refactor go-flags initialization

internal/cmd/BUILD

@@ -1,8 +0,0 @@
-load("@io_bazel_rules_go//go:def.bzl", "go_library")
-
-go_library(
-    name = "go_default_library",
-    srcs = ["cmd.go"],
-    importpath = "github.com/motiejus/code/undocker/internal/cmd",
-    visibility = ["//src/undocker:__subpackages__"],
-)

internal/cmd/cmd.go

@@ -1,20 +0,0 @@
-package cmd
-
-import (
-	"io"
-	"os"
-)
-
-// BaseCommand provides common fields to all commands.
-type BaseCommand struct {
-	Stdin  io.Reader
-	Stdout io.Writer
-	Stderr io.Writer
-}
-
-// Init initializes BaseCommand with default arguments
-func (b *BaseCommand) Init() {
-	b.Stdin = os.Stdin
-	b.Stdout = os.Stdout
-	b.Stderr = os.Stderr
-}

internal/cmdlxcconfig/BUILD

@@ -6,7 +6,6 @@ go_library(
     importpath = "github.com/motiejus/code/undocker/internal/cmdlxcconfig",
     visibility = ["//src/undocker:__subpackages__"],
     deps = [
-        "//src/undocker/internal/cmd:go_default_library",
         "//src/undocker/lxcconfig:go_default_library",
         "@com_github_jessevdk_go_flags//:go_default_library",
         "@org_uber_go_multierr//:go_default_library",

internal/cmdlxcconfig/cmdlxcconfig.go

@@ -2,10 +2,11 @@ package cmdlxcconfig
 
 import (
 	"errors"
+	"fmt"
+	"io"
 	"os"
 
 	goflags "github.com/jessevdk/go-flags"
-	"github.com/motiejus/code/undocker/internal/cmd"
 	"github.com/motiejus/code/undocker/lxcconfig"
 	"go.uber.org/multierr"
 )
@@ -13,7 +14,8 @@ import (
 // Command is "lxcconfig" command
 type (
 	Command struct {
-		cmd.BaseCommand
+		Stdout io.Writer
+
 		PositionalArgs struct {
 			Infile  goflags.Filename `long:"infile" description:"Input tarball"`
 			Outfile string           `long:"outfile" description:"Output path, stdout is '-'"`
@@ -21,9 +23,17 @@ type (
 	}
 )
 
+func NewCommand() *Command {
+	return &Command{
+		Stdout: os.Stdout,
+	}
+}
+
+func (*Command) ShortDesc() string { return "Create an LXC-compatible container configuration" }
+func (*Command) LongDesc() string  { return "" }
+
 // Execute executes lxcconfig Command
 func (c *Command) Execute(args []string) (err error) {
-	c.BaseCommand.Init()
 	if len(args) != 0 {
 		return errors.New("too many args")
 	}
@@ -34,17 +44,18 @@ func (c *Command) Execute(args []string) (err error) {
 	}
 	defer func() { err = multierr.Append(err, rd.Close()) }()
 
-	var out *os.File
+	var out io.Writer
 	outf := string(c.PositionalArgs.Outfile)
-	if outf == "-" {
+	if fname := string(c.PositionalArgs.Outfile); fname == "-" {
-		out = os.Stdout
+		out = c.Stdout
 	} else {
-		out, err = os.Create(outf)
+		outf, err := os.Create(outf)
 		if err != nil {
-			return err
+			return fmt.Errorf("create: %w", err)
 		}
+		defer func() { err = multierr.Append(err, outf.Close()) }()
+		out = outf
 	}
-	defer func() { err = multierr.Append(err, out.Close()) }()
 
 	return lxcconfig.LXCConfig(rd, out)
 }

internal/cmdrootfs/BUILD

@@ -6,7 +6,6 @@ go_library(
     importpath = "github.com/motiejus/code/undocker/internal/cmdrootfs",
     visibility = ["//src/undocker:__subpackages__"],
     deps = [
-        "//src/undocker/internal/cmd:go_default_library",
         "//src/undocker/rootfs:go_default_library",
         "@com_github_jessevdk_go_flags//:go_default_library",
         "@org_uber_go_multierr//:go_default_library",
@@ -18,7 +17,6 @@ go_test(
     srcs = ["cmdrootfs_test.go"],
     embed = [":go_default_library"],
     deps = [
-        "//src/undocker/internal/cmd:go_default_library",
         "@com_github_jessevdk_go_flags//:go_default_library",
         "@com_github_stretchr_testify//assert:go_default_library",
         "@com_github_stretchr_testify//require:go_default_library",

internal/cmdrootfs/cmdrootfs.go

@@ -7,34 +7,37 @@ import (
 	"os"
 
 	goflags "github.com/jessevdk/go-flags"
-	"github.com/motiejus/code/undocker/internal/cmd"
 	"github.com/motiejus/code/undocker/rootfs"
 	"go.uber.org/multierr"
 )
 
 type (
-
-	// Command is "rootfs" command
 	Command struct {
-		cmd.BaseCommand
+		flattener func(io.ReadSeeker, io.Writer) error
+		Stdout    io.Writer
 
