SIP Redirect via Proxy (SIP.js)

Question

I'm trying to create a minimal SIP Proxy that serves one purpose: redirects requests to another domain. The catch is the domain I'm redirecting to requires authorization so I assume I need to rewrite some SIP attributes since SIP authorization is based partly on the domain name of the destination.

I've tried issuing a 302 redirect as well as simply proxying and changing the values of each SIP request but none seem to quit do the trick. I'm using a node.js library (sip.js) and have tried the redirect and proxy modules (https://github.com/kirm/sip.js/blob/master/doc/api.markdown).

Any ideas exactly how I need to modify the SIP data to redirect requests to another domain and enable authentication to take place against that other domain?

Answer 1

Below is a basic node script I got working with my own SIP server. You'll need to replace the credentials and IP address fro your own testing.

The proxy script does not send a redirect response to the client but instead initiates a new transaction to the server on the client's behalf. A SIP server operating in this mode is more correctly called a Back-to-Back User Agent (B2BUA). I haven't added all the functionality needed, such as matching up and passing responses back to the original client; there is a fair bit of work involved in that.

var sip = require('sip');
var digest = require('sip/digest');
var util = require('util');
var os = require('os');
var proxy = require('sip/proxy');

var registry = {
  'user': { user: "user", password: "password", realm: "sipserver.com"},
};

function rstring() { return Math.floor(Math.random()*1e6).toString(); }

sip.start({
  address: "192.168.33.116", // If the IP is not specified here the proxy uses a hostname in the Via header which will causes an issue if it's not fully qualified.
  logger: { 
    send: function(message, address) { debugger; util.debug("send\n" + util.inspect(message, false, null)); },
    recv: function(message, address) { debugger; util.debug("recv\n" + util.inspect(message, false, null)); }
  }
},
function(rq) {
  try {
    if(rq.method === 'INVITE') {  

       proxy.send(sip.makeResponse(rq, 100, 'Trying'));

      //looking up user info
      var username = sip.parseUri(rq.headers.to.uri).user;    
      var creds = registry[username];

      if(!creds) {  
        proxy.send(sip.makeResponse(rq, 404, 'User not found'));
      }
      else {
        proxy.send(rq, function(rs) {

            if(rs.status === 401) {

                // Update the original request so that it's not treated as a duplicate.
                rq.headers['cseq'].seq++;
                rq.headers.via.shift ();
                rq.headers['call-id'] = rstring();

                digest.signRequest(creds, rq, rs, creds);

                proxy.send(rq);
            }
        });
      }
    }
    else {
      proxy.send(sip.makeResponse(rq, 405, 'Method Not Allowed'));
    }
  } catch(e) {
    util.debug(e);
    util.debug(e.stack);

   proxy.send(sip.makeResponse(rq, 500, "Server Internal Error"));
  }
});