Add the cserverseed command

src/main/java/net/earthcomputer/clientcommands/ClientCommands.java

@@ -160,6 +160,7 @@ public static void registerCommands(CommandDispatcher<FabricClientCommandSource>
         RelogCommand.register(dispatcher);
         RenderCommand.register(dispatcher);
         ReplyCommand.register(dispatcher);
+        ServerSeedCommand.register(dispatcher);
         ShrugCommand.register(dispatcher);
         SignSearchCommand.register(dispatcher);
         SnakeCommand.register(dispatcher);

src/main/java/net/earthcomputer/clientcommands/command/ServerSeedCommand.java

@@ -0,0 +1,64 @@
+package net.earthcomputer.clientcommands.command;
+
+import com.google.common.hash.HashCode;
+import com.mojang.brigadier.CommandDispatcher;
+import com.mojang.brigadier.exceptions.CommandSyntaxException;
+import com.mojang.brigadier.exceptions.SimpleCommandExceptionType;
+import com.seedfinding.mccore.rand.seed.WorldSeed;
+import net.fabricmc.fabric.api.client.command.v2.FabricClientCommandSource;
+import net.minecraft.network.chat.Component;
+import net.minecraft.network.chat.ComponentUtils;
+import org.apache.commons.lang3.StringUtils;
+
+import java.util.List;
+
+import static com.mojang.brigadier.arguments.LongArgumentType.*;
+import static net.fabricmc.fabric.api.client.command.v2.ClientCommandManager.*;
+
+public class ServerSeedCommand {
+
+    private static final SimpleCommandExceptionType IMPOSSIBLE_SEED_COMBINATION_EXCEPTION = new SimpleCommandExceptionType(Component.translatable("commands.cserverseed.hashedSeed.impossibleSeedCombination"));
+    private static final SimpleCommandExceptionType ENCHANTMENT_SEED_NOT_SENT_EXCEPTION = new SimpleCommandExceptionType(Component.translatable("commands.cserverseed.enchantmentSeedNotSent"));
+
+    public static void register(CommandDispatcher<FabricClientCommandSource> dispatcher) {
+        dispatcher.register(literal("cserverseed")
+            .then(literal("enchantmentSeed")
+                .executes(ctx -> enchantmentSeed(ctx.getSource())))
+            .then(literal("hashedSeed")
+                .executes(ctx -> hashedSeed(ctx.getSource()))
+                .then(argument("structureSeed", longArg())
+                    .executes(ctx -> fromStructureSeed(ctx.getSource(), getLong(ctx, "structureSeed"))))));
+    }
+
+    private static int enchantmentSeed(FabricClientCommandSource source) throws CommandSyntaxException {
+        int seed = source.getPlayer().getEnchantmentSeed();
+        if (seed == 0) {
+            throw ENCHANTMENT_SEED_NOT_SENT_EXCEPTION.create();
+        }
+        // The enchantment seed is a Java int, which is 32 bits.
+        // However, the server sends the enchantment seed as short to the client.
+        // This causes the 16 higher bits to be ignored, leaving only the 16 lower bits.
+        seed &= 0x0000ffff;
+        source.sendFeedback(Component.translatable("commands.cserverseed.enchantmentSeed", ComponentUtils.copyOnClickText(StringUtils.leftPad(Integer.toBinaryString(seed), 16, '0'))));
+        return seed;
+    }
+
+    private static int hashedSeed(FabricClientCommandSource source) {
+        long hashedSeed = source.getWorld().getBiomeManager().biomeZoomSeed;
+        HashCode seedHash = HashCode.fromLong(hashedSeed);
+        source.sendFeedback(Component.translatable("commands.cserverseed.hashedSeed", ComponentUtils.copyOnClickText(seedHash.toString()), ComponentUtils.copyOnClickText(String.valueOf(seedHash.asLong()))));
+        return (int) hashedSeed;
+    }
+
+    private static int fromStructureSeed(FabricClientCommandSource source, long structureSeed) throws CommandSyntaxException {
+        long hashedSeed = source.getWorld().getBiomeManager().biomeZoomSeed;
+        List<Long> seeds = WorldSeed.fromHash(structureSeed, hashedSeed);
+        if (seeds.isEmpty()) {
+            throw IMPOSSIBLE_SEED_COMBINATION_EXCEPTION.create();
+        }
+        // Collision is extremely unlikely, so just call `getFirst`
+        long worldSeed = seeds.getFirst();
+        source.sendFeedback(Component.translatable("commands.cserverseed.hashedSeed.fromStructureSeed", ComponentUtils.copyOnClickText(String.valueOf(worldSeed))));
+        return (int) worldSeed;
+    }
+}

