rpc: add scanblocks - scan for relevant blocks with descriptors

Co-authored-by: James O'Beirne <james.obeirne@gmail.com>

2 files changed, 201 insertions, 0 deletions

diff --git a/src/rpc/blockchain.cpp b/src/rpc/blockchain.cpp
index ddb7ad0f8d..afd4ef0375 100644
--- a/src/rpc/blockchain.cpp
+++ b/src/rpc/blockchain.cpp
@@ -2204,6 +2204,203 @@ static RPCHelpMan scantxoutset()
     };
 }
 
+/** RAII object to prevent concurrency issue when scanning blockfilters */
+static std::atomic<int> g_scanfilter_progress;
+static std::atomic<int> g_scanfilter_progress_height;
+static std::atomic<bool> g_scanfilter_in_progress;
+static std::atomic<bool> g_scanfilter_should_abort_scan;
+class BlockFiltersScanReserver
+{
+private:
+    bool m_could_reserve{false};
+public:
+    explicit BlockFiltersScanReserver() = default;
+
+    bool reserve() {
+        CHECK_NONFATAL(!m_could_reserve);
+        if (g_scanfilter_in_progress.exchange(true)) {
+            return false;
+        }
+        m_could_reserve = true;
+        return true;
+    }
+
+    ~BlockFiltersScanReserver() {
+        if (m_could_reserve) {
+            g_scanfilter_in_progress = false;
+        }
+    }
+};
+
+static RPCHelpMan scanblocks()
+{
+    return RPCHelpMan{"scanblocks",
+        "\nReturn relevant blockhashes for given descriptors.\n"
+        "This call may take several minutes. Make sure to use no RPC timeout (bitcoin-cli -rpcclienttimeout=0)",
+        {
+            scan_action_arg_desc,
+            scan_objects_arg_desc,
+            RPCArg{"start_height", RPCArg::Type::NUM, RPCArg::Default{0}, "Height to start to scan from"},
+            RPCArg{"stop_height", RPCArg::Type::NUM, RPCArg::DefaultHint{"chain tip"}, "Height to stop to scan"},
+            RPCArg{"filtertype", RPCArg::Type::STR, RPCArg::Default{BlockFilterTypeName(BlockFilterType::BASIC)}, "The type name of the filter"}
+        },
+        {
+            scan_result_status_none,
+            RPCResult{"When action=='start'", RPCResult::Type::OBJ, "", "", {
+                {RPCResult::Type::NUM, "from_height", "The height we started the scan from"},
+                {RPCResult::Type::NUM, "to_height", "The height we ended the scan at"},
+                {RPCResult::Type::ARR, "relevant_blocks", "", {{RPCResult::Type::STR_HEX, "blockhash", "A relevant blockhash"},}},
+                },
+            },
+            RPCResult{"when action=='status' and a scan is currently in progress", RPCResult::Type::OBJ, "", "", {
+                    {RPCResult::Type::NUM, "progress", "Approximate percent complete"},
+                    {RPCResult::Type::NUM, "current_height", "Height of the block currently being scanned"},
+                },
+            },
+            scan_result_abort,
+        },
+        RPCExamples{
+            HelpExampleCli("scanblocks", "start '[\"addr(bcrt1q4u4nsgk6ug0sqz7r3rj9tykjxrsl0yy4d0wwte)\"]' 300000") +
+            HelpExampleCli("scanblocks", "start '[\"addr(bcrt1q4u4nsgk6ug0sqz7r3rj9tykjxrsl0yy4d0wwte)\"]' 100 150 basic") +
+            HelpExampleCli("scanblocks", "status") +
+            HelpExampleRpc("scanblocks", "\"start\", [\"addr(bcrt1q4u4nsgk6ug0sqz7r3rj9tykjxrsl0yy4d0wwte)\"], 300000") +
+            HelpExampleRpc("scanblocks", "\"start\", [\"addr(bcrt1q4u4nsgk6ug0sqz7r3rj9tykjxrsl0yy4d0wwte)\"], 100, 150, \"basic\"") +
+            HelpExampleRpc("scanblocks", "\"status\"")
+        },
+        [&](const RPCHelpMan& self, const JSONRPCRequest& request) -> UniValue
+{
+    UniValue ret(UniValue::VOBJ);
+    if (request.params[0].get_str() == "status") {
+        BlockFiltersScanReserver reserver;
+        if (reserver.reserve()) {
+            // no scan in progress
+            return NullUniValue;
+        }
+        ret.pushKV("progress", g_scanfilter_progress.load());
+        ret.pushKV("current_height", g_scanfilter_progress_height.load());
+        return ret;
+    } else if (request.params[0].get_str() == "abort") {
+        BlockFiltersScanReserver reserver;
+        if (reserver.reserve()) {
