lesavka/server/src/usb_gadget.rs

// server/src/usb_gadget.rs
use std::{fs::{self, OpenOptions}, io::Write, thread, time::Duration};
use anyhow::{Context, Result};
use tracing::{info, warn};

#[derive(Clone)]
pub struct UsbGadget {
    udc_file: &'static str,
}

impl UsbGadget {
    pub fn new(name: &'static str) -> Self {
        Self {
            udc_file: Box::leak(
                format!("/sys/kernel/config/usb_gadget/{name}/UDC").into_boxed_str(),
            ),
        }
    }

    /// Read the controller name currently written to `<gadget>/UDC`
    fn current_udc(&self) -> Result<String> {
        Ok(fs::read_to_string(self.udc_file)?.trim().to_owned())
    }

    /// Helper: busy‑loop (max 10s) until the UDC `state` file equals `wanted`.
    fn wait_state(udc: &str, wanted: &str) -> Result<()> {
        let state_file = format!("/sys/class/udc/{udc}/state");
        for _ in 0..100 {
            let state = fs::read_to_string(&state_file)
                .unwrap_or_default()
                .trim()
                .to_owned();
            if state == wanted {
                return Ok(());
            }
            thread::sleep(Duration::from_millis(100));
        }
        Err(anyhow::anyhow!("🚧 UDC state did not reach '{wanted}' in time"))
            .with_context(|| format!("waiting for {wanted} in {state_file}"))
    }

    /// Force the host to re‑enumerate our HID gadget *safely*.
    pub fn cycle(&self) -> Result<()> {
        let udc_name = std::fs::read_dir("/sys/class/udc")?
            .next()
            .transpose()?
            .context("no UDC present")?
            .file_name()
            .to_string_lossy()
            .into_owned();

        /*–––– DETACH ––––*/
        if !self.current_udc()?.is_empty() {
            info!("🔌 UDC‑cycle: detaching gadget");
            OpenOptions::new()
                .write(true)
                .open(self.udc_file)?
                .write_all(b"")?;
        } else {
            info!("🔌 Gadget already detached");
        }
        Self::wait_state(&udc_name, "not attached")?;

        /*–––– ATTACH ––––*/
        info!("🔌 UDC‑cycle: re‑attaching to {udc_name}");
        OpenOptions::new()
            .write(true)
            .open(self.udc_file)?
            .write_all(udc_name.as_bytes())?;

        Self::wait_state(&udc_name, "configured")?;
        info!("🔌 USB‑gadget cycled successfully 🎉");
        Ok(())
    }
}