 		PositionalArgs struct {
-			Infile  goflags.Filename `long:"infile" description:"Input tarball"`
+			Infile  goflags.Filename `long:"infile" desc:"Input tarball"`
-			Outfile string           `long:"outfile" description:"Output path, stdout is '-'"`
+			Outfile string           `long:"outfile" desc:"Output path, stdout is '-'"`
 		} `positional-args:"yes" required:"yes"`
-
-		flattener func(io.ReadSeeker, io.Writer) error
 	}
 )
 
+func NewCommand() *Command {
+	return &Command{
+		flattener: rootfs.Flatten,
+		Stdout:    os.Stdout,
+	}
+}
+
+func (*Command) ShortDesc() string { return "Flatten a docker container image to a tarball" }
+func (*Command) LongDesc() string  { return "" }
+
 // Execute executes rootfs Command
 func (c *Command) Execute(args []string) (err error) {
 	if len(args) != 0 {
 		return errors.New("too many args")
 	}
-	if c.flattener == nil {
-		c.init()
-	}
 
 	rd, err := os.Open(string(c.PositionalArgs.Infile))
 	if err != nil {
@@ -56,12 +59,3 @@ func (c *Command) Execute(args []string) (err error) {
 
 	return c.flattener(rd, out)
 }
-
-// init() initializes Command with the default options.
-//
-// Since constructors for sub-commands requires lots of boilerplate,
-// command will initialize itself.
-func (c *Command) init() {
-	c.BaseCommand.Init()
-	c.flattener = rootfs.Flatten
-}

internal/cmdrootfs/cmdrootfs_test.go

@@ -8,7 +8,6 @@ import (
 	"testing"
 
 	goflags "github.com/jessevdk/go-flags"
-	"github.com/motiejus/code/undocker/internal/cmd"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 )
@@ -57,7 +56,7 @@ func TestExecute(t *testing.T) {
 		t.Run(tt.name, func(t *testing.T) {
 			dir := t.TempDir()
 			var stdout bytes.Buffer
-			c := &Command{BaseCommand: cmd.BaseCommand{Stdout: &stdout}}
+			c := &Command{Stdout: &stdout}
 			if tt.fixture != nil {
 				tt.fixture(t, dir)
 			}

main.go

@@ -4,29 +4,22 @@ import (
 	"os"
 
 	goflags "github.com/jessevdk/go-flags"
+
 	"github.com/motiejus/code/undocker/internal/cmdlxcconfig"
 	"github.com/motiejus/code/undocker/internal/cmdrootfs"
 )
 
-type (
-	params struct {
-		RootFS    cmdrootfs.Command    `command:"rootfs" description:"Unpack a docker container image to a single filesystem tarball"`
-		LXCConfig cmdlxcconfig.Command `command:"lxcconfig" description:"Create an LXC-compatible container configuration"`
-	}
-)
-
 func main() {
-	if err := run(os.Args); err != nil {
+	flags := goflags.NewParser(nil, goflags.Default)
+
+	rootfs := cmdrootfs.NewCommand()
+	lxcconfig := cmdlxcconfig.NewCommand()
+	flags.AddCommand("rootfs", rootfs.ShortDesc(), rootfs.LongDesc(), rootfs)
+	flags.AddCommand("lxcconfig", lxcconfig.ShortDesc(), lxcconfig.LongDesc(), lxcconfig)
+
+	_, err := flags.Parse()
+	if err != nil {
 		os.Exit(1)
 	}
 	os.Exit(0)
 }
-
-func run(args []string) error {
-	var opts params
-	if _, err := goflags.ParseArgs(&opts, args[1:]); err != nil {
-		return err
-	}
-
-	return nil
-}

rootfs/BUILD

@@ -9,10 +9,6 @@ go_library(
     ],
     importpath = "github.com/motiejus/code/undocker/rootfs",
     visibility = ["//visibility:public"],
-    deps = [
-        "//src/undocker/internal/bytecounter:go_default_library",
-        "@org_uber_go_multierr//:go_default_library",
-    ],
 )
 
 go_test(

rootfs/doc.go

@@ -2,7 +2,7 @@
 // tarball. It will go trough all layers in order and copy every file to the
 // destination archive.
 //
-// Except it will also reasonably process those files.
+// It will also reasonably process those files.
 //
 // == Non-directory will be copied only once ==
 // A non-directory will be copied only once, only from within it's past