httpdirfs/src/cache.h

#ifndef CACHE_H
#define CACHE_H

#include <stdint.h>
#include <unistd.h>

/**
 * \file cache.h
 * \brief cache related structures and functions
 * \details
 * Metadata:
 *   - We store the metadata and the actual data separately in two
 * different folders.
 *   - The metadata file should follow the following format:
 *      - file length (long)
 *      - CURLINFO_FILETIME
 *      - segment count (int)
 *      - individual segments (array of seg)
 * \note
 *   - We are using 'long' to store file size, because the offset in fseek() is
 * in long, because the way we use the cache system, you cannot seek past
 * long. So the biggest file size has to be able to be stored in long. This
 * makes this program architecturally dependent, i.e. i386 vs amd64
 */

/**
 * \brief Type definition for a cache segment
 */
typedef uint8_t Seg;

/**
 * \brief cache in-memory data structure
 */
typedef struct {
    char *p_url; /**< the filename from the http server */
    long time; /**<the modified time of the file */
    long content_length; /**<the size of the file */
    int blksz; /**<the block size of the data file */
    long segbc; /**<segment array byte count */
    Seg *seg; /**< the detail of each segment */
} Cache;

/**************************** External functions ****************************/
/**
 * \brief initialise the cache system directories
 * \details This function basically sets up the following variables:
 *  - META_DIR
 *  - DATA_DIR
 *
 * If these directories do not exist, they will be created.
 * \note Call this when the program starts
 */
void CacheSystem_init(const char *dir);

/**
 * \brief open a cache file set
 * \note Call this when FUSE opens a file
 */
Cache *Cache_open(const char *fn);

/**
 * \brief create a cache file set
 * \note Call this when creating a new LinkTable
 */
Cache *Cache_create(const char *fn, long len, long time);

/**
 * \brief Create directories under the cache directory structure, if they do
 * not already exist
 * \return
 *  -   -1 failed to create metadata directory.
 *  -   -2 failed to create data directory.
 *  -   -3 failed to create both metadata and data directory.
 * \note Call this when creating a new LinkTable
 */
int CacheDir_create(const char *fn);

/**
 * \brief Check if a segment exists.
 * \note Call this when deciding whether to download a file
 */
int Seg_exist(Cache *cf, long start);

/**
 * \brief Set the existence of a segment
 * \param[in] start the starting position of the segment.
 * \param[in] i 1 for exist, 0 for doesn't exist
 * \note Call this after downloading a segment.
 */
void Seg_set(Cache *cf, long start, int i);



/***************************** To be completed ******************************/

/**
 * \brief Close a cache data structure
 * \note Call this when FUSE releases a file
 */
void Cache_close(Cache *cf);

/**
 * \brief Read from a cache file set
 * \details This function performs the following two things:
 *  - check again the metafile to see which segments are available
 *  - return the available segments
 * \note Call this when it is not necessary to download a segment
 */
long Cache_read(const char *fn, long offset, long len, uint8_t *buf);

/**
 * \brief Write to a cache file set
 * \details This function performs the following two things:
 *  - Write to the data file
 *  - Update the metadata file
 * \note Call this after downloading a segment.
 */
long Cache_write(const char *fn, long offset, long len, const uint8_t *buf);

#endif