From 5e112269c311a559bfded814d3c3c438349a1986 Mon Sep 17 00:00:00 2001
From: Jonas Schnelli <dev@jonasschnelli.ch>
Date: Thu, 10 Dec 2020 13:21:54 +0100
Subject: [PATCH] Avoid pruning below the blockfilterindex sync height

---
 src/validation.cpp | 17 +++++++++++++----
 src/validation.h   |  2 +-
 2 files changed, 14 insertions(+), 5 deletions(-)

diff --git a/src/validation.cpp b/src/validation.cpp
index 8f7d36bfd3..6f76d8f5fd 100644
--- a/src/validation.cpp
+++ b/src/validation.cpp
@@ -17,6 +17,7 @@
 #include <cuckoocache.h>
 #include <flatfile.h>
 #include <hash.h>
+#include <index/blockfilterindex.h>
 #include <index/txindex.h>
 #include <logging.h>
 #include <logging/timer.h>
@@ -2249,17 +2250,25 @@ bool CChainState::FlushStateToDisk(
     {
         bool fFlushForPrune = false;
         bool fDoFullFlush = false;
+
         CoinsCacheSizeState cache_state = GetCoinsCacheSizeState(&m_mempool);
         LOCK(cs_LastBlockFile);
         if (fPruneMode && (fCheckForPruning || nManualPruneHeight > 0) && !fReindex) {
+            // make sure we don't prune above the blockfilterindexes bestblocks
+            // pruning is height-based
+            int last_prune = m_chain.Height(); // last height we can prune
+            ForEachBlockFilterIndex([&](BlockFilterIndex& index) {
+               last_prune = std::max(1, std::min(last_prune, index.GetSummary().best_block_height));
+            });
+
             if (nManualPruneHeight > 0) {
                 LOG_TIME_MILLIS_WITH_CATEGORY("find files to prune (manual)", BCLog::BENCH);
 
-                m_blockman.FindFilesToPruneManual(setFilesToPrune, nManualPruneHeight, m_chain.Height());
+                m_blockman.FindFilesToPruneManual(setFilesToPrune, std::min(last_prune, nManualPruneHeight), m_chain.Height());
             } else {
                 LOG_TIME_MILLIS_WITH_CATEGORY("find files to prune", BCLog::BENCH);
 
-                m_blockman.FindFilesToPrune(setFilesToPrune, chainparams.PruneAfterHeight(), m_chain.Height(), IsInitialBlockDownload());
+                m_blockman.FindFilesToPrune(setFilesToPrune, chainparams.PruneAfterHeight(), m_chain.Height(), last_prune, IsInitialBlockDownload());
                 fCheckForPruning = false;
             }
             if (!setFilesToPrune.empty()) {
@@ -3934,7 +3943,7 @@ void PruneBlockFilesManual(int nManualPruneHeight)
     }
 }
 
-void BlockManager::FindFilesToPrune(std::set<int>& setFilesToPrune, uint64_t nPruneAfterHeight, int chain_tip_height, bool is_ibd)
+void BlockManager::FindFilesToPrune(std::set<int>& setFilesToPrune, uint64_t nPruneAfterHeight, int chain_tip_height, int prune_height, bool is_ibd)
 {
     LOCK2(cs_main, cs_LastBlockFile);
     if (chain_tip_height < 0 || nPruneTarget == 0) {
@@ -3944,7 +3953,7 @@ void BlockManager::FindFilesToPrune(std::set<int>& setFilesToPrune, uint64_t nPr
         return;
     }
 
-    unsigned int nLastBlockWeCanPrune = chain_tip_height - MIN_BLOCKS_TO_KEEP;
+    unsigned int nLastBlockWeCanPrune = std::min(prune_height, chain_tip_height - static_cast<int>(MIN_BLOCKS_TO_KEEP));
     uint64_t nCurrentUsage = CalculateCurrentUsage();
     // We don't check to prune until after we've allocated new space for files
     // So we should leave a buffer under our target to account for another allocation
diff --git a/src/validation.h b/src/validation.h
index e85c7bbf1a..30d8c9c17a 100644
--- a/src/validation.h
+++ b/src/validation.h
@@ -361,7 +361,7 @@ private:
      *
      * @param[out]   setFilesToPrune   The set of file indices that can be unlinked will be returned
      */
-    void FindFilesToPrune(std::set<int>& setFilesToPrune, uint64_t nPruneAfterHeight, int chain_tip_height, bool is_ibd);
+    void FindFilesToPrune(std::set<int>& setFilesToPrune, uint64_t nPruneAfterHeight, int chain_tip_height, int prune_height, bool is_ibd);
 
 public:
     BlockMap m_block_index GUARDED_BY(cs_main);