feat: Allow to create tarpc on existing TCP listener

tarpc/src/serde_transport.rs

@@ -210,7 +210,19 @@ pub mod tcp {
         Codec: Serializer<SinkItem> + Deserializer<Item>,
         CodecFn: Fn() -> Codec,
     {
-        let listener = TcpListener::bind(addr).await?;
+        listen_on(TcpListener::bind(addr).await?, codec_fn).await
+    }
+
+    /// Wrap accepted connections from `listener` in TCP transports.
+    pub async fn listen_on<Item, SinkItem, Codec, CodecFn>(
+        listener: TcpListener,
+        codec_fn: CodecFn,
+    ) -> io::Result<Incoming<Item, SinkItem, Codec, CodecFn>>
+    where
+        Item: for<'de> Deserialize<'de>,
+        Codec: Serializer<SinkItem> + Deserializer<Item>,
+        CodecFn: Fn() -> Codec,
+    {
         let local_addr = listener.local_addr()?;
         Ok(Incoming {
             listener,
@@ -662,6 +674,26 @@ mod tests {
         Ok(())
     }
 
+    #[cfg(tcp)]
+    #[tokio::test]
+    async fn tcp_on_existing_transport() -> io::Result<()> {
+        use super::tcp;
+
+        let transport = TcpListener::bind("0.0.0.0:0").await?;
+        let mut listener = tcp::listen_on(transport, SymmetricalJson::<String>::default).await?;
+        let addr = listener.local_addr();
+        tokio::spawn(async move {
+            let mut transport = listener.next().await.unwrap().unwrap();
+            let message = transport.next().await.unwrap().unwrap();
+            transport.send(message).await.unwrap();
+        });
+        let mut transport = tcp::connect(addr, SymmetricalJson::<String>::default).await?;
+        transport.send(String::from("test")).await?;
+        assert_matches!(transport.next().await, Some(Ok(s)) if s == "test");
+        assert_matches!(transport.next().await, None);
+        Ok(())
+    }
+
     #[cfg(all(unix, feature = "unix"))]
     #[tokio::test]
     async fn uds() -> io::Result<()> {