WIP

.gitignore

@@ -1,3 +1,4 @@
+.wineprefix
 .envrc
 /target
 /msvc

Cargo.toml

@@ -6,8 +6,13 @@ edition = "2024"
 # See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
 
 [dependencies]
+bincode = "2.0.1"
+bstr = "1.12.0"
+color-eyre = "0.6.4"
 libc = "0.2.144"
+libp2p = { version = "0.55.0", features = ["tokio", "tcp", "noise", "yamux", "ping", "gossipsub"] }
 log = { version = "0.4.27", features = ["release_max_level_info"] }
+tokio = { version = "1.45.0", features = ["macros", "rt", "sync"] }
 
 [build-dependencies]
 bindgen = "0.71.0"

Justfile

@@ -7,7 +7,7 @@ image_name := "dt-p2p-builder"
 
 steam_library := env("steam_library")
 game_dir := steam_library / "steamapps" / "common" / "Warhammer 40,000 DARKTIDE"
-log_dir := env("appdata") / "Fatshark" / "Darktide" / "console_logs"
+log_dir := env("APPDATA") / "Fatshark" / "Darktide" / "console_logs"
 
 proton_dir := env("HOME") / ".steam" / "steam"
 

src/lib.rs

@@ -1,20 +1,25 @@
-use std::ffi::{CString, c_char};
-use std::sync::OnceLock;
+use std::ffi::{CStr, c_char};
+use std::sync::{OnceLock, RwLock};
 
 mod lua;
 mod plugin;
+mod rpc;
 mod stingray_sdk;
 
+use log::error;
 use plugin::Plugin;
 use stingray_sdk::{GetApiFunction, LoggingApi, LuaApi, PluginApi, PluginApiID};
 
 /// The name that the plugin is registered to the engine as.
 /// Must be unique across all plugins.
-pub const PLUGIN_NAME: &str = "dt_p2p";
+pub const PLUGIN_NAME: &CStr = c"dt_p2p";
 /// The module that Lua functions are assigned to.
-pub const MODULE_NAME: &str = "dt_p2p";
+pub const MODULE_NAME: &CStr = c"dt_p2p";
 
-static PLUGIN: OnceLock<Plugin> = OnceLock::new();
+const CHANNEL_BUFFER_SIZE: usize = 100;
+const EVENTS_PER_TICK: usize = 25;
+
+static PLUGIN: OnceLock<RwLock<Plugin>> = OnceLock::new();
 static LOGGER: OnceLock<LoggingApi> = OnceLock::new();
 static LUA: OnceLock<LuaApi> = OnceLock::new();
 
@@ -30,10 +35,22 @@ macro_rules! global {
     }};
 }
 
+/// A macro to make accessing the plugin instance as mutable a little more convenient.
+#[macro_export]
+macro_rules! plugin_mut {
+    () => {{
+        let lock = $crate::PLUGIN.get().and_then(|l| l.write().ok());
+        if cfg!(debug_assertions) {
+            lock.expect("failed to acquire lock on plugin global")
+        } else {
+            unsafe { lock.unwrap_unchecked() }
+        }
+    }};
+}
+
 #[unsafe(no_mangle)]
 pub extern "C" fn get_name() -> *const c_char {
-    let s = CString::new(PLUGIN_NAME).expect("Failed to create CString from plugin name");
-    s.as_ptr()
+    PLUGIN_NAME.as_ptr()
 }
 
 #[unsafe(no_mangle)]
@@ -44,19 +61,27 @@ pub extern "C" fn setup_game(get_engine_api: GetApiFunction) {
 
     let _ = LUA.get_or_init(|| LuaApi::get(get_engine_api));
 
-    let plugin = PLUGIN.get_or_init(Plugin::new);
+    let plugin = match Plugin::new() {
+        Ok(plugin) => plugin,
+        Err(err) => {
+            error!("Failed to initialize plugin:\n{:?}", err);
+            return;
+        }
+    };
+
     plugin.setup_game();
+    PLUGIN.set(RwLock::new(plugin));
 }
 
 #[unsafe(no_mangle)]
 pub extern "C" fn shutdown_game() {
-    let plugin = global!(PLUGIN);
+    let plugin = plugin_mut!();
     plugin.shutdown_game();
 }
 
 #[unsafe(no_mangle)]
 pub extern "C" fn update_game(dt: f32) {
-    let plugin = global!(PLUGIN);
+    let mut plugin = plugin_mut!();
     plugin.update_game(dt);
 }
 

src/lua.rs

@@ -1,16 +1,334 @@
-use crate::stingray_sdk::lua_State;
-use crate::{LUA, global};
+use std::collections::HashMap;
+use std::panic::catch_unwind;
 
-pub extern "C" fn do_something(l: *mut lua_State) -> i32 {
-    let lua = global!(LUA);
+use bstr::BStr;
+use bstr::ByteSlice as _;
+use color_eyre::Result;
+use color_eyre::eyre;
+use color_eyre::eyre::Context as _;
 
