Refactored most of the CLI tests to run in-process as opposed to using sub-processes (#1059)

* cli: fixed remaining testability indirections for output and logging

* cli: added cli.RunSubcommand() which is used in testing to execute a subcommand in the same process

* tests: refactored most e2e tests to invoke kopia subcommands in-process

* Makefile: enable code coverage for cli/ and internal/

* testing: pass 'testing' tag to unit tests which uses much faster (insecure) password hashing scheme

* Makefile: push coverage from PRs again

* tests: disable buffer management to reduce memory usage on ARM

* cli: fixed misaligned atomic field on ARMHF

also temporarily fixed statup-time benign race condition when setting
default on the timeZone variable, which is the last global variable.

cli/app.go

@@ -79,6 +79,7 @@ type appServices interface {
 	repositoryWriterAction(act func(ctx context.Context, rep repo.RepositoryWriter) error) func(ctx *kingpin.ParseContext) error
 	maybeRepositoryAction(act func(ctx context.Context, rep repo.Repository) error, mode repositoryAccessMode) func(ctx *kingpin.ParseContext) error
 
+	advancedCommand(ctx context.Context)
 	repositoryConfigFileName() string
 	getProgress() *cliProgress
 
@@ -99,6 +100,8 @@ type advancedAppServices interface {
 	passwordPersistenceStrategy() passwordpersist.Strategy
 	getPasswordFromFlags(ctx context.Context, isNew, allowPersistent bool) (string, error)
 	optionsFromFlags(ctx context.Context) *repo.Options
+
+	rootContext() context.Context
 }
 
 // App contains per-invocation flags and state of Kopia CLI.
@@ -116,6 +119,7 @@ type App struct {
 	metricsListenAddr             string
 	keyRingEnabled                bool
 	persistCredentials            bool
+	AdvancedCommands              string
 
 	// subcommands
 	blob        commandBlob
@@ -140,6 +144,7 @@ type App struct {
 	osExit       func(int) // allows replacing os.Exit() with custom code
 	stdoutWriter io.Writer
 	stderrWriter io.Writer
+	rootctx      context.Context
 }
 
 func (c *App) getProgress() *cliProgress {
@@ -185,9 +190,10 @@ func (c *App) setup(app *kingpin.Application) {
 	app.Flag("config-file", "Specify the config file to use.").Default(defaultConfigFileName()).Envar("KOPIA_CONFIG_PATH").StringVar(&c.configPath)
 	app.Flag("trace-storage", "Enables tracing of storage operations.").Default("true").Hidden().BoolVar(&c.traceStorage)
 	app.Flag("metrics-listen-addr", "Expose Prometheus metrics on a given host:port").Hidden().StringVar(&c.metricsListenAddr)
-	app.Flag("timezone", "Format time according to specified time zone (local, utc, original or time zone name)").Default("local").Hidden().StringVar(&timeZone)
+	app.Flag("timezone", "Format time according to specified time zone (local, utc, original or time zone name)").Hidden().StringVar(&timeZone)
 	app.Flag("password", "Repository password.").Envar("KOPIA_PASSWORD").Short('p').StringVar(&c.password)
 	app.Flag("persist-credentials", "Persist credentials").Default("true").Envar("KOPIA_PERSIST_CREDENTIALS_ON_CONNECT").BoolVar(&c.persistCredentials)
+	app.Flag("advanced-commands", "Enable advanced (and potentially dangerous) commands.").Hidden().Envar("KOPIA_ADVANCED_COMMANDS").StringVar(&c.AdvancedCommands)
 
 	c.setupOSSpecificKeychainFlags(app)
 
@@ -235,6 +241,7 @@ func NewApp() *App {
 		osExit:       os.Exit,
 		stdoutWriter: os.Stdout,
 		stderrWriter: os.Stderr,
+		rootctx:      context.Background(),
 	}
 }
 
@@ -268,7 +275,7 @@ func safetyFlagVar(cmd *kingpin.CmdClause, result *maintenance.SafetyParameters)
 
 func (c *App) noRepositoryAction(act func(ctx context.Context) error) func(ctx *kingpin.ParseContext) error {
 	return func(_ *kingpin.ParseContext) error {
-		return act(rootContext())
+		return act(c.rootContext())
 	}
 }
 
@@ -284,7 +291,7 @@ func (c *App) serverAction(sf *serverClientFlags, act func(ctx context.Context,
 			return errors.Wrap(err, "unable to create API client")
 		}
 
