user: implement mlibc as the libc, finally.

It's finally done..

Signed-off-by: kaguya <vpshinomiya@protonmail.com>

user/include/mlibc/options/ansi/generic/environment.cpp

@@ -0,0 +1,168 @@
+#include <errno.h>
+#include <stdlib.h>
+#include <stdio.h>
+
+#include <bits/ensure.h>
+#include <mlibc/allocator.hpp>
+#include <mlibc/debug.hpp>
+
+#include <frg/string.hpp>
+#include <frg/vector.hpp>
+
+namespace {
+	char *empty_environment[] = { nullptr };
+} // namespace
+
+char **environ = empty_environment;
+
+namespace {
+
+size_t find_environ_index(frg::string_view name) {
+	for(size_t i = 0; environ[i]; i++) {
+		frg::string_view view{environ[i]};
+		size_t s = view.find_first('=');
+		if(s == size_t(-1)) {
+			mlibc::infoLogger() << "mlibc: environment string \""
+					<< frg::escape_fmt{view.data(), view.size()}
+					<< "\" does not contain an equals sign (=)" << frg::endlog;
+			continue;
+		}
+		if(view.sub_string(0, s) == name)
+			return i;
+	}
+
+	return -1;
+}
+
+// Environment vector that is mutated by putenv() and setenv().
+// Cannot be global as it is accessed during library initialization.
+frg::vector<char *, MemoryAllocator> &get_vector() {
+	static frg::vector<char *, MemoryAllocator> vector{getAllocator()};
+	return vector;
+}
+
+void update_vector() {
+	auto &vector = get_vector();
+	if(environ == vector.data())
+		return;
+
+	// If the environ variable was changed, we copy the environment.
+	// Note that we must only copy the pointers but not the strings themselves!
+	vector.clear();
+	for(size_t i = 0; environ[i]; i++)
+		vector.push(environ[i]);
+	vector.push(nullptr);
+
+	environ = vector.data();
+}
+
+void assign_variable(frg::string_view name, const char *string, bool overwrite) {
+	auto &vector = get_vector();
+	__ensure(environ == vector.data());
+
+	auto k = find_environ_index(name);
+	if(k != size_t(-1)) {
+		if(overwrite)
+			vector[k] = const_cast<char *>(string);
+	}else{
+		// Last pointer of environ must always be a null delimiter.
+		__ensure(!vector.back());
+		vector.back() = const_cast<char *>(string);
+		vector.push(nullptr);
+	}
+
+	// push() might have re-allocated the vector.
+	environ = vector.data();
+}
+
+void unassign_variable(frg::string_view name) {
+	auto &vector = get_vector();
+	__ensure(environ == vector.data());
+
+	auto k = find_environ_index(name);
+	if(k == size_t(-1))
+		return;
+
+	// Last pointer of environ must always be a null delimiter.
+	__ensure(vector.size() >= 2 && !vector.back());
+	std::swap(vector[k], vector[vector.size() - 2]);
+	vector.pop();
+	vector.back() = nullptr;
+
+	// pop() might have re-allocated the vector.
+	environ = vector.data();
+}
+
+} // anonymous namespace
+
+char *getenv(const char *name) {
+	auto k = find_environ_index(name);
+	if(k == size_t(-1))
+		return nullptr;
+
+	frg::string_view view{environ[k]};
+	size_t s = view.find_first('=');
+	__ensure(s != size_t(-1));
+	return const_cast<char *>(view.data() + s + 1);
+}
+
+namespace mlibc {
+
+int putenv(char *string) {
+	frg::string_view view{string};
+	size_t s = view.find_first('=');
+	if(s == size_t(-1)) {
+		// GLIBC EXTENSION
+		update_vector();
+		unassign_variable(string);
+		return 0;
+	}
+
+	update_vector();
+	assign_variable(view.sub_string(0, s), string, true);
+	return 0;
+}
+
+} // namespace mlibc
+
+#if __MLIBC_POSIX_OPTION
+
+int putenv(char *string) {
+	return mlibc::putenv(string);
+}
+
+int setenv(const char *name, const char *value, int overwrite) {
+	frg::string_view view{name};
+	size_t s = view.find_first('=');
+	if(s != size_t(-1)) {
+		mlibc::infoLogger() << "mlibc: environment variable \""
+				<< frg::escape_fmt{view.data(), view.size()} << "\" contains an equals sign"
+				<< frg::endlog;
+		errno = EINVAL;
+		return -1;
+	}
+
+	// We never free strings here. TODO: Reuse them?
+	char *string;
+	__ensure(asprintf(&string, "%s=%s", name, value) > 0);
+	__ensure(string);
+
+	update_vector();
+	assign_variable(name, string, overwrite);
+	return 0;
+}
+
+int unsetenv(const char *name) {
+	update_vector();
+	unassign_variable(name);
+	return 0;
+}
+
+int clearenv(void) {
+	auto vector = get_vector();
+	vector.clear();
+	update_vector();
+	return 0;
+}
+
+#endif /* __MLIBC_POSIX_OPTION */