feat: report listening sockets

get_listening_sockets() in the shape of napalm-device-types'
ListeningSocketsMixin, whose ss/cgroup reading is Linux's, and with its
rule: read as root first, and without root when that brings nothing back,
which the reading reports as `attributed: False`.

- FreeBSD: `sockstat -46lq -P tcp,udp`, which sees every socket either way.
- OpenBSD: `fstat -n` as root (the sockets nothing is connected to; port 0
  is unbound), `netstat -an` without root, as fstat shows a user only
  their own processes; those sockets come without a process.
- Addresses as ss prints them: `*` becomes 0.0.0.0 or :: by family, IPv6
  without brackets, a zone (`fe80::1%lo0`) becomes the interface. One entry
  per socket, the first process holding it.

No get_kernel_facts on purpose: KernelFactsMixin reports a Linux kernel's
modules and CONFIG_ options, which a BSD kernel does not have.

Fixtures recorded on the FreeBSD 15.1 and OpenBSD 7.9 VMs with test
listeners on 127.0.0.1 and ::1 (NetOrk/netork#798).

tests/test_parse.py

@@ -213,3 +213,59 @@ class TestBoottime:
 
     def test_garbage(self):
         assert parse.boottime("sysctl: unknown oid") is None
+
+
+class TestListeningSockets:
+    """In the shape of napalm-device-types' ListeningSocketDict: ``0.0.0.0`` and
+    ``::`` are every address of their family, as ``ss`` prints them."""
+
+    @staticmethod
+    def _keys(sockets):
+        return {(s["proto"], s["address"], s["port"], s["interface"]) for s in sockets}
+
+    def test_freebsd_sockstat(self):
+        sockets = parse.sockstat(fixture("freebsd-vm", "sudo_sockstat_46lq_P_tcp_udp.txt"))
+        assert self._keys(sockets) == {
+            ("udp", "127.0.0.1", 7779, None),
+            ("tcp", "::1", 7777, None),
+            ("tcp", "127.0.0.1", 7778, None),
+            ("tcp", "::", 22, None),
+            ("tcp", "0.0.0.0", 22, None),
+            ("udp", "::", 514, None),
+            ("udp", "0.0.0.0", 514, None),
+        }
+        sshd = next(s for s in sockets if s["port"] == 22 and s["address"] == "0.0.0.0")
+        assert (sshd["process"], sshd["pid"], sshd["unit"], sshd["container_id"]) == (
+            "sshd",
+            1282,
+            None,
+            None,
+        )
+
+    def test_openbsd_fstat_keeps_only_listening_and_bound_sockets(self):
+        sockets = parse.fstat_sockets(fixture("openbsd-vm", "sudo_fstat_n.txt"))
+        keys = self._keys(sockets)
+        assert ("tcp", "0.0.0.0", 22, None) in keys
+        assert ("tcp", "::", 22, None) in keys
+        assert ("tcp", "::1", 25, None) in keys
+        assert ("tcp", "fe80::1", 25, "lo0") in keys
+        assert ("udp", "10.0.2.15", 68, None) in keys
+        assert ("udp", "127.0.0.1", 7779, None) in keys
+        # connected (ntpd, ssh sessions) and unbound (*:0) sockets are not listening
+        assert not any(s["port"] in (0, 123) or s["process"] == "sshd-session" for s in sockets)
+        smtpd = next(s for s in sockets if s["port"] == 25 and s["address"] == "127.0.0.1")
+        assert (smtpd["process"], smtpd["pid"]) == ("smtpd", 69044)
+
+    def test_openbsd_netstat_without_root_names_no_process(self):
+        sockets = parse.netstat_listening(fixture("openbsd-vm", "netstat_an.txt"))
+        keys = self._keys(sockets)
+        assert ("tcp", "0.0.0.0", 22, None) in keys
+        assert ("tcp", "::", 22, None) in keys
+        assert ("tcp", "fe80::1", 25, "lo0") in keys
+        assert ("udp", "127.0.0.1", 7779, None) in keys
+        assert all(s["process"] is None and s["pid"] is None for s in sockets)
+        assert not any(s["port"] == 123 for s in sockets)  # ntpd's connected sockets
+
+    def test_a_socket_held_by_two_processes_is_listed_once(self):
+        text = "www nginx 901 6 tcp4 *:80 *:*\nwww nginx 900 6 tcp4 *:80 *:*\n"
+        assert [(s["pid"]) for s in parse.sockstat(text)] == [901]