From 38aab0c5e389319115ec6ce2127174688e3c2656 Mon Sep 17 00:00:00 2001
From: Alexander Block <ablock84@gmail.com>
Date: Thu, 16 May 2019 10:12:36 +0200
Subject: [PATCH] Add blocks conflicting with ChainLocks to block index (#2923)

* Print hash of block which conflicts with a ChainLock

* Allow specifying custom block status in `AddToBlockIndex`

* Add blocks (headers) to block index even if they conflict with chainlocks
---
 src/chain.h        |  2 ++
 src/validation.cpp | 25 +++++++++++++++++++------
 2 files changed, 21 insertions(+), 6 deletions(-)

diff --git a/src/chain.h b/src/chain.h
index bff4f3c5fc820..ff72ff684cc58 100644
--- a/src/chain.h
+++ b/src/chain.h
@@ -158,6 +158,8 @@ enum BlockStatus: uint32_t {
     BLOCK_FAILED_VALID       =   32, //!< stage after last reached validness failed
     BLOCK_FAILED_CHILD       =   64, //!< descends from failed block
     BLOCK_FAILED_MASK        =   BLOCK_FAILED_VALID | BLOCK_FAILED_CHILD,
+
+    BLOCK_CONFLICT_CHAINLOCK =   128, //!< conflicts with chainlock system
 };
 
 /** The block chain is a tree shaped structure starting with the
diff --git a/src/validation.cpp b/src/validation.cpp
index 822eb4c8ce9c2..f4095e2ec4e3b 100644
--- a/src/validation.cpp
+++ b/src/validation.cpp
@@ -3074,7 +3074,7 @@ bool ResetBlockFailureFlags(CBlockIndex *pindex) {
     return true;
 }
 
-CBlockIndex* AddToBlockIndex(const CBlockHeader& block)
+CBlockIndex* AddToBlockIndex(const CBlockHeader& block, enum BlockStatus nStatus = BLOCK_VALID_TREE)
 {
     // Check for duplicate
     uint256 hash = block.GetHash();
@@ -3100,9 +3100,14 @@ CBlockIndex* AddToBlockIndex(const CBlockHeader& block)
     }
     pindexNew->nTimeMax = (pindexNew->pprev ? std::max(pindexNew->pprev->nTimeMax, pindexNew->nTime) : pindexNew->nTime);
     pindexNew->nChainWork = (pindexNew->pprev ? pindexNew->pprev->nChainWork : 0) + GetBlockProof(*pindexNew);
-    pindexNew->RaiseValidity(BLOCK_VALID_TREE);
-    if (pindexBestHeader == NULL || pindexBestHeader->nChainWork < pindexNew->nChainWork)
-        pindexBestHeader = pindexNew;
+    if (nStatus & BLOCK_VALID_MASK) {
+        pindexNew->RaiseValidity(nStatus);
+        if (pindexBestHeader == NULL || pindexBestHeader->nChainWork < pindexNew->nChainWork)
+            pindexBestHeader = pindexNew;
+    } else {
+        pindexNew->RaiseValidity(BLOCK_VALID_TREE); // required validity level
+        pindexNew->nStatus |= nStatus;
+    }
 
     setDirtyBlockIndex.insert(pindexNew);
 
@@ -3468,10 +3473,15 @@ static bool AcceptBlockHeader(const CBlockHeader& block, CValidationState& state
         if (mi == mapBlockIndex.end())
             return state.DoS(10, error("%s: prev block not found", __func__), 0, "bad-prevblk");
         pindexPrev = (*mi).second;
+        assert(pindexPrev);
+
         if (pindexPrev->nStatus & BLOCK_FAILED_MASK)
             return state.DoS(100, error("%s: prev block invalid", __func__), REJECT_INVALID, "bad-prevblk");
 
-        assert(pindexPrev);
+        if (pindexPrev->nStatus & BLOCK_CONFLICT_CHAINLOCK)
+            // it's ok-ish, the other node is probably missing the latest chainlock
+            return state.DoS(10, error("%s: prev block %s conflicts with chainlock", __func__, block.hashPrevBlock.ToString()), REJECT_INVALID, "bad-prevblk-chainlock");
+
         if (fCheckpointsEnabled && !CheckIndexAgainstCheckpoint(pindexPrev, state, chainparams, hash))
             return error("%s: CheckIndexAgainstCheckpoint(): %s", __func__, state.GetRejectReason().c_str());
 
@@ -3479,7 +3489,10 @@ static bool AcceptBlockHeader(const CBlockHeader& block, CValidationState& state
             return error("%s: Consensus::ContextualCheckBlockHeader: %s, %s", __func__, hash.ToString(), FormatStateMessage(state));
 
         if (llmq::chainLocksHandler->HasConflictingChainLock(pindexPrev->nHeight + 1, hash)) {
-            return state.DoS(10, error("%s: conflicting with chainlock", __func__), REJECT_INVALID, "bad-chainlock");
+            if (pindex == NULL) {
+                AddToBlockIndex(block, BLOCK_CONFLICT_CHAINLOCK);
+            }
+            return state.DoS(10, error("%s: header %s conflicts with chainlock", __func__, hash.ToString()), REJECT_INVALID, "bad-chainlock");
         }
     }
     if (pindex == NULL)