peer: Add machinery to track the state and validity of remote pongs

This commit refactors some of the bookkeeping around the ping logic
inside of the Brontide. If the pong response is noncompliant with
the spec or if it times out, we disconnect from the peer.

peer/ping_manager_test.go

@@ -0,0 +1,88 @@
+package peer
+
+import (
+	"testing"
+	"time"
+
+	"github.com/lightningnetwork/lnd/lnwire"
+	"github.com/stretchr/testify/require"
+)
+
+// TestPingManager tests three main properties about the ping manager. It
+// ensures that if the pong response exceeds the timeout, that a failure is
+// emitted on the failure channel. It ensures that if the Pong response is
+// not congruent with the outstanding ping then a failure is emitted on the
+// failure channel, and otherwise the failure channel remains empty.
+func TestPingManager(t *testing.T) {
+	t.Parallel()
+
+	testCases := []struct {
+		name     string
+		delay    int
+		pongSize uint16
+		result   bool
+	}{
+		{
+			name:     "Happy Path",
+			delay:    0,
+			pongSize: 4,
+			result:   true,
+		},
+		{
+			name:     "Bad Pong",
+			delay:    0,
+			pongSize: 3,
+			result:   false,
+		},
+		{
+			name:     "Timeout",
+			delay:    2,
+			pongSize: 4,
+			result:   false,
+		},
+	}
+
+	payload := make([]byte, 4)
+	for _, test := range testCases {
+		// Set up PingManager.
+		pingSent := make(chan struct{})
+		disconnected := make(chan struct{})
+		mgr := NewPingManager(&PingManagerConfig{
+			NewPingPayload: func() []byte {
+				return payload
+			},
+			NewPongSize: func() uint16 {
+				return 4
+			},
+			IntervalDuration: time.Second * 2,
+			TimeoutDuration:  time.Second,
+			SendPing: func(ping *lnwire.Ping) {
+				close(pingSent)
+			},
+			OnPongFailure: func(err error) {
+				close(disconnected)
+			},
+		})
+		require.NoError(t, mgr.Start(), "Could not start pingManager")
+
+		// Wait for initial Ping.
+		<-pingSent
+
+		// Wait for pre-determined time before sending Pong response.
+		time.Sleep(time.Duration(test.delay) * time.Second)
+
+		// Send Pong back.
+		res := lnwire.Pong{PongBytes: make([]byte, test.pongSize)}
+		mgr.ReceivedPong(&res)
+
+		// Evaluate result
+		select {
+		case <-time.NewTimer(time.Second / 2).C:
+			require.True(t, test.result)
+		case <-disconnected:
+			require.False(t, test.result)
+		}
+
+		require.NoError(t, mgr.Stop(), "Could not stop pingManager")
+	}
+}