feat(tvix/store): add directoryservice

This adds a DirectoryService trait, and an implementation for it using
sled, and one using a HashMap.

Change-Id: Ida61524b2ca949e1b3a78089a5aa7d9f9800c8d7
Reviewed-on: https://cl.tvl.fyi/c/depot/+/8093
Tested-by: BuildkiteCI
Reviewed-by: raitobezarius <tvl@lahfa.xyz>

tvix/store/src/directoryservice/mod.rs

@@ -0,0 +1,21 @@
+use crate::{proto, Error};
+mod memory;
+mod sled;
+
+pub use self::memory::MemoryDirectoryService;
+pub use self::sled::SledDirectoryService;
+
+/// The base trait all Directory services need to implement.
+/// This is a simple get and put of [crate::proto::Directory], returning their
+/// digest.
+pub trait DirectoryService {
+    /// Get looks up a single Directory message by its digest.
+    /// In case the directory is not found, Ok(None) is returned.
+    fn get(
+        &self,
+        by_what: &proto::get_directory_request::ByWhat,
+    ) -> Result<Option<proto::Directory>, Error>;
+    /// Get uploads a single Directory message, and returns the calculated
+    /// digest, or an error.
+    fn put(&self, directory: proto::Directory) -> Result<Vec<u8>, Error>;
+}