should be good to extend functionality now

.github/workflows/rust.yml

@@ -1,22 +0,0 @@
-name: Rust
-
-on:
-  push:
-    branches: [ "main" ]
-  pull_request:
-    branches: [ "main" ]
-
-env:
-  CARGO_TERM_COLOR: always
-
-jobs:
-  build:
-
-    runs-on: ubuntu-latest
-
-    steps:
-    - uses: actions/checkout@v4
-    - name: Build
-      run: cargo build --verbose
-    - name: Run tests
-      run: cargo test --verbose

README.md

@@ -5,10 +5,25 @@ Production't graden't load balancer.
 
 ## Todo
 - [ ] architecture astronauting
+  - balancer module
+    - just the algorithms i guess
+- 
+  - backend module
+    - manages the backend pool
+    - deals with health / load check
+    - BackendPool for all the backends stored together
+    - Backend for individual backends
+    - has some methods used by balancer module to pick a suitable backend
+  - proxy module 
+    - all the different supported protocols to handle
+    - will create a session / stream context structure (ConnectionContext)
+      - not globally tracked (this might change for UDP!)
+      - mainly some metadata
+  - config module
+    - set up all the stuff or something
 - [ ] stream / session handling (i think wrapper around tokio TcpStream)
 - [ ] basic backend pooling
 - [ ] layer 4 load balancing
-- [ ] load balancing algorithm from the paper (https://www.wcse.org/WCSE_2018/W110.pdf) 
 
 ## notes
 tcp, for nginx (and haproxy, its similar):
@@ -21,7 +36,7 @@ struct ngx_connection_s {
 
     ngx_socket_t        fd;
 
-    ngx_recv_pt         recv; // fn pointer to whatever recv fn used (different for dfferent platforms / protocol
+    ngx_recv_pt         recv; // fn pointer to whatever recv fn used (different for idfferent platforms / protocol
     ngx_send_pt         send; // ditto
     ngx_recv_chain_pt   recv_chain;
     ngx_send_chain_pt   send_chain;
@@ -104,3 +119,10 @@ process to load balance:
 - connect to the server
 - proxy the data (copy_bidirectional? maybe we want some metrics or logging, so might do manually)
 - cleanup when smoeone leavesr or something goes wrong (with TCP, OS / tokio will tell us, with UDP probably just timeout based, and a periodic sweep of all sessions)
+
+
+### UDP
+UDP is connectionless, and i don't think UdpSocket or UdpFramed implement the traits required for tokio copy_bidirectional
+but async write and read don't work on just regular datagrams, so probably not possible.
+
+Would require us to implement our own bidirectional copying / proxying, as well as tracking "active" connections.

src/backend/mod.rs

@@ -0,0 +1,58 @@
+use core::fmt;
+use std::net::SocketAddr;
+use std::sync::RwLock;
+use std::sync::Arc;
+use std::sync::atomic::{AtomicUsize, Ordering};
+
+#[derive(Debug)]
+pub struct Backend {
+    pub id: String,
+    pub address: SocketAddr,
+    pub active_connections: AtomicUsize,
+}
+
+impl Backend {
+    pub fn new(id: String, address: SocketAddr) -> Self {
+        Self {
+            id: id.to_string(),
+            address,
+            active_connections: AtomicUsize::new(0),
+        }
+    }
+
+    // Ordering::Relaxed means the ops could be in any order, but since this
+    // is just a metric, and we assume the underlying system is sane
+    // enough not to behave poorly, so SeqCst is probably overkill.
+    pub fn inc_connections(&self) {
+        self.active_connections.fetch_add(1, Ordering::Relaxed);
+        println!("{} has {} connections open", self.id, self.active_connections.load(Ordering::Relaxed));
+    }
+
+    pub fn dec_connections(&self) {
+        self.active_connections.fetch_sub(1, Ordering::Relaxed);
+        println!("{} has {} connections open", self.id, self.active_connections.load(Ordering::Relaxed));
+    }
+}
+
+impl fmt::Display for Backend {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        write!(f, "{} ({})", self.address, self.id)
+    }
+}
+
+#[derive(Clone, Debug)]
+pub struct BackendPool {
+    pub backends: Arc<RwLock<Vec<Arc<Backend>>>>,
+}
+
+impl BackendPool {
+    pub fn new() -> Self {
+        BackendPool {
+            backends: Arc::new(RwLock::new(Vec::new())),
+        }
+    }
+
+    pub fn add(&self, backend: Backend) {
+        self.backends.write().unwrap().push(Arc::new(backend));
+    }
+}

