Keep prefixes that do not parse out of the prefix tables (closes #114)

UpdatePrefixesBatch now skips a prefix that does not parse, so it never
becomes a row in prefixes_v4 or prefixes_v6 and never counts in the prefix
total in the stats. Before, the prefix handler stored no route for such a
prefix and logged it once per prefix and peer, but still passed it to
UpdatePrefixesBatch, which stored it.

Model: opus-5-5

internal/database/database.go

@@ -855,7 +855,7 @@ func insertPrefixesInTable(
 
 // UpdatePrefixesBatch stores, in a single transaction, the prefixes that are
 // not stored yet, each first seen at its time in prefixes: the IPv4 prefixes
-// first and then the IPv6 prefixes.
+// first and then the IPv6 prefixes. A prefix that does not parse is not stored.
 func (d *Database) UpdatePrefixesBatch(prefixes map[string]time.Time) error {
 	if len(prefixes) == 0 {
 		return nil
@@ -874,6 +874,11 @@ func (d *Database) UpdatePrefixesBatch(prefixes map[string]time.Time) error {
 	prefixesV6 := make(map[string]time.Time)
 
 	for prefix, timestamp := range prefixes {
+		_, err := netip.ParsePrefix(prefix)
+		if err != nil {
+			continue
+		}
+
 		if detectIPVersion(prefix) == ipVersionV4 {
 			prefixesV4[prefix] = timestamp
 		} else {

internal/routewatch/prefixhandler_internal_test.go

@@ -440,6 +440,64 @@ func TestPrefixHandlerRemovesTheRouteOnAnAnnouncementWithoutAnOrigin(
 	}
 }
 
+// TestPrefixHandlerDoesNotStoreAPrefixThatDoesNotParse runs an announcement of
+// "not-a-prefix" and a withdrawal of "also/bad" through the prefix handler into
+// a real database. Neither is stored in the prefix tables: the prefix count in
+// the stats stays 0, both as kept in memory and as counted from the tables when
+// the database is opened again.
+func TestPrefixHandlerDoesNotStoreAPrefixThatDoesNotParse(t *testing.T) {
+	t.Parallel()
+
+	cfg := &config.Config{StateDir: t.TempDir()}
+
+	db, err := database.New(cfg, logger.New())
+	if err != nil {
+		t.Fatalf("failed to create database: %v", err)
+	}
+
+	// Built without NewPrefixHandler's flush timer, so the test flushes itself.
+	h := &PrefixHandler{db: db, logger: logger.New()}
+
+	withdrawal := &ristypes.RISMessage{
+		Type:            ristypes.MessageTypeUpdate,
+		Peer:            testPeerIP,
+		ParsedTimestamp: time.Date(2026, 1, 2, 3, 4, 5, 0, time.UTC),
+		Withdrawals:     []string{"also/bad"},
+	}
+	h.HandleMessage(peerAnnouncement(testPeerIP, "not-a-prefix"))
+	h.HandleMessage(withdrawal)
+	h.flushBatch()
+
+	checkNoPrefixes := func(when string) {
+		t.Helper()
+
+		stats, err := db.GetStatsContext(context.Background())
+		if err != nil {
+			t.Fatalf("GetStatsContext %s: %v", when, err)
+		}
+
+		if stats.Prefixes != 0 {
+			t.Errorf("prefix count %s = %d, want 0", when, stats.Prefixes)
+		}
+	}
+
+	checkNoPrefixes("after the flush")
+
+	err = db.Close()
+	if err != nil {
+		t.Fatalf("Close: %v", err)
+	}
+
+	db, err = database.New(cfg, logger.New())
+	if err != nil {
+		t.Fatalf("failed to open the database again: %v", err)
+	}
+
+	t.Cleanup(func() { _ = db.Close() })
+
+	checkNoPrefixes("after opening the database again")
+}
+
 // TestStateMessagesGoToThePrefixHandlerNotThePeerHandler checks that STATE
 // messages go to the prefix handler, which acts on a down, and not to the peer
 // handler, which would record a peer whose session never comes up as active.