Adding upstream version 5.7.1.upstream/5.7.1

Signed-off-by: Daniel Baumann <daniel.baumann@progress-linux.org>

1 files changed, 896 insertions, 0 deletions

diff --git a/daemon/engine.c b/daemon/engine.c
new file mode 100644
index 0000000..1d387ea
--- /dev/null
+++ b/daemon/engine.c
@@ -0,0 +1,896 @@
+/*  Copyright (C) CZ.NIC, z.s.p.o. <knot-resolver@labs.nic.cz>
+ *  SPDX-License-Identifier: GPL-3.0-or-later
+ */
+
+#include <contrib/cleanup.h>
+#include <ccan/json/json.h>
+#include <ccan/asprintf/asprintf.h>
+#include <dlfcn.h>
+#include <uv.h>
+#include <unistd.h>
+#include <grp.h>
+#include <pwd.h>
+#include <sys/param.h>
+#include <libzscanner/scanner.h>
+#include <sys/un.h>
+
+#include <lua.h>
+#include <lualib.h>
+#include <lauxlib.h>
+#include "daemon/bindings/impl.h"
+
+#include "kresconfig.h"
+#include "daemon/engine.h"
+#include "daemon/ffimodule.h"
+#include "lib/selection.h"
+#include "lib/cache/api.h"
+#include "lib/defines.h"
+#include "lib/cache/cdb_lmdb.h"
+#include "lib/dnssec/ta.h"
+#include "lib/log.h"
+
+/* Magic defaults for the engine. */
+#ifndef LRU_RTT_SIZE
+#define LRU_RTT_SIZE 65536 /**< NS RTT cache size */
+#endif
+#ifndef LRU_REP_SIZE
+#define LRU_REP_SIZE (LRU_RTT_SIZE / 4) /**< NS reputation cache size */
+#endif
+#ifndef LRU_COOKIES_SIZE
+	#if ENABLE_COOKIES
+	#define LRU_COOKIES_SIZE LRU_RTT_SIZE /**< DNS cookies cache size. */
+	#else
+	#define LRU_COOKIES_SIZE LRU_ASSOC /* simpler than guards everywhere */
+	#endif
+#endif
+
+/**@internal Maximum number of incomplete TCP connections in queue.
+* Default is from empirical testing - in our case, more isn't necessarily better.
+* See https://gitlab.nic.cz/knot/knot-resolver/-/merge_requests/968
+* */
+#ifndef TCP_BACKLOG_DEFAULT
+#define TCP_BACKLOG_DEFAULT 128
+#endif
+
+/* Cleanup engine state every 5 minutes */
+const size_t CLEANUP_TIMER = 5*60*1000;
+
+/* Execute byte code */
+#define l_dobytecode(L, arr, len, name) \
+	(luaL_loadbuffer((L), (arr), (len), (name)) || lua_pcall((L), 0, LUA_MULTRET, 0))
+
+/*
+ * Global bindings.
