fail early if web app URI is not reachable (#3520)

Author: Vladimir Kotal

opengrok-indexer/src/main/java/org/opengrok/indexer/index/Indexer.java

@@ -79,6 +79,7 @@
 import org.opengrok.indexer.logger.LoggerUtil;
 import org.opengrok.indexer.util.CtagsUtil;
 import org.opengrok.indexer.util.Executor;
+import org.opengrok.indexer.util.HostUtil;
 import org.opengrok.indexer.util.OptionParser;
 import org.opengrok.indexer.util.PlatformUtils;
 import org.opengrok.indexer.util.Statistics;
@@ -161,9 +162,18 @@ public static void main(String[] argv) {
 
         boolean createDict = false;
 
+        int CONNECT_TIMEOUT = 1000;  // in milliseconds
+
         try {
             argv = parseOptions(argv);
 
+            if (webappURI != null) {
+                if (!HostUtil.isReachable(webappURI, CONNECT_TIMEOUT)) {
+                    System.err.println(webappURI + " is not reachable.");
+                    System.exit(1);
+                }
+            }
+
             /*
              * Attend to disabledRepositories here in case exitWithHelp() will
              * need to report about repos.

opengrok-indexer/src/main/java/org/opengrok/indexer/util/HostUtil.java

@@ -0,0 +1,107 @@
+/*
+ * CDDL HEADER START
+ *
+ * The contents of this file are subject to the terms of the
+ * Common Development and Distribution License (the "License").
+ * You may not use this file except in compliance with the License.
+ *
+ * See LICENSE.txt included in this distribution for the specific
+ * language governing permissions and limitations under the License.
+ *
+ * When distributing Covered Code, include this CDDL HEADER in each
+ * file and include the License file at LICENSE.txt.
+ * If applicable, add the following below this CDDL HEADER, with the
+ * fields enclosed by brackets "[]" replaced with your own identifying
+ * information: Portions Copyright [yyyy] [name of copyright owner]
+ *
+ * CDDL HEADER END
+ */
+
+/*
+ * Copyright (c) 2021, Oracle and/or its affiliates. All rights reserved.
+ */
+package org.opengrok.indexer.util;
+
+import org.opengrok.indexer.logger.LoggerFactory;
+
+import java.io.IOException;
+import java.net.InetAddress;
+import java.net.InetSocketAddress;
+import java.net.Socket;
+import java.net.URI;
+import java.net.URISyntaxException;
+import java.net.UnknownHostException;
+import java.util.logging.Level;
+import java.util.logging.Logger;
+
+/**
+ * Utility class to provide simple host/address methods.
+ */
+public class HostUtil {
+
+    private static final Logger LOGGER = LoggerFactory.getLogger(HostUtil.class);
+
+    private HostUtil() {
+        // private to enforce static
+    }
+
+    /**
+     * @param urlStr URI
+     * @return port number
+     * @throws URISyntaxException on error
+     */
+    public static int urlToPort(String urlStr) throws URISyntaxException {
+        URI uri = new URI(urlStr);
+        return uri.getPort();
+    }
+
+    /**
+     * @param urlStr URI
+     * @return hostname
+     * @throws URISyntaxException on error
+     */
+    public static String urlToHostname(String urlStr) throws URISyntaxException {
+        URI uri = new URI(urlStr);
+        return uri.getHost();
+    }
+
+    /**
+     * @param addr IP address
+     * @param port port number
+     * @param timeOutMillis timeout in milliseconds
+     * @return true if TCP connect works, false otherwise
+     */
+    public static boolean isReachable(InetAddress addr, int port, int timeOutMillis) {
+        try (Socket soc = new Socket()) {
+            soc.connect(new InetSocketAddress(addr, port), timeOutMillis);
+        } catch (IOException e) {
+            return false;
+        }
+
+        return true;
+    }
+
+    public static boolean isReachable(String webappURI, int timeOutMillis) {
+        boolean connectWorks = false;
+
+        try {
+            int port = HostUtil.urlToPort(webappURI);
+            if (port <= 0) {
+                LOGGER.log(Level.SEVERE, "invalid port number for " + webappURI);
+                return false;
+            }
+
+            for (InetAddress addr : InetAddress.getAllByName(HostUtil.urlToHostname(webappURI))) {
+                if (HostUtil.isReachable(addr, port, timeOutMillis)) {
+                    LOGGER.log(Level.FINE, "URI " + webappURI + " is reachable via " + addr.toString());
+                    connectWorks = true;
+                    break;
+                }
+            }
+        } catch (URISyntaxException | UnknownHostException e) {
+            LOGGER.log(Level.WARNING, String.format("URI not valid: %s", webappURI), e);
+        }
+
+        return connectWorks;
+    }
+}