Server snapshot WIP

packages/excalidraw/cloudflare/repository.ts

@@ -9,7 +9,7 @@ import { Network } from "../sync/utils";
 // CFDO II: add senderId, possibly roomId as well
 export class DurableDeltasRepository implements DeltasRepository {
   // there is a 2MB row limit, hence working with max payload size of 1.5 MB
-  // and leaving a buffer for other row metadata
+  // and leaving a ~500kB buffer for other row metadata
   private static readonly MAX_PAYLOAD_SIZE = 1_500_000;
 
   constructor(private storage: DurableObjectStorage) {

packages/excalidraw/cloudflare/room.ts

@@ -2,8 +2,6 @@ import { DurableObject } from "cloudflare:workers";
 import { DurableDeltasRepository } from "./repository";
 import { ExcalidrawSyncServer } from "../sync/server";
 
-import type { ExcalidrawElement } from "../element/types";
-
 /**
  * Durable Object impl. of Excalidraw room.
  */
@@ -11,26 +9,10 @@ export class DurableRoom extends DurableObject {
   private roomId: string | null = null;
   private sync: ExcalidrawSyncServer;
 
-  private snapshot!: {
-    appState: Record<string, any>;
-    elements: Map<string, ExcalidrawElement>;
-    version: number;
-  };
-
   constructor(ctx: DurableObjectState, env: Env) {
     super(ctx, env);
 
     this.ctx.blockConcurrencyWhile(async () => {
-      // CFDO I: snapshot should likely be a transient store
-      // CFDO II: loaded the latest state from the db
-      this.snapshot = {
-        // CFDO: start persisting acknowledged version (not a scene version!)
-        // CFDO: we don't persist appState, should we?
-        appState: {},
-        elements: new Map(),
-        version: 0,
-      };
-
       this.roomId = (await this.ctx.storage.get("roomId")) || null;
     });
 

packages/excalidraw/components/App.tsx

@@ -5367,7 +5367,7 @@ class App extends React.Component<AppProps, AppState> {
           : -1;
 
         if (midPoint && midPoint > -1) {
-          this.store.shouldCaptureIncrement();
+          this.store.scheduleCapture();
           LinearElementEditor.deleteFixedSegment(selectedElements[0], midPoint);
 
           const nextCoords = LinearElementEditor.getSegmentMidpointHitCoords(

packages/excalidraw/delta.ts

@@ -32,7 +32,7 @@ import type {
 } from "./element/types";
 import { orderByFractionalIndex, syncMovedIndices } from "./fractionalIndex";
 import { getNonDeletedGroupIds } from "./groups";
-import { getObservedAppState } from "./store";
+import { getObservedAppState, StoreSnapshot } from "./store";
 import type {
   AppState,
   ObservedAppState,
@@ -1036,7 +1036,10 @@ export class ElementsDelta implements DeltaContainer<SceneElementsMap> {
    * @param modifierOptions defines which of the delta (`deleted` or `inserted`) will be updated
    * @returns new instance with modified delta/s
    */
-  public applyLatestChanges(elements: SceneElementsMap): ElementsDelta {
+  public applyLatestChanges(
+    elements: SceneElementsMap,
+    modifierOptions: "deleted" | "inserted",
+  ): ElementsDelta {
     const modifier =
       (element: OrderedExcalidrawElement) => (partial: ElementPartial) => {
         const latestPartial: { [key: string]: unknown } = {};
@@ -1069,7 +1072,7 @@ export class ElementsDelta implements DeltaContainer<SceneElementsMap> {
             delta.deleted,
             delta.inserted,
             modifier(existingElement),
-            "inserted",
+            modifierOptions,
           );
 
           modifiedDeltas[id] = modifiedDelta;
@@ -1092,7 +1095,10 @@ export class ElementsDelta implements DeltaContainer<SceneElementsMap> {
 
