From f4268471b6f4f6e2444ab0f5ee36505596760ca9 Mon Sep 17 00:00:00 2001
From: David Pedersen <david.pdrsn@gmail.com>
Date: Sun, 30 May 2021 13:24:03 +0200
Subject: [PATCH] Break things into modules

---
 src/body.rs     |  10 +-
 src/error.rs    |  70 ++++
 src/extract.rs  | 154 +++++++++
 src/handler.rs  | 198 ++++++++++++
 src/lib.rs      | 837 ++++--------------------------------------------
 src/response.rs |  79 +++++
 src/routing.rs  | 284 ++++++++++++++++
 7 files changed, 848 insertions(+), 784 deletions(-)
 create mode 100644 src/error.rs
 create mode 100644 src/extract.rs
 create mode 100644 src/handler.rs
 create mode 100644 src/response.rs
 create mode 100644 src/routing.rs

diff --git a/src/body.rs b/src/body.rs
index 7b895383..44152377 100644
--- a/src/body.rs
+++ b/src/body.rs
@@ -1,21 +1,23 @@
 use bytes::Buf;
-use http_body::{Body, Empty};
+use http_body::{Body as _, Empty};
 use std::{
     fmt,
     pin::Pin,
     task::{Context, Poll},
 };
 
+pub use hyper::body::Body;
+
 /// A boxed [`Body`] trait object.
 pub struct BoxBody<D, E> {
-    inner: Pin<Box<dyn Body<Data = D, Error = E> + Send + Sync + 'static>>,
+    inner: Pin<Box<dyn http_body::Body<Data = D, Error = E> + Send + Sync + 'static>>,
 }
 
 impl<D, E> BoxBody<D, E> {
     /// Create a new `BoxBody`.
     pub fn new<B>(body: B) -> Self
     where
-        B: Body<Data = D, Error = E> + Send + Sync + 'static,
+        B: http_body::Body<Data = D, Error = E> + Send + Sync + 'static,
         D: Buf,
     {
         Self {
@@ -40,7 +42,7 @@ impl<D, E> fmt::Debug for BoxBody<D, E> {
     }
 }
 
