upstream: add xextendf() to extend a string with a format

(reallocating as necessary). ok aja@ as part of a larger diff

OpenBSD-Commit-ID: 30796b50d330b3e0e201747fe40cdf9aa70a77f9

1 files changed, 28 insertions, 1 deletions

diff --git a/misc.c b/misc.c
index f25b8cf5c..74e01a4c0 100644
--- a/misc.c
+++ b/misc.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: misc.c,v 1.144 2020/01/23 07:10:22 dtucker Exp $ */
+/* $OpenBSD: misc.c,v 1.145 2020/01/24 23:54:40 djm Exp $ */
 /*
  * Copyright (c) 2000 Markus Friedl.  All rights reserved.
  * Copyright (c) 2005,2006 Damien Miller.  All rights reserved.
@@ -1244,6 +1244,33 @@ tohex(const void *vp, size_t l)
         return (r);
 }
 
+/*
+ * Extend string *sp by the specified format. If *sp is not NULL (or empty),
+ * then the separator 'sep' will be prepended before the formatted arguments.
+ * Extended strings are heap allocated.
+ */
+void
+xextendf(char **sp, const char *sep, const char *fmt, ...)
+{
+        va_list ap;
+        char *tmp1, *tmp2;
+
+        va_start(ap, fmt);
+        xvasprintf(&tmp1, fmt, ap);
+        va_end(ap);
+
+        if (*sp == NULL || **sp == '\0') {
+                free(*sp);
+                *sp = tmp1;
+                return;
+        }
+        xasprintf(&tmp2, "%s%s%s", *sp, sep == NULL ? "" : sep, tmp1);
+        free(tmp1);
+        free(*sp);
+        *sp = tmp2;
+}
+
+
 u_int64_t
 get_u64(const void *vp)
 {