genode/repos/libports/include/libc/args.h

/*
 * \brief  Populate arguments and environment from config
 * \author Christian Prochaska
 * \date   2020-08-14
 */

/*
 * Copyright (C) 2020 Genode Labs GmbH
 *
 * This file is part of the Genode OS framework, which is distributed
 * under the terms of the GNU Affero General Public License version 3.
 */

#ifndef _INCLUDE__LIBC__ARGS_H_
#define _INCLUDE__LIBC__ARGS_H_

/* Genode includes */
#include <libc/component.h>
#include <util/xml_node.h>

/* libc includes */
#include <stdlib.h> /* 'malloc' */

static void populate_args_and_env(Libc::Env &env, int &argc, char **&argv, char **&envp)
{
	using Genode::Xml_node;
	using Genode::Xml_attribute;

	env.config([&] (Xml_node const &node) {

		int envc = 0;

		/* count the number of arguments and environment variables */
		node.for_each_sub_node([&] (Xml_node const &node) {
			/* check if the 'value' attribute exists */
			if (node.has_type("arg") && node.has_attribute("value"))
				++argc;
			else
			if (node.has_type("env") && node.has_attribute("key") && node.has_attribute("value"))
				++envc;
		});

		if (argc == 0 && envc == 0) {
			/*
			 * If argc is zero then argv is still a NULL-terminated array.
			 */
			static char const *args[] = { nullptr, nullptr };
			argc = 0;
			argv = (char**)&args;
			envp = &argv[1];
			return; /* from lambda */
		}

		/* arguments and environment are arranged System V style (but don't count on it) */
		argv = (char**)malloc((argc + envc + 2) * sizeof(char*));
		envp = &argv[argc+1];

		/* read the arguments */
		int arg_i = 0;
		int env_i = 0;
		node.for_each_sub_node([&] (Xml_node const &node) {

			/* insert an argument */
			if (node.has_type("arg")) {

				Xml_attribute attr = node.attribute("value");
				attr.with_raw_value([&] (char const *start, size_t length) {

					size_t const size = length + 1; /* for null termination */

					argv[arg_i] = (char *)malloc(size);

					Genode::copy_cstring(argv[arg_i], start, size);
				});

				++arg_i;
			}
			else

			/* insert an environment variable */
			if (node.has_type("env")) try {

				auto check_attr = [] (Xml_node node, auto key) {
					if (!node.has_attribute(key))
						Genode::warning("<env> node lacks '", key, "' attribute"); };

				check_attr(node, "key");
				check_attr(node, "value");

				Xml_attribute const key   = node.attribute("key");
				Xml_attribute const value = node.attribute("value");

				using namespace Genode;

				/*
				 * An environment variable has the form <key>=<value>, followed
				 * by a terminating zero.
				 */
				size_t const var_size = key  .value_size() + 1
				                      + value.value_size() + 1;

				envp[env_i] = (char*)malloc(var_size);

				size_t pos = 0;

				/* append characters to env variable with zero termination */
				auto append = [&] (char const *s, size_t len) {

					if (pos + len >= var_size) {
						/* this should never happen */
						warning("truncated environment variable: ", node);
						return;
					}

					copy_cstring(envp[env_i] + pos, s, len + 1);
					pos += len;
				};

				key.with_raw_value([&] (char const *start, size_t length) {
					append(start, length); });

				append("=", 1);

				value.with_raw_value([&] (char const *start, size_t length) {
					append(start, length); });

				++env_i;

			}
			catch (Xml_node::Nonexistent_sub_node)  { }
			catch (Xml_node::Nonexistent_attribute) { }
		});

		/* argv and envp are both NULL terminated */
		argv[arg_i] = NULL;
		envp[env_i] = NULL;
	});
}

#endif /* _INCLUDE__LIBC__ARGS_H_ */