test: replace net2 dependency with socket2 (#635)

The proxy's integration tests depend on the `net2` crate, which has been
deprecated and replaced by `socket2`. Since `net2` is no longer actively
maintained, `cargo audit` will warn us about it, so we should replace it
with `socket2`.

While I was making this change, I was curious why we were manually
constructing and binding these sockets at all, rather than just using
`tokio::net::TcpListener::bind`. After some archaeology, I determined
that this was added in linkerd/linkerd2#952, which added a test that
requires a delay between when a socket is _bound_ and when it starts
_listening_. `tokio::net::TcpListener::bind` (as well as the `std::net`
version) perform these operations together. Since this wasn't obvious
from the test code, I went ahead and moved the new `socket2` version of
this into a pair of functions, with comments explaining why we didn't
just use `tokio::net`.

Fixes linkerd/linkerd2#4891

Cargo.lock

@@ -717,9 +717,9 @@ checksum = "bc5729f27f159ddd61f4df6228e827e86643d4d3e7c32183cb30a1c08f604a14"
 
 [[package]]
 name = "libc"
-version = "0.2.65"
+version = "0.2.76"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "1a31a0627fdf1f6a39ec0dd577e101440b7db22672c0901fe00a9a6fbb5c24e8"
+checksum = "755456fae044e6fa1ebbbd1b3e902ae19e73097ed4ed87bb79934a867c007bc3"
 
 [[package]]
 name = "libmimalloc-sys"
@@ -775,7 +775,6 @@ dependencies = [
  "linkerd2-metrics",
  "linkerd2-opencensus",
  "linkerd2-proxy-api",
- "net2",
  "quickcheck",
  "regex 1.3.9",
  "ring",
@@ -910,11 +909,11 @@ dependencies = [
  "linkerd2-app-core",
  "linkerd2-metrics",
  "linkerd2-proxy-api",
- "net2",
  "quickcheck",
  "regex 0.1.80",
  "ring",
  "rustls",
+ "socket2",
  "tokio",
  "tokio-rustls",
  "tonic",
@@ -2138,9 +2137,9 @@ dependencies = [
 
 [[package]]
 name = "redox_syscall"
-version = "0.1.37"
+version = "0.1.57"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "0d92eecebad22b767915e4d529f89f28ee96dbbf5a4810d2b844373f136417fd"
+checksum = "41cc0f7e4d5d4544e8861606a285bb08d3e70712ccc7d2b84d7c0ccfaf4b05ce"
 
 [[package]]
 name = "regex"
@@ -2339,12 +2338,13 @@ checksum = "5c2fb2ec9bcd216a5b0d0ccf31ab17b5ed1d627960edff65bbe95d3ce221cefc"
 
 [[package]]
 name = "socket2"
-version = "0.3.5"
+version = "0.3.12"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "ff606e0486e88f5fc6cfeb3966e434fb409abbc7a3ab495238f70a1ca97f789d"
+checksum = "03088793f677dce356f3ccc2edb1b314ad191ab702a5de3faf49304f7e104918"
 dependencies = [
  "cfg-if",
  "libc",
+ "redox_syscall",
  "winapi 0.3.8",
 ]
 

linkerd/app/Cargo.toml

@@ -39,7 +39,6 @@ http = "0.2"
 hyper = "0.13.7"
 linkerd2-metrics = { path = "../metrics", features = ["test_util"] }
 linkerd2-proxy-api = { git = "https://github.com/linkerd/linkerd2-proxy-api", tag = "v0.1.13", features = ["arbitrary"] }
-net2 = "0.2"
 quickcheck = { version = "0.9", default-features = false }
 ring = "0.16"
 rustls = "0.17"

linkerd/app/integration/Cargo.toml

@@ -29,7 +29,7 @@ linkerd2-app-core = { path = "../core", features = ["mock-orig-dst"] }
 linkerd2-metrics = { path = "../../metrics", features = ["test_util"] }
 linkerd2-proxy-api = { git = "https://github.com/linkerd/linkerd2-proxy-api", tag = "v0.1.13", features = ["arbitrary"] }
 regex = "0.1"
-net2 = "0.2"
+socket2 = "0.3.12"
 quickcheck = { version = "0.9", default-features = false }
 ring = "0.16"
 rustls = "0.17"

