1 | NAME |
1 | NAME |
2 | Convert::Scalar - convert between different representations of perl |
2 | JSON::XS - JSON serialising/deserialising, done correctly and fast |
3 | scalars |
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4 | |
3 | |
5 | SYNOPSIS |
4 | SYNOPSIS |
6 | use Convert::Scalar; |
5 | use JSON::XS; |
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6 | |
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7 | # exported functions, they croak on error |
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8 | # and expect/generate UTF-8 |
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9 | |
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10 | $utf8_encoded_json_text = to_json $perl_hash_or_arrayref; |
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11 | $perl_hash_or_arrayref = from_json $utf8_encoded_json_text; |
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12 | |
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13 | # objToJson and jsonToObj aliases to to_json and from_json |
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14 | # are exported for compatibility to the JSON module, |
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15 | # but should not be used in new code. |
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16 | |
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17 | # OO-interface |
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18 | |
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19 | $coder = JSON::XS->new->ascii->pretty->allow_nonref; |
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20 | $pretty_printed_unencoded = $coder->encode ($perl_scalar); |
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21 | $perl_scalar = $coder->decode ($unicode_json_text); |
7 | |
22 | |
8 | DESCRIPTION |
23 | DESCRIPTION |
9 | This module exports various internal perl methods that change the |
24 | This module converts Perl data structures to JSON and vice versa. Its |
10 | internal representation or state of a perl scalar. All of these work |
25 | primary goal is to be *correct* and its secondary goal is to be *fast*. |
11 | in-place, that is, they modify their scalar argument. No functions are |
26 | To reach the latter goal it was written in C. |
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27 | |
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28 | As this is the n-th-something JSON module on CPAN, what was the reason |
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29 | to write yet another JSON module? While it seems there are many JSON |
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30 | modules, none of them correctly handle all corner cases, and in most |
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31 | cases their maintainers are unresponsive, gone missing, or not listening |
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32 | to bug reports for other reasons. |
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33 | |
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34 | See COMPARISON, below, for a comparison to some other JSON modules. |
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35 | |
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36 | See MAPPING, below, on how JSON::XS maps perl values to JSON values and |
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37 | vice versa. |
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38 | |
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39 | FEATURES |
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40 | * correct unicode handling |
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41 | This module knows how to handle Unicode, and even documents how and |
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42 | when it does so. |
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43 | |
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44 | * round-trip integrity |
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45 | When you serialise a perl data structure using only datatypes |
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46 | supported by JSON, the deserialised data structure is identical on |
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47 | the Perl level. (e.g. the string "2.0" doesn't suddenly become "2" |
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48 | just because it looks like a number). |
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49 | |
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50 | * strict checking of JSON correctness |
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51 | There is no guessing, no generating of illegal JSON texts by |
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52 | default, and only JSON is accepted as input by default (the latter |
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53 | is a security feature). |
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54 | |
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55 | * fast |
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56 | Compared to other JSON modules, this module compares favourably in |
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57 | terms of speed, too. |
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58 | |
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59 | * simple to use |
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60 | This module has both a simple functional interface as well as an OO |
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61 | interface. |
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62 | |
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63 | * reasonably versatile output formats |
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64 | You can choose between the most compact guarenteed single-line |
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65 | format possible (nice for simple line-based protocols), a pure-ascii |
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66 | format (for when your transport is not 8-bit clean, still supports |
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67 | the whole unicode range), or a pretty-printed format (for when you |
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68 | want to read that stuff). Or you can combine those features in |
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69 | whatever way you like. |
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70 | |
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71 | FUNCTIONAL INTERFACE |
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72 | The following convinience methods are provided by this module. They are |
12 | exported by default. |
73 | exported by default: |
13 | |
74 | |
14 | The following export tags exist: |
75 | $json_text = to_json $perl_scalar |
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76 | Converts the given Perl data structure (a simple scalar or a |
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77 | reference to a hash or array) to a UTF-8 encoded, binary string |
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78 | (that is, the string contains octets only). Croaks on error. |
15 | |
79 | |
