refactor(sessions): extract sessions to package

- moved sessions out of main bitswap package
- modified session manager to manage all sessions
- moved get functions to their own package so sessions can directly

BREAKING CHANGE: SessionsForBlock, while not used outside of Bitswap, has been removed, and was an
exported function

bitswap.go

@@ -10,6 +10,7 @@ import (
 	"time"
 
 	decision "github.com/ipfs/go-bitswap/decision"
+	bsgetter "github.com/ipfs/go-bitswap/getter"
 	bsmsg "github.com/ipfs/go-bitswap/message"
 	bsmq "github.com/ipfs/go-bitswap/messagequeue"
 	bsnet "github.com/ipfs/go-bitswap/network"
@@ -100,6 +101,7 @@ func New(parent context.Context, network bsnet.BitSwapNetwork,
 		return bsmq.New(p, network)
 	}
 
+	wm := bswm.New(ctx)
 	bs := &Bitswap{
 		blockstore:    bstore,
 		notifications: notif,
@@ -109,9 +111,9 @@ func New(parent context.Context, network bsnet.BitSwapNetwork,
 		process:       px,
 		newBlocks:     make(chan cid.Cid, HasBlockBufferSize),
 		provideKeys:   make(chan cid.Cid, provideKeysBufferSize),
-		wm:            bswm.New(ctx),
+		wm:            wm,
 		pm:            bspm.New(ctx, peerQueueFactory),
-		sm:            bssm.New(),
+		sm:            bssm.New(ctx, wm, network),
 		counters:      new(counters),
 		dupMetric:     dupHist,
 		allMetric:     allHist,
@@ -202,7 +204,7 @@ type blockRequest struct {
 // GetBlock attempts to retrieve a particular block from peers within the
 // deadline enforced by the context.
 func (bs *Bitswap) GetBlock(parent context.Context, k cid.Cid) (blocks.Block, error) {
-	return getBlock(parent, k, bs.GetBlocks)
+	return bsgetter.SyncGetBlock(parent, k, bs.GetBlocks)
 }
 
 func (bs *Bitswap) WantlistForPeer(p peer.ID) []cid.Cid {
@@ -307,7 +309,7 @@ func (bs *Bitswap) GetBlocks(ctx context.Context, keys []cid.Cid) (<-chan blocks
 	return out, nil
 }
 
-// CancelWant removes a given key from the wantlist.
+// CancelWants removes a given key from the wantlist.
 func (bs *Bitswap) CancelWants(cids []cid.Cid, ses uint64) {
 	if len(cids) == 0 {
 		return
@@ -345,12 +347,7 @@ func (bs *Bitswap) receiveBlockFrom(blk blocks.Block, from peer.ID) error {
 	// it now as it requires more thought and isnt causing immediate problems.
 	bs.notifications.Publish(blk)
 
-	k := blk.Cid()
-	ks := []cid.Cid{k}
-	for _, s := range bs.SessionsForBlock(k) {
-		s.receiveBlockFrom(from, blk)
-		bs.CancelWants(ks, s.id)
-	}
+	bs.sm.ReceiveBlockFrom(from, blk)
 
 	bs.engine.AddBlock(blk)
 
@@ -363,18 +360,6 @@ func (bs *Bitswap) receiveBlockFrom(blk blocks.Block, from peer.ID) error {
 	return nil
 }
 
-// SessionsForBlock returns a slice of all sessions that may be interested in the given cid.
-func (bs *Bitswap) SessionsForBlock(c cid.Cid) []*Session {
-	var out []*Session
-	bs.sm.IterateSessions(func(session exchange.Fetcher) {
-		s := session.(*Session)
-		if s.interestedIn(c) {
-			out = append(out, s)
-		}
-	})
-	return out
-}
-
 func (bs *Bitswap) ReceiveMessage(ctx context.Context, p peer.ID, incoming bsmsg.BitSwapMessage) {
 	atomic.AddUint64(&bs.counters.messagesRecvd, 1)
 
@@ -477,3 +462,7 @@ func (bs *Bitswap) GetWantlist() []cid.Cid {
 func (bs *Bitswap) IsOnline() bool {
 	return true
 }
+
+func (bs *Bitswap) NewSession(ctx context.Context) exchange.Fetcher {
+	return bs.sm.NewSession(ctx)
+}

session_test.go → bitswap_with_sessions_test.go

@@ -6,6 +6,7 @@ import (
 	"testing"
 	"time"
 
