From 5b2d8ffb5a1ebbd1e7c5359a9b924454f9dac031 Mon Sep 17 00:00:00 2001
From: Lennart Poettering <lennart@poettering.net>
Date: Thu, 5 Nov 2020 13:33:52 +0100
Subject: [PATCH] answer: add helper for randomizing RR of answers

---
 src/resolve/resolved-dns-answer.c | 21 +++++++++++++++++++++
 src/resolve/resolved-dns-answer.h |  2 ++
 2 files changed, 23 insertions(+)

diff --git a/src/resolve/resolved-dns-answer.c b/src/resolve/resolved-dns-answer.c
index 051a2a0f25..8591ed0f3b 100644
--- a/src/resolve/resolved-dns-answer.c
+++ b/src/resolve/resolved-dns-answer.c
@@ -4,6 +4,7 @@
 
 #include "alloc-util.h"
 #include "dns-domain.h"
+#include "random-util.h"
 #include "resolved-dns-answer.h"
 #include "resolved-dns-dnssec.h"
 #include "string-util.h"
@@ -898,3 +899,23 @@ int dns_answer_has_dname_for_cname(DnsAnswer *a, DnsResourceRecord *cname) {
 
         return 0;
 }
+
+void dns_answer_randomize(DnsAnswer *a) {
+        size_t n;
+
+        /* Permutes the answer list randomly (Knuth shuffle) */
+
+        n = dns_answer_size(a);
+        if (n <= 1)
+                return;
+
+        for (size_t i = 0; i < n; i++) {
+                size_t k;
+
+                k = random_u64_range(n);
+                if (k == i)
+                        continue;
+
+                SWAP_TWO(a->items[i], a->items[k]);
+        }
+}
diff --git a/src/resolve/resolved-dns-answer.h b/src/resolve/resolved-dns-answer.h
index cc2cd93a33..f90ca67019 100644
--- a/src/resolve/resolved-dns-answer.h
+++ b/src/resolve/resolved-dns-answer.h
@@ -80,6 +80,8 @@ static inline bool dns_answer_isempty(DnsAnswer *a) {
 
 void dns_answer_dump(DnsAnswer *answer, FILE *f);
 
+void dns_answer_randomize(DnsAnswer *a);
+
 DEFINE_TRIVIAL_CLEANUP_FUNC(DnsAnswer*, dns_answer_unref);
 
 #define _DNS_ANSWER_FOREACH(q, kk, a)                                   \
-- 
2.25.1