support: Add TEST_COMPARE_BLOB, support_quote_blob

The declaration of support_test_compare_blob uses unsigned long int,
to avoid including <stddef.h>.

Reviewed-by: Carlos O'Donell <carlos@redhat.com>

support/support_quote_blob.c

@@ -0,0 +1,83 @@
+/* Quote a blob so that it can be used in C literals.
+   Copyright (C) 2018 Free Software Foundation, Inc.
+   This file is part of the GNU C Library.
+
+   The GNU C Library is free software; you can redistribute it and/or
+   modify it under the terms of the GNU Lesser General Public
+   License as published by the Free Software Foundation; either
+   version 2.1 of the License, or (at your option) any later version.
+
+   The GNU C Library is distributed in the hope that it will be useful,
+   but WITHOUT ANY WARRANTY; without even the implied warranty of
+   MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
+   Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public
+   License along with the GNU C Library; if not, see
+   <http://www.gnu.org/licenses/>.  */
+
+#include <support/support.h>
+#include <support/xmemstream.h>
+
+char *
+support_quote_blob (const void *blob, size_t length)
+{
+  struct xmemstream out;
+  xopen_memstream (&out);
+
+  const unsigned char *p = blob;
+  for (size_t i = 0; i < length; ++i)
+    {
+      unsigned char ch = p[i];
+
+      /* Use C backslash escapes for those control characters for
+         which they are defined.  */
+      switch (ch)
+        {
+          case '\a':
+            putc_unlocked ('\\', out.out);
+            putc_unlocked ('a', out.out);
+            break;
+          case '\b':
+            putc_unlocked ('\\', out.out);
+            putc_unlocked ('b', out.out);
+            break;
+          case '\f':
+            putc_unlocked ('\\', out.out);
+            putc_unlocked ('f', out.out);
+            break;
+          case '\n':
+            putc_unlocked ('\\', out.out);
+            putc_unlocked ('n', out.out);
+            break;
+          case '\r':
+            putc_unlocked ('\\', out.out);
+            putc_unlocked ('r', out.out);
+            break;
+          case '\t':
+            putc_unlocked ('\\', out.out);
+            putc_unlocked ('t', out.out);
+            break;
+          case '\v':
+            putc_unlocked ('\\', out.out);
+            putc_unlocked ('v', out.out);
+            break;
+          case '\\':
+          case '\'':
+          case '\"':
+            putc_unlocked ('\\', out.out);
+            putc_unlocked (ch, out.out);
+            break;
+        default:
+          if (ch < ' ' || ch > '~')
+            /* Use octal sequences because they are fixed width,
+               unlike hexadecimal sequences.  */
+            fprintf (out.out, "\\%03o", ch);
+          else
+            putc_unlocked (ch, out.out);
+        }
+    }
+
+  xfclose_memstream (&out);
+  return out.buffer;
+}