Entity message handling

src/main/kotlin/ru/dbotthepony/kstarbound/client/world/ClientWorld.kt

@@ -22,6 +22,7 @@ import ru.dbotthepony.kstarbound.defs.tile.LiquidDefinition
 import ru.dbotthepony.kstarbound.defs.world.WorldTemplate
 import ru.dbotthepony.kstarbound.math.roundTowardsNegativeInfinity
 import ru.dbotthepony.kstarbound.math.roundTowardsPositiveInfinity
+import ru.dbotthepony.kstarbound.network.Connection
 import ru.dbotthepony.kstarbound.network.packets.DamageNotificationPacket
 import ru.dbotthepony.kstarbound.network.packets.DamageRequestPacket
 import ru.dbotthepony.kstarbound.network.packets.HitRequestPacket
@@ -339,6 +340,12 @@ class ClientWorld(
 		client.activeConnection?.send(data)
 	}
 
+	override fun remote(connectionID: Int): Connection? {
+		// connectionID might be of different client (and not of server's),
+		// but we always must send messages to server
+		return client.activeConnection
+	}
+
 	companion object {
 		val ring = listOf(
 			Vector2i(0, 0),

src/main/kotlin/ru/dbotthepony/kstarbound/collect/IdMap.kt

@@ -45,6 +45,14 @@ class IdMap<T : Any>(val min: Int = 0, val max: Int = Int.MAX_VALUE, private val
 		return index
 	}
 
+	override fun get(key: Int): T? {
+		if (map is Int2ObjectMap) {
+			return (map as Int2ObjectMap).get(key)
+		} else {
+			return map[key]
+		}
+	}
+
 	override fun clear() {
 		nextIndex = min - 1
 		map.clear()

src/main/kotlin/ru/dbotthepony/kstarbound/defs/item/ItemDescriptor.kt

@@ -180,13 +180,12 @@ data class ItemDescriptor(
 		it.add("parameters", parameters.deepCopy())
 	}
 
-	fun toJson(): JsonObject? {
+	fun toJson(): JsonElement {
 		if (Starbound.IS_STORE_JSON) {
 			return VersionRegistry.make("Item", toJsonStruct()).toJson()
 		} else {
-			if (isEmpty) {
-				return null
-			}
+			if (isEmpty)
+				return JsonNull.INSTANCE
 
 			return toJsonStruct()
 		}

src/main/kotlin/ru/dbotthepony/kstarbound/item/IContainer.kt

@@ -3,6 +3,10 @@ package ru.dbotthepony.kstarbound.item
 import com.google.gson.JsonArray
 import com.google.gson.JsonElement
 import it.unimi.dsi.fastutil.ints.IntArrayList
+import it.unimi.dsi.fastutil.ints.IntIterable
+import it.unimi.dsi.fastutil.ints.IntIterator
+import it.unimi.dsi.fastutil.ints.IntIterators
+import it.unimi.dsi.fastutil.ints.IntLists
 import ru.dbotthepony.kstarbound.Starbound
 import ru.dbotthepony.kstarbound.defs.item.ItemDescriptor
 import java.util.random.RandomGenerator
@@ -11,6 +15,7 @@ interface IContainer {
 	var size: Int
 	operator fun get(index: Int): ItemStack
 	operator fun set(index: Int, value: ItemStack)
+	fun clear()
 
 	fun ageItems(by: Double): Boolean {
 		var any = false
@@ -109,13 +114,29 @@ interface IContainer {
 		}
 	}
 
-	// puts item into container, returns remaining not put items
+	// returns not inserted items
 	fun add(item: ItemStack, simulate: Boolean = false): ItemStack {
+		return put({ IntIterators.fromTo(0, size) }, item, simulate)
+	}
+
+	// returns not inserted items
+	fun put(slots: IntIterable, item: ItemStack, simulate: Boolean = false): ItemStack {
+		return put(slots::iterator, item, simulate)
+	}
+
+	// returns not inserted items
+	fun put(slots: () -> IntIterator, item: ItemStack, simulate: Boolean = false): ItemStack {
 		val copy = item.copy()
 
