zero, and we can't tell that <tt>deflate()</tt> has done all it can.
As far as we know, <tt>deflate()</tt>
has more output for us.  So we call it again.  But now <tt>deflate()</tt> produces no output
at all, and <tt>avail_out</tt> remains unchanged as <tt>CHUNK</tt>.  That <tt>deflate()</tt> call
wasn't able to do anything, either consume input or produce output, and so it returns
<tt>Z_BUF_ERROR</tt>.  (See, I told you I'd cover this later.)  However this is not a problem at
all.  Now we finally have the d