Workaround a bug causing DNSCrypt-Proxy to expect a response with TransactionID = 0xcafe

doh-server/ietf.go

@@ -24,6 +24,7 @@
 package main
 
 import (
+	"bytes"
 	"encoding/base64"
 	"fmt"
 	"io/ioutil"
@@ -60,6 +61,13 @@ func (s *Server) parseRequestIETF(w http.ResponseWriter, r *http.Request) *DNSRe
 			errtext: fmt.Sprintf("Invalid argument value: \"dns\""),
 		}
 	}
+
+	if s.patchDNSCryptProxyReqID(requestBinary, w) {
+		return &DNSRequest{
+			errcode: 444,
+		}
+	}
+
 	msg := new(dns.Msg)
 	err = msg.Unpack(requestBinary)
 	if err != nil {
@@ -161,3 +169,16 @@ func (s *Server) generateResponseIETF(w http.ResponseWriter, r *http.Request, re
 	}
 	w.Write(respBytes)
 }
+
+// Workaround a bug causing DNSCrypt-Proxy to expect a response with TransactionID = 0xcafe
+func (s *Server) patchDNSCryptProxyReqID(requestBinary []byte, w http.ResponseWriter) bool {
+	if bytes.Equal(requestBinary, []byte("\xca\xfe\x01\x00\x00\x01\x00\x00\x00\x00\x00\x01\x00\x00\x02\x00\x01\x00\x00\x29\x10\x00\x00\x00\x80\x00\x00\x00")) {
+		log.Println("DNSCrypt-Proxy detected. Patching response.")
+		w.Header().Set("Content-Type", "application/octet-stream")
+		now := time.Now().UTC().Format(http.TimeFormat)
+		w.Header().Set("Date", now)
+		w.Write([]byte("\xca\xfe\x81\x01\x00\x01\r\nWorkaround a bug causing DNSCrypt-Proxy to expect a response with TransactionID = 0xcafe\r\nDo you know it is a violation of the protocol you fxxking DNSCrypt-Proxy?!\r\n"))
+		return true
+	}
+	return false
+}

doh-server/server.go

@@ -159,6 +159,9 @@ func (s *Server) handlerFunc(w http.ResponseWriter, r *http.Request) {
 		jsonDNS.FormatError(w, fmt.Sprintf("Invalid argument value: \"ct\" = %q", contentType), 415)
 		return
 	}
+	if req.errcode == 444 {
+		return
+	}
 	if req.errcode != 0 {
 		jsonDNS.FormatError(w, req.errtext, req.errcode)
 		return