box the state service (#879)

* box the state service

* cleanup

zebra-state/src/on_disk.rs

@@ -9,7 +9,7 @@ use std::{
     pin::Pin,
     task::{Context, Poll},
 };
-use tower::{buffer::Buffer, Service};
+use tower::{buffer::Buffer, util::BoxService, Service};
 use tracing::instrument;
 use zebra_chain::serialization::{SerializationError, ZcashDeserialize, ZcashSerialize};
 use zebra_chain::{
@@ -18,6 +18,9 @@ use zebra_chain::{
     Network,
 };
 
+/// Type alias of our wrapped service
+pub type StateService = Buffer<BoxService<Request, Response, Error>, Request>;
+
 #[derive(Clone)]
 struct SledState {
     storage: sled::Db,
@@ -243,23 +246,6 @@ impl From<BlockHeight> for BlockQuery {
     }
 }
 
-/// Returns a type that implements the `zebra_state::Service` using `sled`.
-///
-/// Each `network` has its own separate sled database.
-pub fn init(
-    config: Config,
-    network: Network,
-) -> impl Service<
-    Request,
-    Response = Response,
-    Error = BoxError,
-    Future = impl Future<Output = Result<Response, BoxError>>,
-> + Send
-       + Clone
-       + 'static {
-    Buffer::new(SledState::new(&config, network), 1)
-}
-
 type BoxError = Box<dyn error::Error + Send + Sync + 'static>;
 
 // these hacks are necessary to capture spantraces that can be extracted again
@@ -275,7 +261,7 @@ struct BoxRealError(BoxError);
 
 /// The TracedError wrapper on a type that implements Error
 #[derive(Debug)]
-struct Error(tracing_error::TracedError<BoxRealError>);
+pub struct Error(tracing_error::TracedError<BoxRealError>);
 
 macro_rules! impl_from {
     ($($src:ty,)*) => {$(
@@ -302,3 +288,10 @@ impl Into<BoxError> for Error {
         BoxError::from(self.0)
     }
 }
+
+/// Returns a type that implements the `zebra_state::Service` using `sled`.
+///
+/// Each `network` has its own separate sled database.
+pub fn init(config: Config, network: Network) -> StateService {
+    Buffer::new(BoxService::new(SledState::new(&config, network)), 1)
+}