refactor: Clarify error message when waitForSpan failed

src/eventBus/infra/memoryBus.ts

@@ -1,8 +1,7 @@
 import { EventBus, WatchCallback } from "@/eventBus/infra/eventBus";
+import { TimeoutError } from "@/eventBus/infra/timeoutError";
 import { ErrorMessage } from "@/type/common";
 
-const TIMEOUT_ERROR_MESSAGE: ErrorMessage = { error: true, reason: "timeout" };
-
 export class MemoryBus implements EventBus {
   private watchingEvents: Map<string, WatchCallback[]> = new Map();
 
@@ -17,7 +16,7 @@ export class MemoryBus implements EventBus {
     timeoutMs: number,
     fn: (data: unknown) => Promise<T | undefined>,
   ): Promise<T | ErrorMessage> {
-    return new Promise((resolve) => {
+    return new Promise((resolve, reject) => {
       const callback = async (data: unknown): Promise<void> => {
         const res = await fn(data);
         if (!res) {
@@ -31,7 +30,7 @@ export class MemoryBus implements EventBus {
 
       const timeoutId = setTimeout(() => {
         this.off(eventName, callback);
-        resolve(TIMEOUT_ERROR_MESSAGE);
+        reject(new TimeoutError());
       }, timeoutMs);
 
       this.on(eventName, callback);

src/eventBus/infra/timeoutError.ts

@@ -0,0 +1,7 @@
+import { EchoedError } from "@/echoedError";
+
+export class TimeoutError extends EchoedError {
+  constructor() {
+    super("timeout");
+  }
+}

src/eventBus/spanBus.ts

@@ -1,4 +1,5 @@
 import { EventBus } from "@/eventBus/infra/eventBus";
+import { TimeoutError } from "@/eventBus/infra/timeoutError";
 import {
   JsonReceiveSpanEvent,
   JsonWaitForSpanEvent,
@@ -53,9 +54,20 @@ export class SpanBus {
       filter,
       wantId,
     });
-    const span = await listener;
 
-    return span;
+    try {
+      return await listener;
+    } catch (e) {
+      if (e instanceof TimeoutError) {
+        const waitTime = new Intl.NumberFormat("en").format(waitTimeoutMs);
+        return {
+          error: true,
+          reason: `No matching span found within ${waitTime}ms.`,
+        };
+      }
+
+      throw e;
+    }
   }
 
   private async emitWaitForSpanEvent(event: WaitForSpanEvent): Promise<void> {

src/server/request.ts

@@ -26,9 +26,7 @@ export async function requestWaitForSpanEvent(
   const resp = restoreWaitForSpanEventResponse(jsonResponse);
 
   if ("error" in resp) {
-    throw new EchoedFatalError(
-      `Error happens while waiting for span. ${resp.reason}`,
-    );
+    throw new EchoedFatalError(resp.reason);
   }
 
   return resp.span;