Merge pull request #2658 from TheBlueMatt/forkalert

Detect any sufficiently long fork and alert the user just like any other alert

2 files changed, 89 insertions, 7 deletions

diff --git a/src/init.cpp b/src/init.cpp
index 20d334019d..09871c012c 100644
--- a/src/init.cpp
+++ b/src/init.cpp
@@ -228,7 +228,7 @@ std::string HelpMessage()
     strUsage += "  -rpcthreads=<n>        " + _("Set the number of threads to service RPC calls (default: 4)") + "\n";
     strUsage += "  -blocknotify=<cmd>     " + _("Execute command when the best block changes (%s in cmd is replaced by block hash)") + "\n";
     strUsage += "  -walletnotify=<cmd>    " + _("Execute command when a wallet transaction changes (%s in cmd is replaced by TxID)") + "\n";
-    strUsage += "  -alertnotify=<cmd>     " + _("Execute command when a relevant alert is received (%s in cmd is replaced by message)") + "\n";
+    strUsage += "  -alertnotify=<cmd>     " + _("Execute command when a relevant alert is received or we see a really long fork (%s in cmd is replaced by message)") + "\n";
     strUsage += "  -upgradewallet         " + _("Upgrade wallet to latest format") + "\n";
     strUsage += "  -keypool=<n>           " + _("Set key pool size to <n> (default: 100)") + "\n";
     strUsage += "  -rescan                " + _("Rescan the block chain for missing wallet transactions") + "\n";
diff --git a/src/main.cpp b/src/main.cpp
index 063536820d..e78e055147 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -1376,6 +1376,82 @@ bool IsInitialBlockDownload()
             pindexBest->GetBlockTime() < GetTime() - 24 * 60 * 60);
 }
 
