The Mod Protocol API, aka better validation of mod presence of both-side mods with extra protocol version syncing

fabric-mod-protocol-api-v1/build.gradle

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+version = getSubprojectVersion(project)
+
+moduleDependencies(project, ['fabric-api-base', 'fabric-networking-api-v1'])

fabric-mod-protocol-api-v1/src/client/java/net/fabricmc/fabric/api/client/modprotocol/v1/ClientModProtocolLookup.java

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+/*
+ * Copyright (c) 2016, 2017, 2018, 2019 FabricMC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package net.fabricmc.fabric.api.client.modprotocol.v1;
+
+import it.unimi.dsi.fastutil.objects.Object2IntMap;
+
+import net.minecraft.client.network.ClientCommonNetworkHandler;
+import net.minecraft.network.ClientConnection;
+import net.minecraft.server.network.ServerCommonNetworkHandler;
+import net.minecraft.util.Identifier;
+
+import net.fabricmc.fabric.api.modprotocol.v1.ModProtocol;
+import net.fabricmc.fabric.api.modprotocol.v1.ModProtocolIds;
+import net.fabricmc.fabric.impl.modprotocol.RemoteProtocolStorage;
+
+/**
+ * Utility methods allowing to get protocol versions supported by the server.
+ *
+ * <p>Protocol identifiers can be any valid {@link Identifier}. The default is {@code mod:(mod ID)}.
+ * @see ModProtocolIds
+ */
+public final class ClientModProtocolLookup {
+	/**
+	 * A protocol version returned by {@code getSupportedProtocol} methods, when the server doesn't support the requested protocol.
+	 */
+	public static final int UNSUPPORTED = -1;
+	private ClientModProtocolLookup() { }
+
+	/**
+	 * Gets the protocol version supported by the server.
+	 *
+	 * @param handler the network handler connected to the server
+	 * @param protocolId protocol's id
+	 * @return the protocol version supported by the server
+	 */
+	public static int getSupportedProtocol(ClientCommonNetworkHandler handler, Identifier protocolId) {
+		return RemoteProtocolStorage.getProtocol(handler, protocolId);
+	}
+
+	/**
+	 * Gets the protocol version supported by the server.
+	 *
+	 * @param connection the ClientConnection connected to the server
+	 * @param protocolId protocol's id
+	 * @return the protocol version supported by the server
+	 */
+	public static int getSupportedProtocol(ClientConnection connection, Identifier protocolId) {
+		return RemoteProtocolStorage.getProtocol(connection, protocolId);
+	}
+
+	/**
+	 * Gets the protocol version supported by the server.
+	 *
+	 * @param handler the network handler connected to the server
+	 * @param protocol protocol to check against
+	 * @return the protocol version supported by the server
+	 */
+	public static int getSupportedProtocol(ClientCommonNetworkHandler handler, ModProtocol protocol) {
+		return RemoteProtocolStorage.getProtocol(handler, protocol.id());
+	}
+
+	/**
+	 * Gets the protocol version supported by the server.
+	 *
+	 * @param connection the ClientConnection connected to the server
+	 * @param protocol protocol to check against
+	 * @return the protocol version supported by the server
+	 */
+	public static int getSupportedProtocol(ClientConnection connection, ModProtocol protocol) {
+		return RemoteProtocolStorage.getProtocol(connection, protocol.id());
+	}
+
+	/**
+	 * Gets all protocols supported by the server.
+	 *
+	 * @param handler the network handler connected to the server
+	 * @return the map of protocols to the versions supported by the server
+	 */
+	public static Object2IntMap<Identifier> getAllSupportedProtocols(ServerCommonNetworkHandler handler) {
+		return RemoteProtocolStorage.getMap(handler);
+	}
+
+	/**
+	 * Gets all protocols supported by the server.
+	 *
+	 * @param connection the ClientConnection connected to the server
+	 * @return the map of protocols to the versions supported by the server
+	 */
+	public static Object2IntMap<Identifier> getAllSupportedProtocols(ClientConnection connection) {
+		return RemoteProtocolStorage.getMap(connection);
+	}
+}

fabric-mod-protocol-api-v1/src/client/java/net/fabricmc/fabric/api/client/modprotocol/v1/package-info.java

