
164 | escape sequence, as per RFC4627. The resulting encoded JSON text can |
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165 | be treated as a native unicode string, an ascii-encoded, |
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166 | latin1-encoded or UTF-8 encoded string, or any other superset of |
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167 | ASCII. |
118 | |
168 | |
119 | If $enable is false, then the "encode" method will not escape |
169 | If $enable is false, then the "encode" method will not escape |
120 | Unicode characters unless required by the JSON syntax. This results |
170 | Unicode characters unless required by the JSON syntax or other |
121 | in a faster and more compact format. |
171 | flags. This results in a faster and more compact format. |
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172 | |
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173 | The main use for this flag is to produce JSON texts that can be |
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174 | transmitted over a 7-bit channel, as the encoded JSON texts will not |
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175 | contain any 8 bit characters. |
122 | |
176 | |
123 | JSON::XS->new->ascii (1)->encode ([chr 0x10401]) |
177 | JSON::XS->new->ascii (1)->encode ([chr 0x10401]) |
124 | => ["\ud801\udc01"] |
178 | => ["\ud801\udc01"] |
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179 | |
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180 | $json = $json->latin1 ([$enable]) |
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181 | If $enable is true (or missing), then the "encode" method will |
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182 | encode the resulting JSON text as latin1 (or iso-8859-1), escaping |
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183 | any characters outside the code range 0..255. The resulting string |
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184 | can be treated as a latin1-encoded JSON text or a native unicode |
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185 | string. The "decode" method will not be affected in any way by this |
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186 | flag, as "decode" by default expects unicode, which is a strict |
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187 | superset of latin1. |
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188 | |
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189 | If $enable is false, then the "encode" method will not escape |
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190 | Unicode characters unless required by the JSON syntax or other |
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191 | flags. |
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192 | |
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193 | The main use for this flag is efficiently encoding binary data as |
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194 | JSON text, as most octets will not be escaped, resulting in a |
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195 | smaller encoded size. The disadvantage is that the resulting JSON |
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196 | text is encoded in latin1 (and must correctly be treated as such |
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197 | when storing and transfering), a rare encoding for JSON. It is |
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198 | therefore most useful when you want to store data structures known |
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199 | to contain binary data efficiently in files or databases, not when |
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200 | talking to other JSON encoders/decoders. |
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201 | |
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202 | JSON::XS->new->latin1->encode (["\x{89}\x{abc}"] |
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203 | => ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not) |
125 | |
204 | |
126 | $json = $json->utf8 ([$enable]) |
205 | $json = $json->utf8 ([$enable]) |
127 | If $enable is true (or missing), then the "encode" method will |
206 | If $enable is true (or missing), then the "encode" method will |
128 | encode the JSON result into UTF-8, as required by many protocols, |
207 | encode the JSON result into UTF-8, as required by many protocols, |
129 | while the "decode" method expects to be handled an UTF-8-encoded |
208 | while the "decode" method expects to be handled an UTF-8-encoded |
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203 | |
282 | |
204 | Example, space_before and indent disabled, space_after enabled: |
283 | Example, space_before and indent disabled, space_after enabled: |
205 | |
284 | |
206 | {"key": "value"} |
285 | {"key": "value"} |
207 | |
286 | |
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287 | $json = $json->relaxed ([$enable]) |
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288 | If $enable is true (or missing), then "decode" will accept some |
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289 | extensions to normal JSON syntax (see below). "encode" will not be |
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290 | affected in anyway. *Be aware that this option makes you accept |
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291 | invalid JSON texts as if they were valid!*. I suggest only to use |
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292 | this option to parse application-specific files written by humans |
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293 | (configuration files, resource files etc.) |
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294 | |
