refactor(tvix/castore): B3Digest UX improvements

- Switch from B3_LEN to B3Digest::LENGTH
 - make repr(transparent) with underlying [u8; Self::LENGTH]
 - impl AsRef<[u8; B3Digest::LENGTH]> for B3Digest
 - impl Deref<Target = [u8; Self::LENGTH]> for B3Digest

Change-Id: If4ff077bbd79de1fce4201259bda46c839a7765a
Reviewed-on: https://cl.tvl.fyi/c/depot/+/13258
Tested-by: BuildkiteCI
Reviewed-by: Ilan Joselevich <personal@ilanjoselevich.com>
Autosubmit: flokli <flokli@flokli.de>
Reviewed-by: edef <edef@edef.eu>

tvix/castore/src/blobservice/object_store.rs

@@ -78,8 +78,8 @@ fn derive_blob_path(base_path: &Path, digest: &B3Digest) -> Path {
     base_path
         .child("blobs")
         .child("b3")
-        .child(HEXLOWER.encode(&digest.as_slice()[..2]))
+        .child(HEXLOWER.encode(&digest[..2]))
-        .child(HEXLOWER.encode(digest.as_slice()))
+        .child(HEXLOWER.encode(&digest[..]))
 }
 
 #[instrument(level=Level::TRACE, skip_all,fields(base_path=%base_path,chunk.digest=%digest),ret(Display))]
@@ -87,8 +87,8 @@ fn derive_chunk_path(base_path: &Path, digest: &B3Digest) -> Path {
     base_path
         .child("chunks")
         .child("b3")
-        .child(HEXLOWER.encode(&digest.as_slice()[..2]))
+        .child(HEXLOWER.encode(&digest[..2]))
-        .child(HEXLOWER.encode(digest.as_slice()))
+        .child(HEXLOWER.encode(&digest[..]))
 }
 
 #[async_trait]

tvix/castore/src/digests.rs

@@ -2,10 +2,13 @@ use bytes::Bytes;
 use data_encoding::BASE64;
 use thiserror::Error;
 
-pub const B3_LEN: usize = blake3::OUT_LEN;
-
 #[derive(PartialEq, Eq, Hash)]
-pub struct B3Digest([u8; B3_LEN]);
+#[repr(transparent)]
+pub struct B3Digest([u8; Self::LENGTH]);
+
+impl B3Digest {
+    pub const LENGTH: usize = blake3::OUT_LEN;
+}
 
 // TODO: allow converting these errors to crate::Error
 #[derive(Error, Debug, PartialEq)]
@@ -14,9 +17,17 @@ pub enum Error {
     InvalidDigestLen(usize),
 }
 
-impl B3Digest {
+impl AsRef<[u8; B3Digest::LENGTH]> for B3Digest {
-    pub fn as_slice(&self) -> &[u8] {
+    fn as_ref(&self) -> &[u8; Self::LENGTH] {
-        &self.0[..]
+        &self.0
+    }
+}
+
+impl std::ops::Deref for B3Digest {
+    type Target = [u8; Self::LENGTH];
+
+    fn deref(&self) -> &Self::Target {
+        &self.0
     }
 }
 
@@ -67,13 +78,13 @@ impl TryFrom<Vec<u8>> for B3Digest {
     }
 }
 
-impl From<&[u8; B3_LEN]> for B3Digest {
+impl From<&[u8; B3Digest::LENGTH]> for B3Digest {
-    fn from(value: &[u8; B3_LEN]) -> Self {
+    fn from(value: &[u8; B3Digest::LENGTH]) -> Self {
         Self(*value)
     }
 }
 
-impl From<B3Digest> for [u8; B3_LEN] {
+impl From<B3Digest> for [u8; B3Digest::LENGTH] {
     fn from(value: B3Digest) -> Self {
         value.0
     }

tvix/castore/src/directoryservice/redb.rs

@@ -11,10 +11,10 @@ use super::{
 };
 use crate::{
     composition::{CompositionContext, ServiceBuilder},
-    digests, proto, B3Digest, Error,
+    proto, B3Digest, Error,
 };
 
-const DIRECTORY_TABLE: TableDefinition<[u8; digests::B3_LEN], Vec<u8>> =
+const DIRECTORY_TABLE: TableDefinition<[u8; B3Digest::LENGTH], Vec<u8>> =
     TableDefinition::new("directory");
 
 #[derive(Clone)]
@@ -81,11 +81,11 @@ impl DirectoryService for RedbDirectoryService {
 
         // Retrieves the protobuf-encoded Directory for the corresponding digest.
         let db_get_resp = tokio::task::spawn_blocking({
-            let digest_as_array: [u8; digests::B3_LEN] = digest.to_owned().into();
+            let digest = *digest.as_ref();
             move || -> Result<_, redb::Error> {
                 let txn = db.begin_read()?;
                 let table = txn.open_table(DIRECTORY_TABLE)?;
-                Ok(table.get(digest_as_array)?)
+                Ok(table.get(digest)?)
             }
         })
         .await?
@@ -139,9 +139,8 @@ impl DirectoryService for RedbDirectoryService {
                 let txn = db.begin_write()?;
                 {
                     let mut table = txn.open_table(DIRECTORY_TABLE)?;
-                    let digest_as_array: [u8; digests::B3_LEN] = digest.clone().into();
                     table.insert(
-                        digest_as_array,
+                        digest.as_ref(),
                         proto::Directory::from(directory).encode_to_vec(),
                     )?;
                 }
@@ -225,10 +224,8 @@ impl DirectoryPutter for RedbDirectoryPutter<'_> {
                             // Looping over all the verified directories, queuing them up for a
                             // batch insertion.
                             for directory in directories {
-                                let digest_as_array: [u8; digests::B3_LEN] =
-                                    directory.digest().into();
                                 table.insert(
-                                    digest_as_array,
+                                    directory.digest().as_ref(),
                                     proto::Directory::from(directory).encode_to_vec(),
                                 )?;
                             }

tvix/castore/src/lib.rs

@@ -25,7 +25,7 @@ pub mod tonic;
 // Used as user agent in various HTTP Clients
 const USER_AGENT: &str = concat!(env!("CARGO_PKG_NAME"), "/", env!("CARGO_PKG_VERSION"));
 
-pub use digests::{B3Digest, B3_LEN};
+pub use digests::B3Digest;
 pub use errors::{DirectoryError, Error, ValidateNodeError};
 pub use hashing_reader::{B3HashingReader, HashingReader};