Extract verify_pack_index for reuse from verify_pack

The dumb HTTP transport should verify an index is completely valid
before trying to use it.  That requires checking the header/footer
but also checking the complete content SHA-1.  All of this logic is
already in the front half of verify_pack, so pull it out into a new
function that can be reused.

Signed-off-by: Shawn O. Pearce <spearce@spearce.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

pack-check.c

@@ -133,14 +133,13 @@ static int verify_packfile(struct packed_git *p,
 	return err;
 }
 
-int verify_pack(struct packed_git *p)
+int verify_pack_index(struct packed_git *p)
 {
 	off_t index_size;
 	const unsigned char *index_base;
 	git_SHA_CTX ctx;
 	unsigned char sha1[20];
 	int err = 0;
-	struct pack_window *w_curs = NULL;
 
 	if (open_pack_index(p))
 		return error("packfile %s index not opened", p->pack_name);
@@ -154,8 +153,18 @@ int verify_pack(struct packed_git *p)
 	if (hashcmp(sha1, index_base + index_size - 20))
 		err = error("Packfile index for %s SHA1 mismatch",
 			    p->pack_name);
+	return err;
+}
+
+int verify_pack(struct packed_git *p)
+{
+	int err = 0;
+	struct pack_window *w_curs = NULL;
+
+	err |= verify_pack_index(p);
+	if (!p->index_data)
+		return -1;
 
-	/* Verify pack file */
 	err |= verify_packfile(p, &w_curs);
 	unuse_pack(&w_curs);
 

pack.h

@@ -57,6 +57,7 @@ struct pack_idx_entry {
 
 extern const char *write_idx_file(const char *index_name, struct pack_idx_entry **objects, int nr_objects, unsigned char *sha1);
 extern int check_pack_crc(struct packed_git *p, struct pack_window **w_curs, off_t offset, off_t len, unsigned int nr);
+extern int verify_pack_index(struct packed_git *);
 extern int verify_pack(struct packed_git *);
 extern void fixup_pack_header_footer(int, unsigned char *, const char *, uint32_t, unsigned char *, off_t);
 extern char *index_pack_lockfile(int fd);