+ */
+struct args *the_args;
+
+
+/** Print help and available commands. */
+static int l_help(lua_State *L)
+{
+	static const char *help_str =
+		"help()\n    show this help\n"
+		"quit()\n    quit\n"
+		"hostname()\n    hostname\n"
+		"package_version()\n    return package version\n"
+		"user(name[, group])\n    change process user (and group)\n"
+		"log_level(level)\n    logging level (crit, err, warning, notice, info or debug)\n"
+		"log_target(target)\n    logging target (syslog, stderr, stdout)\n"
+		"log_groups(groups)\n    turn on debug log for selected groups\n"
+		"option(opt[, new_val])\n    get/set server option\n"
+		"mode(strict|normal|permissive)\n    set resolver strictness level\n"
+		"reorder_RR([true|false])\n    set/get reordering of RRs within RRsets\n"
+		"resolve(name, type[, class, flags, callback])\n    resolve query, callback when it's finished\n"
+		"todname(name)\n    convert name to wire format\n"
+		"tojson(val)\n    convert value to JSON\n"
+		"net\n    network configuration\n"
+		"cache\n    network configuration\n"
+		"modules\n    modules configuration\n"
+		"kres\n    resolver services\n"
+		"trust_anchors\n    configure trust anchors\n"
+		"debugging\n    debugging configuration\n"
+		;
+	lua_pushstring(L, help_str);
+	return 1;
+}
+
+static bool update_privileges(int uid, int gid)
+{
+	if ((gid_t)gid != getgid()) {
+		if (setregid(gid, gid) < 0) {
+			return false;
+		}
+	}
+	if ((uid_t)uid != getuid()) {
+		if (setreuid(uid, uid) < 0) {
+			return false;
+		}
+	}
+	return true;
+}
+
+/** Set process user/group. */
+static int l_setuser(lua_State *L)
+{
+	int n = lua_gettop(L);
+	if (n < 1 || !lua_isstring(L, 1))
+		lua_error_p(L, "user(user[, group])");
+
+	/* Fetch UID/GID based on string identifiers. */
+	struct passwd *user_pw = getpwnam(lua_tostring(L, 1));
+	if (!user_pw)
+		lua_error_p(L, "invalid user name");
+	int uid = user_pw->pw_uid;
+	int gid = getgid();
+	if (n > 1 && lua_isstring(L, 2)) {
+		struct group *group_pw = getgrnam(lua_tostring(L, 2));
+		if (!group_pw)
+			lua_error_p(L, "invalid group name");
+		gid = group_pw->gr_gid;
+	}
+	/* Drop privileges */
+	bool ret = update_privileges(uid, gid);
+	if (!ret) {
+		lua_error_maybe(L, errno);
+	}
+	lua_pushboolean(L, ret);
+	return 1;
+}
+
+/** Quit current executable. */
+static int l_quit(lua_State *L)
+{
+	engine_stop(the_worker->engine);
+	return 0;
+}
+
+/** Toggle verbose mode. */
+static int l_verbose(lua_State *L)
+{
+	kr_log_deprecate(SYSTEM, "use log_level() instead of verbose()\n");
+
+	if (lua_isboolean(L, 1) || lua_isnumber(L, 1)) {
+		kr_log_level_set(lua_toboolean(L, 1) == true ? LOG_DEBUG : LOG_DEFAULT_LEVEL);
+	}
+
+	lua_pushboolean(L, kr_log_level == LOG_DEBUG);
+	return 1;
+}
+
+static int l_log_level(lua_State *L)
+{
+	const int params = lua_gettop(L);
+	if (params > 1) {
+		goto bad_call;
+	} else if (params == 1) {  // set
+		const char *lvl_str = lua_tostring(L, 1);
+		if (!lvl_str)
+			goto bad_call;
+		kr_log_level_t lvl = kr_log_name2level(lvl_str);
+		if (lvl < 0)
+			lua_error_p(L, "unknown log level '%s'", lvl_str);
+		kr_log_level_set(lvl);
+	}
+	// get
+	lua_pushstring(L, kr_log_level2name(kr_log_level));
+	return 1;
+bad_call:
+	lua_error_p(L, "takes one string parameter or nothing");
+}
+
+static int l_log_target(lua_State *L)
+{
+	const int params = lua_gettop(L);
+	if (params > 1)
+		goto bad_call;
+	// set
+	if (params == 1) {
+		const char *t_str = lua_tostring(L, 1);
+		if (!t_str)
+			goto bad_call;
+		kr_log_target_t t;
+		if (strcmp(t_str, "syslog") == 0) {
+			t = LOG_TARGET_SYSLOG;
+		} else if (strcmp(t_str, "stdout") == 0) {
