feat: add rtu_over_tcp server

Cargo.toml

@@ -70,6 +70,13 @@ tcp-server = [
     "tokio/macros",
     "tokio/rt-multi-thread",
 ]
+rtu-over-tcp-server = [
+    "rtu",
+    "server",
+    "socket2/all",
+    "tokio/macros",
+    "tokio/rt-multi-thread",
+]
 # The following features are internal and must not be used in dependencies.
 sync = ["dep:futures", "tokio/time", "tokio/rt"]
 server = ["dep:futures"]
@@ -117,6 +124,11 @@ name = "tcp-server"
 path = "examples/tcp-server.rs"
 required-features = ["tcp-server"]
 
+[[example]]
+name = "rtu-over-tcp-server"
+path = "examples/rtu-over-tcp-server.rs"
+required-features = ["rtu-over-tcp-server"]
+
 [[example]]
 name = "tls-client"
 path = "examples/tls-client.rs"

examples/rtu-over-tcp-server.rs

@@ -0,0 +1,214 @@
+// SPDX-FileCopyrightText: Copyright (c) 2017-2023 slowtec GmbH <[email protected]>
+// SPDX-License-Identifier: MIT OR Apache-2.0
+
+//! # RTU over TCP server example
+//!
+//! This example shows how to start a server and implement basic register
+//! read/write operations.
+
+use std::{
+    collections::HashMap,
+    net::SocketAddr,
+    sync::{Arc, Mutex},
+    time::Duration,
+};
+
+use futures::future;
+use tokio::net::TcpListener;
+
+use tokio_modbus::{
+    prelude::*,
+    server::rtu_over_tcp::{accept_tcp_connection, Server},
+};
+
+struct ExampleService {
+    input_registers: Arc<Mutex<HashMap<u16, u16>>>,
+    holding_registers: Arc<Mutex<HashMap<u16, u16>>>,
+}
+
+impl tokio_modbus::server::Service for ExampleService {
+    type Request = SlaveRequest<'static>;
+    type Response = Response;
+    type Error = std::io::Error;
+    type Future = future::Ready<Result<Self::Response, Self::Error>>;
+
+    fn call(&self, req: Self::Request) -> Self::Future {
+        println!("{}", req.slave);
+        match req.request {
+            Request::ReadInputRegisters(addr, cnt) => {
+                match register_read(&self.input_registers.lock().unwrap(), addr, cnt) {
+                    Ok(values) => future::ready(Ok(Response::ReadInputRegisters(values))),
+                    Err(err) => future::ready(Err(err)),
+                }
+            }
+            Request::ReadHoldingRegisters(addr, cnt) => {
+                match register_read(&self.holding_registers.lock().unwrap(), addr, cnt) {
+                    Ok(values) => future::ready(Ok(Response::ReadHoldingRegisters(values))),
+                    Err(err) => future::ready(Err(err)),
+                }
+            }
+            Request::WriteMultipleRegisters(addr, values) => {
+                match register_write(&mut self.holding_registers.lock().unwrap(), addr, &values) {
+                    Ok(_) => future::ready(Ok(Response::WriteMultipleRegisters(
+                        addr,
+                        values.len() as u16,
+                    ))),
+                    Err(err) => future::ready(Err(err)),
+                }
+            }
+            Request::WriteSingleRegister(addr, value) => {
+                match register_write(
+                    &mut self.holding_registers.lock().unwrap(),
+                    addr,
+                    std::slice::from_ref(&value),
+                ) {
+                    Ok(_) => future::ready(Ok(Response::WriteSingleRegister(addr, value))),
+                    Err(err) => future::ready(Err(err)),
+                }
+            }
+            _ => {
+                println!("SERVER: Exception::IllegalFunction - Unimplemented function code in request: {req:?}");
+                // TODO: We want to return a Modbus Exception response `IllegalFunction`. https://github.com/slowtec/tokio-modbus/issues/165
+                future::ready(Err(std::io::Error::new(
+                    std::io::ErrorKind::AddrNotAvailable,
+                    "Unimplemented function code in request".to_string(),
+                )))
+            }
+        }
+    }
+}
+
+impl ExampleService {
+    fn new() -> Self {
+        // Insert some test data as register values.
+        let mut input_registers = HashMap::new();
+        input_registers.insert(0, 1234);
+        input_registers.insert(1, 5678);
+        let mut holding_registers = HashMap::new();
+        holding_registers.insert(0, 10);
+        holding_registers.insert(1, 20);
+        holding_registers.insert(2, 30);
+        holding_registers.insert(3, 40);
+        Self {
+            input_registers: Arc::new(Mutex::new(input_registers)),
+            holding_registers: Arc::new(Mutex::new(holding_registers)),
+        }
+    }
+}
+
+/// Helper function implementing reading registers from a HashMap.
+fn register_read(
+    registers: &HashMap<u16, u16>,
+    addr: u16,
