powdb-storage 0.28.0

//! PowDB storage engine: catalog, tables, heap files, B+tree indexes, and the
//! write-ahead log.
//!
//! # Public API boundary
//!
//! `btree`, `disk`, `format`, `heap`, `page`, `row`, and `wal` are marked
//! `#[doc(hidden)]`. They stay `pub` and code that imports them still compiles:
//! the attribute hides a module from the generated documentation without
//! restricting access to it. What it withdraws is the implication that these
//! are an interface. They are `pub` because sibling crates in this workspace
//! link against them, and they carry no compatibility promise.
//!
//! `row` is the clearest case. It is the raw on-disk row encoding, which the
//! `powdb-query` executor decodes and patches in place on its fast paths, so it
//! has to be reachable across the crate boundary. It also moves whenever the
//! storage format moves, and that is a format-version event governed by
//! `docs/FORMAT.md`, not a crate-API event.
//!
//! The supported entry points are the `powdb` facade crate and the `Engine`
//! API in `powdb-query`. See `docs/STABILITY.md` for what a version bump
//! promises.

#[doc(hidden)]
pub mod btree;
pub mod catalog;
pub mod data_dir;
pub mod dir_lock;
#[doc(hidden)]
pub mod disk;
pub mod error;
#[doc(hidden)]
pub mod format;
#[doc(hidden)]
pub mod heap;
#[doc(hidden)]
pub mod page;
pub mod pj1;
#[doc(hidden)]
pub mod row;
pub mod stored_json_path;
pub mod table;
pub mod types;
pub mod view;
#[doc(hidden)]
pub mod wal;

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

/// Create a database data directory with owner-only permissions.
///
/// On Unix the directory is created (and, if it already exists, tightened) to
/// `0700` so that the heap files, WAL, and indexes it contains — which hold all
/// row data — are not world- or group-readable under a typical umask. This is
/// the same posture PostgreSQL enforces on its data directory: locking the
/// directory down protects every file inside it regardless of each file's own
/// mode. On non-Unix platforms this is a plain recursive create.
pub fn create_data_dir_secure(data_dir: &Path) -> io::Result<()> {
    #[cfg(unix)]
    {
        use std::os::unix::fs::{DirBuilderExt, PermissionsExt};
        std::fs::DirBuilder::new()
            .recursive(true)
            .mode(0o700)
            .create(data_dir)?;
        // `recursive(true)` does not re-apply the mode to a directory that
        // already existed, so tighten an existing dir explicitly. Widening one
        // is a different act from tightening one, and both used to happen
        // without a word: a 0o555 snapshot mount or a 0o500 directory an
        // operator had deliberately frozen came back 0o700 and writable.
        let current = std::fs::metadata(data_dir)?.permissions().mode() & 0o7777;
        if current == 0o700 {
            return Ok(());
        }
        if current == 0o000 {
            // The owner had no access at all. Whatever that directory is for,
            // handing ourselves read, write and execute on it is not a
            // permission fix, it is a decision the owner did not make.
            return Err(io::Error::new(
                io::ErrorKind::PermissionDenied,
                format!(
                    "{}: data directory mode is 0000 (the owner has no access);                      refusing to widen it, set it to 0700 to use it",
                    data_dir.display()
                ),
            ));
        }
        tracing::warn!(
            data_dir = %data_dir.display(),
            old_mode = format!("{current:04o}"),
            new_mode = "0700",
            "changing data directory mode from {current:04o} to 0700"
        );
        std::fs::set_permissions(data_dir, std::fs::Permissions::from_mode(0o700))?;
        Ok(())
    }
    #[cfg(not(unix))]
    {
        std::fs::create_dir_all(data_dir)
    }
}

/// Validate that `data_dir` is an existing directory suitable for read-only
/// snapshot serving, **without mutating it**. Unlike [`create_data_dir_secure`]
/// this never creates the directory and never calls `set_permissions`: a
/// read-only open must leave the directory byte-for-byte unchanged. It only
/// confirms the path exists and is a directory; the actual read access is then
/// proven by opening the catalog and heap files read-only.
pub fn validate_data_dir_read_only(data_dir: &Path) -> io::Result<()> {
    let meta = std::fs::metadata(data_dir)?;
    if !meta.is_dir() {
        return Err(io::Error::new(
            io::ErrorKind::InvalidInput,
            format!("{} is not a directory", data_dir.display()),
        ));
    }
    Ok(())
}

#[cfg(all(test, unix))]
mod tests {
    use super::*;
    use std::os::unix::fs::PermissionsExt;

    fn mode_of(dir: &Path) -> u32 {
        std::fs::metadata(dir).unwrap().permissions().mode() & 0o7777
    }

