fs/StandardDirectory: add GetUserRuntimeDir()

src/Listen.cxx

@@ -32,6 +32,7 @@
 #include "net/SocketUtil.hxx"
 #include "system/Error.hxx"
 #include "fs/AllocatedPath.hxx"
+#include "fs/StandardDirectory.hxx"
 #include "fs/XDG.hxx"
 #include "util/Domain.hxx"
 #include "util/RuntimeError.hxx"
@@ -85,7 +86,7 @@ ListenXdgRuntimeDir(ClientListener &listener) noexcept
 		   use $XDG_RUNTIME_DIR */
 		return false;
 
-	Path xdg_runtime_dir = Path::FromFS(getenv("XDG_RUNTIME_DIR"));
+	const auto xdg_runtime_dir = GetUserRuntimeDir();
 	if (xdg_runtime_dir.IsNull())
 		return false;
 

src/fs/StandardDirectory.cxx

@@ -282,6 +282,16 @@ GetUserCacheDir() noexcept
 #endif
 }
 
+AllocatedPath
+GetUserRuntimeDir() noexcept
+{
+#ifdef USE_XDG
+	return SafePathFromFS(getenv("XDG_RUNTIME_DIR"));
+#else
+	return nullptr;
+#endif
+}
+
 #ifdef _WIN32
 
 AllocatedPath

src/fs/StandardDirectory.hxx

@@ -43,6 +43,13 @@ GetUserMusicDir() noexcept;
 AllocatedPath
 GetUserCacheDir() noexcept;
 
+/**
+ * Obtains the runtime directory for the current user.
+ */
+[[gnu::const]]
+AllocatedPath
+GetUserRuntimeDir() noexcept;
+
 #ifdef _WIN32
 
 /**