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::ffi::{CStr, c_char};
-use std::sync::OnceLock;
+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");
+    PLUGIN_NAME.as_ptr()
-    s.as_ptr()
 }
 
 #[unsafe(no_mangle)]
@@ -44,19 +61,29 @@ 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))
+        .expect("Failed to set global plugin instance");
 }
 
 #[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 +1,393 @@
-use crate::stingray_sdk::lua_State;
+use std::collections::HashMap;
-use crate::{LUA, global};
+use std::ffi::CStr;
+use std::panic::catch_unwind;
 
-pub extern "C" fn do_something(l: *mut lua_State) -> i32 {
+use bstr::BStr;
+use bstr::ByteSlice as _;
+use color_eyre::Result;
+use color_eyre::eyre;
+use color_eyre::eyre::Context as _;
+
+use crate::plugin::Identifier;
+use crate::plugin::ModCallbacks;
+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 = '.';
+
+// 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 = global!(LUA);
 
-    if let Some(name) = lua.tolstring(l, 1) {
+    // We need to drop as many things as possible before the `lua_error` call
-        lua.pushstring(
+    // will longjmp and thereby ignoring Rust's cleanup.
-            l,
+    {
-            format!("[do_something] Hello from Rust, {}", name.to_string_lossy()),
+        let lua = LuaState::new(l, lua);
-        );
+
-        1
+        let res = catch_unwind(|| {
-    } else {
+            let mut plugin = plugin_mut!();
+            f(&mut plugin, &lua)
+        });
+        match res {
+            Ok(Ok(i)) => {
+                return i;
+            }
+            Ok(Err(err)) => lua.pushstring(format!("{:?}", err)),
+            Err(err) => lua.pushstring(format!("{:?}", err)),
+        }
+    }
+
+    lua.error(l);
     0
+}
+
+#[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 = global!(LUA);
+
+    // We need to drop as many things as possible before the `lua_error` call
+    // will longjmp and thereby ignoring Rust's cleanup.
+    {
+        let lua = LuaState::new(l, lua);
+
+        let mut plugin = plugin_mut!();
+        match f(&mut plugin, &lua) {
+            Ok(Ok(i)) => {
+                return i;
+            }
+            Ok(Err(err)) => lua.pushstring(format!("{:?}", err)),
+            Err(err) => lua.pushstring(format!("{:?}", err)),
+        }
+    }
+
+    lua.error(l);
+    0
+}
+
+/// 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, callbacks: table)`
+pub extern "C" fn register_mod(l: *mut lua_State) -> i32 {
+    lua_wrapper(l, |plugin, lua| {
+        if !lua.istable(1) {
+            eyre::bail!("bad argument #1, expected a mod object");
+        }
+
+        let name = {
+            lua.getfield(1, c"name");
+            if !lua.isstring(-1) {
+                eyre::bail!("bad argument #1, not a mod object");
+            }
+
+            lua.tostring(-1)
+        };
+
+        let callbacks = match lua.r#type(2) {
+            LuaType::Nil => ModCallbacks::default(),
+            LuaType::Table => {
+                let get_callback = |name: &CStr| {
+                    lua.getfield(2, name);
+
+                    match lua.r#type(-1) {
+                        LuaType::Nil => Ok(None),
+                        LuaType::Function => Ok(Some(lua.lib_ref(LUA_REGISTRYINDEX))),
+                        x => {
+                            eyre::bail!(
+                                "bad argument #2, expected a function for field {}, got {}",
+                                name.to_string_lossy(),
+                                x
+                            );
+                        }
+                    }
+                };
+
+                ModCallbacks {
+                    on_session_joined: get_callback(c"on_session_joined")?,
+                    on_session_left: get_callback(c"on_session_left")?,
+                    on_user_joined: get_callback(c"on_user_joined")?,
+                    on_user_left: get_callback(c"on_user_left")?,
+                }
+            }
+            x => {
+                eyre::bail!("bad argument #2, expected a table got {}", x);
+            }
+        };
+
+        plugin.register_mod(name, callbacks);
+
+        // TODO: Register unload and disable handlers?
+        // Will likely have to monkey-patch the mod object.
+        // DMF doesn't expose a good way to hook into it, and it wouldn't be feasible to expect a
+        // DMF update to allow it.
+
+        Ok(0)
+    })
+}
+
+// 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, must be number or a version string",
+                    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)]
+pub enum LuaKey<'a> {
+    String(&'a [u8]),
+    Number(f64),
+}
+
+impl Eq for LuaKey<'_> {}
+
+impl std::hash::Hash for LuaKey<'_> {
+    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::get_from_stack(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))
+    }
+
+    /// Gets the value from the stack at `idx`
+    pub fn get_from_stack(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),
+        }
+    }
+
+    /// Pushes the value onto a Lua stack
+    pub fn push_to_stack(&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_to_stack(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)
+            .wrap_err("Failed to add RPC listener")?;
+
+        Ok(0)
+    })
+}
+
+// Called with `(server_name: string, peer_id: string, player_id: string)`
+pub extern "C" fn join_session(l: *mut lua_State) -> i32 {
+    lua_wrapper(l, |plugin, lua| {
+        if !lua.isstring(1) {
+            eyre::bail!("bad argument #1, expected a string");
+        }
+
+        if !lua.isstring(2) {
+            eyre::bail!("bad argument #2, expected a string");
+        }
+
+        if !lua.isstring(3) {
+            eyre::bail!("bad argument #3, expected a string");
+        }
+
+        let server_name = lua.tostring(1);
+        let peer_id = lua.tostring(2);
+        let player_id = lua.tostring(3);
+
+        plugin
+            .join_session(lua, server_name, peer_id, player_id)
+            .wrap_err("Failed to join session")?;
+
+        Ok(0)
+    })
+}
+
+// Called with `()`
+pub extern "C" fn leave_session(l: *mut lua_State) -> i32 {
+    lua_wrapper(l, |plugin, lua| {
+        plugin
+            .leave_session(lua)
+            .wrap_err("Failed to leave session")?;
+
+        Ok(0)
+    })
+}

