// fsearch.c: runs the "file" command on all byte offsets in an image file

// license: GPL. See gnu.org for details
// requires: an external "file" command and a Unixable OS (cygwin works)
// caution: fsearch yeilds lots of false positives.
// compile: cc fsearch.c -o fsearch
// usage: fsearch imagefile


#include <stdio.h>
#include <stdlib.h>

int main(int argc, char **argv)
{
  FILE *in, *out;
  int t;
  char *buffer;
  char syss[1024];
  char resultsfile[1024], fname[1024];

  int fsize, wsize;

  if (argc < 2) {
    fprintf(stderr, "%s must be called with a filename argument\n", argv[0]);
    exit(1);
  }
  // the name of the results file
  snprintf(resultsfile, 1024, "%s.results.txt", argv[1]);

  // zero out the results file if it exists
  out = fopen(resultsfile, "wb");
  if (out == NULL) {
    fprintf(stderr, "couldn't write to filesystem\n");
    exit(1);
  }
  fclose(out);

  strcpy(fname, argv[1]);

  in = fopen(fname, "rb");
  if (in == NULL) {
    fprintf(stderr, "couldn't read %s\n", fname);
    exit(1);
  }
  // fetch the filesize
  fseek(in, 0, SEEK_END);
  fsize = ftell(in);
  fclose(in);

  buffer = malloc(fsize);
  if (buffer == NULL) {
    fprintf(stderr, "couldn't allocate buffer memory\n");
    exit(1);
  }
  in = fopen(fname, "rb");
  if (in == NULL) {
    fprintf(stderr, "couldn't open %s for reading\n", fname);
    free(buffer);
    exit(1);
  }
  if (fread(buffer, 1, fsize, in) < fsize) {
    fprintf(stderr, "trouble reading %s\n", fname);
    free(buffer);
    exit(1);
  }
  fclose(in);
  for (t = 0; t < fsize - 1; t++) {
    out = fopen("filetype-guess", "wb");
    if (out == NULL) {
      fprintf(stderr, "couldn't open 'filetype-guess' for writing\n");
      free(buffer);
      exit(1);
    }
    if (fsize - t > 512)
      wsize = 512;
    else
      wsize = fsize - t;
    fwrite(buffer + t, 1, wsize, out);
    fclose(out);
    sprintf(syss, "echo 0x%x - $(file filetype-guess) >> %s", t, resultsfile);
    system(syss);
  }
  free(buffer);

#ifdef WIN32
  system("del filetype-guess 2> NUL");
#else
  system("rm filetype-guess 2> /dev/null");
#endif

  exit(0);
}