add public RemoveAddress API

after discussion with @ebuchman (https://github.com/tendermint/go-p2p/pull/10#discussion_r96471729)

addrbook.go

@@ -252,15 +252,21 @@ func (a *AddrBook) MarkAttempt(addr *NetAddress) {
 	ka.markAttempt()
 }
 
+// MarkBad currently just ejects the address. In the future, consider
+// blacklisting.
 func (a *AddrBook) MarkBad(addr *NetAddress) {
+	a.RemoveAddress(addr)
+}
+
+// RemoveAddress removes the address from the book.
+func (a *AddrBook) RemoveAddress(addr *NetAddress) {
 	a.mtx.Lock()
 	defer a.mtx.Unlock()
 	ka := a.addrLookup[addr.String()]
 	if ka == nil {
 		return
 	}
-	// We currently just eject the address.
-	// In the future, consider blacklisting.
+	log.Info("Remove address from book", "addr", addr)
 	a.removeFromAllBuckets(ka)
 }
 

addrbook_test.go

@@ -9,6 +9,9 @@ import (
 	"github.com/stretchr/testify/assert"
 )
 
+	"github.com/stretchr/testify/assert"
+)
+
 func createTempFileName(prefix string) string {
 	f, err := ioutil.TempFile("", prefix)
 	if err != nil {
@@ -148,3 +151,19 @@ func randIPv4Address(t *testing.T) *NetAddress {
 		}
 	}
 }
+
+func TestAddrBookRemoveAddress(t *testing.T) {
+	fname := createTempFileName("addrbook_test")
+	book := NewAddrBook(fname, true)
+
+	addr := randIPv4Address()
+	book.AddAddress(addr, addr)
+	assert.Equal(t, 1, book.Size())
+
+	book.RemoveAddress(addr)
+	assert.Equal(t, 0, book.Size())
+
+	nonExistingAddr := randIPv4Address()
+	book.RemoveAddress(nonExistingAddr)
+	assert.Equal(t, 0, book.Size())
+}

pex_reactor.go

@@ -111,10 +111,14 @@ func (r *PEXReactor) AddPeer(p *Peer) {
 }
 
 // RemovePeer implements Reactor by removing peer from the address book.
+//
+// The peer will be proposed to us by other peers (PexAddrsMessage) or himself
+// and we will add him again upon successful connection. Note that other peers
+// will remove him too. The peer will need to send first requests to others by
+// himself (he will have an addrbook or the seeds).
 func (r *PEXReactor) RemovePeer(p *Peer, reason interface{}) {
 	addr := NewNetAddressString(p.ListenAddr)
-	// addr will be ejected from the book
-	r.book.MarkBad(addr)
+	r.book.RemoveAddress(addr)
 }
 
 // Receive implements Reactor by handling incoming PEX messages.