ntended to be called within a waitable procedure
invoked by a-sync (which supplies the &rsquo;await&rsquo; and &rsquo;resume&rsquo; arguments).
This procedure is implemented using a-sync-read-watch!.  Unlike the
await-getblock! procedure, the watch will continue after a complete
block of data has been received in order to receive further blocks.
The watch will not end until end-of-file or an exceptional condition
(&rsquo;excpt) is reached.  In the event of that happening, this procedure
will end and return 