+			t = LOG_TARGET_STDOUT;
+		} else if (strcmp(t_str, "stderr") == 0) {
+			t = LOG_TARGET_STDERR;
+		} else {
+			lua_error_p(L, "unknown log target '%s'", t_str);
+		}
+		kr_log_target_set(t);
+	}
+	// get
+	const char *t_str = NULL;
+	switch (kr_log_target) {
+	case LOG_TARGET_SYSLOG: t_str = "syslog"; break;
+	case LOG_TARGET_STDERR: t_str = "stderr"; break;
+	case LOG_TARGET_STDOUT: t_str = "stdout"; break;
+	} // -Wswitch-enum
+	lua_pushstring(L, t_str);
+	return 1;
+bad_call:
+	lua_error_p(L, "takes one string parameter or nothing");
+}
+
+static int l_log_groups(lua_State *L)
+{
+	const int params = lua_gettop(L);
+	if (params > 1)
+		goto bad_call;
+	if (params == 1) {  // set
+		if (!lua_istable(L, 1))
+			goto bad_call;
+		kr_log_group_reset();
+
+		int idx = 1;
+		lua_pushnil(L);
+		while (lua_next(L, 1) != 0) {
+			const char *grp_str = lua_tostring(L, -1);
+			if (!grp_str)
+				goto bad_call;
+
+			enum kr_log_group grp = kr_log_name2grp(grp_str);
+			if (grp >= 0) {
+				kr_log_group_add(grp);
+			} else {
+				kr_log_warning(SYSTEM, "WARNING: unknown log group '%s'\n", lua_tostring(L, -1));
+			}
+
+			++idx;
+			lua_pop(L, 1);
+		}
+	}
+	// get
+	lua_newtable(L);
+	int i = 1;
+	for (enum kr_log_group grp = LOG_GRP_SYSTEM; grp < LOG_GRP_REQDBG; grp++) {
+		const char *name = kr_log_grp2name(grp);
+		if (kr_fails_assert(name))
+			continue;
+		if (kr_log_group_is_set(grp)) {
+			lua_pushinteger(L, i);
+			lua_pushstring(L, name);
+			lua_settable(L, -3);
+			i++;
+		}
+	}
+	return 1;
+bad_call:
+	lua_error_p(L, "takes a table of string groups as parameter or nothing");
+}
+
+char *engine_get_hostname(struct engine *engine) {
+	static char hostname_str[KNOT_DNAME_MAXLEN];
+	if (!engine) {
+		return NULL;
+	}
+
+	if (!engine->hostname) {
+		if (gethostname(hostname_str, sizeof(hostname_str)) != 0)
+			return NULL;
+		return hostname_str;
+	}
+	return engine->hostname;
+}
+
+int engine_set_hostname(struct engine *engine, const char *hostname) {
+	if (!engine || !hostname) {
+		return kr_error(EINVAL);
+	}
+
+	char *new_hostname = strdup(hostname);
+	if (!new_hostname) {
+		return kr_error(ENOMEM);
+	}
+	if (engine->hostname) {
+		free(engine->hostname);
+	}
+	engine->hostname = new_hostname;
+	network_new_hostname(&engine->net, engine);
+
+	return 0;
+}
+
+/** Return hostname. */
+static int l_hostname(lua_State *L)
+{
+	struct engine *engine = the_worker->engine;
+	if (lua_gettop(L) == 0) {
+		lua_pushstring(L, engine_get_hostname(engine));
+		return 1;
+	}
+	if ((lua_gettop(L) != 1) || !lua_isstring(L, 1))
+		lua_error_p(L, "hostname takes at most one parameter: (\"fqdn\")");
+
+	if (engine_set_hostname(engine, lua_tostring(L, 1)) != 0)
+		lua_error_p(L, "setting hostname failed");
+
+	lua_pushstring(L, engine_get_hostname(engine));
+	return 1;
+}
+
+/** Return server package version. */
+static int l_package_version(lua_State *L)
+{
+	lua_pushliteral(L, PACKAGE_VERSION);
+	return 1;
+}
+
+/** Load root hints from zonefile. */
+static int l_hint_root_file(lua_State *L)
+{
+	struct kr_context *ctx = &the_worker->engine->resolver;
+	const char *file = lua_tostring(L, 1);
+
+	const char *err = engine_hint_root_file(ctx, file);
+	if (err) {
+		if (!file) {
+			file = ROOTHINTS;
+		}
+		lua_error_p(L, "error when opening '%s': %s", file, err);
+	} else {
+		lua_pushboolean(L, true);
+		return 1;
+	}
+}
+
+/** @internal for engine_hint_root_file */
+static void roothints_add(zs_scanner_t *zs)
+{
+	struct kr_zonecut *hints = zs->process.data;
+	if (!hints) {
+		return;
+	}
+	if (zs->r_type == KNOT_RRTYPE_A || zs->r_type == KNOT_RRTYPE_AAAA) {
