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
print_tar_number(char * s,int len,uint64 val)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
read_tar_number(const char * s,int len)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
tarChecksum(char * header)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
tarCreateHeader(char * h,const char * filename,const char * linktarget,pgoff_t size,mode_t mode,uid_t uid,gid_t gid,time_t mtime)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 }
207