-		// first, try to put into not empty slots first
-		for (i in 0 until size) {
-			val itemThere = this[i]
+		var itr = slots.invoke()
+
+		while (itr.hasNext()) {
+			val slot = itr.nextInt()
+
+			if (slot !in 0 until size)
+				continue
+
+			val itemThere = this[slot]
 
 			if (itemThere.isStackable(copy)) {
 				val newCount = (itemThere.size + copy.size).coerceAtMost(itemThere.maxStackSize)
@@ -131,21 +152,29 @@ interface IContainer {
 			}
 		}
 
-		// then try to move into empty slots
-		for (i in 0 until size) {
-			val itemThere = this[i]
+		itr = slots.invoke()
+
+		while (itr.hasNext()) {
+			val slot = itr.nextInt()
+
+			if (slot !in 0 until size)
+				continue
+
+			val itemThere = this[slot]
 
 			if (itemThere.isEmpty) {
-				if (copy.size > copy.maxStackSize) {
-					if (!simulate)
-						this[i] = copy.copy(copy.maxStackSize)
+				if (itemThere.isEmpty) {
+					if (copy.size > copy.maxStackSize) {
+						if (!simulate)
+							this[slot] = copy.copy(copy.maxStackSize)
 
-					copy.size -= copy.maxStackSize
-				} else {
-					if (!simulate)
-						this[i] = copy
+						copy.size -= copy.maxStackSize
+					} else {
+						if (!simulate)
+							this[slot] = copy
 
-					return ItemStack.EMPTY
+						return ItemStack.EMPTY
+					}
 				}
 			}
 		}
@@ -153,7 +182,153 @@ interface IContainer {
 		return copy
 	}
 
-	fun clear()
+	fun take(slot: Int, amount: Long): ItemStack {
+		if (slot !in 0 until size || amount <= 0L)
+			return ItemStack.EMPTY
+
+		val item = this[slot]
+
+		if (item.isEmpty)
+			return item
+
+		if (item.size > amount) {
+			val copy = item.copy(amount)
+			item.shrink(amount)
+			return copy
+		} else {
+			this[slot] = ItemStack.EMPTY
+			return item
+		}
+	}
+
+	fun takeExact(slot: Int, amount: Long): Boolean {
+		if (amount <= 0L)
+			return true
+
+		if (slot !in 0 until size)
+			return false
+
+		val item = this[slot]
+
+		if (item.isEmpty)
+			return false
+
+		if (item.size > amount) {
+			item.shrink(amount)
+			return true
+		} else {
+			return false
+		}
+	}
+
+	fun swap(slot: Int, item: ItemStack, tryCombine: Boolean = true): ItemStack {
+		val existingItem = this[slot]
+
+		if (item.isEmpty && existingItem.isEmpty) {
+			return ItemStack.EMPTY
+		} else if (item.isEmpty && existingItem.isNotEmpty) {
+			// If we are passed in nothing, simply return what's there, if anything.
+			this[slot] = ItemStack.EMPTY
+			return existingItem
+		} else if (item.isNotEmpty && existingItem.isEmpty) {
+			// place into slot
+			// use put because item might be bigger than max stack size
+			return put(IntLists.singleton(slot), item)
+		} else {
+			// If something is there, try to stack with it first.  If we can't stack,
+			// then swap.
+
+			if (tryCombine && existingItem.isStackable(item)) {
+				return put(IntLists.singleton(slot), item)
+			} else {
+				this[slot] = ItemStack.EMPTY
+				val slots = IntArrayList(IntIterators.fromTo(0, size))
+				slots.removeInt(slot)
+				slots.add(0, slot)
+
+				val remaining = put(slots, item)
+
+				if (remaining.isNotEmpty && this[slot].isStackable(remaining)) {
+					// damn
+					this[slot].grow(remaining.size)
+				}
+
+				return existingItem
+			}
+		}
+	}
+
+	fun take(descriptor: ItemDescriptor, exactMatch: Boolean = false, simulate: Boolean = false): Boolean {
+		var toTake = descriptor.count
+
+		if (toTake <= 0L)
+			return true
+
+		val extractSlots = IntArrayList()
+
+		for (slot in 0 until size) {
+			val item = this[slot]
+
+			if (item.matches(descriptor, exactMatch)) {
+				toTake -= item.size
+				if (!simulate) extractSlots.add(slot)
+				if (toTake <= 0L) break
+			}
+		}
+
+		if (simulate || toTake > 0L)
+			return toTake <= 0L
+
+		toTake = descriptor.count
+
+		for (slot in extractSlots) {
+			if (this[slot].size <= toTake) {
+				toTake -= this[slot].size
+				this[slot] = ItemStack.EMPTY
+			} else {
+				this[slot].shrink(toTake)
+				break
+			}
+		}
+
+		return true
+	}
+
+	fun take(descriptor: ItemStack, exactMatch: Boolean = false, simulate: Boolean = false): Boolean {
+		var toTake = descriptor.size
+
+		if (toTake <= 0L)
+			return true
+
+		val extractSlots = IntArrayList()
+
+		for (slot in 0 until size) {
+			val item = this[slot]
+
+			if (item.matches(descriptor, exactMatch)) {
+				toTake -= item.size
+				if (!simulate) extractSlots.add(slot)
+				if (toTake <= 0L) break
+			}
+		}
+
+		if (simulate || toTake > 0L)
+			return toTake <= 0L
+
+		toTake = descriptor.size
+
+		for (slot in extractSlots) {
+			if (this[slot].size <= toTake) {
+				toTake -= this[slot].size
+				this[slot] = ItemStack.EMPTY
+			} else {
+				this[slot].shrink(toTake)
+				break
+			}
+		}
+
+		return true
+	}
 
