NkSIP implements and advanced and very efficient run-time configuration system. As explained in the reference guide, it has two types of configuration options:
- Global configuration options. They are defined as standard Erlang environment variables for nksip application. Any started Service can override most of them.
- Service configuration options. They are defined when starting the Service calling
nksip:start/2. - Call Config
During NkSIP startup, the global configuration values from the nksip application environment are extracted, defining defaults for missing values, and storing them in an ETS table.
It also generates and compiles on the fly the module nksip_config_cache, copying commonly used values as functions in it, for example nksip_config_cache:global_id/0. The on-disk file nksip_config_cache.erl is only a mockup to make it easier to understand the process. Now any process can call any on this functions to get common config values without calling to access the ETS table.
When a Service starts, it copies all configuration values from the global config, allowing it to change any of its values for this specific application.
Then it generates and compiles on the fly a module called with the same name as the internal name of the application. This module has a number of functions that also work as a cache configuration (like the previous nksip_config_cache), but specific for this Service. It has functions as name/0 (for the user name of the application), spec/0 for the full service specification, etc.
This module also includes all the functions in the callback module, and all the detected plugin callbacks.
Each time a new call process is started, NkSIP copies three values in the process registry: the current log level, the application and the call-id. These values are read-only and only used to speed the logging process.