tests: topotest for ZEBRA_BFD_DEST_REGISTER SBFD tail

Verifies the wire-payload extension landed in the previous patch.
The test process spawns a Python ZAPI client inside r1's network
namespace, performs the ZEBRA_HELLO / ZEBRA_BFD_CLIENT_REGISTER /
ZEBRA_BFD_DEST_REGISTER handshake against zebra, and asserts that
bfdd's session table reflects what was sent.

Three cases:

* test_zapi_sbfd_register_creates_session - register frame carries
  the full SBFD tail (bfd_regext_flags + bfd_mode + remote_discr +
  srv6_source_ipv6 + seg_list[2] + bfd_name="zapi-sbfd-test").
  Asserts a bfdd peer with the expected destination materialises
  and that bfd_name was preserved through the tail.

* test_zapi_classical_register_still_accepted - register frame omits
  the SBFD tail entirely (no flags word), exercising both the encoder
  gate (lib/bfd.c emits no tail when bfd_regext_flags == 0) and the
  decoder's STREAM_READABLE-gated tail handling.

* test_zapi_sbfd_register_deduplicates_by_bfd_name - repeats the
  SBFD register from the first test and asserts the peer count for
  the same destination does not grow. This catches a key-table
  asymmetry (bs_peer_find uses bpc->bfd_name in the lookup key, so
  ptm_bfd_sess_new must populate bs->key.bfdname on insert - see
  the production change in the previous patch).

Author: rajshekhar-nexthop

tests/topotests/bfd_zapi_sbfd_topo1/__init__.py

@@ -0,0 +1,7 @@
+hostname r1
+!
+interface r1-eth0
+ ipv6 address 2001:db8:1::1/64
+!
+bfd
+!