src/plugin.rs

@@ -1,26 +1,671 @@
-use log::info;
+use std::collections::HashMap;
+use std::hash::{DefaultHasher, Hash, Hasher as _};
+use std::mem;
+use std::ops::Deref;
+use std::thread;
+use std::thread::JoinHandle;
 
-use crate::{LUA, MODULE_NAME, PLUGIN_NAME, global, lua};
+use bstr::{BStr, BString};
+use color_eyre::Result;
+use color_eyre::eyre;
+use color_eyre::eyre::Context as _;
+use libp2p::PeerId;
+use libp2p::futures::StreamExt;
+use libp2p::gossipsub;
+use libp2p::gossipsub::{
+    AllowAllSubscriptionFilter, Event, IdentTopic, IdentityTransform, Message, TopicHash,
+};
+use libp2p::noise;
+use libp2p::swarm::SwarmEvent;
+use libp2p::tcp;
+use libp2p::yamux;
+use tokio::sync::mpsc;
+use tokio::sync::mpsc::Receiver;
+use tokio::sync::mpsc::UnboundedSender;
+use tokio::sync::mpsc::error::TryRecvError;
 
-pub(crate) struct Plugin {}
+use crate::lua;
+use crate::lua::{LuaValue, NAMESPACE_SEPARATOR};
+use crate::rpc::RPC;
+use crate::stingray_sdk::{LUA_REGISTRYINDEX, LuaRef, LuaState};
+use crate::{CHANNEL_BUFFER_SIZE, EVENTS_PER_TICK};
+use crate::{LUA, MODULE_NAME, global};
+
+type ModName = BString;
+
+#[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 }
+    }
+}
+
+impl From<Identifier<'_>> for String {
+    fn from(value: Identifier<'_>) -> Self {
+        format!("{}", value)
+    }
+}
+
+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, bincode::Encode, bincode::Decode)]
+// To avoid having to implement `bincode` for `bstr` types, we use raw `Vec<u8>` here,
+// which can be turned into `BString` cheaply.
+pub(crate) enum SwarmMessage {
+    // To avoid extra cloning, or having to deal with lifetimes,
+    // this message type contains the Lua args already encoded.
+    Rpc(Vec<u8>),
+    SessionJoin {
+        /// The in-game player ID for this peer
+        player_id: Vec<u8>,
+        /// A list of mod names this peer has enabled
+        mods: Vec<Vec<u8>>,
+    },
+    SessionLeave,
+}
+
+#[derive(Debug)]
+pub(crate) enum SwarmTask {
+    Message { topic: Topic, msg: SwarmMessage },
+    Subscribe(Topic),
+    Unsubscribe(Vec<Topic>),
+}
+
+#[derive(Clone, Debug)]
+pub(crate) struct Topic(IdentTopic);
+
+impl Eq for Topic {}
+impl PartialEq for Topic {
+    fn eq(&self, other: &Self) -> bool {
+        self.0.hash() == other.0.hash()
+    }
+}
+
+impl Hash for Topic {
+    fn hash<H: std::hash::Hasher>(&self, state: &mut H) {
+        self.0.hash().hash(state);
+    }
+}
+
+impl std::fmt::Display for Topic {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "{}", self.0)
+    }
+}
+
+impl std::ops::Deref for Topic {
+    type Target = IdentTopic;
+
+    fn deref(&self) -> &Self::Target {
+        &self.0
+    }
+}
+
+impl From<Topic> for TopicHash {
+    fn from(value: Topic) -> Self {
+        Self::from(value.0)
+    }
+}
+
+#[derive(Debug)]
+struct Player {
+    id: BString,
+    mods: Vec<ModName>,
+}
+
+#[derive(Default)]
+pub(crate) struct ModCallbacks {
+    pub on_session_joined: Option<LuaRef>,
+    pub on_session_left: Option<LuaRef>,
+    pub on_user_joined: Option<LuaRef>,
+    pub on_user_left: Option<LuaRef>,
+}
+
+struct Session {
+    online: bool,
+    address: String,
+    peer_id: BString,
+    topics: HashMap<TopicHash, Topic>,
+    peers: HashMap<PeerId, Player>,
+}
+
+impl Session {
+    pub fn new_topic(&mut self, topic: impl Into<String>) -> &Topic {
+        self.topics
+            .entry(TopicHash::from_raw(topic.into()))
+            .or_insert_with_key(|topic| {
+                Topic(IdentTopic::new(format!("{}/{}", self.address, topic)))
