Be stricter in processing unrequested blocks

AcceptBlock will no longer process an unrequested block, unless it has not
been previously processed and has more work than chainActive.Tip()

Github-Pull: #5875
Rebased-From: 9be0e6837b878f72bd087ce32b7a2f2ffb2fd544

5 files changed, 33 insertions, 22 deletions

diff --git a/src/main.cpp b/src/main.cpp
index efb7fb3f87..760cda5dee 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -296,7 +296,8 @@ void FinalizeNode(NodeId nodeid) {
 }
 
 // Requires cs_main.
-void MarkBlockAsReceived(const uint256& hash) {
+// Returns a bool indicating whether we requested this block.
+bool MarkBlockAsReceived(const uint256& hash) {
     map<uint256, pair<NodeId, list<QueuedBlock>::iterator> >::iterator itInFlight = mapBlocksInFlight.find(hash);
     if (itInFlight != mapBlocksInFlight.end()) {
         CNodeState *state = State(itInFlight->second.first);
@@ -306,7 +307,9 @@ void MarkBlockAsReceived(const uint256& hash) {
         state->nBlocksInFlight--;
         state->nStallingSince = 0;
         mapBlocksInFlight.erase(itInFlight);
+        return true;
     }
+    return false;
 }
 
 // Requires cs_main.
@@ -2826,7 +2829,7 @@ bool AcceptBlockHeader(const CBlockHeader& block, CValidationState& state, CBloc
     return true;
 }
 
-bool AcceptBlock(CBlock& block, CValidationState& state, CBlockIndex** ppindex, CDiskBlockPos* dbp)
+bool AcceptBlock(CBlock& block, CValidationState& state, CBlockIndex** ppindex, bool fRequested, CDiskBlockPos* dbp)
 {
     const CChainParams& chainparams = Params();
     AssertLockHeld(cs_main);
@@ -2836,13 +2839,18 @@ bool AcceptBlock(CBlock& block, CValidationState& state, CBlockIndex** ppindex,
     if (!AcceptBlockHeader(block, state, &pindex))
         return false;
 
-    // If we're pruning, ensure that we don't allow a peer to dump a copy
-    // of old blocks.  But we might need blocks that are not on the main chain
-    // to handle a reorg, even if we've processed once.
-    if (pindex->nStatus & BLOCK_HAVE_DATA || chainActive.Contains(pindex)) {
-        // TODO: deal better with duplicate blocks.
-        // return state.DoS(20, error("AcceptBlock(): already have block %d %s", pindex->nHeight, pindex->GetBlockHash().ToString()), REJECT_DUPLICATE, "duplicate");
-        return true;
+    // 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.
+    bool fAlreadyHave = pindex->nStatus & BLOCK_HAVE_DATA;
+    bool fHasMoreWork = (chainActive.Tip() ? pindex->nChainWork > chainActive.Tip()->nChainWork : true);
+
+    // TODO: deal better with return value and error conditions for duplicate
+    // and unrequested blocks.
+    if (fAlreadyHave) return true;
+    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 ((!CheckBlock(block, state)) || !ContextualCheckBlock(block, state, pindex->pprev)) {
@@ -2891,21 +2899,22 @@ static bool IsSuperMajority(int minVersion, const CBlockIndex* pstart, unsigned
 }
 
 
-bool ProcessNewBlock(CValidationState &state, CNode* pfrom, CBlock* pblock, CDiskBlockPos *dbp)
+bool ProcessNewBlock(CValidationState &state, CNode* pfrom, CBlock* pblock, bool fForceProcessing, CDiskBlockPos *dbp)
 {
     // Preliminary checks
     bool checked = CheckBlock(*pblock, state);
 
     {
         LOCK(cs_main);
-        MarkBlockAsReceived(pblock->GetHash());
+        bool fRequested = MarkBlockAsReceived(pblock->GetHash());
+        fRequested |= fForceProcessing;
         if (!checked) {
             return error("%s: CheckBlock FAILED", __func__);
         }
 
         // Store to disk
         CBlockIndex *pindex = NULL;
-        bool ret = AcceptBlock(*pblock, state, &pindex, dbp);
+        bool ret = AcceptBlock(*pblock, state, &pindex, fRequested, dbp);
         if (pindex && pfrom) {
             mapBlockSource[pindex->GetBlockHash()] = pfrom->GetId();
         }
@@ -3453,7 +3462,7 @@ bool LoadExternalBlockFile(FILE* fileIn, CDiskBlockPos *dbp)
                 // process in case the block isn't known yet
                 if (mapBlockIndex.count(hash) == 0 || (mapBlockIndex[hash]->nStatus & BLOCK_HAVE_DATA) == 0) {
                     CValidationState state;
-                    if (ProcessNewBlock(state, NULL, &block, dbp))
+                    if (ProcessNewBlock(state, NULL, &block, true, dbp))
                         nLoaded++;
                     if (state.IsError())
                         break;
@@ -3475,7 +3484,7 @@ bool LoadExternalBlockFile(FILE* fileIn, CDiskBlockPos *dbp)
                             LogPrintf("%s: Processing out of order child %s of %s\n", __func__, block.GetHash().ToString(),
                                     head.ToString());
                             CValidationState dummy;
-                            if (ProcessNewBlock(dummy, NULL, &block, &it->second))
+                            if (ProcessNewBlock(dummy, NULL, &block, true, &it->second))
                             {
                                 nLoaded++;
                                 queue.push_back(block.GetHash());
@@ -4462,7 +4471,8 @@ bool static ProcessMessage(CNode* pfrom, string strCommand, CDataStream& vRecv,
         pfrom->AddInventoryKnown(inv);
 
