A fix and test case for Bug#7990 "mysql_stmt_close doesn't

reset mysql->net.last_error": the solution is to clear
MYSQL->net error before performing COM_CLOSE: if the call
succeeds, the connection is usable for other statements.
More comprehensive fix is to clear MYSQL->net for all
recoverable errors at the time they happen, it will be
implemented in 5.0 as it introduces incompatibility in behavior.

libmysql/libmysql.c

@@ -1788,6 +1788,18 @@ static my_bool my_realloc_str(NET *net, ulong length)
 }
 
 
+/* Clear possible error statee of struct NET */
+
+static void net_clear_error(NET *net)
+{
+  if (net->last_errno)
+  {
+    net->last_errno= 0;
+    net->last_error[0]= '\0';
+    strmov(net->sqlstate, not_error_sqlstate);
+  }
+}
+
 /*
   Set statement error code, sqlstate, and error message
   from given errcode and sqlstate.
@@ -4512,6 +4524,11 @@ my_bool STDCALL mysql_stmt_close(MYSQL_STMT *stmt)
 
       if (mysql->unbuffered_fetch_owner == &stmt->unbuffered_fetch_cancelled)
         mysql->unbuffered_fetch_owner= 0;
+      /*
+        Clear NET error state: if the following commands come through
+        successfully, connection will still be usable for other commands.
+      */
+      net_clear_error(&mysql->net);
       if (mysql->status != MYSQL_STATUS_READY)
       {
         /*

tests/mysql_client_test.c

@@ -11534,7 +11534,7 @@ static void test_bug6761(void)
 }
 
 
-/* Bug#8330 - Bug #8330   mysql_stmt_execute crashes (libmysql) */
+/* Bug#8330 - mysql_stmt_execute crashes (libmysql) */
 
 static void test_bug8330()
 {
@@ -11585,6 +11585,26 @@ static void test_bug8330()
 }
 
 
+/* Bug#7990 - mysql_stmt_close doesn't reset mysql->net.last_error */
+
+static void test_bug7990()
+{
+  MYSQL_STMT *stmt;
+  int rc;
+  myheader("test_bug7990");
+
+  stmt= mysql_stmt_init(mysql);
+  rc= mysql_stmt_prepare(stmt, "foo", 3);
+  /*
+    XXX: the fact that we store errno both in STMT and in
+    MYSQL is not documented and is subject to change in 5.0
+  */
+  DIE_UNLESS(rc && mysql_stmt_errno(stmt) && mysql_errno(mysql));
+  mysql_stmt_close(stmt);
+  DIE_UNLESS(!mysql_errno(mysql));
+}
+
+
 /*
   Read and parse arguments and MySQL options from my.cnf
 */