Kamailio rewrite uri

A popular topic in the world of SIP!

In Kamailio (formerly OpenSER), the rewrite_uri function is used to modify the Request-URI (R-URI) of a SIP message. This function is commonly used to perform various tasks, such as:

1. URL rewriting: Modify the R-URI to point to a different destination.
2. Domain rewriting: Replace a domain name in the R-URI with another domain name.
3. Port rewriting: Change the port number in the R-URI.
4. Path rewriting: Modify the path part of the R-URI.

The rewrite_uri function takes three arguments:

1. uri: The original R-URI.
2. new_uri: The new R-URI to be written.
3. flags: Optional flags that control the rewriting process.

Here's an example of how to use the rewrite_uri function in a Kamailio script:

route {
   ...
    rewrite_uri("sip:olddomain.com;transport=udp", "sip:newdomain.com;transport=tcp", lr);
   ...
}

In this example, the rewrite_uri function is used to replace the oldomain.com domain with newdomain.com in the R-URI, and also change the transport protocol from UDP to TCP.

The lr flag stands for "loopback" and is used to indicate that the rewriting should be done in a loopback manner, i.e., the rewritten R-URI should be used as the new R-URI for the next hop.

You can also use regular expressions to match and replace parts of the R-URI using the regmatch and regsub functions:

route {
   ...
    regmatch("sip:([^;]+);transport=udp", "sip:$1;transport=tcp", uri);
   ...
}

In this example, the regular expression sip:([^;]+);transport=udp matches the R-URI and captures the domain name (everything before the first ;) using a capture group (([^;]+)). The regsub function is then used to replace the captured group with the new domain name, resulting in the rewritten R-URI.

These are just a few examples of how you can use the rewrite_uri function in Kamailio. The possibilities are endless, and the function is a powerful tool for manipulating SIP messages in your Kamailio script.