Re: [BuildStream] CAS server resource names & instance names

[Jim MacArthur <jim macarthur codethink co uk>]

On 10/12/2018 13:48, Jürg Billeter wrote:
> On Mon, 2018-12-10 at 13:41 +0000, Jim MacArthur wrote:
> > I don't see how you've got to the conclusion that empty instance and no
> > instance are the same thing. The Bazel protocol does say "For servers
> > which do not support multiple instances, then the `instance_name` is the
> > empty path" but that doesn't necessary imply behaviour for servers which
> > do support it. I can also see mappings to http URLs which look like
> > they'll always include an instance name or empty string, but I wasn't
> > considering them authoritative specifications.
> For example, for Execution.Execute() instance_name is a protobuf string
> field in the ExecuteRequest message. URL mapping is handled internally
> by gRPC, clients can't normally influence it. Protobuf messages don't
> allow distinction between unset string fields and empty string fields
> (the serialization is identical).
>
> I.e., at least for Execution.Execute() empty instance_name and no
> instance_name are identical. It's impossible for the server to treat
> them differently. I don't think it makes sense to distinguish the two
> cases in other places where it would theoretically be possible. That
> would be inconsistent and confusing, in my opinion.
>
> Cheers,
> Jürg
OK, this isn't really a question for BuildStream anymore so let's agree 
that "" and no instance are the same thing in BuildStream's world. 
Google can resolve the ambiguity in protocol buffers.