cli/

persist.rs

//! Shared atomic-write primitives.
//!
//! Several modules (config, app/sys/task manifests, ssh transfer, workspace
//! env files, self-install) each hand-rolled their own "write to a temp file,
//! then rename over the destination" sequence. This module is the single
//! place that logic lives.

use anyhow::{Context, Result};
use std::path::Path;
use tokio::io::AsyncWriteExt;

/// Durably writes `contents` to `path`.
///
/// Creates the parent directory if missing, writes to a uniquely-named temp
/// file in the same directory, fsyncs it, then renames it over `path`. If
/// anything fails after the temp file is created, the temp file is removed.
pub async fn atomic_write(path: &Path, contents: &[u8]) -> Result<()> {
    let parent = path.parent().unwrap_or_else(|| Path::new("."));
    tokio::fs::create_dir_all(parent)
        .await
        .with_context(|| format!("creating {}", parent.display()))?;
    let temp = parent.join(format!(".shine-write-{}", uuid::Uuid::new_v4()));

    if let Err(error) = write_temp(&temp, contents).await {
        let _ = tokio::fs::remove_file(&temp).await;
        return Err(error);
    }

    finalize_temp(&temp, path).await
}

async fn write_temp(temp: &Path, contents: &[u8]) -> Result<()> {
    let mut file = tokio::fs::File::create(temp)
        .await
        .with_context(|| format!("creating {}", temp.display()))?;
    file.write_all(contents)
        .await
        .with_context(|| format!("writing {}", temp.display()))?;
    file.sync_all()
        .await
        .with_context(|| format!("syncing {}", temp.display()))?;
    Ok(())
}

/// Renames `temp` over `dest`, for callers that already wrote/streamed their
/// own temp file (e.g. large-file copies) and only need the finalize step.
///
/// On Windows, an existing `dest` is removed first (`rename` there doesn't
/// replace an existing file). On any failure, `temp` is removed.
pub async fn finalize_temp(temp: &Path, dest: &Path) -> Result<()> {
    #[cfg(windows)]
    if dest.exists() {
        tokio::fs::remove_file(dest)
            .await
            .with_context(|| format!("removing {}", dest.display()))?;
    }
    if let Err(error) = tokio::fs::rename(temp, dest).await {
        let _ = tokio::fs::remove_file(temp).await;
        return Err(error).with_context(|| format!("replacing {}", dest.display()));
    }
    Ok(())
}

/// Loads and parses a TOML file at `path`, or returns `T::default()` if it
/// doesn't exist yet. `what` is a human-readable label used in error
/// messages (e.g. `"app manifest"`).
pub async fn load_toml_or_default<T>(path: &Path, what: &str) -> Result<T>
where
    T: serde::de::DeserializeOwned + Default,
{
    match tokio::fs::read_to_string(path).await {
        Ok(content) => toml::from_str(&content).with_context(|| format!("failed to parse {what}")),
        Err(e) if e.kind() == std::io::ErrorKind::NotFound => Ok(T::default()),
        Err(e) => Err(e).with_context(|| format!("failed to read {what}")),
    }
}

/// Serializes `value` as pretty TOML and atomically writes it to `path`.
/// `what` is a human-readable label used in error messages.
pub async fn save_toml_atomic<T: serde::Serialize>(
    value: &T,
    path: &Path,
    what: &str,
) -> Result<()> {
    let content =
        toml::to_string_pretty(value).with_context(|| format!("failed to serialize {what}"))?;
    atomic_write(path, content.as_bytes())
        .await
        .with_context(|| format!("failed to write {what}"))
}

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

    #[tokio::test]
    async fn atomic_write_creates_missing_parent_directories() {
        let dir = crate::test_support::make_temp_dir("shine-persist").await;
        let path = dir.join("nested/deep/file.txt");

        atomic_write(&path, b"hello").await.unwrap();

        assert_eq!(tokio::fs::read(&path).await.unwrap(), b"hello");
        tokio::fs::remove_dir_all(&dir).await.unwrap();
    }

    #[tokio::test]
    async fn atomic_write_replaces_existing_file() {
        let dir = crate::test_support::make_temp_dir("shine-persist").await;
        let path = dir.join("file.txt");
        tokio::fs::write(&path, b"old").await.unwrap();

        atomic_write(&path, b"new").await.unwrap();

        assert_eq!(tokio::fs::read(&path).await.unwrap(), b"new");
        tokio::fs::remove_dir_all(&dir).await.unwrap();
    }

    #[tokio::test]
    async fn atomic_write_leaves_no_temp_file_behind_on_success() {
        let dir = crate::test_support::make_temp_dir("shine-persist").await;
        let path = dir.join("file.txt");

        atomic_write(&path, b"content").await.unwrap();

        let mut entries = tokio::fs::read_dir(&dir).await.unwrap();
        let mut names = Vec::new();
        while let Some(entry) = entries.next_entry().await.unwrap() {
            names.push(entry.file_name());
        }
        assert_eq!(names, vec![std::ffi::OsString::from("file.txt")]);
        tokio::fs::remove_dir_all(&dir).await.unwrap();
    }

    #[tokio::test]
    async fn finalize_temp_removes_temp_on_rename_failure() {
        let dir = crate::test_support::make_temp_dir("shine-persist").await;
        let temp = dir.join(".shine-write-test");
        tokio::fs::write(&temp, b"content").await.unwrap();
        // A destination inside a nonexistent directory makes rename fail.
        let dest = dir.join("missing-dir").join("dest.txt");

        let result = finalize_temp(&temp, &dest).await;

        assert!(result.is_err());
        assert!(!temp.exists(), "temp file should be cleaned up on failure");
        tokio::fs::remove_dir_all(&dir).await.unwrap();
    }

    #[derive(Debug, Default, PartialEq, serde::Serialize, serde::Deserialize)]
    struct SampleToml {
        #[serde(default)]
        name: String,
        #[serde(default)]
        count: u32,
    }

    #[tokio::test]
    async fn load_toml_or_default_returns_default_when_file_missing() {
        let dir = crate::test_support::make_temp_dir("shine-persist").await;
        let path = dir.join("sample.toml");

        let value: SampleToml = load_toml_or_default(&path, "sample").await.unwrap();

        assert_eq!(value, SampleToml::default());
        tokio::fs::remove_dir_all(&dir).await.unwrap();
    }

    #[tokio::test]
    async fn save_then_load_toml_round_trips() {
        let dir = crate::test_support::make_temp_dir("shine-persist").await;
        let path = dir.join("sample.toml");
        let value = SampleToml {
            name: "hi".to_string(),
            count: 3,
        };

        save_toml_atomic(&value, &path, "sample").await.unwrap();
        let loaded: SampleToml = load_toml_or_default(&path, "sample").await.unwrap();

        assert_eq!(loaded, value);
        tokio::fs::remove_dir_all(&dir).await.unwrap();
    }

    #[tokio::test]
    async fn save_toml_atomic_creates_missing_parent_directory() {
        let dir = crate::test_support::make_temp_dir("shine-persist").await;
        let path = dir.join("nested/sample.toml");
        let value = SampleToml::default();

        save_toml_atomic(&value, &path, "sample").await.unwrap();

        assert!(path.exists());
        tokio::fs::remove_dir_all(&dir).await.unwrap();
    }
}