 	fun toJson(store: Boolean = false): JsonArray {
 		val result = JsonArray(size)

src/main/kotlin/ru/dbotthepony/kstarbound/item/ItemStack.kt

@@ -359,9 +359,9 @@ open class ItemStack(val entry: ItemRegistry.Entry, val config: JsonObject, para
 		return ItemStack(entry, config, parameters.deepCopy(), size)
 	}
 
-	fun toJson(): JsonObject? {
+	fun toJson(): JsonElement {
 		if (isEmpty)
-			return null
+			return JsonNull.INSTANCE
 
 		return createDescriptor().toJson()
 	}

src/main/kotlin/ru/dbotthepony/kstarbound/network/Connection.kt

@@ -245,6 +245,8 @@ abstract class Connection(val side: ConnectionSide, val type: ConnectionType) :
 	}
 
 	companion object {
+		const val SERVER_CONNECTION_ID = 0
+
 		private val LOGGER = LogManager.getLogger()
 
 		private val warpActionCodec = StreamCodec.Pair(WarpAction.CODEC, WarpMode.CODEC).koptional()

src/main/kotlin/ru/dbotthepony/kstarbound/network/PacketRegistry.kt

@@ -24,6 +24,8 @@ import ru.dbotthepony.kstarbound.network.packets.HitRequestPacket
 import ru.dbotthepony.kstarbound.network.packets.DamageRequestPacket
 import ru.dbotthepony.kstarbound.network.packets.EntityCreatePacket
 import ru.dbotthepony.kstarbound.network.packets.EntityDestroyPacket
+import ru.dbotthepony.kstarbound.network.packets.EntityMessagePacket
+import ru.dbotthepony.kstarbound.network.packets.EntityMessageResponsePacket
 import ru.dbotthepony.kstarbound.network.packets.EntityUpdateSetPacket
 import ru.dbotthepony.kstarbound.network.packets.PingPacket
 import ru.dbotthepony.kstarbound.network.packets.PongPacket
@@ -483,8 +485,8 @@ class PacketRegistry(val isLegacy: Boolean) {
 			LEGACY.add(HitRequestPacket::read)
 			LEGACY.add(DamageRequestPacket::read)
 			LEGACY.add(::DamageNotificationPacket)
-			LEGACY.skip("EntityMessage")
-			LEGACY.skip("EntityMessageResponse")
+			LEGACY.add(::EntityMessagePacket)
+			LEGACY.add(::EntityMessageResponsePacket)
 			LEGACY.add(::UpdateWorldPropertiesPacket)
 			LEGACY.add(::StepUpdatePacket)
 

