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 シリアライザ/デシリアライザ |
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5 | (http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html) |
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6 | |
4 | SYNOPSIS |
7 | SYNOPSIS |
5 | use JSON::XS; |
8 | use JSON::XS; |
6 | |
9 | |
7 | # exported functions, they croak on error |
10 | # exported functions, they croak on error |
8 | # and expect/generate UTF-8 |
11 | # and expect/generate UTF-8 |
9 | |
12 | |
10 | $utf8_encoded_json_text = to_json $perl_hash_or_arrayref; |
13 | $utf8_encoded_json_text = encode_json $perl_hash_or_arrayref; |
11 | $perl_hash_or_arrayref = from_json $utf8_encoded_json_text; |
14 | $perl_hash_or_arrayref = decode_json $utf8_encoded_json_text; |
12 | |
15 | |
13 | # OO-interface |
16 | # OO-interface |
14 | |
17 | |
15 | $coder = JSON::XS->new->ascii->pretty->allow_nonref; |
18 | $coder = JSON::XS->new->ascii->pretty->allow_nonref; |
16 | $pretty_printed_unencoded = $coder->encode ($perl_scalar); |
19 | $pretty_printed_unencoded = $coder->encode ($perl_scalar); |
17 | $perl_scalar = $coder->decode ($unicode_json_text); |
20 | $perl_scalar = $coder->decode ($unicode_json_text); |
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21 | |
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22 | # Note that JSON version 2.0 and above will automatically use JSON::XS |
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23 | # if available, at virtually no speed overhead either, so you should |
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24 | # be able to just: |
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25 | |
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26 | use JSON; |
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27 | |
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28 | # and do the same things, except that you have a pure-perl fallback now. |
18 | |
29 | |
19 | DESCRIPTION |
30 | DESCRIPTION |
20 | This module converts Perl data structures to JSON and vice versa. Its |
31 | This module converts Perl data structures to JSON and vice versa. Its |
21 | primary goal is to be *correct* and its secondary goal is to be *fast*. |
32 | primary goal is to be *correct* and its secondary goal is to be *fast*. |
22 | To reach the latter goal it was written in C. |
33 | To reach the latter goal it was written in C. |
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34 | |
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35 | Beginning with version 2.0 of the JSON module, when both JSON and |
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36 | JSON::XS are installed, then JSON will fall back on JSON::XS (this can |
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37 | be overridden) with no overhead due to emulation (by inheriting |
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38 | constructor and methods). If JSON::XS is not available, it will fall |
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39 | back to the compatible JSON::PP module as backend, so using JSON instead |
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40 | of JSON::XS gives you a portable JSON API that can be fast when you need |
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41 | and doesn't require a C compiler when that is a problem. |
23 | |
42 | |
24 | As this is the n-th-something JSON module on CPAN, what was the reason |
43 | As this is the n-th-something JSON module on CPAN, what was the reason |
25 | to write yet another JSON module? While it seems there are many JSON |
44 | to write yet another JSON module? While it seems there are many JSON |
26 | modules, none of them correctly handle all corner cases, and in most |
45 | modules, none of them correctly handle all corner cases, and in most |
27 | cases their maintainers are unresponsive, gone missing, or not listening |
46 | cases their maintainers are unresponsive, gone missing, or not listening |
28 | to bug reports for other reasons. |
47 | to bug reports for other reasons. |
29 | |
48 | |
30 | See COMPARISON, below, for a comparison to some other JSON modules. |
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31 | |
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32 | See MAPPING, below, on how JSON::XS maps perl values to JSON values and |
49 | See MAPPING, below, on how JSON::XS maps perl values to JSON values and |
33 | vice versa. |
50 | vice versa. |
34 | |
51 | |
35 | FEATURES |
52 | FEATURES |
36 | * correct unicode handling |
53 | * correct Unicode handling |
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54 | |
37 | This module knows how to handle Unicode, and even documents how and |
55 | This module knows how to handle Unicode, documents how and when it |
38 | when it does so. |
56 | does so, and even documents what "correct" means. |
39 | |
57 | |
40 | * round-trip integrity |
58 | * round-trip integrity |
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59 | |
41 | When you serialise a perl data structure using only datatypes |
60 | When you serialise a perl data structure using only data types |
42 | supported by JSON, the deserialised data structure is identical on |
61 | supported by JSON and Perl, the deserialised data structure is |
43 | the Perl level. (e.g. the string "2.0" doesn't suddenly become "2" |
62 | identical on the Perl level. (e.g. the string "2.0" doesn't suddenly |
44 | just because it looks like a number). |
63 | become "2" just because it looks like a number). There *are* minor |
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64 | exceptions to this, read the MAPPING section below to learn about |
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65 | those. |
45 | |
66 | |
46 | * strict checking of JSON correctness |
67 | * strict checking of JSON correctness |
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68 | |
47 | There is no guessing, no generating of illegal JSON texts by |
69 | There is no guessing, no generating of illegal JSON texts by |
48 | default, and only JSON is accepted as input by default (the latter |
70 | default, and only JSON is accepted as input by default (the latter |
49 | is a security feature). |
71 | is a security feature). |
50 | |
72 | |
51 | * fast |
73 | * fast |
52 | Compared to other JSON modules, this module compares favourably in |
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53 | terms of speed, too. |
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54 | |
74 | |
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75 | Compared to other JSON modules and other serialisers such as |
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76 | Storable, this module usually compares favourably in terms of speed, |
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77 | too. |
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78 | |
55 | * simple to use |
79 | * simple to use |
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80 | |
56 | This module has both a simple functional interface as well as an OO |
81 | This module has both a simple functional interface as well as an |
57 | interface. |
82 | object oriented interface interface. |
58 | |
83 | |
59 | * reasonably versatile output formats |
84 | * reasonably versatile output formats |
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85 | |
60 | You can choose between the most compact guarenteed single-line |
86 | You can choose between the most compact guaranteed-single-line |
61 | format possible (nice for simple line-based protocols), a pure-ascii |
87 | format possible (nice for simple line-based protocols), a pure-ASCII |
62 | format (for when your transport is not 8-bit clean, still supports |
88 | format (for when your transport is not 8-bit clean, still supports |
63 | the whole unicode range), or a pretty-printed format (for when you |
89 | the whole Unicode range), or a pretty-printed format (for when you |
64 | want to read that stuff). Or you can combine those features in |
90 | want to read that stuff). Or you can combine those features in |
65 | whatever way you like. |
91 | whatever way you like. |
66 | |
92 | |
67 | FUNCTIONAL INTERFACE |
93 | FUNCTIONAL INTERFACE |
68 | The following convinience methods are provided by this module. They are |
94 | The following convenience methods are provided by this module. They are |
69 | exported by default: |
95 | exported by default: |
70 | |
96 | |
71 | $json_text = to_json $perl_scalar |
97 | $json_text = encode_json $perl_scalar |
72 | Converts the given Perl data structure (a simple scalar or a |
98 | Converts the given Perl data structure to a UTF-8 encoded, binary |
73 | reference to a hash or array) to a UTF-8 encoded, binary string |
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74 | (that is, the string contains octets only). Croaks on error. |
99 | string (that is, the string contains octets only). Croaks on error. |
75 | |
100 | |
76 | This function call is functionally identical to: |
101 | This function call is functionally identical to: |
77 | |
102 | |
78 | $json_text = JSON::XS->new->utf8->encode ($perl_scalar) |
103 | $json_text = JSON::XS->new->utf8->encode ($perl_scalar) |
79 | |
104 | |
80 | except being faster. |
105 | Except being faster. |
81 | |
106 | |
82 | $perl_scalar = from_json $json_text |
107 | $perl_scalar = decode_json $json_text |
83 | The opposite of "to_json": expects an UTF-8 (binary) string and |
108 | The opposite of "encode_json": expects an UTF-8 (binary) string and |
84 | tries to parse that as an UTF-8 encoded JSON text, returning the |
109 | tries to parse that as an UTF-8 encoded JSON text, returning the |
85 | resulting simple scalar or reference. Croaks on error. |
110 | resulting reference. Croaks on error. |
86 | |
111 | |
87 | This function call is functionally identical to: |
112 | This function call is functionally identical to: |
88 | |
113 | |
89 | $perl_scalar = JSON::XS->new->utf8->decode ($json_text) |
114 | $perl_scalar = JSON::XS->new->utf8->decode ($json_text) |
90 | |
115 | |
91 | except being faster. |
116 | Except being faster. |
92 | |
117 | |
93 | $is_boolean = JSON::XS::is_bool $scalar |
118 | $is_boolean = JSON::XS::is_bool $scalar |
94 | Returns true if the passed scalar represents either JSON::XS::true |
119 | Returns true if the passed scalar represents either JSON::XS::true |
95 | or JSON::XS::false, two constants that act like 1 and 0, |
120 | or JSON::XS::false, two constants that act like 1 and 0, |
96 | respectively and are used to represent JSON "true" and "false" |
121 | respectively and are used to represent JSON "true" and "false" |
97 | values in Perl. |
122 | values in Perl. |
98 | |
123 | |
99 | See MAPPING, below, for more information on how JSON values are |
124 | See MAPPING, below, for more information on how JSON values are |
100 | mapped to Perl. |
125 | mapped to Perl. |
101 | |
126 | |
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127 | A FEW NOTES ON UNICODE AND PERL |
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128 | Since this often leads to confusion, here are a few very clear words on |
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129 | how Unicode works in Perl, modulo bugs. |
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130 | |
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131 | 1. Perl strings can store characters with ordinal values > 255. |
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132 | This enables you to store Unicode characters as single characters in |
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133 | a Perl string - very natural. |