src/balancer/mod.rs

@@ -0,0 +1,9 @@
+pub mod round_robin;
+
+use std::fmt::Debug;
+use std::sync::Arc;
+use crate::backend::Backend;
+
+pub trait Balancer: Debug + Send + Sync + 'static {
+    fn choose_backend(&mut self) -> Option<Arc<Backend>>;
+}

src/balancer/round_robin.rs

@@ -0,0 +1,33 @@
+use std::sync::{Arc, RwLock};
+use std::fmt::Debug;
+use crate::backend::{Backend, BackendPool};
+use crate::balancer::Balancer;
+
+// only the main thread for receiving connections should be
+// doing the load balancing. alternatively, each thread
+// that handles load balancing should get their own instance.
+#[derive(Debug)]
+pub struct RoundRobinBalancer {
+    pool: BackendPool,
+    index: usize,
+}
+
+impl RoundRobinBalancer {
+    pub fn new(pool: BackendPool) -> RoundRobinBalancer {
+        Self {
+            pool,
+            index: 0,
+        }
+    }
+}
+
+impl Balancer for RoundRobinBalancer {
+    fn choose_backend(&mut self) -> Option<Arc<Backend>> {
+        let backends = self.pool.backends.read().unwrap();
+        if backends.is_empty() { return None; }
+
+        let backend = backends[self.index % backends.len()].clone();
+        self.index = self.index.wrapping_add(1);
+        Some(backend)
+    }
+}

src/config.rs

@@ -0,0 +1,6 @@
+// TODO: "routing" rules
+// backends defined as ip + port
+// define sets of backends
+// allowed set operations for now is just union
+// rules are ip + mask and ports, maps to some of the sets
+//  defined earlier, along with a routing strategy

src/main.rs

@@ -1,55 +1,52 @@
-macro_rules! info {
+extern crate core;
-    ($($arg:tt)*) => {{
-        print!("info: ");
-        println!($($arg)*);
-    }};
-}
 
-macro_rules! error {
+mod balancer;
-    ($($arg:tt)*) => {
+mod config;
-        eprint!("error: ");
+mod backend;
-        eprintln!($($arg)*);
+mod proxy;
-    };
-}
-
-mod netutils;
-
-use anywho::Error;
-use netutils::{Backend, tunnel};
-use std::sync::Arc;
 
 use tokio::net::TcpListener;
-use tokio::sync::Mutex;
+use tokio::io::{AsyncReadExt, AsyncWriteExt};
+use std::sync::Arc;
+use std::sync::atomic::AtomicU64;
+use crate::backend::{Backend, BackendPool};
+use crate::balancer::Balancer;
+use crate::balancer::round_robin::RoundRobinBalancer;
+use crate::proxy::tcp::proxy_tcp_connection;
+
+static NEXT_CONN_ID: AtomicU64 = AtomicU64::new(1);
 
 #[tokio::main]
-async fn main() -> Result<(), Error> {
+async fn main() -> Result<(), Box<dyn std::error::Error>> {
-    let backends = Arc::new(vec![
+    let pool = BackendPool::new();
-        Backend::new("127.0.0.1:8081".to_string()),
-        Backend::new("127.0.0.1:8082".to_string()),
-    ]);
 
-    let current_index = Arc::new(Mutex::new(0));
+    pool.add(Backend::new(
+        "backend 1".into(),
+        "127.0.0.1:8081".parse().unwrap(),
+    ));
 
-    info!("enginewhy starting on 0.0.0.0:8080");
+    pool.add(Backend::new(
-    info!("backends: {:?}", backends);
+        "backend 2".into(),
+        "127.0.0.1:8082".parse().unwrap(),
+    ));
 
-    let listener = TcpListener::bind("0.0.0.0:8080").await?;
+    let mut balancer = RoundRobinBalancer::new(pool.clone());
+
+    let listener = TcpListener::bind("127.0.0.1:8080").await?;
 
     loop {
-        let (client, addr) = listener.accept().await?;
+        let (socket, _) = listener.accept().await?;
-        info!("new connection from {}", addr);
 
-        let backend = {
+        let conn_id = NEXT_CONN_ID.fetch_add(1, std::sync::atomic::Ordering::SeqCst);
-            let mut index = current_index.lock().await;
-            let selected_backend = backends[*index].clone();
-            *index = (*index + 1) % backends.len();
-            selected_backend
-        };
 
