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

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