Add AgentManager::ping

The GraphQL query `nodeStatusList` will use this method rather than
creating a raw `Ping` message.

CHANGELOG.md

@@ -9,6 +9,8 @@ Versioning](https://semver.org/spec/v2.0.0.html).
 
 ### Added
 
+- `AgentManager::ping` method to measure the latency between the agent manager
+  and a host.
 - `AgentManager::reboot` method to reboot a host.
 
 ## [0.18.0] - 2024-02-26

examples/minireview.rs

@@ -94,6 +94,10 @@ impl AgentManager for Manager {
         bail!("Not supported")
     }
 
+    async fn ping(&self, hostname: &str) -> Result<i64, Error> {
+        bail!("Host {hostname} is unreachable")
+    }
+
     async fn reboot(&self, hostname: &str) -> Result<(), Error> {
         bail!("Host {hostname} is unreachable")
     }

src/graphql.rs

@@ -86,6 +86,14 @@ pub trait AgentManager: Send + Sync {
     ) -> Result<HashMap<String, Vec<(String, String)>>, anyhow::Error>;
     async fn send_and_recv(&self, key: &str, msg: &[u8]) -> Result<Vec<u8>, anyhow::Error>;
 
+    /// Sends a ping message to the given host and waits for a response. Returns
+    /// the round-trip time in microseconds.
+    async fn ping(&self, _hostname: &str) -> Result<i64, anyhow::Error> {
+        // TODO: This body is only to avoid breaking changes. It should be
+        // removed when all the implementations are updated. See #144.
+        anyhow::bail!("not implemented")
+    }
+
     /// Reboots the node with the given hostname.
     async fn reboot(&self, _hostname: &str) -> Result<(), anyhow::Error> {
         // TODO: This body is only to avoid breaking changes. It should be
@@ -568,6 +576,10 @@ impl AgentManager for MockAgentManager {
         unimplemented!()
     }
 
+    async fn ping(&self, _hostname: &str) -> Result<i64, anyhow::Error> {
+        unimplemented!()
+    }
+
     async fn reboot(&self, _hostname: &str) -> Result<(), anyhow::Error> {
         unimplemented!()
     }

src/graphql/node/status.rs

@@ -72,6 +72,8 @@ async fn load(
                     },
                 );
 
+                // TODO: Refactor this code to use `AgentManager::ping` after
+                // `review` implements it. See #144.
                 let start = Utc::now().timestamp_micros();
                 if let Ok(response) = agents.send_and_recv(&key, &ping_msg).await {
                     let end = Utc::now().timestamp_micros();