Use a clearer style to issue commands to remote helpers

This style is overkill for some commands, but it's worthwhile to use
the same style to issue all commands, and it's useful to avoid
open-coding string lengths.

Signed-off-by: Daniel Barkalow <barkalow@iabervon.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

transport-helper.c

@@ -37,7 +37,10 @@ static struct child_process *get_helper(struct transport *transport)
 		die("Unable to run helper: git %s", helper->argv[0]);
 	data->helper = helper;
 
-	write_in_full(data->helper->in, "capabilities\n", 13);
+	strbuf_addstr(&buf, "capabilities\n");
+	write_in_full(helper->in, buf.buf, buf.len);
+	strbuf_reset(&buf);
+
 	file = fdopen(helper->out, "r");
 	while (1) {
 		if (strbuf_getline(&buf, file, '\n') == EOF)
@@ -78,11 +81,12 @@ static int fetch_with_fetch(struct transport *transport,
 		const struct ref *posn = to_fetch[i];
 		if (posn->status & REF_STATUS_UPTODATE)
 			continue;
-		write_in_full(helper->in, "fetch ", 6);
-		write_in_full(helper->in, sha1_to_hex(posn->old_sha1), 40);
-		write_in_full(helper->in, " ", 1);
-		write_in_full(helper->in, posn->name, strlen(posn->name));
-		write_in_full(helper->in, "\n", 1);
+
+		strbuf_addf(&buf, "fetch %s %s\n",
+			    sha1_to_hex(posn->old_sha1), posn->name);
+		write_in_full(helper->in, buf.buf, buf.len);
+		strbuf_reset(&buf);
+
 		if (strbuf_getline(&buf, file, '\n') == EOF)
 			exit(128); /* child died, message supplied already */
 	}
@@ -119,7 +123,10 @@ static struct ref *get_refs_list(struct transport *transport, int for_push)
 	FILE *file;
 
 	helper = get_helper(transport);
-	write_in_full(helper->in, "list\n", 5);
+
+	strbuf_addstr(&buf, "list\n");
+	write_in_full(helper->in, buf.buf, buf.len);
+	strbuf_reset(&buf);
 
 	file = fdopen(helper->out, "r");
 	while (1) {