add API to gracefully terminate name server & resolver

src/container.rs

@@ -137,11 +137,12 @@ impl Container {
 
     pub fn spawn(&self, cmd: &[&str]) -> Result<Child> {
         let mut command = Command::new("docker");
+        command.stdout(Stdio::piped()).stderr(Stdio::piped());
         command.args(["exec", "-t", &self.inner.id]).args(cmd);
 
         let inner = command.spawn()?;
         Ok(Child {
-            inner,
+            inner: Some(inner),
             _container: self.inner.clone(),
         })
     }
@@ -164,13 +165,22 @@ struct Inner {
 // runs inside of, to prevent the scenario of the container being destroyed _before_
 // the child is killed
 pub struct Child {
-    inner: process::Child,
+    inner: Option<process::Child>,
     _container: Arc<Inner>,
 }
 
+impl Child {
+    pub fn wait(mut self) -> Result<Output> {
+        let output = self.inner.take().expect("unreachable").wait_with_output()?;
+        output.try_into()
+    }
+}
+
 impl Drop for Child {
     fn drop(&mut self) {
-        let _ = self.inner.kill();
+        if let Some(mut inner) = self.inner.take() {
+            let _ = inner.kill();
+        }
     }
 }
 

src/name_server.rs

@@ -152,7 +152,7 @@ impl<'a> NameServer<'a, Stopped> {
         Ok(NameServer {
             container,
             zone_file,
-            state: Running { _child: child },
+            state: Running { child },
         })
     }
 }
@@ -188,7 +188,7 @@ impl<'a> NameServer<'a, Signed> {
         Ok(NameServer {
             container,
             zone_file,
-            state: Running { _child: child },
+            state: Running { child },
         })
     }
 
@@ -209,6 +209,31 @@ impl<'a> NameServer<'a, Signed> {
     }
 }
 
+impl<'a> NameServer<'a, Running> {
+    /// gracefully terminates the name server collecting all logs
+    pub fn terminate(self) -> Result<String> {
+        let pidfile = "/run/nsd/nsd.pid";
+        // if `terminate` is called right after `start` NSD may not have had the chance to create
+        // the PID file so if it doesn't exist wait for a bit before invoking `kill`
+        let kill = format!(
+            "test -f {pidfile} || sleep 1
+kill -TERM $(cat {pidfile})"
+        );
+        self.container.status_ok(&["sh", "-c", &kill])?;
+        let output = self.state.child.wait()?;
+
+        if !output.status.success() {
+            return Err("could not terminate the `unbound` process".into());
+        }
+
+        assert!(
+            output.stderr.is_empty(),
+            "stderr should be returned if not empty"
+        );
+        Ok(output.stdout)
+    }
+}
+
 impl<'a, S> NameServer<'a, S> {
     pub fn ipv4_addr(&self) -> Ipv4Addr {
         self.container.ipv4_addr()
@@ -238,7 +263,7 @@ pub struct Signed {
 }
 
 pub struct Running {
-    _child: Child,
+    child: Child,
 }
 
 fn primary_ns(ns_count: usize) -> FQDN<'static> {
@@ -345,4 +370,14 @@ mod tests {
 
         Ok(())
     }
+
+    #[test]
+    fn terminate_works() -> Result<()> {
+        let ns = NameServer::new(FQDN::ROOT)?.start()?;
+        let logs = ns.terminate()?;
+
+        assert!(logs.contains("nsd starting"));
+
+        Ok(())
+    }
 }

src/recursive_resolver.rs

@@ -7,7 +7,7 @@ use crate::Result;
 
 pub struct RecursiveResolver {
     container: Container,
-    _child: Child,
+    child: Child,
 }
 
 impl RecursiveResolver {
@@ -37,15 +37,33 @@ impl RecursiveResolver {
 
         let child = container.spawn(&["unbound", "-d"])?;
 
-        Ok(Self {
-            _child: child,
-            container,
-        })
+        Ok(Self { child, container })
     }
 
     pub fn ipv4_addr(&self) -> Ipv4Addr {
         self.container.ipv4_addr()
     }
+
+    /// gracefully terminates the name server collecting all logs
+    pub fn terminate(self) -> Result<String> {
+        let pidfile = "/run/unbound.pid";
+        let kill = format!(
+            "test -f {pidfile} || sleep 1
+kill -TERM $(cat {pidfile})"
+        );
+        self.container.status_ok(&["sh", "-c", &kill])?;
+        let output = self.child.wait()?;
+
+        if !output.status.success() {
+            return Err("could not terminate the `unbound` process".into());
+        }
+
+        assert!(
+            output.stderr.is_empty(),
+            "stderr should be returned if not empty"
+        );
+        Ok(output.stdout)
+    }
 }
 
 fn unbound_conf(use_dnssec: bool) -> String {
@@ -229,4 +247,15 @@ mod tests {
 
         Ok(())
     }
+
+    #[test]
+    fn terminate_works() -> Result<()> {
+        let resolver = RecursiveResolver::start(&[], &[])?;
+        let logs = resolver.terminate()?;
+
+        eprintln!("{logs}");
+        assert!(logs.contains("start of service"));
+
+        Ok(())
+    }
 }