Feature/mod prohibition check

common/src/main/java/net/eternalempires/mod/common/network/AbstractEternalEmpiresPayload.java

@@ -51,11 +51,6 @@
  */
 @Slf4j
 public abstract class AbstractEternalEmpiresPayload implements CustomPacketPayload {
-
-    @NotNull
-    public static final CustomPacketPayload.Type<@NotNull UpdateDiscordRpcPayload> TYPE =
-            new CustomPacketPayload.Type<>(ResourceLocation.fromNamespaceAndPath(Constants.MOD_ID, "mod"));
-
     protected final byte[] data;
 
     @Nullable
@@ -170,5 +165,16 @@ protected String extractJsonField(final @NotNull String fieldName) {
      * @apiNote Will likely be moved in the future to a more robust handling.
      * @param service this is an instance of the RichPresenceService.
      */
-    public abstract void handlePayload(@NotNull RichPresenceService service);
+    public void handlePayload(@NotNull RichPresenceService service) {};
+
+    /**
+     * Handles the payload without requiring any external service dependencies.
+     * This variant exists to support subclasses such as
+     * {@link net.eternalempires.mod.common.network.packet.ModCheckPayload},
+     * which perform their own internal processing without relying on
+     * {@link net.eternalempires.mod.common.util.discord.RichPresenceService}.
+     * Default implementation is a no-op; subclasses should override to provide
+     * concrete handling logic.
+     */
+    public void handlePayload() {}
 }

common/src/main/java/net/eternalempires/mod/common/network/packet/ModCheckPayload.java

@@ -0,0 +1,190 @@
+/*
+ * MIT License
+ *
+ * Copyright (c) 2025 EternalEmpires.net
+ *
+ * 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:
+ *s
+ * 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 net.eternalempires.mod.common.network.packet;
+
+import io.netty.buffer.ByteBuf;
+import lombok.extern.slf4j.Slf4j;
+import net.eternalempires.mod.common.Constants;
+import net.eternalempires.mod.common.network.AbstractEternalEmpiresPayload;
+import net.eternalempires.mod.common.util.modlistcheck.ModCheckHandler;
+import net.minecraft.network.FriendlyByteBuf;
+import net.minecraft.network.RegistryFriendlyByteBuf;
+import net.minecraft.network.codec.StreamCodec;
+import net.minecraft.network.protocol.common.custom.CustomPacketPayload;
+import net.minecraft.resources.ResourceLocation;
+import org.jetbrains.annotations.NotNull;
+
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * This is effectively a custom-payload-packet that is sent from the minecraft server through the plugin-message-channel.
+ * This packet that gets send to the client upon joining so client can validate present mods.
+ * It's data will be (de)serialized as json and transferred byte-wise.
+ *
+ * @see AbstractEternalEmpiresPayload
+ *
+ * @since 09/07/2025
+ * @author EternalEmpires
+ */
+@Slf4j
+public class ModCheckPayload extends AbstractEternalEmpiresPayload {
+
+    public static final @NotNull CustomPacketPayload.Type<ModCheckPayload> TYPE =
+            new CustomPacketPayload.Type<>(ResourceLocation.fromNamespaceAndPath(Constants.MOD_ID, "modcheck"));
+
+    public static final @NotNull StreamCodec<ByteBuf, ModCheckPayload> BYTEBUF_CODEC =
+            StreamCodec.of((buf, value) -> buf.writeBytes(value.data),
+                    buf -> {
+                        final byte[] data = new byte[buf.readableBytes()];
+                        buf.readBytes(data);
+                        return new ModCheckPayload(data);
+                    });
+
+    public static final @NotNull StreamCodec<RegistryFriendlyByteBuf, ModCheckPayload> FORGE_CODEC =
+            StreamCodec.of(
+                    (buf, packet) -> buf.writeBytes(packet.data),
+                    buf -> {
+                        byte[] data = new byte[buf.readableBytes()];
+                        buf.readBytes(data);
+                        return new ModCheckPayload(data);
+                    }
+            );
+
+    public static final @NotNull StreamCodec<FriendlyByteBuf, ModCheckPayload> FABRIC_CODEC =
+            StreamCodec.of((buf, value) -> buf.writeBytes(value.data),
+                    buf -> {
+                        final byte[] data = new byte[buf.readableBytes()];
+                        buf.readBytes(data);
+                        return new ModCheckPayload(data);
+                    });
+
+    /**
+     * Constructs a new payload by reading all remaining bytes
+     * from the provided {@link FriendlyByteBuf}.
+     *
+     * @param buffer the buffer containing the raw packet data
+     */
+    public ModCheckPayload(@NotNull FriendlyByteBuf buffer) {
+        super(buffer);
+    }
+
+    /**
+     * Constructs a new payload from a raw byte array.
+     *
+     * @param data the raw packet data
+     */
+    public ModCheckPayload(byte @NotNull [] data) {
+        super(data);
+    }
+
+    /**
+     * Returns the unique type identifier for this custom payload.
+     * Used by Minecraft’s networking system to distinguish packet types.
+     *
+     * @return the {@link Type} of this payload
+     */
+    @Override
+    public @NotNull Type<? extends CustomPacketPayload> type() {
+        return TYPE;
+    }
+
+    /**
+     * Extracts a list of mod IDs from the JSON data contained in this payload.
+     * <p>
+     * Looks for a {@code "modIds"} array inside the {@code "data"} object.
+     * If found, the array is parsed into a list of trimmed strings.
+     * <p>
+     * In case of malformed JSON or unexpected structure, an empty list is returned.
+     *
+     * @return a list of mod IDs provided by the server
+     */
+    private @NotNull List<String> extractModIds() {
+        try {
+            List<String> modIds = new ArrayList<>();
+
+            // Extract the "data" object first, then get "modIds" from within it
+            String dataJson = extractJsonField("data");
+            if (dataJson != null) {
+                // Parse the nested modIds array from the data object
+                // The dataJson should contain something like: {"modIds":["mod1","mod2","mod3"]}
+                int modIdsStart = dataJson.indexOf("\"modIds\":");
+                if (modIdsStart != -1) {
+                    int arrayStart = dataJson.indexOf("[", modIdsStart);
+                    int arrayEnd = dataJson.indexOf("]", arrayStart);
+
+                    if (arrayStart != -1 && arrayEnd != -1) {
+                        String modIdsArray = dataJson.substring(arrayStart + 1, arrayEnd);
+                        String[] mods = modIdsArray.replace("\"", "").split(",");
+                        for (String mod : mods) {
+                            String trimmed = mod.trim();
+                            if (!trimmed.isEmpty()) {
+                                modIds.add(trimmed);
+                            }
+                        }
+                    }
+                }
+            }
+
+            return modIds;
+        } catch (Exception e) {
+            log.error("[EternalEmpires] Failed to extract mod IDs from JSON", e);
+            return new ArrayList<>();
+        }
+    }
+
+    /**
+     * Processes this payload on the client.
+     * <p>
+     * Specifically, it checks whether the payload type matches
+     * {@code "prohibited_mod_ids"}. If so, it extracts the mod IDs and
+     * delegates validation to {@link ModCheckHandler}.
+     * <p>
+     * Logs the JSON, handles empty or malformed cases, and ensures the
+     * client is disconnected if disallowed mods are detected.
+     */
+    @Override
+    public void handlePayload() {
+        log.info("[EternalEmpires] Received JSON: {}", json);
+
+        final String type = getTypeField();
+
+        if (!"prohibited_mod_ids".equalsIgnoreCase(type)) {
+            log.info("[EternalEmpires] Ignoring non-disallowed_mod_ids payload: type={}", type);
+            return;
+        }
+
+        List<String> serverDisallowedMods = extractModIds();
+        if (serverDisallowedMods.isEmpty()) {
+            log.warn("[EternalEmpires] No mod IDs found in server packet");
+            return;
+        }
+
+        log.info("[EternalEmpires] Server disallowed mods: {}", serverDisallowedMods);
+
+        // Delegate to the loader-specific handler
+        ModCheckHandler.performModCheck(serverDisallowedMods);
+    }
+}

