1 | NAME |
1 | NAME |
2 | JSON::XS - JSON serialising/deserialising, done correctly and fast |
2 | EV - perl interface to libevent, monkey.org/~provos/libevent/ |
3 | |
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4 | JSON::XS - 正しくて高速な JSON |
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5 | シリアライザ/デシリアライザ |
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6 | (http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html) |
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7 | |
3 | |
8 | SYNOPSIS |
4 | SYNOPSIS |
9 | use JSON::XS; |
5 | use EV; |
10 | |
6 | |
11 | # exported functions, they croak on error |
7 | # TIMER |
12 | # and expect/generate UTF-8 |
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13 | |
8 | |
14 | $utf8_encoded_json_text = to_json $perl_hash_or_arrayref; |
9 | my $w = EV::timer 2, 0, sub { |
15 | $perl_hash_or_arrayref = from_json $utf8_encoded_json_text; |
10 | warn "is called after 2s"; |
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11 | }; |
16 | |
12 | |
17 | # OO-interface |
13 | my $w = EV::timer 2, 1, sub { |
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14 | warn "is called roughly every 2s (repeat = 1)"; |
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15 | }; |
18 | |
16 | |
19 | $coder = JSON::XS->new->ascii->pretty->allow_nonref; |
17 | undef $w; # destroy event watcher again |
20 | $pretty_printed_unencoded = $coder->encode ($perl_scalar); |
18 | |
21 | $perl_scalar = $coder->decode ($unicode_json_text); |
19 | # IO |
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20 | |
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21 | my $w = EV::timer_abs 0, 60, sub { |
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22 | warn "is called every minute, on the minute, exactly"; |
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23 | }; |
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24 | |
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25 | my $w = EV::io \*STDIN, EV::READ | EV::PERSIST, sub { |
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26 | my ($w, $events) = @_; # all callbacks get the watcher object and event mask |
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27 | if ($events & EV::TIMEOUT) { |
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28 | warn "nothign received on stdin for 10 seconds, retrying"; |
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29 | } else { |
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30 | warn "stdin is readable, you entered: ", <STDIN>; |
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31 | } |
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32 | }; |
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33 | $w->timeout (10); |
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34 | |
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35 | # MAINLOOP |
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36 | EV::dispatch; # loop as long as watchers are active |
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37 | EV::loop; # the same thing |
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38 | EV::loop EV::LOOP_ONCE; |
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39 | EV::loop EV::LOOP_ONSHOT; |
22 | |
40 | |
23 | DESCRIPTION |
41 | DESCRIPTION |
24 | This module converts Perl data structures to JSON and vice versa. Its |
42 | This module provides an interface to libevent |
25 | primary goal is to be *correct* and its secondary goal is to be *fast*. |
43 | (<http://monkey.org/~provos/libevent/>). You probably should acquaint |
26 | To reach the latter goal it was written in C. |
44 | yourself with its documentation and source code to be able to use this |
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45 | module fully. |
27 | |
46 | |
28 | As this is the n-th-something JSON module on CPAN, what was the reason |
47 | Please note thta this module disables the libevent EPOLL method by |
29 | to write yet another JSON module? While it seems there are many JSON |
48 | default, see BUGS, below, if you need to enable it. |
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 | |
49 | |
34 | See COMPARISON, below, for a comparison to some other JSON modules. |
50 | BASIC INTERFACE |
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51 | $EV::NPRI |
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52 | How many priority levels are available. |
35 | |
53 | |
36 | See MAPPING, below, on how JSON::XS maps perl values to JSON values and |
54 | $EV::DIED |
37 | vice versa. |
55 | Must contain a reference to a function that is called when a |
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56 | callback throws an exception (with $@ containing thr error). The |
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57 | default prints an informative message and continues. |
38 | |
58 | |
39 | FEATURES |
59 | If this callback throws an exception it will be silently ignored. |
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 | |
60 | |
44 | * round-trip integrity |
61 | $time = EV::now |
45 | When you serialise a perl data structure using only datatypes |
62 | Returns the time in (fractional) seconds since the epoch. |
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 | |
63 | |
50 | * strict checking of JSON correctness |
64 | $version = EV::version |
51 | There is no guessing, no generating of illegal JSON texts by |
65 | $method = EV::method |
52 | default, and only JSON is accepted as input by default (the latter |
66 | Return version string and event polling method used. |
53 | is a security feature). |
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54 | |
67 | |
55 | * fast |
68 | EV::loop $flags # EV::LOOP_ONCE, EV::LOOP_ONESHOT |
56 | Compared to other JSON modules, this module compares favourably in |
69 | EV::loopexit $after |
57 | terms of speed, too. |
70 | Exit any active loop or dispatch after $after seconds or immediately |
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71 | if $after is missing or zero. |
58 | |
72 | |
59 | * simple to use |
73 | EV::dispatch |
60 | This module has both a simple functional interface as well as an OO |
74 | Same as "EV::loop 0". |
61 | interface. |
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62 | |
75 | |
63 | * reasonably versatile output formats |
76 | EV::event $callback |
64 | You can choose between the most compact guarenteed single-line |
77 | Creates a new event watcher waiting for nothing, calling the given |
65 | format possible (nice for simple line-based protocols), a pure-ascii |
78 | callback. |
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 | |
79 | |
71 | FUNCTIONAL INTERFACE |
80 | my $w = EV::io $fileno_or_fh, $eventmask, $callback |
72 | The following convinience methods are provided by this module. They are |
81 | my $w = EV::io_ns $fileno_or_fh, $eventmask, $callback |
73 | exported by default: |
82 | As long as the returned watcher object is alive, call the $callback |
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83 | when the events specified in $eventmask happen. Initially, the |
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84 | timeout is disabled. |
74 | |
85 | |
75 | $json_text = to_json $perl_scalar |
86 | Youc an additionall set a timeout to occur on the watcher, but note |
76 | Converts the given Perl data structure to a UTF-8 encoded, binary |
87 | that this timeout will not be reset when you get an I/O event in the |
77 | string (that is, the string contains octets only). Croaks on error. |
88 | EV::PERSIST case, and reaching a timeout will always stop the |
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89 | watcher even in the EV::PERSIST case. |
78 | |
90 | |
79 | This function call is functionally identical to: |
91 | If you want a timeout to occur only after a specific time of |
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92 | inactivity, set a repeating timeout and do NOT use EV::PERSIST. |
