try again

cmd/server/main.go

@@ -341,15 +341,12 @@ func buildDiagramsNetURL(r *http.Request, id string, xml string) string {
 	}
 	base := fmt.Sprintf("%s://%s/diagram?id=%s", scheme, r.Host, url.QueryEscape(id))
 	// Request AWS library for custom shapes (e.g., aws4) to render correctly.
-	// Use the fragment form (#U) to point at a downloadable URL.
+	// Provide both query param (url=) and fragment (#U) so different draw.io deployments can fetch the diagram.
+	// We intentionally avoid embedding the XML inline to keep headers small for Tomcat-based self-hosted instances.
 	encodedURL := url.QueryEscape(base)
-	redirect := fmt.Sprintf("%s/?splash=0&ui=min&libs=aws4", drawioBaseURL)
-	// Also embed the XML directly via `data=` so self-hosted instances that block remote fetches can still open it.
-	if xml != "" {
-		data := base64.StdEncoding.EncodeToString([]byte(xml))
-		redirect += "&data=" + url.QueryEscape(data)
-	}
-	return fmt.Sprintf("%s#U%s", redirect, encodedURL)
+	redirect := fmt.Sprintf("%s/?splash=0&ui=min&libs=aws4&url=%s#U%s", drawioBaseURL, encodedURL, encodedURL)
+	_ = xml // kept for signature compatibility; may be used in future fallbacks
+	return redirect
 }
 
 func addCORS(w http.ResponseWriter) {