src/main/kotlin/ru/dbotthepony/kstarbound/network/packets/EntityMessagePacket.kt

@@ -0,0 +1,83 @@
+package ru.dbotthepony.kstarbound.network.packets
+
+import com.google.gson.JsonArray
+import ru.dbotthepony.kommons.io.readUUID
+import ru.dbotthepony.kommons.io.writeBinaryString
+import ru.dbotthepony.kommons.io.writeUUID
+import ru.dbotthepony.kommons.util.Either
+import ru.dbotthepony.kstarbound.client.ClientConnection
+import ru.dbotthepony.kstarbound.io.readInternedString
+import ru.dbotthepony.kstarbound.json.readJsonArray
+import ru.dbotthepony.kstarbound.json.writeJsonArray
+import ru.dbotthepony.kstarbound.network.Connection
+import ru.dbotthepony.kstarbound.network.IClientPacket
+import ru.dbotthepony.kstarbound.network.IServerPacket
+import ru.dbotthepony.kstarbound.server.ServerConnection
+import ru.dbotthepony.kstarbound.world.World
+import java.io.DataInputStream
+import java.io.DataOutputStream
+import java.util.*
+import java.util.function.Consumer
+import java.util.function.Function
+
+class EntityMessagePacket(val entity: Either<Int, String>, val message: String, val arguments: JsonArray, val id: UUID, val sourceConnection: Int) : IClientPacket, IServerPacket {
+	constructor(stream: DataInputStream, isLegacy: Boolean) : this(
+		if (stream.readBoolean()) Either.right(stream.readInternedString()) else Either.left(stream.readInt()),
+		stream.readInternedString(),
+		stream.readJsonArray(),
+		stream.readUUID(),
+		stream.readUnsignedShort()
+	)
+
+	override fun write(stream: DataOutputStream, isLegacy: Boolean) {
+		stream.writeBoolean(entity.isRight)
+
+		if (entity.isLeft) {
+			stream.writeInt(entity.left())
+		} else {
+			stream.writeBinaryString(entity.right())
+		}
+
+		stream.writeBinaryString(message)
+		stream.writeJsonArray(arguments)
+		stream.writeUUID(id)
+		stream.writeShort(sourceConnection)
+	}
+
+	private fun handle(connection: Connection, world: World<*, *>) {
+		if (entity.isLeft) {
+			val entity = world.entities[entity.left()]
+
+			if (entity == null) {
+				connection.send(EntityMessageResponsePacket(Either.left("No such entity ${this@EntityMessagePacket.entity}"), id))
+			} else {
+				entity.dispatchMessage(connection.connectionID, message, arguments)
+					.thenAccept(Consumer {
+						connection.send(EntityMessageResponsePacket(Either.right(it), id))
+					})
+					.exceptionally(Function {
+						connection.send(EntityMessageResponsePacket(Either.left(it.message ?: "Internal server error"), id))
+						null
+					})
+			}
+		} else {
+			TODO("messages to unique entities")
+		}
+	}
+
+	override fun play(connection: ServerConnection) {
+		connection.enqueue {
+			handle(connection, this)
+		}
+	}
+
+	override fun play(connection: ClientConnection) {
+		connection.enqueue {
+			val world = world
+
+			if (world != null) {
+				handle(connection, world)
+			}
+		}
+	}
+}

src/main/kotlin/ru/dbotthepony/kstarbound/network/packets/EntityMessageResponsePacket.kt

