Allow setting nMinimumChainWork on command line

src/init.cpp

@@ -354,6 +354,9 @@ std::string HelpMessage(HelpMessageMode mode)
     strUsage += HelpMessageOpt("-maxorphantx=<n>", strprintf(_("Keep at most <n> unconnectable transactions in memory (default: %u)"), DEFAULT_MAX_ORPHAN_TRANSACTIONS));
     strUsage += HelpMessageOpt("-maxmempool=<n>", strprintf(_("Keep the transaction memory pool below <n> megabytes (default: %u)"), DEFAULT_MAX_MEMPOOL_SIZE));
     strUsage += HelpMessageOpt("-mempoolexpiry=<n>", strprintf(_("Do not keep transactions in the mempool longer than <n> hours (default: %u)"), DEFAULT_MEMPOOL_EXPIRY));
+    if (showDebug) {
+        strUsage += HelpMessageOpt("-minimumchainwork=<hex>", strprintf("Minimum work assumed to exist on a valid chain in hex (default: %s, testnet: %s)", defaultChainParams->GetConsensus().nMinimumChainWork.GetHex(), testnetChainParams->GetConsensus().nMinimumChainWork.GetHex()));
+    }
     strUsage += HelpMessageOpt("-persistmempool", strprintf(_("Whether to save the mempool on shutdown and load on restart (default: %u)"), DEFAULT_PERSIST_MEMPOOL));
     strUsage += HelpMessageOpt("-blockreconstructionextratxn=<n>", strprintf(_("Extra transactions to keep in memory for compact block reconstructions (default: %u)"), DEFAULT_BLOCK_RECONSTRUCTION_EXTRA_TXN));
     strUsage += HelpMessageOpt("-par=<n>", strprintf(_("Set the number of script verification threads (%u to %d, 0 = auto, <0 = leave that many cores free, default: %d)"),
@@ -970,6 +973,20 @@ bool AppInitParameterInteraction()
     else
         LogPrintf("Validating signatures for all blocks.\n");
 
+    if (gArgs.IsArgSet("-minimumchainwork")) {
+        const std::string minChainWorkStr = gArgs.GetArg("-minimumchainwork", "");
+        if (!IsHexNumber(minChainWorkStr)) {
+            return InitError(strprintf("Invalid non-hex (%s) minimum chain work value specified", minChainWorkStr));
+        }
+        nMinimumChainWork = UintToArith256(uint256S(minChainWorkStr));
+    } else {
+        nMinimumChainWork = UintToArith256(chainparams.GetConsensus().nMinimumChainWork);
+    }
+    LogPrintf("Setting nMinimumChainWork=%s\n", nMinimumChainWork.GetHex());
+    if (nMinimumChainWork < UintToArith256(chainparams.GetConsensus().nMinimumChainWork)) {
+        LogPrintf("Warning: nMinimumChainWork set below default value of %s\n", chainparams.GetConsensus().nMinimumChainWork.GetHex());
+    }
+
     // mempool limits
     int64_t nMempoolSizeMax = gArgs.GetArg("-maxmempool", DEFAULT_MAX_MEMPOOL_SIZE) * 1000000;
     int64_t nMempoolSizeMin = gArgs.GetArg("-limitdescendantsize", DEFAULT_DESCENDANT_SIZE_LIMIT) * 1000 * 40;

src/net_processing.cpp

@@ -466,7 +466,7 @@ void FindNextBlocksToDownload(NodeId nodeid, unsigned int count, std::vector<con
     // Make sure pindexBestKnownBlock is up to date, we'll need it.
     ProcessBlockAvailability(nodeid);
 
-    if (state->pindexBestKnownBlock == nullptr || state->pindexBestKnownBlock->nChainWork < chainActive.Tip()->nChainWork || state->pindexBestKnownBlock->nChainWork < UintToArith256(consensusParams.nMinimumChainWork)) {
+    if (state->pindexBestKnownBlock == nullptr || state->pindexBestKnownBlock->nChainWork < chainActive.Tip()->nChainWork || state->pindexBestKnownBlock->nChainWork < nMinimumChainWork) {
         // This peer has nothing interesting.
         return;
     }

src/test/util_tests.cpp

@@ -253,6 +253,31 @@ BOOST_AUTO_TEST_CASE(util_IsHex)
     BOOST_CHECK(!IsHex("0x0000"));
 }
 
