How to handle slow clients with "push-streamed" response bodies?

[konnextv]

I am kind of lost right now, I am using a setup kind of similar to the send_file.rs example.
Only difference is that I use the async_stream::stream! macro to wrap a loop that yields from a bounded channel.

However fast I push things into the channel, they are almost instantly yielded even if the client consuming the body is doing so very slowly.

Q: Where does the body go and get buffered? How can I control or check the length of that buffer?

[konnextv]

Update: I did more research on this and found out that you can get the number of unsent (or unACKed) bytes in a TCP buffer with ioctl SIOCOUTQ (on UNIX). I will dive deeper into this and look for a way to facilitate this using hyper, but maybe someone did exactly this and could give me a pointer in the right direction.
Will update with further findings.

[konnextv]

I played around with the max_buf_size of the hyper connection but that did not change the behaviour, there is still no backpressure if I feed data faster than the other side of the TCP connection processes it. There really must be some growing buffer on the OS level that I cannot grasp yet.