16 | :utf8 all functions with utf8 in their name |
80 | This function call is functionally identical to: |
17 | :taint all functions with taint in their name |
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18 | :refcnt all functions with refcnt in their name |
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19 | :ok all *ok-functions. |
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20 | |
81 | |
21 | utf8 scalar[, mode] |
82 | $json_text = JSON::XS->new->utf8->encode ($perl_scalar) |
22 | Returns true when the given scalar is marked as utf8, false |
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23 | otherwise. If the optional mode argument is given, also forces the |
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24 | interpretation of the string to utf8 (mode true) or plain bytes |
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25 | (mode false). The actual (byte-) content is not changed. The return |
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26 | value always reflects the state before any modification is done. |
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27 | |
83 | |
28 | This function is useful when you "import" utf8-data into perl, or |
84 | except being faster. |
29 | when some external function (e.g. storing/retrieving from a |
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30 | database) removes the utf8-flag. |
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31 | |
85 | |
32 | utf8_on scalar |
86 | $perl_scalar = from_json $json_text |
33 | Similar to "utf8 scalar, 1", but additionally returns the scalar |
87 | The opposite of "to_json": expects an UTF-8 (binary) string and |
34 | (the argument is still modified in-place). |
88 | tries to parse that as an UTF-8 encoded JSON text, returning the |
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89 | resulting simple scalar or reference. Croaks on error. |
35 | |
90 | |
36 | utf8_off scalar |
91 | This function call is functionally identical to: |
37 | Similar to "utf8 scalar, 0", but additionally returns the scalar |
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38 | (the argument is still modified in-place). |
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39 | |
92 | |
40 | utf8_valid scalar [Perl 5.7] |
93 | $perl_scalar = JSON::XS->new->utf8->decode ($json_text) |
41 | Returns true if the bytes inside the scalar form a valid utf8 |
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42 | string, false otherwise (the check is independent of the actual |
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43 | encoding perl thinks the string is in). |
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44 | |
94 | |
45 | utf8_upgrade scalar |
95 | except being faster. |
46 | Convert the string content of the scalar in-place to its |
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47 | UTF8-encoded form (and also returns it). |
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48 | |
96 | |
49 | utf8_downgrade scalar[, fail_ok=0] |
97 | OBJECT-ORIENTED INTERFACE |
50 | Attempt to convert the string content of the scalar from |
98 | The object oriented interface lets you configure your own encoding or |
51 | UTF8-encoded to ISO-8859-1. This may not be possible if the string |
99 | decoding style, within the limits of supported formats. |
52 | contains characters that cannot be represented in a single byte; if |
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53 | this is the case, it leaves the scalar unchanged and either returns |
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54 | false or, if "fail_ok" is not true (the default), croaks. |
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55 | |
100 | |
56 | utf8_encode scalar |
101 | $json = new JSON::XS |
57 | Convert the string value of the scalar to UTF8-encoded, but then |
102 | Creates a new JSON::XS object that can be used to de/encode JSON |
58 | turn off the "SvUTF8" flag so that it looks like bytes to perl |
103 | strings. All boolean flags described below are by default |
59 | again. (Might be removed in future versions). |
104 | *disabled*. |
60 | |
105 | |
61 | utf8_length scalar |
106 | The mutators for flags all return the JSON object again and thus |
62 | Returns the number of characters in the string, counting wide UTF8 |
107 | calls can be chained: |
63 | characters as a single character, independent of wether the scalar |
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64 | is marked as containing bytes or mulitbyte characters. |
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65 | |
108 | |
66 | unmagic scalar, type |
109 | my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]}) |
67 | Remove the specified magic from the scalar (DANGEROUS!). |
110 | => {"a": [1, 2]} |
68 | |
111 | |
69 | weaken scalar |
112 | $json = $json->ascii ([$enable]) |
70 | Weaken a reference. (See also WeakRef). |
113 | If $enable is true (or missing), then the "encode" method will not |
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114 | generate characters outside the code range 0..127 (which is ASCII). |
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115 | Any unicode characters outside that range will be escaped using |
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116 | either a single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL |
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117 | escape sequence, as per RFC4627. The resulting encoded JSON text can |
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118 | be treated as a native unicode string, an ascii-encoded, |
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119 | latin1-encoded or UTF-8 encoded string, or any other superset of |
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120 | ASCII. |
71 | |
121 | |
72 | taint scalar |
122 | If $enable is false, then the "encode" method will not escape |
73 | Taint the scalar. |
123 | Unicode characters unless required by the JSON syntax or other |
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124 | flags. This results in a faster and more compact format. |
74 | |
125 | |
75 | tainted scalar |
126 | The main use for this flag is to produce JSON texts that can be |
76 | returns true when the scalar is tainted, false otherwise. |
127 | transmitted over a 7-bit channel, as the encoded JSON texts will not |
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128 | contain any 8 bit characters. |
77 | |
129 | |
78 | untaint scalar |
130 | JSON::XS->new->ascii (1)->encode ([chr 0x10401]) |
79 | Remove the tainted flag from the specified scalar. |
131 | => ["\ud801\udc01"] |
80 | |
132 | |
81 | grow scalar, newlen |
133 | $json = $json->latin1 ([$enable]) |
82 | Sets the memory area used for the scalar to the given length, if the |
134 | If $enable is true (or missing), then the "encode" method will |
83 | current length is less than the new value. This does not affect the |
135 | encode the resulting JSON text as latin1 (or iso-8859-1), escaping |
84 | contents of the scalar, but is only useful to "pre-allocate" memory |
136 | any characters outside the code range 0..255. The resulting string |
85 | space if you know the scalar will grow. The return value is the |
137 | can be treated as a latin1-encoded JSON text or a native unicode |
