add REFER handling

kamailio/default.cfg

@@ -344,6 +344,8 @@ route
     route(HANDLE_REGISTER);
     #!endif
 
+    route(HANDLE_REFER);
+
     route(HANDLE_IN_DIALOG_REQUESTS);
 
     route(PREPARE_INITIAL_REQUESTS);
@@ -526,6 +528,26 @@ route[HANDLE_MESSAGE]
     #!endif
 }
 
+route[HANDLE_REFER]
+{
+    if (!is_method("REFER")) {
+        return;
+    }
+
+    if(is_present_hf("Referred-By")) {
+       $var(referred_by) = $hdr(Referred-By);
+    } else {
+       $var(referred_by) = $_s(<sip:$Au>;created=true);
+    }
+    $xavp(regcfg=>match_received) = $su;
+    if(registered("location", "$rz:$Au", 2, 1) == 1) {
+        $var(referred_by) = $_s($var(referred_by);endpoint_id=$(xavp(ulattrs=>token){re.subst,/(.*)@(.*)/\1/});account_id=$(xavp(ulattrs=>token){re.subst,/(.*)@(.*)/\2/}));
+    }
+
+    remove_hf_re("^Referred-By");
+    append_hf("Referred-By: $var(referred_by)\r\n");
+
+}
 
 route[HANDLE_IN_DIALOG_REQUESTS]
 {