Query Logs (PostgreSQL): strip null bytes from answer field before insert

[daedaevibin]

Closes #2048

Problem

The Query Logs (PostgreSQL) app throws Npgsql.PostgresException (22021) when bulk-inserting DNS query logs containing null bytes (0x00) in the answer field. PostgreSQL rejects these as invalid UTF-8, causing the entire batch insert to fail and query logs to be lost.

Reproduction

1. Create a TXT record with a null byte via the API:

curl -sk 'https://server:7742/api/zones/records/add' \
  -H 'Authorization: Bearer <token>' \
  -d 'domain=null.test.local&zone=test.local&type=TXT&characterStringsBase64=aGVsbG8Ad29ybGQ='

2. Query it through the DNS server: dig @127.0.0.1 null.test.local TXT

3. The query log app throws:

Npgsql.PostgresException (0x80004005): 22021: invalid byte sequence for encoding "UTF8": 0x00
  Where: unnamed portal parameter $11

Root Cause

DnsTXTRecordData.ToZoneFileEntry() calls Encoding.UTF8.GetString() on raw TXT record bytes. When the wire data contains 0x00, this produces a C# string with an embedded null character. Npgsql passes it to PostgreSQL which rejects it.

QNAME is safe — the DNS wire format prevents null bytes in domain names. Only the answer field (built from record.RDATA.ToString()) is affected.

Fix

Strip null bytes from the answer field in BulkInsertLogsAsync before passing it as a Npgsql parameter:

paramAnswer.Value = answer?.Replace("\0", "");

Verified

• Full solution build succeeds (TechnitiumLibrary + DnsServer)
• Reproduction confirmed on Technitium DNS Server v15.4 with PostgreSQL

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Note: I tested this against a live v15.4 instance. The null byte only appeared in the answer field during reproduction; other fields were clean.