tests/topotests/bfd_zapi_sbfd_topo1/r1/frr.conf

@@ -0,0 +1,381 @@
+#!/usr/bin/env python
+#
+# test_bfd_zapi_sbfd_topo1.py
+#
+# Verifies the ZAPI wire-payload extension: a ZEBRA_BFD_DEST_REGISTER
+# message that carries the appended SBFD/SRv6 tail (bfd_mode, remote_discr,
+# srv6_source_ipv6, seg_num, seg_list[], bfd_name) is decoded by bfdd and the
+# resulting bfd_session reflects those fields. A second register without the
+# SBFD tail acts as a back-compatibility regression check that the previous wire format
+# senders are still accepted.
+#
+# Topology: single router r1 running zebra + bfdd. The test process opens
+# zebra's ZAPI socket from inside r1's namespace via r1.popen("python3 -c"),
+# performs the ZEBRA_HELLO + ZEBRA_BFD_CLIENT_REGISTER + ZEBRA_BFD_DEST_REGISTER
+# handshake, and then asserts the bfdd-side session state via vtysh.
+
+import json
+import os
+import sys
+import time
+
+import pytest
+
+CWD = os.path.dirname(os.path.realpath(__file__))
+sys.path.append(os.path.join(CWD, "../"))
+
+# pylint: disable=C0413
+from lib.common_config import required_linux_kernel_version
+from lib.topogen import Topogen, TopoRouter, get_topogen
+
+pytestmark = [pytest.mark.bfdd]
+
+
+# ZAPI wire-protocol constants — mirror lib/zclient.h / lib/route_types.txt.
+ZSERV_PATH = "/var/run/frr/zserv.api"
+ZEBRA_HEADER_MARKER = 254
+ZSERV_VERSION = 6
+ZEBRA_HEADER_SIZE = 10  # length(2)+marker(1)+version(1)+vrf(4)+command(2)
+
+# Subset of `enum zclient_msg_type` from lib/zclient.h. Counted positionally
+# from ZEBRA_INTERFACE_ADD (=0). Verified against FRR base commit
+# 25d64c41b8 (origin/frr-10.4.1 at the time of this patch); re-verify on
+# each upstream FRR rebase with:
+#   grep -nE '^[[:space:]]+ZEBRA_(HELLO|BFD_DEST_REGISTER|BFD_CLIENT_REGISTER),' \
+#         lib/zclient.h
+# A stale value will produce no protocol NAK from zebra — the test fails as
+# a `_wait_for_peer` timeout rather than a wire-level error.
+ZEBRA_HELLO = 19
+ZEBRA_BFD_DEST_REGISTER = 27
+ZEBRA_BFD_CLIENT_REGISTER = 35
+
+# enum bfd_mode_type from bfdd/bfd.h.
+BFD_MODE_TYPE_BFD = 0
+BFD_MODE_TYPE_SBFD_INIT = 2
+
+# Position of ZEBRA_ROUTE_SHARP in lib/route_types.txt — we identify as
+# sharpd, the canonical dev/test ZAPI client.
+ZEBRA_ROUTE_SHARP = 23
+
+VRF_DEFAULT = 0
+
+
+def build_topo(tgen):
+    tgen.add_router("r1")
+    sw = tgen.add_switch("s1")
+    sw.add_link(tgen.gears["r1"])
+
+
+def setup_module(mod):
+    tgen = Topogen(build_topo, mod.__name__)
+    tgen.start_topology()
+    for rname, router in tgen.routers().items():
+        router.load_frr_config(
+            os.path.join(CWD, "{}/frr.conf".format(rname)),
+            [(TopoRouter.RD_ZEBRA, None), (TopoRouter.RD_BFD, None)],
+        )
+    tgen.start_router()
+
+
+def teardown_module(mod):
+    get_topogen().stop_topology()
+
+
+# Inline Python script that runs inside r1's namespace, opens the ZAPI
+# socket, performs the BFD client handshake, and emits one
+# ZEBRA_BFD_DEST_REGISTER. Two forms are exercised, selected by argv[1]:
+#   "sbfd"      — appends the SBFD tail (bfd_mode/seg_num/bfd_name).
+#   "classical" — omits the tail entirely, mimicking a sender without the SBFD tail.
+# Exit code 0 indicates the socket exchange succeeded; non-zero plus a
+# diagnostic on stderr indicates a wire-level failure.
+ZAPI_CLIENT_SCRIPT = r"""
+import os, socket, struct, sys, time
+
+ZSERV_PATH = "/var/run/frr/zserv.api"
+ZEBRA_HEADER_MARKER = 254
+ZSERV_VERSION = 6
+ZEBRA_HEADER_SIZE = 10
+
+ZEBRA_HELLO = 19
+ZEBRA_BFD_DEST_REGISTER = 27
+ZEBRA_BFD_CLIENT_REGISTER = 35
+
+BFD_MODE_TYPE_SBFD_INIT = 2
+ZEBRA_ROUTE_SHARP = 23
+VRF_DEFAULT = 0
+
+
+def header(command, vrf_id=VRF_DEFAULT):
+    return struct.pack(
+        "!HBBIH", ZEBRA_HEADER_SIZE, ZEBRA_HEADER_MARKER, ZSERV_VERSION,
+        vrf_id, command,
+    )
+
+
+def finalize(buf):
+    # length prefix at offset 0 covers the whole frame
+    return struct.pack("!H", len(buf)) + buf[2:]
+
+
+def send(sock, buf):
+    sock.sendall(finalize(buf))
+
+
+def hello(sock):
+    buf = bytearray(header(ZEBRA_HELLO))
+    buf += struct.pack("!B", ZEBRA_ROUTE_SHARP)     # redist_default
+    buf += struct.pack("!H", 0)                     # instance
+    buf += struct.pack("!I", 0)                     # session_id
+    buf += struct.pack("!B", 0)                     # synchronous=false
+    send(sock, buf)
+
+
+def bfd_client_register(sock):
+    buf = bytearray(header(ZEBRA_BFD_CLIENT_REGISTER))
+    buf += struct.pack("!I", os.getpid())
+    send(sock, buf)
+
+
+def bfd_dest_register(sock, kind, dst_addr):
+    # Mirrors lib/bfd.c::zclient_bfd_command, HAVE_BFDD path. Encodes a
+    # multihop IPv6 register so the body length is identical between the
+    # SBFD and classical variants up to the appended tail.