src/main/java/net/earthcomputer/clientcommands/mixin/commands/serverseed/ClientPacketListenerMixin.java

@@ -0,0 +1,21 @@
+package net.earthcomputer.clientcommands.mixin.commands.serverseed;
+
+import com.llamalad7.mixinextras.sugar.Local;
+import net.minecraft.client.multiplayer.ClientPacketListener;
+import net.minecraft.network.protocol.game.ClientboundContainerSetDataPacket;
+import net.minecraft.world.entity.player.Player;
+import net.minecraft.world.inventory.EnchantmentMenu;
+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;
+
+@Mixin(ClientPacketListener.class)
+public class ClientPacketListenerMixin {
+    @Inject(method = "handleContainerSetData", at = @At(value = "INVOKE", target = "Lnet/minecraft/world/inventory/AbstractContainerMenu;setData(II)V", shift = At.Shift.AFTER))
+    private void onContainerData(ClientboundContainerSetDataPacket packet, CallbackInfo ci, @Local Player player) {
+        if (player.containerMenu instanceof EnchantmentMenu menu) {
+            player.enchantmentSeed = menu.getEnchantmentSeed();
+        }
+    }
+}

src/main/resources/assets/clientcommands/lang/en_us.json

@@ -224,6 +224,12 @@
   "commands.creply.messageTooLong": "Your reply was too long (maximum: %s, given: %s)",
   "commands.creply.noTargetFound": "Could not find a target to reply to",
 
+  "commands.cserverseed.enchantmentSeed": "Lower 16 bits of the enchantment seed: %s",
+  "commands.cserverseed.enchantmentSeedNotSent": "The server has not sent the partial enchantment seed yet!",
+  "commands.cserverseed.hashedSeed": "First 8 bytes of the hashed world seed: %s (decimal: %s)",
+  "commands.cserverseed.hashedSeed.fromStructureSeed": "Found world seed: %s",
+  "commands.cserverseed.hashedSeed.impossibleSeedCombination": "Impossible seed combination!",
+
   "commands.csignsearch.starting": "Searching signs",
 
   "commands.csnap.airborne": "You cannot snap while airborne",

src/main/resources/clientcommands.aw

@@ -24,6 +24,10 @@ accessible method net/minecraft/world/entity/projectile/FishingHook canHitEntity
 accessible method net/minecraft/world/entity/player/Inventory addResource (ILnet/minecraft/world/item/ItemStack;)I
 accessible method net/minecraft/world/entity/player/Inventory hasRemainingSpaceForItem (Lnet/minecraft/world/item/ItemStack;Lnet/minecraft/world/item/ItemStack;)Z
 
+# cserverseed
+accessible field net/minecraft/world/entity/player/Player enchantmentSeed I
+accessible field net/minecraft/world/level/biome/BiomeManager biomeZoomSeed J
+
 # chat
 accessible method net/minecraft/client/Minecraft openChatScreen (Ljava/lang/String;)V
 

src/main/resources/mixins.clientcommands.json

@@ -70,6 +70,7 @@
     "commands.generic.CommandSuggestionsMixin",
     "commands.glow.LivingEntityRenderStateMixin",
     "commands.reply.ClientPacketListenerMixin",
+    "commands.serverseed.ClientPacketListenerMixin",
     "commands.snap.MinecraftMixin",
     "dataqueryhandler.ClientPacketListenerMixin",
     "events.ClientPacketListenerMixin",