fix: duplicated shared prefix with custom delimiter when listing (#16111)

cmd/erasure-server-pool.go

@@ -1254,7 +1254,20 @@ func (z *erasureServerPools) ListObjectVersions(ctx context.Context, bucket, pre
 	}
 	for _, obj := range objects {
 		if obj.IsDir && obj.ModTime.IsZero() && delimiter != "" {
-			loi.Prefixes = append(loi.Prefixes, obj.Name)
+			// Only add each once.
+			// With slash delimiter we only get the directory once.
+			found := false
+			if delimiter != slashSeparator {
+				for _, p := range loi.Prefixes {
+					if found {
+						break
+					}
+					found = p == obj.Name
+				}
+			}
+			if !found {
+				loi.Prefixes = append(loi.Prefixes, obj.Name)
+			}
 		} else {
 			loi.Objects = append(loi.Objects, obj)
 		}
@@ -1334,7 +1347,20 @@ func (z *erasureServerPools) ListObjects(ctx context.Context, bucket, prefix, ma
 	}
 	for _, obj := range objects {
 		if obj.IsDir && obj.ModTime.IsZero() && delimiter != "" {
-			loi.Prefixes = append(loi.Prefixes, obj.Name)
+			// Only add each once.
+			// With slash delimiter we only get the directory once.
+			found := false
+			if delimiter != slashSeparator {
+				for _, p := range loi.Prefixes {
+					if found {
+						break
+					}
+					found = p == obj.Name
+				}
+			}
+			if !found {
+				loi.Prefixes = append(loi.Prefixes, obj.Name)
+			}
 		} else {
 			loi.Objects = append(loi.Objects, obj)
 		}

cmd/object-api-listobjects_test.go

@@ -315,18 +315,20 @@ func _testListObjects(obj ObjectLayer, instanceType string, t1 TestErrHandler, v
 	t, _ := t1.(*testing.T)
 	testBuckets := []string{
 		// This bucket is used for testing ListObject operations.
-		"test-bucket-list-object",
+		0: "test-bucket-list-object",
 		// This bucket will be tested with empty directories
-		"test-bucket-empty-dir",
+		1: "test-bucket-empty-dir",
 		// Will not store any objects in this bucket,
 		// Its to test ListObjects on an empty bucket.
-		"empty-bucket",
+		2: "empty-bucket",
 		// Listing the case where the marker > last object.
-		"test-bucket-single-object",
+		3: "test-bucket-single-object",
 		// Listing uncommon delimiter.
-		"test-bucket-delimiter",
+		4: "test-bucket-delimiter",
 		// Listing prefixes > maxKeys
-		"test-bucket-max-keys-prefixes",
+		5: "test-bucket-max-keys-prefixes",
+		// Listing custom delimiters
+		6: "test-bucket-custom-delimiter",
 	}
 	for _, bucket := range testBuckets {
 		err := obj.MakeBucketWithLocation(context.Background(), bucket, MakeBucketOptions{
@@ -366,6 +368,10 @@ func _testListObjects(obj ObjectLayer, instanceType string, t1 TestErrHandler, v
 		{testBuckets[5], "foo/201910/2112", "content", nil},
 		{testBuckets[5], "foo/201910_txt", "content", nil},
 		{testBuckets[5], "201910/foo/bar/xl.meta/1.txt", "content", nil},
+		{testBuckets[6], "aaa", "content", nil},
+		{testBuckets[6], "bbb_aaa", "content", nil},
+		{testBuckets[6], "bbb_aaa", "content", nil},
+		{testBuckets[6], "ccc", "content", nil},
 	}
 	for _, object := range testObjects {
 		md5Bytes := md5.Sum([]byte(object.content))
@@ -788,6 +794,15 @@ func _testListObjects(obj ObjectLayer, instanceType string, t1 TestErrHandler, v
 				{Name: "201910/foo/bar/xl.meta/1.txt"},
 			},
 		},
+		// ListObjectsResult-40
+		{
+			IsTruncated: false,
+			Objects: []ObjectInfo{
+				{Name: "aaa"},
+				{Name: "ccc"},
+			},
+			Prefixes: []string{"bbb_"},
+		},
 	}
 
 	testCases := []struct {
@@ -918,6 +933,8 @@ func _testListObjects(obj ObjectLayer, instanceType string, t1 TestErrHandler, v
 		{testBuckets[5], "foo/201910", "", "", 1000, resultCases[38], nil, true},
 		// Test listing with prefix match with 'xl.meta'
 		{testBuckets[5], "201910/foo/bar", "", "", 1000, resultCases[39], nil, true},
+		// Test listing with custom prefix
+		{testBuckets[6], "", "", "_", 1000, resultCases[40], nil, true},
 	}
 
 	for i, testCase := range testCases {