         CValidationState state;
-        ProcessNewBlock(state, pfrom, &block);
+        // Process all blocks from whitelisted peers, even if not requested.
+        ProcessNewBlock(state, pfrom, &block, pfrom->fWhitelisted, NULL);
         int nDoS;
         if (state.IsInvalid(nDoS)) {
             pfrom->PushMessage("reject", strCommand, state.GetRejectCode(),
diff --git a/src/main.h b/src/main.h
index 3b25217869..669ea7128a 100644
--- a/src/main.h
+++ b/src/main.h
@@ -153,10 +153,11 @@ void UnregisterNodeSignals(CNodeSignals& nodeSignals);
  * @param[out]  state   This may be set to an Error state if any error occurred processing it, including during validation/connection/etc of otherwise unrelated blocks during reorganisation; or it may be set to an Invalid state if pblock is itself invalid (but this is not guaranteed even when the block is checked). If you want to *possibly* get feedback on whether pblock is valid, you must also install a CValidationInterface (see validationinterface.h) - this will have its BlockChecked method called whenever *any* block completes validation.
  * @param[in]   pfrom   The node which we are receiving the block from; it is added to mapBlockSource and may be penalised if the block is invalid.
  * @param[in]   pblock  The block we want to process.
+ * @param[in]   fForceProcessing Process this block even if unrequested; used for non-network block sources and whitelisted peers.
  * @param[out]  dbp     If pblock is stored to disk (or already there), this will be set to its location.
  * @return True if state.IsValid()
  */
-bool ProcessNewBlock(CValidationState &state, CNode* pfrom, CBlock* pblock, CDiskBlockPos *dbp = NULL);
+bool ProcessNewBlock(CValidationState &state, CNode* pfrom, CBlock* pblock, bool fForceProcessing, CDiskBlockPos *dbp);
 /** Check whether enough disk space is available for an incoming block */
 bool CheckDiskSpace(uint64_t nAdditionalBytes = 0);
 /** Open a block file (blk?????.dat) */
@@ -400,8 +401,8 @@ bool ContextualCheckBlock(const CBlock& block, CValidationState& state, CBlockIn
 /** Check a block is completely valid from start to finish (only works on top of our current best block, with cs_main held) */
 bool TestBlockValidity(CValidationState &state, const CBlock& block, CBlockIndex *pindexPrev, bool fCheckPOW = true, bool fCheckMerkleRoot = true);
 
-/** Store block on disk. If dbp is provided, the file is known to already reside on disk */
-bool AcceptBlock(CBlock& block, CValidationState& state, CBlockIndex **pindex, CDiskBlockPos* dbp = NULL);
+/** Store block on disk. If dbp is non-NULL, the file is known to already reside on disk */
+bool AcceptBlock(CBlock& block, CValidationState& state, CBlockIndex **pindex, bool fRequested, CDiskBlockPos* dbp);
 bool AcceptBlockHeader(const CBlockHeader& block, CValidationState& state, CBlockIndex **ppindex= NULL);
 
 
diff --git a/src/miner.cpp b/src/miner.cpp
index dfabfd48d0..f5919ca3af 100644
--- a/src/miner.cpp
+++ b/src/miner.cpp
@@ -434,7 +434,7 @@ static bool ProcessBlockFound(CBlock* pblock, CWallet& wallet, CReserveKey& rese
 
     // Process this block the same as if we had received it from another node
     CValidationState state;
-    if (!ProcessNewBlock(state, NULL, pblock))
+    if (!ProcessNewBlock(state, NULL, pblock, true, NULL))
         return error("BitcoinMiner: ProcessNewBlock, block not accepted");
 
     return true;
diff --git a/src/rpcmining.cpp b/src/rpcmining.cpp
index d58d438573..528d5406f4 100644
--- a/src/rpcmining.cpp
+++ b/src/rpcmining.cpp
@@ -164,7 +164,7 @@ Value generate(const Array& params, bool fHelp)
             ++pblock->nNonce;
         }
         CValidationState state;
-        if (!ProcessNewBlock(state, NULL, pblock))
+        if (!ProcessNewBlock(state, NULL, pblock, true, NULL))
             throw JSONRPCError(RPC_INTERNAL_ERROR, "ProcessNewBlock, block not accepted");
         ++nHeight;
         blockHashes.push_back(pblock->GetHash().GetHex());
@@ -650,7 +650,7 @@ Value submitblock(const Array& params, bool fHelp)
     CValidationState state;
     submitblock_StateCatcher sc(block.GetHash());
     RegisterValidationInterface(&sc);
-    bool fAccepted = ProcessNewBlock(state, NULL, &block);
+    bool fAccepted = ProcessNewBlock(state, NULL, &block, true, NULL);
     UnregisterValidationInterface(&sc);
     if (fBlockPresent)
     {
diff --git a/src/test/miner_tests.cpp b/src/test/miner_tests.cpp
index e3e9061cce..9e4fd8513e 100644
--- a/src/test/miner_tests.cpp
+++ b/src/test/miner_tests.cpp
@@ -84,7 +84,7 @@ BOOST_AUTO_TEST_CASE(CreateNewBlock_validity)
         pblock->hashMerkleRoot = pblock->BuildMerkleTree();
         pblock->nNonce = blockinfo[i].nonce;
         CValidationState state;
-        BOOST_CHECK(ProcessNewBlock(state, NULL, pblock));
+        BOOST_CHECK(ProcessNewBlock(state, NULL, pblock, true, NULL));
         BOOST_CHECK(state.IsValid());
         pblock->hashPrevBlock = pblock->GetHash();
     }