proxy: Always return valid URL

[sboeuf]

Even when we are not allocating some IO streams, the caller can expect to receive a valid URL.

[sboeuf]

@dlespiau @sameo Let's get this merge unless you have some objections !

[coveralls]

Coverage increased (+0.05%) to 70.278% when pulling ad1edd3 on sboeuf/always_return_url into 664f4fa on master.

[coveralls]

Coverage increased (+0.5%) to 70.725% when pulling ad1edd3 on sboeuf/always_return_url into 664f4fa on master.

[dlespiau]

What's the use case for that?

[sboeuf]

In virtcontainers, we decided to retrieve the URL from the registerVM(), which is performed when we start the VM. Then we store this URL so that we can check that for the same pod, we are getting all the time the same URL.
But the problem is that when we start the VM, we sometimes have no containers described in the pod, they will come later by calling CreateContainer, meaning the registerVM returns an empty URL, and all the logic explained above does not work.
@sameo can you confirm ?

[dlespiau]

Sounds a good enough reason to me. It wasn't really designed to cache the URL + check, but why not.

lgtm