snap7-server

In-process S7 PLC simulator for testing and development. Pure Rust — no FFI, no native C dependency. Responds to real S7Comm read/write requests over TCP.

Part of the rs-snap7 workspace.

Features

Capability	Status
S7Comm read/write dispatch — handles `ReadVar` / `WriteVar` requests	✅
Multi-item read/write — single-PDU multi-area operations	✅
DataStore — thread-safe in-memory store by `(area, db, offset)`	✅
Area registration — PI, PA, MK, DB, timer, counter, etc.	✅
CPU state tracking — RUN / STOP with state-change callbacks	✅
Read / write event callbacks	✅
Max connections limit	✅
Ephemeral port support — `127.0.0.1:0` for tests	✅
Pure Rust, zero native dependencies	✅

Use cases

Add to your project

[dev-dependencies]
snap7-server = "0.1"
tokio = { version = "1", features = ["rt-multi-thread", "macros"] }

Quick start

use snap7_server::{S7Server, ServerConfig, DataStore};
use std::net::SocketAddr;

#[tokio::main]
async fn main() -> anyhow::Result<()> {
    // Pre-seed data block 1
    let store = DataStore::new();
    store.write_bytes(1, 0, &[0xDE, 0xAD, 0xBE, 0xEF]);

    let cfg = ServerConfig {
        bind_addr: "127.0.0.1:10200".parse()?,
        max_connections: 8,
    };
    let server = S7Server::bind(cfg).await?;
    println!("listening on {}", server.local_addr()?);

    server.serve(store).await?;
    Ok(())
}

Ephemeral port (tests)

let cfg = ServerConfig {
    bind_addr: "127.0.0.1:0".parse()?,  // OS assigns a free port
    max_connections: 4,
};
let server = S7Server::bind(cfg).await?;
let addr = server.local_addr()?;
tokio::spawn(server.serve(store));

// connect snap7-client to `addr`

API

Type	Purpose
`S7Server`	Binds TCP socket, accepts connections
`ServerConfig`	`bind_addr` + `max_connections`
`DataStore`	Thread-safe in-memory data block store; read/write by `(db, offset)`

Notes

Implements TPKT / COTP / S7Comm handshake and dispatch.
Supports multi-item read/write (ReadVar / WriteVar).
Does not implement S7CommPlus, SZL, or block upload — those return protocol errors.

License

MIT — see LICENSE.

snap7-server 0.1.4