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134 | |
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135 | 2. Perl does *not* associate an encoding with your strings. |
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136 | ... until you force it to, e.g. when matching it against a regex, or |
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137 | printing the scalar to a file, in which case Perl either interprets |
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138 | your string as locale-encoded text, octets/binary, or as Unicode, |
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139 | depending on various settings. In no case is an encoding stored |
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140 | together with your data, it is *use* that decides encoding, not any |
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141 | magical meta data. |
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142 | |
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143 | 3. The internal utf-8 flag has no meaning with regards to the encoding |
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144 | of your string. |
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145 | Just ignore that flag unless you debug a Perl bug, a module written |
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146 | in XS or want to dive into the internals of perl. Otherwise it will |
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147 | only confuse you, as, despite the name, it says nothing about how |
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148 | your string is encoded. You can have Unicode strings with that flag |
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149 | set, with that flag clear, and you can have binary data with that |
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150 | flag set and that flag clear. Other possibilities exist, too. |
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151 | |
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152 | If you didn't know about that flag, just the better, pretend it |
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153 | doesn't exist. |
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154 | |
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155 | 4. A "Unicode String" is simply a string where each character can be |
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156 | validly interpreted as a Unicode code point. |
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157 | If you have UTF-8 encoded data, it is no longer a Unicode string, |
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158 | but a Unicode string encoded in UTF-8, giving you a binary string. |
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159 | |
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160 | 5. A string containing "high" (> 255) character values is *not* a UTF-8 |
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161 | string. |
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162 | It's a fact. Learn to live with it. |
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163 | |
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164 | I hope this helps :) |
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165 | |
102 | OBJECT-ORIENTED INTERFACE |
166 | OBJECT-ORIENTED INTERFACE |
103 | The object oriented interface lets you configure your own encoding or |
167 | The object oriented interface lets you configure your own encoding or |
104 | decoding style, within the limits of supported formats. |
168 | decoding style, within the limits of supported formats. |
105 | |
169 | |
106 | $json = new JSON::XS |
170 | $json = new JSON::XS |
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113 | |
177 | |
114 | my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]}) |
178 | my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]}) |
115 | => {"a": [1, 2]} |
179 | => {"a": [1, 2]} |
116 | |
180 | |
117 | $json = $json->ascii ([$enable]) |
181 | $json = $json->ascii ([$enable]) |
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182 | $enabled = $json->get_ascii |
118 | If $enable is true (or missing), then the "encode" method will not |
183 | If $enable is true (or missing), then the "encode" method will not |
119 | generate characters outside the code range 0..127 (which is ASCII). |
184 | generate characters outside the code range 0..127 (which is ASCII). |
120 | Any unicode characters outside that range will be escaped using |
185 | Any Unicode characters outside that range will be escaped using |
121 | either a single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL |
186 | either a single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL |
122 | escape sequence, as per RFC4627. The resulting encoded JSON text can |
187 | escape sequence, as per RFC4627. The resulting encoded JSON text can |
123 | be treated as a native unicode string, an ascii-encoded, |
188 | be treated as a native Unicode string, an ascii-encoded, |
124 | latin1-encoded or UTF-8 encoded string, or any other superset of |
189 | latin1-encoded or UTF-8 encoded string, or any other superset of |
125 | ASCII. |
190 | ASCII. |
126 | |
191 | |
127 | If $enable is false, then the "encode" method will not escape |
192 | If $enable is false, then the "encode" method will not escape |
128 | Unicode characters unless required by the JSON syntax or other |
193 | Unicode characters unless required by the JSON syntax or other |
129 | flags. This results in a faster and more compact format. |
194 | flags. This results in a faster and more compact format. |
130 | |
195 | |
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196 | See also the section *ENCODING/CODESET FLAG NOTES* later in this |
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197 | document. |
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198 | |
131 | The main use for this flag is to produce JSON texts that can be |
199 | The main use for this flag is to produce JSON texts that can be |
132 | transmitted over a 7-bit channel, as the encoded JSON texts will not |
200 | transmitted over a 7-bit channel, as the encoded JSON texts will not |
133 | contain any 8 bit characters. |
201 | contain any 8 bit characters. |
134 | |
202 | |
135 | JSON::XS->new->ascii (1)->encode ([chr 0x10401]) |
203 | JSON::XS->new->ascii (1)->encode ([chr 0x10401]) |
136 | => ["\ud801\udc01"] |
204 | => ["\ud801\udc01"] |
137 | |
205 | |
138 | $json = $json->latin1 ([$enable]) |
206 | $json = $json->latin1 ([$enable]) |
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207 | $enabled = $json->get_latin1 |
139 | If $enable is true (or missing), then the "encode" method will |
208 | If $enable is true (or missing), then the "encode" method will |
140 | encode the resulting JSON text as latin1 (or iso-8859-1), escaping |
209 | encode the resulting JSON text as latin1 (or iso-8859-1), escaping |
141 | any characters outside the code range 0..255. The resulting string |
210 | any characters outside the code range 0..255. The resulting string |
142 | can be treated as a latin1-encoded JSON text or a native unicode |
211 | can be treated as a latin1-encoded JSON text or a native Unicode |
143 | string. The "decode" method will not be affected in any way by this |
212 | string. The "decode" method will not be affected in any way by this |
144 | flag, as "decode" by default expects unicode, which is a strict |
213 | flag, as "decode" by default expects Unicode, which is a strict |
145 | superset of latin1. |
214 | superset of latin1. |
146 | |
215 | |
147 | If $enable is false, then the "encode" method will not escape |
216 | If $enable is false, then the "encode" method will not escape |
148 | Unicode characters unless required by the JSON syntax or other |
217 | Unicode characters unless required by the JSON syntax or other |
149 | flags. |
218 | flags. |
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219 | |
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220 | See also the section *ENCODING/CODESET FLAG NOTES* later in this |
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221 | document. |
150 | |
222 | |
151 | The main use for this flag is efficiently encoding binary data as |
223 | The main use for this flag is efficiently encoding binary data as |
152 | JSON text, as most octets will not be escaped, resulting in a |
224 | JSON text, as most octets will not be escaped, resulting in a |
153 | smaller encoded size. The disadvantage is that the resulting JSON |
225 | smaller encoded size. The disadvantage is that the resulting JSON |
154 | text is encoded in latin1 (and must correctly be treated as such |
226 | text is encoded in latin1 (and must correctly be treated as such |
155 | when storing and transfering), a rare encoding for JSON. It is |
227 | when storing and transferring), a rare encoding for JSON. It is |
156 | therefore most useful when you want to store data structures known |
228 | therefore most useful when you want to store data structures known |
157 | to contain binary data efficiently in files or databases, not when |
229 | to contain binary data efficiently in files or databases, not when |
158 | talking to other JSON encoders/decoders. |
230 | talking to other JSON encoders/decoders. |
159 | |
231 | |
160 | JSON::XS->new->latin1->encode (["\x{89}\x{abc}"] |
232 | JSON::XS->new->latin1->encode (["\x{89}\x{abc}"] |
161 | => ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not) |
233 | => ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not) |
162 | |
234 | |
163 | $json = $json->utf8 ([$enable]) |
235 | $json = $json->utf8 ([$enable]) |
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236 | $enabled = $json->get_utf8 |
164 | If $enable is true (or missing), then the "encode" method will |
237 | If $enable is true (or missing), then the "encode" method will |
165 | encode the JSON result into UTF-8, as required by many protocols, |
238 | encode the JSON result into UTF-8, as required by many protocols, |
166 | while the "decode" method expects to be handled an UTF-8-encoded |
239 | while the "decode" method expects to be handled an UTF-8-encoded |
167 | string. Please note that UTF-8-encoded strings do not contain any |
240 | string. Please note that UTF-8-encoded strings do not contain any |
168 | characters outside the range 0..255, they are thus useful for |
241 | characters outside the range 0..255, they are thus useful for |
169 | bytewise/binary I/O. In future versions, enabling this option might |
242 | bytewise/binary I/O. In future versions, enabling this option might |
170 | enable autodetection of the UTF-16 and UTF-32 encoding families, as |
243 | enable autodetection of the UTF-16 and UTF-32 encoding families, as |
171 | described in RFC4627. |
244 | described in RFC4627. |
172 | |
245 | |
173 | If $enable is false, then the "encode" method will return the JSON |
246 | If $enable is false, then the "encode" method will return the JSON |
174 | string as a (non-encoded) unicode string, while "decode" expects |
247 | string as a (non-encoded) Unicode string, while "decode" expects |
175 | thus a unicode string. Any decoding or encoding (e.g. to UTF-8 or |
248 | thus a Unicode string. Any decoding or encoding (e.g. to UTF-8 or |
176 | UTF-16) needs to be done yourself, e.g. using the Encode module. |
249 | UTF-16) needs to be done yourself, e.g. using the Encode module. |
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250 | |