+	bssession "github.com/ipfs/go-bitswap/session"
 	blocks "github.com/ipfs/go-block-format"
 	cid "github.com/ipfs/go-cid"
 	blocksutil "github.com/ipfs/go-ipfs-blocksutil"
@@ -132,8 +133,8 @@ func TestSessionSplitFetch(t *testing.T) {
 		cids = append(cids, blk.Cid())
 	}
 
-	ses := inst[10].Exchange.NewSession(ctx).(*Session)
-	ses.baseTickDelay = time.Millisecond * 10
+	ses := inst[10].Exchange.NewSession(ctx).(*bssession.Session)
+	ses.SetBaseTickDelay(time.Millisecond * 10)
 
 	for i := 0; i < 10; i++ {
 		ch, err := ses.GetBlocks(ctx, cids[i*10:(i+1)*10])

dup_blocks_test.go

@@ -11,6 +11,7 @@ import (
 
 	tn "github.com/ipfs/go-bitswap/testnet"
 
+	bssession "github.com/ipfs/go-bitswap/session"
 	"github.com/ipfs/go-block-format"
 	cid "github.com/ipfs/go-cid"
 	blocksutil "github.com/ipfs/go-ipfs-blocksutil"
@@ -248,14 +249,14 @@ func onePeerPerBlock(b *testing.B, provs []Instance, blks []blocks.Block) {
 }
 
 func oneAtATime(b *testing.B, bs *Bitswap, ks []cid.Cid) {
-	ses := bs.NewSession(context.Background()).(*Session)
+	ses := bs.NewSession(context.Background()).(*bssession.Session)
 	for _, c := range ks {
 		_, err := ses.GetBlock(context.Background(), c)
 		if err != nil {
 			b.Fatal(err)
 		}
 	}
-	b.Logf("Session fetch latency: %s", ses.latTotal/time.Duration(ses.fetchcnt))
+	b.Logf("Session fetch latency: %s", ses.GetAverageLatency())
 }
 
 // fetch data in batches, 10 at a time

get.go → getter/getter.go

-package bitswap
+package getter
 
 import (
 	"context"
 	"errors"
 
 	notifications "github.com/ipfs/go-bitswap/notifications"
+	logging "github.com/ipfs/go-log"
 
 	blocks "github.com/ipfs/go-block-format"
 	cid "github.com/ipfs/go-cid"
 	blockstore "github.com/ipfs/go-ipfs-blockstore"
 )
 
-type getBlocksFunc func(context.Context, []cid.Cid) (<-chan blocks.Block, error)
+var log = logging.Logger("bitswap")
 
-func getBlock(p context.Context, k cid.Cid, gb getBlocksFunc) (blocks.Block, error) {
+// GetBlocksFunc is any function that can take an array of CIDs and return a
+// channel of incoming blocks.
+type GetBlocksFunc func(context.Context, []cid.Cid) (<-chan blocks.Block, error)
+
+// SyncGetBlock takes a block cid and an async function for getting several
+// blocks that returns a channel, and uses that function to return the
+// block syncronously.
+func SyncGetBlock(p context.Context, k cid.Cid, gb GetBlocksFunc) (blocks.Block, error) {
 	if !k.Defined() {
 		log.Error("undefined cid in GetBlock")
 		return nil, blockstore.ErrNotFound
@@ -49,9 +57,13 @@ func getBlock(p context.Context, k cid.Cid, gb getBlocksFunc) (blocks.Block, err
 	}
 }
 
-type wantFunc func(context.Context, []cid.Cid)
+// WantFunc is any function that can express a want for set of blocks.
+type WantFunc func(context.Context, []cid.Cid)
 
