Adds a check for the minimum version as well.

consul/util.go

@@ -96,8 +96,8 @@ func ensurePath(path string, dir bool) error {
 }
 
 // CanServersUnderstandProtocol checks to see if all the servers in the given
-// list understand the given protocol version or higher. If there are no servers
+// list understand the given protocol version. If there are no servers in the
-// in the list then this will return false.
+// list then this will return false.
 func CanServersUnderstandProtocol(members []serf.Member, version uint8) (bool, error) {
 	numServers, numWhoGrok := 0, 0
 	for _, m := range members {
@@ -106,13 +106,18 @@ func CanServersUnderstandProtocol(members []serf.Member, version uint8) (bool, e
 		}
 		numServers++
 
-		vsn_str := m.Tags["vsn_max"]
+		vsn_min, err := strconv.Atoi(m.Tags["vsn_min"])
-		vsn, err := strconv.Atoi(vsn_str)
 		if err != nil {
 			return false, err
 		}
 
-		if vsn >= int(version) {
+		vsn_max, err := strconv.Atoi(m.Tags["vsn_max"])
+		if err != nil {
+			return false, err
+		}
+
+		v := int(version)
+		if (v >= vsn_min) && (v <= vsn_max) {
 			numWhoGrok++
 		}
 	}

consul/util_test.go

@@ -136,6 +136,7 @@ func TestUtil_CanServersUnderstandProtocol(t *testing.T) {
 	// Add a non-server member.
 	members = append(members, serf.Member{
 		Tags: map[string]string{
+			"vsn_min": fmt.Sprintf("%d", ProtocolVersionMin),
 			"vsn_max": fmt.Sprintf("%d", ProtocolVersionMax),
 		},
 	})
@@ -155,6 +156,7 @@ func TestUtil_CanServersUnderstandProtocol(t *testing.T) {
 	members = append(members, serf.Member{
 		Tags: map[string]string{
 			"role":    "consul",
+			"vsn_min": fmt.Sprintf("%d", ProtocolVersionMin),
 			"vsn_max": fmt.Sprintf("%d", ProtocolVersionMax),
 		},
 	})
@@ -185,6 +187,7 @@ func TestUtil_CanServersUnderstandProtocol(t *testing.T) {
 	members = append(members, serf.Member{
 		Tags: map[string]string{
 			"role":    "consul",
+			"vsn_min": fmt.Sprintf("%d", ProtocolVersionMin),
 			"vsn_max": fmt.Sprintf("%d", ProtocolVersionMax-1),
 		},
 	})
@@ -200,6 +203,17 @@ func TestUtil_CanServersUnderstandProtocol(t *testing.T) {
 			t.Fatalf("bad: %v != %v", grok, expected)
 		}
 	}
+
+	// Try a version that's too low for the minimum.
+	{
+		grok, err := CanServersUnderstandProtocol(members, 0)
+		if err != nil {
+			t.Fatalf("err: %v", err)
+		}
+		if grok {
+			t.Fatalf("server should not grok")
+		}
+	}
 }
 
 func TestIsConsulServer(t *testing.T) {