Finding entities: Handle task cancellation

I can't assume entity fetches will always work, because user might e g close window

Author: nevyn

Sources/allonet2/AlloClient.swift

@@ -27,18 +27,18 @@ open class AlloClient : AlloSessionDelegate, ObservableObject, Identifiable
         guard let aeid = self.avatarId else { return nil }
         return place.entities[aeid]
     }
-    public func findAvatar() async -> Entity
+    /// Fetch the convenience accessor for our own avatar Entity, so that we can modify it. This will only throw in case of task cancellation.
+    public func findAvatar() async throws -> Entity
     {
         var avatarId: EntityID? = self.avatarId
-        while avatarId == nil
+        var iter = self.$avatarId.values.compactMap({ $0 }).makeAsyncIterator()
+        while let maybeId = await iter.next()
         {
-            var iter = self.$avatarId.values.makeAsyncIterator()
-            if let next = await iter.next()
-            {
-                avatarId = next
-            }
+            try Task.checkCancellation()
+            if maybeId != nil { avatarId = maybeId; break }
         }
-        return await place.findEntity(id: avatarId!)
+        try Task.checkCancellation()
+        return try await place.findEntity(id: avatarId!)
     }
     @Published public private(set) var isAnnounced: Bool = false
     public private(set) var placeName: String?

Sources/allonet2/Place.swift

@@ -23,9 +23,11 @@ public class Place
     }
 
     /// Wait for a specific entity to come in and return its convenience structure.
-    public func findEntity(id: EntityID) async -> Entity
+    public func findEntity(id: EntityID) async throws -> Entity
     {
-        let edata = await state.findEntity(id)
+        let edata = try await state.findEntity(id)
+        try Task.checkCancellation()
+        // Cancellation should be the only reason why we get nil back, which should make the below force-unwrap safe with the above check
         return entities[edata.id]!
     }
 

Sources/allonet2/PlaceContents.swift

@@ -34,13 +34,16 @@ public class PlaceState
     }
 
     /// Wait for a specific entity to come in.
-    public func findEntity(_ id: EntityID) async -> EntityData
+    public func findEntity(_ id: EntityID) async throws -> EntityData
     {
         if let ent = current.entities[id] {
             return ent
         }
         var iter = observers.subjectFor(id).values.makeAsyncIterator()
-        return await iter.next()!
+        if let ent = await iter.next() {
+            return ent
+        }
+        throw CancellationError()
     }
 
     internal func callChangeObservers()