-    if let Some(name) = lua.tolstring(l, 1) {
-        lua.pushstring(
-            l,
-            format!("[do_something] Hello from Rust, {}", name.to_string_lossy()),
-        );
-        1
-    } else {
-        0
+use crate::plugin::Identifier;
+use crate::plugin::Plugin;
+use crate::stingray_sdk::LUA_REGISTRYINDEX;
+use crate::stingray_sdk::{LuaState, LuaType, lua_State};
+use crate::{LUA, global, plugin_mut};
+
+pub const NAMESPACE_SEPARATOR: char = '.';
+
+static RPC_CALLBACK_KEY: &str = "dt-p2p.rpc-callbacks";
+
+// As a minor optimization, only `catch_unwind` in debug mode.
+#[cfg(debug_assertions)]
+fn lua_wrapper<F>(l: *mut lua_State, f: F) -> i32
+where
+    F: FnOnce(&mut Plugin, &LuaState) -> Result<i32> + std::panic::UnwindSafe,
+{
+    let lua = LuaState::new(l, global!(LUA));
+
+    let res = catch_unwind(|| {
+        let mut plugin = plugin_mut!();
+        f(&mut plugin, &lua)
+    });
+    match res {
+        Ok(Ok(i)) => i,
+        Ok(Err(err)) => lua.lib_error(format!("{:?}", err)),
+        Err(err) => lua.lib_error(format!("{:?}", err)),
     }
 }
+
+#[cfg(not(debug_assertions))]
+fn lua_wrapper<F>(l: *mut lua_State, f: F) -> i32
+where
+    F: FnOnce(&mut Plugin, &LuaState) -> Result<i32>,
+{
+    let lua = LuaState::new(l, global!(LUA));
+    let plugin = plugin_mut!();
+
+    let res = f(&mut plugin, &lua);
+    match res {
+        Ok(i) => i,
+        Err(err) => lua.lib_error(format!("{:?}", err)),
+    }
+}
+
+/// Returns the namespace and name for a RPC.
+///
+/// The namespace may either be part of the name, separated by `NAMESPACE_SEPARATOR`
+/// or omitted, in which case the mod name is used as fallback.
+fn get_identifier<'a>(lua: &'a LuaState) -> Result<Identifier<'a>> {
+    lua.getfield(1, c"name");
+    if !lua.isstring(-1) {
+        eyre::bail!("bad argument #1, not a mod object");
+    }
+
+    let mod_name = lua.tostring(-1);
+    let name = lua.tostring(2);
+
+    let (namespace, name) = name
+        .split_once_str(&[NAMESPACE_SEPARATOR as u8])
+        .map(|(namespace, name)| (BStr::new(namespace), BStr::new(name)))
+        .unwrap_or((mod_name, name));
+
+    Ok(Identifier::new(namespace, name))
+}
+
+// Called with `(mod: table, name: string, opts: table)`
+pub extern "C" fn create_rpc(l: *mut lua_State) -> i32 {
+    lua_wrapper(l, |plugin, lua| {
+        lua.getfield(1, c"version");
+        if !lua.istable(1) {
+            eyre::bail!("bad argument #1, expected a mod object");
+        }
+
+        if !lua.isstring(2) {
+            eyre::bail!("bad argument #2, expected a string");
+        }
+
+        if !lua.istable(3) {
+            eyre::bail!("bad argument #3, expected a table");
+        }
+
+        let _version = match lua.r#type(-1) {
+            LuaType::Nil => {
+                eyre::bail!("bad argument #1, mod object doesn't provide a 'version' field");
+            }
+            LuaType::Number => lua.tostring(-1),
+            LuaType::String => {
+                let version = lua.tostring(-1);
+                // TODO: parse as date or semver-like
+                version
+            }
+            x => {
+                eyre::bail!("invalid type {} for 'version' field", x)
+            }
+        };
+
+        let id = get_identifier(lua).wrap_err("failed to determine RPC name")?;
+        plugin.create_rpc(id);
+
+        Ok(0)
+    })
+}
+
+type LuaMap<'a> = HashMap<LuaKey<'a>, LuaValue<'a>>;
+
+#[derive(bincode::BorrowDecode, bincode::Encode, PartialEq)]
+enum LuaKey<'a> {
+    String(&'a [u8]),
+    Number(f64),
+}
+
+impl<'a> Eq for LuaKey<'a> {}
+
+impl<'a> std::hash::Hash for LuaKey<'a> {
+    fn hash<H: std::hash::Hasher>(&self, state: &mut H) {
+        match self {
+            LuaKey::String(s) => s.hash(state),
+            LuaKey::Number(n) => (*n as u128).hash(state),
+        }
+    }
+}
+
+#[derive(bincode::BorrowDecode, bincode::Encode)]
+pub enum LuaValue<'a> {
+    Nil,
+    Boolean(bool),
+    Number(f64),
+    String(&'a [u8]),
+    Table(LuaMap<'a>),
+}
+
+impl<'a> LuaValue<'a> {
+    fn parse_table(lua: &'a LuaState, idx: i32) -> Result<Self> {
+        let mut values = LuaMap::default();
+        //
+        // `nil` as initial key tells `lua_next` to pick the first key.
+        lua.pushnil();
+
+        loop {
+            if lua.next(idx) <= 0 {
+                break;
+            }
+
+            let key = match lua.r#type(-2) {
+                LuaType::Number => LuaKey::Number(lua.tonumber(-2)),
+                LuaType::String => LuaKey::String(lua.tostring(-2)),
+                t => eyre::bail!("Unsupported type {} for args table key", t),
+            };
+
+            let value = Self::parse(lua, -1)?;
+
+            values.insert(key, value);
+
+            // Pop the value, but keep the key so `lua_next` knows where to continue
+            lua.pop();
+        }
+
+        // Pop the last key
+        lua.pop();
+
+        Ok(LuaValue::Table(values))
+    }
+
+    pub fn parse(lua: &'a LuaState, idx: i32) -> Result<Self> {
