Add some DNS fallthrough functionality.

Author: wrouesnel

Diff for: .travis.yml

@@ -6,15 +6,16 @@ cache:
   - tools/bin
 script:
 - CONCURRENT_LINTERS=1 LINTER_DEADLINE=180s make all
-- tools/bin/goveralls -coverprofile=cover.out -service=travis-ci"
+- tools/bin/goveralls -coverprofile=cover.out -service=travis-ci
 - make release
 deploy:
-  skip_cleanup: true
   provider: releases
   api_key:
-    secure: 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
+    secure: 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
+  skip_cleanup: true
   file_glob: true
-  file: release/*.tar.gz
+  file: release/*
   on:
     tags: true
+    branch: master
     repo: wrouesnel/dns-over-https-proxy

Diff for: Makefile

@@ -97,7 +97,7 @@ lint: tools
 		--enable-all \
 		--line-length=120 \
 		--disable=testify --disable=test --disable=goimports --disable=gofmt \
-		--disable=gotype $(GO_DIRS)
+		--disable=gotype --disable=gocyclo $(GO_DIRS)
 
 fmt: tools
 	gofmt -s -w $(GO_SRC)

Diff for: README.md

@@ -10,7 +10,10 @@ A and AAAA records (as no API to convert them to Go-DNS format is yet written,
 and the Google API is still in flux).
 
 ## Usage
-Just run it!
+Just run it! Remember if you're behind a corporate proxy you will need to set your
+`http_proxy` and `https_proxy` environment variables to contact the Google DNS servers
+through them. It might also be advisable use a local caching proxy in front of this
+if it's going to be a daily driver.
 
 By default it binds to port 53, so if you have a local resolver it will fail to
 start. You can test it by binding to a high port and using dig like so:

Diff for: cmd/dns-over-https-proxy/main.go

@@ -14,10 +14,13 @@ import (
 	"syscall"
 
 	"encoding/json"
-	"fmt"
 	"net"
 	"net/http"
 
+	"strings"
+
+	"fmt"
+
 	"github.com/miekg/dns"
 	"github.com/wrouesnel/go.log"
 )
@@ -28,6 +31,17 @@ var (
 	defaultServer = flag.String("default", "https://dns.google.com/resolve",
 		"DNS-over-HTTPS service endpoint")
 
+	prefixServer = flag.String("primary-dns", "",
+		"If set all DNS queries are attempted against this DNS server first before trying HTTPS")
+
+	suffixServer = flag.String("fallback-dns", "",
+		"If set all failed (i.e. NXDOMAIN and others) DNS queries are attempted against this DNS server after HTTPS fails.") // nolint: lll
+
+	fallthroughStatuses = flag.String("fallthrough-statuses", "NXDOMAIN",
+		"Comma-separated list of statuses which should cause server fallthrough")
+	neverDefault = flag.String("no-fallthrough", "",
+		"Comma-separated list of suffixes which will not be allowed to fallthrough (most useful with prefix DNS")
+
 	//routeList = flag.String("route", "",
 	//	"List of routes where to send queries (subdomain=IP:port)")
 	//routes map[string]string
@@ -157,7 +171,20 @@ func route(w dns.ResponseWriter, req *dns.Msg) {
 	//		return
 	//	}
 	//}
-	proxy(*defaultServer, w, req)
+
+	fallthroughs := make(map[int]struct{})
+	for _, v := range strings.Split(*fallthroughStatuses, ",") {
+		rcode, found := dns.StringToRcode[v]
+		if !found {
+			log.Fatalln("Could not find matching Rcode integer for", v)
+		}
+
+		fallthroughs[rcode] = struct{}{}
+	}
+
+	noFallthrough := strings.Split(*neverDefault, ",")
+
+	proxy(*defaultServer, *prefixServer, *suffixServer, fallthroughs, noFallthrough, w, req)
 }
 
 //func isTransfer(req *dns.Msg) bool {
@@ -183,41 +210,17 @@ func route(w dns.ResponseWriter, req *dns.Msg) {
 //	return false
 //}
 
