feat: friendly way to inform user there's an error (#12)

src/util/ConcurrentQueue.ts

@@ -1,15 +1,15 @@
 import { nextTickAsync } from './nextTick';
 
 export abstract class ConcurrentQueue<T, R = unknown> {
-  protected items: [T, (result: R) => void, (error: unknown) => void][] = [];
+  protected items: [T, (result: R) => void, (error: unknown) => void, void | (() => void)][] = [];
 
   constructor(protected maxConcurrent = 5) {}
 
   abstract handler(item: T): Promise<R>;
 
-  public async add(item: T): Promise<R> {
+  public async add(item: T, onPreProcess?: () => void): Promise<R> {
     return new Promise((resolve, reject) => {
-      this.items.push([item, resolve, reject]);
+      this.items.push([item, resolve, reject, onPreProcess]);
       this.runWorkerIfFree();
     });
   }
@@ -32,9 +32,11 @@ export abstract class ConcurrentQueue<T, R = unknown> {
   private async processQueue() {
     let item: (typeof this.items)[0] | void;
     while ((item = this.items.shift())) {
-      const [payload, resolve, reject] = item;
+      const [payload, resolve, reject, onPreProcess] = item;
 
       try {
+        onPreProcess?.();
+
         resolve(await this.handler(payload));
       } catch (error: unknown) {
         reject(error);

src/util/WorkerEventBus.ts

@@ -1,10 +1,12 @@
 import { nanoid } from 'nanoid';
+import { DecryptError } from '~/decrypt-worker/util/DecryptError';
 
 type WorkerServerHandler<P, R> = (payload: P) => R | Promise<R>;
 
 interface SerializedError {
   message: string;
   stack?: string;
+  code?: string;
 }
 
 interface WorkerClientRequestPayload<P = unknown> {
@@ -39,6 +41,7 @@ export class WorkerClientBus<T = string> {
     if (error) {
       const wrappedError = new Error(error.message, { cause: error });
       wrappedError.stack = error.stack;
+      Object.assign(wrappedError, { code: error.code ?? null });
       reject(wrappedError);
     } else {
       resolve(result as never);
@@ -77,8 +80,12 @@ export class WorkerServerBus {
     } else {
       try {
         result = await handler(payload);
-      } catch (e: unknown) {
-        error = e;
+      } catch (err: unknown) {
+        if (err instanceof DecryptError) {
+          error = err.toJSON();
+        } else {
+          error = err;
+        }
       }
     }