Pagination for wlm/stats api

CHANGELOG.md

@@ -8,6 +8,7 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 - Add support for linux riscv64 platform ([#18156](https://github.com/opensearch-project/OpenSearch/pull/18156))
 - [Rule based auto-tagging] Add get rule API ([#17336](https://github.com/opensearch-project/OpenSearch/pull/17336))
 - [Rule based auto-tagging] Add Delete Rule API ([#18184](https://github.com/opensearch-project/OpenSearch/pull/18184))
+- Add paginated wlm/stats API ([#17638](https://github.com/opensearch-project/OpenSearch/pull/17638))
 - Implement parallel shard refresh behind cluster settings ([#17782](https://github.com/opensearch-project/OpenSearch/pull/17782))
 - Bump OpenSearch Core main branch to 3.0.0 ([#18039](https://github.com/opensearch-project/OpenSearch/pull/18039))
 - Update API of Message in index to add the timestamp for lag calculation in ingestion polling ([#17977](https://github.com/opensearch-project/OpenSearch/pull/17977/))

client/rest-high-level/src/test/java/org/opensearch/client/RestHighLevelClientTests.java

@@ -882,7 +882,8 @@ public void testApiNamingConventions() throws Exception {
             "cluster.delete_weighted_routing",
             "cluster.put_decommission_awareness",
             "cluster.get_decommission_awareness",
-            "cluster.delete_decommission_awareness", };
+            "cluster.delete_decommission_awareness",
+            "wlm_stats_list" };
         List<String> booleanReturnMethods = Arrays.asList("security.enable_user", "security.disable_user", "security.change_password");
         Set<String> deprecatedMethods = new HashSet<>();
         deprecatedMethods.add("indices.force_merge");

rest-api-spec/src/main/resources/rest-api-spec/api/wlm_stats_list.json

@@ -0,0 +1,44 @@
+{
+  "wlm_stats_list": {
+    "stability": "experimental",
+    "documentation": {
+      "url": "https://docs.opensearch.org/docs/latest/tuning-your-cluster/availability-and-recovery/workload-management/wlm-feature-overview/",
+      "description": "This API endpoint returns a list of WLM stats with pagination support."
+    },
+    "url": {
+      "paths": [
+        {
+          "path": "/_list/wlm_stats",
+          "methods": ["GET"]
+        }
+      ]
+    },
+    "params": {
+      "size": {
+        "type": "int",
+        "required": false,
+        "description": "Number of results per page"
+      },
+      "next_token": {
+        "type": "string",
+        "required": false,
+        "description": "Pagination token for next page"
+      },
+      "sort": {
+        "type": "string",
+        "required": false,
+        "description": "Sort field"
+      },
+      "order": {
+        "type": "string",
+        "required": false,
+        "description": "Sort order (asc or desc)"
+      },
+      "v": {
+        "type": "boolean",
+        "required": false,
+        "description": "Whether to include headers"
+      }
+    }
+  }
+}

rest-api-spec/src/main/resources/rest-api-spec/test/wlm_stats/10_basic.yml

@@ -0,0 +1,135 @@
+---
+"Custom size param still returns headers":
+  - skip:
+        version: " - 3.0.0"
+        reason: "wlm_stats_list API added after 3.0.0"
+  - do:
+      wlm_stats_list:
+        size: 1
+        v: true
+  - is_true: $body
+  - match:
+      $body: /TOTAL_REJECTIONS/
+
+---
+"Sort by node_id asc does not error":
+  - skip:
+      version: " - 3.0.0"
+      reason: "wlm_stats_list API added after 3.0.0"
+  - do:
+      wlm_stats_list:
+        sort: node_id
+        order: asc
+  - is_true: $body
+  - match:
+      $body: /DEFAULT_WORKLOAD_GROUP/
+
+---
+"Sort by workload_group_id desc does not error":
+  - skip:
+      version: " - 3.0.0"
+      reason: "wlm_stats_list API added after 3.0.0"
+  - do:
+      wlm_stats_list:
+        sort: workload_group
+        order: desc
+  - is_true: $body
+  - match:
+      $body: /DEFAULT_WORKLOAD_GROUP/
+
+---
+"Invalid sort field returns error":
+  - skip:
+      version: " - 3.0.0"
+      reason: "wlm_stats_list API added after 3.0.0"
+  - do:
+      catch: bad_request
+      wlm_stats_list:
+        sort: memory_usage
+        order: desc
+  - match:
+      error.reason: "Invalid value for 'sort'. Allowed: 'node_id', 'workload_group'"
+
+---
+"Invalid sort order returns error":
+  - skip:
+      version: " - 3.0.0"
+      reason: "wlm_stats_list API added after 3.0.0"
+  - do:
+      catch: bad_request
+      wlm_stats_list:
+        order: upside_down
+  - match:
+          error.reason: "Invalid value for 'order'. Allowed: 'asc', 'desc'"
+
+---
+"Invalid token returns 400":
+  - skip:
+      version: " - 3.0.0"
+      reason: "wlm_stats_list API added after 3.0.0"
+  - do:
+      catch: bad_request
+      wlm_stats_list:
+        next_token: "abcdef123456"
+
+  - match: { error: "Pagination state has changed (e.g., new workload groups added or removed). Please restart pagination from the beginning by omitting the 'next_token' parameter." }
+
+---
+"Default request returns 200 and contains expected keys":
+  - skip:
+      version: " - 3.0.0"
+      reason: "wlm_stats_list API added after 3.0.0"
+  - do:
+      wlm_stats_list:
+        v: true
+  - is_true: $body
+  - match:
+      $body: /WORKLOAD_GROUP_ID/
+
+---
+"Max allowed size param returns success":
+  - skip:
+      version: " - 3.0.0"
+      reason: "wlm_stats_list API added after 3.0.0"
+  - do:
+      wlm_stats_list:
+        size: 100
+  - is_true: $body
+
+---
+"Too large page size returns error":
+  - skip:
+      version: " - 3.0.0"
+      reason: "wlm_stats_list API added after 3.0.0"
+  - do:
+      catch: bad_request
+      wlm_stats_list:
+        size: 1000
+  - match:
+      error.reason: "Invalid value for 'size'. Allowed range: 1 to 100"
+
+---
+"Negative page size returns error":
+  - skip:
+      version: " - 3.0.0"
+      reason: "wlm_stats_list API added after 3.0.0"
+  - do:
+      catch: bad_request
+      wlm_stats_list:
+        size: -1
+  - match:
+      error.reason: "Invalid value for 'size'. Allowed range: 1 to 100"
+
+
+---
+"Sort param omitted uses default 'node_id'":
+  - skip:
+      version: " - 3.0.0"
+      reason: "wlm_stats_list API added after 3.0.0"
+  - do:
+      wlm_stats_list:
+        size: 1
+        v: true
+  - is_true: $body
+  - match:
+      $body: /NODE_ID/

server/src/main/java/org/opensearch/action/admin/cluster/wlm/WlmStatsResponse.java

@@ -33,7 +33,7 @@ public class WlmStatsResponse extends BaseNodesResponse<WlmStats> implements ToX
         super(in);
     }
 
-    WlmStatsResponse(ClusterName clusterName, List<WlmStats> nodes, List<FailedNodeException> failures) {
+    public WlmStatsResponse(ClusterName clusterName, List<WlmStats> nodes, List<FailedNodeException> failures) {
         super(clusterName, nodes, failures);
     }