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Usage notes

 

1. The function performed by the channel exit is defined by the provider of the exit. The exit, however, must conform to the rules defined here and in the associated control block, the MQCXP.

2. The ChannelDefinition parameter passed to the channel exit may be one of several versions. See the Vfield in the MQCD structure for more information.

3. If the channel exit receives an MQCD structure with the Vfield set to a value greater than MQCD_VERSION_1, the exit should use the ConnectionName field in MQCD, in preference to the ShortConnectionName field.

4. In general, channel exits are allowed to change the length of message data. This may arise as a result of the exit adding data to the message, or removing data from the message, or compressing or encrypting the message. However, special restrictions apply if the message is a segment that contains only part of a logical message. In particular, there must be no net change in the length of the message as a result of the actions of complementary sending and receiving exits.

   For example, it is permissible for a sending exit to shorten the message by compressing it, but the complementary receiving exit must restore the original length of the message by decompressing it, so that there is no net change in the length of the message.

   This restriction arises because changing the length of a segment would cause the offsets of later segments in the message to be incorrect, and this would inhibit the queue manager’s ability to recognize that the segments formed a complete logical message.

 

Parent topic:

MQ_CHANNEL_EXIT – Channel exit

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