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Add and use symbolic constants for tar header offsets and file types. 

Because symbolic constants in a header file are better than magic
constants embedded in the code.

Patch by me, reviewed by Tom Lane, Dagfinn Ilmari Mannsåker, and
Tristan Partin.

Discussion: http://postgr.es/m/CA+TgmoZNbLwhmCrNtkJAvi8FLkwFdMeVU3myV2HQQpA5bvbRZg@mail.gmail.com
This commit is contained in:
Robert Haas 2023-08-01 13:50:42 -04:00
parent deae1657ee
commit 6050b6a92d
5 changed files with 80 additions and 42 deletions
Show Stats Download Patch File Download Diff File Expand all files Collapse all files

22
src/bin/pg_basebackup/bbstreamer_tar.c
View File

@ -286,22 +286,20 @@ bbstreamer_tar_header(bbstreamer_tar_parser *mystreamer)
/*
* Parse key fields out of the header.
*
* FIXME: It's terrible that we use hard-coded values here instead of some
* more principled approach. It's been like this for a long time, but we
* ought to do better.
*/
strlcpy(member->pathname, &buffer[0], MAXPGPATH);
strlcpy(member->pathname, &buffer[TAR_OFFSET_NAME], MAXPGPATH);
if (member->pathname[0] == '\0')
pg_fatal("tar member has empty name");
member->size = read_tar_number(&buffer[124], 12);
member->mode = read_tar_number(&buffer[100], 8);
member->uid = read_tar_number(&buffer[108], 8);
member->gid = read_tar_number(&buffer[116], 8);
member->is_directory = (buffer[156] == '5');
member->is_link = (buffer[156] == '2');
member->size = read_tar_number(&buffer[TAR_OFFSET_SIZE], 12);
member->mode = read_tar_number(&buffer[TAR_OFFSET_MODE], 8);
member->uid = read_tar_number(&buffer[TAR_OFFSET_UID], 8);
member->gid = read_tar_number(&buffer[TAR_OFFSET_GID], 8);
member->is_directory =
(buffer[TAR_OFFSET_TYPEFLAG] == TAR_FILETYPE_DIRECTORY);
member->is_link =
(buffer[TAR_OFFSET_TYPEFLAG] == TAR_FILETYPE_SYMLINK);
if (member->is_link)
strlcpy(member->linktarget, &buffer[157], 100);
strlcpy(member->linktarget, &buffer[TAR_OFFSET_LINKNAME], 100);
/* Compute number of padding bytes. */
mystreamer->pad_bytes_expected = tarPaddingBytesRequired(member->size);

7
src/bin/pg_basebackup/walmethods.c
View File

@ -1131,7 +1131,7 @@ tar_close(Walfile *f, WalCloseMethod method)
* possibly also renaming the file. We overwrite the entire current header
* when done, including the checksum.
*/
print_tar_number(&(tf->header[124]), 12, filesize);
print_tar_number(&(tf->header[TAR_OFFSET_SIZE]), 12, filesize);
if (method == CLOSE_NORMAL)
@ -1139,9 +1139,10 @@ tar_close(Walfile *f, WalCloseMethod method)
* We overwrite it with what it was before if we have no tempname,
* since we're going to write the buffer anyway.
*/
strlcpy(&(tf->header[0]), tf->base.pathname, 100);
strlcpy(&(tf->header[TAR_OFFSET_NAME]), tf->base.pathname, 100);
print_tar_number(&(tf->header[148]), 8, tarChecksum(((TarMethodFile *) f)->header));
print_tar_number(&(tf->header[TAR_OFFSET_CHECKSUM]), 8,
tarChecksum(((TarMethodFile *) f)->header));
if (lseek(tar_data->fd, tf->ofs_start, SEEK_SET) != ((TarMethodFile *) f)->ofs_start)
{
f->wwmethod->lasterrno = errno;

