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From "Timothy Bish (JIRA)" <>
Subject [jira] [Closed] (AMQ-5453) AMQP interop: Active broker does not respect the "drain" flag.
Date Fri, 27 Mar 2015 15:03:54 GMT


Timothy Bish closed AMQ-5453.
       Resolution: Duplicate
    Fix Version/s: AMQ-5413

Closing this as it is directed at the ACTIVEMQ6 project which has an open issue covering this
and a 5.x bug is already open AMQ-5413

> AMQP interop: Active broker does not respect the "drain" flag.
> --------------------------------------------------------------
>                 Key: AMQ-5453
>                 URL:
>             Project: ActiveMQ
>          Issue Type: Bug
>          Components: AMQP
>    Affects Versions: 6.0.0
>            Reporter: Alan Conway
>             Fix For: AMQ-5413
> The drain flag on the AMQP flow performative allows a client to request confirmation
that it has received the last available message that it has credit to receive.
> To reproduce using the qpid-send, qpid-receive clients from
Create a JMS queue 'foo' on the active broker then run:
> $ qpid-send -a -b localhost:5455 --content-string XXX --connection-options='{protocol:amqp1.0}'
> $ qpid-receive -a -b localhost:5455 --connection-options='{protocol:amqp1.0}'
--log-enable trace+:Protocol
> qpid-receive hangs, the  last line of output is:
> 2014-11-24 15:15:46 [Protocol] trace [58e8ee08-0f33-426b-b77a-450f7c3d976c]: 0 ->
@flow(19) [next-incoming-id=2, incoming-window=2147483647, next-outgoing-id=0, outgoing-window=0,
handle=0, delivery-count=1, link-credit=1, drain=true]
> This shows that qpid-receive sent a flow with drain=true but never received a response.
> Why is this important? Without the drain flag it is impossible for a client to implement
the simple behavior "get the next message" correctly. The flow response tells the client immediately
"there are no more messages available for you". Without it the client can only use a timeout
which is unreliable (if too short the client may give up while the message is in flight) and
inefficient (if too long the client will wait needlessly for messages that the broker knows
are not presently available)
> The spec 2.6.7 is a little ambiguous about whether this is a SHOULD or a MUST behavior
but without it it is impossible to implement the use cases described in the following section.
> AMQP 1.0 specification 2.7.6
> drain
> The drain flag indicates how the sender SHOULD behave when insufficient messages are
available to consume the current link-credit. If set, the sender will (after sending all available
messages) advance the delivery-count as much as possible, consuming all link-credit, and send
the flow state to the receiver. Only the receiver can independently modify this field. The
sender's value is always the last known value indicated by the receiver.
> If the link-credit is less than or equal to zero, i.e., the delivery-count is the same
as or greater than the delivery-limit, a sender MUST NOT send more messages. If the link-credit
is reduced by the receiver when transfers are in-flight, the receiver MAY either handle the
excess messages normally or detach the link with a transfer-limit-exceeded error code.
> Figure 2.40: Flow Control
>      +----------+                                    +----------+
>      |  Sender  |---------------transfer------------>| Receiver |
>      +----------+                                    +----------+
>       \        / <----------------flow--------------- \        /
>        +------+                                        +------+
>           |
>           |
>           |
>  if link-credit <= 0 then pause 
> If the sender's drain flag is set and there are no available messages, the sender MUST
advance its delivery-count until link-credit is zero, and send its updated flow state to the

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