--- a/configure.in	Tue Sep 18 18:41:01 2012 +0300
+++ b/configure.in	Tue Sep 18 18:44:46 2012 +0300
@@ -2806,6 +2806,7 @@
 src/plugins/lazy-expunge/Makefile
 src/plugins/listescape/Makefile
 src/plugins/mail-log/Makefile
+src/plugins/mailbox-alias/Makefile
 src/plugins/notify/Makefile
 src/plugins/pop3-migration/Makefile
 src/plugins/quota/Makefile

--- a/src/plugins/Makefile.am	Tue Sep 18 18:41:01 2012 +0300
+++ b/src/plugins/Makefile.am	Tue Sep 18 18:44:46 2012 +0300
@@ -21,6 +21,7 @@
 	listescape \
 	notify \
 	mail-log \
+	mailbox-alias \
 	quota \
 	imap-quota \
 	pop3-migration \

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/plugins/mailbox-alias/Makefile.am	Tue Sep 18 18:44:46 2012 +0300
@@ -0,0 +1,18 @@
+AM_CPPFLAGS = \
+	-I$(top_srcdir)/src/lib \
+	-I$(top_srcdir)/src/lib-mail \
+	-I$(top_srcdir)/src/lib-imap \
+	-I$(top_srcdir)/src/lib-index \
+	-I$(top_srcdir)/src/lib-storage
+
+NOPLUGIN_LDFLAGS =
+lib20_mailbox_alias_plugin_la_LDFLAGS = -module -avoid-version
+
+module_LTLIBRARIES = \
+	lib20_mailbox_alias_plugin.la
+
+lib20_mailbox_alias_plugin_la_SOURCES = \
+	mailbox-alias-plugin.c
+
+noinst_HEADERS = \
+	mailbox-alias-plugin.h

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/plugins/mailbox-alias/mailbox-alias-plugin.c	Tue Sep 18 18:44:46 2012 +0300
@@ -0,0 +1,335 @@
+/* Copyright (c) 2012 Dovecot authors, see the included COPYING file */
+
+#include "lib.h"
+#include "str.h"
+#include "mail-storage-hooks.h"
+#include "mail-storage-private.h"
+#include "mailbox-list-private.h"
+#include "mailbox-alias-plugin.h"
+
+#define MAILBOX_ALIAS_USER_CONTEXT(obj) \
+	MODULE_CONTEXT(obj, mailbox_alias_user_module)
+#define MAILBOX_ALIAS_CONTEXT(obj) \
+	MODULE_CONTEXT(obj, mailbox_alias_storage_module)
+#define MAILBOX_ALIAS_LIST_CONTEXT(obj) \
+	MODULE_CONTEXT(obj, mailbox_alias_mailbox_list_module)
+
+struct mailbox_alias {
+	const char *old_vname, *new_vname;
+};
+
+struct mailbox_alias_user {
+	union mail_user_module_context module_ctx;
+
+	ARRAY_DEFINE(aliases, struct mailbox_alias);
+};
+
+struct mailbox_alias_mailbox_list {
+	union mailbox_list_module_context module_ctx;
+};
+
+struct mailbox_alias_mailbox {
+	union mailbox_module_context module_ctx;
+};
+
+enum mailbox_symlink_existence {
+	MAILBOX_SYMLINK_EXISTENCE_NONEXISTENT,
+	MAILBOX_SYMLINK_EXISTENCE_SYMLINK,
+	MAILBOX_SYMLINK_EXISTENCE_NOT_SYMLINK
+};
+
+static MODULE_CONTEXT_DEFINE_INIT(mailbox_alias_user_module,
+				  &mail_user_module_register);
+static MODULE_CONTEXT_DEFINE_INIT(mailbox_alias_storage_module,
+				  &mail_storage_module_register);
+static MODULE_CONTEXT_DEFINE_INIT(mailbox_alias_mailbox_list_module,
+				  &mailbox_list_module_register);
+
+const char *mailbox_alias_plugin_version = DOVECOT_VERSION;
+
+static const char *
+mailbox_alias_find_new(struct mail_user *user, const char *new_vname)
+{
+	struct mailbox_alias_user *auser = MAILBOX_ALIAS_USER_CONTEXT(user);
+	const struct mailbox_alias *alias;
+
+	array_foreach(&auser->aliases, alias) {