86 | modified scalar (the scalar is modified in-place). |
138 | string. The "decode" method will not be affected in any way by this |
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139 | flag, as "decode" by default expects unicode, which is a strict |
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140 | superset of latin1. |
87 | |
141 | |
88 | refcnt scalar[, newrefcnt] |
142 | If $enable is false, then the "encode" method will not escape |
89 | Returns the current reference count of the given scalar and |
143 | Unicode characters unless required by the JSON syntax or other |
90 | optionally sets it to the given reference count. |
144 | flags. |
91 | |
145 | |
92 | refcnt_inc scalar |
146 | The main use for this flag is efficiently encoding binary data as |
93 | Increments the reference count of the given scalar inplace. |
147 | JSON text, as most octets will not be escaped, resulting in a |
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148 | smaller encoded size. The disadvantage is that the resulting JSON |
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149 | text is encoded in latin1 (and must correctly be treated as such |
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150 | when storing and transfering), a rare encoding for JSON. It is |
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151 | therefore most useful when you want to store data structures known |
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152 | to contain binary data efficiently in files or databases, not when |
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153 | talking to other JSON encoders/decoders. |
94 | |
154 | |
95 | refcnt_dec scalar |
155 | JSON::XS->new->latin1->encode (["\x{89}\x{abc}"] |
96 | Decrements the reference count of the given scalar inplace. Use |
156 | => ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not) |
97 | "weaken" instead if you understand what this function is fore. |
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98 | Better yet: don't use this module in this case. |
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99 | |
157 | |
100 | refcnt_rv scalar[, newrefcnt] |
158 | $json = $json->utf8 ([$enable]) |
101 | Works like "refcnt", but dereferences the given reference first. |
159 | If $enable is true (or missing), then the "encode" method will |
102 | This is useful to find the reference count of arrays or hashes, |
160 | encode the JSON result into UTF-8, as required by many protocols, |
103 | which cnanot be passed directly. Remember that taking a reference of |
161 | while the "decode" method expects to be handled an UTF-8-encoded |
104 | some object increases it's reference count, so the reference count |
162 | string. Please note that UTF-8-encoded strings do not contain any |
105 | used by the *_rv-functions tend to be one higher. |
163 | characters outside the range 0..255, they are thus useful for |
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164 | bytewise/binary I/O. In future versions, enabling this option might |
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165 | enable autodetection of the UTF-16 and UTF-32 encoding families, as |
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166 | described in RFC4627. |
106 | |
167 | |
107 | refcnt_inc_rv scalar |
168 | If $enable is false, then the "encode" method will return the JSON |
108 | Works like "refcnt_inc", but dereferences the given reference first. |
169 | string as a (non-encoded) unicode string, while "decode" expects |
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170 | thus a unicode string. Any decoding or encoding (e.g. to UTF-8 or |
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171 | UTF-16) needs to be done yourself, e.g. using the Encode module. |
109 | |
172 | |
110 | refcnt_dec_rv scalar |
173 | Example, output UTF-16BE-encoded JSON: |
111 | Works like "refcnt_dec", but dereferences the given reference first. |
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112 | |
174 | |
113 | ok scalar |
175 | use Encode; |
114 | uok scalar |
176 | $jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object); |
115 | rok scalar |
177 | |
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178 | Example, decode UTF-32LE-encoded JSON: |
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179 | |
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180 | use Encode; |
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181 | $object = JSON::XS->new->decode (decode "UTF-32LE", $jsontext); |
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182 | |
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183 | $json = $json->pretty ([$enable]) |
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184 | This enables (or disables) all of the "indent", "space_before" and |
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185 | "space_after" (and in the future possibly more) flags in one call to |
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186 | generate the most readable (or most compact) form possible. |
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187 | |
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188 | Example, pretty-print some simple structure: |
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189 | |
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190 | my $json = JSON::XS->new->pretty(1)->encode ({a => [1,2]}) |
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191 | => |
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192 | { |
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193 | "a" : [ |
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194 | 1, |
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195 | 2 |
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196 | ] |
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197 | } |
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198 | |
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199 | $json = $json->indent ([$enable]) |
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200 | If $enable is true (or missing), then the "encode" method will use a |
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201 | multiline format as output, putting every array member or |
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202 | object/hash key-value pair into its own line, identing them |
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203 | properly. |
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204 | |
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205 | If $enable is false, no newlines or indenting will be produced, and |
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206 | the resulting JSON text is guarenteed not to contain any "newlines". |
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207 | |
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208 | This setting has no effect when decoding JSON texts. |
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209 | |
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210 | $json = $json->space_before ([$enable]) |
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211 | If $enable is true (or missing), then the "encode" method will add |
