From 776e0d7ccc70a446a9a06edde936a09d246b704f Mon Sep 17 00:00:00 2001
From: Frank Denis <github@pureftpd.org>
Date: Sat, 7 Sep 2019 16:19:47 +0200
Subject: [PATCH] New feature: query_meta

---
 ChangeLog                                  |  2 +
 dnscrypt-proxy/config.go                   |  3 ++
 dnscrypt-proxy/example-dnscrypt-proxy.toml |  8 ++++
 dnscrypt-proxy/plugin_querymeta.go         | 43 ++++++++++++++++++++++
 dnscrypt-proxy/plugins.go                  |  4 ++
 dnscrypt-proxy/proxy.go                    |  1 +
 6 files changed, 61 insertions(+)
 create mode 100644 dnscrypt-proxy/plugin_querymeta.go

diff --git a/ChangeLog b/ChangeLog
index 7e940caf..1d820792 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -15,6 +15,8 @@ hashes.
  - DoH servers on a non-standard port, with stamps that don't include
 IP addresses, and without working system resolvers can now be properly
 bootstrapped.
+ - A new option, `query_meta`, is now available to add optional records
+to client queries.
 
 * Version 2.0.25
  - The example IP address for network probes didn't work on Windows.
diff --git a/dnscrypt-proxy/config.go b/dnscrypt-proxy/config.go
index 7f65fda7..0dadc621 100644
--- a/dnscrypt-proxy/config.go
+++ b/dnscrypt-proxy/config.go
@@ -82,6 +82,7 @@ type Config struct {
 	HTTPProxyURL             string                     `toml:"http_proxy"`
 	RefusedCodeInResponses   bool                       `toml:"refused_code_in_responses"`
 	BlockedQueryResponse     string                     `toml:"blocked_query_response"`
+	QueryMeta                []string                   `toml:"query_meta"`
 }
 
 func newConfig() Config {
@@ -351,6 +352,8 @@ func ConfigLoad(proxy *Proxy, svcFlag *string) error {
 	proxy.cacheMinTTL = config.CacheMinTTL
 	proxy.cacheMaxTTL = config.CacheMaxTTL
 
+	proxy.queryMeta = config.QueryMeta
+
 	if len(config.QueryLog.Format) == 0 {
 		config.QueryLog.Format = "tsv"
 	} else {
diff --git a/dnscrypt-proxy/example-dnscrypt-proxy.toml b/dnscrypt-proxy/example-dnscrypt-proxy.toml
index f54875a7..8455f8dd 100644
--- a/dnscrypt-proxy/example-dnscrypt-proxy.toml
+++ b/dnscrypt-proxy/example-dnscrypt-proxy.toml
@@ -230,6 +230,14 @@ netprobe_address = '9.9.9.9:53'
 # offline_mode = false
 
 
+## Additional data to attach to outgoing queries.
+## These strings will be added as TXT records to queries.
+## Do not use, except on servers explicitly asking for extra data
+## to be present.
+
+# query_meta = ["key1:value1", "key2:value2", "key3:value3"]
+
+
 ## Automatic log files rotation
 
 # Maximum log files size in MB
diff --git a/dnscrypt-proxy/plugin_querymeta.go b/dnscrypt-proxy/plugin_querymeta.go
new file mode 100644
index 00000000..68398f31
--- /dev/null
+++ b/dnscrypt-proxy/plugin_querymeta.go
@@ -0,0 +1,43 @@
+package main
+
+import (
+	"github.com/miekg/dns"
+)
+
+type PluginQueryMeta struct {
+	queryMetaRR *dns.TXT
+}
+
+func (plugin *PluginQueryMeta) Name() string {
+	return "query_log"
+}
+
+func (plugin *PluginQueryMeta) Description() string {
+	return "Log DNS queries."
+}
+
+func (plugin *PluginQueryMeta) Init(proxy *Proxy) error {
+	queryMetaRR := new(dns.TXT)
+	queryMetaRR.Hdr = dns.RR_Header{Name: ".", Rrtype: dns.TypeTXT,
+		Class: dns.ClassINET, Ttl: 86400}
+	queryMetaRR.Txt = proxy.queryMeta
+	plugin.queryMetaRR = queryMetaRR
+	return nil
+}
+
+func (plugin *PluginQueryMeta) Drop() error {
+	return nil
+}
+
+func (plugin *PluginQueryMeta) Reload() error {
+	return nil
+}
+
+func (plugin *PluginQueryMeta) Eval(pluginsState *PluginsState, msg *dns.Msg) error {
+	questions := msg.Question
+	if len(questions) == 0 {
+		return nil
+	}
+	msg.Extra = []dns.RR{plugin.queryMetaRR}
+	return nil
+}
diff --git a/dnscrypt-proxy/plugins.go b/dnscrypt-proxy/plugins.go
index b678e577..4cb78683 100644
--- a/dnscrypt-proxy/plugins.go
+++ b/dnscrypt-proxy/plugins.go
@@ -83,6 +83,10 @@ type PluginsState struct {
 
 func InitPluginsGlobals(pluginsGlobals *PluginsGlobals, proxy *Proxy) error {
 	queryPlugins := &[]Plugin{}
+
+	if len(proxy.queryMeta) != 0 {
+		*queryPlugins = append(*queryPlugins, Plugin(new(PluginQueryMeta)))
+	}
 	if len(proxy.whitelistNameFile) != 0 {
 		*queryPlugins = append(*queryPlugins, Plugin(new(PluginWhitelistName)))
 	}
diff --git a/dnscrypt-proxy/proxy.go b/dnscrypt-proxy/proxy.go
index d639acea..ad3d1d7d 100644
--- a/dnscrypt-proxy/proxy.go
+++ b/dnscrypt-proxy/proxy.go
@@ -64,6 +64,7 @@ type Proxy struct {
 	logMaxAge                    int
 	logMaxBackups                int
 	blockedQueryResponse         string
+	queryMeta                    []string
 	showCerts                    bool
 }