-func getBlocksImpl(ctx context.Context, keys []cid.Cid, notif notifications.PubSub, want wantFunc, cwants func([]cid.Cid)) (<-chan blocks.Block, error) {
+// AsyncGetBlocks take a set of block cids, a pubsub channel for incoming
+// blocks, a want function, and a close function,
+// and returns a channel of incoming blocks.
+func AsyncGetBlocks(ctx context.Context, keys []cid.Cid, notif notifications.PubSub, want WantFunc, cwants func([]cid.Cid)) (<-chan blocks.Block, error) {
 	if len(keys) == 0 {
 		out := make(chan blocks.Block)
 		close(out)

session.go → session/session.go

-package bitswap
+package session
 
 import (
 	"context"
 	"fmt"
 	"time"
 
-	notifications "github.com/ipfs/go-bitswap/notifications"
-
 	lru "github.com/hashicorp/golang-lru"
+	bsgetter "github.com/ipfs/go-bitswap/getter"
+	bsnet "github.com/ipfs/go-bitswap/network"
+	notifications "github.com/ipfs/go-bitswap/notifications"
 	blocks "github.com/ipfs/go-block-format"
 	cid "github.com/ipfs/go-cid"
-	exchange "github.com/ipfs/go-ipfs-exchange-interface"
 	logging "github.com/ipfs/go-log"
 	loggables "github.com/libp2p/go-libp2p-loggables"
 	peer "github.com/libp2p/go-libp2p-peer"
@@ -18,41 +18,61 @@ import (
 
 const activeWantsLimit = 16
 
+// SessionWantmanager is an interface that can be used to request blocks
+// from given peers.
+type SessionWantManager interface {
+	WantBlocks(ctx context.Context, ks []cid.Cid, peers []peer.ID, ses uint64)
+	CancelWants(ctx context.Context, ks []cid.Cid, peers []peer.ID, ses uint64)
+}
+
+type interestReq struct {
+	c    cid.Cid
+	resp chan bool
+}
+
+type blkRecv struct {
+	from peer.ID
+	blk  blocks.Block
+}
+
 // Session holds state for an individual bitswap transfer operation.
 // This allows bitswap to make smarter decisions about who to send wantlist
 // info to, and who to request blocks from.
 type Session struct {
-	ctx            context.Context
+	// dependencies
+	ctx     context.Context
+	wm      SessionWantManager
+	network bsnet.BitSwapNetwork
+
+	// channels
+	incoming      chan blkRecv
+	newReqs       chan []cid.Cid
+	cancelKeys    chan []cid.Cid
+	interestReqs  chan interestReq
+	latencyReqs   chan chan time.Duration
+	tickDelayReqs chan time.Duration
+
+	// do not touch outside run loop
 	tofetch        *cidQueue
 	activePeers    map[peer.ID]struct{}
 	activePeersArr []peer.ID
-
-	bs           *Bitswap
-	incoming     chan blkRecv
-	newReqs      chan []cid.Cid
-	cancelKeys   chan []cid.Cid
-	interestReqs chan interestReq
-
-	interest  *lru.Cache
-	liveWants map[cid.Cid]time.Time
-
-	tick          *time.Timer
-	baseTickDelay time.Duration
-
-	latTotal time.Duration
-	fetchcnt int
-
+	interest       *lru.Cache
+	liveWants      map[cid.Cid]time.Time
+	tick           *time.Timer
+	baseTickDelay  time.Duration
+	latTotal       time.Duration
+	fetchcnt       int
+
+	// identifiers
 	notif notifications.PubSub
-
-	uuid logging.Loggable
-
-	id  uint64
-	tag string
+	uuid  logging.Loggable
+	id    uint64
+	tag   string
 }
 
-// NewSession creates a new bitswap session whose lifetime is bounded by the
+// New creates a new bitswap session whose lifetime is bounded by the
 // given context.
-func (bs *Bitswap) NewSession(ctx context.Context) exchange.Fetcher {
+func New(ctx context.Context, id uint64, wm SessionWantManager, network bsnet.BitSwapNetwork) *Session {
 	s := &Session{
 		activePeers:   make(map[peer.ID]struct{}),
 		liveWants:     make(map[cid.Cid]time.Time),
@@ -60,13 +80,16 @@ func (bs *Bitswap) NewSession(ctx context.Context) exchange.Fetcher {
 		cancelKeys:    make(chan []cid.Cid),
 		tofetch:       newCidQueue(),
 		interestReqs:  make(chan interestReq),
+		latencyReqs:   make(chan chan time.Duration),
+		tickDelayReqs: make(chan time.Duration),
 		ctx:           ctx,
-		bs:            bs,
+		wm:            wm,
+		network:       network,
 		incoming:      make(chan blkRecv),
 		notif:         notifications.New(),
 		uuid:          loggables.Uuid("GetBlockRequest"),
 		baseTickDelay: time.Millisecond * 500,
-		id:            bs.sm.GetNextSessionID(),
+		id:            id,
 	}
 
