Allow zero key length in key and prefix for DynamoDb.

linera-views/src/backends/dynamo_db.rs

@@ -130,9 +130,10 @@ const VISIBLE_MAX_VALUE_SIZE: usize = RAW_MAX_VALUE_SIZE
     - 1
     - 1;
 
-/// Fundamental constant in DynamoDB: The maximum size of a key is 1024 bytes
+/// Fundamental constant in DynamoDB: The maximum size of a key is 1024 bytes.
+/// We decrease by 1 because we append a [1] as prefix.
 /// See https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/HowItWorks.NamingRulesDataTypes.html
-const MAX_KEY_SIZE: usize = 1024;
+const MAX_KEY_SIZE: usize = 1023;
 
 /// Fundamental constants in DynamoDB: The maximum size of a [`TransactWriteItem`] is 4 MB.
 /// See https://docs.aws.amazon.com/amazondynamodb/latest/APIReference/API_TransactWriteItems.html
@@ -167,12 +168,17 @@ const MAX_BATCH_GET_ITEM_SIZE: usize = 40;
 /// The second attribute is the actual key value, which is generated by concatenating the
 /// context prefix. `The Vec<u8>` expression is obtained from `self.derive_key`.
 fn build_key(start_key: &[u8], key: Vec<u8>) -> HashMap<String, AttributeValue> {
+    let mut prefixed_key = vec![1];
+    prefixed_key.extend(key);
     [
         (
             PARTITION_ATTRIBUTE.to_owned(),
             AttributeValue::B(Blob::new(start_key.to_vec())),
         ),
-        (KEY_ATTRIBUTE.to_owned(), AttributeValue::B(Blob::new(key))),
+        (
+            KEY_ATTRIBUTE.to_owned(),
+            AttributeValue::B(Blob::new(prefixed_key)),
+        ),
     ]
     .into()
 }
@@ -183,12 +189,17 @@ fn build_key_value(
     key: Vec<u8>,
     value: Vec<u8>,
 ) -> HashMap<String, AttributeValue> {
+    let mut prefixed_key = vec![1];
+    prefixed_key.extend(key);
     [
         (
             PARTITION_ATTRIBUTE.to_owned(),
             AttributeValue::B(Blob::new(start_key.to_vec())),
         ),
-        (KEY_ATTRIBUTE.to_owned(), AttributeValue::B(Blob::new(key))),
+        (
+            KEY_ATTRIBUTE.to_owned(),
+            AttributeValue::B(Blob::new(prefixed_key)),
+        ),
         (
             VALUE_ATTRIBUTE.to_owned(),
             AttributeValue::B(Blob::new(value)),
@@ -199,7 +210,6 @@ fn build_key_value(
 
 /// Checks that a key is of the correct size
 fn check_key_size(key: &[u8]) -> Result<(), DynamoDbStoreInternalError> {
-    ensure!(!key.is_empty(), DynamoDbStoreInternalError::ZeroLengthKey);
     ensure!(
         key.len() <= MAX_KEY_SIZE,
         DynamoDbStoreInternalError::KeyTooLong
@@ -216,7 +226,7 @@ fn extract_key(
         .get(KEY_ATTRIBUTE)
         .ok_or(DynamoDbStoreInternalError::MissingKey)?;
     match key {
-        AttributeValue::B(blob) => Ok(&blob.as_ref()[prefix_len..]),
+        AttributeValue::B(blob) => Ok(&blob.as_ref()[1 + prefix_len..]),
         key => Err(DynamoDbStoreInternalError::wrong_key_type(key)),
     }
 }
@@ -602,6 +612,8 @@ impl DynamoDbStoreInternal {
     ) -> Result<QueryOutput, DynamoDbStoreInternalError> {
         let _guard = self.acquire().await;
         let start_key = start_key.to_vec();
+        let mut prefixed_key_prefix = vec![1];
+        prefixed_key_prefix.extend(key_prefix);
         let response = self
             .client
             .query()
@@ -611,7 +623,10 @@ impl DynamoDbStoreInternal {
                 "{PARTITION_ATTRIBUTE} = :partition and begins_with({KEY_ATTRIBUTE}, :prefix)"
             ))
             .expression_attribute_values(":partition", AttributeValue::B(Blob::new(start_key)))
-            .expression_attribute_values(":prefix", AttributeValue::B(Blob::new(key_prefix)))
+            .expression_attribute_values(
+                ":prefix",
+                AttributeValue::B(Blob::new(prefixed_key_prefix)),
+            )
             .set_exclusive_start_key(start_key_map)
             .send()
             .boxed_sync()
@@ -746,7 +761,8 @@ impl DynamoDbStoreInternal {
                             .ok_or(DynamoDbStoreInternalError::MissingKey)?;
 
                         if let AttributeValue::B(blob) = key_attr {
-                            let key = blob.as_ref();
+                            let prefixed_key = blob.as_ref();
+                            let key = &prefixed_key[1..]; // Remove the [1] prefix
                             if let Some(indices) = key_to_index.get(key) {
                                 if let Some((&last, rest)) = indices.split_last() {
                                     let value = extract_value_owned(&mut item)?;
@@ -966,10 +982,6 @@ pub enum DynamoDbStoreInternalError {
     #[error("The transact must have length at most MAX_TRANSACT_WRITE_ITEM_SIZE")]
     TransactUpperLimitSize,
 
-    /// Keys have to be of non-zero length.
-    #[error("The key must be of strictly positive length")]
-    ZeroLengthKey,
-
     /// The key must have at most 1024 bytes
     #[error("The key must have at most 1024 bytes")]
     KeyTooLong,
@@ -978,10 +990,6 @@ pub enum DynamoDbStoreInternalError {
     #[error("The key prefix must have at most 1024 bytes")]
     KeyPrefixTooLong,
 
-    /// Key prefixes have to be of non-zero length.
-    #[error("The key_prefix must be of strictly positive length")]
-    ZeroLengthKeyPrefix,
-
     /// The journal is not coherent
     #[error(transparent)]
     JournalConsistencyError(#[from] JournalConsistencyError),

linera-views/src/test_utils/mod.rs

@@ -176,7 +176,7 @@ pub async fn run_reads<S: KeyValueStore>(store: S, key_values: Vec<(Vec<u8>, Vec
     store.write_batch(batch).await.unwrap();
     for key_prefix in keys
         .iter()
-        .flat_map(|key| (0..key.len()).map(|u| &key[..=u]))
+        .flat_map(|key| (0..=key.len()).map(|u| &key[..u]))
     {
         // Getting the find_keys_by_prefix / find_key_values_by_prefix
         let len_prefix = key_prefix.len();