[freetds] dblib question - handling bad login name/password from auser

Lowden, James K LowdenJK at bernstein.com
Mon Apr 26 13:23:36 EDT 2004

> From: Andy Cranston [mailto:a.cranston at selwaymoore.com]
> Sent: April 26, 2004 11:59 AM
> However I'd like to write my own handlers.  The main reason 
> being to catch
> an invalid login attempt via:
>   dbproc = dbopen(login, DEFAULT_SERVER);
> Instead of the program bombing out I'd like to be able to gracefully
> reprompt for another username and password.
> Am I right in thinking I need to amend the handler routines 
> to do this?  If
> so any suggestions on a "clean" way to do this.  


You might want to check simply that you got a non-null dbproc.  There are several possible causes for not being able to log in (user error being only the most common with a working setup).   Passing the message to the user (using your handler) will at least provide the information to the person who needs it, whether or not it's understood. ;-)

The simplest way in general to pass information from the handler to the main code is through a global variable.  In a threaded environment, that translates to thread local storage or a per-thread map.  When you call a db-lib function that causes the library or the server to emit a message or error, you are assured that your handler will be invoked before the function returns.  The sequence is always

	call dbsomething
	[a bad thing happens]
	handler invoked
	dbsomething returns

IOW, you never have to worry about a race condition.  Or, at any rate, behavior in exception to my description would be considered a bug.  I don't believe I've seen that written down anywhere, but I can't think of any exceptions.  


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