From 7d42a95d1206db12ccd2ce7ab2f1e3d483e66ba1 Mon Sep 17 00:00:00 2001
From: Peter Hutterer <peter.hutterer@who-t.net>
Date: Fri, 17 Apr 2026 18:50:49 +1000
Subject: [PATCH] util: replace strcat memcpy in strv_join

Repeatedly using strcat means we rescan the string, making it O(n^2).
Use memcpy and an offset instead because we can't affort to waste
nanoseconds here.

Assisted-by: Claude:claude-opus-4-6
Part-of: <https://gitlab.freedesktop.org/libinput/libei/-/merge_requests/388>
---
 src/util-strings.c | 12 +++++++++---
 1 file changed, 9 insertions(+), 3 deletions(-)

diff --git a/src/util-strings.c b/src/util-strings.c
index 41c1d95..6e6140a 100644
--- a/src/util-strings.c
+++ b/src/util-strings.c
@@ -150,11 +150,17 @@ strv_join(char **strv, const char *joiner)
 	slen += (count - 1) * strlen(joiner);
 
 	str = xalloc(slen + 1); /* trailing \0 */
+	size_t jlen = strlen(joiner);
+	size_t offset = 0;
 	for (s = strv; *s; s++) {
-		strcat(str, *s);
+		size_t l = strlen(*s);
+		memcpy(str + offset, *s, l);
+		offset += l;
 		--count;
-		if (count > 0)
-			strcat(str, joiner);
+		if (count > 0) {
+			memcpy(str + offset, joiner, jlen);
+			offset += jlen;
+		}
 	}
 
 	return str;