+		kr_zonecut_add(hints, zs->r_owner, zs->r_data, zs->r_data_length);
+	}
+}
+const char* engine_hint_root_file(struct kr_context *ctx, const char *file)
+{
+	if (!file) {
+		file = ROOTHINTS;
+	}
+	if (strlen(file) == 0 || !ctx) {
+		return "invalid parameters";
+	}
+	struct kr_zonecut *root_hints = &ctx->root_hints;
+
+	zs_scanner_t zs;
+	if (zs_init(&zs, ".", 1, 0) != 0) {
+		return "not enough memory";
+	}
+	if (zs_set_input_file(&zs, file) != 0) {
+		zs_deinit(&zs);
+		return "failed to open root hints file";
+	}
+
+	kr_zonecut_set(root_hints, (const uint8_t *)"");
+	zs_set_processing(&zs, roothints_add, NULL, root_hints);
+	zs_parse_all(&zs);
+	zs_deinit(&zs);
+	return NULL;
+}
+
+/** Unpack JSON object to table */
+static void l_unpack_json(lua_State *L, JsonNode *table)
+{
+	/* Unpack POD */
+	switch(table->tag) {
+		case JSON_STRING: lua_pushstring(L, table->string_); return;
+		case JSON_NUMBER: lua_pushnumber(L, table->number_); return;
+		case JSON_BOOL:   lua_pushboolean(L, table->bool_); return;
+		default: break;
+	}
+	/* Unpack object or array into table */
+	lua_newtable(L);
+	JsonNode *node = NULL;
+	json_foreach(node, table) {
+		/* Push node value */
+		switch(node->tag) {
+		case JSON_OBJECT: /* as array */
+		case JSON_ARRAY:  l_unpack_json(L, node); break;
+		case JSON_STRING: lua_pushstring(L, node->string_); break;
+		case JSON_NUMBER: lua_pushnumber(L, node->number_); break;
+		case JSON_BOOL:   lua_pushboolean(L, node->bool_); break;
+		default: continue;
+		}
+		/* Set table key */
+		if (node->key) {
+			lua_setfield(L, -2, node->key);
+		} else {
+			lua_rawseti(L, -2, lua_objlen(L, -2) + 1);
+		}
+	}
+}
+
+/** @internal Recursive Lua/JSON serialization. */
+static JsonNode *l_pack_elem(lua_State *L, int top)
+{
+	switch(lua_type(L, top)) {
+	case LUA_TSTRING:  return json_mkstring(lua_tostring(L, top));
+	case LUA_TNUMBER:  return json_mknumber(lua_tonumber(L, top));
+	case LUA_TBOOLEAN: return json_mkbool(lua_toboolean(L, top));
+	case LUA_TTABLE:   break; /* Table, iterate it. */
+	default:           return json_mknull();
+	}
+	/* Use absolute indexes here, as the table may be nested. */
+	JsonNode *node = NULL;
+	lua_pushnil(L);
+	while(lua_next(L, top) != 0) {
+		bool is_array = false;
+		if (!node) {
+			is_array = (lua_type(L, top + 1) == LUA_TNUMBER);
+			node = is_array ? json_mkarray() : json_mkobject();
+			if (!node) {
+				return NULL;
+			}
+		} else {
+			is_array = node->tag == JSON_ARRAY;
+		}
+
+		/* Insert to array/table. */
+		JsonNode *val = l_pack_elem(L, top + 2);
+		if (is_array) {
+			json_append_element(node, val);
+		} else {
+			const char *key = lua_tostring(L, top + 1);
+			json_append_member(node, key, val);
+		}
+		lua_pop(L, 1);
+	}
+	/* Return empty object for empty tables. */
+	return node ? node : json_mkobject();
+}
+
+/** @internal Serialize to string */
+static char *l_pack_json(lua_State *L, int top)
+{
+	JsonNode *root = l_pack_elem(L, top);
+	if (!root) {
+		return NULL;
+	}
+	char *result = json_encode(root);
+	json_delete(root);
+	return result;
+}
+
+static int l_tojson(lua_State *L)
+{
+	auto_free char *json_str = l_pack_json(L, lua_gettop(L));
+	if (!json_str) {
+		return 0;
+	}
+	lua_pushstring(L, json_str);
+	return 1;
+}
+
+static int l_fromjson(lua_State *L)
+{
+	if (lua_gettop(L) != 1 || !lua_isstring(L, 1))
+		lua_error_p(L, "a JSON string is required");
+
+	const char *json_str = lua_tostring(L, 1);
+	JsonNode *root_node = json_decode(json_str);
+
+	if (!root_node)
+		lua_error_p(L, "invalid JSON string");
+	l_unpack_json(L, root_node);
+	json_delete(root_node);
+
+	return 1;
+}
+
+/*
+ * Engine API.
