WIP: layered settings

This might be something we could use for config/sa/thread specific
settings.

diff --git a/src/libstrongswan/settings/layered_settings.h b/src/libstrongswan/settings/layered_settings.h
new file mode 100644 (file)
index 0000000..ec32b82
--- /dev/null
+++ b/src/libstrongswan/settings/layered_settings.h
@@ -0,0 +1,114 @@
+/*
+ * Copyright (C) 2015 Tobias Brunner
+ * Hochschule fuer Technik Rapperswil
+ *
+ * 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 of the License, or (at your
+ * option) any later version.  See <http://www.fsf.org/copyleft/gpl.txt>.
+ *
+ * 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.
+ */
+
+/**
+ * @defgroup layered_settings_t layered_settings
+ * @{ @ingroup settings
+ */
+
+#ifndef LAYERED_SETTINGS_H_
+#define LAYERED_SETTINGS_H_
+
+typedef struct layered_settings_t layered_settings_t;
+
+#include "settings.h"
+
+/**
+ * This class enables layering of settings_t objects.
+ *
+ * Each instance of layered_settings_t is created with a base settings layer.
+ * On top of that two layers may be added, one permanent and one is thread
+ * specific (each layer may in turn be an instance of layered_settings_t).
+ *
+ * When settings are queried from an instance of layered_settings_t the thread
+ * specific overlay is searched first, if set, then the overlay layer, if set,
+ * and then the base.
+ *
+ * The same applies if settings are set or loaded (so the thread specific layer
+ * is modified first).
+ *
+ * To access individual layers use the appropriate getter method.
+ */
+struct layered_settings_t {
+
+       /**
+        * Implements the settings_t interface.
+        *
+        * FIXME: enumeration could get tricky, but we already have similar code for
+        * the fallback feature
+        * The add_fallback feature is also a bit tricky especially if an overlay
+        * gets added after a fallback was defined. Do we set the fallback on that
+        * overlay again?
+        * load_files[_section]() as well as the setters will only be called on the
+        * highest overlay by default (if we'd replace lib->settings with an instance
+        * of this we might have to use get_base() to reload the settings although
+        * thread-specific settings should probably be removed on e.g. ike-sa
+        * checkin)
+        */
+       settings_t settings;
+
+       /**
+        * Set the overlay settings layer.
+        *
+        * @param overlay       overlay settings FIXME: do we adopt this?
+        * @return                      FIXME: should we return a previous overlay? (would easily allow to remove a layer by setting it NULL)
+        */
+       settings_t *(*set_overlay)(layered_settings_t *this, settings_t *overlay);
+
+       /**
+        * Set the thread-specific overlay settings layer.
+        *
+        * @param overlay       thread-specific overlay settings FIXME: do we adopt this?
+        * @return                      FIXME: should we return a previous overlay? (would easily allow to remove a layer by setting it NULL)
+        */
+       settings_t *(*set_overlay_local)(layered_settings_t *this,
+                                                                        settings_t *overlay);
+
+       /**
+        * Get the base settings layer.
+        *
+        * @return                      base settings_t object
+        */
+       settings_t *(*get_base)(layered_settings_t *this);
+
+       /**
+        * Get the overlay settings layer.
+        *
+        * @return                      overlay settings_t object
+        */
+       settings_t *(*get_overlay)(layered_settings_t *this);
+
+       /**
+        * Get the thread-specific overlay settings layer.
+        *
+        * @return                      thread-specific overlay settings_t object
+        */
+       settings_t *(*get_overlay_local)(layered_settings_t *this);
+
+       /**
+        * Destroy a layered_settings_t instance.
+        */
+       void (*destroy)(layered_settings_t *this);
+};
+
+/**
+ * Create a layered settings object.
+ *
+ * @param base                 base settings FIXME: Do we adopt this?
+ * @return                             instance
+ */
+layered_settings_t *layered_settings_create(settings_t *base);
+
+#endif /** LAYERED_SETTINGS_H_ @}*/