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+/*
+ * Copyright (c) 2016, 2017, 2018, 2019 FabricMC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+/**
+ * The Mod Protocol API (client side), version 1.
+ *
+ * <p>See {@link net.fabricmc.fabric.api.modprotocol.v1}</p>
+ */
+
+@ApiStatus.Experimental
+package net.fabricmc.fabric.api.client.modprotocol.v1;
+
+import org.jetbrains.annotations.ApiStatus;

fabric-mod-protocol-api-v1/src/client/java/net/fabricmc/fabric/impl/modprotocol/client/ClientModProtocolInit.java

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+/*
+ * Copyright (c) 2016, 2017, 2018, 2019 FabricMC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package net.fabricmc.fabric.impl.modprotocol.client;
+
+import java.util.HashMap;
+
+import net.minecraft.util.Identifier;
+
+import net.fabricmc.api.ClientModInitializer;
+import net.fabricmc.fabric.api.client.networking.v1.ClientConfigurationNetworking;
+import net.fabricmc.fabric.impl.modprotocol.ModProtocolImpl;
+import net.fabricmc.fabric.impl.modprotocol.ModProtocolInit;
+import net.fabricmc.fabric.impl.modprotocol.ModProtocolManager;
+import net.fabricmc.fabric.impl.modprotocol.RemoteProtocolStorage;
+import net.fabricmc.fabric.impl.modprotocol.payload.ModProtocolRequestS2CPayload;
+import net.fabricmc.fabric.impl.modprotocol.payload.ModProtocolResponseC2SPayload;
+
+public final class ClientModProtocolInit implements ClientModInitializer {
+	public void onInitializeClient() {
+		ClientConfigurationNetworking.registerGlobalReceiver(ModProtocolRequestS2CPayload.ID, (payload, context) -> {
+			var map = new HashMap<Identifier, ModProtocolImpl>(payload.modProtocol().size());
+
+			for (ModProtocolImpl protocol : payload.modProtocol()) {
+				map.put(protocol.id(), protocol);
+			}
+
+			ModProtocolManager.ValidationResult validate = ModProtocolManager.validateClient(map);
+
+			if (validate.isSuccess()) {
+				((RemoteProtocolStorage) context.networkHandler()).fabric$setRemoteProtocol(validate.supportedProtocols());
+				context.responseSender().sendPacket(new ModProtocolResponseC2SPayload(validate.supportedProtocols()));
+				return;
+			}
+
+			var b = new StringBuilder();
+			b.append("Disconnected due to mismatched protocols!").append('\n');
+			b.append("Missing entries:").append('\n');
+			ModProtocolManager.appendTextEntries(validate.missing(), ModProtocolManager.LOCAL_MOD_PROTOCOLS_BY_ID, -1, text -> b.append(" - ").append(text.getString()));
+
+			context.responseSender().disconnect(ModProtocolManager.constructMessage(validate.missing(), ModProtocolManager.LOCAL_MOD_PROTOCOLS_BY_ID));
+			ModProtocolInit.LOGGER.warn(b.toString());
+		});
+	}
+}

fabric-mod-protocol-api-v1/src/client/java/net/fabricmc/fabric/mixin/modprotocol/client/ClientCommonNetworkHandlerMixin.java

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+/*
+ * Copyright (c) 2016, 2017, 2018, 2019 FabricMC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package net.fabricmc.fabric.mixin.modprotocol.client;
+
+import it.unimi.dsi.fastutil.objects.Object2IntMap;
+import org.spongepowered.asm.mixin.Final;
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.Shadow;
+
+import net.minecraft.client.network.ClientCommonNetworkHandler;
+import net.minecraft.network.ClientConnection;
+import net.minecraft.util.Identifier;
+
+import net.fabricmc.fabric.impl.modprotocol.RemoteProtocolStorage;
+
+@Mixin(ClientCommonNetworkHandler.class)
+public class ClientCommonNetworkHandlerMixin implements RemoteProtocolStorage {
+	@Shadow
+	@Final
+	protected ClientConnection connection;
+
+	@Override
+	public Object2IntMap<Identifier> fabric$getRemoteProtocol() {
+		return ((RemoteProtocolStorage) this.connection).fabric$getRemoteProtocol();
+	}
+
+	@Override
+	public void fabric$setRemoteProtocol(Object2IntMap<Identifier> protocol) {
+		((RemoteProtocolStorage) this.connection).fabric$setRemoteProtocol(protocol);
+	}
+}

fabric-mod-protocol-api-v1/src/client/java/net/fabricmc/fabric/mixin/modprotocol/client/ClientConfigurationNetworkHandlerMixin.java