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212 | an extra optional space before the ":" separating keys from values |
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213 | in JSON objects. |
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214 | |
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215 | If $enable is false, then the "encode" method will not add any extra |
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216 | space at those places. |
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217 | |
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218 | This setting has no effect when decoding JSON texts. You will also |
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219 | most likely combine this setting with "space_after". |
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220 | |
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221 | Example, space_before enabled, space_after and indent disabled: |
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222 | |
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223 | {"key" :"value"} |
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224 | |
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225 | $json = $json->space_after ([$enable]) |
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226 | If $enable is true (or missing), then the "encode" method will add |
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227 | an extra optional space after the ":" separating keys from values in |
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228 | JSON objects and extra whitespace after the "," separating key-value |
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229 | pairs and array members. |
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230 | |
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231 | If $enable is false, then the "encode" method will not add any extra |
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232 | space at those places. |
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233 | |
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234 | This setting has no effect when decoding JSON texts. |
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235 | |
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236 | Example, space_before and indent disabled, space_after enabled: |
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237 | |
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238 | {"key": "value"} |
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239 | |
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240 | $json = $json->canonical ([$enable]) |
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241 | If $enable is true (or missing), then the "encode" method will |
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242 | output JSON objects by sorting their keys. This is adding a |
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243 | comparatively high overhead. |
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244 | |
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245 | If $enable is false, then the "encode" method will output key-value |
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246 | pairs in the order Perl stores them (which will likely change |
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247 | between runs of the same script). |
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248 | |
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249 | This option is useful if you want the same data structure to be |
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250 | encoded as the same JSON text (given the same overall settings). If |
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251 | it is disabled, the same hash migh be encoded differently even if |
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252 | contains the same data, as key-value pairs have no inherent ordering |
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253 | in Perl. |
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254 | |
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255 | This setting has no effect when decoding JSON texts. |
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256 | |
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257 | $json = $json->allow_nonref ([$enable]) |
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258 | If $enable is true (or missing), then the "encode" method can |
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259 | convert a non-reference into its corresponding string, number or |
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260 | null JSON value, which is an extension to RFC4627. Likewise, |
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261 | "decode" will accept those JSON values instead of croaking. |
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262 | |
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263 | If $enable is false, then the "encode" method will croak if it isn't |
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264 | passed an arrayref or hashref, as JSON texts must either be an |
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265 | object or array. Likewise, "decode" will croak if given something |
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266 | that is not a JSON object or array. |
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267 | |
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268 | Example, encode a Perl scalar as JSON value with enabled |
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269 | "allow_nonref", resulting in an invalid JSON text: |
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270 | |
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271 | JSON::XS->new->allow_nonref->encode ("Hello, World!") |
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272 | => "Hello, World!" |
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273 | |
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274 | $json = $json->shrink ([$enable]) |
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275 | Perl usually over-allocates memory a bit when allocating space for |
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276 | strings. This flag optionally resizes strings generated by either |
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277 | "encode" or "decode" to their minimum size possible. This can save |
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278 | memory when your JSON texts are either very very long or you have |
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279 | many short strings. It will also try to downgrade any strings to |
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280 | octet-form if possible: perl stores strings internally either in an |
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281 | encoding called UTF-X or in octet-form. The latter cannot store |
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282 | everything but uses less space in general (and some buggy Perl or C |
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283 | code might even rely on that internal representation being used). |
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284 | |
