add Windows network utilities and abstraction layer

Create a struct NetApi, which contains various network related functions
that will be used. This is done so that these operations can be injected
as a dependency and thus replaced with mock operation for the purpose of
testing.

There are also functions which operate solely on the Registry, those are
left out of the NetApi since they can already be abstracted by struct Reg.

Signed-off-by: Heiko Hund <heiko@openvpn.net>

openvpn/win/netutil.hpp

@@ -0,0 +1,154 @@
+//    OpenVPN -- An application to securely tunnel IP networks
+//               over a single port, with support for SSL/TLS-based
+//               session authentication and key exchange,
+//               packet encryption, packet authentication, and
+//               packet compression.
+//
+//    Copyright (C) 2024 OpenVPN Inc.
+//
+//    This program is free software: you can redistribute it and/or modify
+//    it under the terms of the GNU Affero General Public License Version 3
+//    as published by the Free Software Foundation.
+//
+//    This program is distributed in the hope that it will be useful,
+//    but WITHOUT ANY WARRANTY; without even the implied warranty of
+//    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+//    GNU Affero General Public License for more details.
+//
+//    You should have received a copy of the GNU Affero General Public License
+//    along with this program in the COPYING file.
+//    If not, see <http://www.gnu.org/licenses/>.
+
+// Windows network related utilities
+
+#pragma once
+
+#include <string>
+#include "openvpn/win/reg.hpp"
+
+namespace openvpn {
+namespace Win {
+
+struct NetApi
+{
+    /**
+     * Get the string interface UUID (with braces) for an interface alias name
+     *
+     * @param  itf_name         the interface alias name
+     * @return std::wstring     the wide IID string
+     */
+    static std::wstring get_itf_id(const std::string &itf_name)
+    {
+        DWORD err;
+        NET_LUID luid;
+        std::wstring iid;
+        err = ::ConvertInterfaceAliasToLuid(wstring::from_utf8(itf_name).c_str(), &luid);
+        if (err)
+        {
+            goto out;
+        }
+
+        IID guid;
+        err = ::ConvertInterfaceLuidToGuid(&luid, &guid);
+        if (err)
+        {
+            goto out;
+        }
+
+        PWSTR iid_str;
+        if (::StringFromIID(guid, &iid_str) != S_OK)
+        {
+            goto out;
+        }
+
+        iid = iid_str;
+        ::CoTaskMemFree(iid_str);
+
+    out:
+        return iid;
+    }
+
+    /**
+     * @brief Check if an interface is connected and up
+     *
+     * @param  iid_str  the interface GUID string
+     * @return bool     true if the interface is connected and up,
+     *                  false otherwise or in case an error happened
+     */
+    static bool interface_connected(const std::wstring &iid_str)
+    {
+        GUID iid;
+        MIB_IF_ROW2 itf_row;
+
+        // Get LUID from GUID string
+        if (::IIDFromString(iid_str.c_str(), &iid) != S_OK
+            || ::ConvertInterfaceGuidToLuid(&iid, &itf_row.InterfaceLuid) != NO_ERROR)
+        {
+            return false;
+        }
+
+        // Look up interface status
+        if (::GetIfEntry2(&itf_row) != NO_ERROR)
+        {
+            return false;
+        }
+
+        // Check if interface is connected and up
+        if (itf_row.MediaConnectState != MediaConnectStateConnected
+            || itf_row.OperStatus != IfOperStatusUp)
+        {
+            return false;
+        }
+
+        return true;
+    }
+};
+
+/**
+ * @brief Read interface specific domain suffix
+ *
+ * It can be either be the one assigned by DHCP or manually.
+ *
+ * @tparam REG          the Registry abstraction to use (default: Win::Reg)
+ * @param  itf_guid     The interface GUID string
+ * @return std::wstring The domain found, or the empty string
+ */
+template <typename REG = Win::Reg>
+static std::wstring interface_dns_domain(const std::wstring &itf_guid)
+{
+    typename REG::Key itf_key(std::wstring(REG::subkey_ipv4_itfs) + L"\\" + itf_guid);
+
+    auto [domain, error] = REG::get_string(itf_key, L"DhcpDomain");
+    if (!error && !domain.empty())
+    {
+        return domain;
+    }
+    else
+    {
+        auto [domain, error] = REG::get_string(itf_key, L"Domain");
+        if (!error && !domain.empty())
+        {
+            return domain;
+        }
+    }
+
+    return {};
+}
+
+/**
+ * @brief Checks if DHCP is enabled for an interface
+ *
+ * @tparam REG      the Registry abstraction to use (default: Win::Reg)
+ * @param  itf_key  REG::Key of the interface to check for
+ * @return bool     true if DHCP is enabled, false if
+ *                  disabled or an error occurred
+ */
+template <typename REG = Win::Reg>
+static bool dhcp_enabled_on_itf(typename REG::Key &itf_key)
+{
+    auto [dhcp, error] = REG::get_dword(itf_key, L"EnableDHCP");
+    return !error && dhcp ? true : false;
+}
+
+} // namespace Win
+} // namespace openvpn