common/src/main/java/net/eternalempires/mod/common/network/packet/UpdateDiscordRpcPayload.java

@@ -26,12 +26,14 @@
 
 import io.netty.buffer.ByteBuf;
 import lombok.extern.slf4j.Slf4j;
+import net.eternalempires.mod.common.Constants;
 import net.eternalempires.mod.common.network.AbstractEternalEmpiresPayload;
 import net.eternalempires.mod.common.util.discord.RichPresenceService;
 import net.minecraft.network.FriendlyByteBuf;
 import net.minecraft.network.RegistryFriendlyByteBuf;
 import net.minecraft.network.codec.StreamCodec;
 import net.minecraft.network.protocol.common.custom.CustomPacketPayload;
+import net.minecraft.resources.ResourceLocation;
 import org.jetbrains.annotations.NotNull;
 import org.jetbrains.annotations.Nullable;
 
@@ -48,6 +50,10 @@
 @Slf4j
 public final class UpdateDiscordRpcPayload extends AbstractEternalEmpiresPayload {
 
+    @NotNull
+    public static final CustomPacketPayload.Type<@NotNull UpdateDiscordRpcPayload> TYPE =
+            new CustomPacketPayload.Type<>(ResourceLocation.fromNamespaceAndPath(Constants.MOD_ID, "mod"));
+
     @NotNull
     public static final StreamCodec<@NotNull ByteBuf, @NotNull UpdateDiscordRpcPayload> BYTEBUF_CODEC =
             StreamCodec.of((buf, value) -> buf.writeBytes(value.data),

common/src/main/java/net/eternalempires/mod/common/util/modlistcheck/IModListProvider.java

@@ -0,0 +1,62 @@
+/*
+ * MIT License
+ *
+ * Copyright (c) 2025 EternalEmpires.net
+ *
+ * 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:
+ *s
+ * 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 net.eternalempires.mod.common.util.modlistcheck;
+
+import org.jetbrains.annotations.NotNull;
+
+import java.util.Map;
+import java.util.Set;
+
+
+/**
+ * Abstraction for retrieving information about installed mods on the client.
+ * Each supported mod loader (e.g., Fabric, Forge, NeoForge) must provide its
+ * own implementation of this interface so that {@link ModCheckHandler} can
+ * query the installed mods in a loader-agnostic way.
+ * Implementations are expected to return both the set of installed mod IDs and
+ * a mapping from mod ID to a user-friendly display name.
+ *
+ * @see ModCheckHandler
+ *
+ * @since 09/07/2025
+ * @author EternalEmpires
+ */
+public interface IModListProvider {
+
+    /**
+     * Gets the set of installed mod IDs on the client.
+     *
+     * @return a non-null set of mod IDs (may be empty, but never null)
+     */
+    @NotNull Set<@NotNull String> getInstalledModIds();
+
+    /**
+     * Gets a map of mod ID to mod display name for all installed mods.
+     *
+     * @return a non-null map where keys are non-null mod IDs and values are
+     * non-null display names (may be empty, but never null)
+     */
+    @NotNull Map<@NotNull String, @NotNull String> getModIdToNameMap();
+}