xapian-applications/omega/loadfile.cc

   1 /* loadfile.cc: load a file into a std::string.
   2  *
   3  * Copyright (C) 2006,2010,2012,2015 Olly Betts
   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 2 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, write to the Free Software
  17  * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA  02110-1301 USA
  18  */
  19
  20 #include <config.h>
  21
  22 #ifdef HAVE_POSIX_FADVISE
  23 # ifdef __linux__
  24 #  define _POSIX_C_SOURCE 200112L // for posix_fadvise from fcntl.h
  25 #  define _DEFAULT_SOURCE 1 // Needed to get lstat() for glibc >= 2.20
  26 #  define _BSD_SOURCE 1 // Needed to get lstat() for glibc < 2.20
  27 # endif
  28 #endif
  29
  30 #include "loadfile.h"
  31
  32 #include <algorithm>
  33 #include <cerrno>
  34 #include <string>
  35
  36 #include "safefcntl.h"
  37 #include <sys/types.h>
  38 #include "safesysstat.h"
  39 #include "safeunistd.h"
  40
  41 using namespace std;
  42
  43 int
  44 load_file_fd(const string &file_name, size_t max_to_read, int flags,
  45              string &output, bool &truncated)
  46 {
  47     (void)flags; // Avoid possible "unused" warning.
  48     mode_t mode = O_RDONLY;
  49 #if defined O_NOATIME && O_NOATIME != 0
  50     if (flags & NOATIME) mode |= O_NOATIME;
  51 #endif
  52
  53     int fd = open(file_name.c_str(), mode);
  54 #if defined O_NOATIME && O_NOATIME != 0
  55     if (fd < 0 && (mode & O_NOATIME)) {
  56         mode &= ~O_NOATIME;
  57         fd = open(file_name.c_str(), mode);
  58     }
  59 #endif
  60     if (fd < 0) return -1;
  61
  62 #ifdef HAVE_POSIX_FADVISE
  63     if (flags & NOCACHE)
  64         posix_fadvise(fd, 0, 0, POSIX_FADV_NOREUSE); // or POSIX_FADV_SEQUENTIAL
  65 #endif
  66
  67     struct stat st;
  68     if (fstat(fd, &st) < 0) {
  69         int errno_save = errno;
  70         close(fd);
  71         errno = errno_save;
  72         return -1;
  73     }
  74
  75     if (!S_ISREG(st.st_mode)) {
  76         close(fd);
  77         errno = EINVAL;
  78         return -1;
  79     }
  80
  81     char blk[4096];
  82     size_t n = st.st_size;
  83     truncated = (max_to_read && max_to_read < n);
  84     if (truncated) {
  85         n = max_to_read;
  86         truncated = true;
  87     }
  88
  89     output.resize(0);
  90     output.reserve(n);
  91     while (n) {
  92         int c = read(fd, blk, min(n, sizeof(blk)));
  93         if (c <= 0) {
  94             if (c < 0 && errno == EINTR) continue;
  95             break;
  96         }
  97         output.append(blk, c);
  98         n -= c;
  99     }
 100
 101 #ifdef HAVE_POSIX_FADVISE
 102     if (flags & NOCACHE)
 103         posix_fadvise(fd, 0, 0, POSIX_FADV_DONTNEED);
 104 #endif
 105
 106     return fd;
 107 }
 108
 109 bool
 110 load_file(const string &file_name, size_t max_to_read, int flags,
 111           string &output, bool &truncated) {
 112     int fd = load_file_fd(file_name, max_to_read, flags, output, truncated);
 113     if (fd >= 0)
 114         close(fd);
 115     return (fd >= 0);
 116 }