Lua Dialplan Tips and Tricks

Long Running Operations (Autoservcie)¶

Before starting long running operations, an autoservice should be started using the autoservice_start() function. An autoservice will ensure that the user hears a continuous stream of audio while your lua code works in the background. This autoservice will automatically be stopped before executing applications and dialplan functions and will be restarted afterwards. The autoservice can be stopped using autoservice_stop() and the autoservice_status() function will return true if an autoservice is currently running.

app.startmusiconhold()

autoservice_start()
do_expensive_db_query()
autoservice_stop()

app.stopmusiconhold()

Defining Extensions Dynamically¶

Since extensions are functions in pbx_lua, any function can be used, including closures. A function can be defined that returns extension functions and used to populate the extensions table.

extensions.lua

extensions = {}
extensions.default = {}

function sip_exten(e)
 return function()
 app.dial("SIP/" .. e)
 end
end

extensions.default[100] = sip_exten(100)
extensions.default[101] = sip_exten(101)

Creating Custom Aliases for Built-in Constructs¶

If you don't like the app table being named 'app' or if you think typing 'channel' to access the channel table is too much work, you can rename them.

I prefer less typing

function my_exten(context, extensions)
 c = channel
 a = app

 c.my_variable = "my new channel variable"
 a.dial("SIP/100")
end

Re-purposing The print Function¶

Lua has a built in "print" function that outputs things to stdout, but for Asterisk, we would rather have the output go in the verbose log. To do so, we could rewrite the print function as follows.

function print(...)
 local msg = ""
 for i=1,select('#', ...) do
 if i == 1 then
 msg = msg .. tostring(select(i, ...))
 else
 msg = msg .. "\t" .. tostring(select(i, ...))
 end
 end

 app.verbose(msg)
end

Splitting Configuration into Multiple Files¶

The require method can be used to load lua modules located in LUA_PATH. The dofile method can be used to include any file by path name.

Using External Modules¶

Lua modules can be loaded using the standard require lua method. Some of the functionality provided by various lua modules is already included in Asterisk (e.g. func_odbc provides what LuaSQL provides). It is generally better to use code built-in to Asterisk over external lua modules. Specifically, the func_odbc module uses a connection pool to provide database resources, where as with LuaSQL each channel would have to make a new connection to the database on its own.

Compile extensions.lua¶

The luac program can be used to compile your extensions.lua file into lua bytecode. This will slightly increase performance as pbx_lua will no longer need to parse extensions.lua on load. The luac compiler will also detect and report any syntax errors. To use luac, rename your extensions.lua file and then run luac as follows.

Assume you name your extensions.lua file extensions.lua.lua

luac -o extensions.lua extensions.lua.lua

The pbx_lua module automatically knows the difference between a lua text file and a lua bytecode file.