rpc: Round verificationprogress to exactly 1 for a recent tip

This requires a new lock annotation, but all relevant callers already
held the lock.

src/node/interfaces.cpp

@@ -326,7 +326,8 @@ public:
     }
     double getVerificationProgress() override
     {
-        return chainman().GuessVerificationProgress(WITH_LOCK(chainman().GetMutex(), return chainman().ActiveChain().Tip()));
+        LOCK(chainman().GetMutex());
+        return chainman().GuessVerificationProgress(chainman().ActiveTip());
     }
     bool isInitialBlockDownload() override
     {
@@ -409,6 +410,7 @@ public:
     std::unique_ptr<Handler> handleNotifyBlockTip(NotifyBlockTipFn fn) override
     {
         return MakeSignalHandler(::uiInterface.NotifyBlockTip_connect([fn, this](SynchronizationState sync_state, const CBlockIndex* block) {
+            LOCK(chainman().GetMutex());
             fn(sync_state, BlockTip{block->nHeight, block->GetBlockTime(), block->GetBlockHash()},
                chainman().GuessVerificationProgress(block));
         }));

src/validation.cpp

@@ -5558,10 +5558,9 @@ bool Chainstate::ResizeCoinsCaches(size_t coinstip_size, size_t coinsdb_size)
     return ret;
 }
 
-//! Guess how far we are in the verification process at the given block index
-//! require cs_main if pindex has not been validated yet (because m_chain_tx_count might be unset)
 double ChainstateManager::GuessVerificationProgress(const CBlockIndex* pindex) const
 {
+    AssertLockHeld(GetMutex());
     const ChainTxData& data{GetParams().TxData()};
     if (pindex == nullptr) {
         return 0.0;
@@ -5573,13 +5572,24 @@ double ChainstateManager::GuessVerificationProgress(const CBlockIndex* pindex) c
     }
 
     const int64_t nNow{TicksSinceEpoch<std::chrono::seconds>(NodeClock::now())};
+    const auto block_time{
+        (Assume(m_best_header) && std::abs(nNow - pindex->GetBlockTime()) <= Ticks<std::chrono::seconds>(2h) &&
+         Assume(m_best_header->nHeight >= pindex->nHeight)) ?
+            // When the header is known to be recent, switch to a height-based
+            // approach. This ensures the returned value is quantized when
+            // close to "1.0", because some users expect it to be. This also
+            // avoids relying too much on the exact miner-set timestamp, which
+            // may be off.
+            nNow - (m_best_header->nHeight - pindex->nHeight) * GetConsensus().nPowTargetSpacing :
+            pindex->GetBlockTime(),
+    };
 
     double fTxTotal;
 
     if (pindex->m_chain_tx_count <= data.tx_count) {
         fTxTotal = data.tx_count + (nNow - data.nTime) * data.dTxRate;
     } else {
-        fTxTotal = pindex->m_chain_tx_count + (nNow - pindex->GetBlockTime()) * data.dTxRate;
+        fTxTotal = pindex->m_chain_tx_count + (nNow - block_time) * data.dTxRate;
     }
 
     return std::min<double>(pindex->m_chain_tx_count / fTxTotal, 1.0);

src/validation.h

@@ -1147,7 +1147,7 @@ public:
     bool IsInitialBlockDownload() const;
 
     /** Guess verification progress (as a fraction between 0.0=genesis and 1.0=current tip). */
-    double GuessVerificationProgress(const CBlockIndex* pindex) const;
+    double GuessVerificationProgress(const CBlockIndex* pindex) const EXCLUSIVE_LOCKS_REQUIRED(GetMutex());
 
     /**
      * Import blocks from an external file

test/functional/rpc_blockchain.py

@@ -286,7 +286,13 @@ class BlockchainTest(BitcoinTestFramework):
         future = 2 * 60 * 60
         self.nodes[0].setmocktime(self.nodes[0].getblockchaininfo()["time"] + future + 1)
         assert_greater_than(1, self.nodes[0].getblockchaininfo()["verificationprogress"])
+
+        self.log.info("Check that verificationprogress is exactly 1 for a recent block tip")
         self.nodes[0].setmocktime(self.nodes[0].getblockchaininfo()["time"] + future)
+        assert_equal(1, self.nodes[0].getblockchaininfo()["verificationprogress"])
+
+        self.log.info("Check that verificationprogress is less than 1 as soon as a new header comes in")
+        self.nodes[0].submitheader(self.generateblock(self.nodes[0], output="raw(55)", transactions=[], submit=False, sync_fun=self.no_op)["hex"])
         assert_greater_than(1, self.nodes[0].getblockchaininfo()["verificationprogress"])
 
     def _test_y2106(self):