resolve: add CURLOPT_DNS_SHUFFLE_ADDRESSES

This patch adds CURLOPT_DNS_SHUFFLE_ADDRESSES to explicitly request
shuffling of IP addresses returned for a hostname when there is more
than one. This is useful when the application knows that a round robin
approach is appropriate and is willing to accept the consequences of
potentially discarding some preference order returned by the system's
implementation.

Closes #1694

1 files changed, 70 insertions, 0 deletions

diff --git a/tests/unit/unit1608.c b/tests/unit/unit1608.c
new file mode 100644
index 000000000..9ae474ba9
--- /dev/null
+++ b/tests/unit/unit1608.c
@@ -0,0 +1,70 @@
+/***************************************************************************
+ *                                  _   _ ____  _
+ *  Project                     ___| | | |  _ \| |
+ *                             / __| | | | |_) | |
+ *                            | (__| |_| |  _ <| |___
+ *                             \___|\___/|_| \_\_____|
+ *
+ * Copyright (C) 1998 - 2018, Daniel Stenberg, <daniel@haxx.se>, et al.
+ *
+ * This software is licensed as described in the file COPYING, which
+ * you should have received as part of this distribution. The terms
+ * are also available at https://curl.haxx.se/docs/copyright.html.
+ *
+ * You may opt to use, copy, modify, merge, publish, distribute and/or sell
+ * copies of the Software, and permit persons to whom the Software is
+ * furnished to do so, under the terms of the COPYING file.
+ *
+ * This software is distributed on an "AS IS" basis, WITHOUT WARRANTY OF ANY
+ * KIND, either express or implied.
+ *
+ ***************************************************************************/
+#include "curlcheck.h"
+
+#include "hostip.h"
+
+#define NUM_ADDRS 8
+static struct Curl_addrinfo addrs[NUM_ADDRS];
+
+static CURLcode unit_setup(void)
+{
+  int i;
+  for(i = 0; i < NUM_ADDRS - 1; i++) {
+    addrs[i].ai_next = &addrs[i + 1];
+  }
+
+  return CURLE_OK;
+}
+
+static void unit_stop(void)
+{
+
+}
+
+UNITTEST_START
+{
+  int i;
+  CURLcode code;
+  struct Curl_addrinfo* addrhead = addrs;
+
+  struct Curl_easy *easy = curl_easy_init();
+  abort_unless(easy, "out of memory");
+
+  code = curl_easy_setopt(easy, CURLOPT_DNS_SHUFFLE_ADDRESSES, 1L);
+  abort_unless(code == CURLE_OK, "curl_easy_setopt failed");
+
+  /* Shuffle repeatedly and make sure that the list changes */
+  for(i = 0; i < 10; i++) {
+    if(CURLE_OK != Curl_shuffle_addr(easy, &addrhead))
+      break;
+    if(addrhead != addrs)
+      break;
+  }
+
+  curl_easy_cleanup(easy);
+
+  abort_unless(addrhead != addrs, "addresses are not being reordered");
+
+  return 0;
+}
+UNITTEST_STOP