From 881ab4fc82fe3cf36b227cf1ba704448df160745 Mon Sep 17 00:00:00 2001
From: furszy <matiasfurszyfer@protonmail.com>
Date: Mon, 16 Jun 2025 11:28:04 -0400
Subject: [PATCH] support multiple block status checks in
 CheckBlockDataAvailability

---
 src/node/blockstorage.cpp       | 14 +++++++++++---
 src/node/blockstorage.h         |  2 +-
 src/test/blockmanager_tests.cpp | 13 +++++++++++++
 3 files changed, 25 insertions(+), 4 deletions(-)

diff --git a/src/node/blockstorage.cpp b/src/node/blockstorage.cpp
index 37bf1799aa4..a8ff110c3ad 100644
--- a/src/node/blockstorage.cpp
+++ b/src/node/blockstorage.cpp
@@ -623,10 +623,18 @@ const CBlockIndex& BlockManager::GetFirstBlock(const CBlockIndex& upper_block, u
     return *last_block;
 }
 
-bool BlockManager::CheckBlockDataAvailability(const CBlockIndex& upper_block, const CBlockIndex& lower_block)
+bool BlockManager::CheckBlockDataAvailability(const CBlockIndex& upper_block, const CBlockIndex& lower_block, BlockStatus block_status)
 {
-    if (!(upper_block.nStatus & BLOCK_HAVE_DATA)) return false;
-    return &GetFirstBlock(upper_block, BLOCK_HAVE_DATA, &lower_block) == &lower_block;
+    if (!(upper_block.nStatus & block_status)) return false;
+    const auto& first_block = GetFirstBlock(upper_block, block_status, &lower_block);
+    // Special case: the genesis block has no undo data
+    if (block_status & BLOCK_HAVE_UNDO && lower_block.nHeight == 0 && first_block.nHeight == 1) {
+        // This might indicate missing data, or it could simply reflect the expected absence of undo data for the genesis block.
+        // To distinguish between the two, check if all required block data *except* undo is available up to the genesis block.
+        BlockStatus flags{block_status & ~BLOCK_HAVE_UNDO};
+        return first_block.pprev && first_block.pprev->nStatus & flags;
+    }
+    return &first_block == &lower_block;
 }
 
 // If we're using -prune with -reindex, then delete block files that will be ignored by the
diff --git a/src/node/blockstorage.h b/src/node/blockstorage.h
index d8b716e98b1..8cb398fea64 100644
--- a/src/node/blockstorage.h
+++ b/src/node/blockstorage.h
@@ -414,7 +414,7 @@ public:
     //! Check if all blocks in the [upper_block, lower_block] range have data available.
     //! The caller is responsible for ensuring that lower_block is an ancestor of upper_block
     //! (part of the same chain).
-    bool CheckBlockDataAvailability(const CBlockIndex& upper_block, const CBlockIndex& lower_block) EXCLUSIVE_LOCKS_REQUIRED(::cs_main);
+    bool CheckBlockDataAvailability(const CBlockIndex& upper_block, const CBlockIndex& lower_block, BlockStatus block_status = BLOCK_HAVE_DATA) EXCLUSIVE_LOCKS_REQUIRED(::cs_main);
 
     /**
      * @brief Returns the earliest block with specified `status_mask` flags set after
diff --git a/src/test/blockmanager_tests.cpp b/src/test/blockmanager_tests.cpp
index db59931ba78..ff99a1ee4ff 100644
--- a/src/test/blockmanager_tests.cpp
+++ b/src/test/blockmanager_tests.cpp
@@ -126,6 +126,14 @@ BOOST_FIXTURE_TEST_CASE(blockmanager_block_data_availability, TestChain100Setup)
     CBlockIndex* lower_block = chainman->ActiveChain()[tip.nHeight / 2];
     BOOST_CHECK(blockman.CheckBlockDataAvailability(tip, *lower_block));
 
+    // Ensure we don't fail due to the expected absence of undo data in the genesis block
+    CBlockIndex* upper_block = chainman->ActiveChain()[2];
+    CBlockIndex* genesis = chainman->ActiveChain()[0];
+    BOOST_CHECK(blockman.CheckBlockDataAvailability(*upper_block, *genesis, BlockStatus{BLOCK_HAVE_DATA | BLOCK_HAVE_UNDO}));
+    // Ensure we detect absence of undo data in the first block
+    chainman->ActiveChain()[1]->nStatus &= ~BLOCK_HAVE_UNDO;
+    BOOST_CHECK(!blockman.CheckBlockDataAvailability(tip, *genesis, BlockStatus{BLOCK_HAVE_DATA | BLOCK_HAVE_UNDO}));
+
     // Prune half of the blocks
     int height_to_prune = tip.nHeight / 2;
     CBlockIndex* first_available_block = chainman->ActiveChain()[height_to_prune + 1];
@@ -136,6 +144,11 @@ BOOST_FIXTURE_TEST_CASE(blockmanager_block_data_availability, TestChain100Setup)
     BOOST_CHECK_EQUAL(&blockman.GetFirstBlock(tip, BLOCK_HAVE_DATA), first_available_block);
     BOOST_CHECK(blockman.CheckBlockDataAvailability(tip, *first_available_block));
     BOOST_CHECK(!blockman.CheckBlockDataAvailability(tip, *last_pruned_block));
+
+    // Simulate that the first available block is missing undo data and
+    // detect this by using a status mask.
+    first_available_block->nStatus &= ~BLOCK_HAVE_UNDO;
+    BOOST_CHECK(!blockman.CheckBlockDataAvailability(tip, *first_available_block, BlockStatus{BLOCK_HAVE_DATA | BLOCK_HAVE_UNDO}));
 }
 
 BOOST_FIXTURE_TEST_CASE(blockmanager_block_data_part, TestChain100Setup)