portlist: exclude services bound to IPv6 loopback address

Fixes #1683

Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

portlist/netstat.go

@@ -42,7 +42,10 @@ func parsePort(s string) int {
 }
 
 func isLoopbackAddr(s string) bool {
-	return strings.HasPrefix(s, "127.0.0.1:") || strings.HasPrefix(s, "127.0.0.1.")
+	return strings.HasPrefix(s, "127.0.0.1:") ||
+		strings.HasPrefix(s, "127.0.0.1.") ||
+		strings.HasPrefix(s, "[::1]:") ||
+		strings.HasPrefix(s, "::1.")
 }
 
 type nothing struct{}

portlist/netstat_test.go

@@ -5,6 +5,7 @@
 package portlist
 
 import (
+	"encoding/json"
 	"testing"
 )
 
@@ -41,6 +42,10 @@ udp6       0      0 :::5354                 :::*
 // macOS
 tcp4       0      0  *.23                   *.*                    LISTEN     
 tcp6       0      0  *.24                   *.*                    LISTEN
+tcp4      0      0  *.8185                 *.*                    LISTEN
+tcp4       0      0  127.0.0.1.8186         *.*                    LISTEN
+tcp6       0      0  ::1.8187               *.*                    LISTEN
+
 udp6       0      0  *.5453                 *.*                               
 udp4       0      0  *.5553                 *.*                               
 
@@ -73,14 +78,21 @@ func TestParsePortsNetstat(t *testing.T) {
 		Port{"udp", 5354, "", ""},
 		Port{"udp", 5453, "", ""},
 		Port{"udp", 5553, "", ""},
+		Port{"tcp", 8185, "", ""}, // but not 8186 or 8187 on localhost
 		Port{"udp", 9353, "iTunes", ""},
 	}
 
 	pl := parsePortsNetstat(netstatOutput)
+	jgot, _ := json.MarshalIndent(pl, "", "\t")
+	jwant, _ := json.MarshalIndent(want, "", "\t")
+	if len(pl) != len(want) {
+		t.Fatalf("Got:\n%s\n\nWant:\n%s\n", jgot, jwant)
+	}
 	for i := range pl {
 		if pl[i] != want[i] {
 			t.Errorf("row#%d\n got: %#v\n\nwant: %#v\n",
 				i, pl[i], want[i])
+			t.Fatalf("Got:\n%s\n\nWant:\n%s\n", jgot, jwant)
 		}
 	}
 }