First stab at a handler framework; a basic chain-of-responsibility pattern

This is intended to make middleware a forefront technology.

Signed-off-by: Erik Hollensbe <linux@hollensbe.org>

Cargo.toml

@@ -8,3 +8,4 @@ edition = "2021"
 [dependencies]
 hyper = { version = "*", features = [ "http1", "http2", "server", "runtime", "tcp", "stream" ] }
 http = "*"
+async-trait = "*"

src/handler.rs

@@ -0,0 +1,50 @@
+use crate::Params;
+
+use async_trait::async_trait;
+use hyper::{Error, Request, Response};
+
+pub type HandlerFunc<T, R> =
+    dyn Fn(&Request<T>, &Params, Option<&Response<R>>) -> Result<Response<R>, Error>;
+
+#[async_trait]
+pub trait Handler<R>
+where
+    Self: Send + Sync + 'static,
+{
+    async fn perform(&self, response: Option<&Response<R>>) -> Result<Response<R>, Error>;
+}
+
+pub struct BasicHandler<T, R>
+where
+    T: Send + Sync + 'static,
+    R: Send + Sync + 'static,
+{
+    req: Request<T>,
+    params: Params,
+    next: Option<&'static BasicHandler<T, R>>,
+    func: &'static HandlerFunc<T, R>,
+}
+
+impl<T, R> BasicHandler<T, R>
+where
+    T: Send + Sync + 'static,
+    R: Send + Sync + 'static,
+{
+}
+
+#[async_trait]
+impl<T, R> Handler<R> for BasicHandler<T, R>
+where
+    Self: Send + Sync,
+    R: Copy + Send + Sync + Sized + 'static,
+    T: Copy + Send + Sync + Sized + 'static,
+{
+    async fn perform(&self, response: Option<&Response<R>>) -> Result<Response<R>, Error> {
+        let response = (*self.func)(&self.req, &self.params, response)?;
+        if self.next.is_some() {
+            return Ok(self.next.unwrap().perform(Some(&response)).await?);
+        }
+
+        Ok(response)
+    }
+}

src/lib.rs

@@ -1,8 +1,13 @@
-#[cfg(test)]
-mod tests {
-    #[test]
-    fn it_works() {
-        let result = 2 + 2;
-        assert_eq!(result, 4);
-    }
+pub mod handler;
+
+use crate::handler::BasicHandler;
+
+use std::collections::BTreeMap;
+
+#[derive(Debug, Clone)]
+pub struct Params(BTreeMap<String, String>);
+
+pub struct App {
+    #[allow(dead_code)] // FIXME remove
+    routes: BTreeMap<String, BasicHandler<hyper::Body, hyper::Body>>,
 }