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: segment.rs
    path of file: ./repos/zbox/src/content
    
    the code of the file until where you have to start completion: use std::fmt::{self, Debug};
use std::io::{Error as IoError, ErrorKind, Read, Result as IoResult, Write};
use std::ops::{Index, IndexMut, Range};
use std::sync::{Arc, RwLock};

use log::debug;
use serde::{Deserialize, Serialize};

use super::chunk::Chunk;
use super::{Store, StoreWeakRef};
use crate::base::lru::{Lru, Meter, PinChecker};
use crate::base::IntoRef;
use crate::error::{Error, Result};
use crate::trans::cow::{Cow, CowCache, CowRef, Cowable, IntoCow};
use crate::trans::trans::{Action, Transable};
use crate::trans::{Eid, EntityType, Finish, Id, TxMgrRef, TxMgrWeakRef, Txid};
use crate::volume::{
    Arm, Reader as VolReader, VolumeRef, VolumeWeakRef, Writer as VolWriter,
};

/// Segment Data
#[derive(Default)]
pub struct SegData {
    id: Eid,
    action: Option<Action>,
    data: Vec<u8>,
}

impl SegData {
    fn new(id: &Eid) -> Self {
        SegData {
            id: id.clone(),
            action: None,
            data: Vec::new(),
        }
    }

    // Note: offset is in the segment data
    #[inline]
    pub fn read(&self, dst: &mut [u8], offset: usize) -> usize {
        let read_len = dst.len();
        assert!(offset + read_len <= self.data.len());
        dst.copy_from_slice(&self.data[offset..(offset + read_len)]);
        read_len
    }

    pub fn add_to_trans(
        data_id: &Eid,
        action: Action,
        txid: Txid,
        txmgr: &TxMgrRef,
    ) -> Result<()> {
        // create a segment data stub and add it to transaction.
        // Note: because it is just a stub in tx, only id is used and its data
        // element will always be empty.
        let mut stub = Self::new(data_id);
        stub.action = Some(action);
        let mut txmgr = txmgr.write().unwrap();
        txmgr.add_to_trans(
            data_id,
            txid,
            stub.into_ref(),
            action,
            EntityType::Direct,
            Arm::default(),
        )
    }

    // Check if seg data is in transaction
    #[inline]
    pub fn in_trans(&self) -> bool {
        self.action.is_some()
    }

    fn load(id: &Eid, vol: &VolumeRef) -> Result<Self> {
        let mut rdr = VolReader::new(id, vol)?;
        let mut buf = Vec::new();
        rdr.read_to_end(&mut buf)?;

        Ok(SegData {
            id: id.clone(),
            action: None,
            data: buf,
        })
    }

    fn save(&self, vol: &VolumeWeakRef) -> Result<()> {
        let mut wtr = VolWriter::new(&self.id, vol)?;
        wtr.write_all(&self.data[..])?;
        wtr.finish()?;
        Ok(())
    }
}

impl Id for SegData {
    #[inline]
    fn id(&self) -> &Eid {
    
    fn multiple_segs_spans() {
        let seg_id = Eid::new();
        let seg2_id = Eid::new();
        let mut seg = Segment::new();
        seg.append_chunk(5);
        seg.append_chunk(5);
        seg.append_chunk(5);
        let mut seg2 = Segment::new();
        seg2.append_chunk(5);
        seg2.append_chunk(5);
        seg2.append_chunk(5);
        seg2.append_chunk(5);
        let mut elst = EntryList::new();
        elst.append(&seg_id, &Span::new(0, 1, 0, 5, 0));
        elst.append(&seg_id, &Span::new(2, 3, 0, 5, 5));
        elst.append(&seg2_id, &Span::new(1, 2, 0, 5, 10));
        elst.append(&seg2_id, &Span::new(3, 4, 0, 5, 15));
        test_split_off(&elst, &seg, &seg2);
        test_split_to(&elst, &seg, &seg2);

        // split off in the middle
        let half = elst.len() / 2;
        let mut dst = elst.clone();
        let split = dst.split_off(half, &seg);
        dst.check();
        split.check();
        assert_eq!(dst.len(), half);
        assert_eq!(dst.offset(), 0);
        assert_eq!(dst.iter().count(), 1);
        assert_eq!(dst.iter().nth(0).unwrap().iter().count(), 2);
        assert_eq!(split.len(), half);
        assert_eq!(split.offset(), half);
        assert_eq!(split.iter().count(), 1);
        assert_eq!(split.iter().nth(0).unwrap().iter().count(), 2);

        // split off at 1/3
        let at = elst.len() / 3;
        let mut dst = elst.clone();
        let split = dst.split_off(at, &seg);
        dst.check();
        split.check();
        assert_eq!(dst.len(), at);
        assert_eq!(dst.offset(), 0);
        assert_eq!(dst.iter().count(), 1);
        assert_eq!(dst.iter().nth(0).unwrap().iter().count(), 2);
        assert_eq!(split.len(), 10);
        assert_eq!(split.offset(), 10);
        assert_eq!(split.iter().count(), 1);
        assert_eq!(split.iter().nth(0).unwrap().iter().count(), 2);

        // split off at 2/3
        let at = elst.len() * 2 / 3;
        let mut dst = elst.clone();
        let split = dst.split_off(at, &seg2);
        dst.check();
        split.check();
        assert_eq!(dst.len(), at);
        assert_eq!(dst.offset(), 0);
        assert_eq!(dst.iter().count(), 2);
        assert_eq!(dst.iter().nth(0).unwrap().iter().count(), 2);
        assert_eq!(dst.iter().nth(1).unwrap().iter().count(), 1);
        assert_eq!(split.len(), 5);
        assert_eq!(split.offset(), 15);
        assert_eq!(split.iter().count(), 1);
        assert_eq!(split.iter().nth(0).unwrap().iter().count(), 1);

        // split to in the middle
        let half = elst.len() / 2;
        let mut dst = elst.clone();
        let split = dst.split_to(half, &seg);
        dst.check();
        split.check();
        assert_eq!(dst.len(), half);
        assert_eq!(dst.offset(), half);
        assert_eq!(split.len(), half);
        assert_eq!(split.offset(), 0);

        // split to at 1/3
        let at = elst.len() / 3;
        let mut dst = elst.clone();
        let split = dst.split_to(at, &seg);
        dst.check();
        split.check();
        assert_eq!(dst.len(), elst.len() - at);
        assert_eq!(dst.offset(), at);
        assert_eq!(dst.iter().count(), 2);
        assert_eq!(dst.iter().nth(0).unwrap().iter().count(), 1);
        assert_eq!(dst.iter().nth(1).unwrap().iter().count(), 2);
        assert_eq!(split.len(), 5);
        assert_eq!(split.offset(), 0);
        assert_eq!(split.iter().count(), 1);

        // split to at 2/3
        let at = elst.len() * 2 / 3;
        let mut dst = elst.clone();
        let split = dst.split_to(at, &seg2);
        dst.check();
        split.check();
        assert_eq!(dst.len(), elst.len() - at);
        assert_eq!(dst.offset(), at);
        assert_eq!(dst.iter().nth(0).unwrap().iter().count(), 2);
        assert_eq!(dst.iter().nth(0).unwrap().seg_id(), &seg2_id);
        assert_eq!(split.len(), 10);
        assert_eq!(split.offset(), 0);
        assert_eq!(split.iter().nth(0).unwrap().iter().count(), 2);
        assert_eq!(split.iter().nth(0).unwrap().seg_id(), &seg_id);
    }