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295 | If $enable is false (the default), then "decode" will only accept |
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296 | valid JSON texts. |
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297 | |
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298 | Currently accepted extensions are: |
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299 | |
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300 | * list items can have an end-comma |
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301 | JSON *separates* array elements and key-value pairs with commas. |
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302 | This can be annoying if you write JSON texts manually and want |
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303 | to be able to quickly append elements, so this extension accepts |
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304 | comma at the end of such items not just between them: |
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305 | |
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306 | [ |
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307 | 1, |
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308 | 2, <- this comma not normally allowed |
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309 | ] |
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310 | { |
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311 | "k1": "v1", |
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312 | "k2": "v2", <- this comma not normally allowed |
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313 | } |
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314 | |
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315 | * shell-style '#'-comments |
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316 | Whenever JSON allows whitespace, shell-style comments are |
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317 | additionally allowed. They are terminated by the first |
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318 | carriage-return or line-feed character, after which more |
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319 | white-space and comments are allowed. |
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320 | |
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321 | [ |
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322 | 1, # this comment not allowed in JSON |
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323 | # neither this one... |
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324 | ] |
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325 | |
208 | $json = $json->canonical ([$enable]) |
326 | $json = $json->canonical ([$enable]) |
209 | If $enable is true (or missing), then the "encode" method will |
327 | If $enable is true (or missing), then the "encode" method will |
210 | output JSON objects by sorting their keys. This is adding a |
328 | output JSON objects by sorting their keys. This is adding a |
211 | comparatively high overhead. |
329 | comparatively high overhead. |
212 | |
330 | |
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236 | Example, encode a Perl scalar as JSON value with enabled |
354 | Example, encode a Perl scalar as JSON value with enabled |
237 | "allow_nonref", resulting in an invalid JSON text: |
355 | "allow_nonref", resulting in an invalid JSON text: |
238 | |
356 | |
239 | JSON::XS->new->allow_nonref->encode ("Hello, World!") |
357 | JSON::XS->new->allow_nonref->encode ("Hello, World!") |
240 | => "Hello, World!" |
358 | => "Hello, World!" |
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359 | |
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360 | $json = $json->allow_blessed ([$enable]) |
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361 | If $enable is true (or missing), then the "encode" method will not |
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362 | barf when it encounters a blessed reference. Instead, the value of |
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363 | the convert_blessed option will decide wether "null" |
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364 | ("convert_blessed" disabled or no "to_json" method found) or a |
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365 | representation of the object ("convert_blessed" enabled and |
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366 | "to_json" method found) is being encoded. Has no effect on "decode". |
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367 | |
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368 | If $enable is false (the default), then "encode" will throw an |
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369 | exception when it encounters a blessed object. |
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370 | |
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371 | $json = $json->convert_blessed ([$enable]) |
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372 | If $enable is true (or missing), then "encode", upon encountering a |
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373 | blessed object, will check for the availability of the "TO_JSON" |
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374 | method on the object's class. If found, it will be called in scalar |
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375 | context and the resulting scalar will be encoded instead of the |
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376 | object. If no "TO_JSON" method is found, the value of |
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377 | "allow_blessed" will decide what to do. |
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378 | |
