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Commit4a095e9

Browse files
robertmhaaspull[bot]
authored andcommitted
Add and use symbolic constants for tar header offsets and file types.
Because symbolic constants in a header file are better than magicconstants embedded in the code.Patch by me, reviewed by Tom Lane, Dagfinn Ilmari Mannsåker, andTristan Partin.Discussion:http://postgr.es/m/CA+TgmoZNbLwhmCrNtkJAvi8FLkwFdMeVU3myV2HQQpA5bvbRZg@mail.gmail.com
1 parente1025c8 commit4a095e9

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5 files changed

+80
-42
lines changed

5 files changed

+80
-42
lines changed

‎src/bin/pg_basebackup/bbstreamer_tar.c‎

Lines changed: 10 additions & 12 deletions
Original file line numberDiff line numberDiff line change
@@ -286,22 +286,20 @@ bbstreamer_tar_header(bbstreamer_tar_parser *mystreamer)
286286

287287
/*
288288
* Parse key fields out of the header.
289-
*
290-
* FIXME: It's terrible that we use hard-coded values here instead of some
291-
* more principled approach. It's been like this for a long time, but we
292-
* ought to do better.
293289
*/
294-
strlcpy(member->pathname,&buffer[0],MAXPGPATH);
290+
strlcpy(member->pathname,&buffer[TAR_OFFSET_NAME],MAXPGPATH);
295291
if (member->pathname[0]=='\0')
296292
pg_fatal("tar member has empty name");
297-
member->size=read_tar_number(&buffer[124],12);
298-
member->mode=read_tar_number(&buffer[100],8);
299-
member->uid=read_tar_number(&buffer[108],8);
300-
member->gid=read_tar_number(&buffer[116],8);
301-
member->is_directory= (buffer[156]=='5');
302-
member->is_link= (buffer[156]=='2');
293+
member->size=read_tar_number(&buffer[TAR_OFFSET_SIZE],12);
294+
member->mode=read_tar_number(&buffer[TAR_OFFSET_MODE],8);
295+
member->uid=read_tar_number(&buffer[TAR_OFFSET_UID],8);
296+
member->gid=read_tar_number(&buffer[TAR_OFFSET_GID],8);
297+
member->is_directory=
298+
(buffer[TAR_OFFSET_TYPEFLAG]==TAR_FILETYPE_DIRECTORY);
299+
member->is_link=
300+
(buffer[TAR_OFFSET_TYPEFLAG]==TAR_FILETYPE_SYMLINK);
303301
if (member->is_link)
304-
strlcpy(member->linktarget,&buffer[157],100);
302+
strlcpy(member->linktarget,&buffer[TAR_OFFSET_LINKNAME],100);
305303

306304
/* Compute number of padding bytes. */
307305
mystreamer->pad_bytes_expected=tarPaddingBytesRequired(member->size);

‎src/bin/pg_basebackup/walmethods.c‎

Lines changed: 4 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -1131,17 +1131,18 @@ tar_close(Walfile *f, WalCloseMethod method)
11311131
* possibly also renaming the file. We overwrite the entire current header
11321132
* when done, including the checksum.
11331133
*/
1134-
print_tar_number(&(tf->header[124]),12,filesize);
1134+
print_tar_number(&(tf->header[TAR_OFFSET_SIZE]),12,filesize);
11351135

11361136
if (method==CLOSE_NORMAL)
11371137

11381138
/*
11391139
* We overwrite it with what it was before if we have no tempname,
11401140
* since we're going to write the buffer anyway.
11411141
*/
1142-
strlcpy(&(tf->header[0]),tf->base.pathname,100);
1142+
strlcpy(&(tf->header[TAR_OFFSET_NAME]),tf->base.pathname,100);
11431143

1144-
print_tar_number(&(tf->header[148]),8,tarChecksum(((TarMethodFile*)f)->header));
1144+
print_tar_number(&(tf->header[TAR_OFFSET_CHECKSUM]),8,
1145+
tarChecksum(((TarMethodFile*)f)->header));
11451146
if (lseek(tar_data->fd,tf->ofs_start,SEEK_SET)!= ((TarMethodFile*)f)->ofs_start)
11461147
{
11471148
f->wwmethod->lasterrno=errno;

‎src/bin/pg_dump/pg_backup_tar.c‎

Lines changed: 8 additions & 8 deletions
Original file line numberDiff line numberDiff line change
@@ -975,20 +975,20 @@ isValidTarHeader(char *header)
975975
intsum;
976976
intchk=tarChecksum(header);
977977

978-
sum=read_tar_number(&header[148],8);
978+
sum=read_tar_number(&header[TAR_OFFSET_CHECKSUM],8);
979979

