MySQL column definitions from fetch or execute response should be used prior to prepare response when decoding rows using cursors

Author: BillyYccc

vertx-mysql-client/src/main/java/io/vertx/mysqlclient/impl/codec/ExtendedQueryCommandCodec.java

@@ -32,7 +32,7 @@ class ExtendedQueryCommandCodec<R> extends ExtendedQueryCommandBaseCodec<R, Exte
   ExtendedQueryCommandCodec(ExtendedQueryCommand<R> cmd) {
     super(cmd);
     if (cmd.fetch() > 0 && statement.isCursorOpen) {
-      // restore the state we need for decoding fetch response
+      // restore the state we need for decoding fetch response based on the prepared statement
       columnDefinitions = statement.rowDesc.columnDefinitions();
     }
   }
@@ -42,7 +42,10 @@ void encode(MySQLEncoder encoder) {
     super.encode(encoder);
 
     if (statement.isCursorOpen) {
-      decoder = new RowResultDecoder<>(cmd.collector(), statement.rowDesc);
+      if (decoder == null) {
+        // restore the state we need for decoding if column definitions are not included in the fetch response
+        decoder = new RowResultDecoder<>(cmd.collector(), statement.rowDesc);
+      }
       sendStatementFetchCommand(statement.statementId, cmd.fetch());
     } else {
       Tuple params = cmd.params();
@@ -96,8 +99,6 @@ void decodePayload(ByteBuf payload, int payloadLength) {
             // need to reset packet number so that we can send a fetch request
             sequenceId = 0;
             // send fetch after cursor opened
-            decoder = new RowResultDecoder<>(cmd.collector(), statement.rowDesc);
-
             statement.isCursorOpen = true;
 
             sendStatementFetchCommand(statement.statementId, cmd.fetch());

vertx-mysql-client/src/main/java/io/vertx/mysqlclient/impl/codec/QueryCommandBaseCodec.java

@@ -94,7 +94,8 @@ protected void handleResultsetColumnDefinitions(ByteBuf payload) {
 
   protected void handleResultsetColumnDefinitionsDecodingCompleted() {
     commandHandlerState = CommandHandlerState.HANDLING_ROW_DATA_OR_END_PACKET;
-    decoder = new RowResultDecoder<>(cmd.collector(), /*cmd.isSingleton()*/ new MySQLRowDesc(columnDefinitions, format));
+    MySQLRowDesc mySQLRowDesc = new MySQLRowDesc(columnDefinitions, format); // use the column definitions if provided by execute or fetch response instead of prepare response
+    decoder = new RowResultDecoder<>(cmd.collector(), mySQLRowDesc);
   }
 
   protected void handleRows(ByteBuf payload, int payloadLength) {

vertx-mysql-client/src/test/java/io/vertx/mysqlclient/MySQLPooledConnectionTest.java

@@ -17,7 +17,9 @@
 import io.vertx.ext.unit.Async;
 import io.vertx.ext.unit.TestContext;
 import io.vertx.ext.unit.junit.VertxUnitRunner;
+import io.vertx.sqlclient.Cursor;
 import io.vertx.sqlclient.PoolOptions;
+import io.vertx.sqlclient.Row;
 import io.vertx.sqlclient.SqlConnection;
 import org.junit.After;
 import org.junit.Before;
@@ -84,4 +86,19 @@ public void testTransactionRollbackUnfinishedOnRecycle(TestContext ctx) {
       });
     }));
   }
+
+  @Test
+  public void testQueryConstantWithCursor(TestContext ctx) {
+    connector.accept(ctx.asyncAssertSuccess(conn -> {
+      conn.prepare("SELECT 1")
+        .onComplete(ctx.asyncAssertSuccess(ps -> {
+          Cursor cursor = ps.cursor();
+          cursor.read(1024).onComplete(ctx.asyncAssertSuccess(result -> {
+            ctx.assertEquals(1, result.size());
+            Row row = result.iterator().next();
+            ctx.assertEquals(1, row.getInteger(0));
+          }));
+        }));
+    }));
+  }
 }