Add the inferproxy byte forwarder with its two limits

Implemented-By: Laguna S 2.1 (OpenCode)

crates/inferproxy/tests/bucket.rs

@@ -0,0 +1,70 @@
+//! Tests for the accept-rate limiter. Do not edit: these define the required behaviour.
+
+use inferproxy::{Limits, TokenBucket};
+use std::time::{Duration, Instant};
+
+#[test]
+fn default_limits() {
+    let want = Limits {
+        max_connections: 8,
+        burst: 10,
+        per_second: 2,
+    };
+    assert_eq!(Limits::default(), want);
+}
+
+#[test]
+fn starts_full_and_empties() {
+    let t0 = Instant::now();
+    let mut b = TokenBucket::new(3, 2, t0);
+    assert!(b.take(t0));
+    assert!(b.take(t0));
+    assert!(b.take(t0));
+    assert!(!b.take(t0), "a fourth take at the same instant must fail");
+}
+
+#[test]
+fn refills_at_the_given_rate() {
+    let t0 = Instant::now();
+    let mut b = TokenBucket::new(1, 2, t0);
+    assert!(b.take(t0));
+    assert!(
+        !b.take(t0 + Duration::from_millis(499)),
+        "half a second at 2/s is one token"
+    );
+    assert!(b.take(t0 + Duration::from_millis(500)));
+    assert!(!b.take(t0 + Duration::from_millis(500)));
+}
+
+#[test]
+fn partial_refills_add_up() {
+    // Ten checks 100 ms apart at 2/s must add up to two tokens, not zero.
+    let t0 = Instant::now();
+    let mut b = TokenBucket::new(1, 2, t0);
+    assert!(b.take(t0));
+    let granted = (1..=10)
+        .filter(|i| b.take(t0 + Duration::from_millis(100 * i)))
+        .count();
+    assert_eq!(granted, 2);
+}
+
+#[test]
+fn never_holds_more_than_the_burst() {
+    let t0 = Instant::now();
+    let mut b = TokenBucket::new(2, 100, t0);
+    let later = t0 + Duration::from_secs(3600);
+    assert!(b.take(later));
+    assert!(b.take(later));
+    assert!(
+        !b.take(later),
+        "an hour of refill must still stop at the burst size"
+    );
+}
+
+#[test]
+fn a_clock_that_does_not_advance_is_harmless() {
+    let t0 = Instant::now();
+    let mut b = TokenBucket::new(1, 2, t0 + Duration::from_secs(10));
+    assert!(b.take(t0), "an earlier `now` must not panic or underflow");
+    assert!(!b.take(t0));
+}

