Re: Handling protocol not supported error message when working with protocol 2 and 3

"Francisco Figueiredo Jr." <fxjrlists@yahoo.com.br> writes:
> I'm finishing the implementation of the protocol 3.0 and now I'm working 
> in how to connect to server using protocol 3.0 when the server doesn't 
> support it 7.3- .

I'd suggest using the same methods libpq does.  You do have to be
prepared to accept an old-format error message.
        regards, tom lane