Initial import. Most things seem working.

This includes an abortive attempt to do a gtk4 dialog (which I don't
think is possible, as gtk4 doesn't allow embedding toplevels anymore),
and an iced dialog, which I just never started writing.

util/src/lib.rs

@@ -0,0 +1,50 @@
+use std::{ffi::CStr, io};
+use xcb::x;
+
+pub const BSCREENSAVER_WM_CLASS: &[u8] = b"bscreensaver\0Bscreensaver\0";
+
+pub fn init_logging(env_name: &str) {
+    env_logger::builder()
+        .format_timestamp_millis()
+        .parse_env(env_name)
+        .init();
+}
+
+pub fn create_atom(conn: &xcb::Connection, name: &[u8]) -> xcb::Result<x::Atom> {
+    let cookie = conn.send_request(&x::InternAtom {
+        only_if_exists: false,
+        name,
+    });
+    Ok(conn.wait_for_reply(cookie)?.atom())
+}
+
+pub fn destroy_gc(conn: &xcb::Connection, gc: x::Gcontext) -> xcb::Result<()> {
+    conn.send_and_check_request(&x::FreeGc {
+        gc,
+    })?;
+    Ok(())
+}
+
+pub fn destroy_window(conn: &xcb::Connection, window: x::Window) -> xcb::Result<()> {
+    conn.send_and_check_request(&x::DestroyWindow {
+        window,
+    })?;
+    Ok(())
+}
+
+pub fn get_username() -> io::Result<String> {
+    // SAFETY: libc must be sane
+    let uid = unsafe { libc::getuid() };
+    // SAFETY: libc must be sane
+    let pwd = unsafe { libc::getpwuid(uid) };
+    // SAFETY: null-check occurs on same line
+    if pwd.is_null() || unsafe { *pwd }.pw_name.is_null() {
+        Err(io::Error::new(io::ErrorKind::NotFound, "Username not found".to_string()))
+    } else {
+        // SAFETY: libc must be sane; null checks performed above
+        let cstr = unsafe { CStr::from_ptr((*pwd).pw_name) };
+        cstr.to_str()
+            .map_err(|_| io::Error::new(io::ErrorKind::InvalidData, "Invalid UTF-8 data in username".to_string()))
+            .map(|s| s.to_string())
+    }
+}