fix(core) bootstrap panic

@jbenet @mappum

License: MIT
Signed-off-by: Brian Tiger Chow <brian@perfmode.com>

core/bootstrap.go

@@ -11,6 +11,7 @@ import (
 	inet "github.com/jbenet/go-ipfs/net"
 	peer "github.com/jbenet/go-ipfs/peer"
 	dht "github.com/jbenet/go-ipfs/routing/dht"
+	math2 "github.com/jbenet/go-ipfs/util/math2"
 )
 
 const (
@@ -68,10 +69,7 @@ func bootstrap(ctx context.Context,
 		}
 	}
 
-	var randomSubset []peer.Peer
-	for _, val := range rand.Perm(numCxnsToCreate) {
-		randomSubset = append(randomSubset, notConnected[val])
-	}
+	var randomSubset = randomSubsetOfPeers(notConnected, numCxnsToCreate)
 	if err := connect(ctx, r, randomSubset); err != nil {
 		return err
 	}
@@ -119,3 +117,12 @@ func toPeer(ps peer.Peerstore, bootstrap *config.BootstrapPeer) (peer.Peer, erro
 	p.AddAddress(maddr)
 	return p, nil
 }
+
+func randomSubsetOfPeers(in []peer.Peer, max int) []peer.Peer {
+	n := math2.IntMin(max, len(in))
+	var out []peer.Peer
+	for _, val := range rand.Perm(n) {
+		out = append(out, in[val])
+	}
+	return out
+}

core/bootstrap_test.go

@@ -0,0 +1,20 @@
+package core
+
+import (
+	"testing"
+
+	peer "github.com/jbenet/go-ipfs/peer"
+	testutil "github.com/jbenet/go-ipfs/util/testutil"
+)
+
+func TestSubsetWhenMaxIsGreaterThanLengthOfSlice(t *testing.T) {
+	var ps []peer.Peer
+	sizeofSlice := 100
+	for i := 0; i < sizeofSlice; i++ {
+		ps = append(ps, testutil.RandPeer())
+	}
+	out := randomSubsetOfPeers(ps, 2*sizeofSlice)
+	if len(out) != len(ps) {
+		t.Fail()
+	}
+}

util/math2/math2.go

@@ -0,0 +1,9 @@
+package math2
+
+// IntMin returns the smaller of x or y.
+func IntMin(x, y int) int {
+	if x < y {
+		return x
+	}
+	return y
+}