Fixes and test cases for Bug#8880 "Commands out of sync error with cursors"

and Bug#9159 "Server crash during mysql_stmt_close".
The patch adds support for single-row result sets in cursors.


libmysql/libmysql.c:
  If we wanted a cursor, and the server wasn't able to create one,
  buffer all rows on client. Currently this is possible only for
  single row result sets and some SHOW commands.
sql/sql_prepare.cc:
  Properly free resources if there was a request to open a cursor which
  wasn't fullfilled.
  Give error on attempt to open a cursor for a statement not returning
  a result set.
sql/sql_select.h:
  Initialize Item_arena of Cursor object. A case when a cursor object
  is created but not used is possible with single-row result sets.
tests/mysql_client_test.c:
  Test cases for Bug#8880 and Bug#9159

libmysql/libmysql.c

@@ -2862,6 +2862,17 @@ int STDCALL mysql_stmt_execute(MYSQL_STMT *stmt)
       mysql->status= MYSQL_STATUS_READY;
       stmt->read_row_func= stmt_read_row_from_cursor;
     }
+    else if (stmt->flags & CURSOR_TYPE_READ_ONLY)
+    {
+      /*
+        This is a single-row result set, a result set with no rows, EXPLAIN,
+        SHOW VARIABLES, or some other command which either a) bypasses the
+        cursors framework in the server and writes rows directly to the
+        network or b) is more efficient if all (few) result set rows are
+        precached on client and server's resources are freed.
+      */
+      DBUG_RETURN(mysql_stmt_store_result(stmt));
+    }
     else
     {
       stmt->mysql->unbuffered_fetch_owner= &stmt->unbuffered_fetch_cancelled;

sql/sql_prepare.cc

@@ -1970,6 +1970,7 @@ void mysql_stmt_execute(THD *thd, char *packet, uint packet_length)
 {
   ulong stmt_id= uint4korr(packet);
   ulong flags= (ulong) ((uchar) packet[4]);
+  Cursor *cursor= 0;
   /*
     Query text for binary log, or empty string if the query is not put into
     binary log.
@@ -2007,15 +2008,17 @@ void mysql_stmt_execute(THD *thd, char *packet, uint packet_length)
         statement: we can't open a cursor for it.
       */
       flags= 0;
+      my_error(ER_SP_BAD_CURSOR_QUERY, MYF(0));
+      goto err;
     }
     else
     {
       DBUG_PRINT("info",("Using READ_ONLY cursor"));
       if (!stmt->cursor &&
-          !(stmt->cursor= new (&stmt->main_mem_root) Cursor()))
+          !(cursor= stmt->cursor= new (&stmt->main_mem_root) Cursor()))
         DBUG_VOID_RETURN;
       /* If lex->result is set, mysql_execute_command will use it */
-      stmt->lex->result= &stmt->cursor->result;
+      stmt->lex->result= &cursor->result;
     }
   }
 #ifndef EMBEDDED_LIBRARY
@@ -2061,11 +2064,10 @@ void mysql_stmt_execute(THD *thd, char *packet, uint packet_length)
     my_pthread_setprio(pthread_self(), WAIT_PRIOR);
   thd->protocol= &thd->protocol_simple;         // Use normal protocol
 
-  if (flags & (ulong) CURSOR_TYPE_READ_ONLY)
+  if (cursor && cursor->is_open())
   {
-    if (stmt->cursor->is_open())
-      stmt->cursor->init_from_thd(thd);
-    stmt->cursor->state= stmt->state;
+    cursor->init_from_thd(thd);
+    cursor->state= stmt->state;
   }
   else
   {

sql/sql_select.h

@@ -370,7 +370,7 @@ public:
   void close();
 
   void set_unit(SELECT_LEX_UNIT *unit_arg) { unit= unit_arg; }
-  Cursor() :join(0), unit(0) {}
+  Cursor() :Item_arena(TRUE), join(0), unit(0) {}
   ~Cursor();
 };
 

tests/mysql_client_test.c

@@ -12740,6 +12740,73 @@ static void test_bug8378()
   mysql_close(lmysql);
 }
 
+
+MYSQL_STMT *open_cursor(char *query)
+{
+  int rc;
+  const ulong type= (ulong)CURSOR_TYPE_READ_ONLY;
+
+  MYSQL_STMT *stmt= mysql_stmt_init(mysql);
+  rc= mysql_stmt_prepare(stmt, query, strlen(query));
+  check_execute(stmt, rc);
+
+  mysql_stmt_attr_set(stmt, STMT_ATTR_CURSOR_TYPE, (void*) &type);
+  return stmt;
+}
+
+
+static void test_bug8880()
+{
+  MYSQL_STMT *stmt_list[2], **stmt;
+  MYSQL_STMT **stmt_list_end= (MYSQL_STMT**) stmt_list + 2;
+  int rc;
+
+  myheader("test_bug8880");
+
+  mysql_query(mysql, "drop table if exists t1");
+  mysql_query(mysql, "create table t1 (a int not null primary key, b int)");
+  rc= mysql_query(mysql, "insert into t1 values (1,1)");
+  myquery(rc);                                  /* one check is enough */
+  /*
+    when inserting 2 rows everything works well
+    mysql_query(mysql, "INSERT INTO t1 VALUES (1,1),(2,2)");
+  */
+  for (stmt= stmt_list; stmt < stmt_list_end; stmt++)
+    *stmt= open_cursor("select a from t1");
+  for (stmt= stmt_list; stmt < stmt_list_end; stmt++)
+  {
+    rc= mysql_stmt_execute(*stmt);
+    check_execute(*stmt, rc);
+  }
+  for (stmt= stmt_list; stmt < stmt_list_end; stmt++)
+    mysql_stmt_close(*stmt);
+}
+
+
+static void test_bug9159()
+{
+  MYSQL_STMT *stmt;
+  int rc;
+  const char *stmt_text= "select a, b from t1";
+  const unsigned long type= CURSOR_TYPE_READ_ONLY;
+
+  myheader("test_bug9159");
+
+  mysql_query(mysql, "drop table if exists t1");
+  mysql_query(mysql, "create table t1 (a int not null primary key, b int)");
+  rc= mysql_query(mysql, "insert into t1 values (1,1)");
+  myquery(rc);
+
+  stmt= mysql_stmt_init(mysql);
+  mysql_stmt_prepare(stmt, stmt_text, strlen(stmt_text));
+  mysql_stmt_attr_set(stmt, STMT_ATTR_CURSOR_TYPE, (const void *)&type);
+
+  mysql_stmt_execute(stmt);
+  mysql_stmt_close(stmt);
+  rc= mysql_query(mysql, "drop table if exists t1");
+  myquery(rc);
+}
+
 /*
   Read and parse arguments and MySQL options from my.cnf
 */
@@ -12962,6 +13029,8 @@ static struct my_tests_st my_tests[]= {
   { "test_bug8330", test_bug8330 },
   { "test_bug7990", test_bug7990 },
   { "test_bug8378", test_bug8378 },
+  { "test_bug8880", test_bug8880 },
+  { "test_bug9159", test_bug9159 },
   { 0, 0 }
 };