1 files changed, 46 insertions, 9 deletions
diff --git a/nihil.posix/getenv.ccm b/nihil.posix/getenv.ccm
index 465f7e7..5967bf7 100644
--- a/nihil.posix/getenv.ccm
+++ b/nihil.posix/getenv.ccm
@@ -1,11 +1,15 @@
-/*
- * This source code is released into the public domain.
- */
-
+// This source code is released into the public domain.
 module;
 
+#include <cerrno>
 #include <expected>
 #include <string>
+#include <system_error>
+#include <vector>
+
+#include <unistd.h>
+
+#include "nihil.hh"
 
 export module nihil.posix:getenv;
 
@@ -13,11 +17,44 @@ import nihil.error;
 
 namespace nihil {
 
-/*
- * Find a variable by the given name in the environment by calling getenv_r().
- */
 
-export [[nodiscard]] auto getenv(std::string_view varname)
-	-> std::expected<std::string, error>;
+// Find a variable by the given name in the environment by calling getenv_r() if available,
+// or getenv() if not.  In either case the value is copied, so will not be affected by
+// future calls to setenv().
+export [[nodiscard]] auto getenv(std::string_view varname) -> std::expected<std::string, error>
+{
+	auto cvarname = std::string(varname);
+
+#ifdef NIHIL_HAVE_GETENV_R
+	// Start with a buffer of this size, and double it every iteration.
+	constexpr auto bufinc = std::size_t{1024};
+
+	auto buf = std::vector<char>(bufinc);
+	for (;;) {
+		auto const ret = ::getenv_r(cvarname.c_str(), buf.data(), buf.size());
+
+		if (ret == 0)
+			return {std::string(buf.data())};
+
+		if (ret == -1 && errno == ERANGE) {
+			buf.resize(buf.size() * 2);
+			continue;
+		}
+
+		return std::unexpected(error(std::errc(errno)));
+	}
+#else  // NIHIL_HAVE_GETENV_R
+	errno = 0;
+	auto *v = ::getenv(cvarname.c_str()); // NOLINT
+
+	if (v != nullptr)
+		return {std::string(v)};
+
+	if (errno != 0)
+		return std::unexpected(error(std::errc(errno)));
+
+	return std::unexpected(error(std::errc::no_such_file_or_directory));
+#endif // NIHIL_HAVE_GETENV_R
+}
 
 } // namespace nihil