spiegel_podman/cmd/podman

Podman CLI

The following is an example of how to add a new primary command (manifest) and a sub-command (inspect) to the Podman CLI. This is example code, the production code has additional error checking and the business logic provided.

See items below for details on building, installing, contributing to Podman:

• Readme
• Contributing
• Podman Usage
• Trouble Shooting
• Code Of Conduct

Adding a new command podman manifest

$ mkdir -p $GOPATH/src/github.com/containers/podman/cmd/podman/manifest

Create the file $GOPATH/src/github.com/containers/podman/cmd/podman/manifest/manifest.go

package manifest

import (
    "github.com/containers/podman/cmd/podman/registry"
    "github.com/containers/podman/cmd/podman/validate"
    "github.com/containers/podman/pkg/domain/entities"
    "github.com/spf13/cobra"
)

var (
    // podman _manifests_
    manifestCmd = &cobra.Command{
        Use:               "manifest",
        Short:             "Manage manifests",
        Args:              cobra.ExactArgs(1),
        Long:              "Manage manifests",
        Example:           "podman manifest IMAGE",
        TraverseChildren:  true,
        RunE:              validate.SubCommandExists, // Report error if there is no sub command given
    }
)
func init() {
    // Subscribe command to podman
    registry.Commands = append(registry.Commands, registry.CliCommand{
        Command: manifestCmd,
    })
}

To "wire" in the manifest command, edit the file $GOPATH/src/github.com/containers/podman/cmd/podman/main.go to add:

package main

import	_ "github.com/containers/podman/cmd/podman/manifest"

Adding a new sub command podman manifest list

Create the file $GOPATH/src/github.com/containers/podman/cmd/podman/manifest/inspect.go

package manifest

import (
    "github.com/containers/podman/cmd/podman/registry"
    "github.com/containers/podman/pkg/domain/entities"
    "github.com/spf13/cobra"
)

var (
    // podman manifests _inspect_
    inspectCmd = &cobra.Command{
        Use:     "inspect IMAGE",
        Short:   "Display manifest from image",
        Long:    "Displays the low-level information on a manifest identified by image name or ID",
        RunE:    inspect,
        Annotations: map[string]string{
            // Add this annotation if this command cannot be run rootless
            // registry.ParentNSRequired: "",
        },
        Example: "podman manifest inspect DEADBEEF",
    }
)

func init() {
    // Subscribe inspect sub command to manifest command
    registry.Commands = append(registry.Commands, registry.CliCommand{
        Command: inspectCmd,
        // The parent command to proceed this command on the CLI
        Parent:  manifestCmd,
    })

    // This is where you would configure the cobra flags using inspectCmd.Flags()
}

// Business logic: cmd is inspectCmd, args is the positional arguments from os.Args
func inspect(cmd *cobra.Command, args []string) error {
    // Business logic using registry.ImageEngine()
    // Do not pull from libpod directly use the domain objects and types
    return nil
}

Helper functions

The complete set can be found in the validate package, here are some examples:

• cobra.Command{ Args: validate.NoArgs } used when the command does not accept errors
• cobra.Command{ Args: validate.IdOrLatestArgs } used to ensure either a list of ids given or the --latest flag
• cobra.Command{ RunE: validate.SubCommandExists } used to validate a subcommand given to a command
• validate.ChoiceValue used to create a pflag.Value that validate user input against a provided slice of values. For example:

  flags := cobraCommand.Flags()
  created := validate.ChoiceValue(&opts.Sort, "command", "created", "id", "image", "names", "runningfor", "size", "status")
  flags.Var(created, "sort", "Sort output by: "+created.Choices())
  

Adding CLI flags

When adding a new cli option that accepts a string array, there are two options to choose from: StringSlice() and StringArray(). They differ slightly in their behavior: StringSlice() allows the values to be comma separated so --opt v1,v2 --opt v3 results in []string{"v1", "v2", "v3"}, while StringArray() would result in []string{"v1,v2", "v3"}. Thus it is impossible to use values with comma in StringSlice(), which makes it unsuitable for flags that accept arbitrary values such as file paths as example. Also, because StringSlice() uses the csv lib to parse the values, it has special escaping rules for things like quotes, see https://github.com/containers/podman/issues/20064 for an example of how complicated things can get because of this. Thus use StringSlice() only when the option accepts predefined values that do not contain special characters, for example --cap-add and --cap-drop are a good example for this. Using --cap-add NET_ADMIN,NET_RAW is equal to --cap-add NET_ADMIN --cap-add NET_RAW so it is better suited to save some typing for users. When in doubt always choose StringArray() over StringSlice().