2 files changed, 38 insertions, 2 deletions
diff --git a/src/index/blockfilterindex.cpp b/src/index/blockfilterindex.cpp
index f2c3d66ebd..65a5f03a8e 100644
--- a/src/index/blockfilterindex.cpp
+++ b/src/index/blockfilterindex.cpp
@@ -31,6 +31,12 @@ constexpr char DB_FILTER_POS = 'P';
 constexpr unsigned int MAX_FLTR_FILE_SIZE = 0x1000000; // 16 MiB
 /** The pre-allocation chunk size for fltr?????.dat files */
 constexpr unsigned int FLTR_FILE_CHUNK_SIZE = 0x100000; // 1 MiB
+/** Maximum size of the cfheaders cache
+ *  We have a limit to prevent a bug in filling this cache
+ *  potentially turning into an OOM. At 2000 entries, this cache
+ *  is big enough for a 2,000,000 length block chain, which
+ *  we should be enough until ~2047. */
+constexpr size_t CF_HEADERS_CACHE_MAX_SZ{2000};
 
 namespace {
 
@@ -377,13 +383,32 @@ bool BlockFilterIndex::LookupFilter(const CBlockIndex* block_index, BlockFilter&
     return ReadFilterFromDisk(entry.pos, filter_out);
 }
 
-bool BlockFilterIndex::LookupFilterHeader(const CBlockIndex* block_index, uint256& header_out) const
+bool BlockFilterIndex::LookupFilterHeader(const CBlockIndex* block_index, uint256& header_out)
 {
+    LOCK(m_cs_headers_cache);
+
+    bool is_checkpoint{block_index->nHeight % CFCHECKPT_INTERVAL == 0};
+
+    if (is_checkpoint) {
+        // Try to find the block in the headers cache if this is a checkpoint height.
+        auto header = m_headers_cache.find(block_index->GetBlockHash());
+        if (header != m_headers_cache.end()) {
+            header_out = header->second;
+            return true;
+        }
+    }
+
     DBVal entry;
     if (!LookupOne(*m_db, block_index, entry)) {
         return false;
     }
 
+    if (is_checkpoint &&
+        m_headers_cache.size() < CF_HEADERS_CACHE_MAX_SZ) {
+        // Add to the headers cache if this is a checkpoint height.
+        m_headers_cache.emplace(block_index->GetBlockHash(), entry.header);
+    }
+
     header_out = entry.header;
     return true;
 }
diff --git a/src/index/blockfilterindex.h b/src/index/blockfilterindex.h
index 436d52515f..7ca43540c7 100644
--- a/src/index/blockfilterindex.h
+++ b/src/index/blockfilterindex.h
@@ -10,6 +10,14 @@
 #include <flatfile.h>
 #include <index/base.h>
 
+/** Interval between compact filter checkpoints. See BIP 157. */
+static constexpr int CFCHECKPT_INTERVAL = 1000;
+
+struct FilterHeaderHasher
+{
+    size_t operator()(const uint256& hash) const { return ReadLE64(hash.begin()); }
+};
+
 /**
  * BlockFilterIndex is used to store and retrieve block filters, hashes, and headers for a range of
  * blocks by height. An index is constructed for each supported filter type with its own database
@@ -30,6 +38,9 @@ private:
     bool ReadFilterFromDisk(const FlatFilePos& pos, BlockFilter& filter) const;
     size_t WriteFilterToDisk(FlatFilePos& pos, const BlockFilter& filter);
 
+    Mutex m_cs_headers_cache;
+    std::unordered_map<uint256, uint256, FilterHeaderHasher> m_headers_cache GUARDED_BY(m_cs_headers_cache);
+
 protected:
     bool Init() override;
 
@@ -54,7 +65,7 @@ public:
     bool LookupFilter(const CBlockIndex* block_index, BlockFilter& filter_out) const;
 
     /** Get a single filter header by block. */
-    bool LookupFilterHeader(const CBlockIndex* block_index, uint256& header_out) const;
+    bool LookupFilterHeader(const CBlockIndex* block_index, uint256& header_out);
 
     /** Get a range of filters between two heights on a chain. */
     bool LookupFilterRange(int start_height, const CBlockIndex* stop_index,