Can device act as CoAP service and client at the same time?

[waatff]

Hi!
I want to write some software utilizing OpenThread and CoAP. I've seen samples of coap server and coap client in NCS. However, I want to ask whether it's possible or not for a device to act as CoAP server and client simultaneously?

My nRF Connect's version is v2.4.0 and I'm using nrf52840dk for prototyping.

[Achim Kraus]

For CoAP in general, that's possible and called "role-exchange". The message format for request and responses is the same, only the "code" uses different values for requests and responses. But I don't know, If the specific implementation used there supports it.

[ArunRuchir]

Hi,

Upon searching I got this and have some specific need to make CoAP Server send some very specific data to OTBR (or other server). This will be once in a while and not regular. 
So,can some one guide how to make a CoAP Server becoming CoAP client momentarily and back to server ? 

Regards

Arun

[Achim Kraus]

In general, UDP sockets are always acting as server&client at the same time. CoAP messages are also designed to act as both request and response, the only difference is the contained code, 0.xy is a request, 2.xy a success response, 4.xy a client error, and 5.xy a server error. So, it's easy to send&receive UDP massage with the same socket, you pass the received messages to the parser and then you check the code and split it.

I just don't know, if the zephyr's coap client&server are able to do so, I mainly use the message encoding and parsing, but not the message handling of zephyr.