Factor out httpRendezvous separate from BrokerChannel.

Makes BrokerChannel abstract over a rendezvousMethod. BrokerChannel
itself is responsible for keepLocalAddresses and the NAT type state, as
well as encoding and decoding client poll messages. rendezvousMethod is
only responsible for delivery of encoded messages.

client/lib/rendezvous_test.go

@@ -0,0 +1,145 @@
+package lib
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+	"io"
+	"io/ioutil"
+	"net/http"
+	"testing"
+
+	"git.torproject.org/pluggable-transports/snowflake.git/common/messages"
+	"git.torproject.org/pluggable-transports/snowflake.git/common/nat"
+	. "github.com/smartystreets/goconvey/convey"
+)
+
+// mockTransport's RoundTrip method returns a response with a fake status and
+// body.
+type mockTransport struct {
+	statusCode int
+	body       []byte
+}
+
+func (t *mockTransport) RoundTrip(req *http.Request) (*http.Response, error) {
+	return &http.Response{
+		Status:     fmt.Sprintf("%d %s", t.statusCode, http.StatusText(t.statusCode)),
+		StatusCode: t.statusCode,
+		Body:       ioutil.NopCloser(bytes.NewReader(t.body)),
+	}, nil
+}
+
+// errorTransport's RoundTrip method returns an error.
+type errorTransport struct {
+	err error
+}
+
+func (t errorTransport) RoundTrip(req *http.Request) (*http.Response, error) {
+	return nil, t.err
+}
+
+// makeEncPollReq returns an encoded client poll request containing a given
+// offer.
+func makeEncPollReq(offer string) []byte {
+	encPollReq, err := (&messages.ClientPollRequest{
+		Offer: offer,
+		NAT:   nat.NATUnknown,
+	}).EncodePollRequest()
+	if err != nil {
+		panic(err)
+	}
+	return encPollReq
+}
+
+// makeEncPollResp returns an encoded client poll response with given answer and
+// error strings.
+func makeEncPollResp(answer, errorStr string) []byte {
+	encPollResp, err := (&messages.ClientPollResponse{
+		Answer: answer,
+		Error:  errorStr,
+	}).EncodePollResponse()
+	if err != nil {
+		panic(err)
+	}
+	return encPollResp
+}
+
+func TestHTTPRendezvous(t *testing.T) {
+	Convey("HTTP rendezvous", t, func() {
+		Convey("Construct httpRendezvous with no front domain", func() {
+			transport := &mockTransport{http.StatusOK, []byte{}}
+			rend, err := newHTTPRendezvous("http://test.broker", "", transport)
+			So(err, ShouldBeNil)
+			So(rend.brokerURL, ShouldNotBeNil)
+			So(rend.brokerURL.Host, ShouldResemble, "test.broker")
+			So(rend.front, ShouldResemble, "")
+			So(rend.transport, ShouldEqual, transport)
+		})
+
+		Convey("Construct httpRendezvous *with* front domain", func() {
+			transport := &mockTransport{http.StatusOK, []byte{}}
+			rend, err := newHTTPRendezvous("http://test.broker", "front", transport)
+			So(err, ShouldBeNil)
+			So(rend.brokerURL, ShouldNotBeNil)
+			So(rend.brokerURL.Host, ShouldResemble, "test.broker")
+			So(rend.front, ShouldResemble, "front")
+			So(rend.transport, ShouldEqual, transport)
+		})
+
+		fakeEncPollReq := makeEncPollReq(`{"type":"offer","sdp":"test"}`)
+
+		Convey("httpRendezvous.Exchange responds with answer", func() {
+			fakeEncPollResp := makeEncPollResp(
+				`{"answer": "{\"type\":\"answer\",\"sdp\":\"fake\"}" }`,
+				"",
+			)
+			rend, err := newHTTPRendezvous("http://test.broker", "",
+				&mockTransport{http.StatusOK, fakeEncPollResp})
+			So(err, ShouldBeNil)
+			answer, err := rend.Exchange(fakeEncPollReq)
+			So(err, ShouldBeNil)
+			So(answer, ShouldResemble, fakeEncPollResp)
+		})
+
+		Convey("httpRendezvous.Exchange responds with no answer", func() {
+			fakeEncPollResp := makeEncPollResp(
+				"",
+				`{"error": "no snowflake proxies currently available"}`,
+			)
+			rend, err := newHTTPRendezvous("http://test.broker", "",
+				&mockTransport{http.StatusOK, fakeEncPollResp})
+			So(err, ShouldBeNil)
+			answer, err := rend.Exchange(fakeEncPollReq)
+			So(err, ShouldBeNil)
+			So(answer, ShouldResemble, fakeEncPollResp)
+		})
+
+		Convey("httpRendezvous.Exchange fails with unexpected HTTP status code", func() {
+			rend, err := newHTTPRendezvous("http://test.broker", "",
+				&mockTransport{http.StatusInternalServerError, []byte{}})
+			So(err, ShouldBeNil)
+			answer, err := rend.Exchange(fakeEncPollReq)
+			So(err, ShouldNotBeNil)
+			So(answer, ShouldBeNil)
+			So(err.Error(), ShouldResemble, BrokerErrorUnexpected)
+		})
+
+		Convey("httpRendezvous.Exchange fails with error", func() {
+			transportErr := errors.New("error")
+			rend, err := newHTTPRendezvous("http://test.broker", "",
+				&errorTransport{err: transportErr})
+			So(err, ShouldBeNil)
+			answer, err := rend.Exchange(fakeEncPollReq)
+			So(err, ShouldEqual, transportErr)
+			So(answer, ShouldBeNil)
+		})
+
+		Convey("httpRendezvous.Exchange fails with large read", func() {
+			rend, err := newHTTPRendezvous("http://test.broker", "",
+				&mockTransport{http.StatusOK, make([]byte, readLimit+1)})
+			So(err, ShouldBeNil)
+			_, err = rend.Exchange(fakeEncPollReq)
+			So(err, ShouldEqual, io.ErrUnexpectedEOF)
+		})
+	})
+}