Be even stricter in processing unrequested blocks

Github-Pull: #6224
Rebased-From: bfc30b34374d71928acee5ff41282f09cedfd5e4 6b1066fab41523d25d75b45a10e4b0f61d7c61d0 04b5d235f1560b8285591b963d3636f7ddf74563 59b49cd07482494d9a99068af502be9ceda41ed2

1 files changed, 14 insertions, 3 deletions

diff --git a/src/main.cpp b/src/main.cpp
index 8f82abf4d9..e2f31d9fd3 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -2847,9 +2847,15 @@ bool AcceptBlock(CBlock& block, CValidationState& state, CBlockIndex** ppindex,
 
     // Try to process all requested blocks that we don't have, but only
     // process an unrequested block if it's new and has enough work to
-    // advance our tip.
+    // advance our tip, and isn't too many blocks ahead.
     bool fAlreadyHave = pindex->nStatus & BLOCK_HAVE_DATA;
     bool fHasMoreWork = (chainActive.Tip() ? pindex->nChainWork > chainActive.Tip()->nChainWork : true);
+    // Blocks that are too out-of-order needlessly limit the effectiveness of
+    // pruning, because pruning will not delete block files that contain any
+    // blocks which are too close in height to the tip.  Apply this test
+    // regardless of whether pruning is enabled; it should generally be safe to
+    // not process unrequested blocks.
+    bool fTooFarAhead = (pindex->nHeight > int(chainActive.Height() + MIN_BLOCKS_TO_KEEP));
 
     // TODO: deal better with return value and error conditions for duplicate
     // and unrequested blocks.
@@ -2857,6 +2863,7 @@ bool AcceptBlock(CBlock& block, CValidationState& state, CBlockIndex** ppindex,
     if (!fRequested) {  // If we didn't ask for it:
         if (pindex->nTx != 0) return true;  // This is a previously-processed block that was pruned
         if (!fHasMoreWork) return true;     // Don't process less-work chains
+        if (fTooFarAhead) return true;      // Block height is too high
     }
 
     if ((!CheckBlock(block, state)) || !ContextualCheckBlock(block, state, pindex->pprev)) {
@@ -4478,8 +4485,12 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
         pfrom->AddInventoryKnown(inv);
 
         CValidationState state;
-        // Process all blocks from whitelisted peers, even if not requested.
-        ProcessNewBlock(state, pfrom, &block, pfrom->fWhitelisted, NULL);
+        // Process all blocks from whitelisted peers, even if not requested,
+        // unless we're still syncing with the network.
+        // Such an unrequested block may still be processed, subject to the
+        // conditions in AcceptBlock().
+        bool forceProcessing = pfrom->fWhitelisted && !IsInitialBlockDownload();
+        ProcessNewBlock(state, pfrom, &block, forceProcessing, NULL);
         int nDoS;
         if (state.IsInvalid(nDoS)) {
             pfrom->PushMessage("reject", strCommand, state.GetRejectCode(),