Change BIP65/66 enforcement to match Dogecoin (#1403)

* Introduce first estimates at BIP lock-in blocks

* Introduce Dogecoin BIP parameters

* Re-introduce supermajority rules for BIP65

* Add BIP65 supermajority rules

* Tighten v3 block constraints

* Don't enforce coinbase in v2 blocks

* Correct testnet majority params

* Change to using base version when checking supermajority

1 files changed, 26 insertions, 4 deletions

diff --git a/src/validation.cpp b/src/validation.cpp
index eb02a1dd2..b233e1044 100644
--- a/src/validation.cpp
+++ b/src/validation.cpp
@@ -84,6 +84,11 @@ CAmount maxTxFee = DEFAULT_TRANSACTION_MAXFEE;
 
 CTxMemPool mempool(::minRelayTxFee);
 
+/**
+ * Returns true if there are nRequired or more blocks of minVersion or above
+ * in the last Consensus::Params::nMajorityWindow blocks, starting at pstart and going backwards.
+ */
+static bool IsSuperMajority(int minVersion, const CBlockIndex* pstart, unsigned nRequired, const Consensus::Params& consensusParams);
 static void CheckBlockIndex(const Consensus::Params& consensusParams);
 
 /** Constant stuff for coinbase transactions we create: */
@@ -1858,8 +1863,9 @@ bool ConnectBlock(const CBlock& block, CValidationState& state, CBlockIndex* pin
         flags |= SCRIPT_VERIFY_DERSIG;
     }
 
-    // Start enforcing CHECKLOCKTIMEVERIFY (BIP65) rule
-    if (pindex->nHeight >= chainparams.GetConsensus().BIP65Height) {
+    // Start enforcing CHECKLOCKTIMEVERIFY, (BIP65) for block.nVersion=4
+    // blocks, when 75% of the network has upgraded:
+    if (block.GetBaseVersion() >= 4 && IsSuperMajority(4, pindex->pprev, chainparams.GetConsensus().nMajorityEnforceBlockUpgrade, chainparams.GetConsensus())) {
         flags |= SCRIPT_VERIFY_CHECKLOCKTIMEVERIFY;
     }
 
@@ -3025,11 +3031,15 @@ bool ContextualCheckBlockHeader(const CBlockHeader& block, CValidationState& sta
     // Reject outdated version blocks when 95% (75% on testnet) of the network has upgraded:
     // check for version 2, 3 and 4 upgrades
     // Dogecoin: Version 2 enforcement was never used
-    if((block.GetBaseVersion() < 3 && nHeight >= consensusParams.BIP66Height) ||
-       (block.GetBaseVersion() < 4 && nHeight >= consensusParams.BIP65Height))
+    if((block.GetBaseVersion() < 3 && nHeight >= consensusParams.BIP66Height))
             return state.Invalid(false, REJECT_OBSOLETE, strprintf("bad-version(0x%08x)", block.GetBaseVersion()),
                                  strprintf("rejected nVersion=0x%08x block", block.GetBaseVersion()));
 
+    // Dogecoin: Introduce supermajority rules for v4 blocks
+    if (block.GetBaseVersion() < 4 && IsSuperMajority(4, pindexPrev, consensusParams.nMajorityRejectBlockOutdated, consensusParams))
+        return state.Invalid(error("%s : rejected nVersion=3 block", __func__),
+                             REJECT_OBSOLETE, "bad-version");
+
     return true;
 }
 
@@ -3262,6 +3272,18 @@ static bool AcceptBlock(const std::shared_ptr<const CBlock>& pblock, CValidation
     return true;
 }
 
+static bool IsSuperMajority(int minVersion, const CBlockIndex* pstart, unsigned nRequired, const Consensus::Params& consensusParams)
+{
+    unsigned int nFound = 0;
+    for (int i = 0; i < consensusParams.nMajorityWindow && nFound < nRequired && pstart != NULL; i++)
+    {
+        if (pstart->nVersion >= minVersion)
+            ++nFound;
+        pstart = pstart->pprev;
+    }
+    return (nFound >= nRequired);
+}
+
 bool ProcessNewBlock(const CChainParams& chainparams, const std::shared_ptr<const CBlock> pblock, bool fForceProcessing, bool *fNewBlock)
 {
     {