net: change FindNode() to not return a node and rename it

All callers of `CConnman::FindNode()` use its return value `CNode*` only
as a boolean null/notnull. So change that method to return `bool`.

This removes the dangerous pattern of handling a `CNode` object (the
return value of `FindNode()`) without holding `CConnman::m_nodes_mutex`
and without having that object's reference count incremented for the
duration of the usage.

Also rename the method to better describe what it does.

src/net.cpp

@@ -331,26 +331,16 @@ bool IsLocal(const CService& addr)
     return mapLocalHost.count(addr) > 0;
 }
 
-CNode* CConnman::FindNode(const std::string& addrName)
+bool CConnman::AlreadyConnectedToHost(const std::string& host) const
 {
     LOCK(m_nodes_mutex);
-    for (CNode* pnode : m_nodes) {
-        if (pnode->m_addr_name == addrName) {
-            return pnode;
-        }
-    }
-    return nullptr;
+    return std::ranges::any_of(m_nodes, [&host](CNode* node) { return node->m_addr_name == host; });
 }
 
-CNode* CConnman::FindNode(const CService& addr)
+bool CConnman::AlreadyConnectedToAddressPort(const CService& addr_port) const
 {
     LOCK(m_nodes_mutex);
-    for (CNode* pnode : m_nodes) {
-        if (static_cast<CService>(pnode->addr) == addr) {
-            return pnode;
-        }
-    }
-    return nullptr;
+    return std::ranges::any_of(m_nodes, [&addr_port](CNode* node) { return node->addr == addr_port; });
 }
 
 bool CConnman::AlreadyConnectedToAddress(const CNetAddr& addr) const
@@ -393,10 +383,8 @@ CNode* CConnman::ConnectNode(CAddress addrConnect, const char *pszDest, bool fCo
             return nullptr;
 
         // Look for an existing connection
-        CNode* pnode = FindNode(static_cast<CService>(addrConnect));
-        if (pnode)
-        {
-            LogPrintf("Failed to open new connection, already connected\n");
+        if (AlreadyConnectedToAddressPort(addrConnect)) {
+            LogInfo("Failed to open new connection to %s, already connected", addrConnect.ToStringAddrPort());
             return nullptr;
         }
     }
@@ -426,9 +414,7 @@ CNode* CConnman::ConnectNode(CAddress addrConnect, const char *pszDest, bool fCo
                 }
                 // It is possible that we already have a connection to the IP/port pszDest resolved to.
                 // In that case, drop the connection that was just created.
-                LOCK(m_nodes_mutex);
-                CNode* pnode = FindNode(static_cast<CService>(addrConnect));
-                if (pnode) {
+                if (AlreadyConnectedToAddressPort(addrConnect)) {
                     LogPrintf("Not opening a connection to %s, already connected to %s\n", pszDest, addrConnect.ToStringAddrPort());
                     return nullptr;
                 }
@@ -2996,8 +2982,9 @@ void CConnman::OpenNetworkConnection(const CAddress& addrConnect, bool fCountFai
         if (IsLocal(addrConnect) || banned_or_discouraged || AlreadyConnectedToAddress(addrConnect)) {
             return;
         }
-    } else if (FindNode(std::string(pszDest)))
+    } else if (AlreadyConnectedToHost(pszDest)) {
         return;
+    }
 
     CNode* pnode = ConnectNode(addrConnect, pszDest, fCountFailure, conn_type, use_v2transport);
 

src/net.h

@@ -1365,8 +1365,23 @@ private:
 
     uint64_t CalculateKeyedNetGroup(const CNetAddr& ad) const;
 
-    CNode* FindNode(const std::string& addrName);
-    CNode* FindNode(const CService& addr);
+    /**
+     * Determine whether we're already connected to a given "host:port".
+     * Note that for inbound connections, the peer is likely using a random outbound
+     * port on their side, so this will likely not match any inbound connections.
+     * @param[in] host String of the form "host[:port]", e.g. "localhost" or "localhost:8333" or "1.2.3.4:8333".
+     * @return true if connected to `host`.
+     */
+    bool AlreadyConnectedToHost(const std::string& host) const;
+
+    /**
+     * Determine whether we're already connected to a given address:port.
+     * Note that for inbound connections, the peer is likely using a random outbound
+     * port on their side, so this will likely not match any inbound connections.
+     * @param[in] addr_port Address and port to check.
+     * @return true if connected to addr_port.
+     */
+    bool AlreadyConnectedToAddressPort(const CService& addr_port) const;
 
     /**
      * Determine whether we're already connected to a given address.