+    buf = bytearray(header(ZEBRA_BFD_DEST_REGISTER))
+    buf += struct.pack("!I", os.getpid())
+
+    dst = socket.inet_pton(socket.AF_INET6, dst_addr)
+    src = socket.inet_pton(socket.AF_INET6, "2001:db8:1::1")
+
+    # Layout per lib/bfd.c::zclient_bfd_command (HAVE_BFDD path).
+    # min_rx/min_tx are uint32; detection_multiplier, mhop, hops, ifname_len,
+    # cbit and profile_len are each uint8. The stream_putc/stream_putl mix
+    # is easy to misencode from Python; keep the sizes lined up below.
+    buf += struct.pack("!H", socket.AF_INET6) + dst       # dst family + addr
+    buf += struct.pack("!II", 300000, 300000)             # min_rx, min_tx
+    buf += struct.pack("!B", 3)                           # det_mult
+    buf += struct.pack("!B", 1)                           # is_multihop = 1
+    buf += struct.pack("!H", socket.AF_INET6) + src       # src family + addr
+    buf += struct.pack("!B", 1)                           # hops/ttl
+    buf += struct.pack("!B", 0)                           # ifname_len = 0 (mhop)
+    buf += struct.pack("!B", 0)                           # cbit
+    buf += struct.pack("!B", 0)                           # profile_len = 0
+
+    if kind == "sbfd":
+        # Optional-field tail with BFD_REGEXT_FLAG_* indicating which fields
+        # follow. Mirrors the encoder in lib/bfd.c::zclient_bfd_command.
+        BFD_REGEXT_FLAG_BFD_MODE     = 0x0001
+        BFD_REGEXT_FLAG_REMOTE_DISCR = 0x0002
+        BFD_REGEXT_FLAG_SRV6_SOURCE  = 0x0004
+        BFD_REGEXT_FLAG_SEG_LIST     = 0x0008
+        BFD_REGEXT_FLAG_BFD_NAME     = 0x0010
+
+        seg_list = [
+            socket.inet_pton(socket.AF_INET6, "2001:db8:a::100"),
+            socket.inet_pton(socket.AF_INET6, "2001:db8:a::200"),
+        ]
+        bfd_name = b"zapi-sbfd-test"
+
+        flags = (BFD_REGEXT_FLAG_BFD_MODE
+                 | BFD_REGEXT_FLAG_REMOTE_DISCR
+                 | BFD_REGEXT_FLAG_SRV6_SOURCE
+                 | BFD_REGEXT_FLAG_SEG_LIST
+                 | BFD_REGEXT_FLAG_BFD_NAME)
+        buf += struct.pack("!H", flags)                     # bfd_regext_flags
+        buf += struct.pack("!B", BFD_MODE_TYPE_SBFD_INIT)   # bfd_mode
+        buf += struct.pack("!I", 0x000186A0)                # remote_discr = 100000
+        buf += src                                          # srv6_source_ipv6
+        buf += struct.pack("!B", len(seg_list))             # seg_num
+        for sid in seg_list:
+            buf += sid
+        buf += struct.pack("!B", len(bfd_name)) + bfd_name
+    elif kind == "classical":
+        # A sender without the optional tail: no tail bytes at all.
+        pass
+    else:
+        raise SystemExit("unknown kind {!r}".format(kind))
+
+    send(sock, buf)
+
+
+def main():
+    if len(sys.argv) != 3:
+        raise SystemExit("usage: {} sbfd|classical <dst-ipv6>".format(sys.argv[0]))
+    kind = sys.argv[1]
+    dst_addr = sys.argv[2]
+
+    deadline = time.time() + 10.0
+    while time.time() < deadline:
+        try:
+            sock = socket.socket(socket.AF_UNIX, socket.SOCK_STREAM)
+            sock.connect(ZSERV_PATH)
+            break
+        except (FileNotFoundError, ConnectionRefusedError, OSError) as exc:
+            last_err = exc
+            time.sleep(0.2)
+    else:
+        raise SystemExit("zserv connect failed: {}".format(last_err))
+
+    try:
+        hello(sock)
+        bfd_client_register(sock)
+        bfd_dest_register(sock, kind, dst_addr)
+        # Give zebra a beat to forward the register to bfdd before we close.
+        time.sleep(0.5)
+    finally:
+        sock.close()
+
+
+main()
+"""
+
+
+def _run_zapi_client(net_node, kind, dst_addr):
+    """Run the inline ZAPI client inside `net_node`'s network namespace.
+
+    `net_node` is the mininet Router (tgen.net[name]) — it exposes `cmd`
+    without the higher-level TopoRouter wrappers. The inline script
+    raises SystemExit on ZAPI handshake failure, but `cmd()` swallows
+    the exit code; we append a sentinel echo so the caller can surface
+    a real diagnostic instead of silently timing out at `_wait_for_peer`.
+    """
+    script = ZAPI_CLIENT_SCRIPT.replace("'", "'\\''")
+    output = net_node.cmd(
+        "python3 -c '{}' {} {} 2>&1; echo __ZAPI_EXIT__=$?".format(
+            script, kind, dst_addr))
+    assert "__ZAPI_EXIT__=0" in output, (
+        "ZAPI client ({} -> {}) failed; output:\n{}".format(
+            kind, dst_addr, output))
+    return output
+
+
+def _show_bfd_peers(net_node):
+    """Read bfdd's session table as JSON; return list of peer dicts."""
+    raw = net_node.cmd("vtysh -c 'show bfd peers json'")
+    raw = raw.strip()
+    if not raw:
+        return []
+    return json.loads(raw)
+
+
+def _wait_for_peer(net_node, predicate, timeout=10.0):
+    """Poll `show bfd peers json` until predicate matches one peer."""
+    deadline = time.time() + timeout
+    last = []
+    while time.time() < deadline:
+        last = _show_bfd_peers(net_node)
+        for peer in last:
+            if predicate(peer):
+                return peer
+        time.sleep(0.3)
+    raise AssertionError(
+        "no bfd peer matched predicate within {}s; last seen: {}".format(
+            timeout, last))
+
+
+SBFD_DST = "2001:db8:2::1"
+CLASSICAL_DST = "2001:db8:2::2"
+
+
+def test_zapi_sbfd_register_creates_session():
+    """
+    Drive the new ZAPI tail end-to-end: a ZEBRA_BFD_DEST_REGISTER with
+    `bfd_mode=SBFD_INIT` + a non-empty `bfd_name` + a 2-SID seg_list
+    materialises as a bfdd session whose peer/source addresses match
+    what was sent. `bfd_name` being preserved through the tail is the
+    load-bearing assertion — it is the only new field already
+    surfaced by `show bfd peers json` without bfdd-side debug counters.
+    """
+    if required_linux_kernel_version("4.5") is not True:
+        pytest.skip("Kernel requirements are not met")
+
+    tgen = get_topogen()
+    if tgen.routers_have_failure():
+        pytest.skip(tgen.errors)
+
+    r1 = tgen.net["r1"]
+    _run_zapi_client(r1, "sbfd", SBFD_DST)
+
+    peer = _wait_for_peer(
+        r1, lambda p: p.get("peer") == SBFD_DST,
+    )
+    assert peer.get("bfd-name") == "zapi-sbfd-test", (
+        "bfd_name from ZAPI SBFD tail not preserved: {!r}".format(peer))
+
+
+def test_zapi_classical_register_still_accepted():
+    """
+    Back-compat: a register frame without the SBFD tail (the previous wire
+    format, and the extended wire format that classical-BFD callers like
+    BGP/OSPF continue to produce) must still create a
+    working bfdd session. The decoder's `STREAM_READABLE > 0` gate is
+    what enables this; the encoder's matching gate is what keeps
+    classical-BFD wire bytes byte-for-byte unchanged.
+    """
+    if required_linux_kernel_version("4.5") is not True:
+        pytest.skip("Kernel requirements are not met")
+
+    tgen = get_topogen()
+    if tgen.routers_have_failure():
+        pytest.skip(tgen.errors)
+
+    r1 = tgen.net["r1"]
+    _run_zapi_client(r1, "classical", CLASSICAL_DST)
+
+    peer = _wait_for_peer(
+        r1, lambda p: p.get("peer") == CLASSICAL_DST,
+    )
+    # Classical-BFD register: bfd_name was not carried, so the session
+    # comes up without one. (Default formatting may omit the key
+    # entirely or emit an empty string; accept both.)
+    assert not peer.get("bfd-name"), (
+        "classical register unexpectedly carries bfd-name: {!r}".format(peer))
+
+
+def test_zapi_sbfd_register_deduplicates_by_bfd_name():
+    """
+    Re-registering the *same* SBFD session — same peer/local/vrf/bfd_name
+    — must reuse the existing `bfd_session`. The load-bearing piece is
+    that `bs_peer_find` uses `bpc->bfd_name` in the key; for that lookup
+    to match the previously-inserted session, `ptm_bfd_sess_new` must
+    also have populated `bs->key.bfdname` (set by the SBFD register path). Without
+    that, a re-register would silently create a duplicate session and
+    bfdd's peer count would grow on every flap.
+
+    Self-contained: uses a distinct destination address so the test
+    does not depend on other tests' session state and can be reordered
+    or run in isolation.
+    """
+    if required_linux_kernel_version("4.5") is not True:
+        pytest.skip("Kernel requirements are not met")
+
+    tgen = get_topogen()
+    if tgen.routers_have_failure():
+        pytest.skip(tgen.errors)
+
+    r1 = tgen.net["r1"]
+    dedupe_dst = "2001:db8:2::3"
+
+    def count_with_dst(dst):
+        return sum(1 for p in _show_bfd_peers(r1) if p.get("peer") == dst)
+
+    # Issue two back-to-back identical SBFD registers; expect exactly
+    # one session afterwards.
+    _run_zapi_client(r1, "sbfd", dedupe_dst)
+    _wait_for_peer(r1, lambda p: p.get("peer") == dedupe_dst)
+    after_first = count_with_dst(dedupe_dst)
+    assert after_first == 1, (
+        "first SBFD register did not produce exactly one session "
+        "(got {})".format(after_first))
+
+    _run_zapi_client(r1, "sbfd", dedupe_dst)
+    # Negative-test timing window: we're asserting that the count
+    # *did not grow*, so there's no event to poll for. The inline
+    # client already sleeps 0.5s post-send, and we add another 0.5s
+    # here; on a loaded CI runner this can be bumped if the dedupe
+    # assertion ever flakes.
+    time.sleep(0.5)
+    after_second = count_with_dst(dedupe_dst)
+    assert after_second == 1, (
+        "duplicate SBFD session created on same-name re-register "
+        "(after_first={}, after_second={})".format(
+            after_first, after_second))