80 | |
93 | |
81 | $json_text = JSON::XS->new->utf8->encode ($perl_scalar) |
94 | Eventmask can be one or more of these constants ORed together: |
82 | |
95 | |
83 | except being faster. |
96 | EV::READ wait until read() wouldn't block anymore |
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97 | EV::WRITE wait until write() wouldn't block anymore |
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98 | EV::PERSIST stay active after a (non-timeout) event occured |
84 | |
99 | |
85 | $perl_scalar = from_json $json_text |
100 | The "io_ns" variant doesn't add/start the newly created watcher. |
86 | The opposite of "to_json": expects an UTF-8 (binary) string and |
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87 | tries to parse that as an UTF-8 encoded JSON text, returning the |
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88 | resulting reference. Croaks on error. |
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89 | |
101 | |
90 | This function call is functionally identical to: |
102 | my $w = EV::timer $after, $repeat, $callback |
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103 | my $w = EV::timer_ns $after, $repeat, $callback |
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104 | Calls the callback after $after seconds. If $repeat is true, the |
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105 | timer will be restarted after the callback returns. This means that |
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106 | the callback would be called roughly every $after seconds, prolonged |
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107 | by the time the callback takes. |
91 | |
108 | |
92 | $perl_scalar = JSON::XS->new->utf8->decode ($json_text) |
109 | The "timer_ns" variant doesn't add/start the newly created watcher. |
93 | |
110 | |
94 | except being faster. |
111 | my $w = EV::timer_abs $at, $interval, $callback |
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112 | my $w = EV::timer_abs_ns $at, $interval, $callback |
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113 | Similar to EV::timer, but the time is given as an absolute point in |
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114 | time ($at), plus an optional $interval. |
95 | |
115 | |
96 | $is_boolean = JSON::XS::is_bool $scalar |
116 | If the $interval is zero, then the callback will be called at the |
97 | Returns true if the passed scalar represents either JSON::XS::true |
117 | time $at if that is in the future, or as soon as possible if its in |
98 | or JSON::XS::false, two constants that act like 1 and 0, |
118 | the past. It will not automatically repeat. |
99 | respectively and are used to represent JSON "true" and "false" |
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100 | values in Perl. |
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101 | |
119 | |
102 | See MAPPING, below, for more information on how JSON values are |
120 | If the $interval is nonzero, then the watcher will always be |
103 | mapped to Perl. |
121 | scheduled to time out at the next "$at + integer * $interval" time. |
104 | |
122 | |
105 | A FEW NOTES ON UNICODE AND PERL |
123 | This can be used to schedule a callback to run at very regular |
106 | Since this often leads to confusion, here are a few very clear words on |
124 | intervals, as long as the processing time is less then the interval |
107 | how Unicode works in Perl, modulo bugs. |
125 | (otherwise obviously events will be skipped). |
108 | |
126 | |
109 | 1. Perl strings can store characters with ordinal values > 255. |
127 | Another way to think about it (for the mathematically inclined) is |
110 | This enables you to store unicode characters as single characters in |
128 | that "timer_abs" will try to tun the callback at the next possible |
111 | a Perl string - very natural. |
129 | time where "$time = $at (mod $interval)", regardless of any time |
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130 | jumps. |
112 | |
131 | |
113 | 2. Perl does *not* associate an encoding with your strings. |
132 | The "timer_abs_ns" variant doesn't add/start the newly created |
114 | Unless you force it to, e.g. when matching it against a regex, or |
133 | watcher. |
115 | printing the scalar to a file, in which case Perl either interprets |
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116 | your string as locale-encoded text, octets/binary, or as Unicode, |
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117 | depending on various settings. In no case is an encoding stored |
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118 | together with your data, it is *use* that decides encoding, not any |
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119 | magical metadata. |
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120 | |
134 | |
121 | 3. The internal utf-8 flag has no meaning with regards to the encoding |
135 | my $w = EV::signal $signum, $callback |
122 | of your string. |
136 | my $w = EV::signal_ns $signum, $callback |
123 | Just ignore that flag unless you debug a Perl bug, a module written |
137 | Call the callback when signal $signum is received. |
124 | in XS or want to dive into the internals of perl. Otherwise it will |
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125 | only confuse you, as, despite the name, it says nothing about how |
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126 | your string is encoded. You can have unicode strings with that flag |
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127 | set, with that flag clear, and you can have binary data with that |
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128 | flag set and that flag clear. Other possibilities exist, too. |
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129 | |
138 | |
130 | If you didn't know about that flag, just the better, pretend it |
139 | The "signal_ns" variant doesn't add/start the newly created watcher. |
131 | doesn't exist. |
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132 | |
140 | |
133 | 4. A "Unicode String" is simply a string where each character can be |
141 | THE EV::Event CLASS |
134 | validly interpreted as a Unicode codepoint. |
142 | All EV functions creating an event watcher (designated by "my $w =" |
135 | If you have UTF-8 encoded data, it is no longer a Unicode string, |
143 | above) support the following methods on the returned watcher object: |
136 | but a Unicode string encoded in UTF-8, giving you a binary string. |
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137 | |
144 | |
138 | 5. A string containing "high" (> 255) character values is *not* a UTF-8 |
145 | $w->add ($timeout) |
139 | string. |
146 | Stops and (re-)starts the event watcher, setting the optional |
140 | Its a fact. Learn to live with it. |
147 | timeout to the given value, or clearing the timeout if none is |
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148 | given. |
141 | |
149 | |
142 | I hope this helps :) |
150 | $w->start |
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151 | Stops and (re-)starts the event watcher without touching the |
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152 | timeout. |
143 | |
153 | |
144 | OBJECT-ORIENTED INTERFACE |
154 | $w->del |
145 | The object oriented interface lets you configure your own encoding or |
155 | $w->stop |
146 | decoding style, within the limits of supported formats. |
156 | Stop the event watcher if it was started. |
147 | |
157 | |
148 | $json = new JSON::XS |
158 | $current_callback = $w->cb |
149 | Creates a new JSON::XS object that can be used to de/encode JSON |
159 | $old_callback = $w->cb ($new_callback) |
150 | strings. All boolean flags described below are by default |
160 | Return the previously set callback and optionally set a new one. |
151 | *disabled*. |
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152 | |
