client/SubConn: do not recreate addrConn if UpdateAddresses is called with the same addresses

clientconn.go

@@ -801,16 +801,31 @@ func (ac *addrConn) connect() error {
 	return nil
 }
 
+func equalAddresses(a, b []resolver.Address) bool {
+	if len(a) != len(b) {
+		return false
+	}
+	for i, v := range a {
+		if !v.Equal(b[i]) {
+			return false
+		}
+	}
+	return true
+}
+
 // tryUpdateAddrs tries to update ac.addrs with the new addresses list.
 //
-// If ac is Connecting, it returns false. The caller should tear down the ac and
-// create a new one. Note that the backoff will be reset when this happens.
-//
 // If ac is TransientFailure, it updates ac.addrs and returns true. The updated
 // addresses will be picked up by retry in the next iteration after backoff.
 //
 // If ac is Shutdown or Idle, it updates ac.addrs and returns true.
 //
+// If the addresses is the same as the old list, it does nothing and returns
+// true.
+//
+// If ac is Connecting, it returns false. The caller should tear down the ac and
+// create a new one. Note that the backoff will be reset when this happens.
+//
 // If ac is Ready, it checks whether current connected address of ac is in the
 // new addrs list.
 //  - If true, it updates ac.addrs and returns true. The ac will keep using
@@ -827,6 +842,10 @@ func (ac *addrConn) tryUpdateAddrs(addrs []resolver.Address) bool {
 		return true
 	}
 
+	if equalAddresses(ac.addrs, addrs) {
+		return true
+	}
+
 	if ac.state == connectivity.Connecting {
 		return false
 	}

clientconn_test.go

@@ -970,7 +970,7 @@ func (s) TestUpdateAddresses_RetryFromFirstAddr(t *testing.T) {
 		{Addr: lis3.Addr().String()},
 	}
 	rb := manual.NewBuilderWithScheme("whatever")
-	rb.InitialState(resolver.State{Addresses: addrsList})
+	rb.InitialState(resolver.State{Addresses: addrsList[0:2]})
 
 	client, err := Dial("whatever:///this-gets-overwritten",
 		WithTransportCredentials(insecure.NewCredentials()),