@@ -0,0 +1,60 @@
+package ru.dbotthepony.kstarbound.network.packets
+
+import com.google.gson.JsonElement
+import ru.dbotthepony.kommons.io.readUUID
+import ru.dbotthepony.kommons.io.writeBinaryString
+import ru.dbotthepony.kommons.io.writeUUID
+import ru.dbotthepony.kommons.util.Either
+import ru.dbotthepony.kstarbound.client.ClientConnection
+import ru.dbotthepony.kstarbound.io.readEither
+import ru.dbotthepony.kstarbound.io.readInternedString
+import ru.dbotthepony.kstarbound.io.writeEither
+import ru.dbotthepony.kstarbound.json.readJsonElement
+import ru.dbotthepony.kstarbound.json.writeJsonElement
+import ru.dbotthepony.kstarbound.network.IClientPacket
+import ru.dbotthepony.kstarbound.network.IServerPacket
+import ru.dbotthepony.kstarbound.server.ServerConnection
+import ru.dbotthepony.kstarbound.world.entities.AbstractEntity
+import java.io.DataInputStream
+import java.io.DataOutputStream
+import java.util.UUID
+
+class EntityMessageResponsePacket(val response: Either<String, JsonElement>, val id: UUID) : IServerPacket, IClientPacket {
+	constructor(stream: DataInputStream, isLegacy: Boolean) : this(
+		stream.readEither(isLegacy, { readInternedString() }, { readJsonElement() }),
+		stream.readUUID())
+
+	override fun write(stream: DataOutputStream, isLegacy: Boolean) {
+		// ah yes, Variant<> in EntityMessagePacket, but Either<> in EntityMessageResponsePacket
+		stream.writeEither(response, isLegacy, { writeBinaryString(it) }, { writeJsonElement(it) })
+		stream.writeUUID(id)
+	}
+
+	override fun play(connection: ServerConnection) {
+		connection.enqueue {
+			val message = pendingEntityMessages.asMap().remove(id)
+
+			if (message != null) {
+				if (response.isLeft) {
+					message.completeExceptionally(AbstractEntity.MessageCallException(response.left()))
+				} else {
+					message.complete(response.right())
+				}
+			}
+		}
+	}
+
+	override fun play(connection: ClientConnection) {
+		connection.enqueue {
+			val message = world?.pendingEntityMessages?.asMap()?.remove(this@EntityMessageResponsePacket.id)
+
+			if (message != null) {
+				if (response.isLeft) {
+					message.completeExceptionally(AbstractEntity.MessageCallException(response.left()))
+				} else {
+					message.complete(response.right())
+				}
+			}
+		}
+	}
+}

src/main/kotlin/ru/dbotthepony/kstarbound/server/world/ServerWorld.kt

@@ -31,6 +31,7 @@ import ru.dbotthepony.kstarbound.defs.world.WorldStructure
 import ru.dbotthepony.kstarbound.defs.world.WorldTemplate
 import ru.dbotthepony.kstarbound.json.builder.JsonFactory
 import ru.dbotthepony.kstarbound.json.jsonArrayOf
+import ru.dbotthepony.kstarbound.network.Connection
 import ru.dbotthepony.kstarbound.network.IPacket
 import ru.dbotthepony.kstarbound.network.packets.DamageNotificationPacket
 import ru.dbotthepony.kstarbound.network.packets.DamageRequestPacket
@@ -304,7 +305,7 @@ class ServerWorld private constructor(
 			val broken = entity.damageTileEntity(occupySpaces, sourcePosition, actualDamage)
 
 			if (source != null && broken) {
-				source.receiveMessage("tileEntityBroken", jsonArrayOf(
+				source.dispatchMessage(Connection.SERVER_CONNECTION_ID, "tileEntityBroken", jsonArrayOf(
 					damagePositions.firstOrNull { p -> actualPositions.any { it.position == p } } ?: entity.tilePosition,
 					entity.type.jsonName,
 					(entity as? WorldObject)?.config?.key))
@@ -341,7 +342,7 @@ class ServerWorld private constructor(
 				topMost = topMost.coerceAtLeast(result)
 