-impl<D, E> Body for BoxBody<D, E>
+impl<D, E> http_body::Body for BoxBody<D, E>
 where
     D: Buf,
 {
diff --git a/src/error.rs b/src/error.rs
new file mode 100644
index 00000000..0b8088b7
--- /dev/null
+++ b/src/error.rs
@@ -0,0 +1,70 @@
+use std::convert::Infallible;
+
+use http::{Response, StatusCode};
+use tower::BoxError;
+
+#[derive(Debug, thiserror::Error)]
+#[non_exhaustive]
+pub enum Error {
+    #[error("failed to deserialize the request body")]
+    DeserializeRequestBody(#[source] serde_json::Error),
+
+    #[error("failed to serialize the response body")]
+    SerializeResponseBody(#[source] serde_json::Error),
+
+    #[error("failed to consume the body")]
+    ConsumeRequestBody(#[source] hyper::Error),
+
+    #[error("URI contained no query string")]
+    QueryStringMissing,
+
+    #[error("failed to deserialize query string")]
+    DeserializeQueryString(#[source] serde_urlencoded::de::Error),
+
+    #[error("failed generating the response body")]
+    ResponseBody(#[source] BoxError),
+
+    #[error("handler service returned an error")]
+    Service(#[source] BoxError),
+
+    #[error("request extension of type `{type_name}` was not set")]
+    MissingExtension { type_name: &'static str },
+}
+
+impl From<Infallible> for Error {
+    fn from(err: Infallible) -> Self {
+        match err {}
+    }
+}
+
+pub(crate) fn handle_error<B>(error: Error) -> Result<Response<B>, Error>
+where
+    B: Default,
+{
+    fn make_response<B>(status: StatusCode) -> Result<Response<B>, Error>
+    where
+        B: Default,
+    {
+        let mut res = Response::new(B::default());
+        *res.status_mut() = status;
+        Ok(res)
+    }
+
+    match error {
+        Error::DeserializeRequestBody(_)
+        | Error::QueryStringMissing
+        | Error::DeserializeQueryString(_) => make_response(StatusCode::BAD_REQUEST),
+
+        Error::MissingExtension { .. } | Error::SerializeResponseBody(_) => {
+            make_response(StatusCode::INTERNAL_SERVER_ERROR)
+        }
+
+        Error::Service(err) => match err.downcast::<Error>() {
+            Ok(err) => Err(*err),
+            Err(err) => Err(Error::Service(err)),
+        },
+
+        err @ Error::ConsumeRequestBody(_) => Err(err),
+        err @ Error::ResponseBody(_) => Err(err),
+    }
+}
diff --git a/src/extract.rs b/src/extract.rs
new file mode 100644
index 00000000..acfccf6f
--- /dev/null
+++ b/src/extract.rs
@@ -0,0 +1,154 @@
+use crate::{body::Body, Error};
+use futures_util::{future, ready};
+use http::Request;
+use pin_project::pin_project;
+use serde::de::DeserializeOwned;
+use std::{
+    future::Future,
+    pin::Pin,
+    task::{Context, Poll},
+};
+
+pub trait FromRequest: Sized {
+    type Future: Future<Output = Result<Self, Error>> + Send;
+
+    fn from_request(req: &mut Request<Body>) -> Self::Future;
+}
+
+impl<T> FromRequest for Option<T>
+where
+    T: FromRequest,
+{
+    type Future = OptionFromRequestFuture<T::Future>;
+
+    fn from_request(req: &mut Request<Body>) -> Self::Future {
+        OptionFromRequestFuture(T::from_request(req))
+    }
+}
+
+#[pin_project]
+pub struct OptionFromRequestFuture<F>(#[pin] F);
+
+impl<F, T> Future for OptionFromRequestFuture<F>
+where
+    F: Future<Output = Result<T, Error>>,
+{
+    type Output = Result<Option<T>, Error>;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let value = ready!(self.project().0.poll(cx));
+        Poll::Ready(Ok(value.ok()))
+    }
+}
+
+#[derive(Debug, Clone, Copy)]
+pub struct Query<T>(T);
+
+impl<T> Query<T> {
+    pub fn into_inner(self) -> T {
+        self.0
+    }
+}
+
+impl<T> FromRequest for Query<T>
+where
+    T: DeserializeOwned + Send,
+{
+    type Future = future::Ready<Result<Self, Error>>;
+
+    fn from_request(req: &mut Request<Body>) -> Self::Future {
+        let result = (|| {
+            let query = req.uri().query().ok_or(Error::QueryStringMissing)?;
+            let value = serde_urlencoded::from_str(query).map_err(Error::DeserializeQueryString)?;
+            Ok(Query(value))
+        })();
+
+        future::ready(result)
+    }
+}
+
+#[derive(Debug, Clone, Copy)]
+pub struct Json<T>(T);
+
+impl<T> Json<T> {
+    pub fn into_inner(self) -> T {
+        self.0
+    }
+}
+
+impl<T> FromRequest for Json<T>
+where
+    T: DeserializeOwned,
+{
+    type Future = future::BoxFuture<'static, Result<Self, Error>>;
+
+    fn from_request(req: &mut Request<Body>) -> Self::Future {
+        // TODO(david): require the body to have `content-type: application/json`
+
+        let body = std::mem::take(req.body_mut());
+
+        Box::pin(async move {
+            let bytes = hyper::body::to_bytes(body)
+                .await
+                .map_err(Error::ConsumeRequestBody)?;
+            let value = serde_json::from_slice(&bytes).map_err(Error::DeserializeRequestBody)?;
+            Ok(Json(value))
+        })
+    }
+}
+
+#[derive(Debug, Clone, Copy)]
+pub struct Extension<T>(T);
+
+impl<T> Extension<T> {
+    pub fn into_inner(self) -> T {
+        self.0
+    }
+}
+
+impl<T> FromRequest for Extension<T>
+where
+    T: Clone + Send + Sync + 'static,
+{
+    type Future = future::Ready<Result<Self, Error>>;
+
+    fn from_request(req: &mut Request<Body>) -> Self::Future {
+        let result = (|| {
+            let value = req
+                .extensions()
+                .get::<T>()
+                .ok_or_else(|| Error::MissingExtension {
+                    type_name: std::any::type_name::<T>(),
+                })
+                .map(|x| x.clone())?;
+            Ok(Extension(value))
+        })();
+
+        future::ready(result)
+    }
+}
+
+// TODO(david): can we add a length limit somehow? Maybe a const generic?
+#[derive(Debug, Clone)]
+pub struct Bytes(bytes::Bytes);
+
+impl Bytes {
+    pub fn into_inner(self) -> bytes::Bytes {
+        self.0
+    }
+}
+
+impl FromRequest for Bytes {
+    type Future = future::BoxFuture<'static, Result<Self, Error>>;
+
+    fn from_request(req: &mut Request<Body>) -> Self::Future {
+        let body = std::mem::take(req.body_mut());
+
+        Box::pin(async move {
+            let bytes = hyper::body::to_bytes(body)
+                .await
+                .map_err(Error::ConsumeRequestBody)?;
+            Ok(Bytes(bytes))
+        })
+    }
+}
diff --git a/src/handler.rs b/src/handler.rs
new file mode 100644
index 00000000..7c651bff
--- /dev/null
+++ b/src/handler.rs
@@ -0,0 +1,198 @@
+use crate::{body::Body, error::Error, extract::FromRequest, response::IntoResponse};
+use async_trait::async_trait;
+use futures_util::future;
+use http::{Request, Response};
+use std::{
+    future::Future,
+    marker::PhantomData,
+    task::{Context, Poll},
+};
+use tower::{BoxError, Layer, Service, ServiceExt};
+
+mod sealed {
+    pub trait HiddentTrait {}
+    pub struct Hidden;
+    impl HiddentTrait for Hidden {}
+}
+
+#[async_trait]
+pub trait Handler<B, In>: Sized {
+    type Response: IntoResponse<B>;
+
+    // This seals the trait. We cannot use the regular "sealed super trait" approach
+    // due to coherence.
+    #[doc(hidden)]
+    type Sealed: sealed::HiddentTrait;
+
+    async fn call(self, req: Request<Body>) -> Result<Self::Response, Error>;
+
+    fn layer<L>(self, layer: L) -> Layered<L::Service, In>
+    where
+        L: Layer<HandlerSvc<Self, B, In>>,
+    {
+        Layered::new(layer.layer(HandlerSvc::new(self)))
+    }
+}
+
+#[async_trait]
+impl<F, Fut, B, Res> Handler<B, ()> for F
+where
+    F: Fn(Request<Body>) -> Fut + Send + Sync,
+    Fut: Future<Output = Result<Res, Error>> + Send,
+    Res: IntoResponse<B>,
+{
+    type Response = Res;
+
+    type Sealed = sealed::Hidden;
+
+    async fn call(self, req: Request<Body>) -> Result<Self::Response, Error> {
+        self(req).await
+    }
+}
+
+macro_rules! impl_handler {
+    ( $head:ident $(,)? ) => {
+        #[async_trait]
+        #[allow(non_snake_case)]
+        impl<F, Fut, B, Res, $head> Handler<B, ($head,)> for F
+        where
+            F: Fn(Request<Body>, $head) -> Fut + Send + Sync,
+            Fut: Future<Output = Result<Res, Error>> + Send,
+            Res: IntoResponse<B>,
+            $head: FromRequest + Send,
+        {
+            type Response = Res;
+
+            type Sealed = sealed::Hidden;
+
+            async fn call(self, mut req: Request<Body>) -> Result<Self::Response, Error> {
+                let $head = $head::from_request(&mut req).await?;
+                let res = self(req, $head).await?;
+                Ok(res)
+            }
+        }
+    };
+
+    ( $head:ident, $($tail:ident),* $(,)? ) => {
+        #[async_trait]
+        #[allow(non_snake_case)]
+        impl<F, Fut, B, Res, $head, $($tail,)*> Handler<B, ($head, $($tail,)*)> for F
+        where
+            F: Fn(Request<Body>, $head, $($tail,)*) -> Fut + Send + Sync,
+            Fut: Future<Output = Result<Res, Error>> + Send,
+            Res: IntoResponse<B>,
+            $head: FromRequest + Send,
+            $( $tail: FromRequest + Send, )*
+        {
+            type Response = Res;
+
+            type Sealed = sealed::Hidden;
+
+            async fn call(self, mut req: Request<Body>) -> Result<Self::Response, Error> {
+                let $head = $head::from_request(&mut req).await?;
+                $(
+                    let $tail = $tail::from_request(&mut req).await?;
+                )*
+                let res = self(req, $head, $($tail,)*).await?;
+                Ok(res)
+            }
+        }
+
+        impl_handler!($($tail,)*);
+    };
+}
+
+impl_handler!(T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15, T16);
+
+pub struct Layered<S, T> {
+    svc: S,
+    _input: PhantomData<fn() -> T>,
+}
+
+impl<S, T> Clone for Layered<S, T>
+where
+    S: Clone,
+{
+    fn clone(&self) -> Self {
+        Self::new(self.svc.clone())
+    }
+}
+
+#[async_trait]
+impl<S, B, T> Handler<B, T> for Layered<S, T>
+where
+    S: Service<Request<Body>, Response = Response<B>> + Send,
+    S::Error: Into<BoxError>,
+    S::Future: Send,
+{
+    type Response = S::Response;
+
+    type Sealed = sealed::Hidden;
+
+    async fn call(self, req: Request<Body>) -> Result<Self::Response, Error> {
+        self.svc
+            .oneshot(req)
+            .await
+            .map_err(|err| Error::Service(err.into()))
+    }
+}
+
+impl<S, T> Layered<S, T> {
+    pub(crate) fn new(svc: S) -> Self {
+        Self {
+            svc,
+            _input: PhantomData,
+        }
+    }
+}
+
+pub struct HandlerSvc<H, B, T> {
+    handler: H,
+    _input: PhantomData<fn() -> (B, T)>,
+}
+
+impl<H, B, T> HandlerSvc<H, B, T> {
+    pub(crate) fn new(handler: H) -> Self {
+        Self {
+            handler,
+            _input: PhantomData,
+        }
+    }
+}
+
+impl<H, B, T> Clone for HandlerSvc<H, B, T>
+where
+    H: Clone,
+{
+    fn clone(&self) -> Self {
+        Self {
+            handler: self.handler.clone(),
+            _input: PhantomData,
+        }
+    }
+}
+
+impl<H, B, T> Service<Request<Body>> for HandlerSvc<H, B, T>
+where
+    H: Handler<B, T> + Clone + Send + 'static,
+    H::Response: 'static,
+{
+    type Response = Response<B>;
+    type Error = Error;
+    type Future = future::BoxFuture<'static, Result<Self::Response, Self::Error>>;
+
+    fn poll_ready(&mut self, _cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+        // HandlerSvc can only be constructed from async functions which are always ready, or from
+        // `Layered` which bufferes in `<Layered as Handler>::call` and is therefore also always
+        // ready.
+        Poll::Ready(Ok(()))
+    }
+
+    fn call(&mut self, req: Request<Body>) -> Self::Future {
+        let handler = self.handler.clone();
+        Box::pin(async move {
+            let res = Handler::call(handler, req).await?.into_response()?;
+            Ok(res)
+        })
+    }
+}
diff --git a/src/lib.rs b/src/lib.rs
index 82378f51..ad3068e0 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -4,14 +4,19 @@
 
