Task Management: Make TaskInfo parsing forwards compatible (#24073)

TaskInfo is stored as a part of TaskResult and therefore can be read by nodes with an older version. If we add any additional information to TaskInfo (for #23250, for example), nodes with an older version should be able to ignore it, otherwise they will not be able to read TaskResults stored by newer nodes.

Author: imotov

core/src/main/java/org/elasticsearch/tasks/TaskInfo.java

@@ -183,7 +183,7 @@ public XContentBuilder toXContent(XContentBuilder builder, Params params) throws
     }
 
     public static final ConstructingObjectParser<TaskInfo, Void> PARSER = new ConstructingObjectParser<>(
-            "task_info", a -> {
+            "task_info", true, a -> {
                 int i = 0;
                 TaskId id = new TaskId((String) a[i++], (Long) a[i++]);
                 String type = (String) a[i++];
@@ -196,11 +196,11 @@ public XContentBuilder toXContent(XContentBuilder builder, Params params) throws
                 String parentTaskIdString = (String) a[i++];
 
                 RawTaskStatus status = statusBytes == null ? null : new RawTaskStatus(statusBytes);
-                TaskId parentTaskId = parentTaskIdString == null ? TaskId.EMPTY_TASK_ID : new TaskId((String) parentTaskIdString);
+                TaskId parentTaskId = parentTaskIdString == null ? TaskId.EMPTY_TASK_ID : new TaskId(parentTaskIdString);
                 return new TaskInfo(id, type, action, description, status, startTime, runningTimeNanos, cancellable, parentTaskId);
             });
     static {
-        // Note for the future: this has to be backwards compatible with all changes to the task storage format
+        // Note for the future: this has to be backwards and forwards compatible with all changes to the task storage format
         PARSER.declareString(constructorArg(), new ParseField("node"));
         PARSER.declareLong(constructorArg(), new ParseField("id"));
         PARSER.declareString(constructorArg(), new ParseField("type"));

core/src/test/java/org/elasticsearch/tasks/TaskResultTests.java

@@ -26,6 +26,7 @@
 import org.elasticsearch.common.io.stream.StreamInput;
 import org.elasticsearch.common.xcontent.ToXContent;
 import org.elasticsearch.common.xcontent.XContentBuilder;
+import org.elasticsearch.common.xcontent.XContentFactory;
 import org.elasticsearch.common.xcontent.XContentParser;
 import org.elasticsearch.common.xcontent.XContentType;
 import org.elasticsearch.test.ESTestCase;
@@ -65,7 +66,7 @@ public void testXContentRoundTrip() throws IOException {
         try (XContentBuilder builder = XContentBuilder.builder(randomFrom(XContentType.values()).xContent())) {
             result.toXContent(builder, ToXContent.EMPTY_PARAMS);
             try (XContentBuilder shuffled = shuffleXContent(builder);
-                    XContentParser parser = createParser(shuffled)) {
+                 XContentParser parser = createParser(shuffled)) {
                 read = TaskResult.PARSER.apply(parser, null);
             }
         } catch (IOException e) {
@@ -74,16 +75,52 @@ public void testXContentRoundTrip() throws IOException {
         assertEquals(result, read);
     }
 
+    public void testTaskInfoIsForwardCompatible() throws IOException {
+        TaskInfo taskInfo = randomTaskInfo();
+        TaskInfo read;
+        try (XContentBuilder builder = XContentBuilder.builder(randomFrom(XContentType.values()).xContent())) {
+            builder.startObject();
+            taskInfo.toXContent(builder, ToXContent.EMPTY_PARAMS);
+            builder.endObject();
+            try (XContentBuilder withExtraFields = addRandomUnknownFields(builder)) {
+                try (XContentBuilder shuffled = shuffleXContent(withExtraFields)) {
+                    try (XContentParser parser = createParser(shuffled)) {
+                        read = TaskInfo.PARSER.apply(parser, null);
+                    }
+                }
+            }
+        } catch (IOException e) {
+            throw new IOException("Error processing [" + taskInfo + "]", e);
+        }
+        assertEquals(taskInfo, read);
+    }
+
+    private XContentBuilder addRandomUnknownFields(XContentBuilder builder) throws IOException {
+        try (XContentParser parser = createParser(builder)) {
+            Map<String, Object> map = parser.mapOrdered();
+            int numberOfNewFields = randomIntBetween(2, 10);
+            for (int i = 0; i < numberOfNewFields; i++) {
+                if (randomBoolean()) {
+                    map.put("unknown_field" + i, randomAlphaOfLength(20));
+                } else {
+                    map.put("unknown_field" + i, Collections.singletonMap("inner", randomAlphaOfLength(20)));
+                }
+            }
+            XContentBuilder xContentBuilder = XContentFactory.contentBuilder(parser.contentType());
+            return xContentBuilder.map(map);
+        }
+    }
+
     private static TaskResult randomTaskResult() throws IOException {
         switch (between(0, 2)) {
-        case 0:
-            return new TaskResult(randomBoolean(), randomTaskInfo());
-        case 1:
-            return new TaskResult(randomTaskInfo(), new RuntimeException("error"));
-        case 2:
-            return new TaskResult(randomTaskInfo(), randomTaskResponse());
-        default:
-            throw new UnsupportedOperationException("Unsupported random TaskResult constructor");
+            case 0:
+                return new TaskResult(randomBoolean(), randomTaskInfo());
+            case 1:
+                return new TaskResult(randomTaskInfo(), new RuntimeException("error"));
+            case 2:
+                return new TaskResult(randomTaskInfo(), randomTaskResponse());
+            default:
+                throw new UnsupportedOperationException("Unsupported random TaskResult constructor");
         }
     }