Merge bitcoin/bitcoin#33454: net: support overriding the proxy selection in ConnectNode()

c76de2eea1 net: support overriding the proxy selection in ConnectNode() (Vasil Dimov)

Pull request description:

  Normally `ConnectNode()` would choose whether to use a proxy and which one. Make it possible to override this from the callers and same for `OpenNetworkConnection()` - pass down the proxy to `ConnectNode()`.

  Document both functions.

  This is useful if we want to open connections to IPv4 or IPv6 peers through the Tor SOCKS5 proxy.

  Also have `OpenNetworkConnection()` return whether the connection succeeded or not. This can be used when the caller needs to keep track of how many (successful) connections were opened.

  ---

  This is part of [#29415 Broadcast own transactions only via short-lived Tor or I2P connections](https://github.com/bitcoin/bitcoin/pull/29415). Putting it in its own PR to reduce the size of #29415 and because it does not depend on the other commits from there.

ACKs for top commit:
  stratospher:
    ACK c76de2e.
  optout21:
    ACK c76de2eea1
  mzumsande:
    Code Review ACK c76de2eea1
  andrewtoth:
    ACK c76de2eea1

Tree-SHA512: 1d266e4280cdb1d0599971fa8b5da58b1b7451635be46abb15c0b823a1e18cf6e7bcba4a365ad198e6fd1afee4097d81a54253fa680c8b386ca6b9d68d795ff0

src/net.cpp

@@ -373,7 +373,12 @@ static CService GetBindAddress(const Sock& sock)
     return addr_bind;
 }
 
-CNode* CConnman::ConnectNode(CAddress addrConnect, const char *pszDest, bool fCountFailure, ConnectionType conn_type, bool use_v2transport)
+CNode* CConnman::ConnectNode(CAddress addrConnect,
+                             const char* pszDest,
+                             bool fCountFailure,
+                             ConnectionType conn_type,
+                             bool use_v2transport,
+                             const std::optional<Proxy>& proxy_override)
 {
     AssertLockNotHeld(m_unused_i2p_sessions_mutex);
     assert(conn_type != ConnectionType::INBOUND);
@@ -439,7 +444,13 @@ CNode* CConnman::ConnectNode(CAddress addrConnect, const char *pszDest, bool fCo
 
     for (auto& target_addr: connect_to) {
         if (target_addr.IsValid()) {
-            const bool use_proxy{GetProxy(target_addr.GetNetwork(), proxy)};
+            bool use_proxy;
+            if (proxy_override.has_value()) {
+                use_proxy = true;
+                proxy = proxy_override.value();
+            } else {
+                use_proxy = GetProxy(target_addr.GetNetwork(), proxy);
+            }
             bool proxyConnectionFailed = false;
 
             if (target_addr.IsI2P() && use_proxy) {
@@ -2872,7 +2883,7 @@ void CConnman::ThreadOpenConnections(const std::vector<std::string> connect, std
             const bool count_failures{((int)outbound_ipv46_peer_netgroups.size() + outbound_privacy_network_peers) >= std::min(m_max_automatic_connections - 1, 2)};
             // Use BIP324 transport when both us and them have NODE_V2_P2P set.
             const bool use_v2transport(addrConnect.nServices & GetLocalServices() & NODE_P2P_V2);
-            OpenNetworkConnection(addrConnect, count_failures, std::move(grant), /*strDest=*/nullptr, conn_type, use_v2transport);
+            OpenNetworkConnection(addrConnect, count_failures, std::move(grant), /*pszDest=*/nullptr, conn_type, use_v2transport);
         }
     }
 }
@@ -2981,7 +2992,13 @@ void CConnman::ThreadOpenAddedConnections()
 }
 
 // if successful, this moves the passed grant to the constructed node
-void CConnman::OpenNetworkConnection(const CAddress& addrConnect, bool fCountFailure, CountingSemaphoreGrant<>&& grant_outbound, const char *pszDest, ConnectionType conn_type, bool use_v2transport)
+bool CConnman::OpenNetworkConnection(const CAddress& addrConnect,
+                                     bool fCountFailure,
+                                     CountingSemaphoreGrant<>&& grant_outbound,
+                                     const char* pszDest,
+                                     ConnectionType conn_type,
+                                     bool use_v2transport,
+                                     const std::optional<Proxy>& proxy_override)
 {
     AssertLockNotHeld(m_unused_i2p_sessions_mutex);
     assert(conn_type != ConnectionType::INBOUND);
@@ -2990,24 +3007,24 @@ void CConnman::OpenNetworkConnection(const CAddress& addrConnect, bool fCountFai
     // Initiate outbound network connection
     //
     if (m_interrupt_net->interrupted()) {
-        return;
+        return false;
     }
     if (!fNetworkActive) {
-        return;
+        return false;
     }
     if (!pszDest) {
         bool banned_or_discouraged = m_banman && (m_banman->IsDiscouraged(addrConnect) || m_banman->IsBanned(addrConnect));
         if (IsLocal(addrConnect) || banned_or_discouraged || AlreadyConnectedToAddress(addrConnect)) {
-            return;
+            return false;
         }
     } else if (AlreadyConnectedToHost(pszDest)) {
-        return;
+        return false;
     }
 
-    CNode* pnode = ConnectNode(addrConnect, pszDest, fCountFailure, conn_type, use_v2transport);
+    CNode* pnode = ConnectNode(addrConnect, pszDest, fCountFailure, conn_type, use_v2transport, proxy_override);
 
     if (!pnode)
-        return;
+        return false;
     pnode->grantOutbound = std::move(grant_outbound);
 
     m_msgproc->InitializeNode(*pnode, m_local_services);
@@ -3025,6 +3042,8 @@ void CConnman::OpenNetworkConnection(const CAddress& addrConnect, bool fCountFai
         pnode->ConnectionTypeAsString().c_str(),
         pnode->ConnectedThroughNetwork(),
         GetNodeCount(ConnectionDirection::Out));
+
+    return true;
 }
 
 Mutex NetEventsInterface::g_msgproc_mutex;