New file. Sample base64 encoder-decoder.

+/* GNU mailutils - a suite of utilities for electronic mail
+   Copyright (C) 1999, 2000, 2001, 2002 Free Software Foundation, Inc.
+
+   This program is free software; you can redistribute it and/or modify
+   it under the terms of the GNU General Public License as published by
+   the Free Software Foundation; either version 2, or (at your option)
+   any later version.
+
+   This program 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 General Public License for more details.
+
+   You should have received a copy of the GNU General Public License
+   along with this program; if not, write to the Free Software
+   Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.  */
+
+#include <unistd.h>
+#include <stdio.h>
+#include <assert.h>
+#include <ctype.h>
+#include <mailutils/mailutils.h>
+
+int
+main (int argc, char * argv [])
+{
+  stream_t in, out, flt;
+  unsigned char buffer;
+  int c, verbose = 0;
+  int printable = 0;
+  size_t size, total = 0;
+  int mode = MU_FILTER_ENCODE;
+  char *input = NULL, *output = NULL;
+
+  while ((c = getopt (argc, argv, "dehi:o:pv")) != EOF)
+    switch (c)
+      {
+      case 'i':
+	input = optarg;
+	break;
+
+      case 'o':
+	output = optarg;
+	break;
+	
+      case 'd':
+	mode = MU_FILTER_DECODE;
+	break;
+	
+      case 'e':
+	mode = MU_FILTER_ENCODE;
+	break;
+
+      case 'p':
+	printable = 1;
+	break;
+	
+      case 'v':
+	verbose = 1;
+	break;
+
+      case 'h':
+	printf ("usage: base64 [-vpde][-i infile][-o outfile]\n");
+	exit (0);
+	  
+      default:
+	exit (1);
+      }
+
+  if (input)
+    c = file_stream_create (&in, input, MU_STREAM_READ);
+  else
+    c = stdio_stream_create (&in, stdin, 0);
+  assert (c == 0);
+  assert (filter_create (&flt, in, "base64", mode, MU_STREAM_READ) == 0);
+  assert (stream_open (in) == 0);
+
+  if (output)
+    c = file_stream_create (&out, output, MU_STREAM_WRITE|MU_STREAM_CREAT);
+  else
+    c = stdio_stream_create (&out, stdout, 0);
+  assert (c == 0);
+  assert (stream_open (out) == 0);
+  
+  while (stream_read (flt, &buffer, sizeof (buffer), total, &size) == 0
+	 && size > 0)
+    {
+      if (printable && !isprint (buffer))
+	{
+	  char outbuf[24];
+	  sprintf (outbuf, "\\%03o", (unsigned int) buffer);
+	  stream_write (out, outbuf, strlen (outbuf), total, NULL);
+	}
+      else
+	stream_write (out, &buffer, size, total, NULL);
+      total += size;
+    }
+
+  stream_write (out, "\n", 1, total, NULL);
+  stream_close (in);
+  stream_close (out);
+  if (verbose)
+    fprintf (stderr, "total: %lu bytes\n", (unsigned long) total);
+  return 0;
+}