When the option is set to `true`, the module will generate
CAPTCHA challenges for incoming subscription requests. The option
also implies that option `drop` is set to `true`. Note that
the module won't generate CAPTCHA challenges for messages: they
will still be rejected if `drop` is set to `true`.
Fixes#2246
The callback is supposed to provide known options and their default
values, as long as the documentation. Passing default values into
get_mod functions is now deprecated: all defaults should be provided
by the Mod:mod_options/1 callback.
This is a boolean option. If set to `true` and some server's JID
is in user's roster, then messages from any user of this server are
accepted even if no subscription present.
The option is enabled by default.
The changes are very similar to those from previous commit:
* Now there is no need to pass validating function in
gen_mod:get_opt() and gen_mod:get_module_opt() functions,
because the modules' configuration keeps already validated values.
* New functions gen_mod:get_opt/2 and gen_mod:get_module_opt/3 are
introduced.
* Functions gen_mod:get_opt/4 and get_module_opt/5 are deprecated.
If the functions are still called, the "function" argument is
simply ignored.
* Validating callback Mod:listen_opt_type/1 is introduced to validate
listening options at startup.
Evgeniy Khramtsov