Should we go ahead and rename XxxConfiguration to XxxServer then?  I'm still trying to get
back in the groove on this stuff - looking at the code now.  I'll comment more on the issues
you mentioned later regarding creating filters.  I have a feeling those wrappers you created
may come in handy for setting up the chain giving us another degree of freedom.

Alex

On 10/11/07, David Jencks < david_jencks@yahoo.com> wrote:
After a lot of discussion on IRC with Alex we think we have an approach we like for providing the acceptors to the servers, so i coded most of it up and committed it (rev 583683).  Lets see if I can describe it:

- the acceptors get to be components, and they each get a reference to a thread pool (Executor).
- there's a DatagramAcceptor and a SocketAcceptor, so the server can be sure to get the kind it expects.
- these wrap the Mina acceptor classes to
-- install a final filter
-- assure that some parts of the IoAcceptorConfiguration are configured correctly (right now, that ThreadModel.MANUAL is set which appears to mean we are using an external thread pool)

Each server has 2 (will be one for non-udp protocols such as ldap) Acceptor references.  On start it binds stuff at its port to the acceptor and on stop it unbinds.  It supplies a (partially configured) IoAcceptorConfiguration to the bind method along with the actual protocol handler and the address to bind to.

We were thinking of allowing configuration of a non-default AcceptorConfiguration through spring which code-wise would be pretty easy but would be much easier with xbean-ization of mina.  Alex added the xbean tags and pushed snapshots of mina and I added an experimental mina-xbean-spring module to apacheds to build the xbean fluff.  NOTE THAT this new module uses mina 1.1.4-SNAPSHOT whereas everything else uses mina 1.1.2, so to use xbeanized mina components we need to adjust the mina version.  We're hoping the mina guys will pick this up and move it to the mina project.

Among other side effects the ApacheDS module isn't needed in the servers I've worked on (everything except ldap and ldaps AFAICT). 

Alex thought that the filters in one of these acceptors ought to be configurable by spring but looking into it more I don't quite see how.... it looks like we'd need a filter factory rather than a list of filters.  We could presumably take a list of filters and add them to the factory one by one as we do with the final filter now.  I might be missing something here since I haven't looked at the mina code at all.

One bit left to do is renaming the XXXConfiguration to XXXServer or something more appropriate and checking to see if anything can be pruned.

Of course comments are more than welcome...

thanks
david jencks

On Oct 10, 2007, at 1:00 PM, Alex Karasulu wrote:

Hi David,

On 10/10/07, David Jencks < david_jencks@yahoo.com> wrote:

On Oct 10, 2007, at 11:35 AM, Alex Karasulu wrote:

Ok I had some sleep and low and behold the ideas came to me :).  I think I have a clear picture of
what we need to do to handle this properly.  Let me describe that here then try to figure out how
that fits with what you have done and described below.

First if Emmanuel is right about NTP needing both protocol end points on the same port for both
transport protocols (UDP/TCP) then there is no need to have twice the configuration. Then
something like these combinations would suffice:

<ntpServer port=123>
   <#directoryService/>
   <#udpAcceptor/>
   <#tcpAcceptor/>
</ntpServer>

Configures both UDP and TCP transports on port 123.

<ntpServer port=123>
   <#directoryService/>
   <#tcpAcceptor/>
</ntpServer>

Configures only TCP on port 123.

<ntpServer port=123>
   <#directoryService/>
   <#udpAcceptor/>
</ntpServer>

Configures only UDP on port 123.

Note that I did not pass in <#apacheDS/> which is not needed since this service will depend on the
core directory service plus the MINA components.  Depending on which IoAcceptor is set the respective
transport protocol is used.  If both are set then both transports are to be used.

So instead of having the NtpServer class just deal with setting up a single endpoint for one transport
protocol it will handle all endpoints for all transport protocols and no more configuration bean.  The
component is wired directly but how it's wired determines what is enabled.

