Add connection trust flag, and more tests with small caches

Thanks to observations and feedback from @ccampbell.

Peer.go

@@ -8,6 +8,7 @@ import (
 	"github.com/anacrolix/torrent/peer_protocol"
 )
 
+// Peer connection info, handed about publicly.
 type Peer struct {
 	Id     [20]byte
 	IP     net.IP
@@ -16,6 +17,8 @@ type Peer struct {
 	// Peer is known to support encryption.
 	SupportsEncryption bool
 	peer_protocol.PexPeerFlags
+	// Whether we can ignore poor or bad behaviour from the peer.
+	Trusted bool
 }
 
 func (me *Peer) FromPex(na krpc.NodeAddr, fs peer_protocol.PexPeerFlags) {

client.go

@@ -19,12 +19,12 @@ import (
 	"github.com/anacrolix/dht/v2"
 	"github.com/anacrolix/dht/v2/krpc"
 	"github.com/anacrolix/log"
-	"github.com/anacrolix/missinggo"
 	"github.com/anacrolix/missinggo/bitmap"
 	"github.com/anacrolix/missinggo/perf"
 	"github.com/anacrolix/missinggo/pproffd"
 	"github.com/anacrolix/missinggo/pubsub"
 	"github.com/anacrolix/missinggo/slices"
+	"github.com/anacrolix/missinggo/v2"
 	"github.com/anacrolix/missinggo/v2/conntrack"
 	"github.com/anacrolix/sync"
 	"github.com/davecgh/go-spew/spew"
@@ -690,7 +690,7 @@ func (cl *Client) establishOutgoingConn(t *Torrent, addr IpPort) (c *connection,
 
 // Called to dial out and run a connection. The addr we're given is already
 // considered half-open.
-func (cl *Client) outgoingConnection(t *Torrent, addr IpPort, ps peerSource) {
+func (cl *Client) outgoingConnection(t *Torrent, addr IpPort, ps peerSource, trusted bool) {
 	cl.dialRateLimiter.Wait(context.Background())
 	c, err := cl.establishOutgoingConn(t, addr)
 	cl.lock()
@@ -706,6 +706,7 @@ func (cl *Client) outgoingConnection(t *Torrent, addr IpPort, ps peerSource) {
 	}
 	defer c.Close()
 	c.Discovery = ps
+	c.trusted = trusted
 	cl.runHandshookConn(c, t)
 }
 
@@ -1212,6 +1213,7 @@ func (cl *Client) AddDHTNodes(nodes []string) {
 }
 
 func (cl *Client) banPeerIP(ip net.IP) {
+	cl.logger.Printf("banning ip %v", ip)
 	if cl.badPeerIPs == nil {
 		cl.badPeerIPs = make(map[string]struct{})
 	}

client_test.go

@@ -228,7 +228,7 @@ func fileCachePieceResourceStorage(fc *filecache.Cache) storage.ClientImpl {
 	return storage.NewResourcePieces(fc.AsResourceProvider())
 }
 
-func TestClientTransferSmallCache(t *testing.T) {
+func testClientTransferSmallCache(t *testing.T, setReadahead bool, readahead int64) {
 	testClientTransfer(t, testClientTransferParams{
 		LeecherStorage: NewFileCacheClientStorageFactory(FileCacheClientStorageFactoryParams{
 			SetCapacity: true,
@@ -237,14 +237,26 @@ func TestClientTransferSmallCache(t *testing.T) {
 			Capacity: 5,
 			Wrapper:  fileCachePieceResourceStorage,
 		}),
-		SetReadahead: true,
+		SetReadahead: setReadahead,
 		// Can't readahead too far or the cache will thrash and drop data we
 		// thought we had.
-		Readahead:          0,
+		Readahead:          readahead,
 		ExportClientStatus: true,
 	})
 }
 
+func TestClientTransferSmallCachePieceSizedReadahead(t *testing.T) {
+	testClientTransferSmallCache(t, true, 5)
+}
+
+func TestClientTransferSmallCacheLargeReadahead(t *testing.T) {
+	testClientTransferSmallCache(t, true, 15)
+}
+
+func TestClientTransferSmallCacheDefaultReadahead(t *testing.T) {
+	testClientTransferSmallCache(t, false, -1)
+}
+
 func TestClientTransferVarious(t *testing.T) {
 	// Leecher storage
 	for _, ls := range []storageFactory{
@@ -342,6 +354,7 @@ func testClientTransfer(t *testing.T, ps testClientTransferParams) {
 		cfg.DownloadRateLimiter = ps.LeecherDownloadRateLimiter
 	}
 	cfg.Seed = false
+	//cfg.Debug = true
 	leecher, err := NewClient(cfg)
 	require.NoError(t, err)
 	defer leecher.Close()

