1 EXTCAP: DEVELOPER GUIDE
2 =======================
4 The extcap interface is a versatile plugin interface that allows external binaries
5 to act as capture interfaces directly in wireshark. It is used in scenarios, where
6 the source of the capture is not a traditional capture model (live capture from an
7 interface, from a pipe, from a file, etc). The typical example is connecting esoteric
8 hardware of some kind to the main wireshark app.
10 Without extcap, a capture can always be achieved by directly writing to a capture file:
12 the-esoteric-binary --the-strange-flag --interface=stream1 --file dumpfile.pcap &
13 wireshark dumpfile.pcap
15 but the extcap interface allows for such a connection to be easily established and
16 configured using the wireshark GUI.
18 The extcap subsystem is made of multiple extcap binaries that are automatically
19 called by the GUI in a row. In the following chapters we will refer to them as
22 Extcaps may be any binary or script within the extcap directory. Please note, that
23 scripts need to be executable without prefacing a script interpreter before the call.
25 WINDOWS USER: Because of restrictions directly calling the script may not always work.
26 In such a case, a batch file may be provided, which then in turn executes the script.
27 Please refer to doc/extcap_example.py for more information.
31 The actual capture is run after a setup process that can be made manually by the
32 user or automatically by the GUI. All the steps performed are done for every extcap.
34 Let's go through those steps.
36 STEP1: the extcap is queried for its interfaces.
38 extcapbin --extcap-interfaces
40 This call must print the existing interfaces for this extcap and must return 0.
41 The output must conform to the grammar specified for extcap, and it is specified
42 in the doc/extcap.4 generated man page (in the build dir).
46 $ extcapbin --extcap-interfaces
47 extcap {version=1.0}{help=Some help url}
48 interface {value=example1}{display=Example interface 1 for extcap}
49 interface {value=example2}{display=Example interface 2 for extcap}
51 The version for the extcap sentence (which may exist as often as wanted, but only
52 the last one will be used) will be used for displaying the version information of
53 the extcap interface in the about dialog of Wireshark (Qt only).
55 The value for each interface will be used in subsequent calls as the interface name
58 Using the help argument, an interface may provide a generic help url for the extcap
61 STEP2: the extcap is queried for valid DLTs (Data Link Types) for all the
62 interfaces returned by the step 1.
64 extcapbin --extcap-dlts --extcap-interface IFACE
66 This call must print the valid DLTs for the interface specified. This call is
67 made for all the interfaces and must return 0.
71 $ extcapbin --extcap-interface IFACE --extcap-dlts
72 dlt {number=147}{name=USER1}{display=Demo Implementation for Extcap}
74 A binary or script, which neither provides an interface list or a DLT list will
75 not show up in the extcap interfaces list.
78 STEP3: the extcap is queried for the configuration options for an interface.
80 extcapbin --extcap-interface IFACE --extcap-config
82 Each interface can have custom options that are valid for this interface only.
83 Those config options are specified on the command line when running the actual
84 capture. To allow an end-user to specify certain options, such options may be
85 provided using the extcap config argument.
87 To share which options are available for an interface, the extcap responds to
88 the command --extcap-config, that shows all the available options (aka additional command
91 Those options are automatically presented via a dialog to the user for the individual
96 $ extcapbin --extcap-interface IFACE --extcap-config
97 arg {number=0}{call=--delay}{display=Time delay}{tooltip=Time delay between packages}{type=integer}{range=1,15}{required=true}
98 arg {number=1}{call=--message}{display=Message}{tooltip=Package message content}{placeholder=Please enter a message here ...}{type=string}
99 arg {number=2}{call=--verify}{display=Verify}{tooltip=Verify package content}{type=boolflag}
100 arg {number=3}{call=--remote}{display=Remote Channel}{tooltip=Remote Channel Selector}{type=selector}
101 arg {number=4}{call=--server}{display=IP address for log server}{type=string}{validation=\\b(?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\\.){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\\b}
102 value {arg=3}{value=if1}{display=Remote1}{default=true}
103 value {arg=3}{value=if2}{display=Remote2}{default=false}
105 Now the user can click on the options and change them. They are sent to the
106 extcap when the capture is launched.