crates/inferproxy/tests/forward.rs

@@ -0,0 +1,156 @@
+//! End-to-end tests for the forwarder. Do not edit: these define the required behaviour.
+//!
+//! Each test starts a small TCP server as the upstream, runs `serve` on a Unix socket in a
+//! temporary directory, and talks to it as a client would.
+
+use inferproxy::{Limits, serve};
+use std::io::{Read, Write};
+use std::net::{Shutdown, TcpListener};
+use std::os::unix::net::{UnixListener, UnixStream};
+use std::path::PathBuf;
+use std::sync::atomic::{AtomicU32, Ordering};
+use std::thread;
+use std::time::Duration;
+
+static NEXT: AtomicU32 = AtomicU32::new(0);
+
+fn socket_path() -> PathBuf {
+    let n = NEXT.fetch_add(1, Ordering::SeqCst);
+    let dir = std::env::temp_dir().join(format!("inferproxy-test-{}-{n}", std::process::id()));
+    std::fs::create_dir_all(&dir).unwrap();
+    dir.join("infer.sock")
+}
+
+/// An upstream that reads until the client stops sending, then answers with what it read,
+/// upper-cased, and closes. This is the shape of one HTTP exchange with `Connection: close`.
+fn shouting_upstream() -> String {
+    let listener = TcpListener::bind("127.0.0.1:0").unwrap();
+    let addr = listener.local_addr().unwrap().to_string();
+    thread::spawn(move || {
+        for stream in listener.incoming() {
+            let mut stream = stream.unwrap();
+            thread::spawn(move || {
+                let mut got = Vec::new();
+                stream.read_to_end(&mut got).unwrap();
+                stream.write_all(&got.to_ascii_uppercase()).unwrap();
+            });
+        }
+    });
+    addr
+}
+
+/// An upstream that accepts and then holds every connection open without reading or writing.
+fn silent_upstream() -> String {
+    let listener = TcpListener::bind("127.0.0.1:0").unwrap();
+    let addr = listener.local_addr().unwrap().to_string();
+    thread::spawn(move || {
+        let mut held = Vec::new();
+        for stream in listener.incoming() {
+            held.push(stream.unwrap());
+        }
+    });
+    addr
+}
+
+fn start(upstream: String, limits: Limits) -> PathBuf {
+    let path = socket_path();
+    let listener = UnixListener::bind(&path).unwrap();
+    thread::spawn(move || serve(listener, upstream, limits));
+    path
+}
+
+fn exchange(path: &PathBuf, request: &[u8]) -> Vec<u8> {
+    let mut s = UnixStream::connect(path).unwrap();
+    s.set_read_timeout(Some(Duration::from_secs(5))).unwrap();
+    s.write_all(request).unwrap();
+    s.shutdown(Shutdown::Write).unwrap();
+    let mut got = Vec::new();
+    s.read_to_end(&mut got).unwrap();
+    got
+}
+
+/// True if the proxy closed the connection without sending anything.
+fn was_refused(path: &PathBuf) -> bool {
+    let mut s = UnixStream::connect(path).unwrap();
+    s.set_read_timeout(Some(Duration::from_millis(500)))
+        .unwrap();
+    let mut buf = [0u8; 1];
+    matches!(s.read(&mut buf), Ok(0))
+}
+
+#[test]
+fn forwards_both_ways_and_passes_the_half_close_on() {
+    let path = start(shouting_upstream(), Limits::default());
+    assert_eq!(exchange(&path, b"hello, box"), b"HELLO, BOX");
+}
+
+#[test]
+fn forwards_more_than_one_buffer() {
+    let path = start(shouting_upstream(), Limits::default());
+    let request: Vec<u8> = (0..300_000u32).map(|i| b'a' + (i % 26) as u8).collect();
+    assert_eq!(exchange(&path, &request), request.to_ascii_uppercase());
+}
+
+#[test]
+fn serves_connections_one_after_another() {
+    let path = start(
+        shouting_upstream(),
+        Limits {
+            max_connections: 1,
+            burst: 100,
+            per_second: 100,
+        },
+    );
+    for i in 0..5 {
+        let msg = format!("request {i}");
+        assert_eq!(
+            exchange(&path, msg.as_bytes()),
+            msg.to_ascii_uppercase().as_bytes()
+        );
+    }
+}
+
+#[test]
+fn refuses_connections_over_the_open_limit() {
+    let limits = Limits {
+        max_connections: 2,
+        burst: 100,
+        per_second: 100,
+    };
+    let path = start(silent_upstream(), limits);
+    let _a = UnixStream::connect(&path).unwrap();
+    let _b = UnixStream::connect(&path).unwrap();
+    thread::sleep(Duration::from_millis(200)); // let the proxy take both
+    assert!(
+        was_refused(&path),
+        "a third open connection must be closed at once"
+    );
+}
+
+#[test]
+fn refuses_connections_over_the_rate_limit() {
+    let limits = Limits {
+        max_connections: 100,
+        burst: 3,
+        per_second: 1,
+    };
+    let path = start(shouting_upstream(), limits);
+    for i in 0..3 {
+        assert_eq!(
+            exchange(&path, b"x"),
+            b"X",
+            "connection {i} is within the burst"
+        );
+    }
+    assert!(
+        was_refused(&path),
+        "the fourth connection in the same instant must be refused"
+    );
+}
+
+#[test]
+fn an_unreachable_upstream_closes_the_client() {
+    // Port 1 on localhost refuses connections.
+    let path = start("127.0.0.1:1".to_string(), Limits::default());
+    assert!(was_refused(&path));
+}