yaacov/add-cobra-command

Adding a Cobra Command

kubectl-mtv uses a two-layer pattern: thin Cobra wiring in cmd/ delegates to business logic in pkg/cmd/.

Architecture

cmd/<verb>/<resource>.go        -> Cobra command (flags, args, RunE)
pkg/cmd/<verb>/<resource>/      -> Business logic (K8s calls, output)

The parent verb (e.g. cmd/get/get.go) registers subcommands. The root (cmd/kubectl-mtv.go) registers top-level verbs via rootCmd.AddCommand().

Flags Over Positional Args

Always prefer named flags (--name my-plan) over positional arguments. The MCP layer maps flags directly to JSON flags objects. Positional args require special handling and are harder for LLMs to discover.

Use cobra.NoArgs and define all parameters as flags:

cmd := &cobra.Command{
    Use:  "host",
    Args: cobra.NoArgs,
    // ...
}
cmd.Flags().StringVarP(&hostName, "name", "M", "", "Host name")

Step-by-Step Checklist

1. Add business logic

Create pkg/cmd/<verb>/<resource>/list.go (or appropriate name):

package resource

import (
    "context"
    "fmt"
    "strings"

    metav1 "k8s.io/apimachinery/pkg/apis/meta/v1"
    "k8s.io/cli-runtime/pkg/genericclioptions"

    "github.com/yaacov/kubectl-mtv/pkg/util/client"
    "github.com/yaacov/kubectl-mtv/pkg/util/output"
    "github.com/yaacov/kubectl-mtv/pkg/util/watch"
)

func ListItems(ctx context.Context, configFlags *genericclioptions.ConfigFlags, namespace, outputFormat string, useUTC bool) error {
    dynamicClient, err := client.GetDynamicClient(configFlags)
    if err != nil {
        return fmt.Errorf("failed to get client: %v", err)
    }

    items, err := dynamicClient.Resource(client.YourGVR).Namespace(namespace).List(ctx, metav1.ListOptions{})
    if err != nil {
        return fmt.Errorf("failed to list: %v", err)
    }

    allItems := make([]map[string]interface{}, 0, len(items.Items))
    for _, item := range items.Items {
        allItems = append(allItems, createItem(item, useUTC))
    }

    switch strings.ToLower(outputFormat) {
    case "json":
        return output.PrintJSONWithEmpty(allItems, "No items found.")
    case "yaml":
        return output.PrintYAMLWithEmpty(allItems, "No items found.")
    default:
        return printTable(allItems)
    }
}

func List(ctx context.Context, configFlags *genericclioptions.ConfigFlags, namespace string, watchMode bool, outputFormat string, useUTC bool) error {
    return watch.WrapWithWatch(watchMode, outputFormat, func() error {
        return ListItems(ctx, configFlags, namespace, outputFormat, useUTC)
    }, watch.DefaultInterval)
}

2. Add Cobra command

Create cmd/<verb>/<resource>.go:

package verb

import (
    "context"
    "time"

    "github.com/spf13/cobra"
    "k8s.io/cli-runtime/pkg/genericclioptions"

    "github.com/yaacov/kubectl-mtv/pkg/cmd/<verb>/<resource>"
    "github.com/yaacov/kubectl-mtv/pkg/cmd/help"
    "github.com/yaacov/kubectl-mtv/pkg/util/client"
    "github.com/yaacov/kubectl-mtv/pkg/util/completion"
    "github.com/yaacov/kubectl-mtv/pkg/util/flags"
)

func NewResourceCmd(kubeConfigFlags *genericclioptions.ConfigFlags, globalConfig GlobalConfigGetter) *cobra.Command {
    outputFormatFlag := flags.NewOutputFormatTypeFlag()
    var watch bool
    var name string

    cmd := &cobra.Command{
        Use:          "resource",
        Short:        "Get resources",
        Long:         `Detailed description of the resource.`,
        Example: `  # List all resources
  kubectl-mtv get resources

  # Get a specific resource
  kubectl-mtv get resource --name my-resource --output yaml`,
        Args:         cobra.NoArgs,
        SilenceUsage: true,
        RunE: func(cmd *cobra.Command, args []string) error {
            ctx := cmd.Context()
            if !watch {
                var cancel context.CancelFunc
                ctx, cancel = context.WithTimeout(ctx, 30*time.Second)
                defer cancel()
            }

            namespace := client.ResolveNamespaceWithAllFlag(
                globalConfig.GetKubeConfigFlags(), globalConfig.GetAllNamespaces())

            return resource.List(ctx, globalConfig.GetKubeConfigFlags(),
                namespace, watch, outputFormatFlag.GetValue(), globalConfig.GetUseUTC())
        },
    }

    cmd.Flags().StringVarP(&name, "name", "N", "", "Resource name")
    cmd.Flags().VarP(outputFormatFlag, "output", "o", "Output format (table, json, yaml)")
    cmd.Flags().BoolVarP(&watch, "watch", "w", false, "Watch for changes")
    help.MarkMCPHidden(cmd, "watch")

    // Register completions
    _ = cmd.RegisterFlagCompletionFunc("output", func(cmd *cobra.Command, args []string, toComplete string) ([]string, cobra.ShellCompDirective) {
        return outputFormatFlag.GetValidValues(), cobra.ShellCompDirectiveNoFileComp
    })

    return cmd
}

3. Register subcommand

In the parent verb file (e.g. cmd/get/get.go):

resourceCmd := NewResourceCmd(kubeConfigFlags, globalConfig)
resourceCmd.Aliases = []string{"resources"}
cmd.AddCommand(resourceCmd)

4. Add GVR (if new CRD)

In pkg/util/client/client.go:

YourGVR = schema.GroupVersionResource{
    Group:    Group,    // "forklift.konveyor.io"
    Version:  Version,  // "v1beta1"
    Resource: "yourresources",
}

5. Add completion (if name-based)

In pkg/util/completion/completion.go, add a function that lists resource names for shell completion.

6. Update category (if new top-level verb)

In pkg/cmd/help/generator.go, update getCategory():

case "get", "describe", "health", "yournewverb":
    return "read"

This controls whether the MCP layer exposes the command via mtv_read or mtv_write.

7. Verify MCP discovery

Commands under known verbs are auto-discovered via help --machine. Run kubectl-mtv help --machine and verify your command appears with correct category and flags.

Key Packages

| Package | Purpose | |---------|---------| | pkg/util/flags/ | Shared flag types (OutputFormatTypeFlag, ProviderTypeFlag) | | pkg/util/client/ | K8s dynamic client, GVR constants, namespace helpers | | pkg/util/output/ | Table, JSON, YAML printers | | pkg/util/watch/ | WrapWithWatch for --watch mode | | pkg/util/completion/ | Shell completion for flag values | | pkg/util/config/ | GlobalConfigGetter interface | | pkg/cmd/help/ | MarkMCPHidden, category assignment |

Conventions

• Use cobra.NoArgs -- pass everything via flags.
• Add plural alias (Aliases = []string{"resources"}).
• Set SilenceUsage: true on all commands.
• Add 30s context timeout for non-watch commands.
• Use help.MarkMCPHidden(cmd, "watch") for interactive/TUI flags.
• Follow the GlobalConfigGetter interface for accessing global config.