feat: close transports that implement io.Closer

This way, transports with shared resources (e.g., reused sockets) can clean them
up.

fixes https://github.com/libp2p/go-libp2p/issues/999

swarm.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"errors"
 	"fmt"
+	"io"
 	"strings"
 	"sync"
 	"sync/atomic"
@@ -176,6 +177,27 @@ func (s *Swarm) teardown() error {
 	// Wait for everything to finish.
 	s.refs.Wait()
 
+	// Now close out any transports (if necessary). Do this after closing
+	// all connections/listeners.
+	s.transports.Lock()
+	transports := s.transports.m
+	s.transports.m = nil
+	s.transports.Unlock()
+
+	var wg sync.WaitGroup
+	for _, t := range transports {
+		if closer, ok := t.(io.Closer); ok {
+			wg.Add(1)
+			go func(c io.Closer) {
+				defer wg.Done()
+				if err := closer.Close(); err != nil {
+					log.Errorf("error when closing down transport %T: %s", c, err)
+				}
+			}(closer)
+		}
+	}
+	wg.Wait()
+
 	return nil
 }
 

swarm_listen.go

@@ -40,7 +40,17 @@ func (s *Swarm) Listen(addrs ...ma.Multiaddr) error {
 func (s *Swarm) AddListenAddr(a ma.Multiaddr) error {
 	tpt := s.TransportForListening(a)
 	if tpt == nil {
-		return ErrNoTransport
+		// TransportForListening will return nil if either:
+		// 1. No transport has been registered.
+		// 2. We're closed (so we've nulled out the transport map.
+		//
+		// Distinguish between these two cases to avoid confusing users.
+		select {
+		case <-s.proc.Closing():
+			return ErrSwarmClosed
+		default:
+			return ErrNoTransport
+		}
 	}
 
 	list, err := tpt.Listen(a)

swarm_transport.go

@@ -20,7 +20,10 @@ func (s *Swarm) TransportForDialing(a ma.Multiaddr) transport.Transport {
 	s.transports.RLock()
 	defer s.transports.RUnlock()
 	if len(s.transports.m) == 0 {
-		log.Error("you have no transports configured")
+		// make sure we're not just shutting down.
+		if s.transports.m != nil {
+			log.Error("you have no transports configured")
+		}
 		return nil
 	}
 
@@ -48,7 +51,10 @@ func (s *Swarm) TransportForListening(a ma.Multiaddr) transport.Transport {
 	s.transports.RLock()
 	defer s.transports.RUnlock()
 	if len(s.transports.m) == 0 {
-		log.Error("you have no transports configured")
+		// make sure we're not just shutting down.
+		if s.transports.m != nil {
+			log.Error("you have no transports configured")
+		}
 		return nil
 	}
 
@@ -77,6 +83,9 @@ func (s *Swarm) AddTransport(t transport.Transport) error {
 
 	s.transports.Lock()
 	defer s.transports.Unlock()
+	if s.transports.m == nil {
+		return ErrSwarmClosed
+	}
 	var registered []string
 	for _, p := range protocols {
 		if _, ok := s.transports.m[p]; ok {

transport_test.go

@@ -4,6 +4,7 @@ import (
 	"context"
 	"testing"
 
+	swarm "github.com/libp2p/go-libp2p-swarm"
 	swarmt "github.com/libp2p/go-libp2p-swarm/testing"
 
 	"github.com/libp2p/go-libp2p-core/peer"
@@ -14,6 +15,7 @@ import (
 type dummyTransport struct {
 	protocols []int
 	proxy     bool
+	closed    bool
 }
 
 func (dt *dummyTransport) Dial(ctx context.Context, raddr ma.Multiaddr, p peer.ID) (transport.CapableConn, error) {
@@ -35,13 +37,44 @@ func (dt *dummyTransport) Proxy() bool {
 func (dt *dummyTransport) Protocols() []int {
 	return dt.protocols
 }
+func (dt *dummyTransport) Close() error {
+	dt.closed = true
+	return nil
+}
 
 func TestUselessTransport(t *testing.T) {
 	ctx, cancel := context.WithCancel(context.Background())
 	defer cancel()
-	swarm := swarmt.GenSwarm(t, ctx)
-	err := swarm.AddTransport(new(dummyTransport))
+	s := swarmt.GenSwarm(t, ctx)
+	err := s.AddTransport(new(dummyTransport))
 	if err == nil {
 		t.Fatal("adding a transport that supports no protocols should have failed")
 	}
 }
+
+func TestTransportClose(t *testing.T) {
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+	s := swarmt.GenSwarm(t, ctx)
+	tpt := &dummyTransport{protocols: []int{1}}
+	if err := s.AddTransport(tpt); err != nil {
+		t.Fatal(err)
+	}
+	_ = s.Close()
+	if !tpt.closed {
+		t.Fatal("expected transport to be closed")
+	}
+
+}
+
+func TestTransportAfterClose(t *testing.T) {
+	ctx, cancel := context.WithCancel(context.Background())
+	defer cancel()
+	s := swarmt.GenSwarm(t, ctx)
+	s.Close()
+
+	tpt := &dummyTransport{protocols: []int{1}}
+	if err := s.AddTransport(tpt); err != swarm.ErrSwarmClosed {
+		t.Fatal("expected swarm closed error, got: ", err)
+	}
+}