feat(dial): implement the Timeout interface on dial errors

dial_error.go

@@ -2,6 +2,7 @@ package swarm
 
 import (
 	"fmt"
+	"os"
 	"strings"
 
 	"github.com/libp2p/go-libp2p-core/peer"
@@ -20,6 +21,10 @@ type DialError struct {
 	Skipped    int
 }
 
+func (e *DialError) Timeout() bool {
+	return os.IsTimeout(e.Cause)
+}
+
 func (e *DialError) recordErr(addr ma.Multiaddr, err error) {
 	if len(e.DialErrors) >= maxDialDialErrors {
 		e.Skipped++
@@ -48,11 +53,7 @@ func (e *DialError) Error() string {
 
 // Unwrap implements https://godoc.org/golang.org/x/xerrors#Wrapper.
 func (e *DialError) Unwrap() error {
-	// If we have a context error, that's the "ultimate" error.
-	if e.Cause != nil {
-		return e.Cause
-	}
-	return nil
+	return e.Cause
 }
 
 var _ error = (*DialError)(nil)