-		return act(rootContext(), apiClient)
+		return act(c.rootContext(), apiClient)
 	}
 }
 
@@ -348,8 +355,8 @@ func (c *App) repositoryWriterAction(act func(ctx context.Context, rep repo.Repo
 	})
 }
 
-func rootContext() context.Context {
-	return context.Background()
+func (c *App) rootContext() context.Context {
+	return c.rootctx
 }
 
 type repositoryAccessMode struct {
@@ -359,7 +366,7 @@ type repositoryAccessMode struct {
 
 func (c *App) maybeRepositoryAction(act func(ctx context.Context, rep repo.Repository) error, mode repositoryAccessMode) func(ctx *kingpin.ParseContext) error {
 	return func(kpc *kingpin.ParseContext) error {
-		ctx := rootContext()
+		ctx := c.rootContext()
 
 		if err := withProfiling(func() error {
 			c.mt.startMemoryTracking(ctx)
@@ -398,7 +405,7 @@ func (c *App) maybeRepositoryAction(act func(ctx context.Context, rep repo.Repos
 		}); err != nil {
 			// print error in red
 			log(ctx).Errorf("ERROR: %v", err.Error())
-			os.Exit(1)
+			c.osExit(1)
 		}
 
 		return nil
@@ -436,15 +443,20 @@ func (c *App) maybeRunMaintenance(ctx context.Context, rep repo.Repository) erro
 	return errors.Wrap(err, "error running maintenance")
 }
 
-func advancedCommand(ctx context.Context) {
-	if os.Getenv("KOPIA_ADVANCED_COMMANDS") != "enabled" {
-		log(ctx).Errorf(`
+func (c *App) advancedCommand(ctx context.Context) {
+	if c.AdvancedCommands != "enabled" {
+		_, _ = errorColor.Fprintf(c.stderrWriter, `
 This command could be dangerous or lead to repository corruption when used improperly.
 
 Running this command is not needed for using Kopia. Instead, most users should rely on periodic repository maintenance. See https://kopia.io/docs/advanced/maintenance/ for more information.
 To run this command despite the warning, set KOPIA_ADVANCED_COMMANDS=enabled
 
 `)
-		os.Exit(1)
+
+		c.osExit(1)
 	}
 }
+
+func init() {
+	kingpin.EnableFileExpansion = false
+}

cli/command_blob_delete.go

@@ -11,16 +11,20 @@ import (
 
 type commandBlobDelete struct {
 	blobIDs []string
+
+	svc appServices
 }
 
 func (c *commandBlobDelete) setup(svc appServices, parent commandParent) {
 	cmd := parent.Command("delete", "Delete blobs by ID").Alias("remove").Alias("rm")
 	cmd.Arg("blobIDs", "Blob IDs").Required().StringsVar(&c.blobIDs)
 	cmd.Action(svc.directRepositoryWriteAction(c.run))
+
+	c.svc = svc
 }
 
 func (c *commandBlobDelete) run(ctx context.Context, rep repo.DirectRepositoryWriter) error {
-	advancedCommand(ctx)
+	c.svc.advancedCommand(ctx)
 
 	for _, b := range c.blobIDs {
 		err := rep.BlobStorage().DeleteBlob(ctx, blob.ID(b))

cli/command_blob_gc.go

@@ -15,6 +15,8 @@ type commandBlobGC struct {
 	parallel int
 	prefix   string
 	safety   maintenance.SafetyParameters
+
+	svc appServices
 }
 
 func (c *commandBlobGC) setup(svc appServices, parent commandParent) {
@@ -24,10 +26,12 @@ func (c *commandBlobGC) setup(svc appServices, parent commandParent) {
 	cmd.Flag("prefix", "Only GC blobs with given prefix").StringVar(&c.prefix)
 	safetyFlagVar(cmd, &c.safety)
 	cmd.Action(svc.directRepositoryWriteAction(c.run))
+
+	c.svc = svc
 }
 
 func (c *commandBlobGC) run(ctx context.Context, rep repo.DirectRepositoryWriter) error {
-	advancedCommand(ctx)
+	c.svc.advancedCommand(ctx)
 
 	opts := maintenance.DeleteUnreferencedBlobsOptions{
 		DryRun:   c.delete != "yes",

cli/command_blob_show.go

@@ -5,7 +5,6 @@ import (
 	"context"
 	"encoding/json"
 	"io"
-	"os"
 
