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#include "c.h"
#include <sys/stat.h>
#include "pgtar.h"
/*
* Print a numeric field in a tar header. The field starts at *s and is of
* length len; val is the value to be written.
*
* Per POSIX, the way to write a number is in octal with leading zeroes and
* one trailing space (or NUL, but we use space) at the end of the specified
* field width.
*
* However, the given value may not fit in the available space in octal form.
* If that's true, we use the GNU extension of writing \200 followed by the
* number in base-256 form (ie, stored in binary MSB-first). (Note: here we
* support only non-negative numbers, so we don't worry about the GNU rules
* for handling negative numbers.)
*/
void
print_tar_number(char *s, int len, uint64 val)
{
if (val < (((uint64) 1) << ((len - 1) * 3)))
{
/* Use octal with trailing space */
s[--len] = ' ';
while (len)
{
s[--len] = (val & 7) + '0';
val >>= 3;
}
}
else
{
/* Use base-256 with leading \200 */
s[0] = '\200';
while (len > 1)
{
s[--len] = (val & 255);
val >>= 8;
}
}
}
/*
* Read a numeric field in a tar header. The field starts at *s and is of
* length len.
*
* The POSIX-approved format for a number is octal, ending with a space or
* NUL. However, for values that don't fit, we recognize the GNU extension
* of \200 followed by the number in base-256 form (ie, stored in binary
* MSB-first). (Note: here we support only non-negative numbers, so we don't
* worry about the GNU rules for handling negative numbers.)
*/
uint64
read_tar_number(const char *s, int len)
{
uint64 result = 0;
if (*s == '\200')
{
/* base-256 */
while (--len)
{
result <<= 8;
result |= (unsigned char) (*++s);
}
}
else
{
/* octal */
while (len-- && *s >= '0' && *s <= '7')
{
result <<= 3;
result |= (*s - '0');
s++;
}
}
return result;
}
/*
* Calculate the tar checksum for a header. The header is assumed to always
* be 512 bytes, per the tar standard.
*/
int
tarChecksum(char *header)
{
int i,
sum;
/*
* Per POSIX, the checksum is the simple sum of all bytes in the header,
* treating the bytes as unsigned, and treating the checksum field (at
* offset 148) as though it contained 8 spaces.
*/
sum = 8 * ' '; /* presumed value for checksum field */
for (i = 0; i < 512; i++)
if (i < 148 || i >= 156)
sum += 0xFF & header[i];
return sum;
}
/*
* Fill in the buffer pointed to by h with a tar format header. This buffer
* must always have space for 512 characters, which is a requirement of
* the tar format.
*/
enum tarError
tarCreateHeader(char *h, const char *filename, const char *linktarget,
pgoff_t size, mode_t mode, uid_t uid, gid_t gid, time_t mtime)
{
if (strlen(filename) > 99)
return TAR_NAME_TOO_LONG;
if (linktarget && strlen(linktarget) > 99)
return TAR_SYMLINK_TOO_LONG;
memset(h, 0, 512); /* assume tar header size */
/* Name 100 */
strlcpy(&h[0], filename, 100);
if (linktarget != NULL || S_ISDIR(mode))
{
/*
* We only support symbolic links to directories, and this is
* indicated in the tar format by adding a slash at the end of the
* name, the same as for regular directories.
*/
int flen = strlen(filename);
flen = Min(flen, 99);
h[flen] = '/';
h[flen + 1] = '\0';
}
/* Mode 8 - this doesn't include the file type bits (S_IFMT) */
print_tar_number(&h[100], 8, (mode & 07777));
/* User ID 8 */
print_tar_number(&h[108], 8, uid);
/* Group 8 */
print_tar_number(&h[116], 8, gid);
/* File size 12 */
if (linktarget != NULL || S_ISDIR(mode))
/* Symbolic link or directory has size zero */
print_tar_number(&h[124], 12, 0);
else
print_tar_number(&h[124], 12, size);
/* Mod Time 12 */
print_tar_number(&h[136], 12, mtime);
/* Checksum 8 cannot be calculated until we've filled all other fields */
if (linktarget != NULL)
{
/* Type - Symbolic link */
h[156] = '2';
/* Link Name 100 */
strlcpy(&h[157], linktarget, 100);
}
else if (S_ISDIR(mode))
{
/* Type - directory */
h[156] = '5';
}
else
{
/* Type - regular file */
h[156] = '0';
}
/* Magic 6 */
strcpy(&h[257], "ustar");
/* Version 2 */
memcpy(&h[263], "00", 2);
/* User 32 */
/* XXX: Do we need to care about setting correct username? */
strlcpy(&h[265], "postgres", 32);
/* Group 32 */
/* XXX: Do we need to care about setting correct group name? */
strlcpy(&h[297], "postgres", 32);
/* Major Dev 8 */
print_tar_number(&h[329], 8, 0);
/* Minor Dev 8 */
print_tar_number(&h[337], 8, 0);
/* Prefix 155 - not used, leave as nulls */
/* Finally, compute and insert the checksum */
print_tar_number(&h[148], 8, tarChecksum(h));
return TAR_OK;
}
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