Add CI testing against OpenSearch 3.6.0

Signed-off-by: Sean Chittenden <sean.chittenden@crowdstrike.com>

Author: sean-

.github/workflows/test-compatibility.yml

@@ -38,6 +38,7 @@ jobs:
           - { opensearch_version: 3.3.2 }
           - { opensearch_version: 3.4.0 }
           - { opensearch_version: 3.5.0 }
+          - { opensearch_version: 3.6.0 }
           - { opensearch_version: latest }
     steps:
       - uses: actions/checkout@v6

CHANGELOG.md

@@ -6,6 +6,7 @@ Inspired from [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
 
 ### Added
 
+- Add `primary_terms_map` and `split_shards_metadata` fields to ClusterState index metadata for OpenSearch >=3.6.0 compatibility
 - Add `InsecureSkipVerify` config option to disable TLS certificate verification without constructing a custom `http.Transport`, preserving `DefaultTransport` connection pooling, HTTP/2, and timeout defaults ([#786](https://github.com/opensearch-project/opensearch-go/issues/786))
 - Add `DisableResponseBuffering` config option to skip eager `io.ReadAll` buffering of response bodies in `Perform()`, reducing per-request allocations and TTFB for proxy and streaming use cases ([#786](https://github.com/opensearch-project/opensearch-go/issues/786))
 - Add per-attempt `RequestTimeout` to bound individual HTTP round-trips, preventing indefinite hangs on stalled connections ([#786](https://github.com/opensearch-project/opensearch-go/issues/786))
@@ -110,6 +111,7 @@ Inspired from [Keep a Changelog](https://keepachangelog.com/en/1.0.0/)
 
 ### Changed
 
+- Test against Opensearch 3.6.0 ([#817](https://github.com/opensearch-project/opensearch-go/pull/817))
 - Consolidate test utilities into two canonical packages: opensearchtransport/testutil (env helpers, polling, version comparison) and opensearchapi/testutil (client-dependent helpers, test suite, JSON comparison)
 - Rename `singleConnectionPool` to `singleServerPool` and `statusConnectionPool` to `multiServerPool` for clarity ([#786](https://github.com/opensearch-project/opensearch-go/pull/786))
 - Refactor Client struct to use embedded mutex pattern for improved thread safety ([#775](https://github.com/opensearch-project/opensearch-go/pull/775))

opensearchapi/api_cluster-state.go

@@ -180,6 +180,32 @@ type ClusterStateMetaDataIndex struct {
 	} `json:"rollover_info"`
 	System          bool            `json:"system"`
 	IngestionStatus json.RawMessage `json:"ingestion_status"` // Available in OpenSearch 3.3.0+
+
+	// Added in OpenSearch 3.6.0 (opensearch-project/OpenSearch@ed2e1006,
+	// server/src/main/java/org/opensearch/cluster/metadata/IndexMetadata.java:1057-1059).
+	PrimaryTermsMap     map[string]int               `json:"primary_terms_map,omitempty"`
+	SplitShardsMetadata *ClusterStateSplitShardsMeta `json:"split_shards_metadata,omitempty"`
+}
+
+// ClusterStateSplitShardsMeta contains shard-split metadata for an index.
+// Added in OpenSearch 3.6.0 (opensearch-project/OpenSearch@ed2e1006,
+// server/src/main/java/org/opensearch/cluster/metadata/SplitShardsMetadata.java).
+type ClusterStateSplitShardsMeta struct {
+	NumOfRootShards         int                                 `json:"num_of_root_shards"`
+	MaxShardID              int                                 `json:"max_shard_id"`
+	InProgressSplitShardID  []int                               `json:"in_progress_split_shard_id,omitempty"`
+	ActiveShardIDs          []int                               `json:"active_shard_ids"`
+	RootShardsToAllChildren map[string][]ClusterStateShardRange `json:"root_shards_to_all_children"`
+	ParentToChildShards     map[string][]ClusterStateShardRange `json:"parent_to_child_shards"`
+}
+
+// ClusterStateShardRange describes the hash-range owned by a single shard.
+// Added in OpenSearch 3.6.0 (opensearch-project/OpenSearch@ed2e1006,
+// server/src/main/java/org/opensearch/cluster/metadata/ShardRange.java).
+type ClusterStateShardRange struct {
+	ShardID int `json:"shard_id"`
+	Start   int `json:"start"`
+	End     int `json:"end"`
 }
 
 // ClusterStateMetaDataStream is a sub type of ClusterStateMetaData containing information about a data stream