+ */
+
+static int init_resolver(struct engine *engine)
+{
+	/* Note: whole *engine had been zeroed by engine_init(). */
+	struct kr_context * const ctx = &engine->resolver;
+	/* Default options (request flags). */
+	ctx->options.REORDER_RR = true;
+
+	/* Open resolution context */
+	ctx->trust_anchors = trie_create(NULL);
+	ctx->negative_anchors = trie_create(NULL);
+	ctx->vld_limit_crypto = KR_VLD_LIMIT_CRYPTO_DEFAULT;
+	ctx->pool = engine->pool;
+	ctx->modules = &engine->modules;
+	ctx->cache_rtt_tout_retry_interval = KR_NS_TIMEOUT_RETRY_INTERVAL;
+	/* Create OPT RR */
+	ctx->downstream_opt_rr = mm_alloc(engine->pool, sizeof(knot_rrset_t));
+	ctx->upstream_opt_rr = mm_alloc(engine->pool, sizeof(knot_rrset_t));
+	if (!ctx->downstream_opt_rr || !ctx->upstream_opt_rr) {
+		return kr_error(ENOMEM);
+	}
+	knot_edns_init(ctx->downstream_opt_rr, KR_EDNS_PAYLOAD, 0, KR_EDNS_VERSION, engine->pool);
+	knot_edns_init(ctx->upstream_opt_rr, KR_EDNS_PAYLOAD, 0, KR_EDNS_VERSION, engine->pool);
+	/* Use default TLS padding */
+	ctx->tls_padding = -1;
+	/* Empty init; filled via ./lua/postconfig.lua */
+	kr_zonecut_init(&ctx->root_hints, (const uint8_t *)"", engine->pool);
+	lru_create(&ctx->cache_cookie, LRU_COOKIES_SIZE, NULL, NULL);
+
+	/* Load basic modules */
+	engine_register(engine, "iterate", NULL, NULL);
+	engine_register(engine, "validate", NULL, NULL);
+	engine_register(engine, "cache", NULL, NULL);
+
+	return array_push(engine->backends, kr_cdb_lmdb());
+}
+
+static int init_state(struct engine *engine)
+{
+	/* Initialize Lua state */
+	engine->L = luaL_newstate();
+	if (engine->L == NULL) {
+		return kr_error(ENOMEM);
+	}
+	/* Initialize used libraries. */
+	luaL_openlibs(engine->L);
+	/* Global functions */
+	lua_pushcfunction(engine->L, l_help);
+	lua_setglobal(engine->L, "help");
+	lua_pushcfunction(engine->L, l_quit);
+	lua_setglobal(engine->L, "quit");
+	lua_pushcfunction(engine->L, l_hostname);
+	lua_setglobal(engine->L, "hostname");
+	lua_pushcfunction(engine->L, l_package_version);
+	lua_setglobal(engine->L, "package_version");
+	lua_pushcfunction(engine->L, l_verbose);
+	lua_setglobal(engine->L, "verbose");
+	lua_pushcfunction(engine->L, l_log_level);
+	lua_setglobal(engine->L, "log_level");
+	lua_pushcfunction(engine->L, l_log_target);
+	lua_setglobal(engine->L, "log_target");
+	lua_pushcfunction(engine->L, l_log_groups);
+	lua_setglobal(engine->L, "log_groups");
+	lua_pushcfunction(engine->L, l_setuser);
+	lua_setglobal(engine->L, "user");
+	lua_pushcfunction(engine->L, l_hint_root_file);
+	lua_setglobal(engine->L, "_hint_root_file");
+	lua_pushliteral(engine->L, libknot_SONAME);
+	lua_setglobal(engine->L, "libknot_SONAME");
+	lua_pushliteral(engine->L, libzscanner_SONAME);
+	lua_setglobal(engine->L, "libzscanner_SONAME");
+	lua_pushcfunction(engine->L, l_tojson);
+	lua_setglobal(engine->L, "tojson");
+	lua_pushcfunction(engine->L, l_fromjson);
+	lua_setglobal(engine->L, "fromjson");
+	/* Random number generator */
+	lua_getfield(engine->L, LUA_GLOBALSINDEX, "math");
+	lua_getfield(engine->L, -1, "randomseed");
+	lua_remove(engine->L, -2);
+	lua_Number seed = kr_rand_bytes(sizeof(lua_Number));
+	lua_pushnumber(engine->L, seed);
+	lua_call(engine->L, 1, 0);
+	return kr_ok();
+}
+
+/**
+ * Start luacov measurement and store results to file specified by
+ * KRESD_COVERAGE_STATS environment variable.