+bool fLargeWorkForkFound = false;
+bool fLargeWorkInvalidChainFound = false;
+CBlockIndex *pindexBestForkTip = NULL, *pindexBestForkBase = NULL;
+
+void CheckForkWarningConditions()
+{
+    // If our best fork is no longer within 72 blocks (+/- 12 hours if no one mines it)
+    // of our head, drop it
+    if (pindexBestForkTip && nBestHeight - pindexBestForkTip->nHeight >= 72)
+        pindexBestForkTip = NULL;
+
+    if (pindexBestForkTip || nBestInvalidWork > nBestChainWork + (pindexBest->GetBlockWork() * 6).getuint256())
+    {
+        if (!fLargeWorkForkFound)
+        {
+            std::string strCmd = GetArg("-alertnotify", "");
+            if (!strCmd.empty())
+            {
+                std::string warning = std::string("'Warning: Large-work fork detected, forking after block ") +
+                                      pindexBestForkBase->phashBlock->ToString() + std::string("'");
+                boost::replace_all(strCmd, "%s", warning);
+                boost::thread t(runCommand, strCmd); // thread runs free
+            }
+        }
+        if (pindexBestForkTip)
+        {
+            printf("CheckForkWarningConditions: Warning: Large valid fork found\n  forking the chain at height %d (%s)\n  lasting to height %d (%s).\nChain state database corruption likely.\n",
+                   pindexBestForkBase->nHeight, pindexBestForkBase->phashBlock->ToString().c_str(),
+                   pindexBestForkTip->nHeight, pindexBestForkTip->phashBlock->ToString().c_str());
+            fLargeWorkForkFound = true;
+        }
+        else
+        {
+            printf("CheckForkWarningConditions: Warning: Found invalid chain at least ~6 blocks longer than our best chain.\nChain state database corruption likely.\n");
+            fLargeWorkInvalidChainFound = true;
+        }
+    }
+    else
+    {
+        fLargeWorkForkFound = false;
+        fLargeWorkInvalidChainFound = false;
+    }
+}
+
+void CheckForkWarningConditionsOnNewFork(CBlockIndex* pindexNewForkTip)
+{
+    // If we are on a fork that is sufficiently large, set a warning flag
+    CBlockIndex* pfork = pindexNewForkTip;
+    CBlockIndex* plonger = pindexBest;
+    while (pfork && pfork != plonger)
+    {
+        while (plonger && plonger->nHeight > pfork->nHeight)
+            plonger = plonger->pprev;
+        if (pfork == plonger)
+            break;
+        pfork = pfork->pprev;
+    }
+
+    // We define a condition which we should warn the user about as a fork of at least 7 blocks
+    // who's tip is within 72 blocks (+/- 12 hours if no one mines it) of ours
+    // We use 7 blocks rather arbitrarily as it represents just under 10% of sustained network
+    // hash rate operating on the fork.
+    // or a chain that is entirely longer than ours and invalid (note that this should be detected by both)
+    // We define it this way because it allows us to only store the highest fork tip (+ base) which meets
+    // the 7-block condition and from this always have the most-likely-to-cause-warning fork
+    if (pfork && (!pindexBestForkTip || (pindexBestForkTip && pindexNewForkTip->nHeight > pindexBestForkTip->nHeight)) &&
+            pindexNewForkTip->nChainWork - pfork->nChainWork > (pfork->GetBlockWork() * 7).getuint256() &&
+            nBestHeight - pindexNewForkTip->nHeight < 72)
+    {
+        pindexBestForkTip = pindexNewForkTip;
+        pindexBestForkBase = pfork;
+    }
+
+    CheckForkWarningConditions();
+}
+
 void static InvalidChainFound(CBlockIndex* pindexNew)
 {
     if (pindexNew->nChainWork > nBestInvalidWork)
@@ -1391,8 +1467,7 @@ void static InvalidChainFound(CBlockIndex* pindexNew)
     printf("InvalidChainFound:  current best=%s  height=%d  log2_work=%.8g  date=%s\n",
       hashBestChain.ToString().c_str(), nBestHeight, log(nBestChainWork.getdouble())/log(2.0),
       DateTimeStrFormat("%Y-%m-%d %H:%M:%S", pindexBest->GetBlockTime()).c_str());
-    if (pindexBest && nBestInvalidWork > nBestChainWork + (pindexBest->GetBlockWork() * 6).getuint256())
-        printf("InvalidChainFound: Warning: Displayed transactions may not be correct! You may need to upgrade, or other nodes may need to upgrade.\n");
+    CheckForkWarningConditions();
 }
 
 void static InvalidBlockFound(CBlockIndex *pindex) {
@@ -2103,11 +2178,14 @@ bool AddToBlockIndex(CBlock& block, CValidationState& state, const CDiskBlockPos
 
     if (pindexNew == pindexBest)
     {
+        // Clear fork warning if its no longer applicable
+        CheckForkWarningConditions();
         // Notify UI to display prev block's coinbase if it was ours
         static uint256 hashPrevBestCoinBase;
         UpdatedTransaction(hashPrevBestCoinBase);
         hashPrevBestCoinBase = block.GetTxHash(0);
-    }
+    } else
+        CheckForkWarningConditionsOnNewFork(pindexNew);
 
     if (!pblocktree->Flush())
         return state.Abort(_("Failed to sync block index"));
@@ -3066,11 +3144,15 @@ string GetWarnings(string strFor)
         strStatusBar = strMiscWarning;
     }
 
-    // Longer invalid proof-of-work chain
-    if (pindexBest && nBestInvalidWork > nBestChainWork + (pindexBest->GetBlockWork() * 6).getuint256())
+    if (fLargeWorkForkFound)
+    {
+        nPriority = 2000;
+        strStatusBar = strRPC = _("Warning: The network does not appear to fully agree! Some miners appear to be experiencing issues.");
+    }
+    else if (fLargeWorkInvalidChainFound)
     {
         nPriority = 2000;
-        strStatusBar = strRPC = _("Warning: Displayed transactions may not be correct! You may need to upgrade, or other nodes may need to upgrade.");
+        strStatusBar = strRPC = _("Warning: We do not appear to fully agree with our peers! You may need to upgrade, or other nodes may need to upgrade.");
     }
 
     // Alerts