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379 | The "TO_JSON" method may safely call die if it wants. If "TO_JSON" |
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380 | returns other blessed objects, those will be handled in the same |
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381 | way. "TO_JSON" must take care of not causing an endless recursion |
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382 | cycle (== crash) in this case. The name of "TO_JSON" was chosen |
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383 | because other methods called by the Perl core (== not by the user of |
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384 | the object) are usually in upper case letters and to avoid |
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385 | collisions with the "to_json" function. |
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386 | |
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387 | This setting does not yet influence "decode" in any way, but in the |
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388 | future, global hooks might get installed that influence "decode" and |
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389 | are enabled by this setting. |
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390 | |
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391 | If $enable is false, then the "allow_blessed" setting will decide |
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392 | what to do when a blessed object is found. |
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393 | |
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394 | $json = $json->filter_json_object ([$coderef->($hashref)]) |
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395 | When $coderef is specified, it will be called from "decode" each |
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396 | time it decodes a JSON object. The only argument is a reference to |
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397 | the newly-created hash. If the code references returns a single |
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398 | scalar (which need not be a reference), this value (i.e. a copy of |
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399 | that scalar to avoid aliasing) is inserted into the deserialised |
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400 | data structure. If it returns an empty list (NOTE: *not* "undef", |
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401 | which is a valid scalar), the original deserialised hash will be |
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402 | inserted. This setting can slow down decoding considerably. |
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403 | |
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404 | When $coderef is omitted or undefined, any existing callback will be |
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405 | removed and "decode" will not change the deserialised hash in any |
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406 | way. |
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407 | |
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408 | Example, convert all JSON objects into the integer 5: |
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409 | |
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410 | my $js = JSON::XS->new->filter_json_object (sub { 5 }); |
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411 | # returns [5] |
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412 | $js->decode ('[{}]') |
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413 | # throw an exception because allow_nonref is not enabled |
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414 | # so a lone 5 is not allowed. |
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415 | $js->decode ('{"a":1, "b":2}'); |
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416 | |
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417 | $json = $json->filter_json_single_key_object ($key [=> |
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418 | $coderef->($value)]) |
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419 | Works remotely similar to "filter_json_object", but is only called |
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420 | for JSON objects having a single key named $key. |
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421 | |
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422 | This $coderef is called before the one specified via |
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423 | "filter_json_object", if any. It gets passed the single value in the |
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424 | JSON object. If it returns a single value, it will be inserted into |
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425 | the data structure. If it returns nothing (not even "undef" but the |
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426 | empty list), the callback from "filter_json_object" will be called |
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427 | next, as if no single-key callback were specified. |
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428 | |
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429 | If $coderef is omitted or undefined, the corresponding callback will |
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430 | be disabled. There can only ever be one callback for a given key. |
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431 | |
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432 | As this callback gets called less often then the |
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433 | "filter_json_object" one, decoding speed will not usually suffer as |
