Wharf CLI plugins

By using the Hashicorp Go Plugin System over RPC¹ each build target environment needs only to be included in the $PATH.

Sample interface

This is not final!

type Flag struct {
    Name         string
    ShortName    string
    Description  string
    IsArgument   bool
    IsRequired   bool
    DefaultValue string
    // Type Type // some enum of types, ex file, existingFile, etc. 
    //           // just for potential future autocompletion
}

type Arguments = map[string]string // flag name: argument value

type Build struct {
    BuildID    int
    Step       wharf.Step
    Definition wharf.Definition
}

// Builder is the interface for the wharf command to talk to the builder plugin
type Builder interface {
    CanBuild(build Build, args Arguments) bool
    Build(build Build, args Arguments)
    Flags() []Flag
    Version() string
}

Sample use case: --help

$ wharf build kubernetes --help
Usage: wharf build kubernetes

Wharf flags:
  -h, --help                        Show this help.
  --version                         Show the version of the 'kubernetes' plugin.
  --build                           Set the build ID.
  -v, --verbose                     Enable verbose logging.
  
Plugin flags (kubernetes):
  --kubeconfig="~/.kube/config"     Path to the kubeconfig to use.

In the background, the Wharf CLI did this:

1. Spin up the kubernetes plugin, for example named wharf-build-kubernetes
2. Connect to it via RPC
3. Ask for its flags via Builder.Flags()
4. Combine with some Wharf flags, such as the --help and --version flags
5. Print output.
6. Exit.

Sample use case: Building

$ wharf build kubernetes --build 2355
I0302 13:57.215113  wharf                   build.go:23] Starting build: 2355
I0302 13:57.215113  wharf                   build.go:23] Running step: build/web
I0302 13:57.215113  wharf-build-kubernetes  main.go:23] Checking connection with Kubernetes cluster...
I0302 13:57.215113  wharf-build-kubernetes  main.go:23] Creating pod 'wharf-docker-2355'
I0302 13:57.215113  wharf-build-kubernetes  main.go:23] Waiting for pod to initialize...

In the background, the Wharf CLI did this:

1. Read .wharf-ci.yml
2. Log Starting build: 2355
3. Log Running step: build/web
4. Spin up the kubernetes plugin, for example named wharf-build-kubernetes
5. Connect to it via RPC
6. Pass it the build/web step to build via Builder.Build(...)
7. Wait for it to complete
8. Continue to the next step…