This commit adds a new test file, `tests/test_cli.py`, containing
unit tests for the `_os_timezone` function in `netsleuth.cli`.
The tests cover:
- Happy paths (TZ variable, /etc/localtime symlink, /etc/timezone file)
- The edge case of an `OSError` exception being thrown when reading the
/etc/timezone file.
Co-authored-by: Horizontal42 <75383519+Horizontal42@users.noreply.github.com>
Stayed unprivileged on both platforms deliberately. Windows: echo_once()
gained a df: bool param setting IP_FLAG_DF on the IP_OPTION_INFORMATION
struct's Flags field (present but unused until now), and classify_status()
learned IP_PACKET_TOO_BIG (11009) - the same unprivileged IcmpSendEcho2
API the rest of the ICMP tier already uses, no new capability needed.
Unix deliberately does not hand-roll raw ICMP echo requests - unprivileged
SOCK_DGRAM/IPPROTO_ICMP checksum and identifier handling varies enough
across kernel versions that shipping it without a Linux/macOS box to
verify on felt like the wrong risk to take. Shells out to system
ping -M do -s <size> (Linux) / ping -D -s <size> (macOS/BSD) instead,
the same subprocess-and-parse pattern traceroute.py's system tiers
already use. Matches "frag"/"too long" loosely in the output rather than
an exact phrase, since a locally-cached-PMTU failure and a genuine
on-path ICMP response word themselves differently across ping
implementations - same "parse by shape" principle traceparse.py already
established.
classify_pmtu() distinguishes a path that's just narrower (a frag-needed
signal was seen - PMTUD is working, normal behind a VPN) from an actual
blackhole (large packets vanish with no ICMP reply at all - the "SSH
connects then hangs" symptom). path.pmtu_below_iface_mtu flags separately
when the path MTU is narrower than the local NIC's own MTU, which is
exactly what makes this class of problem invisible locally.
Opt-in --pmtud, excluded from --full. Live-verified on Windows against
real cloudflare.com/google.com - found the full 1500-byte MTU in 11
probes each, matching the expected binary-search depth, correct probe
history in the JSON output.
Part of plans/zesty-zooming-wilkinson.md (gitignored).