 Improvements to make:
 
-Break stuff up into modules
-
 Support extracting headers, perhaps via `headers::Header`?
 
 Tests
 
 */
 
+use self::{
+    body::{Body, BoxBody},
+    extract::FromRequest,
+    handler::{Handler, HandlerSvc},
+    response::IntoResponse,
+    routing::{EmptyRouter, RouteAt},
+};
 use async_trait::async_trait;
 use bytes::Bytes;
 use futures_util::{future, ready};
@@ -28,10 +33,15 @@ use std::{
 };
 use tower::{BoxError, Layer, Service, ServiceExt};
 
-mod body;
-pub use body::BoxBody;
+pub mod body;
+pub mod extract;
+pub mod handler;
+pub mod response;
+pub mod routing;
 
-pub use hyper::body::Body;
+mod error;
+
+pub use self::error::Error;
 
 pub fn app() -> App<EmptyRouter> {
     App {
@@ -57,712 +67,6 @@ impl<R> App<R> {
     }
 }
 
-#[derive(Debug, Clone)]
-pub struct RouteAt<R> {
-    app: App<R>,
-    route_spec: Bytes,
-}
-
-impl<R> RouteAt<R> {
-    pub fn get<F, B, T>(self, handler_fn: F) -> RouteBuilder<Route<HandlerSvc<F, B, T>, R>>
-    where
-        F: Handler<B, T>,
-    {
-        self.add_route(handler_fn, Method::GET)
-    }
-
-    pub fn get_service<S, B>(self, service: S) -> RouteBuilder<Route<S, R>>
-    where
-        S: Service<Request<Body>, Response = Response<B>> + Clone,
-        S::Error: Into<BoxError>,
-    {
-        self.add_route_service(service, Method::GET)
-    }
-
-    pub fn post<F, B, T>(self, handler_fn: F) -> RouteBuilder<Route<HandlerSvc<F, B, T>, R>>
-    where
-        F: Handler<B, T>,
-    {
-        self.add_route(handler_fn, Method::POST)
-    }
-
-    pub fn post_service<S, B>(self, service: S) -> RouteBuilder<Route<S, R>>
-    where
-        S: Service<Request<Body>, Response = Response<B>> + Clone,
-        S::Error: Into<BoxError>,
-    {
-        self.add_route_service(service, Method::POST)
-    }
-
-    fn add_route<H, B, T>(
-        self,
-        handler: H,
-        method: Method,
-    ) -> RouteBuilder<Route<HandlerSvc<H, B, T>, R>>
-    where
-        H: Handler<B, T>,
-    {
-        self.add_route_service(HandlerSvc::new(handler), method)
-    }
-
-    fn add_route_service<S>(self, service: S, method: Method) -> RouteBuilder<Route<S, R>> {
-        let new_app = App {
-            router: Route {
-                service,
-                route_spec: RouteSpec {
-                    method,
-                    spec: self.route_spec.clone(),
-                },
-                fallback: self.app.router,
-                handler_ready: false,
-                fallback_ready: false,
-            },
-        };
-
-        RouteBuilder {
-            app: new_app,
-            route_spec: self.route_spec,
-        }
-    }
-}
-
-pub struct RouteBuilder<R> {
-    app: App<R>,
-    route_spec: Bytes,
-}
-
-impl<R> Clone for RouteBuilder<R>
-where
-    R: Clone,
-{
-    fn clone(&self) -> Self {
-        Self {
-            app: self.app.clone(),
-            route_spec: self.route_spec.clone(),
-        }
-    }
-}
-
-impl<R> RouteBuilder<R> {
-    pub fn at(self, route_spec: &str) -> RouteAt<R> {
-        self.app.at(route_spec)
-    }
-
-    pub fn get<F, B, T>(self, handler_fn: F) -> RouteBuilder<Route<HandlerSvc<F, B, T>, R>>
-    where
-        F: Handler<B, T>,
-    {
-        self.app.at_bytes(self.route_spec).get(handler_fn)
-    }
-
-    pub fn get_service<S, B>(self, service: S) -> RouteBuilder<Route<S, R>>
-    where
-        S: Service<Request<Body>, Response = Response<B>> + Clone,
-        S::Error: Into<BoxError>,
-    {
-        self.app.at_bytes(self.route_spec).get_service(service)
-    }
-
-    pub fn post<F, B, T>(self, handler_fn: F) -> RouteBuilder<Route<HandlerSvc<F, B, T>, R>>
-    where
-        F: Handler<B, T>,
-    {
-        self.app.at_bytes(self.route_spec).post(handler_fn)
-    }
-
-    pub fn post_service<S, B>(self, service: S) -> RouteBuilder<Route<S, R>>
-    where
-        S: Service<Request<Body>, Response = Response<B>> + Clone,
-        S::Error: Into<BoxError>,
-    {
-        self.app.at_bytes(self.route_spec).post_service(service)
-    }
-
-    pub fn into_service(self) -> IntoService<R> {
-        IntoService {
-            app: self.app,
-            poll_ready_error: None,
-        }
-    }
-}
-
-#[derive(Debug, thiserror::Error)]
-#[non_exhaustive]
-pub enum Error {
-    #[error("failed to deserialize the request body")]
-    DeserializeRequestBody(#[source] serde_json::Error),
-
-    #[error("failed to serialize the response body")]
-    SerializeResponseBody(#[source] serde_json::Error),
-
-    #[error("failed to consume the body")]
-    ConsumeRequestBody(#[source] hyper::Error),
-
-    #[error("URI contained no query string")]
-    QueryStringMissing,
-
-    #[error("failed to deserialize query string")]
-    DeserializeQueryString(#[source] serde_urlencoded::de::Error),
-
-    #[error("failed generating the response body")]
-    ResponseBody(#[source] BoxError),
-
-    #[error("handler service returned an error")]
-    Service(#[source] BoxError),
-
-    #[error("request extension of type `{type_name}` was not set")]
-    MissingExtension { type_name: &'static str },
-}
-
-impl From<Infallible> for Error {
-    fn from(err: Infallible) -> Self {
-        match err {}
-    }
-}
-
-mod sealed {
-    pub trait HiddentTrait {}
-    pub struct Hidden;
-    impl HiddentTrait for Hidden {}
-}
-
-#[async_trait]
-pub trait Handler<B, In>: Sized {
-    type Response: IntoResponse<B>;
-
-    // This seals the trait. We cannot use the regular "sealed super trait" approach
-    // due to coherence.
-    #[doc(hidden)]
-    type Sealed: sealed::HiddentTrait;
-
-    async fn call(self, req: Request<Body>) -> Result<Self::Response, Error>;
-
-    fn layer<L>(self, layer: L) -> Layered<L::Service, In>
-    where
-        L: Layer<HandlerSvc<Self, B, In>>,
-    {
-        Layered::new(layer.layer(HandlerSvc::new(self)))
-    }
-}
-
-pub trait IntoResponse<B> {
-    fn into_response(self) -> Result<Response<B>, Error>;
-}
-
-impl<B> IntoResponse<B> for Response<B> {
-    fn into_response(self) -> Result<Response<B>, Error> {
-        Ok(self)
-    }
-}
-
-impl IntoResponse<Body> for &'static str {
-    fn into_response(self) -> Result<Response<Body>, Error> {
-        Ok(Response::new(Body::from(self)))
-    }
-}
-
-impl IntoResponse<Body> for String {
-    fn into_response(self) -> Result<Response<Body>, Error> {
-        Ok(Response::new(Body::from(self)))
-    }
-}
-
-impl IntoResponse<Body> for Bytes {
-    fn into_response(self) -> Result<Response<Body>, Error> {
-        Ok(Response::new(Body::from(self)))
-    }
-}
-
-impl IntoResponse<Body> for &'static [u8] {
-    fn into_response(self) -> Result<Response<Body>, Error> {
-        Ok(Response::new(Body::from(self)))
-    }
-}
-
-impl IntoResponse<Body> for Vec<u8> {
