Return Result when creating DaprHttpServer (#253)

Especially when running custom docker setups, the container that
contains the sidecar may not be running exactly when the Rust code
starts running.

With this patch, this can be handled on the user side (e.g. the
connection can be retried multiple times with timeouts in between).

Signed-off-by: Leon Matthes <leon.matthes@kdab.com>
Co-authored-by: Mike Nguyen <hey@mike.ee>

dapr/src/server/http.rs

@@ -84,6 +84,12 @@ pub struct DaprHttpServer {
 
 impl DaprHttpServer {
     /// Creates a new instance of the Dapr HTTP server with default options.
+    ///
+    /// # Panics
+    ///
+    /// This function panics if the Dapr Sidecar cannot be reached!
+    /// For a non-panicking version that allows you to handle any errors yourself, see:
+    /// [DaprHttpServer::try_new_with_dapr_port]
     pub async fn new() -> Self {
         let dapr_port: u16 = std::env::var("DAPR_GRPC_PORT")
             .unwrap_or("3501".into())
@@ -92,19 +98,38 @@ impl DaprHttpServer {
         Self::with_dapr_port(dapr_port).await
     }
 
+    /// Creates a new instance of the Dapr HTTP server that connects to the Dapr sidecar on the
+    /// given dapr_port.
+    ///
+    /// # Panics
+    ///
+    /// This function panics if the Dapr Sidecar cannot be reached!
+    /// For a non-panicking version that allows you to handle any errors yourself, see:
+    /// [DaprHttpServer::try_new_with_dapr_port]
     pub async fn with_dapr_port(dapr_port: u16) -> Self {
-        let dapr_addr = format!("https://127.0.0.1:{}", dapr_port);
-
-        let cc = match TonicClient::connect(dapr_addr).await {
+        match Self::try_new_with_dapr_port(dapr_port).await {
             Ok(c) => c,
             Err(err) => panic!("failed to connect to dapr: {}", err),
-        };
+        }
+    }
+
+    /// Creates a new instance of the Dapr HTTP server that connects to the Dapr sidecar on the
+    /// given dapr_port.
+    ///
+    /// In contrast to the other functions that create a DaprHttpServer, this function does
+    /// not panic, but instead returns a Result.
+    pub async fn try_new_with_dapr_port(
+        dapr_port: u16,
+    ) -> Result<Self, Box<dyn std::error::Error>> {
+        let dapr_addr = format!("https://127.0.0.1:{}", dapr_port);
+
+        let cc = TonicClient::connect(dapr_addr).await?;
         let rt = ActorRuntime::new(cc);
 
-        DaprHttpServer {
+        Ok(DaprHttpServer {
             actor_runtime: Arc::new(rt),
             shutdown_signal: None,
-        }
+        })
     }
 
     pub fn with_graceful_shutdown<F>(self, signal: F) -> Self
@@ -138,7 +163,7 @@ impl DaprHttpServer {
             .unwrap_or(8080);
 
         let address = format!("127.0.0.1:{}", port.unwrap_or(default_port));
-        let listener = TcpListener::bind(address).await.unwrap();
+        let listener = TcpListener::bind(address).await?;
 
         let server = axum::serve(listener, app.into_make_service());