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// Package httpserver implements an HTTPS server which handles DNS requests
// over HTTPS.
//
// It implements DNS Queries over HTTPS (DoH), as specified in RFC 8484:
// https://tools.ietf.org/html/rfc8484.
package httpserver
import (
"encoding/base64"
"io"
"io/ioutil"
"mime"
"net/http"
"blitiri.com.ar/go/dnss/internal/trace"
"blitiri.com.ar/go/log"
"github.com/miekg/dns"
)
// Server is an HTTPS server that implements DNS over HTTPS, see the
// package-level documentation for more references.
type Server struct {
Addr string
Upstream string
CertFile string
KeyFile string
Insecure bool
}
// ListenAndServe starts the HTTPS server.
func (s *Server) ListenAndServe() {
mux := http.NewServeMux()
mux.HandleFunc("/dns-query", s.Resolve)
mux.HandleFunc("/resolve", s.Resolve)
srv := http.Server{
Addr: s.Addr,
Handler: mux,
}
log.Infof("HTTPS listening on %s", s.Addr)
var err error
if s.Insecure {
err = srv.ListenAndServe()
} else {
err = srv.ListenAndServeTLS(s.CertFile, s.KeyFile)
}
log.Fatalf("HTTPS exiting: %s", err)
}
// Resolve incoming DoH requests.
func (s *Server) Resolve(w http.ResponseWriter, req *http.Request) {
tr := trace.New("httpserver", "/resolve")
defer tr.Finish()
tr.Printf("from:%v", req.RemoteAddr)
tr.Printf("method:%v", req.Method)
req.ParseForm()
// Identify DoH requests:
// - GET requests have a "dns=" query parameter.
// - POST requests have a content-type = application/dns-message.
if req.Method == "GET" && req.FormValue("dns") != "" {
tr.Printf("DoH:GET")
dnsQuery, err := base64.RawURLEncoding.DecodeString(
req.FormValue("dns"))
if err != nil {
tr.Error(err)
http.Error(w, err.Error(), http.StatusBadRequest)
return
}
s.resolveDoH(tr, w, dnsQuery)
return
}
if req.Method == "POST" {
ct, _, err := mime.ParseMediaType(req.Header.Get("Content-Type"))
if err != nil {
tr.Error(err)
http.Error(w, err.Error(), http.StatusBadRequest)
return
}
if ct == "application/dns-message" {
tr.Printf("DoH:POST")
// Limit the size of request to 4k.
dnsQuery, err := ioutil.ReadAll(io.LimitReader(req.Body, 4092))
if err != nil {
tr.Error(err)
http.Error(w, err.Error(), http.StatusBadRequest)
return
}
s.resolveDoH(tr, w, dnsQuery)
return
}
}
// Could not found how to handle this request.
tr.Errorf("unknown request type")
http.Error(w, "unknown request type", http.StatusUnsupportedMediaType)
}
// Resolve DNS over HTTPS requests, as specified in RFC 8484.
func (s *Server) resolveDoH(tr *trace.Trace, w http.ResponseWriter, dnsQuery []byte) {
r := &dns.Msg{}
err := r.Unpack(dnsQuery)
if err != nil {
tr.Error(err)
http.Error(w, err.Error(), http.StatusBadRequest)
return
}
tr.Question(r.Question)
// Do the DNS request, get the reply.
fromUp, err := exchange(tr, r, s.Upstream)
if err != nil {
err = tr.Errorf("dns exchange error: %v", err)
http.Error(w, err.Error(), http.StatusFailedDependency)
return
}
if fromUp == nil {
err = tr.Errorf("no response from upstream")
http.Error(w, err.Error(), http.StatusRequestTimeout)
return
}
tr.Answer(fromUp)
packed, err := fromUp.Pack()
if err != nil {
err = tr.Errorf("cannot pack reply: %v", err)
http.Error(w, err.Error(), http.StatusFailedDependency)
return
}
// Write the response back.
w.Header().Set("Content-type", "application/dns-message")
// TODO: set cache-control based on the response.
w.WriteHeader(http.StatusOK)
w.Write(packed)
}
func exchange(tr *trace.Trace, r *dns.Msg, addr string) (*dns.Msg, error) {
reply, err := dns.Exchange(r, addr)
if err == nil && !reply.Truncated {
tr.Printf("UDP exchange successful")
return reply, err
}
// If we had issues over UDP, or the message was truncated, retry over
// TCP. We don't try beyond that.
if err != nil {
tr.Printf("error on UDP exchange: %v", err)
} else if reply.Truncated {
tr.Printf("UDP exchange returned truncated reply: %v", reply.MsgHdr)
}
tr.Printf("retrying on TCP")
c := &dns.Client{
Net: "tcp",
}
reply, _, err = c.Exchange(r, addr)
return reply, err
}
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