Break things into modules

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),
+    }
+}