feat(plugin-stack-persistence): parse persisted metadata at the storage boundary

.changeset/fep-2612-parse-metadata.md

@@ -0,0 +1,5 @@
+---
+"@stackflow/plugin-stack-persistence": major
+---
+
+`StackSnapshotStrategy` now exposes `metadata.create` and `metadata.parse`, storage loads unknown metadata, and composed strategies persist and validate schema/version envelopes.

extensions/plugin-stack-persistence/src/StackSnapshotMetadataDefinition.ts

@@ -0,0 +1,15 @@
+import type { Stack, StackSnapshot } from "@stackflow/core";
+
+export type Result<Value> =
+  | {
+      ok: true;
+      value: Value;
+    }
+  | {
+      ok: false;
+    };
+
+export interface StackSnapshotMetadataDefinition<Metadata> {
+  create(args: { stack: Stack; snapshot: StackSnapshot }): Metadata;
+  parse(data: unknown): Result<Metadata>;
+}

extensions/plugin-stack-persistence/src/StackSnapshotStorage.ts

@@ -1,6 +1,6 @@
 import type { StackSnapshotRecord } from "./StackSnapshotRecord";
 
 export interface StackSnapshotStorage<Metadata> {
-  load(): StackSnapshotRecord<Metadata> | null;
+  load(): StackSnapshotRecord<unknown> | null;
   save(record: StackSnapshotRecord<Metadata>): Promise<void>;
 }

extensions/plugin-stack-persistence/src/StackSnapshotStrategy.ts

@@ -1,8 +1,8 @@
-import type { Stack, StackSnapshot } from "@stackflow/core";
+import type { StackSnapshotMetadataDefinition } from "./StackSnapshotMetadataDefinition";
 import type { StackSnapshotRecord } from "./StackSnapshotRecord";
 
 export interface StackSnapshotStrategy<Metadata> {
-  createMetadata(args: { stack: Stack; snapshot: StackSnapshot }): Metadata;
+  metadata: StackSnapshotMetadataDefinition<Metadata>;
 
   shouldReuse(args: {
     record: StackSnapshotRecord<Metadata>;

extensions/plugin-stack-persistence/src/composeStrategies.ts

@@ -1,13 +1,20 @@
 import type { StackSnapshotStrategy } from "./StackSnapshotStrategy";
 
+const COMPOSED_METADATA_SCHEMA = "stackflow.compose-strategies";
+const COMPOSED_METADATA_VERSION = 1;
+
+type StrategiesMetadataData<
+  Strategies extends Record<string, StackSnapshotStrategy<any>>,
+> = {
+  [Key in keyof Strategies]: ReturnType<Strategies[Key]["metadata"]["create"]>;
+};
+
 export type StrategiesMetadata<
   Strategies extends Record<string, StackSnapshotStrategy<any>>,
 > = {
-  [Key in keyof Strategies]: Strategies[Key] extends StackSnapshotStrategy<
-    infer Metadata
-  >
-    ? Metadata
-    : never;
+  readonly schema: typeof COMPOSED_METADATA_SCHEMA;
+  readonly version: typeof COMPOSED_METADATA_VERSION;
+  readonly data: StrategiesMetadataData<Strategies>;
 };
 
 export function composeStrategies<
@@ -18,21 +25,72 @@ export function composeStrategies<
   const keys = Object.keys(strategies) as Array<keyof Strategies>;
 
   return {
-    createMetadata(args) {
-      return Object.fromEntries(
-        keys.map((key) => [key, strategies[key].createMetadata(args)]),
-      ) as StrategiesMetadata<Strategies>
+    metadata: {
+      create(args) {
+        return {
+          schema: COMPOSED_METADATA_SCHEMA,
+          version: COMPOSED_METADATA_VERSION,
+          data: Object.fromEntries(
+            keys.map((key) => [key, strategies[key].metadata.create(args)]),
+          ),
+        } as StrategiesMetadata<Strategies>;
+      },
+      parse(data) {
+        if (data === null || typeof data !== "object") {
+          return { ok: false };
+        }
+
+        const metadata = data as Record<PropertyKey, unknown>;
+
+        if (
+          !Object.hasOwn(metadata, "schema") ||
+          !Object.hasOwn(metadata, "version") ||
+          !Object.hasOwn(metadata, "data") ||
+          metadata.schema !== COMPOSED_METADATA_SCHEMA ||
+          metadata.version !== COMPOSED_METADATA_VERSION ||
+          metadata.data === null ||
+          typeof metadata.data !== "object"
+        ) {
+          return { ok: false };
+        }
+
+        const metadataData = metadata.data as Record<PropertyKey, unknown>;
+
+        if (
+          Object.keys(metadataData).length !== keys.length ||
+          !keys.every((key) => Object.hasOwn(metadataData, key))
+        ) {
+          return { ok: false };
+        }
+
+        const parsedEntries: Array<[PropertyKey, unknown]> = [];
+
+        for (const key of keys) {
+          const result = strategies[key].metadata.parse(metadataData[key]);
+
+          if (!result.ok) {
+            return { ok: false };
+          }
+
+          parsedEntries.push([key, result.value]);
+        }
+
+        return {
+          ok: true,
+          value: {
+            schema: COMPOSED_METADATA_SCHEMA,
+            version: COMPOSED_METADATA_VERSION,
+            data: Object.fromEntries(parsedEntries),
+          } as StrategiesMetadata<Strategies>,
+        };
+      },
     },
     shouldReuse({ record, initialContext }) {
-      if (!keys.every((key) => Object.hasOwn(record.metadata, key))) {
-        return false;
-      }
-
       return keys.every((key) => {
         return strategies[key].shouldReuse({
           record: {
             ...record,
-            metadata: record.metadata[key],
+            metadata: record.metadata.data[key],
           },
           initialContext,
         });