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285 | The actual definition of what shrink does might change in future |
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286 | versions, but it will always try to save space at the expense of |
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287 | time. |
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288 | |
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289 | If $enable is true (or missing), the string returned by "encode" |
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290 | will be shrunk-to-fit, while all strings generated by "decode" will |
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291 | also be shrunk-to-fit. |
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292 | |
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293 | If $enable is false, then the normal perl allocation algorithms are |
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294 | used. If you work with your data, then this is likely to be faster. |
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295 | |
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296 | In the future, this setting might control other things, such as |
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297 | converting strings that look like integers or floats into integers |
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298 | or floats internally (there is no difference on the Perl level), |
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299 | saving space. |
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300 | |
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301 | $json = $json->max_depth ([$maximum_nesting_depth]) |
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302 | Sets the maximum nesting level (default 512) accepted while encoding |
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303 | or decoding. If the JSON text or Perl data structure has an equal or |
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304 | higher nesting level then this limit, then the encoder and decoder |
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305 | will stop and croak at that point. |
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306 | |
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307 | Nesting level is defined by number of hash- or arrayrefs that the |
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308 | encoder needs to traverse to reach a given point or the number of |
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309 | "{" or "[" characters without their matching closing parenthesis |
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310 | crossed to reach a given character in a string. |
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311 | |
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312 | Setting the maximum depth to one disallows any nesting, so that |
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313 | ensures that the object is only a single hash/object or array. |
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314 | |
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315 | The argument to "max_depth" will be rounded up to the next nearest |
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316 | power of two. |
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317 | |
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318 | See SECURITY CONSIDERATIONS, below, for more info on why this is |
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319 | useful. |
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320 | |
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321 | $json_text = $json->encode ($perl_scalar) |
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322 | Converts the given Perl data structure (a simple scalar or a |
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323 | reference to a hash or array) to its JSON representation. Simple |
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324 | scalars will be converted into JSON string or number sequences, |
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325 | while references to arrays become JSON arrays and references to |
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326 | hashes become JSON objects. Undefined Perl values (e.g. "undef") |
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327 | become JSON "null" values. Neither "true" nor "false" values will be |
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328 | generated. |
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329 | |
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330 | $perl_scalar = $json->decode ($json_text) |
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331 | The opposite of "encode": expects a JSON text and tries to parse it, |
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332 | returning the resulting simple scalar or reference. Croaks on error. |
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333 | |
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334 | JSON numbers and strings become simple Perl scalars. JSON arrays |
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335 | become Perl arrayrefs and JSON objects become Perl hashrefs. "true" |
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336 | becomes 1, "false" becomes 0 and "null" becomes "undef". |
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337 | |
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338 | ($perl_scalar, $characters) = $json->decode_prefix ($json_text) |
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339 | This works like the "decode" method, but instead of raising an |
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340 | exception when there is trailing garbage after the first JSON |
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341 | object, it will silently stop parsing there and return the number of |
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342 | characters consumed so far. |
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343 | |
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344 | This is useful if your JSON texts are not delimited by an outer |
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345 | protocol (which is not the brightest thing to do in the first place) |
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346 | and you need to know where the JSON text ends. |
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347 | |
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348 | JSON::XS->new->decode_prefix ("[1] the tail") |
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349 | => ([], 3) |
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350 | |
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351 | MAPPING |
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352 | This section describes how JSON::XS maps Perl values to JSON values and |
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353 | vice versa. These mappings are designed to "do the right thing" in most |
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354 | circumstances automatically, preserving round-tripping characteristics |
