caldir-core 0.15.1

Core library for caldir calendar storage, sync, and provider protocol
Documentation 
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//! Write a file atomically: the contents land in a temp file in the same
//! directory and are renamed into place, so a concurrent reader (a file
//! watcher, another caldir process) never sees a partially written file.

use std::io::Write;
use std::path::Path;

pub(crate) fn atomic_write(path: &Path, contents: &[u8]) -> std::io::Result<()> {
    let parent = path.parent().ok_or_else(|| {
        std::io::Error::new(
            std::io::ErrorKind::InvalidInput,
            "path has no parent directory",
        )
    })?;

    std::fs::create_dir_all(parent)?;
    let mut tmp = tempfile::NamedTempFile::new_in(parent)?;
    tmp.write_all(contents)?;
    tmp.persist(path).map_err(|e| e.error)?;

    Ok(())
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn writes_and_replaces_contents() {
        let dir = tempfile::tempdir().unwrap();
        let path = dir.path().join("nested").join("file.txt");

        atomic_write(&path, b"one").unwrap();
        assert_eq!(std::fs::read(&path).unwrap(), b"one");

        atomic_write(&path, b"two").unwrap();
        assert_eq!(std::fs::read(&path).unwrap(), b"two");
        // No temp file left behind.
        assert_eq!(
            std::fs::read_dir(path.parent().unwrap()).unwrap().count(),
            1
        );
    }
}