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251 | See also the section *ENCODING/CODESET FLAG NOTES* later in this |
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252 | document. |
177 | |
253 | |
178 | Example, output UTF-16BE-encoded JSON: |
254 | Example, output UTF-16BE-encoded JSON: |
179 | |
255 | |
180 | use Encode; |
256 | use Encode; |
181 | $jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object); |
257 | $jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object); |
… | |
… | |
200 | 2 |
276 | 2 |
201 | ] |
277 | ] |
202 | } |
278 | } |
203 | |
279 | |
204 | $json = $json->indent ([$enable]) |
280 | $json = $json->indent ([$enable]) |
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281 | $enabled = $json->get_indent |
205 | If $enable is true (or missing), then the "encode" method will use a |
282 | If $enable is true (or missing), then the "encode" method will use a |
206 | multiline format as output, putting every array member or |
283 | multiline format as output, putting every array member or |
207 | object/hash key-value pair into its own line, identing them |
284 | object/hash key-value pair into its own line, indenting them |
208 | properly. |
285 | properly. |
209 | |
286 | |
210 | If $enable is false, no newlines or indenting will be produced, and |
287 | If $enable is false, no newlines or indenting will be produced, and |
211 | the resulting JSON text is guarenteed not to contain any "newlines". |
288 | the resulting JSON text is guaranteed not to contain any "newlines". |
212 | |
289 | |
213 | This setting has no effect when decoding JSON texts. |
290 | This setting has no effect when decoding JSON texts. |
214 | |
291 | |
215 | $json = $json->space_before ([$enable]) |
292 | $json = $json->space_before ([$enable]) |
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293 | $enabled = $json->get_space_before |
216 | If $enable is true (or missing), then the "encode" method will add |
294 | If $enable is true (or missing), then the "encode" method will add |
217 | an extra optional space before the ":" separating keys from values |
295 | an extra optional space before the ":" separating keys from values |
218 | in JSON objects. |
296 | in JSON objects. |
219 | |
297 | |
220 | If $enable is false, then the "encode" method will not add any extra |
298 | If $enable is false, then the "encode" method will not add any extra |
… | |
… | |
226 | Example, space_before enabled, space_after and indent disabled: |
304 | Example, space_before enabled, space_after and indent disabled: |
227 | |
305 | |
228 | {"key" :"value"} |
306 | {"key" :"value"} |
229 | |
307 | |
230 | $json = $json->space_after ([$enable]) |
308 | $json = $json->space_after ([$enable]) |
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309 | $enabled = $json->get_space_after |
231 | If $enable is true (or missing), then the "encode" method will add |
310 | If $enable is true (or missing), then the "encode" method will add |
232 | an extra optional space after the ":" separating keys from values in |
311 | an extra optional space after the ":" separating keys from values in |
233 | JSON objects and extra whitespace after the "," separating key-value |
312 | JSON objects and extra whitespace after the "," separating key-value |
234 | pairs and array members. |
313 | pairs and array members. |
235 | |
314 | |
… | |
… | |
241 | Example, space_before and indent disabled, space_after enabled: |
320 | Example, space_before and indent disabled, space_after enabled: |
242 | |
321 | |
243 | {"key": "value"} |
322 | {"key": "value"} |
244 | |
323 | |
245 | $json = $json->relaxed ([$enable]) |
324 | $json = $json->relaxed ([$enable]) |
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325 | $enabled = $json->get_relaxed |
246 | If $enable is true (or missing), then "decode" will accept some |
326 | If $enable is true (or missing), then "decode" will accept some |
247 | extensions to normal JSON syntax (see below). "encode" will not be |
327 | extensions to normal JSON syntax (see below). "encode" will not be |
248 | affected in anyway. *Be aware that this option makes you accept |
328 | affected in anyway. *Be aware that this option makes you accept |
249 | invalid JSON texts as if they were valid!*. I suggest only to use |
329 | invalid JSON texts as if they were valid!*. I suggest only to use |
250 | this option to parse application-specific files written by humans |
330 | this option to parse application-specific files written by humans |
… | |
… | |
253 | If $enable is false (the default), then "decode" will only accept |
333 | If $enable is false (the default), then "decode" will only accept |
254 | valid JSON texts. |
334 | valid JSON texts. |
255 | |
335 | |
256 | Currently accepted extensions are: |
336 | Currently accepted extensions are: |
257 | |
337 | |
258 | * list items can have an end-comma |
338 | * list items can have an end-comma |
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339 | |
259 | JSON *separates* array elements and key-value pairs with commas. |
340 | JSON *separates* array elements and key-value pairs with commas. |
260 | This can be annoying if you write JSON texts manually and want |
341 | This can be annoying if you write JSON texts manually and want |
261 | to be able to quickly append elements, so this extension accepts |
342 | to be able to quickly append elements, so this extension accepts |
262 | comma at the end of such items not just between them: |
343 | comma at the end of such items not just between them: |
263 | |
344 | |
… | |
… | |
268 | { |
349 | { |
269 | "k1": "v1", |
350 | "k1": "v1", |
270 | "k2": "v2", <- this comma not normally allowed |
351 | "k2": "v2", <- this comma not normally allowed |
271 | } |
352 | } |
272 | |
353 | |
|
|
354 | * shell-style '#'-comments |
|
|
355 | |
|
|
356 | Whenever JSON allows whitespace, shell-style comments are |
|
|
357 | additionally allowed. They are terminated by the first |
|
|
358 | carriage-return or line-feed character, after which more |
|
|
359 | white-space and comments are allowed. |
|
|
360 | |
|
|
361 | [ |
|
|
362 | 1, # this comment not allowed in JSON |
|
|
363 | # neither this one... |
|
|
364 | ] |
|
|
365 | |
273 | $json = $json->canonical ([$enable]) |
366 | $json = $json->canonical ([$enable]) |
|
|
367 | $enabled = $json->get_canonical |
274 | If $enable is true (or missing), then the "encode" method will |
368 | If $enable is true (or missing), then the "encode" method will |
275 | output JSON objects by sorting their keys. This is adding a |
369 | output JSON objects by sorting their keys. This is adding a |
276 | comparatively high overhead. |
370 | comparatively high overhead. |
277 | |
371 | |
278 | If $enable is false, then the "encode" method will output key-value |
372 | If $enable is false, then the "encode" method will output key-value |
279 | pairs in the order Perl stores them (which will likely change |
373 | pairs in the order Perl stores them (which will likely change |
280 | between runs of the same script). |
374 | between runs of the same script). |
281 | |
375 | |
282 | This option is useful if you want the same data structure to be |
376 | This option is useful if you want the same data structure to be |
283 | encoded as the same JSON text (given the same overall settings). If |
377 | encoded as the same JSON text (given the same overall settings). If |
284 | it is disabled, the same hash migh be encoded differently even if |
378 | it is disabled, the same hash might be encoded differently even if |
285 | contains the same data, as key-value pairs have no inherent ordering |
379 | contains the same data, as key-value pairs have no inherent ordering |
286 | in Perl. |
380 | in Perl. |
287 | |
381 | |
288 | This setting has no effect when decoding JSON texts. |
382 | This setting has no effect when decoding JSON texts. |
289 | |
383 | |
|
|
384 | This setting has currently no effect on tied hashes. |
|
|
385 | |
290 | $json = $json->allow_nonref ([$enable]) |
386 | $json = $json->allow_nonref ([$enable]) |
|
|
387 | $enabled = $json->get_allow_nonref |
291 | If $enable is true (or missing), then the "encode" method can |
388 | If $enable is true (or missing), then the "encode" method can |
292 | convert a non-reference into its corresponding string, number or |
389 | convert a non-reference into its corresponding string, number or |
293 | null JSON value, which is an extension to RFC4627. Likewise, |
390 | null JSON value, which is an extension to RFC4627. Likewise, |
294 | "decode" will accept those JSON values instead of croaking. |
391 | "decode" will accept those JSON values instead of croaking. |
295 | |
392 | |
… | |
… | |
302 | "allow_nonref", resulting in an invalid JSON text: |
399 | "allow_nonref", resulting in an invalid JSON text: |
303 | |
400 | |
304 | JSON::XS->new->allow_nonref->encode ("Hello, World!") |
401 | JSON::XS->new->allow_nonref->encode ("Hello, World!") |
305 | => "Hello, World!" |
402 | => "Hello, World!" |
306 | |
403 | |
|
|
404 | $json = $json->allow_unknown ([$enable]) |
|
|
405 | $enabled = $json->get_allow_unknown |
|
|
406 | If $enable is true (or missing), then "encode" will *not* throw an |
|
|
407 | exception when it encounters values it cannot represent in JSON (for |
|
|
408 | example, filehandles) but instead will encode a JSON "null" value. |
|
|
409 | Note that blessed objects are not included here and are handled |
|
|
410 | separately by c<allow_nonref>. |
|
|
411 | |
|
|
412 | If $enable is false (the default), then "encode" will throw an |
|
|
413 | exception when it encounters anything it cannot encode as JSON. |
|
|
414 | |
|
|
415 | This option does not affect "decode" in any way, and it is |
|
|
416 | recommended to leave it off unless you know your communications |
|
|
417 | partner. |
|
|
418 | |
307 | $json = $json->allow_blessed ([$enable]) |
419 | $json = $json->allow_blessed ([$enable]) |
|
|
420 | $enabled = $json->get_allow_blessed |
308 | If $enable is true (or missing), then the "encode" method will not |
421 | If $enable is true (or missing), then the "encode" method will not |
309 | barf when it encounters a blessed reference. Instead, the value of |
422 | barf when it encounters a blessed reference. Instead, the value of |
310 | the convert_blessed option will decide wether "null" |
423 | the convert_blessed option will decide whether "null" |
311 | ("convert_blessed" disabled or no "to_json" method found) or a |
424 | ("convert_blessed" disabled or no "TO_JSON" method found) or a |
312 | representation of the object ("convert_blessed" enabled and |
425 | representation of the object ("convert_blessed" enabled and |
313 | "to_json" method found) is being encoded. Has no effect on "decode". |
426 | "TO_JSON" method found) is being encoded. Has no effect on "decode". |
314 | |
427 | |
315 | If $enable is false (the default), then "encode" will throw an |
428 | If $enable is false (the default), then "encode" will throw an |
316 | exception when it encounters a blessed object. |
429 | exception when it encounters a blessed object. |
317 | |
430 | |
318 | $json = $json->convert_blessed ([$enable]) |
431 | $json = $json->convert_blessed ([$enable]) |
|
|
432 | $enabled = $json->get_convert_blessed |
319 | If $enable is true (or missing), then "encode", upon encountering a |
433 | If $enable is true (or missing), then "encode", upon encountering a |
320 | blessed object, will check for the availability of the "TO_JSON" |
434 | blessed object, will check for the availability of the "TO_JSON" |
321 | method on the object's class. If found, it will be called in scalar |
