Added simple logic for dry run on prune containers

[kaushik94]

- What I did
Implemented a simple dry run mode for containers

- How I did it
When checking for containers that are stale, moby does a daemon.ContainerRm. In dry run mode, I simply disabled this line and returned the container id and size to be removed.

- How to verify it
do
docker run hello-world
docker containers prune --dry-run

use this branch for cli side changes: docker/cli#3226

- Description for the changelog

changed:
container/prune.go -> accept a new parameter dryRun
container_routes.go -> Post a url with dryRun param to backend

TODO: Add tests

- A picture of a cute animal (not mandatory but encouraged)

[cpuguy83]

I would probably promote dryRun to a full option rather than a filter argument.

[kaushik94]

@cpuguy83 when I remove this line, it is complaining me invalid parameters.

[cpuguy83]

This is probably because you are passing dryRun as a filter rather than a configuration option.
It looks like we don't currently accept any options on prune other than filter.

This would need to be added at the API level.

[kaushik94]

@cpuguy83 can you give an example of any top level options. Like --all? Can you show me the file to add this.

[cpuguy83]

It will need to be decoded here:

moby/api/server/router/container/container_routes.go

Lines 713 to 728 in f416e99

	func (s *containerRouter) postContainersPrune(ctx context.Context, w http.ResponseWriter, r *http.Request, vars map[string]string) error {
	if err := httputils.ParseForm(r); err != nil {
	return err
	}
	pruneFilters, err := filters.FromJSON(r.Form.Get("filters"))
	if err != nil {
	return errdefs.InvalidParameter(err)
	}
	pruneReport, err := s.backend.ContainersPrune(ctx, pruneFilters)
	if err != nil {
	return err
	}
	return httputils.WriteJSON(w, http.StatusOK, pruneReport)
	}

The backend interface definition will need to be updated here:

moby/api/server/router/container/backend.go

Line 67 in f416e99

ContainersPrune(ctx context.Context, pruneFilters filters.Args) (*types.ContainersPruneReport, error)

The options will need to be encoded here:

moby/client/container_prune.go

Lines 13 to 36 in f416e99

	func (cli *Client) ContainersPrune(ctx context.Context, pruneFilters filters.Args) (types.ContainersPruneReport, error) {
	var report types.ContainersPruneReport
	if err := cli.NewVersionError("1.25", "container prune"); err != nil {
	return report, err
	}
	query, err := getFiltersQuery(pruneFilters)
	if err != nil {
	return report, err
	}
	serverResp, err := cli.post(ctx, "/containers/prune", query, nil, nil)
	defer ensureReaderClosed(serverResp)
	if err != nil {
	return report, err
	}
	if err := json.NewDecoder(serverResp.body).Decode(&report); err != nil {
	return report, fmt.Errorf("Error retrieving disk usage: %v", err)
	}
	return report, nil
	}

[cpuguy83]

This is duplicated in the else block.
I think this can be:

Suggested change

	if (!dryRunMode) {
	if !dryRunMode {
	if err := daemon.ContainerRm(c.ID, &types.ContainerRmConfig{}); err != nil {
	logrus.Warnf("failed to prune container %s: %v", c.ID, err)
	continue
	}
	}
	if cSize > 0 {
	rep.SpaceReclaimed += uint64(cSize)
	}
	rep.ContainersDeleted = append(rep.ContainersDeleted, c.ID)

Note: Don't use GH's UI to accept the change, as the commit won't be signed and it will be rejected by CI.

[kaushik94]

@cpuguy83 when I try to make a change to the existing API, it complains with the following error:

# github.com/docker/cli/vendor/github.com/docker/docker/client
vendor/github.com/docker/docker/client/interface_stable.go:10:5: cannot use &Client literal (type *Client) as type APIClient in assignment:
	*Client does not implement APIClient (wrong type for ContainersPrune method)
		have ContainersPrune(context.Context, filters.Args) (types.ContainersPruneReport, error)
		want ContainersPrune(context.Context, filters.Args, bool) (types.ContainersPruneReport, error)

This is probably because docker implements a ContainerPrune declaration already. How do I build the moby with my CLI?
I used to just make previously but that doesn't work. Can you please tell me steps to compile my own CLI and then attach that CLI to moby as described here

[kaushik94]

@cpuguy83 I was able to build the moby code by hacking the vendor/github.com directory of docker/cli. But the tests are still failing on the CLI PR. Can you please help me with understanding. Thanks a ton.

[kaushik94]

Please don't close this PR. I have started working on this again.