Use a p2p dbus connection during tests

This removes the requirement of having the DBus daemon running locally,
which is particularly helpful e.g. in a container or for CI.

src/policy_checker/dbus.rs

@@ -36,14 +36,30 @@ pub async fn restrictions_for(user: Uid) -> anyhow::Result<Vec<Restriction>, any
 
     #[cfg(feature = "integration_test")]
     let proxy = {
+        use tokio::net::UnixStream;
+
         // During integration testing, we want to connect to a private
         // bus name to avoid clashes with existing system services.
-        let connection = zbus::Connection::session().await?;
-        let dbus_name = std::env::var("TEST_DBUS_SERVICE_NAME")
-            .expect("The test has not set the TEST_DBUS_SERVICE_NAME environment variable to the private bus name prior to attempting name resolution");
+        let socket_path = std::env::var("TEST_DBUS_SOCKET")
+            .expect("The test has not set the TEST_DBUS_SOCKET environment variable to the unix socket to connect to");
+
+        let socket = loop {
+            match UnixStream::connect(&socket_path).await {
+                Ok(stream) => break stream,
+                Err(e) if e.kind() == std::io::ErrorKind::ConnectionRefused => {
+                    tokio::task::yield_now().await;
+                    continue;
+                }
+                Err(e) => anyhow::bail!(e),
+            }
+        };
+
+        let connection = zbus::ConnectionBuilder::unix_stream(socket)
+            .p2p()
+            .build()
+            .await?;
+
         MalcontentDnsProxy::builder(&connection)
-            .destination(zbus_names::UniqueName::try_from(dbus_name).unwrap())
-            .unwrap()
             .build()
             .await
             .expect("Unable to build DBus proxy object")