 	"github.com/pkg/errors"
 
@@ -17,6 +16,8 @@ import (
 type commandBlobShow struct {
 	blobShowDecrypt bool
 	blobShowIDs     []string
+
+	out textOutput
 }
 
 func (c *commandBlobShow) setup(svc appServices, parent commandParent) {
@@ -24,11 +25,13 @@ func (c *commandBlobShow) setup(svc appServices, parent commandParent) {
 	cmd.Flag("decrypt", "Decrypt blob if possible").BoolVar(&c.blobShowDecrypt)
 	cmd.Arg("blobID", "Blob IDs").Required().StringsVar(&c.blobShowIDs)
 	cmd.Action(svc.directRepositoryReadAction(c.run))
+
+	c.out.setup(svc)
 }
 
 func (c *commandBlobShow) run(ctx context.Context, rep repo.DirectRepository) error {
 	for _, blobID := range c.blobShowIDs {
-		if err := c.maybeDecryptBlob(ctx, os.Stdout, rep, blob.ID(blobID)); err != nil {
+		if err := c.maybeDecryptBlob(ctx, c.out.stdout(), rep, blob.ID(blobID)); err != nil {
 			return errors.Wrap(err, "error presenting blob")
 		}
 	}

cli/command_content_delete.go

@@ -10,16 +10,20 @@ import (
 
 type commandContentDelete struct {
 	ids []string
+
+	svc appServices
 }
 
 func (c *commandContentDelete) setup(svc appServices, parent commandParent) {
 	cmd := parent.Command("delete", "Remove content").Alias("remove").Alias("rm")
 	cmd.Arg("id", "IDs of content to remove").Required().StringsVar(&c.ids)
 	cmd.Action(svc.directRepositoryWriteAction(c.run))
+
+	c.svc = svc
 }
 
 func (c *commandContentDelete) run(ctx context.Context, rep repo.DirectRepositoryWriter) error {
-	advancedCommand(ctx)
+	c.svc.advancedCommand(ctx)
 
 	for _, contentID := range toContentIDs(c.ids) {
 		if err := rep.ContentManager().DeleteContent(ctx, contentID); err != nil {

cli/command_content_rewrite.go

@@ -19,6 +19,7 @@ type commandContentRewrite struct {
 	contentRewriteSafety        maintenance.SafetyParameters
 
 	contentRange contentRangeFlags
+	svc          appServices
 }
 
 func (c *commandContentRewrite) setup(svc appServices, parent commandParent) {
@@ -33,10 +34,12 @@ func (c *commandContentRewrite) setup(svc appServices, parent commandParent) {
 	c.contentRange.setup(cmd)
 	safetyFlagVar(cmd, &c.contentRewriteSafety)
 	cmd.Action(svc.directRepositoryWriteAction(c.runContentRewriteCommand))
+
+	c.svc = svc
 }
 
 func (c *commandContentRewrite) runContentRewriteCommand(ctx context.Context, rep repo.DirectRepositoryWriter) error {
-	advancedCommand(ctx)
+	c.svc.advancedCommand(ctx)
 
 	return maintenance.RewriteContents(ctx, rep, &maintenance.RewriteContentsOptions{
 		ContentIDRange: c.contentRange.contentIDRange(),

cli/command_content_show.go

@@ -14,6 +14,8 @@ type commandContentShow struct {
 	ids        []string
 	indentJSON bool
 	decompress bool
+
+	out textOutput
 }
 
 func (c *commandContentShow) setup(svc appServices, parent commandParent) {
@@ -23,6 +25,8 @@ func (c *commandContentShow) setup(svc appServices, parent commandParent) {
 	cmd.Flag("json", "Pretty-print JSON content").Short('j').BoolVar(&c.indentJSON)
 	cmd.Flag("unzip", "Transparently decompress the content").Short('z').BoolVar(&c.decompress)
 	cmd.Action(svc.directRepositoryReadAction(c.run))
+
+	c.out.setup(svc)
 }
 
 func (c *commandContentShow) run(ctx context.Context, rep repo.DirectRepository) error {
@@ -41,5 +45,5 @@ func (c *commandContentShow) contentShow(ctx context.Context, r repo.DirectRepos
 		return errors.Wrapf(err, "error getting content %v", contentID)
 	}
 
