Support closures as handlers (#19)

Author: srijs

lambda-runtime/src/runtime.rs

@@ -1,4 +1,4 @@
-use std::{error::Error, result};
+use std::{error::Error, marker::PhantomData, result};
 
 use serde;
 use serde_json;
@@ -12,7 +12,19 @@ use tokio::runtime::Runtime as TokioRuntime;
 const MAX_RETRIES: i8 = 3;
 
 /// Functions acting as a handler must conform to this type.
-pub type Handler<E, O> = fn(E, Context) -> Result<O, HandlerError>;
+pub trait Handler<E, O> {
+    /// Run the handler.
+    fn run(&mut self, event: E, ctx: Context) -> Result<O, HandlerError>;
+}
+
+impl<F, E, O> Handler<E, O> for F
+where
+    F: FnMut(E, Context) -> Result<O, HandlerError>,
+{
+    fn run(&mut self, event: E, ctx: Context) -> Result<O, HandlerError> {
+        (*self)(event, ctx)
+    }
+}
 
 /// Creates a new runtime and begins polling for events using Lambda's Runtime APIs.
 ///
@@ -22,9 +34,9 @@ pub type Handler<E, O> = fn(E, Context) -> Result<O, HandlerError>;
 ///
 /// # Panics
 /// The function panics if the Lambda environment variables are not set.
-pub fn start<E, O>(f: Handler<E, O>, runtime: Option<TokioRuntime>)
+pub fn start<E, O>(f: impl Handler<E, O>, runtime: Option<TokioRuntime>)
 where
-    for<'invocation> E: serde::Deserialize<'invocation>,
+    E: serde::de::DeserializeOwned,
     O: serde::Serialize,
 {
     start_with_config(f, &EnvConfigProvider::new(), runtime)
@@ -53,9 +65,9 @@ macro_rules! lambda {
 /// The function panics if the `ConfigProvider` returns an error from the `get_runtime_api_endpoint()`
 /// or `get_function_settings()` methods. The panic forces AWS Lambda to terminate the environment
 /// and spin up a new one for the next invocation.
-pub(crate) fn start_with_config<E, O, C>(f: Handler<E, O>, config: &C, runtime: Option<TokioRuntime>)
+pub(crate) fn start_with_config<E, O, C>(f: impl Handler<E, O>, config: &C, runtime: Option<TokioRuntime>)
 where
-    for<'invocation> E: serde::Deserialize<'invocation>,
+    E: serde::de::DeserializeOwned,
     O: serde::Serialize,
     C: ConfigProvider,
 {
@@ -100,12 +112,15 @@ where
 ///
 /// # Panics
 /// The function panics if we cannot instantiate a new `RustRuntime` object.
-pub(crate) fn start_with_runtime_client<E, O>(f: Handler<E, O>, func_settings: FunctionSettings, client: RuntimeClient)
-where
-    for<'invocation> E: serde::Deserialize<'invocation>,
+pub(crate) fn start_with_runtime_client<E, O>(
+    f: impl Handler<E, O>,
+    func_settings: FunctionSettings,
+    client: RuntimeClient,
+) where
+    E: serde::de::DeserializeOwned,
     O: serde::Serialize,
 {
-    let lambda_runtime: Runtime<E, O>;
+    let mut lambda_runtime: Runtime<_, E, O>;
     match Runtime::new(f, func_settings, MAX_RETRIES, client) {
         Ok(r) => lambda_runtime = r,
         Err(e) => {
@@ -119,15 +134,16 @@ where
 
 /// Internal representation of the runtime object that polls for events and communicates
 /// with the Runtime APIs
-pub(super) struct Runtime<E, O> {
+pub(super) struct Runtime<F, E, O> {
     runtime_client: RuntimeClient,
-    handler: Handler<E, O>,
+    handler: F,
     max_retries: i8,
     settings: FunctionSettings,
+    _phan: PhantomData<(E, O)>,
 }
 
 // generic methods implementation
-impl<E, O> Runtime<E, O> {
+impl<F, E, O> Runtime<F, E, O> {
     /// Creates a new instance of the `Runtime` object populated with the environment
     /// settings.
     ///
@@ -142,11 +158,11 @@ impl<E, O> Runtime<E, O> {
     /// fails the init if this function returns an error. If we cannot find the
     /// `AWS_LAMBDA_RUNTIME_API` variable in the environment the function panics.
     pub(super) fn new(
-        f: Handler<E, O>,
+        f: F,
         config: FunctionSettings,
         retries: i8,
         client: RuntimeClient,
-    ) -> result::Result<Runtime<E, O>, RuntimeError> {
+    ) -> result::Result<Self, RuntimeError> {
         debug!(
             "Creating new runtime with {} max retries for endpoint {}",
             retries,
@@ -157,21 +173,23 @@ impl<E, O> Runtime<E, O> {
             settings: config,
             handler: f,
             max_retries: retries,
+            _phan: PhantomData,
         })
     }
 }
 
 // implementation of methods that require the Event and Output types
 // to be compatible with `serde`'s Deserialize/Serialize.
-impl<'env, E, O> Runtime<E, O>
+impl<F, E, O> Runtime<F, E, O>
 where
-    for<'de> E: serde::Deserialize<'de>,
+    F: Handler<E, O>,
+    E: serde::de::DeserializeOwned,
     O: serde::Serialize,
 {
     /// Starts the main event loop and begin polling or new events. If one of the
     /// Runtime APIs returns an unrecoverable error this method calls the init failed
     /// API and then panics.
-    fn start(&self) {
+    fn start(&mut self) {
         debug!("Beginning main event loop");
         loop {
             let (event, ctx) = self.get_next_event(0, None);
@@ -238,8 +256,8 @@ where
 
     /// Invoke the handler function. This method is split out of the main loop to
     /// make it testable.
-    pub(super) fn invoke(&self, e: E, ctx: Context) -> Result<O, HandlerError> {
-        (self.handler)(e, ctx)
+    pub(super) fn invoke(&mut self, e: E, ctx: Context) -> Result<O, HandlerError> {
+        (&mut self.handler).run(e, ctx)
     }
 
     /// Attempts to get the next event from the Runtime APIs and keeps retrying