+        match lua.r#type(idx) {
+            LuaType::None | LuaType::Nil => Ok(LuaValue::Nil),
+            LuaType::Boolean => Ok(LuaValue::Boolean(lua.toboolean(-1))),
+            LuaType::Number => Ok(LuaValue::Number(lua.tonumber(-1))),
+            LuaType::String => Ok(LuaValue::String(lua.tostring(-1))),
+            LuaType::Table => Self::parse_table(lua, -1),
+            x => eyre::bail!("Unknown or unsupported Lua type {}", x),
+        }
+    }
+
+    pub fn push(&self, lua: &LuaState) {
+        match self {
+            LuaValue::Nil => lua.pushnil(),
+            LuaValue::Boolean(bool) => lua.pushboolean(*bool),
+            LuaValue::Number(num) => lua.pushnumber(*num),
+            LuaValue::String(s) => lua.pushstring(*s),
+            LuaValue::Table(table) => Self::push_table(lua, table),
+        }
+    }
+
+    fn push_table(lua: &LuaState, table: &LuaMap) {
+        let (narr, nrec) = table.iter().fold((0, 0), |(narr, nrec), (k, _)| match k {
+            LuaKey::String(_) => (narr, nrec + 1),
+            LuaKey::Number(_) => (narr + 1, nrec),
+        });
+
+        lua.createtable(narr, nrec);
+        let tbl_index = lua.gettop();
+
+        for (k, v) in table.iter() {
+            match k {
+                LuaKey::String(s) => lua.pushstring(*s),
+                LuaKey::Number(num) => lua.pushnumber(*num),
+            }
+
+            v.push(lua);
+
+            lua.settable(tbl_index);
+        }
+    }
+}
+
+// Called with `(mod: table, name: string, args: table)`
+pub extern "C" fn send_rpc(l: *mut lua_State) -> i32 {
+    lua_wrapper(l, |plugin, lua| {
+        if !lua.istable(1) {
+            eyre::bail!("bad argument #1, expected a mod object");
+        }
+
+        if !lua.isstring(2) {
+            eyre::bail!("bad argument #2, expected a string");
+        }
+
+        if !lua.istable(3) {
+            eyre::bail!("bad argument #3, expected a table");
+        }
+
+        let id = get_identifier(lua).wrap_err("failed to determine RPC name")?;
+        let args = LuaValue::parse_table(lua, 3).wrap_err("Failed to parse args table")?;
+
+        plugin.send_rpc(id, args).wrap_err("Failed to send RPC")?;
+
+        Ok(0)
+    })
+}
+
+// Called with `(mod: table, name: string, callback: Fn(args))`
+pub extern "C" fn receive_rpc(l: *mut lua_State) -> i32 {
+    lua_wrapper(l, |plugin, lua| {
+        if !lua.istable(1) {
+            eyre::bail!("bad argument #1, expected a mod object");
+        }
+
+        if !lua.isstring(2) {
+            eyre::bail!("bad argument #2, expected a string");
+        }
+
+        if !lua.isfunction(3) {
+            eyre::bail!("bad argument #3, expected a function");
+        }
+
+        let id = get_identifier(lua).wrap_err("failed to determine RPC name")?;
+
+        // We will utilize Lua's _references_ to store the callback functions. Since we're doing
+        // the bookkeeping on the Rust side, we don't need to worry about any structured layout on
+        // the Lua side.
+
+        lua.pushvalue(3);
+        let fn_ref = lua.lib_ref(LUA_REGISTRYINDEX);
+
+        plugin.add_rpc_listener(id, fn_ref);
+
+        Ok(0)
+    })
+}
+
+// Called with `(mod: table, callback: Fn(peer_id))`
+pub extern "C" fn on_peer_connected(l: *mut lua_State) -> i32 {
+    lua_wrapper(l, |plugin, lua| {
+        if !lua.istable(1) {
+            eyre::bail!("bad argument #1, expected a mod object");
+        }
+
+        if !lua.isfunction(2) {
+            eyre::bail!("bad argument #2, expected a function");
+        }
+
+        lua.getfield(1, c"name");
+        if !lua.isstring(-1) {
+            eyre::bail!("bad argument #1, not a mod object");
+        }
+
+        let mod_name = lua.tostring(-1);
+        lua.pushvalue(3);
+        let fn_ref = lua.lib_ref(LUA_REGISTRYINDEX);
+
+        plugin.add_connect_listener(mod_name, fn_ref);
+
+        Ok(0)
+    })
+}
+
+// Called with `(mod: table, callback: Fn(peer_id))`
+pub extern "C" fn on_peer_disconnected(l: *mut lua_State) -> i32 {
+    lua_wrapper(l, |plugin, lua| {
+        if !lua.istable(1) {
+            eyre::bail!("bad argument #1, expected a mod object");
+        }
+
+        if !lua.isfunction(2) {
+            eyre::bail!("bad argument #2, expected a function");
+        }
+
+        lua.getfield(1, c"name");
+        if !lua.isstring(-1) {
+            eyre::bail!("bad argument #1, expected a mod object");
+        }
+
+        let mod_name = lua.tostring(-1);
+        lua.pushvalue(3);
+        let fn_ref = lua.lib_ref(LUA_REGISTRYINDEX);
+
+        plugin.add_disconnect_listener(mod_name, fn_ref);
+
+        Ok(0)
+    })
+}
+
+// Called with `(dt: float)`
+pub extern "C" fn update(l: *mut lua_State) -> i32 {
+    lua_wrapper(l, |plugin, lua| {
+        if !lua.isnumber(1) {
+            eyre::bail!("bad argument #1, expected a number");
+        }
+
+        let dt = lua.tonumber(1);
+        plugin.lua_update(dt, lua)?;
+
+        Ok(0)
+    })
+}

