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 static off_t ceil_div(off_t dividend, off_t divisor) {
  16   return (dividend - 1) / divisor + 1;
  17 }
  18
  19 void reverse_file(const char* input_filename, FILE* output_stream) {
  20   const off_t mmap_chunk_size = 512 << 20;
  21
  22   int fd = open(input_filename, O_RDONLY);
  23   if (fd == -1) err(EX_NOINPUT, "Could not open specified file");
  24
  25   struct stat stats;
  26   if (fstat(fd, &stats) == -1) err(EX_NOINPUT, "Could not stat input");
  27
  28   long page_size = sysconf(_SC_PAGE_SIZE);
  29   off_t num_chunks = ceil_div(stats.st_size, mmap_chunk_size);
  30   for (off_t chunk = num_chunks - 1; chunk >= 0; chunk--) {
  31     off_t start_offset = chunk * mmap_chunk_size;
  32     off_t end_offset = (chunk + 1) * mmap_chunk_size;
  33     if (end_offset > stats.st_size) {
  34       end_offset = stats.st_size;
  35     }
  36     off_t pages = ceil_div(end_offset - start_offset, page_size);
  37     long map_size = pages * page_size;
  38     char *m = mmap(NULL, map_size, PROT_READ, MAP_SHARED, fd, start_offset);
  39     if (m == MAP_FAILED) err(EX_NOINPUT, "Could not mmap chunk %lld of %lld", chunk, num_chunks);
  40
  41     for (off_t p = (end_offset - start_offset) - 1; p >= 0; p--) {
  42       if (fputc(m[p], output_stream) == EOF) errx(EX_IOERR, "Could not write");
  43     }
  44
  45     if (munmap(m, map_size) == -1) err(EX_IOERR, "Could not unmap chunk %lld of %lld", chunk, num_chunks);
  46   }
  47
  48   if (close(fd) == -1) err(EX_IOERR, "Could not close input");
  49 }
  50
  51 /* Copy data from input to output until EOF is reached. */
  52 static void copy(FILE* input, FILE* output) {
  53   for (;;) {
  54     int c = fgetc(input);
  55     if (c == EOF) {
  56       if (ferror(input)) errx(EX_IOERR, "Could not read");
  57       if (!feof(input)) errx(EX_IOERR, "Unexpected end of file");
  58       break;
  59     }
  60     if (fputc(c, output) == EOF) errx(EX_IOERR, "Could not write");
  61   }
  62 }
  63
  64 void reverse_stream(FILE* input_stream, FILE* output_stream) {
  65   char* temp_filename;
  66   FILE* temp_file;
  67   make_temporary_file(&temp_filename, &temp_file);
  68
  69   copy(input_stream, temp_file);
  70   if (fclose(temp_file) != 0) err(EX_IOERR, "Could not close temporary file");
  71
  72   reverse_file(temp_filename, output_stream);
  73
  74   if (unlink(temp_filename) == -1) err(EX_IOERR, "Could not remove temporary file");
  75   free(temp_filename);
  76 }