From 1e6c0ef4d6cfaa5d985c6812286603b25ee420f8 Mon Sep 17 00:00:00 2001
From: Paul Duncan <pabs@pablotron.org>
Date: Mon, 29 Apr 2024 12:02:51 -0400
Subject: add rand-bytes.h

---
 rand-bytes.h | 20 ++++++++++++++++++++
 1 file changed, 20 insertions(+)
 create mode 100644 rand-bytes.h

diff --git a/rand-bytes.h b/rand-bytes.h
new file mode 100644
index 0000000..b9d38d4
--- /dev/null
+++ b/rand-bytes.h
@@ -0,0 +1,20 @@
+#ifndef RAND_BYTES_H
+#define RAND_BYTES_H
+
+#include <stddef.h> // size_t
+#include <sys/random.h> // getrandom()
+#include <err.h> // errx()
+
+// Fill `buf` with `len` random bytes using `getrandom()`.
+//
+// Prints an error and exits with an error code if `len` random bytes
+// could not be read.
+static void rand_bytes(void * const buf, const size_t len) {
+  const ssize_t got = getrandom(buf, len, 0);
+  if (got < (ssize_t) len) {
+    // print error message, exit with error
+    errx(-1, "getrandom() failed");
+  }
+}
+
+#endif /* RAND_BYTES_H */
-- 
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