fix(blahd): reject UNIX domain socket for now

It's too complex to bother with for the current `axum` API. Let's wait
for axum 0.8 release.

Ref: tokio-rs/axum#2479

blahd/Cargo.toml

@@ -21,6 +21,7 @@ parking_lot = "0.12" # Maybe no better performance, just that we hate poisoning.
 rand = "0.8"
 reqwest = "0.12"
 rusqlite = "0.32"
+rustix = { version = "0.38", features = ["net"] }
 sd-notify = "0.4"
 serde = { version = "1", features = ["derive"] }
 serde-constant = "0.1"
@@ -45,6 +46,7 @@ nix = { version = "0.29.0", features = ["fs", "process", "signal"] }
 reqwest = { version = "0.12.7", features = ["json"] }
 rstest = { version = "0.22.0", default-features = false }
 scopeguard = "1.2.0"
+tempfile = "3.12.0"
 
 [lints]
 workspace = true

blahd/config.example.toml

@@ -24,6 +24,7 @@ address = "localhost:8080"
 
 # Use systemd socket activation mechanism to get listener fd from envvars.
 # See also sd_listen_fds(3) and systemd.socket(5).
+# NB. Currently only TCP sockets are supported. UNIX domain socket is TODO.
 #systemd = true
 
 [server]

blahd/src/bin/blahd.rs

@@ -1,9 +1,8 @@
-use std::net::TcpListener;
-use std::os::fd::FromRawFd;
+use std::os::fd::{FromRawFd, OwnedFd};
 use std::path::PathBuf;
 use std::sync::Arc;
 
-use anyhow::{anyhow, Context, Result};
+use anyhow::{anyhow, bail, Context, Result};
 use blahd::config::{Config, ListenConfig};
 use blahd::{AppState, Database};
 
@@ -56,30 +55,44 @@ fn main() -> Result<()> {
 async fn main_serve(db: Database, config: Config) -> Result<()> {
     let st = AppState::new(db, config.server);
 
-    let listener = match &config.listen {
-        ListenConfig::Address(addr) => {
-            tracing::info!("listening on {addr:?}");
+    let (listener_display, listener) = match &config.listen {
+        ListenConfig::Address(addr) => (
+            format!("address {addr:?}"),
             tokio::net::TcpListener::bind(addr)
                 .await
-                .context("failed to listen on socket")?
-        }
+                .context("failed to listen on socket")?,
+        ),
         ListenConfig::Systemd(_) => {
-            tracing::info!("listening on fd from environment");
+            use rustix::net::{getsockname, SocketAddrAny};
+
             let [fd] = sd_notify::listen_fds()
                 .context("failed to get fds from sd_listen_fds(3)")?
                 .collect::<Vec<_>>()
                 .try_into()
-                .map_err(|_| anyhow!("more than one fds available from sd_listen_fds(3)"))?;
+                .map_err(|_| anyhow!("expecting exactly one fd from LISTEN_FDS"))?;
             // SAFETY: `fd` is valid by sd_listen_fds(3) protocol.
-            let listener = unsafe { TcpListener::from_raw_fd(fd) };
-            listener
-                .set_nonblocking(true)
-                .context("failed to set socket non-blocking")?;
-            tokio::net::TcpListener::from_std(listener)
-                .context("failed to register async socket")?
+            let listener = unsafe { OwnedFd::from_raw_fd(fd) };
+
+            let addr = getsockname(&listener).context("failed to getsockname")?;
+            match addr {
+                SocketAddrAny::V4(_) | SocketAddrAny::V6(_) => {
+                    let listener = std::net::TcpListener::from(listener);
+                    listener
+                        .set_nonblocking(true)
+                        .context("failed to set socket non-blocking")?;
+                    let listener = tokio::net::TcpListener::from_std(listener)
+                        .context("failed to register async socket")?;
+                    (format!("tcp socket {addr:?} from LISTEN_FDS"), listener)
+                }
+                // Unix socket support for axum is currently overly complex.
+                // WAIT: https://github.com/tokio-rs/axum/pull/2479
+                _ => bail!("unsupported socket type from LISTEN_FDS: {addr:?}"),
+            }
         }
     };
 
+    tracing::info!("listening on {listener_display}");
+
     let router = blahd::router(Arc::new(st));
     let _ = sd_notify::notify(true, &[sd_notify::NotifyState::Ready]);
 

blahd/tests/socket_activate.rs

@@ -2,7 +2,8 @@ use std::ffi::CString;
 use std::fs::File;
 use std::io::{Seek, Write};
 use std::net::TcpListener;
-use std::os::fd::{AsFd, AsRawFd};
+use std::os::fd::{AsFd, AsRawFd, OwnedFd};
+use std::os::unix::net::UnixListener;
 use std::process::abort;
 use std::ptr::null;
 use std::time::Duration;
@@ -13,6 +14,7 @@ use nix::sys::memfd::{memfd_create, MemFdCreateFlag};
 use nix::sys::signal::{kill, Signal};
 use nix::sys::wait::{waitpid, WaitStatus};
 use nix::unistd::{alarm, dup2, fork, getpid, ForkResult};
+use rstest::rstest;
 use tokio::io::stderr;
 
 const TIMEOUT_SEC: u32 = 1;
@@ -28,10 +30,22 @@ systemd = true
 base_url = "http://example.com"
 "#;
 
-#[test]
-fn socket_activate() {
-    let listener = TcpListener::bind("127.0.0.1:0").unwrap();
-    let local_port = listener.local_addr().unwrap().port();
+#[rstest]
+#[case::tcp(false)]
+#[case::unix(true)]
+fn socket_activate(#[case] unix_socket: bool) {
+    let socket_dir;
+    let (local_port, listener) = if unix_socket {
+        socket_dir = tempfile::tempdir().unwrap();
+        let listener = UnixListener::bind(socket_dir.path().join("socket")).unwrap();
+        // Port is unused.
+        (0, OwnedFd::from(listener))
+    } else {
+        let listener = TcpListener::bind("127.0.0.1:0").unwrap();
+        let local_port = listener.local_addr().unwrap().port();
+        (local_port, OwnedFd::from(listener))
+    };
+
     let rt = tokio::runtime::Builder::new_current_thread()
         .enable_all()
         .build()
@@ -89,11 +103,11 @@ fn socket_activate() {
             }
         }
         ForkResult::Parent { child } => {
-            {
-                scopeguard::defer! {
-                    let _ = kill(child, Signal::SIGKILL);
-                }
+            let guard = scopeguard::guard((), |()| {
+                let _ = kill(child, Signal::SIGKILL);
+            });
 
+            if !unix_socket {
                 let resp = rt.block_on(async {
                     let url = format!("http://127.0.0.1:{local_port}/_blah/room?filter=public");
                     let fut = async {
@@ -111,13 +125,20 @@ fn socket_activate() {
                         .unwrap()
                 });
                 assert_eq!(resp, r#"{"rooms":[]}"#);
+                // Trigger the killer.
+                drop(guard);
             }
 
             let st = waitpid(child, None).unwrap();
-            assert!(
-                matches!(st, WaitStatus::Signaled(_, Signal::SIGKILL, _)),
-                "unexpected exit status {st:?}",
-            );
+            if unix_socket {
+                // Fail with unsupported error.
+                assert!(matches!(st, WaitStatus::Exited(_, 1)));
+            } else {
+                assert!(
+                    matches!(st, WaitStatus::Signaled(_, Signal::SIGKILL, _)),
+                    "unexpected exit status {st:?}",
+                );
+            }
         }
     }
 }