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1NAME 1NAME
2 JSON::XS - JSON serialising/deserialising, done correctly and fast 2 EV - perl interface to libev, a high performance full-featured event
3 3 loop
4 JSON::XS - 正しくて高速な JSON
5 シリアライザ/デシリアライザ
6 (http://fleur.hio.jp/perldoc/mix/lib/JSON/XS.html)
7 4
8SYNOPSIS 5SYNOPSIS
9 use JSON::XS; 6 use EV;
7
8 # TIMERS
9
10 my $w = EV::timer 2, 0, sub {
11 warn "is called after 2s";
12 };
13
14 my $w = EV::timer 2, 2, sub {
15 warn "is called roughly every 2s (repeat = 2)";
16 };
17
18 undef $w; # destroy event watcher again
19
20 my $w = EV::periodic 0, 60, 0, sub {
21 warn "is called every minute, on the minute, exactly";
22 };
23
24 # IO
25
26 my $w = EV::io *STDIN, EV::READ, sub {
27 my ($w, $revents) = @_; # all callbacks receive the watcher and event mask
28 warn "stdin is readable, you entered: ", <STDIN>;
29 };
30
31 # SIGNALS
32
33 my $w = EV::signal 'QUIT', sub {
34 warn "sigquit received\n";
35 };
36
37 # CHILD/PID STATUS CHANGES
10 38
11 # exported functions, they croak on error 39 my $w = EV::child 666, sub {
12 # and expect/generate UTF-8 40 my ($w, $revents) = @_;
13 41 my $status = $w->rstatus;
14 $utf8_encoded_json_text = to_json $perl_hash_or_arrayref; 42 };
15 $perl_hash_or_arrayref = from_json $utf8_encoded_json_text; 43
16 44 # MAINLOOP
17 # OO-interface 45 EV::loop; # loop until EV::unloop is called or all watchers stop
18 46 EV::loop EV::LOOP_ONESHOT; # block until at least one event could be handled
19 $coder = JSON::XS->new->ascii->pretty->allow_nonref; 47 EV::loop EV::LOOP_NONBLOCK; # try to handle same events, but do not block
20 $pretty_printed_unencoded = $coder->encode ($perl_scalar);
21 $perl_scalar = $coder->decode ($unicode_json_text);
22 48
23DESCRIPTION 49DESCRIPTION
24 This module converts Perl data structures to JSON and vice versa. Its 50 This module provides an interface to libev
25 primary goal is to be *correct* and its secondary goal is to be *fast*. 51 (<http://software.schmorp.de/pkg/libev.html>).
26 To reach the latter goal it was written in C.
27 52
28 As this is the n-th-something JSON module on CPAN, what was the reason 53BASIC INTERFACE
29 to write yet another JSON module? While it seems there are many JSON 54 $EV::DIED
30 modules, none of them correctly handle all corner cases, and in most 55 Must contain a reference to a function that is called when a
31 cases their maintainers are unresponsive, gone missing, or not listening 56 callback throws an exception (with $@ containing thr error). The
32 to bug reports for other reasons. 57 default prints an informative message and continues.
33 58
34 See COMPARISON, below, for a comparison to some other JSON modules. 59 If this callback throws an exception it will be silently ignored.
35 60
36 See MAPPING, below, on how JSON::XS maps perl values to JSON values and 61 $time = EV::time
37 vice versa. 62 Returns the current time in (fractional) seconds since the epoch.
38 63
39 FEATURES 64 $time = EV::now
40 * correct unicode handling 65 Returns the time the last event loop iteration has been started.
41 This module knows how to handle Unicode, and even documents how and 66 This is the time that (relative) timers are based on, and refering
42 when it does so. 67 to it is usually faster then calling EV::time.
43 68
44 * round-trip integrity 69 $method = EV::ev_method
45 When you serialise a perl data structure using only datatypes 70 Returns an integer describing the backend used by libev
46 supported by JSON, the deserialised data structure is identical on 71 (EV::METHOD_SELECT or EV::METHOD_EPOLL).
47 the Perl level. (e.g. the string "2.0" doesn't suddenly become "2"
48 just because it looks like a number).
49 72
50 * strict checking of JSON correctness 73 EV::loop [$flags]
51 There is no guessing, no generating of illegal JSON texts by 74 Begin checking for events and calling callbacks. It returns when a
52 default, and only JSON is accepted as input by default (the latter 75 callback calls EV::unloop.
