Check if a listing is still active (#184)

* check if a listing is still active

* upgrade dependencies

lib/services/listings/listingActiveTester.js

@@ -0,0 +1,68 @@
+import fetch from 'node-fetch';
+import { randomBetween, sleep } from '../../utils.js';
+
+const maxAttempts = 3;
+
+/**
+ * Check if a listing is still active with up to 3 attempts and exponential backoff.
+ * Backoff waits are capped and the last wait is at most 2000 ms.
+ *
+ * Rules:
+ * - HTTP 200 => return 1
+ * - HTTP 401/403 => return -1 (most certainly detected as a bot)
+ * - HTTP 404 => return 0
+ * - Other statuses or network errors => retry until attempts are exhausted
+ *
+ * @returns {Promise<Integer>} 1 if active, o if not active and -1 if detected as bot
+ */
+export default async function checkIfListingIsActive(link) {
+  await sleep(randomBetween(50, 100));
+
+  for (let attempt = 1; attempt <= maxAttempts; attempt++) {
+    try {
+      const res = await fetch(link, {
+        headers: {
+          'User-Agent':
+            'Mozilla/5.0 (Macintosh; Intel Mac OS X 10_15_7) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/118.0.0.0 Safari/537.36',
+          'Accept-Language': 'de-DE,de;q=0.9,en;q=0.8',
+        },
+      });
+
+      if (res.status === 200) {
+        return 1;
+      }
+      if (res.status === 401) return -1;
+      if (res.status === 403) return -1;
+      if (res.status === 404) return 0;
+
+      // For any other status, only retry if attempts remain
+      if (attempt < maxAttempts) {
+        await sleep(backoffDelay(attempt));
+        continue;
+      }
+
+      return 0;
+    } catch {
+      // Network error: retry if attempts remain
+      if (attempt < maxAttempts) {
+        await sleep(backoffDelay(attempt));
+        continue;
+      }
+      return 0;
+    }
+  }
+
+  return 0;
+}
+
+/**
+ * Exponential backoff delay with cap.
+ * attempt: 1 -> 500ms, 2 -> 1000ms, 3 -> 2000ms (cap)
+ * @param {number} attempt 1-based attempt index
+ * @returns {number} delay in ms
+ */
+function backoffDelay(attempt) {
+  const base = 500;
+  const cap = 2000;
+  return Math.min(base * 2 ** (attempt - 1), cap);
+}