document bitswap more

exchange/bitswap/bitswap.go

@@ -22,7 +22,8 @@ import (
 var log = eventlog.Logger("bitswap")
 
 // Number of providers to request for sending a wantlist to
-const maxProvidersPerRequest = 6
+// TODO: if a 'non-nice' strategy is implemented, consider increasing this value
+const maxProvidersPerRequest = 3
 
 // New initializes a BitSwap instance that communicates over the
 // provided BitSwapNetwork. This function registers the returned instance as
@@ -211,6 +212,7 @@ func (bs *bitswap) loop(parent context.Context) {
 	for {
 		select {
 		case <-broadcastSignal.C:
+			// Resend unfulfilled wantlist keys
 			bs.sendWantlistToProviders(ctx, bs.wantlist.Keys())
 		case ks := <-bs.batchRequests:
 			// TODO: implement batching on len(ks) > X for some X
@@ -224,6 +226,13 @@ func (bs *bitswap) loop(parent context.Context) {
 			for _, k := range ks {
 				bs.wantlist.Add(k)
 			}
+			// NB: send want list to providers for the first peer in this list.
+			//		the assumption is made that the providers of the first key in
+			//		the set are likely to have others as well.
+			//		This currently holds true in most every situation, since when
+			//		pinning a file, you store and provide all blocks associated with
+			//		it. Later, this assumption may not hold as true if we implement
+			//		newer bitswap strategies.
 			providers := bs.routing.FindProvidersAsync(ctx, ks[0], maxProvidersPerRequest)
 
 			err := bs.sendWantListTo(ctx, providers)
@@ -263,7 +272,6 @@ func (bs *bitswap) receiveBlock(ctx context.Context, block *blocks.Block) {
 func (bs *bitswap) ReceiveMessage(ctx context.Context, p peer.Peer, incoming bsmsg.BitSwapMessage) (
 	peer.Peer, bsmsg.BitSwapMessage) {
 	log.Debugf("ReceiveMessage from %s", p)
-	log.Debugf("Message wantlist: %v", incoming.Wantlist())
 
 	if p == nil {
 		log.Error("Received message from nil peer!")
@@ -279,15 +287,17 @@ func (bs *bitswap) ReceiveMessage(ctx context.Context, p peer.Peer, incoming bsm
 	// Record message bytes in ledger
 	// TODO: this is bad, and could be easily abused.
 	// Should only track *useful* messages in ledger
-	bs.strategy.MessageReceived(p, incoming) // FIRST
+	// This call records changes to wantlists, blocks received,
+	// and number of bytes transfered.
+	bs.strategy.MessageReceived(p, incoming)
 
-	for _, block := range incoming.Blocks() {
-		go bs.receiveBlock(ctx, block)
-	}
+	go func() {
+		for _, block := range incoming.Blocks() {
+			bs.receiveBlock(ctx, block)
+		}
+	}()
 
 	for _, key := range incoming.Wantlist() {
-		// TODO: might be better to check if we have the block before checking
-		//			if we should send it to someone
 		if bs.strategy.ShouldSendBlockToPeer(key, p) {
 			if block, errBlockNotFound := bs.blockstore.Get(key); errBlockNotFound != nil {
 				continue
@@ -303,12 +313,12 @@ func (bs *bitswap) ReceiveMessage(ctx context.Context, p peer.Peer, incoming bsm
 				}
 
 				blkmsg.AddBlock(block)
-				bs.strategy.MessageSent(p, blkmsg)
 				bs.send(ctx, p, blkmsg)
 			}
 		}
 	}
 
+	// TODO: consider changing this function to not return anything
 	return nil, nil
 }
 
@@ -326,7 +336,7 @@ func (bs *bitswap) send(ctx context.Context, p peer.Peer, m bsmsg.BitSwapMessage
 }
 
 func (bs *bitswap) sendToPeersThatWant(ctx context.Context, block *blocks.Block) {
-	log.Debugf("Sending %v to peers that want it", block.Key())
+	log.Debugf("Sending %s to peers that want it", block)
 
 	for _, p := range bs.strategy.Peers() {
 		if bs.strategy.BlockIsWantedByPeer(block.Key(), p) {