jens@0: /*
jens@0:  *  Chunk.h
jens@0:  *  Ottoman
jens@0:  *
jens@0:  *  Created by Jens Alfke on 8/27/09.
jens@0:  *  Copyright 2009 Jens Alfke. All rights reserved.
jens@0:  *  BSD-Licensed: See the file "LICENSE.txt" for details.
jens@0:  */
jens@0: 
jens@0: #ifndef _MOOSEYARD_CHUNK_
jens@0: #define _MOOSEYARD_CHUNK_
jens@0: #include "File.h"
jens@0: 
jens@0: namespace Mooseyard {
jens@0:     
jens@0:     class KeyValueChunk;
jens@0:     
jens@0: #pragma pack(2)
jens@0:     
jens@0:     /** An item stored in a file. It's prefixed with its length, so that the entire file
jens@0:         can be scanned for chunks easily. */
jens@0:     class Chunk {
jens@0:     public:
jens@0:         uint32_t size() const                       {return _size;}
jens@0:         uint16_t type() const;
jens@0:         
jens@0:         /** If this is a KeyValueChunk, returns itself cast to that type, else NULL. */
jens@0:         const KeyValueChunk* asKeyValue() const;
jens@0:         
jens@0:         /** Write a Chunk to the file, in pieces a la writev. */
jens@0:         static size_t writeMultiple (File *file, uint16_t type,
jens@0:                                      Blob blobs[], int count)  throw(File::Error);
jens@0:         
jens@0:         static size_t writePadding (File *file);
jens@0: 
jens@0:         static const uint16_t kChunkTypePadding = 0;
jens@0: 
jens@0:         const void* end() const                     {return offsetBy(this,_size);}
jens@0: 
jens@0:     protected:
jens@0:         Chunk (uint32_t size, uint16_t type)        :_size(size), _keyLength(0xFFFF), _type(type) { }
jens@0: 
jens@0:     private:
jens@0:         // This is mapped to data in the file! Don't mess with it!
jens@0:         LittleEndian<uint32_t> _size;
jens@0:         LittleEndian<uint16_t> _keyLength;          // Used by KeyValueChunk; else 0xFFFF
jens@0:         LittleEndian<uint16_t> _type;               // Not used by KeyValueChunk
jens@0:         friend class KeyValueChunk;
jens@0:     };
jens@0:     
jens@0:     
jens@0:     /** A key/value pair as stored in the memory-mapped file. */
jens@0:     class KeyValueChunk :public Chunk {
jens@0:     public:
jens@0:         Blob key() const;
jens@0:         Blob value() const;
jens@0:         
jens@0:         bool hasKey (Blob key) const;
jens@0:         
jens@0:         void validate() const  throw(File::Error);
jens@0:         
jens@0:         /** Write a KeyValueChunk to a file. */
jens@0:         static size_t write (File* file, FilePosition pos, Blob key, Blob value)  throw(File::Error);
jens@0: 
jens@0:         static const uint16_t kChunkType = 1;
jens@0: 
jens@0:     private:
jens@0:         const char* valuePtr() const;
jens@0:     };    
jens@0:    
jens@0: #pragma options align=reset
jens@0:     
jens@0:     
jens@0:     /** An iterator over all the Chunks in a file. */
jens@0:     class ChunkIterator {
jens@0:     public:
jens@0:         ChunkIterator (File*, FilePosition start);
jens@0:         
jens@0:         const Chunk* chunk() const              {return _chunk;}
jens@0:         FilePosition position() const           {return _pos;}
jens@0:         bool atEOF() const;
jens@0:         bool next();
jens@0:         
jens@0:         operator const Chunk*() const           {return _chunk;}
jens@0:         virtual bool hasValue() const           {return _chunk != NULL;}
jens@0:         operator bool() const                   {return hasValue();}
jens@0:         ChunkIterator& operator++()             {next(); return *this;}
jens@0:     private:
jens@0:         void _loadChunk();
jens@0:         File *_file;
jens@0:         FilePosition _pos, _length;
jens@0:         const Chunk* _chunk;
jens@0:     };
jens@0:     
jens@0: }
jens@0: 
jens@0: #endif _MOOSEYARD_CHUNK_