+		if (strcmp(alias->new_vname, new_vname) == 0)
+			return alias->old_vname;
+	}
+	return NULL;
+}
+
+static int mailbox_symlink_exists(struct mailbox_list *list, const char *vname,
+				  enum mailbox_symlink_existence *existence_r)
+{
+	struct mailbox_alias_mailbox_list *alist =
+		MAILBOX_ALIAS_LIST_CONTEXT(list);
+	struct stat st;
+	const char *symlink_name, *symlink_path;
+
+	symlink_name = alist->module_ctx.super.get_storage_name(list, vname);
+	symlink_path = mailbox_list_get_path(list, symlink_name,
+					     MAILBOX_LIST_PATH_TYPE_DIR);
+	if (lstat(symlink_path, &st) < 0) {
+		if (errno == ENOENT) {
+			*existence_r = MAILBOX_SYMLINK_EXISTENCE_NONEXISTENT;
+			return 0;
+		}
+		mailbox_list_set_critical(list,
+					  "lstat(%s) failed: %m", symlink_path);
+		return -1;
+	}
+	if (S_ISLNK(st.st_mode))
+		*existence_r = MAILBOX_SYMLINK_EXISTENCE_SYMLINK;
+	else
+		*existence_r = MAILBOX_SYMLINK_EXISTENCE_NOT_SYMLINK;
+	return 0;
+}
+
+static int mailbox_is_alias_symlink(struct mailbox *box)
+{
+	enum mailbox_symlink_existence existence;
+
+	if (mailbox_alias_find_new(box->storage->user, box->vname) == NULL)
+		return 0;
+	if (mailbox_symlink_exists(box->list, box->vname, &existence) < 0) {
+		mail_storage_copy_list_error(box->storage, box->list);
+		return -1;
+	}
+	return existence == MAILBOX_SYMLINK_EXISTENCE_SYMLINK ? 1 : 0;
+}
+
+static int
+mailbox_has_aliases(struct mailbox_list *list, const char *old_vname)
+{
+	struct mailbox_alias_user *auser =
+		MAILBOX_ALIAS_USER_CONTEXT(list->ns->user);
+	const struct mailbox_alias *alias;
+	enum mailbox_symlink_existence existence;
+	int ret = 0;
+
+	array_foreach(&auser->aliases, alias) {
+		if (strcmp(alias->old_vname, old_vname) == 0) {
+			if (mailbox_symlink_exists(list, alias->new_vname,
+						   &existence) < 0)
+				ret = -1;
+			if (existence == MAILBOX_SYMLINK_EXISTENCE_SYMLINK)
+				return 1;
+		}
+	}
+	return ret;
+}
+
+static int
+mailbox_alias_create_symlink(struct mailbox *box,
+			     const char *old_name, const char *new_name)
+{
+	const char *old_path, *new_path, *fname;
+
+	old_path = mailbox_list_get_path(box->list, old_name,
+					 MAILBOX_LIST_PATH_TYPE_DIR);
+	new_path = mailbox_list_get_path(box->list, new_name,
+					 MAILBOX_LIST_PATH_TYPE_DIR);
+	fname = strrchr(old_path, '/');
+	i_assert(fname != NULL);
+	fname++;
+	i_assert(strncmp(new_path, old_path, fname-old_path) == 0);
+
+	if (symlink(fname, new_path) < 0) {
+		if (errno == EEXIST) {
+			mail_storage_set_error(box->storage, MAIL_ERROR_EXISTS,
+					       "Mailbox already exists");
+			return -1;
+		}
+		mail_storage_set_critical(box->storage,
+			"symlink(%s, %s) failed: %m", fname, new_path);
+		return -1;
+	}
+	return 0;
+}
+
+static const char *
+mailbox_alias_get_storage_name(struct mailbox_list *list, const char *vname)
+{
+	struct mailbox_alias_mailbox_list *alist =
+		MAILBOX_ALIAS_LIST_CONTEXT(list);
+	const char *old_vname;
+	enum mailbox_symlink_existence existence;
