From 4d3d475c27432278769280f55fc85bdacb275890 Mon Sep 17 00:00:00 2001
From: kenshinx <kenshin.acs@gmail.com>
Date: Wed, 15 Feb 2017 01:08:08 +0800
Subject: [PATCH] Support for larger UDP DNS responses #30
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As [RFC6891](https://tools.ietf.org/html/rfc6891) define, Extension Mechanisms for DNS(EDNS(0)) can make UDP DNS response packets reach max 65535 bytes and breakthrough the early [RFC1035](‘https://tools.ietf.org/html/rfc1035’) 512 limitation.
---
 godns.conf  | 2 ++
 resolver.go | 4 ++++
 settings.go | 1 +
 3 files changed, 7 insertions(+)

diff --git a/godns.conf b/godns.conf
index 5a23165..9a5e1d4 100644
--- a/godns.conf
+++ b/godns.conf
@@ -18,6 +18,8 @@ timeout = 5  # 5 seconds
 # Match the PR15, https://github.com/kenshinx/godns/pull/15
 interval = 200 # 200 milliseconds
 
+setedns0 = false #Support for larger UDP DNS responses
+
 [redis]
 host = "127.0.0.1"
 port = 6379
diff --git a/resolver.go b/resolver.go
index 2cac6bd..e20b9d8 100644
--- a/resolver.go
+++ b/resolver.go
@@ -34,6 +34,10 @@ func (r *Resolver) Lookup(net string, req *dns.Msg) (message *dns.Msg, err error
 		WriteTimeout: r.Timeout(),
 	}
 
+	if net == "udp" && settings.ResolvConfig.SetEDNS0 {
+		req = req.SetEdns0(65535, true)
+	}
+
 	qname := req.Question[0].Name
 
 	res := make(chan *dns.Msg, 1)
diff --git a/settings.go b/settings.go
index d1a5dfa..2f8d22c 100644
--- a/settings.go
+++ b/settings.go
@@ -37,6 +37,7 @@ type ResolvSettings struct {
 	ResolvFile string `toml:"resolv-file"`
 	Timeout    int
 	Interval   int
+	SetEDNS0   bool
 }
 
 type DNSServerSettings struct {