   public applyTo(
     elements: SceneElementsMap,
-    snapshot: Map<string, OrderedExcalidrawElement>,
+    elementsSnapshot: Map<
+      string,
+      OrderedExcalidrawElement
+    > = StoreSnapshot.empty().elements,
   ): [SceneElementsMap, boolean] {
     let nextElements = toBrandedType<SceneElementsMap>(new Map(elements));
     let changedElements: Map<string, OrderedExcalidrawElement>;
@@ -1106,7 +1112,7 @@ export class ElementsDelta implements DeltaContainer<SceneElementsMap> {
     try {
       const applyDeltas = ElementsDelta.createApplier(
         nextElements,
-        snapshot,
+        elementsSnapshot,
         flags,
       );
 

packages/excalidraw/history.ts

@@ -159,7 +159,13 @@ export class History {
     entry: HistoryEntry,
     prevElements: SceneElementsMap,
   ) {
-    const updatedEntry = HistoryEntry.applyLatestChanges(entry, prevElements);
+    const inversedEntry = HistoryEntry.inverse(entry);
+    const updatedEntry = HistoryEntry.applyLatestChanges(
+      inversedEntry,
+      prevElements,
+      "inserted",
+    );
+
     return stack.push(updatedEntry);
   }
 }

packages/excalidraw/store.ts

@@ -474,14 +474,13 @@ export class StoreDelta {
   public static applyLatestChanges(
     delta: StoreDelta,
     elements: SceneElementsMap,
+    modifierOptions: "deleted" | "inserted",
   ): StoreDelta {
-    const inversedDelta = this.inverse(delta);
-
     return this.create(
-      inversedDelta.elements.applyLatestChanges(elements),
-      inversedDelta.appState,
+      delta.elements.applyLatestChanges(elements, modifierOptions),
+      delta.appState,
       {
-        id: inversedDelta.id,
+        id: delta.id,
       },
     );
   }

packages/excalidraw/sync/protocol.ts

@@ -4,6 +4,7 @@ import type { DTO } from "../utility-types";
 export type CLIENT_DELTA = DTO<StoreDelta>;
 export type CLIENT_CHANGE = DTO<StoreChange>;
 
+export type RESTORE_PAYLOAD = {};
 export type RELAY_PAYLOAD = CLIENT_CHANGE;
 export type PUSH_PAYLOAD = CLIENT_DELTA;
 export type PULL_PAYLOAD = { lastAcknowledgedVersion: number };
@@ -15,6 +16,7 @@ export type CHUNK_INFO = {
 };
 
 export type CLIENT_MESSAGE = (
+  | { type: "restore"; payload: RESTORE_PAYLOAD }
   | { type: "relay"; payload: RELAY_PAYLOAD }
   | { type: "pull"; payload: PULL_PAYLOAD }
   | { type: "push"; payload: PUSH_PAYLOAD }
@@ -48,7 +50,8 @@ export type SERVER_MESSAGE =
   | {
       type: "rejected";
       payload: { deltas: Array<CLIENT_DELTA>; message: string };
-    };
+    }
+  | { type: "restored"; payload: { elements: Array<ExcalidrawElement> } };
 
 export interface DeltasRepository {
   save(delta: CLIENT_DELTA): SERVER_DELTA | null;

packages/excalidraw/sync/server.ts

@@ -3,7 +3,6 @@ import { Network, Utils } from "./utils";
 
 import type {
   DeltasRepository,
-  CLIENT_MESSAGE,
   PULL_PAYLOAD,
   PUSH_PAYLOAD,
   SERVER_MESSAGE,
@@ -11,7 +10,10 @@ import type {
   CHUNK_INFO,
   RELAY_PAYLOAD,
   CLIENT_MESSAGE_BINARY,
+  CLIENT_MESSAGE,
+  ExcalidrawElement,
 } from "./protocol";
+import { StoreDelta } from "../store";
 
