Abstract IO structure for rproxy
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$Id: abstract-io.txt,v 1.1 2000/08/04 07:19:38 mbp Exp $

* Short reads and writes:

Are short reads and writes allowed?  I think the code is a bit
confused about this at the moment. 

At the OS level, we know this: that network reads can be short, and
that any call can be short if we're signalled in the middle.  

In the case of an interrupted call, we'll get rc=-1 and errno=EINTR or
EAGAIN. 

* Non-blocking:

Squid is select-driven.  I think we need to restructure librsync to
allow the caller to push data through.  This might be hard, but we can
get there by splitting up the processing loop and having the minimum
amount of state on the stack.

* Error handling:

Particularly as we're ignoring SIGPIPE, we should be careful to check
the return code on all calls, and respond appropriately if there was
an error.

* Abstract mapptr

We could make mapptr abstract by either allowing some other underlying
mechanism rather than POSIX I/O, or by allowing different mapptr
implementations.  I'm not sure why this would be useful, so I think
I'll leave it out for now.