+ * Do nothing if the variable is not set.
+ */
+static void init_measurement(struct engine *engine)
+{
+	const char * const statspath = getenv("KRESD_COVERAGE_STATS");
+	if (!statspath)
+		return;
+
+	char * snippet = NULL;
+	int ret = asprintf(&snippet,
+		"_luacov_runner = require('luacov.runner')\n"
+		"_luacov_runner.init({\n"
+		"	statsfile = '%s',\n"
+		"	exclude = {'test', 'tapered', 'lua/5.1'},\n"
+		"})\n"
+		"jit.off()\n", statspath
+	);
+	if (kr_fails_assert(ret > 0))
+		return;
+
+	ret = luaL_loadstring(engine->L, snippet);
+	if (kr_fails_assert(ret == 0)) {
+		free(snippet);
+		return;
+	}
+	lua_call(engine->L, 0, 0);
+	free(snippet);
+}
+
+int init_lua(struct engine *engine) {
+	if (!engine) {
+		return kr_error(EINVAL);
+	}
+
+	/* Use libdir path for including Lua scripts */
+	char l_paths[MAXPATHLEN] = { 0 };
+	#pragma GCC diagnostic push
+	#pragma GCC diagnostic ignored "-Wformat" /* %1$ is not in C standard */
+	/* Save original package.path to package._path */
+	snprintf(l_paths, MAXPATHLEN - 1,
+		 "if package._path == nil then package._path = package.path end\n"
+		 "package.path = '%1$s/?.lua;%1$s/?/init.lua;'..package._path\n"
+		 "if package._cpath == nil then package._cpath = package.cpath end\n"
+		 "package.cpath = '%1$s/?%2$s;'..package._cpath\n",
+		 LIBDIR, LIBEXT);
+	#pragma GCC diagnostic pop
+
+	int ret = l_dobytecode(engine->L, l_paths, strlen(l_paths), "");
+	if (ret != 0) {
+		lua_pop(engine->L, 1);
+		return ret;
+	}
+	return 0;
+}
+
+
+int engine_init(struct engine *engine, knot_mm_t *pool)
+{
+	if (engine == NULL) {
+		return kr_error(EINVAL);
+	}
+
+	memset(engine, 0, sizeof(*engine));
+	engine->pool = pool;
+
+	/* Initialize state */
+	int ret = init_state(engine);
+	if (ret != 0) {
+		engine_deinit(engine);
+		return ret;
+	}
+	init_measurement(engine);
+	/* Initialize resolver */
+	ret = init_resolver(engine);
+	if (ret != 0) {
+		engine_deinit(engine);
+		return ret;
+	}
+	/* Initialize network */
+	network_init(&engine->net, uv_default_loop(), TCP_BACKLOG_DEFAULT);
+
+	/* Initialize lua */
+	ret = init_lua(engine);
+	if (ret != 0) {
+		engine_deinit(engine);
+		return ret;
+	}
+
+	return ret;
+}
+
+/** Unregister a (found) module */
+static void engine_unload(struct engine *engine, struct kr_module *module)
+{
+	auto_free char *name = module->name ? strdup(module->name) : NULL;
+	kr_module_unload(module); /* beware: lua/C mix, could be confusing */
+	/* Clear in Lua world, but not for embedded modules ('cache' in particular). */
+	if (name && !kr_module_get_embedded(name)) {
+		lua_pushnil(engine->L);
+		lua_setglobal(engine->L, name);
+	}
+	free(module);
+}
+
+void engine_deinit(struct engine *engine)
+{
+	if (!engine || kr_fails_assert(engine->L))
+		return;
+	/* Only close sockets and services; no need to clean up mempool. */
+
+	/* Network deinit is split up.  We first need to stop listening,
+	 * then we can unload modules during which we still want
+	 * e.g. the endpoint kind registry to work (inside ->net),
+	 * and this registry deinitialization uses the lua state. */
+	network_close_force(&engine->net);
+	for (size_t i = 0; i < engine->modules.len; ++i) {
+		engine_unload(engine, engine->modules.at[i]);
+	}
+	kr_zonecut_deinit(&engine->resolver.root_hints);