 				if (source != null && health?.isDead == true) {
-					source.receiveMessage("tileBroken", jsonArrayOf(
+					source.dispatchMessage(Connection.SERVER_CONNECTION_ID, "tileBroken", jsonArrayOf(
 						pos, if (isBackground) "background" else "foreground",
 						tile!!.tile(isBackground).material.id ?: tile.tile(isBackground).material.key, // TODO: explicit string identifiers support
 						tile.dungeonId,
@@ -644,6 +645,10 @@ class ServerWorld private constructor(
 		server.channels.connectionByID(data.destinationConnection)?.send(data)
 	}
 
+	override fun remote(connectionID: Int): Connection? {
+		return server.channels.connectionByID(connectionID)
+	}
+
 	@JsonFactory
 	data class MetadataJson(
 		val playerStart: Vector2d,

src/main/kotlin/ru/dbotthepony/kstarbound/world/World.kt

@@ -1,5 +1,7 @@
 package ru.dbotthepony.kstarbound.world
 
+import com.github.benmanes.caffeine.cache.Cache
+import com.github.benmanes.caffeine.cache.Caffeine
 import com.google.gson.JsonElement
 import com.google.gson.JsonNull
 import com.google.gson.JsonObject
@@ -26,6 +28,7 @@ import ru.dbotthepony.kstarbound.defs.world.WorldStructure
 import ru.dbotthepony.kstarbound.defs.world.WorldTemplate
 import ru.dbotthepony.kstarbound.json.mergeJson
 import ru.dbotthepony.kstarbound.math.*
+import ru.dbotthepony.kstarbound.network.Connection
 import ru.dbotthepony.kstarbound.network.IPacket
 import ru.dbotthepony.kstarbound.network.packets.DamageNotificationPacket
 import ru.dbotthepony.kstarbound.network.packets.DamageRequestPacket
@@ -43,13 +46,17 @@ import ru.dbotthepony.kstarbound.world.entities.tile.TileEntity
 import ru.dbotthepony.kstarbound.world.physics.CollisionPoly
 import ru.dbotthepony.kstarbound.world.physics.CollisionType
 import ru.dbotthepony.kstarbound.world.physics.Poly
+import java.util.*
 import java.util.concurrent.CompletableFuture
 import java.util.concurrent.CopyOnWriteArrayList
+import java.util.concurrent.TimeUnit
+import java.util.concurrent.TimeoutException
 import java.util.concurrent.atomic.AtomicInteger
 import java.util.concurrent.locks.ReentrantLock
 import java.util.function.Predicate
 import java.util.random.RandomGenerator
 import java.util.stream.Stream
+import kotlin.collections.ArrayList
 import kotlin.math.roundToInt
 
 abstract class World<This : World<This, ChunkType>, ChunkType : Chunk<This, ChunkType>>(val template: WorldTemplate) : ICellAccess {
@@ -573,6 +580,18 @@ abstract class World<This : World<This, ChunkType>, ChunkType : Chunk<This, Chun
 	protected abstract fun networkHitRequest(data: HitRequestPacket)
 	protected abstract fun networkDamageRequest(data: DamageRequestPacket)
 
+	abstract fun remote(connectionID: Int): Connection?
+
+	// this *could* have been divided into per-entity map and beheaded world's map
+	//  but we can't, because response packets contain only message UUID, and don't contain entity ID
+	val pendingEntityMessages: Cache<UUID, CompletableFuture<JsonElement>> = Caffeine.newBuilder()
+		.maximumSize(32000L) // some unreachable value unless there is a malicious actor
+		.expireAfterWrite(1L, TimeUnit.MINUTES)
+		.executor(Starbound.EXECUTOR)
+		.scheduler(Starbound)
+		.removalListener<UUID, CompletableFuture<JsonElement>> { key, value, cause -> if (!cause.wasEvicted()) value?.completeExceptionally(TimeoutException("Did not receive response from remote in time")) }
+		.build()
+
 	companion object {
 		private val LOGGER = LogManager.getLogger()
 

