Channel-exit programs
If you want to do some additional processing (for example, encryption or
data compression) you can write your own channel-exit programs, or sometimes
use SupportPacs. The Transaction Processing SupportPacs library for WebSphere MQ is
available on the Internet at URL:
WebSphere MQ calls channel-exit programs at defined places in the processing carried
out by the MCA. There are six types of channel exit:
- Security exit
- Used for security checking, such as authentication of the partner.
- Message exit
- Used for operations on the message, for example, encryption prior to
transmission.
- Send and receive exits
- Used for operations on split messages, for example, data compression
and decompression.
- Message-retry exit
- Used when there is a problem putting the message to the destination.
- Channel auto-definition exit
- Used to modify the supplied default definition for an automatically
defined receiver or server-connection channel.
The sequence of processing is as follows:
- The security exits are called after the initial data negotiation between
both ends of the channel. These must end successfully for the startup phase
to complete and to allow messages to be transferred.
- The message exit is called by the sending MCA, and then the send exit
is called for each part of
the message that is transmitted to the receiving MCA.
- The receiving MCA calls the receive exit when it receives each part of
the message, and then calls the message exit when the whole message has been
received.
This is illustrated in Figure 10.
The message-retry exit is used to determine how
many times the receiving MCA will attempt to put a message to the destination
queue before taking alternative action.
For more information about channel exits, see Channel-exit programs.