mdw@git.distorted.org.uk Git - disorder/blob - lib/hreader.c

   1 /*
   2  * This file is part of DisOrder
   3  * Copyright (C) 2010 Richard Kettlewell
   4  *
   5  * This program is free software: you can redistribute it and/or modify
   6  * it under the terms of the GNU General Public License as published by
   7  * the Free Software Foundation, either version 3 of the License, or
   8  * (at your option) any later version.
   9  *
  10  * This program is distributed in the hope that it will be useful,
  11  * but WITHOUT ANY WARRANTY; without even the implied warranty of
  12  * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
  13  * GNU General Public License for more details.
  14  *
  15  * You should have received a copy of the GNU General Public License
  16  * along with this program.  If not, see <http://www.gnu.org/licenses/>.
  17  */
  18 /** @file lib/hreader.c
  19  * @brief Hands-off reader - read files without keeping them open
  20  */
  21 #include "hreader.h"
  22 #include "mem.h"
  23 #include <string.h>
  24 #include <fcntl.h>
  25
  26 static int hreader_fill(struct hreader *h, off_t offset);
  27
  28 void hreader_init(const char *path, struct hreader *h) {
  29   memset(h, 0, sizeof *h);
  30   h->path = xstrdup(path);
  31   h->bufsize = 65536;
  32   h->buffer = xmalloc_noptr(h->bufsize);
  33 }
  34
  35 int hreader_read(struct hreader *h, void *buffer, size_t n) {
  36   int r = hreader_pread(h, buffer, n, h->read_offset);
  37   if(r > 0)
  38     h->read_offset += r;
  39   return r;
  40 }
  41
  42 int hreader_pread(struct hreader *h, void *buffer, size_t n, off_t offset) {
  43   size_t bytes_read = 0;
  44
  45   while(bytes_read < n) {
  46     // If the desired byte range is outside the file, fetch new contents
  47     if(offset < h->buf_offset || offset >= h->buf_offset + (off_t)h->bytes) {
  48       int r = hreader_fill(h, offset);
  49       if(r < 0)
  50         return -1;                      /* disaster! */
  51       else if(r == 0)
  52         break;                          /* end of file */
  53     }
  54     // Figure out how much we can read this time round
  55     size_t left = h->bytes - (offset - h->buf_offset);
  56     // Truncate the read if we don't want that much
  57     if(left > (n - bytes_read))
  58       left = n - bytes_read;
  59     memcpy((char *)buffer + bytes_read,
  60            h->buffer + (offset - h->buf_offset),
  61            left);
  62     offset += left;
  63     bytes_read += left;
  64   }
  65   return bytes_read;
  66 }
  67
  68 static int hreader_fill(struct hreader *h, off_t offset) {
  69   int fd = open(h->path, O_RDONLY);
  70   if(fd < 0)
  71     return -1;
  72   int n = pread(fd, h->buffer, h->bufsize, offset);
  73   close(fd);
  74   if(n < 0)
  75     return -1;
  76   h->buf_offset = offset;
  77   h->bytes = n;
  78   return n;
  79 }
  80
  81 /*
  82 Local Variables:
  83 c-basic-offset:2
  84 comment-column:40
  85 fill-column:79
  86 indent-tabs-mode:nil
  87 End:
  88 */