From c3a422347ce3da25637a6f1239e676db530df01d Mon Sep 17 00:00:00 2001
From: Tulir Asokan <tulir@maunium.net>
Date: Mon, 25 Aug 2025 18:36:03 +0300
Subject: [PATCH] bridgev2/portal: validate capabilities when updating
 disappearing timer

---
 bridgev2/errors.go    | 2 ++
 bridgev2/portal.go    | 7 +++++++
 event/capabilities.go | 7 +++++++
 3 files changed, 16 insertions(+)

diff --git a/bridgev2/errors.go b/bridgev2/errors.go
index c023dcdf..026a95f4 100644
--- a/bridgev2/errors.go
+++ b/bridgev2/errors.go
@@ -67,6 +67,8 @@ var (
 	ErrPowerLevelsNotSupported         error = WrapErrorInStatus(errors.New("this bridge does not support changing group power levels")).WithIsCertain(true).WithErrorAsMessage().WithSendNotice(false)
 	ErrRemoteEchoTimeout                     = WrapErrorInStatus(errors.New("remote echo timed out")).WithIsCertain(false).WithSendNotice(true).WithErrorReason(event.MessageStatusTooOld)
 	ErrRemoteAckTimeout                      = WrapErrorInStatus(errors.New("remote ack timed out")).WithIsCertain(false).WithSendNotice(true).WithErrorReason(event.MessageStatusTooOld)
+
+	ErrDisappearingTimerUnsupported error = WrapErrorInStatus(errors.New("invalid disappearing timer")).WithIsCertain(true)
 )
 
 // Common login interface errors
diff --git a/bridgev2/portal.go b/bridgev2/portal.go
index 24365df9..5e0a9137 100644
--- a/bridgev2/portal.go
+++ b/bridgev2/portal.go
@@ -1488,6 +1488,10 @@ func handleMatrixRoomMeta[APIType any, ContentType any](
 			portal.sendSuccessStatus(ctx, evt, 0, "")
 			return EventHandlingResultIgnored
 		}
+		if !sender.Client.GetCapabilities(ctx, portal).DisappearingTimer.Supports(typedContent) {
+			portal.sendRoomMeta(ctx, nil, time.Now(), event.StateBeeperDisappearingTimer, "", portal.Disappear.ToEventContent())
+			return EventHandlingResultFailed.WithMSSError(ErrDisappearingTimerUnsupported)
+		}
 	}
 	var prevContent ContentType
 	if evt.Unsigned.PrevContent != nil {
@@ -1508,6 +1512,9 @@ func handleMatrixRoomMeta[APIType any, ContentType any](
 	})
 	if err != nil {
 		log.Err(err).Msg("Failed to handle Matrix room metadata")
+		if evt.Type == event.StateBeeperDisappearingTimer {
+			portal.sendRoomMeta(ctx, nil, time.Now(), event.StateBeeperDisappearingTimer, "", portal.Disappear.ToEventContent())
+		}
 		return EventHandlingResultFailed.WithMSSError(err)
 	}
 	if changed {
diff --git a/event/capabilities.go b/event/capabilities.go
index f44d6600..20f87bce 100644
--- a/event/capabilities.go
+++ b/event/capabilities.go
@@ -76,6 +76,13 @@ type DisappearingTimerCapability struct {
 	OmitEmptyTimer bool `json:"omit_empty_timer,omitempty"`
 }
 
+func (dtc *DisappearingTimerCapability) Supports(content *BeeperDisappearingTimer) bool {
+	if dtc == nil || content.Type == DisappearingTypeNone {
+		return true
+	}
+	return slices.Contains(dtc.Types, content.Type) && slices.Contains(dtc.Timers, content.Timer)
+}
+
 type CapabilityMsgType = MessageType
 
 // Message types which are used for event capability signaling, but aren't real values for the msgtype field.