-func proxy(addr string, w dns.ResponseWriter, req *dns.Msg) {
-	var err error
-	//transport := "udp"
-	//if _, ok := w.RemoteAddr().(*net.TCPAddr); ok {
-	//	transport = "tcp"
-	//}
-	//if isTransfer(req) {
-	//	if transport != "tcp" {
-	//		dns.HandleFailed(w, req)
-	//		return
-	//	}
-	//	t := new(dns.Transfer)
-	//	c, err := t.In(req, addr)
-	//	if err != nil {
-	//		dns.HandleFailed(w, req)
-	//		return
-	//	}
-	//	if err = t.Out(w, req, c); err != nil {
-	//		dns.HandleFailed(w, req)
-	//		return
-	//	}
-	//	return
-	//}
-	//c := &dns.Client{Net: "tcp"}
-	//resp, _, err := c.Exchange(req, addr)
-	//if err != nil {
-	//	dns.HandleFailed(w, req)
-	//	return
-	//}
+func dnsRequestProxy(addr string, transport string, req *dns.Msg) (*dns.Msg, error) {
+	c := &dns.Client{Net: transport}
+	resp, _, err := c.Exchange(req, addr)
+	return resp, err
+}
 
+func httpDNSRequestProxy(addr string, _ string, req *dns.Msg) (*dns.Msg, error) {
 	httpreq, err := http.NewRequest(http.MethodGet, addr, nil)
 	if err != nil {
 		log.Errorln("Error setting up request:", err)
-		dns.HandleFailed(w, req)
-		return
+		return nil, err
 	}
 
 	qry := httpreq.URL.Query()
@@ -233,9 +236,7 @@ func proxy(addr string, w dns.ResponseWriter, req *dns.Msg) {
 
 	httpresp, err := http.DefaultClient.Do(httpreq)
 	if err != nil {
-		log.Errorln("Error sending DNS response:", err)
-		dns.HandleFailed(w, req)
-		return
+		return nil, err
 	}
 	defer httpresp.Body.Close() // nolint: errcheck
 
@@ -244,9 +245,7 @@ func proxy(addr string, w dns.ResponseWriter, req *dns.Msg) {
 	decoder := json.NewDecoder(httpresp.Body)
 	err = decoder.Decode(&dnsResp)
 	if err != nil {
-		log.Errorln("Malformed JSON DNS response:", err)
-		dns.HandleFailed(w, req)
-		return
+		return nil, err
 	}
 
 	// Parse the google Questions to DNS RRs
@@ -298,9 +297,76 @@ func proxy(addr string, w dns.ResponseWriter, req *dns.Msg) {
 		Extra:    extras,
 	}
 
-	// Write the response
-	err = w.WriteMsg(&resp)
-	if err != nil {
-		log.Errorln("Error writing DNS response:", err)
+	return &resp, nil
+}
+
+func isSuccess(fallthroughStatuses map[int]struct{}, resp *dns.Msg) bool {
+	if resp == nil {
+		return false
+	}
+	_, found := fallthroughStatuses[resp.Rcode]
+	return !found
+}
+
+func continueFallthrough(noFallthrough []string, req *dns.Msg) bool {
+	for _, f := range noFallthrough {
+		if f == "" {
+			continue
+		}
+		for _, q := range req.Question {
+			if strings.HasSuffix(q.Name, f) {
+				return false
+			}
+		}
 	}
+	return true
+}
+
+type proxyFunc func() (*dns.Msg, error)
+
+func proxy(addr string, prefixServer string, suffixServer string, fallthroughStatuses map[int]struct{},
+	noFallthrough []string, w dns.ResponseWriter, req *dns.Msg) {
+
+	qryCanFallthrough := continueFallthrough(noFallthrough, req)
+
+	transport := "udp"
+	if _, ok := w.RemoteAddr().(*net.TCPAddr); ok {
+		transport = "tcp"
+	}
+
+	proxyFuncs := []proxyFunc{}
+
+	// If prefix server set, try prefix server...
+	if prefixServer != "" {
+		proxyFuncs = append(proxyFuncs, func() (*dns.Msg, error) { return dnsRequestProxy(prefixServer, transport, req) })
+
+	}
+
+	proxyFuncs = append(proxyFuncs, func() (*dns.Msg, error) { return httpDNSRequestProxy(addr, transport, req) })
+
+	// If prefix server set, try prefix server...
+	if suffixServer != "" {
+		proxyFuncs = append(proxyFuncs, func() (*dns.Msg, error) { return dnsRequestProxy(suffixServer, transport, req) })
+
+	}
+
+	for _, proxyFunc := range proxyFuncs {
+		resp, err := proxyFunc()
+		if err == nil && (isSuccess(fallthroughStatuses, resp) || !qryCanFallthrough) {
+			// Write the response
+			err = w.WriteMsg(resp)
+			if err != nil {
+				log.Errorln("Error writing DNS response:", err)
+				dns.HandleFailed(w, req)
+			}
+			return
+		}
+
+		if !qryCanFallthrough {
+			dns.HandleFailed(w, req)
+			return
+		}
+	}
+
+	dns.HandleFailed(w, req)
 }