sync: Fix timeout when establishing serial RTU connections

CHANGELOG.md

@@ -9,6 +9,7 @@
 - TCP Server: Stabilize "tcp-server" feature
 - TCP Client: Allow to attach a generic transport layer, e.g. for TLS support
 - RTU Server: Remove `NewService` trait and pass instance directly
+- Fix (sync): No timeout while establishing serial RTU connections
 
 ### Breaking Changes
 

src/client/sync/rtu.rs

@@ -7,7 +7,6 @@ use super::{block_on_with_timeout, Context};
 
 use tokio_serial::{SerialPortBuilder, SerialStream};
 
-use crate::client::rtu::connect_slave as async_connect_slave;
 use crate::slave::Slave;
 
 /// Connect to no particular Modbus slave device for sending
@@ -41,8 +40,10 @@ pub fn connect_slave_with_timeout(
         .enable_time()
         .build()?;
     // SerialStream::open requires a runtime at least on cfg(unix).
-    let serial = runtime.block_on(async { SerialStream::open(builder) })?;
-    let async_ctx = block_on_with_timeout(&runtime, timeout, async_connect_slave(serial, slave))?;
+    let serial = block_on_with_timeout(&runtime, timeout, async {
+        SerialStream::open(builder).map_err(Into::into)
+    })?;
+    let async_ctx = crate::client::rtu::attach_slave(serial, slave);
     let sync_ctx = Context {
         runtime,
         async_ctx,