commit 55f4814dfb5c196bb66416d4f3ba367498602489 Author: David Fifield david@bamsoftware.com Date: Sun Jul 18 10:39:51 2021 -0600

Change the representation of domain fronting in HTTP rendezvous.

Formerly, BrokerChannel represented the broker URL and possible domain fronting as bc.url *url.URL bc.Host string That is, bc.url is the URL of the server which we contact directly, and bc.Host is the Host header to use in the request. With no domain fronting, bc.url points directly at the broker itself, and bc.Host is blank. With domain fronting, we do the following reshuffling: if front != "" { bc.Host = bc.url.Host bc.url.Host = front } That is, we alter bc.url to reflect that the server to which we send requests directly is the CDN, not the broker, and store the broker's own URL in the HTTP Host header.

The above representation was always confusing to me, because in my mental model, we are always conceptually communicating with the broker; but we may optionally be using a CDN proxy in the middle. The new representation is bc.url *url.URL bc.front string bc.url is the URL of the broker itself, and never changes. bc.front is the optional CDN front domain, and likewise never changes after initialization. When domain fronting is in use, we do the swap in the http.Request struct, not in BrokerChannel itself: if bc.front != "" { request.Host = request.URL.Host request.URL.Host = bc.front }

Compare to the representation in meek-client:

https://gitweb.torproject.org/pluggable-transports/meek.git/tree/meek-client... var options struct { URL string Front string } https://gitweb.torproject.org/pluggable-transports/meek.git/tree/meek-client... if ok { // if front is set info.Host = info.URL.Host info.URL.Host = front } --- client/lib/lib_test.go | 12 ++++++------ client/lib/rendezvous.go | 23 +++++++++++------------ 2 files changed, 17 insertions(+), 18 deletions(-)

diff --git a/client/lib/lib_test.go b/client/lib/lib_test.go index 03c53dd..9087eed 100644 --- a/client/lib/lib_test.go +++ b/client/lib/lib_test.go @@ -172,14 +172,14 @@ func TestSnowflakeClient(t *testing.T) {

Convey("Dialers", t, func() { Convey("Can construct WebRTCDialer.", func() { - broker := &BrokerChannel{Host: "test"} + broker := &BrokerChannel{front: "test"} d := NewWebRTCDialer(broker, nil, 1) So(d, ShouldNotBeNil) So(d.BrokerChannel, ShouldNotBeNil) - So(d.BrokerChannel.Host, ShouldEqual, "test") + So(d.BrokerChannel.front, ShouldEqual, "test") }) SkipConvey("WebRTCDialer can Catch a snowflake.", func() { - broker := &BrokerChannel{Host: "test"} + broker := &BrokerChannel{} d := NewWebRTCDialer(broker, nil, 1) conn, err := d.Catch() So(conn, ShouldBeNil) @@ -201,8 +201,8 @@ func TestSnowflakeClient(t *testing.T) { b, err := NewBrokerChannel("http://test.broker", "", transport, false) So(b.url, ShouldNotBeNil) So(err, ShouldBeNil) - So(b.Host, ShouldResemble, "") So(b.url.Host, ShouldResemble, "test.broker") + So(b.front, ShouldResemble, "") So(b.transport, ShouldNotBeNil) })

@@ -210,8 +210,8 @@ func TestSnowflakeClient(t *testing.T) { b, err := NewBrokerChannel("http://test.broker", "front", transport, false) So(b.url, ShouldNotBeNil) So(err, ShouldBeNil) - So(b.Host, ShouldResemble, "test.broker") - So(b.url.Host, ShouldResemble, "front") + So(b.url.Host, ShouldResemble, "test.broker") + So(b.front, ShouldResemble, "front") So(b.transport, ShouldNotBeNil) })

diff --git a/client/lib/rendezvous.go b/client/lib/rendezvous.go index b89f432..caa4ae4 100644 --- a/client/lib/rendezvous.go +++ b/client/lib/rendezvous.go @@ -32,10 +32,8 @@ const (

// Signalling Channel to the Broker. type BrokerChannel struct { - // The Host header to put in the HTTP request (optional and may be - // different from the host name in URL). - Host string url *url.URL + front string // Optional front domain to replace url.Host in requests. transport http.RoundTripper // Used to make all requests. keepLocalAddresses bool NATType string @@ -61,14 +59,12 @@ func NewBrokerChannel(broker string, front string, transport http.RoundTripper, return nil, err } log.Println("Rendezvous using Broker at:", broker) - bc := new(BrokerChannel) - bc.url = targetURL - if front != "" { // Optional front domain. + if front != "" { log.Println("Domain fronting using:", front) - bc.Host = bc.url.Host - bc.url.Host = front } - + bc := new(BrokerChannel) + bc.url = targetURL + bc.front = front bc.transport = transport bc.keepLocalAddresses = keepLocalAddresses bc.NATType = nat.NATUnknown @@ -92,7 +88,7 @@ func limitedRead(r io.Reader, limit int64) ([]byte, error) { func (bc *BrokerChannel) Negotiate(offer *webrtc.SessionDescription) ( *webrtc.SessionDescription, error) { log.Println("Negotiating via BrokerChannel...\nTarget URL: ", - bc.Host, "\nFront URL: ", bc.url.Host) + bc.url.Host, "\nFront URL: ", bc.front) // Ideally, we could specify an `RTCIceTransportPolicy` that would handle // this for us. However, "public" was removed from the draft spec. // See https://developer.mozilla.org/en-US/docs/Web/API/RTCConfiguration#RTCIceTran... @@ -126,8 +122,11 @@ func (bc *BrokerChannel) Negotiate(offer *webrtc.SessionDescription) ( if nil != err { return nil, err } - if "" != bc.Host { // Set true host if necessary. - request.Host = bc.Host + if bc.front != "" { + // Do domain fronting. Replace the domain in the URL's with the + // front, and store the original domain the HTTP Host header. + request.Host = request.URL.Host + request.URL.Host = bc.front } resp, err := bc.transport.RoundTrip(request) if nil != err {