svxreflector: side-effecting calls inside assert() are compiled out under -DNDEBUG (empty UDP datagrams, broken cipher AAD)

[MarkRose]

Summary

Several side-effecting calls in the reflector are wrapped in assert(...). When the project is compiled with -DNDEBUG (i.e. any optimized/release build, which is what most distributions ship), assert() expands to nothing and the calls — along with their side effects — are removed entirely. This silently breaks reflector behavior in release builds.

Location

src/svxlink/reflector/Reflector.cpp:

415:    assert(header.pack(ss) && msg.pack(ss));   // sendUdpDatagram(), proto >= 3.0 branch
436:    assert(header.pack(ss) && msg.pack(ss));   // sendUdpDatagram(), V2 branch
911:  assert(m_aad.unpack(ss));                    // udpCipherDataReceived()
1017:      assert(aadss.seekg(0));                 // udpDatagramReceived()
1024:      assert(iaad.iv_cntr == 0);             // udpDatagramReceived()  (see note)

Impact (in a -DNDEBUG build)

• Lines 415 / 436 — the outgoing message is never serialized into ss, so the reflector transmits empty UDP datagrams.
• Line 911 — the AAD is never unpacked, breaking UDP cipher handling.
• Line 1017 — the stream is never rewound, so the following InitialAAD unpack reads from the wrong offset.

These are functional-correctness failures that appear only in release builds and not in debug builds, which makes them easy to miss.

Separately, line 1024 asserts on attacker-controlled datagram content (iaad.iv_cntr). In a debug build a malformed initial-AAD datagram aborts the process (a remote DoS); it should be validated and rejected, not asserted.

Suggested fix

Replace each side-effecting assert() with an explicit call whose result is checked and handled, e.g.:

if (!header.pack(ss) || !msg.pack(ss))
{
  std::cout << "*** WARNING: Packing UDP datagram failed for "
            << udp_addr << ":" << udp_port << std::endl;
  return false;
}

if (!m_aad.unpack(ss)) { /* log + ignore datagram */ return true; }

aadss.seekg(0);

and convert assert(iaad.iv_cntr == 0) into a normal validation that drops the datagram when the check fails.