How to determine server's decoding capability before sending entity?

Hi, all.

Before sending a POST request to HTTP/1.1 server, whose body is encoded in
the coding defined by Content-Encoding header, how do I know the server's
capability to decode the request's body?

HEAD method seems to be only for GET method, and response for OPTIONS
request may not return any information about that.

It is the only way that receive 415 Unsupported media type after sending
the request with the body?

Thanks in advance.