Implement serialization of diff in one go

CHANGELOG.md

@@ -9,6 +9,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ### Changed
 
+- Functions in `AppReplicationExt::replicate_with` now accept bytes cursor for memory reuse and return serialization errors.
 - Rename `ReplicationCore` into `RepliconCore` with its module for clarity.
 - Store changes in `WorldDiff` in `Vec` instead of `HashMap` to increase performance.
 - `MapNetworkEntities` now accepts generic `Mapper` and doesn't have error handling and deserialiation functions now accept `NetworkEntityMap`. This allowed us to lazily map entities on client without extra allocation.

src/client.rs

@@ -1,5 +1,5 @@
 use bevy::{
-    ecs::{component::Tick, system::Command, world::EntityMut},
+    ecs::{component::Tick, system::SystemState, world::EntityMut},
     prelude::*,
     utils::{Entry, HashMap},
 };
@@ -8,8 +8,7 @@ use bevy_renet::{renet::RenetClient, transport::NetcodeClientPlugin, RenetClient
 use serde::{Deserialize, Serialize};
 
 use crate::{
-    prelude::ReplicationRules,
-    replicon_core::{ComponentDiff, Mapper, WorldDiff, REPLICATION_CHANNEL_ID},
+    replicon_core::{Mapper, WorldDiff, REPLICATION_CHANNEL_ID},
     Replication,
 };
 
@@ -47,21 +46,16 @@ impl Plugin for ClientPlugin {
 }
 
 impl ClientPlugin {
-    fn diff_receiving_system(
-        mut commands: Commands,
-        mut last_tick: ResMut<LastTick>,
-        mut client: ResMut<RenetClient>,
-    ) {
+    fn diff_receiving_system(world: &mut World, state: &mut SystemState<ResMut<RenetClient>>) {
+        let mut client = state.get_mut(world);
         let mut last_message = None;
         while let Some(message) = client.receive_message(REPLICATION_CHANNEL_ID) {
             last_message = Some(message);
         }
 
         if let Some(last_message) = last_message {
-            let world_diff: WorldDiff = bincode::deserialize(&last_message)
-                .expect("server should send only world diffs over replication channel");
-            *last_tick = world_diff.tick.into();
-            commands.apply_world_diff(world_diff);
+            WorldDiff::deserialize_to_world(world, last_message)
+                .expect("server should send only valid world diffs");
         }
     }
 
@@ -95,55 +89,6 @@ impl From<LastTick> for Tick {
     }
 }
 
-trait ApplyWorldDiffExt {
-    fn apply_world_diff(&mut self, world_diff: WorldDiff);
-}
-
-impl ApplyWorldDiffExt for Commands<'_, '_> {
-    fn apply_world_diff(&mut self, world_diff: WorldDiff) {
-        self.add(ApplyWorldDiff(world_diff));
-    }
-}
-
-struct ApplyWorldDiff(WorldDiff);
-
-impl Command for ApplyWorldDiff {
-    fn apply(self, world: &mut World) {
-        world.resource_scope(|world, mut entity_map: Mut<NetworkEntityMap>| {
-            world.resource_scope(|world, replication_rules: Mut<ReplicationRules>| {
-                for (entity, components) in self.0.entities {
-                    let mut entity = entity_map.get_by_server_or_spawn(world, entity);
-                    for component_diff in components {
-                        match component_diff {
-                            ComponentDiff::Changed((replication_id, component)) => {
-                                let replication_info = replication_rules.get_info(replication_id);
-                                (replication_info.deserialize)(
-                                    &mut entity,
-                                    &mut entity_map,
-                                    &component,
-                                );
-                            }
-                            ComponentDiff::Removed(replication_id) => {
-                                let replication_info = replication_rules.get_info(replication_id);
-                                (replication_info.remove)(&mut entity);
-                            }
-                        }
-                    }
-                }
-            });
-
-            for server_entity in self.0.despawns {
-                // The entity might have already been deleted with the last diff,
-                // but the server might not yet have received confirmation from the
-                // client and could include the deletion in the latest diff.
-                if let Some(client_entity) = entity_map.remove_by_server(server_entity) {
-                    world.entity_mut(client_entity).despawn_recursive();
-                }
-            }
-        });
-    }
-}
-
 /// Set with replication and event systems related to client.
 #[derive(SystemSet, Debug, Hash, PartialEq, Eq, Clone, Copy)]
 pub enum ClientSet {
@@ -172,7 +117,7 @@ impl NetworkEntityMap {
         self.client_to_server.insert(client_entity, server_entity);
     }
 
