I am using Openfire REST api plugin to use api services. I want to retrieve chat messages and attachments sent/received by a user. I do not see any api to accomplish this task. Can anyone suggest how can i perform the above mentioned activity.
The REST API does not provide such functionality. It primarily facilitates administrative functionality.
You would probably be best served by finding a XMPP library that exposes functionality in an API that is easy for you to consume. A number of great libraries are listed on XMPP | XMPP Libraries & Tools, but others do exist that might be equally useful to you.