Re: libpq support for NegotiateProtocolVersion

On 14.11.22 19:11, Jacob Champion wrote:
>> If we want to address this, maybe this should be handled
>> in the polling loop before we pass off the input buffer to the
>> per-message-type handlers.
>
> I thought it was supposed to be handled by this code:
>
>> /*
>> * Can't process if message body isn't all here yet.
>> */
>> msgLength -= 4;
>> avail = conn->inEnd - conn->inCursor;
>> if (avail < msgLength)
>> {
>> /*
>> * Before returning, try to enlarge the input buffer if
>> * needed to hold the whole message; see notes in
>> * pqParseInput3.
>> */
>> if (pqCheckInBufferSpace(conn->inCursor + (size_t) msgLength,
>> conn))
>> goto error_return;
>> /* We'll come back when there is more data */
>> return PGRES_POLLING_READING;
>> }
>
> But after this block, we still treat EOF as if we need to get more data.
> If we know that the message was supposed to be fully buffered, can we
> just avoid the return to the pooling loop altogether and error out
> whenever we see EOF?

I agree this doesn't make sense together. Digging through the history,
this code is ancient and might have come about during the protocol 2/3
transition. (Protocol 2 didn't have length fields in the message IIRC.)

I think for the current code, the following would be an appropriate
adjustment:

diff --git a/src/interfaces/libpq/fe-connect.c
b/src/interfaces/libpq/fe-connect.c
index 746e9b4f1efc..d15fb96572d9 100644
--- a/src/interfaces/libpq/fe-connect.c
+++ b/src/interfaces/libpq/fe-connect.c
@@ -3412,8 +3412,7 @@ PQconnectPoll(PGconn *conn)
/* Get the type of request. */
if (pqGetInt((int *) &areq, 4, conn))
{
- /* We'll come back when there are more data */
- return PGRES_POLLING_READING;
+ goto error_return;
}
msgLength -= 4;

And then the handling of the 'v' message in my patch would also be
adjusted like that.