-    fn into_response(self) -> Result<Response<Body>, Error> {
-        Ok(Response::new(Body::from(self)))
-    }
-}
-
-impl IntoResponse<Body> for std::borrow::Cow<'static, str> {
-    fn into_response(self) -> Result<Response<Body>, Error> {
-        Ok(Response::new(Body::from(self)))
-    }
-}
-
-impl IntoResponse<Body> for std::borrow::Cow<'static, [u8]> {
-    fn into_response(self) -> Result<Response<Body>, Error> {
-        Ok(Response::new(Body::from(self)))
-    }
-}
-
-// TODO(david): rename this to Json when its in another module
-pub struct JsonBody<T>(T);
-
-impl<T> IntoResponse<Body> for JsonBody<T>
-where
-    T: Serialize,
-{
-    fn into_response(self) -> Result<Response<Body>, Error> {
-        let bytes = serde_json::to_vec(&self.0).map_err(Error::SerializeResponseBody)?;
-        let len = bytes.len();
-        let mut res = Response::new(Body::from(bytes));
-
-        res.headers_mut().insert(
-            header::CONTENT_TYPE,
-            HeaderValue::from_static("application/json"),
-        );
-
-        res.headers_mut()
-            .insert(header::CONTENT_LENGTH, HeaderValue::from(len));
-
-        Ok(res)
-    }
-}
-
-#[async_trait]
-impl<F, Fut, B, Res> Handler<B, ()> for F
-where
-    F: Fn(Request<Body>) -> Fut + Send + Sync,
-    Fut: Future<Output = Result<Res, Error>> + Send,
-    Res: IntoResponse<B>,
-{
-    type Response = Res;
-
-    type Sealed = sealed::Hidden;
-
-    async fn call(self, req: Request<Body>) -> Result<Self::Response, Error> {
-        self(req).await
-    }
-}
-
-macro_rules! impl_handler {
-    ( $head:ident $(,)? ) => {
-        #[async_trait]
-        #[allow(non_snake_case)]
-        impl<F, Fut, B, Res, $head> Handler<B, ($head,)> for F
-        where
-            F: Fn(Request<Body>, $head) -> Fut + Send + Sync,
-            Fut: Future<Output = Result<Res, Error>> + Send,
-            Res: IntoResponse<B>,
-            $head: FromRequest + Send,
-        {
-            type Response = Res;
-
-            type Sealed = sealed::Hidden;
-
-            async fn call(self, mut req: Request<Body>) -> Result<Self::Response, Error> {
-                let $head = $head::from_request(&mut req).await?;
-                let res = self(req, $head).await?;
-                Ok(res)
-            }
-        }
-    };
-
-    ( $head:ident, $($tail:ident),* $(,)? ) => {
-        #[async_trait]
-        #[allow(non_snake_case)]
-        impl<F, Fut, B, Res, $head, $($tail,)*> Handler<B, ($head, $($tail,)*)> for F
-        where
-            F: Fn(Request<Body>, $head, $($tail,)*) -> Fut + Send + Sync,
-            Fut: Future<Output = Result<Res, Error>> + Send,
-            Res: IntoResponse<B>,
-            $head: FromRequest + Send,
-            $( $tail: FromRequest + Send, )*
-        {
-            type Response = Res;
-
-            type Sealed = sealed::Hidden;
-
-            async fn call(self, mut req: Request<Body>) -> Result<Self::Response, Error> {
-                let $head = $head::from_request(&mut req).await?;
-                $(
-                    let $tail = $tail::from_request(&mut req).await?;
-                )*
-                let res = self(req, $head, $($tail,)*).await?;
-                Ok(res)
-            }
-        }
-
-        impl_handler!($($tail,)*);
-    };
-}
-
-impl_handler!(T1, T2, T3, T4, T5, T6, T7, T8, T9, T10, T11, T12, T13, T14, T15, T16);
-
-pub struct Layered<S, T> {
-    svc: S,
-    _input: PhantomData<fn() -> T>,
-}
-
-impl<S, T> Clone for Layered<S, T>
-where
-    S: Clone,
-{
-    fn clone(&self) -> Self {
-        Self::new(self.svc.clone())
-    }
-}
-
-#[async_trait]
-impl<S, B, T> Handler<B, T> for Layered<S, T>
-where
-    S: Service<Request<Body>, Response = Response<B>> + Send,
-    S::Error: Into<BoxError>,
-    S::Future: Send,
-{
-    type Response = S::Response;
-
-    type Sealed = sealed::Hidden;
-
-    async fn call(self, req: Request<Body>) -> Result<Self::Response, Error> {
-        self.svc
-            .oneshot(req)
-            .await
-            .map_err(|err| Error::Service(err.into()))
-    }
-}
-
-impl<S, T> Layered<S, T> {
-    fn new(svc: S) -> Self {
-        Self {
-            svc,
-            _input: PhantomData,
-        }
-    }
-}
-
-pub struct HandlerSvc<H, B, T> {
-    handler: H,
-    _input: PhantomData<fn() -> (B, T)>,
-}
-
-impl<H, B, T> HandlerSvc<H, B, T> {
-    fn new(handler: H) -> Self {
-        Self {
-            handler,
-            _input: PhantomData,
-        }
-    }
-}
-
-impl<H, B, T> Clone for HandlerSvc<H, B, T>
-where
-    H: Clone,
-{
-    fn clone(&self) -> Self {
-        Self {
-            handler: self.handler.clone(),
-            _input: PhantomData,
-        }
-    }
-}
-
-impl<H, B, T> Service<Request<Body>> for HandlerSvc<H, B, T>
-where
-    H: Handler<B, T> + Clone + Send + 'static,
-    H::Response: 'static,
-{
-    type Response = Response<B>;
-    type Error = Error;
-    type Future = future::BoxFuture<'static, Result<Self::Response, Self::Error>>;
-
-    fn poll_ready(&mut self, _cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
-        // HandlerSvc can only be constructed from async functions which are always ready, or from
-        // `Layered` which bufferes in `<Layered as Handler>::call` and is therefore also always
-        // ready.
-        Poll::Ready(Ok(()))
-    }
-
-    fn call(&mut self, req: Request<Body>) -> Self::Future {
-        let handler = self.handler.clone();
-        Box::pin(async move {
-            let res = Handler::call(handler, req).await?.into_response()?;
-            Ok(res)
-        })
-    }
-}
-
-pub trait FromRequest: Sized {
-    type Future: Future<Output = Result<Self, Error>> + Send;
-
-    fn from_request(req: &mut Request<Body>) -> Self::Future;
-}
-
-impl<T> FromRequest for Option<T>
-where
-    T: FromRequest,
-{
-    type Future = OptionFromRequestFuture<T::Future>;
-
-    fn from_request(req: &mut Request<Body>) -> Self::Future {
-        OptionFromRequestFuture(T::from_request(req))
-    }
-}
-
-#[pin_project]
-pub struct OptionFromRequestFuture<F>(#[pin] F);
-
-impl<F, T> Future for OptionFromRequestFuture<F>
-where
-    F: Future<Output = Result<T, Error>>,
-{
-    type Output = Result<Option<T>, Error>;
-
-    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
-        let value = ready!(self.project().0.poll(cx));
-        Poll::Ready(Ok(value.ok()))
-    }
-}
-
-#[derive(Debug, Clone, Copy)]
-pub struct Query<T>(T);
-
-impl<T> Query<T> {
-    pub fn into_inner(self) -> T {
-        self.0
-    }
-}
-
-impl<T> FromRequest for Query<T>
-where
-    T: DeserializeOwned + Send,
-{
-    type Future = future::Ready<Result<Self, Error>>;
-
-    fn from_request(req: &mut Request<Body>) -> Self::Future {
-        let result = (|| {
