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From Gregg Wonderly <ge...@cox.net>
Subject Re: OSGi
Date Thu, 26 Jan 2017 02:04:28 GMT
This would be a DHCP like lease scheme.

Gregg

> On Jan 25, 2017, at 7:30 PM, Michał Kłeczek (XPro Sp. z o. o.) <michal.kleczek@xpro.biz>
wrote:
> 
> I also think about adding leasing to the scheme.
> If CodeBaseModule can be leased (and the client is capable of handling declines of lease
renewals) - it would be quite straightforward to implement auto-upgrade: the lease for a module
"mymodule" ver 1.1 expires and you have to ask the code server for a new CodeBaseModule -
which in turn could return a newer patched version of it.
> 
> Cheers,
> Michal
> 
> Michał Kłeczek (XPro Sp. z o. o.) wrote:
>> So for a client and a service to be able to communicate they must agree on a common
set of interchangeable CodeRepositories that would allow them to have a common understanding
of names.
>> In other words - to be able to work - any party first has to contact a CodeRepository
that can authenticate itself as a particular principal. The issue is that to find the CodeRepository
one needs to communicate with ServiceRegistrar. And to communicate with ServiceRegistrar you
need a CodeRepository!!!. So there needs to be some bootstrapping in place:
>> - either ServiceRegistrar and CodeRepository constitute as single entity
>> - there is a bootstrap well known CodeRepository (Maven central?) - its implementation
is based on a well known URL and its implementation code is shipped with the framework.
>> 
>> Thanks,
>> Michal
>> 
>> Michał Kłeczek (XPro Sp. z o. o.) wrote:
>>> Honestly - since I am fixed ( :-) ) on having mobile code treated as any other
object - I see it something like:
>>> 
>>> interface CodeBaseModule {
>>>   ClassLoader createLoader() throws AnyImportantException;
>>> }
>>> 
>>> interface CodeRepository {
>>>   CodeBaseModule getCodeBaseModule(String name, Version version);
>>>   boolean isSameNamespace(CodeRepository other);
>>> }
>>> 
>>> class NamedCodeBase {
>>>   String name; Version version; 
>>>   CodeRepository repository;
>>>   boolean equals(Object other) { //check name, version and repo }
>>> }
>>> 
>>> Now the question is about the implementation of "isSameNamespace". Since the
protocol(s) to access code repository might differ (and there might be multiple available
at the same time), location based equality won't work (although is the easiest to implement).
My rough idea is for the CodeRepository to be able to authenticate as any of a set of Principals
( ie. satisfy the ServerMinPrincipal constraint ). Two CodeRepository instances are interchangeable
if intersection of their principal sets is non-empty.
>>> 
>>> At first I thought about having a global naming scheme - then cryptographic hash
would constitute the part of the name. But that would make names obscure and difficult to
remember and write by hand.
>>> So I came up with an idea to abstract it away - according to "all problems in
CS can be solved by introducing another level of indirection" :)
>>> 
>>> Thanks,
>>> Michal
>>> 
>>> Peter wrote:
>>>> codebase identity
>>>> 
>>>> So River codebase identity is currently any number of space delimited RFC
3986 normalised URI strings.
>>>> 
>>>> httpmd uses a location filename and message digest.
>>>> 
>>>> But should location be part of identity?  How can you relocate a codebase
once remote objects are deployed?
>>>> 
>>>> OSGi and Maven use a name and version to identify a codebase.  
>>>> 
>>>> Might we also need codebase signers (if any) to be part of identity?
>>>> 
>>>> If no, why not and if yes why?
>>>> 
>>>> Regards,
>>>> 
>>>> Peter.
>>>> 
>>>> Sent from my Samsung device.
>>>>  
>>>>   Include original message
>>>> ---- Original message ----
>>>> From: "Michał Kłeczek (XPro Sp. z o. o.)" <michal.kleczek@xpro.biz>
<mailto:michal.kleczek@xpro.biz>
>>>> Sent: 26/01/2017 08:30:58 am
>>>> To: dev@riverapache.org <mailto:dev@riverapache.org>
>>>> Subject: Re: OSGi
>>>> 
>>>> I haven't been aware of ObjectSpace Voyager. I just briefly looked at it
 
>>>> and it seems like it is based on Java 1.x (ancient beast) and - as I  
>>>> understand it - the issues you describe are mainly caused by having only
 
>>>> a single class name space (single ClassLoader). 
>>>> 
>>>> But sending IMHO class bytes in-band is not necessary (nor good). 
>>>> 
>>>> What is needed is: 
>>>> 1. Encoding dependency information in codebases (either in-band or by  
>>>> providing a downloadable descriptor) so that it is possible to recreate 

>>>> proper ClassLoader structure (hierarchy or rather graph - see below) on 

>>>> the client. 
>>>> 2. Provide non-hierarchical class loading to support arbitrary object  
>>>> graph deserialization (otherwise there is a problem with "diamond  
>>>> shaped" object graphs). 
>>>> 
>>>> A separate issue is with the definition of codebase identity. I guess  
>>>> originally Jini designers wanted to avoid this issue and left it  
>>>> undefined... but it is unavoidable :) 
>>>> 
>>>> Thanks, 
>>>> Michal 
>>>> 
>>>> Gregg Wonderly wrote: 
>>>>>  That’s what I was suggesting.  The code works, but only if you put
the required classes into codebases or class paths.  It’s not a problem with mobile code,
it’s a problem with resolution of objects in mobile code references.  That’s why I mentioned
ObjectSpace Voyager.  It automatically sent/sends class definitions with object graphs to
the remote VM. 
>>>>> 
>>>>>  Gregg 
>>>>> 
>>>>>>  On Jan 23, 2017, at 3:03 PM, Michał Kłeczek (XPro Sp. z o. o.)<michal.kleczek@xpro.biz>
<mailto:michal.kleczek@xpro.biz>  wrote: 
>>>>>> 
>>>>>>  The problem is that we only support (smart) proxies that reference
only objects of classes from their own code base. 
>>>>>>  We do not support cases when a (smart) proxy wraps a (smart) proxy
of another service (annotated with different codebase). 
>>>>>> 
>>>>>>  This precludes several scenarios such as for example "dynamic exporters"
- exporters that are actually smart proxies. 
>>>>>> 
>>>>>>  Thanks, 
>>>>>>  Michal 
>>>>>> 
>>>>>> 
>>>> 
>>>> 
>>>> 
>>>> 
>>> 
>> 
> 


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