+            })
+    }
+
+    pub fn get_topic(&self, topic: impl Into<String>) -> Option<&Topic> {
+        let hash = TopicHash::from_raw(topic.into());
+        self.topics.get(&hash)
+    }
+}
+
+pub(crate) struct Plugin {
+    swarm_thread: JoinHandle<Result<()>>,
+    event_rx: Receiver<SwarmEvent<Event>>,
+    send_tx: UnboundedSender<SwarmTask>,
+    session: Session,
+    rpcs: HashMap<Topic, RPC>,
+    mods: HashMap<ModName, ModCallbacks>,
+}
 
 impl Plugin {
-    pub fn new() -> Self {
+    pub fn new() -> Result<Self> {
-        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, send_rx) = mpsc::unbounded_channel::<SwarmTask>();
+
+        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 send_rx = send_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")?;
+                            }
+                            task = send_rx.recv() => {
+                                let Some(task) = task else {
+                                    eyre::bail!("Task queue closed prematurely");
+                                };
+
+                                let behavior = swarm.behaviour_mut();
+
+                                match task{
+                                    SwarmTask::Message { topic, msg } => {
+                                        let data = bincode::encode_to_vec(msg, bincode::config::standard())
+                                            .wrap_err("Failed to encode swarm message")?;
+                                        behavior
+                                            .publish(topic, data)
+                                            .wrap_err("Failed to send message")?;
+                                    },
+                                    SwarmTask::Subscribe(topic) => {
+                                        behavior
+                                            .subscribe(&topic)
+                                            .wrap_err_with(|| format!("Failed to subscribe to topic {}", topic))?;
+                                    },
+                                    SwarmTask::Unsubscribe(topics) => {
+                                        for topic in topics {
+                                            behavior.unsubscribe(&topic);
+                                        }
+                                    }
+                                }
+                            }
+                        }
+                    }
+                })
+            })
+            .wrap_err("Failed to create p2p-swarm thread")?;
+
+        log::info!("Plugin initialized");
+
+        Ok(Self {
+            swarm_thread,
+            event_rx,
+            send_tx,
+            session: Session {
+                online: false,
+                address: Default::default(),
+                peer_id: Default::default(),
+                topics: Default::default(),
+                peers: Default::default(),
+            },
+            rpcs: Default::default(),
+            mods: 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);
+        // Internal API
+        // TODO: Maybe useful to move these to a separate module, e.g. `P2PInternal`?
+        lua.add_module_function(MODULE_NAME, c"join_session", lua::join_session);
+        lua.add_module_function(MODULE_NAME, c"leave_session", lua::leave_session);
+
+        // User-facing API
+        lua.add_module_function(MODULE_NAME, c"register_mod", lua::register_mod);
+        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);
+
+        log::debug!("Lua functions registered");
     }
 