+    cnt: u16,
+) -> Result<Vec<u16>, std::io::Error> {
+    let mut response_values = vec![0; cnt.into()];
+    for i in 0..cnt {
+        let reg_addr = addr + i;
+        if let Some(r) = registers.get(&reg_addr) {
+            response_values[i as usize] = *r;
+        } else {
+            // TODO: Return a Modbus Exception response `IllegalDataAddress` https://github.com/slowtec/tokio-modbus/issues/165
+            println!("SERVER: Exception::IllegalDataAddress");
+            return Err(std::io::Error::new(
+                std::io::ErrorKind::AddrNotAvailable,
+                format!("no register at address {reg_addr}"),
+            ));
+        }
+    }
+
+    Ok(response_values)
+}
+
+/// Write a holding register. Used by both the write single register
+/// and write multiple registers requests.
+fn register_write(
+    registers: &mut HashMap<u16, u16>,
+    addr: u16,
+    values: &[u16],
+) -> Result<(), std::io::Error> {
+    for (i, value) in values.iter().enumerate() {
+        let reg_addr = addr + i as u16;
+        if let Some(r) = registers.get_mut(&reg_addr) {
+            *r = *value;
+        } else {
+            // TODO: Return a Modbus Exception response `IllegalDataAddress` https://github.com/slowtec/tokio-modbus/issues/165
+            println!("SERVER: Exception::IllegalDataAddress");
+            return Err(std::io::Error::new(
+                std::io::ErrorKind::AddrNotAvailable,
+                format!("no register at address {reg_addr}"),
+            ));
+        }
+    }
+
+    Ok(())
+}
+
+#[tokio::main]
+async fn main() -> Result<(), Box<dyn std::error::Error>> {
+    let socket_addr = "127.0.0.1:5502".parse().unwrap();
+
+    tokio::select! {
+        _ = server_context(socket_addr) => unreachable!(),
+        _ = client_context(socket_addr) => println!("Exiting"),
+    }
+
+    Ok(())
+}
+
+async fn server_context(socket_addr: SocketAddr) -> anyhow::Result<()> {
+    println!("Starting up server on {socket_addr}");
+    let listener = TcpListener::bind(socket_addr).await?;
+    let server = Server::new(listener);
+    let new_service = |_socket_addr| Ok(Some(ExampleService::new()));
+    let on_connected = |stream, socket_addr| async move {
+        accept_tcp_connection(stream, socket_addr, new_service)
+    };
+    let on_process_error = |err| {
+        eprintln!("{err}");
+    };
+    server.serve(&on_connected, on_process_error).await?;
+    Ok(())
+}
+
+async fn client_context(socket_addr: SocketAddr) {
+    tokio::join!(
+        async {
+            // Give the server some time for starting up
+            tokio::time::sleep(Duration::from_secs(1)).await;
+
+            println!("CLIENT: Connecting client...");
+            let transport = tokio::net::TcpStream::connect(socket_addr).await.unwrap();
+            let mut ctx = tokio_modbus::prelude::rtu::attach_slave(transport, Slave(1));
+
+            println!("CLIENT: Reading 2 input registers...");
+            let response = ctx.read_input_registers(0x00, 2).await.unwrap();
+            println!("CLIENT: The result is '{response:?}'");
+            assert_eq!(response, [1234, 5678]);
+
+            println!("CLIENT: Writing 2 holding registers...");
+            ctx.write_multiple_registers(0x01, &[7777, 8888])
+                .await
+                .unwrap();
+
+            // Read back a block including the two registers we wrote.
+            println!("CLIENT: Reading 4 holding registers...");
+            let response = ctx.read_holding_registers(0x00, 4).await.unwrap();
+            println!("CLIENT: The result is '{response:?}'");
+            assert_eq!(response, [10, 7777, 8888, 40]);
+
+            // Now we try to read with an invalid register address.
+            // This should return a Modbus exception response with the code
+            // IllegalDataAddress.
+            println!("CLIENT: Reading nonexisting holding register address... (should return IllegalDataAddress)");
+            let response = ctx.read_holding_registers(0x100, 1).await;
+            println!("CLIENT: The result is '{response:?}'");
+            assert!(response.is_err());
+            // TODO: How can Modbus client identify Modbus exception responses? E.g. here we expect IllegalDataAddress
+            // Question here: https://github.com/slowtec/tokio-modbus/issues/169
+
+            println!("CLIENT: Done.")
+        },
+        tokio::time::sleep(Duration::from_secs(5))
+    );
+}

src/server/mod.rs

@@ -12,6 +12,9 @@ pub mod rtu;
 #[cfg(feature = "tcp-server")]
 pub mod tcp;
 
+#[cfg(feature = "rtu-over-tcp-server")]
+pub mod rtu_over_tcp;
+
 mod service;
 pub use self::service::Service;