feat: add support for direct connections (#350)

* feat: add support for direct connections

* refactor: simplify a bit, change comments, extend tests

* fix: compiler warning about unused variable

* docs: add section on direct connections to the tutorial

---------

Co-authored-by: Maksim Fedyarov <m.fedyarov@omp.ru>
Co-authored-by: Stanislav Angelovič <stanislav.angelovic@protonmail.com>

tests/integrationtests/TestFixture.h

@@ -39,6 +39,11 @@
 #include <atomic>
 #include <chrono>
 
+#include <sys/types.h>
+#include <sys/socket.h>
+#include <sys/stat.h>
+#include <sys/un.h>
+
 namespace sdbus { namespace test {
 
 class TestFixture : public ::testing::Test
@@ -59,28 +64,6 @@ public:
         s_proxyConnection->leaveEventLoop();
     }
 
-    template <typename _Fnc>
-    static bool waitUntil(_Fnc&& fnc, std::chrono::milliseconds timeout = std::chrono::seconds(5))
-    {
-        using namespace std::chrono_literals;
-
-        std::chrono::milliseconds elapsed{};
-        std::chrono::milliseconds step{5ms};
-        do {
-            std::this_thread::sleep_for(step);
-            elapsed += step;
-            if (elapsed > timeout)
-                return false;
-        } while (!fnc());
-
-        return true;
-    }
-
-    static bool waitUntil(std::atomic<bool>& flag, std::chrono::milliseconds timeout = std::chrono::seconds(5))
-    {
-        return waitUntil([&flag]() -> bool { return flag; }, timeout);
-    }
-
 private:
     void SetUp() override
     {
@@ -106,6 +89,101 @@ public:
     std::unique_ptr<TestProxy> m_proxy;
 };
 
+class TestFixtureWithDirectConnection : public ::testing::Test
+{
+private:
+    void SetUp() override
+    {
+        int sock = openUnixSocket();
+        createClientAndServerConnections(sock);
+        createAdaptorAndProxyObjects();
+    }
+
+    void TearDown() override
+    {
+        m_proxy.reset();
+        m_adaptor.reset();
+        m_proxyConnection->leaveEventLoop();
+        m_adaptorConnection->leaveEventLoop();
+    }
+
+    static int openUnixSocket()
+    {
+        int sock = socket(AF_UNIX, SOCK_STREAM|SOCK_CLOEXEC, 0);
+        assert(sock >= 0);
+
+        sockaddr_un sa;
+        memset(&sa, 0, sizeof(sa));
+        sa.sun_family = AF_UNIX;
+        snprintf(sa.sun_path, sizeof(sa.sun_path), "%s", DIRECT_CONNECTION_SOCKET_PATH.c_str());
+
+        unlink(DIRECT_CONNECTION_SOCKET_PATH.c_str());
+
+        umask(0000);
+        [[maybe_unused]] int r = bind(sock, (const sockaddr*) &sa, sizeof(sa.sun_path));
+        assert(r >= 0);
+
+        r = listen(sock, 5);
+        assert(r >= 0);
+
+        return sock;
+    }
+
+    void createClientAndServerConnections(int sock)
+    {
+        std::thread t([&]()
+        {
+            auto fd = accept4(sock, NULL, NULL, /*SOCK_NONBLOCK|*/SOCK_CLOEXEC);
+            m_adaptorConnection = sdbus::createServerBus(fd);
+            // This is necessary so that createDirectBusConnection() below does not block
+            m_adaptorConnection->enterEventLoopAsync();
+        });
+
+        m_proxyConnection = sdbus::createDirectBusConnection("unix:path=" + DIRECT_CONNECTION_SOCKET_PATH);
+        m_proxyConnection->enterEventLoopAsync();
+
+        t.join();
+    }
+
+    void createAdaptorAndProxyObjects()
+    {
+        assert(m_adaptorConnection != nullptr);
+        assert(m_proxyConnection != nullptr);
+
+        m_adaptor = std::make_unique<TestAdaptor>(*m_adaptorConnection, OBJECT_PATH);
+        // Destination parameter can be empty in case of direct connections
+        m_proxy = std::make_unique<TestProxy>(*m_proxyConnection, EMPTY_DESTINATION, OBJECT_PATH);
+    }
+
+public:
+    std::unique_ptr<sdbus::IConnection> m_adaptorConnection;
+    std::unique_ptr<sdbus::IConnection> m_proxyConnection;
+    std::unique_ptr<TestAdaptor> m_adaptor;
+    std::unique_ptr<TestProxy> m_proxy;
+};
+
+template <typename _Fnc>
+inline bool waitUntil(_Fnc&& fnc, std::chrono::milliseconds timeout = std::chrono::seconds(5))
+{
+    using namespace std::chrono_literals;
+
+    std::chrono::milliseconds elapsed{};
+    std::chrono::milliseconds step{5ms};
+    do {
+        std::this_thread::sleep_for(step);
+        elapsed += step;
+        if (elapsed > timeout)
+            return false;
+    } while (!fnc());
+
+    return true;
+}
+
+inline bool waitUntil(std::atomic<bool>& flag, std::chrono::milliseconds timeout = std::chrono::seconds(5))
+{
+    return waitUntil([&flag]() -> bool { return flag; }, timeout);
+}
+
 }}
 
 #endif /* SDBUS_CPP_INTEGRATIONTESTS_TESTFIXTURE_H_ */