Add example

example-vhost.conf

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+geo $ipv4 {
+    0.0.0.0/0 ipv4;
+}
+server {
+	#Listen SSL+HTTP/2
+	listen 443 ssl http2;
+	listen [::]:443 ssl http2;
+
+	#Server Name here
+
+	include /etc/nginx/snippets/legacy-js.conf;
+
+	location / {
+		proxy_pass (...);
+		include /etc/nginx/proxy_params.conf;
+		# IP Legacy Banner
+		sub_filter_types text/html;
+		include /etc/nginx/snippets/legacy-banner.conf;
+		if ($ipv4 ~ "^$") {
+	                set $legacy "<!-- uses IPv6 --></body>";
+		}
+		sub_filter "script-src 'unsafe-inline'" "script-src 'unsafe-inline'";
+		sub_filter "</body>" $legacy;
+	}
+}
+

snippets/legacy-banner.conf

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+set $legacy "
+<script src='/legacywarn.js'></script>
+<style>
+#legacywarnoverlay {
+  position: fixed;
+  width: 100%;
+  left: 0;
+  right: 0;
+  bottom: 0;
+  background-color: rgba(0,0,0,0.9);
+  z-index: 2;
+  cursor: pointer;
+  text-align: center;
+}
+#legacywarnoverlay p {
+  padding: 10px;
+  color: white;
+}
+#legacywarnoverlay p a {
+  text-decoration: underline;
+  color: white;
+}
+#legavywarnoverlay p a:hover {
+  text-decoration: none;
+}
+</style>
+<div id='legacywarnoverlay'>
+<p>Du besuchst diese Seite mit einem <strong>veralteten</strong> IPv4-Internetzugang. M&ouml;glicherweise treten in Zukunft Probleme mit der Erreichbarkeit und Performance auf. Bitte Frage deinen Internetanbieter oder Netzwerkadministrator nach IPv6-Unterst&uuml;tzung.<br>
+You are visiting this site with an <strong>outdated</strong> IPv4 internet access. Possibly in the future you may experience problems with accessibility and performance. Please ask your ISP or network administrator for IPv6 support.<br>
+<a href='https://margau.net/ipv6' target='_blank'>Weitere Infos | More Information</a><br>Klicke zum schlie&szlig;en | Click to close</p></div></body>";

snippets/legacy-js.conf

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+location /legacywarn.js {
+return 200 "
+function legacywarnon() {
+  document.getElementById('legacywarnoverlay').style.display = 'block';
+}
+
+function legacywarnoff() {
+  document.getElementById('legacywarnoverlay').style.display = 'none';
+  document.cookie = 'legacywarn=true; max-age=60*60*24 ; path=/';
+}
+document.addEventListener('DOMContentLoaded', function(){
+  document.getElementById('legacywarnoverlay').onclick = legacywarnoff;
+    if (document.cookie.indexOf('legacywarn=') > -1) {
+      document.getElementById('legacywarnoverlay').style.display = 'none';
+      console.log('Hide Legacy IP warn');
+    }
+  });";
+}