src/plugin.rs

@@ -1,26 +1,382 @@
-use log::info;
+use std::collections::HashMap;
+use std::hash::{DefaultHasher, Hash as _, Hasher as _};
+use std::thread;
+use std::thread::JoinHandle;
 
-use crate::{LUA, MODULE_NAME, PLUGIN_NAME, global, lua};
+use bstr::{BStr, BString, ByteSlice};
+use color_eyre::eyre::Context as _;
+use color_eyre::{Result, eyre};
+use libp2p::futures::StreamExt;
+use libp2p::gossipsub::{AllowAllSubscriptionFilter, Event, IdentityTransform, TopicHash};
+use libp2p::swarm::SwarmEvent;
+use libp2p::{gossipsub, noise, tcp, yamux};
+use tokio::sync::mpsc::Receiver;
+use tokio::sync::mpsc::error::TryRecvError;
+use tokio::sync::mpsc::{self, UnboundedSender};
 
-pub(crate) struct Plugin {}
+use crate::lua::{LuaValue, NAMESPACE_SEPARATOR};
+use crate::rpc::{RPC, RPCMessage};
+use crate::stingray_sdk::{LUA_REGISTRYINDEX, LuaRef, LuaState};
+use crate::{CHANNEL_BUFFER_SIZE, EVENTS_PER_TICK, lua};
+use crate::{LUA, MODULE_NAME, global};
+
+#[derive(Clone, Copy, Debug)]
+pub struct Identifier<'a> {
+    name: &'a BStr,
+    namespace: &'a BStr,
+}
+
+impl<'a> Identifier<'a> {
+    pub fn new(namespace: &'a BStr, name: &'a BStr) -> Self {
+        Self { namespace, name }
+    }
+
+    pub(crate) fn to_topic(self) -> TopicHash {
+        TopicHash::from_raw(format!("{}", self))
+    }
+}
+
+impl std::fmt::Display for Identifier<'_> {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "{}{}{}", self.namespace, NAMESPACE_SEPARATOR, self.name)
+    }
+}
+
+#[derive(Debug)]
+struct NamespacedMap<T> {
+    map: HashMap<BString, HashMap<BString, T>>,
+}
+
+impl<T> NamespacedMap<T> {
+    pub fn insert(&mut self, id: Identifier, val: T) {
+        if !self.map.contains_key(id.namespace) {
+            self.map.insert(id.namespace.to_owned(), Default::default());
+        }
+
+        let map = self
+            .map
+            .get_mut(id.namespace)
+            .expect("entry is verified to exist");
+        map.insert(id.name.to_owned(), val);
+    }
+
+    pub fn get(&self, id: &Identifier) -> Option<&T> {
+        self.map.get(id.namespace).and_then(|map| map.get(id.name))
+    }
+}
+
+impl<T> Default for NamespacedMap<T> {
+    fn default() -> Self {
+        Self {
+            map: Default::default(),
+        }
+    }
+}
+
+enum Task {}
+
+pub(crate) struct Plugin {
+    swarm_thread: JoinHandle<Result<()>>,
+    event_rx: Receiver<SwarmEvent<Event>>,
+    send_tx: UnboundedSender<RPCMessage>,
+    rpcs: HashMap<TopicHash, RPC>,
+    connect_listeners: HashMap<TopicHash, LuaRef>,
+    disconnect_listeners: HashMap<TopicHash, LuaRef>,
+}
 
 impl Plugin {
-    pub fn new() -> Self {
-        Self {}
+    pub fn new() -> Result<Self> {
+        let mut swarm = libp2p::SwarmBuilder::with_new_identity()
+            .with_tokio()
+            .with_tcp(
+                tcp::Config::default(),
+                noise::Config::new,
+                yamux::Config::default,
+            )
+            .wrap_err("Failed to configure transport")?
+            .with_behaviour(|key| {
+                let message_id_fn = |msg: &gossipsub::Message| {
+                    let mut s = DefaultHasher::new();
+                    msg.data.hash(&mut s);
+                    gossipsub::MessageId::from(s.finish().to_string())
+                };
+
+                let config = gossipsub::ConfigBuilder::default()
+                    .validation_mode(gossipsub::ValidationMode::Strict)
+                    .message_id_fn(message_id_fn)
+                    .build()
+                    .wrap_err("Failed to create gossipsub config")?;
+
+                // TODO: Benchmark if compression would be beneficial.
+                let behavior: gossipsub::Behaviour<IdentityTransform, AllowAllSubscriptionFilter> =
+                    gossipsub::Behaviour::new(
+                        gossipsub::MessageAuthenticity::Signed(key.clone()),
+                        config,
+                    )?;
+
+                Ok(behavior)
+            })
+            .wrap_err("Failed to configure behavior")?
+            .build();
+
+        swarm
+            .listen_on(
+                "/ipv4/0.0.0.0/tcp/0"
+                    .parse()
+                    .expect("listen address invalid"),
+            )
+            .wrap_err("failed to listen on IPv4 socket")?;
+
+        // TODO: Connect to first hard coded relay server(s), which should then
+        // fan out to online peers.
+        // Maybe a cheap server (e.g. AWS free tier instance) is already enough to handle all
+        // session negotiations. If not, then a system is needed where each mod user also becomes
+        // available for that, and the hosted server merely acts as load balancer between them.
+        //
+        // swarm.dial(RELAY_SERVER)
+
+        let (event_tx, event_rx) = mpsc::channel::<SwarmEvent<Event>>(CHANNEL_BUFFER_SIZE);
+        // Since the `Sender` will be on the sync side, and we want to avoid blocking, we make this
+        // unbounded to limit the chance for it to actually block.
+        let (send_tx, rpc_rx) = mpsc::unbounded_channel::<RPCMessage>();
+
+        let swarm_thread = thread::Builder::new()
+            .name("p2p-swarm".into())
+            .spawn(move || {
+                let rt = tokio::runtime::Builder::new_current_thread()
+                    .build()
+                    .wrap_err("Failed to create tokio runtime")?;
+
+                let mut swarm = swarm;
+                let mut rpc_rx = rpc_rx;
+
+                rt.block_on(async move {
+                    loop {
+                        tokio::select! {
+                            event = swarm.select_next_some() => {
+                                event_tx.send(event).await.wrap_err("Failed to queue event")?;
+                            }
+                            msg = rpc_rx.recv() => {
+                                let Some(msg) = msg else {
+                                    eyre::bail!("RPC queue closed prematurely");
+                                };
+                                swarm.behaviour_mut().publish(msg.topic, msg.data).wrap_err("Failed to send RPC")?;
+                            }
+                        }
+                    }
+                })
+            })
+            .wrap_err("Failed to create p2p-swarm thread")?;
+
+        Ok(Self {
+            swarm_thread,
+            event_rx,
+            send_tx,
+            rpcs: Default::default(),
+            connect_listeners: Default::default(),
+            disconnect_listeners: Default::default(),
+        })
     }
 
     pub fn setup_game(&self) {
-        info!("[setup_game] Hello, world! This is {}!", PLUGIN_NAME);
-
         let lua = global!(LUA);
-        lua.add_module_function(MODULE_NAME, "do_something", lua::do_something);
+        lua.add_module_function(MODULE_NAME, c"update", lua::update);
+
+        lua.add_module_function(MODULE_NAME, c"create_rpc", lua::create_rpc);
+        lua.add_module_function(MODULE_NAME, c"send_rpc", lua::send_rpc);
+        lua.add_module_function(MODULE_NAME, c"receive_rpc", lua::receive_rpc);
+
+        // TODO: Handle mod reloads
+        lua.add_module_function(MODULE_NAME, c"on_peer_connected", lua::on_peer_connected);
+        lua.add_module_function(
+            MODULE_NAME,
+            c"on_peer_disconnected",
+            lua::on_peer_disconnected,
+        );
+
+        log::info!("Plugin initialized");
     }
 
     pub fn shutdown_game(&self) {
-        info!("[shutdown_game] Goodbye, world!");
+        // TODO: Find a way to send a close command, and make it blocking.
     }
 
