tauri-plugin-hot-update 0.1.0

//! On-disk store: the thin I/O shell around the pure state machine.
//!
//! Layout inside the app data dir (design doc, "On-disk layout"):
//!
//! ```text
//! hot-update/
//!   bundles/seq-<N>/    # one dir per extracted bundle
//!   state.json          # the persisted machine::State
//! ```
//!
//! Rules:
//! - `state.json` is written atomically (temp file in the same dir + fsync +
//!   rename), so a crash mid-write can never leave a half-written pointer.
//! - A missing, truncated, or otherwise unparseable `state.json` loads as a
//!   fresh [`State`] — never a panic. The app then serves embedded (the
//!   fail-safe floor) and the machine rebuilds state from there.
//! - Everything under `bundles/` that is not a referenced `seq-<N>` dir is
//!   plugin-owned garbage (orphans from a kill between extraction and state
//!   write, stale temp dirs) and is swept by boot GC.
//! - Seqs are allocated above every seq ever seen on disk *or* in the state,
//!   so a stale orphan dir can never alias a future bundle.

use std::collections::BTreeSet;
use std::fs;
use std::io;
use std::path::{Path, PathBuf};
use std::sync::Mutex;

use crate::machine::{Effect, State};

const STATE_FILE: &str = "state.json";
const BUNDLES_DIR: &str = "bundles";
const SEQ_PREFIX: &str = "seq-";

/// Handle to the `hot-update/` directory. All state mutations go through
/// [`Store::update`], which serializes load→transition→persist cycles behind
/// a mutex so a mid-session ack and a finishing download cannot lose updates.
#[derive(Debug)]
pub struct Store {
    root: PathBuf,
    write_lock: Mutex<()>,
}

impl Store {
    /// `root` is the `hot-update/` directory itself (created lazily).
    pub fn new(root: PathBuf) -> Self {
        Self {
            root,
            write_lock: Mutex::new(()),
        }
    }

    #[cfg(test)]
    pub fn root(&self) -> &Path {
        &self.root
    }

    fn state_path(&self) -> PathBuf {
        self.root.join(STATE_FILE)
    }

    /// The `bundles/` directory: final `seq-<N>` homes and the update
    /// pipeline's temp files/dirs (anything non-`seq-<N>` here is swept by
    /// boot GC, which is what makes crashed downloads self-cleaning).
    pub(crate) fn bundles_dir(&self) -> PathBuf {
        self.root.join(BUNDLES_DIR)
    }

    /// Directory a bundle seq lives in (`hot-update/bundles/seq-<N>`).
    pub fn bundle_dir(&self, seq: u64) -> PathBuf {
        self.bundles_dir().join(format!("{SEQ_PREFIX}{seq}"))
    }

    /// Load `state.json`. Missing or corrupt files yield a fresh state —
    /// recovery is "serve embedded and start over", never a panic.
    pub fn load_state(&self) -> State {
        let path = self.state_path();
        let bytes = match fs::read(&path) {
            Ok(bytes) => bytes,
            Err(e) if e.kind() == io::ErrorKind::NotFound => return State::default(),
            Err(e) => {
                log::warn!("hot-update: failed to read {}: {e}; starting fresh", path.display());
                return State::default();
            }
        };
        match serde_json::from_slice(&bytes) {
            Ok(state) => state,
            Err(e) => {
                log::warn!(
                    "hot-update: corrupt state.json ({e}); discarding it and starting fresh"
                );
                State::default()
            }
        }
    }

    /// Persist the state atomically: write `state.json.tmp` in the same
    /// directory, fsync, then rename over `state.json`.
    pub fn save_state(&self, state: &State) -> io::Result<()> {
        fs::create_dir_all(&self.root)?;
        let path = self.state_path();
        let tmp = self.root.join(format!("{STATE_FILE}.tmp"));
        let json = serde_json::to_vec_pretty(state).map_err(io::Error::other)?;
        {
            let mut file = fs::File::create(&tmp)?;
            io::Write::write_all(&mut file, &json)?;
            file.sync_all()?;
        }
        fs::rename(&tmp, &path)
    }

    /// Serialized load → transition → persist. The transition runs on the
    /// freshest on-disk state and its result is persisted before returning.
    pub fn update<T>(&self, transition: impl FnOnce(State) -> (State, T)) -> io::Result<T> {
        let _guard = self.write_lock.lock().unwrap_or_else(|e| e.into_inner());
        let (state, out) = transition(self.load_state());
        self.save_state(&state)?;
        Ok(out)
    }

    /// Seqs of the `seq-<N>` dirs that exist under `bundles/`.
    pub fn present_seqs(&self) -> BTreeSet<u64> {
        let Ok(entries) = fs::read_dir(self.bundles_dir()) else {
            return BTreeSet::new();
        };
        entries
            .flatten()
            .filter(|entry| entry.path().is_dir())
            .filter_map(|entry| parse_seq(&entry.file_name().to_string_lossy()))
            .collect()
    }

    /// Entries under `bundles/` that are not `seq-<N>` dirs — stale temp
    /// dirs and other debris from interrupted extractions.
    pub fn foreign_entries(&self) -> Vec<PathBuf> {
        let Ok(entries) = fs::read_dir(self.bundles_dir()) else {
            return Vec::new();
        };
        entries
            .flatten()
            .filter(|entry| {
                let name = entry.file_name().to_string_lossy().into_owned();
                parse_seq(&name).is_none() || !entry.path().is_dir()
            })
            .map(|entry| entry.path())
            .collect()
    }

    /// Next seq: strictly above everything the state references and
    /// everything present on disk, so orphan dirs are never aliased.
    pub fn allocate_seq(&self, state: &State) -> u64 {
        let disk_max = self.present_seqs().into_iter().max().unwrap_or(0);
        let state_max = [state.committed, state.last_good, state.staged, state.booting]
            .into_iter()
            .flatten()
            .chain(state.versions.keys().copied())
            .max()
            .unwrap_or(0);
        disk_max.max(state_max) + 1
    }

    /// Execute deletion effects, best-effort: a failed delete is logged and
    /// left for the next boot's GC.
    pub fn apply_effects(&self, effects: &[Effect]) {
        for effect in effects {
            match effect {
                Effect::DeleteBundle(seq) => self.delete_path(&self.bundle_dir(*seq)),
            }
        }
    }

    /// Remove foreign (non-`seq-<N>`) debris under `bundles/`.
    pub fn sweep_foreign_entries(&self) {
        for path in self.foreign_entries() {
            self.delete_path(&path);
        }
    }

    fn delete_path(&self, path: &Path) {
        let result = if path.is_dir() {
            fs::remove_dir_all(path)
        } else {
            fs::remove_file(path)
        };
        match result {
            Ok(()) => log::debug!("hot-update: removed {}", path.display()),
            Err(e) if e.kind() == io::ErrorKind::NotFound => {}
            Err(e) => log::warn!(
                "hot-update: failed to remove {} ({e}); leaving it for next boot's GC",
                path.display()
            ),
        }
    }
}

fn parse_seq(name: &str) -> Option<u64> {
    name.strip_prefix(SEQ_PREFIX)?.parse().ok()
}

#[cfg(test)]
mod tests;