Writing your own message channel agents

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Overview

WebSphere MQ products allow you to write your own message channel agent (MCA) programs or to install one from an independent software vendor. You might want to do this to make a WebSphere MQ product interoperate over your own, proprietary communications protocol or to send messages over a protocol that WebSphere MQ does not support. (You cannot write your own MCA to interoperate with a WebSphere MQ-supplied MCA at the other end.)

If you decide to use an MCA that was not supplied by WebSphere MQ, you need to consider the following.

Message sending and receiving

You need to write a sending application that gets messages from wherever your application puts them, for example from a transmission queue, and sends them out on a protocol with which you want to communicate. You also need to write a receiving application that takes messages from this protocol and puts them onto destination queues. The sending and receiving applications use the message queue interface (MQI) calls, not any special interfaces.

You need to ensure that messages are delivered once and once only. Syncpoint coordination can be used to help with this.

Channel control function

You need to provide your own administration functions to control channels. You cannot use WebSphere MQ channel administration functions either for configuring (for example, the DEFINE CHANNEL command) or monitoring (for example, DISPLAY CHSTATUS) your channels.

Initialization file

You need to provide your own initialization file, if you require one.

Application data conversion

You will probably want to allow for data conversion for messages you send to a different system. If so, use the MQGMO_CONVERT option on the MQGET call when retrieving messages from wherever your application puts them, for example the transmission queue.

User exits

Consider whether you need user exits. If so, you can use the same interface definitions that WebSphere MQ uses.

Triggering

If your application puts messages to a transmission queue, you can set up the transmission queue attributes so that your sending MCA is triggered when messages arrive on the queue.

Channel initiator

You may need to provide your own channel initiator.

 

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IBM is a trademark of the IBM Corporation in the United States, other countries, or both.