🧵 Service::handle now blocking

Otherwise the `Server::run` becomes `!Send`, making it impossible for
users to run it in spawned tasks in multi-threadded runtimes (e.g
`tokio::task::spawn`). Implementers can still handle methods
asynchronously by returning a stream. Although that means they can not
keep a reference to the server around in their async handling logic and
are limited to only be able to send owned types.

An alternative here would be to accept `Server::run` being `!Send` but
givne the widespread use of multi-threaded runtimes and (especially)
`tokio::task::spawn`, I have a strong feeling that it would make the API
very unattractive for the majority of the potential users.

Author: zeenix

zlink/src/server/mod.rs

@@ -158,7 +158,7 @@ where
         writer: &mut WriteConnection<<Listener::Socket as Socket>::WriteHalf>,
     ) -> crate::Result<Option<Service::ReplyStream>> {
         let mut stream = None;
-        match self.service.handle(call).await {
+        match self.service.handle(call) {
             Reply::Single(reply) => writer.send_reply(reply, Some(false)).await?,
             Reply::Error(err) => writer.send_error(err).await?,
             Reply::Multi(s) => stream = Some(s),

zlink/src/server/service.rs

@@ -1,6 +1,6 @@
 //! Serice-related API.
 
-use core::{fmt::Debug, future::Future};
+use core::fmt::Debug;
 
 use futures_util::Stream;
 use serde::{Deserialize, Serialize};
@@ -40,12 +40,14 @@ where
         Self: 'ser;
 
     /// Handle a method call.
+    ///
+    /// While this methos is no async, it can return a reply stream that can be used to
+    /// ascynchronously send out replies. The main use case for allowing to return a stream is
+    /// multiple replies but it can be used for single reply as well.
     fn handle<'ser>(
         &'ser mut self,
         method: Call<Self::MethodCall<'_>>,
-    ) -> impl Future<
-        Output = Reply<Option<Self::ReplyParams<'ser>>, Self::ReplyStream, Self::ReplyError<'ser>>,
-    >;
+    ) -> Reply<Option<Self::ReplyParams<'ser>>, Self::ReplyStream, Self::ReplyError<'ser>>;
 }
 
 /// A service method call reply.