-        info!("routing client {} to backend {}", addr, backend);
+        if let Some(backend) = balancer.choose_backend() {
-
+            tokio::spawn(async move {
-        if let Err(e) = tunnel(client, backend).await {
+                if let Err(e) = proxy_tcp_connection(conn_id, socket, backend).await {
-            error!("proxy failed for {}: {}", addr, e);
+                    eprintln!("error: conn_id={} proxy failed: {}", conn_id, e);
+                }
+            });
+        } else {
+            eprintln!("error: no backendsd for conn_id={}", conn_id);
         }
     }
 }

src/netutils.rs

@@ -1,52 +0,0 @@
-use std::fmt;
-use tokio::io;
-use tokio::net::TcpStream;
-
-use std::error::Error;
-
-#[derive(Clone, Debug)]
-pub struct Backend {
-    address: String,
-}
-
-impl Backend {
-    pub fn new(address: String) -> Self {
-        Backend { address }
-    }
-}
-
-impl fmt::Display for Backend {
-    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
-        write!(f, "{}", self.address)
-    }
-}
-
-pub async fn tunnel(client_stream: TcpStream, backend: Backend) -> Result<(), Box<dyn Error>> {
-    let backend_address: String = backend.address.clone();
-
-    tokio::spawn(async move {
-        let backend_stream: TcpStream = match TcpStream::connect(&backend_address).await {
-            Ok(s) => {
-                info!("connected to backend {backend_address}");
-                s
-            }
-            Err(e) => {
-                error!("failed connecting to backend {backend_address}: {e}");
-                return;
-            }
-        };
-
-        let (mut read_client, mut write_client) = client_stream.into_split();
-        let (mut read_backend, mut write_backend) = backend_stream.into_split();
-
-        let client_to_backend =
-            tokio::spawn(async move { io::copy(&mut read_client, &mut write_backend).await });
-
-        let backend_to_client =
-            tokio::spawn(async move { io::copy(&mut read_backend, &mut write_client).await });
-
-        let _ = tokio::join!(client_to_backend, backend_to_client);
-    });
-
-    Ok(())
-}

src/proxy/mod.rs

@@ -0,0 +1,43 @@
+use std::net::SocketAddr;
+use std::sync::Arc;
+use std::time::Instant;
+use crate::backend::Backend;
+
+pub mod tcp;
+
+pub struct ConnectionContext {
+    pub id: u64,
+    pub client_addr: SocketAddr,
+    pub start_time: Instant,
+    pub backend: Arc<Backend>,
+    pub bytes_transferred: u64,
+}
+
+impl ConnectionContext {
+    pub fn new(id: u64, client_addr: SocketAddr, backend: Arc<Backend>) -> Self {
+        backend.inc_connections();
+
+        Self {
+            id,
+            client_addr,
+            start_time: Instant::now(),
+            backend,
+            bytes_transferred: 0,
+        }
+    }
+}
+
+impl Drop for ConnectionContext {
+    fn drop(&mut self) {
+        self.backend.dec_connections();
+        let duration = self.start_time.elapsed();
+
+        println!("info: conn_id={} closed. client={} backend={} bytes={} duration={:.2?}",
+            self.id,
+            self.client_addr,
+            self.backend.address,
+            self.bytes_transferred,
+            duration.as_secs_f64()
+        );
+    }
+}

src/proxy/tcp.rs

@@ -0,0 +1,26 @@
+use std::sync::Arc;
+use tokio::io;
+use tokio::net::TcpStream;
+use anywho::Error;
+use crate::backend::Backend;
+use crate::proxy::ConnectionContext;
+
+pub async fn proxy_tcp_connection(connection_id: u64, mut client_stream: TcpStream, backend: Arc<Backend>) -> Result<(), Error> {
+    let client_addr = client_stream.peer_addr()?;
+
+    let mut ctx = ConnectionContext::new(connection_id, client_addr, backend.clone());
+
+    #[cfg(debug_assertions)]
+    println!("info: conn_id={} connecting to {}", connection_id, ctx.backend.id);
+
+    let mut backend_stream = TcpStream::connect(&backend.address).await?;
+
+    let (tx, rx) = io::copy_bidirectional(
+        &mut client_stream,
+        &mut backend_stream,
+    ).await?;
+
+    ctx.bytes_transferred = tx + rx;
+
+    Ok(())
+}