add --succeed-on-exists flag to make s3 repo init idempotent (#324)

* [Minor #323] add --success-on-exists flag to make  idempotent

Co-authored-by: ryanfkeepers <ryanfkeepers@gmail.com>
Co-authored-by: Keepers <104464746+ryanfkeepers@users.noreply.github.com>

src/cli/repo/s3.go

@@ -9,6 +9,7 @@ import (
 
 	"github.com/alcionai/corso/cli/config"
 	"github.com/alcionai/corso/cli/utils"
+	"github.com/alcionai/corso/internal/kopia"
 	"github.com/alcionai/corso/pkg/account"
 	"github.com/alcionai/corso/pkg/credentials"
 	"github.com/alcionai/corso/pkg/logger"
@@ -18,10 +19,11 @@ import (
 
 // s3 bucket info from flags
 var (
-	accessKey string
-	bucket    string
-	endpoint  string
-	prefix    string
+	accessKey       string
+	bucket          string
+	endpoint        string
+	prefix          string
+	succeedIfExists bool
 )
 
 // called by repo.go to map parent subcommands to provider-specific handling.
@@ -41,6 +43,10 @@ func addS3Commands(parent *cobra.Command) *cobra.Command {
 	cobra.CheckErr(c.MarkFlagRequired("bucket"))
 	fs.StringVar(&endpoint, "endpoint", "s3.amazonaws.com", "Server endpoint for S3 communication.")
 	fs.StringVar(&prefix, "prefix", "", "Prefix applied to objects in the bucket.")
+	fs.BoolVar(&succeedIfExists, "succeed-if-exists", false, "Exit with success if the repo has already been initialized.")
+	// In general, we don't want to expose this flag to users and have them mistake it
+	// for a broad-scale idempotency solution.  We can un-hide it later the need arises.
+	cobra.CheckErr(fs.MarkHidden("succeed-if-exists"))
 	return c
 }
 
@@ -88,6 +94,9 @@ func initS3Cmd(cmd *cobra.Command, args []string) error {
 
 	r, err := repository.Initialize(ctx, a, s)
 	if err != nil {
+		if succeedIfExists && kopia.IsRepoAlreadyExistsError(err) {
+			return nil
+		}
 		return errors.Wrap(err, "Failed to initialize a new S3 repository")
 	}
 	defer utils.CloseRepo(ctx, r)

src/internal/kopia/conn.go

@@ -8,6 +8,7 @@ import (
 	"github.com/kopia/kopia/repo/blob"
 	"github.com/pkg/errors"
 
+	"github.com/alcionai/corso/internal/common"
 	"github.com/alcionai/corso/pkg/storage"
 )
 
@@ -20,6 +21,19 @@ var (
 	errConnect = errors.New("connecting repo")
 )
 
+type ErrorRepoAlreadyExists struct {
+	common.Err
+}
+
+func RepoAlreadyExistsError(e error) error {
+	return ErrorRepoAlreadyExists{*common.EncapsulateError(e)}
+}
+
+func IsRepoAlreadyExistsError(e error) bool {
+	var erae ErrorRepoAlreadyExists
+	return errors.As(e, &erae)
+}
+
 type conn struct {
 	storage storage.Storage
 	repo.Repository
@@ -47,6 +61,9 @@ func (w *conn) Initialize(ctx context.Context) error {
 
 	// todo - issue #75: nil here should be a storage.NewRepoOptions()
 	if err = repo.Initialize(ctx, bst, nil, cfg.CorsoPassword); err != nil {
+		if errors.Is(err, repo.ErrAlreadyInitialized) {
+			return RepoAlreadyExistsError(err)
+		}
 		return errors.Wrap(err, errInit.Error())
 	}