systemfd

systemfd is the 1% of systemd that's useful for development. It's a tiny process that opens a bunch of sockets and passes them to another process so that that process can then restart itself without dropping connections. For that it uses ths systemd socket passing protocol (LISTEN_FDS + LISTEN_PID) environment variables. Currently this only supports unix systems.

Teaser when combined with catch-watch you can get automatically reloading development servers:

$ systemfd -s http::5000 -- cargo watch -x run

To see how to implement a server ready for systemfd see below.

This program was inspired by catflap but follows systemd semantics and supports multiple sockets.

Installation

You can get systemfd by installing it with cargo:

$ cargo install systemfd

Usage

systemfd can create one or multiple sockets as specified on the command line and then invokes another application. Each time you pass the -s (or --socket) parameter a new socket is created. The value for the parameter is a socket specification in the format [TYPE::]VALUE where TYPE defaults to tcp or unix depending on the value. The following types exist:

• tcp: creates a tcp listener
• http: creates a tcp listener for http usage (prints a http url in the info output)
• https: creates a tcp listener for https usage (prints a https url in the info output)
• unix: creates a unix listener socket
• udp: creates a udp socket

VALUE depends on the socket type. The following formats are supported:

• <port>: an integer port value, assumes 127.0.0.1 as host
• <host>:<port>: binds to a specific network interface and port
• <unix-path>: requests a specific unix socket

Examples:

$ systemfd -s http::5000 -- my-server-executable $ systemfd -s http::5000 -s https::5443 -- my-server-executable $ systemfd -s 5000 -- my-server-executable $ systemfd -s udp::1567 -- my-game-server-executable

When systemfd starts it will print out the socket it created. This can be disabled by passing -q. Additionally if a port is set to 0 a random port is picked.

Usage with actix-web and listenfd

And here is an example actix-web server that supports this by using the listenfd crate:

```rust use listenfd::ListenFdManager; use actix_web::{server, App, Path};

fn index(info: Path<(String, u32)>) -> String { format!("Hello {}! id:{}", info.0, info.1) }

fn main() { let mut manager = ListenFdManager::fromenv(); let mut server = server::new( || App::new() .resource("/{name}/{id}/index.html", |r| r.with(index))); server = if let Some(listener) = manager.taketcp_listener(0)? { server.listener(listener) } else { server.bind("127.0.0.1:3000").unwrap() }; server.run(); } ```