net: attempts to connect to all resolved addresses when connecting to a node

Prior to this, when establishing a network connection via CConnman::ConnectNode,
if the connection needed address resolution, a single address would be picked
at random from the resolved addresses and our node will try to connect to it. However,
this would lead to the behavior of ConnectNode being unpredictable when the address
was resolved to various ips (e.g. the address resolving to IPv4 and IPv6, but we only
support one of them).

This patches the aforementioned behavior by going over all resolved IPs until we find one
we can connect to or until we exhaust them.

1 files changed, 91 insertions, 75 deletions

diff --git a/src/net.cpp b/src/net.cpp
index e388f05b03..f8ed487ccc 100644
--- a/src/net.cpp
+++ b/src/net.cpp
@@ -412,6 +412,9 @@ CNode* CConnman::ConnectNode(CAddress addrConnect, const char *pszDest, bool fCo
     // Resolve
     const uint16_t default_port{pszDest != nullptr ? GetDefaultPort(pszDest) :
                                                      m_params.GetDefaultPort()};
+
+    // Collection of addresses to try to connect to: either all dns resolved addresses if a domain name (pszDest) is provided, or addrConnect otherwise.
+    std::vector<CAddress> connect_to{};
     if (pszDest) {
         std::vector<CService> resolved{Lookup(pszDest, default_port, fNameLookup && !HaveNameProxy(), 256)};
         if (!resolved.empty()) {
@@ -432,8 +435,16 @@ CNode* CConnman::ConnectNode(CAddress addrConnect, const char *pszDest, bool fCo
                     LogPrintf("Not opening a connection to %s, already connected to %s\n", pszDest, addrConnect.ToStringAddrPort());
                     return nullptr;
                 }
+                // Add the address to the resolved addresses vector so we can try to connect to it later on
+                connect_to.push_back(addrConnect);
             }
+        } else {
+            // For resolution via proxy
+            connect_to.push_back(addrConnect);
         }
+    } else {
+        // Connect via addrConnect directly
+        connect_to.push_back(addrConnect);
     }
 
     // Connect
@@ -443,94 +454,99 @@ CNode* CConnman::ConnectNode(CAddress addrConnect, const char *pszDest, bool fCo
     assert(!addr_bind.IsValid());
     std::unique_ptr<i2p::sam::Session> i2p_transient_session;
 
-    if (addrConnect.IsValid()) {
-        const bool use_proxy{GetProxy(addrConnect.GetNetwork(), proxy)};
-        bool proxyConnectionFailed = false;
+    for (auto& target_addr: connect_to) {
+        if (target_addr.IsValid()) {
+            const bool use_proxy{GetProxy(target_addr.GetNetwork(), proxy)};
+            bool proxyConnectionFailed = false;
 
-        if (addrConnect.IsI2P() && use_proxy) {
-            i2p::Connection conn;
-            bool connected{false};
+            if (target_addr.IsI2P() && use_proxy) {
+                i2p::Connection conn;
+                bool connected{false};
 
-            if (m_i2p_sam_session) {
-                connected = m_i2p_sam_session->Connect(addrConnect, conn, proxyConnectionFailed);
-            } else {
-                {
-                    LOCK(m_unused_i2p_sessions_mutex);
-                    if (m_unused_i2p_sessions.empty()) {
-                        i2p_transient_session =
-                            std::make_unique<i2p::sam::Session>(proxy, &interruptNet);
-                    } else {
-                        i2p_transient_session.swap(m_unused_i2p_sessions.front());
-                        m_unused_i2p_sessions.pop();
+                if (m_i2p_sam_session) {
+                    connected = m_i2p_sam_session->Connect(target_addr, conn, proxyConnectionFailed);
+                } else {
+                    {
+                        LOCK(m_unused_i2p_sessions_mutex);
+                        if (m_unused_i2p_sessions.empty()) {
+                            i2p_transient_session =
+                                std::make_unique<i2p::sam::Session>(proxy, &interruptNet);
+                        } else {
+                            i2p_transient_session.swap(m_unused_i2p_sessions.front());
+                            m_unused_i2p_sessions.pop();
+                        }
                     }
-                }
-                connected = i2p_transient_session->Connect(addrConnect, conn, proxyConnectionFailed);
-                if (!connected) {
-                    LOCK(m_unused_i2p_sessions_mutex);
-                    if (m_unused_i2p_sessions.size() < MAX_UNUSED_I2P_SESSIONS_SIZE) {
-                        m_unused_i2p_sessions.emplace(i2p_transient_session.release());
+                    connected = i2p_transient_session->Connect(target_addr, conn, proxyConnectionFailed);
+                    if (!connected) {
+                        LOCK(m_unused_i2p_sessions_mutex);
+                        if (m_unused_i2p_sessions.size() < MAX_UNUSED_I2P_SESSIONS_SIZE) {
+                            m_unused_i2p_sessions.emplace(i2p_transient_session.release());
+                        }
                     }
                 }
-            }
 