-            let query = req.uri().query().ok_or(Error::QueryStringMissing)?;
-            let value = serde_urlencoded::from_str(query).map_err(Error::DeserializeQueryString)?;
-            Ok(Query(value))
-        })();
-
-        future::ready(result)
-    }
-}
-
-#[derive(Debug, Clone, Copy)]
-pub struct Json<T>(T);
-
-impl<T> Json<T> {
-    pub fn into_inner(self) -> T {
-        self.0
-    }
-}
-
-impl<T> FromRequest for Json<T>
-where
-    T: DeserializeOwned,
-{
-    type Future = future::BoxFuture<'static, Result<Self, Error>>;
-
-    fn from_request(req: &mut Request<Body>) -> Self::Future {
-        // TODO(david): require the body to have `content-type: application/json`
-
-        let body = std::mem::take(req.body_mut());
-
-        Box::pin(async move {
-            let bytes = hyper::body::to_bytes(body)
-                .await
-                .map_err(Error::ConsumeRequestBody)?;
-            let value = serde_json::from_slice(&bytes).map_err(Error::DeserializeRequestBody)?;
-            Ok(Json(value))
-        })
-    }
-}
-
-#[derive(Debug, Clone, Copy)]
-pub struct Extension<T>(T);
-
-impl<T> Extension<T> {
-    pub fn into_inner(self) -> T {
-        self.0
-    }
-}
-
-impl<T> FromRequest for Extension<T>
-where
-    T: Clone + Send + Sync + 'static,
-{
-    type Future = future::Ready<Result<Self, Error>>;
-
-    fn from_request(req: &mut Request<Body>) -> Self::Future {
-        let result = (|| {
-            let value = req
-                .extensions()
-                .get::<T>()
-                .ok_or_else(|| Error::MissingExtension {
-                    type_name: std::any::type_name::<T>(),
-                })
-                .map(|x| x.clone())?;
-            Ok(Extension(value))
-        })();
-
-        future::ready(result)
-    }
-}
-
-// TODO(david): rename this to Bytes when its in another module
-// TODO(david): can we add a length limit somehow? Maybe a const generic?
-#[derive(Debug, Clone)]
-pub struct BytesBody(Bytes);
-
-impl BytesBody {
-    pub fn into_inner(self) -> Bytes {
-        self.0
-    }
-}
-
-impl FromRequest for BytesBody {
-    type Future = future::BoxFuture<'static, Result<Self, Error>>;
-
-    fn from_request(req: &mut Request<Body>) -> Self::Future {
-        let body = std::mem::take(req.body_mut());
-
-        Box::pin(async move {
-            let bytes = hyper::body::to_bytes(body)
-                .await
-                .map_err(Error::ConsumeRequestBody)?;
-            Ok(BytesBody(bytes))
-        })
-    }
-}
-
-#[derive(Clone, Copy)]
-pub struct EmptyRouter(());
-
-impl<R> Service<R> for EmptyRouter {
-    type Response = Response<Body>;
-    type Error = Infallible;
-    type Future = future::Ready<Result<Self::Response, Self::Error>>;
-
-    fn poll_ready(&mut self, _cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
-        Poll::Ready(Ok(()))
-    }
-
-    fn call(&mut self, _req: R) -> Self::Future {
-        let mut res = Response::new(Body::empty());
-        *res.status_mut() = StatusCode::NOT_FOUND;
-        future::ok(res)
-    }
-}
-
-pub struct Route<H, F> {
-    service: H,
-    route_spec: RouteSpec,
-    fallback: F,
-    handler_ready: bool,
-    fallback_ready: bool,
-}
-
-impl<H, F> Clone for Route<H, F>
-where
-    H: Clone,
-    F: Clone,
-{
-    fn clone(&self) -> Self {
-        Self {
-            service: self.service.clone(),
-            fallback: self.fallback.clone(),
-            route_spec: self.route_spec.clone(),
-            // important to reset readiness when cloning
-            handler_ready: false,
-            fallback_ready: false,
-        }
-    }
-}
-
-#[derive(Clone)]
-struct RouteSpec {
-    method: Method,
-    spec: Bytes,
-}
-
-impl RouteSpec {
-    fn matches<B>(&self, req: &Request<B>) -> bool {
-        // TODO(david): support dynamic placeholders like `/users/:id`
-        req.method() == self.method && req.uri().path().as_bytes() == self.spec
-    }
-}
-
-impl<H, F, HB, FB> Service<Request<Body>> for Route<H, F>
-where
-    H: Service<Request<Body>, Response = Response<HB>>,
-    H::Error: Into<Error>,
-    HB: http_body::Body + Send + Sync + 'static,
-    HB::Error: Into<BoxError>,
-
-    F: Service<Request<Body>, Response = Response<FB>>,
-    F::Error: Into<Error>,
-    FB: http_body::Body<Data = HB::Data> + Send + Sync + 'static,
-    FB::Error: Into<BoxError>,
-{
-    type Response = Response<BoxBody<HB::Data, Error>>;
-    type Error = Error;
-    type Future = future::Either<BoxResponseBody<H::Future>, BoxResponseBody<F::Future>>;
-
-    fn poll_ready(&mut self, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
-        loop {
-            if !self.handler_ready {
-                ready!(self.service.poll_ready(cx)).map_err(Into::into)?;
-                self.handler_ready = true;
-            }
-
-            if !self.fallback_ready {
-                ready!(self.fallback.poll_ready(cx)).map_err(Into::into)?;
-                self.fallback_ready = true;
-            }
-
-            if self.handler_ready && self.fallback_ready {
-                return Poll::Ready(Ok(()));
-            }
-        }
-    }
-
-    fn call(&mut self, req: Request<Body>) -> Self::Future {
-        if self.route_spec.matches(&req) {
-            assert!(
-                self.handler_ready,
-                "handler not ready. Did you forget to call `poll_ready`?"
-            );
-            self.handler_ready = false;
-            future::Either::Left(BoxResponseBody(self.service.call(req)))
-        } else {
-            assert!(
-                self.fallback_ready,
-                "fallback not ready. Did you forget to call `poll_ready`?"
-            );
-            self.fallback_ready = false;
-            // TODO(david): this leads to each route creating one box body, probably not great
-            future::Either::Right(BoxResponseBody(self.fallback.call(req)))
-        }
-    }
-}
-
-#[pin_project]
-pub struct BoxResponseBody<F>(#[pin] F);
-
-impl<F, B, E> Future for BoxResponseBody<F>
-where
-    F: Future<Output = Result<Response<B>, E>>,
-    E: Into<Error>,
-    B: http_body::Body + Send + Sync + 'static,
-    B::Error: Into<BoxError>,
-{
-    type Output = Result<Response<BoxBody<B::Data, Error>>, Error>;
-
-    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
-        let response: Response<B> = ready!(self.project().0.poll(cx)).map_err(Into::into)?;
-        let response = response.map(|body| {
-            // TODO(david): attempt to downcast this into `Error`
-            let body = body.map_err(|err| Error::ResponseBody(err.into()));
-            BoxBody::new(body)
-        });
-        Poll::Ready(Ok(response))
-    }
-}
-
 pub struct IntoService<R> {
     app: App<R>,
     poll_ready_error: Option<Error>,
@@ -792,12 +96,16 @@ where
 
