Username command & fix commands a bit

src/main/java/land/chipmunk/chipmunkmod/command/CommandManager.java

@@ -28,7 +28,8 @@ public class CommandManager {
       dispatcher.execute(command, commandSource);
     } catch (CommandSyntaxException e) {
       commandSource.sendError(Texts.toText(e.getRawMessage()));
-      commandSource.sendError(getContext(e));
+      final Text context = getContext(e);
+      if (context != null) commandSource.sendError(context);
     } catch (CommandException e) {
       commandSource.sendError(e.getTextMessage());
     } catch (RuntimeException e) {
@@ -67,5 +68,6 @@ public class CommandManager {
   static {
     TestCommand.register(dispatcher);
     CoreCommand.register(dispatcher);
+    UsernameCommand.register(dispatcher);
   }
 }

src/main/java/land/chipmunk/chipmunkmod/commands/UsernameCommand.java

@@ -0,0 +1,67 @@
+package land.chipmunk.chipmunkmod.commands;
+
+import com.mojang.brigadier.Command;
+import com.mojang.brigadier.CommandDispatcher;
+import com.mojang.brigadier.context.CommandContext;
+import static com.mojang.brigadier.arguments.StringArgumentType.greedyString;
+import static com.mojang.brigadier.arguments.StringArgumentType.getString;
+import static land.chipmunk.chipmunkmod.command.CommandManager.literal;
+import static land.chipmunk.chipmunkmod.command.CommandManager.argument;
+import net.fabricmc.fabric.api.client.command.v2.FabricClientCommandSource;
+import net.minecraft.client.MinecraftClient;
+import net.minecraft.client.gui.screen.ConnectScreen;
+import net.minecraft.client.gui.screen.TitleScreen;
+import net.minecraft.client.gui.screen.multiplayer.MultiplayerScreen;
+import net.minecraft.client.network.ServerInfo;
+import net.minecraft.client.network.ServerAddress;
+import net.minecraft.client.util.Session;
+import net.minecraft.text.Text;
+import com.mojang.brigadier.exceptions.CommandSyntaxException;
+import com.mojang.brigadier.exceptions.SimpleCommandExceptionType;
+import java.util.Optional;
+import land.chipmunk.chipmunkmod.mixin.MinecraftClientAccessor;
+
+public class UsernameCommand {
+  private static final Session ORIGINAL_SESSION = ((MinecraftClientAccessor) MinecraftClient.getInstance()).session();
+  private static final SimpleCommandExceptionType USERNAME_TOO_LONG = new SimpleCommandExceptionType(Text.translatable("The specified username is longer than 16 characters"));
+
+  public static void register (CommandDispatcher<FabricClientCommandSource> dispatcher) {
+    dispatcher.register(
+      literal("username")
+        .then(
+          literal("set")
+            .then(
+              argument("username", greedyString())
+                .executes(c -> updateUsername(c))
+            )
+        )
+        .then(
+          literal("revert")
+            .executes(c -> updateSession(c, ORIGINAL_SESSION))
+        )
+    );
+  }
+
+  public static int updateUsername (CommandContext<FabricClientCommandSource> context) throws CommandSyntaxException {
+    final String username = getString(context, "username");
+    if (username.length() > 16) throw USERNAME_TOO_LONG.create();
+    final Session session = new Session(username, "", "", Optional.empty(), Optional.empty(), Session.AccountType.MOJANG);
+    return updateSession(context, session);
+  }
+
+  public static int updateSession (CommandContext<FabricClientCommandSource> context, Session session) throws CommandSyntaxException {
+    final FabricClientCommandSource source = context.getSource();
+
+    final MinecraftClient client = source.getClient();
+
+    ((MinecraftClientAccessor) client).session(session);
+
+    // TODO: Put this in a separate class
+    final ServerInfo info = client.getCurrentServerEntry();
+    client.world.disconnect();
+    client.disconnect();
+    ConnectScreen.connect(new MultiplayerScreen(new TitleScreen()), client, ServerAddress.parse(info.address), info);
+
+    return Command.SINGLE_SUCCESS;
+  }
+}

src/main/java/land/chipmunk/chipmunkmod/mixin/MinecraftClientAccessor.java

@@ -0,0 +1,16 @@
+package land.chipmunk.chipmunkmod.mixin;
+
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.Mutable;
+import org.spongepowered.asm.mixin.gen.Accessor;
+import net.minecraft.client.util.Session;
+
+@Mixin(net.minecraft.client.MinecraftClient.class)
+public interface MinecraftClientAccessor {
+  @Accessor("session")
+  Session session ();
+
+  @Mutable
+  @Accessor("session")
+  void session (Session session);
+}

src/main/resources/chipmunkmod.mixins.json

@@ -11,7 +11,8 @@
     "ClientPlayNetworkHandlerAccessor",
     "ClientConnectionMixin",
     "ClientPlayerEntityMixin",
-    "ClientPlayNetworkHandlerMixin"
+    "ClientPlayNetworkHandlerMixin",
+    "MinecraftClientAccessor"
   ],
   "injectors": {
     "defaultRequire": 1