How can I use Apple's Core Audio C API to create a simple, real-time I/O stream on OS X?

After spending quite a while traversing the extensive Core Audio docs maze, I'm still unsure of what part of the C API I should be using to create a basic audio sample I/O stream in OS X.

When I say "I/O stream" I mean a low-latency stream that is spawned for a specific audio device (with params such as sample rate, number of channels, bit depth, etc) and receives/requests buffers of interleaved audio samples to be played back by the device with.

I would really appreciate it if someone could point me towards the header and associated functions that I need to achieve this (perhaps even an example) :) Thanks!

PS: Normally I would use PortAudio to achieve this, however in this case I'm interested in accessing the Core Audio framework directly in order to assist a friend in creating a purely Rust portable audio platform. Also, I've posted this question to the Apple developer forums but have not yet received a response so I thought I'd try here. If there is a more suitable exchange/forum to ask at, please let me know.