imag/libimagstore/src/lazyfile.rs

use error::{StoreError, StoreErrorKind};
use std::io::{Seek, SeekFrom};
use std::path::{Path, PathBuf};
use std::fs::{File, OpenOptions};

/**
 * LazyFile type
 *
 * A lazy file is either absent, but a path to it is available, or it is present.
 */
#[derive(Debug)]
pub enum LazyFile {
    Absent(PathBuf),
    File(File)
}

fn open_file<A: AsRef<Path>>(p: A) -> ::std::io::Result<File> {
    OpenOptions::new().write(true).read(true).open(p)
}

fn create_file<A: AsRef<Path>>(p: A) -> ::std::io::Result<File> {
    OpenOptions::new().write(true).read(true).create(true).open(p)
}

impl LazyFile {

    /**
     * Create a new LazyFile instance from a Path
     */
    pub fn new(p: PathBuf) -> LazyFile {
        LazyFile::Absent(p)
    }

    /**
     * Create a new LazyFile instance from an already existing file
     */
    pub fn new_with_file(f: File) -> LazyFile {
        LazyFile::File(f)
    }

    /**
     * Get the file behind a LazyFile object
     */
    pub fn get_file(&mut self) -> Result<&File, StoreError> {
        match self.get_file_mut() {
            Ok(file) => Ok(&*file),
            Err(e) => Err(e)
        }
    }

    /**
     * Get the mutable file behind a LazyFile object
     */
    pub fn get_file_mut(&mut self) -> Result<&mut File, StoreError> {
        let file = match *self {
            LazyFile::File(ref mut f) => return {
                // We seek to the beginning of the file since we expect each
                // access to the file to be in a different context
                f.seek(SeekFrom::Start(0)).map_err(|e|
                    StoreError::new(
                        StoreErrorKind::FileNotCreated, Some(Box::new(e))));
                Ok(f)
            },
            LazyFile::Absent(ref p) => {
                try!(open_file(p).map_err(|e| {
                    StoreError::new(StoreErrorKind::FileNotFound,
                                    Some(Box::new(e)))
                }))
            }
        };
        *self = LazyFile::File(file);
        if let LazyFile::File(ref mut f) = *self {
            return Ok(f);
        }
        unreachable!()
    }

    /**
     * Create a file out of this LazyFile object
     */
    pub fn create_file(&mut self) -> Result<&mut File, StoreError> {
        let file = match *self {
            LazyFile::File(ref mut f) => return Ok(f),
            LazyFile::Absent(ref p) => {
                try!(create_file(p).map_err(|e| {
                    StoreError::new(StoreErrorKind::FileNotFound,
                                    Some(Box::new(e)))
                }))
            }
        };
        *self = LazyFile::File(file);
        if let LazyFile::File(ref mut f) = *self {
            return Ok(f);
        }
        unreachable!()
    }
}

#[cfg(test)]
mod test {
    use super::LazyFile;
    use std::io::{Read, Write, Seek, SeekFrom};
    use std::path::PathBuf;
    use std::fs::File;
    use tempdir::TempDir;

    fn get_dir() -> TempDir {
        TempDir::new("test-image").unwrap()
    }

    #[test]
    fn lazy_file() {
        let dir = get_dir();
        let mut path = PathBuf::from(dir.path());
        path.set_file_name("test1");
        let mut lf = LazyFile::new(path);

        write!(lf.create_file().unwrap(), "Hello World").unwrap();
        dir.close().unwrap();
    }

    #[test]
    fn lazy_file_with_file() {
        let dir = get_dir();
        let mut path = PathBuf::from(dir.path());
        path.set_file_name("test2");
        let mut lf = LazyFile::new(path.clone());

        {
            let mut file = lf.create_file().unwrap();

            file.write(b"Hello World").unwrap();
            file.sync_all().unwrap();
        }

        {
            let mut file = lf.get_file().unwrap();
            let mut s = Vec::new();
            file.read_to_end(&mut s).unwrap();
            assert_eq!(s, "Hello World".to_string().into_bytes());
        }

        dir.close().unwrap();
    }
}