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 extern void free_delta_index(struct delta_index *index);
  23
  24 /*
  25  * create_delta: create a delta from given index for the given buffer
  26  *
  27  * This function may be called multiple times with different buffers using
  28  * the same delta_index pointer.  If max_delta_size is non-zero and the
  29  * resulting delta is to be larger than max_delta_size then NULL is returned.
  30  * On success, a non-NULL pointer to the buffer with the delta data is
  31  * returned and *delta_size is updated with its size.  The returned buffer
  32  * must be freed by the caller.
  33  */
  34 extern void *
  35 create_delta(const struct delta_index *index,
  36              const void *buf, unsigned long bufsize,
  37              unsigned long *delta_size, unsigned long max_delta_size);
  38
  39 /*
  40  * diff_delta: create a delta from source buffer to target buffer
  41  *
  42  * If max_delta_size is non-zero and the resulting delta is to be larger
  43  * than max_delta_size then NULL is returned.  On success, a non-NULL
  44  * pointer to the buffer with the delta data is returned and *delta_size is
  45  * updated with its size.  The returned buffer must be freed by the caller.
  46  */
  47 static inline void *
  48 diff_delta(const void *src_buf, unsigned long src_bufsize,
  49            const void *trg_buf, unsigned long trg_bufsize,
  50            unsigned long *delta_size, unsigned long max_delta_size)
  51 {
  52         struct delta_index *index = create_delta_index(src_buf, src_bufsize);
  53         if (index) {
  54                 void *delta = create_delta(index, trg_buf, trg_bufsize,
  55                                            delta_size, max_delta_size);
  56                 free_delta_index(index);
  57                 return delta;
  58         }
  59         return NULL;
  60 }
  61
  62 /*
  63  * patch_delta: recreate target buffer given source buffer and delta data
  64  *
  65  * On success, a non-NULL pointer to the target buffer is returned and
  66  * *trg_bufsize is updated with its size.  On failure a NULL pointer is
  67  * returned.  The returned buffer must be freed by the caller.
  68  */
  69 extern void *patch_delta(const void *src_buf, unsigned long src_size,
  70                          const void *delta_buf, unsigned long delta_size,
  71                          unsigned long *dst_size);
  72
  73 /* the smallest possible delta size is 4 bytes */
  74 #define DELTA_SIZE_MIN  4
  75
  76 /*
  77  * This must be called twice on the delta data buffer, first to get the
  78  * expected source buffer size, and again to get the target buffer size.
  79  */
  80 static inline unsigned long get_delta_hdr_size(const unsigned char **datap,
  81                                                const unsigned char *top)
  82 {
  83         const unsigned char *data = *datap;
  84         unsigned char cmd;
  85         unsigned long size = 0;
  86         int i = 0;
  87         do {
  88                 cmd = *data++;
  89                 size |= (cmd & ~0x80) << i;
  90                 i += 7;
  91         } while (cmd & 0x80 && data < top);
  92         *datap = data;
  93         return size;
  94 }
  95
  96 #endif