connection.go

@@ -55,6 +55,7 @@ type connection struct {
 	headerEncrypted bool
 	cryptoMethod    mse.CryptoMethod
 	Discovery       peerSource
+	trusted         bool
 	closed          missinggo.Event
 	// Set true after we've added our ConnStats generated during handshake to
 	// other ConnStat instances as determined when the *Torrent became known.
@@ -1568,3 +1569,19 @@ func (c *connection) remoteIpPort() IpPort {
 func (c *connection) String() string {
 	return fmt.Sprintf("connection %p", c)
 }
+
+func (c *connection) trust() connectionTrust {
+	return connectionTrust{c.trusted, c.netGoodPiecesDirtied()}
+}
+
+type connectionTrust struct {
+	Implicit            bool
+	NetGoodPiecesDirted int64
+}
+
+func (l connectionTrust) Less(r connectionTrust) bool {
+	var ml missinggo.MultiLess
+	ml.NextBool(!l.Implicit, !r.Implicit)
+	ml.StrictNext(l.NetGoodPiecesDirted == r.NetGoodPiecesDirted, l.NetGoodPiecesDirted < r.NetGoodPiecesDirted)
+	return ml.Less()
+}

misc.go

@@ -4,7 +4,7 @@ import (
 	"errors"
 	"net"
 
-	"github.com/anacrolix/missinggo"
+	"github.com/anacrolix/missinggo/v2"
 	"golang.org/x/time/rate"
 
 	"github.com/anacrolix/torrent/metainfo"
@@ -107,7 +107,7 @@ func chunkIndexSpec(index pp.Integer, pieceLength, chunkSize pp.Integer) chunkSp
 }
 
 func connLessTrusted(l, r *connection) bool {
-	return l.netGoodPiecesDirtied() < r.netGoodPiecesDirtied()
+	return l.trust().Less(r.trust())
 }
 
 func connIsIpv6(nc interface {

torrent.go

@@ -1548,8 +1548,7 @@ func (t *Torrent) pieceHashed(piece pieceIndex, correct bool) {
 		}
 	} else {
 		if len(touchers) != 0 {
-			// Don't increment stats above connection-level for every involved
+			// Don't increment stats above connection-level for every involved connection.
-			// connection.
 			t.allStats((*ConnStats).incrementPiecesDirtiedBad)
 			for _, c := range touchers {
 				// Y u do dis peer?!
@@ -1557,17 +1556,21 @@ func (t *Torrent) pieceHashed(piece pieceIndex, correct bool) {
 			}
 			slices.Sort(touchers, connLessTrusted)
 			if t.cl.config.Debug {
-				t.logger.Printf("dropping first corresponding conn from trust: %v", func() (ret []int64) {
+				t.logger.Printf("conns by trust for piece %d: %v",
+					piece,
+					func() (ret []connectionTrust) {
 						for _, c := range touchers {
-						ret = append(ret, c.netGoodPiecesDirtied())
+							ret = append(ret, c.trust())
 						}
 						return
 					}())
 			}
 			c := touchers[0]
+			if !c.trust().Implicit {
 				t.cl.banPeerIP(c.remoteAddr.IP)
 				c.Drop()
 			}
+		}
 		t.onIncompletePiece(piece)
 		p.Storage().MarkNotComplete()
 	}
@@ -1702,13 +1705,12 @@ func (t *Torrent) VerifyData() {
 	}
 }
 
-// Start the process of connecting to the given peer for the given torrent if
+// Start the process of connecting to the given peer for the given torrent if appropriate.
-// appropriate.
 func (t *Torrent) initiateConn(peer Peer) {
 	if peer.Id == t.cl.peerID {
 		return
 	}
-	if t.cl.badPeerIPPort(peer.IP, peer.Port) {
+	if t.cl.badPeerIPPort(peer.IP, peer.Port) && !peer.Trusted {
 		return
 	}
 	addr := IpPort{peer.IP, uint16(peer.Port)}
@@ -1716,15 +1718,17 @@ func (t *Torrent) initiateConn(peer Peer) {
 		return
 	}
 	t.halfOpen[addr.String()] = peer
-	go t.cl.outgoingConnection(t, addr, peer.Source)
+	go t.cl.outgoingConnection(t, addr, peer.Source, peer.Trusted)
 }
 
+// Adds each a trusted, pending peer for each of the Client's addresses.
 func (t *Torrent) AddClientPeer(cl *Client) {
 	t.AddPeers(func() (ps []Peer) {
 		for _, la := range cl.ListenAddrs() {
 			ps = append(ps, Peer{
 				IP:      missinggo.AddrIP(la),
 				Port:    missinggo.AddrPort(la),
+				Trusted: true,
 			})
 		}
 		return