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
  41 main(int argc, char * argv[])
  42 {
  43         struct stat sb;
  44         char *newcontent = NULL;
  45         size_t newcontentlength = 0;
  46         char *oldcontent = NULL;
  47         int ret;
  48         int dstfd;
  49         const char *dst = NULL;
  50         ssize_t readsize, writesize;
  51         int i;
  52
  53         if (argc < 2) {
  54                 usage();
  55         }
  56
  57         dst = argv[1];
  58
  59         for (i = 2; i < argc; i++) {
  60                 newcontentlength += strlen(argv[i]) + 1 /* space or newline */;
  61         }
  62         newcontentlength += 1; /* NUL */
  63
  64         newcontent = malloc(newcontentlength);
  65         if (newcontent == NULL) {
  66                 err(EX_UNAVAILABLE, "malloc() failed");
  67         }
  68
  69         newcontent[0] = '\0';
  70
  71         for (i = 2; i < argc; i++) {
  72                 strlcat(newcontent, argv[i], newcontentlength);
  73                 if (i < argc - 1) {
  74                         strlcat(newcontent, " ", newcontentlength);
  75                 } else {
  76                         strlcat(newcontent, "\n", newcontentlength);
  77                 }
  78         }
  79
  80         dstfd = open(dst, O_RDWR | O_CREAT | O_APPEND, DEFFILEMODE);
  81         if (dstfd < 0) {
  82                 err(EX_NOINPUT, "open(%s)", dst);
  83         }
  84
  85         ret = fstat(dstfd, &sb);
  86         if (ret < 0) {
  87                 err(EX_NOINPUT, "fstat(%s)", dst);
  88         }
  89
  90         if (!S_ISREG(sb.st_mode)) {
  91                 err(EX_USAGE, "%s is not a regular file", dst);
  92         }
  93
  94         if (sb.st_size != newcontentlength) {
  95                 /* obvious new content must be different than old */
  96                 goto replace;
  97         }
  98
  99         oldcontent = malloc(newcontentlength);
 100         if (oldcontent == NULL) {
 101                 err(EX_UNAVAILABLE, "malloc(%lu) failed", newcontentlength);
 102         }
 103
 104         readsize = read(dstfd, oldcontent, newcontentlength);
 105         if (readsize == -1) {
 106                 err(EX_UNAVAILABLE, "read() failed");
 107         } else if (readsize != newcontentlength) {
 108                 errx(EX_UNAVAILABLE, "short read of file");
 109         }
 110
 111         if (0 == memcmp(oldcontent, newcontent, newcontentlength)) {
 112                 /* binary comparison succeeded, just exit */
 113                 free(oldcontent);
 114                 ret = close(dstfd);
 115                 if (ret < 0) {
 116                         err(EX_UNAVAILABLE, "close() failed");
 117                 }
 118
 119                 exit(0);
 120         }
 121
 122 replace:
 123         ret = ftruncate(dstfd, 0);
 124         if (ret < 0) {
 125                 err(EX_UNAVAILABLE, "ftruncate() failed");
 126         }
 127
 128         writesize = write(dstfd, newcontent, newcontentlength);
 129         if (writesize == -1) {
 130                 err(EX_UNAVAILABLE, "write() failed");
 131         } else if (writesize != newcontentlength) {
 132                 errx(EX_UNAVAILABLE, "short write of file");
 133         }
 134
 135         ret = close(dstfd);
 136         if (ret < 0) {
 137                 err(EX_NOINPUT, "close(dst)");
 138         }
 139
 140         return 0;
 141 }
 142
 143 void
 144 usage(void)
 145 {
 146         fprintf(stderr, "Usage: %s <dst> <new> <contents> <...>\n",
 147             getprogname());
 148         exit(EX_USAGE);
 149 }