From 363b2dca3746c0e6a5b519b6e375a5f44799e695 Mon Sep 17 00:00:00 2001
From: ValdikSS <iam@valdikss.org.ru>
Date: Thu, 7 Dec 2017 22:38:21 +0300
Subject: [PATCH] Flush DNS cache if --dns-addr is used

---
 dnsredir.c   | 16 ++++++++++++++++
 dnsredir.h   |  2 ++
 goodbyedpi.c |  1 +
 3 files changed, 19 insertions(+)

diff --git a/dnsredir.c b/dnsredir.c
index 3ba931d..c530592 100644
--- a/dnsredir.c
+++ b/dnsredir.c
@@ -50,6 +50,22 @@ typedef struct udp_connrecord {
 static time_t last_cleanup = 0;
 static udp_connrecord_t *conntrack = NULL;
 
+void flush_dns_cache() {
+    BOOL WINAPI (*DnsFlushResolverCache)();
+
+    HMODULE dnsapi = LoadLibrary("dnsapi.dll");
+    if (dnsapi == NULL)
+    {
+        printf("Can't load dnsapi.dll to flush DNS cache!\n");
+        exit(EXIT_FAILURE);
+    }
+
+    DnsFlushResolverCache = GetProcAddress(dnsapi, "DnsFlushResolverCache");
+    if (DnsFlushResolverCache == NULL || !DnsFlushResolverCache())
+        printf("Can't flush DNS cache!");
+    FreeLibrary(dnsapi);
+}
+
 inline static void construct_key(const uint32_t srcip, const uint16_t srcport, char *key) {
     debug("Construct key enter\n");
     if (key) {
diff --git a/dnsredir.h b/dnsredir.h
index 013048f..f23215c 100644
--- a/dnsredir.h
+++ b/dnsredir.h
@@ -15,3 +15,5 @@ int dns_handle_incoming(const uint32_t srcip, const uint16_t srcport,
 int dns_handle_outgoing(const uint32_t srcip, const uint16_t srcport,
                         const uint32_t dstip, const uint16_t dstport,
                         const char *packet_data, const UINT packet_dataLen);
+
+void flush_dns_cache();
diff --git a/goodbyedpi.c b/goodbyedpi.c
index 8178046..e9bb413 100644
--- a/goodbyedpi.c
+++ b/goodbyedpi.c
@@ -337,6 +337,7 @@ int main(int argc, char *argv[]) {
                         exit(EXIT_FAILURE);
                     }
                     add_filter_str(IPPROTO_UDP, 53);
+                    flush_dns_cache();
                 }
                 break;
             case 'g':