[REST API compatibility] special handling for _freeze (#79861)

x-pack/plugin/build.gradle

@@ -118,6 +118,11 @@ tasks.named("yamlRestTestV7CompatTransform").configure{ task ->
   task.replaceValueInMatch("_type", "_doc")
   task.addAllowedWarningRegex("\\[types removal\\].*")
   task.addAllowedWarningRegexForTest("Including \\[accept_enterprise\\] in get license.*", "Installing enterprise license")
+
+  task.replaceValueTextByKeyValue("catch",
+    'bad_request',
+    '/It is no longer possible to freeze indices, but existing frozen indices can still be unfrozen/',
+    "Cannot freeze write index for data stream")
 }
 
 

x-pack/plugin/frozen-indices/src/main/java/org/elasticsearch/xpack/frozen/rest/action/RestFreezeIndexAction.java

@@ -6,34 +6,62 @@
  */
 package org.elasticsearch.xpack.frozen.rest.action;
 
+import org.elasticsearch.action.admin.indices.get.GetIndexRequest;
+import org.elasticsearch.action.admin.indices.get.GetIndexResponse;
 import org.elasticsearch.action.support.ActiveShardCount;
 import org.elasticsearch.action.support.IndicesOptions;
 import org.elasticsearch.client.node.NodeClient;
 import org.elasticsearch.common.Strings;
 import org.elasticsearch.core.RestApiVersion;
 import org.elasticsearch.protocol.xpack.frozen.FreezeRequest;
 import org.elasticsearch.rest.BaseRestHandler;
+import org.elasticsearch.rest.BytesRestResponse;
 import org.elasticsearch.rest.RestRequest;
+import org.elasticsearch.rest.RestResponse;
+import org.elasticsearch.rest.action.RestBuilderListener;
 import org.elasticsearch.rest.action.RestToXContentListener;
+import org.elasticsearch.xcontent.XContentBuilder;
 import org.elasticsearch.xpack.core.frozen.action.FreezeIndexAction;
 
 import java.util.List;
 
 import static org.elasticsearch.rest.RestRequest.Method.POST;
+import static org.elasticsearch.rest.RestStatus.GONE;
 
 public final class RestFreezeIndexAction extends BaseRestHandler {
 
-    public static final String DEPRECATION_WARNING = "Frozen indices are deprecated because they provide no benefit given improvements "
+    private static final String FREEZE_REMOVED = "It is no longer possible to freeze indices, but existing frozen indices can still be "
+        + "unfrozen";
+
+    private static final String UNFREEZE_DEPRECATED = "Frozen indices are deprecated because they provide no benefit given improvements "
         + "in heap memory utilization. They will be removed in a future release.";
-    private static final RestApiVersion DEPRECATION_VERSION = RestApiVersion.V_8;
 
     @Override
     public List<Route> routes() {
-        return List.of(Route.builder(POST, "/{index}/_unfreeze").deprecated(DEPRECATION_WARNING, DEPRECATION_VERSION).build());
+        return List.of(
+            Route.builder(POST, "/{index}/_freeze").deprecated(FREEZE_REMOVED, RestApiVersion.V_7).build(),
+            Route.builder(POST, "/{index}/_unfreeze").deprecated(UNFREEZE_DEPRECATED, RestApiVersion.V_8).build()
+        );
     }
 
     @Override
     protected RestChannelConsumer prepareRequest(RestRequest request, NodeClient client) {
+        if (request.getRestApiVersion() == RestApiVersion.V_7 && request.path().endsWith("/_freeze")) {
+            // translate to a get indices request, so that we'll 404 on non-existent indices
+            final GetIndexRequest getIndexRequest = new GetIndexRequest();
+            getIndexRequest.indices(Strings.splitStringByCommaToArray(request.param("index")));
+            getIndexRequest.masterNodeTimeout(request.paramAsTime("master_timeout", getIndexRequest.masterNodeTimeout()));
+            getIndexRequest.indicesOptions(IndicesOptions.fromRequest(request, getIndexRequest.indicesOptions()));
+            return channel -> client.admin().indices().getIndex(getIndexRequest, new RestBuilderListener<>(channel) {
+                @Override
+                public RestResponse buildResponse(GetIndexResponse getIndexResponse, XContentBuilder builder) throws Exception {
+                    builder.close();
+                    // but if the index *does* exist, we still just respond with 410 -- there's no such thing as _freeze anymore
+                    return new BytesRestResponse(channel, GONE, new UnsupportedOperationException(FREEZE_REMOVED));
+                }
+            });
+        }
+
         FreezeRequest freezeRequest = new FreezeRequest(Strings.splitStringByCommaToArray(request.param("index")));
         freezeRequest.timeout(request.paramAsTime("timeout", freezeRequest.timeout()));
         freezeRequest.masterNodeTimeout(request.paramAsTime("master_timeout", freezeRequest.masterNodeTimeout()));

x-pack/plugin/src/yamlRestTestV7Compat/resources/rest-api-spec/test/freeze.gone/10_basic_compat.yml

@@ -0,0 +1,40 @@
+---
+setup:
+  - skip:
+      version: "9.0.0 - "
+      reason: "compatible from 8.x to 7.x"
+      features:
+        - "headers"
+        - "warnings_regex"
+  - do:
+      index:
+        index: some-test-index-1
+        id: 1
+        body: { foo: bar }
+
+---
+"Freezing a non-existent index throws 404":
+  - do:
+      headers:
+        Content-Type: "application/vnd.elasticsearch+json;compatible-with=7"
+        Accept: "application/vnd.elasticsearch+json;compatible-with=7"
+      indices.freeze:
+        index: some-test-index-404
+      catch: missing
+
+---
+"Freezing an index throws 410":
+  - do:
+      headers:
+        Content-Type: "application/vnd.elasticsearch+json;compatible-with=7"
+        Accept: "application/vnd.elasticsearch+json;compatible-with=7"
+      indices.freeze:
+        index: some-test-index-1
+      catch: /It is no longer possible to freeze indices, but existing frozen indices can still be unfrozen/
+
+---
+"Without compat headers throws 400":
+  - do:
+      indices.freeze:
+        index: some-test-index-1
+      catch: /no handler found for uri/