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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). 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. (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. (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): 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. 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 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. |
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