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#include "cache.h"

/*
* A signature file has a very simple fixed format: three lines
* of "object <sha1>" + "type <typename>" + "tag <tagname>",
* followed by some free-form signature that git itself doesn't
* care about, but that can be verified with gpg or similar.
*
* The first three lines are guaranteed to be at least 63 bytes:
* "object <sha1>\n" is 48 bytes, "type tag\n" at 9 bytes is the
* shortest possible type-line, and "tag .\n" at 6 bytes is the
* shortest single-character-tag line.
*
* We also artificially limit the size of the full object to 8kB.
* Just because I'm a lazy bastard, and if you can't fit a signature
* in that size, you're doing something wrong.
*/

// Some random size
#define MAXSIZE (8192)

/*
* We refuse to tag something we can't verify. Just because.
*/
static int verify_object(unsigned char *sha1, const char *expected_type)
{
int ret = -1;
char type[100];
unsigned long size;
void *buffer = read_sha1_file(sha1, type, &size);

if (buffer) {
if (!strcmp(type, expected_type))
ret = check_sha1_signature(sha1, buffer, size, type);
free(buffer);
}
return ret;
}

static int verify_tag(char *buffer, unsigned long size)
{
int typelen;
char type[20];
unsigned char sha1[20];
const char *object, *type_line, *tag_line, *tagger_line;

if (size < 64 || size > MAXSIZE-1)
return -1;
buffer[size] = 0;

/* Verify object line */
object = buffer;
if (memcmp(object, "object ", 7))
return -1;
if (get_sha1_hex(object + 7, sha1))
return -1;

/* Verify type line */
type_line = object + 48;
if (memcmp(type_line - 1, "\ntype ", 6))
return -1;

/* Verify tag-line */
tag_line = strchr(type_line, '\n');
if (!tag_line)
return -1;
tag_line++;
if (memcmp(tag_line, "tag ", 4) || tag_line[4] == '\n')
return -1;

/* Get the actual type */
typelen = tag_line - type_line - strlen("type \n");
if (typelen >= sizeof(type))
return -1;
memcpy(type, type_line+5, typelen);
type[typelen] = 0;

/* Verify that the object matches */
if (get_sha1_hex(object + 7, sha1))
return -1;
if (verify_object(sha1, type))
return -1;

/* Verify the tag-name: we don't allow control characters or spaces in it */
tag_line += 4;
for (;;) {
unsigned char c = *tag_line++;
if (c == '\n')
break;
if (c > ' ')
continue;
return -1;
}

/* Verify the tagger line */
tagger_line = tag_line;

if (memcmp(tagger_line, "tagger", 6) || (tagger_line[6] == '\n'))
return -1;

/* The actual stuff afterwards we don't care about.. */
return 0;
}

int main(int argc, char **argv)
{
unsigned long size;
char buffer[MAXSIZE];
unsigned char result_sha1[20];

if (argc != 1)
usage("cat <signaturefile> | git-mktag");

// Read the signature
size = 0;
for (;;) {
int ret = read(0, buffer + size, MAXSIZE - size);
if (!ret)
break;
if (ret < 0) {
if (errno == EAGAIN)
continue;
break;
}
size += ret;
}

// Verify it for some basic sanity: it needs to start with "object <sha1>\ntype\ntagger "
if (verify_tag(buffer, size) < 0)
die("invalid tag signature file");

if (write_sha1_file(buffer, size, "tag", result_sha1) < 0)
die("unable to write tag file");
printf("%s\n", sha1_to_hex(result_sha1));
return 0;
}
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