[net_processing] Introduce SetupAddressRelay

Idempotent function that initializes m_addr_known for connections that support
address relay (anything other than block-relay-only). Unused until the next
commit.

Author: amitiuttarwar

src/net_processing.cpp

@@ -226,7 +226,7 @@ struct Peer {
     std::vector<CAddress> m_addrs_to_send;
     /** Probabilistic filter of addresses that this peer already knows.
      *  Used to avoid relaying addresses to this peer more than once. */
-    const std::unique_ptr<CRollingBloomFilter> m_addr_known;
+    std::unique_ptr<CRollingBloomFilter> m_addr_known;
     /** Whether a getaddr request to this peer is outstanding. */
     bool m_getaddr_sent{false};
     /** Guards address sending timers. */
@@ -612,6 +612,14 @@ class PeerManagerImpl final : public PeerManager
      * @param[in]   vRecv           The raw message received
      */
     void ProcessGetCFCheckPt(CNode& peer, CDataStream& vRecv);
+
+    /** Checks if address relay is permitted with peer. Initializes
+     * `m_addr_known` bloom filter if needed.
+     *
+     *  @return   True if address relay is enabled with peer
+     *            False if address relay is disallowed
+     */
+    bool SetupAddressRelay(CNode& node, Peer& peer);
 };
 } // namespace
 
@@ -4423,6 +4431,22 @@ class CompareInvMempoolOrder
 };
 }
 
+bool PeerManagerImpl::SetupAddressRelay(CNode& node, Peer& peer)
+{
+    // We don't participate in addr relay with outbound block-relay-only
+    // connections to prevent providing adversaries with the additional
+    // information of addr traffic to infer the link.
+    if (node.IsBlockOnlyConn()) return false;
+
+    if (!RelayAddrsWithPeer(peer)) {
+        // First addr message we have received from the peer, initialize
+        // m_addr_known
+        peer.m_addr_known = std::make_unique<CRollingBloomFilter>(5000, 0.001);
+    }
+
+    return true;
+}
+
 bool PeerManagerImpl::SendMessages(CNode* pto)
 {
     PeerRef peer = GetPeerRef(pto->GetId());