108 There are two kind of options available:
110 * file, integer, string, boolean, boolflag - are value based options and each expect
111 a single value via the command-line call
112 * selector, checkbox - are selections and can be presented multiple times in the command
113 line. Both expect subsequent "value" items in the config list, with the corresponding
114 argument selected via arg
117 STEP4: the capture. Once the interfaces are listed and configuration is customized
118 by the user, the capture is run.
120 extcapbin --extcap-interface IFACE [params] --capture [--extcap-capture-filter CFILTER]
123 To run the capture, the extcap must implement the --capture, --extcap-capture-filter
125 They are automatically added by wireshark that opens the fifo for reading. All
126 the other options are automatically added to run the capture. The extcap interface
127 is used like all other interfaces (meaning that capture on multiple interfaces, as
128 well as stopping and restarting the capture is supported).
133 The extcap interface provides the possibility for generating a GUI dialog to
134 set and adapt settings for the extcap binary.
136 All options must provide a number, by which they are identified. No NUMBER may be
137 provided twice. Also all options must present the elements CALL and DISPLAY, where
138 call provides the arguments name on the command-line and display the name in the GUI.
140 Additionally TOOLTIP and PLACEHOLDER may be provided, which will give the user an
141 explanation within the GUI, about what to enter into this field.
143 These options do have types, for which the following types are being supported:
145 * INTEGER, UNSIGNED, LONG, DOUBLE - this provides a field for entering a numeric value
146 of the given data type. A DEFAULT value may be provided, as well as a RANGE
148 arg {number=0}{call=--delay}{display=Time delay}{tooltip=Time delay between packages}
149 {type=integer}{range=1,15}{default=0}
151 * STRING - Let the user provide a string to the capture
153 arg {number=1}{call=--server}{display=IP Address}{tooltip=IP Address for log server}{type=string}{validation=\\b(?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\\.){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\\b}
155 - validation allows to provide a regular expression string, which is used to check
156 the user input for validity beyond normal data type or range checks. Back-slashes
157 must be escaped (as in \\b for \b)
159 * PASSWORD - Let the user provide a masked string to the capture. Password strings are
160 not saved, when the extcap configuration is being saved
162 arg {number=0}{call=--password}{display=The user password}{tooltip=The password for the connection}{type=password}
164 * BOOLEAN,BOOLFLAG - this provides the possibility to set a true/false value.
165 BOOLFLAG values will only appear in the command-line if set to true, otherwise they
166 will not be added to the command-line call for the extcap interface
168 arg {number=2}{call=--verify}{display=Verify}{tooltip=Verify package content}{type=boolflag}
170 * FILESELECT - Let the user provide a filepath to the capture. If MUSTEXIST is
171 being provided, the GUI checks if the file exists.
173 arg {number=3}{call=--logfile}{display=Logfile}{tooltip=A file for log messages}{type=fileselect}{mustexist=false}
175 * SELECTOR, RADIO, MULTICHECK - an optionfield, where the user may choose one or
176 more options from. If PARENT is provided for the value items, the option fields
177 for MULTICHECK and SELECTOR are being presented in a tree-like structure. SELECTOR
178 and RADIO values must present a default value, which will be the value provided to
179 the extcap binary for this argument
181 arg {number=3}{call=--remote}{display=Remote Channel}{tooltip=Remote Channel Selector}{type=selector}
182 value {arg=3}{value=if1}{display=Remote1}{default=true}
183 value {arg=3}{value=if2}{display=Remote2}{default=false}
186 VALIDATION OF ARGUMENTS
187 =======================
188 Arguments may be set with "{required=true}" which enforces a value being provided, before
189 a capture can be started using the extcap options dialog. This is not being checked, if
190 the extcap is started via a simple double-click. The necessary fields are marked for the
191 customer, to ensure a visibility for the end customer of the required argument.