53 is a security feature).
54 76
55 * fast 77 The $flags argument can be one of the following:
56 Compared to other JSON modules, this module compares favourably in
57 terms of speed, too.
58 78
59 * simple to use 79 0 as above
60 This module has both a simple functional interface as well as an OO 80 EV::LOOP_ONESHOT block at most once (wait, but do not loop)
61 interface. 81 EV::LOOP_NONBLOCK do not block at all (fetch/handle events but do not wait)
62 82
63 * reasonably versatile output formats 83 EV::unloop [$how]
64 You can choose between the most compact guarenteed single-line 84 When called with no arguments or an argument of EV::UNLOOP_ONE,
65 format possible (nice for simple line-based protocols), a pure-ascii 85 makes the innermost call to EV::loop return.
66 format (for when your transport is not 8-bit clean, still supports
67 the whole unicode range), or a pretty-printed format (for when you
68 want to read that stuff). Or you can combine those features in
69 whatever way you like.
70 86
71FUNCTIONAL INTERFACE 87 When called with an argument of EV::UNLOOP_ALL, all calls to
72 The following convinience methods are provided by this module. They are 88 EV::loop will return as fast as possible.
73 exported by default:
74 89
75 $json_text = to_json $perl_scalar 90 WATCHER
76 Converts the given Perl data structure to a UTF-8 encoded, binary 91 A watcher is an object that gets created to record your interest in some
77 string (that is, the string contains octets only). Croaks on error. 92 event. For instance, if you want to wait for STDIN to become readable,
93 you would create an EV::io watcher for that:
78 94
79 This function call is functionally identical to: 95 my $watcher = EV::io *STDIN, EV::READ, sub {
96 my ($watcher, $revents) = @_;
97 warn "yeah, STDIN should not be readable without blocking!\n"
98 };
80 99
81 $json_text = JSON::XS->new->utf8->encode ($perl_scalar) 100 All watchers can be active (waiting for events) or inactive (paused).
101 Only active watchers will have their callbacks invoked. All callbacks
102 will be called with at least two arguments: the watcher and a bitmask of
103 received events.
82 104
83 except being faster. 105 Each watcher type has its associated bit in revents, so you can use the
106 same callback for multiple watchers. The event mask is named after the
107 type, i..e. EV::child sets EV::CHILD, EV::prepare sets EV::PREPARE,
108 EV::periodic sets EV::PERIODIC and so on, with the exception of IO
109 events (which can set both EV::READ and EV::WRITE bits), and EV::timer
110 (which uses EV::TIMEOUT).
84 111
85 $perl_scalar = from_json $json_text 112 In the rare case where one wants to create a watcher but not start it at
86 The opposite of "to_json": expects an UTF-8 (binary) string and 113 the same time, each constructor has a variant with a trailing "_ns" in
87 tries to parse that as an UTF-8 encoded JSON text, returning the 114 its name, e.g. EV::io has a non-starting variant EV::io_ns and so on.
88 resulting reference. Croaks on error.
89 115
90 This function call is functionally identical to: 116 Please note that a watcher will automatically be stopped when the
117 watcher object is destroyed, so you *need* to keep the watcher objects
118 returned by the constructors.
91 119
92 $perl_scalar = JSON::XS->new->utf8->decode ($json_text) 120 Also, all methods changing some aspect of a watcher (->set, ->priority,
121 ->fh and so on) automatically stop and start it again if it is active,
122 which means pending events get lost.
93 123
94 except being faster. 124 WATCHER TYPES
125 Now lets move to the existing watcher types and asociated methods.
95 126
96 $is_boolean = JSON::XS::is_bool $scalar 127 The following methods are available for all watchers. Then followes a
97 Returns true if the passed scalar represents either JSON::XS::true 128 description of each watcher constructor (EV::io, EV::timer,
98 or JSON::XS::false, two constants that act like 1 and 0, 129 EV::periodic, EV::signal, EV::child, EV::idle, EV::prepare and
99 respectively and are used to represent JSON "true" and "false" 130 EV::check), followed by any type-specific methods (if any).
100 values in Perl.
101 131
102 See MAPPING, below, for more information on how JSON values are 132 $w->start
103 mapped to Perl. 133 Starts a watcher if it isn't active already. Does nothing to an
134 already active watcher. By default, all watchers start out in the
135 active state (see the description of the "_ns" variants if you need
136 stopped watchers).
