Review comments

README.md

@@ -187,7 +187,7 @@ pub trait Handler<E, O>: Send {
 
 `Handler` provides a default implementation that enables you to provide a Rust closure or function pointer to the `lambda!()` macro.
 
-If your handler is synchronous, you can just return a `Result` from it; if your handler is asynchronous, you can return a `Future` from it.
+Your `Handler` needs to return something which implements `IntoFuture`; `Result` implements `IntoIterator`, so most synchronous `Handler`s will return a `Result`.
 
 Optionally, you can pass your own instance of Tokio runtime to the `lambda!()` macro. See our [`with_custom_runtime.rs` example](https://github.com/awslabs/aws-lambda-rust-runtime/tree/master/lambda-runtime/examples/with_custom_runtime.rs)
 

lambda-runtime-client/src/client.rs

@@ -129,13 +129,13 @@ pub struct RuntimeClient {
 impl RuntimeClient {
     /// Creates a new instance of the Runtime APIclient SDK. The http client has timeouts disabled and
     /// will always send a `Connection: keep-alive` header.
-    pub fn new(endpoint: String, task_executor: TaskExecutor) -> Result<Self, ApiError> {
+    pub fn new(endpoint: String, task_executor: TaskExecutor) -> Self {
         debug!("Starting new HttpRuntimeClient for {}", endpoint);
         // start a tokio core main event loop for hyper
 
         let http_client = Client::builder().executor(task_executor).build_http();
 
-        Ok(RuntimeClient { http_client, endpoint })
+        RuntimeClient { http_client, endpoint }
     }
 }
 

lambda-runtime-client/src/lib.rs

@@ -36,8 +36,7 @@
 //! fn main() {
 //!     let tokio_runtime = TokioRuntime::new().expect("Could not make tokio runtime");
 //!     let runtime_endpoint = String::from("http://localhost:8080");
-//!     let client = RuntimeClient::new(runtime_endpoint, tokio_runtime.executor())
-//!         .expect("Could not initialize client");
+//!     let client = RuntimeClient::new(runtime_endpoint, tokio_runtime.executor());
 //!
 //!     let (event_data, event_context) = client.next_event().wait()
 //!         .expect("Could not retrieve next event");

lambda-runtime/src/runtime.rs

@@ -126,12 +126,7 @@ where
         }
     }
 
-    match RuntimeClient::new(endpoint, task_executor) {
-        Ok(client) => start_with_runtime_client(f, function_config, client),
-        Err(e) => {
-            panic!("Could not create runtime client SDK: {}", e);
-        }
-    }
+    start_with_runtime_client(f, function_config, RuntimeClient::new(endpoint, task_executor))
 }
 
 /// Starts the rust runtime with the given Runtime API client.
@@ -398,8 +393,7 @@ pub(crate) mod tests {
                 .get_runtime_api_endpoint()
                 .expect("Could not get runtime endpoint"),
             runtime.executor(),
-        )
-        .expect("Could not initialize client");
+        );
         let handler = |_e: String, _c: context::Context| -> Result<String, HandlerError> { Ok("hello".to_string()) };
         let retries: i8 = 3;
         let runtime = Runtime::new(