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+/*
+ * Copyright (c) 2016, 2017, 2018, 2019 FabricMC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package net.fabricmc.fabric.mixin.modprotocol.client;
+
+import org.spongepowered.asm.mixin.Mixin;
+import org.spongepowered.asm.mixin.injection.At;
+import org.spongepowered.asm.mixin.injection.Inject;
+import org.spongepowered.asm.mixin.injection.callback.CallbackInfo;
+
+import net.minecraft.client.MinecraftClient;
+import net.minecraft.client.network.ClientCommonNetworkHandler;
+import net.minecraft.client.network.ClientConfigurationNetworkHandler;
+import net.minecraft.client.network.ClientConnectionState;
+import net.minecraft.network.ClientConnection;
+import net.minecraft.network.packet.s2c.config.SelectKnownPacksS2CPacket;
+
+import net.fabricmc.fabric.impl.modprotocol.ModProtocolManager;
+import net.fabricmc.fabric.impl.modprotocol.RemoteProtocolStorage;
+
+@Mixin(ClientConfigurationNetworkHandler.class)
+public abstract class ClientConfigurationNetworkHandlerMixin extends ClientCommonNetworkHandler {
+	protected ClientConfigurationNetworkHandlerMixin(MinecraftClient client, ClientConnection connection, ClientConnectionState connectionState) {
+		super(client, connection, connectionState);
+	}
+
+	@Inject(method = "onSelectKnownPacks", at = @At("HEAD"), cancellable = true)
+	private void preventJoiningIncompatibleServers(SelectKnownPacksS2CPacket packet, CallbackInfo ci) {
+		if (((RemoteProtocolStorage) this.connection).fabric$getRemoteProtocol() == null && !ModProtocolManager.SERVER_REQUIRED.isEmpty()) {
+			this.client.execute(() -> this.connection.disconnect(ModProtocolManager.constructMessage(ModProtocolManager.SERVER_REQUIRED, ModProtocolManager.LOCAL_MOD_PROTOCOLS_BY_ID)));
+			ci.cancel();
+		}
+	}
+}

fabric-mod-protocol-api-v1/src/client/resources/fabric-mod-protocol-api-v1.client.mixins.json

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+{
+  "required": true,
+  "package": "net.fabricmc.fabric.mixin.modprotocol.client",
+  "compatibilityLevel": "JAVA_17",
+  "mixins": [
+    "ClientCommonNetworkHandlerMixin"
+  ],
+  "injectors": {
+    "defaultRequire": 1
+  },
+  "client": [
+    "ClientConfigurationNetworkHandlerMixin"
+  ]
+}

fabric-mod-protocol-api-v1/src/main/java/net/fabricmc/fabric/api/modprotocol/v1/ModProtocol.java

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+/*
+ * Copyright (c) 2016, 2017, 2018, 2019 FabricMC
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package net.fabricmc.fabric.api.modprotocol.v1;
+
+import it.unimi.dsi.fastutil.ints.IntList;
+import org.jetbrains.annotations.ApiStatus;
+
+import net.minecraft.util.Identifier;
+
+/**
+ * Interface representing registered ModProtocol. Can be used for further lookups.
+ */
+@ApiStatus.NonExtendable
+public interface ModProtocol {
+	/**
+	 * @return Identifier associated with this Mod Protocol
+	 */
+	Identifier id();
+	/**
+	 * @return Display name of this protocol
+	 */
+	String name();
+	/**
+	 * @return Display version of this protocol
+	 */
+	String version();
+	/**
+	 * @return Protocol versions supported by this protocol
+	 */
+	IntList protocol();
+	/**
+	 * @return Client requirement of this protocol
+	 */
+	boolean requireClient();
+	/**
+	 * @return Server requirement of this protocol
+	 */
+	boolean requireServer();
+}