### Description fix_nated_contact() and removing and appending a contact will malform the SIP packet. I read somewhere that all of the *_hf functions are applied only when the packet is sent out again. Perhaps things are working as intended and I am just asking too much of these functions.

#### Reproduction In my onreply_route for 200 OK with SDP:

fix_nated_contact(); #dlg_setflag(1); # I want the contact in the dialog table to be the fixed one #Then I want to replace that contact with a contact to Kamailio's public IP and route it to Asterisk #for ACK response. This contact must be here for Asterisk to relay this back to me. remove_hf("Contact"); append_hf("Contact: sip:$sel(cfg_get.global.publicIP):5060\r\n"); # insert_hf same problem

### Troubleshooting This results in two contacts, but does not malform. remove_hf after the nat_fix_contact is the issue. fix_nated_contact(); insert_hf("Contact: sip:$sel(cfg_get.global.publicIP):5060\r\n");

#### SIP Traffic The inbound 200 OK CSeq: 9865 INVITE Contact: sip:424242143@devicePrivateIP:5060 Content-Type: application/sdp

After fix_nated_contact(); remove_hf("Contact"); append_hf("Contact: sip:serverIP:5060\r\n"); CSeq: 9865 INVITE sip:424242143@devicePublicIP:1026Content-Type: application/sdp

### Possible Solutions

I managed to get the functionality I wanted with either of these, but they result in two contact headers. I have also noticed that a remove->append->remove->append ignores the remove between appends.

Workaround 1 remove_hf("Contact"); insert_hf("Contact: sip:$tU@$si:$sp\r\n"); dlg_setflag(1); insert_hf("Contact: sip:$sel(cfg_get.global.publicIP):5060\r\n");

Workaround 2 fix_nated_contact(); dlg_setflag(1); insert_hf("Contact: sip:$sel(cfg_get.global.publicIP):5060\r\n");

### Additional Information

* **Kamailio Version**: kamailio 4.4.5 (x86_64/linux) f98162

* **Operating System**: Linux 3.10.0-514.2.2.el7.x86_64 # 1 SMP Tue Dec 6 23:06:41 UTC 2016 x86_64 x86_64 x86_64 GNU/Linux