QuincyGao created an issue (kamailio/kamailio#4190)

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### Description

<!-- Explain what you did, what you expected to happen, and what actually happened. --> I want to use opensips as SBC, When the agent registers to kamailio, the contact content is modified to the ip and port of kamailio, and then Register is forwarded to the agent.

remove_hf("Contact") can't remove the whole Contact( field, vlue).

here is my config: ``` route[REGISTRAR] { if (!is_method("REGISTER")) return;

if(isflagset(FLT_NATS)) { setbflag(FLB_NATB); #!ifdef WITH_NATSIPPING # do SIP NAT pinging setbflag(FLB_NATSIPPING); #!endif } fix_nated_contact(); if (!save("location","0x02")) { #if (!save("location")) { sl_reply_error(); } $fs="udp:172.16.4.111:5461"; $du="sip:172.16.4.114:5060"; remove_hf("Contact"); $var(contact) = "Contact: <sip:" +$fU+"@"+"172.16.4.111:5461>;expires=120\r\n" ; append_hf("$var(contact)"); route(RELAY); exit; } ``` here is the sip message: ``` 2025/03/26 16:36:07.706093 172.16.4.111:5461 -> 172.16.4.114:5060 REGISTER sip:172.16.4.111:5460 SIP/2.0 Via: SIP/2.0/UDP 172.16.4.111:5461;branch=z9hG4bKfc7e.d2df36f3b5681afeb71e442e645de38d.0 Via: SIP/2.0/UDP 172.16.80.3:49309;received=172.16.80.3;rport=49309;branch=z9hG4bKPj8ab8bd1d3c3a4c1bb0cd639540fa3183 Max-Forwards: 69 From: sip:1008@172.16.4.111;tag=95f7f5601f8b40458a1efe6923ab0a29 To: sip:1008@172.16.4.111 Call-ID: f84b643f5d284d18a0d8175e1ef4d747 CSeq: 33264 REGISTER User-Agent: MicroSIP/3.21.6 sip:1008@172.16.80.3:49309;obExpires: 120 Allow: PRACK, INVITE, ACK, BYE, CANCEL, UPDATE, INFO, SUBSCRIBE, NOTIFY, REFER, MESSAGE, OPTIONS Content-Length: 0 Contact: sip:1008@172.16.4.111:5461;expires=120 ``` you can see the problem is that: `sip:1008@172.16.80.3:49309;obExpires: 120` , `sip:1008@172.16.80.3:49309` is the value of the Contact field after fix_nated_contact(). ### Troubleshooting

#### Reproduction

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#### Debugging Data

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``` (paste your debugging data here) ```

#### Log Messages

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#### SIP Traffic

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``` (paste your sip traffic here) ```

### Possible Solutions

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### Additional Information

* **Kamailio Version** - output of `kamailio -v`

``` version: kamailio 5.8.5 (x86_64/linux) flags: USE_TCP, USE_TLS, USE_SCTP, TLS_HOOKS, USE_RAW_SOCKS, DISABLE_NAGLE, USE_MCAST, DNS_IP_HACK, SHM_MMAP, PKG_MALLOC, MEM_JOIN_FREE, Q_MALLOC, F_MALLOC, TLSF_MALLOC, DBG_SR_MEMORY, USE_FUTEX, FAST_LOCK-ADAPTIVE_WAIT, USE_DNS_CACHE, USE_DNS_FAILOVER, USE_NAPTR, USE_DST_BLOCKLIST, HAVE_RESOLV_RES, TLS_PTHREAD_MUTEX_SHARED ADAPTIVE_WAIT_LOOPS 1024, MAX_RECV_BUFFER_SIZE 262144, MAX_SEND_BUFFER_SIZE 262144, MAX_URI_SIZE 1024, BUF_SIZE 65535, DEFAULT PKG_SIZE 8MB poll method support: poll, epoll_lt, epoll_et, sigio_rt, select. id: compiled on 11:27:01 Mar 21 2025 with gcc 4.8.5

```

* **Operating System**:

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``` Centos7.9 ```