fd_reader(
fd) ->reader
Wrap an arbitrary fd for cooperative reads on the event loop
Returns a reader for fd (e.g. stdin, fd 0) that integrates with the
event loop. :read(maxlen, opts) yields the current coroutine until at
least one byte is available, returning the bytes, or nil,"closed" on
EOF, or nil,"cancelled"/err. :read_available(maxlen) drains all
currently-readable bytes without yielding.
The fd must be in non-blocking mode (see set_nonblocking) and must be
epoll-able (a TTY or pipe, not a regular file). Only one coroutine may
wait on a given fd at a time.
read reports EOF only from a non-blocking fd. On a fd flipped to
blocking, a raw-mode tty (VMIN=0, VTIME>0) returns zero bytes on idle --
a phantom EOF -- so read re-asserts non-blocking and keeps reading. A
caller that flips the flag mid-read gets it flipped back.