anyhow for Application Errors

// Cargo.toml: anyhow = "1"
use anyhow::{Context, Result, bail};

fn run() -> Result<()> {
    let config = std::fs::read_to_string("config.toml")
        .context("reading config.toml")?;        // adds breadcrumb if it fails

    let port: u16 = config.trim().parse()
        .with_context(|| format!("parsing port from {config:?}"))?;

    if port == 0 {
        bail!("port cannot be zero");            // shorthand for return Err(anyhow!())
    }
    println!("listening on :{port}");
    Ok(())
}

fn main() {
    if let Err(e) = run() {
        eprintln!("error: {e:#}");               // {:#} prints full causal chain
        std::process::exit(1);
    }
}