The Mangler Module - SDP mangling

Gabriel Vasile

   FhG FOKUS

   Copyright © 2003 FhG FOKUS
     __________________________________________________________________

   List of Examples

   1. Set db_url parameter
   2. sdp_mangle_ip usage
   3. sdp_mangle_port usage
   4. encode_contact usage
   5. decode_contact usage
   6. decode_contact_header usage

1. Overview

   This is a module to help with SDP mangling - changing data in the SDP.

2. Parameters

   2.1. contact_flds_separator (string)

2.1. contact_flds_separator (string)

   First char of this parameter is used as separator for encoding/decoding
   Contact header. If you set this parameter to "-", then an encoded uri
   might look sip:user-password-ip-port-protocol@PublicIP

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("mangler", "contact_flds_separator", "-")
...

3. Functions

   3.1. sdp_mangle_ip(pattern, newip)
   3.2. sdp_mangle_port(offset)
   3.3. encode_contact(encoding_prefix)
   3.4. decode_contact()
   3.5. decode_contact_header()

3.1.  sdp_mangle_ip(pattern, newip)

   Changes IP addresses inside SDP package in lines describing connections
   like c=IN IP4 . Currently this function 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 ip address/mask pair used to match IP's located inside
       SDP package in lines c=IN IP4 ip. This line will only be changed 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");
...

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");
...

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. "*" (asterisk) 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 public ip--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");
...

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 is converted to sip:username:password@ip:port;parameters
   and will set destination 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.

   Example 5. decode_contact usage
...
if (uri =~ "^enc*") { decode_contact(); }
...

3.5.  decode_contact_header()

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

   The function returns negative on error, 1 on success.

   Example 6. decode_contact_header usage
...
if (uri =~ "^enc*") { decode_contact_header(); }
...