+	kr_cache_close(&engine->resolver.cache);
+
+	/* The LRUs are currently malloc-ated and need to be freed. */
+	lru_free(engine->resolver.cache_cookie);
+
+	network_deinit(&engine->net);
+	ffimodule_deinit(engine->L);
+	lua_close(engine->L);
+
+	/* Free data structures */
+	array_clear(engine->modules);
+	array_clear(engine->backends);
+	kr_ta_clear(engine->resolver.trust_anchors);
+	trie_free(engine->resolver.trust_anchors);
+	kr_ta_clear(engine->resolver.negative_anchors);
+	trie_free(engine->resolver.negative_anchors);
+	free(engine->hostname);
+}
+
+int engine_pcall(lua_State *L, int argc)
+{
+	return lua_pcall(L, argc, LUA_MULTRET, 0);
+}
+
+int engine_cmd(lua_State *L, const char *str, bool raw)
+{
+	if (L == NULL) {
+		return kr_error(ENOEXEC);
+	}
+
+	/* Evaluate results */
+	lua_getglobal(L, "eval_cmd");
+	lua_pushstring(L, str);
+	lua_pushboolean(L, raw);
+
+	/* Check result. */
+	return engine_pcall(L, 2);
+}
+
+int engine_load_sandbox(struct engine *engine)
+{
+	/* Init environment */
+	int ret = luaL_dofile(engine->L, LIBDIR "/sandbox.lua");
+	if (ret != 0) {
+		kr_log_error(SYSTEM, "error %s\n", lua_tostring(engine->L, -1));
+		lua_pop(engine->L, 1);
+		return kr_error(ENOEXEC);
+	}
+	ret = ffimodule_init(engine->L);
+	return ret;
+}
+
+int engine_loadconf(struct engine *engine, const char *config_path)
+{
+	if (kr_fails_assert(config_path))
+		return kr_error(EINVAL);
+
+	char cwd[PATH_MAX];
+	get_workdir(cwd, sizeof(cwd));
+	kr_log_debug(SYSTEM, "loading config '%s' (workdir '%s')\n", config_path, cwd);
+
+	int ret = luaL_dofile(engine->L, config_path);
+	if (ret != 0) {
+		kr_log_error(SYSTEM, "error while loading config: "
+			"%s (workdir '%s')\n", lua_tostring(engine->L, -1), cwd);
+		lua_pop(engine->L, 1);
+	}
+	return ret;
+}
+
+int engine_start(struct engine *engine)
+{
+	/* Clean up stack */
+	lua_settop(engine->L, 0);
+
+	return kr_ok();
+}
+
+void engine_stop(struct engine *engine)
+{
+	if (!engine) {
+		return;
+	}
+	uv_stop(uv_default_loop());
+}
+
+/** @internal Find matching module */
+static size_t module_find(module_array_t *mod_list, const char *name)
+{
+	size_t found = mod_list->len;
+	for (size_t i = 0; i < mod_list->len; ++i) {
+		struct kr_module *mod = mod_list->at[i];
+		if (strcmp(mod->name, name) == 0) {
+			found = i;
+			break;
+		}
+	}
+	return found;
+}
+
+int engine_register(struct engine *engine, const char *name, const char *precedence, const char* ref)
+{
+	if (kr_fails_assert(engine && name))
+		return kr_error(EINVAL);
+	/* Make sure module is unloaded */
+	(void) engine_unregister(engine, name);
+	/* Find the index of referenced module. */
+	module_array_t *mod_list = &engine->modules;
+	size_t ref_pos = mod_list->len;
+	if (precedence && ref) {
+		ref_pos = module_find(mod_list, ref);
+		if (ref_pos >= mod_list->len) {
+			return kr_error(EIDRM);
+		}
+	}
+	/* Attempt to load binary module */
+	struct kr_module *module = malloc(sizeof(*module));
+	if (!module) {
+		return kr_error(ENOMEM);
+	}
+	module->data = engine; /*< some outside modules may still use this value */
+
+	int ret = kr_module_load(module, name, LIBDIR "/kres_modules");
+	if (ret == 0) {
+		/* We have a C module, loaded and init() was called.