    /// Records the message of every `tracing` event emitted on this thread.
    ///
    /// `tracing-subscriber` is not a dependency of this crate and the whole
    /// question here is "did the warning happen, and did it name the modes",
    /// which a dozen lines of `Subscriber` answers directly.
    #[derive(Clone, Default)]
    struct RecordedWarnings(std::sync::Arc<std::sync::Mutex<Vec<String>>>);

    impl RecordedWarnings {
        fn messages(&self) -> Vec<String> {
            self.0.lock().unwrap_or_else(|e| e.into_inner()).clone()
        }
    }

    impl tracing::Subscriber for RecordedWarnings {
        fn enabled(&self, metadata: &tracing::Metadata<'_>) -> bool {
            *metadata.level() <= tracing::Level::WARN
        }

        fn new_span(&self, _: &tracing::span::Attributes<'_>) -> tracing::span::Id {
            tracing::span::Id::from_u64(1)
        }

        fn record(&self, _: &tracing::span::Id, _: &tracing::span::Record<'_>) {}

        fn record_follows_from(&self, _: &tracing::span::Id, _: &tracing::span::Id) {}

        fn event(&self, event: &tracing::Event<'_>) {
            struct Render(String);
            impl tracing::field::Visit for Render {
                fn record_debug(
                    &mut self,
                    field: &tracing::field::Field,
                    value: &dyn std::fmt::Debug,
                ) {
                    self.0.push_str(&format!(" {}={value:?}", field.name()));
                }
            }
            let mut render = Render(format!("{}", event.metadata().level()));
            event.record(&mut render);
            self.0
                .lock()
                .unwrap_or_else(|e| e.into_inner())
                .push(render.0);
        }

        fn enter(&self, _: &tracing::span::Id) {}

        fn exit(&self, _: &tracing::span::Id) {}
    }

    /// Tightening a loose mode is right, but doing it in silence is not: an
    /// operator who froze a snapshot at 0555 got a writable 0700 directory
    /// back and no way to know it had happened. So the warning itself is what
    /// this pins: asserting only that the mode ends at 0700 asserts what the
    /// code did before the warning was added, and stays green if it is deleted.
    #[test]
    fn widening_a_data_directory_mode_is_announced() {
        let dir = tempfile::tempdir().unwrap();
        std::fs::set_permissions(dir.path(), std::fs::Permissions::from_mode(0o555)).unwrap();

        let recorded = RecordedWarnings::default();
        tracing::subscriber::with_default(recorded.clone(), || {
            create_data_dir_secure(dir.path()).expect("a 0555 directory is still usable");
        });

        assert_eq!(mode_of(dir.path()), 0o700);
        let warnings = recorded.messages();
        assert_eq!(
            warnings.len(),
            1,
            "widening a directory must emit exactly one warning, got: {warnings:?}"
        );
        let warning = &warnings[0];
        for expected in ["WARN", "0555", "0700"] {
            assert!(
                warning.contains(expected),
                "the warning must name {expected}, got: {warning}"
            );
        }
    }

    /// The other half of the announcement: a directory already at 0700 is not
    /// widened, so it must say nothing at all. Without this, "announce every
    /// call" would satisfy the test above.
    #[test]
    fn a_directory_already_at_0700_is_announced_to_nobody() {
        let dir = tempfile::tempdir().unwrap();
        std::fs::set_permissions(dir.path(), std::fs::Permissions::from_mode(0o700)).unwrap();

        let recorded = RecordedWarnings::default();
        tracing::subscriber::with_default(recorded.clone(), || {
            create_data_dir_secure(dir.path()).unwrap();
        });

        assert!(
            recorded.messages().is_empty(),
            "a directory that was already 0700 was not changed and must not warn, got: {:?}",
            recorded.messages()
        );
    }

    /// A 0000 directory is one the owner deliberately shut. Widening it to
    /// 0700 and writing into it is a decision they did not make.
    #[test]
    fn a_zero_mode_data_directory_is_refused_rather_than_widened() {
        let dir = tempfile::tempdir().unwrap();
        std::fs::set_permissions(dir.path(), std::fs::Permissions::from_mode(0o000)).unwrap();

        let error = create_data_dir_secure(dir.path())
            .expect_err("a 0000 directory must be refused, not widened");

        assert_eq!(error.kind(), io::ErrorKind::PermissionDenied);
        assert!(
            error.to_string().contains("0000"),
            "the refusal must name the mode, got: {error}"
        );
        assert_eq!(mode_of(dir.path()), 0o000, "the mode must be left alone");

        // Restore so the temp dir can be removed.
        std::fs::set_permissions(dir.path(), std::fs::Permissions::from_mode(0o700)).unwrap();
    }

    #[test]
    fn a_directory_already_at_0700_is_left_alone() {
        let dir = tempfile::tempdir().unwrap();
        std::fs::set_permissions(dir.path(), std::fs::Permissions::from_mode(0o700)).unwrap();
        create_data_dir_secure(dir.path()).unwrap();
        assert_eq!(mode_of(dir.path()), 0o700);
    }
}