SOLR-13284: fallback to json instead of NPE and 500 code, when wt is omitted or wrong.

solr/CHANGES.txt

@@ -108,6 +108,9 @@ Bug Fixes
 * SOLR-13254: Correct message that is logged in solrj's ConnectionManager when an exception
   occurred while reconnecting to ZooKeeper. (hu xiaodong via Christine Poerschke)
 
+* SOLR-13284: NullPointerException with 500 http status on omitted or wrong wt param. 
+  It's fixed by fallback to json (Munendra S N via Mikhail Khludnev)
+
 Improvements
 ----------------------
 * SOLR-12999: Index replication could delete segments before downloading segments from master if there is not enough

solr/core/src/java/org/apache/solr/api/V2HttpCall.java

@@ -17,8 +17,12 @@
 
 package org.apache.solr.api;
 
-import javax.servlet.http.HttpServletRequest;
+import static org.apache.solr.common.cloud.ZkStateReader.COLLECTION_PROP;
-import javax.servlet.http.HttpServletResponse;
+import static org.apache.solr.common.util.PathTrie.getPathSegments;
+import static org.apache.solr.servlet.SolrDispatchFilter.Action.ADMIN;
+import static org.apache.solr.servlet.SolrDispatchFilter.Action.PROCESS;
+import static org.apache.solr.servlet.SolrDispatchFilter.Action.REMOTEQUERY;
+
 import java.lang.invoke.MethodHandles;
 import java.util.HashMap;
 import java.util.HashSet;
@@ -29,7 +33,9 @@ import java.util.Map;
 import java.util.Set;
 import java.util.function.Supplier;
 
-import com.google.common.collect.ImmutableSet;
+import javax.servlet.http.HttpServletRequest;
+import javax.servlet.http.HttpServletResponse;
+
 import org.apache.solr.client.solrj.SolrRequest;
 import org.apache.solr.common.SolrException;
 import org.apache.solr.common.cloud.DocCollection;
@@ -45,7 +51,6 @@ import org.apache.solr.handler.RequestHandlerUtils;
 import org.apache.solr.logging.MDCLoggingContext;
 import org.apache.solr.request.SolrQueryRequest;
 import org.apache.solr.request.SolrRequestHandler;
-import org.apache.solr.response.QueryResponseWriter;
 import org.apache.solr.response.SolrQueryResponse;
 import org.apache.solr.security.AuthorizationContext;
 import org.apache.solr.servlet.HttpSolrCall;
@@ -54,13 +59,7 @@ import org.apache.solr.servlet.SolrRequestParsers;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
-import static org.apache.solr.common.cloud.ZkStateReader.COLLECTION_PROP;
+import com.google.common.collect.ImmutableSet;
-import static org.apache.solr.common.params.CommonParams.JSON;
-import static org.apache.solr.common.params.CommonParams.WT;
-import static org.apache.solr.common.util.PathTrie.getPathSegments;
-import static org.apache.solr.servlet.SolrDispatchFilter.Action.ADMIN;
-import static org.apache.solr.servlet.SolrDispatchFilter.Action.PROCESS;
-import static org.apache.solr.servlet.SolrDispatchFilter.Action.REMOTEQUERY;
 
 // class that handle the '/v2' path
 public class V2HttpCall extends HttpSolrCall {
@@ -366,13 +365,6 @@ public class V2HttpCall extends HttpSolrCall {
     return parts;
   }
 
-  @Override
-  protected QueryResponseWriter getResponseWriter() {
-    String wt = solrReq.getParams().get(WT, JSON);
-    if (core != null) return core.getResponseWriters().get(wt);
-    return SolrCore.DEFAULT_RESPONSE_WRITERS.get(wt);
-  }
-
   @Override
   protected ValidatingJsonMap getSpec() {
     return api == null ? null : api.getSpec();

solr/core/src/java/org/apache/solr/servlet/HttpSolrCall.java

@@ -724,12 +724,20 @@ public class HttpSolrCall {
     writeResponse(solrResp, respWriter, Method.getMethod(req.getMethod()));
   }
 
