LibCore: Introduce Directory

Core::Directory represents an existing directory on the system, and it
holds an actual file descriptor so that the user can be sure the
directory stays in existence.

Userland/Libraries/LibCore/Directory.h

@@ -0,0 +1,70 @@
+/*
+ * Copyright (c) 2022, kleines Filmröllchen <filmroellchen@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/Error.h>
+#include <AK/Format.h>
+#include <AK/LexicalPath.h>
+#include <AK/Noncopyable.h>
+#include <AK/Optional.h>
+#include <LibCore/Stream.h>
+#include <dirent.h>
+#include <sys/stat.h>
+
+namespace Core {
+
+class DirIterator;
+
+// Deal with real system directories. Any Directory instance always refers to a valid existing directory.
+class Directory {
+    AK_MAKE_NONCOPYABLE(Directory);
+
+public:
+    Directory(Directory&&);
+    ~Directory();
+
+    // When this flag is set, both the directory attempted to instantiate as well as all of its parents are created with mode 0755 if necessary.
+    enum class CreateDirectories : bool {
+        No,
+        Yes,
+    };
+
+    static ErrorOr<Directory> create(LexicalPath path, CreateDirectories);
+    static ErrorOr<Directory> create(String path, CreateDirectories);
+    static ErrorOr<Directory> adopt_fd(int fd, Optional<LexicalPath> path = {});
+
+    ErrorOr<NonnullOwnPtr<Stream::File>> open(StringView filename, Stream::OpenMode mode) const;
+    ErrorOr<struct stat> stat() const;
+    ErrorOr<DirIterator> create_iterator() const;
+
+    ErrorOr<LexicalPath> path() const;
+
+    static ErrorOr<bool> is_valid_directory(int fd);
+
+private:
+    Directory(int directory_fd, Optional<LexicalPath> path);
+    static ErrorOr<void> ensure_directory(LexicalPath const& path);
+
+    Optional<LexicalPath> m_path;
+    int m_directory_fd;
+};
+
+}
+
+namespace AK {
+template<>
+struct Formatter<Core::Directory> : Formatter<StringView> {
+    ErrorOr<void> format(FormatBuilder& builder, Core::Directory const& directory)
+    {
+        auto path = directory.path();
+        if (path.is_error())
+            return Formatter<StringView>::format(builder, "<unknown>");
+        return Formatter<StringView>::format(builder, path.release_value().string());
+    }
+};
+
+}