Add a null UI method

There are cases when, if you pass a NULL UI_METHOD, the called
function will use an internal default.  This is well and good, but
there may be cases when this is undesirable and one would rather send
in a UI that does absolutely nothing (sort of a /dev/null).  UI_null()
is the UI_METHOD for this purpose.

Reviewed-by: Rich Salz <rsalz@openssl.org>
(Merged from https://github.com/openssl/openssl/pull/2744)

2 files changed, 27 insertions, 1 deletions

diff --git a/crypto/ui/build.info b/crypto/ui/build.info
index fcb45af7eb..c5d17fb744 100644
--- a/crypto/ui/build.info
+++ b/crypto/ui/build.info
@@ -1,3 +1,3 @@
 LIBS=../../libcrypto
 SOURCE[../../libcrypto]=\
-        ui_err.c ui_lib.c ui_openssl.c ui_util.c
+        ui_err.c ui_lib.c ui_openssl.c ui_null.c ui_util.c
diff --git a/crypto/ui/ui_null.c b/crypto/ui/ui_null.c
new file mode 100644
index 0000000000..9e5f6fca59
--- /dev/null
+++ b/crypto/ui/ui_null.c
@@ -0,0 +1,26 @@
+/*
+ * Copyright 2017 The OpenSSL Project Authors. All Rights Reserved.
+ *
+ * Licensed under the OpenSSL license (the "License").  You may not use
+ * this file except in compliance with the License.  You can obtain a copy
+ * in the file LICENSE in the source distribution or at
+ * https://www.openssl.org/source/license.html
+ */
+
+#include "ui_locl.h"
+
+static const UI_METHOD ui_null = {
+    "OpenSSL NULL UI",
+    NULL,                        /* opener */
+    NULL,                        /* writer */
+    NULL,                        /* flusher */
+    NULL,                        /* reader */
+    NULL,                        /* closer */
+    NULL
+};
+
+/* The method with all the built-in thingies */
+const UI_METHOD *UI_null(void)
+{
+    return &ui_null;
+}