104 137
105A FEW NOTES ON UNICODE AND PERL 138 $w->stop
106 Since this often leads to confusion, here are a few very clear words on 139 Stop a watcher if it is active. Also clear any pending events
107 how Unicode works in Perl, modulo bugs. 140 (events that have been received but that didn't yet result in a
141 callback invocation), regardless of wether the watcher was active or
142 not.
108 143
109 1. Perl strings can store characters with ordinal values > 255. 144 $bool = $w->is_active
110 This enables you to store unicode characters as single characters in 145 Returns true if the watcher is active, false otherwise.
111 a Perl string - very natural.
112 146
113 2. Perl does *not* associate an encoding with your strings. 147 $current_data = $w->data
114 Unless you force it to, e.g. when matching it against a regex, or 148 $old_data = $w->data ($new_data)
115 printing the scalar to a file, in which case Perl either interprets 149 Queries a freely usable data scalar on the watcher and optionally
116 your string as locale-encoded text, octets/binary, or as Unicode, 150 changes it. This is a way to associate custom data with a watcher:
117 depending on various settings. In no case is an encoding stored
118 together with your data, it is *use* that decides encoding, not any
119 magical metadata.
120 151
121 3. The internal utf-8 flag has no meaning with regards to the encoding 152 my $w = EV::timer 60, 0, sub {
122 of your string. 153 warn $_[0]->data;
123 Just ignore that flag unless you debug a Perl bug, a module written
124 in XS or want to dive into the internals of perl. Otherwise it will
125 only confuse you, as, despite the name, it says nothing about how
126 your string is encoded. You can have unicode strings with that flag
127 set, with that flag clear, and you can have binary data with that
128 flag set and that flag clear. Other possibilities exist, too.
129
130 If you didn't know about that flag, just the better, pretend it
131 doesn't exist.
132
133 4. A "Unicode String" is simply a string where each character can be
134 validly interpreted as a Unicode codepoint.
135 If you have UTF-8 encoded data, it is no longer a Unicode string,
136 but a Unicode string encoded in UTF-8, giving you a binary string.
137
138 5. A string containing "high" (> 255) character values is *not* a UTF-8
139 string.
140 Its a fact. Learn to live with it.
141
142 I hope this helps :)
143
144OBJECT-ORIENTED INTERFACE
145 The object oriented interface lets you configure your own encoding or
146 decoding style, within the limits of supported formats.
147
148 $json = new JSON::XS
149 Creates a new JSON::XS object that can be used to de/encode JSON
150 strings. All boolean flags described below are by default
151 *disabled*.
152
153 The mutators for flags all return the JSON object again and thus
154 calls can be chained:
155
156 my $json = JSON::XS->new->utf8->space_after->encode ({a => [1,2]})
157 => {"a": [1, 2]}
158
159 $json = $json->ascii ([$enable])
160 If $enable is true (or missing), then the "encode" method will not
161 generate characters outside the code range 0..127 (which is ASCII).
162 Any unicode characters outside that range will be escaped using
163 either a single \uXXXX (BMP characters) or a double \uHHHH\uLLLLL
164 escape sequence, as per RFC4627. The resulting encoded JSON text can
165 be treated as a native unicode string, an ascii-encoded,
166 latin1-encoded or UTF-8 encoded string, or any other superset of
167 ASCII.
168
169 If $enable is false, then the "encode" method will not escape
170 Unicode characters unless required by the JSON syntax or other
171 flags. This results in a faster and more compact format.
172
173 The main use for this flag is to produce JSON texts that can be
174 transmitted over a 7-bit channel, as the encoded JSON texts will not
175 contain any 8 bit characters.
176
177 JSON::XS->new->ascii (1)->encode ([chr 0x10401])
178 => ["\ud801\udc01"]
179
180 $json = $json->latin1 ([$enable])
181 If $enable is true (or missing), then the "encode" method will
182 encode the resulting JSON text as latin1 (or iso-8859-1), escaping
183 any characters outside the code range 0..255. The resulting string
184 can be treated as a latin1-encoded JSON text or a native unicode
185 string. The "decode" method will not be affected in any way by this
186 flag, as "decode" by default expects unicode, which is a strict
187 superset of latin1.
188
189 If $enable is false, then the "encode" method will not escape
190 Unicode characters unless required by the JSON syntax or other
191 flags.
