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

Hi all,

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- .

As suggested in a previous mail about how to handle with both protocol 
versions, I'm trying first to connect using version 3.0. The problem is 
if the server is a 7.3 or earlier, it would answer with a non supported 
protocol error message, but as I'm in the protocol 3.0 version mode, I 
would expect a error message in the new format and not in the 2.0 format.

How I could handle it?

I know this error happens early in the connection establishment, when I 
send the StartupPacket and I could use this info to do some choices 
about when to use the version 2 or 3. The problem is that I also could 
get a lot of errors when sending the startup packet, as password 
incorrect, database and others.

I was thinking about examining the first 4 bytes ( as this is where the 
message length is located) and try if these bytes could be translated to 
"FATA" which would mean the "FATAL:  unsupported frontend protocol\n" 
error.  But I think this would be a big hack. Is there a more elegant 
solution?


I know this question was alread raised some time ago, but I couldn't 
find it.

Thanks in advance.


-- 
Regards,

Francisco Figueiredo Jr.

------
"My grandfather once told me that there are two
kinds of people: those
who work and those who take the credit. He told me
to try to be in the
first group; there was less competition there."
- Indira Gandhi

"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

Tom Lane wrote:

> "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.
> 

Yes, I'm prepared, but the problem is how can I in advance know which 
format the message is, as I'm expecing a 3 version and comes a 2 version 
error message?
Uhmmmm, I could see in the following line in libpq how it does it:
if (beresp == 'E' && (msgLength < 8 || msgLength > 30000))

So this is how it checks ahead, if the value is very large, the 
msgLength would be bigger than 30000 and this would mean a string error 
and so the 2.0 version error message. I think I will get this approach too.

Thanks Tom Lane.




>             regards, tom lane
> 


-- 
Regards,

Francisco Figueiredo Jr.

------
"My grandfather once told me that there are two
kinds of people: those
who work and those who take the credit. He told me
to try to be in the
first group; there was less competition there."
- Indira Gandhi