git/chunk-format.h
Derrick Stolee 5f0879f54b chunk-format: create read chunk API
Add the capability to read the table of contents, then pair the chunks
with necessary logic using read_chunk_fn pointers. Callers will be added
in future changes, but the typical outline will be:

 1. initialize a 'struct chunkfile' with init_chunkfile(NULL).
 2. call read_table_of_contents().
 3. for each chunk to parse,
    a. call pair_chunk() to assign a pointer with the chunk position, or
    b. call read_chunk() to run a callback on the chunk start and size.
 4. call free_chunkfile() to clear the 'struct chunkfile' data.

We are re-using the anonymous 'struct chunkfile' data, as it is internal
to the chunk-format API. This gives it essentially two modes: write and
read. If the same struct instance was used for both reads and writes,
then there would be failures.

Helped-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Derrick Stolee <dstolee@microsoft.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2021-02-18 13:38:16 -08:00

69 lines
1.9 KiB
C

#ifndef CHUNK_FORMAT_H
#define CHUNK_FORMAT_H
#include "git-compat-util.h"
struct hashfile;
struct chunkfile;
#define CHUNK_TOC_ENTRY_SIZE (sizeof(uint32_t) + sizeof(uint64_t))
/*
* Initialize a 'struct chunkfile' for writing _or_ reading a file
* with the chunk format.
*
* If writing a file, supply a non-NULL 'struct hashfile *' that will
* be used to write.
*
* If reading a file, use a NULL 'struct hashfile *' and then call
* read_table_of_contents(). Supply the memory-mapped data to the
* pair_chunk() or read_chunk() methods, as appropriate.
*
* DO NOT MIX THESE MODES. Use different 'struct chunkfile' instances
* for reading and writing.
*/
struct chunkfile *init_chunkfile(struct hashfile *f);
void free_chunkfile(struct chunkfile *cf);
int get_num_chunks(struct chunkfile *cf);
typedef int (*chunk_write_fn)(struct hashfile *f, void *data);
void add_chunk(struct chunkfile *cf,
uint32_t id,
size_t size,
chunk_write_fn fn);
int write_chunkfile(struct chunkfile *cf, void *data);
int read_table_of_contents(struct chunkfile *cf,
const unsigned char *mfile,
size_t mfile_size,
uint64_t toc_offset,
int toc_length);
#define CHUNK_NOT_FOUND (-2)
/*
* Find 'chunk_id' in the given chunkfile and assign the
* given pointer to the position in the mmap'd file where
* that chunk begins.
*
* Returns CHUNK_NOT_FOUND if the chunk does not exist.
*/
int pair_chunk(struct chunkfile *cf,
uint32_t chunk_id,
const unsigned char **p);
typedef int (*chunk_read_fn)(const unsigned char *chunk_start,
size_t chunk_size, void *data);
/*
* Find 'chunk_id' in the given chunkfile and call the
* given chunk_read_fn method with the information for
* that chunk.
*
* Returns CHUNK_NOT_FOUND if the chunk does not exist.
*/
int read_chunk(struct chunkfile *cf,
uint32_t chunk_id,
chunk_read_fn fn,
void *data);
#endif