     #[inline]
     fn poll_ready(&mut self, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
-        self.app.router.poll_ready(cx).map_err(Into::into)
+        if let Err(err) = ready!(self.app.router.poll_ready(cx)).map_err(Into::into) {
+            self.poll_ready_error = Some(err);
+        }
+
+        Poll::Ready(Ok(()))
     }
 
     fn call(&mut self, req: T) -> Self::Future {
         if let Some(poll_ready_error) = self.poll_ready_error.take() {
-            match handle_error::<B>(poll_ready_error) {
+            match error::handle_error::<B>(poll_ready_error) {
                 Ok(res) => {
                     return HandleErrorFuture(Kind::Response(Some(res)));
                 }
@@ -834,44 +142,12 @@ where
             KindProj::Error(err) => Poll::Ready(Err(err.take().unwrap())),
             KindProj::Future(fut) => match ready!(fut.poll(cx)) {
                 Ok(res) => Poll::Ready(Ok(res)),
-                Err(err) => Poll::Ready(handle_error(err.into())),
+                Err(err) => Poll::Ready(error::handle_error(err.into())),
             },
         }
     }
 }
 
-fn handle_error<B>(error: Error) -> Result<Response<B>, Error>
-where
-    B: Default,
-{
-    fn make_response<B>(status: StatusCode) -> Result<Response<B>, Error>
-    where
-        B: Default,
-    {
-        let mut res = Response::new(B::default());
-        *res.status_mut() = status;
-        Ok(res)
-    }
-
-    match error {
-        Error::DeserializeRequestBody(_)
-        | Error::QueryStringMissing
-        | Error::DeserializeQueryString(_) => make_response(StatusCode::BAD_REQUEST),
-
-        Error::MissingExtension { .. } | Error::SerializeResponseBody(_) => {
-            make_response(StatusCode::INTERNAL_SERVER_ERROR)
-        }
-
-        Error::Service(err) => match err.downcast::<Error>() {
-            Ok(err) => Err(*err),
-            Err(err) => Err(Error::Service(err)),
-        },
-
-        err @ Error::ConsumeRequestBody(_) => Err(err),
-        err @ Error::ResponseBody(_) => Err(err),
-    }
-}
-
 #[cfg(test)]
 mod tests {
     #![allow(warnings)]
@@ -909,44 +185,45 @@ mod tests {
             Ok(Response::new(Body::empty()))
         }
 