161 | |
153 | The mutators for flags all return the JSON object again and thus |
162 | $current_fh = $w->fh |
154 | calls can be chained: |
163 | $old_fh = $w->fh ($new_fh) |
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164 | Returns the previously set filehandle and optionally set a new one. |
155 | |
165 | |
156 | my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]}) |
166 | $current_eventmask = $w->events |
157 | => {"a": [1, 2]} |
167 | $old_eventmask = $w->events ($new_eventmask) |
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168 | Returns the previously set event mask and optionally set a new one. |
158 | |
169 | |
159 | $json = $json->ascii ([$enable]) |
170 | $w->timeout ($after, $repeat) |
160 | If $enable is true (or missing), then the "encode" method will not |
171 | Resets the timeout (see "EV::timer" for details). |
161 | generate characters outside the code range 0..127 (which is ASCII). |
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162 | Any unicode characters outside that range will be escaped using |
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163 | either a single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL |
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164 | escape sequence, as per RFC4627. The resulting encoded JSON text can |
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165 | be treated as a native unicode string, an ascii-encoded, |
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166 | latin1-encoded or UTF-8 encoded string, or any other superset of |
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167 | ASCII. |
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168 | |
172 | |
169 | If $enable is false, then the "encode" method will not escape |
173 | $w->timeout_abs ($at, $interval) |
170 | Unicode characters unless required by the JSON syntax or other |
174 | Resets the timeout (see "EV::timer_abs" for details). |
171 | flags. This results in a faster and more compact format. |
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172 | |
175 | |
173 | The main use for this flag is to produce JSON texts that can be |
176 | $w->priority_set ($priority) |
174 | transmitted over a 7-bit channel, as the encoded JSON texts will not |
177 | Set the priority of the watcher to $priority (0 <= $priority < |
175 | contain any 8 bit characters. |
178 | $EV::NPRI). |
176 | |
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177 | JSON::XS->new->ascii (1)->encode ([chr 0x10401]) |
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178 | => ["\ud801\udc01"] |
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179 | |
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180 | $json = $json->latin1 ([$enable]) |
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181 | If $enable is true (or missing), then the "encode" method will |
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182 | encode the resulting JSON text as latin1 (or iso-8859-1), escaping |
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183 | any characters outside the code range 0..255. The resulting string |
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184 | can be treated as a latin1-encoded JSON text or a native unicode |
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185 | string. The "decode" method will not be affected in any way by this |
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186 | flag, as "decode" by default expects unicode, which is a strict |
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187 | superset of latin1. |
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188 | |
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189 | If $enable is false, then the "encode" method will not escape |
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190 | Unicode characters unless required by the JSON syntax or other |
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191 | flags. |
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192 | |
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193 | The main use for this flag is efficiently encoding binary data as |
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194 | JSON text, as most octets will not be escaped, resulting in a |
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195 | smaller encoded size. The disadvantage is that the resulting JSON |
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196 | text is encoded in latin1 (and must correctly be treated as such |
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197 | when storing and transfering), a rare encoding for JSON. It is |
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198 | therefore most useful when you want to store data structures known |
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199 | to contain binary data efficiently in files or databases, not when |
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200 | talking to other JSON encoders/decoders. |
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201 | |
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202 | JSON::XS->new->latin1->encode (["\x{89}\x{abc}"] |
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203 | => ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not) |
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204 | |
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205 | $json = $json->utf8 ([$enable]) |
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206 | If $enable is true (or missing), then the "encode" method will |
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207 | encode the JSON result into UTF-8, as required by many protocols, |
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208 | while the "decode" method expects to be handled an UTF-8-encoded |
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209 | string. Please note that UTF-8-encoded strings do not contain any |
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210 | characters outside the range 0..255, they are thus useful for |
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211 | bytewise/binary I/O. In future versions, enabling this option might |
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212 | enable autodetection of the UTF-16 and UTF-32 encoding families, as |
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213 | described in RFC4627. |
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214 | |
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215 | If $enable is false, then the "encode" method will return the JSON |
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216 | string as a (non-encoded) unicode string, while "decode" expects |
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217 | thus a unicode string. Any decoding or encoding (e.g. to UTF-8 or |
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218 | UTF-16) needs to be done yourself, e.g. using the Encode module. |
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219 | |
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220 | Example, output UTF-16BE-encoded JSON: |
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221 | |
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222 | use Encode; |
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223 | $jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object); |
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224 | |
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225 | Example, decode UTF-32LE-encoded JSON: |
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226 | |
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227 | use Encode; |
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228 | $object = JSON::XS->new->decode (decode "UTF-32LE", $jsontext); |
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229 | |
