Re: Protocol de-synchronisation bug, bogus query sent

On 06/19/2014 06:44 AM, Craig Ringer wrote:
> The whole code block around connection.c:3082 appears to be attempting
> to send an empty query in order to elicit an 'I' (EmptyQueryResponse)
> message. It sends a malformed protocol message:
>
> SOCK_put_string(self->sock, "Q ");
> SOCK_flush_output(self->sock);
>
> so the server just waits for the rest of the message, never responding.
>
> When the connection is killed by program exit later, the server will log:
>
> LOG: unexpected EOF within message length word
> LOG: disconnection: session time: 0:00:08.910 user=Administrator
> database=XXXX host=127.0.0.1 port=53705
> LOG: could not receive data from client: No connection could be made
> because the target machine actively refused it.
>
>
> That's because the V3 protocol specifies that the message format for
> Query is:
>
> 'Q'
> [32 bit integer]
> [query string]
>
> http://www.postgresql.org/docs/current/static/protocol-message-formats.html
>
> ... but psqlODBC just sends:
>
> 'Q'
> '\x20'
> '\x00'
>
> If it is really necessary to go through this empty-query dance, then for
> the V3 protocol the correct message would be:
>
> /* Send an empty query to elicit an 'I' (EmptyQueryResponse)
> * from the server */
> SOCK_put_char(self->sock, 'Q');
> SOCK_put_int(self->sock, 5, 4);
> SOCK_put_char(self->sock, '\0');

Hmm. Just before that code, there's this:

> if (!beforeV2)
> break;

So we shouldn't even get there with protocol version 3. But if you
managed to hit that, apparently we do. Can you debug that further?
- Heikki