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: wal.rs
    path of file: ./repos/mini-lsm/mini-lsm/src
    
    the code of the file until where you have to start completion: use std::fs::{File, OpenOptions};
use std::hash::Hasher;
use std::io::{BufWriter, Read, Write};
use std::path::Path;
use std::sync::Arc;

use anyhow::{bail, Context, Result};
use bytes::{Buf, BufMut, Bytes};
use crossbeam_skiplist::SkipMap;
use parking_lot::Mutex;

pub struct Wal {
    file: Arc<Mutex<BufWriter<File>>>,
}

impl Wal {
    pub fn create(path: impl AsRef<Path>) -> Re
    
    pub fn put(&self, key: &[u8], value: &[u8]) -> Result<()> {
        let mut file = self.file.lock();
        let mut buf: Vec<u8> =
            Vec::with_capacity(key.len() + value.len() + std::mem::size_of::<u16>());
        let mut hasher = crc32fast::Hasher::new();
        hasher.write_u16(key.len() as u16);
        buf.put_u16(key.len() as u16);
        hasher.write(key);
        buf.put_slice(key);
        hasher.write_u16(value.len() as u16);
        buf.put_u16(value.len() as u16);
        buf.put_slice(value);
        hasher.write(value);
        // add checksum: week 2 day 7
        buf.put_u32(hasher.finalize());
        file.write_all(&buf)?;
        Ok(())
    }