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230 | $json = $json->pretty ([$enable]) |
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231 | This enables (or disables) all of the "indent", "space_before" and |
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232 | "space_after" (and in the future possibly more) flags in one call to |
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233 | generate the most readable (or most compact) form possible. |
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234 | |
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235 | Example, pretty-print some simple structure: |
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236 | |
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237 | my $json = JSON::XS->new->pretty(1)->encode ({a => [1,2]}) |
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238 | => |
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239 | { |
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240 | "a" : [ |
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241 | 1, |
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242 | 2 |
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243 | ] |
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244 | } |
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245 | |
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246 | $json = $json->indent ([$enable]) |
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247 | If $enable is true (or missing), then the "encode" method will use a |
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248 | multiline format as output, putting every array member or |
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249 | object/hash key-value pair into its own line, identing them |
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250 | properly. |
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251 | |
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252 | If $enable is false, no newlines or indenting will be produced, and |
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253 | the resulting JSON text is guarenteed not to contain any "newlines". |
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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 = $json->space_before ([$enable]) |
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258 | If $enable is true (or missing), then the "encode" method will add |
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259 | an extra optional space before the ":" separating keys from values |
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260 | in JSON objects. |
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261 | |
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262 | If $enable is false, then the "encode" method will not add any extra |
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263 | space at those places. |
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264 | |
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265 | This setting has no effect when decoding JSON texts. You will also |
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266 | most likely combine this setting with "space_after". |
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267 | |
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268 | Example, space_before enabled, space_after and indent disabled: |
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269 | |
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270 | {"key" :"value"} |
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271 | |
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272 | $json = $json->space_after ([$enable]) |
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273 | If $enable is true (or missing), then the "encode" method will add |
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274 | an extra optional space after the ":" separating keys from values in |
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275 | JSON objects and extra whitespace after the "," separating key-value |
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276 | pairs and array members. |
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277 | |
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278 | If $enable is false, then the "encode" method will not add any extra |
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279 | space at those places. |
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280 | |
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281 | This setting has no effect when decoding JSON texts. |
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282 | |
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283 | Example, space_before and indent disabled, space_after enabled: |
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284 | |
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285 | {"key": "value"} |
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286 | |
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287 | $json = $json->relaxed ([$enable]) |
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288 | If $enable is true (or missing), then "decode" will accept some |
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289 | extensions to normal JSON syntax (see below). "encode" will not be |
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290 | affected in anyway. *Be aware that this option makes you accept |
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291 | invalid JSON texts as if they were valid!*. I suggest only to use |
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292 | this option to parse application-specific files written by humans |
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293 | (configuration files, resource files etc.) |
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294 | |
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295 | If $enable is false (the default), then "decode" will only accept |
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296 | valid JSON texts. |
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297 | |
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298 | Currently accepted extensions are: |
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299 | |
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300 | * list items can have an end-comma |
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301 | JSON *separates* array elements and key-value pairs with commas. |
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302 | This can be annoying if you write JSON texts manually and want |
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303 | to be able to quickly append elements, so this extension accepts |
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304 | comma at the end of such items not just between them: |
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305 | |
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306 | [ |
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307 | 1, |
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308 | 2, <- this comma not normally allowed |
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309 | ] |
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310 | { |
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311 | "k1": "v1", |
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312 | "k2": "v2", <- this comma not normally allowed |
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313 | } |
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314 | |
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315 | * shell-style '#'-comments |
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316 | Whenever JSON allows whitespace, shell-style comments are |
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317 | additionally allowed. They are terminated by the first |
