Add leveldb-backed storage layer (#4)

* Add storage abstraction layer for metadata persistence

* Add LevelDB-backed implementation of `MetadataStore`

Author: ekkolon

Cargo.lock

@@ -15,7 +15,12 @@ categories = ["database", "network-programming"]
 
 [workspace.dependencies]
 thiserror = "2"
+tracing = "0.1"
+
 base64 = "0.22"
 blake3 = "1.8"
 dashmap = "6.1"
 tokio = { version = "1.49", default-features = false }
+
+# Chosen over `leveldb` crate which requires C++ LevelDB via FFI.
+rusty-leveldb = "1"

Cargo.toml

@@ -12,9 +12,11 @@ categories.workspace = true
 
 [dependencies]
 thiserror.workspace = true
+tracing.workspace = true
 base64 = { workspace = true }
 blake3 = { workspace = true }
 dashmap = { workspace = true }
+rusty-leveldb = { workspace = true }
 
 [dev-dependencies]
 tokio = { workspace = true, features = ["full"] }

minikv-core/Cargo.toml

@@ -0,0 +1,13 @@
+/// Unified error type for minikv.
+#[derive(Debug, thiserror::Error)]
+pub enum Error {
+    /// Errors from the rusty-leveldb storage engine.
+    #[error("LevelDB error: {0}")]
+    LevelDb(String),
+}
+
+impl From<rusty_leveldb::Status> for Error {
+    fn from(s: rusty_leveldb::Status) -> Self {
+        Error::LevelDb(s.to_string())
+    }
+}

minikv-core/src/error.rs

@@ -1,3 +1,7 @@
+pub mod error;
 pub mod hashing;
 pub mod locking;
+pub mod storage;
 pub mod volumes;
+
+pub use error::Error;