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355 | (what you put in comes out as something equivalent). |
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356 | |
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357 | For the more enlightened: note that in the following descriptions, |
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358 | lowercase *perl* refers to the Perl interpreter, while uppcercase *Perl* |
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359 | refers to the abstract Perl language itself. |
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360 | |
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361 | JSON -> PERL |
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362 | object |
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363 | A JSON object becomes a reference to a hash in Perl. No ordering of |
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364 | object keys is preserved (JSON does not preserver object key |
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365 | ordering itself). |
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366 | |
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367 | array |
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368 | A JSON array becomes a reference to an array in Perl. |
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369 | |
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370 | string |
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371 | A JSON string becomes a string scalar in Perl - Unicode codepoints |
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372 | in JSON are represented by the same codepoints in the Perl string, |
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373 | so no manual decoding is necessary. |
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374 | |
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375 | number |
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376 | A JSON number becomes either an integer or numeric (floating point) |
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377 | scalar in perl, depending on its range and any fractional parts. On |
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378 | the Perl level, there is no difference between those as Perl handles |
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379 | all the conversion details, but an integer may take slightly less |
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380 | memory and might represent more values exactly than (floating point) |
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381 | numbers. |
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382 | |
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383 | true, false |
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384 | These JSON atoms become 0, 1, respectively. Information is lost in |
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385 | this process. Future versions might represent those values |
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386 | differently, but they will be guarenteed to act like these integers |
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387 | would normally in Perl. |
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388 | |
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389 | null |
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390 | A JSON null atom becomes "undef" in Perl. |
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391 | |
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392 | PERL -> JSON |
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393 | The mapping from Perl to JSON is slightly more difficult, as Perl is a |
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394 | truly typeless language, so we can only guess which JSON type is meant |
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395 | by a Perl value. |
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396 | |
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397 | hash references |
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398 | Perl hash references become JSON objects. As there is no inherent |
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399 | ordering in hash keys (or JSON objects), they will usually be |
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400 | encoded in a pseudo-random order that can change between runs of the |
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401 | same program but stays generally the same within a single run of a |
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402 | program. JSON::XS can optionally sort the hash keys (determined by |
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403 | the *canonical* flag), so the same datastructure will serialise to |
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404 | the same JSON text (given same settings and version of JSON::XS), |
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405 | but this incurs a runtime overhead and is only rarely useful, e.g. |
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406 | when you want to compare some JSON text against another for |
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407 | equality. |
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408 | |
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409 | array references |
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410 | Perl array references become JSON arrays. |
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411 | |
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412 | other references |
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413 | Other unblessed references are generally not allowed and will cause |
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414 | an exception to be thrown, except for references to the integers 0 |
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415 | and 1, which get turned into "false" and "true" atoms in JSON. You |
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416 | can also use "JSON::XS::false" and "JSON::XS::true" to improve |
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417 | readability. |
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418 | |
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419 | to_json [\0,JSON::XS::true] # yields [false,true] |
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420 | |
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421 | blessed objects |
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422 | Blessed objects are not allowed. JSON::XS currently tries to encode |
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423 | their underlying representation (hash- or arrayref), but this |
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424 | behaviour might change in future versions. |
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425 | |
116 | pok scalar |
426 | simple scalars |
117 | nok scalar |
427 | Simple Perl scalars (any scalar that is not a reference) are the |
118 | niok scalar |
428 | most difficult objects to encode: JSON::XS will encode undefined |
119 | Calls SvOK, SvUOK, SvROK, SvPOK, SvNOK or SvNIOK on the given |
