Reduce dial timeouts when there are lots of peers in the backlog

client.go

@@ -387,6 +387,10 @@ func doDial(dial func() (net.Conn, error), ch chan dialResult, utp bool) {
 	}
 }
 
+func reducedDialTimeout(max time.Duration, halfOpenLimit int, pendingPeers int) time.Duration {
+	return max / time.Duration((pendingPeers+halfOpenLimit)/halfOpenLimit)
+}
+
 // Start the process of connecting to the given peer for the given torrent if
 // appropriate.
 func (me *Client) initiateConn(peer Peer, t *torrent) {
@@ -405,6 +409,7 @@ func (me *Client) initiateConn(peer Peer, t *torrent) {
 		// this address so that peers associate our local address with our
 		// listen address.
 
+		dialTimeout := reducedDialTimeout(dialTimeout, me.halfOpenLimit, len(t.Peers))
 		// Initiate connections via TCP and UTP simultaneously. Use the first
 		// one that succeeds.
 		left := 2

client_test.go

@@ -3,6 +3,7 @@ package torrent
 import (
 	"os"
 	"testing"
+	"time"
 
 	"bitbucket.org/anacrolix/go.torrent/testutil"
 	"bitbucket.org/anacrolix/go.torrent/util"
@@ -75,3 +76,24 @@ func TestUnmarshalPEXMsg(t *testing.T) {
 		t.FailNow()
 	}
 }
+
+func TestReducedDialTimeout(t *testing.T) {
+	for _, _case := range []struct {
+		Max             time.Duration
+		HalfOpenLimit   int
+		PendingPeers    int
+		ExpectedReduced time.Duration
+	}{
+		{dialTimeout, 40, 0, dialTimeout},
+		{dialTimeout, 40, 1, dialTimeout},
+		{dialTimeout, 40, 39, dialTimeout},
+		{dialTimeout, 40, 40, dialTimeout / 2},
+		{dialTimeout, 40, 80, dialTimeout / 3},
+		{dialTimeout, 40, 4000, dialTimeout / 101},
+	} {
+		reduced := reducedDialTimeout(_case.Max, _case.HalfOpenLimit, _case.PendingPeers)
+		if reduced != _case.ExpectedReduced {
+			t.Fatalf("expected %s, got %s", _case.ExpectedReduced, reduced)
+		}
+	}
+}