Implement disk-based DataCache with no eviction

mountpoint-s3-client/src/object_client.rs

@@ -31,6 +31,11 @@ impl ETag {
         &self.etag
     }
 
+    /// Unpack the [String] contained by the [ETag] wrapper
+    pub fn into_inner(self) -> String {
+        self.etag
+    }
+
     /// Creating default etag for tests
     #[doc(hidden)]
     pub fn for_tests() -> Self {

mountpoint-s3/Cargo.toml

@@ -14,7 +14,7 @@ anyhow = { version = "1.0.64", features = ["backtrace"] }
 async-channel = "1.8.0"
 async-lock = "2.6.0"
 async-trait = "0.1.57"
-bytes = "1.2.1"
+bytes = { version = "1.2.1", features = ["serde"] }
 clap = { version = "4.1.9", features = ["derive"] }
 crc32c = "0.6.3"
 ctrlc = { version = "3.2.3", features = ["termination"] }
@@ -36,6 +36,10 @@ nix = "0.26.2"
 time = { version = "0.3.17", features = ["macros", "formatting"] }
 const_format = "0.2.30"
 serde_json = "1.0.95"
+serde = { version = "1.0.190", features = ["derive"] }
+bincode = "1.3.3"
+sha2 = "0.10.6"
+hex = "0.4.3"
 
 [target.'cfg(target_os = "linux")'.dependencies]
 procfs = { version = "0.15.1", default-features = false }

mountpoint-s3/src/checksums.rs

@@ -151,6 +151,16 @@ impl ChecksummedBytes {
         }
         Ok(())
     }
+
+    /// Provide the underlying bytes and the associated checksum,
+    /// which may be recalculated if the checksum covers a larger slice than the current slice.
+    /// Validation may or may not be triggered, and **bytes or checksum may be corrupt** even if result returns [Ok].
+    ///
+    /// If you are only interested in the underlying bytes, **you should use `into_bytes()`**.
+    pub fn into_inner(self) -> Result<(Bytes, Crc32c), IntegrityError> {
+        self.shrink_to_fit()?;
+        Ok((self.curr_slice, self.checksum))
+    }
 }
 
 impl Default for ChecksummedBytes {

mountpoint-s3/src/data_cache.rs

@@ -4,6 +4,7 @@
 //! reducing both the number of requests as well as the latency for the reads.
 //! Ultimately, this means reduced cost in terms of S3 billing as well as compute time.
 
+pub mod disk_data_cache;
 pub mod in_memory_data_cache;
 
 use std::ops::RangeBounds;