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|
318 | carriage-return or line-feed character, after which more |
|
|
319 | white-space and comments are allowed. |
|
|
320 | |
|
|
321 | [ |
|
|
322 | 1, # this comment not allowed in JSON |
|
|
323 | # neither this one... |
|
|
324 | ] |
|
|
325 | |
|
|
326 | $json = $json->canonical ([$enable]) |
|
|
327 | If $enable is true (or missing), then the "encode" method will |
|
|
328 | output JSON objects by sorting their keys. This is adding a |
|
|
329 | comparatively high overhead. |
|
|
330 | |
|
|
331 | If $enable is false, then the "encode" method will output key-value |
|
|
332 | pairs in the order Perl stores them (which will likely change |
|
|
333 | between runs of the same script). |
|
|
334 | |
|
|
335 | This option is useful if you want the same data structure to be |
|
|
336 | encoded as the same JSON text (given the same overall settings). If |
|
|
337 | it is disabled, the same hash migh be encoded differently even if |
|
|
338 | contains the same data, as key-value pairs have no inherent ordering |
|
|
339 | in Perl. |
|
|
340 | |
|
|
341 | This setting has no effect when decoding JSON texts. |
|
|
342 | |
|
|
343 | $json = $json->allow_nonref ([$enable]) |
|
|
344 | If $enable is true (or missing), then the "encode" method can |
|
|
345 | convert a non-reference into its corresponding string, number or |
|
|
346 | null JSON value, which is an extension to RFC4627. Likewise, |
|
|
347 | "decode" will accept those JSON values instead of croaking. |
|
|
348 | |
|
|
349 | If $enable is false, then the "encode" method will croak if it isn't |
|
|
350 | passed an arrayref or hashref, as JSON texts must either be an |
|
|
351 | object or array. Likewise, "decode" will croak if given something |
|
|
352 | that is not a JSON object or array. |
|
|
353 | |
|
|
354 | Example, encode a Perl scalar as JSON value with enabled |
|
|
355 | "allow_nonref", resulting in an invalid JSON text: |
|
|
356 | |
|
|
357 | JSON::XS->new->allow_nonref->encode ("Hello, World!") |
|
|
358 | => "Hello, World!" |
|
|
359 | |
|
|
360 | $json = $json->allow_blessed ([$enable]) |
|
|
361 | If $enable is true (or missing), then the "encode" method will not |
|
|
362 | barf when it encounters a blessed reference. Instead, the value of |
|
|
363 | the convert_blessed option will decide wether "null" |
|
|
364 | ("convert_blessed" disabled or no "to_json" method found) or a |
|
|
365 | representation of the object ("convert_blessed" enabled and |
|
|
366 | "to_json" method found) is being encoded. Has no effect on "decode". |
|
|
367 | |
|
|
368 | If $enable is false (the default), then "encode" will throw an |
|
|
369 | exception when it encounters a blessed object. |
|
|
370 | |
|
|
371 | $json = $json->convert_blessed ([$enable]) |
|
|
372 | If $enable is true (or missing), then "encode", upon encountering a |
|
|
373 | blessed object, will check for the availability of the "TO_JSON" |
|
|
374 | method on the object's class. If found, it will be called in scalar |
|
|
375 | context and the resulting scalar will be encoded instead of the |
|
|
376 | object. If no "TO_JSON" method is found, the value of |
|
|
377 | "allow_blessed" will decide what to do. |
|
|
378 | |
|
|
379 | The "TO_JSON" method may safely call die if it wants. If "TO_JSON" |
|
|
380 | returns other blessed objects, those will be handled in the same |
|
|
381 | way. "TO_JSON" must take care of not causing an endless recursion |
|
|
382 | cycle (== crash) in this case. The name of "TO_JSON" was chosen |
|
|
383 | because other methods called by the Perl core (== not by the user of |
|
|
384 | the object) are usually in upper case letters and to avoid |
|
|
385 | collisions with the "to_json" function. |
|
|
386 | |
|
|
387 | This setting does not yet influence "decode" in any way, but in the |
|
|
388 | future, global hooks might get installed that influence "decode" and |
|
|
389 | are enabled by this setting. |
|
|
390 | |
|
|
391 | If $enable is false, then the "allow_blessed" setting will decide |
|
|
392 | what to do when a blessed object is found. |
|
|
393 | |
|
|
394 | $json = $json->filter_json_object ([$coderef->($hashref)]) |
|
|
395 | When $coderef is specified, it will be called from "decode" each |
|
|
396 | time it decodes a JSON object. The only argument is a reference to |
|
|
397 | the newly-created hash. If the code references returns a single |
|
|
398 | scalar (which need not be a reference), this value (i.e. a copy of |
|
|
399 | that scalar to avoid aliasing) is inserted into the deserialised |
|
|
400 | data structure. If it returns an empty list (NOTE: *not* "undef", |
|
|
401 | which is a valid scalar), the original deserialised hash will be |
|
|
402 | inserted. This setting can slow down decoding considerably. |
|
|
403 | |
|
|
404 | When $coderef is omitted or undefined, any existing callback will be |
|
|
405 | removed and "decode" will not change the deserialised hash in any |
|
|
406 | way. |
|
|
407 | |
|
|
408 | Example, convert all JSON objects into the integer 5: |
|
|
409 | |
|
|
410 | my $js = JSON::XS->new->filter_json_object (sub { 5 }); |
|
|
411 | # returns [5] |
|
|
412 | $js->decode ('[{}]') |
|
|
413 | # throw an exception because allow_nonref is not enabled |
|
|
414 | # so a lone 5 is not allowed. |
|
|
415 | $js->decode ('{"a":1, "b":2}'); |
|
|
416 | |
|
|
417 | $json = $json->filter_json_single_key_object ($key [=> |
|
|
418 | $coderef->($value)]) |
|
|
419 | Works remotely similar to "filter_json_object", but is only called |
|
|
420 | for JSON objects having a single key named $key. |
|
|
421 | |
|
|
422 | This $coderef is called before the one specified via |
|
|
423 | "filter_json_object", if any. It gets passed the single value in the |
|
|
424 | JSON object. If it returns a single value, it will be inserted into |
|
|
425 | the data structure. If it returns nothing (not even "undef" but the |
|
|
426 | empty list), the callback from "filter_json_object" will be called |
|
|
427 | next, as if no single-key callback were specified. |
|
|
428 | |
|
|
429 | If $coderef is omitted or undefined, the corresponding callback will |
|
|
430 | be disabled. There can only ever be one callback for a given key. |
|
|
431 | |
|
|
432 | As this callback gets called less often then the |
|
|
433 | "filter_json_object" one, decoding speed will not usually suffer as |
|
|
434 | much. Therefore, single-key objects make excellent targets to |
|
|
435 | serialise Perl objects into, especially as single-key JSON objects |
|
|
436 | are as close to the type-tagged value concept as JSON gets (its |
|
|
437 | basically an ID/VALUE tuple). Of course, JSON does not support this |
|
|
438 | in any way, so you need to make sure your data never looks like a |
|
|
439 | serialised Perl hash. |
|
|
440 | |
|
|
441 | Typical names for the single object key are "__class_whatever__", or |
|
|
442 | "$__dollars_are_rarely_used__$" or "}ugly_brace_placement", or even |
|
|
443 | things like "__class_md5sum(classname)__", to reduce the risk of |
|
|
444 | clashing with real hashes. |
|
|
445 | |
|
|
446 | Example, decode JSON objects of the form "{ "__widget__" => <id> }" |
|
|
447 | into the corresponding $WIDGET{<id>} object: |
|
|
448 | |
|
|
449 | # return whatever is in $WIDGET{5}: |
|
|
450 | JSON::XS |
|
|
451 | ->new |
|
|
452 | ->filter_json_single_key_object (__widget__ => sub { |
|
|
453 | $WIDGET{ $_[0] } |
|
|
454 | }) |
|
|
455 | ->decode ('{"__widget__": 5') |
|
|
456 | |
|
|
457 | # this can be used with a TO_JSON method in some "widget" class |
|
|
458 | # for serialisation to json: |
|
|
459 | sub WidgetBase::TO_JSON { |
|
|
460 | my ($self) = @_; |
|
|
461 | |
|
|
462 | unless ($self->{id}) { |
|
|
463 | $self->{id} = ..get..some..id..; |
|
|
464 | $WIDGET{$self->{id}} = $self; |
|
|
465 | } |
|
|
466 | |
|
|
467 | { __widget__ => $self->{id} } |
|
|
468 | } |
|
|
469 | |
|
|
