git/delta.h
Matt Cooper d6a09e795d odb: guard against data loss checking out a huge file
This introduces an additional guard for platforms where `unsigned long`
and `size_t` are not of the same size. If the size of an object in the
database would overflow `unsigned long`, instead we now exit with an
error.

A complete fix will have to update _many_ other functions throughout the
codebase to use `size_t` instead of `unsigned long`. It will have to be
implemented at some stage.

This commit puts in a stop-gap for the time being.

Helped-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Matt Cooper <vtbassmatt@gmail.com>
Signed-off-by: Johannes Schindelin <johannes.schindelin@gmx.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
2021-11-03 11:22:27 -07:00

105 lines
3.4 KiB
C

#ifndef DELTA_H
#define DELTA_H
/* opaque object for delta index */
struct delta_index;
/*
* create_delta_index: compute index data from given buffer
*
* This returns a pointer to a struct delta_index that should be passed to
* subsequent create_delta() calls, or to free_delta_index(). A NULL pointer
* is returned on failure. The given buffer must not be freed or altered
* before free_delta_index() is called. The returned pointer must be freed
* using free_delta_index().
*/
struct delta_index *
create_delta_index(const void *buf, unsigned long bufsize);
/*
* free_delta_index: free the index created by create_delta_index()
*
* Given pointer must be what create_delta_index() returned, or NULL.
*/
void free_delta_index(struct delta_index *index);
/*
* sizeof_delta_index: returns memory usage of delta index
*
* Given pointer must be what create_delta_index() returned, or NULL.
*/
unsigned long sizeof_delta_index(struct delta_index *index);
/*
* create_delta: create a delta from given index for the given buffer
*
* This function may be called multiple times with different buffers using
* the same delta_index pointer. If max_delta_size is non-zero and the
* resulting delta is to be larger than max_delta_size then NULL is returned.
* On success, a non-NULL pointer to the buffer with the delta data is
* returned and *delta_size is updated with its size. The returned buffer
* must be freed by the caller.
*/
void *
create_delta(const struct delta_index *index,
const void *buf, unsigned long bufsize,
unsigned long *delta_size, unsigned long max_delta_size);
/*
* diff_delta: create a delta from source buffer to target buffer
*
* If max_delta_size is non-zero and the resulting delta is to be larger
* than max_delta_size then NULL is returned. On success, a non-NULL
* pointer to the buffer with the delta data is returned and *delta_size is
* updated with its size. The returned buffer must be freed by the caller.
*/
static inline void *
diff_delta(const void *src_buf, unsigned long src_bufsize,
const void *trg_buf, unsigned long trg_bufsize,
unsigned long *delta_size, unsigned long max_delta_size)
{
struct delta_index *index = create_delta_index(src_buf, src_bufsize);
if (index) {
void *delta = create_delta(index, trg_buf, trg_bufsize,
delta_size, max_delta_size);
free_delta_index(index);
return delta;
}
return NULL;
}
/*
* patch_delta: recreate target buffer given source buffer and delta data
*
* On success, a non-NULL pointer to the target buffer is returned and
* *trg_bufsize is updated with its size. On failure a NULL pointer is
* returned. The returned buffer must be freed by the caller.
*/
void *patch_delta(const void *src_buf, unsigned long src_size,
const void *delta_buf, unsigned long delta_size,
unsigned long *dst_size);
/* the smallest possible delta size is 4 bytes */
#define DELTA_SIZE_MIN 4
/*
* This must be called twice on the delta data buffer, first to get the
* expected source buffer size, and again to get the target buffer size.
*/
static inline unsigned long get_delta_hdr_size(const unsigned char **datap,
const unsigned char *top)
{
const unsigned char *data = *datap;
size_t cmd, size = 0;
int i = 0;
do {
cmd = *data++;
size |= st_left_shift(cmd & 0x7f, i);
i += 7;
} while (cmd & 0x80 && data < top);
*datap = data;
return cast_size_t_to_ulong(size);
}
#endif