refactor: Introduce GetFirstStoredBlock helper function

Author: fjahr

src/index/base.cpp

@@ -75,11 +75,7 @@ bool BaseIndex::Init()
         if (!m_best_block_index) {
             // index is not built yet
             // make sure we have all block data back to the genesis
-            const CBlockIndex* block = active_chain.Tip();
-            while (block->pprev && (block->pprev->nStatus & BLOCK_HAVE_DATA)) {
-                block = block->pprev;
-            }
-            prune_violation = block != active_chain.Genesis();
+            prune_violation = node::GetFirstStoredBlock(active_chain.Tip()) != active_chain.Genesis();
         }
         // in case the index has a best block set and is not fully synced
         // check if we have the required blocks to continue building the index

src/node/blockstorage.cpp

@@ -397,6 +397,16 @@ bool BlockManager::IsBlockPruned(const CBlockIndex* pblockindex)
     return (m_have_pruned && !(pblockindex->nStatus & BLOCK_HAVE_DATA) && pblockindex->nTx > 0);
 }
 
+const CBlockIndex* GetFirstStoredBlock(const CBlockIndex* start_block) {
+    AssertLockHeld(::cs_main);
+    assert(start_block);
+    const CBlockIndex* last_block = start_block;
+    while (last_block->pprev && (last_block->pprev->nStatus & BLOCK_HAVE_DATA)) {
+        last_block = last_block->pprev;
+    }
+    return last_block;
+}
+
 // If we're using -prune with -reindex, then delete block files that will be ignored by the
 // reindex.  Since reindexing works by starting at block file 0 and looping until a blockfile
 // is missing, do the same here to delete any later block files after a gap.  Also delete all

src/node/blockstorage.h

@@ -181,6 +181,9 @@ class BlockManager
     }
 };
 
+//! Find the first block that is not pruned
+const CBlockIndex* GetFirstStoredBlock(const CBlockIndex* start_block) EXCLUSIVE_LOCKS_REQUIRED(::cs_main);
+
 void CleanupBlockRevFiles();
 
 /** Open a block file (blk?????.dat) */

src/rpc/blockchain.cpp

@@ -787,10 +787,9 @@ static RPCHelpMan pruneblockchain()
 
     PruneBlockFilesManual(active_chainstate, height);
     const CBlockIndex* block = CHECK_NONFATAL(active_chain.Tip());
-    while (block->pprev && (block->pprev->nStatus & BLOCK_HAVE_DATA)) {
-        block = block->pprev;
-    }
-    return uint64_t(block->nHeight);
+    const CBlockIndex* last_block = node::GetFirstStoredBlock(block);
+
+    return static_cast<uint64_t>(last_block->nHeight);
 },
     };
 }
@@ -1217,11 +1216,7 @@ RPCHelpMan getblockchaininfo()
     obj.pushKV("pruned", node::fPruneMode);
     if (node::fPruneMode) {
         const CBlockIndex* block = CHECK_NONFATAL(tip);
-        while (block->pprev && (block->pprev->nStatus & BLOCK_HAVE_DATA)) {
-            block = block->pprev;
-        }
-
-        obj.pushKV("pruneheight",        block->nHeight);
+        obj.pushKV("pruneheight", node::GetFirstStoredBlock(block)->nHeight);
 
         // if 0, execution bypasses the whole if block.
         bool automatic_pruning{args.GetIntArg("-prune", 0) != 1};