lib-storage: Added mail_storage_service_all_init_mask()

This allows providing a usermask hint to the userdb iteration lookup. For example
with LDAP this allows setting the base based on the @Domain.

src/lib-storage/mail-storage-service.c

@@ -1529,6 +1529,12 @@ mail_storage_service_all_iter_deinit(struct mail_storage_service_ctx *ctx)
 }
 
 void mail_storage_service_all_init(struct mail_storage_service_ctx *ctx)
+{
+	mail_storage_service_all_init_mask(ctx, "");
+}
+
+void mail_storage_service_all_init_mask(struct mail_storage_service_ctx *ctx,
+					const char *user_mask_hint)
 {
 	enum auth_master_flags flags = 0;
 
@@ -1542,7 +1548,8 @@ void mail_storage_service_all_init(struct mail_storage_service_ctx *ctx)
 		flags |= AUTH_MASTER_FLAG_DEBUG;
 	ctx->iter_conn = auth_master_init(auth_master_get_socket_path(ctx->conn),
 					  flags);
-	ctx->auth_list = auth_master_user_list_init(ctx->iter_conn, "", NULL);
+	ctx->auth_list = auth_master_user_list_init(ctx->iter_conn,
+						    user_mask_hint, NULL);
 }
 
 int mail_storage_service_all_next(struct mail_storage_service_ctx *ctx,

src/lib-storage/mail-storage-service.h

@@ -111,6 +111,11 @@ int mail_storage_service_lookup_next(struct mail_storage_service_ctx *ctx,
 void mail_storage_service_user_free(struct mail_storage_service_user **user);
 /* Initialize iterating through all users. */
 void mail_storage_service_all_init(struct mail_storage_service_ctx *ctx);
+/* Same as mail_storage_service_all_init(), but give a user mask hint to the
+   userdb iteration lookup. This itself isn't yet guaranteed to filter out any
+   usernames. */
+void mail_storage_service_all_init_mask(struct mail_storage_service_ctx *ctx,
+					const char *user_mask_hint);
 /* Iterate through all usernames. Returns 1 if username was returned, 0 if
    there are no more users, -1 if error. */
 int mail_storage_service_all_next(struct mail_storage_service_ctx *ctx,