SETUP/replacecontents/replacecontents.c

   1 /*
   2  * Copyright (c) 2013 Apple Inc. All rights reserved.
   3  *
   4  * @APPLE_LICENSE_HEADER_START@
   5  *
   6  * This file contains Original Code and/or Modifications of Original Code
   7  * as defined in and that are subject to the Apple Public Source License
   8  * Version 2.0 (the 'License'). You may not use this file except in
   9  * compliance with the License. Please obtain a copy of the License at
  10  * http://www.opensource.apple.com/apsl/ and read it before using this
  11  * file.
  12  *
  13  * The Original Code and all software distributed under the License are
  14  * distributed on an 'AS IS' basis, WITHOUT WARRANTY OF ANY KIND, EITHER
  15  * EXPRESS OR IMPLIED, AND APPLE HEREBY DISCLAIMS ALL SUCH WARRANTIES,
  16  * INCLUDING WITHOUT LIMITATION, ANY WARRANTIES OF MERCHANTABILITY,
  17  * FITNESS FOR A PARTICULAR PURPOSE, QUIET ENJOYMENT OR NON-INFRINGEMENT.
  18  * Please see the License for the specific language governing rights and
  19  * limitations under the License.
  20  *
  21  * @APPLE_LICENSE_HEADER_END@
  22  */
  23
  24 #include <stdio.h>
  25 #include <stdlib.h>
  26 #include <unistd.h>
  27 #include <string.h>
  28 #include <stdbool.h>
  29 #include <errno.h>
  30 #include <err.h>
  31 #include <sysexits.h>
  32
  33 #include <sys/stat.h>
  34 #include <sys/fcntl.h>
  35 #include <sys/param.h>
  36 #include <sys/time.h>
  37
  38 void usage(void);
  39
  40 int main(int argc, char * argv[])
  41 {
  42         struct stat sb;
  43         char *newcontent = NULL;
  44         size_t newcontentlength = 0;
  45         char *oldcontent = NULL;
  46         int ret;
  47         int dstfd;
  48         const char *dst = NULL;
  49         ssize_t readsize, writesize;
  50         int i;
  51
  52         if (argc < 2) {
  53                 usage();
  54         }
  55
  56         dst = argv[1];
  57
  58         for (i=2; i < argc; i++) {
  59                 newcontentlength += strlen(argv[i]) + 1 /* space or newline */;
  60         }
  61         newcontentlength += 1; /* NUL */
  62
  63         newcontent = malloc(newcontentlength);
  64         if (newcontent == NULL)
  65                 err(EX_UNAVAILABLE, "malloc() failed");
  66
  67         newcontent[0] = '\0';
  68
  69         for (i=2; i < argc; i++) {
  70                 strlcat(newcontent, argv[i], newcontentlength);
  71                 if (i < argc - 1) {
  72                         strlcat(newcontent, " ", newcontentlength);
  73                 } else {
  74                         strlcat(newcontent, "\n", newcontentlength);
  75                 }
  76         }
  77
  78         dstfd = open(dst, O_RDWR | O_CREAT | O_APPEND, DEFFILEMODE);
  79         if (dstfd < 0)
  80                 err(EX_NOINPUT, "open(%s)", dst);
  81
  82         ret = fstat(dstfd, &sb);
  83         if (ret < 0)
  84                 err(EX_NOINPUT, "fstat(%s)", dst);
  85
  86         if (!S_ISREG(sb.st_mode))
  87                 err(EX_USAGE, "%s is not a regular file", dst);
  88
  89         if (sb.st_size != newcontentlength) {
  90                 /* obvious new content must be different than old */
  91                 goto replace;
  92         }
  93
  94         oldcontent = malloc(newcontentlength);
  95         if (oldcontent == NULL)
  96                 err(EX_UNAVAILABLE, "malloc(%lu) failed", newcontentlength);
  97
  98         readsize = read(dstfd, oldcontent, newcontentlength);
  99         if (readsize == -1)
 100                 err(EX_UNAVAILABLE, "read() failed");
 101         else if (readsize != newcontentlength)
 102                 errx(EX_UNAVAILABLE, "short read of file");
 103
 104         if (0 == memcmp(oldcontent, newcontent, newcontentlength)) {
 105                 /* binary comparison succeeded, just exit */
 106                 free(oldcontent);
 107                 ret = close(dstfd);
 108                 if (ret < 0)
 109                         err(EX_UNAVAILABLE, "close() failed");
 110
 111                 exit(0);
 112         }
 113
 114 replace:
 115         ret = ftruncate(dstfd, 0);
 116         if (ret < 0)
 117                 err(EX_UNAVAILABLE, "ftruncate() failed");
 118
 119         writesize = write(dstfd, newcontent, newcontentlength);
 120         if (writesize == -1)
 121                 err(EX_UNAVAILABLE, "write() failed");
 122         else if (writesize != newcontentlength)
 123                 errx(EX_UNAVAILABLE, "short write of file");
 124
 125         ret = close(dstfd);
 126         if (ret < 0)
 127                 err(EX_NOINPUT, "close(dst)");
 128
 129         return 0;
 130 }
 131
 132 void usage(void)
 133 {
 134         fprintf(stderr, "Usage: %s <dst> <new> <contents> <...>\n",
 135                         getprogname());
 136         exit(EX_USAGE);
 137 }