-    fn get_by_server_or_spawn<'a>(
+    pub(super) fn get_by_server_or_spawn<'a>(
         &mut self,
         world: &'a mut World,
         server_entity: Entity,
@@ -189,7 +134,7 @@ impl NetworkEntityMap {
         }
     }
 
-    fn remove_by_server(&mut self, server_entity: Entity) -> Option<Entity> {
+    pub(super) fn remove_by_server(&mut self, server_entity: Entity) -> Option<Entity> {
         let client_entity = self.server_to_client.remove(&server_entity);
         if let Some(client_entity) = client_entity {
             self.client_to_server.remove(&client_entity);

src/lib.rs

@@ -89,30 +89,34 @@ If your component doesn't implement serde traits or you want to serialize it par
 you can use [`AppReplicationExt::replicate_with`]:
 
 ```rust
-use bevy::{ecs::world::EntityMut, prelude::*, ptr::Ptr, utils::HashMap};
-# use bevy_replicon::prelude::*;
+# use std::io::Cursor;
+# use bevy::{ecs::world::EntityMut, prelude::*, ptr::Ptr, utils::HashMap};
+# use bevy_replicon::{prelude::*, renet::Bytes};
 # use serde::{Deserialize, Serialize};
 # let mut app = App::new();
 # app.add_plugins(ReplicationPlugins);
 app.replicate_with::<Transform>(serialize_transform, deserialize_transform);
 
 /// Serializes only translation.
-fn serialize_transform(component: Ptr) -> Vec<u8> {
+fn serialize_transform(
+    component: Ptr,
+    cursor: &mut Cursor<&mut Vec<u8>>,
+) -> Result<(), bincode::Error> {
     // SAFETY: Function called for registered `ComponentId`.
     let transform: &Transform = unsafe { component.deref() };
-    bincode::serialize(&transform.translation)
-        .unwrap_or_else(|e| panic!("Vec3 should be serialzable: {e}"))
+    bincode::serialize_into(cursor, &transform.translation)
 }
 
 /// Deserializes translation and creates [`Transform`] from it.
 fn deserialize_transform(
     entity: &mut EntityMut,
     _entity_map: &mut NetworkEntityMap,
-    component: &[u8],
-) {
-    let translation: Vec3 = bincode::deserialize(component)
-        .unwrap_or_else(|e| panic!("bytes from server should be Vec3: {e}"));
+    cursor: &mut Cursor<Bytes>,
+) -> Result<(), bincode::Error> {
+    let translation: Vec3 = bincode::deserialize_from(cursor)?;
     entity.insert(Transform::from_translation(translation));
+
+    Ok(())
 }
 ```
 
@@ -138,8 +142,9 @@ necessary components after replication. If you want to avoid one frame delay, pu
 your initialization systems to [`ClientSet::Receive`]:
 
 ```rust
-use bevy::{ecs::world::EntityMut, prelude::*, ptr::Ptr, utils::HashMap};
-# use bevy_replicon::prelude::*;
+# use std::io::Cursor;
+# use bevy::{ecs::world::EntityMut, prelude::*, ptr::Ptr, utils::HashMap};
+# use bevy_replicon::{prelude::*, renet::Bytes};
 # use serde::{Deserialize, Serialize};
 # let mut app = App::new();
 # app.add_plugins(ReplicationPlugins);
@@ -166,8 +171,8 @@ fn player_init_system(
 
 #[derive(Component, Deserialize, Serialize)]
 struct Player;
-# fn serialize_transform(_: Ptr) -> Vec<u8> { unimplemented!() }
-# fn deserialize_transform(_: &mut EntityMut, _: &mut NetworkEntityMap, _: &[u8]) {}
+# fn serialize_transform(_: Ptr, _: &mut Cursor<&mut Vec<u8>>) -> Result<(), bincode::Error> { unimplemented!() }
+# fn deserialize_transform(_: &mut EntityMut, _: &mut NetworkEntityMap, _: &mut Cursor<Bytes>) -> Result<(), bincode::Error> { unimplemented!() }
 ```
 
 If your game have save states you probably want to re-use the same logic to