     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) {}
+    pub fn update_game(&mut self, dt: f32) {
+        if let Err(err) = self.update(dt) {
+            log::error!("{:?}", err);
+            // TODO: Exit application or find a better way to report the error
+        }
+    }
+
+    pub fn update(&mut self, _dt: f32) -> 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.
+        }
+
+        let lua = {
+            let lua = global!(LUA);
+            let l = lua.getscriptenvironmentstate();
+            LuaState::new(l, lua)
+        };
+
+        // 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:
+                        Message {
+                            topic,
+                            data,
+                            source,
+                            sequence_number: _,
+                        },
+                }) => {
+                    log::debug!(
+                        "Received message {message_id} from {propagation_source} for topic {}",
+                        topic
+                    );
+
+                    let Some(topic) = self.session.topics.get(&topic) else {
+                        log::warn!("Received message for unknown topic {}", topic);
+                        continue;
+                    };
+
+                    let Ok((msg, _)) = bincode::borrow_decode_from_slice::<SwarmMessage, _>(
+                        &data,
+                        bincode::config::standard(),
+                    ) else {
+                        log::error!(
+                            "Failed to decode data for message {message_id} on topic {}",
+                            topic
+                        );
+                        continue;
+                    };
+
+                    match msg {
+                        SwarmMessage::Rpc(rpc_args) => {
+                            let Some(rpc) = self.rpcs.get(topic) else {
+                                log::warn!("Topic {} does not have an RPC", topic);
+                                continue;
+                            };
+
+                            let Ok((args, _)) = bincode::borrow_decode_from_slice::<LuaValue<'_>, _>(
+                                &rpc_args,
+                                bincode::config::standard(),
+                            ) else {
+                                log::error!(
+                                    "Failed to decode data for message {message_id} on topic {}",
+                                    topic
+                                );
+                                continue;
+                            };
+
+                            args.push_to_stack(&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 '{}'", topic)
+                                })?;
+                            }
+                        }
+                        SwarmMessage::SessionJoin { player_id, mods } => match source {
+                            Some(peer_id) => {
+                                let id = BString::new(player_id);
+                                let mods = mods.into_iter().map(ModName::new).collect::<Vec<_>>();
+                                let peer = Player { id, mods };
+
+                                // TODO: Check if a corresponding player is in the lobby
+
+                                {
+                                    let callbacks = self
+                                        .mods
+                                        .iter()
+                                        .filter(|(name, _)| peer.mods.contains(name))
+                                        .filter_map(|(_, cbs)| cbs.on_user_joined);
+
+                                    lua.pushstring(peer.id.clone());
+                                    let arg_index = lua.gettop();
+
+                                    for fn_ref in callbacks {
+                                        lua.pushnumber(fn_ref as f64);
+                                        lua.gettable(LUA_REGISTRYINDEX);
+                                        lua.pushvalue(arg_index);
+                                        lua.pcall(1, 0)
+                                            .wrap_err("on_user_joined handler failed")?;
+                                    }
+                                }
+
+                                self.session.peers.insert(peer_id, peer);
+                            }
+                            None => {
+                                log::warn!(
+                                    "Got SessionJoin event without a source peer_id. Don't know how to handle."
+                                );
+                            }
+                        },
+                        SwarmMessage::SessionLeave => match source {
+                            Some(peer_id) => {
+                                if let Some(peer) = self.session.peers.remove(&peer_id) {
+                                    let callbacks = self
+                                        .mods
+                                        .iter()
+                                        .filter(|(name, _)| peer.mods.contains(name))
+                                        .filter_map(|(_, cbs)| cbs.on_user_left);
+
+                                    lua.pushstring(peer.id);
+                                    let arg_index = lua.gettop();
+
+                                    for fn_ref in callbacks {
+                                        lua.pushnumber(fn_ref as f64);
+                                        lua.gettable(LUA_REGISTRYINDEX);
