Merge #9053: IBD using chainwork instead of height and not using header timestamps

e141beb IsInitialBlockDownload no longer uses header-only timestamps. (Gregory Maxwell)
2082b55 Remove GetTotalBlocksEstimate and checkpoint tests that test nothing. (Gregory Maxwell)
fd46136 IBD check uses minimumchain work instead of checkpoints. (Gregory Maxwell)

7 files changed, 19 insertions, 48 deletions

diff --git a/src/Makefile.test.include b/src/Makefile.test.include
index 5ce1bbb896..4e4cca14ca 100644
--- a/src/Makefile.test.include
+++ b/src/Makefile.test.include
@@ -50,7 +50,6 @@ BITCOIN_TESTS =\
   test/bip32_tests.cpp \
   test/blockencodings_tests.cpp \
   test/bloom_tests.cpp \
-  test/Checkpoints_tests.cpp \
   test/coins_tests.cpp \
   test/compress_tests.cpp \
   test/crypto_tests.cpp \
diff --git a/src/chainparams.cpp b/src/chainparams.cpp
index 5850016ae2..a57ab632e4 100644
--- a/src/chainparams.cpp
+++ b/src/chainparams.cpp
@@ -96,6 +96,9 @@ public:
         consensus.vDeployments[Consensus::DEPLOYMENT_SEGWIT].nStartTime = 1479168000; // November 15th, 2016.
         consensus.vDeployments[Consensus::DEPLOYMENT_SEGWIT].nTimeout = 1510704000; // November 15th, 2017.
 
+        // The best chain should have at least this much work.
+        consensus.nMinimumChainWork = uint256S("0x0000000000000000000000000000000000000000002cb971dd56d1c583c20f90");
+
         /**
          * The message start string is designed to be unlikely to occur in normal data.
          * The characters are rarely used upper ASCII, not valid as UTF-8, and produce
@@ -191,6 +194,9 @@ public:
         consensus.vDeployments[Consensus::DEPLOYMENT_SEGWIT].nStartTime = 1462060800; // May 1st 2016
         consensus.vDeployments[Consensus::DEPLOYMENT_SEGWIT].nTimeout = 1493596800; // May 1st 2017
 
+        // The best chain should have at least this much work.
+        consensus.nMinimumChainWork = uint256S("0x0000000000000000000000000000000000000000000000198b4def2baa9338d6");
+
         pchMessageStart[0] = 0x0b;
         pchMessageStart[1] = 0x11;
         pchMessageStart[2] = 0x09;
@@ -224,6 +230,7 @@ public:
         fRequireStandard = false;
         fMineBlocksOnDemand = false;
 
+
         checkpointData = (CCheckpointData) {
             boost::assign::map_list_of
             ( 546, uint256S("000000002a936ca763904c3c35fce2f3556c559c0214345d31b1bcebf76acb70")),
@@ -265,6 +272,9 @@ public:
         consensus.vDeployments[Consensus::DEPLOYMENT_SEGWIT].nStartTime = 0;
         consensus.vDeployments[Consensus::DEPLOYMENT_SEGWIT].nTimeout = 999999999999ULL;
 
+        // The best chain should have at least this much work.
+        consensus.nMinimumChainWork = uint256S("0x00");
+
         pchMessageStart[0] = 0xfa;
         pchMessageStart[1] = 0xbf;
         pchMessageStart[2] = 0xb5;
diff --git a/src/checkpoints.cpp b/src/checkpoints.cpp
index aefddce464..d22c188c16 100644
--- a/src/checkpoints.cpp
+++ b/src/checkpoints.cpp
@@ -55,16 +55,6 @@ namespace Checkpoints {
         return fWorkBefore / (fWorkBefore + fWorkAfter);
     }
 
