This code uses Tokio's TcpListener and the rmodbus library to make an async TCP modbus server in Rust. It can handle concurrent connections using Tokio's green threads.
By default, this listens for modbus client connections on port 5502.
$ cargo build
$ cargo run
Listening on 0.0.0.0:5502
Client connected: 127.0.0.1:38758
16-bit registers from address 0 to 9: [0, 0, 200, 214, 249, 169, 0, 0, 0, 0]
Responding to client 127.0.0.1:38758 with: [c0, 48, 0, 0, 0, 6, 1, 10, 0, 2, 0, 4]
16-bit registers from address 0 to 9: [0, 0, 200, 214, 249, 169, 0, 0, 0, 0]
Responding to client 127.0.0.1:38758 with: [44, 25, 0, 0, 0, b, 1, 3, 8, 0, c8, 0, d6, 0, f9, 0, a9]
16-bit registers from address 0 to 9: [0, 0, 200, 214, 249, 169, 0, 0, 0, 0]
Responding to client 127.0.0.1:38758 with: [8e, 37, 0, 0, 0, b, 1, 4, 8, 0, 0, 0, 0, 0, 0, 0, 0]
Client connected: 127.0.0.1:38770
16-bit registers from address 0 to 9: [0, 0, 233, 80, 160, 89, 0, 0, 0, 0]
Responding to client 127.0.0.1:38770 with: [22, ed, 0, 0, 0, 6, 1, 10, 0, 2, 0, 4]
16-bit registers from address 0 to 9: [0, 0, 233, 80, 160, 89, 0, 0, 0, 0]
Responding to client 127.0.0.1:38770 with: [a8, d9, 0, 0, 0, b, 1, 3, 8, 0, e9, 0, 50, 0, a0, 0, 59]
16-bit registers from address 0 to 9: [0, 0, 233, 80, 160, 89, 0, 0, 0, 0]
Run cargo fmt to format the code and cargo clippy to lint the code.