-        let app =
-            app()
-                // routes with functions
-                .at("/")
-                .get(root)
-                // routes with closures
-                .at("/users")
-                .get(|_: Request<Body>, pagination: Query<Pagination>| async {
+        let app = app()
+            // routes with functions
+            .at("/")
+            .get(root)
+            // routes with closures
+            .at("/users")
+            .get(
+                |_: Request<Body>, pagination: extract::Query<Pagination>| async {
                     let pagination = pagination.into_inner();
                     assert_eq!(pagination.page, 1);
                     assert_eq!(pagination.per_page, 30);
                     Ok::<_, Error>("users#index".to_string())
-                })
-                .post(
-                    |_: Request<Body>,
-                     payload: Json<UsersCreate>,
-                     _state: Extension<Arc<State>>| async {
-                        let payload = payload.into_inner();
-                        assert_eq!(payload.username, "bob");
-                        Ok::<_, Error>(JsonBody(
-                            serde_json::json!({ "username": payload.username }),
-                        ))
-                    },
-                )
-                // routes with a service
-                .at("/service")
-                .get_service(service_fn(root))
-                // routes with layers applied
-                .at("/large-static-file")
-                .get(
-                    large_static_file.layer(
-                        ServiceBuilder::new()
-                            .layer(TimeoutLayer::new(Duration::from_secs(30)))
-                            .layer(CompressionLayer::new())
-                            .into_inner(),
-                    ),
-                )
-                .into_service();
+                },
+            )
+            .post(
+                |_: Request<Body>,
+                 payload: extract::Json<UsersCreate>,
+                 _state: extract::Extension<Arc<State>>| async {
+                    let payload = payload.into_inner();
+                    assert_eq!(payload.username, "bob");
+                    Ok::<_, Error>(response::Json(
+                        serde_json::json!({ "username": payload.username }),
+                    ))
+                },
+            )
+            // routes with a service
+            .at("/service")
+            .get_service(service_fn(root))
+            // routes with layers applied
+            .at("/large-static-file")
+            .get(
+                large_static_file.layer(
+                    ServiceBuilder::new()
+                        .layer(TimeoutLayer::new(Duration::from_secs(30)))
+                        .layer(CompressionLayer::new())
+                        .into_inner(),
+                ),
+            )
+            .into_service();
 
