Message Policies in XDI2

[Markus Sabadello]

I implemented support for message policies in XDI messages.

This means that an XDI client can specify that a message should only be executed if certain conditions are made.

This is the "client-side counterpart" to XDI link contracts.

I.e. instead of the XDI endpoint enforcing a certain policy, the XDI client itself can send a policy along with the message.

See here for Drummond's description of this feature:

https://wiki.oasis-open.org/xdi/XdiMessagePatterns#ConditionalExecutionRules

In the XDI Local Messenger there's an example where you can try this:

http://xdi2.projectdanube.org/XDILocalMessenger?category=5&sample=1

It's a $mod operation that only gets executed if a literal value in the target graph is $greater than 80.

Markus

[Drummond Reed]

Markus, very cool. Quite clean and elegantly done.

=Drummond 

Markus

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[Markus Sabadello]

One question I had was whether the server should return an error if the message policy is not met, or simply not execute the message and be silent.

This also takes us to the question of error codes, and I found this page that Mike had created:

https://wiki.oasis-open.org/xdi/MessagingErrorCode

Is this consistent with your thinking, i.e. we would develop a dictionary of such error codes?

Markus

[Davis, Peter]

I think you need to respond with an error, either to allow software to recover gracefully, or a the very least, prove a user an explanation that might help them fix the problem.

=peterd

Peter Davis: Neustar, Inc.

Distinguished Engineer

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[Markus Sabadello]

The question is, is it really a "problem" that needs to be reported as an "error" so that it can be "fixed", if the client itself is asking to conditionally execute the operation. The condition met or not met might both be perfectly within the intentions of the client.

Markus