-    int GetTotalBlocksEstimate(const CCheckpointData& data)
-    {
-        const MapCheckpoints& checkpoints = data.mapCheckpoints;
-
-        if (checkpoints.empty())
-            return 0;
-
-        return checkpoints.rbegin()->first;
-    }
-
     CBlockIndex* GetLastCheckpoint(const CCheckpointData& data)
     {
         const MapCheckpoints& checkpoints = data.mapCheckpoints;
diff --git a/src/checkpoints.h b/src/checkpoints.h
index cd25ea5379..04346f35ff 100644
--- a/src/checkpoints.h
+++ b/src/checkpoints.h
@@ -19,9 +19,6 @@ struct CCheckpointData;
 namespace Checkpoints
 {
 
-//! Return conservative estimate of total number of blocks, 0 if unknown
-int GetTotalBlocksEstimate(const CCheckpointData& data);
-
 //! Returns last CBlockIndex* in mapBlockIndex that is a checkpoint
 CBlockIndex* GetLastCheckpoint(const CCheckpointData& data);
 
diff --git a/src/consensus/params.h b/src/consensus/params.h
index 0e73cace83..20efc68ade 100644
--- a/src/consensus/params.h
+++ b/src/consensus/params.h
@@ -61,6 +61,7 @@ struct Params {
     int64_t nPowTargetSpacing;
     int64_t nPowTargetTimespan;
     int64_t DifficultyAdjustmentInterval() const { return nPowTargetTimespan / nPowTargetSpacing; }
+    uint256 nMinimumChainWork;
 };
 } // namespace Consensus
 
diff --git a/src/main.cpp b/src/main.cpp
index 4cc886afb5..44031e69e7 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -1746,13 +1746,14 @@ bool IsInitialBlockDownload()
         return false;
     if (fImporting || fReindex)
         return true;
-    if (fCheckpointsEnabled && chainActive.Height() < Checkpoints::GetTotalBlocksEstimate(chainParams.Checkpoints()))
+    if (chainActive.Tip() == NULL)
         return true;
-    bool state = (chainActive.Height() < pindexBestHeader->nHeight - 24 * 6 ||
-            std::max(chainActive.Tip()->GetBlockTime(), pindexBestHeader->GetBlockTime()) < GetTime() - nMaxTipAge);
-    if (!state)
-        latchToFalse.store(true, std::memory_order_relaxed);
-    return state;
+    if (chainActive.Tip()->nChainWork < UintToArith256(chainParams.GetConsensus().nMinimumChainWork))
+        return true;
+    if (chainActive.Tip()->GetBlockTime() < (GetTime() - nMaxTipAge))
+        return true;
+    latchToFalse.store(true, std::memory_order_relaxed);
+    return false;
 }
 
 bool fLargeWorkForkFound = false;
@@ -1780,7 +1781,7 @@ void CheckForkWarningConditions()
 {
     AssertLockHeld(cs_main);
     // Before we get past initial download, we cannot reliably alert about forks
-    // (we assume we don't get stuck on a fork before the last checkpoint)
+    // (we assume we don't get stuck on a fork before finishing our initial sync)
     if (IsInitialBlockDownload())
         return;
 
diff --git a/src/test/Checkpoints_tests.cpp b/src/test/Checkpoints_tests.cpp
deleted file mode 100644
index 1b7d368e13..0000000000
--- a/src/test/Checkpoints_tests.cpp
+++ /dev/null
@@ -1,27 +0,0 @@
-// Copyright (c) 2011-2015 The Bitcoin Core developers
-// Distributed under the MIT software license, see the accompanying
-// file COPYING or http://www.opensource.org/licenses/mit-license.php.
-
-//
-// Unit tests for block-chain checkpoints
-//
-
-#include "checkpoints.h"
-
-#include "uint256.h"
-#include "test/test_bitcoin.h"
-#include "chainparams.h"
-
-#include <boost/test/unit_test.hpp>
-
-using namespace std;
-
-BOOST_FIXTURE_TEST_SUITE(Checkpoints_tests, BasicTestingSetup)
-
-BOOST_AUTO_TEST_CASE(sanity)
-{
-    const CCheckpointData& checkpoints = Params(CBaseChainParams::MAIN).Checkpoints();
-    BOOST_CHECK(Checkpoints::GetTotalBlocksEstimate(checkpoints) >= 134444);
-}
-
-BOOST_AUTO_TEST_SUITE_END()