IPP Mail Archive: IPP> NOT - 7 issues in the IPPGET spec

IPP Mail Archive: IPP> NOT - 7 issues in the IPPGET spec

IPP> NOT - 7 issues in the IPPGET spec

From: Hastings, Tom N (hastings@cp10.es.xerox.com)
Date: Fri Jul 27 2001 - 20:47:43 EDT

  • Next message: Michael Sweet: "Re: IPP> Duplicate ippget events"

    The IPPGET spec that was sent to the IETF last Friday, 7/20, has 7 issues
    that have been raised since then. I've collected them into a single note
    and sent them to the IPP FAX DL (ifx@pwg.org) for their IPPFAX WG meeting in
    Toronto, August 1. IPPFAX REQUIRES support of IPPGET. However, the IPPGET
    spec is an IPP document, so discussion of it should go on the IPP DL. So
    here are the 7 issues.

    If you have a comment think about whether or not to start a new thread. If
    the comment is just about one issue, I suggest a new thread.

    3. IPPGET Delivery Method (<draft-ietf-ipp-notify-get-04.txt>), I posted
    Monday, 7/23, at:

    ISSUE 01 (see section 12): Should we use application/multiplexed
    (draft-herriot-application-multiplexed-03.txt) which can chunk mime types
    using content lengths, instead of multi-part/related, which uses boundary

    ISSUE 02: For Event Wait Mode, OK to make each successive response after
    the first a complete IPP response, instead of just the Event Notification
    Attributes Groups?

    Then each response looks like a complete response with its own status code.
    Also complete responses might be necessary on some other transport. Also we
    can move the "notify-interval" attribute back to the Operation Attributes
    Group where it belongs, since it applies to all events being returned in
    that response.

    ISSUE 03: OK to clarify that the Per-Job Subscription Object and the
    associated Job object MUST persist after the job completes (job completed,
    canceled, or aborted) in the Job Retention or Job History phases (see
    [RFC2911] section

    Otherwise, a Notification Recipient that is polling would not get the Event
    Notification, if it polled after the job completed, but before the Event
    Lease Time expired.

    ISSUE 04: OK to clarify that a client or a Printer MAY disconnect the
    underlying transport connect for any operation, including the Event No Wait
    Get-Notifications operation and the Event Wait Get-Notifications operation
    when the Printer isn't willing to honor the initial request or reneges in a
    later response?

    So a client could keep the connection open for multiple Event No Wait
    Get-Notifications. Before a Printer disconnects it needs to wait enough
    time to make sure that any IPP response has had time to get back to the
    client before disconnecting, otherwise the client might not see the

    ISSUE 05: OK to add 'successful-ok-events-complete' status code for a
    Get-Notifications response whether Event No Wait or Event Wait mode?

    Here is more detail:

    The Printer MUST return the 'successful-ok-events-complete' status code to
    indicate when this return is the last return for all Subscription objects
    that match the request, whether or not there are Event Notifications being
    returned. This condition occurs for Event Wait Mode Notification Recipients
    waiting for responses when the Subscription Object is: (1) canceled with a
    Cancel-Subscription operation, (2) deleted when the Per-Printer Subscription
    lease time expires, or (3) when the 'job-completed' event occurs for a
    Per-Job Subscription. This condition also occurs for a Get-Notifications
    request that a Notification Recipient makes after the job completes, but
    before the Event Lease Time expires.

    Here is a complete table of combinations of "notify-wait", "status-code",
    "notify-interval", and Event Notification Attributes Groups for
    Get-Notification initial (Wait and No Wait) Responses and subsequent Event
    Wait Mode Responses (which may be staying in Wait Mode or may be requesting
    the Notification Recipient to leave Wait Mode):
      client sends: Printer returns: Notification
      "notify-wait" "status-code" "notify-get-interval" Attribute Groups
      ------------- ------------- --------------------- ----------------
    1.'false'/omitted 'successful-ok' MUST return N maybe
    2.'false'/omitted 'not-found' MUST NOT MUST NOT
    3.'false'/omitted 'busy' MUST return N MUST NOT
    4.'false'/omitted 'events-complete' MUST NOT 'job-completed'

    5. 'true' 'not-found' MUST NOT MUST NOT
    6. 'true' 'busy' MUST return N MUST NOT
    7. 'true' 'successful-ok' MUST NOT MUST
    8. 'true' 'successful-ok' MUST return N maybe
    9. 'true' 'events-complete' MUST NOT 'job-completed'
                                                              or maybe other
    1-4: client requests Event No Wait
    5-9: client request Event No Wait
    2,5: Subscription object not found, or was canceled earlier; client should
    NOT try again.
    3,6: server busy, tells client to try later; client should try again in N
    4: client polled after job completed, but before Event Lease Time expired,
    and got the 'job-completed' event, so the client shouldn't bother trying
    again; client should NOT try again later.
    7: Printer returns one or more Event Notifications and is ok to stay in
    Event Wait Mode; the client waits for more.
    8: Printer wants to leave Event Wait mode. Can happen on the first
    response (with events) or happen on a subsequent response with or without
    Event Notifications; the client should try again in N seconds.
    9. Printer either (1) returns 'job-completed' event or (2) the Subscription
    Object was canceled by either a Cancel-Job or a Per-Printer Subscription
    expired without being renewed. For case (1), at least one event MUST be
    returned, while for case (2), it is unlikely that any Events are returned;
    the client should NOT try again.

    ISSUE 06: Section 12 says: "The Printer MAY chunk the responses, but this
    has no significance to the IPP semantics." Is this sufficient, or is
    HTTP/1.1 chunking REQUIRED in order to support the multi-part/related MIME

    ISSUE 07: For Event No Wait mode, should we add a way for the Notification
    Recipient to have the Printer filter out returning Event Notifications that
    the Notification Recipient has already received in order to reduce the
    duplicates (that will usually happen, else events will be lost)? Or should
    we just depend on most usage using Event Wait Mode, so that there aren't
    duplicates? It has been suggested on the mailing list that the Notification
    Recipient could supply pairs of the "notify-sequence-number" and
    "subscription-id" and the Printer would only return events with a higher
    sequence number.


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