Automatic merge from submit-queue. If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>.
move cached_discovery to client-go/discovery
**Release note**:
```release-note
NONE
```
Moves the cmd/util CachedDiscoveryClient to client-go
cc @soltysh @deads2k
Kubernetes-commit: f2ea83bef88f9d2783abe0c00de563db13ec04f4
Automatic merge from submit-queue. If you want to cherry-pick this change to another branch, please follow the instructions <a href="https://github.com/kubernetes/community/blob/master/contributors/devel/cherry-picks.md">here</a>.
client-go: remove import of github.com/gregjones/httpcache
Moves NewCacheRoundTripper from `k8s.io/client-go/transport` to its own package. This prevents Kubernetes clients from requiring its dependencies.
This change removes the following transitive imports from `k8s.io/client-go/kubernetes`
```
github.com/google/btree
github.com/gregjones/httpcache
github.com/gregjones/httpcache/diskcache
github.com/peterbourgon/diskv
```
```release-note
NONE
```
Kubernetes-commit: 4a77bd53e88a719c612086df69a52899bbdd85af
Automatic merge from submit-queue (batch tested with PRs 51480, 49616, 50123, 50846, 50404)
Kubectl to use http caching to cache openapi responses from the server
**What this PR does / why we need it**:
This PR is trying to address the problems raised in #50254
> * uses a disk-based cache that is not safe between processes (does not use atomic fs operations)
> * writes get/list responses to disk that should not be cached (like kubectl get secrets)
> * is vulnerable to partially written cache responses being used as responses to future requests
> * breaks uses of the client transport that make use of websockets
> * defaults to enabling the cache for any client builder using RecommendedConfigOverrideFlags or DefaultClientConfig which affects more components than just kubectl
All of these points are addressed by this pull-request:
1. It now uses atomic fs operations
2. Doesn't cache by default, only if requested by the client (and it's only done by openapi client)
3. Fixed because of atomic fs operations
4. Found the reason for the bug: Cache wrapper couldn't be unwrapped. I implemented the `WrappedRoundTripper` interface.
5. Since 2. is fixed, I think that should be fine
@smarterclayton @liggitt
**Which issue this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close that issue when PR gets merged)*: fixes#50254
**Special notes for your reviewer**:
**Release note**:
```release-note
Allows kubectl to use http caching mechanism for the OpenAPI schema. The cache directory can be configured through `--cache-dir` command line flag to kubectl. If set to empty string, caching will be disabled.
```
Kubernetes-commit: 0f2c2bd847ca7a66035b2289e83359ef4c923617
Automatic merge from submit-queue (batch tested with PRs 50254, 50174, 50179)
Revert "Merge pull request #47353 from apelisse/http-cache"
Some issues were discovered with the caching merged in #47353:
* uses a disk-based cache that is not safe between processes (does not use atomic fs operations)
* writes get/list responses to disk that should not be cached (like `kubectl get secrets`)
* is vulnerable to partially written cache responses being used as responses to future requests
* breaks uses of the client transport that make use of websockets
* defaults to enabling the cache for any client builder using RecommendedConfigOverrideFlags or DefaultClientConfig which affects more components than just kubectl
This reverts commit fc89743dca6b563063b74728c3b28100cf674d9d, reversing changes made to 29ab38e898988c36e2de34f77fa33be556eb21bd.
Kubernetes-commit: 187e6ab0bc35f696d8f5f574fab9aa457f253d34
Automatic merge from submit-queue
go-client: Use httpcache client for all requests, even though only openapi returns ETags for caching
**What this PR does / why we need it**: Use HTTP ETag for caching Swagger spec download
This also adds a new command-line flag "cachedir" to specify where the cache should keep its file. It defaults to `$HOME/.kube/http-cache`.
**Which issue this PR fixes** *(optional, in `fixes #<issue number>(, fixes #<issue_number>, ...)` format, will close that issue when PR gets merged)*: partly #38637
**Special notes for your reviewer**:
Because this adds a bunch of dependencies, and removes a couple of files, I do recommend reading each commit individually.
**Release note**:
```release-note
```
Kubernetes-commit: fc89743dca6b563063b74728c3b28100cf674d9d
Kubernetes Publisher
Kubernetes Publisher