fix: correct consumers handling when custom_id is used

Right now, when a consumer has the `username` equal to the
`custom_id` of another consumer, decK fails because of the
way the consumers are handled in the internal in-memory DB.

```
_format_version: "3.0"
consumers:
- custom_id: foo
  id: ce49186d-7670-445d-a218-897631b29ada
  username: Foo
- custom_id: bar
  id: 7820f383-7b77-4fcc-af7f-14ff3e256693
  username: foo
```

```
$ deck sync
Error: inserting consumer into state: inserting consumer Foo: entity already exists
```

This commit fixes this defect by modifying the way consumers are
looked up in the in-memory DB.

CHANGELOG.md

@@ -61,6 +61,13 @@
 - [v0.2.0](#v020)
 - [v0.1.0](#v010)
 
+## Unreleased
+
+### Fixes
+
+- Fix Consumers handling when a consumer's `custom_id` is equal to the `username` of another consumer.
+  [#986](https://github.com/Kong/deck/pull/986)
+
 ## [v1.24.0]
 
 > Release date: 2023/07/24

state/consumer.go

@@ -54,10 +54,23 @@ func (k *ConsumersCollection) Add(consumer Consumer) error {
 	if !utils.Empty(consumer.Username) {
 		searchBy = append(searchBy, *consumer.Username)
 	}
+
+	// search separately by id+username and by custom_id.
+	//
+	// This is because the custom_id is unique, but it may be equal to
+	// the username of another consumer. If we search by both id+username and
+	// custom_id, we may get a false positive.
+	_, err := getConsumer(txn, []string{"Username", "id"}, searchBy...)
+	if err == nil {
+		return fmt.Errorf("inserting consumer %v: %w", consumer.Console(), ErrAlreadyExists)
+	} else if !errors.Is(err, ErrNotFound) {
+		return err
+	}
+
 	if !utils.Empty(consumer.CustomID) {
-		searchBy = append(searchBy, *consumer.CustomID)
+		searchBy = []string{*consumer.CustomID}
 	}
-	_, err := getConsumer(txn, searchBy...)
+	_, err = getConsumer(txn, []string{"CustomID"}, searchBy...)
 	if err == nil {
 		return fmt.Errorf("inserting consumer %v: %w", consumer.Console(), ErrAlreadyExists)
 	} else if !errors.Is(err, ErrNotFound) {
@@ -72,10 +85,9 @@ func (k *ConsumersCollection) Add(consumer Consumer) error {
 	return nil
 }
 
-func getConsumer(txn *memdb.Txn, IDs ...string) (*Consumer, error) {
+func getConsumer(txn *memdb.Txn, indexes []string, IDs ...string) (*Consumer, error) {
 	for _, id := range IDs {
-		res, err := multiIndexLookupUsingTxn(txn, consumerTableName,
-			[]string{"Username", "id", "CustomID"}, id)
+		res, err := multiIndexLookupUsingTxn(txn, consumerTableName, indexes, id)
 		if errors.Is(err, ErrNotFound) {
 			continue
 		}
@@ -99,7 +111,7 @@ func (k *ConsumersCollection) Get(userNameOrID string) (*Consumer, error) {
 
 	txn := k.db.Txn(false)
 	defer txn.Abort()
-	return getConsumer(txn, userNameOrID)
+	return getConsumer(txn, []string{"Username", "id"}, userNameOrID)
 }
 
 // Update udpates an existing consumer.
@@ -128,7 +140,7 @@ func (k *ConsumersCollection) Update(consumer Consumer) error {
 }
 
 func deleteConsumer(txn *memdb.Txn, userNameOrID string) error {
-	consumer, err := getConsumer(txn, userNameOrID)
+	consumer, err := getConsumer(txn, []string{"Username", "id"}, userNameOrID)
 	if err != nil {
 		return err
 	}

tests/integration/sync_test.go

@@ -3519,3 +3519,33 @@ func Test_Sync_CreateCertificateWithSNIs(t *testing.T) {
 		},
 	}, ignoredFields)
 }
+
+// test scope:
+//   - 3.0.0+
+//   - konnect
+func Test_Sync_ConsumersWithCustomIDAndUsername(t *testing.T) {
+	runWhenKongOrKonnect(t, ">=3.0.0")
+
+	client, err := getTestClient()
+	if err != nil {
+		t.Errorf(err.Error())
+	}
+
+	err = sync("testdata/sync/024-consumers-with-custom_id-and-username/kong3x.yaml")
+	require.NoError(t, err)
+
+	testKongState(t, client, false, utils.KongRawState{
+		Consumers: []*kong.Consumer{
+			{
+				ID:       kong.String("ce49186d-7670-445d-a218-897631b29ada"),
+				Username: kong.String("Foo"),
+				CustomID: kong.String("foo"),
+			},
+			{
+				ID:       kong.String("7820f383-7b77-4fcc-af7f-14ff3e256693"),
+				Username: kong.String("foo"),
+				CustomID: kong.String("bar"),
+			},
+		},
+	}, nil)
+}

tests/integration/testdata/sync/024-consumers-with-custom_id-and-username/kong3x.yaml

@@ -0,0 +1,8 @@
+_format_version: "3.0"
+consumers:
+- custom_id: foo
+  id: ce49186d-7670-445d-a218-897631b29ada
+  username: Foo
+- custom_id: bar
+  id: 7820f383-7b77-4fcc-af7f-14ff3e256693
+  username: foo