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 requires a container manager client API available via a socket.  Both `docker` and `podman` are compatible with the [socket API](https://docs.docker.com/engine/api/v1.24/).  This RFC proposes that `pack` is extended to support a "daemonless" mode.  In a "daemonless" mode `pack` will directly use a container manager client API.  This avoids running a `docker` or `podman` daemon and avoids opening up a local socket.  This will allow to use pack as a full-userspace, standalone application on the OS supported by podman (currently 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)).
+
+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 dificulties 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?
+--->