From 404b01c436122b951e9e06ed26d79dba4651685e Mon Sep 17 00:00:00 2001
From: Sjors Provoost <sjors@sprovoost.nl>
Date: Thu, 30 May 2024 15:55:02 +0200
Subject: rpc: getblocktemplate getTipHash() via Miner interface

---
 src/interfaces/mining.h |  5 +++++
 src/node/interfaces.cpp |  8 ++++++++
 src/rpc/mining.cpp      | 12 +++++-------
 3 files changed, 18 insertions(+), 7 deletions(-)

diff --git a/src/interfaces/mining.h b/src/interfaces/mining.h
index 603d8475d3..8ed273252b 100644
--- a/src/interfaces/mining.h
+++ b/src/interfaces/mining.h
@@ -5,6 +5,8 @@
 #ifndef BITCOIN_INTERFACES_MINING_H
 #define BITCOIN_INTERFACES_MINING_H
 
+#include <uint256.h>
+
 namespace node {
 struct NodeContext;
 } // namespace node
@@ -25,6 +27,9 @@ public:
     //! If this chain is exclusively used for testing
     virtual bool isTestChain() = 0;
 
+    //! Returns the hash for the tip of this chain, 0 if none
+    virtual uint256 getTipHash() = 0;
+
     /**
      * Check a block is completely valid from start to finish.
      * Only works on top of our current best block.
diff --git a/src/node/interfaces.cpp b/src/node/interfaces.cpp
index a528afcff0..bd200e8d29 100644
--- a/src/node/interfaces.cpp
+++ b/src/node/interfaces.cpp
@@ -845,6 +845,14 @@ public:
         return chainman().GetParams().IsTestChain();
     }
 
+    uint256 getTipHash() override
+    {
+        LOCK(::cs_main);
+        CBlockIndex* tip{chainman().ActiveChain().Tip()};
+        if (!tip) return uint256{0};
+        return tip->GetBlockHash();
+    }
+
     bool testBlockValidity(BlockValidationState& state, const CBlock& block, bool check_merkle_root) override
     {
         LOCK(::cs_main);
diff --git a/src/rpc/mining.cpp b/src/rpc/mining.cpp
index a9968b6e5f..9762d7648d 100644
--- a/src/rpc/mining.cpp
+++ b/src/rpc/mining.cpp
@@ -672,7 +672,6 @@ static RPCHelpMan getblocktemplate()
     UniValue lpval = NullUniValue;
     std::set<std::string> setClientRules;
     Chainstate& active_chainstate = chainman.ActiveChainstate();
-    CChain& active_chain = active_chainstate.m_chain;
     if (!request.params[0].isNull())
     {
         const UniValue& oparam = request.params[0].get_obj();
@@ -707,9 +706,8 @@ static RPCHelpMan getblocktemplate()
                 return "duplicate-inconclusive";
             }
 
-            CBlockIndex* const pindexPrev = active_chain.Tip();
             // testBlockValidity only supports blocks built on the current Tip
-            if (block.hashPrevBlock != pindexPrev->GetBlockHash()) {
+            if (block.hashPrevBlock != miner.getTipHash()) {
                 return "inconclusive-not-best-prevblk";
             }
             BlockValidationState state;
@@ -761,7 +759,7 @@ static RPCHelpMan getblocktemplate()
         else
         {
             // NOTE: Spec does not specify behaviour for non-string longpollid, but this makes testing easier
-            hashWatchedChain = active_chain.Tip()->GetBlockHash();
+            hashWatchedChain = miner.getTipHash();
             nTransactionsUpdatedLastLP = nTransactionsUpdatedLast;
         }
 
@@ -806,7 +804,7 @@ static RPCHelpMan getblocktemplate()
     static CBlockIndex* pindexPrev;
     static int64_t time_start;
     static std::unique_ptr<CBlockTemplate> pblocktemplate;
-    if (pindexPrev != active_chain.Tip() ||
+    if (!pindexPrev || pindexPrev->GetBlockHash() != miner.getTipHash() ||
         (mempool.GetTransactionsUpdated() != nTransactionsUpdatedLast && GetTime() - time_start > 5))
     {
         // Clear pindexPrev so future calls make a new block, despite any failures from here on
@@ -814,7 +812,7 @@ static RPCHelpMan getblocktemplate()
 
         // Store the pindexBest used before CreateNewBlock, to avoid races
         nTransactionsUpdatedLast = mempool.GetTransactionsUpdated();
-        CBlockIndex* pindexPrevNew = active_chain.Tip();
+        CBlockIndex* pindexPrevNew = chainman.m_blockman.LookupBlockIndex(miner.getTipHash());
         time_start = GetTime();
 
         // Create new block
@@ -946,7 +944,7 @@ static RPCHelpMan getblocktemplate()
     result.pushKV("transactions", std::move(transactions));
     result.pushKV("coinbaseaux", std::move(aux));
     result.pushKV("coinbasevalue", (int64_t)pblock->vtx[0]->vout[0].nValue);
-    result.pushKV("longpollid", active_chain.Tip()->GetBlockHash().GetHex() + ToString(nTransactionsUpdatedLast));
+    result.pushKV("longpollid", miner.getTipHash().GetHex() + ToString(nTransactionsUpdatedLast));
     result.pushKV("target", hashTarget.GetHex());
     result.pushKV("mintime", (int64_t)pindexPrev->GetMedianTimePast()+1);
     result.pushKV("mutable", std::move(aMutable));
-- 
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