src/port/tar.c

   1 #include "c.h"
   2
   3 #include <sys/stat.h>
   4
   5 #include "pgtar.h"
   6
   7 /*
   8  * Print a numeric field in a tar header.  The field starts at *s and is of
   9  * length len; val is the value to be written.
  10  *
  11  * Per POSIX, the way to write a number is in octal with leading zeroes and
  12  * one trailing space (or NUL, but we use space) at the end of the specified
  13  * field width.
  14  *
  15  * However, the given value may not fit in the available space in octal form.
  16  * If that's true, we use the GNU extension of writing \200 followed by the
  17  * number in base-256 form (ie, stored in binary MSB-first).  (Note: here we
  18  * support only non-negative numbers, so we don't worry about the GNU rules
  19  * for handling negative numbers.)
  20  */
  21 void
  22 print_tar_number(char *s, int len, uint64 val)
  23 {
  24         if (val < (((uint64) 1) << ((len - 1) * 3)))
  25         {
  26                 /* Use octal with trailing space */
  27                 s[--len] = ' ';
  28                 while (len)
  29                 {
  30                         s[--len] = (val & 7) + '0';
  31                         val >>= 3;
  32                 }
  33         }
  34         else
  35         {
  36                 /* Use base-256 with leading \200 */
  37                 s[0] = '\200';
  38                 while (len > 1)
  39                 {
  40                         s[--len] = (val & 255);
  41                         val >>= 8;
  42                 }
  43         }
  44 }
  45
  46
  47 /*
  48  * Read a numeric field in a tar header.  The field starts at *s and is of
  49  * length len.
  50  *
  51  * The POSIX-approved format for a number is octal, ending with a space or
  52  * NUL.  However, for values that don't fit, we recognize the GNU extension
  53  * of \200 followed by the number in base-256 form (ie, stored in binary
  54  * MSB-first).  (Note: here we support only non-negative numbers, so we don't
  55  * worry about the GNU rules for handling negative numbers.)
  56  */
  57 uint64
  58 read_tar_number(const char *s, int len)
  59 {
  60         uint64          result = 0;
  61
  62         if (*s == '\200')
  63         {
  64                 /* base-256 */
  65                 while (--len)
  66                 {
  67                         result <<= 8;
  68                         result |= (unsigned char) (*++s);
  69                 }
  70         }
  71         else
  72         {
  73                 /* octal */
  74                 while (len-- && *s >= '0' && *s <= '7')
  75                 {
  76                         result <<= 3;
  77                         result |= (*s - '0');
  78                         s++;
  79                 }
  80         }
  81         return result;
  82 }
  83
  84
  85 /*
  86  * Calculate the tar checksum for a header. The header is assumed to always
  87  * be 512 bytes, per the tar standard.
  88  */
  89 int
  90 tarChecksum(char *header)
  91 {
  92         int                     i,
  93                                 sum;
  94
  95         /*
  96          * Per POSIX, the checksum is the simple sum of all bytes in the header,
  97          * treating the bytes as unsigned, and treating the checksum field (at
  98          * offset 148) as though it contained 8 spaces.
  99          */
 100         sum = 8 * ' ';                          /* presumed value for checksum field */
 101         for (i = 0; i < 512; i++)
 102                 if (i < 148 || i >= 156)
 103                         sum += 0xFF & header[i];
 104         return sum;
 105 }
 106
 107
 108 /*
 109  * Fill in the buffer pointed to by h with a tar format header. This buffer
 110  * must always have space for 512 characters, which is a requirement of
 111  * the tar format.
 112  */
 113 enum tarError
 114 tarCreateHeader(char *h, const char *filename, const char *linktarget,
 115                                 pgoff_t size, mode_t mode, uid_t uid, gid_t gid, time_t mtime)
 116 {
 117         if (strlen(filename) > 99)
 118                 return TAR_NAME_TOO_LONG;
 119
 120         if (linktarget && strlen(linktarget) > 99)
 121                 return TAR_SYMLINK_TOO_LONG;
 122
 123         memset(h, 0, 512);                      /* assume tar header size */
 124
 125         /* Name 100 */
 126         strlcpy(&h[0], filename, 100);
 127         if (linktarget != NULL || S_ISDIR(mode))
 128         {
 129                 /*
 130                  * We only support symbolic links to directories, and this is
 131                  * indicated in the tar format by adding a slash at the end of the
 132                  * name, the same as for regular directories.
 133                  */
 134                 int                     flen = strlen(filename);
 135
 136                 flen = Min(flen, 99);
 137                 h[flen] = '/';
 138                 h[flen + 1] = '\0';
 139         }
 140
 141         /* Mode 8 - this doesn't include the file type bits (S_IFMT)  */
 142         print_tar_number(&h[100], 8, (mode & 07777));
 143
 144         /* User ID 8 */
 145         print_tar_number(&h[108], 8, uid);
 146
 147         /* Group 8 */
 148         print_tar_number(&h[116], 8, gid);
 149
 150         /* File size 12 */
 151         if (linktarget != NULL || S_ISDIR(mode))
 152                 /* Symbolic link or directory has size zero */
 153                 print_tar_number(&h[124], 12, 0);
 154         else
 155                 print_tar_number(&h[124], 12, size);
 156
 157         /* Mod Time 12 */
 158         print_tar_number(&h[136], 12, mtime);
 159
 160         /* Checksum 8 cannot be calculated until we've filled all other fields */
 161
 162         if (linktarget != NULL)
 163         {
 164                 /* Type - Symbolic link */
 165                 h[156] = '2';
 166                 /* Link Name 100 */
 167                 strlcpy(&h[157], linktarget, 100);
 168         }
 169         else if (S_ISDIR(mode))
 170         {
 171                 /* Type - directory */
 172                 h[156] = '5';
 173         }
 174         else
 175         {
 176                 /* Type - regular file */
 177                 h[156] = '0';
 178         }
 179
 180         /* Magic 6 */
 181         strcpy(&h[257], "ustar");
 182
 183         /* Version 2 */
 184         memcpy(&h[263], "00", 2);
 185
 186         /* User 32 */
 187         /* XXX: Do we need to care about setting correct username? */
 188         strlcpy(&h[265], "postgres", 32);
 189
 190         /* Group 32 */
 191         /* XXX: Do we need to care about setting correct group name? */
 192         strlcpy(&h[297], "postgres", 32);
 193
 194         /* Major Dev 8 */
 195         print_tar_number(&h[329], 8, 0);
 196
 197         /* Minor Dev 8 */
 198         print_tar_number(&h[337], 8, 0);
 199
 200         /* Prefix 155 - not used, leave as nulls */
 201
 202         /* Finally, compute and insert the checksum */
 203         print_tar_number(&h[148], 8, tarChecksum(h));
 204
 205         return TAR_OK;
 206 }