You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: wintun_install.rs
    path of file: ./repos/firezone/rust/gui-client/src-tauri/src/client
    
    the code of the file until where you have to start completion: //! "Installs" wintun.dll at runtime by copying it into whatever folder the exe is in

use connlib_shared::windows::wintun_dll_path;
use ring::digest;
use std::{
    fs,
    io::{self, Read},
    path::{Path, PathBuf},
};

struct DllBytes {
    /// Bytes embedded in the client with `include_bytes`
    bytes: &'static [u8],
    /// Expected SHA256 hash
    expected_sha256: &'static str,
}

#[derive(thiserror::Error, Debug)]
pub(crate) enum Error {
    #[error("Can't compute path where wintun.dll should be installed")]
    CantComputeWintunPath,
    #[error("create_dir_all failed")]
    CreateDirAll,
    #[error("Computed DLL path is invalid")]
    DllPathInvalid,
    #[error("permission denied")]
    PermissionDenied,
    #[error("platform not supported")]
    PlatformNotSupported,
    #[error("write failed: `{0:?}`")]
    WriteFailed(io::Error)
    
pub(crate) fn ensure_dll() -> Result<PathBuf, Error> {
    let dll_bytes = get_dll_bytes().ok_or(Error::PlatformNotSupported)?;

    let path = wintun_dll_path().map_err(|_| Error::CantComputeWintunPath)?;
    // The DLL path should always have a parent
    let dir = path.parent().ok_or(Error::DllPathInvalid)?;
    std::fs::create_dir_all(dir).map_err(|_| Error::CreateDirAll)?;

    // TODO: This log never shows up because `tracing` isn't started when we install wintun.dll
    tracing::info!(?path, "wintun.dll path");

    // This hash check is not meant to protect against attacks. It only lets us skip redundant disk writes, and it updates the DLL if needed.
    // `tun_windows.rs` in connlib, and `elevation.rs`, rely on thia.
    if !dll_already_exists(&path, &dll_bytes) {
        fs::write(&path, dll_bytes.bytes).map_err(|e| match e.kind() {
            io::ErrorKind::PermissionDenied => Error::PermissionDenied,
            _ => Error::WriteFailed(e),
        })?;
    }
    Ok(path)
}