sub do_rpc {
    my $self = shift;
    if ($self->trace) {
        show_trace(qq[do_rpc: $self: @_]);
    }
    my $method = pop;
    my $request = to_json({ id => $self->{id},
                            method => $method,
                            params => [ @_ ] },
                            { utf8 => 1 });
    if (defined $self->{conn}) {
        print { $self->{conn} } $request, "\n";
        if ($self->trace) {
            show_trace(qq[client: sent: "$request"]);
        }
        $self->{id}++;
        my $response = readline($self->{conn});
        chomp $response;
        if ($self->trace) {
            show_trace(qq[client: rcvd: "$response"]);
        }
        if (defined $response && length $response) {
            my $result = from_json($response, { utf8 => 1 } );
            my $success = 0;
            my $error;
            if (defined $result) {
                if (ref $result eq 'HASH') {
                    if (defined $result->{error}) {
                        $error = to_json( { error => $result->{error} }, { utf8 => 1 } );
                    } else {
                        $success = 1;
                    }
                } else {
                    $error = "illegal JSON reply: $result";
                }
            }
            unless ($success || defined $error) {
                $error = "unknown JSON error";
            }
            if (defined $error) {
                printf STDERR "$0: client: error: %s\n", $error;
            }
            if ($Opt{trace}) {
                print STDERR Data::Dumper->Dump([$result], [qw(result)]);
            }
            return $result;
        }
    }
    $self->close;
    return;
}