Introduce new ObjectPart type

The `ObjectPart` type represents a slice of the content of an S3 object. It contains the information required to identify the object it belongs to and its offset in it. It also maintains checksums to validate its integrity. The new type is used in the prefetcher and replaces both `ChecksummedBytes` and `Part`.

Signed-off-by: Alessandro Passaro <[email protected]>

mountpoint-s3/src/data_cache.rs

@@ -8,20 +8,12 @@ mod cache_directory;
 mod disk_data_cache;
 mod in_memory_data_cache;
 
-use mountpoint_s3_client::types::ETag;
 use thiserror::Error;
 
-pub use crate::checksums::ChecksummedBytes;
 pub use crate::data_cache::cache_directory::ManagedCacheDir;
 pub use crate::data_cache::disk_data_cache::{CacheLimit, DiskDataCache, DiskDataCacheConfig};
 pub use crate::data_cache::in_memory_data_cache::InMemoryDataCache;
-
-/// Struct representing a key for accessing an entry in a [DataCache].
-#[derive(Clone, Debug, Hash, PartialEq, Eq)]
-pub struct CacheKey {
-    pub s3_key: String,
-    pub etag: ETag,
-}
+use crate::part::{ObjectId, ObjectPart};
 
 /// Indexes blocks within a given object.
 pub type BlockIndex = u64;
@@ -44,26 +36,20 @@ pub type DataCacheResult<Value> = Result<Value, DataCacheError>;
 /// Data cache for fixed-size checksummed buffers.
 ///
 /// TODO: Deletion and eviction of cache entries.
-/// TODO: Some version information (ETag) independent from [CacheKey] to allow smarter eviction?
+/// TODO: Some version information (ETag) independent from [ObjectId] to allow smarter eviction?
 pub trait DataCache {
-    /// Get block of data from the cache for the given [CacheKey] and [BlockIndex], if available.
+    /// Get block of data from the cache for the given [ObjectId] and [BlockIndex], if available.
     ///
     /// Operation may fail due to errors, or return [None] if the block was not available in the cache.
     fn get_block(
         &self,
-        cache_key: &CacheKey,
+        cache_key: &ObjectId,
         block_idx: BlockIndex,
         block_offset: u64,
-    ) -> DataCacheResult<Option<ChecksummedBytes>>;
+    ) -> DataCacheResult<Option<ObjectPart>>;
 
-    /// Put block of data to the cache for the given [CacheKey] and [BlockIndex].
-    fn put_block(
-        &self,
-        cache_key: CacheKey,
-        block_idx: BlockIndex,
-        block_offset: u64,
-        bytes: ChecksummedBytes,
-    ) -> DataCacheResult<()>;
+    /// Put block of data to the cache.
+    fn put_block(&self, bytes: ObjectPart, block_idx: BlockIndex) -> DataCacheResult<()>;
 
     /// Returns the block size for the data cache.
     fn block_size(&self) -> u64;