Use random port for application service

internal/b/blueprints.go

@@ -18,10 +18,16 @@ import (
 	"crypto/rand"
 	"encoding/hex"
 	"fmt"
+	"net"
 	"strconv"
 	"strings"
 )
 
+var (
+	// HostnameRunningComplement is the hostname of Complement from the perspective of a Homeserver.
+	HostnameRunningComplement = "host.docker.internal"
+)
+
 // KnownBlueprints lists static blueprints
 var KnownBlueprints = map[string]*Blueprint{
 	BlueprintCleanHS.Name:                     &BlueprintCleanHS,
@@ -190,6 +196,22 @@ func normaliseUser(u string, hsName string) (string, error) {
 	return u, nil
 }
 
+// Asks the kernel for a free open port that is ready to use.
+// via https://github.com/phayes/freeport/blob/95f893ade6f232a5f1511d61735d89b1ae2df543/freeport.go#L7-L20
+func getFreePort() (int, error) {
+	addr, err := net.ResolveTCPAddr("tcp", "localhost:0")
+	if err != nil {
+		return 0, err
+	}
+
+	l, err := net.ListenTCP("tcp", addr)
+	if err != nil {
+		return 0, err
+	}
+	defer l.Close()
+	return l.Addr().(*net.TCPAddr).Port, nil
+}
+
 func normalizeApplicationService(as ApplicationService) (ApplicationService, error) {
 	hsToken := make([]byte, 32)
 	_, err := rand.Read(hsToken)
@@ -206,6 +228,18 @@ func normalizeApplicationService(as ApplicationService) (ApplicationService, err
 	as.HSToken = hex.EncodeToString(hsToken)
 	as.ASToken = hex.EncodeToString(asToken)
 
+	if as.URL == "" {
+		// Since, we're just checking and not reserving the port, we could
+		// potentially run into an issue where the port is no longer available when
+		// we actually try to bind to it later on
+		port, err := getFreePort()
+		if err != nil {
+			return as, err
+		}
+
+		as.URL = fmt.Sprintf("http://%s:%d", HostnameRunningComplement, port)
+	}
+
 	return as, err
 }
 

internal/b/hs_with_application_service.go

@@ -15,7 +15,6 @@ var BlueprintHSWithApplicationService = MustValidate(Blueprint{
 			ApplicationServices: []ApplicationService{
 				{
 					ID:              "my_as_id",
-					URL:             "http://host.docker.internal:9111",
 					SenderLocalpart: "the-bridge-user",
 					RateLimited:     false,
 				},

tests/msc2716_test.go

@@ -13,6 +13,7 @@ import (
 	"io/ioutil"
 	"net/http"
 	"net/url"
+	"regexp"
 	"testing"
 	"time"
 
@@ -60,6 +61,9 @@ var createPrivateRoomOpts = map[string]interface{}{
 	"room_version": "org.matrix.msc2716v3",
 }
 
+// Find the URL and port of the application service in some registration yaml text
+var asURLRegexp = regexp.MustCompile(`url: '(.+):(\d+)'`)
+
 func TestImportHistoricalMessages(t *testing.T) {
 	deployment := Deploy(t, b.BlueprintHSWithApplicationService)
 	defer deployment.Destroy(t)
@@ -312,6 +316,13 @@ func TestImportHistoricalMessages(t *testing.T) {
 		t.Run("Historical events from batch_send do not get pushed out as application service transactions", func(t *testing.T) {
 			t.Parallel()
 
+			asRegistration := deployment.HS["hs1"].ApplicationServices["my_as_id"]
+			asURLMatches := asURLRegexp.FindStringSubmatch(asRegistration)
+			if asURLMatches == nil {
+				t.Fatalf("Unable to find application service `url` in registration=%s", asRegistration)
+			}
+			asPort := asURLMatches[2]
+
 			// Create a listener and handler to stub an application service listening
 			// for transactions from a homeserver.
 			handler := mux.NewRouter()
@@ -343,13 +354,22 @@ func TestImportHistoricalMessages(t *testing.T) {
 			}).Methods("PUT")
 
 			srv := &http.Server{
-				Addr:    ":9111",
+				Addr:    fmt.Sprintf(":%s", asPort),
 				Handler: handler,
 			}
 			go func() {
-				srv.ListenAndServe()
+				if err := srv.ListenAndServe(); err != http.ErrServerClosed {
+					// Note that running s.t.FailNow is not allowed in a separate goroutine
+					// Tests will likely fail if the server is not listening anyways
+					t.Logf("Failed to listen and serve our fake application service: %s", err)
+				}
+			}()
+			defer func() {
+				err := srv.Shutdown(context.Background())
+				if err != nil {
+					t.Fatalf("Failed to shutdown our fake application service: %s", err)
+				}
 			}()
-			defer srv.Shutdown(context.Background())
 			// ----------------------------------------------------------
 
 			// Create the room all of the action is going to happen in