Added systemd type=notify support

[solarkennedy]

This adds support to spectatord let systemd know when it is ready.

This is better than just a "fire and forget" type of thing where systemd can't really be sure if spectatord is actually ready to take traffic

https://www.freedesktop.org/software/systemd/man/latest/sd_notify.html#

[bplotnick]

is sizeof(addr) correct? I think it will include padding after the null terminator. from https://github.com/systemd/systemd/blob/51190631968f2a69acf5da3e3412b003805538f2/src/basic/socket-util.c#L1387-L1396, we can see the correct way. adapted for the fact that we already know the length:

Suggested change

	// Handle abstract namespace sockets (starting with '@')
	if (notify_socket[0] == '@') {
	addr.sun_path[0] = '\0';
	std::strncpy(addr.sun_path + 1, notify_socket + 1, sizeof(addr.sun_path) - 2);
	} else {
	std::strncpy(addr.sun_path, notify_socket, sizeof(addr.sun_path) - 1);
	}
	// Send the notification
	ssize_t result = sendto(fd, state.c_str(), state.size(), MSG_NOSIGNAL,
	reinterpret_cast<struct sockaddr*>(&addr), sizeof(addr));
	socklen_t addr_len;
	// Handle abstract namespace sockets (starting with '@')
	if (notify_socket[0] == '@') {
	addr.sun_path[0] = '\0';
	std::memcpy(addr.sun_path + 1, notify_socket + 1, sizeof(addr.sun_path) - 1);
	// abstract sockets treated as byte array, not c string
	addr_len = offsetof(struct sockaddr_un, sun_path) + notify_socket_len;
	} else {
	std::memcpy(addr.sun_path, notify_socket, sizeof(addr.sun_path));
	addr.sun_path[str_len] = '\0';
	// abstract sockets treated as c string. +1 for null termination
	addr_len = offsetof(struct sockaddr_un, sun_path) + notify_socket_len + 1;
	}
	// Send the notification
	ssize_t result = sendto(fd, state.c_str(), state.size(), MSG_NOSIGNAL,
	reinterpret_cast<struct sockaddr*>(&addr), addr_len);

[solarkennedy]

classic