src/main/kotlin/ru/dbotthepony/kstarbound/world/entities/AbstractEntity.kt

@@ -7,11 +7,9 @@ import it.unimi.dsi.fastutil.bytes.ByteArrayList
 import it.unimi.dsi.fastutil.io.FastByteArrayOutputStream
 import it.unimi.dsi.fastutil.objects.ObjectArrayList
 import org.apache.logging.log4j.LogManager
-import ru.dbotthepony.kommons.io.koptional
 import ru.dbotthepony.kommons.io.nullable
 import ru.dbotthepony.kommons.util.Either
 import ru.dbotthepony.kstarbound.math.AABB
-import ru.dbotthepony.kommons.util.KOptional
 import ru.dbotthepony.kstarbound.math.vector.Vector2d
 import ru.dbotthepony.kstarbound.client.StarboundClient
 import ru.dbotthepony.kstarbound.client.render.LayeredRenderer
@@ -30,6 +28,7 @@ import ru.dbotthepony.kstarbound.network.packets.EntityCreatePacket
 import ru.dbotthepony.kstarbound.network.packets.EntityDestroyPacket
 import ru.dbotthepony.kstarbound.network.packets.HitRequestPacket
 import ru.dbotthepony.kstarbound.network.packets.DamageRequestPacket
+import ru.dbotthepony.kstarbound.network.packets.EntityMessagePacket
 import ru.dbotthepony.kstarbound.network.syncher.InternedStringCodec
 import ru.dbotthepony.kstarbound.network.syncher.MasterElement
 import ru.dbotthepony.kstarbound.network.syncher.NetworkedGroup
@@ -43,6 +42,8 @@ import ru.dbotthepony.kstarbound.world.World
 import ru.dbotthepony.kstarbound.world.castRay
 import ru.dbotthepony.kstarbound.world.physics.Poly
 import java.io.DataOutputStream
+import java.util.UUID
+import java.util.concurrent.CompletableFuture
 import java.util.function.Consumer
 import java.util.function.Predicate
 
@@ -179,10 +180,6 @@ abstract class AbstractEntity : Comparable<AbstractEntity> {
 
 	}
 
-	open fun receiveMessage(name: String, arguments: JsonArray): JsonElement? {
-		return null
-	}
-
 	var removalReason: RemovalReason? = null
 		private set
 
@@ -459,6 +456,43 @@ abstract class AbstractEntity : Comparable<AbstractEntity> {
 		}
 	}
 
+	/**
+	 * Entities can send other entities potentially remote messages and get
+	 * responses back from them, and should implement this to receive and respond
+	 * to messages.  If the message is NOT handled, should return Nothing,
+	 * otherwise should return some Json value.
+	 * This will only ever be called on master entities.
+	 */
+	protected open fun handleMessage(connection: Int, message: String, arguments: JsonArray): JsonElement? {
+		return null
+	}
+
+	// doesn't write stacktrace
+	class MessageCallException(message: String) : RuntimeException(message, null, true, false)
+
+	fun dispatchMessage(sourceConnection: Int, message: String, arguments: JsonArray): CompletableFuture<JsonElement> {
+		if (isRemote) {
+			val connection = world.remote(connectionID) ?: return CompletableFuture.failedFuture(NoSuchElementException("Can't dispatch entity message, no such connection $connectionID"))
+			val future = CompletableFuture<JsonElement>()
+			val uuid = UUID(world.random.nextLong(), world.random.nextLong())
+			world.pendingEntityMessages.put(uuid, future)
+			connection.send(EntityMessagePacket(Either.left(entityID), message, arguments, uuid, sourceConnection))
+			return future
+		} else {
+			val response = try {
+				handleMessage(sourceConnection, message, arguments)
+			} catch (err: Throwable) {
+				return CompletableFuture.failedFuture(err)
+			}
+
+			if (response == null) {
+				return CompletableFuture.failedFuture(MessageCallException("Message '$message' was not handled"))
+			} else {
+				return CompletableFuture.completedFuture(response)
+			}
+		}
+	}
+
 	open fun render(client: StarboundClient, layers: LayeredRenderer) {
 
