blockchain: add KeyImageSpent request

storage/blockchain/src/service/read.rs

@@ -34,7 +34,7 @@ use crate::{
         free::{compact_history_genesis_not_included, compact_history_index_to_height_offset},
         types::{BlockchainReadHandle, ResponseResult},
     },
-    tables::{BlockHeights, BlockInfos, OpenTables, Tables},
+    tables::{BlockHeights, BlockInfos, KeyImages, OpenTables, Tables},
     types::{Amount, AmountIndex, BlockHash, BlockHeight, KeyImage, PreRctOutputId},
 };
 
@@ -100,6 +100,7 @@ fn map_request(
         R::GeneratedCoins(height) => generated_coins(env, height),
         R::Outputs(map) => outputs(env, map),
         R::NumberOutputsWithAmount(vec) => number_outputs_with_amount(env, vec),
+        R::KeyImageSpent(set) => key_image_spent(env, set),
         R::KeyImagesSpent(set) => key_images_spent(env, set),
         R::CompactChainHistory => compact_chain_history(env),
         R::FindFirstUnknown(block_ids) => find_first_unknown(env, &block_ids),
@@ -414,6 +415,21 @@ fn number_outputs_with_amount(env: &ConcreteEnv, amounts: Vec<Amount>) -> Respon
     Ok(BlockchainResponse::NumberOutputsWithAmount(map))
 }
 
+/// [`BlockchainReadRequest::KeyImageSpent`].
+#[inline]
+fn key_image_spent(env: &ConcreteEnv, key_image: KeyImage) -> ResponseResult {
+    // Single-threaded, no `ThreadLocal` required.
+    let env_inner = env.env_inner();
+    let tx_ro = env_inner.tx_ro()?;
+    let table_key_images = env_inner.open_db_ro::<KeyImages>(&tx_ro)?;
+
+    match key_image_exists(&key_image, &table_key_images) {
+        Ok(false) => Ok(BlockchainResponse::KeyImagesSpent(false)), // Key image was NOT found.
+        Ok(true) => Ok(BlockchainResponse::KeyImagesSpent(true)),   // Key image was found.
+        Err(e) => Err(e),                                           // A database error occurred.
+    }
+}
+
 /// [`BlockchainReadRequest::KeyImagesSpent`].
 #[inline]
 fn key_images_spent(env: &ConcreteEnv, key_images: HashSet<KeyImage>) -> ResponseResult {

types/src/blockchain.rs

@@ -98,6 +98,11 @@ pub enum BlockchainReadRequest {
     /// The input is a list of output amounts.
     NumberOutputsWithAmount(Vec<u64>),
 
+    /// Check that a single key image is not spent.
+    ///
+    /// Input is a key image hash.
+    KeyImageSpent([u8; 32]),
+
     /// Check that all key images within a set are not spent.
     ///
     /// Input is a set of key images.
@@ -198,6 +203,13 @@ pub enum BlockchainResponse {
     /// - Value = count of outputs with the same amount
     NumberOutputsWithAmount(HashMap<u64, usize>),
 
+    /// Response to [`BlockchainReadRequest::KeyImageSpent`].
+    ///
+    /// The inner value is `true` if the key image
+    /// was spent (existed in the database already),
+    /// else `false`.
+    KeyImageSpent(bool),
+
     /// Response to [`BlockchainReadRequest::KeyImagesSpent`].
     ///
     /// The inner value is `true` if _any_ of the key images