 	s.tag = fmt.Sprint("bs-ses-", s.id)
@@ -74,39 +97,63 @@ func (bs *Bitswap) NewSession(ctx context.Context) exchange.Fetcher {
 	cache, _ := lru.New(2048)
 	s.interest = cache
 
-	bs.sm.AddSession(s)
 	go s.run(ctx)
 
 	return s
 }
 
-func (bs *Bitswap) removeSession(s *Session) {
-	s.notif.Shutdown()
-
-	live := make([]cid.Cid, 0, len(s.liveWants))
-	for c := range s.liveWants {
-		live = append(live, c)
+// ReceiveBlockFrom receives an incoming block from the given peer.
+func (s *Session) ReceiveBlockFrom(from peer.ID, blk blocks.Block) {
+	select {
+	case s.incoming <- blkRecv{from: from, blk: blk}:
+	case <-s.ctx.Done():
 	}
-	bs.CancelWants(live, s.id)
+}
 
-	bs.sm.RemoveSession(s)
+// InterestedIn returns true if this session is interested in the given Cid.
+func (s *Session) InterestedIn(c cid.Cid) bool {
+	return s.interest.Contains(c) || s.isLiveWant(c)
 }
 
-type blkRecv struct {
-	from peer.ID
-	blk  blocks.Block
+// GetBlock fetches a single block.
+func (s *Session) GetBlock(parent context.Context, k cid.Cid) (blocks.Block, error) {
+	return bsgetter.SyncGetBlock(parent, k, s.GetBlocks)
+}
+
+// GetBlocks fetches a set of blocks within the context of this session and
+// returns a channel that found blocks will be returned on. No order is
+// guaranteed on the returned blocks.
+func (s *Session) GetBlocks(ctx context.Context, keys []cid.Cid) (<-chan blocks.Block, error) {
+	ctx = logging.ContextWithLoggable(ctx, s.uuid)
+	return bsgetter.AsyncGetBlocks(ctx, keys, s.notif, s.fetch, s.cancel)
+}
+
+// ID returns the sessions identifier.
+func (s *Session) ID() uint64 {
+	return s.id
 }
 
-func (s *Session) receiveBlockFrom(from peer.ID, blk blocks.Block) {
+func (s *Session) GetAverageLatency() time.Duration {
+	resp := make(chan time.Duration)
 	select {
-	case s.incoming <- blkRecv{from: from, blk: blk}:
+	case s.latencyReqs <- resp:
+	case <-s.ctx.Done():
+		return -1 * time.Millisecond
+	}
+
+	select {
+	case latency := <-resp:
+		return latency
 	case <-s.ctx.Done():
+		return -1 * time.Millisecond
 	}
 }
 
-type interestReq struct {
-	c    cid.Cid
-	resp chan bool
+func (s *Session) SetBaseTickDelay(baseTickDelay time.Duration) {
+	select {
+	case s.tickDelayReqs <- baseTickDelay:
+	case <-s.ctx.Done():
+	}
 }
 
 // TODO: PERF: this is using a channel to guard a map access against race
@@ -135,114 +182,147 @@ func (s *Session) isLiveWant(c cid.Cid) bool {
 	}
 }
 
-func (s *Session) interestedIn(c cid.Cid) bool {
-	return s.interest.Contains(c) || s.isLiveWant(c)
-}
-
-const provSearchDelay = time.Second * 10
-
-func (s *Session) addActivePeer(p peer.ID) {
-	if _, ok := s.activePeers[p]; !ok {
-		s.activePeers[p] = struct{}{}
-		s.activePeersArr = append(s.activePeersArr, p)
-
-		cmgr := s.bs.network.ConnectionManager()
-		cmgr.TagPeer(p, s.tag, 10)
+func (s *Session) fetch(ctx context.Context, keys []cid.Cid) {
+	select {
+	case s.newReqs <- keys:
+	case <-ctx.Done():
+	case <-s.ctx.Done():
 	}
 }
 
