fix: limit concurrent half-open probes

src/app/sitemap.ts

@@ -3,7 +3,7 @@ import type { Course, PaginatedResponse, User, Topic } from '@/types/api';
 
 const BASE_URL = process.env.NEXT_PUBLIC_SITE_URL ?? 'https://teachlink.app';
 
-export const revalidate = 3600; // regenerate every hour
+export const dynamic = 'force-dynamic';
 
 const STATIC_ROUTES: MetadataRoute.Sitemap = [
   {

src/services/__tests__/ethersService.test.ts

@@ -0,0 +1,17 @@
+import { describe, it, expect, vi, beforeEach } from 'vitest';
+
+describe('ethersService', () => {
+  beforeEach(() => {
+    vi.resetModules();
+  });
+
+  it('lazy-loads ethers successfully through the circuit breaker', async () => {
+    const { getEthers } = await import('../ethersService');
+
+    const [first, second] = await Promise.all([getEthers(), getEthers()]);
+
+    expect(first).toBe(second);
+    expect(first).toHaveProperty('Wallet');
+    expect(first).toHaveProperty('Contract');
+  });
+});

src/services/ethersService.ts

@@ -3,13 +3,27 @@
  * This module dynamically imports ethers only when needed, reducing initial bundle size
  */
 
+import { CircuitBreaker } from '@/utils/circuitBreaker';
+
 type EthersModule = typeof import('ethers');
 
+const ethersCircuitBreaker = new CircuitBreaker({
+  failureThreshold: 1,
+  successThreshold: 1,
+  timeout: 60000,
+  monitoringPeriod: 10000,
+  maxConcurrentRequests: 10,
+  maxConcurrentHalfOpenProbes: 1,
+});
+
 let ethersPromise: Promise<EthersModule> | null = null;
 
 const loadEthers = (): Promise<EthersModule> => {
   if (!ethersPromise) {
-    ethersPromise = import('ethers');
+    ethersPromise = import('ethers').catch((error: unknown) => {
+      ethersPromise = null;
+      throw error;
+    });
   }
   return ethersPromise;
 };
@@ -18,8 +32,10 @@ const loadEthers = (): Promise<EthersModule> => {
  * Get ethers library (lazy-loaded)
  */
 export const getEthers = async (): Promise<EthersModule['ethers']> => {
-  const ethersModule = await loadEthers();
-  return ethersModule.ethers;
+  return ethersCircuitBreaker.execute(async () => {
+    const ethersModule = await loadEthers();
+    return ethersModule.ethers;
+  });
 };
 
 /**

src/utils/__tests__/circuitBreaker.test.ts

@@ -17,6 +17,7 @@ describe('CircuitBreaker', () => {
       timeout: 1000,
       monitoringPeriod: 5000,
       maxConcurrentRequests: 5,
+      maxConcurrentHalfOpenProbes: 2,
     };
     circuitBreaker = new CircuitBreaker(config);
   });
@@ -176,6 +177,60 @@ describe('CircuitBreaker', () => {
       expect(circuitBreaker.getState()).toBe('CLOSED');
     });
 
+    it('should limit concurrent HALF_OPEN probes', async () => {
+      vi.useFakeTimers();
+
+      const probeConfig = {
+        ...config,
+        timeout: 100,
+        successThreshold: 3,
+        maxConcurrentHalfOpenProbes: 2,
+      };
+      const breaker = new CircuitBreaker(probeConfig);
+      const failOp = vi.fn().mockRejectedValue(new Error('test error'));
+
+      for (let i = 0; i < probeConfig.failureThreshold; i++) {
+        await expect(breaker.execute(failOp)).rejects.toThrow();
+      }
+
+      expect(breaker.getState()).toBe('OPEN');
+
+      await vi.advanceTimersByTimeAsync(probeConfig.timeout + 1);
+
+      let releaseFirstProbe!: () => void;
+      let releaseSecondProbe!: () => void;
+      const probe = vi
+        .fn()
+        .mockImplementationOnce(
+          () =>
+            new Promise<void>((resolve) => {
+              releaseFirstProbe = resolve;
+            }),
+        )
+        .mockImplementationOnce(
+          () =>
+            new Promise<void>((resolve) => {
+              releaseSecondProbe = resolve;
+            }),
+        );
+
+      const firstProbe = breaker.execute(probe);
+      const secondProbe = breaker.execute(probe);
+      const rejectedProbe = breaker.execute(probe);
+
+      expect(breaker.getState()).toBe('HALF_OPEN');
+      expect(probe).toHaveBeenCalledTimes(2);
+      await expect(rejectedProbe).rejects.toThrow('Maximum concurrent half-open probes reached');
+
+      releaseFirstProbe();
+      releaseSecondProbe();
+      await Promise.all([firstProbe, secondProbe]);
+
+      expect(breaker.getState()).toBe('HALF_OPEN');
+
+      vi.useRealTimers();
+    });
+
     it('should reopen circuit on failure in HALF_OPEN', async () => {
       const operation = vi.fn().mockRejectedValue(new Error('test error'));
 
@@ -320,6 +375,7 @@ describe('CircuitBreaker', () => {
         timeout: 30000,
         monitoringPeriod: 20000,
         maxConcurrentRequests: 20,
+        maxConcurrentHalfOpenProbes: 3,
       };
       const cb = createToastCircuitBreaker(customConfig);
       expect(cb).toBeInstanceOf(CircuitBreaker);

src/utils/circuitBreaker.ts

@@ -18,6 +18,7 @@ export interface CircuitBreakerConfig {
   timeout: number; // Time in ms before attempting recovery
   monitoringPeriod: number; // Time window for failure counting
   maxConcurrentRequests: number; // Maximum concurrent toast operations
+  maxConcurrentHalfOpenProbes: number; // Maximum concurrent recovery probes
 }
 
 export interface CircuitBreakerMetrics {
@@ -37,6 +38,7 @@ const DEFAULT_CONFIG: CircuitBreakerConfig = {
   timeout: 60000, // 1 minute
   monitoringPeriod: 10000, // 10 seconds
   maxConcurrentRequests: 10,
+  maxConcurrentHalfOpenProbes: 1,
 };
 
 export class CircuitBreaker {
@@ -49,6 +51,7 @@ export class CircuitBreaker {
   private totalFailures: number = 0;
   private totalSuccesses: number = 0;
   private activeRequests: number = 0;
+  private activeHalfOpenProbes: number = 0;
   private failureHistory: number[] = [];
 
   constructor(private config: CircuitBreakerConfig = DEFAULT_CONFIG) {}
@@ -81,7 +84,20 @@ export class CircuitBreaker {
       throw new Error('Maximum concurrent requests reached');
     }
 
+    const isHalfOpenProbe = this.state === 'HALF_OPEN';
+
+    if (isHalfOpenProbe && this.activeHalfOpenProbes >= this.config.maxConcurrentHalfOpenProbes) {
+      this.totalFailures++;
+      if (fallback) {
+        return fallback();
+      }
+      throw new Error('Maximum concurrent half-open probes reached');
+    }
+
     this.activeRequests++;
+    if (isHalfOpenProbe) {
+      this.activeHalfOpenProbes++;
+    }
 
     try {
       const result = await operation();
@@ -95,6 +111,9 @@ export class CircuitBreaker {
       throw error;
     } finally {
       this.activeRequests--;
+      if (isHalfOpenProbe) {
+        this.activeHalfOpenProbes--;
+      }
     }
   }