+BOOST_AUTO_TEST_CASE(util_IsHexNumber)
+{
+    BOOST_CHECK(IsHexNumber("0x0"));
+    BOOST_CHECK(IsHexNumber("0"));
+    BOOST_CHECK(IsHexNumber("0x10"));
+    BOOST_CHECK(IsHexNumber("10"));
+    BOOST_CHECK(IsHexNumber("0xff"));
+    BOOST_CHECK(IsHexNumber("ff"));
+    BOOST_CHECK(IsHexNumber("0xFfa"));
+    BOOST_CHECK(IsHexNumber("Ffa"));
+    BOOST_CHECK(IsHexNumber("0x00112233445566778899aabbccddeeffAABBCCDDEEFF"));
+    BOOST_CHECK(IsHexNumber("00112233445566778899aabbccddeeffAABBCCDDEEFF"));
+
+    BOOST_CHECK(!IsHexNumber(""));   // empty string not allowed
+    BOOST_CHECK(!IsHexNumber("0x")); // empty string after prefix not allowed
+    BOOST_CHECK(!IsHexNumber("0x0 ")); // no spaces at end,
+    BOOST_CHECK(!IsHexNumber(" 0x0")); // or beginning,
+    BOOST_CHECK(!IsHexNumber("0x 0")); // or middle,
+    BOOST_CHECK(!IsHexNumber(" "));    // etc.
+    BOOST_CHECK(!IsHexNumber("0x0ga")); // invalid character
+    BOOST_CHECK(!IsHexNumber("x0"));    // broken prefix
+    BOOST_CHECK(!IsHexNumber("0x0x00")); // two prefixes not allowed
+
+}
+
 BOOST_AUTO_TEST_CASE(util_seed_insecure_rand)
 {
     SeedInsecureRand(true);

src/utilstrencodings.cpp

@@ -65,6 +65,19 @@ bool IsHex(const std::string& str)
     return (str.size() > 0) && (str.size()%2 == 0);
 }
 
+bool IsHexNumber(const std::string& str)
+{
+    size_t starting_location = 0;
+    if (str.size() > 2 && *str.begin() == '0' && *(str.begin()+1) == 'x') {
+        starting_location = 2;
+    }
+    for (auto c : str.substr(starting_location)) {
+        if (HexDigit(c) < 0) return false;
+    }
+    // Return false for empty string or "0x".
+    return (str.size() > starting_location);
+}
+
 std::vector<unsigned char> ParseHex(const char* psz)
 {
     // convert hex dump to vector

src/utilstrencodings.h

@@ -38,7 +38,13 @@ std::string SanitizeString(const std::string& str, int rule = SAFE_CHARS_DEFAULT
 std::vector<unsigned char> ParseHex(const char* psz);
 std::vector<unsigned char> ParseHex(const std::string& str);
 signed char HexDigit(char c);
+/* Returns true if each character in str is a hex character, and has an even
+ * number of hex digits.*/
 bool IsHex(const std::string& str);
+/**
+* Return true if the string is a hex number, optionally prefixed with "0x"
+*/
+bool IsHexNumber(const std::string& str);
 std::vector<unsigned char> DecodeBase64(const char* p, bool* pfInvalid = nullptr);
 std::string DecodeBase64(const std::string& str);
 std::string EncodeBase64(const unsigned char* pch, size_t len);

src/validation.cpp

@@ -83,6 +83,7 @@ int64_t nMaxTipAge = DEFAULT_MAX_TIP_AGE;
 bool fEnableReplacement = DEFAULT_ENABLE_REPLACEMENT;
 
 uint256 hashAssumeValid;
+arith_uint256 nMinimumChainWork;
 
 CFeeRate minRelayTxFee = CFeeRate(DEFAULT_MIN_RELAY_TX_FEE);
 CAmount maxTxFee = DEFAULT_TRANSACTION_MAXFEE;
@@ -1035,8 +1036,6 @@ CAmount GetBlockSubsidy(int nHeight, const Consensus::Params& consensusParams)
 
 bool IsInitialBlockDownload()
 {
-    const CChainParams& chainParams = Params();
-
     // Once this function has returned false, it must remain false.
     static std::atomic<bool> latchToFalse{false};
     // Optimization: pre-test latch before taking the lock.
@@ -1050,7 +1049,7 @@ bool IsInitialBlockDownload()
         return true;
     if (chainActive.Tip() == nullptr)
         return true;
-    if (chainActive.Tip()->nChainWork < UintToArith256(chainParams.GetConsensus().nMinimumChainWork))
+    if (chainActive.Tip()->nChainWork < nMinimumChainWork)
         return true;
     if (chainActive.Tip()->GetBlockTime() < (GetTime() - nMaxTipAge))
         return true;
@@ -1670,7 +1669,7 @@ static bool ConnectBlock(const CBlock& block, CValidationState& state, CBlockInd
         if (it != mapBlockIndex.end()) {
             if (it->second->GetAncestor(pindex->nHeight) == pindex &&
                 pindexBestHeader->GetAncestor(pindex->nHeight) == pindex &&
-                pindexBestHeader->nChainWork >= UintToArith256(chainparams.GetConsensus().nMinimumChainWork)) {
+                pindexBestHeader->nChainWork >= nMinimumChainWork) {
                 // This block is a member of the assumed verified chain and an ancestor of the best header.
                 // The equivalent time check discourages hash power from extorting the network via DOS attack
                 //  into accepting an invalid block through telling users they must manually set assumevalid.

src/validation.h

@@ -186,6 +186,9 @@ extern bool fEnableReplacement;
 /** Block hash whose ancestors we will assume to have valid scripts without checking them. */
 extern uint256 hashAssumeValid;
 
+/** Minimum work we will assume exists on some valid chain. */
+extern arith_uint256 nMinimumChainWork;
+
 /** Best header we've seen so far (used for getheaders queries' starting points). */
 extern CBlockIndex *pindexBestHeader;