fix: avoid panic for sentinel blocks in debug builds (#427)

The workaround with the available heights also doesn't work in debug builds. I just didn't realize since I was always running release builds lately. Now while working on integration tests, this became an issue again.

Author: xdustinface

dash-spv/src/storage/blocks.rs

@@ -1,10 +1,9 @@
 //! Block storage for persisting full blocks that contain wallet-relevant transactions.
 
-use std::collections::HashSet;
 use std::path::PathBuf;
 
 use crate::error::StorageResult;
-use crate::storage::segments::{Persistable, SegmentCache};
+use crate::storage::segments::SegmentCache;
 use crate::storage::PersistentStorage;
 use crate::types::HashedBlock;
 use async_trait::async_trait;
@@ -29,9 +28,6 @@ pub trait BlockStorage: Send + Sync + 'static {
 pub struct PersistentBlockStorage {
     /// Block storage segments.
     blocks: RwLock<SegmentCache<HashedBlock>>,
-    /// Set of available block heights used for fast lookups and to bypass sentinel loading and gap
-    /// detection asserts (in debug builds) in the underlying segment implementation.
-    available_heights: HashSet<CoreBlockHeight>,
 }
 
 impl PersistentBlockStorage {
@@ -46,24 +42,10 @@ impl PersistentStorage for PersistentBlockStorage {
 
         tracing::debug!("Opening PersistentBlockStorage from {:?}", blocks_folder);
 
-        let mut blocks: SegmentCache<HashedBlock> =
-            SegmentCache::load_or_new(&blocks_folder).await?;
-
-        let mut available_heights = HashSet::new();
-
-        if let (Some(start), Some(end)) = (blocks.start_height(), blocks.tip_height()) {
-            let hashed_blocks = blocks.get_items(start..end + 1).await?;
-            let sentinel = HashedBlock::sentinel();
-            for (i, hashed_block) in hashed_blocks.iter().enumerate() {
-                if hashed_block != &sentinel {
-                    available_heights.insert(start + i as CoreBlockHeight);
-                }
-            }
-        }
+        let blocks: SegmentCache<HashedBlock> = SegmentCache::load_or_new(&blocks_folder).await?;
 
         Ok(Self {
             blocks: RwLock::new(blocks),
-            available_heights,
         })
     }
 
@@ -78,17 +60,11 @@ impl PersistentStorage for PersistentBlockStorage {
 #[async_trait]
 impl BlockStorage for PersistentBlockStorage {
     async fn store_block(&mut self, height: u32, hashed_block: HashedBlock) -> StorageResult<()> {
-        self.available_heights.insert(height);
         self.blocks.write().await.store_items_at_height(&[hashed_block], height).await
     }
 
     async fn load_block(&self, height: u32) -> StorageResult<Option<HashedBlock>> {
-        // This early return avoids unnecessary disk lookups and bypasses sentinel loading and gap
-        // detection asserts (in debug builds) in the underlying segment implementation.
-        if !self.available_heights.contains(&height) {
-            return Ok(None);
-        }
-        Ok(self.blocks.write().await.get_items(height..height + 1).await?.first().cloned())
+        self.blocks.write().await.get_item(height).await
     }
 }
 

dash-spv/src/storage/segments.rs

@@ -260,6 +260,20 @@ impl<I: Persistable> SegmentCache<I> {
         Ok(items)
     }
 
+    /// Get a single item by height. Returns `None` for sentinel (empty) slots.
+    /// Unlike `get_items()`, this does not assert dense storage — safe for sparse data.
+    pub async fn get_item(&mut self, height: u32) -> StorageResult<Option<I>> {
+        let segment_id = Self::height_to_segment_id(height);
+        let offset = Self::height_to_offset(height);
+        let segment = self.get_segment_mut(&segment_id).await?;
+        let item = segment.get_single(offset);
+        if *item == I::sentinel() {
+            Ok(None)
+        } else {
+            Ok(Some(item.clone()))
+        }
+    }
+
     pub async fn store_items(&mut self, items: &[I]) -> StorageResult<()> {
         self.store_items_at_height(items, self.next_height()).await
     }
@@ -479,6 +493,12 @@ impl<I: Persistable> Segment<I> {
         self.last_accessed = std::time::Instant::now();
     }
 
+    /// Get a single item by offset, returning the raw value (may be a sentinel).
+    pub fn get_single(&mut self, offset: u32) -> &I {
+        self.last_accessed = Instant::now();
+        &self.items[offset as usize]
+    }
+
     pub fn get(&mut self, range: Range<u32>) -> &[I] {
         debug_assert!(range.start < self.items.len() as u32);
         debug_assert!(range.end <= self.items.len() as u32);