-	return showContentWithFlags(bytes.NewReader(data), c.decompress, c.indentJSON)
+	return showContentWithFlags(c.out.stdout(), bytes.NewReader(data), c.decompress, c.indentJSON)
 }

cli/command_diff.go

@@ -2,7 +2,6 @@ package cli
 
 import (
 	"context"
-	"os"
 	"strings"
 
 	"github.com/pkg/errors"
@@ -18,6 +17,8 @@ type commandDiff struct {
 	diffSecondObjectPath string
 	diffCompareFiles     bool
 	diffCommandCommand   string
+
+	out textOutput
 }
 
 func (c *commandDiff) setup(svc appServices, parent commandParent) {
@@ -27,6 +28,8 @@ func (c *commandDiff) setup(svc appServices, parent commandParent) {
 	cmd.Flag("files", "Compare files by launching diff command for all pairs of (old,new)").Short('f').BoolVar(&c.diffCompareFiles)
 	cmd.Flag("diff-command", "Displays differences between two repository objects (files or directories)").Default(defaultDiffCommand()).Envar("KOPIA_DIFF").StringVar(&c.diffCommandCommand)
 	cmd.Action(svc.repositoryReaderAction(c.run))
+
+	c.out.setup(svc)
 }
 
 func (c *commandDiff) run(ctx context.Context, rep repo.Repository) error {
@@ -47,7 +50,7 @@ func (c *commandDiff) run(ctx context.Context, rep repo.Repository) error {
 		return errors.New("arguments do diff must both be directories or both non-directories")
 	}
 
-	d, err := diff.NewComparer(os.Stdout)
+	d, err := diff.NewComparer(c.out.stdout())
 	if err != nil {
 		return errors.Wrap(err, "error creating comparer")
 	}

cli/command_index_optimize.go

@@ -13,6 +13,8 @@ type commandIndexOptimize struct {
 	optimizeDropDeletedOlderThan time.Duration
 	optimizeDropContents         []string
 	optimizeAllIndexes           bool
+
+	svc appServices
 }
 
 func (c *commandIndexOptimize) setup(svc appServices, parent commandParent) {
@@ -22,10 +24,12 @@ func (c *commandIndexOptimize) setup(svc appServices, parent commandParent) {
 	cmd.Flag("drop-contents", "Drop contents with given IDs").StringsVar(&c.optimizeDropContents)
 	cmd.Flag("all", "Optimize all indexes, even those above maximum size.").BoolVar(&c.optimizeAllIndexes)
 	cmd.Action(svc.directRepositoryWriteAction(c.runOptimizeCommand))
+
+	c.svc = svc
 }
 
 func (c *commandIndexOptimize) runOptimizeCommand(ctx context.Context, rep repo.DirectRepositoryWriter) error {
-	advancedCommand(ctx)
+	c.svc.advancedCommand(ctx)
 
 	opt := content.CompactOptions{
 		MaxSmallBlobs: c.optimizeMaxSmallBlobs,

cli/command_index_recover.go

@@ -13,6 +13,8 @@ import (
 type commandIndexRecover struct {
 	blobIDs []string
 	commit  bool
+
+	svc appServices
 }
 
 func (c *commandIndexRecover) setup(svc appServices, parent commandParent) {
@@ -20,10 +22,12 @@ func (c *commandIndexRecover) setup(svc appServices, parent commandParent) {
 	cmd.Flag("blobs", "Names of pack blobs to recover from (default=all packs)").StringsVar(&c.blobIDs)
 	cmd.Flag("commit", "Commit recovered content").BoolVar(&c.commit)
 	cmd.Action(svc.directRepositoryWriteAction(c.run))
+
+	c.svc = svc
 }
 
 func (c *commandIndexRecover) run(ctx context.Context, rep repo.DirectRepositoryWriter) error {
-	advancedCommand(ctx)
+	c.svc.advancedCommand(ctx)
 
 	var totalCount int
 

cli/command_ls.go

@@ -113,7 +113,7 @@ func (c *commandList) printDirectoryEntry(ctx context.Context, e fs.Entry, prefi
 		info = fmt.Sprintf("%v%v", c.nameToDisplay(prefix, e), errorSummary)
 	}
 