192
193 The main use for this flag is efficiently encoding binary data as
194 JSON text, as most octets will not be escaped, resulting in a
195 smaller encoded size. The disadvantage is that the resulting JSON
196 text is encoded in latin1 (and must correctly be treated as such
197 when storing and transfering), a rare encoding for JSON. It is
198 therefore most useful when you want to store data structures known
199 to contain binary data efficiently in files or databases, not when
200 talking to other JSON encoders/decoders.
201
202 JSON::XS->new->latin1->encode (["\x{89}\x{abc}"]
203 => ["\x{89}\\u0abc"] # (perl syntax, U+abc escaped, U+89 not)
204
205 $json = $json->utf8 ([$enable])
206 If $enable is true (or missing), then the "encode" method will
207 encode the JSON result into UTF-8, as required by many protocols,
208 while the "decode" method expects to be handled an UTF-8-encoded
209 string. Please note that UTF-8-encoded strings do not contain any
210 characters outside the range 0..255, they are thus useful for
211 bytewise/binary I/O. In future versions, enabling this option might
212 enable autodetection of the UTF-16 and UTF-32 encoding families, as
213 described in RFC4627.
214
215 If $enable is false, then the "encode" method will return the JSON
216 string as a (non-encoded) unicode string, while "decode" expects
217 thus a unicode string. Any decoding or encoding (e.g. to UTF-8 or
218 UTF-16) needs to be done yourself, e.g. using the Encode module.
219
220 Example, output UTF-16BE-encoded JSON:
221
222 use Encode;
223 $jsontext = encode "UTF-16BE", JSON::XS->new->encode ($object);
224
225 Example, decode UTF-32LE-encoded JSON:
226
227 use Encode;
228 $object = JSON::XS->new->decode (decode "UTF-32LE", $jsontext);
229
230 $json = $json->pretty ([$enable])
231 This enables (or disables) all of the "indent", "space_before" and
232 "space_after" (and in the future possibly more) flags in one call to
233 generate the most readable (or most compact) form possible.
234
235 Example, pretty-print some simple structure:
236
237 my $json = JSON::XS->new->pretty(1)->encode ({a => [1,2]})
238 =>
239 {
240 "a" : [
241 1,
242 2
243 ]
244 } 154 };
155 $w->data ("print me!");
245 156
246 $json = $json->indent ([$enable]) 157 $current_cb = $w->cb
247 If $enable is true (or missing), then the "encode" method will use a 158 $old_cb = $w->cb ($new_cb)
248 multiline format as output, putting every array member or 159 Queries the callback on the watcher and optionally changes it. You
249 object/hash key-value pair into its own line, identing them 160 can do this at any time without the watcher restarting.
250 properly.
251 161
252 If $enable is false, no newlines or indenting will be produced, and 162 $current_priority = $w->priority
253 the resulting JSON text is guarenteed not to contain any "newlines". 163 $old_priority = $w->priority ($new_priority)
164 Queries the priority on the watcher and optionally changes it.
165 Pending watchers with higher priority will be invoked first. The
166 valid range of priorities lies between EV::MAXPRI (default 2) and
167 EV::MINPRI (default -2). If the priority is outside this range it
168 will automatically be normalised to the nearest valid priority.
254 169
255 This setting has no effect when decoding JSON texts. 170 The default priority of any newly-created weatcher is 0.
256 171
257 $json = $json->space_before ([$enable]) 172 $w->trigger ($revents)
258 If $enable is true (or missing), then the "encode" method will add 173 Call the callback *now* with the given event mask.
259 an extra optional space before the ":" separating keys from values
260 in JSON objects.
261 174
262 If $enable is false, then the "encode" method will not add any extra 175 $w = EV::io $fileno_or_fh, $eventmask, $callback
263 space at those places. 176 $w = EV::io_ns $fileno_or_fh, $eventmask, $callback
177 As long as the returned watcher object is alive, call the $callback
178 when the events specified in $eventmask.
264 179
265 This setting has no effect when decoding JSON texts. You will also 180 The $eventmask can be one or more of these constants ORed together:
266 most likely combine this setting with "space_after".
267 181
268 Example, space_before enabled, space_after and indent disabled: 182 EV::READ wait until read() wouldn't block anymore
183 EV::WRITE wait until write() wouldn't block anymore
269 184
270 {"key" :"value"} 185 The "io_ns" variant doesn't start (activate) the newly created
186 watcher.
