p2p: Introduce data struct to track connection counts by network

Connman uses this new map to keep a count of active OUTBOUND_FULL_RELAY and
MANUAL connections. Unused until next commit.

Co-authored-by: Martin Zumsande <mzumsande@gmail.com>

src/net.cpp

@@ -1135,6 +1135,9 @@ void CConnman::DisconnectNodes()
                 // close socket and cleanup
                 pnode->CloseSocketDisconnect();
 
+                // update connection count by network
+                if (pnode->IsManualOrFullOutboundConn()) --m_network_conn_counts[pnode->addr.GetNetwork()];
+
                 // hold in disconnected pool until all refs are released
                 pnode->Release();
                 m_nodes_disconnected.push_back(pnode);
@@ -2035,6 +2038,9 @@ void CConnman::OpenNetworkConnection(const CAddress& addrConnect, bool fCountFai
     {
         LOCK(m_nodes_mutex);
         m_nodes.push_back(pnode);
+
+        // update connection count by network
+        if (pnode->IsManualOrFullOutboundConn()) ++m_network_conn_counts[pnode->addr.GetNetwork()];
     }
 }
 

src/net.h

@@ -465,6 +465,22 @@ public:
         return m_conn_type == ConnectionType::MANUAL;
     }
 
+    bool IsManualOrFullOutboundConn() const
+    {
+        switch (m_conn_type) {
+        case ConnectionType::INBOUND:
+        case ConnectionType::FEELER:
+        case ConnectionType::BLOCK_RELAY:
+        case ConnectionType::ADDR_FETCH:
+                return false;
+        case ConnectionType::OUTBOUND_FULL_RELAY:
+        case ConnectionType::MANUAL:
+                return true;
+        } // no default case, so the compiler can warn about missing cases
+
+        assert(false);
+    }
+
     bool IsBlockOnlyConn() const {
         return m_conn_type == ConnectionType::BLOCK_RELAY;
     }
@@ -1048,6 +1064,9 @@ private:
     std::atomic<NodeId> nLastNodeId{0};
     unsigned int nPrevNodeCount{0};
 
+    // Stores number of full-tx connections (outbound and manual) per network
+    std::array<unsigned int, Network::NET_MAX> m_network_conn_counts GUARDED_BY(m_nodes_mutex) = {};
+
     /**
      * Cache responses to addr requests to minimize privacy leak.
      * Attack example: scraping addrs in real-time may allow an attacker

src/test/util/net.h

@@ -29,7 +29,10 @@ struct ConnmanTestMsg : public CConnman {
     {
         LOCK(m_nodes_mutex);
         m_nodes.push_back(&node);
+
+        if (node.IsManualOrFullOutboundConn()) ++m_network_conn_counts[node.addr.GetNetwork()];
     }
+
     void ClearTestNodes()
     {
         LOCK(m_nodes_mutex);