ServerCall.Listener<RequestT> startCall(ServerCall<RequestT,ResponseT> call, Metadata headers)
nulllistener for the incoming call. Implementations are free to call methods on
callbefore this method has returned.
Metadata is not thread-safe, the caller must not access (read or write)
headers after this point.
If the implementation throws an exception,
call will be closed with an error.
Implementations must not throw an exception if they started processing that may use
call on another thread.
call- object for responding to the remote client.