470 | $json = $json->shrink ([$enable]) |
|
|
471 | Perl usually over-allocates memory a bit when allocating space for |
|
|
472 | strings. This flag optionally resizes strings generated by either |
|
|
473 | "encode" or "decode" to their minimum size possible. This can save |
|
|
474 | memory when your JSON texts are either very very long or you have |
|
|
475 | many short strings. It will also try to downgrade any strings to |
|
|
476 | octet-form if possible: perl stores strings internally either in an |
|
|
477 | encoding called UTF-X or in octet-form. The latter cannot store |
|
|
478 | everything but uses less space in general (and some buggy Perl or C |
|
|
479 | code might even rely on that internal representation being used). |
|
|
480 | |
|
|
481 | The actual definition of what shrink does might change in future |
|
|
482 | versions, but it will always try to save space at the expense of |
|
|
483 | time. |
|
|
484 | |
|
|
485 | If $enable is true (or missing), the string returned by "encode" |
|
|
486 | will be shrunk-to-fit, while all strings generated by "decode" will |
|
|
487 | also be shrunk-to-fit. |
|
|
488 | |
|
|
489 | If $enable is false, then the normal perl allocation algorithms are |
|
|
490 | used. If you work with your data, then this is likely to be faster. |
|
|
491 | |
|
|
492 | In the future, this setting might control other things, such as |
|
|
493 | converting strings that look like integers or floats into integers |
|
|
494 | or floats internally (there is no difference on the Perl level), |
|
|
495 | saving space. |
|
|
496 | |
|
|
497 | $json = $json->max_depth ([$maximum_nesting_depth]) |
|
|
498 | Sets the maximum nesting level (default 512) accepted while encoding |
|
|
499 | or decoding. If the JSON text or Perl data structure has an equal or |
|
|
500 | higher nesting level then this limit, then the encoder and decoder |
|
|
501 | will stop and croak at that point. |
|
|
502 | |
|
|
503 | Nesting level is defined by number of hash- or arrayrefs that the |
|
|
504 | encoder needs to traverse to reach a given point or the number of |
|
|
505 | "{" or "[" characters without their matching closing parenthesis |
|
|
506 | crossed to reach a given character in a string. |
|
|
507 | |
|
|
508 | Setting the maximum depth to one disallows any nesting, so that |
|
|
509 | ensures that the object is only a single hash/object or array. |
|
|
510 | |
|
|
511 | The argument to "max_depth" will be rounded up to the next highest |
|
|
512 | power of two. If no argument is given, the highest possible setting |
|
|
513 | will be used, which is rarely useful. |
|
|
514 | |
|
|
515 | See SECURITY CONSIDERATIONS, below, for more info on why this is |
|
|
516 | useful. |
|
|
517 | |
|
|
518 | $json = $json->max_size ([$maximum_string_size]) |
|
|
519 | Set the maximum length a JSON text may have (in bytes) where |
|
|
520 | decoding is being attempted. The default is 0, meaning no limit. |
|
|
521 | When "decode" is called on a string longer then this number of |
|
|
522 | characters it will not attempt to decode the string but throw an |
|
|
523 | exception. This setting has no effect on "encode" (yet). |
|
|
524 | |
|
|
525 | The argument to "max_size" will be rounded up to the next highest |
|
|
526 | power of two (so may be more than requested). If no argument is |
|
|
527 | given, the limit check will be deactivated (same as when 0 is |
|
|
528 | specified). |
|
|
529 | |
|
|
530 | See SECURITY CONSIDERATIONS, below, for more info on why this is |
|
|
531 | useful. |
|
|
532 | |
|
|
533 | $json_text = $json->encode ($perl_scalar) |
|
|
534 | Converts the given Perl data structure (a simple scalar or a |
|
|
535 | reference to a hash or array) to its JSON representation. Simple |
|
|
536 | scalars will be converted into JSON string or number sequences, |
|
|
537 | while references to arrays become JSON arrays and references to |
|
|
538 | hashes become JSON objects. Undefined Perl values (e.g. "undef") |
|
|
539 | become JSON "null" values. Neither "true" nor "false" values will be |
|
|
540 | generated. |
|
|
541 | |
|
|
542 | $perl_scalar = $json->decode ($json_text) |
|
|
543 | The opposite of "encode": expects a JSON text and tries to parse it, |
|
|
544 | returning the resulting simple scalar or reference. Croaks on error. |
|
|
545 | |
|
|
546 | JSON numbers and strings become simple Perl scalars. JSON arrays |
|
|
547 | become Perl arrayrefs and JSON objects become Perl hashrefs. "true" |
|
|
548 | becomes 1, "false" becomes 0 and "null" becomes "undef". |
|
|
549 | |
|
|
550 | ($perl_scalar, $characters) = $json->decode_prefix ($json_text) |
|
|
551 | This works like the "decode" method, but instead of raising an |
|
|
552 | exception when there is trailing garbage after the first JSON |
|
|
553 | object, it will silently stop parsing there and return the number of |
|
|
554 | characters consumed so far. |
|
|
555 | |
|
|
556 | This is useful if your JSON texts are not delimited by an outer |
|
|
557 | protocol (which is not the brightest thing to do in the first place) |
|
|
558 | and you need to know where the JSON text ends. |
|
|
559 | |
|
|
560 | JSON::XS->new->decode_prefix ("[1] the tail") |
|
|
561 | => ([], 3) |
|
|
562 | |
|
|
563 | MAPPING |
|
|
564 | This section describes how JSON::XS maps Perl values to JSON values and |
|
|
565 | vice versa. These mappings are designed to "do the right thing" in most |
|
|
566 | circumstances automatically, preserving round-tripping characteristics |
|
|
567 | (what you put in comes out as something equivalent). |
|
|
568 | |
|
|
569 | For the more enlightened: note that in the following descriptions, |
|
|
570 | lowercase *perl* refers to the Perl interpreter, while uppcercase *Perl* |
|
|
571 | refers to the abstract Perl language itself. |
|
|
572 | |
|
|
573 | JSON -> PERL |
|
|
574 | object |
|
|
575 | A JSON object becomes a reference to a hash in Perl. No ordering of |
|
|
576 | object keys is preserved (JSON does not preserver object key |
|
|
577 | ordering itself). |
|
|
578 | |
|
|
579 | array |
|
|
580 | A JSON array becomes a reference to an array in Perl. |
|
|
581 | |
|
|
582 | string |
|
|
583 | A JSON string becomes a string scalar in Perl - Unicode codepoints |
|
|
584 | in JSON are represented by the same codepoints in the Perl string, |
|
|
585 | so no manual decoding is necessary. |
|
|
586 | |
|
|
587 | number |
|
|
588 | A JSON number becomes either an integer, numeric (floating point) or |
|
|
589 | string scalar in perl, depending on its range and any fractional |
|
|
590 | parts. On the Perl level, there is no difference between those as |
|
|
591 | Perl handles all the conversion details, but an integer may take |
|
|
592 | slightly less memory and might represent more values exactly than |
|
|
593 | (floating point) numbers. |
|
|
594 | |
|
|
595 | If the number consists of digits only, JSON::XS will try to |
|
|
596 | represent it as an integer value. If that fails, it will try to |
|
|
597 | represent it as a numeric (floating point) value if that is possible |
|
|
598 | without loss of precision. Otherwise it will preserve the number as |
|
|
599 | a string value. |
|
|
600 | |
|
|
601 | Numbers containing a fractional or exponential part will always be |
|
|
602 | represented as numeric (floating point) values, possibly at a loss |
|
|
603 | of precision. |
|
|
604 | |
|
|
605 | This might create round-tripping problems as numbers might become |
|
|
606 | strings, but as Perl is typeless there is no other way to do it. |
|
|
607 | |
|
|
608 | true, false |
|
|
609 | These JSON atoms become "JSON::XS::true" and "JSON::XS::false", |
|
|
610 | respectively. They are overloaded to act almost exactly like the |
|
|
611 | numbers 1 and 0. You can check wether a scalar is a JSON boolean by |
|
|
612 | using the "JSON::XS::is_bool" function. |
|
|
613 | |
|
|
614 | null |
|
|
615 | A JSON null atom becomes "undef" in Perl. |
