media types and descriptors, explain more deeply

[philips]

During last weeks call we discussed how the basic JSON objects in OCI shouldn't embed their own media types because they are not designed to be discovered or detected. Instead the media type should be declared explicitly in a descriptor and the contents verified via digest before interpretation.

This is a safety mechanism in the system so that people follow a strict flow of logic when interpreting things off the wire. We should make this thinking explicit in the overview of the spec.

cc @stevvooe

[wking]

On Tue, Dec 13, 2016 at 11:04:19PM -0800, Brandon Philips wrote: During last weeks call we discussed how the basic JSON objects in OCI shouldn't embed their own media types…

Isn't this being addressed in #411?

[stevvooe]

@philips Was there more we needed here?

[vbatts]

@stevvooe are we going to strip/make-OPTIONAL mediaType on everything except for descriptor objects?

[stevvooe]

@stevvooe are we going to strip/make-OPTIONAL mediaType on everything except for descriptor objects?

This is the plan. Most are reserved fields.

Did you we need implementation direction for descriptor usage here? I am not sure what is actionable on this issue.

[vbatts]

right on.

…

On Tue, Jan 31, 2017 at 1:10 PM, Stephen Day ***@***.***> wrote: @stevvooe <https://github.com/stevvooe> are we going to strip/make-OPTIONAL mediaType on everything except for descriptor objects? This is the plan. Most are reserved fields. Did you we need implementation direction for descriptor usage here? I am not sure what is actionable on this issue. — You are receiving this because you commented. Reply to this email directly, view it on GitHub <#493 (comment)>, or mute the thread <https://github.com/notifications/unsubscribe-auth/AAEF6cVHakMxAJryT1ckxfvbS3LPcgNoks5rX3j4gaJpZM4LMmRg> .

[philips]

@stevvooe I think what needs to happen is an entry in the descriptor spec about how this is the only place mediaType should appear and removal of mediaType from other objects as necessary.

[wking]

On Wed, Feb 01, 2017 at 05:21:04AM -0800, Brandon Philips wrote: I think what needs to happen is an entry in the descriptor spec about how this is the only place mediaType should appear and removal of mediaType from other objects as necessary.

Hasn't this already happened between #411 (and the follow-up #531)? Or are you interested in dropping the reserved-field entries [1,2]? Or are you interested in dropping the context based, descriptor-mediaType value restrictions [3]? I'm fine with dropping the reserved fields. But I think dropping the context based value restrictions will make manifest(-lists) much less reliable, because we'd no longer be recommending the use of OCI types or requiring implementations to support them. [1]: #411 (comment) [2]: https://github.com/opencontainers/image-spec/blame/5fccf471dfc2e02d5509daf0feddeab86f80510a/manifest.md#L23 [3]: https://github.com/opencontainers/image-spec/blame/5fccf471dfc2e02d5509daf0feddeab86f80510a/manifest.md#L52

[stevvooe]

@wking Yes, that should cover it. Closing this.

@philips If you disagree, feel free to re-open and I'll tackle this directly.