do not propagate IOException from the servlet

Author: vladak

opengrok-web/src/main/java/org/opengrok/web/servlet/MetricsServlet.java

@@ -18,7 +18,7 @@
  */
 
 /*
- * Copyright (c) 2020, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2020, 2025, Oracle and/or its affiliates. All rights reserved.
  */
 package org.opengrok.web.servlet;
 
@@ -27,19 +27,33 @@
 import jakarta.servlet.http.HttpServletRequest;
 import jakarta.servlet.http.HttpServletResponse;
 import org.opengrok.indexer.Metrics;
+import org.opengrok.indexer.logger.LoggerFactory;
 
 import java.io.IOException;
 import java.io.PrintWriter;
+import java.io.Serial;
+import java.util.logging.Logger;
+import java.util.logging.Level;
 
 @WebServlet("/metrics/prometheus")
 public class MetricsServlet extends HttpServlet {
 
+    @Serial
     private static final long serialVersionUID = 0L;
 
+    private static final Logger logger = LoggerFactory.getLogger(MetricsServlet.class);
+
     @Override
-    protected void doGet(final HttpServletRequest req, final HttpServletResponse resp) throws IOException {
+    protected void doGet(final HttpServletRequest req, final HttpServletResponse resp) {
         try (PrintWriter pw = resp.getWriter()) {
             pw.print(Metrics.getPrometheusRegistry().scrape());
+        } catch (IOException e) {
+            try {
+                resp.sendError(HttpServletResponse.SC_INTERNAL_SERVER_ERROR,
+                        String.format("failed to write the output data: %s", e.getMessage()));
+            } catch (IOException ex) {
+                logger.log(Level.WARNING, String.format("failed to send error code: %s", e.getMessage()));
+            }
         }
     }
 }