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434 | much. Therefore, single-key objects make excellent targets to |
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435 | serialise Perl objects into, especially as single-key JSON objects |
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436 | are as close to the type-tagged value concept as JSON gets (its |
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437 | basically an ID/VALUE tuple). Of course, JSON does not support this |
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438 | in any way, so you need to make sure your data never looks like a |
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439 | serialised Perl hash. |
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440 | |
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441 | Typical names for the single object key are "__class_whatever__", or |
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442 | "$__dollars_are_rarely_used__$" or "}ugly_brace_placement", or even |
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443 | things like "__class_md5sum(classname)__", to reduce the risk of |
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444 | clashing with real hashes. |
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445 | |
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446 | Example, decode JSON objects of the form "{ "__widget__" => <id> }" |
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447 | into the corresponding $WIDGET{<id>} object: |
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448 | |
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449 | # return whatever is in $WIDGET{5}: |
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450 | JSON::XS |
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451 | ->new |
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452 | ->filter_json_single_key_object (__widget__ => sub { |
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453 | $WIDGET{ $_[0] } |
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454 | }) |
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455 | ->decode ('{"__widget__": 5') |
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456 | |
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457 | # this can be used with a TO_JSON method in some "widget" class |
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458 | # for serialisation to json: |
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459 | sub WidgetBase::TO_JSON { |
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460 | my ($self) = @_; |
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461 | |
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462 | unless ($self->{id}) { |
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463 | $self->{id} = ..get..some..id..; |
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464 | $WIDGET{$self->{id}} = $self; |
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465 | } |
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466 | |
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467 | { __widget__ => $self->{id} } |
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468 | } |
241 | |
469 | |
242 | $json = $json->shrink ([$enable]) |
470 | $json = $json->shrink ([$enable]) |
243 | Perl usually over-allocates memory a bit when allocating space for |
471 | Perl usually over-allocates memory a bit when allocating space for |
244 | strings. This flag optionally resizes strings generated by either |
472 | strings. This flag optionally resizes strings generated by either |
245 | "encode" or "decode" to their minimum size possible. This can save |
473 | "encode" or "decode" to their minimum size possible. This can save |
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278 | crossed to reach a given character in a string. |
506 | crossed to reach a given character in a string. |
279 | |
507 | |
280 | Setting the maximum depth to one disallows any nesting, so that |
508 | Setting the maximum depth to one disallows any nesting, so that |
281 | ensures that the object is only a single hash/object or array. |
509 | ensures that the object is only a single hash/object or array. |
282 | |
510 | |
283 | The argument to "max_depth" will be rounded up to the next nearest |
511 | The argument to "max_depth" will be rounded up to the next highest |
284 | power of two. |
512 | power of two. If no argument is given, the highest possible setting |
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513 | will be used, which is rarely useful. |
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514 | |
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515 | See SECURITY CONSIDERATIONS, below, for more info on why this is |
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516 | useful. |
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517 | |
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518 | $json = $json->max_size ([$maximum_string_size]) |
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519 | Set the maximum length a JSON text may have (in bytes) where |
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520 | decoding is being attempted. The default is 0, meaning no limit. |
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521 | When "decode" is called on a string longer then this number of |
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522 | characters it will not attempt to decode the string but throw an |
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523 | exception. This setting has no effect on "encode" (yet). |
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524 | |
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525 | The argument to "max_size" will be rounded up to the next highest |
