posix: add tempfile()

1 files changed, 142 insertions, 0 deletions

diff --git a/nihil.posix/posix.tempfile.cc b/nihil.posix/posix.tempfile.cc
new file mode 100644
index 0000000..942594c
--- /dev/null
+++ b/nihil.posix/posix.tempfile.cc
@@ -0,0 +1,142 @@
+/*
+ * This source code is released into the public domain.
+ */
+
+module;
+
+#include <algorithm>
+#include <coroutine>
+#include <expected>
+#include <filesystem>
+#include <random>
+#include <string>
+
+#include <fcntl.h>
+#include <unistd.h>
+
+module nihil.posix;
+
+import :getenv;
+import :open;
+
+namespace nihil {
+
+temporary_file::temporary_file(nihil::fd &&fd,
+			       std::filesystem::path path) noexcept
+	: m_fd(std::move(fd))
+	, m_path(std::move(path))
+{
+}
+
+temporary_file::temporary_file(nihil::fd &&fd) noexcept
+	: m_fd(std::move(fd))
+{
+}
+
+temporary_file::temporary_file(temporary_file &&other) noexcept
+	: m_fd(std::move(other.m_fd))
+	, m_path(std::move(other.m_path))
+{
+}
+
+auto temporary_file::operator=(this temporary_file &self,
+			       temporary_file &&other)
+	noexcept -> temporary_file &
+{
+	if (&self != &other) {
+		if (self.m_fd)
+			self.release();
+
+		self.m_fd = std::move(other.m_fd);
+		self.m_path = std::move(other.m_path);
+	}
+
+	return self;
+}
+
+temporary_file::~temporary_file()
+{
+	if (m_fd)
+		release();
+}
+
+auto temporary_file::release(this temporary_file &self) -> void
+{
+	if (!self.m_fd)
+		throw std::logic_error(
+			"release() called on already-released tempfile");
+
+	if (!self.m_path.empty()) {
+		auto ec = std::error_code(); // ignore errors
+		remove(self.path(), ec);
+
+		self.m_path.clear();
+	}
+
+	std::ignore = self.m_fd.close();
+}
+
+auto temporary_file::path(this temporary_file const &self)
+	-> std::filesystem::path const &
+{
+	if (self.m_path.empty())
+		throw std::logic_error(
+			"path() called on unlinked temporary_file");
+
+	return self.m_path;
+}
+
+auto temporary_file::fd(this temporary_file &self) -> nihil::fd &
+{
+	if (!self.m_fd)
+		throw std::logic_error("fd() called on empty temporary_file");
+
+	return self.m_fd;
+}
+
+auto tempfile(tempfile_flags_t flags) -> std::expected<temporary_file, error>
+{
+	auto rng = std::default_random_engine(std::random_device{}());
+
+	auto random_name = [&] -> std::string {
+		auto constexpr length = std::size_t{12};
+		auto constexpr randchars = std::string_view(
+			"abcdefghijklmnopqrstuvwxyz"
+			"ABCDEFGHIJKLMNOPQRSTUVWXYZ"
+			"0123456789");
+
+		auto dist = std::uniform_int_distribution<>(
+				0, randchars.size() - 1);
+		auto ret = std::string(length, 0);
+		std::ranges::generate_n(ret.begin(), length,
+					[&] -> char {
+						return randchars[dist(rng)];
+					});
+		return ret;
+	};
+
+	auto dir = std::filesystem::path(getenv("TMPDIR").value_or("/tmp"));
+
+	// Keep trying until we don't get EEXIST.
+	for (;;) {
+		auto filename = dir / (random_name() + ".tmp");
+		auto fd = nihil::open(filename, O_RDWR | O_CREAT | O_EXCL,
+				      0600);
+		if (!fd) {
+			if (fd.error() == std::errc::file_exists)
+				continue;
+			return std::unexpected(fd.error());
+		}
+
+		if (flags & tempfile_unlink) {
+			auto ec = std::error_code();
+			remove(filename, ec);
+			return temporary_file(std::move(*fd));
+		} else {
+			return temporary_file(std::move(*fd),
+					      std::move(filename));
+		}
+	}
+}
+
+} // namespace nihil