# Functions

## `sdp_mangle_ip(pattern, newip)`

Changes IP addresses inside SDP document 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 - An 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.

### `sdp_mangle_ip` usage

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

## `sdp_mangle_port(offset)`

Changes ports in SDP document in lines starting a media section 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.

### `sdp_mangle_port` usage

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

## `encode_contact(encoding_prefix)`

This function will encode URIs inside the "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.

### `encode_contact` usage

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

## `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.

### `decode_contact` usage

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

## `decode_contact_header()`

This function will decode URIs inside the "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.

### `decode_contact_header` usage

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