indexes, refactor: Remove CBlockIndex* uses in index Init methods

Replace overriden index Init() methods that use the best block
CBlockIndex* pointer with pure CustomInit() callbacks that are passed
the block hash and height.

This gets rid of more CBlockIndex* pointer uses so indexes can work
outside the bitcoin-node process. It also simplifies the initialization
call sequence so index implementations are not responsible for
initializing the base class.

There is a slight change in behavior here since now the best block
pointer is loaded and checked before the custom index init functions are
called instead of while they are called.

src/index/base.cpp

@@ -359,7 +359,10 @@ bool BaseIndex::Start()
     // Need to register this ValidationInterface before running Init(), so that
     // callbacks are not missed if Init sets m_synced to true.
     RegisterValidationInterface(this);
-    if (!Init()) {
+    if (!Init()) return false;
+
+    const CBlockIndex* index = m_best_block_index.load();
+    if (!CustomInit(index ? std::make_optional(interfaces::BlockKey{index->GetBlockHash(), index->nHeight}) : std::nullopt)) {
         return false;
     }
 

src/index/base.h

@@ -63,6 +63,9 @@ private:
     std::thread m_thread_sync;
     CThreadInterrupt m_interrupt;
 
+    /// Read best block locator and check that data needed to sync has not been pruned.
+    bool Init();
+
     /// Sync the index with the block index starting from the current best block.
     /// Intended to be run in its own thread, m_thread_sync, and can be
     /// interrupted with m_interrupt. Once the index gets in sync, the m_synced
@@ -90,10 +93,8 @@ protected:
 
     void ChainStateFlushed(const CBlockLocator& locator) override;
 
-    const CBlockIndex* CurrentIndex() { return m_best_block_index.load(); };
-
     /// Initialize internal state from the database and block index.
-    [[nodiscard]] virtual bool Init();
+    [[nodiscard]] virtual bool CustomInit(const std::optional<interfaces::BlockKey>& block) { return true; }
 
     /// Write update index entries for a newly connected block.
     virtual bool WriteBlock(const CBlock& block, const CBlockIndex* pindex) { return true; }

src/index/blockfilterindex.cpp

@@ -109,7 +109,7 @@ BlockFilterIndex::BlockFilterIndex(std::unique_ptr<interfaces::Chain> chain, Blo
     m_filter_fileseq = std::make_unique<FlatFileSeq>(std::move(path), "fltr", FLTR_FILE_CHUNK_SIZE);
 }
 
-bool BlockFilterIndex::Init()
+bool BlockFilterIndex::CustomInit(const std::optional<interfaces::BlockKey>& block)
 {
     if (!m_db->Read(DB_FILTER_POS, m_next_filter_pos)) {
         // Check that the cause of the read failure is that the key does not exist. Any other errors
@@ -124,7 +124,7 @@ bool BlockFilterIndex::Init()
         m_next_filter_pos.nFile = 0;
         m_next_filter_pos.nPos = 0;
     }
-    return BaseIndex::Init();
+    return true;
 }
 
 bool BlockFilterIndex::CommitInternal(CDBBatch& batch)

src/index/blockfilterindex.h

@@ -41,7 +41,7 @@ private:
     bool AllowPrune() const override { return true; }
 
 protected:
-    bool Init() override;
+    bool CustomInit(const std::optional<interfaces::BlockKey>& block) override;
 
     bool CommitInternal(CDBBatch& batch) override;
 

src/index/coinstatsindex.cpp

@@ -345,7 +345,7 @@ std::optional<CCoinsStats> CoinStatsIndex::LookUpStats(const CBlockIndex* block_
     return stats;
 }
 
-bool CoinStatsIndex::Init()
+bool CoinStatsIndex::CustomInit(const std::optional<interfaces::BlockKey>& block)
 {
     if (!m_db->Read(DB_MUHASH, m_muhash)) {
         // Check that the cause of the read failure is that the key does not
@@ -357,13 +357,9 @@ bool CoinStatsIndex::Init()
         }
     }
 
-    if (!BaseIndex::Init()) return false;
-
-    const CBlockIndex* pindex{CurrentIndex()};
-
-    if (pindex) {
+    if (block) {
         DBVal entry;
-        if (!LookUpOne(*m_db, {pindex->GetBlockHash(), pindex->nHeight}, entry)) {
+        if (!LookUpOne(*m_db, *block, entry)) {
             return error("%s: Cannot read current %s state; index may be corrupted",
                          __func__, GetName());
         }

src/index/coinstatsindex.h

@@ -39,7 +39,7 @@ private:
     bool AllowPrune() const override { return true; }
 
 protected:
-    bool Init() override;
+    bool CustomInit(const std::optional<interfaces::BlockKey>& block) override;
 
     bool CommitInternal(CDBBatch& batch) override;