Hi Hilarie,
1. I believe that the protocol requirements stipulate the use of
independent "channels", and those were put in exactly for the the case
you are discussing for preview. If channels don't solve the problem,
we need to know why.
draft-ietf-opes-protocol-reqs-03 does not mention the "channels", does it?
Till this weekend I was not aware that the "channels" concept already
implies that each fragment of an application message is sent in its own
callout message via the channel.
Is this correct? If yes, I appreciate this concept very much and I think
it is exactly what I thought about solving the out-of-sync and preview
problems.
2. For the SMTP case, let's suppose that the site policy
requires virus
scanning, but some subscribers to the OPES box want potential viruses
removed, and some simply want them flagged. Assume a message has been
sent to several recipients of a domain with an OPES virus scanning
service, and its body is denoted as "A" (identified by its hash, I
suppose). If it's the OPES processor that holds the user preferences,
then it can handle the process of sending A to a callout server for
virus scanning and asking for both removal and flagging, possibly in
one request, but at worst in two. Ah, I see, you'd like to eliminate
the two requests, and have a request type that asks for multiple
services and multiple replies. This is different from asking for
multiple services and one reply. A notation for this might
be something
like:
Request(data=D; service=A AND service=B)
Reply(data=A(B(D)))
Request(data=D; service=A; service=B)
Reply(data=A(D); data=B(D))
Have I captured the requirement correctly?
I am not sure. Please have a look into my posting "SMTP filtering use case".
3. I know the arguments for simple formats, but please give something
specific about your objection to BEEP. My objection to XML encoding
is that it requires many instructions to parse it into tag pairs and
parameters, to create a parse tree, and to traverse the tree. When
comparing this to direct indexing, or even scans for end-of-header,
end-of-line, XML is very slow. But, experience has shown that there
are distinct limits to what can be accomplished with fixed parameters
positions and bit encodings, and even TCP has had a great deal of
trouble staying within its header limitations. Up at the
application layer,
I think some compromise will be necessary. I'd thought BEEP
was actually
a good point to begin looking for that compromise point. What is so
awful about it?
I am really sorry that I started to name protocols. I didn't want to get
into this discussion now. On the other hand it shows that existing
protocols have interesting concepts that are very worth to be known and
understood while discussing OPES protocol needs and I doubt that I would
really look in the protocol's details without this discussion.
Unfortunately I had only a brief look into RFC 3080 (BEEP core) before
sending my first message last week. And in there I found all examples
full of XML structure, always repeating same Content-Type header with
every single small message and that little PASCAL reminding "END" literal.
So on my first glance it did not look very efficient to me.
I thought that if each application message's fragment is encapsulated
in its own BEEP message this would be a big overhead. Seems that this
is not so.
By learning a little more about it over the weekend and starting to
understand the "channels" concept, I agree that BEEP is very worth to
be considered.
It is not "awful" (and I never said so).
But still we should not elect the one or other protocol now.
What we rather need is a common understanding about the best concepts
and how they could fulfill the requirements and solve the questions
and problems that we list.
What other BEEP documents than RFC 3080 should be studied?
Is there a good summary about the concepts that could help OPES?
If not, could somebody compile one?
Martin