-	col.Println(info) //nolint:errcheck
+	col.Fprintln(c.out.stdout(), info) //nolint:errcheck
 
 	if c.recursive {
 		if subdir, ok := e.(fs.Directory); ok {

cli/command_manifest_delete.go

@@ -10,16 +10,20 @@ import (
 
 type commandManifestDelete struct {
 	manifestRemoveItems []string
+
+	svc appServices
 }
 
 func (c *commandManifestDelete) setup(svc appServices, parent commandParent) {
 	cmd := parent.Command("delete", "Remove manifest items").Alias("remove").Alias("rm")
 	cmd.Arg("item", "Items to remove").Required().StringsVar(&c.manifestRemoveItems)
 	cmd.Action(svc.repositoryWriterAction(c.run))
+
+	c.svc = svc
 }
 
 func (c *commandManifestDelete) run(ctx context.Context, rep repo.RepositoryWriter) error {
-	advancedCommand(ctx)
+	c.svc.advancedCommand(ctx)
 
 	for _, it := range toManifestIDs(c.manifestRemoveItems) {
 		if err := rep.DeleteManifest(ctx, it); err != nil {

cli/command_manifest_show.go

@@ -51,7 +51,7 @@ func (c *commandManifestShow) showManifestItems(ctx context.Context, rep repo.Re
 			c.out.printStdout("// label %v:%v\n", k, v)
 		}
 
-		if showerr := showContentWithFlags(bytes.NewReader(b), false, true); showerr != nil {
+		if showerr := showContentWithFlags(c.out.stdout(), bytes.NewReader(b), false, true); showerr != nil {
 			return showerr
 		}
 	}

cli/command_repository_connect.go

@@ -31,7 +31,7 @@ func (c *commandRepositoryConnect) setup(svc advancedAppServices, parent command
 		cc := cmd.Command(prov.name, "Connect to repository in "+prov.description)
 		f.setup(svc, cc)
 		cc.Action(func(_ *kingpin.ParseContext) error {
-			ctx := rootContext()
+			ctx := svc.rootContext()
 			st, err := f.connect(ctx, false)
 			if err != nil {
 				return errors.Wrap(err, "can't connect to storage")

cli/command_repository_create.go

@@ -49,7 +49,7 @@ func (c *commandRepositoryCreate) setup(svc advancedAppServices, parent commandP
 		cc := cmd.Command(prov.name, "Create repository in "+prov.description)
 		f.setup(svc, cc)
 		cc.Action(func(_ *kingpin.ParseContext) error {
-			ctx := rootContext()
+			ctx := svc.rootContext()
 			st, err := f.connect(ctx, true)
 			if err != nil {
 				return errors.Wrap(err, "can't connect to storage")

cli/command_repository_repair.go

@@ -30,7 +30,7 @@ func (c *commandRepositoryRepair) setup(svc advancedAppServices, parent commandP
 		cc := cmd.Command(prov.name, "Repair repository in "+prov.description)
 		f.setup(svc, cc)
 		cc.Action(func(_ *kingpin.ParseContext) error {
-			ctx := rootContext()
+			ctx := svc.rootContext()
 			st, err := f.connect(ctx, false)
 			if err != nil {
 				return errors.Wrap(err, "can't connect to storage")

cli/command_repository_sync.go

@@ -21,6 +21,8 @@ import (
 )
 
 type commandRepositorySyncTo struct {
+	nextSyncOutputTime *timetrack.Throttle
+
 	repositorySyncUpdate               bool
 	repositorySyncDelete               bool
 	repositorySyncDryRun               bool
@@ -30,7 +32,6 @@ type commandRepositorySyncTo struct {
 
 	lastSyncProgress       string
 	syncProgressMutex      sync.Mutex
-	nextSyncOutputTime     timetrack.Throttle
 	setTimeUnsupportedOnce sync.Once
 
 	out textOutput
@@ -47,13 +48,16 @@ func (c *commandRepositorySyncTo) setup(svc advancedAppServices, parent commandP
 
 	c.out.setup(svc)
 
+	// needs to be 64-bit aligned on ARM
+	c.nextSyncOutputTime = new(timetrack.Throttle)
+
 	for _, prov := range storageProviders {
 		// Set up 'sync-to' subcommand
 		f := prov.newFlags()
 		cc := cmd.Command(prov.name, "Synchronize repository data to another repository in "+prov.description)
 		f.setup(svc, cc)
 		cc.Action(func(_ *kingpin.ParseContext) error {
-			ctx := rootContext()
+			ctx := svc.rootContext()
 			st, err := f.connect(ctx, false)
 			if err != nil {
 				return errors.Wrap(err, "can't connect to storage")

cli/command_show.go

@@ -2,7 +2,6 @@ package cli
 
 import (
 	"context"
-	"os"
 