435 | method on the object's class. If found, it will be called in scalar |
322 | context and the resulting scalar will be encoded instead of the |
436 | context and the resulting scalar will be encoded instead of the |
323 | object. If no "TO_JSON" method is found, the value of |
437 | object. If no "TO_JSON" method is found, the value of |
… | |
… | |
327 | returns other blessed objects, those will be handled in the same |
441 | returns other blessed objects, those will be handled in the same |
328 | way. "TO_JSON" must take care of not causing an endless recursion |
442 | way. "TO_JSON" must take care of not causing an endless recursion |
329 | cycle (== crash) in this case. The name of "TO_JSON" was chosen |
443 | cycle (== crash) in this case. The name of "TO_JSON" was chosen |
330 | because other methods called by the Perl core (== not by the user of |
444 | because other methods called by the Perl core (== not by the user of |
331 | the object) are usually in upper case letters and to avoid |
445 | the object) are usually in upper case letters and to avoid |
332 | collisions with the "to_json" function. |
446 | collisions with any "to_json" function or method. |
333 | |
447 | |
334 | This setting does not yet influence "decode" in any way, but in the |
448 | This setting does not yet influence "decode" in any way, but in the |
335 | future, global hooks might get installed that influence "decode" and |
449 | future, global hooks might get installed that influence "decode" and |
336 | are enabled by this setting. |
450 | are enabled by this setting. |
337 | |
451 | |
… | |
… | |
378 | |
492 | |
379 | As this callback gets called less often then the |
493 | As this callback gets called less often then the |
380 | "filter_json_object" one, decoding speed will not usually suffer as |
494 | "filter_json_object" one, decoding speed will not usually suffer as |
381 | much. Therefore, single-key objects make excellent targets to |
495 | much. Therefore, single-key objects make excellent targets to |
382 | serialise Perl objects into, especially as single-key JSON objects |
496 | serialise Perl objects into, especially as single-key JSON objects |
383 | are as close to the type-tagged value concept as JSON gets (its |
497 | are as close to the type-tagged value concept as JSON gets (it's |
384 | basically an ID/VALUE tuple). Of course, JSON does not support this |
498 | basically an ID/VALUE tuple). Of course, JSON does not support this |
385 | in any way, so you need to make sure your data never looks like a |
499 | in any way, so you need to make sure your data never looks like a |
386 | serialised Perl hash. |
500 | serialised Perl hash. |
387 | |
501 | |
388 | Typical names for the single object key are "__class_whatever__", or |
502 | Typical names for the single object key are "__class_whatever__", or |
… | |
… | |
413 | |
527 | |
414 | { __widget__ => $self->{id} } |
528 | { __widget__ => $self->{id} } |
415 | } |
529 | } |
416 | |
530 | |
417 | $json = $json->shrink ([$enable]) |
531 | $json = $json->shrink ([$enable]) |
|
|
532 | $enabled = $json->get_shrink |
418 | Perl usually over-allocates memory a bit when allocating space for |
533 | Perl usually over-allocates memory a bit when allocating space for |
419 | strings. This flag optionally resizes strings generated by either |
534 | strings. This flag optionally resizes strings generated by either |
420 | "encode" or "decode" to their minimum size possible. This can save |
535 | "encode" or "decode" to their minimum size possible. This can save |
421 | memory when your JSON texts are either very very long or you have |
536 | memory when your JSON texts are either very very long or you have |
422 | many short strings. It will also try to downgrade any strings to |
537 | many short strings. It will also try to downgrade any strings to |
… | |
… | |
440 | converting strings that look like integers or floats into integers |
555 | converting strings that look like integers or floats into integers |
441 | or floats internally (there is no difference on the Perl level), |
556 | or floats internally (there is no difference on the Perl level), |
442 | saving space. |
557 | saving space. |
443 | |
558 | |
444 | $json = $json->max_depth ([$maximum_nesting_depth]) |
559 | $json = $json->max_depth ([$maximum_nesting_depth]) |
|
|
560 | $max_depth = $json->get_max_depth |
445 | Sets the maximum nesting level (default 512) accepted while encoding |
561 | Sets the maximum nesting level (default 512) accepted while encoding |
446 | or decoding. If the JSON text or Perl data structure has an equal or |
562 | or decoding. If a higher nesting level is detected in JSON text or a |
447 | higher nesting level then this limit, then the encoder and decoder |
563 | Perl data structure, then the encoder and decoder will stop and |
448 | will stop and croak at that point. |
564 | croak at that point. |
449 | |
565 | |
450 | Nesting level is defined by number of hash- or arrayrefs that the |
566 | Nesting level is defined by number of hash- or arrayrefs that the |
451 | encoder needs to traverse to reach a given point or the number of |
567 | encoder needs to traverse to reach a given point or the number of |
452 | "{" or "[" characters without their matching closing parenthesis |
568 | "{" or "[" characters without their matching closing parenthesis |
453 | crossed to reach a given character in a string. |
569 | crossed to reach a given character in a string. |
454 | |
570 | |
455 | Setting the maximum depth to one disallows any nesting, so that |
571 | Setting the maximum depth to one disallows any nesting, so that |
456 | ensures that the object is only a single hash/object or array. |
572 | ensures that the object is only a single hash/object or array. |
457 | |
573 | |
458 | The argument to "max_depth" will be rounded up to the next highest |
|
|
459 | power of two. If no argument is given, the highest possible setting |
574 | If no argument is given, the highest possible setting will be used, |
460 | will be used, which is rarely useful. |
575 | which is rarely useful. |
|
|
576 | |
|
|
577 | Note that nesting is implemented by recursion in C. The default |
|
|
578 | value has been chosen to be as large as typical operating systems |
|
|
579 | allow without crashing. |
461 | |
580 | |
462 | See SECURITY CONSIDERATIONS, below, for more info on why this is |
581 | See SECURITY CONSIDERATIONS, below, for more info on why this is |
463 | useful. |
582 | useful. |
464 | |
583 | |
465 | $json = $json->max_size ([$maximum_string_size]) |
584 | $json = $json->max_size ([$maximum_string_size]) |
|
|
585 | $max_size = $json->get_max_size |
466 | Set the maximum length a JSON text may have (in bytes) where |
586 | Set the maximum length a JSON text may have (in bytes) where |
467 | decoding is being attempted. The default is 0, meaning no limit. |
587 | decoding is being attempted. The default is 0, meaning no limit. |
468 | When "decode" is called on a string longer then this number of |
588 | When "decode" is called on a string that is longer then this many |
469 | characters it will not attempt to decode the string but throw an |
589 | bytes, it will not attempt to decode the string but throw an |
470 | exception. This setting has no effect on "encode" (yet). |
590 | exception. This setting has no effect on "encode" (yet). |
471 | |
591 | |
472 | The argument to "max_size" will be rounded up to the next highest |
|
|
473 | power of two (so may be more than requested). If no argument is |
|
|
474 | given, the limit check will be deactivated (same as when 0 is |
592 | If no argument is given, the limit check will be deactivated (same |
475 | specified). |
593 | as when 0 is specified). |
476 | |
594 | |
477 | See SECURITY CONSIDERATIONS, below, for more info on why this is |
595 | See SECURITY CONSIDERATIONS, below, for more info on why this is |
478 | useful. |
596 | useful. |
479 | |
597 | |
480 | $json_text = $json->encode ($perl_scalar) |
598 | $json_text = $json->encode ($perl_scalar) |
… | |
… | |
505 | and you need to know where the JSON text ends. |
623 | and you need to know where the JSON text ends. |
506 | |
624 | |
507 | JSON::XS->new->decode_prefix ("[1] the tail") |
625 | JSON::XS->new->decode_prefix ("[1] the tail") |
508 | => ([], 3) |
626 | => ([], 3) |
509 | |
627 | |
|
|
628 | INCREMENTAL PARSING |
|
|
629 | In some cases, there is the need for incremental parsing of JSON texts. |
|
|
630 | While this module always has to keep both JSON text and resulting Perl |
|
|
631 | data structure in memory at one time, it does allow you to parse a JSON |
|
|
632 | stream incrementally. It does so by accumulating text until it has a |
|
|
633 | full JSON object, which it then can decode. This process is similar to |
|
|
634 | using "decode_prefix" to see if a full JSON object is available, but is |
|
|
635 | much more efficient (and can be implemented with a minimum of method |
|
|
636 | calls). |
|
|
637 | |
|
|
638 | JSON::XS will only attempt to parse the JSON text once it is sure it has |
|
|
639 | enough text to get a decisive result, using a very simple but truly |
|
|
640 | incremental parser. This means that it sometimes won't stop as early as |
|
|
641 | the full parser, for example, it doesn't detect mismatched parentheses. |
|
|
642 | The only thing it guarantees is that it starts decoding as soon as a |
|
|
643 | syntactically valid JSON text has been seen. This means you need to set |
|
|
644 | resource limits (e.g. "max_size") to ensure the parser will stop parsing |
|
|
645 | in the presence if syntax errors. |
|
|
646 | |
|
|
647 | The following methods implement this incremental parser. |
|
|
648 | |
|
|
649 | [void, scalar or list context] = $json->incr_parse ([$string]) |
|
|
650 | This is the central parsing function. It can both append new text |
|
|
651 | and extract objects from the stream accumulated so far (both of |
|
|
652 | these functions are optional). |
|
|
653 | |
|
|
654 | If $string is given, then this string is appended to the already |
|
|
655 | existing JSON fragment stored in the $json object. |
|
|
656 | |
|
|
657 | After that, if the function is called in void context, it will |
|
|
658 | simply return without doing anything further. This can be used to |
|
|
659 | add more text in as many chunks as you want. |
|
|
660 | |
|
|
661 | If the method is called in scalar context, then it will try to |
|
|
662 | extract exactly *one* JSON object. If that is successful, it will |
|
|
663 | return this object, otherwise it will return "undef". If there is a |
|
|
664 | parse error, this method will croak just as "decode" would do (one |
|
|
665 | can then use "incr_skip" to skip the errornous part). This is the |
|
|
666 | most common way of using the method. |
|
|
667 | |
|
|
668 | And finally, in list context, it will try to extract as many objects |
|
|
669 | from the stream as it can find and return them, or the empty list |
|
|
670 | otherwise. For this to work, there must be no separators between the |
|
|
671 | JSON objects or arrays, instead they must be concatenated |
|
|
672 | back-to-back. If an error occurs, an exception will be raised as in |
|
|
673 | the scalar context case. Note that in this case, any |
|
|
674 | previously-parsed JSON texts will be lost. |
|
|
675 | |
|
|
676 | Example: Parse some JSON arrays/objects in a given string and return |
|
|
677 | them. |
|
|
678 | |
|
|
679 | my @objs = JSON::XS->new->incr_parse ("[5][7][1,2]"); |
|
|
680 | |
|
|
681 | $lvalue_string = $json->incr_text |
|
|
682 | This method returns the currently stored JSON fragment as an lvalue, |
