Merge bitcoin/bitcoin#26780: rpc: simplify scan blocks

b922f6b5262884f42d7483f1e9af35650bdb53a7 rpc: scanblocks, add "completed" flag to the result obj (furszy)
ce50acc54fa313a92d48ed03e46ce8aabcf267e5 rpc: scanblocks, do not traverse the whole chain block by block (furszy)

Pull request description:

  Coming from https://github.com/bitcoin/bitcoin/pull/23549#pullrequestreview-1105712566

  The current `scanblocks` flow walks-through every block in the active chain
  until hits the chain tip or processes 10k blocks, then calls `lookupFilterRange`
  function to obtain all filters from that particular range.

  This is only done to obtain the heights range to look up the block
  filters. Which is unneeded.

  As `scanblocks` only lookup block filters in the active chain, we can
  directly calculate the lookup range heights, by using the chain tip,
  without requiring to traverse the chain block by block.

ACKs for top commit:
  achow101:
    ACK b922f6b5262884f42d7483f1e9af35650bdb53a7
  TheCharlatan:
    ACK b922f6b5262884f42d7483f1e9af35650bdb53a7

Tree-SHA512: 0587e6d9cf87a59184adb2dbc26a4e2bce3a16233594c6c330f69feb49bf7dc63fdacf44fc20308e93441159ebc604c63eb7de19204d3e745a2ff16004892b45

1 files changed, 53 insertions, 52 deletions

diff --git a/src/rpc/blockchain.cpp b/src/rpc/blockchain.cpp
index 49921794bf..11484a9d8d 100644
--- a/src/rpc/blockchain.cpp
+++ b/src/rpc/blockchain.cpp
@@ -2325,6 +2325,7 @@ static RPCHelpMan scanblocks()
                 {RPCResult::Type::ARR, "relevant_blocks", "Blocks that may have matched a scanobject.", {
                     {RPCResult::Type::STR_HEX, "blockhash", "A relevant blockhash"},
                 }},
+                {RPCResult::Type::BOOL, "completed", "true if the scan process was not aborted"}
             }},
             RPCResult{"when action=='status' and a scan is currently in progress", RPCResult::Type::OBJ, "", "", {
                     {RPCResult::Type::NUM, "progress", "Approximate percent complete"},
@@ -2362,8 +2363,7 @@ static RPCHelpMan scanblocks()
         // set the abort flag
         g_scanfilter_should_abort_scan = true;
         return true;
-    }
-    else if (request.params[0].get_str() == "start") {
+    } else if (request.params[0].get_str() == "start") {
         BlockFiltersScanReserver reserver;
         if (!reserver.reserve()) {
             throw JSONRPCError(RPC_INVALID_PARAMETER, "Scan already in progress, use action \"abort\" or \"status\"");
@@ -2387,27 +2387,28 @@ static RPCHelpMan scanblocks()
         ChainstateManager& chainman = EnsureChainman(node);
 
         // set the start-height
-        const CBlockIndex* block = nullptr;
+        const CBlockIndex* start_index = nullptr;
         const CBlockIndex* stop_block = nullptr;
         {
             LOCK(cs_main);
             CChain& active_chain = chainman.ActiveChain();
-            block = active_chain.Genesis();
-            stop_block = active_chain.Tip();
+            start_index = active_chain.Genesis();
+            stop_block = active_chain.Tip(); // If no stop block is provided, stop at the chain tip.
             if (!request.params[2].isNull()) {
-                block = active_chain[request.params[2].getInt<int>()];
-                if (!block) {
+                start_index = active_chain[request.params[2].getInt<int>()];
+                if (!start_index) {
                     throw JSONRPCError(RPC_MISC_ERROR, "Invalid start_height");
                 }
             }
             if (!request.params[3].isNull()) {
                 stop_block = active_chain[request.params[3].getInt<int>()];
-                if (!stop_block || stop_block->nHeight < block->nHeight) {
+                if (!stop_block || stop_block->nHeight < start_index->nHeight) {
                     throw JSONRPCError(RPC_MISC_ERROR, "Invalid stop_height");
                 }
             }
         }
-        CHECK_NONFATAL(block);
+        CHECK_NONFATAL(start_index);
+        CHECK_NONFATAL(stop_block);
 
         // loop through the scan objects, add scripts to the needle_set
         GCSFilter::ElementSet needle_set;
@@ -2420,64 +2421,64 @@ static RPCHelpMan scanblocks()
         }
         UniValue blocks(UniValue::VARR);
         const int amount_per_chunk = 10000;
-        const CBlockIndex* start_index = block; // for remembering the start of a blockfilter range
         std::vector<BlockFilter> filters;
-        const CBlockIndex* start_block = block; // for progress reporting
-        const int total_blocks_to_process = stop_block->nHeight - start_block->nHeight;
+        int start_block_height = start_index->nHeight; // for progress reporting
+        const int total_blocks_to_process = stop_block->nHeight - start_block_height;
 
         g_scanfilter_should_abort_scan = false;
         g_scanfilter_progress = 0;
-        g_scanfilter_progress_height = start_block->nHeight;
+        g_scanfilter_progress_height = start_block_height;
+        bool completed = true;
 
