1. Mangler Module

Gabriel Vasile

FhG FOKUS

1.1. Overview
1.2. Parameters
1.2.1. contact_flds_separator (string)
1.3. Functions
1.3.1. sdp_mangle_ip(pattern, newip)
1.3.2. sdp_mangle_port(offset)
1.3.3. encode_contact(encoding_prefix)
1.3.4. decode_contact()
1.3.5. decode_contact_header()

1.1. Overview

This is a module to help with SDP mangling. Still in testing.

1.2. Parameters

1.2.1. contact_flds_separator (string)

First char of this parameter is used as separator for encoding/decoding Contact header.

Warning

First char of this field must be set to a value which is not used inside username,password or other fields of contact.Otherwise it is possible for the decoding step to fail/produce wrong results.

Default value is "*".

Example 1. Set db_url parameter

...
modparam("module", "contact_flds_separator", "-")
...

then an encoded uri might look sip:user-password-ip-port-protocol@PublicIP

1.3. Functions

1.3.1.  sdp_mangle_ip(pattern, newip)

Changes IP addresses inside SDP package in lines describing connections like c=IN IP4 Currently in only changes IP4 addresses since IP6 probably will not need to traverse NAT :)

The function returns negative on error, or number of replacements + 1.

Meaning of the parameters is as follows:

  • pattern - A pair ip/mask used to match IP's located inside SDP package in lines c=IN IP4 ip. This lines will only be mangled if located IP is in the network described by this pattern. Examples of valid patterns are "10.0.0.0/255.0.0.0" or "10.0.0.0/8" etc.

  • newip - A string representing the new IP to be put inside SDP package if old IP address matches pattern.

Example 2. sdp_mangle_ip usage

...
sdp_mangle_ip("10.0.0.0/8","193.175.135.38");
...

1.3.2.  sdp_mangle_port(offset)

Changes ports inside SDP package in lines describing media like m=audio 13451.

The function returns negative on error, or number of replacements + 1.

Meaning of the parameters is as follows:

  • offset - A string representing an integer which will be added/subtracted from the located port.

Example 3. sdp_mangle_port usage

...
sdp_mangle_port("-12000");
...

1.3.3.  encode_contact(encoding_prefix)

This function will encode uri-s inside Contact header in the following manner sip:username:password@ip:port;transport=protocol goes sip:enc_pref*username*ip*port*protocol@public_ip * is the default separator.

The function returns negative on error, 1 on success.

Meaning of the parameters is as follows:

  • encoding_prefix - Something to allow us to determine that a contact is encoded publicip--a routable IP,most probably you should put your external IP of your NAT box.

Example 4. encode_contact usage

...
if (src_ip == 10.0.0.0/8) encode_contact("enc_prefix","193.175.135.38"); 
...

1.3.4.  decode_contact()

This function will decode the URI in first line in packets which come with encoded URI in the following manner sip:enc_pref*username*ip*port*protocol*src_ip*src_port*src_proto@public_ip;parameters goes to sip:username:password@ip:port;parameters and will set dst_uri to sip:src_ip:src_port;transport=src_proto (so that the next forward() or t_relay() will send the message back to src_ip:src_port using src_proto). It uses the default set parameter for contact encoding separator.

The function returns negative on error, 1 on success.

Meaning of the parameters is as follows:

Example 5. decode_contact usage

...
if (uri =~ "^enc*") { decode_contact(); }
...

1.3.5.  decode_contact_header()

This function will decode URIs inside Contact header in the same manner as decode_contact. The difference is no dst_uri is set (src_ip, src_port and src_proto are ignored) and instead of changing the request uri, the Contact header uris are modified. It uses the default set parameter for contact encoding separator.

The function returns negative on error, 1 on success.

Meaning of the parameters is as follows:

Example 6. decode_contact_header usage

...
if (uri =~ "^enc*") { decode_contact_header(); }
...