block_log.hpp

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#pragma once
#include <fc/filesystem.hpp>
#include <scorum/protocol/block.hpp>
 
namespace scorum {
namespace chain {
 
using namespace scorum::protocol;
 
namespace detail {
class block_log_impl;
}
 
/* The block log is an external append only log of the blocks. Blocks should only be written
 * to the log after they irreverisble as the log is append only. The log is a doubly linked
 * list of blocks. There is a secondary index file of only block positions that enables O(1)
 * random access lookup by block number.
 *
 * +---------+----------------+---------+----------------+-----+------------+-------------------+
 * | Block 1 | Pos of Block 1 | Block 2 | Pos of Block 2 | ... | Head Block | Pos of Head Block |
 * +---------+----------------+---------+----------------+-----+------------+-------------------+
 *
 * +----------------+----------------+-----+-------------------+
 * | Pos of Block 1 | Pos of Block 2 | ... | Pos of Head Block |
 * +----------------+----------------+-----+-------------------+
 *
 * The block log can be walked in order by deserializing a block, skipping 8 bytes, deserializing a
 * block, repeat... The head block of the file can be found by seeking to the position contained
 * in the last 8 bytes the file. The block log can be read backwards by jumping back 8 bytes, following
 * the position, reading the block, jumping back 8 bytes, etc.
 *
 * Blocks can be accessed at random via block number through the index file. Seek to 8 * (block_num - 1)
 * to find the position of the block in the main file.
 *
 * The main file is the only file that needs to persist. The index file can be reconstructed during a
 * linear scan of the main file.
 */
 
class block_log
{
public:
    block_log();
    ~block_log();
 
    void open(const fc::path& file);
    void close();
    bool is_open() const;
 
    static fc::path block_log_index_path(const fc::path& block_log_file);
 
    uint64_t append(const signed_block& b);
    void flush();
    std::pair<signed_block, uint64_t> read_block(uint64_t file_pos) const;
    optional<signed_block> read_block_by_num(uint32_t block_num) const;
 
    uint64_t get_block_pos(uint32_t block_num) const;
    signed_block read_head() const;
    const optional<signed_block>& head() const;
 
    static const uint64_t npos = std::numeric_limits<uint64_t>::max();
 
private:
    void construct_index();
 
    std::unique_ptr<detail::block_log_impl> my;
};
}
}