Implement ScyllaDb as a KeyValueStoreClient (#887)

* Implement the basic functionality of the ScyllaDb database as a KeyValueStoreClient.

Cargo.toml

@@ -34,6 +34,7 @@ aws-sdk-dynamodb = "0.14.0"
 aws-sdk-s3 = "0.14.0"
 aws-smithy-http = "0.44.0"
 aws-types = "0.14.0"
+scylla = "0.8.1"
 axum = "0.6.2"
 bcs = "0.1.3"
 bincode = "1.3.3"

linera-views/Cargo.toml

@@ -11,12 +11,13 @@ license = "Apache-2.0"
 edition = "2021"
 
 [package.metadata.docs.rs]
-features = ["rocksdb", "aws", "test"]
+features = ["scylladb", "rocksdb", "aws", "test"]
 targets = ["x86_64-unknown-linux-gnu", "wasm32-unknown-unknown"]
 
 [features]
 test = ["anyhow", "tokio/macros", "tokio/parking_lot"]
 aws = ["aws-config", "aws-sdk-dynamodb", "aws-sdk-s3", "aws-smithy-http", "aws-types"]
+scylladb = ["scylla"]
 db_timings = []
 metrics = ["dep:hex", "dep:metrics"]
 
@@ -43,6 +44,7 @@ anyhow = { workspace = true, optional = true }
 tracing = { workspace = true }
 http = { workspace = true }
 rand = { workspace = true }
+scylla = { workspace = true, optional = true }
 rocksdb = { workspace = true, optional = true }
 aws-config = { workspace = true, optional = true }
 aws-sdk-dynamodb = { workspace = true, optional = true }

linera-views/src/common.rs

@@ -47,17 +47,27 @@ pub const MIN_VIEW_TAG: u8 = 1;
 /// is possible with the way the comparison operators for vectors are built.
 ///
 /// The statement is that p is a prefix of v if and only if p <= v < upper_bound(p).
-pub(crate) fn get_upper_bound(key_prefix: &[u8]) -> Bound<Vec<u8>> {
+pub(crate) fn get_upper_bound_option(key_prefix: &[u8]) -> Option<Vec<u8>> {
     let len = key_prefix.len();
     for i in (0..len).rev() {
         let val = key_prefix[i];
         if val < u8::MAX {
             let mut upper_bound = key_prefix[0..i + 1].to_vec();
             upper_bound[i] += 1;
-            return Excluded(upper_bound);
+            return Some(upper_bound);
         }
     }
-    Unbounded
+    None
+}
+
+/// The upper bound that can be used in ranges when accessing
+/// a container. That is a vector v is a prefix of p if and only if
+/// v belongs to the interval (Included(p), get_upper_bound(p)).
+pub(crate) fn get_upper_bound(key_prefix: &[u8]) -> Bound<Vec<u8>> {
+    match get_upper_bound_option(key_prefix) {
+        None => Unbounded,
+        Some(upper_bound) => Excluded(upper_bound),
+    }
 }
 
 /// Computes an interval so that a vector has `key_prefix` as a prefix