pack-objects: use fixup_pack_header_footer()'s validation mode

When limiting the pack size, a new header has to be written to the
pack and a new SHA1 computed.  Make sure that the SHA1 of what is being
read back matches the SHA1 of what was written.

Signed-off-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

builtin-pack-objects.c

@@ -492,9 +492,9 @@ static void write_pack_file(void)
 		} else if (nr_written == nr_remaining) {
 			sha1close(f, sha1, CSUM_FSYNC);
 		} else {
-			int fd = sha1close(f, NULL, 0);
+			int fd = sha1close(f, sha1, 0);
 			fixup_pack_header_footer(fd, sha1, pack_tmp_name,
-						 nr_written, NULL, 0);
+						 nr_written, sha1, offset);
 			close(fd);
 		}
 

csum-file.c

@@ -42,11 +42,11 @@ int sha1close(struct sha1file *f, unsigned char *result, unsigned int flags)
 		sha1flush(f, offset);
 		f->offset = 0;
 	}
+	SHA1_Final(f->buffer, &f->ctx);
+	if (result)
+		hashcpy(result, f->buffer);
 	if (flags & (CSUM_CLOSE | CSUM_FSYNC)) {
 		/* write checksum and close fd */
-		SHA1_Final(f->buffer, &f->ctx);
-		if (result)
-			hashcpy(result, f->buffer);
 		sha1flush(f, 20);
 		if (flags & CSUM_FSYNC)
 			fsync_or_die(f->fd, f->name);