xadhoom created an issue (kamailio/kamailio#4203)

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### Description

Enabled json logging engine, with the following setup: - kam cmd line params: `--log-engine=json:Mp` - prefix: `log_prefix=", "callid": "$ci","srcip": "$si", "ts": $TV(Sn), "method": "$rm", "mt": $mt, "ua": "$(ua{s.escape.common})", "cseq": "$hdr(CSeq)", "status": $rs "` - another prefix (same result): `log_prefix=", "callid": "$ci", "ts": $TV(Sn) "`

What I see that certain json lines are truncated, for example - one line is interrupted by another json entry - one line starts "truncated"

### Troubleshooting What I can observe is that seems to happens always with same "kind" of line, usually internal logs, which don't have callid etc.

#### Log Messages

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The following first 3 lines are ok, then the latest is corrupted: ``` { "time": "2025-04-04T15:51:44.448427533Z", "idx": 193, "pid": 200, "level": "DEBUG", "module": "core", "file": "core/receive.c", "line": 128, "function": "sip_check_fline", "message": "first line indicates a SIP reply" } { "time": "2025-04-04T15:51:44.448682606Z", "idx": 194, "pid": 201, "level": "DEBUG", "module": "core", "file": "core/receive.c", "line": 128, "function": "sip_check_fline", "message": "first line indicates a SIP reply" } { "time": "2025-04-04T15:52:14.448279053Z", "idx": 195, "pid": 202, "level": "DEBUG", "module": "core", "file": "core/receive.c", "line": 128, "function": "sip_check_fline", "message": "first line indicates a SIP reply" } { "time": "2025-04-04T15:52:14.448505797Z", "idx": 196, "pid": 203, "level": "DEBUG", "module": "core", "file": "core/receive.c"{ "time": "2025-04-04T15:52:14.448508084Z", "idx": 195, "pid": 202, "level": "DEBUG", "module": "core", "file": "core/parser/msg, "line": 128, "function": "sip_check_fline", "message": "first line indicates a SIP reply" } ```

or (notice 2nd line or 5th one)

``` { "time": "2025-04-04T16:13:33.789641936Z", "idx": 221, "pid": 228, "level": "DEBUG", "module": "core", "file": "core/receive.c"{ "time": "2025-04-04T16:13:33.789642978Z", "idx": 222, "pid": 229, "level": "DEBUG", "module": "core", "file": "core/xavp.c", ", "line": 265, "function": "ksr_evrt_pre_routing", "callid": "5715efe40e9b7721-264@127.0.0.1", "ts": 1743783213.789640 , "message": "event route core:pre-routing not defined" } line": 630, "function": "xavp_destroy_list", "callid": "5715efe40e9b7720-264@127.0.0.1", "ts": 1743783213.789527 , "message": "destroying xavp list (nil)" } { "time": "2025-04-04T16:13:33.789646470Z", "idx": 222, "pid": 229, "level": "DEBUG", "module": "core", "file": "core/xavp.c", "line": 630, "function": "xavp_destroy_list", "callid": "5715efe40e9b7720-264@127.0.0.1", "ts": 1743783213.789527 , "message": "destroying xavp list (nil)" } { "time": "2025-04-04T16:13:33.789648201Z", "idx": 221, "pid": 228, "level": "DEBUG", "module": "tm", "file": "t_lookup.c", "line": 1579, "function": "t_check_msg", "callid": "5715efe40e9b7721-264@127.0.0.1", "ts": 1743783213.789640 , "message": "msg (0x7f{ "time": "2025-04-04T16:13:33.789649346Z", "idx": 222, "pid": 229, "level": "DEBUG", "module": "core", "file": "core/receive.c"8f7a693c50) id=2/228 global id=1/228 T start=0xffffffffffffffff" } , "line": 637, "function": "receive_msg", "callid": "5715efe40e9b7720-264@127.0.0.1", "ts": 1743783213.789527 , "message": "cleaning up" } { "time": "2025-04-04T16:13:33.789652839Z", "idx": 221, "pid": 228, "level": "DEBUG", "module": "tm", "file": "t_lookup.c", "line": 1424, "function": "t_reply_matching", "callid": "5715efe40e9b7721-264@127.0.0.1", "ts": 1743783213.789640 , "message": "t_reply_matching: hash 26404 label 0 branch 0" } ```

### Additional Information

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

``` 6.0.1 ```

happens also with 5.8.x

* **Operating System**:

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``` Debian noble, docker container ```