Merge #9293: [0.13 Backport] IBD using chainwork instead of height and not using header timestamp (#9053)

5998a09 IsInitialBlockDownload no longer uses header-only timestamps. (Gregory Maxwell)
5b93eee Remove GetTotalBlocksEstimate and checkpoint tests that test nothing. (Gregory Maxwell)
ad20cdd IBD check uses minimumchain work instead of checkpoints. (Gregory Maxwell)
4c71fc4 Remove duplicate nBlocksEstimate cmp (we already checked IsIBD()) (Matt Corallo)

8 files changed, 21 insertions, 52 deletions

diff --git a/doc/release-process.md b/doc/release-process.md
index 41c1ac8556..ccc4bcd230 100644
--- a/doc/release-process.md
+++ b/doc/release-process.md
@@ -10,6 +10,7 @@ Before every minor and major release:
 * Update [bips.md](bips.md) to account for changes since the last release.
 * Update version in sources (see below)
 * Write release notes (see below)
+* Update `src/chainparams.cpp` nMinimumChainWork with information from the getblockchaininfo rpc.
 
 Before every major release:
 
diff --git a/src/Makefile.test.include b/src/Makefile.test.include
index ef30eeb4ae..0878d8234c 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 3ad9f4d2d3..69514617b6 100644
--- a/src/chainparams.cpp
+++ b/src/chainparams.cpp
@@ -97,6 +97,9 @@ 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
@@ -194,6 +197,9 @@ 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;
@@ -228,6 +234,7 @@ public:
         fMineBlocksOnDemand = false;
         fTestnetToBeDeprecatedFieldRPC = true;
 
+
         checkpointData = (CCheckpointData) {
             boost::assign::map_list_of
             ( 546, uint256S("000000002a936ca763904c3c35fce2f3556c559c0214345d31b1bcebf76acb70")),
@@ -270,6 +277,9 @@ 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 d97017d0c4..7aa876d650 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 191bcff4cc..5f04c19162 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -1747,13 +1747,14 @@ 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;
@@ -1781,7 +1782,7 @@ 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;
 
@@ -3110,13 +3111,10 @@ bool ActivateBestChain(CValidationState &state, const CChainParams& chainparams,
                     }
                 }
                 // Relay inventory, but don't relay old inventory during initial block download.
-                int nBlockEstimate = 0;
-                if (fCheckpointsEnabled)
-                    nBlockEstimate = Checkpoints::GetTotalBlocksEstimate(chainparams.Checkpoints());
                 {
                     LOCK(cs_vNodes);
                     BOOST_FOREACH(CNode* pnode, vNodes) {
-                        if (nNewHeight > (pnode->nStartingHeight != -1 ? pnode->nStartingHeight - 2000 : nBlockEstimate)) {
+                        if (nNewHeight > (pnode->nStartingHeight != -1 ? pnode->nStartingHeight - 2000 : 0)) {
                             BOOST_REVERSE_FOREACH(const uint256& hash, vHashes) {
                                 pnode->PushBlockHash(hash);
                             }
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()