Let me take some of that back. If we find an Acknowledgment Message
in persistent storage, we can only reuse it if it is not piggybacked on
another message. Is this really too much complexity? Should we just
create a new Acknowledgment Message? This kind of search probably takes
more cycles then just creating from scratch. . .
Regards,
David Fischer
Drummond Group.
-----Original Message-----
From: David Fischer
[mailto:]
Sent: Tuesday, October 16, 2001
1:40 PM
To: Arvola Chan;
Cc:
Subject: RE: [ebxml-cppa] Comments
on reliable messaging in the 1.0.5 draft
Arvola, I think I need some clarification.
<<comments inline>>
David.
-----Original Message-----
From: Arvola Chan
[mailto:]
Sent: Tuesday, October 16, 2001 12:39
PM
To:
Cc:
Subject: [ebxml-cppa] Comments on
reliable messaging in the 1.0.5 draft
David:
Here are some inlined comments on section
7.5 ebXML Reliable Messaging Protocol.
Regards,
-Arvola
7.5.2
Receiving Message Behavior
If this is an Acknowledgment Message as defined in section 7
then:
1
Look for a message in persistent storage that has a MessageId that is the same as
the value of RefToMessageId on the received
Message
2
If a message is found in persistent storage then mark the
persisted message as delivered
If an AckRequested element is present
that is targeted to a role in which the Receiving MSH is acting (see section
2.2.10 and 2.2.11) then do the following:
1
If the message is a duplicate (i.e. there is a MessageId held in persistent storage that was received
earlier that contains the same value as the MessageId in the received
message) generate an Acknowledgment Message (see section 7).
The Receiving MSH
MUST NOT deliver the message to the application interface.
The above paragraph does not
clearly explain how duplicate request messages are to be handled. The
pointer to section 7 is imprecise. The section 7.5.3 Generating an
Acknowledgment Message also does not provide information on how
Acknowledgment messages for duplicate messages should be generated. The
required information is actually included in section 7.5.2 but in a rather
convoluted form (see below).
<<The second paragraph is
section 7 defines what an Acknowledgment Message is -- which is the
intention of this link.>>
2
If the message is not a duplicate (there
is no MessageId held in persistent storage that corresponds
to the MessageId in the received
message) then do the following:
a
Save the MessageId of the received
message in persistent storage. As
an implementation decision, the whole message MAY be stored if there are
other reasons for doing so
b
Generate an Acknowledgment
Message in response (this may be as part of another message). The Receiving MSH MUST NOT send an Acknowledgment Message until the message has be
safely stored in persistent
storage. Delivery of an Acknowledgment Message constitutes
an obligation by the Receiving
MSH to deliver the message to the application or forward to the next MSH
in the message path as appropriate.
Look in persistent storage for the first response
to the received message (i.e. it contains a RefToMessageId that matches the
MessageId of the received
message).
(1) If a response message was found in persistent storage then resend the
persisted message back to the MSH that sent the received message
The above discussions (in red) are really in the wrong place as the enclosing
item #2 indicates that the message is not a duplicate.
<<we
are not looking for a duplicate here. We are looking to see if a
response (Acknowledgment Message) has previously been sent. If so,
send the same one again. If not, do the following. Maybe it
would help to say "Acknowledgment Message" instead of
"response".>>
(2) If no
response message was found in persistent storage,
then:
(a) if syncReply is set to true and if the CPA indicates an
application response is included, ignore the received message (i.e. no
message was generated in response to the received message, or the processing
of the earlier message is not yet complete)
If the incoming message message is a duplicate and syncReply
is true but no message has been returned in response to the received
message, then it must be the case that processing of the earlier message is
not yet complete. In that case, the received message cannot be ignored.
Instead, it is necessary to wait for completion of the earlier message and
then return the response synchronously. (By the way, this clarification does
not belong in this section because of the inconsistency (cited in red) above.
<<Somehow just saying ignore seems wrong, I know.
However, we certainly do not need to contact the Application and request a
business reply again. Either the first message is still doing that or
the whole thing is hung and there is nothing the MSH can do. I
don't know what else to do besides ignore the resent message and wait
for the completion of the old -- which will send an Acknowledgment when it
is finished (if it ever finishes).>>
(b) Otherwise,
generate an Acknowledgment
Message .
