Return 200 on join before time out (#1493)

* Return 200 on join afer 15 seconds if nothing better has happened by that point

* Return 202 instead, 20 second timeout

clientapi/routing/joinroom.go

@@ -16,9 +16,11 @@ package routing
 
 import (
 	"net/http"
+	"time"
 
 	"github.com/matrix-org/dendrite/clientapi/auth/authtypes"
 	"github.com/matrix-org/dendrite/clientapi/httputil"
+	"github.com/matrix-org/dendrite/clientapi/jsonerror"
 	roomserverAPI "github.com/matrix-org/dendrite/roomserver/api"
 	"github.com/matrix-org/dendrite/userapi/api"
 	"github.com/matrix-org/dendrite/userapi/storage/accounts"
@@ -74,16 +76,32 @@ func JoinRoomByIDOrAlias(
 	}
 
 	// Ask the roomserver to perform the join.
+	done := make(chan util.JSONResponse, 1)
+	go func() {
+		defer close(done)
 		rsAPI.PerformJoin(req.Context(), &joinReq, &joinRes)
 		if joinRes.Error != nil {
-		return joinRes.Error.JSONResponse()
+			done <- joinRes.Error.JSONResponse()
-	}
+		} else {
-
+			done <- util.JSONResponse{
-	return util.JSONResponse{
 				Code: http.StatusOK,
 				// TODO: Put the response struct somewhere internal.
 				JSON: struct {
 					RoomID string `json:"room_id"`
 				}{joinRes.RoomID},
 			}
+		}
+	}()
+
+	// Wait either for the join to finish, or for us to hit a reasonable
+	// timeout, at which point we'll just return a 200 to placate clients.
+	select {
+	case <-time.After(time.Second * 20):
+		return util.JSONResponse{
+			Code: http.StatusAccepted,
+			JSON: jsonerror.Unknown("The room join will continue in the background."),
+		}
+	case result := <-done:
+		return result
+	}
 }