From 889617043c62bc7994df83161a69775ecdd88e7b Mon Sep 17 00:00:00 2001
From: Marten Seemann <martenseemann@gmail.com>
Date: Mon, 25 Oct 2021 15:10:40 +0200
Subject: [PATCH] emit the EvtPeerConnectednessChanged event

---
 p2p/host/basic/basic_host.go              |  5 ++
 p2p/host/basic/peer_connectedness.go      | 73 +++++++++++++++++++++++
 p2p/host/basic/peer_connectedness_test.go | 49 +++++++++++++++
 3 files changed, 127 insertions(+)
 create mode 100644 p2p/host/basic/peer_connectedness.go
 create mode 100644 p2p/host/basic/peer_connectedness_test.go

diff --git a/p2p/host/basic/basic_host.go b/p2p/host/basic/basic_host.go
index 0950a803e9..958dd8763b 100644
--- a/p2p/host/basic/basic_host.go
+++ b/p2p/host/basic/basic_host.go
@@ -183,6 +183,11 @@ func NewHost(n network.Network, opts *HostOpts) (*BasicHost, error) {
 	if h.emitters.evtLocalAddrsUpdated, err = h.eventbus.Emitter(&event.EvtLocalAddressesUpdated{}, eventbus.Stateful); err != nil {
 		return nil, err
 	}
+	evtPeerConnectednessChanged, err := h.eventbus.Emitter(&event.EvtPeerConnectednessChanged{})
+	if err != nil {
+		return nil, err
+	}
+	h.Network().Notify(newPeerConnectWatcher(evtPeerConnectednessChanged))
 
 	if !h.disableSignedPeerRecord {
 		cab, ok := peerstore.GetCertifiedAddrBook(n.Peerstore())
diff --git a/p2p/host/basic/peer_connectedness.go b/p2p/host/basic/peer_connectedness.go
new file mode 100644
index 0000000000..a0ba17c3da
--- /dev/null
+++ b/p2p/host/basic/peer_connectedness.go
@@ -0,0 +1,73 @@
+package basichost
+
+import (
+	"sync"
+
+	"github.com/libp2p/go-libp2p-core/event"
+	"github.com/libp2p/go-libp2p-core/network"
+	"github.com/libp2p/go-libp2p-core/peer"
+
+	ma "github.com/multiformats/go-multiaddr"
+)
+
+type peerConnectWatcher struct {
+	emitter event.Emitter
+
+	mutex     sync.Mutex
+	connected map[peer.ID]struct{}
+}
+
+var _ network.Notifiee = &peerConnectWatcher{}
+
+func newPeerConnectWatcher(emitter event.Emitter) *peerConnectWatcher {
+	return &peerConnectWatcher{
+		emitter:   emitter,
+		connected: make(map[peer.ID]struct{}),
+	}
+}
+
+func (w *peerConnectWatcher) Listen(network.Network, ma.Multiaddr)         {}
+func (w *peerConnectWatcher) ListenClose(network.Network, ma.Multiaddr)    {}
+func (w *peerConnectWatcher) OpenedStream(network.Network, network.Stream) {}
+func (w *peerConnectWatcher) ClosedStream(network.Network, network.Stream) {}
+
+func (w *peerConnectWatcher) Connected(n network.Network, conn network.Conn) {
+	p := conn.RemotePeer()
+	w.handleTransition(p, n.Connectedness(p))
+}
+
+func (w *peerConnectWatcher) Disconnected(n network.Network, conn network.Conn) {
+	p := conn.RemotePeer()
+	w.handleTransition(p, n.Connectedness(p))
+}
+
+func (w *peerConnectWatcher) handleTransition(p peer.ID, state network.Connectedness) {
+	if changed := w.checkTransition(p, state); !changed {
+		return
+	}
+	w.emitter.Emit(event.EvtPeerConnectednessChanged{
+		Peer:          p,
+		Connectedness: state,
+	})
+}
+
+func (w *peerConnectWatcher) checkTransition(p peer.ID, state network.Connectedness) bool {
+	w.mutex.Lock()
+	defer w.mutex.Unlock()
+	switch state {
+	case network.Connected:
+		if _, ok := w.connected[p]; ok {
+			return false
+		}
+		w.connected[p] = struct{}{}
+		return true
+	case network.NotConnected:
+		if _, ok := w.connected[p]; ok {
+			delete(w.connected, p)
+			return true
+		}
+		return false
+	default:
+		return false
+	}
+}
diff --git a/p2p/host/basic/peer_connectedness_test.go b/p2p/host/basic/peer_connectedness_test.go
new file mode 100644
index 0000000000..9b44302282
--- /dev/null
+++ b/p2p/host/basic/peer_connectedness_test.go
@@ -0,0 +1,49 @@
+package basichost
+
+import (
+	"context"
+	"testing"
+	"time"
+
+	"github.com/libp2p/go-libp2p-core/network"
+
+	"github.com/libp2p/go-libp2p-core/event"
+	"github.com/libp2p/go-libp2p-core/peer"
+	swarmt "github.com/libp2p/go-libp2p-swarm/testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestPeerConnectedness(t *testing.T) {
+	h1, err := NewHost(swarmt.GenSwarm(t), nil)
+	require.NoError(t, err)
+	defer h1.Close()
+	h2, err := NewHost(swarmt.GenSwarm(t), nil)
+	require.NoError(t, err)
+
+	sub1, err := h1.EventBus().Subscribe(&event.EvtPeerConnectednessChanged{})
+	require.NoError(t, err)
+	defer sub1.Close()
+	sub2, err := h2.EventBus().Subscribe(&event.EvtPeerConnectednessChanged{})
+	require.NoError(t, err)
+	defer sub2.Close()
+
+	ctx, cancel := context.WithTimeout(context.Background(), 5*time.Second)
+	defer cancel()
+	require.NoError(t, h1.Connect(ctx, peer.AddrInfo{ID: h2.ID(), Addrs: h2.Addrs()}))
+	require.Equal(t, (<-sub1.Out()).(event.EvtPeerConnectednessChanged), event.EvtPeerConnectednessChanged{
+		Peer:          h2.ID(),
+		Connectedness: network.Connected,
+	})
+	require.Equal(t, (<-sub2.Out()).(event.EvtPeerConnectednessChanged), event.EvtPeerConnectednessChanged{
+		Peer:          h1.ID(),
+		Connectedness: network.Connected,
+	})
+
+	// now close h2. This will disconnect it from h1.
+	require.NoError(t, h2.Close())
+	require.Equal(t, (<-sub1.Out()).(event.EvtPeerConnectednessChanged), event.EvtPeerConnectednessChanged{
+		Peer:          h2.ID(),
+		Connectedness: network.NotConnected,
+	})
+}