Bugfix: Allow mining on top of old tip blocks for testnet (fixes testnet-in-a-box use case)

src/chainparams.cpp

@@ -125,6 +125,7 @@ public:
         nMinerThreads = 0;
         nTargetTimespan = 3.5 * 24 * 60 * 60; // 3.5 days
         nTargetSpacing = 2.5 * 60; // 2.5 minutes
+        nMaxTipAge = 24 * 60 * 60;
 
         /**
          * Build the genesis block. Note that the output of the genesis coinbase cannot
@@ -209,6 +210,7 @@ public:
         nMinerThreads = 0;
         nTargetTimespan = 3.5 * 24 * 60 * 60; // 3.5 days
         nTargetSpacing = 2.5 * 60; // 2.5 minutes
+        nMaxTipAge = 0x7fffffff;
 
         //! Modify the testnet genesis block so the timestamp is valid for a later start.
         genesis.nTime = 1317798646;
@@ -268,6 +270,7 @@ public:
         nTargetTimespan = 3.5 * 24 * 60 * 60; // 3.5 days
         nTargetSpacing = 2.5 * 60; // 2.5 minutes
         bnProofOfWorkLimit = ~uint256(0) >> 1;
+        nMaxTipAge = 24 * 60 * 60;
         genesis.nTime = 1296688602;
         genesis.nBits = 0x207fffff;
         genesis.nNonce = 0;

src/chainparams.h

@@ -69,6 +69,7 @@ public:
     int64_t TargetTimespan() const { return nTargetTimespan; }
     int64_t TargetSpacing() const { return nTargetSpacing; }
     int64_t Interval() const { return nTargetTimespan / nTargetSpacing; }
+    int64_t MaxTipAge() const { return nMaxTipAge; }
     /** Make miner stop after a block is found. In RPC, don't return until nGenProcLimit blocks are generated */
     bool MineBlocksOnDemand() const { return fMineBlocksOnDemand; }
     /** In the future use NetworkIDString() for RPC fields */
@@ -98,6 +99,7 @@ protected:
     int64_t nTargetTimespan;
     int64_t nTargetSpacing;
     int nMinerThreads;
+    long nMaxTipAge;
     std::vector<CDNSSeedData> vSeeds;
     std::vector<unsigned char> base58Prefixes[MAX_BASE58_TYPES];
     CBaseChainParams::Network networkID;

src/main.cpp

@@ -1257,6 +1257,7 @@ CAmount GetBlockValue(int nHeight, const CAmount& nFees)
 
 bool IsInitialBlockDownload()
 {
+    const CChainParams& chainParams = Params();
     LOCK(cs_main);
     if (fImporting || fReindex || chainActive.Height() < Checkpoints::GetTotalBlocksEstimate())
         return true;
@@ -1264,7 +1265,7 @@ bool IsInitialBlockDownload()
     if (lockIBDState)
         return false;
     bool state = (chainActive.Height() < pindexBestHeader->nHeight - 24 * 6 ||
-            pindexBestHeader->GetBlockTime() < GetTime() - 24 * 60 * 60);
+            pindexBestHeader->GetBlockTime() < GetTime() - chainParams.MaxTipAge());
     if (!state)
         lockIBDState = true;
     return state;