+                                        lua.pushvalue(arg_index);
+                                        lua.pcall(1, 0).wrap_err("on_user_left handler failed")?;
+                                    }
+                                }
+                            }
+                            None => {
+                                log::warn!(
+                                    "Got SessionLeave event without a source peer_id. Don't know how to handle."
+                                );
+                            }
+                        },
+                    }
+                }
+                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: Start a timeout to wait for a `SwarmMessage::SessionJoin` to show a
+                    // warning when a client connected but didn't join the session.
+                    // Not sure if that should ever happen.
+                }
+                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
+                    );
+                    if self.session.peers.contains_key(&peer_id) {
+                        log::warn!("Peer dropped connection without properly leaving session!");
+                        // TODO: Start a timeout and if the peer doesn't come back, remove the peer
+                        // and trigger "user left" callbacks.
+                        // TODO: Maybe also check if a corresponding player is still in the game
+                        // lobby.
+                    }
+                }
+                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 register_mod(&mut self, name: &BStr, callbacks: ModCallbacks) {
+        self.mods.insert(name.to_owned(), callbacks);
+    }
+
+    pub(crate) fn create_rpc(&mut self, id: Identifier) {
+        let rpc = RPC::new();
+        let topic = self.session.new_topic(id);
+        self.rpcs.insert(topic.clone(), rpc);
+    }
+
+    pub(crate) fn send_rpc(&self, id: Identifier, args: LuaValue<'_>) -> Result<()> {
+        let Some(topic) = self.session.get_topic(id) else {
+            eyre::bail!("Topic for this RPC does not exist");
+        };
+
+        if !self.rpcs.contains_key(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")?;
+
+        // TODO: Add metrics/profiling for size of the encoded args
+
+        let msg = SwarmTask::Message {
+            topic: topic.clone(),
+            msg: SwarmMessage::Rpc(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: LuaRef) -> Result<()> {
+        let topic = self.session.new_topic(id);
+        let Some(rpc) = self.rpcs.get_mut(topic) else {
+            eyre::bail!("RPC '{}' does not exist", id);
+        };
+
+        rpc.add_listener(fn_ref);
+        self.send_tx
+            .send(SwarmTask::Subscribe(topic.clone()))
+            .wrap_err("Failed to subscribe to RPC topic")?;
+
+        Ok(())
+    }
+
+    pub(crate) fn join_session(
+        &mut self,
+        lua: &LuaState,
+        server_name: &BStr,
+        peer_id: &BStr,
+        player_id: &BStr,
+    ) -> Result<()> {
+        self.session.peer_id = peer_id.to_owned();
+        self.session.address = format!("/{:08X}", hash(server_name));
+
+        let session_topic = self.session.new_topic("session").clone();
+
+        self.send_tx
+            .send(SwarmTask::Subscribe(session_topic.clone()))
+            .wrap_err("Failed to subscribe to session topic")?;
+
+        // TODO: Is there a way to do this without the intermediate `Vec`?
+        // Probably not, since we cannot keep an immutable reference on `self.rpcs`, while
+        // also trying to get a mutable reference on `self` for `self.subscribe`.
+        let topics = self.rpcs.keys().cloned().collect::<Vec<_>>();
+        for topic in topics {
+            self.send_tx
+                .send(SwarmTask::Subscribe(topic.clone()))
+                .wrap_err_with(|| format!("Failed to subscribe to {}", topic))?;
+        }
+
+        self.session.online = true;
+
+        let msg = SwarmTask::Message {
+            topic: session_topic,
+            msg: SwarmMessage::SessionJoin {
+                player_id: player_id.to_vec(),
+                mods: self.mods.keys().map(|name| name.to_vec()).collect(),
+            },
+        };
+        self.send_tx
+            .send(msg)
+            .wrap_err("Failed to queue RPC call")?;
+
+        // TODO: Do I want to wait for a reply or some sort of confirmation?
+        // Currently, we just assume this works always.
+
+        for fn_ref in self.mods.values().filter_map(|cbs| cbs.on_session_joined) {
+            lua.pushnumber(fn_ref as f64);
+            lua.gettable(LUA_REGISTRYINDEX);
+            lua.pcall(0, 0)
+                .wrap_err("on_session_joined handler failed")?;
+        }
+
+        Ok(())
+    }
+
+    pub(crate) fn leave_session(&mut self, lua: &LuaState) -> Result<()> {
+        if !self.session.online {
+            log::warn!("There is no session to leave");
+            return Ok(());
+        }
+
+        let topics = mem::take(&mut self.session.topics);
+        self.send_tx
+            .send(SwarmTask::Unsubscribe(topics.into_values().collect()))
+            .wrap_err("Failed to queue unsubscribe task")?;
+
+        self.session.online = false;
+
+        for fn_ref in self.mods.values().filter_map(|cbs| cbs.on_session_left) {
+            lua.pushnumber(fn_ref as f64);
+            lua.gettable(LUA_REGISTRYINDEX);
+            lua.pcall(0, 0).wrap_err("on_session_left handler failed")?;
+        }
+
+        Ok(())
+    }
 }
 
