Add helper function for checking header continuity

Author: sdaftuar

src/net_processing.cpp

@@ -565,6 +565,8 @@ class PeerManagerImpl final : public PeerManager
      * occasional non-connecting header (this can happen due to BIP 130 headers
      * announcements for blocks interacting with the 2hr (MAX_FUTURE_BLOCK_TIME) rule). */
     void HandleFewUnconnectingHeaders(CNode& pfrom, Peer& peer, const std::vector<CBlockHeader>& headers);
+    /** Return true if the headers connect to each other, false otherwise */
+    bool CheckHeadersAreContinuous(const std::vector<CBlockHeader>& headers) const;
 
     void SendBlockTransactions(CNode& pfrom, Peer& peer, const CBlock& block, const BlockTransactionsRequest& req);
 
@@ -2241,6 +2243,18 @@ void PeerManagerImpl::HandleFewUnconnectingHeaders(CNode& pfrom, Peer& peer,
     }
 }
 
+bool PeerManagerImpl::CheckHeadersAreContinuous(const std::vector<CBlockHeader>& headers) const
+{
+    uint256 hashLastBlock;
+    for (const CBlockHeader& header : headers) {
+        if (!hashLastBlock.IsNull() && header.hashPrevBlock != hashLastBlock) {
+            return false;
+        }
+        hashLastBlock = header.GetHash();
+    }
+    return true;
+}
+
 void PeerManagerImpl::ProcessHeadersMessage(CNode& pfrom, Peer& peer,
                                             const std::vector<CBlockHeader>& headers,
                                             bool via_compact_block)
@@ -2271,21 +2285,18 @@ void PeerManagerImpl::ProcessHeadersMessage(CNode& pfrom, Peer& peer,
         return;
     }
 
+    // At this point, the headers connect to something in our block index.
+    if (!CheckHeadersAreContinuous(headers)) {
+        Misbehaving(peer, 20, "non-continuous headers sequence");
+        return;
+    }
+
     {
         LOCK(cs_main);
 
-        uint256 hashLastBlock;
-        for (const CBlockHeader& header : headers) {
-            if (!hashLastBlock.IsNull() && header.hashPrevBlock != hashLastBlock) {
-                Misbehaving(peer, 20, "non-continuous headers sequence");
-                return;
-            }
-            hashLastBlock = header.GetHash();
-        }
-
         // If we don't have the last header, then they'll have given us
         // something new (if these headers are valid).
-        if (!m_chainman.m_blockman.LookupBlockIndex(hashLastBlock)) {
+        if (!m_chainman.m_blockman.LookupBlockIndex(headers.back().GetHash())) {
             received_new_header = true;
         }
     }