New issue: Unitialized Partner Links

["Monica J. Martin" <Monica.Martin@Sun.COM>]

Background: Questions were raised if it is valid to have partnerLinks 
declared in a BPEL process which are not referenced by any messaging 
activity (receive, invoke, onMessage, onEvent, etc) whereby they are 
declared but not referenced. If they are to be used, they need to be 
initialized to be used (and of course referenced in a message activity). 
The specification talks about in Section 6.2 that partner links can be 
dynamically bound outside of the process as well. If the partner role is 
uninitialized a fault will occur (see Section 10.3):

    If an <invoke> activity is used on a partnerLink whose partnerRole
    EPR is not initialized then a bpel:uninitializedPartnerRole fault
    MUST be thrown."

In reviewing this question, we uncovered a potential gap when copying 
one partner link to another in an assign where a partnerLink role is 
unitialized. 
                                                                              


Example:
<?xml version="1.0" encoding="utf-8" ?>
<process name="fhMatchingCatches1"
targetNamespace="http://www.seebeyond.com/eInsight/MatchingCatches1";
   xmlns:tns="http://www.seebeyond.com/eInsight/MatchingCatches1";   
xmlns:bpel="http://schemas.xmlsoap.org/ws/2004/03/business-process/";>   
xmlns:ns0="http://stc.com/FaultTest/MatchingCatches1";
   xmlns="http://schemas.xmlsoap.org/ws/2004/03/business-process/";>
   <import namespace="http://stc.com/FaultTest/MatchingCatches1";
   location="MatchingCatches1.wsdl"
   importType="http://schemas.xmlsoap.org/wsdl/";></import>
   <partnerLinks>
       <partnerLink name="faulttestLink" partnerLinkType="ns0:SLT" 
myRole="server"/>
       <partnerLink name="unusedPartnerLink1" partnerLinkType="ns0:PLT2" 
myRole="role1"/> <!-notice that these are not used
       in the business process -->             
       <partnerLink name="unusedPartnerLink2" partnerLinkType="ns0:PLT3" 
partnerRole="role2"/>
   </partnerLinks>
    <variables>
       <variable name="MatchingCatches1_Output" 
messageType="ns0:FaultTest"></variable>
       <variable name="MatchingCatches1_Input" 
messageType="ns0:FaultTest"></variable>
    </variables>   
   <sequence>
      <receive name="MatchingCatches1" partnerLink="faulttestLink" 
portType="ns0:FaultTest" operation="MatchingCatches1"            
variable="MatchingCatches1_Output" createInstance="yes"/>
      <assign name="Assign">
           <copy>
               <from>&apos;Scenario Passes Thru&apos;</from>
               <to>$MatchingCatches1_Input.part/retString</to>
           </copy>
      </assign>
       <reply name="Reply"
       partnerLink="faulttestLink" portType="ns0:FaultTest"
           operation="MatchingCatches1"
           variable="MatchingCatches1_Input"/>
   </sequence>                        

Use case: One use case was identified that may explain why this was 
allowed (if only indirectly): A partner link (not used by any messaging 
activity) can be used as the source for an endpoint reference. A set of 
unused partner links, and some BPEL logic to choose one of them to be 
assigned to a partner link that is actually used. The unused partner 
links would be bound to concrete addresses during deployment.

<process>
  partnerLink alpha
  partnerLink beta
  partnerLink gamma
  sequence    ...
    if some-condition
      assign from beta to alpha
    else
      assign from gamma to alpha
    invoke operation bar on alpha ...
</process>

However, the example and use case uncover the potential gap. 
UninitializedVariable and UnitializedPartnerRole faults exist but 
neither really applies to copying one partner link to another in an 
assign. What if we execute:
  assign from beta to alpha

And, beta (for the selected EPR) is not initialized? The 
UninitializedVariable fault still works, but Variables are distinction 
from PartnerLinks in BPEL. This is a problem that exists and should be 
addressed regardless of the declaration and referencing question that 
prompted this discovery. 
                                                                                                                        
Question: In Section 12, we discuss partner links in several contexts, 
such as for example, that any partner links defined in the <scope> must 
be set before variables defined in the same <scope> whose initialization 
logic refers to those partner links. However, unless identified, I don't 
see any restrictions for a partner link to be declared but remain 
unused, nor any restrictions on assignment.

Conceptual Proposal: Suggest we consider two explicit restrictions that 
specify that it is invalid: 1) to have partnerLinks declared in an 
executable BPEL process which are not referenced by any messaging 
activity (receive, invoke, onMessage, onEvent, etc). If they are to be 
used, they need to be initialized to be used. 2) for an assignment from 
an uninitialized partnerLink role. It causes an UninitializedVariable fault.