Rebuild file from original file and differences file in RAM

See more:

C

disk

compression

FileIO

Dear friends, I am trying to implement a program that reconstructs a binary file, starting from the old file and a file of differences. The work is based on the ingenious thesis Olin Percival, Naive differences of executable code, http://www.daemonology.net/bsdiff/ , 2003. I want to use the rebuilder (bspatch) on a microcontroller ARM M4. I'm trying to eliminate disk access with operations on simple vectors. The operation is not trivial because the Olin program is complicated! Of course in addition to the file pointer, the Olin program uses functions to access the file, such as fgetc FSEEK that must be replaced. To start I am working in C in visual studio and when the program will work on the PC i will move it on ARM M4.
To begin with, I add static vectors of char as long as the files in input,then I copy-paste the files in to the vectors. From this point on I no longer want to make disk accesses. However, the program keeps making unwanted disk access.

Has anyone ever replaced a file pointer with a vector of char to use only RAM?

Look the original program of Olin (found in the link) there is a Visual Studio project.

Thank You and Happy Happy Happy New Year
Stefano Fredella

Ok, I try to explain one specific problem:
 
I have these two functions and i do not want pass FILE* f. I want pass a chars vector 
How can I change that?
 
<pre lang="c++">
typedef void BZFILE;
 
BZFILE* BZ_API(BZ2_bzReadOpen) 
                   ( int*  bzerror, 
                     FILE* f, 
                     int   verbosity,
                     int   small,
                     void* unused,
                     int   nUnused )
{
   bzFile* bzf = NULL;
   int     ret;
 
   BZ_SETERR(BZ_OK);
 
   if (f == NULL || 
       (small != 0 && small != 1) ||
       (verbosity < 0 || verbosity > 4) ||
       (unused == NULL && nUnused != 0) ||
       (unused != NULL && (nUnused < 0 || nUnused > BZ_MAX_UNUSED)))
      { BZ_SETERR(BZ_PARAM_ERROR); return NULL; };
 
   if (ferror(f))
      { BZ_SETERR(BZ_IO_ERROR); return NULL; };
 
   bzf = malloc ( sizeof(bzFile) );
   if (bzf == NULL) 
      { BZ_SETERR(BZ_MEM_ERROR); return NULL; };
 
   BZ_SETERR(BZ_OK);
 
   bzf->initialisedOk = False;
   bzf->handle        = f;
   bzf->bufN          = 0;
   bzf->writing       = False;
   bzf->strm.bzalloc  = NULL;
   bzf->strm.bzfree   = NULL;
   bzf->strm.opaque   = NULL;
 
   while (nUnused > 0) {
      bzf->buf[bzf->bufN] = *((UChar*)(unused)); bzf->bufN++;
      unused = ((void*)( 1 + ((UChar*)(unused))  ));
      nUnused--;
   }
 
   ret = BZ2_bzDecompressInit ( &(bzf->strm), verbosity, small );
   if (ret != BZ_OK)
      { BZ_SETERR(ret); free(bzf); return NULL; };
 
   bzf->strm.avail_in = bzf->bufN;
   bzf->strm.next_in  = bzf->buf;
 
   bzf->initialisedOk = True;
   return bzf;   
}
 
int BZ_API(BZ2_bzRead) 
           ( int*    bzerror, 
             BZFILE* b, 
             void*   buf, 
             int     len )
{
   Int32   n, ret;
   bzFile* bzf = (bzFile*)b;
 
   BZ_SETERR(BZ_OK);
 
   if (bzf == NULL || buf == NULL || len < 0)
      { BZ_SETERR(BZ_PARAM_ERROR); return 0; };
 
   if (bzf->writing)
      { BZ_SETERR(BZ_SEQUENCE_ERROR); return 0; };
 
   if (len == 0)
      { BZ_SETERR(BZ_OK); return 0; };
 
   bzf->strm.avail_out = len;
   bzf->strm.next_out = buf;
 
   while (True) {
 
      if (ferror(bzf->handle)) 
         { BZ_SETERR(BZ_IO_ERROR); return 0; };
 
      if (bzf->strm.avail_in == 0 && !myfeof(bzf->handle)) {
         n = fread ( bzf->buf, sizeof(UChar), 
                     BZ_MAX_UNUSED, bzf->handle );
         if (ferror(bzf->handle))
            { BZ_SETERR(BZ_IO_ERROR); return 0; };
         bzf->bufN = n;
         bzf->strm.avail_in = bzf->bufN;
         bzf->strm.next_in = bzf->buf;
      }
 
      ret = BZ2_bzDecompress ( &(bzf->strm) );
 
      if (ret != BZ_OK && ret != BZ_STREAM_END)
         { BZ_SETERR(ret); return 0; };
 
      if (ret == BZ_OK && myfeof(bzf->handle) && 
          bzf->strm.avail_in == 0 && bzf->strm.avail_out > 0)
         { BZ_SETERR(BZ_UNEXPECTED_EOF); return 0; };
 
      if (ret == BZ_STREAM_END)
         { BZ_SETERR(BZ_STREAM_END);
           return len - bzf->strm.avail_out; };
      if (bzf->strm.avail_out == 0)
         { BZ_SETERR(BZ_OK); return len; };
 
   }
 
   return 0; /*not reached*/
}
static Bool myfeof ( FILE* f )
{
   Int32 c = fgetc ( f );
   if (c == EOF) return True;
   ungetc ( c, f );
   return False;
}
</pre>