Drop connection if an unknown error occurs

This fixes a potential infinite loop when an unknown error occurs and
will happen every time the connection is handled. This was causing an
infinite loop in some situation.

Fixes dedis/cothority#1851

network/router.go

@@ -334,6 +334,12 @@ func (r *Router) handleConn(remote *ServerIdentity, c Conn) {
 				r.triggerConnectionErrorHandlers(remote)
 				return
 			}
+			if err == ErrUnknown {
+				// The error might not be recoverable so the connection is dropped
+				log.Lvlf5("%v drops %v connection: unknown", r.ServerIdentity, remote)
+				r.triggerConnectionErrorHandlers(remote)
+				return
+			}
 			// Temporary error, continue.
 			log.Lvl3(r.ServerIdentity, "Error with connection", address, "=>", err)
 			continue

network/router_test.go

@@ -560,3 +560,48 @@ func waitTimeout(timeout time.Duration, repeat int,
 	}
 
 }
+
+type testConn struct{}
+
+func (c *testConn) Receive() (*Envelope, error) {
+	return nil, ErrUnknown
+}
+
+func (c *testConn) Close() error {
+	return nil
+}
+
+func (c *testConn) Local() Address {
+	return ""
+}
+
+func (c *testConn) Remote() Address {
+	return ""
+}
+
+func (c *testConn) Rx() uint64 {
+	return 0
+}
+
+func (c *testConn) Tx() uint64 {
+	return 0
+}
+
+func (c *testConn) Send(msg Message) (uint64, error) {
+	return 0, nil
+}
+
+func (c *testConn) Type() ConnType {
+	return "testConn"
+}
+
+// This test insures that an unknown error cannot end up as an infinite loop
+// when handling a connection
+func TestRouterHandleUnknownError(t *testing.T) {
+	router, err := NewTestRouterTCP(0)
+	require.NoError(t, err)
+
+	router.wg.Add(1)
+	// The test will leak 1 goroutine if the connection is not dropped
+	go router.handleConn(router.ServerIdentity, &testConn{})
+}

network/tcp.go

@@ -266,6 +266,8 @@ func handleError(err error) error {
 	if netErr.Timeout() {
 		return ErrTimeout
 	}
+
+	log.Errorf("Unknown error caught: %s", err.Error())
 	return ErrUnknown
 }