Implemented plugin update folder

proxy/src/main/java/com/velocitypowered/proxy/VelocityServer.java

@@ -423,18 +423,23 @@ private void loadPlugins() {
 
     try {
       Path pluginPath = Path.of("plugins");
+      Path updatePath = configuration.isUpdateFolderEnabled() ? pluginPath.resolve(configuration.getUpdateFolderName()) : null;
 
       if (!pluginPath.toFile().exists()) {
         Files.createDirectory(pluginPath);
-      } else {
-        if (!pluginPath.toFile().isDirectory()) {
-          logger.warn("Plugin location {} is not a directory, continuing without loading plugins",
-              pluginPath);
-          return;
-        }
+      }
 
-        pluginManager.loadPlugins(pluginPath);
+      if (updatePath != null && !updatePath.toFile().exists()) {
+        Files.createDirectory(updatePath);
       }
+
+      if (!pluginPath.toFile().isDirectory()) {
+        logger.warn("Plugin location {} is not a directory, continuing without loading plugins",
+            pluginPath);
+        return;
+      }
+
+      pluginManager.loadPlugins(pluginPath, updatePath);
     } catch (Exception e) {
       logger.error("Couldn't load plugins", e);
     }

proxy/src/main/java/com/velocitypowered/proxy/config/VelocityConfiguration.java

@@ -435,6 +435,14 @@ public boolean isLogPlayerConnections() {
     return advanced.isLogPlayerConnections();
   }
 
+  public boolean isUpdateFolderEnabled() {
+    return !advanced.getUpdateFolderName().isEmpty();
+  }
+
+  public String getUpdateFolderName() {
+    return advanced.getUpdateFolderName();
+  }
+
   public boolean isAcceptTransfers() {
     return this.advanced.isAcceptTransfers();
   }
@@ -763,6 +771,8 @@ private static class Advanced {
     @Expose
     private boolean logPlayerConnections = true;
     @Expose
+    private String updateFolderName = ".update";
+    @Expose
     private boolean acceptTransfers = false;
     @Expose
     private boolean enableReusePort = false;
@@ -800,6 +810,7 @@ private Advanced(CommentedConfig config) {
         this.announceProxyCommands = config.getOrElse("announce-proxy-commands", true);
         this.logCommandExecutions = config.getOrElse("log-command-executions", false);
         this.logPlayerConnections = config.getOrElse("log-player-connections", true);
+        this.updateFolderName = config.getOrElse("update-folder", ".update");
         this.acceptTransfers = config.getOrElse("accepts-transfers", false);
         this.enableReusePort = config.getOrElse("enable-reuse-port", false);
         this.commandRateLimit = config.getIntOrElse("command-rate-limit", 25);
@@ -866,6 +877,10 @@ public boolean isLogPlayerConnections() {
       return logPlayerConnections;
     }
 
+    public String getUpdateFolderName() {
+      return updateFolderName;
+    }
+
     public boolean isAcceptTransfers() {
       return this.acceptTransfers;
     }

proxy/src/main/java/com/velocitypowered/proxy/plugin/VelocityPluginManager.java

@@ -35,6 +35,7 @@
 import com.velocitypowered.proxy.plugin.loader.VelocityPluginContainer;
 import com.velocitypowered.proxy.plugin.loader.java.JavaPluginLoader;
 import com.velocitypowered.proxy.plugin.util.PluginDependencyUtils;
+import edu.umd.cs.findbugs.annotations.Nullable;
 import edu.umd.cs.findbugs.annotations.SuppressFBWarnings;
 import java.io.IOException;
 import java.nio.file.DirectoryStream;
@@ -82,19 +83,19 @@ public void registerPlugin(PluginContainer plugin) {
   /**
    * Loads all plugins from the specified {@code directory}.
    *
-   * @param directory the directory to load from
+   * @param pluginDirectory the directory to load from
    * @throws IOException if we could not open the directory
    */
   @SuppressFBWarnings(value = "RCN_REDUNDANT_NULLCHECK_WOULD_HAVE_BEEN_A_NPE",
       justification = "I looked carefully and there's no way SpotBugs is right.")
-  public void loadPlugins(Path directory) throws IOException {
-    checkNotNull(directory, "directory");
-    checkArgument(directory.toFile().isDirectory(), "provided path isn't a directory");
+  public void loadPlugins(Path pluginDirectory, @Nullable Path updateDirectory) throws IOException {
+    checkNotNull(pluginDirectory, "directory");
+    checkArgument(pluginDirectory.toFile().isDirectory(), "provided path isn't a directory");
 
