Sample loadable extension for sieve.

+/* 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 Lesser 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 Lesser General Public License for more details.
+
+   You should have received a copy of the GNU Lesser General Public License
+   along with this program; if not, write to the Free Software
+   Foundation, Inc., 675 Mass Ave, Cambridge, MA 02139, USA.  */
+
+/*  This is an example on how to write extension tests for GNU sieve.
+    It provides test "numaddr".
+
+    Syntax:   numaddr [":over" / ":under"] <header-names: string-list>
+              <limit: number>
+
+    The "numaddr" test counts Internet addresses in structured headers
+    that contain addresses.  It returns true if the total number of
+    addresses satisfies the requested relation:
+
+    If the argument is ":over" and the number of addresses is greater than
+    the number provided, the test is true; otherwise, it is false.
+
+    If the argument is ":under" and the number of addresses is less than
+    the number provided, the test is true; otherwise, it is false.
+
+    If the argument is empty, ":over" is assumed. */
+
+#ifdef HAVE_CONFIG_H
+# include <config.h>
+#endif  
+
+#include <stdlib.h>
+#include <mailutils/libsieve.h>
+
+struct val_ctr {
+  header_t hdr;
+  size_t limit;
+  size_t count;
+};
+
+static int
+_count_items (void *item, void *data)
+{
+  char *name = item;
+  struct val_ctr *vp = data;
+  char *val;
+  address_t addr;
+  size_t count = 0;
+  
+  if (header_aget_value (vp->hdr, name, &val))
+    return 0;
+  if (address_create (&addr, val) == 0)
+    {
+      address_get_count (addr, &count);
+      address_destroy (&addr);
+      vp->count += count;
+    }
+  free (val);
+  return vp->count >= vp->limit;
+}
+  
+static int
+numaddr_test (sieve_machine_t mach, list_t args, list_t tags)
+{
+  sieve_value_t *h, *v;
+  struct val_ctr vc;
+  int rc;
+  
+  if (sieve_get_debug_level (mach) & MU_SIEVE_DEBUG_TRACE)
+    sieve_debug (mach, "NUMADDR\n");
+
+  h = sieve_value_get (args, 0);
+  if (!h)
+    {
+      sieve_error (mach, "numaddr: can't get argument 1");
+      sieve_abort (mach);
+    }
+  v = sieve_value_get (args, 1);
+  if (!v)
+    {
+      sieve_error (mach, "numaddr: can't get argument 2");
+      sieve_abort (mach);
+    }
+
+  message_get_header (sieve_get_message (mach), &vc.hdr);
+  vc.count = 0;
+  vc.limit = v->v.number;
+
+  rc = sieve_vlist_do (h, _count_items, &vc);
+  
+  if (sieve_tag_lookup (tags, "under", NULL))
+    rc = !rc;
+  return rc;
+}
+
+static sieve_data_type numaddr_req_args[] = {
+  SVT_STRING_LIST,
+  SVT_NUMBER,
+  SVT_VOID
+};
+
+static sieve_tag_def_t numaddr_tags[] = {
+  { "over", SVT_VOID },
+  { "under", SVT_VOID },
+  { NULL }
+};
+
+static sieve_tag_group_t numaddr_tag_groups[] = {
+  { numaddr_tags, NULL },
+  { NULL }
+};
+
+
+int
+SIEVE_EXPORT(numaddr,init) (sieve_machine_t mach)
+{
+  return sieve_register_test (mach, "numaddr", numaddr_test,
+			      numaddr_req_args, numaddr_tag_groups, 1);
+}