Handling the Optional Runtime Path

The runtime directory isn't always available, so it's an Option. This guide shows the right way to check if it exists and use it.

When you look at the BaseDir struct, you’ll notice one field is different from the others. The runtime field is not a PathBuf, but an Option<PathBuf>.

This is intentional. The runtime directory is not always available, and this guide explains why it’s optional and how you should handle it in your code.

Why is it an Option?

The XDG specification defines $XDG_RUNTIME_DIR as the location for temporary, non-essential files for running applications, like sockets or PID files.

Unlike the config or data directories, the spec does not provide a default fallback path based on $HOME. If the $XDG_RUNTIME_DIR environment variable is not set, there is no standard location for these files.

Because of this, xdgdir will return None for the runtime path if the variable is missing or empty. It can’t just invent a path for you.

How to Handle It

Since the runtime path can be missing, you must check for it before you use it. The best way to do this is with an if let statement. This lets you safely unwrap the Option and run code only when the path exists.

Here is an example showing how to do it correctly.

Rust
use xdgdir::BaseDir;

fn main() {
    let dirs = BaseDir::new("my-app").unwrap();

    if let Some(runtime_path) = dirs.runtime {
        // The runtime directory exists, so we can use it.
        // For example, we could create a path for a socket file.
        let socket_path = runtime_path.join("app.sock");
        println!("Socket path would be: {}", socket_path.display());

    } else {
        // The runtime directory is not set.
        // Your application should handle this case.
        println!("$XDG_RUNTIME_DIR is not set.");
        println!("Features that need a runtime directory might be disabled.");
    }
}

By checking the Option, you make sure your app doesn’t crash if the runtime directory isn’t available. Your app could choose to disable features that depend on it, or maybe create its own temporary directory somewhere else as a fallback.