Move handling of unconnecting headers into own function

src/net_processing.cpp

@@ -560,6 +560,11 @@ private:
                                const std::vector<CBlockHeader>& headers,
                                bool via_compact_block)
         EXCLUSIVE_LOCKS_REQUIRED(!m_peer_mutex);
+    /** Various helpers for headers processing, invoked by ProcessHeadersMessage() */
+    /** Deal with state tracking and headers sync for peers that send the
+     * 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);
 
     void SendBlockTransactions(CNode& pfrom, Peer& peer, const CBlock& block, const BlockTransactionsRequest& req);
 
@@ -2194,6 +2199,48 @@ void PeerManagerImpl::SendBlockTransactions(CNode& pfrom, Peer& peer, const CBlo
     m_connman.PushMessage(&pfrom, msgMaker.Make(NetMsgType::BLOCKTXN, resp));
 }
 
+/**
+ * Special handling for unconnecting headers that might be part of a block
+ * announcement.
+ *
+ * We'll send a getheaders message in response to try to connect the chain.
+ *
+ * The peer can send up to MAX_UNCONNECTING_HEADERS in a row that
+ * don't connect before given DoS points.
+ *
+ * Once a headers message is received that is valid and does connect,
+ * nUnconnectingHeaders gets reset back to 0.
+ */
+void PeerManagerImpl::HandleFewUnconnectingHeaders(CNode& pfrom, Peer& peer,
+        const std::vector<CBlockHeader>& headers)
+{
+    const CNetMsgMaker msgMaker(pfrom.GetCommonVersion());
+
+    LOCK(cs_main);
+    CNodeState *nodestate = State(pfrom.GetId());
+
+    nodestate->nUnconnectingHeaders++;
+
+    // Try to fill in the missing headers.
+    m_connman.PushMessage(&pfrom, msgMaker.Make(NetMsgType::GETHEADERS, m_chainman.ActiveChain().GetLocator(m_chainman.m_best_header), uint256()));
+    LogPrint(BCLog::NET, "received header %s: missing prev block %s, sending getheaders (%d) to end (peer=%d, nUnconnectingHeaders=%d)\n",
+            headers[0].GetHash().ToString(),
+            headers[0].hashPrevBlock.ToString(),
+            m_chainman.m_best_header->nHeight,
+            pfrom.GetId(), nodestate->nUnconnectingHeaders);
+
+    // Set hashLastUnknownBlock for this peer, so that if we
+    // eventually get the headers - even from a different peer -
+    // we can use this peer to download.
+    UpdateBlockAvailability(pfrom.GetId(), headers.back().GetHash());
+
+    // The peer may just be broken, so periodically assign DoS points if this
+    // condition persists.
+    if (nodestate->nUnconnectingHeaders % MAX_UNCONNECTING_HEADERS == 0) {
+        Misbehaving(peer, 20, strprintf("%d non-connecting headers", nodestate->nUnconnectingHeaders));
+    }
+}
+
 void PeerManagerImpl::ProcessHeadersMessage(CNode& pfrom, Peer& peer,
                                             const std::vector<CBlockHeader>& headers,
                                             bool via_compact_block)
@@ -2208,36 +2255,24 @@ void PeerManagerImpl::ProcessHeadersMessage(CNode& pfrom, Peer& peer,
 
     bool received_new_header = false;
     const CBlockIndex *pindexLast = nullptr;
+
+    // Do these headers connect to something in our block index?
+    bool headers_connect_blockindex{WITH_LOCK(::cs_main, return m_chainman.m_blockman.LookupBlockIndex(headers[0].hashPrevBlock) != nullptr)};
+
+    if (!headers_connect_blockindex) {
+        if (nCount <= MAX_BLOCKS_TO_ANNOUNCE) {
+            // If this looks like it could be a BIP 130 block announcement, use
+            // special logic for handling headers that don't connect, as this
+            // could be benign.
+            HandleFewUnconnectingHeaders(pfrom, peer, headers);
+        } else {
+            Misbehaving(peer, 10, "invalid header received");
+        }
+        return;
+    }
+
     {
         LOCK(cs_main);
-        CNodeState *nodestate = State(pfrom.GetId());
-
-        // If this looks like it could be a block announcement (nCount <=
-        // MAX_BLOCKS_TO_ANNOUNCE), use special logic for handling headers that
-        // don't connect:
-        // - Send a getheaders message in response to try to connect the chain.
-        // - The peer can send up to MAX_UNCONNECTING_HEADERS in a row that
-        //   don't connect before giving DoS points
-        // - Once a headers message is received that is valid and does connect,
-        //   nUnconnectingHeaders gets reset back to 0.
-        if (!m_chainman.m_blockman.LookupBlockIndex(headers[0].hashPrevBlock) && nCount <= MAX_BLOCKS_TO_ANNOUNCE) {
-            nodestate->nUnconnectingHeaders++;
-            m_connman.PushMessage(&pfrom, msgMaker.Make(NetMsgType::GETHEADERS, m_chainman.ActiveChain().GetLocator(m_chainman.m_best_header), uint256()));
-            LogPrint(BCLog::NET, "received header %s: missing prev block %s, sending getheaders (%d) to end (peer=%d, nUnconnectingHeaders=%d)\n",
-                     headers[0].GetHash().ToString(),
-                     headers[0].hashPrevBlock.ToString(),
-                     m_chainman.m_best_header->nHeight,
-                     pfrom.GetId(), nodestate->nUnconnectingHeaders);
-            // Set hashLastUnknownBlock for this peer, so that if we
-            // eventually get the headers - even from a different peer -
-            // we can use this peer to download.
-            UpdateBlockAvailability(pfrom.GetId(), headers.back().GetHash());
-
-            if (nodestate->nUnconnectingHeaders % MAX_UNCONNECTING_HEADERS == 0) {
-                Misbehaving(peer, 20, strprintf("%d non-connecting headers", nodestate->nUnconnectingHeaders));
-            }
-            return;
-        }
 
         uint256 hashLastBlock;
         for (const CBlockHeader& header : headers) {