Factor out generic state listener

internal/api/rust/dynamic_slice.go

@@ -6,6 +6,8 @@ import (
 	"golang.org/x/exp/slices"
 )
 
+// This is a recurring pattern in the FFI bindings where a room list or timeline has delta updates
+// sent to it. Rather than reimplementing all the functions over and over, define it once here.
 type DynamicSlice[T any] struct {
 	Slice []T
 }

internal/api/rust/generic_state_listener.go

@@ -0,0 +1,28 @@
+package rust
+
+// This is a recurring pattern in the ffi bindings, where a param is an interface
+// which has a single OnUpdate(T) method. Rather than having many specific impls,
+// just have a generic one which can be listened to via a channel. Using a channel
+// means we can time out more easily using select {}.
+type genericStateListener[T any] struct {
+	ch       chan T
+	isClosed bool
+}
+
+func newGenericStateListener[T any]() *genericStateListener[T] {
+	return &genericStateListener[T]{
+		ch: make(chan T),
+	}
+}
+
+func (l *genericStateListener[T]) Close() {
+	l.isClosed = true
+	close(l.ch)
+}
+
+func (l *genericStateListener[T]) OnUpdate(state T) {
+	if l.isClosed {
+		return
+	}
+	l.ch <- state
+}

internal/api/rust/room_listener.go

@@ -5,6 +5,8 @@ import (
 	"sync/atomic"
 )
 
+// This is a more ergonomic way to listen for updates from the FFI layer, as it will allow you to listen
+// for non-existing rooms without crashing.
 type RoomsListener struct {
 	listeners  map[int32]func(roomID string) (cancel bool)
 	listenerID atomic.Int32

internal/api/rust/rust.go

@@ -729,26 +729,3 @@ func eventTimelineItemToEvent(item *matrix_sdk_ffi.EventTimelineItem) *api.Event
 	}
 	return &complementEvent
 }
-
-type genericStateListener[T any] struct {
-	ch       chan T
-	isClosed bool
-}
-
-func newGenericStateListener[T any]() *genericStateListener[T] {
-	return &genericStateListener[T]{
-		ch: make(chan T),
-	}
-}
-
-func (l *genericStateListener[T]) Close() {
-	l.isClosed = true
-	close(l.ch)
-}
-
-func (l *genericStateListener[T]) OnUpdate(state T) {
-	if l.isClosed {
-		return
-	}
-	l.ch <- state
-}