robt 0.2.0

Read only, immutable Btree for indexing key,value
Documentation 
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use fs2::FileExt;
use log::{info, trace};
use mkit::thread;

use std::{convert::TryFrom, ffi, fs, mem, path};

use crate::{Error, Result};

pub enum Flusher {
    File {
        file: ffi::OsString,
        fpos: u64,
        th: Option<thread::Thread<Vec<u8>, u64, Result<u64>>>,
        tx: Option<thread::Tx<Vec<u8>, u64>>,
    },
    None,
}

impl Drop for Flusher {
    fn drop(&mut self) {
        match self {
            Flusher::File { file, .. } => info!(target: "robt-flush", "drop {:?}", file),
            Flusher::None => (),
        }
    }
}

impl Flusher {
    pub fn new(file: &ffi::OsStr, create: bool, chan_size: usize) -> Result<Flusher> {
        let (fd, fpos) = if create {
            (create_file_a(file)?, 0)
        } else {
            let fpos = err_at!(IOError, fs::metadata(file))?
                .len()
                .saturating_sub(1);
            (open_file_a(file)?, fpos)
        };

        let ffpp = file.to_os_string();
        let (th, tx) = thread::Thread::new_sync(
            "flusher",
            chan_size,
            move |rx: thread::Rx<Vec<u8>, u64>| move || thread_flush(ffpp, fd, rx, fpos),
        );

        let val = Flusher::File {
            file: file.to_os_string(),
            fpos,
            th: Some(th),
            tx: Some(tx),
        };

        Ok(val)
    }

    pub fn empty() -> Flusher {
        Flusher::None
    }

    pub fn to_fpos(&self) -> Option<u64> {
        match self {
            Flusher::File { fpos, .. } => Some(*fpos),
            Flusher::None => None,
        }
    }

    pub fn flush(&mut self, data: Vec<u8>) -> Result<()> {
        match self {
            Flusher::File { fpos, tx, .. } => {
                *fpos = tx.as_ref().unwrap().request(data)?
            }
            Flusher::None => (),
        };
        Ok(())
    }

    pub fn close(&mut self) -> Result<u64> {
        match self {
            Flusher::File { tx, th, .. } => {
                mem::drop(tx.take());
                th.take().unwrap().join()?
            }
            Flusher::None => Ok(0),
        }
    }
}

fn thread_flush(
    file: ffi::OsString,
    mut fd: fs::File,
    rx: thread::Rx<Vec<u8>, u64>,
    mut fpos: u64,
) -> Result<u64> {
    info!(target: "robt-flush", "starting {:?} @ fpos {}", file, fpos);

    err_at!(IOError, fd.lock_shared(), "fail read lock for {:?}", file)?;

    for (data, res_tx) in rx {
        write_file!(fd, &data, &file, "flushing file")?;

        fpos += u64::try_from(data.len()).unwrap();
        trace!(target: "robt", "flusher {:?} {} {}", file, data.len(), fpos);
        res_tx.map(|tx| tx.send(fpos).ok());
    }

    err_at!(IOError, fd.sync_all(), "fail sync_all {:?}", file)?;
    err_at!(IOError, fd.unlock(), "fail read unlock {:?}", file)?;

    Ok(fpos)
}

// create a file in append mode for writing.
fn create_file_a(file: &ffi::OsStr) -> Result<fs::File> {
    let os_file = {
        let os_file = path::Path::new(file);
        fs::remove_file(os_file).ok(); // NOTE: ignore remove errors.
        os_file
    };

    match os_file.parent() {
        Some(parent) => err_at!(IOError, fs::create_dir_all(parent))?,
        None => err_at!(InvalidFile, msg: "{:?}", file)?,
    };

    let mut opts = fs::OpenOptions::new();
    Ok(err_at!(
        IOError,
        opts.append(true).create_new(true).open(os_file)
    )?)
}

// open existing file in append mode for writing.
fn open_file_a(file: &ffi::OsStr) -> Result<fs::File> {
    let os_file = path::Path::new(file);
    Ok(err_at!(
        IOError,
        fs::OpenOptions::new().append(true).open(os_file)
    )?)
}

#[cfg(test)]
#[path = "flush_test.rs"]
mod flush_test;