 impl std::fmt::Debug for Plugin {
@@ -28,3 +673,9 @@ impl std::fmt::Debug for Plugin {
         f.write_str("PluginApi")
     }
 }
+
+fn hash(val: impl AsRef<[u8]>) -> u64 {
+    let mut hasher = DefaultHasher::new();
+    hasher.write(val.as_ref());
+    hasher.finish()
+}

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 +1,24 @@
+use std::collections::HashSet;
+
+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()
+    }
+}

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 +203,40 @@ 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),
+    error: unsafe extern "C" fn(*mut lua_State) -> i32,
+    getscriptenvironmentstate: unsafe extern "C" fn() -> *mut lua_State,
+    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 +249,226 @@ impl LuaApi {
         unsafe {
             Self {
                 add_module_function: (*api).add_module_function.unwrap_unchecked(),
-                tolstring: (*api).tolstring.unwrap_unchecked(),
+                createtable: (*api).createtable.unwrap_unchecked(),
+                error: (*api).error.unwrap_unchecked(),
+                getscriptenvironmentstate: (*api).getscriptenvironmentstate.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>>,
+        module: impl AsRef<CStr>,
-        name: impl Into<Vec<u8>>,
+        name: impl AsRef<CStr>,
         cb: extern "C" fn(*mut lua_State) -> i32,
     ) {
-        let module = CString::new(module).expect("Invalid CString");
+        unsafe {
-        let name = CString::new(name).expect("Invalid CString");
+            (self.add_module_function)(module.as_ref().as_ptr(), name.as_ref().as_ptr(), Some(cb))
-
-        unsafe { (self.add_module_function)(module.as_ptr(), name.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>>) {
+    pub fn getscriptenvironmentstate(&self) -> *mut lua_State {
-        let s = CString::new(s).expect("Invalid CString");
+        unsafe { (self.getscriptenvironmentstate)() }
-        unsafe { (self.pushstring)(L, s.as_ptr()) }
+    }
+
+    pub fn error(&self, l: *mut lua_State) {
+        unsafe { (self.error)(l) };
+    }
+}
+
+/// 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 {
+        matches!(self.r#type(idx), LuaType::Function)
+    }
+
+    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 error(&self) {
+        self.api.error(self.l)
+    }
+
+    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()) }
+    }
+
+    /// Creates and returns a reference, in the table at index t, for the object at the top of
+    /// the stack (and pops the object).
+    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) };
     }
 }