A Receiving
MSH node is NOT participating in the reliable messaging protocol for a
received message if that message either; does not contain an AckRequested element, or does
contain an AckRequested element that is not
targeted at the Receiving MSH,
because it is acting in a role other than that specified in the SOAP
actor attribute of the received message. If the Receiving MSH node is operating as
an intermediary along the message's message path, then it MAY use
store-and-forward behavior. However, it MUST NOT filter out perceived
duplicate messages from their normal processing at that node. (see section
11.2)
7.5.3
Generating an Acknowledgment Message
An Acknowledgment
Message MUST be generated whenever a message is received with an AckRequested element that has a
SOAP actor URI which targets the Receiving MSH node.
As a minimum, it MUST contain a MessageData element with a RefToMessageId that contains the
same value as the MessageId element in the message
being acknowledged and an Acknowledgment element.
The above paragraph contradicts an
earlier statement in section 7.5 (before 7.5.1):
<<agreed. Actually, the RefToMessageId is now
in the Acknowledgment element.>>
An Acknowledgment Message MUST contain
a MessageData element with a RefToMessageId that contains the
same value as the MessageId element in the message being acknowledged and an Acknowledgment element as
described in section 7.3.1.
It is important to reiterate
that the Acknowledgment message must be persisted before being sent. Need to
say something about the persist duration for this message. Presumably, this
can be the same as the persist duration for the incoming message. In fact,
the definition of PersistDuration in section 7.4.6 needs to be expanded to
cover "first response" messages.
<<PersistDuration on the response message should be
the same as on the First Message. OK, persistDuration is an
interval. Is this since the original timestamp or since the timestamp
on the response message?>>
Depending on the value of the syncReply parameter, the Acknowledgment Message can be sent
at the same time as the response to the received message. In this case, the
values for the MessageHeader elements of the Acknowledgment Message are
determined by the Service and Action associated with the
business response.
If syncReply is not specified in
the incoming message or is not applicable to the delivery channel being
used, then the CPA must be consulted to determine the delivery channel that
is suitable for the Acknowledgment action. This delivery channel must not
specify the use of Reliable Messaging!
<<OK, what if there is no CPA? Can I change the
above to say "if there is a CPA,
then...">>
If an Acknowledgment Message is being sent
on its own, then the value of the MessageHeader elements MUST be
set as follows:
·
The Service element MUST be set to:
uri:www.oasis-open.org/messageService/
·
The Action element MUST be set to Acknowledgment.
·
The From element MAY be populated
with the To element extracted from the
message received and all child elements from the To element received SHOULD be
included in this From element.
·
The To element MAY be populated with
the From element extracted from the
message received and all child elements from the From element received SHOULD be
included in this To element.
·
The RefToMessageId element MUST be
set to the MessageId of the message
received.
7.5.6
Failed Message Delivery
If
a message sent with an AckRequested element cannot be
delivered, the MSH or process handling the message (as in the case of a
routing intermediary) SHALL send a delivery failure notification to the From Party. The delivery failure
notification message contains:
·
a From element that identifies the
Party who detected the
problem
·
a To element that identifies the From Party that created the message
that could not be delivered
·
a Service element and Action element set as described
in 4.2.3.3.
·
an Error element with a severity
of:
-
Error if the party who detected
the problem could not transmit the message (e.g. the communications
transport was not available)
-
Warning if the message was
transmitted, but an Acknowledgment
Message was not received. This means the message probably was not
delivered.
·
an ErrorCode of DeliveryFailure
It is possible that an error message with an Error element with an ErrorCode set to DeliveryFailure cannot be
delivered successfully for some reason. If this occurs, then the From Party that is the ultimate
destination for the error message MUST be informed of the problem by other
means. How this is done is
outside the scope of this specification
Note: If the From Party MSH
receives an Acknowledgment Message from the To Party MSH,
it SHOULD ignore all other DeliveryFailure or
Acknowledgment Messages.
If syncReply is in use, then the
error message should be returned synchronously. Otherwise, the CPA needs to
be consulted to determine the appropriate delivery channel for the
MessageError action.
