first draft of pack direct podman call rfc

text/0000-pack-direct-podman-call.md

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+# Meta
+[meta]: #meta
+- Name: Pack direct podman call
+- Start Date: 2023-06-16
+- Author(s): dvaumoron
+- Status: Draft
+- RFC Pull Request: (leave blank)
+- CNB Pull Request: (leave blank)
+- CNB Issue: (leave blank)
+- Supersedes: "N/A"
+
+# Summary
+[summary]: #summary
+
+A flag `--daemonless` will be added to the `pack` CLI, the flag presence will switch from the current functioning to one where podman is called directly (without needing a daemon backed socket)
+
+# Definitions
+[definitions]: #definitions
+
+Container Manager Client API: an API such as Docker's `CommonAPIClient` or Podman's `ContainerEngine` allowing interaction with container and OCI image
+
+# Motivation
+[motivation]: #motivation
+
+`pack` currently interacts with a container manager through an API service. Both `docker` and `podman` can run the daemon service, which provides a compatible [socket API](https://docs.docker.com/engine/api/v1.24/). This RFC proposes an alternative "daemonless" mode with direct calls to `podman` without opening up a local socket or running API service. This makes `pack` an userspace, standalone application (currently only on Linux, as Windows and macOS need `podman` machine).
+
+# What it is
+[what-it-is]: #what-it-is
+
+Adding `--daemonless` to the `pack` command which currently need docker call would allow them to work without docker installed.
+
+# How it Works
+[how-it-works]: #how-it-works
+
+The flag will change the initialization of the CommonAPIClient passed to call docker (interface defined in "github.com/docker/docker/client") by an adapter conforming to the used subset [DockerClient](https://github.com/buildpacks/pack/blob/main/pkg/client/docker.go#L14) to call podman as a library (forwarding calls to an initialized instance of [ContainerEngine](https://github.com/containers/podman/blob/main/pkg/domain/entities/engine_container.go#L16)).
+
+In order to ensure correctness, options passed to the lifecycle will probably need to be adapted too (however, it does not seem necessary to change the lifecycle implementation because it already have alternatives to work without the docker socket).
+
+The adapter will look like :
+
+```Go
+type podmanAdapter struct {
+    inner entities.ContainerEngine
+}
+
+func MakePodmanAdapter() DockerClient {
+    // initialization of engine
+    return podmanAdapter{inner: engine}
+}
+
+func (a podmanAdapter) ContainerCreate(ctx context.Context, config *containertypes.Config, hostConfig *containertypes.HostConfig, networkingConfig *networktypes.NetworkingConfig, platform *specs.Platform, containerName string) (containertypes.CreateResponse, error) {
+    // initialization of specGenerator from the different configs
+    report, err := a.inner.ContainerCreate(ctx, specGenerator)
+    if err != nil {
+        return containertypes.CreateResponse{}, err
+    }
+    // initialization of adaptedReport from the report
+    return adaptedReport, nil
+}
+```
+
+# Migration
+[migration]: #migration
+
+The current mode of `pack` operation is the default mode of operation.  The proposed `--daemonless` mode of operation is an optional mode of execution.  We will need to document how to switch between operation modes and the motivations for choosing an appropriate mode of operation.
+
+# Drawbacks
+[drawbacks]: #drawbacks
+
+pack contributor could need to update the podman dependencies in go.mod for bugfixes
+
+# Alternatives
+[alternatives]: #alternatives
+
+pack user could have difficulties to set up docker or podman to work with the pack CLI
+
+# Prior Art
+[prior-art]: #prior-art
+
+N/A
+
+# Unresolved Questions
+[unresolved-questions]: #unresolved-questions
+
+N/A
+
+# Spec. Changes (OPTIONAL)
+[spec-changes]: #spec-changes
+
+N/A
+
+# History
+[history]: #history
+<!--
+## Amended
+### Meta
+[meta-1]: #meta-1
+- Name: (fill in the amendment name: Variable Rename)
+- Start Date: (fill in today's date: YYYY-MM-DD)
+- Author(s): (Github usernames)
+- Amendment Pull Request: (leave blank)
+
+### Summary
+
+A brief description of the changes.
+
+### Motivation
+
+Why was this amendment necessary?
+--->