Scripting: fill in get contexts REST API (elastic#48319)

* Scripting: fill in get contexts REST API

Updates response for `GET /_script_context`, returning a `contexts`
object with a list of context description objects.  The description
includes the context name and a list of methods available.  The
methods list has the signature for the `execute` mathod and any
getters. eg.
```
{
  "contexts": [
     {
       "name" : "moving-function",
       "methods" : [
         {
           "name" : "execute",
           "return_type" : "double",
           "params" : [
             {
               "type" : "java.util.Map",
               "name" : "params"
             },
             {
               "type" : "double[]",
               "name" : "values"
             }
           ]
         }
       ]
     },
     {
       "name" : "number_sort",
       "methods" : [
         {
           "name" : "execute",
           "return_type" : "double",
           "params" : [ ]
         },
         {
           "name" : "getDoc",
           "return_type" : "java.util.Map",
           "params" : [ ]
         },
         {
           "name" : "getParams",
           "return_type" : "java.util.Map",
           "params" : [ ]
         },
         {
           "name" : "get_score",
           "return_type" : "double",
           "params" : [ ]
         }
       ]
     },
...
  ]
}
```

fixes: elastic#47411

Author: stu-elastic

rest-api-spec/src/main/resources/rest-api-spec/test/scripts/20_get_script_context.yml

@@ -4,24 +4,7 @@
       reason: "get_all_contexts introduced in 7.6.0"
   - do:
       get_script_context: {}
-  - match: { contexts.aggregation_selector: {} }
-  - match: { contexts.aggs: {} }
-  - match: { contexts.aggs_combine: {} }
-  - match: { contexts.aggs_init: {} }
-  - match: { contexts.aggs_map: {} }
-  - match: { contexts.aggs_reduce: {} }
-  - match: { contexts.bucket_aggregation: {} }
-  - match: { contexts.field: {} }
-  - match: { contexts.filter: {} }
-  - match: { contexts.ingest: {} }
-  - match: { contexts.interval: {} }
-  - match: { contexts.number_sort: {} }
-  - match: { contexts.processor_conditional: {} }
-  - match: { contexts.score: {} }
-  - match: { contexts.script_heuristic: {} }
-  - match: { contexts.similarity: {} }
-  - match: { contexts.similarity_weight: {} }
-  - match: { contexts.string_sort: {} }
-  - match: { contexts.template: {} }
-  - match: { contexts.terms_set: {} }
-  - match: { contexts.update: {} }
+
+  - is_true: contexts.0.name
+  - is_true: contexts.0.methods.0.return_type
+  - match: { contexts.0.methods.0.name: "execute" }

server/src/main/java/org/elasticsearch/action/admin/cluster/storedscripts/GetScriptContextResponse.java

@@ -28,69 +28,72 @@
 import org.elasticsearch.common.xcontent.XContentBuilder;
 import org.elasticsearch.common.xcontent.XContentParser;
 import org.elasticsearch.rest.RestStatus;
+import org.elasticsearch.script.ScriptContextInfo;
 
 import java.io.IOException;
-import java.util.ArrayList;
 import java.util.Collections;
+import java.util.Comparator;
+import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
 import java.util.Objects;
+import java.util.Set;
+import java.util.function.Function;
 import java.util.stream.Collectors;
 
-import static org.elasticsearch.common.xcontent.XContentParser.Token.END_OBJECT;
-import static org.elasticsearch.common.xcontent.XContentParser.Token.START_OBJECT;
-
 public class GetScriptContextResponse extends ActionResponse implements StatusToXContentObject {
 
     private static final ParseField CONTEXTS = new ParseField("contexts");
-    private final List<String> contextNames;
+    final Map<String,ScriptContextInfo> contexts;
 
     @SuppressWarnings("unchecked")
     public static final ConstructingObjectParser<GetScriptContextResponse,Void> PARSER =
         new ConstructingObjectParser<>("get_script_context", true,
             (a) -> {
-                Map<String, Object> contexts = ((List<String>) a[0]).stream().collect(Collectors.toMap(
-                    name -> name, name -> new Object()
-                ));
+                Map<String,ScriptContextInfo> contexts = ((List<ScriptContextInfo>)a[0]).stream().collect(
+                    Collectors.toMap(ScriptContextInfo::getName, c -> c)
+                );
                 return new GetScriptContextResponse(contexts);
             }
         );
 
     static {
-        PARSER.declareNamedObjects(
-            ConstructingObjectParser.constructorArg(),
-            (p, c, n) ->
-            {
-                // advance empty object
-                assert(p.nextToken() == START_OBJECT);
-                assert(p.nextToken() == END_OBJECT);
-                return n;
-            },
-            CONTEXTS
-        );
+        PARSER.declareObjectArray(ConstructingObjectParser.constructorArg(),
+            (parser, ctx) -> ScriptContextInfo.PARSER.apply(parser, ctx), CONTEXTS);
     }
 
