[Opensim-dev] Error detection when storing an asset

[Oren Hurvitz]

I have found that when OpenSim tries to store an asset using
AssetServicesConnector, it doesn't handle failures well. There are several
problems in AssetServicesConnector.Store(), and some of them seem to be
based on historical considerations that may no longer be relevant, so I'd
like to see if anyone knows about these issues before pushing a change.

AssetServicesConnector.Store() uses SynchronousRestObjectRequester to send
the request. The first problem is that
SynchronousRestObjectRequester.MakeRequest() hides exceptions and just
returns null. This is a mistake: MakeRequest() should propagate exceptions,
so that callers will know that an error occurred. Store() already catches
these exceptions (as it should), so this won't make a big difference in our
case. But of course, this change in behavior to MakeRequest() may affect
other places in the code as well. It's better to fail-fast when errors
occur, and not hide them, because doing so makes the errors much harder to
diagnose once they become apparent. This brings me to the next problem...

The second problem is that AssetServicesConnector.Store() compares the
return value from MakeRequest to string.Empty, but in fact the return value
that is returned in case of error is null. So it mistakenly treats 'null'
as a valid Asset ID, which causes it to cache the asset. This can cause the
operation to appear to have succeeded for a while, since OpenSim will have
the asset available, but the moment the asset is loaded from the asset
server "the jig is up" and the asset will be missing. This can explain many
problems people have had with disappearing assets.

The third problem is a comment found in this method, which says that a
return value of 'null' is considered to be success because of "old asset
servers that don't send any reply back". That's a really old comment (from
2009). Can I assume that we no longer need to support such servers and we
can treat 'null' as the error value that it is?

Oren
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