Hello Sandeep,
Lets address the things one-by-one.
For the 1st mapping, you will have a Async Outbound interface and Sync Inbound interface. As it is Async to Sync scenario, there would be no issues for you to map the file structure to web-service request structure.
I have done it already in SAP PO 7.4 and i haven't faced any issues. As XSD of web-service will have 2 different messages for Request and Response and you can use any one of them in your message mapping. Hence use request structure of the web-service as your target in the 1st mapping.
Now configure the RRB in your receiver channel and in the RRB Service Interface parameters, please mention the new Async outbound interface name. This Aysnc outbound interface must have the structure of Web-service response.
Now, create a mapping Web-service response structure as your source and your proxy interface structure as target. As both the interface are async here, there should not be any problem in assigning the mapping.
Hence in total you need to have 4 interfaces.
1. Async Outbound for File structure
2. Sync Inbound for Web-service
3. Async Outbound for Web-service response structure (this is the extra interface)
4. Async Inbound for proxy interface structure
Regards,
Nitin