tor: add method Reconnect to reset connection

A new method, Reconnect, is added to tor controller which can be used to
reset the current connection. This will be later used in healthcheck to
help us reset the connection to Tor Daemon.

tor/controller_test.go

@@ -276,3 +276,87 @@ func TestReadResponse(t *testing.T) {
 		})
 	}
 }
+
+// TestReconnectTCMustBeRunning checks that the tor controller must be running
+// while calling Reconnect.
+func TestReconnectTCMustBeRunning(t *testing.T) {
+	// Create a dummy controller.
+	c := &Controller{}
+
+	// Reconnect should fail because the TC is not started.
+	require.Equal(t, errTCNotStarted, c.Reconnect())
+
+	// Set the started flag.
+	c.started = 1
+
+	// Set the stopped flag so the TC is stopped.
+	c.stopped = 1
+
+	// Reconnect should fail because the TC is stopped.
+	require.Equal(t, errTCStopped, c.Reconnect())
+}
+
+// TestReconnectSucceed tests a reconnection will succeed when the tor
+// controller is up and running.
+func TestReconnectSucceed(t *testing.T) {
+	// Create mock server and client connection.
+	proxy := createTestProxy(t)
+	defer proxy.cleanUp()
+
+	// Create a tor controller and mark the controller as started.
+	c := &Controller{
+		conn:        proxy.clientConn,
+		started:     1,
+		controlAddr: proxy.serverAddr,
+	}
+
+	// Accept the connection inside a goroutine. We will also write some
+	// data so that the reconnection can succeed. We will mock three writes
+	// and two reads inside our proxy server,
+	//   - write protocol info
+	//   - read auth info
+	//   - write auth challenge
+	//   - read auth challenge
+	//   - write OK
+	go func() {
+		// Accept the new connection.
+		server, err := proxy.server.Accept()
+		require.NoError(t, err, "failed to accept")
+
+		// Write the protocol info.
+		resp := "250-PROTOCOLINFO 1\n" +
+			"250-AUTH METHODS=NULL\n" +
+			"250 OK\n"
+		_, err = server.Write([]byte(resp))
+		require.NoErrorf(t, err, "failed to write protocol info")
+
+		// Read the auth info from the client.
+		buf := make([]byte, 65535)
+		_, err = server.Read(buf)
+		require.NoError(t, err)
+
+		// Write the auth challenge.
+		resp = "250 AUTHCHALLENGE SERVERHASH=fake\n"
+		_, err = server.Write([]byte(resp))
+		require.NoErrorf(t, err, "failed to write auth challenge")
+
+		// Read the auth challenge resp from the client.
+		_, err = server.Read(buf)
+		require.NoError(t, err)
+
+		// Write OK resp.
+		resp = "250 OK\n"
+		_, err = server.Write([]byte(resp))
+		require.NoErrorf(t, err, "failed to write response auth")
+	}()
+
+	// Reconnect should succeed.
+	require.NoError(t, c.Reconnect())
+
+	// Check that the old connection is closed.
+	_, err := proxy.clientConn.ReadLine()
+	require.Contains(t, err.Error(), "use of closed network connection")
+
+	// Check that the connection has been updated.
+	require.NotEqual(t, proxy.clientConn, c.conn)
+}