980980
if (sum!=chk)
981981
return false;
982982

983983
/* POSIX tar format */
984-
if (memcmp(&header[257],"ustar\0",6)==0&&
985-
memcmp(&header[263],"00",2)==0)
984+
if (memcmp(&header[TAR_OFFSET_MAGIC],"ustar\0",6)==0&&
985+
memcmp(&header[TAR_OFFSET_VERSION],"00",2)==0)
986986
return true;
987987
/* GNU tar format */
988-
if (memcmp(&header[257],"ustar \0",8)==0)
988+
if (memcmp(&header[TAR_OFFSET_MAGIC],"ustar \0",8)==0)
989989
return true;
990990
/* not-quite-POSIX format written by pre-9.3 pg_dump */
991-
if (memcmp(&header[257],"ustar00\0",8)==0)
991+
if (memcmp(&header[TAR_OFFSET_MAGIC],"ustar00\0",8)==0)
992992
return true;
993993

994994
return false;
@@ -1151,7 +1151,7 @@ _tarGetHeader(ArchiveHandle *AH, TAR_MEMBER *th)
11511151

11521152
/* Calc checksum */
11531153
chk=tarChecksum(h);
1154-
sum=read_tar_number(&h[148],8);
1154+
sum=read_tar_number(&h[TAR_OFFSET_CHECKSUM],8);
11551155

11561156
/*
11571157
* If the checksum failed, see if it is a null block. If so, silently
@@ -1175,9 +1175,9 @@ _tarGetHeader(ArchiveHandle *AH, TAR_MEMBER *th)
11751175
}
11761176

11771177
/* Name field is 100 bytes, might not be null-terminated */
1178-
strlcpy(tag,&h[0],100+1);
1178+
strlcpy(tag,&h[TAR_OFFSET_NAME],100+1);
11791179

1180-
len=read_tar_number(&h[124],12);
1180+
len=read_tar_number(&h[TAR_OFFSET_SIZE],12);
11811181

11821182
pg_log_debug("TOC Entry %s at %llu (length %llu, checksum %d)",
11831183
tag, (unsigned long long)hPos, (unsigned long long)len,sum);

‎src/include/pgtar.h‎

Lines changed: 39 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -23,6 +23,45 @@ enum tarError
2323
TAR_SYMLINK_TOO_LONG
2424
};
2525

26+
/*
27+
* Offsets of fields within a 512-byte tar header.
28+
*
29+
* "tar number" values should be generated using print_tar_number() and can be
30+
* read using read_tar_number(). Fields that contain strings are generally
31+
* both filled and read using strlcpy().
32+
*
33+
* The value for the checksum field can be computed using tarChecksum().
34+
*
35+
* Some fields are not used by PostgreSQL; see tarCreateHeader().
36+
*/
37+
enumtarHeaderOffset
38+
{
39+
TAR_OFFSET_NAME=0,/* 100 byte string */
40+
TAR_OFFSET_MODE=100,/* 8 byte tar number, excludes S_IFMT */
41+
TAR_OFFSET_UID=108,/* 8 byte tar number */
42+
TAR_OFFSET_GID=116,/* 8 byte tar number */
43+
TAR_OFFSET_SIZE=124,/* 8 byte tar number */
44+
TAR_OFFSET_MTIME=136,/* 12 byte tar number */
45+
TAR_OFFSET_CHECKSUM=148,/* 8 byte tar number */
46+
TAR_OFFSET_TYPEFLAG=156,/* 1 byte file type, see TAR_FILETYPE_* */
47+
TAR_OFFSET_LINKNAME=157,/* 100 byte string */
48+
TAR_OFFSET_MAGIC=257,/* "ustar" with terminating zero byte */
49+
TAR_OFFSET_VERSION=263,/* "00" */
50+
TAR_OFFSET_UNAME=265,/* 32 byte string */
51+
TAR_OFFSET_GNAME=297,/* 32 byte string */
52+
TAR_OFFSET_DEVMAJOR=329,/* 8 byte tar number */
53+
TAR_OFFSET_DEVMINOR=337,/* 8 byte tar number */
54+
TAR_OFFSET_PREFIX=345/* 155 byte string */
55+
/* last 12 bytes of the 512-byte block are unassigned */
56+
};
57+
58+
enumtarFileType
59+
{
60+
TAR_FILETYPE_PLAIN='0',
61+
TAR_FILETYPE_SYMLINK='2',
62+
TAR_FILETYPE_DIRECTORY='5'
63+
};
64+
2665
externenumtarErrortarCreateHeader(char*h,constchar*filename,
2766
constchar*linktarget,pgoff_tsize,
2867
mode_tmode,uid_tuid,gid_tgid,

