auto login protocol retry (was Re: ignore --tdsver)

Bob,
You bring up an interesting point.

There may be some sites that model what a 'good' application does.   Hunting with a number 
of rejected requests from the same source server may look like an unauthorized probe.

Explaining why a previously vetted application has changed behavior that now violates site 
policy would tend to inhibit acceptance of the new release.


James,
   Would you consider the auto login feature not be compiled in unless the package builder
   specifies a configure option to use it?

   Benefits for making auto login feature configured at build time only include:
   1. Increased confidence in the user community that using the new release does not 
produce unexpected changes in behavior.  This will tend to speed migration to the new release.

   2. There is a low probability that the un-compiled feature can be blamed for some error.

   3. Any proven existing troubleshooting procedure might be vetted with minimal change.

   4. Applications linked to the new release are not likely to leverage the un-compiled
      feature for malicious intent nor suspicious mistake.

   5. Re-qualifying existing applications built to the new release is easier when existing 
test plans are not required to cover a new feature.

Thank you for considering this.
-Mike Slifcak



Bob Hetzel wrote:
> James,
> 
> Regarding re-trying the login with each protocol until it finds a good 
> one... is there any chance that'll cause an account lock-out if a place has 
> really tight security settings?
> 
> I guess the real question I'm asking is... how far will it get when it 
> fails due to the wrong tds version for that server?  If it fails before 
> sending the username/password then there would probably not be a problem. 
> After that point, it might be.  This would probably only be an issue if 
> using a windows logon (rather than a sql only account), but I did just 
> stumble onto this:
> 
> http://technet.microsoft.com/en-us/library/bb326598.aspx
> 
> referenced from
> 
> http://www.derkeiler.com/Newsgroups/microsoft.public.sqlserver.security/2008-01/msg00016.html
> 
>     Bob
> 
> On 9/8/2011 11:08 PM, James K. Lowden wrote:
>> On Thu, 08 Sep 2011 12:22:14 -0500
>> "Craig A. Berry"<[email protected]>  wrote:
>>
>>> 5.0 may not be a sensible default in this day and age.  But I'm not
>>> sure there is a different one that makes sense either.
>> I'd like to riff on that a bit.  The right default might be "auto",
>> which is currently supported in, er, CVS HEAD.
>>
>> The recent discussion of dbsetversion() is illustrative.  The
>> documentation says if you don't call it, you get TDS 4.2.  That makes
>> sense: recompile old code, link to new library, get same behavior.  To
>> get new behavior, call the (previously nonexistent) function.
>>
>> But it also doesn't make sense.  Write brand new code, and to get
>> modern behavior you have call the (otherwise meaningless) function.
>> ODBC has been stuck with this for a decade, cf. SQL_ATTR_ODBC_VERSION.
>> You actually call the API to change the API.
>>
>> Larry Wall mentioned a similar artifact once in writing about Perl 6.
>> He remembered IIRC a setting in VMS mumble something like SET EXTENDED
>> ON to make it DTRT.  He observed that thereafter *every* script needed
>> that boilerplate in its preamble.  One gets the sense Larry is not a fan
>> of boilerplate or, for that matter, preambles.
>>
>> That's the world of binary interfaces and closed source.  Free
>> software lets you set the "default defaults" with ./configure.  Because
>> you control the source, you can set the default at compile time, which
>> is why the inoperability of dbset[l]version went unremarked-on for
>> years.
>>
>> If we were to remove --with-tdsver (which we won't) we'd remove
>> only the ability to set the compiled-in default.  If you don't use that
>> configure option, you get 5.0.  It has to be *something*, even if it's
>> an invalid value that forces you to use one of the runtime or
>> programatic methods to set it to something valid.
>>
>> Which brings us back to: what should it be?
>>
>> Which makes me ask: what's a configure file for, anyway?
>>
>> freetds.conf associates a hostname, port, and TDS version with a local
>> name.  Hostname is converted to an IP address by DNS or similar.  Port
>> is discoverable on Microsoft servers using 1434.  And TDS version can
>> be found by starting high and working down.  Old servers reject
>> logins using newer versions of the protocol; from their perspective the
>> new version is a protocol violation.  By trying successively lower
>> version, a client can discover the highest one supported by a server.
>>
>> What that means to me is that FreeTDS in its next release should
>> normally be run without a configuration file or environment variables.
>> The default-default TDS version should be 0, which tells the login
>> function to keep trying TDS flavors as long as something accepts the
>> tcp/ip connection.
>>
>> That said, there is miniscule overhead in retrying logins, and it is
>> unnecessary if you know which TDS version the server wants, and for
>> some applications a few hundred milliseconds' delay to log in
>> matters.  The spirit of the project demands that users be able to nail
>> things down, even to the point of setting the compiled-in default
>> behavior.
>>
>> End of Riff.  Thanks for listening.
>>
>> --jkl
>> _______________________________________________
>> FreeTDS mailing list
>> [email protected]
>> http://lists.ibiblio.org/mailman/listinfo/freetds
> _______________________________________________
> FreeTDS mailing list
> [email protected]
> http://lists.ibiblio.org/mailman/listinfo/freetds
>