Add a smoke test for server-side cursor support

integration-tests/mysql-client-tests/java/MySQLConnectorTest.java

@@ -1,8 +1,10 @@
 import java.sql.Connection;
 import java.sql.DriverManager;
+import java.sql.PreparedStatement;
 import java.sql.SQLException;
 import java.sql.Statement;
 import java.sql.ResultSet;
+import java.sql.ResultSetMetaData;
 
 public class MySQLConnectorTest {
 
@@ -62,6 +64,59 @@ public class MySQLConnectorTest {
     };
 
     public static void main(String[] args) {
+        testStatements(args);
+        testServerSideCursors(args);
+        System.exit(0);
+    }
+
+    // testServerSideCursors does a simple smoke test with server-side cursors to make sure
+    // results can be read. Note that we don't test results here; this is just a high level
+    // smoke test that we can execute server-side cursors logic without the server erroring out.
+    // This test was added for a regression where server-side cursor logic was getting
+    // corrupted result set memory and sending invalid data to the client, which caused the
+    // server to error out and crash the connection. If any errors are encountered, a stack trace
+    // is printed and this function exits with a non-zero code.
+    // For more details, see: https://github.com/dolthub/dolt/issues/9125
+    private static void testServerSideCursors(String[] args) {
+        String user = args[0];
+        String port = args[1];
+        String db   = args[2];
+
+        try {
+            String url = "jdbc:mysql://127.0.0.1:" + port + "/" + db +
+                         "?useServerPrepStmts=true&useCursorFetch=true";
+            Connection conn = DriverManager.getConnection(url, user, "");
+
+            executePreparedQuery(conn, "SELECT 1;");
+            executePreparedQuery(conn, "SELECT database();");
+            executePreparedQuery(conn, "SHOW COLLATION;");
+            executePreparedQuery(conn, "SHOW COLLATION;");
+            executePreparedQuery(conn, "SHOW COLLATION;");
+        } catch (SQLException ex) {
+            System.out.println("An error occurred.");
+            ex.printStackTrace();
+            System.exit(1);
+        }
+    }
+
+    // executePreparedQuery executes the specified |query| using |conn| as a prepared statement,
+    // and uses server-side cursor to fetch results. This method does not do any validation of
+    // results from the query. It is simply a smoke test to ensure the connection doesn't crash.
+    private static void executePreparedQuery(Connection conn, String query) throws SQLException {
+        PreparedStatement stmt = conn.prepareStatement(query, ResultSet.TYPE_FORWARD_ONLY);
+        stmt.setFetchSize(25); // needed to ensure a server-side cursor is used
+
+        ResultSet rs = stmt.executeQuery();
+        while (rs.next()) {}
+
+        rs.close();
+        stmt.close();
+    }
+
+    // testStatements executes the queries from |queries| and asserts their results from
+    // |expectedResults|. If any errors are encountered, a stack trace is printed and this
+    // function exits with a non-zero code.
+    private static void testStatements(String[] args) {
         Connection conn = null;
 
         String user = args[0];
@@ -109,7 +164,6 @@ public static void main(String[] args) {
                     }
                 }
             }
-            System.exit(0);
         } catch (SQLException ex) {
             System.out.println("An error occurred.");
             ex.printStackTrace();