-        while (block) {
+        const CBlockIndex* end_range = nullptr;
+        do {
             node.rpc_interruption_point(); // allow a clean shutdown
             if (g_scanfilter_should_abort_scan) {
-                LogPrintf("scanblocks RPC aborted at height %d.\n", block->nHeight);
+                completed = false;
                 break;
             }
-            const CBlockIndex* next = nullptr;
-            {
-                LOCK(cs_main);
-                CChain& active_chain = chainman.ActiveChain();
-                next = active_chain.Next(block);
-                if (block == stop_block) next = nullptr;
-            }
-            if (start_index->nHeight + amount_per_chunk == block->nHeight || next == nullptr) {
-                LogPrint(BCLog::RPC, "Fetching blockfilters from height %d to height %d.\n", start_index->nHeight, block->nHeight);
-                if (index->LookupFilterRange(start_index->nHeight, block, filters)) {
-                    for (const BlockFilter& filter : filters) {
-                        // compare the elements-set with each filter
-                        if (filter.GetFilter().MatchAny(needle_set)) {
-                            if (filter_false_positives) {
-                                // Double check the filter matches by scanning the block
-                                const CBlockIndex& blockindex = *CHECK_NONFATAL(WITH_LOCK(cs_main, return chainman.m_blockman.LookupBlockIndex(filter.GetBlockHash())));
-
-                                if (!CheckBlockFilterMatches(chainman.m_blockman, blockindex, needle_set)) {
-                                    continue;
-                                }
-                            }
 
-                            blocks.push_back(filter.GetBlockHash().GetHex());
-                            LogPrint(BCLog::RPC, "scanblocks: found match in %s\n", filter.GetBlockHash().GetHex());
+            // split the lookup range in chunks if we are deeper than 'amount_per_chunk' blocks from the stopping block
+            int start_block = !end_range ? start_index->nHeight : start_index->nHeight + 1; // to not include the previous round 'end_range' block
+            end_range = (start_block + amount_per_chunk < stop_block->nHeight) ?
+                    WITH_LOCK(::cs_main, return chainman.ActiveChain()[start_block + amount_per_chunk]) :
+                    stop_block;
+
+            if (index->LookupFilterRange(start_block, end_range, filters)) {
+                for (const BlockFilter& filter : filters) {
+                    // compare the elements-set with each filter
+                    if (filter.GetFilter().MatchAny(needle_set)) {
+                        if (filter_false_positives) {
+                            // Double check the filter matches by scanning the block
+                            const CBlockIndex& blockindex = *CHECK_NONFATAL(WITH_LOCK(cs_main, return chainman.m_blockman.LookupBlockIndex(filter.GetBlockHash())));
+
+                            if (!CheckBlockFilterMatches(chainman.m_blockman, blockindex, needle_set)) {
+                                continue;
+                            }
                         }
+
+                        blocks.push_back(filter.GetBlockHash().GetHex());
                     }
                 }
-                start_index = block;
-
-                // update progress
-                int blocks_processed = block->nHeight - start_block->nHeight;
-                if (total_blocks_to_process > 0) { // avoid division by zero
-                    g_scanfilter_progress = (int)(100.0 / total_blocks_to_process * blocks_processed);
-                } else {
-                    g_scanfilter_progress = 100;
-                }
-                g_scanfilter_progress_height = block->nHeight;
             }
-            block = next;
-        }
-        ret.pushKV("from_height", start_block->nHeight);
-        ret.pushKV("to_height", g_scanfilter_progress_height.load());
+            start_index = end_range;
+
+            // update progress
+            int blocks_processed = end_range->nHeight - start_block_height;
+            if (total_blocks_to_process > 0) { // avoid division by zero
+                g_scanfilter_progress = (int)(100.0 / total_blocks_to_process * blocks_processed);
+            } else {
+                g_scanfilter_progress = 100;
+            }
+            g_scanfilter_progress_height = end_range->nHeight;
+
+        // Finish if we reached the stop block
+        } while (start_index != stop_block);
+
+        ret.pushKV("from_height", start_block_height);
+        ret.pushKV("to_height", start_index->nHeight); // start_index is always the last scanned block here
         ret.pushKV("relevant_blocks", blocks);
+        ret.pushKV("completed", completed);
     }
     else {
         throw JSONRPCError(RPC_INVALID_PARAMETER, strprintf("Invalid action '%s'", request.params[0].get_str()));