271 187
272 $json = $json->space_after ([$enable]) 188 $w->set ($fileno_or_fh, $eventmask)
273 If $enable is true (or missing), then the "encode" method will add 189 Reconfigures the watcher, see the constructor above for details. Can
274 an extra optional space after the ":" separating keys from values in 190 be called at any time.
275 JSON objects and extra whitespace after the "," separating key-value
276 pairs and array members.
277 191
278 If $enable is false, then the "encode" method will not add any extra 192 $current_fh = $w->fh
279 space at those places. 193 $old_fh = $w->fh ($new_fh)
194 Returns the previously set filehandle and optionally set a new one.
280 195
281 This setting has no effect when decoding JSON texts. 196 $current_eventmask = $w->events
197 $old_eventmask = $w->events ($new_eventmask)
198 Returns the previously set event mask and optionally set a new one.
282 199
283 Example, space_before and indent disabled, space_after enabled: 200 $w = EV::timer $after, $repeat, $callback
201 $w = EV::timer_ns $after, $repeat, $callback
202 Calls the callback after $after seconds. If $repeat is non-zero, the
203 timer will be restarted (with the $repeat value as $after) after the
204 callback returns.
284 205
285 {"key": "value"} 206 This means that the callback would be called roughly after $after
207 seconds, and then every $repeat seconds. The timer does his best not
208 to drift, but it will not invoke the timer more often then once per
209 event loop iteration, and might drift in other cases. If that isn't
210 acceptable, look at EV::periodic, which can provide long-term stable
211 timers.
286 212
287 $json = $json->relaxed ([$enable]) 213 The timer is based on a monotonic clock, that is, if somebody is
288 If $enable is true (or missing), then "decode" will accept some 214 sitting in front of the machine while the timer is running and
289 extensions to normal JSON syntax (see below). "encode" will not be 215 changes the system clock, the timer will nevertheless run (roughly)
290 affected in anyway. *Be aware that this option makes you accept 216 the same time.
291 invalid JSON texts as if they were valid!*. I suggest only to use
292 this option to parse application-specific files written by humans
293 (configuration files, resource files etc.)
294 217
295 If $enable is false (the default), then "decode" will only accept 218 The "timer_ns" variant doesn't start (activate) the newly created
296 valid JSON texts. 219 watcher.
297 220
298 Currently accepted extensions are: 221 $w->set ($after, $repeat)
222 Reconfigures the watcher, see the constructor above for details. Can
223 be at any time.
299 224
300 * list items can have an end-comma 225 $w->again
301 JSON *separates* array elements and key-value pairs with commas. 226 Similar to the "start" method, but has special semantics for
302 This can be annoying if you write JSON texts manually and want 227 repeating timers:
303 to be able to quickly append elements, so this extension accepts
304 comma at the end of such items not just between them:
305 228
229 If the timer is active and non-repeating, it will be stopped.
230
231 If the timer is active and repeating, reset the timeout to occur
232 $repeat seconds after now.
233
234 If the timer is inactive and repeating, start it using the repeat
235 value.
236
237 Otherwise do nothing.
238
239 This behaviour is useful when you have a timeout for some IO
240 operation. You create a timer object with the same value for $after
241 and $repeat, and then, in the read/write watcher, run the "again"
242 method on the timeout.
243
244 $w = EV::periodic $at, $interval, $reschedule_cb, $callback
245 $w = EV::periodic_ns $at, $interval, $reschedule_cb, $callback
246 Similar to EV::timer, but is not based on relative timeouts but on
247 absolute times. Apart from creating "simple" timers that trigger
248 "at" the specified time, it can also be used for non-drifting
249 absolute timers and more complex, cron-like, setups that are not
250 adversely affected by time jumps (i.e. when the system clock is
251 changed by explicit date -s or other means such as ntpd). It is also
252 the most complex watcher type in EV.
253
254 It has three distinct "modes":
255
256 * absolute timer ($interval = $reschedule_cb = 0)
257 This time simply fires at the wallclock time $at and doesn't
258 repeat. It will not adjust when a time jump occurs, that is, if
259 it is to be run at January 1st 2011 then it will run when the
260 system time reaches or surpasses this time.
261
262 * non-repeating interval timer ($interval > 0, $reschedule_cb = 0)
263 In this mode the watcher will always be scheduled to time out at
264 the next "$at + N * $interval" time (for some integer N) and
265 then repeat, regardless of any time jumps.
