Added headers for CRR Cascaded

[SylvainSenechal]

ISSUE : CLDSRVCLT-14

Crr cascaded design : https://github.com/scality/citadel/pull/349

Related PRs :
Arsenal : scality/Arsenal#2628
Cloudserver : scality/cloudserver#6179
Backbeat : Not done yet
S3utils : scality/s3utils#395

[bert-e]

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[bert-e]

Waiting for approval

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[maeldonn]

To document errors:

/// Returned when a version of an object already exists
@error("client")
@httpError(409)
structure ConflictException {
    @required
    message: String
}

@http(method: "PUT", uri: "/_/backbeat/data/{Bucket}/{Key+}?v2")
@unsignedPayload
operation PutData {
    input: PutDataInput,
    output: PutDataOutput,
    errors: [ConflictException]
}

[SylvainSenechal]

First I added some tests in this codebase, but they were too functional and not really oriented toward just testing the client itself. + we already have test testing the client itself for putData/putMetadata

So I added the tests in Cloudserver : They are functional tests using CloudserverClient with the micro version id, testing 409 error, actual api behavior etc. I think they are better in cloudserver than in here

[francoisferrand]

as discussed (late) in the design, not an input parameter : PutData should minimize work/logic related to metadata, and should simply return the current microVersionId (instead of "x-scal-cascade-loop-detected")

this will reduce coupling, while giving all flexibility for backbeat to take all decisions.

[francoisferrand]

PutMetadata is a generic api, used in many more cases than CRR.
→ api should stay generic, no reason to introduce "crr cascaded" vocabulary : stick to some generic concept, like "conflict" or "already have microVersionId"

[SylvainSenechal]

I thought about this but I thought it would be better for future maintainers to understand what this field is used for.
I dont wanna go with conflict as this would already be used for microVersionId that are too old, but I'll find something for the equality around "already have micro version id"

[SylvainSenechal]

edit: name updated, let me know if you have other name ideas

[francoisferrand]

nit: to make the semantic explicit, field could be name something like IfMicroVersionIdOlderThan (i.e. semantics is part of the API)

[SylvainSenechal]

Leaving for now, what do other ppl think about the naming ?