Tag Archives: Event Socket Library

Using fs_cli and ESL

If you work with FreeSWITCH there’s a good chance every time you do, you run fs_cli and attempt to read the firehose of data shown when making a call to make sense of what’s going on and why what you’re trying to do isn’t working.

But, if you are also using the Event Socket Language service built into FreeSWITCH (Which you totally should) either for programming FreeSWITCH behaviour, or for realtime charging with CGrateS, then you’ll find that fs_cli will fail to connect.

That’s because we’ve edited the event_socket.conf.xml file, and fs_cli uses the event socket to connect to FreeSWITCH as well.

But there’s a simple fix,

Create a new file in /etc/fs_cli.conf and populate it with the info needed to connect to your ESL session you defined in event_socket.conf.xml, so if this is is your

<configuration name="event_socket.conf" description="Socket Client">
    <param name="nat-map" value="false"/>
    <param name="listen-ip" value=""/>
    <param name="listen-port" value="8021"/>
    <param name="password" value="mysupersecretpassword"/>
    <param name="apply-inbound-acl" value="NickACL"/>

Then your /etc/fs_cli.conf should look like:

; Put me in /etc/fs_cli.conf or ~/.fs_cli_conf
;overide any default options here
loglevel => 6
log-uuid => false

host     =>
port     => 8021
password => mysupersecretpassword
debug    => 7

And that’s it, now you can run fs_cli and connect to the terminal once more!

FreeSWITCH + ESL = Programmable Voice

No great secret, I’m a big Python fan.

Recently I’ve been working on a few projects with FreeSWITCH, and looking at options for programmatically generating dialplans, instead of static XML files.

Why not Static XML?

So let’s say I define a static XML dialplan.

It works great, but if I want to change the way a call routes I need to do it from the dialplan,

That’s not ideal if you’re using a distributed cluster of FreeSWITCH instances, or if you want to update on the fly.

Static XML means we have to define our dialplan when setting up the server, and would have to reconfigure the server to change it.

So what about mod_xml_curl?

When I’ve done this in the past I’ve relied on the mod_xml_curl module.

mod_xml_curl gets the XML dialplan using Curl from a web server, and so you setup a web server using Flask/PHP/etc, and dynamically generate the dialplan when the call comes in.

This sounds good, except you can’t update it on the fly.

mod_xml_curl means call routing decisions are made at the start of the call, and can’t be changed midway through the call.

So what’s ESL?

ESL is the Event Socket Library, essentially a call comes in, an ESL request is made to an external server.

For each step in the dialplan, an ESL request will be sent to the external server which tells it to do,

ESL allows us to use all FreeSWITCH’s fantastic modules, without being limited as to having to perform the call routing logic in FreeSWITCH.

So how do I use ESL?

You’ll need two create an ESL server,

Luckily there’s premade examples for popular languages;

Once you’ve got a basic server defined we’ll need to put some config in our XML Dialplan to say “transfer all your thinking to ESL!”;

<!-- Send everything that's numbers to ESL for Processing --> 
    <extension name="esl_route">
      <condition field="destination_number" expression="^\d*$">
        <action application="socket" data=""/>
        <action application="log" data="ERR Made it past ESL - Play error."/>
        <action application="playback" data="ivr/ivr-call_cannot_be_completed_as_dialed"/>

In the above example my ESL server is on / port 5000.

Now any calls coming in will be transfered to ESL and where it goes from there, is something you define in your prefered programming language.

In the next post I’ll cover how I’ve been addressing this using Python and Greenswitch.