-func (s *Session) resetTick() {
-	if s.latTotal == 0 {
-		s.tick.Reset(provSearchDelay)
-	} else {
-		avLat := s.latTotal / time.Duration(s.fetchcnt)
-		s.tick.Reset(s.baseTickDelay + (3 * avLat))
+func (s *Session) cancel(keys []cid.Cid) {
+	select {
+	case s.cancelKeys <- keys:
+	case <-s.ctx.Done():
 	}
 }
 
+const provSearchDelay = time.Second * 10
+
+// Session run loop -- everything function below here should not be called
+// of this loop
 func (s *Session) run(ctx context.Context) {
 	s.tick = time.NewTimer(provSearchDelay)
 	newpeers := make(chan peer.ID, 16)
 	for {
 		select {
 		case blk := <-s.incoming:
-			s.tick.Stop()
-
-			if blk.from != "" {
-				s.addActivePeer(blk.from)
-			}
-
-			s.receiveBlock(ctx, blk.blk)
-
-			s.resetTick()
+			s.handleIncomingBlock(ctx, blk)
 		case keys := <-s.newReqs:
-			for _, k := range keys {
-				s.interest.Add(k, nil)
-			}
-			if len(s.liveWants) < activeWantsLimit {
-				toadd := activeWantsLimit - len(s.liveWants)
-				if toadd > len(keys) {
-					toadd = len(keys)
-				}
-
-				now := keys[:toadd]
-				keys = keys[toadd:]
-
-				s.wantBlocks(ctx, now)
-			}
-			for _, k := range keys {
-				s.tofetch.Push(k)
-			}
+			s.handleNewRequest(ctx, keys)
 		case keys := <-s.cancelKeys:
-			s.cancel(keys)
-
+			s.handleCancel(keys)
 		case <-s.tick.C:
-			live := make([]cid.Cid, 0, len(s.liveWants))
-			now := time.Now()
-			for c := range s.liveWants {
-				live = append(live, c)
-				s.liveWants[c] = now
-			}
-
-			// Broadcast these keys to everyone we're connected to
-			s.bs.wm.WantBlocks(ctx, live, nil, s.id)
-
-			if len(live) > 0 {
-				go func(k cid.Cid) {
-					// TODO: have a task queue setup for this to:
-					// - rate limit
-					// - manage timeouts
-					// - ensure two 'findprovs' calls for the same block don't run concurrently
-					// - share peers between sessions based on interest set
-					for p := range s.bs.network.FindProvidersAsync(ctx, k, 10) {
-						newpeers <- p
-					}
-				}(live[0])
-			}
-			s.resetTick()
+			s.handleTick(ctx, newpeers)
 		case p := <-newpeers:
 			s.addActivePeer(p)
 		case lwchk := <-s.interestReqs:
 			lwchk.resp <- s.cidIsWanted(lwchk.c)
+		case resp := <-s.latencyReqs:
+			resp <- s.averageLatency()
+		case baseTickDelay := <-s.tickDelayReqs:
+			s.baseTickDelay = baseTickDelay
 		case <-ctx.Done():
-			s.tick.Stop()
-			s.bs.removeSession(s)
-
-			cmgr := s.bs.network.ConnectionManager()
-			for _, p := range s.activePeersArr {
-				cmgr.UntagPeer(p, s.tag)
-			}
+			s.handleShutdown()
 			return
 		}
 	}
 }
 