+            // reserve was possible which means no scan was running
+            return false;
+        }
+        // set the abort flag
+        g_scanfilter_should_abort_scan = true;
+        return true;
+    }
+    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\"");
+        }
+        const std::string filtertype_name{request.params[4].isNull() ? "basic" : request.params[4].get_str()};
+
+        BlockFilterType filtertype;
+        if (!BlockFilterTypeByName(filtertype_name, filtertype)) {
+            throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, "Unknown filtertype");
+        }
+
+        BlockFilterIndex* index = GetBlockFilterIndex(filtertype);
+        if (!index) {
+            throw JSONRPCError(RPC_MISC_ERROR, "Index is not enabled for filtertype " + filtertype_name);
+        }
+
+        NodeContext& node = EnsureAnyNodeContext(request.context);
+        ChainstateManager& chainman = EnsureChainman(node);
+
+        // set the start-height
+        const CBlockIndex* block = nullptr;
+        const CBlockIndex* stop_block = nullptr;
+        {
+            LOCK(cs_main);
+            CChain& active_chain = chainman.ActiveChain();
+            block = active_chain.Genesis();
+            stop_block = active_chain.Tip();
+            if (!request.params[2].isNull()) {
+                block = active_chain[request.params[2].getInt<int>()];
+                if (!block) {
+                    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) {
+                    throw JSONRPCError(RPC_MISC_ERROR, "Invalid stop_height");
+                }
+            }
+        }
+        CHECK_NONFATAL(block);
+
+        // loop through the scan objects, add scripts to the needle_set
+        GCSFilter::ElementSet needle_set;
+        for (const UniValue& scanobject : request.params[1].get_array().getValues()) {
+            FlatSigningProvider provider;
+            std::vector<CScript> scripts = EvalDescriptorStringOrObject(scanobject, provider);
+            for (const CScript& script : scripts) {
+                needle_set.emplace(script.begin(), script.end());
+            }
+        }
+        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;
+
+        g_scanfilter_should_abort_scan = false;
+        g_scanfilter_progress = 0;
+        g_scanfilter_progress_height = start_block->nHeight;
+
+        while (block) {
+            node.rpc_interruption_point(); // allow a clean shutdown
+            if (g_scanfilter_should_abort_scan) {
+                LogPrintf("scanblocks RPC aborted at height %d.\n", block->nHeight);
+                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)) {
+                            blocks.push_back(filter.GetBlockHash().GetHex());
+                            LogPrint(BCLog::RPC, "scanblocks: found match in %s\n", 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());
+        ret.pushKV("relevant_blocks", blocks);
+    }
+    else {
+        throw JSONRPCError(RPC_INVALID_PARAMETER, "Invalid command");
+    }
+    return ret;
+},
+    };
+}
+
 static RPCHelpMan getblockfilter()
 {
     return RPCHelpMan{"getblockfilter",
@@ -2439,6 +2636,7 @@ void RegisterBlockchainRPCCommands(CRPCTable& t)
         {"blockchain", &verifychain},
         {"blockchain", &preciousblock},
         {"blockchain", &scantxoutset},
+        {"blockchain", &scanblocks},
         {"blockchain", &getblockfilter},
         {"hidden", &invalidateblock},
         {"hidden", &reconsiderblock},
diff --git a/src/rpc/client.cpp b/src/rpc/client.cpp
index 612dbbdacf..8688263ef5 100644
--- a/src/rpc/client.cpp
+++ b/src/rpc/client.cpp
@@ -83,6 +83,9 @@ static const CRPCConvertParam vRPCConvertParams[] =
     { "sendmany", 8, "fee_rate"},
     { "sendmany", 9, "verbose" },
     { "deriveaddresses", 1, "range" },
+    { "scanblocks", 1, "scanobjects" },
+    { "scanblocks", 2, "start_height" },
+    { "scanblocks", 3, "stop_height" },
     { "scantxoutset", 1, "scanobjects" },
     { "addmultisigaddress", 0, "nrequired" },
     { "addmultisigaddress", 1, "keys" },