Re: [equinox-dev] [prov] ECF in P2, was request handler orientation

[Jeff McAffer <Jeff_McAffer@xxxxxxxxxx>]

:-)  Thanks.  I think I will
flip it around without piped streams since the handler already forks jobs
etc.  Feel free to pick apart the upcoming proposal.

Jeff

Stefan Liebig <Stefan.Liebig@xxxxxxxxxxxx>
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09/01/2007 11:11 AM

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Subject	Re: [equinox-dev] [prov] ECF in P2, was request handler orientation

Jeff, shall I start to revive the push model? I think
I have some backups ;-)

Stefan

Jeff McAffer wrote: 

Thanks for all the comments and info Scott (and others).  First, this
thread started with something completely unrelated to ECF.  I was
just interested in whether the call to RequestHandler.download() happen
in the MirrorRequest or somewhere in the ArtifactRepository (or elsewhere).
 In the end I think that that has been resolved and the call will
be moved as I restructure some of the code. 

As for using ECF, I am all for using it and so far have not found it to
be particularly limiting or limited.  If it were then I expect that
we would work with you to understand how we should use it or to enhance
it to suit the requirements.  For example, my recent questions about
chaining InputStreams.  Given your advice I am going to revisit the
approach I proposed and Stefan implemented to see if we can flip it around
to use OutputStreams and have ECF *push* data through the pipe rather than
having clients *pull* data out of the pipe.  Should be resaonbly straightforward
as this is what Stefan had originally (sorry Stefan :-)  Anyway, having
said that, depending on how complex this gets, it may be worth our will
to still maintain an insulating later between p2 and whatever handler technology
we are using.  Your points about potential complexity here are well
taken and that will have to weigh into the consideration.

There is a valid question of whether or not we expose handlers and ECF
in the p2 API.  We would do well to avoid it if possible.  Not
because there is anything wrong with ECF rather if we can implement p2
without exposing ECF then it is likely simpler as there would likely be
less API and fewer concepts.  Of course, that might come at the expense
of flexibility...  We will have to see. 

Finally, we will certainly take you up on your offer of assistance in structuring
the handler code and other bits.   Thanks 

Jeff

Scott Lewis <slewis@xxxxxxxxxxxxx>
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08/31/2007 09:20 PM

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Subject	Re: [equinox-dev] [prov] ECF in P2, was request handler orientation

I admit I'm a little confused by this thread, as it seems bring up a 
range of issues...some of which are related to ECF functionality and 
some of which don't seem (to me) to be directly related to ECF per se 
(but rather the provisioning request handlers?).

RE: Stefan's original comments about the ECF proxy handling and 
authentication structure...the API supports both proxy and arbitrary 
auth mechanisms for whatever protocol/provider implementation is used 
for the underlying file transfer (http/ftp/efs/bittorrent/etc).  ECF
exposes extension points for adding support for other protocols (e.g. 
private ones like a repository-specific protocol).

RE: defining request handlers externally...I think the current version
of ECFHandler (version I looked at few weeks ago anyway) is overly tied
to a *particular* (default) protocol/provider (http via URLConnection).
 
I think this handler could be abstracted and made pluggable, but I 
haven't yet given much thought to how this would be done as I'm not yet
familiar enough with all the provisioning code to understand the 
external API requirements on request handlers.

Pascal Rapicault wrote:
> In scenarios where size matters, or where only one well-known transport
is
> to be used, the handler give us the ability to remove our dependency
on
> ECF.
> So to me, to know whether or not the handler should be kept, we have
to
> answer the following questions:
>
> * Size
> - Is ECF small enough for scenarios where size matters?
>   

What would be considered 'small enough'?  I know zero bytes of code
is 
best :), but that seems a little 'severe'.  Of course ECF's pluggable
transport nature could be sacrificed and a return to the JRE-provided 
URLConnection could be used instead, but this returns things to the 
state prior to the equinox provisioning work (i.e. bound to a specific
transport...e.g. http).

I guess I'm not clear on what benefit removing the dependency on ECF 
would have other than a fairly small change in code size, and it's costs
(return to lack of flexibility in transports) would be pretty clear.  
Besides, what's the problem?

> - Can the removal of the dependency on ECF be achieved by another
way (for
> example having a new DownloadManager)?
>
> * Pluggability
> - Can any transport be plugged into ECF, if not what is missing from
the
> API?
>   

This is a very important question.  I would assert than any file 
transfer protocol of interest can be plugged into the ECF filetransfer
API...but if this turns out to be wrong for some transport and API 
changes (as opposed to additions) are needed, then I would like to know
about that as soon as possible.

> - How more complex would the handler have to become, which other
> infrastructure would we have to have when ECF is not present (e.g.
how do
> we know which transports are supported)?
>   

I would guess that the handler would have to become significantly more
complex without ECF, because if multiple/pluggable transports are 
desired/required then *some* abstraction has to be introduced to provide
pluggability/flexibility at the transport level.  ECF is essentially
that abstraction.

> - How complex is it to plug a new transport?
>
> * Functionality
> - What does ECF brings us?
>   
I would offer that it provides a consistent API to get pluggable file 
transfer protocols, suspendable/resumeable transfers, and other goals 
for transport pluggability as described here

http://wiki.eclipse.org/Equinox_Provisioning_Plan

...and probably other places.

> - Will ECF be able to overcome its current limitations? Is the ECF
team
> aware of these?
>   
RE: the current (implementation) limitations WRT proxy handling...we have:

https://bugs.eclipse.org/bugs/show_bug.cgi?id=181544
https://bugs.eclipse.org/bugs/show_bug.cgi?id=192286

Beyond these, I'm not exactly clear on what people are suggesting are 
the limitations of ECF API or specific protocol implementations.  If
there are specific limitations (outside the proxy issues) that I/we 
should know about then I would appreciate bug and/or enhancement 
requests.  We are completely able and willing to address any such
limitations as they are identified.

> Can any one take a look at this?
>   

By take a look at this do you mean looking at 
redesigning/reimplementing/generalizing the provisioning request handler
(ECFHandler as current impl) structure or something else?  In either
case, I can probably contribute if that's desired.  But I would like
to 
understand better what the current deficiencies are (beyond full impl 
support for proxy handling).

Scott


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