kill stale connections

The weave protocol already effectively performs heartbeating -
FetchAll is performed at regular intervals. Hence we can detect stale
connections by the lack of receiving any data for approximately that
interval (we use x2).

We use the same interval to set a time limit on the handshake too, and
any subsequent interactions prior to the connection being fully
established.

Fixes #272.

router/connection.go

@@ -285,8 +285,8 @@ func (conn *LocalConnection) handshake(acceptNewPeer bool) error {
 	// ourself. Only when we add this connection to the conn.local
 	// peer will it be visible from multiple go-routines.
 	tcpConn := conn.TCPConn
-	tcpConn.SetKeepAlive(true)
 	tcpConn.SetLinger(0)
+	conn.extendReadDeadline()
 
 	enc := gob.NewEncoder(tcpConn)
 
@@ -428,6 +428,7 @@ func (conn *LocalConnection) receiveTCP(decoder *gob.Decoder, usingPassword bool
 	var err error
 	for {
 		var msg []byte
+		conn.extendReadDeadline()
 		if conn.CheckFatal(decoder.Decode(&msg)) != nil {
 			return
 		}
@@ -501,6 +502,10 @@ func (conn *LocalConnection) receiveTCP(decoder *gob.Decoder, usingPassword bool
 	}
 }
 
+func (conn *LocalConnection) extendReadDeadline() {
+	conn.TCPConn.SetReadDeadline(time.Now().Add(ReadTimeout))
+}
+
 // Heartbeats
 
 // Heartbeating serves two purposes: a) keeping NAT paths alive, and

router/consts.go

@@ -22,6 +22,7 @@ const (
 	SlowHeartbeat      = 10 * time.Second
 	FetchAllInterval   = 30 * time.Second
 	FragTestInterval   = 5 * time.Minute
+	ReadTimeout        = 2 * FetchAllInterval
 	PMTUVerifyAttempts = 8
 	PMTUVerifyTimeout  = 10 * time.Millisecond // gets doubled with every attempt
 	MaxDuration        = time.Duration(math.MaxInt64)