mark 1.21.6 as supported and adjust dependency resolution

build.gradle.kts

@@ -12,7 +12,7 @@ plugins {
 val buildNum = System.getenv("GITHUB_RUN_NUMBER") ?: "SNAPSHOT"
 
 group = "win.templeos.lualink"
-version = "1.21.5-$buildNum"
+version = "1.21.6-$buildNum"
 
 repositories {
     mavenLocal()
@@ -34,7 +34,7 @@ dependencies {
     // Kotlin (downloaded and loaded at runtime)
     paperLibrary(kotlin("stdlib"))
     // Paper API
-    compileOnly("io.papermc.paper:paper-api:1.20-R0.1-SNAPSHOT")
+    compileOnly("io.papermc.paper:paper-api:1.21.6-R0.1-SNAPSHOT")
     // LuaJava (cannot be easily relocated or downloaded at runtime)
     implementation("party.iroiro.luajava:luajava:$luaJavaVersion") // Use our fork of the LuaJava library
     implementation("party.iroiro.luajava:luajit:$luaJavaVersion")
@@ -64,7 +64,7 @@ modrinth {
     versionNumber.set(version.toString())
     versionType.set("release")
     uploadFile.set(tasks.shadowJar.get())
-    gameVersions.addAll("1.21.4", "1.21.5")
+    gameVersions.addAll("1.21.4", "1.21.5", "1.21.6")
     loaders.addAll("paper", "purpur")
     changelog.set(System.getenv("GIT_COMMIT_MESSAGE"))
 }
@@ -81,7 +81,7 @@ hangarPublish {
         platforms {
             register(Platforms.PAPER) {
                 jar.set(tasks.shadowJar.flatMap { it.archiveFile })
-                platformVersions.set(listOf("1.21.4", "1.21.5"))
+                platformVersions.set(listOf("1.21.4", "1.21.5", "1.21.6"))
             }
         }
     }
@@ -92,7 +92,7 @@ tasks {
         // Configure the Minecraft version for our task.
         // This is the only required configuration besides applying the plugin.
         // Your plugin's jar (or shadowJar if present) will be used automatically.
-        minecraftVersion("1.21.5")
+        minecraftVersion("1.21.6")
 
         // Make sure runServer is ran with -add-opens=java.base/java.util=ALL-UNNAMED
         jvmArgs(

src/main/java/win/templeos/lualink/PluginLibrariesLoader.java

@@ -15,6 +15,7 @@
 import org.eclipse.aether.graph.Dependency;
 import org.eclipse.aether.repository.RemoteRepository;
 import org.eclipse.aether.util.repository.AuthenticationBuilder;
+import org.slf4j.Logger;
 
 import java.io.File;
 import java.io.FileInputStream;
@@ -50,7 +51,7 @@ public void classloader(final @NotNull PluginClasspathBuilder classpathBuilder)
                 throw new IOException("File 'paper-libraries.json' not found in the classpath.");
             // Extracting file contents to new MavenLibraryResolver instance.
             final MavenLibraryResolver iLibraries = gson.fromJson(new InputStreamReader(stream, StandardCharsets.UTF_8), PluginLibraries.class)
-                    .toMavenLibraryResolver();
+                    .toMavenLibraryResolver(classpathBuilder.getContext().getLogger(), RepositoryContext.INTERNAL);
             // Adding library(-ies) to the PluginClasspathBuilder.
             classpathBuilder.addLibrary(iLibraries);
         } catch (final IOException e) {
@@ -77,7 +78,7 @@ public void classloader(final @NotNull PluginClasspathBuilder classpathBuilder)
             try {
                 // Extracting file contents to new MavenLibraryResolver instance.
                 final MavenLibraryResolver eDependencies = gson.fromJson(new InputStreamReader(new FileInputStream(eLibrariesFile), StandardCharsets.UTF_8), PluginLibraries.class)
-                        .toMavenLibraryResolver();
+                        .toMavenLibraryResolver(classpathBuilder.getContext().getLogger(), RepositoryContext.USER_SPECIFIED);
                 // Adding library(-ies) to the PluginClasspathBuilder.
                 classpathBuilder.addLibrary(eDependencies);
             } catch (final FileNotFoundException e) {
@@ -88,12 +89,40 @@ public void classloader(final @NotNull PluginClasspathBuilder classpathBuilder)
 
     private record PluginLibraries(Map<String, RepositoryInfo> repositories, List<String> dependencies) {
 
