plugin/transfer: configure notify source address (#8192)

Signed-off-by: houyuwushang <liuluoqianqiu@outlook.com>

plugin/transfer/notify_test.go

@@ -0,0 +1,27 @@
+package transfer
+
+import (
+	"net"
+	"testing"
+)
+
+func TestNotifyClientSource(t *testing.T) {
+	c := notifyClient(&xfr{})
+	if c.Dialer != nil {
+		t.Fatalf("expected no dialer without a source address, got %#v", c.Dialer)
+	}
+
+	source := net.ParseIP("2001:db8::53")
+	c = notifyClient(&xfr{source: source})
+	if c.Dialer == nil {
+		t.Fatal("expected dialer for source address")
+	}
+
+	addr, ok := c.Dialer.LocalAddr.(*net.UDPAddr)
+	if !ok {
+		t.Fatalf("expected UDP local address, got %T", c.Dialer.LocalAddr)
+	}
+	if !addr.IP.Equal(source) {
+		t.Fatalf("expected source address %s, got %s", source, addr.IP)
+	}
+}