From cb94db119f4643f49da63520d64efc99fb0c0795 Mon Sep 17 00:00:00 2001
From: Fabian Jahr <fjahr@protonmail.com>
Date: Thu, 24 Dec 2020 00:11:40 +0100
Subject: [PATCH] validation, index: Add unspendable coinbase helper functions

Making the checks to identify BIP30 available outside of validation.cpp is needed for reporting and tracking statistics on specific blocks and the UTXO set correctly.
---
 src/index/coinstatsindex.cpp |  6 +-----
 src/validation.cpp           | 15 +++++++++++++--
 src/validation.h             |  6 ++++++
 3 files changed, 20 insertions(+), 7 deletions(-)

diff --git a/src/index/coinstatsindex.cpp b/src/index/coinstatsindex.cpp
index d3559b1b75e..271e5bb1f68 100644
--- a/src/index/coinstatsindex.cpp
+++ b/src/index/coinstatsindex.cpp
@@ -144,17 +144,13 @@ bool CoinStatsIndex::CustomAppend(const interfaces::BlockInfo& block)
             }
         }
 
-        // TODO: Deduplicate BIP30 related code
-        bool is_bip30_block{(block.height == 91722 && block.hash == uint256S("0x00000000000271a2dc26e7667f8419f2e15416dc6955e5a6c6cdf3f2574dd08e")) ||
-                            (block.height == 91812 && block.hash == uint256S("0x00000000000af0aed4792b1acee3d966af36cf5def14935db8de83d6f9306f2f"))};
-
         // Add the new utxos created from the block
         assert(block.data);
         for (size_t i = 0; i < block.data->vtx.size(); ++i) {
             const auto& tx{block.data->vtx.at(i)};
 
             // Skip duplicate txid coinbase transactions (BIP30).
-            if (is_bip30_block && tx->IsCoinBase()) {
+            if (IsBIP30Unspendable(*pindex) && tx->IsCoinBase()) {
                 m_total_unspendable_amount += block_subsidy;
                 m_total_unspendables_bip30 += block_subsidy;
                 continue;
diff --git a/src/validation.cpp b/src/validation.cpp
index 37e68cfe4a1..e6fa63b5640 100644
--- a/src/validation.cpp
+++ b/src/validation.cpp
@@ -2083,8 +2083,7 @@ bool Chainstate::ConnectBlock(const CBlock& block, BlockValidationState& state,
     // Now that the whole chain is irreversibly beyond that time it is applied to all blocks except the
     // two in the chain that violate it. This prevents exploiting the issue against nodes during their
     // initial block download.
-    bool fEnforceBIP30 = !((pindex->nHeight==91842 && pindex->GetBlockHash() == uint256S("0x00000000000a4d0a398161ffc163c503763b1f4360639393e0e4c8e300e0caec")) ||
-                           (pindex->nHeight==91880 && pindex->GetBlockHash() == uint256S("0x00000000000743f190a18c5577a3c2d2a1f610ae9601ac046a38084ccb7cd721")));
+    bool fEnforceBIP30 = !IsBIP30Repeat(*pindex);
 
     // Once BIP34 activated it was not possible to create new duplicate coinbases and thus other than starting
     // with the 2 existing duplicate coinbase pairs, not possible to create overwriting txs.  But by the
@@ -5290,3 +5289,15 @@ Chainstate& ChainstateManager::ActivateExistingSnapshot(CTxMemPool* mempool, uin
     m_active_chainstate = m_snapshot_chainstate.get();
     return *m_snapshot_chainstate;
 }
+
+bool IsBIP30Repeat(const CBlockIndex& block_index)
+{
+    return (block_index.nHeight==91842 && block_index.GetBlockHash() == uint256S("0x00000000000a4d0a398161ffc163c503763b1f4360639393e0e4c8e300e0caec")) ||
+           (block_index.nHeight==91880 && block_index.GetBlockHash() == uint256S("0x00000000000743f190a18c5577a3c2d2a1f610ae9601ac046a38084ccb7cd721"));
+}
+
+bool IsBIP30Unspendable(const CBlockIndex& block_index)
+{
+    return (block_index.nHeight==91722 && block_index.GetBlockHash() == uint256S("0x00000000000271a2dc26e7667f8419f2e15416dc6955e5a6c6cdf3f2574dd08e")) ||
+           (block_index.nHeight==91812 && block_index.GetBlockHash() == uint256S("0x00000000000af0aed4792b1acee3d966af36cf5def14935db8de83d6f9306f2f"));
+}
diff --git a/src/validation.h b/src/validation.h
index fb6d59f92ed..a8ef7a8b3ae 100644
--- a/src/validation.h
+++ b/src/validation.h
@@ -1082,4 +1082,10 @@ bool DeploymentEnabled(const ChainstateManager& chainman, DEP dep)
  */
 const AssumeutxoData* ExpectedAssumeutxo(const int height, const CChainParams& params);
 
+/** Identifies blocks that overwrote an existing coinbase output in the UTXO set (see BIP30) */
+bool IsBIP30Repeat(const CBlockIndex& block_index);
+
+/** Identifies blocks which coinbase output was subsequently overwritten in the UTXO set (see BIP30) */
+bool IsBIP30Unspendable(const CBlockIndex& block_index);
+
 #endif // BITCOIN_VALIDATION_H