server: Add DynamicService trait and adapter

CHANGELOG.md

@@ -7,6 +7,8 @@
 
 - Server: Remove `Sync` and `Unpin` trait bounds from `Service::call()` future
   result.
+- Server: Add `DynamicService`/`DynamicServiceAdapter` opt-in for dynamic
+  dispatch.
 
 ## v0.10.0 (2024-01-03)
 

src/server/mod.rs

@@ -16,7 +16,7 @@ pub mod tcp;
 pub mod rtu_over_tcp;
 
 mod service;
-pub use self::service::Service;
+pub use self::service::{DynamicService, DynamicServiceAdapter, Service};
 
 /// Cause for termination
 #[derive(Debug, Clone)]

src/server/service.rs

@@ -1,7 +1,7 @@
 // SPDX-FileCopyrightText: Copyright (c) 2017-2024 slowtec GmbH <[email protected]>
 // SPDX-License-Identifier: MIT OR Apache-2.0
 
-use std::{future::Future, ops::Deref};
+use std::{future::Future, ops::Deref, pin::Pin};
 
 /// A Modbus server service.
 pub trait Service {
@@ -36,3 +36,42 @@ where
         self.deref().call(req)
     }
 }
+
+/// A Modbus server service that uses dynamic dispatch.
+pub trait DynamicService {
+    /// Requests handled by the service.
+    type Request;
+
+    /// Responses given by the service.
+    type Response;
+
+    /// Errors produced by the service.
+    type Error;
+
+    /// Process the request and return the response asynchronously.
+    #[allow(clippy::type_complexity)]
+    fn call(
+        &self,
+        req: Self::Request,
+    ) -> Pin<Box<dyn Future<Output = Result<Self::Response, Self::Error>> + Send>>;
+}
+
+/// An adapter that allows to use a [`DynamicService`] as a [`Service`].
+#[derive(Debug, Clone)]
+pub struct DynamicServiceAdapter<T> {
+    delegate: T,
+}
+
+impl<T> Service for DynamicServiceAdapter<T>
+where
+    T: DynamicService,
+{
+    type Request = T::Request;
+    type Response = T::Response;
+    type Error = T::Error;
+    type Future = Pin<Box<dyn Future<Output = Result<Self::Response, Self::Error>> + Send>>;
+
+    fn call(&self, req: Self::Request) -> Self::Future {
+        self.delegate.call(req)
+    }
+}