fix: avoid field spillover in parsing DS API responses

internal/emqx/api/ds.go

@@ -103,8 +103,8 @@ func GetDSReplicationStatus(requester req.RequesterInterface) (DSReplicationStat
 		return status, emperror.Wrap(err, "failed to retrieve DS DBs")
 	}
 
-	dbStatus := DSDBReplicationStatus{}
 	for _, db := range dsDatabases {
+		dbStatus := DSDBReplicationStatus{}
 		path := fmt.Sprintf("api/v5/ds/storages/%s", db)
 		body, err := get(requester, path)
 		if err != nil {

internal/emqx/api/ds_test.go

@@ -0,0 +1,98 @@
+package api
+
+import (
+	"net/http"
+	"net/url"
+	"testing"
+
+	req "github.com/emqx/emqx-operator/internal/requester"
+	"github.com/stretchr/testify/assert"
+	"github.com/stretchr/testify/require"
+)
+
+func mockRequesterURLs(responses map[string]string) *req.MockRequester {
+	return req.NewMockRequester(
+		func(method string, u url.URL, body []byte, header http.Header) (*http.Response, []byte, error) {
+			responseBody, ok := responses[u.Path]
+			if ok {
+				return &http.Response{StatusCode: 200}, []byte(responseBody), nil
+			}
+			return &http.Response{StatusCode: 501}, []byte{}, nil
+		},
+	)
+}
+
+func TestGetDSReplicationStatusTransitions(t *testing.T) {
+	// DB "messages" has a shard with a transition; DB "sessions" has a shard
+	// without transitions. Before the fix, `dbStatus` was reused across loop
+	// iterations, so "sessions" would inherit "messages"' transitions because
+	// the `omitempty` tag causes the field to be absent from the JSON.
+	r := mockRequesterURLs(map[string]string{
+		"api/v5/ds/storages": `["messages", "sessions"]`,
+		"api/v5/ds/storages/messages": `{
+			"name": "messages",
+			"shards": [{
+				"id": "0",
+				"replicas": [{"site": "site-a", "status": "up"}],
+				"transitions": [{"site": "site-b", "transition": "joining"}]
+			}]
+		}`,
+		"api/v5/ds/storages/sessions": `{
+			"name": "sessions",
+			"shards": [{
+				"id": "0",
+				"replicas": [{"site": "site-a", "status": "up"}]
+			}]
+		}`,
+	})
+
+	status, err := GetDSReplicationStatus(r)
+	require.NoError(t, err)
+	require.Len(t, status.DBs, 2)
+
+	messages := status.DBs[0]
+	sessions := status.DBs[1]
+
+	assert.Equal(t, "messages", messages.Name)
+	assert.Len(t, messages.Shards[0].Transitions, 1, "messages should have 1 transition")
+
+	assert.Equal(t, "sessions", sessions.Name)
+	assert.Empty(t, sessions.Shards[0].Transitions,
+		"sessions must NOT inherit transitions from messages (omitempty bug)")
+}
+
+func TestGetDSCluster(t *testing.T) {
+	r := mockRequesterURLs(map[string]string{
+		"api/v5/ds/sites": `["site-a", "site-b"]`,
+		"api/v5/ds/sites/site-a": `{
+			"node": "emqx@node1",
+			"up": true,
+			"shards": [{"storage": "messages", "id": "0", "status": "up"}]
+		}`,
+		"api/v5/ds/sites/site-b": `{
+			"node": "emqx@node2",
+			"up": false,
+			"shards": [{"storage": "messages", "id": "0", "status": "joining"}]
+		}`,
+	})
+
+	cluster, err := GetDSCluster(r)
+	require.NoError(t, err)
+	require.Len(t, cluster.Sites, 2)
+
+	assert.Equal(t, "site-a", cluster.Sites[0].ID)
+	assert.Equal(t, "emqx@node1", cluster.Sites[0].Node)
+	assert.True(t, cluster.Sites[0].Up)
+
+	assert.Equal(t, "site-b", cluster.Sites[1].ID)
+	assert.False(t, cluster.Sites[1].Up)
+}
+
+func TestGetDSAPIError(t *testing.T) {
+	var err error
+	r := mockRequesterURLs(map[string]string{})
+	_, err = GetDSReplicationStatus(r)
+	assert.Error(t, err)
+	_, err = GetDSCluster(r)
+	assert.Error(t, err)
+}