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526 | power of two (so may be more than requested). If no argument is |
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527 | given, the limit check will be deactivated (same as when 0 is |
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528 | specified). |
285 | |
529 | |
286 | See SECURITY CONSIDERATIONS, below, for more info on why this is |
530 | See SECURITY CONSIDERATIONS, below, for more info on why this is |
287 | useful. |
531 | useful. |
288 | |
532 | |
289 | $json_text = $json->encode ($perl_scalar) |
533 | $json_text = $json->encode ($perl_scalar) |
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301 | |
545 | |
302 | JSON numbers and strings become simple Perl scalars. JSON arrays |
546 | JSON numbers and strings become simple Perl scalars. JSON arrays |
303 | become Perl arrayrefs and JSON objects become Perl hashrefs. "true" |
547 | become Perl arrayrefs and JSON objects become Perl hashrefs. "true" |
304 | becomes 1, "false" becomes 0 and "null" becomes "undef". |
548 | becomes 1, "false" becomes 0 and "null" becomes "undef". |
305 | |
549 | |
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550 | ($perl_scalar, $characters) = $json->decode_prefix ($json_text) |
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551 | This works like the "decode" method, but instead of raising an |
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552 | exception when there is trailing garbage after the first JSON |
|
|
553 | object, it will silently stop parsing there and return the number of |
|
|
554 | characters consumed so far. |
|
|
555 | |
|
|
556 | This is useful if your JSON texts are not delimited by an outer |
|
|
557 | protocol (which is not the brightest thing to do in the first place) |
|
|
558 | and you need to know where the JSON text ends. |
|
|
559 | |
|
|
560 | JSON::XS->new->decode_prefix ("[1] the tail") |
|
|
561 | => ([], 3) |
|
|
562 | |
306 | MAPPING |
563 | MAPPING |
307 | This section describes how JSON::XS maps Perl values to JSON values and |
564 | This section describes how JSON::XS maps Perl values to JSON values and |
308 | vice versa. These mappings are designed to "do the right thing" in most |
565 | vice versa. These mappings are designed to "do the right thing" in most |
309 | circumstances automatically, preserving round-tripping characteristics |
566 | circumstances automatically, preserving round-tripping characteristics |
310 | (what you put in comes out as something equivalent). |
567 | (what you put in comes out as something equivalent). |
… | |
… | |
326 | A JSON string becomes a string scalar in Perl - Unicode codepoints |
583 | A JSON string becomes a string scalar in Perl - Unicode codepoints |
327 | in JSON are represented by the same codepoints in the Perl string, |
584 | in JSON are represented by the same codepoints in the Perl string, |
328 | so no manual decoding is necessary. |
585 | so no manual decoding is necessary. |
329 | |
586 | |
330 | number |
587 | number |
331 | A JSON number becomes either an integer or numeric (floating point) |
588 | A JSON number becomes either an integer, numeric (floating point) or |
332 | scalar in perl, depending on its range and any fractional parts. On |
589 | string scalar in perl, depending on its range and any fractional |
333 | the Perl level, there is no difference between those as Perl handles |
590 | parts. On the Perl level, there is no difference between those as |
334 | all the conversion details, but an integer may take slightly less |
591 | Perl handles all the conversion details, but an integer may take |
335 | memory and might represent more values exactly than (floating point) |
592 | slightly less memory and might represent more values exactly than |
336 | numbers. |
593 | (floating point) numbers. |
|
|
594 | |
|
|
595 | If the number consists of digits only, JSON::XS will try to |
|
|
596 | represent it as an integer value. If that fails, it will try to |
|
|
597 | represent it as a numeric (floating point) value if that is possible |
|
|
598 | without loss of precision. Otherwise it will preserve the number as |
|
|
599 | a string value. |
|
|
600 | |
|
|
601 | Numbers containing a fractional or exponential part will always be |
|
|
602 | represented as numeric (floating point) values, possibly at a loss |
|
|
603 | of precision. |
|
|
604 | |
|
|
605 | This might create round-tripping problems as numbers might become |
|
|
606 | strings, but as Perl is typeless there is no other way to do it. |
337 | |
607 | |
338 | true, false |
608 | true, false |
339 | These JSON atoms become 0, 1, respectively. Information is lost in |
609 | These JSON atoms become "JSON::XS::true" and "JSON::XS::false", |
340 | this process. Future versions might represent those values |
610 | respectively. They are overloaded to act almost exactly like the |
341 | differently, but they will be guarenteed to act like these integers |
611 | numbers 1 and 0. You can check wether a scalar is a JSON boolean by |
342 | would normally in Perl. |
612 | using the "JSON::XS::is_bool" function. |
343 | |
613 | |
344 | null |
614 | null |
345 | A JSON null atom becomes "undef" in Perl. |
615 | A JSON null atom becomes "undef" in Perl. |
346 | |
616 | |
347 | PERL -> JSON |
617 | PERL -> JSON |
… | |
… | |
371 | can also use "JSON::XS::false" and "JSON::XS::true" to improve |
641 | can also use "JSON::XS::false" and "JSON::XS::true" to improve |
372 | readability. |
642 | readability. |
373 | |
643 | |
374 | to_json [\0,JSON::XS::true] # yields [false,true] |
644 | to_json [\0,JSON::XS::true] # yields [false,true] |
375 | |
645 | |
|
|
646 | JSON::XS::true, JSON::XS::false |
|
|
647 | These special values become JSON true and JSON false values, |
|
|
648 | respectively. You can also use "\1" and "\0" directly if you want. |
