discovery: add banman for channel announcements

This commit introduces a ban manager that marks peers as banned if
they send too many invalid channel announcements to us. Expired
entries are purged after a certain period of time (currently 48 hours).

discovery/ban_test.go

@@ -0,0 +1,60 @@
+package discovery
+
+import (
+	"testing"
+	"time"
+
+	"github.com/lightninglabs/neutrino/cache"
+	"github.com/stretchr/testify/require"
+)
+
+// TestPurgeBanEntries tests that we properly purge ban entries on a timer.
+func TestPurgeBanEntries(t *testing.T) {
+	t.Parallel()
+
+	b := newBanman()
+
+	// Ban a peer by repeatedly incrementing its ban score.
+	peer1 := [33]byte{0x00}
+
+	for i := 0; i < banThreshold; i++ {
+		b.incrementBanScore(peer1)
+	}
+
+	// Assert that the peer is now banned.
+	require.True(t, b.isBanned(peer1))
+
+	// A call to purgeBanEntries should not remove the peer from the index.
+	b.purgeBanEntries()
+	require.True(t, b.isBanned(peer1))
+
+	// Now set the peer's last update time to two banTimes in the past so
+	// that we can assert that purgeBanEntries does remove it from the
+	// index.
+	banInfo, err := b.peerBanIndex.Get(peer1)
+	require.NoError(t, err)
+
+	banInfo.lastUpdate = time.Now().Add(-2 * banTime)
+
+	b.purgeBanEntries()
+	_, err = b.peerBanIndex.Get(peer1)
+	require.ErrorIs(t, err, cache.ErrElementNotFound)
+
+	// Increment the peer's ban score again but don't get it banned.
+	b.incrementBanScore(peer1)
+	require.False(t, b.isBanned(peer1))
+
+	// Assert that purgeBanEntries does nothing.
+	b.purgeBanEntries()
+	banInfo, err = b.peerBanIndex.Get(peer1)
+	require.Nil(t, err)
+
+	// Set its lastUpdate time to 2 resetDelta's in the past so that
+	// purgeBanEntries removes it.
+	banInfo.lastUpdate = time.Now().Add(-2 * resetDelta)
+
+	b.purgeBanEntries()
+
+	_, err = b.peerBanIndex.Get(peer1)
+	require.ErrorIs(t, err, cache.ErrElementNotFound)
+}