LLMQ: bound locked transaction requests

src/llmq/quorums_instantsend.cpp

@@ -1393,12 +1393,26 @@ bool CInstantSendManager::RemoveISLockByTxId(const uint256& txid)
 void CInstantSendManager::AskNodesForLockedTx(const uint256& txid)
 {
     std::vector<CNode*> nodesToAskFor;
-    g_connman->ForEachNode([&](CNode* pnode) {
-        LOCK(pnode->cs_filter);
+    nodesToAskFor.reserve(4);
+
+    auto maybe_add_to_nodesToAskFor = [&nodesToAskFor, &txid](CNode* pnode) {
+        if (nodesToAskFor.size() >= 4) {
+            return;
+        }
+        LOCK(pnode->cs_inventory);
         if (pnode->filterInventoryKnown.contains(txid)) {
             pnode->AddRef();
             nodesToAskFor.emplace_back(pnode);
         }
+    };
+
+    g_connman->ForEachNode([&](CNode* pnode) {
+        // Check masternodes first
+        if (pnode->fZnode) maybe_add_to_nodesToAskFor(pnode);
+    });
+    g_connman->ForEachNode([&](CNode* pnode) {
+        // Check non-masternodes next
+        if (!pnode->fZnode) maybe_add_to_nodesToAskFor(pnode);
     });
     {
         LOCK(cs_main);

src/llmq/quorums_instantsend.h

@@ -74,6 +74,8 @@ class CInstantSendDb
 
 class CInstantSendManager : public CRecoveredSigsListener
 {
+    friend struct CInstantSendRequestTestAccess;
+
 private:
     CCriticalSection cs;
     CInstantSendDb db;

src/test/CMakeLists.txt

@@ -67,6 +67,7 @@ add_executable(test_firo
   ${CMAKE_CURRENT_SOURCE_DIR}/random_tests.cpp
   ${CMAKE_CURRENT_SOURCE_DIR}/reverselock_tests.cpp
   ${CMAKE_CURRENT_SOURCE_DIR}/rpc_tests.cpp
+  ${CMAKE_CURRENT_SOURCE_DIR}/quorums_instantsend_request_tests.cpp
   ${CMAKE_CURRENT_SOURCE_DIR}/sanity_tests.cpp
   ${CMAKE_CURRENT_SOURCE_DIR}/scheduler_tests.cpp
   ${CMAKE_CURRENT_SOURCE_DIR}/scriptnum10.h

src/test/quorums_instantsend_request_tests.cpp

@@ -0,0 +1,93 @@
+// Copyright (c) 2026 The Firo developers
+// Distributed under the MIT software license, see the accompanying
+// file COPYING or http://www.opensource.org/licenses/mit-license.php.
+
+#include "dbwrapper.h"
+#include "llmq/quorums_instantsend.h"
+#include "net.h"
+#include "test/test_bitcoin.h"
+
+#include <boost/test/unit_test.hpp>
+
+#include <memory>
+#include <vector>
+
+namespace llmq
+{
+
+struct CInstantSendRequestTestAccess {
+    static void AskNodesForLockedTx(CInstantSendManager& manager, const uint256& txid)
+    {
+        manager.AskNodesForLockedTx(txid);
+    }
+};
+
+} // namespace llmq
+
+namespace
+{
+
+struct InstantSendRequestSetup : BasicTestingSetup {
+    CDBWrapper db;
+    llmq::CInstantSendManager manager;
+    std::vector<std::unique_ptr<CNode> > nodes;
+
+    InstantSendRequestSetup() : db(boost::filesystem::temp_directory_path() / boost::filesystem::unique_path(), 1 << 20, true, false),
+                                manager(db)
+    {
+        g_connman = std::make_unique<CConnman>(0x1337, 0x1337);
+    }
+
+    ~InstantSendRequestSetup()
+    {
+        LOCK(g_connman->cs_vNodes);
+        g_connman->vNodes.clear();
+    }
+
+    void AddNode(bool masternode, bool knowsTx, const uint256& txid)
+    {
+        auto node = std::make_unique<CNode>(nodes.size(), NODE_NETWORK, 0, INVALID_SOCKET, CAddress(), 0, 0);
+        node->fZnode = masternode;
+        node->fSuccessfullyConnected = true;
+        if (knowsTx) {
+            LOCK(node->cs_inventory);
+            node->filterInventoryKnown.insert(txid);
+        }
+        {
+            LOCK(g_connman->cs_vNodes);
+            g_connman->vNodes.emplace_back(node.get());
+        }
+        nodes.emplace_back(std::move(node));
+    }
+};
+
+} // namespace
+
+BOOST_FIXTURE_TEST_SUITE(quorums_instantsend_request_tests, InstantSendRequestSetup)
+
+BOOST_AUTO_TEST_CASE(asks_at_most_four_peers_and_prefers_masternodes)
+{
+    uint256 txid;
+    txid.SetHex("01");
+
+    AddNode(false, true, txid);
+    AddNode(false, true, txid);
+    AddNode(false, true, txid);
+    AddNode(true, true, txid);
+    AddNode(true, false, txid);
+    AddNode(true, true, txid);
+    AddNode(true, true, txid);
+    AddNode(false, true, txid);
+
+    llmq::CInstantSendRequestTestAccess::AskNodesForLockedTx(manager, txid);
+
+    const std::vector<bool> expected{true, false, false, true, false, true, true, false};
+    for (size_t i = 0; i < nodes.size(); ++i) {
+        LOCK(nodes[i]->cs_inventory);
+        BOOST_CHECK_EQUAL(nodes[i]->setAskFor.count(txid), expected[i] ? 1 : 0);
+        BOOST_CHECK_EQUAL(nodes[i]->GetRefCount(), 0);
+    }
+    g_connman->RemoveAskFor(txid);
+}
+
+BOOST_AUTO_TEST_SUITE_END()