Field caps to support project_routing also in the body of the request (#138681)

* Field caps to support project_routing also in the body of the request

* Update docs/changelog/138681.yaml

Author: piergm

docs/changelog/138681.yaml

@@ -0,0 +1,5 @@
+pr: 138681
+summary: Field caps to support `project_routing` also in the body of the request
+area: Search
+type: enhancement
+issues: []

server/src/main/java/org/elasticsearch/action/fieldcaps/FieldCapabilitiesRequest.java

@@ -280,7 +280,10 @@ public ResolvedIndexExpressions getResolvedIndexExpressions() {
         return resolvedIndexExpressions;
     }
 
-    public void projectRouting(String projectRouting) {
+    public void projectRouting(@Nullable String projectRouting) {
+        if (this.projectRouting != null) {
+            throw new IllegalArgumentException("project_routing is already set to [" + this.projectRouting + "]");
+        }
         this.projectRouting = projectRouting;
     }
 

server/src/main/java/org/elasticsearch/rest/action/RestFieldCapabilitiesAction.java

@@ -107,12 +107,14 @@ public RestChannelConsumer prepareRequest(final RestRequest request, final NodeC
     private static final ParseField INDEX_FILTER_FIELD = new ParseField("index_filter");
     private static final ParseField RUNTIME_MAPPINGS_FIELD = new ParseField("runtime_mappings");
     private static final ParseField FIELDS_FIELD = new ParseField("fields");
+    private static final ParseField PROJECT_ROUTING = new ParseField("project_routing");
 
     private static final ObjectParser<FieldCapabilitiesRequest, Void> PARSER = new ObjectParser<>("field_caps_request");
 
     static {
         PARSER.declareObject(FieldCapabilitiesRequest::indexFilter, (p, c) -> parseTopLevelQuery(p), INDEX_FILTER_FIELD);
         PARSER.declareObject(FieldCapabilitiesRequest::runtimeFields, (p, c) -> p.map(), RUNTIME_MAPPINGS_FIELD);
         PARSER.declareStringArray(fromList(String.class, FieldCapabilitiesRequest::fields), FIELDS_FIELD);
+        PARSER.declareString(FieldCapabilitiesRequest::projectRouting, PROJECT_ROUTING);
     }
 }