get rtt time differently

hbd/server/main.py

@@ -173,14 +173,20 @@ async def _run_async(config, config_path=None):
             f"Warning: Could not reset IPV6_V6ONLY not supported or dual-stack is unavailable. Error: {e}"
         )
 
-    # 3. Bind to all interfaces (::) on a specific port
-
-    # UDP server endpoint (handler wired to handle_datagram with context)
     bind_addr = ("::", config.get("hb_port", 50003))
     sock.bind(bind_addr)
     logger.info("Starting UDP server on %s:%s", *bind_addr)
 
-    def udp_handler(msg, addr, transport):
+    # Try to enable kernel receive timestamps (Linux SO_TIMESTAMPNS).
+    # If supported, read datagrams via recvmsg() so RTT uses the kernel
+    # timestamp rather than the time.time() call after asyncio scheduling.
+    use_kernel_ts = udp.enable_kernel_timestamps(sock)
+    if use_kernel_ts:
+        logger.info("SO_TIMESTAMPNS enabled: using kernel receive timestamps for RTT")
+    else:
+        logger.info("SO_TIMESTAMPNS not available: using time.time() for RTT")
+
+    def udp_handler(msg, addr, transport, recv_ts=None):
         ctx = dict(
             config=config,
             hbdclass=hbdclass,
@@ -190,13 +196,22 @@ async def _run_async(config, config_path=None):
             threshold_checker=threshold_checker,
             DEBUG=config.get("debug", 0),
             verbose=config.get("verbose", False),
+            recv_ts=recv_ts,
         )
         udp.handle_datagram(msg, addr, transport, ctx)
 
-    transport, protocol = await loop.create_datagram_endpoint(
+    if use_kernel_ts:
-        lambda: udp.EchoServerProtocol(config=config, handler=udp_handler),
+        # recvmsg path: manage the socket ourselves with loop.add_reader()
-        sock=sock,
+        sock.setblocking(False)
-    )
+        transport = udp.RecvmsgTransport(loop, sock)
+        reader = udp.make_recvmsg_reader(sock, udp_handler, transport)
+        loop.add_reader(sock.fileno(), reader)
+        protocol = None
+    else:
+        transport, protocol = await loop.create_datagram_endpoint(
+            lambda: udp.EchoServerProtocol(config=config, handler=udp_handler),
+            sock=sock,
+        )
 
     # Restore connection timers for hosts loaded from pickle
     restore_ctx = dict(

hbd/server/udp.py

@@ -1,6 +1,9 @@
 """UDP listener and datagram processing."""
 
 import asyncio
+import socket
+import struct
+import time
 import zlib
 import logging
 
@@ -11,6 +14,98 @@ from . import notify as notify_mod
 logger = logging.getLogger(__name__)
 eventlog = notify_mod.eventlog
 
+# SO_TIMESTAMPNS: kernel attaches a struct timespec to each received datagram.
+# The constant is not exposed by Python's socket module on all platforms,
+# so fall back to the Linux value (35) when absent.
+_SO_TIMESTAMPNS = getattr(socket, 'SO_TIMESTAMPNS', 35)
+# struct timespec uses two native C longs: tv_sec and tv_nsec
+_TIMESPEC = struct.Struct('@ll')
+
+
+def enable_kernel_timestamps(sock) -> bool:
+    """Try to enable SO_TIMESTAMPNS on *sock*.
+
+    Returns True if the kernel will supply receive timestamps, False otherwise
+    (non-Linux, older kernel, or insufficient permissions).
+    """
+    try:
+        sock.setsockopt(socket.SOL_SOCKET, _SO_TIMESTAMPNS, 1)
+        return True
+    except OSError:
+        return False
+
+
+def _extract_kernel_ts(ancdata) -> float | None:
+    """Parse recvmsg ancillary data and return the kernel receive time.
+
+    Returns seconds as a float, or None if no SO_TIMESTAMPNS cmsg is present.
+    """
+    for cmsg_level, cmsg_type, cmsg_data in ancdata:
+        if cmsg_level == socket.SOL_SOCKET and cmsg_type == _SO_TIMESTAMPNS:
+            if len(cmsg_data) >= _TIMESPEC.size:
+                sec, nsec = _TIMESPEC.unpack_from(cmsg_data)
+                return sec + nsec * 1e-9
+    return None
+
+
+class RecvmsgTransport:
+    """Thin wrapper used when SO_TIMESTAMPNS is active (add_reader path).
+
+    Exposes the same sendto() / close() interface as asyncio's DatagramTransport
+    so the rest of the code does not need to know which path is in use.
+    """
+    def __init__(self, loop, sock):
+        self._loop = loop
+        self._sock = sock
+
+    def sendto(self, data, addr):
+        try:
+            self._sock.sendto(data, addr)
+        except Exception as e:
+            logger.debug("sendto failed: %s", e)
+
+    def close(self):
+        try:
+            self._loop.remove_reader(self._sock.fileno())
+        except Exception:
+            pass
+        try:
+            self._sock.close()
+        except Exception:
+            pass
+
+
+def make_recvmsg_reader(sock, handler, transport):
+    """Return a callback suitable for loop.add_reader().
+
+    Reads one datagram per call using recvmsg() so that kernel timestamps in
+    the ancillary data are accessible.  Falls back to time.time() gracefully
+    if the cmsg is missing.
+
+    handler(msg, addr, transport, kernel_ts) – same signature as udp_handler
+    in main.py with the optional kernel_ts argument.
+    """
+    BUFSIZE = 65536
+    ANCBUFSIZE = 128  # enough for one struct timespec cmsg
+
+    def _read():
+        try:
+            data, ancdata, _, addr = sock.recvmsg(BUFSIZE, ANCBUFSIZE)
+        except BlockingIOError:
+            return
+        except OSError as e:
+            logger.warning("recvmsg error: %s", e)
+            return
+        try:
+            kernel_ts = _extract_kernel_ts(ancdata)
+            msg = parse_message(data)
+            if msg:
+                handler(msg, addr, transport, kernel_ts)
+        except Exception:
+            logger.exception("Error processing datagram from %s", addr)
+
+    return _read
+
 
 class EchoServerProtocol(asyncio.DatagramProtocol):
     def __init__(self, config=None, handler=None):
@@ -79,7 +174,6 @@ def _make_timer_callbacks(uname, host, watchhosts, ctx):
             msg_to_websockets("host", host.stateinfo())
 
     async def on_overdue(connection):
-        import time
         if connection.getstate() != connection.__class__.UP:
             return
         now = time.time()
@@ -109,7 +203,6 @@ def restore_connection_timers(hbdclass, ctx):
     lastbeat so that clients that vanished during hbd's downtime are detected.
     For OVERDUE connections, the UNKNOWN drop timer is restored.
     """
-    import time
     now = time.time()
     cfg = ctx.get("config", {})
     grace = cfg.get("grace", 2)
@@ -170,7 +263,7 @@ def handle_datagram(msg: dict, addr, transport, ctx: dict):
     """
     if not msg:
         return
-    now = __import__("time").time()
+    now = ctx.get("recv_ts") or time.time()
     
     # Log message to journal
     msg_journal = ctx.get("msg_journal")
@@ -222,7 +315,7 @@ def handle_datagram(msg: dict, addr, transport, ctx: dict):
     if msg.get("ID") == "HTB":
         host.doesack = msg.get("acks", -1)
         # send ACK back
-        rmsg = {"time": __import__("time").time()}
+        rmsg = {"time": time.time()}
         opkt = dicttos("ACK", rmsg)
         try:
             transport.sendto(opkt, addr)