Stdio.Buffer peculiar state?

>What does it take to get a right-hand endpoint of -1 for read and data there?

It just indicates an empty range.

Basically, the buffer is 8k, byte 0..-1, inclusive (an empty range,
unlike 0..0, inclusive) is already read data, the data is the same
size (also 0 bytes long).

So, it's simply an empty buffer.

>It seems like the connection is now stuck in a busy loop reading 0 bytes
>all the time from the network.

If you do read and the connection is closed or there is no data
available and it's in nonblocking mode you will indeed read 0 bytes.

However, unless the connection is closed it should not be a busy loop
(you can check fd->errno())