In order to make this work and still be typesafe we either have to:

I like the idea of making it type safe.  This can be achieved by making getter/setter pairs for specific
transport types on the XxxServer use more specific interfaces that are already present in MINA:

DatagramAcceptor or
SocketAcceptor

This would best settle the type safety issue IMO.

- create different classes for the tcp and udp IoAcceptor instances so you can't hook up the wrong one

They already exist as stated above so this option is best I think.  WDYT?

or

- wrap the IoAcceptor get the appropriate BaseIoAcceptorConfig from the wrapper.  This would work if all uses of udp use the same acceptor config and all uses of tcp use the same tcp config.  I'm not qualified to guess if this is the case now and in the forseeable future.  In this case the XXXServer class (currently typically XXXConfiguration) could get a list of IoAcceptorwrapper objects instead of just one or two.

Another aspect I don't know about here is exactly how MINA distributes threads between udp and tcp.  My guess is that MINA has a thread pool that it uses for all incoming requests, whether udp or tcp. 

Yes this is the case.  We have two pools: one for the logical request handling and one for the protocol
codec IO handling.  A thread from one pool hands off the req/resp object to the other.

If we want to preserve a single thread pool for all requests this may take some hoop-jumping-through with separate configuration of the tcp and udp IoAcceptors.  On the other hand I've heard rumors that you can get spring to call a method and use the result as the reference value, so we might be able to do something with  that and preserve a single MinaBean.


Anyway if someone wants to explain the desired model here or point me to docs that would be great.

I have some ideas but I'm not so confident.  You're right about more experimentation being needed.  Slowly as we
chug along and get rid of these distracting issues of configuration we'll be able to best move the MINA component
assembly out of the ApacheDS object.
If the other protocols obey the same requirements where both transport endpoints are needed on the
same port then we can follow this same pattern.  We just have to watch for the special cases if they
do exist. 

Now what impact does this have on OSGi and on configuration in DIT for the future.  I don't know that
yet and it's something to think about.

Ok now inline for discussing your changes ...

On 10/10/07, David Jencks <david_jencks@yahoo.com > wrote:
In rev 583375  I moved all the non-ldap protocol servers into independent components and provided 2 NTP implementations as a basis for further discussion.

Ok so you broke it out to have a UdpNtpServer and a TcpNtpServer which are in them selves what you
deem one implementation approach I guess right?

Then there is this NtpConfiguration which starts both together as a configuration bean + manager for the
other two services?

NtpConfiguration illustrates the approach of a single component to configure both udp and tcp versions of the same protocol.  This could trivially be enhanced with flags to enable/disable the tcp or udp choices.  If we decide on this approach I would rename the class NtpServer.

server.xml configuration of this looks like:

  <ntpConfiguration ipPort="80123">
    <apacheDs>#apacheDS</apacheDs>
  </ntpConfiguration>

Ok then this would be close to what I was pointing out above but it uses this ApacheDS reference
instead of feeding in the MINA components.  I would like to see these configuration objects go away
all together without even the ServiceConfiguration base class.  Instead an AbstractServer object can
be defined and used for server implementations like NtpServer with the base configuration details in
it.

This way we don't have a configuration bean + additional code to start and stop subordinate services.
So let me list it out:

AbstractServer (or AbstractService )

    Replaces ServiceConfiguration as base class for protocol servers.  This is the common
    denominator for all servers running in ApacheDS.  It may need some properties moved
    into some subtypes since the present ServiceConfiguration has more than the common
    denominator. 

Is this any different from renaming ServiceConfiguration to AbstractService?  I tried to avoid extra renamings since I thought it would make the actual changes into components harder to see.

Well there might be more to it like removing some properties that are not common across the board but
yes this is what it looks like is going to happen.  However note that now the semantics are clear that what
is being wired is the actual component and not just a bean used to hold configuration information.  Subtypes
of that server/service will now hold the logic and structures to manage the runtime state of the component.
I think that's the main goal with this whole get rid of configuration beans effort.

SNIP ...

Alex