+
+	/* access the old mailbox so that e.g. full text search won't
+	   index the mailbox twice. this also means that deletion must be
+	   careful to delete the symlink, box->name. */
+	old_vname = mailbox_alias_find_new(list->ns->user, vname);
+	if (old_vname != NULL &&
+	    mailbox_symlink_exists(list, vname, &existence) == 0 &&
+	    existence != MAILBOX_SYMLINK_EXISTENCE_NOT_SYMLINK)
+		vname = old_vname;
+
+	return alist->module_ctx.super.get_storage_name(list, vname);
+}
+
+static int
+mailbox_alias_create(struct mailbox *box, const struct mailbox_update *update,
+		     bool directory)
+{
+	struct mailbox_alias_mailbox *abox = MAILBOX_ALIAS_CONTEXT(box);
+	struct mailbox_alias_mailbox_list *alist =
+		MAILBOX_ALIAS_LIST_CONTEXT(box->list);
+	const char *symlink_name;
+	int ret;
+
+	ret = abox->module_ctx.super.create(box, update, directory);
+	if (mailbox_alias_find_new(box->storage->user, box->vname) == NULL)
+		return ret;
+	if (ret < 0 && mailbox_get_last_mail_error(box) != MAIL_ERROR_EXISTS)
+		return ret;
+
+	/* all the code so far has actually only created the original
+	   mailbox. now we'll create the symlink if it's missing. */
+	symlink_name = alist->module_ctx.super.
+		get_storage_name(box->list, box->vname);
+	return mailbox_alias_create_symlink(box, box->name, symlink_name);
+}
+
+static int mailbox_alias_delete(struct mailbox *box)
+{
+	struct mailbox_alias_mailbox *abox = MAILBOX_ALIAS_CONTEXT(box);
+	struct mailbox_alias_mailbox_list *alist =
+		MAILBOX_ALIAS_LIST_CONTEXT(box->list);
+	const char *symlink_name;
+	int ret;
+
+	ret = mailbox_has_aliases(box->list, box->vname);
+	if (ret < 0)
+		return -1;
+	if (ret > 0) {
+		mail_storage_set_error(box->storage, MAIL_ERROR_NOTPOSSIBLE,
+			"Can't delete mailbox while it has aliases");
+		return -1;
+	}
+
+	if (mailbox_is_alias_symlink(box)) {
+		/* we're deleting an alias mailbox. we'll need to handle this
+		   explicitly since box->name points to the original mailbox */
+		symlink_name = alist->module_ctx.super.
+			get_storage_name(box->list, box->vname);
+		if (mailbox_list_delete_symlink(box->list, symlink_name) < 0) {
+			mail_storage_copy_list_error(box->storage, box->list);
+			return -1;
+		}
+		return 0;
+	}
+
+	return abox->module_ctx.super.delete(box);
+}
+
+static int mailbox_alias_rename(struct mailbox *src, struct mailbox *dest,
+				bool rename_children)
+{
+	struct mailbox_alias_mailbox *abox = MAILBOX_ALIAS_CONTEXT(src);
+	int ret;
+
+	if (mailbox_is_alias_symlink(src)) {
+		mail_storage_set_error(src->storage, MAIL_ERROR_NOTPOSSIBLE,
+				       "Can't rename alias mailboxes");
+		return -1;
+	}
+	if (mailbox_is_alias_symlink(dest)) {
+		mail_storage_set_error(src->storage, MAIL_ERROR_NOTPOSSIBLE,
+				       "Can't rename to mailbox alias");
+		return -1;
+	}
+	ret = mailbox_has_aliases(src->list, src->vname);
+	if (ret < 0)
+		return -1;
+	if (ret > 0) {
+		mail_storage_set_error(src->storage, MAIL_ERROR_NOTPOSSIBLE,
