Improve error handling for malformed query cursors (#3066)

* Add reproducer for malformed cursor handling

Signed-off-by: Simeon Widdis <[email protected]>

* Handle malformed query cursors

Signed-off-by: Simeon Widdis <[email protected]>

* Move malformed cursor test to correct file

Signed-off-by: Simeon Widdis <[email protected]>

* Apply spotless

Signed-off-by: Simeon Widdis <[email protected]>

---------

Signed-off-by: Simeon Widdis <[email protected]>

Author: Swiddis

integ-test/src/test/java/org/opensearch/sql/legacy/CursorIT.java

@@ -440,6 +440,17 @@ public void noPaginationWithNonJDBCFormat() throws IOException {
     assertThat(rows.length, equalTo(1000));
   }
 
+  @Test
+  public void testMalformedCursorGracefullyHandled() throws IOException {
+    ResponseException result =
+        assertThrows(
+            "Expected query with malformed cursor to raise error, but didn't",
+            ResponseException.class,
+            () -> executeCursorQuery("d:a11b4db33f"));
+    assertTrue(result.getMessage().contains("Malformed cursor"));
+    assertEquals(result.getResponse().getStatusLine().getStatusCode(), 400);
+  }
+
   public void verifyWithAndWithoutPaginationResponse(
       String sqlQuery, String cursorQuery, int fetch_size, boolean shouldFallBackToV1)
       throws IOException {

legacy/src/main/java/org/opensearch/sql/legacy/executor/cursor/CursorResultExecutor.java

@@ -20,6 +20,7 @@
 import org.opensearch.action.search.SearchResponse;
 import org.opensearch.client.Client;
 import org.opensearch.common.unit.TimeValue;
+import org.opensearch.core.rest.RestStatus;
 import org.opensearch.rest.BytesRestResponse;
 import org.opensearch.rest.RestChannel;
 import org.opensearch.search.SearchHit;
@@ -36,6 +37,7 @@
 import org.opensearch.sql.legacy.pit.PointInTimeHandler;
 import org.opensearch.sql.legacy.pit.PointInTimeHandlerImpl;
 import org.opensearch.sql.legacy.rewriter.matchtoterm.VerificationException;
+import org.opensearch.sql.opensearch.response.error.ErrorMessageFactory;
 
 public class CursorResultExecutor implements CursorRestExecutor {
 
@@ -58,7 +60,15 @@ public void execute(Client client, Map<String, String> params, RestChannel chann
     } catch (IllegalArgumentException | JSONException e) {
       Metrics.getInstance().getNumericalMetric(MetricName.FAILED_REQ_COUNT_CUS).increment();
       LOG.error("Error parsing the cursor", e);
-      channel.sendResponse(new BytesRestResponse(channel, e));
+      channel.sendResponse(
+          new BytesRestResponse(
+              RestStatus.BAD_REQUEST,
+              "application/json; charset=UTF-8",
+              ErrorMessageFactory.createErrorMessage(
+                      new IllegalArgumentException(
+                          "Malformed cursor: unable to extract cursor information"),
+                      RestStatus.BAD_REQUEST.getStatus())
+                  .toString()));
     } catch (OpenSearchException e) {
       int status = (e.status().getStatus());
       if (status > 399 && status < 500) {