Linux: make davmail notify readyness to systemd

src/init/davmail.service

@@ -6,7 +6,7 @@ Documentation=http://davmail.sourceforge.net/sslsetup.html
 After=network.target
 
 [Service]
-Type=simple
+Type=notify
 User=davmail
 PermissionsStartOnly=true
 AmbientCapabilities=CAP_NET_BIND_SERVICE

src/java/davmail/DavGateway.java

@@ -28,6 +28,7 @@
 import davmail.pop.PopServer;
 import davmail.smtp.SmtpServer;
 import davmail.ui.tray.DavGatewayTray;
+import davmail.util.SystemdNotify;
 import org.apache.log4j.Logger;
 
 import java.awt.*;
@@ -158,7 +159,9 @@ public static void start() {
         if (showStartupBanner) {
             DavGatewayTray.info(new BundleMessage("LOG_DAVMAIL_GATEWAY_LISTENING", currentVersion, messages));
         }
-        if (!errorMessages.isEmpty()) {
+        if (errorMessages.isEmpty()) {
+            SystemdNotify.ready();
+        } else {
             DavGatewayTray.error(new BundleMessage("LOG_MESSAGE", errorMessages));
         }
 

src/java/davmail/util/SystemdNotify.java

@@ -0,0 +1,106 @@
+// Based on this answer https://stackoverflow.com/a/36945256/784804
+
+/*
+ * Copyright (c) 2018 Ian Kirk
+ * 
+ * Permission is hereby granted, free of charge, to any person obtaining a copy
+ * of this software and associated documentation files (the "Software"), to deal
+ * in the Software without restriction, including without limitation the rights
+ * to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+ * copies of the Software, and to permit persons to whom the Software is
+ * furnished to do so, subject to the following conditions:
+ * 
+ * The above copyright notice and this permission notice shall be included in all
+ * copies or substantial portions of the Software.
+ * 
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+ * AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+ * LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+ * OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+ * SOFTWARE.
+ */
+package davmail.util;
+
+import com.sun.jna.Library;
+import com.sun.jna.Native;
+
+public final class SystemdNotify {
+
+  interface SystemD extends Library {
+
+    final SystemD INSTANCE = Native.load(SYSTEMD_SO, SystemD.class);
+
+    int sd_notify(int unset_environment, String state);
+  }
+
+  private static final String SYSTEMD_SO = "systemd";
+  private static final String READY      = "READY=1";
+  private static final String RELOADING  = "RELOADING=1";
+  private static final String STOPPING   = "STOPPING=1";
+  private static final String STATUS     = "STATUS=%s";
+  private static final String WATCHDOG   = "WATCHDOG=1";
+  private static final String MAINPID    = "MAINPID=%d";
+  private static final String ERRNO      = "ERRNO=%d";
+  private static final String BUSERROR   = "BUSERROR=%s";
+  private static String       osType;
+
+  public static void busError(final String error) {
+    notify(String.format(BUSERROR, error));
+  }
+
+  public static void errno(final int errno) {
+    notify(String.format(ERRNO, errno));
+  }
+
+  public static void mainPid(final long pid) {
+    notify(String.format(MAINPID, pid));
+  }
+
+  public static void notify(final String message) {
+
+    if (!osType().startsWith("linux"))
+      return;
+
+    try {
+      final int returnCode = SystemD.INSTANCE.sd_notify(0, message);
+      if (returnCode < 0)
+        throw new RuntimeException(
+          String.format("sd_notify returned %d", returnCode));
+    } catch (final Exception e) {
+      throw new RuntimeException(e);
+    }
+  }
+
+  public static void ready() {
+    notify(READY);
+  }
+
+  public static void reloading() {
+    notify(RELOADING);
+  }
+
+  public static void status(final String text) {
+    notify(String.format(STATUS, text));
+  }
+
+  public static void stopping() {
+    notify(STOPPING);
+  }
+
+  public static void watchdog() {
+    notify(WATCHDOG);
+  }
+
+  synchronized static private String osType() {
+    if (osType == null) {
+      osType = System.getProperty("os.name").toLowerCase();
+    }
+    return osType;
+  }
+
+  private SystemdNotify() {
+    throw new RuntimeException("This class should not be instantiated");
+  }
+}