193 Additionally text and number arguments may also be checked using a regular expression,
194 which is provided using the validation attribute (see example above). The syntax for
195 such a check is the same as for Qt RegExp classes. This feature is only active in the
196 Qt version of Wireshark.
201 An extcap utility can provide configuration for controls to use in an interface toolbar.
202 This controls are bidirectional and can be used to control the extcap utility while
205 This is useful in scenarios where configuration can be done based on findings in the
206 capture process, setting temporary values or give other inputs without restarting the
211 $ extcapbin --extcap-interfaces
212 extcap {version=1.0}{display=Example extcap interface}
213 interface {value=example1}{display=Example interface 1 for extcap}
214 interface {value=example2}{display=Example interface 2 for extcap}
215 control {number=0}{type=string}{display=Message}{tooltip=Package message content. Must start with a capital letter.}{validation=[A-Z]+}{required=true}
216 control {number=1}{type=selector}{display=Time delay}{tooltip=Time delay between packages}
217 control {number=2}{type=boolean}{display=Verify}{default=true}{tooltip=Verify package content}
218 control {number=3}{type=button}{display=Turn on}{tooltip=Turn on or off}
219 control {number=4}{type=button}{role=logger}{display=Log}{tooltip=Show capture log}
220 value {control=1}{value=1}{display=1 sec}
221 value {control=1}{value=2}{display=2 sec}{default=true}
223 All controls will be presented as GUI elements in a toolbar specific to the extcap
224 utility. The extcap must not rely on using those controls (they are optional) because
225 of other capturing tools not using GUI (e.g. tshark, tfshark).
230 The controls are similar to the ARGUMENTS, but without the CALL element. All controls
231 may be given a default value at startup and most can be changed during capture, both
232 by the extcap and the user (depending on the type of control).
234 All controls must provide a NUMBER, by which they are identified. No NUMBER may be
235 provided twice. Also all options must present the elements TYPE and DISPLAY, where
236 TYPE provides the type of control to add to the toolbar and DISPLAY the name in the GUI.
238 Additionally TOOLTIP and PLACEHOLDER may be provided, which will give the user an
239 explanation within the GUI.
241 All controls, except from the logger, help and restore buttons, may be disabled
242 (and enabled) in GUI by the extcap during capture. This can be because of set-once
243 operations, or operations which takes some time to complete.
245 All control values which are changed by the user (not equal to the default value) will
246 be sent to the extcap utility when starting a capture. The extcap utility may choose
247 to discard initial values and set new values, depending on implementation.
249 This TYPEs are defined as controls:
251 * BOOLEAN - This provides a checkbox with the possibility to set a true/false value.
253 The extcap utility can set a default value at startup, and can change (set) and receive
254 value changes while capturing. When starting a capture the GUI will send the value if
255 different from the default value.
257 The payload is one byte with binary value 0 or 1.
259 Valid Commands: Set value, Enable, Disable.
261 * BUTTON - This provides a button with different ROLEs:
263 ** CONTROL - This button will send a signal when pressed.
264 This is the default if no role is configured.
265 The button is only enabled when capturing.
267 The extcap utility can set the button text at startup, and can change (set) the
268 button text and receive button press signals while capturing. The button is
269 disabled and the button text is restored to the default text when not capturing.
271 The payload is either the button text or empty (signal).
273 Valid Commands: Set value, Enable, Disable.
275 ** LOGGER - This provides a logger mechanism where the extcap utility can send log
276 entries to be presented in a log window. This communication is unidirectional.
278 The payload is the log entry, and should be ended with a newline.
279 Maximum length is 65535 bytes.
281 Valid Commands: Set log entry, Add log entry.
283 The Set command will clear the log before adding the entry.
285 ** HELP - This button opens the help page, if configured.
286 This role has no controls and will not be used in communication.
288 Valid Commands: NONE.
290 ** RESTORE - This button will restore all control values to default.