     GetScriptContextResponse(StreamInput in) throws IOException {
         super(in);
         int size = in.readInt();
-        ArrayList<String> contextNames = new ArrayList<>(size);
+        HashMap<String, ScriptContextInfo> contexts = new HashMap<>(size);
         for (int i = 0; i < size; i++) {
-            contextNames.add(in.readString());
+            ScriptContextInfo info = new ScriptContextInfo(in);
+            contexts.put(info.name, info);
         }
-        this.contextNames = Collections.unmodifiableList(contextNames);
+        this.contexts = Collections.unmodifiableMap(contexts);
+    }
+
+    // TransportAction constructor
+    GetScriptContextResponse(Set<ScriptContextInfo> contexts) {
+        this.contexts = Map.copyOf(contexts.stream().collect(
+            Collectors.toMap(ScriptContextInfo::getName, Function.identity())
+        ));
+    }
+
+    // Parser constructor
+    private GetScriptContextResponse(Map<String,ScriptContextInfo> contexts) {
+        this.contexts = Map.copyOf(contexts);
     }
 
-    GetScriptContextResponse(Map<String,Object> contexts) {
-        List<String> contextNames = new ArrayList<>(contexts.keySet());
-        contextNames.sort(String::compareTo);
-        this.contextNames = Collections.unmodifiableList(contextNames);
+    private List<ScriptContextInfo> byName() {
+        return contexts.values().stream().sorted(Comparator.comparing(ScriptContextInfo::getName)).collect(Collectors.toList());
     }
 
     @Override
     public void writeTo(StreamOutput out) throws IOException {
-        out.writeInt(this.contextNames.size());
-        for (String context: this.contextNames) {
-            out.writeString(context);
+        out.writeInt(contexts.size());
+        for (ScriptContextInfo context: contexts.values()) {
+            context.writeTo(out);
         }
     }
 
@@ -101,11 +104,11 @@ public RestStatus status() {
 
     @Override
     public XContentBuilder toXContent(XContentBuilder builder, Params params) throws IOException {
-        builder.startObject().startObject(CONTEXTS.getPreferredName());
-        for (String contextName: this.contextNames) {
-            builder.startObject(contextName).endObject();
+        builder.startObject().startArray(CONTEXTS.getPreferredName());
+        for (ScriptContextInfo context: byName()) {
+            context.toXContent(builder, params);
         }
-        builder.endObject().endObject(); // CONTEXTS
+        builder.endArray().endObject(); // CONTEXTS
         return builder;
     }
 
@@ -122,11 +125,11 @@ public boolean equals(Object o) {
             return false;
         }
         GetScriptContextResponse that = (GetScriptContextResponse) o;
-        return contextNames.equals(that.contextNames);
+        return contexts.equals(that.contexts);
     }
 
     @Override
     public int hashCode() {
-        return Objects.hash(contextNames);
+        return Objects.hash(contexts);
     }
 }

server/src/main/java/org/elasticsearch/action/admin/cluster/storedscripts/TransportGetScriptContextAction.java

@@ -22,12 +22,12 @@
 import org.elasticsearch.action.support.ActionFilters;
 import org.elasticsearch.action.support.HandledTransportAction;
 import org.elasticsearch.common.inject.Inject;
+import org.elasticsearch.script.ScriptContextInfo;
 import org.elasticsearch.script.ScriptService;
 import org.elasticsearch.tasks.Task;
 import org.elasticsearch.transport.TransportService;
 
-import java.util.Map;
-import java.util.stream.Collectors;
+import java.util.Set;
 
 public class TransportGetScriptContextAction extends HandledTransportAction<GetScriptContextRequest, GetScriptContextResponse> {
 
@@ -41,9 +41,7 @@ public TransportGetScriptContextAction(TransportService transportService, Action
 
     @Override
     protected void doExecute(Task task, GetScriptContextRequest request, ActionListener<GetScriptContextResponse> listener) {
-        Map<String,Object> contexts = scriptService.getContextNames().stream().collect(
-            Collectors.toMap(name -> name, name -> new Object())
-        );
+        Set<ScriptContextInfo> contexts = scriptService.getContextInfos();
         listener.onResponse(new GetScriptContextResponse(contexts));
     }
 }