-        public MavenLibraryResolver toMavenLibraryResolver() {
+        public MavenLibraryResolver toMavenLibraryResolver(final @NotNull Logger logger, final @NotNull RepositoryContext context) {
             final MavenLibraryResolver resolver = new MavenLibraryResolver();
             // Adding repositories to library resolver.
             repositories.entrySet().stream()
                     .map(entry -> {
-                        final RemoteRepository.Builder builder = new RemoteRepository.Builder(entry.getKey(), "default", entry.getValue().url);
+                        // Preparing the RemoteRepository builder.
+                        // This is filled in the next step, and re-used later to apply authentication credentials if specified.
+                        RemoteRepository.Builder builder;
+                        // Field 'MavenLibraryResolver.MAVEN_CENTRAL_DEFAULT_MIRROR' was added in one of the recent Paper versions and may not be available on < 1.21.6.
+                        try {
+                            // Replacing Maven Central repository with a pre-configured mirror.
+                            // See: https://docs.papermc.io/paper/dev/getting-started/paper-plugins/#loaders
+                            if (entry.getValue().url.contains("maven.org") == true || entry.getValue().url.contains("maven.apache.org") == true) {
+                                if (context == RepositoryContext.INTERNAL) {
+                                    builder = new RemoteRepository.Builder(entry.getKey(), "default", MavenLibraryResolver.MAVEN_CENTRAL_DEFAULT_MIRROR);
+                                } else {
+                                    logger.warn("Found at least one Maven Central repository in use that was not automatically replaced. Adjust contents of 'libraries.json' to get rid of this warning.");
+                                    logger.warn("While the plugin should work as usual, please keep in mind that downloading from Maven Central may be against their TOS and can be subject to a rate-limit.");
+                                    logger.warn("- " + entry.getValue().url + " (" + context + ")");
+                                    builder = new RemoteRepository.Builder(entry.getKey(), "default", entry.getValue().url);
+                                }
+                            } else {
+                                builder = new RemoteRepository.Builder(entry.getKey(), "default", entry.getValue().url);
+                            }
+                        } catch (final NoSuchFieldError e) {
+                            if (context == RepositoryContext.INTERNAL) {
+                                builder = new RemoteRepository.Builder(entry.getKey(), "default", "https://maven-central.storage-download.googleapis.com/maven2");
+                            } else {
+                                logger.warn("Replacing Maven Central repository with pre-configured mirror failed. As of now, this feature is available only on Paper 1.21.6 #11 and higher.");
+                                logger.warn("While the plugin should work as usual, please keep in mind that downloading from Maven Central may be against their TOS and can be subject to a rate-limit.");
+                                logger.warn("- " + entry.getValue().url + " (" + context + ")");
+                                builder = new RemoteRepository.Builder(entry.getKey(), "default", entry.getValue().url);
+                            }
+                        }
                         // Building and adding Authentication if specified.
                         if (entry.getValue().username != null && entry.getValue().password != null)
                             builder.setAuthentication(new AuthenticationBuilder().addUsername(entry.getValue().username).addPassword(entry.getValue().password).build());
@@ -115,6 +144,13 @@ public MavenLibraryResolver toMavenLibraryResolver() {
      */
     private record RepositoryInfo(@NotNull String url, @Nullable String username, @Nullable String password) { /* DATA ONLY */ }
 
+    /**
+     * Represents the context in which the library is being resolved.
+     */
+    private enum RepositoryContext {
+        INTERNAL, USER_SPECIFIED
+    }
+
     /**
      * Converts JSON repository definition to {@link RepositoryInfo} object.
      *

src/main/kotlin/win/templeos/lualink/lua/LuaCommand.kt

@@ -29,12 +29,12 @@ class LuaCommand(private val command: LuaValue) : Command(command.get("metadata"
             this.aliases = aliasList.values.map { it.toString() }.toMutableList()
         }
     }
-    override fun execute(sender: CommandSender, commandLabel: String, args: Array<out String>?): Boolean {
+    override fun execute(sender: CommandSender, commandLabel: String, args: Array<out String>): Boolean {
         command.get("handler").call(sender, args)
         return true
     }
 
-    override fun tabComplete(sender: CommandSender, alias: String, args: Array<out String>?): MutableList<String> {
+    override fun tabComplete(sender: CommandSender, alias: String, args: Array<out String>): MutableList<String> {
         val tabCompleteHandler = command.get("metadata").get("tabComplete")
         if (tabCompleteHandler.type() != Lua.LuaType.FUNCTION) {
             // Default behavior: Return online player names
@@ -43,7 +43,7 @@ class LuaCommand(private val command: LuaValue) : Command(command.get("metadata"
         val result = tabCompleteHandler.call(sender, args)[0]
         if (result.type() == Lua.LuaType.TABLE) {
             val list = result.toJavaObject() as HashMap<*, *>
-            return (if (args != null) list.values.filter { it.toString().contains(args.last(), true) } else list.values).toMutableList() as MutableList<String>
+            return (list.values.filter { it.toString().contains(args.last(), true) }).toMutableList() as MutableList<String>
         }
         // Default behavior: Return online player names
         return null!!

src/main/resources/libraries.json

@@ -1,4 +1,5 @@
 // External libraries to be loaded for use with scripts. Server must be restarted for the changes to take effect.
+// IMPORTANT: If you wish to resolve libraries from Maven Central, you're strongly advised to instead use a mirror.
 {
   "repositories": {
     // "RepositoryName": "https://repo.example.com/releases"