From 3019ad78f92b53e4ca5ca5277d8a33f0cfdb02a1 Mon Sep 17 00:00:00 2001
From: UdjinM6 <UdjinM6@users.noreply.github.com>
Date: Thu, 1 Dec 2022 19:34:11 +0300
Subject: [PATCH] fix(consensus)!: avoid using the same mn twice in one indexed
 quorum (#5086)

---
 src/llmq/utils.cpp | 24 ++++++++++++++++++++++--
 1 file changed, 22 insertions(+), 2 deletions(-)

diff --git a/src/llmq/utils.cpp b/src/llmq/utils.cpp
index ddf803380a..da4ec2fd0d 100644
--- a/src/llmq/utils.cpp
+++ b/src/llmq/utils.cpp
@@ -341,10 +341,21 @@ std::vector<std::vector<CDeterministicMNCPtr>> BuildNewQuorumQuarterMembers(cons
     auto idx = 0;
     for (auto i = 0; i < nQuorums; ++i) {
         auto usedMNsCount = MnsUsedAtHIndexed[i].GetAllMNsCount();
+        auto updated{false};
+        auto initial_loop_idx = idx;
         while (quarterQuorumMembers[i].size() < quarterSize && (usedMNsCount + quarterQuorumMembers[i].size() < sortedCombinedMnsList.size())) {
+            bool skip{true};
             if (!MnsUsedAtHIndexed[i].HasMN(sortedCombinedMnsList[idx]->proTxHash)) {
-                quarterQuorumMembers[i].push_back(sortedCombinedMnsList[idx]);
-            } else {
+                try {
+                    // NOTE: AddMN is the one that can throw exceptions, must be exicuted first
+                    MnsUsedAtHIndexed[i].AddMN(sortedCombinedMnsList[idx]);
+                    quarterQuorumMembers[i].push_back(sortedCombinedMnsList[idx]);
+                    updated = true;
+                    skip = false;
+                } catch (const std::runtime_error& e) {
+                }
+            }
+            if (skip) {
                 if (firstSkippedIndex == 0) {
                     firstSkippedIndex = idx;
                     skipList.push_back(idx);
@@ -355,6 +366,15 @@ std::vector<std::vector<CDeterministicMNCPtr>> BuildNewQuorumQuarterMembers(cons
             if (++idx == sortedCombinedMnsList.size()) {
                 idx = 0;
             }
+            if (idx == initial_loop_idx) {
+                // we made full "while" loop
+                if (!updated) {
+                    // there are not enough MNs, there is nothing we can do here
+                    return std::vector<std::vector<CDeterministicMNCPtr>>(nQuorums);
+                }
+                // reset and try again
+                updated = false;
+            }
         }
     }