rpc: Implement the auth:get_rpc_protocol method.

crates/arti-rpcserver/src/connection/auth.rs

@@ -9,6 +9,55 @@ use std::sync::Arc;
 use super::Connection;
 use tor_rpcbase as rpc;
 
+/// Declare the get_rpc_protocol method.
+mod get_rpc_protocol {
+    use super::Connection;
+    use std::sync::Arc;
+    use tor_rpcbase as rpc;
+
+    /// Method to inquire about the RPC protocol.
+    #[derive(Debug, serde::Deserialize)]
+    struct GetRpcProtocol {}
+
+    /// Reply to the [`GetRpcProtocol`] method
+    #[derive(Debug, serde::Serialize)]
+    struct GetProtocolReply {
+        /// The version of the RPC protocol that this server speaks.
+        // TODO RPC: Should this be a list?
+        version: RpcProtocolId,
+    }
+
+    /// Identifier for a version of this RPC meta-protocol.
+    #[derive(Debug, Copy, Clone, serde::Serialize)]
+    enum RpcProtocolId {
+        /// Alpha version of the protocol.  Things might break between here and the
+        /// stable protocol.
+        ///
+        /// TODO RPC: CHange this to v0.
+        #[serde(rename = "alpha")]
+        Alpha,
+    }
+    rpc::decl_method! {"auth:get_rpc_protocol" => GetRpcProtocol}
+    impl rpc::Method for GetRpcProtocol {
+        type Output = GetProtocolReply;
+        type Update = rpc::NoUpdates;
+    }
+
+    /// Describe which version of the RPC protocol our connection implements.
+    async fn conn_get_rpc_protocol(
+        _conn: Arc<Connection>,
+        _method: Box<GetRpcProtocol>,
+        _ctx: Box<dyn rpc::Context>,
+    ) -> Result<GetProtocolReply, rpc::RpcError> {
+        Ok(GetProtocolReply {
+            version: RpcProtocolId::Alpha,
+        })
+    }
+    rpc::rpc_invoke_fn! {
+        conn_get_rpc_protocol(Connection, GetRpcProtocol);
+    }
+}
+
 /// The authentication scheme as enumerated in the spec.
 ///
 /// Conceptually, an authentication scheme answers the question "How can the