     Map<String, PluginDescription> foundCandidates = new LinkedHashMap<>();
-    JavaPluginLoader loader = new JavaPluginLoader(server, directory);
+    JavaPluginLoader loader = new JavaPluginLoader(server, pluginDirectory);
 
-    try (DirectoryStream<Path> stream = Files.newDirectoryStream(directory,
+    try (DirectoryStream<Path> stream = Files.newDirectoryStream(pluginDirectory,
         p -> p.toFile().isFile() && p.toString().endsWith(".jar"))) {
       for (Path path : stream) {
         try {
@@ -122,6 +123,11 @@ public void loadPlugins(Path directory) throws IOException {
       return;
     }
 
+    // Update plugins if an update folder is defined
+    if (updateDirectory != null) {
+      updatePlugins(pluginDirectory, updateDirectory, foundCandidates, loader);
+    }
+
     List<PluginDescription> sortedPlugins = PluginDependencyUtils.sortCandidates(
         new ArrayList<>(foundCandidates.values()));
 
@@ -182,6 +188,67 @@ protected void configure() {
     }
   }
 
+  private void updatePlugins(
+      Path pluginDirectory,
+      Path updateDirectory,
+      Map<String, PluginDescription> found,
+      JavaPluginLoader loader
+  ) throws IOException {
+    checkNotNull(updateDirectory, "updateDirectory");
+
+    List<PluginDescription> availableUpdates = new ArrayList<>();
+    JavaPluginLoader updateLoader = new JavaPluginLoader(server, updateDirectory);
+    try (
+        DirectoryStream<Path> stream = Files.newDirectoryStream(updateDirectory, path -> path.toFile().isFile() && path.toString().endsWith(".jar"))
+    ) {
+      for (Path path : stream) {
+        try {
+          availableUpdates.add(updateLoader.loadCandidate(path));
+        } catch (Exception e) {
+          logger.error("Unable to load plugin candidate {}", path, e);
+        }
+      }
+    }
+
+    for (PluginDescription availableUpdate : availableUpdates) {
+      PluginDescription potentialMatch = found.get(availableUpdate.getId());
+
+      // This should not happen but acts as a failsafe
+      if (availableUpdate.getSource().isEmpty()) {
+        logger.warn("No source found for plugin {} found", availableUpdate.getId());
+        continue;
+      }
+
+      if (potentialMatch != null) {
+        if (potentialMatch.getSource().isEmpty()) {
+          logger.warn("No source for plugin {} found, continuing without update.",
+              potentialMatch.getId());
+          continue;
+        }
+
+        // Remove outdated plugin file
+        try {
+          Files.deleteIfExists(potentialMatch.getSource().get());
+        } catch (IOException e) {
+          logger.error("Unable to delete plugin {} from plugins folder at {}",
+              potentialMatch.getId(), pluginDirectory.toString(), e);
+          continue;
+        }
+      }
+
+      Path newPath = pluginDirectory.resolve(availableUpdate.getSource().get().getFileName());
+      try {
+        Files.move(availableUpdate.getSource().get(), newPath);
+        logger.info("Successfully updated plugin {} to version {}",
+            availableUpdate.getId(), availableUpdate.getVersion());
+        PluginDescription movedDescription = loader.loadCandidate(newPath);
+        found.put(movedDescription.getId(), movedDescription);
+      } catch (Exception e) {
+        logger.error("Unable to update plugin {}", availableUpdate.getId(), e);
+      }
+    }
+  }
+
   @Override
   public Optional<PluginContainer> fromInstance(Object instance) {
     checkNotNull(instance, "instance");

proxy/src/main/resources/default-velocity.toml

@@ -146,6 +146,9 @@ log-command-executions = false
 # and disconnecting from the proxy.
 log-player-connections = true
 
+# The name of the update folder, set to "" to disable the update folder
+update-folder = ".update"
+
 # Allows players transferred from other hosts via the
 # Transfer packet (Minecraft 1.20.5) to be received.
 accepts-transfers = false