|
|
683 | that is, you can manipulate it. This *only* works when a preceding |
|
|
684 | call to "incr_parse" in *scalar context* successfully returned an |
|
|
685 | object. Under all other circumstances you must not call this |
|
|
686 | function (I mean it. although in simple tests it might actually |
|
|
687 | work, it *will* fail under real world conditions). As a special |
|
|
688 | exception, you can also call this method before having parsed |
|
|
689 | anything. |
|
|
690 | |
|
|
691 | This function is useful in two cases: a) finding the trailing text |
|
|
692 | after a JSON object or b) parsing multiple JSON objects separated by |
|
|
693 | non-JSON text (such as commas). |
|
|
694 | |
|
|
695 | $json->incr_skip |
|
|
696 | This will reset the state of the incremental parser and will remove |
|
|
697 | the parsed text from the input buffer so far. This is useful after |
|
|
698 | "incr_parse" died, in which case the input buffer and incremental |
|
|
699 | parser state is left unchanged, to skip the text parsed so far and |
|
|
700 | to reset the parse state. |
|
|
701 | |
|
|
702 | The difference to "incr_reset" is that only text until the parse |
|
|
703 | error occured is removed. |
|
|
704 | |
|
|
705 | $json->incr_reset |
|
|
706 | This completely resets the incremental parser, that is, after this |
|
|
707 | call, it will be as if the parser had never parsed anything. |
|
|
708 | |
|
|
709 | This is useful if you want to repeatedly parse JSON objects and want |
|
|
710 | to ignore any trailing data, which means you have to reset the |
|
|
711 | parser after each successful decode. |
|
|
712 | |
|
|
713 | LIMITATIONS |
|
|
714 | All options that affect decoding are supported, except "allow_nonref". |
|
|
715 | The reason for this is that it cannot be made to work sensibly: JSON |
|
|
716 | objects and arrays are self-delimited, i.e. you can concatenate them |
|
|
717 | back to back and still decode them perfectly. This does not hold true |
|
|
718 | for JSON numbers, however. |
|
|
719 | |
|
|
720 | For example, is the string 1 a single JSON number, or is it simply the |
|
|
721 | start of 12? Or is 12 a single JSON number, or the concatenation of 1 |
|
|
722 | and 2? In neither case you can tell, and this is why JSON::XS takes the |
|
|
723 | conservative route and disallows this case. |
|
|
724 | |
|
|
725 | EXAMPLES |
|
|
726 | Some examples will make all this clearer. First, a simple example that |
|
|
727 | works similarly to "decode_prefix": We want to decode the JSON object at |
|
|
728 | the start of a string and identify the portion after the JSON object: |
|
|
729 | |
|
|
730 | my $text = "[1,2,3] hello"; |
|
|
731 | |
|
|
732 | my $json = new JSON::XS; |
|
|
733 | |
|
|
734 | my $obj = $json->incr_parse ($text) |
|
|
735 | or die "expected JSON object or array at beginning of string"; |
|
|
736 | |
|
|
737 | my $tail = $json->incr_text; |
|
|
738 | # $tail now contains " hello" |
|
|
739 | |
|
|
740 | Easy, isn't it? |
|
|
741 | |
|
|
742 | Now for a more complicated example: Imagine a hypothetical protocol |
|
|
743 | where you read some requests from a TCP stream, and each request is a |
|
|
744 | JSON array, without any separation between them (in fact, it is often |
|
|
745 | useful to use newlines as "separators", as these get interpreted as |
|
|
746 | whitespace at the start of the JSON text, which makes it possible to |
|
|
747 | test said protocol with "telnet"...). |
|
|
748 | |
|
|
749 | Here is how you'd do it (it is trivial to write this in an event-based |
|
|
750 | manner): |
|
|
751 | |
|
|
752 | my $json = new JSON::XS; |
|
|
753 | |
|
|
754 | # read some data from the socket |
|
|
755 | while (sysread $socket, my $buf, 4096) { |
|
|
756 | |
|
|
757 | # split and decode as many requests as possible |
|
|
758 | for my $request ($json->incr_parse ($buf)) { |
|
|
759 | # act on the $request |
|
|
760 | } |
|
|
761 | } |
|
|
762 | |
|
|
763 | Another complicated example: Assume you have a string with JSON objects |
|
|
764 | or arrays, all separated by (optional) comma characters (e.g. "[1],[2], |
|
|
765 | [3]"). To parse them, we have to skip the commas between the JSON texts, |
|
|
766 | and here is where the lvalue-ness of "incr_text" comes in useful: |
|
|
767 | |
|
|
768 | my $text = "[1],[2], [3]"; |
|
|
769 | my $json = new JSON::XS; |
|
|
770 | |
|
|
771 | # void context, so no parsing done |
|
|
772 | $json->incr_parse ($text); |
|
|
773 | |
|
|
774 | # now extract as many objects as possible. note the |
|
|
775 | # use of scalar context so incr_text can be called. |
|
|
776 | while (my $obj = $json->incr_parse) { |
|
|
777 | # do something with $obj |
|
|
778 | |
|
|
779 | # now skip the optional comma |
|
|
780 | $json->incr_text =~ s/^ \s* , //x; |
|
|
781 | } |
|
|
782 | |
|
|
783 | Now lets go for a very complex example: Assume that you have a gigantic |
|
|
784 | JSON array-of-objects, many gigabytes in size, and you want to parse it, |
|
|
785 | but you cannot load it into memory fully (this has actually happened in |
|
|
786 | the real world :). |
|
|
787 | |
|
|
788 | Well, you lost, you have to implement your own JSON parser. But JSON::XS |
|
|
789 | can still help you: You implement a (very simple) array parser and let |
|
|
790 | JSON decode the array elements, which are all full JSON objects on their |
|
|
791 | own (this wouldn't work if the array elements could be JSON numbers, for |
|
|
792 | example): |
|
|
793 | |
|
|
794 | my $json = new JSON::XS; |
|
|
795 | |
|
|
796 | # open the monster |
|
|
797 | open my $fh, "<bigfile.json" |
|
|
798 | or die "bigfile: $!"; |
|
|
799 | |
|
|
800 | # first parse the initial "[" |
|
|
801 | for (;;) { |
|
|
802 | sysread $fh, my $buf, 65536 |
|
|
803 | or die "read error: $!"; |
|
|
804 | $json->incr_parse ($buf); # void context, so no parsing |
|
|
805 | |
|
|
806 | # Exit the loop once we found and removed(!) the initial "[". |
|
|
807 | # In essence, we are (ab-)using the $json object as a simple scalar |
|
|
808 | # we append data to. |
|
|
809 | last if $json->incr_text =~ s/^ \s* \[ //x; |
|
|
810 | } |
|
|
811 | |
|
|
812 | # now we have the skipped the initial "[", so continue |
|
|
813 | # parsing all the elements. |
|
|
814 | for (;;) { |
|
|
815 | # in this loop we read data until we got a single JSON object |
|
|
816 | for (;;) { |
|
|
817 | if (my $obj = $json->incr_parse) { |
|
|
818 | # do something with $obj |
|
|
819 | last; |
|
|
820 | } |
|
|
821 | |
|
|
822 | # add more data |
|
|
823 | sysread $fh, my $buf, 65536 |
|
|
824 | or die "read error: $!"; |
|
|
825 | $json->incr_parse ($buf); # void context, so no parsing |
|
|
826 | } |
|
|
827 | |
|
|
828 | # in this loop we read data until we either found and parsed the |
|
|
829 | # separating "," between elements, or the final "]" |
|
|
830 | for (;;) { |
|
|
831 | # first skip whitespace |
|
|
832 | $json->incr_text =~ s/^\s*//; |
|
|
833 | |
|
|
834 | # if we find "]", we are done |
|
|
835 | if ($json->incr_text =~ s/^\]//) { |
|
|
836 | print "finished.\n"; |
|
|
837 | exit; |
|
|
838 | } |
|
|
839 | |
|
|
840 | # if we find ",", we can continue with the next element |
|
|
841 | if ($json->incr_text =~ s/^,//) { |
|
|
842 | last; |
|
|
843 | } |
|
|
844 | |
|
|
845 | # if we find anything else, we have a parse error! |
|
|
846 | if (length $json->incr_text) { |
|
|
847 | die "parse error near ", $json->incr_text; |
|
|
848 | } |
|
|
849 | |
|
|
850 | # else add more data |
|
|
851 | sysread $fh, my $buf, 65536 |
|
|
852 | or die "read error: $!"; |
|
|
853 | $json->incr_parse ($buf); # void context, so no parsing |
|
|
854 | } |
|
|
855 | |
|
|
856 | This is a complex example, but most of the complexity comes from the |
|
|
857 | fact that we are trying to be correct (bear with me if I am wrong, I |
|
|
858 | never ran the above example :). |
|
|
859 | |
510 | MAPPING |
860 | MAPPING |
511 | This section describes how JSON::XS maps Perl values to JSON values and |
861 | This section describes how JSON::XS maps Perl values to JSON values and |
512 | vice versa. These mappings are designed to "do the right thing" in most |
862 | vice versa. These mappings are designed to "do the right thing" in most |
513 | circumstances automatically, preserving round-tripping characteristics |
863 | circumstances automatically, preserving round-tripping characteristics |
514 | (what you put in comes out as something equivalent). |
864 | (what you put in comes out as something equivalent). |
515 | |
865 | |
516 | For the more enlightened: note that in the following descriptions, |
866 | For the more enlightened: note that in the following descriptions, |
517 | lowercase *perl* refers to the Perl interpreter, while uppcercase *Perl* |
867 | lowercase *perl* refers to the Perl interpreter, while uppercase *Perl* |
518 | refers to the abstract Perl language itself. |
868 | refers to the abstract Perl language itself. |
519 | |
869 | |
520 | JSON -> PERL |
870 | JSON -> PERL |
521 | object |
871 | object |
522 | A JSON object becomes a reference to a hash in Perl. No ordering of |
872 | A JSON object becomes a reference to a hash in Perl. No ordering of |
523 | object keys is preserved (JSON does not preserver object key |
873 | object keys is preserved (JSON does not preserve object key ordering |
524 | ordering itself). |
874 | itself). |
525 | |
875 | |
526 | array |
876 | array |
527 | A JSON array becomes a reference to an array in Perl. |
877 | A JSON array becomes a reference to an array in Perl. |
528 | |
878 | |
529 | string |
879 | string |
… | |
… | |
535 | A JSON number becomes either an integer, numeric (floating point) or |
885 | A JSON number becomes either an integer, numeric (floating point) or |
536 | string scalar in perl, depending on its range and any fractional |
886 | string scalar in perl, depending on its range and any fractional |
537 | parts. On the Perl level, there is no difference between those as |
887 | parts. On the Perl level, there is no difference between those as |
538 | Perl handles all the conversion details, but an integer may take |
888 | Perl handles all the conversion details, but an integer may take |
539 | slightly less memory and might represent more values exactly than |
889 | slightly less memory and might represent more values exactly than |
540 | (floating point) numbers. |
890 | floating point numbers. |
541 | |
891 | |
542 | If the number consists of digits only, JSON::XS will try to |
892 | If the number consists of digits only, JSON::XS will try to |
543 | represent it as an integer value. If that fails, it will try to |
893 | represent it as an integer value. If that fails, it will try to |
544 | represent it as a numeric (floating point) value if that is possible |
894 | represent it as a numeric (floating point) value if that is possible |
545 | without loss of precision. Otherwise it will preserve the number as |
895 | without loss of precision. Otherwise it will preserve the number as |
546 | a string value. |
896 | a string value (in which case you lose roundtripping ability, as the |
|
|
897 | JSON number will be re-encoded toa JSON string). |
547 | |
898 | |
548 | Numbers containing a fractional or exponential part will always be |
899 | Numbers containing a fractional or exponential part will always be |
549 | represented as numeric (floating point) values, possibly at a loss |
900 | represented as numeric (floating point) values, possibly at a loss |
550 | of precision. |
901 | of precision (in which case you might lose perfect roundtripping |
|
|
902 | ability, but the JSON number will still be re-encoded as a JSON |
