tokio_modbus/
slave.rs

1// SPDX-FileCopyrightText: Copyright (c) 2017-2025 slowtec GmbH <post@slowtec.de>
2// SPDX-License-Identifier: MIT OR Apache-2.0
3
4//! Modbus devices
5
6use std::{fmt, num::ParseIntError, str::FromStr};
7
8/// Slave identifier
9pub type SlaveId = u8;
10
11/// A single byte for addressing Modbus slave devices.
12#[derive(Debug, Clone, Copy, PartialEq, Eq, PartialOrd, Ord)]
13pub struct Slave(pub SlaveId);
14
15impl Slave {
16    /// The special address for sending a broadcast message to all
17    /// connected Modbus slave devices at once. Broadcast messages
18    /// are one-way and sent from the master to all slaves, i.e.
19    /// a request without a response.
20    ///
21    /// Some devices may use a custom id from the reserved range
22    /// 248-255 for broadcasting.
23    #[must_use]
24    pub const fn broadcast() -> Self {
25        Slave(0)
26    }
27
28    /// The minimum address of a single Modbus slave device.
29    #[must_use]
30    pub const fn min_device() -> Self {
31        Slave(1)
32    }
33
34    /// The maximum address of a single Modbus slave device.
35    #[must_use]
36    pub const fn max_device() -> Self {
37        Slave(247)
38    }
39
40    /// The reserved address for sending a message to a directly
41    /// connected Modbus TCP device, i.e. if not forwarded through
42    /// a TCP/RTU gateway according to the unit identifier.
43    ///
44    /// [Modbus Messaging on TCP/IP Implementation Guide](http://www.modbus.org/docs/Modbus_Messaging_Implementation_Guide_V1_0b.pdf), page 23
45    /// "On TCP/IP, the Modbus server is addressed using its IP address; therefore,
46    /// the Modbus Unit Identifier is useless. The value 0xFF has to be used."
47    #[must_use]
48    pub const fn tcp_device() -> Self {
49        Slave(255)
50    }
51
52    /// Check if the [`SlaveId`] is used for broadcasting
53    #[must_use]
54    pub fn is_broadcast(self) -> bool {
55        self == Self::broadcast()
56    }
57
58    /// Check if the [`SlaveId`] addresses a single device
59    #[must_use]
60    pub fn is_single_device(self) -> bool {
61        self >= Self::min_device() && self <= Self::max_device()
62    }
63
64    /// Check if the [`SlaveId`] is reserved
65    #[must_use]
66    pub fn is_reserved(self) -> bool {
67        self > Self::max_device()
68    }
69}
70
71impl From<SlaveId> for Slave {
72    fn from(from: SlaveId) -> Self {
73        Slave(from)
74    }
75}
76
77impl From<Slave> for SlaveId {
78    fn from(from: Slave) -> Self {
79        from.0
80    }
81}
82
83impl FromStr for Slave {
84    type Err = ParseIntError;
85
86    fn from_str(s: &str) -> Result<Self, Self::Err> {
87        let slave_id = match s.parse::<u8>() {
88            Ok(slave_id) => Ok(slave_id),
89            Err(err) => {
90                if let Some(stripped) = s.strip_prefix("0x") {
91                    u8::from_str_radix(stripped, 16)
92                } else {
93                    Err(err)
94                }
95            }
96        }?;
97        Ok(Slave(slave_id))
98    }
99}
100
101impl fmt::Display for Slave {
102    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
103        write!(f, "{} (0x{:0>2X})", self.0, self.0)
104    }
105}
106
107/// Stateful management of the currently active device.
108///
109/// RTU devices are addressed by their assigned *slave id*.
110///
111/// TCP devices are either addressed directly (= implicitly) by using the
112/// reserved *unit id* `Slave::tcp_device() = 0xFF` (default) or indirectly
113/// through an TCP/RTU gateway by setting the *unit id* to the desired
114/// *slave id*.
115///
116/// The names *slave id* and *unit id* are used synonymously depending
117/// on the context. This library consistently adopted the term *slave*.
118pub trait SlaveContext {
119    /// Select a slave device for all subsequent outgoing requests.
120    fn set_slave(&mut self, slave: Slave);
121}
122
123#[cfg(test)]
124mod tests {
125    use super::*;
126
127    #[test]
128    fn parse_dec() {
129        assert_eq!(Slave(0), Slave::from_str("0").unwrap());
130        assert_eq!(Slave(123), Slave::from_str("123").unwrap());
131        assert_eq!(Slave(255), Slave::from_str("255").unwrap());
132        assert!(Slave::from_str("-1").is_err());
133        assert!(Slave::from_str("256").is_err());
134    }
135
136    #[test]
137    fn parse_hex() {
138        assert_eq!(Slave(0), Slave::from_str("0x00").unwrap());
139        assert_eq!(Slave(123), Slave::from_str("0x7b").unwrap());
140        assert_eq!(Slave(123), Slave::from_str("0x7B").unwrap());
141        assert_eq!(Slave(255), Slave::from_str("0xff").unwrap());
142        assert_eq!(Slave(255), Slave::from_str("0xFF").unwrap());
143        assert!(Slave::from_str("0X00").is_err());
144        assert!(Slave::from_str("0x100").is_err());
145        assert!(Slave::from_str("0xfff").is_err());
146        assert!(Slave::from_str("0xFFF").is_err());
147    }
148
149    #[test]
150    fn format() {
151        assert!(format!("{}", Slave(123)).contains("123"));
152        assert!(format!("{}", Slave(0x7B)).contains("0x7B"));
153        assert!(!format!("{}", Slave(0x7B)).contains("0x7b"));
154    }
155}
tokio_modbus/slave.rs

tokio_modbus/
slave.rs