+			"Can't rename mailbox while it has aliases");
+		return -1;
+	}
+
+	return abox->module_ctx.super.rename(src, dest, rename_children);
+}
+
+static void mailbox_alias_mail_user_created(struct mail_user *user)
+{
+	struct mail_user_vfuncs *v = user->vlast;
+	struct mailbox_alias_user *auser;
+	struct mailbox_alias *alias;
+	string_t *oldkey, *newkey;
+	const char *old_vname, *new_vname;
+	unsigned int i;
+
+	auser = p_new(user->pool, struct mailbox_alias_user, 1);
+	auser->module_ctx.super = *v;
+	user->vlast = &auser->module_ctx.super;
+
+	p_array_init(&auser->aliases, user->pool, 8);
+
+	oldkey = t_str_new(32);
+	newkey = t_str_new(32);
+	str_append(oldkey, "mailbox_alias_old");
+	str_append(newkey, "mailbox_alias_new");
+	for (i = 2;; i++) {
+		old_vname = mail_user_plugin_getenv(user, str_c(oldkey));
+		new_vname = mail_user_plugin_getenv(user, str_c(newkey));
+		if (old_vname == NULL || new_vname == NULL)
+			break;
+
+		alias = array_append_space(&auser->aliases);
+		alias->old_vname = old_vname;
+		alias->new_vname = new_vname;
+
+		str_truncate(oldkey, 0);
+		str_truncate(newkey, 0);
+		str_printfa(oldkey, "mailbox_alias_old%u", i);
+		str_printfa(newkey, "mailbox_alias_new%u", i);
+	}
+
+	MODULE_CONTEXT_SET(user, mailbox_alias_user_module, auser);
+}
+
+static void mailbox_alias_mailbox_list_created(struct mailbox_list *list)
+{
+	struct mailbox_list_vfuncs *v = list->vlast;
+	struct mailbox_alias_mailbox_list *alist;
+
+	alist = p_new(list->pool, struct mailbox_alias_mailbox_list, 1);
+	alist->module_ctx.super = *v;
+	list->vlast = &alist->module_ctx.super;
+
+	v->get_storage_name = mailbox_alias_get_storage_name;
+	MODULE_CONTEXT_SET(list, mailbox_alias_mailbox_list_module, alist);
+}
+
+static void mailbox_alias_mailbox_allocated(struct mailbox *box)
+{
+	struct mailbox_vfuncs *v = box->vlast;
+	struct mailbox_alias_mailbox *abox;
+
+	abox = p_new(box->pool, struct mailbox_alias_mailbox, 1);
+	abox->module_ctx.super = *v;
+	box->vlast = &abox->module_ctx.super;
+
+	v->create = mailbox_alias_create;
+	v->delete = mailbox_alias_delete;
+	v->rename = mailbox_alias_rename;
+	MODULE_CONTEXT_SET(box, mailbox_alias_storage_module, abox);
+}
+
+static struct mail_storage_hooks mailbox_alias_mail_storage_hooks = {
+	.mail_user_created = mailbox_alias_mail_user_created,
+	.mailbox_list_created = mailbox_alias_mailbox_list_created,
+	.mailbox_allocated = mailbox_alias_mailbox_allocated
+};
+
+void mailbox_alias_plugin_init(struct module *module)
+{
+	mail_storage_hooks_add(module, &mailbox_alias_mail_storage_hooks);
+}
+
+void mailbox_alias_plugin_deinit(void)
+{
+	mail_storage_hooks_remove(&mailbox_alias_mail_storage_hooks);
+}

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/plugins/mailbox-alias/mailbox-alias-plugin.h	Tue Sep 18 18:44:46 2012 +0300
@@ -0,0 +1,7 @@
+#ifndef MAILBOX_ALIAS_PLUGIN_H
+#define MAILBOX_ALIAS_PLUGIN_H
+
+void mailbox_alias_plugin_init(struct module *module);
+void mailbox_alias_plugin_deinit(void);
+
+#endif