nihil.posix/open_in_path.ccm


1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51

// This source code is released into the public domain.
export module nihil.posix:open_in_path;

import nihil.std;
import nihil.core;

import :fd;
import :getenv;
import :open;
import :paths;

namespace nihil {

// Find an executable in the given path, which should be a colon-separated list of directories, and
// open it with O_EXEC.  If the file can't be found or can't be opened, returns an appropriate error.
export [[nodiscard]] auto
open_in_path(std::filesystem::path const &file, std::string_view path) -> std::expected<fd, error>
{
	// Absolute pathname skips the search.
	if (file.is_absolute())
		return open(file, open_exec);

	// Default to ENOENT as the error.
	auto err = error(std::errc::no_such_file_or_directory);

	for (auto &&dir : path | std::views::split(':')) {
		// An empty $PATH element means cwd.
		auto sdir = dir.empty() ? std::filesystem::path(".")
		                        : std::filesystem::path(std::string_view(dir));

		if (auto ret = open(sdir / file, open_exec); ret)
			return ret;
		// If we get an error other than ENOENT, cache it to return to the caller.
		// This means we can propagate open() errors.
		else if (ret.error().root_cause() != std::errc::no_such_file_or_directory)
			err = std::move(ret.error());
	}

	return std::unexpected(std::move(err));
}

// Find an executable in $PATH and open it.  If $PATH is not set, uses _PATH_DEFPATH.
// If the file can't be found or can't be opened, returns an appropriate error.
export [[nodiscard]] auto
open_in_path(std::filesystem::path const &file) -> std::expected<fd, error>
{
	auto const path = getenv("PATH").value_or(std::string(paths::defpath)); // NOLINT
	return open_in_path(file, path);
}

} // namespace nihil