|
|
903 | number). |
551 | |
904 | |
552 | This might create round-tripping problems as numbers might become |
905 | Note that precision is not accuracy - binary floating point values |
553 | strings, but as Perl is typeless there is no other way to do it. |
906 | cannot represent most decimal fractions exactly, and when converting |
|
|
907 | from and to floating point, JSON::XS only guarantees precision up to |
|
|
908 | but not including the leats significant bit. |
554 | |
909 | |
555 | true, false |
910 | true, false |
556 | These JSON atoms become "JSON::XS::true" and "JSON::XS::false", |
911 | These JSON atoms become "JSON::XS::true" and "JSON::XS::false", |
557 | respectively. They are overloaded to act almost exactly like the |
912 | respectively. They are overloaded to act almost exactly like the |
558 | numbers 1 and 0. You can check wether a scalar is a JSON boolean by |
913 | numbers 1 and 0. You can check whether a scalar is a JSON boolean by |
559 | using the "JSON::XS::is_bool" function. |
914 | using the "JSON::XS::is_bool" function. |
560 | |
915 | |
561 | null |
916 | null |
562 | A JSON null atom becomes "undef" in Perl. |
917 | A JSON null atom becomes "undef" in Perl. |
563 | |
918 | |
… | |
… | |
586 | an exception to be thrown, except for references to the integers 0 |
941 | an exception to be thrown, except for references to the integers 0 |
587 | and 1, which get turned into "false" and "true" atoms in JSON. You |
942 | and 1, which get turned into "false" and "true" atoms in JSON. You |
588 | can also use "JSON::XS::false" and "JSON::XS::true" to improve |
943 | can also use "JSON::XS::false" and "JSON::XS::true" to improve |
589 | readability. |
944 | readability. |
590 | |
945 | |
591 | to_json [\0,JSON::XS::true] # yields [false,true] |
946 | encode_json [\0, JSON::XS::true] # yields [false,true] |
592 | |
947 | |
593 | JSON::XS::true, JSON::XS::false |
948 | JSON::XS::true, JSON::XS::false |
594 | These special values become JSON true and JSON false values, |
949 | These special values become JSON true and JSON false values, |
595 | respectively. You cna alos use "\1" and "\0" directly if you want. |
950 | respectively. You can also use "\1" and "\0" directly if you want. |
596 | |
951 | |
597 | blessed objects |
952 | blessed objects |
598 | Blessed objects are not allowed. JSON::XS currently tries to encode |
953 | Blessed objects are not directly representable in JSON. See the |
599 | their underlying representation (hash- or arrayref), but this |
954 | "allow_blessed" and "convert_blessed" methods on various options on |
600 | behaviour might change in future versions. |
955 | how to deal with this: basically, you can choose between throwing an |
|
|
956 | exception, encoding the reference as if it weren't blessed, or |
|
|
957 | provide your own serialiser method. |
601 | |
958 | |
602 | simple scalars |
959 | simple scalars |
603 | Simple Perl scalars (any scalar that is not a reference) are the |
960 | Simple Perl scalars (any scalar that is not a reference) are the |
604 | most difficult objects to encode: JSON::XS will encode undefined |
961 | most difficult objects to encode: JSON::XS will encode undefined |
605 | scalars as JSON null value, scalars that have last been used in a |
962 | scalars as JSON "null" values, scalars that have last been used in a |
606 | string context before encoding as JSON strings and anything else as |
963 | string context before encoding as JSON strings, and anything else as |
607 | number value: |
964 | number value: |
608 | |
965 | |
609 | # dump as number |
966 | # dump as number |
610 | to_json [2] # yields [2] |
967 | encode_json [2] # yields [2] |
611 | to_json [-3.0e17] # yields [-3e+17] |
968 | encode_json [-3.0e17] # yields [-3e+17] |
612 | my $value = 5; to_json [$value] # yields [5] |
969 | my $value = 5; encode_json [$value] # yields [5] |
613 | |
970 | |
614 | # used as string, so dump as string |
971 | # used as string, so dump as string |
615 | print $value; |
972 | print $value; |
616 | to_json [$value] # yields ["5"] |
973 | encode_json [$value] # yields ["5"] |
617 | |
974 | |
618 | # undef becomes null |
975 | # undef becomes null |
619 | to_json [undef] # yields [null] |
976 | encode_json [undef] # yields [null] |
620 | |
977 | |
621 | You can force the type to be a string by stringifying it: |
978 | You can force the type to be a JSON string by stringifying it: |
622 | |
979 | |
623 | my $x = 3.1; # some variable containing a number |
980 | my $x = 3.1; # some variable containing a number |
624 | "$x"; # stringified |
981 | "$x"; # stringified |
625 | $x .= ""; # another, more awkward way to stringify |
982 | $x .= ""; # another, more awkward way to stringify |
626 | print $x; # perl does it for you, too, quite often |
983 | print $x; # perl does it for you, too, quite often |
627 | |
984 | |
628 | You can force the type to be a number by numifying it: |
985 | You can force the type to be a JSON number by numifying it: |
629 | |
986 | |
630 | my $x = "3"; # some variable containing a string |
987 | my $x = "3"; # some variable containing a string |
631 | $x += 0; # numify it, ensuring it will be dumped as a number |
988 | $x += 0; # numify it, ensuring it will be dumped as a number |
632 | $x *= 1; # same thing, the choise is yours. |
989 | $x *= 1; # same thing, the choice is yours. |
633 | |
990 | |
634 | You can not currently output JSON booleans or force the type in |
991 | You can not currently force the type in other, less obscure, ways. |
635 | other, less obscure, ways. Tell me if you need this capability. |
992 | Tell me if you need this capability (but don't forget to explain why |
|
|
993 | it's needed :). |
636 | |
994 | |
637 | COMPARISON |
995 | Note that numerical precision has the same meaning as under Perl (so |
638 | As already mentioned, this module was created because none of the |
996 | binary to decimal conversion follows the same rules as in Perl, |
639 | existing JSON modules could be made to work correctly. First I will |
997 | which can differ to other languages). Also, your perl interpreter |
640 | describe the problems (or pleasures) I encountered with various existing |
998 | might expose extensions to the floating point numbers of your |
641 | JSON modules, followed by some benchmark values. JSON::XS was designed |
999 | platform, such as infinities or NaN's - these cannot be represented |
642 | not to suffer from any of these problems or limitations. |
1000 | in JSON, and it is an error to pass those in. |
643 | |
1001 | |
644 | JSON 1.07 |
1002 | ENCODING/CODESET FLAG NOTES |
645 | Slow (but very portable, as it is written in pure Perl). |
1003 | The interested reader might have seen a number of flags that signify |
|
|
1004 | encodings or codesets - "utf8", "latin1" and "ascii". There seems to be |
|
|
1005 | some confusion on what these do, so here is a short comparison: |
646 | |
1006 | |
647 | Undocumented/buggy Unicode handling (how JSON handles unicode values |
1007 | "utf8" controls whether the JSON text created by "encode" (and expected |
648 | is undocumented. One can get far by feeding it unicode strings and |
1008 | by "decode") is UTF-8 encoded or not, while "latin1" and "ascii" only |
649 | doing en-/decoding oneself, but unicode escapes are not working |
1009 | control whether "encode" escapes character values outside their |
|
|
1010 | respective codeset range. Neither of these flags conflict with each |
|
|
1011 | other, although some combinations make less sense than others. |
|
|
1012 | |
|
|
1013 | Care has been taken to make all flags symmetrical with respect to |
|
|
1014 | "encode" and "decode", that is, texts encoded with any combination of |
|
|
1015 | these flag values will be correctly decoded when the same flags are used |
|
|
1016 | - in general, if you use different flag settings while encoding vs. when |
|
|
1017 | decoding you likely have a bug somewhere. |
|
|
1018 | |
|
|
1019 | Below comes a verbose discussion of these flags. Note that a "codeset" |
|
|
1020 | is simply an abstract set of character-codepoint pairs, while an |
|
|
1021 | encoding takes those codepoint numbers and *encodes* them, in our case |
|
|
1022 | into octets. Unicode is (among other things) a codeset, UTF-8 is an |
|
|
1023 | encoding, and ISO-8859-1 (= latin 1) and ASCII are both codesets *and* |
|
|
1024 | encodings at the same time, which can be confusing. |
|
|
1025 | |
|
|
1026 | "utf8" flag disabled |
|
|
1027 | When "utf8" is disabled (the default), then "encode"/"decode" |
|
|
1028 | generate and expect Unicode strings, that is, characters with high |
|
|
1029 | ordinal Unicode values (> 255) will be encoded as such characters, |
|
|
1030 | and likewise such characters are decoded as-is, no canges to them |
|
|
1031 | will be done, except "(re-)interpreting" them as Unicode codepoints |
|
|
1032 | or Unicode characters, respectively (to Perl, these are the same |
|
|
1033 | thing in strings unless you do funny/weird/dumb stuff). |
|
|
1034 | |
|
|
1035 | This is useful when you want to do the encoding yourself (e.g. when |
|
|
1036 | you want to have UTF-16 encoded JSON texts) or when some other layer |
|
|
1037 | does the encoding for you (for example, when printing to a terminal |
|
|
1038 | using a filehandle that transparently encodes to UTF-8 you certainly |
|
|
1039 | do NOT want to UTF-8 encode your data first and have Perl encode it |
|
|
1040 | another time). |
|
|
1041 | |
|
|
1042 | "utf8" flag enabled |
|
|
1043 | If the "utf8"-flag is enabled, "encode"/"decode" will encode all |
|
|
1044 | characters using the corresponding UTF-8 multi-byte sequence, and |
|
|
1045 | will expect your input strings to be encoded as UTF-8, that is, no |
|
|
1046 | "character" of the input string must have any value > 255, as UTF-8 |
|
|
1047 | does not allow that. |
|
|
1048 | |
|
|
1049 | The "utf8" flag therefore switches between two modes: disabled means |
|
|
1050 | you will get a Unicode string in Perl, enabled means you get an |
|
|
1051 | UTF-8 encoded octet/binary string in Perl. |
|
|
1052 | |
|
|
1053 | "latin1" or "ascii" flags enabled |
|
|
1054 | With "latin1" (or "ascii") enabled, "encode" will escape characters |
|
|
1055 | with ordinal values > 255 (> 127 with "ascii") and encode the |
|
|
1056 | remaining characters as specified by the "utf8" flag. |
|
|
1057 | |
|
|
1058 | If "utf8" is disabled, then the result is also correctly encoded in |
|
|
1059 | those character sets (as both are proper subsets of Unicode, meaning |
|
|
1060 | that a Unicode string with all character values < 256 is the same |
|
|
1061 | thing as a ISO-8859-1 string, and a Unicode string with all |
|
|
1062 | character values < 128 is the same thing as an ASCII string in |
650 | properly). |
1063 | Perl). |
651 | |
1064 | |
652 | No roundtripping (strings get clobbered if they look like numbers, |
1065 | If "utf8" is enabled, you still get a correct UTF-8-encoded string, |
653 | e.g. the string 2.0 will encode to 2.0 instead of "2.0", and that |
1066 | regardless of these flags, just some more characters will be escaped |
654 | will decode into the number 2. |
1067 | using "\uXXXX" then before. |
655 | |
1068 | |
656 | JSON::PC 0.01 |
1069 | Note that ISO-8859-1-*encoded* strings are not compatible with UTF-8 |
657 | Very fast. |
1070 | encoding, while ASCII-encoded strings are. That is because the |
|
|
1071 | ISO-8859-1 encoding is NOT a subset of UTF-8 (despite the ISO-8859-1 |
|
|
1072 | *codeset* being a subset of Unicode), while ASCII is. |
658 | |
1073 | |
659 | Undocumented/buggy Unicode handling. |
