storage_backend.hpp

00001 /*
00002  * Copyright (C) 2015 Pavel Kirienko <pavel.kirienko@gmail.com>
00003  */
00004 
00005 #ifndef UAVCAN_PROTOCOL_DYNAMIC_NODE_ID_SERVER_STORAGE_BACKEND_HPP_INCLUDED
00006 #define UAVCAN_PROTOCOL_DYNAMIC_NODE_ID_SERVER_STORAGE_BACKEND_HPP_INCLUDED
00007 
00008 #include <uavcan/build_config.hpp>
00009 #include <uavcan/marshal/types.hpp>
00010 
00011 namespace uavcan
00012 {
00013 namespace dynamic_node_id_server
00014 {
00015 /**
00016  * This interface is used by the server to read and write stable storage.
00017  * The storage is represented as a key-value container, where keys and values are ASCII strings up to 32
00018  * characters long, not including the termination byte. Fixed block size allows for absolutely straightforward
00019  * and efficient implementation of storage backends, e.g. based on text files.
00020  * Keys and values may contain only non-whitespace, non-formatting printable characters.
00021  */
00022 class UAVCAN_EXPORT IStorageBackend
00023 {
00024 public:
00025     /**
00026      * Maximum length of keys and values. One pair takes twice as much space.
00027      */
00028     enum { MaxStringLength = 32 };
00029 
00030     /**
00031      * It is guaranteed that the server will never require more than this number of key/value pairs.
00032      * Total storage space needed is (MaxKeyValuePairs * MaxStringLength * 2), not including storage overhead.
00033      */
00034     enum { MaxKeyValuePairs = 512 };
00035 
00036     /**
00037      * This type is used to exchange data chunks with the backend.
00038      * It doesn't use any dynamic memory; please refer to the Array<> class for details.
00039      */
00040     typedef MakeString<MaxStringLength>::Type String;
00041 
00042     /**
00043      * Read one value from the storage.
00044      * If such key does not exist, or if read failed, an empty string will be returned.
00045      * This method should not block for more than 50 ms.
00046      */
00047     virtual String get(const String& key) const = 0;
00048 
00049     /**
00050      * Create or update value for the given key. Empty value should be regarded as a request to delete the key.
00051      * This method should not block for more than 50 ms.
00052      * Failures will be ignored.
00053      */
00054     virtual void set(const String& key, const String& value) = 0;
00055 
00056     virtual ~IStorageBackend() { }
00057 };
00058 
00059 }
00060 }
00061 
00062 #endif // Include guard