common/emgauwa-lib/src/utils.rs

use std::ffi::CString;
use std::io::{Error, ErrorKind};

pub fn load_settings<T>(config_name: &str, env_prefix: &str) -> T
where
	for<'de> T: serde::Deserialize<'de>,
{
	let default_file = config::File::with_name(&format!("emgauwa-{}", config_name)).required(false);

	config::Config::builder()
		.add_source(default_file)
		.add_source(
			config::Environment::with_prefix(&format!("EMGAUWA_{}", env_prefix))
				.prefix_separator("__")
				.separator("__"),
		)
		.build()
		.expect("Error building settings")
		.try_deserialize::<T>()
		.expect("Error reading settings")
}

// https://blog.lxsang.me/post/id/28.0
pub fn drop_privileges(user: &str, group: &str) -> Result<(), Error> {
	// the group id need to be set first, otherwise,
	// when the user privileges drop, it is unable to
	// drop the group privileges
	// get the gid from username
	if let Ok(cstr) = CString::new(group.as_bytes()) {
		let p = unsafe { libc::getgrnam(cstr.as_ptr()) };
		if p.is_null() {
			eprintln!("Unable to getgrnam of group: {}", group);
			return Err(Error::last_os_error());
		}
		if unsafe { libc::setgid((*p).gr_gid) } != 0 {
			eprintln!("Unable to setgid of group: {}", group);
			return Err(Error::last_os_error());
		}
	} else {
		return Err(Error::new(
			ErrorKind::Other,
			"Cannot create CString from String (group)!",
		));
	}
	// drop the user privileges
	// get the uid from username
	if let Ok(cstr) = CString::new(user.as_bytes()) {
		let p = unsafe { libc::getpwnam(cstr.as_ptr()) };
		if p.is_null() {
			eprintln!("Unable to getpwnam of user: {}", user);
			return Err(Error::last_os_error());
		}
		if unsafe { libc::setuid((*p).pw_uid) } != 0 {
			eprintln!("Unable to setuid of user: {}", user);
			return Err(Error::last_os_error());
		}
	} else {
		return Err(Error::new(
			ErrorKind::Other,
			"Cannot create CString from String (user)!",
		));
	}
	Ok(())
}