Fix Cluster kind and multiple /clusters/ in URLs

[ntnn]

Summary

See #2811 and #3517

The KCPRequestInfo handler didn't have any actual use and its existence had been questioned before (I'll post the link to the comment if I find it again) and it was the major contributor for the multiple /cluster/... issue.

What Type of PR Is This?

/kind bug
/kind cleanup

Related Issue(s)

Fixes #2811
Fixes #3517

Release Notes

Fix CRDs with kind `Cluster` leading to errors
Fix URLs with multiple `/cluster/...` segments being silently ignored

[ntnn]

One places where this was used was in the cache server, where it would prune the cluster anyhow:

kcp/pkg/cache/server/config.go

Lines 169 to 194 in 339e173

	func(rq *http.Request) (string, string, error) {
	if serverConfig.Config.RequestInfoResolver == nil {
	return "", "", errors.New("no RequestInfoResolver provided")
	}
	// the k8s request info resolver expects a cluster-less path, but the client we're using knows how to
	// add the cluster we are targeting to the path before this round-tripper fires, so we need to strip it
	// to use the k8s library
	parts := strings.Split(rq.URL.Path, "/")
	if len(parts) < 4 {
	return "", "", fmt.Errorf("RequestInfoResolver: got invalid path: %v", rq.URL.Path)
	}
	if parts[1] != "clusters" {
	return "", "", fmt.Errorf("RequestInfoResolver: got path without cluster prefix: %v", rq.URL.Path)
	}
	// we clone the request here to safely mutate the URL path, but this cloned request is never realized
	// into anything on the network, just inspected by the k8s request info libraries
	clone := rq.Clone(rq.Context())
	clone.URL.Path = strings.Join(parts[3:], "/")
	requestInfo, err := serverConfig.Config.RequestInfoResolver.NewRequestInfo(clone)
	if err != nil {
	return "", "", err
	}
	return requestInfo.Resource, requestInfo.Verb, nil
	},
	"customresourcedefinitions")
	rt = rest.AddUserAgent(rt, "kcp-cache-server")

[ntnn]

/cherry-pick release-0.28

[kcp-ci-bot]

@ntnn: once the present PR merges, I will cherry-pick it on top of release-0.28 in a new PR and assign it to you.

In response to this:

/cherry-pick release-0.28

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.

[ntnn]

Using this instead of t.Context for the cherry-pick to 0.28

[ntnn]

This would be a new e2e package but I didn't see any other that would be fitting.

[ntnn]

/retest

[embik]

/approve

[kcp-ci-bot]

LGTM label has been added.

Git tree hash: 7b6987a5fd53bc34da241b3f07fbb748b03eb985

[kcp-ci-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: embik

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Needs approval from an approver in each of these files:

• OWNERS [embik]

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[ntnn]

/retest

Known flake #3522

[ntnn]

/retest

Known flake #3522

[kcp-ci-bot]

@ntnn: #3537 failed to apply on top of branch "release-0.28":

Applying: Move regex into test file
Applying: Return an error if attempts are made to parse a cluster when one is already present in context
Applying: Don't build longer and longer chains with each call
Applying: Remove KCPRequestInfoResolver
Using index info to reconstruct a base tree...
M	pkg/server/config.go
Falling back to patching base and 3-way merge...
Auto-merging pkg/server/config.go
CONFLICT (content): Merge conflict in pkg/server/config.go
error: Failed to merge in the changes.
hint: Use 'git am --show-current-patch=diff' to see the failed patch
Patch failed at 0004 Remove KCPRequestInfoResolver
When you have resolved this problem, run "git am --continue".
If you prefer to skip this patch, run "git am --skip" instead.
To restore the original branch and stop patching, run "git am --abort".

In response to this:

/cherry-pick release-0.28

Instructions for interacting with me using PR comments are available here. If you have questions or suggestions related to my behavior, please file an issue against the kubernetes/test-infra repository.