291 This role has no controls and will not be used in communication.
292 The button is only enabled when not capturing.
294 Valid Commands: NONE.
296 * SELECTOR - This provides a combo box with fixed values which can be selected.
298 The extcap utility can set default values at startup, and add and remove values and
299 receive change in value selection while capturing. When starting a capture the GUI
300 will send the value if different from the default value.
302 The payload is a string with the value, and optionally a string with a display
303 value if this is different from the value. This two string values are separated
306 Valid Commands: Set selected value, Add value, Remove value, Enable, Disable.
308 If value is empty the Remove command will remove all entries.
310 * STRING - This provides a text edit line with the possibility to set a string or any
311 value which can be represented in a string (integer, float, date, etc.).
313 The extcap utility can set a default string value at startup, and can change (set) and
314 receive value changes while capturing. When starting a capture the GUI will send the
315 value if different from the default value.
317 The payload is a string with the value. Maximum length is 32767 bytes.
319 Valid Commands: Set value, Enable, Disable.
321 The element VALIDATION allows to provide a regular expression string, which is used
322 to check the user input for validity beyond normal data type or range checks.
323 Back-slashes must be escaped (as in \\b for \b).
328 In addition to the controls it's possible to send a single message from the extcap
329 utility to the user. This message can be put in the status bar or displayed in a
330 information, warning or error dialog which must be accepted by the user. This message
331 does not use the NUMBER argument so this can have any value.
336 The protocol used to communicate over the control pipes has a fixed size header of
337 6 bytes and a payload with 0 - 65535 bytes.
341 +----+----+----+----+----+----+----+----+
342 | Sync Pipe Indication (1 byte) |
343 +----+----+----+----+----+----+----+----+
345 | (3 bytes network order) |
346 +----+----+----+----+----+----+----+----+
347 | Control Number (1 byte) |
348 +----+----+----+----+----+----+----+----+
350 +----+----+----+----+----+----+----+----+
352 | (0 - 65535 bytes) |
353 +----+----+----+----+----+----+----+----+
355 Sync Pipe Indication:
356 The common sync pipe indication. This protocol uses the value 'T'.
359 Payload length + 2 bytes for control number and command.
362 Unique number to identify the control. This number also gives the order of
363 the controls in the interface toolbar.
365 Command: Control type:
367 1 = Set boolean / button / logger / selector / string
368 2 = Add logger / selector
370 4 = Enable boolean / button / selector / string
371 5 = Disable boolean / button / selector / string
372 6 = Statusbar message none
373 7 = Information message none
374 8 = Warning message none
375 9 = Error message none
378 The length of the following payload. Maximum length is 65535 bytes.
380 The Initialized command will be sent from the GUI to the extcap utility when all
381 user changed control values are sent after starting a capture. This is an indication
382 that the GUI is ready to receive control values.
384 The GUI will only send Initialized and Set commands. The extcap utility shall not
385 send the Initialized command.
387 Messages with unknown control number or command will be silently ignored.
392 To have extcap support, the specific extcap must be compiled. Examples for autotools and
393 cmake compiling the extcap plugin androiddump are provided within wireshark.
394 The extcap subsystem and the bundled extcaps are compiled by default.
396 Additionally there is an example python script available in doc/extcap_example.py.
398 When developing a new extcap, it must be created under extcap/ directory and
399 added to the makefiles. Once compiled it will be under the extcap/ directory
402 If the current extcaps configuration is copied, the new extcap will need specific
403 configuration flags like --enable-<newextcap> or -DBUILD_<newextcap>
405 Since this is a plugin, the developer must ensure that the extcap dir will be
406 loaded. To see which dir is loaded, they must open HELP->ABOUT->FOLDER and look
407 for "Extcap Path". If there is a system path (like /usr/local/lib/wireshark/extcap/)
408 the extcaps in the build dir are not loaded. To load them, wireshark must be
409 loaded with WIRESHARK_RUN_FROM_BUILD_DIRECTORY=1. Now the "Extcap path" should
410 point to the extcap dir under your build environment.