Re: [9front] [PATCH] git/fs: remove trailing null bytes from parent file

[ori@eigenstate.org]

Quoth Michael Forney <mforney@mforney.org>:
> 
> Previously, due to the way the size of buf was calculated, the parent
> file had one trailing null byte for each parent.
> ---
> diff 370bfd26ce5ffd9a06a314a20d1691cc6b15b712 2a5737d2ef4ea7920f6d4e5f47487837568b751c
> --- a/sys/src/cmd/git/fs.c	Wed Jan  5 22:38:56 2022
> +++ b/sys/src/cmd/git/fs.c	Thu Jan  6 00:52:21 2022
> @@ -380,8 +380,8 @@
>  	char *buf, *p;
>  	int i, n;
>  
> -	n = o->commit->nparent * (40 + 2);
> -	buf = emalloc(n);
> +	n = o->commit->nparent * (40 + 1);
> +	buf = emalloc(n + 1);
>  	p = buf;
>  	for (i = 0; i < o->commit->nparent; i++)
>  		p += sprint(p, "%H\n", o->commit->parent[i]);
> 

I think this needs to be:

	n = o->commit->nparent * (40 + 1) + 1;

because we need 41 bytes per line *and* room
for the trailing nul.

While we're here, let's nuke the sprint, and
compute the number of bytes we wrote in.

diff 370bfd26ce5ffd9a06a314a20d1691cc6b15b712 uncommitted
--- a/sys/src/cmd/git/fs.c
+++ b/sys/src/cmd/git/fs.c
@@ -377,18 +377,18 @@
 static void
 readcommitparent(Req *r, Object *o)
 {
-	char *buf, *p;
+	char *buf, *p, *e;
 	int i, n;
 
-	n = o->commit->nparent * (40 + 2);
+	n = o->commit->nparent * (40 + 1) + 1;
 	buf = emalloc(n);
 	p = buf;
+	e = buf + n;
 	for (i = 0; i < o->commit->nparent; i++)
-		p += sprint(p, "%H\n", o->commit->parent[i]);
-	readbuf(r, buf, n);
+		p = seprint(p, e, "%H\n", o->commit->parent[i]);
+	readbuf(r, buf, p - buf);
 	free(buf);
 }
-