-            if (connected) {
-                sock = std::move(conn.sock);
-                addr_bind = CAddress{conn.me, NODE_NONE};
+                if (connected) {
+                    sock = std::move(conn.sock);
+                    addr_bind = CAddress{conn.me, NODE_NONE};
+                }
+            } else if (use_proxy) {
+                LogPrintLevel(BCLog::PROXY, BCLog::Level::Debug, "Using proxy: %s to connect to %s\n", proxy.ToString(), target_addr.ToStringAddrPort());
+                sock = ConnectThroughProxy(proxy, target_addr.ToStringAddr(), target_addr.GetPort(), proxyConnectionFailed);
+            } else {
+                // no proxy needed (none set for target network)
+                sock = ConnectDirectly(target_addr, conn_type == ConnectionType::MANUAL);
             }
-        } else if (use_proxy) {
-            LogPrintLevel(BCLog::PROXY, BCLog::Level::Debug, "Using proxy: %s to connect to %s:%s\n", proxy.ToString(), addrConnect.ToStringAddr(), addrConnect.GetPort());
-            sock = ConnectThroughProxy(proxy, addrConnect.ToStringAddr(), addrConnect.GetPort(), proxyConnectionFailed);
-        } else {
-            // no proxy needed (none set for target network)
-            sock = ConnectDirectly(addrConnect, conn_type == ConnectionType::MANUAL);
+            if (!proxyConnectionFailed) {
+                // If a connection to the node was attempted, and failure (if any) is not caused by a problem connecting to
+                // the proxy, mark this as an attempt.
+                addrman.Attempt(target_addr, fCountFailure);
+            }
+        } else if (pszDest && GetNameProxy(proxy)) {
+            std::string host;
+            uint16_t port{default_port};
+            SplitHostPort(std::string(pszDest), port, host);
+            bool proxyConnectionFailed;
+            sock = ConnectThroughProxy(proxy, host, port, proxyConnectionFailed);
+        }
+        // Check any other resolved address (if any) if we fail to connect
+        if (!sock) {
+            continue;
         }
-        if (!proxyConnectionFailed) {
-            // If a connection to the node was attempted, and failure (if any) is not caused by a problem connecting to
-            // the proxy, mark this as an attempt.
-            addrman.Attempt(addrConnect, fCountFailure);
+
+        NetPermissionFlags permission_flags = NetPermissionFlags::None;
+        std::vector<NetWhitelistPermissions> whitelist_permissions = conn_type == ConnectionType::MANUAL ? vWhitelistedRangeOutgoing : std::vector<NetWhitelistPermissions>{};
+        AddWhitelistPermissionFlags(permission_flags, target_addr, whitelist_permissions);
+
+        // Add node
+        NodeId id = GetNewNodeId();
+        uint64_t nonce = GetDeterministicRandomizer(RANDOMIZER_ID_LOCALHOSTNONCE).Write(id).Finalize();
+        if (!addr_bind.IsValid()) {
+            addr_bind = GetBindAddress(*sock);
         }
-    } else if (pszDest && GetNameProxy(proxy)) {
-        std::string host;
-        uint16_t port{default_port};
-        SplitHostPort(std::string(pszDest), port, host);
-        bool proxyConnectionFailed;
-        sock = ConnectThroughProxy(proxy, host, port, proxyConnectionFailed);
-    }
-    if (!sock) {
-        return nullptr;
-    }
+        CNode* pnode = new CNode(id,
+                                std::move(sock),
+                                target_addr,
+                                CalculateKeyedNetGroup(target_addr),
+                                nonce,
+                                addr_bind,
+                                pszDest ? pszDest : "",
+                                conn_type,
+                                /*inbound_onion=*/false,
+                                CNodeOptions{
+                                    .permission_flags = permission_flags,
+                                    .i2p_sam_session = std::move(i2p_transient_session),
+                                    .recv_flood_size = nReceiveFloodSize,
+                                    .use_v2transport = use_v2transport,
+                                });
+        pnode->AddRef();
 
-    NetPermissionFlags permission_flags = NetPermissionFlags::None;
-    std::vector<NetWhitelistPermissions> whitelist_permissions = conn_type == ConnectionType::MANUAL ? vWhitelistedRangeOutgoing : std::vector<NetWhitelistPermissions>{};
-    AddWhitelistPermissionFlags(permission_flags, addrConnect, whitelist_permissions);
+        // We're making a new connection, harvest entropy from the time (and our peer count)
+        RandAddEvent((uint32_t)id);
 
-    // Add node
-    NodeId id = GetNewNodeId();
-    uint64_t nonce = GetDeterministicRandomizer(RANDOMIZER_ID_LOCALHOSTNONCE).Write(id).Finalize();
-    if (!addr_bind.IsValid()) {
-        addr_bind = GetBindAddress(*sock);
+        return pnode;
     }
-    CNode* pnode = new CNode(id,
-                             std::move(sock),
-                             addrConnect,
-                             CalculateKeyedNetGroup(addrConnect),
-                             nonce,
-                             addr_bind,
-                             pszDest ? pszDest : "",
-                             conn_type,
-                             /*inbound_onion=*/false,
-                             CNodeOptions{
-                                 .permission_flags = permission_flags,
-                                 .i2p_sam_session = std::move(i2p_transient_session),
-                                 .recv_flood_size = nReceiveFloodSize,
-                                 .use_v2transport = use_v2transport,
-                             });
-    pnode->AddRef();
-
-    // We're making a new connection, harvest entropy from the time (and our peer count)
-    RandAddEvent((uint32_t)id);
 
-    return pnode;
+    return nullptr;
 }
 
 void CNode::CloseSocketDisconnect()