let the list images fails fast if the glance API is not responding

[Andrea Rosa]

The list method of the images.py file (for both v1 and v2) version returns a generators over a list of images.
In case the client can't talk correctly with the glance API we have an exception but this exception is actually raised only once the generator is consumed.
The reason for this is that inside the nested paginate method the client trigger the API call to get the list of images [1] and as that method is a generator the excpetion is not caught immediately.
That leads to some ugly behaviour by the callers of the client method, for example in nova we have to "force" a consume of the generator to catch any potential excpetions [2].
I think the client should fails fast if it gets an error from the API, to do that it should be enough to separate the fetching of the images from the generator.

What do you think?

[1] https://github.com/openstack/python-glanceclient/blob/14b9ba29811d63aa6b61e877376cc538c32aeadc/glanceclient/v2/images.py#L108

[2] https://github.com/openstack/nova/blob/f03bbbab68408e0b3a311256962211b4f5d2cd1e/nova/image/glance.py#L251-L254

[Cyril Roelandt (cyril-roelandt)]

Failing early makes sense to me. You seem to know the code well, so do you know where the exception you are talking about is raised? I think it would also make sense to check the value of "resp" at https://github.com/openstack/python-glanceclient/blob/14b9ba29811d63aa6b61e877376cc538c32aeadc/glanceclient/v2/images.py#L108 .

[Andrea Rosa (andrea-rosa-m)]

I am not very familiar with glanceclient code but my understanding is that the line you pointed out could raise some exception as response back from the API server.
I agree with you that check the response code is a good thing to do.
Hope this helps

[Cao ShuFeng (caosf-fnst)]

If you really want to implement this, I suggest that we add a "retrieve_all=False" param to the list() function.
So that we can keep backward compatibility.
Maybe like this[1].

[1]: https://github.com/openstack/python-neutronclient/blob/master/neutronclient/v2_0/client.py#L353

[Cyril Roelandt (cyril-roelandt)]

Failing early makes sense to me. You seem to know the code well, so do you know where the exception you are talking about is raised? I think it would also make sense to check the value of "resp" at https://github.com/openstack/python-glanceclient/blob/14b9ba29811d63aa6b61e877376cc538c32aeadc/glanceclient/v2/images.py#L108 .

[Cyril Roelandt (cyril-roelandt)]

Oops, sorry for the repost :)

[Andrea Rosa (andrea-rosa-m)]

@caosf-fnst I am not going to work on this bug, in my opinion this is a low priority one and it could be classified as a wishlist, what do you think?