+		 * Now we need to prepare the lua side. */
+		lua_State *L = engine->L;
+		lua_getglobal(L, "modules_create_table_for_c");
+		lua_pushpointer(L, module);
+		if (lua_isnil(L, -2)) {
+			/* When loading the three embedded modules, we don't
+			 * have the "modules_*" lua function yet, but fortunately
+			 * we don't need it there.  Let's just check they're embedded.
+			 * TODO: solve this better *without* breaking stuff. */
+			lua_pop(L, 2);
+			if (module->lib != RTLD_DEFAULT) {
+				ret = kr_error(1);
+				lua_pushliteral(L, "missing modules_create_table_for_c()");
+			}
+		} else {
+			ret = engine_pcall(L, 1);
+		}
+		if (kr_fails_assert(ret == 0)) {  /* probably not critical, but weird */
+			kr_log_error(SYSTEM, "internal error when loading C module %s: %s\n",
+					module->name, lua_tostring(L, -1));
+			lua_pop(L, 1);
+		}
+
+	} else if (ret == kr_error(ENOENT)) {
+		/* No luck with C module, so try to load and .init() lua module. */
+		ret = ffimodule_register_lua(engine, module, name);
+		if (ret != 0) {
+			kr_log_error(SYSTEM, "failed to load module '%s'\n", name);
+		}
+
+	} else if (ret == kr_error(ENOTSUP)) {
+		/* Print a more helpful message when module is linked against an old resolver ABI. */
+		kr_log_error(SYSTEM, "module '%s' links to unsupported ABI, please rebuild it\n", name);
+	}
+
+	if (ret != 0) {
+		engine_unload(engine, module);
+		return ret;
+	}
+
+	/* Push to the right place in engine->modules */
+	if (array_push(engine->modules, module) < 0) {
+		engine_unload(engine, module);
+		return kr_error(ENOMEM);
+	}
+	if (precedence) {
+		struct kr_module **arr = mod_list->at;
+		size_t emplacement = mod_list->len;
+		if (strcasecmp(precedence, ">") == 0) {
+			if (ref_pos + 1 < mod_list->len)
+				emplacement = ref_pos + 1; /* Insert after target */
+		}
+		if (strcasecmp(precedence, "<") == 0) {
+			emplacement = ref_pos; /* Insert at target */
+		}
+		/* Move the tail if it has some elements. */
+		if (emplacement + 1 < mod_list->len) {
+			memmove(&arr[emplacement + 1], &arr[emplacement], sizeof(*arr) * (mod_list->len - (emplacement + 1)));
+			arr[emplacement] = module;
+		}
+	}
+
+	return kr_ok();
+}
+
+int engine_unregister(struct engine *engine, const char *name)
+{
+	module_array_t *mod_list = &engine->modules;
+	size_t found = module_find(mod_list, name);
+	if (found < mod_list->len) {
+		engine_unload(engine, mod_list->at[found]);
+		array_del(*mod_list, found);
+		return kr_ok();
+	}
+
+	return kr_error(ENOENT);
+}
+