‎src/port/tar.c‎

Lines changed: 19 additions & 19 deletions
Original file line numberDiff line numberDiff line change
@@ -120,10 +120,10 @@ tarCreateHeader(char *h, const char *filename, const char *linktarget,
120120
if (linktarget&&strlen(linktarget)>99)
121121
returnTAR_SYMLINK_TOO_LONG;
122122

123-
memset(h,0,512);/* assume tar header size */
123+
memset(h,0,TAR_BLOCK_SIZE);
124124

125125
/* Name 100 */
126-
strlcpy(&h[0],filename,100);
126+
strlcpy(&h[TAR_OFFSET_NAME],filename,100);
127127
if (linktarget!=NULL||S_ISDIR(mode))
128128
{
129129
/*
@@ -139,68 +139,68 @@ tarCreateHeader(char *h, const char *filename, const char *linktarget,
139139
}
140140

141141
/* Mode 8 - this doesn't include the file type bits (S_IFMT) */
142-
print_tar_number(&h[100],8, (mode&07777));
142+
print_tar_number(&h[TAR_OFFSET_MODE],8, (mode&07777));
143143

144144
/* User ID 8 */
145-
print_tar_number(&h[108],8,uid);
145+
print_tar_number(&h[TAR_OFFSET_UID],8,uid);
146146

147147
/* Group 8 */
148-
print_tar_number(&h[116],8,gid);
148+
print_tar_number(&h[TAR_OFFSET_GID],8,gid);
149149

150150
/* File size 12 */
151151
if (linktarget!=NULL||S_ISDIR(mode))
152152
/* Symbolic link or directory has size zero */
153-
print_tar_number(&h[124],12,0);
153+
print_tar_number(&h[TAR_OFFSET_SIZE],12,0);
154154
else
155-
print_tar_number(&h[124],12,size);
155+
print_tar_number(&h[TAR_OFFSET_SIZE],12,size);
156156

157157
/* Mod Time 12 */
158-
print_tar_number(&h[136],12,mtime);
158+
print_tar_number(&h[TAR_OFFSET_MTIME],12,mtime);
159159

160160
/* Checksum 8 cannot be calculated until we've filled all other fields */
161161

162162
if (linktarget!=NULL)
163163
{
164164
/* Type - Symbolic link */
165-
h[156]='2';
165+
h[TAR_OFFSET_TYPEFLAG]=TAR_FILETYPE_SYMLINK;
166166
/* Link Name 100 */
167-
strlcpy(&h[157],linktarget,100);
167+
strlcpy(&h[TAR_OFFSET_LINKNAME],linktarget,100);
168168
}
169169
elseif (S_ISDIR(mode))
170170
{
171171
/* Type - directory */
172-
h[156]='5';
172+
h[TAR_OFFSET_TYPEFLAG]=TAR_FILETYPE_DIRECTORY;
173173
}
174174
else
175175
{
176176
/* Type - regular file */
177-
h[156]='0';
177+
h[TAR_OFFSET_TYPEFLAG]=TAR_FILETYPE_PLAIN;
178178
}
179179

180180
/* Magic 6 */
181-
strcpy(&h[257],"ustar");
181+
strcpy(&h[TAR_OFFSET_MAGIC],"ustar");
182182

183183
/* Version 2 */
184-
memcpy(&h[263],"00",2);
184+
memcpy(&h[TAR_OFFSET_VERSION],"00",2);
185185

186186
/* User 32 */
187187
/* XXX: Do we need to care about setting correct username? */
188-
strlcpy(&h[265],"postgres",32);
188+
strlcpy(&h[TAR_OFFSET_UNAME],"postgres",32);
189189

190190
/* Group 32 */
191191
/* XXX: Do we need to care about setting correct group name? */
192-
strlcpy(&h[297],"postgres",32);
192+
strlcpy(&h[TAR_OFFSET_GNAME],"postgres",32);
193193

194194
/* Major Dev 8 */
195-
print_tar_number(&h[329],8,0);
195+
print_tar_number(&h[TAR_OFFSET_DEVMAJOR],8,0);
196196

197197
/* Minor Dev 8 */
198-
print_tar_number(&h[337],8,0);
198+
print_tar_number(&h[TAR_OFFSET_DEVMINOR],8,0);
199199

200200
/* Prefix 155 - not used, leave as nulls */
201201

202202
/* Finally, compute and insert the checksum */
203-
print_tar_number(&h[148],8,tarChecksum(h));
203+
print_tar_number(&h[TAR_OFFSET_CHECKSUM],8,tarChecksum(h));
204204

205205
returnTAR_OK;
206206
}

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