-    pub fn update_game(&self, _dt: f32) {}
+    // WARN: Due to how the instance of `Plugin` is currently stored and
+    // accessed by Lua functions, things will likely break if we attempt to get a `lua_State` here
+    // and trigger out own Lua functions.
+    pub fn update_game(&mut self, _dt: f32) {}
+
+    pub fn lua_update(&mut self, _dt: f64, lua: &LuaState) -> Result<()> {
+        if self.swarm_thread.is_finished() {
+            eyre::bail!("p2p-swarm thread terminated prematurely",);
+            // TODO: Move `self.swarm_thread` into a data structure that I can move it out of here,
+            // so that I can call `.join` and get the error it ended with.
+        }
+
+        // Limit the amount of events we handle per tick to avoid potential large spikes in
+        // frame time.
+        // TODO: Add a system to monitor the amount of incoming vs processed events, and add
+        // warnings when this cannot catch up.
+        // TODO: Check if it might become necessary to create a more elaborate system that can
+        // change this limit dynamically based on the amount of incoming messages.
+        // This must be able to eventually catch up.
+        for _ in 0..EVENTS_PER_TICK {
+            let event = match self.event_rx.try_recv() {
+                Ok(event) => event,
+                Err(TryRecvError::Empty) => break,
+                Err(TryRecvError::Disconnected) => {
+                    eyre::bail!("p2p-swarm channel disconnected prematurely");
+                }
+            };
+
+            match event {
+                SwarmEvent::Behaviour(Event::Message {
+                    propagation_source,
+                    message_id,
+                    message: msg,
+                }) => {
+                    log::debug!("Received message {message_id} from {propagation_source}");
+                    let Some(rpc) = self.rpcs.get(&msg.topic) else {
+                        log::error!("Receive message for unknown topic {}", msg.topic);
+                        continue;
+                    };
+
+                    let Ok((args, _)) = bincode::borrow_decode_from_slice::<LuaValue<'_>, _>(
+                        &msg.data,
+                        bincode::config::standard(),
+                    ) else {
+                        log::error!(
+                            "Failed to decode data for message {message_id} on topic {}",
+                            msg.topic
+                        );
+                        continue;
+                    };
+
+                    args.push(lua);
+                    let args_index = lua.gettop();
+
+                    for fn_ref in rpc.listeners() {
+                        lua.rawgeti(LUA_REGISTRYINDEX, *fn_ref);
+                        lua.pushvalue(args_index);
+                        lua.pcall(1, 0).wrap_err_with(|| {
+                            format!("Failed to call listener for RPC '{}'", msg.topic)
+                        })?;
+                    }
+                }
+                SwarmEvent::Behaviour(Event::GossipsubNotSupported { peer_id }) => {
+                    log::warn!(
+                        "Peer {peer_id} does not support Gossipsub. Are they really a dt-p2p user?"
+                    );
+                }
+                SwarmEvent::ConnectionEstablished {
+                    peer_id,
+                    connection_id,
+                    endpoint: _,
+                    num_established,
+                    concurrent_dial_errors: _,
+                    established_in,
+                } => {
+                    log::info!(
+                        "Connection {} established with {} in {} ms. Total: {}",
+                        connection_id,
+                        peer_id,
+                        established_in.as_millis(),
+                        num_established
+                    );
+                    // TODO: Establish mods shared with this peer
+                    // TODO: Call `on_peer_connected` listeners for the corresponding mods
+                }
+                SwarmEvent::ConnectionClosed {
+                    peer_id,
+                    connection_id,
+                    endpoint: _,
+                    num_established,
+                    cause,
+                } => {
+                    log::info!(
+                        "Connection {} with {} closed for reason {:?}. Total: {}",
+                        connection_id,
+                        peer_id,
+                        cause,
+                        num_established
+                    );
+                    // TODO: Call `on_peer_disconnected` listeners for active mods
+                    // TODO: Re-establish active mods
+                    // With a peer dropping out, the amount of active mods may change if there is
+                    // now only a single peer left for a mod.
+                }
+                SwarmEvent::IncomingConnectionError {
+                    connection_id,
+                    local_addr: _,
+                    send_back_addr: _,
+                    error,
+                } => {
+                    log::error!("Error on incoming connection {connection_id}: {error}");
+                }
+                SwarmEvent::OutgoingConnectionError {
+                    connection_id,
+                    peer_id: _,
+                    error,
+                } => {
+                    log::error!("Error on outgoing connection {connection_id}: {error}");
+                }
+                SwarmEvent::ListenerError { listener_id, error } => {
+                    log::error!("Listener {listener_id} failed: {error}");
+                }
+                SwarmEvent::NewListenAddr {
+                    listener_id,
+                    address,
+                } => {
+                    log::debug!("Listening on {address} with ID {listener_id}");
+                }
+                // TODO: Maybe add tracing information for the events we don't handle
+                _ => {}
+            }
+        }
+
+        Ok(())
+    }
+
+    pub(crate) fn create_rpc(&mut self, id: Identifier) {
+        let rpc = RPC::new();
+        self.rpcs.insert(id.to_topic(), rpc);
+    }
+
+    pub(crate) fn send_rpc(&self, id: Identifier, args: LuaValue<'_>) -> Result<()> {
+        if !self.rpcs.contains_key(&id.to_topic()) {
+            eyre::bail!("RPC '{}' does not exist", id);
+        }
+
+        let args = bincode::encode_to_vec(args, bincode::config::standard())
+            .wrap_err("Failed to encode RPC args")?;
+
+        let msg = RPCMessage::new(id, args);
+        self.send_tx
+            .send(msg)
+            .wrap_err("Failed to queue RPC call")?;
+
+        Ok(())
+    }
+
+    pub(crate) fn add_rpc_listener(&mut self, id: Identifier, fn_ref: i32) -> Result<()> {
+        let Some(rpc) = self.rpcs.get_mut(&id.to_topic()) else {
+            eyre::bail!("RPC '{}' does not exist", id);
+        };
+
+        rpc.add_listener(fn_ref);
+
+        Ok(())
+    }
+
+    pub(crate) fn add_connect_listener(&mut self, mod_name: &BStr, fn_ref: i32) {
+        let key = TopicHash::from_raw(mod_name.to_str_lossy());
+        self.connect_listeners.insert(key, fn_ref);
+    }
+
+    pub(crate) fn add_disconnect_listener(&mut self, mod_name: &BStr, fn_ref: i32) {
+        let key = TopicHash::from_raw(mod_name.to_str_lossy());
+        self.disconnect_listeners.insert(key, fn_ref);
+    }
 }
 
