Exception handling advise needed for samba-tool

[Andrew Bartlett]

On Tue, 2013-04-09 at 13:40 +0200, Jelmer Vernooij wrote:
> On Tue, Apr 09, 2013 at 12:01:21AM -0700, Matthieu Patou wrote:
> > On 04/08/2013 04:18 PM, Andrew Bartlett wrote:
> > >I'm trying to make the exceptions from samba-tool domain classicupgrade
> > >less intimidating, so I tried this:
> > >
> > >diff --git a/python/samba/netcmd/domain.py
> > >b/python/samba/netcmd/domain.py
> > >index 4ba305c..c47b7be 100644
> > >--- a/python/samba/netcmd/domain.py
> > >+++ b/python/samba/netcmd/domain.py
> > >@@ -1313,9 +1313,12 @@ class cmd_domain_classicupgrade(Command):
> > >          s3conf.load(smbconf)
> > >          samba3 = Samba3(smbconf, s3conf)
> > >-        logger.info("Provisioning")
> > >-        upgrade_from_samba3(samba3, logger, targetdir,
> > >session_info=system_session(),
> > >-                            useeadb=eadb, dns_backend=dns_backend,
> > >use_ntvfs=use_ntvfs)
> > >+        logger.info("Preparing to Upgrade")
> > >+        try:
> > >+            upgrade_from_samba3(samba3, logger, targetdir,
> > >session_info=system_session(),
> > >+                                useeadb=eadb, dns_backend=dns_backend,
> > >use_ntvfs=use_ntvfs)
> > >+        except ProvisioningError, e:
> > >+            raise CommandError("Upgrade failed: ", e)
> > >But I still get:
> > >
> > >ERROR(<class 'samba.provision.ProvisioningError'>): Upgrade failed:  -
> > >ProvisioningError: Could not open '/tmp/secrets.tdb', the Samba3 secrets
> > >database: [Errno 2] No such file or directory.  Perhaps you specified
> > >the incorrect smb.conf, --testparm or --dbdir option?
> > >   File "bin/python/samba/netcmd/domain.py", line 1319, in run
> > >     useeadb=eadb, dns_backend=dns_backend, use_ntvfs=use_ntvfs)
> > >   File "bin/python/samba/upgrade.py", line 575, in upgrade_from_samba3
> > >     raise ProvisioningError("Could not open '%s', the Samba3 secrets
> > >database: %s.  Perhaps you specified the incorrect smb.conf, --testparm
> > >or --dbdir option?" % (samba3.privatedir_path("secrets.tdb"), str(e)))
> > >
> > >Can you remind me of the correct syntax to turn that into just:
> > >
> > >Upgrade failed: Could not open '/tmp/secrets.tdb', the Samba3 secrets
> > >database: [Errno 2] No such file or directory.  Perhaps you specified
> > >the incorrect smb.conf, --testparm or --dbdir option?
> > I think that as long as you raise an exception you will get the call
> > trace, try to see if you can just print the exception or just get
> > the error message.
> > 
> > You can have a look at samba_upgradeprovision around line 1160 I did
> > that there.
> The infrastructure is meant to deal with exceptions and display them properly.
> They shouldn't be caught and written to standard output manually.
> 
> Having a single place where exceptions are handled means we can avoid
> reinventing the wheel everywhere and e.g. have environment variables to
> force the dumping of tracebacks or having Python bring up a debugger whenever
> an exception is raised. It also makes whitebox testing of the code easier
> since you don't have to parse the output but you can just catch the
> exception and introspect it.
> 
> How samba-tool handles various exceptions should really be documented better.
> Sorry. The ubershort summary:
> 
>  * CommandError exceptions are expected, should only be raised by the
>    command code (not library code), should have a user-comprehensible
>    description. They're meant for general user-visible errors. When they're
>    printed there is no traceback printed.
>  * Any other internal errors should be caught by the command code
>    and re-raise a CommandError. You can attach an internal exception to a
>    CommandError for debugging purposes.
>  * Any internal errors that are not explicitly caught are reported with a
>    traceback. They're the Python equivalent of a segmentation error.
> 
> (it's gotten more complicated over time, and we special case more exceptions
>  than just CommandError now. I don't have the source code with me to
>  look at the moment)

So, how do I get just the error string out of the ProvisioningError into
the CommandError?

Thanks,

Andrew Bartlett

-- 
Andrew Bartlett                                http://samba.org/~abartlet/
Authentication Developer, Samba Team           http://samba.org