+  /**
+   * Returns {@link QueryResponseWriter} to be used.
+   * When {@link CommonParams#WT} not specified in the request or specified value doesn't have
+   * corresponding {@link QueryResponseWriter} then, returns the default query response writer
+   * Note: This method must not return null
+   */
   protected QueryResponseWriter getResponseWriter() {
-    if (core != null) return core.getQueryResponseWriter(solrReq);
+    String wt = solrReq.getParams().get(CommonParams.WT);
-    QueryResponseWriter respWriter = SolrCore.DEFAULT_RESPONSE_WRITERS.get(solrReq.getParams().get(CommonParams.WT));
+    if (core != null) {
-    if (respWriter == null) respWriter = SolrCore.DEFAULT_RESPONSE_WRITERS.get("standard");
+      return core.getQueryResponseWriter(wt);
-    return respWriter;
+    } else {
-
+      return SolrCore.DEFAULT_RESPONSE_WRITERS.getOrDefault(wt,
+          SolrCore.DEFAULT_RESPONSE_WRITERS.get("standard"));
+    }
   }
 
   protected void handleAdmin(SolrQueryResponse solrResp) {

solr/core/src/test/org/apache/solr/handler/V2ApiIntegrationTest.java

@@ -29,6 +29,7 @@ import org.apache.solr.client.solrj.SolrServerException;
 import org.apache.solr.client.solrj.impl.BinaryResponseParser;
 import org.apache.solr.client.solrj.impl.CloudSolrClient;
 import org.apache.solr.client.solrj.impl.HttpSolrClient;
+import org.apache.solr.client.solrj.impl.NoOpResponseParser;
 import org.apache.solr.client.solrj.impl.XMLResponseParser;
 import org.apache.solr.client.solrj.request.CollectionAdminRequest;
 import org.apache.solr.client.solrj.request.V2Request;
@@ -114,6 +115,34 @@ public class V2ApiIntegrationTest extends SolrCloudTestCase {
     assertEquals("Command not found!", Utils.getObjectByPath(result, false, "/spec[0]/commands/XXXX"));
   }
 
+  @SuppressWarnings("rawtypes")
+  @Test
+  public void testWTParam() throws Exception {
+    V2Request request = new V2Request.Builder("/c/" + COLL_NAME + "/get/_introspect").build();
+    // TODO: If possible do this in a better way
+    request.setResponseParser(new NoOpResponseParser("bleh"));
+
+    Map resp = resAsMap(cluster.getSolrClient(), request);
+    String respString = resp.toString();
+
+    assertFalse(respString.contains("<body><h2>HTTP ERROR 500</h2>"));
+    assertFalse(respString.contains("500"));
+    assertFalse(respString.contains("NullPointerException"));
+    assertFalse(respString.contains("<p>Problem accessing /solr/____v2/c/collection1/get/_introspect. Reason:"));
+    // since no-op response writer is used, doing contains match
+    assertTrue(respString.contains("/c/collection1/get"));
+
+    // no response parser
+    request.setResponseParser(null);
+    resp = resAsMap(cluster.getSolrClient(), request);
+    respString = resp.toString();
+
+    assertFalse(respString.contains("<body><h2>HTTP ERROR 500</h2>"));
+    assertFalse(respString.contains("<p>Problem accessing /solr/____v2/c/collection1/get/_introspect. Reason:"));
+    assertEquals("/c/collection1/get", Utils.getObjectByPath(resp, true, "/spec[0]/url/paths[0]"));
+    assertEquals(respString, 0, Utils.getObjectByPath(resp, true, "/responseHeader/status"));
+  }
+
   @Test
   public void testSingleWarning() throws Exception {
     NamedList resp = cluster.getSolrClient().request(

solr/solr-ref-guide/src/response-writers.adoc

@@ -39,7 +39,11 @@ The `wt` parameter selects the Response Writer to be used. The list below descri
 
 == JSON Response Writer
 
-The default Solr Response Writer is the `JsonResponseWriter`, which formats output in JavaScript Object Notation (JSON), a lightweight data interchange format specified in specified in RFC 4627. If you do not set the `wt` parameter in your request, you will get JSON by default.
+The default Solr Response Writer is the `JsonResponseWriter`, which formats output in JavaScript Object Notation (JSON), a lightweight data interchange format specified in specified in RFC 4627.
+The default response writer is used when,
+
+* `wt` parameter is not specified in the request
+* non-existent response writer is specified
 
 Here is a sample response for a simple query like `q=id:VS1GB400C3`: