Implement from_sort_value Parameter in Get Snapshots API

docs/reference/snapshot-restore/apis/get-snapshot-api.asciidoc

@@ -140,14 +140,19 @@ Allows setting a sort order for the result. Defaults to `start_time`, i.e. sorti
 (Optional, string)
 Sort order. Valid values are `asc` for ascending and `desc` for descending order. Defaults to `asc`, meaning ascending order.
 
+`after_value`::
+(Optional, string)
+Value of the current sort column after which to start pagination. Can either be a string snapshot- or repository name when sorting by
+snapshot or repository name, a millisecond time value or a number when sorting by index- or shard count.
+
 `after`::
 (Optional, string)
 Offset identifier to start pagination from as returned by the `next` field in the response body.
 
 `offset`::
 (Optional, integer)
 Numeric offset to start pagination from based on the snapshots matching this request. Using a non-zero value for this parameter is mutually
-exclusive with using the `after` parameter. Defaults to `0`.
+exclusive with using the `after` or `after_value` parameters. Defaults to `0`.
 
 `slm_policy_filter`::
 (Optional, string)
@@ -158,11 +163,11 @@ created by an SLM policy but not those snapshots that were not created by an SLM
 policy you can use the special pattern `_none` that will match all snapshots without an SLM policy.
 
 NOTE: The `after` parameter and `next` field allow for iterating through snapshots with some consistency guarantees regarding concurrent
-creation or deletion of snapshots. It is guaranteed that  any snapshot that exists at the beginning of the iteration and not concurrently
+creation or deletion of snapshots. It is guaranteed that any snapshot that exists at the beginning of the iteration and is not concurrently
 deleted will be seen during the iteration. Snapshots concurrently created may be seen during an iteration.
 
-NOTE: The parameters `size`, `order`, `after`, `offset`, `slm_policy_filter` and `sort` are not supported when using `verbose=false` and
-the sort order for requests with `verbose=false` is undefined.
+NOTE: The parameters `size`, `order`, `after`, `after_value`, `offset`, `slm_policy_filter` and `sort` are not supported when using
+`verbose=false` and the sort order for requests with `verbose=false` is undefined.
 
 [role="child_attributes"]
 [[get-snapshot-api-response-body]]
@@ -628,3 +633,84 @@ The API returns the following response:
 // TESTRESPONSE[s/"end_time_in_millis": 1593094752019/"end_time_in_millis": $body.snapshots.1.end_time_in_millis/]
 // TESTRESPONSE[s/"duration_in_millis": 0/"duration_in_millis": $body.snapshots.0.duration_in_millis/]
 // TESTRESPONSE[s/"duration_in_millis": 1/"duration_in_millis": $body.snapshots.1.duration_in_millis/]
+
+
+The following request returns information for all snapshots that come after `snapshot_1` when sorted by snapshot name in the default
+ascending order.
+
+[source,console]
+----
+GET /_snapshot/my_repository/*?sort=name&after_value=snapshot_1
+----
+
+The API returns the following response:
+
+[source,console-result]
+----
+{
+  "snapshots": [
+    {
+      "snapshot": "snapshot_2",
+      "uuid": "vdRctLCxSketdKb54xw67g",
+      "repository": "my_repository",
+      "version_id": <version_id>,
+      "version": <version>,
+      "indices": [],
+      "data_streams": [],
+      "feature_states": [],
+      "include_global_state": true,
+      "state": "SUCCESS",
+      "start_time": "2020-07-06T21:55:18.130Z",
+      "start_time_in_millis": 1593093628851,
+      "end_time": "2020-07-06T21:55:18.130Z",
+      "end_time_in_millis": 1593094752019,
+      "duration_in_millis": 1,
+      "failures": [],
+      "shards": {
+        "total": 0,
+        "failed": 0,
+        "successful": 0
+      }
+    },
+    {
+      "snapshot": "snapshot_3",
+      "uuid": "dRctdKb54xw67gvLCxSket",
+      "repository": "my_repository",
+      "version_id": <version_id>,
+      "version": <version>,
+      "indices": [],
+      "data_streams": [],
+      "feature_states": [],
+      "include_global_state": true,
+      "state": "SUCCESS",
+      "start_time": "2020-07-06T21:55:18.129Z",
+      "start_time_in_millis": 1593093628850,
+      "end_time": "2020-07-06T21:55:18.129Z",
+      "end_time_in_millis": 1593094752018,
+      "duration_in_millis": 0,
+      "failures": [],
+      "shards": {
+        "total": 0,
+        "failed": 0,
+        "successful": 0
+      }
+    }
+  ],
+  "total": 2,
+  "remaining": 0
+}
+----
+// TESTRESPONSE[s/"uuid": "vdRctLCxSketdKb54xw67g"/"uuid": $body.snapshots.0.uuid/]
+// TESTRESPONSE[s/"uuid": "dRctdKb54xw67gvLCxSket"/"uuid": $body.snapshots.1.uuid/]
+// TESTRESPONSE[s/"version_id": <version_id>/"version_id": $body.snapshots.0.version_id/]
+// TESTRESPONSE[s/"version": <version>/"version": $body.snapshots.0.version/]
+// TESTRESPONSE[s/"start_time": "2020-07-06T21:55:18.130Z"/"start_time": $body.snapshots.0.start_time/]
+// TESTRESPONSE[s/"start_time": "2020-07-06T21:55:18.129Z"/"start_time": $body.snapshots.1.start_time/]
+// TESTRESPONSE[s/"start_time_in_millis": 1593093628851/"start_time_in_millis": $body.snapshots.0.start_time_in_millis/]
+// TESTRESPONSE[s/"start_time_in_millis": 1593093628850/"start_time_in_millis": $body.snapshots.1.start_time_in_millis/]
+// TESTRESPONSE[s/"end_time": "2020-07-06T21:55:18.130Z"/"end_time": $body.snapshots.0.end_time/]
+// TESTRESPONSE[s/"end_time": "2020-07-06T21:55:18.129Z"/"end_time": $body.snapshots.1.end_time/]
+// TESTRESPONSE[s/"end_time_in_millis": 1593094752019/"end_time_in_millis": $body.snapshots.0.end_time_in_millis/]
+// TESTRESPONSE[s/"end_time_in_millis": 1593094752018/"end_time_in_millis": $body.snapshots.1.end_time_in_millis/]
+// TESTRESPONSE[s/"duration_in_millis": 1/"duration_in_millis": $body.snapshots.0.duration_in_millis/]
+// TESTRESPONSE[s/"duration_in_millis": 0/"duration_in_millis": $body.snapshots.1.duration_in_millis/]

qa/smoke-test-http/src/test/java/org/elasticsearch/http/snapshots/RestGetSnapshotsIT.java

@@ -36,6 +36,7 @@
 import java.util.Map;
 
 import static org.elasticsearch.snapshots.AbstractSnapshotIntegTestCase.assertSnapshotListSorted;
+import static org.elasticsearch.snapshots.AbstractSnapshotIntegTestCase.matchAllPattern;
 import static org.hamcrest.Matchers.empty;
 import static org.hamcrest.Matchers.in;
 import static org.hamcrest.Matchers.is;
@@ -241,6 +242,60 @@ public void testFilterBySLMPolicy() throws Exception {
         );
     }
 
+    public void testSortAfterStartTime() throws IOException {
+        final String repoName = "test-repo";
+        AbstractSnapshotIntegTestCase.createRepository(logger, repoName, "fs");
+        final SnapshotInfo snapshot1 = AbstractSnapshotIntegTestCase.createFullSnapshot(logger, repoName, "snapshot-1");
+        final SnapshotInfo snapshot2 = AbstractSnapshotIntegTestCase.createFullSnapshot(logger, repoName, "snapshot-2");
+        final SnapshotInfo snapshot3 = AbstractSnapshotIntegTestCase.createFullSnapshot(logger, repoName, "snapshot-3");
+
+        final List<SnapshotInfo> allSnapshotInfo = clusterAdmin().prepareGetSnapshots(matchAllPattern())
+                .setSnapshots(matchAllPattern())
+                .setSort(GetSnapshotsRequest.SortBy.START_TIME)
+                .get()
+                .getSnapshots();
+        assertThat(allSnapshotInfo, is(List.of(snapshot1, snapshot2, snapshot3)));
+
+        final long startTime1 = snapshot1.startTime();
+        final long startTime2 = snapshot2.startTime();
+        final long startTime3 = snapshot3.startTime();
+
+        assertThat(allAfterStartTimeAscending(startTime1 - 1), is(allSnapshotInfo));
+        assertThat(allAfterStartTimeAscending(startTime1), is(List.of(snapshot2, snapshot3)));
+        assertThat(allAfterStartTimeAscending(startTime2), is(List.of(snapshot3)));
+        assertThat(allAfterStartTimeAscending(startTime3), empty());
+
+        final List<SnapshotInfo> allSnapshotInfoDesc = clusterAdmin().prepareGetSnapshots(matchAllPattern())
+                .setSnapshots(matchAllPattern())
+                .setSort(GetSnapshotsRequest.SortBy.START_TIME)
+                .setOrder(SortOrder.DESC)
+                .get()
+                .getSnapshots();
+        assertThat(allSnapshotInfoDesc, is(List.of(snapshot3, snapshot2, snapshot1)));
+
+        assertThat(allBeforeStartTimeDescending(startTime3 + 1), is(allSnapshotInfoDesc));
+        assertThat(allBeforeStartTimeDescending(startTime3), is(List.of(snapshot2, snapshot1)));
+        assertThat(allBeforeStartTimeDescending(startTime2), is(List.of(snapshot1)));
+        assertThat(allBeforeStartTimeDescending(startTime1), empty());
+    }
+
+    private List<SnapshotInfo> allAfterStartTimeAscending(long timestamp) throws IOException {
+        final Request request = baseGetSnapshotsRequest("*");
+        request.addParameter("sort", GetSnapshotsRequest.SortBy.START_TIME.toString());
+        request.addParameter("after_value", String.valueOf(timestamp));
+        final Response response = getRestClient().performRequest(request);
+        return readSnapshotInfos(response).getSnapshots();
+    }
+
+    private List<SnapshotInfo> allBeforeStartTimeDescending(long timestamp) throws IOException {
+        final Request request = baseGetSnapshotsRequest("*");
+        request.addParameter("sort", GetSnapshotsRequest.SortBy.START_TIME.toString());
+        request.addParameter("after_value", String.valueOf(timestamp));
+        request.addParameter("order", SortOrder.DESC.toString());
+        final Response response = getRestClient().performRequest(request);
+        return readSnapshotInfos(response).getSnapshots();
+    }
+
     private static List<SnapshotInfo> getAllSnapshotsForPolicies(String... policies) throws IOException {
         final Request requestWithPolicy = new Request(HttpGet.METHOD_NAME, "/_snapshot/*/*");
         requestWithPolicy.addParameter("slm_policy_filter", Strings.arrayToCommaDelimitedString(policies));