Add option to disable fallback on Want-Blocks

Add an option to disable fallback on `Want-Blocks` when a peer does not
support `Want-Haves`.

Assure connection to peer before checking whether a peer supports
`Want-Haves` to reduce false negatives.

Refactor default connection manger settings to constants.

Fixes #3

broadcaster.go

@@ -150,8 +150,14 @@ func (cs *channeledSender) start() {
 }
 
 func (cs *channeledSender) supportsHaves() bool {
-	// TODO open stream to detect this as that is more reliable
-	// TODO cache supported protocol IDs for the recipient
+	// Assure connection to peer before checking protocols list. Otherwise, GetProtocols
+	// silently returns empty protocols list.
+	if addrs := cs.c.h.Peerstore().Addrs(cs.id); len(addrs) == 0 {
+		return false
+	} else if err := cs.c.h.Connect(cs.ctx, peer.AddrInfo{ID: cs.id, Addrs: addrs}); err != nil {
+		logger.Errorw("Failed to connect to peer in order to determine Want-Haves support", "peer", cs.id, "err", err)
+		return false
+	}
 	protocols, err := cs.c.h.Peerstore().GetProtocols(cs.id)
 	if err != nil {
 		return false
@@ -174,8 +180,13 @@ func (cs *channeledSender) sendUnsent() {
 	var wlt bitswap_message_pb.Message_Wantlist_WantType
 	if cs.supportsHaves() {
 		wlt = bitswap_message_pb.Message_Wantlist_Have
-	} else {
+	} else if cs.c.fallbackOnWantBlock {
 		wlt = bitswap_message_pb.Message_Wantlist_Block
+	} else {
+		logger.Warnw("Peer does not support Want-Haves and fallback on Want-Blocks is disabled. Skipping broadcast.", "peer", cs.id, "skipped", len(cs.unsentCids))
+		// Clear unsent CIDs.
+		cs.unsentCids = make(map[cid.Cid]struct{})
+		return
 	}
 	msg := message.New(false)
 	for c := range cs.unsentCids {

options.go

@@ -20,6 +20,11 @@ var kuboBootstrapPeers = []string{
 	"/ip4/104.131.131.82/udp/4001/quic/p2p/QmaCpDMGvV2BGHeYERUEnRQAwe3N8SzbUtfsmvsqQLuvuJ", // mars.i.ipfs.io
 }
 
+const (
+	defaultConnMngrLowWaterMark  = 0xff
+	defaultConnMngrHighWaterMark = 0xfff
+)
+
 type (
 	Option  func(*options) error
 	options struct {
@@ -34,6 +39,7 @@ type (
 		findByMultihash              bool
 		messageSenderBuffer          int
 		recipientsRefreshInterval    time.Duration
+		fallbackOnWantBlock          bool
 
 		maxBroadcastBatchSize int
 		maxBroadcastBatchWait time.Duration
@@ -49,6 +55,7 @@ func newOptions(o ...Option) (*options, error) {
 		messageSenderBuffer:       100,
 		findByMultihash:           true,
 		recipientsRefreshInterval: 10 * time.Second,
+		fallbackOnWantBlock:       true,
 		maxBroadcastBatchSize:     100,
 		maxBroadcastBatchWait:     100 * time.Millisecond,
 	}
@@ -59,7 +66,7 @@ func newOptions(o ...Option) (*options, error) {
 	}
 
 	if opts.h == nil {
-		manager, err := connmgr.NewConnManager(500, 5000)
+		manager, err := connmgr.NewConnManager(defaultConnMngrLowWaterMark, defaultConnMngrHighWaterMark)
 		if err != nil {
 			return nil, err
 		}