1074 | Surprisingly, "decode" will ignore these flags and so treat all |
|
|
1075 | input values as governed by the "utf8" flag. If it is disabled, this |
|
|
1076 | allows you to decode ISO-8859-1- and ASCII-encoded strings, as both |
|
|
1077 | strict subsets of Unicode. If it is enabled, you can correctly |
|
|
1078 | decode UTF-8 encoded strings. |
660 | |
1079 | |
661 | No roundtripping. |
1080 | So neither "latin1" nor "ascii" are incompatible with the "utf8" |
|
|
1081 | flag - they only govern when the JSON output engine escapes a |
|
|
1082 | character or not. |
662 | |
1083 | |
663 | Has problems handling many Perl values (e.g. regex results and other |
1084 | The main use for "latin1" is to relatively efficiently store binary |
664 | magic values will make it croak). |
1085 | data as JSON, at the expense of breaking compatibility with most |
|
|
1086 | JSON decoders. |
665 | |
1087 | |
666 | Does not even generate valid JSON ("{1,2}" gets converted to "{1:2}" |
1088 | The main use for "ascii" is to force the output to not contain |
667 | which is not a valid JSON text. |
1089 | characters with values > 127, which means you can interpret the |
|
|
1090 | resulting string as UTF-8, ISO-8859-1, ASCII, KOI8-R or most about |
|
|
1091 | any character set and 8-bit-encoding, and still get the same data |
|
|
1092 | structure back. This is useful when your channel for JSON transfer |
|
|
1093 | is not 8-bit clean or the encoding might be mangled in between (e.g. |
|
|
1094 | in mail), and works because ASCII is a proper subset of most 8-bit |
|
|
1095 | and multibyte encodings in use in the world. |
668 | |
1096 | |
669 | Unmaintained (maintainer unresponsive for many months, bugs are not |
1097 | JSON and ECMAscript |
670 | getting fixed). |
1098 | JSON syntax is based on how literals are represented in javascript (the |
|
|
1099 | not-standardised predecessor of ECMAscript) which is presumably why it |
|
|
1100 | is called "JavaScript Object Notation". |
671 | |
1101 | |
672 | JSON::Syck 0.21 |
1102 | However, JSON is not a subset (and also not a superset of course) of |
673 | Very buggy (often crashes). |
1103 | ECMAscript (the standard) or javascript (whatever browsers actually |
|
|
1104 | implement). |
674 | |
1105 | |
675 | Very inflexible (no human-readable format supported, format pretty |
1106 | If you want to use javascript's "eval" function to "parse" JSON, you |
676 | much undocumented. I need at least a format for easy reading by |
1107 | might run into parse errors for valid JSON texts, or the resulting data |
677 | humans and a single-line compact format for use in a protocol, and |
1108 | structure might not be queryable: |
678 | preferably a way to generate ASCII-only JSON texts). |
|
|
679 | |
1109 | |
680 | Completely broken (and confusingly documented) Unicode handling |
1110 | One of the problems is that U+2028 and U+2029 are valid characters |
681 | (unicode escapes are not working properly, you need to set |
1111 | inside JSON strings, but are not allowed in ECMAscript string literals, |
682 | ImplicitUnicode to *different* values on en- and decoding to get |
1112 | so the following Perl fragment will not output something that can be |
683 | symmetric behaviour). |
1113 | guaranteed to be parsable by javascript's "eval": |
684 | |
1114 | |
685 | No roundtripping (simple cases work, but this depends on wether the |
1115 | use JSON::XS; |
686 | scalar value was used in a numeric context or not). |
|
|
687 | |
1116 | |
688 | Dumping hashes may skip hash values depending on iterator state. |
1117 | print encode_json [chr 0x2028]; |
689 | |
1118 | |
690 | Unmaintained (maintainer unresponsive for many months, bugs are not |
1119 | The right fix for this is to use a proper JSON parser in your javascript |
691 | getting fixed). |
1120 | programs, and not rely on "eval" (see for example Douglas Crockford's |
|
|
1121 | json2.js parser). |
692 | |
1122 | |
693 | Does not check input for validity (i.e. will accept non-JSON input |
1123 | If this is not an option, you can, as a stop-gap measure, simply encode |
694 | and return "something" instead of raising an exception. This is a |
1124 | to ASCII-only JSON: |
695 | security issue: imagine two banks transfering money between each |
|
|
696 | other using JSON. One bank might parse a given non-JSON request and |
|
|
697 | deduct money, while the other might reject the transaction with a |
|
|
698 | syntax error. While a good protocol will at least recover, that is |
|
|
699 | extra unnecessary work and the transaction will still not succeed). |
|
|
700 | |
1125 | |
701 | JSON::DWIW 0.04 |
1126 | use JSON::XS; |
702 | Very fast. Very natural. Very nice. |
|
|
703 | |
1127 | |
704 | Undocumented unicode handling (but the best of the pack. Unicode |
1128 | print JSON::XS->new->ascii->encode ([chr 0x2028]); |
705 | escapes still don't get parsed properly). |
|
|
706 | |
1129 | |
707 | Very inflexible. |
1130 | Note that this will enlarge the resulting JSON text quite a bit if you |
|
|
1131 | have many non-ASCII characters. You might be tempted to run some regexes |
|
|
1132 | to only escape U+2028 and U+2029, e.g.: |
708 | |
1133 | |
709 | No roundtripping. |
1134 | # DO NOT USE THIS! |
|
|
1135 | my $json = JSON::XS->new->utf8->encode ([chr 0x2028]); |
|
|
1136 | $json =~ s/\xe2\x80\xa8/\\u2028/g; # escape U+2028 |
|
|
1137 | $json =~ s/\xe2\x80\xa9/\\u2029/g; # escape U+2029 |
|
|
1138 | print $json; |
710 | |
1139 | |
711 | Does not generate valid JSON texts (key strings are often unquoted, |
1140 | Note that *this is a bad idea*: the above only works for U+2028 and |
712 | empty keys result in nothing being output) |
1141 | U+2029 and thus only for fully ECMAscript-compliant parsers. Many |
|
|
1142 | existing javascript implementations, however, have issues with other |
|
|
1143 | characters as well - using "eval" naively simply *will* cause problems. |
713 | |
1144 | |
714 | Does not check input for validity. |
1145 | Another problem is that some javascript implementations reserve some |
|
|
1146 | property names for their own purposes (which probably makes them |
|
|
1147 | non-ECMAscript-compliant). For example, Iceweasel reserves the |
|
|
1148 | "__proto__" property name for its own purposes. |
|
|
1149 | |
|
|
1150 | If that is a problem, you could parse try to filter the resulting JSON |
|
|
1151 | output for these property strings, e.g.: |
|
|
1152 | |
|
|
1153 | $json =~ s/"__proto__"\s*:/"__proto__renamed":/g; |
|
|
1154 | |
|
|
1155 | This works because "__proto__" is not valid outside of strings, so every |
|
|
1156 | occurence of ""__proto__"\s*:" must be a string used as property name. |
|
|
1157 | |
|
|
1158 | If you know of other incompatibilities, please let me know. |
715 | |
1159 | |
716 | JSON and YAML |
1160 | JSON and YAML |
717 | You often hear that JSON is a subset (or a close subset) of YAML. This |
1161 | You often hear that JSON is a subset of YAML. This is, however, a mass |
718 | is, however, a mass hysteria and very far from the truth. In general, |
1162 | hysteria(*) and very far from the truth (as of the time of this |
719 | there is no way to configure JSON::XS to output a data structure as |
1163 | writing), so let me state it clearly: *in general, there is no way to |
720 | valid YAML. |
1164 | configure JSON::XS to output a data structure as valid YAML* that works |
|
|
1165 | in all cases. |
721 | |
1166 | |
722 | If you really must use JSON::XS to generate YAML, you should use this |
1167 | If you really must use JSON::XS to generate YAML, you should use this |
723 | algorithm (subject to change in future versions): |
1168 | algorithm (subject to change in future versions): |
724 | |
1169 | |
725 | my $to_yaml = JSON::XS->new->utf8->space_after (1); |
1170 | my $to_yaml = JSON::XS->new->utf8->space_after (1); |
726 | my $yaml = $to_yaml->encode ($ref) . "\n"; |
1171 | my $yaml = $to_yaml->encode ($ref) . "\n"; |
727 | |
1172 | |
728 | This will usually generate JSON texts that also parse as valid YAML. |
1173 | This will *usually* generate JSON texts that also parse as valid YAML. |
729 | Please note that YAML has hardcoded limits on (simple) object key |
1174 | Please note that YAML has hardcoded limits on (simple) object key |
730 | lengths that JSON doesn't have, so you should make sure that your hash |
1175 | lengths that JSON doesn't have and also has different and incompatible |
|
|
1176 | unicode character escape syntax, so you should make sure that your hash |
731 | keys are noticably shorter than the 1024 characters YAML allows. |
1177 | keys are noticeably shorter than the 1024 "stream characters" YAML |
|
|
1178 | allows and that you do not have characters with codepoint values outside |
|
|
1179 | the Unicode BMP (basic multilingual page). YAML also does not allow "\/" |
|
|
1180 | sequences in strings (which JSON::XS does not *currently* generate, but |
|
|
1181 | other JSON generators might). |
732 | |
1182 | |
733 | There might be other incompatibilities that I am not aware of. In |
1183 | There might be other incompatibilities that I am not aware of (or the |
|
|
1184 | YAML specification has been changed yet again - it does so quite often). |
734 | general you should not try to generate YAML with a JSON generator or |
1185 | In general you should not try to generate YAML with a JSON generator or |
735 | vice versa, or try to parse JSON with a YAML parser or vice versa: |
1186 | vice versa, or try to parse JSON with a YAML parser or vice versa: |
736 | chances are high that you will run into severe interoperability |
1187 | chances are high that you will run into severe interoperability problems |
737 | problems. |
1188 | when you least expect it. |
|
|
1189 | |
|
|
1190 | (*) I have been pressured multiple times by Brian Ingerson (one of the |
|
|
1191 | authors of the YAML specification) to remove this paragraph, despite |
|
|
1192 | him acknowledging that the actual incompatibilities exist. As I was |
|
|
1193 | personally bitten by this "JSON is YAML" lie, I refused and said I |
|
|
1194 | will continue to educate people about these issues, so others do not |
|
|
1195 | run into the same problem again and again. After this, Brian called |
|
|
1196 | me a (quote)*complete and worthless idiot*(unquote). |
|
|
1197 | |
|
|
1198 | In my opinion, instead of pressuring and insulting people who |
|
|
1199 | actually clarify issues with YAML and the wrong statements of some |
|
|
1200 | of its proponents, I would kindly suggest reading the JSON spec |
|
|
1201 | (which is not that difficult or long) and finally make YAML |
|
|
1202 | compatible to it, and educating users about the changes, instead of |
|
|
1203 | spreading lies about the real compatibility for many *years* and |
|
|
1204 | trying to silence people who point out that it isn't true. |
|
|
1205 | |
|
|
1206 | Addendum/2009: the YAML 1.2 spec is still incompatible with JSON, |
|
|
1207 | even though the incompatibilities have been documented (and are |
|
|
1208 | known to Brian) for many years and the spec makes explicit claims |
|
|
1209 | that YAML is a superset of JSON. It would be so easy to fix, but |
|
|
1210 | apparently, bullying people and corrupting userdata is so much |
|
|
1211 | easier. |
738 | |
1212 | |
739 | SPEED |
1213 | SPEED |
740 | It seems that JSON::XS is surprisingly fast, as shown in the following |
1214 | It seems that JSON::XS is surprisingly fast, as shown in the following |
741 | tables. They have been generated with the help of the "eg/bench" program |
1215 | tables. They have been generated with the help of the "eg/bench" program |
