Transfer buffers instead of copying them

packages/kate-core/source/os/apis/processes.ts

@@ -43,9 +43,8 @@ export class KateProcesses {
     const cart = await Cart.parse_metadata(blob, this.os.kernel.version);
     const has_proper_offset = cart.files.every((x) => x.offset !== null);
     const file_map = new Map(cart.files.map((x) => [x.path, x]));
-    let data_map: Map<string, Cart.DataFile> | null = null;
     if (!has_proper_offset) {
-      data_map = (await Cart.parse_whole(blob, this.os.kernel.version)).file_map;
+      throw new Error(`Running this cartridge is not supported without installation.`);
     }
 
     const storage = await this.os.object_store.cartridge(cart, false).get_local_storage();
@@ -56,28 +55,17 @@ export class KateProcesses {
       filesystem: {
         read: async (path) => {
           const node = file_map.get(path);
-          if (node == null) {
+          if (node == null || node.offset == null) {
             throw new Error(`File not found in ${cart.id}: ${path}`);
           }
-          if (data_map != null) {
-            const data = data_map.get(path)!.data;
-            return {
-              path: node.path,
-              mime: node.mime,
-              data,
-            };
-          } else if (node.offset != null) {
-            const data = new Uint8Array(
-              await blob.slice(node.offset, node.offset + node.size).arrayBuffer()
-            );
-            return {
-              path: node.path,
-              mime: node.mime,
-              data,
-            };
-          } else {
-            throw new Error(`Cannot read file ${path} in ${cart.id}`);
-          }
+          const data = new Uint8Array(
+            await blob.slice(node.offset, node.offset + node.size).arrayBuffer()
+          );
+          return {
+            path: node.path,
+            mime: node.mime,
+            data,
+          };
         },
       },
     });

packages/kate-core/source/os/ipc/cart_fs.ts

@@ -4,14 +4,14 @@
  * file, You can obtain one at https://mozilla.org/MPL/2.0/.
  */
 
-import { EMessageFailed, handler } from "./handlers";
+import { EMessageFailed, WithTransfer, handler } from "./handlers";
 import { TC } from "../../utils";
 
 export default [
   handler("kate:cart.read-file", TC.spec({ path: TC.str }), async (os, process, ipc, { path }) => {
     try {
       const file = await process.file_system.read(path);
-      return { mime: file.mime, bytes: file.data };
+      return new WithTransfer({ mime: file.mime, bytes: file.data }, [file.data.buffer]);
     } catch (error) {
       console.error(`[Kate] failed to read file ${path} from ${process.cartridge.id}`);
       throw new EMessageFailed("kate.cart-fs.file-not-found", `Failed to read file ${path}`);

packages/kate-core/source/os/ipc/device-file.ts

@@ -6,7 +6,7 @@
 
 import type { KateOS } from "../os";
 import { TC, make_id } from "../../utils";
-import { EMessageFailed, auth_handler, handler } from "./handlers";
+import { EMessageFailed, WithTransfer, auth_handler, handler } from "./handlers";
 import { DeviceFileHandle } from "../apis";
 import * as UI from "../ui";
 import { Process } from "../../kernel";
@@ -122,7 +122,7 @@ export default [
     async (os, env, ipc, { id }) => {
       const file = (await device_ipc.resolve(os, env, id)).handle;
       const data = await file.arrayBuffer();
-      return new Uint8Array(data);
+      return new WithTransfer(new Uint8Array(data), [data]);
     }
   ),
 ];

packages/kate-core/source/os/ipc/handlers.ts

@@ -36,6 +36,10 @@ export class EMessageFailed extends Error {
   }
 }
 
+export class WithTransfer {
+  constructor(readonly value: unknown, readonly transfer: Transferable[]) {}
+}
+
 export function handler<A, B>(
   type: string,
   parser: Handler<A, B>["parser"],

packages/kate-core/source/os/ipc/ipc.ts

@@ -5,7 +5,7 @@
  */
 
 import type { KateOS } from "../os";
-import { EMessageFailed, type Handler } from "./handlers";
+import { EMessageFailed, WithTransfer, type Handler } from "./handlers";
 import { TC, make_id } from "../../utils";
 import CaptureMessages from "./capture";
 import CartFSMessages from "./cart_fs";
@@ -110,12 +110,16 @@ export class KateIPCServer {
               value: result,
             });
           }
-          process.send({
-            type: "kate:reply",
-            id: payload.id,
-            ok: true,
-            value: result,
-          });
+          const [value, transfer] = this.unpack_transfers(result);
+          process.send(
+            {
+              type: "kate:reply",
+              id: payload.id,
+              ok: true,
+              value: value,
+            },
+            transfer
+          );
         } catch (error: unknown) {
           console.error(
             `[kate:ipc] Error handling ${payload.type} from ${process.id}`,
@@ -137,6 +141,14 @@ export class KateIPCServer {
     }
   };
 
+  private unpack_transfers(x: unknown): [unknown, Transferable[]] {
+    if (x instanceof WithTransfer) {
+      return [x.value, x.transfer];
+    } else {
+      return [x, []];
+    }
+  }
+
   private async mark_suspicious_activity(ev: Message, process: Process) {
     console.debug(`[Kate] suspicious IPC activity from ${process.id}`, ev);
     this.remove_process(process);