add 'copy link' button to upload view

template/upload.html

@@ -11,10 +11,27 @@
       <h1><a href="/">datatrash</a></h1>
       <p>
         datei-link:
-        <a href="{url}">
+        <a id="link" href="{url}">
           {url}
         </a>
       </p>
+      <button id="copy" class="main button" onclick="copyToClipboard()">
+        link kopieren
+      </button>
     </main>
+    <script lang="javascript">
+      function copyToClipboard() {
+        const button = document.getElementById("copy");
+        if (!navigator.clipboard) {
+          button.innerText = "nicht unterstützt";
+          return;
+        }
+        const anchor = document.getElementById("link");
+        navigator.clipboard.writeText(anchor.href).then(
+          _ => { button.innerText = "kopiert!"; },
+          _ => { button.innerText = "nicht unterstützt"; },
+        );
+      }
+    </script>
   </body>
 </html>