Virtual Filesystem & Storage

Modern cross-platform applications often struggle with filesystem differences across operating systems: POSIX permissions, Windows path separators, Android Scoped Storage, iOS sandboxes, and Web browser sandboxes (OPFS/IndexedDB).

Strata solves this with a unified virtual filesystem (strata_vfs) and a zero-dependency append-only storage engine (strata_storage).

---

Universal Virtual Filesystem (strata_vfs)

strata_vfs exposes an asynchronous, unified filesystem API without requiring developers to scatter #[cfg(...)] conditionals throughout application code.

Standard Virtual Roots

• app_data(): Persistent configuration and application database.
  • Linux: ~/.config/<app>/
  • macOS: ~/Library/Application Support/<app>/
  • Windows: %APPDATA%/<app>/
  • Web: Origin Private File System (OPFS)
• cache(): Disposable cached assets and precompiled shaders.
• documents(): User-facing document exports and saved workspaces.
• temp(): Ephemeral scratch directory automatically cleaned on process exit.

use strata_vfs::prelude::*;

async fn save_user_preferences(prefs: &UserPrefs) -> Result<(), VfsError> {
    let vfs = StrataVfs::new();
    let config_path = vfs.app_data().join("preferences.json");

    let bytes = serde_json::to_vec_pretty(prefs)?;
    vfs.write(&config_path, &bytes).await?;

    Ok(())
}

---

Bitcask WAL Storage Engine (StrataKV)

Rather than bundling bulky C libraries such as SQLite (which adds 1.2MB of binary size) or RocksDB (which adds complex C++ dependencies), Strata implements a pure-Rust key-value engine modeled after Bitcask:

Principles of Bitcask

1. Append-Only Write-Ahead Log (WAL): All writes, updates, and deletes are appended sequentially to the active disk log. Sequential disk writes saturate NVMe and SSD bandwidth with zero random write overhead.
2. In-Memory Hash Index: Key pointers (file offset and payload length) are stored in an in-memory hash table.
3. Instant $O(1)$ Reads: Fetching any record requires exactly one disk seek at the cached byte offset.
4. Crash Safety: In the event of a sudden power outage, unwritten buffers are recovered automatically by replaying the append-only log up to the last valid checksum.

use strata_storage::StrataKV;

async fn track_session() -> Result<(), StorageError> {
    let kv = StrataKV::open("session_store").await?;

    // Atomic sequential append
    kv.put(b"last_login", b"2026-11-01T00:30:00Z").await?;

    // O(1) direct retrieval
    if let Some(val) = kv.get(b"last_login").await? {
        println!("Last login: {}", String::from_utf8_lossy(&val));
    }

    Ok(())
}

---

Hardware Secure Keystore

For sensitive credentials, encryption keys, and authentication tokens, strata_storage provides direct access to platform hardware security modules:

• Apple: macOS Keychain / iOS Secure Enclave (Security.framework).
• Android: Android Keystore Provider with hardware-backed TEE / StrongBox.
• Windows: Data Protection API (DPAPI) and Windows Hello TPM.
• Linux: FreeDesktop Secret Service DBus interface (GNOME Keyring / KWallet).
• Web: Web Cryptography API (crypto.subtle).

use strata_storage::keystore::SecureKeystore;

async fn store_secret(token: &str) -> Result<(), KeystoreError> {
    let keystore = SecureKeystore::new("com.larvance.strata")?;
    keystore.set_secret("auth_bearer_token", token.as_bytes())?;
    Ok(())
}