|
|
616 | |
|
|
617 | PERL -> JSON |
|
|
618 | The mapping from Perl to JSON is slightly more difficult, as Perl is a |
|
|
619 | truly typeless language, so we can only guess which JSON type is meant |
|
|
620 | by a Perl value. |
|
|
621 | |
|
|
622 | hash references |
|
|
623 | Perl hash references become JSON objects. As there is no inherent |
|
|
624 | ordering in hash keys (or JSON objects), they will usually be |
|
|
625 | encoded in a pseudo-random order that can change between runs of the |
|
|
626 | same program but stays generally the same within a single run of a |
|
|
627 | program. JSON::XS can optionally sort the hash keys (determined by |
|
|
628 | the *canonical* flag), so the same datastructure will serialise to |
|
|
629 | the same JSON text (given same settings and version of JSON::XS), |
|
|
630 | but this incurs a runtime overhead and is only rarely useful, e.g. |
|
|
631 | when you want to compare some JSON text against another for |
|
|
632 | equality. |
|
|
633 | |
|
|
634 | array references |
|
|
635 | Perl array references become JSON arrays. |
|
|
636 | |
|
|
637 | other references |
|
|
638 | Other unblessed references are generally not allowed and will cause |
|
|
639 | an exception to be thrown, except for references to the integers 0 |
|
|
640 | and 1, which get turned into "false" and "true" atoms in JSON. You |
|
|
641 | can also use "JSON::XS::false" and "JSON::XS::true" to improve |
|
|
642 | readability. |
|
|
643 | |
|
|
644 | to_json [\0,JSON::XS::true] # yields [false,true] |
|
|
645 | |
|
|
646 | JSON::XS::true, JSON::XS::false |
|
|
647 | These special values become JSON true and JSON false values, |
|
|
648 | respectively. You can also use "\1" and "\0" directly if you want. |
|
|
649 | |
|
|
650 | blessed objects |
|
|
651 | Blessed objects are not allowed. JSON::XS currently tries to encode |
|
|
652 | their underlying representation (hash- or arrayref), but this |
|
|
653 | behaviour might change in future versions. |
|
|
654 | |
|
|
655 | simple scalars |
|
|
656 | Simple Perl scalars (any scalar that is not a reference) are the |
|
|
657 | most difficult objects to encode: JSON::XS will encode undefined |
|
|
658 | scalars as JSON null value, scalars that have last been used in a |
|
|
659 | string context before encoding as JSON strings and anything else as |
|
|
660 | number value: |
|
|
661 | |
|
|
662 | # dump as number |
|
|
663 | to_json [2] # yields [2] |
|
|
664 | to_json [-3.0e17] # yields [-3e+17] |
|
|
665 | my $value = 5; to_json [$value] # yields [5] |
|
|
666 | |
|
|
667 | # used as string, so dump as string |
|
|
668 | print $value; |
|
|
669 | to_json [$value] # yields ["5"] |
|
|
670 | |
|
|
671 | # undef becomes null |
|
|
672 | to_json [undef] # yields [null] |
|
|
673 | |
|
|
674 | You can force the type to be a string by stringifying it: |
|
|
675 | |
|
|
676 | my $x = 3.1; # some variable containing a number |
|
|
677 | "$x"; # stringified |
|
|
678 | $x .= ""; # another, more awkward way to stringify |
|
|
679 | print $x; # perl does it for you, too, quite often |
|
|
680 | |
|
|
681 | You can force the type to be a number by numifying it: |
|
|
682 | |
|
|
683 | my $x = "3"; # some variable containing a string |
|
|
684 | $x += 0; # numify it, ensuring it will be dumped as a number |
|
|
685 | $x *= 1; # same thing, the choise is yours. |
|
|
686 | |
|
|
687 | You can not currently output JSON booleans or force the type in |
|
|
688 | other, less obscure, ways. Tell me if you need this capability. |
|
|
689 | |
|
|
690 | COMPARISON |
|
|
691 | As already mentioned, this module was created because none of the |
|
|
692 | existing JSON modules could be made to work correctly. First I will |
|
|
693 | describe the problems (or pleasures) I encountered with various existing |
|
|
694 | JSON modules, followed by some benchmark values. JSON::XS was designed |
|
|
695 | not to suffer from any of these problems or limitations. |
|
|
696 | |
|
|
697 | JSON 1.07 |
|
|
698 | Slow (but very portable, as it is written in pure Perl). |
|
|
699 | |
|
|
700 | Undocumented/buggy Unicode handling (how JSON handles unicode values |
|
|
701 | is undocumented. One can get far by feeding it unicode strings and |
|
|
702 | doing en-/decoding oneself, but unicode escapes are not working |
|
|
703 | properly). |
|
|
704 | |
|
|
705 | No roundtripping (strings get clobbered if they look like numbers, |
|
|
706 | e.g. the string 2.0 will encode to 2.0 instead of "2.0", and that |
|
|
707 | will decode into the number 2. |
|
|
708 | |
|
|
709 | JSON::PC 0.01 |
|
|
710 | Very fast. |
|
|
711 | |
|
|
712 | Undocumented/buggy Unicode handling. |
|
|
713 | |
|
|
714 | No roundtripping. |
|
|
715 | |
|
|
716 | Has problems handling many Perl values (e.g. regex results and other |
|
|
717 | magic values will make it croak). |
|
|
718 | |
|
|
719 | Does not even generate valid JSON ("{1,2}" gets converted to "{1:2}" |
|
|
720 | which is not a valid JSON text. |
|
|
721 | |
|
|
722 | Unmaintained (maintainer unresponsive for many months, bugs are not |
|
|
723 | getting fixed). |
|
|
724 | |
|
|
725 | JSON::Syck 0.21 |
|
|
726 | Very buggy (often crashes). |
|
|
727 | |
|
|
728 | Very inflexible (no human-readable format supported, format pretty |
|
|
729 | much undocumented. I need at least a format for easy reading by |
|
|
730 | humans and a single-line compact format for use in a protocol, and |
|
|
731 | preferably a way to generate ASCII-only JSON texts). |
|
|
732 | |
|
|
733 | Completely broken (and confusingly documented) Unicode handling |
|
|
734 | (unicode escapes are not working properly, you need to set |
|
|
735 | ImplicitUnicode to *different* values on en- and decoding to get |
|
|
736 | symmetric behaviour). |
|
|
737 | |
|
|
738 | No roundtripping (simple cases work, but this depends on wether the |
|
|
739 | scalar value was used in a numeric context or not). |
|
|
740 | |
|
|
741 | Dumping hashes may skip hash values depending on iterator state. |
|
|
742 | |
|
|
743 | Unmaintained (maintainer unresponsive for many months, bugs are not |
|
|
744 | getting fixed). |
|
|
745 | |
|
|
746 | Does not check input for validity (i.e. will accept non-JSON input |
|
|
747 | and return "something" instead of raising an exception. This is a |
|
|
748 | security issue: imagine two banks transfering money between each |
|
|
749 | other using JSON. One bank might parse a given non-JSON request and |
|
|
750 | deduct money, while the other might reject the transaction with a |
|
|
751 | syntax error. While a good protocol will at least recover, that is |
|
|
752 | extra unnecessary work and the transaction will still not succeed). |
|
|
753 | |
|
|
754 | JSON::DWIW 0.04 |
|
|
755 | Very fast. Very natural. Very nice. |
|
|
756 | |
|
|
757 | Undocumented unicode handling (but the best of the pack. Unicode |
|
|
758 | escapes still don't get parsed properly). |
|
|
759 | |
|
|
760 | Very inflexible. |
|
|
761 | |
|
|
762 | No roundtripping. |
|
|
763 | |
|
|
764 | Does not generate valid JSON texts (key strings are often unquoted, |
|
|
765 | empty keys result in nothing being output) |
|
|
766 | |
|
|
767 | Does not check input for validity. |
|
|
768 | |
|
|
769 | JSON and YAML |
|
|
770 | You often hear that JSON is a subset (or a close subset) of YAML. This |
|
|
771 | is, however, a mass hysteria and very far from the truth. In general, |
|
|
772 | there is no way to configure JSON::XS to output a data structure as |
|
|
773 | valid YAML. |
|
|
774 | |
|
|
775 | If you really must use JSON::XS to generate YAML, you should use this |
|
|
776 | algorithm (subject to change in future versions): |
|
|
777 | |
|
|
778 | my $to_yaml = JSON::XS->new->utf8->space_after (1); |
|
|
779 | my $yaml = $to_yaml->encode ($ref) . "\n"; |
|
|
780 | |
|
|
781 | This will usually generate JSON texts that also parse as valid YAML. |
|
|