16
src/bin/pg_dump/pg_backup_tar.c
View File

@ -975,20 +975,20 @@ isValidTarHeader(char *header)
int sum;
int chk = tarChecksum(header);
sum = read_tar_number(&header[148], 8);
sum = read_tar_number(&header[TAR_OFFSET_CHECKSUM], 8);
if (sum != chk)
return false;
/* POSIX tar format */
if (memcmp(&header[257], "ustar\0", 6) == 0 &&
memcmp(&header[263], "00", 2) == 0)
if (memcmp(&header[TAR_OFFSET_MAGIC], "ustar\0", 6) == 0 &&
memcmp(&header[TAR_OFFSET_VERSION], "00", 2) == 0)
return true;
/* GNU tar format */
if (memcmp(&header[257], "ustar \0", 8) == 0)
if (memcmp(&header[TAR_OFFSET_MAGIC], "ustar \0", 8) == 0)
return true;
/* not-quite-POSIX format written by pre-9.3 pg_dump */
if (memcmp(&header[257], "ustar00\0", 8) == 0)
if (memcmp(&header[TAR_OFFSET_MAGIC], "ustar00\0", 8) == 0)
return true;
return false;
@ -1151,7 +1151,7 @@ _tarGetHeader(ArchiveHandle *AH, TAR_MEMBER *th)
/* Calc checksum */
chk = tarChecksum(h);
sum = read_tar_number(&h[148], 8);
sum = read_tar_number(&h[TAR_OFFSET_CHECKSUM], 8);
/*
* If the checksum failed, see if it is a null block. If so, silently
@ -1175,9 +1175,9 @@ _tarGetHeader(ArchiveHandle *AH, TAR_MEMBER *th)
}
/* Name field is 100 bytes, might not be null-terminated */
strlcpy(tag, &h[0], 100 + 1);
strlcpy(tag, &h[TAR_OFFSET_NAME], 100 + 1);
len = read_tar_number(&h[124], 12);
len = read_tar_number(&h[TAR_OFFSET_SIZE], 12);
pg_log_debug("TOC Entry %s at %llu (length %llu, checksum %d)",
tag, (unsigned long long) hPos, (unsigned long long) len, sum);

39
src/include/pgtar.h
View File

@ -23,6 +23,45 @@ enum tarError
TAR_SYMLINK_TOO_LONG
};
/*
* Offsets of fields within a 512-byte tar header.
*
* "tar number" values should be generated using print_tar_number() and can be
* read using read_tar_number(). Fields that contain strings are generally
* both filled and read using strlcpy().
*
* The value for the checksum field can be computed using tarChecksum().
*
* Some fields are not used by PostgreSQL; see tarCreateHeader().
*/
enum tarHeaderOffset
{
TAR_OFFSET_NAME = 0, /* 100 byte string */
TAR_OFFSET_MODE = 100, /* 8 byte tar number, excludes S_IFMT */
TAR_OFFSET_UID = 108, /* 8 byte tar number */
TAR_OFFSET_GID = 116, /* 8 byte tar number */
TAR_OFFSET_SIZE = 124, /* 8 byte tar number */
TAR_OFFSET_MTIME = 136, /* 12 byte tar number */
TAR_OFFSET_CHECKSUM = 148, /* 8 byte tar number */
TAR_OFFSET_TYPEFLAG = 156, /* 1 byte file type, see TAR_FILETYPE_* */
TAR_OFFSET_LINKNAME = 157, /* 100 byte string */
TAR_OFFSET_MAGIC = 257, /* "ustar" with terminating zero byte */
TAR_OFFSET_VERSION = 263, /* "00" */
TAR_OFFSET_UNAME = 265, /* 32 byte string */
TAR_OFFSET_GNAME = 297, /* 32 byte string */
TAR_OFFSET_DEVMAJOR = 329, /* 8 byte tar number */
TAR_OFFSET_DEVMINOR = 337, /* 8 byte tar number */
TAR_OFFSET_PREFIX = 345 /* 155 byte string */
/* last 12 bytes of the 512-byte block are unassigned */
};
enum tarFileType
{
TAR_FILETYPE_PLAIN = '0',
TAR_FILETYPE_SYMLINK = '2',
TAR_FILETYPE_DIRECTORY = '5'
};
extern enum tarError tarCreateHeader(char *h, const char *filename,
const char *linktarget, pgoff_t size,
mode_t mode, uid_t uid, gid_t gid,

