# Module commands

Introduced in MaxScale 2.1, the module commands are special, module-specific
commands. They allow the modules to expand beyond the capabilities of the
module API. Currently, only MaxAdmin implements an interface to the module
commands.

All registered module commands can be shown with `maxadmin list functions` and
they can be executed with `maxadmin call function <domain> <name> ARGS...` where
_<domain>_ is the domain where the module registered the function and _<name>_
is the name of the function. _ARGS_ is a function specific list of arguments.

## Developer reference

The module command API is defined in the _modulecmd.h_ header. It consists of
various functions to register and call module commands. Read the function
documentation in the header for more details.

The following example registers the module command _my_command_ in the _my_module_ domain.

```
#include <maxscale/modulecmd.h>

bool my_simple_cmd(const MODULECMD_ARG *argv)
{
    printf("%d arguments given\n", argv->argc);
}

int main(int argc, char **argv)
{
    modulecmd_arg_type_t my_args[] =
    {
        {MODULECMD_ARG_BOOLEAN, "This is a boolean parameter"},
        {MODULECMD_ARG_STRING | MODULECMD_ARG_OPTIONAL, "This is an optional string parameter"}
    };

    // Register the command
    modulecmd_register_command("my_module", "my_command", my_simple_cmd, 2, my_args);

    // Find the registered command
    const MODULECMD *cmd = modulecmd_find_command("my_module", "my_command");

    // Parse the arguments for the command
    const void *arglist[] = {"true", "optional string"};
    MODULECMD_ARG *arg = modulecmd_arg_parse(cmd, arglist, 2);

    // Call the module command
    modulecmd_call_command(cmd, arg);

    // Free the parsed arguments
    modulecmd_arg_free(arg);
    return 0;
}
```

The array of _modulecmd_arg_type_t_ type is used to tell what kinds of arguments
the command expects. The first argument is a SERVER which will be replaced with a
pointer to a server. The second argument is an optional string argument.

Arguments are passed to the parsing function as an array of void pointers. They
are interpreted as the types the command expects.

When the module command is executed, the _argv_ parameter for the
_my_simple_cmd_ contains the parsed arguments received from the caller of the
command.