Lua/C DHCP example #1

ldhcp-ex1.c

#include <stdio.h>
#include <string.h>
#include <lua.h>
#include <lualib.h>
#include <lauxlib.h>
#include <arpa/inet.h>

/* Get/set opcode */
static int msg_op(lua_State *L)
{
	char *msg = lua_touserdata(L, 1);
	if (lua_isnumber(L, 2)) {
		msg[0] = lua_tointeger(L, 2) & 0xFF;
	}
	lua_pushnumber(L, msg[0]);
	return 1;
}

/* Get/set "your address" */
static int msg_yiaddr(lua_State *L)
{
	char *msg = lua_touserdata(L, 1);
	if (lua_isstring(L, 2)) {
		inet_pton(AF_INET, lua_tostring(L, 2), msg + 16);
		return 0;
	}
	char strbuf[INET_ADDRSTRLEN] = {'\0'};
	inet_ntop(AF_INET, msg + 16, strbuf, sizeof(strbuf));
	lua_pushstring(L, strbuf); /* Make a copy */
	return 1;
}

/* Get "client hardware address" */
static int msg_chaddr(lua_State *L)
{
	char *msg = lua_touserdata(L, 1);
	lua_pushlstring(L, msg + 28, 16);
	return 1;
}

/* Register 'msg' meta table */
static int msg_register(lua_State *L)
{
	static const luaL_Reg wrap[] = {
		{ "op",     &msg_op },
		{ "yiaddr", &msg_yiaddr },
		{ "chaddr", &msg_chaddr },
		{ NULL, NULL }
	};
	luaL_newmetatable(L, "msg");
	lua_pushvalue(L, -1);
	lua_setfield(L, -2, "__index");
	luaL_openlib(L, NULL, wrap, 0);
	lua_pop(L, 1);
	return 0;
}

static int on_recv(lua_State *L, int cb_ref, char *buf, size_t len)
{
	lua_rawgeti(L, LUA_REGISTRYINDEX, cb_ref);
	lua_pushlightuserdata(L, buf);
	luaL_getmetatable(L, "msg");
	lua_setmetatable(L, -2);
	lua_pushinteger(L, len);
	return lua_pcall(L, 2, 1, 0);
}

/* Convenience stuff */
static void close_state(lua_State **L) { lua_close(*L); }
#define cleanup(x) __attribute__((cleanup(x)))
#define auto_lclose cleanup(close_state)

int main(int argc, char *argv[])
{
	/* Create VM state */
	auto_lclose lua_State *L = luaL_newstate();
	if (!L)
		return 1;
	luaL_openlibs(L);
	/* Load config file */
	if (argc > 1) {
		luaL_loadfile(L, argv[1]); /* (1) */
		int ret = lua_pcall(L, 0, 0, 0);
		if (ret != 0) {
			fprintf(stderr, "%s\n", lua_tostring(L, -1));
			return 1;
		}
	}
	/* Read out config */
	lua_getglobal(L, "address"); /* (2) */
	lua_getglobal(L, "port");
	printf("address: %s, port: %ld\n", /* (3) */
		lua_tostring(L, -2), lua_tointeger(L, -1));
	lua_settop(L, 0); /* (4) */
	/* Register bindings */
	msg_register(L);
	lua_getglobal(L, "callback");
	int cb_ref = luaL_ref(L, LUA_REGISTRYINDEX);
	/* Prepare mock datagram. */
	char dhcp_req[512] = {
		0x01, 0x01, 0x06, 0x00
	};
	char dgram[sizeof(dhcp_req)];
	/* Call a few times, no I/O yet. */
	const size_t nr_calls = 1000000;
	for (unsigned i = 0; i < nr_calls; ++i) {
		dgram[0] = 0x01; /* reset to DHCPDISCOVER */
		int ret = on_recv(L, cb_ref, dgram, sizeof(dgram));
		if (ret != 0) {
			printf("%s\n", lua_tostring(L, -1));
			return 1;
		}

		lua_pop(L, 1);
	}
	return 0;
}