extensions/plugin-stack-persistence/src/index.ts

@@ -1,15 +1,19 @@
 export {
   composeStrategies,
-  type StrategiesMetadata
+  type StrategiesMetadata,
 } from "./composeStrategies";
 export {
   StackSnapshotRecordLoadError,
   StackSnapshotRecordSaveError,
 } from "./errors";
-export { StackSnapshotRecord } from "./StackSnapshotRecord";
-export { StackSnapshotStorage } from "./StackSnapshotStorage";
-export { StackSnapshotStrategy } from "./StackSnapshotStrategy";
+export type {
+  Result,
+  StackSnapshotMetadataDefinition,
+} from "./StackSnapshotMetadataDefinition";
+export type { StackSnapshotRecord } from "./StackSnapshotRecord";
+export type { StackSnapshotStorage } from "./StackSnapshotStorage";
+export type { StackSnapshotStrategy } from "./StackSnapshotStrategy";
 export {
-  StackPersistencePluginOptions,
+  type StackPersistencePluginOptions,
   stackPersistencePlugin,
 } from "./stackPersistencePlugin";

extensions/plugin-stack-persistence/src/stackPersistencePlugin.ts

@@ -1,8 +1,8 @@
-import type {
-  StackflowActions,
-  StackflowPlugin,
-} from "@stackflow/core";
-import { StackSnapshotRecordSaveError, StackSnapshotRecordLoadError } from "./errors";
+import type { StackflowActions, StackflowPlugin } from "@stackflow/core";
+import {
+  StackSnapshotRecordLoadError,
+  StackSnapshotRecordSaveError,
+} from "./errors";
 import type { StackSnapshotStorage } from "./StackSnapshotStorage";
 import type { StackSnapshotStrategy } from "./StackSnapshotStrategy";
 
@@ -11,52 +11,68 @@ export type StackPersistencePluginOptions<Metadata> = {
   strategy: StackSnapshotStrategy<Metadata>;
   onRecordLoadError?: (error: StackSnapshotRecordLoadError) => void;
   onRecordSaveError?: (error: StackSnapshotRecordSaveError) => void;
-  onLoadError?: NonNullable<ReturnType<StackflowPlugin>['onLoadError']>;
-}
+  onLoadError?: NonNullable<ReturnType<StackflowPlugin>["onLoadError"]>;
+};
 
-export function stackPersistencePlugin<Metadata>(
-  { storage, strategy, onRecordLoadError, onRecordSaveError, onLoadError }: StackPersistencePluginOptions<Metadata>,
-): StackflowPlugin {
+export function stackPersistencePlugin<Metadata>({
+  storage,
+  strategy,
+  onRecordLoadError,
+  onRecordSaveError,
+  onLoadError,
+}: StackPersistencePluginOptions<Metadata>): StackflowPlugin {
   return () => {
     const saveIfIdle = (actions: StackflowActions) => {
       const stack = actions.getStack();
 
       if (stack.globalTransitionState !== "idle") return;
 
       const snapshot = actions.captureSnapshot();
-      const metadata = strategy.createMetadata({ stack, snapshot });
+      const metadata = strategy.metadata.create({ stack, snapshot });
 
-      storage.save({
-        snapshot,
-        metadata
-      }).catch(error => {
-        const saveError = new StackSnapshotRecordSaveError(error);
+      storage
+        .save({
+          snapshot,
+          metadata,
+        })
+        .catch((error) => {
+          const saveError = new StackSnapshotRecordSaveError(error);
 
-        if (onRecordSaveError) return onRecordSaveError(saveError);
-        else throw saveError;
-      });
-    }
+          if (onRecordSaveError) return onRecordSaveError(saveError);
+          else throw saveError;
+        });
+    };
 
     return {
       key: "@stackflow/plugin-stack-persistence",
       provideSnapshot({ initialContext }) {
         try {
           const record = storage.load();
 
-          if (!record)
-            return null;
-          if (strategy?.shouldReuse({ record, initialContext }) === false)
+          if (!record) return null;
+
+          const parsedMetadata = strategy.metadata.parse(record.metadata);
+
+          if (!parsedMetadata.ok) return null;
+
+          const parsedRecord = {
+            ...record,
+            metadata: parsedMetadata.value,
+          };
+
+          if (!strategy.shouldReuse({ record: parsedRecord, initialContext })) {
             return null;
+          }
 
-          return record.snapshot;
+          return parsedRecord.snapshot;
         } catch (error) {
           onRecordLoadError?.(new StackSnapshotRecordLoadError(error));
 
           return null;
         }
       },
       onLoadError(...args) {
-        return onLoadError?.(...args) ?? { policy: "recover" }
+        return onLoadError?.(...args) ?? { policy: "recover" };
       },
       onInit({ actions }) {
         saveIfIdle(actions);