Documentation -> Manuals -> Manual 3.3 -> Templating opensips.cfg Files

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Templating opensips.cfg Files v3.3

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1.  Generic Preprocessing Support

OpenSIPS 3.0+ releases offer script writers full support for piping the opensips.cfg file (including any other files imported by it) to a generic preprocessing command. This may be useful in scenarios where opensips.cfg must be parameterized (e.g. listening interfaces, ports, DB connectors, etc.) and deployed to multiple servers, in an automated fashion. The system administrator may achieve this using the "-p <cmdline>" (preprocessor) option. For example:

opensips -f opensips.cfg -p /bin/cat

... is a basic use of the "-p" option, by supplying it with an "echo" preprocessor that receives input via standard input and mirrors it to standard output. From here, it's just a matter of choosing a templating language which fits the deployment requirements. Some basic substitutions can be done using, for example, sed:

opensips -f opensips.cfg -p "/bin/sed s/PRIVATE_IP/10.0.0.10/g"

2.  Common Templating Languages + Examples

Below are some examples of using more advanced templating languages on top of opensips.cfg, for cases where the target environment requires complex decision-making (if statements which enable/disable features, for loops over multiple listening interfaces, etc.).

2.1  GNU m4

GNU m4 is a simplistic preprocessor with a mild learning curve, equipped with textual substitution, if statements and file includes among the most notable features. Here is an example integration with opensips.cfg:

listen = udp:PRIVATE_IP:5060
loadmodule "proto_udp.so"

opensips.cfg.m4

divert(-1)
define(`PRIVATE_IP', `127.0.0.1')
divert(0)dnl

env.m4

... and we start OpenSIPS using the below command, which will pipe opensips.cfg.m4 to m4's standard input, and then read the resulting file from its standard output:

opensips -f opensips.cfg.m4 -p "m4 env.m4 -"

2.2  Jinja2

Jinja2 is a modern templating language with a rich feature set, including textual replacement, if statements, for loops, a plethora of filters, file includes, and the list goes on! Unlike m4, Jinja2 does not currently have a standalone binary, rather it is provided via a Python package. Here is a way of integrating it with opensips.cfg:

First, install the jinja2 Python module with: "pip install jinja2". Next, prepare the files:

listen = udp:{{ private_ip }}:5060
loadmodule "proto_udp.so"

opensips.cfg.j2

import sys
import json
from jinja2 import Template

t = Template("".join(sys.stdin.readlines()))

with open('env.json') as f:
    print(t.render(json.load(f)))

opensips-preproc.py

{
    "private_ip": "127.0.0.1"
}

env.json

... and we start OpenSIPS using:

opensips -f opensips.cfg.j2 -p "python opensips-preproc.py"

2.3  Embedded Ruby

Embedded Ruby (ERB) provides an easy to use, powerful templating system for Ruby. Using ERB, actual Ruby code can be added to any plain text document for the purposes of generating document information details and/or flow control. Let's see how it integrates with opensips.cfg!

First, install the ERB package (for Debian/Ubuntu: "apt install ruby-ejs"). Next, prepare the files:

listen = udp:<%= private_ip %>:5060
loadmodule "proto_udp.so"

opensips.cfg.erb

#!/usr/bin/env ruby
require 'erb'
require './env.rb'

template = ERB.new($stdin.read, nil, '-')
$stdout.write template.result($erb_context)

~/src/opensips-preproc.rb

$erb_context = binding
private_ip   = '127.0.0.1'

env.rb

... and OpenSIPS is now started using:

opensips -f opensips.cfg.erb -p "ruby opensips-preproc.rb"

3.  Debugging Preprocessor Output

Since the output of the preprocessor is never written to any file and is just consumed by OpenSIPS on each run, script developers may still visualize and debug the generated file during development by using a wrapper script over the preprocessing command such as the following:

#!/bin/bash

m4 env.m4 - | tee >(grep -v __OSSPP_ >/tmp/opensips.cfg)

~/src/preprocessor.sh

... and now we start OpenSIPS using:

opensips -f opensips.cfg.m4 -p ~/src/preprocessor.sh

The same technique can be used for any other preprocessor.