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tag: v1.4.2-rc4
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#include "cache.h"
#include "tag.h"

/*
* A signature file has a very simple fixed format: four lines
* of "object <sha1>" + "type <typename>" + "tag <tagname>" +
* "tagger <committer>", followed by a blank line, a free-form tag
* message and a signature block 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;
}

#ifdef NO_C99_FORMAT
#define PD_FMT "%d"
#else
#define PD_FMT "%td"
#endif

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)
return error("wanna fool me ? you obviously got the size wrong !");

buffer[size] = 0;

/* Verify object line */
object = buffer;
if (memcmp(object, "object ", 7))
return error("char%d: does not start with \"object \"", 0);

if (get_sha1_hex(object + 7, sha1))
return error("char%d: could not get SHA1 hash", 7);

/* Verify type line */
type_line = object + 48;
if (memcmp(type_line - 1, "\ntype ", 6))
return error("char%d: could not find \"\\ntype \"", 47);

/* Verify tag-line */
tag_line = strchr(type_line, '\n');
if (!tag_line)
return error("char" PD_FMT ": could not find next \"\\n\"", type_line - buffer);
tag_line++;
if (memcmp(tag_line, "tag ", 4) || tag_line[4] == '\n')
return error("char" PD_FMT ": no \"tag \" found", tag_line - buffer);

/* Get the actual type */
typelen = tag_line - type_line - strlen("type \n");
if (typelen >= sizeof(type))
return error("char" PD_FMT ": type too long", type_line+5 - buffer);

memcpy(type, type_line+5, typelen);
type[typelen] = 0;

/* Verify that the object matches */
if (verify_object(sha1, type))
return error("char%d: could not verify object %s", 7, sha1_to_hex(sha1));

/* 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 error("char" PD_FMT ": could not verify tag name", tag_line - buffer);
}

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

if (memcmp(tagger_line, "tagger", 6) || (tagger_line[6] == '\n'))
return error("char" PD_FMT ": could not find \"tagger\"", tagger_line - buffer);

/* TODO: check for committer info + blank line? */
/* Also, the minimum length is probably + "tagger .", or 63+8=71 */

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

#undef PD_FMT

int main(int argc, char **argv)
{
unsigned long size = 4096;
char *buffer = malloc(size);
unsigned char result_sha1[20];

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

setup_git_directory();

if (read_pipe(0, &buffer, &size)) {
free(buffer);
die("could not read from stdin");
}

/* 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_type, result_sha1) < 0)
die("unable to write tag file");

free(buffer);

printf("%s\n", sha1_to_hex(result_sha1));
return 0;
}
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