38
src/port/tar.c
View File

@ -120,10 +120,10 @@ tarCreateHeader(char *h, const char *filename, const char *linktarget,
if (linktarget && strlen(linktarget) > 99)
return TAR_SYMLINK_TOO_LONG;
memset(h, 0, 512); /* assume tar header size */
memset(h, 0, TAR_BLOCK_SIZE);
/* Name 100 */
strlcpy(&h[0], filename, 100);
strlcpy(&h[TAR_OFFSET_NAME], filename, 100);
if (linktarget != NULL || S_ISDIR(mode))
{
/*
@ -139,68 +139,68 @@ tarCreateHeader(char *h, const char *filename, const char *linktarget,
}
/* Mode 8 - this doesn't include the file type bits (S_IFMT) */
print_tar_number(&h[100], 8, (mode & 07777));
print_tar_number(&h[TAR_OFFSET_MODE], 8, (mode & 07777));
/* User ID 8 */
print_tar_number(&h[108], 8, uid);
print_tar_number(&h[TAR_OFFSET_UID], 8, uid);
/* Group 8 */
print_tar_number(&h[116], 8, gid);
print_tar_number(&h[TAR_OFFSET_GID], 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);
print_tar_number(&h[TAR_OFFSET_SIZE], 12, 0);
else
print_tar_number(&h[124], 12, size);
print_tar_number(&h[TAR_OFFSET_SIZE], 12, size);
/* Mod Time 12 */
print_tar_number(&h[136], 12, mtime);
print_tar_number(&h[TAR_OFFSET_MTIME], 12, mtime);
/* Checksum 8 cannot be calculated until we've filled all other fields */
if (linktarget != NULL)
{
/* Type - Symbolic link */
h[156] = '2';
h[TAR_OFFSET_TYPEFLAG] = TAR_FILETYPE_SYMLINK;
/* Link Name 100 */
strlcpy(&h[157], linktarget, 100);
strlcpy(&h[TAR_OFFSET_LINKNAME], linktarget, 100);
}
else if (S_ISDIR(mode))
{
/* Type - directory */
h[156] = '5';
h[TAR_OFFSET_TYPEFLAG] = TAR_FILETYPE_DIRECTORY;
}
else
{
/* Type - regular file */
h[156] = '0';
h[TAR_OFFSET_TYPEFLAG] = TAR_FILETYPE_PLAIN;
}
/* Magic 6 */
strcpy(&h[257], "ustar");
strcpy(&h[TAR_OFFSET_MAGIC], "ustar");
/* Version 2 */
memcpy(&h[263], "00", 2);
memcpy(&h[TAR_OFFSET_VERSION], "00", 2);
/* User 32 */
/* XXX: Do we need to care about setting correct username? */
strlcpy(&h[265], "postgres", 32);
strlcpy(&h[TAR_OFFSET_UNAME], "postgres", 32);
/* Group 32 */
/* XXX: Do we need to care about setting correct group name? */
strlcpy(&h[297], "postgres", 32);
strlcpy(&h[TAR_OFFSET_GNAME], "postgres", 32);
/* Major Dev 8 */
print_tar_number(&h[329], 8, 0);
print_tar_number(&h[TAR_OFFSET_DEVMAJOR], 8, 0);
/* Minor Dev 8 */
print_tar_number(&h[337], 8, 0);
print_tar_number(&h[TAR_OFFSET_DEVMINOR], 8, 0);
/* Prefix 155 - not used, leave as nulls */
/* Finally, compute and insert the checksum */
print_tar_number(&h[148], 8, tarChecksum(h));
print_tar_number(&h[TAR_OFFSET_CHECKSUM], 8, tarChecksum(h));
return TAR_OK;
}