266
267 This can be used to create timers that do not drift with respect
268 to system time:
269
270 my $hourly = EV::periodic 0, 3600, 0, sub { print "once/hour\n" };
271
272 That doesn't mean there will always be 3600 seconds in between
273 triggers, but only that the the clalback will be called when the
274 system time shows a full hour (UTC).
275
276 Another way to think about it (for the mathematically inclined)
277 is that EV::periodic will try to run the callback in this mode
278 at the next possible time where "$time = $at (mod $interval)",
279 regardless of any time jumps.
280
281 * manual reschedule mode ($reschedule_cb = coderef)
282 In this mode $interval and $at are both being ignored. Instead,
283 each time the periodic watcher gets scheduled, the reschedule
284 callback ($reschedule_cb) will be called with the watcher as
285 first, and the current time as second argument.
286
287 *This callback MUST NOT stop or destroy this or any other
288 periodic watcher, ever*. If you need to stop it, return 1e30 and
289 stop it afterwards.
290
291 It must return the next time to trigger, based on the passed
292 time value (that is, the lowest time value larger than to the
293 second argument). It will usually be called just before the
294 callback will be triggered, but might be called at other times,
306 [ 295 too.
307 1, 296
308 2, <- this comma not normally allowed 297 This can be used to create very complex timers, such as a timer
309 ] 298 that triggers on each midnight, local time (actually 24 hours
299 after the last midnight, to keep the example simple. If you know
300 a way to do it correctly in about the same space (without
301 requiring elaborate modules), drop me a note :):
302
303 my $daily = EV::periodic 0, 0, sub {
304 my ($w, $now) = @_;
305
306 use Time::Local ();
307 my (undef, undef, undef, $d, $m, $y) = localtime $now;
308 86400 + Time::Local::timelocal 0, 0, 0, $d, $m, $y
310 { 309 }, sub {
311 "k1": "v1", 310 print "it's midnight or likely shortly after, now\n";
312 "k2": "v2", <- this comma not normally allowed
313 } 311 };
314 312
315 * shell-style '#'-comments 313 The "periodic_ns" variant doesn't start (activate) the newly created
316 Whenever JSON allows whitespace, shell-style comments are 314 watcher.
317 additionally allowed. They are terminated by the first
318 carriage-return or line-feed character, after which more
319 white-space and comments are allowed.
320 315
316 $w->set ($at, $interval, $reschedule_cb)
317 Reconfigures the watcher, see the constructor above for details. Can
318 be at any time.
319
320 $w->again
321 Simply stops and starts the watcher again.
322
323 $w = EV::signal $signal, $callback
324 $w = EV::signal_ns $signal, $callback
325 Call the callback when $signal is received (the signal can be
326 specified by number or by name, just as with kill or %SIG).
327
328 EV will grab the signal for the process (the kernel only allows one
329 component to receive a signal at a time) when you start a signal
330 watcher, and removes it again when you stop it. Perl does the same
331 when you add/remove callbacks to %SIG, so watch out.
332
333 You can have as many signal watchers per signal as you want.
334
335 The "signal_ns" variant doesn't start (activate) the newly created
336 watcher.
337
338 $w->set ($signal)
339 Reconfigures the watcher, see the constructor above for details. Can
340 be at any time.
341
342 $current_signum = $w->signal
343 $old_signum = $w->signal ($new_signal)
344 Returns the previously set signal (always as a number not name) and
345 optionally set a new one.
346
347 $w = EV::child $pid, $callback
348 $w = EV::child_ns $pid, $callback
349 Call the callback when a status change for pid $pid (or any pid if
350 $pid is 0) has been received. More precisely: when the process
351 receives a SIGCHLD, EV will fetch the outstanding exit/wait status
352 for all changed/zombie children and call the callback.
353
354 You can access both status and pid by using the "rstatus" and "rpid"
355 methods on the watcher object.
356
357 You can have as many pid watchers per pid as you want.
358
359 The "child_ns" variant doesn't start (activate) the newly created
360 watcher.
361
362 $w->set ($pid)
363 Reconfigures the watcher, see the constructor above for details. Can
364 be at any time.
365
366 $current_pid = $w->pid
367 $old_pid = $w->pid ($new_pid)
368 Returns the previously set process id and optionally set a new one.
369
370 $exit_status = $w->rstatus
371 Return the exit/wait status (as returned by waitpid, see the waitpid
372 entry in perlfunc).
