server: debug fixes

Signed-off-by: Jens Axboe <axboe@kernel.dk>
diff --git a/server.c b/server.c
index 8bbac70..79c1041 100644
--- a/server.c
+++ b/server.c
@@ -385,10 +385,11 @@
 {
 	char buffer[1024];
 	va_list args;
+	size_t len;
 
 	va_start(args, format);
-	snprintf(buffer, sizeof(buffer), format, args);
+	len = vsnprintf(buffer, sizeof(buffer), format, args);
 	va_end(args);
 
-	return fio_server_text_output(buffer, strlen(buffer));
+	return fio_server_text_output(buffer, len);
 }