p2p: Remove data race bug in netaddr stringer (#5048)

## Description

Remove concurrent write access bug by removing the memoized string representation of a `NetAddress`.

Closes: #5047

p2p/netaddress.go

@@ -17,18 +17,15 @@ import (
 	tmp2p "github.com/tendermint/tendermint/proto/tendermint/p2p"
 )
 
+// EmptyNetAddress defines the string representation of an empty NetAddress
+const EmptyNetAddress = "<nil-NetAddress>"
+
 // NetAddress defines information about a peer on the network
 // including its ID, IP address, and port.
 type NetAddress struct {
 	ID   ID     `json:"id"`
 	IP   net.IP `json:"ip"`
 	Port uint16 `json:"port"`
-
-	// TODO:
-	// Name string `json:"name"` // optional DNS name
-
-	// memoize .String()
-	str string
 }
 
 // IDAddressString returns id@hostPort. It strips the leading
@@ -213,16 +210,15 @@ func (na *NetAddress) Same(other interface{}) bool {
 // String representation: <ID>@<IP>:<PORT>
 func (na *NetAddress) String() string {
 	if na == nil {
-		return "<nil-NetAddress>"
+		return EmptyNetAddress
 	}
-	if na.str == "" {
-		addrStr := na.DialString()
-		if na.ID != "" {
-			addrStr = IDAddressString(na.ID, addrStr)
-		}
-		na.str = addrStr
+
+	addrStr := na.DialString()
+	if na.ID != "" {
+		addrStr = IDAddressString(na.ID, addrStr)
 	}
-	return na.str
+
+	return addrStr
 }
 
 func (na *NetAddress) DialString() string {

p2p/netaddress_test.go

@@ -2,12 +2,35 @@ package p2p
 
 import (
 	"net"
+	"sync"
 	"testing"
 
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 )
 
+func TestNetAddress_String(t *testing.T) {
+	tcpAddr, err := net.ResolveTCPAddr("tcp", "127.0.0.1:8080")
+	require.Nil(t, err)
+
+	netAddr := NewNetAddress("deadbeefdeadbeefdeadbeefdeadbeefdeadbeef", tcpAddr)
+
+	var wg sync.WaitGroup
+
+	for i := 0; i < 10; i++ {
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			_ = netAddr.String()
+		}()
+	}
+
+	wg.Wait()
+
+	s := netAddr.String()
+	require.Equal(t, "deadbeefdeadbeefdeadbeefdeadbeefdeadbeef@127.0.0.1:8080", s)
+}
+
 func TestNewNetAddress(t *testing.T) {
 	tcpAddr, err := net.ResolveTCPAddr("tcp", "127.0.0.1:8080")
 	require.Nil(t, err)