linkerd/app/integration/src/controller.rs

@@ -333,17 +333,16 @@ where
     B::Error: Into<Box<dyn std::error::Error + Send + Sync>>,
     B::Data: Send + 'static,
 {
-    let addr = SocketAddr::from(([127, 0, 0, 1], 0));
-    let listener = net2::TcpBuilder::new_v4().expect("Tcp::new_v4");
-    listener.bind(addr).expect("Tcp::bind");
-    let addr = listener.local_addr().expect("Tcp::local_addr");
-    let listener = listener.listen(1024).expect("listen");
-
     let (listening_tx, listening_rx) = tokio::sync::oneshot::channel();
     let (drain_signal, drain) = drain::channel();
+
+    // Bind an ephemeral port but do not start listening yet.
+    let (sock, addr) = crate::bind_ephemeral();
+
     let task = tokio::spawn(
         cancelable(drain.clone(), async move {
-            let mut listener = tokio::net::TcpListener::from_std(listener)?;
+            // Start listening on the socket.
+            let mut listener = crate::listen(sock);
             let mut listening_tx = Some(listening_tx);
 
             if let Some(delay) = delay {

linkerd/app/integration/src/lib.rs

@@ -14,6 +14,7 @@ pub use http::{HeaderMap, Request, Response, StatusCode};
 pub use http_body::Body as HttpBody;
 pub use linkerd2_app as app;
 pub use linkerd2_app_core::drain;
+use socket2::Socket;
 pub use std::collections::HashMap;
 use std::fmt;
 pub use std::future::Future;
@@ -286,3 +287,35 @@ pub async fn cancelable<E: Send + 'static>(
         }
     }
 }
+
+/// Binds a socket to an ephemeral port without starting listening on it.
+///
+/// Some tests require us to introduce a delay between binding the server
+/// socket and listening on it. However, `tokio::net`'s
+/// `TcpListener::bind` function both binds the socket _and_ starts
+/// listening on it, so we can't just use that. Instead, we must manually
+/// construct the socket using `socket2`'s lower-level interface to libc
+///  socket APIs, and _then_ convert it into a Tokio `TcpListener`.
+pub(crate) fn bind_ephemeral() -> (Socket, SocketAddr) {
+    use socket2::{Domain, Protocol, Type};
+
+    let addr = SocketAddr::from(([127, 0, 0, 1], 0));
+    let sock =
+        Socket::new(Domain::ipv4(), Type::stream(), Some(Protocol::tcp())).expect("Socket::new");
+    sock.bind(&addr.into()).expect("Socket::bind");
+    let addr = sock
+        .local_addr()
+        .expect("Socket::local_addr")
+        .as_std()
+        .expect("must be AF_INET");
+    (sock, addr)
+}
+
+/// Start listening on a socket previously bound using `socket2`, returning a
+/// Tokio `TcpListener`.
+pub(crate) fn listen(sock: Socket) -> TcpListener {
+    sock.listen(1024)
+        .expect("socket should be able to start listening");
+    TcpListener::from_std(sock.into_tcp_listener())
+        .expect("socket should be able to set nonblocking")
+}

linkerd/app/integration/src/server.rs

@@ -201,10 +201,8 @@ impl Server {
         let srv_conn_count = Arc::clone(&conn_count);
         let version = self.version;
 
-        let addr = SocketAddr::from(([127, 0, 0, 1], 0));
-        let listener = net2::TcpBuilder::new_v4().expect("Tcp::new_v4");
-        listener.bind(addr).expect("Tcp::bind");
-        let addr = listener.local_addr().expect("Tcp::local_addr");
+        // Bind an ephemeral port but do not start listening yet.
+        let (sock, addr) = crate::bind_ephemeral();
 
         let (drain_signal, drain) = drain::channel();
         let tls_config = self.tls.clone();
@@ -223,8 +221,9 @@ impl Server {
                     let _ = listening_tx.take().unwrap().send(());
                     delay.await;
                 }
-                let listener = listener.listen(1024).expect("Tcp::listen");
-                let mut listener = TcpListener::from_std(listener).expect("from_std");
+
+                // After the delay, start listening on the socket.
+                let mut listener = crate::listen(sock);
 
                 if let Some(listening_tx) = listening_tx {
                     let _ = listening_tx.send(());