 	}

src/main/kotlin/ru/dbotthepony/kstarbound/world/entities/tile/ContainerObject.kt

@@ -1,8 +1,12 @@
 package ru.dbotthepony.kstarbound.world.entities.tile
 
 import com.google.gson.JsonArray
+import com.google.gson.JsonElement
+import com.google.gson.JsonNull
 import com.google.gson.JsonObject
 import com.google.gson.JsonPrimitive
+import it.unimi.dsi.fastutil.ints.IntIterators
+import it.unimi.dsi.fastutil.ints.IntLists
 import it.unimi.dsi.fastutil.io.FastByteArrayInputStream
 import it.unimi.dsi.fastutil.io.FastByteArrayOutputStream
 import org.apache.logging.log4j.LogManager
@@ -23,8 +27,6 @@ import ru.dbotthepony.kstarbound.defs.`object`.ObjectDefinition
 import ru.dbotthepony.kstarbound.item.IContainer
 import ru.dbotthepony.kstarbound.item.ItemStack
 import ru.dbotthepony.kstarbound.math.Interpolator
-import ru.dbotthepony.kstarbound.math.vector.Vector2d
-import ru.dbotthepony.kstarbound.math.vector.Vector2i
 import ru.dbotthepony.kstarbound.network.syncher.NetworkedElement
 import ru.dbotthepony.kstarbound.network.syncher.networkedBoolean
 import ru.dbotthepony.kstarbound.network.syncher.networkedFloat
@@ -186,6 +188,49 @@ class ContainerObject(config: Registry.Entry<ObjectDefinition>) : WorldObject(co
 		}
 	}
 
+	override fun handleMessage(connection: Int, message: String, arguments: JsonArray): JsonElement? {
+		return when (message.lowercase()) {
+			"startcrafting" -> startCrafting()
+			"stopcrafting" -> stopCrafting()
+			"burncontainercontents" -> burnContainerContents()
+
+			// returns not inserted items
+			"additems" -> items.add(ItemDescriptor(arguments[0]).build()).toJson()
+			"putitems" -> items.put(IntLists.singleton(arguments[0].asInt), ItemDescriptor(arguments[1]).build()).toJson()
+			"takeitems" -> items.take(arguments[0].asInt, arguments[1].asLong).toJson()
+			"swapitems" -> items.swap(arguments[0].asInt, ItemDescriptor(arguments[1]).build(), if (arguments.size() >= 3) arguments[2].asBoolean else true).toJson()
+			"applyaugment" -> TODO("applyaugment")
+			"consumeitems" -> JsonPrimitive(items.take(ItemDescriptor(arguments[0])))
+			"consumeitemsat" -> JsonPrimitive(items.takeExact(arguments[0].asInt, arguments[1].asLong))
+			"clearcontainer" -> {
+				val result = JsonArray()
+
+				for (slot in 0 until items.size) {
+					if (items[slot].isNotEmpty) {
+						result.add(items[slot].toJson())
+					}
+				}
+
+				items.clear()
+				result
+			}
+
+			else -> super.handleMessage(connection, message, arguments)
+		}
+	}
+
+	private fun startCrafting(): JsonElement {
+		return JsonNull.INSTANCE
+	}
+
+	private fun stopCrafting(): JsonElement {
+		return JsonNull.INSTANCE
+	}
+
+	private fun burnContainerContents(): JsonElement {
+		return JsonNull.INSTANCE
+	}
+
 	// Networking of this container to legacy clients is incredibly stupid,
 	// and networks entire state each time something has changed.
 	inner class Container(size: Int) : NetworkedElement(), IContainer {