[GitHub] [druid] paul-rogers commented on a change in pull request #11828: Refactor ResponseContext

[GitBox <gi...@apache.org>]

paul-rogers commented on a change in pull request #11828:
URL: https://github.com/apache/druid/pull/11828#discussion_r759866927



##########
File path: processing/src/main/java/org/apache/druid/query/context/ResponseContextDeserializer.java
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@@ -0,0 +1,74 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+package org.apache.druid.query.context;
+
+import com.fasterxml.jackson.core.JsonParser;
+import com.fasterxml.jackson.core.JsonToken;
+import com.fasterxml.jackson.databind.DeserializationContext;
+import com.fasterxml.jackson.databind.deser.std.StdDeserializer;
+
+import java.io.IOException;
+
+/**
+ * Deserialize a response context. The response context is created for single-thread use.
+ * (That is, it is non-concurrent.) Clients of this code should convert the
+ * context to concurrent if it will be used across threads.
+ */
+@SuppressWarnings("serial")
+public class ResponseContextDeserializer extends StdDeserializer<ResponseContext>
+{
+  public ResponseContextDeserializer()
+  {
+    super(ResponseContext.class);
+  }
+
+  @Override
+  public ResponseContext deserialize(
+      final JsonParser jp,
+      final DeserializationContext ctxt
+  ) throws IOException
+  {
+    if (jp.currentToken() != JsonToken.START_OBJECT) {
+      throw ctxt.wrongTokenException(jp, ResponseContext.class, JsonToken.START_OBJECT, null);
+    }
+
+    // TODO(gianm): Check if we need concurrent response context here
+    final ResponseContext retVal = ResponseContext.createEmpty();
+
+    jp.nextToken();
+
+    ResponseContext.Keys keys = ResponseContext.Keys.instance();
+    while (jp.currentToken() == JsonToken.FIELD_NAME) {
+      final ResponseContext.Key key = keys.keyOf(jp.getText());

Review comment:
       @gianm, excellent point. This can occur during a rolling upgrade when, say, the historical is newer than the broker.
   
   To handle this, added code to "freewheel" over the JSON value, whether it be a scalar or structured. Added tests to match.
   
   This seems like a generic operation, might we have something in one of the utilities? A quick search didn't find anything. 




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