|
|
649 | |
376 | blessed objects |
650 | blessed objects |
377 | Blessed objects are not allowed. JSON::XS currently tries to encode |
651 | Blessed objects are not allowed. JSON::XS currently tries to encode |
378 | their underlying representation (hash- or arrayref), but this |
652 | their underlying representation (hash- or arrayref), but this |
379 | behaviour might change in future versions. |
653 | behaviour might change in future versions. |
380 | |
654 | |
… | |
… | |
490 | Does not generate valid JSON texts (key strings are often unquoted, |
764 | Does not generate valid JSON texts (key strings are often unquoted, |
491 | empty keys result in nothing being output) |
765 | empty keys result in nothing being output) |
492 | |
766 | |
493 | Does not check input for validity. |
767 | Does not check input for validity. |
494 | |
768 | |
|
|
769 | JSON and YAML |
|
|
770 | You often hear that JSON is a subset (or a close subset) of YAML. This |
|
|
771 | is, however, a mass hysteria and very far from the truth. In general, |
|
|
772 | there is no way to configure JSON::XS to output a data structure as |
|
|
773 | valid YAML. |
|
|
774 | |
|
|
775 | If you really must use JSON::XS to generate YAML, you should use this |
|
|
776 | algorithm (subject to change in future versions): |
|
|
777 | |
|
|
778 | my $to_yaml = JSON::XS->new->utf8->space_after (1); |
|
|
779 | my $yaml = $to_yaml->encode ($ref) . "\n"; |
|
|
780 | |
|
|
781 | This will usually generate JSON texts that also parse as valid YAML. |
|
|
782 | Please note that YAML has hardcoded limits on (simple) object key |
|
|
783 | lengths that JSON doesn't have, so you should make sure that your hash |
|
|
784 | keys are noticably shorter than the 1024 characters YAML allows. |
|
|
785 | |
|
|
786 | There might be other incompatibilities that I am not aware of. In |
|
|
787 | general you should not try to generate YAML with a JSON generator or |
|
|
788 | vice versa, or try to parse JSON with a YAML parser or vice versa: |
|
|
789 | chances are high that you will run into severe interoperability |
|
|
790 | problems. |
|
|
791 | |
495 | SPEED |
792 | SPEED |
496 | It seems that JSON::XS is surprisingly fast, as shown in the following |
793 | It seems that JSON::XS is surprisingly fast, as shown in the following |
497 | tables. They have been generated with the help of the "eg/bench" program |
794 | tables. They have been generated with the help of the "eg/bench" program |
498 | in the JSON::XS distribution, to make it easy to compare on your own |
795 | in the JSON::XS distribution, to make it easy to compare on your own |
499 | system. |
796 | system. |
500 | |
797 | |
501 | First comes a comparison between various modules using a very short JSON |
798 | First comes a comparison between various modules using a very short |
502 | string: |
799 | single-line JSON string: |
503 | |
800 | |
504 | {"method": "handleMessage", "params": ["user1", "we were just talking"], "id": null} |
801 | {"method": "handleMessage", "params": ["user1", "we were just talking"], \ |
|
|
802 | "id": null, "array":[1,11,234,-5,1e5,1e7, true, false]} |
505 | |
803 | |
506 | It shows the number of encodes/decodes per second (JSON::XS uses the |
804 | It shows the number of encodes/decodes per second (JSON::XS uses the |
507 | functional interface, while JSON::XS/2 uses the OO interface with |
805 | functional interface, while JSON::XS/2 uses the OO interface with |
508 | pretty-printing and hashkey sorting enabled). Higher is better: |
806 | pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink). |
|
|
807 | Higher is better: |
509 | |
808 | |
|
|
809 | Storable | 15779.925 | 14169.946 | |
|
|
810 | -----------+------------+------------+ |
510 | module | encode | decode | |
811 | module | encode | decode | |
511 | -----------|------------|------------| |
812 | -----------|------------|------------| |
512 | JSON | 11488.516 | 7823.035 | |
813 | JSON | 4990.842 | 4088.813 | |
513 | JSON::DWIW | 94708.054 | 129094.260 | |
814 | JSON::DWIW | 51653.990 | 71575.154 | |
514 | JSON::PC | 63884.157 | 128528.212 | |
815 | JSON::PC | 65948.176 | 74631.744 | |
|
|
816 | JSON::PP | 8931.652 | 3817.168 | |
515 | JSON::Syck | 34898.677 | 42096.911 | |
817 | JSON::Syck | 24877.248 | 27776.848 | |
516 | JSON::XS | 654027.064 | 396423.669 | |
818 | JSON::XS | 388361.481 | 227951.304 | |
517 | JSON::XS/2 | 371564.190 | 371725.613 | |
819 | JSON::XS/2 | 227951.304 | 218453.333 | |
|
|
820 | JSON::XS/3 | 338250.323 | 218453.333 | |
|
|
821 | Storable | 16500.016 | 135300.129 | |
518 | -----------+------------+------------+ |
822 | -----------+------------+------------+ |
519 | |
823 | |
520 | That is, JSON::XS is more than six times faster than JSON::DWIW on |
824 | That is, JSON::XS is about five times faster than JSON::DWIW on |
521 | encoding, more than three times faster on decoding, and about thirty |
825 | encoding, about three times faster on decoding, and over fourty times |
522 | times faster than JSON, even with pretty-printing and key sorting. |
826 | faster than JSON, even with pretty-printing and key sorting. It also |
|
|
827 | compares favourably to Storable for small amounts of data. |
523 | |
828 | |
524 | Using a longer test string (roughly 18KB, generated from Yahoo! Locals |
829 | Using a longer test string (roughly 18KB, generated from Yahoo! Locals |
525 | search API (http://nanoref.com/yahooapis/mgPdGg): |
830 | search API (http://nanoref.com/yahooapis/mgPdGg): |
526 | |
831 | |
527 | module | encode | decode | |
832 | module | encode | decode | |
528 | -----------|------------|------------| |
833 | -----------|------------|------------| |
529 | JSON | 273.023 | 44.674 | |
834 | JSON | 55.260 | 34.971 | |
530 | JSON::DWIW | 1089.383 | 1145.704 | |
