Throw 404 for head requests for prefixes without trailing "/" (#5966)

Minio server returns 403 (access denied) for head requests to prefixes
without trailing "/", this is different from S3 behaviour. S3 returns
404 in such cases.

Fixes #6080

cmd/fs-v1-helpers.go

@@ -199,7 +199,7 @@ func osErrToFSFileErr(err error) error {
 		return errFileAccessDenied
 	}
 	if isSysErrNotDir(err) {
-		return errFileAccessDenied
+		return errFileNotFound
 	}
 	if isSysErrPathNotFound(err) {
 		return errFileNotFound
@@ -218,8 +218,7 @@ func fsStatDir(ctx context.Context, statDir string) (os.FileInfo, error) {
 		return nil, err
 	}
 	if !fi.IsDir() {
-		logger.LogIf(ctx, errFileAccessDenied)
-		return nil, errFileAccessDenied
+		return nil, errFileNotFound
 	}
 	return fi, nil
 }
@@ -244,8 +243,7 @@ func fsStatFile(ctx context.Context, statFile string) (os.FileInfo, error) {
 		return nil, err
 	}
 	if fi.IsDir() {
-		logger.LogIf(ctx, errFileAccessDenied)
-		return nil, errFileAccessDenied
+		return nil, errFileNotFound
 	}
 	return fi, nil
 }

cmd/fs-v1-helpers_test.go

@@ -136,7 +136,7 @@ func TestFSStats(t *testing.T) {
 			srcFSPath:   path,
 			srcVol:      "success-vol",
 			srcPath:     "path",
-			expectedErr: errFileAccessDenied,
+			expectedErr: errFileNotFound,
 		},
 		// Test case - 6.
 		// Test case with src path segment > 255.

cmd/fs-v1.go

@@ -696,7 +696,7 @@ func (fs *FSObjects) getObjectInfoWithLock(ctx context.Context, bucket, object s
 	}
 
 	if _, err := fs.statBucketDir(ctx, bucket); err != nil {
-		return oi, toObjectErr(err, bucket)
+		return oi, err
 	}
 
 	if strings.HasSuffix(object, slashSeparator) && !fs.isObjectDir(bucket, object) {