I am trying to build an app for iOS that can connect to computers running macOS or windows, and control a few stuff on those computers. Another application will be installed on those computers so that the app on iOS can connect to them. But at first I need to discover those computers in the network that has my app installed and running. What is a good way of doing that? I thought about using broadcasting, multicasting or bonjour. Are there any other options? Which one is best for my situation?
I am planning on doing two different applications for macOS and windows, one with objective c and other with c#, so the networking stuff should be available for both of those. Thanks in advance
The simplest option by far would be to use IP/UDP broadcast packets. The application on the computers (running whatever OS) can all sit there listening on a predefined UDP port (e.g. 9999), and when the iOS device wants to ‘scan’ the network, it will send out an IP/UDP broadcast packet with the destination port of 9999. Upon receiving the broadcast packet(s), the application on the computers can respond since it now knows the IP address of the iOS device, and you can take things from there.
The cleanest way to handle a computer leaving the network is for the application that is running on the computer to communicate this fact to the iOS device since it already knows the IP address of the iOS device. But if keeping a current list of computers is crucial, then some sort of a polling mechanism is unavoidable because the computers may crash for whatever reason without having the chance to send the bye-bye message.
Multicasting can be utilized as follows: computers periodically send IGMP joins for a predefined multicast group (e.g. 224.1.1.1), and iOS device sends the multicast UDP packet destined to 224.1.1.1 when it wants to ‘scan’ the network. The multicast UDP packet(s) will be received by the computers since they have already joined the multicast group of 224.1.1.1, and then the computers can start communicating with the iOS device now that the IP address is known. However, this seems overly complex, and does not really offer any advantages. The whole point of using multicast is to save bandwidth, but the amount of bandwidth saved will be minuscule. Unless you are going to send the same data in substantial quantities from the iOS device to all the computers, there is simply no reason to go down this path.
As for Bonjour, unfortunately I am unable to comment as I have no experience with it, but I would still vote for simple broadcasting to keep things platform independent… well, at least on the computers side. 🙂