429 | scalars as JSON null value, scalars that have last been used in a |
120 | scalar, respectively. |
430 | string context before encoding as JSON strings and anything else as |
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431 | number value: |
121 | |
432 | |
122 | CANDIDATES FOR FUTURE RELEASES |
433 | # dump as number |
123 | The following API functions (perlapi) are considered for future |
434 | to_json [2] # yields [2] |
124 | inclusion in this module If you want them, write me. |
435 | to_json [-3.0e17] # yields [-3e+17] |
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436 | my $value = 5; to_json [$value] # yields [5] |
125 | |
437 | |
126 | sv_upgrade |
438 | # used as string, so dump as string |
127 | sv_pvn_force |
439 | print $value; |
128 | sv_pvutf8n_force |
440 | to_json [$value] # yields ["5"] |
129 | the sv2xx family |
441 | |
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442 | # undef becomes null |
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443 | to_json [undef] # yields [null] |
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444 | |
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445 | You can force the type to be a string by stringifying it: |
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446 | |
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447 | my $x = 3.1; # some variable containing a number |
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448 | "$x"; # stringified |
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449 | $x .= ""; # another, more awkward way to stringify |
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450 | print $x; # perl does it for you, too, quite often |
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451 | |
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452 | You can force the type to be a number by numifying it: |
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453 | |
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454 | my $x = "3"; # some variable containing a string |
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455 | $x += 0; # numify it, ensuring it will be dumped as a number |
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456 | $x *= 1; # same thing, the choise is yours. |
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457 | |
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458 | You can not currently output JSON booleans or force the type in |
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459 | other, less obscure, ways. Tell me if you need this capability. |
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460 | |
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461 | COMPARISON |
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462 | As already mentioned, this module was created because none of the |
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463 | existing JSON modules could be made to work correctly. First I will |
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464 | describe the problems (or pleasures) I encountered with various existing |
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465 | JSON modules, followed by some benchmark values. JSON::XS was designed |
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466 | not to suffer from any of these problems or limitations. |
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467 | |
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468 | JSON 1.07 |
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469 | Slow (but very portable, as it is written in pure Perl). |
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470 | |
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471 | Undocumented/buggy Unicode handling (how JSON handles unicode values |
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472 | is undocumented. One can get far by feeding it unicode strings and |
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473 | doing en-/decoding oneself, but unicode escapes are not working |
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474 | properly). |
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475 | |
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476 | No roundtripping (strings get clobbered if they look like numbers, |
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477 | e.g. the string 2.0 will encode to 2.0 instead of "2.0", and that |
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|
478 | will decode into the number 2. |
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479 | |
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480 | JSON::PC 0.01 |
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481 | Very fast. |
|
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482 | |
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483 | Undocumented/buggy Unicode handling. |
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484 | |
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485 | No roundtripping. |
|
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486 | |
|
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487 | Has problems handling many Perl values (e.g. regex results and other |
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488 | magic values will make it croak). |
|
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489 | |
|
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490 | Does not even generate valid JSON ("{1,2}" gets converted to "{1:2}" |
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491 | which is not a valid JSON text. |
|
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492 | |
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493 | Unmaintained (maintainer unresponsive for many months, bugs are not |
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494 | getting fixed). |
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495 | |
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496 | JSON::Syck 0.21 |
|
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497 | Very buggy (often crashes). |
|
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498 | |
|
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499 | Very inflexible (no human-readable format supported, format pretty |
|
|
500 | much undocumented. I need at least a format for easy reading by |
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501 | humans and a single-line compact format for use in a protocol, and |
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502 | preferably a way to generate ASCII-only JSON texts). |
|
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503 | |
|
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504 | Completely broken (and confusingly documented) Unicode handling |
|
|
505 | (unicode escapes are not working properly, you need to set |
|
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506 | ImplicitUnicode to *different* values on en- and decoding to get |
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507 | symmetric behaviour). |
|
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508 | |
|
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509 | No roundtripping (simple cases work, but this depends on wether the |