 impl std::fmt::Debug for Plugin {

src/plugin_api.h

@@ -155,6 +155,17 @@ typedef int (*lua_Writer)(lua_State *L, const void *p, size_t sz, void *ud);
 typedef void *(*lua_Alloc)(void *ud, void *ptr, size_t osize, size_t nsize);
 typedef struct luaL_Reg luaL_Reg;
 
+#define LUA_REGISTRYINDEX (-10000)
+#define LUA_ENVIRONINDEX (-10001)
+#define LUA_GLOBALSINDEX (-10002)
+
+#define LUA_OK 0
+#define LUA_YIELD 1
+#define LUA_ERRRUN 2
+#define LUA_ERRSYNTAX 3
+#define LUA_ERRMEM 4
+#define LUA_ERRERR 5
+
 /*
         Interface to access Lua services.
 */

src/rpc.rs

@@ -0,0 +1,43 @@
+use std::collections::HashSet;
+
+use libp2p::gossipsub::TopicHash;
+
+use crate::plugin::Identifier;
+use crate::stingray_sdk::LuaRef;
+
+#[derive(Debug)]
+pub(crate) struct RPC {
+    listeners: HashSet<LuaRef>,
+}
+
+impl RPC {
+    pub fn new() -> Self {
+        Self {
+            listeners: Default::default(),
+        }
+    }
+
+    pub(crate) fn add_listener(&mut self, fn_ref: LuaRef) {
+        self.listeners.insert(fn_ref);
+    }
+
+    pub(crate) fn listeners(&self) -> impl Iterator<Item = &LuaRef> {
+        self.listeners.iter()
+    }
+}
+
+#[derive(Debug)]
+pub(crate) struct RPCMessage {
+    pub topic: TopicHash,
+    pub data: Vec<u8>,
+}
+
+impl RPCMessage {
+    pub(crate) fn new(id: Identifier, data: impl Into<Vec<u8>>) -> Self {
+        let topic = id.to_topic();
+        Self {
+            topic,
+            data: data.into(),
+        }
+    }
+}

src/stingray_sdk.rs

@@ -11,13 +11,22 @@ mod bindings {
 use std::ffi::CStr;
 use std::ffi::CString;
 use std::os::raw::c_char;
+use std::os::raw::c_int;
 use std::os::raw::c_void;
 
 pub use bindings::GetApiFunction;
+use bindings::LUA_OK;
 pub use bindings::PluginApi;
 pub use bindings::PluginApiID;
 use bindings::lua_CFunction;
+use bindings::lua_Integer;
+use bindings::lua_Number;
 pub use bindings::lua_State;
+pub use bindings::{LUA_ENVIRONINDEX, LUA_GLOBALSINDEX, LUA_REGISTRYINDEX};
+
+use bstr::BStr;
+use color_eyre::Result;
+use color_eyre::eyre;
 use log::Level;
 
 impl std::default::Default for PluginApi {
@@ -131,6 +140,17 @@ impl log::Log for LoggingApi {
     fn flush(&self) {}
 }
 
+#[repr(i32)]
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+pub enum LuaStatus {
+    Ok = bindings::LUA_OK as i32,
+    Yield = bindings::LUA_YIELD as i32,
+    ErrRun = bindings::LUA_ERRRUN as i32,
+    ErrSyntax = bindings::LUA_ERRSYNTAX as i32,
+    ErrMem = bindings::LUA_ERRMEM as i32,
+    ErrErr = bindings::LUA_ERRERR as i32,
+}
+
 #[repr(i32)]
 #[derive(Clone, Copy, Debug, PartialEq, Eq)]
 pub enum LuaType {
@@ -183,10 +203,38 @@ impl std::fmt::Display for LuaType {
     }
 }
 