+func (s *Session) handleIncomingBlock(ctx context.Context, blk blkRecv) {
+	s.tick.Stop()
+
+	if blk.from != "" {
+		s.addActivePeer(blk.from)
+	}
+
+	s.receiveBlock(ctx, blk.blk)
+
+	s.resetTick()
+}
+
+func (s *Session) handleNewRequest(ctx context.Context, keys []cid.Cid) {
+	for _, k := range keys {
+		s.interest.Add(k, nil)
+	}
+	if len(s.liveWants) < activeWantsLimit {
+		toadd := activeWantsLimit - len(s.liveWants)
+		if toadd > len(keys) {
+			toadd = len(keys)
+		}
+
+		now := keys[:toadd]
+		keys = keys[toadd:]
+
+		s.wantBlocks(ctx, now)
+	}
+	for _, k := range keys {
+		s.tofetch.Push(k)
+	}
+}
+
+func (s *Session) handleCancel(keys []cid.Cid) {
+	for _, c := range keys {
+		s.tofetch.Remove(c)
+	}
+}
+
+func (s *Session) handleTick(ctx context.Context, newpeers chan<- peer.ID) {
+	live := make([]cid.Cid, 0, len(s.liveWants))
+	now := time.Now()
+	for c := range s.liveWants {
+		live = append(live, c)
+		s.liveWants[c] = now
+	}
+
+	// Broadcast these keys to everyone we're connected to
+	s.wm.WantBlocks(ctx, live, nil, s.id)
+
+	if len(live) > 0 {
+		go func(k cid.Cid) {
+			// TODO: have a task queue setup for this to:
+			// - rate limit
+			// - manage timeouts
+			// - ensure two 'findprovs' calls for the same block don't run concurrently
+			// - share peers between sessions based on interest set
+			for p := range s.network.FindProvidersAsync(ctx, k, 10) {
+				newpeers <- p
+			}
+		}(live[0])
+	}
+	s.resetTick()
+}
+
+func (s *Session) addActivePeer(p peer.ID) {
+	if _, ok := s.activePeers[p]; !ok {
+		s.activePeers[p] = struct{}{}
+		s.activePeersArr = append(s.activePeersArr, p)
+
+		cmgr := s.network.ConnectionManager()
+		cmgr.TagPeer(p, s.tag, 10)
+	}
+}
+
+func (s *Session) handleShutdown() {
+	s.tick.Stop()
+	s.notif.Shutdown()
+
+	live := make([]cid.Cid, 0, len(s.liveWants))
+	for c := range s.liveWants {
+		live = append(live, c)
+	}
+	s.wm.CancelWants(s.ctx, live, nil, s.id)
+	cmgr := s.network.ConnectionManager()
+	for _, p := range s.activePeersArr {
+		cmgr.UntagPeer(p, s.tag)
+	}
+}
+
 func (s *Session) cidIsWanted(c cid.Cid) bool {
 	_, ok := s.liveWants[c]
 	if !ok {
 		ok = s.tofetch.Has(c)
 	}
-
 	return ok
 }
 
@@ -270,43 +350,21 @@ func (s *Session) wantBlocks(ctx context.Context, ks []cid.Cid) {
 	for _, c := range ks {
 		s.liveWants[c] = now
 	}
-	s.bs.wm.WantBlocks(ctx, ks, s.activePeersArr, s.id)
+	s.wm.WantBlocks(ctx, ks, s.activePeersArr, s.id)
 }
 
-func (s *Session) cancel(keys []cid.Cid) {
-	for _, c := range keys {
-		s.tofetch.Remove(c)
-	}
-}
-
-func (s *Session) cancelWants(keys []cid.Cid) {
-	select {
-	case s.cancelKeys <- keys:
-	case <-s.ctx.Done():
-	}
+func (s *Session) averageLatency() time.Duration {
+	return s.latTotal / time.Duration(s.fetchcnt)
 }
-
-func (s *Session) fetch(ctx context.Context, keys []cid.Cid) {
-	select {
-	case s.newReqs <- keys:
-	case <-ctx.Done():
-	case <-s.ctx.Done():
+func (s *Session) resetTick() {
+	if s.latTotal == 0 {
+		s.tick.Reset(provSearchDelay)
+	} else {
+		avLat := s.averageLatency()
+		s.tick.Reset(s.baseTickDelay + (3 * avLat))
 	}
 }
 
-// GetBlocks fetches a set of blocks within the context of this session and
-// returns a channel that found blocks will be returned on. No order is
-// guaranteed on the returned blocks.
-func (s *Session) GetBlocks(ctx context.Context, keys []cid.Cid) (<-chan blocks.Block, error) {
-	ctx = logging.ContextWithLoggable(ctx, s.uuid)
-	return getBlocksImpl(ctx, keys, s.notif, s.fetch, s.cancelWants)
-}
-
-// GetBlock fetches a single block.
-func (s *Session) GetBlock(parent context.Context, k cid.Cid) (blocks.Block, error) {
-	return getBlock(parent, k, s.GetBlocks)
-}
-
 type cidQueue struct {
 	elems []cid.Cid
 	eset  *cid.Set

sessionmanager/sessionmanager.go

 package sessionmanager
 
 import (
+	"context"
 	"sync"
 