 	"github.com/pkg/errors"
 
@@ -13,12 +12,16 @@ import (
 
 type commandShow struct {
 	path string
+
+	out textOutput
 }
 
 func (c *commandShow) setup(svc appServices, parent commandParent) {
 	cmd := parent.Command("show", "Displays contents of a repository object.").Alias("cat")
 	cmd.Arg("object-path", "Path").Required().StringVar(&c.path)
 	cmd.Action(svc.repositoryReaderAction(c.run))
+
+	c.out.setup(svc)
 }
 
 func (c *commandShow) run(ctx context.Context, rep repo.Repository) error {
@@ -34,7 +37,7 @@ func (c *commandShow) run(ctx context.Context, rep repo.Repository) error {
 
 	defer r.Close() //nolint:errcheck
 
-	_, err = iocopy.Copy(os.Stdout, r)
+	_, err = iocopy.Copy(c.out.stdout(), r)
 
 	return errors.Wrap(err, "unable to copy data")
 }

cli/command_snapshot_list.go

@@ -252,7 +252,7 @@ func (c *commandSnapshotList) outputManifestFromSingleSource(ctx context.Context
 		elidedCount = 0
 		previousOID = oid
 
-		col.Print(fmt.Sprintf("  %v %v %v\n", formatTimestamp(m.StartTime), oid, strings.Join(bits, " "))) //nolint:errcheck
+		col.Fprint(c.out.stdout(), fmt.Sprintf("  %v %v %v\n", formatTimestamp(m.StartTime), oid, strings.Join(bits, " "))) //nolint:errcheck
 
 		count++
 

cli/inproc.go

@@ -0,0 +1,55 @@
+package cli
+
+import (
+	"context"
+	"io"
+
+	"github.com/alecthomas/kingpin"
+	"github.com/pkg/errors"
+
+	"github.com/kopia/kopia/repo/logging"
+)
+
+// RunSubcommand executes the subcommand asynchronously in current process
+// with flags in an isolated CLI environment and returns standard output and standard error.
+func (c *App) RunSubcommand(ctx context.Context, argsAndFlags []string) (stdout, stderr io.Reader, wait func() error, kill func()) {
+	kpapp := kingpin.New("test", "test")
+
+	stdoutReader, stdoutWriter := io.Pipe()
+	stderrReader, stderrWriter := io.Pipe()
+
+	c.stdoutWriter = stdoutWriter
+	c.stderrWriter = stderrWriter
+	c.rootctx = logging.WithLogger(ctx, logging.Writer(stderrWriter))
+
+	c.Attach(kpapp)
+
+	var exitCode int
+
+	resultErr := make(chan error, 1)
+
+	c.osExit = func(ec int) {
+		exitCode = ec
+	}
+
+	go func() {
+		defer close(resultErr)
+		defer stderrWriter.Close() //nolint:errcheck
+		defer stdoutWriter.Close() //nolint:errcheck
+
+		_, err := kpapp.Parse(argsAndFlags)
+		if err != nil {
+			resultErr <- err
+			return
+		}
+
+		if exitCode != 0 {
+			resultErr <- errors.Errorf("exit code %v", exitCode)
+			return
+		}
+	}()
+
+	return stdoutReader, stderrReader, func() error {
+		return <-resultErr
+	}, func() {}
+}

cli/show_utils.go

@@ -7,7 +7,6 @@ import (
 	"fmt"
 	"io"
 	"io/ioutil"
-	"os"
 	"time"
 
 	"github.com/pkg/errors"
@@ -17,9 +16,9 @@ import (
 )
 
 // TODO - remove this global.
-var timeZone string
+var timeZone = "local"
 
-func showContentWithFlags(rd io.Reader, unzip, indentJSON bool) error {
+func showContentWithFlags(w io.Writer, rd io.Reader, unzip, indentJSON bool) error {
 	if unzip {
 		gz, err := gzip.NewReader(rd)
 		if err != nil {
@@ -43,7 +42,7 @@ func showContentWithFlags(rd io.Reader, unzip, indentJSON bool) error {
 		rd = ioutil.NopCloser(&buf2)
 	}
 
-	if _, err := iocopy.Copy(os.Stdout, rd); err != nil {
+	if _, err := iocopy.Copy(w, rd); err != nil {
 		return errors.Wrap(err, "error copying data")
 	}