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

   1 #define _FILE_OFFSET_BITS 64
   2
   3 #include "temp_file.h"
   4
   5 #include <err.h>
   6 #include <fcntl.h>
   7 #include <stdio.h>
   8 #include <stdlib.h>
   9 #include <sys/mman.h>
  10 #include <sys/stat.h>
  11 #include <sys/types.h>
  12 #include <sysexits.h>
  13 #include <unistd.h>
  14
  15 void reverse_file(const char* input_filename, FILE* output_stream) {
  16   int fd = open(input_filename, O_RDONLY);
  17   if (fd == -1) err(EX_NOINPUT, "Could not open specified file");
  18
  19   struct stat stats;
  20   if (fstat(fd, &stats) == -1) err(EX_NOINPUT, "Could not stat input");
  21
  22   long page_size = sysconf(_SC_PAGE_SIZE);
  23   off_t pages = (stats.st_size - 1) / page_size + 1;
  24   long map_size = pages * page_size;
  25   char *m = mmap(NULL, map_size, PROT_READ, MAP_SHARED, fd, 0);
  26   if (m == MAP_FAILED) err(EX_NOINPUT, "Could not mmap input");
  27
  28   for (off_t p = stats.st_size - 1; p >= 0; p--) {
  29     if (fputc(m[p], output_stream) == EOF) errx(EX_IOERR, "Could not write");
  30   }
  31
  32   if (munmap(m, map_size) == -1) err(EX_IOERR, "Could not unmap input");
  33   if (close(fd) == -1) err(EX_IOERR, "Could not close input");
  34 }
  35
  36 /* Copy data from input to output until EOF is reached. */
  37 static void copy(FILE* input, FILE* output) {
  38   for (;;) {
  39     int c = fgetc(input);
  40     if (c == EOF) {
  41       if (ferror(input)) errx(EX_IOERR, "Could not read");
  42       if (!feof(input)) errx(EX_IOERR, "Unexpected end of file");
  43       break;
  44     }
  45     if (fputc(c, output) == EOF) errx(EX_IOERR, "Could not write");
  46   }
  47 }
  48
  49 void reverse_stream(FILE* input_stream, FILE* output_stream) {
  50   char* temp_filename;
  51   FILE* temp_file;
  52   make_temporary_file(&temp_filename, &temp_file);
  53
  54   copy(input_stream, temp_file);
  55   if (fclose(temp_file) != 0) err(EX_IOERR, "Could not close temporary file");
  56
  57   reverse_file(temp_filename, output_stream);
  58
  59   if (unlink(temp_filename) == -1) err(EX_IOERR, "Could not remove temporary file");
  60   free(temp_filename);
  61 }