Store a new prefix's earliest timestamp as first_seen (closes #112)

A batch's prefix times were taken from each peer's last update for the
prefix, and the latest of those was kept. The prefix tables hold only
first_seen, written when the prefix is new, so a prefix announced by
two peers seconds apart in one batch was stored first seen at the
later time, and the IP lookup could answer with a first_seen after the
route's last_seen. The flush now keeps, for each prefix, the earliest
timestamp among all of the batch's updates for it.

Model: opus-5-5

internal/routewatch/prefixhandler.go

@@ -347,8 +347,19 @@ func (h *PrefixHandler) flushBatch() {
 
 	lastUpdates := make(map[prefixAndPeer]prefixUpdate)
 
+	// Each prefix the batch names, announced or withdrawn, with the earliest
+	// timestamp among all of its updates, not only each peer's last one: the
+	// prefix tables store only first_seen, written when the prefix is new and
+	// never changed after.
+	prefixesToUpdate := make(map[string]time.Time)
+
 	for _, update := range batch {
 		lastUpdates[prefixAndPeer{update.prefix, update.peer}] = update
+
+		seen, exists := prefixesToUpdate[update.prefix]
+		if !exists || update.timestamp.Before(seen) {
+			prefixesToUpdate[update.prefix] = update.timestamp
+		}
 	}
 
 	// Collect routes to upsert and delete
@@ -357,16 +368,7 @@ func (h *PrefixHandler) flushBatch() {
 		routesToDelete []database.LiveRouteDeletion
 	)
 
-	// Collect unique prefixes to update
-	prefixesToUpdate := make(map[string]time.Time)
-
 	for _, update := range lastUpdates {
-		// Track prefix for both announcements and withdrawals
-		seen, exists := prefixesToUpdate[update.prefix]
-		if !exists || update.timestamp.After(seen) {
-			prefixesToUpdate[update.prefix] = update.timestamp
-		}
-
 		// An announcement is stored when its path gives an origin, or when it
 		// ends in an AS set of several members: that route is stored with
 		// origin 0 (none). An announcement with an empty path is not stored.

internal/routewatch/prefixhandler_internal_test.go

@@ -83,6 +83,52 @@ func TestPrefixHandlerStoresPrefixesTheIPLookupFinds(t *testing.T) {
 	}
 }
 
+// TestPrefixHandlerStoresANewPrefixFirstSeenAtItsEarliestUpdate announces a
+// prefix the database does not hold yet twice in one batch, the second time 5
+// seconds after the first, through the prefix handler into a real database. The
+// prefix is stored first seen at the time of the first announcement, whether
+// the two come from two peers or from one, and the IP lookup answers with that
+// time.
+func TestPrefixHandlerStoresANewPrefixFirstSeenAtItsEarliestUpdate(
+	t *testing.T,
+) {
+	t.Parallel()
+
+	const (
+		otherPeerIP = "2001:db8:ffff::2"
+		secondAfter = 5 * time.Second
+	)
+
+	tests := []struct {
+		name                  string
+		firstPeer, secondPeer string
+	}{
+		{name: "two peers", firstPeer: testPeerIP, secondPeer: otherPeerIP},
+		{name: "one peer", firstPeer: testPeerIP, secondPeer: testPeerIP},
+	}
+
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			t.Parallel()
+
+			first := peerAnnouncement(tt.firstPeer, testV4Prefix)
+			second := peerAnnouncement(tt.secondPeer, testV4Prefix)
+			second.ParsedTimestamp = first.ParsedTimestamp.Add(secondAfter)
+			db := handleBatches(t, [][]*ristypes.RISMessage{{first, second}})
+
+			info, err := db.GetIPInfo("192.0.2.1")
+			if err != nil {
+				t.Fatalf("GetIPInfo(192.0.2.1): %v", err)
+			}
+
+			if !info.FirstSeen.Equal(first.ParsedTimestamp) {
+				t.Errorf("first_seen of %s = %s, want %s", testV4Prefix,
+					info.FirstSeen, first.ParsedTimestamp)
+			}
+		})
+	}
+}
+
 // TestPrefixHandlerAppliesEachPeersLastUpdateInABatch runs updates for one
 // prefix through the prefix handler into a real database. All updates carry the
 // same timestamp, as updates within one second of the feed do. Within a batch,