From a8b0ea58e60bb0326b7f7c8f3c736d89ce9ef1df Mon Sep 17 00:00:00 2001
From: Lexi Winter <lexi@le-fay.org>
Date: Sun, 29 Jun 2025 19:19:23 +0100
Subject: wip macOS port

---
 nihil.posix/fd.ccm | 157 +++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 157 insertions(+)
 create mode 100644 nihil.posix/fd.ccm

(limited to 'nihil.posix/fd.ccm')

diff --git a/nihil.posix/fd.ccm b/nihil.posix/fd.ccm
new file mode 100644
index 0000000..b937f46
--- /dev/null
+++ b/nihil.posix/fd.ccm
@@ -0,0 +1,157 @@
+/*
+ * This source code is released into the public domain.
+ */
+
+module;
+
+#include <coroutine>
+#include <expected>
+#include <ranges>
+#include <span>
+#include <stdexcept>
+#include <system_error>
+
+export module nihil.posix:fd;
+
+import nihil.error;
+import nihil.monad;
+
+namespace nihil {
+
+/*
+ * fd: a file descriptor.
+ */
+
+export struct fd final {
+	// Construct an empty (invalid) fd.
+	fd() noexcept;
+
+	// Construct an fd from an exising file destrictor, taking ownership.
+	fd(int fd_) noexcept;
+
+	// Destructor.  Close the fd, discarding any errors.
+	~fd();
+
+	// Move from another fd, leaving the moved-from fd in an invalid state.
+	fd(fd &&other) noexcept;
+	auto operator=(this fd &, fd &&other) noexcept -> fd &;
+
+	// Not copyable.
+	fd(fd const &) = delete;
+	fd& operator=(this fd &, fd const &) = delete;
+
+	// Return true if this fd is valid (open).
+	[[nodiscard]] explicit operator bool(this fd const &self) noexcept;
+
+	// Close the wrapped fd.
+	[[nodiscard]] auto close(this fd &self) -> std::expected<void, error>;
+
+	// Return the stored fd.
+	[[nodiscard]] auto get(this fd const &self) -> int;
+
+	// Release the stored fd and return it.  The caller must close it.
+	[[nodiscard]] auto release(this fd &&self) -> int;
+
+	// Write data from the provided buffer to the fd.  Returns the
+	// number of bytes written.
+	[[nodiscard]] auto write(this fd &self, std::span<std::byte const>) 
+		-> std::expected<std::size_t, error>;
+
+	// Read data from the fd to the provided buffer.  Returns a
+	// subspan containing the data which was read.
+	[[nodiscard]] auto read(this fd &self, std::span<std::byte>)
+		-> std::expected<std::span<std::byte>, error>;
+
+private:
+	static constexpr int invalid_fileno = -1;
+
+	int m_fileno = invalid_fileno;
+};
+
+// Create a copy of this fd by calling dup().
+export [[nodiscard]] auto dup(fd const &self) -> std::expected<fd, error>;
+
+// Create a copy of this fd by calling dup2().  Note that because this results
+// in the existing fd and the new fd both being managed by an fd instance,
+// there are two potential cases that can cause problems:
+//
+// - dup()ing an fd to itself (a no-op)
+// - dup()ing an fd to an fd which is already managed by an fd instance
+//
+// In both of these cases, either use raw_dup() instead, or immediately call
+// release() on the returned fd to prevent the fd instance from closing it.
+export [[nodiscard]] auto dup(fd const &self, int newfd)
+	-> std::expected<fd, error>;
+
+// Create a copy of this fd by calling dup().
+export [[nodiscard]] auto raw_dup(fd const &self)
+	-> std::expected<int, error>;
+
+// Create a copy of this fd by calling dup2().
+export [[nodiscard]] auto raw_dup(fd const &self, int newfd)
+	-> std::expected<int, error>;
+
+// Return the fnctl flags for this fd.
+export [[nodiscard]] auto getflags(fd const &self)
+	-> std::expected<int, error>;
+
+// Replace the fnctl flags for this fd.
+export [[nodiscard]] auto replaceflags(fd &self, int newflags)
+	-> std::expected<void, error>;
+
+// Add bits to the fcntl flags for this fd.  Returns the new flags.
+export [[nodiscard]] auto setflags(fd &self, int newflags)
+	-> std::expected<int, error>;
+
+// Remove bits from the fcntl flags for this fd.  Returns the new flags.
+export [[nodiscard]] auto clearflags(fd &self, int clrflags)
+	-> std::expected<int, error>;
+
+// Return the fd flags for this fd.
+export [[nodiscard]] auto getfdflags(fd const &self)
+	-> std::expected<int, error>;
+
+// Replace the fd flags for this fd.
+export [[nodiscard]] auto replacefdflags(fd &self, int newflags)
+	-> std::expected<void, error>;
+
+// Add bits to the fd flags for this fd.  Returns the new flags.
+export [[nodiscard]] auto setfdflags(fd &self, int newflags)
+	-> std::expected<int, error>;
+
+// Remove bits from the fd flags for this fd.  Returns the new flags.
+export [[nodiscard]] auto clearfdflags(fd &self, int clrflags)
+	-> std::expected<int, error>;
+
+// Create two fds by calling pipe() and return them.
+export [[nodiscard]] auto pipe() -> std::expected<std::pair<fd, fd>, error>;
+
+/*
+ * Write data to a file descriptor from the provided range.  Returns the
+ * number of bytes written.
+ */
+export [[nodiscard]] auto write(fd &file,
+				std::ranges::contiguous_range auto &&range)
+	-> std::expected<std::size_t, error>
+requires(sizeof(std::ranges::range_value_t<decltype(range)>) == 1)
+{
+	return file.write(as_bytes(std::span(range)));
+}
+
+/*
+ * Read data from a file descriptor into the provided buffer.  Returns a
+ * span containing the data that was read.
+ */
+export [[nodiscard]] auto read(fd &file,
+			       std::ranges::contiguous_range auto &&range)
+	-> std::expected<
+		std::span<std::ranges::range_value_t<decltype(range)>>,
+		error>
+requires(sizeof(std::ranges::range_value_t<decltype(range)>) == 1)
+{
+	auto bspan = as_writable_bytes(std::span(range));
+	auto rspan = co_await file.read(bspan);
+	co_return std::span(range).subspan(0, rspan.size());
+}
+
+} // namespace nihil
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