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510 | scalar value was used in a numeric context or not). |
|
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511 | |
|
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512 | Dumping hashes may skip hash values depending on iterator state. |
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513 | |
|
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514 | Unmaintained (maintainer unresponsive for many months, bugs are not |
|
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515 | getting fixed). |
|
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516 | |
|
|
517 | Does not check input for validity (i.e. will accept non-JSON input |
|
|
518 | and return "something" instead of raising an exception. This is a |
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519 | security issue: imagine two banks transfering money between each |
|
|
520 | other using JSON. One bank might parse a given non-JSON request and |
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521 | deduct money, while the other might reject the transaction with a |
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522 | syntax error. While a good protocol will at least recover, that is |
|
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523 | extra unnecessary work and the transaction will still not succeed). |
|
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524 | |
|
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525 | JSON::DWIW 0.04 |
|
|
526 | Very fast. Very natural. Very nice. |
|
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527 | |
|
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528 | Undocumented unicode handling (but the best of the pack. Unicode |
|
|
529 | escapes still don't get parsed properly). |
|
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530 | |
|
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531 | Very inflexible. |
|
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532 | |
|
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533 | No roundtripping. |
|
|
534 | |
|
|
535 | Does not generate valid JSON texts (key strings are often unquoted, |
|
|
536 | empty keys result in nothing being output) |
|
|
537 | |
|
|
538 | Does not check input for validity. |
|
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539 | |
|
|
540 | SPEED |
|
|
541 | It seems that JSON::XS is surprisingly fast, as shown in the following |
|
|
542 | tables. They have been generated with the help of the "eg/bench" program |
|
|
543 | in the JSON::XS distribution, to make it easy to compare on your own |
|
|
544 | system. |
|
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545 | |
|
|
546 | First comes a comparison between various modules using a very short JSON |
|
|
547 | string: |
|
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548 | |
|
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549 | {"method": "handleMessage", "params": ["user1", "we were just talking"], "id": null} |
|
|
550 | |
|
|
551 | It shows the number of encodes/decodes per second (JSON::XS uses the |
|
|
552 | functional interface, while JSON::XS/2 uses the OO interface with |
|
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553 | pretty-printing and hashkey sorting enabled). Higher is better: |
|
|
554 | |
|
|
555 | module | encode | decode | |
|
|
556 | -----------|------------|------------| |
|
|
557 | JSON | 11488.516 | 7823.035 | |
|
|
558 | JSON::DWIW | 94708.054 | 129094.260 | |
|
|
559 | JSON::PC | 63884.157 | 128528.212 | |
|
|
560 | JSON::Syck | 34898.677 | 42096.911 | |
|
|
561 | JSON::XS | 654027.064 | 396423.669 | |
|
|
562 | JSON::XS/2 | 371564.190 | 371725.613 | |
|
|
563 | -----------+------------+------------+ |
|
|
564 | |
|
|
565 | That is, JSON::XS is more than six times faster than JSON::DWIW on |
|
|
566 | encoding, more than three times faster on decoding, and about thirty |
|
|
567 | times faster than JSON, even with pretty-printing and key sorting. |
|
|
568 | |
|
|
569 | Using a longer test string (roughly 18KB, generated from Yahoo! Locals |
|
|
570 | search API (http://nanoref.com/yahooapis/mgPdGg): |
|
|
571 | |
|
|
572 | module | encode | decode | |
|
|
573 | -----------|------------|------------| |
|
|
574 | JSON | 273.023 | 44.674 | |
|
|
575 | JSON::DWIW | 1089.383 | 1145.704 | |
|
|
576 | JSON::PC | 3097.419 | 2393.921 | |
|
|
577 | JSON::Syck | 514.060 | 843.053 | |
|
|
578 | JSON::XS | 6479.668 | 3636.364 | |
|
|
579 | JSON::XS/2 | 3774.221 | 3599.124 | |
|
|
580 | -----------+------------+------------+ |
|
|
581 | |
|
|
582 | Again, JSON::XS leads by far. |
|
|
583 | |
|
|
584 | On large strings containing lots of high unicode characters, some |
|
|
585 | modules (such as JSON::PC) seem to decode faster than JSON::XS, but the |
|
|
586 | result will be broken due to missing (or wrong) unicode handling. Others |
|
|
587 | refuse to decode or encode properly, so it was impossible to prepare a |
|
|
588 | fair comparison table for that case. |
|
|
589 | |
|
|
590 | SECURITY CONSIDERATIONS |
|
|
591 | When you are using JSON in a protocol, talking to untrusted potentially |
|
|
592 | hostile creatures requires relatively few measures. |
|
|
593 | |
|
|
594 | First of all, your JSON decoder should be secure, that is, should not |
|
|
595 | have any buffer overflows. Obviously, this module should ensure that and |
|
|
596 | I am trying hard on making that true, but you never know. |
|
|
597 | |
|
|
598 | Second, you need to avoid resource-starving attacks. That means you |
|
|
599 | should limit the size of JSON texts you accept, or make sure then when |
|
|
600 | your resources run out, thats just fine (e.g. by using a separate |
|
|
601 | process that can crash safely). The size of a JSON text in octets or |
|
|
602 | characters is usually a good indication of the size of the resources |
|
|
603 | required to decode it into a Perl structure. |
|
|
604 | |
|
|
605 | Third, JSON::XS recurses using the C stack when decoding objects and |
|
|
606 | arrays. The C stack is a limited resource: for instance, on my amd64 |
|
|
607 | machine with 8MB of stack size I can decode around 180k nested arrays |
|
|
608 | but only 14k nested JSON objects (due to perl itself recursing deeply on |
|
|
609 | croak to free the temporary). If that is exceeded, the program crashes. |
|
|
610 | to be conservative, the default nesting limit is set to 512. If your |
|
|
611 | process has a smaller stack, you should adjust this setting accordingly |
|
|
612 | with the "max_depth" method. |
|
|
613 | |
|
|
614 | And last but least, something else could bomb you that I forgot to think |
|
|
615 | of. In that case, you get to keep the pieces. I am always open for |
|
|
616 | hints, though... |
|
|
617 | |
|
|
618 | BUGS |
|
|
619 | While the goal of this module is to be correct, that unfortunately does |
|
|
620 | not mean its bug-free, only that I think its design is bug-free. It is |
|
|
621 | still relatively early in its development. If you keep reporting bugs |
|
|
622 | they will be fixed swiftly, though. |
130 | |
623 | |
131 | AUTHOR |
624 | AUTHOR |
132 | Marc Lehmann <schmorp@schmorp.de> |
625 | Marc Lehmann <schmorp@schmorp.de> |
133 | http://home.schmorp.de/ |
626 | http://home.schmorp.de/ |
134 | |
627 | |