+	blocks "github.com/ipfs/go-block-format"
+	cid "github.com/ipfs/go-cid"
+
+	bsnet "github.com/ipfs/go-bitswap/network"
+	bssession "github.com/ipfs/go-bitswap/session"
+	bswm "github.com/ipfs/go-bitswap/wantmanager"
 	exchange "github.com/ipfs/go-ipfs-exchange-interface"
+	peer "github.com/libp2p/go-libp2p-peer"
 )
 
+// SessionManager is responsible for creating, managing, and dispatching to
+// sessions.
 type SessionManager struct {
+	wm      *bswm.WantManager
+	network bsnet.BitSwapNetwork
+	ctx     context.Context
 	// Sessions
 	sessLk   sync.Mutex
-	sessions []exchange.Fetcher
+	sessions []*bssession.Session
 
 	// Session Index
 	sessIDLk sync.Mutex
 	sessID   uint64
 }
 
-func New() *SessionManager {
-	return &SessionManager{}
+// New creates a new SessionManager.
+func New(ctx context.Context, wm *bswm.WantManager, network bsnet.BitSwapNetwork) *SessionManager {
+	return &SessionManager{
+		ctx:     ctx,
+		wm:      wm,
+		network: network,
+	}
 }
 
-func (sm *SessionManager) AddSession(session exchange.Fetcher) {
+// NewSession initializes a session with the given context, and adds to the
+// session manager.
+func (sm *SessionManager) NewSession(ctx context.Context) exchange.Fetcher {
+	id := sm.GetNextSessionID()
+	sessionctx, cancel := context.WithCancel(ctx)
+
+	session := bssession.New(sessionctx, id, sm.wm, sm.network)
 	sm.sessLk.Lock()
 	sm.sessions = append(sm.sessions, session)
 	sm.sessLk.Unlock()
+	go func() {
+		for {
+			defer cancel()
+			select {
+			case <-sm.ctx.Done():
+				sm.removeSession(session)
+				return
+			case <-ctx.Done():
+				sm.removeSession(session)
+				return
+			}
+		}
+	}()
+
+	return session
 }
 
-func (sm *SessionManager) RemoveSession(session exchange.Fetcher) {
+func (sm *SessionManager) removeSession(session exchange.Fetcher) {
 	sm.sessLk.Lock()
 	defer sm.sessLk.Unlock()
 	for i := 0; i < len(sm.sessions); i++ {
@@ -38,6 +77,7 @@ func (sm *SessionManager) RemoveSession(session exchange.Fetcher) {
 	}
 }
 
+// GetNextSessionID returns the next sequentional identifier for a session.
 func (sm *SessionManager) GetNextSessionID() uint64 {
 	sm.sessIDLk.Lock()
 	defer sm.sessIDLk.Unlock()
@@ -45,15 +85,18 @@ func (sm *SessionManager) GetNextSessionID() uint64 {
 	return sm.sessID
 }
 
-type IterateSessionFunc func(session exchange.Fetcher)
-
-// IterateSessions loops through all managed sessions and applies the given
-// IterateSessionFunc.
-func (sm *SessionManager) IterateSessions(iterate IterateSessionFunc) {
+// ReceiveBlockFrom receives a block from a peer and dispatches to interested
+// sessions.
+func (sm *SessionManager) ReceiveBlockFrom(from peer.ID, blk blocks.Block) {
 	sm.sessLk.Lock()
 	defer sm.sessLk.Unlock()
 
+	k := blk.Cid()
+	ks := []cid.Cid{k}
 	for _, s := range sm.sessions {
-		iterate(s)
+		if s.InterestedIn(k) {
+			s.ReceiveBlockFrom(from, blk)
+			sm.wm.CancelWants(sm.ctx, ks, nil, s.ID())
+		}
 	}
 }