delta.h

   1 #ifndef DELTA_H
   2 #define DELTA_H
   3
   4 /* opaque object for delta index */
   5 struct delta_index;
   6
   7 /*
   8  * create_delta_index: compute index data from given buffer
   9  *
  10  * This returns a pointer to a struct delta_index that should be passed to
  11  * subsequent create_delta() calls, or to free_delta_index().  A NULL pointer
  12  * is returned on failure.  The given buffer must not be freed nor altered
  13  * before free_delta_index() is called.  The returned pointer must be freed
  14  * using free_delta_index().
  15  */
  16 extern struct delta_index *
  17 create_delta_index(const void *buf, unsigned long bufsize);
  18
  19 /*
  20  * free_delta_index: free the index created by create_delta_index()
  21  *
  22  * Given pointer must be what create_delta_index() returned, or NULL.
  23  */
  24 extern void free_delta_index(struct delta_index *index);
  25
  26 /*
  27  * create_delta: create a delta from given index for the given buffer
  28  *
  29  * This function may be called multiple times with different buffers using
  30  * the same delta_index pointer.  If max_delta_size is non-zero and the
  31  * resulting delta is to be larger than max_delta_size then NULL is returned.
  32  * On success, a non-NULL pointer to the buffer with the delta data is
  33  * returned and *delta_size is updated with its size.  The returned buffer
  34  * must be freed by the caller.
  35  */
  36 extern void *
  37 create_delta(const struct delta_index *index,
  38              const void *buf, unsigned long bufsize,
  39              unsigned long *delta_size, unsigned long max_delta_size);
  40
  41 /*
  42  * diff_delta: create a delta from source buffer to target buffer
  43  *
  44  * If max_delta_size is non-zero and the resulting delta is to be larger
  45  * than max_delta_size then NULL is returned.  On success, a non-NULL
  46  * pointer to the buffer with the delta data is returned and *delta_size is
  47  * updated with its size.  The returned buffer must be freed by the caller.
  48  */
  49 static inline void *
  50 diff_delta(const void *src_buf, unsigned long src_bufsize,
  51            const void *trg_buf, unsigned long trg_bufsize,
  52            unsigned long *delta_size, unsigned long max_delta_size)
  53 {
  54         struct delta_index *index = create_delta_index(src_buf, src_bufsize);
  55         if (index) {
  56                 void *delta = create_delta(index, trg_buf, trg_bufsize,
  57                                            delta_size, max_delta_size);
  58                 free_delta_index(index);
  59                 return delta;
  60         }
  61         return NULL;
  62 }
  63
  64 /*
  65  * patch_delta: recreate target buffer given source buffer and delta data
  66  *
  67  * On success, a non-NULL pointer to the target buffer is returned and
  68  * *trg_bufsize is updated with its size.  On failure a NULL pointer is
  69  * returned.  The returned buffer must be freed by the caller.
  70  */
  71 extern void *patch_delta(const void *src_buf, unsigned long src_size,
  72                          const void *delta_buf, unsigned long delta_size,
  73                          unsigned long *dst_size);
  74
  75 /* the smallest possible delta size is 4 bytes */
  76 #define DELTA_SIZE_MIN  4
  77
  78 /*
  79  * This must be called twice on the delta data buffer, first to get the
  80  * expected source buffer size, and again to get the target buffer size.
  81  */
  82 static inline unsigned long get_delta_hdr_size(const unsigned char **datap,
  83                                                const unsigned char *top)
  84 {
  85         const unsigned char *data = *datap;
  86         unsigned char cmd;
  87         unsigned long size = 0;
  88         int i = 0;
  89         do {
  90                 cmd = *data++;
  91                 size |= (cmd & ~0x80) << i;
  92                 i += 7;
  93         } while (cmd & 0x80 && data < top);
  94         *datap = data;
  95         return size;
  96 }
  97
  98 #endif