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: reader.rs
    path of file: ./repos/fjall/src/journal
    
    the code of the file until where you have to start completion: use super::marker::Marker;
use lsm_tree::{serde::Deserializable, DeserializeError};
use std::{
    fs::{File, OpenOptions},
    io::{BufReader, Seek},
    path::Path,
};

/// Reads and emits throug
    
    fn next(&mut self) -> Option<Self::Item> {
        match Marker::deserialize(&mut self.reader) {
            Ok(abc) => {
                self.last_valid_pos = self
                    .reader
                    .stream_position()
                    .expect("should get stream position of journal reader");

                Some(Ok((self.last_valid_pos, abc)))
            }
            Err(e) => match e {
                DeserializeError::Io(e) => match e.kind() {
                    std::io::ErrorKind::UnexpectedEof | std::io::ErrorKind::Other => {
                        let stream_pos = self
                            .reader
                            .stream_position()
                            .expect("should get stream position of journal reader");

                        if stream_pos > self.last_valid_pos {
                            self.truncate_file_to_last_valid_pos()
                                .expect("should truncate journal");
                        }
                        None
                    }
                    _ => Some(Err(crate::Error::Io(e))),
                },
                DeserializeError::InvalidTag(_) | DeserializeError::InvalidTrailer => {
                    let stream_pos = self
                        .reader
                        .stream_position()
                        .expect("should get stream position of journal reader");

                    if stream_pos > self.last_valid_pos {
                        self.truncate_file_to_last_valid_pos()
                            .expect("should truncate journal");
                    }
                    None
                }
            },
        }
    }