373
374 $pid = $w->rpid
375 Return the pid of the awaited child (useful when you have installed
376 a watcher for all pids).
377
378 $w = EV::idle $callback
379 $w = EV::idle_ns $callback
380 Call the callback when there are no pending io, timer/periodic,
381 signal or child events, i.e. when the process is idle.
382
383 The process will not block as long as any idle watchers are active,
384 and they will be called repeatedly until stopped.
385
386 The "idle_ns" variant doesn't start (activate) the newly created
387 watcher.
388
389 $w = EV::prepare $callback
390 $w = EV::prepare_ns $callback
391 Call the callback just before the process would block. You can still
392 create/modify any watchers at this point.
393
394 See the EV::check watcher, below, for explanations and an example.
395
396 The "prepare_ns" variant doesn't start (activate) the newly created
397 watcher.
398
399 $w = EV::check $callback
400 $w = EV::check_ns $callback
401 Call the callback just after the process wakes up again (after it
402 has gathered events), but before any other callbacks have been
403 invoked.
404
405 This is used to integrate other event-based software into the EV
406 mainloop: You register a prepare callback and in there, you create
407 io and timer watchers as required by the other software. Here is a
408 real-world example of integrating Net::SNMP (with some details left
409 out):
410
411 our @snmp_watcher;
412
413 our $snmp_prepare = EV::prepare sub {
414 # do nothing unless active
415 $dispatcher->{_event_queue_h}
416 or return;
417
418 # make the dispatcher handle any outstanding stuff
419
420 # create an IO watcher for each and every socket
421 @snmp_watcher = (
422 (map { EV::io $_, EV::READ, sub { } }
423 keys %{ $dispatcher->{_descriptors} }),
321 [ 424 );
322 1, # this comment not allowed in JSON
323 # neither this one...
324 ]
325 425
326 $json = $json->canonical ([$enable]) 426 # if there are any timeouts, also create a timer
327 If $enable is true (or missing), then the "encode" method will 427 push @snmp_watcher, EV::timer $event->[Net::SNMP::Dispatcher::_TIME] - EV::now, 0, sub { }
328 output JSON objects by sorting their keys. This is adding a 428 if $event->[Net::SNMP::Dispatcher::_ACTIVE];
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 } 429 };
469 430
470 $json = $json->shrink ([$enable]) 431 The callbacks are irrelevant, the only purpose of those watchers is
471 Perl usually over-allocates memory a bit when allocating space for 432 to wake up the process as soon as one of those events occurs (socket
472 strings. This flag optionally resizes strings generated by either 433 readable, or timer timed out). The corresponding EV::check watcher
473 "encode" or "decode" to their minimum size possible. This can save 434 will then clean up:
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).
480 435
481 The actual definition of what shrink does might change in future 436 our $snmp_check = EV::check sub {
482 versions, but it will always try to save space at the expense of 437 # destroy all watchers
438 @snmp_watcher = ();
439
440 # make the dispatcher handle any new stuff
441 };
442
443 The callbacks of the created watchers will not be called as the
444 watchers are destroyed before this cna happen (remember EV::check
445 gets called first).
446
447 The "check_ns" variant doesn't start (activate) the newly created
483 time. 448 watcher.
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
563MAPPING
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
690COMPARISON
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
854SECURITY 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).
892 449
893THREADS 450THREADS
894 This module is *not* guarenteed to be thread safe and there are no plans 451 Threads are not supported by this in any way. Perl pseudo-threads is
895 to change this until Perl gets thread support (as opposed to the 452 evil stuff and must die.
896 horribly slow so-called "threads" which are simply slow and bloated
897 process simulations - use fork, its *much* faster, cheaper, better).
898 453
899 (It might actually work, but you ahve ben warned). 454SEE ALSO
900 455 L<EV::DNS>, L<EV::AnyEvent>.
901BUGS
902 While the goal of this module is to be correct, that unfortunately does
903 not mean its bug-free, only that I think its design is bug-free. It is
904 still relatively early in its development. If you keep reporting bugs
905 they will be fixed swiftly, though.
906
907 Please refrain from using rt.cpan.org or any other bug reporting
908 service. I put the contact address into my modules for a reason.
909 456
910AUTHOR 457AUTHOR
911 Marc Lehmann <schmorp@schmorp.de> 458 Marc Lehmann <schmorp@schmorp.de>
912 http://home.schmorp.de/ 459 http://home.schmorp.de/
913 460

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