Enforce timeout for system DNS resolution

src/net.rs

@@ -126,10 +126,16 @@ pub(crate) async fn resolve_host_with_doh_tls(
         return Ok(vec![SocketAddr::new(ip, 0)]);
     }
     let Some(dns_server) = dns_server else {
-        return tokio::net::lookup_host((host, 0))
-            .await
-            .map(|addrs| addrs.collect())
-            .map_err(|err| FetchError::Runtime(format!("lookup {host}: {err}")));
+        return resolve_system_host_with(
+            host,
+            timeout,
+            Box::pin(async move {
+                tokio::net::lookup_host((host, 0))
+                    .await
+                    .map(|addrs| addrs.collect())
+            }),
+        )
+        .await;
     };
 
     let addrs = if is_doh_dns_server(dns_server) {
@@ -144,6 +150,23 @@ pub(crate) async fn resolve_host_with_doh_tls(
         .collect())
 }
 
+type SystemLookupFuture<'a> =
+    Pin<Box<dyn Future<Output = std::io::Result<Vec<SocketAddr>>> + Send + 'a>>;
+
+async fn resolve_system_host_with(
+    host: &str,
+    timeout: TimeoutBudget,
+    system_lookup: SystemLookupFuture<'_>,
+) -> Result<Vec<SocketAddr>, FetchError> {
+    timeout
+        .run(async move {
+            system_lookup
+                .await
+                .map_err(|err| FetchError::Runtime(format!("lookup {host}: {err}")))
+        })
+        .await
+}
+
 async fn resolve_host_family(
     host: &str,
     port: u16,
@@ -1408,6 +1431,20 @@ async fn timeout_fetch<T>(
 mod tests {
     use super::*;
 
+    #[tokio::test]
+    async fn system_host_resolution_honors_timeout_budget() {
+        let timeout = Duration::from_millis(10);
+        let err = resolve_system_host_with(
+            "example.com",
+            TimeoutBudget::new(Some(timeout)),
+            Box::pin(std::future::pending::<std::io::Result<Vec<SocketAddr>>>()),
+        )
+        .await
+        .unwrap_err();
+
+        assert_eq!(err.to_string(), "request timed out after 10ms");
+    }
+
     #[test]
     fn host_header_value_brackets_ipv6_literals() {
         let url = Url::parse("http://[::1]/").unwrap();