         // state shared by all routes, could hold db connection etc
         struct State {}
diff --git a/src/response.rs b/src/response.rs
new file mode 100644
index 00000000..f41b1cb9
--- /dev/null
+++ b/src/response.rs
@@ -0,0 +1,79 @@
+use crate::{Body, Error};
+use bytes::Bytes;
+use http::{header, HeaderValue, Response};
+use serde::Serialize;
+
+pub trait IntoResponse<B> {
+    fn into_response(self) -> Result<Response<B>, Error>;
+}
+
+impl<B> IntoResponse<B> for Response<B> {
+    fn into_response(self) -> Result<Response<B>, Error> {
+        Ok(self)
+    }
+}
+
+impl IntoResponse<Body> for &'static str {
+    fn into_response(self) -> Result<Response<Body>, Error> {
+        Ok(Response::new(Body::from(self)))
+    }
+}
+
+impl IntoResponse<Body> for String {
+    fn into_response(self) -> Result<Response<Body>, Error> {
+        Ok(Response::new(Body::from(self)))
+    }
+}
+
+impl IntoResponse<Body> for Bytes {
+    fn into_response(self) -> Result<Response<Body>, Error> {
+        Ok(Response::new(Body::from(self)))
+    }
+}
+
+impl IntoResponse<Body> for &'static [u8] {
+    fn into_response(self) -> Result<Response<Body>, Error> {
+        Ok(Response::new(Body::from(self)))
+    }
+}
+
+impl IntoResponse<Body> for Vec<u8> {
+    fn into_response(self) -> Result<Response<Body>, Error> {
+        Ok(Response::new(Body::from(self)))
+    }
+}
+
+impl IntoResponse<Body> for std::borrow::Cow<'static, str> {
+    fn into_response(self) -> Result<Response<Body>, Error> {
+        Ok(Response::new(Body::from(self)))
+    }
+}
+
+impl IntoResponse<Body> for std::borrow::Cow<'static, [u8]> {
+    fn into_response(self) -> Result<Response<Body>, Error> {
+        Ok(Response::new(Body::from(self)))
+    }
+}
+
+pub struct Json<T>(pub T);
+
+impl<T> IntoResponse<Body> for Json<T>
+where
+    T: Serialize,
+{
+    fn into_response(self) -> Result<Response<Body>, Error> {
+        let bytes = serde_json::to_vec(&self.0).map_err(Error::SerializeResponseBody)?;
+        let len = bytes.len();
+        let mut res = Response::new(Body::from(bytes));
+
+        res.headers_mut().insert(
+            header::CONTENT_TYPE,
+            HeaderValue::from_static("application/json"),
+        );
+
+        res.headers_mut()
+            .insert(header::CONTENT_LENGTH, HeaderValue::from(len));
+
+        Ok(res)
+    }
+}
diff --git a/src/routing.rs b/src/routing.rs
new file mode 100644
index 00000000..5fbaf3ff
--- /dev/null
+++ b/src/routing.rs
@@ -0,0 +1,284 @@
+use crate::{
+    body::{Body, BoxBody},
+    error::Error,
+    handler::{Handler, HandlerSvc},
+    App, IntoService,
+};
+use bytes::Bytes;
+use futures_util::{future, ready};
+use http::{Method, Request, Response, StatusCode};
+use pin_project::pin_project;
+use std::{
+    convert::Infallible,
+    future::Future,
+    pin::Pin,
+    task::{Context, Poll},
+};
+use tower::{BoxError, Layer, Service};
+
+#[derive(Clone, Copy)]
+pub struct EmptyRouter(pub(crate) ());
+
+impl<R> Service<R> for EmptyRouter {
+    type Response = Response<Body>;
+    type Error = Infallible;
+    type Future = future::Ready<Result<Self::Response, Self::Error>>;
+
+    fn poll_ready(&mut self, _cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+        Poll::Ready(Ok(()))
+    }
+
+    fn call(&mut self, _req: R) -> Self::Future {
+        let mut res = Response::new(Body::empty());
+        *res.status_mut() = StatusCode::NOT_FOUND;
+        future::ok(res)
+    }
+}
+
+#[derive(Debug, Clone)]
+pub struct RouteAt<R> {
+    pub(crate) app: App<R>,
+    pub(crate) route_spec: Bytes,
+}
+
+impl<R> RouteAt<R> {
+    pub fn get<F, B, T>(self, handler_fn: F) -> RouteBuilder<Route<HandlerSvc<F, B, T>, R>>
+    where
+        F: Handler<B, T>,
+    {
+        self.add_route(handler_fn, Method::GET)
+    }
+
+    pub fn get_service<S, B>(self, service: S) -> RouteBuilder<Route<S, R>>
+    where
+        S: Service<Request<Body>, Response = Response<B>> + Clone,
+        S::Error: Into<BoxError>,
+    {
+        self.add_route_service(service, Method::GET)
+    }
+
+    pub fn post<F, B, T>(self, handler_fn: F) -> RouteBuilder<Route<HandlerSvc<F, B, T>, R>>
+    where
+        F: Handler<B, T>,
+    {
+        self.add_route(handler_fn, Method::POST)
+    }
+
+    pub fn post_service<S, B>(self, service: S) -> RouteBuilder<Route<S, R>>
+    where
+        S: Service<Request<Body>, Response = Response<B>> + Clone,
+        S::Error: Into<BoxError>,
+    {
+        self.add_route_service(service, Method::POST)
+    }
+
+    fn add_route<H, B, T>(
+        self,
+        handler: H,
+        method: Method,
+    ) -> RouteBuilder<Route<HandlerSvc<H, B, T>, R>>
+    where
+        H: Handler<B, T>,
+    {
+        self.add_route_service(HandlerSvc::new(handler), method)
+    }
+
+    fn add_route_service<S>(self, service: S, method: Method) -> RouteBuilder<Route<S, R>> {
+        let new_app = App {
+            router: Route {
+                service,
+                route_spec: RouteSpec {
+                    method,
+                    spec: self.route_spec.clone(),
+                },
+                fallback: self.app.router,
+                handler_ready: false,
+                fallback_ready: false,
+            },
+        };
+
+        RouteBuilder {
+            app: new_app,
+            route_spec: self.route_spec,
+        }
+    }
+}
+
+pub struct RouteBuilder<R> {
+    app: App<R>,
+    route_spec: Bytes,
+}
+
+impl<R> Clone for RouteBuilder<R>
+where
+    R: Clone,
+{
+    fn clone(&self) -> Self {
+        Self {
+            app: self.app.clone(),
+            route_spec: self.route_spec.clone(),
+        }
+    }
+}
+
+impl<R> RouteBuilder<R> {
+    pub fn at(self, route_spec: &str) -> RouteAt<R> {
+        self.app.at(route_spec)
+    }
+
+    pub fn get<F, B, T>(self, handler_fn: F) -> RouteBuilder<Route<HandlerSvc<F, B, T>, R>>
+    where
+        F: Handler<B, T>,
+    {
+        self.app.at_bytes(self.route_spec).get(handler_fn)
+    }
+
+    pub fn get_service<S, B>(self, service: S) -> RouteBuilder<Route<S, R>>
+    where
+        S: Service<Request<Body>, Response = Response<B>> + Clone,
+        S::Error: Into<BoxError>,
+    {
+        self.app.at_bytes(self.route_spec).get_service(service)
+    }
+
+    pub fn post<F, B, T>(self, handler_fn: F) -> RouteBuilder<Route<HandlerSvc<F, B, T>, R>>
+    where
+        F: Handler<B, T>,
+    {
+        self.app.at_bytes(self.route_spec).post(handler_fn)
+    }
+
+    pub fn post_service<S, B>(self, service: S) -> RouteBuilder<Route<S, R>>
+    where
+        S: Service<Request<Body>, Response = Response<B>> + Clone,
+        S::Error: Into<BoxError>,
+    {
+        self.app.at_bytes(self.route_spec).post_service(service)
+    }
+
+    pub fn into_service(self) -> IntoService<R> {
+        IntoService {
+            app: self.app,
+            poll_ready_error: None,
+        }
+    }
+}
+
+pub struct Route<H, F> {
+    service: H,
+    route_spec: RouteSpec,
+    fallback: F,
+    handler_ready: bool,
+    fallback_ready: bool,
+}
+
+impl<H, F> Clone for Route<H, F>
+where
+    H: Clone,
+    F: Clone,
+{
+    fn clone(&self) -> Self {
+        Self {
+            service: self.service.clone(),
+            fallback: self.fallback.clone(),
+            route_spec: self.route_spec.clone(),
+            // important to reset readiness when cloning
+            handler_ready: false,
+            fallback_ready: false,
+        }
+    }
+}
+
+#[derive(Clone)]
+struct RouteSpec {
+    method: Method,
+    spec: Bytes,
+}
+
+impl RouteSpec {
+    fn matches<B>(&self, req: &Request<B>) -> bool {
+        // TODO(david): support dynamic placeholders like `/users/:id`
+        req.method() == self.method && req.uri().path().as_bytes() == self.spec
+    }
+}
+
+impl<H, F, HB, FB> Service<Request<Body>> for Route<H, F>
+where
+    H: Service<Request<Body>, Response = Response<HB>>,
+    H::Error: Into<Error>,
+    HB: http_body::Body + Send + Sync + 'static,
+    HB::Error: Into<BoxError>,
+
+    F: Service<Request<Body>, Response = Response<FB>>,
+    F::Error: Into<Error>,
+    FB: http_body::Body<Data = HB::Data> + Send + Sync + 'static,
+    FB::Error: Into<BoxError>,
+{
+    type Response = Response<BoxBody<HB::Data, Error>>;
+    type Error = Error;
+    type Future = future::Either<BoxResponseBody<H::Future>, BoxResponseBody<F::Future>>;
+
+    fn poll_ready(&mut self, cx: &mut Context<'_>) -> Poll<Result<(), Self::Error>> {
+        loop {
+            if !self.handler_ready {
+                ready!(self.service.poll_ready(cx)).map_err(Into::into)?;
+                self.handler_ready = true;
+            }
+
+            if !self.fallback_ready {
+                ready!(self.fallback.poll_ready(cx)).map_err(Into::into)?;
+                self.fallback_ready = true;
+            }
+
+            if self.handler_ready && self.fallback_ready {
+                return Poll::Ready(Ok(()));
+            }
+        }
+    }
+
+    fn call(&mut self, req: Request<Body>) -> Self::Future {
+        if self.route_spec.matches(&req) {
+            assert!(
+                self.handler_ready,
+                "handler not ready. Did you forget to call `poll_ready`?"
+            );
+
+            self.handler_ready = false;
+
+            future::Either::Left(BoxResponseBody(self.service.call(req)))
+        } else {
+            assert!(
+                self.fallback_ready,
+                "fallback not ready. Did you forget to call `poll_ready`?"
+            );
+
+            self.fallback_ready = false;
+
+            // TODO(david): this leads to each route creating one box body, probably not great
+            future::Either::Right(BoxResponseBody(self.fallback.call(req)))
+        }
+    }
+}
+
+#[pin_project]
+pub struct BoxResponseBody<F>(#[pin] F);
+
+impl<F, B, E> Future for BoxResponseBody<F>
+where
+    F: Future<Output = Result<Response<B>, E>>,
+    E: Into<Error>,
+    B: http_body::Body + Send + Sync + 'static,
+    B::Error: Into<BoxError>,
+{
+    type Output = Result<Response<BoxBody<B::Data, Error>>, Error>;
+
+    fn poll(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Self::Output> {
+        let response: Response<B> = ready!(self.project().0.poll(cx)).map_err(Into::into)?;
+        let response = response.map(|body| {
+            // TODO(david): attempt to downcast this into `Error`
+            let body = body.map_err(|err| Error::ResponseBody(err.into()));
+            BoxBody::new(body)
+        });
+        Poll::Ready(Ok(response))
+    }
+}