Fix creating rooms when the default is set to v12 (#3670)

This should fix https://github.com/element-hq/dendrite/issues/3669
We'd potentially send an empty string to `GenerateCreateContent`, even
if we set the correct `roomVersion` before.

### Pull Request Checklist

<!-- Please read
https://matrix-org.github.io/dendrite/development/contributing before
submitting your pull request -->

* [x] I have added Go unit tests or [Complement integration
tests](https://github.com/matrix-org/complement) for this PR _or_ I have
justified why this PR doesn't need tests
* [x] Pull request includes a [sign off
below](https://element-hq.github.io/dendrite/development/contributing#sign-off)
_or_ I have already signed off privately

---------

Signed-off-by: Till Faelligen <2353100+S7evinK@users.noreply.github.com>

clientapi/routing/createroom.go

@@ -200,7 +200,7 @@ func createRoom(
 		if createRequest.Preset == spec.PresetTrustedPrivateChat {
 			additionalCreators = createRequest.Invite
 		}
-		createContent, err := roomserverAPI.GenerateCreateContent(ctx, createRequest.RoomVersion, userID.String(), createRequest.CreationContent, additionalCreators)
+		createContent, err := roomserverAPI.GenerateCreateContent(ctx, roomVersion, userID.String(), createRequest.CreationContent, additionalCreators)
 		if err != nil {
 			util.GetLogger(ctx).WithError(err).Error("GenerateCreateContent failed")
 			return util.JSONResponse{

federationapi/routing/backfill.go

@@ -37,7 +37,7 @@ func Backfill(
 	var err error
 
 	// Check the room ID's format.
-	if _, _, err = gomatrixserverlib.SplitID('!', roomID); err != nil {
+	if _, err = spec.NewRoomID(roomID); err != nil {
 		return util.JSONResponse{
 			Code: http.StatusBadRequest,
 			JSON: spec.MissingParam("Bad room ID: " + err.Error()),

federationapi/routing/threepid.go

@@ -394,10 +394,11 @@ func sendToRemoteServer(
 	}
 	// Fallback to the room's server if the sender's domain is the same as
 	// the current server's
-	_, remoteServers[1], err = gomatrixserverlib.SplitID('!', inv.RoomID)
+	roomID, err := spec.NewRoomID(inv.RoomID)
 	if err != nil {
 		return
 	}
+	remoteServers[1] = roomID.Domain()
 
 	for _, server := range remoteServers {
 		err = federation.ExchangeThirdPartyInvite(ctx, cfg.Matrix.ServerName, server, proto)

roomserver/internal/perform/perform_admin.go

@@ -192,7 +192,7 @@ func (r *Admin) PerformAdminPurgeRoom(
 	roomID string,
 ) error {
 	// Validate we actually got a room ID and nothing else
-	if _, _, err := gomatrixserverlib.SplitID('!', roomID); err != nil {
+	if _, err := spec.NewRoomID(roomID); err != nil {
 		return err
 	}
 

roomserver/internal/perform/perform_peek.go

@@ -114,11 +114,11 @@ func (r *Peeker) performPeekRoomByID(
 	roomID = req.RoomIDOrAlias
 
 	// Get the domain part of the room ID.
-	_, domain, err := gomatrixserverlib.SplitID('!', roomID)
+	specRoomID, err := spec.NewRoomID(roomID)
 	if err != nil {
 		return "", api.ErrInvalidID{Err: fmt.Errorf("room ID %q is invalid: %w", roomID, err)}
 	}
-
+	domain := specRoomID.Domain()
 	// handle federated peeks
 	// FIXME: don't create an outbound peek if we already have one going.
 	if !r.Cfg.Matrix.IsLocalServerName(domain) {

roomserver/internal/perform/perform_unpeek.go

@@ -49,7 +49,7 @@ func (r *Unpeeker) performUnpeekRoomByID(
 	roomID, userID, deviceID string,
 ) (err error) {
 	// Get the domain part of the room ID.
-	_, _, err = gomatrixserverlib.SplitID('!', roomID)
+	_, err = spec.NewRoomID(roomID)
 	if err != nil {
 		return api.ErrInvalidID{Err: fmt.Errorf("room ID %q is invalid: %w", roomID, err)}
 	}