 /**
  * Core excalidraw sync logic.
@@ -24,7 +26,22 @@ export class ExcalidrawSyncServer {
     Map<CHUNK_INFO["position"], CLIENT_MESSAGE_BINARY["payload"]>
   >();
 
-  constructor(private readonly repository: DeltasRepository) {}
+  // CFDO II: load from the db
+  private elements = new Map<string, ExcalidrawElement>();
+
+  constructor(private readonly repository: DeltasRepository) {
+    // CFDO II: load from the db
+    const deltas = this.repository.getAllSinceVersion(0);
+
+    for (const delta of deltas) {
+      const storeDelta = StoreDelta.load(delta.payload);
+
+      // CFDO II: fix types (everywhere)
+      const [nextElements] = storeDelta.elements.applyTo(this.elements as any);
+
+      this.elements = nextElements;
+    }
+  }
 
   // CFDO: optimize, should send a message about collaborators (no collaborators => no need to send ephemerals)
   public onConnect(client: WebSocket) {
@@ -48,11 +65,12 @@ export class ExcalidrawSyncServer {
       return;
     }
 
-    const { type, payload, chunkInfo } = rawMessage;
-
     // if there is chunkInfo, there are more than 1 chunks => process them first
-    if (chunkInfo) {
-      return this.processChunks(client, { type, payload, chunkInfo });
+    if (rawMessage.chunkInfo) {
+      return this.processChunks(client, {
+        ...rawMessage,
+        chunkInfo: rawMessage.chunkInfo,
+      });
     }
 
     return this.processMessage(client, rawMessage);
@@ -132,6 +150,8 @@ export class ExcalidrawSyncServer {
     }
 
     switch (type) {
+      case "restore":
+        return this.restore(client);
       case "relay":
         return this.relay(client, parsedPayload as RELAY_PAYLOAD);
       case "pull":
@@ -147,6 +167,15 @@ export class ExcalidrawSyncServer {
     }
   }
 
+  private restore(client: WebSocket) {
+    return this.send(client, {
+      type: "restored",
+      payload: {
+        elements: Array.from(this.elements.values()),
+      },
+    });
+  }
+
   private relay(client: WebSocket, payload: RELAY_PAYLOAD) {
     // CFDO I: we should likely apply these to the snapshot
     return this.broadcast(
@@ -191,10 +220,38 @@ export class ExcalidrawSyncServer {
   }
 
   private push(client: WebSocket, delta: PUSH_PAYLOAD) {
-    // CFDO I: apply latest changes to delt & apply the deltas to the snapshot
-    const [acknowledged, savingError] = Utils.try(() =>
-      this.repository.save(delta),
-    );
+    const [storeDelta, applyingError] = Utils.try(() => {
+      // update the "deleted" delta according to the latest changes (in case of concurrent changes)
+      const storeDelta = StoreDelta.applyLatestChanges(
+        StoreDelta.load(delta),
+        this.elements as any,
+        "deleted",
+      );
+
+      // apply the delta to the elements snapshot
+      const [nextElements] = storeDelta.elements.applyTo(this.elements as any);
+
+      this.elements = nextElements;
+
+      return storeDelta;
+    });
+
+    if (applyingError) {
+      // CFDO: everything should be automatically rolled-back in the db -> double-check
+      return this.send(client, {
+        type: "rejected",
+        payload: {
+          message: applyingError
+            ? applyingError.message
+            : "Couldn't apply the delta.",
+          deltas: [delta],
+        },
+      });
+    }
+
+    const [acknowledged, savingError] = Utils.try(() => {
+      return this.repository.save(storeDelta);
+    });
 
     if (savingError || !acknowledged) {
       // CFDO: everything should be automatically rolled-back in the db -> double-check
@@ -204,7 +261,7 @@ export class ExcalidrawSyncServer {
           message: savingError
             ? savingError.message
             : "Coudn't persist the delta.",
-          deltas: [delta],
+          deltas: [storeDelta],
         },
       });
     }