Add basic two-way junction

872da89e · Frank Sauerburger · 872da89e · 872da89e · 872da89e · 872da89e
Verified Commit 872da89e authored 4 months ago by Frank Sauerburger
--- a/.gitignore
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--- a/Cargo.toml
+++ b/Cargo.toml
+[package]
+name = "tcpjunction"
+version = "0.1.0"
+edition = "2021"
+[dependencies]
+tokio = { version = "1.41.1", features = ["rt", "rt-multi-thread", "macros", "net", "io-util", "time"] }
+signal-hook = "0.3.17"
--- a/src/main.rs
+++ b/src/main.rs
+use tokio::io;
+use tokio::net::TcpListener;
+use tokio::net::TcpStream;
+use std::sync::{Arc, Mutex};
+use signal_hook::{consts::SIGUSR1, iterator::Signals};
+use std::time::Duration;
+use tokio::time::{sleep, timeout};
+struct State {
+    a_up: bool,
+    b_up: bool,
+    a: String,
+    b: String,
+    prefer_a: bool
+}
+impl State {
+    fn use_a(&self) -> bool {
+        match (self.a_up, self.b_up) {
+            (true, true) => self.prefer_a,
+            (false, true) => false,
+            (true, false) => true,
+            (false, false) => self.prefer_a,
+        }
+    }
+    fn addr(&self) -> String {
+        if self.use_a() {
+            self.a.clone()
+        } else {
+            self.b.clone()
+        }
+    }
+    fn mark_up(&mut self, probe_a: bool) {
+        if probe_a && !self.a_up {
+            self.a_up = true;
+            println!("Marked a as up")
+        } else if !probe_a && !self.b_up {
+            self.b_up = true;
+            println!("Marked b as up")
+        }
+    }
+    fn mark_down(&mut self, probe_a: bool) {
+        if probe_a && self.a_up {
+            self.a_up = false;
+            println!("Marked a as down")
+        } else if !probe_a && self.b_up {
+            self.b_up = false;
+            println!("Marked b as down")
+        }
+    }
+}
+type SharedState = Arc<Mutex<State>>;
+#[tokio::main]
+async fn main() {
+    let server = TcpListener::bind("0.0.0.0:8080").await.unwrap();
+    let state: SharedState = Arc::new(Mutex::new(State {
+        a_up: false,
+        b_up: false,
+        prefer_a: true,
+        a: "localhost:8001".to_string(),
+        b: "localhost:8002".to_string(),
+    }));
+    {
+        let state = state.clone();
+        tokio::spawn(async move {
+            let mut signals = Signals::new([SIGUSR1]).unwrap();
+            for _ in signals.forever() {
+                let mut state = state.lock().unwrap();
+                state.prefer_a = !state.prefer_a;
+                println!("Update to server preference: prefer_a={:?}", state.prefer_a)
+            }
+        });
+    }
+    {
+        let state = state.clone();
+        tokio::spawn(async move {
+            probe_upstream(true, state).await
+        });
+    }
+    {
+        let state = state.clone();
+        tokio::spawn(async move {
+            probe_upstream(false, state).await
+        });
+    }
+    loop {
+        let (socket, _) = server.accept().await.unwrap();
+        let state = state.clone();
+        tokio::spawn(async move {
+            handle_client(socket, state).await;
+        });
+    }
+}
+async fn handle_client(client: TcpStream, state: SharedState) {
+    let address = state.lock().unwrap().addr();
+    let server = TcpStream::connect(address.as_str()).await.unwrap();
+    let (mut eread, mut ewrite) = client.into_split();
+    let (mut oread, mut owrite) = server.into_split();
+    tokio::spawn(async move { io::copy(&mut eread, &mut owrite).await });
+    tokio::spawn(async move { io::copy(&mut oread, &mut ewrite).await });
+}
+async fn probe_upstream(probe_a: bool, state: SharedState) {
+    loop {
+        let address = match probe_a {
+            true => state.lock().unwrap().a.clone(),
+            false => state.lock().unwrap().b.clone(),
+        };
+        let upstream  = timeout(
+            Duration::from_millis(1000),
+            TcpStream::connect(address.as_str())
+        ).await;
+        match upstream  {
+            Ok(Ok(_)) => state.lock().unwrap().mark_up(probe_a),
+            _ => state.lock().unwrap().mark_down(probe_a),
+        }
+        sleep(Duration::from_millis(1000)).await;
+    }
+}
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