Store the routing table in the database (part of #122)

A new routes table holds one row per prefix and origin AS: the peer set
as the bitset's bytes, and the two kept routes, each with its peer's
number, AS path and time in seconds. A new route_peers table holds each
peer's number and address.

WriteRouteChanges writes one TakeChanges result in a transaction.
ReadRouteTable reads both tables into a new routing table, through the
new Table.Load, which records no change. It fails on a row that names a
peer number missing from route_peers. Nothing uses them yet.

Model: opus-5-5

internal/routetable/routetable.go

@@ -218,6 +218,53 @@ func (t *Table) PeerDown(peer string) {
 	}
 }
 
+// Load puts one prefix and origin AS pair that the database holds into the
+// table, as startup does with each row it reads. The change's peers join the
+// pair's peer set, and its routes are kept as an announcement's would be.
+// Unlike an update, Load records no change, so TakeChanges does not hand the
+// pair back to be written again. Loading a pair twice changes nothing.
+//
+// The caller makes sure that every peer change names, in its peer set or in
+// its routes, has a number in Params.PeerNumbers.
+func (t *Table) Load(change Change) {
+	t.mu.Lock()
+	defer t.mu.Unlock()
+
+	// A removed pair has no peers, and a pair without peers is not in the
+	// table.
+	if change.Peers == nil || change.Peers.None() || !change.Prefix.IsValid() {
+		return
+	}
+
+	prefix := change.Prefix.Masked()
+	o := t.findOrAddOrigin(prefix, change.OriginASN)
+	wasWithoutKeptRoute := o.withoutKeptRoute()
+
+	for peer := range change.Peers.EachSet() {
+		if !o.peers.Test(peer) {
+			o.peers.Set(peer)
+
+			t.familyOf(prefix.Addr()).routes++
+			t.peerPrefixes[peer]++
+		}
+	}
+
+	// Oldest first, as they were announced, so that two routes with the same
+	// time are kept in the order they had.
+	for _, r := range slices.Backward(change.Routes) {
+		peer := t.peerNumbers[r.Peer]
+
+		t.dropKeptRoute(o, peer)
+		t.keepIfNewest(o, route{
+			peer: peer,
+			path: slices.Clone(r.ASPath),
+			time: r.Time,
+		})
+	}
+
+	t.countOriginWithoutKeptRoute(o, wasWithoutKeptRoute)
+}
+
 // TakeChanges returns the prefix and origin AS pairs that changed since it last
 // ran, in prefix order, each with its current content. It also returns the
 // peers numbered since then, by address. It then clears both records.
@@ -413,6 +460,17 @@ func (t *Table) recordChange(
 ) {
 	t.changed[pair{prefix: prefix, asn: o.asn}] = struct{}{}
 
+	t.countOriginWithoutKeptRoute(o, wasWithoutKeptRoute)
+
+	if o.peers.None() {
+		t.removeOrigin(prefix, o)
+	}
+}
+
+// countOriginWithoutKeptRoute brings the count of origins without a kept route
+// up to date after a change to o. wasWithoutKeptRoute says whether o was such
+// an origin before the change.
+func (t *Table) countOriginWithoutKeptRoute(o *origin, wasWithoutKeptRoute bool) {
 	if wasWithoutKeptRoute {
 		t.originsWithoutKeptRoute--
 	}
@@ -420,10 +478,6 @@ func (t *Table) recordChange(
 	if o.withoutKeptRoute() {
 		t.originsWithoutKeptRoute++
 	}
-
-	if o.peers.None() {
-		t.removeOrigin(prefix, o)
-	}
 }
 
 // countKeptTime adds delta to the number of kept routes with time at.