+pub type LuaRef = i32;
+
 pub struct LuaApi {
     add_module_function: unsafe extern "C" fn(*const c_char, *const c_char, lua_CFunction),
-    tolstring: unsafe extern "C" fn(*mut lua_State, i32, *mut usize) -> *const c_char,
+    createtable: unsafe extern "C" fn(*mut lua_State, i32, i32),
+    getfield: unsafe extern "C" fn(*mut lua_State, i32, *const c_char),
+    gettable: unsafe extern "C" fn(*mut lua_State, i32),
+    gettop: unsafe extern "C" fn(*mut lua_State) -> i32,
+    isnumber: unsafe extern "C" fn(*mut lua_State, i32) -> c_int,
+    isnil: unsafe extern "C" fn(*mut lua_State, i32) -> c_int,
+    isstring: unsafe extern "C" fn(*mut lua_State, i32) -> c_int,
+    istable: unsafe extern "C" fn(*mut lua_State, i32) -> c_int,
+    lib_argerror: unsafe extern "C" fn(*mut lua_State, i32, *const c_char) -> i32,
+    lib_checklstring: unsafe extern "C" fn(*mut lua_State, i32, *mut usize) -> *const c_char,
+    lib_error: unsafe extern "C" fn(*mut lua_State, *const c_char, ...) -> i32,
+    lib_ref: unsafe extern "C" fn(*mut lua_State, i32) -> i32,
+    next: unsafe extern "C" fn(*mut lua_State, i32) -> i32,
+    objlen: unsafe extern "C" fn(*mut lua_State, i32) -> usize,
+    pcall: unsafe extern "C" fn(*mut lua_State, i32, i32, i32) -> i32,
+    pop: unsafe extern "C" fn(*mut lua_State),
+    pushboolean: unsafe extern "C" fn(*mut lua_State, i32),
+    pushinteger: unsafe extern "C" fn(*mut lua_State, lua_Integer),
+    pushnil: unsafe extern "C" fn(*mut lua_State),
+    pushnumber: unsafe extern "C" fn(*mut lua_State, lua_Number),
     pushstring: unsafe extern "C" fn(*mut lua_State, *const c_char),
+    pushvalue: unsafe extern "C" fn(*mut lua_State, i32),
+    rawgeti: unsafe extern "C" fn(*mut lua_State, i32, i32),
+    r#type: unsafe extern "C" fn(*mut lua_State, i32) -> i32,
+    settable: unsafe extern "C" fn(*mut lua_State, i32),
+    toboolean: unsafe extern "C" fn(*mut lua_State, i32) -> i32,
+    tolstring: unsafe extern "C" fn(*mut lua_State, i32, *mut usize) -> *const c_char,
+    tonumber: unsafe extern "C" fn(*mut lua_State, i32) -> f64,
 }
 
 impl LuaApi {
@@ -199,40 +247,211 @@ impl LuaApi {
         unsafe {
             Self {
                 add_module_function: (*api).add_module_function.unwrap_unchecked(),
-                tolstring: (*api).tolstring.unwrap_unchecked(),
+                createtable: (*api).createtable.unwrap_unchecked(),
+                getfield: (*api).getfield.unwrap_unchecked(),
+                gettable: (*api).gettable.unwrap_unchecked(),
+                gettop: (*api).gettop.unwrap_unchecked(),
+                isnumber: (*api).isnumber.unwrap_unchecked(),
+                isnil: (*api).isnil.unwrap_unchecked(),
+                isstring: (*api).isstring.unwrap_unchecked(),
+                istable: (*api).istable.unwrap_unchecked(),
+                lib_argerror: (*api).lib_argerror.unwrap_unchecked(),
+                lib_checklstring: (*api).lib_checklstring.unwrap_unchecked(),
+                lib_error: (*api).lib_error.unwrap_unchecked(),
+                lib_ref: (*api).lib_ref.unwrap_unchecked(),
+                next: (*api).next.unwrap_unchecked(),
+                objlen: (*api).objlen.unwrap_unchecked(),
+                pcall: (*api).pcall.unwrap_unchecked(),
+                pop: (*api).pop.unwrap_unchecked(),
+                pushboolean: (*api).pushboolean.unwrap_unchecked(),
+                pushinteger: (*api).pushinteger.unwrap_unchecked(),
+                pushnil: (*api).pushnil.unwrap_unchecked(),
+                pushnumber: (*api).pushnumber.unwrap_unchecked(),
                 pushstring: (*api).pushstring.unwrap_unchecked(),
+                pushvalue: (*api).pushvalue.unwrap_unchecked(),
+                rawgeti: (*api).rawgeti.unwrap_unchecked(),
+                r#type: (*api).type_.unwrap_unchecked(),
+                settable: (*api).settable.unwrap_unchecked(),
+                toboolean: (*api).toboolean.unwrap_unchecked(),
+                tolstring: (*api).tolstring.unwrap_unchecked(),
+                tonumber: (*api).tonumber.unwrap_unchecked(),
             }
         }
     }
 
