Set linger on p2p connections (ava-labs#2646)

Co-authored-by: Patrick O'Grady <[email protected]>

network/network.go

@@ -49,6 +49,11 @@ const (
 	TimeSinceLastMsgReceivedKey = "timeSinceLastMsgReceived"
 	TimeSinceLastMsgSentKey     = "timeSinceLastMsgSent"
 	SendFailRateKey             = "sendFailRate"
+
+	// lingerTimeout is the amount of time (in seconds) we allow for the
+	// remaining data in a connection to be flushed before forcibly closing the
+	// connection (TCP RST).
+	lingerTimeout = 15
 )
 
 var (
@@ -731,6 +736,7 @@ func (n *network) Dispatch() error {
 			n.metrics.acceptFailed.Inc()
 			continue
 		}
+		n.setLinger(conn)
 
 		// Note: listener.Accept is rate limited outside of this package, so a
 		// peer can not just arbitrarily spin up goroutines here.
@@ -1124,6 +1130,7 @@ func (n *network) dial(ctx context.Context, nodeID ids.NodeID, ip *trackedIP) {
 				)
 				continue
 			}
+			n.setLinger(conn)
 
 			n.peerConfig.Log.Verbo("starting to upgrade connection",
 				zap.String("direction", "outbound"),
@@ -1144,6 +1151,24 @@ func (n *network) dial(ctx context.Context, nodeID ids.NodeID, ip *trackedIP) {
 	}()
 }
 
+// setLinger sets the linger on [conn], if it is a [*net.TCPConn], to
+// [lingerTimeout].
+func (n *network) setLinger(conn net.Conn) {
+	tcpConn, ok := conn.(*net.TCPConn)
+	if !ok {
+		return
+	}
+
+	// If a connection is closed, we allow a grace period for the unsent
+	// data in the connection to be flushed before forcibly closing the
+	// connection (TCP RST).
+	if err := tcpConn.SetLinger(lingerTimeout); err != nil {
+		n.peerConfig.Log.Warn("failed to set no linger",
+			zap.Error(err),
+		)
+	}
+}
+
 // upgrade the provided connection, which may be an inbound connection or an
 // outbound connection, with the provided [upgrader].
 //