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.cpp

@@ -0,0 +1,100 @@
+/*
+ * Copyright (c) 2022, kleines Filmröllchen <filmroellchen@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include "Directory.h"
+#include "DirIterator.h"
+#include "System.h"
+#include <dirent.h>
+
+namespace Core {
+
+// We assume that the fd is a valid directory.
+Directory::Directory(int fd, Optional<LexicalPath> path)
+    : m_path(move(path))
+    , m_directory_fd(fd)
+{
+}
+
+Directory::Directory(Directory&& other)
+    : m_path(move(other.m_path))
+    , m_directory_fd(other.m_directory_fd)
+{
+    other.m_directory_fd = -1;
+}
+
+Directory::~Directory()
+{
+    if (m_directory_fd != -1)
+        MUST(System::close(m_directory_fd));
+}
+
+ErrorOr<bool> Directory::is_valid_directory(int fd)
+{
+    auto stat = TRY(System::fstat(fd));
+    return stat.st_mode & S_IFDIR;
+}
+
+ErrorOr<Directory> Directory::adopt_fd(int fd, Optional<LexicalPath> path)
+{
+    // This will also fail if the fd is invalid in the first place.
+    if (!TRY(Directory::is_valid_directory(fd)))
+        return Error::from_errno(ENOTDIR);
+    return Directory { fd, move(path) };
+}
+
+ErrorOr<Directory> Directory::create(String path, CreateDirectories create_directories)
+{
+    return create(LexicalPath { move(path) }, create_directories);
+}
+
+ErrorOr<Directory> Directory::create(LexicalPath path, CreateDirectories create_directories)
+{
+    if (create_directories == CreateDirectories::Yes)
+        TRY(ensure_directory(path));
+    // FIXME: doesn't work on Linux probably
+    auto fd = TRY(System::open(path.string(), O_CLOEXEC));
+    return adopt_fd(fd, move(path));
+}
+
+ErrorOr<void> Directory::ensure_directory(LexicalPath const& path)
+{
+    if (path.basename() == "/")
+        return {};
+
+    TRY(ensure_directory(path.parent()));
+
+    auto return_value = System::mkdir(path.string(), 0755);
+    // We don't care if the directory already exists.
+    if (return_value.is_error() && return_value.error().code() != EEXIST)
+        return return_value;
+
+    return {};
+}
+
+ErrorOr<LexicalPath> Directory::path() const
+{
+    if (!m_path.has_value())
+        return Error::from_string_literal("Directory wasn't created with a path");
+    return m_path.value();
+}
+
+ErrorOr<NonnullOwnPtr<Stream::File>> Directory::open(StringView filename, Stream::OpenMode mode) const
+{
+    auto fd = TRY(System::openat(m_directory_fd, filename, Stream::File::open_mode_to_options(mode)));
+    return Stream::File::adopt_fd(fd, mode);
+}
+
+ErrorOr<struct stat> Directory::stat() const
+{
+    return System::fstat(m_directory_fd);
+}
+
+ErrorOr<DirIterator> Directory::create_iterator() const
+{
+    return DirIterator { TRY(path()).string() };
+}
+
+}