742 | in the JSON::XS distribution, to make it easy to compare on your own |
1216 | in the JSON::XS distribution, to make it easy to compare on your own |
743 | system. |
1217 | system. |
744 | |
1218 | |
745 | First comes a comparison between various modules using a very short |
1219 | First comes a comparison between various modules using a very short |
746 | single-line JSON string: |
1220 | single-line JSON string (also available at |
|
|
1221 | <http://dist.schmorp.de/misc/json/short.json>). |
747 | |
1222 | |
748 | {"method": "handleMessage", "params": ["user1", "we were just talking"], \ |
1223 | {"method": "handleMessage", "params": ["user1", |
749 | "id": null, "array":[1,11,234,-5,1e5,1e7, true, false]} |
1224 | "we were just talking"], "id": null, "array":[1,11,234,-5,1e5,1e7, |
|
|
1225 | 1, 0]} |
750 | |
1226 | |
751 | It shows the number of encodes/decodes per second (JSON::XS uses the |
1227 | It shows the number of encodes/decodes per second (JSON::XS uses the |
752 | functional interface, while JSON::XS/2 uses the OO interface with |
1228 | functional interface, while JSON::XS/2 uses the OO interface with |
753 | pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink). |
1229 | pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink. |
754 | Higher is better: |
1230 | JSON::DWIW/DS uses the deserialise function, while JSON::DWIW::FJ uses |
|
|
1231 | the from_json method). Higher is better: |
755 | |
1232 | |
756 | Storable | 15779.925 | 14169.946 | |
|
|
757 | -----------+------------+------------+ |
|
|
758 | module | encode | decode | |
1233 | module | encode | decode | |
759 | -----------|------------|------------| |
1234 | --------------|------------|------------| |
760 | JSON | 4990.842 | 4088.813 | |
1235 | JSON::DWIW/DS | 86302.551 | 102300.098 | |
761 | JSON::DWIW | 51653.990 | 71575.154 | |
1236 | JSON::DWIW/FJ | 86302.551 | 75983.768 | |
762 | JSON::PC | 65948.176 | 74631.744 | |
1237 | JSON::PP | 15827.562 | 6638.658 | |
763 | JSON::PP | 8931.652 | 3817.168 | |
1238 | JSON::Syck | 63358.066 | 47662.545 | |
764 | JSON::Syck | 24877.248 | 27776.848 | |
1239 | JSON::XS | 511500.488 | 511500.488 | |
765 | JSON::XS | 388361.481 | 227951.304 | |
1240 | JSON::XS/2 | 291271.111 | 388361.481 | |
766 | JSON::XS/2 | 227951.304 | 218453.333 | |
1241 | JSON::XS/3 | 361577.931 | 361577.931 | |
767 | JSON::XS/3 | 338250.323 | 218453.333 | |
1242 | Storable | 66788.280 | 265462.278 | |
768 | Storable | 16500.016 | 135300.129 | |
|
|
769 | -----------+------------+------------+ |
1243 | --------------+------------+------------+ |
770 | |
1244 | |
771 | That is, JSON::XS is about five times faster than JSON::DWIW on |
1245 | That is, JSON::XS is almost six times faster than JSON::DWIW on |
772 | encoding, about three times faster on decoding, and over fourty times |
1246 | encoding, about five times faster on decoding, and over thirty to |
773 | faster than JSON, even with pretty-printing and key sorting. It also |
1247 | seventy times faster than JSON's pure perl implementation. It also |
774 | compares favourably to Storable for small amounts of data. |
1248 | compares favourably to Storable for small amounts of data. |
775 | |
1249 | |
776 | Using a longer test string (roughly 18KB, generated from Yahoo! Locals |
1250 | Using a longer test string (roughly 18KB, generated from Yahoo! Locals |
777 | search API (http://nanoref.com/yahooapis/mgPdGg): |
1251 | search API (<http://dist.schmorp.de/misc/json/long.json>). |
778 | |
1252 | |
779 | module | encode | decode | |
1253 | module | encode | decode | |
780 | -----------|------------|------------| |
1254 | --------------|------------|------------| |
781 | JSON | 55.260 | 34.971 | |
1255 | JSON::DWIW/DS | 1647.927 | 2673.916 | |
782 | JSON::DWIW | 825.228 | 1082.513 | |
1256 | JSON::DWIW/FJ | 1630.249 | 2596.128 | |
783 | JSON::PC | 3571.444 | 2394.829 | |
|
|
784 | JSON::PP | 210.987 | 32.574 | |
1257 | JSON::PP | 400.640 | 62.311 | |
785 | JSON::Syck | 552.551 | 787.544 | |
1258 | JSON::Syck | 1481.040 | 1524.869 | |
786 | JSON::XS | 5780.463 | 4854.519 | |
1259 | JSON::XS | 20661.596 | 9541.183 | |
787 | JSON::XS/2 | 3869.998 | 4798.975 | |
1260 | JSON::XS/2 | 10683.403 | 9416.938 | |
788 | JSON::XS/3 | 5862.880 | 4798.975 | |
1261 | JSON::XS/3 | 20661.596 | 9400.054 | |
789 | Storable | 4445.002 | 5235.027 | |
1262 | Storable | 19765.806 | 10000.725 | |
790 | -----------+------------+------------+ |
1263 | --------------+------------+------------+ |
791 | |
1264 | |
792 | Again, JSON::XS leads by far (except for Storable which non-surprisingly |
1265 | Again, JSON::XS leads by far (except for Storable which non-surprisingly |
793 | decodes faster). |
1266 | decodes a bit faster). |
794 | |
1267 | |
795 | On large strings containing lots of high unicode characters, some |
1268 | On large strings containing lots of high Unicode characters, some |
796 | modules (such as JSON::PC) seem to decode faster than JSON::XS, but the |
1269 | modules (such as JSON::PC) seem to decode faster than JSON::XS, but the |
797 | result will be broken due to missing (or wrong) unicode handling. Others |
1270 | result will be broken due to missing (or wrong) Unicode handling. Others |
798 | refuse to decode or encode properly, so it was impossible to prepare a |
1271 | refuse to decode or encode properly, so it was impossible to prepare a |
799 | fair comparison table for that case. |
1272 | fair comparison table for that case. |
800 | |
1273 | |
801 | SECURITY CONSIDERATIONS |
1274 | SECURITY CONSIDERATIONS |
802 | When you are using JSON in a protocol, talking to untrusted potentially |
1275 | When you are using JSON in a protocol, talking to untrusted potentially |
… | |
… | |
806 | have any buffer overflows. Obviously, this module should ensure that and |
1279 | have any buffer overflows. Obviously, this module should ensure that and |
807 | I am trying hard on making that true, but you never know. |
1280 | I am trying hard on making that true, but you never know. |
808 | |
1281 | |
809 | Second, you need to avoid resource-starving attacks. That means you |
1282 | Second, you need to avoid resource-starving attacks. That means you |
810 | should limit the size of JSON texts you accept, or make sure then when |
1283 | should limit the size of JSON texts you accept, or make sure then when |
811 | your resources run out, thats just fine (e.g. by using a separate |
1284 | your resources run out, that's just fine (e.g. by using a separate |
812 | process that can crash safely). The size of a JSON text in octets or |
1285 | process that can crash safely). The size of a JSON text in octets or |
813 | characters is usually a good indication of the size of the resources |
1286 | characters is usually a good indication of the size of the resources |
814 | required to decode it into a Perl structure. While JSON::XS can check |
1287 | required to decode it into a Perl structure. While JSON::XS can check |
815 | the size of the JSON text, it might be too late when you already have it |
1288 | the size of the JSON text, it might be too late when you already have it |
816 | in memory, so you might want to check the size before you accept the |
1289 | in memory, so you might want to check the size before you accept the |
… | |
… | |
819 | Third, JSON::XS recurses using the C stack when decoding objects and |
1292 | Third, JSON::XS recurses using the C stack when decoding objects and |
820 | arrays. The C stack is a limited resource: for instance, on my amd64 |
1293 | arrays. The C stack is a limited resource: for instance, on my amd64 |
821 | machine with 8MB of stack size I can decode around 180k nested arrays |
1294 | machine with 8MB of stack size I can decode around 180k nested arrays |
822 | but only 14k nested JSON objects (due to perl itself recursing deeply on |
1295 | but only 14k nested JSON objects (due to perl itself recursing deeply on |
823 | croak to free the temporary). If that is exceeded, the program crashes. |
1296 | croak to free the temporary). If that is exceeded, the program crashes. |
824 | to be conservative, the default nesting limit is set to 512. If your |
1297 | To be conservative, the default nesting limit is set to 512. If your |
825 | process has a smaller stack, you should adjust this setting accordingly |
1298 | process has a smaller stack, you should adjust this setting accordingly |
826 | with the "max_depth" method. |
1299 | with the "max_depth" method. |
827 | |
1300 | |
828 | And last but least, something else could bomb you that I forgot to think |
1301 | Something else could bomb you, too, that I forgot to think of. In that |
829 | of. In that case, you get to keep the pieces. I am always open for |
1302 | case, you get to keep the pieces. I am always open for hints, though... |
830 | hints, though... |
|
|
831 | |
1303 | |
|
|
1304 | Also keep in mind that JSON::XS might leak contents of your Perl data |
|
|
1305 | structures in its error messages, so when you serialise sensitive |
|
|
1306 | information you might want to make sure that exceptions thrown by |
|
|
1307 | JSON::XS will not end up in front of untrusted eyes. |
|
|
1308 | |
832 | If you are using JSON::XS to return packets to consumption by javascript |
1309 | If you are using JSON::XS to return packets to consumption by JavaScript |
833 | scripts in a browser you should have a look at |
1310 | scripts in a browser you should have a look at |
834 | <http://jpsykes.com/47/practical-csrf-and-json-security> to see wether |
1311 | <http://blog.archive.jpsykes.com/47/practical-csrf-and-json-security/> |
835 | you are vulnerable to some common attack vectors (which really are |
1312 | to see whether you are vulnerable to some common attack vectors (which |
836 | browser design bugs, but it is still you who will have to deal with it, |
1313 | really are browser design bugs, but it is still you who will have to |
837 | as major browser developers care only for features, not about doing |
1314 | deal with it, as major browser developers care only for features, not |
838 | security right). |
1315 | about getting security right). |
|
|
1316 | |
|
|
1317 | THREADS |
|
|
1318 | This module is *not* guaranteed to be thread safe and there are no plans |
|
|
1319 | to change this until Perl gets thread support (as opposed to the |
|
|
1320 | horribly slow so-called "threads" which are simply slow and bloated |
|
|
1321 | process simulations - use fork, it's *much* faster, cheaper, better). |
|
|
1322 | |
|
|
1323 | (It might actually work, but you have been warned). |
839 | |
1324 | |
840 | BUGS |
1325 | BUGS |
841 | While the goal of this module is to be correct, that unfortunately does |
1326 | While the goal of this module is to be correct, that unfortunately does |
842 | not mean its bug-free, only that I think its design is bug-free. It is |
1327 | not mean it's bug-free, only that I think its design is bug-free. If you |
843 | still relatively early in its development. If you keep reporting bugs |
|
|
844 | they will be fixed swiftly, though. |
1328 | keep reporting bugs they will be fixed swiftly, though. |
|
|
1329 | |
|
|
1330 | Please refrain from using rt.cpan.org or any other bug reporting |
|
|
1331 | service. I put the contact address into my modules for a reason. |
|
|
1332 | |
|
|
1333 | SEE ALSO |
|
|
1334 | The json_xs command line utility for quick experiments. |
845 | |
1335 | |
846 | AUTHOR |
1336 | AUTHOR |
847 | Marc Lehmann <schmorp@schmorp.de> |
1337 | Marc Lehmann <schmorp@schmorp.de> |
848 | http://home.schmorp.de/ |
1338 | http://home.schmorp.de/ |
849 | |
1339 | |