userspace: Implement chown utility

userspace/programs/CMakeLists.txt

@@ -4,6 +4,7 @@ set(USERSPACE_PROGRAMS
 	cat
 	cat-mmap
 	chmod
+	chown
 	cp
 	dd
 	dhcp-client

userspace/programs/chown/CMakeLists.txt

@@ -0,0 +1,9 @@
+set(SOURCES
+	main.cpp
+)
+
+add_executable(chown ${SOURCES})
+banan_link_library(chown ban)
+banan_link_library(chown libc)
+
+install(TARGETS chown OPTIONAL)

userspace/programs/chown/main.cpp

@@ -0,0 +1,109 @@
+#include <ctype.h>
+#include <errno.h>
+#include <grp.h>
+#include <pwd.h>
+#include <stdarg.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <sys/types.h>
+#include <unistd.h>
+
+void usage(const char* argv0, int ret)
+{
+	FILE* out = (ret == 0) ? stdout : stderr;
+	fprintf(out, "usage: %s [OWNER][:[GROUP]] FILE...\n", argv0);
+	fprintf(out, "  Change the owner and/or group of each FILE.\n");
+	exit(ret);
+}
+
+[[noreturn]] void print_error_and_exit(const char* format, ...)
+{
+	va_list args;
+	va_start(args, format);
+	vfprintf(stderr, format, args);
+	va_end(args);
+	exit(1);
+	__builtin_unreachable();
+}
+
+const passwd* get_user(const char* string)
+{
+	bool is_numeric = true;
+	for (size_t i = 0; string[i] && is_numeric; i++)
+		if (!isdigit(string[i]))
+			is_numeric = false;
+	if (is_numeric)
+		return getpwuid(atoll(string));
+	return getpwnam(string);
+}
+
+const group* get_group(const char* string)
+{
+	bool is_numeric = true;
+	for (size_t i = 0; string[i] && is_numeric; i++)
+		if (!isdigit(string[i]))
+			is_numeric = false;
+	if (is_numeric)
+		return getgrgid(atoll(string));
+	return getgrnam(string);
+}
+
+int main(int argc, char** argv)
+{
+	if (argc <= 2)
+		usage(argv[0], 1);
+
+	uid_t uid = -1;
+	gid_t gid = -1;
+
+	const char* owner_string = argv[1];
+
+	const char* colon = strchr(owner_string, ':');
+	if (colon == owner_string)
+	{
+		const auto* group = get_group(owner_string + 1);
+		if (group == nullptr)
+			print_error_and_exit("could not find group %s\n", owner_string + 1);
+		gid = group->gr_gid;
+	}
+	else if (colon == nullptr)
+	{
+		const auto* user = get_user(owner_string);
+		if (user == nullptr)
+			print_error_and_exit("could not find user %s\n", owner_string);
+		uid = user->pw_uid;
+	}
+	else
+	{
+		char* user_name = strndup(owner_string, colon - owner_string);
+		if (user_name == nullptr)
+			print_error_and_exit("strndup: %s\n", strerror(errno));
+		const auto* user = get_user(user_name);
+		if (user == nullptr)
+			print_error_and_exit("could not find user %s\n", user_name);
+		free(user_name);
+		uid = user->pw_uid;
+		if (colon[1] == '\0')
+			gid = user->pw_gid;
+		else
+		{
+			const auto* group = get_group(colon + 1);
+			if (group == nullptr)
+				print_error_and_exit("could not find group %s\n", colon + 1);
+			gid = group->gr_gid;
+		}
+	}
+
+	int ret = 0;
+	for (int i = 2; i < argc; i++)
+	{
+		if (chown(argv[i], uid, gid) == -1)
+		{
+			perror("chown");
+			ret = 1;
+		}
+	}
+
+	return ret;
+}