Store relay states in a slice for consistent ordering (#1422)

hostmap.go

@@ -4,6 +4,7 @@ import (
 	"errors"
 	"net"
 	"net/netip"
+	"slices"
 	"sync"
 	"sync/atomic"
 	"time"
@@ -69,15 +70,20 @@ type HostMap struct {
 type RelayState struct {
 	sync.RWMutex
 
-	relays        map[netip.Addr]struct{} // Set of VpnIp's of Hosts to use as relays to access this peer
-	relayForByIp  map[netip.Addr]*Relay   // Maps VpnIps of peers for which this HostInfo is a relay to some Relay info
-	relayForByIdx map[uint32]*Relay       // Maps a local index to some Relay info
+	relays        []netip.Addr          // Ordered set of VpnIp's of Hosts to use as relays to access this peer
+	relayForByIp  map[netip.Addr]*Relay // Maps VpnIps of peers for which this HostInfo is a relay to some Relay info
+	relayForByIdx map[uint32]*Relay     // Maps a local index to some Relay info
 }
 
 func (rs *RelayState) DeleteRelay(ip netip.Addr) {
 	rs.Lock()
 	defer rs.Unlock()
-	delete(rs.relays, ip)
+	for idx, val := range rs.relays {
+		if val == ip {
+			rs.relays = append(rs.relays[:idx], rs.relays[idx+1:]...)
+			return
+		}
+	}
 }
 
 func (rs *RelayState) UpdateRelayForByIpState(vpnIp netip.Addr, state int) {
@@ -122,16 +128,16 @@ func (rs *RelayState) GetRelayForByIp(ip netip.Addr) (*Relay, bool) {
 func (rs *RelayState) InsertRelayTo(ip netip.Addr) {
 	rs.Lock()
 	defer rs.Unlock()
-	rs.relays[ip] = struct{}{}
+	if !slices.Contains(rs.relays, ip) {
+		rs.relays = append(rs.relays, ip)
+	}
 }
 
 func (rs *RelayState) CopyRelayIps() []netip.Addr {
+	ret := make([]netip.Addr, len(rs.relays))
 	rs.RLock()
 	defer rs.RUnlock()
-	ret := make([]netip.Addr, 0, len(rs.relays))
-	for ip := range rs.relays {
-		ret = append(ret, ip)
-	}
+	copy(ret, rs.relays)
 	return ret
 }