835 | JSON::DWIW | 825.228 | 1082.513 | |
531 | JSON::PC | 3097.419 | 2393.921 | |
836 | JSON::PC | 3571.444 | 2394.829 | |
532 | JSON::Syck | 514.060 | 843.053 | |
837 | JSON::PP | 210.987 | 32.574 | |
533 | JSON::XS | 6479.668 | 3636.364 | |
838 | JSON::Syck | 552.551 | 787.544 | |
534 | JSON::XS/2 | 3774.221 | 3599.124 | |
839 | JSON::XS | 5780.463 | 4854.519 | |
|
|
840 | JSON::XS/2 | 3869.998 | 4798.975 | |
|
|
841 | JSON::XS/3 | 5862.880 | 4798.975 | |
|
|
842 | Storable | 4445.002 | 5235.027 | |
535 | -----------+------------+------------+ |
843 | -----------+------------+------------+ |
536 | |
844 | |
537 | Again, JSON::XS leads by far. |
845 | Again, JSON::XS leads by far (except for Storable which non-surprisingly |
|
|
846 | decodes faster). |
538 | |
847 | |
539 | On large strings containing lots of high unicode characters, some |
848 | On large strings containing lots of high unicode characters, some |
540 | modules (such as JSON::PC) seem to decode faster than JSON::XS, but the |
849 | modules (such as JSON::PC) seem to decode faster than JSON::XS, but the |
541 | result will be broken due to missing (or wrong) unicode handling. Others |
850 | result will be broken due to missing (or wrong) unicode handling. Others |
542 | refuse to decode or encode properly, so it was impossible to prepare a |
851 | refuse to decode or encode properly, so it was impossible to prepare a |
… | |
… | |
553 | Second, you need to avoid resource-starving attacks. That means you |
862 | Second, you need to avoid resource-starving attacks. That means you |
554 | should limit the size of JSON texts you accept, or make sure then when |
863 | should limit the size of JSON texts you accept, or make sure then when |
555 | your resources run out, thats just fine (e.g. by using a separate |
864 | your resources run out, thats just fine (e.g. by using a separate |
556 | process that can crash safely). The size of a JSON text in octets or |
865 | process that can crash safely). The size of a JSON text in octets or |
557 | characters is usually a good indication of the size of the resources |
866 | characters is usually a good indication of the size of the resources |
558 | required to decode it into a Perl structure. |
867 | required to decode it into a Perl structure. While JSON::XS can check |
|
|
868 | the size of the JSON text, it might be too late when you already have it |
|
|
869 | in memory, so you might want to check the size before you accept the |
|
|
870 | string. |
559 | |
871 | |
560 | Third, JSON::XS recurses using the C stack when decoding objects and |
872 | Third, JSON::XS recurses using the C stack when decoding objects and |
561 | arrays. The C stack is a limited resource: for instance, on my amd64 |
873 | arrays. The C stack is a limited resource: for instance, on my amd64 |
562 | machine with 8MB of stack size I can decode around 180k nested arrays |
874 | machine with 8MB of stack size I can decode around 180k nested arrays |
563 | but only 14k nested JSON objects (due to perl itself recursing deeply on |
875 | but only 14k nested JSON objects (due to perl itself recursing deeply on |
… | |
… | |
565 | to be conservative, the default nesting limit is set to 512. If your |
877 | to be conservative, the default nesting limit is set to 512. If your |
566 | process has a smaller stack, you should adjust this setting accordingly |
878 | process has a smaller stack, you should adjust this setting accordingly |
567 | with the "max_depth" method. |
879 | with the "max_depth" method. |
568 | |
880 | |
569 | And last but least, something else could bomb you that I forgot to think |
881 | And last but least, something else could bomb you that I forgot to think |
570 | of. In that case, you get to keep the pieces. I am alway sopen for |
882 | of. In that case, you get to keep the pieces. I am always open for |
571 | hints, though... |
883 | hints, though... |
|
|
884 | |
|
|
885 | If you are using JSON::XS to return packets to consumption by javascript |
|
|
886 | scripts in a browser you should have a look at |
|
|
887 | <http://jpsykes.com/47/practical-csrf-and-json-security> to see wether |
|
|
888 | you are vulnerable to some common attack vectors (which really are |
|
|
889 | browser design bugs, but it is still you who will have to deal with it, |
|
|
890 | as major browser developers care only for features, not about doing |
|
|
891 | security right). |
|
|
892 | |
|
|
893 | THREADS |
|
|
894 | This module is *not* guarenteed to be thread safe and there are no plans |
|
|
895 | to change this until Perl gets thread support (as opposed to the |
|
|
896 | horribly slow so-called "threads" which are simply slow and bloated |
|
|
897 | process simulations - use fork, its *much* faster, cheaper, better). |
|
|
898 | |
|
|
899 | (It might actually work, but you ahve ben warned). |
572 | |
900 | |
573 | BUGS |
901 | BUGS |
574 | While the goal of this module is to be correct, that unfortunately does |
902 | While the goal of this module is to be correct, that unfortunately does |
575 | not mean its bug-free, only that I think its design is bug-free. It is |
903 | not mean its bug-free, only that I think its design is bug-free. It is |
576 | still relatively early in its development. If you keep reporting bugs |
904 | still relatively early in its development. If you keep reporting bugs |
577 | they will be fixed swiftly, though. |
905 | they will be fixed swiftly, though. |
578 | |
906 | |
|
|
907 | Please refrain from using rt.cpan.org or any other bug reporting |
|
|
908 | service. I put the contact address into my modules for a reason. |
|
|
909 | |
579 | AUTHOR |
910 | AUTHOR |
580 | Marc Lehmann <schmorp@schmorp.de> |
911 | Marc Lehmann <schmorp@schmorp.de> |
581 | http://home.schmorp.de/ |
912 | http://home.schmorp.de/ |
582 | |
913 | |