782 | Please note that YAML has hardcoded limits on (simple) object key |
|
|
783 | lengths that JSON doesn't have, so you should make sure that your hash |
|
|
784 | keys are noticably shorter than the 1024 characters YAML allows. |
|
|
785 | |
|
|
786 | There might be other incompatibilities that I am not aware of. In |
|
|
787 | general you should not try to generate YAML with a JSON generator or |
|
|
788 | vice versa, or try to parse JSON with a YAML parser or vice versa: |
|
|
789 | chances are high that you will run into severe interoperability |
|
|
790 | problems. |
|
|
791 | |
|
|
792 | SPEED |
|
|
793 | It seems that JSON::XS is surprisingly fast, as shown in the following |
|
|
794 | tables. They have been generated with the help of the "eg/bench" program |
|
|
795 | in the JSON::XS distribution, to make it easy to compare on your own |
|
|
796 | system. |
|
|
797 | |
|
|
798 | First comes a comparison between various modules using a very short |
|
|
799 | single-line JSON string: |
|
|
800 | |
|
|
801 | {"method": "handleMessage", "params": ["user1", "we were just talking"], \ |
|
|
802 | "id": null, "array":[1,11,234,-5,1e5,1e7, true, false]} |
|
|
803 | |
|
|
804 | It shows the number of encodes/decodes per second (JSON::XS uses the |
|
|
805 | functional interface, while JSON::XS/2 uses the OO interface with |
|
|
806 | pretty-printing and hashkey sorting enabled, JSON::XS/3 enables shrink). |
|
|
807 | Higher is better: |
|
|
808 | |
|
|
809 | Storable | 15779.925 | 14169.946 | |
|
|
810 | -----------+------------+------------+ |
|
|
811 | module | encode | decode | |
|
|
812 | -----------|------------|------------| |
|
|
813 | JSON | 4990.842 | 4088.813 | |
|
|
814 | JSON::DWIW | 51653.990 | 71575.154 | |
|
|
815 | JSON::PC | 65948.176 | 74631.744 | |
|
|
816 | JSON::PP | 8931.652 | 3817.168 | |
|
|
817 | JSON::Syck | 24877.248 | 27776.848 | |
|
|
818 | JSON::XS | 388361.481 | 227951.304 | |
|
|
819 | JSON::XS/2 | 227951.304 | 218453.333 | |
|
|
820 | JSON::XS/3 | 338250.323 | 218453.333 | |
|
|
821 | Storable | 16500.016 | 135300.129 | |
|
|
822 | -----------+------------+------------+ |
|
|
823 | |
|
|
824 | That is, JSON::XS is about five times faster than JSON::DWIW on |
|
|
825 | encoding, about three times faster on decoding, and over fourty times |
|
|
826 | faster than JSON, even with pretty-printing and key sorting. It also |
|
|
827 | compares favourably to Storable for small amounts of data. |
|
|
828 | |
|
|
829 | Using a longer test string (roughly 18KB, generated from Yahoo! Locals |
|
|
830 | search API (http://nanoref.com/yahooapis/mgPdGg): |
|
|
831 | |
|
|
832 | module | encode | decode | |
|
|
833 | -----------|------------|------------| |
|
|
834 | JSON | 55.260 | 34.971 | |
|
|
835 | JSON::DWIW | 825.228 | 1082.513 | |
|
|
836 | JSON::PC | 3571.444 | 2394.829 | |
|
|
837 | JSON::PP | 210.987 | 32.574 | |
|
|
838 | JSON::Syck | 552.551 | 787.544 | |
|
|
839 | JSON::XS | 5780.463 | 4854.519 | |
|
|
840 | JSON::XS/2 | 3869.998 | 4798.975 | |
|
|
841 | JSON::XS/3 | 5862.880 | 4798.975 | |
|
|
842 | Storable | 4445.002 | 5235.027 | |
|
|
843 | -----------+------------+------------+ |
|
|
844 | |
|
|
845 | Again, JSON::XS leads by far (except for Storable which non-surprisingly |
|
|
846 | decodes faster). |
|
|
847 | |
|
|
848 | On large strings containing lots of high unicode characters, some |
|
|
849 | modules (such as JSON::PC) seem to decode faster than JSON::XS, but the |
|
|
850 | result will be broken due to missing (or wrong) unicode handling. Others |
|
|
851 | refuse to decode or encode properly, so it was impossible to prepare a |
|
|
852 | fair comparison table for that case. |
|
|
853 | |
|
|
854 | SECURITY CONSIDERATIONS |
|
|
855 | When you are using JSON in a protocol, talking to untrusted potentially |
|
|
856 | hostile creatures requires relatively few measures. |
|
|
857 | |
|
|
858 | First of all, your JSON decoder should be secure, that is, should not |
|
|
859 | have any buffer overflows. Obviously, this module should ensure that and |
|
|
860 | I am trying hard on making that true, but you never know. |
|
|
861 | |
|
|
862 | Second, you need to avoid resource-starving attacks. That means you |
|
|
863 | should limit the size of JSON texts you accept, or make sure then when |
|
|
864 | your resources run out, thats just fine (e.g. by using a separate |
|
|
865 | process that can crash safely). The size of a JSON text in octets or |
|
|
866 | characters is usually a good indication of the size of the resources |
|
|
867 | required to decode it into a Perl structure. While JSON::XS can check |
|
|
868 | the size of the JSON text, it might be too late when you already have it |
|
|
869 | in memory, so you might want to check the size before you accept the |
|
|
870 | string. |
|
|
871 | |
|
|
872 | Third, JSON::XS recurses using the C stack when decoding objects and |
|
|
873 | arrays. The C stack is a limited resource: for instance, on my amd64 |
|
|
874 | machine with 8MB of stack size I can decode around 180k nested arrays |
|
|
875 | but only 14k nested JSON objects (due to perl itself recursing deeply on |
|
|
876 | croak to free the temporary). If that is exceeded, the program crashes. |
|
|
877 | to be conservative, the default nesting limit is set to 512. If your |
|
|
878 | process has a smaller stack, you should adjust this setting accordingly |
|
|
879 | with the "max_depth" method. |
|
|
880 | |
|
|
881 | And last but least, something else could bomb you that I forgot to think |
|
|
882 | of. In that case, you get to keep the pieces. I am always open for |
|
|
883 | hints, though... |
|
|
884 | |
|
|
885 | If you are using JSON::XS to return packets to consumption by javascript |
|
|
886 | scripts in a browser you should have a look at |
|
|
887 | <http://jpsykes.com/47/practical-csrf-and-json-security> to see wether |
|
|
888 | you are vulnerable to some common attack vectors (which really are |
|
|
889 | browser design bugs, but it is still you who will have to deal with it, |
|
|
890 | as major browser developers care only for features, not about doing |
|
|
891 | security right). |
|
|
892 | |
|
|
893 | THREADS |
|
|
894 | This module is *not* guarenteed to be thread safe and there are no plans |
|
|
895 | to change this until Perl gets thread support (as opposed to the |
|
|
896 | horribly slow so-called "threads" which are simply slow and bloated |
|
|
897 | process simulations - use fork, its *much* faster, cheaper, better). |
|
|
898 | |
|
|
899 | (It might actually work, but you ahve ben warned). |
|
|
900 | |
179 | |
901 | BUGS |
180 | BUGS |
902 | While the goal of this module is to be correct, that unfortunately does |
181 | Lots. Libevent itself isn't well tested and rather buggy, and this |
903 | not mean its bug-free, only that I think its design is bug-free. It is |
182 | module is quite new at the moment. |
904 | still relatively early in its development. If you keep reporting bugs |
|
|
905 | they will be fixed swiftly, though. |
|
|
906 | |
183 | |
907 | Please refrain from using rt.cpan.org or any other bug reporting |
184 | Please note that the epoll method is not, in general, reliable in |
908 | service. I put the contact address into my modules for a reason. |
185 | programs that use fork (even if no libveent calls are being made in the |
|
|
186 | forked process). If your program behaves erratically, try setting the |
|
|
187 | environment variable "EVENT_NOEPOLL" first when running the program. |
|
|
188 | |
|
|
189 | In general, if you fork, then you can only use the EV module in one of |
|
|
190 | the children. |
|
|
191 | |
|
|
192 | SEE ALSO |
|
|
193 | L<EV::DNS>, L<event(3)>, L<event.h>, L<evdns.h>. |
|
|
194 | L<EV::AnyEvent>. |
909 | |
195 | |
910 | AUTHOR |
196 | AUTHOR |
911 | Marc Lehmann <schmorp@schmorp.de> |
197 | Marc Lehmann <schmorp@schmorp.de> |
912 | http://home.schmorp.de/ |
198 | http://home.schmorp.de/ |
913 | |
199 | |