REST generate_etag documentation

[mbj4668]

The documentation for generate_etag says:

Result  :: binary() | {weak | strong, binary()}
Default  - no etag value

I think it should be:

Result  :: undefined | binary() | {weak | strong, binary()}
Default :: undefined

Returning undefined seems to work, and I have a use case where I need to do this.

[essen]

You conditionally generate an etag?

[mbj4668]

My use case is that I have a REST callback module that handles different resources, and for some of them I can't generate an etag.

In general I like the API where I can implement the default behavior explicitly, and not just by not implementing the function. It is more flexible.

[essen]

Asking only to make sure there's a use case for this.

I have no problem with adding undefined along with a test. The expires callback also allows undefined explicitly.

[mbj4668]

Great, thanks!

[essen]

OK for the etag we want to call generate_etag only once, but if it's currently undefined we call the function. So the only way to make it work as intended is make sure that when the function returns undefined we mark the etag as no_call. I will add a test first.

[essen]

Done. Closing, thanks!