From 48eecea7e54095f4ecf9d9d092778cca0cb2d3a2 Mon Sep 17 00:00:00 2001
From: Evan Duffield <evan@dashpay.io>
Date: Tue, 11 Aug 2015 12:06:07 -0700
Subject: [PATCH] pull changes from bitcoin for FindMostWorkChain

---
 src/main.cpp | 24 +++++++++++++++++++-----
 1 file changed, 19 insertions(+), 5 deletions(-)

diff --git a/src/main.cpp b/src/main.cpp
index b4bd95b01e..36c9930cf1 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -2504,15 +2504,29 @@ static CBlockIndex* FindMostWorkChain() {
         CBlockIndex *pindexTest = pindexNew;
         bool fInvalidAncestor = false;
         while (pindexTest && !chainActive.Contains(pindexTest)) {
-            assert(pindexTest->nStatus & BLOCK_HAVE_DATA);
             assert(pindexTest->nChainTx || pindexTest->nHeight == 0);
-            if (pindexTest->nStatus & BLOCK_FAILED_MASK) {
-                // Candidate has an invalid ancestor, remove entire chain from the set.
-                if (pindexBestInvalid == NULL || pindexNew->nChainWork > pindexBestInvalid->nChainWork)
+
+            // Pruned nodes may have entries in setBlockIndexCandidates for
+            // which block files have been deleted.  Remove those as candidates
+            // for the most work chain if we come across them; we can't switch
+            // to a chain unless we have all the non-active-chain parent blocks.
+            bool fFailedChain = pindexTest->nStatus & BLOCK_FAILED_MASK;
+            bool fMissingData = !(pindexTest->nStatus & BLOCK_HAVE_DATA);
+            if (fFailedChain || fMissingData) {
+                // Candidate chain is not usable (either invalid or missing data)
+                if (fFailedChain && (pindexBestInvalid == NULL || pindexNew->nChainWork > pindexBestInvalid->nChainWork))
                     pindexBestInvalid = pindexNew;
                 CBlockIndex *pindexFailed = pindexNew;
+                // Remove the entire chain from the set.
                 while (pindexTest != pindexFailed) {
-                    pindexFailed->nStatus |= BLOCK_FAILED_CHILD;
+                    if (fFailedChain) {
+                        pindexFailed->nStatus |= BLOCK_FAILED_CHILD;
+                    } else if (fMissingData) {
+                        // If we're missing data, then add back to mapBlocksUnlinked,
+                        // so that if the block arrives in the future we can try adding
+                        // to setBlockIndexCandidates again.
+                        mapBlocksUnlinked.insert(std::make_pair(pindexFailed->pprev, pindexFailed));
+                    }
                     setBlockIndexCandidates.erase(pindexFailed);
                     pindexFailed = pindexFailed->pprev;
                 }