update bootstrapPeers to be func() []peer.AddrInfo (#716)

* update bootstrapPeers to internally be func() []peer.AddrInfo

* add BootstrapPeersFunc and add test

dht.go

@@ -126,10 +126,10 @@ type IpfsDHT struct {
 
 	autoRefresh bool
 
-	// A set of bootstrap peers to fallback on if all other attempts to fix
+	// A function returning a set of bootstrap peers to fallback on if all other attempts to fix
 	// the routing table fail (or, e.g., this is the first time this node is
 	// connecting to the network).
-	bootstrapPeers []peer.AddrInfo
+	bootstrapPeers func() []peer.AddrInfo
 
 	maxRecordAge time.Duration
 
@@ -473,15 +473,16 @@ func (dht *IpfsDHT) fixLowPeers(ctx context.Context) {
 	// We should first use non-bootstrap peers we knew of from previous
 	// snapshots of the Routing Table before we connect to the bootstrappers.
 	// See https://github.com/libp2p/go-libp2p-kad-dht/issues/387.
-	if dht.routingTable.Size() == 0 {
-		if len(dht.bootstrapPeers) == 0 {
+	if dht.routingTable.Size() == 0 && dht.bootstrapPeers != nil {
+		bootstrapPeers := dht.bootstrapPeers()
+		if len(bootstrapPeers) == 0 {
 			// No point in continuing, we have no peers!
 			return
 		}
 
 		found := 0
-		for _, i := range rand.Perm(len(dht.bootstrapPeers)) {
-			ai := dht.bootstrapPeers[i]
+		for _, i := range rand.Perm(len(bootstrapPeers)) {
+			ai := bootstrapPeers[i]
 			err := dht.Host().Connect(ctx, ai)
 			if err == nil {
 				found++

dht_options.go

@@ -269,7 +269,18 @@ func RoutingTableFilter(filter RouteTableFilterFunc) Option {
 // and refresh our Routing Table if it becomes empty.
 func BootstrapPeers(bootstrappers ...peer.AddrInfo) Option {
 	return func(c *dhtcfg.Config) error {
-		c.BootstrapPeers = bootstrappers
+		c.BootstrapPeers = func() []peer.AddrInfo {
+			return bootstrappers
+		}
+		return nil
+	}
+}
+
+// BootstrapPeersFunc configures the function that returns the bootstrapping nodes that we will
+// connect to to seed and refresh our Routing Table if it becomes empty.
+func BootstrapPeersFunc(getBootstrapPeers func() []peer.AddrInfo) Option {
+	return func(c *dhtcfg.Config) error {
+		c.BootstrapPeers = getBootstrapPeers
 		return nil
 	}
 }

dht_test.go

@@ -2051,6 +2051,39 @@ func TestBootStrapWhenRTIsEmpty(t *testing.T) {
 	}, 5*time.Second, 500*time.Millisecond)
 }
 
+func TestBootstrapPeersFunc(t *testing.T) {
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+	var lock sync.Mutex
+
+	bootstrapFuncA := func() []peer.AddrInfo {
+		return []peer.AddrInfo{}
+	}
+	dhtA := setupDHT(ctx, t, false, BootstrapPeersFunc(bootstrapFuncA))
+
+	bootstrapPeersB := []peer.AddrInfo{}
+	bootstrapFuncB := func() []peer.AddrInfo {
+		lock.Lock()
+		defer lock.Unlock()
+		return bootstrapPeersB
+	}
+
+	dhtB := setupDHT(ctx, t, false, BootstrapPeersFunc(bootstrapFuncB))
+	require.Equal(t, 0, len(dhtB.host.Network().Peers()))
+
+	addrA := peer.AddrInfo{
+		ID:    dhtA.self,
+		Addrs: dhtA.host.Addrs(),
+	}
+
+	lock.Lock()
+	bootstrapPeersB = []peer.AddrInfo{addrA}
+	lock.Unlock()
+
+	dhtB.fixLowPeers(ctx)
+	require.NotEqual(t, 0, len(dhtB.host.Network().Peers()))
+}
+
 func TestPreconnectedNodes(t *testing.T) {
 	ctx, cancel := context.WithCancel(context.Background())
 	defer cancel()

fullrt/dht.go

@@ -142,7 +142,7 @@ func NewFullRT(h host.Host, protocolPrefix protocol.ID, options ...Option) (*Ful
 
 	var bsPeers []*peer.AddrInfo
 
-	for _, ai := range dhtcfg.BootstrapPeers {
+	for _, ai := range dhtcfg.BootstrapPeers() {
 		tmpai := ai
 		bsPeers = append(bsPeers, &tmpai)
 	}

internal/config/config.go

@@ -57,7 +57,7 @@ type Config struct {
 		DiversityFilter     peerdiversity.PeerIPGroupFilter
 	}
 
-	BootstrapPeers []peer.AddrInfo
+	BootstrapPeers func() []peer.AddrInfo
 
 	// test specific Config options
 	DisableFixLowPeers          bool