fix: handle SIGHUP in launcher-patcher to prevent exits before updating (#1641)

### Motivation
The launcher-patcher tries to update the launcher.jar after the node &
launcher exit. This process did not work when `screen` or `tmux` was
used to start the launcher due to the fact that they send a `SIGHUG`
signal and the JVM handles the signal and stops the still running
(waiting) launcher-patcher. This required users to download the launcher
themselves when we did changes to the launcher.

### Modification
Introduced a handler for `SIGHUP` in the launcher-patcher that ignores
the signal. Furthermore, this introduces a 5 second timeout when waiting
for the launcher to exit before running the patcher as the launcher
should not take that long to stop and to prevent replacing the next
running launcher instance getting replaced while running.

### Result
Launcher updates are properly working when using `screen` or `tmux`

---------

Co-authored-by: Pasqual Koschmieder <git@derklaro.dev>

Author: 0utplay

launcher/patcher/src/main/java/eu/cloudnetservice/launcher/patcher/CloudNetLauncherPatcher.java

@@ -17,40 +17,61 @@
 package eu.cloudnetservice.launcher.patcher;
 
 import java.io.IOException;
+import java.io.PrintStream;
 import java.io.UncheckedIOException;
 import java.nio.file.Files;
 import java.nio.file.Path;
 import java.nio.file.StandardCopyOption;
+import java.util.concurrent.TimeUnit;
 import lombok.NonNull;
+import sun.misc.Signal;
+import sun.misc.SignalHandler;
 
 public final class CloudNetLauncherPatcher {
 
   public static void main(@NonNull String[] args) {
-    // validate that we got all required args to run (<pid> <old launcher> <new launcher>)
+    try {
+      // the jvm has a signal handler for SIGHUP, which exists the jvm when received
+      // tmux and screen use SIGHUP to signal the process that the session closed; however,
+      // this shouldn't prevent the patching process from running anyway
+      Signal.handle(new Signal("HUP"), SignalHandler.SIG_IGN);
+    } catch (Throwable throwable) {
+      printf(System.err, "Unable to register signal handler: %s", throwable.getMessage());
+    }
+
+    // validate that we got all required args to run (<pid> <launcher path> <new launcher path>)
     if (args.length == 3) {
       var launcherPid = Long.parseLong(args[0]);
-      var oldLauncherPath = Path.of(args[1]);
+      var launcherPath = Path.of(args[1]);
       var newLauncherPath = Path.of(args[2]);
-      // just for debug reasons
-      // CHECKSTYLE.OFF: Launcher has no proper logger
-      System.out.printf("Picked up options: %s -> %s (pid: %d)%n", oldLauncherPath, newLauncherPath, launcherPid);
-      // CHECKSTYLE.ON
+      printf(System.out, "Picked up options:");
+      printf(System.out, " - Launcher PID: %d", launcherPid);
+      printf(System.out, " - Launcher Path: %s", launcherPath);
+      printf(System.out, " - New Launcher Path: %s", newLauncherPath);
+
       // wait for the process to terminate by joining it (to block the current thread)
-      ProcessHandle.of(launcherPid).ifPresent(handle -> handle.onExit().join());
-      // the process doesn't exist or terminated - run the updater now
-      // CHECKSTYLE.OFF: Launcher has no proper logger
-      System.out.printf("Running patcher on file %s%n", oldLauncherPath);
-      // CHECKSTYLE.ON
-      replaceOldLauncher(oldLauncherPath, newLauncherPath);
+      ProcessHandle.of(launcherPid).ifPresent(handle -> handle.onExit()
+        .orTimeout(5, TimeUnit.SECONDS)
+        .exceptionally(__ -> {
+          printf(System.err, "Launcher process did not terminate in time, running patcher anyway");
+          return null;
+        })
+        .join());
+
+      printf(System.out, "Copying new launcher file...");
+      replaceOldLauncher(launcherPath, newLauncherPath);
     }
   }
 
   private static void replaceOldLauncher(@NonNull Path oldPath, @NonNull Path newPath) {
     try {
-      // move the new file to the location of the old file
       Files.copy(newPath, oldPath, StandardCopyOption.REPLACE_EXISTING);
     } catch (IOException exception) {
       throw new UncheckedIOException(exception);
     }
   }
+
+  private static void printf(@NonNull PrintStream target, @NonNull String format, @NonNull Object... args) {
+    target.printf(format + "%n", args);
+  }
 }