Perform data-serialization as sendMessage-time

src/core/main/worker/content_preparer.ts

@@ -1,6 +1,6 @@
 import features from "../../../features";
 import log from "../../../log";
-import type { IManifest, IManifestMetadata } from "../../../manifest";
+import type { IManifest } from "../../../manifest";
 import { createRepresentationFilterFromFnString } from "../../../manifest";
 import type { IMediaSourceInterface } from "../../../mse";
 import MainMediaSourceInterface from "../../../mse/main_media_source_interface";
@@ -13,7 +13,6 @@ import type {
 import { WorkerMessageType } from "../../../multithread_types";
 import type { IPlayerError } from "../../../public_types";
 import idGenerator from "../../../utils/id_generator";
-import objectAssign from "../../../utils/object_assign";
 import type {
   CancellationError,
   CancellationSignal,
@@ -76,7 +75,7 @@ export default class ContentPreparer {
   public initializeNewContent(
     sendMessage: (msg: IWorkerMessage, transferables?: Transferable[]) => void,
     context: IContentInitializationData,
-  ): Promise<IManifestMetadata> {
+  ): Promise<IManifest> {
     return new Promise((res, rej) => {
       this.disposeCurrentContent();
       const contentCanceller = this._contentCanceller;
@@ -222,30 +221,23 @@ export default class ContentPreparer {
           return;
         }
 
-        const sentManifest = manifest.getMetadataSnapshot();
         manifest.addEventListener(
           "manifestUpdate",
           (updates) => {
             if (manifest === null) {
               // TODO log warn?
               return;
             }
-
-            // Remove `periods` key to reduce cost of an unnecessary manifest
-            // clone.
-            const snapshot = objectAssign(manifest.getMetadataSnapshot(), {
-              periods: [],
-            });
             sendMessage({
               type: WorkerMessageType.ManifestUpdate,
               contentId,
-              value: { manifest: snapshot, updates },
+              value: { manifest, updates },
             });
           },
           contentCanceller.signal,
         );
         unbindRejectOnCancellation();
-        res(sentManifest);
+        res(manifest);
       }
     });
   }

src/multithread_types.ts

@@ -772,17 +772,53 @@ export interface IRepresentationChangeWorkerMessage {
   };
 }
 
+/** Message sent by the Worker when the Manifest is first loaded. */
 export interface IManifestReadyWorkerMessage {
+  /** Identify this particular message. */
   type: WorkerMessageType.ManifestReady;
+  /** The `contentId` linked to this Manifest. */
   contentId: string;
-  value: { manifest: IManifestMetadata };
+  value: {
+    /**
+     * The actual `Manifest` loaded.
+     *
+     * When possible, this should be a `Manifest` instance.
+     *
+     * Only if this is not possible (e.g. because the `Manifest` cannot be
+     * communicated as is between both Worker and main_thread) might you convert
+     * it to another object also respecting the `IManifestMetadata` interface.
+     *
+     * However doing this might lead to some loss of performance and minor
+     * features.
+     */
+    manifest: IManifestMetadata;
+  };
 }
 
+/** Message sent by the Worker everytime the Manifest is updated. */
 export interface IManifestUpdateWorkerMessage {
+  /** Identify this particular message. */
   type: WorkerMessageType.ManifestUpdate;
+  /** The `contentId` linked to this Manifest. */
   contentId: string | undefined;
   value: {
-    manifest: IManifestMetadata; // TODO only subpart that changed?
+    /**
+     * The new manifest once updated.
+     *
+     * When possible, this should be a `Manifest` instance to improve
+     * performance and allow some advanced features.
+     *
+     * Only if this is not possible (e.g. because the `Manifest` cannot be
+     * communicated as is between both Worker and main_thread) might you convert
+     * it to another object also respecting the `IManifestMetadata` interface.
+     * In that last case, you're also authorized to reset the `periods` property
+     * of that `IManifestMetadata` to an empty array to save up message-passing
+     * performance.
+     */
+    manifest: IManifestMetadata;
+    /**
+     * Object describing what has changed in this update.
+     */
     updates: IPeriodsUpdateResult;
   };
 }

src/worker_entry_point.ts

@@ -14,7 +14,8 @@ import {
 } from "./core/main/worker/globals";
 import log from "./experimental/tools/mediaCapabilitiesProber/log";
 import features from "./features";
-import type { IWorkerMessage } from "./multithread_types";
+import Manifest from "./manifest/classes";
+import { WorkerMessageType, type IWorkerMessage } from "./multithread_types";
 import DashFastJsParser from "./parsers/manifest/dash/fast-js-parser";
 import DashWasmParser from "./parsers/manifest/dash/wasm-parser";
 import createDashPipelines from "./transports/dash";
@@ -45,7 +46,15 @@ initializeWorkerMain(
   },
 );
 
+/**
+ * Perform a `postMessage` to main thread with the given message.
+ * Arguments follow the `postMessage` API.
+ * @param {Object} msg
+ * @param {Array.<Object>} [transferables]
+ */
 function sendMessage(msg: IWorkerMessage, transferables?: Transferable[]): void {
+  updateMessageFormat(msg);
+
   log.debug("<--- Sending to Main:", msg.type);
   if (transferables === undefined) {
     postMessage(msg);
@@ -57,3 +66,28 @@ function sendMessage(msg: IWorkerMessage, transferables?: Transferable[]): void
     );
   }
 }
+
+/**
+ * Ensure that we're sending data that can be serialized, as this is a
+ * requirement for the `postMessage` browser API.
+ *
+ * If necessary, mutations are done in place.
+ * @param {Object} msg
+ */
+function updateMessageFormat(msg: IWorkerMessage): void {
+  if (
+    msg.type === WorkerMessageType.ManifestReady ||
+    msg.type === WorkerMessageType.ManifestUpdate
+  ) {
+    if (msg.value.manifest instanceof Manifest) {
+      msg.value.manifest = msg.value.manifest.getMetadataSnapshot();
+      if (msg.type === WorkerMessageType.ManifestUpdate) {
+        // Remove `periods` key to reduce cost of an unnecessary manifest
+        // clone.
+        msg.value.manifest.periods = [];
+      }
+    } else {
+      log.warn("Worker: the Manifest instance should be communicated to `sendMessage`.");
+    }
+  }
+}