git.scottworley.com Git - overonion/blob - reverse_lib.c

   1 #define _GNU_SOURCE
   2 #define _FILE_OFFSET_BITS 64
   3
   4 #include <err.h>
   5 #include <fcntl.h>
   6 #include <stdio.h>
   7 #include <stdlib.h>
   8 #include <sys/mman.h>
   9 #include <sys/stat.h>
  10 #include <sys/types.h>
  11 #include <sysexits.h>
  12 #include <unistd.h>
  13
  14 void reverse_file(const char* input_filename, FILE* output_stream) {
  15   int fd = open(input_filename, O_RDONLY);
  16   if (fd == -1) err(EX_NOINPUT, "Could not open specified file");
  17
  18   struct stat stats;
  19   if (fstat(fd, &stats) == -1) err(EX_NOINPUT, "Could not stat input");
  20
  21   long page_size = sysconf(_SC_PAGE_SIZE);
  22   off_t pages = (stats.st_size - 1) / page_size + 1;
  23   long map_size = pages * page_size;
  24   char *m = mmap(NULL, map_size, PROT_READ, MAP_SHARED, fd, 0);
  25   if (m == MAP_FAILED) err(EX_NOINPUT, "Could not mmap input");
  26
  27   for (off_t p = stats.st_size - 1; p >= 0; p--) {
  28     if (fputc(m[p], output_stream) == EOF) errx(EX_IOERR, "Could not write");
  29   }
  30
  31   if (munmap(m, map_size) == -1) err(EX_IOERR, "Could not unmap input");
  32   if (close(fd) == -1) err(EX_IOERR, "Could not close input");
  33 }
  34
  35 /* Create a temporary file in $TMPDIR, or /tmp if TMPDIR is not set.
  36  * Caller must free temp_filename and fclose temp_file.  Succeeds or terminates
  37  * the process. */
  38 static void make_temporary_file(char** temp_filename, FILE** temp_file) {
  39   char* TMPDIR = getenv("TMPDIR");
  40   if (TMPDIR == NULL) {
  41     TMPDIR = "/tmp";
  42   }
  43   if (asprintf(temp_filename, "%s/reverse.XXXXXX", TMPDIR) == -1) {
  44     errx(EX_OSERR, "Could not assemble temporary filename");
  45   }
  46   int fd = mkstemp(*temp_filename);
  47   if (fd == -1) err(EX_IOERR, "Could not make a temporary file");
  48   *temp_file = fdopen(fd, "w");
  49   if (*temp_file == NULL) err(EX_IOERR, "Could not open temporary file");
  50 }
  51
  52 /* Copy data from input to output until EOF is reached. */
  53 static void copy(FILE* input, FILE* output) {
  54   for (;;) {
  55     int c = fgetc(input);
  56     if (c == EOF) {
  57       if (ferror(input)) errx(EX_IOERR, "Could not read");
  58       if (!feof(input)) errx(EX_IOERR, "Unexpected end of file");
  59       break;
  60     }
  61     if (fputc(c, output) == EOF) errx(EX_IOERR, "Could not write");
  62   }
  63 }
  64
  65 void reverse_stream(FILE* input_stream, FILE* output_stream) {
  66   char* temp_filename;
  67   FILE* temp_file;
  68   make_temporary_file(&temp_filename, &temp_file);
  69
  70   copy(input_stream, temp_file);
  71   if (fclose(temp_file) != 0) err(EX_IOERR, "Could not close temporary file");
  72
  73   reverse_file(temp_filename, output_stream);
  74
  75   if (unlink(temp_filename) == -1) err(EX_IOERR, "Could not remove temporary file");
  76   free(temp_filename);
  77 }