     pub fn add_module_function(
         &self,
-        module: impl Into<Vec<u8>>,
-        name: impl Into<Vec<u8>>,
+        module: impl AsRef<CStr>,
+        name: impl AsRef<CStr>,
         cb: extern "C" fn(*mut lua_State) -> i32,
     ) {
-        let module = CString::new(module).expect("Invalid CString");
-        let name = CString::new(name).expect("Invalid CString");
-
-        unsafe { (self.add_module_function)(module.as_ptr(), name.as_ptr(), Some(cb)) }
+        unsafe {
+            (self.add_module_function)(module.as_ref().as_ptr(), name.as_ref().as_ptr(), Some(cb))
         }
-
-    pub fn tolstring(&self, L: *mut lua_State, idx: i32) -> Option<&CStr> {
-        let mut len: usize = 0;
-
-        let c = unsafe { (self.tolstring)(L, idx, &mut len as *mut _) };
-
-        if len == 0 {
-            None
-        } else {
-            // Safety: As long as `len > 0`, Lua guarantees the constraints that `CStr::from_ptr`
-            // requires.
-            Some(unsafe { CStr::from_ptr(c) })
-        }
-    }
-
-    pub fn pushstring(&self, L: *mut lua_State, s: impl Into<Vec<u8>>) {
-        let s = CString::new(s).expect("Invalid CString");
-        unsafe { (self.pushstring)(L, s.as_ptr()) }
+    }
+}
+
+/// A wrapper that combines a lua_State and a LuaApi to make calling functions more convenient.
+pub struct LuaState<'a> {
+    l: *mut lua_State,
+    api: &'a LuaApi,
+}
+
+impl<'a> LuaState<'a> {
+    pub fn new(l: *mut lua_State, api: &'a LuaApi) -> Self {
+        Self { l, api }
+    }
+
+    pub fn gettop(&self) -> i32 {
+        unsafe { (self.api.gettop)(self.l) }
+    }
+
+    pub fn pushvalue(&self, idx: i32) {
+        unsafe { (self.api.pushvalue)(self.l, idx) }
+    }
+
+    pub fn isnil(&self, idx: i32) -> bool {
+        let is_nil = unsafe { (self.api.isnil)(self.l, idx) };
+        is_nil > 0
+    }
+
+    pub fn isnumber(&self, idx: i32) -> bool {
+        let is_number = unsafe { (self.api.isnumber)(self.l, idx) };
+        is_number > 0
+    }
+
+    pub fn isstring(&self, idx: i32) -> bool {
+        let is_string = unsafe { (self.api.isstring)(self.l, idx) };
+        is_string > 0
+    }
+
+    pub fn isfunction(&self, idx: i32) -> bool {
+        let is_fn = unsafe { (self.api.isfunction)(self.l, idx) };
+        is_fn > 0
+    }
+
+    pub fn istable(&self, idx: i32) -> bool {
+        let is_table = unsafe { (self.api.istable)(self.l, idx) };
+        is_table > 0
+    }
+
+    pub fn r#type(&self, idx: i32) -> LuaType {
+        let t = unsafe { (self.api.r#type)(self.l, idx) };
+        t.into()
+    }
+
+    pub fn tonumber(&self, idx: i32) -> f64 {
+        unsafe { (self.api.tonumber)(self.l, idx) }
+    }
+
+    pub fn toboolean(&self, idx: i32) -> bool {
+        let n = unsafe { (self.api.toboolean)(self.l, idx) };
+        n != 0
+    }
+
+    pub fn tostring(&self, idx: i32) -> &BStr {
+        let bytes = unsafe {
+            let mut len = 0usize;
+            // `c_char` is `i8` by default, but printable characters are all > 0, so we don't care.
+            let c = (self.api.tolstring)(self.l, idx, &mut len) as *const u8;
+            std::slice::from_raw_parts(c, len)
+        };
+        BStr::new(bytes)
+    }
+
+    pub fn objlen(&self, idx: i32) -> usize {
+        unsafe { (self.api.objlen)(self.l, idx) }
+    }
+
+    pub fn pushnil(&self) {
+        unsafe { (self.api.pushnil)(self.l) };
+    }
+
+    pub fn pushnumber(&self, n: f64) {
+        unsafe { (self.api.pushnumber)(self.l, n) };
+    }
+
+    pub fn pushinteger(&self, n: isize) {
+        unsafe { (self.api.pushinteger)(self.l, n) };
+    }
+
+    pub fn pushstring(&self, s: impl Into<Vec<u8>>) {
+        let s = CString::new(s).expect("Invalid CString");
+        unsafe { (self.api.pushstring)(self.l, s.as_ptr()) };
+    }
+
+    pub fn pushboolean(&self, b: bool) {
+        unsafe { (self.api.pushboolean)(self.l, b as i32) }
+    }
+
+    pub fn gettable(&self, idx: i32) {
+        unsafe { (self.api.gettable)(self.l, idx) }
+    }
+
+    pub fn getfield(&self, idx: i32, k: impl AsRef<CStr>) {
+        unsafe { (self.api.getfield)(self.l, idx, k.as_ref().as_ptr()) }
+    }
+
+    pub fn createtable(&self, narr: i32, nrec: i32) {
+        unsafe { (self.api.createtable)(self.l, narr, nrec) }
+    }
+
+    pub fn settable(&self, idx: i32) {
+        unsafe { (self.api.settable)(self.l, idx) }
+    }
+
+    pub fn rawgeti(&self, idx: i32, n: i32) {
+        unsafe { (self.api.rawgeti)(self.l, idx, n) }
+    }
+
+    pub fn call(&self, nargs: i32, nresults: i32) {
+        self.pcall(nargs, nresults).unwrap()
+    }
+
+    pub fn pcall(&self, nargs: i32, nresults: i32) -> Result<()> {
+        // TODO: Re-create the engine's error handler function to populate the stack trace and
+        // local variables.
+        let res = unsafe { (self.api.pcall)(self.l, nargs, nresults, 0) };
+        if res as u32 == LUA_OK {
+            return Ok(());
+        }
+
+        let err = self.tostring(-1);
+        eyre::bail!("pcall failed: {}", err)
+    }
+
+    pub fn next(&self, idx: i32) -> i32 {
+        unsafe { (self.api.next)(self.l, idx) }
+    }
+
+    pub fn lib_argerror(&self, narg: i32, msg: impl AsRef<CStr>) -> i32 {
+        unsafe { (self.api.lib_argerror)(self.l, narg, msg.as_ref().as_ptr()) }
+    }
+
+    pub fn lib_checklstring(&self, idx: i32) -> &BStr {
+        let bytes = unsafe {
+            let mut len = 0usize;
+            // `c_char` is `i8` by default, but printable characters are all > 0, so we don't care.
+            let c = (self.api.lib_checklstring)(self.l, idx, &mut len) as *const u8;
+            std::slice::from_raw_parts(c, len)
+        };
+        BStr::new(bytes)
+    }
+
+    // Lua's `luaL_error` does have printf-like formatting capabilities,
+    // but since we can just use `format!()`, we don't need to bother handling the varargs here.
+    pub fn lib_error(&self, msg: impl Into<Vec<u8>>) -> i32 {
+        let s = CString::new(msg).expect("Invalid CString");
+        unsafe { (self.api.lib_error)(self.l, s.as_ptr()) }
+    }
+
+    pub fn lib_ref(&self, t: i32) -> LuaRef {
+        unsafe { (self.api.lib_ref)(self.l, t) }
+    }
+
+    // NOTE: This is not like the standard `lua_pop`, it only pops one value at a time.
+    // If more values need to be popped, use `settop(-x)`.
+    pub fn pop(&self) {
+        unsafe { (self.api.pop)(self.l) };
     }
 }