1 files changed, 57 insertions, 0 deletions
diff --git a/lib/libutil++/stringf.cc b/lib/libutil++/stringf.cc
new file mode 100644
index 000000000000..8c24167d70ac
--- /dev/null
+++ b/lib/libutil++/stringf.cc
@@ -0,0 +1,57 @@
+/*-
+ * SPDX-License-Identifier: BSD-2-Clause
+ *
+ * Copyright (c) 2025 Chelsio Communications, Inc.
+ * Written by: John Baldwin <jhb@FreeBSD.org>
+ */
+
+#include <cstdarg>
+#include <cstdio>
+#include <string>
+
+#include "libutil++.hh"
+
+static int
+stringf_write(void *cookie, const char *buf, int len)
+{
+	std::string *str = reinterpret_cast<std::string *>(cookie);
+	try {
+		str->append(buf, len);
+	} catch (std::bad_alloc) {
+		errno = ENOMEM;
+		return (-1);
+	} catch (std::length_error) {
+		errno = EFBIG;
+		return (-1);
+	}
+	return (len);
+}
+
+std::string
+freebsd::stringf(const char *fmt, va_list ap)
+{
+	std::string str;
+	freebsd::FILE_up fp(fwopen(reinterpret_cast<void *>(&str),
+	    stringf_write));
+
+	vfprintf(fp.get(), fmt, ap);
+
+	if (ferror(fp.get()))
+		throw std::bad_alloc();
+	fp.reset(nullptr);
+
+	return str;
+}
+
+std::string
+freebsd::stringf(const char *fmt, ...)
+{
+	std::va_list ap;
+	std::string str;
+
+	va_start(ap, fmt);
+	str = freebsd::stringf(fmt, ap);
+	va_end(ap);
+
+	return str;
+}