daemon/io: configurable idle timeout for incoming TCP connection

The idle timeout was set equal to the timeout for the arrival of the first request after connection had been established. For DNS over TCP it was a half of maximal allowed RTT and it often led to prematurely closing of incoming connection.

daemon/bindings.c

@@ -793,6 +793,37 @@ static int net_outgoing(lua_State *L, int family)
 static int net_outgoing_v4(lua_State *L) { return net_outgoing(L, AF_INET); }
 static int net_outgoing_v6(lua_State *L) { return net_outgoing(L, AF_INET6); }
 
+static int net_tcp_in_idle(lua_State *L)
+{
+	struct engine *engine = engine_luaget(L);
+	struct network *net = &engine->net;
+
+	/* Only return current idle timeout. */
+	if (lua_gettop(L) == 0) {
+		lua_pushnumber(L, net->tcp.in_idle_timeout);
+		return 1;
+	}
+
+	if ((lua_gettop(L) != 1)) {
+		lua_pushstring(L, "net.tcp_in_idle takes one parameter: (\"idle timeout\")");
+		lua_error(L);
+	}
+
+	if (lua_isnumber(L, 1)) {
+		int idle_timeout = lua_tointeger(L, 1);
+		if (idle_timeout <= 0) {
+			lua_pushstring(L, "net.tcp_in_idle parameter has to be positive number");
+			lua_error(L);
+		}
+		net->tcp.in_idle_timeout = idle_timeout;
+	} else {
+		lua_pushstring(L, "net.tcp_in_idle parameter has to be positive number");
+		lua_error(L);
+	}
+	lua_pushboolean(L, true);
+	return 1;
+}
+
 int lib_net(lua_State *L)
 {
 	static const luaL_Reg lib[] = {
@@ -810,6 +841,7 @@ int lib_net(lua_State *L)
 		{ "tls_sticket_secret_file", net_tls_sticket_secret_file },
 		{ "outgoing_v4",  net_outgoing_v4 },
 		{ "outgoing_v6",  net_outgoing_v6 },
+		{ "tcp_in_idle",  net_tcp_in_idle },
 		{ NULL, NULL }
 	};
 	register_lib(L, "net", lib);