From 094afb02fe937d95098cc141fbc62cf61871d59b Mon Sep 17 00:00:00 2001
From: Noratrieb <48135649+Noratrieb@users.noreply.github.com>
Date: Mon, 26 Aug 2024 01:56:38 +0200
Subject: [PATCH] Initial commit

---
 .gitignore  |   2 +
 Cargo.lock  | 462 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 Cargo.toml  |   9 +
 README.md   |   7 +
 default.nix |   6 +
 src/main.rs | 123 ++++++++++++++
 6 files changed, 609 insertions(+)
 create mode 100644 .gitignore
 create mode 100644 Cargo.lock
 create mode 100644 Cargo.toml
 create mode 100644 README.md
 create mode 100644 default.nix
 create mode 100644 src/main.rs

diff --git a/.gitignore b/.gitignore
new file mode 100644
index 0000000..97e3b2f
--- /dev/null
+++ b/.gitignore
@@ -0,0 +1,2 @@
+/result
+/target
diff --git a/Cargo.lock b/Cargo.lock
new file mode 100644
index 0000000..4a83d92
--- /dev/null
+++ b/Cargo.lock
@@ -0,0 +1,462 @@
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+# It is not intended for manual editing.
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diff --git a/Cargo.toml b/Cargo.toml
new file mode 100644
index 0000000..ed1512f
--- /dev/null
+++ b/Cargo.toml
@@ -0,0 +1,9 @@
+[package]
+name = "qotdd"
+version = "0.1.0"
+edition = "2021"
+
+[dependencies]
+eyre = "0.6.12"
+rand = "0.8.5"
+tokio = { version = "1.39.3", features = ["full"] }
diff --git a/README.md b/README.md
new file mode 100644
index 0000000..921fd3b
--- /dev/null
+++ b/README.md
@@ -0,0 +1,7 @@
+# qotdd
+
+Quote of The Day Daemon.
+
+A small service implementing the Quote of the Day protocol according to [RFC 865](https://datatracker.ietf.org/doc/html/rfc865).
+
+Protects against DoS amplification attacks by aggressively rate-limiting every source IP.
diff --git a/default.nix b/default.nix
new file mode 100644
index 0000000..8aedacb
--- /dev/null
+++ b/default.nix
@@ -0,0 +1,6 @@
+{ pkgs ? import <nixpkgs> { } }: pkgs.rustPlatform.buildRustPackage {
+  src = pkgs.lib.cleanSource ./.;
+  pname = "qotdd";
+  version = "0.1.0";
+  cargoLock.lockFile = ./Cargo.lock;
+}
diff --git a/src/main.rs b/src/main.rs
new file mode 100644
index 0000000..79a230e
--- /dev/null
+++ b/src/main.rs
@@ -0,0 +1,123 @@
+use std::{
+    collections::HashMap,
+    net::{IpAddr, Ipv4Addr, SocketAddr},
+    time::Duration,
+};
+
+use eyre::{bail, ensure, Context, Result};
+use rand::seq::SliceRandom;
+use tokio::{io::AsyncWriteExt, net::TcpListener};
+
+#[tokio::main(flavor = "current_thread")]
+async fn main() -> Result<()> {
+    let port: u16 = match std::env::var("QUOTDD_PORT") {
+        Ok(port) => match port.parse() {
+            Ok(port) => port,
+            Err(err) => {
+                bail!("error: invalid port passed in QUOTDD_PORT: {err}");
+            }
+        },
+        Err(_) => 17,
+    };
+
+    let quotes = [
+        "Quickness is the essence of the war. ~ Sun Tsu",
+        "Pretend inferiority and encourage his arrogance. ~ Sun Tsu",
+    ];
+
+    ensure!(!quotes.is_empty(), "Quotes are empty");
+
+    let addr = SocketAddr::new(IpAddr::V4(Ipv4Addr::UNSPECIFIED), port);
+
+    eprintln!("info: Listening on socket {}", addr);
+
+    let listener = TcpListener::bind(addr)
+        .await
+        .wrap_err_with(|| format!("binding on port {port}"))?;
+
+    let mut reset = tokio::time::interval(Duration::from_secs(60));
+
+    let mut limits = RateLimits::default();
+
+    loop {
+        tokio::select! {
+            result = tcp_loop(&listener, &quotes, &mut limits) => {
+                result?;
+            }
+            _ = reset.tick() => {
+                limits.lower();
+            }
+        }
+    }
+}
+
+async fn tcp_loop(listener: &TcpListener, quotes: &[&str], limits: &mut RateLimits) -> Result<()> {
+    let (mut conn, peer) = listener.accept().await.wrap_err("accepting connection")?;
+
+    if !limits.accept(peer.ip()) {
+        conn.shutdown().await.wrap_err("closing connection")?;
+        return Ok(());
+    }
+
+    let quote = quotes.choose(&mut rand::thread_rng()).unwrap();
+
+    conn.write_all(quote.as_bytes())
+        .await
+        .wrap_err("writing quote")?;
+    conn.write_all(b"\n").await.wrap_err("writing quote")?;
+
+    conn.shutdown().await.wrap_err("closing connection")?;
+    Ok(())
+}
+
+// To avoid DoS amplification attacks, we ratelimit our service based on the IP.
+// Sorry, but you're not getting many quotes...
+#[derive(Default)]
+struct RateLimits {
+    ips: HashMap<IpAddr, usize>,
+}
+
+impl RateLimits {
+    fn accept(&mut self, addr: IpAddr) -> bool {
+        let count = self.ips.entry(addr).or_default();
+        let old = *count;
+        *count += 1;
+        old < 10
+    }
+
+    fn lower(&mut self) {
+        self.ips
+            .values_mut()
+            .for_each(|v| *v = v.saturating_sub(10));
+        self.ips.retain(|_, v| *v > 0);
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use std::net::{IpAddr, Ipv4Addr};
+
+    use crate::RateLimits;
+
+    #[test]
+    fn ratelimit() {
+        let mut limits = RateLimits::default();
+        let ip = IpAddr::V4(Ipv4Addr::LOCALHOST);
+
+        for _ in 0..10 {
+            assert!(limits.accept(ip))
+        }
+
+        for _ in 0..10 {
+            assert!(!limits.accept(ip))
+        }
+
+        limits.lower();
+
+        assert!(!limits.accept(ip));
+
+        limits.lower();
+
+        assert!(limits.accept(ip));
+    }
+}