parentDirIsObject() to return quickly with inexistant parent (#11204)

Rewrite parentIsObject() function. Currently if a client uploads
a/b/c/d, we always check if c, b, a are actual objects or not.

The new code will check with the reverse order and quickly quit if 
the segment doesn't exist.

So if a, b, c in 'a/b/c' does not exist in the first place, then returns
false quickly.

cmd/erasure-common.go

@@ -18,8 +18,8 @@ package cmd
 
 import (
 	"context"
-	"path"
 	"sort"
+	"strings"
 	"sync"
 
 	"github.com/minio/minio/pkg/sync/errgroup"
@@ -207,24 +207,29 @@ func (er erasureObjects) getLoadBalancedDisks(optimized bool) []StorageAPI {
 // object is "a/b/c/d", stat makes sure that objects ""a/b/c""
 // "a/b" and "a" do not exist.
 func (er erasureObjects) parentDirIsObject(ctx context.Context, bucket, parent string) bool {
-	var isParentDirObject func(string) bool
-	isParentDirObject = func(p string) bool {
-		if p == "." || p == SlashSeparator {
+	path := ""
+	segments := strings.Split(parent, slashSeparator)
+	for _, s := range segments {
+		if s == "" {
+			break
+		}
+		path += s
+		isObject, pathNotExist := er.isObject(ctx, bucket, path)
+		if pathNotExist {
 			return false
 		}
-		if er.isObject(ctx, bucket, p) {
+		if isObject {
 			// If there is already a file at prefix "p", return true.
 			return true
 		}
-		// Check if there is a file as one of the parent paths.
-		return isParentDirObject(path.Dir(p))
+		path += slashSeparator
 	}
-	return isParentDirObject(parent)
+	return false
 }
 
 // isObject - returns `true` if the prefix is an object i.e if
 // `xl.meta` exists at the leaf, false otherwise.
-func (er erasureObjects) isObject(ctx context.Context, bucket, prefix string) (ok bool) {
+func (er erasureObjects) isObject(ctx context.Context, bucket, prefix string) (ok, pathDoesNotExist bool) {
 	storageDisks := er.getDisks()
 
 	g := errgroup.WithNErrs(len(storageDisks))
@@ -246,5 +251,6 @@ func (er erasureObjects) isObject(ctx context.Context, bucket, prefix string) (o
 	// ignored if necessary.
 	readQuorum := getReadQuorum(len(storageDisks))
 
-	return reduceReadQuorumErrs(ctx, g.Wait(), objectOpIgnoredErrs, readQuorum) == nil
+	err := reduceReadQuorumErrs(ctx, g.Wait(), objectOpIgnoredErrs, readQuorum)
+	return err == nil, err == errPathNotFound
 }

cmd/erasure-common_test.go

@@ -66,6 +66,10 @@ func TestErasureParentDirIsObject(t *testing.T) {
 			parentIsObject: true,
 			objectName:     objectName,
 		},
+		{
+			parentIsObject: false,
+			objectName:     "new-dir",
+		},
 		{
 			parentIsObject: false,
 			objectName:     "",

cmd/storage-errors.go

@@ -67,6 +67,9 @@ var errVolumeExists = StorageErr("volume already exists")
 // errIsNotRegular - not of regular file type.
 var errIsNotRegular = StorageErr("not of regular file type")
 
+// errPathNotFound - cannot find the path.
+var errPathNotFound = StorageErr("path not found")
+
 // errVolumeNotFound - cannot find the volume.
 var errVolumeNotFound = StorageErr("volume not found")
 

cmd/storage-rest-client.go

@@ -82,6 +82,8 @@ func toStorageErr(err error) error {
 		return errFileNameTooLong
 	case errFileAccessDenied.Error():
 		return errFileAccessDenied
+	case errPathNotFound.Error():
+		return errPathNotFound
 	case errIsNotRegular.Error():
 		return errIsNotRegular
 	case errVolumeNotEmpty.Error():

cmd/xl-storage.go

@@ -1757,10 +1757,10 @@ func (s *xlStorage) CheckFile(ctx context.Context, volume string, path string) e
 	}
 
 	// Stat a volume entry.
-	_, err = os.Stat(volumeDir)
+	_, err = os.Stat(pathJoin(volumeDir, path))
 	if err != nil {
 		if osIsNotExist(err) {
-			return errVolumeNotFound
+			return errPathNotFound
 		}
 		return err
 	}

cmd/xl-storage_test.go

@@ -1596,14 +1596,14 @@ func TestXLStorageCheckFile(t *testing.T) {
 		{
 			srcVol:      "success-vol",
 			srcPath:     "nonexistent-file",
-			expectedErr: errFileNotFound,
+			expectedErr: errPathNotFound,
 		},
 		// TestXLStorage case - 4.
 		// TestXLStorage case with non-existent file path.
 		{
 			srcVol:      "success-vol",
 			srcPath:     "path/2/success-file",
-			expectedErr: errFileNotFound,
+			expectedErr: errPathNotFound,
 		},
 		// TestXLStorage case - 5.
 		// TestXLStorage case with path being a directory.
@@ -1617,7 +1617,7 @@ func TestXLStorageCheckFile(t *testing.T) {
 		{
 			srcVol:      "non-existent-vol",
 			srcPath:     "success-file",
-			expectedErr: errVolumeNotFound,
+			expectedErr: errPathNotFound,
 		},
 	}